Title of Invention	SOL-CEL PROCESS FOR THE MANUFACTURE OF A MOULD
Abstract	Sol-gel process for the manufacture of a mould having at least one portion transparent to UV rays, comprising the following stages: providing a container which is a negative of the said at least one portion transparent to UV of the mould which is to be manufactured and internally defining a chamber, the said chamber having at least one first surface which is substantially the negative of a corresponding outer surface of the said at least one transparent portion of the mould being manufactured, and at least one second surface which is substantially a negative of at least one corresponding inner surface of the said at least one transparent portion of the mould being manufactured, wherein the container comprises at least one insert defining the said at least one second surface of the chamber, filling the chamber with a sol, gelling the sol, obtaining a gel, wherein the gelling step c) comprises a step of extracting the said at least one insert at a predetermined time during the gelling of the sol to prevent the formation of cracks in the gel that is forming, heating the gel and a corresponding solvent for a programmed period of time consequently achieving predetermined temperature and pressure values, and evaporating the said solvent, the said heating giving rise to drying of the gel, densifying or sintering the gel which is dry through heating to a predetermined temperature, with the consequent formation of the said transparent portion of the mould, with a vitreous consistency and transparent to at least UV rays, the said mould being suitable for the formation of pultrusion or extrusion products or the moulding of plastics materials through a process of photocatalytic synthesis.

Title of Invention

SOL-CEL PROCESS FOR THE MANUFACTURE OF A MOULD

Abstract

Sol-gel process for the manufacture of a mould having at least one portion transparent to UV rays, comprising the following stages: providing a container which is a negative of the said at least one portion transparent to UV of the mould which is to be manufactured and internally defining a chamber, the said chamber having at least one first surface which is substantially the negative of a corresponding outer surface of the said at least one transparent portion of the mould being manufactured, and at least one second surface which is substantially a negative of at least one corresponding inner surface of the said at least one transparent portion of the mould being manufactured, wherein the container comprises at least one insert defining the said at least one second surface of the chamber, filling the chamber with a sol, gelling the sol, obtaining a gel, wherein the gelling step c) comprises a step of extracting the said at least one insert at a predetermined time during the gelling of the sol to prevent the formation of cracks in the gel that is forming, heating the gel and a corresponding solvent for a programmed period of time consequently achieving predetermined temperature and pressure values, and evaporating the said solvent, the said heating giving rise to drying of the gel, densifying or sintering the gel which is dry through heating to a predetermined temperature, with the consequent formation of the said transparent portion of the mould, with a vitreous consistency and transparent to at least UV rays, the said mould being suitable for the formation of pultrusion or extrusion products or the moulding of plastics materials through a process of photocatalytic synthesis.

Full Text	SOL-GEL PROCESS FOR THE MANUFACTURE OF MOULDS FOR PHOTOCATALYTIC PROCESSES This invention relates to a sol-gel process for the manufacture of moulds suitable for the formation of materials using photocatalysis processes. This invention also relates to a pultrusion process, an extrusion process and a moulding process in which a mould manufactured in accordance with the abovementioned method is provided. In particular the invention lies in the field of the processing of various materials, including composite materials and silicones, and pultrusion, extrusion and moulding processes are of particular interest in that sector. As is known, composite materials (or reinforced plastics) are obtained through the combination of a thermohardening resin, such as polyesters or epoxides, with a reinforcement based on glass fibre, carbon fibre, fabric or other material. This association imparts particular mechanical strength properties to the material which can be utilized in a wide range of industrial sectors. As far as silicones are concerned, these are organosilicon compounds comprising polymers based on a silicon-oxygen chain and organic functional groups linked to the silicon atoms; their special feature is that they are particularly resistant to temperature, chemical attack and oxidation, and are excellent electrical insulators. Silicones may be subdivided into various application classes, including liquids, emulsions, lubricants, resins, elastomers. They obviously have very wide application extending from adhesives to lubricants, insulating agents and prostheses. It is known that in the main industrial processes, and in particular in the processes of pultrusion (for composite materials), extrusion and moulding, both composite materials and silicones undergo a cross- linking treatment known as polymerization which generally takes place through thermal means, in particular by placing the material in contact with a heated mould in which it undergoes polymerization and plastic deformation and in which it takes up the final or semi-final shape of the end product. In the known art moulds are generally made of metal, because they have to withstand high mechanical loads as a result of the plastic deformation stresses on the material being formed, and thermal loads due to the repeated thermal polymerization cycles which they perform. Moulds of this type are disadvantageously characterized by a particularly high mass; as a conseguence of this moulds made of metal create more than insignificant logistical difficulties. Furthermore, the manufacture of moulds from metal requires mechanical finishing machining of the rough piece downstream from the operation of casting or plastically deforming the piece in order to obtain a mould which is consistent with a desired shape. Mechanical machining of the mould takes place through the removal of swarf, generally by milling, or, in some cases, by turning or other machining, and is as a result very costly in that it requires complex equipment, particularly when moulds of large size are being machined. As a result the manufacture of metal moulds has the further disadvantage that it requires rather long machining times; this is another factor having an adverse effect on the costs of manufacture of such moulds, which also reflects the various disadvantages affecting moulds made of metal. As mentioned previously, there are various processes in industry in which the use of moulds is required; specifically the processes of pultrusion, extrusion and moulding will also be described below with reference to the equipment used. These processes, which are known, constitute the main but not the only methods of producing and forming composite and silicone materials in accordance with processes according to this invention. Pultrusion is an operation used to manufacture composite materials and is the production process normally used in the production of pipes, articles having a hollow cross section and various sections, in which continuous layers of reinforced fibre are impregnated with catalysed resin and then caused to pass through a heated metal mask using an appropriate machine which "draws" the composite material. A continuous line of product which can then be cut and dispatched for subsequent processing is obtained in this way. The extrusion process on the other hand consists of feeding the material which has to be shaped, for example a silicone, which is then thrust, for example by means of a piston or continuous thrust means comprising for example rotating screws, through a die having a shape which reproduces the cross section of the required section. Again in this case a continuous line of generally semi-finished product which is then sent to stations for subsequent processing is produced. Moulding on the other hand consists of placing the material which has to be moulded, for example a silicone, in a mould forcing it to fill it and adopt its shape. The material may for example be injected into the mould while it is in the liquid state. Heating of the mould takes place in parallel with polymerization of the material. In each of these processes polymerization takes place through a thermal effect and requires a very precise time, which can in some cases be excessive. This has an adverse effect in terms of low productivity and relatively high production costs. As an alternative to the processes of thermohardening plastics material described, photocatalytic processes for achieving polymerization and, if appropriate, cross-linking of the same, with acceptable results, are known, at least at laboratory level. Unfortunately these processes have not become industrially established because of intrinsic difficulties with the processes themselves. For example, in a photocatalytic process one appreciable difficulty is the nature of the mould, which must have appreciable optical transparency, and mechanical and thermomechanical strength properties. Not to mention a shape appropriate for the purpose, which might require appreciable sophistication. In this situation the technical task underlying this invention is to provide a process for the manufacture of moulds which are capable of overcoming the abovementioned disadvantages. In the context of this technical task it is an important object of the invention to provide a process for the manufacture of moulds which makes it possible to reduce process times and as a consequence to increase productivity, even substantially, in particular in processes of pultrusion, extrusion and moulding using such moulds, achieving the effect of reducing production costs. Another object of the invention is to provide a process for the manufacture of moulds of smaller mass than conventional metal moulds, while maintaining good mechanical and thermal strength. Another object of the invention is to provide a process for the manufacture of moulds which eliminates, or at least reduces as far as possible, the need to carry out mechanical machining on the moulds obtained and therefore which reduces the production costs for the moulds themselves. The technical task specified and the objects specified are substantially achieved through a sol-gel process for the manufacture of moulds having at least one portion transparent to UV rays according to one or more of the technical arrangements claimed below. Thus the object of the following invention comprises a sol-gel process for the manufacture of moulds having at least one portion transparent to UV rays as claimed below. The subject of the invention is a sol-gel process for the manufacture of moulds having at least one portion transparent to UV rays, which comprises the following stages: a) provision of a container (1) which is a negative of the said at least one portion (2a) transparent to UV of the mould (2) which is to be manufactured and internally defining a chamber (3), the said chamber (3) having at least one first surface (3a) which is substantially the negative of a corresponding outer surface (2b) of the said at least one transparent portion (2a) of the mould (2) being manufactured, and at least one second surface (3b) which is substantially a negative of at least one corresponding inner surface (2c) of the said at least one transparent portion (2a) of the mould (2) being manufactured, b) filling the chamber (3) with a sol, c) gelling the sol, obtaining the so-called gel, d) heating the gel and a corresponding solvent for a programmed period of time consequently achieving predetermined temperature and pressure values preferably higher than the critical values for the solvent present in the gel, and evaporation of the said solvent, the said heating giving rise to drying of the gel, e) densification and/or sintering of the dried gel through heating to a predetermined temperature, preferably higher than the temperature at which drying stage d) takes place, with the consequent formation of the said transparent portion (2a) of the mould, with a vitreous consistency and transparent to at least UV rays, the said mould being suitable for the formation of pultrusion and/or extrusion products and/or the moulding of plastics materials through a process of photocatalytic synthesis. In the process of the invention the outer surface (2b) of the said at least one transparent portion (2a) of the mould (2) being manufactured can face the external environment in the operating condition of the mould (2) and allow UV rays to pass towards the interior, while the inner surface (2c) of the said at least one transparent portion (2a) of the mould (2) is in the operating condition in contact with the product being formed and polymerized. In the process according to the invention the container (1) can comprise at least one insert (5) defining the said at least one second surface (3b) of the chamber (3) . In the process according to the invention the said at least one insert (5) can be incompressible. In the process according to the invention the said at least one insert (5) can be cylindrical. In the process according to the invention the stage d) of gelling the sol can comprise an operation of extraction of the said at least one insert (5) . In the process according to the invention the extraction of the said at least one insert (5) can take place at a predetermined time in the gelling stage to prevent the formation of cracks in the forming gel. In the process according to the invention the container (1) can be caused to rotate to assist extraction of the said at least one insert (5) making use of the centrifugal forces acting on the forming gel. In the process according to the invention the container . (1) can be caused to rotate axially so that, under the effect of the centrifugal force, the sol adopts the shape of the container bounded externally by the inner surface of the container and internally by the equipotential surface at right angles to the centrifugal force field. In the process according to the invention the container (1) can comprise a plurality of inserts (5). In the process according to the invention stage b) can be preceded by the following stages: - preparation of an aqueous or water/alcohol suspension containing at least one metal alkoxide, effecting hydrolysis of the above suspension, obtaining the sol. In the process according to the invention a phase c') in which the solvent is replaced with an aprotic solvent can be included between stage c) and stage d). In the process according to the invention a stage c') in which the gel is placed in an autoclave and subjected to a flow of inert gas can be included between stage c') and stage d). In the process according to the invention a stage d') of depressurization of the autoclave with a consequent escape of vapours, with possible recovery of the said vapours, can be included between stage d) and stage e). In the process according to the invention a stage d') which consists of flowing an inert gas through the autoclave containing the gel can be included between stage d') and stage e). In the process according to the invention a stage d'') which comprises cooling the dried gel and removing it from the autoclave can be included between stage d') and stage e). In the process according to the invention the aprotic solvent used in stage c') can be selected from the group comprising acetone, dioxan and hydrofuran. In the process according to the invention stage a) also can comprise the operation of positioning and attaching at least one insert (5) within the chamber (3). In the process according to the invention the mould (2) can be wholly transparent to UV rays. In the process according to the invention the mould (2) can comprise a portion (2a) which is transparent to at least UV rays and a portion (9) which is not transparent to UV rays. In the process according to the invention the mould (2) can comprise a half-mould 2a) which is transparent to at least UV rays and a half-mould (9) which is not transparent to UV rays. In the process according to the invention a surface (9a) of the said portion (9) which is not transparent to UV rays, facing the product being formed, can be coated with a reflecting material (10) . In the process according to the invention the reflecting material (10) can be an aluminium film (10). A further subject of the invention is a pultrusion process, which comprises the following stages: preparing a predetermined number of continuous fibres, - providing a mould (2) which is transparent to UV rays using the procedure according to Claim 1, the said mould (2) having a through cavity (4) shaped to plastically deform the said continuous fibres, impregnating the said continuous fibres with a suitable preferably thermohardening resin, - causing the said continuous fibres so impregnated to pass through the mould (2), - polymerizing the said continuous fibres through UV rays as they pass through the mould (2). A further subject of the invention is an extrusion process, which comprises the following stages: - preparing a material for extrusion, - providing a mould (2) which is transparent to at least UV rays using the process according to Claim 1, the said mould (2) having a through cavity (4) shaped to plastically deform the material being extruded, - providing thrust means to force the material being extruded to pass through the mould (2), - application of a thrust in the direction of the mould (2) to the material being extruded, - forcing the material being extruded to pass through the mould (2) imposing plastic deformation on the material being extruded as it passes through the mould (2), - polymerizing the material by exposing it to UV rays as it passes through the mould (2). The material being extruded can belong to the group comprising materials based on silicone and rubber. A preferably thermohardening catalyst can be added to the material being extruded to polymerize the material being extruded when it is exposed to UV rays. A further subject of the invention is a moulding process, which comprises the following stages: - preparing a material for moulding, - providing a mould (2) comprising at least two mating portions of which at least one is transparent to UV rays using the process according to Claim 1, the said mould (2) defining internally a cavity (4) which can be wholly exposed to UV rays, - joining the said portions of the mould (2), inserting the material to be moulded within the cavity (4), - polymerizing the material by exposing it to UV rays while it is within the cavity (4). The material being moulded can belong to the group comprising materials based on silicone and rubber, or thermohardening materials. Preferably a thermohardening catalyst can be added to the material being moulded to polymerize the material being moulded when it is exposed to UV rays. The moulding process to the invention can comprise injection or compression moulding. A description of a preferred embodiment of a sol-gel process for the manufacture of moulds having at least one portion transparent to UV rays is described below by way of example but not exclusively in accordance with the appended drawings in which: - Figure 1 illustrates a view in cross section of a container for the manufacture of a mould according to the invention, - Figure 2 illustrates a view in cross section of a mould according to a preferred embodiment, - Figures 3 to 5 illustrate a view in cross section of a mould according to further embodiments, - Figure 6 illustrates views in cross section of a mould according to a further embodiment, - Figure 7 illustrates a view in cross section of two containers for the manufacture of the mould in Figure 6' - Figures 8 and 9 illustrate a view in cross section of a mould according to further embodiments. A preferred embodiment of a sol-gel process for the manufacture of moulds having at least one portion transparent to UV rays according to the invention comprises the following stages: a) providing a container 1 having the negative shape with at least one transparent portion 2a of the mould 2 which is to be manufactured and internally defining a chamber 3, b) filling chamber 3 with a colloidal suspension (sol), c) effecting gelling of the sol, obtaining the so- called gel, d) heating the gel and a corresponding solvent in an autoclave for a programmed period of time consequently reaching predetermined temperature and pressure values substantially higher than the critical values for the solvent, and extrusion of that solvent giving rise to drying of the gel, e) densification and/or sintering of the dried gel by heating to a predetermined temperature, preferably higher than the temperature specified in stage d), with the consequent formation of a vitreous body transparent to at least UV rays. The colloidal suspension (sol) in stage b) is prepared in a preceding stage a') by mixing one or more precursors containing metal alkoxides with a solvent. This solvent may be water or a water/alcohol mixture, and gives rise to an aqueous or water/alcohol suspension respectively. Preferably, also, the metal in each precursor is an element belonging to groups 3, 4, 5 of the Periodic system. The metals generally used for the formation of a precursor are silicon and, sometimes, aluminium. In order to be able to carry out stage b) it is also necessary that hydrolysis of the suspension produced in stage a') be carried out in a further preceding stage a'), yielding the sol. This is generally achieved by the addition of an acid or basic catalyst to the suspension. This catalyst is preferably an aqueous solution of hydrochloric acid. It should also be added that once hydrolysis is complete, before starting gelling, it is possible to add a colloidal suspension of an oxide of a metal present in a precursor of the suspension in paragraph b) to the sol. For example, in the case where a precursor comprising or constituting a silicon alkoxide is used, a colloidal suspension prepared by mixing water, pyrolytic silica and an acid or a base may be added to the sol. This also makes it possible to adjust the pH value of the suspension; it is in fact known that pH is one of the factors having the greatest influence on the gelling stage, in particular the duration of that stage and the strength of the gel obtained. In fact it has been found experimentally that increasing the pH value brings about a reduction in the time required for gelling, achieving a period of the order of a few minutes, and in parallel with this imparts greater strength to the gel obtained, thus making it possible to manufacture products of larger dimensions. In detail the improved results in terms of strength of the gel are obtained from a sol having a pH value of between 3 and 6. In order to increase the pH of the suspension it may be brought into solution in a controlled gradual way with for example ammonium hydroxide. The sol so obtained can then be poured into container 1 and proceed to the gelling stage. This stage takes place through maintaining the sol at a temperature below 40°C for a time varying from a few minutes to several hours. The gel so obtained has a gelatinous consistency and a porous structure and is immersed in the solvent, in particular water or a water/alcohol mixture as described previously. In order to be able to proceed to stage d) of drying of the gel it is necessary to provide for replacement of the solvent in that this drying preferably takes place at a temperature and pressure above the critical temperature and pressure for the solvent, and, when excessive water is present, achieving these pressures and temperatures would be extremely harmful to the integrity of the gel, given the agressivity of water towards the gel at high temperatures. In this respect, during a stage c') between the gelling stage c) and the subsequent stage d) of heating chamber 3 and drying the gel, the solvent present in chamber 3 and in the pores of the gel is replaced by an aprotic solvent, for example by washing the gel. This aprotic solvent is preferably selected from the group comprising acetone, dioxan and hydrofuran and is decidedly less aggressive towards the gel at high temperatures than water. The gel so prepared, with a level of solvent compatible with the specifications for the solvent extraction autoclave in question at supercritical conditions or "quasi-supercritical" conditions as described in the known art (Joseph G. Van Lierop et al. - US 4,806,328) is placed directly in the autoclave. The gel is then subjected to a further stage c') of passing through an inert gas, preferably nitrogen, at the pressure necessary to achieve a total pressure greater than the critical pressure for the aprotic solvent when the temperature exceeds the critical temperature for that aprotic solvent. Exceeding the critical conditions in this way has the advantage that a gel which better matches the desired dimensions is obtained in comparison with a gel which is obtained by drying at conditions below the critical conditions. As an alternative, during stage c') the inert gas is passed through at the pressure necessary to achieve total pressure and temperature values below the critical values for the aprotic solvent previously introduced, but compatible with the rules for extraction under subcritical conditions described in the known art (US 5,966,832; US 5,875,564; US 5,473,826; US 5,343,633; PCT/EP 2003/014759). The gel is then heated; after this heating the aprotic solvent evaporates substantially completely and drying of the gel takes place. Subsequently in a stage d') the autoclave is depressurized with the consequent escape of vapours. These vapours may be recovered where this is considered to be convenient or necessary. In a subsequent stage d') an inert gas, preferably nitrogen, is caused to flow through the autoclave containing the gel in order to remove residual traces of vapours. In a subsequent stage d'') the dried gel is cooled and removed from the autoclave. In order to impart the desired transparency properties to the dried gel, a final sintering stage e) is provided in which the gel is heated to a predetermined temperature, preferably higher than the temperature at which drying stage d) takes place, in which vitrification of the gel occurs. Said stage e) is generally effected by placing the gel in a furnace, not illustrated, and increasing the temperature of the furnace above 100°C and up to even 900°C in an atmosphere which may also contain oxygen, used to calcine the gel. After this treatment, gases containing chlorine or its precursors may be introduced in order to eliminate any residual hydroxides in the gel, reaching a temperature of between 100°C and 1250°C. The temperature of the furnace is finally increased to between 900°C and 1650°C in such a way as to bring about densification of the gel and therefore its vitrification, obtaining a mould having a vitreous consistency which is transparent to at least UV rays. Some of the characteristics of the device used to effect the abovementioned process will now be described. As mentioned previously, the performance of stage a) requires the provision of a container 1, illustrated in Figure 1, which defines within it a chamber 3. The sol is then poured into chamber 3. Advantageously chamber 3 is a negative of the final shape or a portion of the final shape of mould 2 which it is desired to obtain, with dimensions which are suitably enlarged to take into account the progressive shrinkage acting on the sol during the gelling stage and subsequent shrinkage associated with the stages of drying and densification and/or sintering. Mould 2 is illustrated in Figure 2. In detail, chamber 3 has at least a first surface 3a which is substantially of a shape which is a negative of a corresponding outer surface 2b of at least one transparent portion 2a of mould 2 being manufactured, and at least one second surface 3b which is substantially a negative of at least one corresponding inner surface 2c of said at least one transparent portion 2a of mould 2 being manufactured. This inner surface 2c defines a cavity 4, preferably a through cavity, within the mould. In relation to Figure 2, in the working condition, outer surface 2b of the said at least one transparent portion 2a of mould 2 being manufactured faces the external environment and allows the passage of UV rays towards the interior, while inner surface 2c of the said at least one transparent portion 2a of mould 2 is in contact with the material which has to be formed and polymerized. In detail, means may be provided externally to mould 2 to generate UV rays. These means for the generation of UV rays must face mould 2, in particular the outer surface 2b of transparent portion 2a. In this way, in the working condition, the UV rays will be directed towards mould 2, and by virtue of the transparency of mould 2 to UV rays will pass through it reaching internal cavity 4. The material which has to be shaped and polymerized, generally a composite material or a silicone, is suitably introduced into cavity 4 to undergo polymerization through the UV rays generated as just described. The material which has to be formed and polymerized is then exposed to the UV rays while it is within the mould. Advantageously polymerization takes place through exposing the material which has to be shaped and polymerized while it is in movement through cavity 4 of mould 2. It is however conceivable that the flow of material which has to be formed and polymerized may be temporarily stopped in order to permit completion of the polymerization process. In the non-working condition, cavity 4 is empty and is therefore not filled with any material which has to be formed. Coupling means, not illustrated, may also be provided to secure mould 2 to a device, for example a pultrusion, extrusion or moulding device. One of the most critical operations for manufacturing moulds according to the invention is the production of cavity 4, for reasons which will be clarified below. In order to make the said cavity 4 (see for example Figures 1-5) it may be necessary to use an insert 5 which has to be attached to container 1, in particular within chamber 3. In general, in order to make cavity 4 at least one insert 5 which has to be attached to the container to define the second surface 3b of chamber 3 is required. In this respect stage a) also comprises a stage of positioning and attaching insert 5 within chamber 3. According to a first embodiment illustrated in Figures 1 and 2, mould 2 is made as a single block. This mould 2, produced using the sol-gel process described previously, is wholly transparent to UV rays and has an outer cylindrical surface 2b and an inner surface 2c which is also cylindrical. In order to make this mould 2, first surface 3a and second surface 3b of chamber 3 are cylindrical. Within chamber 3 there is also housed an insert 5 defining a second surface 3b which is substantially a negative of the inner surface 2c of mould 2 which has to be manufactured. Insert 5 is preferably incompressible so as to withstand the compression forces generated by the surrounding sol during the gelling stage. In general it is preferable to use cylindrical inserts 5 to generate cylindrical cavities 4 within mould 2 and therefore passages of constant cross section for the material being polymerized which passes through it. As an alternative it is possible to use inserts 5 of a frustoconical shape, not illustrated, which can be more easily removed from the gel but which can only be used in circumstances where a cavity 4 having a variable cross section for passage of the material being polymerized is necessary. In a wholly similar way it is possible to obtain different embodiments of a wholly transparent mould 2 as illustrated in Figures 3 to 5 and in any event in accordance with other embodiments not illustrated and corresponding combinations. For example, using a container 1 comprising a plurality of inserts 5 it is possible to obtain a mould 2 having a plurality of cavities 4. Figure 3 in particular illustrates a cylindrical mould 2 having three cylindrical cavities 4 in line extending parallel to each other in as many directions. Figure 4 illustrates a mould 2 having a substantially square cross section with three cavities of rectangular cross section in line and extending in directions parallel to each other. Finally, Figure 5 illustrates a mould 2 having a substantially square cross section with four parallel cylindrical cavities arranged alongside the corners of a square. When an insert 5 is present, gelling stage d) also provides for an operation of extracting insert 5 from the sol as it is gelling. The removal of inserts 5 has proved to be a quite complex operation in that, while it is forming from the sol, the gel has a "syneresis" stage, that is a stage during which the material of which it is formed "migrates" in the direction of the centre of mass thus reducing its volume. It is obvious that in this situation any inserts 5 present will.tend to be tightly gripped by the forming gel, which has a gelatinous and not very strong consistency. It is therefore necessary to remove these inserts 5 before they are excessively gripped by the gel, but in any event not before the gel has developed sufficient robustness to be able to support the presence of an internal cavity 4. It is therefore necessary to remove each insert 5 at a well-specified time in order to avoid irreversible damage to the gel which would compromise its integrity. For this purpose it is possible to cause container 1 to rotate, preferably about an axis of symmetry of insert 5 which has to be removed, in order to assist removal of said insert 5 making use of the occurrence of centrifugal forces acting on the gelling sol, as illustrated in the known art (US 6,799,442). In a further version it may be convenient to prepare cylindrical mould 2 completely on the basis of the centrifugal force acting on the sol located in a suitable horizontal cylindrical container which is caused to rotate rapidly axially as described in the known art (US 4,680,045). In this arrangement the sol, whose volume occupies a predetermined fraction of the volume of the container, under the effect of the centrifugal force adopts the cylindrical shape of the container bounded externally by the inner surface of the container, and internally by the equipotential surface, which is also cylindrical, perpendicular to the centrifugal force field present during the gelling stage. The process and device described above make it possible to obtain moulds which are wholly transparent to UV rays. Figure 2 also indicates, diagrammatically in that it is known, a localized source of UV rays through the number 6. It is however advantageous to use one or more sources 6 of UV rays which are distributed over and face the entire periphery of mould 2 to generate uniform irradiation of all the material which has to be formed and polymerized. In another embodiment, illustrated in Figure 6, mould 2 is made of two half-moulds 7 which are transparent to UV rays and identical to each other in such a way that they can be placed together accurately obtaining a wholly transparent mould 2. As may be seen from Figure 7, in order to make the two half-moulds 7 two identical containers 1 are required, each of which has internally a chamber 3 defining a first hemicylindrical surface 8a which is substantially a negative of an outer hemicylindrical surface 7a of half-mould 7 being manufactured, a second hemicylindrical surface 8b which is substantially a negative of an inner hemicylindrical surface 7b of half-mould 7 and two flat closure surfaces 8b in the form of negatives of two flat contact surfaces 7c in each half-mould 7 to allow the two half-moulds 7 to be mated together. Advantageously in this case it is not necessary to attach inserts 5 within chamber 3. It is however possible to use a single container to consecutively make the two half-moulds 7. In accordance with embodiments not illustrated here the process described can be extended to the manufacture of wholly transparent moulds 2 also comprising more than two transparent portions 2a joined together. As described in the following two embodiments it is also possible to manufacture a mould 2 comprising a portion 2a transparent to UV rays made using the sol- gel process described and a portion 9 which is not transparent to UV rays. This portion 9 which is not transparent to UV rays may be manufactured using conventional materials, for example metal, and may also be machined using machine tools. Advantageously, furthermore, a surface 9a of this non-transparent portion 9 facing the product which has to be shaped and polymerized may be coated with a reflecting material 10 for reasons which will be specified below. Figure 8 illustrates a particular embodiment comprising a half-mould transparent to UV rays (corresponding to previously mentioned transparent portion 2a) and a half-mould 9 which is not transparent to UV rays. The two half-moulds define cavity 4 for passage of the material being shaped and polymerized. In this configuration the UV rays originate from one or more sources 6 of UV rays facing the transparent half-mould and are directed towards the interior of mould 2, in particular towards cavity 4. In a further embodiment illustrated in Figure 9, an inner surface 9a of non-transparent half-mould 9 facing cavity 4 and therefore, in the working condition, the product being shaped and polymerized, is coated with a reflecting material 10, for example a film of aluminium 10. This makes it possible to reflect any UV rays which are otherwise dispersed towards the product and therefore increase the polymerizing efficiency of mould 2. It is also possible to use moulds 2 obtained as described above in accordance with the process of manufacture to carry out processes having industrial applications in which it is convenient to polymerize the working material through UV rays. introduced into mould 2 by exerting a pulling force in a direction of progress. In mould 2 the fibres converge and are coated by the coating layers if these are present, giving rise to a composite material. These may also be provided for subsequent compacting of the fibres. In addition to this means may also subsequently be used to shape or dimension the compacted composite material. A non-restrictive embodiment of an extrusion process comprises the following stages: - preparing a material which has to be extruded, providing a mould 2 which is at least partly transparent to UV rays using the process previously described, having a through cavity 4 shaped to plastically deform the material being extruded, - the provision of thrust means to force the material being extruded to pass through mould 2, - application of a thrust in the direction of the mould to the material being extruded, - forcing the material being extruded to pass through mould 2 imposing plastic deformation on the material being extruded during its passage through mould 2, polymerizing the material through UV rays as it passes through the mould. Similarly to the pultrusion process, in an extrusion process a mould 2 which is at least partly transparent to UV rays manufactured as described previously is provided. The material being extruded preferably belongs to the group comprising materials based on silicone and there is provision for the addition of a catalyst, for example a thermohardening catalyst, to polymerize the material being moulded when it is exposed to UV rays. The material which is to be extruded is also preferably present in a semi-liquid state or in any event has sufficient malleability to be plastically deformed. Thrust means to force the material being extruded to pass through mould 2 are also provided. In this respect the mould must have a through cavity 4 shaped to plastically deform the material being extruded. The thrust means may be provided by means of pistons or rotary screws. A thrust in the direction of mould 2 is therefore applied to the material being extruded by the thrust means, forcing it to pass through mould 2 and imposing plastic deformation upon it. While the material being extruded passes through mould 2 it is exposed to UV rays which activate its polymerization. A non-restrictive embodiment of a moulding process comprises the following stages: preparing a material which is to be moulded, providing through the process previously described two half-moulds which can be joined together, of which at least one is transparent to UV rays, internally defining a cavity 4 which can be wholly exposed to UV rays, - joining the two half-moulds, - inserting the material which has to be moulded within cavity 4, - polymerizing the material through UV rays while it is within cavity 4. Similarly to the pultrusion and extrusion processes, in a moulding process a mould which is at least partly transparent to UV rays manufactured in accordance with what has been described previously is provided. The mould is constructed as at least two portions which can be joined together, of which at least one is transparent to UV rays, and defines within it a cavity 4 which can be wholly exposed to UV rays. The material which has to be moulded preferably belongs to the group of materials based on silicone and rubbers and provision is made for the addition of a catalyst, for example a thermohardening catalyst, to polymerize the material being moulded when exposed to UV rays. The material being moulded is also preferably present in a semi-liquid state or in any event has sufficient malleability to be forced to fill the cavity present within the mould. The process provides for insertion of the material to be moulded within cavity 4. This takes place preferably through at least one hole made in at least one portion of the mould through which it is injected under pressure within cavity 4. The material being moulded is then forced to match the shape of cavity 4. Once injection has taken place it is then possible to polymerize the material by exposing it to UV rays while it is still in cavity 4. Obviously the mould used may be used for the injection moulding of thermohardening materials. In addition to this the technology mentioned above also makes possible the compression moulding of thermohardening material. It should also be noted that inserts, for example of metal, but advantageously also of quartz, may be positioned within the mould in order to be able to obtain hollow pieces. This invention provides major advantages. First of all the use of moulds which are transparent to UV rays makes it possible to polymerize the material being formed by UV rays while it still lies in the mould and this appreciably reduces processing times, in particular because of the possibility of using UV rays whose polymerizing action is appreciably faster than in the case where heated moulds are used. This has the advantageous effect of substantially increasing the productivity of production plants such as, as in the examples mentioned, pultrusion, extrusion and moulding plants. In addition to this, the material which has to be shaped and polymerized may be advantageously exposed to UV rays while it is in movement within the mould, thus bringing about the advantage of regularizing production and further increasing productivity. A further advantage is provided by reducing the production costs of the moulds, in that the sol-gel process for the manufacture of moulds transparent to UV provides as a result moulds having a surface which is defined with high accuracy and which does not require any further machining by machine tools. Economic advantage also lies in the fact that the substantial increase in productivity also has a positive effect in a tangible reduction in costs per unit product, in particular fixed costs, including the costs of making the moulds. These moulds are subject to shrinkage during the stages of gelling, drying and sintering, but the amount of such reduction in size is considered in advance by suitably increasing the initial dimensions of the chamber which contains the sol. The final effect is therefore that of obtaining moulds with high dimensional accuracy and high transparency and sharpness . First of all the use of moulds which are transparent to UV rays makes it possible to polymerize the material being formed by UV rays while it still lies in the mould and this appreciably reduces processing times, in particular because of the possibility of using UV rays whose polymerizing action is appreciably faster than in the case where heated moulds are used. This has the advantageous effect of substantially increasing the productivity of production plants such as, as in the examples mentioned, pultrusion, extrusion and moulding plants. In addition to this, the material which has to be shaped and polymerized may be advantageously exposed to UV rays while it is in movement within the mould, thus bringing about the advantage of regularizing production and further increasing productivity. A further advantage is provided by reducing the production costs of the moulds, in that the sol-gel process for the manufacture of moulds transparent to UV provides as a result moulds having a surface which is defined with high accuracy and which does not require any further machining by machine tools. Economic advantage also lies in the fact that the substantial increase in productivity also has a positive effect in a tangible reduction in costs per unit product, in particular fixed costs, including the costs of making the moulds. These moulds are subject to shrinkage during the stages of gelling, drying and sintering, but the amount of such reduction in size is considered in advance by suitably increasing the initial dimensions of the chamber which contains the sol. The final effect is therefore that of obtaining moulds with high dimensional accuracy and high transparency and sharpness. WE CLAIM: 1. Sol-gel process for the manufacture of a mould having at least one portion transparent to UV rays, comprising the following stages: a) providing a container which is a negative of the said at least one portion transparent to UV of the mould which is to be manufactured and internally defining a chamber, the said chamber having at least one first surface which is substantially the negative of a corresponding outer surface of the said at least one transparent portion of the mould being manufactured, and at least one second surface which is substantially a negative of at least one corresponding inner surface of the said at least one transparent portion of the mould being manufactured, wherein the container comprises at least one insert defining the said at least one second surface of the chamber. b) filling the chamber with a sol, c) gelling the sol, obtaining a gel, wherein the gelling step c) comprises a step of extracting the said at least one insert at a predetermined time during the gelling of the sol to prevent the formation of cracks in the gel that is forming, d) heating the gel and a corresponding solvent for a programmed period of time consequently achieving predetermined temperature and pressure values, and evaporating the said solvent, the said heating giving rise to drying of the gel, e) densifying or sintering the gel which is dry through heating to a predetermined temperature, with the consequent formation of the said transparent portion of the mould, with a vitreous consistency and transparent to at least UV rays, the said mould being suitable for the formation of pultrusion or extrusion products or the moulding of plastics materials through a process of photocatalytic synthesis. 2. Process as claimed in claim 1, wherein the outer surface of the said at least one transparent portion of the mould being manufactured faces the external environment in the operating condition of the mould and allows UV rays to pass towards the interior, while the inner surface of the said at least one transparent portion of the mould is in the operating condition in contact with the product being formed and polymerized. 3. Process as claimed in claim 1, wherein the said at least one insert is incompressible. 4. Process as claimed in claim 1, wherein the said at least one insert is cylindrical. 5. Process as claimed in claim 1, wherein the container is caused to rotate to assist extraction of the said at least one insert making use of the centrifugal forces acting on the gel that is forming. 6. Process as claimed in claim 1, wherein the container is caused to rotate axially so that, under the effect of the centrifugal force, the sol adopts the shape of the container bounded externally by the inner surface of the container and internally by an equipotential surface at right angles to a force field of the centrifugal force. 7. Process as claimed in claim 1, wherein the container comprises a plurality of inserts. 8. Process as claimed in claim 1, wherein stage b) is preceded by the following stages: • preparing an aqueous or water/alcohol suspension containing at least one metal alkoxide; • effecting hydrolysis of the above suspension, obtaining the sol. 9. Process as claimed in claim 1, wherein a phase c') in which the solvent is replaced with an aprotic solvent is included between stage c) and stage d). 10. Process as claimed in claim 9, wherein a stage c") in which the gel is placed in an autoclave and subjected to a flow of inert gas is included between stage c') and stage d). 11. Process as claimed in claim 10, wherein a stage d') of depressurization of the autoclave with a consequent escape of vapours, with optional recovery of the said vapours, is included between stage d) and stage e). 12. Process as claimed in claim 11, wherein a stage d") which consists of flowing an inert gas through the autoclave containing the gel is included between stage d') and stage e). 13. Process as claimed in claim 12, wherein a stage d'") which comprises cooling dried gel and removing it from the autoclave is included between stage d") and stage e). 14. Process as claimed in claim 9, wherein the aprotic solvent used in stage c') is selected from the group consisting of acetone, dioxan and hydrofuran. 15. Process as claimed in claim 1, wherein during stage a) said at least one insert is positioned and attached within the chamber. 16. Process as claimed in claim 1, wherein the mould is wholly transparent to UV rays. 17. Process as claimed in claim 1, wherein the mould comprises a portion which is transparent to at least UV rays and a second portion which is not transparent to UV rays. 18. Process as claimed in claim 17, wherein the mould comprises a half-mould which is transparent to at least UV rays and a second half-mould which is not transparent to UV rays. 19. Process as claimed in claim 17, wherein a surface of the said second portion which is not transparent to UV rays, facing the product being formed, is coated with a reflecting material. 20. Process as claimed in claim 19, wherein the reflecting material is an aluminium film. 21. Process as claimed in claim 1, wherein the temperature and pressure of heating in stage d) is at values higher than the critical values for the solvent present in the gel. 22. Pultrusion process, comprising the following stages: • preparing continuous fibres; • providing a mould which is transparent to UV rays by using the procedure as claimed in claim 1, the said mould having a through cavity shaped to plastically deform the said continuous fibres; • impregnating the said continuous fibres with a suitable resin; • causing the said continuous fibres so impregnated to pass through the mould, and • polymerizing the said continuous fibres through UV rays as they pass through the mould. 23. Extrusion process, comprising the following stages: • preparing a material for extrusion; • providing a mould which is transparent to at least UV rays by using the process according to claim 1, the said mould having a through cavity shaped to plastically deform the material being extruded; • providing thrust means to force the material being extruded to pass through the mould; • applying of a thrust in the direction of the mould to the material being extruded; • forcing the material being extruded to pass through the mould imposing plastic deformation on the material being extruded as it passes through the mould, and • polymerizing the material by exposing it to UV rays as it passes through the mould. 24. Extrusion process as claimed in claim 23, in which the material being extruded belongs to the group comprising materials based on silicone and rubber. 25. Extrusion process as claimed in claim 23, in which a catalyst is added to the material being extruded to polymerize the material being extruded when it is exposed to UV rays. 26. Moulding process, comprising the following stages: • preparing a material for moulding; • providing a mould comprising at least two mating portions of which at least one is transparent to UV rays by using the process as claimed in claim 1, the said mould defining internally a cavity which can be wholly exposed to UV rays; • joining the said at least two mating portions of the mould; • inserting the material to be moulded within the cavity, and • polymerizing the material by exposing it to UV rays while it is within the cavity. 27. Moulding process as claimed in claim 26, wherein the material being moulded belongs to the group comprising materials based on silicone and rubber, or thermohardening materials. 28. Moulding process as claimed in claim 26, wherein a catalyst is added to the material being moulded to polymerize the material being moulded when it is exposed to UV rays. 29. Moulding process as claimed in claim 26, wherein it comprises injection or compression moulding. ABSTRACT Title: Sol-gel process for the manufacture of a mould. Sol-gel process for the manufacture of a mould having at least one portion transparent to UV rays, comprising the following stages: providing a container which is a negative of the said at least one portion transparent to UV of the mould which is to be manufactured and internally defining a chamber, the said chamber having at least one first surface which is substantially the negative of a corresponding outer surface of the said at least one transparent portion of the mould being manufactured, and at least one second surface which is substantially a negative of at least one corresponding inner surface of the said at least one transparent portion of the mould being manufactured, wherein the container comprises at least one insert defining the said at least one second surface of the chamber, filling the chamber with a sol, gelling the sol, obtaining a gel, wherein the gelling step c) comprises a step of extracting the said at least one insert at a predetermined time during the gelling of the sol to prevent the formation of cracks in the gel that is forming, heating the gel and a corresponding solvent for a programmed period of time consequently achieving predetermined temperature and pressure values, and evaporating the said solvent, the said heating giving rise to drying of the gel, densifying or sintering the gel which is dry through heating to a predetermined temperature, with the consequent formation of the said transparent portion of the mould, with a vitreous consistency and transparent to at least UV rays, the said mould being suitable for the formation of pultrusion or extrusion products or the moulding of plastics materials through a process of photocatalytic synthesis.

Full Text

SOL-GEL PROCESS FOR THE MANUFACTURE OF MOULDS FOR
PHOTOCATALYTIC PROCESSES
This invention relates to a sol-gel process for the
manufacture of moulds suitable for the formation of
materials using photocatalysis processes.
This invention also relates to a pultrusion process, an
extrusion process and a moulding process in which a
mould manufactured in accordance with the
abovementioned method is provided.
In particular the invention lies in the field of the
processing of various materials, including composite
materials and silicones, and pultrusion, extrusion and
moulding processes are of particular interest in that
sector.
As is known, composite materials (or reinforced
plastics) are obtained through the combination of a
thermohardening resin, such as polyesters or epoxides,
with a reinforcement based on glass fibre, carbon
fibre, fabric or other material. This association
imparts particular mechanical strength properties to
the material which can be utilized in a wide range of
industrial sectors.
As far as silicones are concerned, these are
organosilicon compounds comprising polymers based on a
silicon-oxygen chain and organic functional groups
linked to the silicon atoms; their special feature is
that they are particularly resistant to temperature,
chemical attack and oxidation, and are excellent
electrical insulators. Silicones may be subdivided into
various application classes, including liquids,

emulsions, lubricants, resins, elastomers. They
obviously have very wide application extending from
adhesives to lubricants, insulating agents and
prostheses.
It is known that in the main industrial processes, and
in particular in the processes of pultrusion (for
composite materials), extrusion and moulding, both
composite materials and silicones undergo a cross-
linking treatment known as polymerization which
generally takes place through thermal means, in
particular by placing the material in contact with a
heated mould in which it undergoes polymerization and
plastic deformation and in which it takes up the final
or semi-final shape of the end product.
In the known art moulds are generally made of metal,
because they have to withstand high mechanical loads as
a result of the plastic deformation stresses on the
material being formed, and thermal loads due to the
repeated thermal polymerization cycles which they
perform.
Moulds of this type are disadvantageously characterized
by a particularly high mass; as a conseguence of this
moulds made of metal create more than insignificant
logistical difficulties.
Furthermore, the manufacture of moulds from metal
requires mechanical finishing machining of the rough
piece downstream from the operation of casting or
plastically deforming the piece in order to obtain a
mould which is consistent with a desired shape.
Mechanical machining of the mould takes place through
the removal of swarf, generally by milling, or, in some
cases, by turning or other machining, and is as a
result very costly in that it requires complex
equipment, particularly when moulds of large size are
being machined.

As a result the manufacture of metal moulds has the
further disadvantage that it requires rather long
machining times; this is another factor having an
adverse effect on the costs of manufacture of such
moulds, which also reflects the various disadvantages
affecting moulds made of metal.
As mentioned previously, there are various processes in
industry in which the use of moulds is required;
specifically the processes of pultrusion, extrusion and
moulding will also be described below with reference to
the equipment used. These processes, which are known,
constitute the main but not the only methods of
producing and forming composite and silicone materials
in accordance with processes according to this
invention.
Pultrusion is an operation used to manufacture
composite materials and is the production process
normally used in the production of pipes, articles
having a hollow cross section and various sections, in
which continuous layers of reinforced fibre are
impregnated with catalysed resin and then caused to
pass through a heated metal mask using an appropriate
machine which "draws" the composite material. A
continuous line of product which can then be cut and
dispatched for subsequent processing is obtained in
this way.
The extrusion process on the other hand consists of
feeding the material which has to be shaped, for
example a silicone, which is then thrust, for example
by means of a piston or continuous thrust means
comprising for example rotating screws, through a die
having a shape which reproduces the cross section of
the required section. Again in this case a continuous
line of generally semi-finished product which is then
sent to stations for subsequent processing is produced.

Moulding on the other hand consists of placing the
material which has to be moulded, for example a
silicone, in a mould forcing it to fill it and adopt
its shape. The material may for example be injected
into the mould while it is in the liquid state. Heating
of the mould takes place in parallel with
polymerization of the material.
In each of these processes polymerization takes place
through a thermal effect and requires a very precise
time, which can in some cases be excessive. This has an
adverse effect in terms of low productivity and
relatively high production costs.
As an alternative to the processes of thermohardening
plastics material described, photocatalytic processes
for achieving polymerization and, if appropriate,
cross-linking of the same, with acceptable results, are
known, at least at laboratory level.
Unfortunately these processes have not become
industrially established because of intrinsic
difficulties with the processes themselves. For
example, in a photocatalytic process one appreciable
difficulty is the nature of the mould, which must have
appreciable optical transparency, and mechanical and
thermomechanical strength properties. Not to mention a
shape appropriate for the purpose, which might require
appreciable sophistication.
In this situation the technical task underlying this
invention is to provide a process for the manufacture
of moulds which are capable of overcoming the
abovementioned disadvantages.
In the context of this technical task it is an
important object of the invention to provide a process
for the manufacture of moulds which makes it possible

to reduce process times and as a consequence to
increase productivity, even substantially, in
particular in processes of pultrusion, extrusion and
moulding using such moulds, achieving the effect of
reducing production costs.
Another object of the invention is to provide a process
for the manufacture of moulds of smaller mass than
conventional metal moulds, while maintaining good
mechanical and thermal strength.
Another object of the invention is to provide a process
for the manufacture of moulds which eliminates, or at
least reduces as far as possible, the need to carry out
mechanical machining on the moulds obtained and
therefore which reduces the production costs for the
moulds themselves.
The technical task specified and the objects specified
are substantially achieved through a sol-gel process
for the manufacture of moulds having at least one
portion transparent to UV rays according to one or more
of the technical arrangements claimed below.
Thus the object of the following invention comprises a
sol-gel process for the manufacture of moulds having at
least one portion transparent to UV rays as claimed
below.
The subject of the invention is a sol-gel process for
the manufacture of moulds having at least one portion
transparent to UV rays, which comprises the following
stages:
a) provision of a container (1) which is a negative
of the said at least one portion (2a) transparent to UV
of the mould (2) which is to be manufactured and
internally defining a chamber (3), the said chamber (3)
having at least one first surface (3a) which is

substantially the negative of a corresponding outer
surface (2b) of the said at least one transparent
portion (2a) of the mould (2) being manufactured, and
at least one second surface (3b) which is substantially
a negative of at least one corresponding inner surface
(2c) of the said at least one transparent portion (2a)
of the mould (2) being manufactured,
b) filling the chamber (3) with a sol,
c) gelling the sol, obtaining the so-called gel,
d) heating the gel and a corresponding solvent for a
programmed period of time consequently achieving
predetermined temperature and pressure values
preferably higher than the critical values for the
solvent present in the gel, and evaporation of the said
solvent, the said heating giving rise to drying of the
gel,
e) densification and/or sintering of the dried gel
through heating to a predetermined temperature,
preferably higher than the temperature at which drying
stage d) takes place, with the consequent formation of
the said transparent portion (2a) of the mould, with a
vitreous consistency and transparent to at least UV
rays, the said mould being suitable for the formation
of pultrusion and/or extrusion products and/or the
moulding of plastics materials through a process of
photocatalytic synthesis.
In the process of the invention the outer surface (2b)
of the said at least one transparent portion (2a) of
the mould (2) being manufactured can face the external
environment in the operating condition of the mould (2)
and allow UV rays to pass towards the interior, while
the inner surface (2c) of the said at least one
transparent portion (2a) of the mould (2) is in the
operating condition in contact with the product being
formed and polymerized.
In the process according to the invention the container
(1) can comprise at least one insert (5) defining the

said at least one second surface (3b) of the chamber (3) .
In the process according to the invention the said at
least one insert (5) can be incompressible.
In the process according to the invention the said at
least one insert (5) can be cylindrical.
In the process according to the invention the stage d)
of gelling the sol can comprise an operation of
extraction of the said at least one insert (5) .
In the process according to the invention the
extraction of the said at least one insert (5) can take
place at a predetermined time in the gelling stage to
prevent the formation of cracks in the forming gel.
In the process according to the invention the container
(1) can be caused to rotate to assist extraction of the
said at least one insert (5) making use of the
centrifugal forces acting on the forming gel.
In the process according to the invention the container .
(1) can be caused to rotate axially so that, under the
effect of the centrifugal force, the sol adopts the
shape of the container bounded externally by the inner
surface of the container and internally by the
equipotential surface at right angles to the
centrifugal force field.
In the process according to the invention the container
(1) can comprise a plurality of inserts (5).
In the process according to the invention stage b) can
be preceded by the following stages:
- preparation of an aqueous or water/alcohol suspension
containing at least one metal alkoxide,

effecting hydrolysis of the above suspension,
obtaining the sol.
In the process according to the invention a phase c')
in which the solvent is replaced with an aprotic
solvent can be included between stage c) and stage d).
In the process according to the invention a stage c')
in which the gel is placed in an autoclave and
subjected to a flow of inert gas can be included
between stage c') and stage d).
In the process according to the invention a stage d')
of depressurization of the autoclave with a consequent
escape of vapours, with possible recovery of the said
vapours, can be included between stage d) and stage e).
In the process according to the invention a stage d')
which consists of flowing an inert gas through the
autoclave containing the gel can be included between
stage d') and stage e).
In the process according to the invention a stage d'')
which comprises cooling the dried gel and removing it
from the autoclave can be included between stage d')
and stage e).
In the process according to the invention the aprotic
solvent used in stage c') can be selected from the
group comprising acetone, dioxan and hydrofuran.
In the process according to the invention stage a) also
can comprise the operation of positioning and attaching
at least one insert (5) within the chamber (3).
In the process according to the invention the mould (2)
can be wholly transparent to UV rays.

In the process according to the invention the mould (2)
can comprise a portion (2a) which is transparent to at
least UV rays and a portion (9) which is not
transparent to UV rays.
In the process according to the invention the mould (2)
can comprise a half-mould 2a) which is transparent to
at least UV rays and a half-mould (9) which is not
transparent to UV rays.
In the process according to the invention a surface
(9a) of the said portion (9) which is not transparent
to UV rays, facing the product being formed, can be
coated with a reflecting material (10) .
In the process according to the invention the
reflecting material (10) can be an aluminium film (10).
A further subject of the invention is a pultrusion
process, which comprises the following stages:
preparing a predetermined number of continuous
fibres,
- providing a mould (2) which is transparent to UV rays
using the procedure according to Claim 1, the said
mould (2) having a through cavity (4) shaped to
plastically deform the said continuous fibres,
impregnating the said continuous fibres with a
suitable preferably thermohardening resin,
- causing the said continuous fibres so impregnated to
pass through the mould (2),
- polymerizing the said continuous fibres through UV
rays as they pass through the mould (2).
A further subject of the invention is an extrusion
process, which comprises the following stages:
- preparing a material for extrusion,
- providing a mould (2) which is transparent to at
least UV rays using the process according to Claim 1,

the said mould (2) having a through cavity (4) shaped
to plastically deform the material being extruded,
- providing thrust means to force the material being
extruded to pass through the mould (2),
- application of a thrust in the direction of the mould
(2) to the material being extruded,
- forcing the material being extruded to pass through
the mould (2) imposing plastic deformation on the
material being extruded as it passes through the mould
(2),
- polymerizing the material by exposing it to UV rays
as it passes through the mould (2).
The material being extruded can belong to the group
comprising materials based on silicone and rubber.
A preferably thermohardening catalyst can be added to
the material being extruded to polymerize the material
being extruded when it is exposed to UV rays.
A further subject of the invention is a moulding
process, which comprises the following stages:
- preparing a material for moulding,
- providing a mould (2) comprising at least two mating
portions of which at least one is transparent to UV
rays using the process according to Claim 1, the said
mould (2) defining internally a cavity (4) which can be
wholly exposed to UV rays,
- joining the said portions of the mould (2),
inserting the material to be moulded within the
cavity (4),
- polymerizing the material by exposing it to UV rays
while it is within the cavity (4).
The material being moulded can belong to the group
comprising materials based on silicone and rubber, or
thermohardening materials.

Preferably a thermohardening catalyst can be added to
the material being moulded to polymerize the material
being moulded when it is exposed to UV rays.
The moulding process to the invention can comprise
injection or compression moulding.
A description of a preferred embodiment of a sol-gel
process for the manufacture of moulds having at least
one portion transparent to UV rays is described below
by way of example but not exclusively in accordance
with the appended drawings in which:
- Figure 1 illustrates a view in cross section of a
container for the manufacture of a mould according to
the invention,
- Figure 2 illustrates a view in cross section of a
mould according to a preferred embodiment,
- Figures 3 to 5 illustrate a view in cross section of
a mould according to further embodiments,

- Figure 6 illustrates views in cross section of a
mould according to a further embodiment,
- Figure 7 illustrates a view in cross section of two
containers for the manufacture of the mould in Figure
6'
- Figures 8 and 9 illustrate a view in cross section of
a mould according to further embodiments.
A preferred embodiment of a sol-gel process for the
manufacture of moulds having at least one portion
transparent to UV rays according to the invention
comprises the following stages:
a) providing a container 1 having the negative shape
with at least one transparent portion 2a of the
mould 2 which is to be manufactured and internally
defining a chamber 3,
b) filling chamber 3 with a colloidal suspension
(sol),
c) effecting gelling of the sol, obtaining the so-
called gel,

d) heating the gel and a corresponding solvent in an
autoclave for a programmed period of time
consequently reaching predetermined temperature
and pressure values substantially higher than the
critical values for the solvent, and extrusion of
that solvent giving rise to drying of the gel,
e) densification and/or sintering of the dried gel by
heating to a predetermined temperature, preferably
higher than the temperature specified in stage d),
with the consequent formation of a vitreous body
transparent to at least UV rays.
The colloidal suspension (sol) in stage b) is prepared
in a preceding stage a') by mixing one or more
precursors containing metal alkoxides with a solvent.
This solvent may be water or a water/alcohol mixture,
and gives rise to an aqueous or water/alcohol
suspension respectively.
Preferably, also, the metal in each precursor is an
element belonging to groups 3, 4, 5 of the Periodic
system. The metals generally used for the formation of
a precursor are silicon and, sometimes, aluminium.
In order to be able to carry out stage b) it is also
necessary that hydrolysis of the suspension produced in
stage a') be carried out in a further preceding stage
a'), yielding the sol. This is generally achieved by
the addition of an acid or basic catalyst to the
suspension. This catalyst is preferably an aqueous
solution of hydrochloric acid.
It should also be added that once hydrolysis is
complete, before starting gelling, it is possible to
add a colloidal suspension of an oxide of a metal
present in a precursor of the suspension in paragraph
b) to the sol. For example, in the case where a
precursor comprising or constituting a silicon alkoxide
is used, a colloidal suspension prepared by mixing

water, pyrolytic silica and an acid or a base may be
added to the sol. This also makes it possible to adjust
the pH value of the suspension; it is in fact known
that pH is one of the factors having the greatest
influence on the gelling stage, in particular the
duration of that stage and the strength of the gel
obtained. In fact it has been found experimentally that
increasing the pH value brings about a reduction in the
time required for gelling, achieving a period of the
order of a few minutes, and in parallel with this
imparts greater strength to the gel obtained, thus
making it possible to manufacture products of larger
dimensions. In detail the improved results in terms of
strength of the gel are obtained from a sol having a pH
value of between 3 and 6. In order to increase the pH
of the suspension it may be brought into solution in a
controlled gradual way with for example ammonium
hydroxide.
The sol so obtained can then be poured into container 1
and proceed to the gelling stage. This stage takes
place through maintaining the sol at a temperature
below 40°C for a time varying from a few minutes to
several hours. The gel so obtained has a gelatinous
consistency and a porous structure and is immersed in
the solvent, in particular water or a water/alcohol
mixture as described previously.
In order to be able to proceed to stage d) of drying of
the gel it is necessary to provide for replacement of
the solvent in that this drying preferably takes place
at a temperature and pressure above the critical
temperature and pressure for the solvent, and, when
excessive water is present, achieving these pressures
and temperatures would be extremely harmful to the
integrity of the gel, given the agressivity of water
towards the gel at high temperatures. In this respect,
during a stage c') between the gelling stage c) and the
subsequent stage d) of heating chamber 3 and drying the

gel, the solvent present in chamber 3 and in the pores
of the gel is replaced by an aprotic solvent, for
example by washing the gel. This aprotic solvent is
preferably selected from the group comprising acetone,
dioxan and hydrofuran and is decidedly less aggressive
towards the gel at high temperatures than water.
The gel so prepared, with a level of solvent compatible
with the specifications for the solvent extraction
autoclave in question at supercritical conditions or
"quasi-supercritical" conditions as described in the
known art (Joseph G. Van Lierop et al. - US 4,806,328)
is placed directly in the autoclave. The gel is then
subjected to a further stage c') of passing through an
inert gas, preferably nitrogen, at the pressure
necessary to achieve a total pressure greater than the
critical pressure for the aprotic solvent when the
temperature exceeds the critical temperature for that
aprotic solvent. Exceeding the critical conditions in
this way has the advantage that a gel which better
matches the desired dimensions is obtained in
comparison with a gel which is obtained by drying at
conditions below the critical conditions.
As an alternative, during stage c') the inert gas is
passed through at the pressure necessary to achieve
total pressure and temperature values below the
critical values for the aprotic solvent previously
introduced, but compatible with the rules for
extraction under subcritical conditions described in
the known art (US 5,966,832; US 5,875,564; US
5,473,826; US 5,343,633; PCT/EP 2003/014759).
The gel is then heated; after this heating the aprotic
solvent evaporates substantially completely and drying
of the gel takes place.
Subsequently in a stage d') the autoclave is
depressurized with the consequent escape of vapours.

These vapours may be recovered where this is considered
to be convenient or necessary.
In a subsequent stage d') an inert gas, preferably
nitrogen, is caused to flow through the autoclave
containing the gel in order to remove residual traces
of vapours. In a subsequent stage d'') the dried gel
is cooled and removed from the autoclave. In order to
impart the desired transparency properties to the dried
gel, a final sintering stage e) is provided in which
the gel is heated to a predetermined temperature,
preferably higher than the temperature at which drying
stage d) takes place, in which vitrification of the gel
occurs. Said stage e) is generally effected by placing
the gel in a furnace, not illustrated, and increasing
the temperature of the furnace above 100°C and up to
even 900°C in an atmosphere which may also contain
oxygen, used to calcine the gel. After this treatment,
gases containing chlorine or its precursors may be
introduced in order to eliminate any residual
hydroxides in the gel, reaching a temperature of
between 100°C and 1250°C. The temperature of the
furnace is finally increased to between 900°C and
1650°C in such a way as to bring about densification of
the gel and therefore its vitrification, obtaining a
mould having a vitreous consistency which is
transparent to at least UV rays.
Some of the characteristics of the device used to
effect the abovementioned process will now be
described.
As mentioned previously, the performance of stage a)
requires the provision of a container 1, illustrated in
Figure 1, which defines within it a chamber 3. The sol
is then poured into chamber 3.
Advantageously chamber 3 is a negative of the final
shape or a portion of the final shape of mould 2 which

it is desired to obtain, with dimensions which are
suitably enlarged to take into account the progressive
shrinkage acting on the sol during the gelling stage
and subsequent shrinkage associated with the stages of
drying and densification and/or sintering. Mould 2 is
illustrated in Figure 2.
In detail, chamber 3 has at least a first surface 3a
which is substantially of a shape which is a negative
of a corresponding outer surface 2b of at least one
transparent portion 2a of mould 2 being manufactured,
and at least one second surface 3b which is
substantially a negative of at least one corresponding
inner surface 2c of said at least one transparent
portion 2a of mould 2 being manufactured. This inner
surface 2c defines a cavity 4, preferably a through
cavity, within the mould.
In relation to Figure 2, in the working condition,
outer surface 2b of the said at least one transparent
portion 2a of mould 2 being manufactured faces the
external environment and allows the passage of UV rays
towards the interior, while inner surface 2c of the
said at least one transparent portion 2a of mould 2 is
in contact with the material which has to be formed and
polymerized.
In detail, means may be provided externally to mould 2
to generate UV rays. These means for the generation of
UV rays must face mould 2, in particular the outer
surface 2b of transparent portion 2a. In this way, in
the working condition, the UV rays will be directed
towards mould 2, and by virtue of the transparency of
mould 2 to UV rays will pass through it reaching
internal cavity 4. The material which has to be shaped
and polymerized, generally a composite material or a
silicone, is suitably introduced into cavity 4 to
undergo polymerization through the UV rays generated as
just described. The material which has to be formed and

polymerized is then exposed to the UV rays while it is
within the mould. Advantageously polymerization takes
place through exposing the material which has to be
shaped and polymerized while it is in movement through
cavity 4 of mould 2. It is however conceivable that the
flow of material which has to be formed and polymerized
may be temporarily stopped in order to permit
completion of the polymerization process.
In the non-working condition, cavity 4 is empty and is
therefore not filled with any material which has to be
formed.
Coupling means, not illustrated, may also be provided
to secure mould 2 to a device, for example a
pultrusion, extrusion or moulding device.
One of the most critical operations for manufacturing
moulds according to the invention is the production of
cavity 4, for reasons which will be clarified below.
In order to make the said cavity 4 (see for example
Figures 1-5) it may be necessary to use an insert 5
which has to be attached to container 1, in particular
within chamber 3. In general, in order to make cavity 4
at least one insert 5 which has to be attached to the
container to define the second surface 3b of chamber 3
is required. In this respect stage a) also comprises a
stage of positioning and attaching insert 5 within
chamber 3.
According to a first embodiment illustrated in Figures
1 and 2, mould 2 is made as a single block. This mould
2, produced using the sol-gel process described
previously, is wholly transparent to UV rays and has an
outer cylindrical surface 2b and an inner surface 2c
which is also cylindrical. In order to make this mould
2, first surface 3a and second surface 3b of chamber 3
are cylindrical. Within chamber 3 there is also housed

an insert 5 defining a second surface 3b which is
substantially a negative of the inner surface 2c of
mould 2 which has to be manufactured. Insert 5 is
preferably incompressible so as to withstand the
compression forces generated by the surrounding sol
during the gelling stage.
In general it is preferable to use cylindrical inserts
5 to generate cylindrical cavities 4 within mould 2 and
therefore passages of constant cross section for the
material being polymerized which passes through it. As
an alternative it is possible to use inserts 5 of a
frustoconical shape, not illustrated, which can be more
easily removed from the gel but which can only be used
in circumstances where a cavity 4 having a variable
cross section for passage of the material being
polymerized is necessary.
In a wholly similar way it is possible to obtain
different embodiments of a wholly transparent mould 2
as illustrated in Figures 3 to 5 and in any event in
accordance with other embodiments not illustrated and
corresponding combinations. For example, using a
container 1 comprising a plurality of inserts 5 it is
possible to obtain a mould 2 having a plurality of
cavities 4. Figure 3 in particular illustrates a
cylindrical mould 2 having three cylindrical cavities 4
in line extending parallel to each other in as many
directions. Figure 4 illustrates a mould 2 having a
substantially square cross section with three cavities
of rectangular cross section in line and extending in
directions parallel to each other. Finally, Figure 5
illustrates a mould 2 having a substantially square
cross section with four parallel cylindrical cavities
arranged alongside the corners of a square.
When an insert 5 is present, gelling stage d) also
provides for an operation of extracting insert 5 from
the sol as it is gelling. The removal of inserts 5 has

proved to be a quite complex operation in that, while
it is forming from the sol, the gel has a "syneresis"
stage, that is a stage during which the material of
which it is formed "migrates" in the direction of the
centre of mass thus reducing its volume. It is obvious
that in this situation any inserts 5 present will.tend
to be tightly gripped by the forming gel, which has a
gelatinous and not very strong consistency. It is
therefore necessary to remove these inserts 5 before
they are excessively gripped by the gel, but in any
event not before the gel has developed sufficient
robustness to be able to support the presence of an
internal cavity 4. It is therefore necessary to remove
each insert 5 at a well-specified time in order to
avoid irreversible damage to the gel which would
compromise its integrity.
For this purpose it is possible to cause container 1 to
rotate, preferably about an axis of symmetry of insert
5 which has to be removed, in order to assist removal
of said insert 5 making use of the occurrence of
centrifugal forces acting on the gelling sol, as
illustrated in the known art (US 6,799,442).
In a further version it may be convenient to prepare
cylindrical mould 2 completely on the basis of the
centrifugal force acting on the sol located in a
suitable horizontal cylindrical container which is
caused to rotate rapidly axially as described in the
known art (US 4,680,045).
In this arrangement the sol, whose volume occupies a
predetermined fraction of the volume of the container,
under the effect of the centrifugal force adopts the
cylindrical shape of the container bounded externally
by the inner surface of the container, and internally
by the equipotential surface, which is also
cylindrical, perpendicular to the centrifugal force
field present during the gelling stage.

The process and device described above make it possible
to obtain moulds which are wholly transparent to UV
rays. Figure 2 also indicates, diagrammatically in that
it is known, a localized source of UV rays through the
number 6. It is however advantageous to use one or more
sources 6 of UV rays which are distributed over and
face the entire periphery of mould 2 to generate
uniform irradiation of all the material which has to be
formed and polymerized.
In another embodiment, illustrated in Figure 6, mould 2
is made of two half-moulds 7 which are transparent to
UV rays and identical to each other in such a way that
they can be placed together accurately obtaining a
wholly transparent mould 2. As may be seen from Figure
7, in order to make the two half-moulds 7 two identical
containers 1 are required, each of which has internally
a chamber 3 defining a first hemicylindrical surface 8a
which is substantially a negative of an outer
hemicylindrical surface 7a of half-mould 7 being
manufactured, a second hemicylindrical surface 8b which
is substantially a negative of an inner hemicylindrical
surface 7b of half-mould 7 and two flat closure
surfaces 8b in the form of negatives of two flat
contact surfaces 7c in each half-mould 7 to allow the
two half-moulds 7 to be mated together. Advantageously
in this case it is not necessary to attach inserts 5
within chamber 3.
It is however possible to use a single container to
consecutively make the two half-moulds 7.
In accordance with embodiments not illustrated here the
process described can be extended to the manufacture of
wholly transparent moulds 2 also comprising more than
two transparent portions 2a joined together.

As described in the following two embodiments it is
also possible to manufacture a mould 2 comprising a
portion 2a transparent to UV rays made using the sol-
gel process described and a portion 9 which is not
transparent to UV rays. This portion 9 which is not
transparent to UV rays may be manufactured using
conventional materials, for example metal, and may also
be machined using machine tools. Advantageously,
furthermore, a surface 9a of this non-transparent
portion 9 facing the product which has to be shaped and
polymerized may be coated with a reflecting material 10
for reasons which will be specified below.
Figure 8 illustrates a particular embodiment comprising
a half-mould transparent to UV rays (corresponding to
previously mentioned transparent portion 2a) and a
half-mould 9 which is not transparent to UV rays. The
two half-moulds define cavity 4 for passage of the
material being shaped and polymerized. In this
configuration the UV rays originate from one or more
sources 6 of UV rays facing the transparent half-mould
and are directed towards the interior of mould 2, in
particular towards cavity 4.
In a further embodiment illustrated in Figure 9, an
inner surface 9a of non-transparent half-mould 9 facing
cavity 4 and therefore, in the working condition, the
product being shaped and polymerized, is coated with a
reflecting material 10, for example a film of aluminium
10. This makes it possible to reflect any UV rays which
are otherwise dispersed towards the product and
therefore increase the polymerizing efficiency of mould
2.
It is also possible to use moulds 2 obtained as
described above in accordance with the process of
manufacture to carry out processes having industrial
applications in which it is convenient to polymerize
the working material through UV rays.

introduced into mould 2 by exerting a pulling force in
a direction of progress.
In mould 2 the fibres converge and are coated by the
coating layers if these are present, giving rise to a
composite material. These may also be provided for
subsequent compacting of the fibres. In addition to
this means may also subsequently be used to shape or
dimension the compacted composite material.
A non-restrictive embodiment of an extrusion process
comprises the following stages:
- preparing a material which has to be extruded,
providing a mould 2 which is at least partly
transparent to UV rays using the process previously
described, having a through cavity 4 shaped to
plastically deform the material being extruded,
- the provision of thrust means to force the material
being extruded to pass through mould 2,
- application of a thrust in the direction of the mould
to the material being extruded,
- forcing the material being extruded to pass through
mould 2 imposing plastic deformation on the material
being extruded during its passage through mould 2,
polymerizing the material through UV rays as it
passes through the mould.
Similarly to the pultrusion process, in an extrusion
process a mould 2 which is at least partly transparent
to UV rays manufactured as described previously is
provided.
The material being extruded preferably belongs to the
group comprising materials based on silicone and there
is provision for the addition of a catalyst, for
example a thermohardening catalyst, to polymerize the
material being moulded when it is exposed to UV rays.
The material which is to be extruded is also preferably

present in a semi-liquid state or in any event has
sufficient malleability to be plastically deformed.
Thrust means to force the material being extruded to
pass through mould 2 are also provided. In this respect
the mould must have a through cavity 4 shaped to
plastically deform the material being extruded.
The thrust means may be provided by means of pistons or
rotary screws.
A thrust in the direction of mould 2 is therefore
applied to the material being extruded by the thrust
means, forcing it to pass through mould 2 and imposing
plastic deformation upon it.
While the material being extruded passes through mould
2 it is exposed to UV rays which activate its
polymerization.
A non-restrictive embodiment of a moulding process
comprises the following stages:
preparing a material which is to be moulded,
providing through the process previously described two
half-moulds which can be joined together, of which at
least one is transparent to UV rays, internally
defining a cavity 4 which can be wholly exposed to UV
rays,
- joining the two half-moulds,
- inserting the material which has to be moulded within
cavity 4,
- polymerizing the material through UV rays while it is
within cavity 4.
Similarly to the pultrusion and extrusion processes, in
a moulding process a mould which is at least partly
transparent to UV rays manufactured in accordance with
what has been described previously is provided. The
mould is constructed as at least two portions which can

be joined together, of which at least one is
transparent to UV rays, and defines within it a cavity
4 which can be wholly exposed to UV rays.
The material which has to be moulded preferably belongs
to the group of materials based on silicone and rubbers
and provision is made for the addition of a catalyst,
for example a thermohardening catalyst, to polymerize
the material being moulded when exposed to UV rays. The
material being moulded is also preferably present in a
semi-liquid state or in any event has sufficient
malleability to be forced to fill the cavity present
within the mould.
The process provides for insertion of the material to
be moulded within cavity 4. This takes place preferably
through at least one hole made in at least one portion
of the mould through which it is injected under
pressure within cavity 4. The material being moulded is
then forced to match the shape of cavity 4.
Once injection has taken place it is then possible to
polymerize the material by exposing it to UV rays while
it is still in cavity 4.
Obviously the mould used may be used for the injection
moulding of thermohardening materials.
In addition to this the technology mentioned above also
makes possible the compression moulding of
thermohardening material.
It should also be noted that inserts, for example of
metal, but advantageously also of quartz, may be
positioned within the mould in order to be able to
obtain hollow pieces.
This invention provides major advantages.

First of all the use of moulds which are transparent to
UV rays makes it possible to polymerize the material
being formed by UV rays while it still lies in the
mould and this appreciably reduces processing times, in
particular because of the possibility of using UV rays
whose polymerizing action is appreciably faster than in
the case where heated moulds are used. This has the
advantageous effect of substantially increasing the
productivity of production plants such as, as in the
examples mentioned, pultrusion, extrusion and moulding
plants.
In addition to this, the material which has to be
shaped and polymerized may be advantageously exposed to
UV rays while it is in movement within the mould, thus
bringing about the advantage of regularizing production
and further increasing productivity.
A further advantage is provided by reducing the
production costs of the moulds, in that the sol-gel
process for the manufacture of moulds transparent to UV
provides as a result moulds having a surface which is
defined with high accuracy and which does not require
any further machining by machine tools. Economic
advantage also lies in the fact that the substantial
increase in productivity also has a positive effect in
a tangible reduction in costs per unit product, in
particular fixed costs, including the costs of making
the moulds.
These moulds are subject to shrinkage during the stages
of gelling, drying and sintering, but the amount of
such reduction in size is considered in advance by
suitably increasing the initial dimensions of the chamber which contains the sol. The final effect is
therefore that of obtaining moulds with high
dimensional accuracy and high transparency and
sharpness .

First of all the use of moulds which are transparent to
UV rays makes it possible to polymerize the material
being formed by UV rays while it still lies in the
mould and this appreciably reduces processing times, in
particular because of the possibility of using UV rays
whose polymerizing action is appreciably faster than in
the case where heated moulds are used. This has the
advantageous effect of substantially increasing the
productivity of production plants such as, as in the
examples mentioned, pultrusion, extrusion and moulding
plants.
In addition to this, the material which has to be
shaped and polymerized may be advantageously exposed to
UV rays while it is in movement within the mould, thus
bringing about the advantage of regularizing production
and further increasing productivity.
A further advantage is provided by reducing the
production costs of the moulds, in that the sol-gel
process for the manufacture of moulds transparent to UV
provides as a result moulds having a surface which is
defined with high accuracy and which does not require
any further machining by machine tools. Economic
advantage also lies in the fact that the substantial
increase in productivity also has a positive effect in
a tangible reduction in costs per unit product, in
particular fixed costs, including the costs of making
the moulds.
These moulds are subject to shrinkage during the stages
of gelling, drying and sintering, but the amount of
such reduction in size is considered in advance by
suitably increasing the initial dimensions of the chamber which contains the sol. The final effect is
therefore that of obtaining moulds with high
dimensional accuracy and high transparency and
sharpness.

WE CLAIM:
1. Sol-gel process for the manufacture of a mould having at least one portion transparent to
UV rays, comprising the following stages:
a) providing a container which is a negative of the said at least one portion
transparent to UV of the mould which is to be manufactured and internally
defining a chamber, the said chamber having at least one first surface which is
substantially the negative of a corresponding outer surface of the said at least one
transparent portion of the mould being manufactured, and at least one second
surface which is substantially a negative of at least one corresponding inner
surface of the said at least one transparent portion of the mould being
manufactured, wherein the container comprises at least one insert defining the
said at least one second surface of the chamber.
b) filling the chamber with a sol,
c) gelling the sol, obtaining a gel, wherein the gelling step c) comprises a step of
extracting the said at least one insert at a predetermined time during the gelling
of the sol to prevent the formation of cracks in the gel that is forming,
d) heating the gel and a corresponding solvent for a programmed period of time
consequently achieving predetermined temperature and pressure values, and
evaporating the said solvent, the said heating giving rise to drying of the gel,
e) densifying or sintering the gel which is dry through heating to a predetermined
temperature, with the consequent formation of the said transparent portion of the
mould, with a vitreous consistency and transparent to at least UV rays, the said
mould being suitable for the formation of pultrusion or extrusion products or the
moulding of plastics materials through a process of photocatalytic synthesis.
2. Process as claimed in claim 1, wherein the outer surface of the said at least one
transparent portion of the mould being manufactured faces the external environment in
the operating condition of the mould and allows UV rays to pass towards the interior,
while the inner surface of the said at least one transparent portion of the mould is in the
operating condition in contact with the product being formed and polymerized.

3. Process as claimed in claim 1, wherein the said at least one insert is incompressible.
4. Process as claimed in claim 1, wherein the said at least one insert is cylindrical.
5. Process as claimed in claim 1, wherein the container is caused to rotate to assist
extraction of the said at least one insert making use of the centrifugal forces acting on
the gel that is forming.
6. Process as claimed in claim 1, wherein the container is caused to rotate axially so that,
under the effect of the centrifugal force, the sol adopts the shape of the container
bounded externally by the inner surface of the container and internally by an
equipotential surface at right angles to a force field of the centrifugal force.
7. Process as claimed in claim 1, wherein the container comprises a plurality of inserts.
8. Process as claimed in claim 1, wherein stage b) is preceded by the following stages:

• preparing an aqueous or water/alcohol suspension containing at least one metal
alkoxide;
• effecting hydrolysis of the above suspension, obtaining the sol.

9. Process as claimed in claim 1, wherein a phase c') in which the solvent is replaced with
an aprotic solvent is included between stage c) and stage d).
10. Process as claimed in claim 9, wherein a stage c") in which the gel is placed in an
autoclave and subjected to a flow of inert gas is included between stage c') and stage d).
11. Process as claimed in claim 10, wherein a stage d') of depressurization of the autoclave
with a consequent escape of vapours, with optional recovery of the said vapours, is
included between stage d) and stage e).

12. Process as claimed in claim 11, wherein a stage d") which consists of flowing an inert
gas through the autoclave containing the gel is included between stage d') and stage e).
13. Process as claimed in claim 12, wherein a stage d'") which comprises cooling dried gel
and removing it from the autoclave is included between stage d") and stage e).
14. Process as claimed in claim 9, wherein the aprotic solvent used in stage c') is selected
from the group consisting of acetone, dioxan and hydrofuran.
15. Process as claimed in claim 1, wherein during stage a) said at least one insert is
positioned and attached within the chamber.
16. Process as claimed in claim 1, wherein the mould is wholly transparent to UV rays.
17. Process as claimed in claim 1, wherein the mould comprises a portion which is
transparent to at least UV rays and a second portion which is not transparent to UV rays.
18. Process as claimed in claim 17, wherein the mould comprises a half-mould which is
transparent to at least UV rays and a second half-mould which is not transparent to UV
rays.
19. Process as claimed in claim 17, wherein a surface of the said second portion which is not
transparent to UV rays, facing the product being formed, is coated with a reflecting
material.
20. Process as claimed in claim 19, wherein the reflecting material is an aluminium film.
21. Process as claimed in claim 1, wherein the temperature and pressure of heating in stage
d) is at values higher than the critical values for the solvent present in the gel.

22. Pultrusion process, comprising the following stages:
• preparing continuous fibres;
• providing a mould which is transparent to UV rays by using the procedure as claimed
in claim 1, the said mould having a through cavity shaped to plastically deform the
said continuous fibres;
• impregnating the said continuous fibres with a suitable resin;
• causing the said continuous fibres so impregnated to pass through the mould, and
• polymerizing the said continuous fibres through UV rays as they pass through the
mould.

23. Extrusion process, comprising the following stages:
• preparing a material for extrusion;
• providing a mould which is transparent to at least UV rays by using the process according to
claim 1, the said mould having a through cavity shaped to plastically deform the material
being extruded;
• providing thrust means to force the material being extruded to pass through the mould;
• applying of a thrust in the direction of the mould to the material being extruded;
• forcing the material being extruded to pass through the mould imposing plastic deformation
on the material being extruded as it passes through the mould, and
• polymerizing the material by exposing it to UV rays as it passes through the mould.
24. Extrusion process as claimed in claim 23, in which the material being extruded belongs
to the group comprising materials based on silicone and rubber.
25. Extrusion process as claimed in claim 23, in which a catalyst is added to the material
being extruded to polymerize the material being extruded when it is exposed to UV rays.

26. Moulding process, comprising the following stages:
• preparing a material for moulding;
• providing a mould comprising at least two mating portions of which at least one is
transparent to UV rays by using the process as claimed in claim 1, the said mould defining
internally a cavity which can be wholly exposed to UV rays;
• joining the said at least two mating portions of the mould;
• inserting the material to be moulded within the cavity, and
• polymerizing the material by exposing it to UV rays while it is within the cavity.

27. Moulding process as claimed in claim 26, wherein the material being moulded belongs
to the group comprising materials based on silicone and rubber, or thermohardening
materials.
28. Moulding process as claimed in claim 26, wherein a catalyst is added to the material
being moulded to polymerize the material being moulded when it is exposed to UV rays.
29. Moulding process as claimed in claim 26, wherein it comprises injection or compression
moulding.

ABSTRACT

Title: Sol-gel process for the manufacture of a mould.
Sol-gel process for the manufacture of a mould having at least one portion transparent to UV rays,
comprising the following stages: providing a container which is a negative of the said at least one
portion transparent to UV of the mould which is to be manufactured and internally defining a
chamber, the said chamber having at least one first surface which is substantially the negative of a
corresponding outer surface of the said at least one transparent portion of the mould being
manufactured, and at least one second surface which is substantially a negative of at least one
corresponding inner surface of the said at least one transparent portion of the mould being
manufactured, wherein the container comprises at least one insert defining the said at least one
second surface of the chamber, filling the chamber with a sol, gelling the sol, obtaining a gel,
wherein the gelling step c) comprises a step of extracting the said at least one insert at a
predetermined time during the gelling of the sol to prevent the formation of cracks in the gel that is
forming, heating the gel and a corresponding solvent for a programmed period of time consequently
achieving predetermined temperature and pressure values, and evaporating the said solvent, the said
heating giving rise to drying of the gel, densifying or sintering the gel which is dry through heating
to a predetermined temperature, with the consequent formation of the said transparent portion of the
mould, with a vitreous consistency and transparent to at least UV rays, the said mould being
suitable for the formation of pultrusion or extrusion products or the moulding of plastics materials
through a process of photocatalytic synthesis.

SOL-CEL PROCESS FOR THE MANUFACTURE OF A MOULD

Documents:

Inventors:

PCT Conventions: