Title of Invention	"METHOD FOR PRODUCING A SCREEN PRINTING STENCIL"
Abstract	A method for producing a screen printing stencil, in particular for printing textiles, in which a support (1) coated on its outer surface with a lacquer layer (L) is exposed to a laser beam (S) in order to introduce a desired pattern into said lacquer layer, is distinguished by the fact that the radiation wavelength of the laser beam (S) is greater than 450 nm.

Full Text

Description The invention relates to a method for producing a screen printing stencil, Such a method has already been disclosed in EP 0593806BI.. Here, for producing a screen printing stencil, in particular for printing textiles, a support coated on its outer surface with a lacquer layer is exposed to a laser beam in order to introduce a desired pattern into the lacquer layer. It is the object of the invention to develop the method of the type stated at the outset so that it can be carried out economically. The achievement of the object is stated in the characterizing clause of Patent Claim 1. Advantageous embodiments of the invention are described in the subclaims. A process according to the invention for producing a screen printing stencil is distinguished by the fact that the radiation wavelength of the laser beam is greater than 450 nm. There are already a number of lasers which emit in the longer wavelength radiation range and have a comparatively high radiant power. Such lasers can be produced more cheaply than the shorter wavelength radiation range with approximately the same beam output power, so that the cost of producing screen printing stencils can be reduced by their use. Owing to their higher beam output power, it is also possible to use less sensitive lacquer layers, which further increases the cost-efficiency of the production method. Furthermore, at higher beam output power, comparatively thicker lacquer layers or thicker multilayer systems can be used if this should be required for strength or adhesion reasons or for increasing the sensitivity, so that the method according to the invention leads to further advantages in this respect too. The radiation wavelength of the laser beam is above 450 nm, preferably in the visible spectral range, since lasers operating in this spectral range are particularly economically available on the market and furthermore the sensitivity of the lacquer layer can be relatively easily adjusted. The radiation wavelength of the laser beam can, however, also be in the infrared spectral range, since here too economical lasers are available and the sensitivity adjustment of the lacquer layer is possible in a corresponding manner. In principle, it is possible directly to remove or burn off the lacquer layer or a layer system consisting of several lacquer layers one on top of the other by means of the laser beam, or only to expose and thus crosslink said layer or system by means of the laser beam if the lacquer is a crosslinkable or polymerizable material. In the last-mentioned case, this procedure is followed by a development step in order to wash out the unexposed lacquer layers. In the case of polymerization by laser radiation, the procedure can preferably be carried out at a radiation wavelength of about 488 nm and at an optical radiant power of 150 mW, in order to obtain optimum exposure results. An acousto-optical modulator is an economical means for switching the laser beam on and off, the use of which modulator makes the method according to the invention more commercially favourable. The on/off frequency of the laser beam is preferably in the range from 1.0 to 1.3 MHz, which can be realized by an acousto-optical modulator, so that sufficiently crisp contours of the pattern to be introduced into the lacquer layer can also be obtained. Of course, it would also be possible to use an electro-optical modulator instead of the acousto-optical modulator. In principle, the support used may be a flat or cylindrical support. Said supports may be perforated supports or those having a closed wall surface. In the last-mentioned case, the introduction of the pattern in the lacquer layer and the development step are followed by a further step in which the bared parts of the lacquer layer are filled with metal in order to form a screen printing stencil, which is then removed from the support. Several possibilities are available for applying the lacquer layer. Thus, the lacquer for forming the lacquer layer can be sprayed on by a nozzle means. This also applies to a layer system consisting of several layers, a drying process being carried out after the application of each layer. Spraying on the lacquer can be carried out in the case of both flat and cylindrical supports. In the case of cylindrical supports, the lacquer layer can also be applied by means of a ring coater. For this purpose, the cylindrical support is set up vertically and the ring coater surrounding it is moved along its vertical axis. If the support is a support having a closed wall surface, it is preferable to use an immersion ring coater, which is moved from top to bottom to apply the lacquer layer. In the case of a cylindrical support which is already perforated, the ring coater can be moved either from top to bottom or from bottom to top in order to apply the lacquer. By repeating the stated processes and carrying out a drying step in each case, it is thus also possible to form several lacquer layers one on top of the other, if this is required. To form the lacquer layer, it is possible, for example, to apply a lacquer which has at least one negative liquid resist with at least one photoinitiator present therein. This lacquer layer is crosslinkable or curable by laser radiation, and its sensitivity to radiation can be adjusted by means of the photoinitiator used in each case. Thus, different photoinitiators are used for the visible spectral range and the infrared spectral range, for example a metallocene or a metallocene-containing mixture for the visible spectral range. The lacquer may contain a thinner which can be readily evaporated off, in order to obtain a viscosity suitable for application of the lacquer layer. Instead or in addition, however, it may also contain a monomer which causes the lacquer in the initial state to be less viscous or solid. This monomer is used instead of a solvent and is subsequently incorporated into the chains of the lacquer or resin system, leading to more rapid curing of the lacquer. In a further embodiment of the invention, the lacquer may furthermore contain a dye whose colour is preferably complementary to the colour corresponding to the radiation wavelength, which leads to better radiation absorption and higher crosslinking efficiency. The dye may be, for example, Zapon red. In a further embodiment of the invention, a further organic lacquer layer which essentially protects the photoinitiator-containing lacquer layer against the effects of oxygen may be applied to the lacquer layer before the latter is irradiated. By means of this further organic lacquer layer, the sensitivity of the lacquer layer underneath or its polymerizability can thus be considerably increased. The further organic lacquer layer may be, for example, a gelatine layer or a layer which contains at least one thermoplastic dissolved in water. This may be a polyvinyl alcohol which may additionally contain a fatty alcohol polyglycol ether, resulting in a further increase in the sensitivity of the polymerizable lacquer layer underneath. The use of demineralized water furthermore prevents opacity of the further lacquer layer, so that no reduction in the sensitivity of the total layer system can occur. Accordingly, the present invention relates to a method for producing a screen printing stencil, in particular for printing textiles, in which a support coated on its outer surface with a lacquer layer is exposed to a laser beam in order to introduce a desired pattern into said lacquer layer, the radiation wavelength of the laser beam is greater than 4 50 nm, characterised in that the on/off frequency of the laser beam is in the range from 1.0 to 1.3 MHZ. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Embodiments of the invention are described in more detail below with reference to the accompanying drawings. Fig.l. shows a process step for coating a hollow cylindrical support with a photosensitive lacquer layer; Fig.2. shows a corresponding process step in which the photosensitive lacquer layer is sprayed onto the hollow cylindrical support; Fig. 3 shows an exposure apparatus for exposing the photosensitive lacquer layer; Fig. 4 shows a side view of the exposure apparatus according to Fig. 3; Fig. 5 shows a further exposure apparatus for exposing the photosensitive lacquer layer; Fig. 6 shows a side view of the further exposure apparatus according to Fig. 5 and Fig. 7 shows a process step for developing the photosensitive lacquer layer. Fig. 1 shows a hollow cylindrical support which is coated with a liquid photopolymer using an immersion ring coater 2. Here, the hollow cylindrical support 1 consists of metal and has a closed lateral surface. The liquid photopolymer is present in an annular trough 3 and cannot flow out of the trough 3, owing to a rubber lip 4 providing a seal against the support 1. The rubber lip 4 is held between an upper part 5 of the ring coater and a lower part 6 of the ring coater. The photopolymer has approximately the viscosity of a viscous engine oil and, as a result of an upward movement of the ring coater 2, can be applied to the outer surface of the support 1. If, in contrast, the hollow cylindrical support 1 consists of a circular sieve, the photopolymer cannot flow through the circular sieve 1 into its interior during the downward movement of the ring coater 2. The reason for this is that the static pressure applied to the viscous photopolymer corresponds only to the height of the liquid in the trough 3 of the ring coater 2 and is therefore very small. Furthermore, this static pressure acts on a longitudinal section of the circular sieve 1 only for a very short time, that is to say for the time required by the ring coater 2 at its downward speed to pass through the height of the liquid level in the trough 3. The circular sieve 1 has such a narrow mesh or has such small holes that the small static pressure is sufficient to force the polymer into the holes and fill them within the available time, but said pressure is not sufficient to exert excessive pressure on, and thus to tear, the liquid membrane forming against the interior of the circular sieve 1 in each small capillary hole. Emergence of photopolymer in the interior of the circular sieve 1 is thus substantially impossible, even when the speed of lowering of the ring coater 2 is reduced. Both in the case of the hollow cylinder having a closed wall surface and in the case of the circular sieve, the speed of lowering of the ring coater 2 is chosen so that the polymer layer L remaining on the circular sieve 1 has the desired thickness. The thickness of the photopolymer layer is larger if the ring coater 2 is lowered rapidly, whereas the thickness is smaller the slower the downward movement of the ring coater 2. This is understandable if it is considered that the photopolymer is a solution of (photosensitive) resins in a solvent which can be readily evaporated. The circular sieve 1 withdrawn from the trough 3 entrains a correspondingly thick liquid film with it. The innermost layer of this liquid film adheres to the circular sieve 1, while the outer layers of the liquid film flow back downwards into the trough 3 under their weight. The outermost layers flow back the most rapidly. During this process, the solvent evaporates off. The thinner the liquid layer has become, the greater are the specific solvent losses of the remaining layer and hence its increase in viscosity, since the amount of solvent evaporating off per unit time depends only on the ambient temperature and the surface area and therefore remains essentially constant. Finally, a viscosity is reached which is so high that the speed of the outermost layers flowing away downwards corresponds to the speed of lowering and hence the photopolymer can no longer reach the trough 3. This coating process therefore gives uniform thicknesses of the photopolymer layer even when the support does not have an exactly cylindrical surface but is, for example, slightly dented. If the cylindrical support 1 is in the form of a circular sieve, the ring coater 2 could also be moved from bottom to top. In this case, it would be expedient to replace the rubber lip 4 by an 0 ring which fits tightly against the circular sieve and by means of which at least some of the photopolymer is also forced into the sieve openings. However, regardless of whether it has a closed or perforated wall surface, the hollow cylindrical support 1 can alternatively also be coated by means of an atom izer nozzle 8 if it is rotated according to Fig. 2 in the direction of the arrow 7, i.e. about its longitudinal axis 9. The atomizer nozzle 8 is moved in the direction of the longitudinal axis 9 of the support 1. The photopolymer which is present in a cup 10 above the atomizer nozzle 8 is sucked out of the cup 10 by an injector-like apparatus in the interior of the atomizer nozzle 8 and is ejected, together with the compressed air which operates the injector and is supplied through a hose 11, through a mouthpiece 12 of the atomizer nozzle 8 and is atomized there in a manner known per se. This is achieved, for example, by an air jet which is under more than 2 bar gauge pressure and in which intensive ultrasonic waves occur, by means of which the photopolymer is broken up into very small liquid particles. Owing to the rotary movement of the support 1 and the simultaneous feed movement of the atomizer nozzle 8 in the axial direction of the support 1, the photopolymer mist is uniformly distributed over the surface of the support 1. The liquid photopolymer or lacquer used may be an acrylic resin or an acrylate resin. This is based on a mixture of monomeric and polymeric acrylates and/or methacrylates. The monomer of the acrylic acid or of the acrylate has the following structural formula: (Formula Removed) The radical R may be H, CH3, CH2-CH3 or CH2 -CH2 - CH2 -CH3. In these cases, the monomer is then referred to as acrylic acid, methyl acrylate, ethyl acrylate or butyl acrylate, respectively. After the polymerization, a long-chain polymer of the following form results. (Formula Removed) The polymers are then accordingly called: poly-acrylic acid, polymethyl acrylate, polyethyl acrylate or polybutyl acrylate. On the other hand, methacrylic acid and meth-acrylates have the following structural composition: (Formula Removed) The radical R may be H, CH3, CH2-CH3, CH2-CH2-CH3 or CH(CH3)-CH3. Depending on the radical R, the compound is then referred to as methacrylic acid, methvl methacrylate, ethyl methacrylate, propyl methacrylate or isopropyl methacrylate. Accordingly, the polymerization gives compounds of the formula: (FormulaRemoved) These are now polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate and polyisopropyl methacrylate. The mixture of monomeric and polymeric acrylic and methacrylic acid or monomeric and polymeric acrylates and methacrylates, mentioned at the outset, may also contain ethyl alcohol. This is practical if the viscosity is already too high for processing, owing to a relatively high content of relatively long chains. A relatively large part of the lacquer or resist is then already present as polymer. In this case, however, a further accelerator may be added to improve the reactivity or polymerizability, for example a diacrylate, such as an ethylene glycol dimethacrylate, which has the following structural composition: (FormulaRemoved) The following monomers may also be added to the resin mixtures described above: styrene, a-methylstyrene, vinyltoluene, 2-chlorostyrene, 2,5-dichlorostyrene, vinylpyridine, tert-butyl acrylate, methyl methacrylate, divinylbenzene. All these monomers initially ensure an improved viscosity of the resins in the initial state and can theref ore replace some of the solvent, said monomers being firmly incorporated in the resin skeleton during the polymerization, thus accelerating the curing process. Epoxy resins or aminoplasts may also be copolymerized with the acrylates described. A metallocene is preferably used as photo-initiator for making the resin layer sensitive to the visible spectral range. For example, the product CGI 784 from Ciba-Geigy may be used here and has the following structural formula: (FormulaRemoved) This is bis(eta 5-2,4-cyclopentadien-l-yl)-bis[2,6-difluoro-3-(lH-pyrrol-1-yl)phenyl]titanium. It may be mixed with other substances if necessary. This photoinitiator is added to the resin in the form of a solution. Possible solvents are: trimethylol-propane triacetate, hexanediol diacrylate, N-vinyl-pyrrolidone, acetone, toluene or methyl ethyl ketone. From 0.3 to 10% by weight, based on the dry resin weight, of photoinitiator are used. This is the resin weight without the non-copolymerizing solvent (e.g. ethanol). Such a photoresist has a high sensitivity at a radiation wavelength of, for example, X = 488 nm, good polymerization results being achieved on exposure to a laser whose beam output power is 150 mW. A specific example of a lacquer composition is described below. All work for the preparation of the lacquer would have to be carried out in red light, a) Composition: 1750.0 g of NL 143 No. 5011, photoresist from Morton Electronic Materials; 70.0 g of photoinitiator solution according to formulation b) ; 17.5 g of red dye No. 171294 from Manoukian; 700.0 g of ethyl acetate p.a. from Riedel-de-Haen. b) Working up the photoinitiator CGI 7 84 IP from Ciba- Geigy: Since carrier material is added to the photoinitiator for safety reasons, the CGI 784 IP must be separated therefrom by extraction. An appropriate amount of photoinitiator is mixed with three times the amount of methyl ethyl ketone p.a. (MEK) and stirred for one hour at room temperature (by means of a magnetic stirrer). Thereafter, filtration is effected through a slot-type suction filter and rinsing with MEK is carried out until the yellow colour disappears. The filtrate is transferred to a tapered flask and evaporated down by means of a Rotavapor at 3 5°C. The highly viscous (almost solvent-free) residue is dissolved in the appropriate amount of ethyl acetate (by means of Rotavapor at 35°C) and stored in a tightly closed opaque vessel. The concentration of the prepared photoinitiator is 200 mg of CGI 784 IP/g of solution. c) Mixing of the lacquer: The ethyl acetate p.a. is initially taken and the photoinitiator solution is added (any initiator which has crystallized thus goes into solution) and stirring is carried out, after which the red dye and then the NL 143 are introduced and thoroughly stirred. The prepared lacquer is filtered through a slot-type suction filter and then stored in a tightly closed opaque vessel. After the lacquer thus prepared has been applied to the hollow cylindrical support 1 by means of the ring coater or immersion ring coater 2, the photosensitive lacquer layer is dried as completely as possible, i.e. the solvent which had to be introduced into the photopolymer for process engineering reasons is evaporated off. For this purpose, the stencils which were already air-dried during the coating process are further dried in a warm-air oven so that no solvent residues remain in the layer. At the same time, important properties are introduced or at least influenced by this drying. The adhesion of the photosensitive lacquer layer to the metallic surface of the support is improved by relatively high temperatures, whereas at the same time the optical resolving power is reduced. The drying is therefore carried out at temperatures between 2 0°C and 85°C and must be effected very carefully with respect to time and temperature in order uniformly to obtain the stated properties. In the case of lacquer layers which require a monomer for better or more rapid crosslinking, it should be noted that said monomer may evaporate off only to a small extent, if at all, during the drying process. In this case, the photopolymer will of course remain liquid, resulting in a tacky surface of the lacquer layer. However, the viscosity of this layer, established by evaporation of the thinner, is very high and, moreover, the layer can be rendered thixotropic in its rheological properties by suitable additives or fillers, so that the still uncrosslinked polymer layer cannot flow away. Depending on the characteristics of the polymer layer or lacquer layer L, the drying can either be carried out in such a way that the hollow cylindrical support 1 is placed in the drying oven, i.e. the axis 9 of the support 1 is vertical, or, in the case of relatively low viscosity of the lacquer layer, the support 1 is pushed onto horizontal spindles and the latter are optionally even caused to rotate, so that the polymer layer is prevented from flowing away at the beginning of the drying process. After the photopolymer layer has been applied to the surface of the cylindrical support 1, said layer is covered with a further organic lacquer layer L1, this being effected by means of dip coating. The immersion ring coater (rubber doctor blade) already mentioned can once again be used for this purpose. For example, the further organic lacquer layer L1 may be a gelatine layer or a layer which contains at least one thermoplastic dissolved in water. The thermoplastic may be a polyvinyl alcohol which may additionally contain a fatty alcohol polyglycol ether. An example of such a further organic lacquer layer is given below. This is a 5% strength PVA solution containing 0.1% of Genapol T250. More precisely, the solution contains 100 g of polyvinyl alcohol, Article No. 318 from Riedel-de-Haen, 2 g of Genapol T250 from Hoechst and 1898 g of demineralized water. The Genapol T250 is a fatty alcohol polyglycol ether. For the preparation, first 1600 g of demineralized water are heated to the boil and 100 g of PVA are added while stirring. After the PVA (polyvinyl alcohol) has dissolved, 2 g of Genapol T250 are added and stirring is carried out until a transparent solution is obtained. Thereafter, the solution is made up to 2000 g with demineralized water, cooled and filtered through a slot-type suction filter. The solution is initially stored in a tightly closable vessel. It can then be transferred to the ring coater in order appropriately to coat the photopolymer layer L already present on the hollow cylindrical support 1. A further drying process is then carried out for up to not more than one hour at about 6 0°C or lower, as already described above. The following process step involving exposure with the aid of a laser is described with reference to Fig. 3 to 6. By means of this laser, the photopolymer layer to be cross linked is exposed in a punctiform fashion at the points to be crosslinked in accordance with the pattern and is thus solidified. These points subsequently remain after the development of the photopolymer layer. A cylinder 13, which is understood as meaning the support 1 coated with the photopolymer, is placed between a chuck 15 and a tail stock 16 in a rotary exposure apparatus 14. By closing the chuck 15, a shaft encoder 17 is nonrotatably connected to the cylinder 13. Said encoder Is arranged on the right side of a spindle head 18 of the rotary exposure apparatus 14. The rotary drive of the cylinder 13 and of the apparatus parts connected to this is effected by means of a main drive motor 19 via a V-belt drive 20 with vibration damping. While the cylinder 13 rotates, an optics cradle 21 is moved along guides 22 with the aid of a feed spindle 23 and a stepping motor 24 coupled to said feed spindle. A torsional vibration damper 24 is mounted at the right shaft end of the stepping motor 24. The guides 22 and the feed spindle 23 are mounted on a guide bed 2 6 or machine bed of the rotary exposure apparatus 14. Fig. 3 and 4 show a laser 27 which is carried by the optics cradle 21 and whose laser beam S is deflected by a deflecting mirror 28 from the originally vertical direction to a horizontal direction, so that it is then focused via an optical system 29 radially onto the surface of the cylinder 13. Guide elements (rollers, sliding guides) can be provided for stabilizing the stencil wall in the radial and tangential direction, but this is of course possible only in the case of those photopolymers which already have a dry, i.e. solid, surface in the uncrosslinked state. Fig. 5 and 6 show a stationary laser 27 which is mounted on the tailstock end of the rotary exposure apparatus 14 by means of a bracket 30. For the purpose of the punctiform exposure of the surface of the cylinder 13 at the focal point of the optical system 29, the laser radiation is switched on or off, for example by means of an acousto-optical modulator. For the purposes required here, quartz glass is preferably used as the interaction or switching medium since it is transparent to light in the wavelength range under discussion and also has a sufficiently high sound velocity, which is required for sufficiently rapid switching through of the modulator. Although the first-order beam, that is to say the beam reflected at the compaction zones in the interaction medium, is most expediently used because this makes it possible to achieve a 0:100 pulse duty factor of the radiant power, it is however also entirely possible to use the zero-order beam for the surface exposure of the cylinder 13 and to accept the resulting partial preliminary cross-linking in the parts which remain uncrosslinked. The development process for the photopolymers, which essentially consists in dissolving away the uncrosslinked polymers from the surface film, is also quite capable of dissolving away partially crosslinked parts. In the present case, the laser 27 is an argon ion laser whose radiation wavelength is 488 nm and which has an optical radiant power of 150 mW. By means of the acousto-optical modulator, it is possible to produce on and off frequencies for the laser beam S which are in the range between 1 MHz and 1.3 MHz. The diameter of the focal spot after focusing may be, for example, 20 µm. However, it may also be larger for producing other pattern structures. If it is intended, for example, to produce hexagons having a width across flats of 33 0 µm, the resulting diameter of the focal spot could be, for example, 45 µm. In a further process step, the uppermost or further organic layer L1 (PVA layer) present on the hollow cylindrical support 1 is now washed away. For this purpose, the cylinder 13 is rinsed with water at room temperature. This is followed by the development of the photoresist layer L. For this purpose, the cylinder is immersed in a developer medium which is present in a trough 31, and the parts not crosslinked by the action of light are dissolved away from the photopolymer layer L present on the hollow cylinder. The developer liquid may expediently consist of an alkaline solution. This may be, for example, a 1% strength sodium carbonate solution, in which development is effected for about 1.5 minutes. To support the development process, unused developer solution can be applied from a spray 32 onto the surface of the cylinder 13. During the development process, the cylinder 13 revolves in the direction indicated by the arrow 33. The cylinder 13 is then again rinsed with water, this being effected until the foaming disappears. The cylinder 13 developed in this manner is then dried at about 60°C or less for not more than one hour, preferably 15 minutes. If the hollow cylindrical support is a prefabricated sieve, the screen printing stencil is now complete. However, if the hollow cylindrical support 1 is one having a closed wall surface, a galvanization process is subsequently carried out in order to introduce metal into the gaps formed in the lacquer as a result of the development. This results in a screen printing stencil on the surface of the hollow cylinder 1 according to the pattern of the lacquer layer L, said stencil subsequently being removed from the hollow cylinder 1. WE CLAIM: 1. Method for producing a screen printing stencil, in particular for printing textiles, in which a support (1) coated on its outer surface with a lacquer layer (L) is exposed to a laser beam (S) in order to introduce a desired pattern into said lacquer layer, the radiation wavelength of the laser beam (S) is greater than 450 nm, characterised in that the on/off frequency of the laser beam (S) is in the range from 1.0 to 1.3 MHz. 2. Method as claimed in claim 1, wherein the said radiation wavelength of the laser beam (S) is in the visible spectral range. 3. Method as claimed in claim 1, wherein the said radiation wavelength of the laser beam (S) is 488 nm. 4. Method as claimed in claim 1, wherein the said radiation wavelength of the laser beam (S) is in the infrared spectral range. 5. Method as claimed in claims 1 to 4, wherein the optical radiant power of the laser beam (S) is 150 mW. 6. Method as claimed in any one of claims 1 to 5, wherein the said lacquer layer (L) is burnt away by means of the laser beam (S). 7. Method as claimed in any one of claims 1 to 5, wherein the said lacquer layer (L) z's a polymerizable layer which is crosslinked in parts by the incident laser beam (S) and is subsequently developed. 8. Method as claimed in claim 7, wherein the aarfu lacquer which has at least one negative liquid resist with at least one photoinitiator present therein is applied for forming the lacquer layer (L). 9. Method as claimed in claim 8, wherein the said iacquer Contains a thinner which can be readily evaporated off. 10 Method as claimed in claims 8 or 9, wherein the said-lacquer ^contains a dye whose colour is preferably complementary to the colour corresponding to the radiation wavelength. 11. Method as claimed in any one of claims 1 to 10, wherein an another organic lacquer layer (LI) is applied to the lacquer layer (L) before the latter is irradiated. 12. Method as claimed in claim 11, wherein the said organic lacquer layer (LI) is a gelatine layer. 13. Method as claimed in claim 11, wherein the said organic lacquer layer (LI) contains at least one thermoplastic dissolved in water. 14. Method as claimed in claim 13, wherein the said thermoplastic is a polyvinyl alcohol. 15. Method as claimed in claims 13 or 14, wherein the said thermoplastic additionally contains a fatty alcohol polyglycol ether. ^ 16. Method as claimed in claims1 4-3 ^""Pl or—1-wnerein the/water is demineralized. 17. Method as claimed in any of the preceding claims, wherein the said support (1) used is a metallic hollow cylinder having a perforated lateral surface. 18. Method as claimed in any one of the preceding claims, wherein the said support (1) provided is a metallic cylinder which has a closed lateral surface and on which, after removal of the lacquer layer (L) in accordance with the pattern, metal is galvanically applied in order to obtain a screen printing stencil. 19. Method as claimed in claim(M, wherein the said lacquer layer (L) f and/or the another lacquer layer (LI) are applied by means of a ring coater (2) with the hollow cylinder (1) arranged vertically. 20. Method as claimed in claim 6, wnerein the said lacquer layer (L) and/or the another lacquer layer (LI) Jx applied by means of an immersion ring coater (2) which is moved from top to bottom, with the cylinder (1) arranged vertically. 21. Method as claimed in any of the preceding claims, wherein a drying step is carried out immediately after the application of the lacquer layer (L) or of the another lacquer layer (LI) or after the development. 22. Method as claimed in any of the preceding claims, wherein the said contains a monomer. 23. Method for producing a screen printing stencil substantially as herein described with reference to the accompanying drawings.

Documents:

1856-del-1996-abstract.pdf

1856-DEL-1996-Claims.pdf

1856-del-1996-complete specification (granted).pdf

1856-del-1996-correspondence-others.pdf

1856-del-1996-correspondence-po.pdf

1856-del-1996-description (complete).pdf

1856-del-1996-drawings.pdf

1856-DEL-1996-Form-1.pdf

1856-del-1996-form-13.pdf

1856-del-1996-form-2.pdf

1856-DEL-1996-Form-3.pdf

1856-del-1996-form-4.pdf

1856-del-1996-gpa.pdf

1856-del-1996-petition-others.pdf

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