Title of Invention	A METHOD OF CUTTING A GLAZING UNIT AND A GLAZING UNIT THEREOF
Abstract	The invention relates to a method of cutting a glazing unit without applying a breaking force, the glazing unit comprising a glass sheet having two main faces, said method comprising the steps of applying a treatment to the glass sheet that generates stresses such that at least one region in compression and at least one region in extension, the distribution of the stresses being biaxial, isotropic and self balanced in its thickness, the stresses being such that the K factor is between 0.05 and 0.4 Mps.m1/2, said K factor being defined by K = [∫ZỚZ2- H(Ớ2).dz]1/2, in which z is a position in the thickness, Ớ2 is the intensity of the isotropic biaxial stress at the position z, H(Ớ2) is equal to 1 if Ớ2 is greater than 0 and is equal to 0 if Ớ2 is less than or equal to 0, with the convention that extension is denoted by positive values and compression by negative values; and scoring a subcrack deeper than 10 m along the desired line of cutting of the treated glass, the subcrack reaching that region of the glazing in extension.

Title of Invention

A METHOD OF CUTTING A GLAZING UNIT AND A GLAZING UNIT THEREOF

Abstract

The invention relates to a method of cutting a glazing unit without applying a breaking force, the glazing unit comprising a glass sheet having two main faces, said method comprising the steps of applying a treatment to the glass sheet that generates stresses such that at least one region in compression and at least one region in extension, the distribution of the stresses being biaxial, isotropic and self balanced in its thickness, the stresses being such that the K factor is between 0.05 and 0.4 Mps.m1/2, said K factor being defined by K = [∫ZỚZ2- H(Ớ2).dz]1/2, in which z is a position in the thickness, Ớ2 is the intensity of the isotropic biaxial stress at the position z, H(Ớ2) is equal to 1 if Ớ2 is greater than 0 and is equal to 0 if Ớ2 is less than or equal to 0, with the convention that extension is denoted by positive values and compression by negative values; and scoring a subcrack deeper than 10 m along the desired line of cutting of the treated glass, the subcrack reaching that region of the glazing in extension.

Full Text	gLAZING CUT WITHOUT BREAKING -IT- The invention relates to a method of cutting a glazing unit without it being necessary to apply a breaking force. A glass is usually cut according to the following successive steps: - scoring a subcrack along the desired line of cutting, then - application of a (breaking) force so that the subcrack propagates as a crack through the thickness of the glass, thereby breaking it as expected. However, after a glass has been cut it may be desired to improve its mechanical strength, for example its edge bending strength. To do this, a chemical toughening (or tempering) treatment may be carried out on the cut glass, generally by immersing it in a bath of molten potassium nitrate. Chemically toughened glasses therefore have their definitive shape before the chemical toughening treatment and they are not intended to be cut after the toughening has been carried out. WO 98/46537 teaches particular glass compositions obtained by chemical toughening (potassium ion exchange) for producing windows in the aeronautical field. No cutting is envisaged after the chemical toughening. EP 793 132 teaches cells formed from a pair of glass plates having electrodes on their surface, and at least one of the plates of which has undergone a chemical toughening treatment. The glass, intended to be incorporated into such a cell, is chemically toughened, then notched and broken into as many individual elements as will be incorporated into the cell. The chemical toughening treatment is carried out here on a - 2 - thickness of at most 2 0 μm. The above document teaches that, after having notched a glass, it is usually necessary to apply pressure in order to break it and that, in the case of a chemically toughened glass, if the chemically toughened layer is too thick it may be extremely difficult to break it. The object of EP 793 132 is to carry out a chemical toughening treatment allowing the glass to be broken in a conventional manner. To do this, glass having a maximum thickness of 2 mm is chemically treated over a maximum thickness of 20 μm. EP 875 4 90 discloses a continuous process for producing glass hardened by chemical toughening. The glass must have a maximum thickness of 1.2 mm and it is toughened in less than two hours. The chemical toughening treatment is carried out over a maximum thickness of 30 μm. The glass may be wound. The glass may be covered with layers, for example metal layers, produced by sputtering, and may have an application as an LCD or DTR. The chemically treated glass may be cut into plates or sheets. That document does not teach the particular conditions for cutting the glass without breaking it. EP 982 121 discloses three-layer structures, at least one of which, on the surface, is made of glass and includes notches. The notches may have a zero width. Preferably, the layer just below the notched glass is flexible (e.g., it is a polymer). Thus the trilayer has more flexibility thanks to the notches. The notched glass may have been chemically toughened. If the notch has a nonzero width, it may be filled with a polymer having a refractive index identical to that of the notched glass. The envisaged applications are: security card, windows for buildings, smart cards, photomasks. The notches may be left visible so as to have a mirror effect. - 3 - EP 964 112 teaches a panel comprising a glass sheet having, over part of its thickness, grooves arranged horizontally and parallel to one another. These cuts are preferably produced by a laser. That document does not teach the chemical toughening of the glass. FR 1 598 242, FR 2 053 664 and FR 2 063 482 teach the chemical toughening in the presence of screens that protect certain areas from the toughening. The cut is then produced in these areas. This treatment necessarily generates an imbalance of the stresses in the thickness, compared with a thermally toughened pane without a screen. Thus, these glazing units are not in self-equilibrium in the thickness. Furthermore, a ribbon thus treated is not homogeneous and has to be cut in the. areas protected by the screens These documents do not therefore teach how to produce a glazing unit that can be cut, without breaking it after scoring, at whatever point on its surface, whereas this is the case for the glazing units according to the invention because of their homogeneity. In addition, the screens recommended by those documents impair the effect of the thermal toughening at the edges, just at the points where strengthening by the toughening treatment would in general be expected. An unusual behavior of glass, when it is cut after having been treated in a certain way, has now been discovered. When the essential parameters of the invention are achieved, the crack caused by the scoring propagates all by itself through the treated glazing, that is to say without it being necessary to apply a breaking force. Within the scope of the present application, the term "glazing" has a very general sense, without any shape limitation, covering all glass-based articles and in general comprising two generally parallel main faces, and especially the frames shown in figure 8. - 4 - According to the invention, it has been discovered that a glass treated so as to have a K factor of between 0.05 and 0.4 MPa.m.1/2 could be cut without it being necessary to apply a breaking force, the K factor being defined by K = [ I oz2.H(az).dz]1/2 in which z is a position in the thickness, ơz is the intensity of the approximately isotropic biaxial stress at the position z, H(ƠZ) is equal to 1 if ơz is greater than 0 and is equal to 0 if ơz is less than or equal to 0, with the convention that extension is denoted by positive values and compression by negative values. In fact, for such a glass, the subcrack itself propagates as a crack passing through the thickness of the glass, even in the absence of a breaking force. It is necessary for the subcrack to reach that region of the glazing in extension and to be deeper than 10 μm. In particular, the invention allows the cutting, without breaking, of glass sheets of any thickness, especially less than 500 μm, but also greater than 1.2 mm and even greater than 2.6 mm, thicknesses that it is not usually known to cut directly by means of a laser in the case of a glazing unit outside the invention. The cutting according to the invention also generally results in an edge that does not cut one's hand, this being an advantage from the standpoint of safety. In general, the cutting without breaking according to the invention is carried out on glass having a thickness of less than or equal to 5.2 mm. Thus, the invention relates to a method of cutting a glazing unit that includes a glass sheet having two main faces, said method not involving the application - 5 - of a breaking force, said method comprising the following steps: - application of a treatment to the glass sheet that generates stresses and at least one region in compression and at least one region in extension, the distribution of the stresses being biaxial, approximately isotropic and self-balanced in its thickness, said stresses being such that the K factor is between 0.05 and 0.4 MPa.m1/2; - scoring a subcrack deeper than 10 μm along the desired line of cutting, said subcrack reaching that region of the glazing in extension. The stresses giving the glass its property of being able to be cut without breaking may be conferred on any type of glass by a suitable treatment, and especially: - a chemical toughening treatment or - the production of at least one thin layer or - the subjection of the glass to approximately isotropic biaxial bending during the scoring operation. The first two treatments mentioned above result intrinsically in an approximately isotropic biaxial stress distribution. These first two treatments also result in stresses that are residual after cutting. The third treatment (subjection to biaxial bending) does not result in residual stresses after cutting, since the flexural forces disappear as soon as the glass is broken. The treatment gives the glass an approximately isotropic biaxial stress distribution, which means that the stresses are exerted in directions parallel to the glazing and, for a given depth, with approximately the same intensity in all directions parallel to the glazing. These biaxial stresses are generally isotropic in a plane parallel to the glazing. These stresses are self-balanced in the thickness of the glazing, which means that the extensional stresses balance out the - 6 - compressive stresses, which also amounts to saying that {Ơ(z)dz = 0 in which Ơ(z) represents the stress at the position z in the thickness of the glazing. The invention makes it possible to produce a glazing unit that can be cut according to the invention at any point whatsoever. Such a glazing unit may have a large surface, especially greater than 10 cm, or even greater than 20 cm, or indeed greater than 50 cm or indeed greater than 1 m in all directions parallel to its main faces (the case of flat glazing). Before said treatment, the glass may have no internal stress. It may especially be a float glass. The glass may be of any composition, and especially of the soda- lime type, or it may have one of the compositions described in FR 97/04508 or WO 96/11887. If it is chosen to carry out the treatment by chemical toughening, the glass must contain an alkali metal oxide. This oxide may be Na20 or Li20 and be present in the glass in an amount, for example, from 1 to 2 0% by weight. The chemical toughening treatment consists in replacing the alkali metal ions initially in the glass with other, larger alkali metal ions. If the initial oxide is Na20, a chemical toughening by treatment with KN03 is applied, so as to at least partly replace Na+ ions with K+ ions. If the initial oxide is Li20, a chemical toughening by treatment with NaN03 or KN03 is applied, so as at least partly to replace Li+ ions with Na* or K+ ions, depending on the case. In particular, if the treatment is a chemical toughening treatment, the glass cut according to the invention has a better edge strength. The toughening may therefore result in a K+ or Na+ ion concentration gradient perpendicular to at i least one of the main faces and decreasing from said main face. To measure the K factor in the glass, the technique of - 7 - biasographe may be used. This technique is well known to those skilled in the art, and reference may in particular be made to the work "Photoelasticity of glass" by H. Aben and C. Guillemet, Springer-Verlag 1993, page 150. The technique of biasographe gives a stress intensity profile, such as for example curve (1) shown in figure 1, representing the change in the stress Ơ as a function of the depth in the glass (the x-axis is perpendicular to the glazing) . All the stresses Ơi corresponding to a thickness dzi are therefore measured over the entire curve (1) , the value of dzi being, for example, 8 μm. In practice, the K factor is then determined from the formula: K = (∑Ơi2.dzi)1/2. The biasographe technique requires access to the edge of the glazing. To use this technique, it is preferable for the width of the glazing to be equal to at least five times its thickness. Other photoelasticity methods may also be used, such as a stratorefractometer. To obtain a glazing unit having a K factor of between 0.05 and 0.4 MPa.m1/2, it may be made to undergo chemical toughening. This chemical toughening must be carried out for a long enough time and at a high enough temperature for the K factor to be between 0.05 and 0.4 MPa.m1/2. By routine tests, a person skilled in the art may find the time and temperature allowing such values to be obtained. In general, the chemical toughening is carried out by immersing the glazing unit to be treated in a hot bath of the chosen salt (generally NaN03 or KN03) . This bath contains the concentrated salt. The chemical toughening is generally carried out between 380°C and 520°C, and in any manner at a temperature below the softening point of the glass to be treated. The chemical toughening causes ionic exchange at the surface of the treated glass over a depth which may possibly range up to, for example, 50 m. This ionic exchange is the cause of alkali metal ion concentration gradients. In general, this gradient is characterized by a reduction in the concentration of ions provided by the chemical toughening (generally K+ or Na+) from the main face toward the core of the glazing. This gradient exists between the surface and, for example, a depth of at most 50 m. This gradient is shown in figure 2 by dots whose density decreases on moving further towards the inside of the glazing. The depth of the gradient is exaggerated in the figures in order to aid comprehension. The chemically toughened glazing units of the prior art, given the fact that they are not cut after the chemical toughening, have the same composition over their entire surface, including the edge. Figure 2a) shows in cross section the edge of a glazing unit chemically treated after cutting. The cut gave rise to the edge (2) . The scored line of the subcrack (3) is visible on the edge and shown in figure 2a) by a bolder line (it will be recalled that a subcrack is always visible on the cut edge of a glazing unit with the naked eye if the glazing is thick enough or with a microscope in the case of excessively thin glazing, for example with a thickness of less than 500 m) . The chemical toughening of the glazing after cutting gives rise to alkali metal ion exchange between the glazing and the toughening mediμm. This exchange created an alkali metal ion concentration gradient from the surface of the glazing toward the inside of the glazing, this gradient existing from the parallel main faces ((4) and (5) in figure 2) of the glazing and to a sufficient distance from the edges (including that denoted (2)), for example from the point (6) on the surface of a main face and perpendicular to this face toward the core of the glazing. This point (6) may generally be at least 1 mm from the edge. This gradient - 9 - does not exist along the edge in a direction perpendicular to the main faces, but it does exist on the edge in a direction parallel to the main faces of the glazing and at a sufficient distance from said main faces. Figure 2b) shows a glazing unit according to the invention, which was cut after the chemical toughening treatment. It will be understood that, in this case, the edge (2) cut according to the invention has a composition that varies depending on whether one is close to or far from the parallel main faces of the glazing. The surface of the edge cut according to the invention has a surface concentration gradient of alkali metal ions between the main face in which the subcrack was formed and the core of the glazing. This is in fact the fundamental difference from a glass cut before being treated by chemical toughening (the case shown in figure 2a) ) for which this gradient along the edge does not exist. In the case of the present invention, the edge cut according to the invention does have this gradient and has the mark of the subcrack, it being possible however, for this mark to be removed subsequently, for example by abrasion or polishing. Thus, the invention also relates to a glazing unit having such an edge with no subcrack visible. If the chemical toughening is carried out in a potassium nitrate bath, the surface concentration of potassium ions is a maximum along the edge at the end of the edge, that is to say at the corner between the edge and the main face on which the subcrack was formed. This variation in the surface ion concentration Cion along the edge is shown schematically by the curve on the left-hand side of figure 2b). However, this edge does not have a concentration gradient in a direction parallel to the main faces of the glazing (the faces denoted 4) and 5) of figure 2a) ) . The edge having the subcrack therefore does not have an alkali metal ion - 10 - concentration in the direction perpendicular to said edge. The treatment conferring the stresses on the glass may also be the application of at least one thin film. The film must be deposited so that it is in compression at the moment of scoring. This may in particular be achieved by hot deposition (generally at between 400 and 700°C) of a film whose expansion coefficient is less than that of the substrate. The film is then put into compression during cooling. The cut is then made after the coated glass has returned to room temperature. The film may be produced in particular by sol-gel or screen printing or CVD processes. The film may also be produced at low temperature by the process of magnetron sputtering or plasma CVD, and especially when the film is made of silicon nitride. It is possible to check that the film is in compression, as it has a natural tendency to give the coated substrate convexity, seen from the side with the film. The film has a thickness allowing the desired stress intensity factor to be obtained, in general, the film has a thickness ranging from 1 to 20 urn. Preferably, the film contains a stress ranging from 200 MPa to 5 GPa, for example about 3 00 MPa. A person skilled in the art will know how to measure the stress in a film on the glass. This stress in the film may especially be measured from the change in the curvature of the glass, or from the stress that it induces in the glass, this stress usually being evaluated by photoelasticity. The film may especially be made of silicon nitride, silicon carbonitride, silicon carbide, silicon oxycarbide, silicon oxycarbonitride, titanium oxide, titanium nitride, titanium carbonitride, titanium carbide, titanium oxycarbide or titanium oxycarbo- nitride . -li- lt is also possible to apply a film in compression on each side of the substrate. When the glass is coated only on one side with a film in compression, the scoring may be done on the side with the film. For the scoring, a force may be applied to the glazing that tends to reduce the convexity conferred on the coated glass by the film, but this is not essential. When the glass is coated on both its faces with a film in compression, the scoring may be done on one or other of the faces. The treatment conferring the stress on the :. glass may also be the application of an approximately isotropic biaxial bending force. A suitable biaxial bending force may be applied by heating the two main faces • of the glazing to different temperatures and by opposing the deformation that this temperature difference naturally tends to induce by applying a force to the glazing. The scoring is performed, and hence the breaking, as long as the temperature difference and the force opposing the deformation exist. In this case, the bending forces are generated by the combination, on the one hand, of the application of different temperatures to the main faces and, on the other hand, of forces opposing the deformation that the temperature difference induces. Figure 3 illustrates one embodiment according to this principle. This figure shows a glazing unit having two main faces (7) and (8) and a plate (9) having a number of holes (10) . The glazing unit may be pressed against the plate since it is sucked against it by suction being exerted through the holes. The plate is heated to a different temperature from the starting temperature of the glazing so that the face (8) has a different temperature from that of the face (7) . The creation of this temperature difference between the two faces of the glazing is why stress is created in the glazing while it rests pressed against the plate. This is because if the glazing were left to assume its equilibrium shape, it would not contain any stress. If - 12 - the face (8) is hotter than the face (7) , it is the face {8) that is in compression as long as the glazing remains pressed. In this case, the scoring may be done on the face (7) , that is to say the face in extension. The subcrack on this face therefore immediately reaches the region in extension and a subcrack of very shallow depth, while still remaining deeper than 10 m may be sufficient. If the face (8) is cooler than the face (7) , it is the latter face that is in compression as long as the glazing remains pressed. In this case, the scoring may be done on the face (7), that is to say the face in compression, in which case, since the subcrack has to be deeper than the thickness in compression in order to reach the region in extension, it must be deeper than half the thickness of the glazing. In the case of the application of a bending force, the scoring must be done while said force is being exerted. The forces applied so as to generate the stress in the glass are much less than the conventional breaking forces. For example, for a glazing unit having a thickness ranging from 0.1 to 5.2 mm, these bending forces may be between 3 and 70 MPa, extends understood that the thinner the glazing the higher the force must be. In general, for glazing having a thickness ranging from 1 to 5.2 mm, these bending forces may be between 3 and 2 0 MPa. In fact, as soon as the scoring is done, the subcrack propagates right into the thickness of the glass and it would be possible to immediately stop the bending forces just after scoring without this having any influence on the breaking. To cut the glass having a suitable K factor without breaking it, the surface of the glass is scored along a line corresponding to that of the desired cut. This scoring results in a subcrack (also called a blind crack by those skilled in the art) . The scoring may especially be done using a scoring wheel or by a diamond or by laser. Usually, and more particularly for - 13 - glazing having a thickness ranging from 1 to 3 mm, the subcrack has a depth of 100 to 1 000 m. Usually, the subcrack has a depth of between 10% and 2 0%, for example about 15%, of the glazing thickness. When a scoring wheel or a diamond is used, the scoring is done with a load sufficient to obtain a sufficient depth of the subcrack, which must be able to propagate without the application of a breaking force. When a scoring wheel or a diamond is used, the scoring is preferably done under a cutting oil (also called "petrol" by those skilled in the art) . When a scoring wheel is used, it is preferable to use a scoring wheel with a large angle, for example 145°. The angle of the scoring wheel is the angle a as shown in figure 4. For a given scoring wheel or diamond, it is also possible by routine tests to find a load suitable for the scoring. This is because an insufficient load results in no fracture, while an excessively high load results in an uncontrolled fracture, that is to say a fracture that does not always follow the line of scoring. When the essential parameters of the invention have been achieved, the crack caused by the scoring propagates all by itself through the treated glazing, that is to say without it being necessary to apply a breaking force. It is possible to accelerate the propagation of the crack by at least one of the following means: - with water: a little water may be placed in the subcrack; to do this, it is possible, for example, to wet the glazing before cutting, wetting only that part (typically a few mm) of the glazing corresponding to the end of the scoring; - by increasing the scoring load at the end of scoring. The scoring must result in a subcrack. The scoring may be carried out on a main face of the glazing that is in - 14 - compression or, if it exists, on a main face of the glazing that is in extension. When the scoring is carried out on a main face in compression (especially in the case of a surface treated by chemical toughening or by a film in compression) , the subcrack is deeper than the thickness in compression ec so as to reach the region in extension. Preferably, especially if the treatment is a chemical toughening treatment, the subcrack has a depth of 5 to 20 times the value of the thickness in compression ec. In the case of a chemical toughening treatment, the thickness in compression may be evaluated from the depth of ion exchange Pe, which may be determined JTT x Mv x ev x Am a) either by Pe = - — : 32 xaxmr in which: a represents the initial molar % of alkali metal oxide in the glass (for example Na20 or Li20) ; mi represents the total initial mass (before toughening) of the glass in grams; Mv represents the molar mass of the glass in g/mol; Am represents the rate of uptake of the glass during toughening in grams; and ev represents the thickness of the glass in micrometers, Pe thus being obtained in micrometers; b) or by a microprobe profile, in which case it is defined by the depth for which the content of ions provided by the toughening is equal to that of the glass matrix to within 5%. In the case of a treatment by formation of a film, the thickness in compression is equal to the thickness of the film, provided that the film is in compression and that no external force deforms the glazing substantially. - 15 - In the case of a treatment by the application of bending forces, if the scoring is carried out on the side in compression, the thickness in compression is equal to one half of the thickness of the glazing. In the case of a treatment by the application of bending forces, if the scoring is carried out on the side in extension, the subcrack may be shallower, while still remaining greater than 10 μm. The invention makes it possible in particular to cut a glass sheet having a thickness of at least 0.3 mm, or at least 0.7 mm, or at least 1.2 mm or greater than 1.5 mm or even at least 2.6 mm, without breaking it. In general, the glass sheet has a thickness of less than 20 mm, for example at most 5.2 mm. The glazing may in particular have a thickness ranging from 0.7 mm to 5.2 mm, for example 2.6 to 5.2 mm. The cutting according to the invention starts by the scoring of a subcrack on the surface of a glass, and the propagation of a crack through the entire thickness of the inorganic part of the glazing that has undergone the cut is observed. In fact, in the case of a laminated glazing unit that is the association of at least two glass sheets placed on either side of a polymer interlayer, one of the glass sheets being treated according to the invention and scored according to the invention, it is clear that the crack propagates only through the sheet that was scored and not the other glass sheet lying on the other side of the polymer interlayer. The invention also relates to a glazing unit comprising a glass sheet having two main faces and at least one edge, said glazing unit having a distribution of stresses through its thickness, said stresses being biaxial, approximately isotropic and self-balanced, and the K factor of which is between 0.05 and 0.4 MPa.m1/2. - 16 - The invention makes it possible to produce cutting profiles that the prior art does not allow to be produced. According to the invention, it is possible to cut glass along a curved line with a very small radius of curvature, and to do so even with a thick glass. At least at one point along the line of cutting, the radius of curvature may be less than 4 0 mm, or even less than 3 0 mm, or even less than 2 0 mm or even less than 10 mm or even less than 5 mm. In general, the radius of curvature is greater than 3 mm. Such radii of curvature of the cutting may be obtained for glazing with a thickness of even greater than 1 mm, or indeed greater than 2.6 mm. In general, to produce radii of curvature of less than 10 mm, it is preferable for the glazing to have a thickness of less than 5.2 mm, in particular, it is thus possible to cut magnetic recording disks, that is to say to make, simultaneously, their peripheral circular cut and their central circular hole. According to the invention, it is possible to make a cut along a curved line changing in concavity, and even linking inverse concavities with very small radii of curvature, such as those that have just been given. Figure 5 illustrates one form of cut produced on a glazing unit (11) , said cut having a change of concavity at the point (12) . Linked to the point (12) are two curves of different concavity. In figure 5, the curve on either side of the point (12) has the same radius of curvature in absolute value, which may be very small as already explained. According to the invention, it is possible to cut the glass over a very small width. A glazing unit generally has a thickness, a width and a length (at least equal to the width). In general, the glazing to be cut - 17 - according to the invention has an approximately- constant thickness. In general, it is flat. According to the invention, the width of glazing cut may even be less than 1.5 times the thickness, and even less than 1.2 times the thickness, and even less than 1 times the thickness and even less than or equal to 0.7 times the thickness. In general, the width of glazing cut is greater than 0.1 times the thickness. Thus, the invention makes it possible in particular to produce glass strips of square or rectangular cross section having the width given above and especially a width of magnitude similar to that of the thickness or even less than that of the thickness. According to the invention, it is possible to cut a glazing unit along a line of cutting that includes an angle. This angle may, for example, range from 60° to 120° and in particular be 90°. Remarkably, the cut results in a piece having a concave angle a1 and a piece having a convex angle a2 being obtained (see figure 6) . To do this the cut has not to be the result of intersection of two different lines of cutting that meet, said intersection forming the desired angle, the two lines of cutting being continued beyond their intersection. To produce the angle according to the invention, there are two options: 1) a hole may be made at the point chosen for the angle before the cutting and then the cutting is carried out by making two different scored lines that meet at the site of the hole, the hole possibly having a diameter of 0.2 to 2 mm for example; or 2) a hole is not made at the place chosen for the angle, rather a scored line is made that at every point satisfies the abovementioned condition as regards the radius of curvature, which must therefore be at least 3 mm. Thus, the angle is in fact a curve of very small radius of curvature. It is possible to repeat the scoring several times provided that the various scored lines meet so that their tangents coincide at the - 18 - points of intersection. If it is desired to do the scoring by hand, it may be preferable to produce a hole at the place desired for the angle. If the scoring is done by a machine, a hole need not be made prior to the scoring provided that the scoring complies with the minimum radius of curvature given above. With this type of machine, the tracing is generally carried out in one single step, that is to say the scoring object is placed once on the glass and does not leave it until the end of the scoring. Figure 6 shows two glazing pieces after the cutting according to the invention. It may be seen that the cut has a rounded angle of small radius of curvature producing, in the two cut parts, two angles that fit together perfectly. This angle was produced without forming a hole prior to the cutting. According to the prior art, it was known how to make 90° angles, but by the intersection of lines of cutting that cross each other, that is to say that continue after their point of intersection. Figure 7 illustrates this way of cutting ordinary glass according to the prior art, with lines of cutting (13) traversing the entire surface of the glazing, and resulting in square or rectangular pieces (14) . The angles of all the pieces cut in this way are convex, none of the cut pieces having a concave angle. According to the invention, it is possible to cut and remove a full shape even from the inside of a glass plate without said cut intersecting the original external border of the glazing. Thus, a full shape, whose external border has the shape of the cut, is removed from the rest of the glazing, which then has an internal border having the shape of the cut and an external border remaining unchanged with respect to the original external border (before cutting). To do this, the scoring is carried out along a line that joins up - 19 - with itself without intersecting with the external border of the glazing and resulting in the cutting, on the one hand, of a full shape and, on the other hand, of a holed shape, the external outline of the holed shape corresponding to the original external outline of the glazing, the internal outline of the holed shape corresponding to the external outline of the full shape. This full shape may be a circle or have a radius of curvature as already mentioned. Figure 8 illustrates this possibility. In this figure, a full shape (15) has been cut from the inside of a plate, which then appears as a holed shape (16). The external outline of the full shape corresponds to the internal outline (17) of the holed shape. The external outline (18) of the holed shape is the same as the original plate before cutting. The full shape may be a circle or may include a small radius of curvature, as already mentioned. The full shape may also include one or more angles as already mentioned, it being understood that these angles have to be made according to the abovementioned conditions, that is to say with the formation of a hole prior to the cutting or without the prior formation of a hole, but by the scoring complying with a minimum radius of curvature of 3 mm. Thus, a full shape may be cut with a polygonal outline. In particular, the polygonal shape may include three, four, five or six angles, or even more. Thus, it is possible to cut a full shape having the shape of a square or rectangle after having made a cut with four 90° angles (this is the case for the cut shape shown in figure 8). The holed shape therefore has the shape of a frame, said frame shape having an internal border of square or rectangular shape and an external border of square or rectangular shape. This frame also has a cross section of square or rectangular shape. The holed shape (or frame) thus obtained is especially applicable as an insert piece between two glazing units, such as in flat FED (field emission display) screens. The holed shape may have a very small edge width ((19) in figure 8), that is to say one - 20 - corresponding to what was already mentioned as regards thin strips. The full shape may be separated from the holed shape, preferably by extraction from that side with the initial scoring. The full shape may generally be extracted by hand. To make extraction easier, especially for greater glazing thicknesses, a thermal extraction operation may also be carried out, which consists in heating (for example to between 90 and 220°C) firstly the entire cut glazing, but for which the full shape and the holed shape have not yet been separated, and then secondly the central part of the glazing comprising the full shape to be extracted is cooled. The contraction caused by the cooling allows the full shape to be more easily extracted. The cutting according to the invention may be carried out by scoring the surface of a glass sheet treated in accordance with the invention (chemical, film, or bending treatment), said sheet forming part of a laminated glazing unit. In this case, the crack caused by the scoring propagates through the thickness of the treated sheet and stops at the polymer interlayer usually placed between the sheets of a laminated glazing unit. In this way, a multitude of parallel linear cracks may be produced through the treated sheet of the laminated glazing unit, passing through said sheet as far as the polymer interlayer. The cracks thus created act as mirrors for light passing through the glazing. The aesthetically attractive glazing thus obtained may serve as a light deflector. Figure 9 illustrates this application. It shows that the light rays (20) are reflected at the interfaces (21) of the cracks created in accordance with the invention through the treated sheet (22) of the laminated glazing unit (2 3) comprising the combination of two glass sheets separated by a polymer layer (24). In this application, the cracks may be separated from one another by a distance of, for example, 2 mm to 10 mm. In general, it is desirable for the distance between two cracks to - 21 - represent 4 0 to 80% of the thickness of the cracked sheet. Of course, it is also possible to carry out conventional cutting, that is to say passing through the entire surface of the glazing, in order to cut square or rectangular shapes. Pieces of this type may serve as protective glazing for LCD (liquid-crystal display) cells. The present invention, particularly when it involves a chemical toughening treatment, is very beneficial for the cutting of glazing in the electronic field. This chemical toughening technique is particularly applicable to glass capable of ion exchange, as is the case in electronics for glass having in particular a high strain point, for example CS77 glass sold by Saint-Gobain Glass France. The composition of such glass is described, for example, in EP 0 914 299. The cutting technique is therefore applicable in lines for the manufacture of accessories for electronics (such as spacers or inserts) , of screens (plasma, LCD, TFT, FED screen) and of field emission displays, and in lines for manufacturing vacuum glazing. The use of chemical toughening gives the edges, especially the cut edges, high mechanical strength. With the cutting techniques of the prior art, it is necessary for the components to be brought into contact with the surface of the glass and to be held thereon, for the scoring and/or breaking, in order to cut the glass. This is a drawback if a surface of the glass has already received printing, as any contact with this printing may damage it. Thanks to the technique according to the invention, and more particularly when it employs chemical toughening, it is therefore possible to print the glass after the stress-generating treatment and then to cut it with the minimum of contact with components. In particular, it is therefore possible to produce a motherglass, to print patterns on the surface and then - 22 - to carry out the manufacturing cycles in order only thereafter to cut each screen (telephone, palmtop or portable computer screen). All the examples start with the chemical toughening of a glass plate, produced as follows, the essential parameters of said toughening (time and temperature) being given in table 1. The starting glasses used were the following: CS77: glass sold by Saint-Gobain Glass France; Px: glass of the PLANILUX brand sold by Saint- Gobain Glass France; C0211: glass sold by Corning. Chemical toughening for the examples A flat glass with the dimensions 300 x 200 x e mm was taken, "e" representing the thickness that was toughened in a potassium nitrate bath at a temperature T for a time "t". The treatments produced core stresses in the sheet. Cutting principle for the examples The glass plates were cut, using a diamond or a scoring wheel, into various cut shapes corresponding to various applications. The cuts using a scoring wheel were all made according to the principle below. The scoring was done with a scoring wheel of the VITRUM brand sold by Adler, said scoring wheel having an angle of 145° and a diameter of 5 mm with cutting fluid and with a load so that the subcrack is deeper than the exchange depth Pa. For the examples illustrating the invention, it was noticed that the subcrack propagated through the entire thickness of the glass without it being necessary to apply a breaking force (see the "propagation" line in table 1) . In certain cases, the propagation was initiated at the end of the scored line by adding - 23 - water, which penetrated by capillary effect into the subcrack. In other cases, the propagation was initiated by increasing the load at the end of the scored line. For all the examples, the K factor in the glass was measured by a biasographe on glass strips 10 mm in width, except in the case of examples 5 and 6 for which the glass strips were 3 mm in width. In table 1, the following expressions and abbreviations are used: - Pe: ion exchange depth,- - ∆ load: increase in load; - Propagation and type: it was judged whether the crack propagation proceeded correctly (guided propagation) or whether it was uncontrolled, which means that the glass does not break along the line of scoring, or whether it does not occur, which means that in the end the glass has not broken. Examples 1 and 2: frames Before the chemical toughening treatment, four holes 1 mm in diameter were produced in the corners of the plate with a diamond drill bit, said holes being placed 4 mm from the edges of said plate. After the chemical toughening treatment, the plate was cut along straight lines parallel to the edges of the plate and between the holes, so as to draw a frame. The glass rectangle between the holes could be extracted so as to recover a frame (see figure 8). Example 3; daylight reflection A laminated glazing unit was produced with, on the one hand, the chemically treated plate and, on the other hand, a pane of ordinary soda-lime glass (not chemically treated) 2 mm in thickness, placing between them, in the conventional manner, a film of polyvinyl butyral (PVB). - 24 - After one end of the glazing unit had been immersed in water (to about'5 mm), a first series of straight and parallel scored lines was produced by the scoring wheel on that side of the glazing that was chemically toughened, said scored lines being separated from one another by 8 mm and finishing at the edge immersed in water. The water plays its role by initiating the propagation of each crack. A second series of scored lines was then produced, between the scored lines of the first series, so that in the end the plate had scored lines approximately every 4 mm. It was noted that all the cracks caused by the scored lines propagated as far as the PVB film, that is to say they passed through the entire thickness of the chemically toughened glass pane. The glazing unit could then act as a reflector for light passing through it, thanks to the mirror effect of each of the cracks (see figure 9). Example 4: cutting a circle A circle 60 mm in diameter was cut in the chemically toughened glass using a scoring wheel of the VITRUM brand sold by Adler, said scoring wheel having an angle of 145° and a diameter of 5 mm and said scoring wheel being mounted on a circular glass cutter with a handle, having the reference Bohle 530.0 section 1.19. The glass disk could be extracted by thermal extraction without either the disk or the rest of the plate breaking. Example 5: cutting film glass Using a diamond, a glass sheet 300 urn in thickness was cut after it had been chemically toughened, without initiation, either with water or by a load increase. The cut is made easily along the scored line without uncontrolled breaking. The K factor in the glass was measured by a biasographe on strips 3 mm in width. - 25 - Example 6: (comparative example) The procedure was as in the case of example 5, except that the chemical toughening was carried out so that the K factor reached the value mentioned in table 1. Examples 7 to 9 (comparative examples) The procedure was as in the case of example 2, except that the chemical toughening was carried out so that the K factor reached the value mentioned in table 1. - 26 - Table 1 27 We Claim 1. A method of cutting a glazing unit without applying a breaking force, the glazing unit comprising a glass sheet having two main faces, said method comprising the steps of: - application of a treatment to the glass sheet that generates stresses such that at least one region in compression and at least one region in extension, the distribution of the stresses being biaxial, isotropic and self balanced in its thickness, said stresses being such that the K factor is between 0.05 and 0.4 Mpa.m1/2, said K factor being defined by K =[ ∫zỢz2.H(Ợ2).dz]1/2 in which z is a position in the thickness, Ợ2 is the intensity of the isotropic biaxial stress at the position z, H(Ợ2) is equal to 1 if Ợ2 is greater than 0 and is equal to 0 if Ợ2 is less than or equal to 0, with the convention that extension is denoted by positive values and compression by negative values; and then 28 - scoring a subcrack deeper than 10 m along the desired line of cutting of the treated glass, said subcrack reaching that region of the glazing in extension. 2. The method as claimed in the preceding claims, wherein, before treatment, the glass contains an alkali metal oxide and wherein the treatment is a chemical toughening treatment. 3. The method as claimed in the preceding claims, wherein, the chemical toughening results in a K+ or Na+ ion gradient perpendicular to at least one of the main faces and decreasing from said main face. 4. The method as claimed in claims 2 or 3, wherein, the chemical toughening results in ionic exchange over a depth of at most 50 m. 5. The method as claimed in claim 1, wherein the treatment is the application by deposition of a film in compression. 6. The method as claimed in the preceding claim, wherein the film has a thickness ranging from 1 to 20 m. 7. The method as claimed in preceding claim, wherein the film contains a stress ranging from 200 Mpa to 5 Gpa. 29 8. The method as claimed in claim 1, wherein the treatment is the application of isotropic biaxial bending forces. 9. The method as claimed in the preceding claim, wherein the bending forces are generated by the combination, on the one hand, of the application of different temperatures to the main faces, and on the other hand, of forces that oppose the deformation that the temperature difference induces. 10.The method as claimed in claims 8 or 9, wherein the bending forces are between 3 and 20 Mpa. 11.The method as claimed in one of the preceding claims, wherein the glazing has a thickness ranging from 0.7 to 5.2 mm. 12.The method as claimed in the preceding claims, wherein the glazing has a thickness ranging from 2.6 to 5.2 mm. 13.The method as claimed in one of the preceding claims, wherein the scoring is carried out on a main face in compression and produces a subcrack that passes through the region in compression in order to reach the region in extension. 14.The method as claimed in one of claims 1 to 12, wherein the scoring is carried out on a main face in extension. 30 15.The method as claimed in one of the preceding claims, wherein the scoring is carried out along a line that joins up with itself without intersecting the external border of the glazing and resulting in the cutting, on the one hand, of a full shape and, on the other hand, of a holed shape corresponding to the original external outline of the holed shape corresponding to the original external outline of the glazing, the internal outline of the holed shape corresponding to the external outline of the full shape. 16.The method as claimed in one of the preceding claims, wherein the scoring is carried out along a line having, at least one point, a radius of curvature of less than 5 mm. 17.A glazing unit comprising a glass sheet having two main forces and at least one edge, said glazing unit having a distribution of stresses in its thickness, said stresses being biaxial, isotropic and self-balanced, and the K factor of which is between 0.05 and 0.4 MPa.m1/2, said K factor being defined by K = [ ∫z Ớ2 2. H (Ớ2).dz]1/2 in which z is a position in the thickness, Ớ2 is the stress at the position z, H (Ớ2) is equal to 1 if Ớ2 is greater than 0 and is equal to 31 0 if Ớ2 is less than or equal to 0, with the convention that extension is denoted by positive values and compression by negative values. 18. The glazing unit as claimed in the preceding claims, comprising an alkali metal ion gradient perpendicular to at least one of the main faces and decreasing from said main face. 19. The glazing unit as claimed in the preceding claims, wherein the gradient perpendicular to at least one of the main faces exists at the surface of at least one edge. 20. The glazing unit as claimed in the preceding claim, wherein the edge has the scored line of a cutting subcrack. 21. The glazing unit as claimed in one of the preceding claims, wherein at least one edge has no alkali metal ion gradient in the direction perpendicular to said edge. 22. The glazing unit as claimed in one of the preceding claims, comprising a thickness ranging from 0.7 to 5.2 mm. 23. The glazing unit as claimed in claim 22, comprising a thickness ranging from 2.6 to 5.2 mm. 32 24.The glazing unit as claimed in one of the preceding claims, wherein one of its borders has, at least one point, a radius of curvature of less than 5 mm. 25.The glazing unit as claimed in one of the preceding glazing unt claims, wherein at least partly in the form of a strip with a square or rectangular cross section having a width of less than 1.5 times its thickness. 26.The glazing unit as claimed in the preceding claim, comprising at least partly a width of less than 1 times its thickness. 27.The glazing unit as claimed in one of the preceding claims, comprising a frame shape with a square or rectangular cross section, said frame shape having an internal border of square or rectangular shape and an external border of square or rectangular shape. 28. A flat field emission display, comprising an insert having a glazing unit as claimed in one of the preceding claims. 29. A laminated glazing unit, the glass sheets of which constitutes a glazing unit as claimed in one of the claims 17 to 19 and comprising a multitude of parallel linear cracks passing through it as far as the polymer interlayer. 33 30.The glazing unit as clamed in the preceding claims, wherein the cracks are separated from one another by a distance of 2 mm to 10 mm. 31.The glazing unit as claimed in claims 29 or 30, wherein the distance between two cracks represents 40 to 80% of the thickness of the cracked sheet. DATED THIS 4TH DAY OF NOVEMBER 2004 The invention relates to a method of cutting a glazing unit without applying a breaking force, the glazing unit comprising a glass sheet having two main faces, said method comprising the steps of applying a treatment to the glass sheet that generates stresses such that at least one region in compression and at least one region in extension, the distribution of the stresses being biaxial, isotropic and self balanced in its thickness, the stresses being such that the K factor is between 0.05 and 0.4 Mps.m1/2, said K factor being defined by K = [∫ZỚZ2- H(Ớ2).dz]1/2, in which z is a position in the thickness, Ớ2 is the intensity of the isotropic biaxial stress at the position z, H(Ớ2) is equal to 1 if Ớ2 is greater than 0 and is equal to 0 if Ớ2 is less than or equal to 0, with the convention that extension is denoted by positive values and compression by negative values; and scoring a subcrack deeper than 10 m along the desired line of cutting of the treated glass, the subcrack reaching that region of the glazing in extension.

Full Text

gLAZING CUT WITHOUT BREAKING -IT-
The invention relates to a method of cutting a glazing
unit without it being necessary to apply a breaking
force.
A glass is usually cut according to the following
successive steps:
- scoring a subcrack along the desired line of
cutting, then
- application of a (breaking) force so that the
subcrack propagates as a crack through the thickness of
the glass, thereby breaking it as expected.
However, after a glass has been cut it may be desired
to improve its mechanical strength, for example its
edge bending strength. To do this, a chemical
toughening (or tempering) treatment may be carried out
on the cut glass, generally by immersing it in a bath
of molten potassium nitrate. Chemically toughened
glasses therefore have their definitive shape before
the chemical toughening treatment and they are not
intended to be cut after the toughening has been
carried out.
WO 98/46537 teaches particular glass compositions
obtained by chemical toughening (potassium ion
exchange) for producing windows in the aeronautical
field. No cutting is envisaged after the chemical
toughening.
EP 793 132 teaches cells formed from a pair of glass
plates having electrodes on their surface, and at least
one of the plates of which has undergone a chemical
toughening treatment. The glass, intended to be
incorporated into such a cell, is chemically toughened,
then notched and broken into as many individual
elements as will be incorporated into the cell. The
chemical toughening treatment is carried out here on a

- 2 -
thickness of at most 2 0 μm. The above document teaches
that, after having notched a glass, it is usually
necessary to apply pressure in order to break it and
that, in the case of a chemically toughened glass, if
the chemically toughened layer is too thick it may be
extremely difficult to break it. The object of
EP 793 132 is to carry out a chemical toughening
treatment allowing the glass to be broken in a
conventional manner. To do this, glass having a maximum
thickness of 2 mm is chemically treated over a maximum
thickness of 20 μm.
EP 875 4 90 discloses a continuous process for producing
glass hardened by chemical toughening. The glass must
have a maximum thickness of 1.2 mm and it is toughened
in less than two hours. The chemical toughening
treatment is carried out over a maximum thickness of
30 μm. The glass may be wound. The glass may be covered
with layers, for example metal layers, produced by
sputtering, and may have an application as an LCD or
DTR. The chemically treated glass may be cut into
plates or sheets. That document does not teach the
particular conditions for cutting the glass without
breaking it.
EP 982 121 discloses three-layer structures, at least
one of which, on the surface, is made of glass and
includes notches. The notches may have a zero width.
Preferably, the layer just below the notched glass is
flexible (e.g., it is a polymer). Thus the trilayer has
more flexibility thanks to the notches. The notched
glass may have been chemically toughened. If the notch
has a nonzero width, it may be filled with a polymer
having a refractive index identical to that of the
notched glass. The envisaged applications are: security
card, windows for buildings, smart cards, photomasks.
The notches may be left visible so as to have a mirror
effect.

- 3 -
EP 964 112 teaches a panel comprising a glass sheet
having, over part of its thickness, grooves arranged
horizontally and parallel to one another. These cuts
are preferably produced by a laser. That document does
not teach the chemical toughening of the glass.
FR 1 598 242, FR 2 053 664 and FR 2 063 482 teach the
chemical toughening in the presence of screens that
protect certain areas from the toughening. The cut is
then produced in these areas. This treatment
necessarily generates an imbalance of the stresses in
the thickness, compared with a thermally toughened pane
without a screen. Thus, these glazing units are not in
self-equilibrium in the thickness. Furthermore, a
ribbon thus treated is not homogeneous and has to be
cut in the. areas protected by the screens These
documents do not therefore teach how to produce a
glazing unit that can be cut, without breaking it after
scoring, at whatever point on its surface, whereas this
is the case for the glazing units according to the
invention because of their homogeneity. In addition,
the screens recommended by those documents impair the
effect of the thermal toughening at the edges, just at
the points where strengthening by the toughening
treatment would in general be expected.
An unusual behavior of glass, when it is cut after
having been treated in a certain way, has now been
discovered.
When the essential parameters of the invention are
achieved, the crack caused by the scoring propagates
all by itself through the treated glazing, that is to
say without it being necessary to apply a breaking
force. Within the scope of the present application, the
term "glazing" has a very general sense, without any
shape limitation, covering all glass-based articles and
in general comprising two generally parallel main
faces, and especially the frames shown in figure 8.

- 4 -
According to the invention, it has been discovered that
a glass treated so as to have a K factor of between
0.05 and 0.4 MPa.m.1/2 could be cut without it being
necessary to apply a breaking force, the K factor being
defined by
K = [ I oz2.H(az).dz]1/2
in which z is a position in the thickness, ơz is the
intensity of the approximately isotropic biaxial stress
at the position z, H(ƠZ) is equal to 1 if ơz is greater
than 0 and is equal to 0 if ơz is less than or equal to
0, with the convention that extension is denoted by
positive values and compression by negative values.
In fact, for such a glass, the subcrack itself
propagates as a crack passing through the thickness of
the glass, even in the absence of a breaking force. It
is necessary for the subcrack to reach that region of
the glazing in extension and to be deeper than 10 μm.
In particular, the invention allows the cutting,
without breaking, of glass sheets of any thickness,
especially less than 500 μm, but also greater than
1.2 mm and even greater than 2.6 mm, thicknesses that
it is not usually known to cut directly by means of a
laser in the case of a glazing unit outside the
invention. The cutting according to the invention also
generally results in an edge that does not cut one's
hand, this being an advantage from the standpoint of
safety. In general, the cutting without breaking
according to the invention is carried out on glass
having a thickness of less than or equal to 5.2 mm.
Thus, the invention relates to a method of cutting a
glazing unit that includes a glass sheet having two
main faces, said method not involving the application

- 5 -
of a breaking force, said method comprising the
following steps:
- application of a treatment to the glass sheet
that generates stresses and at least one region in
compression and at least one region in extension, the
distribution of the stresses being biaxial,
approximately isotropic and self-balanced in its
thickness, said stresses being such that the K factor
is between 0.05 and 0.4 MPa.m1/2;
- scoring a subcrack deeper than 10 μm along the
desired line of cutting, said subcrack reaching that
region of the glazing in extension.
The stresses giving the glass its property of being
able to be cut without breaking may be conferred on any
type of glass by a suitable treatment, and especially:
- a chemical toughening treatment or
- the production of at least one thin layer or
- the subjection of the glass to approximately
isotropic biaxial bending during the scoring operation.
The first two treatments mentioned above result
intrinsically in an approximately isotropic biaxial
stress distribution. These first two treatments also
result in stresses that are residual after cutting. The
third treatment (subjection to biaxial bending) does
not result in residual stresses after cutting, since
the flexural forces disappear as soon as the glass is
broken.
The treatment gives the glass an approximately
isotropic biaxial stress distribution, which means that
the stresses are exerted in directions parallel to the
glazing and, for a given depth, with approximately the
same intensity in all directions parallel to the
glazing. These biaxial stresses are generally isotropic
in a plane parallel to the glazing. These stresses are
self-balanced in the thickness of the glazing, which
means that the extensional stresses balance out the

- 6 -
compressive stresses, which also amounts to saying that
{Ơ(z)dz = 0 in which Ơ(z) represents the stress at the
position z in the thickness of the glazing. The
invention makes it possible to produce a glazing unit
that can be cut according to the invention at any point
whatsoever. Such a glazing unit may have a large
surface, especially greater than 10 cm, or even greater
than 20 cm, or indeed greater than 50 cm or indeed
greater than 1 m in all directions parallel to its main
faces (the case of flat glazing).
Before said treatment, the glass may have no internal
stress. It may especially be a float glass. The glass
may be of any composition, and especially of the soda-
lime type, or it may have one of the compositions
described in FR 97/04508 or WO 96/11887.
If it is chosen to carry out the treatment by chemical
toughening, the glass must contain an alkali metal
oxide. This oxide may be Na20 or Li20 and be present in
the glass in an amount, for example, from 1 to 2 0% by
weight. The chemical toughening treatment consists in
replacing the alkali metal ions initially in the glass
with other, larger alkali metal ions. If the initial
oxide is Na20, a chemical toughening by treatment with
KN03 is applied, so as to at least partly replace Na+
ions with K+ ions. If the initial oxide is Li20, a
chemical toughening by treatment with NaN03 or KN03 is
applied, so as at least partly to replace Li+ ions with
Na* or K+ ions, depending on the case. In particular, if
the treatment is a chemical toughening treatment, the
glass cut according to the invention has a better edge
strength. The toughening may therefore result in a K+
or Na+ ion concentration gradient perpendicular to at
i least one of the main faces and decreasing from said
main face.
To measure the K factor in the glass, the technique of

- 7 -
biasographe may be used. This technique is well known
to those skilled in the art, and reference may in
particular be made to the work "Photoelasticity of
glass" by H. Aben and C. Guillemet, Springer-Verlag
1993, page 150.
The technique of biasographe gives a stress intensity
profile, such as for example curve (1) shown in
figure 1, representing the change in the stress Ơ as a
function of the depth in the glass (the x-axis is
perpendicular to the glazing) . All the stresses Ơi
corresponding to a thickness dzi are therefore measured
over the entire curve (1) , the value of dzi being, for
example, 8 μm. In practice, the K factor is then
determined from the formula:
K = (∑Ơi2.dzi)1/2.
The biasographe technique requires access to the edge
of the glazing. To use this technique, it is preferable
for the width of the glazing to be equal to at least
five times its thickness. Other photoelasticity methods
may also be used, such as a stratorefractometer.
To obtain a glazing unit having a K factor of between
0.05 and 0.4 MPa.m1/2, it may be made to undergo
chemical toughening. This chemical toughening must be
carried out for a long enough time and at a high enough
temperature for the K factor to be between 0.05 and
0.4 MPa.m1/2. By routine tests, a person skilled in the
art may find the time and temperature allowing such
values to be obtained. In general, the chemical
toughening is carried out by immersing the glazing unit
to be treated in a hot bath of the chosen salt
(generally NaN03 or KN03) . This bath contains the
concentrated salt. The chemical toughening is generally
carried out between 380°C and 520°C, and in any manner
at a temperature below the softening point of the glass
to be treated. The chemical toughening causes ionic

exchange at the surface of the treated glass over a
depth which may possibly range up to, for example,
50 m. This ionic exchange is the cause of alkali metal
ion concentration gradients. In general, this gradient
is characterized by a reduction in the concentration of
ions provided by the chemical toughening (generally K+
or Na+) from the main face toward the core of the
glazing. This gradient exists between the surface and,
for example, a depth of at most 50 m. This gradient is
shown in figure 2 by dots whose density decreases on
moving further towards the inside of the glazing. The
depth of the gradient is exaggerated in the figures in
order to aid comprehension.
The chemically toughened glazing units of the prior
art, given the fact that they are not cut after the
chemical toughening, have the same composition over
their entire surface, including the edge. Figure 2a)
shows in cross section the edge of a glazing unit
chemically treated after cutting. The cut gave rise to
the edge (2) . The scored line of the subcrack (3) is
visible on the edge and shown in figure 2a) by a bolder
line (it will be recalled that a subcrack is always
visible on the cut edge of a glazing unit with the
naked eye if the glazing is thick enough or with a
microscope in the case of excessively thin glazing, for
example with a thickness of less than 500 m) . The
chemical toughening of the glazing after cutting gives
rise to alkali metal ion exchange between the glazing
and the toughening mediμm. This exchange created an
alkali metal ion concentration gradient from the
surface of the glazing toward the inside of the
glazing, this gradient existing from the parallel main
faces ((4) and (5) in figure 2) of the glazing and to a
sufficient distance from the edges (including that
denoted (2)), for example from the point (6) on the
surface of a main face and perpendicular to this face
toward the core of the glazing. This point (6) may
generally be at least 1 mm from the edge. This gradient

- 9 -
does not exist along the edge in a direction
perpendicular to the main faces, but it does exist on
the edge in a direction parallel to the main faces of
the glazing and at a sufficient distance from said main
faces.
Figure 2b) shows a glazing unit according to the
invention, which was cut after the chemical toughening
treatment. It will be understood that, in this case,
the edge (2) cut according to the invention has a
composition that varies depending on whether one is
close to or far from the parallel main faces of the
glazing. The surface of the edge cut according to the
invention has a surface concentration gradient of
alkali metal ions between the main face in which the
subcrack was formed and the core of the glazing. This
is in fact the fundamental difference from a glass cut
before being treated by chemical toughening (the case
shown in figure 2a) ) for which this gradient along the
edge does not exist. In the case of the present
invention, the edge cut according to the invention does
have this gradient and has the mark of the subcrack, it
being possible however, for this mark to be removed
subsequently, for example by abrasion or polishing.
Thus, the invention also relates to a glazing unit
having such an edge with no subcrack visible.
If the chemical toughening is carried out in a
potassium nitrate bath, the surface concentration of
potassium ions is a maximum along the edge at the end
of the edge, that is to say at the corner between the
edge and the main face on which the subcrack was
formed. This variation in the surface ion concentration
Cion along the edge is shown schematically by the curve
on the left-hand side of figure 2b). However, this edge
does not have a concentration gradient in a direction
parallel to the main faces of the glazing (the faces
denoted 4) and 5) of figure 2a) ) . The edge having the
subcrack therefore does not have an alkali metal ion

- 10 -
concentration in the direction perpendicular to said
edge.
The treatment conferring the stresses on the glass may
also be the application of at least one thin film. The
film must be deposited so that it is in compression at
the moment of scoring. This may in particular be
achieved by hot deposition (generally at between 400
and 700°C) of a film whose expansion coefficient is
less than that of the substrate. The film is then put
into compression during cooling. The cut is then made
after the coated glass has returned to room
temperature. The film may be produced in particular by
sol-gel or screen printing or CVD processes. The film
may also be produced at low temperature by the process
of magnetron sputtering or plasma CVD, and especially
when the film is made of silicon nitride. It is
possible to check that the film is in compression, as
it has a natural tendency to give the coated substrate
convexity, seen from the side with the film.
The film has a thickness allowing the desired stress
intensity factor to be obtained, in general, the film
has a thickness ranging from 1 to 20 urn. Preferably,
the film contains a stress ranging from 200 MPa to
5 GPa, for example about 3 00 MPa. A person skilled in
the art will know how to measure the stress in a film
on the glass. This stress in the film may especially be
measured from the change in the curvature of the glass,
or from the stress that it induces in the glass, this
stress usually being evaluated by photoelasticity.
The film may especially be made of silicon nitride,
silicon carbonitride, silicon carbide, silicon
oxycarbide, silicon oxycarbonitride, titanium oxide,
titanium nitride, titanium carbonitride, titanium
carbide, titanium oxycarbide or titanium oxycarbo-
nitride .

-li-
lt is also possible to apply a film in compression on
each side of the substrate. When the glass is coated
only on one side with a film in compression, the
scoring may be done on the side with the film. For the
scoring, a force may be applied to the glazing that
tends to reduce the convexity conferred on the coated
glass by the film, but this is not essential. When the
glass is coated on both its faces with a film in
compression, the scoring may be done on one or other of
the faces.
The treatment conferring the stress on the :. glass may
also be the application of an approximately isotropic
biaxial bending force. A suitable biaxial bending force
may be applied by heating the two main faces • of the
glazing to different temperatures and by opposing the
deformation that this temperature difference naturally
tends to induce by applying a force to the glazing. The
scoring is performed, and hence the breaking, as long
as the temperature difference and the force opposing
the deformation exist. In this case, the bending forces
are generated by the combination, on the one hand, of
the application of different temperatures to the main
faces and, on the other hand, of forces opposing the
deformation that the temperature difference induces.
Figure 3 illustrates one embodiment according to this
principle. This figure shows a glazing unit having two
main faces (7) and (8) and a plate (9) having a number
of holes (10) . The glazing unit may be pressed against
the plate since it is sucked against it by suction
being exerted through the holes. The plate is heated to
a different temperature from the starting temperature
of the glazing so that the face (8) has a different
temperature from that of the face (7) . The creation of
this temperature difference between the two faces of
the glazing is why stress is created in the glazing
while it rests pressed against the plate. This is
because if the glazing were left to assume its
equilibrium shape, it would not contain any stress. If

- 12 -
the face (8) is hotter than the face (7) , it is the
face {8) that is in compression as long as the glazing
remains pressed. In this case, the scoring may be done
on the face (7) , that is to say the face in extension.
The subcrack on this face therefore immediately reaches
the region in extension and a subcrack of very shallow
depth, while still remaining deeper than 10 m may be
sufficient. If the face (8) is cooler than the face
(7) , it is the latter face that is in compression as
long as the glazing remains pressed. In this case, the
scoring may be done on the face (7), that is to say the
face in compression, in which case, since the subcrack
has to be deeper than the thickness in compression in
order to reach the region in extension, it must be
deeper than half the thickness of the glazing.
In the case of the application of a bending force, the
scoring must be done while said force is being exerted.
The forces applied so as to generate the stress in the
glass are much less than the conventional breaking
forces. For example, for a glazing unit having a
thickness ranging from 0.1 to 5.2 mm, these bending
forces may be between 3 and 70 MPa, extends understood
that the thinner the glazing the higher the force must
be. In general, for glazing having a thickness ranging
from 1 to 5.2 mm, these bending forces may be between 3
and 2 0 MPa. In fact, as soon as the scoring is done,
the subcrack propagates right into the thickness of the
glass and it would be possible to immediately stop the
bending forces just after scoring without this having
any influence on the breaking.
To cut the glass having a suitable K factor without
breaking it, the surface of the glass is scored along a
line corresponding to that of the desired cut. This
scoring results in a subcrack (also called a blind
crack by those skilled in the art) . The scoring may
especially be done using a scoring wheel or by a
diamond or by laser. Usually, and more particularly for

- 13 -
glazing having a thickness ranging from 1 to 3 mm, the
subcrack has a depth of 100 to 1 000 m. Usually, the
subcrack has a depth of between 10% and 2 0%, for
example about 15%, of the glazing thickness.
When a scoring wheel or a diamond is used, the scoring
is done with a load sufficient to obtain a sufficient
depth of the subcrack, which must be able to propagate
without the application of a breaking force. When a
scoring wheel or a diamond is used, the scoring is
preferably done under a cutting oil (also called
"petrol" by those skilled in the art) . When a scoring
wheel is used, it is preferable to use a scoring wheel
with a large angle, for example 145°. The angle of the
scoring wheel is the angle a as shown in figure 4. For
a given scoring wheel or diamond, it is also possible
by routine tests to find a load suitable for the
scoring. This is because an insufficient load results
in no fracture, while an excessively high load results
in an uncontrolled fracture, that is to say a fracture
that does not always follow the line of scoring.
When the essential parameters of the invention have
been achieved, the crack caused by the scoring
propagates all by itself through the treated glazing,
that is to say without it being necessary to apply a
breaking force. It is possible to accelerate the
propagation of the crack by at least one of the
following means:
- with water: a little water may be placed in the
subcrack; to do this, it is possible, for example, to
wet the glazing before cutting, wetting only that part
(typically a few mm) of the glazing corresponding to
the end of the scoring;
- by increasing the scoring load at the end of
scoring.
The scoring must result in a subcrack. The scoring may
be carried out on a main face of the glazing that is in

- 14 -
compression or, if it exists, on a main face of the
glazing that is in extension. When the scoring is
carried out on a main face in compression (especially
in the case of a surface treated by chemical toughening
or by a film in compression) , the subcrack is deeper
than the thickness in compression ec so as to reach the
region in extension. Preferably, especially if the
treatment is a chemical toughening treatment, the
subcrack has a depth of 5 to 20 times the value of the
thickness in compression ec.
In the case of a chemical toughening treatment, the
thickness in compression may be evaluated from the
depth of ion exchange Pe, which may be determined
JTT x Mv x ev x Am
a) either by Pe = - — :
32 xaxmr
in which:
a represents the initial molar % of alkali metal
oxide in the glass (for example Na20 or Li20) ;
mi represents the total initial mass (before
toughening) of the glass in grams;
Mv represents the molar mass of the glass in
g/mol;
Am represents the rate of uptake of the glass
during toughening in grams; and
ev represents the thickness of the glass in
micrometers,
Pe thus being obtained in micrometers;
b) or by a microprobe profile, in which case it is
defined by the depth for which the content of ions
provided by the toughening is equal to that of the
glass matrix to within 5%.
In the case of a treatment by formation of a film, the
thickness in compression is equal to the thickness of
the film, provided that the film is in compression and
that no external force deforms the glazing
substantially.

- 15 -
In the case of a treatment by the application of
bending forces, if the scoring is carried out on the
side in compression, the thickness in compression is
equal to one half of the thickness of the glazing. In
the case of a treatment by the application of bending
forces, if the scoring is carried out on the side in
extension, the subcrack may be shallower, while still
remaining greater than 10 μm.
The invention makes it possible in particular to cut a
glass sheet having a thickness of at least 0.3 mm, or
at least 0.7 mm, or at least 1.2 mm or greater than
1.5 mm or even at least 2.6 mm, without breaking it. In
general, the glass sheet has a thickness of less than
20 mm, for example at most 5.2 mm. The glazing may in
particular have a thickness ranging from 0.7 mm to
5.2 mm, for example 2.6 to 5.2 mm.
The cutting according to the invention starts by the
scoring of a subcrack on the surface of a glass, and
the propagation of a crack through the entire thickness
of the inorganic part of the glazing that has undergone
the cut is observed. In fact, in the case of a
laminated glazing unit that is the association of at
least two glass sheets placed on either side of a
polymer interlayer, one of the glass sheets being
treated according to the invention and scored according
to the invention, it is clear that the crack propagates
only through the sheet that was scored and not the
other glass sheet lying on the other side of the
polymer interlayer.
The invention also relates to a glazing unit comprising
a glass sheet having two main faces and at least one
edge, said glazing unit having a distribution of
stresses through its thickness, said stresses being
biaxial, approximately isotropic and self-balanced, and
the K factor of which is between 0.05 and 0.4 MPa.m1/2.

- 16 -
The invention makes it possible to produce cutting
profiles that the prior art does not allow to be
produced.
According to the invention, it is possible to cut glass
along a curved line with a very small radius of
curvature, and to do so even with a thick glass. At
least at one point along the line of cutting, the
radius of curvature may be less than 4 0 mm, or even
less than 3 0 mm, or even less than 2 0 mm or even less
than 10 mm or even less than 5 mm. In general, the
radius of curvature is greater than 3 mm. Such radii of
curvature of the cutting may be obtained for glazing
with a thickness of even greater than 1 mm, or indeed
greater than 2.6 mm. In general, to produce radii of
curvature of less than 10 mm, it is preferable for the
glazing to have a thickness of less than 5.2 mm, in
particular, it is thus possible to cut magnetic
recording disks, that is to say to make,
simultaneously, their peripheral circular cut and their
central circular hole.
According to the invention, it is possible to make a
cut along a curved line changing in concavity, and even
linking inverse concavities with very small radii of
curvature, such as those that have just been given.
Figure 5 illustrates one form of cut produced on a
glazing unit (11) , said cut having a change of
concavity at the point (12) . Linked to the point (12)
are two curves of different concavity. In figure 5, the
curve on either side of the point (12) has the same
radius of curvature in absolute value, which may be
very small as already explained.
According to the invention, it is possible to cut the
glass over a very small width. A glazing unit generally
has a thickness, a width and a length (at least equal
to the width). In general, the glazing to be cut

- 17 -
according to the invention has an approximately-
constant thickness. In general, it is flat. According
to the invention, the width of glazing cut may even be
less than 1.5 times the thickness, and even less than
1.2 times the thickness, and even less than 1 times the
thickness and even less than or equal to 0.7 times the
thickness. In general, the width of glazing cut is
greater than 0.1 times the thickness. Thus, the
invention makes it possible in particular to produce
glass strips of square or rectangular cross section
having the width given above and especially a width of
magnitude similar to that of the thickness or even less
than that of the thickness.
According to the invention, it is possible to cut a
glazing unit along a line of cutting that includes an
angle. This angle may, for example, range from 60° to
120° and in particular be 90°. Remarkably, the cut
results in a piece having a concave angle a1 and a
piece having a convex angle a2 being obtained (see
figure 6) . To do this the cut has not to be the result
of intersection of two different lines of cutting that
meet, said intersection forming the desired angle, the
two lines of cutting being continued beyond their
intersection. To produce the angle according to the
invention, there are two options:
1) a hole may be made at the point chosen for the
angle before the cutting and then the cutting is
carried out by making two different scored lines that
meet at the site of the hole, the hole possibly having
a diameter of 0.2 to 2 mm for example; or
2) a hole is not made at the place chosen for the
angle, rather a scored line is made that at every point
satisfies the abovementioned condition as regards the
radius of curvature, which must therefore be at least
3 mm. Thus, the angle is in fact a curve of very small
radius of curvature. It is possible to repeat the
scoring several times provided that the various scored
lines meet so that their tangents coincide at the

- 18 -
points of intersection.
If it is desired to do the scoring by hand, it may be
preferable to produce a hole at the place desired for
the angle. If the scoring is done by a machine, a hole
need not be made prior to the scoring provided that the
scoring complies with the minimum radius of curvature
given above. With this type of machine, the tracing is
generally carried out in one single step, that is to
say the scoring object is placed once on the glass and
does not leave it until the end of the scoring.
Figure 6 shows two glazing pieces after the cutting
according to the invention. It may be seen that the cut
has a rounded angle of small radius of curvature
producing, in the two cut parts, two angles that fit
together perfectly. This angle was produced without
forming a hole prior to the cutting. According to the
prior art, it was known how to make 90° angles, but by
the intersection of lines of cutting that cross each
other, that is to say that continue after their point
of intersection. Figure 7 illustrates this way of
cutting ordinary glass according to the prior art, with
lines of cutting (13) traversing the entire surface of
the glazing, and resulting in square or rectangular
pieces (14) . The angles of all the pieces cut in this
way are convex, none of the cut pieces having a concave
angle.
According to the invention, it is possible to cut and
remove a full shape even from the inside of a glass
plate without said cut intersecting the original
external border of the glazing. Thus, a full shape,
whose external border has the shape of the cut, is
removed from the rest of the glazing, which then has an
internal border having the shape of the cut and an
external border remaining unchanged with respect to the
original external border (before cutting). To do this,
the scoring is carried out along a line that joins up

- 19 -
with itself without intersecting with the external
border of the glazing and resulting in the cutting, on
the one hand, of a full shape and, on the other hand,
of a holed shape, the external outline of the holed
shape corresponding to the original external outline of
the glazing, the internal outline of the holed shape
corresponding to the external outline of the full
shape. This full shape may be a circle or have a radius
of curvature as already mentioned. Figure 8 illustrates
this possibility. In this figure, a full shape (15) has
been cut from the inside of a plate, which then appears
as a holed shape (16). The external outline of the full
shape corresponds to the internal outline (17) of the
holed shape. The external outline (18) of the holed
shape is the same as the original plate before cutting.
The full shape may be a circle or may include a small
radius of curvature, as already mentioned. The full
shape may also include one or more angles as already
mentioned, it being understood that these angles have
to be made according to the abovementioned conditions,
that is to say with the formation of a hole prior to
the cutting or without the prior formation of a hole,
but by the scoring complying with a minimum radius of
curvature of 3 mm. Thus, a full shape may be cut with a
polygonal outline. In particular, the polygonal shape
may include three, four, five or six angles, or even
more. Thus, it is possible to cut a full shape having
the shape of a square or rectangle after having made a
cut with four 90° angles (this is the case for the cut
shape shown in figure 8). The holed shape therefore has
the shape of a frame, said frame shape having an
internal border of square or rectangular shape and an
external border of square or rectangular shape. This
frame also has a cross section of square or rectangular
shape. The holed shape (or frame) thus obtained is
especially applicable as an insert piece between two
glazing units, such as in flat FED (field emission
display) screens. The holed shape may have a very small
edge width ((19) in figure 8), that is to say one

- 20 -
corresponding to what was already mentioned as regards
thin strips. The full shape may be separated from the
holed shape, preferably by extraction from that side
with the initial scoring. The full shape may generally
be extracted by hand. To make extraction easier,
especially for greater glazing thicknesses, a thermal
extraction operation may also be carried out, which
consists in heating (for example to between 90 and
220°C) firstly the entire cut glazing, but for which
the full shape and the holed shape have not yet been
separated, and then secondly the central part of the
glazing comprising the full shape to be extracted is
cooled. The contraction caused by the cooling allows
the full shape to be more easily extracted.
The cutting according to the invention may be carried
out by scoring the surface of a glass sheet treated in
accordance with the invention (chemical, film, or
bending treatment), said sheet forming part of a
laminated glazing unit. In this case, the crack caused
by the scoring propagates through the thickness of the
treated sheet and stops at the polymer interlayer
usually placed between the sheets of a laminated
glazing unit. In this way, a multitude of parallel
linear cracks may be produced through the treated sheet
of the laminated glazing unit, passing through said
sheet as far as the polymer interlayer. The cracks thus
created act as mirrors for light passing through the
glazing. The aesthetically attractive glazing thus
obtained may serve as a light deflector. Figure 9
illustrates this application. It shows that the light
rays (20) are reflected at the interfaces (21) of the
cracks created in accordance with the invention through
the treated sheet (22) of the laminated glazing unit
(2 3) comprising the combination of two glass sheets
separated by a polymer layer (24). In this application,
the cracks may be separated from one another by a
distance of, for example, 2 mm to 10 mm. In general, it
is desirable for the distance between two cracks to

- 21 -
represent 4 0 to 80% of the thickness of the cracked
sheet.
Of course, it is also possible to carry out
conventional cutting, that is to say passing through
the entire surface of the glazing, in order to cut
square or rectangular shapes. Pieces of this type may
serve as protective glazing for LCD (liquid-crystal
display) cells.
The present invention, particularly when it involves a
chemical toughening treatment, is very beneficial for
the cutting of glazing in the electronic field. This
chemical toughening technique is particularly
applicable to glass capable of ion exchange, as is the
case in electronics for glass having in particular a
high strain point, for example CS77 glass sold by
Saint-Gobain Glass France. The composition of such
glass is described, for example, in EP 0 914 299. The
cutting technique is therefore applicable in lines for
the manufacture of accessories for electronics (such as
spacers or inserts) , of screens (plasma, LCD, TFT, FED
screen) and of field emission displays, and in lines
for manufacturing vacuum glazing. The use of chemical
toughening gives the edges, especially the cut edges,
high mechanical strength. With the cutting techniques
of the prior art, it is necessary for the components to
be brought into contact with the surface of the glass
and to be held thereon, for the scoring and/or
breaking, in order to cut the glass. This is a drawback
if a surface of the glass has already received
printing, as any contact with this printing may damage
it. Thanks to the technique according to the invention,
and more particularly when it employs chemical
toughening, it is therefore possible to print the glass
after the stress-generating treatment and then to cut
it with the minimum of contact with components. In
particular, it is therefore possible to produce a
motherglass, to print patterns on the surface and then

- 22 -
to carry out the manufacturing cycles in order only
thereafter to cut each screen (telephone, palmtop or
portable computer screen).
All the examples start with the chemical toughening of
a glass plate, produced as follows, the essential
parameters of said toughening (time and temperature)
being given in table 1. The starting glasses used were
the following:
CS77: glass sold by Saint-Gobain Glass France;
Px: glass of the PLANILUX brand sold by Saint-
Gobain Glass France;
C0211: glass sold by Corning.
Chemical toughening for the examples
A flat glass with the dimensions 300 x 200 x e mm was
taken, "e" representing the thickness that was
toughened in a potassium nitrate bath at a temperature
T for a time "t". The treatments produced core stresses
in the sheet.
Cutting principle for the examples
The glass plates were cut, using a diamond or a scoring
wheel, into various cut shapes corresponding to various
applications. The cuts using a scoring wheel were all
made according to the principle below. The scoring was
done with a scoring wheel of the VITRUM brand sold by
Adler, said scoring wheel having an angle of 145° and a
diameter of 5 mm with cutting fluid and with a load so
that the subcrack is deeper than the exchange depth Pa.
For the examples illustrating the invention, it was
noticed that the subcrack propagated through the entire
thickness of the glass without it being necessary to
apply a breaking force (see the "propagation" line in
table 1) . In certain cases, the propagation was
initiated at the end of the scored line by adding

- 23 -
water, which penetrated by capillary effect into the
subcrack. In other cases, the propagation was initiated
by increasing the load at the end of the scored line.
For all the examples, the K factor in the glass was
measured by a biasographe on glass strips 10 mm in
width, except in the case of examples 5 and 6 for which
the glass strips were 3 mm in width.
In table 1, the following expressions and abbreviations
are used:
- Pe: ion exchange depth,-
- ∆ load: increase in load;
- Propagation and type: it was judged whether the
crack propagation proceeded correctly (guided
propagation) or whether it was uncontrolled, which
means that the glass does not break along the line of
scoring, or whether it does not occur, which means that
in the end the glass has not broken.
Examples 1 and 2: frames
Before the chemical toughening treatment, four holes
1 mm in diameter were produced in the corners of the
plate with a diamond drill bit, said holes being placed
4 mm from the edges of said plate. After the chemical
toughening treatment, the plate was cut along straight
lines parallel to the edges of the plate and between
the holes, so as to draw a frame. The glass rectangle
between the holes could be extracted so as to recover a
frame (see figure 8).
Example 3; daylight reflection
A laminated glazing unit was produced with, on the one
hand, the chemically treated plate and, on the other
hand, a pane of ordinary soda-lime glass (not
chemically treated) 2 mm in thickness, placing between
them, in the conventional manner, a film of polyvinyl
butyral (PVB).

- 24 -
After one end of the glazing unit had been immersed in
water (to about'5 mm), a first series of straight and
parallel scored lines was produced by the scoring wheel
on that side of the glazing that was chemically
toughened, said scored lines being separated from one
another by 8 mm and finishing at the edge immersed in
water. The water plays its role by initiating the
propagation of each crack. A second series of scored
lines was then produced, between the scored lines of
the first series, so that in the end the plate had
scored lines approximately every 4 mm. It was noted
that all the cracks caused by the scored lines
propagated as far as the PVB film, that is to say they
passed through the entire thickness of the chemically
toughened glass pane. The glazing unit could then act
as a reflector for light passing through it, thanks to
the mirror effect of each of the cracks (see figure 9).
Example 4: cutting a circle
A circle 60 mm in diameter was cut in the chemically
toughened glass using a scoring wheel of the VITRUM
brand sold by Adler, said scoring wheel having an angle
of 145° and a diameter of 5 mm and said scoring wheel
being mounted on a circular glass cutter with a handle,
having the reference Bohle 530.0 section 1.19. The
glass disk could be extracted by thermal extraction
without either the disk or the rest of the plate
breaking.
Example 5: cutting film glass
Using a diamond, a glass sheet 300 urn in thickness was
cut after it had been chemically toughened, without
initiation, either with water or by a load increase.
The cut is made easily along the scored line without
uncontrolled breaking. The K factor in the glass was
measured by a biasographe on strips 3 mm in width.

- 25 -
Example 6: (comparative example)
The procedure was as in the case of example 5, except
that the chemical toughening was carried out so that
the K factor reached the value mentioned in table 1.
Examples 7 to 9 (comparative examples)
The procedure was as in the case of example 2, except
that the chemical toughening was carried out so that
the K factor reached the value mentioned in table 1.

- 26 -
Table 1

27
We Claim
1. A method of cutting a glazing unit without applying a breaking force, the
glazing unit comprising a glass sheet having two main faces, said method
comprising the steps of:
- application of a treatment to the glass sheet that generates
stresses such that at least one region in compression and at least
one region in extension, the distribution of the stresses being
biaxial, isotropic and self balanced in its thickness, said stresses
being such that the K factor is between 0.05 and 0.4 Mpa.m1/2, said
K factor being defined by
K =[ ∫zỢz2.H(Ợ2).dz]1/2
in which z is a position in the thickness, Ợ2 is the intensity of the
isotropic biaxial stress at the position z, H(Ợ2) is equal to 1 if Ợ2 is
greater than 0 and is equal to 0 if Ợ2 is less than or equal to 0, with
the convention that extension is denoted by positive values and
compression by negative values; and then

28
- scoring a subcrack deeper than 10 m along the desired line of
cutting of the treated glass, said subcrack reaching that region of
the glazing in extension.
2. The method as claimed in the preceding claims, wherein, before
treatment, the glass contains an alkali metal oxide and wherein the
treatment is a chemical toughening treatment.
3. The method as claimed in the preceding claims, wherein, the chemical
toughening results in a K+ or Na+ ion gradient perpendicular to at least
one of the main faces and decreasing from said main face.
4. The method as claimed in claims 2 or 3, wherein, the chemical toughening
results in ionic exchange over a depth of at most 50 m.
5. The method as claimed in claim 1, wherein the treatment is the
application by deposition of a film in compression.
6. The method as claimed in the preceding claim, wherein the film has a
thickness ranging from 1 to 20 m.
7. The method as claimed in preceding claim, wherein the film contains a
stress ranging from 200 Mpa to 5 Gpa.

29
8. The method as claimed in claim 1, wherein the treatment is the
application of isotropic biaxial bending forces.
9. The method as claimed in the preceding claim, wherein the bending
forces are generated by the combination, on the one hand, of the
application of different temperatures to the main faces, and on the other
hand, of forces that oppose the deformation that the temperature
difference induces.
10.The method as claimed in claims 8 or 9, wherein the bending forces are
between 3 and 20 Mpa.
11.The method as claimed in one of the preceding claims, wherein the
glazing has a thickness ranging from 0.7 to 5.2 mm.
12.The method as claimed in the preceding claims, wherein the glazing has a
thickness ranging from 2.6 to 5.2 mm.
13.The method as claimed in one of the preceding claims, wherein the
scoring is carried out on a main face in compression and produces a
subcrack that passes through the region in compression in order to reach
the region in extension.
14.The method as claimed in one of claims 1 to 12, wherein the scoring is
carried out on a main face in extension.

30
15.The method as claimed in one of the preceding claims, wherein the
scoring is carried out along a line that joins up with itself without
intersecting the external border of the glazing and resulting in the cutting,
on the one hand, of a full shape and, on the other hand, of a holed shape
corresponding to the original external outline of the holed shape
corresponding to the original external outline of the glazing, the internal
outline of the holed shape corresponding to the external outline of the full
shape.
16.The method as claimed in one of the preceding claims, wherein the
scoring is carried out along a line having, at least one point, a radius of
curvature of less than 5 mm.
17.A glazing unit comprising a glass sheet having two main forces and at
least one edge, said glazing unit having a distribution of stresses in its
thickness, said stresses being biaxial, isotropic and self-balanced, and the
K factor of which is between 0.05 and 0.4 MPa.m1/2, said K factor being
defined by
K = [ ∫z Ớ2 2. H (Ớ2).dz]1/2
in which z is a position in the thickness, Ớ2 is the stress at the
position z, H (Ớ2) is equal to 1 if Ớ2 is greater than 0 and is equal to

31
0 if Ớ2 is less than or equal to 0, with the convention that extension
is denoted by positive values and compression by negative values.
18. The glazing unit as claimed in the preceding claims, comprising an alkali
metal ion gradient perpendicular to at least one of the main faces and
decreasing from said main face.
19. The glazing unit as claimed in the preceding claims, wherein the
gradient perpendicular to at least one of the main faces exists at the
surface of at least one edge.
20. The glazing unit as claimed in the preceding claim, wherein the edge has
the scored line of a cutting subcrack.
21. The glazing unit as claimed in one of the preceding claims, wherein at
least one edge has no alkali metal ion gradient in the direction
perpendicular to said edge.
22. The glazing unit as claimed in one of the preceding claims, comprising a
thickness ranging from 0.7 to 5.2 mm.
23. The glazing unit as claimed in claim 22, comprising a thickness ranging
from 2.6 to 5.2 mm.

32
24.The glazing unit as claimed in one of the preceding claims, wherein one of
its borders has, at least one point, a radius of curvature of less than 5
mm.
25.The glazing unit as claimed in one of the preceding glazing unt claims,
wherein at least partly in the form of a strip with a square or rectangular
cross section having a width of less than 1.5 times its thickness.
26.The glazing unit as claimed in the preceding claim, comprising at least
partly a width of less than 1 times its thickness.
27.The glazing unit as claimed in one of the preceding claims, comprising a
frame shape with a square or rectangular cross section, said frame shape
having an internal border of square or rectangular shape and an external
border of square or rectangular shape.
28. A flat field emission display, comprising an insert having a glazing unit as
claimed in one of the preceding claims.
29. A laminated glazing unit, the glass sheets of which constitutes a glazing
unit as claimed in one of the claims 17 to 19 and comprising a multitude
of parallel linear cracks passing through it as far as the polymer interlayer.

33
30.The glazing unit as clamed in the preceding claims, wherein the cracks are
separated from one another by a distance of 2 mm to 10 mm.
31.The glazing unit as claimed in claims 29 or 30, wherein the distance
between two cracks represents 40 to 80% of the thickness of the cracked
sheet.
DATED THIS 4TH DAY OF NOVEMBER 2004

The invention relates to a method of cutting a glazing unit without applying a
breaking force, the glazing unit comprising a glass sheet having two main
faces, said method comprising the steps of applying a treatment to the glass
sheet that generates stresses such that at least one region in compression
and at least one region in extension, the distribution of the stresses being
biaxial, isotropic and self balanced in its thickness, the stresses being such
that the K factor is between 0.05 and 0.4 Mps.m1/2, said K factor being
defined by K = [∫ZỚZ2- H(Ớ2).dz]1/2, in which z is a position in the thickness, Ớ2
is the intensity of the isotropic biaxial stress at the position z, H(Ớ2) is equal to
1 if Ớ2 is greater than 0 and is equal to 0 if Ớ2 is less than or equal to 0, with
the convention that extension is denoted by positive values and compression
by negative values; and scoring a subcrack deeper than 10 m along the
desired line of cutting of the treated glass, the subcrack reaching that region
of the glazing in extension.

Documents:

1657-kolnp-2004-granted-abstract.pdf

1657-kolnp-2004-granted-claims.pdf

1657-kolnp-2004-granted-correspondence.pdf

1657-kolnp-2004-granted-description (complete).pdf

1657-kolnp-2004-granted-drawings.pdf

1657-kolnp-2004-granted-examination report.pdf

1657-kolnp-2004-granted-form 1.pdf

1657-kolnp-2004-granted-form 18.pdf

1657-kolnp-2004-granted-form 2.pdf

1657-kolnp-2004-granted-form 3.pdf

1657-kolnp-2004-granted-form 5.pdf

1657-kolnp-2004-granted-gpa.pdf

1657-kolnp-2004-granted-reply to examination report.pdf

1657-kolnp-2004-granted-specification.pdf

1657-kolnp-2004-granted-translated copy of priority document.pdf

« Previous Patent

Next Patent »

Patent Number

228126

Indian Patent Application Number

1657/KOLNP/2004

PG Journal Number

05/2009

Publication Date

30-Jan-2009

Grant Date

28-Jan-2009

Date of Filing

04-Nov-2004

Name of Patentee

SAINT GOBAIN GLASS FRANCE

Applicant Address

18 AVENUE D'ALSACE, F-92400 COURBEVOIE

Inventors:

#	Inventor's Name	Inventor's Address
1	GAUM OLIVLER	31 RUE VOLTAIRE 92300 LEVALLOIS-PERRET
2	VALLADEAU SERGE	6 RUE FALDHERBE 93700 DRANCY

PCT International Classification Number

C03B 33/033

PCT International Application Number

PCT/FR2003/

PCT International Filing date

2003-05-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	02/05956	2002-05-07	France