FR2703043A1 - Composition for enamelling glass substrates, application to laminated glazing and products obtained - Google Patents

Abstract

The enamel composition contains a frit which has antiadhesive properties and a medium made up essentially of volatile components. The enamel composition is advantageously employed for coating at least a part of the internal face of a laminated glazing.

Description

COMPOSITION FOR ENAMELLING GLASS SUBSTRATES,
APPLICATION TO SHEET GLASS AND PRODUCTS OBTAINED
The present invention relates to an enamel composition intended to cover, at least in part, a glass substrate and particularly suitable for coating the faces of glass substrates (or sheets) oriented towards the inside of a laminated glazing.

 The invention also relates to methods of manufacturing glazed glazing and in particular laminated glazed glazing, said methods using the above-mentioned composition, as well as the products obtained according to said methods.

 Enamels are well known in the state of the art and used in particular on glass substrates such as vehicle glazing or building glazing. They allow, among other things, to form borders, decorative layers or protective layers. Thus, in automobile glazing, enamels are used to hide the collector strips of heating networks or to hide and protect the heating networks themselves. They are also and above all used to protect bonding cords used for mounting glazing in bodywork bays against UV radiation, at the same time as they mask said cords.

 In general, the enamel is deposited by screen printing. It is in fact known to deposit, in this mode, the enamel on the substrate, to dry the layer thus obtained to allow its adhesion to the glass, to possibly deposit other layers which are also dried, before heat treatment. '' all the enamel layers at high temperature to vitrify the enamel and obtain the final coating.

 In the case of laminated glazing, it is known to deposit the enamel by screen printing on an external face of the glazing, before drying and then baking said enamel, the firing of the enamel taking place during the simultaneous bending of the substrates for the glazing curved puff pastry. However, simultaneous bending of the superimposed substrates in their final order with simultaneous baking of the enamel layer is only possible in the case where the enamel is outside the glazing. In the opposite case, where it is desired to provide a laminated glazing with an enamel layer on a substrate face intended to be brought into contact with another glazing substrate, the simultaneous firing of the enamel with the bending poses There are many problems. The enamel contains organic components which, at the firing temperature, give off reaction products in gaseous form, which cannot escape outside the space between the two substrates. The risks of bonding of the substrates to one another during the melting of the enamel are also significant.

 It is known, to remedy these problems, to bake the enamel on a flat substrate before bending. Thus, patent application DE-A-39 20 573 proposes to subject the enamelled substrate still planar to firing at high temperature (of the order of 6000C), to allow said substrate to cool before superimposing it on a second substrate and to simultaneously bend the two substrates. This process makes it possible to solve the problems associated with the reaction gases, bonding being avoided by the use of separating agents between the two substrates, but imposes a number of requirements. The enamelled substrate must in fact remain flat and not present any internal stress which could lead to deformations during bending. The transport of the substrates on conveyor rolls among others, can cause slight but sufficient deformations so that the glazings thus produced have optical qualities insufficient. In addition, a high temperature treatment before bending is expensive and may cause irreversible optical defects.

Another process, described in the patent application
DE 42 01 275.9, proposes to resort to a pre-bending and a simultaneous firing of the enamel, however reversing the order of the substrates so as to present the face covered with enamel on the outside. After the substrates thus pre-curved have cooled down, the place of the substrates is swapped and said substrates are curved to their final shape, the enamelled substrate this time having its face covered with enamel inside the laminated glazing.

However, this method requires the use of an additional bending step as well as an additional step of cooling and inverting the substrates while increasing costs.

 A first object of the invention is therefore to remedy the problems of enamelling inside a laminated glazing by proposing a simple and effective solution making it possible to obtain products of satisfactory quality at a lower cost and for a improved productivity.

 More particularly, the object of the invention is to develop an enamel composition making possible simultaneous bending of the glass substrates of a laminated glazing and a firing of the enamel in question when said enamel is on a face of substrate inside the laminated glazing and, more generally, to develop an enamel composition which can be used with advantage in all traditional enamelling processes.

 The object of the invention is also to develop an enameling method, and in particular an enamelling method on a substrate face inside a laminated glazing, said method using the abovementioned enamel composition.

 These aims are achieved, firstly, thanks to an enamel composition for a glass substrate, said composition comprising a frit having non-stick properties and a volatile medium.

 By anti-adhesive properties ("anti-stick") is understood, according to the invention, a non-adhesion of the enamel layer deposited on a substrate with respect to an element coming into contact with it during the bending operation.

 By volatile medium is meant, according to the invention, a medium comprising solvents which can be removed by evaporation at a temperature below about 2000C and, optionally, one or more resins which can be removed, in particular by carbonization, at a temperature below that inducing deformations of the glass, preferably at a temperature below 4000C.

 The invention also covers a method of enamelling a glass substrate using the enamel composition according to the invention.

 The invention also advantageously provides a solution to the enamelling of a face of a glass substrate inside a laminated glazing.

 The invention also relates to a glazing unit comprising at least one glass substrate provided, on at least part of one of its faces, with a layer of the enamel composition according to the invention. Advantageously, the glazing is a laminated glazing comprising two glass substrates and a plastic interlayer, one of the substrates being coated, on at least part of its face oriented towards the thermoplastic interlayer sheet, with an enamel composition according to the invention.

 The enamel composition according to the invention has a direct influence on the enameling processes using this composition. The presence of a very volatile medium makes it possible to work, in the first place, at low temperatures, therefore at costs all the lower as the temperatures are low and without risk of deformation of the glass substrate covered with enamel. The solvents making up this volatile medium can, for example, be chosen from terpene derivatives such as gamma-terpineol or beta-terpineol. According to the application and / or according to the choice of the components of the enamel composition, the medium may also contain a resin allowing the adhesion of the enamel to the glass substrate after drying. an ester of an acrylic acid such as a polyalkylacrylate, in particular polybutylmethacrylate or polymethyl methacrylate, can be used.

 Furthermore, the fact of using a frit having non-stick properties makes it possible to avoid problems of gluing of enamel during a bending step. The frits having non-stick properties according to the invention may consist of frits containing elements forming crystalline phases such as the elements described in patent EP 0 370 183 and in particular titanium oxide or zirconium oxide, or frits containing oxidizable metals in the form in particular of powder, such as those described in patents EP 0 362 136 and EP 0 466 343 and in particular zinc in the form of powder, or refractory products having melting points higher than 6500C .

 The enamel composition according to the invention can also advantageously contain a frit with a low melting point, that is to say a frit whose melting temperature is less than approximately 4500C and, preferably, less than approximately 4000C, this frit improving the adhesion of the enameled layer before final baking. Such a frit is necessary to deposit another layer of enamel on the first layer, this second enamel being generally called upon to fulfill different functions.

This is the case of conductive enamel layers based on silver paste that one wishes to deposit on a glazing to form heating networks that the first layer of enamel comes to hide from view.

 In this application, the low-melting frit-free enamel composition does not allow satisfactory adhesion of the second layer of enamel with respect to the first; it is therefore advisable to add to the enamel composition a frit with a low melting point, this frit allowing sufficient adhesion of the two layers of enamel and avoiding the problems of delamination of said enamels after firing. This frit may consist in particular of lead silicates, lead oxides or boric derivatives. Said frit is used in such proportions that the non-stick properties are not affected.

 The enamel composition according to the invention can be used in all enamelling processes and is particularly suitable for enamelling the faces of glass substrates located inside curved laminated glazing.

 The method according to the invention, as defined above, makes it possible to enamel the faces of substrates located inside curved laminated glazings as simply and effectively as traditional methods of enameling on faces of substrates made of glass located on the outside of curved laminated panes without fear of the problems of sticking or the problems of evacuation of gaseous reaction products previously mentioned.

 According to an embodiment of the present invention, a layer of the enamel composition is deposited comprising a frit having non-stick properties, a volatile medium and, optionally, a frit with a low melting point on at least part of '' at least one face of glass substrate intended to form part of a laminated glazing, said enamel is subjected to a precooking at a temperature below the deformation temperature of the glass, in particular by gravity, then the enameled substrate is associated with a second glass substrate in the order of their final arrangement within the glazing and the two substrates are simultaneously bent, the final baking of the enamel being carried out during bending.

 Advantageously, the deposition of the enamel layer is done by screen printing. Pre-baking takes place around 2000C in the case where the volatile medium does not contain resin and around 400 "C in the case where the volatile medium contains a resin. This low-temperature pre-baking is made possible in particular by the choice of the volatile medium as indicated above and makes it possible to release the gaseous reaction products without risking deformation of the glass substrates due to the relatively low working temperature. The bending is then carried out normally by gravity around 600 "C according to a method known per se, then the curved substrates are separated before being assembled again after intercalation of a sheet of thermoplastic material between said substrates.

 According to another embodiment of the present invention, a layer of the enamel composition according to the invention is deposited comprising a frit with a low melting point (such as that described in the example below) and a resin on at least part of at least one face of glass substrate intended to form part of a laminated glazing, said enamel is subjected to drying before depositing a second layer of conductive enamel by screen printing on the first layer of enamel previously mentioned. A drying of the new enamel is then carried out and then the substrate thus enamelled is subjected to a pre-baking step at a temperature below the temperature of deformation of the glass by gravity before assembling the enameled substrate to a second glass substrate. in the order of their final arrangement within the laminated glazing and to carry out a simultaneous bending of said substrates, the final firing of the enamels being carried out during the bomba ge.

 Here again, the precooking step makes it possible to release the gaseous reaction products at the same time as a pre-attachment of the enamels is carried out by melting the low-melting frit. The precooking taking place according to this embodiment at a temperature of the order of 4000C, there is moreover no risk of optical deformation of the substrates. The two drying stages are carried out at temperatures varying between 80 and 100 C.

 Advantageously, for enamel compositions comprising a frit with a very low melting point, of the order of 2000 ° C., such as a frit based on boric acid derivatives and not comprising resin, the process is simplified by eliminating the second drying step, the first taking place around 2000C and the precooking also taking place around 200 "C.

 The applications of the methods according to the invention are diverse.

 The main applications relate to the production of glazing, in particular curved laminated automobile glazing and, preferably, to the production of convex laminated automotive glazing covered with enamel on a face of substrate located inside the laminated glazing.

 An example of application relates to the production of a laminated automotive glazing provided with a heating network on a part of the face of the external substrate located inside the laminated glazing, as described in the publication US 4,373,130. A heating network is used to defrost the wipers on the other side of the above-mentioned external substrate and it constitutes a second layer deposited on a first layer of enamel used to mask it. The second deposited layer, when it is conductive, can also extend beyond the first enamel layer, for example to come into contact with another conductive layer of the glazing.

 The method according to the invention allows the production of glazing thus enamelled, as well as the production of any other glazed curved laminated glazing. The enamel composition according to the invention can also be advantageously used in any enamelling process.

 The glazings obtained according to the invention thus comprise at least one glass substrate coated, on at least part of one of its faces, with an enamel composition according to the invention and whose optical qualities are preserved.

 The example which follows illustrates, in a non-exhaustive manner, an enamel composition according to the invention and the associated method of glazing laminated glazing.

EXAMPLE
In this example, the enamel composition produced comprises a frit having non-stick properties, a volatile medium with resin and a frit with a low melting point in the following proportions by weight
80 parts of a frit having non-stick properties and of the following composition
PbO 38%
Cr2O3 20%
CuO 19%
SiO2 6%
MnO 4%
TiO2
B203 1%
Au203 0.5%
ZrO2 2.5%
20 parts of a volatile medium formed of 18 parts of terpene derivatives of the gamma-terpineol (1-methylcyclohexane 1-ol 4-isopropylene) and beta-terpineol type and 2 parts of a polybutylmethacrylate resin,
s 10 parts of a frit with a low melting point of the following composition
Pb304 60%
PbSiO3 22%
H3BO3 18%
This enamel is deposited by screen printing on the face of a glass sheet intended to be the face 2 of a laminated glazing, this face being oriented towards the interlayer, face 1 being the face oriented towards the outside of said glazing. The enamel is then dried at around 80-100 C, then a layer of conductive enamel based on silver paste is deposited on the first layer of enamel before being subjected in turn to drying around 1000C. The enamelled glass substrate is then subjected to a precooking around 4000C before associating it with a second sheet of glass which is placed above and the stack is subjected to bending according to traditional methods by gravity.

Claims (17)

 1. An enamel composition for a glass substrate comprising at least one frit having non-stick properties and a medium formed essentially of volatile components.  2. An enamel composition according to claim 1, characterized in that the frit having non-stick properties contains elements forming crystalline phases, such as titanium oxide, zirconium oxide.  3. An enamel composition according to claim 1, characterized in that the frit having non-stick properties contains oxidizable metals in the form in particular of powder, such as zinc powder, or refractory products having higher melting points. at 650 C.  4. Enamel composition according to one of the preceding claims, characterized in that the medium contains solvents having a melting point below 200 "C, such as terpene derivatives and, in particular, gammaterpineols or beta-terpineols .  5. Enamel composition according to claim 4, characterized in that the medium also contains one or more resins such as esters of acrylic acid.  6. Enamel composition according to one of the preceding claims, characterized in that the composition further comprises at least one low-melting frit based on components such as lead silicates, lead oxides or boric derivatives and whose melting temperature is around 400 "C and below.  7. An enamel composition according to claim 6, characterized in that the frit with a low melting point has a melting point of the order of 200 C.  8. A method of enamelling a glass substrate, characterized in that it uses an enamel composition according to one of claims 1 to 7.  9. The enameling method according to claim 8, on at least part of at least one face of glass substrate intended to form part of a laminated glazing, in which an enamel composition according to the is deposited by screen printing. one of claims 1 to 7, said enamel is precooked at a temperature below the glass deformation temperature by gravity and then the enamelled substrate is associated with a second glass substrate in the order of their final arrangement within the glazing and the two substrates are simultaneously bent, the final baking of the enamel being carried out during bending.  10. Enamelling method according to claim 9, characterized in that the face of the enamelled substrate corresponds to the face 2 of the laminated glazing, the association being effected by placing the second glass substrate on the enamelled face.  11. Enamelling method consisting in depositing a layer of the enamel composition according to claim 6 on at least part of at least one face of glass substrate intended to form part of a laminated glazing, in subjecting said enamel drying before depositing a layer of conductive enamel on the previous enamel, subjecting the enameled substrate to a new drying and then pre-cooking said enameled substrate before associating it with a second glass substrate by superposition of this second glass substrate in the order of their final arrangement within the glazing and to carry out a simultaneous bending of said substrates, the final firing of the enamels being carried out during bending.  12. A method of enamelling consisting in depositing a layer of the enamel composition according to claim 7 on at least part of at least one face of glass substrate intended to form part of a laminated glazing, in subjecting said enamel drying before depositing on the previous enamel a layer of conductive enamel, subjecting the enameled substrate to a precooking before associating it with a second glass substrate by superposition of this second glass substrate in the order of their final arrangement within the glazing and to carry out a simultaneous bending of said substrates, the final firing of the enamels being done during bending.  13. Enamelling method according to one of the preceding claims, characterized in that the drying or drying takes place at a temperature between 80 and 2000C.  14. Enamelling method according to one of the preceding claims, characterized in that the precooking takes place between 200 and 4000C approximately, the bending taking place at approximately 6000C.  15. Glazing comprising at least one glass substrate, characterized in that at least one glass substrate is coated, on at least part of one of its faces, with an enamel composition as defined in the claims 1 to 7.  16. Glazing according to claim 15, characterized in that it comprises two sheets of glass and a plastic interlayer, the face coated with enamel being an inner face and in particular the inner face oriented towards the interlayer of the sheet. of exterior glass.  17. Glazing according to one of claims 15 or 16, characterized in that it comprises an electrically conductive layer belonging to a heating network on the first layer of enamel deposited.