EP0777633A1

EP0777633A1 - Curable squeegee paste for printing on glass surfaces, and method for making same

Info

Publication number: EP0777633A1
Application number: EP96920876A
Authority: EP
Inventors: Wolfgang Schäfer; Walter Goerenz; Helmut Schmidt; Martin Mennig; Axel Kalleder
Original assignee: Saint Gobain Vitrage SA
Current assignee: Saint Gobain Vitrage SA
Priority date: 1995-06-08
Filing date: 1996-05-31
Publication date: 1997-06-11
Also published as: MX9700914A; CZ40497A3; PL318504A1; WO1996041773A1; JPH10504013A

Abstract

A curable squeegee paste for printing on glass surfaces, including at least one glass composition, one or more inorganic coloured pigments and a binder providing the flow properties required both for printing and for achieving sufficient solidity after drying. The inorganic pigments are coated as they are with a layer of glass or a gel of a suitable thermally solidified vitrifiable composition. The pigments are coated using a sol-gel method.

Description

BAKING PRINTABLE PASTE FOR PRINTING SURFACES

OF GLASS AND PROCESS FOR PRODUCING THE SAME

The present invention relates to a baking printing paste for printing glass surfaces, comprising at least one glass composition (for example a glass frit), one or more inorganic colored pigments and an organic and / or inorganic binder to impart the flow properties necessary for the printing operation and to achieve sufficient mechanical strength of the printed layer after drying. The invention also relates to a process for the preparation of such a printing paste.

Enamel-type baking inks are often applied for decorative purposes or for technical reasons on glass bodies, for example on glass sheets, and are fired at high temperatures. This technique is applied on a large scale for automotive glazing when the glazing is mounted, using the bonding technique, in the window frames of the bodywork. In this case, a frame-shaped layer made of an opaque baking ink for visible light and UV radiation is usually applied by screen printing on the glazing. The applied layer, after an operation of drying, is cooked during a subsequent bending and / or quenching operation. The purpose of the baked enamel layer is to prevent the adhesive region from being seen from the outside through the glazing and also to protect the adhesive from UV rays which can lead to spalling of the adhesive. over time. The printing pastes known for the preparation of such enamel-type layers contain as color pigments minerals with high melting point, for example copper-chromium-manganese spinel (CuO-Cr ₂ O ₃ -MnO) for the black color, mixtures of this spinel with titanium dioxide (TiO ₂ ) for the gray color, or mixtures of spinels formed by Sn, V, Fe, Zr, Si, Co, Al, Ni and Ca for others desired colors. Known printing pastes also include a glass frit which is present in the printing paste, like pigments, in the form of a finely ground powder and which, during the cooking operation (carried out, by example, at a temperature between 500 and 750-800 ° C) melts by partially or completely coating the colored pigments, so that after cooling, an enamel-like layer is firmly united on the surface of the glass substrate.

In known printing pastes, thermally and chemically stable inorganic materials or substances are used as colored pigments, that is to say only substances which do not thermally decompose at cooking temperature or chemically react with d 'other constituents of the printing paste or with the ambient atmosphere and therefore do not change their color or other properties. This means that we are limited in the choice of appropriate colored pigments and that we only use very stable minerals (generally oxides), namely the aforementioned spinels. For example, magnetite (Fe ₃ O) cannot so far be used as a colored pigment, because at the firing temperature it oxidizes to hematite (Fe ₂ O ₃ ) which as such no longer has the properties of desired coloring.

When the printed glass objects are glazings, for example automobile glazings, the recycling of printed glazings by adding to the vitrifiable mixture of cullet provided with these known enamel layers during the melting of the glass frequently gives rise to difficulties. When it comes to minerals with a very high melting point, it can indeed happen that the colored pigments remain contained as such in the molten glass. With other colored pigments which s distribute as dissolved oxides in the molten glass, it can also happen that they undesirably influence the properties of the glass, by modifying, for example, the viscosity of the molten glass, the color of the glazing obtained and / or other physical properties of molten glass and / or glazing. For this reason, it has hitherto not been possible to recycle glazing which is provided with a layer of baked enamel of known compositions, for example for the manufacture of high optical quality float glass.

The object of the invention is to prepare, for printing glass surfaces, baking printing pastes having a greater field of application and which can use a greater variety of components, in particular as regards the possibility of using less stable colored pigments.

The invention resides in the fact that the pigments present in the dough ready for printing and baking are coated as such with a layer of a glass or a gel (or xerogel) with a suitable vitrifiable composition thermally solidified. The printing paste suitable for cooking according to the present invention thus comprises at least one glass composition, one or more pigments and an organic and / or inorganic binder, the pigments being coated as such with a layer of a glass or a gel of a thermally solidified vitrifiable composition.

Generally and advantageously according to the invention, the pigments, present in the uncooked dough, are coated with a layer with a thickness of 0.5 to 5 μm of a glass or a gel of a thermally solidified vitrifiable composition.

By "composition" is meant by extension, one or more components. By “glass composition” is meant a vitrifiable composition (for example a glass frit) or a composition made vitreous (case, for example, where the composition forms the glass layer coating the pigments, as explained later).

The glass composition of the printing paste according to the invention can therefore be in the form of a powder of a glass frit or of vitreous or vitrifiable coatings of the pigment grains. The printing paste may also comprise a glass composition in the form of the coatings of the pigments and one or more compositions in the form of glass frit powder (s). In this case, the coating of the nature of a glass or of a gel of the pigmentary grains may have a different composition or which corresponds, in whole or in part, to the composition of a glass frit of the printing paste.

Preferably, the printing paste comprises at least one glass composition with a low melting point, that is to say with a melting point lower than the deformation temperature of the glass of the substrate to be printed or at the baking temperature. of the printed substrate, that is to say in most cases less than 750-800 ° C. and generally less than 650 ° C.

In the case in particular where the coatings of the pigments have a low melting point (when, for example, the pigments used are sufficiently stable at the usual cooking temperatures of between 500 and 800 ° C.), it is possible to reduce the amount of composition of glass in the form of glass frit powder in the printing paste ready to bake or even to completely dispense with the contribution of this glass powder to the printing paste. The glass composition is then present in the printing paste in whole or in part in the form of glass coatings surrounding the pigments. In this embodiment of the invention, a remarkably uniform and homogeneous distribution of the pigments in the baked enamel layer is automatically ensured, because neither accumulations of pigments nor large regions of pure glass matrix without coated pigments cannot form.

In the case on the other hand, where the coatings of the pigments have a high melting point, in particular greater than 750-800 ° C., (when for example the pigments used as they tend to transform at the usual cooking temperatures), the dough d printing according to the invention preferably comprises, in addition to the coatings, at least one composition in the form of a frit with a low melting point. The use according to the invention of pigments which are completely enclosed in a sealed coating of a thermally densified glass or gel as a preliminary stage of an appropriate glass has various favorable effects. For example, due to the coating, particles in principle more or less spherical with round or rounded surface are formed. In this way, flow properties of the printing paste which are more favorable are obtained, whereby the proportion and composition of the binder used in particular to obtain certain flow properties necessary for printing can be optimized ( for example, the amount of binder used can be reduced). Another essential advantage of the invention consists in that the printing paste, independently of the binder, largely contains grains or more or less spherical bodies having a glassy or vitrifiable surface. This has the consequence that, during the cooking operation, the bodies with a glassy or vitrifiable surface agglomerate more easily at their points of contact, so that the cooking operation can possibly take place at a lower temperature or that, for a predetermined cooking temperature, a vitreous or vitrifiable composition with a higher melting point (for example with a melting point greater than 750 ° C., in particular greater than 1000 ° C.) can be used, in particular for coating the pigments.

The invention therefore leads, even when using the colored pigments used up to now, to notable advantages as regards the quality of the layers of baked enamel. It also offers the advantage that the printing pastes, insofar as the glass composition is formed only by coating the grains of pigments, can be baked at lower temperatures. Indeed, in certain circumstances, it is not necessary to choose the high baking temperature to the point that the glass composition melts completely, but it may be sufficient in this case that the glass spheres containing a grain of pigment constitute by simple sintering a coherent layer. In this way, for example, more or less porous enamel layers can be obtained, which may be desirable in many cases.

The invention also makes it possible to use colored pigments which are chemically less stable than the minerals with high melting point hitherto employed. Because the pigments are coated in a closed protective envelope, they do not come into immediate contact either with the ambient atmosphere or with any reactive agents in the printing paste during the baking process. The composition and the thickness of the protective coating of the nature of a glass or a gel must, in this case, be chosen so that the protective action remains intact at least for the duration of the operation. proper cooking.

In this way, it is now possible to use pigments which until now have been out of the question because they changed color or they completely lost their coloring function by oxidation or reduction during the cooking operation. For example, using the invention, it is now possible to use as colored pigments also iron oxides, such as magnetite (Fe ₃ O ₄ ) and / or hematite (Fe O ₃ ), or even carbon in the form of carbon black or graphite or titanium nitride, etc. In this way, it is also now possible to use pigments which do not interfere when recycling glazed glass panes, because that they are completely burnt at the melting point of the glass and escape in the gaseous state, such as for example carbon or which dissolve in the molten glass and become constituents of the glasses in the form of oxides which are not bothersome, such as certain metal oxides.

In principle, the protective coating of the nature of a glass or a gel around the pigments may consist of the oxides of the most diverse elements, in particular the oxides of the elements silicon, lead, bismuth, zinc, titanium, zirconium, aluminum, boron, phosphorus, calcium, magnesium, sodium and / or potassium. For example, coatings of pure SiO ₂ , as well as coatings from the two-component system SiO ₂ -B ₂ O ₃ in proportions of the order of 70 to 90% by weight of Si0 ₂ and from 10 to 30 % by weight of B ₂ O ₃ were found to be satisfactory. Coatings from the ternary system PbO-B ₂ O ₃ -SiO ₂ in proportions of the order of 70 to 90% by weight of PbO, from 5 to 15% by weight of B ₂ O ₃ and from 5 to 15% by weight of SiO ₂ or from the four-component system PbO- B ₂ O ₃ -SiO ₂ -ZnO have also proved useful for the purposes of the invention, especially those from this four-component system in proportions of the from 65 to 92% by weight of PbO, from 5 to 20% by weight of B ₂ O ₃ , from 2 to 10% by weight of SiO ₂ and from 1 to 5% by weight of ZnO. The coating of the colored pigments by means of the nature layer of a glass or a gel is carried out using the known sol-gel process, according to which the colored pigments are embedded in a soil which is densified by subsequent heat treatment in the field of the resulting glass transformation temperature. Other characteristics and advantages of the invention will become apparent in the light of the following examples of embodiment of the printing paste according to the invention.

EXAMPLE 1 A printing paste based on a four-component glass d is prepared. following composition: 83.0% by weight of PbO, 13.0% by weight of B ₂ O ₃ , 2.4% by weight of SiO ₂ and 1.6% by weight of ZnO, as low-point glass composition with a melting temperature of about 610 ° C, and copper chromite (CuCr ₂ O ₄ ) as a colored pigment. The glass composition must be present in the printing paste exclusively in the form of a coating of the nature of a glass or of the nature of a gel densified around the grains of pigments.

To this end, 120.0 g of lead (II) nitrate are dissolved in a round flask with two 1-liter necks, fitted with a reflux condenser and a drop-shaped funnel.

4.2 g of zinc acetate dihydrate in 600 ml of water. The solution of 12.0 ml of 0.1 M nitric acid and then of 7.98 ml of triethoxysilane (TEOS) are added. After heating the solution to 60 ° C., a mixture of 37.81 ml of trimethyl borate (TMB) in 24 ml of ethanol is added dropwise. The solution is stirred at this temperature for 3 hours. This gives a colorless transparent floor. By disintegration with ultrasound, 97.4 g of powdered copper chromite (CuCr ₂ O ₄ ) are dispersed in the soil thus obtained.

The pigment and soil dispersion is subjected to a drying operation by blowing hot air or by “spraying” for which the temperature of the spray nozzle is maintained at 130 ° C. In this way a black powder is obtained which consists of grains of the pigment coated with the dried gel. Due to the raw materials used for synthesis, the gel layer contains residual organic radicals. These residual organic radicals are eliminated by a heat treatment of 2 hours at 475 ° C. The coating is thus simultaneously densified. 43 g of an organic binder, for example a screen printing oil which contains 18% by weight of a resinous component and 82% by weight of a low volatile solvent such as l, are added to the powder obtained in this way. 'turpentine. After careful mixing and homogenization of the mixture, the ready-to-use printing paste is obtained. The printing paste is applied according to the usual screen printing process to a sheet of float glass and dried for 5 minutes at a temperature between 120 and 180 ° C. Next, the printed layer is baked at a temperature of about 600 ° C. The decorative layer of the nature of an enamel thus obtained consists of 50% of the glass component and 50% of the pigment.

EXAMPLE 2

A printing paste based on a three-component glass having the following composition is prepared: 89.6% by weight of PbO, 5.2% by weight of B ₂ O ₃ and 5.2% by weight of SiO ₂ as a composition of low melting point glass having a melting temperature of about 580 ° C, and of graphite as a colored pigment. The glass composition must be present in the printing paste again exclusively in the form of the coating of the nature of a glass on the graphite grains. According to the procedure described in Example 1, a colorless transparent sol is prepared from 26.59 g of lead nitrate Pb (NO ₃ ) ₂ , from 100 ml of water, 2.6 ml of nitric acid 0.1 M, 3.61 g of tetraethoxysilane (TEOS) and 3.10 g of trimethyl borate (TMB) in 3.0 ml of ethanol. By ultrasonic disintegration, 8.6 g of graphite are dispersed in the soil thus obtained. The dispersion is again subjected to a spray drying operation under the same conditions as in Example 1. The black powder obtained in this way is subjected to a heat treatment for 2 hours at 475 ° C. by which the residual organic radicals in the layer of gel coating the pigment are eliminated. Then, 15.0 g of the corresponding gel are added to the powder instead of an organic binder. In this way, the proportion of glass bodies of the enamel fired subsequently is raised. After mixing and homogenization, the ready-to-use printing paste is obtained which is applied by the screen printing process to sheets of float glass and which is baked at baking temperatures between 500 and 700 ° C. Cullet with such enamel layers can be added to the mixture of a float glass melt without inconvenience because the carbon forming the colored pigment burns CO ₂ in the molten glass and escapes upon gaseous state.

EXAMPLE 3 A printing paste is prepared which contains a glass frit powder with low melting point as a glass composition and colored pigments formed by magnetite grains provided with a coating of glass with high melting point.

The high melting point coating of the magnetite grains consists of a glass d bicomponent borosilicate having the composition of 83% by weight of B ₂ O ₃ and 17% by weight of SiO ₂ and has a melting temperature of approximately 1110 ° C. The coating of glass with a high melting point does not melt during the cooking operation, but completely retains its protective action during this process and does not dissolve until a possible reflow of the cullet provided with the layer in the glass. molten during the recycling process.

For the preparation of the soil, 7 ml of ethanol are mixed with 81.07 g of tetraethoxysilane (TEOS) and 15 ml of 0.15 M hydrochloric acid. After the hydrolysis of TEOS, 32.22 are added dropwise. ml trimethyl borate (TMB). The solution is then stirred for 2 hours at 50 ° C. Then 15 ml of 0.15 M hydrochloric acid and 20 g of magnetite powder are added, which is dispersed in an ultrasonic bath. The dispersion thus obtained is carried out as described in Example 1 by spray drying.

The powder obtained in this way, consisting of coated grains of pigment, is subjected to a heat treatment at a temperature of 700 ° C. in a nitrogen atmosphere with a heating rate of 1 K / min, a holding time of 1 hour. at 700 ° C, then a cooling rate of approximately 5 K / min.

9.0 g of the powder thus prepared are mixed and homogenized

21.0 g of a glass frit powder and 12.0 g of an oil for screen printing. This gives the ready-to-use printing paste which is applied and baked on a sheet of float glass in the same way as that described in Examples 1 and 2.

EXAMPLE 4 A printing paste is prepared as described in Example 3 which contains a low melting point frit in the form of glass powder, as well as colored pigments consisting of magnetite and which are coated with a layer. glass of high melting point formed of a borosilicate glass. The borosilicate glass consists of 84.1% by weight of B ₂ O ₃ and 15.9% by weight of SiO ₂ and has a melting temperature of approximately 1130 ° C. The soil preparation is carried out in the same way as in Example 3, using in this case 7 ml of ethanol, in total 34.8 ml of 0.15 M hydrochloric acid, 93.87 g of tetraethoxysilane, 21.78 g of trimethyl borate and 20 g of magnetite powder. Spray drying is also carried out as described in the previous examples.

The thermal post-treatment of the powder obtained after spray-drying with a view to densifying the coating of the nature of a gel with elimination of organic radicals takes place in this case at 800 ° C. in a nitrogen atmosphere. By the coating of the magnetite grains carried out in this way, the temperature necessary for the oxidation of the magnetite moves from 280 ° C to 780 ° C, measured by differential thermal analysis at a heating rate of 10 K / min in the air.

As described in Example 3, the pigment powder thus prepared formed by magnetite grains coated with glass is transformed into printing paste. Glass sheets with such enamel are recyclable and can be incorporated into the float glass mixture

EXAMPLE 5

As described in Example 3, a printing paste is prepared which contains a low-melting glass frit in the form of glass powder, as well as colored pigments formed by magnetite which are surrounded by a coating of glass with high melting point. The glass coating consists in this case of a phosphoborosilicate glass having the composition of 67.4% by weight of SiO ₂ , 21.7% by weight of P ₂ O ₅ and 10.9% by weight of B ₂ O ₃ . This glass has a melting temperature of around 1170 ° C.

The soil preparation is carried out again in a similar manner to that of Example 1 using 20 ml of ethanol, 87.6 ml of hydrochloric acid

0.15 M, 270 ml of tetraethoxysilane (TEOS), 117.7 ml of trimethyl borate

(TMB), 27.2 g of P ₂ O ₅ and 50 g of magnetite. The ethanol, TEOS and half of the hydrochloric acid are mixed. After the hydrolysis of TEOS, the TMB is added dropwise and the solution is stirred for 2 hours at 50 ° C. The remainder of the hydrochloric acid is then added, then the P ₂ O ₅ and finally the magnetite powder and dispersed for 5 minutes in an ultrasonic bath. The spray drying takes place as in Example 1. For thermal densification, the powder obtained after spray drying and consisting of coated grains of pigment is subjected to heat treatment at 720 ° C. in an atmosphere of nitrogen with a heating speed of 1 K / min, a holding time at 720 ° C of 1 hour and a speed of cooling of approximately 5 K / min.

The pigment powder thus prepared, consisting of magnetite grains coated with glass, is converted in the manner described in Example 3 into a printing paste. Glass sheets coated with such enamel are recyclable and can be incorporated by mixing with the amount of float glass.

Claims

1. Printing paste suitable for baking for printing glass surfaces, comprising at least one glass composition, one or more pigments and an organic and / or inorganic binder, the pigments being coated as such with a layer of a glass or gel of a thermally solidified vitrifiable composition.

2. Printing paste according to claim 1, characterized in that the pigments are coated with a layer with a thickness of 0.5 to 5 μm from a glass or a gel of a thermally solidified vitrifiable composition .

3. Printing paste according to one of claims 1 or 2, characterized in that it comprises at least one glass composition with low melting point.

4. Printing paste according to one of claims 1 to 3, characterized in that it comprises a glass composition in the form of a glass frit powder.

5. Printing paste according to claim 4, characterized in that the coating of the nature of a glass or of the nature of a gel of the pigments has another composition with a higher melting temperature than the frit of glass.

6. Printing paste according to claim 4, characterized in that the coating of the nature of a glass or of the nature of a gel of the pigments has the same composition as the glass frit.

7. Printing paste according to one of claims 1 to 3, characterized in that the glass composition is formed exclusively by coating the nature of a glass or the nature of a gel of the pigments.

8. Printing paste according to one of claims 1 to 7, characterized in that the glass layer coating the pigments consists of oxides of the elements Si, Pb, Bi, Zn, Ti, Zr, Al, B, P, Ca, Mg, Na and / or K.

9. Printing paste according to one of claims 1 to 8, characterized in that the layer of thermally solidified glass or gel coating the pigments consists of the four-component system PbO-B ₂ O ₃ -SiO ₂ -ZnO with 65 to 92% by weight of PbO, 5 to 20% by weight of B ₂ O ₃ , 2 to 10% by weight of SiO ₂ and 1 to 5% by weight of ZnO.

10. Printing paste according to one of claims 1 to 8, characterized in that the layer of thermally solidified glass or gel coating the pigments consists of the three-component system PbO-B ₂ O ₃ -SiO ₂ with 70 90% by weight of PbO, 5 to 15% by weight of B ₂ O ₃ and 5 to 15% by weight of SiO ₂ .

11. Printing paste according to one of claims 1 to 5, characterized in that the layer of thermally solidified glass or gel coating the pigments consists of the two-component system SiO ₂ -B ₂ O ₃ with 70 to 90 % by weight of SiO ₂ and 10 to 30% by weight of B ₂ O ₃ .

12. Printing paste according to one of claims 1 to 5, characterized in that the layer of thermally solidified gel coating the pigments consists of SiO ₂ .

13. Printing paste according to one of claims 1 to 12, characterized in that the pigments are provided with a coating prepared by the sol-gel process.

14. Printing paste according to one of claims 1 to 13, characterized in that the pigments consist as such of materials which are liable to change at the baking temperature by chemical reaction with other constituents of the printing paste and / or with the ambient atmosphere and which are protected by the coating of thermally solidified glass or gel against contact with reactive agents during the cooking operation.

15. Printing paste according to one of claims 1 to 14, characterized in that the pigments and the coating of thermally solidified glass or gel consist of materials and / or oxides which, during the remelting of the substrates of glass coated with printing paste, dissolve in oxides having no harmful effects on the molten glass or escape from the molten glass forming a gas.

16. Printing paste according to one of claims 1 to 15, characterized in that the pigments consist of carbon in the form of carbon black or graphite, magnetite, hematite or titanium nitride.

17. Process for preparing a printing paste suitable for cooking comprising at least one glass composition, one or more pigments and an organic and / or inorganic binder, characterized in that the pigments are coated by the sol- gel of a layer of a gel of a vitrifiable composition, which is converted into the corresponding glass by a heat treatment at temperatures within the range of the resulting glass transformation temperature.

18. The method of claim 17, characterized in that use is made of pigments consisting of materials sensitive to redox conditions and that the heat treatment of the gel-coated pigments is carried out in an atmosphere of protective gas.

19. Glass substrate coated on at least part of at least one face with a layer formed from a printing paste comprising at least one glass composition, one or more pigments and one organic binder and / or inorganic, and in which the pigments are coated with a layer of a glass or of a gel of a thermally solidified vitrifiable composition.