Enamel composition

Abstract

The invention relates to an enamel composition comprising a glass frit, pigments and an organic medium, wherein the chemical composition of said glass frit comprises the following elements, within the limits defined below, expressed in molar percentages: P2O5: 10-80%, ZnO: 5-65%, Bi2O3: 2-35%, the sum of the molar contents of P2O5, ZnO and Bi2O3 being at least 80%.

Description

Title of the invention: Enamel composition

[0001] The present invention relates to enamel compositions, methods of manufacturing enameled glazing using these enamel compositions, as well as enameled glazing obtained by these methods.

[0002] An enamel composition is a fluid (liquid or pasty) composition comprising pigments, a glass frit and an organic medium. Deposited on substrates, for example glass, they confer aesthetic and functional properties (in particular protection against ultraviolet radiation). The pigments confer the desired color and optical density, while the organic medium, which generally comprises a resin and / or a solvent, allows the composition to be deposited on the substrate. Enameling comprises depositing the enamel composition on the substrate to obtain a wet enamel layer, then firing this wet enamel layer, generally at temperatures ranging from 400 to 600°C in the case of glass substrates, firing sometimes preceded by drying.Firing allows, thanks to the fusion of the glass frit, to create a vitreous or vitrocrystalline binder with strong adhesion to the substrate and capable of maintaining and encapsulating the pigment particles.

[0003] Enamel compositions, and in particular the chemical composition of the glass frit, must meet a large number of requirements. In the case of glass substrates, particularly soda-lime-silica glass, it is important that the glass frit can melt or at least soften significantly at the firing or shaping temperatures that the glass substrate can withstand. It is also important that the coefficient of thermal expansion of the glass frit is close to that of the glass substrate, in order to avoid creating thermomechanical stresses that could weaken the substrate. Finally, the enamel must have excellent chemical resistance, not only to water but also to acids, and mechanical resistance.

[0004] Enamelled glazing has multiple applications. In the field of automotive glazing, for example, it is common to place a strip of enamel, generally black, around the edges of windshields, roofs and rear windows in order to protect and conceal the glazing mounting systems as well as the connections of various sensors. In the field of glazing for buildings or household appliances, decorative enamels of various colors can be used.

[0005] The glass frits currently used are based on bismuth and / or zinc borosilicate. The use of boron is, however, subject to restrictions due to its negative effects on health and the environment.

[0006] The aim of the invention is to provide enamel compositions free of boron or with a low boron content.

[0007] To this end, the invention relates to an enamel composition comprising a glass frit, pigments and an organic medium, in which the chemical composition of said glass frit comprises the following elements, within the limits defined below, expressed in molar percentages: - P2O5: 10-80% - ZnO: 5-65% - Bi2O3: 2-35%, the sum of the molar contents of P2O5, ZnO and Bi2O3 being at least 80%.

[0008] Another subject of the invention is a method for obtaining enameled glazing comprising a step of depositing an enamel composition according to the invention on at least a portion of at least one face of a glass sheet to obtain a wet enamel layer and then a step of firing said wet enamel layer.

[0009] Preferably, the sum of the molar contents of P2O5, ZnO and Bi2O3 is at least 90%, or even at least 95%. It may even be at least 98%, or even 100%.

[0010] In addition to the aforementioned oxides, the chemical composition of the glass frit may comprise one or more oxides, in particular chosen from SiO2, Al2O3, Li2O, Na2O, K2O, MgO, CaO SrO, BaO, ZrO2 and TiO2. These oxides may in particular make it possible to adjust the coefficient of thermal expansion of the frit or its glass transition temperature. For example, SiO2 makes it possible to increase the glass transition temperature and reduce the coefficient of thermal expansion while alkali oxides have the opposite effect.

[0011] Preferably, the chemical composition of the glass frit comprises less than 5 mol% of boron, expressed in the form B2O3, in particular less than 2 mol% of boron, or even does not comprise boron.

[0012] According to a first embodiment: - the molar content of P2O5 is between 40 and 80%, in particular between 45 and 75%, or even between 50 and 70%, - the molar content of ZnO is between 5 and 45%, in particular between 10 and 40%, or even between 15 and 35%, - the molar content of Bi2O3 is between 2 and 35%, in particular between 5 and 30%, or even between 10 and 25%.

[0013] Such glasses have low softening points, with glass transition temperatures generally between 350 and 430°C, and coefficients of linear thermal expansion between 89 and 130.107 / K.

[0014] According to a second embodiment: - the molar content of P2O5 is between 10 and 35%, in particular between 15 and 30%, or even between 20 and 25% - the molar content of ZnO is between 40 and 65%, in particular between 45 and 60%, or even between 50 and 55% - the molar content of Bi2O3 is between 10 and 35%, in particular between 15 and 30%, or even between 20 and 25%.

[0015] Such glasses have slightly higher softening points, with glass transition temperatures generally between 450 and 480°C, and coefficients of linear thermal expansion between 80 and 95.10 7 / K. These compositions are preferred because these properties are very close to those of the enamel compositions usually used, which comprise bismuth borosilicate frits.

[0016] In the enamel composition, the weight ratio between the pigment content and the glass frit content is preferably between 1:5 and 1:1, in particular between 1:4 and 1:2.

[0017] The weight ratio between the organic medium content and the total pigment and glass frit content is preferably between 1:10 and 1:3, in particular between 1:8 and 1:5.

[0018] The pigments preferably comprise one or more oxides, in particular chosen from transition metal oxides, for example oxides of chromium, copper, iron, manganese, cobalt, titanium, or nickel. The pigments have, for example, a spinel-type structure, possibly partially substituted. They may be, for example, copper and / or iron chromates, which are black pigments particularly suitable for enamelling automotive glazing. In addition to black, the pigments may impart any color, such as white, red, blue, green, yellow, etc.

[0019] The organic medium comprises a resin and / or an organic solvent, generally both. The nature of the resin and / or the solvent is advantageously adapted to the drying method. In the case of drying by infrared radiation, the solvent is advantageously chosen from vegetable oils (for example pine oil or terpineol), mineral oils and other petroleum fractions and glycol derivatives (for example glycol and propanol ethers, in particular butyldiglycol acetate) and the resin is for example a cellulose derivative. In the case of drying by ultraviolet radiation, the resin is preferably a photo-crosslinkable acrylic resin.

[0020] The enamel composition may further comprise additives intended to improve the processing or the properties of the final enamel, such as sticking inhibitors and / or opacifiers. The sticking inhibitors are intended to prevent, before and during firing, any sticking between the enamel and other elements which may come into contact with it, for example another sheet of glass or glass shaping tools (for example bending and / or tempering). These may in particular be refractory particles.

[0021] The pigments and the glass frit are dispersed in the organic medium, the latter facilitating the deposition of the enamel composition and ensuring a certain cohesion of the wet enamel before the firing step. The medium is then removed at the latest during the firing step, and if necessary at least partially during any prior drying and / or pre-firing steps.

[0022] The glass sheet is preferably made of soda-lime-silica glass, but other types of glass (borosilicate, aluminosilicate, etc.) may be used. The glass sheet is generally flat when the enamel composition is deposited, but may be curved subsequently, as explained in more detail in the rest of the text. The glass sheet may, prior to the enamel deposition, have been at least partially coated with a coating, in particular based on thin layers, such as a solar control or low-emissivity stack, for example comprising at least one electrically conductive thin layer, in particular metallic (in particular silver) or a transparent conductive oxide (for example ITO).

[0023] The step of depositing the enamel composition is preferably carried out by screen printing.

[0024] To do this, a screen printing screen is placed on the glass sheet, which comprises meshes, some of which are sealed, then the enamel composition is deposited on the screen in order to coat the screen, then a doctor is applied in order to force the transfer of the enamel composition from the screen to the glass sheet, in the areas where the meshes of the screen are not sealed, so as to form a layer of wet enamel.

[0025] The deposition of the enamel composition can also be carried out by digital printing, for example by inkjet. The deposition of the enamel composition can also be carried out by spraying or by roller coating, in particular for depositions on large surfaces, in particular on the entire surface of the glass sheet.

[0026] Depending on the intended application, the deposition of the enamel composition may be carried out on all or part of one face of the glass sheet. For example, in the case of a sill, used on a building facade, the enamel composition may be deposited over the entire surface of one of the faces of the glass sheet. In most cases, the enamel composition will be deposited on only part of the surface of one face of the glass sheet, for example on 2 to 70%, in particular on 5 to 50%, or even on 10 to 40% of the surface. In the case of automotive glazing, in particular windshield, rear window, roof or quarter panel, the enamel composition is generally deposited in the form of a peripheral strip. This will also be the case for oven doors or glazing incorporating a Marie-Louise. In other cases, the enamel can be deposited in the form of aesthetic or functional patterns, for example to form a decoration or a logo.

[0027] The deposition step makes it possible to deposit a layer of wet enamel having a thickness preferably between 10 and 50 μm, in particular between 15 and 30 μm.

[0028] The deposition step is advantageously followed by a drying step, which will make it possible to eliminate at least part of the solvent contained in the organic medium. Such drying is preferably carried out at a temperature between 120 and 180°C.

[0029] The firing step is preferably carried out at a temperature ranging from 400 to 700°C. When the glass sheet is intended to be thermally toughened and / or curved, the firing is preferably carried out during the thermal toughening and / or bending step of the glass sheet. The bending can in particular be carried out by gravity (the glass deforming under its own weight) or by pressing, at temperatures typically ranging from 550 to 680°C. When the glass sheet is intended to be integrated into a laminated glazing unit, the glass sheet can be curved with another glass sheet.

[0030] After the firing step, the enamel layer is preferably opaque. Its optical density is preferably at least 2, or even at least 3. In particular for automotive glazing applications, the enamel may be black. Its clarity L* measured in reflection on the glass side is then preferably less than 10, in particular less than 5.

[0031] In some cases, it may be advantageous to carry out a pre-baking step before the baking step. This is particularly the case when the enamel layer risks adhering to bending tools or to another sheet of glass during bending. The pre-baking step makes it possible to avoid these disadvantages by carrying out at least partial pre-baking of the enamel layer. The pre-baking step is preferably carried out at temperatures ranging from 400 to 650°C.

[0032] The invention also relates to enamelled glazing obtained (or capable of being obtained) by the process of the invention.

[0033] It may for example be a building glazing, in particular residential or tertiary. The glass sheet may be integrated into a facade, or into multiple glazing (double or triple), by being secured to another glass sheet by means of a peripheral frame providing a cavity between the two glass sheets, or into laminated glazing, by being secured to another glass sheet by means of a polymeric interlayer, in particular polyvinyl butyral. It may also be an oven door or a refrigerator or freezer door, in particular commercial.

[0034] It may also be automotive glazing, for example a windshield, a rear window, a roof, a side window, or even a quarter window. In this case, the glazing is preferably curved glazing, which may also be laminated or tempered.

[0035] Examples

[0036] The following examples illustrate the invention in a non-limiting manner.

[0037] Glass frits were obtained by melting, then quenching and grinding. In a first step, a mixture of ammonium dihydrogen phosphate and zinc oxide was gradually heated to 550°C to remove water and ammonia, and then to 1100°C to obtain a precursor of Zn(PO3)2. This precursor was then mixed with appropriate amounts of ZnO, NH4H2PO4 and Bi2O3, the mixture being melted by heating to temperatures ranging from 900 to 1100°C. After refining for 30 minutes, the molten glass was quenched onto brass blocks. The glass was then ground using a planetary mill to obtain powders with a particle size of less than 1 pm.

[0038] Table 1 below shows the compositions tested (in molar percentages) and the properties measured (glass transition temperature Tg, dilatometric softening temperature Td, crystallization temperature Te and coefficient of linear thermal expansion CTE from 50 to 300°C). The temperatures Tg and Te were determined by differential thermal analysis (DTA) and the temperature Td and the CTE were determined by dilatometry on solid glass specimens after melting and quenching. The temperatures Tg, Td, and Te are expressed in °C and the CTE in 10 7 / K. Only certain glasses crystallize, so the temperature Te is not given for all examples.

[0039] [Tables 1] p2o5 ZnO Bi2O3 Tg Td Te CTE 1 50 35 15 393 407 - 109 2 55 30 15 401 410 560 97 3 60 25 15 408 418 - 108 4 65 20 15 410 429 - 95 5 70 15 15 423 440 - 89 6 65 30 5 362 376 - 125 7 65 25 10 396 408 - 105 8 65 20 15 410 429 - 95 9 65 15 20 408 425 - 98 10 65 10 25 409 424 - 98 11 25 55 20 468 474 568 86 12 25 50 25 465 471 569 91 13 20 55 25 464 469 565 92

[0040] For reference, the following properties were measured for a commercial bismuth zinc borosilicate frit: Tg = 460°C, Td = 472°C, Te = 531°C and CTE = 81.10 7 / K.

[0041] An enamel composition was prepared with the frit of Example 11. To do this, a mixture of powders comprising 25% by weight of black pigment (Tomatec 42-302 A) and 75% by weight of frit were mixed with an organic medium (Vibrantz 80 007F-ME), according to a powder:medium weight ratio of 85:15. The paste obtained was deposited by screen printing on a 4 mm thick glass sheet so as to obtain a wet enamel 25 μm thick. The enamel was then fired for 180 seconds in a gradient oven.

[0042] Enamel layers with good properties were obtained for firing temperatures above 595°C. The black enamel had a reflection clarity L* (glass side) of 2.6, an optical density of 2.3, good adhesion to the substrate and good chemical resistance. Adhesion to the substrate was evaluated by 10 N sclerometer resistance and chemical resistance was evaluated by color variation after immersion in 0.1 N sulfuric acid for 2 hours at 80°C.

Claims

Claims

1. Enamel composition comprising a glass frit, pigments and an organic medium, wherein the chemical composition of said glass frit comprises the following elements, within the limits defined below, expressed in molar percentages: - P2O5: 10-80% - ZnO: 5-65% - Bi2O3: 2-35%, the sum of the molar contents of P2O5, ZnO and Bi2O3 being at least 80%.

2. Enamel composition according to the preceding claim, such that the sum of the molar contents of P2O5, ZnO and Bi2O3 is at least 90%.

3. An enamel composition according to one of the preceding claims, such that the chemical composition of the glass frit does not include boron.

4. Enamel composition according to one of the preceding claims, in which the molar content of P2O5 is between 10 and 35%, in particular between 15 and 30%, the molar content of ZnO is between 40 and 65%, in particular between 45 and 60%, and the molar content of Bi2 O3 is between 10 and 35%, in particular between 15 and 30%.

5. Enamel composition according to one of claims 1 to 3, in which the molar content of P2O5 is between 40 and 80%, in particular between 45 and 75%, the molar content of ZnO is between 5 and 45%, in particular between 10 and 40%, and the molar content of Bi2O3 is between 2 and 35%, in particular between 5 and 30%.

6. Enamel composition according to one of the preceding claims, in which the weight ratio between the pigment content and the glass frit content is between 1:5 and 1:1, in particular between 1:4 and 1:

2.

7. Method for obtaining enamelled glazing comprising a step of depositing an enamel composition according to one of the preceding claims on at least a portion of at least one face of a glass sheet to obtain a wet enamel layer and then a step of firing said wet enamel layer.

8. Method according to the preceding claim, in which the step of depositing the enamel composition is carried out by screen printing or by digital printing.

9. Enamelled glazing obtained by the process according to one of claims 7 or 8.

10. Enamelled glazing according to the preceding claim, in which the enamel layer is opaque.