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: 10-35%, the sum of the molar contents of P2O5, ZnO and Bi2O3 being at least 80%.

Description

Enamel composition

[0001] The present invention relates to enamel compositions, methods of manufacturing enameled glazings using these enamel compositions, as well as enameled glazings 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). Pigments are colored mineral particles that confer the desired color and optical density, while the organic medium, which generally comprises a resin and / or a solvent, allows the deposition of the composition on the substrate. Enameling involves 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] Enameled glazing has multiple applications. In the field of automotive glazing, for example, it is common to place a strip of enamel, usually black, around the edges of windshields, roofs, and rear windows to protect and conceal the glazing mounting systems and the connections of various sensors. In the field of glazing for buildings or household appliances, decorative enamels of various colors can be used.

[0005] Glass frits currently used are based on bismuth and / or zinc borosilicate. However, the use of boron is 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: 10-35%, 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 part 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% boron, expressed as B2O3, in particular less than 2 mol% boron, or even does not comprise boron.

[0012] According to a first preferred 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 10 and 35%, in particular between 10 and 30%, or even between 10 and 25%.

[0013] Such glasses have low softening points, with glass transition temperatures typically between 350 and 430°C, and coefficients of linear thermal expansion between 89 and 130.10 -7 / K, preferably between 89 and 110.10 -7 / K.

[0014] According to a second preferred 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 somewhat higher softening points, with glass transition temperatures typically 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 commonly used enamel compositions, which include 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 chromium, copper, iron, manganese, cobalt, titanium, or nickel oxides. 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 enameling automotive windows. 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 photocrosslinkable acrylic resin.

[0020] The enamel composition may further comprise additives intended to improve the processing or properties of the final enamel, such as bonding inhibitors and / or opacifiers. Bonding inhibitors are intended to prevent, before and during firing, any bonding between the enamel and other elements that may come into contact with it, for example another sheet of glass or glass shaping tools (for example bending and / or tempering). These may include 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 stage. The medium is then removed at the latest during the firing stage, and if necessary at least partially during any preliminary drying and / or pre-firing stages.

[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 later in 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 thin electrically conductive 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 includes meshes, some of which are closed, then the enamel composition is deposited on the screen in order to coat the screen, then a doctor blade 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 closed, so as to form a layer of wet enamel.

[0025] The enamel composition can also be applied by digital printing, for example by inkjet. The enamel composition can also be applied by spraying or roller coating, particularly for large surface applications, including the entire surface of the glass sheet.

[0026] Depending on the intended application, the enamel composition can be deposited on all or part of one side of the glass sheet. For example, in the case of a sill, used on a building facade, the enamel composition can be deposited on the entire surface of one of the sides of the glass sheet. In most cases, the enamel composition will be deposited on only part of the surface of one side 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 windshields, rear windows, roofs or quarter panels, the enamel composition is generally deposited in the form of a peripheral band. 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, firing is preferably carried out during the thermal toughening and / or bending step of the glass sheet. 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. Particularly 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-firing step before the firing step. This is particularly the case when the enamel layer risks adhering to bending tools or another sheet of glass during bending. The pre-firing step makes it possible to avoid these disadvantages by carrying out at least partial pre-firing of the enamel layer. The pre-firing 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] For example, it may be a building glazing, particularly 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 creating a cavity between the two glass sheets, or into laminated glazing, by being secured to another glass sheet by means of a polymeric interlayer, particularly polyvinyl butyral. It may also be an oven door or a refrigerator or freezer door, particularly commercial.

[0034] It can 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 can 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. First, 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 µm.

[0038] Table 1 below shows the tested compositions (in molar percentages) and the measured properties (glass transition temperature Tg, dilatometric softening temperature Td, crystallization temperature Tc and coefficient of linear thermal expansion CTE from 50 to 300°C). The temperatures Tg and Tc 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 tempering. The temperatures Tg, Td, and Tc are expressed in °C and the CTE in 10 -7 / K. Only some glasses crystallize, so the temperature Tc is not given for all examples.

[0039] P2O5ZnOBi2O3TgTdTcCTE1503515393407-1092553015401410560973602515408418-1084652015410429-955701515423440-8966525103 96408-1057652015410429-958651520408425-989651025409424-98102555204684745688611255025465471569911220552546446956592

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

[0041] An enamel composition was prepared with the frit of Example 10. 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 assessed by 10 N sclerometer resistance and chemical resistance was assessed by color variation after immersion in 0.1 N sulfuric acid for 2 hours at 80°C.

Claims

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: 10-35%, the sum of the molar contents of P2O5, ZnO and Bi2O3 being at least 80%. Enamel composition according to the preceding claim, such that the sum of the molar contents of P2O5, ZnO and Bi2O3 is at least 90%. Enamel composition according to the preceding claim, such that the sum of the molar contents of P2O5, ZnO and Bi2O3 is at least 95%. Enamel composition according to one of the preceding claims, such that 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. Enamel composition according to one of the preceding claims, such that the chemical composition of the glass frit does not comprise boron. 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 Bi2O3 is between 10 and 35%, in particular between 15 and 30%. Enamel composition according to one of claims 1 to 5, 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 10 and 35%, in particular between 10 and 30%. 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. Enamel composition according to one of the preceding claims, in which the weight ratio between the organic medium content and the total content of pigments and glass frit is preferably between 1:10 and 1:3, in particular between 1:8 and 1:

5. Enamel composition according to one of the preceding claims, in which the pigments comprise one or more oxides, in particular chosen from transition metal oxides 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. 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. Enamelled glazing obtained by the process according to one of claims 11 or 12. Enamelled glazing according to the preceding claim, in which the enamel layer is opaque.