Glass substrate coated with silicate paint of a composition providing better resistance to breakage of the assembly

Abstract

Glass substrate comprising a paint coating comprising the following mass proportions - 31.4 to 33.1% of SiO2, - 10.5 to 11.1% of Na2O, - 1.7 to 1.8% of Al2O3, - 4.4 to 4.7% of K2O, - 23.4 to 23.8% of MnO2, - 7.3 to 7.4% of Fe2O3, and - 18.2 to 21.3% of CuO; method of manufacturing the same. Figure for abstract Figure 1.

Description

Title of the invention: Glass substrate coated with silicate paint of a composition providing better resistance to breakage of the assembly

[0001] Black enamel is used on automotive glazing such as windshields, rear windows, side windows, for the purpose of opacification. This use of black enamel is the cause of several problems: - the need for non-stick properties, when two sheets of glass intended for the same laminated glazing are bent together by gravity sagging, with one face of one of the two sheets of glass facing the other sheet of glass and in contact with the latter bearing a printing coating, which must not stick to the counter-glass at the risk of breaking it; - optical defects due to the different thermal conductivities of glass and enamel, which induce defects and irregularities in the areas of the glass devoid of enamel close to enameled areas when the assembly is subjected to heat treatments of the bending type already mentioned; - mechanical weakening.

[0002] The use of silicate paint instead of enamel has provided significant improvements in terms of optical quality, particularly in areas of glazing (windshields) crossed by the field of a camera. However, this type of material also greatly degrades the mechanical strength of the glass due to a large difference in thermal expansion between the two materials. The ease of implementation of silicate paint is also not very good since it requires a high level of humidity to prevent rapid heterogeneous drying and carbonate precipitation.

[0003] Silicate paint reduces the mechanical strength of glass much more than enamel, although it improves the optical quality of laminated glass. The difference in thermal expansion is the main parameter that influences the creation of stress in the coating, and therefore the mechanical weakening of the glass substrate. Thus, the coefficient of thermal expansion of enamel is closer to that of glass than that of silicate paint.

[0004] On the other hand, the pigments used in black silicate enamels and paints are generally black spinels of Fe, Cr, Cu or Mn, depending on the nature of the coating (compatibility with water, etc.). The coefficient of thermal expansion of black spinels depends greatly on the transition metals in the formulation.

[0005] The inventors therefore sought formulations of silicate paints providing the improved optical quality of the coated substrate mentioned above (compared to the enameled substrate), and a coefficient of thermal expansion of the dry paint as close as possible to that of the substrate, so as to reduce the stress in the coating and therefore the mechanical weakening (degradation, reduction in mechanical strength) of the painted substrate. This aim has been achieved by the invention which, consequently, relates to a glass substrate comprising a paint coating comprising the following proportions by mass - 31.4 to 33.1% of SiO2, - 10.5 to 11.1% of Na2O, - 1.7 to 1.8% of Al2O3, - 4.4 to 4.7% of K2O, - 23.4 to 23.8% of MnO2, - 7.3 to 7.4% of Fe2O3, and - 18.2 to 21.3% of CuO.

[0006] The inventors have established that such silicate paints provide good mechanical resistance, resistance to breaking in bending, established by tripod tests which will be seen in detail below. The glass substrate designates a sheet of mineral glass such as float, soda-lime, aluminosilicate, borosilicate or equivalent, possibly hardened, thermally tempered or chemically reinforced, flat or curved.

[0007] Preferably, the dry thickness of the coating is between 6.1 and 6.9, preferably between 6.3 and 6.7 μm.

[0008] Another object of the invention consists of a method for manufacturing a glass substrate as described above, characterized in that at least one of its two faces is printed with a liquid thickness of between 20 and 25 μm of an aqueous silicate paint, comprising 15 to 50% by mass of organic fraction and the remainder of mineral fraction consisting of a refractory pigment powder and a silicate binder powder in proportions by mass indicated above, then the paint is dried at a temperature at most equal to 160°C, then subjected to baking at a temperature of between 550 and 650°C for 5 to 10 min (corresponding to a thermal cycle of bending by gravity slump, in particular of two sheets of glass together intended to constitute a laminated glazing by bonding by means of a transparent interlayer adhesive layer of the polyvinyl butyral (PVB), polyurethane (PU) type,ethylene-vinyl acetate copolymer (EVA) or equivalent).

[0009] Preferably, the organic fraction of the paint comprises at least 80% by mass of water, optionally at least one organic solvent and additives such as thickeners, surfactants.

[0010] Preferably, the operation of printing the glass substrate is carried out by screen printing.

[0011] The invention will be better understood in light of the following embodiment.

[0012] A silicate paint marketed by ICD (United States of America) under the reference OPH-CG1-231 is used, which is a suspension in 85% by mass of water of the oxide composition recorded in Table 1 below as Composition 1. The first four oxides (of Si, Na, Al and K) are binders, the last three (of Mn, Fe and Cu) are pigments.

[0013] A pigment paste marketed by Pemco (Belgium) under the reference DV 154140 is used, comprising the following pigments in % by mass: 76.8% CuO, 17.4% MnO2 and 5.8% Fe2O3. The black pigments are collected by calcining this pigment paste at 450°C for 10 min, and 10% by mass is mixed with a quantity of silicate paint from ICD above containing 90% by mass of the aforementioned Composition 1 of oxides. A silicate paint of Composition 2 recorded in Table 1 below is obtained.

[0014] [Tables 1] Composition 1 2 SiO2 34.9 31.4 Na2O 11.7 10.5 A12O3 1.9 1.7 k2o 4.9 4.4 MnO2 24.1 23.4 Fe2O3 7.4 7.3 CuO 15.1 21.3

[0015] Silicate paint of Composition 1 and Composition 2 was deposited on 3.85 mm thick, 70 mm X 70 mm float glass sheets by screen printing. 30 glass sheets were coated on the full face with each of the two compositions in order to obtain statistical accuracy. The painted glass sheets were dried, then baked for 400 s at 610 °C, corresponding to a thermal cycle for laminated glazing.

[0016] The paint thickness characteristics, the optical properties of the painted glass substrate and the paint surface roughness obtained from Composition 1, recorded in Table 2 below, and from Composition 2, recorded in Table 3 below, were first measured.

[0017] [Tables2] Sample No. Thickness (pm) L* a* b* OD Gloss Ra Rz 1 5.51 4.79 0.19 -0.2 3.67 10.3 0.559 5.21 10 5.17 4.77 0.29 -0.23 3.69 10.7 0.434 3.33 20 5.16 4.62 0.18 -0.17 3.62 10.2 0.429 3.76 30 4.85 4.92 0.14 -0.11 3.6 10.7 0.44 4.40 Mean 5.2 4.78 0.20 -0.18 3.65 10.48 0.47 4.18 Standard Deviation 0.3 0.12 0.06 0.05 0.04 0.26 0.06 0.82

[0018] [Tables3] Sample No. Thickness (pm) L* a* b* OD Gloss Ra Rz 1 6.35 5.79 0.38 -0.13 3.68 6.8 1.47 12.3 10 6.62 5.44 0.22 0.06 4.01 7.4 1.87 15.5 20 6.54 5.01 0.33 -0.16 3.89 6.9 1.92 14.9 30 6.56 5.4 0.21 -0.05 3.76 6 1.26 10.8 Mean 6.5 5.41 0.29 -0.07 3.84 6.78 1.63 13.38 Standard Deviation 0.1 0.32 0.08 0.10 0.15 0.58 0.32 2.21

[0019] It is found that Composition 2 in accordance with the invention maintains at least the positive characteristics of Composition 1 which is outside the invention. The slight variation in L* is due to the refractive property of the black pigments. The coating thickness, Optical Density, gloss and roughness Rz also increase for Composition 2 due to the large particle size of the black pigments, which is visible on the Scanning Electron Microscope images.

[0020] The characterization of the improvement in mechanical strength provided to the glass substrate by Composition 2 compared to Composition 1 is now described. The tripod test is used to determine the mechanical embrittlement of the printed glass. The test consists of applying an increasing load at a constant speed (10 mm / min) until the sample breaks.

[0021] Each sheet of glass is placed printed side down on three balls forming an equilateral triangle, arranged on a circle with a radius of 20 mm. The balls have a diameter of 1 cm, making it possible to overcome any edge effects of the glass such as poor condition of the edges. The force is applied vertically from above by through a 10 mm diameter ring, and centered in relation to the three balls. The device stops its descent when it reaches the safety threshold, defined by the application of a force of 0.8 kg. The device is then confined (closing a door) to protect against shards of broken glass. The descent is restarted until the breakage, and the value of the force in daN is recorded.

[0022] The calibration coefficient K makes it possible to calculate the stress as a function of the applied force according to the equation

[0023] [Math.l] ^(Mpa) ~ K* F(daN) With - o = stress in Mpa, - F = Force applied in daN, - K = coefficient = 9.4091 (1 / e2) + 0.018, - e = thickness of the specimen (mm).

[0024] [Fig. 1] represents the probability of rupture or breakage of the samples as a function of the applied stress in MPa in the case of the use of Composition 1 (dotted line) and Composition 2 (solid line). The stress corresponding to 20% of ruptures is 49.2 MPa for Composition 1, 52.0 MPa for Composition 2 (+ 6%), the stress corresponding to 50% of ruptures is 51.2% for Composition 1, 55.2% for Composition 2 (+ 8%).

Claims

Claims

1. A glass substrate comprising a paint coating comprising the following mass proportions: -31.4 to 33.1% SiO2, -10.5 to 11.1% Na2O, -1.7 to 1.8% Al2O3, -4.4 to 4.7% K2O, -23.4 to 23.8% MnO2, -7.3 to 7.4% Fe2O3, and -18.2 to 21.3% CuO.

2. Glass substrate according to claim 1, characterized in that the dry thickness of the coating is between 6.1 and 6.9, preferably between 6.3 and 6.7 μm.

3. A method of manufacturing a glass substrate according to one of the preceding claims, characterized in that at least one of its two faces is printed with a liquid thickness of between 20 and 25 μm of an aqueous silicate paint, comprising 15 to 50% by mass of organic fraction and the remainder of mineral fraction consisting of a refractory pigment powder and a silicate binder powder in proportions by mass according to claim 1, then the paint is dried at a temperature at most equal to 160°C, then subjected to firing at a temperature of between 550 and 650°C for 5 to 10 min.

4. Method according to claim 3, characterized in that the organic fraction of the paint comprises at least 80% by mass of water, optionally at least one organic solvent and additives such as thickeners, surfactants.

5. Method according to one of claims 3 or 4, characterized in that the operation consisting of printing the glass substrate is carried out by screen printing.

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