Glass substrate coated with silicate paint having a composition providing better strength at break for same
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-16
- Publication Date
- 2026-04-08
AI Technical Summary
Conventional black enamel and silicate paint coatings on glass substrates face issues such as non-stick properties, optical defects, and mechanical weakening due to thermal conductivity differences and expansion mismatches, which affect the durability and performance of laminated glazing, particularly in automotive applications.
A silicate paint composition with specific mass proportions (31.4-33.1% SiO2, 10.5-11.1% Na2O, 1.7-1.8% Al2O3, 4.4-4.7% K2O, 23.4-23.8% MnO2, 7.3-7.4% Fe2O3, and 18.2-21.3% CuO) is applied to match the thermal expansion coefficient of glass, enhancing mechanical strength and optical quality, and a manufacturing process involving screen printing and controlled thermal cycling is used to achieve a uniform and robust coating.
The silicate paint composition significantly improves the mechanical strength and resistance to breakage of glass substrates, as demonstrated by tripod tests, while maintaining excellent optical properties and reducing stress-induced degradation, thereby enhancing the overall performance of laminated glazing.
Smart Images
Figure FR2024050634_28112024_PF_FP_ABST
Abstract
Description
Description Title of the invention: Glass substrate coated with silicate paint of a composition providing improved overall resistance to breakage [1] Black enamel is used on automotive glass such as windshields, rear windows, and side windows for the purpose of opacity. This use of black enamel causes several problems: - the need for non-stick properties, when two sheets of glass intended for the same laminated glazing are curved together by gravity sagging, with one face of one of the two sheets of glass oriented towards the other sheet of glass and in contact with it 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 the glass and the enamel, which induce defects and irregularities in the areas of the glass without enamel near enameled areas when the whole is subjected to heat treatments of the type of curvature already mentioned; - a mechanical weakening. [2] The use of silicate paint instead of enamel has provided significant improvements in optical quality, particularly in areas of glazing (windshields) traversed by a camera's field of view. However, this type of material also considerably degrades the mechanical strength of the glass due to a large difference in thermal expansion between the two materials. The ease of application of silicate paint is also not very good, as it requires a high humidity level to prevent rapid, uneven drying and carbonate precipitation. [3]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 influencing 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. [4]On the other hand, the pigments used in black silicate enamels and paints are generally black spine lies of Fe, Cr, Cu or Mn, depending on the nature of the coating (compatibility with water...). The coefficient of thermal expansion of black spinels depends greatly on the transition metals in the formulation. [5] The inventors therefore sought silicate paint formulations 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 stress in the coating and thus the mechanical weakening (degradation, reduction in mechanical strength) of the painted substrate. This objective was achieved by the invention, which consequently relates to a glass substrate comprising a paint coating having the following mass proportions - 31.4 to 33.1% SiO2, - 10.5 to 11.1% Na2O, - 1.7 to 1.8% of A12O3, - 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. [6] The inventors have established that such silicate paints provide good mechanical strength, resistance to flexural breakage, as established by tripod tests which will be described in detail below. The glass substrate means a sheet of mineral glass such as float, soda-lime, aluminosilicate, borosilicate or equivalent, optionally hardened, thermally tempered or chemically strengthened, flat or curved. [7]Preferably, the dry thickness of the coating is between 6.1 and 6.9, preferably between 6.3 and 6.7 um. [8] 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 imprinted 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 the mass proportions indicated above, then the paint is dried at a temperature not exceeding 160 °C, then subjected to baking at a temperature between 550 and 650 °C for 5 to 10 min (corresponding to a thermal cycle of curvature by gravity slump, in particular two sheets of glass together intended to form a laminated glazing by bonding using a transparent interlayer adhesive layer of the type polyvinyl butyral (PVB), polyurethane (PU), ethylene-vinyl acetate (EVA) copolymer or equivalent). [9]Preferably, the organic fraction of the paint comprises at least 80% by mass of water, possibly 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. [1 l]The invention will be better understood in the light of the following embodiment example.
[0012] We use a silicate paint marketed by the ICD Company (United States of America) under the reference OPH-CG 1-231, which is a suspension in 85% by mass of water of the composition of oxides 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 reference DV 154140 is used, comprising the following pigments in mass percentages: 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 minutes, and 10% by mass of this mixture is combined with a quantity of silicate paint from ICD (see above) containing 90% by mass of the aforementioned Composition 1 of oxides. The resulting silicate paint has Composition 2, as shown in Table 1 below.
[0014] [Table 1]
[0015] Silicate paints of Composition 1 and Composition 2 were screen-printed onto 3.85 mm thick, 70 mm x 70 mm sheets of float glass. Thirty sheets of glass were fully coated with each of the two compositions. in order to obtain statistical precision. The painted glass sheets were dried, then baked for 400 s at 610 °C, corresponding to a thermal cycle for laminated glazing.
[0016] We first measured the paint thickness characteristics, the optical properties of the painted glass substrate and the surface roughness of the paint obtained from Composition 1, recorded in Table 2 below, and from Composition 2, recorded in Table 3 below.
[0017] [Table 2]
[0018] [Table 3]
[0019] It is observed that Composition 2, according to the invention, maintains at least the positive characteristics of Composition 1, which is outside the scope of the invention. The slight variation in L* is due to the refractive properties 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 in scanning electron microscope images.
[0020] The characterization of the improvement in mechanical resistance 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 (10mm / 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 20 mm radius. The balls have a diameter of 1 cm, eliminating any edge effects such as poor edge condition. The force is applied vertically from above via a 10 mm diameter ring, centered on 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 (by closing a door) to protect against broken glass shards. The descent is restarted until breakage occurs, and the force value is recorded in daN.
[0022] The calibration coefficient K allows the stress to be calculated as a function of the applied force according to the equation
[0023] [Math 1] a(Mpa) = K. F( daN ) With - o = stress in MPa - F = Force applied in daN - K = coefficient = 9.4091 (1 / e 2 ) + 0.018, - e = thickness of the specimen (mm).
[0024] [Fig. 1] represents the probability of sample failure or breakage as a function of the applied stress in MPa for Composition 1 (dashed line) and Composition 2 (solid line). The stress corresponding to 20% failure is 49.2 MPa for Composition 1 and 52.0 MPa for Composition 2 (+6%), while the stress corresponding to 50% failure is 51.2% for Composition 1 and 55.2% for Composition 2 (+8%).
Claims
Claims 1. 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% of A12O3, - 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. Method for 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.