Method for hydrophobizing aerospace assembly glass

Abstract

The invention relates to a method for hydrophobizing a glass substrate, preferably an aircraft cabin glazing, comprising the following consecutive steps: forming a primer layer, preferably silica, on one of the main surfaces of the glass substrate; and grafting a layer of a C3-C8-alkyl trialkoxysilane and / or a layer of a C3-C8-alkyl trichlorosilane onto the primer layer. A step of polishing, optionally using a water / alcohol mixture. The invention also relates to a hydrophobic glass substrate, which is obtained by means of this method and comprises a transparent glass substrate, which is covered on one of the main faces thereof with a primer layer of silica, which is grafted with a C3-C8 alkylsilyl group.

Description

[0001] The present invention relates to a glass substrate, in particular an aircraft cockpit glazing, the surface of which is made hydrophobic by grafting a non-fluorinated alkylsilane, and to a method for manufacturing such a substrate.

[0002] In the field of transportation, and in particular for the windshields of aircraft such as airplanes and helicopters, hydrophobic properties are sought. For this purpose, the certification bodies (aviation regulations CS25 and FAR25) require a sufficiently large and transparent glazing area to ensure sufficient visibility in the event of rain without pilot intervention. These transparent vision areas can be created by wiping the rainwater with a windshield wiper. The flow of raindrops is facilitated by the hydrophobic properties of the glazing surface.

[0003] Several types of aircraft glazings are used, but they generally consist of a laminated assembly composed of several sheets of structural material bonded together using an adhesive or what are referred to as "interlayers". The outermost sheet of structural material in the glazing is usually made of glass, which has an inherent hydrophilic property. In order to limit the visual interference caused by rain, it is therefore necessary to apply a method for hydrophobization to the outer surface of such a glass sheet.

[0004] The hydrophobization method must allow for the efficient drainage of rainwater and the maintenance of the optical quality of the glazing. A high contact angle (θ) of the water droplets is sought, which on the one hand reduces the wetted surface area of the glazing and on the other hand increases the aerodynamic force exerted on the water droplets, enabling them to flow during flight. In addition, the hydrophobic treatment reduces the adhesion force of the droplets, thereby prompting them to flow under the action of gravity or under the action of the aerodynamic force. Thus, the hydrophobic coating prevents the formation of a continuous water film, which is the most severe optical deterioration.

[0005] Two parameters that can be used to characterize the hydrophobic properties of the glazing surface are:

[0006] - the contact angle (θ) of a water droplet deposited on a horizontal substrate, and

[0007] - the roll-off volume of a water droplet deposited on an inclined surface.

[0008] Of course, the hydrophobicity of the window must withstand wear for as long as possible, especially wear caused by dust present in the atmosphere, as well as the effects of the natural environment (water, which causes hydrolysis of deposits, and UV radiation) and the industrial environment (cleaning products). However, known hydrophobic treatments do not guarantee sufficient hydrophobicity of the assembled glass throughout its lifetime.

[0009] Therefore, when the droplet contact angle is less than 50°, visibility in the case of rain is usually insufficient.

[0010] The method for hydrophobicizing assembled glass must be capable of being implemented in-situ, i.e., on the assembled glass installed on an aircraft, in order to enable quick and easy maintenance. This is called regeneration of the hydrophobic function. Thus, a good hydrophobic treatment, in addition to being durable, must require a limited amount of equipment (including safety equipment), a limited number of steps, and a short implementation time.

[0011] It is known that the hydrophobicity of vehicle assembled glass is usually enhanced by grafting perfluoroalkylsilanes onto the outer surface of the glass plate after a silica primer layer has been pre-created, typically by sol-gel method, magnetron sputtering, or chemical vapor deposition (CVD).

[0012] However, perfluorinated compounds are considered harmful to the environment and human health. The persistent nature of these compounds in the environment and the human body, combined with their adverse effects on health, has recently increased the regulatory pressure regarding their use, especially via the European REACH and POP regulations. This may lead to a large-scale ban on these compounds by 2025 or at the latest by 2030.

[0013] The aim of the present invention is to provide a method for hydrophobicizing a glass substrate intended for use in the aviation industry, which method enables the obtaining of an assembled glass having satisfactory and durable hydrophobic properties (which can be regenerated on an aircraft) without the use of perfluorinated compounds.

[0014] As part of its research aimed at finding non-toxic molecules capable of replacing the perfluoroalkylsilanes hitherto used for hydrophobicizing glass substrates, the applicant has tested a large number of hydrophobic functional silanes having short, i.e., non-hydrolyzable hydrocarbon chains containing 1 to 8 carbon atoms (C1 to C8).

[0015] All the alkylsilanes tested enabled a satisfactory water droplet contact angle (θ) to be achieved after deposition, i.e., greater than 50°, or even greater than 95°, and for some even greater than 100°, and the roll-off volume differed very little from the roll-off volume obtained after grafting 1H,1H,2H,2H-perfluoroalkyltriethoxysilane (SiF5E). However, after exposure to water and UV, a deterioration of the hydrophobic performance was observed.

[0016] The present invention is based on the following finding: that fatty chain C3 to C8 alkylsilanes provide satisfactory durability with respect to both hydrolysis and UV. Alkyl chains shorter than C3 provide insufficient hydrolysis resistance, while longer alkyl chains (>C8) produce deposits that are overly sensitive to UV.

[0017] The present application thus relates to a method for hydrophobizing a glass substrate, the method comprising the following successive steps:

[0018] - forming a primer layer on one of the main surfaces of the glass substrate, the primer layer preferably being silica,

[0019] - grafting a layer of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane onto the primer layer.

[0020] Another technical problem encountered during testing was that the obtained alkylsilane deposits had a milky appearance, especially in the case of application by wiping. The treated surface of the assembled glass was slightly scattering, thereby unacceptably reducing the transparency and gloss of the assembled glass. This problem can be overcome by means of a polishing step carried out after the step of grafting the layer of C3-C8) alkyltrialkoxysilane and / or C3-C8) alkyltrichlorosilane. The polishing step is advantageously carried out by rubbing the surface with a cloth dipped in a solvent which is advantageously a mixture of water and alcohol until specular light reflection is re-established over the entire treated surface. The water / alcohol mixture is preferably a water / isopropanol mixture and contains 30 to 90% by weight of water, preferably 50 to 80% by weight of water.

[0021] Thus, the method for hydrophobizing a glass substrate according to the invention further comprises an additional polishing step after the grafting step.

[0022] The present application also relates to a glass substrate obtained by the above method. Such a hydrophobic glass substrate comprises a transparent glass substrate having on one of its main faces a primer layer, which is preferably silica, and the primer layer is grafted with a C3-C8 alkylsilyl group.

[0023] The glass substrate obtained by the method of the invention is preferably an aircraft cockpit window, in particular an aircraft windshield.

[0024] According to a first embodiment, the C3-C8 alkyltrialkoxysilane is an alkyltrialkoxysilane of the formula C n H 2n+1 SiR3, where n = 3-8, preferably n = 5-8, and each R represents C 1-3 alkoxy, preferably methoxy or ethoxy.

[0025] According to one embodiment, the C3-C8 alkyltrichlorosilane is preferably an alkyltrichlorosilane of the formula C n H 2n+1 SiR3, where n = 3-8, preferably n = 5-8, and each R represents a chlorine atom.

[0026] Optimal performance is obtained using a trialkoxysilane or trichlorosilane of the formula C n H 2n+1 SiR3 (where n = 8).

[0027] n = 5-8 means that n can take any integer value from 5 to 8, including the limiting values.

[0028] In order to obtain good durability of the hydrophobic coating on the glass substrate, it is necessary to pre-form a primer layer, preferably a silica primer layer, on the surface to be treated.

[0029] In order for this primer layer to effectively anchor the hydrophobic coating of alkyltrialkoxysilane and / or alkyltrichlorosilane to the substrate, it is important that it contains as many reactive silanol groups (Si-OH) as possible, i.e., capable of reacting with the silanol groups released by the hydrolysis of alkoxy or chlorine atoms.

[0030] Furthermore, it is recommended to perform a step of polishing the substrate before the step of forming the primer layer, for example by means of a felt impregnated with an aqueous solution of fine abrasive particles, followed by rinsing with water and drying. In the case of regeneration of the hydrophobic function, this step is even essential to completely eliminate the pre-existing degraded layer.

[0031] The silica primer layer is formed in a sol-gel step, in which tetrachlorosilane and / or tetraalkoxysilane, preferably tetraethoxysilane, is hydrolyzed in an acidic water-alcohol medium.

[0032] To carry out this step, an appropriate amount of tetrachlorosilane and / or tetraalkoxysilane is dissolved in a water / alcohol mixture, which is usually an acidic water / isopropanol mixture containing 3 to 50% by weight, preferably 5 to 15% by weight, of water, and the pH of the water has been pre-adjusted to a value of 0 to 3. The content of tetrachlorosilane and / or tetraalkoxysilane in this water-alcohol solution is advantageously 0.1 to 1% by weight, preferably 0.15 to 0.8% by weight.

[0033] Preferably, the water-alcohol solution is not applied immediately after the dissolution of the tetrachlorosilane / tetraalkoxysilane, but hydrolysis is allowed to proceed at room temperature (20-25 °C) for a period of 2 minutes to 2 hours, preferably 3 minutes to 1 hour, especially 5 minutes to 30 minutes.

[0034] In principle, the acidic hydroalcoholic solution of tetrachlorosilane / tetraalkoxysilane can be applied by any technique capable of forming a thin liquid film on the surface of the substrate. By way of example, mention may be made of application by dipping, curtain coating, spraying or wiping. Wiping is most suitable for regeneration operations on aircraft. Spraying or atomization is preferably used, as well as application by means of a cloth immersed in the hydroalcoholic solution of tetrachlorosilane / tetraalkoxysilane.

[0035] After application to the surface of the glass substrate, the formed liquid film is left to dry for a period of at least 2 minutes, preferably at least 15 minutes.

[0036] After drying the first deposit, the hydroalcoholic solution of tetrachlorosilane / tetraalkoxysilane can be applied again until the desired thickness of the silica primer layer is obtained.

[0037] The silica primer layer advantageously has a thickness of 5 nm to 250 nm, preferably 10 nm to 100 nm, in particular 15 nm to 75 nm.

[0038] The grafting of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane is carried out after drying the silica primer layer at room temperature for at least 2 minutes.

[0039] Similar to the formation of the silica primer layer, the step of grafting alkyltrialkoxysilane or alkyltrichlorosilane is carried out by a sol-gel step in which the alkyltrialkoxysilane and / or alkyltrichlorosilane is hydrolyzed in an acidic hydroalcoholic medium. It can be implemented in a manner similar to that used for forming the primer layer.

[0040] The grafting composition is an acidic hydroalcoholic (water / isopropanol) solution of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane. The content of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane in the acidic hydroalcoholic solution is preferably 0.1% to 4% by weight, and in particular 1 to 3.5% by weight.

[0041] The water / alcohol mixture in which the alkyltrialkoxysilane and / or alkyltrichlorosilane is dissolved contains 5 to 70% by weight, preferably 10 to 50% by weight, of water.

[0042] The hydroalcoholic solution of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane is advantageously left at room temperature for a period of about 10 minutes to about 3 hours to enable hydrolysis, and is then applied to the glass substrate, which is covered with a silica primer layer on one of its main faces, by spraying, sprinkling or wiping.

[0043] Procedures known in the art of hydrophobic coating are used to evaluate the hydrophobicity of the deposit:

[0044] Contact angle measurement:

[0045] The contact angle (θ) of water droplets at equilibrium was measured on 2 μl droplets using a Krüss MSA (Mobile Surface Analyzer) goniometer. The droplets were observed using a high-speed camera, which took pictures, and the contact angle was subsequently recorded from the pictures. The higher the value of the contact angle, the more hydrophobic the surface of the test sample.

[0046] Roll-off volume measurement:

[0047] The roll-off volume was measured with the assembly glass inclined at 45°. A series of calibrated droplets of increasing volume were positioned on the surface of the inclined glass plate with the aid of a micropipette. Above a certain volume, the droplets would flow by gravity on the surface of the inclined assembly glass. The roll-off volume is the minimum droplet volume that allows the droplet to flow under its own weight. This measurement was carried out with a precision of 1 μL.

[0048] The overall goal is to achieve the lowest possible roll-off volume.

[0049] Hydrolysis resistance:

[0050] The hydrolysis resistance was determined by immersing a glass plate with the hydrophobic coating to be tested in a 35 g / L saline solution at 35 °C and pH = 9 (adjusted with NaOH) for 7 days. After this treatment, the contact angle was measured again.

[0051] UV resistance:

[0052] The UV radiation resistance (under the conditions of standard ASTM G-154) was determined using a QUV-B type QUV device equipped with fluorescent lamps having a maximum irradiance at 313 nm.

[0053] UV exposure test alternative:

[0054] - Irradiation phases (fluorescent lamps), lasting for 16 hours at a temperature of 70 °C

[0055] - Dark phases, where the sample was exposed to a humid heat environment at a temperature of 40 °C, producing condensation on the surface of the sample, lasting for 8 hours

[0056] The total exposure time of this test was 150 hours. Examples

[0057] Samples of glass substrates were functionalized with different alkyltrialkoxysilanes as follows:

[0058] A 10 cm × 10 cm sample was cleaned by polishing with a felt impregnated with an aqueous suspension containing 20% cerium oxide particles. The polished sample was rinsed with distilled water and dried with a dry cloth.

[0059] To form a silica primer layer, a 0.3 wt% solution of tetraethoxysilane (TEOS) was prepared in a mixture of 10% acidic water (0.3 N HCl) and 90% isopropanol.

[0060] After reacting for 30 minutes at room temperature, the solution was applied to the surface of the glass substrate using a soaked cloth. It was left to dry for about 2 minutes.

[0061] Subsequently, immediately, a 1.6% solution of an alkyltriethoxysilane in a mixture of 10% acidic water (0.3 N HCl) and 90% isopropanol was applied by wiping onto the silica primer layer thus obtained.

[0062] It was left to dry at room temperature for 15 minutes, and then polished using a cloth dipped in a water / alcohol mixture containing 70 wt% water and 30 wt% isopropanol to remove white marks until all scattered residues disappeared from the surface of the assembled glass.

[0063] Table 1 shows the contact angle (θ) of water droplets after depositing the hydrophobic coating, the rolling-off volume (V 45° ) on a 45° surface after deposition, and the contact angle of all samples prepared in this way after hydrolysis and UV exposure, compared with samples according to the prior art using perfluoroalkyltrialkoxysilanes.

[0064] [Table 1]

[0065]

[0066] It was observed that substrates treated with alkyltriethoxysilanes having long alkyl chains (C5 and C8) were less sensitive to hydrolysis but more sensitive to UV. The hydrolysis stability of the methylsilane-based coating was insufficient (contact angle below 50 °C). By extrapolating the degradation observed after UV exposure, it seems that alkyl chains containing more than 8 carbons would provide insufficient durability with respect to this environmental factor.

[0067] In summary, in order to achieve satisfactory durability in terms of sensitivity to hydrolysis and UV, alkylsilanes having C 3-8 chains were proven to be the best.

Claims

1. A method for hydrophobizing a glass substrate, preferably an aircraft cockpit glazing, the method comprising the following successive steps: - forming a primer layer on one of the main surfaces of the glass substrate, the primer layer being preferably silica, - grafting a layer of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane onto the primer layer, wherein the C3-C8 alkyltrialkoxysilane is an alkyltrialkoxysilane of the formula C n H 2n+1 SiR3, where n = 3-8, each R represents a C 1-3 alkoxy group, preferably a methoxy or ethoxy group, and wherein the C3-C8 alkyltrichlorosilane is an alkyltrichlorosilane of the formula C n H 2n+1 SiR3, where n = 3-8, each R represents a chlorine atom.

2. The method according to claim 1, wherein After the grafting step, it further comprises a polishing step using a cloth immersed in a water / alcohol mixture, preferably a water / isopropanol mixture, the water / alcohol mixture containing 30 wt% to 90 wt% water, preferably 50 wt% to 80 wt% water.

3. The method according to any one of the preceding claims, characterized in that, The C3-C8 alkyltrialkoxysilane is an alkyltrialkoxysilane of the formula C n H 2n+1 SiR3, where n = 5-8, and each R represents a C 1-3 alkoxy group, preferably a methoxy or ethoxy group.

4. The method according to any one of claims 1 or 2, characterized in that The C3-C8 alkyltrichlorosilane is an alkyltrichlorosilane of the formula C n H 2n+1 SiR3, where n = 5-8 and each R represents a chlorine atom.

5. The method according to claim 3 or 4, characterized in that, n＝8。 6. The method according to any one of the preceding claims, characterized in that, The primer layer is made of silica and the silica primer layer is formed in a sol-gel step in which tetrachlorosilane and / or tetraalkoxysilane, preferably tetraethoxysilane, is hydrolyzed in an acidic water-alcohol medium.

7. The method according to claim 6, characterized in that, The sol-gel step for forming the silica primer layer is carried out with an acidic water-alcohol solution containing 0.1 wt% to 1 wt% of tetrachlorosilane and / or tetraalkoxysilane in a water / alcohol mixture containing 3 to 50 wt%, preferably 5 to 15 wt% water, the pH value of the water having been pre-adjusted to a value of 0 to 3.

8. The method according to claim 7, wherein The water-alcohol solution of tetrachlorosilane and / or tetraalkoxysilane is left for a period of 2 minutes to 2 hours, preferably 3 minutes to 1 hour, especially 5 to 30 minutes at room temperature and is then applied to the glass substrate by dipping, curtain coating, spraying or wiping.

9. The method according to any one of the preceding claims, characterized in that The step of grafting C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane is carried out by a sol-gel step in which the C3-C8 alkyltrialkoxysilane and / or the C3-C8 alkyltrichlorosilane is hydrolyzed in an acidic water-alcohol medium.

10. The method according to claim 9, wherein The step of grafting C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane is carried out using an acidic water-alcohol solution containing 0.1 wt% to 4 wt%, preferably 1 to 3.5 wt% of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane in a water / alcohol mixture containing 5 to 70 wt%, preferably 10 to 50 wt% water.

11. The method according to claim 10, wherein the water-alcohol solution of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane is left for a period of about 10 minutes to about 3 hours at room temperature and is then applied by spraying or wiping onto a glass substrate having one of its main faces covered with the silica primer layer.

12. The method according to any one of the preceding claims, characterized in that, The grafting of C3-C8 alkyltrialkoxysilane and / or C3-C8 alkyltrichlorosilane is carried out after the silica primer layer has been dried at room temperature for at least 2 minutes.

13. A hydrophobic glass substrate obtained by means of the method according to any one of the preceding claims, comprising a transparent glass substrate having on one of its major faces a silica primer layer grafted with a C3-C8 alkylsilyl group, the alkyl group corresponding to the formula (C n H 2n+1 ), where n = 3 - 8.

14. The hydrophobic glass substrate according to the previous claim, wherein n = 5-8, preferably wherein n = 8.

15. The hydrophobic glass substrate according to claim 13 or 14, wherein The silica primer layer has a thickness of 5 nm to 250 nm, preferably 10 nm to 100 nm, especially 15 nm to 75 nm.

16. The hydrophobic glass substrate according to any one of claims 13 to 15, characterized in that, It is an aircraft cockpit glazing.

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