Method of hydrophobizing glass substrate

Abstract

The invention relates to a method for hydrophobizing a glass substrate, said method comprising the following consecutive steps:-forming a primer layer, preferably silica, on one of the main surfaces of the glass substrate,-grafting a layer of C8-C16-alkyltrialkoxysilane and / or C8-C16-alkyltrichlorosilane onto said primer layer. The invention also relates to a hydrophobic glass substrate obtained by means of this method and comprising a transparent glass substrate covered on one of the main faces thereof with a primer layer of silica grafted with a C8-C16-alkylsilyl group.

Description

[0001] The present invention relates to a glass substrate whose surface has been made hydrophobic by grafting a non-fluorinated alkylsilane, and to a method for manufacturing such a substrate.

[0002] In the field of transport, hydrophobic properties are sought for side windows and windscreens, in particular for motor vehicles, where for obvious safety reasons the transparency of the glazed unit must be optimized even in the case of rain. The raindrops should adhere as little as possible to the outer surface of the glazed unit and should rather flow easily under the action of gravity or an aerodynamic flow.

[0003] Two parameters used to characterize the hydrophobic properties of the surface of a glazed unit are the contact angle (θ) of a water droplet and the contact angle hysteresis (Δθ).

[0004] The hydrophobicity of the glass must of course withstand wear and chemical attack by the environment (water, UV radiation) for as long as possible.

[0005] It is known that the hydrophobicity of vehicle glazed units is usually increased by grafting one of the perfluoroalkylsilanes onto the surface of a glass sheet after a silica primer layer has been pre-created by the sol-gel process, magnetron sputtering or chemical vapour deposition (CVD).

[0006] However, perfluorinated compounds are considered harmful to the environment and human health. The persistent nature of these compounds in the environment and in the human body, combined with their adverse effects on health, has recently increased the regulatory pressure regarding their use, particularly via the European REACH and POP regulations. This could lead to a large-scale ban on these compounds by 2025 or at the latest by 2030.

[0007] The object of the present invention is to provide a method for hydrophobizing a glass substrate, in particular a glass substrate intended for the automotive industry, which makes it possible to obtain a glazed unit with satisfactory and durable hydrophobic properties without using perfluorinated compounds.

[0008] As part of its research aimed at finding non-toxic molecules capable of replacing the perfluoroalkylsilanes hitherto used for hydrophobizing glass substrates, the applicant has tested a large number of hydrophobic functional silanes with hydrocarbon fatty chains.

[0009] Nearly all of the alkylsilanes tested made it possible to achieve a satisfactory water droplet contact angle (θ), i.e., greater than 90°, or even greater than 95°, and some even greater than 100°, with a hysteresis (Δθ) lower than the hysteresis (Δθ) obtained after grafting 1H,1H,2H,2H-perfluoroalkyltriethoxysilane (SiF5E), satisfactory resistance to ultraviolet radiation, and satisfactory corrosion resistance.

[0010] The technical problem encountered is the short service life of the hydrophobic coatings prepared in this way. Some of them have insufficient resistance to mechanical wear.

[0011] The present invention is based on the following finding: different from alkylsilanes with shorter or longer hydrocarbon chains, alkylsilanes with C8 to C 16 alkylsilanes with aliphatic chains make it possible to produce durable hydrophobic coatings on glass substrates, i.e., coatings with satisfactory resistance to mechanical wear, UV resistance, and corrosion resistance.

[0012] The present application thus relates to a method for hydrophobizing a glass substrate, the method comprising the following successive steps:

[0013] - forming a primer layer on one of the main surfaces of the glass substrate, the primer layer preferably being silica,

[0014] - grafting a layer of C8-C 16 alkyltrialkoxysilane and / or C8-C 16 alkyltrichlorosilane onto the primer layer.

[0015] 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, the primer layer preferably being silica, the primer layer being grafted with C8-C 16 alkylsilyl, preferably linear C8-C 16 alkylsilyl.

[0016] The glass substrate obtained by the method of the present invention is preferably a side window of a motor vehicle.

[0017] According to a first embodiment, the C8-C 16 alkyltrialkoxysilane is an alkyltrialkoxysilane with a linear chain of the formula CH3(CH2) n SiR3, where n = 7-15, preferably n = 7-11, and each R represents a C1-C3 alkoxy group, preferably methoxy or ethoxy.

[0018] According to another embodiment, the C8-C 16 alkyltrichlorosilane is of the formula CH3(CH2) nAlkyltrichlorosilanes of SiR3, where n = 7 - 15, preferably n = 7 - 11, and each R represents a chlorine atom.

[0019] n = 7 - 15 means that n can take any integer value from 7 to 15, including the limiting values.

[0020] The best results, especially the best UV resistance and the best salt corrosion resistance, are obtained with a straight-chain C 10 alkyl chain (n = 9).

[0021] To obtain good durability of the hydrophobic coating on a glass substrate, a primer layer, preferably a silica primer layer, must be formed in advance on the surface to be treated. For the primer layer to effectively anchor the hydrophobic coating of the alkylsilane 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 the alkoxy groups of the alkyltrialkoxysilane or the chlorine atoms of the alkyltrichlorosilane. It is also important to ensure that the silica primer layer is sufficiently condensed before depositing the acidic aqueous alcohol solution containing the alkyltrialkoxysilane and / or alkyltrichlorosilane. This is because if the silica layer is not sufficiently condensed, there is a risk that it will be removed or damaged during the preparation of the hydrophobic functional layer.

[0022] Therefore, it is recommended to dry the primer layer at room temperature for at least 5 minutes, preferably 15 minutes, before grafting the C8 - C 16 alkyltrialkoxysilane or C8 - C 16 alkyltrichlorosilane. After the step of drying the primer layer, the step of grafting the C8 - C 16 alkyltrialkoxysilane and / or C8 - C 16 alkyltrichlorosilane onto the silica primer layer is advantageously carried out in less than two hours, preferably less than one hour.

[0023] In addition, it is recommended to carry out a step of polishing the substrate before the step of forming the primer layer, for example using a felt impregnated with an aqueous suspension of fine abrasive particles, followed by rinsing with water and drying.

[0024] The silica primer layer is formed in a sol - gel step, in which silicon tetrachloride and / or tetraalkoxysilane, preferably tetraethoxysilane, is hydrolyzed in an acidic aqueous alcohol medium.

[0025] To carry out this step, a suitable amount of silicon tetrachloride or tetraalkoxysilane is dissolved in a water / alcohol mixture, typically a water / isopropanol mixture, the pH of the water having been pre-adjusted to a value of 1 to 3. The content of silicon tetrachloride and / or tetraalkoxysilane in this water-alcohol solution is advantageously 0.1 to 1% by weight, preferably 0.15 to 0.8% by weight. The molar ratio of water to the silica precursor, i.e. to silicon tetrachloride or tetraalkoxysilane, is typically 400 to 600, preferably 450 to 550, and in particular 480 to 520.

[0026] Preferably, the water-alcohol solution is not applied immediately after the dissolution of silicon tetrachloride and / or tetraalkoxysilane, but hydrolysis is allowed to proceed at room temperature (20 - 25 °C) for a period of 30 minutes to 4 hours, preferably 40 minutes to 3.5 hours, and in particular 45 minutes to 3 hours. During this period, it is advisable to stir the solution to ensure good homogeneity of the reaction medium. It is generally not necessary to supply heat energy to the solution during this hydrolysis step.

[0027] In principle, the acidic water-alcohol solution of tetraalkoxysilane or silicon tetrachloride can be applied by any technique capable of forming a thin liquid film on the surface of the substrate. By way of example, application by dipping, curtain coating, spraying or wiping can be mentioned. Spraying or atomization will be preferably used, as well as application by means of a cloth immersed in the water-alcohol solution of tetraalkoxysilane and / or silicon tetrachloride.

[0028] After application to the surface of the glass substrate, the formed liquid film is left to dry for a period of at least 5 minutes, preferably at least 15 minutes.

[0029] After the first deposit has been dried, the water-alcohol solution can be applied again until the desired thickness of the silica primer layer is obtained.

[0030] The silica primer layer advantageously has a thickness of 5 nm to 250 nm, preferably 10 nm to 100 nm, and in particular 15 nm to 75 nm.

[0031] Similar to the formation of the silica primer layer, the step of grafting alkyltrialkoxysilane and / or alkyltrichlorosilane is carried out by a sol-gel step in which alkyltrialkoxysilane and / or alkyltrichlorosilane are hydrolyzed in an acidic water-alcohol medium. It can be carried out in a manner similar to that used for forming the primer layer, except that the grafting of alkyltrialkoxysilane or alkyltrichlorosilane is preferably carried out in a single application step.

[0032] The grafting composition is an acidic water-alcohol (water / isopropanol) solution of C8-C 16 alkyltrialkoxysilane and / or C8-C 16 alkyltrichlorosilane. The C8-C in the acidic water-alcohol solution16 The content of alkyltrialkoxysilane and / or C8-C 16 alkyltrichlorosilane is preferably 1 to 4% by weight, and in particular 2.5 to 3.5% by weight, preferably the straight-chain C8-C of the formula CH3(CH2) n SiR3 16 alkyltrialkoxysilane, where n = 7-11 and R represents C 1-3 alkoxy group.

[0033] The H2O / C8-C of the acidic hydroalcoholic solution for grafting 16 alkyltrialkoxysilane or H2O / C8-C 16 The molar ratio of alkyltrichlorosilane is 70 to 200, preferably 80 to 150, and in particular 90 to 140.

[0034] C8-C 16 alkyltrialkoxysilane or C8-C 16 The hydroalcoholic solution of alkyltrialkoxysilane is advantageously left for a period of about 30 minutes to about 3 hours at room temperature, preferably with stirring, to allow the C8-C 16 alkyltrialkoxysilane or C8-C 16 alkyltrialkoxysilane to hydrolyze, and then sprayed, atomized or wiped onto a glass substrate covered with a silica primer layer on one of its main surfaces.

[0035] In some cases, the inventors have encountered the technical problem of obtaining a milky appearance of the alkylsilane deposit. This visual problem is observed more particularly in the case of application by wiping. The treated surface of the assembled glass unit is slightly scattering, thereby unacceptably reducing the transparency and gloss of the assembled glass unit. This problem can be overcome by a polishing step carried out after the step of grafting the C8-C 16 alkyltrialkoxysilane and / or C8-C 16 alkyltrichlorosilane layer. This 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.

[0036] Standard procedures known in the art of hydrophobic coatings are used to evaluate the hydrophobicity of the deposit:

[0037] Contact angle measurement:

[0038] The contact angle (θ) of water droplets at equilibrium was measured on 3 μl droplets using a Krüss DSA-100 goniometer (drop shape analyzer). The droplets were observed using a high-speed camera, which took photographs, and the contact angle was subsequently recorded from the photographs. The higher the value of the contact angle, the more hydrophobic the surface of the test sample.

[0039] Contact angle hysteresis measurement:

[0040] Contact angle hysteresis was also measured using a Krüss DSA-100 goniometer. A 5 μl drop of water was deposited on the hydrophobic surface of the sample to be tested. Water was then injected into the droplet (at a rate of 0.5 μl / min) to increase the volume of the droplet. The increase in volume was accompanied by an increase in the contact angle. The volume was increased until a contact angle plateau was reached. The value of the contact angle at this plateau (average of at least 3 repetitions) is called the advancing angle (θ a ). The device then gradually withdrew water from the droplet to return it to a smaller volume. Withdrawal was continued until a contact angle plateau was reached. The value of the contact angle at this plateau (average of at least 3 repetitions) is called the receding angle (θ r ).

[0041] Hysteresis (Δθ) is the difference between the advancing angle and the receding angle:

[0042] Δθ = θ a - θ r

[0043] The aim is generally to obtain the lowest possible contact angle hysteresis for water droplets.

[0044] Opel test: Standard EN 1096-2 or DIN61200

[0045] The abrasion test consists of rubbing the hydrophobic surface of the sample with a wool felt of hardness H1 subjected to a pressure load of 0.397 kg / cm 2 over an area of 1.5 cm 2 at a rate of 50 reciprocating cycles per minute and a rotational speed of 6 rpm. The sample is considered satisfactory when the contact angle θ is still greater than 90° after 5000 reciprocating cycles and the sample has no optical defects.

[0046] Salt corrosion resistance was measured by a test called the neutral salt spray (NSS) test as described in standard NF ISO 9227. This test involves spraying fine droplets of neutral (pH 7) brine (50 g / l NaCl solution) onto a substrate inclined at 20° relative to the vertical line at a temperature of 35 °C and 100% relative humidity for a period of 14 days. After 7 days and optimally at the end of the 14-day test, the contact angle should always be greater than 90° and the hysteresis less than 30°.

[0047] UV resistance:

[0048] Measurements are carried out using a 4000W xenon arc lamp (under the conditions of standard SAE J 1885 or SAE-J 2527 (2004)).

[0049] The sample is continuously exposed to radiation whose spectrum is similar to the solar spectrum on the ground. The irradiance at a wavelength of 340 nm is 0.55 W / m 2 / nm.

[0050] In the context of the present application, if after 1000 hours of exposure to UV radiation, the contact angle is still greater than 70° and the hysteresis is less than 30°, the sample is considered satisfactory. Examples

[0051] Samples of glass substrates are functionalized with different alkyltrialkoxysilanes in the following manner:

[0052] 10 cm × 10 cm samples are cleaned by polishing with a felt impregnated with an aqueous suspension containing 20% cerium oxide particles. The polished samples are rinsed with distilled water and dried with compressed air.

[0053] To form a silica primer layer, a 0.3% solution of tetraethoxysilane (TEOS) is prepared in a mixture of isopropyl alcohol and water at pH = 1 (0.1N HCl in softened water). The H2O / TEOS ratio is 500. Stirring is carried out at room temperature for 1 hour. The solution prepared in this way can be used for about 4 hours.

[0054] After stirring at room temperature for 1 hour, the solution is sprayed onto the cleaned glass samples and left to dry for about 15 minutes.

[0055] Subsequently, a 3% solution of alkyltriethoxysilane in an acidic isopropyl alcohol / water mixture (0.1N HCl, pH = 1) with an H2O / alkyltriethoxysilane molar ratio of 94.5, which was prepared 1 hour ago and kept under mechanical stirring, is applied immediately by spraying onto the silica primer layer thus obtained.

[0056] It is left to dry at room temperature for 15 minutes, and then the excess (whitish traces) is removed by wiping with a cloth impregnated with isopropyl alcohol.

[0057] Table 1 shows the contact angle (θ), hysteresis (Δθ), salt corrosion resistance, ultraviolet (UV) resistance, and abrasion resistance (Opel test) of the water droplets of all the samples thus prepared, compared with samples according to the prior art prepared with perfluoroalkyltrialkoxysilanes.

[0058] [Table 1]

[0059]

[0060] It was observed that only the glass plates with a layer of C8-C 16 alkylsilane grafted on the silica primer layer exhibited sufficiently durable hydrophobic properties. For short-chain alkylsilanes (branched C5 and C6), the abrasion resistance was insufficient.

[0061] It should be noted that C 10 alkylsilanes enable the acquisition of hydrophobic glass substrates with particularly highly durable hydrophobic properties: salt corrosion resistance greater than 14 days and UV resistance greater than 1000 hours.

Claims

1. A method for hydrophobizing a glass substrate, the method comprising the following consecutive steps: - Forming a primer layer on one of the main surfaces of the glass substrate, the primer layer preferably being silica, - Graft a layer of C8-C 16 alkyltrialkoxysilane and / or C8-C 16 alkyltrichlorosilane onto the primer layer, - Optionally, a polishing step using a cloth dipped in a water / alcohol mixture containing 30 wt% to 90 wt% of water, wherein the C8-C 16 alkyltrialkoxysilane is a straight-chain alkylsilane of the formula CH3(CH2) n SiR3, where n = 7-15, each R represents a C 1-3 alkoxy group, preferably a methoxy or ethoxy group, and the C8-C 16 alkyltrichlorosilane is a straight-chain alkyltrichlorosilane of the formula CH3(CH2) n SiR3, where n = 7-15, and each R represents a chlorine atom.

2. The method according to claim 1, wherein The C8-C 16 alkyltrialkoxysilane is a straight-chain alkyltrialkoxysilane of the formula CH3(CH2) n SiR3, where n = 7-11, and each R represents a C 1-3 alkoxy group, preferably a methoxy or ethoxy group.

3. The method according to claim 1, characterized in that, The C8-C 16 alkyltrichlorosilane is a straight-chain alkyltrichlorosilane of the formula CH3(CH2) n SiR3, where n = 7-11 and each R represents a chlorine atom.

4. 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.

5. The method according to claim 4, wherein 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 tetraalkoxysilane and / or tetrachlorosilane.

6. The method according to claim 5, wherein the H2O / tetraalkoxysilane or H2O / tetrachlorosilane molar ratio of the acidic water-alcohol solution is from 400 to 600, preferably from 450 to 550, in particular from 480 to 520.

7. The method according to any one of claims 5 to 6, characterized in that, The water-alcohol solution of tetraalkoxysilane and / or tetrachlorosilane is left for a period of about 30 minutes to about 4 hours at room temperature and is then applied to the glass substrate by dipping, curtain coating, spraying or wiping.

8. The method according to any one of the preceding claims, characterized in that, Grafting C8-C 16 alkyltrialkoxysilane and / or C8-C 16 The step of alkyltrichlorosilane is carried out by a sol-gel step, wherein the C8-C 16 alkyltrialkoxysilane and / or the C8-C 16 alkyltrichlorosilane is hydrolyzed in an acidic hydroalcoholic medium.

9. The method according to claim 8, characterized in that, Grafting C8-C 16 alkyltrialkoxysilanes and / or C8-C 16 The step of alkyltrichlorosilanes is carried out with an acidic aqueous alcohol solution containing 1 wt% to 4 wt% of C8-C 16 alkyltrialkoxysilanes and / or C8-C 16 alkyltrichlorosilanes, preferably a straight-chain C8-C of the formula CH3(CH2) n SiR3, where n = 7 - 11 and R represents C 16 alkyltrialkoxysilanes, and 1-3 alkoxy groups.

10. The method according to claim 9, wherein the H2O / alkyltrialkoxysilane or H2O / alkyltrichlorosilane molar ratio of the acidic water-alcohol solution is from 70 to 200, preferably from 80 to 150, in particular from 90 to 140.

11. The method according to claim 9 or 10, wherein the aqueous alcohol solution of the C8-C 16 alkyltrialkoxysilane and / or C8-C 16 alkyltrichlorosilane is left for a period of about 30 minutes to about 3 hours at room temperature and then applied by spraying or wiping onto a glass substrate having the silica primer layer on one of its major surfaces.

12. The method according to any one of the preceding claims, characterized in that Grafted C8-C 16 alkyltrialkoxysilane and / or C8-C 16 alkyltrichlorosilane is carried out after the silica primer layer has been dried at room temperature for at least 5 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 main faces a silica primer layer grafted with a linear C8-C 16 alkylsilyl, wherein the linear C8-C 16 alkyl has the formula CH3(CH2) n , where n = 7 - 15.

14. The hydrophobic glass substrate according to claim 13, wherein n is from 7 to 11, including the limiting values, preferably wherein n = 9.

15. The hydrophobic glass substrate according to any one of claims 13 or 14, characterized in that, The silica primer layer has a thickness of 5 nm to 250 nm, preferably 10 nm to 100 nm, in particular 15 nm to 75 nm.

16. The hydrophobic glass substrate according to any one of claims 13 to 15, characterized in that, It is a side window of a motor vehicle.

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