Method for hydrophobicizing a glass substrate

Abstract

The invention relates to a method for hydrophobicizing a glass substrate, the method comprising the following consecutive steps: - forming a primary layer, preferably of silica, on one of the main surfaces of the glass substrate; - grafting a layer of C8-C16)-alkyltrialkoxysilane and / or C8-C16-alkyltrichlorosilane onto the primary layer. The invention also relates to a hydrophobic glass substrate obtained by means of this method and comprising a transparent glass substrate, which is covered, on one of its main faces, with a primary layer of silica, this primary layer of silica being grafted with C8-C16-alkylsilyl groups.

Description

PROCESS FOR HYDROPHOBIZING A GLASS SUBSTRATE

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

[0002] Hydrophobic properties are sought after for side windows and windshields in the transport sector, particularly for motor vehicles, where it is essential, for obvious safety reasons, to optimize the transparency of the glazing even in the rain. Raindrops must adhere as little as possible to the outer surface of the glazing and, on the contrary, flow easily under the effect of gravity or aerodynamic flows.

[0003] The two parameters used to characterize the hydrophobic nature of a glazing surface are the contact angle (θ) of a water droplet and the hysteresis of the contact angle (Δθ).

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

[0005] It is known to increase the hydrophobicity of vehicle glazing by grafting one of the perfluorinated alkylsilanes onto the surface of the glass sheet, generally after first creating a silica primer layer using a sol-gel process, magnetron sputtering or chemical vapor deposition (CVD).

[0006] Perfluorinated compounds are, however, 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 health effects, has recently increased regulatory pressure regarding their use, particularly through the European REACH and POP regulations. This could lead to a mass ban on these compounds by 2025 or, at the latest, 2030.

[0007] The present invention aims to propose a process for hydrophobizing glass substrates, in particular intended for the automotive industry, which makes it possible to obtain glazing having a satisfactory and persistent hydrophobic character without the use of perfluorinated compounds.

[0008] As part of its research aimed at finding non-toxic molecules capable of replacing the perfluorinated alkylsilanes used until now for the hydrophobization of glass substrates, the Applicant tested a large number of hydrophobic functional silanes with a hydrocarbon fatty chain.

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

[0010] The technical problem encountered was the short lifespan of the hydrophobic coatings thus prepared. Some of them had insufficient resistance to mechanical abrasion.

[0011] The present invention is based on the discovery that C8-C fatty chain alkylsilanes 16allowed, unlike alkylsilanes with shorter or longer hydrocarbon chains, to produce durable hydrophobic coatings on glass substrates, i.e. those with satisfactory resistance to mechanical abrasion, UV resistance and corrosion resistance.

[0012] The present application thus relates to a process for hydrophobizing a glass substrate comprising the following successive steps: - formation of a primary layer, preferably made of silica, on one of the main surfaces of the glass substrate, - grafting of a layer of trialkoxy-(C8-C alkyl 16 )-silanes and / or trichloro-(C8-C alkyl 16 )-silanes on the primer layer.

[0013] The present application also relates to a glass substrate obtained by the above process. This hydrophobic glass substrate comprises a transparent glass substrate, covered, on one of its main faces, with a primary layer, preferably made of silica, said primary layer being grafted with groups (C8-alkyl 16 )-silyl, preferably of (C8-C linear alkyl) groups 16 )-silyl.

[0014] The glass substrate obtained by the method of the invention is preferably an automotive side glazing.

[0015] According to a first embodiment, trialkoxy-(C8-C alkyl 16 )-silane is a straight-chain alkyl trialkoxyalkylsilane of formula CH3(CH2) n SiR3where n = 7 -15, preferably n = 7 - 11, and each R represents a C alkoxy group 1-3 , preferably a methoxy or ethoxy group.

[0016] According to another embodiment, trichloro-(C8-C10 alkyl) 16)-silane is a trichloroalkylsilane of formula CH3(CH2) n SiR3where n = 7 - 15, preferably n = 7 - 11, and each R represents a chlorine atom.

[0017] By n = 7 -15, we mean that n can take all integer values ​​between 7 and 15, inclusive.

[0018] The best results, including the best UV resistance and the best resistance to saline corrosion, were obtained with a linear C alkyl chain 10 (n = 9).

[0019] To achieve good durability of the hydrophobic coating on the glass substrate, it is essential to first form a primer layer, preferably silica, on the surface to be treated. For this primer layer to be effective in anchoring the hydrophobic alkylsilane coating to the substrate, it is important that it contains as many active silanol (Si-OH) groups as possible, i.e., groups capable of reacting with the silanol groups released by the hydrolysis of the alkoxy functions of the alkyl-trialkoxy-silane or the chlorine atoms of the alkyltrichlorosilanes. It is also important to ensure that the silica primer layer is sufficiently condensed before the deposition of the acidic hydroalcoholic solution containing the alkyltrialkoxysilane and / or the alkyltrichlorosilane. If the silica layer were insufficiently condensed, it would risk being removed or damaged during the creation of the hydrophobic functional layer.

[0020] It is therefore recommended to implement the grafting of trialkoxy-(C8-C alkyl 16 )-silane or trichloro-(C8-C alkyl 16 )-silane after at least 5 minutes of drying of the primer layer at room temperature, preferably 15. The step of grafting the trialkoxy-(C8-C alkyl 16 )-silane and / or trichloro-(C8-C alkyl 16 )-silane on the silica primer layer advantageously occurs less than two hours, preferably less than one hour after this step of drying the primer layer.

[0021] Furthermore, it is recommended to precede the step of forming the primer layer with a step of polishing the substrate, for example using a felt impregnated with an aqueous suspension of fine abrasive particles, followed by rinsing with water and drying.

[0022] The formation of the primary silica layer is carried out by a sol-gel step in which a tetrachlorosilane and / or a tetraalkoxysilane, preferably tetraethoxysilane, is hydrolyzed in an acidic hydro-alcoholic medium.

[0023] To carry out this step, an appropriate amount of tetrachlorosilane or tetraalkoxysilane is dissolved in a water / alcohol mixture, typically a water / isopropanol mixture, the pH of the water having been previously adjusted to a value between 1 and 3. The tetrachlorosilane and / or tetraalkoxysilane content of this hydroalcoholic solution is advantageously between 0.1 and 1% by weight, preferably between 0.15 and 0.8% by weight. The molar ratio of water to the silica precursor, i.e. tetrachlorosilane or tetraalkoxysilane, is generally between 400 and 600, preferably between 450 and 550 and in particular between 480 and 520.

[0024] It is preferable not to apply the hydroalcoholic solution immediately after dissolving the tetrachlorosilane and / or tetraalkoxysilane, but to allow the hydrolysis to take place at room temperature (20 – 25 °C) for a period of between 30 minutes and 4 hours, preferably between 40 minutes and 3.5 hours, in particular between 45 minutes and 3 hours. During this time, it is recommended to stir the solution to ensure good homogeneity of the reaction medium. It is generally not necessary to supply thermal energy to the solution during this hydrolysis step.

[0025] The acidic hydroalcoholic solution of tetraalkoxysilane or tetrachlorosilane can be applied in principle by any technique allowing the formation of a thin liquid film on the surface of the substrate. Examples include application by immersion, by liquid curtain, by spraying or by wiping. Preferably, spraying, or nebulization, and application using a cloth soaked in the hydroalcoholic solution of tetraalkoxysilane or tetrachlorosilane will be used.

[0026] After application to the surface of the glass substrate, the liquid film formed is left to dry for a period of at least 5 minutes, preferably at least 15 minutes.

[0027] After the first deposit has dried, it is possible to repeat the application of the hydro-alcoholic solution until the desired thickness of silica primer layer is obtained.

[0028] The silica primer layer advantageously has a thickness of between 5 nm and 250 nm, preferably between 10 nm and 100 nm, in particular between 15 nm and 75 nm.

[0029] The step of grafting the alkyltrialkoxysilane and / or the alkyltrichlorosilane is carried out, like the formation of the silica primer layer, by a sol-gel step in which the alkyltrialkoxysilane and / or the alkyltrichlorosilane is hydrolyzed in an acidic hydro-alcoholic medium. It can be carried out in a similar manner to that used for the formation of the primer layer, except that the grafting of the alkyltrialkoxysilane or the alkyltrichlorosilane is preferably carried out in a single application step.

[0030] The grafting composition is a hydroalcoholic (water / isopropanol) solution of C8-C10 alkyl acid 16 )-trialkoxysilane and / or (C8-C alkyl 16 )-trichlorosilane. The content of (C8-C alkyl 16)-trialkoxysilane and / or (C8-C alkyl 16 )-trichlorosilane of the acidic hydroalcoholic solution is preferably between 1 and 4% by weight and in particular between 2.5 and 3.5% by weight, preferably of trialkoxy-(C8-C alkyl 16 )-linear silane of formula CH3(CH2) n SiR3where n = 7 – 11, and R represents a C alkoxy group 1-3 .

[0031] The molar ratio H2O / (C8-C alkyl 16 )-trialkoxysilane or H2O / (C8-C alkyl 16 )-trichlorosilane of the acidic hydroalcoholic solution used for grafting is between 70 and 200, preferably between 80 and 150, in particular between 90 and 140.

[0032] The hydroalcoholic solution of (C8-C alkyl 16 )-trialkoxysilane or (C8-C alkyl 16)-trialkoxysilane is advantageously left at room temperature for a period of about 30 minutes to about 3 hours, preferably with stirring, to allow hydrolysis of the (C8-C alkyl 16 )-trialkoxysilane or (C8-C alkyl 16 )-trialkoxysilane, before being applied by spraying, watering or wiping on the glass substrate covered on one of its main faces with the primary layer of silica.

[0033] In some cases, the inventors encountered a technical problem consisting of the milky appearance of the alkylsilane deposits obtained. This optical problem was observed more particularly in the case of application by wiping. The treated surface of the glazing was slightly diffusive, thus unacceptably reducing the transparency and brightness of the glazing. This problem was overcome thanks to a polishing step, implemented after the grafting step of the trialkoxy-(C8-C alkyl) layer 16 )-silanes and / or trichloro-(C8-C alkyl 16)-silanes. This polishing step is advantageously carried out by rubbing the surface using a cloth soaked in a solvent, advantageously a mixture of water and alcohol, until specular reflection of the light is restored by the entire treated surface. The water / alcohol mixture is preferably a water / isopropanol mixture and contains from 30% to 90% by weight of water, preferably from 50% to 80% by weight of water.

[0034] To assess the hydrophobicity of deposits, standardized procedures known in the technical field of hydrophobic coatings are used:

[0035] Contact angle measurement:

[0036] The contact angle of a water droplet (θ) at equilibrium is measured using a Krüss DSA-100 goniometer (Drop Shape Analyzer) on a 3 µl droplet. The droplet is observed using a high-speed camera that takes pictures from which the contact angle is then recorded. The higher the contact angle, the more hydrophobic the surface of the sample being tested.

[0037] Contact angle hysteresis measurement:

[0038] Contact angle hysteresis is also performed using a Krüss DSA goniometer. The device places a 5 µl drop of water on the hydrophobic surface of the sample to be tested. Water is then injected (at a rate of 0.5 µl / min) into the drop to increase its volume. The increase in volume is accompanied by an increase in the contact angle. The increase in volume is continued until a plateau in the contact angle is reached. This is called the advance angle (θ a ) the value (average over at least 3 repetitions) of the contact angle at the plateau. The device then gradually sucks the water from the droplet so as to return to a smaller volume. The suction is continued until a contact angle plateau is obtained. The recoil angle (θ) is called r ) the value (average over at least three repetitions) of the contact angle at the plate.

[0039] Hysteresis (Δθ) is the difference between the advance angle and the recoil angle:

[0040] Δθ = θ a -θ r

[0041] We generally seek to obtain the lowest possible hysteresis of the contact angle of the water droplet.

[0042] Opel test: EN 1096-2 or DIN61200 standard

[0043] Opel friction test ® consists of rubbing the hydrophobic surface of the sample with a sheep wool felt of hardness H1 subjected to a pressure load of 0.397 kg / cm 2 , on a surface of 1.5 cm 2 , at a speed of 50 back-and-forth cycles per minute and a rotation speed of 6 revolutions per minute. A sample is considered satisfactory when, after 5000 back-and-forth cycles, the contact angle θ is still greater than 90° and the sample is free from optical defects.

[0044] Salt corrosion resistance, measured by a test called the Neutral Salt Mist test (NSM test) as described in NF ISO 9227. This test consists of spraying fine droplets of neutral (pH 7) salt water (50 g / l NaCl solution) at a temperature of 35°C and 100% relative humidity, for a period of 14 days, onto substrates inclined at 20° to the vertical. After 7 days, and even better at the end of the 14-day test, the contact angle must still be greater than 90° and the hysteresis less than 30°. UV resistance:

[0045] Measurement made using a device called a Weather-O-meter ® equipped with a xenon arc lamp with a power of 4000 W (under the conditions of standard SAEJ 1885 or SAE-J 2527(2004))

[0046] The sample is continuously exposed to radiation whose spectrum is similar to the solar spectrum at ground level. The irradiance at the wavelength of 340 nm is 0.55 W / m2 / nm

[0047] For the purposes of this application, a sample is deemed satisfactory when, after 1000 hours of exposure to UV radiation, the contact angle is still greater than 70° and the hysteresis less than 30°. Example

[0048] Glass substrate samples are functionalized with different alkyltrialkoxysilanes as follows:

[0049] A 10 cm x 10 cm sample is cleaned by polishing using a felt impregnated with an aqueous suspension containing 20% ​​cerium oxide particles. The polished sample is rinsed with distilled water and dried with compressed air.

[0050] To form the silica primer layer, a 0.3% tetraethoxysilane (TEOS) solution is prepared in a mixture of isopropanol and water at pH=1 (0.1 N HCl in demineralized water). The H2O / TEOS ratio is 500. Stir for one hour at room temperature. The solution thus prepared can be used for about 4 hours.

[0051] After stirring for one hour at room temperature, the solution is sprayed onto the cleaned glass sample and allowed to dry for approximately 15 minutes.

[0052] Immediately after, a 3% solution of alkyltriethoxysilane in a mixture of isopropanol / acid water (0.1 N HCl, pH=1) with a molar ratio of H2O / alkyltriethoxysilane of 94.5, prepared one hour earlier and maintained under mechanical stirring, is sprayed onto the silica primer layer thus obtained.

[0053] Leave to dry for 15 minutes at room temperature and remove the excess (whitish traces) by wiping with a cloth soaked in isopropanol.

[0054] Table 1 shows the contact angle of a water droplet (θ), hysteresis (Δθ), salt corrosion resistance, ultraviolet (UV) resistance and abrasion resistance (Opel test) of all the samples thus prepared, in comparison with a state-of-the-art sample prepared with a perfluoroalkyltrialkoxysilane.

[0055] Alkyl chain lengthθΔθSalt corrosionUVTest Opel-C191°17°< 2 days---C591°28°> 7 days>1300 h< 5000 hC 6 (ramifié) 103°29°> 7 days>1000 h< 5000 h-C8108 °25°> 7 days>1000 h>10000 hC 10 105°20°> 14 days>1000 h>10000 hC 16 103°24°> 7 days>1000 h>10000 h1H,1H,2H,2H– perfluorooctyl-103°36°> 7 days>2000 h>10000 h

[0056] It is observed that only glass sheets grafted with a layer of (C8-C alkyl 16 )-silanes, on a silica primer layer, have a sufficiently durable hydrophobic character. For shorter chain alkylsilanes (C5 and C6 branched) the abrasion resistance is insufficient.

[0057] It can be noted that the (C alkyl 10 )- silane allows to obtain hydrophobic glass substrates with a particularly high durability of hydrophobic properties: resistance to saline corrosion greater than 14 days and UV resistance greater than 1000 hours.

Claims

A method for hydrophobizing a glass substrate comprising the following successive steps:- formation of a primary layer, preferably of silica, on one of the main surfaces of the glass substrate,- grafting of a layer of trialkoxy-(C8-C alkyl 16 )-silane and / or trichloro-(C8-C alkyl 16 )-silane on the primer layer,- optionally a polishing step using a cloth soaked in a water / alcohol mixture containing from 30% to 90% by weight of water, in which the trialkoxy(C8-C alkyl 16 )-silane is a linear alkylsilane of formula CH3(CH2) n SiR3 where n = 7 - 15, each R representing a C alkoxy group 1-3 , preferably a methoxy or ethoxy group, and trichloro(C8-C10 alkyl) 16 )-silane is a linear trichloroalkylsilane of formula CH3(CH2) n SiR3 where n = 7 - 15, and each R representing a chlorine atom. Process according to claim 1, characterized in that the trialkoxy(C8-C10 alkyl) 16 )-silane is a linear trialkoxyalkylsilane of formula CH3(CH2) n SiR3where n = 7 – 11, and each R represents a C alkoxy group 1-3 , preferably a methoxy or ethoxy group. Process according to claim 1, characterized in that the trichloro(C8-C10 alkyl) 16 )-silane is a linear trichloroalkylsilane of formula CH3(CH2) n SiR3 where n = 7 – 11, and each R represents a chlorine atom. Method according to any one of the preceding claims, characterized in that the primary layer is made of silica and that the formation of the primary silica layer is carried out by a sol-gel step in which a tetrachlorosilane and / or tetraalkoxysilane, preferably a tetraethoxysilane, is hydrolyzed in an acidic hydro-alcoholic medium. Method according to claim 4, characterized in that the sol-gel step for the formation of the primary silica layer is carried out with an acidic hydroalcoholic solution containing from 0.1% to 1% by weight of tetraalkoxysilane and / or tetrachlorosilane. Method according to claim 5, in which the molar ratio H2O / tetraalkoxysilane or H2O / tetrachlorosilane of the acidic hydroalcoholic solution is between 400 and 600, preferably between 450 and 550, in particular between 480 and 520. Method according to any one of claims 5 to 6, characterized in that the hydro-alcoholic solution of tetraalkoxysilane and / or tetrachlorosilane is left at room temperature for a period of approximately 30 minutes to approximately 4 hours, before being applied to the glass substrate by immersion, liquid curtain, spraying or wiping. Process according to any one of the preceding claims, characterized in that the step of grafting trialkoxy-(C8-C alkyl 16 )-silane and / or trichloro-(C8-C alkyl 16 )-silane is made by a sol-gel step in which the trialkoxy-(C8-C alkyl 16 )-silane and / or trichloro-(C8-C alkyl 16 )-silane is hydrolyzed in an acidic hydro-alcoholic medium. Process according to claim 8, characterized in that the step of grafting trialkoxy-(C8-C alkyl 16 )-silane and / or trichloro-(C8-C alkyl 16 )-silane is implemented with an acidic hydroalcoholic solution containing from 1% to 4% by weight of trialkoxy-(C8-C alkyl 16 )-silane and / or trichloro-(C8-C alkyl 16 )-silane, preferably trialkoxy-(C8-C alkyl 16 )-linear silane of formula CH3(CH2) n SiR3where n = 7 – 11, and R represents a C alkoxy group 1-3 . Method according to claim 9, in which the molar ratio H2O / trialkoxyalkylsilane or H2O / trichloroalkylsilane of the acidic hydroalcoholic solution is between 70 and 200, preferably between 80 and 150, in particular between 90 and 140. A method according to claim 9 or 10, wherein the hydro-alcoholic solution of trialkoxy-(C8-C alkyl 16 )-silane and / or trichloro-(C8-C alkyl 16 )-silane is left at room temperature for a period of approximately 30 minutes to approximately 3 hours, before being applied by spraying or wiping onto the glass substrate covered on one of its main faces with the primary layer of silica. Process according to any one of the preceding claims, characterized in that the grafting of trialkoxy-(C8-C alkyl 16 )-silane and / or trichloro-(C8-C alkyl 16)-silane is implemented after at least 5 minutes of drying of the silica primer layer at room temperature. Hydrophobic glass substrate obtained by the process according to any one of the preceding claims, comprising a transparent glass substrate, covered, on one of its main faces, with a primary layer of silica, said primary layer of silica being grafted with (linear C8-C alkyl) groups 16 )-silyl, in which the linear C8-C alkyl 16 has a formula CH3(CH2) n , where n=7-15. Hydrophobic glass substrate according to claim 13, in which n is between 7 and 11, limits inclusive, preferably in which n=9 Hydrophobic glass substrate according to one of claims 13 or 14, characterized in that the primary silica layer has a thickness of between 5 nm and 250 nm, preferably between 10 nm and 100 nm, in particular between 15 nm and 75 nm. Hydrophobic glass substrate according to one of claims 13 to 15, characterized in that it is automotive side glazing.