GB2269330A - Water repellent window glass and method for preparation thereof - Google Patents

Abstract

A window glass capable of maintaining good water repellent performance for a long time can be manufactured by applying a mixture comprising a ceramics sol and a fluorine containing compound to the surface of the glass and forming a ceramic coated layer on the glass by heating.

Description

2269330 Water Repellent Window Glass and Method for Preparation Thereof

The present invention relates to a technique for forming a coated layer on glass such as a sunroof or a window glass for motor vehicles, that provides water repellancy thereto.

One technique for coating a water repellent agent on a window glass is disclosed in Japanese Patent Laid-opened Gazette No. Hei 4-124047. In this technique, first the surface of the glass is coated with a vehicle, which is obtained from the product of the hydrolysis and polycondensation of a metal oxide in the presence of water, alcohol and a catalyst. Then the coated glass is heated to form a coated layer comprising the metal oxide.

The surface of the coated layer comprising the metal oxide is then treated with hydrofluoric bcid or by plasma etching to form fine unevenness on the surface thereof.

Finally treated coated layer is coated with a fluorinated silicon water repellent agent that contains a polyfluoroalkyl group (hereinafter referreCto as Rf group). According to this treating process for providing water repellancy, the elution of alkaline components from the glass substance can be prevented.

2 However, this technique has a disadvantage in that it reduces operation efficiency because it absolutely requires at least two coating procedures; a first procedure for coating the metal oxide on the surface of the glass, and a second procedure for coating a water repellent agent for providing water repellancy over the layer of the coated metal oxide.

Besides, inasmuch as the uppermost layer on the glass, where the fluorine compound is coated, receives the strongest exposure to sunlight, the fluorine compound in the layer tends to absorb thermal energy from the sunlight. For this reason.' the layer cannot gain sufficient weather resistance and durability, and is thus another disadvantage for this prior art technique.

A technique capable of solving the above problem is described in Japanese Patent Laid-opened Gazette No. Sho 58-122979, wherein the coating of a mixture consisting of two different compounds to the surface of the glass is disclosed. This technique comprises (1) mixing of either an alkoxysilane compound or a halogenated silane compound with an Rf group containing silane compound, (2) attaching the resulting mixture onto the glass, and then (3) heating the attached mixture to strengthen the bonding thereof to the contacted surface to thereby improve the adhesion and the water repellancy of the glass.

In the prior art described above, a silicon-based composition comprising a silane compound is used as a

3 component of the coating layer. However, since the hardness of the coated layer comprising a silicon-based composition is generally low, the layer has the disadvantage of being easily abraded, even by the repeated operation of wipers on motor vehicles or the like.

The present invention was accomplished in view of the above problems, and relates to a water repellent window glass comprising a glass substrate and a ceramic layer formed on the surface of said substrate, wherein said substrate being the heated product of a mixture which comprises a ceramic sol and a fluorine containing compound, wherein said ceramic sol is a metal oxide in sol such as zirconia sol and said fluorine containing compound is a nonionic organofluorine compound, N-E3-(trimethoxysilyl) propyll-N-n-propylperfluorooctyl sulfonamide or the like, which is in a concentration of from 0.2% to 0.5% by weight and capable of forming bonds to the metal in the ceramic sol as a group of the fluorine containing compound.

The present invention further relates to a method for preparing a water repellent window glass, which comprises coating a mixture comprising a ceramic sol and a fluorine containing compound onto a glass substrate and heating said coated glass substrate, wherein said mixture are subjected to an aging step, which comprises dipping said glass substrate into said mixture and removing said substrate from said mixture at a rate with the range of 5 mm/min to 50 mm/min, and said heating step is carried out at a temperature of from 200 to 4001C.

According to the present invention, the coated layer is formed on the glass by coating the mixture in sol prepared by mixing the ceramic sol having excellent adhesion to the glass and the fluorine containing compound having water repellancy, so that the fluorine containing compound invades into the inside of the ceramic coated layer and is fixed therein. Because the fluorine containing compound remains in the coated layer even if the surface of the coated layer had been abraded, the water and oil repellent properties are maintained in good condition over a long time. In addition, the present invention can be effective in saving time and labor as well as improving the operation efficiency because the process for coating the glass surface can be accomplished by one operation.

Figs. 1 through 4 illustrate the examples according to the present invention. Fig. 1 is a fluorine containing compound concentrationdulling value correlation graph for explaining the relationship between the concentrations of the fluorine containing compound and the dulling value. Fig. 2 shows the relationships between the speed for pulling up glass and the water repellent performance, and between the speed for pulling up glass and the transmission factor. Fig. 3 shows the relationships between the heating temperature and the water repellent performance, and between the heating t emperature and the water resistance. Fig. 4 is a shielding ratio - wave length correlation graph which shows the shielding percentage of zirconia against ultraviolet rays.

In the present invention, "ceramic sol" is defined as a suspension of fine ceramic particles dispersed in a dispersing vehicle. The ceramic sol is capable of forming a coated layer of the ceramic by heating a ceramic sol coating. A ceramic sol can form a coated layer that causes little deterioration of the transparency of glass is preferable.

For a concrete example of the ceramic sol, zirconia sol (including zirconia containing compound in sol), which is a metal oxide in sol, can be exemplified. Among these, the zirconia sol dispersed in an organic solvent obtainable by replacing water of the zirconia sol dispersed in water with an organic solvent by adding said organic solvent to the zirconia sol in water (see Japanese Patent Application laid-opened Gazette No. Hei 3-218928.) is particularly preferable, because a transparent and crystalline coated layer can be formed by using it in the mixture with the fluorine containing compound. As the examples of the organic solvent for substituting zirconia, ketones, carboxylic acids, esters, alcohols, polyhydric alcohols, glycols and solvents having hydrophilic groups such as COOH, -OH and the like in their molecules or the mixtures 6 of two or more of the foregoing organic solvents are exemplified.

In the present invention, "zirconia so]" is defined as a suspension in an organic solvent wherein fine zirconia particles are dispersed.

Zirconia, which is a component of the zirconia so], has excellent chemical stability and is stable for acids and alkalis. For this reason, it hardly decomposes or melts, and can lower the dissolution of the coated layer caused by the adhesion of acids or alkalis derived from outside the glass material. In addition, it functions to inhibit the elution of alkaline components f - rom the inside of the glass material, thereby affording improved weather resistance to the coated layer. Furthermore, the coated layer formed with the zirconia sol can provide an additional advantage of more sufficiently shielding ultraviolet rays as well as providing a higher hardness to the layer in comparison with the coated layer comprising a non-metal oxide such as silica.

In the present invention, "glass" is defined as a glass for motor vehicles as represented by soda-lime silicate glass, etc.

In the present invention, "fluorine containing compound" is defined as a compound that contains fluorine elements therein. Preferably, the fluorine containing compound is one that can exhibit high water repellancy when it is contained in the ceramic coated layer and that 1 0 -. 0. 0 has high transmissivity of rays.

Alternatively, in view of making the water repellent performance to last for a long time, it is preferable to use a compound which can form bonds by polycondensation reaction etc. with the zirconia contained in the ceramic sol.

When using the zirconia sol dispersed in the organic solvent for forming the coated layer, a nonionic organofluorine surfactant or N-[3(trimethoxysilyl) propyll-N-n-propylperfluorooctyl sulfonamide and the like can be exemplified as the fluorine containing compound which undergoes a polycondensation reaction with the zirconia sol. The reaction can be accomplished by aging a mixture thereof. The resulting coating exhibits good water repellancy.

In that case, it is preferable to adjust the content ratio of the fluorine containing compound in the mixture in sol to a concentration in the range of from 0.2% to 0.5% by weight. In the above range, the mixture in sol prepared can ensure having both the water. repellancy and transmissivity in good condition.

For forming the coated layer specified in the present invention, the mixture containing the ceramic sol and the fluorine containing compound is applied onto the surface of the glass and then heated.

In the above procedure, it is further preferable to form the coated layer described above by employing a sol- gel process. The mixing ratio for both the ceramic sol and the fluorine containing compound can be selected in the range which does not cause a defect. In general, an increase in the content of the fluorine containing compound enhances the water repellancy, but may cause whitening etc. of the coated layer, transparency less, dispersion of the contact angle and/or separation of the coated layer from the glass due to uneven coating.

Any application method may be employed without restriction as far as the method for applying the mixture in sol to the glass. However, a method of readily forming the layer in an uniform thickness is preferably employed.

As a preferable example, a dipping method is employed for the formation of the coated layer in the sol-gel process.

In the dipping method, the thickness of the layer can be adjusted by either varying the speed for pulling up the glass or repeating the dipping procedure, and should be determined in a range where the whitening etc. and detachment of the layer may not occur. In general, an increase in the thickness of the coated.layer will lead to such defects. The application of the mixture in sol may be carried out for either both sides of the glass or the one side thereof in accordance with the requirements. In addition, a coated layer thickness capable of providing both the water repellent property and transmissivity in good condition can be obtained by varying the speed of pull up the glass to be within the range of from 5 mm/min. to 50 9 mm/min.

The heating condition can be selected within a temperature range, wherein the ceramics can be stable and in consideration the thermal resistance of the fluorine containing compound, so as to form the coated layer in good condition.

When the zirconia sol is used for coating, it is preferable to set the heating temperature within the range of from 200 to 400 'C. If the temperature is lower than 200 C, abrasion resistance of the coated layer tends to decrease, and if the temperature is higher than 4001C, the water repellent performance tends to decline as well. The time for heating can be selected properly in connection with the heating temperature and it is not specifically restricted. In general, the time is preferably within the range of from about 3 to about 120 min.

Considering the reaction time required for the polycondensation reaction between the zirconia sol and the fluorine containing compound, it is preferable to age the mixture before coating. This aging is preferably conducted in a clean room at a temperature maintained within the range of from 23C to 26C and a relative humidity of from 45% to 55%.

Now the process for forming the water repellent window glass having a water repellent ceramic coated layer is explained by employing the solgel process which can readily take the fluorine containing compound in the coated - 1 ayer.

The preparation of the sol according to the sol-gel process is described first.

For the ceramic sol, Zirconia sol (Zr02)(manufactured by Nihon Shokubai Co., Ltd.) prepared by making zirconia, which is a transparent ceramics as well as a metal oxide, in sol, is used as an intermediate vehicle for improving the adhesion of various fluorine containing compounds exemplified below to the glass surface. The fluorine containing compound should be mixed in an amount so as to sufficient water repellent performance. That is, the contact angle indicative for tKe water repellent ability, should be at least about 80 degrees. It is preferable to prepare the mixing ratio for the fluorine containing compound so as to be more than about 0.2% by weight. Concerning the proportions of water and an organic solvent, it is preferably 50% and 47%, respectively, when the proportion of zirconia in the sol is 3%.

However, as can be seen from the results in Fig. 1, a dulling value (scattering transmissJon factor/ total transmission factor) through the glass becomes high as the concentration of the fluorine containing compound increases, thereby causing defects such as whitening etc. of the coated layer. For this reason, it is necessary to select the concentration of the fluorine containing compound in the mixture to be about 0.5% by weight or less in order to lower the dulling value. As a results, the concentration of the fluorine containing compound is preferably determined in a concentration range of from about 0.2% to about 0.5% by weight in order to retain both the water repellent property and transmission factor. As the sufficient values in the water repellent property and the dulling value can be obtained in the above range, it is feasible to adjust the concentration of the fluorine containing compound according to the places for use and the usages, depending upon the importance either in the water repellent performance or the dulling value.

In Fig. 1, the dulling value (%) was measured by using a phase meter comprising a light source unit having an incandescent lamp as light source and a light receiving unit having an integrated lamp and is obtained according to the following formula.

Dulling value = Scattering transmission factor 1 total transmission factor Total transmission factor = T: 1 Ti x 100 Scattering transmission factor =(T4- T3X T2 /TO X 100 Ti Quantity of incident rays T2 Transmission quantity of total rays through test sample T3 Quantity of rays scattered by apparatus T4 Quantity of rays scattered by apparatus and test sample After to mixing the zirconia sol with the fluorine containing compound, it is preferable to leave the mixture in sol for aging. During the aging, the molecules of the fluorine containing compound individually conduct polycondensation reactions with the zirconia sol to make them bond to zirconia as a group. This makes the scattering of the fluorine containing compound from the coated layer difficult, even if the layer absorbs thermal energy from sunlight, etc. The period for the aging is, preferably, in a range of from about 1 hour to about 50 hours. If the period is shorter than the above range, the adhesion of the coated layer to the glass is insufficient, thus the layer easily detaches from the glass. On the contrary, if the period is longer than the above range, the coated layer tends to be uneven.

[Fluorine containing compounds used] 1) Nonionic organofluorine surfactant; 2) N-[3-(trimethoxysilyl)propyl]-N-n-propylperflucrooctyl sulfonamide.

Now the application method for forming the coated layer according to the sol-gel process will be explained.

Since dipping is preferable as the application method for coating, the foregoing method is described based on the dipping method.

Washed glass is soaked in a mixture in sol prepared according to the procedure described above. Then the glass is vertically pulled up over the surface of the sol 13 at a speed of from about 5 mm/min. to about 50 mm/min. If the speed is less than about 5 mm/min., the coated layer becomes thick as shown in Fig. 2, and the light transmissivity through the glass becomes insufficient. On the other hand, when the speed is more than about 50 mm/min the coated layer becomes thin, and the quantity of the fluorine containing compound contained in the layer decreases. In this case, the coated layer cannot exhibit sufficient water repellent performance. Moreover, the resulting layer is uneven. As a result, it is necessary for the formation of the coated layer to vary the speed for pulling up the glass to be within the range of from about 5 mm/min. to about 50 mm/min. in order to simultaneously possess both good transmission factor and water repellent property therein. Therefore, it is feasible to determine the thickness of the coated layer suitable for the respective fluorine containing compound by properly adjusting the thickness of the coated layer depending upon the places for use and the usages.

In Fig. 2, water repellancy is dete.rmined by measuring the contact angle on the surface of the coated layer after forming the water repellent coated layer.

In the present invention, the contact angle was measured by gauging droplets of distillated water having a diameter of 1.5 mm dropped on the surface with a contact angle gauge (produced by Kyowa Kaimen Kagakusha) at room temperature.

1 The transmission factor was determined by the same manner as the one for determining the total transmission factor in Fig.l.

Afte.r pulling up the glass, the applied glass is treated by heating to strengthen the adhesion between the coated layer applied by the dipping method and the glass. The crystallization of zirconia in the mixture proceeds as the heating temperature elevates, increasing the adhesion between the coated layer and the glass as well as the hardness of the coated layer, thereby improving the durability and the abrasion resistance of the coated layer. In the present invention, it 'is preferable to fix the temperature for the heating in a range of from about 200 C to about 400 C. Because, if the heating is performed at the temperature of about 200 C or less, the adhesion between the coated layer and the glass and the hardness of the coated layer will not be stabilized, while if it is performed at the temperature exceeding about 400C, the groups of the fluorine containing compound in the mixture in so] where polycondensation reaction w.as conducted during the aging may be liberated and then scatter due to the heat, thereby providing a possibility of deteriorating both the initial water repellent performance and water durability of the coated layer (see Fig. 3). Yet it is possible to obtain good initial water repellent performance and water resistance at a heating temperature of about 200 OC. However, both the adhesion between the coated layer and the glass and the hardness of the coated layer g'radually increase as the heating temperature is elevated over 200C, albeit the water resistance lowers in some cases, though the initial water repellent property is not affected.

Therefore, it is preferable to select the temperature in a vicinal range of 200C for a prescribed period as a condition for the heating.

In the above examination, the determination of the water durability was based on the results obtained by measuring the contact angle on the surface of the coated glass after soaking the glass in a bath maintained at 40 C for 336 hours and then washing the glass by way of ultrasonic cleaning together with detergent.

Now we explain about the formation of the coated layer according to the sol-gel process with greater detail.

One example of the mixture sol comprises 0.2% by weight of the fluorine containing compound, 3% by weight of Zr02, 50% by weight of propyleneglycolmethylether, and 46.8% by weight of water. By leaving the mixture for aging for approximately 24 hours, the optimal sol preparation can be obtained due to having polycondensation reaction. The glass washed by grinding the coated surface with a glass detergent such as cerium oxide or the like is then put into the aged mixture in sol. By pulling up the glass in the vertical direction from the surface of the mixture in sol at a speed of 12 mm/min., a coated layer having a thickness of 0.04,u m can be applied onto the glass. '-The coated layer of the above thickness gives a high light transmission factor of about 80%. Following to the application of the mixture in sol to the glass, the coated layer is heated at 200C for 2 hours, thereby obtaining sufficient water repellancy to provide a contact angle in the range of from about 80 to about 110 degrees.

The foregoing condition gave the similar results in the standard test on front glass for motor vehicles (JIS R3212, Provision 3.7), which results indicated excellent water resistance of the coated layer.

As described above, the formation of the coated layer having excellent water and oil repellent properties and weather resistance can be accomplished by employing the sol-gel process described above.

Since the coated layer according to the present invention is preferably based on zirconia, which is stable for acids and alkalis as a chemical property thereof, it is possible to prevent the outstanding deterioration of the water repellent performance caused by the elution of components in the coated layer by acid rains. In addition, zirconia has a higher hardness than silane and silica which have been conventionally used for the coating. Therefore the coated layer containing zirconia has an advantage of providing less abrasion of the layer which may be caused by the repeated movements of wipers and resistance to flaws made by sands. Moreover, with regard to the transmissivity for ultraviolet rays, the zirconia sol can shield the rays up to 60% against the rays having 320 nm wave lengths, while glasses allow the penetration of ultraviolet rays with the wave length of more than 300 nm and, silane and silica allow that of more than 200 nm. In this regards, the transmission factor for ultraviolet rays which is shown in Fig. 4 means the percent of shielding ultraviolet rays through the zirconia sol placed in a cell which is measured by using spectrophotometer.

The water repellent window glass manufactured in the examples described above is suitable to be used for motor vehicle window glasses as described above, it is naturally applicable for other uses such as door mirrors, sunroofs, lamps or the like for motor vehicles use, allowing to provide them good water repellent property.

The present application claims priority under 35 U.S.C. 9 119 from previously f iled Japanese Patent Application-No. Hei 4-210082, filed August 6, 1992, in Japan, the entire contents of which are hereby incorporated by reference. EXAMPLES Now the present invention is described in detail according to the Examples.

With zirconia sol (manufactured by Nihon Shokubai Co., Ltd.) was mixed one of the fluorine containing compounds described below to prepare the mixture so as to contain 0.2% by weight of the fluorine containing compound, 3% by 18 - weight of Zr02, 50% by weight of propyleneglycolmethylether, and 46.'8% by weight of water, then left the resulting mixture for aging in a clean room maintained at the temperature of 25 C and relative humidity of 50% for 24 hours. Then the mixture was applied to the both sides of the glass by dipping method and followed by heating of the coated glass. The application of the mixture to the glass was accomplished by pulling the dipped glass vertically upward from the surface of the mixture at the speed indicated in Table 1 as shown below, affording the ceramic coated layer.

E The fluorine containing compounds used Nonionic organofluorine surfactant (manufactured by Mitsubishi Material Co., Ltd.: EFTOP EF-352) N-E3-(trimethoxysilyl)propyll-N-n-propylperfluoroocty1 sulfonamide (manufactured by Mitsubishi Material Co., Ltd.: MF-160) The water repellent performance, which is shown as the contact angle to distillated water was in the good range of 85 to 110 degrees. The transmission factor for the coated glass was from 80% to 85%. Similar values to the above were obtained after conducting the standard test on the front glass for motor vehicles (JIS R3212, Provision 3.7), which proves the excellent durability of the coated glass.

The glass without coating was also checked for the comparison, which indicated the contact angle of about 20 degrees an.d the transmission factor of about 87%.

19 - The results are shown in Table 1.

Table 1

Examples Fluorine Speed of Heating Thickness Contact Transm- DurabiliContaining Pulling Condi- of Angle ission ty Compound' Up Glass tion Layer Factor' (mm/min.) C /hr) m m) (degree) 1 A 12 200/2 0.04 85-100 80-83 Good 2 B 12 200/2 0.04 100-110 82-85 Good Comparative 20 87 Example

1: Fluorine containing compound used:

A: Nonionic organofluorine surfactant (Manufactured by Mitsubishi Material Co., Ltd.: EFTOP EF-352) B: N-[3-(trimethoxysilyl)propyl-N-n-propylperfluoroocty1 sulfonamide (Manufactured by Mitsubishi Material Co., Ltd.: MF-160) 2: Transmission factor of visible rays -

Claims (14)

1. A water repellant window glass comprising a glass substrate and a ceramic layer formed on the surface of said substrate, said ceramic layer being the heated product of a mixture which comprises a ceramic sol and a fluorine containing compound.

2. A water repellent window glass as claimed in claim 1, wherein the ceramics sol is a metal oxide in sol.

3. A water repellent window glass as claimed in claim 2, wherein the metal oxide in sol is zirconia sol dispersed in an organic solvent which is obtained by replacing water in the zirconia sol dispersed in water with the organic solvent by adding the organic solvent to the zirconia sol in water.

4. A water repellent window glass as claimed in any one of the preceding claims wherein the fluorine containing compound is a nonionic organofluorine surfactant or N-[3-(trimethoxysilyl)propyl]-N-npropylperfluorooctyl sulfonamide.

5. A water repellent as claimed in any one of the preceding claims wherein the concentration of the fluorine containing compound in the mixture is prepared to a range of from 0.2% to 0.5% by weight and the fluorine containing compound bonds to zirconia in the ceramics sol as a group of the fluorine containing compound.

6. A method for preparing a water repellent window glass, which comprises: coating a mixture comprising a ceramic sol and a fluorine containing compound onto a glass substrate; and heating said coated glass substrate.

7. The method as claimed in claim 6, wherein said mixture of ceramic sol and fluorine containing compound is subjected to an aging step prior to said coating step.

8. The method as claimed in claim 6 or claim 7, wherein said coating step comprises dipping said glass substrate into said mixture of ceramic sol and fluorine containing compound and removing said substrate from said mixture at a rate within the range of 5 mm/min to 50 mm/min.

9. The method as claimed in any one of claims 6 to 8, wherein said heating step is carried out at a temperature of from 200 to 400 0 C.

10. A glass article comprising a glass substrate having formed thereon a ceramic layer, said ceramic layer comprising the polycondensation reaction product between a ceramic material and a fluorine containing compound.

11. A mixture comprising a ceramic sol and a fluorine containing compound.

12. A water repellent window glass as claimed in claim 1 substantially as hereinbefore specifically described with reference to the accompanying figures of the drawings.

13. A method as claimed in claim 6 substantially as hereinbefore specifically described with reference to the accompanying figures of the drawings.

14. Use of a mixture as claimed in claim 11 to form a water repellent coating on a window glass.

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