JPH11181355A - Material having heat-resistant water-repellent coating layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a material having a coating layer with excellent water repellency and heat resistance by applying an aqueous emulsion containing a fluorocarbonsilane hydrolyzate and a silicate to at least either surface of a substrate and drying the film. SOLUTION: An aqueous emulsion is prepared containing 0.1-20 wt.%, in terms of a fluorocarbonsilane, product obtained by hydrolyzing at least one fluorocarbonsilane represented by formula I (wherein Rf is a 3-18C perfluoroalkyl; R' is a 1-3C alkyl; p is 2-4; and n is 2-10) in the presence of a surfactant in an amount to give a weight ratio of l:1 to 10:l and 0.3-10 (in terms of a molar ratio to the fluorocarbonsilane) silicate represented by formula II [wherein R is OCH3 , OCH2 CH3 , or (OCH2 CH2 )m OCH3 ; and m is 1-10]. The pH of this emulsion is adjusted to 7 or higher. This is applied to at least either surface of a substrate and dried at a temp. of 100-300 deg.C for 1-24 hr to form a heat-resistant water-repellent coating layer on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material having a heat-resistant water-repellent coating layer formed by applying a fluorocarbon silane hydrolyzate-containing aqueous emulsion, and more particularly to a pH-adjusted fluorocarbon silane hydrolyzate-containing hydrolyzate-containing material. Metal plate, glass plate, aqueous emulsion
The present invention relates to a material in which a coating layer having water repellency and excellent heat resistance is formed on the surface of a base material by applying and drying the coating on a ceramic plate.

[0002]

2. Description of the Related Art Various proposals have been made for a silane-containing aqueous solution capable of providing water and oil repellency to the surface of a substrate. In order to form a water-repellent transparent film on the surface of a glass substrate and produce a water-repellent glass, a silicon alkoxide represented by Si (OR) ₄ and a substituted silicon in which part of an alkoxyl group is substituted with a fluoroalkyl group A method using a mixed solution of an alkoxide, an alcohol, water, and an acid or a base has been developed (Japanese Patent Laid-Open No. Hei 4-3).
No. 38137). However, silicon alkoxides partially substituted with fluoroalkyl groups are alcohol /
There is a problem that the concentration cannot be increased because it is hardly soluble in an aqueous solvent. Furthermore, this aqueous solution has a problem that its storage property is not good because the reaction proceeds with time and the viscosity increases because the solution containing the silicon alkoxide and the alcohol contains an acid or a base. There is also. Furthermore, there is a problem that the use of alcohol is not good for the environment. An emulsion of an excellent hydrolyzable alkoxysilane compound capable of providing a substrate with water and oil repellency without requiring a special curing operation has been developed (US Pat. No. 5,550,184). ). However, further improvement in heat resistance of the coated surface is desired for some applications.

[0003]

In order to solve the above problems, the present invention provides a material having an excellent water-repellent and heat-resistant coating layer by coating and drying an aqueous emulsion containing a hydrolyzed fluorocarbon silane. The purpose is to provide.

[0004]

Means for Solving the Problems The material having heat resistance repellent coating layer according to the present invention for solving the above _{problems, R f - (CH 2)} p -Si {- (O-CH 2 CH 2 ) _n -OR '｝ ₃ (1) (R _f is a perfluoroalkyl group having 3 to 18 carbon atoms or a mixture thereof, and a plurality of R's are the same or different having 1 to 3 carbon atoms. An alkyl group,
p = 2-4 and n = 2-10. A hydrolyzate formed from at least one fluorocarbon silane represented by the formula (I) in the presence of a surfactant; and Si—R ₄ (2) (R is OCH ₃ , OCH ₂ CH ₃ , and (OCH ₂ CH) ₂ )
1 selected from the group consisting of _m OCH ₃ (m = 1 to 10)
Or two or more groups. And the silicate represented by the formula (1), wherein the content of the fluorocarbon silane in the aqueous emulsion is 0.5.
1 to 20% by weight, the mole fraction of the silicate with respect to the fluorocarbon silane is 0.3 to 10, and the weight of the fluorocarbon silane and the surfactant used for producing a hydrolyzate thereof. The ratio is from 1: 1 to 10: 1 and the p of the aqueous emulsion is
It is characterized by having a heat-resistant water-repellent coating layer formed by applying and drying a fluorocarbon silane hydrolyzate-containing aqueous emulsion having H adjusted to 7 or more on at least one surface of a substrate.

In another material having a heat-resistant water-repellent coating layer according to the present invention, the surfactant used for producing the hydrolyzate of fluorocarbon silane is C ₉ H ₁₉ -C ₆ H _4. A nonionic surfactant represented by —O— (CH ₂ CH ₂ O) ₅₀ —H (3), wherein the content of the fluorocarbon silane is 0.1 to 20% by weight; The mole fraction of the silicate is 0.3 to 10, the weight ratio of the fluorocarbon silane and the surfactant used for producing the hydrolyzate thereof is 1: 1 to 10: 1, and A heat-resistant water-repellent coating formed by applying and drying a fluorocarbon silane hydrolyzate-containing aqueous emulsion whose pH has been adjusted to 4 or more on at least one surface of a substrate. Characterized in that it has a coating layer. In the present specification, a heat-resistant water-repellent coating layer refers to a material obtained by applying and drying a fluorocarbon silane hydrolyzate-containing aqueous emulsion used in the present invention on a substrate at a temperature of at least 350 ° C. It means that the water repellent angle on the surface of the coating layer hardly changes even after being left for a long time.

[0006]

In DETAILED DESCRIPTION OF THE INVENTION The aqueous emulsion to form a heat-resistant water-repellent coating layer, in the hydrolyzable alkoxysilane _{compound, R f - (CH 2)} p -Si {- (O-CH 2 CH 2) _n -OR '} expressed in ₃ (1), R _f is a mixture thereof, or 3 to 18 or a perfluoroalkyl group carbon atoms, a plurality R' identical one to three carbon atoms Alternatively, fluorocarbon silanes having different alkyl groups and p = 2 to 4 and n = 2 to 10 are used. Preferably, R _f is a mixed perfluoroalkyl group having an average of 8 to 12 carbon atoms, R ′ is methyl, p = 2,
And n = 2-4. More preferably, n = 2-3
It is. When n is 2, a preferred fluorocarbon silane hydrolyzate is a hydrolyzate of perfluoroalkylethyltris (2- (2-methoxyethoxy) ethoxy) silane, and when n is 3, a preferred fluorocarbon silane hydrolyzate is The hydrolyzate is a hydrolyzate of 2-perfluoroalkylethyl tris (2- (2- (2-methoxyethoxy) ethoxy) ethoxy) silane.
Such a fluorocarbon silane is produced by a known method. Two or more fluorocarbon silanes may be used as a mixture.

The aqueous emulsion of the present invention contains a component copolymerized with the hydrolyzate of the fluorocarbon silane in order to improve heat resistance. Hydrolyses in water,
In terms of solubilization, in the present invention, R is represented by Si—R ₄ (2), where R is OCH ₃ , OCH ₂ CH ₃ , and (OC
_{H 2 CH 2) m OCH 3} ( silicate is a m = 1 to 10) 1 or 2 or more groups selected from the group consisting of is used. Oil-soluble Si (OCH ₃ ) ₄ or Si (OCH ₂ CH
₃ ) Dissolution of ₄ in water has conventionally been carried out only with a water / alcohol system, but it has been found that, usually, water is hydrolyzed and dissolved by stirring for 3 hours or more. From the viewpoint of being able to adjust easily can shorten the stirring time and the hydrolyzed fluorocarbon silane aqueous _{emulsions, Si - {(OCH 2 CH} 2) m OCH 3} 4 (m = 1~
The water-soluble silicate represented by 3) is more preferable.
_{i - {(OCH 2 CH 2} ) 2 OCH 3} soluble silicate represented by ₄ is particularly preferred.

The surfactant used in the aqueous emulsion of the present invention forms a stable fluorocarbon silane hydrolyzate. The emulsion retains the alkoxysilane in a substantially totally hydrolyzed state and comprises an effective amount of a surfactant having an HLB value high enough to inhibit self-condensation of the hydrolyzed alkoxysilane compound. It is obtained by emulsifying a hydrolyzable alkoxysilane in water in the presence. Surfactants that can be used in the present invention can be selected from anionic, cationic, nonionic, and amphoteric types. Preferred surfactants have an HLB value greater than 12, more preferably greater than 16. If a surfactant having an HLB value of 12 to 16 is used, a very large amount of surfactant must usually be incorporated in order to obtain a stable emulsion. If the above HLB value is satisfied, two or more compatible surfactants may be mixed and used.

The nonionic HLB value can be obtained by calculation using a calculation formula created by Mr. Griffin of Atlas (currently ICI America) in the United States.
In the case of the anion type or the cation type, there is no method of calculating by calculation at present. However, Atlas has
Focusing on the fact that emulsifiability changes sensitively when the LB value changes, a method for experimentally determining the HLB value by emulsification experiments using standard oils has been established and published. A method of experimentally determining the HLB value has been established by companies other than Atlas, but the HLB value of the anionic or cationic type is larger than 16 regardless of which experimental method is adopted. Specifically, R
_{f -CH 2 CH 2 -O- (CH} 2 CH 2 O) 11 -H, C 9 H 19 -
A nonionic surfactant such as C ₆ H ₄ —O— (CH ₂ CH ₂ O) ₅₀ —H; R _f —CH ₂ CH ₂ SCH ₂ CH (OH) CH ₂ N
A cationic surfactant such as (CH ₃ ) ₃ ⁺ Cl ⁻ , C ₁₂ H _{25
(OCH 2 CH 2) 4 OSO} 3 - NH 4 +, C 12 H 27 -C 6 H 4 -
Anionic surfactants such as SO ₃ ⁻ Na ⁺ can be used. R _f is a perfluoroalkyl group, usually having 3 to 18 carbon atoms. After applying the aqueous emulsion to the substrate and drying, the surfactant usually loses at least the structure of the hydrophilic part in the chemical structure of the surfactant due to heat aging, but the heat aging in a shorter time Those having a hydrophilic portion that can be lost are preferred. Since the hydrophilic portion of polyethylene glycol is decomposed by drying and disappears in a short time, a nonionic surfactant having polyethylene glycol in the molecular chain of the surfactant is specifically mentioned.

The content of the fluorocarbon silane in the aqueous emulsion is at least 0.1% by weight, preferably 2 to 20% by weight, more preferably 7 to 15% by weight. If it is less than 0.1% by weight, water repellency is insufficient,
If it exceeds 20% by weight, it is difficult to obtain the stability of the aqueous emulsion. The molar ratio of silicate to fluorocarbon silane is 0.3 to 10. The mole fraction is 0.
If it is less than 3, the heat resistance of the coating layer is insufficient, while if it is more than 10, the aqueous emulsion gels and the heat resistance of the coating layer is impaired. In terms of ease of handling the aqueous emulsion,
In order to obtain a stable aqueous emulsion, the molar fraction of silicate to fluorocarbon silane must be 0.3 to 5
Is preferred, and 0.4 to 2 is more preferred. The weight ratio between the fluorocarbon silane in the aqueous emulsion and the surfactant used to form the hydrolyzate thereof is from 1: 1 to 1
0: 1, preferably 10: 2 to 10: 5,
More preferably, the ratio is 10: 3. If the proportion of the surfactant is too low, the aqueous emulsion cannot be kept stable. If the proportion is too high, the hydrophilic group tends to remain on the substrate even after drying, and good water repellency cannot be provided.

The inventors of the present invention have proposed a method for applying a fluorocarbon silane hydrolyzate-containing aqueous emulsion to a substrate and drying the coating to form a coating layer having heat resistance so as to maintain water repellency even after 5 hours at 350 ° C. Has surprisingly found that the pH of the aqueous emulsion needs to be adjusted to alkaline. As the pH value is higher, the heat resistance is improved, and the pH is preferably adjusted to 11 or more. However, a nonionic interface represented by C ₉ H ₁₉ —C ₆ H ₄ —O— (CH ₂ CH ₂ O) ₅₀ —H (3) is used as a surfactant to form a hydrolyzate of fluorocarbon silane. It was found that when the activator was used, a heat-resistant water-repellent coating layer was obtained by adjusting the pH of the aqueous emulsion to 4 or more. The pH is adjusted using an appropriate alkali such as aqueous ammonia. The aqueous emulsion of the present invention is a pigment,
Additives such as biocides, ultraviolet absorbers, and antioxidants can be contained in a range that does not affect the properties of the aqueous emulsion and the heat resistance of the coating layer.

The substrate used in the present invention is a substrate that can be used under high temperature conditions, such as a metal plate such as aluminum and stainless steel, a glass plate, a ceramic tile, a brick, concrete, and a stone. The application of the aqueous emulsion to the substrate is performed by a known method such as a dipping method, a spray method, and a spin coating method. When applied to a glass substrate, the dipping method is preferred from the viewpoint that transparency is not impaired. Heating may be used to accelerate the drying process. Usually, drying is performed in a temperature range of 100 to 300 ° C. for 1 to 2 times.
Performed over 4 hours. The substrate on which the aqueous emulsion has been applied and dried is optionally washed after drying with water to remove the remaining surfactant.

[0013]

EXAMPLES The present invention will be described with reference to examples, but the present invention is not limited to these examples. The aqueous emulsions used in the following Examples and Comparative Examples dissolve the surfactant in water, and then slowly added fluorocarbon silane with stirring by a conventional stirring technique to suppress self-condensation of fluorocarbon silane. It was prepared by keeping it in a hydrolyzed state and adding other components.

[0014] (Examples 1-3) fluorocarbons hydrolyzate used _{was, R f - (CH 2)} 2 -Si {- (O-
CH ₂ CH ₂ ) ₂ —OCH ₃ ｝ ₃ . R
_f is F (CF ₂ ) _k CH ₂ CH ₂ (k = 6.1 to ₂ % by weight; k
= 8,62-64% by weight; k = 10,23-30% by weight; k = 12-18,2-6% by weight). The surfactant is R _f
Using nonionic surfactant represented by _{-CH 2 CH 2 -O- (CH 2} CH 2 O) 11 -H. The content in the aqueous emulsion was 30 parts by weight with respect to 100 parts by weight of the fluorocarbon silane. As the silicate, tetrakis [2- (2-methoxyethoxy) ethyl] silicate (Si (DEGM) ₄ ) was used. The pH was adjusted to 10.8 by adding aqueous ammonia using a pH meter. The prepared aqueous emulsion was allowed to stand, and one week later, it was visually observed whether gelation or precipitation had occurred. Stable, like water. Next, a test piece was prepared using an aluminum plate (2.5 cm × 5.0 cm, JIS 1100 having a thickness of 1 mm) as a substrate. The application of the aqueous emulsion was performed by dip coating. Dip coating is 300mm /
Then, it was lowered at a speed of 10 minutes, waited for 10 minutes in that state, and raised at a speed of 50 mm / minute. Drying after application is 60 ° C at 200 ° C.
Minutes. Using the obtained test piece, the transparency of the coated surface was visually observed, and the case where it was the same as before coating was defined as “transparent”. Further, pure water was dropped on the surface of the coated substrate, and the contact angle was measured with a contact angle meter (manufactured by Kyowa Interface Science). Table 1 shows the stability of the aqueous emulsion, the transparency of the coated surface, and the water repellency.

Comparative Examples 1 to 4 In Comparative Examples 1 to 3, after preparing a fluorocarbon silane hydrolyzate-containing aqueous emulsion having the same composition as in Examples 1 to 3, respectively, the pH was adjusted to 2.0 using hydrochloric acid. Was adjusted. In Comparative Example 4, an aqueous emulsion was prepared without adding a silicate, and the pH was adjusted.
Was adjusted to 10.8. Table 1 shows the stability of the aqueous emulsion, the transparency of the coated surface, and the water repellency.

[0016]

[Table 1]

In Examples 1 to 3, even after elapse of 10 hours at 350 ° C., the water repellent angle on the surface of the coating layer was equal to or greater than that before aging, and an excellent heat resistant water repellent coating layer was obtained. It is shown that. The composition was as in Examples 1 to
3, respectively, and it is found that there is a remarkable difference in heat resistance when compared with Comparative Examples 1 to 3 in which the pH is adjusted to 2.0. Further, Comparative Example 4 shows that even if the pH is 10.8, the adhesion of the film becomes poor unless silicate is added. Furthermore, when Examples 1 to 3 are compared, it is understood that the heat resistance is best when the mole fraction is 1.

(Examples 4 to 7) 10% by weight of R _f- (CH
₂ ) ₂ —Si ｛— (O—CH ₂ CH ₂ ) ₂ —OCH ₃ ｝ ₃ (R _f is F (CF ₂ ) _k CH ₂ CH ₂ (k = 6.1 to ₂ % by weight; k = 8,62-64% by weight; k = 10,23-30
% By weight; k = 12 to 18, 2 to 6% by weight) perfluoroalkyl mixture) fluorocarbon silane, 30 parts by weight per 100 parts by weight of fluorocarbon silane
Parts by weight of R _f —CH ₂ CH ₂ —O— (CH ₂ CH ₂ O) ₁₁ —H
And a tetrakis [2- (2-methoxyethoxy) ethyl] silicate (Si (DEGM) ₄ ) so that the molar fraction of the silicate with respect to the fluorocarbon silane becomes 1. Prepare emulsion and adjust pH to 9.8, 10.0, 11.
0, 11.6, and adjusted to Examples 4, 5, 6, 7 respectively.
And Table 2 shows the stability of the aqueous emulsion, the transparency of the coating layer, and the water repellency.

[0019]

[Table 2] Examples 4 to 7 show that as the pH increases, a water-repellent coating layer having improved heat resistance can be obtained even when the aqueous emulsion is alkaline.

(Examples 8 to 13) In place of the surfactant used in Examples 1 to 3, C ₉ H ₁₉ -C ₆ H ₄ -O-
A nonionic surfactant represented by (CH ₂ CH ₂ O) ₅₀ -H was used. Further, in Examples 8 to 10, after the aqueous emulsion was prepared, it was used without adjusting the pH, and in Examples 11 to 13, the pH was adjusted to 1 with ammonia water.
Adjusted to 0.8. Table 3 shows the results. (Comparative Example 5-9) Comparative Example 5-9 _{also, C 9 H 19 -C 6 H} 4 -
O- (CH ₂ CH ₂ O) a nonionic surfactant represented by ₅₀ -H was used. Further, in Comparative Examples 5 to 7, the pH was adjusted to 2.0 using hydrochloric acid. In Comparative Examples 8 and 9, an aqueous emulsion was prepared without adding silicate, and in Comparative Example 9, the pH was adjusted to 10.8.

[0021]

[Table 3]

Example 8, Example 11, Comparative Example 5, Example 9, Example 12, Comparative Example 6, Example 10, Example 13, and Comparative Example 7 had the same composition, respectively.
Although these are examples in which pH is different, C ₉ H ₁₉
When a surfactant represented by —C ₆ H ₄ —O— (CH ₂ CH ₂ O) ₅₀ —H is used, by adjusting the pH to 4.0 or more, excellent heat resistance and water repellency can be obtained. This shows that a coating layer can be formed. Further, Comparative Examples 8 and 9 show that pH
This indicates that no excellent coating layer can be obtained unless silicate is added even if is adjusted to 4.0 or more.

(Examples 14 and 15) Examples 14 and 1
5 used an aqueous emulsion prepared in the same manner as in Examples 1 and 2, respectively. Instead of the aluminum plate used in Examples 1 and 2, a stainless steel plate (2.5 cm × 5.
0 cm, thickness 1 mm, grade 304). Table 4 shows the results. (Comparative Examples 10 to 11) In Comparative Examples 10 and 11, aqueous emulsions having the same composition as in Examples 14 and 15 were prepared, and the pH was adjusted to 2.0. Table 4 shows the results.

[0024]

[Table 4]

Examples 14 to 15 and Comparative Examples 10 to 11
Indicates that when stainless steel is used as the base material, an excellent heat-resistant water-repellent coating layer can be formed regardless of the pH value of the aqueous emulsion. However, Example 14 where the aqueous emulsion was of the same composition
Comparing Comparative Example 10 with Comparative Example 10 and Example 15 with Comparative Example 11, it can be seen that the example has a larger water repellent angle than before aging, whereas the comparative example does not show such a change. I understand. Therefore, it is considered that the pH value of the aqueous emulsion has a large effect on the heat resistance of the coating layer when used in an environment having more severe temperature conditions for many years. By adjusting the pH to 7 or more, A water-repellent coating layer having stable heat resistance can be obtained.

(Examples 16 and 17) Examples 16 and 1
7 used an aqueous emulsion prepared in the same manner as in Examples 1 and 2, respectively. Instead of the aluminum plate used in Examples 1 and 2, a slide glass (2.5 cm ×
Preclin glass (trade name, manufactured by Matsunami) having a size of 7.5 cm and a thickness of 1.2 mm was used. The application of the aqueous emulsion was carried out by dip coating in the same manner as in Examples 1 and 2, but the lifting speed was 10 mm / min. Also, the coated surface was observed with an optical microscope (400 ×), and when nothing was seen, it was regarded as “transparent”. When nothing was visually observed, but when clouding was confirmed by microscopic observation, it was regarded as “slightly cloudy”. When some cloudiness was found by visual inspection, it was described as "slightly cloudy". Table 5 shows the results. (Comparative Examples 12 and 13) In Comparative Example 12, an aqueous emulsion having the same composition as in Example 16 was prepared, and the pH was adjusted to 2.0. In Comparative Example 13, no silicate was added.
Table 5 shows the results.

[0027]

[Table 5] Comparing Examples 16 to 17 with Comparative Example 12, it can be seen that, even when a glass plate is used as the base material, heat resistance is improved by adjusting the aqueous emulsion to alkaline. In addition, comparing Examples 16 to 17 with Comparative Example 13, it can be seen that even if the pH is 10.8, the heat resistance is significantly impaired unless silicate is added.

[0028]

As described above, the coating layer obtained by adjusting the pH of the fluorocarbon silane hydrolyzate-containing aqueous emulsion and then coating and drying the substrate provides excellent water repellency and heat resistance. can do.

Claims (2)

[Claims] 1. A _{R f - (CH 2) p} -Si {- (O-CH 2 CH 2) n -OR '} 3 (1) (R f 3 to 18 amino perfluoroalkyl radical carbon atoms Or a mixture thereof, wherein a plurality of R ′ are the same or different alkyl groups having 1 to 3 carbon atoms,
p = 2-4 and n = 2-10. A hydrolyzate formed from at least one fluorocarbon silane represented by the formula (I) in the presence of a surfactant; and Si—R ₄ (2) (R is OCH ₃ , OCH ₂ CH ₃ , and (OCH ₂ CH) ₂ )
1 selected from the group consisting of _m OCH ₃ (m = 1 to 10)
Or two or more groups. And a silicate represented by the formula (1), wherein the content of the fluorocarbon silane in the aqueous emulsion is 0.1%.
1 to 20% by weight, the mole fraction of the silicate with respect to the fluorocarbon silane is 0.3 to 10, and the weight of the fluorocarbon silane and the surfactant used for producing a hydrolyzate thereof. The ratio is from 1: 1 to 10: 1 and the p of the aqueous emulsion is
A material having a heat-resistant water-repellent coating layer formed by applying and drying a fluorocarbon silane hydrolyzate-containing aqueous emulsion having H adjusted to 7 or more on at least one surface of a substrate. Wherein _{R f - (CH 2) p} -Si {- (O-CH 2 CH 2) n -OR '} 3 (1) (R f 3 to 18 amino perfluoroalkyl group carbon atoms Or a mixture thereof, wherein a plurality of R ′ are the same or different alkyl groups having 1 to 3 carbon atoms,
p = 2-4 and n = 2-10. ) In the presence of a nonionic surfactant represented by C ₉ H ₁₉ —C ₆ H ₄ —O— (CH ₂ CH ₂ O) ₅₀ —H (3) from at least one fluorocarbon silane a hydrolyzate _{generated, Si-R 4 (2)} (R is OCH _3, OCH ₂ CH _3, and (OCH ₂ CH ₂₎
1 selected from the group consisting of _m OCH ₃ (m = 1 to 10)
Or two or more groups. And the silicate represented by the formula (1), wherein the content of the fluorocarbon silane in the aqueous emulsion is 0.5.
1 to 20% by weight, the mole fraction of the silicate with respect to the fluorocarbon silane is 0.3 to 10, and the weight of the fluorocarbon silane and the surfactant used for producing a hydrolyzate thereof. The ratio is from 1: 1 to 10: 1 and the p of the aqueous emulsion is
A material having a heat-resistant water-repellent coating layer formed by applying and drying a fluorocarbon silane hydrolyzate-containing aqueous emulsion having H adjusted to 4 or more on at least one surface of a substrate.