JPH1179789A - Method of forming water-repellent thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain a high quality water-repellent thin film in a large amt. by applying an excessive amt. of a coating liquid for the formation of a water-repellent thin film on the surface of a substrate such as glass and removing the excess coating material. SOLUTION: The base body consists of glass, metal, ceramic material, resin, etc., and especially, glass is preferable because the a glass base body has hydroxyl groups on the surface and firmly bonds with a water-repellent liquid to form a transparent thin film. The water-repellent liquid contains a perfluoro group- contg. compd., preferably a perfluoro group-contg. silane compd. and its hydrolyzed condensed material. As for the coating means of the water-repellent liquid, squeegee coating method is preferably used. After the water-repellent liquid is dropped on the surface of the base body, an elastic, preferably a sponge squeegee is used to spread the liquid. After coating, the liquid is dried for 1 to 25 hours to bond to the substrate. The excess coating material is removed by wiping till color irregularity or haze disappears. Especially, it is preferable to spray a starch-contg. powder which can adsorp the excess coating material and then to remove by using a brush or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a water-repellent thin film by applying a coating liquid for forming a water-repellent thin film on a surface of glass or the like.

[0002]

2. Description of the Related Art Conventionally, a method for forming a water-repellent thin film is to apply a coating liquid for forming a water-repellent thin film to paper or the like, spread a treatment liquid on a substrate, and leave it as it is until it becomes a transparent state without any problem in appearance. I was wiping while replacing the paper.

In this method, there is no problem with a small amount and a small area, but a large amount and a large area require a great deal of labor and time, and there are many variations in the degree of application (amount, strength, time, etc.).
As a result, there were many irregularities in appearance and variations in performance, which were unsuitable for mass production. Further, in the case of mechanization, it is necessary to frequently change the paper or the like to which the coating liquid for forming a water-repellent thin film is adhered during the process, so that the mechanization is difficult.

[0004] That is, the conventional method has the following three problems. 1) Since the coating liquid for forming the water-repellent thin film is applied to paper or the like by applying it, it is difficult to make the liquid amount, coating time, number of coatings, pressing force (coating force) uniform and automatic, and it is difficult to perform manually. Contact angle (contact angle of water with substrate)
Therefore, it is not suitable for a large amount of processing.

2) If the evaporating property of the coating liquid for forming a water-repellent thin film is improved, processing can be performed in a short time. However, the area that can be processed becomes small, and the processing in a small area unit is combined to cope with a large area. There is a need. If the evaporation property is poor, a large area can be processed at once, but there are problems such as that it takes a lot of time to finish, the coating liquid is spread too thin, and the film thickness is too thin due to excessive wiping, and the performance is insufficient. Was.

3) When considering mechanization for the above-mentioned improvement, it is necessary to replace paper or the like in the middle of painting, and the mechanization using a robot or the like becomes complicated and difficult. If the same product is used without replacing the paper or the like, the finishing time is gradually increased, and the old coating liquid for forming a water-repellent thin film is accumulated, and the performance is reduced.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a water-repellent thin film capable of stably obtaining a large amount of a high-quality water-repellent thin film.

[0008]

SUMMARY OF THE INVENTION The present invention is a method for forming a water-repellent thin film on a surface of a substrate using a coating solution for forming a water-repellent thin film. A method for forming a water-repellent thin film, comprising: a coating step of coating, and a subsequent step of removing a surplus of the coating liquid for forming a water-repellent thin film.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A feature of the present invention is that a coating liquid for forming a water-repellent thin film (hereinafter, simply referred to as a water-repellent liquid) is applied.
This is to wipe off the “excess” of the water-repellent liquid. The “excess” (hereinafter simply referred to as “excess”) of the water-repellent liquid is a part where the reflected color unevenness and transmission haze are developed. Therefore, it is important to wipe off the portion where the color unevenness and haze disappear. is there.

In the present invention, a water-repellent liquid that reacts with the substrate (when a film is previously formed on the substrate, the film material) is used. According to the present invention, an excessive amount of the water-repellent liquid is applied to the surface of the substrate and allowed to react (for example, dried), and thereafter, an excessive amount of the water-repellent liquid (unreacted and not adhered) is removed.

The substrate on which the water-repellent liquid is applied is glass,
Examples thereof include metals, ceramics, resins, and substrates subjected to a surface treatment thereof. Particularly, glass and various kinds of surface-treated glass are preferable. The reason is that the water-repellent liquid chemically reacts with the hydroxyl groups on the surface of the substrate to form a strong bond, and the excess water-repellent liquid that does not react is wiped off later, so that a uniform, uniform and transparent water-repellent thin film (hereinafter simply referred to as Water-repellent film)
Is important, and it is preferable to have an active hydroxyl group on the substrate surface. For example, a layer made of SiO ₂ is formed on a substrate in advance, and the Si 2
A water-repellent liquid can be applied on the layer made of O ₂ . In addition, the shape of the base may include not only a flat surface but also a curved surface shape.

The water-repellent liquid in the present invention contains a compound (active ingredient) for forming a water-repellent film. The water-repellent liquid may be composed of only the active ingredient, but contains an organic solvent capable of appropriately dissolving or diluting the active ingredient as needed.

As the active ingredient, a compound containing a perfluorinated group is exemplified. As the perfluorinated group-containing compound, a perfluorinated group-containing silane compound is preferable. Further, in order to chemically bond the perfluorinated group-containing compound to a silanol group (—Si—OH) on the surface of glass or the like, it is necessary to use —Si—OR, —Si—Cl, and —Si—NC.
It preferably has a hydrolyzable reactive group such as O.

Here, the perfluorinated group-containing silane compound is used as the perfluorinated group-containing compound because the silanol group on the surface of the substrate and the hydrolyzable reactive group of the perfluorinated group-containing silane compound are chemically bonded. This is because a siloxane bond (Si-O-Si) can be formed, and durability of water repellency can be exhibited.

As the silane compound having a perfluorinated group in the present invention, one or more compounds selected from chlorosilane, alkoxysilane, and isocyanate silane having a perfluorinated group can be mentioned. The following can be illustrated as the perfluorinated group-containing silane compound. In the following, Rf is a perfluoroalkyl group having 4 to 16 carbon atoms, Me is a methyl group, Et is an ethyl group,
m is an integer of 1 or more, and n is an integer of 4 to 16.

[0016]

## STR1 ## Rf (CH ₂ ) ₂ SiCl ₃ , Rf (CH ₂ )
₂ SiMeCl ₂ , (RfCH ₂ CH ₂ ) ₂ SiCl
₂ , Rf (CH ₂ ) ₂ Si (OMe) ₃ , RfCONH
(CH ₂ ) ₃ Si (OEt) ₃ , RfCONH (CH
₂ ) ₂ NH (CH ₂ ) ₃ Si (OEt) ₃ , RfSO ₂
NMe (CH ₂ ) ₂ CONH (CH ₂ ) ₃ Si (OE
t) ₃ , Rf (CH ₂ ) ₂ OCO (CH ₂ ) ₂ S (CH
₂ ) ₃ Si (OMe) ₃ , Rf (CH ₂ ) ₂ OCONH
(CH ₂ ) ₃ Si (OEt) ₃ , Rf (CH ₂ ) ₂ NH
(CH ₂ ) ₂ Si (OMe) ₃ , Rf (CH ₂ ) ₂ NH
(CH ₂ ) ₂ Si (OCH ₂ CH ₂ OMe) ₃ , CF _{3
CF 2 CF 2 O [CF (} CF 3) CF 2 O] m --CF
(CF ₃ ) CONH (CH ₂ ) ₃ Si (OMe) ₃ , R
f (CH ₂ ) ₂ Si (NCO) ₃ , Cl ₃ Si (CH
₂ ) ₂ (CF ₂ ) _n (CH ₂ ) ₂ SiCl ₃ , Cl ₂ M
eSi (CH ₂ ) ₂ (CF ₂ ) _n (CH ₂ ) ₂ SiMe
Cl ₂ , (MeO) ₃ Si (CH ₂ ) ₂ (CF ₂ ) _n
(CH ₂ ) ₂ Si (OMe) ₃ , (MeO) ₂ MeSi
(CH ₂ ) ₂ (CF ₂ ) _n (CH ₂ ) ₂ --SiMe
(OMe) ₂ , (OCN) ₃ Si (CH ₂ ) ₂ (CF
₂ ) _n (CH ₂ ) ₂ Si (NCO) ₃ , (OCN) ₂ M
_{eSi (CH 2) 2 (CF} 2) n (CH 2) 2 --Si
Me (NCO) ₂ .

As the silane compound having a perfluorinated group, a condensate obtained by hydrolyzing these compounds or a silane compound having a perfluoroalkyl group having an ether bond may be used. Further, two or more of the above-described perfluorinated group-containing silane compounds may be appropriately selected and used as a co-condensate. Further, another silane compound may be added to the above-described perfluorinated group-containing silane compound and used as a mixture.

Particularly preferred is a cold-curable Rf
(CH ₂ ) ₂ SiCl ₃ , Rf (CH ₂ ) ₂ Si (NC
O) ₃ and the like. Alkoxysilanes form a strong siloxane bond by dehydration condensation upon heating, but chlorosilanes and isocyanatesilanes can be firmly bonded to hydroxyl groups on the surface of glass and the like at room temperature, requiring no heating process, easy handling, and industrial use This is because it is suitable for

The concentration of the active ingredient in the water-repellent liquid is determined in consideration of workability and stability in forming the water-repellent film, the thickness of the water-repellent film, and economy. In particular, the content is preferably 0.2 to 12% by weight based on the total weight of the water-repellent liquid in terms of the solid content of the active ingredient. If the amount is less than 0.2% by weight, sufficient water repellency cannot be obtained. If the amount exceeds 12% by weight, more water repellent remains on the surface of the substrate than necessary and a long time is required for subsequent wiping, and the amount of water repellent to be wiped off And is industrially useless.

In the present invention, the organic solvent contained in the water-repellent liquid includes acetates, aromatic hydrocarbons,
Examples include halogenated hydrocarbons, ketones, and ethers. However, as an active ingredient, Rf (CH ₂ ) ₂ S
When a compound having an isocyanate group such as i (NCO) ₃ is used, an organic solvent having a reactive functional group (such as a hydroxyl group) is not desirable because it reacts with the isocyanate group. In addition, isopropyl alcohol (IPA)
Organic solvents having functional groups with low reactivity, such as, for example, can be used. The organic solvent is not limited to one type, and two or more types can be used as a mixture.

When a hydrocarbon-based solvent is used, cissing may occur immediately after the application of the water-repellent liquid. This is due to the fact that a fluorine compound (active ingredient) reacts on the surface of the substrate to form a water-repellent film, but not yet. This occurs because the water-repellent liquid that has not dried is repelled. In this case, the concentration of the water-repellent liquid and the evaporation rate of the solvent are adjusted so that the thickness of the water-repellent film at the repelled portion is equal to or larger than a monomolecular film. In this case, it is preferable that the thickness unevenness caused by the repelling is 3 μm or less.

From such a viewpoint, R as an active ingredient
When f (CH ₂ ) ₂ Si (NCO) ₃ is used, an organic solvent is preferably an acetate-based solvent, specifically, butyl acetate or ethyl acetate. When a fluorine-based solvent is used, repelling during coating is eliminated by adjusting the evaporation rate, and a smooth dry water-repellent film can be formed.

The film thickness when the water-repellent liquid is applied is 1 at the thinnest part.
The thickness is preferably not less than μm and not more than 10 μm in the thick portion. Further, it is preferable that the coating can be uniformly performed at about 3 μm on the entire surface of the substrate to be coated. If it is less than 1 μm, sufficient water repellency cannot be obtained, and if it exceeds 10 μm, the time required for wiping becomes long. If a thickness unevenness of 3 μm or more exists on the surface of the substrate to be coated, unevenness occurs in subsequent wiping, and uniform wiping in the surface becomes difficult.

As a means for applying the water repellent liquid, various conventional methods such as dip coating, spin coating,
Spray coat, curtain (flow) coat, die head coat, blade coat, wipe coat, squeegee coat and the like can be mentioned. The squeegee coating method allows a small amount of liquid to be applied to a large-area substrate, and can be easily applied in a short time without masking to only one side of a substrate having a curved surface. It is particularly preferable because it can be continuously supplied to the substrate without deterioration, and even if the water-repellent liquid is expensive, it can be processed at a necessary minimum amount and at low cost.

In order to secure the thickness of the applied water-repellent liquid, it is preferable to use an elastic body, particularly a plate-like elastic body. That is, in the coating step, it is preferable that after the water-repellent liquid is dropped on the surface of the substrate, it is spread over the surface of the substrate by an elastic body. As the material of the elastic body, rubber, foam, cloth, or the like can be used, and foam is preferable because it absorbs the water-repellent liquid to some extent and easily spreads the liquid uniformly. Specifically, a sponge squeegee is suitable. If a foam such as a sponge squeegee is used, it can follow even if the substrate surface on which the coating is performed has a curvature with a radius of curvature of 1000 mm or less. Further, when the radius of curvature is small, the squeegee itself may have a curvature.

The foam is preferably resistant to the water-repellent liquid, has open cells (in which case the liquid is well absorbed), and is preferably smooth. The material is preferably polyurethane or polyethylene. When butyl acetate is used as the solvent, it is preferable to use polyethylene.

Even a sponge of closed cells can be applied without trouble by making a slit and / or a hole at the tip to make it easy to absorb the water-repellent liquid. As a specific example, as shown in FIG. 5, several slits (cuts) 6 of 1 to 15 mm are inserted in the height direction from the lower surface of the squeegee, or in the thickness direction (application direction) below the squeegee. Hole 7 of about 0.1 to 1 mm (preferably through hole)
By opening the sponge, the sponge can absorb the liquid by capillary action. The slit 6 is preferably inserted in a direction parallel to the length direction (a direction perpendicular to the application direction). The hole 7 is about 3 to 5 mm below the squeegee,
Preferably, they are arranged in a staggered manner parallel to each other. The number, size, and design of the slits 6 and the holes 7 are not particularly limited as long as thickness unevenness does not occur after application.

The reaction between the water-repellent liquid after application of the liquid-repellent liquid and the substrate surface is usually carried out by drying. Drying time is 1 minute to 75
Time is preferred. If it is less than 1 minute, the evaporating and drying of the diluting solvent is not sufficient, and the binding reaction of the water repellent liquid to the substrate cannot be sufficiently obtained.
If the time exceeds 75 hours, the reaction of the water-repellent liquid proceeds too much, and subsequent wiping is not easy. In particular, when a room temperature curing type water-repellent liquid is used, it is preferably 1 to 25 hours.

The drying temperature after application of the water-repellent liquid is from room temperature to 300
C is preferred. When the temperature is lower than room temperature, the binding reaction to the substrate does not proceed and the reaction requires a long time. When the temperature is higher than 300 ° C., the water-repellent liquid is gradually decomposed, and the water-repellency is reduced. In particular, when a room-temperature-curable water-repellent liquid is used, the temperature is preferably from room temperature to 200 ° C.

The surplus is removed (wiped) until the color unevenness disappears and the original transparency of the substrate such as glass can be exhibited. In order to exhibit water repellency, theoretically, the film thickness may be a monomolecular layer or more. Also, the durability of the water-repellent film,
Considering the economic effect, the thickness is preferably 2 μm or less. For example, when a heat-curable water-repellent liquid is used, the film thickness after wiping the water-repellent liquid is preferably 5 to 60 nm, and when a room-temperature-curable water-repellent liquid is used, the film thickness is preferably 5 to 60 nm.

As a method of removing (wiping off) the surplus,
It is preferable to use powders of paper, cloth (such as ash and towel), porous silica fine particles, foamed polyethylene, starch, and cellulose. In particular, it is preferable to remove the excess of the water-repellent liquid by spraying a powder capable of adsorbing the excess of the water-repellent liquid on the surface to which the liquid-repellent liquid is applied, and then removing the powder. The size of the powder is not particularly limited, for example,
A material having a particle size of about several tens μm is used. Also, the shape of the powder is not particularly limited. It is preferable to remove the powder with a brush, cloth, or the like.

Even if the water-repellent liquid is wiped off only with a brush such as PVC (vinyl chloride resin), the excess water-repellent liquid is merely kneaded on the substrate and is not wiped off. on the other hand,
If the brush is wiped off through the powder that itself has adsorptive properties, the water-repellent liquid will be absorbed by the adsorptive powder and removed, and the brush will not be contaminated with the water-repellent liquid. By supplying water, a large amount of surplus water-repellent liquid can be continuously removed. In particular, the use of powder containing starch and / or cellulose provides high wiping efficiency, is safe,
This is preferable because the cost is low.

[0033] The material of the brush is not particularly limited, but PVC is preferred from the viewpoint of difficulty in generating static electricity and physical strength. The thickness of the brush bristles is preferably from 0.1 to 0.5 mm, most preferably about 0.2 mm. If it is less than 0.1 mm, the physical force for removing powder is weak, and if it is more than 0.5 mm, it is not too hard. The length of the brush hair is 2
It is preferably from 0 to 50 mm, especially about 40 mm. 20mm
If it is less than 50 mm, the followability will be poor, and if it exceeds 50 mm, the powder will be dispersed.

As another surplus removal (wiping) method, a method of dissolving and removing the surplus water-repellent liquid with a solvent capable of dissolving the surplus water-repellent liquid is also preferable. The reason is,
Dissolving only the unreacted water-repellent liquid and wiping it chemically is because, in some cases, it is easier to finish with a smooth, uniform and high surface fluorine concentration than in the case of mechanical wiping. Specifically, the surplus of the water-repellent liquid is touched (rubbed) with a surface coated with a solvent capable of dissolving a surplus of the water-repellent liquid, and the surplus is dissipated to paper, cloth, foam, etc. Dissolve in and absorb. According to this removing (wiping) method, there is no scattering of powder and the like, and the cost is low.

Examples of such solvents include aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, alcohols, ketones, esters, alcohol esters, ketone esters, ethers, ketone alcohols, ether alcohols. , Ketone ethers, ester ethers, and fluorocarbons. Particularly, lower alcohols are preferred. Furthermore, IPA is preferred from the viewpoints of solubility in a water-repellent liquid, drying speed at wiping, and safety and cost.

[0036]

【Example】

[Example 1] A water-repellent film was formed on a front door glass having a curvature radius of 1000 mm in the height direction as follows. In perfluoro (2-n-butyltetrahydrofuran) (boiling point 100 ° C., specific gravity 1.77), fluoroalkylsilyl isocyanate (C ₈
F ₁₇ C ₂ H ₄ Si (NCO) ₃ ) was dropped onto a glass surface after dropping a water-repellent liquid containing 4% by weight (in terms of the solid content concentration of the active ingredient) on the glass surface.
Using a foamed polyurethane plate-like sponge squeegee, it was run by pushing the sponge into the glass surface.

FIG. 1 is a side view showing a state of a squeegee when a water-repellent liquid is applied. Reference numeral 1 denotes a squeegee, 2 denotes a holder, 3 denotes a water-repellent liquid, and 4 denotes a substrate (glass). FIG. 2 is a plan view showing a locus of a squeegee in a coating process. The length of the squeegee is 300 mm.
The vehicle was run by overlapping 0 to 20 mm. If a pool of the water-repellent liquid (ink) was conspicuous at the overlapping portion (boundary portion), the ink pool was reduced by running the apparatus again without discharging ink.

In this example, as shown in FIG. 2, the water-repellent liquid was spread over the entire glass by coating four times. The supply of the water-repellent liquid was performed by a nozzle located in front of the squeegee. Except within 10mm each side of squeegee, between 0.5 ~ 5c
In c, control was performed so as not to protrude from the squeegee.

In the water-repellent liquid application using the sponge squeegee, the amount of the ink was minimized and the amount of the liquid was controlled so that the liquid did not protrude from the squeegee (pool of ink). The coating liquid of the water-repellent liquid could be spread over the entire glass.

After applying as described above and drying at 25 ° C. for 60 minutes, as a surplus removal step, starch powder (particle size: several tens nm) is sprayed on the surface to which the water-repellent liquid has been applied. , 20
0mmφ rotating brush (made of PVC, hair length 40mm,
This powder was removed by a hair thickness of 0.2 mm). If the rotation speed is too high, the powder in the brush advancing direction is scattered around and the finishing ability is reduced.
0 rpm or less and 50 to 2 depending on the degree of wiping.
It was rotated at about 00 rpm. Tilt the brush about 5 to 10 degrees to the direction of travel so that the powder is guided to the center of the brush,
It ran on the glass in a state where it was pushed in for 5 to 15 mm.

FIG. 3 is a side view showing the state of the brush in the surplus removing step. Reference numeral 5 denotes a brush. FIG.
FIG. 5 is a plan view showing a locus of a brush in a surplus removing step. As described above, a transparent and uniform water-repellent film was formed. The film thickness was 10 to 30 nm.

The foamed polyurethane plate-like sponge squeegee used in this example absorbs the water-repellent liquid well. Therefore, even if the supply of liquid varies, coating can be performed relatively uniformly, and coating can be performed even at the glass edge portion.

Example 2 n-butyl acetate (boiling point: 126 ° C.,
Specific gravity 0.87), the fluoroalkylsilyl isocyanate (C ₈ F ₁₇ C ₂ H ₄ Si (NC
O) Repellent on the front door glass in the same manner as in Example 1 except that a water-repellent liquid containing 7% by weight of ₃ ) (in terms of the solid content concentration of the active ingredient) was used, and a foamed polyethylene plate-like sponge squeegee was used. The aqueous solution was spread and dried. As a surplus component removing step, instead of the method using the starch powder of Example 1,
By using a towel impregnated with IPA and rubbing several times, the “excess” of the water-repellent liquid was wiped off. In addition, IPA was sprayed on a towel using a mist sprayer to be impregnated. By this soaking method, the IPA uniformly soaked into the towel. The amount of soak is 1-3 c per 30 cm ² of toweling
c. As a result of wiping off the “excess” of the water-repellent liquid, a transparent and uniform water-repellent film was formed. The film thickness is 10-3
It was 0 nm. The workability was also good.

Further, the foamed polyethylene plate-shaped sponge squeegee used in this example has a small water-repellent liquid absorption amount,
As a result, the usage is also reduced. Since the "surplus" is reduced, wiping can be performed in a short time.

[0045]

Conventionally, since the application step and the wiping (finishing) step were performed manually at the same time, skill was required and the amount of water-repellent liquid, the number of times of rubbing, the strength, and the frequency of replacing paper and the like were required. Variations such as were inevitable. In the present invention, since the coating process and the wiping process are separated, and the coating is uniformly performed and the surplus amount is constantly determined, each process can be automated (by a robot), mass-produced by mechanization, and high quality water repellent. A large number of films can be obtained stably. In addition, the quality was stable, and the processing time per sheet was reduced from 5 to 20 minutes by the conventional manual operation to 5 minutes, which was greatly reduced.

[Brief description of the drawings]

FIG. 1 is a side view showing a state of a squeegee when a water-repellent liquid is applied in Example 1.

FIG. 2 is a plan view showing a locus of a squeegee in a coating process of Example 1.

FIG. 3 is a side view showing a state of a brush in a surplus removing step of Example 1.

FIG. 4 is a plan view showing a locus of a brush in a surplus removing step of Example 1.

5A is a perspective view and FIG. 5B is a side view showing an example of a sponge squeegee used in the present invention.

[Explanation of symbols]

 1: Squeegee 2: Holder 3: Water-repellent liquid 4: Base 5: Brush 6: Slit 7: Hole

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C09K 3/18 101 C09K 3/18 101

Claims (5)

[Claims] 1. A method for forming a water-repellent thin film on a surface of a substrate using a coating solution for forming a water-repellent thin film, comprising: a coating step of excessively applying the coating solution for forming a water-repellent thin film to the surface of the substrate; A method for forming a water-repellent thin film, comprising: a step of removing a surplus of the coating liquid for forming a water-repellent thin film. 2. The method for forming a water-repellent thin film according to claim 1, wherein, in the coating step, a coating liquid for forming a water-repellent thin film is dropped on the surface of the substrate and then spread over the surface of the substrate with an elastic body. 3. In the excess removing step, a powder capable of adsorbing an excess of the coating liquid for forming a water-repellent thin film is sprayed on a surface to which the coating liquid for forming a water-repellent thin film is applied, and then the powder is dispersed. 3. The method for forming a water-repellent thin film according to claim 1, wherein the removing removes an excess of the coating liquid for forming a water-repellent thin film. 4. The method for forming a water-repellent thin film according to claim 3, wherein the powder is a powder containing starch and / or cellulose. 5. The method of claim 1, wherein in the step of removing the excess, the excess of the coating liquid for forming a water-repellent thin film is dissolved and removed with a solvent capable of dissolving the excess of the coating liquid for forming a water-repellent thin film.
The method for forming a water-repellent thin film according to the above.