JP2001294779A - Resin covered material having excellent outdoor stain resistance and surface treating method of resin covered material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin covered material having excellent outdoor stain resistance and hydrophilicity in its surface. SOLUTION: A silica coating film containing no binder is formed on the surface of a resin covered material to a maximum dried film thickness of <=3 μm to render the contact angle of the surface to water <=60 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin coating material mainly used outdoors, and more particularly to a resin coating material provided with a hydrophilically-treated coating having excellent hydrophilicity against outdoor contamination on the surface of a substrate, and It relates to the surface treatment method.

[0002]

2. Description of the Related Art Various resin-coated metal plates are used for soundproof walls and guard rails on highways and the like, or for outdoor applications such as building exterior walls, roofing materials, shutters and shutters. In this way, the metal plate installed outdoors has dust,
There has been a problem that the surface is easily stained by the adhesion of exhaust gas, iron powder, and the like, the appearance is impaired, and much effort is required to clean the stain.

[0003] In order to solve such a problem, the contact angle with water on the surface of the resin-coated metal plate is 60 ° or less, preferably 40 ° or less.
Means that impart a hydrophilicity of less than or equal to ° and allow the dirt adhering to the surface to be washed away with rainwater have been effective.

[0004] As a method of preventing this kind of dirt, WO
JP-A-94-6870 discloses an organic paint in which a hydrophilic substance such as an organosilicate or a condensate of an organosilicate is blended, and WO-94-6879 discloses an alkoxysilyl group on a coating film surface. It has been proposed to form and hydrolyze to hydrophilic silanol groups by contact with rainwater or acid treatment to make them hydrophilic.
However, in these methods, there is a problem that the storability of the paint is such that a hydrolysis reaction occurs in the paint about one week after the preparation of the paint, and the storability and workability of the paint are extremely poor. Also, depending on the type of paint, it may not be possible to add it, and even if it can be added, the contact angle with water can be reduced only to about 60 °, and a sufficient pollution control effect cannot be obtained. is there.

Japanese Patent Application Laid-Open No. 10-158585 discloses a method of applying a coating composed of acidic colloidal silica, an amine compound, a coloring pigment (inorganic filler) and water or a hydrophilic organic solvent to, for example, a metal surface and drying the coating. Has been proposed. In the case of the standard colloidal silica having a pH of 9 to 11, which is dissolved in a strongly alkaline amine compound having a pH of 12 or more, an acidic colloidal silica is added. It is a method of forming a coating film. The coating obtained by this method is as thick as 2 to 200 μm,
Moreover, since it contains a large amount of the inorganic filler as 10 to 80 parts by weight, there is a problem in processability and durability of the processed portion,
There is a problem that it is not suitable for use in precoating, in which a coating is previously provided on the surface of a metal plate.

Further, Japanese Patent Application Laid-Open No. HEI 8-80474 discloses a method of forming a clear coating mainly composed of polyvinyl alcohol resin and colloidal silica to a thickness of 3 μm or less on the outermost layer of a coated metal plate as a base material. Has been proposed. According to this method, the period during which the problem of contamination occurs during outdoor use is about one year from the beginning of use, in which the surface of the coated metal plate shows hydrophobicity, and thereafter the surface is gradually hydrophilized. This is a technique aimed at preventing only contamination in the early stage of use. However, in practice, the resin deteriorates after several years, causing chalking or yellowing, and the color tone of the base material is significantly changed.

[0007] WO-96-29375 proposes a method of applying a dispersion of a photocatalytic semiconductor material such as titanium oxide to the surface of a substrate. In this method, when a titanium oxide is exposed to sunlight, an oxygen atom in the titanium oxide reacts with water to form a hydroxyl group (−).
Although OH) exhibits hydrophilicity, an antifouling effect is brought about, but the effect is reduced by half in the shade in winter when the sunlight dose is small. When the base material surface is covered with a resin, it is necessary to provide an inorganic protective layer such as silicone between the photocatalyst layer and the titanium oxide so that the resin is not decomposed by the strong photocatalytic function of the titanium oxide. There is a disadvantage that the original color tone of the base material is changed.

[0008]

Accordingly, the present invention provides a resin-coated material represented by a resin-coated metal plate having a hydrophilic surface without the above-mentioned problems of the prior art.
It is an object of the present invention to provide an advantageous surface treatment method.

[0009]

Means for Solving the Problems The inventors of the present invention paid attention to contaminants adhering to a coated metal plate actually used outdoors, and examined the contaminants. It was found that SiO ₂ ) was mainly used, and that the surface to which the contaminants had adhered was hydrophilized and the progress of the stain was slow as a result of comparison with the surface state at the beginning of use without the stain. Therefore, if the above-mentioned organosilica or colloidal silica is adhered to the surface in some form, the surface may show hydrophilicity and exhibit an antifouling effect, but these silicas have no adhesiveness to the resin. For this reason, the method is generally applied to the surface of a base material via a so-called binder such as a resin, so that the above-described problem has been encountered. Also, JP-A-10-15858
No. 5 stipulates that coatings formed of acidic colloidal silica alone do not work on organic base materials such as ceramic base materials, inorganic base materials, wood, paper, and fibers. However, the inventors have continued their research without being bound by such established concepts, and as a result, have found that there is a method capable of forming a silica coating without using a resin binder on the surface, and have completed the present invention. Was.

That is, the gist of the present invention is as follows. (1) A silica coating not containing a binder is formed on the surface of the substrate at a maximum dry coating thickness of 3 μm or less, and the silica coating has a surface-to-water contact angle of less than 60 °. Resin coating material with excellent outdoor pollution resistance. (2) A silica coating containing no binder is formed on the surface of the substrate in a non-uniform manner so as to have a coverage of 5% to 95%, and the silica coating has a surface-to-water contact angle of 6%.
A resin coating material having excellent outdoor pollution resistance characterized by being less than 0 °. (3) A silica film containing no binder is coated on the surface of the substrate with a maximum dry coating thickness of 3 μm or less and a coverage of 5% or more and 9% or less.
A resin coating material having excellent outdoor pollution resistance, characterized in that the silica coating film is formed so as to have a surface-to-water contact angle of 60 ° or less. (4) A surface treatment of a resin coating material characterized by thinly applying an acidic colloidal silica sol having a pH of less than 6 to the surface of a substrate and then drying it to obtain the resin coating material described in (1) to (3) above. Method.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a resin coating material of the present invention provided with a coating having excellent resistance to outdoor pollution will be described in detail with reference to the drawings. First, FIG. 1 shows an electron micrograph of a fluorine-coated steel sheet to which the present invention is applied, and FIG. 2 shows a schematic structure of the surface thereof. The resin coating material having excellent resistance to outdoor contamination includes a silica coating 2 made of simple silica containing no binder such as resin on a surface of a base material, for example, a resin-coated metal plate (hereinafter, simply referred to as “metal plate”) 1.
Are scattered like islands, that is, formed unevenly.

Here, the metal plate 1 is provided on the surface of a metal plate used as a material for an outdoor building such as a soundproof wall, a guardrail, an outer wall material of a building, a roofing material, a shutter, a shutter or the like on a highway. A resin coating layer is formed by applying a resin or laminating a resin film, and the types of the metal plate and the resin are not particularly limited. For example, suitable metal sheets include hot-dip galvanized steel sheet, hot-dip 5% aluminum-galvanized steel sheet (Galfan), hot-dip galvanized steel sheet 5%
Examples of the coating resin such as an aluminum-galvanized steel sheet (galvalume) or a stainless steel sheet include fluorine resin, polyester resin, vinyl chloride resin, urethane resin and the like. The substrate used in the present invention,
In addition to the metal plate 1, a resin-coated ceramic, which will be described later, may be used, but a metal plate will be described below as a typical example.

The silica coating 2 is formed on the surface of the metal plate 1 which is a resin-coated base material without any binder.
Maximum dry coating thickness 3 μm or less, preferably 0.1 to 2 μm
It is important that the film is formed sparsely, that is, unevenly so that the surface coverage (area ratio) is 5% or more and 95% or less. In addition, the coating film 2 of silica alone containing no binder has a pH of 6
An acidic colloidal silica sol having a pH of less than 2, preferably 2 or more and 5 or less, is thinly applied to the surface of the metal plate 1 and dried by a hot air drier or the like. The range of the surface coverage is
This is one of the conditions necessary for firmly attaching the acidic colloidal silica sol to the surface of the metal plate 1.

In general, a colloidal solution of pure silicic anhydride shows acidity, but has a low stability. Therefore, it is common to add a sodium salt or an ammonium salt to adjust the pH to a weak alkalinity of 9 to 11 before use. is there. FIG. 3 shows the relationship between the pH and the stability of the colloidal silica sol. However, a coating using such a weakly alkaline colloidal silica sol, for example, a silica coating 2 coated on the surface of a metal plate 1 becomes in a dusty state after drying, and easily touches with a fingertip. Not only does it peel off, it cannot be strongly adhered to the metal plate 1, but it is easily washed off when exposed to rain and wind outdoors.

On the other hand, in the case of a coating using an acidic colloidal silica sol, according to the findings of the present inventors, the silica coating 2 is formed on the surface of the metal plate 1 with a maximum dry coating thickness of 3 μm or less. Is 0.1 to 2 μm or less, and / or has a surface coverage of 5% to 95%, preferably 10% to 70%, and more preferably 40 to 7%.
If you coat it mottled (unequally) so that it is 0%,
It has been found that this silica coating can be firmly attached to the surface of the metal plate 1.

In the present invention, in order to form a silica coating 2 having a maximum dry coating thickness of 3 μm or less on the surface of a base material such as a metal plate 1, a very thin sol water film in a wet state is required.
It is necessary to apply to the surface. This coating film
It changes to strongly acidic with the evaporation of water during drying, and rapidly gels on the surface of the metal plate 1.
Is considered to adhere firmly to the surface of the metal plate 1.
In particular, since a thin sol water film is applied, it is affected by trace amounts of acidic substances, negative charges, terminal groups, anions, etc. on the surface, which promotes gelation during drying and improves the adhesion of the film It is considered to be one of the causes.

Here, the maximum dry film thickness is determined, for example, by embedding a metal plate 1 in a room temperature dry-type embedding resin, cutting the metal plate 1 in the plate thickness direction, and measuring the thickness of the silica coating 2 on the cut surface with an optical microscope. Obtained by

As described above, when the maximum dry film thickness exceeds 3 μm, the coating 2 is not firmly adhered as described above. However, when the film thickness exceeds 3 μm, further depending on the type of the metal plate 1, There are also disadvantages that the color tone changes and the film is easily peeled off by processing. The silica coating 2 having a maximum dry film thickness of 0.1 μm or more is advantageous for exhibiting good resistance to outdoor contamination, and the silica coating 2 having a maximum dry film thickness of about 2 μm or less has a color tone of the base material. This is advantageous in suppressing the change in the thickness and ensuring the workability of the silica coating.

Setting the surface coverage of the silica coating 2 to 5% or more and 95% or less means that the coating covers the surface of the metal plate 1 in a non-uniform state so that the coating exhibits a mottled pattern. ing. That is, since the gel film of colloidal silica has a property that it is difficult to form a continuous film, it is inevitably a thick film to form a continuous and uniform film, and as a result, from the surface of the metal plate 1 It is easy to peel off. The reason for this is not clear, but is presumed to be that the thicker the film, the thicker the film in the wet state, and the above-mentioned gelation does not sufficiently occur.

Here, the surface coverage can be determined by, for example, observing or elemental analysis with a scanning electron microscope, and calculating the average coverage per visual field or analysis surface by image processing or mapping. The reason for limiting the coverage is as described above. However, the lower the coverage, the more advantageous the change in color tone of the metal plate 1 is. However, if the coverage is less than 5%, the effect of resistance to outdoor pollution will not be sufficiently exhibited, while if it exceeds 95%, a part of the coating tends to be missing, which is not preferable. Therefore, in applications where processing is severe, the coating itself may cause cohesive failure and may be partially missing.

Even if the surface of the metal plate is not completely covered with the silica coating 2, that is, even if the surface coverage is not 100%, the reason why good outdoor contamination resistance is exhibited is that the metal plate surface has This is because the diameter of the formed raindrop is usually 5 mm or more, and if this size is such a size, a capillary phenomenon acts between the silica coating showing hydrophilicity and the resin part showing hydrophobicity.

As described above, it is important that the silica coating 2 formed on the surface of the metal plate 1 satisfies a maximum dry coating thickness of 3 μm or less and a surface coverage of 5% to 95%. In the case of, the silica coating 2 has a maximum dry coating thickness of 3
It is known that when the thickness is set to be equal to or less than μm, the surface coverage becomes about 95% under the above-described film forming characteristics. However, it is a preferred embodiment to control both the film thickness and the surface coverage toward the target in order to obtain the desired effect.

Incidentally, FIG. 1 shows a metal plate having a surface coverage of about 40% by computer image analysis, a maximum thickness of about 1 μm by cross-sectional observation, and a coating 2 of silica alone formed on the surface of the metal plate. As shown in the photomicrograph, relatively large cracks are observed in the coating 2 in FIG. This is because water contained in the silica coating 2 was rapidly evaporated by irradiation with an electron beam under a vacuum in an electron microscope, and the silica coating 2 formed according to the present invention has There is no such a large crack, and even if such a crack occurs, its film adhesion is good.

In the present invention, the silica coating 2 formed on the surface of the metal plate has a large number of hydroxyl groups as compared with the surface characteristics of the resin coating, and therefore shows hydrophilicity. Therefore, the surface to water contact angle needs to be 60 ° or less, and preferably 40 ° or less. The reason is that, when water (rainfall) adheres to the resin-coated metal plate with dirt, the thinner the water film is formed on the resin surface, the higher the hydrophilicity of the resin surface, and the dirt is deposited on the water film. It is easily taken in and washed away. On the other hand, it is considered that a water film is not easily formed on the hydrophobic surface, and dirt is likely to be left on the surface even when it is rained. Whether it is hydrophilic or hydrophobic can be evaluated by the surface-to-water contact angle. According to the study by the inventors, if the contact angle exceeds 60 °, the antifouling function due to hydrophilicity is recognized but insufficient, and the contact angle is 60 °.
° or less is preferable, and it is still more effective if it is 40 ° or less. In addition, such a surface-water contact angle (≦ 60 °)
In order to obtain a silica coating having the following properties, acidic colloidal silica having a pH of less than 6 is used, and the maximum dry coating thickness is 3 μm or less, or the surface coverage is 5% to 95%.
A method of applying a thin film and drying it is effective.

Next, a specific method for imparting excellent outdoor contamination resistance to the surface of a metal plate will be described in detail. The process according to the invention is preferably carried out at a pH below 6, preferably at pH 2
Basically, the acidic colloidal silica sol of No. 5 is thinly applied to the surface of a metal plate and dried. The application of the acidic colloidal silica sol to the metal plate surface is performed by mist spray,
Spraying and ringer, dipping and ringer or roll coating can be used. For example, in a continuous coating facility, the coating device may be installed after the top coat baking process, preferably after the shape correction leveler process, and after the coil winding process.

The reason why the pH adjustment of the colloidal silica sol is effective is that when the pH exceeds 6 and becomes weakly alkaline,
A film cannot be formed because it gels in a solution. Therefore, in the present invention, it is important to use a colloidal silica sol whose pH is adjusted to less than 6. For example, a general weakly alkaline colloidal silica sol having a pH of about 9 is not preferable because it changes to strongly alkaline with evaporation of water during drying. Further, as shown in FIG. 3, the colloidal silica sol is extremely stable and does not gel in the pH range of 8 to 11, and shows solubility when the pH exceeds 11, so that the colloidal silica sol is stable even when applied to the surface of the metal plate. Drying while dissolving, no gelled film can be formed.

Here, it is also possible to form the film by acidifying the resin surface in advance by, for example, applying an acidic solution, applying a weak alkali colloidal silica sol thinly, and gelling the resin surface when drying. However, it is difficult to adjust the amount and concentration of an acid to obtain a silica coating film having good adhesion, so that it is not a preferable method. Also, this problem is to neutralize the acidic colloidal silica sol on the metal plate surface,
The same applies to the case of gelation.

In particular, in order to reduce the maximum dry film thickness of the silica film to 3 μm or less, for example, in the case of treatment by spraying and Ringer's method, the squeezing pressure of the ringer is adjusted to reduce the wet film thickness of the acidic colloidal silica sol. About 25
g / m ² (about 20 μm) or less and obtained by drying.

Similarly, to make the surface coverage of the silica coating 5% or more and 95% or less, the wet film thickness is about 25 g / m 2.
It is preferred that the drying be performed at a thickness of ² (about 20 μm) or less.
Then, the surface coverage of the silica coating can be made 5% to 95%.

Next, an acidic colloidal silica sol having a pH of less than 6 is applied thinly on the surface of the metal plate and dried to form a silica coating. The adhesion amount of the silica coating varies depending on the surface condition of the metal plate such as the surface roughness, but can be easily adjusted by changing the application conditions such as the concentration of the processing solution and the ringer squeezing pressure in the above-mentioned application method. In this drying, it is only necessary to remove water,
It is sufficient to leave the material to dry naturally, but in the case of industrial continuous production, it is possible to perform sufficient drying by exposing it to warm air at about 80 ° C. for about 5 seconds. Further, in order to promote gelation, the warm air may be charged with a negative charge.

Further, alcohol such as methanol is added to the acidic colloidal silica sol to speed up drying, and a nonionic surfactant or a water-soluble emulsion resin is added to improve the processability of the metal plate. Alternatively, a small amount of an organic coloring pigment may be added for adjusting the color tone.

In the case where these are added, since the silica particles have a negative charge, non-ionic or anionic ones or those which are stable under acidic conditions and do not disturb the charge balance can be used. Lithium silicate, a silane derivative, a silane coupling agent, colloidal alumina, and the like can be added without being used as an additive.

Since the present invention forms a silica coating on the resin surface of a metal plate, it can also be applied to a painted ceramic molded article such as a ceramic tile used for an outer wall of a general house. In addition, since the unit price of colloidal silica sol is low, and the present invention has a small burden on the processing equipment,
It can exhibit excellent performance at low cost.

[0034]

Inventive Example 1 A fluororesin film-laminated metal plate (1.6 mm thick, color white) in which a vinylidene fluoride resin film of 40 μm thickness used as an outer wall material of a highway is laminated via an adhesive. in the final manufacturing process of), acidic colloidal silica sol (manufactured by Nissan Chemical Industries, Snowtex -O, pH 3, the SiO ₂ content 20 mass%) was added dropwise to the fluorine resin film surface by the mist spray, the linear pressure of a pair of acid-resistant rubber roll It was squeezed at 5 kg / cm and dried with warm air at 80 ° C. for 5 seconds to obtain a fluororesin film-laminated metal plate having excellent outdoor stain resistance.

Inventive Example 2 A color metal plate (plate thickness 0.35 mm, color light gray) on which a 20 μm-thick polyester top coat, which is used as a general housing metal-based siding material, is painted and baked, P of acidic colloidal silica sol
Except that H was set to 4, the same treatment as in Inventive Example 1 was performed to obtain a color metal plate having excellent outdoor stain resistance.

Inventive Example 3 A nonionic surfactant (Surflon S-132 manufactured by Asahi Glass Co., Ltd.) was added to the acidic colloidal silica sol used in Inventive Example 1 in an amount of 0.1%.
The same treatment as in Inventive Example 1 was performed except that the solution having a pH of 4 to which 1 part by weight was added was roll-coated according to a two-roll reverse method, to obtain a fluororesin film-laminated metal plate having excellent outdoor stain resistance.

Comparative Example 1 The same treatment as that of Inventive Example 1 was carried out except that colloidal silica used was a generally weakly alkaline one (Nissan Chemical Industries, Snowtex Soo 20, pH 10, SiO ₂ content 20 mass%). . Comparative Example 2 The same treatment as that of Inventive Example 2 was performed except that the weakly alkaline colloidal silica used in Comparative Example 1 was used. Comparative Example 3 The same treatment as in Inventive Example 1 was performed except that the acidic colloidal silica sol used in Inventive Example 1 was adjusted to pH 6 with an alkaline 1 / 10N aqueous sodium hydroxide solution. Comparative Example 4 The fluororesin film-laminated metal plate used in Invention Example 1 was used as a comparative example. Comparative Example 5 The color metal plate used in Inventive Example 2 was directly used for comparison. Comparative Example 6 Same as Invention Example 3 except that the maximum dry film thickness was 5 μm.

With respect to each of the above-mentioned invention examples and comparative examples, the results obtained by measuring the obtained coating and conducting various tests were as follows.
It is shown in Table 1. Here, the maximum dry film thickness was obtained by embedding each metal plate after the treatment in a room temperature dry-type embedding resin, cutting it in the thickness direction, and calculating the maximum thickness of the silica coating on the cut surface from an optical microscope photograph. The measurement limit of this method was about 1 μm, and it was not possible to measure Comparative Examples 1 to 3 where the silica coating did not adhere.

The surface coverage was determined by observing any five places on the surface of each metal plate after treatment with a scanning electron microscope at a magnification of 100, and calculating the coverage per visual field by image processing.
The average was calculated in 5% units. In addition, Comparative Examples 1 to 3 described the measurement results of the silica coating that was not adhered but was present on the surface.

The colorability was determined by measuring the color difference (ΔE) before and after the treatment at any five points on the surface of each metal plate after the treatment with a color difference meter. Although the determination is affected by the base color, ΔE is 1 or less, indicating that the coloring is small and good.

The adhesion is determined by adding Si to the surface of each metal plate after the treatment.
The adhesive tape containing no is pressure-bonded and then peeled off, and the adhesive surface is analyzed by fluorescent X-ray. If no Si is detected (no peeling of the silica coating), the evaluation is evaluated as ○. .

The contact angle was determined by forming a water droplet on the surface of each metal plate after treatment at 25 ° C. with approximately 0.05 cc of pure water, and measuring the contact angle of the water droplet with a contact angle measuring device. The measurement was performed at five places, and the average value was rounded in units of 5 degrees in consideration of errors. It is said that when the contact angle is 60 degrees or less, preferably 40 degrees or less, the stain resistance in actual outdoor use is good.

In the outdoor exposure test, each of the treated metal sheets was turned northward at a point 20 m away from a high-traffic national road in the Chiba Works of Kawa Iron and Steel Co., Ltd. in the industrial area of Chiba City, Chiba Prefecture. After arranging at an inclination angle of 60 ° and exposing for 1 year, the degree of contamination at 3, 6, and 12 months was compared with that before exposure (ΔL; lightness index). The measurement was performed at five places on the surface of the metal plate, and the average value was rounded in integer units in consideration of errors. The judgment is influenced by the base color, but if ΔL is 3 or less compared with the visual evaluation, it is judged that the stain resistance is good.

[0044]

[Table 1]

[0045]

The metal sheet of the present invention having excellent resistance to outdoor contamination is characterized by exhibiting excellent resistance to outdoor contamination by forming a silica gel coating on the surface of the metal plate using an acidic colloidal silica sol. In addition, it is possible to impart low resistance to outdoor contamination to various resin coating materials at low cost.

[Brief description of the drawings]

FIG. 1 is an electron microscope photograph of a fluorine-coated steel sheet according to the present invention.

FIG. 2 is a schematic view of a surface structure of the fluorine-coated steel sheet shown in FIG.

FIG. 3 is a diagram showing a relationship between pH and stability of a colloidal silica sol.

[Explanation of symbols]

 1 metal plate 2 silica coating

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D075 CA34 CA37 DB01 DB11 DC03 DC05 EA12 EC03 4H020 AA01 AB02 4J038 AA011 HA441 MA14 NA05 NA06

Claims (4)

[Claims] 1. A silica coating containing no binder is formed on the surface of a substrate to a maximum dry coating thickness of 3 μm or less, and the silica coating has a surface to water contact angle of less than 60 °. Characterized resin coating material with excellent outdoor pollution resistance. 2. A binder-free silica coating is formed on the surface of a substrate so as to have a surface coverage of 5% or more and 95% or less, and the silica coating has a surface-to-water contact. A resin covering material having an angle of less than 60 ° and excellent in outdoor stain resistance. 3. A silica coating containing no binder is formed on the surface of the base material such that the maximum dry coating thickness is 3 μm or less and the surface coverage is 5% or more and 95% or less. And the silica coating has a surface to water contact angle of 60.
° or less, a resin coating material having excellent outdoor pollution resistance. 4. The method according to claim 1, wherein an acidic colloidal silica sol having a pH of less than 6 is thinly applied to the surface of the substrate and then dried.
A surface treatment method for a resin coating material, wherein the method is a resin coating material according to any one of claims 1 to 3.