JPH0228237A - Curable fluororesin coating compound - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a curable fluororesin paint, and more specifically, a paint containing glass fibers in the paint component and producing a semi-gloss or matte paint film. The present invention relates to room temperature curable or thermosetting fluororesin paints.

[Conventional technology]

Fluororesin paints have traditionally been widely used in architectural applications due to their characteristics such as high weather resistance against outdoor exposure, as well as excellent stain resistance and chemical resistance. The most commonly used paints are paints whose main component is fluoroolefin thermoplastic resins (hereinafter referred to as thermoplastic fluororesins) such as vinyl fluoride resin and vinylidene fluoride resin. Since this type of paint requires baking at a temperature higher than the melting point of the thermoplastic fluororesin after painting, it could not be widely used as an architectural paint.

In order to solve these problems, Japanese Patent Application Laid-Open No. 57-341
No. 07, JP-A No. 59-102962, JP-A No. 62-174213, and other publications describe paints containing a thermosetting fluororesin in which a functional group is introduced into the fluororesin. By using a paint that combines a thermosetting fluororesin and an appropriate curing agent.

It is now possible to obtain a cured coating film at room temperature or at a relatively low baking temperature of up to 200°C, and it has become possible to apply coatings to objects for which high-temperature baking processes were not possible. .

[Problems to be Solved by the Invention] Thermosetting fluororesins are manufactured by copolymerizing fluorine-containing vinyl monomers, vinyl monomers having reactive groups such as hydroxyl groups, and other general-purpose vinyl monomers. It has lower crystallinity than fluororesin, and therefore the transparency and gloss of the thermosetting fluororesin coating tend to be higher. Therefore, thermosetting fluororesin is suitable when a high gloss coating is required, but on the other hand, it has a semi-glossy or matte gloss (60
It was difficult to obtain a coating film with a specular gloss of 50% or less.

To reduce the gloss of the paint film - for boat fishing.

For example, a method is known in which gloss modifiers such as finely divided silicic anhydride and finely divided polytetrafluoroethylene are dispersed in paints, but when this method is adopted for thermosetting fluororesin paints, weather resistance and There was a problem that chemical resistance and flexibility were significantly impaired.

The problem to be solved by the present invention is to provide a curable fluororesin paint that can form a semi-gloss or matte coating without impairing weather resistance, chemical resistance, flexibility, etc. .

[Means to solve the problem]

The present invention aims to solve the above problems.

(1) Fluororesin having hydroxyl groups.

A curable fluororesin paint (hereinafter referred to as the fluororesin paint of the present invention) containing glass fibers whose surface has been treated with (2) a curing agent and (3) a silane-based covering agent is provided.

The fluororesin having a hydroxyl group is used in the present invention.

For example, a fluorine-containing vinyl monomer, a copolymerizable vinyl monomer having a hydroxyl group, and other copolymerizable vinyl monomers can be used for bulk polymerization or solution polymerization using a radical polymerization initiator. It can be produced by polymerization using a known polymerization method such as emulsion polymerization.

Examples of the fluorine-containing vinyl monomer include vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, bromotrifluoroethylene, and chlorotrifluoroethylene.

fluoropropylene, hexafluoro7'CI pyrene, (/n-)fluoroalkyl trifluorovinyl ether (however, the number of carbon atoms in the (per)fluoroalkyl group is an integer of 1 to 18), etc. Can be mentioned.

The amount of fluorine-containing vinyl monomer used is polymerizable vinyl A/-
The range of 10 to 90% by weight of E-summer is preferable, and 20% by weight.
A range of 85% by weight is particularly preferred.

Examples of copolymerizable vinyl monomers having a hydroxyl group include hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, and hydroxybutyl vinyl ether; Examples include (meth)acrylate.

The amount of the copolymerizable vinyl monomer having a hydroxyl group to be used is such that the hydroxyl value of the fluororesin having a hydroxyl group is 30 in terms of solid content.
The amount is preferably in the range of 9 to 70 ■KOH/.

Examples of other copolymerizable vinyl monomers include vinyl acetate, vinyl propionate, vinyl butyrate, etc.
Vinyl Jionate, Vinyl Cabroate, Vinyl Caprate,
Vinyl esters of linear or segmented aliphatic carboxylic acids such as vinyl caprate, vinyl persate, vinyl laurate, vinyl stearate; Aromatic carboxylic acid vinyl esters such as benzoic acid vinyl ester, pt-butyl benzoic acid vinyl ester, and salicylic acid vinyl ester; Vinyl septamers having epoxy groups such as glycidyl vinyl ether and glycizol methacrylate; acrylic acid, methacrylate Acid, maleic acid, maleic anhydride: Itaconic acid, itaconic anhydride, fumaric acid, monoethyl maleate, motuptil maleate, motuptil fumarate, motuptil itaconate, monovinyl adipate, monovinyl sepacate, etc. to sulfini containing carboxyl groups mo/-r; dimethylaminoethyl vinyl ether, dimethylaminopropyl vinyl ether, N,N-dimef/l/7
Vinyl monomers containing amino groups such as minopropyl (meth)acrylamide and dimethylamine ethyl (meth)acrylate; such as vinyl chloride and vinylidene chloride;
Halodane-containing vinyl monomers excluding fluorine; styrene, α
- Aromatic vinyl monomers such as methylstyrene and vinyltoluene; ) Acrylic acid ester; (meth)acrylonitrile, (meth)acrylamide, N-methylol (meth)acrylamide, etc. are mentioned.

What is the number average molecular weight of a fluororesin having hydroxyl groups?

The range of 1.000 to 300,000 is preferable, and 5.0
A range of 00 to 200.000 is particularly preferred.

Typical commercial products of fluororesin having hydroxyl groups are 1
For example, "Fluonate 700J, [Fluoney] K701J" manufactured by Dainippon Ink and Chemicals (Musei).

Examples include Lumiflon LF100 J, r Lumiflon LF200 J, r Lumiflon LF400J, r Lumiflon LF601 J, and r Lumiflon LF700J manufactured by Asahi Glass.

The amount of the fluororesin having a hydroxyl group used is preferably in the range of 20 to 70% by weight of the solid content of the fluororesin paint of the present invention.

Examples of the curing agent used in the present invention include aminoplast, polyisocyanate, block polyisocyanate, polybasic acid, polybasic acid anhydride, polyepoxy compound,
Equal parts of silane coupling agents containing epoxy groups or incyanate groups can be mentioned.

Examples of aminoplasts include amino group-containing compounds such as melamine, urea, acetoguanamine, benzoguanamine, and spiroguanamine.

Examples include condensates obtained by reacting aldehyde group-containing compounds such as formaldehyde, acetaldehyde, and glyoxol by a known and commonly used method, and etherified products obtained by reacting these condensates with alcohols. In particular, from the viewpoint of compatibility with the fluororesin, it is desirable to use methyl etherified methylolmelamine.

A typical commercially available product of the methyl etherified methylol melamine is "Suit 9" manufactured by Dainippon Ink & Chemicals.
- Beckamin L105J, Mitsui Toatsu Chemical Co., Ltd. [Synul 303J, r Cymel 370J.

Examples include "Nikaratsuku MW24XJ" manufactured by Sansho Chemical ■.

Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as xylene diisocyanate and inphorone diisocyanate; tolylene diisocyanate and 4,4'-diphenylmethane diisocyanate. organic diisocyanates such as aromatic diisocyanates such as;

Or these organic diisocyanates and polyhydric alcohol,
Examples include adducts with low-molecular polyester resins or water, polymers of organic diisocyanates, incyanate biuret bodies, and the like.

Typical commercial products of the polyisocyanate include 1, for example, "Parnock DN" manufactured by Dainippon Ink and Chemicals Co., Ltd.
-950J, ``Parnock DN-981'', ``Takene'' D14ONJ manufactured by Takeda Pharmaceutical Company Limited.

Examples include "Takenate D170J,""CoronateHLJ" manufactured by Nippon Polyurethane Industry ■, and "r-Coronate EHJ."

Examples of the blocked polyisocyanate include those obtained by reacting the above polyisocyanate with a known blocking agent.

As a polybasic acid, for example - two or more cals in the molecule?
Examples include acrylic resins or polyester resins having xyl groups, pyromellitic acid, trimellitic acid, and the like.

Examples of polybasic acid anhydrides include acrylic resins having two or more acid anhydride groups in the molecule, trimellitic anhydride, pyromellitic anhydride, and the like.

Examples of polyepoxy compounds include polyhydric alcohol esters such as ethylene glycol, glycerin, pentaerythritol, and sorbitol, -
Examples include acrylic resins having two or more epoxy groups in the molecule.

The amount of curing agent used is 2 to 5 of the fluororesin having hydroxyl groups.
A range of 0% by weight is preferred.

When using aminoplast, polyincyanate or blocked polyisocyanate as a curing agent, a curing catalyst can be blended into the fluororesin coating material of the present invention.

When the curing agent is an aminoplast, examples of the curing catalyst include p-toluenesulfonic acid, phosphoric acid, monoalkyl ester of phosphoric acid, dialkyl ester of phosphoric acid,
Examples include dinonylnaphthalenedisulfonic acid, dodecylbenzenesulfonic acid, and organic amine-blocked products of these compounds.

As a curing catalyst when the curing agent is polyincyanate or block polyisocyanate.

For example, diptyltin diacetate, diptyltin dioctate, dibutyltin silaurylate, triethylamine,
Examples include dimethylaminoethanol.

The fluororesin paint of the present invention can be used as a two-component room-temperature-curing paint when a compound having a free isocyanate group is used as a curing agent, and as a thermosetting-liquid paint in other cases.

The glass fibers used in the production of the glass fibers surface-treated with a silane coupling agent used in the present invention include E
Examples include glass fiber and C glass fiber. The size of the glass fiber is 1 to 30 μm in diameter.

The length is preferably in the range of 1 to 200 μm. The thickness of the special coating film using fluororesin paint is usually in the range of 30 to 70 μm, so if the diameter of the glass fiber is larger than 30 μm,
This is not preferable because the glass fibers protrude from the surface of the coating film, causing cracks in the coating film and the glass fibers tending to fall off from the coating film. If the diameter of the glass fiber is smaller than 1 μm, the strength of the coating film tends to decrease, which is not preferable. When the length of the glass fiber is longer than 200 μm, it is not preferable because it tends to become difficult to uniformly disperse the glass fiber in the fluororesin paint.

The amount of glass fiber surface-treated with a silane coupling agent is 1 to 80% of the solid content of the fluororesin paint of the present invention.
A weight percent range is preferred. The amount of glass fiber used is 80
If it is more than 5% by weight, the paint film tends to crack and become very brittle, but if it is less than 5% by weight,
This is not preferable because it tends to make it difficult to obtain a sufficient matting effect.

Since the surface of glass is generally covered with hydrophilic groups such as hydroxyl groups, it has poor wettability with paint and is not compatible with paint. Therefore, simply adding glass fibers to a paint makes it difficult to disperse them uniformly in the paint, and as a result of the ubiquitous presence of glass fibers in the resulting paint film, it is difficult for water to pass through, and corrosion resistance and weather resistance are impaired. It is on a declining trend.

On the other hand, the glass surface is a chloropropyl type.

There are known methods of treatment with silane coupling agents such as vinyl type, Mercagt type, and amino type.
For example, in the production of composite materials made by laminating polyester resin and glass fiber cloth, it is widely applied to improve the compatibility between the polyester resin and glass fiber cloth and to improve their strength. There is.

Also in the fluororesin paint of the present invention, it is useful to treat the surface of the glass fiber with a silane coupling agent as described below in order to improve the compatibility between the fluororesin having hydroxyl groups and the glass fiber. It was revealed.

Examples of the silane coupling agent used in the production of glass fibers surface-treated with the silane coupling agent used in the present invention include the general formula % (where R is a hydrogen atom, a methyl group, or an ethyl group). , X represents a methoxy group, ethoxy group, β-methoxyethoxy group, n represents 1, 2 or 3, y represents a vinyl group; Alkyl group; β-(3,4-
an alkyl group containing an epoxy group such as 2I (oxycyclohexyl)ethyl group, 3-glycidoxyglobyl group;
-Aminozolopyl group, N-(2-aminoethyl)-3-
It represents an alkyl group containing an amino group such as an aminopropyl group or an N-phenyl-3-aminopropyl group; an alkyl group containing a chlorine atom such as a chloromethyl group or a 3-chloropropyl group. Examples include silane coupling agents consisting of compounds represented by:

Treatment of glass fibers with a silane coupling agent is usually carried out as follows.

That is, a silane-based coupling agent is dissolved in an organic solvent such as a ketone-based, ester-based, or hydrocarbon-based solvent, and glass fibers are added to the solution while stirring and heating the solution. The treatment is carried out at 25-70°C until the organic solvent is evaporated to dryness. The amount of silane coupling agent used is 5
A range of 60% by weight is preferred.

In order to obtain the fluororesin paint of the present invention, the above-described fluororesin having a hydroxyl group and, if necessary, a curing agent and a colorant are dispersed or dissolved in an organic solvent using a dispersion mixer such as a sand mill or a ball mill. Thereafter, glass fibers surface-treated with the silane coupling agent may be added and dispersed. When obtaining a two-component paint that cures at room temperature, the curing agent may be dispersed or dissolved before coating. The non-volatile content concentration is preferably in the range of 30 to 75% by weight, and more preferably in the range of 35 to 70% by weight, based on the total amount of the paint. In order to supplement the adhesion with the material, it is common practice to first coat the base material with a primer paint. As a resin component of primer paint.

Examples of alkyd resins include alkyd resins, epoxy resins, and acrylic resins.In order to improve adhesion to the base material and improve corrosion resistance, alkyd resins include epoxy-modified alkyd resins, phenol-modified alkyd resins, etc. It is preferable to use resin and acrylic modified alkyd resin. Also, when using epoxy resin or acrylic resin.

It is preferable to use it together with a curing agent.

Examples of curing agents for epoxy resins used in primer paints include aminoplasts, polyisocyanates, block polyisocyanates, and polyamines.

Examples of curing agents for acrylic resins used in primer paints include aminoplasts, polyincyanates, and block polyisocyanates.

Pigment components used in primer paints vary depending on the type of base material, but if the base material is iron or galvanized steel, lead-based pigments such as red lead and cyanamide lead; zinc chromate, chromic acid Antirust pigments such as chromate pigments such as strontium are preferred.

The composition of the primer paint is 10 to 60% by weight of the above resin,
A range of 0 to 50% by weight of pigment and 10 to 40% by weight of solvent is preferred.

The primer paint is applied to the substrate with a brush, wool roller, spray, roll coater, etc., and cured at a temperature of 20° C. to 200° C. for 40 seconds to 7 days. Dry coating thickness is 5-80
A range of μm is appropriate. In order to further improve the coating performance, the same type of fc is also coated with different types of primer paints. Please be careful, especially when the base material is aluminum material, and the total amount of chromium on the surface is 50 da/
Primer coating can be omitted only if chromic acid treatment of m2 or more is applied.

The fluororesin paint of the present invention can be applied by spray painting, brush painting,
A coating film can be formed on a substrate coated with a primer, if necessary, by a known and commonly used method such as roller coating or a roll coater.

Curing of the coating film in the room temperature curable fluororesin paint of the present invention using a compound having a free incyanate group is as follows:
1 to 7 days at room temperature or 1 minute to 60 days at 50 to 120℃
Can be cured under conditions of minutes.

The coating film of the fluororesin paint of the present invention using other curing agents can be cured under conditions of 60 to 250°C for 5 seconds to 40 minutes.

The fluororesin paint of the present invention can be used as an exterior paint for buildings, roof tiles, pre-coated metal (PCM), enamel paint or clear paint for office equipment, surface protection paint for ceramic products, FRP, etc.

Next, the present invention will be explained in more detail using synthesis examples, formulation examples, comparative formulation examples, and coating examples, and the effects of the present invention will be clarified through examples and comparative examples. The examples are not limited in any way.

Note that all parts and percentages hereinafter are based on weight.

〔Example〕

Example 1 (Treatment of glass fiber) 20 parts of 3-glycidoglopyltrimethoxysilane was added to 100 parts of xylene and stirred well to obtain a xylene solution of 3-glycidopropyltrimethoxysilane. This solution was kept at 25°C and stirred using E glass fibers (diameter 1).
3 μm, length 20-50 μm) was added little by little. After the addition of the glass fibers was completed, the temperature of the solution was raised to 60° C. and the solvent was evaporated to obtain glass fibers surface-treated with a silane coupling agent (hereinafter referred to as glass fibers A).

(Preparation of fluororesin paint of the present invention) (2) Titanium oxide 15.5 parts (3) Xylene 8.0 parts (4) Glass fiber A 6.0 parts (5) Butyl acetate 2.0 parts (6) Diptyl tin dilauryl) 0.05% solution
0.5 parts (1) to (3)? - After thoroughly kneading with Lumil, add the mixture of (4) to (6) with stirring, and then add (by applying force and stirring) before coating.
A curable fluororesin paint was obtained.

Example 2 A curable fluororesin paint was obtained in the same manner as in Example 1, except that the amount of glass fiber A added was changed to 30.0 parts.

Comparative Example 1 A curable fluororesin paint was obtained in the same manner as in Example 1, except that glass fiber A was not added.

Comparative Example 2 In Example 1, "Syroid+404J (fine particle anhydrous silica manufactured by Fuji Depison Chemical ■)" was used instead of glass fiber A.
A curable fluororesin paint was obtained in the same manner as in Example 1, except that 2.1 parts were used.

(Preparation of primer paint) After adding 18 parts of titanium oxide to 20 parts of Ebicuron 1050-70XJ (a 70% solution of epoxy resin manufactured by Dainippon Ink & Chemicals) and dispersing it,
6 J (Polyamide resin manufactured by Dainippon Ink & Chemicals)
A primer paint was obtained by adding 11 parts and 6 parts of butyl cellosolve and stirring.

(Creation of painted board for test) Aluminum board (JIS Al 100X) was coated with degreasing liquid (
"Fine Cleaner 315" manufactured by Nippon Parkerizing Co., Ltd.
J) for 10 minutes and then dried.

Next, the aluminum plate was degreased and then immersed in a chemical conversion treatment solution (manufactured by Nippon Parkerizing Co., Ltd. [M Nderant 713J) for 2 minutes, and then dried. The above primer paint was applied to a chemical conversion treated aluminum plate by air spraying to a dry film thickness of 5 μm.

It was dried at room temperature (20° C.) for 48 hours.

The aluminum plate coated with this primer was coated with each of the curable fluororesin paints obtained in each Example and Comparative Example using T-Air Spray to a dry film thickness of 30 μm, and left at room temperature (20°C). After drying for 7 hours, m-piece sheet metals for testing were obtained.

(1) Weather resistance test The coating film of the above test plate was subjected to an accelerated weather resistance test for 500 hours using an apparatus compliant with the ASTM (American Society for Testing and Materials) G23 test standard, and then the gloss retention rate and Just looking for color difference.

(2) Light resistance test A Toshiba germicidal lamp was used on the coating film of the above-mentioned test coated board.
After irradiating with ultraviolet light from a distance of 15 cm for 1,000 hours, gloss retention and color difference were determined.

[Gloss retention rate (GR)]

G00 specular gloss was measured before and after the accelerated weathering test or ultraviolet irradiation test in accordance with the JIS-K5400 test standard, and the value after the test was expressed as a percentage of the value before the test.

[Color Difference (ΔE)] Measurements were made before and after the accelerated weathering test or the ultraviolet irradiation test under optical conditions in accordance with the test standard of JIS-28722, and the one color difference (ΔE) was determined by Hunter's color difference formula.

(3) Pencil hardness test The test was conducted in accordance with the test standard for the "pencil scratch test" of JIS-K5400. However, the hardness of the coating film was determined based on the pencil hardness when the coating surface was scratched.

(4) Moisture Test The coated test plate described above was subjected to a wetness test for 3,000 hours in accordance with the JIS ZO236 test standard using an anti-static device, and then the presence of pristar on the surface of the coating film was determined.

[Pristar Judgment Criteria]

◎: Prista has not occurred.

○: Prista size &8 according to the evaluation criteria specified in ASTM D714. Pristors with a density of about rFEWJ are generated.

Δ: Blister density r excluding the above blister of MEDIUM J or higher is generated.

×: More significant pristal than above occurs.

Table 1 shows the test results conducted according to the above test methods (1) to (4).

Table 1 As is clear from the test results shown in Table 1, the coating film made of the fluororesin paint of the present invention has a lower initial gloss than the current paint (comparative example 2), despite its low initial gloss. Far superior to the coating performance of ! ! In fact, it shows that the film performance even exceeds that of the current full-gloss paint (Comparative Example 1).

〔Effect of the invention〕

The fluororesin paint of the present invention is a curable fluororesin paint that can form a semi-gloss or matte coating without impairing weather resistance, chemical resistance, flexibility, etc. Therefore, by using the fluororesin paint of the present invention, it is possible to apply a semi-gloss or matte coating to objects to be coated, for which a high-temperature baking process was conventionally impossible.

Agent: Patent Attorney Katsutoshi Takahashi

Claims (1)

[Claims] 1. A curable fluorine resin characterized by containing (1) a fluororesin having a hydroxyl group, (2) a curing agent, and (3) a glass fiber surface-treated with a silane coupling agent. resin paint. 2. Claim 1, wherein the diameter of the glass fiber is in the range of 1 to 30 μm, and the length of the glass fiber is in the range of 1 to 200 μm.
Curable fluororesin paint as described. 3. The curable fluororesin paint according to claim 1, wherein the glass fiber is E glass fiber or C glass fiber. 4. The silane coupling agent has the general formula YSiX_nR_3_-_n (wherein R represents a hydrogen atom, methyl group or ethyl group, X represents a methoxy group, ethoxy group, β-methoxyethoxy group, and n is 1 , 2 or 3.Y represents a vinyl group, an alkyl group containing an olefin, an alkyl group containing an epoxy group, an alkyl group containing an amino group, or an alkyl group containing a chlorine atom) The curable fluororesin paint according to claim 1. 5. The curable fluororesin paint according to claim 1, wherein the amount of the silane coupling agent used is in the range of 5 to 60% by weight of the glass fiber. 6. The curable fluororesin paint according to claim 1, wherein the amount of glass fiber surface-treated with a silane coupling agent is in the range of 5 to 80% by weight of the solid content of the paint. 7. A claim that the fluororesin having a hydroxyl group is a copolymer obtained by copolymerizing a polymerizable vinyl monomer consisting of a fluorine-containing vinyl monomer, a copolymerizable vinyl monomer having a hydroxyl group, and another copolymerizable vinyl monomer. The curable fluororesin paint according to item 1. 8. The fluorine-containing vinyl monomer includes vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, bromotrifluoroethylene, chlorotrifluoroethylene, pentafluoropropylene, hexafluoropropylene, and (per)fluoroalkylfluorovinyl ether ( The curable fluororesin coating material according to claim 7, wherein the number of carbon atoms in the (per)fluoroalkyl group is an integer of 1 to 18. 9. Claim 7 or 8, wherein the amount of the fluorine-containing vinyl monomer used is in the range of 5 to 90% by weight of the polymerizable vinyl monomer.
Curable fluororesin paint as described. 10. The curable fluororesin coating material according to claim 7, wherein the copolymerizable vinyl monomer having a hydroxyl group is selected from the group consisting of hydroxyalkyl vinyl ether, hydroxyalkyl acrylate, and hydroxyalkyl methacrylate. 11. The curable fluororesin according to claim 7 or 10, wherein the amount of the copolymerizable vinyl monomer having a hydroxyl group is such that the hydroxyl value of the fluororesin having a hydroxyl group is in the range of 30 to 70 mgKOH/g in terms of solid content. paint. 12. The number average molecular weight of the fluororesin having a hydroxyl group is 1
2. The curable fluororesin paint according to claim 1, which has a molecular weight in the range of . 13. The curable fluororesin paint according to claim 1, wherein the amount of the fluororesin having a hydroxyl group used is in the range of 20 to 70% by weight based on the solid content of the paint. 14. The curing agent according to claim 1, wherein the curing agent is selected from the group consisting of aminoplast, polyisocyanate, blocked polyisocyanate, polybasic acid, polybasic acid anhydride, polyepoxy compound, and epoxy group- or isocyanate group-containing silane coupling agent. Curable fluororesin paint. 15. The curable fluororesin paint according to claim 1, wherein the amount of the curing agent used is in the range of 2 to 50% by weight of the fluororesin having hydroxyl groups. 16. The curable fluororesin paint according to claim 1, wherein the nonvolatile content is in the range of 30 to 75% by weight of the paint. 17. A matte paint comprising the curable fluororesin paint according to claim 1. 18. A coated metal substrate, characterized in that a cured coating film of a primer paint is provided on the metal substrate as necessary, and then a cured coating film of the curable fluororesin paint according to claim 1 is provided.