JP2014167035A - Coating material composition for reflecting mirror for solar heat collection, and reflecting mirror for solar heat collection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating material composition that can form a cured coating film layer excellent in heat resistance, weatherability, scratch resistance and impact resistance and having a self-cleaning function over a long period of time, and to provide a reflecting mirror for solar heat collection that has the cured coating film layer.SOLUTION: A coating material composition for coating glass for the production of a reflecting mirror for solar heat collection comprises (A) to (C) as given below: (A) a fluoroolefin copolymer having at least one kind of crosslinkable functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, an epoxy group, an oxetane group, an alkoxysilyl group and an isocyanate group; (B) at least one kind of curing agent selected from the group consisting of an isocyanate curing agent, a blocked isocyanate curing agent and an amino resin; and (C) a multimer of a tetrafunctional hydrolyzable silane compound.

Description

  The present invention relates to a coating composition for a solar heat collecting reflector, and a solar heat collecting reflector formed by the coating composition.

  In recent years, from the viewpoint of global environmental problems, many attempts have been made to reduce the amount of fossil fuel used. As one of them, a solar heat collection system using solar heat is known. Examples of the solar heat collection system include a solar heat collection system having a heat collection tube provided with a heat medium such as water or an inorganic salt, and a reflecting mirror that reflects sunlight and collects the heat collection tube. In the solar heat collecting system, sunlight is reflected by a reflecting mirror and collected in a heat collecting tube, and heat energy is obtained by heating the heat medium of the heat collecting tube with the heat of the sunlight.

Reflectors for solar heat collection are required to reflect sunlight efficiently, but when used outdoors for a long period of time, solar dust collects dust, dirt, sand, earth, insect dead bodies, etc. in the atmosphere. It adheres on the glass reflecting surface of the reflector for use and cannot collect solar heat efficiently. In order to solve these problems, the solar heat collecting reflector is regularly washed with a brush or the like. However, unlike general mirrors used indoors, solar heat collecting reflectors have a large area, and large heavy machinery must be used for cleaning, which increases maintenance costs. It was. Moreover, if it cleans regularly with a brush etc., the glass surface will be damaged, As a result, it becomes impossible to collect solar heat efficiently.
That is, it is required to form a cured coating film having a self-cleaning function for a long period of time and having excellent weather resistance on the glass reflecting surface side of the solar heat collecting reflector.
On the other hand, in general buildings and the like, it has been proposed that a fluorine-containing paint composition containing a silane compound is used as a paint in order to reduce contamination on the surface of a coated film.

JP-A-9-165550

The present invention is a coating composition for producing a solar heat collecting reflector, which is excellent in heat resistance, weather resistance, scratch resistance and impact resistance, and has a self-cleaning function over a long period of time. It aims at providing the coating composition which can form a layer.
Another object of the present invention is to provide a solar heat collecting reflector having a cured coating film layer that has excellent heat resistance, weather resistance, scratch resistance and impact resistance and has a self-cleaning function over a long period of time.

The present invention employs the following configuration in order to solve the above problems.
[1] A solar heat collecting reflector coating composition containing the following (A) to (C).
(A) a fluoroolefin copolymer having at least one crosslinkable functional group selected from the group consisting of a hydroxyl group, a carboxy group, an amino group, an epoxy group, an oxetanyl group, an alkoxysilyl group and an isocyanate group;
(B) at least one curing agent selected from the group consisting of an isocyanate curing agent, a blocked isocyanate curing agent and an amino resin,
(C) a multimer of tetrafunctional hydrolyzable silane compounds [2] on the solar light incident surface side of the solar heat collecting reflector laminated in the order of the glass substrate, the reflective metal layer, and the cured coating film layer (a), A solar heat collecting reflector having a cured coating layer (b) formed from the glass coating composition according to [1].

If the coating composition for glass coating of the solar heat collecting reflector of the present invention is used, a cured coating layer having excellent heat resistance, weather resistance, scratch resistance and impact resistance and having a self-cleaning function over a long period of time ( b) can be formed on the solar light incident surface side of the solar heat collecting reflector.
In addition, the solar heat collecting reflector of the present invention has a cured coating film layer formed on the sunlight incident surface side having excellent heat resistance, weather resistance, scratch resistance and impact resistance, and a self-cleaning function over a long period of time. have.

It is sectional drawing which showed an example of embodiment of the reflective mirror for solar heat collection of this invention.

[Coating composition for glass application of solar heat collecting reflector]
The solar heat collecting reflector coating composition of the present invention (hereinafter also simply referred to as “coating composition”) forms a cured coating layer (b) on the solar light incident surface side of the solar heat collecting reflector. A fluoroolefin copolymer having at least one crosslinkable functional group selected from the group consisting of a hydroxyl group, a carboxy group, an amino group, an epoxy group, an oxetanyl group, an alkoxysilyl group and an isocyanate group Containing.

[Fluoroolefin copolymer (A)]
The fluoroolefin copolymer (A) is a fluoroolefin copolymer having a crosslinkable group, a repeating unit based on the fluoroolefin, and a monomer having a crosslinkable group copolymerizable with the fluoroolefin ( Hereinafter, it is a copolymer having a repeating unit based on “monomer (a1)”. As the fluoroolefin copolymer (A), from the viewpoint of coating workability and the like, a repeating unit based on fluoroolefin, a repeating unit based on monomer (a1), and other than fluoroolefin and monomer (a1) A fluoroolefin copolymer (A1) having a repeating unit based on another monomer (hereinafter referred to as “monomer (a2)”) is preferred.

A fluoroolefin is a compound in which one or more hydrogen atoms of an olefin hydrocarbon (general formula C _n H _2n ) are substituted with a fluorine atom.
2-8 are preferable and, as for carbon number of a fluoro olefin, 2-6 are more preferable.
The number of fluorine atoms in the fluoroolefin (hereinafter referred to as “fluorine addition number”) is preferably 2 or more, and more preferably 3-4. If the fluorine addition number is 2 or more, the weather resistance of the inclined coating film 15 is improved. In the fluoroolefin, one or more hydrogen atoms not substituted with fluorine atoms may be substituted with chlorine atoms.

As the fluoroolefin, one or more selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, vinylidene fluoride and vinyl fluoride is preferable, and tetrafluoroethylene and chlorotrifluoroethylene are more preferable.
A fluoro olefin may be used individually by 1 type, and may use 2 or more types together.
As the repeating unit based on fluoroolefin, a repeating unit directly formed by polymerization of fluoroolefin is preferable.

The monomer (a1) is a monomer having a crosslinkable group. The said crosslinkable group is group which reacts with crosslinkable groups or a hardening | curing agent, and forms a crosslink. Examples of the crosslinkable group include a hydroxyl group, a carboxy group, an amino group, an epoxy group, an oxetanyl group, an alkoxysilyl group, and an isocyanate group.
As the repeating unit based on the monomer (a1), a repeating unit directly formed by polymerization of the monomer (a1) is preferable.

Examples of the monomer having a hydroxyl group include allyl alcohol; hydroxyalkyl vinyl ethers such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether and cyclohexanediol monovinyl ether; hydroxyalkyl allyl ethers such as 2-hydroxyethyl allyl ether; Examples thereof include hydroxyalkyl carboxylic acid vinyl esters such as ethyl carboxylic acid vinyl ester; (meth) acrylic acid hydroxyalkyl esters such as hydroxyethyl (meth) acrylate and the like.
Examples of the monomer having a carboxyl group include crotonic acid and undecenoic acid.
Examples of the monomer having a hydrolyzable silyl group include triethoxyvinylsilane.
Examples of the monomer having an oxetanyl group include 3-ethyl-3-vinyloxymethyl oxetane, 3-methyl-3-methacryloylmethyl oxetane, and the like.
Examples of the monomer having an epoxy group include glycidyl vinyl ether and glycidyl allyl ether.
Examples of the monomer having an amino group include aminopropyl vinyl ether and aminopropyl allyl ether.
Examples of the monomer having an isocyanate group include isocyanatopropyl (meth) acrylate.
A monomer (a1) may be used individually by 1 type, and may use 2 or more types together.

  Further, the repeating unit based on the monomer (a1) may be formed by introducing a crosslinkable group by chemically converting a part of the polymerized unit of the polymer after obtaining the polymer. For example, a method of introducing a hydroxyl group by saponifying a polymer obtained by copolymerizing a carboxylic acid vinyl ester, a polymer obtained by copolymerizing a monomer having a hydroxyl group with a polyvalent carboxylic acid or an anhydride thereof to form a carboxyl A method of introducing a group, a method of introducing a hydrolyzable silyl group by reacting an isocyanate alkyl alkoxysilane with a polymer copolymerized with a monomer having a hydroxyl group, and a polymer copolymerizing a monomer having a hydroxyl group Examples include a method of introducing an isocyanate group by reacting a polyvalent isocyanate compound.

  The monomer (a2) is preferably a vinyl monomer, that is, a compound having a carbon-carbon double bond. Examples of the vinyl monomer include vinyl ether, allyl ether, carboxylic acid vinyl ester, carboxylic acid allyl ester, and olefin.

Examples of the vinyl ether include cycloalkyl vinyl ethers such as cyclohexyl vinyl ether; alkyl vinyl ethers such as nonyl vinyl ether, 2-ethylhexyl vinyl ether, hexyl vinyl ether, ethyl vinyl ether, n-butyl vinyl ether, and t-butyl vinyl ether.
Examples of the allyl ether include alkyl allyl ethers such as ethyl allyl ether and hexyl allyl ether.

Examples of the carboxylic acid vinyl ester include vinyl esters of carboxylic acids such as acetic acid, butyric acid, pivalic acid, benzoic acid, and propionic acid. Moreover, as a vinyl ester of a carboxylic acid having a branched alkyl group, commercially available Veova-9, Veova-10 (both manufactured by Shell Chemical Co., Ltd., trade name), etc. may be used.
Examples of the carboxylic acid allyl ester include allyl esters of carboxylic acids mentioned in the above carboxylic acid vinyl ester.
Examples of the olefin include ethylene, propylene, isobutylene and the like.
A monomer (a2) may be used individually by 1 type, and may use 2 or more types together.

  As the fluoroolefin copolymer (A), a fluoroolefin copolymer (A1) is preferable, and a copolymer of chlorotrifluoroethylene (CTFE), cyclohexyl vinyl ether (CHVE), alkyl vinyl ether and hydroxyalkyl vinyl ether; CTFE , A copolymer of an aliphatic carboxylic acid vinyl ester and a hydroxyalkyl vinyl ether; or a copolymer using tetrafluoroethylene (TFE) instead of CTFE in these copolymers.

  The proportion of the repeating unit based on the fluoroolefin in the fluoroolefin copolymer (A1) is preferably from 30 to 70 mol%, more preferably from 40 to 60 mol%, based on all the repeating units in the fluoroolefin copolymer. . If the repeating unit based on fluoroolefin is more than the said lower limit, the weather resistance of a coating film will improve. If the repeating unit based on a fluoro olefin is below the said upper limit, the adhesiveness with the glass surface of a fluoro olefin type copolymer (A1) will improve.

The proportion of repeating units based on the monomer (a1) in the fluoroolefin copolymer (A1) is preferably 0.5 to 30 mol%, more preferably 1 to 20 mol%. If the ratio of the repeating unit based on a monomer (a1) is more than the said lower limit, adhesiveness with a glass surface will improve. When the ratio of the repeating unit based on the monomer (a1) is not more than the above upper limit value, the scratch resistance of the coating film is improved.
The proportion of the repeating unit based on the monomer (a2) in the fluoroolefin copolymer (A1) is preferably 0.5 to 50 mol%, more preferably 1 to 40 mol%. If the ratio of the repeating unit based on a monomer (a2) is more than the said lower limit, the solubility to the solvent of a fluoroolefin type copolymer (A1) will improve, and coating workability | operativity will improve. If the ratio of the repeating unit based on a monomer (a2) is below the said upper limit, adhesiveness with a glass surface will improve.

  The number average molecular weight of the fluoroolefin copolymer (A) is preferably 2,000 to 100,000, and more preferably 6,000 to 30,000. If the number average molecular weight of the fluoroolefin copolymer (A) is not less than the lower limit, the water resistance and salt water resistance of the coating film will be good. If the number average molecular weight of a fluoroolefin type copolymer (A) is below the said upper limit, the smoothness of a coating film will become favorable.

  The hydroxyl value of the fluoroolefin copolymer (A) is preferably 5 to 250 mgKOH / g, more preferably 10 to 150 mgKOH / g. If it is more than a lower limit, adhesiveness with a glass surface will improve. If it is below the upper limit, the crack resistance of the cured coating film under a temperature cycle at a high temperature of 100 ° C. or higher and a low temperature of 10 ° C. or lower is difficult to decrease.

As the fluoroolefin copolymer (A), trade name “Lumiflon” (manufactured by Asahi Glass Co., Ltd.), trade name “Fluonate” (manufactured by Dainippon Ink & Chemicals, Inc.) The product name “Zaflon” (manufactured by Toa Gosei Co., Ltd.), the product name “Zeffle” (manufactured by Daikin Industries, Ltd.) and the like are commercially available.
A fluoroolefin type copolymer (A) may be used individually by 1 type, and may use 2 or more types together.

  A hardening | curing agent (B) plays the role which hardens the application layer which apply | coated the coating composition by reacting with the crosslinkable group of a fluoro olefin type copolymer (A), and forming a crosslinked structure. As the curing agent (B), a compound having two or more functional groups having reactivity with the crosslinkable group is appropriately selected according to the type of the crosslinkable group possessed by the fluoroolefin copolymer (A). . As the curing agent, an isocyanate curing agent, a blocked isocyanate curing agent, and an amino resin are preferable.

<Isocyanate curing agent>
As said isocyanate type hardening | curing agent, a non-yellowing polyisocyanate and a non-yellowing polyisocyanate modified body are mentioned.
Examples of the non-yellowing polyisocyanate include alicyclic polyisocyanates such as isophorone diisocyanate (IPDI) and dicyclohexylmethane diisocyanate (HMDI); and aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI).

Examples of the non-yellowing polyisocyanate-modified product include the following modified products (b1) to (b4).
(B1) Isocyanurate of aliphatic diisocyanate or alicyclic diisocyanate.
(B2) A modified product having a structure represented by -C (= O) -NH-, wherein aliphatic diisocyanate or alicyclic diisocyanate is modified with polyol or polyamine.
(B3) A modified product having a structure represented by -C (= O) -NH-, in which a part of the isocyanate group of an aliphatic diisocyanate or an alicyclic diisocyanate isocyanurate is modified with a polyol.
(B4) A modified body comprising a mixture of the modified body (b1) and the modified body (b2).

<Blocked isocyanate curing agent>
The blocked isocyanate curing agent is a blocked isocyanate curing agent in which the isocyanate group of the isocyanate curing agent is blocked.

The isocyanate group can be blocked with epsilon caprolactam (E-CAP), methyl ethyl ketone oxime (MEK-OX), methyl isobutyl ketone oxime (MIBK-OX), pyraridine, triazine (TA) or the like.

<Amino resin>
Examples of the amino resin include melamine resin, guanamine resin, sulfoamide resin, urea resin, aniline resin, and the like. Especially, a melamine resin is preferable at the point that a cure rate is quick.
Specific examples of the melamine resin include alkyl etherified melamine resins that are alkyl etherified. Among these, a melamine resin substituted with a methoxy group and / or a butoxy group can be used more preferably.

  The coating composition of the present invention is used as a two-component coating composition in which a curing agent (B) is not added and a curing agent (B) is added immediately before forming a cured coating layer (b). Alternatively, it may be used as a one-pack type coating composition containing both the fluoroolefin copolymer (A) and the curing agent (B).

The content of the fluoroolefin copolymer (A) when using the coating composition of the present invention is 10 with respect to the total content of the fluoroolefin copolymer (A) and the curing agent (B). -90 mass% is preferable, 20-80 mass% is more preferable, 30-70 mass% is further more preferable.
If the said content of a fluoro olefin type copolymer (A) is 10 mass% or more, the weather resistance of a cured coating film layer (b) will improve. If the content of the fluoroolefin copolymer (A) is 90% by mass or less, it is easy to suppress the occurrence of cracks in the cured coating layer (b), and the cured coating layer (b) and the glass surface Adhesion with is improved. Moreover, it becomes easy to form the cured coating film layer (b) excellent in durability, scratch resistance and impact resistance.

  As for content of the hardening | curing agent (B) in the coating composition of this invention, 1.0-60.0 mass parts is preferable with respect to 100 mass parts of fluoroolefin type copolymers (A), and 5.0-50. 0.0 part by mass is more preferable. If content of a hardening | curing agent is more than the said lower limit, a fluoro olefin type copolymer (A) can fully be bridge | crosslinked. If content of a hardening | curing agent is below the said upper limit, it will be easy to suppress that an unreacted hardening | curing agent remains in a cured coating film and affects the performance of a coating film.

[Multimer of tetrafunctional hydrolyzable silane compound (C)]
The tetrafunctional hydrolyzable silane compound is a compound in which four hydrolyzable groups are directly bonded to a silicon atom. A multimer of tetrafunctional hydrolyzable silane compounds (hereinafter simply referred to as “multimer (C)”). ) Is obtained by condensation of this compound by condensation.
Examples of the hydrolyzable group include an alkoxy group, an alkoxyalkyl group, an acyloxy group, an aryloxy group, an aminooxy group, an amide group, a ketoxime group, an isocyanate group, and a halogen atom. A group obtained by removing a hydrogen atom from a hydroxyl group of a monohydric alcohol such as an alkoxy group or an alkoxyalkyl group is preferred. Of these, an alkoxy group is particularly preferable, and the alkoxy group preferably has 4 or less carbon atoms, particularly preferably 1 or 2.

The degree of multimerization of the multimer (C) is preferably such that the composition does not produce a gel product. The degree of multimerization means the number of condensation molecules of the tetrafunctional hydrolyzable silane compound. The multimer (C) is preferably a tetraalkoxysilane multimer. As the straight-chain tetraalkoxysilane, a compound represented by the following formula 1 is preferable.
RO (Si (OR) ₂ O) _n R Formula 1
(In Formula 1, n represents the multimerization degree of the multimer, and R represents an alkyl group having 1 to 4 carbon atoms. The n Rs in the multimer may be the same as or different from each other. .)
The normally available multimer is a mixture of multimers having different n, and the degree of multimerization is indicated by average n. In Formula 1, as R, there are a methyl group, an ethyl group, a propyl group, and a butyl group, and a methyl group and an ethyl group are preferable. As the multimer (C), a tetramethoxysilane multimer and a tetraethoxysilane multimer are more preferable, and a tetraethoxysilane multimer is most preferable.

The degree of multimerization of a tetrafunctional hydrolyzable silane compound such as tetraalkoxysilane or a multimer thereof may be represented by “silica content”. The “silica content” is a mass ratio of silica (SiO ₂ ) produced from the compound, and can be obtained by measuring the amount of silica produced by stably hydrolyzing and firing the compound. The “silica content” also indicates the ratio of silica generated per molecule of the compound, and is a value calculated by the following formula.
Silica content (parts by mass) = degree of multimerization × molecular weight of SiO ₂ / molecular weight of the compound When the tetrafunctional hydrolyzable silane compound is a tetraalkoxysilane multimer, by setting the silica content to 40 parts by mass or more, Further, when the tetrafunctional hydrolyzable silane compound is a multimer of a compound other than tetraalkoxysilane, the coating composition containing the multimer (C) can be produced over a long period of time by setting the silica content to 35 parts by mass or more. The glass surface can be prevented from being stained.

  As the multimer (C), commercially available products may be used, MKC silicate MS51, MS56 manufactured by Mitsubishi Chemical Corporation; methyl silicate 51 (multimer of tetramethoxysilane) manufactured by Colcoat, ethyl silicate 40, 40T, 48 (Both are tetraethoxysilane multimers); Matsumoto Kosho's ORGATIX SI series; Tama Chemical Co., Ltd. ethyl silicates 40 and 45 (both tetraethoxysilane multimers). Of these, tetraethoxysilane having a silica content of 45% by mass or more is preferable, and ethyl silicate 48 and ethyl silicate 45 are particularly preferable.

  When the multimer (C) is a tetramethoxysilane multimer or a tetraethoxysilane multimer, the content ratio in the coating composition is 5 to 50 with respect to 100 parts by mass of the fluoroolefin copolymer (A). It is preferable that it is a mass part. By setting the content ratio to 5 parts by mass or more, the effect of preventing the occurrence of contamination on the glass surface is increased, and by setting the content to 50 parts by mass or less, it is possible to obtain a good coating film with no poor curing of the coating film.

  As for the ratio of the multimer (C) in a coating composition, it is further more preferable that the quantity beyond the incompatible point with respect to a fluoroolefin type copolymer (A) is mix | blended. This incompatible point is a coating film obtained by applying a solution prepared by dissolving the fluoroolefin copolymer (A) and the multimer (C) in a solvent to the surface of a glass plate and drying at 20 ° C. It is the “mass of the minimum multimer (C) that does not become cloudy relative to the mass of the fluoroolefin copolymer (A)” that can be confirmed by the presence or absence of white turbidity. When the multimer (C) is blended in excess of the incompatible point, it is possible to more effectively prevent the occurrence of dirt on the glass surface. Although this mechanism is not clear, the fluoroolefin copolymer (A) and multimer (C) undergo phase separation after coating, and the multimer (C) is formed near the surface of the cured coating film formed on the glass surface. ) Is hydrolyzed and the surface becomes hydrophilic, so that the occurrence of contamination on the glass surface can be more effectively prevented. This incompatible point has different values depending on the type of the fluoroolefin copolymer (A), the type of multimer (C), and the degree of multimerization.

  The coating composition of the present invention may contain a curing catalyst (D) for the purpose of accelerating the curing reaction and imparting good chemical performance and physical performance to the cured coating film layer (b) that is a cured product. . In particular, when curing at a low temperature in a short time, it is preferable to contain a curing catalyst (D). What is necessary is just to select a curing catalyst (D) suitably according to the combination of a crosslinkable functional group and a hardening | curing agent.

  For example, when the crosslinkable functional group is a hydroxyl group and the curing agent is an isocyanate curing agent or a blocked isocyanate curing agent, the curing catalyst (D) may be tin octylate, tributyltin dilaurate, dibutyltin dilaurate. Of these, tin catalysts and zirconium catalysts are preferred. A zirconium chelate etc. are mentioned as a zirconium catalyst. Moreover, as a commercial item of a zirconium compound, "K-KAT XC-4205" (Enomoto Kasei company make, brand name) etc. are mentioned.

For example, when the crosslinkable functional group is a hydroxyl group and the curing agent is an amino resin, the curing catalyst (D) is preferably a blocked acid catalyst. Examples of the blocked acid catalyst include various amine salts such as carboxylic acid, sulfonic acid, and phosphoric acid. Particularly preferred are higher alkyl-substituted sulfonic acid amine salts such as p-toluenesulfonic acid and diethanolamine salt of dodecylbenzenesulfonic acid and triethylamine salt.
A curing catalyst (D) may be used individually by 1 type, and may use 2 or more types together.

  When the coating composition of the present invention is applied to the solar incident surface side surface of the solar heat collecting reflector glass to form a coating film, the multimer (C) is hydrolyzed near the surface of the coating film. In view of this, the coating composition may contain a catalyst that promotes hydrolysis. Examples of the catalyst include metal compound catalysts such as metal chelates, metal esters, and metal alkoxides. Preferred examples of the metal include aluminum. More specifically, aluminum monoacetylacetonate bis (ethyl acetoacetate), aluminum tris (acetylacetonate), etc. are mentioned. The ratio of the catalyst in the coating composition is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the multimer (C).

The coating composition of this invention is a composition containing each said component which forms a cured coating film layer (b). Furthermore, in order to apply the coating composition of the present invention, it is preferable to use a solvent mixed with the coating composition.
As the solvent for applying the coating composition of the present invention, conventionally used solvents such as toluene, xylene, methyl ethyl ketone, butyl acetate, etc. can be used. Solvents are preferred.
The weak solvent is preferably a weak solvent species that can be used for the polymerization of the fluoroolefin copolymer (A) or solvent substitution, and more preferably mineral spirits and mineral terpenes.
The content of the solvent in the coating composition is appropriately determined in consideration of the solubility of the fluoroolefin copolymer (A), an appropriate viscosity when applied as a coating material, a coating method, and the like.

  5.0-80.0 mass% is preferable and, as for content of the solvent contained in a coating composition (100 mass%), 10.0-60.0 mass% is more preferable. If content of a solvent is more than the said lower limit, application | coating operation | work will become easy. If the content of the solvent is not more than the above upper limit value, it is easy to remove the solvent and form a cured coating film. Moreover, it becomes possible to suppress the peeling of the coating film resulting from the solvent. In addition, the armpit is a phenomenon in which many foam marks are generated on the surface of the coating film and the appearance of the coating film is lowered.

The coating composition of the present invention may further contain a light stabilizer, an ultraviolet absorber and the like as necessary. Examples of the light stabilizer include hindered amine light stabilizers and the like. For example, MARX LA62, MARX LA67 (above, manufactured by Adeka Argus Chemical Co., Ltd., trade name), TINUVIN 292, TINUVIN 144, TINUVIN-123, TINUVIN 440 (above TIVA)・ Specialty Chemicals, trade name).
Examples of ultraviolet absorbers include benzophenone compounds, benzotriazole compounds, triazine compounds, and cyanoacrylate compounds. Examples of the compound include Viosorb 130, Viosorb 582, Viosorb 583 (manufactured by Kyodo Pharmaceutical Co., Ltd., trade name), Tinuvin 320, Tinuvin 982, Tinuvin 1130, Tinuvin 400 (manufactured by Ciba Specialty Chemicals, trade name), and the like. It is done.

  You may mix | blend surfactant with the coating composition of this invention. The surfactant can control the surface tension, and is effective when adjusting the surface concentration to a specific component. The surfactant may be any of nonionic type, cationic type, anionic type, ROLEX ASE (made by Daiichi Kogyo Co., Ltd., trade name), “Surflon”, a fluorosurfactant (made by Asahi Glass Co., Ltd., trade name) Acrylic “Modaflow” (manufactured by Monsanto, trade name), “Leo Fat” series (trade name, manufactured by Kao), and the like.

In the coating composition of the present invention, a silane coupling agent may be blended for the purpose of improving the adhesion to the glass surface.
Examples of the silane coupling agent include a silane coupling agent having at least one functional group selected from the group consisting of an epoxy group, a vinyl group, an amino group, a (meth) acryloyl group, a styryl group, a mercapto group, and an isocyanate group. It is done. Of these, a silane coupling agent having an epoxy group is preferable.

The coating composition of the present invention may contain other resins other than the fluoroolefin copolymer (A).
Other resins include non-fluorinated resins such as acrylic resins, polyester resins, acrylic polyol resins, polyester polyol resins, urethane resins, acrylic silicone resins, silicone resins, alkyd resins, epoxy resins, oxetane resins, and fluoroolefin based copolymers. Fluorine resins other than the combined (A) can be mentioned. The other resin may be a resin that has a crosslinkable group and is cured by being crosslinked by the curing agent (B).
When mix | blending other resin with the coating composition of this invention, 1-200 mass parts is preferable with respect to 100 mass parts of fluoroolefin copolymer (A).

The coating composition of the present invention can be produced by mixing the above essential components and various additives added as necessary. The mixing order and addition order are not particularly limited.
The coating composition of the present invention can be produced using various equipment used for usual coating, such as a ball mill, paint shaker, sand mill, jet mill, rocking mill, attritor, three rolls, kneader.
As a method of coating using the coating composition of the present invention, any method such as spray coating, brush coating, dipping method, roll coater, flow coater and the like can be applied.

10-200 degreeC is preferable and, as for the curing temperature of the coating composition of this invention, 25-160 degreeC is more preferable.
When the curing temperature is 10 ° C. or higher, the crosslinking proceeds sufficiently and a tough multilayer coating film is easily obtained. In addition, the multimer (C) is hydrolyzed on the surface of the coating film, and the coating film surface tends to become hydrophilic. Moreover, if the curing temperature is 200 ° C. or lower, poor appearance of the coating film hardly occurs and the reflectance of the mirror does not decrease.
Although hardening time changes with hardening temperature, when hardening temperature is 25-160 degreeC, 5 minutes-24 hours are preferable.

  There is no restriction | limiting in particular as a heating method of the coating composition of this invention, The tunnel furnace etc. in which a sealing-type hardening furnace and continuous hardening are possible are mentioned. The heating source is not particularly limited and can be performed by a method such as hot air circulation, infrared heating, high-frequency heating or the like. Of these, from the viewpoint of continuous productivity, a tunnel furnace, and a method of obtaining a uniform and uniform cured film with heat transfer, hot air circulation and infrared heating are preferred.

  The thickness of the coating film is preferably 0.05 to 40 μm, and more preferably 0.1 to 10 μm. If the film thickness is equal to or greater than the lower limit, dirt is unlikely to adhere to the glass surface. If the film thickness is less than or equal to the upper limit, the reflectivity of the mirror is unlikely to decrease.

  When the coating composition of the present invention described above is used, a highly hydrophilic cured coating film layer (b) can be formed on the glass surface of the solar heat collecting reflector. The cured coating layer (b) is a highly hydrophilic coating in addition to improving weather resistance by containing fluorine atoms, and thus has a self-cleaning function over a long period of time.

[Reflector for solar heat collection]
The solar heat collecting reflector of the present invention is a mirror that reflects sunlight in a solar heat collecting system that collects solar heat and uses it as thermal energy.
FIG. 1 is a cross-sectional view showing an example of an embodiment of a solar heat collecting reflector (hereinafter simply referred to as “reflecting mirror”) according to the present invention.
As shown in FIG. 1, the reflecting mirror 10 includes a glass substrate 11, a metal layer 12 formed on the glass substrate 11, a cured coating film layer (a) 13 formed on the metal layer 12, and a glass substrate. On the opposite side of the metal layer 12 and the cured coating layer (a) 13, there is a cured coating layer (b) 14 formed by the coating composition of the present invention.

As the glass substrate 11, known glass for mirrors can be used, and examples thereof include soda lime glass. Since the solar heat collecting reflector is used outdoors such as in the desert and may be damaged by collision with sand or the like, tempered glass is preferable as the glass substrate.
As for the thickness of the glass substrate 11, 0.5-10 mm is preferable.

  The substrate for the solar heat collecting reflector may be a transparent substrate, and is not limited to a glass substrate, and other transparent substrates can be used as long as they have transparency. As the transparent substrate other than the glass substrate, a transparent resin substrate is preferable. For example, transparent resin substrates, such as an acrylic resin, a polycarbonate resin, and a polyester resin, are mentioned. The thickness of the transparent resin substrate is preferably 0.5 to 10 mm.

  The shape of the transparent substrate is not limited to a plate-like body having a flat surface, and may be a plate-like body having a curved surface or a molded body. It is preferable that the thickness of the plate-like body or the molded body is substantially constant. For example, a hemisphere, a semi-cylindrical body, a plate-like body having a paraboloid, and the like may be mentioned, and these reflecting surfaces may be inside or outside a curved surface.

The metal layer 12 is a metal layer having a role of reflecting sunlight. Examples of the metal forming the metal layer 12 include Ag.
As for the thickness of the metal layer 12, 300-1500 mg / m < ² > is preferable.

The cured coating film layer (a) 13 is a layer formed for preventing corrosion of the metal layer 12 and improving mechanical durability, and is generally formed of a coating called a back coating. As the back coating, a coating containing a metal compound imparting rust prevention and corrosion resistance and a resin binder such as an alkyd resin, an epoxy resin, or an acrylic resin is preferable.
The thickness of the cured coating layer (a) 13 is preferably 10 to 150 μm.
The cured coating layer (a) is provided on the side opposite to the glass substrate of the metal layer from the viewpoint of protecting the metal layer. Another layer may exist between the metal layer and the cured coating layer (a). As another layer, for example, a metal protective layer mainly composed of copper for the purpose of protecting the metal layer, or a layer composed of a silane coupling agent for improving the adhesion of the cured coating film layer (a). Etc.

[Manufacturing method of solar heat collecting reflector]
The reflecting mirror of the present invention can be manufactured by a known manufacturing method except that the coating composition of the present invention is used. Hereinafter, the manufacturing method of the reflecting mirror will be described as an example of the manufacturing method of the reflecting mirror of the present invention.
As a manufacturing method of the reflecting mirror, on the opposite side of the surface having the metal layer and the cured coating layer (a) of the glass substrate in which the metal layer and the cured coating layer (a) are laminated on one side, A method of forming the cured coating layer (b) by applying the coating composition of the invention to form a coating layer and curing it is mentioned.

Examples of the method for forming the metal layer on the glass substrate include an electroless plating method, a vacuum deposition method, and a sputtering method. The cured coating layer (a) on the metal layer can be formed by a known method using a back coating.
The coating composition of the present invention can be applied using a brush, roller, spray, flow coater, applicator or the like. What is necessary is just to select the application quantity of the coating composition of this invention suitably so that a dry film thickness may become in the said range. The temperature for thermosetting the coating composition of the present invention is preferably from room temperature to 200 ° C.

  The reflective mirror of the present invention described above has a cured coating film layer (b) that is formed of the coating composition of the present invention and has excellent weather resistance and high hydrophilicity. It has a function and can collect solar heat stably over a long period of time.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited by the following description.
Examples 1 to 3 are production examples, Example 4 is an example, and Example 5 is a comparative example.

<Production of fluoropolymer (A)>
[Example 1]
In a pressure resistant reactor with a stainless steel stirrer having an internal volume of 2500 mL, 590 g of xylene, 170 g of ethanol, 129 g of 4-hydroxybutyl vinyl ether (HBVE) which is monomer (a2-1), and monomer (a3) Charged with 206 g of ethyl vinyl ether (EVE) and 208 g of cyclohexyl vinyl ether (CHVE), 11 g of calcium carbonate, and 3.5 g of perbutyl perpivalate (PBPV), the dissolved oxygen in the liquid was removed by degassing with nitrogen. Removed.
Next, 660 g of fluoroolefin, chlorotrifluoroethylene (CTFE), was introduced, the temperature was gradually raised, and the reaction was continued while maintaining the temperature at 65 ° C. After reacting for 10 hours, the reaction was stopped by cooling the reactor with water. After cooling the reaction solution to room temperature, unreacted monomers were purged, and the resulting reaction solution was filtered through diatomaceous earth to remove solids. Next, part of xylene and ethanol were removed by distillation under reduced pressure to obtain a xylene solution (nonvolatile content 60%) of the fluoroolefin copolymer (A1).

<Manufacture of coating composition>
[Example 2]
To 100 g of the xylene solution (nonvolatile content 60%) of the fluoroolefin copolymer (A1) obtained in Example 1, an HDI nurate type polyisocyanate resin (manufactured by Nippon Polyurethane Co., Ltd., trade name) 10.7 g of "Coronate HX"), 5.0 g of ethyl silicate 48 (manufactured by Colcoat, tetraethoxysilane multimer) as a multimer (C), 100 g of xylene, and a curing catalyst (D) Dibutyltin dilaurate (diluted 4 to 10 times with xylene to 3 g) and 0.1 g of aluminum tris (acetylacetonate) were added and mixed to obtain a coating composition I.

[Example 3]
To 100 g of the xylene solution (nonvolatile content 60%) of the fluoroolefin copolymer (A1) obtained in Example 1, an HDI nurate type polyisocyanate resin (manufactured by Nippon Polyurethane Co., Ltd., trade name) 10.7 g of “Coronate HX”), 100 g of xylene, and dibutyltin dilaurate as a curing catalyst (D) (diluted 4 to 10 times with xylene to 3 g) are mixed and mixed. Composition II was obtained.

<Manufacture and evaluation of solar heat collecting reflectors>
[Example 4]
One side of the glass substrate is subjected to silver plating treatment so that the thickness becomes 800 mg / m ² , and then a lead-free epoxy resin-based back coating for mirrors (Dainippon Paint Co., Ltd.) on the silver plating film “SM trade name COAT DF”) was applied with a curtain flow coater so that the film thickness of the dried coating film was 60 μm, and cured in a drying furnace at 180 ° C. Then, the reflective mirror with a rust prevention hardening coating film was obtained by cooling to room temperature with a cooler.
Next, the coating composition I obtained in Example 2 was applied on the sunlight incident surface of the reflector with a rust-proof cured coating film so as to have a film thickness of 5 μm and dried in an oven at 150 ° C. for 20 minutes. By curing and forming a cured coating layer, a solar heat collecting reflector for testing was obtained.

[Example 5]
A solar heat collecting reflector was obtained in the same manner as in Example 4 except that the coating composition II was used instead of the coating composition I.
An actual exposure test was carried out on the solar heat collecting reflectors obtained in [Example 4] and [Example 5].

(Actual exposure test)
A solar heat collecting reflector was installed outdoors in Naha City, Okinawa Prefecture, and the degree of contamination on the glass surface was evaluated by comparing just before and after one year.
1. The degree of dirt on the glass surface The degree of dirt on the glass surface was evaluated according to the following criteria.
“O”: No sand, earth, or mud adheres to the glass surface.
“×”: Sand, soil, or mud is attached to the glass surface.

  The evaluation results of Example 4 and Example 5 are shown in Table 1.

  As shown in Table 1, in Example 4 using the coating composition of the present invention, dirt on the glass surface was adhered as compared to Example 5 using the coating composition containing no multimer (C). There wasn't.

  10; reflector 11; glass substrate 12; metal layer 13; cured coating layer (a) 14; cured coating layer (b))

Claims (2)

A solar heat collecting reflector coating composition containing the following (A) to (C).
(A) a fluoroolefin copolymer having at least one crosslinkable functional group selected from the group consisting of a hydroxyl group, a carboxy group, an amino group, an epoxy group, an oxetanyl group, an alkoxysilyl group and an isocyanate group;
(B) at least one curing agent selected from the group consisting of an isocyanate curing agent, a blocked isocyanate curing agent and an amino resin,
(C) Multimer of tetrafunctional hydrolyzable silane compound   From the glass coating composition according to claim 1, on the solar light incident surface side of the solar heat collecting reflector laminated in the order of the glass substrate, the metal layer reflecting sunlight, and the cured coating layer (a). A solar heat collecting reflector having the formed cured coating layer (b).