Transparent coatings, laminates, and solar cell protective covers

Abstract

To provide a transparent coating that can form a hardened coating layer with excellent flame retardancy, transparency, and weather resistance. [Solution] The transparent coating contains a curable fluororesin (A), a flame retardant (B), and a curing agent (C). The flame retardant (B) is dissolved in butyl acetate and xylene, respectively, at a temperature of 23°C, at an active ingredient concentration of 10% by mass or more.

Description

[Technical Field]

[0001] This disclosure relates to transparent coatings, laminates, and solar cell protective covers. [Background technology]

[0002] It is known that resin is used as the surface coating material for solar cell modules. Patent Document 1 discloses the use of fluororesin as the coating material in order to obtain a flame-retardant coating material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-302925 [Overview of the project] [Problems that the invention aims to solve]

[0004] This disclosure aims to provide a transparent coating capable of forming a hardened coating layer with excellent flame retardancy, transparency, and weather resistance. Furthermore, this disclosure aims to provide a laminate and a solar cell protective cover with excellent flame retardancy, transparency, and weather resistance. [Means for solving the problem]

[0005] This disclosure relates to a transparent coating comprising a curable fluororesin (A), a flame retardant (B), and a curing agent (C), characterized in that the flame retardant (B) dissolves in butyl acetate and xylene, respectively, at a temperature of 23°C, at an active ingredient concentration of 10% by mass or more.

[0006] Preferably, the flame retardant (B) is an organophosphate ester represented by the following formula (1) or a polymer thereof, and the molecular weight of the flame retardant (B) is 1000 or less.

[0007] [ka]

[0008] In the above formula (1), R , , , , , , , , is a group represented by the following formula (2) or (3), and R 2 , R 3 , R 4 , and R 5 are each independently a substituted or unsubstituted aromatic hydrocarbon group.

[0009]

Chemical formula

[0010] It is preferable that the content of the flame retardant (B) is 5% by mass or more and 40% by mass or less with respect to the solid content of the curable fluororesin (A) in the transparent paint. The curable fluororesin (A) has units derived from fluorine-containing monomers, and it is preferable that the fluorine-containing monomer is at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, 2,3,3,3-tetrafluoropropene, and 1,3,3,3-tetrafluoropropene. It is preferable that the acid value of the curable fluororesin (A) is 35 mgKOH / g or less, and the hydroxyl value of the curable fluororesin (A) is 29 mgKOH / g or more and 150 mgKOH / g or less. It is preferable that the curing agent (C) is an isocyanate-based curing agent or an amino resin-based curing agent. It is preferable that the transparent paint further contains an ultraviolet absorber (D). It is preferable that the transparent paint is a paint for a solar cell protection cover provided on the sunlight irradiation surface side of the solar cell. The curable fluororesin (A) has units derived from fluorine-containing monomers and units derived from curable functional group-containing monomers, the fluorine-containing monomer is tetrafluoroethylene, the flame retardant (B) is an organic phosphate ester represented by the above formula (1) or a multimer thereof, ​The molecular weight of the flame retardant (B) is 500 or more and 1000 or less. The amount of the flame retardant (B) is 5% by mass or more and 40% by mass or less relative to the solid content of the curable fluororesin (A) in the transparent coating. It is preferable that the curing agent (C) is an isocyanate-based curing agent or an amino resin-based curing agent.

[0011] This disclosure also relates to a laminate comprising a transparent substrate and a transparent layer provided on the transparent substrate, wherein the transparent layer is a hardened coating layer of the transparent paint described above.

[0012] It is preferable that the total light transmittance of the laminate is 85% or more. It is preferable that the thickness of the hardened coating layer is 10 μm or more and 100 μm or less. The transparent substrate is preferably a polyethylene terephthalate substrate, a polycarbonate substrate, an acrylic resin substrate, or a fluororesin substrate. It is preferable that the total light transmittance of the transparent substrate is 85% or more. It is preferable that the hardened coating layer is provided directly on the transparent substrate. Preferably, one or both sides of the transparent substrate are subjected to corona treatment or plasma treatment.

[0013] This disclosure relates to a solar cell protective cover provided on the solar light irradiation side of a solar cell, wherein the solar cell protective cover comprises the laminate described above. [Effects of the Invention]

[0014] The transparent coatings of this disclosure can form a hardened coating layer with excellent flame retardancy, transparency, and weather resistance. The laminates and solar cell protective covers of this disclosure also exhibit excellent flame retardancy, transparency, and weather resistance. [Modes for carrying out the invention]

[0015] The details of this disclosure are described below.

[0016] [Transparent paint] This disclosure relates to a transparent coating. The transparent coating of this disclosure is particularly suitable for use in the manufacture of solar cell protective covers. In order to ensure the flame retardancy of solar cell protective covers, it is known that fluororesin is used as a coating material as a conventional method. In order to reduce the weight of solar cells, it is desirable to be able to ensure sufficient flame retardancy of the solar cell protective cover even when the fluororesin layer is thin. However, when attempting to incorporate a flame retardant into the fluororesin in order to ensure sufficient flame retardancy, a problem arises in that clouding occurs during mixing, reducing the transparency of the fluororesin layer.

[0017] Therefore, the transparent coating of this disclosure comprises a curable fluororesin (A), a flame retardant (B), and a curing agent (C). By including a flame retardant (B) in addition to the curable fluororesin (A), the cured coating layer formed by the transparent coating of this disclosure exhibits even greater flame retardancy. Furthermore, the flame retardant (B) contained in the transparent coating of this disclosure dissolves in butyl acetate and xylene, respectively, at a temperature of 23°C, at an active ingredient concentration of 10% by mass or more. By using such a flame retardant (B), the flame retardant (B) and the curable fluororesin (A) are suitably compatible without clouding, and a decrease in the transparency of the cured coating layer can be suppressed. Therefore, the cured coating layer formed by the transparent coating of this disclosure can achieve both transparency and flame retardancy.

[0018] Furthermore, the transparent coatings disclosed herein also have the advantage of forming a weather-resistant hardened coating layer. Here, a glass substrate is used as the substrate for the solar cell protective cover, but in recent years, the use of a resin substrate has also been considered for weight reduction. The above advantages can be obtained regardless of which substrate the hardened coating layer is formed on, but they are particularly noticeable when forming a hardened coating layer on a resin substrate that is susceptible to the effects of sunlight, especially a hydrocarbon-based resin substrate.

[0019] As described above, the transparent coating of this disclosure can form a hardened coating layer with excellent flame retardancy, transparency, and weather resistance. Because the transparent coating of this disclosure can form a hardened coating layer with excellent flame retardancy, solar cells equipped with solar cell protective covers manufactured using this transparent coating can be safely installed in houses and other buildings. Furthermore, because the transparent coating of this disclosure can form a hardened coating layer with excellent transparency, solar cells equipped with solar cell protective covers manufactured using this transparent coating transmit sunlight well, resulting in good power generation efficiency. In addition, because the transparent coating of this disclosure can form a hardened coating layer with excellent weather resistance, solar cells equipped with solar cell protective covers manufactured using this transparent coating can be used for a long period of several decades. For these reasons, the transparent coating of this disclosure is particularly suitable for use in the manufacture of solar cell protective covers. However, the applications of the transparent coating of this disclosure are not limited to solar cell protective covers. The transparent coating of this disclosure can be suitably used in applications other than solar cell protective covers where flame retardancy, transparency, and weather resistance are desirable. Other applications will be described later.

[0020] As described above, the transparent coating of this disclosure comprises a curable fluororesin (A), a flame retardant (B), and a curing agent (C). The flame retardant (B) dissolves in butyl acetate and xylene at a temperature of 23°C at an active ingredient concentration of 10% by mass or more. In other words, the flame retardant (B) dissolves in butyl acetate at a temperature of 23°C at an active ingredient concentration of 10% by mass or more, and the flame retardant (B) also dissolves in xylene at a temperature of 23°C at an active ingredient concentration of 10% by mass or more.

[0021] Hereinafter, "dissolving in butyl acetate and xylene at a temperature of 23°C at a concentration of 10% by mass or more of the active ingredient" may be described as "having a specified solubility."

[0022] <Curing type fluororesin (A)> The transparent coatings of this disclosure include a curable fluororesin (A). The curable fluororesin (A) is a fluororesin having a curable functional group. Examples of curable functional groups include hydroxyl groups (excluding hydroxyl groups contained in carboxyl groups; the same applies hereinafter), carboxyl groups, groups represented by -COOCO-, amino groups, glycidyl groups, silyl groups, silanate groups, isocyanate groups, and the like. The curable functional group is appropriately selected in accordance with the ease of manufacturing the fluororesin and the curing system. Among these, hydroxyl groups, carboxyl groups, groups represented by -COOCO-, amino groups, and silyl groups are preferred as curable functional groups in terms of good curing reactivity. Hydroxyl groups and carboxyl groups are preferred as curable functional groups in terms of the ease of obtaining the fluororesin and good curing reactivity. The curable fluororesin (A) may have one or more curable functional groups.

[0023] The curable fluororesin (A) has at least units derived from a fluorine-containing monomer (A1) (hereinafter sometimes referred to as "fluorine-containing monomer (A1) units"). Curable functional groups are introduced into the fluororesin, for example, by copolymerizing a fluorine-containing monomer (A1) with a curable functional group-containing monomer (A2). The curable fluororesin (A) obtained by the above copolymerization includes, for example, fluorine-containing monomer (A1) units and units derived from a curable functional group-containing monomer (A2) (hereinafter sometimes referred to as "curable functional group-containing monomer (A2) units"). If the fluorine-containing monomer (A1) has a curable functional group, the fluorine-containing monomer (A1) also functions as the curable functional group-containing monomer (A2), so the addition of the curable functional group-containing monomer (A2) may be omitted during copolymerization.

[0024] <Fluorine-containing monomer (A1)> Examples of fluorine-containing monomers (A1) include tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), hexanefluoropropylene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, vinylidene fluoride (VdF), vinyl fluoride (VF), and fluorovinyl ether. One or more of these fluorine-containing monomers (A1) can be used.

[0025] In particular, in terms of improving flame retardancy and weather resistance, the fluorine-containing monomer (A1) is preferably at least one selected from the group consisting of TFE, CTFE, hexanefluoropropylene, 2,3,3,3-tetrafluoropropene, and 1,3,3,3-tetrafluoropropene, and more preferably TFE.

[0026] <Curable functional group-containing monomer (A2)> Examples of curable functional group-containing monomers (A2) include hydroxyl group-containing monomers, carboxyl group-containing monomers, acid anhydride monomers, amino group-containing monomers, and silicone-based vinyl monomers. One or more curable functional group-containing monomers (A2) can be used.

[0027] The curable fluororesin (A) comprises fluorine-containing monomer (A1) units and curable functional group-containing monomer (A2) units, wherein the curable functional group-containing monomer (A2) units are preferably at least one monomer unit selected from the group consisting of hydroxyl group-containing monomers, carboxyl group-containing monomers, acid anhydride monomers, amino group-containing monomers, and silicone-based vinyl monomers.

[0028] (Hydroxyl group-containing monomer) Examples of hydroxyl group-containing monomers include hydroxyl group-containing vinyl ethers such as hydroxyethyl vinyl ether (e.g., 2-hydroxyethyl vinyl ether), 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, hydroxybutyl vinyl ether (e.g., 4-hydroxybutyl vinyl ether), 4-hydroxy-2-methylbutyl vinyl ether, 5-hydroxypentyl vinyl ether, and 6-hydroxyhexyl vinyl ether; hydroxyl group-containing allyl ethers such as 2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, and glycerol monoallyl ether; and hydroxyalkyl esters of (meth)acrylic acid such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. Among these, hydroxyl group-containing vinyl ethers are preferred as hydroxyl group-containing monomers due to their excellent polymerization reactivity and curability of functional groups, with hydroxybutyl vinyl ether and hydroxyethyl vinyl ether being more preferred, and 4-hydroxybutyl vinyl ether and 2-hydroxyethyl vinyl ether being even more preferred. Note that carboxyl group-containing monomers, as described later, are not included in the hydroxyl group-containing monomers.

[0029] (carboxyl group-containing monomer) Examples of carboxyl group-containing monomers include unsaturated carboxylic acids, carboxyl group-containing vinyl ether monomers, and alkenyl esters of polybasic carboxylic acids.

[0030] Examples of unsaturated carboxylic acids include unsaturated monocarboxylic acids, unsaturated dicarboxylic acids, and their monoesters. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, vinyl acetic acid, crotonic acid, cinnamic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, and fumaric acid monoester. Among these, crotonic acid, itaconic acid, maleic acid, maleic acid monoester, fumaric acid, and fumaric acid monoester are preferred as unsaturated carboxylic acids due to their low homopolymerizability and difficulty in forming homopolymers.

[0031] Examples of carboxyl group-containing vinyl ether monomers include 3-allyloxypropionic acid, 3-(2-alyroxyethoxycarbonyl)propionic acid, 3-(2-alyroxybutoxycarbonyl)propionic acid, 3-(2-vinyloxyethoxycarbonyl)propionic acid, and 3-(2-vinyloxybutoxycarbonyl)propionic acid. Among these, 3-(2-alyroxyethoxycarbonyl)propionic acid is preferred due to its good monomer stability and polymerization reactivity.

[0032] Examples of alkenyl esters of polybasic carboxylic acids include vinyl phthalate and vinyl pyromellitic acid.

[0033] (acid anhydride monomer) Examples of acid anhydride monomers include unsaturated dicarboxylic acid anhydrides such as maleic anhydride.

[0034] (Amino group-containing monomer) Examples of monomers containing an amino group include CH2=CH-O-(CH2) x Amino vinyl ethers represented by -NH2 (x=0~10); CH2=CH-O-CO(CH2) x Examples include amines represented by -NH2(x=1~10); aminomethylstyrene; vinylamine; acrylamide; vinylacetamide; vinylformamide, etc.

[0035] (Silicone-based vinyl monomer) Examples of silicone vinyl monomers include silicone (meth)acrylic acid esters, vinylsilanes, and silicone vinyl ethers.

[0036] Examples of silicone-based (meth)acrylic acid esters include CH2=CHCO2(CH2)3Si(OCH3)3, CH2=CHCO2(CH2)3Si(OC2H5)3, CH2=C(CH3)CO2(CH2)3Si(OCH3)3, CH2=C(CH3)CO2(CH2)3Si(OC2H5)3, CH2=CHCO2(CH2)3SiCH3(OC2H5)2, CH2=C(CH3)CO2(CH2)3SiC2H5(OCH3)2, CH2=C(CH3)CO2(CH2)3Si( CH3)2(OC2H5), CH2=C(CH3)CO2(CH2)3Si(CH3)2OH, CH2=CH(CH2)3Si(OCOCH3)3, CH2=C(CH3)CO2(CH2)3SiC2H5(OCOCH3)2, CH2=C(CH3 )CO2(CH2)3SiCH3(N(CH3)COCH3)2, CH2=CHCO2(CH2)3SiCH3[ON(CH3)C2H5]2, CH2=C(CH3)CO2(CH2)3SiC6H5[ON(CH3)C2H5]2, etc.

[0037] Examples of vinylsilanes include vinyltrichlorosilane and its partial hydrolysates. Specific examples of vinylsilanes include CH2=CHSi[ON=C(CH3)(C2H5)]3, CH2=CHSi(OCH3)3, CH2=CHSi(OC2H5)3, CH2=CHSiCH3(OCH3)2, CH2=CHSi(OCOCH3)3, CH2=CHSi(CH3)2(OC2H5), CH2=CHSi(CH3)2SiCH3(OCH3)2, CH2=CHSiC2H5(OCOCH3)2, CH2=CHSiCH3〔ON(CH3)C2H5〕2, vinyltrichlorosilane, and their partial hydrolysates.

[0038] Examples of silicone-based vinyl ethers include trimethoxysilylethyl vinyl ether, triethoxysilylethyl vinyl ether, trimethoxysilylbutyl vinyl ether, methyldimethoxysilylethyl vinyl ether, trimethoxysilylpropyl vinyl ether, and triethoxysilylpropyl vinyl ether.

[0039] <Other monomers (A3)> For copolymerization of the curable fluororesin (A), only a fluorine-containing monomer (A1) and a monomer containing a curable functional group (A2) may be used, or other monomers (A3) copolymerizable with these may be used in addition. Examples of other copolymerizable monomers (A3) include vinyl carboxylate esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caproate, vinyl versaticate, vinyl laurate, vinyl stearate, vinyl cyclohexylcarboxylate, vinyl benzoate, and p-t-butylbenzoate vinyl; alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, and cyclohexyl vinyl ether; and fluorine-free olefins such as ethylene, propylene, n-butene, and isobutene. One or more of the other monomers (A3) can be used.

[0040] The above describes fluorine-containing monomers (A1), monomers containing curable functional groups (A2), and other monomers (A3). Below, we will further describe curable fluororesins (A).

[0041] Examples of curable fluororesins (A) include the resins shown in (1) to (4) below. Among these, the perfluoroolefin resin shown in (1) below is preferred due to its excellent weather resistance and moisture resistance. (1) Perfluoroolefin resins mainly composed of perfluoroolefin units (2) CTFE-based resins mainly composed of CTFE units (3) VdF-based resins mainly composed of VdF units (4) Fluoroalkyl group-containing resins mainly composed of fluoroalkyl units

[0042] First, the perfluoroolefin resins shown in (1) above will be described. In terms of excellent weather resistance, copolymerizability, and chemical resistance, TFE-based resins are preferred as perfluoroolefin resins. Examples of TFE-based resins include copolymers of TFE and other monomers (A3); copolymers of TFE and at least one of hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE), VdF, CTFE, VF, and fluorovinyl ether; and copolymers of TFE and at least one of hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE), VdF, CTFE, VF, and fluorovinyl ether with other monomers (A3).

[0043] Examples of perfluoroolefin resins having curable functional groups include copolymers of TFE / isobutylene / hydroxybutyl vinyl ether / other monomers (A3), copolymers of TFE / vinyl versatate / hydroxybutyl vinyl ether / other monomers (A3), and copolymers of TFE / VdF / hydroxybutyl vinyl ether / other monomers (A3).

[0044] Examples of TFE-based curing resins include the Zeffle GK series manufactured by Daikin Industries, Ltd.

[0045] Next, the CTFE-based resins shown in (2) above will be described. Examples of CTFE-based resins include copolymers of CTFE / hydroxybutyl vinyl ether / other monomers (A3). Examples of CTFE-based curable resins include Lumiflon manufactured by AGC Inc. and Eternal manufactured by Changxing Chemical Industry Co., Ltd.

[0046] Next, the VdF-based resins shown in (3) above will be described. Examples of VdF-based resins include copolymers of VdF / TFE / hydroxybutyl vinyl ether / other monomers (A3).

[0047] Next, the fluoroalkyl group-containing resins shown in (4) above will be described. Examples of fluoroalkyl group-containing resins include CF3CF2 (CF2CF2) n Examples include CH2CH2OCOCH=CH2 (a mixture of n=3 and n=4) / 2-hydroxyethyl methacrylate / stearyl acrylate copolymers. Examples of fluoroalkyl group-containing resins include Unidyne and F-Tone manufactured by Daikin Industries, Ltd., and Zonyl manufactured by DuPont.

[0048] In terms of good compatibility with the curing agent (C), the acid value of the curable fluororesin (A) is preferably 35 mgKOH / g or less, more preferably 28.8 mgKOH / g or less, even more preferably 12 mgKOH / g or less, and most preferably 5 mgKOH / g or less.

[0049] The acid value of the curable fluororesin (A) is not particularly limited in its lower limit and may be 0.0 mg KOH / g or higher. In terms of improving the adhesion of the transparent coating to the substrate and having good compatibility with the curing agent (C), the acid value of the curable fluororesin (A) is preferably 0.6 mg KOH / g or higher, and more preferably 2 mg KOH / g or higher.

[0050] In terms of improving affinity with solvents, the hydroxyl value of the curable fluororesin (A) is preferably 180 mg KOH / g or less, more preferably 170 mg KOH / g or less, even more preferably 160 mg KOH / g or less, and particularly preferably 150 mg KOH / g or less.

[0051] In terms of improving the adhesion of the transparent coating to the substrate and improving the curing reactivity with the curing agent (C), the hydroxyl value of the curable fluororesin (A) is preferably 29 mg KOH / g or more, more preferably 40 mg KOH / g or more, and even more preferably 50 mg KOH / g or more.

[0052] The acid value of curable fluororesin (A) can be measured by acid-base titration using a basic substance. The hydroxyl value of curable fluororesin (A) can be calculated from the weight of curable fluororesin (A) and the number of moles of -OH groups. The number of moles of -OH groups can be determined by NMR measurement, IR measurement, titration, elemental analysis, etc.

[0053] Curable fluororesin (A) can be produced by copolymerizing a fluorine-containing monomer (A1), a monomer containing a curable functional group (A2), and any other monomer (A3) using conventionally known methods.

[0054] The content of the curable fluororesin (A) is preferably 20% by mass or more and 90% by mass or less, relative to the total amount of nonvolatile matter in the transparent coating. When the transparent coating of this disclosure is a solvent-type coating, the concentration of the curable fluororesin (A) relative to the total amount of the transparent coating is preferably 5 to 95% by mass, and more preferably 10 to 70% by mass.

[0055] <Flame retardant (B)> The transparent coating of this disclosure contains a flame retardant (B), which enables the formation of a coating film cured layer with excellent flame retardancy. Furthermore, by using a flame retardant (B) having predetermined solubility, the flame retardant (B) and the curable fluororesin (A) are suitably compatible without clouding, and a decrease in the transparency of the coating film cured layer can be suppressed.

[0056] Whether or not the flame retardant (B) has the required solubility can be confirmed by the following method. First, under conditions of 23°C, weigh 3.5 g of butyl acetate into a 10 mL glass screw-top bottle, add an amount of flame retardant (B) to the butyl acetate that results in an active ingredient concentration of 10% by mass or more, close the lid, and shake by hand for 10 minutes to obtain the evaluation solution. Visually check the appearance of the evaluation solution, and if the appearance is clear (transparent), it is determined that the flame retardant (B) has dissolved into the butyl acetate. Next, under conditions of 23°C, weigh 3.5 g of xylene into a 10 mL glass screw-top bottle, add an amount of flame retardant (B) to the xylene that results in an active ingredient concentration of 10% by mass or more, close the lid, and shake by hand for 10 minutes to obtain the evaluation solution. Visually check the appearance of the evaluation solution, and if the appearance is clear (transparent), it is determined that the flame retardant (B) has dissolved into the xylene. A flame retardant (B) that is soluble in both butyl acetate and xylene is determined to have the required solubility.

[0057] In terms of forming a good transparent coating film, it is preferable that the flame retardant (B) dissolves in butyl acetate and xylene at a temperature of 23°C at an active ingredient concentration of 20% by mass or more, and more preferably 30% by mass or more. There is no particular upper limit, but in terms of ease of manufacture, the flame retardant (B) may dissolve in butyl acetate and xylene at a temperature of 23°C at an active ingredient concentration of 80% by mass or less.

[0058] The flame retardant (B) is not particularly limited as long as it has the required solubility. Examples of flame retardants (B) include phosphorus-based flame retardants, halogen-based flame retardants, nitrogen-based flame retardants, silicone-based flame retardants, etc. One or more types of flame retardants (B) can be used.

[0059] In terms of suppressing the decrease in transparency of the coating film hardening layer, as the flame retardant (B), a phosphorus-based flame retardant is preferable, an organic phosphate ester-based flame retardant is more preferable, and an organic phosphate ester represented by the following formula (1) or its multimer is even more preferable. Hereinafter, the "organic phosphate ester represented by formula (1)" may be referred to as compound (1). Compound (1) and its multimer are excellent in solubility in each of butyl acetate and xylene, and thus tend to be preferably compatible with the curable fluororesin (A) without becoming turbid.

[0060]

Chemical formula

[0061] In formula (1), R 1 is a divalent group derived from a compound selected from the group consisting of hydroquinone, resorcinol, catechol, bis(4-hydroxydiphenyl)methane, bisphenol A, dihydroxydiphenyl, dihydroxynaphthalene, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)ketone, and bis(4-hydroxyphenyl)sulfide. The divalent group derived from these compounds means a group in which two hydroxyl groups of these compounds are both replaced by bonds.

[0062] In formula (1), R 1 is preferably a group represented by the following formula (2) or formula (3). In formula (2) and formula (3), * represents a bond. The group represented by formula (2) corresponds to a divalent group derived from hydroquinone when the bond is located at the 4-position of the phenyl group, corresponds to a divalent group derived from resorcinol when the bond is located at the 3-position of the phenyl group, and corresponds to a divalent group derived from catechol when the bond is located at the 2-position of the phenyl group. As the group represented by formula (2), a divalent group derived from resorcinol is preferable. The group represented by formula (3) corresponds to a divalent group derived from bisphenol A. In formula (1), R 1 may be a group having no halogen atom.

[0063] [ka]

[0064] In formula (1), R 2 , R 3 , R 4 , and R 5 Each of these is independently a substituted or unsubstituted aromatic hydrocarbon group. The aromatic hydrocarbon group may be a monocyclic group or a fused ring group. The number of carbon atoms in the aromatic hydrocarbon group is, for example, 6 to 14. Examples of aromatic hydrocarbon groups include phenyl, naphthyl, phenantrenyl, and anthryl groups. In terms of increasing the solubility of butyl acetate and xylene, aromatic hydrocarbon groups with 6 to 10 carbon atoms are preferred, and phenyl groups are more preferred.

[0065] When the aromatic hydrocarbon group has substituents, examples of such substituents include C1-C6 alkyl groups and C1-C6 alkyl groups substituted with phenyl groups. The above C1-C6 alkyl groups may be linear or branched. Examples of C1-C6 alkyl groups include methyl, ethyl, propyl, butyl, pentyl, and hexyl groups. In terms of increasing solubility in butyl acetate and xylene, C1-C4 alkyl groups are preferred as C1-C6 alkyl groups, and methyl, propyl (e.g., isopropyl), and butyl groups are more preferred. When the aromatic hydrocarbon group has substituents, the number of substituents is 1 to 5, and preferably 1 or 2. In formula (1), R 2 , R 3 , R 4 , and R 5 This group may not contain a halogen atom.

[0066] R 2 , R 3 , R 4 , and R 5 The unsubstituted aromatic hydrocarbon group represented by is preferably a phenyl group. 2 , R 3 , R 4, and R 5 The substituted aromatic hydrocarbon group represented by is preferably a methylphenyl group, a dimethylphenyl group (e.g., a 2,6-dimethylphenyl group), an isopropylphenyl group, and a butylphenyl group.

[0067] Compound (1) is particularly preferred if it is represented by formulas (1-1) and (1-2) because it exhibits excellent solubility in both butyl acetate and xylene, and is suitably compatible with curable fluororesin (A) without causing turbidity. As a commercially available product of the compound represented by formula (1-1), PX-200 manufactured by Daihachi Chemical Industry Co., Ltd. can be used. As a commercially available product of the compound represented by formula (1-2), CR-741 manufactured by Daihachi Chemical Industry Co., Ltd., FP-600 manufactured by ADEKA Corporation, etc. can be used.

[0068] [ka]

[0069] [ka]

[0070] The polymer of compound (1) is, for example, the compound represented by formula (4).

[0071] [ka]

[0072] R in equation (4) 11 , R 12 , R 13 , R 14 , and R 15 R in equation (1) 1 , R 2 , R 3 , R 4 , and R 5This is synonymous with the following: n represents the number of repeating structural units of the polymer. n is preferably a number greater than 1 and less than or equal to 5. The flame retardant (B) may be a mixture of polymers of phosphate esters with different n numbers. In the case of a mixture of polymers of phosphate esters with different n numbers, n represents the average value of the different n numbers. In terms of improving solubility in butyl acetate and xylene, it is preferable to appropriately select the n number such that the molecular weight of the flame retardant (B) is 1000 or less.

[0073] Compound (4) is particularly preferred if it is represented by formula (4-1) because it has excellent solubility in both butyl acetate and xylene, and is suitably compatible with curable fluororesin (A) without causing turbidity.

[0074] [ka]

[0075] In terms of improving solubility in butyl acetate and xylene, the molecular weight of flame retardant (B) is preferably 1000 or less. The molecular weight of flame retardant (B) is not particularly limited to a lower limit, but in terms of adjusting the solubility in butyl acetate and xylene to a suitable range, it is preferably 100 or more, more preferably 200 or more, even more preferably 300 or more, even more preferably 400 or more, even more preferably 450 or more, and particularly preferably 500 or more. The molecular weight of flame retardant (B) can be determined from the chemical formula of flame retardant (B).

[0076] In terms of forming a coating film cured layer with excellent flame retardancy, the content of the flame retardant (B) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more, relative to the solid content of the cured fluororesin (A) in the transparent coating.

[0077] In terms of suppressing a decrease in the transparency of the cured coating layer, the content of the flame retardant (B) is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, relative to the solid content of the cured fluororesin (A) in the transparent coating. In this disclosure, the content of the flame retardant (B) relative to the solid content of the cured fluororesin (A) (unit: mass%) corresponds to the content of the flame retardant (B) per 100 parts by mass of the solid content of the cured fluororesin (A) (unit: parts by mass).

[0078] <Hardening agent (C)> The transparent coating of this disclosure contains a curing agent (C), which allows for the formation of a hardened coating layer using the transparent coating of this disclosure. Specifically, a hardened coating layer is formed by a curing reaction between the hardened fluororesin (A) and the curing agent (C) in the transparent coating of this disclosure. Examples of the curing agent (C) include isocyanate-based curing agents, amino resin-based curing agents, epoxy-based curing agents, carbonyl group-containing curing agents, and acid anhydride-based curing agents. One or more types of curing agents (C) can be used.

[0079] The curing agent (C) can be appropriately selected according to the curable functional group of the curable fluororesin (A). If the curable functional group is a hydroxyl group, the curing agent (C) is preferably an isocyanate-based curing agent or an amino resin-based curing agent.

[0080] Isocyanate-based curing agents are compounds having isocyanate groups. Examples of isocyanate-based curing agents include polyisocyanates. In this disclosure, polyisocyanate means a compound having two or more isocyanate groups in its molecule.

[0081] Examples of polyisocyanates include diisocyanates. Diisocyanates are not particularly limited, but examples include diisocyanates in which an isocyanate group is bonded to an aliphatic group, such as trimethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, norbornane diisocyanate; and diisocyanates in which an isocyanate group is bonded to an aromatic group, such as tolylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, tollidine diisocyanate, and naphthalene diisocyanate.

[0082] The isocyanate-based curing agent may be a polyisocyanate obtained by trimerizing diisocyanate. Alternatively, the polyisocyanate, which is a trimer of diisocyanate, may exist as a polymer formed by the polymerization of these.

[0083] As an isocyanate-based curing agent, polyisocyanates having an isocyanurate structure are preferred. Polyisocyanates having an isocyanurate structure may also be polymers obtained by polymerization of such polyisocyanates. Polyisocyanates having an isocyanurate structure may be monocyclic compounds having only one isocyanurate ring, or they may be polycyclic compounds obtained by polymerization of such monocyclic compounds.

[0084] Specific examples of isocyanate-based curing agents include 2,4-tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, lysine methyl ester diisocyanate, methylcyclohexyl diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, n-pentane-1,4-diisocyanate, trimers thereof, adducts thereof, biurets thereof, isocyanurates thereof, polymers thereof having two or more isocyanate groups, and further blocked isocyanates.

[0085] Examples of commercially available isocyanate-based curing agents include: Sumijoul N3300 (manufactured by Sumika Covestro Urethane Co., Ltd.), Desmodule N3600 (manufactured by Sumika Covestro Urethane Co., Ltd.), Desmodule T, L, IL, HL series (manufactured by Sumika Covestro Urethane Co., Ltd.), Desmodule 2460M (manufactured by Sumika Covestro Urethane Co., Ltd.), Sumijoul 44 series (manufactured by Sumika Covestro Urethane Co., Ltd.), SBU Isocyanate series (manufactured by Sumika Covestro Urethane Co., Ltd.), Desmodule E, M series (manufactured by Sumika Covestro Urethane Co., Ltd.), Sumijoul HT (manufactured by Sumika Covestro Urethane Co., Ltd.), Desmodule N series (manufactured by Sumika Covestro Urethane Co., Ltd.), Desmodule Z4470 series (manufactured by Sumika Covestro Urethane Co., Ltd.), and Duranate TPA-1. 00 (manufactured by Asahi Kasei Corporation), Duranate TKA-100 (manufactured by Asahi Kasei Corporation), Duranate 24A-100 (manufactured by Asahi Kasei Corporation), Duranate 22A-75P (manufactured by Asahi Kasei Corporation), and Duranate P301-75E (manufactured by Asahi Kasei Corporation), Duranate MF-K60B (manufactured by Asahi Kasei Corporation), Duranate SBB-70P (manufactured by Asahi Kasei Corporation), Duranate SBN-70D (manufactured by Asahi Kasei Corporation) Examples include (manufactured by Asahi Kasei Corporation), Duranate MF-B60B (manufactured by Asahi Kasei Corporation), Duranate 17B-60P (manufactured by Asahi Kasei Corporation), Duranate TPA-B80E (manufactured by Asahi Kasei Corporation), Duranate E402-B80B (manufactured by Asahi Kasei Corporation), Duranate WM44-L70G (manufactured by Asahi Kasei Corporation), Duranate TLA-100 (manufactured by Asahi Kasei Corporation), Coronate HX (manufactured by Tosoh Corporation), etc.

[0086] Amino resin-based curing agents are curing agents that contain amino resins. Examples of amino resin-based curing agents include urea resins, melamine resins, benzoguanamine resins, glycoluryl resins, methylolated melamine resins (melamine obtained by methylolating melamine), and alkyl etherated melamine resins (methylolated melamine obtained by etherating methylolated melamine with alcohols such as methanol, ethanol, and butanol).

[0087] The content of the curing agent (C) is preferably 0.1 to 5 equivalents, more preferably 0.5 to 1.5 equivalents, per equivalent of the curable functional group in the curable fluororesin (A). Furthermore, the content of the curing agent (C) is preferably 0.1 to 50 parts by mass, more preferably 10 to 40 parts by mass, and even more preferably 15 to 25 parts by mass, per 100 parts by mass of the curable fluororesin (A).

[0088] <UV absorber (D)> To improve the weather resistance of the hardened coating layer by absorbing ultraviolet rays from sunlight, the transparent coatings of this disclosure may optionally contain an ultraviolet absorber (D). Examples of ultraviolet absorbers (D) include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers (e.g., hydroxyphenyltriazine), benzoate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, nickel complex salt-based ultraviolet absorbers, oxalic acid anilide-based ultraviolet absorbers, and the like.

[0089] Examples of commercially available UV absorbers (D) are given below, but UV absorbers (D) are not limited to these. One or more types of UV absorbers (D) can be used.

[0090] Examples of commercially available benzophenone-based UV absorbers include Ubinal 3049 and Ubinal 3050 (both manufactured by BASF); Sumisorb 110, Sumisorb 130, and Sumisorb 200 (all manufactured by Sumitomo Chemical Co., Ltd.). Examples of commercially available benzotriazole-based UV absorbers include Chinuvin 900, Chinuvin PS, Chinuvin 384, Chinuvin 109, Chinuvin 928, and Chinuvin 1130 (all manufactured by BASF); Sumisorb 250, Sumisorb 300, Sumisorb 320, Sumisorb 340, and Sumisorb 350 (all manufactured by Sumitomo Chemical Co., Ltd.); and Adekastab LA-32 and Adekastab LA-31 (both manufactured by Asahi Denka Co., Ltd.). Examples of commercially available triazine-based UV absorbers include Tinuvin 400, Tinuvin 405, and Tinuvin 479 (all manufactured by BASF). An example of a commercially available benzoate-based UV absorber is Sumisorb 400 (manufactured by Sumitomo Chemical Co., Ltd.). Examples of commercially available cyanoacrylate-based UV absorbers include Ubinal 3055 and Ubinal 3039 (manufactured by BASF). An example of a commercially available other UV absorber is propanedioic acid [(4-methoxyphenyl)-methylene]-dimethyl ester.

[0091] By appropriately selecting the ultraviolet absorber, yellowing can be effectively suppressed even during long-term exposure. In this respect, benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers, which have absorption capabilities from the long-wavelength side, are preferred as ultraviolet absorber (D). Triazine-based ultraviolet absorbers are more preferred as ultraviolet absorber (D) because they have particularly excellent ultraviolet absorption capabilities.

[0092] The amount of ultraviolet absorber (D) is preferably 0.1 to 50 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of curable fluororesin (A). In addition, two or more types of ultraviolet absorbers (D) may be added in combination from the viewpoint of broadly covering the ultraviolet absorption wavelength range.

[0093] <Solvent> Examples of solvents include organic solvents. Examples of organic solvents include aliphatic esters such as ethyl acetate, butyl acetate, isopropyl acetate, and isobutyl acetate; aliphatic glycol ether esters such as propylene glycol methyl ether acetate; aromatic hydrocarbons such as xylene, toluene, and solvent naphtha; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; cyclic ethers such as tetrahydrofuran and dioxane; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; glycol ethers such as propylene glycol methyl ether, ethyl cellosolve, and cellosolve acetate; diethylene glycol esters such as carbitol acetate; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, and mineral spirits; and mixed solvents thereof.

[0094] One or more solvents can be used. It is preferable to use a mixture of two or more solvents as the solvent in order to form a highly transparent, less cloudy, cured coating layer.

[0095] In terms of forming a highly transparent, less cloudy cured coating layer, aliphatic esters and aromatic hydrocarbons, as well as mixed solvents thereof, are preferred as solvents; butyl acetate and xylene, as well as mixed solvents thereof, are more preferred; and a mixed solvent of butyl acetate and xylene is particularly preferred.

[0096] When using a mixed solvent of aliphatic esters (preferably butyl acetate) and aromatic hydrocarbons (preferably xylene), in order to form a highly transparent, less cloudy cured coating layer, the ratio of the mass M2 of aromatic hydrocarbons to the mass M1 of aliphatic esters (M2 / M1) is preferably 0.01 to 0.80, more preferably 0.05 to 0.70, even more preferably 0.10 to 0.55, and even more preferably 0.15 to 0.30.

[0097] It is preferable to use a combination of two or more solvents with different volatility in order to obtain appropriate drying properties for the transparent coating during application and appropriate leveling properties for the formed coating film. In addition to the paintability of the transparent coating, it is preferable to prepare a flame retardant solution by pre-dissolving the flame retardant (B) in a solvent in order to uniformly mix the curable fluororesin (A) and the flame retardant (B), and then mix the flame retardant solution with other transparent coating components (for example, curable fluororesin (A), curing agent (C), any other transparent coating components, the remaining solvent, etc.). The solvent that can be used when preparing the flame retardant solution may be only one type of solvent or a mixture of two or more solvents. In order to obtain a highly transparent cured coating layer with little clouding, it is preferable that the solvent that can be used when preparing the flame retardant solution be a mixture of two or more solvents.

[0098] <Additives> The transparent coatings of this disclosure may further contain various additives, provided that their flame retardancy, transparency, and weather resistance are not impaired. Examples of additives include light stabilizers (radical trapping agents), adhesion improvers, flexibility improvers, surface hydrophilizers, heat shielding agents, coupling agents (e.g., silane-based coupling agents, metal-based coupling agents), antioxidants, fillers, defoamers, thickeners, leveling agents, curing accelerators, fillers, gelling inhibitors, pigments, inorganic powders, metal powders, silica, and dispersants. However, in order to form a highly transparent cured coating layer, it is preferable that the transparent coatings do not contain colored additives. Specifically, it is preferable that the transparent coatings do not contain silica, inorganic powders, metal powders, pigments, etc. Furthermore, by using a flame retardant (B) having a predetermined solubility, the components of the transparent coatings become suitably compatible, so the transparent coatings do not need to contain dispersants.

[0099] <Method for manufacturing transparent paint> The transparent coatings of this disclosure can be prepared by mixing or dispersing a curable fluororesin (A), a flame retardant (B), a curing agent (C), and other components as needed, in a solvent. The mixing and dispersion methods are not particularly limited and can be carried out using known devices such as mixers, roll mills, paint shakers, bead mills, and kneaders. The transparent coatings of this disclosure may be one-component transparent coatings in which the curable fluororesin (A) and the curing agent (C) are mixed in advance. Alternatively, the transparent coatings of this disclosure may be two-component transparent coatings in which the curable fluororesin (A) and the curing agent (C) are mixed immediately before application.

[0100] The transparent coatings of this disclosure can form a hardened coating layer with excellent flame retardancy, transparency, and weather resistance, and are therefore particularly suitable for use in the manufacture of solar cell protective covers provided on the sunlight-irradiated side of solar cells. However, the applications of the transparent coatings of this disclosure are not limited to these. The transparent coatings of this disclosure can also be suitably used in applications other than solar cell protective covers where flame retardancy, transparency, and weather resistance are desirable. Examples of applications other than solar cell protective covers include resin glass; windows and light-gathering parts of automobiles, trains, airplanes, etc.; roofs of buildings, parking lots, etc.; flame-retardant partition sheets for data centers; sound barriers and windbreaks for roads; light covers for automobiles, motorcycles, etc.; lighting protective covers; agricultural materials, etc. Furthermore, the transparent coatings of this disclosure can also be used as backsheets for solar cells where flame retardancy and weather resistance are desirable.

[0101] [Laminated structure] This disclosure also relates to a laminate. The laminate of this disclosure comprises a transparent substrate and a transparent layer. In this disclosure, "transparent" in the transparent substrate and transparent layer means that the total light transmittance is 85% or more. The transparent layer is provided on the transparent substrate. The transparent layer is a coating-cured layer of the transparent coating of this disclosure described above. As described above, the transparent coating of this disclosure can form a coating-cured layer with excellent flame retardancy, transparency, and weather resistance. Therefore, the laminate of this disclosure having such a coating-cured layer also has excellent flame retardancy, transparency, and weather resistance. The coating-cured layer is provided on one or both sides of the transparent substrate.

[0102] Since it is desirable for the laminate to have high transparency, the total light transmittance of the laminate is preferably 85% or higher, and more preferably 90% or higher. The upper limit of the total light transmittance of the laminate is not particularly limited, but for ease of manufacturing, it may be, for example, 99% or less. When the coating film cured layer of the transparent coating of this disclosure is provided on a transparent substrate, diffuse reflection of light on the surface of the transparent substrate is reduced, and the transparency of the laminate is increased. The total light transmittance of the laminate can be measured using a haze meter in accordance with ASTM D1003.

[0103] <Transparent base material> The transparent substrate can be any transparent substrate commonly used as a protective cover for solar cells. While a glass substrate may be used as the transparent substrate, a resin substrate is preferred in terms of reducing the weight of the solar cell. Examples of resins that make up the resin substrate include polycarbonate, polyethylene terephthalate (PET), acrylic resin, fluororesin, polyethylene, polypropylene, polystyrene, polyimide, epoxy resin, and the like.

[0104] In terms of good strength and transparency, the transparent substrate is preferably a PET substrate, polycarbonate substrate, acrylic resin substrate, or fluororesin substrate. Furthermore, while hydrocarbon resin substrates such as PET substrates, polycarbonate substrates, acrylic resin substrates, and fluororesin substrates tend to be susceptible to the effects of sunlight, the weather resistance of the coating-cured layer of the transparent coating of this disclosure is excellent, so even if the laminate has a hydrocarbon resin substrate, the weather resistance of the laminate can be improved. When the transparent substrate is a resin substrate, the laminate of this disclosure is a transparent resin laminate in which a transparent resin substrate and a coating-cured layer which is a transparent layer are laminated together.

[0105] When a laminate is used as a protective cover for a solar cell, the transparent substrate is preferably water-impermeable in order to sufficiently prevent moisture from penetrating into the solar cell. Examples of water-impermeable substrates include PET substrates.

[0106] In terms of enhancing the transparency of the laminate, the total light transmittance of the transparent substrate is preferably 85% or higher, and more preferably 90% or higher. While there is no particular upper limit to the total light transmittance of the transparent substrate, it may be, for example, 99% or less, for ease of manufacturing. The total light transmittance of the transparent substrate can be measured using a haze meter in accordance with ASTM D1003.

[0107] To improve the adhesion of the layers to the transparent substrate, the transparent substrate may be surface-treated, provided that the transparency of the laminate is not impaired. The surface treatment may be applied to one side of the transparent substrate or to both sides. Examples of surface treatments include corona treatment, plasma treatment, chemical conversion treatment, and vapor deposition treatment (e.g., Si vapor deposition treatment). Conventional known methods can be appropriately employed for any of these treatments. In addition, vapor deposition treatment may be omitted in order to enhance the transparency of the laminate.

[0108] In order to improve the adhesion of the curable fluororesin (A) in the transparent coating to the transparent substrate by introducing polar functional groups such as hydroxyl groups and carbonyl groups to the surface of the transparent substrate, it is preferable that one or both sides of the transparent substrate are corona-treated or plasma-treated.

[0109] The thickness of the transparent substrate is preferably 10 to 500 μm, and more preferably 50 to 300 μm.

[0110] <Cured coating layer> The hardened coating layer is a layer formed by curing a coating film created by applying the transparent paint of this disclosure to a substrate by heating or the like.

[0111] In terms of good weather resistance, chemical resistance, and moisture resistance, the film thickness of the hardened coating layer is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, and even more preferably 10 μm or more. The upper limit of the film thickness of the hardened coating layer is not particularly limited, but in terms of reducing the weight of the laminate, it is preferably 1000 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. The film thickness of the hardened coating layer can be measured, for example, using a magnetic / eddy current type film thickness gauge.

[0112] In order to reduce the refraction of light between layers and improve the transparency of the laminate, and to reduce the weight of the laminate, it is preferable that the coating-cured layer be provided directly on the transparent substrate without an intermediate layer, as described later. When the coating-cured layer is provided directly on the transparent substrate, it is preferable that one or both sides of the transparent substrate be corona-treated or plasma-treated in order to ensure good adhesion of the coating-cured layer to the transparent substrate.

[0113] When the coating-cured layer of this disclosure is directly applied to a transparent substrate, it is preferable that the surface of the transparent substrate has hydroxyl groups and the acid value of the curable fluororesin (A) contained in the transparent coating is within the above range. Due to the interaction between the hydroxyl groups of the transparent substrate and the carboxyl groups of the curable fluororesin (A), the coating-cured layer tends to adhere well to the transparent substrate. When the coating-cured layer of this disclosure is directly applied to a transparent substrate, it is more preferable that one or both sides of the transparent substrate are corona-treated or plasma-treated, the surface of the transparent substrate has hydroxyl groups, and the acid value of the curable fluororesin (A) contained in the transparent coating is within the above range. Corona treatment or plasma treatment increases the number of hydroxyl groups on the surface of the transparent substrate, which tends to further improve the adhesion of the coating-cured layer to the transparent substrate. In terms of improving adhesion, it is preferable that the transparent substrate is a resin substrate composed of a resin having hydroxyl groups.

[0114] Furthermore, when the coating-cured layer of this disclosure is directly applied to a transparent substrate, it is preferable that the surface of the transparent substrate has carboxyl groups and that the hydroxyl value of the curable fluororesin (A) contained in the transparent coating is within the above range. Due to the interaction between the carboxyl groups of the transparent substrate and the hydroxyl groups of the curable fluororesin (A), the coating-cured layer tends to adhere well to the transparent substrate. When the coating-cured layer of this disclosure is directly applied to a transparent substrate, it is even more preferable that one or both sides of the transparent substrate are corona-treated or plasma-treated, that the surface of the transparent substrate has carboxyl groups, and that the hydroxyl value of the curable fluororesin (A) contained in the transparent coating is within the above range. Corona treatment or plasma treatment increases the number of carboxyl groups on the surface of the transparent substrate, which tends to further improve the adhesion of the coating-cured layer to the transparent substrate. In terms of improving adhesion, it is preferable that the transparent substrate is a resin substrate composed of a resin having carboxyl groups.

[0115] <Middle class> The laminate of this disclosure may optionally include an intermediate layer between the transparent substrate and the coating-cured layer. An example of the intermediate layer is a resin layer. Examples of resins constituting the resin layer include acrylic resin, urethane resin, polyester resin, fluororesin, and silicone resin. However, the intermediate layer does not have to be a silicone layer in order to improve the transparency of the laminate. Furthermore, the intermediate layer may be omitted in order to improve the transparency of the laminate.

[0116] <Barrier layer> The laminate of this disclosure may optionally include a barrier layer on the side of the coating-cured layer opposite to the side facing the transparent substrate. Conventionally known barrier layers can be appropriately selected and used. Examples of barrier layers include those described in Japanese Patent Publication No. 2000-294817 (e.g., paragraphs 0017, 0021, 0027), Japanese Patent Publication No. 2000-277770 (e.g., paragraphs 0017, 0021, 0027), Japanese Patent Publication No. 2007-173449 (e.g., paragraphs 0028-0034), Japanese Patent Publication No. 2014-017431 (e.g., paragraphs 0011, 0018, 0031-0043), etc., but are not limited to these. Furthermore, the barrier layer may be provided on one or both sides of the transparent substrate.

[0117] <Method for manufacturing laminates> The method for forming a hardened coating layer using the transparent coating of this disclosure is not particularly limited, but for example, it is a method in which the transparent coating of this disclosure is applied to a transparent substrate to form a coating film, and the coating film is hardened by a hardening reaction between a fluororesin (A) and a hardener (C) to form a hardened coating layer. The above coating is not particularly limited and can be carried out by known methods. Examples of coating methods include dipping, casting, roll coating, curtain flow coating, bar coating, spray coating, spin coating, die coating, gravure coating, etc. The above hardening can be appropriately selected from room temperature drying, heat drying, baking drying, UV curing, etc., depending on the components of the transparent coating.

[0118] [Solar protective cover] This disclosure also relates to a solar cell protective cover. The solar cell protective cover of this disclosure is provided on the side of the solar cell that is exposed to sunlight. The solar cell protective cover comprises the laminate of this disclosure as described above. As described above, the laminate of this disclosure has excellent flame retardancy, so when used as a solar cell protective cover, solar cells can be safely installed in houses and other buildings. Also, as described above, the laminate of this disclosure has excellent transparency, so when used as a solar cell protective cover, sunlight is transmitted well, resulting in good power generation efficiency of the solar cell. Also, as described above, the laminate of this disclosure has excellent weather resistance, so when used as a solar cell protective cover, solar cells can be used for a long period of time, such as several decades.

[0119] The solar cell protective cover may comprise only the laminate of this disclosure, or may further comprise other components as needed. The other components may be conventionally known components, such as reinforcing materials and adhesive layers for the solar cell module.

[0120] A solar cell protective cover is provided on the solar cell. The solar cell comprises, for example, a solar cell module, a solar cell protective cover, and a backsheet. The solar cell module has, for example, solar cells and a sealing layer that seals the solar cells. The solar cell module has a sun-irradiating surface (light-receiving surface) and an opposite surface (back surface). The solar cell protective cover is provided on the sun-irradiating surface side of the solar cell relative to the solar cell module. The backsheet is provided on the side of the solar cell opposite to the sun-irradiating surface relative to the solar cell module. Note that conventionally known solar cell modules and backsheets can be used without particular limitation.

[0121] When a coating hardening layer is provided on one side of the substrate of the laminate, the coating hardening layer is provided on the side facing the sunlight irradiation surface relative to the substrate. In this case, the substrate is provided on the sunlight irradiation surface of the solar cell module, and the coating hardening layer is provided on the substrate. When coating hardening layers are provided on both sides of the substrate of the laminate, a first coating hardening layer is provided on the sunlight irradiation surface of the solar cell module, the substrate is provided on the first coating hardening layer, and a second coating hardening layer is provided on the substrate.

[0122] <Manufacturing method for solar cell protective covers> Solar cell protective covers can be manufactured using conventionally known methods. The transparent substrate or the hardened coating layer may be directly painted onto the solar cell module. Alternatively, a solar cell protective cover having a laminate of the transparent substrate and the hardened coating layer may be prepared in advance, and this protective cover may be bonded to the solar cell module.

[0123] While embodiments of this disclosure have been described above, it will be understood that a variety of modifications to the form and details are possible without departing from the spirit and scope of the claims. [Examples]

[0124] The present disclosure will be specifically illustrated below with examples, but this disclosure is not limited to these examples. Unless otherwise specified in the following examples, "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0125] Table 1 shows the flame retardants used in the following reference examples and embodiments. Note that PX-200, CR-741, and FP-600 are represented by the chemical formulas described in the embodiments. Also, HCA is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0126] [Table 1]

[0127] [Solubility of butyl acetate as a flame retardant] Under conditions of 23°C, 3.5 g of butyl acetate was weighed into a 10 mL glass screw-top bottle. The amount of flame retardant required to achieve the solid content concentration (active ingredient concentration) shown in Table 2 was added, the bottle was sealed, and the mixture was shaken by hand for 10 minutes to obtain the evaluation solution. The appearance of the evaluation solution was visually inspected. If the appearance of the evaluation solution was clear, it was determined that the flame retardant had dissolved in the butyl acetate. The results are shown in Table 2.

[0128] [Table 2]

[0129] [Solubility of xylene in flame retardants] Under conditions of 23°C, 3.5 g of xylene was weighed into a 10 mL glass screw-top bottle. An amount of flame retardant corresponding to the solid content concentration (active ingredient concentration) shown in Table 3 was added, the bottle was capped, and the mixture was shaken by hand for 10 minutes to obtain the evaluation solution. The appearance of the evaluation solution was visually inspected. If the appearance of the evaluation solution was clear, it was determined that the flame retardant had dissolved in the xylene. The results are shown in Table 3.

[0130] [Table 3]

[0131] As shown in Tables 2 and 3, PX-200, CR-741, and FP-600 exhibited the specified solubility. On the other hand, HCA did not exhibit the specified solubility.

[0132] [Compatibility of flame retardants with fluororesins] The compatibility of the flame retardant with fluororesin was confirmed by following steps 1-3 below.

[0133] Step 1 (Preparation of flame retardant solution) The flame retardant PX-200 listed in Table 1 was pre-dissolved in a mixed solvent of butyl acetate / xylene (mass ratio: 50 / 50) to an active ingredient concentration of 30 mass% to prepare a flame retardant solution of PX-200. For CR-741, the flame retardant solution of CR-741 was prepared by dissolving it in the above mixed solvent of butyl acetate / xylene (mass ratio: 50 / 50) to an active ingredient concentration of 50 mass%. For FP-600, the flame retardant solution of FP-600 was prepared by dissolving it in the above mixed solvent of butyl acetate / xylene (mass ratio: 50 / 50) to an active ingredient concentration of 50 mass%. Since HCA did not dissolve in the mixed solvent of butyl acetate / xylene (mass ratio: 50 / 50), HCA was added to the above mixed solvent to an active ingredient concentration of 30 mass%, and the mixture was stirred at 500 rpm for 30 minutes using a dissolver to prepare an HCA mixture.

[0134] Step 2 (Mixing with GK-570) 10 g of Zeffle GK-570 (resin solids content 65 mass%) manufactured by Daikin Industries, Ltd. was weighed into a 20 mL glass screw bottle. The flame retardant solution of PX-200 (active ingredient concentration 30 mass%) was added in the amount shown in Table 4 relative to the resin solids content of GK-570. The contents of the screw bottle were then manually stirred at 23°C to prepare the mixed solution. Mixed solutions for CR-741 and FP-600 were prepared using the same method.

[0135] Regarding HCA, significant separation and sedimentation were observed during the preparation of the flame retardant solution in step 1, making it impossible to dissolve. Therefore, it was determined that it could not be mixed with GK-570, and the subsequent casting to the glass plate was canceled.

[0136] Step 3 (Casting the film onto the glass plate) The mixed solutions prepared in step 2 above were drop-cast onto glass plates and allowed to stand and dry at 23°C for two days to obtain evaluation films. The appearance of the evaluation films was visually inspected. If the appearance of the evaluation film was clear, it was determined that the flame retardant was compatible with the fluororesin. The results are shown in Table 4. In Table 4, "phr" indicates the amount of flame retardant added in parts by mass relative to the resin solid content of 100 parts by mass of Zeffle GK-570.

[0137] [Table 4]

[0138] As shown in Table 4, by using a flame retardant having a predetermined solubility, the flame retardant and the fluororesin became suitably compatible, and a film with a clear appearance was formed.

[0139] The components other than the flame retardant used in the following examples are as follows: GK-570: Manufactured by Daikin Industries, Ltd. Zeffle GK-570 (TFE-vinyl monomer copolymer solution, solid content concentration 65%, hydroxyl value 63 mg KOH / g, acid value 3-4 mg KOH / g) Chinuvin 400: Manufactured by BASF. Chinuvin 400 (hydroxyphenyltriazine-based UV absorber) Chinuvin 479: Manufactured by BASF. Chinuvin 479 (hydroxyphenyltriazine-based UV absorber) TPA-100: Manufactured by Asahi Kasei Corporation. Duranate TPA-100 (isocyanurate-based curing agent)

[0140] [Preparation of transparent paint] The components were mixed to obtain the compositions shown in Table 5, and the transparent coatings of Examples 1-2 and Comparative Examples 1-2 were obtained. In Table 5, "-" indicates that the corresponding component was not included. Also, in Table 5, the amount of fluororesin added, "100" parts by mass, indicates the amount of resin solids.

[0141] [Table 5]

[0142] [Formation of laminates] A transparent coating (each of the transparent coatings from Examples 1-2 and Comparative Examples 1-2) was applied to a substrate to form a coating film. As the substrate, a PET substrate of E5101 (total light transmittance of 89% and thickness of 250 μm, corona-treated on one side) manufactured by Toyobo Co., Ltd. was used. The transparent coatings listed in Table 5 were applied to the corona-treated side of the PET substrate using a bar coater. After curing these coated PET sheets at room temperature for 18 hours, they were dried in a forced-air dryer at 150°C for 5 minutes, and then dried in a forced-air dryer at 50°C for 3 days. As a result, a laminate was obtained having a substrate and a hardened coating layer with a dry coating film thickness of 50 μm on the substrate.

[0143] [Transparency (total light transmittance)] The total light transmittance of the laminate obtained above was measured using a haze meter (Haze Guard II, manufactured by Toyo Seiki Co., Ltd.) in accordance with ASTM D1003.

[0144] [Flame retardant] The laminate obtained above was used as a test specimen, and a combustion test was conducted on this specimen in accordance with the UL-94V standard. The flame retardancy of the test specimen was evaluated by visual observation during the combustion test from the following perspectives. A: After ignition, the fire spontaneously extinguished during combustion. B: After ignition, it continued to burn without extinguishing itself. C: After ignition, it burned out immediately without extinguishing itself.

[0145] These results are shown in Table 6. For Comparative Example 3, instead of the laminate, a PET substrate without a cured transparent coating layer was used for evaluation.

[0146] [Table 6]

[0147] [Accelerated weather resistance] As representative samples, a laminate formed using the transparent coating of Example 1, a laminate formed using the transparent coating of Comparative Example 1, and a PET substrate without a cured coating layer of the transparent coating were subjected to accelerated weathering tests. The accelerated weathering tests were conducted for 240 hours using an iSuper UV tester SUV manufactured by Iwasaki Electric Co., Ltd. The test conditions were 12 hours of irradiation (illuminance: 100 mW / cm²). 2 (Black panel temperature: 63°C, relative humidity: 60%, deionized water shower performed at a frequency of 10 seconds / 1 hour during irradiation), condensation for 12 hours (illuminance: 0 mW / cm²) 2 The settings were configured to repeat a cycle of the following conditions: Black panel temperature: room temperature, relative humidity: 100%.

[0148] (Visual appearance) The appearance of the laminate after the accelerated weathering test was visually observed, and its weather resistance was evaluated from the following perspectives. A: No abnormalities B: Slight yellowing present C: Significant yellowing present.

[0149] (color difference) Brightness of the laminate before and after accelerated weathering test (L * The color difference (△E) before and after the accelerated weathering test was measured using a colorimeter (CR-400 manufactured by Konica Minolta, Inc.), and the color saturation (a* value) and hue (b* value) were measured. * ) was sought.

[0150] (Total light transmittance) The total light transmittance of the laminate after accelerated weathering testing was measured using a haze meter (Haze Guard II, manufactured by Toyo Seiki Co., Ltd.) in accordance with ASTM D1003.

[0151] These results are shown in Table 7. For Comparative Example 3, instead of the laminate, a PET substrate without a cured transparent coating layer was used for evaluation.

[0152] [Table 7]

[0153] The results shown in Tables 6 and 7 demonstrate that the transparent coating of this disclosure can form a hardened coating layer with excellent flame retardancy, transparency, and weather resistance. Furthermore, the laminate of this disclosure exhibits excellent flame retardancy, transparency, and weather resistance. In addition, because it possesses such a laminate, the solar cell protective cover of this disclosure is judged to have excellent flame retardancy, transparency, and weather resistance. [Industrial applicability]

[0154] The transparent coatings of this disclosure can be suitably used as coatings for solar cell protective covers.

Claims

1. It comprises a curable fluororesin (A), a flame retardant (B), and a curing agent (C), A transparent coating characterized in that the flame retardant (B) dissolves in butyl acetate and xylene at a temperature of 23°C in an active ingredient concentration of 10% by mass or more.

2. The flame retardant (B) is an organophosphate ester or a polymer thereof represented by the following formula (1): The transparent paint according to claim 1, wherein the molecular weight of the flame retardant (B) is 1000 or less. 【Chemistry 1】 (In formula (1) above, R １ R is a group represented by the following formula (2) or (3), ２ , R ３ , R ４ , and R ５ Each of these is independently a substituted or unsubstituted aromatic hydrocarbon group. 【Chemistry 2】

3. The transparent paint according to claim 1 or 2, wherein the amount of the flame retardant (B) is 5% by mass or more and 40% by mass or less with respect to the solid content of the curable fluororesin (A) in the transparent paint.

4. The curable fluororesin (A) has units derived from fluorine-containing monomers, The transparent coating according to claim 1 or 2, wherein the fluorine-containing monomer is at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, hexanefluoropropylene, 2,3,3,3-tetrafluoropropene, and 1,3,3,3-tetrafluoropropene.

5. The acid value of the curable fluororesin (A) is 35 mg KOH / g or less. The transparent coating according to claim 1 or 2, wherein the hydroxyl value of the curable fluororesin (A) is 29 mg KOH / g or more and 150 mg KOH / g or less.

6. The transparent coating according to claim 1 or 2, wherein the curing agent (C) is an isocyanate-based curing agent or an amino resin-based curing agent.

7. The transparent coating according to claim 1 or 2, further comprising an ultraviolet absorber (D).

8. The transparent paint according to claim 1 or 2, wherein the transparent paint is a paint for a solar cell protective cover provided on the solar cell's sunlight-irradiated side.

9. The curable fluororesin (A) has units derived from a fluorine-containing monomer and units derived from a monomer containing a curable functional group, The fluorine-containing monomer is tetrafluoroethylene, The flame retardant (B) is an organophosphate ester or a polymer thereof represented by the following formula (1): The molecular weight of the flame retardant (B) is 500 or more and 1000 or less. The amount of the flame retardant (B) is 5% by mass or more and 40% by mass or less relative to the solid content of the curable fluororesin (A) in the transparent coating. The transparent coating according to claim 1 or 2, wherein the curing agent (C) is an isocyanate-based curing agent or an amino resin-based curing agent. 【Transformation 3】 (In the above formula (1), R １ is a group represented by the following formula (2) or (3), and R ２ , R ３ , R ４ , and R ５ are each independently a substituted or unsubstituted aromatic hydrocarbon group.) 【Chemistry 4】

10. A laminate comprising a transparent substrate and a transparent layer provided on the transparent substrate, A laminate in which the transparent layer is a hardened coating layer of the transparent paint described in claim 1 or 2.

11. The laminate according to claim 10, wherein the total light transmittance of the laminate is 85% or more.

12. The laminate according to claim 10, wherein the thickness of the hardened coating layer is 10 μm or more and 100 μm or less.

13. The laminate according to claim 10, wherein the transparent substrate is a polyethylene terephthalate substrate, a polycarbonate substrate, an acrylic resin substrate, or a fluororesin substrate.

14. The laminate according to claim 10, wherein the total light transmittance of the transparent substrate is 85% or more.

15. The laminate according to claim 10, wherein the coating film curing layer is provided directly on the transparent substrate.

16. The laminate according to claim 10, wherein one or both sides of the transparent substrate are subjected to corona treatment or plasma treatment.

17. A solar cell protective cover provided on the side of the solar cell that is exposed to sunlight, A solar cell protective cover comprising the laminate described in claim 10.

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