JP2013199604A - Curable coating composition, laminated polyester resin film, and solar cell backsheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating agent which has transparency and can impart wet-heat resistance and hydrolysis resistance to various commercially available PET films to prevent film degradation by being applied thereto.SOLUTION: There are provided a curable coating composition containing an epoxy resin of an epoxy equivalent of 170-750, a hydroxyl-containing resin other than the epoxy resin, and an organic polyisocyanate compound, a laminated polyester film prepared by laminating a cured film of the curable coating composition on a polyester resin film, and a multilayer structure solar cell backsheet containing at least the laminated polyester film.

Description

  The present invention relates to a curable coating composition, a laminated polyester resin film, and a solar battery back sheet.

The present invention is, for example, an overlay film for the purpose of surface protection, improvement in gloss, prevention of discoloration / deterioration of a marking film used on a surface of a railway vehicle, automobile, vending machine, etc. The present invention relates to a highly weather-resistant film / sheet used mainly for the purpose of protection and prevention of discoloration, such as a surface protection film for plastic windows and exterior signs, a liquid crystal display reflection sheet, and a solar cell backsheet.
The above-mentioned high weather resistance films and sheets are commonly intended to shield and protect objects from harsh external environments, such as exposure to ultraviolet rays from direct sunlight, large temperature changes, and exposure to wind and rain. Even if there is an environmental change, it is necessary to be able to reliably protect an object without being broken for a long time.
For example, a solar cell back sheet is a sheet intended to shield and protect a solar cell body from a severe external environment. Since the solar cell panel is installed outdoors, it is necessary to operate stably over a long period of time even when there is an environmental change such as exposure to ultraviolet rays by direct sunlight, a large change in temperature, and exposure to wind and rain. Of course, the back sheet itself is also required to have transparency and weather resistance so that the solar cell can be visually recognized.
In order to satisfy the above-mentioned stringent quality, the polyester resin film applied to such a solar battery back sheet is not limited to a polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate. These additives are added and kneaded, and melt extrusion is performed so as to obtain a required thickness.
However, the production method as described above has a drawback that although a polyester resin film having a certain degree of transparency and weather resistance can be obtained, the production process is multi-step and cannot be easily obtained.

PET films have excellent properties such as mechanical strength, heat resistance, optical properties, and chemical resistance, but have the disadvantage of low hydrolysis resistance. Therefore, in a film used outdoors for a long time, such as a solar battery back sheet, the hydrolysis resistance is a factor of the use limit.
Therefore, in order to improve the hydrolysis resistance of the PET film, a method of adding a hydrolysis resistance agent such as carbodiimide during the film production process is known. However, a film containing such a hydrolysis-resistant agent has a risk of causing health damage due to generation of gas due to by-products contained in the film depending on the manufacturing process or use environment. Further, transparency is lost due to the influence of a hydrolysis-resistant agent and the like, and as a result, there are problems in that the intended use is limited and the production cost is increased. In addition, when higher hydrolysis resistance is required, a film such as polyethylene naphthalate or polyimide film is used, but there is a problem that it is very expensive compared with PET film. In particular, solar cell backsheets have been increasingly demanded for cost reduction, the use of the film is difficult, and a low-cost film having high hydrolysis resistance is required.

Patent Document 1 describes a polyurethane-based curable surface coating composition comprising a hydroxyl group-containing acrylic resin and an organic polyisocyanate compound, to which an ultraviolet absorber and / or a hindered amine light stabilizer is added. The obtained highly weather-resistant polyester film is suggested to be applied to a solar battery back sheet, which has sufficient weather resistance even under the influence of heat, light and water, and excellent film adhesion. ing.
However, in this technique, although weather resistance can be imparted to the polyester film, it is necessary to add a hydrolysis-resistant agent during film production. In this method, the film that can be produced is limited, and there are problems such as health damage due to the influence of additives, a decrease in transparency, and an increase in production cost.
Patent Document 2 describes a polyurethane-based curable surface coating composition in which an organic polyisocyanate compound and an epoxy resin are combined with an ionomer-type polyurethane resin, on which the surface is coated on a polyester resin film. A solar cell backsheet coated and cured with the coating composition is also described.
However, the cured film obtained from the curable surface coating composition described in this technology has not been sufficiently weather-resistant yet, but it has been a reality.

JP 2005-015557 A JP 2010-016286 A

  Accordingly, an object of the present invention is to provide a coating that can impart moisture resistance and hydrolysis resistance by coating a variety of commercially available PET films and can prevent deterioration of the film. Is to provide an agent.

  In order to solve the above problems, the present inventor applied a coating composition containing a specific epoxy resin, a resin containing a hydroxyl group other than an epoxy resin, and an organic polyisocyanate compound to a PET film as a result of intensive studies. The present inventors have found that the above problems can be solved and have completed the invention.

  That is, the present invention is a curable coating composition containing an epoxy resin having an epoxy equivalent of 170 to 750, a resin containing a hydroxyl group other than an epoxy resin, and an organic polyisocyanate compound, Provided are a laminated polyester film having a cured film laminated on a polyester resin film, and a solar battery backsheet having a multilayer structure including at least the laminated polyester film.

  According to the present invention, it is possible to impart moisture resistance and hydrolysis resistance by coating a variety of commercially available PET films that are transparent and prevent deterioration of the film. Moreover, the transparency and the manufacturing cost reduction which were difficult to realize with the conventional hydrolysis-resistant PET film can be realized, and the solar cell backsheet can be manufactured at low cost.

It is a figure which shows the one aspect | mode of the layer structure of the solar cell backsheet using the curable coating composition of this invention. It is a figure which shows the one aspect | mode of the layer structure of the solar cell backsheet using the curable coating composition of this invention. It is a figure which shows the one aspect | mode of the layer structure of the solar cell backsheet using the curable coating composition of this invention.

  Examples of the epoxy resin used in the present invention include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AD type epoxy resin, etc .; orthocresol novolac type epoxy resin, phenol Novolac epoxy resin, naphthol novolac epoxy resin, bisphenol A novolac epoxy resin, brominated phenol novolac epoxy resin, alkylphenol novolac epoxy resin, bisphenol S novolac epoxy resin, alkoxy group-containing novolac epoxy resin, brominated phenol Novolac type epoxy resins such as novolac type epoxy resins; other phenol aralkyl type epoxy resins (commonly known as zylock trees) Epoxidized products), diglycidyl ether of resorcin, diglycidyl ether of hydroquinone, diglycidyl ether of catechol, biphenyl type epoxy resin, tetramethylbiphenyl type epoxy resin, sulfur-containing epoxy resin, stilbene type epoxy resin, etc. Resin, alicyclic epoxy resin such as hydrogenated bisphenol A type epoxy resin, triglycidyl isocyanurate, triphenylmethane type epoxy resin, tetraphenylethane type epoxy resin, dicyclopentadiene-phenol addition reaction type epoxy resin, biphenyl modified Novolac epoxy resin (epoxidized polyhydric phenol resin with phenolic nuclei linked by bismethylene group), alkoxy group-containing novolac epoxy resin, tetrabromobisphenol Such type epoxy resin. Moreover, the said epoxy resin may be used independently and may mix 2 or more types.

  The epoxy resin is not limited as long as the epoxy equivalent is 150 to 750, but bisphenol-type epoxy resin, hydrogenated bisphenol-type epoxy resin and alicyclic epoxy resin are more preferable because of excellent weather resistance and adhesion. These may be used alone or in combination.

  Furthermore, among these epoxy resins, in particular, the epoxy resin itself has a low viscosity, is excellent in compatibility with the main agent, and can be well balanced in the physical properties of the heat resistance and strength of the cured coating film. Epoxy resins are preferred. As the bisphenol type epoxy resin, bisphenol A is particularly excellent in fluidity at normal temperature when mixed with the main agent, and particularly in the balance between the rigidity of the cured coating film, the hydrolysis resistance, and the heat and humidity resistance. Type epoxy resin is preferred. The epoxy equivalent of the bisphenol A type epoxy resin is particularly preferably in the range of 150 to 750, particularly in the range of 150 to 300 from the viewpoint of fluidity.

  Examples of such an epoxy resin include DIC Corporation, trade names: Epicron 850, 860, 1050, and 2050. These may be used alone or in any combination of two or more.

  In this invention, it is excellent in a cured coating film to use 2-20 parts, especially 12-20 parts of epoxy resins per 100 parts of mass conversion total of the resin containing hydroxyl groups other than an epoxy resin, and an organic polyisocyanate compound. It is preferable in order to combine flexibility, adhesion and hydrolysis resistance.

  As a resin containing a hydroxyl group other than the epoxy resin used in the present invention (hereinafter referred to as a resin containing a hydroxyl group), the hydroxyl value of the resin is 1 to 200 mgKOH / g, and differential scanning calorimetry (DSC method). The glass transition temperature is preferably 30 to 110 ° C. and the number average molecular weight is preferably 5,000 to 50,000.

  The resin containing a hydroxyl group used in the present invention has a hydroxyl value satisfying 1 to 200 mgKOH / g, and particularly having a hydroxyl value in the range of 4 to 100 mgKOH / g. From the viewpoint of strength and adhesion. When the hydroxyl value is less than 1, curing of the coating film hardly proceeds and durability and strength are inferior. On the other hand, when the hydroxyl value is larger than 200, the shrinkage of curing is too large, and the adhesion is deteriorated.

  The resin containing a hydroxyl group used in the present invention satisfies a glass transition temperature of 30 to 110 ° C. in order to form a coating film having excellent adhesion on a flexible substrate such as a plastic film. The glass transition temperature is more preferably 40 to 70 ° C. When glass transition temperature is lower than 30 degreeC, it is inferior to blocking resistance, and when higher than 110 degreeC, fluid adhesiveness and applicability | paintability fall.

  The hydroxyl group-containing resin used in the present invention satisfies the number average molecular weight of 5,000 to 50,000, preferably the number average molecular weight of 10,000 to 30,000. It is more preferable in terms of excellent properties and weather resistance. The above-described resin containing a hydroxyl group having a molecular weight dissolves in an organic solvent, and exhibits outstanding hydrolysis resistance and weather resistance without significantly impairing the fluidity of the solution.

Examples of the resin containing a hydroxyl group used in the present invention include an acrylic resin, a polyester resin, a urethane resin, a fluorine resin, and the like. These may be used alone or in combination of two or more.

  The acrylic resin containing a hydroxyl group used in the present invention refers to a linear (linear) resin containing a hydroxyl group obtained by polymerization using an acrylic ester or a methacrylic ester as an essential component. Hereinafter, acrylic and methacryl are collectively referred to as (meth) acryl.

  Such an acrylic resin can be easily obtained, for example, by copolymerizing a carboxylic acid group-containing monomer such as (meth) acrylic acid, itaconic acid, maleic anhydride, etc. as necessary with (meth) acrylic acid ester as an essential component. Can be manufactured. Examples of (meth) acrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and tert-butyl. (Meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, isobornyl (meth) acrylate Etc.

  In carrying out copolymerization using (meth) acrylic acid ester as an essential component, for example, hydroxyl-containing (meth) acrylic acid ester such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, etc. By using together, the hydroxyl-containing (meth) acrylic resin by which the hydroxyl group was introduce | transduced into the side chain of the acrylic resin frame | skeleton can be obtained.

  Such an acrylic resin containing a hydroxyl group is linear (linear), and, as long as it does not significantly impair the characteristics such as low viscosity and excellent flexibility of the cured film, Polymerized by using a small amount of a polymerizable monomer containing 2 to 6 (meth) acryloyl groups such as glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate and hexa (meth) acrylate. An acrylic resin may be used.

  As an acrylic resin containing a hydroxyl group, for example, there are “ACRIDIC” series manufactured by DIC Corporation and “ACRITT” series manufactured by Taisei Fine Chemical Co., Ltd. For example, as a commercial item of an acrylic resin, the product name: ACRYDIC A-808-T and A-809 made from DIC Corporation can be mentioned.

  The polyester resin containing a hydroxyl group used in the present invention refers to a linear resin containing an excess hydroxyl group obtained by reacting glycol with dibasic acid or a derivative thereof as essential components. Of course, in place of the dibasic acid, an ester-forming derivative such as a dibasic acid anhydride or a dibasic acid lower alkyl ester is used, and not only in a polycondensation reaction, but also in an addition reaction or an ester exchange reaction, a polyester resin Can also be obtained.

  Examples of the polyester resin include aliphatic glycols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, decanediol, and cyclohexanedimethanol, and succinic acid, adipic acid, sebacic acid, and suberin fumarate. Aliphatic polyester resins obtained by reacting acid, azelaic acid, aliphatic dibasic acid such as 1,10-decamethylenedicarboxylic acid and cyclohexanedicarboxylic acid as essential raw material components, and fats such as ethylene glycol, propylene glycol and butanediol An aromatic polyester resin obtained by reacting an aromatic glycol with an aromatic dibasic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid as an essential raw material component.

  Such a hydroxyl group-containing polyester resin is linear (linear), so long as it does not significantly impair the characteristics such as low viscosity and excellent flexibility of the cured film, the above-mentioned glycol or dibasic acid is used. A polyester resin obtained by using a small amount of a compound containing 3 to 4 active hydrogen groups such as a hydroxyl group or a carboxy group, such as trimellitic acid, pyromellitic acid, tromethylolpropane and pentaerythritol. There may be.

  The polyester resin tends to have a higher Tg by containing more benzene rings and naphthalene rings in the main chain. For example, the target substrate to be coated is PET (polyethylene terephthalate) or PBT (polyethylene). Since affinity with butylene terephthalate) or PEN (polyethylene naphthalate) increases, it is preferable to use an aromatic polyester resin rather than an aliphatic polyester resin in the present invention. However, since more benzene rings and naphthalene rings are contained in the main chain, crystallinity, melting point, etc. tend to increase, and fluidity and applicability tend to be lowered.

  Therefore, the polyester resin is preferably a polyester resin having a glass transition temperature (Tg) of 30 to 110 ° C. in a differential scanning calorimetry (DSC method). In the present invention, Tg is 40 to 70, which is obtained by using 25 mol% or more of aliphatic glycol having 2 to 4 carbon atoms in all alcohols and 30 mol% or more of aromatic dibasic acid in all polybasic acids. It is more preferable to use an aromatic polyester resin at ° C.

  Examples of the polyester resin containing a hydroxyl group include “Byron” series manufactured by Toyobo Co., Ltd., “Eritel” series manufactured by Unitika Ltd., and more specifically, for example, manufactured by Unitika Ltd., trade name: Elitel UE-3210. XA-0611.

  With the polyurethane resin containing a hydroxyl group used in the present invention, for example, a polyisocyanate compound and a compound containing at least two hydroxyl groups in one molecule are reacted at a ratio such that the hydroxyl group is excessive with respect to the isocyanate group. Can be obtained. Examples of the polyisocyanate compound used at that time include hexamethylene diisocyanate, toluene diisocyanate, m-xylylene diisocyanate, and isophorone diisocyanate. Examples of the compound containing at least two hydroxyl groups in one molecule include the polyhydric alcohols, polyester diol, polyethylene glycol, polypropylene glycol, and polycarbonate diol.

  The fluororesin containing a hydroxyl group used in the present invention refers to a linear (linear) resin containing a hydroxyl group obtained by polymerizing a fluorovinyl monomer as an essential component. Examples of the fluorovinyl monomer include vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, 1,1,3,3,3-pentafluoropropylene, 2,2,3,3-tetra Including pure fluoroolefins such as fluoropropylene, 1,1,2-trifluoropropylene or 3,3,3-trifluoropropylene, chlorotrifluoroethylene, bromotrifluoroethylene, 1- Examples include so-called broad-sense fluoroolefins including compounds having a halogen atom other than fluorine atoms, such as chloro-1,2-difluoroethylene or 1,1-dichloro-2,2-difluoroethylene. It is done.

Furthermore, as an essential component of the fluororesin, for copolymerization, for example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxyl-containing (meth) acrylate such as hydroxybutyl (meth) acrylate, or By using a hydroxyl group-containing vinyl ether such as 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, or 4-hydroxybutyl vinyl ether in combination, a hydroxyl group-containing fluororesin having a hydroxyl group introduced into the side chain of the fluororesin skeleton can be obtained.
Examples of the fluororesin containing a hydroxyl group include “Fluonate” series manufactured by DIC Corporation.

  Examples of the organic polyisocyanate compound used in the present invention include organic compounds having at least two isocyanate groups in the molecule. Examples of the organic polyisocyanate compound include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), lysine diisocyanate, trimethylhexamethylene diisocyanate, Polyisocyanates such as 1,3- (isocyanatomethyl) cyclohexane, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate; derivatives of polyisocyanates such as adducts, burettes and isocyanurates of these polyisocyanates (modified) Etc.).

  The organic polyisocyanate compound may be appropriately selected depending on the application to be used. However, an aromatic system such as tolylene diisocyanate may turn yellow, and if more excellent weather resistance is required, It is preferable to use alicyclic. It is not preferable that the cured coating film is colored on a transparent substrate such as a polyester resin film and the transparency is lowered in view of deterioration of visibility. Therefore, preferred in the present invention are aliphatic or cycloaliphatic organic polyisocyanates, such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), adducts, burettes, isocyanurates of these polyisocyanates, etc. It is preferable to use a polyisocyanate derivative (modified product).

  As such an organic polyisocyanate compound, for example, manufactured by Sumika Bayer Urethane Co., Ltd., trade names: Sumijour N3200, N3300, BL3175, N3400, N3600, VPLS2102; manufactured by Asahi Kasei Chemicals Corporation, Product name: Duranate E-402-90T etc. are mentioned.

In the present invention, the weight ratio between the epoxy resin, the hydroxyl group-containing resin, and the organic polyisocyanate compound that is the curing agent varies depending on the type of the main agent and curing agent used, the content of each functional group, etc. However, when the total amount in terms of weight is 100%, the proportion of use in the curing agent is usually 0.1 to 30%, particularly from the viewpoint of adhesion of the cured coating film and hydrolysis resistance, It is preferable to set it as 1 to 10%.
Furthermore, the organic polyisocyanate compound used in the present invention is blended so that the isocyanate group of the organic polyisocyanate compound is equivalent to 0.5 to 10.0 with respect to the hydroxyl group of the resin containing the hydroxyl group. Preferably, it is 0.8-5.0.

  A certain level of performance is manifested with only the organic polyisocyanate compound, but a high degree of hydrolysis resistance can be imparted to the cured coating film by actively using the organic polyisocyanate compound and the epoxy resin together.

  The curable coating composition of the present invention can contain, for example, an antioxidant and a light stabilizer in order to prevent the cured product from being deteriorated by light, heat, water or the like.

  As said antioxidant, a phenol type, phosphoric acid type, and a sulfur type are mentioned, for example. Specific phosphoric acid antioxidants include triphenyl phosphite, diphenylisodecyl phosphite, phenylisodecyl phosphite, 4,4′-butylidene-bis (3-methyl-6-tert-butylphenylditridecyl) ) Phosphite, octadecyl phosphite, tris (nonylphenyl) phosphite, tris (mono and / or dinonylphenyl) phosphite, diisodecylpentaerythritol diphosphite, 9,10-dihydro-9-oxa-10-phospha Phenanthrene = 10-oxide, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9 , 10-Dihydro-9-oxa-10-phos Aphenanthrene, tris (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis (2 , 6-di-t-butyl-4-methylphenyl) phosphite, 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite, tetraphenyltetra (tridecyl) pentaerythritol tetraphosphite, 2,2'-ethylidenebis (4,6-di-t-butylphenol) fluorophosphite, 4,4'-isopropylidene-diphenolalkyl (C12-C15) phosphite, bis (nonylphenyl) pentaerythritol diphos Fight, Dibutyl hydrogen phosphite, Dis Allyl pentaerythritol diphosphite, include phosphorous ester compound.

  As the light stabilizer, there are those used as the above-mentioned antioxidant, but benzotriazole, benzophenone, salicylate, cyanoacrylate, oxalic acid derivative, hindered amine (HALS), hindered phenol, etc. Can be mentioned. Specific hindered amine light stabilizers include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 3 ″, 4 ″, 2- (2′-hydroxy-5′-t-octyl). Phenyl) benzotriazole, 2- (2′-hydroxy-4′-t-octoxyphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole, 2 -(2'-hydroxy-3 ', 5'-di-t-amylphenyl) benzotriazole, 2- (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole, 2- (2' -Hydroxy-3 ′, 5′-bis (α, α-dimethylbenzyl) phenylbenzotriazole, 2- [2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6) '-Tetraphthalimidomethyl) -5'-methylphenyl] benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'- Hydroxy-3 ', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H- Condensation with benzotriazol-2-yl) phenol, methyl-3- [3-tert-butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenylpropionate-polyethylene glycol (molecular weight about 300) 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzof Enone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2′-carboxybenzophenone, 2-hydroxy-4-methoxy-5-sulfoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, 2,2′-dihydroxy- Polymer of 4,4′-dimethoxy-5-sodiumsulfoxybenzophenone, bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane, 4- (2-acryloyloxyethoxy) -2-hydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimeth A mixture of cibenzophenone and other 4-substituted benzophenones, phenyl salicylate, 2,5-di-t-butyl-4-hydroxybenzoic acid-n-hexadecyl ester, 4-t-butylphenyl salicylate, 4-t-octylphenyl salicylate, 2,4-di-t-butylphenyl-3 ′, 5′-di-t-butyl-4′-hydroxybenzoate, ethyl (β, β-diphenyl) cyanoacrylate, 2-ethylhexyl (β, β-diphenyl) cyanoacrylate, 2-ethoxy-2′-ethylsuccinic acid bisanilide, 2-ethoxy-5-tert-butyl-2′-ethylsuccinic acid bisanilide, succinic acid anilide derivatives, indole, azomethine , Phenyl-4-piperidinyl carbonate, [4- (4-hydroxy-3,5-di-t-butylphenyl Propionyl] -N- (4-hydroxy-3,5-di-t-butylphenyl) methyl-2,2,6,6-tetramethylpiperidine, 1,1 ′-(1,2-ethanediyl) bis (3 , 3,5,5-tetramethylpiperazinone), bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis- [N-methyl-2,2,6,6-tetramethyl- Piperidinyl sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) -2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalo 1, 2,3,4-butanecarboxylic acid, 2,2,6,6-tetramethyl-4-piperidinol and tridecyl alcohol condensate, 1,2,3,4-butanecarboxylic acid and 1 , 2,2,6,6-pentamethyl- A condensate of piperidinol and tridecyl alcohol, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) -1,2,3,4-butanetetracarboxylate, tetrakis (1,2,2, 6,6-pentamethyl-4-piperidyl) -1,2,3,4-butanetetracarboxylate, poly [[6- (1,1,3,3-tetramethylbutylamino) -1,3,5- Triazine-2,4-diyl] [(2,2,6,6-tetramethylpiperidine) imino] hexamethylene [(2,2,6,6-tetramethylpiperidyl) imino]], poly [6-morpholino- s-triazine-2,4-diyl-2,2,6,6-tetramethylpiperidylimino-hexamethylene] [2,2,6,6-tetramethylpiperidylimino]], 1,2,3,4- Butanteto Carboxylic acid, 2,2,6,6-tetramethyl-4-piperidinol and β, β, β ′, β′-tetramethyl-3,9- (2,4,8,10-tetraoxaspiro [5 5] undecane) condensate with diethanol, 1,6-hexamethylenebis (N, N-dimethylsemicarbazide), 1,1,1 ′, 1′-tetramethyl-4,4 ′-(methylene-di-p -Phenylene) disemicarbazide and the like.

  As such ultraviolet absorbers, antioxidants, and light stabilizers, phosphoric acid-based antioxidants and / or hindered amine-based light stabilizers are preferable in that a cured film having better weather resistance can be obtained. In comparison with the same amount used, the hindered amine light stabilizer has a higher effect of improving weather resistance than the phosphoric acid antioxidant.

  These additives may be added in consideration of the toughness of the cured coating film itself and the adhesiveness that can follow the flexibility of the substrate to be coated, depending on the target level of weather resistance. It is preferable to use 0.1 to 15 parts, particularly 1 to 5 parts with respect to 100 parts by mass of the solid content of the coating film.

  The curable coating composition of the present invention can contain a carbodiimide compound. The carbodiimide group present in the carbodiimide compound is generated by hydrolysis of the ester group in either or both of the ester bond in the polyester resin and when the substrate to be coated is a polyester resin such as a PET film. Reacts instantly with carboxyl groups. Carbodiimide groups also react with water. Therefore, the carbodiimide compound contributes not only to the cured coating film but also to the hydrolysis resistance of the substrate itself by utilizing such a reaction mechanism.

  Moreover, this carbodiimide compound can improve the hydrolysis resistance of a cured coating film by using a resin containing a hydroxyl group, an organic polyisocyanate compound, and an epoxy resin, but the carbodiimide group reacts with an isocyanate group. Or, since carbodiimide groups react with each other to form a crosslinked structure, the hydrolysis resistance of the cured coating film can be further improved by considering the isocyanate equivalent and the amount used of the organic polyisocyanate compound to be used. I can do it.

  As such a carbodiimide compound, for example, an organic isocyanate compound can be obtained by a decarboxylation reaction in the presence of a carbodiimidization catalyst such as phospholene oxide. Furthermore, monocarbodiimide obtained from organic monoisocyanate, polycarbodiimide obtained by capping a part of organic diisocyanate with monoalcohol or monoamine, polycarbodiimide obtained by combined use of organic monoisocyanate and organic diisocyanate, and the like can be mentioned. Examples of the organic isocyanate compound include organic monoisocyanate compounds such as phenyl isocyanate and tertiary butyl-1-phenyl isocyanate, and known conventional organic polyisocyanate compounds as described above. Specific products include DIPC (Kawaguchi Kagaku), Stabakzol (registered trademark) I (Bayer), Carbodilite (registered trademark) HMV-8CA (Nisshinbo), ELASTOSTAB (elasto stub; registered trademark) H01 (elastomer gran) AG) and the like. In the present invention, considering compatibility with a hydroxyl group-containing (meth) acrylic resin or the like, the carbodiimide compound is preferably a tetramethylxylylene diisocyanate (TMXDI) carbodiimide compound. In the present invention, the carbodiimide compound may be added in consideration of adhesion and hydrolysis resistance that can follow the flexibility of the substrate to be coated, but with respect to 100 parts by mass of the solid content of the cured coating film. 0.1 to 10 parts, preferably 1 to 5 parts.

  The curable coating composition of the present invention can contain a polycarbonate resin. Polycarbonate resin can improve the hydrolysis resistance of a cured coating film more by using together the resin containing a hydroxyl group, an organic polyisocyanate compound, and an epoxy resin.

  Polyester resins contain ester bonds and thus have poor hydrolysis resistance. Polyether resins contain ether bonds and therefore have the disadvantage of low weather resistance and low heat resistance. Does not have such a drawback. Due to the high cohesive strength of the polycarbonate group, the cured coating film can be made more excellent in heat resistance, weather resistance, oil resistance, and chemical resistance. In the present invention, the polycarbonate resin may be added in consideration of adhesion that can follow the flexibility of the substrate to be coated and hydrolysis resistance, but with respect to 100 parts by mass of the solid content of the cured coating film. 0.1 to 10 parts, preferably 1 to 5 parts.

  As this polycarbonate resin, for example, a polycarbonate resin obtained using only dialkyl carbonate and 1,6-hexanediol can be used, but in terms of lower crystallinity, as the diol, It is preferable to use a polycarbonate diol obtained by copolymerizing 1,4-butanediol, 1,5-pentanediol or 1,4-cyclohexanedimethanol.

  Examples of such a polycarbonate diol include those having a number average molecular weight of 500 to 2000 and a hydroxyl value of 30 to 500 mgKOH / g. Among them, the number average molecular weight is 800 to 1200 and is liquid at room temperature and excellent in compatibility. A hydroxyl value of 50 to 250 mgKOH / g is preferred.

  As the polycarbonate diol, for example, trade names “T5650J”, “T5651”, “T5652”, “T4671”, “T4672”, which are copolymer polycarbonate diols manufactured by Asahi Kasei Chemicals Corporation, or Ube Industries, Ltd. "UM-CARB90 (1/3)", "UM-CARB90 (1/1)" and the like are commercially available.

  From the viewpoint of adjusting the viscosity, the curable coating composition of the present invention, particularly the main component described above, can contain an organic solvent that does not have reactivity with the raw material included therein and dissolves the raw material. Specifically, for example, hydrocarbon solvents such as toluene and xylene, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, ether solvents such as dioxane and ethylene glycol diethyl ether , Aliphatic hydrocarbons such as pentane, hexane and heptane.

  If necessary, the curable coating composition of the present invention may contain other additives. Examples of the additive include additives generally used in resin compositions that form films and coating films. Examples of additives include leveling agents; inorganic fine particles such as colloidal silica and alumina sol; organic fine particles based on polymethyl methacrylate; antifoaming agents; anti-sagging agents; silane coupling agents; viscosity modifiers; Metal deactivator; Peroxide decomposing agent; Flame retardant; Reinforcing agent; Plasticizer; Lubricant; Rust preventive agent; Fluorescent whitening agent; Inorganic heat absorber; Flameproof agent; A pigment or the like.

  For example, the pigment used in the present invention is preferably titanium dioxide having an average particle size of 0.5 to 1.5 μm. When the rutile-type titanium dioxide having this particle size range is contained in the coating composition, the absorption of near infrared rays inside the cured coating film thereof can be selectively suppressed to a lower level. Such unique properties cannot be achieved with titanium dioxide having an average particle size of less than 0.5 μm. Further, titanium dioxide having an average particle diameter exceeding 1.5 μm is not preferable because it deteriorates the surface smoothness of the cured coating film.

  Titanium dioxide with an average particle size of 0.5 to 1.5 μm takes into account the toughness of the cured coating film itself and the adhesion that can follow the flexibility of the substrate to be coated, depending on the desired level of weather resistance In addition, it may be added to the main agent and / or the curing agent, but is preferably 30 to 250 parts per 100 parts in total in terms of non-volatile content of all curable components in terms of excellent weather resistance, and more particularly It is more preferable to use 120 to 210 parts in that the whiteness can be as high as when a fluororesin is used.

  The curable coating composition of the present invention is usually prepared by preparing a main component premix in which components other than the organic polyisocyanate compound that is a curing agent are blended in advance, and mixing this with the organic polyisocyanate compound. I can do it.

The curable coating composition of the present invention can be applied to various substrates and dried to laminate a cured coating film having adhesion on the substrate. The coating amount on the substrate is not particularly limited, but for example, selecting from the range of 1 to ²⁰ g / m ² , especially 5 to 10 g / m ² can give excellent weather resistance in a small amount. This is preferable. For this coating, for example, a gravure coater, a micro gravure coater, a reverse coater, a bar coater, a roll coater, a die coater or the like can be used.

  As the base material in this case, for example, paper, olefin resin, acrylonitrile-butadiene-styrene copolymer (ABS resin), polyvinyl chloride resin, fluororesin, poly (meth) acrylic resin, carbonate resin, Examples thereof include a polyamide resin, a polyimide resin, a polyphenylene ether resin, a synthetic resin film obtained from a polyphenylene sulfide resin and a polyester resin, a metal foil such as a copper foil and an aluminum foil. The thickness of the substrate is not particularly limited, and can be selected, for example, from 10 to 400 μm. However, the curable coating composition of the present invention can be applied to a substrate with a small amount of application and drying at a low temperature in a short time. Since it exhibits excellent adhesion without giving any influence such as sag and can provide excellent weather resistance, it is most suitable to be applied to a substrate having a softening temperature of 180 ° C. or less at 30 to 80 μm.

  Due to low temperature and short time drying, there is no inconvenience such as warping of the substrate or peeling of the coating film, and excellent adhesion to the substrate can be obtained and deterioration of the laminate can be prevented more effectively. In this respect, it is preferable to use a polyester resin film as the base material. The laminated polyester resin film in which the cured coating film of the curable coating composition of the present invention is laminated on the polyester resin film has the above-described excellent properties.

  Examples of the polyester resin film in this case include PET, PBT, PEN, and a film of a copolymerized polyester resin such as 1,4-cyclohexanedimethanol copolymerized polyethylene terephthalate (PET-G). Moreover, either a stretched film or an unstretched film may be used. The polyester resin film may be white or colored, but transparency is required when it is prepared by selecting raw materials so that the cured coating film of the curable coating composition of the present invention is transparent or used. In this case, it is preferable to select and use a transparent polyester resin film because the laminated polyester resin film can be made transparent. Of course, if necessary, as a polyester resin film, a pattern can be applied to the surface before and after lamination of the cured coating film.

  In particular, from the drying at a relatively low temperature of 160 ° C. or less for a short time of 1 minute or less, the above-mentioned inconvenience is not caused to the thin film base material, and excellent adhesion to the base material is obtained, and the moisture resistance of the laminated body is obtained. As a base material, it is more preferable to use a PET film in that deterioration based on heat resistance and hydrolysis resistance can be more effectively prevented. The laminated polyester resin film in which the cured coating film of the coating composition of the present invention is laminated on a PET film has the above-described excellent properties.

  In order to improve the adhesion between the polyester resin film and the cured coating film, a surface treatment may be performed on the surface on which the cured coating film of the polyester resin film is formed. Examples of the surface treatment include corona treatment, plasma treatment, ozone treatment, flame treatment, and radiation treatment.

  In obtaining the laminated polyester resin film in which the cured coating film of the curable coating composition of the present invention is laminated on the polyester resin film, the cured coating film 1 may be provided only on one side of the polyester resin film 2. It may be provided on both sides. The layer structure of the laminated polyester resin film in which the cured coating film 1 is provided on one side of the polyester resin film 2 is as shown in FIG. A polyester resin-based or polyurethane resin-based easy-adhesive coating agent 3 is applied to the PET surface 2 on the side opposite to the cured coating film 1 of the coating composition of the present invention of the laminated polyester resin film of FIG. A laminated polyester resin film as shown in FIG. 2 that can be adhered to the material can also be obtained. For distribution, a release paper (release film) is further laminated on the outside of the easy-adhesive coating agent 3 and, when in use, the laminate polyester resin film can be adhered to the substrate by peeling it off. . These laminated polyester resin films shown in FIGS. 1 and 2 can be used for a solar battery back sheet.

  For applications that receive light, heat, water, and other effects that cause deterioration from only one side, it is generally sufficient to provide a cured coating only on that side of the two surfaces of the polyester resin film. effective. However, when there is a possibility of receiving the action of light, heat or water from both sides, it is desirable to provide both sides.

  A laminated polyester resin film having a multilayer structure including at least a laminated polyester resin film in which a cured film of the curable coating composition of the present invention is laminated on a polyester resin film can also be used as a solar cell backsheet.

  In order to give a further excellent gas barrier property to the solar cell back sheet, it is preferable to provide a thin film of, for example, aluminum, aluminum oxide, silicon oxide, tin oxide or magnesium oxide in the intermediate layer. For example, an adhesive having excellent adhesion between a polyester resin film and an intermediate layer having a gas barrier property on the surface of the polyester resin film 2 opposite to the cured coating film 1 of the coating composition of the present invention of the laminated polyester resin film of FIG. 4, a flexible thin film (intermediate layer) 5 of a metal or metal oxide having a gas barrier property such as a soft aluminum layer is laminated, and a polyester resin film and a gas barrier property are further formed outside the intermediate layer 5. Including a structure in which another polyester resin film 2 is laminated via an adhesive 4 excellent in adhesiveness with a certain intermediate layer so that the gas barrier intermediate layer 5 is sandwiched between the polyester resin films, The polyester resin film surface of was coated with a cured coating film of the coating composition of the present invention, Can be obtained solar cell back sheet (see FIG. 3.).

  In addition, it replaces with the polyester resin film with which the surface is untreated, PET film layer by using two polyester resin films provided with vapor deposition thin films, such as aluminum, aluminum oxide, silicon oxide, tin oxide, and magnesium oxide, on one side No adhesive layer 4 is provided between the intermediate layer 5 and the intermediate layer 5, and a cured coating film of the coating composition of the present invention is laminated on the surface opposite to the surface of the deposited thin film, and the respective deposited thin film sides are bonded to each other. It is possible to obtain a solar battery back sheet similar to that shown in FIG.

Hereinafter, the present invention will be specifically described with reference to examples. In the examples, “part” is based on weight.
The number average molecular weight of the resin containing a hydroxyl group used in the present invention was determined under the following conditions using a gel permeation chromatograph (GPC); HLC-8220 manufactured by Tosoh Corporation
Detector: RI (differential refractometer)
Measurement conditions: Column temperature 40 ° C. Solvent Tetrahydrofuran Further, the glass transition temperature of the resin containing a hydroxyl group used in the present invention was determined under the following conditions.
Measuring device: DSC220C manufactured by Seiko Electronics Corporation
Measuring method: DSC (Differential Scanning Calorimetry) method

Examples 1-7, Comparative Examples 1-4
As shown in Table 1 and Table 2 below, using a resin containing a hydroxyl group, an organic polyisocyanate compound, an epoxy resin, a carbodiimide compound, a polycarbonate resin, an antioxidant, and a light stabilizer, the main component and the curing agent component A two-part type of the present invention and a conventional curable coating composition were prepared.
With a bar coater, the obtained curable coating composition was immediately applied to the corona-treated surface of a corona-treated PET film (thickness 50 μm) manufactured by Toyobo Co., Ltd. so that the coating amount was 7 g / m ² . Each layer was dried at 100 ° C. for 30 seconds to obtain each laminated polyester resin film having the layer structure of FIG.
The weather resistance was determined by using the heat and humidity resistance including the influence of hydrolysis resistance as an index. This weather resistance was evaluated using a laminated polyester resin film instead of the cured coating film itself. In evaluating weather resistance, each laminated polyester resin film was subjected to a pressure cooker test (PCT) to determine how much the breaking strength and elongation strength of the laminated polyester resin film changed before and after the test. PCT was performed under conditions of a temperature of 121 ° C. × humidity of 100% × 50 hours, and each strength was measured with a Tensilon universal material testing machine manufactured by A & D Corporation.
The strength retention ratios before and after PCT are shown in Tables 1 and 2 below, where 90% or more is ◎, 89 to 70% is ○, 69 to 40% is Δ, and 39% or less is ×.

Elitel UE-3210: Polyester resin (Unitika Ltd.) Solid content: 100%, Tg: 45 ° C., hydroxyl value: 4 mg KOH / g, number average molecular weight: 20,000
Elitel UE-3220: Polyester resin (Unitika Ltd.) Solid content: 100%, Tg: 5 ° C., hydroxyl value: 3 mgKOH / g, number average molecular weight: 25,000
ACRYDIC A-808-T: hydroxyl group-containing acrylic resin (DIC Corporation), solid content: 50%, Tg: 70 ° C., hydroxyl value: 20 mgKOH / g
ACRYDIC A-809: Hydroxyl-containing acrylic resin (DIC Corporation), solid content: 50%, Tg: 41 ° C., hydroxyl value: 20 mgKOH / g
Epicron 860: Bisphenol A type epoxy resin (DIC Corporation), solid content: 100%, epoxy equivalent: 240
Epicron 3050: Bisphenol A type epoxy resin (DIC Corporation) Solid content: 100%, epoxy equivalent: 800
DURANOL T-5651: Polycarbonate diol (Asahi Kasei Chemicals Corporation), solid content: 100% Number average molecular weight: 1000 Hydroxyl value: 100-120 mgKOH / g
IRGAFOS 168: Phosphorous antioxidant (BASF Japan Ltd.) Solid content: 100%
Tinuvin 123: Light stabilizer (HALS) (BASF Japan Ltd.) Solid content: 100%
ELASTOSTAB H01: Carbodiimide resin (Nisshinbo Chemical Co., Ltd.) Solid content: 100%
Sumidur N3300: HDI polyisocyanate (Sumika Bayer Urethane Co., Ltd.) Solid content: 100%

Since the curable coating composition of the present invention has more excellent weather resistance, for example, surface protection of a marking film used by being attached to the surface of a railway vehicle, an automobile, a vending machine, etc., gloss improvement, discoloration Protecting precision parts and preventing discoloration mainly as overlay films for the purpose of preventing deterioration, surface protection films for plastic windows and exterior signs for vehicles and houses, liquid crystal display reflection sheets, solar cell back sheets, etc. It is possible to provide a highly weather-resistant film or sheet used for the purpose described above.

1 Cured product (cured coating film) of the coating composition of the present invention
2 PET film 3 Adhesive coating agent 4 Adhesive 5 Soft aluminum

Claims (9)

  Epoxy resin having an epoxy equivalent of 170 to 750, a curable coating composition containing a resin containing a hydroxyl group other than an epoxy resin and an organic polyisocyanate compound   2. The curable coating composition according to claim 1, wherein the epoxy resin is at least one resin selected from the group consisting of a bisphenol-type epoxy resin, a hydrogenated bisphenol-type epoxy resin, and an alicyclic epoxy resin.   The curable coating composition according to claim 1 or 2, wherein the epoxy resin is a bisphenol A type epoxy resin.   The hydroxyl group value of the resin containing the hydroxyl group is 1 to 200 mgKOH / g, the glass transition temperature is 30 to 110 ° C. in the differential scanning calorimetry (DSC method), and the number average molecular weight is 5,000 to 50,000. The curable coating composition according to any one of claims 1 to 3.   The curable coating composition according to any one of claims 1 to 4, wherein the resin containing a hydroxyl group is one or more resins selected from the group consisting of an acrylic resin, a polyester resin, a urethane resin, and a fluorine resin. object.   Furthermore, the curable coating composition as described in any one of Claims 1-5 containing antioxidant and / or a light stabilizer.   Furthermore, the curable coating composition as described in any one of Claims 1-6 containing a polycarbonate resin and / or a carbodiimide compound.   A laminated polyester resin film in which a cured film of the curable coating composition according to any one of claims 1 to 7 is laminated on a polyester resin film.   A solar cell back sheet having a multilayer structure comprising the laminated polyester resin film according to claim 8.

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