WO2013146180A1 - Solar cell back protection sheet and solar cell module - Google Patents

Abstract

This solar cell back surface protective sheet includes a polymer layer in direct contact with one surface on a polyester support body containing polyester and an end-capping agent, and said polymer layer contains, in the molecule, a composite polymer comprising 15-85% siloxane structural units represented by general formula (S-1): -(Si(R¹¹)(R¹²)-O)_n1- and 85-15 mass% non-siloxane-based structural units including a carboxyl group, and a crosslinking agent-derived structural part which comprises 45-85 mass% of a pigment with a bulk specific gravity of 0.50-0.85 g/cm³ and which crosslinks the aforementioned composite polymer, wherein this solar cell back surface protective sheet has excellent adhesion all throughout aging in hot and humid conditions, excellent adhesion after UV irradiation, excellent coloring, and high fracture elongation retention after hot and humid storage and after heat-resistant storage (R¹¹ and R¹² are a hydrogen atom, a halogen atom, or a monovalent organic group; n1 is a natural number).

Description

Solar cell back surface protection sheet and solar cell module

The present invention relates to a back surface protection sheet for solar cells and a solar cell module.

Solar cells are a power generation system that emits no carbon dioxide during power generation and has a low environmental load, and has been rapidly spreading in recent years.

The solar cell module is usually a front glass on the side where sunlight enters, and a back surface protection sheet for solar cells (so-called back sheet) disposed on the side opposite to the side on which sunlight enters (back side) Between the front glass and the solar cell, and between the solar cell and the back sheet, respectively, EVA (ethylene-vinyl acetate) resin. Etc. are sealed.

A solar cell back surface protection sheet (back sheet) is used on the back surface of a solar cell, and has durability (hydrolysis resistance, heat resistance, light resistance) as a protection sheet, adhesion to a solar cell sealing material, etc. Is required. As the back sheet, as described in Patent Documents 1 to 6, a coating type back sheet has been proposed.
The coating type backsheet is a functional layer coating solution in which a functional material is dissolved or dispersed in an organic solvent or water on a support sheet such as polyester, and is applied to the support sheet at room temperature or a moderately high temperature. Created.
The advantage of the coating type back sheet is that the manufacturing cost can be reduced as compared with the laminate type back sheet. On the other hand, since the functional layer is provided by coating without using an adhesive, the drawback is that the adhesion between the support sheet and the functional layer and its durability are inferior. On the other hand, in order to improve the adhesion between the functional layer and the support sheet and its durability, Patent Document 6 proposes a coating-type back sheet using a curable functional group-containing fluoropolymer paint.

With the recent progress of solar cells, solar cell back sheets are increasingly required to have weather resistance (hydrolysis resistance, heat resistance, light resistance). In order to provide this function, the primary structure (amount of terminal carboxylic acid, molecular weight, etc.) or higher order of the polyester film, which is a support sheet occupying most of the coating type back sheet, as described in Patent Documents 7 and 8. Techniques for controlling the structure (plane orientation, etc.) and techniques for introducing a hydrolysis-resistant agent into a support sheet as described in Patent Documents 9 and 10 are known.

Further, Patent Document 11 is excellent in weather resistance, in which a polymer layer containing Typake R-780-2, which is a fine particle of titanium oxide, is coated on a polyester support containing polyester and a carbodiimide compound as an end-capping agent. A back surface protection sheet for solar cells is described. In Patent Document 12, a polymer layer containing a composite polymer containing siloxane and an acrylic structural unit and Typek R-780-2, which is titanium oxide fine particles, is coated on a polyester support, and has high light reflectance. A polymer sheet for solar cell backsheets having good adhesion and adhesion durability is described.

Special table 2010-519742 JP 2011-29397 A JP 2011-165967 A JP 2011-184488 A JP 2007-150084 A JP 2007-35694 A JP 2007-70430 A JP 2009-256621 A JP 2002-187965 A JP 2011-222580 A JP 2012-17456 A JP 2012-4546 A

However, none of the solar cell back surface protective sheets described in Patent Documents 1 to 12 has satisfactory performance. For example, the back surface protection sheet for solar cells described in Patent Document 3 has a high reflectance by providing a silicone-based weather-resistant coating layer on a titanium dioxide-containing polyester support and adjusting the amount of terminal carboxylic acid groups of the polyester support. Although it is described that weather resistance is imparted to the film, the weather resistance performance was insufficient from recent requirements. Moreover, if the amount of terminal carboxylic acid groups is further reduced to provide weather resistance that meets recent requirements, there is a problem that the adhesion between the polyester support and the weather-resistant coating layer deteriorates.
Although the back surface protection sheet for solar cells described in Patent Document 6 describes that light resistance can be improved by providing a coating layer using a curable functional group-containing fluoropolymer paint on a water-impermeable sheet, The heat resistance and heat resistance are not taken into consideration, and the inventors have found that it is insufficient. Moreover, although the water-impermeable sheet | seat is used as a support body in the same literature, there also existed a problem that the weather resistance of a support body was inadequate.
When using a highly weather-resistant support sheet as in Patent Documents 7 to 10, if a functional coating layer is provided, there is a problem that the adhesion between the support and the functional coating layer and its durability deteriorate. I found out that For example, the solar cell back surface protective sheet described in Patent Document 10 is described as being able to improve the adhesion between the base material layer and the surface layer by providing a surface layer made of thermoplastic polyester on the base material layer containing the carbodiimide compound. However, the weather resistance required in recent years was insufficient.
In Patent Documents 11 and 12, a polymer layer containing Typek R-780-2, which is titanium oxide fine particles, is coated on a polyester support, but both of them have recently required adhesion before and after wet heat aging. It was not enough.

The present invention aims to solve the above problems. The problem to be solved by the present invention is that the adhesiveness is good before and after wet heat aging, the adhesiveness after UV irradiation is good, the coloring is good, the elongation at break after wet heat storage and after heat resistant storage It is providing the back surface protection sheet for solar cells with a high retention rate.

In order to solve the above-mentioned problems, the present inventors diligently studied to introduce a terminal blocker into a polyester support, a specific binder in a functional polymer layer adjacent to the polyester support, and a specific By adding a pigment having a specific gravity in a specific addition amount and further adding a cross-linking agent, it has been found that a back protective sheet for a solar cell that can simultaneously solve all the above problems can be obtained. .

The present invention which is a specific means for solving the above-mentioned problems is as follows.
[1] A polyester support containing polyester and a terminal blocker, and a polymer layer in direct contact with at least one surface of the polyester support, wherein the polymer layer has the following general formula (S -1) containing 15 to 85% by mass of the siloxane structural unit and 85 to 15% by mass of the non-siloxane structural unit, and the non-siloxane structural unit includes a composite polymer containing a carboxyl group, The pigment having a bulk specific gravity of 0.50 to 0.85 g / cm ³ is 45 to 85% by mass with respect to the total mass of the polymer layer, and the polymer layer is derived from a crosslinking agent that crosslinks the composite polymer. The back surface protection sheet for solar cells characterized by including a structure part.
Formula (S-1)
-(Si (R ¹¹ ) (R ¹² ) -O) _n1-
[In the general formula (S-1), R ¹¹ and R ¹² each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, and R ¹¹ and R ¹² may be the same or different. n1 represents a natural number. When n1 is 2 or more, the plurality of R ¹¹ and R ¹² may be the same as or different from each other. ]
[2] In the back protective sheet for solar cells according to [1], the non-polysiloxane structural unit of the composite polymer is preferably an acrylic structural unit.
[3] In the back protective sheet for solar cells according to [1] or [2], it is preferable that 0.1 to 5.0% by mass of the end-capping agent is added to the polyester support. .
[4] In the back surface protective sheet for a solar cell according to any one of [1] to [3], the end-capping agent is preferably polycarbodiimide.
[5] In the back protective sheet for a solar cell according to [4], the polycarbodiimide is preferably a polycarbodiimide having a molecular weight of 2000 to 50000.
[6] In the back protective sheet for a solar cell according to [4] or [5], the polycarbodiimide is preferably a polycarbodiimide having a melting point of 80 to 170 ° C.
[7] In the back protective sheet for a solar cell according to any one of [1] to [6], the pigment is preferably titanium dioxide.
[8] In the back protective sheet for solar cells according to any one of [1] to [7], the crosslinking agent is preferably at least one selected from oxazoline compounds and carbodiimide compounds.
[9] In the back surface protective sheet for a solar cell according to any one of [1] to [8], the end-capping agent is preferably a cyclic carbodiimide compound.
[10] A solar cell module comprising the solar cell back surface protective sheet according to any one of [1] to [9].

The polyester film of the present invention has good adhesiveness before and after wet heat aging, good adhesiveness after UV irradiation, good coloration, and high elongation at break after wet heat storage and heat resistant storage. high.

It is the schematic which shows an example of the cross section of the back surface protection sheet for solar cells of this invention. It is the schematic which shows another example of the cross section of the back surface protection sheet for solar cells of this invention. It is the schematic which shows another example of the cross section of the back surface protection sheet for solar cells of this invention. It is the schematic which shows an example of the cross section of the solar cell module using the back surface protection sheet for solar cells of this invention.

Hereinafter, the back surface protection sheet for solar cells and solar cell module of this invention are demonstrated in detail.
The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Back protection sheet for solar cells]
The back surface protection sheet for solar cells of the present invention has a polyester support containing polyester and a terminal sealing agent, and a polymer layer in direct contact with at least one surface on the polyester support, the polymer layer comprising: A compound containing 15 to 85% by mass of a siloxane structural unit represented by the following general formula (S-1) and 85 to 15% by mass of a non-siloxane structural unit in the molecule, and the non-siloxane structural unit containing a carboxyl group 45 to 85% by mass of a pigment containing a polymer, wherein the polymer layer has a bulk specific gravity of 0.50 to 0.85 g / cm ³ , based on the total mass of the polymer layer, It contains a structural part derived from a crosslinking agent that crosslinks the polymer.
Formula (S-1)
-(Si (R ¹¹ ) (R ¹² ) -O) _n1-
[In the general formula (S-1), R ¹¹ and R ¹² each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, and R ¹¹ and R ¹² may be the same or different. n1 represents a natural number. When n1 is 2 or more, the plurality of R ¹¹ and R ¹² may be the same as or different from each other. ]
By adopting such a configuration, the back surface protection sheet for solar cells of the present invention has good adhesiveness before and after wet heat aging, good adhesiveness after ultraviolet irradiation, good coloring, wet heat High elongation at break after storage and after heat-resistant storage. That is, the back surface protection sheet for solar cells of the present invention improves the weather resistance (wet heat resistance, heat resistance and light resistance) of the polyester support itself and the polymer layer (preferably the coating layer), and at the same time, the polyester support and the polymer layer. The weather resistance of the adhesion between (preferably the coating layer) can also be increased.
Hereinafter, the preferable structure of the back surface protection sheet for solar cells of this invention is demonstrated.

<Configuration>
First, preferred configurations of the back surface protection sheet for solar cells of the present invention are described in FIGS.
The back protective sheet for a solar cell shown in FIG. 1 has a polymer layer 3 disposed adjacent to the polyester support 16 adjacent to one side of the polyester support 16, and the polymer layer 3 is the outermost layer. An outer layer (back layer) is formed.
In the back surface protection sheet for a solar cell shown in FIG. 2, the polymer layer 3 is disposed adjacent to one surface side of the polyester support 16, and a second back layer (overcoat layer) 4 is further formed thereon. Arranged to form the outermost layer. It is further preferable that the overcoat layer 4 is further provided on the polymer layer 3 as described above.
The back surface protective sheet shown in FIG. 3 is provided with the easy-adhesion layer 2 and the white layer 1 on the side of the polyester support 16 opposite to the side on which the polymer layer 3 is provided.

Next, the details of preferred embodiments of each layer will be described for the back surface protective sheet for solar cell of the present invention.

<Polyester support>
The back surface protection sheet for solar cells of this invention has the polyester support body containing polyester and terminal blocker.

-polyester-
The polyester used for the polyester support is preferably a linear saturated polyester synthesized from an aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof. Specific examples of such polyester include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylenedimethylene terephthalate), polyethylene-2,6-naphthalate and the like.
Among these, polyethylene terephthalate (PET) or polyethylene-2,6-naphthalate (PEN) is particularly preferable, and PET is more particularly preferable from the viewpoint of the balance between mechanical properties and cost.

In the present invention, the terminal carboxyl group content AV of the polyester is preferably 3 to 20 eq / ton. More preferably, it is 4 to 17 eq / ton, and further preferably 5 to 15 eq / ton. Exceeding this range is not preferable because the sealant cannot sufficiently react with the carboxylic acid and the heat-and-moisture resistance deteriorates. On the other hand, below this range, the number of carboxylic acid groups on the surface becomes too small, and the adhesion with the polymer layer deteriorates, which is not preferable.

The carboxyl group content in the polyester should be adjusted according to the polymerization catalyst species before film formation, the solid phase polymerization conditions after normal polymerization, and the film formation conditions (film formation temperature and time, stretching conditions and thermal relaxation conditions), etc. Is possible. In particular, it is preferable to control by the solid phase polymerization conditions before the polymer support is formed into a film.
The carboxyl group content (AV) A. Pohl, Anal. Chem. 26 (1954) 2145, and can be measured. Specifically, the target polyester is pulverized and dried in a vacuum dryer at 60 ° C. for 30 minutes. Next, 0.1000 g of the polyester immediately after drying is weighed, 5 ml of benzyl alcohol is added, and then dissolved by stirring with heating at 205 ° C. for 2 minutes. The solution was cooled, 15 ml of chloroform was added, phenol red was used as an indicator, and neutralization point (pH = 7.3 ± 0.10.0) with an alkali reference solution (0.01 N KOH-benzyl alcohol mixed solution). Titrate to 1) and calculate from the appropriate amount.

In the solar cell protective sheet of the present invention, the polyester preferably has an intrinsic viscosity IV (molecular weight) in the range of 0.6 to 1.2 dl / g. More preferably, it is dl / g at 0.65 to 1.00, and further preferably 0.70 to 0.95 dl / g. In order to improve the hydrolysis resistance, it is preferable to increase the intrinsic viscosity. However, when the intrinsic viscosity exceeds 1.2 dl / g, it is necessary to lengthen the solid phase polymerization time when producing the polyester resin, and the cost is remarkably high. Therefore, it may not be preferable. On the other hand, if it is less than 0.6 dl / g, the degree of polymerization is low, so that the heat resistance and hydrolysis resistance are remarkably lowered, which is not preferable.
The IV value was obtained by pulverizing the target polyester and dissolving it in 0.01 g / ml using a 1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent. Using a viscometer (AVL-6C, Asahi Kasei Techno System Co., Ltd.). The sample is dissolved at 120 ° C. for 15 to 30 minutes.

The polyester is preferably solid-phase polymerized after polymerization. Thereby, it becomes easy to achieve control to a preferable carboxyl group content and intrinsic viscosity. Solid-phase polymerization may be a continuous method (a method in which a tower is filled with a resin, which is slowly heated for a predetermined time and then sent out), or a batch method (a resin is charged into a container). , A method of heating for a predetermined time). Specifically, for solid phase polymerization, Japanese Patent No. 2621563, Japanese Patent No. 3121876, Japanese Patent No. 3136774, Japanese Patent No. 3603585, Japanese Patent No. 3616522, Japanese Patent No. 3617340, Japanese Patent No. 3680523, Japanese Patent No. 3717392 are disclosed. The method described in Japanese Patent No. 4167159 can be applied.

長 く By increasing the solid phase polymerization time, the IV of the polyester increases and the AV decreases. AV increases by increasing the solid-state polymerization temperature. Preferred solid phase polymerization conditions are 180 ° C. or higher and 230 ° C. or lower, more preferably 190 ° C. or higher and 220 ° C. or lower, more preferably 195 ° C. or higher and 210 ° C. or lower, and the solid phase polymerization time is preferably 10 hours or longer and 70 hours or shorter, more preferably 14 hours to 50 hours, more preferably 16 hours to 35 hours. The solid phase polymerization is preferably carried out in a vacuum or in an inert air stream.

-End sealant-
The polyester support contains an end capping agent. By introducing the end-capping agent into the polyester support, the moisture resistance and heat resistance of the polyester support itself can be improved, and the adhesion to the polymer layer described below and its durability can be significantly improved. Can do.
The mechanism for improving the weather resistance of the polyester support itself is derived from the reaction of the end-capping agent with the terminal carboxylic acid of the polyester molecular chain. It is known that the terminal carboxylic acid of the polyester molecular chain causes an autocatalytic reaction by an acid and promotes the decomposition of the polyester molecule in a high temperature environment or a high humidity environment. By inactivating the terminal carboxylic acid with an end-capping agent, the weather resistance (wet heat resistance and heat resistance) of the polyester support itself is improved.
The mechanism for improving the adhesion between the polymer layer and the polyester support and the durability thereof is derived from the fact that the end-capping agent builds a crosslinked structure between the polyester support and the polymer layer. As described later, by introducing a carboxyl group into the composite polymer contained in the polymer layer, the end-capping agent can react with not only the polyester support but also the composite polymer. A cross-linked structure is constructed between them, and they are firmly adhered to each other, and the weather resistance is dramatically improved.

The back protective sheet for a solar cell of the present invention preferably contains 0.1 to 5.0% by mass of the end-capping agent in the polyester support with respect to the polyester support. The content of 2.0% by mass is more preferable, and the content of 0.2 to 1.0% by mass is particularly preferable from the viewpoint of improving the adhesion between the polyester support and the polymer layer after wet heat aging.
Furthermore, if the content of the end-capping agent with respect to the polyester support is 0.1% by mass or more, it is possible to achieve an improvement in weather resistance due to the effect of reducing the terminal carboxylic acid content (AV) of the polyester in the polyester support. On the other hand, if the content of the end-capping agent with respect to the polyester support is 5.0% by mass or less, the addition of the end-capping agent can suppress a decrease in the glass transition temperature (Tg) of the polyester, resulting in weather resistance. It is possible to suppress a decrease in property and an increase in heat shrinkage. This is because the increase in hydrolyzability caused by the increase in the reactivity of the polyester relative to the decrease in the Tg is suppressed, or the mobility of the polyester molecules that increase due to the decrease in the Tg is likely to increase. This is to suppress heat shrinkage that occurs in the process.

Examples of the terminal blocking agent include carbodiimide compounds, oxazoline compounds, epoxy compounds, carbonate compounds, and the like, and carbodiimide compounds having high affinity with a polyester support are particularly preferable.

(1) Carbodiimide compound The carbodiimide compound having a carbodiimide group includes a monofunctional carbodiimide and a polyfunctional carbodiimide. Examples of the monofunctional carbodiimide include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, and t-butyl. Examples include isopropyl carbodiimide, diphenyl carbodiimide, di-t-butyl carbodiimide, and di-β-naphthyl carbodiimide. Particularly preferred are dicyclohexylcarbodiimide and diisopropylcarbodiimide.
As the polyfunctional carbodiimide, carbodiimide having a polymerization degree of 3 to 15 is preferably used. Specifically, 1,5-naphthalene carbodiimide, 4,4′-diphenylmethane carbodiimide, 4,4′-diphenyldimethylmethane carbodiimide, 1,3-phenylene carbodiimide, 1,4-phenylene diisocyanate, 2,4-tolylene Carbodiimide, 2,6-tolylene carbodiimide, mixture of 2,4-tolylene carbodiimide and 2,6-tolylene carbodiimide, hexamethylene carbodiimide, cyclohexane-1,4-carbodiimide, xylylene carbodiimide, isophorone carbodiimide, isophorone carbodiimide, Dicyclohexylmethane-4,4′-carbodiimide, methylcyclohexanecarbodiimide, tetramethylxylylene carbodiimide, 2,6-diisopropylphenylcarbodiimide and 1, , And the like can be exemplified 5- triisopropylbenzene-2,4-carbodiimide.
Moreover, it can select from the compound obtained by superposing | polymerizing aliphatic diisocyanate, alicyclic diisocyanate, aromatic diisocyanate, and these mixtures as polycarbodiimide. Specific examples of the polycarbodiimide include poly (1,6-hexamethylenecarbodiimide), poly (4,4′-methylenebiscyclohexylcarbodiimide), poly (1,3-cyclohexylenecarbodiimide), poly (1,4-cycloheximide). Silenecarbodiimide), poly (4,4′-dicyclohexylmethanecarbodiimide), poly (4,4′-diphenylmethanecarbodiimide), poly (3,3′-dimethyl-4,4′-diphenylmethanecarbodiimide), poly (naphthylenecarbodiimide) ), Poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide), poly (tolylcarbodiimide), poly (diisopropylcarbodiimide), poly (methyl-diisopropylphenylenecarbodiimide), poly (1,3,5-trii) Examples include polycarbodiimides such as propylbenzene) polycarbodiimide, poly (1,3,5-triisopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide, poly (triethylphenylenecarbodiimide), and poly (triisopropylphenylenecarbodiimide). Can do.

The carbodiimide compound is preferably a carbodiimide compound having high heat resistance because an isocyanate gas is generated by thermal decomposition. In order to improve heat resistance, the higher the molecular weight (degree of polymerization), the more preferable is polycarbodiimide. The weight average molecular weight of the polycarbodiimide compound is preferably 2000 or more, and more preferably 10,000 or more, from the viewpoint of volatility. Further, the upper limit of the weight average molecular weight of the polycarbodiimide compound is preferably 50000 or less from the viewpoint of improving the adhesion between the polyester support and the polymer layer after wet heat aging and after ultraviolet irradiation, and more preferably 30000 or less. preferable.
Further, once thermal decomposition occurs, further thermal decomposition is likely to occur. Therefore, it is necessary to devise measures such as setting the extrusion temperature of the polyester as low as possible.
A cyclic carbodiimide compound described in JP2011-153209A is also effective for suppressing the generation of isocyanate-based gas.

In the back surface protective sheet for a solar cell of the present invention, the melting point of the polycarbodiimide is preferably 80 to 170 ° C. from the viewpoint of uniformity when the polyester and the polycarbodiimide are kneaded and mixed, and is 80 to 160 ° C. Is more preferable, and 80 to 150 ° C. is particularly preferable.

In addition, the polycarbodiimide compound is preferably a compound obtained by polymerizing aromatic diisocyanate from the viewpoint of hydrolysis resistance, and is a polycarbodiimide having a unit structure represented by the following general formula (1). Preferably there is.
General formula (1)

[R ₁ , R ₂ , R ₃ and R ₄ each independently represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom. n represents the number of repeating units. ]

Examples of the polycarbodiimide having a unit structure represented by the general formula (1) obtained by polymerizing aromatic diisocyanate include poly (1,3,5-triisopropylphenylene-2,4-carbodiimide), poly (1 , 5-diisopropylphenylene-2,4-carbodiimide) and copolymers thereof.

The following polycarbodiimides can be used as commercial products.
-Starvacol P400: polycarbodiimide, weight average molecular weight of about 20000, melting point 150 ° C., manufactured by Rhein Chemie Japan Co., Ltd.
-Starvacol P100: polycarbodiimide, weight average molecular weight of about 10,000, melting point 120 ° C., manufactured by Rhein Chemie Japan Co., Ltd.)
・ Starbazole P: polycarbodiimide, weight average molecular weight 3000, melting point 80 ° C., manufactured by Rhein Chemie Japan Co., Ltd. ・ Carbodilite HMV-8CA: polycarbodiimide, weight average molecular weight about 3000, melting point 80 ° C., manufactured by Nisshinbo Chemical Co., Ltd. ・ STABILIZER9000 : Polycarbodiimide, weight average molecular weight of about 20000, melting point 150 ° C., manufactured by Rhein Chemie)

(2) Epoxy compound Moreover, as a preferable example of an epoxy compound, a glycidyl ester compound, a glycidyl ether compound, etc. are mentioned.
Specific examples of glycidyl ester compounds include benzoic acid glycidyl ester, t-Bu-benzoic acid glycidyl ester, P-toluic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, pelargonic acid glycidyl ester, stearic acid glycidyl ester, lauric acid glycidyl ester , Glycidyl palmitate, glycidyl behenate, glycidyl versatate, glycidyl oleate, glycidyl linoleate, glycidyl linolein, glycidyl behenol, glycidyl stearol, diglycidyl terephthalate, isophthalic acid Diglycidyl ester, phthalic acid diglycidyl ester, naphthalenedicarboxylic acid diglycidyl ester Ter, methylterephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, cyclohexanedicarboxylic acid diglycidyl ester, adipic acid diglycidyl ester, succinic acid diglycidyl ester, sebacic acid diglycidyl ester, dodecane Examples thereof include diglycidyl diacid, octadecanedicarboxylic acid diglycidyl ester, trimellitic acid triglycidyl ester, and pyromellitic acid tetraglycidyl ester. These may be used alone or in combination of two or more.
Specific examples of the glycidyl ether compound include phenyl glycidyl ether, O-phenyl glycidyl ether, 1,4-bis (β, γ-epoxypropoxy) butane, 1,6-bis (β, γ- Epoxypropoxy) hexane, 1,4-bis (β, γ-epoxypropoxy) benzene, 1- (β, γ-epoxypropoxy) -2-ethoxyethane, 1- (β, γ-epoxypropoxy) -2-benzyl Oxyethane, 2,2-bis- [р- (β, γ-epoxypropoxy) phenyl] propane and 2,2-bis- (4-hydroxyphenyl) propane and 2,2-bis- (4-hydroxyphenyl) Examples thereof include bisglycidyl polyether obtained by reaction of bisphenol such as methane and epichlorohydrin, and these use one kind or two or more kinds. Door can be.

(3) Oxazoline Compound The oxazoline compound is preferably a bisoxazoline compound, specifically 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-2-oxazoline). 2,2′-bis (4,4-dimethyl-2-oxazoline), 2,2′-bis (4-ethyl-2-oxazoline), 2,2′-bis (4,4′-diethyl-2) -Oxazoline), 2,2'-bis (4-propyl-2-oxazoline), 2,2'-bis (4-butyl-2-oxazoline), 2,2'-bis (4-hexyl-2-oxazoline) ), 2,2′-bis (4-phenyl-2-oxazoline), 2,2′-bis (4-cyclohexyl-2-oxazoline), 2,2′-bis (4-benzyl-2-oxazoline), 2,2'-p-phenylenebis (2 Oxazoline), 2,2'-m-phenylenebis (2-oxazoline), 2,2'-o-phenylenebis (2-oxazoline), 2,2'-p-phenylenebis (4-methyl-2-oxazoline) ), 2,2′-p-phenylenebis (4,4-dimethyl-2-oxazoline), 2,2′-m-phenylenebis (4-methyl-2-oxazoline), 2,2′-m-phenylene Bis (4,4-dimethyl-2-oxazoline), 2,2′-ethylenebis (2-oxazoline), 2,2′-tetramethylenebis (2-oxazoline), 2,2′-hexamethylenebis (2 -Oxazoline), 2,2'-octamethylenebis (2-oxazoline), 2,2'-decamethylenebis (2-oxazoline), 2,2'-ethylenebis (4-methyl-2-oxazoline), 2 , 2 ' Tetramethylene bis (4,4-dimethyl-2-oxazoline), 2,2'-9,9'-diphenoxyethane bis (2-oxazoline), 2,2'-cyclohexylene bis (2-oxazoline) and 2 , 2′-diphenylenebis (2-oxazoline) and the like. Of these, 2,2′-bis (2-oxazoline) is most preferably used from the viewpoint of reactivity with polyester. Furthermore, as long as the objective of this invention is achieved, the bisoxazoline compound mentioned above may be used individually by 1 type, or may use 2 or more types together.

<Polymer layer>
The back protective sheet for solar cells of the present invention has a polymer layer that is in direct contact with at least one surface on the polyester support, and the polymer layer is represented by the following general formula (S-1) in the molecule. 15 to 85% by mass of a siloxane structural unit and 85 to 15% by mass of a non-siloxane structural unit, and the non-siloxane structural unit includes a composite polymer containing a carboxyl group, and the polymer layer has a bulk specific gravity of 0.1. 45 to 85% by mass of a pigment of 50 to 0.85 g / cm ³ is contained with respect to the total mass of the polymer layer, and the polymer layer contains a structural part derived from a crosslinking agent that crosslinks the composite polymer.

The polymer layer in the present invention can be applied to any layer constituting the back sheet as long as it is in direct contact with at least one surface on the polyester support. The polymer layer can be applied as, for example, an adhesive layer that bonds a functional layer such as a reflective layer, a back layer, or a reflective layer and a polyester support. From the viewpoint of excellent durability in heat and moisture and other wet heat environments and UV irradiation environments, the backsheet component layer is a layer exposed to the external environment when used as a solar cell module, that is, as a back layer. It is particularly preferable to use it.
Since the polymer layer is exposed to the outdoor environment, the polymer layer itself deteriorates (breaks and changes in quality) and adherence to the substrate even when exposed to heat, water vapor, or ultraviolet rays for a long time. It is necessary not to occur.

-Composite polymer-
In order to achieve the deterioration of the polymer layer itself (cracking and alteration) and the deterioration of adhesion to the substrate, the polymer layer has a mass ratio represented by the general formula (S-1) in the molecule. Contains a siloxane structural unit of 15 to 85% by mass and a non-siloxane structural unit of 85 to 15% by mass, and the non-siloxane structural unit contains a composite polymer containing a carboxyl group. By using the composite polymer, the adhesive strength between the layers, the adhesive strength between the polyester support and the battery side substrate (especially a sealing material such as EVA) is improved, and deterioration due to heat, moisture or ultraviolet rays is suppressed. . Therefore, the adhesive strength can be kept high over a long period of time under environmental conditions that are exposed to heat, moisture or ultraviolet rays for a long time, and long-term durability can be ensured. That is, the weather resistance (moisture and heat resistance, heat resistance and weather resistance) of the polymer layer is improved.

In order to improve the adhesion to the polyester support, the composite polymer contains a carboxyl group. The end sealant contained in the polyester support undergoes a crosslinking reaction at the interface between the polymer layer and the polyester support to create a primary structure, thereby improving the adhesion between the polyester support and the coating layer and its durability. It is to do.
The composite polymer in the present invention is a block copolymer in which (poly) siloxane and at least one polymer are copolymerized. The (poly) siloxane and the copolymerized polymer may be one kind alone, or two or more kinds.

Formula (S-1)
-(Si (R ¹¹ ) (R ¹² ) -O) _n1-
[In the general formula (S-1), R ¹¹ and R ¹² each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, and R ¹¹ and R ¹² may be the same or different. n1 represents a natural number. When n1 is 2 or more, the plurality of R ¹¹ and R ¹² may be the same as or different from each other. ]
The portion of “— (Si (R ¹¹ ) (R ¹² ) —O) _n1 —” which is the (poly) siloxane segment in the composite polymer ((poly) siloxane structural unit represented by the general formula (S-1)) In the formula, R ¹¹ and R ¹² may be the same or different and each represents a hydrogen atom, a halogen atom, or a monovalent organic group.
“— (Si (R ¹¹ ) (R ¹² ) —O) _n1 —” is a (poly) siloxane segment derived from various (poly) siloxanes having a linear, branched or cyclic structure.
Examples of the halogen atom represented by R ¹¹ and R ¹² include a fluorine atom, a chlorine atom, and an iodine atom.
The “monovalent organic group” represented by R ¹¹ and R ¹² is a group that can be covalently bonded to a Si atom, and may be unsubstituted or may have a substituent. Examples of the monovalent organic group include an alkyl group (e.g., methyl group, ethyl group), an aryl group (e.g., phenyl group), an aralkyl group (e.g., benzyl group, phenylethyl), and an alkoxy group (e.g. : Methoxy group, ethoxy group, propoxy group, etc.), aryloxy group (eg, phenoxy group etc.), mercapto group, amino group (eg: amino group, diethylamino group etc.), amide group and the like.
The composite polymer may have a carboxyl group in the repeating part of the siloxane structural unit represented by the general formula (S-1) or in the repeating part of the non-siloxane structural unit. . Among them, the composite polymer preferably has a carboxyl group at a repeating portion of the non-siloxane structural unit. That is, the composite polymer may not have a carboxyl group in the “monovalent organic group” represented by R ¹¹ and R ¹² .
R ¹¹ and R ¹² are each independently a hydrogen atom, chlorine atom, bromine atom, unsubstituted or substituted, in terms of adhesion to adjacent materials such as a polyester support and durability in a humid heat environment. Alkyl groups having 1 to 4 carbon atoms (particularly methyl group, ethyl group), unsubstituted or substituted phenyl group, unsubstituted or substituted alkoxy group, mercapto group, unsubstituted amino group, amide group And more preferably an unsubstituted or substituted alkoxy group (preferably an alkoxy group having 1 to 4 carbon atoms) from the viewpoint of durability in a moist heat environment.

The n1 is preferably 1 to 5000, and more preferably 1 to 1000.

The ratio of the portion of “— (Si (R ¹¹ ) (R ¹² ) —O) _n1 —” (the (poly) siloxane structural unit represented by the general formula (S-1)) in the composite polymer is The content is 15 to 85% by mass with respect to the total mass, and among them, the range of 20 to 80% by mass is preferable from the viewpoint of adhesion to a polyester support and durability in a moist heat environment.
If the ratio of the polysiloxane moiety is less than 15% by mass, the adhesion to the polyester support and the adhesion durability when exposed to a moist heat environment are inferior, and if it exceeds 85% by mass, the liquid becomes unstable.

Further, the non-siloxane structural unit copolymerized with the siloxane structural unit (the structural portion derived from the polymer) is not particularly limited except that it does not have a siloxane structure, and is derived from an arbitrary polymer. Any of the polymer segments may be used. Examples of the polymer (precursor polymer) that is a precursor of the polymer segment include various polymers such as a vinyl polymer, a polyester polymer, and a polyurethane polymer. From the viewpoint of easy preparation and excellent hydrolysis resistance, vinyl polymers and polyurethane polymers are preferred, and vinyl polymers are particularly preferred.

Representative examples of the vinyl polymer include various polymers such as an acrylic polymer, a carboxylic acid vinyl ester polymer, an aromatic vinyl polymer, and a fluoroolefin polymer. Among these, it is particularly preferable that the non-polysiloxane structural unit of the composite polymer is an acrylic structural unit because a carboxyl group can be introduced and design flexibility is high.
In addition, the polymer which comprises a non-siloxane type structural unit may be single 1 type, and 2 or more types of combined use may be sufficient as it.

In addition, the precursor polymer forming the non-siloxane structural unit is preferably one containing at least one of an acid group and a neutralized acid group and / or a hydrolyzable silyl group. Among such precursor polymers, the vinyl polymer includes, for example, (a) a vinyl monomer containing an acid group and a vinyl monomer containing a hydrolyzable silyl group and / or a silanol group. (2) a method of reacting a polycarboxylic acid anhydride with a vinyl polymer containing a previously prepared hydroxyl group and hydrolyzable silyl group and / or silanol group, 3) Utilizing various methods such as a method in which a vinyl polymer containing an acid anhydride group and a hydrolyzable silyl group and / or silanol group prepared in advance is reacted with a compound having active hydrogen (water, alcohol, amine, etc.). Can be prepared.

In the polymer layer in the present invention, the composite polymer may be used alone as a binder, or may be used in combination with other polymers. When other polymers are used in combination, the ratio of the composite polymer in the present invention is preferably 30% by mass or more, more preferably 60% by mass or more of the total binder. When the ratio of the composite polymer is 30% by mass or more, the adhesiveness with the polymer base material and the durability under a moist heat environment are more excellent.

The molecular weight of the composite polymer is preferably 5,000 to 100,000, and more preferably 10,000 to 50,000.

For the preparation of the composite polymer, (i) the precursor polymer is reacted with the polysiloxane having the structure of the general formula (S-1) [-(Si (R ¹¹ ) (R ¹² ) -O) _n1- ]. Process, (ii) Silane compound having a structure of “— (Si (R ¹¹ ) (R ¹² ) —O) _n1 —” in which R ¹ and / or R ² is a hydrolyzable group in the presence of a precursor polymer A method of hydrolyzing and condensing can be used.
Examples of the silane compound used in the method (ii) include various silane compounds, and alkoxysilane compounds are particularly preferable.

When preparing the composite polymer by the method (i), for example, water and a catalyst are added to the mixture of the precursor polymer and polysiloxane as necessary, and the temperature is about 20 to 150 ° C. for about 30 minutes to 30 hours ( (Preferably, the reaction can be performed at 50 to 130 ° C. for 1 to 20 hours). As a catalyst, various silanol condensation catalysts, such as an acidic compound, a basic compound, and a metal containing compound, can be added.
When preparing a composite polymer by the method (ii), for example, water and a silanol condensation catalyst are added to a mixture of a precursor polymer and an alkoxysilane compound, and the temperature is about 20 to 150 ° C. for 30 minutes to 30 minutes. It can be prepared by carrying out hydrolysis condensation for about an hour (preferably at 50 to 130 ° C. for 1 to 20 hours).

-Pigment-
The pigment can impart an ultraviolet shielding effect that prevents the polyester support from being irradiated with ultraviolet rays. By including a pigment in the polymer layer, light resistance (particularly ultraviolet resistance) can be improved, and yellowing of the polyester support and deterioration of mechanical strength can be suppressed.
In order to dramatically improve the ultraviolet shielding effect of the pigment, it is necessary that the mass ratio of the pigment to the total mass of the polymer layer is 45% or more and 85% or less. In this method, by increasing the mass ratio of the pigment, fine voids are formed between the pigment particles, and irregular reflection of the voids is utilized.
At this time, by setting the bulk specific gravity to 0.50 to 0.85 g / cm ³ , the pigments are densely packed, and the polymer layer can be toughened by improving the cohesive force, and the polymer layer does not become brittle. Can be. By controlling the bulk specific gravity of the pigment in this way, the adhesion between the polyester support and the polymer layer can be maintained high even if the mass ratio of the pigment is set so as to be within the range of the present invention.

Examples of the pigment include inorganic materials such as titanium dioxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, ultramarine, cobalt blue, cerulean blue, chromium oxide, cobalt green, carbon black, and iron black. A pigment can be appropriately selected and contained.
As the inorganic pigment that can be used in the present invention, a white pigment is particularly preferable, and titanium dioxide is particularly preferable.
Hereinafter, although the case where titanium dioxide is used as the pigment contained in the polymer layer will be described, the pigment particles other than titanium dioxide as exemplified above are used for the shape, particle size, content, bulk density, and the like of the pigment particles. The same applies to the case.

When polyethylene terephthalate (PET) is selected as the polyester support, it is necessary to shield the ultraviolet rays and prevent the ultraviolet rays from being irradiated to the PET because the PET may cause a decrease in mechanical strength and coloring problems due to exposure to the ultraviolet rays. There is. Titanium dioxide is preferable as the white pigment having an ultraviolet shielding effect.

There are rutile type, anatase type, and brookite type in the crystal system of titanium dioxide. Of these, as the titanium dioxide used in the present invention, the rutile type is preferred. The titanium dioxide used in the present invention may be surface-treated with aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), alkanolamine compound, silicon compound or the like, if necessary.

The average particle diameter of titanium dioxide is preferably 0.03 to 0.8 μm, more preferably about 0.15 to 0.5 μm in terms of volume average particle diameter. When the average particle size is within the above range, the ultraviolet ray shielding efficiency is high and good design properties can be obtained. The average particle diameter of titanium dioxide can be measured by a laser scattering method.

In the present invention, in particular, by using titanium dioxide having a bulk specific gravity of 0.50 g / cm ³ or more, the titanium dioxide is densely packed and the polymer layer becomes tough. On the other hand, when titanium dioxide having a bulk specific gravity exceeding 0.85 g / cm ³ is used, the dispersibility of titanium dioxide is deteriorated and the surface state of the coating layer is deteriorated. By setting the bulk specific gravity to 0.50 g / cm ³ or more and 0.85 g / cm ³ or less, titanium dioxide is tightly packed and the coating film becomes tough, so that even if the mass ratio of titanium dioxide is set high, it adheres Sex can be maintained high. The bulk specific gravity of titanium dioxide used for the polymer layer is particularly preferably 0.60 g / cm ³ or more and 0.80 g / cm ³ or less.

The bulk specific gravity of the pigment in the present specification is a value measured by the following method.
(1) The pigment is passed through a sieve having an aperture of 1.0 mm.
(2) About the above-mentioned pigment, about 100 g of pigment is weighed (m) and gently put into a 250 mL graduated cylinder. If necessary, the top surface of the pigment layer is carefully leveled without compaction and the volume (V) is measured.
(3) The bulk specific gravity is determined according to the following formula.
Bulk specific gravity = m / V (Unit: g / cm ³ )

Further, by setting the mass ratio of titanium dioxide having a bulk specific gravity in the above range to 45 mass% or more with respect to the total mass of the polymer layer, voids are formed between the titanium dioxide particles. As a result, the ultraviolet rays that have entered the polymer layer are irregularly reflected in the gaps, thereby reducing the transmittance of the ultraviolet rays and increasing the shielding effect. However, if the mass ratio of titanium dioxide is increased too much, voids increase too much, the polymer layer becomes brittle, and adhesion decreases, so the mass ratio of titanium dioxide to the total mass of the polymer layer is 85 mass% or less. And The mass ratio of titanium dioxide having a bulk specific gravity within the above range with respect to the total mass of the polymer layer is preferably 50% by mass to 75% by mass.

The content of titanium dioxide in the polymer layer is preferably in the range of 3 to 15 g / m ² . When the pigment content is 3 g / m ² or more, necessary shielding properties can be obtained. Further, when the content of titanium dioxide in the polymer layer is 15 g / m ² or less, the planar shape of the polymer layer is easily maintained, and the film strength is more excellent. In particular, the pigment content is more preferably in the range of 4 to 10 g / m ² .

-Crosslinking agent-
The crosslinking agent can form a stronger film structure by crosslinking between the composite polymers, and can prevent deterioration (cracking or alteration) of the polymer layer itself. Thereby, the adhesiveness after wet heat aging, specifically, the adhesion to the polyester support when exposed to a wet heat environment, and the adhesion between layers can be improved.

Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among the crosslinking agents, crosslinking agents such as oxazoline compounds and carbodiimide compounds are preferable.
Furthermore, by selecting the cross-linking agent from at least one selected from oxazoline-based compounds and carbodiimide-based compounds that are carboxyl group-reactive cross-linking agents, not only forms a cross-linked structure between the composite polymers in the polymer layer. A crosslinked structure between the composite polymer in the polymer layer and the polyester support can also be formed, and the adhesion between the polyester support and the polymer layer is significantly improved.

Specific examples of the oxazoline-based crosslinking agent include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2- Oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2'-bis- (2-oxazoline), 2,2'-methylene-bis- (2-oxazoline), 2,2′-ethylene-bis- (2-oxazoline), 2,2′-trimethylene-bis- (2-oxazoline), 2,2′-tetramethylene-bis- (2-oxazoline) ), 2,2′-hexamethylene-bis- (2-oxazoline), 2,2′-octamethylene-bis- (2-oxazoline), 2,2′-ethylene-bis- (4,4 ′) Dimethyl-2-oxazoline), 2,2'-p-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene- Examples thereof include bis- (4,4′-dimethyl-2-oxazoline), bis- (2-oxazolinylcyclohexane) sulfide, and bis- (2-oxazolinyl norbornane) sulfide. Furthermore, (co) polymers of these compounds are also preferably used.
Further, as compounds having an oxazoline group, aqueous dispersion type Epocross “K-1010E”, “K-1020E”, “K-1030E”, K2010E, same K2020E, same K2030E, aqueous solution type same WS-500, same Commercial products such as WS-700 (all manufactured by Nippon Shokubai Chemical Co., Ltd.) can also be used.

Specific examples of the carbodiimide-based crosslinking agent include dicyclohexylmethane carbodiimide, tetramethylxylylene carbodiimide, dicyclohexylmethane carbodiimide, and the like. A carbodiimide compound described in JP-A-2009-235278 is also preferable. Specifically, carbodiimide-based crosslinking agents such as Carbodilite SV-02, Carbodilite V-02, Carbodilite V-02-L2, Carbodilite V-04, Carbodilite E-01, Carbodilite E-02 (all Nisshinbo Chemical Co., Ltd.) (Commercially available) can also be used.

Further, the mass ratio of the structural part derived from the crosslinking agent in the polymer layer to the composite polymer is preferably 1 to 30% by mass, more preferably 10 to 25% by mass. When the content of the cross-linking agent is 1% by mass or more, the strength of the polymer layer and the adhesion after wet heat aging are excellent, and when it is 30% by mass or less, the pot life of the coating solution can be kept long.

-Additive-
You may add surfactant, a filler, etc. to the polymer layer of this invention as needed.
As the surfactant, a known surfactant such as an anionic or nonionic surfactant can be used. When a surfactant is added, the addition amount is preferably 0.1 to 15 mg / m ² , more preferably 0.5 to 5 mg / m ² . The addition amount of the surfactant, if it is 0.1 mg / m ² or more, good layer formation by suppressing the occurrence of cissing can be obtained, if it is 15 mg / m ² or less, it is possible to perform the bonding well .

<Other functional layers>
The back surface protection sheet for solar cells of this invention may have another functional layer other than a polyester support body and a polymer layer. As other functional layers, an overcoat layer, a reflective layer, an easy adhesion layer (undercoat layer), and the like can be provided.

In particular, when the polymer layer in direct contact with at least one surface on the polyester support is used on a layer exposed to the external environment, that is, a so-called back layer side, an overcoat layer as a second back layer on the polymer layer Is particularly preferable.

(1) Overcoat layer Since the back surface protection sheet for solar cells of the present invention enhances the shielding property of ultraviolet rays by forming voids between the pigment particles, water vapor easily enters from the voids to the inside. By filling the space only on the surface of the polymer layer with the coat layer, the adhesion durability of the polymer layer is further improved.

The overcoat layer is preferably a resin layer obtained by removing titanium dioxide from the composition of the polymer layer, and it is also preferable to replace the composite polymer with a fluorine resin layer.

-Fluoropolymer-
The fluoropolymer used in the overcoat layer is not particularly limited as long as it is a polymer having a repeating unit represented by-(CFX ¹ -CX ² X ³ )-(however, X ¹ , X ² and X ³ are hydrogen) An atom, a fluorine atom, a chlorine atom, or a perfluoroalkyl group having 1 to 3 carbon atoms). Specific examples of the polymer include polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), polyvinyl fluoride (hereinafter sometimes referred to as PVF), and polyvinylidene fluoride (hereinafter referred to as PVDF). ), Polychloroethylene trifluoride (hereinafter sometimes referred to as PCTFE), polytetrafluoropropylene (hereinafter sometimes referred to as HFP), and the like.

These polymers may be a homopolymer obtained by polymerizing a single monomer, or may be a copolymer obtained by copolymerizing two or more kinds. Examples thereof include a copolymer of tetrafluoroethylene and tetrafluoropropylene (abbreviated as P (TFE / HFP)), a copolymer of tetrafluoroethylene and vinylidene fluoride (abbreviated as P (TFE / VDF)), etc. Can be mentioned.

Further, the polymer used for the overcoat layer may be a polymer obtained by copolymerizing a fluorine-based monomer represented by-(CFX ¹ -CX ² X ³ )-and another monomer. Examples of these are copolymers of tetrafluoroethylene and ethylene (abbreviated as P (TFE / E)), copolymers of tetrafluoroethylene and propylene (abbreviated as P (TFE / P)), tetrafluoroethylene and vinyl ether. Copolymer (abbreviated as P (TFE / VE)), copolymer of tetrafluoroethylene and perfluorovinyl ether (abbreviated as P (TFE / FVE)), copolymer of chlorotrifluoroethylene and vinyl ether (P (CTFE) / VE), a copolymer of chlorotrifluoroethylene and perfluorovinyl ether (abbreviated as P (CTFE / FVE)), and the like.

These fluoropolymers may be used by dissolving the polymer in an organic solvent, or may be used by dispersing polymer fine particles in water. The latter is preferred because of its low environmental burden. Aqueous dispersions of fluoropolymers are described in, for example, JP-A Nos. 2003-231722, 2002-20409, and No. 9-194538.
The fluorine-based polymer may be obtained commercially, for example, Lumiflon LF200 (manufactured by Asahi Glass Co., Ltd.), Zeffle GK-570 (manufactured by Daikin Industries, Ltd.), Obligato SW0011F (fluorine-based binder, AGC Co-Tech). Etc.) can be preferably used in the present invention.

As the binder for the overcoat layer, the above-mentioned fluoropolymers may be used alone or in combination of two or more. Moreover, you may use together resin other than fluorine-type polymers, such as an acrylic resin, a polyester resin, a polyurethane resin, a polyolefin resin, and a silicone resin, in the range which does not exceed 50 mass% of all the binders. However, when the resin other than the fluorine-based polymer exceeds 50% by mass, the weather resistance may be lowered when used for the back sheet.

The content ratio of the fluoropolymer in the overcoat layer is preferably in the range of 0.1 to 2.0 g / m ² . When the content ratio of the fluoropolymer is 0.1 g / m ² or more, scratch resistance can be improved. Moreover, when the content ratio of the fluorine-based polymer is 2 g / m ² or less, the ratio of the fluorine-based polymer is not too large, and the overcoat layer is sufficiently cured.
Among the above ranges, from the viewpoint of the surface strength of the overcoat layer, a range of 0.3 to 1.5 g / m ² is preferable, and a range of 0.5 to 1.5 g / m ² is more preferable.

-Organic lubricant-
The overcoat layer preferably contains at least one organic lubricant. By containing an organic lubricant, it is possible to suppress slippage deterioration (that is, increase in the dynamic friction coefficient) that is likely to occur when using a fluorine-containing polymer. The ease of sticking is remarkably eased. Further, it is possible to improve the surface repellency of the coating liquid that is likely to occur when a fluorine-containing polymer is used, and it is possible to form a weather-resistant layer containing a fluorine-based polymer having a good surface shape.

The organic lubricant is preferably contained in the overcoat layer in the range of 0.2 to 500 mg / m ² . When the content ratio of the organic lubricant is 0.2 mg / m ² or more, the scratch resistance is sufficiently improved by the effect of reducing the dynamic friction coefficient due to the inclusion of the organic lubricant. Further, when the content ratio of the organic lubricant is 500 mg / m ² or less, coating unevenness and aggregates are less likely to occur when the overcoat layer is formed by coating, and repelling failure is less likely to occur.
Within the above range, from the viewpoint of the effect of reducing the dynamic friction coefficient and application suitability, the range of 1 mg / m ² to 300 mg / m ² is more preferred, the range of 5 mg / m ² to 200 mg / m ² is particularly preferred, and 10 mg / m 2. A range of ² to 150 mg / m ² is more particularly preferred.

Examples of the organic lubricant include synthetic wax compounds, natural wax compounds, surfactant compounds, inorganic compounds, organic resin compounds, and the like. Among them, the organic lubricant contained in the weather resistant layer containing the fluorine polymer is a polyolefin compound, a synthetic wax compound, or a natural wax compound in terms of the surface strength of the weather resistant layer containing the fluorine polymer. And at least one selected from surfactant-based compounds.

Examples of the polyolefin compound include olefin waxes such as polyethylene wax and polypropylene wax.

Examples of the synthetic wax compounds include esters such as stearic acid, oleic acid, erucic acid, lauric acid, behenic acid, palmitic acid, adipic acid, amides, bisamides, ketones, metal salts and derivatives thereof, and Fischer-Tropsch wax ( Examples include synthetic hydrocarbon waxes (other than olefin waxes), phosphate esters, hydrogenated castor oil, hydrogenated waxes of hydrogenated castor oil derivatives, and the like.

Examples of the natural wax compounds include plant waxes such as carnauba wax, candelilla wax and wood wax, petroleum waxes such as paraffin wax and microcrystalline wax, mineral waxes such as montan wax, animals such as beeswax and lanolin. And waxes.

Examples of the surfactant compound include a cationic surfactant such as an alkylamine salt, an anionic surfactant such as an alkyl sulfate ester salt, a nonionic surfactant such as polyoxyethylene alkyl ether, and an alkylbetaine. Amphoteric surfactants, fluorosurfactants and the like.

The organic lubricant may be a commercially available product, specifically,
Examples of organic lubricants for polyolefin compounds include Chemipearl series (for example, Chemipearl W700, W900, W950, etc.) manufactured by Mitsui Chemicals, and Polylon P-502 manufactured by Chukyo Yushi Co., Ltd. ,
Examples of synthetic wax-based organic lubricants include Hymicron L-271 and Hydrin L-536 manufactured by Chukyo Yushi Co., Ltd.
Examples of natural wax-based organic lubricants include Hydrin L-703-35, Cellosol 524, and Cellosol R-586 manufactured by Chukyo Yushi Co., Ltd.
Examples of surfactant-based organic lubricants include the NIKKOL series (for example, NIKKOL SCS, etc.) manufactured by Nikko Chemicals Co., Ltd., and the Emar series (for example, EMAL 40, etc.) manufactured by Kao Corporation.

Among the above, it is preferable to add a polyethylene wax compound as the organic lubricant from the viewpoint of scratch resistance and surface improvement, and among them, the use of Chemipearl series manufactured by Mitsui Chemicals Co., Ltd. It is more preferable from the viewpoint that it can be greatly improved and scratch resistance and surface improvement can be improved.

-Other additives to the overcoat layer-
You may add colloidal silica, a silane coupling agent, a crosslinking agent, surfactant, etc. to the said overcoat layer as needed.

Colloidal silica may be added to the overcoat layer to improve the surface shape.
The colloidal silica to be used is one in which fine particles mainly composed of silicon oxide are present as colloidal with water or unit price alcohols or diols or a mixture thereof as a dispersion medium.
The colloidal silica particles have an average primary particle size of about several nm to 100 nm.
The average particle diameter can be measured from an electron micrograph taken with a scanning electron microscope (SEM) or the like, or can be measured with a particle size distribution meter using a dynamic light scattering method or a static light scattering method. .
The shape of the colloidal silica particles may be spherical, or may be one in which these are connected in a bead shape.
Colloidal silica particles are commercially available. Examples thereof include the Snowtex series manufactured by Nissan Chemical Industries, the Cataloid-S series manufactured by Catalytic Chemical Industries, and the Rebacil series manufactured by Bayer.
Specifically, for example, Snowtex ST-20, ST-30, ST-40, ST-C, ST-N, ST-20L, ST-O, ST-OL, ST-S, manufactured by Nissan Chemical Industries, Ltd. ST-XS, ST-XL, ST-YL, ST-ZL, ST-OZL, ST-AK, Snowtex-AK series, Snowtex-PS series, Snowtex-UP series, and the like.
Among these colloidal silicas, it is preferable to use beads having a bead shape such as Snowtex-UP series.
The amount of colloidal silica added is preferably 0.3 to 1.0% by mass, and more preferably 0.5 to 0.8% by mass. When the addition amount is 0.3% by mass or more, a planar improvement effect is obtained, and when the addition amount is 1.0% by mass or less, aggregation of the coating liquid can be prevented.

When using the colloidal silica for the overcoat layer, it is preferable to add a silane coupling agent from the viewpoint of improving the surface condition. As the silane coupling agent, an alkoxysilane compound is preferable, and examples thereof include tetraalkoxysilane and trialkoxysilane. Among these, trialkoxysilane is preferable, and an alkoxysilane compound having an amino group is particularly preferable. When a silane coupling agent is added, the addition amount is preferably 0.3 to 1.0% by mass, particularly preferably 0.5 to 0.8% by mass with respect to the overcoat layer. . When the addition amount is 0.3% by mass or more, a surface improvement effect is obtained, and when the addition amount is 1.0% by mass or less, aggregation of the coating liquid can be prevented.

A cross-linking structure derived from the cross-linking agent can be obtained by adding a cross-linking agent to form an overcoat layer.
Examples of the crosslinking agent used for the overcoat layer include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Examples of carbodiimide crosslinking agents include, for example, Carbodilite V-02-L2 (manufactured by Nisshinbo Co., Ltd.), and examples of oxazoline crosslinking agents include, for example, Epocross WS-700 and Epocross K-2020E (both from Nippon Shokubai Co., Ltd.) Etc.).

As the surfactant used in the overcoat layer, known anionic or nonionic surfactants can be used. When a surfactant is added, the addition amount is preferably 0 to 15 mg / m ² , more preferably 0.5 to 5 mg / m ² . The addition amount of the surfactant, if it is 0.1 mg / m ² or more, good layer formation by suppressing the occurrence of cissing can be obtained, if it is 15 mg / m ² or less, it is possible to perform the bonding well .

(2) Reflective layer-White pigment-
The reflective layer includes a white pigment, and has a function of increasing power generation efficiency by irregularly reflecting light that has passed through the cell out of sunlight incident from the front surface of the solar cell module and returning it to the cell.
The light reflectance at a wavelength of 550 nm of the surface (outermost surface) on which the reflective layer of the back surface protective sheet for solar cells is disposed is controlled by the above-mentioned or later numerical range of the white pigment content and layer thickness in the reflective layer. By doing so, it can be adjusted in the direction of increasing the reflectance.

The volume average particle size of the white pigment is preferably 0.03 μm to 0.8 μm, more preferably 0.15 μm to 0.5 μm. By setting the volume average particle diameter of the white pigment within this range, it is possible to suppress a decrease in light reflection efficiency.
The volume average particle diameter of the white pigment is a value measured by Microtrac FRA manufactured by Honeywell.

The preferred content of the white pigment in the reflective layer varies depending on the type and average particle size of the white pigment used, but if the content of the white pigment in the reflective layer is not too small, the reflectivity and design can be sufficiently exerted. If not too much, it is preferable from the viewpoint of adhesiveness with the sealing material. From the viewpoint of sufficiently exerting these functions, the content of the white pigment in the reflective layer is preferably 3 g / m ² to 20 g / m ² , more preferably 5 g / m ² to 17 g / m ² .
From the same viewpoint, the volume fraction of the white pigment with respect to all the binders contained in the reflective layer is preferably 15 to 200%, more preferably 20 to 150%, and particularly preferably 20 to 100%. It is.

The thickness of the reflective layer is preferably 30 μm or less, more preferably 1 μm to 20 μm, particularly preferably 1.5 μm to 10 μm, and particularly preferably 2 to 8 μm. By setting the film thickness to 1 μm or more, the decorativeness and reflectance can be sufficiently expressed, and by setting the film thickness to 30 μm or less, the deterioration of the surface condition is suppressed and the adhesion with the sealing material after wet heat aging is improved. can do.

-binder-
The reflective layer contains at least one binder.

The binder suitable for the reflective layer is polyester, polyurethane, acrylic resin, polyolefin or the like, and acrylic resin or polyolefin is preferable from the viewpoint of durability. As the acrylic resin, a composite resin of acrylic and silicone is also preferable. Examples of preferred binders include Chemipearl S-120 and S-75N (both manufactured by Mitsui Chemicals) as examples of polyolefins, and Julimer ET-410 and SEK-301 (both Nippon Pure Chemicals) as examples of acrylic resins. Examples of the composite resin of acrylic and silicone include Ceranate WSA1060, WSA1070 (both manufactured by DIC Corporation), H7620, H7630, H7650 (both manufactured by Asahi Kasei Chemicals Corporation), and the like.

-Crosslinking agent-
The reflective layer preferably contains a crosslinking agent, so that the binder resin contained in the reflective layer forming composition can be crosslinked to form a reflective layer having adhesiveness and strength.
Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, an oxazoline-based cross-linking agent (compound having an oxazoline group) is particularly preferable from the viewpoint of ensuring adhesion after aging with wet heat with the sealing material of the solar cell module.

-Other additives-
The reflective layer can further contain various additives such as a surfactant, fine particles other than the white pigment, an ultraviolet absorber, and an antioxidant, and in particular, a reflective layer for forming the reflective layer. The composition for use is preferably prepared using a surfactant for the dispersion stability of the white pigment.

As the surfactant, for example, known surfactants such as anionic, cationic, and nonionic surfactants can be used. Specifically, Demole EP (manufactured by Kao Corporation), NAROACTY CL95 [ Sanyo Chemical Industries, Ltd.]. The surfactant may be a single species or a plurality of species.

-Formation of reflective layer-
The composition for forming a reflective layer for forming the reflective layer is prepared by mixing the binder, white pigment, other binder resin, inorganic oxide filler, crosslinking agent, additive and the like with a coating solvent. Can do.

As the reflective layer in the solar cell back surface protective sheet of the present invention, a reflective layer having a configuration described in [0034] to [0044] and [0048] of JP2011-165967A can also be preferably used.

(3) Easy adhesion layer (undercoat layer)
The easy-adhesion layer (meaning an undercoat layer of a reflective layer, also referred to as an undercoat layer) is formed by applying an easy-adhesion layer forming composition (also referred to as an undercoat layer-forming composition) on a polyester support. Can do.
The undercoat layer forming composition preferably contains at least an aqueous binder.
As the aqueous binder, polyester, polyurethane, acrylic resin, polyolefin and the like can be used. The main component of the other layer is preferably a polyester resin.
Furthermore, in addition to the water-based binder, it may contain an epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, oxazoline-based crosslinking agent, anionic or nonionic surfactant, silica filler or the like. The preferred ranges of these additives and the like are the same as the preferred ranges of these additives and the like in the reflective layer.
The content of the aqueous binder with respect to the total solid mass of the undercoat layer forming composition is preferably 50% by mass to 100% by mass, and more preferably 70% by mass to 100% by mass.

The undercoat layer may contain various additives such as an inorganic oxide filler and fine particles other than the inorganic oxide filler described later, an ultraviolet absorber, an antioxidant, and a surfactant.

The method for applying the undercoat layer-forming aqueous composition is not particularly limited.
As a coating method, for example, a gravure coater or a bar coater can be used.
The coating amount of the undercoat layer-forming aqueous composition is preferably less than 10 μm, more preferably from 0.05 μm to 2 μm, particularly preferably from 0.1 μm to 1 in terms of the layer thickness after drying, from the viewpoints of adhesiveness and planarity. It is preferable to apply to a polyester support so as to be 5 μm.

Water is preferably used as a coating solvent for the undercoat layer-forming aqueous composition, and 60% by mass or more of the solvent contained in the undercoat layer-forming aqueous composition is preferably water. The aqueous composition is preferable in that it is difficult to load the environment, and the ratio of water is 60% by mass or more, which is advantageous in terms of explosion-proof property and safety.
The proportion of water in the undercoat layer-forming aqueous composition is preferably larger from the viewpoint of environmental load, and more preferably 70% by mass or more of water in the total solvent.

(Manufacturing method of back surface protection sheet for solar cell)
There is no restriction | limiting in particular in the manufacturing method of the back surface protection sheet for solar cells of this invention. Hereinafter, the preferable manufacturing method of the back surface protection sheet for solar cells of this invention is demonstrated.

<Manufacture of polyester support>
Although the case where PET is used as the polyester support will be described, the present invention is not limited to the case where the polyester support is PET.
First, polyethylene terephthalate is prepared. Polyethylene terephthalate is manufactured by one of the following processes. (1) Using terephthalic acid and ethylene glycol as raw materials, a low molecular weight polyethylene terephthalate or oligomer is obtained by direct esterification reaction, and then a polymer is obtained by polycondensation reaction using antimony trioxide or titanium compound as a catalyst. And (2) a process in which dimethyl terephthalate and ethylene glycol are used as raw materials, a low molecular weight product is obtained by a transesterification reaction, and a polymer is obtained by a subsequent polycondensation reaction using antimony trioxide or a titanium compound as a catalyst. Here, the reaction proceeds even without a catalyst, but in the transesterification reaction, the esterification usually proceeds using a compound such as manganese, calcium, magnesium, zinc, lithium and titanium as a catalyst. After the exchange reaction is substantially completed, a phosphorus compound may be added for the purpose of inactivating the catalyst used in the reaction. It is preferable to solid-phase polymerize the obtained PET pellets to increase the intrinsic viscosity.

It is preferred to extrude a melt of a composition comprising polyester and end capping agent from a die.
As a method for adding a terminal blocking agent to the polyester constituting the film, the polyester is formed by using a vented twin-screw kneading extruder in which the terminal blocking agent is directly mixed with polyester pellets and heated to a temperature of 270 to 275 ° C. A method of kneading into a high-concentration master pellet is effective. At this time, the intrinsic viscosity IV of the polyester is higher than usual and is preferably 0.7 to 1.6. The intrinsic viscosity IV is more preferably 1.2 to 1.4. When the intrinsic viscosity IV is less than 0.7, the amount of carboxyl ends of the master pellet is increased, and the reaction with the end-capping agent occurs when the master pellet is formed. In some cases, the carboxyl end amount may not be reduced. On the other hand, if the intrinsic viscosity IV is greater than 1.6, the melt viscosity becomes too high, and the extrusion may not be stable and master pellets may not be produced. If the temperature of the extruder is raised to lower the melt viscosity, the end-capping agent may be thermally decomposed and the effect may not appear.

Next, the obtained polyester pellets are dried under reduced pressure, for example, at a temperature of 180 ° C. for 3 hours or more, and then, for example, at a temperature of 265 to 280 ° C. (more preferably) under a nitrogen stream or reduced pressure so that the intrinsic viscosity does not decrease. Is preferably supplied to an extruder heated to a temperature of 270 to 275 ° C. and extruded from a slit-shaped die.
Then, it cools on a casting roll and an unstretched film is obtained. At this time, it is preferable to use various types of filters, for example, filters made of materials such as sintered metal, porous ceramic, sand and wire mesh, in order to remove foreign substances and denatured polymers. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property. When laminating films, a plurality of different polymers are melt laminated using two or more extruders and manifolds or merge blocks.

The melt (melt) extruded from the die is cooled and solidified on a cast roll or the like to become an unstretched film.

<Extension>
Next, the unstretched film thus obtained is stretched in the machine direction using the difference in peripheral speed of the roll (MD stretching) using a longitudinal stretching machine in which several rolls are arranged, and subsequently A biaxial stretching method in which transverse stretching is performed with a tenter (TD stretching) will be described.

First, it is preferable to MD-stretch an unstretched film. In MD stretching, first, stretching is performed at a low temperature, and then the temperature is raised, and two-stage stretching is performed, whereby orientation crystallization occurs and the orientation can be increased. The first low-temperature stretching (MD1 stretching) is carried out with a heating roll group in the range of (Tg-20) to (Tg + 10) ° C., more preferably in the range of (Tg-10) to (Tg + 5) ° C. Preferably, the film is stretched 1.1 to 3.0 times, more preferably 1.2 to 2.5 times, and still more preferably 1.5 to 2.0 times, and then higher than the MD stretching 1 temperature (Tg + 10) MD stretching 2 is performed at ~ (Tg + 50). A more preferable temperature is (Tg + 15) (˜Tg + 30). The preferred draw ratio of MD stretch 2 is 1.2 to 4.0 times, more preferably 1.5 to 3.0 times. The MD stretching ratio of MD stretching 1 and MD stretching 2 is preferably 2.0 to 6.0 times, more preferably 3.0 to 5.5 times, still more preferably 3.5 to 5 times. .0 times. After stretching, it is preferably cooled by a cooling roll group having a temperature of 20 to 50 ° C.

Next, stretching in the width direction is preferably performed using a tenter. The draw ratio is preferably 2.0 to 6.0 times, more preferably 3.0 to 5.5 times, and still more preferably 3.5 to 5.0 times. The temperature is preferably in the range of (Tg) to (Tg + 50) ° C., more preferably in the range of (Tg) to (Tg + 30) ° C. (TD stretching).
It is preferable to perform heat setting treatment after TD stretching. In the heat setting treatment, the film is heat-treated at a temperature of 150 to 230 ° C., more preferably 165 to 220 ° C., and further preferably 170 to 210 ° C. while relaxing the film under tension or in the width direction. The heat treatment time is preferably in the range of 0.5 to 10 seconds. Thereafter, after cooling to 25 ° C., the film edge can be removed to obtain a polyester support.

The polyester support preferably has a surface treated by corona treatment, flame treatment, low pressure plasma treatment, atmospheric pressure plasma treatment, or ultraviolet treatment. By applying these surface treatments to the application surface before application of the polymer layer, it is possible to further enhance the adhesiveness when exposed to a wet heat environment. Among these, by performing the corona treatment, a more excellent adhesive improvement effect can be obtained.
By increasing the number of carboxyl groups and hydroxyl groups on the surface of the polyester support by these surface treatments, the adhesion between the polyester support and the polymer layer is enhanced. Alternatively, stronger adhesion can be obtained when a carbodiimide-based crosslinking agent) is used in combination. This is more remarkable in the case of corona treatment. Therefore, it is particularly preferable that the surface of the polyester support on the side where the coating layer is formed is subjected to corona treatment.

<Formation of polymer layer>
The polymer layer can be formed by a method in which a polymer sheet is bonded to a polyester support, a method in which the polymer layer is coextruded when forming the polyester support, a method by coating, or the like. Especially, the method by application | coating is preferable at the point which is easy and can form in a thin film with uniformity. In the case of coating, as a coating method, for example, a known coating method such as a gravure coater or a bar coater can be used.

The coating solution may be an aqueous system using water as an application solvent, or a solvent system using an organic solvent such as toluene or methyl ethyl ketone. Among these, from the viewpoint of environmental burden, it is preferable to use water as a solvent. A coating solvent may be used individually by 1 type, and may mix and use 2 or more types.

The coating solution for the polymer layer is preferably an aqueous coating solution in which 50% by mass or more, preferably 60% by mass or more, of the solvent contained therein is water. The aqueous coating solution is preferable in terms of environmental load, and is advantageous in that the environmental load is particularly reduced when the ratio of water is 50% by mass or more. The proportion of water in the coating liquid for the polymer layer is preferably larger from the viewpoint of environmental load, and more preferably 90% by weight or more of water is contained in the total solvent. The solvent residual ratio in the polymer layer is preferably 0.05% by mass or less, more preferably 0.025% by mass or less, based on the mass of the polymer layer (mass of the coating film). The content is particularly preferably 001% by mass or less.

After the application, a drying process for drying under desired conditions may be provided.

In the case where other functional layers are provided in addition to the polymer layer that is in direct contact with at least one surface on the polyester support, a method of forming by coating in the same manner as the polymer layer is preferable.

[Solar cell module]
The back surface protection sheet for a solar cell of the present invention seals a transparent base material (a front base material such as a glass substrate) disposed on the side on which sunlight is incident, and an element structure portion (solar cell element and the same). In a solar cell having a laminated structure of “transparent front base material / element structure portion / back sheet” in which a sealing material is included) and a solar cell back sheet are laminated. Here, the back sheet is a back surface protection sheet disposed on the side where the front base material is not located when viewed from the element structure portion of the battery side substrate.
In the present specification, a battery part having a laminated structure of “transparent front substrate / element structure part” in which an element structure part is disposed on a transparent substrate disposed on the side on which sunlight is incident. Is called “battery side substrate”.

Specifically, the solar cell module of the present invention is provided on a transparent base material (a front base material such as a glass substrate) on which sunlight enters and the base material, and the solar cell element and the solar cell element An element structure portion having a sealing material for sealing, and the above-described solar cell back surface protective sheet of the present invention disposed on the opposite side of the element structure portion on the side where the substrate is located, It has a laminated structure of “transparent front substrate / element structure portion / back sheet”. Specifically, an element structure portion in which a solar cell element that converts light energy of sunlight into electrical energy is disposed, and a transparent front base material that is disposed on a side where sunlight directly enters, An element structure portion (for example, solar cell) including a solar cell element is disposed between the front substrate and the back sheet between the back surface protective sheet for a solar cell of the present invention and an ethylene-vinyl acetate (EVA) system. It is preferable that the structure is sealed and bonded using a sealing material such as.

FIG. 4 schematically shows an example of the configuration of the solar cell module of the present invention. This solar cell module 10 includes a solar cell element 20 that converts light energy of sunlight into electric energy, a transparent substrate 24 on which sunlight is incident, and the solar cell back surface protective sheet 12 of the present invention described above. It is arranged between the substrate and the solar cell back surface protective sheet 12 and sealed with an ethylene-vinyl acetate sealing material 22. The back protective sheet for a solar cell of this embodiment is provided with a second back layer (overcoat layer) 4 that is arbitrarily disposed in contact with the polymer layer 3 on one surface side of the polyester support 16 and the other side. The easy adhesion layer 2 and the white layer 1 are provided as other layers on the surface side (the side on which sunlight is incident). The polymer layer 3 is preferably provided directly on the polyester support 16 as a so-called back layer only on the opposite side of the sealing material 22 across the polyester support 16.

About members other than a solar cell module, a photovoltaic cell, and the back surface protection sheet for solar cells, for example, it describes in detail in "Solar power generation system constituent material" (supervised by Eiichi Sugimoto, Industrial Research Institute, Inc., 2008 issue). Has been.

The transparent substrate only needs to have a light-transmitting property through which sunlight can be transmitted, and can be appropriately selected from substrates that transmit light. From the viewpoint of power generation efficiency, the higher the light transmittance, the better. For such a substrate, for example, a glass substrate, a transparent resin such as an acrylic resin, or the like can be suitably used.

Examples of the solar cell element include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, III-V groups such as copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, and gallium-arsenic. Various known solar cell elements such as II-VI group compound semiconductor systems can be applied.

The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the examples shown below. Unless otherwise specified, “part” is based on mass.

Example 1
<Preparation of polyester support>
-Step 1: Esterification-
A slurry of 100 kg of high-purity terephthalic acid (manufactured by Mitsui Chemicals Co., Ltd.) and 45 kg of ethylene glycol (manufactured by Nippon Shokubai Chemical Industry Co., Ltd.) is charged with about 123 kg of bis (hydroxyethyl) terephthalate in advance, at a temperature of 250 ° C. and a pressure of 1 . The esterification reaction tank maintained at 2 × 10 ⁵ Pa was sequentially supplied over 4 hours, and the esterification reaction was further performed over 1 hour after the completion of the supply. Thereafter, 123 kg of the obtained esterification reaction product was transferred to a polycondensation reaction tank.

-Step 2: Preparation of polymer pellet A-
Subsequently, 0.3% by mass of ethylene glycol was added to the polycondensation reaction tank to which the esterification reaction product had been transferred, based on the resulting polymer. After stirring for 5 minutes, an ethylene glycol solution of cobalt acetate and manganese acetate was added in the resulting polymer so that the cobalt element equivalent value and the manganese element equivalent value were 30 ppm and 15 ppm, respectively. After further stirring for 5 minutes, a 2% by mass ethylene glycol solution of a titanium alkoxide compound was added so that the titanium element equivalent value was 5 ppm in the obtained polymer. Five minutes later, a 10% by mass ethylene glycol solution of ethyl diethylphosphonoacetate was added so that the phosphorus element equivalent value was 5 ppm in the resulting polymer. Thereafter, while stirring the low polymer at 30 rpm, the reaction system was gradually heated from 250 ° C. to 285 ° C. and the pressure was reduced to 40 Pa. The time to reach the final temperature and final pressure was both 60 minutes. When the predetermined stirring torque was reached, the reaction system was purged with nitrogen, returned to normal pressure, and the polycondensation reaction was stopped. And it discharged to cold water in the shape of a strand, and it cut immediately, and produced polymer pellet A (diameter about 3 mm, length about 7 mm). The time from the start of decompression to the arrival of the predetermined stirring torque was 3 hours.
As the titanium alkoxide compound, the titanium alkoxide compound (Ti content = 4.44 mass%) synthesized in Example 1 of paragraph No. [0083] of JP-A-2005-340616 was used.

-Step 3: Solid phase polymerization (Preparation of polymer pellet B)-
The polymer pellet A obtained above was held in a vacuum vessel maintained at 40 Pa at a temperature of 220 ° C. for 30 hours to carry out solid phase polymerization to produce a polymer pellet B.

-Step 4: Production of polymer with end-capping agent introduced (Production of polymer pellet C)-
90 parts by mass of polymer pellet B and 10 parts by mass of the following end-capping agent are blended, supplied to a twin-screw kneader, melt-kneaded at 280 ° C., discharged in water into strands, cut with a cutter, and chip Turned into. This is designated as PET-C.
Terminal blocker: Starvacol P400 ... polycarbodiimide, weight average molecular weight of about 20000, manufactured by Rhein Chemie Japan

-Step 5: Production of film-like polyester support-
The polymer pellet B and polymer pellet C produced as described above were mixed so that the ratio of the terminal blocking agent to the total mass of the pellet was 0.4% by mass, then dried at 180 ° C. for 3 hours, and then extruded. It was put into a machine, melted at 280 ° C., cast on a metal drum, and an unstretched base having a thickness of about 3 mm was produced. Thereafter, the film is stretched 3.4 times in the MD direction (longitudinal direction: Machine Direction) at 90 ° C., and further stretched 4.5 times in the TD direction (transverse direction: Transverse Direction) at 120 ° C., and the film surface is 200 ° C. A heat setting treatment was performed for 15 seconds, and thermal relaxation was performed at 190 ° C. in the MD and TD directions by 5% and 11%, respectively. Thus, a biaxially stretched polyethylene terephthalate support (hereinafter referred to as “PET-1”) having a thickness of 300 μm was obtained.

<Lamination of easy-adhesive layer>
-Preparation of coating solution for forming easy-adhesive layer-
Components in the following composition were mixed to prepare a coating solution for forming an easily adhesive layer.
-Composition of coating liquid-
・ Polyolefin resin aqueous dispersion: 5.2 parts (Binder: Chemipearl S-75N, manufactured by Mitsui Chemicals, solid content: 24% by mass)
Polyoxyalkylene alkyl ether 7.8 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Oxazoline compound (crosslinking agent) 0.8 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
Silica fine particle aqueous dispersion: 2.9 parts (Aerosil OX-50, manufactured by Nippon Aerosil Co., Ltd., volume average particle diameter = 0.15 μm, solid content: 10% by mass)
・ Distilled water ... 83.3 parts

-Formation of an easily adhesive layer-
The obtained coating solution was applied to one side of the above PET-1 that had been corona-treated on both sides in advance so as to have a binder amount of 0.09 g / m ² and dried at 180 ° C. for 1 minute. An easy-adhesive layer was formed.

--- Corona treatment conditions ---
・ Equipment: Solid state corona treatment machine 6KVA model made by Pillar ・ Electrode and dielectric roll gap clearance: 1.6 mm
・ Processing frequency: 9.6 kHz
Processing speed: 20 m / min Processing intensity: 0.375 kV A / min / m ²

<Lamination of reflection layer>
-Preparation of titanium dioxide dispersion-
Components in the following composition were mixed, and the mixture was subjected to a dispersion treatment for 1 hour by a dynomill type disperser.
-Composition of titanium dioxide dispersion for reflective layer-
・ Titanium dioxide (bulk specific gravity = 0.75 g / cm ³ ) 46.5% by mass
(Taipeke CR-95, manufactured by Ishihara Sangyo Co., Ltd., 100% solid content)
・ Polyvinyl alcohol: 23.0% by mass
(PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10% by mass)
・ Surfactant ... 0.6% by mass
(Demol EP, manufactured by Kao Corporation, solid content: 25% by mass)
・ Distilled water: 29.9% by mass

-Preparation of reflection layer coating solution 1-
Components in the following composition were mixed to prepare a reflection layer forming coating solution 1.
-Composition of coating liquid 1-
-Titanium dioxide dispersion for reflective layer-71.4 parts-Polyacrylic resin aqueous dispersion-17.1 parts (Binder: Jurimer ET410, manufactured by Nippon Pure Chemicals Co., Ltd., solid content: 30 mass %)
Polyoxyalkylene alkyl ether: 2.7 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Oxazoline compound (crosslinking agent) 1.8 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
・ Distilled water: 7.0 parts

-Formation of reflective layer-
The obtained reflective layer-forming coating solution 1 is applied onto the above easy-adhesive layer and dried at 180 ° C. for 1 minute, and a white layer (reflective layer) having a titanium dioxide content of 6.0 g / m ^2. Formed.

<Lamination of back layer>
-Synthesis of composite polymers-
[Synthesis Example 1]: Synthesis of Composite Polymer Water Dispersion P-1--Step 1--
In a reaction vessel equipped with a stirrer and a dropping funnel and purged with nitrogen gas, 81 parts of propylene glycol mono-n-propyl ether (PNP), 360 parts of isopropyl alcohol (IPA), 110 parts of phenyltrimethoxysilane (PTMS), and dimethyl 71 parts of dimethoxysilane (DMDMS) was charged, and the temperature was raised to 80 ° C. with stirring in a nitrogen gas atmosphere.

--- Step 2--
Next, at the same temperature in this reaction vessel, 260 parts of methyl methacrylate (MMA), 200 parts of n-butyl methacrylate (BMA), 110 parts of n-butyl acrylate (BA), 30 parts of acrylic acid (AA), 3-methacryloyl A mixture of 19 parts of oxypropyltrimethoxysilane (MPTMS), 31.5 parts of tert-butylperoxy-2-ethylhexanoate (TBPO), and 31.5 parts of PNP was added dropwise over 4 hours. Thereafter, the mixture was heated and stirred at the same temperature for 2.5 hours to obtain an acrylic polymer solution having a weight average molecular weight of 29,300 and containing a carboxyl group and a hydrolyzable silyl group.

--- Step 3--
Next, 54.8 parts of deionized water was added thereto, and heating and stirring were continued for 16 hours to hydrolyze the alkoxysilane and further condense with an acrylic polymer, so that the nonvolatile content (NV) = 56.3 mass%. A solution of a composite polymer having a site derived from a carboxyl group-containing acrylic polymer and a polysiloxane site, with a solution acid value = 22.3 mgKOH / g, was obtained.

--- Step 4--
Next, 42 parts of triethylamine (TEA) was added to this solution while stirring at the same temperature, followed by stirring for 10 minutes. Thereby, 100% of the contained carboxyl groups were neutralized.

--- Step 5--
Thereafter, 1250.0 parts of deionized water was added dropwise at the same temperature over 1.5 hours for phase inversion emulsification, and then the mixture was heated to 50 ° C. and stirred for 30 minutes. Subsequently, over 3.0 hours at an internal temperature of 40 ° C., a part of water was removed under reduced pressure together with the organic solvent. Thus, an aqueous dispersion P-1 of a composite polymer containing a portion derived from a carboxyl group-containing acrylic polymer and a polysiloxane portion having a solid content concentration of 40% by mass and an average particle size of 110 nm was obtained. The aqueous dispersion P-1 has a polysiloxane moiety of about 25% by mass and an acrylic polymer part of about 75% by mass.
Table 1 shows the types and amounts of materials used in the synthesis of the composite polymer aqueous dispersion P-1.

-Preparation of pigment (titanium dioxide) dispersion for back layer-
Components in the following composition were mixed, and the mixture was subjected to a dispersion treatment for 1 hour by a dynomill type disperser.
-Composition of pigment (titanium dioxide) dispersion for back layer-
・ Titanium dioxide (bulk specific gravity = 0.75 g / cm ³ ) 46.5% by mass
(Taipeke CR-95, manufactured by Ishihara Sangyo Co., Ltd., 100% solid content)
・ Polyvinyl alcohol: 23.0% by mass
(PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10% by mass)
・ Surfactant ... 0.6% by mass
(Demol EP, manufactured by Kao Corporation, solid content: 25% by mass)
・ Distilled water: 29.9% by mass

-Preparation of coating solution 1 for forming the back layer-
Components in the following composition were mixed to prepare a coating solution 1 for forming a back layer.
-Composition of coating liquid 1 for forming the back layer-
-Said composite polymer aqueous dispersion P-1 (solid content concentration 40 mass%)
... 34.1 parts · Oxazoline compound (crosslinking agent H-1) ... 10.9 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25 mass%)
-Pigment for back layer (titanium dioxide) dispersion ... 48.2 parts-Polyoxyalkylene alkyl ether ... 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1 mass %)
・ Distilled water: 5.3 parts

-Formation of back layer-
The obtained back layer-forming coating solution 1 has a dry coating amount of titanium dioxide of 9. The resultant was applied at 0 g / m ² and dried at 180 ° C. for 1 minute to form a back layer having a dry thickness of 10 μm.
As described above, the back protective sheet for solar cell of Example 1 was produced.

(Examples 2 to 4, Comparative Examples 1 and 2)
In Example 1, the composite polymer aqueous dispersion P-1 used for the preparation of the coating solution for forming the back layer was prepared by synthesizing the following composite polymer aqueous dispersions P-2 to P-4 (solid content concentration: 40 mass). %: Examples 2 to 4), composite polymer aqueous dispersions P-5 and P-6 (solid content concentration 40% by mass; Comparative Examples 1 and 2) The back surface protection sheet for solar cells of each Example and the comparative example was produced.

[Synthesis Example 2]: Synthesis of Composite Polymer Aqueous Dispersion P-2 In the synthesis of Composite Polymer Aqueous Dispersion P-1, the amount of monomer used was changed to the following amount in the same manner as in Synthesis Example 1. Thus, a composite polymer aqueous dispersion P-2 was synthesized.
The ratio of the monomers used is as follows: phenyltrimethoxysilane (PTMS): 210 parts, dimethyldimethoxysilane (DMDMS): 166 parts, 3-methacryloyloxypropyltrimethoxysilane (MPTMS): 24 parts, methyl methacrylate (MMA): 200 parts N-butyl methacrylate (BMA): 100 parts, n-butyl acrylate (BA) 70 parts, acrylic acid (AA) 30 parts. In the aqueous dispersion P-2, the polysiloxane part is about 50% by mass, and the acrylic polymer part is about 50% by mass.

[Synthesis Example 3]: Synthesis of Composite Polymer Aqueous Dispersion P-3 In the synthesis of Composite Polymer Aqueous Dispersion P-1, the amount of monomer used was changed to the following amount in the same manner as in Synthesis Example 1. Thus, a composite polymer aqueous dispersion P-3 was synthesized.
The ratio of the monomers used is as follows: phenyltrimethoxysilane (PTMS): 70 parts, dimethyldimethoxysilane (DMDMS): 50 parts, 3-methacryloyloxypropyltrimethoxysilane (MPTMS): 15 parts, methyl methacrylate (MMA): 275 parts N-butyl methacrylate (BMA): 215 parts, n-butyl acrylate (BA) 145 parts, and acrylic acid (AA) 30 parts. In the aqueous dispersion P-3, the polysiloxane part is about 15% by mass, and the acrylic polymer part is about 85% by mass.

[Synthesis Example 4]: Synthesis of Composite Polymer Water Dispersion P-4 In the synthesis of Composite Polymer Water Dispersion P-1, the amount of monomer used was changed to the following amount in the same manner as in Synthesis Example 1. Thus, a composite polymer aqueous dispersion P-4 was synthesized.
The ratio of the monomers used is as follows: phenyltrimethoxysilane (PTMS): 320 parts, dimethyldimethoxysilane (DMDMS): 244 parts, 3-methacryloyloxypropyltrimethoxysilane (MPTMS): 36 parts, methyl methacrylate (MMA): 90 parts N-butyl methacrylate (BMA): 60 parts, n-butyl acrylate (BA): 20 parts, and acrylic acid (AA): 30 parts. In the aqueous dispersion P-4, the polysiloxane part is about 85% by mass, and the acrylic polymer part is about 15% by mass.

[Synthesis Example 5]: Synthesis of Composite Polymer Aqueous Dispersion P-5 In the synthesis of Composite Polymer Aqueous Dispersion P-1, the amount of monomer used was changed to the following amount in the same manner as in Synthesis Example 1 above. Thus, a composite polymer aqueous dispersion P-5 was synthesized.
The ratio of the monomers used was 60 parts phenyltrimethoxysilane (PTMS), 25 parts dimethyldimethoxysilane (DMDMS), 15 parts 3-methacryloyloxypropyltrimethoxysilane (MPTMS), 300 parts methyl methacrylate (MMA), n-butyl. Methacrylate (BMA) 220 parts, n-butyl acrylate (BA) 150 parts, and acrylic acid (AA) 30 parts. The aqueous dispersion P-5 has a polysiloxane moiety of about 13% by mass and is not classified as a composite polymer in the present invention.

[Synthesis Example 6]: Synthesis of Composite Polymer Aqueous Dispersion P-6 Except that the amount of monomer used in the synthesis of Composite Polymer Aqueous Dispersion P-1 was changed to the following amount, the same as Synthesis Example 1 above. Thus, a composite polymer aqueous dispersion P-6 was synthesized.
The proportions of monomers used were 360 parts of phenyltrimethoxysilane (PTMS), 320 parts of dimethyldimethoxysilane (DMDMS), 40 parts of 3-methacryloyloxypropyltrimethoxysilane (MPTMS), 20 parts of methyl methacrylate (MMA), n-butyl 20 parts of methacrylate (BMA), 10 parts of n-butyl acrylate (BA) and 30 parts of acrylic acid (AA) were used. The aqueous dispersion P-6 has a polysiloxane moiety of about 90% by mass and is not classified as a composite polymer in the present invention. The aqueous dispersion had agglomerated and had poor stability.

(Comparative Example 3)
In Example 1, except that the composite polymer aqueous dispersion P-1 used for the preparation of the coating solution for forming the back layer was replaced with the following composite polymer aqueous dispersion P-101, the same as in Example 1, The back surface protection sheet for solar cells of Comparative Example 3 was produced.

[Synthesis Example-101]: Synthesis of Composite Polymer Water Dispersion P-101 In a reaction vessel equipped with a stirrer and a dropping funnel and purged with nitrogen gas, 14 parts of dimethylolbutanoic acid, Plaxel CD220 (polycarbonate diol (PCD), Daicel) Chemical Industry Co., Ltd., average molecular weight 2000) 57 parts, chain extender (short chain diol component) 4 parts, the following compound A (both terminal polysiloxane diol) 25 parts, and a predetermined amount of acetone are added and dissolved uniformly. Solution concentration was prepared.

Next, a predetermined amount (NCO / OH 2.0) of hexamethylene diisocyanate (HDI) was added, the reaction was performed at 80 ° C., the reaction was performed until the predetermined NCO% was reached, and then cooled to 50 ° C. Furthermore, a predetermined amount (an amount equivalent to the hydrophilic group —COOH) of ion-exchanged water of 30% by mass with respect to the solid content and a neutralizing agent (triethylamine (TEA)) is added, and the inside of the system is uniformly distributed. After emulsification, an ethylenediamine (EDI) component (an amount equal to the measured NCO%) was added to extend the chain. The acetone in the system was recovered by vacuum degassing.
As described above, a composite polymer aqueous dispersion P-101 having a polysiloxane structural unit and a urethane-based structural unit as a non-polysiloxane was synthesized.
The composite polymer aqueous dispersion P-101 has about 25% by mass of the polysiloxane moiety and about 75% by mass of the urethane-based polymer part.
The solid content concentration of the composite polymer aqueous dispersion P-101 was 40% by mass.

(Examples 5 to 8)
In Example 1, the composite polymer aqueous dispersion P-1 used for the preparation of the coating solution for forming the back layer was synthesized by the following method, and the composite polymer aqueous dispersions P-7, P-8, P-9 and P Except that each was replaced with −10, the back protective sheet for solar cell of each example was produced in the same manner as in Example 1.

[Synthesis Example-7]: Synthesis of Composite Polymer Water Dispersion P-7 In the synthesis of Composite Polymer Water Dispersion P-1, 110 parts of phenyltrimethoxysilane (PTMS) and dimethyldimethoxysilane (DMDMS) 71 added first Except that 100 parts of phenyltrimethoxysilane (PTMS), 10 parts of 3-aminopropyltriethoxysilane (APTES) and 71 parts of dimethyldimethoxysilane (DMDMS) were changed to P-1 A composite polymer aqueous dispersion P-7 was synthesized in the same manner as in the above.
The aqueous dispersion P-7 has a polysiloxane moiety of about 25% by mass and an acrylic polymer part of about 75% by mass.

[Synthesis Example 8]: Synthesis of Composite Polymer Aqueous Dispersion P-8 In the synthesis of composite polymer aqueous dispersion P-7, 10 parts of 3-aminopropyltriethoxysilane (APTES) was added to 3-mercaptopropyltrimethoxylane ( MPTMS) A composite polymer aqueous dispersion P-8 was synthesized in the same manner as the composite polymer aqueous dispersion P-7 except that the amount was changed to 10 parts.
In the aqueous dispersion P-8, the polysiloxane part is about 25% by mass, and the acrylic polymer part is about 75% by mass.

[Synthesis Example 9]: Synthesis of Composite Polymer Water Dispersion P-9 In the synthesis of Composite Polymer Water Dispersion P-7, 10 parts of 3-aminopropyltriethoxysilane (APTES) was added to 3-glycidoxypropyltrimethoxy. A composite polymer aqueous dispersion P-9 was synthesized in the same manner as the synthesis of the composite polymer aqueous dispersion P-7 except that the amount was changed to 10 parts of silane (GPTMS).
In the aqueous dispersion P-9, the polysiloxane part is about 25% by mass, and the acrylic polymer part is about 75% by mass.

[Synthesis Example-10]: Synthesis of Composite Polymer Aqueous Dispersion P-10 In the synthesis of composite polymer aqueous dispersion P-7, 10 parts of 3-aminopropyltriethoxysilane (APTES) was added to p-styryltrimethoxysilane (STMS). ) A composite polymer aqueous dispersion P-10 was synthesized in the same manner as in the synthesis of the composite polymer aqueous dispersion P-7 except that the amount was changed to 10 parts.
In the aqueous dispersion P-10, the polysiloxane part is about 25% by mass, and the acrylic polymer part is about 75% by mass.

(Examples 9 to 13)
In Example 1, in the process 5 for producing the polyester support, the ratio of the end-capping agent was 0.05% by mass, 0.1%, 1.0% by mass, 5.0% by mass, and 7.5% by mass. % Back protection sheet for solar cell of each example, except that it was replaced by PET-2, PET-3, PET-4, PET-5, and PET-6, respectively. Was made.

(Examples 14 to 17)
In Example 1, except that in Step 4 of the production of the polyester support, the terminal blocking agents to be added were changed to the following PET-a to PET-d prepared by changing the terminal blocking agents a to d. In the same manner as in Example 1, solar cell back surface protective sheets of the respective examples were produced.
End-capping agent a: polycarbodiimide, weight average molecular weight of about 1500
End-capping agent b: polycarbodiimide, weight average molecular weight of about 2000
End-capping agent c: polycarbodiimide, weight average molecular weight of about 50,000
End-capping agent d: polycarbodiimide, weight average molecular weight of about 60,000

[Production Method of Terminal Sealant a]
1,000 parts of 2,4,6-triisopropylphenyl 1,3-diisocyanate (TRIDI) and 5 parts of 3-methyl-1-phenyl-2-phospholene oxide were heated to 170 ° C. over 1 hour, Thereafter, the end-capping agent a was synthesized by reacting for 1 hour without changing the temperature.
It was found that the end-capping agent a obtained from GPC had a weight average molecular weight (Mw) of 1500.

[Production Method of Terminal Sealant b]
1,000 parts of 2,4,6-triisopropylphenyl 1,3-diisocyanate (TRIDI) and 5 parts of 3-methyl-1-phenyl-2-phospholene oxide were heated to 170 ° C. over 1 hour, Thereafter, the end-capping agent b was synthesized by reacting for 2 hours without changing the temperature.
The end-capping agent b obtained from GPC was found to have a weight average molecular weight (Mw) of 2000.

[Preparation Method of Terminal Sealant c]
1,000 parts of 2,4,6-triisopropylphenyl 1,3-diisocyanate (TRIDI) and 15 parts of 3-methyl-1-phenyl-2-phospholene oxide were heated to 170 ° C. over 1 hour, Thereafter, the end-capping agent c was synthesized by reacting for 15 hours without changing the temperature.
It turned out that the weight average molecular weight (Mw) of the terminal blocker c obtained from GPC is 50000.

[Production Method of Terminal Sealant d]
1,000 parts of 2,4,6-triisopropylphenyl 1,3-diisocyanate (TRIDI) and 15 parts of 3-methyl-1-phenyl-2-phospholene oxide were heated to 170 ° C. over 1 hour, Thereafter, the end-capping agent d was synthesized by reacting for 20 hours without changing the temperature.
The end-capping agent d obtained from GPC was found to have a weight average molecular weight (Mw) of 60000.

(Example 18)
In Example 1, the same procedure as in Example 1 was performed except that, in Step 4 of the production of the polyester support, the terminal blocking agent to be added was changed to PET-e prepared by changing to the following terminal blocking agent e. Thus, a back surface protective sheet for a solar cell of Example 18 was produced.
End-capping agent e: “Epocross” RPS-1005, manufactured by Nippon Shokubai Co., Ltd., oxazoline compound, weight average molecular weight of about 35000

(Example 19)
In Example 1, the same procedure as in Example 1 was performed except that, in Step 4 of the production of the polyester support, the terminal blocking agent to be added was changed to PET-f prepared by changing to the following terminal blocking agent f. Thus, a back protective sheet for a solar cell of Example 19 was produced.
End-capping agent f: “Epofriend” AT-501, manufactured by Daicel Chemical Industries, Ltd., epoxy compound, weight average molecular weight of about 25000

(Example 20)
In Example 1, the same procedure as in Example 1 except that, in Step 4 of the production of the polyester support, the terminal blocking agent to be added was changed to the following PET-g prepared by changing to the terminal blocking agent g. Thus, a back protective sheet for a solar cell of Example 20 was produced.
End-capping agent g: cyclic carbodiimide compound described in paragraph [0171] of JP2011-153209A, weight average molecular weight 252

(Comparative Example 4)
In Example 1, the solar cell of Comparative Example 4 was prepared in the same manner as in Example 1 except that in Step 5 of preparing the polyester support, PET-7 was prepared without adding the end-capping agent. A back protective sheet was prepared.

(Examples 21 to 23)
In Example 1, except that the titanium dioxide used for the preparation of the coating solution for forming the back layer was replaced with the following titanium dioxides (Taipeku CR-85, Taipaque CR-93, and Taipaque CR-Super 70), respectively. In the same manner as in Example 1, the solar cell back surface protective sheet of each example was produced. In addition, the bulk specific gravity of each pigment is a value measured by the method described in this specification.
・ Tipeke CR-85
Ishihara Sangyo Co., Ltd., 100% solid content
Bulk specific gravity = 0.52 g / cm ³
・ Tipeke CR-93
Ishihara Sangyo Co., Ltd., 100% solid content
Bulk specific gravity = 0.64 g / cm ³
・ Tipeke CR-Super70
Ishihara Sangyo Co., Ltd., 100% solid content
Bulk specific gravity = 0.80 g / cm ³

(Comparative Examples 5 and 6)
In Example 1, the same manner as in Example 1 except that the titanium dioxide used for the preparation of the coating solution for forming the back layer was replaced with the following titanium dioxides (Typaque R-780-2, Taipaque CR-63), respectively. Thus, back protection sheets for solar cells of each comparative example were produced.
・ Tipeke R-780-2
Ishihara Sangyo Co., Ltd., 100% solid content
Bulk specific gravity = 0.41 g / cm ³
・ Tipeke CR-63
Ishihara Sangyo Co., Ltd., 100% solid content
Bulk specific gravity = 0.90 g / cm ³

(Example 24)
Titanium dioxide in the same manner as in Example 1 except that the back layer was formed using the back layer forming coating solution 2 prepared as follows instead of the back layer forming coating solution 1 in Example 1. The back surface protection sheet for solar cells of Example 24 whose mass ratio is 45% was produced.
-Preparation of coating solution 2 for forming the back layer-
Components in the following composition were mixed to prepare a back layer forming coating solution 2.
-Composition of coating solution 2 for forming the back layer-
-Said composite polymer aqueous dispersion P-1 (solid content concentration 40 mass%)
34.1 parts oxazoline compound (crosslinking agent) 10.9 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
-Titanium dioxide dispersion for back layer used in Example 1 ... 30.1 parts-Polyoxyalkylene alkyl ether ... 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, Ltd., solid content: 1% by mass)
・ Distilled water ... 23.4 parts

(Example 25)
Titanium dioxide in the same manner as in Example 1 except that the back layer was formed using the back layer forming coating solution a prepared as follows instead of the back layer forming coating solution 1 in Example 1. The back surface protection sheet for solar cells of Example 25 whose mass ratio is 45% was produced.
-Preparation of coating solution a for forming the back layer-
Components in the following composition were mixed to prepare a back layer forming coating solution a.
-Composition of coating solution a for forming the back layer-
-Said composite polymer aqueous dispersion P-1 (solid content concentration 40 mass%)
34.1 parts oxazoline compound (crosslinking agent) 10.9 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
-Titanium dioxide dispersion for back layer used in Example 1 ... 111.1 parts-Polyoxyalkylene alkyl ether ... 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, Ltd., solid content: 1% by mass)
·Distilled water

(Example 26)
Titanium dioxide in the same manner as in Example 1 except that the back layer was formed using the back layer forming coating solution 3 prepared as follows instead of the back layer forming coating solution 1 in Example 1. The back surface protection sheet for solar cells of Example 26 whose mass ratio is 85% was produced.
-Preparation of coating solution 3 for forming the back layer-
Components in the following composition were mixed to prepare a back layer forming coating solution 3.
-Composition of back layer forming coating solution 3-
-Said composite polymer aqueous dispersion P-1 (solid content concentration 40 mass%)
34.1 parts oxazoline compound (crosslinking agent) 10.9 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
-Titanium dioxide dispersion for back layer of Example 1 ... 284.5 parts-Polyoxyalkylene alkyl ether ... 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1 mass %)

(Comparative Example 7)
Titanium dioxide in the same manner as in Example 1 except that the back layer was formed using the back layer forming coating solution 4 prepared as follows instead of the back layer forming coating solution 1 in Example 1. The back surface protection sheet for solar cells of the comparative example 7 whose mass ratio is 40% was produced.
-Preparation of coating solution 4 for forming the back layer-
Components in the following composition were mixed to prepare a coating solution 4 for forming a back layer.
-Composition of coating solution 4 for forming the back layer-
-Said composite polymer aqueous dispersion P-1 (solid content concentration 40 mass%)
34.1 parts oxazoline compound (crosslinking agent) 10.9 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
-Titanium dioxide dispersion for back layer of Example 1 ... 24.4 parts-Polyoxyalkylene alkyl ether ... 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1 mass %)
・ Distilled water ... 29.1 parts

(Comparative Example 8)
Titanium dioxide in the same manner as in Example 1 except that the back layer was formed using the back layer forming coating solution 5 prepared as follows instead of the back layer forming coating solution 1 in Example 1. The back surface protection sheet for solar cells of the comparative example 8 whose mass ratio is 90% was produced.
-Preparation of coating solution 5 for forming the back layer-
Components in the following composition were mixed to prepare a back layer forming coating solution 5.
-Composition of coating liquid 5 for forming the back layer-
-Said composite polymer aqueous dispersion P-1 (solid content concentration 40 mass%)
34.1 parts oxazoline compound (crosslinking agent) 10.9 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
-Titanium dioxide dispersion for back layer of Example 1 ... 603.0 parts-Polyoxyalkylene alkyl ether ... 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, Ltd., solid content: 1 mass %)

(Comparative Example 9)
Titanium dioxide in the same manner as in Example 1 except that the back layer was formed using the back layer forming coating solution 6 prepared as follows instead of the back layer forming coating solution 1 in Example 1. The back surface protection sheet for solar cells of the comparative example 9 which does not contain in a back layer was produced.
-Preparation of coating solution 6 for forming the back layer-
Components in the following composition were mixed to prepare a back layer forming coating solution 6.
--- Composition weight of coating liquid 6 for forming the back layer / the composite polymer aqueous dispersion P-1 (solid content: 40% by mass)
34.1 parts oxazoline compound (crosslinking agent) 10.9 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
Polyoxyalkylene alkyl ether: 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Distilled water: 53.5 parts

(Example 27)
In Example 1, the same procedure as in Example 1 was performed except that the crosslinking agent (H-1) used in the preparation of the coating solution for forming the back layer was replaced with the following carbodiimide crosslinking agent (H-2). The solar cell back surface protective sheet of Example 27 was produced.
Carbodiimide type cross-linking agent (H-2): Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 25% by mass

(Example 28)
In Example 1, the same procedure as in Example 1 was performed except that the crosslinking agent (H-1) used in the preparation of the coating solution for forming the back layer was replaced with the following isocyanate crosslinking agent (H-3). The solar cell back surface protective sheet of Example 28 was produced.
・ Isocyanate-based crosslinking agent (H-3): Takelac W-6061, manufactured by Mitsui Chemicals, solid content: 25% by mass

(Comparative Example 10)
A cross-linking agent was obtained in the same manner as in Example 1 except that the back layer was formed using the back layer forming coating solution 7 prepared as follows instead of the back layer forming coating solution 1 in Example 1. The back surface protection sheet for solar cells of the comparative example 19 which does not contain in a back layer was produced.
-Preparation of coating solution 7 for back layer formation-
Components in the following composition were mixed to prepare a back layer forming coating solution 7.
-Composition of coating solution 7 for forming the back layer-
-Said composite polymer aqueous dispersion P-1 (solid content concentration 40 mass%)
... 34.1 parts-Titanium dioxide dispersion for back layer of Example 1 ... 24.4 parts-Polyoxyalkylene alkyl ether ... 1.5 parts (Naroacty CL95, Sanyo Chemical Industries, Ltd.) Manufactured, solid content: 1% by mass)
・ Distilled water: 40.0 parts

(Example 29)
In Example 1, the second back layer forming coating solution 1 prepared by further mixing the following components on the surface coated with the back layer was applied so that the dry thickness was 1.5 μm, and 180 ° C. Was dried for 1 minute to form a second back layer, and a back protective sheet for a solar cell of Example 29 having a back layer with a multilayer structure in which the binder of the second back layer was a silicone resin was produced. In addition, the structure of the back surface protection sheet for solar cells of Example 29 and Example 30 mentioned later was the structure of FIG.
-Preparation of coating solution 1 for forming the second back layer-
Components in the following composition were mixed to prepare a second back layer forming coating solution 1.
--- Second back layer forming coating solution 1--
-Said composite polymer aqueous dispersion P-1 (solid content concentration 40 mass%)
・ ・ ・ 19.2 parts ・ Colloidal silica ・ ・ ・ 0.2 parts (Snowtex UP, Nissan Chemical Co., Ltd., concentration 20% by mass)
Silane coupling agent: 4.8 parts (TSL8340, manufactured by Momentive Performance Materials, concentration: 1% by mass)
・ Organic lubricant: 12.8 parts (Chemipearl W950, manufactured by Mitsui Chemicals, Ltd., concentration 5% by mass)
Nonionic surfactant: 3.7 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, Ltd., concentration 1% by mass)
-Oxazoline compound (crosslinking agent) 6.2 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
・ Distilled water: 53.1 parts

(Example 30)
In Example 1, the following components were further mixed on the surface coated with the back layer, and the prepared second back layer forming coating solution 2 was applied so that the dry thickness was 1.5 μm, and 180 ° C. Was dried for 1 minute to form a second back layer, and a back protective sheet for a solar cell of Example 30 having a back layer with a multilayer structure in which the binder of the second back layer was a fluororesin was produced.
-Preparation of second back layer forming coating solution 2-
Components in the following composition were mixed to prepare a second back layer forming coating solution 2.
--- Second back layer forming coating solution 2--
・ Fluorine binder: 21.4 parts (Obligato SW0011F, manufactured by AGC Co-Tech Co., Ltd., concentration: 36% by mass)
・ Colloidal silica: 0.2 parts (Snowtex UP, manufactured by Nissan Chemical Co., Ltd., concentration: 20% by mass)
Silane coupling agent: 4.8 parts (TSL8340, manufactured by Momentive Performance Materials, concentration: 1% by mass)
・ Organic lubricant: 12.8 parts (Chemipearl W950, manufactured by Mitsui Chemicals, Ltd., concentration 5% by mass)
Nonionic surfactant: 3.7 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, Ltd., concentration 1% by mass)
-Oxazoline compound (crosslinking agent) 6.2 parts (Epocross WS-700, manufactured by Nippon Shokubai Chemical Industry Co., Ltd., solid content: 25% by mass)
・ Distilled water: 50.9 parts

Regarding the constitution of the polymer base material and the back layer of the back surface protective sheet for solar cell prepared in each Example and Comparative Example, those having a single back layer are shown in Table 1 below, and those having a back layer in multiple layers are shown in Table 3 below. Indicated.

(Evaluation)
The following evaluation was performed about the back surface protection sheet for solar cells produced by said each Example and comparative example. The evaluation results are shown in Table 2 and Table 4 below.

-Evaluation of adhesion-
(1) Adhesiveness before aging with wet heat Six back scratches were made on the back layer surface of the back protection sheet for solar cells with a single-edged razor to form 25 squares. A Mylar tape (polyester tape) was affixed thereon and peeled by manually pulling it in the 180 ° direction along the sample surface. At this time, the adhesive strength of the back layer was ranked according to the following evaluation criteria according to the number of peeled cells.
In this evaluation, the evaluation ranks 4 to 5 are practically acceptable.
--Evaluation criteria--
5: There was no cell which peeled (0 cell).
4: The peeled square was from 0 square to less than 0.5 square.
3: The square which peeled was 0.5 square or more and less than 2 squares.
2: The square which peeled was 2 squares or more and less than 10 squares.
1: The square which peeled was 10 squares or more.

(2) Adhesion after wet heat aging The back protective sheet for solar cells was held for 100 hours under an environmental condition of 120 ° C. and 100% relative humidity, and then conditioned for 1 hour under an environment of 25 ° C. and 60% relative humidity. . Thereafter, the adhesive strength of the back layer was evaluated in the same manner as in the evaluation of “(1) Adhesiveness before wet heat aging”.
In this evaluation, the evaluation ranks 3 to 5 are practically acceptable ranges.

(3) Adhesiveness after ultraviolet (UV) irradiation About the prepared back surface protection sheet for solar cells, peaked at the wavelength in the ultraviolet region using a super energy irradiation tester (UE-1DEc type) manufactured by Suga Test Instruments Co., Ltd. The back layer surface was irradiated with light having an energy of 100 mW / cm ² having a thickness of 120 hours. Immediately after the irradiation, the adhesive strength of the back layer was evaluated in the same manner as in the evaluation of “(1) Adhesiveness before wet heat aging”.
The temperature of the back sheet during light irradiation was controlled at 63 ° C.
In this evaluation, the evaluation ranks 3 to 5 are practically acceptable ranges.

-Evaluation of design-
Using the super-energy irradiation tester (UE-1DEc type) manufactured by Suga Test Instruments Co., Ltd., the back surface protection sheet for the solar cell produced was backed with 100 mW / cm ² energy light having a peak in the wavelength of the ultraviolet region. The layer surface was irradiated for 120 hours. After irradiation, the back layer surface was visually observed, and the presence or absence of coloring was ranked according to the following evaluation criteria.
Evaluation ranks 3 and 2 are practically acceptable ranges.
--Evaluation criteria--
3: There was no coloring.
2: There was slight coloring.
1: There was remarkable coloring.

-Evaluation of elongation at break-
(1) Evaluation of breaking elongation retention ratio after storage with moisture and heat resistance About the manufactured solar cell back surface protective sheet, after the shape of the measurement sample was cut out to 2.5 cm × 20 cm, the environmental conditions were 120 ° C. and relative humidity 100%. Held under for 120 hours. Then, about the produced back surface protection sheet for solar cells, the fracture | rupture elongation when it pulled by the distance between chuck | zippers of 12.5 cm and the tension | pulling speed of 1.25 cm / min was measured. At this time, the number of samples was set to n = 5, and after measuring about each of the longitudinal direction and the width direction of the back surface protection sheet for solar cells, those average values were made into breaking elongation E1. At this time, the elongation at break of the sample before storage with moisture and heat resistance was also measured and set as the elongation at break E0. Using the obtained breaking elongations E1 and E0, the breaking elongation retention after storage under heat and moisture resistance was calculated by the following equation (1).
Breaking elongation retention after storage with moisture and heat resistance (%) = E1 / E0 × 100 (1) Formula It is practically acceptable that the elongation at break after storage with moisture and heat is 50% or more. It is preferable that the breaking elongation retention after storage with moisture and heat resistance is 70% or more.

(2) Evaluation of elongation at break after heat-resistant storage-
About the produced back surface protection sheet for solar cells, after the shape of the measurement sample was cut out to 2.5 cm × 20 cm, it was held at 190 ° C. under dry environmental conditions for 120 hours, and then the elongation at break after the above heat and heat resistant storage The elongation at break was measured in the same manner as in the evaluation method. At this time, the number of samples was set to n = 5, and after measuring for each of the longitudinal direction and the width direction of the backsheet, the average value thereof was defined as the breaking elongation E2. At this time, the breaking elongation of the sample before heat-resistant storage was also measured and set as the breaking elongation E0. Using the obtained breaking elongations E2 and E0, the breaking elongation retention after heat-resistant storage was calculated by the following equation (2).
Breaking elongation retention after heat-resistant storage (%) = E2 / E0 × 100 (2) Formula Within a practically acceptable range, the breaking elongation retention after heat-resistant storage is 50% or more. In addition, it is preferable that the breaking elongation retention after heat-resistant storage is 75% or more.

From Tables 1 to 4, the back protective sheet for solar cells of the present invention has good adhesiveness before and after wet heat aging, good adhesiveness after UV irradiation, good coloring, and after wet heat storage. It was also found that the retention rate at break after heat-resistant storage was high.
Further, from Comparative Example 5, the type R-780-2 used in JP 2012-17456 A and JP 2012-4546 A, which is below the lower limit of the bulk specific gravity range of the pigment of the present invention, is used. It was found that adhesion durability and coloring were poor. That is, a composite containing a siloxane and an acrylic structural unit disclosed in JP2012-4546A on a polyester support containing a carbodiimide compound disclosed in JP2012-17456A as a terminal blocking agent. Even when the coating layer containing the polymer and the white pigment was combined, it was found that the adhesion durability and coloring were worse than the solar cell back surface protective sheet of the present invention, and the weather resistance and designability were inferior.

(Example 101)
-Creation of solar cell module-
3 mm thick tempered glass, EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), crystalline solar cell, EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), and back of Example 1 The sheets were superposed in this order, and hot-pressed using a vacuum laminator (Nisshinbo Co., Ltd., vacuum laminating machine) to adhere to EVA. At this time, the back surface protection sheet for solar cells prepared in Example 1 was disposed such that the side on which the reflective layer and the easy-adhesion layer were formed (the reflective layer being the outermost layer among them) was in contact with the EVA sheet.
In this way, a crystalline solar cell module was produced. When the produced solar cell module was operated for power generation, it showed good power generation performance as a solar cell.

(Examples 102 to 129)
Using the backsheet samples produced in Examples 2 to 29, solar cell modules were produced in the same manner as in Example 101. In addition, the structure of the solar cell module produced in Example 28 and 29 was the structure of FIG.
When the power generation operation was performed using the produced solar cell module, all showed good power generation performance as a solar cell.

DESCRIPTION OF SYMBOLS 1 Reflective layer 2 Easy-adhesion layer 3 Polymer layer (back layer) arrange | positioned adjacent to the polyester support body
4 Second back layer (overcoat layer)
DESCRIPTION OF SYMBOLS 12 Back surface protection sheet 16 for solar cell modules Polyester support body 22 Sealing material 20 Solar cell element 24 Transparent front substrate (tempered glass)
10 Solar cell module

Claims (10)

1. A polyester support containing polyester and end-capping agent;
   Having a polymer layer in direct contact with at least one surface on the polyester support;
   The polymer layer contains 15 to 85% by mass of a siloxane structural unit represented by the following general formula (S-1) and 85 to 15% by mass of a non-siloxane structural unit in the molecule, and the non-siloxane structural unit is Including a composite polymer containing carboxyl groups,
   The polymer layer contains 45 to 85% by mass of a pigment having a bulk specific gravity of 0.50 to 0.85 g / cm ³ with respect to the total mass of the polymer layer;
   The said polymer layer contains the structure part derived from the crosslinking agent which bridge | crosslinks the said composite polymer, The back surface protection sheet for solar cells characterized by the above-mentioned.
   Formula (S-1)
   -(Si (R ¹¹ ) (R ¹² ) -O) _n1-
   [In the general formula (S-1), R ¹¹ and R ¹² each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, and R ¹¹ and R ¹² may be the same or different. n1 represents a natural number. When n1 is 2 or more, the plurality of R ¹¹ and R ¹² may be the same as or different from each other. ]
2. The back protective sheet for a solar cell according to claim 1, wherein the non-polysiloxane structural unit of the composite polymer is an acrylic structural unit.
3. The solar cell back surface protective sheet according to claim 1 or 2, wherein the end sealant is added in an amount of 0.1 to 5.0 mass% to the polyester support.
4. The back protective sheet for a solar cell according to any one of claims 1 to 3, wherein the end-capping agent is polycarbodiimide.
5. The back protective sheet for a solar cell according to claim 4, wherein the polycarbodiimide is a polycarbodiimide having a molecular weight of 2000 to 50000.
6. The solar cell back surface protective sheet according to claim 4 or 5, wherein the polycarbodiimide is a polycarbodiimide having a melting point of 80 to 170 ° C.
7. The back protective sheet for a solar cell according to any one of claims 1 to 6, wherein the pigment is titanium dioxide.
8. The solar cell back surface protective sheet according to any one of claims 1 to 7, wherein the crosslinking agent is at least one selected from an oxazoline-based compound and a carbodiimide-based compound.
9. The back protective sheet for a solar cell according to any one of claims 1 to 8, wherein the end-capping agent is a cyclic carbodiimide compound.
10. A solar cell module comprising the solar cell back surface protective sheet according to any one of claims 1 to 9.

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