WO2013024902A1

WO2013024902A1 - Back sheet for solar cell, method for manufacturing same, and solar cell module

Info

Publication number: WO2013024902A1
Application number: PCT/JP2012/070928
Authority: WO
Inventors: 伊藤　維成; 畠山　晶
Original assignee: 富士フイルム株式会社
Priority date: 2011-08-17
Filing date: 2012-08-17
Publication date: 2013-02-21
Also published as: JP2013058748A; JP5722287B2; TW201318853A

Abstract

The purpose of the present invention is to provide a back sheet for a solar cell having a high reflection performance, durability, and a high adhesion strength with respect to a sealing material. This back sheet (1) for a solar cell has: a polymer substrate (10); a pigment layer (12) provided on a first surface of the polymer substrate (10), the pigment layer including a binder and a pigment; a topcoat layer (14) provided on the pigment layer; and a composite polymer layer (16) provided on a second surface of the polymer substrate (10), the composite polymer layer containing a composite polymer that is represented by the following general formula (1) and that includes, in the molecule, siloxane structural units in a mass ratio of 15-85 mass% and non-siloxane structural units in a mass ratio of 85-15 mass%.

Description

SOLAR CELL BACK SHEET, ITS MANUFACTURING METHOD, AND SOLAR CELL MODULE

The present invention relates to a solar cell backsheet, a manufacturing method thereof, 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 side glass on the side on which sunlight is incident and a solar cell back surface protection sheet (solar cell backsheet, on the side opposite to the side on which sunlight is incident (back side), (Hereinafter also referred to simply as “back sheet”), the solar cell is sandwiched between the front glass and the solar cell, and between the solar cell and the back sheet. Are sealed with EVA (ethylene-vinyl acetate) resin or the like.

The back sheet has a function of preventing moisture from entering from the back surface of the solar cell module, and conventionally glass or fluororesin has been used, but in recent years, polyester has been used from the viewpoint of cost. It has become to. And a back sheet is not a mere polymer sheet, but may have various functions as shown below.

As a function imparted to the solar cell backsheet, for example, a backsheet having a reflective performance by adding a white pigment such as titanium oxide may be required. This is to increase power generation efficiency by irregularly reflecting light that has passed through the cell out of sunlight incident from the front side of the module and returning it to the cell. As such a white film, a white resin film such as a method of applying a coating liquid or a white paint containing a white pigment on a stretched polyester film, a white polyester film containing a white pigment or forming a void by foaming or stretching The method of laminating is mentioned. Among these, since the material cost is low and it is easy to obtain a high reflectance, a titanium polyester kneaded type white polyester film is widely used (see, for example, JP-A-2008-130642). .

Japanese Patent Laid-Open No. 2008-130642 proposes to use a white resin film of a titanium oxide wrought type, but when maintaining the reflection performance by increasing the thickness of the base material, a large amount of titanium oxide is required. , Leading to higher material costs.

The present invention has been made in view of the above, and provides a solar cell backsheet having a low manufacturing cost, high reflection performance and durability, and high adhesive strength with a sealing material, and a method for manufacturing the backsheet. The purpose is to provide. Another object of the present invention is to provide a solar cell module that can stably maintain power generation performance over a long period of time.

Specific means for achieving the above object are as follows.
<1> a polymer substrate;
A pigment layer provided on the first surface of the polymer substrate and comprising a binder and a pigment;
An overcoat layer provided on the pigment layer and containing a binder;
A non-siloxane provided on the second surface of the polymer substrate and having a mass ratio of 15 to 85 mass% and a mass ratio of 85 to 15 mass% represented by the following general formula (1) in the molecule A composite polymer layer containing a composite polymer comprising a system structural unit;
A solar cell backsheet.

[In General Formula (1), R ¹ and R ² each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, and R ¹ and R ² may be the same or different. n represents an integer of 1 or more. The plurality of R ¹ and R ² may be the same as or different from each other. ]
<2>
<1> The solar cell backsheet according to <1>, comprising a binder and having an undercoat layer having a thickness of 2 μm or less between the polymer substrate and the pigment layer.
<3>
The solar cell backsheet according to <1> or <2>, wherein at least one layer provided on the polymer base material contains a fluorosurfactant.
<4>
The solar cell backsheet according to any one of <1> to <3>, wherein a ratio of the pigment to the total of the binder and the pigment in the pigment layer is 40 to 95% by mass.
<5>
The solar cell backsheet according to any one of <1> to <4>, wherein the thickness of the topcoat layer is 0.1 μm or more and 30 μm or less.
<6>
The solar cell backsheet according to any one of <1> to <5>, wherein a ratio of the pigment to the total of the binder and the pigment in the pigment layer is 50 to 95% by mass.
<7>
The solar cell backsheet according to any one of <1> to <6>, wherein the ratio of the pigment to the total of the binder and the pigment in the pigment layer is 70 to 95% by mass.
<8>
The solar cell backsheet according to any one of <1> to <7>, wherein the thickness of the topcoat layer is from 0.3 μm to 20 μm.
<9>
The solar cell backsheet according to any one of <1> to <8>, wherein the thickness of the overcoat layer is 0.5 μm or more and 10 μm or less.
<10>
<1> to <9>, wherein at least one layer provided on the first surface of the polymer substrate contains 5 to 50% by mass of a crosslinking agent-derived structure with respect to the binder contained in the layer The solar cell backsheet according to any one of the above.
<11>
The solar cell backsheet according to <10>, wherein at least one of the crosslinking agents is a crosslinking agent having a carbodiimide group or an oxazoline group.
<12>
Between the polymer substrate and the pigment layer, a binder is included, and an undercoat layer having a thickness of 2 μm or less is formed. The solar cell backsheet according to any one of <1> to <11>, comprising at least one resin selected from the group consisting of:
<13>
Any one of <1> to <12> containing a binder and having an undercoat layer having a thickness of 2 μm or less between the polymer substrate and the pigment layer, wherein the undercoat layer and the overcoat layer contain an inorganic oxide filler The back sheet for solar cells as described in 2.
<14>
The solar cell according to any one of <1> to <13>, wherein at least one surface of the polymer substrate is surface-treated by at least one method of corona treatment, atmospheric pressure plasma treatment, glow discharge treatment, and flame treatment. Back sheet.
<15>
The solar cell according to any one of <1> to <14>, wherein the polymer base material includes 0.1 to 10% by mass of an end-capping agent based on the total mass of the polyester resin and the polyester resin. Polymer sheet.
<16>
The base polymer base material contains inorganic particles or organic particles, the average particle size of the particles is 0.1 to 10 μm, and the content of the particles is 0 to 50% by mass with respect to the total mass of the polymer base material <1> to the polymer sheet for solar cell according to any one of <15>.
<17>
The solar cell backsheet according to any one of <1> to <16>, wherein the polymer base material has a thermal shrinkage rate of about 0 to 0.5% at 150 ° C. for about 30 minutes.
<18>
The solar cell backsheet according to any one of <1> to <17>, wherein the polymer substrate comprises a polyester resin having a carboxyl group content of 35 equivalents / ton or less.
<19>
The solar cell backsheet according to any one of <1> to <18>, wherein the reflectance with respect to light having a wavelength of 550 nm on the side where the pigment layer is provided is 70% or more.
<20>
The solar cell backsheet according to any one of <1> to <19>, wherein all of the layers provided on the first surface of the polymer base material are layers formed by coating.
<21>
A melt extrusion step of melt-extruding a raw material resin for a polymer substrate into a sheet,
Cooling the melt-extruded sheet-shaped resin, and forming a resin sheet,
A first stretching step of stretching the resin sheet in a first direction;
An undercoat layer forming step of applying and forming an undercoat layer on at least one surface of the resin sheet stretched in the first direction;
A second stretching step of stretching the resin sheet coated with the undercoat layer in a second direction orthogonal to the first direction;
A method for producing a solar cell backsheet, wherein the solar cell backsheet according to any one of <2> to <20> is produced.
<22>
A solar cell module comprising: a transparent substrate on which sunlight is incident; a solar cell element; and the solar cell backsheet according to any one of <1> to <20>.

According to the present invention, it is possible to provide a solar cell backsheet having a low manufacturing cost, high reflection performance and durability, and high adhesive strength with a sealing material, and a method for manufacturing the same. Moreover, according to this invention, the solar cell module which can maintain electric power generation performance stably over a long term can be provided.

It is a schematic sectional drawing which shows an example (1st Embodiment) of the layer structure of the solar cell backsheet which concerns on this invention. It is a schematic sectional drawing which shows the other example (2nd Embodiment) of the laminated constitution of the solar cell backsheet which concerns on this invention.

Hereinafter, the solar cell backsheet and solar cell module of the present invention will be described 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 expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Back sheet for solar cells]
The solar cell backsheet of the present invention (appropriately referred to as “backsheet”) is provided on the first surface of the polymer substrate, the polymer substrate, the pigment layer containing the binder and the pigment, and the pigment layer. An overcoating layer containing a binder, a siloxane structural unit provided on the second surface of the polymer substrate and having a mass ratio of 15 to 85% by mass represented by the following general formula (1) in the molecule; And a composite polymer layer containing a composite polymer containing a non-siloxane structural unit having a mass ratio of 85 to 15% by mass.

In General Formula (1), R ¹ and R ² each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, and R ¹ and R ² may be the same or different. n represents an integer of 1 or more. The plurality of R ¹ and R ² may be the same as or different from each other.
With such a configuration, the production cost is kept low, the solar cell back sheet has high reflection performance and durability (light resistance and heat and moisture resistance), and has high adhesive strength with the sealing material.
In addition, due to the above characteristics of the backsheet of the present invention, the solar cell module provided with the backsheet of the present invention has excellent power generation performance due to the high light reflectivity of the backsheet of the present invention, and over time in a humid heat environment. It is possible to stably maintain the power generation performance over a long period without causing peeling or the like.
Hereinafter, the structure of the solar cell backsheet of this invention is demonstrated concretely.

<Configuration>
FIG. 1 shows an example (first embodiment) of a layer configuration of a solar cell backsheet according to the present invention. In the solar cell backsheet 1 of the first embodiment, a pigment layer 12 and an overcoat layer 14 are provided on the first surface of the polymer substrate 10, and on the second surface of the polymer substrate 10. A composite polymer layer 16 containing a composite polymer is provided.
FIG. 2 shows another example (second embodiment) of the layer configuration of the solar cell backsheet according to the present invention. The solar cell backsheet 2 of the second embodiment is provided with an undercoat layer 11 having a thickness of 2 μm or less, a pigment layer 12, and an overcoat layer 14 on the first surface of the polymer substrate 10. A composite polymer layer 16 containing a composite polymer is provided on the second surface of the material 10.
1 and 2 do not limit the present invention at all, and may have other layers.

<Polymer substrate>
Examples of the polymer substrate include polyester, polyolefin such as polypropylene and polyethylene, or fluorine-based polymer such as polyvinyl fluoride. Among these, polyester is preferable from the viewpoint of cost and mechanical strength.

The polyester used as the polymer substrate (support) in the present invention is 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. Of these, polyethylene terephthalate or polyethylene-2,6-naphthalate is particularly preferable from the viewpoint of balance between mechanical properties and cost.

The polyester may be a homopolymer or a copolymer. Further, polyester may be blended with other kinds of resins such as polyimide in a small amount.

When polymerizing the polyester in the present invention, it is preferable to use an Sb-based, Ge-based or Ti-based compound as a catalyst from the viewpoint of keeping the carboxyl group content below a predetermined range, and among these, a Ti-based compound is particularly preferable. In the case of using a Ti-based compound, an embodiment in which polymerization is performed by using the Ti-based compound as a catalyst in a range of 1 ppm to 30 ppm, more preferably 3 ppm to 15 ppm is preferable. When the proportion of the Ti-based compound is within the above range, the terminal carboxyl group can be adjusted to the following range, and the hydrolysis resistance of the polymer substrate can be kept low.

In the present invention, the carboxyl group content in the polyester is preferably 50 equivalents / ton or less, more preferably 35 equivalents / ton or less. When the carboxyl group content is 35 equivalents / ton or less, hydrolysis resistance is maintained, and a decrease in adhesiveness when subjected to wet heat aging can be remarkably suppressed. The lower limit of the carboxyl group content is desirably 2 equivalents / ton or more from the viewpoint of maintaining adhesiveness with a layer (for example, a pigment layer) formed on the polymer substrate. “Equivalent / ton” represents a molar equivalent per ton.
The carboxyl group content in the polyester can be adjusted by the polymerization catalyst species and the film forming conditions (film forming temperature and time).

It is preferable that the polymer substrate is surface-treated by at least one method of corona treatment, atmospheric pressure plasma treatment, glow discharge treatment, and flame treatment (for example, flame treatment using a flame introduced with a silane compound). Even if the surface treatment is performed only on one surface of the substrate, the surface treatment may be performed on both surfaces of the substrate. For example, when forming the other functional layer mentioned later on a polymer base material by application | coating, it is preferable that the surface treatment is given to both surfaces. Among these, in the present invention, it is preferable to use corona treatment or glow discharge treatment.
A preferred embodiment of the corona treatment is a corona treatment in a treatment strength range of 150 to 500 J / m ² at an output of 0.1 to 3.0 kw / electrode 1 m (representing an output per 1 m of electrode) with respect to the polymer substrate. It is the aspect which gives.
In the corona treatment, the output is more preferably 0.5 to 2.5 kw / electrode 1 m, and particularly preferably 0.7 to 1.7 kw / electrode 1 m. More preferably treated intensity range is 160 ~ 450J / m ^2, and particularly preferably 170 ~ 360J / m ^2.

Glow discharge treatment is a method called low-pressure plasma treatment or vacuum plasma treatment, and is a method of generating a plasma by discharge in a gas (plasma gas) in a low-pressure atmosphere to treat the substrate surface. The low-pressure plasma used in the process of the present invention is a non-equilibrium plasma generated under conditions where the plasma gas pressure is low. The treatment of the present invention is performed by placing a film to be treated (polymer substrate) in this low-pressure plasma atmosphere.

In the glow discharge treatment of the present invention, as a method for generating plasma, methods such as direct current glow discharge, high frequency discharge, and microwave discharge can be used. The power source used for discharging may be direct current or alternating current. When alternating current is used, a range of about 30 Hz to 20 MHz is preferable.
When alternating current is used, a commercial frequency of 50 or 60 Hz may be used, or a high frequency of about 10 to 50 kHz may be used. A method using a high frequency of 13.56 MHz is also preferable.

As the plasma gas used in the glow discharge treatment of the present invention, an inorganic gas such as oxygen gas, nitrogen gas, water vapor gas, argon gas, helium gas can be used, and in particular, oxygen gas or oxygen gas and argon gas The mixed gas is preferable. Specifically, it is desirable to use a mixed gas of oxygen gas and argon gas. When oxygen gas and argon gas are used, the ratio between the two is preferably oxygen gas: argon gas = 100: 0 to 30:70, more preferably 90:10 to 70:30, as a partial pressure ratio. In addition, a method in which a gas such as water entering the processing container due to a leak or water vapor coming out of the object to be processed is used as the plasma gas without introducing a gas into the processing container.

The plasma gas pressure needs to be low enough to achieve non-equilibrium plasma conditions. The specific plasma gas pressure is preferably in the range of 0.005 to 10 Torr (0.666 to 1333 Pa), more preferably about 0.008 to 3 Torr (1.067 to 400 Pa). If the pressure of the plasma gas is 0.666 Pa or more, the effect of improving adhesiveness is sufficient, and if it is 1333 Pa or less, the increase in current is suppressed and the discharge is stabilized.

The plasma output cannot be generally specified depending on the shape and size of the processing container and the shape of the electrode, but is preferably about 100 to 2500 W, more preferably about 500 to 1500 W.
The treatment time of the glow discharge treatment of the present invention is preferably 0.05 to 100 seconds, more preferably about 0.5 to 30 seconds. If the treatment time is 0.05 seconds or more, the effect of improving adhesiveness is sufficient, and if it is 100 seconds or less, problems such as deformation and coloring of the film to be treated can be prevented.

Discharge treatment intensity of the glow discharge treatment of the present invention will depend on the plasma power and treatment time, preferably in the range of 0.01 ~ 10kV · A · min ^{/ m 2, 0.1 ~ 7kV ·} A · min / ^{m 2} Gayori preferable.
Discharge treatment intensity that is sufficient adhesion improving effect of the 0.01 kV · A · min / m ² or more is obtained, and such deformation and coloration of the processed film by a 10 kV · A · min / m ² or less You can avoid problems.

In the glow discharge treatment of the present invention, it is also preferable to heat the film to be treated in advance. By this method, better adhesiveness can be obtained in a shorter time than when heating is not performed. The heating temperature is preferably in the range of 40 ° C. to the softening temperature of the film to be treated + 20 ° C., more preferably in the range of 70 ° C. to the softening temperature of the film to be processed. By setting the heating temperature to 40 ° C. or higher, a sufficient adhesive improvement effect can be obtained. Moreover, the handleability of a favorable film is securable during a process by making heating temperature below into the softening temperature of a to-be-processed film.
Specific methods for raising the temperature of the film to be treated in vacuum include heating with an infrared heater, heating by contacting with a hot roll, and the like.

The polymer base material of the present invention may contain an end-capping agent. Specifically, the polymer base material may contain 0.1 to 10% by mass of the end-capping agent with respect to the total mass of the polyester resin and the polyester resin. . The amount of the end-capping agent added relative to the total mass of the polyester resin constituting the polymer substrate is more preferably 0.2 to 5% by mass, still more preferably 0.3 to 2% by mass.

Since the hydrolysis of the polyester is accelerated by the catalytic effect of H ⁺ generated from the terminal carboxylic acid or the like, an end-capping agent that reacts with the terminal carboxylic acid is added to improve the hydrolysis resistance (weather resistance). It is effective.
If the end-capping agent is less than the above range, the effect of improving the weather resistance is hardly exhibited.

Examples of the end capping agent include epoxy compounds, carbodiimide compounds, oxazoline compounds, carbonate compounds, etc., but carbodiimide having high affinity with PET and high end capping ability is preferable.

It is preferable that terminal blocker (especially carbodiimide terminal blocker) is high molecular weight. This can reduce volatilization during melt film formation. The molecular weight is preferably 200 to 100,000, more preferably 2000 to 80,000, still more preferably 10,000 to 50,000. If the molecular weight of the end-capping agent (especially carbodiimide end-capping agent) is within the above range, it is easy to uniformly disperse in the polyester, and it is easy to fully express the weather resistance improving effect. It is difficult and it becomes easy to express an effect of improving weather resistance.
In addition, the molecular weight of terminal blocker means a weight average molecular weight.

Carbodiimide end-capping agent:
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, t-butylisopropylcarbodiimide, and diphenylcarbodiimide. , Di-t-butylcarbodiimide, di-β-naphthylcarbodiimide, and the like. 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 , And the like can be exemplified 3,5-triisopropyl-2,4-carbodiimide.

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, it is preferable that the molecular weight (degree of polymerization) is high, and it is more preferable that the terminal of the carbodiimide compound has a structure with high heat resistance. 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.

The terminal blocker carbodiimide preferably has a cyclic structure (for example, those described in JP-A-2011-153209). These exhibit the same effect as the above high molecular weight carbodiimide even at low molecular weight. This is because the terminal carboxylic acid of the polyester and the cyclic carbodiimide undergo a ring-opening reaction, one reacts with this polyester, and the other with the ring-opening reacts with another polyester to increase the molecular weight, thus suppressing the generation of isocyanate gas. It is to do.

Among those having a cyclic structure, in the present invention, the terminal blocking agent is a carbodiimide compound having a carbodiimide group and a cyclic structure in which the first nitrogen and the second nitrogen are bonded by a bonding group. It is preferable.
Further, the end capping agent has a cyclic structure in which at least one carbodiimide group adjacent to the aromatic ring is present, and the first nitrogen and the second nitrogen of the carbodiimide group adjacent to the aromatic ring are bonded by a bonding group. More preferred is carbodiimide (also referred to as aromatic cyclic carbodiimide).
The aromatic cyclic carbodiimide may have a plurality of cyclic structures.
The aromatic cyclic carbodiimide is preferably an aromatic carbodiimide having no ring structure in which the first nitrogen and the second nitrogen of two or more carbodiimide groups are bonded by a linking group in the molecule, that is, a monocyclic ring. Can be used.

The cyclic structure has one carbodiimide group (—N═C═N—), and the first nitrogen and the second nitrogen are bonded by a bonding group. One cyclic structure has only one carbodiimide group. For example, when there are a plurality of cyclic structures in the molecule, such as a spiro ring, one cyclic structure bonded to a spiro atom is included in each cyclic structure. Needless to say, the compound may have a plurality of carbodiimide groups as long as it has a carbodiimide group. The number of atoms in the cyclic structure is preferably 8 to 50, more preferably 10 to 30, further preferably 10 to 20, and particularly preferably 10 to 15.

Here, the number of atoms in the cyclic structure means the number of atoms directly constituting the cyclic structure, and is, for example, 8 for an 8-membered ring and 50 for a 50-membered ring. This is because if the number of atoms in the cyclic structure is smaller than 8, the stability of the cyclic carbodiimide compound is lowered, and it may be difficult to store and use. From the viewpoint of reactivity, the upper limit of the number of ring members is not particularly limited, but cyclic carbodiimide compounds having more than 50 atoms are difficult to synthesize, and the cost may increase significantly. From this viewpoint, the number of atoms in the cyclic structure is preferably selected in the range of 10 to 30, more preferably 10 to 20, and particularly preferably 10 to 15.

Specific examples of the carbodiimide end-capping agent having a cyclic structure include the following compounds. However, the present invention is not limited to the following specific examples.

Epoxy end sealant:
Preferred examples of the epoxy compound include glycidyl ester compounds and glycidyl ether compounds.

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, diglycidyl phthalate, diglycidyl naphthalene dicarboxylate Stell, methyl terephthalic 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 include bisglycidyl polyether obtained by the reaction of bisphenol such as methane and epichlorohydrin, and these use one kind or two or more kinds. It is possible.

Oxazoline-based end-capping agent:
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-phenylenebis (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'-tetramethylenebis ( 4, 4-dimethyl-2-oxazoline), 2,2'-9,9'-diphenoxyethanebis (2-oxazoline), 2,2'-cyclohexylenebis (2-oxazoline) and 2,2'-diphenylene Examples thereof include bis (2-oxazoline). 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.

It is necessary to knead such a terminal blocker into the polyester film. That is, the above-described effect cannot be obtained unless the polyester molecule is directly reacted. This is because the polyester and the end-capping agent do not react even when added to the coating layer on PET.

In the present invention, inorganic particles or organic particles can be mixed in the polyester film (polymer substrate). Thereby, the reflectance (whiteness) of light can be improved and the power generation efficiency of a solar cell can be raised.

The average particle size of the particles contained in the polyester film is preferably 0.1 to 10 μm, more preferably 0.1 to 5 μm, and still more preferably 0.15 to 1 μm, and the content is based on the total mass of the film. 0 to 50% by mass, preferably 1 to 10% by mass, and more preferably 2 to 5% by mass.
If the average particle size of the particles is 0.1 to 10 μm, the whiteness of the film can be made 50 or more without increasing the addition amount.
Further, if the addition amount of the particles is 1% by mass or more, it becomes easy to set the whiteness to 50 or more, and if it is 50% by mass or less, an increase in the film weight is suppressed and handling in processing and the like is easy. Become. In addition, the average particle diameter and content mentioned here refer to the average value of each layer when the film used as the substrate has a multilayer structure. That is, (particle diameter of each layer, content) × (thickness of each layer / thickness of all layers) is calculated for each layer, and the sum is obtained.

In addition, the average particle diameter of the particle | grains contained in the polymer base material of this invention is calculated | required by the electron microscope method. Specifically, the following method is used.
The particles are observed with a scanning electron microscope, the magnification is appropriately changed according to the size of the particles, and the photographed image is enlarged and copied. Next, the outer circumference of each particle is traced for at least 200 particles randomly selected. The equivalent circle diameters of the particles are measured from these trace images with an image analysis apparatus, and the average value thereof is taken as the average particle diameter.

The particles may be either inorganic particles or organic particles, or a combination of both. Thereby, the reflectance of light can be improved and the power generation efficiency of a solar cell can be raised. Suitable inorganic particles include, for example, wet and dry silica, colloidal silica, calcium carbonate, aluminum silicate, calcium phosphate, alumina, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc white), antimony oxide, oxidation Cerium, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (lead white), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, titanium mica, talc, clay, Kaolin, lithium fluoride, calcium fluoride, and the like can be used, and titanium dioxide and barium sulfate are particularly preferable. The titanium oxide may be either anatase type or rutile type. The particle surface may be subjected to inorganic treatment such as alumina or silica, or may be subjected to organic treatment such as silicon or alcohol.

Among these particles, titanium dioxide is preferable, and the polymer base material can exhibit excellent durability even under light irradiation by containing titanium dioxide. Specifically, when UV irradiation is performed at 63 ° C., 50% Rh, irradiation intensity of 100 mW / cm ² for 100 hours, the elongation at break is preferably 35% or more, more preferably 40% or more. As described above, the polymer base material of the present invention is more suitable as a back surface protective film of a solar cell used outdoors because photodecomposition and deterioration are suppressed even by light irradiation.

Titanium dioxide includes rutile type and anatase type, but it is preferable to add titanium dioxide particles mainly composed of rutile type to the polymer substrate of the present invention. The anatase type has a very high spectral reflectance of ultraviolet rays, whereas the rutile type has a characteristic that the absorption rate of ultraviolet rays is large (spectral reflectance is small). The present inventor pays attention to such a difference in spectral characteristics in the crystal form of titanium dioxide, and can improve the light resistance in the polyester film for protecting the back surface of the solar cell by utilizing the rutile-type ultraviolet absorption performance. Thereby, it is excellent in the film durability under light irradiation, even if it does not add another ultraviolet absorber substantially. For this reason, problems such as contamination due to bleeding out of the ultraviolet absorber and a decrease in adhesion are unlikely to occur.

In addition, as described above, the titanium dioxide particles according to the present invention are mainly composed of rutile type, but the term “main body” as used herein means that the amount of rutile type titanium dioxide in all titanium dioxide particles is 50% by mass. It means that it is over.
Moreover, it is preferable that the amount of anatase type titanium dioxide in all the titanium dioxide particles is 10 mass% or less. More preferably, it is 5 mass% or less, Most preferably, it is 0 mass%. If the content of anatase type titanium dioxide exceeds the above upper limit, the amount of rutile type titanium dioxide in the total titanium dioxide particles may be reduced, resulting in insufficient ultraviolet absorption performance. Since the photocatalytic action is strong, the light resistance also tends to be lowered by this action. Rutile titanium dioxide and anatase titanium dioxide can be distinguished by X-ray structure diffraction and spectral absorption characteristics.

The rutile titanium dioxide particles of the present invention may be subjected to an inorganic treatment such as alumina or silica on the particle surface, or an organic treatment such as silicon or alcohol. Rutile titanium dioxide may be subjected to particle size adjustment and coarse particle removal using a purification process before blending with the polyester composition. As industrial means of the purification process, for example, a jet mill or a ball mill can be applied as a pulverizing means, and as a classification means, for example, dry or wet centrifugation can be applied.

In the present invention, organic particles can also be used. Those that can withstand the heat in the polyester film are preferable, for example, those made of a cross-linked resin are used, and specifically, polystyrene cross-linked with divinylbenzene is used. The size and addition amount of the particles are the same as in the case of inorganic particles.
Various known methods can be used for adding particles to the film as a method using a known method. The following method can be mentioned as the typical method.

(A) A method of adding particles before the end of the ester exchange reaction or esterification reaction during the synthesis of polyethylene terephthalate, or adding the particles before the start of the polycondensation reaction.
(B) A method in which particles are added to polyethylene terephthalate and melt kneaded.
(C) Producing master pellets (or master batch (MB)) with a large amount of particles added in the methods (A) and (B), kneading these and polyethylene terephthalate containing no particles, A method of containing a predetermined amount of particles.
(D) The method of using the master pellet of said (C) as it is.

Among these, a master batch method (MB method: (C) above) in which a polyester resin and particles are mixed in advance by an extruder is preferable. Further, it is possible to adopt a method in which a polyester resin and particles that have not been dried in advance are put into an extruder and MB is produced while moisture and air are deaerated. Furthermore, it is preferable to prepare an MB using a polyester resin that has been slightly dried in advance to suppress an increase in the acid value of the polyester. In this case, a method of extruding while degassing, a method of extruding without deaeration with a sufficiently dried polyester resin, and the like can be mentioned.

For example, when preparing MB, it is preferable to reduce the moisture content of the polyester resin to be charged in advance by drying. The drying conditions are preferably 100 to 200 ° C., more preferably 120 to 180 ° C., for 1 hour or longer, more preferably 3 hours or longer, and even more preferably 6 hours or longer. Thereby, it is sufficiently dried so that the moisture content of the polyester resin is preferably 50 ppm or less, more preferably 30 ppm or less. The premixing method is not particularly limited, and may be a batch method or a single-screw or biaxial or more kneading extruder. When making MB while degassing, melt the polyester resin at a temperature of 250 ° C to 300 ° C, preferably 270 ° C to 280 ° C, and provide one, preferably two or more degassing ports in the pre-kneader. It is preferable to adopt a method such as performing continuous suction deaeration of 0.05 MPa or more, more preferably 0.1 MPa or more, and maintaining the reduced pressure in the mixer.

The polymer base material of the present invention may contain many fine cavities (voids) inside. Thereby, higher whiteness can be suitably obtained. In that case, the apparent specific gravity is 0.7 or more and 1.3 or less, preferably 0.9 or more and 1.3 or less, more preferably 1.05 or more and 1.2 or less. If it is less than 0.7, the film is not elastic and processing at the time of producing the solar cell module becomes difficult. If it exceeds 1.3, the weight of the film is large, which may be an obstacle when considering the reduction of the weight of the solar cell.

The fine cavities can be formed from particles and / or a thermoplastic resin incompatible with the polyester described below. In addition, the void derived from the thermoplastic resin incompatible with the particles or polyester means that there are voids around the particles or the thermoplastic resin, and can be confirmed by, for example, a cross-sectional photograph of the film using an electron microscope. .

The resin added to the polyester film for forming the voids is preferably a resin incompatible with the polyester, which can scatter light and increase the light reflectance. Preferred incompatible resins include polyolefin resins such as polyethylene, polypropylene, polybutene, polymethylpentene, polystyrene resins, polyacrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, polysulfone resins, cellulose resins, And fluorine-based resins are preferably used. These incompatible resins may be homopolymers or copolymers, and two or more incompatible resins may be used in combination. Among these, polyolefin resins and polystyrene resins such as polypropylene and polymethylpentene having a low surface tension are preferable, and polymethylpentene is most preferable. Polymethylpentene has a relatively large difference in surface tension from polyester and a high melting point, so it has a low affinity with polyester in the polyester film-forming step, and is easy to form voids, which is particularly preferable as an incompatible resin. Is.
When the incompatible resin is contained, the amount thereof is 0 to 30% by mass, more preferably 1 to 20% by mass, and further preferably 2 to 15% by mass with respect to the entire polyester film. When the content is less than the above range, the film has poor reflectivity. Conversely, when the content is more than the above range, the apparent density of the entire film is too low, and film breakage occurs during stretching. It is easy and productivity may be reduced.

When the particles are added, the average particle size of the particles is preferably 0.1 to 10 μm, more preferably 0.1 to 5 μm, and still more preferably 0.15 to 1 μm. Within this range, a high reflectance (whiteness) is obtained, and a decrease in mechanical strength is suppressed. The content of the particles is 0 to 50% by mass, preferably 1 to 10% by mass, and more preferably 2 to 5% by mass with respect to the total mass of the film. Within this range, the reflectance (whiteness) is high, and the reduction in mechanical strength due to voids is suppressed. Preferable particles include those having a low affinity with polyester, specifically, barium sulfate and the like.

These white polyesters, that is, a particle-containing and void-forming polyester film, may have a single layer or a laminated structure composed of two or more layers. As a laminated structure, it is preferable to combine a high whiteness (layer with many voids and particles) and a low whiteness (layer with few voids and particles). Light reflection efficiency can be increased with a layer having high voids or particles, but a decrease in mechanical strength (embrittlement) is likely to occur due to voids or particles, and it is preferable to combine with a layer with low whiteness to compensate for this. For this reason, a layer with high whiteness is preferably used for the outer layer, and may be used on one side or on both sides. Moreover, when the high white layer which used the titanium dioxide for the particle | grains is used for an outer layer, since it has UV absorption ability, it also has the effect of improving light resistance.

In the case of adding particles, the high whiteness layer preferably has a particle amount of 5% by mass to 50% by mass, more preferably 6% by mass to 20% by mass. In the case of forming a cavity, the apparent specific gravity of the high whiteness layer is preferably 0.7 or more and 1.2 or less, more preferably 0.8 or more and 1.1 or less. On the other hand, in the case of adding particles, the low whiteness layer preferably has a particle amount of 0% by mass to less than 5% by mass, more preferably 1% by mass to 4% by mass. In the case of cavity formation, the apparent specific gravity of the low whiteness layer is preferably 0.9 or more and 1.4 or less and higher density than the high white layer, more preferably 1.0 or more and 1.3 or less and high whiteness. It is denser than the layer. The low white layer may be free of particles or cavities.

Preferred layer configurations include high white layer / low white layer, high white layer / low white layer / high white layer, high white layer / low white layer / high white layer / low white layer, high white layer / low white layer / high Examples include white layer / low white layer / high white layer.
The thickness ratio of each layer is not particularly limited, but the thickness of each layer is preferably 1% or more and 99% or less, more preferably 2% or more and 95% or less of the total layer thickness. Above or below this range, it is difficult to obtain the effects of increasing the reflection efficiency and imparting light resistance (UV). The thickness of all layers of the polyester film is not particularly limited as long as it can be formed as a film, but is usually 20 to 500 μm, preferably 25 to 300 μm.
As the method for laminating the polyester film in the present invention, a so-called coextrusion method using two or three or more melt extruders is preferably used.

In the present invention, it is also preferable to use a fluorescent whitening agent such as thiofediyl in order to increase the whiteness. A preferable addition amount is 0.01% by mass or more and 1% by mass or less, more preferably 0.05% by mass or more and 0.5% by mass or less, and further preferably 0.1% by mass or more and 0.3% by mass or less. . If it is less than this range, it is difficult to obtain the effect of improving the light reflectivity, and if it exceeds this range, yellowing occurs due to thermal decomposition during extrusion and the reflectivity decreases. As such a fluorescent whitening agent, for example, OB-1 manufactured by Eastman Kodak Company can be used.

The white polyester film that can be used as the polymer substrate of the present invention has an illuminance of 100 mW / cm ² , a temperature of 60 ° C., a relative humidity of 50% RH, an irradiation time of 48 hours, and a yellowish change amount (Δb Value) is preferably less than 5. The Δb value is more preferably less than 4, and still more preferably less than 3. This is useful in that the color change can be reduced even if it is irradiated with sunlight for a long time. Such an effect is particularly prominent when irradiated from the back sheet side of the solar cell module.

The heat shrinkage ratio of the polymer substrate at 150 ° C. for about 30 minutes is preferably 0 to 0.5%, more preferably the heat shrinkage is 0.05% to 0.5%, and more preferably 0 0.1 to 0.45%, more preferably 0.15% to 0.4%. The amount of heat shrinkage here refers to the average value of MD (film transport direction) and TD (direction orthogonal to the film transport direction) of measured values before and after storage at 150 ° C. for 30 minutes.
When the thermal shrinkage is not more than the upper limit value of the above preferred range, peeling between layers of the solar cell backsheet of the present invention is less likely to occur due to the shrinkage. On the other hand, when the amount of heat shrinkage is 0.05% or more, it is preferable from the viewpoint that wrinkles due to dimensional change (sag) due to thermal expansion during heat treatment are less likely to occur.

The thickness of the polymer substrate is preferably 100 to 350 μm, more preferably 120 to 300 μm, and particularly preferably 200 to 300 μm.
From the viewpoint of the withstand voltage performance of the solar cell module, the thickness of the polymer substrate is preferably 100 μm or more. On the other hand, when the thickness is 350 μm or less, especially in the case of a polyester base material, the hydrolysis resistance is good, the effect of improving wet heat durability is exhibited, and it can withstand long-term use. Moreover, it is preferable from a viewpoint of sheet productivity that it is 350 micrometers or less.
In the present invention, when the thickness of the polymer substrate is 120 μm or more and 300 μm or less and the carboxyl group content in the polyester constituting the polymer substrate is 35 equivalents / ton or less, the effect of improving wet heat durability is further improved. Is played.

<Undercoat layer>
In the solar cell backsheet of the present invention, an undercoat layer having a thickness of 2 μm or less may be provided between the polymer substrate (support) and the pigment layer. In the backsheet of the present invention, by providing such a thin undercoat layer, the adhesiveness after wet heat aging, film strength, and surface state of the pigment layer are simultaneously improved despite the high proportion of pigment in the pigment layer. be able to. In particular, when the thickness of the undercoat layer is 2 μm or less, when the content ratio of the pigment in the pigment layer is increased, coating repelling defects and pigment unevenness are less likely to occur.
However, if the thickness of the undercoat layer is too thin, the adhesiveness after wet heat aging may deteriorate. Therefore, the thickness of the undercoat layer is preferably 0.05 μm to 2 μm, more preferably 0.1 μm to 1. 5 μm. When the thickness is 0.05 μm or more, it is easy to ensure necessary adhesiveness.

(Undercoat layer binder)
The undercoat layer is configured to contain a binder. In the present invention, as the binder, the undercoat layer preferably contains at least one resin selected from the group consisting of polyolefin resin, polyurethane resin, polyvinyl alcohol resin, polyacrylic resin, and polyester resin. Polyester, polyurethane, acrylic resin It is more preferable to use polyolefin. These binders may be used alone or in combination of two or more.

As the polyolefin resin, for example, a modified polyolefin copolymer is preferable. Commercially available products may be used as the polyolefin resin. For example, Arrow Base SE-1013N, SD-1010, TC-4010, TD-4010 (both manufactured by Unitika Ltd.), Hitech S3148, S3121, S8512. (Both manufactured by Toho Chemical Co., Ltd.), Chemipearl S-120, S-75N, V100, EV210H (both manufactured by Mitsui Chemicals, Inc.) and the like. Among them, in the present invention, it is preferable to use Arrow Base SE-1013N, manufactured by Unitika Ltd., which is a terpolymer of low density polyethylene, acrylic acid ester, and maleic anhydride.

As the acrylic resin, for example, a polymer containing polymethyl methacrylate, polyethyl acrylate, or the like is preferable. As the acrylic resin, a commercially available product may be used. For example, AS-563A (manufactured by Daicel Einchem Co., Ltd.) can be preferably used.

As the polyester resin, for example, polyethylene terephthalate (PET), polyethylene-2,6-naphthalate (PEN) and the like are preferable. As the polyester resin, a commercially available product may be used. For example, Vylonal MD-1245 (manufactured by Toyobo Co., Ltd.) can be preferably used.
As the polyurethane resin, for example, a carbonate-based urethane resin is preferable, and for example, Superflex 460 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) can be preferably used.

Among these, it is preferable to use a polyolefin resin from the viewpoint of ensuring adhesion between the polymer support and the pigment layer. These polymers may be used alone or in combination of two or more. When two or more of these polymers are used in combination, a combination of an acrylic resin and a polyolefin resin is preferable.

(Undercoat layer additive)
The undercoat layer may contain various additives, and preferably contains a crosslinking agent, an inorganic oxide filler, and a surfactant.
It is more preferable to contain a crosslinking agent because the durability of the undercoat layer can be improved. Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, it is preferable to use a carbodiimide-based crosslinking agent or an oxazoline-based crosslinking agent from the viewpoint of ensuring adhesiveness after wet heat aging, from the viewpoint of improving the adhesiveness after wet heat aging. That is, in the present invention, the undercoat layer preferably includes a crosslinked structure derived from at least one of a carbodiimide compound-based crosslinking agent and an oxazoline compound-based crosslinking agent.

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 can also be preferably used.
Further, as an oxazoline-based cross-linking agent, Epocros K2010E, Epocros K2020E, Epocros K2030E, Epocros WS500, Epocros WS700 (all manufactured by Nippon Shokubai Chemical Co., Ltd.) and the like can be used.

Specific examples of carbodiimide crosslinking agents include Carbodilite V-02-L2 (Nisshinbo Chemical Co., Ltd.), Carbodilite SV-02 (Nisshinbo Chemical Co., Ltd.), Carbodilite E-01 (Nisshinbo Chemical Co., Ltd.) ) And the like.

In the backsheet of the present invention, the undercoat layer preferably contains 5 to 50% by mass of a crosslinking agent, more preferably 10 to 40% by mass, more preferably 20 to 40% by mass with respect to the binder. % Crosslinking agent is particularly preferred. In particular, when the addition amount of the crosslinking agent is 5% by mass or more, a sufficient crosslinking effect is obtained while maintaining the strength and adhesiveness of the undercoat layer, and when it is 50% by mass or less, the pot life of the coating liquid is lengthened. If it is 40% by mass or less, the coated surface can be improved.

The undercoat layer preferably contains an inorganic oxide filler.
Examples of the inorganic oxide filler include silica, calcium carbonate, magnesium oxide, magnesium carbonate, and tin oxide. Among them, tin oxide and fine particles of silica are preferable, and silica is more preferable in that the decrease in adhesiveness when exposed to a wet heat atmosphere is small.

The particle size of the inorganic oxide filler is preferably about 10 to 700 nm, more preferably about 20 to 300 nm in terms of volume average particle size. When the particle size is within this range, better easy adhesion can be obtained. The particle size is a value measured by a laser analysis / scattering particle size distribution measuring apparatus LA950 (manufactured by Horiba, Ltd.).

The shape of the inorganic oxide filler is not particularly limited, and any shape such as a spherical shape, an irregular shape, or a needle shape can be used.

The content of the inorganic oxide filler is preferably in the range of 5 to 400% by mass with respect to the binder in the undercoat layer. If the content of the inorganic fine particles is 5% by mass or more, good adhesiveness can be maintained when exposed to a humid heat atmosphere, and if it is 400% by mass or less, the surface shape of the pigment layer laminated on the undercoat layer can be maintained. It becomes difficult to get worse.
In particular, the content of the inorganic oxide filler is more preferably in the range of 50 to 300% by mass.

The undercoat layer preferably contains an anionic or nonionic surfactant. The range of the surfactant that can be used for the undercoat layer is the same as the range of the surfactant that can be used for the pigment layer described later. Of these, nonionic surfactants are preferred.
When a surfactant is added to the undercoat layer, the addition amount is preferably 0.1 to 10 mg / m ² , more preferably 0.5 to 3 mg / m ² . When the addition amount of the surfactant is 0.1 mg / m ² or more, generation of a repelling is suppressed and good layer formation is obtained, and when it is 10 mg / m ² or less, the polymer substrate and the pigment layer Adhesion can be performed satisfactorily.

<Pigment layer>
The pigment layer in the present invention includes a binder and a pigment. The pigment layer may further include other components such as various additives as necessary.

The main function of the pigment layer in the present invention is to reflect the light that passes through the solar cells and reaches the back sheet without being used for power generation out of the incident light, and returns the solar cells to the solar cells. It is to increase power generation efficiency.

(Pigment)
The pigment layer contains at least one pigment.
Examples of the pigment include inorganic pigments such as titanium oxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, ultramarine blue, bitumen, and carbon black, and organic pigments such as phthalocyanine blue and phthalocyanine green. It can be appropriately selected and contained. Of these, titanium oxide and barium sulfate are preferable in that high whiteness and reflectance can be obtained.

The pigment layer in the present invention preferably contains a pigment in the range of 2.5 to 8.5 g / m ² . When the content of the pigment in the pigment layer is 2.5 g / m ² or more, the light reflectance tends to be improved particularly effectively. Further, when the content of the pigment in the pigment layer is 8.5 g / m ² or less, the surface shape of the pigment layer tends to be particularly good, and the film strength tends to be improved.
Among these, a more preferable content of the pigment is in the range of 4.5 to 8.0 g / m ² .

The average particle diameter of the pigment is preferably 0.03 to 0.8 μm in volume average particle diameter, more preferably about 0.15 to 0.5 μm. When the average particle size is within the above range, the light reflection efficiency is high. The average particle diameter is a value measured by a laser analysis / scattering particle size distribution measuring apparatus LA950 (manufactured by Horiba, Ltd.).

The ratio of the pigment (P / P + B ratio) to the total of the binder and the pigment in the pigment layer is preferably 40 to 95% by mass. When the ratio of the pigment (P / P + B ratio) is 40% by mass or more, high light reflectance can be obtained. On the other hand, when the ratio of the pigment (P / P + B ratio) is 95% by mass or less, it is possible to reduce the cost by suppressing the amount of the pigment used and to obtain high adhesion with the adjacent layer. From these viewpoints, the ratio of the pigment (P / P + B ratio) is more preferably 50 to 95% by mass, and further preferably 70 to 95% by mass.

(Binder for pigment layer)
The pigment layer contains at least one binder.
Suitable binders for the pigment layer include polyester resin, polyurethane resin, acrylic resin, polyolefin resin, and the like. From the viewpoint of durability, polyolefin resin, acrylic resin, and siloxane-modified acrylic resin are preferable. These polymers may be used alone or in combination of two or more. When two or more of these polymers are used in combination, a combination of an acrylic resin and a polyolefin resin is preferable. Examples of preferred binders include Chemipearl S-120 and S-75N (both manufactured by Mitsui Chemicals) as examples of polyolefins, Arrow Base SE-1013N (manufactured by Unitika), and Julimer ET- as examples of acrylic resins. 410, SEK-301 (both manufactured by Nippon Pure Chemicals Co., Ltd.), AS-563A (manufactured by Daicel Finechem Co., Ltd.), as examples of siloxane-modified acrylic resins, Ceranate WSA1060, WSA1070 (both manufactured by DIC Corporation), H7620, H7630, H7650 (both manufactured by Asahi Kasei Chemicals Corporation) and the like can be mentioned.

(Pigment layer additive)
In addition to the binder and the pigment, additives such as a crosslinking agent, a surfactant, and a filler may be further added to the pigment layer in the present invention as necessary.

Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Of these, carbodiimide-based and oxazoline-based crosslinking agents are preferable, and specifically, those usable for the above-described undercoat layer can be suitably used.
When a crosslinking agent is added, the addition amount is preferably 5 to 50% by mass, more preferably 10 to 40% by mass with respect to the binder in the pigment layer. When the addition amount of the crosslinking agent is 5% by mass or more, a sufficient crosslinking effect is obtained while maintaining the strength and adhesiveness of the pigment layer, and when it is 50% by mass or less, the pot life of the coating solution can be kept long. .

Examples of the surfactant include known surfactants such as anionic and nonionic surfactants. 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 .

In addition to the above pigment, an inorganic oxide filler such as silica may be added to the pigment layer in the present invention. When adding an inorganic oxide filler, the addition amount is preferably 20% by mass or less, more preferably 15% by mass or less, based on the binder in the pigment layer. When the added amount of the inorganic oxide filler is 20% by mass or less, a necessary reflectance can be obtained while suppressing a decrease in the ratio of the pigment.

(Physical properties of the pigment layer)
In the backsheet of the present invention, when a white pigment is added to the pigment layer to form a reflective layer, the light reflectance at 550 nm on the surface on which the pigment layer is provided is preferably 70% or more, and 75% More preferably.
The light reflectance is a ratio of the amount of light incident from the pigment layer side surface of the back sheet of the present invention reflected by the reflective layer and emitted from the topcoat layer to the incident light amount.
When the light reflectance is 70% or more, the light that passes through the cell and enters the cell can be effectively returned to the cell, and the effect of improving the power generation efficiency is great. By controlling the pigment content in the range of 2.5 to 8.5 g / m ² , the light reflectance can be easily adjusted to 70% or more.

When the pigment layer is formed as a reflective layer, the thickness of the reflective layer is preferably 1 to 20 μm, more preferably 1 to 15 μm, still more preferably 1 to 10 μm, and particularly preferably about 1 to 7 μm. When this thickness is 1 μm or more, necessary decorative properties and reflectance can be obtained, and when it is 20 μm or less, the surface shape can be kept good.

<Overcoat layer>
In the back sheet of the present invention, an overcoat layer is provided on the pigment layer. The topcoat layer is a layer that contains a binder and is provided to improve adhesion to a sealing material such as EVA (ethylene-vinyl acetate) resin. That is, by adhering the pigment layer through the overcoat layer rather than directly adhering to the encapsulant, the adhesiveness with the encapsulant can be maintained high even in a humid heat environment.

(Binder for topcoat layer)
It is preferable that the topcoat layer includes a binder and includes one type selected from the group consisting of a polyolefin resin, a polyurethane resin, a polyvinyl alcohol resin, an acrylic resin, and a polyester resin. Of these, polyolefin resins and acrylic resins are preferable. These binders may be used alone or in combination of two or more. When two or more of these binders are used in combination, a combination of an acrylic resin and a polyolefin resin is preferable.

(Additive for topcoat layer)
In addition to the binder, additives such as a cross-linking agent, a surfactant, and a filler may be added to the topcoat layer in the present invention as necessary.

Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Of these, carbodiimide-based and oxazoline-based crosslinking agents are preferable, and specifically, those usable for the above-described undercoat layer can be suitably used.
When a crosslinking agent is added, the addition amount is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass with respect to the binder in the overcoat layer. When the addition amount of the crosslinking agent is 5% by mass or more, a sufficient crosslinking effect is obtained while maintaining the strength and adhesiveness of the overcoat layer, and when it is 50% by mass or less, the pot life of the coating liquid can be kept long. .

The topcoat layer preferably contains an inorganic oxide filler.
As the inorganic oxide filler, specifically, those usable for the above-mentioned undercoat layer can be suitably used.

The content of the inorganic oxide filler is preferably in the range of 5 to 400% by mass with respect to the binder in the overcoat layer. If the content of the inorganic fine particles is 5% by mass or more, good adhesiveness can be maintained when exposed to a moist heat atmosphere, and if it is 400% by mass or less, the surface state is hardly deteriorated and the adhesiveness to the sealing material. Can be kept high.
In particular, the content of the inorganic oxide filler is more preferably in the range of 50 to 300% by mass.

The thickness of the overcoat layer is preferably 0.1 μm or more and 30 μm or less. If the thickness of the overcoat layer is 0.1 μm or more, it is possible to suppress a decrease in adhesion after being exposed to a humid heat atmosphere, and if it is 30 μm or less, the surface condition is hardly deteriorated and the adhesion to the sealant is kept high. Can do. From these viewpoints, the thickness of the overcoat layer is more preferably from 0.3 μm to 20 μm, and further preferably from 0.5 μm to 10 μm.

<Composite polymer layer>
The backsheet of the present invention is a composite polymer having light resistance and moisture and heat resistance on a second surface (referred to as “back surface” as appropriate) opposite to the surface on which the pigment layer and the topcoat layer of the polymer substrate are provided. A layer is provided.

The composite polymer layer is disposed in contact with the back surface of the polymer substrate or through another layer. The composite polymer layer is configured using at least a specific composite polymer containing a non-siloxane structural unit and a (poly) siloxane structural unit represented by the general formula (1) in the molecule. The composite polymer layer in the present invention is preferably formed directly on the back surface of the polymer base material because the adhesiveness with the polymer base material is improved by the constitution containing the composite polymer. The composite polymer layer is preferably formed as the outermost layer that is exposed to the external environment because it has moisture and heat storage resistance.

This composite polymer layer can be constituted by further using other components depending on the case, and the constituent components differ depending on the intended application. The composite polymer layer can constitute a colored layer that bears the function of reflecting sunlight and imparting appearance design, a back layer disposed on the side opposite to the side on which sunlight is incident, and the like.

For example, when the composite polymer layer is configured as a reflective layer that reflects sunlight toward the incident side, the composite polymer layer can be configured by further using a colorant such as a white pigment.
When two or more composite polymer layers are provided on the polymer substrate, a laminated structure of white layer (composite polymer layer) / composite polymer layer / polymer substrate may be used. The white layer can be configured as a reflective layer. It is possible to further improve the adhesion and adhesion within the back sheet of the reflective layer.
In order to provide a necessary function as a back sheet, it is more preferable to provide two or more composite polymer layers.

-Composite polymer-
The composite polymer layer according to the present invention includes a (poly) siloxane structural unit having a mass ratio of 15 to 85% by mass and a non-siloxane structural unit having a mass ratio of 85 to 15% by mass represented by the general formula (1) in the molecule. And at least one kind of composite polymer. By containing this composite polymer, the adhesion between the polymer substrate as a support and other layers, that is, the peel resistance and shape stability that are easily deteriorated when given heat and moisture, is greatly improved compared to the conventional products. Can be improved.

The composite polymer in the present invention is a block copolymer obtained by copolymerizing (poly) siloxane and at least one polymer. The (poly) siloxane and the copolymerized polymer may be one kind alone, or two or more kinds.

In the part of “— (Si (R ¹ ) (R ² ) —O) _n —” ((poly) siloxane structural unit represented by the general formula (1)), which is the (poly) siloxane segment in the composite polymer, R ¹ and R ² may be the same or different and each represents a hydrogen atom, a halogen atom, or a monovalent organic group.

“— (Si (R ¹ ) (R ² ) —O) _n —” 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 ¹ and R ² include a fluorine atom, a chlorine atom, and an iodine atom.

The “monovalent organic group” represented by R ¹ and R ² is a group capable of covalent bonding with a Si atom, and may be unsubstituted or have a substituent. The monovalent organic group includes, for example, an alkyl group (eg, methyl group, ethyl group, etc.), an aryl group (eg: phenyl group, etc.), an aralkyl group (eg: benzyl group, phenylethyl etc.), and an alkoxy group (eg: A methoxy group, an ethoxy group, a propoxy group, etc.), an aryloxy group (eg, phenoxy group, etc.), a mercapto group, an amino group (eg, amino group, diethylamino group, etc.), an amide group and the like.

Among them, R ¹ and R ² are each independently a hydrogen atom, a chlorine atom, a bromine atom, an unsubstituted or substituted, in terms of adhesion to adjacent materials such as a polymer substrate and durability in a wet and 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.

N is preferably from 1 to 5000, and more preferably from 1 to 1000.

The ratio of “— (Si (R ¹ ) (R ² ) —O) _n —” (the (poly) siloxane structural unit represented by the general formula (1)) in the composite polymer is the total mass of the composite polymer. The content is preferably from 15 to 85% by mass, more preferably from 20 to 80% by mass in terms of adhesion to the polymer substrate and durability in a moist heat environment.
When the ratio of the polysiloxane moiety is less than 15% by mass, the adhesion to the polymer substrate and the adhesion durability when exposed to a wet heat environment are inferior, and when 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 any 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.

Typical 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, an acrylic polymer (that is, an acrylic structural unit as a non-siloxane structural unit) is particularly preferable from the viewpoint of design flexibility.
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, vinyl polymers include, for example, (1) vinyl monomers containing acid groups and vinyl monomers containing hydrolyzable silyl groups and / or silanol groups. (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.

Such a precursor polymer can be produced and obtained using, for example, the method described in paragraph Nos. 0021 to 0078 of JP-A-2009-52011.

In the composite 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) a method in which a precursor polymer is reacted with a polysiloxane having a structure of the general formula (1) [— (Si (R ¹ ) (R ² ) —O) _n —], ii) Hydrolysis of a silane compound having a structure of “— (Si (R ¹ ) (R ² ) —O) _n —” in which R ¹ and / or R ² is a hydrolyzable group in the presence of a precursor polymer Methods such as a condensation method can be used.
Examples of the silane compound used in the method (ii) include various silane compounds, and an alkoxysilane compound is 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 Can be prepared by reacting 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.
In the case of 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 hours. It can be prepared by hydrolytic condensation to a degree (preferably at 50 to 130 ° C. for 1 to 20 hours).

-Crosslinking agent-
In the present invention, the composite polymer layer preferably has a structural portion derived from a cross-linking agent that cross-links between the composite polymers. That is, the composite polymer layer can be formed using a cross-linking agent that can cross-link between the composite polymers. By crosslinking with a crosslinking agent, adhesion after wet heat aging, specifically adhesion to a polymer substrate when exposed to a wet heat environment, and adhesion between layers can be further 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 carbodiimide compounds and oxazoline compounds are preferable.

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'-di Til-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 a compound having an oxazoline group, Epocros K2010E, K2020E, K2030E, WS-500, WS-700 (all manufactured by Nippon Shokubai Chemical Co., Ltd.) and the like can be used.

Specific examples of the carbodiimide-based crosslinking agent include dicyclohexylmethane carbodiimide, tetramethylxylylene carbodiimide, and dicyclohexylmethane carbodiimide. 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.

In the composite polymer layer, the mass ratio of the structural part derived from the crosslinking agent to the composite polymer is preferably 1 to 30% by mass, more preferably 5 to 20% by mass. When the content of the crosslinking agent is 1% by mass or more, the strength of the composite polymer layer and the adhesiveness 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.

In the backsheet of the present invention, since the composite polymer layer contains the above composite polymer, adhesion to the polymer substrate and the like is improved, and further, deterioration resistance (adhesion durability) in a humid heat environment is excellent. For this reason, it is also preferable to be provided as the outermost layer disposed at the position farthest from the polymer substrate. Specifically, for example, there is a back layer disposed on the opposite side (back side) to the side (front side) facing the battery side substrate including the solar cell element.

Only one composite polymer layer may be provided, or a plurality of composite polymer layers may be formed.
The thickness of one layer of the composite polymer layer is usually preferably from 0.3 μm to 22 μm, more preferably from 0.5 μm to 15 μm, still more preferably from 0.8 μm to 12 μm, particularly preferably from 1.0 μm to 8 μm. A range of 2 to 6 μm is most preferable. When the composite polymer layer has a thickness of 0.3 μm or more, more preferably 0.8 μm or more, it is difficult for moisture to penetrate from the surface of the composite polymer layer when exposed to a humid heat environment. Adhesiveness is remarkably improved by making it difficult for moisture to reach the interface with the material. Moreover, when the thickness of the composite polymer layer is 22 μm or less, and further 12 μm or less, the composite polymer layer itself is difficult to become brittle, and the composite polymer layer is less likely to be destroyed when exposed to a humid heat environment. Is improved.

The composite polymer layer in the present invention has a cross-linked structure in which the composite polymer and the polymer molecules of the composite polymer are cross-linked with a cross-linking agent, and the ratio of the structural portion derived from the cross-linking agent to the composite polymer is 1 to 30% by mass. Thus, when the thickness of the composite polymer layer is 0.8 μm to 12 μm, the effect of improving the adhesion after wet heat aging is particularly excellent.

<Other functional layers>
The back sheet of the present invention may have other functional layers.
Examples of other functional layers include an easily adhesive layer and a back layer.

In addition, in order to improve the film surface state on at least one layer formed on the polymer substrate directly or via another layer on the surface (first surface or second surface) of the polymer substrate. It is preferable to contain a surfactant. Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and fluorosurfactants.

The nonionic surfactant used in the present invention is not particularly limited, and conventionally known nonionic surfactants can be used. For example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polystyryl phenyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, glycerin fatty acid partial esters, sorbitan fatty acid partial esters, pentaerythritol Fatty acid partial esters, propylene glycol mono fatty acid esters, sucrose fatty acid partial esters, polyoxyethylene sorbitan fatty acid partial esters, polyoxyethylene sorbitol fatty acid partial esters, polyethylene glycol fatty acid esters, polyglycerin fatty acid partial esters, Polyoxyethylenated castor oil, polyoxyethylene glycerin fatty acid partial esters, fatty acid diethanolamides, N N- bis-2-hydroxyalkylamines, polyoxyethylene alkylamines, triethanolamine fatty acid ester, trialkylamine oxide, polyethylene glycol, copolymers of polyethylene glycol and polypropylene glycol.

The anionic surfactant used in the present invention is not particularly limited, and conventionally known anionic surfactants can be used. For example, fatty acid salts, abietic acid salts, hydroxyalkane sulfonates, alkane sulfonates, dialkyl sulfosuccinate esters, linear alkyl benzene sulfonates, branched alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl phenoxy poly Oxyethylenepropyl sulfonates, polyoxyethylene alkylsulfophenyl ether salts, N-methyl-N-oleyl taurine sodium salt, N-alkylsulfosuccinic acid monoamide disodium salt, petroleum sulfonates, sulfated beef oil, fatty acid alkyl esters Sulfates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, fatty acid monoglyceride sulfates, polyoxyethylene alcohol Ruphenyl ether sulfates, polyoxyethylene styryl phenyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl phenyl ether phosphates, styrene / maleic anhydride Examples thereof include partial saponification products of polymers, partial saponification products of olefin / maleic anhydride copolymers, and naphthalene sulfonate formalin condensates.

The cationic surfactant used in the present invention is not particularly limited, and conventionally known cationic surfactants can be used. Examples thereof include alkylamine salts, quaternary ammonium salts, polyoxyethylene alkylamine salts, and polyethylene polyamine derivatives.

The surfactant contained in the layer on the polymer substrate of the present invention is preferably at least one selected from an anionic surfactant, an amphoteric surfactant and a fluorosurfactant.
In addition, it is particularly preferable that both the topcoat layer and the pigment layer contain a fluorosurfactant.

The amphoteric surfactant used in the present invention is not particularly limited, and conventionally known amphoteric surfactants can be used. Examples thereof include carboxybetaines, aminocarboxylic acids, sulfobetaines, aminosulfuric esters, and imidazolines.

Of the above surfactants, the term “polyoxyethylene” can be read as “polyoxyalkylene” such as polyoxymethylene, polyoxypropylene, polyoxybutylene, etc. These surfactants can also be used.

More preferable surfactants include fluorine-based surfactants containing a perfluoroalkyl group in the molecule. Examples of such fluorosurfactants include anionic types such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and perfluoroalkyl phosphates; amphoteric types such as perfluoroalkyl betaines; Cation type such as trimethylammonium salt; perfluoroalkylamine oxide, perfluoroalkylethylene oxide adduct, oligomer containing perfluoroalkyl group and hydrophilic group, oligomer containing perfluoroalkyl group and lipophilic group, perfluoroalkyl Nonionic types such as an oligomer containing a group, a hydrophilic group and a lipophilic group, and a urethane containing a perfluoroalkyl group and a lipophilic group. In addition, fluorine-based surfactants described in JP-A Nos. 62-170950, 62-226143, and 60-168144 are also preferred.

The surfactant is used in the layer on the polymer substrate of the present invention, preferably in the range of 0.001 to 10% by mass, more preferably 0.01 to 5% by mass with respect to the nonvolatile component. . Moreover, surfactant can be used individually or in combination of 2 or more types.

Specific examples of preferable surfactants are shown below, but the present invention is not limited thereto.

[Method for producing back sheet for solar cell]
In the solar cell backsheet of the present invention, as described above, after forming an undercoat layer on the first surface of the polymer substrate as necessary, a pigment layer and an overcoat layer are sequentially formed, Any method may be used as long as a composite polymer layer can be formed on the surface. In this invention, it can produce suitably by the method including the process (application | coating process) of apply | coating the coating liquid for forming each said layer on a polymer base material one by one, and forming each layer, for example.

<Manufacture of polymer substrate>
(Adjustment of polymer base resin)
In the back sheet of the present invention, the aforementioned resin can be used as a polymer substrate. Such polymer substrates may be obtained synthetically or commercially. When using polyester as a polymer base material, it is preferable to obtain by synthesis. Hereinafter, a method for producing a polyester film as a polymer substrate, and more preferable polyethylene terephthalate (hereinafter, also referred to as PET) will be described.

-Esterification process-
In this invention, the esterification process which provides an esterification reaction and a polycondensation reaction and produces | generates polyester can be provided. In this esterification step, (a) an esterification reaction and (b) a polycondensation reaction in which an esterification reaction product produced by the esterification reaction is subjected to a polycondensation reaction can be provided.

(A) Esterification reaction The amount of the aliphatic diol (preferably ethylene glycol) used is 1.015 to 1.0.1 per mol of the aromatic dicarboxylic acid (preferably terephthalic acid) and, if necessary, its ester derivative. A range of 50 moles is preferred. The amount used is more preferably in the range of 1.02 to 1.30 mol, and still more preferably in the range of 1.025 to 1.10 mol. If the amount used is in the range of 1.015 or more, the esterification reaction proceeds favorably, and if it is in the range of 1.50 mol or less, for example, by-production of diethylene glycol due to dimerization of ethylene glycol is suppressed, and the melting point In addition, many properties such as glass transition temperature, crystallinity, heat resistance, hydrolysis resistance, and weather resistance can be kept good.

PET preferably contains 90% by mole or more of terephthalic acid and ethylene glycol, more preferably 95% by mole or more, and still more preferably 98% by mole or more.
PET may have different properties depending on the catalyst described later, and one or two selected from a germanium (Ge) -based catalyst, an antimony (Sb) -based catalyst, an aluminum (Al) -based catalyst, and a titanium (Ti) -based catalyst. PET that is polymerized using more than one species is preferred, and a Ti-based catalyst is more preferred.

A conventionally known reaction catalyst can be used for the esterification reaction and / or transesterification reaction. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Usually, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst at an arbitrary stage before the polyester production method is completed. As such a method, for example, when a germanium compound is taken as an example, it is preferable to add the germanium compound powder as it is.

The backsheet production method of the present invention preferably includes a step of preparing a polyester resin to be used for melt film formation by an esterification reaction using a Ti-based catalyst.
A film containing a polyester resin esterified using a Ti-based catalyst is preferable because weather resistance is unlikely to decrease. Although not bound by any theory, it is presumed that the reason is as follows. The decrease in weather resistance of the weather resistant polyester film depends to some extent on the hydrolysis of the polyester. The esterification reaction catalyst also promotes the hydrolysis reaction, which is the reverse reaction of esterification, while the Ti catalyst has a low effect of the hydrolysis reaction, which is the reverse reaction. Therefore, even if the esterification reaction catalyst remains to some extent in the film after film formation, the polyester resin esterified using the Ti-based catalyst is more than the polyester resin esterified using another catalyst. The weather resistance can be made relatively high.

Examples of the Ti-based catalyst include oxides, hydroxides, alkoxides, carboxylates, carbonates, oxalates, organic chelate titanium complexes, and halides. The Ti-based catalyst may be used in combination of two or more titanium compounds as long as the effects of the present invention are not impaired.
Examples of Ti-based catalysts include tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, tetra-t-butyl titanate, tetracyclohexyl titanate, tetraphenyl Titanium alkoxide such as titanate and tetrabenzyl titanate, titanium oxide obtained by hydrolysis of titanium alkoxide, titanium-silicon or zirconium composite oxide obtained by hydrolysis of a mixture of titanium alkoxide and silicon alkoxide or zirconium alkoxide, titanium acetate , Titanium oxalate, potassium potassium oxalate, sodium oxalate, potassium titanate, sodium titanate, titanium titanate-aluminum hydroxide mixture, titanium chloride, titanium chloride-aluminum chloride Miniumu mixture, titanium acetylacetonate, an organic chelate titanium complex having an organic acid as a ligand, and the like.

Among Ti-based catalysts, at least one organic chelate titanium complex having an organic acid as a ligand can be suitably used. Examples of the organic acid include citric acid, lactic acid, trimellitic acid, malic acid and the like. Among them, an organic chelate complex having citric acid or citrate as a ligand is preferable.

For example, when a chelate titanium complex having citric acid as a ligand is used, there is little generation of foreign matters such as fine particles, and a polyester resin having better polymerization activity and color tone than other titanium compounds can be obtained. Furthermore, even when using a citric acid chelate titanium complex, by adding it at the stage of the esterification reaction, a polyester resin having better polymerization activity and color tone and having less terminal carboxyl groups can be obtained than when added after the esterification reaction. It is done. In this regard, the titanium catalyst also has a catalytic effect of the esterification reaction. By adding it at the esterification stage, the oligomer acid value at the end of the esterification reaction is lowered, and the subsequent polycondensation reaction is performed more efficiently. In addition, complexes with citric acid as a ligand are more resistant to hydrolysis than titanium alkoxides, etc., and do not hydrolyze in the esterification reaction process, while maintaining the original activity and catalyzing the esterification and polycondensation reactions It is estimated to function effectively as
In general, it is known that as the amount of terminal carboxyl groups increases, the hydrolysis resistance deteriorates. By reducing the amount of terminal carboxyl groups by the addition method of the present invention, improvement in hydrolysis resistance is expected. The
Examples of the citric acid chelate titanium complex are readily available as commercial products such as VERTEC AC-420 manufactured by Johnson Matthey.

To synthesize a Ti-based polyester using such a Ti compound, for example, Japanese Patent Publication No. 8-30119, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 3897756, Japanese Patent No. 396226 Japanese Patent No. 3997866, Japanese Patent No. 3996687, Japanese Patent No. 40000867, Japanese Patent No. 4053837, Japanese Patent No. 4127119, Japanese Patent No. 4134710, Japanese Patent No. 4159154, Japanese Patent No. 4269538, Japanese Patent No. The methods described in JP 2005-340616 A, JP 2005-239940 A, JP 2004-319444 A, JP 2007-204538 A, Japanese Patent No. 3436268, Japanese Patent No. 3780137, and the like can be applied.

In the present invention, an aromatic dicarboxylic acid and an aliphatic diol are polymerized in the presence of a catalyst containing a titanium compound, and at least one of the titanium compounds is an organic chelate titanium complex having an organic acid as a ligand. It is preferable that an esterification reaction process including at least a process of adding an organic chelate titanium complex, a magnesium compound, and a pentavalent phosphate ester having no aromatic ring as a substituent in this order is provided. In this case, in addition to this esterification reaction step, production of a polyester resin comprising a polycondensation step in which a polycondensation product is produced by polycondensation reaction of the esterification reaction product produced in the esterification reaction step The aspect which produces a film with a method is more preferable. The polycondensation step will be described later.

In this case, in the course of the esterification reaction, the addition of a magnesium compound to the presence of an organic chelate titanium complex as a titanium compound, followed by the addition order of adding a specific pentavalent phosphorus compound, thereby providing a titanium catalyst. As the result, the coloring reaction is less and the electrostatic application property is high. At the same time, a polyester resin with improved yellowing when exposed to high temperatures is obtained.
As a result, coloring during polymerization and subsequent coloring during melt film formation are reduced, and yellowishness is reduced compared to conventional antimony (Sb) catalyst-based polyester resins, and germanium catalysts having a relatively high transparency are also obtained. It is possible to provide a polyester resin having a color tone and transparency comparable to a polyester resin and having excellent heat resistance. Moreover, PET resin which has high transparency and few yellowishness is obtained, without using color tone adjusting materials, such as a cobalt compound and a pigment | dye.

This polyester resin can be used for applications requiring high transparency (for example, optical film, industrial squirrel, etc.), and it is not necessary to use an expensive germanium-based catalyst, so that the cost can be greatly reduced. In addition, since foreign matters caused by the catalyst that are likely to occur in the Sb catalyst system are also avoided, the occurrence of failures and quality defects in the film forming process can be reduced, and the cost can be reduced by improving the yield.

In the above, when the aromatic dicarboxylic acid and the aliphatic diol are mixed with a catalyst containing an organic chelate titanium complex that is a titanium compound prior to the addition of the magnesium compound and the phosphorus compound, the organic chelate titanium complex or the like is subjected to an esterification reaction. Therefore, the esterification reaction can be carried out satisfactorily. At this time, you may add a titanium compound in mixing the dicarboxylic acid component and the diol component. Moreover, after mixing a dicarboxylic acid component (or diol component) and a titanium compound, you may mix a diol component (or dicarboxylic acid component). Further, the dicarboxylic acid component, the diol component, and the titanium compound may be mixed at the same time. The mixing is not particularly limited, and can be performed by a conventionally known method.

In the esterification reaction, it is preferable to provide a process in which an organic chelate titanium complex which is a titanium compound and a magnesium compound and a pentavalent phosphorus compound as additives are added in this order. At this time, the esterification reaction proceeds in the presence of the organic chelate titanium complex, and thereafter, the addition of the magnesium compound is started before the addition of the phosphorus compound.

As the pentavalent phosphorus compound, at least one pentavalent phosphate having no aromatic ring as a substituent is used. Examples of the pentavalent phosphate ester include trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, tris phosphate (triethylene glycol), methyl acid phosphate, ethyl acid phosphate, Examples thereof include isopropyl acid phosphate, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate, and triethylene glycol acid phosphate.

Among pentavalent phosphate esters, phosphate esters having a lower alkyl group having 2 or less carbon atoms as a substituent [(OR) ₃ —P═O; R = alkyl group having 1 or 2 carbon atoms] are preferable, Specifically, trimethyl phosphate and triethyl phosphate are particularly preferable.

In particular, when a chelate titanium complex coordinated with citric acid or a salt thereof is used as a catalyst as the titanium compound, the pentavalent phosphate ester has better polymerization activity and color tone than the trivalent phosphate ester, Furthermore, in the case of adding a pentavalent phosphate having 2 or less carbon atoms, the balance of polymerization activity, color tone, and heat resistance can be particularly improved.

静電 Inclusion of magnesium compound improves electrostatic applicability. In this case, although it is easy to color, in this invention, coloring is suppressed and the outstanding color tone and heat resistance are obtained.

Examples of the magnesium compound include magnesium salts such as magnesium oxide, magnesium hydroxide, magnesium alkoxide, magnesium acetate, and magnesium carbonate. Among these, magnesium acetate is most preferable from the viewpoint of solubility in ethylene glycol.

As a preferred embodiment, before the esterification reaction is completed, a chelate titanium complex having 1 ppm to 30 ppm of citric acid or citrate as a ligand is added to the aromatic dicarboxylic acid and the aliphatic diol, In the presence, a magnesium salt of 60 ppm to 90 ppm (more preferably 70 ppm to 80 ppm) weak acid is added, and after addition, 60 ppm to 80 ppm (more preferably 65 ppm to 75 ppm) having no aromatic ring as a substituent 5 An embodiment in which a monovalent phosphate is added.

The esterification reaction may be carried out using a multistage apparatus in which at least two reactors are connected in series under conditions where ethylene glycol is refluxed while removing water or alcohol produced by the reaction from the system. it can.

Dicarboxylic acid and diol can be introduced by preparing a slurry containing them and continuously supplying it to the esterification reaction step.

Further, the esterification reaction described above may be performed in one stage or may be performed in multiple stages.

(B) Polycondensation In the polycondensation, an esterification reaction product generated by the esterification reaction is subjected to a polycondensation reaction to generate a polycondensation product. The polycondensation reaction may be performed in one stage or may be performed in multiple stages.

The esterification reaction product such as an oligomer generated by the esterification reaction is subsequently subjected to a polycondensation reaction. This polycondensation reaction can be suitably performed by supplying it to a multistage polycondensation reaction tank.

For example, the polycondensation reaction conditions in a three-stage reaction tank are as follows: the first reaction tank has a reaction temperature of 255 to 280 ° C., more preferably 265 to 275 ° C., and a pressure of 13.3 × 10 ^−3. ^{~ 1.3 × 10 -3 MPa (100} ~ 10torr), a more preferably ^{6.67 × 10 -3 ~ 2.67 × 10} -3 MPa (50 ~ 20torr), the second reaction vessel, the reaction The temperature is 265 to 285 ° C., more preferably 270 to 280 ° C., and the pressure is 2.67 × 10 ⁻³ to 1.33 × 10 ⁻⁴ MPa (20 to 1 torr), more preferably 1.33 × 10 ^−. The third reaction tank in the final reaction tank has a reaction temperature of 270 to 290 ° C., more preferably 275 to 285 ° C., and a pressure of ³ to 4.0 × 10 ⁻⁴ MPa (10 to 3 torr). ^{1.33 × 10 -3 ~ 1.33 × 10} -5 MPa 10 ~ 0.1 torr), embodiments are preferred and more preferably ^{6.67 × 10 -4 ~ 6.67 × 10} -5 MPa (5 ~ 0.5torr).

The measurement of each element of Ti, Mg, and P was obtained by quantifying each element in PET using high resolution high frequency inductively coupled plasma-mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology). It can carry out by calculating content [ppm] from the obtained result.

-Solid phase polymerization process-
The polyester constituting the substrate may be solid-phase polymerized after polymerization. Thereby, preferable carboxyl group content can be achieved. Solid phase polymerization is a technique in which the degree of polymerization is increased by heating the polymerized polyester in a vacuum or nitrogen gas at a temperature of about 170 ° C. to 240 ° C. for about 5 to 100 hours. 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.
The solid-phase polymerization can be suitably performed using the polyester polymerized by the esterification reaction described above or a commercially available polyester in the form of small pieces such as pellets.

The solid phase polymerization temperature is preferably 190 to 230 ° C, more preferably 200 ° C to 220 ° C, and still more preferably 205 ° C to 215 ° C.
The solid phase polymerization temperature is preferably 10 to 80 hours, more preferably 15 to 50 hours, and still more preferably 20 to 30 hours.
Such heat treatment is preferably performed in a low oxygen atmosphere, for example, in a nitrogen atmosphere or in a vacuum. Furthermore, 1 ppm to 1% of a polyhydric alcohol (ethylene glycol or the like) may be mixed.

Solid-phase polymerization may be carried out in a batch mode (a method in which a resin is placed in a container and stirred while applying heat for a predetermined time), or a continuous mode (a resin is placed in a heated cylinder and this is stirred). It may be carried out by a system in which the gas is passed through the cylinder while being kept flowing for a predetermined time while being heated, and sequentially fed out.

In the production method of the present invention, it is preferable to form a PET film by melt-kneading the polyester after the solid phase polymerization step and extruding it from a die (extrusion die).

In the production method of the present invention, the PET resin can be melted using an extruder. The melting temperature is preferably 250 ° C to 320 ° C, more preferably 260 ° C to 310 ° C, and further preferably 270 ° C to 300 ° C.
The extruder may be uniaxial or multi-axial. More preferably, the inside of the extruder is replaced with nitrogen from the viewpoint that generation of terminal COOH due to thermal decomposition can be further suppressed.

The molten resin (melt) of the molten PET resin is preferably extruded from an extrusion die through a gear pump, a filter or the like. At this time, it may be extruded as a single layer or may be extruded as a multilayer.

The melt-extruded melt is preferably cooled on a support, solidified and formed into a film.
There is no restriction | limiting in particular as a support body, The cooling roll used for normal melt film forming can be used.

The temperature of the cooling roll itself is preferably 10 ° C. to 80 ° C., more preferably 15 ° C. to 70 ° C., and further preferably 20 ° C. to 60 ° C. Further, from the viewpoint of improving the adhesion between the molten resin (melt) and the cooling roll and increasing the cooling efficiency, it is preferable to apply static electricity before the melt contacts the cooling roll.

The thickness of the molten resin (melt) discharged in a band after solidification (before stretching) is in the range of 2600 μm to 6000 μm, and a polyester film having a thickness of 260 μm to 400 μm can be obtained through subsequent stretching. The thickness of the melt after solidification is preferably in the range of 3100 μm to 6000 μm, more preferably in the range of 3300 μm to 5000 μm, and still more preferably in the range of 3500 μm to 4500 μm. When the thickness after solidification and before stretching is 6000 μm or less, wrinkles are unlikely to occur during melt extrusion, and unevenness is suppressed. Moreover, it is preferable that the thickness before stretching after solidification is 2600 μm or more suppresses uneven adhesion to the chill roll (cooling roll for solidification) generated due to weak melt, and is preferable from the viewpoint of reducing unevenness of the film.

(Stretching process)
In the manufacturing method of this invention, the process of extending | stretching the produced extruded film (unstretched film) may be included after the said film forming process. In the production method of the present invention, the substrate is preferably biaxially stretched from the viewpoint of mechanical strength.

(surface treatment)
In the production method of the present invention, the polymer substrate is preferably surface-treated by at least one method of corona treatment, atmospheric pressure plasma treatment, glow discharge treatment, flame treatment, and flame treatment using a silane compound-introduced flame.

<Formation of undercoat layer>
The undercoat layer is preferably formed by applying an undercoat layer forming coating solution to a polymer substrate.
There is no particular limitation on the method for applying the undercoat layer and the solvent of the coating solution used.
As a method of applying and forming an undercoat layer on a polymer substrate, a known coating method is appropriately adopted. For example, any method such as a reverse roll coater, a gravure coater, a rod coater, a bar coater, an air doctor coater, a spray or a coating method using a brush can be used.
The solvent used for the coating solution may be water or an organic solvent such as toluene or methyl ethyl ketone. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.
The coating may be performed on the polymer substrate after biaxial stretching, or may be performed by stretching in a direction different from the initial stretching after coating on the polymer substrate after uniaxial stretching. Furthermore, you may extend | stretch in 2 directions, after apply | coating to the base material before extending | stretching.

You may immerse a polymer base material in the aqueous coating liquid (coating liquid for undercoat layer formation) containing the component which comprises an undercoat layer. From the viewpoint of cost, it is preferable to apply the coating solution for forming the undercoat layer by a so-called in-line coating method in which the film is coated in the film production process.
That is, a melt extrusion step of melt-extruding a raw material resin for a polymer substrate into a sheet,
Cooling the melt-extruded sheet-shaped resin, and forming a resin sheet,
A first stretching step of stretching the resin sheet in a first direction;
An undercoat layer forming step of applying and forming an undercoat layer on at least one surface of the resin sheet stretched in the first direction;
And a second stretching step of stretching the resin sheet on which the undercoat layer has been applied and formed in a second direction orthogonal to the first direction.
More specifically, for example, a resin for forming a base film is extruded, for example, while being used together with an electrostatic adhesion method or the like, cast on a cooling drum to obtain a resin sheet, and then stretched in the longitudinal direction. Next, a method such as stretching in the transverse direction after applying an aqueous coating solution for forming an undercoat layer on one side of the film after longitudinal stretching can be used. The conditions for drying and heat treatment during coating depend on the thickness of the coat and the conditions of the apparatus, but it is preferable that the coating is sent immediately after coating to the stretching step in the perpendicular direction and dried in the preheating zone or stretching zone of the stretching step. In such a case, drying is usually performed at about 50 to 250 ° C.
In addition, you may perform a corona discharge process and other surface activation processes to the film used as a base material.

The solid concentration in the aqueous coating solution for forming the undercoat layer is preferably 30% by mass or less, and particularly preferably 10% by mass or less. The lower limit of the solid content concentration is preferably 1% by mass, more preferably 3% by mass, and particularly preferably 5% by mass. An undercoat layer having a good surface shape can be formed within the above range.

The coating amount of the undercoat layer coating liquid is preferably varied according to the thickness of the subbing layer to obtain, it is preferably 2 g / m ² or less, more preferably ^{0.05g / m 2 ~ 2g / m} 2 More preferably, it is 0.1 g / m ² to 1.5 g / m ² .
When the undercoat layer contains an inorganic oxide filler, the coating amount is preferably 0.005 to 0.5 g / m ² , more preferably 0.005 to 0.3 g / m ² , and A range of 005 to 0.2 g / m ² is particularly preferred.
After the application, a drying process for drying under desired conditions may be provided.

<Formation of pigment layer>
The pigment layer can be formed by a method in which a polymer sheet containing a pigment is bonded to a substrate, a method in which the pigment layer is co-extruded during substrate formation, a method by coating, or the like. Specifically, the pigment layer can be formed by bonding, co-extrusion, coating or the like directly on the surface of the polymer substrate or through an undercoat layer having a thickness of 2 μm or less. The formed pigment layer may be in a state where it is in direct contact with the surface of the polymer substrate or may be in a state where it is laminated via an undercoat layer.
Among the methods described above, the method by coating is preferable because it is simple and can be formed 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 liquid 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. Especially, it is preferable to use water as a solvent from a viewpoint of environmental impact. A coating solvent may be used individually by 1 type, and may mix and use 2 or more types.
It is preferable to apply the pigment layer forming coating solution on the undercoat layer.
The coating amount of the coating liquid for forming the pigment layer is preferably changed according to the desired thickness of the pigment layer, but the surface state of the pigment layer is disturbed due to the thickness of the undercoat layer. Therefore, it is not necessary to change the coating amount for the purpose of changing the reflectance and other physical properties of the pigment layer, and it is preferable to adjust the amount of the pigment contained in the pigment layer. The coating amount of the pigment layer forming coating solution is preferably 5 to 15 g / m ² from the viewpoint of maintaining reflectance and adhesion, more preferably 6 to 12 g / m ² , and even more preferably 7 g / m ^2. ~ 10 g / m ² .
After the application, a drying process for drying under desired conditions may be provided.

<Formation of topcoat layer>
The topcoat layer is preferably formed by applying a topcoat layer forming coating solution on the pigment layer.
There are no particular restrictions on the method for applying the topcoat layer and the solvent of the coating solution used.
As a coating method, for example, a gravure coater or a bar coater can be used.
The solvent used for the coating solution may be water or an organic solvent such as toluene or methyl ethyl ketone. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.
The coating amount of the coating solution for forming the topcoat layer is preferably changed according to the desired thickness of the topcoat layer, preferably 30 g / m ² or less, more preferably 0.5 g / m ² to 20 g / m ² . More preferably 1 g / m ² to 10 g / m ² .
When the topcoat layer contains an inorganic oxide filler, the coating amount is preferably 0.005 to 15 g / m ² , more preferably 0.005 to 10 g / m ² , and 0.005 to 5 g / m ^2. Particularly preferred is m ² .
After the application, a drying process for drying under desired conditions may be provided.

<Formation of composite polymer layer>
The composite polymer layer can be formed by a method in which a polymer sheet is bonded to a polymer substrate, a method in which the composite polymer layer is coextruded when forming the polymer substrate, 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 composite 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 solution for the composite polymer layer is preferably larger from the viewpoint of environmental load, and more preferably 90% by mass or more of water in the total solvent.

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

[Solar cell module]
The solar cell module of the present invention includes a transparent substrate on which sunlight is incident, a solar cell element, and the solar cell backsheet of the present invention. In the solar cell module of the present invention, a solar cell element that converts light energy of sunlight into electric energy is disposed between the transparent substrate on which sunlight is incident and the above-described solar cell backsheet of the present invention. The substrate and the back sheet are preferably sealed with an ethylene-vinyl acetate sealing material.

The sealing material is not limited to EVA (ethylene-vinyl acetate) resin, and PVB (polyvinyl butyral) resin, polyolefin resin, ethylene ionomer resin, and the like can also be used.

Components other than solar cell modules, solar cells, and backsheets are described in detail in, for example, “Solar Power Generation System Constituent Materials” (supervised by Eiichi Sugimoto, Industrial Research Committee, Inc., issued in 2008).

The transparent substrate only needs to have a light-transmitting property through which sunlight can be transmitted, and can be appropriately selected from base materials 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.

Solar cell elements 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, gallium-arsenic, and II Various known solar cell elements such as -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.
The volume average particle size was measured using a laser analysis / scattering particle size distribution measuring apparatus LA950 (manufactured by Horiba, Ltd.).

[Example 1]
<Production of polymer substrate>
-Polymerization of PET-
According to [0033] lines 1 to 11 of JP2011-165698A, a polymer of polyethylene terephthalate was obtained. Specifically, 100 parts by mass of dimethyl terephthalate, 61 parts by mass of ethylene glycol, and 0.06 parts by mass of magnesium acetate tetrahydrate were charged in a transesterification reaction vessel, heated to 150 ° C., melted and stirred. The reaction was advanced while the temperature in the reaction vessel was slowly raised to 235 ° C., and the produced methanol was distilled out of the reaction vessel. When the distillation of methanol was completed, 0.02 parts by mass of trimethyl phosphoric acid was added. After adding trimethyl phosphoric acid, 0.03 parts by mass of antimony trioxide was added, and the reaction product was transferred to a polymerization apparatus.

Then, the temperature in the polymerization apparatus was raised from 235 ° C. to 290 ° C. over 90 minutes, and at the same time, the pressure in the apparatus was reduced from atmospheric pressure to 100 Pa over 90 minutes. When the stirring torque of the contents of the polymerization apparatus reached a predetermined value, the interior of the apparatus was returned to atmospheric pressure with nitrogen gas to complete the polymerization. The valve at the bottom of the polymerization apparatus was opened and the inside of the polymerization apparatus was pressurized with nitrogen gas, and the polymerized polyethylene terephthalate was discharged into water in the form of a strand. The strand was chipped with a cutter. Thus, PET having an intrinsic viscosity IV = 0.58 and an acid value (AV) = 12, was obtained. This was designated as PET-A.

-Solid phase polymerization of polyester-
PET-A was subjected to solid phase polymerization according to [0032] of JP-A-2009-182186. That is, the obtained polymer (PET-A) was pre-dried at 150 to 160 ° C. for 3 hours and then subjected to solid phase polymerization at 205 ° C. for 25 hours in an atmosphere of 100 Torr and nitrogen gas. IV = 8, AV = 0.79 PET-B was obtained. The carboxyl terminal amount AV was measured by the method of Malice (Reference: MJ Malice, F. Huizinga. Anal. Chim. Acta, 22 363 (1960)).

The intrinsic viscosity (IV) was obtained by dissolving the polyester in orthochlorophenol and obtaining the intrinsic viscosity from the following formula from the solution viscosity measured at 25 ° C.
ηsp / C = [η] + K [η] ² · C
Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the weight of dissolved polymer per 100 ml of solvent (1 g / 100 ml in this measurement), and K is the Huggins constant (0.343) The solution viscosity and the solvent viscosity were measured using an Ostwald viscometer.

-Made of polyester film-
These were dried at 180 ° C. for 3 hours using PET-B, melted at 280 ° C., cast onto a metal drum, cooled and solidified to obtain an unstretched sheet.
The unstretched sheet was stretched 3.5 times in the longitudinal direction at 100 ° C., cooled to 25 ° C., and then stretched 4.2 times in the width direction at 130 ° C. Thereafter, heat setting was performed at 210 ° C., relaxation was performed 2% in the width direction, and winding was performed. The thickness after stretching was 250 μm. Thus, a biaxially stretched polyethylene terephthalate substrate S-1 having a thickness of 250 μm (hereinafter sometimes referred to as “biaxially stretched PET film”, “PET substrate”, or “support”) was obtained.

-Thermal shrinkage of a biaxially stretched PET substrate-
A biaxially stretched PET film was sampled into a 5 cm × 15 cm rectangle and a 15 cm side cut out in parallel to MD (film transport direction) was an MD sample, 15 cm parallel to TD (direction perpendicular to the film transport direction) The side cut out was used as a TD sample, and three pieces each were cut out. These samples were cut out at a point where the film forming width was divided into five equal parts, and a total of 15 MD samples and 15 TD samples were produced.
Each sample was conditioned at 25 ° C. and a relative humidity of 60% for 3 hours or more, a pair of 10 cm base length holes were made in this sample, and the distance between the holes was measured with a pin gauge (L1).
Each sample was heat-treated in an air thermostat at 150 ° C. for 30 minutes under no tension. Thereafter, each sample was conditioned at 25 ° C. and a relative humidity of 60% for 3 hours or longer, and the distance between the holes was measured with a pin gauge (L2).
100 × (L1-L2) / L1 was defined as the thermal shrinkage (%) of each sample.
As a result of obtaining the average values of all the MD and TD samples, they are shown as “heat shrinkage” in Table 1.

<Pigment 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)
・ Titanium dioxide (volume average particle size = 0.42 μm): 455.8 parts by mass [Taipeke CR-95, manufactured by Ishihara Sangyo Co., Ltd., solid content: 100% by mass]
・ Polyvinyl alcohol: 227.9 parts by mass [PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10% by mass]
-Surfactant: 5.5 parts by mass [Demol EP, manufactured by Kao Corporation, solid content: 25% by mass]
・ Distilled water ... 310.8 parts by mass

-Preparation of coating solution for pigment layer formation-
Components in the following composition were mixed to prepare a coating solution for forming a pigment layer.
(Composition of coating solution)
-Titanium dioxide dispersion ... 298.5 parts by mass-Polyolefin binder ... 568.7 parts by mass [Arrow Base SE1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass]
Polyoxyalkylene alkyl ether 23.4 parts by mass [Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass]
Oxazoline compound: 58.4 parts by mass [Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25%; crosslinking agent]
・ Distilled water: 51.0 parts by mass

The ratio (mass ratio) of the pigment to the total of the binder (polyolefin-based binder) and the pigment (titanium dioxide) in the composition of the coating liquid for forming the pigment layer was calculated to be 54.2%. The results are shown in Table 1 below.

-Formation of pigment layer-
One side (first side) of the PET substrate (S-1) was subjected to corona treatment under the following conditions using a corona treatment apparatus (solid state corona treatment machine 6KVA model manufactured by Pillar).

Electrode and dielectric roll gap clearance: 1.6mm
Processing frequency: 9.6 kHz
Processing speed: 20 m / min Processing intensity: 0.375 kV · A · min / m ²

Next, the pigment layer forming coating solution was applied to the corona-treated surface of the PET base material (S-1) so that the amount of titanium dioxide was 5.6 g / m ^2, and dried at 170 ° C. for 2 minutes. A layer was formed.

<Overcoat layer>
-Preparation of topcoat layer-
The components in the above composition were mixed to prepare a coating solution for forming an overcoat layer.
(Composition of coating solution for forming top coat layer)
・ Olefin binder: 213.8 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 73.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
Oxazoline compound (crosslinking agent) 45.0 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
Colloidal silica (inorganic pigment) 72.0 parts by mass (Snowtex C, manufactured by Nissan Chemical Co., Ltd., solid content: 20% by mass)
-Surfactant: 45.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Distilled water: 550.7 parts by mass

The ratio (mass ratio) of the pigment to the total of the binder (polyolefin-based binder) and the pigment (colloidal silica) in the composition of the coating solution for forming the overcoat layer was calculated to be 25.0%. Moreover, when the ratio (mass ratio) of the crosslinking agent addition amount (total of carbodiimide compound and oxazoline compound) to the binder addition amount (polyolefin-based binder) in the composition of the coating solution for forming the topcoat layer was calculated as a percentage, 22.2 %Met. The results are shown in Table 1 below.

-Formation of overcoat layer-
The obtained coating solution is applied onto the pigment layer so that the solid content coating amount is 0.6 g / m ² and dried at 170 ° C. for 2 minutes to form an overcoat layer having a dry thickness of about 0.5 μm. did.

<First composite polymer layer>
-Preparation of coating solution for forming first composite polymer layer-
Each component in the following composition was mixed to prepare a coating solution for forming the first composite polymer layer on the back surface.
(Composition of coating solution)
・ Acrylic / silicone binder (binder)
(Ceranate WSA-1070, manufactured by DIC Corporation, solid content: 40% by mass, siloxane structural unit: acrylic structural unit = 30: 70) ... 396.5 parts by mass / carbodiimide compound (crosslinking agent) ... 49 0.0 part by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Industries, Inc., solid content: 20% by mass)
Oxazoline compound (crosslinking agent) 16.8 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
-Titanium dioxide dispersion: 493.9 parts by mass-Distilled water: 28.8 parts by mass

-Formation of first composite polymer layer-
The surface opposite to the surface on which the pigment layer of the support S-1 was formed (sometimes referred to as “back surface”) was subjected to corona treatment under the conditions described above.
Next, the first composite polymer layer forming coating solution was applied to the corona-treated back surface of the support S-1 so that the binder coating amount was 5.1 g / m ² and dried at 175 ° C. for 2 minutes. A first composite polymer layer having a dry thickness of about 5 μm was formed.

<Second composite polymer layer>
-Preparation of coating solution for forming second composite polymer layer-
Each component in the following composition was mixed to prepare a coating solution for forming a second composite polymer layer.
(Composition of coating solution)
・ Acrylic / silicone binder (binder) 77.8 parts by mass (Ceranate WSA-1070, manufactured by DIC Corporation, solid content: 40% by mass)
Carbodiimide compound (crosslinking agent) 15.6 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 20% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Polyethylene wax dispersion: 51.9 parts by mass (Chemical Pearl W950, manufactured by Mitsui Chemicals, solid content: 5% by mass)
Colloidal silica: 1.0 part by mass (Snowtex UP, manufactured by Nissan Chemical Co., Ltd., solid content: 20% by mass)
Aminosilane compound: 19.6 parts by mass (TSL8340, manufactured by Momentive Performance Materials, solid content: 1% by mass)
・ Distilled water: 60.7 parts by mass

-Formation of second composite polymer layer-
The obtained coating liquid for forming the second composite polymer layer was applied onto the first composite polymer layer so that the amount of the binder applied was 1.3 g / m ² , dried at 175 ° C. for 2 minutes, and dried. Formed a second composite polymer layer of about 1.2 μm.

<Evaluation>
-1. Adhesiveness-
[A] Adhesiveness before wet heat aging The sample sheet produced as described above was cut into a width of 20 mm × 150 mm to prepare two sample pieces. These two sample pieces are arranged so that the pigment layer side is inside, and an EVA sheet (EVA sheet: SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.) cut into a width of 20 mm × 100 mm is sandwiched between them. It was made to adhere to EVA by hot pressing using a laminator (vacuum laminator manufactured by Nisshinbo Co., Ltd.). The bonding conditions at this time were as follows.
Using a vacuum laminator, evacuation was performed at 128 ° C. for 3 minutes, followed by pressurization for 2 minutes and temporary adhesion. Thereafter, the main adhesion treatment was performed at 150 ° C. for 30 minutes using a dry oven. In this way, an adhesion evaluation sample was obtained in which the 20 mm portion from one end of the two sample pieces adhered to each other was not bonded to EVA, and the EVA sheet was bonded to the remaining 100 mm portion.
The EVA non-adhered portion of the obtained adhesion evaluation sample was sandwiched between upper and lower clips with Tensilon (RTENT-1210A manufactured by ORIENTEC), a tensile test was performed at a peeling angle of 180 °, and a tensile speed of 300 mm / min, and the adhesive strength was measured. .
Based on the measured adhesive strength, ranking was performed according to the following evaluation criteria. Among these, ranks 4 and 5 are practically acceptable ranges.
<Evaluation criteria>
5: Adhesion was very good (60 N / 20 mm or more)
4: Adhesion was good (30N / 20mm or more and less than 60N / 20mm)
3: Adhesion was slightly poor (20N / 20mm or more and less than 30N / 20mm)
2: Adhesion failure occurred (10N / 20mm or more and less than 20N / 20mm)
1: Adhesion failure was remarkable (less than 10N / 20mm)

[B] Adhesiveness after wet heat aging The obtained sample for adhesion evaluation was held for 48 hours under the environmental conditions of 120 ° C. and 100% RH (wet heat aging), and then the adhesive strength was obtained in the same manner as in [A]. Was measured. Moreover, based on the measured adhesive strength after wet heat aging, the adhesive strength was evaluated by the same method as [A].

[C] Adhesive residual rate before and after wet heat aging of the adhesive ratio [A] of the same adhesion evaluation sample with respect to the adhesive strength before wet heat aging [%; = (after wet heat aging Adhesive strength / [A] Adhesive strength before wet heat aging × 100] was calculated.

-2. Reflectance-
Using a spectrophotometer UV-2450 (manufactured by Shimadzu Corporation) equipped with an integrating sphere attachment device ISR-2200, the reflectance of 550 nm light on the pigment layer side of the sample sheet was measured. The reflectance of the barium sulfate standard plate was measured as a reference, and the reflectance of the sample sheet was calculated using this as 100%.

-3. Light resistance
Using an ultra-energy irradiation tester (manufactured by Suga Test Instruments Co., Ltd.), ultraviolet light having an intensity of 700 W / m ² was irradiated from the composite polymer layer side of the sample sheet obtained above for 48 hours. Thereafter, the chromaticity (L * a * B *) before and after the ultraviolet light irradiation was measured to obtain the color difference ΔE. The greater the value of ΔE, the greater the discoloration due to ultraviolet light, and the lower the quality as a backsheet.

-4. Scratch resistance
The sample was conditioned for 24 hours in an atmosphere of 25 ° C. and 60% RH. Thereafter, the surface of the sample on the side where the composite polymer layer was provided was scratched with a sapphire needle having a tip of 0.1 mmφ at a speed of 1 cm / second. At this time, the load was continuously changed from 0 to 100 g. The surface of the sample after scratching was observed with an optical microscope, and the lowest load at which scratches were observed was taken as a measure of scratch resistance. Larger values indicate better scratch resistance, and practically acceptable is 30 g or more.

-5. Hydrolysis resistance
The PET film prepared above was subjected to environmental conditions of 120 ° C. and 100% RH for 50 hours, 60 hours, 70 hours, 80 hours, 90 hours, 100 hours, 110 hours, 120 hours, 130 hours, 150 hours, 170 hours. The thermo treatment was performed by leaving it for 190 hours and 210 hours. For the PET film after the thermo treatment, the breaking elongation in each MD direction is measured, and based on the obtained measurement value, the breaking elongation after the thermo treatment is divided by the breaking elongation before the thermo treatment, The elongation at break at the thermo treatment time was determined from the following formula. Plotting with the thermo-axis on the horizontal axis and the breaking elongation retention on the vertical axis, the time for heat treatment until the breaking elongation retention reaches 50% (hr; breaking elongation retention half-life) Asked.

Breaking elongation retention [%] =
(Elongation at break after thermo treatment) / (Elongation at break before thermo treatment) × 100

The greater the half-life value of the elongation at break elongation, the higher the hydrolysis resistance of the polymer substrate and the better the weather resistance.

-6. Defect occurrence frequency
The number of coating defects generated when a coating layer was provided on the polymer substrate was counted, and the frequency of occurrence per square meter of coating area was calculated.

[Example 2]
A solar cell backsheet (sample sheet) was prepared in the same manner as in Example 1 except that <Composition of coating solution for forming topcoat layer> in Example 1 was as follows.
<Composition of coating liquid for topcoat layer formation>
・ Olefin binder: 213.8 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 73.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
Oxazoline compound (crosslinking agent) 45.0 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
Titanium dioxide dispersion described in Example 1 31.6 parts by mass Surfactant 45.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass )
・ Distilled water: 591.1 parts by mass

[Example 3]
A solar cell backsheet (sample sheet) was prepared in the same manner as in Example 1 except that <Composition of coating solution for forming topcoat layer> in Example 1 was as follows.
<Composition of coating liquid for topcoat layer formation>
・ Olefin binder: 213.8 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 73.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
Oxazoline compound (crosslinking agent) 45.0 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
-Titanium dioxide dispersion described in Example 1 ... 77.5 parts by mass-Surfactant ... 45.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass )
・ Distilled water: 545.2 parts by mass

[Example 4]
<Undercoat layer>
-Preparation of undercoat layer-
Components in the following composition were mixed to prepare a coating solution for forming an undercoat layer.
<Composition of coating liquid for undercoat layer formation>
・ Polyester binder: 24.0 parts by mass
(Byronal MD1245, manufactured by Toyobo Co., Ltd., solid content 30% by mass)
・ Olefin binder: 35.6 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 24.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
Oxazoline compound (crosslinking agent) 15.0 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Distilled water: 885.9 parts by mass

The ratio (mass ratio) of the crosslinking agent addition amount (total of carbodilite compound and oxazoline compound) to the binder addition amount (total of polyester-based binder and polyolefin-based binder) in the composition of the coating solution for forming the undercoat layer was calculated as a percentage. However, it was 22.2%. The results are shown in Table 1 below.

-Formation of undercoat layer-
The first surface of the PET substrate (S-1) was subjected to corona treatment under the following conditions using a corona treatment device (solid state corona treatment machine 6KVA model manufactured by Pillar).
Electrode and dielectric roll gap clearance: 1.6mm
Processing frequency: 9.6 kHz
Processing speed: 20 m / min Processing intensity: 0.375 kV · A · min / m ²

Next, the undercoat layer-forming coating solution was applied to the corona-treated surface of the PET substrate (S-1) so that the solid content coating amount was 0.12 g / m ² and dried at 170 ° C. for 1 minute. An undercoat layer having a dry thickness of about 0.1 μm was formed.

<Pigment 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)
・ Titanium dioxide (volume average particle size = 0.42 μm): 455.8 parts by mass [Taipeke CR-95, manufactured by Ishihara Sangyo Co., Ltd., solid content: 100% by mass]
・ Polyvinyl alcohol: 227.9 parts by mass [PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10% by mass]
-Surfactant [Demol EP, manufactured by Kao Corporation, solid content: 25% by mass] ... 5.5 parts by mass Distilled water ... 310.8 parts by mass

-Formation of pigment layer-
The obtained coating solution was applied onto the undercoat layer of the support S-1 and dried at 170 ° C. for 2 minutes to form a pigment layer having a titanium dioxide content of 5.6 g / m ² .

<Overcoat layer>
-Preparation of topcoat layer-
Components in the following composition were mixed to prepare a coating solution for forming an overcoat layer.
<Composition of coating liquid for topcoat layer formation>
・ Olefin binder: 213.8 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 73.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
Oxazoline compound (crosslinking agent) 45.0 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
Colloidal silica (inorganic pigment) 72.0 parts by mass (Snowtex C, manufactured by Nissan Chemical Co., Ltd., solid content: 20% by mass)
-Surfactant: 45.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Distilled water: 550.7 parts by mass

The ratio (mass ratio) of the pigment to the total of the binder (polyolefin binder) and the pigment (colloidal silica) in the composition of the coating solution for forming the topcoat layer was calculated to be 25.0%. Moreover, when the ratio (mass ratio) of the amount of the crosslinking agent added (total of the carbodilite compound and the oxazoline compound) to the binder addition amount (polyolefin-based binder) in the composition of the coating solution for forming the topcoat layer was calculated as a percentage, 22. 2%. The results are shown in Table 1 below.

-Formation of overcoat layer-
The obtained coating solution was applied so that the solid content coating amount was 0.6 g / m ² and dried at 170 ° C. for 2 minutes to form an overcoat layer having a dry thickness of about 0.5 μm.

<First composite polymer layer>
-Preparation of coating solution for forming first composite polymer layer-
Each component in the following composition was mixed to prepare a coating solution for forming the first composite polymer layer on the back surface.
(Composition of coating solution)
・ Acrylic / silicone binder (binder)
(Ceranate WSA-1070, manufactured by DIC Corporation, solid content: 40% by mass)
... 396.5 parts by mass-Carbodiimide compound (crosslinking agent) ... 49.0 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 20% by mass)
Oxazoline compound (crosslinking agent) 16.8 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
-Titanium dioxide dispersion: 493.9 parts by mass-Distilled water: 28.8 parts by mass

-Formation of first composite polymer layer-
The surface opposite to the surface on which the pigment layer of the support S-1 was formed (hereinafter sometimes referred to as the back surface) was subjected to corona treatment under the conditions described above.
Next, the first composite polymer layer forming coating solution was applied to the corona-treated back surface of the support S-1 so that the binder coating amount was 5.1 g / m ² and dried at 175 ° C. for 2 minutes. A first composite polymer layer having a dry thickness of about 5 μm was formed.

<Second composite polymer layer>
-Preparation of coating solution for forming second composite polymer layer-
Each component in the following composition was mixed to prepare a coating solution for forming a second composite polymer layer.
(Composition of coating solution)
・ Acrylic / silicone binder (binder, P-1)
(Ceranate WSA-1070, manufactured by DIC Corporation, solid content: 40% by mass)
... 77.8 parts by mass-Carbodiimide compound (crosslinking agent) ... 15.6 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 20% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Polyethylene wax dispersion: 51.9 parts by mass (Chemical Pearl W950, manufactured by Mitsui Chemicals, solid content: 5% by mass)
Colloidal silica: 1.0 part by mass (Snowtex UP, manufactured by Nissan Chemical Co., Ltd., solid content: 20% by mass)
Aminosilane compound: 19.6 parts by mass (TSL8340, manufactured by Momentive Performance Materials, solid content: 1% by mass)
・ Distilled water: 60.7 parts by mass

-Formation of second composite polymer layer-
The obtained coating liquid for forming the second composite polymer layer was applied on the first composite polymer layer so that the amount of the binder applied was 1.3 g / m ² , dried at 175 ° C. for 2 minutes, and dried. A second composite polymer layer of about 1.2 μm was formed.

[Example 5]
A solar cell backsheet (sample sheet) was produced in the same manner as in Example 4 except that <Composition of coating solution for forming topcoat layer> in Example 4 was as follows.
<Composition of coating liquid for topcoat layer formation>
・ Olefin binder: 213.8 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 73.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
Titanium dioxide dispersion described in Example 1 31.6 parts by mass Surfactant 45.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass )
・ Distilled water: 636.1 parts by mass

[Example 6]
A solar cell back sheet (sample sheet) was produced in the same manner as in Example 5 except that <Composition of coating solution for forming undercoat layer> in Example 5 was as follows.
<Composition of coating liquid for undercoat layer formation>
・ Acrylic binder: 25.7 parts by mass
(AS-563A, manufactured by Daicel Finechem Co., Ltd., solid content: 28% by mass)
・ Olefin binder: 35.6 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 24.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Distilled water: 899.2 parts by mass

[Example 7]
A solar cell backsheet (sample sheet) was prepared in the same manner as in Example 6 except that <Composition of coating solution for forming undercoat layer> and <Composition of coating solution for forming pigment layer> in Example 6 were as follows. ) Was produced.
<Composition of coating liquid for undercoat layer formation>
・ Olefin binder: 71.3 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 24.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Distilled water: 889.2 parts by mass

<Composition of pigment layer forming coating solution>
-Titanium dioxide dispersion ... 298.5 parts by mass-Polyolefin binder ... 568.7 parts by mass [Arrow Base SE1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass]
Polyoxyalkylene alkyl ether 23.4 parts by mass [Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass]
・ Oxazoline compound: 29.2 parts by mass [Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25%; crosslinking agent]
・ Distilled water: 80.2 parts by mass

[Example 8]
A solar cell back sheet (sample sheet) was produced in the same manner as in Example 7 except that <Composition of pigment layer forming coating solution> in Example 7 was as follows.
<Composition of pigment layer forming coating solution>
Titanium dioxide dispersion: 298.5 parts by mass Polyolefin binder: 284.3 parts by mass [Arrow Base SE1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass]
・ Polyurethane binder: 191.5 parts by mass [Takelac WS-6021, manufactured by Mitsui Chemicals Polyurethanes, solid content: 30% by mass]
Polyoxyalkylene alkyl ether 23.4 parts by mass [Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass]
Carbodiimide compound (crosslinking agent) 146.0 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
・ Distilled water: 56.3 parts by mass

[Example 9]
A solar cell backsheet (sample sheet) was prepared in the same manner as in Example 8 except that <Composition of pigment layer forming coating solution> in Example 8 was as follows.
<Composition of pigment layer forming coating solution>
Titanium dioxide dispersion: 447.8 parts by mass Polyolefin binder: 89.1 parts by mass [Arrow Base SE1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass]
-Polyurethane binder: 60.0 parts by mass [Takelac WS-6021, manufactured by Mitsui Chemicals Polyurethanes, solid content: 30% by mass]
Polyoxyalkylene alkyl ether 35.1 parts by mass [Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass]
Carbodiimide compound (crosslinking agent) 45.7 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
・ Distilled water ... 322.3 parts by mass

[Example 10]
A solar cell backsheet (sample sheet) was produced in the same manner as in Example 8, except that <Composition of coating solution for forming topcoat layer> in Example 8 was as follows.
<Composition of coating liquid for topcoat layer formation>
・ Olefin binder: 213.8 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
Carbodiimide compound (crosslinking agent) 73.5 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
-Surfactant: 45.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Distilled water: 667.7 parts by mass

[Example 11]
In the same manner as in Example 7 except that <Preparation of coating liquid for forming first composite polymer layer> and <Preparation of coating liquid for forming second composite polymer layer> in Example 7 were as follows, A battery back sheet (sample sheet) was prepared.
-Preparation of coating solution for forming first composite polymer layer-
Each component in the following composition was mixed to prepare a coating solution for forming the first composite polymer layer on the back surface.
(Composition of coating solution)
・ Acrylic / silicone binder (binder)
(Ceranate WSA-1060, manufactured by DIC Corporation, solid content: 35% by mass, siloxane structural unit: acrylic structural unit = 75: 25) ... 396.5 parts by mass, carbodiimide compound (crosslinking agent) ... 49 0.0 part by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Industries, Inc., solid content: 20% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
-Titanium dioxide dispersion: 493.9 parts by mass-Distilled water: 28.8 parts by mass

<Second composite polymer layer>
-Preparation of coating solution for forming second composite polymer layer-
Each component in the following composition was mixed to prepare a coating solution for forming a second composite polymer layer.
(Composition of coating solution)
・ Acrylic / silicone binder (binder) 77.8 parts by mass (Ceranate WSA-1060, manufactured by DIC Corporation, solid content: 35% by mass)
Carbodiimide compound (crosslinking agent) 15.6 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 20% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Polyethylene wax dispersion: 51.9 parts by mass (Chemical Pearl W950, manufactured by Mitsui Chemicals, solid content: 5% by mass)
Colloidal silica: 1.0 part by mass (Snowtex UP, manufactured by Nissan Chemical Co., Ltd., solid content: 20% by mass)
Aminosilane compound: 19.6 parts by mass (TSL8340, manufactured by Momentive Performance Materials, solid content: 1% by mass)
・ Distilled water: 60.7 parts by mass

[Example 12]
A solar cell backsheet (sample sheet) was prepared in the same manner as in Example 7 except that the <composition of the titanium dioxide dispersion> used in <Pigment layer forming coating solution> in Example 7 was as follows. Produced.
(Composition of titanium dioxide dispersion)
・ Titanium dioxide (volume average particle size = 0.44 μm): 455.8 parts by mass [Taipek R-780, manufactured by Ishihara Sangyo Co., Ltd., solid content: 100% by mass]
・ Polyvinyl alcohol: 227.9 parts by mass [PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10% by mass]
-Surfactant: 5.5 parts by mass [Demol EP, manufactured by Kao Corporation, solid content: 25% by mass]
・ Distilled water ... 310.8 parts by mass

[Comparative Example 1]
A solar cell back sheet (sample sheet) was produced in the same manner as in Example 1 except that the <overcoat layer> in Example 1 was not provided.

[Comparative Example 2]
A solar cell back sheet (sample sheet) was produced in the same manner as in Example 6 except that the <overcoat layer> in Example 6 was not formed by coating.

[Comparative Example 3]
A solar cell backsheet (sample sheet) was prepared in the same manner as in Example 6 except that the <composite polymer layer> on the opposite side of the pigment layer of Example 6 was not formed by coating.

[Example 13]
A back sheet for solar cell (sample) was formed in the same manner as in Example 5 except that the <first composite polymer layer> of Example 5 was formed as follows and <second composite polymer layer> was not formed. Sheet).

-Preparation of coating solution for forming first composite polymer layer-
Each component in the following composition was mixed to prepare a coating solution for forming the first composite polymer layer on the back surface.
(Composition of coating solution)
・ Acrylic / silicone binder (binder)
(Ceranate WSA-1070, manufactured by DIC Corporation, solid content: 40% by mass, siloxane structural unit: acrylic structural unit = 30: 70)
... 643.5 parts by mass-Carbodiimide compound (crosslinking agent) ... 49.0 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Industries, Inc., solid content: 20% by mass)
Oxazoline compound (crosslinking agent) 16.8 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
-Surfactant: 15.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
-Titanium dioxide dispersion: 246.9 parts by mass-Distilled water: 28.8 parts by mass

-Formation of first composite polymer layer-
The surface opposite to the surface on which the pigment layer of the support S-1 was formed (hereinafter sometimes referred to as the back surface) was subjected to corona treatment under the conditions described above.
Next, the first composite polymer layer forming coating solution was coated on the corona-treated back surface of the support S-1 so that the binder coating amount was 10.2 / m ² and dried at 175 ° C. for 2 minutes, A first composite polymer layer having a dry thickness of about 10 μm was formed.

[Comparative Example 4]
A titanium oxide kneaded base material (white film) that exhibits a reflectance substantially equivalent to that of Example 1 was produced as follows. In addition, in Comparative Example 4 using a titanium oxide kneaded type base material, the coating layer was not formed, and thus the adhesion and film strength of the coating layer were not measured.

-Production of master batch containing titanium dioxide-
Intrinsic viscosity 0.79 obtained by solid-phase polymerization of polyethylene terephthalate resin having an intrinsic viscosity of 0.58 and an acid value of 12 (eq / ton) at 205 ° C. in a nitrogen stream for 25 hours, an acid value of 7.5 (eq / ton) 50% by mass of polyethylene terephthalate resin (PET-I) was previously dried at 120 ° C. for 8 hours under 10 ⁻³ torr. This was mixed with 50% by mass of rutile type titanium dioxide having an average particle size of 0.3 μm (electron microscopic method), supplied to a vent type twin screw extruder, kneaded and extruded at 275 ° C. while degassing. (Titanium oxide) -containing master batch (MB-I) pellets were prepared. This pellet had an intrinsic viscosity of 0.78 and an acid value of 7.9 (eq / ton).

-Production of film-
Next, a raw material in which 50% by mass of polyethylene terephthalate resin (PET-I) and 50% by mass of the previously prepared MB-I were mixed and melted at 280 ° C. Next, the sheet was extruded onto a cooling drum adjusted to 30 ° C. using a T-die to produce an unstretched sheet.

-Preparation of stretched film-
The obtained unstretched sheet was uniformly heated to 70 ° C. using a heating roll, and stretched 3.5 times at 90 ° C. The obtained uniaxially stretched film was led to a tenter, heated to 140 ° C. and transversely stretched 4.2 times, fixed in width and subjected to a heat treatment at 205 ° C. for 5 seconds, and further 4% in the width direction at 200 ° C. By relaxing, a white film having a thickness of 250 μm was obtained.

[Example 14]
A back sheet for a solar cell (sample sheet) was prepared in the same manner as in Example 1 except that the <Composition of the coating liquid for forming a pigment layer> and <Composition of the coating liquid for forming an overcoat layer> in Example 1 were as follows. ) Was produced.

<Composition of pigment layer forming coating solution>
Titanium dioxide dispersion: 298.5 parts by mass Polyolefin binder: 341.2 parts by mass [Arrow Base SE1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass]
・ Acrylic binder: 164.1 parts by mass
(AS-563A, manufactured by Daicel Finechem Co., Ltd., solid content: 28% by mass)
Fluorosurfactant: 8.5 parts by mass [Methanol solution of fluorosurfactant 6 described in JP 2010-83927 A, solid content: 1% by mass]
Oxazoline compound: 94.9 parts by mass [Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25%; crosslinking agent]
・ Distilled water ... 93.1 parts by mass

<Composition of coating liquid for topcoat layer formation>
・ Olefin binder: 171.0 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content: 20.2% by mass)
・ Acrylic binder: 30.8 parts by mass (AS-563A, manufactured by Daicel Finechem Co., Ltd., solid content: 28% by mass)
・ Oxazoline compound: 45.0 parts by mass (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 5% by mass)
Surfactant: 10.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Fluorosurfactant: 5.0 parts by mass [Methanol solution of fluorosurfactant 6 described in JP2010-83927A, solid content: 1% by mass]
・ Distilled water: 738.2 parts by mass

[Example 15]
In <Formation of pigment layer> and <Formation of first composite polymer layer>, instead of corona-treating the surface of the PET substrate (S-1), a PET substrate subjected to glow treatment under the following conditions was used. Produced the solar cell backsheet (sample sheet) in the same manner as in Example 14.

-Glow discharge treatment-
Both surfaces of a 250 μm thick biaxially stretched polyethylene terephthalate film were subjected to low pressure plasma treatment under the following conditions. This apparatus does not particularly introduce plasma gas. The atmosphere (plasma gas) is therefore degassed from the inflowing air and the polyethylene terephthalate film.
The polyethylene terephthalate film was heated to 145 ° C. using a heating roller before the treatment.

・ Processing atmosphere pressure 0.2 Torr
・ Discharge frequency 30kHz
・ Output 5000w
・ Processing strength 4.2 kV ・ A ・ min / m ²

[Example 16]
A solar cell backsheet (sample sheet) was produced in the same manner as in Example 14 except that the titanium oxide kneaded base material (white film) used in Comparative Example 4 was used.

[Example 17]
A solar cell backsheet (sample sheet) was prepared in the same manner as in Example 14 except that the polymer base material (S-2) to which the end-capping agent was prepared as described below was used.

<Preparation of polymer substrate (S-2)>
-Polymerization of PET-
According to [0033] lines 1 to 11 of JP2011-165698A, a polymer of polyethylene terephthalate was obtained. Specifically, 100 parts by mass of dimethyl terephthalate, 61 parts by mass of ethylene glycol, and 0.06 parts by mass of magnesium acetate tetrahydrate were charged in a transesterification reaction vessel, heated to 150 ° C., melted and stirred. The reaction was advanced while the temperature in the reaction vessel was slowly raised to 235 ° C., and the produced methanol was distilled out of the reaction vessel. When the distillation of methanol was completed, 0.02 parts by mass of trimethyl phosphoric acid was added. After adding trimethyl phosphoric acid, 0.03 parts by mass of antimony trioxide was added, and the reaction product was transferred to a polymerization apparatus. Subsequently, the temperature in the polymerization apparatus was raised from 235 ° C. to 290 ° C. over 90 minutes, and at the same time, the pressure in the apparatus was reduced from atmospheric pressure to 100 Pa over 90 minutes. When the stirring torque of the contents of the polymerization apparatus reached a predetermined value, the inside of the apparatus was returned to atmospheric pressure with nitrogen gas to complete the polymerization. The valve | bulb of the polymerization apparatus lower part was opened, the inside of the polymerization apparatus was pressurized with nitrogen gas, and the polyethylene terephthalate which superposed | polymerized was made into strand shape, and was discharged in water. The strand was chipped with a cutter. Thus, PET having an intrinsic viscosity IV = 0.58 and an acid value (AV) = 12 was obtained. This was designated as PET-A.

-Solid phase polymerization of polyester-
PET-A was subjected to solid phase polymerization according to [0032] of JP-A-2009-182186. That is, the obtained polymer (PET-A) was pre-dried at 150 to 160 ° C. for 3 hours and then subjected to solid phase polymerization at 205 ° C. for 25 hours in an atmosphere of 100 torr and nitrogen gas, and IV = 8, AV = 0. 79 PET-Bs were obtained. The carboxyl terminal amount AV was measured by the method of Malice (reference: MJ Malice, F. Huizinga. Anal. Chim. Acta, 22 363 (1960)).
The intrinsic viscosity (IV) was obtained by dissolving the polyester in orthochlorophenol and obtaining the intrinsic viscosity from the following formula from the solution viscosity measured at 25 ° C.
ηsp / C = [η] + K [η] ² · C
Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the weight of dissolved polymer per 100 ml of solvent (1 g / 100 ml in this measurement), and K is the Huggins constant (0.343) The solution viscosity and the solvent viscosity were measured using an Ostwald viscometer.

-Production of master pellets containing polyester and end-capping agent-
90 parts by mass of the above-mentioned PET-B and 10 parts by mass of the following end-capping agent C) are blended, supplied to a twin-screw kneader, melt-kneaded at 280 ° C., discharged into water in a strand form, and cutter And cut into chips. This was designated as PET-C (master pellet).
End-capping agent a) Carbodiimide: Stabilizer 9000 (manufactured by Raschig), Mw = 20000
End-capping agent b) carbodiimide: N, N′-dicyclohexylcarbodiimide, Mw = 206
End-capping agent c) carbodiimide: cyclic carbodiimide compound (2) described in JP 2011-153209 A [0174] and [0175], Mw = 516
End-capping agent d) Epoxy: chain extender 1 described in JP 2010-116560 A [0115], Mw = 3300
End-capping agent e) Oxazoline: Epocross RPS-1005 (manufactured by Nippon Shokubai Co., Ltd.), Mw = 5000

-Made of polyester film-
Using PET-B and PET-C, these were dried at 180 ° C. for 3 hours and then put into an extruder at a ratio of PET-B / PET-C = 92/8 (mass%) and kneaded at 280 ° C. did. Then, after passing through a gear pump and a filter, it was extruded onto a cooling drum of 25 ° C. to which electrostatic application was applied from a T die, and cooled and solidified to obtain an unstretched sheet. The unstretched sheet was stretched 3.5 times in the longitudinal direction at 100 ° C., cooled to 25 ° C., and then stretched 4.2 times in the width direction at 130 ° C. Thereafter, heat setting was performed at 210 ° C., relaxation was performed 2% in the width direction, and winding was performed. The thickness after stretching was 250 μm.

[Example 18]
A solar cell backsheet (sample sheet) was prepared in the same manner as in Example 4 except that the polymer substrate with an undercoat layer (S-3) prepared as described below was used.
<Preparation of polymer substrate (S-3)>
-Preparation of coating solution for undercoat layer formation-
Each component in the following composition was mixed to prepare a coating solution for forming an undercoat layer.
<Composition of coating solution>
・ Polyester binder: 8.12 parts by mass
(Byronal MD1245, manufactured by Toyobo Co., Ltd., solid content 30% by mass)
Polyolefin binder: 12.06 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., concentration: 20% by mass)
-Carbodiimide compound (crosslinking agent): 8.20 parts by mass (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
・ Oxazoline-based crosslinking agent: 1.00 parts by mass (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., concentration: 25% by mass)
-Surfactant: 5.0 parts by mass (Naroacty CL95, manufactured by Sanyo Chemical Industries, Ltd., solid content: 1% by mass)
・ Distilled water: 65.62 parts by mass

-Formation of undercoat layer-
The first surface of the polymer support was subjected to corona treatment under the following conditions.
・ Electrode and dielectric roll gap clearance: 1.6mm
・ Processing frequency: 9.6 kHz
Processing speed: 20 m / min Processing intensity: 0.375 kV / A / min / m ²

Next, the coating solution for forming the undercoat layer is applied to the corona-treated surface of the polymer support by an in-line coating method after MD stretching and before TD stretching so that the coating amount is 5.1 ml / m ^2. An undercoat layer of 0.1 μm was formed. The TD stretching temperature is 105 ° C., stretched 4.5 times in the TD direction, and heat treatment is performed at 200 ° C. for 15 seconds. The MD relaxation rate is 5% at 190 ° C., and the MD relaxation rate is 11%. -Thermal relaxation was performed in the TD direction.

[Example 19]
A solar cell backsheet (sample sheet) was produced in the same manner as in Example 14 except that the polymer substrate (S-4) with an undercoat layer produced as described below was used.
<Preparation of polymer substrate (S-4)>
-Preparation of coating solution for undercoat layer formation-
Each component in the following composition was mixed to prepare a coating solution for forming an undercoat layer.
<Composition of coating solution>
・ Polyolefin binder: 24.12 parts by mass (Arrow Base SE-1013N, manufactured by Unitika Ltd., concentration: 20% by mass)
・ Oxazoline-based crosslinking agent: 3.90 parts by mass (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., concentration: 25% by mass)
・ Fluorine-based surfactant: 0.19 parts by mass (sodium bis (3, 3, 4, 4, 5, 5, 6, 6-nonafluoro) = 2-sulfonite oxysuccinate, Sankyo Chemical (Made by Co., Ltd., concentration 1% by mass)
・ Distilled water: 71.80 parts by mass

Next, the coating solution for forming the undercoat layer is applied to the corona-treated surface of the polymer support by an in-line coating method after MD stretching and before TD stretching so that the coating amount is 5.1 ml / m ^2. An undercoat layer of 0.1 μm was formed. The TD stretching temperature is 105 ° C., stretched 4.5 times in the TD direction, and heat treatment is performed for 15 seconds at a film surface of 200 ° C. The MD relaxation rate is 5% at 190 ° C., and the TD relaxation rate is 11%. Thermal relaxation was performed in the MD / TD direction.

The film of each Example and Comparative Example obtained was evaluated in the same manner as Example 1. The results are shown in Table 2 below.

From the above Table 2, the solar cell backsheets of the examples all have good adhesiveness, reflectance and light resistance after wet heat aging.
On the other hand, Comparative Examples 1 and 2 did not have an overcoat layer on the pigment layer, and the adhesion after wet heat aging significantly decreased.
Comparative Example 3 did not have a composite polymer layer on the back surface and had low light resistance.
In Comparative Example 4, a pigment kneaded type sheet prepared so as to have a thickness equivalent to that of Example 1 and a reflectance exceeding 80% was produced, and the light resistance was low.

(Example 20)
A tempered glass having a thickness of 3 mm, an EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), a crystalline solar cell, an EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), and the sample of Example 1 Sheets (back sheets for solar cells of the present invention) 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 sample sheet was disposed so that the overcoat layer was in contact with the EVA sheet. Moreover, the adhesion conditions of EVA are as follows.
Using a vacuum laminator, evacuation was performed at 128 ° C. for 3 minutes, followed by pressurization for 2 minutes and temporary adhesion. Thereafter, the main adhesion treatment was performed in a dry oven at 150 ° C. for 30 minutes.
In this way, a crystalline solar cell module was produced. When the generated solar cell module was used for power generation operation, it showed good power generation performance as a solar cell.

The entire disclosure of Japanese Patent Application 2011-178562 is incorporated herein by reference.
All documents, patents, patent applications, and technical standards described herein are specifically and individually described as individual documents, patents, patent applications, and technical standards are incorporated by reference. To the same extent, it is incorporated herein by reference.

Claims

A polymer substrate;
A pigment layer provided on the first surface of the polymer substrate and comprising a binder and a pigment;
An overcoat layer provided on the pigment layer and containing a binder;
Provided on the second surface of the polymer base material, a siloxane structural unit having a mass ratio of 15 to 85 mass% represented by the following general formula (1) in the molecule and a non-mass ratio of 85 to 15 mass% A composite polymer layer containing a composite polymer comprising a siloxane-based structural unit;
A solar cell backsheet.

[In General Formula (1), R 1 and R 2 each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, and R 1 and R 2 may be the same or different. n represents an integer of 1 or more. The plurality of R 1 and R 2 may be the same as or different from each other. ]
The solar cell backsheet according to claim 1, further comprising an undercoat layer containing a binder and having a thickness of 2 µm or less between the polymer substrate and the pigment layer.
The solar cell backsheet according to claim 1 or 2, wherein at least one layer provided on the polymer substrate contains a fluorosurfactant.
The solar cell backsheet according to any one of claims 1 to 3, wherein a ratio of the pigment to a total of the binder and the pigment in the pigment layer is 40 to 95 mass%.
The solar cell backsheet according to any one of claims 1 to 4, wherein a thickness of the overcoat layer is 0.1 µm or more and 30 µm or less.
The solar cell backsheet according to any one of claims 1 to 5, wherein a ratio of the pigment to a total of the binder and the pigment in the pigment layer is 50 to 95 mass%.
The back sheet for a solar cell according to any one of claims 1 to 6, wherein a ratio of the pigment to a total of the binder and the pigment in the pigment layer is 70 to 95% by mass.
The solar cell backsheet according to any one of claims 1 to 7, wherein a thickness of the overcoat layer is from 0.3 µm to 20 µm.
The solar cell backsheet according to any one of claims 1 to 8, wherein a thickness of the overcoat layer is 0.5 µm or more and 10 µm or less.
The at least one layer provided on the first surface of the polymer substrate contains 5 to 50% by mass of a crosslinking agent-derived structure with respect to the binder contained in the layer. The solar cell backsheet according to claim 9.
The solar cell backsheet according to claim 10, wherein at least one of the crosslinking agents is a crosslinking agent having a carbodiimide group or an oxazoline group.
A binder is included between the polymer substrate and the pigment layer, and an undercoat layer having a thickness of 2 μm or less is provided. The undercoat layer and the overcoat layer are made of a polyolefin resin, a polyurethane resin, a polyvinyl alcohol resin, or a polyacrylic resin. The solar cell backsheet according to any one of claims 1 to 11, comprising at least one resin selected from the group consisting of a polyester resin and a polyester resin.
The undercoat layer includes a binder and has a thickness of 2 μm or less between the polymer substrate and the pigment layer, and the undercoat layer and the overcoat layer contain an inorganic oxide filler. The solar cell backsheet according to any one of 12 above.
The surface treatment is performed on at least one surface of the polymer base material by at least one method of corona treatment, glow discharge treatment, atmospheric pressure plasma treatment, and flame treatment. Back sheet for solar cells.
The polymer base material according to any one of claims 1 to 14, wherein the polymer base material includes a polyester resin and 0.1 to 10% by mass of an end-capping agent based on the total mass of the polyester resin. The polymer sheet for solar cells described.
The base polymer base material contains inorganic particles or organic particles, the average particle size of the particles is 0.1 to 10 μm, and the content of the particles is 0 to 50 mass with respect to the total mass of the polymer base material. The solar cell polymer sheet according to any one of claims 1 to 15, wherein the polymer sheet is%.
The solar cell backsheet according to any one of claims 1 to 16, wherein the polymer base material has a thermal shrinkage rate of 0 to 0.5% at 150 ° C for about 30 minutes.
The solar cell backsheet according to any one of claims 1 to 17, wherein the polymer base material comprises a polyester resin having a carboxyl group content of 35 equivalents / ton or less.
The solar cell backsheet according to any one of claims 1 to 18, wherein a reflectance with respect to light having a wavelength of 550 nm on the side on which the pigment layer is provided is 70% or more.
The solar cell backsheet according to any one of claims 1 to 19, wherein all the layers provided on the first surface of the polymer base material are layers formed by coating.
A melt extrusion step of melt-extruding a raw material resin for a polymer substrate into a sheet,
Cooling the melt-extruded sheet-shaped resin, and forming a resin sheet,
A first stretching step of stretching the resin sheet in a first direction;
An undercoat layer forming step of applying and forming an undercoat layer on at least one surface of the resin sheet stretched in the first direction;
A second stretching step of stretching the resin sheet coated with the undercoat layer in a second direction orthogonal to the first direction;
A method for producing a solar cell backsheet, which comprises producing the solar cell backsheet according to any one of claims 2 to 20.
A solar cell module comprising: a transparent substrate on which sunlight is incident; a solar cell element; and the solar cell backsheet according to any one of claims 1 to 20.