JP2016111037A - Solar battery back protection sheet, and solar cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery back protection sheet excellent in adhesion to the sealing material of a solar cell, adhesion (adhesion durability) at the time of long term use, long term durability, and processing suitability, and to provide a solar cell using the same.SOLUTION: In a solar battery back protection sheet having a base material layer (P1 layer) and an easy adhesive layer (P2 layer), the P1 layer is mainly composed of polyester resin, and has the P2 layer at least on one side thereof. The solar battery back protection sheet satisfies following conditions (a)-(c) entirely. (a) Thermal shrinkage after heat treatment at 150°C for 30 minutes is 1.5% or less. (b) Surface roughness (Ra) of the P2 layer is 0.03-0.50 μm(c) Adhesive strength after humidity and heat resistance test is 15 N/cm or more, and adhesive strength retention rate after humidity and heat resistance test is 80% or more.SELECTED DRAWING: Figure 1

Description

  The present invention provides a sheet for protecting a back surface of a solar battery, which has good adhesion to a sealing material of a solar battery cell and has good adhesion (adhesion durability), long-term durability, and processability when used for a long period of time. Related to solar cells.

  In recent years, solar power generation has attracted attention as a semi-permanent and pollution-free next-generation energy source, and solar cells are rapidly spreading. In solar cells, a power generation element is sealed with a transparent sealing material such as ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as EVA), a transparent substrate such as glass, and a solar cell back surface protection A resin sheet called a sheet (hereinafter sometimes referred to as a back sheet) is laminated to be configured. Sunlight is introduced into the solar cell through the transparent substrate. Sunlight introduced into the solar cell is absorbed by the power generation element, and the absorbed light energy is converted into electrical energy. The converted electric energy is taken out by a lead wire connected to the power generation element and used for various electric devices.

  So far, biaxially stretched films using inexpensive and high-performance polyethylene terephthalate (hereinafter sometimes referred to as PET) have been widely used for solar cell back surface protection sheets. Studies have been made to impart barrier properties and electrical characteristics by bonding them together. However, polyester resins such as PET have a problem that adhesion to a sealing material is weak. Therefore, conventionally, it is common to laminate a polyolefin resin sheet excellent in adhesion to a sealing material on a polyester resin such as PET and use the polyolefin resin sheet as a sealing material adhesion surface of a sheet for protecting the back surface of a solar cell. Met.

  Recently, polyester sheets (Patent Documents 1 and 2) that can be easily bonded to a sealing material by providing an easy-adhesion layer on the surface of a biaxially stretched polyester film have been disclosed.

JP 2014-75508 A JP 2006-175664 A

  However, in the method of laminating the above-mentioned polyolefin resin sheet and using the polyolefin resin sheet as the sealing material adhesion surface of the solar cell back surface protection sheet, the cost increases because of lamination, and the moisture resistance of the interfacial polyolefin layer is low. There was a problem.

  In addition, since the conventional easy-adhesion layers listed in Patent Documents 1 and 2 do not have sufficient adhesion to the sealing material, they are sealed during processing of solar cells or when used outdoors as solar cells. There was a problem that it was easy to peel off at the interface with the stopper or between the layers of the easy-adhesion layer.

  In the present invention, in view of conventional problems, a sheet for protecting a back surface of a solar cell having good adhesion with a sealing material for solar cells, adhesion during long-term use (adhesion durability), long-term durability, and processability, And it aims at providing the solar cell using the same.

In order to solve the above problems, the present invention has the following configuration.
That is,
It is a solar cell back surface protection sheet having a base material layer (P1 layer) and an easy-adhesion layer (P2 layer). The P1 layer is mainly composed of a polyester resin, and the P2 layer is formed on at least one side of the P1 layer. And a solar cell back surface protection sheet characterized by satisfying all of the following (a) to (c).

  (A) The heat shrinkage rate after heat treatment at 150 ° C. for 30 minutes is 1.5% or less.

  (B) The surface roughness (Ra) of the P2 layer is 0.03 μm or more and 0.50 μm or less.

  (C) The adhesive strength after the moist heat test is 15 N / cm or more, and the adhesive strength retention after the moist heat test is 80% or more.

  According to the present invention, a solar cell back surface protective sheet having good adhesion to a sealing material of a solar battery cell, adhesion during long-term use (adhesion durability), long-term durability and processability, and the solar battery A solar battery using the back surface protection sheet can be provided.

It is sectional drawing which shows typically an example of a structure of the solar cell using the solar cell back surface protection sheet of this invention.

  The solar cell back surface protection sheet of the present invention is a solar cell back surface protection sheet having a base material layer (P1 layer) and an easy-adhesion layer (P2 layer), and the P1 layer mainly comprises a polyester resin. The P2 layer is provided on at least one side of the P1 layer, and all of the following (a) to (c) are satisfied.

  (A) The heat shrinkage rate after heat treatment at 150 ° C. for 30 minutes is 1.5% or less.

  (B) The surface roughness (Ra) of the P2 layer is 0.03 μm or more and 0.50 μm or less.

  (C) The adhesive strength after the moist heat test is 15 N / cm or more, and the adhesive strength retention after the moist heat test is 80% or more.

  Hereinafter, each component will be described.

(Base material layer (P1 layer))
The P1 layer of the present invention contains a polyester resin as a main component. Here, the main constituent component refers to a constituent component contained in excess of 50% by mass.

  Examples of the polyester resin constituting the P1 layer include polyethylene terephthalate, polyethylene-2,6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, and polylactic acid. The polyester resin is preferably composed mainly of polyethylene terephthalate.

  The polyester resin used in the P1 layer of the present invention includes 1) polycondensation of dicarboxylic acid or an ester-forming derivative thereof (hereinafter collectively referred to as “dicarboxylic acid component”) and a diol component, 2) a carboxyl group in one molecule or It can be obtained by a polycondensation of a compound having an ester-forming derivative group and a hydroxyl group, and a combination of the above 1) and 2). The polycondensation of the polyester resin can be performed by a conventional method.

  As the dicarboxylic acid component in the case of obtaining a polyester resin by the method 1), malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid , Aliphatic dicarboxylic acids such as azelaic acid, methylmalonic acid, ethylmalonic acid, alicyclic dicarboxylic acids such as adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4'-diphenylsulfo Aromatic dicarboxylic acids such as dicarboxylic acid, 5-sodium sulfoisophthalic acid, phenylendanedicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, 9,9′-bis (4-carboxyphenyl) fluorenic acid, or ester derivatives thereof A typical example. These may be used alone or in combination. Further, dicarboxyl obtained by condensing at least one carboxy terminus of the above dicarboxylic acid component with oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid, and derivatives thereof or a combination of a plurality of such oxyacids. Compounds can also be used.

  As the diol component in the case of obtaining a polyester resin by the method 1), ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1, Aliphatic diols such as 3-butanediol, cycloaliphatic diols such as cyclohexanedimethanol, spiroglycol, isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9′-bis A typical example is an aromatic diol such as (4-hydroxyphenyl) fluorene. These may be used alone, or a plurality of types may be used as necessary. In addition, a dihydroxy compound formed by condensing a diol with at least one hydroxy terminal of the diol component described above can also be used.

  Examples of compounds having a carboxyl group or an ester-forming derivative group thereof and a hydroxyl group in one molecule when a polyester resin is obtained by the method 2) include l-lactide, d-lactide, and hydroxybenzoic acid. Examples thereof include oxyacids and derivatives thereof, oligomers of oxyacids, and those obtained by condensing an oxyacid with one carboxyl group of dicarboxylic acid. The compound having a carboxyl group or an ester-forming derivative group thereof and a hydroxyl group in one molecule may be used singly or plural kinds may be used as necessary.

  The polyester resin constituting the P1 layer may be a single type or a blend of two or more types of polyester resins. Here, the term “single species” means that the types and compositions of the components are the same.

  In the present invention, the intrinsic viscosity IV of the polyester resin constituting the P1 layer is preferably 0.65 dl / g or more and 0.80 dl / g or less. When the intrinsic viscosity IV is 0.65 dl / g or more, the moisture and heat resistance of the sheet is easily improved. In addition, when the intrinsic viscosity IV is 0.8 dl / g or less, the extrudability of the resin when producing the P1 layer is good, and sheet molding is likely to be easy.

  In this invention, it is preferable that the terminal carboxyl group amount of the polyester resin which comprises P1 layer is 24 equivalent / tons or less. When the amount of the terminal carboxyl group is 24 equivalents / ton or less, the adhesiveness with the P2 layer may be slightly lowered. However, when the amount is 24 equivalents / ton or less, the moisture and heat resistance of the P1 layer is improved. Long-term durability of the protective sheet is easily improved. The lower limit value of the terminal carboxyl group amount is not particularly limited, but it is difficult to substantially make it less than 1 equivalent / ton.

  In addition, in this invention, "long-term durability" represents the solar cell back surface protection sheet and the overall durability of the solar cell, and is evaluated by an output retention rate after a moisture and heat resistance test described later. Since the long-term durability is a comprehensive evaluation, it varies depending on various factors. For example, when the heat and humidity resistance and the durability of the P2 layer are lowered, the long-term durability is also lowered.

  In this invention, 18500-40000 are preferable, as for the number average molecular weight of the polyester resin which comprises P1 layer, 19000-35000 are more preferable, 20000-33000 are further more preferable. When the number average molecular weight of the polyester resin constituting the P1 layer is 18500 or more, long-term durability is easily improved. Further, when the number average molecular weight of the polyester resin constituting the P1 is 40000 or less, the polymerization becomes easy, and after the polymerization, the resin is easily extruded by an extruder, and the film formation is also easy.

  In the present invention, the P1 layer is preferably uniaxially or biaxially oriented. When the P1 layer is uniaxially or biaxially oriented, long-term durability can be improved by orientation crystallization.

  In the solar cell back surface protective sheet of the present invention, the polyester resin constituting the P1 layer has a minute endothermic peak temperature TmetaP1 (° C.) obtained by differential scanning calorimetry (DSC), which is the melting point of the polyester resin constituting the P1 layer. When TmP1 (° C.) is used, it is preferably in the range of TmP 1-90 ° C. to TmP 1-40 ° C., more preferably in the range of TmP 1-80 ° C. to TmP 1-50 ° C., and TmP 1-75 ° C. More preferably, it falls within the range of TmP1-55 ° C. When the TmetaP1 is TmP1-90 ° C. or higher, the residual stress during stretching can be easily eliminated. As a result, the thermal contraction rate of the P1 layer is reduced, and the bonding with the sealing material tends to be easy in the bonding process when the solar cell back surface protection sheet is incorporated into the solar cell. Moreover, when it integrates in a solar cell and uses it under high temperature after bonding, the curvature of a solar cell system will become small, and long-term durability will become easy to improve. Further, when the TmetaP1 is TmP1-40 ° C. or lower, the oriented crystallinity of the P1 layer is improved and the heat and moisture resistance is easily improved. In the solar cell back surface protection sheet of the present invention, when the TmetaP1 of the P1 layer is in the above range, it is easy to achieve both reduction of the heat shrinkage rate and moisture and heat resistance. In the present invention, the heat shrinkage rate is measured by the method described later.

  In the solar cell back surface protective sheet of the present invention, the melting point TmP1 (° C.) of the polyester resin constituting the P1 layer is preferably 220 ° C. or higher, more preferably 240 ° C. or higher, from the viewpoint of enhancing the heat and humidity resistance of the P1 layer. More preferably, it is not lower than ° C. Although there is no restriction | limiting in particular about the upper limit of melting | fusing point TmP1 (degreeC) of the said P1 layer, The thing of 300 degrees C or less is preferable at the point of productivity.

  In the present invention, for the purpose of imparting properties such as light resistance, light reflectivity, light hiding property, designability, and visibility to the P1 layer, a method of containing particles having respective functions is also preferably used.

  For example, in order to improve both light resistance and light reflectivity, titanium oxide particles are contained in the range of 1% by mass to 30% by mass with respect to the resin composition containing the polyester resin constituting the P1 layer. Is preferred. This makes it possible to exhibit the effect of reducing coloration due to deterioration of the sheet over a long period of time by utilizing the ultraviolet absorbing ability and light reflectivity of the titanium oxide particles. If the content of the titanium oxide particles is 1% by mass or more, sufficient ultraviolet resistance can be easily obtained. If content of the said titanium oxide particle is 30 mass% or less, the adhesiveness between layers will improve easily. The lower limit of the content range of the titanium oxide particles is preferably 1% by mass, more preferably 2% by mass, and further preferably 3% by mass. The upper limit of the content range of the titanium oxide particles is preferably 30% by mass, more preferably 25% by mass, and further preferably 20% by mass.

  In the present invention, it is more preferable to use rutile type titanium oxide as the titanium oxide particles in the case where the titanium oxide particles are contained in the P1 layer in terms of high light reflectivity and light resistance.

  In the present invention, as a method of adding particles to the resin composition containing the polyester resin constituting the P1 layer, a method of melt-kneading the polyester resin and particles using a vent type biaxial kneading extruder or tandem type extruder Is preferably used. Here, when the polyester resin is subjected to a thermal load when the polyester resin contains particles, the polyester resin deteriorates not a little. Therefore, a high-concentration master pellet having a larger amount of particles added than the amount of particles contained in the resin composition containing the polyester resin constituting the P1 layer is prepared, mixed with the polyester resin and diluted, and the predetermined P1 layer The particle content is preferably from the viewpoint of heat and humidity resistance.

  In the present invention, in addition to the above titanium oxide particles, the P1 layer has a heat stabilizer, an oxidation stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, and an organic material as long as the effects of the present invention are not impaired as necessary. Additives such as system / inorganic lubricants, organic / inorganic fine particles, fillers, nucleating agents, dyes, dispersants, coupling agents, bubbles, etc. may be blended.

For example, when a polyester mainly composed of 1,4-cyclohexylenedimethylene terephthalate unit (hereinafter sometimes referred to as CHT unit) is selected as the heat stabilizer, the content of P1 layer It is preferable that it is 20 mass% or less with respect to the whole resin composition containing the polyester resin to comprise. By using polyester having the CHT unit as a main constituent, it is possible to impart moisture and heat resistance to the P1 layer and to control the surface roughness (Ra) of the P1 layer. Thereby, the adhesiveness of P2 layer and P1 layer can be improved. Moreover, since the surface roughness (Ra) of the P2 layer is controlled by the surface roughness (Ra) of the P1 layer, the adhesion between EVA and the P2 layer can be enhanced. The effect of improving the adhesion to EVA is particularly large when the surface roughness (Ra) of the P1 layer is 0.03 μm to 0.50 μm. In addition, surface roughness (Ra) represents arithmetic mean roughness.
In the present invention, the P1 layer may have a laminated structure. For example, a laminated structure of a P11 layer excellent in wet heat resistance and a P12 layer containing a high concentration of an ultraviolet absorber or titanium oxide particles having an ultraviolet absorbing ability is preferably used. When using such P1 layer, it is preferable from a light-resistant viewpoint that the structure of the solar cell back surface protection sheet | seat of this invention will be P12 layer / P11 layer // P2 layer. In this case, as the resin used for the P11 layer and the P12 layer, those exemplified for the P1 layer can be suitably used as appropriate.

  In the solar cell back surface protective sheet of the present invention, the thickness of the P1 layer is preferably 30 μm or more and 500 μm or less. When the thickness of the P1 layer is 30 μm or more, the partial discharge voltage is large, and dielectric breakdown does not easily occur when used under a high voltage, which is preferable as a solar cell back surface protection sheet. Moreover, when the thickness is 500 μm or less, the processability is good, and when used as a solar battery back surface protection sheet, the entire thickness of the solar battery cell is easily reduced, which is preferable. The lower limit of the thickness range of the P1 layer is preferably 30 μm, more preferably 38 μm, and even more preferably 50 μm. The upper limit of the thickness range of the P1 layer is preferably 500 μm, more preferably 400 μm, and even more preferably 300 μm.

(Easily adhesive layer (P2 layer))
The solar cell back surface protection sheet of the present invention has an easy adhesion layer (P2 layer) adjacent to at least one surface of the P1 layer.

  In the solar cell back surface protective sheet of the present invention, the P2 layer preferably includes a urethane resin component, a melamine resin component, and an epoxy resin component.

  In the present invention, the P2 layer is preferably a layer formed from a coating composition containing a urethane resin, a melamine resin, and an epoxy resin, and the total solid content in the coating composition forming the P2 layer On the other hand, it is preferable to contain 80% by mass or more and 90% by mass or less of urethane resin, 7% by mass or more and 17% by mass or less of melamine resin, and 2% by mass or more and 7% by mass or less of epoxy resin.

  When the content of the urethane resin is 80% by mass or more, the P2 layer has flexibility and is difficult to peel off from the EVA layer. When the content of the urethane resin is 90% by mass or less, the urethane resin is sufficiently cross-linked by the melamine resin and the epoxy resin, and the durability of the P2 layer is easily improved.

  When the content of the melamine resin is 7% by mass or more, the durability of the P2 layer tends to be high. When the content of the melamine resin is 17% by mass or less, the P2 layer has flexibility, and cracks and cracks are less likely to occur.

  When the content of the epoxy resin is 2% by mass or more, the durability of the P2 layer tends to be high. When the content of the melamine resin is 7% by mass or less, the P2 layer has flexibility, and cracks and cracks are less likely to occur.

  In the coating composition for forming the P2 layer in the present invention, the content of the olefin resin is preferably 1% by mass or less with respect to the total solid content in the coating composition. When the content of the olefin resin is 1% by mass or less, the adhesion between the P1 layer and the P2 layer tends to be strong.

(Polyester polyurethane resin)
In the solar cell back surface protective sheet of the present invention, the P2 layer is preferably a layer formed from a coating composition containing a polyester polyurethane resin as a urethane resin component.

  In the present invention, the polyester polyurethane resin is a resin containing a urethane bond in the main chain, and is obtained, for example, by a reaction between a polyester polyol compound and a polyisocyanate compound.

  The polyester polyurethane resin preferably has an anionic group from the viewpoint of dispersibility in an aqueous medium. Here, the anionic group means a functional group that becomes an anion in an aqueous medium such as a carboxyl group, a sulfonic acid group, a sulfuric acid group, and a phosphoric acid group.

  In the present invention, the polyester of the polyester polyurethane resin is preferably a polyester synthesized from a dicarboxylic acid component and a diol component shown below.

  Dicarboxylic acid components include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid, ethylmalonic acid, etc. Aliphatic dicarboxylic acids such as aliphatic dicarboxylic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5- Naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid, 5- Sodium sulfoisophthalic acid Phenyl ene boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic acid, 9,9'-bis (4-carboxyphenyl) and aromatic dicarboxylic acids such as fluorene acid are preferably used.

  Examples of the diol component include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, Aromatic diols such as methanol, spiroglycol and isosorbide, aromatic diols such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol and 9,9'-bis (4-hydroxyphenyl) fluorene Etc. are preferably used.

  By using the above-mentioned polyester polyurethane resin, it is easy to form a P2 layer having good adhesion to the P1 layer and excellent durability.

(Isocyanate component used in polyester polyurethane resin)
In the present invention, as the isocyanate component used for the polyester polyurethane resin, one or a mixture of two or more known aromatic, aliphatic and alicyclic diisocyanates can be used. Specific examples of the diisocyanates include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, isophorone diisocyanate, dimaryl diisocyanate, Examples include lysine diisocyanate, hydrogenated 4,4′-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, dimerized isocyanate obtained by converting the carboxyl group of dimer acid to an isocyanate group, and adducts, biurets, and isocyanurates. Further, as the diisocyanates, trifunctional or higher functional polyisocyanates such as triphenylmethane triisocyanate and polymethylene polyphenyl isocyanate may be used.

(Anionic groups to be introduced into polyester polyurethane resin)
In the present invention, in order to introduce an anionic group into the polyester polyurethane resin, a polyol component having a carboxyl group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group or the like can be used. Among these, as the polyol compound having a carboxyl group, 3,5-dihydroxybenzoic acid, 2,2-bis (hydroxymethyl) propionic acid, 2,2-bis (hydroxyethyl) propionic acid, 2,2-bis (Hydroxypropyl) propionic acid, bis (hydroxymethyl) acetic acid, bis (4-hydroxyphenyl) acetic acid, 2,2-bis (4-hydroxyphenyl) pentanoic acid, tartaric acid, N, N-dihydroxyethylglycine, N, N -Bis (2-hydroxyethyl) -3-carboxyl-propionamide and the like.

  The molecular weight of the polyester polyurethane resin can be appropriately adjusted using a chain extender. Examples of the chain extender include compounds having two or more active hydrogens such as amino groups and hydroxyl groups capable of reacting with isocyanate groups. For example, diamine compounds, dihydrazide compounds, and glycols can be used.

(Acid value of polyester polyurethane resin)
In the present invention, the polyester polyurethane resin preferably has an acid value of 25 mg-KOH / g or less. When the acid value of the polyester polyurethane resin is 25 mg-KOH / g or less, when used as a sheet for protecting the back surface of a solar cell, an increase in terminal carboxyl groups due to long-term outdoor use is suppressed, and adhesion It becomes easy to form an easy-adhesion layer excellent in long-term durability without impairing the properties. As a minimum of the range of the acid value of a polyester polyurethane resin, 5 mg-KOH / g is more preferable, and 8 mg-KOH / g is further more preferable. The upper limit of the acid value range of the polyester polyurethane resin is preferably 25 mg-KOH / g, more preferably 20 mg-KOH / g, and still more preferably 15 mg-KOH / g. In addition, although the lower limit of an acid value is not specifically limited, It is difficult to make it substantially less than 0.1 mg-KOH / g.

(Elongation at break of polyester polyurethane resin)
The polyester polyurethane resin used in the present invention preferably has a breaking elongation of 300% or more and 3000% or less when a 150 μm thick sheet made of polyester polyurethane resin is produced.

  A method for producing a 150 μm-thick sheet made of the polyester polyurethane resin is as follows.

  When the polyester polyurethane resin is dissolved or dispersed in a solvent or the like, the polyester polyurethane resin is applied on a glass plate using a film applicator, and then dried for 48 hours at 23 ° C. and 65% RH. Thus, a sheet having a thickness of 150 μm is obtained.

  If the polyester polyresin is not dissolved or dispersed in a solvent or the like and is solid at room temperature (25 ° C.), it is heated and dissolved at a temperature of the softening point temperature of the polyester polyurethane resin + 20 ° C. to form a sheet, A sheet having a thickness of 150 μm is prepared.

  The sheet produced by the above method is cut out to 10 × 100 mm, and the elongation at break is measured based on ASTM-D882 (1997). In addition, the measurement is 10 mm between chucks, the pulling speed is 300 mm / min, the number of measurements is n = 5, and the average value is the elongation at break. In addition, it is determined that a polyester polyurethane resin in which a sheet is difficult to produce under the above-described sheet production conditions is “not measurable”.

  When the breaking elongation of a sheet having a thickness of 150 μm obtained by the above method is 300% or more, it becomes easy to form an easy-adhesive layer excellent in adhesion to a solar cell sealing material (for example, EVA sheet), particularly moisture and heat resistance. Moreover, if it is 3000% or less, it will become easy to set it as an easily bonding layer with little change of adhesiveness (it is excellent in adhesion durability) even if it uses it for a long period of time. In addition, stickiness and blocking are less likely to occur when an easy-adhesion layer is formed, and the processability is likely to be excellent.

(Glass transition temperature Tg of polyester polyurethane resin)
The glass transition temperature Tg of the polyester polyurethane resin when constituting the P2 layer in the present invention is preferably 0 ° C. or higher and 50 ° C. or lower. When the glass transition temperature Tg is 0 ° C. or higher, the adhesion to EVA on the solar battery cell side may be slightly lowered, but it is preferable because it is easily excellent in moisture and heat resistance. Moreover, it is preferable for Tg to be 50 ° C. or lower because the film-forming property when forming the P2 layer is easily improved or the adhesiveness is easily improved. A more preferable range of the glass transition temperature Tg of the polyester polyurethane resin constituting the P2 layer is 0 ° C. or more and 35 ° C. or less, and a more preferable range is 0 ° C. or more and 20 ° C. or less.

  These polyester polyurethane resins can be obtained by using commercially available resins such as “Hydran” (registered trademark) series manufactured by DIC Corporation.

(Crosslinking agent)
In order to enhance durability such as adhesion and heat resistance, moisture resistance, and blocking resistance of the P2 layer in the present invention, it is preferable to use a crosslinking agent. The cross-linking agent as used in the present invention refers to a compound or resin having reactivity that links polymers and changes physical and chemical properties. The cross-linking agent used in the present invention is not particularly limited, and any cross-linking agent can be suitably used as long as it has an effect of increasing the mechanical strength of the P2 layer. For example, an isocyanate cross-linking agent, an epoxy cross-linking agent, a melamine cross-linking agent, an oxazoline cross-linking agent, a carbodiimide cross-linking agent and the like are preferably used, and a melamine cross-linking agent, an epoxy cross-linking agent and a carbodiimide cross-linking agent are particularly preferably used. It is also a preferred technique to select and use two or more of these crosslinking agents. In particular, it is preferable to use a melamine crosslinking agent and an epoxy crosslinking agent in combination since the polyester polyurethane resin having a low acid value used in the present invention can be favorably crosslinked. These cross-linking agents include, for example, the isocyanate cross-linking agent “Elastolon” (registered trademark) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., the melamine cross-linking agent “Beckamine” (registered trademark) manufactured by DIC Corporation, and the oxazoline cross-linking agent “Epocross” manufactured by Nippon Shokubai Co., Ltd. "(Registered trademark), carbodiimide crosslinking agent" Carbodilite "(registered trademark) manufactured by Nisshinbo Chemical Co., Ltd., epoxy crosslinking agent" EPICLON "(registered trademark) manufactured by DIC Corporation, epoxy crosslinking agent" Denacol "manufactured by Nagase ChemteX Corporation ( A commercially available cross-linking agent such as (registered trademark) can be obtained and used.

  As for the addition amount of the crosslinking agent in P2 layer of the solar cell back surface protection sheet of this invention, 10 mass% or more and 20 mass% or less are preferable. Moreover, it is preferable that the crosslinking agent uses a melamine resin as a melamine crosslinking agent, and an epoxy resin as an epoxy crosslinking agent together. The content of the melamine resin is preferably 7% by mass or more and 17% by mass or less with respect to the resin component constituting the P2 layer. The content of the epoxy resin is desirably 2% by mass or more and 7% by mass or less with respect to the resin component constituting the P2 layer. When the content of the crosslinking agent is 10% by mass or more, the durability of the P2 layer is likely to be favorable when bonded to the solar battery cell. Moreover, when content of a crosslinking agent is 20 mass% or less, P2 layer has a softness | flexibility and it becomes difficult to peel.

(Coating composition)
Examples of the solvent for the coating liquid (coating composition) for forming the P2 layer in the solar cell back surface protection sheet of the present invention include toluene, xylene, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, and methyl isobutyl ketone. , Tetrahydrofuran, dimethylformamide, dimethylacetamide, methanol, ethanol, water and the like, and the properties of the coating liquid may be either an emulsion type or a dissolution type. In recent years, environmental protection, resource saving, exhaust problems of organic solvents at the time of manufacture have been emphasized, so water-soluble solvent-based coating liquid or water-based emulsion-type coating liquid Is a preferred form. In the case of a coating liquid mainly composed of water, it may contain a solvent used for emulsifying the resin component or an organic solvent as a dispersion aid. A dissolution type coating composition containing no auxiliary is preferred. Further, the method for emulsifying urethane resin, melamine resin, and epoxy resin in water-based emulsion is not particularly limited, and can be prepared by a device widely known to those skilled in the art as a solid / liquid stirring device or an emulsifier. it can.

  The P2 layer of the present invention is preferably obtained by applying and drying a coating composition containing the urethane resin, melamine resin, and epoxy resin on the P1 layer.

  In the solar cell back surface protective sheet of the present invention, the P2 layer is formed by applying a heat treatment at 150 ° C. or more and 250 ° C. or less after applying the polyester polyurethane resin and a resin composition containing a crosslinking agent to the P1 layer. It is preferable that it is a layer. When the heat treatment temperature is 150 ° C. or higher, the degree of cross-linking of the cross-linking agent contained in the P2 layer is sufficient, and the wet heat property of the easy-adhesion layer is easily improved. Further, when the heat treatment temperature is 250 ° C. or less, thermal degradation of the P1 layer and the P2 layer hardly occurs and the sheet characteristics are easily improved. The lower limit of the heat treatment temperature range is preferably 150 ° C. The upper limit of the heat treatment temperature range is preferably 250 ° C, more preferably 230 ° C, and further preferably 210 ° C.

  In the solar cell back surface protective sheet of the present invention, the thickness of the P2 layer is preferably 0.1 μm or more and 2 μm or less. When the thickness is 0.1 μm or more, the adhesion with the sealing material is improved, and delamination hardly occurs. Moreover, when it is 2 μm or less, it becomes possible to develop an adhesive force in a short time (accelerating the crosslinking reaction between the main agent and the curing agent), and as a result, the moisture and heat resistance of the easy-adhesion layer is easily improved. The lower limit of the thickness range of the P2 layer is preferably 0.1 μm, more preferably 0.15 μm, and still more preferably 0.2 μm. The upper limit of the thickness range of the P2 layer is preferably 2 μm, and more preferably 1 μm.

  The P2 layer is preferably provided by in-line coating during the formation of the P1 layer from the viewpoints of simplifying the manufacturing process, good film forming properties, reduced thickness unevenness, and coating defects.

  In the solar cell back surface protective sheet of the present invention, the P2 layer has a known heat stabilizer, lubricant, antistatic agent, anti-blocking agent, dye, pigment, photosensitizer, surfactant, ultraviolet absorber, etc. Various additives can be added as needed.

(Solar cell backside protection sheet)
The solar cell back surface protection sheet of the present invention has a heat shrinkage ratio of 1.5% or less after heat treatment at 150 ° C. for 30 minutes. When the heat shrinkage ratio is 1.5% or less, generation of wrinkles due to heat shrinkage of the P1 layer at the time of close contact with EVA can be suppressed, and the decrease in adhesion is small even in the subsequent moisture-resistant heat treatment. It can be set as the battery back surface protection sheet.

  Moreover, the sheet | seat for solar cell back surface protection of this invention is 0.03 micrometer or more and 0.50 micrometer or less in the surface roughness (Ra) of P2 layer. When the surface roughness (Ra) of the P2 layer is 0.03 μm or more, it is possible to produce a solar cell back surface protective sheet having high initial adhesive strength, which is less likely to contain bubbles when closely attached to EVA. In addition, in this invention, adhesive strength represents the adhesive strength of P2 layer and EVA sheet | seat measured by the below-mentioned method. In the above measurement, the EVA sheet, the P2 layer, and the P1 layer itself may be destroyed before peeling occurs between the P2 layer and the EVA sheet, but in the present invention, the measurement values obtained in these cases are also the P2 layer. And the adhesive strength of the EVA sheet.

  The sheet for protecting the back surface of the solar cell of the present invention has an adhesive strength after the moisture and heat test of 15 N / cm or more and an adhesive strength retention after the moisture and heat test of 80% or more. Since the adhesive strength after the heat and humidity resistance test is 15 N / cm or more, the solar cell can be used as a protective material without causing a decrease in the output of the solar cell even when the solar cell is placed under severe conditions of high temperature and high humidity outdoors. Can continue to play a role. In addition, since the adhesive strength retention after the moisture and heat resistance test is 80% or more, the sheet serves as a protective material for a long time without causing wrinkles in the sheet for protecting the back surface of the solar cell due to a decrease in adhesion. I can do it.

  The solar cell back surface protective sheet of the present invention is provided with a layer having other functions such as gas barrier property and ultraviolet resistance on one side surface of the P1 layer (however, the surface opposite to the surface in contact with the P2 layer). be able to. As a method of providing these layers, a method of separately preparing materials to be laminated with the P1 layer and thermocompression bonding with a heated group of rolls (thermal laminating method), a method of bonding together with an adhesive (adhesion method) ) In addition, a method of dissolving the material for forming the material to be laminated in a solvent and applying the solution onto the P1 layer prepared in advance (coating method), electromagnetic wave irradiation after applying a curable material onto the P1 layer A method of curing by heat treatment or the like, a method of depositing / sputtering a material to be laminated on the P1 layer, a method combining these, and the like can be used.

The solar cell back surface protection sheet of the present invention preferably has a water vapor transmission rate of 0.0001 g / m ² · day or more and 10 g / m ² · day or less from the viewpoint of gas barrier properties. More preferably, it is 0.0001 g / m ² · day or more and 5 g / m ² · day or less, and most preferably 0.0001 g / m ² · day or more and 3 g / m ² · day or less. By setting it as this range, deterioration inside the solar cell due to permeation of gas from the back sheet to the sealing material can be prevented. Here, the water vapor transmission rate is a value measured according to the JIS-K7129B method (1992). The water vapor transmission rate in the present invention can be adjusted by the thicknesses of the P1 layer and the P2 layer, and the water vapor transmission rate decreases as the thickness increases.

(Method for producing solar cell back surface protection sheet)
The solar cell back surface protection sheet of the present invention can be obtained by, for example, a production method including the following steps (1) to (4).
(1) Step of obtaining a non-oriented polyester film by melting and kneading a resin composition containing a polyester resin constituting the P1 layer with an extruder and then extruding and cooling and solidifying on a cooling drum (2) Unoriented polyester film Using a stretching roll and a stretching nip roll in the longitudinal direction at a stretching temperature of 70 to 120 ° C. and a stretching ratio of 2.0 to 4.0 times to obtain a uniaxially oriented polyester film (however, the stretching roll The surface roughness (Ra) is 0.5 to 1.5 μm, and the nip pressure between the stretching roll and the stretching nip roll is 0.4 to 1.0 MPa)
(3) Step of stretching a uniaxially oriented polyester film in the width direction at a stretching temperature of 70 to 150 ° C. and a stretching ratio of 3.0 to 4.0 to obtain a biaxially oriented polyester film (4) Biaxially oriented polyester The process which relaxes 0-10% in the width direction, heat-processing a film at 205-240 degreeC Hereinafter, an example is given and demonstrated about the manufacturing method of the solar cell back surface protection sheet | seat of this invention. This is an example, and the present invention should not be construed as being limited to the product obtained by such an example.

  First, the manufacturing method of the polyester resin which is a raw material which comprises P1 layer is demonstrated below.

  In the sheet for protecting the back surface of the solar cell of the present invention, the polyester resin used as the raw material for the P1 layer is, for example, polycondensation by diesterification or esterification of dicarboxylic acid or its ester derivative and diol by a well-known method. Can be obtained.

  Examples of the reaction catalyst used for the polycondensation include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, germanium compounds, titanium compounds, and phosphorus compounds. I can do it. Among them, it is preferable to add an antimony compound, a germanium compound, or a titanium compound at an arbitrary stage before the polycondensation of the polyester resin is completed. Moreover, when using a germanium compound, it is preferable to add germanium compound powder as it is.

  In addition, in order to control the number average molecular weight of the polyester resin to 18500-40000, after polycondensing a polyester resin having a molecular weight of about 18000, the number average molecular weight is 190 ° C. to less than the melting point of the polyester resin. So-called solid phase polymerization, in which heating is performed under reduced pressure or a flow of an inert gas such as nitrogen gas, is preferable. Solid phase polymerization is preferably performed in that the number average molecular weight can be increased without increasing the amount of terminal carboxyl groups of the thermoplastic resin.

  Next, the manufacturing method of a P1 layer is demonstrated below.

  In the present invention, the P1 layer may have a single film structure or a laminated structure as described above.

  The manufacturing method when the P1 layer has a single film configuration uses a method (melt cast method) in which the P1 layer raw material is heated and melted in an extruder and extruded from a die onto a cast drum cooled to be processed into a sheet shape. Can do. As another method, the raw material for the P1 layer is dissolved in a solvent, and the solution is extruded from a die onto a support such as a cast drum or an endless belt to form a film, and then the solvent is dried and removed from the film layer. A method of processing into a shape (solution casting method) or the like can also be used.

  In addition, in the manufacturing method when the P1 layer has a laminated structure, when the material of each layer to be laminated is mainly composed of a thermoplastic resin, two different thermoplastic resins are put into two extruders and melted. A method of co-extrusion on a cast drum cooled from a die to process it into a sheet (co-extrusion method), a method of laminating a sheet made of a single film into an extruder, melting and extruding and extruding from the die (Melt lamination method) can be used.

  In the manufacturing method of the solar cell back surface protection sheet of the present invention, the manufacturing method in the case of using a uniaxially or biaxially stretched base material layer as the P1 layer is as follows.

  First, as the step (1), a resin composition containing a polyester resin constituting the P1 layer is charged as a raw material into an extruder (a plurality of extruders in the case of a laminated structure), melted and extruded from a die ( In the case of a laminated structure, it is coextruded) and cooled and solidified on a cooling drum to obtain an unoriented polyester film.

  In the method for producing a solar cell back surface protection sheet of the present invention, as the step (2), the unstretched sheet after being cooled by a cooling drum is guided to a roll group heated to a temperature of 70 to 120 ° C. The film is stretched 2.0 to 4.0 times in the direction (longitudinal direction, that is, the sheet traveling direction). At this time, the unstretched sheet is stretched between a stretching roll and a stretching nip roll. Here, the roughness (Ra) of the P1 layer is adjusted by setting the surface roughness (Ra) of the stretching nip roll to 0.5 to 1.5 μm and the stretching nip pressure to 0.5 to 1.5 MPa, and P2 The roughness (Ra) of the layer can be adjusted so as to fall within the scope of the present application. After stretching, it is preferable to cool with a roll group having a temperature of 20 to 50 ° C.

  Subsequently, in the step (3), the both ends of the sheet are guided to the tenter while being gripped by clips, and in the atmosphere heated to a temperature of 70 to 150 ° C., 3 in the direction perpendicular to the longitudinal direction (width direction). Stretch from 0 to 4.0 times.

  The draw ratio is 2.5 to 5 times in the longitudinal direction and the width direction, respectively, but the area ratio (longitudinal draw ratio x transverse draw ratio) is preferably 6 to 15 times. When the area magnification is 6 times or more, the obtained biaxially stretched sheet is likely to have sufficient long-term durability, and when the area magnification is 15 times or less, it is difficult to break during stretching.

  As the biaxial stretching method, either the sequential biaxial stretching method in which the stretching in the longitudinal direction and the width direction is separated as described above or the simultaneous biaxial stretching method in which the stretching in the longitudinal direction and the width direction is performed simultaneously. It does not matter.

  Since the biaxial stretching method often cannot be relaxed in the longitudinal direction, when the stretching ratio in the longitudinal direction is high, the heat shrinkage stress remains in the film, and when the film becomes a film having a high heat shrinkage rate and is bonded to EVA. A film with low adhesion may be formed. Therefore, the draw ratio in the longitudinal direction is preferably 3.1 times or less. By setting the draw ratio in the longitudinal direction to 3.1 times or less, the thermal shrinkage rate hardly exceeds 1.5%. When the thermal shrinkage rate is larger than 1.5%, the film is wrinkled due to the shrinkage of the film when pasted with EVA, resulting in a film having low adhesion. In addition, when forming the P2 layer by in-line coating provided in the manufacturing process of the P1 layer, in the case of the sequential biaxial stretching method, after the uniaxially stretched sheet, in the case of the unstretched sheet or the simultaneous biaxial stretching method In this case, after forming an unstretched sheet, a coating process may be provided, and a coating composition to be a material of the P2 layer may be applied. At this time, from the viewpoint of improving the wettability of the coating composition on the support and improving the adhesive force, it is also preferable to perform a corona treatment on the surface of the P1 layer as the base material layer immediately before the coating step.

  As the step (4), in order to complete the crystal orientation of the obtained biaxially stretched sheet and to provide flatness and dimensional stability, Relax 0-10% in the direction. The heat treatment time is preferably 1 to 30 seconds. In general, when the heat treatment temperature is low, the thermal contraction rate of the sheet is large. Therefore, it is preferable that the heat treatment temperature is high in order to provide high thermal dimensional stability. However, when the heat treatment temperature is too high, the orientation crystallinity is lowered, and as a result, the formed sheet may be inferior in heat and moisture resistance. Therefore, the lower limit of the heat treatment temperature is 205 ° C, preferably 210 ° C, and more preferably 215 ° C. Moreover, the upper limit of the said heat processing temperature is 240 degreeC, and 235 degreeC is more preferable.

  After the heat treatment, it is gradually cooled down and then cooled to room temperature.

  Subsequently, if necessary, the substrate layer of the solar cell back surface protection sheet of the present invention can be formed by performing a corona discharge treatment or the like in order to further enhance the adhesion to other materials and winding up.

(Another aspect of the method for producing a solar cell back surface protection sheet)
As another aspect of the manufacturing method of the solar cell back surface protection sheet of this invention, the manufacturing method including the following process (1 ')-(4') is mentioned.
(1 ′) On the cooling drum of Tg−70 ° C. or more and Tg−30 ° C. or less of the polyester resin constituting the P1 layer after melt-kneading the resin composition containing the polyester resin constituting the P1 layer with an extruder. Step of obtaining a non-oriented polyester film by cooling and solidifying for 20 seconds to 120 seconds at (2 ') A non-oriented polyester film is stretched at a stretching temperature of 70 to 120 ° C. in the longitudinal direction using a stretching roll and a stretching nip roll. Step of obtaining a uniaxially oriented polyester film by stretching at a magnification of 2.0 to 4.0 times (3 ′) A uniaxially oriented polyester film is stretched in the width direction at a stretching temperature of 70 to 150 ° C. and a stretching ratio of 3.0 to 4. Step of obtaining biaxially oriented polyester film by stretching at 0 times (4 ′) 0-1 in the width direction while heat treating the biaxially oriented polyester film at 205-240 ° C. Step of Relaxing by 0% In another aspect (hereinafter referred to as “this aspect”) of the method for producing the solar cell back surface protection sheet of the present invention, the surface temperature of the cooling drum is configured as the P1 layer in the step (1 ′). The polyester resin is Tg-70 ° C. or higher and Tg-30 ° C. or lower, and the time (residence time) in which the non-oriented polyester film is in contact with the cooling drum is 20 to 120 seconds to cool and solidify. Get.

  By setting the surface temperature of the cooling drum to Tg-30 ° C. or less, thermal crystallization hardly occurs. Moreover, the heating before the next extending | stretching can be made easy by making the surface temperature of the said cooling drum into Tg-70 degreeC or more.

  In this embodiment, the time during which the unoriented polyester film is in contact with the cooling drum (residence time) is 20 seconds to 120 seconds. If the residence time is 20 seconds or longer, the unoriented polyester film is sufficiently cooled and enters the longitudinal stretching step, so that the variation in thermal crystallization is reduced and the surface roughness (Ra) is easily controlled. . In addition, when the residence time is 120 seconds or less, heating when stretching in the longitudinal direction is facilitated without being overcooled. Further, since the residence time of the cooling drum is not too long, it is not necessary to enlarge the drum or reduce the rotation speed of the drum, and it is difficult to increase the cost.

  In this embodiment, by adjusting the surface temperature and the residence time as described above, the surface roughness (Ra) of the P2 layer is adjusted by adjusting the surface roughness (Ra) of the P1 layer under the film forming conditions. It can adjust so that it may enter into the range of this, As a result, adhesiveness with EVA can be improved.

  Next, as the step (2 ′), the unstretched sheet cooled by the cooling drum is guided to a group of rolls heated to a temperature of 70 to 120 ° C., and the longitudinal direction (longitudinal direction, that is, the traveling direction of the sheet). To 2.0 to 4.0 times.

  In this embodiment, the surface roughness (Ra) and the stretching nip pressure, which are essential in the step (2), are mainly used to adjust the surface roughness (Ra) in the step (1 ′). Is not necessarily within the range of the step (2). However, from the point of more reliably controlling the surface roughness (Ra) of the P1 layer and the P2 layer, the surface roughness (Ra) of the stretching nip roll in the step (2 ′) is 0.5 to 1.5 μm, The nip pressure between the stretching roll and the stretching nip roll is preferably 0.5 to 1.5 MPa.

  The steps (3 ′) and (4 ′) in this embodiment are the same as the steps (3) and (4).

  After the heat treatment in the step (4 '), the solution is gradually cooled gradually and then cooled to room temperature.

  Subsequently, if necessary, the substrate layer of the solar cell back surface protection sheet of the present invention can be formed by performing a corona discharge treatment or the like in order to further enhance the adhesion to other materials and winding up.

(Method for forming P2 layer)
As a method of forming the P2 layer on the P1 layer, a known coating method can be used. As the coating method, various methods can be applied. For example, a roll coating method, a dip coating method, a bar coating method, a die coating method, a gravure roll coating method, or a combination of these methods can be used. it can. In addition, a method of providing an easy-adhesion layer in-line using a known coating technique during the formation of a polyester film as a substrate is also a preferable method in terms of simplifying the manufacturing process. In addition to in-line coating, using a plurality of extruders, the P1 layer raw material and the P2 layer raw material are melted in separate extruders and co-extruded on a cast drum cooled from the die to form a sheet. Processing (coextrusion method), P1 layer produced by a single film, P2 layer material is put into an extruder, melt extruded and laminated while extruding from the die (melt laminating method), P1 layer and P2 layer Are prepared separately, and are thermocompression-bonded by a heated roll group (thermal laminating method), a method of bonding via an adhesive (adhesion method), or other, P2 layer raw materials are dissolved or dispersed in a solvent. A method (coating method) of applying the solution onto the P1 layer prepared in advance, a method combining these, and the like can be used.

  In the present invention, a coating method in which formation of the P2 layer is easy is a more preferable method. Examples of the method for forming the P2 layer on the P1 layer by the coating method include the in-line coating method applied during the formation of the P1 layer, and the offline coating method applied to the P1 layer after the film formation. However, the in-line coating method is preferably used because it is efficient because it can be formed simultaneously with the formation of the P1 layer and the adhesiveness between the P2 layer and the P1 layer is high. Furthermore, from the viewpoint of improving the adhesion between the P1 layer and the EVA layer, the P22 layer can be provided by off-line coating on the P21 layer provided on the surface of the P1 layer by in-line coating.

  Moreover, when hardening P2 layer after coating, the hardening method can take a well-known method. For example, thermosetting, a method using active rays such as ultraviolet rays, electron beams, radiation, or a combination of these methods can be applied. In the present invention, a heat curing method using a hot air oven is preferred. Furthermore, in the curing with a hot air oven, the method of increasing the drying temperature stepwise, such as material preheating / constant rate drying / residual rate drying, is preferable because the solvent does not remain in the P2 layer. Furthermore, it is preferable to perform an aging treatment at an arbitrary temperature after the drying step in terms of promoting a crosslinking reaction between the main agent and the curing agent.

  As a method for forming the P2 layer on the P1 layer serving as the base material by the coating method, a coating composition obtained by dissolving / dispersing the material constituting the P2 layer in a solvent is used as the P1 layer as the base material layer. A means for coating and drying on the top is preferably used. In this case, the solvent to be used is arbitrary, but in the in-line coating method, it is preferable to use water from the viewpoint of safety. In that case, a small amount of an organic solvent that dissolves in water may be added in order to improve applicability and solubility. Examples of such organic solvents include aliphatic or alicyclic alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, diols such as ethylene glycol, propylene glycol, diethylene glycol acetylenic diol, Diol derivatives such as methyl cellosorb, ethyl cellosolve propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as methyl acetate, ethyl acetate and amyl acetate, ketones such as acetone and methyl ethyl ketone, N-methylpyrrolidone and the like Amides and the like, and mixtures thereof can be used, but are not limited thereto. In addition, a small amount of a surfactant can be added to the coating composition in order to improve coating properties and solubility.

  The solar cell back surface protection sheet of the present invention obtained by the above-described method may be subjected to a processing such as heat treatment or aging as necessary within the range where the effects of the present invention are not impaired. As the upper limit of the heat treatment temperature, the glass transition temperature of the polyester resin constituting the P1 layer is −10 ° C. or lower, more preferably the glass transition temperature −20 ° C. or lower, more preferably the glass transition temperature − 30 ° C. or lower. The heat treatment time is 5 seconds or more and 48 hours or less. By heat-treating, the adhesion of the solar cell back surface protective sheet of the present invention can be improved. Moreover, in order to improve the adhesiveness of the solar cell back surface protection sheet | seat of this invention obtained by the said method, you may implement a corona treatment and a plasma treatment.

(Solar cell)
The solar cell of the present invention uses the solar cell back surface protective sheet of the present invention. By using the solar cell back surface protective sheet of the present invention, it is possible to increase the durability or to make it thinner as compared to the conventional solar cell. An example of the configuration is shown in FIG. A power generating element connected with a lead wire for taking out electricity (not shown in FIG. 1) is sealed with a transparent sealing material 2 such as EVA resin, a transparent substrate 4 such as glass, and the solar cell of the present invention. Although it is configured by bonding the back surface protection sheet 1, it is not limited to this and can be used for any configuration. In addition, although the example in the single sheet | seat for solar cell back surface protection of this invention was shown in FIG. 1, according to the other required required characteristic, the composite sheet of the sheet | seat for solar cell back surface protection of this invention and another film It is also possible to use.

Here, in the solar cell of the present invention, the solar cell back surface protection sheet 1 described above is installed on the back surface of the sealing material 2 in which the power generating element 3 is sealed. Here, the solar cell back surface protection sheet of the present invention is preferably arranged so that the P2 layer is in contact with the sealing material 2. By adopting this configuration, it becomes possible to increase resistance to ultraviolet rays reflected from the ground, etc., so that a highly durable solar cell or a reduced thickness can be obtained. Converts energy into electrical energy. Arbitrary according to the purpose, such as crystalline silicon, polycrystalline silicon, microcrystalline silicon, amorphous silicon, copper indium selenide, compound semiconductor, dye sensitization A plurality of these elements can be connected in series or in parallel according to the desired voltage or current. Since the transparent substrate 4 having translucency is located on the outermost surface layer of the solar cell, a transparent material having high weather resistance, high contamination resistance, and high mechanical strength characteristics in addition to high transmittance is used.

  In the solar cell of the present invention, the transparent substrate 4 having translucency can be any material as long as it satisfies the above characteristics. Examples thereof include glass, ethylene tetrafluoride-ethylene copolymer (ETFE), polyfluoride. Vinyl fluoride resin (PVF), polyvinylidene fluoride resin (PVDF), polytetrafluoroethylene resin (TFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytrifluoroethylene chloride resin (CTFE) ), Fluorinated resins such as polyvinylidene fluoride resin, olefinic resins, acrylic resins, and mixtures thereof. In the case of glass, it is more preferable to use a tempered glass. Moreover, when using the resin-made translucent base material, what extended | stretched the said resin uniaxially or biaxially from a viewpoint of mechanical strength is also used preferably. In addition, in order to provide these substrates with adhesion to EVA resin, which is the material of the sealing material 2 of the power generating element 3, the surface is subjected to corona treatment, plasma treatment, ozone treatment, and easy adhesion treatment. Is also preferably performed.

  The sealing material 2 for sealing the power generation element 3 covers and fixes the unevenness of the surface of the power generation element 3 with a resin, protects the power generation element from the external environment, and has translucency in addition to the purpose of electrical insulation. A material having high transparency, high weather resistance, high adhesion, and high heat resistance is used to adhere to the base material, the back sheet, and the power generation element. Examples thereof include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA) resin, ethylene-methacrylic acid copolymer (EMAA), Ionomer resins, polyvinyl butyral resins, and mixtures thereof are preferably used.

  As described above, by incorporating the solar cell back surface protective sheet of the present invention into a solar cell system, it is possible to obtain a highly durable and / or thin solar cell system as compared with conventional solar cells. The solar cell of the present invention can be suitably used for various applications without being limited to outdoor use and indoor use such as a solar power generation system and a power source for small electronic components.

(Characteristic measurement method and evaluation method)
(1) Thickness of P1 layer and P2 layer Using a microtome, a small piece cut in a direction perpendicular to the surface of the solar cell back surface protection sheet was created, and the cross section was taken as a field emission scanning electron microscope "JSM-6700F" (JEOL Co., Ltd.) was used to magnify and photograph 3000 times. From the cross-sectional photograph, the thickness of each of the P1 layer and the P2 layer was measured, and the thickness was obtained by calculating back from the magnification. In addition, the thickness used the cross-sectional photograph of five places arbitrarily selected from the mutually different measurement visual field, and used the average value.

(2) Heat shrinkage rate A test piece having a sample width of 10 mm and a length of 100 mm was sampled by taking 5 samples with the side having a length of 100 mm along the longitudinal direction of the sheet and 5 samples with the direction along the width direction. Each is heated for 30 minutes in an environment of 150 ° C. ± 2 ° C. with a load of 3 g. The length of the test piece after standing to cool is measured, and the thermal shrinkage rate is defined by the following formula.

The longitudinal direction, the width direction, and the average of the thermal shrinkage rates of each of the five samples are taken, and the larger thermal shrinkage rate is defined as the thermal shrinkage rate in the present invention.
(3) Adhesive strength evaluation with an EVA sheet Based on JIS K 6854-2 (1999), the adhesive strength with an EVA sheet was measured. An EVA sheet (manufactured by Sunvic Co., Ltd., fast cure type (500 μm thick sheet)) is stacked on the P2 layer side of the solar cell back surface protection sheet, and a 3 mm thick semi-tempered glass is further stacked on the sheet. After evacuation using a laminator, an evaluation sample (pseudo solar cell module sample) was produced by pressing for 15 minutes with a load of 29.4 N / cm ² under 135 ° C. heating conditions. An adhesive strength test sample having a width of 10 mm and a length of 150 mm was prepared for the adhesive strength test.
As for the peeling method, the semi-tempered glass and the EVA sheet were held on one side, the P2 layer and the P1 layer were held on the other side, 180 ° peeling was performed, and the number of measurements was measured at n = 3. The average value of the three measured values was determined as the value of adhesive strength S0 as follows.

S: When the adhesive strength S0 is 40 N / 10 mm or more A: When the adhesive strength S0 is 15 N / 10 mm or more and less than 40 N / 10 mm B: When the adhesive strength S0 is 10 N / 10 mm or more and less than 15 N / 10 mm C: Adhesion When the strength S0 is less than 10 N / 10 mm, S to A are good, and S is the best among them.

(4) Adhesive strength with EVA sheet after moisture and heat resistance test In the same manner as in the above (2), an evaluation sample (pseudo solar cell module sample) was prepared, and a temperature cooker manufactured by Tabay Espec Co., Ltd. was used. The treatment was performed for 48 hours under the conditions of ° C. and relative humidity 100% RH. Then, according to the said (3) term, adhesive strength S1 with the EVA sheet | seat after a wet heat test was measured, and it determined as follows.

S: When the adhesive strength S1 is 40 N / 10 mm or more A: When the adhesive strength S1 is 15 N / 10 mm or more and less than 40 N / 10 mm B: When the adhesive strength S1 is 10 N / 10 mm or more and less than 15 N / 10 mm C: Adhesion When the strength S1 is less than 10 N / 10 mm D: The adhesive strength S1 that cannot be measured due to sheet breakage S to A is good, and among them, S is the best.

(5) Breaking elongation of polyester polyurethane resin When the polyester polyurethane resin is dissolved or dispersed in a solvent or the like, after applying the polyester polyurethane resin solution or the dispersion on the glass plate using a film applicator, It is dried for 48 hours under the conditions of room temperature 23 ° C. and 65% RH to obtain a sheet having a thickness of 150 μm. When the polyester polyurethane resin is not dissolved or dispersed in a solvent or the like and is solid at room temperature (25 ° C.), the polyester polyurethane resin is heated and dissolved at a temperature of the softening point temperature of the polyester polyurethane resin + 20 ° C. to form a sheet. A sheet having a thickness of 150 μm is obtained.

  The formed sheet was cut out to 10 × 100 mm, and the elongation at break was measured based on ASTM-D882 (1997). The measurement was performed with 10 mm between chucks, a pulling speed of 300 mm / min, the number of measurements was n = 5, and the average value was the elongation at break. In addition, it was judged that the polyester polyurethane resin which is difficult to form into a sheet under the above-described sheet preparation conditions was “not measurable”.

(6) Glass transition temperature Tg of polyester polyurethane resin
Differential scanning calorific value obtained when the temperature was increased from −20 ° C. to 200 ° C. in a differential scanning calorimetry (hereinafter referred to as DSC) at a heating rate of 20 ° C./min by a method based on JIS K-7121 (1987). The glass transition temperature Tg in the measurement chart was determined.

(7) Acid value of urethane resin The acid value of the urethane resin was determined by a method based on JIS K-0070 (1992) neutralization titration method.

(8) Adhesive strength retention after the wet heat resistance test (3) For the adhesive strength measured in (4), the adhesive strength retention was calculated by the following equation.
Adhesive strength retention rate (%) = S1 / S0 × 100 (1)
About the obtained adhesive strength retention, it determined as follows.

S: When the adhesive strength retention is 90% or more A: When the adhesive strength retention is 80% or more and less than 90% B: When the adhesive strength retention is 50% or more and less than 80% C: Adhesive strength retention When the rate is less than 50%, S to B are good, and S is the best among them.

(9) Intrinsic viscosity IV
The polyester resin constituting the P1 layer was dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / ml), and the viscosity of the solution at 25 ° C. was measured using an Ostwald viscometer. Similarly, the viscosity of the solvent was measured. [Η] was calculated by the following equation (2) using the obtained solution viscosity and solvent viscosity, and the obtained value was used as the intrinsic viscosity (IV).

ηsp / C = [η] + K [η] ² · C (2)
(Where ηsp = (solution viscosity / solvent viscosity) −1, K is the Huggins constant (assuming 0.343))
If there is insoluble matter in the solution in which the polyester resin is dissolved, the solution is filtered and the weight of the filtrate is measured, and the value obtained by subtracting the weight of the filtrate from the weight of the measurement sample is measured as the measurement sample weight. .

(10) Terminal carboxyl group amount (in the table, described as COOH amount)
The amount of the terminal carboxyl group of the P1 layer was measured under the following conditions according to the method of Malice. 2 g of the polyester resin constituting the P1 layer was dissolved in 50 mL of o-cresol / chloroform (weight ratio 7/3) at a temperature of 80 ° C., titrated with a 0.05N KOH / methanol solution, and the amount of terminal carboxyl groups was measured. , Equivalent / value expressed as 1 ton of polyester. In addition, the indicator at the time of titration uses phenol red, and the place where it changed from yellowish green to light red is set as the end point of titration.

If there is insoluble matter in the solution in which the polyester composition is dissolved, the solution is filtered and the weight of the filtrate is measured, and the value obtained by subtracting the weight of the filtrate from the weight of the measurement sample is measured. To do. (Document M. J. Malice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)).
(11) Output retention rate after wet heat resistance test Output W1 of a solar cell in which a back sheet having the P2 layer adhered to the P1 layer is sealed with transparent EVA and the back sheet after the wet heat resistance test is sealed with transparent EVA The output maintenance rate after the wet heat resistance test is defined as W2 / W1 × 100 using the output W2 of the battery. S: When the output maintenance rate exceeds 90% A: The output maintenance rate exceeds 70% and is 90% or less In the case of B: When the output maintenance ratio exceeds 50% and is 70% or less C: When the output maintenance ratio is 50% or less (12) Glass transition temperature (Tg) of the polyester resin constituting the P1 layer
In accordance with JIS K7121 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used, and a disk session “SSC / 5200” was used for data analysis. Perform the measurement.

  The resin constituting the P1 layer is cut out from the polyester film using a microtome and used for a measurement sample. 5 mg of the obtained measurement sample was weighed in a sample pan, heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1stRUN), held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. To do. Immediately thereafter, the temperature was increased again from 25 ° C. to 300 ° C. at a rate of temperature increase of 20 ° C./minute, and a 2ndRUN differential scanning calorimetry chart (the vertical axis represents thermal energy and the horizontal axis represents temperature) Get. In the 2ndRUN differential scanning calorimetry chart, in the step change portion of the glass transition, a straight line that is equidistant from the extended straight line of each base line in the vertical axis direction and a curve of the step change portion of the glass transition are The glass transition temperature (Tg) (° C.) is determined from the intersecting point. When two or more stepwise changes in glass transition are observed, the glass transition temperature is obtained for each, and the average of these temperatures is taken as the glass transition temperature (Tg) (° C.) of the sample.

  In each of the above measurements, when the longitudinal direction and the width direction of the film to be measured are unknown, the direction having the maximum refractive index in the film is regarded as the longitudinal direction, and the direction orthogonal to the longitudinal direction is regarded as the width direction.

(13) Surface roughness (Ra)
The surface roughness (Ra) of the polyester film was measured under the following conditions in accordance with JIS-B0601 (1994) using a high-definition fine shape measuring instrument of the stylus method.

Measuring device: 3D fine shape measuring instrument (model ET-4000A manufactured by Kosaka Laboratory)
Analysis equipment: 3D surface roughness analysis system (Model TDA-31, manufactured by Kosaka Laboratory)
Stylus: 0.5 μm tip radius, 2 μm diameter, diamond needle pressure: 100 μN
Measurement direction / calculation method: Measure the film longitudinal direction and width direction 10 times each. The average value of the 20 measurements is defined as the surface roughness.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

(Polyester resin raw material)
1. PET raw material A (used in all Examples and Comparative Examples other than Example 11)
A polycondensation reaction was performed using 100 parts by mass of terephthalic acid as the dicarboxylic acid component, 100 parts by mass of ethylene glycol as the diol component, and magnesium acetate, antimony trioxide, and phosphorous acid as the catalyst. Next, the obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours, and then subjected to solid phase polymerization at 220 ° C. and a vacuum degree of 0.3 Torr for 9 hours to have a melting point of 255 ° C. and an intrinsic viscosity of 0.80 dl / g. A polyethylene terephthalate (PET-A) raw material having a terminal carboxyl group amount of 10 equivalents / ton was obtained.

2. PET raw material B (used in Example 11 and Comparative Example 12)
A polycondensation reaction was performed using 100 parts by mass of terephthalic acid as the dicarboxylic acid component, 100 parts by mass of ethylene glycol as the diol component, and magnesium acetate, antimony trioxide, and phosphorous acid as the catalyst. Next, the obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours to obtain a polyethylene terephthalate (PET-B) raw material having a melting point of 255 ° C., an intrinsic viscosity of 0.65 dl / g, and a terminal carboxyl group content of 25 equivalents / ton. It was.
3. PET raw material A-based titanium oxide master (used in all Examples and Comparative Examples except Examples 5 and 11 and Comparative Examples 10 and 12)
Above 1. 100 parts by mass of the PET resin (PET-A) obtained according to the above and 100 parts by mass of rutile titanium oxide particles having an average particle size of 210 nm are melt-kneaded in a vented 290 ° C. extruder to obtain a titanium oxide raw material (PET raw material). a base titanium oxide master, to prepare a PETa-TiO _2).

4). PET raw material B-based titanium oxide master (used in Example 11 and Comparative Example 12)
2. 100 parts by mass of the PET resin (PET-B) obtained according to the above and 100 parts by mass of rutile-type titanium oxide particles having an average particle diameter of 210 nm are melt-kneaded in a vented 290 ° C. extruder to obtain a titanium oxide raw material (PET raw material). B-based titanium oxide master, to prepare a PETb-TiO _2).

5. PET raw material A-based CHT master (used in all Examples and Comparative Examples other than Examples 6 and 11 and Comparative Examples 10 and 12)
2. 100 parts by mass of the PET resin (PET-A) obtained according to the above and 100 parts by mass of the CHT unit are melt-kneaded in a vented 290 ° C. extruder, and the CHT raw material (PET raw material A-based CHT master, PETa-CHT) Was made.

6). PET raw material B base CHT master (used in Example 11 and Comparative Example 12)
2. 100 parts by mass of the PET resin (PET-A) obtained according to the above and 100 parts by mass of the CHT unit are melt-kneaded in a vented 290 ° C. extruder, and the CHT material (PET material B base CHT master, PETb-CHT) Was made.

(Preparation of easy-adhesion layer coating composition)
After preparing a coating composition A to O having a solid content concentration of 20% by mass using water as a diluent solvent and a resin described in the following section, an acetylenic diol surfactant, “Orphine” manufactured by Nisshin Chemical Co., Ltd. "(Registered trademark) EXP4051F was blended in an amount of 0.5% by mass with respect to each coating composition. The compounding amounts of the resins described in the following items are all solid content ratios.

1. Coating composition A (used in Examples 1 to 11 and Comparative Examples 8 to 12)
・ Aqueous polyester polyurethane resin, 90% by mass of “Hydran” (registered trademark) AP-201 manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
2. Coating composition B (used in Example 12)
Water-based polyester polyurethane resin, 63% by mass of “Hydran” (registered trademark) AP-201 manufactured by DIC Corporation
Water-based polyester polyurethane resin, 27% by mass of “Hydran” (registered trademark) AP-70 manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
3. Coating composition C (used in Example 13)
-Aqueous polyester polyurethane resin, 45% by mass of “Hydran” (registered trademark) AP-201 manufactured by DIC Corporation
-Aqueous polyester polyurethane resin, 45% by mass of "Hydran" (registered trademark) AP-70 manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
4). Coating composition D (used in Example 14)
-Aqueous polyester polyurethane resin, 27% by mass of “Hydran” (registered trademark) AP-201 manufactured by DIC Corporation
Water-based polyester polyurethane resin, 63% by mass of “Hydran” (registered trademark) AP-70 manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
5. Coating composition E (used in Example 15)
-Aqueous polyester polyurethane resin, 90% by mass of “Hydran” (registered trademark) AP-70 manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
6). Coating composition F (used in Example 16)
・ Aqueous polyester polyurethane resin, 90% by mass of “Hydran” (registered trademark) AP-201 manufactured by DIC Corporation
・ Melamine cross-linking agent, 10% by mass of “Beckamine” (registered trademark) PM-80 manufactured by DIC Corporation
7). Coating composition G (used in Example 17)
・ Aqueous polyester polyurethane resin, 90% by mass of “Hydran” (registered trademark) AP-201 manufactured by DIC Corporation
-10% by mass of epoxy cross-linking agent, Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
8). Coating composition H (used in Example 18)
Water-based polyester polyurethane resin, 87% by mass of “Hydran” (registered trademark) AP-201 manufactured by DIC Corporation
-3% by mass of ethylene vinyl acetate (EVA) copolymer resin aqueous dispersion, "Aquatex" (registered trademark) HA-1100 manufactured by Chuo Rika Kogyo Co., Ltd.
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
9. Coating composition J (used in Comparative Example 2)
-90% by mass of water-based polyester polyurethane resin, "Hydran" (registered trademark) HW-140F manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
10. Coating composition K (used in Comparative Example 3)
-Aqueous polyester polyurethane resin, 90% by mass of “Hydran” (registered trademark) AP-20 manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
11. Coating composition L (used in Comparative Example 4)
-Aqueous polyester polyurethane resin, 90% by mass of “Hydran” (registered trademark) AP-40F manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
12 Coating composition M (used in Comparative Example 5)
・ Water-based polyester polyurethane resin, 90% by mass of “Hydran” (registered trademark) HW-350 manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741
13. Coating composition N (used in Comparative Example 6)
-100% by mass of water-based polyester polyurethane resin, "Hydran" (registered trademark) AP-201 manufactured by DIC Corporation
14 Coating composition O (used in Comparative Example 7)
Aqueous polyether polyurethane resin, 90% by mass of “Hydran” (registered trademark) WLS-230 manufactured by DIC Corporation
・ Melamine cross-linking agent, 8% by mass of “Becamine” (registered trademark) PM-80 manufactured by DIC Corporation
-Epoxy crosslinking agent, 2% by mass of Nagase ChemteX Corporation "Denacol" (registered trademark) EX-741

(Film production method)
Example 1
The PET raw material A and the PET raw material A-based titanium oxide master (PETa-TiO ₂ ) and the PET raw material A-based CHT master (PETa-CHT) described in the above section (Polyester-based resin raw material) that were vacuum-dried at 180 ° C. for 2 hours. The mixture was prepared so that the amount of particles was the concentration shown in Table 1, melted and kneaded in an extruder at 290 ° C., and introduced into a T die die. Next, the sheet was melt-extruded into a sheet form from a T-die die and adhered and cooled and solidified by an electrostatic application method on a cooling drum maintained at a surface temperature of 25 ° C. to obtain an unstretched sheet.

  Subsequently, the unstretched sheet is preheated with a roll group heated to a temperature of 80 ° C., and then a heated roll having a temperature of 85 ° C. (stretching roll and surface roughness (Ra): 0.5 μm stretching nip roll) is used. The film was stretched 2.8 times at a stretching nip pressure of 0.5 MPa in the longitudinal direction (longitudinal direction), and cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched sheet. After the uniaxially stretched sheet was subjected to corona treatment, the coating composition A described in the above section (Preparation of coating composition for easy-adhesion layer) was applied with a 25 mesh metering bar.

  While holding both ends of the obtained uniaxially stretched sheet with a clip, it is guided to a preheating zone at a temperature of 90 ° C. in the tenter, and is continuously heated at 100 ° C. in a direction perpendicular to the longitudinal direction (width direction). The film was stretched 3.2 times. Subsequently, heat treatment was performed at 200 ° C. for 20 seconds in a heat treatment zone in the tenter, and further relaxation treatment was performed in the 4% width direction at 210 ° C. Then, it was gradually cooled gradually to obtain a biaxially stretched sheet. Moreover, Tg of this film was 80 degreeC. P1 layer thickness, P2 layer thickness, surface roughness (Ra), heat shrinkage ratio, initial adhesive strength, adhesive strength after wet heat resistance test, adhesive strength retention after wet heat resistance test, after wet heat resistance test Table 4 shows the output retention ratio.

  The resulting sheet was evaluated for characteristics. As a result, as shown in Table 4, the sheet is excellent in adhesion, adhesion durability, long-term durability, and processability, and has characteristics suitable for use as a solar cell back surface protection sheet and solar cell. I understood.

(Examples 2-18, Comparative Examples 1-12)
Biaxially stretched sheet in the same manner as in Example 1 except that the type of P1 layer raw material, the type of coating composition, and the production conditions were changed to the raw materials, coating composition, and production method described in Tables 1-3. Got. P1 layer thickness, P2 layer thickness, surface roughness (Ra), heat shrinkage ratio, initial adhesive strength, adhesive strength after wet heat resistance test, adhesive strength retention after wet heat resistance test, after wet heat resistance test Table 4 shows the output retention ratio.

Hereinafter, description of Examples 2 to 18 and Comparative Examples 1 to 12 will be described.

  Since Example 2 has a high heat shrinkage rate, the adhesive strength after the wet heat test is slightly inferior to that of Example 1, but the result is practically satisfactory.

  Since Example 3 has a high surface roughness (Ra), the initial adhesive strength was the same as that of Example 1. However, the adhesive strength retention after the wet heat resistance test is inferior to that of Example 1. However, there was no problem in practical use.

  In Example 4, since much CHT, which is a heat-resistant agent, was added, the adhesive strength retention after the heat and humidity resistance test was better than that of Example 1.

  In Example 5, since the titanium oxide was not contained, the surface roughness (Ra) of the P2 layer was small and the initial adhesive strength was small, but there was no problem in practical use.

  In Example 6, since CHT was not contained, the adhesion after the wet heat test was lowered, but there was no problem in practical use.

  In Example 7, the cast residence time was short, and the crystallinity was likely to be uneven. When the solar cell back sheet was used, the decrease in output was larger than that in Example 1, but it was practical. The result was fine.

  In Example 8, since the cast residence time was long and the film was longitudinally stretched after being sufficiently cooled, the decrease in output after the wet heat test was small.

  In Example 9, since the stretching roll NIP pressure was high, the film was rougher than Example 1, and the adhesive strength was high.

  In Example 10, the stretched NIP pressure was lower and the adhesive strength was lower than that in Example 1, but there was no problem in practical use.

  In Example 11, hydrolysis of the P1 layer may have occurred due to the high amount of carboxyl groups in the raw material, and both the adhesive strength after the moist heat resistance test and the output retention rate after the moist heat resistance test were lowered. Was no problem.

  In Examples 12 to 15, although the breaking elongation of the polyester polyurethane resin contained in the P2 layer was high, there was no problem in practical use, and the adhesive strength after the initial moist heat resistance test was good.

  In Example 16, since the epoxy crosslinking agent was not contained in the P2 layer, the adhesive strength after the wet heat resistance test was slightly inferior, but there was no problem in practical use.

  In Example 17, since the melamine crosslinking agent was not contained in the P2 layer, the adhesive strength after the wet heat resistance test was slightly inferior, but there was no problem in practical use.

  Since Example 18 contained polyolefin resin A ', the adhesive strength with the polyester film was slightly inferior, but it was at a level of no practical problem.

  In Comparative Example 1, when the characteristics were evaluated using only the P1 layer of Example 1, the adhesive strength was insufficient in both the initial stage and after the wet heat resistance test.

  Since the acid value of the polyester polyurethane resin contained in P2 layer was too high, the comparative example 2 was the characteristic inferior to the adhesive strength after a moist heat test.

  In Comparative Examples 3 and 4, since the breaking elongation of the polyester polyurethane resin contained in the P2 layer was too low, the adhesive strength after the wet heat resistance test was inferior.

  In Comparative Example 5, the polyester polyurethane resin contained in the P2 layer had a low elongation at break and an acid value that was too high, so that the adhesive strength after the wet heat resistance test was inferior.

  Since the comparative example 6 did not contain the crosslinking agent in the P2 layer, it was inferior in the adhesive strength after the moist heat resistance test.

In Comparative Example 7, a polyester polyurethane resin was not used as the urethane resin contained in the P2 layer, and the characteristics were inferior in adhesive strength after the wet heat resistance test.
In Comparative Example 8, the film had a large vertical orientation and a high moisture and heat resistance film as the P1 layer. However, since the shrinkage was large when closely contacting with EVA, the initial adhesive strength was poor.

  In Comparative Example 9, since a large amount of titanium and CHT was contained, the clogging of the filter was large, and it was a film that was difficult to form with frequent film tearing. Moreover, the film surface was too rough and it was difficult to adhere to EVA.

  Since Comparative Example 10 did not contain particles, the surface roughness (Ra) was low and the adhesive strength was low.

  The conditions of Comparative Example 11 were also small in the number of particles and insufficient in the stretched NIP pressure, so that the surface roughness (Ra) was insufficient and the film had poor adhesive strength.

  In Comparative Example 12, since the amount of the carboxyl group in the original fabric was high and the stretched NIP pressure was insufficient, the film was poor in surface roughness (Ra) and poor in adhesive strength.

  In the table, the CHT particle amount represents the content of polyester having a CHT unit as a main constituent component.

  In the table, the CHT particle amount represents the content of polyester having a CHT unit as a main constituent component.

  The solar cell back surface protection sheet of the present invention can be suitably used as a back surface protection sheet of a solar cell module. In addition, it can be suitably used as an adhesive sheet in applications where adhesion with an ethylene-vinyl acetate copolymer resin is required.

1: Solar cell back surface protection sheet 2: Sealing material 3: Power generation element 4: Transparent substrate

Claims (12)

It is a solar cell back surface protection sheet having a base material layer (P1 layer) and an easy-adhesion layer (P2 layer). The P1 layer is mainly composed of a polyester resin, and the P2 layer is formed on at least one side of the P1 layer. And a solar cell back surface protection sheet characterized by satisfying all of the following (a) to (c).
(A) The thermal shrinkage after heat treatment at 150 ° C. for 30 minutes is 1.5% or less (b) The surface roughness (Ra) of the P2 layer is 0.03 μm or more and 0.50 μm or less (c) Moisture and heat resistance The adhesive strength after the test is 15 N / cm or more, and the adhesive strength retention after the wet heat resistance test is 80% or more.   The solar cell back surface protection sheet according to claim 1, wherein the P2 layer includes a urethane resin component, a melamine resin component, and an epoxy resin component.   The P2 layer is a layer formed from a coating composition containing a urethane resin, a melamine resin, and an epoxy resin, and the urethane resin is added to the total solid content in the coating composition forming the P2 layer. The solar cell back surface protection sheet according to claim 2, comprising 80% by mass or more and 90% by mass or less, 7% by mass or more and 17% by mass or less of melamine resin, and 2% by mass or more and 7% by mass or less of epoxy resin.   The solar cell back surface protection sheet of Claim 3 whose content of an olefin resin is 1 mass% or less with respect to the total solid in the coating composition which forms the said P2 layer.   The solar cell back surface protection sheet according to any one of claims 2 to 4, wherein the P2 layer is a layer formed from a coating composition containing a polyester polyurethane resin as a urethane resin component.   The sheet for protecting a back surface of a solar cell according to claim 5, wherein an acid value of the polyester polyurethane resin is 25 mg-KOH / g or less.   The sheet for protecting a solar cell according to claim 5 or 6, wherein when the sheet made of the polyester polyurethane resin having a thickness of 150 µm is produced, the breaking elongation of the sheet is 300% or more and 3000% or less.   The sheet | seat for solar cell back surface protection in any one of Claims 1-7 whose amount of terminal carboxyl groups of the polyester resin which comprises P1 layer is 24 equivalent / tons or less. It is a method of manufacturing the solar cell back surface protection sheet in any one of Claims 1-8, Comprising: The manufacturing method of the solar cell back surface protection sheet containing the process of following (1)-(4).
(1) Step of obtaining a non-oriented polyester film by melting and kneading a resin composition containing a polyester resin constituting the P1 layer with an extruder and then extruding and cooling and solidifying on a cooling drum (2) Unoriented polyester film Using a stretching roll and a stretching nip roll in the longitudinal direction at a stretching temperature of 70 to 120 ° C. and a stretching ratio of 2.0 to 4.0 times to obtain a uniaxially oriented polyester film (however, the stretching roll The surface roughness (Ra) is 0.5 to 1.5 μm, and the nip pressure between the stretching roll and the stretching nip roll is 0.4 to 1.0 MPa)
(3) Step of stretching a uniaxially oriented polyester film in the width direction at a stretching temperature of 70 to 150 ° C. and a stretching ratio of 3.0 to 4.0 to obtain a biaxially oriented polyester film (4) Biaxially oriented polyester The process of relaxing 0-10% in the width direction while heat-treating the film at 205-240 ° C. It is a method of manufacturing the solar cell surface protection sheet in any one of Claims 1-8, Comprising: The manufacturing method of the solar cell back surface protection sheet including the process of following (1 ')-(4') .
(1 ′) On the cooling drum of Tg−70 ° C. or more and Tg−30 ° C. or less of the polyester resin constituting the P1 layer after melt-kneading the resin composition containing the polyester resin constituting the P1 layer with an extruder. Step of obtaining a non-oriented polyester film by cooling and solidifying for 20 seconds to 120 seconds at (2 ') A non-oriented polyester film is stretched at a stretching temperature of 70 to 120 ° C. in the longitudinal direction using a stretching roll and a stretching nip roll. Step of obtaining a uniaxially oriented polyester film by stretching at a magnification of 2.0 to 4.0 times (3 ′) A uniaxially oriented polyester film is stretched in the width direction at a stretching temperature of 70 to 150 ° C. and a stretching ratio of 3.0 to 4. Step of obtaining biaxially oriented polyester film by stretching at 0 times (4 ′) 0-1 in the width direction while heat treating the biaxially oriented polyester film at 205-240 ° C. 0% relaxation process   In the step (2 ′), the surface roughness (Ra) of the stretching roll is 0.5 to 1.5 μm, and the nip pressure between the stretching roll and the stretching nip roll is 0.4 to 1.0 MPa. The manufacturing method of the solar cell back surface protection sheet of Claim 10. The solar cell which uses the sheet | seat for solar cell back surface protection in any one of Claims 1-8.

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