JP5262044B2 - Solar cell back surface sealing sheet and solar cell module using the same - Google Patents

Abstract

Provided is a solar cell rear surface sealing sheet having excellent adhesiveness to a filling material which constitutes a solar cell module and excellent storage stability with time. A solar cell module using such solar cell rear surface sealing sheet is also provided. Solar cell rear surface sealing sheets (1A, 1B) have easy-to-adhere coat layers (2a, 2b) on the surfaces to be bonded to the filling material that constitutes the solar cell module. The easy-to-adhere coat layers (2a, 2b) are formed of a coating composition containing 0.1-10 parts by mass of at least one kind of a cross-linking agent selected from among specific compounds and 0.1-10 parts by mass of a polyacrylic acid or its derivative per 100 parts by mass of a water dispersing ionomer type polyurethane resin having a film softening point temperature of 100°C or higher.

Description

  TECHNICAL FIELD The present invention relates to a solar cell back surface sealing sheet, and more specifically, a solar cell back surface sealing sheet having high adhesion with a filler constituting a solar cell module and excellent storage stability over time, and The present invention relates to a solar cell module using a solar cell back surface sealing sheet.

  In recent years, various efforts have been made to suppress carbon dioxide emissions while interest from various countries both inside and outside Japan has increased. Increasing fossil fuel consumption leads to an increase in atmospheric carbon dioxide, and the greenhouse effect raises the Earth's temperature, significantly affecting the global environment. Various studies have been carried out to solve this global problem, and in particular, solar power generation is highly expected in terms of cleanliness and non-pollution.

  Solar cells constitute the heart of a photovoltaic power generation system that directly converts sunlight energy into electricity, and are made of single crystal, polycrystalline, or amorphous silicon semiconductors. As a structure thereof, a single solar cell element (cell) is not used as it is, and generally several to several tens of solar cell elements are wired in series and in parallel, for a long time (about 20 years). In order to protect the cell, various parsing is performed and unitized. The unit built into this package is called a solar cell module. The surface that is exposed to sunlight is generally covered with a glass surface, and the gap is filled with a filler made of thermoplastics (especially ethylene-vinyl acetate copolymer). The back surface is protected by a sealing sheet.

  By the way, since these solar cell modules are mainly used outdoors, sufficient durability and weather resistance are required in the configuration and material structure thereof. In particular, the back surface sealing sheet is required to have a weather resistance and a low water vapor transmission rate (excellent moisture barrier property). This is because if the filler is peeled off or discolored due to the permeation of moisture, or the wiring is corroded, the output of the module itself may be affected.

  Conventionally, as a solar cell back surface sealing sheet, such as polyvinyl fluoride and polyvinylidene fluoride (including a copolymer with ethylene), such as weather resistance, flame retardancy, and a solar cell module filler are often used. “Fluorine-based resins” having good adhesiveness with ethylene-vinyl acetate copolymers have been used (see, for example, Patent Documents 1 and 2).

However, solar cell backside sealing sheets using polyester films such as polyethylene terephthalate with excellent electrical insulation instead of expensive fluororesins have been developed, and the weather resistance improvement, which is a disadvantage of polyester films, has been developed. Is progressing.
For example, a case where an ultraviolet absorber is blended as described in Patent Document 3, a case where the amount of cyclic oligomer in polyester is defined as described in Patent Documents 4 and 5, and a polyester as described in Patent Document 6 Examples of defining the molecular weight are disclosed.
However, as a disadvantage of using such a polyester film, there is a problem of adhesion with a filler (ethylene-vinyl acetate copolymer) constituting the solar cell module.

  As described above, the solar cell needs to maintain its performance for about 20 years, and in order to evaluate its durability, an accelerated test is performed at high temperature and high humidity (85 ° C.-85% relative humidity). At this time, the sheet for sealing the back surface of a solar cell made of a polyester film and the filler ethylene-vinyl acetate copolymer are due to wetting utilizing the intermolecular interactions such as affinity between polar groups and hydrogen bonding. Since it is only adhesion, the adhesiveness immediately after manufacturing the solar cell module is excellent, but it has been confirmed that the adhesiveness is remarkably reduced in the above environment. In order to improve these, the technique (for example, refer patent document 7) which performs a corona treatment to the surface bonded with the filler of a solar cell back surface protection sheet is disclosed, but even if it gives a corona treatment, the said problem The situation has not been improved.

In order to improve this problem, there is a technique for further laminating an adhesive film having good thermal adhesiveness to a filler such as ethylene-vinyl acetate copolymer (EVA) on a sheet for sealing the back surface of a solar cell. Although it is disclosed (see, for example, Patent Document 8), in providing an adhesive film that is thermally bonded to EVA as a filler, the extrusion laminating method improves adhesion to a polyester film as a substrate. Inferior, the dry laminating method has a problem that the workability is remarkably lowered due to blocking of the adhesive film itself.
Thus, a technique (for example, see Patent Document 9) that uses EVA itself, which is a filler for a solar cell module, as the adhesive film is disclosed. EVA for a solar cell module filler will be described later. Consists of a resin composition containing various additives such as peroxides and cross-linking agents, and its processability itself is difficult. At the same time, the filler used for solar cell modules is often chosen by solar cell manufacturers. Therefore, it has a problem that it is restricted in the area where the market can be developed.

  Reflecting the above problems, the inventors have invented a solar cell back sheet provided with an easy-adhesion coat layer having a crosslinked structure (see Patent Document 10). This solar cell back sheet was able to maintain adhesion with EVA as a filler even after storage for 1000 h at 85 ° C.-85% relative humidity (RH).

However, the required performance of solar cells tends to be high in recent years, and it is stored for 3000 to 3500 hours under storage at 85 ° C.-85%, or these accelerated evaluations require a very long evaluation days. The high temperature and high humidity storage test used (PCT test: 105 ° C-100% RH-200h storage, etc.) will be carried out, and the adhesion performance will be greatly improved with no decrease in adhesion even under harsh storage environments. A solar cell backside sealing sheet is desired.
JP-T 8-500214 Japanese translation of PCT publication No. 2002-520820 JP 2001-1111073 A Japanese Patent Laid-Open No. 2002-100788 JP 2002-134771 A JP 2002-26354 A JP 2000-243999 A Japanese Patent Laid-Open No. 10-25357 JP 2000-174296 A JP 2007-48944 A

  The present invention has been made in view of the above circumstances, and uses a solar cell back surface sealing sheet that has high adhesion to the filler constituting the solar cell module and is excellent in storage aging stability, and the same. An object is to provide a solar cell module.

In order to solve the above problems, the present invention employs the following configuration.
[1] A solar cell back surface sealing sheet in which an easy-adhesion coat layer is provided on a surface to be bonded to a filler constituting the solar cell module,
The easy-adhesion coat layer is composed of a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a melamine compound, the following general formula (I) with respect to 100 parts by mass of a water-dispersed ionomer type polyurethane resin having a film softening point temperature of 100 ° C. or higher. It is formed with a coating composition in which 0.1 to 10 parts by mass of a crosslinking agent selected from at least one compound selected from the compounds having the structure represented, and further 0.1 to 10 parts by mass of polyacrylic acid or a derivative thereof. And the polyacrylic acid or a derivative thereof is a sodium salt of polyacrylic acid or an ammonium salt of polyacrylic acid .

(In the formula (I), R1, R2, R3, R4 have hydrogen, halogen, alkyl group, alkoxyl group, (meth) acryloyl group, allyl group, vinyl group, glycidyl group, isocyanate group, mercapto group, amine group. Selected from any of the substituents.)
[2] The solar cell backside sealing sheet according to [1], wherein the water-dispersed ionomer-type polyurethane has a glass transition temperature (Tg) of 50 ° C. or lower.
[3] The water-dispersed ionomer-type polyurethane includes water-dispersed ionomer-type polyurethane (PU-1) having a glass transition temperature (Tg) of 50 ° C. or less and water having a glass transition temperature (Tg) in the range of 50 to 80 ° C. It consists of a mixture of dispersed ionomer type polyurethane (PU-2), and the mass ratio is (PU-1) / (PU-2) = 50/50 to 99/1. The solar cell back surface sealing sheet.
[ 4 ] The solar cell according to any one of [1] to [ 3 ], wherein acetylene diol or an ethylene oxide adduct of acetylene diol is further blended in the coating composition. Sheet for backside sealing.
[ 5 ] The sun according to any one of [1] to [ 4 ], wherein an inorganic filler antiblocking agent or a fatty acid amide slip agent is further blended in the coating composition. Battery back surface sealing sheet.
[ 6 ] The coating composition has a solution state viscosity including a solvent in a range of 50 to 500 mPa · S, and is provided in a range of 0.5 to 10 g / m ² as a dry film. The solar cell back surface sealing sheet according to any one of [1] to [ 5 ].
[ 7 ] The solar cell backside sealing according to any one of [1] to [ 6 ], wherein the coating composition is provided in a dot shape or a stripe shape. Stop sheet.
[ 8 ] The solar cell back surface sealing sheet according to any one of [1] to [ 7 ], wherein the easy-adhesion coat layer is provided on an untreated polyester base material. .
[ 9 ] The solar cell back surface sealing according to any one of [1] to [ 8 ], which has a multilayer structure including at least one polyester layer made of the same material as the polyester base material. Sheet.
[ 10 ] The solar cell backside sealing according to any one of [1] to [ 9 ], wherein the solar cell backside sealing has a multilayer structure including at least one barrier base material provided with an inorganic compound vapor deposition layer. Sheet.
[ 11 ] The solar cell back surface sealing sheet according to any one of [1] to [ 10 ], wherein the sheet has a multilayer structure including at least one base layer having weather resistance.
[ 12 ] The substrate layer having weather resistance is a polyester substrate selected from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polycyclohexanedimethanol-terephthalate (PCT), polycarbonate Base material, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polyethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), tetrafluoroethylene perfluoroalkyl vinyl ether Is it a fluorine-based substrate selected from a copolymer (PFA), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or an acrylic modified product of these fluorine-based substrates? Characterized in that it is selected, a rear surface of a solar cell sealing sheet according to [11].
[ 13 ] The substrate layer having weather resistance is polyethylene terephthalate having a number average molecular weight in the range of 18,000 to 40,000, the cyclic oligomer content is 15 wt% or less, and the intrinsic viscosity is 0.5 dl / g or more. The sheet for sealing a back surface of a solar cell according to [ 11 ] or [ 12 ], wherein the sheet is for sealing a back surface of a solar cell.
[ 14 ] A solar cell module using the solar cell back surface sealing sheet according to any one of [1] to [ 13 ].

  According to the solar cell back surface sealing sheet of the present invention, good lamination strength can be obtained regardless of the type of the ethylene-vinyl acetate copolymer by being laminated in the form of heat fusion with the filler. Furthermore, since there is no reduction in the adhesion between the heat-fusible film and the solar cell back surface sealing sheet even under high temperature and high humidity, not only the poor appearance due to delamination but also the back surface sealing sheet As a result, it is possible to maintain the barrier characteristics and the electric output characteristics of the solar cell.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment.

  The solar cell back surface sealing sheet of the present invention has a “water-dispersed ionomer-type polyurethane having a film softening point temperature of 100 ° C. or higher on a surface to be bonded to a filler, particularly an ethylene-vinyl acetate copolymer, constituting a solar cell module. 0.1 parts or more of a crosslinking agent selected from a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a melamine compound, and a compound having a structure represented by the following general formula (I) with respect to 100 parts by mass of the resin. It is characterized in that an easy-adhesion coat layer comprising 10 to 10 parts by mass and further a coating composition containing 0.1 to 10 parts by mass of polyacrylic acid or a derivative thereof is provided.

(In general formula (I), R1, R2, R3 and R4 are hydrogen, halogen, alkyl group, alkoxyl group, (meth) acryloyl group, allyl group, vinyl group, glycidyl group, isocyanate group, mercapto group, amine group. Selected from any of the substituents possessed.)

<Solar cell backside sealing sheet>
First, the solar cell back surface sealing sheet to which the present invention is applied will be described.
The solar cell back surface sealing sheet to which the present invention is applied has easy-adhesion coat layers 2a and 2b, for example, solar cell back surface sealing sheets 1A and 1B shown in FIGS. 1 (a) and 1 (b). The inner surfaces (surfaces bonded to the filler constituting the solar cell module) of the base materials 3a and 3b made of polyester are provided.
In the solar cell back surface sealing sheet 1B, the first adhesive layer 4, the barrier base material 6, the second adhesive layer 8, and the outermost layer (base material having weather resistance) are provided outside the base material 3b. 9 are provided in order. The barrier base material 6 includes a polyester layer 7 made of the same material as the base material 3b, and an overcoat layer 5a and an inorganic compound vapor deposition layer 5b provided in this order from the first adhesive layer 4 side.

<Easily adhesive coat layer>
The easy-adhesion coat layers 2a and 2b are designed in consideration of the adhesion to the solar cell back surface sealing sheets 1A and 1B and the adhesion to the filler constituting the solar cell module. It is necessary to consider the adhesion to the ethylene-vinyl acetate copolymer often used as a material. Usually, an ethylene-vinyl acetate copolymer used as a filler for a solar cell module has a vinyl acetate content of 10 to 40% by weight, and ensures the heat resistance and physical strength of the solar cell module. Therefore, the ethylene-vinyl acetate copolymer is crosslinked by heat or light.

  In ethylene-vinyl acetate copolymerization, an organic peroxide is usually used for thermal crosslinking, and those that decompose at a temperature of 70 ° C. or higher to generate radicals are used. Usually, those having a decomposition temperature of 50 ° C. or more with a half-life of 10 hours are used, and 2,5-dimethylhexane-2,5-dihydroxyperoxide, 2,5-dimethyl-2,5-di (t-butyl) Peroxy) hexyne-3, di-t-butyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, dicumyl peroxide, α, α 'Bis (t-butylperoxyisopropyl) benzene, n-butyl-4,4-bis- (t-butylperoxy) valerate, t-butylperoxybenzoate, benzoyl peroxide, etc. are used.

In photocuring, a photosensitizer can be used, which is a hydrogen abstraction type (bimolecular reaction type) such as benzophenone, methyl orthobenzoylbenzoate, 4-benzoyl-4'-methyldiphenyl sulfide, isopropylthioxanthone. Etc. can be used.
Internal cleavage type initiators include benzoin ether, benzyl dimethyl ketal, α-hydroxyalkylphenone type, 2-hydroxy-2-methyl-1-phenylpropane, 1-one-1-hydroxycyclohexyl phenyl ketone, alkylphenyl Glyoxylate, diethoxyacetophenone, etc. can be used. In addition, as α-aminoalkylphenone type, 2-methyl-1- [4 (methylthio) phenyl] -2-morpholinopropane-1,2-benzyl-2-dimethylamino-1- (4-morpholino Phenyl) -butanone-1 and the like, and acylphosphine oxide and the like can also be used.

  Moreover, a silane coupling agent can also be mix | blended in consideration of adhesion | attachment with the glass plate which comprises a solar cell module. Specifically, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltrimethoxysilane, γ, glycidoxypropyltri Ethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-chloropropylmethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β (amino Ethyl) -γ-aminopropyltrimethoxysilane and the like can be blended.

  Furthermore, an epoxy group-containing compound may be blended for the purpose of promoting adhesion and curing. Specific examples of the epoxy group-containing compound include triglycidyl tris (2-hydroxyethyl) isocyanurate, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, acrylic glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl Hundreds of compounds, such as glycidyl ether, phenol glycidyl ether, Pt-butylphenyl glycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, glycidyl methacrylate, butyl glycidyl ether To thousands of oligomers and polymers having weight average molecular weights of thousands to hundreds of thousands can be blended.

  Further, an acryloxy group, methacryloxy group or allyl group-containing compound can be added for the purpose of improving the crosslinking, adhesion, mechanical strength, heat resistance, moist heat resistance, weather resistance and the like of the filler. As such compounds, (meth) acrylic acid derivatives such as alkyl esters and amides thereof are the most common, and as alkyl groups, in addition to alkyl groups such as methyl, ethyl, dodecyl, stearyl, lauryl, cyclohexyl Group, tetrahydrofurfuryl group, aminoethyl group, 2-hydroxyethyl group, 3-hydroxypropyl group, 3-chloro-2-hydroxypropyl group and the like. In addition, esters of (meth) acrylic acid and polyfunctional alcohols such as ethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, and pentaerythritol can also be used. A typical amide is acrylamide. Further, as the allyl group-containing compound, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl isophthalate, diallyl maleate and the like can be blended.

Furthermore, an inorganic compound for imparting flame retardancy, an ultraviolet absorber for imparting weather resistance, and an antioxidant for preventing oxidative degradation can be variously blended.
As described above, the ethylene-vinyl acetate copolymer constituting the solar cell module is often a resin composition in which various additives are blended so as to satisfy the function required as the solar cell module. Therefore, in order to consider the adhesiveness between the solar cell backside sealing sheet and the filler constituting the solar cell module, it is not simply an adhesive with ethylene-vinyl acetate copolymer, but a resin composition containing various additives. It is necessary to have the recognition of adhesion to an object, and it is necessary to consider that the various additives described above may be advantageous or disadvantageous for adhesion. Therefore, as a result of sincerity studies to improve the adhesion to the filler, ethylene-vinyl acetate copolymer, it was confirmed that the easy-adhesion coat layer described below is effective.

  As the easy-adhesion coat layers 2a and 2b, the present inventors first represented “water-dispersed ionomer type polyurethane resin, polyfunctional isocyanate compound, polyfunctional epoxy compound, melamine compound, and general formula (I)”. We examined the use of a coating composition containing at least one cross-linking agent selected from compounds having a structure and further polyacrylic acid or a derivative thereof.

"Water-dispersed ionomer type polyurethane resin"
Water-dispersed ionomer-type polyurethane resins include “polyester polyols” obtained using polybasic acids or their ester-forming derivatives and polyols or their ester-forming derivatives, “acrylic polyols” having a hydroxyl group at the terminal / side chain, polyethylene "Polyether polyols" such as glycols and polypropylene glycols, as chain extenders, tolylene diisocyanate, xylylene diisocyanate or its hydrogenated product, hexamethylene diisocyanate, 4-4 'diphenylmethane diisocyanate or its hydrogenated product, isophorone diisocyanate Obtained by reacting these diisocyanates with adducts obtained by reacting these diisocyanates with polyhydric alcohols such as trimethylolpropane and water. In the structure of polyurethane resins obtained by the action of polyisocyanates such as the isurelet body or the isocyanurate body that is a trimer, a hydroxyl group, an amino group, or a sulfonic acid is used to improve water dispersibility. It has a structure obtained by copolymerizing a compound having a hydrophilic functional group such as a group, a carboxylic acid group, or a salt thereof. These hydrophilic functional groups not only give dispersion stability as an emulsion, but also improve adhesion to various substrates, especially polyester substrates, compared to solvent-soluble polyurethane resins. In terms of adhesion to the substrate, carboxylic acid groups, sulfonic acid groups, or salts thereof are particularly preferable.

Next, the present inventors examined the film softening point temperature of this water-dispersed ionomer type polyurethane resin, and decided to use a heat-resistant polyurethane resin having a film softening point temperature of 100 ° C. or higher.
As described above, the water-dispersed ionomer type polyurethane resin can improve adhesion to various substrates by introducing a sulfonic acid group, a carboxylic acid group, or a salt thereof into the structure. . However, in order to improve the adhesion to various substrates compared to solvent-soluble polyurethane resins, the hydrogen bonding and ionic bonding properties of sulfonic acid groups, carboxylic acid groups, or salts thereof and the substrate surface are improved. However, there is a problem that these bonds are weak against water.
Therefore, in order not to cause a decrease in adhesion even when stored in the above-mentioned environment of 85 ° C.-85% RH, the influence of the fluidity of the film in the above storage environment or the permeation of water associated with storage under high humidity. It is necessary to design the molecular structure to prevent. That is, it is necessary to improve the heat resistance of the water-dispersed ionomer type polyurethane resin. From such a viewpoint, the heat flow starting temperature of the water-dispersed ionomer type polyurethane resin used in the present invention is 100 ° C. or more, more preferably A polyurethane resin having a heat resistance of 150 ° C. or higher, more preferably 180 ° C. or higher is preferable.

  In addition, it is also preferable to add a crosslinking agent to the water-dispersed ionomer type polyurethane resin in terms of further improving heat resistance. Examples of such cross-linking agents include tolylene diisocyanate, xylylene diisocyanate or hydrogenated products thereof, hexamethylene diisocyanate, 4-4 ′ diphenylmethane diisocyanate or hydrogenated products thereof, diisocyanates such as isophorone diisocyanate, or these isocyanates. Polyisocyanates such as adducts reacted with polyhydric alcohols such as trimethylolpropane, burettes obtained by reacting with water, or isocyanurates that are trimers, or these polyisocyanates It is possible to use blocked polyisocyanates obtained by blocking with alcohols, lactams, oximes and the like. Furthermore, various crosslinking agents utilizing the hydrophilic group of the ionomer type polyurethane can also be used, and examples thereof include an epoxy compound, a melamine compound, or a compound having a structure represented by the general formula (I). It is done.

  Specifically, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltri Ethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-chloropropylmethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β (amino Examples thereof include various silane coupling agents such as ethyl) -γ-aminopropyltrimethoxysilane and γ-isocyanatopropyltriethoxysilane.

  In particular, when these compounds having the structure represented by the general formula (I) are blended, it is expected to act with various additives blended in EVA of the solar cell filler, such as a silane coupling material. It is expected to improve the adhesion between the coating material and EVA as the filler. The amount of these crosslinking agents is 0.1 to 10 parts per 100 parts of the water-dispersed ionomer type polyurethane resin. When the amount is less than 0.1 part, it is difficult to obtain the effect of adding a crosslinking agent. On the other hand, if it exceeds 10 parts, the pot life as a coating agent is remarkably shortened depending on the type of the additive.

However, as a result of further diligent investigation regarding the present situation that the moisture-and-heat-resistant adhesiveness is insufficient by itself, the present inventors have remarkably determined that the composition of the easy-adhesion coat layers 2a and 2b is as follows. The present inventors have found that the heat adhesion performance is improved and completed the present invention.
That is, the easy-adhesion coat layers 2a and 2b in the present invention have a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a melamine compound, 100 parts by mass of a water-dispersed ionomer type polyurethane resin having a film softening point temperature of 100 ° C. or higher. 0.1 to 10 parts by mass of at least one crosslinking agent selected from the compound having the structure represented by the general formula (I) is blended, and further 0.1 to 10 parts by mass of polyacrylic acid or a derivative thereof. The coating composition was formulated in the range of.

  Examples of such materials include (meth) acrylic acid as a main component as a monomer, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t- as alkyl groups. Polymers obtained by copolymerizing alkyl (meth) acrylate monomers that are butyl, 2-ethylhexyl, and cyclohexyl groups, and (meth) acrylamide, N-alkyl (meth) acrylamide, N, N-dialkyl (meth) Acrylamide (alkyl groups include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, 2-ethylhexyl, cyclohexyl, etc.), N- Alkoxy (meth) acrylamide, N, N-dialkoxy (meth) acrylamide, (the alkoxy group is Amide group-containing monomers such as N-methylol (meth) acrylamide, N-phenyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (Si group, ethoxy group, butoxy group, isobutoxy group, etc.) Hydroxyl group-containing monomers such as (meth) acrylate, glycidyl group-containing monomers such as glycidyl (meth) acrylate, allyl glycidyl ether, silane-containing monomers such as (meth) acryloxypropyltrimethoxysilane, (meth) acryloxypropyltriethoxylane, What copolymerized isocyanate group containing monomers, such as (meth) acryloxypropyl isocyanate, is mentioned. Of these polyacrylic acids or derivatives thereof, the sodium salt or ammonium salt of polyacrylic acid is most preferred, and the sodium salt is particularly preferred.

  The effect of this sodium salt or ammonium salt of polyacrylic acid is presumed as follows. First, the water-dispersed ionomer type polyurethane resin may function as a crosslinking agent. When the carboxyl group of polyacrylic acid and the carboxyl group in the water-dispersed ionomer polyurethane resin are present as free acids (this case is an ammonium salt), it is assumed that a crosslinked structure is formed by associated hydrogen bonds. . Further, when the carboxyl group is present as a salt with sodium ions, it is considered that a cluster-type cross-linked form having sodium ions as nuclei is formed.

  In this way, not only is the cross-linking density of the coating film increased, but also the glass transition temperature (Tg) of polyacrylic acid itself is high, so the restraint point (because the amount of polyacrylic acid added is small, It is thought that the high heat resistance of (which is formed) leads to the improvement of wet heat resistance. Further, in terms of heat resistance of the crosslinked structure, the cluster-type crosslinked structure is more heat resistant than the above-mentioned associated hydrogen bond type, and as a result, it is judged that the sodium salt of polyacrylic acid is preferable. . In addition, although the effect of using sodium salt or ammonium salt of polyacrylic acid will be described later separately, when the amount is less than 0.1 parts by mass, the effect of improving wet heat resistance is low, and when the amount is more than 10 parts by mass, this composition The workability in the process of coating with a wet coating method is reduced.

Further, the glass transition temperature (Tg) of the water-dispersed ionomer type polyurethane is preferably 50 ° C. or lower, more preferably 30 ° C. or lower. Glass transition is a phenomenon different from film softening, and the film softening temperature is attributed to the molecular weight of the polyurethane, while the glass transition temperature is attributed to a component of the molecular skeleton. That is, by doing so, heat resistance can be imparted by increasing the molecular weight while easily causing molecular motion such as micro-Brownian motion at low temperatures.
In addition, since adhesion with EVA as a filler is a laminate by thermocompression bonding, in order to induce interaction between molecules that is considered to contribute to adhesion, molecular mobility at the thermocompression bonding temperature at the time of this lamination It is preferable to use a skeleton that facilitates the expression of.
In other words, when bonding is required, such as thermal bonding, film flow due to heat is utilized in high-temperature, long-time environments that require the use of molecular structural features that have a low glass transition temperature (easy to undergo molecular motion) and that are resistant to moist heat. It is necessary to design molecules without increasing the molecular weight (increasing the molecular weight).

  However, when a water-dispersed ionomer type polyurethane having a glass transition temperature of 50 ° C. or lower, preferably 30 ° C. or lower is used, for example, a manufacturing process of a solar cell back surface sealing film or a back surface sealing film is cut into a sheet and laminated. There is a risk of blocking during the process. Therefore, a water-dispersed ionomer type polyurethane (PU-1) having a glass transition temperature (Tg) of 50 ° C. or less and a water-dispersed ionomer type polyurethane (PU-2) having a glass transition temperature (Tg) in the range of 50 to 80 ° C. The compounding ratio (mass ratio) is preferably in the range of (PU-1) / (PU-2) = 50/50 to 99/1. When the blending ratio of (PU-2) is less than 1, moisture and heat resistant adhesion performance can be obtained, but blocking may occur. When the blending ratio of (PU-2) is more than 50, the above-mentioned adhesive properties in heat and pressure during lamination are difficult to develop, and the initial adhesion strength is difficult to obtain. Preferably it is the range of 70/30-90/10.

Moreover, it is preferable to use an untreated polyester base material as the base materials 3a and 3b on which the water-dispersed ionomer type polyurethane is provided. This is an idea opposite to the improvement in adhesion of various substrates subjected to corona treatment, which has been known in the art.
The present inventors have studied from what part the wet heat and heat adhesion of the easy adhesion coats 2a and 2b is, and the polyurethane coating agent has good adhesion to EVA as a filler. When expected to improve adhesion with EVA as a filler, the next place where there is concern about adhesion is the base material 3a on which the easy adhesion coat layers 2a and 2b and the easy adhesion coat layers 2a and 2b are provided. It paid attention to the adhesiveness with 3b.

  As described above, conventionally, various treatments such as corona treatment have been applied to improve the coating properties and adhesion of various types of coating agents. However, the improvement of various adhesion properties with a substrate subjected to corona treatment is a type using hydrogen bonding as an adhesion mechanism, and this bonding mode is a type that is very weak against water and heat. In other words, as a result of studies to further improve the adhesion between the easy-adhesion coat layers 2a and 2b and the base materials 3a and 3b, various treatments such as corona treatment can be performed by using an untreated polyester base material. It has become possible to significantly improve the wet heat resistance compared to the base material made. Therefore, the main point is to use an adhesion mechanism with excellent water resistance and heat resistance such as intermolecular force and dipole interaction.

  However, when such an adhesion mechanism is used, the untreated polyester base material and the easy-adhesion coat layers 2a and 2b are greatly affected by the wet state when applied by wet coating. Water-dispersed ionomer-type polyurethane is not water-soluble (dissolved at the molecular level), but is a state in which fine particles of polyurethane resin are dispersed in water. In this state, the adhesive properties are greatly affected.

  When a coating agent whose solvent is water is applied to an untreated polyester film (for example, a surface tension of 38 to 50 mN / m), a solvent that is relatively compatible with water, such as alcohols and ketones, is used. It is particularly preferable to add a leveling agent. Typical leveling agents include fluorine, chlorine, and silicon, but these leveling agents affect adhesive properties. More preferably, acetylenic diol or ethylene oxide adduct of acetylenic diol can be mentioned, and it is blended at about 10 to 10000 ppm, more preferably 100 to 5000 ppm in the state of a coating liquid of an easy-adhesion coat composed of the composition described above. It is preferably used between. When it is less than 10 ppm, the coating property is inferior, and when it is more than 10,000 ppm, the dispersion stability of the leveling agent in the state of the coating liquid is inferior.

As described above, as the solar cell backside sealing sheets 1A and 1B, in order to improve the wet and heat resistant adhesion of EVA as a filler, in view of adhesion to EVA, adhesion to base materials 3a and 3b As a result of the examination from the viewpoint of properties, the main points of the resin composition for forming the easy-adhesion coat layers 2a and 2b are summarized as follows.
[Point 1] A water-dispersed ionomer resin having a high molecular weight of a film softening point temperature of 100 ° C. or higher and a glass transition temperature (Tg) of 50 ° C. or lower is preferable. For such a water-dispersed ionomer resin, a crosslinking agent is used. A composition having heat resistance that does not cause heat flow even in an environment of high temperature and high humidity such as an accelerated test, while blending preferably sodium salt of polyacrylic acid and improving adhesion to EVA as a filler. Is used.
[Point 2] Easy-adhesion coat layers 2a and 2b made of such a coating composition are provided on an untreated polyester base material (base materials 3a and 3b). In that case, in order to improve the coating property to an untreated polyester base material, acetylene diol or the ethylene oxide adduct of acetylene diol is mix | blended, and the coating-film adhesiveness of a film | membrane is improved.

  By performing such a material design, it is possible to provide the easy-adhesion coat layers 2a and 2b having excellent wet heat resistance, but there is one problem. That is, since a water-dispersed ionomer resin having a glass transition temperature (Tg) of 50 ° C. or lower is used, it has a blocking effect. As a countermeasure, water-dispersed ionomer type polyurethane is composed of water-dispersed ionomer type polyurethane (PU-1) having a glass transition temperature (Tg) of 50 ° C. or less and water having a glass transition temperature (Tg) in the range of 50 to 80 ° C. It is made of a mixture of dispersed ionomer type polyurethane (PU-2), and the anti-blocking effect can be obtained by blending the mass ratio of (PU-1) / (PU-2) = 50/50 to 99/1. Is possible.

  To further improve the blocking prevention effect, various inorganic filler blocking agents such as silica, calcium carbonate, barium sulfate and alumina, or amide derivatives of fatty acids such as stearic acid and erucic acid (fatty acid amide, amide), etc. Can be included.

In addition, the easy-adhesion coat layer roughens the coating surface of the coating film, thereby providing an easy-adhesion coat layer 2e having a coating film 2d having a shape as shown in FIG. Is possible. The planar shape of the coating film 2d can be formed, for example, in a dot shape as shown in FIG. 2 (b) or a stripe shape as shown in FIGS. 2 (c) and 2 (d).
As shown in FIG. 3, for example, when the easy-adhesion coat 2b is applied and wound in a roll shape, as shown in FIG. Although it contacts the outermost layer 9 in the whole surface, as shown in FIG.3 (b), in the case of the coating film 2d with a coating surface shape, the easily-adhesive coat 2e provided in the base material 3c, and the outermost layer 9a The contact point is only in contact with the apex portion (α) of the easy-adhesion coat layer 2e, and the contact area ratio is small compared to the state of close contact as a whole. It is possible to obtain an anti-blocking effect with the opposite side surface coated with 2e. On the other hand, as for the close contact with EVA, heat lamination is performed by heat or pressure. Therefore, as shown in FIG. 3C, the EVA (filler 14) side is in close contact with the coating surface of this easy-adhesive coat 2e. Is possible.

  In order to form this coated surface shape, for example, it is only necessary to provide vertical streaks or the like in the wet-adhesive coating layer 2e provided on a uniform plane, and the solution viscosity of the coating liquid is in the range of 50 to 500 mPa · S, It is possible to form a coating surface using the plate of the plate to which the easy-adhesion coat 2e is applied, preferably in the range of 100 to 300 mPa · S and exhibiting thixotropic viscosity. It becomes. In other words, in the above viscosity range, leveling is difficult even when heat at the drying temperature is used, so in the case of gravure coating, in the case of a slanted plate, an oblique stripe-shaped easy adhesion coat is provided when applied. In addition, when a coating agent that has been applied once wet, such as a Mayer bar coat, is drawn (or leveled) with a wire rod, stripe stripes can be formed in the flow direction.

  The method of providing the easy-adhesion coats 2a, 2b, 2e is not particularly limited, and can be provided by various coating methods such as gravure coat, reverse coat, roll coat, die coat, comma coat, etc. You may pass through a process or a thermosetting process as needed. In addition, after the polyester resin is extruded in a molten state and cooled with a cooling roll, a film is formed, and then an easy-adhesion coat layer is provided. It is also possible to provide an adhesive coat layer. The method of forming the coated surface shape as shown in FIG. 2 can be provided when it is determined that it is necessary as a countermeasure against blocking, and the coated surface shape can be formed in a form conforming to the above contents. If there is a process that can do this, there is no restriction on the method.

The easy-adhesion coat layers 2a, 2b, and 2e are preferably provided in the range of 0.5 to 10 g / m ² , and more preferably in the range of 5 to 10 g / m ² . In order to improve the wet heat resistant adhesion performance, it is preferable to provide a thicker layer as much as possible, and if it is less than 0.5, the adhesion performance cannot be obtained. Although it may be 10 g / m ² or more, functional saturation has been reached in terms of adhesive properties, and providing more than this significantly reduces the handling properties of the coating process. Therefore, when considering both workability and functionality, it falls within the above range. The solution viscosity may be 50 mPa · S or less, but when it is desired to coat thickly, if the viscosity is too low, it becomes difficult to obtain a stable coating weight. When it is more than 500 mPa · S, the viscosity becomes too high and the workability is inferior, and at the same time, there is a risk of appearance defects accompanying air biting in the coating process. Incidentally, the sodium salt and ammonium salt of polyacrylic acid described above may act as an alkali thickener for water-based paints, and if more than 10 parts by weight is added, the adhesive function may work, but the viscosity of the coating solution It may become too high and processing may become difficult.
By providing such easy-adhesion coat layers 2a, 2b, and 2e, it is possible to improve the adhesion between the solar cell back surface sealing sheets 1A, 1B, and 1C and the solar cell module filler.

  Examples of the base materials 3a, 3b, and 3c on which these easy-adhesion coat layers 2a, 2b, and 2e are provided include fluorine resins, polyolefin resins, polyester resins, polyamide resins, polycarbonate resins, and polyarylate resins. However, in view of heat resistance, strength properties, electrical insulation, etc., polyester resins, particularly biaxially stretched polyester resins are preferred. The polyester resin is obtained by using a polybasic acid or an ester-forming derivative thereof and a polyol or an ester-forming derivative thereof. Polybasic acid components include terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, dimer Two or more acid components such as acid, maleic acid, and itaconic acid, and ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedi as polyol components Contains methanol, trimethylolpropane, pentaerythritol, xylene glycol, dimethylolpropane, poly (ethylene oxide) glycol, poly (tetramethylene oxide) glycol, and also carboxylic acid groups, sulfonic acid groups, amino groups, or salts thereof While polyester obtained may be mentioned by using a polyol component alone or in combination of two or more that it is possible to use polyethylene terephthalate, polybutylene terephthalate, a general polyester such as polyethylene naphthalate. In these substrates, as described above, the surface on which the easy-adhesion coats 2a, 2b, and 2e are applied is preferably untreated.

  The solar cell backside sealing sheets 1A, 1B, and 1C are at least the above-mentioned easy-adhesion coats, considering not only adhesion of EVA as a filler but also gas barrier properties from the viewpoint of protecting the solar cell module. It is preferable that it is a multilayer structure which uses the polyester base material which provided layer 2a, 2b, 2e as an essential component. And in terms of gas barrier property, it is preferable to use the gas barrier base material 6 provided with the inorganic compound vapor deposition layer 5b like the solar cell back surface sealing sheet 1B.

  Examples of the inorganic compound include aluminum oxide, silicon oxide, tin oxide, magnesium oxide, indium oxide, and composite oxides thereof. Any inorganic compound may be used as long as it is transparent and has a gas barrier property such as oxygen and water vapor. Among them, aluminum oxide and silicon oxide are particularly preferable.

  The optimum condition of the thickness of the gas barrier substrate 6 varies depending on the type and configuration of the inorganic oxide used, but generally it is preferably in the range of 5 to 300 m, and the value is appropriately selected. If the film thickness is less than 5 ml, a uniform film cannot be obtained, and the film thickness is not sufficient for exhibiting the barrier function. When the film thickness is larger than 300 nm, the film is subjected to flexibility, and there is a possibility that a crack is easily generated due to external stress. Preferably, it exists in the range of 10-150 m. As a method of providing these vapor deposition layers, it can be formed by a normal vacuum vapor deposition method, but other thin film formation methods such as sputtering, ion plating, and plasma vapor deposition (CVD) are used. Is also possible. If necessary, an overcoat layer 5a composed of an ethylene-vinyl acetate copolymer portion or a completely saponified product and a silane compound is provided on the inorganic compound vapor-deposited layer in order to further improve gas barrier properties. You can also. These overcoat layers 5a can be provided mainly by a technique such as gravure coating.

By providing the easy-adhesion coat layers 2a, 2b, and 2e, which have been described above, the moisture and heat adhesion with EVA as a filler is improved, and it is possible to maintain 3000h in an 85 ° C-85% RH environment and 200h in PCT evaluation. It becomes possible. However, if the evaluation is so severe, the solar cell back surface sealing sheets 1A, 1B, 1C themselves may be damaged. Therefore, it is preferable to use a base material having weather resistance or hydrolysis resistance even in the above severe storage environment.
Such materials include polyester base materials selected from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polycyclohexanedimethanol-terephthalate (PCT), polycarbonate base materials, polyfluorinated base materials. Vinyl (PVF), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polyethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) , A fluorine-based substrate selected from tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or an acrylic modified product of these fluorine-based substrates. Can.

  When a biaxially stretched polyester base material such as polyethylene terephthalate is used as the material for the solar cell back surface sealing sheets 1A, 1B, 1C, there is no particular limitation, but the solar cell back surface sealing sheets 1A, 1B, It is possible to select materials according to the required functions required for 1C. For example, when there is a concern about the effect of shrinkage due to heat when manufacturing a solar cell module, a polyester base material having a heat shrinkage rate of 1% or less, preferably 0.5% or less by performing an annealing treatment is used. It is possible to use. When weather resistance is required, UV absorbers such as benzophenone, benzotriazole, and triazine, hindered phenol-based, phosphorus-based, sulfur-based, tocopherol-based antioxidants, hindered amine-based light stabilizers are also appropriately used. It is possible to mix. When there is a concern about hydrolysis of the polyester base in terms of weather resistance, the number average molecular weight is in the range of 18000 to 40000, the cyclic oligomer content is 15 wt% or less, preferably 0.5 wt% or less, and the intrinsic viscosity is It is preferable to use a polyester base of 0.5 dl / g or more.

  In addition, when the polyester molecule terminal is a carboxylic acid group, it acts as a heat, water, and acid catalyst and is most affected by hydrolysis, so the number average molecular weight is increased without increasing the amount of the terminal carboxylic acid. A solid phase polymerization method that can be used, or a method of sealing a terminal carboxylic acid group with a carbodiimide compound, an epoxy compound, or an oxazoline compound can be used. However, in terms of the above-described heat shrinkage rate and weather resistance, it is possible to select a polyester base material according to the function required as a solar cell module, but it is not limited to these, and is very general. A general-purpose polyester resin such as polyethylene terephthalate can be used as the base material. These base materials can be used as the base material of the gas barrier base material 6 even if it is used for the base materials 3a, 3b, 3c to which the easy-adhesion coat is applied.

  Although the base material used for solar cell backside sealing sheets 1A, 1B, and 1C may be transparent, it is preferable to use a white film from the viewpoint of improving the power generation efficiency of the solar cell element. In particular, when the solar cell back surface sealing sheets 1A, 1B, and 1C have a multi-layer structure, it is possible to provide a white film on at least the base material bonded to the filler. Also, a black film using a black pigment (for example, carbon black) can be used.

For white films, add “white pigments” such as titanium oxide, silica, alumina, calcium carbonate, barium sulfate, or in the case of polyester films, add incompatible polymers and fine particles. It is possible to use a “fine foam type” or the like that is whitened by forming voids at the blend interface during axial stretching.
In the “fine foaming type”, the polymer incompatible with the polyester is preferably a polyolefin resin such as polyethylene, polypropylene, polybutene, polymethylpentene. If necessary, polyalkylene glycol or a copolymer thereof can be used as a compatibilizing agent. Specific examples of the fine particles include organic particles and inorganic particles. Silicon particles, polyimide particles, crosslinked styrene-divinylbenzene copolymer particles, crosslinked polyester particles, fluorine-based particles, and the like are used. As the inorganic particles, calcium carbonate, silicon dioxide, barium sulfate or the like is used.

  When laminating and bonding various substrates including the substrates 3a, 3b, and 3c provided with the easy-adhesion coat layers 2a, 2b, and 2e, a urethane-based adhesive or the like is used, and a dry lamination is known. It is possible to laminate by a technique. In this way, it is possible to obtain solar cell backside sealing sheets 1A, 1B, and 1C having good adhesion to the ethylene-vinyl acetate copolymer resin composition that is a filler of the solar cell module. is there.

<Solar cell module>
Next, the solar cell module M to which the present invention shown in FIG. 4 is applied will be described.
As shown in FIG. 4, the solar cell module M includes a glass plate 11, solar cells 13 as photovoltaic elements provided with wirings 12, and a solar cell back surface sealing sheet 1 </ b> A (or 1 </ b> B, 1 </ b> C). And a filler (14a, 14b) and a frame (spacer) 15 between the glass plate 11 and the solar cell back surface sealing sheet 1A (or 1B, 1C) fixed by the frame (spacer) 15. In addition to being hermetically sealed, the solar cell element 13 is disposed in the sealed space and filled with the filler 14.

As shown in FIG. 5, the solar cell module M is manufactured in a batch system using an apparatus called a laminator 16, and the method is as follows.
[S1] Glass plate 11, filler 14b, solar battery cell 13, filler 14b, solar battery back surface sealing sheet 1A (or 1B, 1C) on heated top plate 10 (approximately 120 to 160 ° C.) set.
[S2] The chambers 17a and 17b are evacuated.
[S3] The chamber 17a is opened to the atmosphere, and the heat-resistant rubber sheet 18 is brought into close contact with the solar cell module M.
[S4] The ethylene / vinyl acetate copolymer as fillers 14a and 14b is melted by the heat / pressure, the solar cell 13 is embedded, and the glass plate 11 / solar cell 13 / solar cell back surface sealing sheet 1A ( Alternatively, 1B and 1C) are bonded and the fillers 14a and 14b are crosslinked and solidified.

  At this time, the step [S4] is classified into a case where a cross-linking reaction is performed in an oven provided in another line after lamination and a case where a cross-linking reaction is performed inside the laminator 16. The former is a type called standard cure, and the latter is a type called fast cure. Each type has advantages / disadvantages, but in the case of fast cure, the time to apply heat is shorter than that of standard cure, so it can affect the adhesion of solar cell backside sealing sheet 1A (or 1B, 1C) However, it is possible to improve the adhesion failure due to the EVA type by using the above-described easy-adhesion coats 2a, 2b, and 2e.

  By using the solar cell backside sealing sheet 1A (or 1B, 1C) of the present invention for this solar cell module M, the heat-fusible film and the solar cell backside sealing sheet 1A (or 1B) even under high temperature and high humidity. 1C) is not accompanied by a decrease in adhesion, so it is possible to maintain not only the poor appearance due to delamination, but also the barrier characteristics as a back surface sealing sheet and the electrical output characteristics as a solar cell. It becomes.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, it is not limited to a following example.

《Design and evaluation of easy adhesion coat》
About the composition of the polyester base material which provides an easy-adhesion coat layer, and an easy-adhesion coat layer, it designed as follows.

[Polyester substrate on which an easy-adhesion coat layer is provided]
<Base-1>
A hydrolysis-resistant polyethylene terephthalate film (thickness: 188 μm: manufactured by Toray Industries, Inc.) obtained by a solid phase polymerization method was used as a substrate. The base material has an oligomer content of 0.5 wt%, a number average molecular weight of 19,500, and an intrinsic viscosity of 0.7 dl / g. This base material is subjected to corona treatment.
<Substrate-2>
A hydrolysis-resistant polyethylene terephthalate film (thickness: 188 μm: manufactured by Toray Industries, Inc.) obtained by a solid phase polymerization method was used as a substrate. The oligomer content of this substrate was 0.5 wt%, the number average molecular weight was 19,500, Intrinsic viscosity is 0.7 dl / g This substrate is not corona treated.
<Base material-3>
A general polyethylene terephthalate film (thickness: 188 μm: manufactured by Toray Industries, Inc.) was used as a base material.

[Composition of easy-adhesion coat layer]
<PU-1>
A water-dispersed ionomer type polyurethane resin (Dainippon Ink Co., Ltd.) having a film flow start temperature of 180 ° C. and a glass transition temperature (Tg) = 25 ° C. was used.
<PU-2>
A water-dispersed ionomer type polyurethane resin (Dainippon Ink Co., Ltd.) having a film flow start temperature of 180 ° C. and a glass transition temperature (Tg) = 55 ° C. was used.
<PU-3>
A water-dispersed ionomer type polyurethane resin (Dainippon Ink Co., Ltd.) having a film flow start temperature of 95 ° C. and a glass transition temperature (Tg) = 25 ° C. was used.
<Crosslinking-1>
Polyisocyanate for water-based urethane (Dainippon Ink Co., Ltd.) was used.
<Crosslinking-2>
An epoxy compound for water-based coating agent (Dainippon Ink Co., Ltd.) was used.
<Crosslinking-3>
A butylated melamine compound (Dainippon Ink Co., Ltd.) was used.
<Crosslinking-4>
β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane (manufactured by Azmax) was used.
<PAA-1>
Polyacrylic acid sodium salt (manufactured by Toa Gosei Co., Ltd.) was used.
<PAA-2>
Polyacrylic acid ammonium salt (manufactured by Toa Gosei Co., Ltd.) was used.
<Leveling agent>
<Anti-blocking agent> using acetylene diol ethylene oxide adduct (produced by Air Products)
Silica powder having a secondary particle diameter of 10 to 50 μm was used.

[Preparation of coating composition]
Materials were blended so as to have the blending formulation shown in Table 1, and coating compositions consisting of samples 1 to 15 were produced.

The adjustment method adjusts the solid content in the coating composition based on the idea that a water-dispersed ionomer-type polyurethane resin weighed in a predetermined amount is diluted with an aqueous solution of polyaglylate. Thereafter, a predetermined amount of a crosslinking agent was blended while stirring, and finally an auxiliary agent such as a leveling agent and an antiblocking agent was blended. In this example, leveling agents are blended in all configurations.
The solution viscosity was adjusted to 100 to 200 mPa · S. The leveling agent was added in an amount of 1000 ppm in the state of the coating liquid, and 3000 ppm was added to the solid content when the anti-blocking agent was added.

[Coating composition coating]
About the samples 1-12, it applied so that the dry application quantity might be set to 5-6 g / m < ² > using the micro gravure.
At that time, the ratio of the micro gravure was adjusted to 1.2 to 1.3 so that the coated surface was flat. Then, dry baking was performed at 150-160 degreeC. About Examples 13-15, it traveled so that the dry coating amount might be set to 5-6 g / m < ² > similarly using the Mayer bar coater. The coating surface at this time was dared so that the wire rod streaks of the bar appeared in stripes in the flow direction. Similarly, dry baking was performed at 150 to 160 ° C. The sample form is as shown in FIG.

[Preparation of evaluation sample]
A fast cure type ethylene-vinyl acetate copolymer resin composition was used as a filler for a solar cell module. Because it is a basic evaluation, the above-mentioned ethylene-vinyl acetate copolymer sheet having the same size and thickness of 600 μm is placed directly on an A4 size tempered glass without using solar cells, and further, a sheet for backside sealing is placed thereon. An easy-adhesion coat-coated base material was provided. After preheating at 40 ° C. for 3 minutes in advance, a laminate was applied at 150 ° C. under vacuum for 6 minutes and pressure bonding for 8 minutes under a pressure of 1 atm. This sample was used in the following evaluation.

[Evaluation of wet heat resistance]
Immediately after laminating the above sample and at an initial temperature of 500, 1000, 1500, 2000, 2500, 3000 hours in an environment of 85 ° C.-85% RH, the laminate strength (15 mm width) was measured using a tensilon and the crosshead speed was 300 mm / Measured in min. Those having a strength of 1 N / 15 mm or more after storage for 3000 hours are marked with ◎, those having a strength of 1 N / 15 mm or more after 2000 h are marked with ◯, and others with x. The passing score is ○ or more.

[Anti-blocking effect]
Evaluation was performed using a single polyester film provided with an easy-adhesion coat layer. The state of this film has a layer structure of “polyester film / easy adhesion coat”. Ten samples of this 100 × 100 mm size cut were stacked so as to be “polyester film / easy adhesion coat” / “polyester film / easy adhesion coat” /... The underlined part) was evaluated with a blocking tester. The load is 10 kg / cm ² and the storage environment is 60-5 days. Samples that gave a peeling sound when peeled off were marked with ×, and Δ, ○, and ◎ were marked according to the peeling sound and the adhesion state (◎ means no peeling sound at all). Since this evaluation is at a level where there is no practical problem even with ×, it is used as reference data for comprehensive evaluation described later.

[Durability evaluation of encapsulant]
The above-mentioned sample forms a part of the solar cell backside sealing sheet, and there is a problem if the member is broken even if the moisture and heat adhesion is good. Therefore, in evaluating the moisture and heat resistance adhesion, it was determined whether measurement was possible or the substrate was destroyed. A sample capable of measuring at least 2000 h was evaluated as “◯”, and a sample with a base material destruction at 2000 h was evaluated as “x” because it was not durable. The pass is ○.

[Comprehensive evaluation]
The pass / fail of the above evaluation results is evaluated overall. However, the greatest specific gravity is the wet heat and heat adhesion, and when the blocking / durability is ○, the wet heat adhesion performance is x, the overall evaluation is x. If the wet heat adhesion performance is more than △, the evaluation of ○, △, and × was performed by combining additional functions such as blocking and durability. This is a performance that can be dealt with, but there is no alternative method for wet heat-resistant adhesion). If the overall evaluation is Δ or more, it was determined to be acceptable.
The results are shown in Table 2.

  Sample 1 is Comparative Example 1, but the wet heat-resistant adhesion performance is maintained up to 1000 h, which was the initial target level, but after that, a decrease in strength is confirmed. On the other hand, the life extension effect of 500-1000h is recognized by mix | blending sodium polyacrylate (Example 1). Furthermore, it became possible to implement | achieve the adhesion performance to 3000 h by using the base material without a corona treatment (Example 2). The same behavior has been confirmed even when ammonium polyacrylate or other crosslinking agent is used (Examples 3 to 5). It can also be seen that the influence of the blending ratio of sodium polyacrylate and the film flow start temperature of water-dispersed ionomer type polyurethane is large (Comparative Examples 2 and 3).

  On the other hand, in terms of blocking resistance as an additional function, an improvement tendency is recognized by blending a material having a high glass transition temperature (Tg), but it has been confirmed that the adhesion performance cannot be obtained if too much is added. (Example 6, Comparative Example 4). In this sense, it can be seen that it is also an effective means to study the blending of the antiblocking agent and the coating surface condition, and it can be seen that these combined effects are most preferable (Examples 7 to 10). However, it was also confirmed that even the most preferable configuration of Example 15 does not have 2000 h without the weather resistance of the base material, so that the overall evaluation results in Δ.

<< Evaluation as solar cell module >>
[Substrate used for solar cell back surface sealing sheet]
<Outermost film layer>
A “pigment dispersion type” white polyethylene terephthalate film (manufactured by Toray) having a thickness of 50 μm was used. The polyester film uses a polyester resin whose hydrolysis resistance is improved by the above-described solid-phase polymerization. This film substrate was used as the outermost film substrate. In addition, a white type of polyvinyl fluoride film (PVF: 25 μm DuPont) obtained by a solvent casting method was also used as the outermost film substrate.
<Gas barrier layer>
A normal biaxially stretched polyethylene terephthalate film having a thickness of 12 μm was provided with an alumina vapor deposition layer of 20 m by PVD, and an overcoat layer of 1 μm of a coating layer made of a silane compound on a completely saponified ethylene-vinyl acetate copolymer. This substrate was used as a gas barrier substrate.

[Production of solar cell backside sealing sheet]
<Urgent film layer> / <Gas barrier layer> / <any of samples 1 to 15> Urethane adhesive {polyester-based main agent + (isophorone diisocyanate / xylylene diisocyanate) -based curing agent} so as to be in a laminated state Lamination was performed by a dry laminating method. The obtained laminate was subjected to engineering for 96 hours in a 50 ° C. environment.
This sample was used as a solar cell back surface sealing sheet. The form of the sample is the same as that shown in FIG.

[Production of solar cell module]
Then, the solar cell module M as shown in FIG. 4 was produced using these samples. A fast cure type ethylene-vinyl acetate copolymer resin composition was used as a filler for a solar cell module. The solar cell used was polycrystalline silicon. A cell sandwiched between the ethylene-vinyl acetate copolymer sheets having the same size and a thickness of 600 μm was placed on an A4-sized tempered glass, and a back-surface sealing sheet was further provided thereon. After preheating at 40 ° C. for 3 minutes in advance, vacuuming at 150 ° C. for 6 minutes, pressure bonding for 8 minutes, laminating at a pressure of 1 atm, and then mounting the frame and terminal box with an aluminum frame .

"Evaluation of output characteristics"
Immediately after laminating the sample and measuring the electrical output characteristics when the accelerated test is performed for 3000 hours in an environment of 85 ° C.-85% RH according to JIS-C8913, and the rate of change of the maximum output before and after the storage evaluation is 80% or more Passed.

<Example 12>
In the case where the outermost layer is a white polyester film and the base material coated with an easy-adhesion coat is Sample 14, the moisture and heat resistance after storage for 3000 hours is an evaluation result equivalent to that of Sample 14, and the battery output characteristic is 94%. I kept it.

<Example 13>
As a result of evaluating the outermost layer as a white polyvinyl fluoride film in the same manner as in Example 12, the moisture and heat resistance after storage for 3000 hours was the same as that of the sample 14, and the battery output characteristic was maintained at 90%.

<Comparative Example 5>
In the case where the outermost layer is a white polyester film and the base material coated with an easy-adhesion coat is Sample 1, the heat-and-moisture-resistant adhesion after storage for 3000 hours is the same as the evaluation result of Sample 1, and floating occurs at 2500 hours. It was. The battery output characteristic in this state was less than 80%.

  From the above results, the sheet for sealing the back surface of the solar cell of the present invention has an adhesive property even after 3000 hours in a harsh environment of 85 ° C.-85% RH regardless of the type of ethylene-vinyl acetate copolymer. Since it is not accompanied by a reduction, it was shown that not only the appearance defect accompanying delamination but also the barrier characteristics as the back surface sealing sheet and the electric output characteristics as the solar cell can be maintained.

FIG. 1 is a cross-sectional view of a solar cell back surface sealing sheet according to the present invention. FIG. 2 is a schematic view of the coated surface of the easy-adhesion coat layer in the solar cell back surface sealing sheet according to the present invention. FIG. 3 is a view for explaining winding of the solar cell back surface sealing sheet in the solar cell back surface sealing sheet according to the present invention. FIG. 4 is a cross-sectional view of the solar cell module according to the present invention. FIG. 5 is a schematic view showing a manufacturing process of the solar cell module according to the present invention.

Explanation of symbols

1A, 1B, 1C ... solar cell back surface sealing sheet, 2a, 2b, 2e ... easy adhesion coating layer, 2c, 2d ... coating film, 3a, 3b, 3c ... substrate, 4 ... first adhesive layer, 5a Inorganic compound vapor deposition layer, 5b ... Overcoat layer, 6 ... Gas barrier substrate, 7 ... Polyester layer, 8 ... Second adhesive layer, 9, 9a ... Outermost layer, 10 ... Top plate, 11 ... Glass plate, 12 ... Wiring, 13 ... solar cell, 14, 14a, 14b ... filler, 15 ... frame, 16 ... laminator, 17a, 17b ... chamber, 18 ... rubber sheet, M ... solar cell module.

Claims (14)

A solar cell back surface sealing sheet provided with an easy-adhesion coat layer on the surface to be bonded to the filler constituting the solar cell module,
The easy-adhesion coat layer is composed of a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a melamine compound, the following general formula (I) with respect to 100 parts by mass of a water-dispersed ionomer type polyurethane resin having a film softening point temperature of 100 ° C. or higher. It is formed with a coating composition in which 0.1 to 10 parts by mass of a crosslinking agent selected from at least one compound selected from the compounds having the structure represented, and further 0.1 to 10 parts by mass of polyacrylic acid or a derivative thereof. And
The sheet for sealing a back surface of a solar cell, wherein the polyacrylic acid or a derivative thereof is a sodium salt of polyacrylic acid or an ammonium salt of polyacrylic acid .

(In the formula (I), R1, R2, R3, R4 have hydrogen, halogen, alkyl group, alkoxyl group, (meth) acryloyl group, allyl group, vinyl group, glycidyl group, isocyanate group, mercapto group, amine group. Selected from any of the substituents.)   The solar cell back surface sealing sheet according to claim 1, wherein the water-dispersed ionomer type polyurethane has a glass transition temperature (Tg) of 50 ° C or lower.   The water-dispersed ionomer type polyurethane includes a water-dispersed ionomer type polyurethane (PU-1) having a glass transition temperature (Tg) of 50 ° C. or less, and a water-dispersed ionomer type having a glass transition temperature (Tg) in the range of 50 to 80 ° C. 2. The solar cell back surface sealing according to claim 1, comprising a mixture of polyurethane (PU-2) and having a mass ratio of (PU-1) / (PU-2) = 50/50 to 99/1. Stop sheet. During the coating composition, wherein the ethylene oxide adduct of acetylene diol or acetylenic diol is further compounded, a rear surface of a solar cell sealing sheet according to any one of claims 1-3. The solar cell back surface sealing sheet according to any one of claims 1 to 4 , wherein an inorganic filler antiblocking agent or a fatty acid amide slip agent is further blended in the coating composition. . The said coating composition is the range of the viscosity of the solution state containing a solvent of 50-500 mPa * S, and is provided in the range of 0.5-10 g / m < ² > as a dry film, It is characterized by the above-mentioned. The sheet | seat for solar cell back surface sealing | blocking as described in any one of 1-5 . The solar cell back surface sealing sheet according to any one of claims 1 to 6 , wherein the coating composition has a coating film surface formed in a dot shape or a stripe shape. The solar cell back surface sealing sheet according to any one of claims 1 to 7 , wherein the easy adhesion coat layer is provided on an untreated polyester base material. The solar cell back surface sealing sheet according to any one of claims 1 to 8 , wherein the solar cell back surface sealing sheet has a multilayer structure including at least one polyester layer made of the same material as the polyester base material. Characterized in that a multilayer structure comprising at least one layer of barrier substrates provided with an inorganic compound deposition layer, a solar cell rear surface sealing sheet according to any one of claims 1-9. Characterized in that a multilayer structure comprising at least one layer of substrate layer having a weather resistance, a solar cell rear surface sealing sheet according to any one of claims 1-10. The substrate layer having weather resistance is a polyester substrate selected from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polycyclohexanedimethanol-terephthalate (PCT), polycarbonate substrate , Polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polyethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), a fluorine-based substrate selected from tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or an acrylic modified product of these fluorine-based substrates. Characterized in that, a rear surface of a solar cell sealing sheet according to claim 11, wherein. The substrate layer having weather resistance is polyethylene terephthalate having a number average molecular weight in the range of 18,000 to 40,000, the cyclic oligomer content is 15 wt% or less, and the intrinsic viscosity is 0.5 dl / g or more. The solar cell back surface sealing sheet according to claim 11 or 12 , characterized in that it is characterized in that: A solar cell module comprising the solar cell back surface sealing sheet according to any one of claims 1 to 13 .

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