JP2012059732A - Back protective sheet for solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back protective sheet for a solar cell, excellent in weather resistance and moisture resistance and remarkably suppressing peeling between layers in long-term use at outdoors, and also to provide a solar cell module excellent in long-term reliability, such as electrical characteristics and mechanical characteristics.SOLUTION: The back protective sheet for a solar cell at least includes: a layer (A layer) mainly composed of a vinylidene fluoride resin; a layer (B layer) mainly composed of an acrylic thermoplastic elastomer; a layer (C layer) comprising one or more selected from a styrene-conjugated diene block copolymer and a hydrogen additive of the copolymer; and a layer (D layer) comprising a polypropylene resin, while the layers are laminated in the order of from the A layer to the D layer.

Description

The present invention relates to a back sheet for a solar cell module.

The solar cell module includes a transparent protective member on the surface side such as a glass substrate, an ethylene-vinyl acetate copolymer (EVA) film for a sealing film filler, a silicon power generation element, an EVA film for a sealing film filler, and a back surface protection. In general, the sheets are laminated in this order, and the EVA film is heated and melted to be crosslinked and cured to be integrated.

Since the solar cell module is mainly used outdoors, sufficient durability and weather resistance are required in its configuration and material structure. In addition, if the sealing film filler peels or discolors due to moisture permeation or corrodes the wiring, it may affect the module output itself. Must be small (excellent in moisture barrier properties). As such a material, for example, a type in which a polyvinyl fluoride resin (PVF) film or a polyvinylidene fluoride resin (PVDF) film having excellent weather resistance is laminated on both sides of an aluminum foil with an adhesive, or a polyester on both sides of an aluminum foil. What laminated | stacked the resin film with the adhesive agent is used.

Those using fluororesin film are excellent in weather resistance and heat resistance of the film itself, but are used for lamination, generally urethane resin adhesive, epoxy resin adhesive, etc. However, this adhesive was inferior in durability such as weather resistance, heat resistance and moisture resistance. Therefore, in long-term use, the adhesive on the layer placed on the back side of the module will change in quality due to heat, moisture, etc., leading to deterioration of electrical and mechanical properties, and peeling and destruction of the film layer. In addition, there is a drawback that the processing cost is high because the three layers are laminated. In addition, the fluorine resin film is softened by the heat of 140 ° C. to 150 ° C. hot press applied at the time of solar cell module creation, and the protrusions of the solar cell element electrode part penetrate the filler layer, and further constitute the back surface protection sheet There is a risk that the solar cell element and the aluminum foil may be short-circuited to adversely affect battery performance by penetrating the fluorine resin film on the inner surface and contacting the aluminum foil in the back surface protective sheet. .

In order to eliminate such drawbacks, a two-layer type protective sheet based on a polyester resin film excellent in weather resistance and strength has been proposed. For example, Patent Document 1 exemplifies a material in which an inorganic oxide is laminated on one side of a polyester film by vapor deposition, and Patent Document 2 exemplifies a material in which PVF is laminated on one side of a polyester film. However, the polyester film has a defect that it is inferior in hydrolysis resistance in a high temperature region, and in a heat and humidity resistance test in accordance with JIS C-8917, it is reliable in terms of long-term stability due to deterioration. It was inferior to.

On the other hand, the film which improved defects, such as mechanical strengths, such as the tearing force of the said fluororesin, is proposed by making it the alloy film of PVDF and PMMA as a fluororesin (patent document 3). However, as with other fluororesin films, this alloy film is insufficient for use as a back surface protection sheet for solar cells to suppress the mechanical strength properties and moisture penetration. In order to compensate for these characteristics, it has been proposed to laminate a fluorine resin film with a sheet of an olefin resin such as polypropylene that can prevent moisture penetration (for example, Patent Document 4). However, PVDF-based films and olefin-based films such as polypropylene are extremely difficult to laminate, and even when laminated using acrylic or urethane adhesives, when used under long-term outdoor direct sunlight, It has been difficult to prevent peeling, and improvement has been demanded.

JP 2000-174296 A JP 2002-83978 A JP-A-2-30528 JP 2001-111077 A

An object of the present invention is to provide a solar cell module having excellent weather resistance, moisture resistance, and long-term reliability such as electrical characteristics and mechanical characteristics, and at least vinylidene fluoride resin as a back surface protection sheet thereof It is an object of the present invention to provide a back surface protection sheet comprising a laminated sheet of a thermoplastic resin having a layer and a polypropylene resin layer, and remarkably suppressing delamination between each layer particularly in long-term outdoor use.

The inventors of the present invention provide a method for maintaining the adhesion between a weatherable vinylidene fluoride resin layer and a moisture-resistant polypropylene resin layer in a long-term outdoor use of a solar cell back surface protection sheet. The inventors have intensively studied to arrive at the present invention.
That is, the present invention includes at least a layer mainly composed of vinylidene fluoride resin (A layer), a layer mainly composed of an acrylic thermoplastic elastomer (B layer), a styrene-conjugated diene block copolymer, and hydrogen thereof. A back surface protection sheet for a solar cell module having a layer composed of one or more selected from additives (C layer) and a layer composed of a polypropylene resin (D layer) and laminated in the order of A layer to D layer It is. The A layer is preferably composed of a resin composition containing 95 to 50 parts by mass of a vinylidene fluoride resin and 5 to 50 parts by mass of a methacrylic ester resin.
It is preferable that the content of acrylic acid-n-butyl in the acrylic thermoplastic elastomer used for the B layer is 50 to 90% by mass.
It is preferable to use a styrene-conjugated diene block copolymer having a conjugated diene content of 50 to 80% by mass for the C layer.

Furthermore, it is preferable that each of the layers A to D has a thickness in the following range.
A layer: 10-50 μm
B layer: 10-30 μm
C layer: 10-30 μm
D layer: 100-300 μm

The manufacturing method of the back surface protection sheet for solar cell modules of this invention melt | dissolves at least the raw material which comprises each layer of AD with each separate extruder, and laminates | stacks with a feed block or a multi-manifold die. It is characterized by.

Moreover, this invention includes the solar cell module using the said back surface protection sheet.

The solar cell back surface protective sheet of the present invention is excellent in weather resistance and moisture resistance, and is particularly peeled between a vinylidene fluoride resin layer and a polypropylene resin layer when laminated on a solar cell module and used outdoors for a long period of time. Therefore, it is possible to provide a solar cell module having excellent long-term reliability such as electrical characteristics and mechanical characteristics of the solar cell module.

The back protective sheet for a solar cell module of the present invention includes a layer (A layer) mainly composed of vinylidene fluoride (PVDF) resin, a layer (B layer) mainly composed of an acrylic thermoplastic elastomer, and aromatic vinyl. -It has each layer of the layer (C layer) which consists of 1 type or more selected from the diene block copolymer and its hydrogenated product, and the layer (D layer) which consists of polypropylene resin, and laminates in order of A layer to D layer It is the made back surface protection sheet for solar cell modules.

The PVDF resin constituting the A layer of the present invention may be a homopolymer of vinylidene fluoride, and is copolymerized with vinylidene fluoride as a main component and other fluorine-containing monomers in a range of up to 50% by mass. A copolymer may also be used. Examples of the fluorine-containing monomer that forms a copolymer with vinylidene fluoride include known fluorine-containing monomers such as hexafluoropropylene, tetrafluoroethylene, hexafluoroisobutylene, and various fluoroalkyl vinyl ethers. The A layer of the present invention contains at least 50% by mass of the PVDF resin. These PVDF resins are excellent in melt flowability among fluorine resins, have a high thermal decomposition temperature and good extrudability, and have excellent weather resistance and mechanical strength of the film. Suitable for use.

Furthermore, in order to give the A layer a heat-fusible property with the B layer mainly composed of an acrylic thermoplastic elastomer, a methacrylate ester-based polymethacrylic acid methyl ester (PMMA) having compatibility with PVDF (PMMA) ( (PMMA) resin is preferably contained. The PMMA resin referred to in the present invention refers to a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and less than 50% by mass of a copolymerizable monomer. Examples of the copolymerizable monomer include acrylates having 2 to 4 carbon atoms such as methacrylic acid esters having 2 to 4 carbon atoms, methyl acrylate and butyl acrylate, styrene, α-methylstyrene, acrylonitrile, Examples include acrylic acid and other ethylenically unsaturated monomers.

When forming the A layer with a mixture of PVDF resin and PMMA resin, the resin component compounding ratio is preferably 95 to 50 parts by mass for PVDF resin and 5 to 50 parts by mass for PMMA resin, more preferably. The PVDF resin is 90 to 70 parts by mass, and the PMMA resin is 30 to 10 parts by mass. When the content of the PVDF resin is less than 50 parts by mass, the weather resistance becomes insufficient when used as a back protective sheet for solar cells, and when the PVDF resin is excessive, sufficient fusion with the B layer is achieved. May not be obtained. By mixing the PMMA-based resin, the heat-fusibility of the B layer with the acrylic thermoplastic elastomer is improved.

On the other hand, to the layer A, inorganic particles such as titanium oxide and organic or inorganic pigments are appropriately added to the resin component for the purpose of providing concealability and enhancing reflectivity to increase the power generation efficiency of the solar cell. May be.

In this invention, 10-50 micrometers is preferable and, as for the thickness of this A layer, More preferably, it is 10-30 micrometers. In such a range, a laminated sheet can be easily produced, and a sheet having sufficient weather resistance when used as a solar cell back surface protective sheet can be obtained.

In the present invention, the acrylic thermoplastic elastomer constituting the B layer is preferably a methyl methacrylate / n-butyl acrylate / methyl methacrylate triblock copolymer from the viewpoint of adhesiveness with the C layer, It is preferable that the content of the acrylic acid-n-butyl component in the elastomer is 50% by mass or more and 90% by mass or less in terms of extrudability when producing the back protective sheet of the present invention described later. Similarly, in order to improve extrudability, a PMMA resin can be contained in a range not exceeding 30 parts by mass when the B layer is 100. This B layer exhibits heat-fusibility in both the A layer and the C layer, and serves as an adhesive for both. The thickness of the B layer is preferably in the range of 10 to 30 μm, more preferably 20 to 30 μm. If the thickness is less than 10 μm, the adhesion may be insufficient, and the method for forming such a thin layer may be limited. Further, as described above, the role of the B layer is to heat-seal both the A layer and the C layer with a sufficient adhesive force, so that usually 30 μm or less is sufficient.

As described above, the back surface protection sheet for solar cells is required to have a property that does not cause weathering deterioration due to direct sunlight, does not deteriorate characteristics due to heat, and does not cause alteration or peeling due to moisture penetration. As a result of intensive studies, the present inventors have laminated an ADF layer of PVDF resin having excellent weather resistance and a D layer of polypropylene resin having an effect of preventing moisture permeation. By providing a plastic elastomer B layer and a C layer made of an aromatic vinyl-diene block copolymer or a hydrogenated product thereof, the back surface protection for solar cell modules does not cause separation between layers even during long-term use. The inventors have found that a sheet can be obtained and have reached the configuration of the present invention. That is, the C layer of the present invention exhibits heat-fusibility in both the B layer and the D layer, and serves as an adhesive for both.

The styrene-conjugated diene block copolymer used in the C layer in the present invention includes a polymer block mainly composed of a styrene monomer and a polymer block mainly composed of a conjugated diene monomer in the structure. Polymer. Styrene monomers include styrene as a main component, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, 1 , 1-diphenylethylene or the like may be contained. The conjugated diene monomer is a compound having a conjugated double bond in its structure. For example, 1,3-butadiene (butadiene), 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl- There are 1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 2-methylpentadiene, etc., among which butadiene and isoprene are preferred. One type or two or more types of conjugated diene monomers can be used. A polymer block mainly composed of a styrene monomer is a polymer block consisting only of a structure derived from a styrene monomer, or a polymer block containing 50% by mass or more of a structure derived from a styrene monomer. It means both. The polymer block mainly composed of a conjugated diene monomer is a polymer block consisting only of a structure derived from a conjugated diene monomer, or a polymer block containing 50% by weight or more of a structure derived from a conjugated diene monomer. Means either. The conjugated diene content of the styrene-conjugated diene block copolymer is preferably 50 to 80% by mass. Conjugated diene content means the ratio of the mass which occupies in all the copolymers of the structure derived from a conjugated diene monomer. One type or two or more types of styrene-conjugated diene block copolymers can be used. A commercially available styrene-conjugated diene block copolymer can be used as it is.

Further, as the styrene-conjugated diene block copolymer used for the C layer, styrene and binary styrene-butadiene block copolymer resin, styrene-isoprene block copolymer resin, ternary styrene-butadiene-styrene block copolymer are used. Examples thereof include resins and styrene-isoprene-styrene copolymers. One or more resins selected from these polymers and hydrogenated products of these polymers can be used. Among them, when a styrene-ethylene-butylene-styrene block copolymer resin (SEBS), which is a hydrogenated resin of a styrene-butadiene-styrene block copolymer resin, is used, the thermal stability is good, which is preferable for producing the back surface protective sheet of the present invention. . The thickness of the C layer is preferably 10 to 30 μm, more preferably 20 to 30 μm, from the viewpoint of providing sufficient adhesive force.

The D layer plays a role of suppressing deterioration of the solar cell module due to moisture in the outdoors. In order to suppress moisture permeation, the thickness is preferably 100 to 300 μm, more preferably 150 to 250 μm. The polypropylene resin used in the D layer of the present invention is not particularly limited, and a sheet having the above thickness may be used regardless of whether it is a propylene homopolymer or a copolymer with another olefin according to the use. Or, general resins used for films can be used.

As mentioned above, the back surface protection sheet for solar cell modules of this invention has A layer, B layer, C layer, and D layer at least in order. An antistatic agent can be coated on both surfaces of the laminated sheet. In addition, a metal oxide film can be deposited for the purpose of improving water vapor permeability and gas permeability.

The method for obtaining the back surface protective sheet of the present invention is not particularly limited. In principle, the films of the respective layers A to D are formed by extrusion molding such as an inflation method or a T-die method. This film can also be produced by forming a four-layer laminate sheet by thermal lamination. As another method, the raw material resin or resin composition of each layer is supplied to a separate extruder, melted and kneaded, supplied to a feed block, and then passed through a T-die to produce a general laminated sheet 4 A laminated sheet of layers can be produced. This method can be efficiently manufactured with few manufacturing steps. Further, it can also be produced by supplying a melt-kneaded resin or a resin composition to a multi-manifold die having a four-layer structure to produce a laminated sheet. This method produces a sheet having a small thickness distribution of each layer. This is preferable.
Further, a two-layer film in which a B layer is formed on one side of the A layer film is prepared, while a two-layer sheet composed of a C layer and a D layer is prepared by a general two-layer coextrusion. It can also be produced by a method of laminating the surface on the B layer side of the two-layer film comprising the A layer and the B layer on the surface on the C layer side of the sheet by a thermal lamination method. The method for obtaining the two-layer film composed of the A layer and the B layer is not particularly limited, and may be a coextrusion method or a method of forming the B layer by coating.

The back surface protective sheet of the present invention is laminated with a high adhesive force between the layers A to D as compared with a sheet having no B layer and / or C layer. Therefore, it has a fluorine-based resin layer with excellent weather resistance and a polyolefin-based resin layer with excellent moisture resistance, and a back protective sheet that can maintain initial characteristics for a long period of time without peeling between each layer in long-term use is obtained. be able to.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these. First, the following resins were used in Examples and Comparative Examples.
(Raw materials used)
1. Layer A (a-1) Vinylidene fluoride resin: Kyner K720 (manufactured by Arkema)
(A-2) Methacrylate resin: Hi-pet HBS000 (Mitsubishi Rayon Co., Ltd.)
(A-3) White pigment: Titanium pigment D962S (manufactured by Sakai Chemical Co., Ltd.)
2. Layer B (b-1) Acrylic thermoplastic elastomer: LA2140E (manufactured by Kuraray Co., Ltd.)
Acrylic acid-n-butyl component content: about 80% methyl methacrylate / acrylic acid-n-butyl / methyl methacrylate triblock copolymer resin (pellet)
(B-2) Acrylic thermoplastic elastomer: LA2250 (manufactured by Kuraray Co., Ltd.)
Acrylic acid-n-butyl component content; about 70% methyl methacrylate / acrylic acid-n-butyl / methyl methacrylate triblock copolymer resin (pellet)
3. C layer
(C-1) Styrene-butadiene-styrene block copolymer: STR1602 (manufactured by Denki Kagaku Kogyo) * Styrene monomer content 40%
(C-2) Completely hydrogenated product of styrene-butadiene block copolymer
: Septon 8007 (Kuraray Co., Ltd.) * Styrene monomer content 30%
4). D layer Polypropylene resin: Prime Polypro F113G (Mitsui Chemicals)

Example 1
As the raw material for the A layer, the above-mentioned resin raw materials (a-1) and (a-2) are each 80 parts by mass, and 22 parts by mass of the raw material (a-3) is blended with respect to 100 parts by mass of the resin. The mixture was blended with a tumbler to obtain a mixture, and kneaded with a φ30 mm twin screw extruder to obtain a compound for layer A.
Next, as the raw materials, the A layer is the above compound, the B layer is the resin (b-1), the C layer is (c-1), and the D layer is the polypropylene resin. A laminate sheet having the thickness of each layer shown in Table 1 was prepared by a feed block method using a φ40 mm single screw extruder for the C layer and a φ65 mm single screw extruder for the D layer, and used as a back protective sheet.
(Example 2)
A back protective sheet was obtained in the same manner as in Example 1 except that (b-2) was used as a raw material used for the B layer.
Example 3
A back protective sheet was obtained in the same manner as in Example 1 except that the above (c-2) was used as a raw material used for the C layer.
(Example 4 and Example 5)
A back protective sheet was obtained in the same manner as in Example 1 except that the blending ratios of (a-1) and (a-2) as shown in Table 1 were used as the raw material for the A layer.

(Comparative Examples 1-3)
A back protective sheet was obtained in the same manner as in Example 1 except that the B layer, the C layer, and the D layer were not provided, and a three-layer configuration was used.
(Comparative Example 4)
A back protective sheet was obtained in the same manner as in Example except that (a-2) was 100 parts by mass and (a-3) was 5 parts by mass as the raw material for the A layer.

(Evaluation methods)
1) Interlayer adhesion (peel strength)
About the back surface protection sheet obtained by each Example and the comparative example, peel strength was measured based on JISK6854-1. (The peeling surface is between the B layer and the C layer for Examples 1 to 5, and each comparative example is shown in Table 2. Note that the sheet of Comparative Example 3 has a thin thickness and can measure the peel strength. There wasn't.

2) Moisture-proofing About the back surface protection sheet obtained by each Example and the comparative example, the water-vapor-permeation rate was measured by 25 degreeC x 90% RH based on JISK7129B. The lower the water vapor transmission rate, the better the moisture resistance.

3) Weather resistance The weather resistance of the back surface protection sheet obtained in each Example and Comparative Example was measured using a sunshine weatherometer in accordance with JIS K7350-2. As an evaluation of the back sheet after 3000 hours of irradiation, color difference measurement was performed according to JIS K7105. Moreover, the surface state of the external appearance was evaluated visually. The evaluation criteria were “◯ = almost no change” and “× = changes such as occurrence of cracks on the film surface”.

4) Moisture and heat resistance of interlayer adhesion The back surface protective sheet obtained in each Example and Comparative Example was evaluated in accordance with JIS C8990 as a moisture and heat resistance evaluation of interlayer adhesion strength. A dump heat test of 1000 hours was performed under conditions of relative humidity (85 ± 5)%. After the test, the peel strength was measured according to JIS K6854-1 as an evaluation of the adhesive strength of the sheet. (The peeling surface was shown in Table 2 for each comparative example between the B layer and the C layer for Examples 1-5.

In the example of Table 1, the quality, weather resistance, and interlayer adhesion are all good, whereas in the comparative example shown in Table 2, Comparative Example 4 in which PVDF is not used for the A layer is an environmental test. In other comparative examples, interlaminar adhesion was particularly poor after a 1000 hour wet heat resistance test.

The back sheet for a solar cell module of the present invention can be applied to a weather resistant decorative sheet provided with a printed layer in addition to the back sheet for a solar cell.

Claims (7)

At least selected from a layer mainly composed of a vinylidene fluoride resin (A layer), a layer mainly composed of an acrylic thermoplastic elastomer (B layer), a styrene-conjugated diene block copolymer, and a hydrogenated product thereof. A back surface protection sheet for a solar cell module, which has each layer of a layer composed of one or more (C layer) and a layer composed of a polypropylene resin (D layer) and is laminated in the order of the A layer to the D layer. The back surface protection sheet for solar cell modules of Claim 1 which A layer consists of a resin composition which contains 95-50 mass parts of vinylidene fluoride type-resins, and 5-50 mass parts of methacrylate ester-type resins. The back surface protection sheet for solar cell modules according to claim 1 or 2, wherein the content of acrylic acid n-butyl in the acrylic thermoplastic elastomer used for the B layer is 50 to 90% by mass. The back surface protection sheet for solar cell modules of any one of Claims 1-3 which used the styrene diconjugated diene block copolymer whose conjugated diene content is 50-80 mass% for C layer. The back surface protection sheet for solar cell modules of any one of Claims 1-5 in which each layer of said AD has the following thickness.
A layer: 10-50 μm
B layer: 10-30 μm
C layer: 10-30 μm
D layer: 100-300 μm The raw material constituting at least each of the layers A to D is melted and extruded by individual extruders, and is laminated by a feed block or a multi-manifold die. The manufacturing method of the back surface protection sheet for solar cell modules as described in any one of. The solar cell module using the back surface protection sheet of any one of Claims 1-5.