Composition for forming solar cell sealing material, sheet for solar cell sealing material, solar cell sealing material, and solar cell module

Abstract

[Problem] To provide a composition for forming a solar cell sealing material that is for producing a solar cell sealing material having excellent heat resistance and durability and that enables high productivity and has excellent slip resistance. [Solution] A composition for forming a solar cell sealing material, said composition comprising: an ethylene / α-olefin copolymer in which the terminal unsaturation amount is not less than 0.26 per 1,000 carbon atoms; a silane coupling agent; an organic peroxide; and a cross-linking aid, wherein the content of the cross-linking aid is less than 0.5 parts by mass with respect to 100 parts by mass of the ethylene / α-olefin copolymer, and a gel fraction measured by a prescribed method is not less than 70 mass%.

Description

Composition for forming solar cell encapsulants, sheets for solar cell encapsulants, solar cell encapsulants, and solar cell modules

[0001] The present invention relates to a composition for forming solar cell encapsulants, a sheet for solar cell encapsulants, a solar cell encapsulant, and a solar cell module.

[0002] Amidst increasingly serious global environmental and energy problems, solar cells are attracting attention as a clean and inexhaustible energy generation method. When solar cells are used outdoors, such as on the roofs of buildings, they are generally used in the form of solar cell modules.

[0003] The solar cell modules described above are generally manufactured by the following procedure. First, crystalline solar cell elements (hereinafter sometimes referred to as power generation elements or cells) formed from polycrystalline silicon, monocrystalline silicon, etc., or thin-film solar cell elements obtained by forming a very thin film of several micrometers on a substrate such as glass using amorphous silicon or crystalline silicon are manufactured. Next, to obtain a crystalline solar cell module, the following layers are laminated in the order of solar cell module protective sheet (front protective sheet) / solar cell encapsulant sheet / crystalline solar cell element / solar cell encapsulant sheet / solar cell module protective sheet (back protective sheet). On the other hand, to obtain a thin-film solar cell module, the following layers are laminated in the order of thin-film solar cell element / solar cell encapsulant sheet / solar cell module protective sheet (back protective sheet). After that, the solar cell module is manufactured by using a lamination method, which involves vacuum suction and heat compression to bond these layers together. Solar cell modules manufactured in this way are weather-resistant and suitable for outdoor use, such as on the roofs of buildings.

[0004] Ethylene-vinyl acetate copolymer (EVA) films are widely used as encapsulating film materials for solar cells due to their excellent transparency, flexibility, and adhesion. For example, Patent Document 1 discloses an encapsulating film with excellent adhesion and film-forming properties, comprising an EVA composition containing a crosslinking agent and trimellitic acid ester. However, when using an EVA composition as a constituent material for solar cell encapsulating materials, there have been concerns that components such as acetic acid gas generated by the decomposition of EVA may affect the solar cell elements.

[0005] In contrast, polyolefin-based materials, particularly ethylene-based materials, also exhibit excellent insulating properties and have been proposed for use as encapsulating film materials (see, for example, Patent Documents 2 and 8). Resin compositions for solar cell encapsulants using ethylene-α-olefin copolymers or ethylene-α-olefin-non-conjugated polyene copolymers have also been proposed (see, for example, Patent Documents 3 to 7).

[0006] Japanese Patent Publication No. 2010-53298, Japanese Patent Publication No. 2006-210906, Japanese Patent Publication No. 2010-258439, International Publication No. 2011 / 162324, International Publication No. 2011 / 153541, Japanese Patent Publication No. 2013-139558, International Publication No. 2012 / 070245, International Publication No. 2024 / 043449

[0007] Solar cell encapsulants using polyolefin-based encapsulation film materials are often manufactured by incorporating organic peroxides, silane coupling agents, crosslinking aids, etc., into the encapsulation film material to improve heat resistance and durability. According to the inventors' research, there was room for further improvement in preventing a decrease in productivity caused by the long impregnation time of additives into the encapsulation film material. Furthermore, there was also room for further improvement in preventing assembly defects caused by the bleed-out of additives, particularly crosslinking aids, contained in the encapsulation film material during the assembly of solar cell modules, resulting in slippage and misalignment of components during the solar cell module production process.

[0008] Furthermore, the inventors' investigations revealed that the polyolefin-based encapsulation film material disclosed in Patent Document 8 requires a long time for crosslinking. As a result, it was found that using this material reduces the productivity of solar cell module assembly, and also necessitates a longer impregnation time for additives into the encapsulation film material, leading to the aforementioned assembly defect problem.

[0009] This invention has been made in view of the problems of the prior art, and its objective is to provide a solar cell encapsulant that is highly productive and has excellent heat resistance and durability, as well as a composition for forming such a solar cell encapsulant and a sheet thereof that is highly productive and has excellent slip resistance.

[0010] As a result of diligent research to achieve the above objectives, the inventors of the present invention have found that the above objectives can be solved by using a material that contains an ethylene-α-olefin copolymer having a specific amount of terminal unsaturated groups, has a specific range of crosslinking agent content, and has a specific range of gel fraction, thereby completing the present invention.

[0011] The present invention relates, for example, to the following [1] to

[13] . [1] A composition comprising an ethylene-α-olefin copolymer (A), a silane coupling agent, an organic peroxide, and a crosslinking aid, wherein the content of the crosslinking aid is less than 0.5 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), wherein the gel fraction measured by the following measurement method is 70% by mass or more, and the ethylene-α-olefin copolymer (A) 1A composition for forming solar cell encapsulants, wherein the total amount of vinyl-type double bonds and vinylidene-type double bonds per 1000 carbon atoms, as determined by H-NMR, is 0.26 or more. <Method for measuring gel fraction> The composition is melt-kneaded in a twin-screw batch melt-kneading apparatus at 90°C with a screw rotation speed of 30 rpm for 5 minutes and formed into a sheet. The obtained sheet is molded in a hot press machine set to 145°C for 3 minutes under pressure of 10 MPa for 15 minutes, and then cooled at 20°C under pressure of 10 MPa for 4 minutes to obtain a sheet-like measurement sample with a thickness of 0.5 mm. 0.10 g of the measurement sample is weighed, wrapped in a 325 mesh stainless steel screen, and immersed in 30 ml of p-xylene in a sealed container at 140°C for 3 hours. Next, the screen is removed and dried at 80°C until it reaches a constant weight. The gel fraction (mass%) is calculated using the following formula. Gel fraction (mass%) = 100 × (W) ３ -W ２ ) / (W １ -W ２ ) (W １ : Mass of the screen and sample before immersion W ２ Screen mass W ３ (Mass of the screen and sample after immersion and drying)

[0012] [2] The composition for forming a solar cell encapsulant according to [1], wherein the content of the organic peroxide is 0.1 to 2 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), the content of the silane coupling agent is 0.1 to 1 part by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), and the 1-minute half-life temperature of the organic peroxide is in the range of 100 to 170°C.

[0013] [3] A composition for forming a solar cell encapsulant according to [1] or [2], comprising 0.005 to 5 parts by mass of at least one selected from the group consisting of ultraviolet absorbers, heat stabilizers, and light stabilizers, per 100 parts by mass of the ethylene-α-olefin copolymer (A).

[0014] [4] The composition for forming a solar cell encapsulant according to any one of [1] to [3], wherein the ethylene·α-olefin copolymer (A) satisfies the following requirements (a1) and (a2): (a1) the density measured in accordance with ASTM D1505 is 0.865 to 0.885 g / cm ３ . (a2) the melt flow rate (MFR) ２ measured in accordance with ASTM D1238 at 190°C under a load of 2.16 kg is 4.0 to 13 g / 10 min.

[0015] [5] The composition for forming a solar cell encapsulant according to any one of [1] to [4], wherein the ethylene·α-olefin copolymer (A) satisfies the following requirement (a3): (a3) the content of structural units derived from ethylene is 80 to 90 mol%, and the content of structural units derived from an α-olefin having 3 to 20 carbon atoms is 10 to 20 mol% (provided that the total of the content of structural units derived from ethylene and the content of structural units derived from the α-olefin is 100 mol%).

[0016] [6] The composition for forming a solar cell encapsulant according to any one of [1] to [5], wherein the amount of vinyl double bonds per 1000 carbon atoms determined by 1 1H-NMR of the ethylene·α-olefin copolymer (A) is 0.08 or more.

[0017] [7] The composition for forming a solar cell encapsulant according to any one of [1] to [6], wherein the ethylene·α-olefin copolymer (A) satisfies the following requirement (a4): (a4) the total amount of vinyl double bonds, vinylidene double bonds, disubstituted olefin double bonds and trisubstituted olefin double bonds per 1000 carbon atoms (total unsaturation content) contained in the ethylene·α-olefin copolymer (A) determined by 1 1H-NMR is 0.50 or more.

[0018] [8] A composition for forming a solar cell encapsulant according to any of [1] to [7] (for example, [1]), wherein the ethylene-α-olefin copolymer (A) satisfies all of the following requirements (a1) to (a3): (a1) Density measured in accordance with ASTM D1505 is 0.865 to 0.885 g / cm³ ３ (a2) Melt flow rate (MFR) measured in accordance with ASTM D1238 under conditions of 190°C and a 2.16 kg load. ２ The amount is 4.0 to 13 g / 10 min. (a3) ​​The content of constituent units derived from ethylene is 80 to 90 mol%, and the content of constituent units derived from α-olefins having 3 to 20 carbon atoms is 10 to 20 mol% (however, the sum of the content of constituent units derived from ethylene and the content of constituent units derived from α-olefins shall be 100 mol%).

[0019] [9] The ethylene-α-olefin copolymer (A) satisfies the following requirement (a4), and the ethylene-α-olefin copolymer (A) 1 A solar cell encapsulant forming composition according to any of the above [1] to [8] (for example, [1]), wherein the number of vinyl double bonds per 1000 carbon atoms determined by H-NMR is 0.08 or more. (a4) The ethylene-α-olefin copolymer (A) contains, 1 The total number of vinyl double bonds, vinylidene double bonds, disubstituted olefin double bonds, and trisubstituted olefin double bonds per 1000 carbon atoms, as determined by H-NMR, is 0.50 or more.

[0020]

[10] The composition for forming a solar cell encapsulant according to [8] or [9], wherein the content of the organic peroxide is 0.1 to 2 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), the content of the silane coupling agent is 0.1 to 1 part by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), the 1-minute half-life temperature of the organic peroxide is in the range of 100 to 170°C, and the composition contains at least one selected from the group consisting of ultraviolet absorbers, heat stabilizers, and light stabilizers in an amount of 0.005 to 5 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A).

[0021]

[11] A sheet for solar cell encapsulant comprising any of the solar cell encapsulant forming compositions described in [1] to

[10] above.

[0022]

[12] A solar cell encapsulant, which is a crosslinked material of the solar cell encapsulant sheet of

[11] .

[0023]

[13] A solar cell module comprising a transparent protective member on the front side, a protective member on the back side, a solar cell element, and a sealing layer including the solar cell sealing material of

[12] , wherein the sealing layer seals the solar cell element between the transparent protective member on the front side and the protective member on the back side.

[0024] According to the present invention, a solar cell encapsulant with high productivity and excellent heat resistance and durability is provided, as well as a composition and sheet for forming such a solar cell encapsulant, which also has high productivity and excellent slip resistance. Therefore, according to the present invention, the productivity of solar cell modules can be improved.

[0025] The following describes specific embodiments of the present invention in detail. However, the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention. Unless otherwise specified, the numerical range represented by "X to Y" means "X or more and Y or less".

[0026] [Composition for forming solar cell encapsulant and its sheet] The composition for forming solar cell encapsulant of the present invention contains an ethylene-α-olefin copolymer (A). The sheet for forming solar cell encapsulant of the present invention is made of the composition for forming solar cell encapsulant of the present invention.

[0027] <Ethylene-α-olefin copolymer (A)> The ethylene-α-olefin copolymer (A) is a copolymer of ethylene and α-olefin.

[0028] <α-olefin> As the α-olefin constituting the ethylene-α-olefin copolymer (A) (hereinafter sometimes simply referred to as "polymer (A)"), typically one or more α-olefins having 3 to 20 carbon atoms can be used.

[0029] Specific examples of α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, 1-octene, 1-decene, and 1-dodecene. Among these, α-olefins with 10 or fewer carbon atoms are preferred, and α-olefins having 3 to 8 carbon atoms, namely propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene, are particularly preferred. 1-butene is especially preferred.

[0030] The monomers constituting copolymer (A) may consist solely of biomass-derived monomers, solely of chemically recycled monomers, solely of fossil fuel-derived monomers, or may contain two or more of the biomass-derived monomers, chemically recycled monomers, and fossil fuel-derived monomers. It is preferable for copolymer (A) to contain constituent units derived from biomass-derived monomers from the viewpoint of reducing environmental impact. It is also preferable for copolymer (A) to contain constituent units derived from chemically recycled monomers from the viewpoint of reducing environmental impact (mainly waste reduction).

[0031] The ethylene-α-olefin copolymer (A) may be a random copolymer or a block copolymer, but a random copolymer is preferred from the viewpoint of flexibility. The content of ethylene-derived constituent units constituting the copolymer (A) (hereinafter sometimes referred to as "ethylene units") is usually 80 to 90 mol%, and the proportion of α-olefin-derived constituent units having 3 to 20 carbon atoms constituting the copolymer (A) (hereinafter sometimes referred to as "α-olefin units") is usually 10 to 20 mol% (however, the total of ethylene units and α-olefin units is set to 100 mol%).

[0032] When the α-olefin unit content is 10 mol% or more, the crystallinity is low and the transparency is high. Furthermore, extrusion molding is possible at low temperatures, for example, at temperatures lower than 130°C. Therefore, it is possible to suppress the crosslinking reaction of the organic peroxide kneaded into copolymer (A) in the extruder, and prevent the formation of gel-like foreign matter in the solar cell encapsulant sheet, which would degrade the appearance of the sheet. In addition, it has high flexibility, which can prevent cracking of the solar cell elements and chipping of thin-film electrodes during the lamination molding of solar cell modules.

[0033] Furthermore, when the α-olefin unit content is 20 mol% or less, the crystallization rate of the copolymer is appropriate. This prevents the sheet extruded from the extruder from becoming sticky, and facilitates peeling of the sheet on the first cooling roll. Also, since the sheet is not sticky, blocking is prevented, and the sheet feed-out performance is good. In addition, when crosslinking the sheet for solar cell encapsulation, crosslinking can be sufficiently advanced, making it possible to obtain a solar cell encapsulation material with high heat resistance.

[0034] In one preferred embodiment, the ethylene-α-olefin copolymer (A) does not contain constituent units derived from monomers other than ethylene and α-olefins having 3 to 20 carbon atoms, such as unconjugated polyenes.

[0035] The density of the copolymer (A), as measured in accordance with ASTM D1505, is typically 0.865 to 0.885 g / cm³. 3 That is the case.

[0036] The density of copolymer (A) can be adjusted by balancing the content ratio of ethylene units and α-olefin units. In other words, increasing the content ratio of ethylene units increases crystallinity and yields a high-density copolymer (A). On the other hand, decreasing the content ratio of ethylene units decreases crystallinity and yields a low-density copolymer (A).

[0037] The density of the ethylene-α-olefin copolymer is 0.885 g / cm³. 3 The following characteristics result in low crystallinity and high transparency. Furthermore, extrusion molding is possible at low temperatures, for example, at temperatures lower than 130°C. This prevents the organic peroxide kneaded into the ethylene-α-olefin copolymer (A) from undergoing a crosslinking reaction in the extruder, thus preventing the formation of gel-like foreign matter in the solar cell encapsulant sheet, which would otherwise degrade the sheet's appearance. In addition, its high flexibility prevents cracking of the solar cell elements and chipping of thin-film electrodes during the lamination molding of solar cell modules.

[0038] On the other hand, the density of the ethylene-α-olefin copolymer is 0.865 g / cm³. 3 As a result, the crystallization rate of the ethylene-α-olefin copolymer is appropriate. This prevents the sheet extruded from the extruder from becoming sticky, and facilitates the peeling of the sheet on the first cooling roll. Furthermore, since the sheet is not sticky, blocking is prevented, and the sheet feedability is good. In addition, when crosslinking the sheet for solar cell encapsulation, crosslinking is sufficiently advanced, making it possible to obtain a solar cell encapsulation material with high heat resistance.

[0039] The melt flow rate (MFR2) of the copolymer (A), measured in accordance with ASTM D1238 under conditions of 190°C and a 2.16 kg load, is typically in the range of 2.0 to 40 g / 10 min, preferably 3.0 to 20 g / 10 min, more preferably 5.0 to 15 g / 10 min, preferably 4.0 to 13 g / 10 min, and more preferably 4.5 to 12 g / 10 min.

[0040] The MFR2 of copolymer (A) can be adjusted by adjusting the polymerization temperature, polymerization pressure, and the molar ratio of ethylene and α-olefin monomers to hydrogen concentration in the polymerization system, as described later.

[0041] When the MFR2 is 2.0 g / 10 min or higher, the fluidity of the ethylene-α-olefin copolymer (A) is good, and sheet formation by extrusion molding is possible. Furthermore, it is possible to prevent gel formation due to shear heat generation during sheet extrusion molding.

[0042] On the other hand, if the MFR2 is 40 g / 10 min or less, adhesion to the roll surface of chill rolls and other materials due to the low molecular weight is prevented, and a sheet of uniform thickness can be easily formed. Furthermore, even sheets thicker than 0.3 mm can be easily formed. In addition, the crosslinking characteristics (especially the crosslinking speed) when crosslinking the sheet for solar cell encapsulating material are good, allowing for sufficient crosslinking and enabling the production of a solar cell encapsulating material with high heat resistance.

[0043] The copolymer (A) contains, 1 The total amount of vinyl-type double bonds and vinylidene-type double bonds per 1000 carbon atoms, as determined by H-NMR (hereinafter sometimes referred to as "terminal unsaturation amount"), is 0.26 or more, preferably 0.27 or more, more preferably 0.28 or more, and even more preferably 0.29 or more. The upper limit may be, for example, 0.6 or 0.5. That is, the terminal unsaturation amount is preferably 0.26 to 0.6, more preferably 0.27 to 0.6, even more preferably 0.28 to 0.5, and particularly preferably 0.29 to 0.5. By keeping the terminal unsaturation amount within the above range, the crosslinking characteristics (especially the crosslinking speed) when crosslinking the solar cell encapsulant sheet are improved, allowing crosslinking to proceed sufficiently and enabling the acquisition of a solar cell encapsulant with high heat resistance.

[0044] The copolymer (A) contains, 1The total amount of vinyl-type double bonds, vinylidene-type double bonds, disubstituted olefin-type double bonds, and trisubstituted olefin-type double bonds per 1000 carbon atoms, as determined by H-NMR (hereinafter sometimes referred to as "total unsaturated amount"), is usually 0.50 or more, preferably 0.60 or more, more preferably 0.65 or more, even more preferably 0.70 or more, and particularly preferably 0.75 or more. The upper limit may be, for example, 5.0. The above unsaturated group refers to a carbon-2 group containing an unsaturated bond. By keeping the total unsaturated amount within the above range, the crosslinking characteristics (especially the crosslinking speed) when crosslinking the sheet for solar cell encapsulating material are improved, allowing crosslinking to proceed sufficiently and enabling the acquisition of a solar cell encapsulating material with high heat resistance.

[0045] The copolymer (A) contains 1 The number of vinyl double bonds per 1000 carbon atoms, as determined by H-NMR, is preferably 0.08 or more, more preferably 0.09 or more, even more preferably 0.10 or more, particularly preferably 0.11 or more, and most preferably 0.12 or more. The upper limit may be, for example, 5.0. By setting the number of vinyl double bonds within the above range, the crosslinking characteristics (especially the crosslinking speed) when crosslinking the sheet for solar cell encapsulating material are improved, allowing crosslinking to proceed sufficiently and enabling the production of a solar cell encapsulating material with high heat resistance.

[0046] The quantitative determination of unsaturated groups (double bonds) in ethylene-α-olefin copolymers is performed. 1 This is performed by 1H-NMR measurement. Signals originating from unsaturated groups (double bonds) include vinyl-type double bonds, vinylidene-type double bonds, disubstituted olefin-type double bonds, and trisubstituted olefin-type double bonds, as shown below. The amount of double bonds is quantified from the integrated intensity of each signal. The main chain methylene signal of the ethylene-α-olefin copolymer is used as the chemical shift standard (1.2 ppm).

[0047]

[0048] In each formula, * indicates a bond with an atom other than a hydrogen atom. The peaks for each hydrogen atom a to e are observed around the following locations: • Peak for hydrogen atom a: 4.60 ppm • Peak for hydrogen atom b: 4.85 ppm • Peak for hydrogen atom c: 5.10 ppm • Peak for hydrogen atom d: 5.25 ppm • Peak for hydrogen atom e: 5.70 ppm

[0049] The quantitative formulas for the amount of double bonds are as follows: • Vinyl type double bond amount = {(integrated intensity of signal b) + (integrated intensity of signal e)} / 3 • Vinylidene type double bond amount = (integrated intensity of signal a) / 2 • Disubstituted olefin type double bond amount = (integrated intensity of signal d) / 2 • Trisubstituted olefin type double bond amount = (integrated intensity of signal c)

[0050] From these results, the amount of each double bond per 1000 carbon atoms (1000C) is determined. If the polymer produced during the manufacturing process of ethylene-α-olefin copolymer (A) has many unsaturated groups, the resulting ethylene-α-olefin copolymer (A) may also contain many unsaturated groups, improving the efficiency of the crosslinking reaction with organic peroxides described later, and enabling the production of solar cell encapsulants with a large gel fraction. The amount of unsaturated groups is, for example, within the range described above.

[0051] The amount of unsaturated groups can be increased or decreased, for example, by adjusting the polymerization temperature, hydrogen content, or organoaluminum oxy compound content in the method for producing the ethylene-α-olefin copolymer (A) described later, or by selecting a metallocene compound.

[0052] (Method for producing ethylene-α-olefin copolymer (A)) The ethylene-α-olefin copolymer (A) can be produced, for example, by a method that includes a polymerization step of copolymerizing ethylene with an α-olefin having 3 to 20 carbon atoms in the presence of an olefin polymerization catalyst containing a metallocene compound (I).

[0053] Various metallocene compounds can be used as metallocene compound (I). For example, metallocene compounds described in Japanese Patent Publication No. 2006-077261, Japanese Patent Publication No. 2008-231265, Japanese Patent Publication No. 2005-314680, etc., can be used. However, metallocene compounds with structures different from those described in these patent documents may be used, or two or more metallocene compounds may be used in combination.

[0054] <Silane coupling agent, organic peroxide> The composition for forming solar cell encapsulants according to the present invention contains a silane coupling agent. The content of the silane coupling agent is usually 0.1 to 1 part by mass, preferably 0.1 to 0.8 parts by mass, more preferably 0.1 to 0.6 parts by mass, even more preferably 0.1 to 0.4 parts by mass, and particularly preferably 0.1 to 0.3 parts by mass, per 100 parts by mass of the copolymer (A).

[0055] The composition for forming solar cell encapsulants according to the present invention contains an organic peroxide. The content of the organic peroxide is usually 0.1 to 2 parts by mass, preferably 0.3 to 1.8 parts by mass, more preferably 0.5 to 1.6 parts by mass, even more preferably 0.6 to 1.4 parts by mass, and particularly preferably 0.7 to 1.3 parts by mass, per 100 parts by mass of the copolymer (A). The 1-minute half-life temperature of the organic peroxide is usually in the range of 100 to 170°C.

[0056] (Silane coupling agent) When the amount of silane coupling agent is above the lower limit, the solar cell encapsulant sheet of the present invention exhibits excellent adhesion. On the other hand, when the amount of silane coupling agent is below the upper limit, a good balance is achieved between the cost and performance of the solar cell encapsulant sheet, and the amount of organic peroxide added to graft the silane coupling agent to the copolymer (A) contained in the solar cell encapsulant sheet during lamination with the solar cell module can be suppressed.

[0057] Ethylene-unsaturated silane compounds are preferably used as silane coupling agents. Conventionally known ethylenically unsaturated silane compounds can be used, and there are no particular restrictions. Examples of ethylenically unsaturated silane compounds include vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxysilane), γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-methacryloxypropyltrimethoxysilane. Preferably, due to their good adhesion, γ-glycidoxypropylmethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltriethoxysilane are used, more preferably γ-methacryloxypropyltrimethoxysilane.

[0058] (Organic Peroxides) When the amount of organic peroxides is above the lower limit, the crosslinking reaction of the solar cell encapsulant sheet can proceed sufficiently. On the other hand, when the amount of organic peroxides is below the upper limit, it is possible to suppress the progress of localized crosslinking reactions, and it is possible to produce a solar cell encapsulant sheet with uniform physical properties.

[0059] Organic peroxides are used as radical initiators during graft modification of copolymer (A) contained in the solar cell encapsulant composition with ethylenically unsaturated silane compounds, and as radical initiators during the crosslinking reaction when laminating the solar cell encapsulant sheet with the solar cell module. By graft-modifying copolymer (A) contained in the solar cell encapsulant sheet with ethylenically unsaturated silane compounds, a solar cell module with good adhesion to glass, backsheet, cells, and electrodes can be obtained. Furthermore, by crosslinking the copolymer (A) that forms the solar cell encapsulant sheet, a solar cell module with excellent heat resistance and adhesion can be obtained.

[0060] The organic peroxide can be any peroxide capable of grafting an ethylenically unsaturated silane compound onto the copolymer (A) contained in the solar cell encapsulant formation composition, or of crosslinking the copolymer (A) contained in the solar cell encapsulant formation composition. However, considering the balance between productivity in extrusion sheet molding and the crosslinking rate during lamination with solar cell modules, it is usually an organic peroxide with a 1-minute half-life temperature of 100 to 170°C. If the 1-minute half-life temperature of the organic peroxide is above the lower limit, it is possible to prevent gel formation in the sheet-like solar cell encapsulant sheet obtained from the copolymer (A) containing the organic peroxide during extrusion sheet molding. If the 1-minute half-life temperature of the organic peroxide is below the upper limit, the crosslinking rate during lamination with solar cell modules is appropriate, and the productivity of solar cell modules is good.

[0061] Known organic peroxides can be used. Specific examples of organic peroxides with a 1-minute half-life temperature in the range of 100 to 170°C are preferably dilauroyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, dibenzoyl peroxide, t-amylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxymaleic acid, 1,1-di(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-amylperoxy)cyclohexane, t-amylperoxyisononanoate, t-amylperoxyn-octoate, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane Examples include hexahexane, t-butyl peroxyisopropyl carbonate, t-butyl peroxy-2-ethylhexyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-amyl-peroxybenzoate, t-butyl peroxyacetate, t-butyl peroxyisononanoate, 2,2-di(t-butylperoxy)butane, and t-butyl peroxybenzoate. More preferably, examples include dilauroyl peroxide, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, t-butyl peroxyisononanoate, t-butyl peroxy-2-ethylhexyl carbonate, t-butyl peroxybenzoate, and even more preferably t-butyl peroxy-2-ethylhexyl carbonate.

[0062] <Crosslinking Aid> The composition for forming solar cell encapsulants according to the present invention contains a crosslinking aid. Conventional crosslinking aids commonly used for olefin resins can be used. Such crosslinking aids are compounds having two or more double bonds in their molecule, and specific examples include monoacrylates such as t-butyl acrylate, lauryl acrylate, cetyl acrylate, stearyl acrylate, 2-methoxyethyl acrylate, ethyl carbitol acrylate, and methoxytripropylene glycol acrylate; monomethacrylates such as t-butyl methacrylate, lauryl methacrylate, cetyl methacrylate, stearyl methacrylate, methoxyethylene glycol methacrylate, and methoxypolyethylene glycol methacrylate; and diacrylates such as 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, and polypropylene glycol diacrylate. Dimethacrylates such as 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, neopentyl glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate; triacrylates such as trimethylolpropane triacrylate, tetramethylolmethane triacrylate, and pentaerythritol triacrylate; trimethacrylates such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate; tetraacrylates such as pentaerythritol tetraacrylate and tetramethylolmethane tetraacrylate; divinyl aromatic compounds such as divinylbenzene and di-i-propenylbenzene; cyanurates such as triallyl cyanurate and triallyl isocyanurate; diallyl compounds such as diallyl phthalate;Triaryl compounds: Oximes such as p-quinone dioxime and p-p'-dibenzoylquinone dioxime; maleimides such as phenylmaleimide are examples, preferably triacrylates such as diacrylates, dimethacrylates, divinyl aromatic compounds, trimethylolpropane triacrylate, tetramethylolmethane triacrylate, and pentaerythritol triacrylate; trimethacrylates such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate; tetraacrylates such as pentaerythritol tetraacrylate and tetramethylolmethane tetraacrylate; cyanurates such as triallyl cyanurate and triallyl isocyanurate; diallyl compounds such as diallyl phthalate; Triaryl compounds: Oximes such as p-quinone dioxime and p-p'-dibenzoylquinone dioxime; maleimides such as phenylmaleimide are examples.

[0063] Among these, triallyl isocyanurate is particularly preferred, as it exhibits an excellent balance between suppressing bubble generation in the solar cell encapsulant after lamination and crosslinking properties.

[0064] The amount of crosslinking aid added is less than 0.5 parts by mass, preferably 0.45 parts by mass or less, and more preferably 0.42 parts by mass or less, per 100 parts by mass of copolymer (A). There is no particular lower limit, but for example, it may be 0.01 parts by mass or more, and 0.25 parts by mass or more, per 100 parts by mass of copolymer (A). Among the additives, the crosslinking aid in particular has a long impregnation time into copolymer (A). When the amount of the crosslinking aid added is within the above range, the impregnation time of the crosslinking agent into copolymer (A) is short, so that compositions for forming solar cell encapsulants, sheets for solar cell encapsulants, and solar cell encapsulants can be manufactured with high productivity, and the slip resistance of the sheets for solar cell encapsulants can be improved.

[0065] (UV absorber, light stabilizer, heat stabilizer) The composition for forming solar cell encapsulants according to the present invention preferably contains at least one additive selected from the group consisting of a UV absorber, a light stabilizer, and a heat stabilizer.

[0066] The amount of these additives blended is preferably 0.005 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, even more preferably 0.05 to 1.0 parts by mass, and particularly preferably 0.08 to 0.5 parts by mass per 100 parts by mass of copolymer (A). Blending the above additives within the above range is preferable because it sufficiently ensures the effect of improving resistance to high temperature and high humidity, resistance to heat cycles, weather resistance, and heat resistance, and also prevents a decrease in the transparency of the solar cell encapsulant sheet and adhesion to glass, backsheet, cells, electrodes, and aluminum.

[0067] Specific examples of UV absorbers include benzophenone-based UV absorbers such as 2-hydroxy-4-n-octyloxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-4-carboxybenzophenone, and 2-hydroxy-4-N-octoxybenzophenone; benzotriazole-based UV absorbers such as 2-(2-hydroxy-3,5-di-t-butylphenyl)benzotriazole and 2-(2-hydroxy-5-methylphenyl)benzotriazole; and salicylic acid ester-based UV absorbers such as phenyl salicylate and p-octylphenyl salicylate.

[0068] Specific examples of light stabilizers include hindered amine and hindered piperidine light stabilizers such as bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate and poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}].

[0069] Specific examples of heat stabilizers include phosphite-based heat stabilizers such as tris(2,4-di-tert-butylphenyl) phosphite, bis[2,4-bis(1,1-dimethylethyl)-6-methylphenyl]ethyl ester phosphorous acid, tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diylbisphosphonate, and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite; lactone-based heat stabilizers such as reaction products of 3-hydroxy-5,7-di-tert-butyl-furan-2-one and o-xylene; and 3,3',3",5,5',5"-hexa-tert-butyl Examples of hindered phenol-based heat stabilizers include ru-a,a',a''-(methylene-2,4,6-triyl)tri-p-cresol, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenyl)benzylbenzene, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; sulfur-based heat stabilizers; and amine-based heat stabilizers.

[0070] Furthermore, these can be used individually or in combination of two or more (for example, a combination of a phosphite-based heat stabilizer and a hindered phenol-based heat stabilizer).

[0071] (Other Additives) The composition for forming solar cell encapsulants according to the present invention may appropriately contain various components other than those described in detail above, to the extent that they do not impair the objectives of the present invention. Examples include various polyolefins other than copolymer (A), styrene-based and ethylene-based block copolymers, propylene-based polymers, etc. The content of these may be 0.0001 to 25 parts by mass, preferably 0.001 to 10 parts by mass, per 100 parts by mass of copolymer (A). Furthermore, the composition for forming solar cell encapsulants according to the present invention may appropriately contain one or more additives selected from various resins and / or rubbers other than polyolefins, plasticizers, fillers, pigments, dyes, antistatic agents, antifungal agents, flame retardants, and dispersants.

[0072] <Gel Fraction> The gel fraction of the solar cell encapsulant-forming composition according to the present invention, as measured by the following measurement method, is 70% by mass or more, preferably 70 to 90% by mass, and more preferably 70 to 85% by mass. If the gel fraction is above the lower limit, the solar cell encapsulant produced from the solar cell encapsulant-forming composition according to the present invention has good heat resistance. If the gel fraction is below the upper limit, the solar cell encapsulant produced from the solar cell encapsulant-forming composition according to the present invention has good flexibility.

[0073] (Method for measuring gel fraction) The composition containing the copolymer (A) described above, a silane coupling agent, an organic peroxide, and a crosslinking aid is melt-kneaded for 5 minutes at 90°C with a screw rotation speed of 30 rpm using a twin-screw batch melt-kneading apparatus and formed into a sheet. The obtained sheet is then molded for 15 minutes under a pressure of 10 MPa after preheating for 3 minutes using a hot press machine set to 160°C, and then cooled for 4 minutes under a pressure of 10 MPa at 20°C to obtain a sheet-like measurement sample with a thickness of 0.5 mm.

[0074] Weigh 0.10 g of the sample, wrap it in a 325 mesh stainless steel screen, and immerse it in 30 ml of p-xylene in a sealed container at 140°C for 3 hours. Next, remove the screen and dry it at 80°C for at least 2 hours until a constant weight is achieved. Calculate the gel fraction (mass%) using the following formula: Gel fraction (mass%) = 100 × (W３ -W ２ ) / (W １ -W ２ ) (W １ : Mass of the screen and sample before immersion W ２ Screen mass W ３ (Mass of the screen and sample after immersion and drying)

[0075] The gel fraction can be adjusted by the amount of organic peroxide and crosslinking aid added, the temperature and molding time of the hot press, and the unsaturated group content of the copolymer (A). As these factors increase, the gel fraction tends to increase as well.

[0076] The composition for forming solar cell encapsulants according to the present invention contains, for example, 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more of the copolymer (A). The upper limit of the copolymer (A) content depends on the content of the additives.

[0077] In one embodiment of the present invention, the composition for forming the solar cell encapsulant preferably satisfies the following requirement (b1): <Requirement (b1)> The volume resistivity measured at a temperature of 100°C and an applied voltage of 1000V in accordance with JIS K6911 is 1.0 × 10 13 ~1.0 x 10 18 Ω·cm, preferably 1.0 × 10⁻⁶ 14 ~1.0 x 10 18 Ω·cm, more preferably 5.0 × 10 14 ~1.0 x 10 18 Ω·cm, most preferably 5.0 × 10 14 ~1.0 x 10 18 The volume resistivity is Ω·cm. Compositions for forming solar cell encapsulants with low volume resistivity tend to have a tendency to generate PID (Potential Induced Degradation). Furthermore, during periods of sunlight irradiation, the module temperature of conventional solar cell modules can exceed, for example, 70°C. Therefore, from the viewpoint of long-term reliability, volume resistivity under high-temperature conditions is required, rather than the volume resistivity at room temperature (23°C) that has been previously reported, and volume resistivity at 100°C is important.

[0078] The volume resistivity can be increased or decreased, for example, by changing the additives contained in the composition for forming the solar cell encapsulant. If the volume resistivity is above the lower limit, the occurrence of PID phenomena can be suppressed. If the volume resistivity is below the upper limit, the composition for forming the solar cell encapsulant or the sheet for the solar cell encapsulant can be prevented from becoming electrostatically charged and attracting dust, which is preferable from the viewpoint of power generation efficiency and long-term reliability of the solar cell module.

[0079] Furthermore, the volume resistivity is 5.0 × 10 14 A value exceeding Ω·cm is desirable because it tends to prolong the occurrence of the PID phenomenon in constant temperature and humidity tests at 85°C and 85% rh. Volume resistivity is measured after the composition for forming the solar cell encapsulant is formed into a sheet, and then crosslinked and flattened using a vacuum laminator, hot press, or crosslinking furnace. In addition, sheets within a module laminate are measured after removing other layers.

[0080] The solar cell encapsulant sheet of the present invention exhibits excellent adhesion, extrusion moldability, and crosslinking properties with various solar cell components such as glass, backsheets, thin-film electrodes, aluminum, and solar cell elements. For this reason, it is suitably used as a solar cell encapsulant sheet for conventionally known solar cell modules.

[0081] While conventional methods can be used to manufacture the solar cell encapsulant sheet of the present invention, it is preferable to manufacture it by a method that includes a step of melting and blending raw materials using a kneader, a Banbar mixer, an extruder, etc. In particular, manufacturing using an extruder capable of continuous production is preferred.

[0082] The thickness of the sheet layer for the solar cell encapsulant is typically 0.01 to 2 mm, preferably 0.05 to 1.5 mm, more preferably 0.1 to 1.2 mm, particularly preferably 0.2 to 1 mm, more preferably 0.3 to 0.9 mm, and most preferably 0.3 to 0.8 mm. A thickness within this range suppresses damage to glass, solar cell elements, thin-film electrodes, etc., during the lamination process, and ensures sufficient light transmittance, thereby enabling high photovoltaic power generation. Furthermore, it is preferable because it allows for lamination molding of solar cell modules at low temperatures.

[0083] There are no particular limitations on the method for forming the sheet for solar cell encapsulant of the present invention, but various known forming methods (such as casting, extrusion sheet forming, inflation molding, injection molding, and compression molding) can be employed. In particular, the most preferred embodiment is to obtain a sheet-shaped solar cell encapsulant by putting a composition obtained by blending the copolymer (A) with other components, which is obtained by manually blending in a bag such as a poly bag or by using a stirring mixer such as a Henschel mixer, tumbler, or super mixer, into an extrusion sheet forming hopper, and performing extrusion sheet forming while melt-kneading.

[0084] The extrusion temperature is typically 70 to 130°C. An extrusion temperature of 70°C or higher results in good productivity of solar cell encapsulant sheets. An extrusion temperature of 130°C or lower suppresses gelation when the solar cell encapsulant-forming composition of the present invention, which contains the copolymer (A) and other components, is extruded to obtain solar cell encapsulant sheets.

[0085] Furthermore, the surface of the uncrosslinked solar cell encapsulant sheet may be embossed. Decorating the surface of the solar cell encapsulant sheet with embossing can prevent blocking between uncrosslinked encapsulant sheets, or between uncrosslinked encapsulant sheets and other sheets. In addition, since the embossing reduces the storage modulus of the solar cell encapsulant sheet, it can act as a cushion for the solar cell element when laminating the solar cell encapsulant sheet with the solar cell element, thereby preventing damage to the solar cell element.

[0086] In one embodiment of the present invention, the total volume V of the recesses per unit area of ​​the solar cell encapsulant sheet. H And the apparent volume V of the sheet for solar cell encapsulation A V as a percentage H / V AThe porosity P (%), expressed as ×100, is preferably 10 to 50%, more preferably 10 to 40%, and even more preferably 15 to 40%. The apparent volume VA of the solar cell encapsulant sheet is obtained by multiplying the unit area by the maximum thickness of the solar cell encapsulant sheet. When the porosity P is equal to or greater than the lower limit, the elastic modulus of the solar cell encapsulant sheet can be sufficiently reduced, and sufficient cushioning can be obtained. Therefore, in the module manufacturing process, when laminating (pressurizing) is performed in two stages, it is possible to suppress cracking of silicon cells or the solder fixing silicon cells to electrodes in crystalline solar cells, and cracking of silver electrodes in thin-film solar cells. In other words, when the porosity of the solar cell encapsulant sheet is equal to or greater than the lower limit, when localized pressure is applied to the solar cell encapsulant sheet, the convex portion to which the pressure is applied deforms so as to collapse, thus preventing the silicon cell from cracking due to large localized pressure applied to, for example, a silicon cell during lamination. Furthermore, if the porosity of the sheet for solar cell encapsulation is above the aforementioned lower limit, there are many air passages, resulting in good degassing during lamination.

[0087] On the other hand, if the porosity P is below the upper limit, sufficient degassing can be achieved during lamination, and air is less likely to remain inside the solar cell module. The porosity P can be calculated as follows: the apparent volume V of the embossed solar cell encapsulant sheet. A (mm 3 ) is the maximum thickness t of the sheet for solar cell encapsulant. max (mm) and unit area (e.g., 1 m) 2 = 1000 x 1000 = 10 6 mm 2 It is calculated by multiplying it with the following formula (3): V A (mm 3 ) = t max (mm) x 10 6 (mm 2 ) (3)

[0088] On the other hand, the actual volume V0 (mm²) of this unit area of ​​solar cell encapsulant sheet 3) is the specific gravity ρ (g / mm²) of the resin constituting the sheet for solar cell encapsulation. 3 ) and unit area (1 m 2 The actual weight W (g) of the solar cell encapsulant sheet per unit area is calculated by applying it to the following formula (4): V0 (mm 3 ) = W / ρ (4)

[0089] The total volume V of recesses per unit area of ​​the sheet used for solar cell encapsulation. H (mm 3 ) is as shown in the following formula (5), "the apparent volume V of the sheet for solar cell encapsulation material" A It is calculated by subtracting the "actual volume V0" from ". H (mm 3 ) = V A -V0 = V A -(W / ρ) (5)

[0090] Therefore, the porosity (%) can be calculated as follows: P(%) = V H / V A × 100 = (V A -(W / ρ) / V A ×100 =1-W / (ρ・V A )×100 =1-W / (ρ・t max 10 6 ) × 100

[0091] The porosity (%) can be calculated using the formula above, but it can also be determined by microscopically photographing the cross-section or embossed surface of an actual solar cell encapsulant sheet and performing image processing.

[0092] The depth of the recess formed by embossing is preferably 20 to 95% of the maximum thickness of the solar cell encapsulant sheet, more preferably 50 to 95%, and even more preferably 65 to 95%. max The percentage of the depth D of the recess relative to the given space is sometimes referred to as the "depth ratio" of the recess.

[0093] The depth of the embossed recesses refers to the height difference D between the highest point of the convex portion and the deepest point of the concave portion of the embossed surface of the solar cell encapsulant sheet. Also, the maximum thickness t of the solar cell encapsulant sheet is specified. max This refers to the distance (in the thickness direction of the solar cell encapsulant sheet) from the highest point of the protrusion on one side of the sheet to the highest point of the protrusion on the other side if one side of the sheet is embossed, or from the highest point of the protrusion on one side to the highest point of the protrusion on the other side if both sides of the sheet are embossed.

[0094] Embossing may be applied to one side or both sides of the solar cell encapsulant sheet. If the depth of the embossed recesses is to be increased, it is preferable to form the embossing on only one side of the solar cell encapsulant sheet. When embossing is applied to only one side of the solar cell encapsulant sheet, the maximum thickness t of the solar cell encapsulant sheet is... max The thickness is 0.01 mm to 2 mm, preferably 0.05 to 1 mm, more preferably 0.1 to 1 mm, even more preferably 0.15 to 1 mm, even more preferably 0.2 to 1 mm, even more preferably 0.2 to 0.9 mm, even more preferably 0.3 to 0.9 mm, and most preferably 0.3 to 0.8 mm. max If the temperature range is within this range, damage to glass, solar cell elements, thin-film electrodes, etc., during the lamination process can be suppressed, and the solar cell module can be laminated even at relatively low temperatures, which is preferable. In addition, the sheet for the solar cell encapsulant can ensure sufficient light transmittance, and the solar cell module using it has a high photovoltaic output.

[0095] Furthermore, the sheet can be used as a solar cell encapsulant sheet in the form of a single sheet cut to the size of the solar cell module, or in the form of a roll that can be cut to size immediately before manufacturing the solar cell module.

[0096] [Solar Cell Encapsulation Sheet] The sheet-like solar cell encapsulant of the present invention (hereinafter also referred to as "solar cell encapsulant sheet") has at least one layer made of the solar cell encapsulant sheet of the present invention. Therefore, the number of layers made of the solar cell encapsulant sheet in the solar cell encapsulant sheet of the present invention may be one or two or more. From the viewpoint of simplifying the structure and reducing costs, and from the viewpoint of minimizing interfacial reflection between layers and effectively utilizing light, it is preferable to have one layer.

[0097] The solar cell encapsulation sheet of the present invention may consist only of a layer made of the solar cell encapsulation material sheet of the present invention, or it may have layers other than the aforementioned layer (hereinafter also referred to as "other layers"). Examples of other layers, if classified by purpose, include hard coat layers for surface or back surface protection, adhesive layers, anti-reflective layers, gas barrier layers, anti-fouling layers, etc. If classified by material, examples include layers made of ultraviolet curable resins, thermosetting resins, polyolefin resins, carboxylic acid-modified polyolefin resins, fluorine-containing resins, cyclic olefin (co)polymers, inorganic compounds, etc.

[0098] There are no particular restrictions on the positional relationship between the layer made of the solar cell encapsulant sheet of the present invention and the other layers, and a preferred layer configuration can be appropriately selected depending on the purpose. That is, the other layers may be provided between two or more layers made of solar cell encapsulant sheets, on the outermost layer of the solar cell encapsulant sheet, or at any other location. Furthermore, the other layers may be provided on only one side of the layer made of the solar cell encapsulant sheet, or on both sides. There are no particular restrictions on the number of other layers, and any number of other layers can be provided, or no other layers may be provided at all.

[0099] From the viewpoint of simplifying the structure and reducing costs, and from the viewpoint of minimizing interfacial reflection and effectively utilizing light, it is sufficient to manufacture a solar cell encapsulation sheet using only the layer made of the solar cell encapsulation sheet of the present invention, without providing any other layers. However, if there are other layers that are necessary or useful in relation to the purpose, such other layers may be provided as appropriate. When other layers are provided, there are no particular restrictions on the method of laminating the layer made of the solar cell encapsulation sheet of the present invention with the other layers, but it is preferable to obtain a laminate by co-extruding using a known melt extruder such as a cast molding machine, extruded sheet molding machine, inflation molding machine, or injection molding machine, or to obtain a laminate by melting or heat laminating the other layer onto one of the pre-formed layers. Alternatively, lamination may be carried out by a dry lamination method or a heat lamination method using a suitable adhesive (for example, maleic anhydride-modified polyolefin resin (such as "Admer" from Mitsui Chemicals, "Modic" from Mitsubishi Chemical Corporation), low (non)crystalline soft polymers such as unsaturated polyolefins, acrylic adhesives including ethylene / acrylic acid ester / maleic anhydride ternary copolymer (such as "Bondine" from Sumika CDF Chemical Co., Ltd.), ethylene / vinyl acetate copolymer, or adhesive resin compositions containing these). Adhesives with heat resistance of about 120 to 150°C are preferably used, and polyester-based or polyurethane-based adhesives are exemplified as suitable. Furthermore, to improve the adhesion between the two layers, for example, silane-based coupling treatment, titanium-based coupling treatment, corona treatment, plasma treatment, etc., may be used.

[0100] [Solar Cell Encapsulation Material] A first aspect of the solar cell encapsulation material of the present invention is a crosslinked sheet made of a composition comprising an ethylene-α-olefin copolymer (A), a silane coupling agent, an organic peroxide, and a crosslinking aid, wherein the content of the crosslinking aid is less than 0.5 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), and the gel fraction measured by the following measurement method is 70% by mass or more.

[0101] <Method for measuring gel fraction> Weigh 0.10 g of the solar cell encapsulant, wrap it in a 325 mesh stainless steel screen, and immerse it in 30 ml of p-xylene in a sealed container at 140°C for 3 hours. Next, remove the screen and dry it at 80°C until it reaches a constant weight. Calculate the gel fraction (mass%) using the following formula: Gel fraction (mass%) = 100 × (W ３ -W ２ ) / (W １ -W ２ ) (W １ : Mass of the screen and sample before immersion W ２ Screen mass W ３ (Mass of the screen and sample after immersion and drying)

[0102] Details of the ethylene-α-olefin copolymer (A) and additives, as well as their content, in the first embodiment of the solar cell encapsulant are the same as described above. Furthermore, a second embodiment of the solar cell encapsulant of the present invention is a solar cell encapsulant comprising a crosslinked product of the solar cell encapsulant sheet of the present invention described above. Organic peroxides and the like described above can be used for crosslinking.

[0103] The solar cell encapsulant of the present invention is in sheet form, and its thickness is typically 0.01 to 2 mm, preferably 0.05 to 1.5 mm, more preferably 0.1 to 1.2 mm, particularly preferably 0.2 to 1 mm, more preferably 0.3 to 0.9 mm, and most preferably 0.3 to 0.8 mm. When the thickness is within this range, damage to glass, solar cell elements, thin-film electrodes, etc., during the lamination process can be suppressed, and a high amount of photovoltaic power can be obtained by ensuring sufficient light transmittance. Furthermore, lamination molding of solar cell modules can be performed at low temperatures.

[0104] [Solar Cell Module] An example of a solar cell module of the present invention is a crystalline solar cell module in which solar cell elements formed from polycrystalline silicon or the like are sandwiched and laminated between solar cell encapsulation sheets or their crosslinking bodies, and both the front and back surfaces are covered with protective sheets. That is, a typical example of the configuration of a solar cell module is a protective sheet for solar cell modules (front protective member) / a sheet made of the solar cell encapsulation sheet or its crosslinking body of the present invention / solar cell elements / a sheet made of the solar cell encapsulation sheet or its crosslinking body of the present invention / a protective sheet for solar cell modules (back protective member).

[0105] As an example, a solar cell module can be described, comprising a transparent protective member on the front side, a protective member on the back side, a solar cell element, and a sealing layer containing the solar cell sealing material of the present invention (i.e., formed by crosslinking a sheet for solar cell sealing material of the present invention), wherein the sealing layer seals the solar cell element between the transparent protective member on the front side and the protective member on the back side.

[0106] It should be noted that a solar cell module, which is one of the preferred embodiments of the present invention, is not limited to the above configuration, and depending on the purpose, some of the above layers may be omitted or other layers may be provided as appropriate. Examples of other layers include an adhesive layer, a shock-absorbing layer, a coating layer, an anti-reflective layer, a back-surface re-reflective layer, and a light-diffusing layer. These layers are not particularly limited, but they may be provided in appropriate positions considering the purpose and characteristics of each layer.

[0107] (Method for manufacturing a solar cell module) The method for manufacturing a solar cell module of the present invention includes, for example, the steps of (i) stacking a transparent protective member on the front side, a sheet for solar cell encapsulation material of the present invention, a solar cell element (cell), a sheet for solar cell encapsulation material of the present invention, and a protective member on the back side in this order to form a laminate, and (ii) pressing and heating the obtained laminate to integrate it.

[0108] In step (i), if the solar cell encapsulant sheet of the present invention has a surface with an uneven shape (embossed shape), it is preferable to position it so that the surface faces the solar cell element.

[0109] In step (ii), the laminate obtained in step (i) is heated and pressurized using a vacuum laminator or a hot press according to a conventional method to integrate (seal) it. During sealing, the solar cell encapsulant of the present invention has high cushioning properties, which prevents damage to the solar cell elements. Furthermore, because it has good degassing properties, there is no air entrapment, and high-quality products can be manufactured with a high yield.

[0110] When manufacturing a solar cell module, the ethylene-α-olefin copolymer (A) that constitutes the solar cell encapsulant sheet is crosslinked and cured. This crosslinking step may be performed simultaneously with step (ii) or after step (ii).

[0111] If the crosslinking process is performed after process (ii), the laminate is vacuum-heated for 3 to 6 minutes at a temperature of 125 to 160°C and a vacuum pressure of 10 Torr or less in process (ii); then pressurized with atmospheric pressure for about 1 to 15 minutes to integrate the laminate. The crosslinking process performed after process (ii) can be carried out by a general method; for example, a tunnel-type continuous crosslinking furnace may be used, or a tray-type batch crosslinking furnace may be used. The crosslinking conditions are usually 130 to 155°C for about 20 to 60 minutes.

[0112] On the other hand, when the crosslinking process is performed simultaneously with process (ii), it can be carried out in the same manner as when the crosslinking process is performed after process (ii), except that the heating temperature in process (ii) is set to 145 to 170°C and the pressurization time by atmospheric pressure is set to 6 to 30 minutes.

[0113] In any case, the manufacturing of the solar cell module of the present invention involves temporarily adhering the solar cell encapsulant sheet to the solar cell elements and protective material at a temperature at which the crosslinking agent does not substantially decompose and the solar cell encapsulant sheet of the present invention melts, and then raising the temperature to ensure sufficient adhesion and crosslinking of the solar cell encapsulant sheet.

[0114] The gel fraction of the solar cell encapsulant of the present invention, measured by the following method, is preferably more than 70% by mass, more more preferably more than 70% by mass and 90% by mass or less, still more preferably more than 70% by mass and 85% by mass or less. When the gel fraction exceeds the above lower limit, the solar cell encapsulant has favorable heat resistance. When the gel fraction is equal to or lower than the above upper limit, the solar cell encapsulant has favorable flexibility.

[0115] (Method for measuring gel fraction) 0.10 g is collected as a measurement sample from the solar cell encapsulant of the present invention. The measurement sample is wrapped in a 325-mesh stainless steel screen, and immersed in 30 mL of p-xylene in a sealed container at 140°C for 3 hours. Next, the screen is taken out and dried at 80°C for 2 hours or more until a constant mass is reached. The gel fraction (% by mass) is calculated by the following formula. Gel fraction (% by mass) = 100 × (W ３ -W ２ ) / (W １ -W ２ ) (W １ : mass of the screen and the measurement sample before immersion, W ２ : mass of the screen, W ３ : mass of the screen and the measurement sample after immersion and drying)

[0116] Hereinafter, the present invention will be described more specifically based on Examples, but the present invention is not limited to these Examples. In the following Examples and Comparative Examples, each measurement method and evaluation method are as follows.

[0117] <Measurement of ethylene / α-olefin copolymer> [Density] The density of the ethylene / α-olefin copolymer was measured in accordance with ASTM D1505.

[0118] [Content ratio (composition) of each constituent unit] The content ratio of the constituent units derived from ethylene and α-olefin in the ethylene / α-olefin copolymer was obtained by analyzing the nuclear magnetic resonance spectrum of the polymer according to the following method.

[0119] (Measurement conditions) Apparatus: ECX400P nuclear magnetic resonance spectrometer manufactured by JEOL Ltd. Measurement nucleus: 13C (125 MHz) Measurement mode: Single pulse Pulse width: 45° (5.25 μsec) Number of points: 32k Measurement range: 20 ppm (-4 to 16 ppm) Repetition time: 7.0 sec Number of integrations: 64 Measurement solvent: Orthodichlorobenzene-d4 Sample concentration: Ca. 20 mg / 0.6 mL Measurement temperature: 120°C Window function: exponential (BF: 0.12 Hz) Chemical shift reference: Orthodichlorobenzene (7.1 ppm)

[0120] [Total Unsaturated Amount] The amount of unsaturated groups per 1000 carbon atoms in an ethylene-α-olefin copolymer (also called "unsaturated amount") is measured at 400 MHz. 1 The unsaturated groups were determined by analyzing the nuclear magnetic resonance spectra of the polymer obtained from 1H-NMR (JEOL ECX400P). Specifically, the amount of unsaturated groups per 1000 carbon atoms was calculated from the integral values ​​of vinyl, vinylidene, disubstituted olefins, and trisubstituted olefins in the total polymer, and these were defined as the vinyl-type double bond amount, vinylidene-type double bond amount, disubstituted olefin-type double bond amount, and trisubstituted olefin-type double bond amount, respectively. Here, the total amount of vinyl-type double bonds, vinylidene-type double bonds, disubstituted olefin-type double bonds, and trisubstituted olefin-type double bonds was defined as the total unsaturated amount, and the total amount of vinyl-type double bonds and vinylidene-type double bonds was defined as the terminal unsaturated amount. For details on the quantitative method of each unsaturated group, please refer to paragraphs

[0161] to

[0164] of Japanese Patent Application Publication No. 2024-146464.

[0121] [Melt Flow Rate (MFR): MFR2] The melt flow rate (MFR) of the ethylene-α-olefin copolymer was determined in accordance with ASTM D1238 under a temperature of 190°C and a load of 2.16 kg.

[0122] [Additive Impregnation Time] In the examples described later, the time required to impregnate the copolymer pellets with the additives was measured. Specifically, the additives were mixed into the copolymer pellets according to the additive mixing amounts described in the examples, and these were left in an oven at 40°C to impregnate the copolymer pellets with the additives. After mixing, the copolymer pellets were observed every 60 minutes, and the time at which it was confirmed that there was no remaining liquid visually, that is, the time at which the additives were no longer visible on the surface of the copolymer pellets, was defined as the additive impregnation time.

[0123] <Evaluation of solar cell encapsulant sheets (uncrosslinked sheets)> [Preparation of measurement samples] Samples of appropriate sizes were cut from the solar cell encapsulant sheets (uncrosslinked sheets) prepared in the examples described below, according to the various measurements.

[0124] [Crosslinkability Evaluation] [MH-ML (S'Max-S'Min)] Using a 5.0 g sample (uncrosslinked sheet) for crosslinkability evaluation, a cure meter test was performed using the measuring device: MDR2000P (manufactured by ALPHA TECHNOLOGIES) under measurement conditions of 160°C and 20 minutes, and S'Max-S'Min was measured as follows.

[0125] The sample was placed in a measuring device, and the torque change obtained under constant temperature and constant shear rate conditions was measured to obtain a vulcanization curve. From this vulcanization curve, the minimum torque value S'Min and the maximum torque value S'Max were determined, and the progress of bridge bridging was confirmed by the degree of torque increase.

[0126] [Glass Adhesion] A transparent glass plate, which is a transparent protective material for the surface side of a solar cell, and a measurement sample (uncrosslinked sheet) measuring 12 cm in length x 7.5 cm in width x 0.5 mm in thickness were laminated and placed in a vacuum laminator (NPC Corporation, LM-110X160S). The laminator was then placed on a hot plate heated to 150°C, the pressure was reduced for 3 minutes, and then heated for 15 minutes to create a laminate of transparent glass plate / solar cell encapsulant (crosslinked sheet) for measuring adhesive strength. Four cuts were made in the solar cell encapsulant layer of this adhesive strength measurement sample at 15 mm intervals along its length, reaching down to the transparent glass plate. Three areas (12 cm in length x 1.5 cm in width) were formed to peel off when measuring the peel strength (glass adhesive strength) of the solar cell encapsulant using a 180-degree peel test. A tensile testing machine (product name "Instron 1123") manufactured by Instron Corporation was used for the measurement. Measurements were taken at 23°C with a 180-degree peel, a span of 30 mm, and a tensile speed of 30 mm / min. The average of three measurements was used.

[0127] [Dynamic Friction Coefficient] The dynamic friction coefficient was measured using an 8.0 cm long x 8.0 cm wide x 0.5 mm thick sample (uncrosslinked sheet) with a universal testing machine, Intesco 2001, under the following conditions. A high dynamic friction coefficient indicates a low amount of additive bleed-out and excellent slip resistance.

[0128] A sample was placed on a glass plate, which served as the substrate. A SUS weight was placed on top of the sample, and a load of 200 gf was applied. The frictional force was measured when the sample was slid at a tensile speed of 300 mm / min, and the coefficient of kinetic friction was calculated from this frictional force.

[0129] <Evaluation of Solar Cell Encapsulation Material (Crosslinked Sheet)> [Preparation of Measurement Samples] Samples of appropriate sizes were cut from the solar cell encapsulation material (crosslinked sheet) prepared in the examples described below, according to the various measurements.

[0130] [Gel Fraction] A sample (cross-linked sheet) for gel fraction measurement was finely cut. 0.10 g of this was weighed, wrapped in a 325-mesh stainless steel screen, and immersed in 30 ml of p-xylene in a sealed container at 140°C for 3 hours. Next, the screen was removed and dried at 80°C for at least 2 hours until a constant weight was achieved. That is, after heating at 80°C for at least 2 hours, weighing and heating at 80°C and weighing were repeated until there was no mass change of more than 0.01 g, and it was confirmed that a constant weight was achieved. The gel fraction (mass %) is expressed by the following formula: Gel fraction (mass %) = 100 × (W3 - W2) / (W1 - W2) (W1: Mass of the screen and sample before immersion W2: Mass of the screen W3: Mass of the screen and sample after immersion and drying)

[0131] [Creep Resistance] A creep resistance evaluation sample (crosslinked sheet) measuring 1 cm wide, 5 cm long, and 0.5 mm thick was marked with a 3 cm lengthwise mark along its length. A 20 g weight was suspended from the sheet, and it was left in a 100°C oven for 1 hour to conduct the creep resistance test. After the test, the length of the mark was measured again, and the elongation rate, expressed by the following formula, was calculated: Elongation rate (%) = (Mark length after test - Mark length before test) / Mark length before test × 100

[0132] The creep resistance test is used as an indicator of crosslinking properties. If the crosslinking is sufficient, the elongation during the creep resistance test will be small; if the crosslinking is insufficient, the elongation during the creep resistance test will be large; and if the crosslinking is even more insufficient, the weight may "fall" during the test.

[0133] <Materials> According to the method described in paragraph

[0181] of Japanese Unexamined Patent Publication No. 2024-146464, the following ethylene / 1-butene copolymers (A-1) to (A-4) were produced by appropriately adjusting the feed amounts of ethylene and 1-butene. The produced ethylene / 1-butene copolymers (A-1) to (A-4) and a commercially available ethylene / 1-butene copolymer (A-5) (LF675 manufactured by LG Chem) were each passed through a single-screw extruder with the die temperature set to 180°C, the strands were cooled in a water tank, and the strands were cut with a pellet cutter to obtain ethylene / 1-butene copolymers (A-1) to (A-5) as pellets.

[0134] Ethylene / 1-butene copolymer (A-1): density = 0.873 g / cm ３ , content of constitutional units derived from ethylene = 84 mol%, MFR₂ = 11.9 g / 10 min, amount of vinyl-type double bonds = 0.13, amount of terminal unsaturation = 0.28, total amount of unsaturation = 0.78 per 1000 C Ethylene / 1-butene copolymer (A-2): density = 0.872 g / cm ３ , content of constitutional units derived from ethylene = 85 mol%, MFR₂ = 5.5 g / 10 min, amount of vinyl-type double bonds = 0.10, amount of terminal unsaturation = 0.35, total amount of unsaturation = 1.11 per 1000 C Ethylene / 1-butene copolymer (A-3): density = 0.872 g / cm ３ , content of constitutional units derived from ethylene = 85 mol%, MFR₂ = 19.2 g / 10 min, amount of vinyl-type double bonds = 0.04, amount of terminal unsaturation = 0.06, total amount of unsaturation = 0.14 per 1000 C Ethylene / 1-butene copolymer (A-4): density = 0.872 g / cm ３ , content of constitutional units derived from ethylene = 85 mol%, MFR₂ = 4.0 g / 10 min, amount of vinyl-type double bonds = 0.03, amount of terminal unsaturation = 0.05, total amount of unsaturation = 0.17 per 1000 C Ethylene / 1-butene copolymer (A-5): density = 0.877 g / cm ３ , MFR ２ = 14.0 g / 10 min), amount of vinyl-type double bonds = 0.05, amount of terminal unsaturation = 0.11, total amount of unsaturation = 0.32 per 1000 C

[0135] <Preparation of Solar Cell Encapsulation Material> [Example 1] To 100 parts by mass of pellets of the manufactured ethylene-α-olefin copolymer (A-1), 0.2 parts by mass of γ-methacryloxypropyltrimethoxysilane, a silane coupling agent, 1.0 part by mass of t-butylperoxy-2-ethylhexyl carbonate, an organic peroxide with a half-life temperature of 166°C at one minute, 0.40 parts by mass of triallyl isocyanurate, a crosslinking aid, and 0.10 parts by mass of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, a light stabilizer were added as additives, and the mixture was left in an oven at 40°C to impregnate the pellets with the additives.

[0136] After confirming that the ethylene-α-olefin copolymer (A-1) pellets were impregnated with a silane coupling agent, organic peroxide, crosslinking aid, and light stabilizer (i.e., after measuring the additive impregnation time), the additive-impregnated pellets were melt-kneaded and molded using a Toyo Seiki Laboplast Mill (twin-screw batch type melt-kneading device) at 90°C, screw rotation speed: 30 rpm, and kneading time: 5 minutes to obtain a sheet for solar cell encapsulation (uncrosslinked sheet) and pellets for physical property measurement. The obtained solar cell encapsulation sheet was preheated for 3 minutes using a hydraulic hot press set to 145°C, molded under a pressure of 10 MPa for 15 minutes, and then cooled at 20°C under a pressure of 10 MPa for 4 minutes to produce a sheet-like solar cell encapsulation (crosslinked sheet) with a thickness of 0.5 mm. The results of the measurement of the physical properties of the sheet are shown in Table 1.

[0137] [Examples 2-3, Comparative Examples 1-5] Except for changing the type of ethylene-α-olefin copolymer used as shown in Table 1 and using the amounts of each material as shown in Table 1, a sheet for solar cell encapsulation (uncrosslinked sheet) was prepared in the same manner as in Example 1, and then a solar cell encapsulation (crosslinked sheet) was obtained. The physical properties are shown in Table 1.

[0138]

[0139] (Comparison of Examples and Comparative Examples) As shown in Table 1 above, in the process of the Examples, the additive could be impregnated into the copolymer pellets in a shorter time than in the Comparative Examples. Therefore, the composition for forming solar cell encapsulants, the sheets for solar cell encapsulants, and the solar cell encapsulants (crosslinked sheets) of the Examples could be manufactured in a shorter time than in the Comparative Examples, and showed superior productivity.

[0140] Furthermore, the solar cell encapsulant formation composition and solar cell encapsulant sheet of the examples exhibited excellent slip resistance due to their high coefficient of dynamic friction, and the solar cell encapsulant of the examples exhibited excellent heat resistance and durability due to its excellent creep resistance.

[0141] Furthermore, the solar cell encapsulant formation composition and solar cell encapsulant sheet of the examples exhibited excellent crosslinking progress due to their high MH-ML ratio, and therefore excellent productivity.

Claims

1. The composition comprises an ethylene-α-olefin copolymer (A), a silane coupling agent, an organic peroxide, and a crosslinking aid, wherein the content of the crosslinking aid is less than 0.5 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), and the gel fraction measured by the following measurement method is 70% by mass or more, and the ethylene-α-olefin copolymer (A) 1 A composition for forming solar cell encapsulants, wherein the total amount of vinyl-type double bonds and vinylidene-type double bonds per 1000 carbon atoms, as determined by H-NMR, is 0.26 or more. <Method for measuring gel fraction> The composition is melt-kneaded in a twin-screw batch melt-kneading apparatus at 90°C with a screw rotation speed of 30 rpm for 5 minutes and formed into a sheet. The obtained sheet is molded in a hot press machine set to 145°C for 3 minutes under pressure of 10 MPa for 15 minutes, and then cooled at 20°C under pressure of 10 MPa for 4 minutes to obtain a sheet-like measurement sample with a thickness of 0.5 mm. 0.10 g of the measurement sample is weighed, wrapped in a 325 mesh stainless steel screen, and immersed in 30 ml of p-xylene in a sealed container at 140°C for 3 hours. Next, the screen is removed and dried at 80°C until it reaches a constant weight. The gel fraction (mass%) is calculated using the following formula. Gel fraction (mass%) = 100 × (W) ３ -W ２ ) / (W １ -W ２ ) (W １ : Mass of the screen and sample before immersion W ２ Screen mass W ３ (Mass of the screen and sample after immersion and drying) 2. The composition for forming a solar cell encapsulant according to claim 1, wherein the content of the organic peroxide is 0.1 to 2 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), the content of the silane coupling agent is 0.1 to 1 part by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), and the 1-minute half-life temperature of the organic peroxide is in the range of 100 to 170°C.

3. The composition for forming a solar cell encapsulant according to claim 1, comprising 0.005 to 5 parts by mass of at least one selected from the group consisting of ultraviolet absorbers, heat stabilizers, and light stabilizers, per 100 parts by mass of the ethylene-α-olefin copolymer (A).

4. The solar cell encapsulant-forming composition according to claim 1, wherein the ethylene-α-olefin copolymer (A) satisfies the following requirements (a1) and (a2): (a1) a density measured in accordance with ASTM D1505 of 0.865 to 0.885 g / cm ３ . (a2) a melt flow rate (MFR) ２ ) measured in accordance with ASTM D1238 under the conditions of 190°C and a 2.16 kg load of 4.0 to 13 g / 10 min.

5. The solar cell encapsulant forming composition according to claim 1, wherein the ethylene-α-olefin copolymer (A) satisfies the following requirement (a3): (a3) ​​The content of constituent units derived from ethylene is 80 to 90 mol%, and the content of constituent units derived from α-olefins having 3 to 20 carbon atoms is 10 to 20 mol% (provided that the sum of the content of constituent units derived from ethylene and the content of constituent units derived from α-olefins is 100 mol%).

6. The ethylene-α-olefin copolymer (A) 1 The composition for forming solar cell encapsulants according to claim 1, wherein the number of vinyl-type double bonds per 1000 carbon atoms, as determined by H-NMR, is 0.08 or more.

7. The solar cell encapsulant forming composition according to claim 1, wherein the ethylene-α-olefin copolymer (A) satisfies the following requirement (a4): (a4) The ethylene-α-olefin copolymer (A) contains, 1 The total number of vinyl double bonds, vinylidene double bonds, disubstituted olefin double bonds, and trisubstituted olefin double bonds per 1000 carbon atoms, as determined by H-NMR, is 0.50 or more.

8. The solar cell encapsulant forming composition according to claim 1, wherein the ethylene-α-olefin copolymer (A) satisfies all of the following requirements (a1) to (a3): (a1) Density measured in accordance with ASTM D1505 is 0.865 to 0.885 g / cm³ ３ (a2) Melt flow rate (MFR) measured in accordance with ASTM D1238 under conditions of 190°C and a 2.16 kg load. ２ The amount is 4.0 to 13 g / 10 min. (a3) ​​The content of constituent units derived from ethylene is 80 to 90 mol%, and the content of constituent units derived from α-olefins having 3 to 20 carbon atoms is 10 to 20 mol% (however, the sum of the content of constituent units derived from ethylene and the content of constituent units derived from α-olefins shall be 100 mol%).

9. The ethylene-α-olefin copolymer (A) satisfies the following requirement (a4), and the ethylene-α-olefin copolymer (A) 1 A composition for forming a solar cell encapsulant according to claim 1, wherein the number of vinyl double bonds per 1000 carbon atoms determined by H-NMR is 0.08 or more. (a4) The ethylene-α-olefin copolymer (A) contains, 1 The total number of vinyl double bonds, vinylidene double bonds, disubstituted olefin double bonds, and trisubstituted olefin double bonds per 1000 carbon atoms, as determined by H-NMR, is 0.50 or more.

10. The composition for forming a solar cell encapsulant according to claim 8, wherein the content of the organic peroxide is 0.1 to 2 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), the content of the silane coupling agent is 0.1 to 1 part by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A), the 1-minute half-life temperature of the organic peroxide is in the range of 100 to 170°C, and the composition contains at least one selected from the group consisting of ultraviolet absorbers, heat stabilizers, and light stabilizers in an amount of 0.005 to 5 parts by mass per 100 parts by mass of the ethylene-α-olefin copolymer (A).

11. A sheet for solar cell encapsulating material, comprising the composition for forming solar cell encapsulating material according to any one of claims 1 to 10.

12. A solar cell encapsulant, which is a crosslinked sheet for solar cell encapsulant according to claim 11.

13. A solar cell module comprising a transparent protective member on the front side, a protective member on the back side, a solar cell element, and a sealing layer containing the solar cell sealing material described in claim 12, wherein the sealing layer seals the solar cell element between the transparent protective member on the front side and the protective member on the back side.

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