Encapsulant sheet for solar cell module, solar cell module and method for producing the same

Abstract

Provided is an encapsulant sheet that has a preferable level of molding property and heat resistance as an encapsulant sheet for a solar cell module. [Solution] This is an encapsulant sheet for solar cell modules, which uses a polyolefin resin as a base resin, has a melting point of 45°C or higher and 60°C or lower, and the temperature difference between the extrapolated melting onset temperature and the melting point is 11°C or lower, and contains a crosslinking agent in a proportion of 0.1% by mass or higher and 1.2% by mass or lower in the resin component.

Description

[Technical field]

[0001] The present invention relates to an encapsulant sheet for a solar cell module, and a method for producing the solar cell module and the encapsulant sheet. [Background technology]

[0002] Conventionally, the layer structure of a solar cell module is such that, from the light-receiving side, a transparent front substrate, a light-receiving side sealing material, a plurality of solar cell elements, a non-light-receiving side sealing material, and a back protective sheet are laminated in this order.

[0003] In such solar cell modules, the encapsulant sheet that encapsulates the solar cell elements is required to have a well-balanced high level of transparency and heat resistance. For example, Patent Document 1 describes a technology related to a solar cell element encapsulant material for solar cell modules, which is an ethylene-unsaturated carboxylic acid copolymer or its ionomer having an unsaturated carboxylic acid content of 4% by weight or more and a melting point of 85°C or more. Patent Document 1 describes that this solar cell element encapsulant material (encapsulant sheet for solar cell modules) exhibits excellent adhesion to solar cell elements and is also excellent in transparency and heat resistance.

[0004] On the other hand, the encapsulant sheet described in Patent Document 1 contains unsaturated carboxylic acid, which leads to corrosion of the solar cell, which is a semiconductor, and reduces the power generation efficiency of the solar cell. Therefore, an encapsulant sheet for solar cell modules using a polyolefin resin instead of an ethylene-unsaturated carboxylic acid copolymer has been developed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-186114 A Summary of the Invention [Problem to be solved by the invention]

[0006] If a sealing material sheet having a polyethylene resin as a base resin is subjected to a necessary and sufficient crosslinking treatment to provide it with sufficient heat resistance to withstand long-term use at high temperatures, there is a problem that the sheet cannot maintain its ability to conform to the unevenness of the surface of the opposing component when modularized (hereinafter referred to as "molding characteristics").

[0007] An object of the present invention is to provide an encapsulant sheet having a preferable level of molding property and heat resistance as an encapsulant sheet for a solar cell module. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by specifying the base resin constituting the encapsulant sheet for a solar cell module as a resin having a temperature difference between the extrapolated melting onset temperature and the melting point of a given value or less, and have thus completed the present invention. Specifically, the present invention provides the following:

[0009] (1) An encapsulant sheet for a solar cell module, the encapsulant sheet having a polyolefin resin as a base resin, a melting point of 45°C or higher and 60°C or lower, and a temperature difference between the extrapolated melting onset temperature and the melting point of 11°C or lower, and containing a crosslinking agent in a proportion of 0.1% by mass or higher and 1.2% by mass or lower in the resin component.

[0010] (2) A solar cell module comprising a solar cell element, the solar cell module comprising a front sealing material layer and a rear sealing material layer for sealing the solar cell element, at least one of the front sealing material layer and the rear sealing material layer being made of the sealing material sheet described in (1).

[0011] (3) The solar cell module according to (2), wherein the encapsulant sheet has a gel fraction of 50% or more and 90% or less.

[0012] (4) A method for producing an encapsulant sheet for a solar cell module obtained by melt-molding an encapsulant composition, the encapsulant composition containing a resin including a polyolefin-based resin as a base resin and a crosslinking agent, the content of the crosslinking agent being in the range of 0.2 mass % or more and 1.2 mass % or less based on the total amount of the encapsulant composition, the encapsulant composition being melt-molded so that the melting point of the obtained encapsulant sheet is 45° C. or more and 60° C. or less, and the temperature difference between the extrapolated melting onset temperature and the melting point is 11° C. or less. Effect of the Invention

[0013] According to the present invention, it is possible to provide an encapsulant sheet having a preferable level of molding property and heat resistance as an encapsulant sheet for a solar cell module. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view that illustrates a layer structure of an encapsulant sheet according to one embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view showing a schematic example of a layer structure of a solar cell module using an encapsulant sheet according to one embodiment of the present invention and a solar cell element. [Diagram 3] FIG. 1 is a graph showing the melting point and the extrapolated melting onset temperature of the "sealant sheet for solar cell module (Example 9)" according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Specific embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments and can be modified as appropriate within the scope of the object of the present invention.

[0016] ≪1. Encapsulating sheet≫ The encapsulant sheet according to the present embodiment is a encapsulant sheet for a solar cell module. Specifically, the encapsulant sheet is a resin sheet that can be used as an encapsulant sheet for covering and laminating solar cell elements in a solar cell module to protect the solar cell elements mainly from physical impact.

[0017] The sealing material sheet according to the present embodiment is characterized in that it has a polyolefin resin as a base resin, a melting point of 45°C or more and 60°C or less, a temperature difference between the extrapolated melting onset temperature and the melting point of 11°C or less, and contains a crosslinking agent in a proportion of 0.1% by mass or more and 1.2% by mass or less in the resin component.

[0018] In this specification, the term "polyolefin resin" and the like are used as a concept including not only "polyolefin resin" but also a copolymer containing, for example, 50% or more (preferably 70% or more, more preferably 80% or more) of a polyolefin main chain and in which a part of the main chain is replaced with another main chain different from polyolefin.

[0019] By including such a polyolefin resin as a base resin, it is possible to impart a preferable level of molding property as an encapsulant sheet for a solar cell module. Not only is the melting point range of the thermal properties of the encapsulant sheet optimized, but also, by specifying the temperature difference of the encapsulant sheet within the above-mentioned specific range, it is possible to impart preferable properties such as molding property required for an encapsulant sheet for a solar cell module. Furthermore, it is possible to impart heat resistance to the finished product stage of the solar cell module.

[0020] For example, the inventors' research has revealed that even if an encapsulant sheet has a polyolefin resin as the base resin and a melting point of 45°C or higher, if the temperature difference between the extrapolated melting onset temperature and the melting point exceeds 11°C, sufficient heat resistance may not be exhibited, and that even if the melting points are approximately the same, if the temperature difference between the extrapolated melting onset temperature and the melting point exceeds a certain value, molding properties will also be adversely affected.

[0021] In this specification, the melting point of the encapsulant sheet refers to a peak melting temperature measured by differential scanning calorimetry (DSC) at a stage after completion of sheeting of an encapsulant sheet obtained by forming an encapsulant composition containing a resin component and other additives into a sheet by a molding method such as extrusion melt molding.

[0022] The extrapolated melting onset temperature of the encapsulant sheet refers to a value determined according to the method described in JIS K 7121-1987 "Method for measuring transition temperature of plastics." Specifically, the melting peak temperature is determined by DSC for the encapsulant sheet before crosslinking after film formation, and the extrapolated melting onset temperature is determined as the temperature at the intersection of a straight line extending the baseline on the low temperature side to the high temperature side and a tangent drawn at the point where the gradient is maximum on the curve on the low temperature side of the melting peak (when two or more overlapping melting peaks appear, the melting peak with the lower melting peak temperature).

[0023] The temperature difference between the extrapolated melting initiation temperature and the melting point of the sealing material sheet according to the present embodiment may be 11° C. or less, preferably 10.5° C. or less, and more preferably 10° C. or less.

[0024] The melting point of the sealing material sheet according to the present embodiment may be 45° C. or more and 60° C. or less, and is preferably 48° C. or more and 57° C. or less, and more preferably 50° C. or more and 55° C. or less. The lower limit of the melting point of the sealing material sheet according to the present embodiment is preferably 48° C. or more, and more preferably 50° C. or more. The upper limit of the melting point of the sealing material sheet according to the present embodiment is preferably 57° C. or less, and more preferably 55° C. or less.

[0025] The MFR of the sealing material sheet according to the present embodiment is not particularly limited, but is preferably 5.0 g / 10 min or more and 50.0 g / 10 min or less, more preferably 8.0 g / 10 min or more and 45.0 g / 10 min or less, and even more preferably 10.0 g / 10 min or more and 40.0 g / 10 min or less, on an average of all layers. The lower limit of the MFR of the sealing material sheet according to the present embodiment is preferably 5.0 g / 10 min or more, more preferably 8.0 g / 10 min or more, and even more preferably 10.0 g / 10 min or more, on an average of all layers. The upper limit of the MFR of the sealing material sheet according to the present embodiment is preferably 50.0 g / 10 min or less, more preferably 45.0 g / 10 min or less, and even more preferably 40.0 g / 10 min or less, on an average of all layers. When the MFR of the encapsulant sheet is 50.0 g / 10 min or less, the encapsulant sheet can be provided with necessary heat resistance, and when the MFR of the encapsulant sheet is 5.0 g / 10 min or more, the encapsulant sheet can be provided with necessary molding properties.

[0026] In this specification, the "MFR" of an encapsulant sheet refers to a value measured at a stage after the encapsulant sheet is formed by forming an encapsulant composition containing a resin component and other additives into a sheet by a molding method such as extrusion melt molding, i.e., in an uncrosslinked state after film formation, under conditions of 190°C and a load of 2.16 kg in accordance with JIS K7210. In addition, when the encapsulant sheet is a multilayer film, the measured value obtained by performing the measurement by the above-mentioned process while the encapsulant sheet is in a multilayer state in which all layers are laminated together is regarded as the MFR value of the multilayer encapsulant sheet.

[0027] The Vicat softening point of the encapsulant sheet is not particularly limited, but is preferably 20° C. or higher and 100° C. or lower, more preferably 25° C. or higher and 95° C. or lower, and even more preferably 30° C. or higher and 90° C. or lower. The lower limit of the Vicat softening point of the encapsulant sheet is preferably 20° C. or higher, more preferably 25° C. or higher, and even more preferably 30° C. or higher. The upper limit of the Vicat softening point of the encapsulant sheet is preferably 100° C. or lower, more preferably 95° C. or lower, and even more preferably 90° C. or lower.

[0028] The total light transmittance of the encapsulant sheet measured in accordance with JIS K 7361 is not particularly limited, but is preferably 70% or more, more preferably 80% or more, and even more preferably 85% or more.

[0029] The haze value of the encapsulating material sheet measured in accordance with JIS K 7136 is not particularly limited, but is preferably 0% or more and 35% or less, more preferably 0% or more and 32% or less, and even more preferably 0% or more and 30% or less.

[0030] When the "encapsulant sheet" is a multilayer film, it is more preferable that each layer has a different MFR within a range that satisfies the essential constituent requirements of the present invention. Specifically, as shown in FIG. 1, it is preferable that a layer having a lower MFR is disposed in the center as a core layer 11, and a layer having a higher MFR is disposed on the outermost layer side as a skin layer 12. The encapsulant sheet according to the present embodiment has sufficiently favorable molding properties even when it is a single-layer encapsulant sheet, but by disposing a layer having a relatively high MFR as the skin layer 12 in this way, the encapsulant sheet can have further improved adhesion and molding properties.

[0031] The thickness (total thickness) of the encapsulant sheet according to the present embodiment is not particularly limited, but is preferably 250 μm or more and 600 μm or less, and more preferably 300 μm or more and 550 μm or less. The lower limit of the thickness (total thickness) of the encapsulant sheet according to the present embodiment is preferably 250 μm or more, and more preferably 300 μm or more. The upper limit of the thickness (total thickness) of the encapsulant sheet according to the present embodiment is preferably 600 μm or less, and more preferably 550 μm or less. If the thickness is 250 μm or more, even if the encapsulant sheet 1 is thinned to a total thickness of about 250 μm, for example, it can have molding properties and heat resistance at a sufficiently preferable level. Note that if the total thickness exceeds 600 μm, the effect of further improving the impact mitigation effect cannot be obtained, so it is preferable that the total thickness is 600 μm or less.

[0032] Furthermore, when the encapsulant sheet according to the present embodiment is used as the encapsulant sheet 1 which is a multilayer sheet, the thickness of the core layer 11 is not particularly limited, but is preferably 200 μm or more and 400 μm or less, and more preferably 250 μm or more and 350 μm or less. When the encapsulant sheet according to the present embodiment is used as the encapsulant sheet 1 which is a multilayer sheet, the lower limit of the thickness of the core layer 11 is preferably 200 μm or more, and more preferably 250 μm or more. When the encapsulant sheet according to the present embodiment is used as the encapsulant sheet 1 which is a multilayer sheet, the upper limit of the thickness of the core layer 11 is preferably 400 μm or less, and more preferably 350 μm or less.

[0033] When the encapsulant sheet according to the present embodiment is the encapsulant sheet 1 which is a multilayer sheet, the thickness of each layer of the skin layer 12 is not particularly limited, but is preferably 30 μm or more and 100 μm or less, and more preferably 25 μm or more and 80 μm or less. When the encapsulant sheet according to the present embodiment is the encapsulant sheet 1 which is a multilayer sheet, the lower limit of the thickness of each layer of the skin layer 12 is preferably 20 μm or more, and more preferably 25 μm or more. When the encapsulant sheet according to the present embodiment is the encapsulant sheet 1 which is a multilayer sheet, the upper limit of the thickness of each layer of the skin layer 12 is preferably 100 μm or less, and more preferably 80 μm or less.

[0034] When the encapsulant sheet according to the present embodiment is the encapsulant sheet 1 as a multilayer sheet, the total thickness of the two skin layers 12 laminated on both sides of the core layer is not particularly limited, but is preferably 1 / 20 to 1 / 3, and more preferably 1 / 15 to 1 / 4, of the total thickness of the encapsulant sheet 1. When the encapsulant sheet according to the present embodiment is the encapsulant sheet 1 as a multilayer sheet, the total thickness of the two skin layers 12 laminated on both sides of the core layer is preferably 1 / 20 or more, and more preferably 1 / 15 or more, of the total thickness of the encapsulant sheet 1. When the encapsulant sheet according to the present embodiment is the encapsulant sheet 1 as a multilayer sheet, the total thickness of the two skin layers 12 laminated on both sides of the core layer is preferably 1 / 3 or less, and more preferably 1 / 4 or less, of the total thickness of the encapsulant sheet 1. By setting the thickness of each layer of the encapsulant sheet 1 in such a range, the heat resistance and molding properties of the encapsulant sheet 1 can be maintained in a good range.

[0035] The encapsulant sheet for the solar cell module according to the present embodiment may be applied to a crystalline solar cell, but is not limited to crystalline solar cells. For example, the encapsulant sheet can be applied to a thin-film solar cell in which a solar cell element is formed on the back side of a transparent front surface by deposition, sputtering, wet coating, etc., a encapsulant layer is laminated on the surface side of the solar cell element, and a transparent back surface substrate is further formed. It can also be applied to a thin-film solar cell in which glass is applied to a transparent front substrate, an encapsulant is laminated, and then a solar cell element is applied to the glass, which is formed by deposition, sputtering, wet coating, etc., and serves as a back surface protective plate. It can also be applied to a solar cell in which the transparent front substrate, solar cell element, and back surface protective sheet are in a flexible sheet shape. Specifically, it can be applied to various solar cells regardless of the type of solar cell, such as a single crystal solar cell, a polycrystalline solar cell, a back contact type solar cell, an amorphous thin-film solar cell, a Cd-Te thin-film solar cell, a compound solar cell, a dye-sensitized solar cell, and a perovskite solar cell.

[0036] The encapsulant composition used in the production of the encapsulant sheet according to the present embodiment will be described below. The encapsulant sheet according to the present embodiment will be described in detail later, but can be produced, for example, by melt molding the encapsulant composition described in detail below.

[0037] [Encapsulant composition] The encapsulant composition (hereinafter, also simply referred to as "encapsulant composition") used in the manufacture of the "encapsulant sheet" of the present invention is a thermally crosslinked resin composition containing a polyolefin resin (preferably a low-density polyethylene resin) as a base resin and a crosslinking agent. In this specification, the "base resin" refers to the resin having the largest content ratio among the resin components of the resin composition containing the base resin. In addition, when the same type of resin with different densities (for example, multiple polyethylenes each having different densities) is used as a mixed resin, the entire mixed resin is considered to be the base resin.

[0038] (Base resin) The base resin of the "encapsulant composition" forming the "encapsulant sheet" of the present invention can be selected from a wide variety of olefin-based resins, so long as the melting point is in the range of 45° C. or more and 60° C. or less, and the temperature difference between the extrapolated melting onset temperature and the melting point is in the range of 11° C. or less. Among these, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (M-LLDPE), and various other polyethylene-based resins can be preferably used.

[0039] Furthermore, among the various polyethylenes mentioned above, linear low density polyethylene (LLDPE) has a narrow crystallinity distribution and uniform crystal size, so not only does it not have large crystal sizes, but it also has low crystallinity and excellent transparency when processed into a sheet as an encapsulant sheet. Therefore, an "encapsulant sheet" made of an "encapsulant composition" using this as a base resin can better prevent a decrease in power generation efficiency due to attenuation of incident light on the solar cell element when it is placed on the light-receiving surface side of the solar cell element in a self-luminous display.

[0040] The density of the polyolefin resin used as the base resin of the "encapsulant composition" is 0.880 g / cm 3 More than 0.920g / cm 3 It is preferable that the density is 0.880 g / cm or less. 3 More than 0.900g / cm 3 It is preferable that the density is 0.880 g / cm or less. 3 More than 0.890g / cm 3 The upper limit of the density of the polyolefin resin used as the base resin of the "encapsulant composition" is 0.920 g / cm or less. 3 It is preferable that the density is 0.900 g / cm or less. 3 It is preferable that the density is 0.890 g / cm or less. 3 It is more preferable that the density of the base resin of the encapsulant composition is 0.880 g / cm or less. 3 By making the density equal to or higher than 0.920 g / cm, the heat resistance of the sealing material sheet can be stably improved to a sufficient level. 3By setting the thickness to the range below, the adhesion of the "encapsulant sheet" to solar cell elements and the like can be maintained at a sufficiently preferable level.

[0041] Furthermore, in this specification, the term "polyethylene resin" includes not only ordinary polyethylene obtained by polymerizing ethylene, but also resins obtained by polymerizing compounds having ethylenically unsaturated bonds such as α-olefins, resins obtained by copolymerizing a plurality of different compounds having ethylenically unsaturated bonds, and modified resins obtained by grafting other chemical species onto these resins.

[0042] Among them, a "silane copolymer obtained by copolymerizing an α-olefin and an ethylenically unsaturated silane compound as a comonomer" can be preferably used as a part of the base resin of the encapsulant composition. By using such a resin, it is possible to obtain sufficient adhesive strength between the "encapsulant sheet" and other laminated members such as a glass protective substrate and a solar cell element.

[0043] The content of the ethylenically unsaturated silane compound when forming a copolymer of an α-olefin and an ethylenically unsaturated silane compound is, for example, preferably 0.001 mass% or more and 15 mass% or less, more preferably 0.01 mass% or more and 5 mass% or less, and even more preferably 0.05 mass% or more and 2 mass% or less, based on the total copolymer mass. The lower limit of the content of the ethylenically unsaturated silane compound when forming a copolymer of an α-olefin and an ethylenically unsaturated silane compound is preferably 0.001 mass% or more, more preferably 0.01 mass% or more, and even more preferably 0.05 mass% or more, based on the total copolymer mass. The upper limit of the content of the ethylenically unsaturated silane compound when forming a copolymer of an α-olefin and an ethylenically unsaturated silane compound is preferably 15 mass% or less, more preferably 5 mass% or less, and even more preferably 2 mass% or less, based on the total copolymer mass.

[0044] (Crosslinking agent) The crosslinking agent used in the "sealant composition" preferably has a one-hour half-life temperature of 120° C. or more and 145° C. or less. This allows the "sealant composition" according to the present invention to be a composition that can be melt extrusion molded at a temperature range of 110° C. or less.

[0045] Specific examples of preferred crosslinking agents that satisfy the above conditions include peroxyketals such as n-butyl 4,4-di(t-butylperoxy)valerate, ethyl 3,3-di(t-butylperoxy)butyrate, and 2,2-di(t-butylperoxy)butane, and dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(t-peroxy)hexyne-3, which can be preferably used as crosslinking agents to be added to the sealing material composition.

[0046] The content of the crosslinking agent in the "encapsulant composition" is preferably 0.2% by mass or more and 1.2% by mass or less, and more preferably 0.4% by mass or more and 0.8% by mass or less, relative to the base resin in the "encapsulant composition". By setting the content of the crosslinking agent within the above range, the molded "encapsulant sheet" can be provided with excellent heat resistance. As described above, the encapsulant sheet of the present invention is formed into a film without causing substantial crosslinking to proceed, and it is assumed that the content of the crosslinking agent in the encapsulant sheet at the sheet stage after film formation is within the range of 0.1% by mass or more and 1.2% by mass or less.

[0047] (Crosslinking aid) The "sealant composition" preferably contains a crosslinking aid in which the functional group of the polyfunctional monomer is an allyl group, a (meth)acrylate group, or a vinyl group. This promotes an appropriate crosslinking reaction to improve the heat resistance of the "sealant sheet" to a high level, and the crosslinking aid reduces the crystallinity of the base resin, such as linear low-density polyethylene, that forms the sealant sheet, thereby maintaining transparency. This improves the heat resistance as described above, and also makes it possible to improve the transparency of the "sealant sheet".

[0048] Specific examples of crosslinking aids that can be used in the "sealing material composition" include polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, and diallyl maleate, poly(meth)acryloxy compounds such as trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA), ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, and 1,9-nonanediol diacrylate, and epoxy compounds such as glycidyl methacrylate containing a double bond and an epoxy group, 4-hydroxybutyl acrylate glycidyl ether, and 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexane dimethanol diglycidyl ether, and trimethylolpropane polyglycidyl ether, which contain two or more epoxy groups. These may be used alone or in combination of two or more. Among the above crosslinking aids, TAIC can be particularly preferably used because it has good compatibility with linear low-density polyethylene, reduces crystallinity by crosslinking, maintains transparency, and is likely to exhibit a significant effect of imparting flexibility at low temperatures.

[0049] The content of the crosslinking aid in the "sealing material composition" is not particularly limited, but is preferably 0.01% by mass or more and 3.0% by mass or less, more preferably 0.05% by mass or more and 2.0% by mass or less, based on the base resin in the "sealing material composition". The lower limit of the content of the crosslinking aid in the "sealing material composition" is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, based on the base resin in the "sealing material composition". The upper limit of the content of the crosslinking aid in the "sealing material composition" is preferably 3.0% by mass or less, more preferably 2.0% by mass or less, based on the base resin in the "sealing material composition".

[0050] [Other additives] The sealing material composition may be appropriately added with an adhesion improver. As the adhesion improver, a known silane coupling agent may be used, but a silane coupling agent having an epoxy group (hereinafter also referred to as an "epoxy-based silane coupling agent") or a silane coupling agent having a mercapto group (hereinafter also referred to as a "mercapto-based silane coupling agent") may be particularly preferably used.

[0051] The encapsulant composition may further contain other components. For example, components such as a weather-resistant masterbatch for imparting weather resistance to the encapsulant sheet, various fillers, crosslinking aids, light stabilizers, ultraviolet absorbers, heat stabilizers, flame retardants, colorants, antioxidants, and nucleating agents are exemplified. The content of these components varies depending on the particle shape, density, and the like, but is preferably within the range of about 0.001% by mass or more and 5% by mass or less in the encapsulant composition. By including these additives, the encapsulant sheet can be provided with stable mechanical strength over a long period of time, and with an effect of preventing yellowing, cracking, and the like.

[0052] <Method of manufacturing encapsulant sheet> The "encapsulant sheet" of the present invention can be produced by a method of melt molding the "encapsulant composition" described in detail above. The melt molding of the encapsulant composition can be performed by a known molding method, specifically, various molding methods such as injection molding, extrusion molding, blow molding, compression molding, and rotational molding. The lower limit of the molding temperature during molding may be a temperature that exceeds the melting point of the encapsulant composition. The upper limit of the molding temperature may be a temperature at which crosslinking does not start during film formation, that is, a temperature at which the gel fraction of the encapsulant composition can be maintained at 10% or less, preferably 0%, depending on the 1-minute half-life temperature of the crosslinking agent used.

[0053] Here, the term "gel fraction (%)" in this specification refers to a value obtained by placing 1.0 g of an encapsulant sheet in a resin mesh, extracting it with 110°C xylene for 12 hours, taking it out together with the resin mesh, drying it, and weighing it, comparing the mass before and after extraction to measure the proportion (mass%) of the residual insolubles. A gel fraction of 0% means that the residual insolubles are substantially 0 and the crosslinking reaction has not substantially started. More specifically, a gel fraction of 0% means that the residual insolubles are completely absent, or that the mass% of the residual insolubles measured by a precision balance is less than 0.05 mass%. The residual insolubles do not include pigment components other than the resin components. When the residual insolubles are mixed with these other than the resin components in the above test, for example, the content of these mixtures in the resin components can be separately measured in advance to calculate the "gel fraction (%)" that should be obtained for the residual insolubles derived from the resin components excluding these mixtures.

[0054] As described above, the encapsulant sheet molded by the above means is formed into a film without causing substantial crosslinking, and it is expected that the content of the above crosslinking agent in the encapsulant sheet at the sheet stage after film formation will be in the range of 0.1 mass % or more and 1.2 mass % or less.

[0055] ≪2. Solar cell module≫ 2, solar cell module 10 according to the present embodiment has a transparent front substrate 2, a front sealing material layer 3, a solar cell element 4, a rear sealing material layer 5, and a rear protective sheet 6 laminated in this order from the light receiving side of the incident light. Solar cell module 10 according to the present embodiment uses the above-mentioned sealing material sheet for at least one of front sealing material layer 3 and rear sealing material layer 5.

[0056] It should be noted that the solar cell module 10 in FIG. 2 is intended to be a crystalline solar cell that uses glass or the like as a transparent front substrate, but the above-mentioned encapsulant sheet 1 for solar cell modules is not limited to application to crystalline solar cells, and as mentioned above, can be applied to various solar cells regardless of the type of solar cell.

[0057] The solar cell module 10 can be manufactured by sequentially stacking components including the encapsulant sheet, integrating them by vacuum suction or the like, and then thermocompression molding the above components into an integrally molded body by a molding method such as lamination. For example, in the case of vacuum thermal lamination, the lamination temperature may be adjusted within a range of 110°C or higher and 170°C or lower depending on the one-minute half-life temperature of the crosslinking agent added to the encapsulant composition for the light-receiving surface side encapsulant 2 and the non-light-receiving surface side transparent encapsulant 3. In this manner, the solar cell module 10 can be manufactured by thermocompression molding the above components into an integrally molded body.

[0058] Of the sealing materials constituting the solar cell module 10, the front sealing material layer 3 and the rear sealing material layer 5 are formed as uncrosslinked films of sealing material compositions for the front sealing material and the rear sealing material, and a process of crosslinking the films so that the gel fraction is 50% or more and 90% or less is carried out during the manufacturing process of the solar cell module. This crosslinking process can be carried out by allowing a crosslinking reaction to proceed during the heat and pressure bonding during lamination carried out during this modularization. Alternatively, if necessary depending on the lamination conditions, a separate thermal crosslinking process may be carried out after modularization.

[0059] In the solar cell module 10 according to the present embodiment, the transparent front substrate 2, the solar cell element 4, and the back protective sheet 6, which are members other than the front sealing material layer 3 and the back sealing material layer 5, can be made of conventionally known materials without any restrictions. The solar cell module 10 according to the present embodiment may also include members other than the above-mentioned members. The sealing material sheet according to the present embodiment is not limited to single crystal type, and can be applied to all solar cell modules such as thin film type. EXAMPLES

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0061] <Production of encapsulant sheets for solar cell modules> Each of the examples and comparative examples was produced using an encapsulant composition having the composition shown in the following Table 1. A linear low-density polyethylene resin (LLDPE) was used as the base resin. The film was formed using a film forming machine having a φ30 mm extruder and a 200 mm wide T-die at an extrusion temperature of 90° C. and a take-up speed of 1.1 m / min to form a sheet with a film thickness of 450 μm in each case, thereby producing the encapsulant sheets of each Example and Comparative Example.

[0062] [Table 1]

[0063] [Table 2]

[0064] In Table 2, the silane coupling agent is vinyltrimethoxysilane. In Table 2, the crosslinking agent is an organic peroxide ("Luperox TBEC" manufactured by Arkema Yoshitomi Co., Ltd.). In Table 2, the crosslinking coagent is triallyl isocyanurate (TAIC). In Table 2, the ultraviolet absorber is KEMISORB79. In Table 2, the light stabilizer is KEMISTAB62 (HALS).

[0065] For the encapsulant sheets of the examples and comparative examples shown in Table 2, the Picat softening point, Shore A hardness (JIS K6253), melt viscosity (Pa s 90°C 2.43×10sec -1 ), thickness, volume resistivity, total light transmittance (JIS K 7361), haze (JIS K 7136), gel fraction, extrapolated melting onset temperature (JIS K 7121-1987), melting point, and temperature difference between the extrapolated melting onset temperature and the melting point are shown in Table 3.

[0066] Picat softening point was measured using a 533HDT tester 6M-2 manufactured by Toyo Seiki Seisakusho. Shore A hardness was measured using an EA617DK-1 manufactured by Esco. Melt viscosity was measured using a Capilograph 1D PMD-C manufactured by Toyo Seiki Seisakusho. Volume resistivity was measured using a Digital Ultra High Resistance / Micro Ammeter 5450 manufactured by ADC. Total light transmittance was measured using a HM-150N manufactured by Murakami Color Research Institute. Haze was measured using a HM-150N manufactured by Murakami Color Research Institute.

[0067] The gel fraction was determined by subjecting a laminate of each encapsulant sheet to a vacuum heating laminator treatment at a set temperature of 150°C, vacuuming for 3 minutes, and atmospheric pressure application for 7 minutes, and then placing 0.1 g of the encapsulant sheet after the treatment in a resin mesh and extracting it with toluene at 60°C for 4 hours, and then taking it out together with the resin mesh and drying and weighing it, and comparing the masses before and after extraction to measure the mass % of the residual insoluble matter.

[0068] The melting point and extrapolated melting start temperature of the encapsulant sheet were measured by the measurement method "differential scanning calorimetry (DSC), measurement method based on JIS K 7121-1987" described in detail above. In the DSC measurement, the temperature is repeatedly increased and decreased in the temperature range of -80 to +200 ° C., with the first increase in temperature, the first decrease in temperature, the second increase in temperature, and the second decrease in temperature. The data analysis this time used the data of the first increase in temperature. The melting point and extrapolated melting start temperature of the encapsulant sheet of Example 9 are shown in FIG. 3. In FIG. 3, the vertical axis represents heat flow (heat capacity) and the horizontal axis represents temperature. From FIG. 3, the melting point of the encapsulant sheet of Example 9 is 51.0 ° C., and the extrapolated melting start temperature is 41.7 ° C., and therefore the temperature difference between the extrapolated melting start temperature and the melting point is 9.3 ° C.

[0069] <Evaluation Example 1: Molding Characteristics 1> A lead wire (250 μm diameter) was placed on the surface of a flat white tempered glass plate, and the lead wire was covered with each of the sealing material sheets of the Examples and Comparative Examples, which were cut to 150 mm × 150 mm. The resulting laminate was subjected to a vacuum heating lamination process (vacuum lamination process) at a set temperature of 150 ° C., 3 minutes of evacuation, and the upper chamber was released to atmospheric pressure, and vacuum pressure was applied for 15 minutes to obtain a solar cell module evaluation sample for each Example and Comparative Example. The resin temperature (achieved temperature) of the sealing material sheet during lamination during this heat treatment was 147 ° C. These solar cell module evaluation samples were visually observed, and the molding characteristics were evaluated according to the following evaluation criteria. (Evaluation Criteria) A: The encapsulant sheet completely conforms to the unevenness of the facing substrate surface. No void formation was observed. B: 2mm 2 Up to 5 bubbles were observed. C: A part of the encapsulant sheet did not completely conform to the unevenness of the opposing substrate surface, and a defective lamination portion (a gap) was formed near the lead wire. The evaluation results are shown in the table below as "molding properties 1".

[0070] <Evaluation Example 2: Molding Characteristics 2> The molding properties were evaluated in the same manner and with the same evaluation criteria as in the above molding property 1, except that 10 lead wires (250 μm diameter) were arranged in a row at intervals of 10 mm. The evaluation results are shown in the table below as "molding properties 2".

[0071] <Evaluation Example 2: Heat Creep Resistance> To evaluate heat resistance, a "heat creep test" was conducted using the method described below. In the "heat creep test," a sheet of sealing material cut to a size of 75 mm x 50 mm and a sheet of semi-tempered glass measuring 75 mm x 50 mm were laminated in this order on a 250 mm square piece of semi-tempered glass, and the laminate was pressed at 150°C for 15 minutes using a vacuum laminator used for manufacturing solar cell modules. The laminate sample was then left standing vertically in an oven at 140°C for 12 hours, and the distance (mm) that the semi-tempered glass shifted was measured.

[0072] [Table 3]

[0073] [Table 4]

[0074] [Table 5]

[0075] As can be seen from the above table, the encapsulant sheet has a polyolefin resin as the base resin, a melting point of 45°C or higher and 60°C or lower, and a temperature difference between the extrapolated melting onset temperature and the melting point of 11°C or lower, and thus has a preferable level of molding property and heat resistance as an encapsulant sheet for solar cell modules. [Explanation of symbols]

[0076] 1. Encapsulating material sheet 11 Core layer 12 Skin Layer 2 Transparent front board 3 Front sealing material layer 4. Solar cell elements 5 Back sealing material layer 6 Back protection sheet

Claims

1. An encapsulant sheet for a solar cell module, comprising: The base resin is polyolefin resin. the polyolefin resin is a linear low-density polyethylene resin composed of an α-olefin having 8 carbon atoms, and the content of the α-olefin is 12 mol %; The melting point is 45°C or more and 60°C or less, and the temperature difference between the extrapolated melting onset temperature and the melting point is 11°C or less; The resin component contains a crosslinking agent in an amount of 0.1% by mass or more and 1.2% by mass or less. Encapsulating sheet.

2. A solar cell module including a solar cell element, a front encapsulant layer and a rear encapsulant layer that encapsulate the solar cell element; At least one of the front sealing material layer and the rear sealing material layer is composed of the sealing material sheet according to claim 1. Solar cell module.

3. The gel fraction of the sealing material sheet is 50% or more and 90% or less. The solar cell module according to claim 2 .

4. A method for producing an encapsulant sheet for a solar cell module obtained by melt molding an encapsulant composition, comprising the steps of: The encapsulant composition contains a resin including a polyolefin-based resin as a base resin and a crosslinking agent, the polyolefin resin is a linear low-density polyethylene resin composed of an α-olefin having 8 carbon atoms, and the content of the α-olefin is 12 mol %; The content of the crosslinking agent is in the range of 0.2 mass % or more and 1.2 mass % or less based on the total amount of the encapsulant composition, The encapsulating material composition is melt-molded so that the melting point of the encapsulating material sheet to be obtained is 45° C. or more and 60° C. or less, and the temperature difference between the extrapolated melting initiation temperature and the melting point is 11° C. or less. A method for producing an encapsulant sheet.

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