Encapsulant sheet for solar cell module and solar cell module

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] An encapsulant sheet for a solar cell module, which uses a polyolefin resin as the base resin, has a melting point of 55°C or higher and 120°C or lower, and the temperature difference between the extrapolated melting onset temperature and the melting point is 20°C or lower, and preferably has a gel fraction of 10% or lower, and the solar cell module has at least one of the front encapsulant layer and the back encapsulant layer constituted by the encapsulant sheet.

Description

[Technical Field]

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

[0002] Conventionally, the layer structure of a solar cell module is a laminate of 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, stacked in this order from the light-receiving side.

[0003] In such solar cell modules, the encapsulant sheet that encapsulates the solar cell elements is required to have a good balance of high levels 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 an ionomer thereof, having an unsaturated carboxylic acid content of 4% by weight or more and a melting point of 85°C or more. Patent Document 1 also 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, encapsulant sheets for solar cell modules using polyolefin resins instead of ethylene-unsaturated carboxylic acid copolymers have been developed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-186114 Summary of the Invention [Problem to be solved by the invention]

[0006] If an encapsulant sheet having a polyethylene resin as a base resin is subjected to a crosslinking treatment to a sufficient degree to provide it with sufficient heat resistance to withstand long-term use at high temperatures, there is a problem in that, when modularized, the sheet is unable to maintain its ability to conform to the irregularities on the surface of the opposing component (hereinafter referred to as "molding characteristics").

[0007] An object of the present invention is to provide an encapsulant sheet that has 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 a base resin constituting an encapsulant sheet for a solar cell module to be a resin whose temperature difference between its extrapolated melting onset temperature and its melting point is equal to or less than a predetermined value, and have thus completed the present invention.

[0009] (1) An encapsulant sheet for a solar cell module, which uses a polyolefin resin as the base resin, has a melting point of 55°C or higher and 120°C or lower, and the temperature difference between the extrapolated melting onset temperature and the melting point is 20°C or lower.

[0010] (2) The encapsulant sheet according to (1), which has a gel fraction of 10% or less.

[0011] (3) A solar cell module including a solar cell element, the solar cell module including a front sealing material layer and a rear sealing material layer that seal the solar cell element, and 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) or (2). [Effects of the Invention]

[0012] 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 explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view schematically illustrating a layer structure of an encapsulant sheet according to one embodiment of the present invention. [Figure 2] 1 is a cross-sectional view schematically showing an 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. [Figure 3] FIG. 1 is a graph showing the melting point and extrapolated melting onset temperature of "encapsulant sheet for solar cell module (Example 3)" according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Specific embodiments of the present invention will be described in detail below, but 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.

[0015] ≪1. Encapsulating material sheet≫ The encapsulant sheet according to the present embodiment is a encapsulant sheet for a solar cell module. Specifically, it is a resin sheet that can be used as a encapsulant sheet that covers and laminates solar cell elements in a solar cell module to protect the solar cell elements mainly from physical impact.

[0016] The sealing material sheet according to the present embodiment is characterized in that it uses a polyolefin resin as a base resin, has a melting point of 55°C or higher and 120°C or lower, and the temperature difference between the extrapolated melting onset temperature and the melting point is 20°C or lower.

[0017] In this specification, the term "polyolefin resin" and the like are used to refer not only to "polyolefin resin" but also to a copolymer containing, for example, 50% or more (preferably 70% or more, more preferably 80% or more) of a polyolefin main chain, in which a part of the main chain is replaced with another main chain different from the polyolefin.

[0018] By including such a polyolefin resin as the base resin, it is possible to impart a desirable level of molding property to the encapsulant sheet for a solar cell module. By optimizing the melting point range of the encapsulant sheet with respect to thermal properties and also specifying the temperature difference of the encapsulant sheet within the above-mentioned specific range, it is possible to impart desirable properties, such as molding property, required for the encapsulant sheet for a solar cell module. Furthermore, it is possible to impart heat resistance to the finished solar cell module.

[0019] 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 55°C or higher, sufficient heat resistance may not be exhibited if the temperature difference between the extrapolated melting onset temperature and the melting point exceeds 20°C, and that even if the melting points are similar, if the temperature difference between the extrapolated melting onset temperature and the melting point exceeds a certain value, molding properties may also be adversely affected.

[0020] Here, in this specification, the melting point of the encapsulant sheet refers to the melting peak temperature measured by differential scanning calorimetry (DSC) at a stage after the completion of sheeting of the 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.

[0021] The extrapolated melting onset temperature of the encapsulant sheet refers to a value determined in accordance with the method described in JIS K 7121-1987 "Method for measuring transition temperatures of plastics." Specifically, the melting peak temperature is determined by DSC for an encapsulant sheet in an uncrosslinked stage after film formation, and the extrapolated melting onset temperature is determined as the temperature at the intersection of a straight line extending the low-temperature baseline toward 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 is used).

[0022] The temperature difference between the extrapolated melting initiation temperature and the melting point of the sealing material sheet according to this embodiment may be 20°C or less, preferably 17°C or less, and more preferably 15°C or less. The melting point of the sealing material sheet according to the present embodiment may be 55° C. or higher and 120° C. or lower, preferably 65° C. or higher and 117° C. or lower, and more preferably 70° C. or higher and 115° C. or lower. The lower limit of the melting point of the sealing material sheet according to the present embodiment is preferably 65° C. or higher, and more preferably 70° C. or higher. The upper limit of the melting point of the sealing material sheet according to the present embodiment is preferably 117° C. or lower, and more preferably 115° C. or lower.

[0023] The MFR of the encapsulant sheet according to the present embodiment is not particularly limited, but is preferably 2.0 g / 10 min or more and 5.0 g / 10 min or less, more preferably 2.2 g / 10 min or more and 4.5 g / 10 min or less, and even more preferably 2.3 g / 10 min or more and 4.0 g / 10 min or less, on average across all layers. The lower limit of the MFR of the encapsulant sheet according to the present embodiment is preferably 2.0 g / 10 min or more, more preferably 2.2 g / 10 min or more, and even more preferably 2.3 g / 10 min or more, on average across all layers. The upper limit of the MFR of the encapsulant sheet according to the present embodiment is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, and even more preferably 4.0 g / 10 min or less, on average across all layers. When the MFR of the encapsulant sheet is 5.0 g / 10 min or less, the encapsulant sheet can be provided with the required heat resistance, and when the MFR of the encapsulant sheet is 3.0 g / 10 min or more, the encapsulant sheet can be provided with the required molding properties.

[0024] In this specification, the "MFR" of an encapsulant sheet refers to a value measured at a stage after the completion of sheet formation 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, i.e., the MFR of the encapsulant sheet in an uncrosslinked state after film formation, in accordance with JIS K 7210, under conditions of 190°C and a load of 2.16 kg. In the case where the encapsulant sheet is a multilayer film, the MFR is the value measured by performing the above-mentioned measurement while the encapsulant sheet is in a multilayer state in which all layers are laminated together.

[0025] The Vicat softening point of the encapsulant sheet is not particularly limited, but is preferably 30° C. or higher and 100° C. or lower, more preferably 35° C. or higher and 95° C. or lower, and even more preferably 40° C. or higher and 90° C. or lower. The lower limit of the Vicat softening point of the encapsulant sheet is preferably 30° C. or higher, more preferably 35° C. or higher, and even more preferably 40° 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.

[0026] 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.

[0027] 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 60% or less, more preferably 0% or more and 57% or less, and even more preferably 0% or more and 55% or less.

[0028] When the "encapsulant sheet" is made into 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 with a lower MFR is disposed in the center as core layer 11, and a layer with a higher MFR is disposed on the outermost side as skin layer 12. The encapsulant sheet according to this embodiment has sufficiently favorable molding properties even when it is a single-layer encapsulant sheet, but by disposing a layer with a relatively high MFR as skin layer 12 in this manner, it is possible to further improve the adhesion and molding properties of the encapsulant sheet.

[0029] The thickness (total thickness) of the encapsulant sheet according to this 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 this 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 this embodiment is preferably 600 μm or less, and more preferably 550 μm or less. If the thickness is 250 μm or more, even when the encapsulant sheet 1 is thinned to a total thickness of, for example, about 250 μm, it is possible to achieve a sufficiently favorable level of both molding properties and heat resistance. Note that if the total thickness exceeds 600 μm, further improvement in the impact mitigation effect cannot be obtained, so it is preferably 600 μm or less.

[0030] 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.

[0031] When the encapsulant sheet according to the present embodiment is used as 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 20 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 used as 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 used as 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.

[0032] When the encapsulant sheet according to the present embodiment is used as 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 used as 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 used as 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 within such a range, the heat resistance and molding characteristics of the encapsulant sheet 1 can be maintained within a good range.

[0033] The encapsulant sheet for a solar cell module according to the present embodiment may be applied to crystalline solar cells, but its application is not limited to crystalline solar cells. For example, it can also be applied to thin-film solar cells in which a solar cell element is formed as a thin film on the back side of a transparent front panel by vapor deposition, sputtering, wet coating, etc., and an encapsulant layer is laminated on the solar cell element side, and a transparent back substrate is further formed. It can also be applied to thin-film solar cells 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 then formed by vapor deposition, sputtering, wet coating, etc., and serves as a back surface protective plate. It can also be applied to solar cells in which the transparent front substrate, solar cell element, and back surface protective sheet are in the form of flexible sheets. Specifically, it can be applied to various solar cells regardless of the type of solar cell, such as monocrystalline solar cells, polycrystalline solar cells, back-contact solar cells, amorphous thin-film solar cells, Cd—Te thin-film solar cells, compound solar cells, dye-sensitized solar cells, and perovskite solar cells.

[0034] The encapsulant composition used in producing the encapsulant sheet according to the present embodiment will be described below in detail. The encapsulant sheet according to the present embodiment can be produced, for example, by melt-molding the encapsulant composition described in detail below.

[0035] [Encapsulant composition] The encapsulant composition (hereinafter also simply referred to as "encapsulant composition") used in producing the "encapsulant sheet" of the present invention is a resin composition having a polyolefin-based resin (preferably a low-density polyethylene-based resin) as a base resin. In this specification, the "base resin" refers to the resin having the largest content ratio among the resin components of a resin composition containing the base resin. In addition, when the same type of resins with different densities (for example, multiple polyethylenes each having a different densities) are used as a mixed resin, the entire mixed resin is considered to be the base resin.

[0036] The base resin of the encapsulant composition can be selected from a wide variety of polyolefin resins, as long as the melting point is in the range of 55° C. or higher and 120° C. or lower, and the temperature difference between the extrapolated melting onset temperature and the melting point is within a range of 20° C. or lower. Among these, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (M-LLDPE), and various polyethylene resins are preferably used.

[0037] Furthermore, among the various polyethylenes mentioned above, linear low-density polyethylene (LLDPE) has a narrow crystallinity distribution and uniform crystal size, so not only are there no large crystals, but the crystallinity itself is low, resulting in excellent transparency when processed into a sheet as an encapsulant sheet. Therefore, when an "encapsulant sheet" made from an "encapsulant composition" using this as the base resin is placed on the light-receiving side of a solar cell element in a solar cell module, it can better prevent a decrease in power generation efficiency due to attenuation of light incident on the solar cell element.

[0038] The density of the polyolefin resin used as the base resin of the "encapsulant composition" is 0.880 g / cm 3 More than 0.930g / cm 3 Preferably, it is 0.880 g / cm or less. 3 More than 0.925g / cm 3 Preferably, it is 0.880 g / cm or less. 3 More than 0.920g / cm 3 The upper limit of the density of the polyolefin resin used as the base resin of the "encapsulant composition" is 0.930 g / cm or less. 3 Preferably, it is 0.925 g / cm or less. 3 Preferably, it is 0.920 g / cm or less. 3 The density of the base resin of the encapsulant composition is more preferably 0.880 g / cm or less. 3 By setting the density to 0.920 g / cm or more, the heat resistance of the sealing material sheet can be stably improved to a sufficient level. 3 By setting the thickness to the following, the adhesion of the "encapsulant sheet" to the solar cell element or the like can be maintained at a sufficiently preferable level.

[0039] Furthermore, the term "polyethylene resin" as used herein 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.

[0040] Among these, a "silane copolymer obtained by copolymerizing an α-olefin with an ethylenically unsaturated silane compound as a comonomer" can be preferably used as part of the base resin of the encapsulant composition. By using such a resin, sufficient adhesive strength can be obtained between the "encapsulant sheet" and other laminated members such as a glass protective substrate or a solar cell element.

[0041] 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 to 15% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.05 to 2% by mass, 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 to 15% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.05 to 2% by mass, 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% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less, based on the total copolymer mass.

[0042] [Other added ingredients] An adhesion improver can be added to the encapsulant composition as appropriate. As the adhesion improver, a known silane coupling agent can 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") can be particularly preferably used.

[0043] A crosslinking agent can be added to the encapsulant composition. The one-hour half-life temperature of the crosslinking agent is preferably 120°C or higher and 145°C or lower. Specific examples of crosslinking agents that can be preferably added to the encapsulant composition 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.

[0044] When a crosslinking agent is contained, the content of the crosslinking agent in the encapsulant composition is 0.02% by mass or more but less than 0.5% by mass, with the upper limit preferably being 0.2% by mass or less, more preferably 0.1% by mass or less. By including a crosslinking agent in such a range, weak crosslinking of the polyolefin-based resin proceeds, improving heat resistance and transparency. Although the MFR of the polyolefin-based resin decreases when the crosslinking agent content is small, the degree of decrease is small. Therefore, weak crosslinking can proceed during melt molding. Furthermore, weak crosslinking of the polyolefin-based resin proceeds even with a small amount of crosslinking agent and essentially no crosslinking aid. Since this molding temperature is above the 1-minute half-life temperature of the crosslinking agent, almost no crosslinking agent remains after molding. Therefore, weak crosslinking is completed at this molding stage.

[0045] The encapsulant composition may further contain other components. Examples include a weather-resistant masterbatch for imparting weather resistance to the encapsulant sheet, various fillers, crosslinking aids, light stabilizers, UV absorbers, heat stabilizers, flame retardants, colorants, antioxidants, nucleating agents, and the like. The content of these components varies depending on the particle shape, density, and the like, but is preferably within a range of approximately 0.001% by mass or more and 5% by mass or less in the encapsulant composition. The inclusion of these additives can impart stable mechanical strength over a long period of time and prevent yellowing, cracking, and the like to the encapsulant sheet.

[0046] <Method of manufacturing encapsulant sheet> The "encapsulant sheet" according to the present embodiment can be produced by a method of melt-molding the "encapsulant composition" described in detail above. The encapsulant composition can be melt-molded by known molding methods, specifically, various molding methods such as injection molding, extrusion molding, blow molding, compression molding, and rotational molding. When the encapsulant sheet is a multilayer sheet, an example of the sheet formation method is a method of molding by co-extrusion using three types of melt-kneading extruders. The lower limit of the molding temperature during molding may be any temperature as long as it exceeds the melting point of the encapsulant composition.

[0047] The melt molding temperature in the production of the encapsulant sheet is preferably at least 30°C higher than the melting point of the resin with the highest melting point among the base resins of the encapsulant composition contained in the encapsulant composition. Specifically, a high temperature of 175°C to 230°C is preferred, and a high temperature in the range of 190°C to 210°C is more preferred.

[0048] Even when the encapsulant composition contains a small amount (for example, less than 0.5% by mass) of a crosslinking agent, the gel fraction of the resulting encapsulant sheet is 25% or less, preferably 10% or less, and more preferably 1% or less, including zero. By setting the gel fraction to 10% or less, it is possible to effectively prevent gel generation during film formation and improve film formability. Furthermore, by setting the gel fraction to 1% or less, it is possible to improve the embedding ability of the encapsulant sheet in the modularization process, i.e., its ability to conform to irregularities.

[0049] ≪2. Solar Cell Module≫ 2, solar cell module 10 according to the present embodiment has a transparent front substrate 2, a front encapsulant layer 3, a solar cell element 4, a rear encapsulant layer 5, and a rear protective sheet 6 laminated in this order from the light-receiving side of incident light. Solar cell module 10 according to the present embodiment uses the above-mentioned encapsulant sheet for at least one of front encapsulant layer 3 and rear encapsulant layer 5.

[0050] The solar cell module 10 in FIG. 2 is intended for 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.

[0051] The solar cell module 10 can be manufactured by sequentially stacking components including an encapsulant sheet, integrating them by vacuum suction or the like, and then heat-pressing the above components into an integrated molded body using a molding method such as lamination. [Example]

[0052] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0053] <Manufacturing of encapsulant sheets for solar cell modules> Polyethylene resins 1 to 6 (represented as "PE1 to PE6" in the table) were prepared as base resins. Table 1 shows the densities, number of moles of α-olefin, number of carbon atoms, and MFR at 190°C of PE1 to PE6.

[0054] The encapsulant composition raw materials described below were mixed in the proportions shown in Table 2 below to form the encapsulant compositions for the encapsulant sheets of the Examples and Comparative Examples, respectively. Each encapsulant composition was extruded using a film molding machine equipped with a 30 mm diameter extruder and a 200 mm wide T-die at an extrusion temperature of 210°C and a take-up speed of 1.1 m / min to produce a resin sheet, and each resin sheet was used to produce the encapsulant sheets (single layer) of the Examples and Comparative Examples. The encapsulant sheets of the Examples and Comparative Examples all had a total thickness of 450 μm. In Table 2, the contents of PE1 to PE6 are expressed in parts by mass relative to 100 parts by mass of the base resin, and the contents of other additives (silane coupling agent, crosslinking agent, UV absorber, light stabilizer) refer to the contents (% by mass) of the total encapsulant composition.

[0055] [Table 1]

[0056] [Table 2]

[0057] In Table 2, the silane coupling agent is vinyltrimethoxysilane. In Table 2, the crosslinking agent is an organic peroxide (Luperox 101). In Table 2, the ultraviolet absorber is KEMISORB79. In Table 2, the light stabilizer is KEMISTAB62 (HALS).

[0058] The encapsulant sheets of the Examples and Comparative Examples listed in Table 2 were measured for Picat softening point, Shore A hardness (JIS K6253), melt viscosity (Pa·s 190°C 2.43×10 sec -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 the temperature difference between the extrapolated melting onset temperature and the melting point are shown in Table 3.

[0059] The Picat softening point was measured using a Toyo Seiki Seisakusho 533HDT testing device 6M-2. The Shore A hardness was measured using an ESCO EA617DK-1. The melt viscosity was measured using a Toyo Seiki Seisakusho Capillograph 1D PMD-C. The volume resistivity was measured using an ADC Digital Ultra-High Resistance / Micro Current Meter 5450. The total light transmittance was measured using a Murakami Color Research Institute HM-150N. The haze was measured using a Murakami Color Research Institute HM-150N.

[0060] The gel fraction was determined by placing 0.1 g of the sealing material sheet in a resin mesh, extracting it with toluene at 60°C for 4 hours, removing it together with the resin mesh, drying it, weighing it, and comparing the masses before and after extraction to determine the mass % of the remaining insoluble matter.

[0061] The melting point and extrapolated melting onset temperature of the encapsulant sheet were measured by the measurement method described in detail above ("differential scanning calorimetry (DSC), measurement method based on JIS K 7121-1987"). DSC measurement involves repeatedly measuring temperature increases and decreases in the temperature range of -80 to +200°C, i.e., an initial heating, an initial cooling, a second heating, and a second cooling. The data analysis this time used the data from the initial heating. The melting point and extrapolated melting onset temperature of the encapsulant sheet of Example 3 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 3 is 106.6°C, and the extrapolated melting onset temperature is 95.1°C. Therefore, the temperature difference between the extrapolated melting onset temperature and the melting point is 11.5°C.

[0062] <Evaluation example 1: Molding characteristics 1> A lead wire (250 μm diameter) was placed on the surface of a flat-surface white tempered glass plate, and the lead wire was covered with each of the encapsulant sheets of the Examples and Comparative Examples, cut to 150 mm × 150 mm. The laminate was then subjected to a vacuum heating lamination process (vacuum lamination process) at a set temperature of 150°C, evacuation for 3 minutes, release of the upper chamber to atmospheric pressure, and vacuum pressure for 7 minutes to obtain a solar cell module evaluation sample for each Example and Comparative Example. The resin temperature (achieved temperature) of the encapsulant 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 conformed to the irregularities of the facing substrate surface, and no void formation was observed. B: 2mm 2 Up to five bubbles were observed. C: A part of the sealing material sheet did not completely conform to the unevenness of the opposing substrate surface, and a defective lamination part (void) was formed in the vicinity of the lead wire. The evaluation results are shown in the table below as "Molding Properties 1."

[0063] <Evaluation example 2: Molding characteristics 2> The molding characteristics were evaluated in the same manner and with the same evaluation criteria as in the above molding characteristics 1, except that 10 lead wires (250 μm diameter) were arranged in a row at 10 mm intervals. The evaluation results are shown in the table below as "molding properties 2."

[0064] <Evaluation Example 3: Heat Creep Resistance> To evaluate heat resistance, a "heat creep test" was conducted using the method described below. In the "heat creep test," one sheet of encapsulant sheet cut to a size of 75 mm x 50 mm and one sheet of 75 mm x 50 mm semi-tempered glass were laminated in this order on a 250 mm square 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. [Table 3]

[0065] As can be seen from the above table, the encapsulant sheet has a polyolefin resin as the base resin, a melting point of 55°C or higher and 120°C or lower, and a temperature difference between the extrapolated melting onset temperature and the melting point of 20°C or lower, and therefore has a preferable level of molding property and heat resistance as an encapsulant sheet for solar cell modules. [Explanation of symbols]

[0066] 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, The base resin is polyethylene resin, The melting point is 106.6°C or higher and 120°C or lower, and the temperature difference between the extrapolated melting onset temperature and the melting point is 20°C or lower. An encapsulant sheet (excluding those in which the polyethylene resin is a propylene-butene copolymer or an ethylene-octene block copolymer).

2. The temperature difference between the extrapolated melting onset temperature and the melting point is 15°C or less. The encapsulant sheet according to claim 1 .

3. The gel fraction is 10% or less The encapsulant sheet according to claim 1 .

4. 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 back sealing material layer is formed from the sealing material sheet according to any one of claims 1 to 3. Solar cell module.

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