Sealing material sheet for solar cell module and solar cell module

Abstract

Provided is a sealing material sheet that is heat resistant and has molding properties at a level preferred for a sealing material sheet for a solar cell module.　This sealing material sheet for a solar cell module comprises a polyolefin-based resin as a base resin, has a melting point of 55-120°C and a temperature difference between the extrapolated melting start temperature and the melting point of 20°C or less, and preferably has a gel fraction of 10% or less, and is a sealing material sheet or a sealing material sheet for a solar cell module, the sealing material sheet comprising a polyolefin-based resin as a base resin, having a melting point of 45-60°C and a temperature difference between the extrapolated melting start temperature and the melting point of 11°C or less, and containing a crosslinking agent at a ratio of 0.1-1.2 mass% in a resin component.

Description

Encapsulant sheet for solar cell module and solar cell module

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

[0002] Conventionally, the layer structure of a solar cell module is configured 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 high level of transparency and heat resistance in a well-balanced manner. For example, Patent Document 1 describes a technology related to a solar cell element encapsulation material for solar cell modules that 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 describes that this solar cell element encapsulation 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 an 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.

[0005] Japanese Patent Application Laid-Open No. 2000-186114

[0006] If an encapsulant sheet having a polyethylene-based resin as a base resin is subjected to a crosslinking treatment to a sufficient extent 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.

[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, the encapsulant sheet having a polyolefin resin as a 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.

[0010] (2) The encapsulating material 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).

[0012] (4) 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 more and 60°C or less, and a temperature difference between the extrapolated melting onset temperature and the melting point of 11°C or less, and containing a crosslinking agent in a proportion of 0.1% by mass or more and 1.2% by mass or less in the resin component.

[0013] (5) A solar cell module including solar cell elements, comprising a front encapsulant layer and a rear encapsulant layer that encapsulate the solar cell elements, and at least one of the front encapsulant layer and the rear encapsulant layer is formed from the encapsulant sheet according to (4).

[0014] (6) The solar cell module according to (5), wherein the encapsulant sheet has a gel fraction of 50% or more and 90% or less.

[0015] (7) A method for producing an encapsulant sheet for a solar cell module obtained by melt-molding an encapsulant composition, wherein the encapsulant composition contains a resin containing a polyolefin-based resin as a base resin and a crosslinking agent, the content of the crosslinking agent is in the range of 0.2 mass % or more and 1.2 mass % or less with respect to the total amount of the encapsulant composition, and the encapsulant composition is 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.

[0016] 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.

[0017] FIG. 1 is a cross-sectional view schematically showing a layer structure of a sealant sheet according to a first embodiment or a second embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of a layer structure of a solar cell module according to a first embodiment or a second embodiment, which is formed using a sealant sheet according to a first embodiment or a second embodiment of the present invention and a solar cell element. FIG. 3 is a graph showing the melting point and extrapolated melting onset temperature of an "sealant sheet for a solar cell module (Example 1-3)" according to one embodiment of the present invention. FIG. 4 is a graph showing the melting point and extrapolated melting onset temperature of an "sealant sheet for a solar cell module (Example 2-9)" according to one embodiment of the present invention.

[0018] 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.

[0019] 1-1. Sealant Sheet of First Embodiment The sealant sheet according to the first embodiment of this invention is a sealant sheet for a solar cell module. Specifically, it is a resin sheet that can be used as a sealant sheet that covers and laminates solar cell elements in a solar cell module to protect the solar cell elements mainly from physical impact.

[0020] The sealing material sheet according to the first embodiment of the present invention is characterized in that it has a polyolefin resin as a base resin, 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.

[0021] 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 and in which a portion of the main chain is replaced with another main chain different from the polyolefin. The same applies to the encapsulant sheet according to the first embodiment of this invention and the encapsulant sheet according to the second embodiment described later.

[0022] 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.

[0023] 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 necessarily 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 approximately the same, 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.

[0024] Here, the melting point of the encapsulant sheet in this specification refers to the peak melting temperature measured by differential scanning calorimetry (DSC) 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. The same applies to the encapsulant sheet according to the first embodiment of this invention and the encapsulant sheet according to the second embodiment described later.

[0025] 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 of the encapsulant sheet in an uncrosslinked stage after film formation is determined by DSC, and the extrapolated melting onset temperature is determined as the temperature at the intersection of a straight line extending the low-temperature baseline 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 is used). The same applies to the encapsulant sheet according to the first embodiment of this invention and the encapsulant sheet according to the second embodiment described below.

[0026] The temperature difference between the extrapolated melting initiation temperature and the melting point of the sealing material sheet according to the first embodiment of this invention 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 first embodiment of this invention may be 55°C or more and 120°C or less, preferably 65°C or more and 117°C or less, and more preferably 70°C or more and 115°C or less. The lower limit of the melting point of the sealing material sheet according to this embodiment is preferably 65°C or more, and more preferably 70°C or more. The upper limit of the melting point of the sealing material sheet according to this embodiment is preferably 117°C or less, and more preferably 115°C or less.

[0027] The MFR of the sealing material sheet according to the first embodiment of this invention 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 sealing material sheet according to the first embodiment of this invention 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 sealing material sheet according to the first embodiment of this invention 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 necessary heat resistance, and when the MFR of the encapsulant sheet of the first embodiment is 3.0 g / 10 min or more, the encapsulant sheet can be provided with the necessary molding properties.

[0028] In this specification, the "MFR" of an encapsulant sheet refers to the value measured in accordance with JIS K7210 at 190°C and a load of 2.16 kg 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. When the encapsulant sheet is a multilayer film, the MFR is measured by the above-mentioned process while the multilayered state in which all layers are laminated together is taken as the MFR value of the multilayer encapsulant sheet. The same applies to the encapsulant sheet according to the first embodiment of this embodiment and the encapsulant sheet according to the second embodiment described later.

[0029] The Vicat softening point of the sealing material sheet according to the first embodiment of this invention 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 sealing material 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 sealing material sheet is preferably 100° C. or lower, more preferably 95° C. or lower, and even more preferably 90° C. or lower.

[0030] The total light transmittance of the sealing material sheet according to the first embodiment of this invention, 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.

[0031] The haze value of the sealing material sheet according to the first embodiment of the present invention, 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.

[0032] 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 with a lower MFR is disposed at the center as a core layer 11, and a layer with a higher MFR is disposed on the outermost side as a skin layer 12. The encapsulant sheet according to this embodiment has sufficiently favorable molding properties even when it is a single-layer encapsulant sheet. However, by disposing a layer with a relatively high MFR as the skin layer 12, the encapsulant sheet can further improve its adhesion and molding properties. The same applies to the encapsulant sheet according to the first embodiment of this embodiment and the encapsulant sheet according to the second embodiment described below.

[0033] The thickness (total thickness) of the encapsulant sheet according to the first 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 first 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 first 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 can have molding properties and heat resistance at a sufficiently favorable level. 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.

[0034] Furthermore, when the encapsulant sheet according to the first embodiment of the present invention 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 first embodiment of the present invention 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 first embodiment of the present invention 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.

[0035] When the encapsulant sheet according to the first embodiment of the present invention 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 first embodiment of the present invention 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 first embodiment of the present invention 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.

[0036] When the encapsulant sheet according to the first embodiment of this 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 first embodiment of this 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 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 first embodiment of this 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 ranges, the heat resistance and molding characteristics of the encapsulant sheet 1 can be maintained within good ranges.

[0037] 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, or the like, and an encapsulant layer is laminated on the solar cell element side, followed by a transparent back substrate. 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, or the like, 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 flexible sheets. Specifically, it can be applied to various solar cells, regardless of the type of solar cell, including 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. The same applies to the encapsulant sheet according to the first embodiment of the present embodiment and the encapsulant sheet according to the second embodiment described below.

[0038] The encapsulant composition used in the production of the encapsulant sheet according to the first embodiment will be described below. The encapsulant sheet according to the first embodiment will be described in detail later, but can be produced, for example, by melt-molding the encapsulant composition described in detail below.

[0039] [Encapsulant composition] The encapsulant composition used in producing the "encapsulant sheet" according to the first embodiment of the present invention (hereinafter also simply referred to as "encapsulant composition of the first embodiment") is a resin composition having a polyolefin resin (preferably a low-density polyethylene resin) as a base resin. In this specification, the term "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 a mixed resin is made of the same type of resin but different densities (for example, multiple polyethylenes each having different densities), the entire mixed resin is referred to as the base resin.

[0040] The base resin of the encapsulant composition of the first embodiment 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 in the range of 20° C. or lower. Among these, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or metallocene linear low-density polyethylene (M-LLDPE), as well as various polyethylene resins, can be preferably used.

[0041] 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, and the encapsulant sheet has excellent transparency when processed into a sheet. Therefore, when an "encapsulant sheet" made of the "encapsulant composition of the first embodiment" using this as a base resin is placed on the light-receiving surface 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.

[0042] The density of the polyolefin resin used as the base resin of the "encapsulant composition of the first embodiment" is 0.880 g / cm ３ 0.930g / cm or more ３ Preferably, it is 0.880 g / cm or less. ３ 0.925g / cm or more ３ Preferably, it is 0.880 g / cm or less. ３ 0.920g / cm or more ３ The upper limit of the density of the polyolefin resin used as the base resin of the "encapsulant composition of the first embodiment" 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 It is more preferable that the density of the base resin of the encapsulant composition of the first embodiment is 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. ３By 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.

[0043] 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. The same applies to the encapsulant composition of the first embodiment and the encapsulant composition of the second embodiment described below.

[0044] Among these, a "silane copolymer obtained by copolymerizing an α-olefin and 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, it is possible to obtain a sufficiently strong adhesive property between the "encapsulant sheet" and other laminate members such as a glass protective substrate or a solar cell element. The same applies to the encapsulant composition of the first embodiment and the encapsulant composition of the second embodiment described below.

[0045] The content of the ethylenically unsaturated silane compound when constituting 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, relative to the total copolymer mass. The lower limit of the content of the ethylenically unsaturated silane compound when constituting 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, relative to the total copolymer mass. The upper limit of the content of the ethylenically unsaturated silane compound when constituting 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, relative to the total copolymer mass. The same applies to the encapsulant composition of the first embodiment and the encapsulant composition of the second embodiment described below.

[0046] [Other Additive Components] An adhesion improver can be added as appropriate to the encapsulant composition of the first embodiment. 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.

[0047] A crosslinking agent can be added to the encapsulant composition of the first embodiment. It is preferable to use a crosslinking agent with a one-hour half-life temperature of 120°C or higher and 145°C or lower. Specific examples of the crosslinking agent that can be preferably used as the crosslinking agent to be added to the encapsulant composition of the first embodiment 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.

[0048] When a crosslinking agent is contained, the content of the crosslinking agent in the encapsulant composition of the first embodiment 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 containing the crosslinking agent in such a range, weak crosslinking of the polyolefin-based resin is promoted, 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 be promoted during melt molding. Furthermore, weak crosslinking of the polyolefin-based resin progresses even with a small amount of crosslinking agent and essentially no crosslinking aid. Since this molding temperature is above the one-minute half-life temperature of the crosslinking agent, almost no crosslinking agent remains after molding. Therefore, weak crosslinking is completed at this molding stage.

[0049] The encapsulant composition of the first embodiment 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 of the first embodiment. The inclusion of these additives can impart stable mechanical strength over a long period of time, and can provide the encapsulant sheet with effects such as prevention of yellowing and cracking.

[0050] <Method for manufacturing encapsulant sheet> The "encapsulant sheet" according to the first embodiment of the present invention can be manufactured by melt-molding the "encapsulant composition of the first embodiment" described in detail above. The melt-molding of the encapsulant composition of the first embodiment can be carried out 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 a sheet-forming 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 a temperature exceeding the melting point of the encapsulant composition.

[0051] The melt molding temperature in the production of the encapsulant sheet according to the first embodiment is preferably the melting point of the resin with the highest melting point among the base resins of the encapsulant composition contained in the encapsulant composition + 30°C or more. 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.

[0052] Even when the encapsulant composition of the first embodiment 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. In particular, 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.

[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 xylene at 110°C for 12 hours, removing the sheet together with the resin mesh, drying it, and weighing it. The masses before and after extraction were compared to measure the proportion (mass %) of residual insoluble matter. A gel fraction of 0% means that the residual insoluble matter is essentially zero, and the crosslinking reaction has not substantially started. More specifically, a "gel fraction of 0%" means that the residual insoluble matter is completely absent, or that the mass % of the residual insoluble matter measured using a precision balance is less than 0.05 mass %. The residual insoluble matter does not include pigment components other than the resin component. If the residual insoluble matter is found to be mixed in the above test with other contaminants, for example, the content of these contaminants in the resin component can be separately measured in advance to calculate the "gel fraction (%)" that should be obtained for the residual insoluble matter derived from the resin component excluding these contaminants. The same applies to the encapsulant composition of the first embodiment and the encapsulant composition of the second embodiment described below.

[0054] 2, a solar cell module 10 according to a first embodiment of the present invention includes 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. The solar cell module 10 according to the first embodiment of the present invention uses the encapsulant sheet of the first embodiment described above for at least one of the front encapsulant layer 3 and the rear encapsulant layer 5.

[0055] 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-described first embodiment of the encapsulant sheet 1 for a solar cell module is not limited to application to crystalline solar cells, and as described above, can be applied to various solar cells regardless of the type of solar cell.

[0056] The solar cell module 10 can be manufactured by sequentially stacking components including the above-described first type of sealing material sheet, integrating them by vacuum suction or the like, and then heat-pressing the above-described components into an integrated molded body using a molding method such as lamination.

[0057] 2-1. Sealant Sheet of Second Embodiment The sealant sheet according to the second embodiment of this invention is a sealant sheet for a solar cell module. Specifically, it is a resin sheet that can be used as a sealant sheet that covers and laminates solar cell elements in a solar cell module to protect the solar cell elements mainly from physical impact.

[0058] The sealing material sheet according to the second embodiment of the present invention is characterized in that it 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 an amount of 0.1% by mass or higher and 1.2% by mass or lower in the resin component.

[0059] 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.

[0060] 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, sufficient heat resistance may not necessarily be exhibited if the temperature difference between the extrapolated melting onset temperature and the melting point exceeds 11°C, 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 may also be adversely affected.

[0061] The temperature difference between the extrapolated melting initiation temperature and the melting point in the sealing material sheet of the second embodiment according to the present embodiment may be 11°C or less, and is preferably 10.5°C or less, and more preferably 10°C or less.

[0062] The melting point of the sealing material sheet of the second embodiment according to the present embodiment may be 45° C. or higher and 60° C. or lower, preferably 48° C. or higher and 57° C. or lower, and more preferably 50° C. or higher and 55° C. or lower. The lower limit of the melting point of the sealing material sheet of the second embodiment according to the present embodiment is preferably 48° C. or higher, and more preferably 50° C. or higher. The upper limit of the melting point of the sealing material sheet of the second embodiment according to the present embodiment is preferably 57° C. or lower, and more preferably 55° C. or lower.

[0063] The MFR of the sealing material sheet according to the second embodiment of this invention 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 average across all layers. The lower limit of the MFR of the sealing material sheet according to the second embodiment of this invention 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 average across all layers. The upper limit of the MFR of the sealing material sheet according to the second embodiment of this invention 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 average across all layers. When the MFR of the sealing material sheet of the second embodiment is 50.0 g / 10 min or less, the sealing material sheet can be provided with the necessary heat resistance, and when the MFR of the sealing material sheet is 5.0 g / 10 min or more, the sealing material sheet can be provided with the necessary molding properties.

[0064] The Vicat softening point of the sealing material sheet according to the second embodiment of this invention 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 sealing material sheet according to the second embodiment of this invention 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 sealing material sheet according to the second embodiment of this invention is preferably 100° C. or lower, more preferably 95° C. or lower, and even more preferably 90° C. or lower.

[0065] The total light transmittance of the encapsulant sheet according to the second embodiment of the present invention 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.

[0066] The haze value of the sealing material sheet according to the second embodiment of the present invention, 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.

[0067] The thickness (total thickness) of the encapsulant sheet according to the second 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 second 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 second 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 can have molding properties and heat resistance at a sufficiently favorable level. 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.

[0068] Furthermore, when the encapsulant sheet according to the second 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 second 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 second 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.

[0069] When the encapsulant sheet according to the second embodiment of the present invention 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 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 second embodiment of the present invention 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 second embodiment of the present invention 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.

[0070] When the encapsulant sheet according to the second embodiment of the present invention 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 second embodiment of the present invention 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 ...3 or less, and more preferably 1 / 15 or more, of the total thickness of the encapsulant sheet 1. When the encapsulant sheet according to the second embodiment of the present invention 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 ranges, the heat resistance and molding characteristics of the encapsulant sheet 1 can be maintained within good ranges.

[0071] The encapsulant composition used in the production of the encapsulant sheet according to the second embodiment of the present invention will be described below in detail. The encapsulant sheet according to the second embodiment of the present invention can be produced, for example, by melt-molding the encapsulant composition described in detail below.

[0072] [Encapsulant composition] The encapsulant composition used in producing the "encapsulant sheet" according to the second embodiment of this invention (hereinafter also simply referred to as "encapsulant composition of the second embodiment") is a thermally crosslinkable resin composition containing a polyolefin resin (preferably a low-density polyethylene resin) as a base resin and a crosslinking agent. In this specification, the term "base resin" refers to the resin with the largest content ratio among the resin components of a resin composition containing the base resin. In addition, when a mixed resin is made of the same type of resin but with different densities (for example, multiple polyethylenes each with a different density), the entire mixed resin is referred to as the base resin.

[0073] (Base Resin) The base resin of the "encapsulant composition of the second embodiment" forming the "encapsulant sheet" according to the second embodiment of this invention can be selected from a wide variety of olefin-based resins, as long as the melting point is in the range 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 in the range of 11° C. or lower. Among these, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (M-LLDPE), and various polyethylene-based resins can be preferably used.

[0074] 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 and the encapsulant sheet has excellent transparency when processed into a sheet. Therefore, when the "encapsulant sheet of the second embodiment" made of the "encapsulant composition of the second embodiment" using this as a base resin is placed on the light-receiving surface 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.

[0075] The density of the polyolefin resin used as the base resin of the "encapsulant composition of the second embodiment" is 0.880 g / cm ３ 0.920g / cm or more ３ Preferably, it is 0.880 g / cm or less. ３ 0.900g / cm or more３ Preferably, it is 0.880 g / cm or less. ３ 0.890g / cm or more ３ The upper limit of the density of the polyolefin resin used as the base resin of the "encapsulant composition of the second embodiment" is 0.920 g / cm or less. ３ Preferably, it is 0.900 g / cm or less. ３ It is preferable that the density is 0.890 g / cm or less. ３ The density of the base resin of the encapsulant composition of the second embodiment 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.

[0076] (Crosslinking Agent) The crosslinking agent used in the "encapsulant composition of the second embodiment" preferably has a one-hour half-life temperature of 120° C. or higher and 145° C. or lower. This allows the "encapsulant composition of the second embodiment" according to the present invention to be a composition that can be melt-extruded at a temperature range of 110° C. or lower.

[0077] 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 the crosslinking agent to be added to the sealing material composition of the second embodiment.

[0078] The content of the crosslinking agent in the "encapsulant composition of the second embodiment" 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 of the second embodiment". 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 according to the second embodiment of this invention is formed into a film without causing substantial crosslinking, and it is expected that the content of the crosslinking agent in the encapsulant sheet at the sheet stage after film formation will be in the range of 0.1% by mass or more and 1.2% by mass or less.

[0079] (Cross-linking aid) The "encapsulant composition of the second embodiment" preferably contains a cross-linking aid that is a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group, more preferably a polyfunctional monomer in which the functional group is an allyl group, a (meth)acrylate group, or a vinyl group. This promotes an appropriate cross-linking reaction, thereby improving the heat resistance of the "encapsulant sheet of the second embodiment" to a high level. In addition, this cross-linking aid reduces the crystallinity of the base resin, such as linear low-density polyethylene, that forms the encapsulant sheet, thereby maintaining transparency. This not only improves the heat resistance as described above, but also makes it possible to further improve the transparency of the "encapsulant sheet of the second embodiment."

[0080] Specific examples of cross-linking aids that can be used in the "sealant composition of the second embodiment" 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, cyclohexanedimethanol diglycidyl ether, and trimethylolpropane polyglycidyl ether, each of which contains 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.

[0081] The content of the cross-linking aid in the "encapsulant composition of the second embodiment" is not particularly limited, but is preferably 0.01% by mass or more and 3.0% by mass or less, and more preferably 0.05% by mass or more and 2.0% by mass or less, relative to the base resin in the "encapsulant composition of the second embodiment". The lower limit of the content of the cross-linking aid in the "encapsulant composition of the second embodiment" is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more, relative to the base resin in the "encapsulant composition of the second embodiment". The upper limit of the content of the cross-linking aid in the "encapsulant composition of the second embodiment" is preferably 3.0% by mass or less, and more preferably 2.0% by mass or less, relative to the base resin in the "encapsulant composition of the second embodiment".

[0082] [Other Additives] An adhesion improver can be added as appropriate to the sealing material composition of the second embodiment. 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.

[0083] The encapsulant composition of the second embodiment may further contain other components. Examples include a weather-resistant masterbatch for imparting weather resistance to the encapsulant sheet of the second embodiment, 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.

[0084] <Method for manufacturing encapsulant sheet> The "encapsulant sheet" according to the second embodiment of the present invention can be manufactured by melt-molding the "encapsulant composition of the second embodiment" described in detail above. The melt-molding of the encapsulant composition of the second embodiment can be carried out by known molding methods, 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 exceeding 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, depending on the one-minute half-life temperature of the crosslinking agent used, that is, a temperature at which the gel fraction of the encapsulant composition of the second embodiment can be maintained at 10% or less, preferably 0%.

[0085] As described above, the encapsulant sheet according to the second embodiment formed by the above means is formed into a film without allowing substantial crosslinking to proceed, and it is expected that the content of the 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.

[0086] 2-2. Solar Cell Module>> Solar cell module 10 according to the second embodiment of the present invention 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, as shown in Fig. 2. Solar cell module 10 according to the present embodiment uses the above-described encapsulant sheet for at least one of front encapsulant layer 3 and rear encapsulant layer 5.

[0087] 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-described encapsulant sheet 1 for solar cell modules is not limited to application to crystalline solar cells, and as described above, can be applied to various solar cells regardless of the type of solar cell.

[0088] The solar cell module 10 according to the second embodiment can be manufactured by sequentially stacking components including an encapsulant sheet, integrating them by vacuum suction or the like, and then thermocompression molding the components into an integrally molded body using a molding method such as lamination. For example, when using vacuum thermal lamination, the lamination temperature may be adjusted to 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 compositions 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 according to the second embodiment can be manufactured by thermocompression molding the components into an integrally molded body.

[0089] For the front sealing material layer 3 and the rear sealing material layer 5 of the solar cell module 10 according to the second embodiment, a process is performed in which the sealing material compositions for the front sealing material and the rear sealing material are formed into films without crosslinking and then crosslinked to a gel fraction of 50% to 90% during the solar cell module manufacturing process. This crosslinking process can be performed by promoting a crosslinking reaction during the heat-pressure bonding step during lamination performed during modularization. Alternatively, if necessary depending on the lamination conditions, a separate thermal crosslinking process may be performed after modularization.

[0090] In the solar cell module 10 according to the second embodiment, conventionally known materials can be used without limitation for the transparent front substrate 2, the solar cell element 4, and the back protective sheet 6, which are components other than the front encapsulant layer 3 and the back encapsulant layer 5. The solar cell module 10 according to the second embodiment may also include components other than the above-mentioned components. The encapsulant sheet according to the second embodiment is not limited to single-crystal solar cell modules, and can be applied to all thin-film and other solar cell modules.

[0091] 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.

[0092] (1) First Embodiment <Production of Encapsulant Sheet for Solar Cell Module> Polyethylene resins 1-1 to 1-6 (respectively referred to as "PE1-1 to 1-6" in the table) were prepared as base resins. The densities, number of moles of α-olefin, number of carbon atoms, and MFR at 190°C of PE1-1 to PE1-6 are as shown in Table 1.

[0093] 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. Each encapsulant composition was extruded using a film molding machine equipped with a φ30 mm 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. The encapsulant sheets (single layer) of the Examples and Comparative Examples were manufactured using these resin sheets. The thickness of each encapsulant sheet in the Examples and Comparative Examples was a total thickness of 450 μm. In Table 2, the contents of PE1-1 to PE1-6 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 content (% by mass) of the total encapsulant composition.

[0094]

[0095]

[0096] In Table 2, the silane coupling agent is vinyltrimethoxysilane. In Table 2, the crosslinking agent is organic peroxide (Luperox 101). In Table 2, the ultraviolet absorber is KEMISORB 79. In Table 2, the light stabilizer is KEMISTAB 62 (HALS).

[0097] The sealing material sheets of the examples and comparative examples shown in Table 2 were measured for their 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 temperature difference between the extrapolated melting onset temperature and the melting point are shown in Table 3.

[0098] The Picat softening point was measured using a 533HDT testing device 6M-2 manufactured by Toyo Seiki Seisakusho. The Shore A hardness was measured using an EA617DK-1 manufactured by ESCO. The melt viscosity was measured using a Capillograph 1D PMD-C manufactured by Toyo Seiki Seisakusho. The volume resistivity was measured using a Digital Ultra-High Resistance / Micro Current Meter 5450 manufactured by ADC. The total light transmittance was measured using an HM-150N manufactured by Murakami Color Research Institute. The haze was measured using an HM-150N manufactured by Murakami Color Research Institute.

[0099] 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 residual insoluble matter.

[0100] 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 a 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. For the encapsulant sheet of Example 1-3, the melting point and extrapolated melting onset temperature are shown in Figure 3. In Figure 3, the vertical axis represents heat flow (heat capacity) and the horizontal axis represents temperature. From Figure 3, the melting point of the encapsulant sheet of Example 1-3 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.

[0101] Evaluation Example 1: Molding Property 1 A lead wire (250 μm diameter) was placed on the surface of a flat-surfaced white tempered glass plate. The lead wire was covered with each of the encapsulant sheets of the Examples and Comparative Examples, which were 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 property was evaluated according to the following evaluation criteria. (Evaluation Criteria) A: The encapsulant sheet completely followed the irregularities of the facing substrate surface. No void formation was observed. B: 2 mm 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 (void) was formed in the vicinity of the lead wire. The evaluation results are shown in the table below as "molding property 1".

[0102] <Evaluation Example 2: Molding Property 2> Except for arranging 10 lead wires (250 μm diameter) in a row at 10 mm intervals, the molding property was evaluated in the same manner and with the same evaluation criteria as in the above-mentioned Molding Property 1. The evaluation results are shown in the table below as "Molding Property 2."

[0103] Evaluation Example 3: Heat Creep Test As a test for evaluating heat resistance, a "heat creep test" was performed by the following method. In the "heat creep test," one sheet of the sealing material sheet cut to a size of 75 mm × 50 mm and one sheet of semi-tempered glass measuring 75 mm × 50 mm were laminated in this order on a 250 mm square semi-tempered glass, and the laminate was pressure-bonded 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) by which the semi-tempered glass shifted was measured.

[0104]

[0105] 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 a solar cell module.

[0106] (2) Second Embodiment <Production of Encapsulant Sheet for Solar Cell Module> Each example and comparative example was produced using an encapsulant composition having the composition shown in Table 4 below. A linear low-density polyethylene resin (LLDPE) was used as the base resin. Film formation was performed using a film forming machine equipped with a φ30 mm extruder and a 200 mm wide T-die at an extrusion temperature of 90°C, a take-up speed of 1.1 m / min, and a film thickness of 450 μm for each example and comparative example, to produce the encapsulant sheets.

[0107]

[0108]

[0109] In Table 5, the silane coupling agent is vinyltrimethoxysilane. In Table 5, the crosslinking agent is an organic peroxide ("Luperox TBEC" manufactured by Arkema Yoshitomi Co., Ltd.). In Table 5, the crosslinking coagent is triallyl isocyanurate (TAIC). In Table 5, the ultraviolet absorber is KEMISORB79. In Table 5, the light stabilizer is KEMISTAB62 (HALS).

[0110] The encapsulant sheets of the Examples and Comparative Examples listed in Table 5 were measured for Picat softening point, Shore A hardness (JIS K6253), melt viscosity (Pa·s 90°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 temperature difference between the extrapolated melting onset temperature and the melting point are shown in Tables 6 to 8.

[0111] The Picat softening point was measured using a 533HDT testing device 6M-2 manufactured by Toyo Seiki Seisakusho. The Shore A hardness was measured using an EA617DK-1 manufactured by ESCO. The melt viscosity was measured using a Capillograph 1D PMD-C manufactured by Toyo Seiki Seisakusho. The volume resistivity was measured using an ADC Digital Ultra-High Resistance / Micro-Current Meter 5450. The total light transmittance was measured using an HM-150N manufactured by Murakami Color Research Institute. The haze was measured using an HM-150N manufactured by Murakami Color Research Institute.

[0112] The gel fraction was determined by measuring the mass % of the residual insoluble matter by comparing the masses before and after extraction, after a laminate of each encapsulant sheet was subjected to a vacuum heating laminator treatment at a set temperature of 150°C, evacuation 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 removing it together with the resin mesh and drying it, weighing it, and comparing the masses before and after extraction.

[0113] 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), a measurement method based on JIS K 7121-1987." DSC measurements are performed in a temperature range of -80 to +200°C, with repeated heating and cooling, including an initial heating, an initial cooling, a second heating, and a second cooling. The data analysis used this data from the initial heating. For the encapsulant sheet of Example 2-9, the melting point and extrapolated melting onset temperature are shown in Figure 4. The vertical axis of Figure 4 represents heat flow (heat capacity), and the horizontal axis represents temperature. From Figure 4, the melting point of the encapsulant sheet of Example 2-9 is 51.0°C, and the extrapolated melting onset temperature is 41.7°C. Therefore, the temperature difference between the extrapolated melting onset temperature and the melting point is 9.3°C.

[0114] Evaluation Example 1: Molding Property 1 A lead wire (250 μm diameter) was placed on the surface of a flat-surfaced white tempered glass plate. The lead wire was covered with each of the encapsulant sheets of the Examples and Comparative Examples, which were 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, and release of atmospheric pressure from the upper chamber. The vacuum pressurization was performed for 15 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 property was evaluated according to the following evaluation criteria. (Evaluation Criteria) A: The encapsulant sheet completely followed the irregularities of the facing substrate surface. No void formation was observed. B: 2 mm 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 (void) was formed in the vicinity of the lead wire. The evaluation results are shown in the table below as "molding property 1".

[0115] Evaluation Example 2: Molding Property 2 Except for arranging 10 lead wires (250 μm diameter) at 10 mm intervals, the molding property was evaluated in the same manner and with the same evaluation criteria as in the above-mentioned Molding Property 1. The evaluation results are shown in the table below as "Molding Property 2."

[0116] Evaluation Example 2: Heat Creep Test As a test for evaluating heat resistance, a "heat creep test" was performed by the following method. In the "heat creep test," one sheet of the encapsulant sheet cut to a size of 75 mm × 50 mm and one sheet of 75 mm × 50 mm semi-tempered glass were laminated in this order on a 250 mm square semi-tempered glass, and the laminate was pressure-bonded 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.

[0117]

[0118]

[0119]

[0120] 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 therefore has a preferable level of molding property and heat resistance as an encapsulant sheet for a solar cell module.

[0121] REFERENCE SIGNS LIST 1 encapsulant sheet 11 core layer 12 skin layer 2 transparent front substrate 3 front encapsulant layer 4 solar cell element 5 rear encapsulant layer 6 rear surface protective sheet

Claims

1. An encapsulant sheet for solar cell modules, 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.

2. The encapsulant sheet according to claim 1, which has a gel fraction of 10% or less.

3. A solar cell module comprising solar cell elements, comprising a front encapsulant layer and a rear encapsulant layer that encapsulate the solar cell elements, wherein at least one of the front encapsulant layer and the rear encapsulant layer is formed from the encapsulant sheet according to claim 1 or 2.

4. An encapsulant sheet for solar cell modules, which uses a polyolefin resin as the 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.

5. A solar cell module comprising solar cell elements, comprising a front encapsulant layer and a rear encapsulant layer for encapsulating the solar cell elements, wherein at least one of the front encapsulant layer and the rear encapsulant layer is formed from the encapsulant sheet according to claim 4.

6. The solar cell module according to claim 5, wherein the gel fraction of the encapsulant sheet is 50% or more and 90% or less.

7. A method for producing an encapsulant sheet for a solar cell module obtained by melt-molding an encapsulant composition, wherein the encapsulant composition contains a resin containing a polyolefin resin as a base resin and a crosslinking agent, the content of the crosslinking agent is in the range of 0.2 mass% to 1.2 mass% of the total amount of the encapsulant composition, and the encapsulant composition is melt-molded so that the melting point of the obtained encapsulant sheet is 45°C to 60°C and the temperature difference between the extrapolated melting onset temperature and the melting point is 11°C or less.

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