Sealing material sheets for solar cell modules and solar cell modules

Abstract

The present invention provides a sealing sheet for solar cell modules that offers a desirable level of molding properties, heat resistance, and effectively suppresses defects during hot press processing. [Solution] A encapsulating sheet for solar cell modules, with a polyolefin resin as the base resin, a melting point of 55°C to 120°C, a temperature difference of 20°C or less between the extracellular melting initiation temperature and the melting point, and a shear rate of 2.43 × 10 sec measured at 190°C. -1 The solar cell module comprises a sealing sheet having a melt viscosity of 1000 Pa·s or more and 4000 Pa·s or less, preferably with a gel fraction of 10% or less, and at least one of the front sealing layer and the back sealing layer being composed of the sealing sheet.

Description

[Technical Field]

[0001] This invention relates to a sealing material sheet for solar cell modules and a solar cell module. [Background technology]

[0002] Conventionally, the layer structure of a solar cell module consists of a transparent front substrate, a light-receiving side encapsulant, multiple solar cell elements, a non-light-receiving side encapsulant, and a back protective sheet, all stacked in that order from the light-receiving side.

[0003] In such solar cell modules, the sealing sheet used to enclose 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 relating to a solar cell element sealing material for solar cell modules, which is an ethylene-unsaturated carboxylic acid copolymer or its ionomer having an unsaturated carboxylic acid content of 4% by weight or more and a melting point of 85°C or higher. Patent Document 1 states that this solar cell element sealing material (sealing sheet for solar cell modules) exhibits excellent adhesion to solar cell elements and also has excellent transparency and heat resistance.

[0004] On the other hand, the encapsulating sheet described in Patent Document 1 contains an unsaturated carboxylic acid, which can lead to corrosion of the semiconductor solar cell and a decrease in the power generation efficiency of the solar cell. Therefore, encapsulating sheets for solar cell modules that use polyolefin resin instead of ethylene-unsaturated carboxylic acid copolymers have been developed. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-186114 [Overview of the project] [Problems that the invention aims to solve]

[0006] When a polyethylene-based resin-based sealing sheet is subjected to a degree of cross-linking necessary to provide sufficient heat resistance for long-term use at high temperatures, a problem arises in that the ability to conform to the surface irregularities of the opposing component (hereinafter referred to as "molding characteristics") cannot be maintained during modularization.

[0007] Furthermore, the inventors' research has revealed that if a sealing material composition is selected for manufacturing the sealing material sheet to achieve good molding characteristics, then during the hot-pressing process of the sealing material sheet, the sealing material composition may flow excessively, causing some of the resin to leak out, or the film thickness of the molded sealing material sheet may become uneven, resulting in problems such as the inability to maintain insulation as a solar cell module.

[0008] The present invention aims to provide a sealing sheet for solar cell modules that possesses a desirable level of molding properties, heat resistance, and can effectively suppress defects during hot press processing. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have discovered that the above problems can be solved by specifying the base resin constituting the encapsulant sheet for solar cell modules to be a resin in which the temperature difference between the extrapolation melting initiation temperature and the melting point is below a predetermined value, and the melt viscosity at a specific shear rate under a specific temperature is within a predetermined range, thereby completing the present invention. Specifically, the present invention provides the following.

[0010] (1) A encapsulating sheet for solar cell modules, having a polyolefin resin as the base resin, a melting point of 55°C to 120°C, and a temperature difference of 20°C or less between the extracellular melting initiation temperature and the melting point, with a shear rate of 2.43 × 10 sec measured at 190°C. -1 A sealing sheet having a melt viscosity of 1000 Pa·s or more and 4000 Pa·s or less.

[0011] The encapsulant sheet according to (1), wherein the gel fraction is 10% or less.

[0012] A solar cell module including a solar cell element, comprising a front encapsulant layer and a back encapsulant layer for encapsulating the solar cell element, wherein at least one of the front encapsulant layer and the back encapsulant layer is composed of the encapsulant sheet according to (1) or (2).

Advantages of the Invention

[0013] According to the present invention, it is possible to provide an encapsulant sheet having a preferable level of moldability as an encapsulant sheet for a solar cell module, having heat resistance, and effectively suppressing problems during hot press processing.

Brief Description of the Drawings

[0014] [Figure 1] It is a cross-sectional view schematically showing the layer structure of the encapsulant sheet of one embodiment of the present invention. [Figure 2] It is a cross-sectional view schematically showing an example of the layer structure of a solar cell module using the encapsulant sheet of one embodiment of the present invention and a solar cell element. [Figure 3] It is a graph showing the melting point and the extrapolated onset melting temperature of the "encapsulant sheet for solar cell module (Example 3)" of one embodiment of the present invention.

Modes for Carrying Out the Invention

[0015] Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0016] ≪1. Encapsulant Sheet≫ The sealing sheet according to this embodiment is a sealing sheet for solar cell modules. Specifically, it is a resin sheet that can be used as a sealing sheet to cover and laminate solar cell elements in a solar cell module, primarily to protect the solar cell elements from physical impact.

[0017] Furthermore, the sealing sheet according to this embodiment is characterized in that it 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 extracellular melting initiation temperature and the melting point is 20°C or less.

[0018] In this specification, the terms "polyolefin resin," etc., are used to include not only "polyolefin resin" but also copolymers that contain, for example, 50% or more (preferably 70% or more, more preferably 80% or more) of the polyolefin main chain, and in which a portion of the main chain is replaced by another main chain different from that of polyolefin.

[0019] By incorporating such polyolefin resins as a base resin, a desirable level of moldability can be imparted to the encapsulating sheet for solar cell modules. Regarding the thermal properties of the encapsulating sheet, not only is the melting point range optimized, but the temperature difference of the encapsulating sheet is also specified within the above-mentioned range, thereby imparting desirable characteristics such as moldability required for encapsulating sheets for solar cell modules. Furthermore, heat resistance can be imparted to the finished solar cell module.

[0020] For example, our research has revealed that even if a sealing sheet using a polyolefin resin as the base resin has a melting point of 55°C or higher, if the temperature difference between the extracellular melting initiation temperature and the melting point exceeds 20°C, sufficient heat resistance may not necessarily be achieved. Furthermore, even with similar melting points, if the temperature difference between the extracellular melting initiation temperature and the melting point exceeds a certain value, it can negatively affect the molding properties.

[0021] Herein, the melting point of the sealing material sheet as used herein refers to the melting peak temperature measured by differential scanning calorimetry (DSC) at the stage after the completion of sheet formation of a sealing material sheet, which is formed by a molding method such as extrusion melt molding, from a sealing material composition comprising a resin component and other additives.

[0022] Furthermore, the extracellular melting initiation temperature of the encapsulant sheet refers to the value obtained in accordance with the method described in JIS K 7121-1987 "Method for Measuring Transition Temperatures of Plastics". Specifically, for the encapsulant sheet in the uncrosslinked stage after film formation, the melting peak temperature is determined by DSC, and the extracellular melting initiation temperature is defined as the temperature at the intersection of a straight line extending from the low-temperature baseline to the high-temperature side and a tangent line drawn at the point where the slope is maximum on the low-temperature side curve of the melting peak (if two or more overlapping melting peaks appear, the melting peak with the lower melting peak temperature is used).

[0023] The temperature difference between the extracellular melting initiation temperature and the melting point in the sealing material sheet according to this embodiment may be 20°C or less, but is preferably 17°C or less, and more preferably 15°C or less. The melting point of the sealing material sheet according to this embodiment may be 55°C or higher and 120°C or lower, but is 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 this 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 this embodiment is preferably 117°C or lower, and more preferably 115°C or lower.

[0024] Furthermore, the sealing sheet according to this embodiment measured a shear rate of 2.43 × 10 sec at a temperature of 190°C. -1 It is characterized by having a melt viscosity of 1000 Pa·s or more and 4000 Pa·s or less.

[0025] The shear rate was measured at a temperature of 190°C for the sealing material sheet, at 2.43 × 10 sec. -1A melt viscosity of 1000 Pa·s or higher suppresses leakage of some resin due to excessive flow during the hot pressing of the encapsulating sheet, and also maintains good uniformity of the film thickness of the encapsulating sheet after the hot pressing, thereby effectively suppressing defects during the hot pressing process. A melt viscosity of 4000 Pa·s or lower of the encapsulating sheet provides a desirable level of molding properties for use as an encapsulating sheet for solar cell modules. In this specification, melt viscosity refers to the melt viscosity measured according to the method in accordance with JIS K7199.

[0026] Furthermore, the shear rate of 2.43 × 10 sec was measured at a temperature of 190°C in the sealing material sheet according to this embodiment. -1 The melt viscosity is preferably 1500 Pa·s or higher, and more preferably 1800 Pa·s or higher. The shear rate measured at 190°C for the sealing sheet according to this embodiment was 2.43 × 10 sec. -1 The melt viscosity is preferably 3000 Pa·s or less, and more preferably 2800 Pa·s or less. The shear rate measured at 190°C for the sealing material sheet according to this embodiment was 2.43 × 10 sec. -1 The melt viscosity is preferably 1500 Pa·s to 3000 Pa·s, and more preferably 1800 Pa·s to 2800 Pa·s.

[0027] The MFR of the sealing sheet according to this embodiment is not particularly limited, but is preferably 2.0 g / 10 min or more and 5.0 g / 10 min or less on average across all layers, 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. The lower limit of the MFR of the sealing sheet according to this embodiment is preferably 2.0 g / 10 min or more on average across all layers, more preferably 2.2 g / 10 min or more, and even more preferably 2.3 g / 10 min or more. The upper limit of the MFR of the sealing sheet according to this embodiment is preferably 5.0 g / 10 min or less on average across all layers, more preferably 4.5 g / 10 min or less, and even more preferably 4.0 g / 10 min or less. A sealing sheet with an MFR of 5.0 g / 10 min or less can provide the sealing sheet with the necessary heat resistance, and a sealing sheet with an MFR of 3.0 g / 10 min or more can provide the sealing sheet with the necessary molding characteristics.

[0028] In this specification, "MFR" of a sealing material sheet refers to the MFR of a sealing material sheet formed by a molding method such as extrusion melt molding from a sealing material composition containing resin components and other additives, after the completion of sheet formation, i.e., in the uncrosslinked state after film formation, measured under conditions of 190°C and a 2.16 kg load in accordance with JIS K7210. In the case of a sealing material sheet being a multilayer film, the MFR of the multilayer sealing material sheet shall be the value obtained by performing the above-mentioned measurement while all layers are integrally laminated in a multilayer state.

[0029] The Vicat softening point of the sealing material sheet is not particularly limited, but is preferably 30°C to 100°C, more preferably 35°C to 95°C, and even more preferably 40°C to 90°C. 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. A Vicat softening point of 30°C or higher effectively suppresses the occurrence of blocking due to the sealing material sheets sticking together. A Vicat softening point of 100°C or lower improves the moldability of the sealing material sheet.

[0030] The Shore A hardness of the sealing material sheet is not particularly limited, but is preferably 50 degrees or higher, more preferably 53 degrees or higher, and even more preferably 55 degrees or higher. The Shore A hardness of the sealing material sheet is preferably 100 degrees or lower, more preferably 99 degrees or lower, and even more preferably 98 degrees or lower. The Shore A hardness of the sealing material sheet is preferably 50 degrees or higher and 100 degrees or lower, more preferably 53 degrees or higher and 99 degrees or lower, and even more preferably 55 degrees or higher and 98 degrees or lower. A Shore A hardness of 50 degrees or higher for the sealing material sheet provides desirable durability as a sealing material sheet for solar cell modules. A Shore A hardness of 100 degrees or lower for the sealing material sheet provides an even more desirable level of molding properties as a sealing material sheet for solar cell modules.

[0031] The total light transmittance of the sealing sheet, as measured in accordance with JIS K 7361, is not particularly limited, but is preferably 70% or higher, more preferably 80% or higher, and even more preferably 85% or higher.

[0032] The haze value of the sealing sheet, measured in accordance with JIS K 7136, is not particularly limited, but is preferably 0% to 60%, more preferably 0% to 57%, and even more preferably 0% to 55%.

[0033] When the "sealing material sheet" is a multilayer film, it is more preferable to have a layer configuration in which the MFR differs for each layer, within the range that satisfies the essential constituent requirements of the present invention. Specifically, as shown in Figure 1, it is preferable to place the layer with the lower MFR in the center as the core layer 11, and the layer with the higher MFR on the outermost side as the skin layer 12. The sealing material sheet according to this embodiment has sufficiently good molding properties even when it is a single-layer sealing material sheet, but by placing the layer with the relatively higher MFR as the skin layer 12 in this way, the adhesion and molding properties of the sealing material sheet can be further improved.

[0034] The thickness (total thickness) of the sealing material 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 sealing material 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 sealing material 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, for example, even if the sealing material sheet 1 is thinned to a total thickness of about 250 μm, it is possible to achieve a sufficiently desirable combination of molding characteristics and heat resistance. If the total thickness exceeds 600 μm, no further improvement in the impact mitigation effect can be obtained, so it is preferable that the total thickness be 600 μm or less.

[0035] Furthermore, when the sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, 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 sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, 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 sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, the upper limit of the thickness of the core layer 11 is preferably 400 μm or less, and more preferably 350 μm or less.

[0036] When the sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, 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 sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, 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 sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, 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.

[0037] When the sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, 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 of the total thickness of the sealing material sheet 1, and more preferably 1 / 15 to 1 / 4. When the sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, the total thickness of the two skin layers 12 laminated on both sides of the core layer is preferably 1 / 20 or more of the total thickness of the sealing material sheet 1, and more preferably 1 / 15 or more. When the sealing material sheet according to this embodiment is a multilayer sealing material sheet 1, the total thickness of the two skin layers 12 laminated on both sides of the core layer is preferably 1 / 3 or less of the total thickness of the sealing material sheet 1, and more preferably 1 / 4 or less. By setting the thickness of each layer of the sealing material sheet 1 within this range, the heat resistance and molding characteristics of the sealing material sheet 1 can be maintained within a good range.

[0038] The encapsulating sheet for solar cell modules according to this embodiment may be applied to crystalline solar cells, but is not limited to crystalline solar cells. For example, it can also be applied to thin-film solar cells in which a thin film of solar cell elements is formed on the back side of a transparent front surface by vapor deposition, sputtering, wet coating, etc., a encapsulating layer is laminated on the side of the solar cell elements, and a transparent back substrate is further formed. It can also be applied to thin-film solar cells in which glass is applied to the transparent front substrate, the encapsulating material is laminated, solar cell elements are applied to the glass, and a back protective plate is formed by vapor deposition, sputtering, wet coating, etc. It can also be applied to solar cells in which the transparent front substrate, solar cell elements, and back protective sheet are in the shape of flexible sheets. Specifically, it can be applied to various types of solar cells, 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, perovskite solar cells, etc.

[0039] The following describes the sealing material composition used in the manufacture of the sealing material sheet according to this embodiment. The sealing material sheet according to this embodiment can be manufactured, for example, by melt-molding the sealing material composition described in detail below, although this will be described in more detail later.

[0040] [Encapsulant composition] The sealing material composition used in the manufacture of the "sealing material sheet" of the present invention (hereinafter also simply referred to as "sealing material composition") is a resin composition in which a polyolefin resin (preferably a low-density polyethylene resin) is used as the base resin. In this specification, "base resin" refers to the resin that has the highest content ratio among the resin components of a resin composition containing the base resin. In the case of a mixed resin consisting of the same type of resin with different densities (for example, multiple polyethylenes with different densities), the entire mixed resin is considered the base resin.

[0041] The base resin of the encapsulating material composition can be a wide variety of polyolefin resins, provided that it has a melting point of 55°C to 120°C and the temperature difference between the extracellular melting initiation temperature and the melting point is within the range of 20°C or less. In particular, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or metallocene-based linear low-density polyethylene (M-LLDPE), as well as various other polyethylene resins, can be preferably used.

[0042] Furthermore, among the various types of polyethylene mentioned above, linear low-density polyethylene (LLDPE) has a narrow crystallinity distribution and uniform crystal sizes, meaning that not only are there no large crystals, but its crystallinity itself is low, resulting in excellent transparency when processed into a sheet as a sealing material sheet. Therefore, a sealing material sheet made from a sealing material composition using this as the base resin can better prevent a decrease in power generation efficiency due to attenuation of incident light to the solar cell element when placed on the light-receiving surface side of the solar cell element in a solar cell module.

[0043] The density of the above-mentioned polyolefin resin used as the base resin of the "sealing material composition" is 0.880 g / cm 3 or more and 0.930 g / cm 3 or less, preferably 0.880 g / cm 3 or more and 0.925 g / cm 3 or less, preferably 0.880 g / cm 3 or more and 0.920 g / cm 3 or less is more preferable. The upper limit of the density of the above-mentioned polyolefin resin used as the base resin of the "sealing material composition" is preferably 0.930 g / cm 3 or less, preferably 0.925 g / cm 3 or less, and more preferably 0.920 g / cm 3 or less. By setting the density of the base resin of the sealing material composition to 0.880 g / cm 3 or more, the heat resistance of the sealing material sheet can be stably improved to a sufficient level. Also, by setting the density to 0.920 g / cm 3 or less, the adhesion of the "sealing material sheet" to the solar cell element or the like can be maintained at a sufficiently preferable level.

[0044] In addition, the "polyethylene resin" in this specification includes not only ordinary polyethylene obtained by polymerizing ethylene, but also resins obtained by polymerizing compounds having ethylenic unsaturated bonds such as α-olefins, resins obtained by copolymerizing a plurality of different compounds having ethylenic unsaturated bonds, and modified resins obtained by grafting another chemical species onto these resins.

[0045] Among them, a "silane copolymer obtained by copolymerizing an α-olefin and an ethylenic unsaturated silane compound as comonomers" can be preferably used as part of the base resin of the sealing material composition. By using such a resin, sufficient strength adhesion can be obtained between the "sealing material sheet" and other laminated members such as a glass protection substrate and a solar cell element.

[0046] The content of the ethylenically unsaturated silane compound in a copolymer of an α-olefin and an ethylenically unsaturated silane compound is preferably, for example, 0.001% by mass or more and 15% by mass or less, more preferably 0.01% by mass or more and 5% by mass or less, and even more preferably 0.05% by mass or more and 2% by mass or less, relative to the total mass of the copolymer. The lower limit of the content of the ethylenically unsaturated silane compound in a copolymer of an α-olefin and an ethylenically unsaturated silane compound is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.05% by mass or more, relative to the total mass of the copolymer. The upper limit of the content of the ethylenically unsaturated silane compound in 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, relative to the total mass of the copolymer.

[0047] [Other additives] Adhesion enhancers may be added to the sealing material composition as appropriate. Known silane coupling agents can be used as adhesion enhancers, but silane coupling agents having epoxy groups (hereinafter also referred to as "epoxy-based silane coupling agents") or silane coupling agents having mercapto groups (hereinafter also referred to as "mercapto-based silane coupling agents") can be used particularly preferably.

[0048] A crosslinking agent can be added to the encapsulating material composition. It is preferable to use a crosslinking agent with a half-life temperature of 120°C to 145°C. Specific examples of crosslinking agents include peroxyketals such as n-butyl 4,4-di(t-butylperoxy)valerate, ethyl 3,3-di(t-butylperoxy)butyrate, and 2,2-di(t-butylperoxy)butane; and dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(t-peroxy)hexyne-3, which can be preferably used as crosslinking agents added to the encapsulating material composition.

[0049] When a crosslinking agent is included, the amount of crosslinking agent in the encapsulant composition is 0.02% by mass or more and less than 0.5% by mass, with an upper limit of preferably 0.2% by mass or less, and more preferably 0.1% by mass or less. Including a crosslinking agent within this range promotes weak crosslinking of the polyolefin resin, improving heat resistance and transparency. Although the MFR of the polyolefin resin decreases due to the small amount of crosslinking agent, the degree of decrease is small. Therefore, weak crosslinking can be promoted during melt molding. Furthermore, even with a small amount of crosslinking agent and virtually no crosslinking aids, weak crosslinking of the polyolefin resin will proceed. In addition, 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.

[0050] The sealing material composition may contain other components. Examples include weather-resistant masterbatches for imparting weather resistance to the sealing material sheet, various fillers, crosslinking aids, light stabilizers, ultraviolet absorbers, heat stabilizers, flame retardants, colorants, antioxidants, and nucleating agents. The content of these components varies depending on their particle shape, density, etc., but it is preferable that each component be in the range of approximately 0.001% to 5% by mass in the sealing material composition. By including these additives, the sealing material sheet can be given stable mechanical strength over a long period of time, as well as effects that prevent yellowing and cracking.

[0051] <Method for manufacturing sealing material sheets> The "sealing material sheet" according to this embodiment can be manufactured by melt molding the "sealing material composition" described in detail above. The melt molding of the sealing material composition can be carried out by known molding methods, specifically, by various molding methods such as injection molding, extrusion molding, hollow molding, compression molding, and rotational molding. As an example of a method for forming a sheet when the sealing material sheet is a multilayer sheet, a method of molding by co-extrusion using three types of melt-kneading extruders can be mentioned. The lower limit of the molding temperature during molding should be a temperature that exceeds the melting point of the sealing material composition.

[0052] In the manufacture of the sealing sheet, the melt molding temperature is preferably 30°C or higher than the melting point of the resin with the highest melting point among the base resins of the sealing composition contained in the sealing 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.

[0053] Even when the encapsulant composition contains a small amount of crosslinking agent (for example, less than 0.5% by mass), 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, setting it to 10% or less effectively prevents gel generation during film formation and improves film formation performance. Furthermore, setting it to 1% or less improves the embedding ability of the encapsulant sheet in the modularization process, i.e., its ability to follow uneven surfaces.

[0054] ≪2. Solar Cell Modules≫ As shown in Figure 2, the solar cell module 10 according to this embodiment has the following components stacked in order from the light-receiving surface side of the incident light: a transparent front substrate 2, a front sealing material layer 3, a solar cell element 4, a back sealing material layer 5, and a back protective sheet 6. The solar cell module 10 according to this embodiment uses the above-mentioned sealing material sheet for at least one of the front sealing material layer 3 and the back sealing material layer 5.

[0055] Although the solar cell module 10 in Figure 2 is assumed to be a crystalline solar cell using glass or the like as the transparent front substrate, the encapsulating sheet 1 for solar cell modules described above is not limited to crystalline solar cells, but as stated above, can be applied to various types of solar cells regardless of the type of solar cell.

[0056] The solar cell module 10 can be manufactured by sequentially stacking components, including a sealing sheet, integrating them by vacuum suction or the like, and then heat-pressing the components together as a single molded body using a molding method such as lamination. [Examples]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0058] <Manufacturing of sealing sheets for solar cell modules> As base resins, polyethylene resins 1 to 7 (referred to as "PE1 to 7" respectively in the table) were prepared. The densities, number of moles of α-olefin, number of carbon atoms, and MFR at 190°C for PE1 to 7 are shown in Table 1.

[0059] The encapsulant composition raw materials described below were mixed in the proportions shown in Table 2 to obtain the encapsulant compositions for the Examples and Comparative Examples, respectively. Each encapsulant composition was extruded using a φ30 mm extruder and a film molding machine with 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 resin sheets. These resin sheets were then used to produce the encapsulant sheets (single layer) for the Examples and Comparative Examples. The thickness of each encapsulant sheet in the Examples and Comparative Examples was 450 μm in total. In Table 2, the content of PE1 to PE7 is the content (parts by mass) per 100 parts by mass of the base resin, while the content of other additives (silane coupling agent, crosslinking agent, UV absorber, light stabilizer) is the content (mass %) in the total amount of the encapsulant composition.

[0060] [Table 1]

[0061] [Table 2]

[0062] 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 UV absorber is KEMISORB79. In Table 2, the light stabilizer is KEMISTAB62(HALS).

[0063] For the sealing material sheets of the examples and comparative examples listed in Table 2, the Vicat softening point, Shore A hardness (JIS K6253), and melt viscosity (Pa·s) were measured at 190℃ for 2.43 × 10 sec. -1 Tables 3 and 4 show the following parameters: thickness, volume resistivity, total light transmittance (JIS K 7361), haze (JIS K 7136), gel fraction, extracellular melting onset temperature (JIS K 7121-1987), melting point, and the temperature difference between the extracellular melting onset temperature and the melting point.

[0064] The Vicat softening point was measured using a 533HDT test apparatus 6M-2 manufactured by Toyo Seiki Seisakusho. The Shore A hardness was measured using an ESCO EA617DK-1. 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.

[0065] The gel fraction was determined by placing 0.1g of the sealing material sheet into a resin mesh, extracting it in toluene at 60°C for 4 hours, then removing the resin mesh, drying it, weighing it, and comparing the mass before and after extraction to measure the mass percentage of residual insoluble matter.

[0066] The melting point and extracorporeal melting onset temperature of the sealing material sheet were measured using the measurement method described in detail above ("Differential Scanning Calorimetry (DSC), measurement method based on JIS K 7121-1987"). DSC measurements are taken by repeatedly heating and cooling the material in the temperature range of -80 to +200°C, with an initial heating, initial cooling, a second heating, and a second cooling. However, the data used in this analysis was the data from the second heating. For the sealing material sheet of Example 3, the melting point and extracorporeal 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 sealing material sheet of Example 3 is 106.6°C, and the extracorporeal melting onset temperature is 95.1°C. Therefore, the temperature difference between the extracorporeal melting onset temperature and the melting point is 11.5°C.

[0067] <Evaluation Example 1: Molding Characteristics 1> Lead wires (250 μm diameter) were placed on the surface of a flat white tempered glass board, and then the lead wires were covered with laminated encapsulating sheets cut to 150 mm x 150 mm for both the example and the comparative example. These laminated sheets were then subjected to vacuum heating and lamination (vacuum lamination) at a set temperature of 150°C, with a vacuum evacuation for 3 minutes, followed by the release of atmospheric pressure from the upper chamber and vacuum pressurization for 7 minutes. Samples for evaluating solar cell modules were obtained for each example and comparative example. The resin temperature (reached temperature) of the encapsulating sheet during lamination was 147°C. These solar cell module evaluation samples were visually observed, and the molding characteristics were evaluated according to the evaluation criteria described below. (Evaluation Criteria) A: The sealing sheet perfectly conformed to the irregularities of the substrate surface it faced. No void formation was observed. B: 2mm 2 Five or fewer bubbles were observed within the specified range. C: A portion of the sealing material sheet did not fully conform to the unevenness of the opposing substrate surface, resulting in a defective laminate area (void) near the lead wire. The evaluation results are recorded in the table below as "Molding Characteristics 1".

[0068] <Evaluation Example 2: Molding Characteristics 2> Except for arranging 10 lead wires (250 μm diameter) at 10 mm intervals, the molding characteristics were evaluated using the same method and evaluation criteria as described in Molding Characteristics 1 above. The evaluation results are listed in the table below as "Molding Characteristics 2".

[0069] <Evaluation Example 3: Molding Characteristics 3> Lead wires (250 μm diameter) were placed on the surface of a flat white tempered glass board, and the lead wires were then covered with laminated encapsulating material sheets cut to 150 mm x 150 mm for both the example and the comparative example. These laminated sheets were then subjected to vacuum heating and lamination (vacuum lamination) at a set temperature of 150°C, with a vacuum evacuation for 3 minutes, followed by the release of the upper chamber to atmospheric pressure and vacuum pressurization for 7 minutes. Samples for evaluating solar cell modules were obtained for each example and comparative example. The resin temperature (reached temperature) of the encapsulating material sheet during lamination was 147°C. For these solar cell module evaluation samples, the thickness was measured at 16 (4 x 4) points in a 120 x 120 mm area at 40 mm intervals, and resin leakage of the encapsulating material was visually observed at the edges of the encapsulating material sheet. The molding characteristics were evaluated according to the evaluation criteria described below. (Evaluation Criteria) A: The thickness variation (difference between maximum and minimum thickness) within a 150mm x 150mm area after heated vacuum lamination was 2mm or less, and no leakage of the sealing material resin was observed at the edges of the sealing material sheet, or if it was observed, the width of the leakage was less than 15mm. B: The thickness variation (difference between maximum and minimum thickness) within a 150mm x 150mm area after heated vacuum lamination was greater than 2mm, and no leakage of the sealing material resin was observed at the edges of the sealing material sheet, or if observed, the width of the leakage was less than 15mm. C: After heated vacuum lamination, the thickness variation (difference between maximum and minimum thickness) within a 150mm x 150mm area was greater than 2mm, and the width of resin leakage from the sealing material at the edge of the sealing material sheet was 15mm or more.

[0070] <Evaluation Example 4: Heat-resistant creep> To evaluate the heat resistance, a "heat creep test" was conducted using the method described below. In the "heat creep test," one sheet of sealing material cut to a size of 75 mm x 50 mm and one sheet of semi-tempered glass measuring 75 mm x 50 mm were sequentially laminated onto a 250 mm square sheet of semi-tempered glass. The laminated samples were then pressed together at 150°C for 15 minutes using a vacuum laminator used for manufacturing solar cell modules. The laminated samples were then left standing vertically in a 140°C oven for 12 hours, and the displacement distance (mm) of the semi-tempered glass was measured.

[0071] [Table 3]

[0072] [Table 4]

[0073] As can be seen from the table above, the base resin is a polyolefin resin, with a melting point of 55°C to 120°C, and a temperature difference of 20°C or less between the extracellular melting initiation temperature and the melting point. The shear rate measured at 190°C was 2.43 × 10 sec. -1 The fact that the encapsulating sheet has a melt viscosity of 1000 Pa·s to 4000 Pa·s indicates that it possesses a desirable level of molding properties and heat resistance as an encapsulating sheet for solar cell modules.

[0074] When the laminated encapsulant sheets of each example were subjected to vacuum heat lamination (vacuum lamination) at a set temperature of 150°C, vacuumed for 3 minutes, the upper chamber was released to atmospheric pressure, and vacuum pressurized for 7 minutes, resin leakage due to excessive flow was visually confirmed. In each of the encapsulant sheets of Examples 1 to 7, there was no resin leakage of the encapsulant at the edges of the encapsulant sheet due to excessive flow during the heat press processing of the encapsulant sheet, or if there was, the width of the resin leakage was less than 15 mm. From this, the shear rate measured at a temperature of 190°C for the encapsulant sheet was 2.43 × 10 sec. -1It was confirmed that a melt viscosity of 1000 Pa·s to 4000 Pa·s effectively suppresses defects during the hot pressing process of the sealing material sheet. [Explanation of Symbols]

[0075] 1. Sealing sheet 11 Core Layers 12 skin layers 2 Transparent front board 3 Front sealing material layer 4. Click the solar cell button. 5 Back sealing material layer 6. Back protective sheet

Claims

1. A sealing sheet for solar cell modules, Using polyolefin resin as the base resin, The melting point is between 55°C and 120°C, and the temperature difference between the extracellular melting initiation temperature and the melting point is 20°C or less. The shear rate measured at 190°C was 2.43 × 10 sec. －１ The melt viscosity is 1000 Pa·s or more and 4000 Pa·s or less. Sealing sheet.

2. The gel fraction is 10% or less. The sealing sheet according to claim 1.

3. A solar cell module equipped with solar cell elements, The solar cell element comprises a front sealing layer and a back sealing layer, At least one of the front sealing layer and the back sealing layer is made of the sealing sheet described in claim 1 or 2. Solar cell module.

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