Sealing material sheets for solar cell modules and solar cell modules

Abstract

The present invention provides a highly flame-retardant sealing sheet for solar cell modules and a solar cell module. [Solution] A sealing sheet for solar cell modules, wherein the sealing sheet uses a polyolefin resin as the base resin and further contains a phosphinate metal salt.

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] Since solar cell modules are generally expected to be used outdoors for extended periods, long-term reliability and safety are becoming increasingly important.

[0007] For example, in residential solar cell modules, it is believed that safety during a fire can be further enhanced by increasing the flame retardancy of the solar cell modules and preventing damage.

[0008] The present invention aims to provide a highly flame-retardant sealing sheet for solar cell modules and a solar cell module. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have discovered that the above problems can be solved by using a polyolefin resin as the base resin and further containing a phosphinate metal salt, and have completed the present invention. Specifically, the present invention provides the following:

[0010] (1) A sealing sheet for solar cell modules, Using polyolefin resin as the base resin, Furthermore, it contains a metal phosphinate salt. Sealing sheet.

[0011] (2) The gel fraction is 10% or less. (1) The sealing sheet described above.

[0012] (3) The melting point is 40°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. The sealing sheet described in (1) or (2).

[0013] (4) A solar cell module comprising solar cell elements, The solar cell element comprises a front sealing layer and a back sealing layer, At least one of the front sealing material layer and the back sealing material layer is composed of the sealing material sheet described in (1) or (2). Solar cell module.

Effect of the Invention

[0014] According to the present invention, a sealing material sheet with high flame retardancy can be provided.

Brief Description of the Drawings

[0015] [Figure 1] It is a cross-sectional view schematically showing the layer structure of the sealing material 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 sealing material sheet of one embodiment of the present invention and a solar cell element.

Mode for Carrying Out the Invention

[0016] 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.

[0017] ≪1. Sealing Material Sheet≫ The sealing material sheet according to the present embodiment is a sealing material sheet for a solar cell module. Specifically, in a solar cell module, it is a resin sheet that can be used as a sealing material sheet for covering and laminating a solar cell element in order to mainly protect the solar cell element from physical impact.

[0018] And the sealing material sheet according to the present embodiment is characterized in that it uses a polyolefin-based resin as a base resin and contains a metal phosphinate.

[0019] 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.

[0020] By incorporating such a polyolefin-based resin as a base resin, and further including a phosphinate metal salt, desirable flame retardancy can be imparted to the encapsulating sheet for solar cell modules.

[0021] The reason why the inclusion of metal phosphinate improves flame retardancy is presumed to be that, at temperatures higher than those of the polyolefin resin contained in the sealing sheet, the metal phosphinate generates a carbonized layer (foamed char) in the combustion residue, thereby improving flame retardancy.

[0022] Furthermore, encapsulating sheets containing phosphinate metal salts have a higher volume resistivity compared to encapsulating sheets that do not contain phosphinate metal salts. Therefore, it is possible to prevent the risk of leakage of electricity collected from solar cell elements through the encapsulating sheet and to improve the effective power generation efficiency.

[0023] Furthermore, encapsulating sheets containing phosphinate metal salts have higher heat resistance compared to encapsulating sheets that do not contain phosphinate metal salts. Therefore, they can be used as encapsulating sheets for solar cell modules that possess sufficient heat resistance to withstand prolonged use at high temperatures.

[0024] Furthermore, it is preferable that the sealing sheet according to this embodiment has a melting point and a temperature difference between the extramelting initiation temperature and the melting point within a predetermined range. By including such a polyolefin resin as the base resin, in addition to flame retardancy, a desirable level of molding properties for a sealing sheet used in solar cell modules can be provided. By optimizing the melting point range of the sealing sheet in terms of its thermal properties, and by specifying the above temperature difference of the sealing sheet within the above-mentioned specific range, desirable characteristics such as molding properties required for a sealing sheet used in solar cell modules can be provided. Furthermore, heat resistance can be provided at the finished product stage when it becomes a solar cell module.

[0025] 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.

[0026] 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).

[0027] In the sealing sheet according to this embodiment, the temperature difference between the extracellular melting initiation temperature and the melting point is preferably 20°C or less, more preferably 17°C or less, and even more preferably 15°C or less.

[0028] The melting point of the sealing material sheet according to this embodiment is preferably 40°C or higher and 120°C or lower, more preferably 43°C or higher and 117°C or lower, and even more preferably 44°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 40°C or higher, more preferably 43°C or higher, and even more preferably 44°C or higher. The upper limit of the melting point of the sealing material sheet according to this embodiment is preferably 120°C or lower, more preferably 117°C or lower, and even more preferably 115°C or lower.

[0029] The MFR of the sealing sheet according to this embodiment is not particularly limited, but is preferably 0.1 g / 10 min or more and 5.0 g / 10 min or less on average across all layers, more preferably 1.0 g / 10 min or more and 4.5 g / 10 min or less, and even more preferably 2.0 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 0.1 g / 10 min or more on average across all layers, more preferably 1.0 g / 10 min or more, and even more preferably 2.0 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 necessary heat resistance, and a sealing sheet with an MFR of 0.1 g / 10 min or more can provide the necessary molding characteristics. The average MFR of all layers can be determined by the weighted average of each layer constituting the sealing sheet.

[0030] 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.

[0031] The Vicat softening point of the sealing material sheet is not particularly limited, but is preferably 30°C to 100°C, more preferably 31°C to 95°C, even more preferably 33°C to 90°C, and still more preferably 35°C to 85°C. The lower limit of the Vicat softening point of the sealing material sheet is preferably 30°C or higher, more preferably 31°C or higher, even more preferably 33°C or higher, and still more preferably 35°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, even more preferably 90°C or lower, and still more preferably 85°C or lower.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] [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.

[0040] The base resin of the sealing material composition can be widely selected from various polyolefin resins. Among them, in addition to low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or metallocene linear low-density polyethylene (M-LLDPE), various polyethylene resins can be preferably used.

[0041] Moreover, among the above-mentioned various polyethylenes, linear low-density polyethylene (LLDPE) has a narrow crystalline distribution and uniform crystal sizes. Therefore, not only are there no large crystal sizes, but the crystallinity itself is low, and it is excellent in transparency when processed into a sheet as a sealing material sheet. Therefore, the "sealing material sheet" composed of the "sealing material composition" using this as the base resin can better prevent the reduction in power generation efficiency due to the attenuation of incident light to the solar cell element when arranged on the light-receiving surface side of the solar cell element in the solar cell module.

[0042] The density of the above polyolefin resin used as the base resin of the "sealing material composition" is preferably 0.880 g / cm 3 or more and 0.930 g / cm 3 or less, more preferably 0.880 g / cm 3 or more and 0.925 g / cm 3 or less, and even more preferably 0.880 g / cm 3 or more and 0.920 g / cm 3 or less. The upper limit of the density of the above polyolefin resin used as the base resin of the "sealing material composition" is preferably 0.930 g / cm 3 or less, more preferably 0.925 g / cm 3 or less, and even 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 same 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.

[0043] Furthermore, the term "polyethylene resin" in this specification 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 multiple different compounds having ethylenically unsaturated bonds, and modified resins obtained by grafting other chemical species onto these resins.

[0044] In particular, a "silane copolymer obtained by copolymerizing α-olefin and an ethylenically unsaturated silane compound as comonomers" can be preferably used as part of the base resin of the encapsulant composition. By using such a resin, sufficient adhesion strength can be obtained between the "encapsulant sheet" and other laminated members such as glass protective substrates and solar cell elements.

[0045] 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.

[0046] [Phosphinate metal salts] The sealing material composition according to this embodiment contains a phosphinate metal salt. By including a predetermined amount of the phosphinate metal salt, flame retardancy can be imparted to the resulting sealing material.

[0047] Examples of phosphinate metal salts include those represented by the following formula.

[0048] [ka] (In formula (I), R 1 , R 2 Each of these is independently a linear or branched alkyl group having 1 to 16 carbon atoms, which may include a phenyl group or a cyclic structure. m+ (This represents a metal ion.)

[0049] Examples of phosphinate metal salts include magnesium phosphinate, calcium phosphinate, aluminum phosphinate, antimony phosphinate, tin phosphinate, germanium phosphinate, titanium phosphinate, iron phosphinate, zirconium phosphinate, cerium phosphinate, bismuth phosphinate, manganese phosphinate, lithium phosphinate, sodium phosphinate, potassium phosphinate, and strontium phosphinate. Among these, aluminum phosphinate (aluminum = tris{diethyl [and butyl(ethyl)]phosphinate}) is preferred.

[0050] The content of the phosphinate metal salt is preferably 3 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the sealing material composition, more preferably 4 parts by mass or more and 40 parts by mass or less, and even more preferably 5 parts by mass or more and 35 parts by mass or less.

[0051] [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.

[0052] 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.

[0053] 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.

[0054] 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, colorants, antioxidants, nucleating agents, and other components. 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.

[0055] <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.

[0056] 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.

[0057] 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 preferably 25% or less, more preferably 10% or less, and even 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.

[0058] ≪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.

[0059] In particular, in the solar cell module 10 according to this embodiment, it is preferable to use the above-mentioned sealing sheet as the back sealing layer 5 rather than the front sealing layer 3. Sealing sheets containing phosphinate metal salts may have a relatively lower total light transmittance compared to sealing sheets that do not contain phosphinate metal salts. Therefore, by using a sealing sheet containing phosphinate metal salts as a back sealing layer located on the opposite side of the light-receiving surface, rather than as the front sealing layer 3 located on the light-receiving surface side, it is possible to provide flame retardancy while maintaining the power generation efficiency of the solar cell module.

[0060] Furthermore, the content of phosphinate metal salts contained in the front and back sealing layers may be adjusted in order to impart flame retardancy to the front and back sealing layers. Specifically, the front and back sealing layers contain phosphinate metal salts, and the content of phosphinate metal salts in the front sealing layer is made smaller than the content of phosphinate metal salts in the back sealing layer (for example, by adjusting the content of phosphinate metal salts in the front sealing layer to be 10 to 50 parts by mass, more preferably 20 to 40 parts by mass, per 100 parts by mass of phosphinate metal salts in the back sealing layer), the total light transmittance of the front sealing layer is improved relative to that of the back sealing layer, making it possible to impart desirable flame retardancy to the sealing sheet while maintaining the power generation efficiency of the solar cell module.

[0061] 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.

[0062] 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]

[0063] 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.

[0064] <Manufacturing of sealing sheets for solar cell modules> As base resins, polyethylene resins 1 to 5 (referred to as "PE1 to 5" 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 5 are shown in Table 1.

[0065] [Table 1]

[0066] Of the polyethylene resins 1 to 5 mentioned above, PE3 was a silane-modified polyethylene resin obtained as follows. Specifically, this silane-modified polyethylene resin PE3 has a density of 0.884 g / cm³. 3 It was obtained by mixing 95 parts by mass of a metallocene-based linear low-density polyethylene resin with an MFR of 3.5 g / 10 min with 5 parts by mass of vinyltrimethoxysilane and 0.15 parts by mass of dicumyl peroxide as a radical generator (reaction catalyst), melting and kneading at 200°C.

[0067] The raw materials for the encapsulating material compositions described below were mixed in the proportions shown in Table 2 to obtain the encapsulating material compositions for the Examples and Comparative Examples, respectively. Each encapsulating material composition was used to produce resin sheets using a film molding machine 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. These resin sheets were then used to produce the encapsulating material sheets (single layer) for the Examples and Comparative Examples. The thickness of each encapsulating material sheet in the Examples and Comparative Examples was 450 μm in total. In Table 2, the content of PE1 to PE5 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, ultraviolet absorber, light stabilizer, phosphinate metal salt) is the content (mass %) in the total amount of the encapsulating material composition.

[0068] [Table 2]

[0069] 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). In Table 2, the phosphinate metal salt is EXOLIT OP945 manufactured by CLARIANT.

[0070] Table 3 shows the Picatto softening point, Shore A hardness (JIS K6253), thickness, total light transmittance (JIS K 7361), haze (JIS K 7136), gel fraction, melting point, extracellular melting onset temperature (JIS K 7121-1987), tensile breaking strength, and tensile breaking elongation for the sealing material sheets of the examples and comparative examples listed in Table 2.

[0071] The Picatto softening point was measured using the 533HDT 6M-2 test apparatus manufactured by Toyo Seiki Seisakusho. The Shore A hardness was measured using the EA617DK-1 manufactured by ESCO.

[0072] Tensile breaking strength and tensile breaking elongation were measured according to JIS K 7161-1:2024 and JIS K 7161-2:2024, with a sample width of 10 mm, a chuck distance of 40 mm, and a tensile speed of 200 mm / min, using an A&D RTG-1210.

[0073] 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.

[0074] The melting point and extrapolation onset temperature of the sealing material sheet were measured using differential scanning calorimetry (DSC) according to JIS K 7121-1987. DSC measurements were taken within a temperature range of -80 to +200°C. For volume resistivity, an ADC 5450 digital ultra-high resistance / micro-current meter was used, and the value was measured after 30 seconds at an applied voltage of 500V in an environment of 23°C, in accordance with JIS K6911-1995.

[0075] <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: 2mm2 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 partially defective laminate area (void) near the lead wire. The evaluation results are recorded in the table below as "Molding Characteristics 1".

[0076] <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".

[0077] <Evaluation Example 3: Combustion Test 1> The combustion performance of solar cell module evaluation samples obtained from the encapsulating material sheets of the examples and comparative examples was measured using a measurement method in accordance with IEC60695-11-10A when the samples were installed horizontally. If a flame retardancy grade of "HB" was obtained, it was indicated as "〇" in Table 3; if "HB" was not obtained, it was indicated as "×".

[0078] <Evaluation Example 4: Combustion Test 2> The combustion performance of solar cell module evaluation samples obtained from the encapsulating material sheets of the examples and comparative examples was measured in a vertical position using a measurement method in accordance with IEC60695-11-10B. If a flame retardancy grade of "V-2," "V-1," or "V-0" was obtained, it was indicated as "〇" in Table 3, and if none of "V-2," "V-1," or "V-0" was obtained, it was indicated as "×."

[0079] <Evaluation Example 5: Heat Creep Resistance Test> 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.

[0080] [Table 3]

[0081] [Table 4]

[0082] As can be seen from the table above, the sealing sheet is highly flame-retardant because it uses a polyolefin resin as its base resin and also contains a phosphinate metal salt.

[0083] Furthermore, the sealing sheet in the example containing the phosphinate metal salt exhibits higher volume resistivity compared to the sealing sheet in the comparative example. In addition, no glass displacement was observed after the heat creep test for the sealing sheet containing the phosphinate metal salt, indicating that it is a sealing sheet with higher heat resistance compared to the sealing sheet in the comparative example. [Explanation of Symbols]

[0084] 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 10 solar modules

Claims

1. A sealing sheet for solar cell modules, Using polyolefin resin as the base resin, Furthermore, it contains a metal phosphinate salt, The melting point is between 40°C and 120°C, and the temperature difference between the extracellular melting initiation temperature and the melting point is 20°C or less. Sealing sheet.

2. The MFR is between 0.1 g / 10 min and 5.0 g / 10 min on average across all layers. The sealing sheet according to claim 1.

3. The Vicat softening point is between 30°C and 100°C. The sealing sheet according to claim 1 or 2.

4. The aforementioned phosphinate metal salt is aluminum phosphinate. The content of the aluminum phosphinate is 3 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the sealing material composition. The sealing sheet according to claim 1 or 2.

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

6. 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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