Sealing sheet for solar cell modules, solar cell module, and method for manufacturing the sealing sheet

Abstract

[Problem] To provide a sealing sheet for solar cell modules that has a desirable level of molding properties and heat resistance. [Solution] A sealing sheet for solar cell modules, wherein the base resin is a polyolefin resin, the polyolefin resin is a linear low-density polyethylene resin composed of α-olefins having 4 or 6 carbon atoms, the α-olefin content is 12 to 13 mol%, the melting point is 45°C to 60°C, the temperature difference between the extracellular melting start temperature and the melting point is 11°C or less, and the resin component contains a crosslinking agent in a proportion of 0.1% to 1.2% by mass. [Selected Figure] Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sealing sheet for solar cell modules, a solar cell module, and a method for manufacturing the sealing sheet. [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] The present invention aims to provide a sealing sheet that has a desirable level of molding properties and heat resistance, suitable for use as a sealing sheet for solar cell modules. [Means for solving the problem]

[0008] As a result of diligent research, the inventors have discovered that the above problem can be solved by specifying the base resin constituting the encapsulating sheet for solar cell modules as a resin in which the temperature difference between the extrapolation melting start temperature and the melting point is below a predetermined value, and have completed the present invention. Specifically, the present invention provides the following.

[0009] (1) A encapsulating sheet for solar cell modules, wherein the base resin is a polyolefin resin, the melting point is 45°C or higher and 60°C or lower, the temperature difference between the extracellular melting initiation temperature and the melting point is 11°C or lower, and the resin component contains a crosslinking agent in a proportion of 0.1% by mass or higher and 1.2% by mass or lower.

[0010] (2) A solar cell module comprising solar cell elements, wherein the module comprises a front sealing layer and a back sealing layer for sealing the solar cell elements, and at least one of the front sealing layer and the back sealing layer is made of the sealing sheet described in (1).

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

[0012] (4) A method for manufacturing a encapsulant sheet for a solar cell module obtained by melt-molding an encapsulant composition, wherein the encapsulant composition contains a resin having a polyolefin resin as a base resin and a crosslinking agent, the amount of the crosslinking agent being in the range of 0.2% by mass or more and 1.2% by mass or less of the total amount of the encapsulant composition, the melting point of the resulting encapsulant sheet being 45°C or more and 60°C or less, and the encapsulant composition is melt-molded such that the temperature difference between the extracellular melting start temperature and the melting point is 11°C or less. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a sealing material sheet that has a desirable level of molding properties and heat resistance as a sealing material sheet for solar cell modules. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic cross-sectional view showing the layer structure of a sealing material sheet according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing an example of the layer configuration of a solar cell module using a sealing sheet and solar cell elements according to one embodiment of the present invention. [Figure 3] This graph shows the melting point and extracellular melting initiation temperature of a "encapsulating material sheet for solar cell modules (Example 9)" according to one embodiment of the present invention. [Modes for carrying out the invention]

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

[0016] ≪1. Sealing Sheet≫ The encapsulant sheet according to this embodiment is an encapsulant sheet for a solar cell module. Specifically, in a solar cell module, it can be used as a resin sheet that covers and laminates solar cell elements in order to mainly protect the solar cell elements from physical impacts.

[0017] The encapsulant sheet according to this embodiment 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 supplementary melting start temperature and the melting point is 11°C or lower, and contains a crosslinking agent in a proportion of 0.1% by mass or more and 1.2% by mass or less in the resin component.

[0018] In this specification, the term "polyolefin resin" etc. is used as a concept that includes not only "polyolefin resin" but also a copolymer that contains, for example, 50% or more (preferably 70% or more, more preferably 80% or more) of the main chain of polyolefin and a part of the main chain is replaced by another main chain different from polyolefin.

[0019] By containing such a polyolefin resin as a base resin, it is possible to impart a preferable level of moldability as an encapsulant sheet for a solar cell module. Not only the optimization of the melting point range for the thermal properties of the encapsulant sheet, but also by specifying the above temperature difference of the encapsulant sheet within the above specific range, it is possible to impart preferable characteristics regarding moldability etc. required for the encapsulant sheet for a solar cell module. Furthermore, heat resistance can be imparted at the completed product stage of the solar cell module.

[0020] For example, in the case of an encapsulant sheet using a polyolefin resin as a base resin and having a melting point of 45°C or higher, if the temperature difference between the supplementary melting start temperature and the melting point exceeds 11°C, sufficient heat resistance may not necessarily be exhibited, and it has been clarified by the research of the present inventors that even with the same degree of melting point, if the temperature difference between the supplementary melting start temperature and the melting point becomes larger than a certain value, it will also have an adverse effect on moldability.

[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 11°C or less, but is preferably 10.5°C or less, and more preferably 10°C or less.

[0024] The melting point of the sealing material sheet according to this embodiment may be 45°C or higher and 60°C or lower, but is 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 according to this 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 according to this embodiment is preferably 57°C or lower, and more preferably 55°C or lower.

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

[0026] 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.

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

[0028] The total light transmittance of the 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.

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

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 30 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] [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 thermal crosslinking resin composition that uses a polyolefin resin (preferably a low-density polyethylene resin) as the base resin and contains a crosslinking agent. In this specification, "base resin" refers to the resin with 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.

[0038] (Base resin) The base resin of the "sealing material composition" that forms the "sealing material sheet" of the present invention can be widely selected from various olefin resins as long as the melting point is 45°C or higher and 60°C or lower, and the temperature difference between the supplementary melting start temperature and the melting point is within 11°C. Among them, in addition to low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or metallocene-based linear low-density polyethylene (M-LLDPE), various polyethylene-based resins can be preferably used.

[0039] Among the above 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 has excellent transparency when processed into a sheet as a sealing material sheet. Therefore, a "sealing material sheet" composed of 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 on the solar cell element when disposed on the light-receiving surface side of the solar cell element in a self-luminous display body.

[0040] 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 0.920 g / cm 3 or less, more preferably 0.880 g / cm 3 or more and 0.900 g / cm 3 or less, and even more preferably 0.880 g / cm 3 or more and 0.890 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 0.920 g / cm 3 or less, more preferably 0.900 g / cm 3 or less, and even more preferably 0.890 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 3By doing the following, the adhesion of the "encapsulating sheet" to the solar cell element and the like can be maintained at a sufficiently favorable level.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] (Crosslinking agent) It is preferable to use a crosslinking agent with a 1-hour half-life temperature of 120°C to 145°C for the "sealing agent composition". This makes it possible to make the "sealing agent composition" according to the present invention a composition that can be melt-extruded in a range of 110°C or less.

[0045] Furthermore, as specific examples of preferred crosslinking agents that satisfy the above conditions, 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 dialkylperoxides such as di-t-butylperoxide, t-butylcumylperoxide, dicumylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(t-peroxy)hexine-3 can be preferably used as crosslinking agents added to the encapsulating material composition.

[0046] The content of the above-mentioned crosslinking agent in the "sealing material composition" is preferably 0.2% by mass or more and 1.2% by mass or less, and more preferably 0.4% by mass or more and 0.8% by mass or less, relative to the base resin in the "sealing material composition". By setting the content of the crosslinking agent within the above range, the molded "sealing material sheet" can be provided with excellent heat resistance. As described above, the sealing material sheet of the present invention is formed without substantially promoting crosslinking, and it is assumed that the content of the above-mentioned crosslinking agent in the sealing material 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.

[0047] (Cross-linking agent) The "sealing material composition" preferably contains a crosslinking aid, which is a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group, more preferably a polyfunctional monomer whose functional group is an allyl group, a (meth)acrylate group, or a vinyl group. This promotes a moderate crosslinking reaction, thereby improving the heat resistance of the "sealing material sheet" to a high level. In addition, this crosslinking aid reduces the crystallinity of the base resin, such as linear low-density polyethylene, that forms the sealing material sheet, thereby maintaining transparency. As a result, in addition to the effect of improving heat resistance as described above, the transparency of the "sealing material sheet" can be made even better.

[0048] Specific examples of crosslinking aids that can be used in the "encapsulating material composition" include polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, and diallyl maleate; poly(meth)acryloxy compounds such as trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA), ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, and 1,9-nonanediol diacrylate; glycidyl methacrylate containing a double bond and an epoxy group; 4-hydroxybutyl acrylate glycidyl ether; and epoxy compounds containing two or more epoxy groups, such as 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and trimethylolpropane polyglycidyl ether. These may be used individually or in combination of two or more. Furthermore, among the above crosslinking aids, TAIC is particularly preferred because it exhibits good compatibility with linear low-density polyethylene, reduces crystallinity through crosslinking while maintaining transparency, and readily demonstrates the effect of providing flexibility at low temperatures.

[0049] Furthermore, the content of the above-mentioned crosslinking aid in the "encapsulating material composition" 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 "encapsulating material composition". The lower limit of the content of the above-mentioned crosslinking aid in the "encapsulating material composition" is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more, relative to the base resin in the "encapsulating material composition". The upper limit of the content of the above-mentioned crosslinking aid in the "encapsulating material composition" is preferably 3.0% by mass or less, and more preferably 2.0% by mass or less, relative to the base resin in the "encapsulating material composition".

[0050] [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.

[0051] 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.

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

[0053] Here, "gel fraction (%)" as used herein refers to the value obtained by placing 1.0 g of the sealing material sheet into a resin mesh, extracting it in xylene at 110°C for 12 hours, removing the resin mesh, drying it, weighing it, and comparing the mass before and after extraction to measure the percentage of residual insoluble matter (mass%). A gel fraction of 0% means that the above residual insoluble matter is substantially zero, and the crosslinking reaction has not substantially started. More specifically, a gel fraction of 0% means that the above residual insoluble matter is completely absent, or that the mass% of the above residual insoluble matter measured by a precision balance is less than 0.05 mass%. The above residual insoluble matter does not include pigment components or other substances other than the resin components. If these impurities other than the resin components are present in the residual insoluble matter as a result of the above test, for example, by separately measuring the content of these impurities in the resin components in advance, the "gel fraction (%)" that should be obtained for the residual insoluble matter derived from the resin components excluding these impurities can be calculated.

[0054] As described above, the sealing material sheet formed by the above means does not cause substantial crosslinking, and it is assumed that the content of the above crosslinking agent in the sealing material 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.

[0055] ≪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.

[0056] 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.

[0057] The solar cell module 10 can be manufactured by sequentially stacking components, including a sealing sheet, integrating them by vacuum suction, and then heat-pressing the components as an integral molded body using a molding method such as lamination. For example, in the case of vacuum heat lamination, the lamination temperature should be adjusted within the range of 110°C to 170°C, depending on the 1-minute half-life temperature of the crosslinking agent added to the sealing material composition for the light-receiving side sealing material 2 and the non-light-receiving side transparent sealing material 3. In this way, the solar cell module 10 can be manufactured by heat-pressing the components as an integral molded body.

[0058] Of the encapsulants constituting the solar cell module 10, the front encapsulant layer 3 and the back encapsulant layer 5 are formed by depositing the encapsulant compositions for the front and back encapsulants without crosslinking, and then crosslinking them so that the gel fraction is between 50% and 90%. This crosslinking process is carried out within the manufacturing process of the solar cell module. This crosslinking process can be performed by allowing the crosslinking reaction to proceed during the heat bonding process during lamination at the time of module assembly. Alternatively, if necessary depending on the lamination conditions, a separate thermal crosslinking process may be performed after module assembly.

[0059] In the solar cell module 10 according to this embodiment, the transparent front substrate 2, solar cell elements 4, and back protective sheet 6, which are components other than the front sealing layer 3 and back sealing layer 5, can be made from conventionally known materials without limitation. Furthermore, the solar cell module 10 according to this embodiment may include components other than those mentioned above. In addition, the sealing sheet according to this embodiment is not limited to monocrystalline type but can be applied to thin-film type and all other types of solar cell modules. [Examples]

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

[0061] <Manufacturing of sealing sheets for solar cell modules> Each example and comparative example was prepared using the respective encapsulating composition having the composition shown in Table 1 below. Linear low-density polyethylene (LLDPE) resin was used as the base resin. The films were formed using a φ30 mm extruder and a film molding machine with a 200 mm wide T-die, at an extrusion temperature of 90°C and a take-up speed of 1.1 m / min, with a film thickness of 450 μm in both cases, to produce sealing material sheets for each example and comparative example.

[0062] [Table 1]

[0063] [Table 2]

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

[0065] For the sealing material sheets of the examples and comparative examples listed in Table 2, the Picatto softening point, Shore A hardness (JIS K6253), and melt viscosity (Pa·s) were measured at 90℃ for 2.43 × 10 sec. -1 Table 3 shows 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.

[0066] The Picatto 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.

[0067] The gel fraction was determined by laminating each sealing material sheet, performing vacuum heating lamination at a set temperature of 150°C, under vacuum for 3 minutes, and under atmospheric pressure for 7 minutes. After treatment, 0.1g of the sealing material sheet was placed in a resin mesh and extracted in toluene at 60°C for 4 hours. The resin mesh was then removed, dried, and weighed, and the mass before and after extraction was compared to determine the mass percentage of residual insoluble matter.

[0068] 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 initial heating. For the sealing material sheet of Example 9, 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 9 is 51.0°C, and the extracorporeal melting onset temperature is 41.7°C. Therefore, the temperature difference between the extracorporeal melting onset temperature and the melting point is 9.3°C.

[0069] <Evaluation Example 1: Molding Characteristics 1> Lead wires (250 μm diameter) were placed on the flat surface of a 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 the upper chamber to atmospheric pressure and vacuum pressurization for 15 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 partially defective laminate area (void) near the lead wire. The evaluation results are recorded in the table below as "Molding Characteristics 1".

[0070] <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".

[0071] <Evaluation Example 3: 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.

[0072] [Table 3]

[0073] [Table 4]

[0074] [Table 5]

[0075] As can be seen from the table above, the encapsulating sheet, which uses a polyolefin resin as the base resin, has a melting point of 45°C to 60°C, and a temperature difference of 11°C or less between the extracellular melting initiation temperature and the melting point, possesses desirable levels of molding properties and heat resistance for use as an encapsulating sheet for solar cell modules. [Explanation of Symbols]

[0076] 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 polyolefin resin is a linear low-density polyethylene resin composed of α-olefins having 4 or 6 carbon atoms, and the α-olefin content is 13 mol%. The melting point is 45°C or higher and 60°C or lower, and the temperature difference between the extracellular melting initiation temperature and the melting point is 11°C or less. The resin component contains a crosslinking agent in a proportion of 0.1% by mass or more and 1.2% by mass or less. Sealing sheet.

2. 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. Solar cell module.

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

4. A method for manufacturing a encapsulant sheet for a solar cell module obtained by melt molding an encapsulant composition, The aforementioned sealing material composition contains a resin having a polyolefin resin as a base resin, and a crosslinking agent. The polyolefin resin is a linear low-density polyethylene resin composed of at least one selected from α-olefins having 4 carbon atoms and α-olefins having 6 carbon atoms, wherein the α-olefin content is 13 mol%. The content of the crosslinking agent is in the range of 0.2% by mass or more and 1.2% by mass or less of the total amount of the sealing material composition. The sealing material composition is melt-molded such that the resulting sealing material sheet has a melting point of 45°C or higher and 60°C or lower, and the temperature difference between the extracellular melting initiation temperature and the melting point is 11°C or less. A method for manufacturing sealing material sheets.

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