JP2013115211A - Sealing material sheet for solar cell module and solar cell module using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyethylene-based crosslinked sealing material sheet.SOLUTION: A composition containing low density polyethylene with a density of 0.900 or lower, a crosslinking agent, and a crosslinking auxiliary agent consisting of a polyfunctional vinyl monomer and/or a polyfunctional epoxy monomer is formed, then a crosslinking treatment by irradiation with ionization radiation is performed to form a sealing material sheet for a solar cell module with the gel fraction of 2% or more and 70% or less, a complex viscosity of 3.0E+4 PaS or more and 1.0E+6 PaS or less at 80°C or more and 100°C or less, and a complex viscosity of 1.0E+5 PaS or more and 4.0E+5 PaS or less at 150°C or more and 200°C or less after crosslinking process under a predetermined condition. The composition is a polyethylene sealing material that has already been crosslinked, therefore a separate crosslinking step is not needed at the time of a modularization into a solar cell, and also the flow can be suppressed in the modularization.

Description

  The present invention relates to a polyethylene-based solar cell module sealing material sheet. More specifically, the present invention relates to a solar cell module sealing material sheet that has been cross-linked by ionizing radiation such as an electron beam and a solar cell module using the same.

  Conventionally, as a sealing material sheet for a solar cell module, a combination of an ethylene-vinyl acetate copolymer resin (EVA) and a crosslinking agent typified by an organic peroxide has been used. In recent years, a sealing material sheet using a polyethylene-based resin instead of EVA has been widely used by taking advantage of excellent water vapor barrier properties.

  As a polyethylene-based sealing material sheet, for example, a sealing material made of a modified ethylene-based resin containing alkoxysilane as a copolymerization component is also known. Moreover, the sealing material sheet | seat which mix | blended a crosslinking agent with such a modified ethylene-type resin, and bridge | crosslinked by the modularization process or the subsequent heating process is known (refer patent document 1).

  Also, a polyethylene-based sealing material sheet obtained by melt extrusion forming a resin composition comprising an α-olefin copolymer having specific physical properties and a silane compound, and the gel fraction of the sealing material sheet at the time of extrusion forming Also known is a sealing material sheet for use in a solar cell module by proceeding with crosslinking until the content reaches about 5 to 29% and further proceeding with crosslinking so that the gel fraction becomes about 70 to 95% in the modularization process. (See Patent Document 2).

  On the other hand, as a method for the crosslinking treatment, in addition to the thermal crosslinking treatment by heating the organic peroxide, the polyethylene-based resin or the like is crosslinked by irradiating with ionizing radiation, so that a sealing material is not used. A technique for improving the heat resistance of a sheet is disclosed (see Patent Document 3). In addition, a technique is disclosed in which linear low density polyethylene having a predetermined density or less is irradiated with ionizing radiation to crosslink, and a long-time heat curing step is omitted without using a cross-linking agent to impart heat resistance ( (See Patent Document 4).

JP 2009-10277 A JP 2011-12246 A JP 2009-249556 A JP 2011-77357 A

  However, as in the sealing material sheets described in Patent Documents 1 and 2, all of the sealing material sheets obtained by subjecting the polyethylene resin to thermal crosslinking treatment leave room for further improvement in heat resistance. It was a thing. In any case, since most of the cross-linking reaction is premised to proceed during the modularization process, large restrictions on heating temperature and time in the modularization process are factors that hinder productivity improvement. It was.

  Moreover, the sealing material sheet obtained by irradiating the polyethylene resin with ionizing radiation, such as the sealing material sheet described in Patent Documents 3 and 4, is free from the restrictions on the modularization conditions as described above. In addition, although the heat resistance can be improved by crosslinking, there is a defect that the transparency is inferior to that in the case where the conventional thermal crosslinking treatment is performed, and there is room for improvement in this respect. In addition, if the irradiation intensity of ionizing radiation is increased in order to obtain sufficient heat resistance, there is a problem that the adhesiveness is lowered.

  The present invention has been made to solve the above problems. The objective of this invention is providing the sealing material sheet for solar cell modules which has high transparency and heat resistance, and makes it possible to improve the productivity of a solar cell module.

  The present inventors have performed a crosslinking treatment by irradiation with ionizing radiation in advance after extrusion formation of the sealing material sheet and before modularization, whereby the gel fraction and the complex viscosity are optimized within a predetermined range. By using a material sheet, it is possible to obtain a polyethylene-based encapsulant sheet excellent in transparency and heat resistance, and by using such an encapsulant sheet, the productivity of the solar cell module is improved. As a result, the present invention has been completed. More specifically, the present invention provides the following.

(1) A low-density polyethylene having a density of 0.900 g / cm ³ or less and a crosslinking aid which is a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group, and has a gel fraction of 2% The complex viscosity at 80 ° C. or more and 100 ° C. or less is 3.0E + 4 Pa · S or more and 1.0E + 6 Pa · S or less, and the complex viscosity at 150 ° C. or more and 200 ° C. or less after crosslinking under the following crosslinking conditions. A solar cell module sealing material sheet having a viscosity of 1.0E + 5 Pa · S or more and 4.0E + 5 Pa · S or less.
Crosslinking conditions: Heat until the resin temperature of the encapsulant sheet reaches 140 ° C. or higher, and then hold the temperature for 5 minutes or longer in a range where the resin temperature is 140 ° C. or higher and 150 ° C. or lower.

  (2) A solar cell module provided with the sealing material layer which consists of a sealing material sheet for solar cell modules as described in (1).

  (3) The solar cell module according to (2), wherein a complex viscosity of the sealing material layer at 150 ° C. or more and 200 ° C. or less is 1.0E + 5 Pa · S or more and 4.0E + 5 Pa · S or less.

  (4) The solar cell module according to (2) or (3), wherein a haze value at a thickness of 400 μm of the sealing material layer is 3% or less.

(5) Density of 0.900 g / cm ³ or less, low density polyethylene, a crosslinking agent, and a crosslinking agent containing a crosslinking aid are melt-molded to obtain an uncrosslinked sealing material sheet Production of a sealing material sheet for a solar cell module comprising a step and a crosslinking step of crosslinking the uncrosslinked sealing material sheet so that the gel fraction becomes 2% or more and 70% or less by irradiation with ionizing radiation Method.

  According to the solar cell module sealing material sheet of the present invention and the solar cell module using the same, a solar cell module sealing material sheet having both high heat resistance and transparency can be provided. In addition, by using this encapsulant sheet, a cross-linking step when forming a solar cell module is unnecessary, and the flow during modularization can be suppressed, so that the productivity of the solar cell module can be improved. .

It is sectional drawing which shows an example of the laminated constitution about the solar cell module using the sealing material sheet of this invention. It is the graph which showed the change of the complex viscosity in 20-110 degreeC of the sealing material sheet | seat of this invention. It is the graph which showed the change of the complex viscosity in 20-200 degreeC of the sealing material layer of the solar cell module of this invention.

  The sealing material sheet of the present invention has extremely preferable heat resistance and transparency as a sealing material sheet for a solar cell module by limiting the gel fraction and the complex viscosity to the predetermined ranges. Features. Hereinafter, the solar cell module encapsulant composition (hereinafter also simply referred to as “encapsulant composition”) and the solar cell module encapsulant sheet (hereinafter simply referred to as “encapsulant sheet”) according to the present invention. And the solar cell module in this order.

<Encapsulant composition>
The sealing material composition used in the present invention contains low density polyethylene having a density of 0.900 g / cm ³ or less, a crosslinking agent, and a crosslinking aid as essential components. Hereinafter, after describing the essential components, other resins and other components will be described.

[Low density polyethylene]
In the present invention, low density polyethylene (LDPE) having a density of 0.900 g / cm ³ or less, preferably linear low density polyethylene (LLDPE) is used. Linear low density polyethylene is a copolymer of ethylene and α- olefin, in the present invention, within the scope thereof density of 0.900 g / cm ³ or less, preferably 0.890 g / cm ³ within the following ranges More preferably, it is the range of 0.870-0.885 g / cm < ³ >. If it is this range, favorable softness | flexibility and transparency can be provided, maintaining sheet workability.

  In the present invention, it is preferable to use a metallocene linear low density polyethylene. Metallocene linear low density polyethylene is synthesized using a metallocene catalyst which is a single site catalyst. Such polyethylene has few side chain branches and a uniform comonomer distribution. For this reason, molecular weight distribution is narrow, it is possible to make it the above ultra-low density, and a softness | flexibility can be provided with respect to a sealing material. As a result of the flexibility, the adhesion between the sealing material and the substrate, such as the adhesion between the sealing material and the transparent front substrate and the adhesion between the sealing material and the back surface protective sheet, is increased.

  In addition, since the crystallinity distribution is narrow and the crystal sizes are uniform, not only a large crystal size does not exist, but also the crystallinity itself is low due to the low density. For this reason, it is excellent in transparency when processed into a sheet shape. Therefore, even if the sealing material which consists of a sealing material composition of this invention is arrange | positioned between a transparent front substrate and a solar cell element, power generation efficiency hardly falls.

  As the α-olefin of the linear low density polyethylene, an α-olefin having no branch is preferably used. Among these, 1-hexene and 1-heptene which are α-olefins having 6 to 8 carbon atoms are preferable. Or 1-octene is particularly preferably used. When the number of carbon atoms of the α-olefin is 6 or more and 8 or less, the sealing material sheet can be given good flexibility and good strength. As a result, the adhesion between the encapsulant sheet and the substrate is further enhanced.

  The melt mass flow rate (MFR) of the low-density polyethylene is MFR at 190 ° C. and a load of 2.16 kg measured according to JIS-K6922-2 (in the present specification, the measurement value under these measurement conditions is hereinafter referred to as MFR). Is preferably 0.5 g / 10 min or more and 40 g / 10 min or less, and more preferably 6 g / 10 min or more and 40 g / 10 min or less.

  The encapsulant sheet of the present invention is a crosslinked encapsulant sheet that undergoes a crosslinking treatment by irradiation with ionizing radiation after melt formation of the encapsulant composition. For this reason, even if the MFR of the low density polyethylene used as a base is high, the fluidity at the time of modularization can be suppressed by the crosslinking treatment after film formation. For this reason, even if it is high MFR like the said range, it can be used conveniently.

  The sealing material composition of the present invention may further contain a silane-modified polyethylene resin. The silane-modified polyethylene resin is obtained by graft-polymerizing an ethylenically unsaturated silane compound as a side chain to linear low-density polyethylene (LLDPE) or the like as a main chain. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to the adhesive force, it can improve the adhesion of the sealing material sheet to other members in the solar cell module.

  The silane-modified polyethylene resin can be produced, for example, by the method described in JP-A-2003-46105. By using the resin as a component of a sealing material composition for a solar cell module, strength and durability can be obtained. In addition, it has excellent weather resistance, heat resistance, water resistance, light resistance, wind pressure resistance, yield resistance, and other characteristics, and is also affected by manufacturing conditions such as thermocompression bonding for manufacturing solar cell modules. Therefore, it is possible to manufacture solar cell modules that have extremely excellent heat-fusibility, are stable and low-cost, and are suitable for various applications.

  Examples of ethylenically unsaturated silane compounds to be graft polymerized with linear low density polyethylene include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinyltripentyloxysilane , One or more selected from vinyltriphenoxysilane, vinyltribenzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane be able to.

  The graft amount, which is the content of the ethylenically unsaturated silane compound, is, for example, 0.001 to 15 masses with respect to a total of 100 mass parts of all the resin components in the sealing material composition containing other polyethylene-based resins described later. Part, preferably 0.01 to 5 parts by mass, particularly preferably 0.05 to 2 parts by mass. In the present invention, when the content of the ethylenically unsaturated silane compound is large, the mechanical strength and heat resistance are excellent. However, when the content is excessive, the tensile elongation and heat-fusibility tend to be inferior.

The content of polyethylene having a density of 0.900 g / cm ³ or less contained in the encapsulant composition is preferably 10 or more and 99 with respect to 100 parts by mass in total of all resin components in the encapsulant composition. It is 50 parts or less and 99 parts by mass or less, more preferably 90 or more and 99 parts by mass or less. Other resin may be included as long as the melting point of the sealing material composition is within a range of less than 80 ° C. These may be used, for example, as an additive resin, or may be used for masterbatching other components described later.

[Crosslinking agent]
A well-known thing can be used for a crosslinking agent, It does not specifically limit, For example, a well-known radical polymerization initiator can be used. Examples of radical polymerization initiators include hydroperoxides such as diisopropylbenzene hydroperoxide and 2,5-dimethyl-2,5-di (hydroperoxy) hexane; di-t-butyl peroxide, t-butyl Cumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-peroxy) hexyne-3, etc. Dialkyl peroxides; diacyl peroxides such as bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, benzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dichlorobenzoyl peroxide; t-butyl peroxyacetate, t-butyl pero Ci-2-ethylhexanoate, t-butyl peroxypivalate, t-butyl peroxyoctoate, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, di-t-butyl peroxyphthalate, 2 , 5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexyne-3, t-butylperoxy-2-ethylhexyl carbonate Oxyesters; organic peroxides such as methyl peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, or azo compounds such as azobisisobutyronitrile and azobis (2,4-dimethylvaleronitrile), dibutyltin Diacetate, dibutyltin dilaurate It can be mentioned dibutyltin dioctoate, dioctyltin dilaurate, dicumyl peroxide, such a silanol condensation catalyst.

  Conventionally, it has been considered that a crosslinking agent such as an organic peroxide is unnecessary when performing a crosslinking treatment by irradiation with ionizing radiation, unlike the case of a thermal crosslinking treatment. However, the encapsulant composition used in the present invention contains a small amount of a crosslinking agent while performing a crosslinking treatment by irradiation with ionizing radiation. By adding this cross-linking agent, it is possible to improve heat resistance and maintain transparency by irradiation with ionizing radiation. The action of the cross-linking agent in the cross-linking treatment by irradiation with ionizing radiation is not clear, but since ionizing radiation has strong energy, cross-linking proceeds, but the crystals that cause HAZE do not loosen and do not participate in cross-linking unless the temperature exceeds a certain temperature. It is estimated that this is because it remains.

  The addition amount of the crosslinking agent to the sealing material composition of the present invention is preferably 0.3 or more and less than 1.5 parts by weight with respect to 100 parts by weight of all components in the sealing material composition. It is more preferably 3 or more and 0.7 parts by mass or less, and further preferably 0.3 or more and less than 0.5 parts by mass. By making the addition amount of the crosslinking agent to the sealing material composition within this range, in addition to heat resistance and adhesion, a sealing material sheet that is particularly excellent in transparency can be obtained. In this case, if the content of the crosslinking agent is less than 0.3 parts by mass, the effect of improving the transparency is insufficient, and if it exceeds 0.7 parts by mass, the load during extrusion increases, As a result of gel generation, the film-forming property is lowered and the transparency is also lowered. In addition, although the sealing material sheet of the present invention can be obtained by performing a crosslinking treatment by irradiation with ionizing radiation, in this case, the addition amount of the crosslinking material is different from the conventional thermal crosslinking, Even if the addition amount of the crosslinking material is less than 0.5 parts by mass, sufficient heat resistance can be obtained. Thereby, the risk of the productivity fall by the gelatinization of the sealing material composition in the sheeting process of a sealing material composition can be reduced, and manufacturing cost can also be reduced by reducing the usage-amount of a crosslinking agent.

  In general, a conventional uncrosslinked sealing material sheet is required to undergo a crosslinking treatment in a modularization process. For this reason, the half-life temperature of the crosslinking agent used for the crosslinking treatment of the uncrosslinked encapsulant sheet is limited by the heating temperature and heating time conditions in the modularization process, and the one-minute half-life temperature is generally less than 185 ° C. Was virtually limited to. However, when the crosslinked sealing material sheet of the present invention is produced, the crosslinking agent can be selected without being subjected to the above-described restrictions. Generally, the upper limit temperature of the cross-linking agent is about 230 ° C. from the viewpoint of resin oxidative degradation, but in the production of the cross-linked encapsulant sheet of the present invention, the half-life temperature for 1 minute is within this range. A crosslinking agent at 185 ° C. or higher can also be freely selected. In addition, by expanding the selection range in this way, there is an advantage that the temperature at which molding can be performed without cross-linking is improved and the productivity is improved.

[Crosslinking aid]
In the present invention, a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group is used as a crosslinking aid. More preferably, the functional group of the polyfunctional monomer is an allyl group, a (meth) acrylate group, or a vinyl group. As a result, an appropriate crosslinking reaction is promoted so that the gel fraction is 70% or less, and in the present invention, this crosslinking aid reduces the crystallinity of the linear low density polyethylene and maintains transparency. As a result, it is possible to obtain a sealing material sheet that is more excellent in transparency and low-temperature flexibility, and specifically, it is possible to obtain transparency and low-temperature flexibility equivalent to those of EVA.

  Specifically, polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, diallyl maleate, trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA) Poly (meth) acryloxy compounds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, Glycidyl methacrylate containing epoxy groups, 4-hydroxybutyl acrylate glycidyl ether and 1,6-hexanediol diglycidyl ether containing two or more epoxy groups, 1 4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and epoxy compounds such as trimethylolpropane polyglycidyl ether. These may be used alone or in combination of two or more.

  Among these, TAIC is preferably used from the viewpoint of good compatibility with low density polyethylene, lowering crystallinity by crosslinking, maintaining transparency, and imparting flexibility at low temperatures. Further, 1,6-hexanediol diacrylate can also be preferably used from the viewpoint of reactivity with the silane coupling agent.

  The content of the crosslinking aid is preferably 0.0 or more and 3 parts by mass or less, more preferably 0.05 or more and 2.0 parts by mass or less with respect to 100 parts by mass of all components of the sealing material composition. The range is as follows. Within this range, an appropriate crosslinking reaction by irradiation with ionizing radiation can be promoted, and the gel fraction of the crosslinked encapsulant sheet before modularization can be 2% or more and 70% or less.

[Adhesion improver]
In the production method of the present invention in which the crosslinking treatment is performed by irradiation with ionizing radiation, it is preferable to add the above-described adhesion improver to the encapsulant composition. This is because when the ionizing radiation is irradiated in a large amount, the enlargement ratio can be suppressed, but the adhesion component on the surface of the sealing material sheet may be damaged and the adhesion may be lowered, but the low molecular weight silane coupling agent It is presumed that the adhesion can be ensured by the seepage effect. Thereby, it becomes possible to irradiate ionizing radiation with stronger intensity, and a more preferable enlargement ratio can be suppressed. As the adhesion improver, a known silane coupling agent can be used. The silane coupling agent is not particularly limited. For example, vinyl-based silane coupling agents such as vinyltrichlorosilane, vinyltrimethoxysilane, and vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-methacryloxypropyldiethoxy. A methacryloxy-based silane coupling agent such as silane or 3-methacryloxypropyltriethoxysilane can be preferably used. In addition, these can also be used individually or in mixture of 2 or more types. Among these, a methacryloxy silane coupling agent can be particularly preferably used.

  When a silane coupling agent is added as an adhesion improver, the content thereof is 0.1 to 10.0 parts by mass with respect to 100 parts by mass of all components of the sealing material composition, and the upper limit is preferably Is 5.0 parts by mass or less. When the content of the silane coupling agent is in the above range, and the polyolefin resin constituting the encapsulant composition contains an appropriate amount of the ethylenically unsaturated silane compound, the adhesion is more preferable. And improve. In addition, when this range is exceeded, the film-forming property is deteriorated, and the so-called bleed-out in which the silane coupling agent aggregates and solidifies with time and is pulverized on the surface of the sealing material sheet is not preferable.

[Radical absorbent]
In the present invention, the gel fraction can be adjusted more finely by adjusting the degree of cross-linking by using the above-mentioned cross-linking auxiliary agent serving as a radical polymerization initiator in combination with the radical absorbent for quenching it. . Examples of such radical absorbents include hindered phenol-based antioxidants, hindered amine-based weather resistance stabilization, and the like. A hindered phenol-based radical absorbent having a high radical absorbing ability near the crosslinking temperature is preferred. The amount of the radical absorbent used is preferably 0.01 to 3 parts by mass, more preferably 0.0 to 2.0 parts by mass in the composition. If it exists in this range, a crosslinking reaction can be suppressed moderately and the gel fraction of the bridge | crosslinking sealing material sheet before modularization can be 70% or less.

[Other ingredients]
The sealing material composition may further contain other components. For example, components such as a weather resistance masterbatch for imparting weather resistance to a sealing material sheet produced from the sealing material composition of the present invention, various fillers, a light stabilizer, an ultraviolet absorber, and a heat stabilizer Illustrated. These contents vary depending on the particle shape, density and the like, but are preferably in the range of 0.001 to 5 parts by mass in the encapsulant composition. By including these additives, it is possible to impart a mechanical strength that is stable over a long period of time, an effect of preventing yellowing, cracking, and the like to the encapsulant composition.

  A weatherproof masterbatch is obtained by dispersing a light stabilizer, an ultraviolet absorber, a heat stabilizer and the above-mentioned antioxidant in a resin such as polyethylene, and adding this to a sealing material composition. Thus, good weather resistance can be imparted to the encapsulant sheet. The weatherproof masterbatch may be prepared and used as appropriate, or a commercially available product may be used. The resin used in the weatherproof masterbatch may be a linear low density polyethylene used in the present invention, or other resins described above.

  These light stabilizers, ultraviolet absorbers, heat stabilizers and antioxidants can be used alone or in combination of two or more.

  Further, other components used in the sealing material composition of the present invention include nucleating agents, dispersants, leveling agents, plasticizers, antifoaming agents, flame retardants and the like.

<Sealing material sheet>
The sealing material sheet of the present invention obtains an uncrosslinked sealing material sheet by a sheeting process in which the above-mentioned sealing material composition is melt-molded at a temperature exceeding its melting point, and then a crosslinking process by irradiation with ionizing radiation. Through this, the sheet-like or film-like sealing material sheet for the solar cell module of the present invention is obtained. In addition, the sheet form in this invention means the film form, and there is no difference in both.

[Sheet making process]
Film formation by melt molding of the above-mentioned sealing material composition is performed by various molding methods such as injection molding, extrusion molding, hollow molding, compression molding, and rotational molding, which are usually used in ordinary thermoplastic resins. . At that time, the lower limit of the molding temperature may be a temperature exceeding the melting point of the encapsulant composition, and the upper limit may be a temperature at which crosslinking does not start during film formation depending on the 1-minute half-life temperature of the crosslinking agent used. There is no particular limitation as long as it is within these ranges. In the method for producing a solar cell module sealing material sheet of the present invention, as described above, since a crosslinking agent having a half-life temperature higher than that of the conventional one can be used, the molding temperature is higher than that of the conventional one. By setting to, it is possible to reduce the load applied to the extruder or the like and increase the productivity of the sealing material sheet.

[Crosslinking process]
The cross-linking process for performing a cross-linking process on the uncross-linked encapsulant sheet after the sheet forming process is performed after the sheet forming process is completed by the cross-linking process by irradiation with ionizing radiation, and the encapsulant sheet is integrated with other members. Before starting the solar cell module integration process. It is a feature of the encapsulant sheet of the present invention that the gel fraction and complex viscosity of the encapsulant sheet are optimized within a predetermined range by such a crosslinking step. Thus, by performing the crosslinking process by irradiation of ionizing radiation, it can be set as the sealing material sheet provided with higher adhesiveness and heat resistance than the case where it manufactures by the crosslinking process by heating.

  About the gel fraction of a sealing material sheet, the irradiation amount of ionizing radiation and the addition amount of a crosslinking agent are adjusted suitably so that it may become 2% or more and 70% or less. The gel fraction is preferably 2% or more and 70% or less, and more preferably 10% or more and 60% or less. If the gel fraction is less than 2%, the effect of suppressing the flow by the crosslinking step before the modularization step is not exhibited, and the sealing material composition flows in the vacuum heating laminate, making it difficult to keep the film thickness constant. . If the gel fraction exceeds 70%, the fluidity of the encapsulant composition becomes too low, and the module is not well embedded in the irregularities of the module, making it difficult to use it as an encapsulant sheet. That is, if the gel fraction is within the above range, the sealing property to the unevenness can be maintained well while suppressing excessive flow. In addition, the dimensional stability at the time of shaping | molding can be made very high by making a gel fraction 30% or more. The heat shrinkage is preferably 45% or less, more preferably 30% or less, and most preferably 20% or less.

  Here, the gel fraction (%) means that 0.1 g of a sealing material sheet is put in a resin mesh, extracted with 60 ° C. toluene for 4 hours, taken out together with the resin mesh, weighed after drying, and mass before and after extraction. Comparison is made to measure the mass% of the remaining insoluble matter, and this is used as the gel fraction.

  Moreover, about the complex viscosity of a sealing material sheet, bridge | crosslinking conditions are adjusted so that the complex viscosity in 80 degreeC or more and 100 degrees C or less may be 3.0E + 4Pa * S or more and 1.0E + 6Pa * S or less. The complex viscosity is preferably 3.0E + 4 Pa · S or more and 1.0E + 6 Pa · S or less, and more preferably 3.0E + 4 Pa · S or more and 5.0E + 5 Pa · S or less.

The complex viscosity of the sealing material sheet of the present invention is that the complex viscosity at 150 ° C. or more and 200 ° C. or less after crosslinking under the following crosslinking conditions is 1.0E + 5 Pa · S or more and 4.0E + 5 Pa · S or less. Features.
Crosslinking conditions: Heat until the resin temperature of the encapsulant sheet reaches 140 ° C. or higher, and then hold the temperature for 5 minutes or longer in a range where the resin temperature is 140 ° C. or higher and 150 ° C. or lower.

  The resin temperature of the encapsulant sheet can be measured by attaching a temperature sensor thermocouple to the upper surface of the encapsulant sheet during heating and using a temperature / humidity data logger. The resin temperature refers to, for example, the resin temperature of the sealing material sheet measured as described above.

  In addition, although the sealing material sheet of this invention can be preferably used as a member which comprises a solar cell module by integrating with another member, it is common in the integration process as a solar cell module. The above crosslinking conditions can be realized by heat laminating treatment depending on conditions. About an example of the lamination conditions for implement | achieving such bridge | crosslinking conditions, a specific example is shown in an Example later.

  By setting the complex viscosity of the encapsulant sheet and the complex viscosity after crosslinking to the above ranges, the fluidity and heat resistance of the encapsulant sheet are optimized, and the film pressure change of the encapsulant sheet during solar cell module production By suppressing the sealing material sheet, the protrusion of the sealing material sheet to the outside of the module end can be prevented, and the sealing material sheet can have sufficient adhesion and wraparound characteristics with respect to unevenness.

  Here, the complex viscosity (Pa · s) is a rotational rheometer (MCR301 manufactured by Anton Paar), parallel plate geometry (diameter 8 mm), stress 0.5 N, strain 5%, angular velocity 0.1 ( 1 / s), measured at conditions of a heating rate of 5 ° C./min, and this is the complex viscosity.

  Regarding the crosslinking treatment by irradiation with ionizing radiation, individual crosslinking conditions are not particularly limited, and may be appropriately set so that the gel fraction and the complex viscosity are in the upper range as a total treatment result. Specifically, it can be performed by ionizing radiation such as electron beam (EB), α-ray, β-ray, γ-ray, neutron beam, etc. Among them, it is preferable to use an electron beam. The acceleration voltage in electron beam irradiation is determined by the thickness of the sheet that is the object to be irradiated, and the thicker the sheet, the larger the acceleration voltage is required. For example, a 0.5 mm-thick sheet is irradiated with 100 kV or more, preferably 200 kV or more. If the acceleration voltage is lower than this, the crosslinking is not sufficiently performed. The irradiation dose is in the range of 5 kGy to 1000 kGy, preferably 5 to 300 kGy. When the irradiation dose is less than 5 kGy, sufficient crosslinking is not performed, and when it exceeds 1000 kGy, there is a concern about deformation or coloring of the sheet due to generated heat. In addition, you may irradiate from both sides. Irradiation may be in an air atmosphere or a nitrogen atmosphere.

  This crosslinking treatment may be performed continuously in-line following the sheet forming step, or may be performed off-line. Further, when the crosslinking treatment is a general heat treatment, generally, the content of the crosslinking agent is 0.5 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of all components of the sealing material sheet. However, in the sealing material sheet of the present invention, if the content of the crosslinking agent is 0.3 parts by mass or more, sufficient heat resistance can be obtained even if the content is less than 0.5 parts by mass. Can do.

<Solar cell module>
FIG. 1: is sectional drawing which shows an example of the layer structure about the solar cell module using the sealing material sheet of this invention. In the solar cell module 1 of the present invention, 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 surface protection sheet 6 are sequentially laminated from the incident light receiving surface side. ing. In the present invention, the sealing agent layer refers to the front sealing material layer 3 and the back sealing material layer 5. The solar cell module 1 of this invention uses said sealing material sheet for at least one of the front sealing material layer 3 and the back sealing material layer 5 which are sealing material layers.

[Method for manufacturing solar cell module]
The solar cell module 1 is, for example, vacuum suction after sequentially laminating members composed of the transparent front substrate 2, the front sealing material layer 3, the solar cell element 4, the back sealing material layer 5, and the back surface protection sheet 6. Then, the above-mentioned members can be manufactured by thermocompression molding as an integrally molded body by a molding method such as a lamination method.

  In the solar cell module 1, the incidental and limited crosslinking reaction of the encapsulant sheet may be further advanced during the above vacuum heating lamination. It is preferable that the gel fraction after the thermocompression bonding of the front sealing material layer 3 and the back sealing material layer 5 using the sealing material sheet of the present invention is 20 to 80%. By setting it as this range, the solar cell module 1 can be equipped with the sealing material layer which has high transparency, and shall have preferable heat resistance.

  In addition, the solar cell module 1 has a complex viscosity of 150 ° C. or more and 200 ° C. or less after the thermocompression bonding of the front sealing material layer 3 and the back sealing material layer 5 using the sealing material sheet of the present invention. It is preferably 0E + 5 Pa · S or more and 4.0E + 5 Pa · S or less. By setting the complex viscosity to 1.0E + 5 Pa · S or more and 4.0E + 5 Pa · S or less, the solar cell module can be provided with sufficient heat resistance and adhesion between the substrates.

  And the flow of the sealing material sheet in a vacuum heating lamination can be suppressed by using the sealing material sheet of this invention. In addition, since there is no cross-linking step by the modularization step or the subsequent heating step, the degree of freedom of the vacuum heating laminating condition in the modularization step is increased because the cross-linking conditions need not be considered, and the time for the modularization step is also increased. Can be shortened and productivity is greatly improved. In particular, the problem of the polyethylene-based encapsulant sheet having a slower crosslinking rate than that of EVA can be solved, and the modularization time can be greatly shortened.

  The haze value after the thermocompression bonding of the front sealing material layer 3 and the back sealing material layer 5 using the sealing material sheet of the present invention is 4% or less, preferably 3% at a thickness of 400 μm. It is as follows. As described above, in the present invention, in the solar cell module that contains a crosslinking agent as a composition, and thus employs a sealing material sheet using a crosslinked polyethylene resin as a sealing material layer. The excellent point of the present invention is that both heat resistance and transparency are achieved.

  In the solar cell module 1 of the present invention, the transparent front substrate 2, the solar cell element 4 and the back surface protection sheet 6 which are members other than the front sealing material layer 3 and the back sealing material layer 5 are made of conventionally known materials. It can be used without particular limitation. Moreover, the solar cell module 1 of this invention may also contain members other than the said member. In addition, the sealing material sheet of this invention is applicable not only to a single crystal type but to all other solar cell modules.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

<Manufacture of sealing material sheet>
The unsealed sealing materials of Examples, Comparative Examples, and Reference Examples were prepared by mixing and melting a sealing material composition having the following composition, and forming a film to a thickness of 460 μm by a conventional T-die method. A sheet was obtained. The film forming temperature was 90 ° C. or higher and lower than 100 ° C.
(Base resin)
A base resin of the encapsulant composition was prepared by mixing and melting 75 parts by mass of the following LLDPE (resin M) and 25 parts by mass of a silane-modified polyethylene resin (resin S).
LLDPE (resin M): polyethylene resin (LLDPE): a metallocene linear low density polyethylene which is a copolymer of ethylene and 1-hexene and has a density of 0.880 g / cm ³ and MFR of ³⁰ g / 10 min. Number average molecular weight 53,000 in terms of polystyrene.
Silane-modified polyethylene resin (resin S): a copolymer of ethylene and 1-hexene, having a density of 0.880 g / cm ³ and a melt mass flow rate (MFR) at 190 ° C. of 8 g / 10 min. A linear low-density polyethylene resin, 98 parts by mass, 2 parts by mass of vinyltrimethoxysilane and 0.1 parts by mass of dicumyl peroxide as a radical generator (reaction catalyst) are mixed at 200 ° C. A silane-modified polyethylene resin having a density of 0.884 g / cm ³ and an MFR of 6 g / 10 min obtained by melting and kneading. Number average molecular weight in terms of polystyrene is 79000.
(Crosslinking agent)
As a cross-linking agent, t-butyl peroxy-2-ethylhexyl carbonate (manufactured by Arkema Yoshitomi Co., Ltd., trade name Luperox TBEC) was used. The indicated amount (parts by mass) was added.
(Crosslinking aid)
Triallyl isocyanurate (manufactured by Statomer, trade name SR533) was used as a crosslinking aid, and 0.5 parts by mass was added to the sealing material compositions of all Examples, Comparative Examples, and Reference Examples.
(Adhesion improver)
A silane coupling agent was used as an adhesion improver. As the silane coupling agent, 3-methacryloxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM503) was used, and 0.5 parts by mass was added only to the sealing material composition of Example 4.
(Other additives)
0.25 mass part of UV absorbers (Kemipro Kasei Co., Ltd., trade name KEMISORB12) were added to the sealing material compositions of all Examples, Comparative Examples, and Reference Examples.
0.6 parts by mass of a weathering stabilizer (manufactured by Ciba Japan Co., Ltd., trade name Tinuvin 770) was added to the sealing material compositions of all Examples, Comparative Examples, and Reference Examples.
An antioxidant (trade name: Irganox 1076, manufactured by Ciba Japan Co., Ltd.) was added to 0.05 parts by mass of the sealing material compositions of all Examples, Comparative Examples, and Reference Examples.

  Next, for the uncrosslinked encapsulant sheets of Examples 1 to 4, Comparative Examples 2 and 3, and Reference Example, the ionizing radiation was irradiated under the crosslinking conditions (ionizing radiation (EB) irradiation intensity) shown in Table 1. Crosslinking treatment was performed to obtain a crosslinked encapsulant sheet. Irradiation with ionizing radiation was performed on both surfaces of the sealing material sheet with the strength shown in Table 1.

  The uncrosslinked encapsulant sheet of Comparative Example 4 was subjected to a thermal crosslinking treatment with an oven under the crosslinking conditions (temperature, time) shown in Table 1 to obtain a crosslinked encapsulant sheet.

  The uncrosslinked sealing material sheet of Comparative Example 1 was not subjected to crosslinking treatment.

  About the sealing material sheet | seat of the Example, the comparative example, and the reference example about the bridge | crosslinking sealing material sheet which performed the crosslinking process on the conditions as shown above, the gel fraction after the said crosslinking process is bridge | crosslinked. About the uncrosslinked sealing material sheet (Comparative Example 1) which was not performed, the gel fraction in an uncrosslinked state was measured after film formation. The results are shown in Table 1.

Moreover, about the sealing material sheet | seat of an Example and a comparative example, about the bridge | crosslinking sealing material sheet which performed the crosslinking process on the conditions as shown above, it does not perform a crosslinking process about the complex viscosity after the said crosslinking process. For the uncrosslinked sealing material sheet (Comparative Example 1), the complex viscosity in an uncrosslinked state after film formation was measured. The measurement was performed by the following test method in the range of 25 to 110 ° C. The result was as shown in FIG. The complex viscosity at 80 ° C. or more and 100 ° C. or less is 3.0E + 4 Pa · S or more and 1.0E + 6 Pa · S or less, and the complex viscosity is out of the range, “X”, Each is shown in the column of complex viscosity 1 in Table 1.
[Test method for complex viscosity]
The complex viscosity was measured using a rotary rheometer (MCR301 manufactured by Anton Paar), parallel plate geometry (diameter 8 mm), stress 0.5 N, strain 5%, angular velocity 0.1 (1 / s), heating rate 5 The measurement was performed under the condition of ° C / min.

Moreover, about the sealing material sheet | seat of an Example and a comparative example, after each said crosslinking process, the additional thermal crosslinking process was performed. As an additional thermal crosslinking treatment, a sealing material sheet (thickness: 460 μm) was sandwiched between Aflex ETFE (thickness: 100 μm) manufactured by Asahi Glass, and a vacuum heating laminator treatment was performed with a laminator. The thermal laminating conditions were as follows (a) to (d), and the cross-linking was advanced by performing a vacuum heating laminator treatment. According to the thermal laminating treatment under the following thermal laminating conditions (a) to (d), the resin temperature of the encapsulant sheet becomes 140 ° C. or higher after 2 minutes, and then held at a temperature of 140 ° C. or higher and 150 ° C. or lower for 6 minutes. Will be. In addition, the progress degree of the bridge | crosslinking at the time of a vacuum heating laminator process is decided by the temperature and heating time of a sealing material sheet, and is not influenced by pressurization conditions. And the complex viscosity of each sealing material sheet after a vacuum heating laminator process, ie, after an additional thermal crosslinking process, was measured, respectively. The measurement was performed in the range of 20 to 200 ° C. The result was as shown in FIG. The complex viscosity at 150 ° C. or more and 200 ° C. or less is 1.0E + 5 Pa · S or more and 4.0E + 5 Pa · S or less, and ○ when the complex viscosity is out of the range. Each is shown in the column of complex viscosity 2 in Table 1.
<Heat lamination conditions> (a) Vacuum drawing: 5.0 minutes
(B) Pressurization (0 kPa to 100 kPa): 1.5 minutes
(C) Pressure holding (100 kPa): 8.0 minutes
(D) Temperature 150 ° C

  In addition, the displacement of the encapsulant sheet resin temperature with the passage of time is, as described above, a temperature sensor thermocouple (ST-14K-060-) at the upper part of the central part of the encapsulant sheet sandwiched between ETFEs. GW5.0-ANP) pasted with ASONE Kapton tape (P-221 12.7mm width 5-5018-01), and temperature profile was measured using temperature / humidity data logger (Ondotori TR-72Ui) It is.

<Evaluation Example 1>
The sealing material sheets of Examples, Comparative Examples and Reference Examples cut to 5.0 × 5.0 cm were laminated on glass substrates (blue plate glass 150 mm × 150 mm × 3.0 mm), respectively, and further, A vacuum heating laminator process was performed in the state where the glass substrates were laminated, and the enlargement ratio of each sealing material sheet after the process was measured.
[Expansion rate (%) test method]
The length of the line drawn in a cross shape at the center of the square sealing material sheet (the value indicated by the diameter of the smallest circle including the cross shape) is the length when compared before and after the lamination process. The ratio was measured and this value was taken as the magnification. The heat laminating conditions were the same as the above (a) to (d). The results are shown in Table 2 for each example and comparative example.

<Evaluation Example 2>
Two sealing material sheets of Examples, Comparative Examples and Reference Examples cut to 7.5 × 5.0 cm are stacked on a glass substrate (white plate float semi-tempered glass JPT3.2 150 mm × 150 mm × 3.2 mm). From above, a glass substrate (white float semi-tempered glass JPT3.2 75 mm × 50 mm × 3.2 mm) is placed and subjected to vacuum heating laminator treatment, and solar cell module evaluation is performed for each of the examples, comparative examples, and reference examples. A sample was obtained. These solar cell module evaluation samples were subjected to a heat-resistant creep test under the following test conditions to evaluate heat resistance. The results are shown in Table 2.
[Test method for heat-resistant creep test (mm)]
The solar cell module evaluation sample was placed vertically and allowed to stand at 150 ° C. for 12 hours, and the moving distance of the glass substrate (white plate semi-tempered glass JPT3.2 75 mm × 50 mm × 3.2 mm) after being left was measured and evaluated. . In this test, a sheet having a moving distance of less than 1.0 mm was evaluated as a sealing material sheet having preferable heat resistance.

<Evaluation Example 3>
The sealing material sheets of Examples, Comparative Examples, and Reference Examples cut to a width of 15 mm were brought into close contact with glass substrates (white plate float semi-tempered glass JPT3.2 75 mm × 50 mm × 3.2 mm), respectively, and vacuum heating laminators The sample for solar cell module evaluation was obtained about each Example, the comparative example, and the reference example. Lamination treatment conditions were the same as the above-described crosslinking conditions (a) to (d). About these solar cell module evaluation samples, the glass adhesion rejection under the following test conditions was measured to evaluate the glass adhesion. The results are shown in Table 2.
[Test method for glass adhesion strength (N / 15 mm)]
Peeling test method: In the above solar cell module evaluation sample, the sealing material sheet in close contact with the glass substrate was vertically peeled (50 mm / min) with a peeling tester (Tensilon Universal Tester RTF-1150-H). A test was conducted to measure the glass adhesion strength. In this test, a sheet having an adhesion strength of 20 N / 15 mm or more was evaluated as a sealing material sheet having preferable adhesion.

<Evaluation Example 4>
Samples for solar cell module evaluation were obtained for Examples, Comparative Examples, and Reference Examples under the same conditions as in Evaluation Example 3 except that a copper plate (75 mm × 50 mm × 0.1 mm) was used instead of the glass substrate. About these solar cell module evaluation samples, the copper adhesion strength under the following test conditions was measured to evaluate the copper adhesion. The results are shown in Table 2.
[Testing method for copper adhesion strength (N / 15 mm)]
Peel test method: A test was conducted under the same method and conditions as in Evaluation Example 3, and the copper adhesion strength was measured.

<Evaluation Example 5>
The sealing material sheets of Examples, Comparative Examples, and Reference Examples cut to 30 mm × 75 mm were respectively laminated on a glass substrate (blue plate glass 30 mm × 75 mm × 3.2 mm), and the sealing material sheets after lamination were laminated. A vacuum heating laminator process is performed with a spacer so that the film thickness is 360 to 400 μm, and the HAZE of each encapsulant sheet after the process is measured (%) by the following test method. Transparency after integration as a module was evaluated. The heat laminating conditions were the same as the above (a) to (d).
[Test method for haze (%)]
According to JISK7136, it measured with Murakami Color Research Institute Co., Ltd. Haze and transmittance system HM150. The results are shown in Table 3.

<Evaluation Example 6>
Only the processing conditions of the heating temperature and laminating time at the time of the processing by the vacuum heating laminator were appropriately changed as shown in Table 4 below, and the other conditions were the same as those in Evaluation Example 3 and the sealing material sheet of Example 1 was used. The solar cell module evaluation sample manufactured for each processing condition was obtained. About these solar cell module evaluation samples, the glass adhesion strength under the same test conditions as in Evaluation Example 3 was measured to evaluate the glass adhesion. The results are shown in Table 4.

  From Table 2 and FIG. 2, the sealing material sheet of the present invention in which the gel fraction and the complex viscosity and the above-described complex viscosity after heat crosslinking are within a predetermined range is a module compared to the sealing material sheet of the comparative example. It can be understood that the flow is moderately suppressed by the crosslinking before the conversion step. Moreover, such a sealing material sheet of the present invention is performed by performing a crosslinking process by irradiation with ionizing radiation by performing a crosslinking process before the modularization process, compared with a case where a crosslinking process by a heating process is performed (Comparative Example 4). It turns out that it is what has become the sealing material sheet excellent in heat resistance.

  Moreover, from Table 2 and FIG. 3, the solar cell module of this invention in which the complex viscosity of a sealing material layer exists in the predetermined range used the sealing material sheet of the comparative example 4 which performed the crosslinking process by heat processing. It turns out that it becomes a solar cell module excellent in heat resistance compared with a thing.

  In addition, as can be seen from the test results for the reference examples in Table 2, when the crosslinking process before the modularization process is sufficiently performed by irradiation with ionizing radiation, the crosslinking process by the heat treatment is performed (Comparative Example 4). It can be seen that the enlargement ratio can be kept lower than that. In this case, the adhesion to glass or copper is slightly lowered, but as can be seen from the test results for Example 4, by adding an adhesion improver to such a sealing material sheet, by irradiation with ionizing radiation. It can be seen that it is possible to prevent a decrease in adhesion due to the crosslinking treatment and to obtain a sealing material sheet having extremely preferable physical properties having both excellent adhesion and heat resistance.

  Moreover, it can be seen from Table 2 that the sealing material sheet of the present invention has sufficient adhesion to glass and copper, which are the main materials of the constituent members of the solar cell module. In particular, as can be seen from the test results for Examples and Comparative Example 4, the encapsulant sheet of the present invention is crosslinked by heat treatment by performing the crosslinking step before the modularization step by crosslinking treatment with ionizing radiation. It turns out that it becomes a sealing material sheet provided with the especially preferable adhesiveness with respect to copper rather than the case where a process is performed. In addition, also about adhesiveness with another base material, it is thought that adhesiveness can be improved by adjusting irradiation conditions suitably for every base material to laminate | stack.

  Also, from Table 3, the encapsulant sheet of the present invention has an encapsulant composition containing at least 0.3 parts by mass of a cross-linking agent when the cross-linking step before the modularization step is performed by cross-linking treatment by irradiation with ionizing radiation. It turns out that it becomes a sealing material sheet provided with the outstanding transparency by adding to a thing. Moreover, from Table 2, it can also be confirmed that such a sealing material sheet has both excellent adhesion and heat resistance.

  In addition, it turns out that the sealing material sheet of this invention can be made into the sealing material sheet provided with sufficiently high glass adhesiveness by heating temperature in a modularization process to 110 degreeC or more from Table 4.

DESCRIPTION OF SYMBOLS 1 Solar cell module 2 Transparent front substrate 3 Front sealing material layer 4 Solar cell element 5 Back sealing material layer 6 Back surface protection sheet

Claims (5)

A low density polyethylene having a density of 0.900 g / cm ³ or less, and a crosslinking aid which is a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group,
The gel fraction is 2% or more and 70% or less,
The complex viscosity at 80 ° C. or more and 100 ° C. or less is 3.0E + 4 Pa · S or more and 1.0E + 6 Pa · S or less,
The sealing material sheet for solar cell modules whose complex viscosity in 150 degreeC or more and 200 degrees C or less after bridge | crosslinking by the following crosslinking conditions is 1.0E + 5Pa * S or more and 4.0E + 5Pa * S or less.
Crosslinking conditions: Heat until the resin temperature of the encapsulant sheet reaches 140 ° C. or higher, and then hold the temperature for 5 minutes or longer in a range where the resin temperature is 140 ° C. or higher and 150 ° C. or lower.   A solar cell module provided with the sealing material layer which consists of a sealing material sheet for solar cell modules of Claim 1.   3. The solar cell module according to claim 2, wherein a complex viscosity of the sealing material layer at 150 ° C. or more and 200 ° C. or less is 1.0E + 5 Pa · S or more and 4.0E + 5 Pa · S or less.   The solar cell module according to claim 2 or 3, wherein a haze value at a thickness of 400 µm of the encapsulant layer is 3% or less. A sheet forming step of obtaining an uncrosslinked encapsulant sheet by melt-molding an encapsulant composition comprising a density of 0.900 g / cm ³ or less, a low density polyethylene, a crosslinking agent, and a crosslinking assistant;
The manufacturing method of the sealing material sheet for solar cell modules provided with the bridge | crosslinking process which bridge | crosslinks the said unbridged sealing material sheet so that a gel fraction may be 2% or more and 70% or less by irradiation of ionizing radiation.

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