JP6089569B2 - SEALING MATERIAL SHEET FOR SOLAR CELL MODULE AND SOLAR CELL MODULE - Google Patents

Description

  The present invention relates to a sealing material sheet for a solar cell module. More specifically, the present invention relates to a polyethylene-based encapsulant sheet for a solar cell module 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 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).

  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 2). 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 3).

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

  However, like the sealing material sheet described in Patent Document 1, all of the sealing material sheets obtained by subjecting the polyethylene resin to thermal crosslinking treatment leave room for further improvement in heat resistance. there were.

  Moreover, the sealing material sheet obtained by irradiating the polyethylene resin with ionizing radiation, such as the sealing material sheet described in Patent Documents 2 and 3, is free from the restrictions on the modularization conditions as described above. In addition, the heat resistance can be improved by crosslinking. However, if the irradiation intensity of ionizing radiation is increased in order to obtain sufficient heat resistance, there is a problem that the embedding characteristics with respect to the unevenness of other members laminated at the time of integration as a solar cell module will be deteriorated. There was room for improvement in this regard.

  The present invention has been made to solve the above problems. An object of this invention is to provide the sealing material sheet for solar cell modules which has heat resistance and an embedding characteristic.

  The present inventors perform the crosslinking treatment by irradiation with ionizing radiation in advance from only one side of the encapsulant sheet after extrusion formation of the encapsulant sheet and before modularization, thereby reducing the encapsulant sheet. By finding that the molecular weight is inclined and distributed in a specific manner from the molecular weight surface side toward the high molecular weight surface side, it is found that a sealing material sheet excellent in heat resistance and unevenness followability can be obtained. It came to be completed. More specifically, the present invention provides the following.

(1) A sealing material sheet for a solar cell module containing low density polyethylene having a density of 0.890 g / cm ³ or less, comprising one low molecular weight surface and another high molecular weight surface, The weight average molecular weight (Mw) in terms of partial polystyrene in the range from the surface of the molecular weight surface to the depth of 30% of the thickness of the sealing material sheet, and the thickness of the sealing material sheet from the surface of the high molecular weight surface The encapsulant sheet having a ratio of 0.5 to less than 1.0 with respect to the weight average molecular weight (Mw) of the portion in the range up to a depth of 30%.

  (2) Molecular weight that is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of polystyrene in the range from the surface of the low molecular weight surface to the depth of 30% of the thickness of the encapsulant sheet Dispersity (Mw / Mn) is 1.6 or more and 2.4 or less, and the molecular weight dispersity in a range from the surface of the high molecular weight surface to a depth of 30% of the thickness of the encapsulant sheet (Mw / Mn) is a sealing material sheet according to (1), which is 2.0 or more and 3.2 or less.

  (3) The sealing material sheet according to (1) or (2), wherein the gel fraction is 0%.

(4) A method for producing a sealing material sheet according to any one of (1) to (3), wherein the sealing material composition comprises a low density polyethylene having a density of 0.890 g / cm ³ or less. The manufacturing method of the sealing material sheet for solar cell modules provided with the sheet forming process formed in a sheet form, and the process of irradiating ionizing radiation only to the single side | surface side of the said sealing material composition formed in the sheet form.

  (5) The encapsulant sheet according to any one of (1) to (3) and a solar cell element are laminated, and the solar cell element is on the low molecular weight surface side of the encapsulant sheet. A stacked solar cell module.

  ADVANTAGE OF THE INVENTION According to this invention, the sealing material sheet for polyethylene-type solar cell modules excellent in heat resistance and the uneven | corrugated followable | trackability with respect to the other member in a solar cell module can be provided.

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.

  The encapsulant sheet for solar cell modules of the present invention (hereinafter also simply referred to as “encapsulant sheet”) is a solar cell module encapsulant by limiting the molecular weight gradient distribution to the above specific range. The sheet is characterized by having extremely preferable heat resistance and unevenness followability with respect to other members in the solar cell module.

The solar cell module encapsulant composition (hereinafter also simply referred to as “encapsulant composition”) for producing the encapsulant sheet of the present invention has a low density of 0.890 g / cm ³ or less. And polyethylene as an essential component.

<Encapsulant composition>
The encapsulant composition used as the material of the encapsulant sheet of the present invention contains a low-density polyethylene, which will be described in detail below, as a base resin, and additionally contains a crosslinking agent, a crosslinking aid, and the like as optional components. It is. The encapsulant sheet of the present invention is characterized in that the molecular weight is distributed in a gradient, but when the encapsulant sheet is a multilayer sheet, the molecular weight of each single-layer encapsulant sheet forming each layer is A sealing material composition using a different resin as a base resin can also be used. Even in such a case, it is possible to laminate a resin having the same molecular weight, and to distribute the molecular weight in a gradient distribution during the ionizing radiation cross-linking treatment described in detail later.

[Low density polyethylene]
In the present invention, low density polyethylene (LDPE) having a density of 0.890 or less, preferably linear low density polyethylene (LLDPE) is used. The linear low density polyethylene is a copolymer of ethylene and α-olefin, and in the present invention, the density thereof is in the range of 0.890 g / cm ³ or less, preferably 0.870 to 0.885 g / cm ^3. Range. 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 sheet. As a result of the flexibility, adhesion between the sealing material sheet and other laminated members constituting the solar cell module such as a glassy transparent front substrate is enhanced.

  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, for example, even when a sealing material sheet made of the sealing material composition of the present invention is disposed between the transparent front substrate and the solar cell element, the power generation efficiency hardly decreases.

  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 sealing material sheet and other members 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 in accordance with JIS-K6922-2 (in the present specification, the measurement value under this measurement condition is hereinafter referred to as MFR). It 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.

  In addition, even if the MFR of the low density polyethylene used as the base is high by performing the crosslinking treatment by irradiation with ionizing radiation after the melt formation of the encapsulant composition, the flow at the time of modularization by the crosslinking treatment after film formation Sex can be suppressed. For this reason, even if it is high MFR like the said range, it can be used conveniently.

  The molecular weight of the raw material low density polyethylene itself is not particularly limited, but in the case of the above metallocene linear low density polyethylene, the number average molecular weight (Mn) in terms of polystyrene (hereinafter simply referred to as “number average molecular weight”). (Also referred to as (Mn) ”) in the range of about 30,000 to 100,000 g / mol, and a weight average molecular weight (Mw) (hereinafter also simply referred to as“ weight average molecular weight (Mw) ”) of about 70000 to 300,000 g / mol. A range is preferable. Further, the molecular weight dispersity (Mw / Mn) of the resin is preferably about 2.2 to 2.4. If it is a low density polyethylene resin having a molecular weight and molecular weight distribution in this range, a solar cell having a predetermined molecular weight distribution and excellent in other physical properties by treatment such as irradiation with ionizing radiation described later. It can be set as the sealing material sheet for modules.

  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 the sealing material composition of the 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 having extremely excellent heat-fusibility, stably and at low cost, and 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 grafting amount, which is the content of the ethylenically unsaturated silane compound, is, for example, 0.001 or more and 15 masses with respect to 100 mass parts in total of all resin components in the sealing material composition containing other polyethylene-based resins described later. Part or less, 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 sealing material composition may further contain an acid-modified polyethylene resin typified by maleic anhydride modification. The acid-modified polyethylene resin is obtained, for example, by graft polymerization using, for example, maleic anhydride or the like as a side chain on linear low density polyethylene (LLDPE) or the like as a main chain. Such a graft polymer has a high polarity of the acid part which contributes to adhesive force, and can improve the adhesiveness of the sealing material sheet to the metal member in the solar cell module.

  The content of the low density polyethylene contained in the encapsulant composition is preferably 10 or more and 99 parts by mass or less, more preferably 50 or more and 99 with respect to 100 parts by mass in total of all resin components in the encapsulant composition. The amount is not more than part by mass, more preferably not less than 90 and not more than 99 parts by mass. 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]
You may add a crosslinking agent to the sealing material composition of this invention as needed. 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 performs the crosslinking treatment by the irradiation of ionizing radiation, and has the following preferable effects by containing a small amount of the crosslinking agent. Can do. This is because the addition of this crosslinking agent makes it possible to improve the heat resistance as well as the 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 in the case of adding the crosslinking agent to the sealing material composition of the present invention is 0.01 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of all components in the sealing material composition. It is preferable that it is 0.01 mass part or more and 0.3 mass part or less. 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 0.01 parts by mass, the effect of improving the transparency is insufficient, and if it exceeds 1.5 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 0.3 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 may be used as a crosslinking aid. Preferably, the functional group of the polyfunctional monomer is an allyl group, a (meth) acrylate group, or a vinyl group. This promotes an appropriate crosslinking reaction, and in the present invention, this crosslinking aid reduces the crystallinity of the low density polyethylene and maintains transparency.

  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 assistant is preferably 0.01 parts by mass or more and 3 parts by mass or less, more preferably 0.05 parts by mass or more and 2 parts by mass with respect to 100 parts by mass of all components of the sealing material composition. It is the range below 0.0 mass part. Within this range, an appropriate crosslinking reaction by irradiation with ionizing radiation can be promoted, and the gel fraction of the crosslinked sealing material sheet before modularization can be maintained at 0%.

[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 adding a silane coupling agent as an adhesion improver, the content is 0.1 parts by mass or more and 10.0 parts by mass or less with respect to 100 parts by mass of all components of the encapsulant composition, and the upper limit. Is preferably 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 parts by weight or more and 3 parts by weight or less, more preferably 0.05 parts by weight or more and 2.0 parts by weight or less 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 made into 0%.

[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 this invention melt-molded said sealing material composition at the temperature exceeding the melting | fusing point, and was set as the sealing material sheet for solar cell modules of this invention of a sheet form or a film form It is. The encapsulant sheet of the present invention has a molecular weight that is inclined and distributed in the thickness direction of the encapsulant, and a low molecular weight surface made of a resin having a relatively small molecular weight and a resin having a relatively large molecular weight. The molecular weight is distributed in a specific manner. In addition, the sheet form in this invention means the film form, and there is no difference in both.

  The molecular weight distribution in the encapsulant sheet is a cross-linking treatment in which an uncrosslinked single-layer encapsulant sheet having a substantially uniform molecular weight distribution is irradiated with ionizing radiation only from one side thereof. Thus, this can be realized by making the one surface side a high molecular weight surface and the other surface a low molecular weight surface. Details of this crosslinking treatment will be described later.

  Also, for example, using a sealing material composition having the same molecular weight, by irradiation with ionizing radiation as described above, a single layer sheet having a relatively low molecular weight and a relatively low molecular weight is used. Even in the case of a multilayer sheet in which a single sheet having a large high molecular weight layer is laminated, the layer structure based on the molecular weight distribution described above can be realized, and a sealing material sheet having the same effect as the present invention and can do.

  The encapsulant sheet of the present invention has a weight average molecular weight (hereinafter also referred to as “low molecular weight portion”) in a range from the surface of the low molecular weight surface to a depth of 30% of the thickness of the encapsulant sheet. Mw) and the ratio of the weight average molecular weight (Mw) of the portion in the range from the surface of the high molecular weight surface to the depth of 30% of the thickness of the encapsulant sheet (hereinafter also referred to as “high molecular weight portion”) Is 0.5 or more and less than 1.0. Further, this ratio is more preferably 0.6 or more and less than 0.85. In addition, it is preferable that this sealing material sheet is 200 micrometers or more in thickness.

  The sealing material sheet of the present invention has a molecular weight dispersity (Mw) which is a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the low molecular weight portion within the range of the weight molecular weight ratio of the present invention. / Mn) is preferably 1.4 or more and 2.6 or less, and more preferably 1.6 or more and 2.4 or less. In addition, the molecular weight dispersity (Mw / Mn) of the high molecular weight part is preferably 1.8 or more and 3.5 or less, and more preferably 2.0 or more and 3.2 or less.

  When the molecular weight dispersity (Mw / Mn) of the low molecular weight portion is less than 1.4 or the molecular weight dispersity (Mw / Mn) of the high molecular weight portion is less than 1.8, the solar cell When a module is used, the heat resistance is insufficient, such being undesirable. Further, when the molecular weight dispersity (Mw / Mn) of the low molecular weight portion exceeds 2.6, or the molecular weight dispersity (Mw / Mn) of the high molecular weight portion exceeds 3.5, a solar cell element or the like In addition, it is not preferable because the unevenness followability with respect to other laminates constituting the solar cell module becomes insufficient.

  The absolute value of the molecular weight of the encapsulant sheet of the present invention is not particularly limited as long as the molecular weight ratio and the dispersion are within the predetermined ranges of the present invention.

  About the weight average molecular weight (Mw) of a high molecular weight part, the weight average molecular weight ratio of said sealing material sheet should just be a range used as 0.5 or more and less than 1.0.

  The molecular weight distribution of the encapsulant sheet is set within the predetermined range of the present invention while the gel fraction is kept at 0% by the crosslinking treatment by irradiation with ionizing radiation, which will be described in detail later. It can be set as the sealing material sheet provided with heat resistance, transparency, and adhesiveness by it.

  The encapsulant sheet of the present invention has a gel weight of 0% and a molecular weight based on a mass average molecular weight. However, at this time, an increase in the molecular weight is relatively small on a number average molecular weight basis. It is suppressed. As a result, the encapsulant sheet of the present invention has an increased degree of dispersion by a crosslinking treatment by irradiation with ionizing radiation. Such a low-density polyethylene-based sealing material having a specific degree of dispersion cannot be obtained by conventional thermal crosslinking treatment, but can be obtained by crosslinking treatment by irradiation with ionizing radiation. According to the cross-linking treatment by irradiation with ionizing radiation, unlike conventional thermal cross-linking, the cross-linking reaction by irradiation with ionizing radiation in which the cross-linking progresses in the encapsulant while the decomposition reaction proceeds irregularly simultaneously. This is because a unique reaction proceeds. The sealing material sheet of the present invention having such a specific degree of dispersion is a sealing material sheet having heat resistance and unevenness followability superior to conventional products, and transparency.

  As described above, the encapsulant sheet of the present invention has a low molecular weight surface while ensuring heat resistance as a whole encapsulant sheet by limiting the molecular weight distribution in the thickness direction to a predetermined specific range. The unevenness followability is extremely preferable.

  Here, the molecular weight can be measured by a conventionally known GPC method after dissolving in a solvent such as THF. The number average molecular weight (Mn), the weight average molecular weight (Mw), and the degree of dispersion d when the polymer having a molecular weight Mi (g / mol) is Ni (pieces) in the encapsulant sheet are defined by the following equations, respectively. It is what is done.

  Number average molecular weight Mn = Σ (MiNi) / ΣNi

Weight average molecular weight Mw = Σ (Mi ² Ni) / ΣMiNi

  Dispersity d = Mw / Mn

  Regarding the gel fraction of the sealing material sheet of the present invention, the gel fraction should be 0% at all stages, including the state after the crosslinking treatment after molding, after the crosslinking treatment, and even after the modularization. Is preferred. By maintaining the gel fraction at 0%, it is possible to improve the unevenness followability of the unevenness of other members laminated up and down during modularization, and to reduce the load at the time of melt extrusion with high productivity stably. An encapsulant sheet can be produced.

  Here, the gel fraction (%) means that 0.1 g of a sealing material sheet is put into a resin mesh, extracted with xylene by heating under reflux for 12 hours, taken out together with the resin mesh, weighed after drying, and before and after extraction. The mass ratio of the residual insoluble matter is measured and the gel fraction is obtained. “Gel fraction 0%” means that the residual insoluble matter is substantially 0 and the crosslinking reaction of the encapsulant composition has not substantially started. More specifically, “gel fraction 0%” in the present invention means that the residual insoluble matter is not present at all, and the residual insoluble matter mass% measured by a precision balance is less than 0.05 mass%. Let's say the case.

Regarding the transparency of the sealing material sheet of the present invention, the haze value at a thickness of 400 μm is preferably 10% or less, more preferably 7% or less. Since the sealing material sheet of the present invention uses a low-density polyethylene resin having a density of 0.890 g / cm ³ or less as the base resin of the sealing material composition, such a preferable transparency for the sealing material sheet. Can be provided. Moreover, even if it uses such a low density polyethylene resin, it can also provide sufficient heat resistance by performing the crosslinking process by ionizing radiation by the method specific to the manufacturing method of this application. In addition, in this specification, the sample of the sealing material sheet which heated the resin temperature to 150 degreeC from the original viewpoint which shows the characteristic in an actual use environment about the haze value of a sealing material sheet is -3. The value when cooled under the condition of ° C./min is the haze value.

  Conventionally, when a crosslinking treatment by ionizing radiation is performed on a sealing material sheet, a crosslinking agent is unnecessary, but by adding an appropriate amount of a crosslinking agent as described above to the sealing material composition. In the crosslinked encapsulant sheet subjected to crosslinking treatment with ionizing radiation, both heat resistance and transparency can be achieved at a higher level.

  The thickness of the encapsulant sheet is preferably 250 μm or more and 600 μm or less, and if it is less than 250 μm, the impact cannot be sufficiently mitigated, and the insulating property becomes insufficient, which is not preferable. Moreover, even if it exceeds 600 micrometers, since the effect beyond it is not acquired and it is uneconomical, it is unpreferable.

[Method for producing sealing material sheet]
The manufacturing method of the sealing material sheet of the present invention includes at least a sheet forming step for forming the sealing material composition described above into a sheet shape, and an uncrosslinked material that is a sealing material composition formed into a sheet shape. It is a manufacturing method provided with the bridge | crosslinking process which irradiates ionizing radiation only from the single side | surface side of a sealing material sheet. It is characterized in that a molecular weight distribution peculiar to the present application is realized by a crosslinking step by irradiation with ionizing radiation.

(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. . In addition, when the sealing material sheet is a multilayer sheet, a molding method by coextrusion can be preferably used. 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. By this crosslinking step, the molecular weight distribution of the encapsulant sheet can be optimized within a predetermined range unique to the present application. Thus, by performing the bridge | crosslinking process by irradiation of ionizing radiation, it can be set as the sealing material sheet which has heat resistance, the uneven | corrugated followable | trackability with respect to the other member in a solar cell module, and transparency.

  Moreover, it is preferable to adjust appropriately the irradiation amount of ionizing radiation, and the addition amount of a crosslinking agent so that it may become 0% also about the gel fraction of a sealing material sheet. Conventionally, when the gel fraction is 0%, the effect of suppressing flow by the crosslinking step before the modularization step is not exhibited, and it is difficult to keep the film thickness of the encapsulant sheet constant due to excessive flow. However, the encapsulant sheet of the present invention avoids such a problem by limiting the molecular weight distribution to a predetermined range by crosslinking treatment by irradiation of electron irradiation rays, and thus the solar cell module. It can be preferably used as a sealing material sheet.

  The cross-linking treatment 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. For crosslinking treatment by irradiation with ionizing radiation, in order to realize the gradient distribution of molecular weight as described above in the thickness direction of the encapsulant sheet, ionization is performed only from one side of the uncrosslinked encapsulant sheet after the sheeting process. It is characterized by irradiating with radiation. Other processing conditions are not particularly limited as long as the molecular weight distribution of the encapsulant sheet falls within the predetermined range described above as a total processing result.

  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 0.02 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. The solar cell module 1 uses the encapsulant sheet of the present invention as at least the front encapsulant layer 3 located directly facing the solar cell element 4. Moreover, the sealing material sheet | seat of this invention is laminated | stacked in the aspect which closely_contact | adheres the low molecular weight surface side to the solar cell element 4, when arrange | positioning the same. Thereby, the unevenness | corrugation of the solar cell element of a sealing material sheet can fully be tracked, the adhesiveness of this interlayer can also be improved, and the crack of a solar cell element, etc. can fully be prevented. In addition, the layer structure of this solar cell module represents a preferable example, and arrangement | positioning of the sealing material sheet | seat of this invention is not limited above. For example, if it is a module of a type in which a thin film solar cell element is disposed on a transparent front substrate, the sealing material sheet of the present invention is used in a mode in which the low molecular weight surface is in close contact with the transparent front substrate. The same effect can be produced.

[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 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 for solar cell module>
As described below, an uncrosslinked preliminary sealing material sheet was formed from a sealing material composition containing a low-density polyethylene resin as a main resin. Then, as shown below, each preliminary sealing material sheet is subjected to crosslinking treatment by irradiation with ionizing radiation under different crosslinking conditions to prepare each crosslinked sealing material sheet, and the sealing of Example 1 and Comparative Example 1 is performed. A stop sheet was obtained. In Comparative Examples 2 and 3, the uncrosslinked preliminary sealing material sheet was used as it was as the sealing material sheet of each Comparative Example without performing the crosslinking treatment.

<Manufacture of preliminary sealing material sheet>
A sealing material composition having the following composition was mixed and melted, and a film was formed by extrusion at 220 ° C. to a thickness of 400 μm by a conventional T-die method.

(Base resin)
One obtained by mixing and melting 75 parts by mass of any of the following two types of LLDPE (resin M1 or M2) and 25 parts by mass of a silane-modified polyethylene resin (resin S) was used as the base resin of the sealing material composition.

LLDPE (Resin M1)
: 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 ³ g / 10 min. Number average molecular weight 100,000 in terms of polystyrene.
LLDPE (Resin M2)
: Polyethylene resin (LLDPE): A metallocene linear low density polyethylene which is a copolymer of ethylene and 1-hexene and has a density of 0.900 g / cm ³ and MFR of 2 g / 10 min. Number average molecular weight of 120,000 in terms of polystyrene.
Silane-modified polyethylene resin (resin S)
A copolymer of ethylene and 1-hexene, a metallocene linear low density polyethylene resin having a density of 0.880 g / cm ³ and a melt mass flow rate (MFR) at 190 ° C. of 3 g / 10 min, 98 Density obtained by mixing 2 parts by mass of vinyltrimethoxysilane and 0.1 part by mass of dicumyl peroxide as a radical generator (reaction catalyst) with respect to parts by mass, and melting and kneading at 200 ° C. Silane-modified polyethylene resin having 0.884 g / cm ³ and MFR of 2 g / 10 min. Number average molecular weight 110000 in terms of polystyrene.
(Crosslinking agent)
As a crosslinking agent, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (Arkema Yoshitomi Co., Ltd., trade name Luperox 101) was used. An amount (parts by mass) shown in Table 1 was added.
(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 and Comparative 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 and Comparative Examples.

<Manufacture of sealing material sheet>
Next, the preliminary sealing material sheets of Example 1 and Comparative Example 1 were subjected to crosslinking treatment by irradiation with ionizing radiation to obtain a crosslinked sealing material sheet. Irradiation conditions were an acceleration voltage of 200 kV and an irradiation dose of 20 kGy. In Example 1, 20 kGy was applied to one side, and Comparative Example 1 was irradiated on both sides to irradiate a total of 40 kGy.

  About Comparative Examples 2-3, the irradiation process of said ionizing radiation was not performed but the sealing material sheet after shaping | molding was used as the sealing material sheet of each comparative example as it was.

  The molecular weight and molecular weight distribution of the sealing material sheets of the above Examples and Comparative Examples, and the gel fraction were measured by the following methods. The results are shown in Table 2.

Molecular weight: The sealing agent sheets of Examples and Comparative Examples were dissolved in o-dichlorobenzene, and the polystyrene-equivalent number average molecular weight, weight average molecular weight, and molecular weight distribution of each sealing material sheet were measured under the following conditions. . In addition, about the sealing material sheet | seat of Example 1 and Comparative Example 1, it cut to the depth range of 120 micrometers from each surface with the microtome, and measured the molecular weight of each surface part with the following measuring method.
Measurement model: GPC / V2000 manufactured by Waterers
Column: Shodex AT-G + AT-806MS × 2 Eluent: o-dichlorobenzene (with 0.3% BHT)
Temperature: Column and injector 145 ° C
Concentration: about 1.0 g / L
Flow rate 1.0ml / min
Solubility: Complete dissolution Detector: Differential refractometer (RI)

  Gel fraction (%): 0.1 g of the sealing material sheets of Examples and Comparative Examples were put into a resin mesh, extracted with 60 ° C. toluene for 4 hours, then taken out together with the resin mesh, weighed after drying treatment, and before and after extraction. A weight comparison was performed to measure the mass% of the remaining insoluble matter, and this was used as the gel fraction. The definition of the gel fraction of 0% is as described above.

<Manufacture of solar cell module evaluation samples>
Moreover, the solar cell module evaluation sample of an Example and a comparative example was manufactured using each sealing material of said Example comparative example.

Samples for solar cell module evaluation are from a transparent front glass substrate (blue plate glass), a front sealing material sheet, a solar cell element, a back surface sealing material sheet, and a back surface protection sheet (Dai Nippon Printing Co., Ltd., model number VPEW 280 μm). Then, the above-mentioned members were manufactured by thermocompression-bonding as an integral molded body by vacuum heating lamination. About a solar cell element, it is set as the structure which arrange | positions the solar cell element demonstrated below on the low molecular weight surface of a sealing material sheet | seat, and 42 solar cell elements of the same kind are each connected to one solar cell module evaluation sample. Electrically connected in series. The thermal lamination conditions were as follows. or,
<Heat lamination conditions> (a) Vacuum drawing: 5.0 minutes
(B) Pressurization (0 kPa to 100 kPa): 1.5 minutes
(C) Pressure holding (100 kPa): 15.0 minutes
(D) Temperature 150 ° C
(Solar cell element)
A crystalline silicon solar cell element manufactured using a polycrystalline silicon substrate. An electrode for collecting current is arranged on the daylighting side. (Q-CELLS, cell Q6LTT-200 / 1520 156mm)

<Evaluation Example 1>
About the sealing material sheet | seat of an Example and a comparative example, it measured about uneven | corrugated followable | trackability, cell protective property, transparency, and heat resistance. The results are shown in Table 3. Each test condition is as follows.

(Unevenness follow-up test)
: About each said solar cell module evaluation sample created using each sealing material sheet | seat of an Example and a comparative example, the uneven | corrugated followable | trackability was evaluated by the following reference | standard visually.
(Evaluation criteria)
A = No bubbles around the wiring connecting the solar cell elements C = No bubbles around the wiring connecting the solar cell elements

(Cell protection performance test)
About the said solar cell module evaluation sample created using each sealing material sheet of an Example and a comparative example, it measured about the microcrack which generate | occur | produces from the curvature of a solar cell element. The results are shown in Table 2. The test conditions are as follows.

Microcrack measurement test of solar cell element: Cell microcracks were observed by EL images for the solar cell module evaluation samples of the above-described Examples and Comparative Examples. The test was performed before and after the cycle test described below. The cycle test used the method based on the temperature cycle test of JIS C8917. Increase from 25 ° C. to 90 ° C. over 45 minutes, hold at this temperature for 90 minutes, then decrease to −40 ° C. over 90 minutes, hold at this temperature for 90 minutes, then increase to 25 ° C. over 45 minutes Let This is one cycle (6 hours). This cycle was repeated 400 cycles to perform a cycle test. Observation of the cell microcrack by the EL image was performed as follows. When current is made to conduct in the forward direction with respect to the solar cell element, electrons of minority carriers are introduced into the p layer, and light emission is generated by recombination of the electrons and holes in the p layer. In the detection step, conventionally known light detection means that can detect the light emission characteristics of light from the solar cell element can be used. In the test, a current of 3 A was passed from the output terminal of the module, EL emission was photographed, and microcracks at a level that could not be confirmed visually or with a microscope were confirmed from the emission image. And the number of the cell in which the microcrack has generate | occur | produced in one solar cell module evaluation sample comprised by 42 cells was measured. The number of microcracks generated before the cycle test was 0 for all microcracks. The measured values were evaluated according to the following evaluation criteria. The results are shown in Table 2.
(Evaluation criteria)
A = Number of microcracks generated 0-2
B = number of microcracks generated 3-7
C = Number of microcracks generated is 8 or more

(Heat resistance test)
Heat-resistant creep (mm): Two sheets of sealing material cut into 5 x 7.5 cm are placed on a large glass plate that has been subjected to graining, and 5 x 7.5 grain glass is placed on top of the sealing material. went. After this, the large format glass is placed vertically and left at 140 ° C. for 12 hours. The moving distance of 5 × 7.5 grain glass after being left was measured and evaluated. The measured values were evaluated according to the following evaluation criteria. The results are shown in Table 3.
(Evaluation criteria)
A = less than 1.5 mm B = 1.5-2
C = 2mm or more

(Transparency test)
Haze (%): Measured in accordance with JISK7136 with Murakami Color Research Laboratory Haze / Transmittance HM150. The value when the sealing material sheet heated to 150 ° C. was cooled under the condition of −3 ° C./min was defined as the haze value. The measured values were evaluated according to the following evaluation criteria. The results are shown in Table 3.
(Evaluation criteria)
A = less than 5 B = 5-7
C = 7 or more

  From Tables 1 to 3, the encapsulant sheet of the present invention in which the molecular weight distribution in the thickness direction of the encapsulant is limited to a specific range is a well-balanced balance of unevenness followability, cell protection performance, transparency, and heat resistance. It turns out that it is the outstanding sealing material sheet which combines.

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 (6)

A sealing material sheet for a solar cell module comprising a single-layer sheet containing low-density polyethylene having a density of 0.890 g / cm ³ or less,
One low molecular weight surface and another high molecular weight surface, and a weight average molecular weight in terms of polystyrene in a range from the surface of the low molecular weight surface to a depth of 30% of the thickness of the encapsulant sheet ( Mw) and the weight average molecular weight (Mw) of the portion ranging from the surface of the high molecular weight surface to a depth of 30% of the thickness of the encapsulant sheet is 0.5 or more and less than 1.0 Is a sealing material sheet. Molecular weight dispersity (which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of polystyrene of the portion ranging from the surface of the low molecular weight surface to the depth of 30% of the thickness of the encapsulant sheet ( Mw / Mn) is 1.6 or more and 2.4 or less,
The molecular weight dispersity (Mw / Mn) of a portion ranging from the surface of the high molecular weight surface to a depth of 30% of the thickness of the encapsulant sheet is 2.0 or more and 3.2 or less. The encapsulant sheet described in 1.   The sealing material sheet according to claim 1 or 2, wherein the gel fraction is 0%. Density 0.890g / cm ³ It is a sealing material sheet for a solar cell module containing the following low density polyethylene,
One low molecular weight surface and another high molecular weight surface, and a weight average molecular weight in terms of polystyrene in a range from the surface of the low molecular weight surface to a depth of 30% of the thickness of the encapsulant sheet ( Mw) and the weight average molecular weight (Mw) of the portion ranging from the surface of the high molecular weight surface to a depth of 30% of the thickness of the encapsulant sheet is 0.5 or more and less than 1.0 Because
A sealing material sheet having a gel fraction of 0%. It is a manufacturing method of the sealing material sheet in any one of Claim 1 to 4 , Comprising: Sheet formation which forms the sealing material composition containing the low density polyethylene of a density of 0.890 g / cm < ³ > or less in a sheet form The manufacturing method of the sealing material sheet for solar cell modules provided with the process and the process of irradiating an ionizing radiation only to the single side | surface side of the said sealing material composition formed in the sheet form. The encapsulant sheet according to any one of claims 1 to 4 ,
A laminate of solar cell elements,
The solar cell module by which the said solar cell element is laminated | stacked on the said low molecular weight surface side of the said sealing material sheet.

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