JP2014072300A - Seal-material sheet and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seal-material sheet for solar battery module use which is thermally resistant while using a polyethylene-based resin, and superior in transparency, and to provide a method for manufacturing such a seal-material sheet.SOLUTION: A seal-material sheet for solar battery module use comprises: a low-melting point layer including no less than 70 mass% of a polyethylene-based resin having a melting point of 50-70°C. The low-melting point layer is composed of a monolayer or multilayer having a value of MFR(melt-mass-flow rate) of no less than 0.1 g/10 min and below 1.0 g/10 min under the condition of a load of 2.16 kg at 190°C, which was measured in conformity with JIS K7210. The polyethylene-based resin preferably has a density of 0.900 g/cmor less, a gel fraction of 25% or less, and a weight-average molecular weight of 120,000-300,000 in terms of polystyrene.

Description

  The present invention relates to a sealing material sheet for a solar cell module and a manufacturing method thereof.

  In recent years, solar cells as a clean energy source have attracted attention due to the growing awareness of environmental issues. The solar cell module constituting the solar cell includes a solar cell element, and this solar cell element plays a role of converting light energy such as sunlight into electric energy.

  Solar cell elements are often manufactured using a single crystal silicon substrate or a polycrystalline silicon substrate. For this reason, the solar cell element is vulnerable to physical impact, and when the solar cell module is mounted outdoors, it is necessary to protect it from rain or the like. Moreover, since the electrical output generated by one solar cell element is small, it is necessary to connect a plurality of solar cell elements in series and parallel so that a practical electrical output can be taken out. For this reason, a solar cell module is usually manufactured by connecting a plurality of solar cell elements and enclosing them with a transparent substrate and a sealing material sheet. Generally, a solar cell module is manufactured by a lamination method or the like in which a transparent front substrate, a sealing material sheet, a solar cell element, a sealing material sheet, a back surface protection sheet, and the like are sequentially laminated, and these are vacuum-sucked and heat-pressed. .

  As a sealing material sheet used for a solar cell module, ethylene-vinyl acetate copolymer resin (EVA) is most commonly used from the viewpoints of workability, workability, manufacturing cost, etc. ing. However, EVA resin has a tendency to gradually decompose with long-term use, and deteriorates inside the solar cell module to decrease its strength or generate acetic acid gas that affects the solar cell element. there is a possibility. For this reason, the sealing material sheet for solar cell modules which uses polyolefin-type resin, such as polyethylene, instead of EVA resin is proposed.

  For example, in Patent Document 1, due to the presence of a predetermined amount of a crosslinking agent in the composition, the MFR of the encapsulant sheet after film formation is lower than that of the raw material polyethylene, thereby being excellent in heat resistance while being transparent. An encapsulant sheet is disclosed.

WO2011 / 152314 International Publication Pamphlet

  However, since the improvement in transparency directly affects the power generation efficiency of the solar cell module, it has been desired to further improve the transparency while imparting heat resistance to the polyethylene resin sealing material sheet.

  The present invention has been made in view of the above circumstances, and can further improve transparency while having heat resistance suitable for a sealing material sheet for a solar cell module while using a polyethylene-based resin. It is an object to provide a sealing material sheet and a manufacturing method thereof.

  The present inventors have pointed out that the use environment temperature of the solar cell module reaches 50 ° C. to 70 ° C. or more and the cause of the decrease in transparency of the polyethylene resin is that the polyethylene resin is a crystalline resin in the first place. We focused on the point that crystallinity is the origin of the decrease in transparency. That is, it is possible to greatly improve transparency by melting part or all of the crystals in a high temperature environment at the time of use.

  However, on the other hand, since it is also necessary to ensure the heat resistance in the solar cell module, a less amount of a crosslinking agent (polymerization initiator) than the conventional general crosslinking treatment is added to the polyethylene resin composition. By adding, a state in which the molecular weight is increased by weakening the degree of crosslinking (hereinafter also referred to as so-called weak crosslinking) is formed, and in this state, transparency is improved by crystal melting, thereby improving heat resistance and transparency. It has been found that transparency can be obtained, which can be achieved at the same time, and cannot be obtained with conventional polyethylene resins, and the present invention has been completed. More specifically, the present invention provides the following.

(1) A low melting point layer containing 70 mass% or more of a polyethylene resin having a melting point of 50 ° C or higher and 70 ° C or lower,
The low-melting-point layer is sealed for a single-layer or multi-layer solar cell module having an MFR at 190 ° C. and a load of 2.16 kg measured according to JIS K7210 of 0.1 g / 10 min or more and less than 1.0 g / 10 min. Material sheet.

(2) The encapsulant sheet according to (1), wherein the density of the polyethylene resin is 0.900 g / cm ³ or less.

  (3) The sealing material sheet according to (1) or (2), wherein the gel fraction is 25% or less.

  (4) The encapsulant sheet according to any one of (1) to (3), wherein the weight average molecular weight in terms of polystyrene is 120,000 to 300,000.

  (5) A solar cell module using the encapsulant sheet according to any one of (1) to (4).

  (6) In the composition, a resin composition containing 70 mass% or more of a polyethylene resin having a melting point of 50 ° C. or more and 70 ° C. or less, and 0.02 mass% or more and less than 0.5 mass% of a crosslinking agent is contained at 100 ° C. The manufacturing method of the sealing material sheet for solar cell modules melt-molded by the film-forming temperature below 250 degreeC above.

  ADVANTAGE OF THE INVENTION According to this invention, the sealing for solar cell modules which can provide further favorable transparency and a softness | flexibility, being equipped with the heat resistance suitable for the sealing material sheet for solar cell modules, using a polyethylene-type resin. A stopping material sheet and a manufacturing method thereof can be provided.

It is sectional drawing which shows an example of the laminated constitution of the solar cell module of this invention. It is a schematic diagram which shows an example of the PID test apparatus in evaluation of an Example.

<Sealing material sheet composition>
The encapsulant sheet composition for producing the encapsulant sheet for the solar cell module of the present invention comprises 70% by mass or more of a polyethylene resin having a melting point of 50 ° C. or more and 70 ° C. or less in the composition, and a crosslinking agent. 0.02 mass% or more and less than 0.5 mass%. And the layer which formed this composition into a film comprises the low melting point layer in this invention, and the sealing material sheet of this invention is a single layer sheet which consists of a low melting point layer, or the multilayer sheet | seat containing a low melting point layer It is.

[Polyethylene resin]
In the present invention, a polyethylene resin having a melting point of 50 ° C. or higher and 70 ° C. or lower is used as the base resin. Preferably it is 60 degrees C or less, More preferably, it is 55 degrees C or less. The melting point can be measured by a conventionally known DSC method. The polyethylene resin is preferably low density polyethylene (LDPE), more preferably linear low density polyethylene (LLDPE). When the melting point is less than 50 ° C., the heat resistance becomes insufficient, and when the melting point exceeds 70 ° C., the crystallinity deterioration when used as a solar cell module is insufficient, and the transparency is not improved.

Preferably a density of 0.900 g / cm ³ or less of low density or polyethylene (LDPE), more preferably a density of use 0.900 g / cm ³ or less linear low density polyethylene (LLDPE). The linear low density polyethylene is a copolymer of ethylene and α-olefin, and in the present invention, the density is 0.900 g / cm ³ or less, preferably 0.870 to 0.890 g / cm ³ . is there. If it is this range, favorable transparency and heat resistance 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 distribution of comonomer. For this reason, molecular weight distribution is narrow and it is possible to make it the above ultra-low density. 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 sheet for solar cell modules which consists of a sealing material sheet 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 α-olefin has 6 to 8 carbon atoms, the solar cell module sealing material sheet can be provided with good flexibility and good strength. As a result, the adhesiveness between the solar cell module sealing material sheet and the base material is increased, and the intrusion of moisture between the solar cell module sealing material sheet and the base material can be suppressed.

  The melt mass flow rate (MFR) of the polyethylene resin is preferably 1.0 g / 10 min or more and 40 g / 10 min or less at 190 ° C. and a load of 2.16 kg, preferably 2 g / 10 min or more and 40 g / 10 min or less. More preferably it is. When the MFR is in the above range, the processability during film formation is excellent.

Unless otherwise specified, MFR in the present specification is a value obtained by the following method.
MFR (g / 10 min): Measured according to JIS K7210. Specifically, the synthetic resin was heated and pressurized at 190 ° C. in a cylindrical container heated by a heater, and the amount of resin extruded per 10 minutes from an opening (nozzle) provided at the bottom of the container was measured. . The test machine used was an extrusion plastometer, and the extrusion load was 2.16 kg.

  The “polyethylene resin” in the present invention includes not only ordinary polyethylene obtained by polymerizing ethylene, but also a resin obtained by polymerizing a compound having an ethylenically unsaturated bond such as α-olefin. Examples include resins obtained by copolymerizing a plurality of different compounds having an ethylenically unsaturated bond, and modified resins obtained by grafting different chemical species to these resins.

  Among these, a silane copolymer obtained by copolymerizing at least an α-olefin and an ethylenically unsaturated silane compound as a comonomer can be preferably used. By using such a resin, adhesion between a member such as a transparent front substrate or a solar cell element and the solar cell module sealing material sheet can be obtained.

  The silane copolymer is described in, for example, JP-A-2003-46105. By using the copolymer as a component of the solar cell module sealing material sheet composition, it is excellent in strength, durability, etc., and weather resistance, heat resistance, water resistance, light resistance, wind pressure resistance, yield resistance In addition, it has excellent heat fusion properties without being affected by manufacturing conditions such as thermocompression bonding for manufacturing solar cell modules, and is stable, low cost, and various. A solar cell module suitable for the application can be manufactured.

  The silane copolymer is a copolymer obtained by copolymerizing at least an α-olefin and an ethylenically unsaturated silane compound as a comonomer and, if necessary, further using another unsaturated monomer as a comonomer. The modified product or condensate is also included.

Specifically, for example, one or more of α-olefins, one or more of ethylenically unsaturated silane compounds, and, if necessary, one or more of other unsaturated monomers. Using a desired reaction vessel, for example, pressure 500-4000 Kg / cm ² position, preferably, 1000-4000 Kg / cm ² position, temperature 100-400 ° C., preferably 150-350 ° C. In the presence of a radical polymerization initiator and, if necessary, a chain transfer agent, random copolymerization is performed simultaneously or stepwise, and if necessary, a random copolymer formed by the copolymerization is formed. A silane compound portion can be modified or condensed to produce a copolymer of an α-olefin and an ethylenically unsaturated silane compound, or a modified or condensed product thereof.

  Examples of the copolymer of an α-olefin and an ethylenically unsaturated silane compound or a modified or condensed product thereof include, for example, one or more α-olefins and, if necessary, other unsaturated monomers. One or two or more kinds are polymerized simultaneously or stepwise in the presence of a radical polymerization initiator and, if necessary, a chain transfer agent, using a desired reaction vessel, and then the polymerization. 1 to 2 or more types of ethylenically unsaturated silane compounds are graft-copolymerized to the polyolefin-based polymer produced by the above, and further, if necessary, a graft copolymer produced by the copolymer is constituted. A silane compound portion can be modified or condensed to produce a copolymer of an α-olefin and an ethylenically unsaturated silane compound or a modified or condensed product thereof. That.

  Examples of the α-olefin include ethylene, propylene, 1-butene, isobutylene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 1-heptene, 1-octene, One or more selected from 1-nonene and 1-decene can be used.

  Examples of the ethylenically unsaturated silane compound include vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tripropoxy silane, vinyl triisopropoxy silane, vinyl tributoxy silane, vinyl tripentyloxy silane, vinyl triphenoxy silane, vinyl tri One or more selected from benzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane can be used.

  As the other unsaturated monomer, for example, one or more selected from vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, and vinyl alcohol can be used.

  Examples of radical polymerization initiators include organic peroxides such as lauroyl peroxide, dipropionyl peroxide, benzoyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, and t-butyl peroxyisobutyrate. Products, molecular oxygen, azo compounds such as azobisisobutyronitrile azoisobutylvaleronitrile, and the like can be used.

  Examples of the chain transfer agent include paraffinic hydrocarbons such as methane, ethane, propane, butane and pentane, α-olefins such as propylene, 1-butene and 1-hexene, and aldehydes such as formaldehyde, acetaldehyde and n-butyraldehyde. Further, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, aromatic hydrocarbons, chlorinated hydrocarbons, and the like can be used.

  Examples of the method of modifying or condensing the silane compound portion constituting the random copolymer, or the method of modifying or condensing the silane compound portion constituting the graft copolymer include, for example, tin, zinc, iron, lead, Using α-olefin and ethylenically unsaturated silane using metal carboxylate such as cobalt, organometallic compound such as titanate and chelate, organic base, inorganic acid, silanol condensation catalyst such as organic acid, etc. Modification of copolymer of α-olefin and ethylenically unsaturated silane compound by performing dehydration condensation reaction between silanols of the silane compound part constituting the random copolymer or graft copolymer with the compound The method of manufacturing a condensate is mentioned.

  As the silane copolymer, any of a random copolymer, an alternating copolymer, a block copolymer, and a graft copolymer can be preferably used. However, the silane copolymer is more preferably a graft copolymer. A graft copolymer obtained by polymerizing polyethylene for polymerization as a main chain and an ethylenically unsaturated silane compound as a side chain is more preferable. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to adhesive strength, it can improve the adhesion of the solar cell module sealing material sheet to other members in the solar cell module. .

  The content of the ethylenically unsaturated silane compound when constituting the copolymer of the α-olefin and the ethylenically unsaturated silane compound is, for example, about 0.001 to 15% by mass relative to the total copolymer mass. Preferably, about 0.01 to 5 mass%, particularly preferably about 0.05 to 2 mass% is desirable. In the present invention, when the content of the ethylenically unsaturated silane compound constituting the copolymer of the α-olefin and the ethylenically unsaturated silane compound is large, the mechanical strength and heat resistance are excellent, but the content is excessive. When it becomes, it exists in the tendency which is inferior to tensile elongation, heat-fusibility, etc.

  The content of the polyethylene resin having a melting point of 50 ° C. or higher and 70 ° C. or lower contained in the encapsulant sheet composition may be 70% by mass or more, preferably 80% by mass in the encapsulant sheet composition. Above, more preferably 90% or more. That is, other resins may be included within the range. As other resin, for example, it may be used as an additive resin, and it can be used to make other components described later as a master batch.

[Crosslinking agent]
In the present invention, the content of the crosslinking agent with respect to the encapsulant sheet composition for solar cell modules is different from the case where the conventional crosslinking treatment of the encapsulant sheet composition for solar cell modules is performed. The crosslinking agent is used so that the content in a specific range is smaller than that in the case of general crosslinking treatment. Content of a crosslinking agent is 0.02 mass% or more and less than 0.5 mass% in the sealing material sheet composition for solar cell modules, Preferably an upper limit is 0.2 mass% or less, More preferably, it is 0.00. 1% by mass or less. If it is less than this range, the weak crosslinking of the polyethylene resin does not proceed and the heat resistance is insufficient. Moreover, when this range is exceeded, film forming property will fall, for example, gel will generate | occur | produce during shaping | molding, and transparency will also fall.

  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 t-- Tylhexanoate, t-butyl peroxypivalate, t-butyl peroxyoctoate, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, di-t-butyl peroxyphthalate, 2,5-dimethyl Peroxyesters such as -2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexyne-3, t-butylperoxy-2-ethylhexyl carbonate; Ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; organic peroxides such as t-amyl-peroxy-2-ethylhexyl carbonate, peroxycarbonates such as t-butylperoxy 2-ethylhexyl carbonate, or Azo Examples include azo compounds such as sisobutyronitrile and azobis (2,4-dimethylvaleronitrile), silanol condensation catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dioctate, dioctyltin dilaurate, and dicumyl peroxide. Can do.

  Of the above, t-butylperoxy 2-ethylhexyl carbonate, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, and the like can be preferably used. These are preferable because the amount of active oxygen is as high as 5% or more, and the 1-minute half-life temperature of the crosslinking agent is 160 to 190 ° C., which is consumed at the time of molding and remains after molding to suppress the progress of excess post-crosslinking. . A one-minute half-life temperature of less than 160 ° C. is not preferable because it is difficult to allow the crosslinking reaction to proceed after sufficiently dispersing the crosslinking agent during molding.

[Crosslinking aid]
In the present invention, the crosslinking aid is an optional component. Here, the crosslinking assistant is, for example, a polyfunctional vinyl monomer and / or a polyfunctional epoxy monomer, and specifically, triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fuma. Polyallyl compounds such as rate and diallyl maleate, trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA), ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6 -Poly (meth) acryloxy compounds such as hexanediol diacrylate and 1,9-nonanediol diacrylate, glycidyl methacrylate containing double bond and epoxy group, 4-hydroxybutyl acrylate glycol Epoxy compounds such as 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexane dimethanol diglycidyl ether, trimethylolpropane polyglycidyl ether and the like containing two or more diyl ethers and epoxy groups Can be mentioned.

[Other ingredients]
The sealing material sheet composition can further contain other components. For example, components such as a weather resistance masterbatch for imparting weather resistance, various fillers, a light stabilizer, an ultraviolet absorber, and a heat stabilizer are exemplified. These contents vary depending on the particle shape, density, and the like, but are preferably in the range of 0.001 to 5 mass% in the encapsulant sheet 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 sheet composition.

  A weather-resistant 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 this is added to the encapsulant sheet 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, as other components used in the solar cell module sealing material sheet composition of the present invention, in addition to the above, an adhesion improver such as a silane coupling agent, a nucleating agent, a dispersing agent, a leveling agent, a plasticizer, Examples include an antifoaming agent and a flame retardant.

<Sealing material sheet>

  The encapsulant sheet for the solar cell module is obtained by subjecting the above encapsulant sheet composition to the above-described weak crosslinking treatment during molding in the process of molding by a conventionally known method, It is a single layer or multilayer sheet or film. In addition, the sheet form in this invention means the film form, and there is no difference in both.

  The sealing material sheet is formed into a sheet 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, as an example of the sheet forming method when the encapsulant sheet is a multilayer film, a method of forming by co-extrusion using two or more types of melt-kneading extruders can be given. However, in any method, in order to promote a weak crosslinking reaction during molding, it is preferable that the film forming temperature is the melting point of the polyethylene resin + 50 ° C. or more. Specifically, the temperature is preferably 100 to 250 ° C., more preferably 190 to 230 ° C. As described above, in the present invention, since the addition of the crosslinking agent is small, the MFR is reduced, but the degree of the reduction is small. For this reason, weak crosslinking can be advanced during melt molding. And even if it is a small amount of crosslinking agents and there is substantially no crosslinking aid, the weak crosslinking of the polyethylene resin proceeds. Since the molding temperature is equal to or higher than the 1 minute half-life temperature of the crosslinking agent, the crosslinking agent hardly remains after molding. For this reason, the weak crosslinking ends at this molding stage.

The solar cell module encapsulant sheet of the present invention that has been weakly cross-linked in this way has, from the standpoint of its physical properties, i) maintained low density and ii) improved heat resistance but sufficient production. It has the characteristic of having film properties. Regarding i), the density of the solar cell module encapsulant sheet of the present invention does not increase at about 0.900 g / cm ³ or less, which is almost equal to the density of the low-density polyethylene resin that is the main raw material, and is melt-molded. The density difference between the resin composition before and after is 0.05 g / cm ^{3 or} less. For this reason, transparency is maintained.

  On the other hand, ii) the heat resistance is such that the MFR is 0.1 g / 10 min or more and less than 1.0 g / 10 min, and preferably the MFR difference of the resin composition before and after melt molding is 1.0 g / 10 min or more and 10.0 g / 10 min. Since it is the following, heat resistance is improving though it is in the range of MFR which can be fabricated. This is the effect of the weak crosslinking treatment in the present invention. Normally, there is a positive correlation between the MFR and the density of the resin. In the present invention, the MFR can be slightly increased within the range of the moldable MFR without changing the density.

In addition, the result of said weak bridge | crosslinking process can be understood also from the gel fraction. The gel fraction of the sealing material sheet of the present invention is 25% or less, preferably 10% or less, more preferably 1% or less including zero. In particular, by setting the content to 10% or less, it is possible to effectively prevent gel generation during film formation and improve the film formability. Furthermore, by setting it to 1% or less, the embedding property of the encapsulant sheet in the modularization process, that is, the unevenness followability can be improved. In addition, the gel fraction here is a value obtained by the following method.
Gel fraction (%): After crosslinking, 1 g of the sealing material sheet is weighed and put into an 80 mesh wire mesh bag. Next, a sample with the wire mesh is put into a Soxhlet extractor, and xylene is refluxed at the boiling point. After 10 hours of continuous extraction, the sample was taken out together with the wire mesh, weighed after drying, and compared with the mass before and after extraction to measure the mass% of the remaining insoluble matter, which was taken as the gel fraction. In addition, about the gel fraction of the sealing material sheet | seat which is a multilayer film, the said process is performed with the multilayer state in which all the layers were laminated | stacked, and the obtained measured value is the said multilayer sealing material sheet. The gel fraction was used.

  As another aspect, the weak crosslinking treatment can be confirmed from the viewpoint of molecular weight. The polystyrene equivalent weight average molecular weight of the encapsulant sheet of the present invention is 120,000 to 300,000, and the ratio of the weight average molecular weight of the encapsulant sheet after weak crosslinking / the polyethylene resin before crosslinking is 1.5 or more. The range is 3.0 or less. From this, it can be understood that although it is made into a macromolecule, a dense cross-linked structure is not formed and a weak cross-link is formed. In addition, the weight average molecular weight in this invention melt | dissolves so that it may become 6 wt% of xylene, a viscosity is measured, and the weight average molecular weight is calculated | required from conversion with the polystyrene sample from the viscosity. As for the molecular weight of the encapsulant sheet, which is a multilayer film, the above-mentioned treatment was carried out with all the layers being laminated, and the obtained measurement value was determined based on the gel content of the multilayer encapsulant sheet. Rate.

  In the sealing material sheet which is a multilayer film, it is more preferable to set it as the sealing material sheet from which MFR for every layer differs. As will be described later, in the solar cell module, the sealing material sheet is generally used with one surface being in close contact with the electrode surface of the solar cell element. In that case, the encapsulant sheet is required to have high adhesion regardless of the unevenness of the electrode surface. Even when the encapsulant sheet of the present invention is a single-layer encapsulant sheet, the encapsulant sheet has preferable transparency, flexibility and heat resistance, but the surface which is in close contact with the electrode surface of the solar cell element. Furthermore, it is more preferable that such molding characteristics are excellent. The encapsulant sheet of the present invention, which is a multilayer film having a different MFR for each layer, can be used as an encapsulant sheet by arranging a layer having a high MFR in close contact with the electrode surface of the solar cell element and using it on the outermost layer. While maintaining the above-described preferable transparency and heat resistance, it is possible to further improve the molding characteristics on the contact surface with the solar cell element.

  For example, in the encapsulant sheet which is a multilayer film composed of three or more layers, the thickness of the outermost layer is 30 μm or more and 120 μm or less, and the intermediate layer and the outermost layer composed of all layers other than the outermost layer The thickness ratio is preferably in the range of outermost layer: intermediate layer: outermost layer = 1: 3: 1 to 1: 8: 1. By doing in this way, the preferable heat resistance as a sealing material sheet can be hold | maintained, the preferable molding characteristic in an outermost layer can be provided, and also manufacturing cost can be suppressed low.

<Solar cell module>
Next, an example of the solar cell module of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of the layer structure of the solar cell module of the present invention. In the solar cell module 1 of the present invention, the transparent front substrate 2, the front sealing material sheet layer 3, the solar cell element 4, the back sealing material sheet layer 5, and the back surface protection sheet 6 are sequentially arranged from the incident light receiving surface side. Are stacked. The solar cell module 1 of the present invention uses the encapsulant sheet of the present invention for at least the front encapsulant sheet layer 3.

  In the solar cell module 1, for example, the transparent front substrate 2, the front sealing material sheet layer 3, the solar cell element 4, the back sealing material sheet layer 5, and the back surface protection sheet 6 are sequentially laminated. It can be manufactured by integration by vacuum suction or the like, and then thermocompression-molding the above-mentioned member as an integral molded body by a molding method such as a lamination method.

  Moreover, the solar cell module 1 is formed on the front sealing material sheet layer 3 on each of the front surface side and the back surface side of the solar cell element 4 by a molding method usually used in a normal thermoplastic resin, for example, T-die extrusion molding. The back sealing material sheet layer 5 is melt-laminated to sandwich the solar cell element 4 with the front sealing material sheet layer 3 and the back sealing material sheet layer 5, and then the transparent front substrate 2 and the back surface protection sheet 6 are bonded. They may be manufactured by a method of sequentially laminating them and then integrating them by vacuum suction or the like and heat-pressing them.

  The solar cell module 1 of the present invention uses the encapsulant sheet of the present invention for at least the front encapsulant sheet layer 3. Thereby, when the temperature is 50 ° C. or higher, preferably 70 ° C. or higher depending on the high temperature environment during use, the crystalline portion of polyethylene is melted and the crystallinity is lowered, thereby improving the transparency. This can be confirmed by haze measurement at 70 ° C. in the Examples. As a haze value at 70 ° C., a thickness of about 600 μm 2% is obtained, which is the same transparency as EVA.

  Here, since the sealing material sheet of the present invention has a low MFR in the range of 0.1 g to 2 g due to the weak crosslinking effect as described above, the viscosity is high, the fluidity is suppressed, and the heat resistance is reduced. Are better. For this reason, even if it becomes the temperature more than melting | fusing point of base resin, it does not flow, but heat resistance and transparency are compatible.

  It should be noted that the sealing material sheet of the present invention crystallizes at low temperatures and decreases in transparency, and the haze rises and falls repeatedly, which is a sealing that improves transparency only at the time of high temperature use during power generation. It is a stopping material sheet. Thus, the concept of changing the transparency according to the temperature is not present in the conventional sealing material sheet, and the sealing material sheet of the present invention is novel in this respect.

  In the solar cell module 1 of the present invention, the back sealing material sheet layer 5, 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 sheet layer 3 are conventionally known. The material can be used without any 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 | seat 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.

[Test Example 1]
<Sealing material sheet composition raw material>
The following raw materials were used as the sealing material sheet composition raw material.
Base resin 1: M-LLDPE pellets having a melting point of 60 ° C., a density of 0.880 g / cm ³ , and an MFR at 190 ° C. of 3.1 g / 10 min were used.
Base resin 2: M-LLDPE pellets having a melting point of 55 ° C., a density of 0.870 g / cm ³ , and an MFR at 190 ° C. of 3.5 g / 10 min were used.
Base resin 3: M-LLDPE pellets having a melting point of 93 ° C., a density of 0.903 g / cm ³ , and an MFR at 190 ° C. of 2.6 g / 10 min were used.
Base resin 4: M-LLDPE pellets having a melting point of 97 ° C., a density of 0.905 g / cm ³ , and an MFR at 190 ° C. of 3.7 g / 10 min were used.
Silane modified transparent resin: with respect to 98 parts by mass of metallocene linear low density polyethylene (M-LLDPE) having a melting point of 60 ° C., a density of 0.881 g / cm ³ and an MFR at 190 ° C. of 2 g / 10 min. 2 parts by mass of vinyltrimethoxysilane and 0.1 part by mass of dicumyl peroxide as a radical generator (reaction catalyst) were mixed, melted and kneaded at 200 ° C. to obtain a silane-modified transparent resin.
Crosslinking agent master batch: Melting point of 60 ° C., density of 0.880 g / cm ³ , MFR at 190 ° C. of 3.1 g / 10 min. A master batch was obtained by impregnating 0.5 parts by mass of 2,5-di (t-butylperoxy) hexane.
Weatherproof masterbatch: 3.8 parts by mass of benzophenol UV absorber and hindered amine light stabilizer 5 with respect to 100 parts by mass of powder obtained by pulverizing Ziegler linear low density polyethylene having a density of 0.880 g / cm ³ Mass parts and 0.5 parts by mass of a phosphorous heat stabilizer were mixed, melted, processed, and pelletized to obtain a master batch.

<Sealing material sheet composition>
Example 1: 70 parts by mass of base resin 1 (melting point: 60 ° C.), 20 parts by mass of a silane-modified transparent resin, 10 parts by mass of a crosslinking agent masterbatch, and 5 parts by mass of a weathering masterbatch were used. It was a thing.
Example 2: 70 parts by mass of base resin 2 (melting point 55 ° C.), 20 parts by mass of a silane-modified transparent resin, 10 parts by mass of a crosslinking agent masterbatch, and 5 parts by mass of a weather resistant masterbatch were used. It was a thing.
Comparative Example 1: 80 parts by mass of base resin 1 (melting point: 60 ° C.), 20 parts by mass of silane-modified transparent resin, and 5 parts by mass of weatherproof masterbatch were used as the sealing material sheet composition of Comparative Example 1.
Comparative Example 2: 80 parts by mass of the base resin 2 (melting point 55 ° C.), 20 parts by mass of the silane-modified transparent resin, and 5 parts by mass of the weather resistant master batch were used as the sealing material sheet composition of Comparative Example 2.
Comparative Example 3: With respect to 100 parts by mass of EVA having a melting mass flow rate of 15 g / 10 min at melting points of 70 ° C. and 190 ° C., 0.38 parts by mass of a benzophenol ultraviolet absorber and 0.5 parts by mass of a hindered amine light stabilizer And 0.05 parts by mass of a phosphorus-based heat stabilizer, 1.5 parts by mass of a crosslinking agent 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, and a crosslinking aid trimethallyl isocyanurate 0.5 mass part was mixed and it was set as the sealing material sheet composition of the comparative example 3.
Comparative Example 4: 80 parts by mass of base resin 1 (melting point: 93 ° C.), 20 parts by mass of silane-modified transparent resin, and 5 parts by mass of weather resistant masterbatch were used as the sealing material sheet composition of Comparative Example 4.
Comparative Example 5: 80 parts by mass of the base resin 2 (melting point 97 ° C.), 20 parts by mass of the silane-modified transparent resin, and 5 parts by mass of the weather resistant masterbatch were used as the sealing material sheet composition of Comparative Example 5.

<Manufacture of sealing material sheet>
Using the above composition, a single layer φ30 mm extruder, a film forming machine having a 200 mm width T die, an extrusion temperature (film formation temperature) of 210 ° C., a take-off speed of 1.1 m / min, and a single layer of 600 μm The sealing material sheet of an example and a comparative example was formed into a film. In addition, EVA of the comparative example 3 was made into extrusion temperature 90 degreeC.

<Evaluation example>
The results of the following evaluations on the sealing material sheets of Examples and Comparative Examples produced by the above methods are summarized in Table 1.

  Haze: About 600 μm of the sealing material sheets of Examples and Comparative Examples, after preparing a test piece of a single film without embossing or the like, according to JISK7136, 25 at Murakami Color Research Laboratory Haze / Transmissivity HM150 Each haze (%) at 70 ° C. was measured.

  Initial power generation efficiency: sandwiching a solar cell element made of polycrystalline silicon between a glass plate (transparent front substrate) having a thickness of 33 mm and the two sealing materials for a solar cell module having a thickness of 600 μm, and a back for a solar cell module Sheets were laminated in this order, and the solar cell element surface was faced up, and pressure-bonded at 150 ° C. for 15 minutes with a vacuum laminator for production of the solar cell module to produce a solar cell module. The end of the laminated module was sealed with foamed rubber (acrylic foam). Moreover, when measuring the power generation efficiency, it was installed outdoors at an inclination of 45 ° C facing south, and the power generation efficiency was evaluated by measuring the amount of power generation per day. The power generation efficiency is a relative value when the EVA of Comparative Example 3 is 100%.

  PID test: Using an apparatus as shown in FIG. 2, after taking an EL emission of each of the above solar cell modules and setting it to an initial state, a voltage of 1000 V was applied in an environment of temperature 60 ° C. and humidity 100%, After 36 hours, EL light emission was photographed again, and the appearance with the initial state was compared to evaluate the degree of deterioration.

  Heat resistance test: Two pieces of the solar cell module sealing materials of the above examples and comparative examples cut into a size of 75 mm × 50 mm on a semi-tempered glass of 250 mm square, the back surface for a solar cell module of 75 mm × 50 mm After laminating one protective sheet in order, the laminate was pressure-bonded at 150 ° C. for 15 minutes with a vacuum laminator for manufacturing a solar cell module, and the laminate sample was tilted at 45 degrees and left in an oven at 120 ° C. for 12 hours. The heat resistance was evaluated with the distance of the semi-tempered glass shifted.

  From the results of Table 1, the sealing material sheet of the present invention has improved transparency at high temperatures when the solar cell module is used, has both heat resistance and transparency, and is superior in PID characteristics. It can be understood that.

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

Claims (6)

A low melting point layer containing 70 mass% or more of a polyethylene resin having a melting point of 50 ° C or higher and 70 ° C or lower;
The low-melting-point layer is sealed for a single-layer or multi-layer solar cell module having an MFR at 190 ° C. and a load of 2.16 kg measured according to JIS K7210 of 0.1 g / 10 min or more and less than 1.0 g / 10 min. Material sheet. The encapsulant sheet according to claim 1, wherein the density of the polyethylene resin is 0.900 g / cm ³ or less.   The encapsulant sheet according to claim 1 or 2, wherein the gel fraction is 25% or less.   The encapsulant sheet according to any one of claims 1 to 3, which has a polystyrene-equivalent weight average molecular weight of 120,000 to 300,000.   The solar cell module using the sealing material sheet in any one of Claim 1 to 4.   In the composition, a polyethylene resin having a melting point of 50 ° C. or more and 70 ° C. or less is 70% by mass or more, a crosslinking agent is 0.02% by mass or more and less than 0.5% by mass, and a resin composition containing 100 ° C. or more and 250 or less The manufacturing method of the sealing material sheet | seat for solar cell modules melt-molded by the film-forming temperature of.

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