JP2014086489A - Method of producing sealing material sheet for solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a polyethylene sealing material sheet for solar cell module having excellent transparency.SOLUTION: In a method of producing a sealing material sheet for solar cell module by depositing a sealing material composition containing low density polyethylene of 0.900 g/cmor less, and then cross-linking by irradiation with ionization radiation, the haze value in the sheet before irradiation with ionization radiation is 3% or less for the thickness of 400 μm. In order to attain such a low haze value or low crystallinity, polyethylene having MFR of 20.0-40.0 g/10 min may be deposited at a deposition temperature of 120°C or less, or quenching may be performed immediately after deposition.

Description

  The present invention relates to a method for producing a sealing material sheet for a polyethylene-based solar cell module, and more particularly to a sealing material sheet that has been subjected to crosslinking treatment with ionizing radiation such as an electron beam.

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

  In this regard, in Patent Document 1 below, linear low density polyethylene having a predetermined density or less is crosslinked by irradiating with ionizing radiation, omitting a long-time heat curing step without using an organic peroxide, and having heat resistance. A technique for imparting is disclosed.

JP 2011-77357 A

  Although the crosslinking treatment by irradiation with ionizing radiation is effective for improving the heat resistance, there is no great effect from the viewpoint of improving the transparency, and the transparency before the crosslinking treatment is reflected almost as it is. In particular, since a normal polyethylene-based resin is crystallized at the time of cooling the melt film formation, a significant improvement in transparency cannot be expected even if it is crosslinked after irradiation with ionizing radiation.

  The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a polyethylene-based sealing material sheet that is improved in heat resistance by irradiation with ionizing radiation and at the same time has excellent transparency. There is.

  The present inventors pay attention to the crystallinity control of polyethylene resin before irradiation with ionizing radiation, create a low crystallinity polyethylene resin sheet state, and perform electron beam irradiation in this transparent sheet state to be transparent. As a result, the present invention has been completed. More specifically, the present invention provides the following.

(1) A method for producing a sealing material sheet for a solar cell module, in which a sealing material composition containing a low density polyethylene having a density of 0.900 g / cm ³ or less is formed and then irradiated with ionizing radiation for crosslinking treatment. Because
The manufacturing method of the sealing material sheet whose haze value in the sheet | seat after the said film formation and before ionizing radiation irradiation is 3.0% or less with a thickness of 400 micrometers.

  (2) The low-density polyethylene has an MFR of 190 ° C. and a load of 2.16 kg measured in accordance with JIS K6922-2 of 20.0 g / 10 min or more and 40.0 g / 10 min or less. The manufacturing method of the sealing material sheet as described in (1) which is 120 degrees C or less.

  (3) The method for producing a sealing material sheet according to (1), wherein a rapid cooling process is performed immediately after the film formation.

  According to the production method and the present invention, it is possible to achieve both heat resistance and transparency required for a sealing material sheet for a solar cell module.

It is sectional drawing which shows typically an example of the laminated constitution of the solar cell module using the sealing material sheet of this invention.

  Hereinafter, the encapsulant composition according to the present invention (hereinafter also simply referred to as the encapsulant composition), the encapsulant sheet for the solar cell module of the present invention (hereinafter also simply referred to as the encapsulant sheet), and the A solar cell module using a sealing material sheet will be described.

<Encapsulant composition>
An example of the sealing material composition used in the present invention has a density of 0.900 g / cm ³ or less and an MFR of 20.0 g / 10 min at 190 ° C. and a load of 2.16 kg measured according to JIS K6922-2. The low density polyethylene which is 40.0 g / 10 min or less is contained as an essential component. Hereinafter, after describing the essential components, other resins and other components will be described.

[Low density polyethylene]
In the present invention, low density polyethylene (LDPE) having a density of 0.900 g / cm ³ or less, preferably linear low density polyethylene (LLDPE) is used. Linear low density polyethylene is a copolymer of ethylene and α- olefin, in the present invention, within the scope thereof density of 0.900 g / cm ³ or less, preferably 0.890 g / cm ³ within the following ranges , more preferably from 0.870 g / cm ³ or more 0.885 g / cm ³ or less. 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 can give a softness | flexibility with respect to a sealing material. As a result of the flexibility, the adhesion between the sealing material and the substrate, such as the adhesion between the sealing material and the transparent front substrate and the adhesion between the sealing material and the back surface protective sheet, is increased.

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

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

  The MFR of the low density polyethylene used in the production method of the present invention is 20.0 g / 10 min or more and 40.0 g / 10 min or less. Moreover, it is more preferable that they are 25.0 g / 10min or more and 35g / 10min or less. In the production method of the present invention, it is essential to perform a crosslinking treatment by irradiation with ionizing radiation after molding the encapsulant composition, and to add a predetermined amount of a crosslinking aid to the encapsulant composition. According to the present invention, it is characterized in that it is a production method that can produce a sealing material sheet having physical properties that are superior to or higher than those of conventional materials using a polyethylene resin having a high MFR that has not been used as a material resin. .

  In the method for producing a sealing material sheet of the present invention, a sealing material composition containing a predetermined amount of a crosslinking aid as an essential component is melt-formed without a crosslinking reaction, and an uncrosslinked gel fraction of 0% is obtained. After the sealing material sheet is formed, a crosslinking treatment is performed by irradiation with ionizing radiation to obtain a crosslinked sealing material sheet. When cross-linking treatment is performed by irradiation with ionizing radiation, fluidity at the time of modularization can be suppressed by cross-linking treatment by irradiation with ionizing radiation after film formation. Therefore, a low-density polyethylene resin having a high MFR to some extent may be selected as a base resin. it can. In general, when crosslinking treatment is performed by irradiation with ionizing radiation, specifically, as described above, a low density polyethylene resin having an MFR of less than 5.0 g / 10 min is used as a base in order to balance workability and heat resistance. It was used as a preferable resin.

  In this specification, the gel fraction (%) refers to 0.1 g of a sealing material sheet placed in a resin mesh, extracted with 60 ° C. toluene for 4 hours, then taken out together with the resin mesh, weighed after drying, Mass comparison before and after extraction is performed to measure the mass% of the remaining insoluble matter, and this is used as the gel fraction. A gel fraction of 0% means that the residual insoluble matter is substantially 0 and that 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.

  Further, in the method for producing a sealing material sheet of the present invention, the cross-linking treatment by ionizing radiation and the cross-linking aid in a predetermined amount range as an essential constituent component of the sealing material composition are suitable for processing. And a balance of heat resistance are realized in a combination of manufacturing conditions different from the conventional one. For this reason, conventionally, even if the MFR was not used as a resin for a thermoplastic encapsulant composition, it is preferably used as a base resin even if it is a high MFR resin of 20.0 g / 10 min or more. Can do. Thereby, the manufacturing cost of the sealing material sheet can be suppressed while providing desired physical properties.

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

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

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

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

The content of polyethylene having a density of 0.900 g / cm ³ or less contained in the encapsulant composition is preferably 10 or more and 100 with respect to 100 parts by mass in total of all resin components in the encapsulant composition. It is not more than part by mass, more preferably not less than 50 parts by mass and not more than 100 parts by mass, and still more preferably not less than 90 parts by mass and not more than 100 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.

  The sealing material composition of the present invention 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 density of the acid-modified polyethylene resin is preferably 0.900 g / cm ³ or less, more preferably 0.890 g / cm ³ or less, and particularly preferably 0.870 g / cm ³ or more. It is. Thereby, heat resistance and the adhesiveness to a metal can be made favorable, suppressing blocking.

  The content of the acid-modified polyethylene resin is preferably 15% by mass or more and 40% by mass or less in all resin components. By setting it as this range, generation | occurrence | production of blocking and acidic gas can be suppressed, and heat resistance and the adhesiveness to a metal can be made favorable.

Specific examples of the acid-modified polyethylene resin include maleic anhydride-modified resin. Specific examples include Admer SF731 (manufactured by Mitsui Chemicals, Inc., density 0.880 g / cm ³ ), Admer SF730 (manufactured by Mitsui Chemicals, Inc., density 0.880 g / cm ³ ), and the like.

The content of the polyethylene resin having a density of 0.900 g / cm ³ or less contained in the encapsulant composition is preferably 10% by mass or more and 99% by mass or less, more preferably 50% by mass or more in the composition. It is 99% by mass or less, more preferably 90% by mass or more and 99% by mass or less. That is, other resins may be included as long as the effects of the present invention are not impaired. These may be used, for example, as an additive resin, or may be used for masterbatching other components described later.

[Crosslinking agent]
In the production method of the present invention, the crosslinking agent is not an essential component of the encapsulant composition. The content of the crosslinking agent in the sealing material composition may be zero. Even when a crosslinking agent is added, the addition amount is preferably 0.4 parts by mass or less, and 0.1 parts by mass or less, with respect to 100 parts by mass of all components in the sealing material composition. It is more preferable that By limiting the amount of the crosslinking agent added to the encapsulant composition below this range, it is possible to suppress the crosslinking of the resin during film formation and the film forming process load, and to form a sheet, especially in terms of durability by chemical crosslinking. It can be set as the excellent sealing material sheet. When the content of the cross-linking agent exceeds 0.4 parts by mass, film formation becomes impossible due to cross-linking during film formation. In the method for producing a sealing material sheet of the present invention, the sealing material composition is subjected to a crosslinking treatment by irradiation with ionizing radiation, and 0.05 parts by mass or more of a crosslinking aid is sealed as an essential component. It is added to the stopping material composition. In this case, the addition amount of the cross-linking material is different from the conventional case of thermal cross-linking or cross-linking by irradiation with ionizing radiation, even if the addition amount of the cross-linking material is less than 0.4 parts by mass. Sufficient heat resistance and electrical resistance can be obtained by advancing crosslinking. Thereby, the risk of productivity reduction due to the gelation of the sealing material composition in the sheet forming step of the sealing material composition can also be reduced, and the production cost can be reduced by reducing the amount of the crosslinking agent used. .

  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.

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-butylperoxy) hexane-3 Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-peroxy) hexyne-3; bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, benzoyl peroxide, Diacyl such as o-methylbenzoyl peroxide and 2,4-dichlorobenzoyl peroxide -Oxides; t-butyl peroxyacetate, t-butylperoxy-2-ethylhexanoate, t-butylperoxypivalate, t-butylperoxyoctoate, t-butylperoxyisopropyl carbonate, t-butyl Peroxybenzoate, di-t-butylperoxyphthalate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexyne-3 , T-butylperoxy-2-ethylhexyl carbonate, 2,5-dimethyl-2,5 di (t-butylperoxy) hexane-3 and other peroxyesters; methyl ethyl ketone peroxide, cyclohexanone peroxide and other ketone peroxides Organic peroxides such as oxides 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.
[Crosslinking aid]
In the production method of the present invention, a crosslinking aid is also an optional component. The crosslinking aid is not particularly limited, and known ones can be used. An example of a crosslinking aid that can be preferably used includes a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group. Further, examples of the crosslinking aid that can be used more preferably include those in which the functional group of the polyfunctional monomer is an allyl group, a (meth) acrylate group, or a vinyl group.

  Specific examples of the crosslinking aid that can be used in the production method of the present invention include polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, diallyl maleate, and trimethylol. Propane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA), ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol Poly (meth) acryloxy compounds such as diacrylate, glycidyl methacrylate containing double bond and epoxy group, 4-hydroxybutyl acrylate glycidyl ether and two or more epoxy groups That 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and epoxy compounds such as trimethylolpropane polyglycidyl ether. These may be used alone or in combination of two or more.

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

  The content of the crosslinking aid is preferably included in a range of 0.05 parts by weight or more and less than 1.0 part by weight, more preferably 0.1 parts per 100 parts by weight of all components of the sealing material composition. It is a range of not less than 0.5 parts by mass.

  By containing the above-mentioned crosslinking aid in the encapsulant composition with the above content, the gel fraction of the crosslinked encapsulant sheet before modularization is promoted by promoting an appropriate crosslinking reaction by irradiation with ionizing radiation. Can be 2% or more and 80% or less.

  Addition of an appropriate amount of a crosslinking aid to the encapsulant composition can appropriately promote the cross-linking reaction by irradiation with ionizing radiation, so that the encapsulant has appropriate heat resistance and surface fluidity. Here, when the crosslinking agent is not contained in the encapsulant composition, if the crosslinking reaction by the irradiation of ionizing radiation is similarly promoted, the irradiation amount of the ionizing radiation is inevitably too strong, The fluidity of the surface is insufficient, resulting in a lack of unevenness followability.

  Moreover, the addition of an appropriate amount of a crosslinking aid to the encapsulant composition can lower the crystallinity of the linear low density polyethylene and maintain transparency. As a result, specifically, it is possible to obtain transparency and heat resistance comparable to those of EVA and a low MFR polyethylene resin, low-temperature flexibility, electrical characteristics, and the like that are superior to those.

[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 large quantities, 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. It is presumed that the adhesion can be ensured by the seepage effect. Thereby, irradiation with stronger EB can be performed, 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. Within this range, the crosslinking reaction can be moderately suppressed. Specifically, the gel fraction of the crosslinked encapsulant sheet before modularization can be made 70% or less.

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

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

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

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

<Method for producing sealing material sheet>
The manufacturing method of the sealing material sheet of the present invention is to obtain an uncrosslinked sealing material sheet having a gel fraction of 0% by a sheeting process in which the above-mentioned sealing material composition is melt-molded at a temperature exceeding its melting point. Then, a crosslinked sealing material sheet having a gel fraction of 2% or more and 80% or less in the form of a sheet or film is obtained through a crosslinking step by irradiation with ionizing radiation. In addition, the sheet form in this invention means the film form, and there is no difference in both.

[Sheet making process]
Film formation by melt molding of the above-mentioned sealing material composition is performed by various molding methods such as injection molding, extrusion molding, hollow molding, compression molding, and rotational molding, which are usually used in ordinary thermoplastic resins. .

  The film formation temperature in the present invention is important in determining the crystallinity of the post-deposition sheet. By using polyethylene having a low density as described above and a high MFR of MFR 20 or more and 40 or less, the film formation temperature can be greatly reduced, and crystallization can be suppressed. Specifically, the film formation temperature is preferably 100 to 120 ° C.

  In the present invention, not only the above-described high MFR low-density polyethylene is formed at a low temperature, but also a low-density polyethylene of MFR 2 to about 15 in the normal range is formed at a high temperature of 180 ° C. to 230 ° C. After the film formation, the post-deposition sheet may be rapidly cooled from about 40 ° C. to about 60 ° C. using a water cooling means using a chill roll. By shortening the cooling time by rapid cooling, crystallization of the sheet after film formation can be suppressed.

  The post-deposition sheet thus obtained has a thickness of 400 μm and less than 3% in terms of haze value.

[Crosslinking process]
The cross-linking treatment step in which the pre-cross-linking encapsulant sheet after the sheet forming step is subjected to a cross-linking treatment by ionizing radiation is performed after the completion of the sheet forming step and the sun integrating the encapsulant with other members. Performed before starting the battery module integration process. By this cross-linking step, a sealing material having a gel fraction of 2% or more and 80% or less is obtained. The cross-linking treatment may be performed continuously in-line following the sheet forming step, or may be performed off-line.

  The cross-linking step is preferably performed using ionizing radiation such as electron beam (EB), α-ray, β-ray, γ-ray, neutron beam, and the like. The acceleration voltage in electron beam irradiation is determined by the thickness of the sheet that is the object to be irradiated, and the thicker the sheet, the larger the acceleration voltage is required. For example, a 0.5 mm-thick sheet is irradiated with 100 kV or more, preferably 200 kV or more. If the acceleration voltage is lower than this, the crosslinking is not sufficiently performed. The irradiation dose is in the range of 1-100 Mrad, preferably 1-30 Mrad. When the irradiation dose is less than 1 Mrad, sufficient crosslinking is not performed, and when it exceeds 50 Mrad, there is a concern about deformation or coloring of the sheet due to generated heat. In addition, you may irradiate from both sides. Irradiation may be in an air atmosphere or a nitrogen atmosphere.

  By passing through the cross-linking step, the gel fraction of the encapsulant becomes 2% or more and 80% or less, and a crosslinked encapsulant is obtained. The gel fraction is preferably 2% or more and 80% or less, and more preferably 30% or more and 80% or less. If the gel fraction is less than 2%, the effect of suppressing the flow by the crosslinking step before the modularization step is not exhibited, and the sealing material composition flows in the vacuum heating laminate, making it difficult to keep the film thickness constant. . When the gel fraction exceeds 80%, the fluidity of the encapsulant composition becomes too low, and the module is not well embedded in the irregularities of the module, making it difficult to use as an encapsulant. That is, if the gel fraction is within the above range, the sealing property to the unevenness can be maintained well while suppressing excessive flow. In addition, the dimensional stability at the time of shaping | molding can be made very high by making a gel fraction 30% or more. The gel fraction (%) is a value obtained by the method of Examples described later. The heat shrinkage is preferably 45% or less, more preferably 30% or less, and most preferably 20% or less.

  The haze value of the sealing material sheet of the present invention is less than 4%, preferably 3.5% or less at a thickness of 400 μm. As described above, in the present invention, transparency can be maintained by reducing the crystallinity of the sheet after film formation to maintain a transparent state, and performing a crosslinking treatment with ionizing radiation as it is.

  In addition, since the sealing material sheet | seat of this invention obtained in this way is bridge | crosslinked, the annealing process etc. are unnecessary again and can be used in a modularization process as it is.

<Sealing material sheet and solar cell module using the same>
Next, an example of a sealing material sheet obtained by the production method of the present invention and a solar cell module using the same 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 above-described encapsulant sheet for at least one of the front encapsulant sheet layer 3 and the back encapsulant sheet layer 5.

  The encapsulant sheet of the present invention is obtained, for example, by molding the above encapsulant sheet composition by a conventionally known method, and is in the form of a sheet or a 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. Thus, the encapsulant sheet sheet of the present invention is obtained by forming the solar cell module encapsulant sheet composition into a sheet.

  The encapsulant sheet formed into a sheet may not be a single layer. In order to improve the adhesiveness between the encapsulant sheet and the filled member such as the transparent front substrate 2, the solar cell element 4, and the back surface protective sheet 6, the encapsulant sheet for the solar cell module of the present invention is formed at the interface. The composition should just be arrange | positioned. By allowing the encapsulant sheet composition of the present invention to be present near the interface, the encapsulant sheet of the present invention can be produced at a lower cost.

  As a method for causing the encapsulant sheet composition of the present invention to be present in the vicinity of the interface, for example, the encapsulant sheet has a structure of three or more layers, that is, two outermost layers and the outermost layer. And a method comprising a multilayer film having at least a core layer sandwiched between layers. In order to produce a filler sheet made of a multilayer film as described above, for example, a conventionally known T-die multilayer coextrusion method can be used.

  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. And the back sealing material sheet layer 5 are 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 protection sheet 6 are 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.

  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 that are members other than the front surface sealing material sheet layer 3 and the back surface sealing material sheet layer 5 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.
<Manufacture of sealing material sheet>
A sealing material composition having the following composition was mixed and melted, and a film was formed at 120 ° C. by a conventional T-die method so as to have a thickness of 400 μm, thereby obtaining an uncrosslinked post-deposition sheet of the example. Moreover, the film-forming temperature was 205 degreeC, and the film | membrane after film-forming of the comparative example was obtained.

75 parts by mass of polyethylene resin (LLDPE): a metallocene linear low density polyethylene which is a copolymer of ethylene and 1-hexene and has a density of 0.880 g / cm ³ and MFR of ³⁰ g / 10 min. Number average molecular weight 55,000 in terms of polystyrene.
25 parts by mass of a silane-modified polyethylene resin: a copolymer of ethylene and 1-hexene, a density of 0.880 g / cm ³ and a melt mass flow rate (MFR) at 190 ° C. of 30 g / 10 min. 2 parts by mass of vinyltrimethoxysilane and 0.1 parts by mass of dicumyl peroxide as a radical generator (reaction catalyst) are mixed with 98 parts by mass of a low-density polyethylene resin, and melted at 200 ° C. A silane-modified polyethylene resin having a density of 0.884 g / cm ³ and an MFR of 18 g / 10 min, obtained by kneading. Number average molecular weight 82,000 in terms of polystyrene.

The haze value (JIS K7136) was measured for the post-deposition sheets of Examples and Comparative Examples. The results are shown in Table 1.
([Test method for haze (%)]
According to JISK7136, it measured with Murakami Color Research Institute Co., Ltd. Haze and transmittance system HM150. In addition, about the sealing material sheet | seat, after carrying out the vacuum heat lamination by the following lamination conditions by the structure of glass 3.2mm / sealing material sheet 400micrometer / glass 3.2mm, the haze was measured.
(Lamination condition)
(A) Vacuum drawing: 5.0 minutes (b) Pressurization (0 kPa to 100 kPa): 1.5 minutes (c) Pressure holding (100 kPa): 7.0 minutes (d) Temperature 150 ° C.

  Next, the post-deposition sheet is irradiated with an electron beam irradiation device (product name EC250 / 15 / 180L, manufactured by Iwasaki Electric Co., Ltd.) at an acceleration voltage of 200 kV and an irradiation intensity of 75 kGy (7.5 Mrad) and sealed. A stop sheet was obtained.

  From Table 1, the haze after film formation is smaller in the examples than in the comparative examples, and the haze increase after electron beam irradiation is 3.1-2.5 = 0.6%. It is smaller than 4.0-3.1 = 0.9%. From this, the sealing material sheet finally obtained by controlling the crystallinity of the post-deposition sheet stage to form a post-deposition sheet with low crystallinity, low density, and low haze, followed by electron beam irradiation It can be understood that the transparency can be enhanced.

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 (3)

A method for producing a sealing material sheet for a solar cell module, in which a sealing material composition containing a low density polyethylene having a density of 0.900 g / cm ³ or less is formed and then subjected to crosslinking treatment by irradiation with ionizing radiation. ,
The manufacturing method of the sealing material sheet whose haze value in the sheet | seat after the said film formation and before ionizing radiation irradiation is 3.0% or less with a thickness of 400 micrometers.   The low-density polyethylene has an MFR of 190 ° C. measured according to JIS K6922-2 and a load of 2.16 kg of 20.0 g / 10 min to 40.0 g / 10 min, and the film formation temperature during the film formation is 120 ° C. or less. The method for producing a sealing material sheet according to claim 1.   The method for producing a sealing material sheet according to claim 1, wherein a rapid cooling process is performed immediately after the film formation.

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