JP6965504B2 - Encapsulant sheet for solar cell modules - Google Patents

Description

The present invention relates to a sealing material sheet for a solar cell module.

In recent years, due to growing awareness of environmental issues, solar cells have been attracting attention as a clean energy source. Currently, solar cell modules having various forms have been developed and proposed. Generally, a solar cell module has a structure in which a transparent front substrate, a solar cell element, and a back surface protective sheet are laminated via a sealing material sheet for the solar cell module.

Each member constituting the solar cell module and the like is constantly exposed to a harsh environment such as strong ultraviolet rays, heat rays, wind and rain, and the like. Therefore, each member constituting the solar cell module needs to have long-term durability under these conditions.

As a composition of the sealing material composition for providing the sealing material sheet for the solar cell module with such durability, EVA (ethylene-vinyl acetate copolymer) is used as a base resin, and a cross-linking agent and a cross-linking agent are used for cross-linking. A configuration containing an auxiliary agent is known (see Patent Document 1). In this case, if the cross-linking reaction of the above composition proceeds during extrusion molding, the load during molding becomes excessive and the productivity decreases or molding becomes impossible. Therefore, the above composition is generally heated at a low temperature of 50 ° C. to 90 ° C. It is molded without being crosslinked by extruding with. Then, the cross-linking treatment is performed after molding, or the cross-linking is performed by heating at the time of modularization.

On the other hand, when the base resin is an olefin resin such as polyethylene, it is known that the adhesion with glass or the like is improved by blending a silane coupling agent, but in order to further improve the adhesion, an alkoxysilane is grafted. A sealing material using a polymerized modified ethylene resin is known (see Patent Document 2). According to this, it is possible to provide a sealing material having durability and adhesiveness while eliminating the need for a cross-linking step.

JP-A-2009-135200 JP-A-2002-23408

The encapsulant sheet of Patent Document 2 does not contain a cross-linking agent. That is, it is a thermoplastic resin film on the premise that the cross-linking treatment is not performed until the final product stage. In this way, when the base resin of the encapsulant sheet is thermoplastic polyethylene, in order to ensure the heat resistance required for the encapsulant sheet, it is necessary to select a resin having a high density to some extent and a high melting point. I don't get it. In fact, it is considered that the inevitable result is that the composition of the silane-modified ethylene-α-olefin copolymer (Example 2) is extruded at a high temperature of 180 ° C. in the examples of the same document.

Increasing the density of the polyethylene-based resin used as the base resin for the encapsulant sheet leads to a decrease in the transparency of the encapsulant sheet, but when the base resin is thermoplastic polyethylene, it has sufficient heat resistance. As long as securing was prioritized, we had to accept the deterioration of transparency to some extent.

On the other hand, by using thermosetting polyethylene, which has a desire for a cross-linking agent, as the base resin, it becomes possible to use polyethylene having a relatively low density. However, even in this case, improvement of adhesion to glass or the like is strongly required for the sealing material sheet for the solar cell module. That is, even in the polyethylene-based encapsulant sheet to be subjected to the cross-linking treatment, for example, the above-mentioned silane-modified ethylene-α-olefin copolymer (hereinafter, also referred to as “silane-modified polyethylene”), a silane coupling agent, or an acid-modified resin. Etc., it was essential to add some adhesive-improving component.

Among these adhesion improving components, the silane coupling agent tends to generate free silane during cross-linking, and the acid-modified resin tends to deteriorate due to moisture. On the other hand, silane-modified polyethylene is superior to other adhesion-improving components in that it is excellent in durability.

However, a so-called post-crosslinking type in which a sealing material sheet using a thermosetting polyethylene as a base resin, which has a desire for a cross-linking agent, is manufactured, and in particular, a cross-linking treatment is performed after the film formation is completed in a limited low temperature range. When silane-modified polyethylene is used in the production of the encapsulant sheet, the film-forming property and the optical characteristics may be deteriorated due to insufficient compatibility with the base resin.

The present invention has been made to solve the above problems, and an object thereof is a thermosetting encapsulant sheet using polyethylene as a base resin and advancing cross-linking in any process after film formation. It is an object of the present invention to provide a sealing material sheet for a solar cell module, which has excellent transparency and sufficient adhesion and durability.

We have optimized the melting point and MFR of silane-modified polyethylene to be added to the encapsulant composition as part of the base resin in the production of encapsulant sheets for thermosetting solar cell modules. By doing so, it was found that the above problems could be solved, and the present invention was completed. More specifically, the present invention provides the following.

Comprising (1) a density of 0.865 g / cm ³ or more 0.900 g / cm ³ or less of polyethylene, copolymerized with comprising silane-modified polyethylene and α- olefin and an ethylenically unsaturated silane compound as comonomers, the A sealing material composition for a solar cell module containing a polyethylene-based resin as a base resin and a cross-linking agent. The polyethylene has a melting point of 50 ° C. or higher and 70 ° C. or lower, and is measured by JIS-K6922-2. The MFR at 190 ° C. and a load of 2.16 kg is 10 g / 10 minutes or more and 20 g / min or less, the melting point of the silane-modified polyethylene is 50 ° C. or more and 70 ° C. or less, and the MFR is 10 g / 10 minutes or more and 20 g. The cross-linking agent has a 1-hour half-life temperature of 125 ° C. or higher and 145 ° C. or lower, and the content of the encapsulant composition in the resin component is 0.2% by mass or more and 0.5. Encapsulant composition for a polyethylene module having a mass% or less.

(2) The encapsulant composition according to (1), wherein the cross-linking agent is a peroxyketal or a dialkyl peroxide.

(3) An encapsulant sheet obtained by forming the encapsulant composition according to (1) or (2) and having a gel fraction of 0% or more and 10% or less.

(4) The encapsulant sheet according to (3), which has a gel fraction of 0%.

(5) A solar cell module in which the encapsulant sheet according to any one of (1) to (4) and a glass substrate are laminated so as to face each other.

(6) The solar cell module according to (5), wherein the gel content of the encapsulant sheet is 50% or more and 90% or less.

(7) A method for producing a sealing material sheet, which is carried out by melt-molding the sealing material composition according to (1) or (2) at a film forming temperature of 90 ° C. or higher and 120 ° C. or lower.

According to the present invention, a thermosetting encapsulant sheet using polyethylene as a base resin and advancing cross-linking in any process after film formation, which is excellent in transparency and has sufficient adhesion and durability. It is possible to provide a sealing material sheet for a solar cell module having the above.

It is sectional drawing which shows an example of the layer structure of the solar cell module of this invention.

<Encapsulant sheet>
The encapsulant sheet of the present invention (hereinafter, also simply referred to as “encapsulant sheet”) is a film-like or sheet-like encapsulant composition obtained by molding a encapsulant composition whose details will be described below by a conventionally known method. It is the one. The sheet shape in the present invention means that the film shape is also included, and there is no difference between the two.

Further, the encapsulant sheet is molded in an uncrosslinked state by limiting the molding temperature to a low temperature range of 90 ° C. to 120 ° C. The cross-linking treatment is performed separately after molding, or is heated to a high temperature at the time of manufacturing the solar cell module described later to complete the cross-linking.

Sealing material sheet, density 0.865 g / cm ³ or more 0.900 g / cm ³ or less, preferably, density 0.880 g / cm ³ or more 0.895 g / cm ³ or less, more preferably, density 0.885 g / cm ³ or more 0.890 g / cm ³ or less of the polyethylene resin is the base resin, 10% 0% gel fraction less, and is formed by a resin film uncrosslinked and more preferably 0%.

However, this uncrosslinked encapsulant sheet contains a predetermined amount of a crosslinking agent, and it is assumed that the crosslinking will proceed during any process until after integration as a solar cell module. This is a so-called thermosetting (or cross-linked) resin film. The gel fraction of the encapsulant sheet after the completion of crosslinking in the finished product stage of the final product solar cell module is preferably 50% or more and 90% or less, and more preferably 60% or more and 80% or less. By adjusting the composition and the amount of the cross-linking agent, the cross-linking aid, and other additives to a preferable range as described above, the cross-linking reaction can be appropriately suppressed so that the gel fraction is within the above range. As a result, it has a water vapor barrier of olefins, has flexibility in a low temperature region more than EVA, and can obtain heat resistance at a high temperature. Can also be an excellent sealing material.

Here, the "gel fraction (%)" in the present specification refers to 1.0 g of a sealing material in a resin mesh, extracted with xylene at 110 ° C. for 12 hours, then taken out together with the resin mesh, dried and weighed. , The mass before and after extraction was compared, the mass% of the residual insoluble matter was measured, and this was used as the gel fraction. The gel fraction of 0% means that the residual insoluble matter is substantially 0 and the cross-linking reaction of the encapsulant composition or the encapsulant sheet has not substantially started. More specifically, "gel fraction 0%" means that the residual insoluble matter is not present at all, and the mass% of the residual insoluble matter measured by a precision balance is less than 0.05% by mass. Suppose to say. The residual insoluble matter does not include pigment components other than the resin component. When a mixture other than these resin components is mixed in the residual insoluble matter by the above test, for example, by separately measuring the content of these mixture in the resin component in advance, these It is possible to calculate the gel fraction that should be originally obtained for the residual insoluble matter derived from the resin component excluding the mixture.

The melt mass flow rate (MFR) of the encapsulant sheet at the stage of uncrosslinking after film formation is MFR at 190 ° C. and a load of 2.16 kg measured by JIS-K6922-2 (hereinafter, this measurement condition in the present specification). The value measured according to (MFR) is preferably 5 g / 10 minutes or more and 25 g / 10 minutes or less, and more preferably 10 g / 10 minutes or more and 20 g / 10 minutes or less. When the MFR is in the above range, it is possible to obtain a sealing material having excellent adhesion to other members of the solar cell module made of glass, metal or the like. Regarding the MFR when the encapsulant sheet is a multilayer film as described below, the measurement is performed by the above treatment while all the layers are integrally laminated, and the obtained measured value is used as the multilayer. It shall be the MFR value of the sealing material sheet of.

The encapsulant sheet of the present invention may be a single-layer film, or may be a multilayer film composed of a core layer and skin layers arranged on both sides of the core layer. The multilayer film in the present specification is a film or sheet having a structure having a skin layer formed into at least one of the outermost layers, preferably both outermost layers, and a core layer which is a layer other than the skin layer. Say that.

When the encapsulant sheet is a multilayer film, it is more preferable to have a layer structure in which the MFR is different for each layer within a range satisfying the essential constituent requirements of the present invention. In this case, a layer having a higher MFR is used. It is preferable to arrange the skin layer on the outermost layer side. The encapsulant sheet of the present invention has sufficiently preferable transparency, heat resistance, and appropriate flexibility even when it is a single-layer encapsulant sheet, but as described above, it is relatively MFR. By arranging the layer having a high value in the outermost layer, it is possible to further improve the adhesion and the molding characteristics while maintaining the above-mentioned preferable transparency and heat resistance as the sealing material sheet.

For example, in a sealing material 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 an intermediate layer and an outermost layer composed of all layers other than the outermost layer. The thickness ratio of the outermost layer: the intermediate layer: the outermost layer is preferably in the range of 1: 3: 1 to 1: 8: 1. By doing so, it is possible to provide preferable molding characteristics in the outermost layer while maintaining preferable heat resistance as a sealing material.

[Encapsulant composition]
The encapsulant composition used for producing the encapsulant sheet of the present invention (hereinafter, also simply referred to as “encapsulant composition”) uses low-density polyethylene as a base resin and silane-modified polyethylene as an essential additive resin. It is a thermosetting resin composition that is mixed with this and is used, and further addition of a cross-linking agent is indispensable. In addition, in this specification, a "base resin" means a resin having the largest content ratio among the resin components of the resin composition in the resin composition containing the base resin.

Further, the encapsulant composition is characterized in that the melting points and MFR of polyethylene used as a base resin and silane-modified polyethylene used as an essential additive resin are both adjusted within the same specific range.

Specifically, the melting points of polyethylene and silane-modified polyethylene used in the encapsulant composition are both 50 ° C. or higher and 70 ° C. or lower, and the melting point difference between them is preferably 20 ° C. or lower, preferably 10 ° C. or lower. Is more preferable.

In the present specification, the melting point of the encapsulant sheet or each resin constituting the encapsulant sheet means the melting point of the resin that can be obtained by measuring by differential scanning calorimetry (DSC). When there are a plurality of valley peaks on the DSC curve, the melting point indicated by the peak having the largest peak area is referred to as the melting point of the resin. When the encapsulant sheet has multiple layers, the average value of the melting points of each layer is used as the melting point of the encapsulant sheet.

Similarly, the MFRs of polyethylene and silane-modified polyethylene used in the encapsulant composition are both 10 g / 10 minutes or more and 20 g / 10 minutes or less, and the difference between their MFRs is 15 g / 10 minutes or less. Is preferable, and it is more preferably within 10 g / 10 minutes.

In this way, by adjusting the melting points and MFRs of polyethylene and silane-modified polyethylene used as the base resin of the encapsulant composition so as to be within the same range, the compatibility between the two resins can be improved, and the film forming property can be improved. It is possible to produce a sealing material sheet having excellent adhesion and durability while avoiding a decrease in transparency.

To total resin components of the sealing material composition, the content ratio of the polyethylene used as the base resin is the content ratio of preferably not more than 95 wt% or more and 85 wt%, whereas the silane modified polyethylene Is preferably 5% by mass or more and 15% by mass or less. As long as the above-mentioned polyethylene and silane-modified polyethylene are contained in the above-mentioned content range, the encapsulant composition may contain other resins as long as the effects of the present invention are not impaired.

(polyethylene)
The above polyethylene used as the base resin of the sealant composition, density 0.865 g / cm ³ or more 0.900 g / cm ³ or less, preferably, density 0.880 g / cm ³ or more 0.895 g / cm ³ or less, more preferably, the density 0.885 g / cm ³ or more 0.890 g / cm ³ or less of polyethylene. By using low-density polyethylene in this way, the transparency of the encapsulant sheet can be improved. Further, according to this, the adhesion to other members constituting the solar cell module such as a glass protective substrate is enhanced, and the risk of cell cracking at the time of crimping each member in the laminating process can be reduced.

The polyethylene used as the base resin of the encapsulant composition is linear low density polyethylene (LLDPE) which is a copolymer of ethylene and α-olefin. The polyethylene is more preferably a metallocene-based linear low-density polyethylene (M-LLDPE). The metallocene-based linear low-density polyethylene is synthesized by using a metallocene catalyst which is a single-site catalyst. Such polyethylene has few side chain branches and a uniform distribution of comonomer. Therefore, the molecular weight distribution is narrow, the density can be made ultra-low as described above, and flexibility can be imparted to the encapsulant. As a result of imparting flexibility to the encapsulant, the adhesion between the encapsulant and glass, metal, etc. is enhanced.

Since the linear low-density polyethylene has a narrow crystallinity distribution and the same crystal size, not only does it not exist with a large crystal size, but also the crystallinity itself is low due to its low density. Therefore, it is excellent in transparency when processed into a sheet as a sealing material. Therefore, when the encapsulant sheet made of the encapsulant composition using this as a base resin is arranged on the light receiving surface side of the solar cell element in the solar cell module, it is caused by the attenuation of the incident light on the solar cell element. It is possible to prevent a decrease in power generation efficiency.

As the α-olefin of the linear low-density polyethylene used as the base resin of the encapsulant composition, propylene having 3 carbon atoms can be mainly used. Conventionally, as the α-olefin of a polyethylene resin used for a sealing material sheet for a solar cell module, 1-hexene, 1-heptene or 1-octene, which are α-olefins having 6 to 8 carbon atoms, are often used. However, the encapsulant composition replaces this with propylene having 3 carbon atoms, and the α-olefin having this specific carbon number is contained in the base resin in an amount of 5 mol% or more and 25 mol% or less, preferably 15 mol% or more and 20 mol% or more. By containing the following, it is possible to provide the sealing agent sheet with sufficient heat resistance by adding a smaller amount of cross-linking agent.

In this case, it is not essential that all the α-olefins in the base resin of the encapsulant composition have 3 carbon atoms, but for example, α-olefin having 8 or more carbon atoms such as 1-octene. It is preferable that it does not contain olefins. Further, the ratio of the α-olefin having 3 carbon atoms to the total α-olefin in the base resin is preferably 50 mol% or more, and most preferably 100 mol%.

By setting the content of the α-olefin having a specific carbon number in the encapsulant sheet to 5 mol% or more in this way, even if the amount of the cross-linking agent added is relatively small, the encapsulant sheet has sufficient heat resistance. It is possible to impart properties, and at the same time, it is possible to suppress deterioration of the light-resistant stabilizer. On the other hand, if this content exceeds 25 mol%, the melting point is lowered and blocking is likely to occur. Therefore, the content is preferably 25 mol% or less.

The "content of α-olefin having a specific carbon number (mol%)" in the encapsulant sheet can be calculated by the following measuring method.
(Measuring method)
The encapsulant sheet is dissolved in an ODCB / C6D6 (4/1) solvent to a concentration of 10 wt%. With the temperature of this solvent at 130 ° C., measurement is performed using 13C-NMR, and a peak peculiar to triad (triplet) is quantified. After calculating the monomer sequence fraction (normalizing the entire sequence to 100%), each monomer ratio (C3 component concentration) is calculated from the sequence fraction.

(Silane-modified polyethylene)
The silane-modified polyethylene used as an essential additive resin in the encapsulant composition is obtained by graft-polymerizing a linear low-density polyethylene (LLDPE) as a main chain with an ethylenically unsaturated silane compound as a side chain. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to the adhesive force, it is possible to improve the adhesiveness of the sealing material to other members in the solar cell module.

The silane-modified polyethylene can be produced, for example, by the method described in JP-A-2003-46105, and by using the resin as a component of the encapsulant composition of the solar cell module, the strength, durability and the like can be improved. It is excellent, and has excellent weather resistance, heat resistance, water resistance, light resistance, wind pressure resistance, haze resistance, and other characteristics, and is not affected by manufacturing conditions such as heat crimping for manufacturing solar cell modules. It is possible to manufacture a solar cell module suitable for various applications with extremely excellent heat fusion property, stably and at low cost.

As the silane-modified polyethylene, any of a random copolymer, an alternating copolymer, a block copolymer, and a graft copolymer can be preferably used, but a graft copolymer is more preferable. 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 the adhesive force, it is possible to improve the adhesiveness of the sealing material for the solar cell module to other members in the solar cell module.

Examples of ethylenically unsaturated silane compounds graft-polymerized with straight-chain low-density polyethylene include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, and vinyltripentyroxysilane. , Vinyl triphenyloxysilane, vinyl tribenzyloxysilane, vinyl trimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, vinyltricarboxysilane, one or more selected from them. be able to.

The optimum density, melting point and MFR of the silane-modified polyethylene can be appropriately and optimally adjusted by adjusting the density, melting point and MFR of the polyethylene-based resin of the main chain.

(Crosslinking agent)
As the cross-linking agent used in the encapsulant composition, the amount of active oxygen is preferably 8.5% or more and 15.00% or less, preferably 8.5% or more and 10.00% or less. By using a cross-linking agent whose amount of active oxygen is in the above range, even when the amount of the cross-linking agent added is limited to the range peculiar to the present invention, the encapsulant sheet is provided with sufficient heat resistance, light resistance, and transparency. Can be prepared.

Further, as the 1-hour half-life temperature of the cross-linking agent used in the encapsulant composition, one having a temperature of 125 ° C. or higher and 145 ° C. or lower can be used. Thereby, the encapsulant composition of the present invention can be made into a composition capable of melt extrusion molding at 120 ° C. or lower.

Specific examples of the cross-linking agent satisfying the above conditions include n-butyl 4,4-di (t-butylperoxy) valerate, ethyl 3,3-di (t-butylperoxy) butyrate, and 2,2-di. Peroxyketals such as (t-butylperoxy) butane, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butyl) Seals dialkyl peroxides such as peroxy) hexane, 2,5-dimethyl-2,5-di (t-peroxy) hexin-3, and peroxyesters such as t-butylperoxy-2-ethylhexyl carbonate. A cross-linking agent added to the stopping material composition can be used. Above all, a cross-linking agent for peroxyketals or dialkyl peroxides can be particularly preferably used for the encapsulant composition of the present invention.

The content of the above-mentioned cross-linking agent in the encapsulant composition is preferably 0.2% by mass or more and 0.5% by mass or less, more preferably 0, based on the total resin components in the encapsulant composition. It is in the range of 0.3% by mass or more and 0.4% by mass or less. By adding a cross-linking agent in this range, sufficient durability can be imparted to the sealing material sheet. Further, if the addition amount is within this range, the generation of unfavorable bubbles derived from the cross-linking agent can be suppressed. The encapsulant sheet of the present invention is formed without substantially advancing cross-linking, and the content of the above-mentioned cross-linking agent in the encapsulant sheet at the sheet stage after film formation is also 0. The range is 2% by mass or more and 0.5% by mass or less.

(Crosslinking aid)
In the encapsulant composition, a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group, more preferably the functional group of the polyfunctional monomer is an allyl group, a (meth) acrylate group, or a vinyl group. It is preferable to contain an agent. This promotes an appropriate cross-linking reaction to improve the adhesion of the encapsulant sheet to glass and metal, and in addition, this cross-linking aid is the crystallinity of the linear low-density polyethylene forming the encapsulant sheet. To maintain transparency. As a result, in addition to the above-mentioned effect of improving the adhesiveness, the transparency and low-temperature flexibility of the encapsulant sheet can be made more excellent.

Specific examples of the cross-linking aid that can be used in the encapsulant composition include polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, and diallyl maleate. Methylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA), ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonane Poly (meth) acryloxy compounds such as diol diacrylate, glycidyl methacrylate containing double bonds and epoxy groups, 4-hydroxybutyl acrylate glycidyl ether and 1,6-hexanediol diglycidyl ether containing two or more epoxy groups, 1 , 4-Butandiol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, trimethylolpropane polyglycidyl ether and other epoxy compounds can be mentioned. These may be used alone or in combination of two or more. In addition, among the above-mentioned cross-linking aids, it also contributes remarkably to the improvement of glass adhesion of the sealing material, has good compatibility with linear low-density polyethylene, lowers crystallinity by cross-linking, maintains transparency, and has a low temperature. TAIC can be preferably used from the viewpoint of imparting flexibility in the above.

The content of the cross-linking aid in the encapsulant composition is preferably 0.01% by mass or more and 3% by mass or less, more preferably 0.05, based on the total resin components in the encapsulant composition. It is mass% or more and 2.0 mass% or less. Within this range, an appropriate cross-linking reaction can be promoted and the adhesion of the encapsulant sheet can be improved.

(Hindered amine-based light-resistant stabilizer)
A hindered amine-based light-resistant stabilizer (HALS) is used as the light-resistant stabilizer in the encapsulant composition. Hindered amine-based photostabilizers are roughly classified according to the bond partner of the nitrogen atom in the piperidine skeleton, NH type (hydrogen is bonded to the nitrogen atom), NR type (alkyl group (R) is bonded to the nitrogen atom), There are three types: N-OR type (alkoxy group (OR) bonded to nitrogen atom). Of these, in the encapsulant composition of the present invention, it is preferable to use an NH-type or NR-type hindered amine-based light-resistant stabilizer.

The N-OR type hindered amine-based light-resistant stabilizer has a faster reaction speed and a higher radical trap function than the NH-type and N-R-type hindered amine-based light-resistant stabilizers. However, in a type of encapsulant sheet such as the encapsulant sheet of the present invention in which cross-linking proceeds at the modularization stage after film formation, it reacts with the cross-linking agent during thermal lamination for modularization. Therefore, it is easy to deteriorate, which often makes it impossible to sufficiently improve the light resistance. By specifying the hindered amine-based light-resistant stabilizer as an NH-type or N-R-type hindered amine-based light-resistant stabilizer, deterioration due to the cross-linking agent is avoided, and the function of capturing radicals generated by light is maintained well. Can be done.

Further, in general, many kinds of compounds are known as hindered amine-based light-resistant stabilizers, from those having a low molecular weight to those having a high molecular weight. When used in a sealing material composition for a solar cell module, bleed-out often occurs when a low molecular weight material, that is, a material having a molecular weight of less than 2000 is used, and in this case, the light transmittance is high. It becomes smaller and less transparent. Since a decrease in the transparency of the encapsulant leads to a decrease in the power generation efficiency of the solar cell module, it is preferable to use a light-resistant stabilizer having a molecular weight of 2000 or more as the light-resistant stabilizer used in the encapsulant composition.

Specific examples of the hindered amine-based light-resistant stabilizer that can be preferably used in the encapsulant composition according to the present invention are those of the NH type and having a molecular weight of 2000 or more, and dibutylamine-1,3,5-triazine. -N, N'-bis (2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine-N- (2,2,6,6-tetramemethyl-4-piperidyl) butylamine Polycondensates can be mentioned. This compound is commercially available as Chimassorb 2020 and is a compound with CAS number 192268-64-7. It has a molecular weight of 2600 to 3400 and a melting point of 130 ° C to 136 ° C.

As another specific example of the hindered amine-based light-resistant stabilizer that can be preferably used in the encapsulant composition according to the present invention, it is assumed that it is an NR type and has a molecular weight of 2000 or more, and butanedioic acid 1- [2- (4-Hydroxy-2,2,6,6-tetramethylpiperidino) ethyl] can be mentioned. This compound is commercially available as KEMISTAB62 and is a compound of CAS No. 65447-77-0. It has a molecular weight of 3100 to 4000 and a melting point of 55 ° C to 70 ° C.

The amount of the above-mentioned hindered amine-based light-resistant stabilizer added to the encapsulant composition may be 0.1% by mass or more and 0.5% by mass or less with respect to the total resin components in the encapsulant composition. More preferably, it is 0.2% by mass or more and 0.4% by mass or less. By setting the content to 0.1% by mass or more, the effect of stabilizing light resistance can be sufficiently obtained. Further, by setting the content to 0.5% by mass or less, bleed-out can be suppressed, and discoloration of the resin due to excessive addition of a hindered amine-based light-resistant stabilizer can also be suppressed.

(Other additives)
The encapsulant composition may further contain other components. For example, an ultraviolet absorber, a heat stabilizer, an adhesion improver, a nucleating agent, a dispersant, a leveling agent, a plasticizer, a defoaming agent, a flame retardant, and various other fillers can be appropriately added. The content ratio of these additives varies depending on the particle shape, density, etc., but is preferably in the range of 0.001% by mass or more and 60% by mass or less in the encapsulant composition. By including these additives, it is possible to impart stable mechanical strength over a long period of time and an effect of preventing yellowing, cracking, etc. to the encapsulant composition.

<Solar cell module>
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, a transparent front substrate 2, a front sealing material 3, a solar cell element 4, a back sealing material 5, and a back surface protective sheet 6 are laminated in this order from the light receiving surface side of incident light. .. The solar cell module 1 of the present invention can be manufactured by using the sealing material sheet of the present invention as the front sealing material 3 and / or the back sealing material 5.

In the solar cell module 1, for example, the members including the transparent front substrate 2, the front encapsulant 3, the solar cell element 4, the back encapsulant 5, and the back surface protective sheet 6 are sequentially laminated and then vacuum suctioned or the like. After being integrated, it can be manufactured by heat-pressing molding the above-mentioned member as an integrally molded body by a molding method such as a lamination method. At this time, the front sealing material 3 made of a single-layer sheet and the glass substrate are laminated, or the adhesion strengthening layer of the front sealing material 3 made of a multilayer sheet is an example of the transparent front substrate 2. By laminating so as to face the glass substrate, the adhesion between the glass substrate and the sealing material can be improved. The above heat crimping is carried out at 110 ° C. or higher, and if a curing step is carried out after the heat crimping, the polyethylene cross-linking reaction further proceeds. The curing step is performed under heating conditions such that the resin temperature of the sealing material sheet is 140 ° C. or higher and 170 ° C. or lower. As a result, the cross-linking of the sealing material sheet can be appropriately advanced, and the heat resistance and light resistance of the solar cell module can be sufficiently enhanced.

The solar cell module of the present invention thus obtained has excellent heat resistance and light resistance, and is extremely high for a long period of time even when exposed to harsh environments such as strong ultraviolet rays, heat rays, wind and rain, etc. It is durable. Further, it can contribute to the improvement of the power generation efficiency of the solar cell module because it is also excellent in transparency.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Manufacturing of encapsulant sheet]
An extruder having a screw diameter of 150 mm and a T-shaped die having a lip width of 1000 mm was used to prepare a sealing material sheet of 650 um at a roll temperature of 25 ° C. and a winding speed of 2.3 m / min under the condition of a die temperature of 110 ° C.
(polyethylene)
Metallocene-based linear low-density polyethylene having different densities, melting points, and MFRs was added as a base resin for the encapsulant sheets of each Example and Comparative Example by 85 parts by mass.
(Silane-modified polyethylene)
5 parts by mass of vinyltrimethoxysilane and 0.1 part by mass of dicumyl peroxide as a radical generator (reaction catalyst) with respect to 95 parts by mass of metallocene-based linear low-density polyethylene having different densities, melting points and MFR. Was mixed, melted and kneaded at 200 ° C. to obtain a silane-modified polyethylene having the density and melting point MFR shown in Table 1 below. Each of these silane-modified polyethylenes having different densities, melting points and MFRs was added to the encapsulant sheets of each Example and Comparative Example by 15 parts by mass.
(Crosslinking agent)
As for the cross-linking agent, the three types of cross-linking agents (A to C) shown in Table 2 were used properly for each encapsulant composition in the formulation as shown in Table 1. The content (mass%) of each cross-linking agent in the resin component of each encapsulant composition is as shown in Table 1. The molecular weight, active oxygen amount, and 1-hour half-life temperature of each of the cross-linking agents (A to C) are as shown in Table 2.
(Silane coupling agent)
Only for the encapsulant composition of Comparative Example, a silane coupling agent (manufactured by "KBM1003" Shinetsu Silicone Co., Ltd.) was added to the resin content of the encapsulant composition at a ratio of 1% by mass.

[Evaluation example 1: Difference in melting point and MFR between polyethylene resin and silane-modified polyethylene resin]
The difference in melting point and MFR between the polyethylene resin used as the base resin of each encapsulant sheet and the silane-modified polyethylene resin is as shown in Table 1.

[Evaluation example 2: Film formation property]
In order to evaluate the film-forming property of each encapsulant sheet, it was confirmed whether or not the resin pressure increased and unmelted matter was generated during the production of each encapsulant sheet (deposition temperature 110 ° C.). The results are shown as "resin pressure increase" and "unmelted material" in the list of film forming properties in Table 3, respectively. The evaluation criteria are as follows.
(Evaluation criteria)
"Increased resin pressure"
30 minutes after the start of film formation, the resin pressure hardly rises from the initial resin pressure (rise rate 0-1%) is A, the rise rate 0-10% is B, and the rise rate 10% or more is C. bottom. The resin pressure was measured by attaching a resin pressure gauge of CZ-200P manufactured by Rika Kogyo Co., Ltd. near the die. The rate of increase in resin pressure was calculated as follows.
When the initial resin pressure is P1 and the resin pressure after 30 minutes is P2, the rate of increase (%) = (P2-P1) × 100 / P1
"Unmelted material" A: Level that cannot be visually confirmed.
B: Occurs when the size is less than 1 mm.
C: Occurs when the size is 1 mm or more.

[Evaluation example 3: Optical characteristics]
A layered laminate in which both sides of each of the above encapsulant sheets are sandwiched between glass substrates (white plate semi-tempered glass (JPT 3.2 75 mm × 50 mm × 3.2 mm)) is evacuated under the following vacuum heating lamination conditions. A heat laminating treatment and a subsequent curing treatment were carried out, and samples for an optical property test were prepared for each of Examples and Comparative Examples. The optical properties (HAZE) (measured by JIS K7136, Murakami Color Research Institute Co., Ltd., haze / transmittance system HM150) were measured for each of these samples. The results are shown in Table 3 as "optical characteristics". The evaluation criteria are as follows.
(Vacuum heating laminating conditions) (a) Evacuation: 4.0 minutes
(B) Pressurization: (0 kPa to 50 kPa): 10 seconds
(C) Pressure retention: (50 kPa): 6 minutes
(D) Temperature: 110 ° C
(Cure conditions) (a) Time 40 minutes, temperature 150 ° C or 160 ° C
(Evaluation criteria) A: Haze less than 5%
B: Haze 5% or more and less than 10%
C: Haze 10% or more

[Evaluation example 4: Heat resistance]
With respect to the encapsulant sheet after the cure treatment in Evaluation Example 3, the gel fraction was measured by the above method to evaluate the heat resistance of the encapsulant sheet after cross-linking. The results are shown in Table 3 as "heat resistance". The evaluation criteria are as follows.
(Evaluation criteria) A: The gel fraction after curing is 60% or more.
B: The gel fraction after the cure treatment is 50% or more and less than 60%.
C: The gel fraction after curing is less than 50%.
[Evaluation example 5: Adhesion]
The uncrosslinked encapsulant sheets of Examples and Comparative Examples are brought into close contact with the glass substrate (white plate semi-tempered glass) used in Evaluation Example 3 above, and a vacuum heating laminator is provided under the same conditions as in Evaluation Example 3 above. After the treatment, samples for adhesion test were prepared for each of the examples and comparative examples.
Peeling test method: A sealing material sheet that is in close contact with the glass substrate is cut to a width of 15 mm, and a vertical peeling (50 mm / min) test is performed with a peeling tester (Tensilon universal testing machine RTF-1150-H). The adhesion of the encapsulant sheet was measured. The results are shown in Table 4 as "adhesion (initial)". The evaluation criteria are as follows.
(Evaluation criteria) A: 40N / 15mm or more
B: 20N / 15mm or more and less than 40N / 15mm
C: less than 20N / 15mm

[Evaluation example 6: Durability]
In order to evaluate the durability of the encapsulant sheet of the present invention, each sample used in Evaluation Example 4 was subjected to a "dump heat test" under the conditions of a test chamber temperature of 85 ° C. and a humidity of 85% in accordance with JIS C8917. , And after 2000 hours, the same adhesion test as in Evaluation Example 4 was performed. The results are shown in Table 4 as the "adhesion maintenance rate". The evaluation criteria are as follows.
(Evaluation Criteria) A: The retention rate of adhesion after the above "dump heat test" is 50% or more with respect to the adhesion in Evaluation Example 5.
B: Same adhesion maintenance rate is 30% or more and less than 50%
C: Same adhesion maintenance rate is less than 30%

From Tables 1 to 3, the encapsulant sheet for the solar cell module of the present invention is a thermosetting encapsulant sheet using polyethylene as a base resin and advancing cross-linking in any process after film formation. It can be seen that the sealing material sheet has excellent transparency and sufficient adhesion and durability.

1 Solar cell module 2 Transparent front substrate 3 Front encapsulant 4 Solar cell element 5 Back encapsulant 6 Back protective sheet

Claims (8)

The gel fraction is 0% or more and 10% or less,
A copolymer of ethylene and alpha-olefins to a linear low density polyethylene, density 0.865 g / cm ³ or more and 0.900 g / cm ³ or less of polyethylene, alpha-olefin and an ethylenically unsaturated silane compound a silane-modified polyethylene obtained by copolymerizing as comonomers bets, the comprise ing polyethylene resin was used as a base resin,
The base resin has an α-olefin having 3 carbon atoms having a content of 5 mol% or more and 25 mol% or less.
The melting point of the polyethylene is 50 ° C. or higher and 70 ° C. or lower, and the MFR at 190 ° C. and a load of 2.16 kg measured by JIS-K6922-2 is 10 g / 10 min or more and 20 g / 10 min or lower.
The melting point of the silane-modified polyethylene is 50 ° C. or higher and 70 ° C. or lower, and the MFR is 10 g / 10 minutes or longer and 20 g / 10 minutes or lower.
Contains a cross-linking agent
The cross-linking agent has a 1-hour half-life temperature of 125 ° C. or higher and 145 ° C. or lower, and a content in the resin component of 0.2% by mass or higher and 0.5% by mass or lower.
By the encapsulant composition for the solar cell module
All layers are formed,
Single-layer or multi-layer encapsulant sheet. The melting point difference between the polyethylene and the silane-modified polyethylene is within 20 ° C., and the MFR difference is 10 g / 10 minutes or less.
The encapsulant sheet according to claim 1. The polyethylene and the silane-modified polyethylene have the same melting point, and the MFR is also the same.
The encapsulant sheet according to claim 1 or 2. The encapsulant sheet is a multi-layer encapsulant sheet, and the MFR of the outermost layer is higher than that of the other layers.
The encapsulant sheet according to any one of claims 1 to 3. The encapsulant sheet according to any one of claims 1 to 4, wherein the cross-linking agent is a peroxyketal or a dialkyl peroxide. Gel fraction is 0%,
The encapsulant sheet according to any one of claims 1 to 5. A solar cell module in which the sealing material sheet according to any one of claims 1 to 6 and a glass substrate are laminated so as to face each other. The solar cell module according to claim 7, wherein the gel content of the encapsulant sheet is 50% or more and 90% or less.

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