JP2012054521A - Sealing material composition for solar cell module and sealing material for solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an olefin-based sealing material for a solar cell module which has excellent flexibility in low temperature region in comparison with EVA and has heat resistance at high temperatures.SOLUTION: A sealing material composition for solar cell module includes: low density polyethylene having a density of 0.940 or less, preferably 0.900 or less; a crosslinking agent containing a crosslinking agent and a crosslinking assistant of such an amount corresponding to a gel fraction after crosslinking at 150°C for 30 minutes of 5% or more and 95% or less; and a crosslinking assistant, where the low density polyethylene has a number-average molecular weight of 30,000 to 90,000. Consequently, the sealing material has flexibility in low temperature region and heat resistance at high temperatures in comparison with EVA, while the sealing material is an olefin-based material. Furthermore, this allows quick crosslinking simultaneous with assembling of module to shorten a manufacturing process time of a module.

Description

  The present invention relates to a sealing material composition for a solar cell module, a sealing material for a solar cell module using the same, a solar cell module incorporating the same, and a method for producing the same.

  In recent years, solar cells as a clean energy source have attracted attention due to the growing awareness of environmental issues. Currently, various types of solar cell modules have been developed and proposed. In general, a solar cell module has a configuration in which a transparent front substrate, a solar cell element, and a back surface protection sheet are laminated via a sealing material (filler).

  As a sealing material for a solar cell module, a configuration mainly containing EVA (ethylene-vinyl acetate copolymer) from the viewpoint of transparency and fluidity and containing a crosslinking agent and a crosslinking aid is known (patent). Reference 1). In this case, the above composition is formed uncrosslinked and crosslinked by heating during modularization.

  Further, as a sealing material for another solar cell module, PBR (propylene-butene copolymer), which is a low crystalline α-olefin having a crystallinity of 40% or less, or EBR (ethylene-butene copolymer). Moreover, the structure containing EPR (ethylene-propylene copolymer) etc., a crosslinking agent, and a crosslinking adjuvant is known (refer patent document 2).

  Furthermore, in applications such as electric wires, it is also known to perform crosslinking by reacting an olefin resin such as HDPE with a crosslinking agent (photoreaction initiator) and a crosslinking aid (see Patent Document 3). .

JP 2009-135200 A JP 2006-210906 A JP-A-5-4235

  The EVA of Patent Document 1 has the advantage of being excellent in transparency and fluidity, but has the basic drawback of poor water vapor barrier properties. Further, EVA has a problem that, for example, the film is hardened due to intramolecular hydrogen bonding in a low temperature region below freezing point, so that the flexibility in the low temperature region is inferior, and this causes cell cracks in the module.

  In Patent Document 2, although the water vapor barrier property is improved by using a low crystalline olefin as a base, the elastic modulus is particularly high near room temperature and the flexibility is not sufficient.

  Further, as in Patent Document 3, in the electric wire field, the olefin resin is cross-linked to increase the strength, but as a solar cell sealing material, there are many other physical properties such as transparency and flexibility. It is required to satisfy simultaneously. And the present condition is that the olefin type bridge | crosslinking type solar cell module sealing material which satisfy | fills all these physical properties has not been obtained yet.

  The present invention has been made in order to solve the above problems, and its purpose is to have an olefinic characteristic of excellent water vapor barrier properties, and to have flexibility in a low temperature region more than EVA, and An object of the present invention is to provide an olefin-based solar cell module sealing material that also has heat resistance at high temperatures.

  The present inventors pay attention to the molecular weight of low-density polyethylene and use an olefin having a low molecular weight and a high MFR (MI) as a base resin and crosslinking it with a predetermined monomer, thereby having an olefin water vapor barrier. In addition, the present inventors have found that it has flexibility in a low temperature region more than EVA, can obtain heat resistance at a high temperature, and is excellent in moldability in a low temperature region even though it is olefin-based. In addition, according to a preferred embodiment, since the crosslinking rate is high and reaches a predetermined gel fraction in a short time, crosslinking is performed, so that a fast cure that does not require a post-crosslinking step in the modularization step is possible, and it is an olefin type. It has also been found that a sealing material excellent in productivity can be obtained, and the present invention has been completed. More specifically, the present invention provides the following.

(1) Low density polyethylene having a density of 0.940 g / cm ³ or less and a number average molecular weight of 30,000 to 90,000 and a gel fraction after crosslinking at 150 ° C. for 30 minutes are 5% to 95%. The sealing material composition for solar cell modules containing the quantity of a crosslinking agent and a crosslinking adjuvant.

  (2) The solar cell module sealing material composition according to (1), wherein the low-density polyethylene has a melt mass flow rate (MFR) of 6 g / 10 min or more and 40 g / 10 min or less at 190 ° C.

(3) The solar cell module sealing material composition according to (1) or (2), wherein the low-density polyethylene has a density of 0.900 g / cm ³ or less.

  (4) The solar cell module sealing material composition according to any one of (1) to (3), wherein the cross-linking agent is contained in an amount of 0.5 to 2.0 parts by mass with respect to 100 parts by mass of the low-density polyethylene. object.

  (5) The solar cell module sealing material according to any one of (1) to (4), wherein the crosslinking aid is contained in an amount of 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the low-density polyethylene. Composition.

  (6) The encapsulant composition for a solar cell module according to any one of (1) to (5), wherein the crosslinking aid is a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group.

  (7) The encapsulant composition for a solar cell module according to (6), wherein the functional group of the polyfunctional monomer is at least one selected from an allyl group, a (meth) acrylate group, and a vinyl group.

  (8) The solar cell module according to (6) or (7), wherein the crosslinking aid is one or more selected from triallyl isocyanurate, 1,6 hexanediol diacrylate, and 1,9 nonanediol diacrylate. Sealing material composition.

  (9) The solar cell module sealing material composition according to any one of (1) to (8) is molded and then subjected to a crosslinking treatment, and the gel fraction after the crosslinking treatment at 150 ° C. for 30 minutes is 5% or more. The sealing material for solar cell modules which is 95% or less.

  (10) A solar cell module including the solar cell module sealing material according to (9).

  (11) After molding the solar cell module sealing material composition according to any one of (1) to (8), a crosslinking treatment is performed in the modularization process of the solar cell module, and the thermal lamination temperature in the modularization process is 135. The manufacturing method of the solar cell module which is 160 to 160 degreeC and heat lamination time is less than 20 minutes.

  The encapsulant using the encapsulant composition for solar cell modules of the present invention has excellent water vapor barrier properties by crosslinking in the subsequent modularization step, and in a lower temperature region than EVA. It has flexibility and can obtain heat resistance at high temperatures, and is excellent in moldability in a low temperature region while being olefin-based. Furthermore, since the crosslinking rate reaches a predetermined gel fraction in a short time and crosslinks, fast curing can be performed without the need for post-crosslinking in the modularization process. An olefin-based solar cell module sealing material can be provided.

It is a graph which shows the measurement result of the Young's modulus in an Example. It is a graph which shows the result of having measured the relationship between the thermal lamination time of the modularization process in an Example, and a gel fraction. It is sectional drawing which shows an example of the laminated constitution of the solar cell module of this invention.

  Hereinafter, it demonstrates in detail in order of the sealing material composition for solar cell modules of this invention, the sealing material for solar cell modules, a solar cell module, and its manufacturing method.

<Sealant composition for solar cell module>
The sealing material composition for solar cell modules of this invention contains the low density polyethylene whose density is 0.940 or less, a crosslinking agent, and a crosslinking adjuvant as an essential component. Hereinafter, after explaining these essential components, other resins and other components will be explained.

[Low density polyethylene]
In the present invention, low density polyethylene (LDPE) having a density of 0.940 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 0.940 g / cm ³ or less, preferably 0.900 g / cm ³ within the following ranges More preferably, it is the range of 0.870-0.890 g / cm < ³ >. Within this range, good flexibility and transparency can be imparted while maintaining sheet processability, and moisture from the end face of the module, specifically between the sealing material and the substrate, can be obtained. Infiltration can be suppressed.

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

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

  As the α-olefin of the linear low density polyethylene, an α-olefin having no branch is preferably used. Among these, 1-hexene and 1-heptene which are α-olefins having 6 to 8 carbon atoms are preferable. Or 1-octene is particularly preferably used. When the α-olefin has 6 to 8 carbon atoms, the solar cell module sealing material can be provided with good flexibility and good strength. As a result, the adhesiveness between the sealing material and the base material is further increased, and the above problem of moisture intrusion can be suppressed.

  The number average molecular weight of the low density polyethylene used in the present invention is from 30,000 to 90,000 in terms of polystyrene, preferably from 30,000 to 70,000, more preferably from 30,000 to 550,000. Thereby, the softness | flexibility in the low-temperature area | region below freezing can be maintained more than EVA. If the number average molecular weight is less than 30,000, moldability as a sealing material becomes difficult, which is not preferable, and if it exceeds 90,000, the moldability and the crosslinking rate are decreased, which is not preferable. In addition, about the softness | flexibility in a low temperature area | region, it can evaluate by measuring a Young's modulus so that it may demonstrate in the Example mentioned later.

  The present invention is also characterized in that heat resistance at high temperatures can be ensured by a combination with a crosslinking aid (monomer) described later, which will be described in the crosslinking aid described later. .

  The number average molecular weight can be measured by dissolving in a solvent such as THF and using a conventionally known GPC method. An example of measurement conditions will be described in Examples.

  The melt mass flow rate (MFR) of the low density polyethylene is preferably 6 g / 10 min or more and 40 g / 10 min or less at 190 ° C. It is preferable that the MFR is in the above range since it has excellent water vapor barrier properties, has flexibility in a low temperature region as compared with EVA, and can obtain heat resistance at high temperatures. The melt mass flow rate (MFR) of the low density polyethylene is more preferably 10 g / 10 min or more and 40 g / 10 min or less at 190 ° C. When the MFR is in the above range, in addition to the above-mentioned performance, the crosslinking rate is further high, and the gel can reach a predetermined gel fraction in a short time and can be crosslinked. This is preferable because it can be cured.

The content of the low-density polyethylene having a density of 0.940 g / cm ³ or less contained in the solar cell module sealing material composition is preferably 10% by mass or more and 99% by mass or less, more preferably in the composition. It is 50 mass% or more and 99% mass or less, More preferably, it is 90 mass% or more and 99% mass or less. In other words, other resins may be contained within this range. For example, other polyethylene resins exceeding 0.940 g / cm ³ can be exemplified. These may be used, for example, as an additive resin, and can be used for masterbatching other components described later.

[Crosslinking agent]
A well-known thing can be used for a crosslinking agent, It does not specifically limit, For example, a well-known radical polymerization initiator can be used. Examples of radical polymerization initiators include hydroperoxides such as diisopropylbenzene hydroperoxide and 2,5-dimethyl-2,5-di (hydroperoxy) hexane; di-t-butyl peroxide, t-butyl Cumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-peroxy) hexyne-3, etc. Dialkyl peroxides; diacyl peroxides such as bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, benzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dichlorobenzoyl peroxide; t-butyl peroxyacetate, t-butyl pero Ci-2-ethylhexanoate, t-butyl peroxypivalate, t-butyl peroxyoctoate, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, di-t-butyl peroxyphthalate, 2 , 5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexyne-3, t-butylperoxy-2-ethylhexyl carbonate Oxyesters; organic peroxides such as methyl peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, or azo compounds such as azobisisobutyronitrile and azobis (2,4-dimethylvaleronitrile), dibutyltin Diacetate, Dibutyltin dilaurate , It may be mentioned dibutyltin dioctoate, dioctyltin dilaurate, dicumyl peroxide, such a silanol condensation catalyst. Of these, organic peroxides having a one-hour half-life temperature of 100 ° C. to 150 ° C. are preferred. As content of a crosslinking agent, it is preferable that 0.5 mass%-2.0 mass% is contained in a composition, More preferably, it is preferable that 0.5 mass%-1.5 mass% is contained, Furthermore, Preferably it is the range of 0.5 mass part-1.0 mass part. If it is less than 0.5 parts by mass, the heat resistance at high temperatures is inferior due to insufficient crosslinking, and the crosslinking time becomes long and cannot be fast cured. If the amount exceeds 2.0 parts by mass, radicals may be generated and foaming may cause problems due to modularization. In addition, unreacted residual crosslinking agent may cause crosslinking during storage, and storage stability as a sealing material may be increased. It is not preferable because it may decrease.

[Crosslinking aid]
In the present invention, a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group is preferable, and a functional group of the polyfunctional monomer is preferably an allyl group, a (meth) acrylate group, or a vinyl group. As a result, an appropriate crosslinking reaction is promoted to make the gel fraction 5% or more and 95% or less, and in the present invention, this crosslinking aid reduces the crystallinity of the low density polyethylene and maintains transparency. And by using this crosslinking aid together, the low-molecular-weight polyethylene as described above is used to obtain flexibility in a low-temperature region, while at the same time achieving both high-temperature heat resistance. is there. That is, the present invention has succeeded in obtaining, for the first time, a preferable elasticity higher than EVA as a sealing material in a polyethylene system.

  Specific crosslinking aids include polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, diallyl maleate, trimethylol propane trimethacrylate (TMPT), trimethylol propane tri Poly (meth) acryloxy compounds such as acrylate (TMPTA), ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, Glycidyl methacrylate containing double bond and epoxy group, 4-hydroxybutyl acrylate glycidyl ether and 1,6-hexanediol diglycidyl containing two or more epoxy groups Ether, and 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, an epoxy compound such as trimethylolpropane polyglycidyl ether. These may be used alone or in combination of two or more.

  Among these, TAIC, 1,6-hexanediol diacrylate, from the viewpoint of good compatibility with low density polyethylene, lowering crystallinity by crosslinking, maintaining transparency, and imparting flexibility in a low temperature region, 1,9-nonanediol diacrylate can be preferably used.

  The amount of the crosslinking aid used is preferably 0.5 to 1.5 parts by mass, more preferably 0.5 to 1.0 parts by mass with respect to 100 parts by mass of the low density polyethylene. More preferably, it is the range of 0.5 mass part-0.7 mass part. Within this range, an appropriate crosslinking reaction can be promoted to reduce the gel fraction to 95% or less, and so-called fast cure can be achieved in which crosslinking in the modularization process described later is completed in one step. Can do. If the amount is less than 0.5 parts by mass, the flexibility and heat resistance are inferior due to insufficient crosslinking, and the crosslinking time becomes long and cannot be fast cured. If the amount exceeds 1.5 parts by mass, the unreacted residual crosslinking aid may bleed out after modularization, or the crosslinking aid may bleed out during storage and storage stability may be reduced.

  As described above, the present invention achieves both of imparting flexibility in a low temperature region with low molecular weight low density polyethylene and heat resistance with a crosslinking aid. For this reason, the selection of the type and amount of the crosslinking aid is also important for achieving compatibility, and the present invention is also characterized by finding the optimum range of the crosslinking aid suitable for combination with low molecular weight polyethylene.

[Radical absorbent]
In the present invention, the gel fraction can be further finely adjusted by adjusting the degree of cross-linking by using the above-mentioned cross-linking agent as a radical polymerization initiator in combination with the radical absorbent for quenching it. Examples of such radical absorbers 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. It is preferable that the usage-amount of a radical absorber is contained in 0.01 to 3 mass% in a composition, More preferably, it is the range of 0.05 mass part-2.0 mass parts. If it exists in this range, a crosslinking reaction can be suppressed moderately and a gel fraction can be 95% or less.

[Other ingredients]
The solar cell module sealing material composition may further contain other components. For example, a weather resistance masterbatch for imparting weather resistance to the encapsulant prepared from the encapsulant composition for solar cell modules of the present invention, various fillers, light stabilizers, ultraviolet absorbers, heat stabilizers, etc. These components 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 solar cell module encapsulant composition. By including these additives, it is possible to impart a long-term stable mechanical strength, an effect of preventing yellowing, cracking, and the like to the encapsulant composition for solar cell modules.

  The weather-resistant masterbatch is a dispersion of a light stabilizer, a UV absorber, a heat stabilizer, the above-mentioned antioxidant, etc., in a resin such as polyethylene, and this is a sealing material composition for a solar cell module. By adding to, favorable weather resistance can be imparted to the solar cell module sealing material. 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.

  In addition to the above, the other components used in the solar cell module encapsulant composition of the present invention include an adhesion improver such as a silane coupling agent, a nucleating agent, a dispersant, a leveling agent, a plasticizer, A foaming agent, a flame retardant, etc. can be mentioned.

<Sealant for solar cell module and solar cell module using the same>
Next, an example of the solar cell module sealing material of the present invention and a solar cell module using the same will be described with reference to the drawings. FIG. 3 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 protection sheet 6 are sequentially laminated from the light receiving surface side of incident light. . The solar cell module 1 of the present invention uses the solar cell module sealing material of the present invention (hereinafter also simply referred to as “sealing material sheet”) as the front sealing material 3 and / or the back sealing material 5.

  The encapsulant sheet of the present invention is obtained, for example, by molding and processing the above encapsulant composition for solar cell modules by a conventionally known method, and is a sheet or film having a thickness of 300 to 650 μm. It is what. 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, by forming the solar cell module sealing material composition into a sheet, a layer made of the solar cell module sealing material composition of the present invention (hereinafter referred to as a layer according to the present invention) is used as the sealing material sheet of the present invention. Or a multilayer sheet provided with the layer according to the present invention. Note that the sealing material sheet is uncrosslinked by setting the molding temperature thereof to, for example, 90 ° C. to 100 ° C., and is heated at a high temperature at the time of manufacturing a solar cell module described later to complete the crosslinking. Focusing on the molecular weight of low-density polyethylene, low-molecular weight, high MFR (MI) olefin is used as a base resin, and this is cross-linked with a predetermined monomer to form at low molding temperature despite being olefin-based. It is also a feature of the present invention that it has excellent properties.

  The encapsulant sheet may be a single layer sheet or a multilayer sheet. In the case of a multilayer sheet, for example, the sealing material sheet may be configured as a two-layer structure, and the layer according to the present invention may be disposed only in one layer. The layer according to the present invention may be disposed. In order to produce a sealing material sheet made of a multilayer film as described above, for example, a conventionally known T-die multilayer coextrusion method can be used.

  In the modularization process, the solar cell module 1 is formed by sequentially laminating, for example, members composed of the transparent front substrate 2, the front sealing material 3, the solar cell element 4, the back sealing material 5, and the back surface protection sheet 6 described above. And then by vacuum suction or the like, and then, by a molding method such as a thermal lamination method, the above-mentioned member can be manufactured by thermocompression molding as an integral molded body.

  Further, the solar cell module 1 has a front sealing material 3 and a rear surface on the front side and the back side of the solar cell element 4 by a molding method usually used in ordinary thermoplastic resins, for example, T-die extrusion molding. The sealing material 5 is melt-laminated, the solar cell element 4 is sanded with the front sealing material 3 and the back sealing material 5, and then the transparent front substrate 2 and the back surface protection sheet 6 are sequentially stacked, You may manufacture by the method of integrating by vacuum suction etc. and carrying out thermocompression bonding.

  In addition, since a sealing material sheet is uncrosslinked at the time of shaping | molding as mentioned above, it bridge | crosslinks in this modularization process. In this case, the heat laminating time in the modularization process is a predetermined temperature, for example, the heat laminating time temperature is 135 ° C. to 160 ° C., and the heat laminating time is within 20 minutes, preferably the heat laminating time temperature is 140 ° C. To 155 ° C. and thermal laminating time is less than 13 minutes, preferably the thermal laminating temperature is 150 ° C. to 160 ° C. and the thermal laminating time is less than 10 minutes to reach a predetermined gel fraction and crosslink Can be completed. In addition, since it may damage a cell when it exceeds 160 degreeC, it is unpreferable. That is, when the MFR is 10 or more in the sealing material of the present invention, fast cure equivalent to EVA is possible while being olefin-based. This point is also an excellent effect of the present invention that could not be obtained with a conventional olefin-based sealing material, and will be described in more detail in Examples described later.

  In the solar cell module 1 of the present invention, the transparent front substrate 2, the solar cell element 4, and the back surface protection sheet 6, which are members other than the front sealing material 3 and the back sealing material 5, are particularly limited to conventionally known materials. It can be used without. 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.

  In the solar cell module of the present invention thus obtained, the gel fraction after crosslinking of the encapsulant sheet is 5% or more and 95% or less, and the lower limit is preferably 20% or more, more preferably 40% or more, and the upper limit. Is preferably 80% or less, more preferably 70% or less. As a result, while having the same degree of transparency as conventional EVA, flexibility higher than EVA can be obtained particularly in a low temperature range from -50 ° C. to 0 ° C. as shown in the examples described later. On the other hand, it has heat resistance in a high temperature region of 80 ° C to 150 ° C. Furthermore, since the gel fraction is reached in a short cross-linking time as described above and the cross-linking is substantially completed, so-called fast cure is possible, and a separate cross-linking step is unnecessary and the sealing material is excellent in productivity.

  In addition, as shown in FIG. 2 of the Example mentioned later, the gel fraction in the present invention is after the crosslinking treatment at 150 ° C. for 30 minutes in the method of the Example, unless particularly specified in temperature and time. Of gel fraction. In addition, the above “completion of crosslinking” means a time point when the gel fraction reaches a steady state (saturate) after increasing.

  The technical idea of the present invention cannot be conceived at all from the field where the transparency and flexibility need not be considered like the wire coating material of Patent Document 3. Patent Document 2 is also a simple idea of simply crosslinking to increase the gel fraction, and the present invention cannot be recalled. The present invention makes it possible to optimally adjust the degree of crosslinking by selecting the type and amount of crosslinking aid based on low density linear low density polyethylene. As a result, the desired gel fraction and elastic modulus can be obtained. As a result, it is possible to obtain physical properties and optical properties that exceed those of EVA while being olefin-based.

  And in the solar cell module, if the water vapor permeability of the encapsulant sheet is high, it adversely affects the solar cell element due to the ingress of moisture from the end face of the encapsulant sheet itself, but the encapsulant sheet of the present invention is Since it is an olefin type and its water vapor permeability is low, it is preferably used. In addition, as a result of increasing the adhesion between the sealing material sheet and the base material, it is possible to effectively suppress the intrusion of moisture from between the transparent front substrate 2 and the back surface protection sheet 6 and the sealing material sheet. Has an effect.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.
<Manufacture of sealing material for solar cell module>
A composition having the composition shown in Table 1 below was mixed and melted, and a film was formed by a conventional T-die method so as to have a thickness of 460 to 480 μm. The film forming temperature was 90 ° C. to 100 ° C.
In addition, mixing of LLDPE and various additives melted and compounded other than the crosslinking agent at 90 ° C., and the crosslinking agent was stirred at 40 ° C. for 15 minutes to prevent deactivation of the crosslinking agent. .
LLDPE1: A metallocene linear low density polyethylene which is a copolymer of ethylene and 1-hexene and has a density of 0.88 g / cm ³ and a melt mass flow rate (MFR) at 190 ° C. of 30 g / 10 min. Number average molecular weight 53,000 in terms of polystyrene.
LLDPE2: A metallocene linear low density polyethylene which is a copolymer of ethylene and 1-hexene and has a density of 0.88 g / cm ³ and a melt mass flow rate (MFR) at 190 ° C. of 8 g / 10 min. Number average molecular weight of 77,000 in terms of polystyrene.

[Molecular weight measurement conditions]
Equipment: Uses Waters GPC system “Waters2695” Detector: RI detector “Waters2414”
Measuring solvent: THF
Flow rate: 1 ml / min
Column: LF-804 x 3 (made by Shodex)
Column oven 40 ° C, injection volume 50μL

Cross-linking agent (TBEC): t-butylperoxy-2-ethylhexyl carbonate (manufactured by Arkema Yoshitomi, trade name Luperox TBEC)
Crosslinking aid A (TAIC): triallyl isocyanurate (Sartomer, trade name SR533)
Crosslinking aid B: 1,6 hexanediol diacrylate (manufactured by Daicel-Cytec, trade name HDDA)
Crosslinking aid C: 1,9 nonanediol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name A-NOD-N)
UV absorber A: Ciba Japan Co., Ltd., trade name CHIMASSORB 81
UV absorber B: manufactured by Chemipro Kasei Co., Ltd., trade name KEMISORB102
Weatherproof stabilizer A: Ciba Japan Co., Ltd., trade name Tinuvin 770
Weathering stabilizer B: Product name ADEKASTAB LA-81, manufactured by ADEKA Corporation
Antioxidant: Ciba Japan Co., Ltd., trade name Irganox 1076
Silane coupling agent A (SC agent A): manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM1003
Silane coupling agent B (SC agent B): manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM503
Silane coupling agent C (SC agent C): Shin-Etsu Chemical Co., Ltd., trade name X-40-2655A
The EVA sealing material of Comparative Example 1 is 1.5 parts by mass of a crosslinking agent (Luperox 101) with respect to 100 parts by mass of EVA (vinyl acetate content 28%, manufactured by Mitsui DuPont Polychemical, trade name EVAFLEX / EV250 grade). Parts, crosslinking aid (SR350) 1.5 parts by weight, antioxidant (NAUGARD-P) 0.2 parts by weight, UV absorber (0.1 parts by weight of Tinuvin 7709 and 0.3 parts by weight of Cyasorb UV-531 ) Was used.

<Test Example 1>
Next, these uncrosslinked sealing materials were treated with a vacuum heating laminator at 155 ° C. for 10 minutes to perform crosslinking (corresponding to thermal lamination in the modularization process), and each of the examples and comparative examples was sealed after crosslinking. The material was obtained. In addition, about Example 7, after processing with a vacuum heating laminator at 120 degreeC, heat crosslinking was performed for 30 minutes in 150 degreeC oven. The post-crosslinking encapsulant was evaluated for gel fraction, physical properties, optical properties, and water vapor permeability. The results are summarized in Table 2. Each test condition is as shown below, and-in the table is not measured.
Gel fraction (%): 0.1 g of the sealing material after cross-linking was put into a resin mesh, extracted with 60 ° C. toluene for 4 hours, then taken out together with the resin mesh, weighed after drying treatment, and the weight was compared before and after extraction. The mass% of insoluble matter was measured and used as the gel fraction.
The sample for measuring the gel fraction is obtained by sandwiching a sealing material (50 mm × 50 mm × thickness of about 0.4 to 0.5 mm) in a 50 μm thick PET film (100 mm × 100 mm) that has been subjected to a release treatment. Then, it was laminated at a predetermined temperature and time by a thermal laminator.
Gap stress (mm): Two sheets of sealing material cut out to 5 × 7.5 cm are placed on a large glass plate that has been subjected to graining, and then 5 × 7.5 grain glass is placed on top of the sealing material. I did it. Thereafter, the large glass is placed vertically and left at 150 ° C. for 12 hours. The moving distance of 5 × 7.5 grain glass after being left was measured and evaluated.
Young's modulus (Pa): A test piece after cross-linking was cut into 5 × 20 mm and measured with a UBM Rheogel E-4000.
Haze (%): Measured in accordance with JISK7136 with Murakami Color Research Laboratory Haze / Transmittance HM150.
Total light transmittance (%): Measured in accordance with JISK 7361 with Murakami Color Research Laboratory Haze / Transmittance HM150.
Yellowness (Yi): Measured with SM Color Computer, Suga Test Instruments Co., Ltd. according to JISK7105.
Water vapor transmission rate (g / m ² · day): Measured by JISK7129B method, 40 ° C. × 90% RH.

<Test Example 2>
For Example 2, Example 7, and Comparative Example 1, the change in elastic modulus (Young's modulus) with temperature was measured. The result is shown in FIG.
<Test Example 3>
For Example 2 and Example 7, the relationship between the thermal lamination time and the gel fraction in the modularization process was measured. The result is shown in FIG.

  As can be seen from FIG. 1, Example 2 and Example 7 have flexibility in a low temperature region of −50 ° C. to 0 ° C. compared to EVA of Comparative Example 1, while 80 ° C. to 150 ° C. It can be understood that the heat resistance is superior to EVA in the high temperature region, and that the elastic performance of EVA or higher is obtained by the present invention while being olefin-based.

  Further, as can be seen from Table 2, the sealing material of the present invention is a cross-link having a gel fraction of 5% or more and 95% or less, and in the present invention, while having an olefin water vapor barrier, It can be understood that the same physical properties as EVA are obtained in terms of flexibility.

  Further, as can be seen from FIG. 3, in Example 2 of MFR30, the gel fraction exceeded 50% at 130 ° C. and then became substantially constant, and it took 22 minutes to saturate, but at 135 ° C., 19 minutes, The gel fraction exceeded 50% in 12 minutes at 140 ° C, 9 minutes at 150 ° C, 8 minutes at 155 ° C, and 6 minutes at 160 ° C. On the other hand, in Example 7 of MFR8, although the gel fraction exceeded 50% and became substantially constant thereafter, it took over 15 minutes at 150 ° C., 13 minutes at 155 ° C., and 11 minutes at 160 ° C. From this curve, it can be understood that in the sealing material of Example 2, the cross-linking reaction proceeds rapidly, and fast curing that does not require a post-crosslinking step in the modularization step is possible.

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

Claims (11)

Low density polyethylene having a density of 0.940 g / cm ³ or less and a number average molecular weight of 30,000 or more and 90,000 or less, and a crosslinking amount in which the gel fraction after crosslinking at 150 ° C. for 30 minutes is 5% or more and 95% or less. A solar cell module encapsulant composition comprising an agent and a crosslinking aid.   2. The encapsulant composition for a solar cell module according to claim 1, wherein the low-density polyethylene has a melt mass flow rate (MFR) of from 6 g / 10 min to 40 g / 10 min at 190 ° C. 3. The solar cell module sealing material composition according to claim 1, wherein the low density polyethylene has a density of 0.900 g / cm ³ or less.   The sealing material composition for solar cell modules in any one of Claim 1 to 3 which contains the said crosslinking agent 0.5 to 2.0 mass parts with respect to 100 mass parts of the said low density polyethylene.   The sealing material composition for solar cell modules in any one of Claim 1 to 4 which contains the said crosslinking adjuvant 0.5 to 1.5 mass parts with respect to 100 mass parts of the said low density polyethylene.   The encapsulant composition for a solar cell module according to any one of claims 1 to 5, wherein the crosslinking aid is a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group.   The sealing material composition for a solar cell module according to claim 6, wherein the functional group of the polyfunctional monomer is at least one selected from an allyl group, a (meth) acrylate group, and a vinyl group.   The solar cell module sealing material according to claim 6 or 7, wherein the crosslinking aid is one or more selected from triallyl isocyanurate, 1,6 hexanediol diacrylate, and 1,9 nonanediol diacrylate. Composition.   The solar cell module encapsulant composition according to any one of claims 1 to 8 is molded and then subjected to a crosslinking treatment, and the gel fraction after the crosslinking treatment at 150 ° C for 30 minutes is from 5% to 95%. Sealant for solar cell module.   A solar cell module provided with the sealing material for solar cell modules of Claim 9.   After the solar cell module encapsulant composition according to any one of claims 1 to 8 is molded, a crosslinking treatment is performed in the modularization step of the solar cell module, and the thermal lamination temperature in the modularization step is from 135 ° C to 160 ° C. And the manufacturing method of the solar cell module whose thermal lamination time is less than 20 minutes.

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