JP2013219154A - Sealing sheet for solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing sheet for a solar cell having thermal creep resistance and light adhesion resistance, and obtained by irradiating a polyethylene resin with ionizing radiation.SOLUTION: In a sealing sheet for a solar cell which seals a resin layer in softened state while adhering to a sealed object, the resin layer contains low density polyethylene of at least 0.91 g/cm, and has a partially crosslinked part by irradiation with ionizing radiation, when viewed from the sheet surface.

Description

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

  In recent years, with increasing awareness of the environment, the supply of energy by solar cell power generation has attracted attention and has been put into practical use.

  Solar cell elements that form the heart of solar cells that directly convert solar energy into electricity are those that use monocrystalline or polycrystalline silicon cells (crystalline silicon cells), amorphous silicon, or compound semiconductors. A thing (thin film cell) or the like is used. Generally, a solar cell element is used by forming a solar cell module in order to connect a plurality of solar cell elements in order to generate a practical electric output and protect the solar cell element.

  In the solar cell module, the light-receiving surface is covered with a transparent front substrate such as glass, and a front surface side sealing sheet, a solar cell element, a back surface side sealing sheet, a back surface protection sheet, and the like are sequentially laminated, and the transparent front substrate is Then, using a dedicated solar cell vacuum laminator, these are vacuum sucked and heated at a temperature equal to or higher than the melting temperature of the resin constituting the sealing sheet (temperature condition of 150 ° C. in the case of EVA) and a pressing process. The sealing sheet is melted and bonded.

  In the method, first, the resin of the sealing sheet is melted in the heating process, and is in close contact with the member in contact with the melted resin in the pressing process, and vacuum laminated. In this laminating step, after the crosslinking agent contained in the sealing sheet, for example, the organic peroxide is thermally decomposed and the EVA crosslinking is promoted, the coupling agent contained in the sealing sheet comes into contact. It is covalently bonded to the member. As a result, the mutual adhesiveness is further improved, the flow of the solar cell element part due to the melting of the sealing sheet in a high temperature state is prevented (creep resistance), and the excellent adhesion to the glass, the power generation element and the back sheet Sex is realized.

  Conventionally, as a sealing sheet for a solar cell module, a combination of an ethylene-vinyl acetate copolymer resin (EVA) and a crosslinking agent typified by an organic peroxide has been used. In recent years, a sealing sheet using a polyethylene resin instead of EVA has been widely used by taking advantage of its excellent water vapor barrier property.

  As a polyethylene-based sealing sheet, for example, a sealing sheet made of a modified ethylene-based resin containing alkoxysilane as a copolymerization component is also known. Moreover, the sealing sheet which mix | blended a crosslinking agent with such modified ethylene resin, and bridge | crosslinked by the modularization process or the subsequent heating process is known (refer patent document 1).

Also, a polyethylene-based sealing sheet obtained by melt extrusion molding a resin composition comprising an α-olefin copolymer having specific physical properties and a silane compound, and the gel fraction of the sealing sheet is 5 at the time of extrusion molding. Also known is a sealing sheet used for a solar cell module by proceeding with crosslinking until about 29% and further proceeding with crosslinking so that the gel fraction is about 70-95% in the modularization step. (See Patent Document 2).
On the other hand, as a method of cross-linking treatment, in addition to thermal cross-linking treatment by heating an organic peroxide, it is sealed without using a cross-linking agent by irradiating polyethylene resin etc. with ionizing radiation for cross-linking. A technique for improving the heat resistance of a sheet is disclosed (see Patent Document 3).
In addition, a technique is disclosed in which low-density polyethylene of a predetermined density or less is irradiated with ionizing radiation to crosslink, and a long-time heat-curing process is omitted without using a cross-linking agent to impart heat resistance (patent) Reference 4).

JP 2009-10277 A JP 2011-12246 A JP 2009-249556 A JP 2011-77357 A

The following (1) to (4) are required for the sealing sheet as characteristics. That is,
(1) Low shrinkage during heating in the modularization process (hereinafter referred to as low shrinkage)
(2) Transparency that does not hinder the incidence of sunlight (hereinafter referred to as transparency)
(3) Good adhesion to the transparent front substrate, solar cell element, and back protection sheet (hereinafter referred to as adhesion)
(4) Flow prevention of solar cell element due to melting of sealing sheet at high temperature (hereinafter referred to as heat resistant creep property)
It is.

A sealing sheet based on an olefin resin such as a polyethylene resin can reduce the crystallinity inherent to the olefin resin by crosslinking with a predetermined monomer. This makes it possible to obtain the same physical properties as conventional EVA in terms of transparency and flexibility while maintaining the water vapor barrier of the olefin resin.
In particular, adhesiveness and heat-resistant creep resistance are in a trade-off relationship from the viewpoint of crosslinking of the sealing sheet. That is, in order to improve the adhesion, it is preferable to keep the degree of crosslinking low because the fluidity increases during heating. On the other hand, in order to improve heat resistance such as low shrinkage and heat-resistant creep resistance, the fluidity can be kept low at a high temperature by increasing the degree of crosslinking.

Like the sealing sheet described in Patent Document 1, all of the sealing sheets obtained by subjecting the polyethylene resin to thermal crosslinking treatment leave room for further improvement in heat resistance.
That is, although it is known to impart heat resistance and flame retardancy with a crosslinking agent, it is necessary to perform sufficient crosslinking to achieve the purpose. For this purpose, it is a conventional technique to add a large amount of a crosslinking agent. In Patent Document 1, a crosslinking agent is added in such an amount that the gel fraction is 30% or more. In this case, the heat resistance and flame retardancy are certainly improved, but conversely the flexibility is lowered and the adhesion cannot be obtained. In addition, if crosslinking proceeds during molding, the film formability deteriorates, so it is necessary to consider that the molding is performed at a low temperature and the crosslinking reaction is performed after the molding.

  Moreover, about the sealing sheet of patent document 2, bridge | crosslinking is advanced to a fixed grade at the time of melt extrusion molding. In this case, since it is necessary to control the progress of crosslinking during melt extrusion molding, there are large restrictions on the heating temperature, processing time, MFR of the material resin, and the like, which hinders the improvement of the productivity of the sealing sheet. It was a factor.

Moreover, as for the sealing sheet of patent document 1 and patent document 2, all the crosslinking agents used in order to bridge | crosslink with light or heat have bad light resistance, and transparency of a sealing sheet is temporally changed. This is one of the factors that significantly reduce the incident sunlight.
Further, in order to obtain a degree of crosslinking for obtaining a sufficient heat-resistant creep property in a sealing sheet that is crosslinked by heat, a long-time heat curing step is required, and an increase in production cost is inevitable.

In contrast to crosslinking by heat, crosslinking by irradiation with ionizing radiation is excellent in productivity because the shrinkage rate during heating in the modularization process is suppressed and a heat curing process is unnecessary. In addition, it has a great advantage in that the amount of the crosslinking agent having poor light resistance that causes a decrease in transparency can be suppressed.
Like the sealing sheet of patent document 3 and 4, the sealing sheet obtained by irradiating an ionizing radiation to a polyethylene-type resin is open | released from the restrictions of the conditions of said modularization process, and is a bridge | crosslinking process. Although the improvement of the heat resistance by can also be expected, there is a defect that the transparency is inferior compared with the case where the conventional thermal crosslinking treatment is performed, and there remains room for improvement in this respect. Moreover, it has not been possible to find a solution to the problem of conflicting heat resistance and adhesion that the adhesion decreases when the irradiation intensity of ionizing radiation is increased in order to obtain sufficient heat resistance.

  Moreover, generally a hindered amine light stabilizer (HALS: Hindered Amine Light Stabilizer) is added to the sealing sheet. HALS, which is a light stabilizer, reacts with ultraviolet rays and peroxides in the sealing material matrix to form NO radicals, and functions as a radical trapping agent. Since the radicals generated in the sealing material matrix are captured and bonded using the NO radicals, the sealing sheet maintains flexibility and maintains the adhesion even when exposed to sunlight for a long time. ing. However, when ionizing radiation such as an electron beam is irradiated on the entire surface, most of the HALS is decomposed at the time of irradiation, resulting in a decrease in light stability, that is, durability in terms of adhesion when exposed to light for a long time. Will be inferior.

  The present invention has been made to solve the above problems. The purpose of the present invention is that the shrinkage rate is low during heating in the modularization process and has transparency that does not hinder the incidence of sunlight, and has good adhesion with a transparent substrate, solar cell element, electrode, back surface protection sheet, etc. It is to supply a sealing sheet for a solar cell module having heat resistance creep resistance.

In view of the above situation, earnest research and development is advanced, and claim 1 of the present invention is a sealing sheet for a solar cell module that seals a softened resin layer in close contact with an object to be sealed, The resin layer contains a low-density polyethylene having a density of 0.91 g / cm ³ or less, and has a cross-linked treatment part that is partially cross-linked as viewed from the sheet surface by ionizing radiation irradiation. It is the sealing sheet to do.

  In the present invention, the cross-linked treatment part that has been partially cross-linked by irradiation with ionizing radiation means a process of increasing the weight average molecular weight by 50000 or more with respect to a portion that has not been cross-linked. ing. Therefore, the concept of the present application can be applied as long as the weight average molecular weight with respect to the uncrosslinked treatment part is 50,000 or more in the subsequent partial crosslinking treatment even if the whole is irradiated with weak ionizing radiation in advance and the whole molecular weight is raised. Is included. In the present invention, the sheet surface is used as a term indicating a sealing sheet surface irradiated with ionizing radiation.

  In addition, according to claim 2 of the present invention, there are a plurality of crosslinking treatment parts partially crosslinked by ionizing radiation irradiation, and the distance between the ends of the crosslinking treatment parts closest to each other in the crosslinking treatment parts. It is 1 mm or more and 160 mm or less, It is a sealing sheet of Claim 1 characterized by the above-mentioned.

  In addition, Claim 3 of the present invention is the encapsulating sheet according to claim 1 or 2, wherein the cross-linked portion partially cross-linked by ionizing radiation irradiation has a line shape. is there.

  In addition, according to claim 4 of the present invention, the cross-linking treatment part has a line shape along the film forming direction of the sealing sheet, and the width of the line shape is 1 mm or more and 160 mm or less. It is a sealing sheet of Claim 3 characterized by the above-mentioned.

According to the first aspect of the present invention, the resin layer of the sealing sheet contains low-density polyethylene having a density of 0.91 g / cm ³ or less, so that sufficient adhesiveness is maintained while maintaining sheet processability. Good flexibility and transparency obtained can be imparted, and peeling of the sealing sheet and entry of moisture from the end face when the solar cell module is obtained can be suppressed. In addition, the cross-linking treatment by ionizing radiation irradiation can eliminate the long-time heat curing process, greatly reduce the manufacturing cost, and adversely affect the transparency used during the thermal cross-linking treatment and photo-crosslinking treatment. Therefore, it is not necessary to use a light-light-resistant crosslinking agent that exerts a low temperature resistance, and therefore, when used in a solar cell module, it is possible to suppress a decrease in heat-resistant creep resistance due to exposure to sunlight for a long time.

By partially crosslinking with ionizing radiation irradiation, the non-crosslinked treatment part retains flexibility compared to the case of full-crosslinking treatment, so that the initial state of the sealing sheet and each member by crosslinking of the entire sealing sheet A decrease in adhesion is suppressed. Moreover, since a solar electronic element and an electrode are supported by the bridge | crosslinking process part, heat resistant creep property is also ensured. That is, it is possible to simultaneously improve adhesion and heat-resistant creep, which have been contradictory properties in the past.
In addition, HALS, which plays a role of maintaining adhesion when used as a solar cell module for a long time, is partially crosslinked by irradiation with ionizing radiation, thereby suppressing decomposition in the unirradiated portion of ionizing radiation, Since more HALS remains, the deterioration of the adhesion for a long period of time can be prevented as compared with the case where the entire surface is crosslinked.

  Furthermore, by providing the structural requirements described in claim 2, the shrinkage that occurs in the encapsulating sheet when the solar cell module is softened by heating at the time of creating the solar cell module and then returned to room temperature, A shrinkage rate of 40% or less that falls within the range can be realized. The shrinkage rate will be described later.

  Furthermore, by providing the structural requirements according to claim 3, when partially cross-linking the encapsulating sheet of the present application, an ionizing property in which a mask is arranged to partially block electronic radiation between the encapsulating sheet and the sealing sheet. By using the radiation irradiation device, the physical properties of the sealing sheet can be improved without reducing in-line productivity.

  Furthermore, by providing the structural requirements according to claim 4, when modularized, the number of cross-linked parts spanning from the electronic member constituting the solar cell module to the edge of the solar cell module is reduced. Separation from the edge of the battery module and intrusion of moisture are more firmly prevented. In the present invention, the electronic member refers to a component that should be kept airtight by the sealing sheet 14 when the solar cell module 10 is formed, such as the solar cell element 11 and the electrode 12 (excluding the external connection terminal portion). Use as a term.

It is the typical schematic which looked at the solar cell module using the sealing sheet which is one form of this invention from the transparent front plate side. It is typical sectional drawing of the AA cross section of FIG. 1 which shows the solar cell module using the sealing sheet which is one form of this invention. It is the fragmentary top view which looked at the 1st form of the sealing sheet which is one form of this invention from the sheet | seat surface. It is the fragmentary top view which looked at the 2nd form of the sealing sheet which is one form of this invention from the sheet | seat surface. It is the fragmentary top view which looked at the 3rd form of the sealing sheet which is one form of this invention from the sheet | seat surface. It is the fragmentary top view which looked at the 4th form of the sealing sheet which is one form of this invention from the sheet | seat surface.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment at all, In the range of the objective of this invention, it can add and change suitably.

  [Sealing sheet]

<Sealing sheet material>
(Polyethylene resin)
The composition for producing the sealing sheet 14 of the present invention contains a polyethylene resin having a density of 0.91 g / cm ³ or less and a polymerization initiator as essential components. Hereinafter, after explaining these essential components, other resins and other components will be explained.

In the present invention, low density polyethylene (LDPE) having a density of 0.91 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, the density of 0.91 g / cm ³ within the following range, preferably 0.890 g / cm ³ or less of Within the range, more preferably 0.870 to 0.885 g / cm ³ . If it is this range, favorable softness | flexibility, transparency, and heat resistance can be provided, maintaining sheet workability.

  In the present invention, it is preferable to use a metallocene linear low density polyethylene as the polyethylene resin. The 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, as shown in FIGS. 1 and 2, the adhesion between the sealing sheet 14 and the transparent front substrate 13, the back surface protection sheet 15, the solar cell element 11, the electrode 12, and other electronic members is improved. Rise.

  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 sheet 14 made of the sealing sheet material of the present invention is disposed between the transparent front substrate 13 and the solar cell element 11, the power generation efficiency of the solar cell module 10 hardly decreases.

  As the α-olefin of the linear low density polyethylene, an α-olefin having no branch is preferably used. Among these, 1-hexene, which is an α-olefin having 6 to 8 carbon atoms, Heptene or 1-octene is particularly preferably used. When the α-olefin has 6 to 8 carbon atoms, the sealing sheet 14 can be given good flexibility and good strength. As a result, the adhesiveness between the sealing sheet 14 and other members is further increased, and the intrusion of moisture between the sealing sheet 14 and other members can be suppressed.

The melt mass flow rate (MFR) of the low-density polyethylene is MFR at 190 ° C. and a load of 2.16 kg measured according to JIS-K6922-2 (in the present specification, the measurement value under these measurement conditions is hereinafter referred to as MFR). Must be 0.5 g / 10 min or more and 40 g / 10 min or less, and more preferably 6 g / 10 min or more and 40 g / 10 min or less.
Due to the MFR being in the above range, the processability during film formation is excellent.

  The encapsulating sheet 14 of the present invention is an encapsulating sheet 14 having a crosslinking treatment portion 14a that is partially crosslinked as viewed from the sheet surface by irradiation with ionizing radiation after melt formation of the encapsulating sheet material. For this reason, even if MFR of the low density polyethylene used as a base is high, the fluidity | liquidity of a modularization process can be suppressed by the crosslinked process part after film forming. For this reason, even if it is high MFR like the said range, it can be used conveniently.

  The molecular weight of the raw material low-density polyethylene itself is the above-mentioned metallocene linear low-density polyethylene, the number average molecular weight (Mn) in terms of polystyrene is about 30,000 to 40,000 g / mol, and the weight average molecular weight (Mw) is 70,000. To about 90000 g / mol. This molecular weight changes with the below-mentioned crosslinking agent and ionizing radiation irradiation.

  The encapsulating sheet material of the present invention may further contain a silane-modified polyethylene resin. The silane-modified polyethylene-based resin is obtained by graft-polymerizing an ethylenically unsaturated silane compound as a side chain to linear low-density polyethylene (LLDPE) or the like serving as a main chain. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to adhesion, the adhesion of the sealing sheet 14 to other members in the solar cell module 10 can be improved.

  The silane-modified polyethylene resin can be produced, for example, by a method described in JP-A-2003-46105. By using the resin as a component of the sealing sheet material of the solar cell module 10, 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 also affects the manufacturing conditions such as thermocompression bonding for manufacturing the solar cell module 10. It is possible to manufacture solar cell modules that have extremely excellent adhesion without receiving, are stable, low cost, and suitable for various applications.

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

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

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

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

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

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

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

  The content of the ethylenically unsaturated silane compound in constituting the copolymer of the α-olefin and the ethylenically unsaturated silane compound is, for example, 0.001 to 15,000 mass with respect to the total copolymer mass. %, Preferably about 0.010 to 5.000% by mass, particularly preferably about 0.050 to 2.000% by mass. In the present invention, when the content of the ethylenically unsaturated silane compound constituting the copolymer of the α-olefin and the ethylenically unsaturated silane compound is large, the mechanical strength and heat resistance are excellent, but the content is excessive. When it becomes, it exists in the tendency which is inferior to tensile elongation, adhesiveness, etc.

  The sealing sheet material may further contain an acid-modified polyethylene resin typified by maleic anhydride modification. The acid-modified polyethylene resin is obtained by graft polymerization using, for example, maleic anhydride or the like as a side chain on linear low-density polyethylene (LLDPE) or the like serving as a main chain. Such a graft polymer has a high polarity of the acid portion that contributes to the adhesive force, and can improve the adhesion of the sealing sheet 14 to the metal member in the solar cell module 10.

  The content of the low density polyethylene contained in the sealing sheet material is preferably 10 or more and 99 parts by weight or less, more preferably 50 or more and 99 parts by weight or less with respect to a total of 100 parts by weight of all resin components in the sealing sheet material. It is below, More preferably, it is 90-99 mass parts. Other resins may be included as long as the melting point of the sealing sheet material is within a range of less than 80 ° C. These may be used, for example, as an additive resin, or may be used for masterbatching other components described later.

(Crosslinking agent)
A well-known thing can be used for a crosslinking agent, It does not specifically limit, For example, a well-known radical polymerization initiator can be used. Examples of radical polymerization initiators include hydroperoxides such as diisopropylbenzene hydroperoxide and 2,5-dimethyl-2,5-di (hydroperoxy) hexane; di-t-butyl peroxide, t-butyl Cumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-peroxy) hexyne-3, etc. Dialkyl peroxides; diacyl peroxides such as bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, benzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dichlorobenzoyl peroxide; t-butyl peroxyacetate, t-butyl pero Ci-2-ethylhexanoate, t-butyl peroxypivalate, t-butyl peroxyoctoate, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, di-t-butyl peroxyphthalate, 2 , 5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexyne-3, t-butylperoxy-2-ethylhexyl carbonate Oxyesters; organic peroxides such as methyl peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, or azo compounds such as azobisisobutyronitrile and azobis (2,4-dimethylvaleronitrile), dibutyltin Diacetate, dibutyltin dilaurate It can be mentioned dibutyltin dioctoate, dioctyltin dilaurate, dicumyl peroxide, such a silanol condensation catalyst.

  Among the above, t-butylperoxy 2-ethylhexyl carbonate, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and the like can be preferably used. Since the active oxygen content is as high as 5% or more, and the one-minute half-life temperature of the polymerization initiator is 160 to 190 ° C., it is consumed at the time of molding and can remain after molding to suppress the progress of excessive post-crosslinking. preferable. A one-minute half-life temperature of less than 160 ° C. is not preferable because it is difficult to allow the crosslinking reaction to proceed after sufficiently dispersing the polymerization initiator during molding. In the present invention, the polymerization initiator is not necessarily essential.

  Conventionally, in the case of performing a crosslinking treatment by irradiation with ionizing radiation, it has been considered that a crosslinking agent such as an organic peroxide is unnecessary unlike the case of the thermal crosslinking treatment. However, the encapsulating sheet material used in the present invention may be subjected to a crosslinking treatment by irradiation with ionizing radiation, and may contain a small amount of a crosslinking agent. By adding this crosslinking agent, it is possible to improve heat-resistant creep resistance by irradiation with ionizing radiation and maintain transparency. Although the action of the crosslinking agent in the crosslinking treatment by irradiation with ionizing radiation is not clear, crosslinking proceeds because ionizing radiation is strong in energy, but the crystals that cause haze do not loosen unless they rise above a certain temperature and participate in crosslinking. It is estimated that this is because it remains without.

  The addition amount of the crosslinking agent to the sealing sheet material of the present invention is preferably 0.01 or more and 1.50 parts by mass or less with respect to 100 parts by mass of all components in the sealing sheet material. More preferably, it is 0.80 parts by mass or less. By setting the addition amount of the crosslinking agent to the sealing sheet material within this range, it is possible to obtain a sealing sheet that is particularly excellent in transparency in addition to heat-resistant creep property and adhesion. In this case, if the content of the crosslinking agent is less than 0.01 parts by mass, the effect of improving the heat resistance creep resistance is insufficient, and if it exceeds 0.80 parts by mass, the load during extrusion increases, The yield (productivity) decreases due to the generation of gel, and the transparency also decreases. In addition, although the sealing sheet 14 of the present invention can be obtained by partially performing a crosslinking treatment when viewed from the sheet surface by irradiation with ionizing radiation, in this case, the addition amount of the crosslinking material is: Unlike the case of conventional thermal crosslinking, sufficient heat resistance can be obtained even if the addition amount of the crosslinking material is less than 0.80 parts by mass. Thereby, the risk of the productivity fall by gelatinization of the sealing sheet material in the sheet-forming process of sealing sheet material can be reduced, and manufacturing cost can also be reduced by reducing the usage-amount of a crosslinking agent.

In general, a conventional uncrosslinked sealing 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 sealing sheet is limited by the heating temperature and heating time conditions in the modularization process, and the half-life temperature for 1 minute is generally less than 185 ° C. It was virtually limited to things. However, when manufacturing the crosslinked sealing sheet 14 of this invention, a crosslinking agent can be selected without receiving said restrictions. In general, the upper limit temperature of the crosslinking agent is about 230 ° C. from the viewpoint of resin oxidative degradation, but in the production of the crosslinked sealing sheet of the present invention, the half-life temperature for 1 minute is 185 within this range. It is possible to freely select a crosslinking agent having a temperature of not lower than ° C. In addition, by expanding the selection range in this way, there is an advantage that the temperature at which molding can be performed without cross-linking is improved and the productivity is improved.

(Crosslinking aid)
In the present invention, a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group may be used as a crosslinking aid. More preferably, the functional group of the polyfunctional monomer is an allyl group, a (meth) acrylate group, or a vinyl group. This promotes an appropriate crosslinking reaction, and in the present invention, this crosslinking aid reduces the crystallinity of the low density polyethylene and maintains transparency.

  Specifically, polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, diallyl maleate, trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA) Poly (meth) acryloxy compounds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, Glycidyl methacrylate containing epoxy groups, 4-hydroxybutyl acrylate glycidyl ether and 1,6-hexanediol diglycidyl ether containing two or more epoxy groups, 1 4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and epoxy compounds such as trimethylolpropane polyglycidyl ether. These may be used alone or in combination of two or more.

  Of these, TAIC is preferably used from the viewpoint of good compatibility with low density polyethylene, lowering crystallinity by crosslinking treatment, 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.

  As content of a crosslinking adjuvant, it is preferable that 0.010 or more and 3.000 mass parts or less are contained with respect to 100 mass parts of all the components of sealing sheet material, More preferably, it is 0.050 or more and 2.000 mass. Part or less. If it is in this range, a moderate crosslinking reaction by irradiation with ionizing radiation can be promoted, and the gel fraction of the sealing sheet subjected to crosslinking treatment before modularization can be made 0%.

(Adhesion improver)
In the production method of the present invention in which the crosslinking treatment is performed by irradiation with ionizing radiation, it is preferable to add an adhesion improver to the sealing sheet material. This is because when the ionizing radiation is irradiated in a large amount, the enlargement ratio can be suppressed, but the adhesion component on the surface of the sealing sheet may be damaged and the adhesion may be lowered, but the low molecular weight silane coupling agent It is presumed that the adhesion can be ensured by the seepage effect. Thereby, it becomes possible to irradiate ionizing radiation with stronger intensity, and more preferable heat-resistant creep property is obtained. 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 a silane coupling agent is added as an adhesion improver, the content thereof is 0.100 or more and 10.000 parts by mass or less with respect to 100 parts by mass of all components of the sealing sheet material, and the upper limit is preferably 5.000 parts by mass or less. When the content of the silane coupling agent is in the above range and the polyolefin resin constituting the sealing sheet material contains an appropriate amount of the ethylenically unsaturated silane compound, the adhesion is more preferably in the range. improves. In addition, when this range is exceeded, the film-forming property is lowered, 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 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 absorbers include hindered phenol-based antioxidants, hindered amine-based light 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 0.010 or more and 3.000 parts by mass or less, and more preferably 0.050 or more and 2.000 parts by mass or less in the composition. If it exists in this range, a crosslinking reaction can be suppressed moderately and the gel fraction of the crosslinked sealing sheet 14 before modularization can be made into less than 1%.

(Other ingredients)
The sealing sheet material can further contain other components. For example, components such as a weather resistance masterbatch for imparting weather resistance to the sealing sheet 14 produced from the sealing sheet material of the present invention, various fillers, a light stabilizer, an ultraviolet absorber, and a heat stabilizer are exemplified. Is done. These contents vary depending on the particle shape, density and the like, but are preferably in the range of 0.001 to 5.000 parts by mass in the sealing sheet material. By including these additives, the sealing sheet material can be provided with a mechanical strength that is stable over a long period of time, an effect of preventing yellowing, cracking, and the like.

  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 sheet material. Good weather resistance can be imparted to the encapsulating sheet. The weatherproof masterbatch may be prepared and used as appropriate, or a commercially available product may be used. The resin used for 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.

  Furthermore, other components used in the encapsulating sheet material of the present invention include nucleating agents, dispersants, leveling agents, plasticizers, antifoaming agents, flame retardants and the like in addition to the above.

[Method for producing sealing sheet]
The encapsulating sheet of the present invention obtains an uncrosslinked encapsulating sheet by a sheet forming process in which the above encapsulating sheet material is melt-molded at a temperature exceeding its melting point, and then a crosslinking treatment process by irradiation with ionizing radiation. Then, it becomes a sealing sheet for the solar cell module of the present invention in the form of a sheet or film. In addition, as an example, by combining the gel fraction and polystyrene-equivalent weight average molecular weight to a predetermined range by the production method as described in detail below, it has extremely preferable heat resistance, transparency, adhesion, etc. It is what. 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 sealing sheet material is carried out 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. At that time, the lower limit of the molding temperature may be a temperature exceeding the melting point of the sealing sheet material, and the upper limit is a temperature at which crosslinking does not start during film formation according to the 1-minute half-life temperature of the crosslinking agent used. It is not particularly limited as long as it is within these ranges. In the manufacturing method of the solar cell module sealing sheet of the present invention, as described above, since a crosslinking agent having a half-life temperature higher than that of the conventional one can be used, the molding temperature is set higher than before. By setting, it is possible to reduce the load applied to the extruder or the like and increase the productivity of the sealing sheet.

  In addition, it is preferable that said uncrosslinked sealing sheet which passed through the sheet forming process has a number average molecular weight of 80000 g / mol to 120,000 g / mol and a weight average molecular weight of 150,000 g / mol to 250,000 g / mol. The present invention has a low gel fraction and a predetermined degree of dispersion by irradiating ionizing radiation to the uncrosslinked sealing sheet in such a molecular weight range and partially subjecting it to a crosslinking treatment as viewed from the sheet surface. It can be set as a sealing sheet. The polystyrene-reduced average molecular weight can be measured by a conventionally known GPC method after being dissolved in a solvent such as tetrahydrofuran (THF).

Here, the molecular weight can be measured by a conventionally known GPC method after dissolving in a solvent such as tetrahydrofuran (THF). And the number average molecular weight Mn and the weight average molecular weight Mw when the polymer of molecular weight Mi (g / mol) is Ni (piece) in a sealing sheet are defined by the following formula | equation, respectively.

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

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

  The thickness of the sealing sheet 14 is preferably 100 μm or more and 600 μm or less, and if it is less than 100 μm, it is not preferable because the impact cannot be sufficiently mitigated and the insulating property becomes insufficient. Moreover, even if it exceeds 600 micrometers, since the effect beyond it is not acquired and it is uneconomical, it is unpreferable.

  Moreover, as for an uncrosslinked sealing sheet, it is desirable that the gel fraction is 0%. The gel fraction (%) is obtained by adding 0.1 g of a sealing sheet to a resin mesh, extracting with 60 ° C. toluene for 4 hours, taking out the resin mesh, weighing it after drying, comparing the mass before and after extraction, and remaining. The mass% of insoluble matter is measured and this is used as the gel fraction. When the gel fraction is 1% or more, the gel generation part becomes a factor that inhibits poor adhesion and transparency.

(Crosslinking process)
A cross-linking process in which the uncrosslinked encapsulating sheet after the sheet forming process is partially cross-linked as viewed from the sheet surface is partially cross-linked as viewed from the sheet surface by irradiation with ionizing radiation. And before the start of the solar cell module forming step of integrating the sealing sheet with other members. It is a feature of the encapsulating sheet 14 of the present invention that the cross-linking portion is formed by such a cross-linking step. Thus, by performing the bridge | crosslinking process by irradiation of ionizing radiation, it can be set as the sealing sheet which has heat resistant creep property, transparency, and the adhesiveness with respect to the other member in a solar cell module.

  In the present application, the crosslinking treatment indicates that the difference in weight average molecular weight of the crosslinking treatment portion 14a of the sealing sheet is increased by 50000 or more with respect to the uncrosslinked treatment portion 14b of the sealing sheet. That is, before the cross-linking step in which a partial cross-linking treatment is performed as viewed from the sheet surface, weak ionizing radiation is irradiated to the entire surface in advance to increase the overall molecular weight. What is necessary is just to enlarge the weight average molecular weight of the bridge | crosslinking process part 14a of a sealing sheet 50000 or more with respect to the non-crosslinking process part 14b of a sealing sheet in the bridge | crosslinking process which performs a crosslinking process. However, it should be noted that if the molecular weight is excessively increased in advance when weakly ionizing radiation is irradiated to the whole in advance, the adhesion is deteriorated.

  The cross-linking treatment in the cross-linking process in which the cross-linking treatment is performed partially when viewed from the sheet surface can be performed by ionizing radiation such as electron beam, α-ray, β-ray, γ-ray, neutron beam, etc. Is preferably used. 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 5 kGy to 100 kGy, preferably 5 to 40 kGy. When the irradiation dose is less than 5 kGy, sufficient crosslinking is not performed, and when it exceeds 100 kGy, there is a concern about deformation or coloring of the sheet due to generated heat. In addition, you may irradiate from both sides.

As for the cross-linking treatment by irradiation with ionizing radiation, as a total processing result, as long as the weight average molecular weight of the cross-linking treatment portion is increased by 50000 or more with respect to the non-cross-linking treatment portion as described above, individual cross-linking is performed. Although the conditions are not particularly limited, as an example, the sealing of the present invention can be carried out by carrying out a crosslinking treatment by irradiation with ionizing radiation with the irradiation dose and voltage within the following conditions (a) and (b). A stop sheet can be manufactured in a preferred embodiment.
(A) Irradiation dose: 5 kGy or more and 40 kGy or less (b) Voltage: In a sealing sheet having a thickness t, the radiation dose transmitted through a portion within the sealing sheet and having a distance of 1/2 t from the irradiation surface is The voltage that is 30% or more and 70% or less with respect to the irradiation dose on the irradiation surface, and that the arrival dose of the irradiation line to the back surface opposite to the irradiation surface is 0% or more and 25% or less with respect to the irradiation surface dose.

  In addition, in the cross-linked portion that has been partially cross-linked as viewed from the sheet surface, the irradiation amount of ionizing radiation and the addition amount of the cross-linking agent are appropriately adjusted so that the gel fraction is less than 1%. When the gel fraction is 1% or more, the gel generation part becomes a factor that inhibits poor adhesion and transparency. By suppressing the gel fraction to less than 1%, the wraparound characteristics of other members laminated up and down in the modularization process are improved, and the load at the time of melt extrusion is reduced, resulting in stable and high productivity. A sealing sheet can be produced.

  This crosslinking treatment may be performed continuously in-line following the sheet forming step, or may be performed off-line. As a means for performing a partial cross-linking treatment when viewed from the sheet surface, a so-called mask is provided with an ionizing radiation irradiation device and a sealing sheet in which holes are formed in a portion where the cross-linking treatment is desired in a material capable of blocking ionizing radiation. It is sufficient to irradiate between. If it carries out continuously in-line, the sealing sheet in which the bridge | crosslinking process part 14a illustrated in FIG. 3 has a line shape can be formed easily. Moreover, what is necessary is just to form offline if it is a pattern as illustrated in FIG.4, FIG.5, FIG.6.

<Shape of partially crosslinked processing section>
In this invention, it has the bridge | crosslinking process part 14a bridge | crosslinked partially by ionizing radiation irradiation seeing from the sheet | seat surface, and the non-crosslinking process part 14b which did not irradiate ionizing radiation, and heat-resistant creep property is provided in the bridge | crosslinking process part 14a By maintaining and maintaining adhesion at the uncrosslinked portion 14b, both heat-resistant creep properties and adhesion are achieved, and the shape of the partially crosslinked crosslinked portion 14a is not particularly limited. Absent.

  The cross-linking treatment part 14a may be provided with a cross-linking treatment part 14a irrespective of the electronic member such as a solar cell element or an electrode to be sealed. Further, as a design for aligning with an electronic member such as a solar cell element or an electrode to be sealed, a cross-linking treatment portion 14a may be provided in accordance with the position of the electric member, or the cross-linking treatment portion 14a is avoided so as to avoid these electronic members. May be provided.

  There are a plurality of crosslinking treatment parts 14a partially crosslinked by ionizing radiation irradiation, and the distance between the ends of the crosslinking treatment parts closest to each other in the crosslinking treatment part 14a is 1 mm or more and 160 mm or less. preferable. Specifically, the distance D between the ends of the cross-linking treatment parts that are closest to each other in the cross-linking treatment part 14a is, specifically, in FIG. 3, FIG. 4, FIG. 5, and FIG. This corresponds to the distance D between the ends of the closest cross-linked portions.

  The shrinkage ratio of the uncrosslinked portion 14b is larger than that of the crosslinked portion 14a. Therefore, in order to realize a shrinkage rate of 40% or less, which is said to be within the allowable range when the solar cell module 11 is displaced when the solar cell module 10 is created, the shortest distance between the cross-linking portions 14a is 160 mm or less. Is desirable. If the shortest distance of the cross-linking treatment portion 14a is larger than 160 mm, the space between the cross-linking treatment portions 14a that support the shrinkage becomes too large and cannot be supported, so that the shrinkage rate exceeds 40%, and defects increase when the solar cell module 10 is produced. In addition, if the shortest distance of the cross-linked portion 14a is less than 1 mm, the cross-linked portion 14a having poor adhesion is too close to each other, resulting in poor adhesion.

  If the cross-linking treatment part 14a is formed in a line shape, the cross-linking treatment part 14a can be formed in-line, so that production by a roll-to-roll is possible, the productivity is excellent, and the manufacturing cost can be greatly reduced.

  When the cross-linking portion 14a is formed in a line shape, if the width W of the line shape is 1 mm or less, the shrinkage rate in the modularization process is suppressed to 40% or less, and the strength for maintaining the heat-resistant creep resistance is reduced. It is not preferable. The present solar cell module 10 often arranges 150 mm square solar cell elements 11 at intervals of 10 mm, and when the line-shaped width W is 160 mm or more, the cross-linking treatment portion 14 a having poor adhesion is formed on the solar cell element 11. Since the site | part which covers the whole arises, it is not preferable.

  On the other hand, when the cross-linking portion 14a pattern as shown in FIGS. 4, 5, and 6 is formed off-line, the productivity is inferior to the line shape, but when the solar cell module is formed, the four edge portions are formed. In addition, it becomes easy to provide an uncrosslinked treatment portion 14b that is not irradiated with ionizing radiation in a frame shape. By providing the uncrosslinked portion 14b having excellent adhesion in a frame shape, it becomes possible to firmly bond the four edges when modularized, and the sealing sheet and each member for long-term use. It is possible to form the solar cell module 10 having excellent durability that is difficult to occur due to poor adhesion and moisture intrusion.

  In addition, by controlling the size of the cross-linked portion 14a, it becomes possible to firmly bond the edge without requiring alignment, and the sealing sheet and each member are in close contact with each other for long-term use. It is possible to form a solar cell module with excellent durability that is difficult to be caused by defects or moisture intrusion.

  That is, as shown in FIGS. 4, 5, and 6, if the solar cell module 10 has a shape that is independent in the front-rear direction and the left-right direction as viewed from the seat surface, the solar cell module 10 is at least in the front-rear direction. Before and after the cross-linking treatment part 14a partially cross-linked by ionizing radiation irradiation as viewed from the top surface of the sealing sheet 14 from the shortest distance from the edge to the electronic member constituting the solar cell module 10 By making the cross-section dimension R1 in the front-rear direction, which is the longest part in the direction, shorter, the uncrosslinked section 14b having excellent adhesion is surely inserted between the module edge and the electronic component. Therefore, when modularized, it becomes possible to firmly bond the edge in the front-rear direction, resulting in poor adhesion between the sealing sheet and each member and intrusion of moisture for long-term use It is possible to form an excellent solar cell module 10 to the pile durability. In this case, the current solar cell module 10 has a shortest distance of the distance from the edge of the solar cell module 10 to the electronic member constituting the solar cell module 10, the so-called frame portion is often about 15 mm, and therefore the front-rear direction. It is preferable that the cross-linking portion dimension R1 in the front-rear direction, which is the longest portion of the cross-linking portion, is 15 mm or less.

  Similarly, when the solar cell module 10 is used, the sealing sheet 14 is shorter than the shortest distance among the distances from the edge of the solar cell module 10 to the electronic member constituting the solar cell module 10 in the left-right direction. A module is obtained by shortening the cross-linking treatment portion dimension R2 in the left-right direction which is the longest portion in the left-right direction of the cross-linking treatment portion 14a partially cross-linked by ionizing radiation irradiation as viewed from above. Since the uncrosslinked portion 14b having excellent adhesion always enters between the edge and the electronic component, it is possible to firmly bond the edge in the left-right direction when modularized, for long-term use It becomes possible to form the solar cell module 10 having excellent durability that is unlikely to occur due to poor adhesion between the sealing sheet and each member or moisture intrusion. In this case, the present solar cell module 10 has a shortest distance among the distances from the edge of the module to the electronic member constituting the solar cell, the so-called frame portion is often about 15 mm, and therefore the longest portion in the left-right direction. It is preferable that the cross-linking portion dimension R2 in the left-right direction is 15 mm or less.

  3 is the shortest distance among the distances from the edge of the module to the electronic member constituting the solar cell in at least the left-right direction when the solar cell module 10 can be said to be applicable to the line shape shown in FIG. More, the width W of the line shape that is the longest portion in the left-right direction of the cross-linking treatment portion 14a partially cross-linked by ionizing radiation irradiation as viewed from the upper surface of the sealing sheet 14 is made shorter. As a result, an uncrosslinked portion 14b having excellent adhesion is surely inserted between the module edge and the electronic component, so that it is possible to firmly bond the edge in the left and right direction when modularized. On the other hand, it is possible to form the solar cell module 10 having excellent durability that is difficult to occur due to poor adhesion between the sealing sheet and each member and moisture intrusion. In this case, the current solar cell module 10 is often the shortest distance among the distances from the edge of the solar cell module 10 to the electronic member constituting the solar cell module 10, so-called frame portion is often about 15 mm, and therefore has a line shape. The width W is preferably 15 mm or less.

The sealing sheet for the solar cell module desirably has a thermal shrinkage rate of a predetermined value or less in order to maintain a high yield rate at the time of module manufacture. For example, 150 degreeC, vacuum drawing: 5 minutes, pressurization: (0 kPa-100 kPa): 1.5 minutes, pressure holding (100 kPa): 7.0 minutes When the lamination process is performed on general conditions, The heat shrinkage ratio is preferably 45% or less, more preferably 30% or less, and most preferably 20% or less. According to the production method of the present invention, for example, even when a high MFR resin having an MFR of 15.0 g / 10 min or more is used, the shrinkage rate can be suppressed to 45% or less.

[Solar cell module]
FIG. 2 is a cross-sectional view showing an example of the layer structure of the solar cell module 10 using the first embodiment (FIG. 3) of the sealing sheet 14 of the present invention. The solar cell module 10 of the present invention has a configuration of a transparent front substrate 13, a front side sealing sheet 14, a solar cell element 11, a back side sealing sheet 14, and a back surface protective sheet 15 from the incident light receiving surface side. Yes, the sealing sheet of the present invention is used for at least one sealing sheet 14.

<Method for manufacturing solar cell module>
For example, the solar cell module 10 is formed by sequentially laminating members including the transparent front substrate 13, the front-side sealing sheet 14, the solar cell element 11, the back-side sealing sheet 14, and the back-side protection sheet 15, and then vacuuming. It can be manufactured by integration by 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.

  According to the manufacturing method of the solar cell module 10 using the sealing sheet 14 of this invention, said thermocompression-bonding process can be performed at 110 degreeC or more and 140 degrees C or less. When a conventional EVA sealing material is used, heating exceeding 140 ° C. is generally essential. In addition, since a general polyethylene-based sealing sheet has a low crosslinking rate, when it is used, for example, when laminating is performed at a temperature of 140 ° C. or lower, heating for a long time is required. There have been inconveniences such as a large change in film thickness or the need for re-curing after integration. According to the manufacturing method of the solar cell module 10 using the sealing sheet 14 of this invention, manufacture of the solar cell module 10 can be implemented in a preferable aspect also in the range of 110 degreeC or more and 140 degrees C or less. For this reason, the range of selection of laminating conditions such as the type and amount of the crosslinking agent, the heating temperature and the time is widened, and by optimizing them, higher productivity than the conventional method can be realized.

  And in the manufacturing method of the solar cell module 10 using the sealing sheet 14 of this invention, the flow of the sealing sheet 14 in a vacuum heating lamination can be suppressed by using the sealing sheet 14 of this invention. In addition, since there is no cross-linking treatment in the modularization process or the subsequent heating process, the degree of freedom of the vacuum heating lamination conditions in the modularization process is increased as much as it is not necessary to consider the cross-linking conditions. Can be shortened and productivity is greatly improved. In particular, the problem of the polyethylene-based encapsulating sheet that the crosslinking speed is slower than that of the EVA system can be solved, and the time for the modularization process can be greatly shortened.

  Moreover, in the manufacturing method of the solar cell module 10 using the sealing sheet 14 of the present invention, the haze value after the thermocompression bonding of the front side sealing sheet 14 and the rear side sealing sheet 14 in the solar cell module 10 is The haze value at a thickness of 400 μm is 7% or less, preferably 4% or less. As described above, in the present invention, a solar cell module that includes a cross-linking agent as a sealing sheet material, and thus employs a sealing sheet using a cross-linked polyethylene resin as a sealing layer. The solar cell module 10 having both heat resistance and transparency can be manufactured, which is an excellent point of the present invention.

  In the solar cell module 10 of the present invention, the transparent front substrate 13, the solar cell element 11 and the back surface protection sheet 15 which are members other than the front sealing sheet 14 and the back sealing sheet 14 are made of conventionally known materials. It can be used without particular limitation. Moreover, the solar cell module 10 of this invention may also contain members other than the said member. In addition, the sealing sheet 14 of this invention is applicable not only to a single crystal type but to all the solar cell modules 10 other than a thin film type.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

[Manufacture of sealing sheet]
As described below, an uncrosslinked sealing sheet was formed from a sealing sheet material composition containing a low-density polyethylene resin as a main resin, and a sealing sheet of Comparative Example 1 was obtained. The sealing sheet of Comparative Example 1 is subjected to a crosslinking treatment by irradiation with ionizing radiation under predetermined conditions as described below to produce a crosslinked sealing sheet that is crosslinked as a whole. A stop sheet was used. Further, a mask having a film thickness of 400 μm or more is placed on the sealing sheet of Comparative Example 1 above, and a crosslinking treatment is performed by irradiation with ionizing radiation under predetermined conditions to produce a partially crosslinked sealing sheet. The sealing sheet of Example 1 was obtained.

(Uncrosslinked sealing sheet)
An uncrosslinked sealing sheet was prepared using the sealing sheet material composition formulated as follows.
Silane-modified transparent resin: with a density of 0.881 g / cm3 and a metallocene linear low-density polyethylene (M-LLDPE) 98.0 parts by mass with an MFR at 190 ° C. of 2 g / 10 min. 2.0 parts by mass of methoxysilane and 0.1 parts by mass of dicumyl peroxide as a radical generator (reaction catalyst) are mixed, melted and kneaded at 200 ° C., and at a density of 0.884 g / cm 3 and 190 ° C. A silane-modified transparent resin (hereinafter referred to as “resin S”) having an MFR of 1.8 g / 10 min was obtained. The metallocene-based linear low-density polyethylene has a raw material-based number average molecular weight (Mn) in terms of polystyrene of 32000 g / mol, a weight average molecular weight (Mw) of 72000 g / mol, and a dispersity (Mw / Mn) of 2 .3.
Weatherproof masterbatch: 3.8 parts by mass of benzophenol UV absorber and 5 parts by mass of hindered amine light stabilizer with respect to 100 parts by mass of powder obtained by pulverizing Ziegler linear low density polyethylene having a density of 0.880 g / cm 3 Part and 0.5 parts by mass of a phosphorous heat stabilizer were mixed, melted, processed, and pelletized to obtain a master batch.
Crosslinker compound resin: 2,5-dimethyl-2,5-di (based on 100.0 parts by mass of M-LLDPE pellets having a density of 0.880 g / cm 3 and MFR at 190 ° C. of 3.1 g / 10 min. Compound pellets were obtained by impregnating 0.1 part by mass of (t-butylperoxy) hexane.
Extrusion temperature of a composition in which 20 parts by mass of resin S, 5 parts by mass of weathering masterbatch, and 80 parts by mass of cross-linking compound compound resin were blended using a film forming machine having a φ30 mm extruder and a 200 mm wide T die. Molding was performed at 210 ° C. and a take-off speed of 1.1 m / min to prepare a sealing sheet having a thickness of 400 μm.

(Comparative Example 1)
Comparative example 1: It was set as the comparative example 1 without irradiating the non-crosslinked sealing sheet created above with an electron beam.

(Comparative Example 2)
Using the electron beam irradiation apparatus (product name EC250 / 15 / 180L, manufactured by Iwasaki Electric Co., Ltd.) for the sealing sheet of Comparative Example 1, an electron beam is irradiated at an acceleration voltage of 200 kV and an irradiation dose of 20 kGy. A finished sealing sheet was prepared and used as Comparative Example 2.

Example 1
With respect to the sealing sheet of Comparative Example 1, an adhesive tape having a width of 10 mm and a thickness of 400 μm is used as a mask, and is adhered in parallel to the flow direction of the sealing sheet at intervals of 10 mm. Using a line irradiation apparatus, an electron beam was irradiated under the same conditions as in Comparative Example 2 to produce a sealing sheet that was partially crosslinked in a stripe shape.

  The gel fraction, heat shrinkage rate, and molecular weight of the sealing sheets of the above Examples and Comparative Examples were measured. The method for measuring the gel fraction is as described above.

Moreover, as a result of measuring the number average molecular weight according to the following method and conditions for the uncrosslinked encapsulated sheets after film formation in each of the examples and comparative examples, the number average molecular weight in terms of polystyrene of the encapsulated sheet is 97300. there were.

Molecular weight: The sealing sheets of Examples and Comparative Examples were dissolved in o-dichlorobenzene, and the polystyrene-equivalent number average molecular weight, weight average molecular weight, and molecular weight distribution of each sealing sheet were measured under the following conditions.
Measurement model: GPC / V2000 manufactured by Waterers
Column: Shodex AT-G + AT-806MS × 2 Eluent: o-dichlorobenzene (with 0.3% BHT)
Temperature: Column and injector 145 ° C
Concentration: about 1.0 g / L
Flow rate 1.0ml / min
Solubility: Complete dissolution Detector: Differential refractometer (RI)

  Table 1 shows the measurement results of the crosslinking conditions, gel fraction, and molecular weight of Examples and Comparative Examples. The sealing sheet in a present Example and a comparative example was all the sealing sheet excellent in transparency.

[Evaluation]
About the sealing sheet of an Example and a comparative example, it measured about glass adhesive strength, heat-resistant creep, and heat shrinkage rate. The results are shown in Table 2. Each test condition is as follows.

<Evaluation method>
About the sealing sheet of an Example and a comparative example, it measured about glass contact | adhesion intensity | strength, a 150 degreeC perpendicular | vertical shift test, and a heat contraction rate. The results are shown in Table 2. Each test condition is as follows.

<Evaluation 1: Glass adhesion strength>
Each of the sealing sheets of Examples and Comparative Examples cut to a width of 15 mm was brought into close contact with a glass substrate (white plate semi-tempered glass JPT3.2 75 mm × 50 mm × 3.2 mm) and vacuumed at 150 ° C. for 18 minutes. It processes with a heating laminator, the solar cell module evaluation sample is obtained about each Example and a comparative example, The sealing sheet closely_contact | adhered on a glass substrate is peeled tester (Tensilon universal testing machine RTF-1150- H) was subjected to a vertical peel (50 mm / min) test to determine the glass adhesion strength. The glass adhesion strength by this measurement is a guideline indicating adhesion, and the larger the value, the higher the adhesion.

<Evaluation 2: Thermal shrinkage>
The heat which is the shrinkage ratio of the side length of the test piece in the MD direction before and after heating after placing the test piece of 100 mm × 100 mm sealing sheet in the sealing sheet on talc heated to 150 ° C. and leaving it to stand for 10 minutes. Shrinkage (%) was measured. The thermal shrinkage rate (%) by this measurement is a guideline indicating the shrinkage rate during heating in the modularization process. The MD direction is a longitudinal direction that is a discharge direction in the sheet forming process. Moreover, in the modularization process which actually produces a solar cell module, the sealing sheet is pinched | interposed into the transparent front substrate and the back surface protection sheet. Therefore, no warping or wrinkling occurs. However, in this test conducted with the sealing sheet alone, warping and wrinkles may occur, and in this case, the maximum value where the cross-linking effect is the strongest and the minimum value where the cross-linking effect is the weakest The average of was taken as the measured value.

<Evaluation 3: Slip test>
The sealing sheets of Examples and Comparative Examples cut into 7.5 × 5.0 cm on large glass plates subjected to graining were used as glass substrates (white plate float semi-tempered glass JPT3.2 150 mm × 150 mm × 3.2 mm). Two pieces are placed on top of each other, and a glass substrate (white plate float semi-tempered glass JPT3.2 75 mm × 50 mm × 3.2 mm) is placed on top of each other, and processed with a vacuum heating laminator at 150 ° C. for 18 minutes. Samples for solar cell module evaluation were obtained for Examples and Comparative Examples. The solar cell module evaluation sample was placed vertically and allowed to stand at 150 ° C. for 12 hours, and the moving distance of the glass substrate (white plate semi-tempered glass JPT3.2 75 mm × 50 mm × 3.2 mm) after being left was measured and evaluated. . In this test, the results of the movement distance are shown in Table 1. The value of the shear test by this measurement serves as a guideline indicating the heat resistant creep property, and it is understood that the smaller the numerical value, the better the heat resistant creep property.

  From Tables 1 and 2, by partially performing a crosslinking treatment by irradiation with ionizing radiation, an adhesive sheet that is difficult to be realized simultaneously with an encapsulating sheet that has been completely uncrosslinked or an encapsulating sheet that has been entirely crosslinked. It turns out that it is the outstanding sealing sheet which has heat resistant creep property.

  The sealing sheet which concerns on this invention has industrial applicability as a sealing material etc. which seal various members, such as a solar cell element and an electrode which comprise a solar cell module.

10: Solar cell module 11: Solar cell element 12: Electrode 13: Transparent front substrate 14: Sealing sheet 14a: Crosslinking treatment part (crosslinking treatment part) of sealing sheet
14b: Uncrosslinked treatment part (uncrosslinked treatment part) of sealing sheet
15: Back protection sheet
D: Distance between the ends of the cross-linked portions closest to each other in the cross-linked portions
W: Line shape width R1: Cross-linking treatment part dimension in the front-rear direction R2: Cross-linking treatment part dimension in the left-right direction

Claims (4)

A sealing sheet for a solar cell module that seals a softened resin layer in close contact with an object to be sealed, wherein the resin layer contains at least a low-density polyethylene having a density of 0.91 g / cm ³ or less. And the sealing sheet | seat characterized by having the bridge | crosslinking process part partially bridge | crosslinked by seeing from the sheet | seat surface by ionizing radiation irradiation.   There are a plurality of cross-linking treatment parts that are partially cross-linked by irradiation with ionizing radiation, and the distance between the ends of the cross-linking treatment parts that are closest to each other is 1 to 160 mm. The sealing sheet according to claim 1.   The encapsulating sheet according to claim 1 or 2, wherein the cross-linked portion partially cross-linked by ionizing radiation irradiation has a line shape.   The said bridge | crosslinking process part has a line shape along the film forming direction of the said sealing sheet, The width | variety of this line shape is 1 mm or more and 160 mm or less, The sealing of Claim 3 characterized by the above-mentioned. Sheet.

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