JP7359277B2 - Encapsulant sheet for solar cell module and solar cell module using the same - Google Patents

Description

The present invention relates to an encapsulant sheet for a solar cell module and a solar cell module using the same. In particular, the present invention relates to a sealing material sheet that can be preferably used in a double-sided glass protective substrate type solar cell module, and a double-sided glass protective substrate type solar cell module using the same.

In recent years, with increasing awareness of environmental issues, solar cells have been attracting attention as a clean energy source. Currently, solar cell modules having various forms are being developed and proposed. Solar cell modules have various layer configurations, but the front protection substrate and back protection substrate have particularly excellent barrier properties to prevent moisture from entering the module and long-term durability under harsh usage conditions. A solar cell module has also been devised in which each of the substrates is a protective substrate made of glass (see Patent Document 1). In this specification, a solar cell module having a configuration in which the protective substrates disposed on both outermost surfaces of the module body are glass substrates is referred to as a "double-sided glass protective substrate type solar cell module."

Conventionally, encapsulant sheets used in solar cell modules, including double-sided glass protection substrate type solar cell modules, have been made of ethylene-vinyl acetate copolymer resin ( EVA) has been mainly used. However, EVA resin tends to gradually decompose with long-term use, and may generate acetic acid gas that affects solar cell elements. Therefore, in recent years, there has been an increasing demand for encapsulant sheets for solar cell modules that use polyethylene resin instead of EVA resin (see Patent Document 2).

Generally, in an encapsulant sheet for a solar cell module that uses polyethylene resin as a base resin, transparency and flexibility can be improved by lowering the density. However, lower density also causes the problem of insufficient heat resistance. Therefore, in the encapsulant sheet of Patent Document 2, heat resistance is imparted by a crosslinking agent. In this case, it is true that heat resistance improves, but if cross-linking is carried out to a sufficient degree to provide sufficient heat resistance to withstand long-term use at high temperatures, during modularization, There was a problem in that the ability to follow the irregularities on the surface of the facing member (hereinafter referred to as "molding characteristics") could not be maintained. In addition, in manufacturing processes that require crosslinking treatment, as crosslinking progresses during molding, film formability deteriorates, so consideration must be taken such as performing molding at a low temperature and repeating the crosslinking reaction after molding. Further improvements were also needed in terms of gender.

For example, in order to achieve both heat resistance and molding properties without going through crosslinking treatment, we have developed a skin layer that is a mixture of two or more resins with different melting points, and a sealing layer that contains a crystal nucleating agent such as inorganic particles. An encapsulant sheet has been disclosed that is designed to achieve both heat resistance and molding properties while eliminating the need for crosslinking treatment by forming a multilayer sheet that combines a core layer made of a material composition (Patent Document (See 3).

Japanese Patent Application Publication No. 2013-9258164 Japanese Patent Application Publication No. 2009-10277 International Publication No. 2012/073971

In recent years, double-sided glass protection substrate type solar cell modules, which have become increasingly popular, often have a frameless structure that eliminates the metal frame that surrounds the side surfaces of the module (see Patent Document 1). In this case, in addition to achieving both heat resistance and molding properties as described above, due to the structure of the solar cell module, high tensile shear adhesive strength at room temperature (JIS J6850 Adhesives - Tensile shear adhesive strength test of rigid adhered materials) adhesive strength) is required for the encapsulant sheet. There has not yet been an encapsulant sheet that can meet all three requirements at a high level: heat resistance, molding properties, and high tensile shear adhesive strength at room temperature.

The present invention has been made in view of the above circumstances, and although it is an encapsulant sheet using polyethylene resin, it does not require a crosslinking process, has high productivity, and has excellent heat resistance and molding properties. Another object of the present invention is to provide an encapsulant sheet for solar cell modules that also has a high level of tensile shear adhesive strength at room temperature.

As a result of extensive studies, the present inventors have determined that the encapsulant sheet is a multilayer sheet consisting of a skin layer, a core layer, and a skin layer, and that the melting point of the core layer is maintained at 70°C or higher, and We have discovered that the above problems can be solved by containing a silane-modified polyethylene resin in a predetermined amount range, and further specifying this silane-modified polyethylene resin to have a specific high molecular weight range. The invention was completed. More specifically, the present invention provides the following.

(1) An encapsulant sheet for a solar cell module, the encapsulant sheet is a multilayer sheet that uses polyethylene resin as a base resin and includes a core layer and skin layers disposed on both outermost surfaces. The core layer has a density of 0.880 g/cm ³ or more and 0.930 g/cm ³ or less, and a melting point of 70° C. or more, and the skin layer has a density of 0.880 g/cm 3 or more and 0.930 g/cm ³ or less. 900 g/cm ³ or less and a melting point of 90° C. or less, the skin layer contains a silane-modified polyethylene resin, and the weight average molecular weight of the silane-modified polyethylene resin contained in the skin layer is 70,000 in terms of polystyrene. or more and 120,000 or less, and the amount of polymerized silane in the total resin components of the skin layer is 300 ppm or more and 2,000 ppm or less.

(2) The encapsulant sheet according to (1), wherein the silane-modified polyethylene resin contained in the skin layer has a weight average molecular weight in terms of polystyrene of from 90,000 to 120,000.

(3) The encapsulant sheet according to (1) or (2), wherein the core layer and the skin layer both have melting points of 70°C or higher and 80°C or lower.

(4) A solar cell module in which a transparent front substrate, a sealing material on the light-receiving surface side, a solar cell element, a sealing material on the non-light-receiving surface side, and a back protection substrate are sequentially laminated, and the transparent front substrate, the sealing material on the light-receiving surface side A solar cell module, wherein the encapsulant and the encapsulant on the non-light-receiving surface side are the encapsulant sheet according to any one of (1) to (3).

(5) The solar cell module according to (4), wherein the transparent front substrate and the back protection substrate are both glass protection substrates.

(6) The module according to (5) is a frameless module in which there is no protective frame that surrounds the side surfaces of the module laminate sandwiched between glass protective substrates and maintains the shape of the module laminate. solar cell module.

(7) On the surface of the solar cell element, there is a convex portion formed by protruding a part of the surface in a linear or dotted manner, and the convex portion is a part of the encapsulant sheet laminated on the surface. From (4), the thickness of the convex portion is 50% or more and 90% or less of the thickness of the encapsulant sheet laminated on the surface of the solar cell element. 6) The solar cell module according to any one of 6).

According to the present invention, although the encapsulant sheet uses polyethylene resin, it does not require a crosslinking process and has high productivity.In addition to heat resistance and molding properties, it also has high tensile shear strength at room temperature. It is possible to provide an encapsulant sheet for solar cell modules that also has a high level of adhesive strength.

FIG. 1 is a cross-sectional view schematically showing the layer structure of the sealing material sheet of the present invention. 1 is a drawing schematically showing an example of the layer structure of a double-sided glass protective substrate type solar cell module using the encapsulant sheet of the present invention. FIG. 1 is a cross-sectional view schematically showing an example of the layer structure of a solar cell module using the encapsulant sheet of the present invention and a thin film solar cell element. FIG. 4 is a partially enlarged view of FIG. 3, and is a drawing for explaining the molding characteristics of the encapsulant sheet of the present invention when used in a thin-film solar cell module. FIG. 2 is a partially enlarged cross-sectional view of a conventional solar cell module in which a conventional encapsulant sheet with poor molding properties is used in a thin-film solar cell module.

Hereinafter, an encapsulant composition that can be used for manufacturing an encapsulant sheet for a solar cell module of the present invention, an encapsulant sheet for a solar cell module of the present invention, and an encapsulant sheet of the present invention will be used. The solar cell modules that were developed will be explained one by one.

<Encapsulant composition>
The encapsulant sheet of the present invention can be manufactured by melt-molding the encapsulant composition described in detail below. As for the encapsulant composition, the encapsulant composition for the core layer and the encapsulant composition for the skin layer are used separately for each layer. Then, by forming a multilayer sheet with a three-layer structure in which the core layer is the inner layer and the skin layer is the outermost layer using each of the sealing material compositions for the core layer and the skin layer, for example, as shown in FIG. The encapsulant sheet of the present invention, typified by the encapsulant sheet 1 shown in Fig. 1, can be manufactured. In this specification, the skin layer refers to a layer disposed on both outermost surfaces of a multilayer encapsulant sheet, and the core layer refers to an inner layer other than the skin layer in the multilayer encapsulant sheet. say about. Although the core layer itself may have a multilayer internal structure, the three-layer encapsulant sheet 1 in which skin layers are laminated on both sides of a single-layer core layer is representative of the present invention. This embodiment is a typical embodiment, and the present invention will be explained below focusing on this sealing material sheet 1.

[Encapsulant composition for core layer]
The encapsulant composition for the core layer is a thermoplastic encapsulant composition that uses polyethylene resin as a base resin, does not contain a crosslinking agent, and does not require a crosslinking process when molding the encapsulant sheet. . Furthermore, in addition to low density polyethylene resin (LDPE) used as the base resin, other resins such as silane-modified polyethylene resin and other components are contained in appropriate amounts within the range that does not impede the effects of the present invention. There may be.

The base resin of the encapsulant composition for the core layer is low density polyethylene resin (LDPE), linear low density polyethylene resin (LLDPE), or metallocene linear low density polyethylene resin (M-LLDPE). can be preferably used. Among them, from the viewpoint of long-term reliability of the solar cell module, low-density polyethylene resin (LDPE) can be particularly preferably used as the encapsulant composition for the core layer. In this specification, the term "base resin" refers to a resin having the highest content ratio among the resin components of the resin composition in a resin composition containing the base resin.

It is preferable that the encapsulant composition for the core layer further contains a predetermined amount of a silane-modified polyethylene resin in addition to the above-mentioned base resin. Silane-modified polyethylene resin is not necessarily an essential component in the encapsulant composition for the core layer, but when adding the silane-modified polyethylene resin to the encapsulant composition for the core layer, it is necessary to add it to the encapsulant composition for the core layer. It is preferable to use a silane-modified polyethylene resin having a weight average molecular weight in terms of polystyrene of 70,000 or more (hereinafter also referred to as a "high molecular weight type silane-modified polyethylene resin").

Regarding the amount of high molecular weight type silane-modified resin added to the encapsulant composition for the core layer, the ratio is such that the amount of polymerized silane in the total resin components of the core layer 11 is 30 ppm or more and 2000 ppm or less. It is preferable that this be contained in the sealing material composition for use in the present invention. By including an appropriate amount of such a high molecular weight type silane-modified polyethylene resin in the encapsulant composition for the core layer, it is possible to contribute to improving the high tensile shear adhesive strength of the encapsulant sheet 1 at room temperature. Can be done. The amount of polymerized silane in each layer of the sealing material can be determined by quantifying the element in each layer by, for example, ICP emission spectroscopy or the like, thereby determining the amount present in the resin component. Details of the polymer type silane modified resin that can be used for the sealing material sheet 1 will be described later.

The density of the encapsulant composition for the core layer is 0.880 g/cm 3 or more and 0.930 g/cm ³ or less, preferably 0.880 g/cm ^{3 or} more and 0.920 g/cm ³ or less, more preferably 0.880 g/cm 3 or more and 0.920 g/cm 3 or less is 0.885 g/cm ³ or more and 0.895 g/cm ³ or less. By setting the density of the encapsulant composition for the core layer within the above range, the encapsulant sheet 1 can be provided with heat resistance and molding properties in a well-balanced manner without undergoing crosslinking treatment.

The melting point of the encapsulant composition for the core layer should just be 70°C or more and 110°C or less, and preferably 73°C or more and 90°C or less. As long as the melting point of the core layer 11 of the encapsulant sheet 1 can be maintained within the above range, the encapsulant composition for the core layer can be prepared by appropriately mixing polyethylene resins having different melting points. For example, according to a resin composition formed by mixing three types of polyethylene resins with melting points of 60° C., 90° C., and 97° C., 65 parts by mass, 8 parts by mass, and 32 parts by mass, respectively, the melting point of the entire core layer is can be set to 74°C. Further, examples of blending such material resins can be illustrated as preferred examples of resin blending of the sealing material composition for the core layer.

Here, the melting point in this specification refers to the average value of melting points calculated from the unique melting points of each component contained in the object to be measured and their blending ratio.

For example, the melting point as defined above of the encapsulant sheet or each resin layer constituting it can be measured and obtained by differential scanning calorimetry (DSC). When there are multiple peaks in the valley of the DSC curve, the melting point of the peak with the largest peak area can be taken as the melting point of the sealing material sheet or each of the resin layers.

Another method for determining the melting point defined above from the encapsulant sheet is to determine whether the linear expansion coefficient increases or decreases when the measured linear expansion coefficient is expressed as a function of resin temperature in accordance with JIS K7179. It is also possible to approximate the temperature by measuring the linear expansion peak temperature, which is the temperature at the maximum value when the temperature changes to . According to this method, the melting point as defined above can be determined from a finished product such as a sealing material sheet within a variation range of approximately 2° C. or less.

As described above, by maintaining the melting point of the encapsulant composition for the core layer at 70° C. or higher, the necessary heat resistance can be imparted to the encapsulant sheet 1. In addition, the encapsulant composition for the core layer is The melting point of the core layer encapsulating material composition should generally be about 110°C or less, and in order to sufficiently improve the molding properties of the encapsulant sheet 1, the melting point of the encapsulant composition for the core layer should be 90°C or less. It is more preferable.

The melt mass flow rate (MFR) of the encapsulant composition for the core layer may be 3.0 g/10 min or more and less than 5.0 g/10 min, and within that range, the MFR is 0.8 g/10 min or more and 5.0 g/10 min. It is possible to use a suitable mixture of polyethylene resins of less than By setting the MFR of the core layer encapsulant composition within the above range, the encapsulant sheet 1 can be provided with heat resistance and molding properties in a well-balanced manner.

In addition, MFR in this specification is a value obtained by the following method unless otherwise specified.
MFR (g/10min): Measured according to JIS K7210. Specifically, synthetic resin was heated and pressurized at 190°C in a cylindrical container heated by a heater, and the amount of resin extruded per 10 minutes from an opening (nozzle) provided at the bottom of the container was measured. . The test machine used was an extrusion type plastometer, and the extrusion load was 2.16 kg.
In addition, the MFR of a multilayer encapsulant sheet was measured by the above process while all the layers were in a multilayer state in which they were laminated in one layer, and the obtained measured value was taken as the MFR value of the multilayer encapsulant sheet. .

[Encapsulant composition for skin layer]
Like the sealing material composition for the core layer, the skin layer sealing material composition is also a thermoplastic sealing material composition that uses polyethylene resin as a base resin and does not contain a crosslinking agent. Further, it is similar to the encapsulant composition for the core layer in that it may contain other components in appropriate amounts within a range that does not impede the effects of the present invention. However, the encapsulant composition for the skin layer must contain a specific amount of a silane-modified polyethylene resin (high molecular weight type silane-modified polyethylene resin) with a weight average molecular weight of 70,000 or more in terms of polystyrene. This point differs from the encapsulant composition for the core layer.

As the base resin of the encapsulant composition for the skin layer, similar to the encapsulant composition for the core layer, low density polyethylene resin (LDPE), linear low density polyethylene resin (LLDPE), or metallocene resin can be used. A linear low density polyethylene resin (M-LLDPE) can be preferably used. Among them, from the viewpoint of molding properties, metallocene linear low density polyethylene resin (M-LLDPE) can be particularly preferably used as a composition for the skin layer.

In addition to the above-mentioned base resin, the sealant composition for the skin layer used in the sealant sheet 1 further contains a predetermined amount of a silane-modified polyethylene resin as an essential resin component. The silane-modified polyethylene resin contained in this skin layer composition has a weight average molecular weight of 70,000 or more in terms of polystyrene (hereinafter also referred to as "high molecular weight type silane-modified polyethylene resin"). limited to).

Further, this high molecular weight type silane-modified resin is contained in the sealing material composition for the skin layer in such a ratio that the amount of polymerized silane in the total resin components of the skin layer is 300 ppm or more and 2000 ppm or less. By containing an appropriate amount of such a high molecular weight type silane-modified polyethylene resin in the sealing material composition for the skin layer, extremely high tensile shear adhesive strength at room temperature can be imparted to the sealing material sheet 1. . Details of the polymer type silane modified resin that can be used for the sealing material sheet 1 will be described later.

The density of the sealant composition for the skin layer is 0.880 g/cm ³ or more and 0.910 g/cm ³ or less, more preferably 0.899 g/cm ³ or less. By setting the density of the sealant composition for the skin layer within the above range, the adhesion of the sealant sheet 1 can be maintained within a preferable range.

The melting point of the sealing material composition for the skin layer may be 70°C or more and 90°C or less, and preferably 70°C or more and 80°C or less. As with the core layer, as long as the melting point of the skin layer can be maintained within the above range, polyethylene resins having different melting points can be appropriately mixed to form a sealing material composition for the skin layer. For example, according to a resin composition formed by mixing three types of polyethylene resins with melting points of 60°C, 90°C, and 97°C, respectively, 65 parts by mass, 20 parts by mass, and 20 parts by mass, the melting point of the entire skin layer is can be set to 73°C. Further, examples of blending such material resins can be illustrated as preferred examples of resin blending of the sealing material composition for the core layer. By setting the melting point of the sealing material composition for the skin layer to 70° C. or higher, the necessary heat resistance can be imparted to the sealing material sheet 1. Furthermore, by setting the melting point of the skin layer encapsulant composition to 90° C. or lower, the molding characteristics of the encapsulant sheet during integration into a solar cell module can be maintained within a preferable range.

The melt mass flow rate (MFR) of the sealant composition for the skin layer may be 3.0 g/10 min or more and less than 5.0 g/10 min, and within that range, the MFR is 0.8 g/10 min or more and less than 5.0 g/10 min. It is possible to use a suitable mixture of polyethylene resins. By setting the MFR of the skin layer sealant composition within the above range, the sealant sheet 1 can be provided with heat resistance and molding properties in a well-balanced manner.

[Silane-modified polyethylene resin]
It is essential that the encapsulant sheet 1 contains a silane-modified polyethylene resin at least in the skin layer 12, and furthermore, the silane-modified polyethylene resin contained in the skin layer 12 is It must be a molecular weight type silane-modified polyethylene resin. Hereinafter, first, a general "silane-modified polyethylene resin" will be explained, and then details of a "high molecular weight type silane-modified polyethylene resin", which is an important component of the present invention, will be explained.

The silane-modified polyethylene resin is obtained by graft polymerizing an ethylenically unsaturated silane compound as a side chain to a linear low-density polyethylene resin (LLDPE) as a main chain. In addition, the "silane-modified polyethylene resin" in this specification is obtained by copolymerizing at least an α-olefin and an ethylenically unsaturated silane compound as a comonomer, and if necessary, further using other unsaturated monomers as a comonomer. It is a copolymer, and includes modified products and condensates of the copolymer.

Further, as a copolymer of an α-olefin and an ethylenically unsaturated silane compound, or a modified or condensed product thereof, for example, one or more α-olefins and, if necessary, other unsaturated One or more monomers are polymerized simultaneously or in stages in the same manner as above in the presence of a radical polymerization initiator and, if necessary, a chain transfer agent. Then, one or more ethylenically unsaturated silane compounds are graft copolymerized to the polyolefin polymer produced by the polymerization, and if necessary, the graft copolymer produced by the copolymer is A copolymer of an α-olefin and an ethylenically unsaturated silane compound or a modified or condensed product thereof can be produced by modifying or condensing a portion of the silane compound constituting the copolymer.

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 include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinyltripentyloxysilane, vinyltriphenoxysilane, and vinyltripropoxysilane. One or more selected from benzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane can be used.

As other unsaturated monomers, 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 radical polymerization initiator include organic peroxides such as lauroyl peroxide, dipropionyl peroxide, benzoyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, and t-butyl peroxyisobutyrate. Azo compounds, such as molecular oxygen, azobisisobutyronitrile, azoisobutylvaleronitrile, etc., can be used.

Examples of chain transfer agents 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. , acetone, methyl ethyl ketone, ketones such as cyclohexanone, aromatic hydrocarbons, chlorinated hydrocarbons, etc. can be used.

Examples of the method of modifying or condensing the silane compound portion constituting the random copolymer or the method of modifying or condensing the silane compound portion constituting the graft copolymer include tin, zinc, iron, lead, Using organic metal compounds such as metal carboxylates such as cobalt, titanate esters and chelates, organic bases, inorganic acids, and silanol condensation catalysts such as organic acids, α-olefin and ethylenically unsaturated silane Modification of the copolymer of α-olefin and ethylenically unsaturated silane compound or Examples include methods for producing condensates.

As the silane-modified polyethylene resin, any of random copolymers, alternating copolymers, block copolymers, and graft copolymers can be preferably used, but graft copolymers are preferable. More preferred is a graft copolymer in which polymerizable polyethylene is used as the main chain and an ethylenically unsaturated silane compound is polymerized as the side chain. Such a graft copolymer has a high degree of freedom in the silanol groups that contribute to adhesive strength, so it can improve the adhesion of the encapsulant sheet to other components in the solar cell module, especially the glass substrate. can.

The content of the ethylenically unsaturated silane compound when constituting the silane-modified polyethylene resin is, for example, about 0.001 to 15% by mass, preferably 0.01 to 5% by mass, based on the total mass of the copolymer. %, particularly preferably 0.05 to 2% by mass. When the content of the ethylenically unsaturated silane compound constituting the copolymer of α-olefin and ethylenically unsaturated silane compound is within the above range, the adhesion of the encapsulant sheet to the glass is significantly improved. do. If the content of the silane compound exceeds the above range, the tensile elongation and heat fusion properties of the encapsulant sheet tend to be poor, which is not preferable.

In the encapsulant sheet 1, among the silane-modified polyethylene resins described above, a "high molecular weight type silane-modified polyethylene resin" having a specific molecular weight range is used as an essential component of the encapsulant composition for the skin layer. Used as additive resin.

The molecular weight of the above-mentioned "high molecular weight type silane-modified polyethylene resin" used as an essential additive resin in the sealing material composition for the skin layer has a weight average molecular weight in terms of polystyrene of 70,000 or more and 120,000 or less, preferably It is 90,000 or more and 120,000 or less. In addition, if the molecular weight of the silane-modified polyethylene resin exceeds 120,000, the compatibility with the base resin, which is assumed to be preferably about 3.0 g / 10 min or more and 5.0 g / 10 min or less, deteriorates. Undesirable.

The molecular weight of each resin component constituting the encapsulant sheet 1 can be measured using a conventionally known GPC method. Note that since polyolefins are difficult to dissolve in solvents at room temperature, it is preferable to use trichlorobenzene, o-dichlorobenzene, or the like as a solvent and perform measurement at a high temperature of 140° C. or higher and 150° C. or lower. Particularly in the case of the encapsulant sheet 1, in order to measure the molecular weight of the silane-modified polyethylene resin contained in the skin layer 12, the skin layer of the encapsulant sheet 1, which is a multilayer sheet, is separated and GPC-FTIR By combining molecular weight measurement and component analysis, etc., it is possible to specify the molecular weight of the silane-modified polyethylene resin by reading the molecular weight corresponding to the component identified by IR. In addition, the number average molecular weight Mn, weight average molecular weight Mw, and dispersion degree d when there are Ni (Ni) polymers with a molecular weight Mi (g/mol) in the skin layer of the encapsulant sheet 1 are defined by the following formulas, respectively. be done.
Number average molecular weight Mn=Σ(MiNi)/ΣNi
Weight average molecular weight Mw=Σ(Mi ² Ni)/ΣMiNi
Dispersion degree d=Mw/Mn

[Other additive ingredients]
An adhesion improver can be added as appropriate to each of the encapsulant compositions for the core layer and the skin layer that constitute the encapsulant sheet 1, particularly to the encapsulant composition for the skin layer. . As the adhesion improver, a known silane coupling agent can be used, but a silane coupling agent having an epoxy group (hereinafter also referred to as "epoxy silane coupling agent") or a silane having a mercapto group may be used. Coupling (hereinafter also referred to as "mercapto silane coupling agent") can be particularly preferably used.

Each of the encapsulant compositions for the core layer and the skin layer may further contain other components. For example, components such as a weather-resistant masterbatch, various fillers, light stabilizers, ultraviolet absorbers, and heat stabilizers for imparting weather resistance to the encapsulant sheet are exemplified. Although the content of these components varies depending on the particle shape, density, etc., it is preferable that each content is within the range of about 0.001% by mass or more and about 5% by mass in the encapsulant composition. By including these additives, the encapsulant sheet can be given stable mechanical strength over a long period of time and the effect of preventing yellowing, cracking, etc.

<Encapsulant sheet>
The encapsulant sheet of the present invention can be manufactured by melt-molding the above-mentioned encapsulant composition.

As shown in FIG. 1, the encapsulant sheet 1 has a core layer 11, and skin layers 12 are formed on both sides of the core layer 11. However, even if the encapsulant sheet has a core layer having a multilayer structure and other functional layers are disposed within the core layer, the sheet may include a core layer and a skin layer that meet the constituent requirements of the present invention, and As long as the encapsulant sheet has the other constituent features of the present invention, it is within the scope of the present invention.

The MFR of the three-layer encapsulant sheet 1 including the core layer 11 and the skin layer 12 is 3.0 g/10 min or more and less than 5.0 g/10 min, and 3.3 g/10 min or more and 3. Preferably it is less than 8g/10min. When the MFR of the encapsulant sheet 1 is less than 5.0 g/10 min, the encapsulant sheet 1 can be provided with the necessary heat resistance, and the MFR is 3.0 g/10 min or more. This allows the encapsulant sheet 1 to have necessary molding characteristics.

The total thickness of the three-layer encapsulant sheet 1 including the core layer 11 and the skin layer 12 is preferably 250 μm or more and 600 μm or less, more preferably 300 μm or more and 550 μm or less. If the total thickness is less than 250 μm, the impact cannot be sufficiently alleviated, but if the total thickness is 250 μm or more, for example, even if the sealing material sheet 1 is thinned to a total thickness of about 250 μm. , it is possible to combine molding properties and heat resistance at sufficiently desirable levels. In addition, if the total thickness exceeds 600 μm, it is difficult to obtain an effect of further improving the impact mitigation effect, it cannot meet the demand for thinner solar cell modules, and it is unfavorable because it is uneconomical.

Further, the thickness of the core layer 11 in the encapsulant sheet 1 is 200 μm or more and 400 μm or less, preferably 250 μm or more and 350 μm or less. Further, the thickness of each layer of the skin layer 12 is 30 μm or more and 100 μm or less, preferably 35 μm or more and 80 μm or less. Further, the total thickness of the two skin layers 12 laminated on both sides of the core layer is 1/20 or more and 1/3 or less of the total thickness of the encapsulant sheet 1, preferably 1/15. It is 1/4 or less. By setting the thickness of each layer of the encapsulant sheet 1 within such a range, the heat resistance and molding properties of the encapsulant sheet 1 can be maintained within a favorable range.

The sealing material sheet 1 is formed into a sheet by various molding methods commonly used for ordinary thermoplastic resins, such as injection molding, extrusion molding, blow molding, compression molding, and rotational molding. An example of a method for producing a multilayer film in the case where the encapsulant sheet is a multilayer film includes a method in which it is formed by coextrusion using three types of melt-kneading extruders.

However, in any of the above molding methods, the melt molding temperature in manufacturing the encapsulant sheet 1 is at least 30°C above the melting point of the base resin of the encapsulant composition for the core layer contained in the encapsulant composition. It is preferable that Specifically, the temperature is preferably in the range of 175°C to 230°C, more preferably in the range of 190°C to 210°C. Since the encapsulant composition used for the encapsulant sheet 1 is a thermoplastic composition that does not contain a crosslinking agent, there is no need to take into consideration the undesirable control of crosslinking progress during melt molding. As a result, in the production of encapsulant sheets using polyethylene resin as a base resin, there is a solution to the temperature limitations when using thermosetting encapsulant compositions that require crosslinking treatment, which was common in the past. The melt forming temperature can be set in a higher temperature range to improve productivity. Thereby, the encapsulant sheet 1 can be manufactured with higher productivity than conventional thermosetting encapsulant sheets.

<Solar cell module>
The encapsulant sheet 1 can be used for general purposes in various conventionally known solar cell modules. Generally, in a solar cell module, an encapsulant is placed on both sides of the solar cell element in such a manner that it is sandwiched and sealed, but the encapsulant sheet 1 is placed as an encapsulant on both sides of the solar cell element. Alternatively, only the sealing material on either side can be the sealing material sheet 1.

As mentioned above, the encapsulant sheet can be used for various solar cell modules, including solar cell modules with double-sided glass protection substrates with a laminated glass structure, or solar cells such as thin-film solar cell modules. It can be particularly preferably used in a solar cell module in which a protrusion with a relatively large height, such as a lead wire, is formed on the element.

[Double-sided glass protection substrate type solar cell module]
FIG. 2 is a cross-sectional view showing an example of the layer structure of a double-sided glass protection substrate type solar cell module 10 that can be constructed using the encapsulant sheet 1 of the present invention. The solar cell module 10 includes, from the light-receiving surface side of incident light, a transparent front substrate 2, a sealing material 1A on the light-receiving surface side, a solar cell element 3, a sealing material 1B on the non-light-receiving surface side, and a back protection substrate 4. The solar cell element 3 is sealed between a sealing material 1A on the light-receiving surface side and a sealing material 1B on the non-light-receiving surface side.

In the double-sided glass protection substrate type solar cell module 10, the transparent front substrate 2 and the back protection substrate 4 are both glass protection substrates. As this glass protective substrate, various glass plate materials conventionally used as light-transmitting substrate materials constituting solar cell modules can be used without particular limitation. Solar cell module 10 may include members other than the above members.

Further, there is no particular restriction on the solar cell element 3 either. In addition to crystalline silicon solar cells produced using single-crystal silicon substrates or polycrystalline silicon substrates, thin-film solar cells (CIGS) using amorphous silicon, microcrystalline silicon, or chalcopyrite-based compounds are also preferably used. be able to.

For the back protection substrate 4, a resin sheet can be used that has physical properties such as water vapor barrier properties and weather resistance that are normally required for a protective layer disposed as the outermost layer of a solar cell module. Further, the back protection substrate 4 may be a glass substrate similar to the transparent front substrate 2. Since the sealing material sheet 1 has good adhesion to both metal and glass, it can be preferably used even when the back protection substrate 4 is a glass substrate.

In a typical solar cell module in which the back protection substrate is made of a weather-resistant resin film, in order to maintain the shape of the laminate made up of the sheet-like members that make up the solar cell module, A protective frame made of metal or the like is provided to surround the side surface of this laminate. However, in the case of a double-sided glass protection substrate type solar cell module 10 sandwiched between glass protection substrates, a solar cell module with a so-called frameless structure that eliminates such a protection frame is used to reduce weight. Many are also offered.

This double-sided glass protective substrate type solar cell module 10 with a frameless structure has a high tensile shear adhesive strength at room temperature (adhesive strength according to JIS J6850 adhesive - tensile shear adhesive strength test method for rigid adherend materials). Required for fasteners. The encapsulant sheet 1 of the present invention is an encapsulant sheet that has special tensile shear adhesive strength by specifying the molecular weight of the adhesive resin contained in the skin layer to a high range, so it is frameless. It can be particularly preferably used in a solar cell module 10 having a double-sided glass protective substrate structure.

[Thin film solar cell module]
FIG. 3 is a cross-sectional view showing an example of the layer structure of a thin film solar cell module 10A that can be constructed using the encapsulant sheet 1 of the present invention. The solar cell module 10A includes, from the incident light receiving surface side, a transparent front substrate 2, a thin film solar cell element 3 disposed on the surface of the transparent front substrate 2, a sealing material (sealing material sheet 1), and It has a structure in which back protection substrates 4 are laminated in order. In the thin film solar cell module 10A, the sealing material (sealing material sheet 1) is laminated on the non-light receiving surface side of the solar cell element 3.

Here, in the solar cell module 10A, as shown in FIG. 4, unevenness exists on the non-light receiving surface side of the solar cell element 3 due to the metal electrode 31 and the lead wire 32 for current collection. When using a conventional encapsulant sheet with polyethylene resin as the base resin, if you try to ensure heat resistance by cross-linking or simply increasing the density, as shown in Figure 5, the voids V will increase due to insufficient molding properties. Formation may occur, which has been a problem.

However, when the encapsulant sheet 1, which has both high heat resistance and molding properties, is placed on this uneven surface, the encapsulant sheet 1 can be used to protect the solar cell element 3, as shown in FIG. It can sufficiently wrap around the unevenness caused by the metal electrode 31 and the current collection lead wire 32 on the surface of the light-receiving surface, thereby preventing the formation of the above-mentioned void V. That is, the encapsulant sheet 1 can be particularly preferably used when the surface of the solar cell element has irregularities formed by convex portions such as the lead wires 32, as in the solar cell module 10A. When the thickness of the convex portion of the unevenness is 50% or more and 90% or less of the thickness of the encapsulant sheet 1, the molding properties of the encapsulant sheet are particularly well exhibited, and as described above, the molding properties of the encapsulant sheet are particularly well exhibited. Formation of voids V due to the presence of surface irregularities of the element can be sufficiently prevented.

More specifically, when the lead wire 32 is a lead wire with a thickness (d ₁ ) of approximately 250 μm or more, the encapsulant sheet 1 exhibits a special effect that is significantly different from conventional products. . For example, as shown in FIG. 5, when thick lead wires 32 are arranged, when a conventional sealing material sheet 1 made of general polyethylene resin is placed on the uneven surface, As a rough guide, when the thickness (d ₁ ) of the lead wire 32 with respect to the thickness (d ₂ ) of the encapsulant sheet 1 exceeds 50%, the above-mentioned formation of the void V becomes a problem. It often happened. However, as shown in FIG. 4, when the encapsulant sheet 1 is disposed on such an uneven surface, the thickness (d 1 ) of the lead wire 32 is smaller than the thickness (d ₂ ) of the encapsulant sheet ₁ . ) is 90% or less, the formation of the voids V described above can be sufficiently prevented. In addition, in the present invention, when a plurality of lead wires are stacked, such as when the lead wires are arranged to intersect, The total thickness is considered to be the "thickness of the lead wire", that is, the "thickness of the convex portion" mentioned above.

[Method for manufacturing solar cell module]
The solar cell module 10 is constructed by sequentially installing the constituent members of the solar cell module including a transparent front substrate 2, a sealing material 1A on the light-receiving surface side, a solar cell element 3, a sealing material 1B on the non-light-receiving surface side, a back protection substrate 4, etc. After lamination, they are integrated by vacuum suction or the like, and then the above-mentioned members can be manufactured by heat-pressing molding as an integral molded body by a molding method such as a lamination method.

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

<Manufacture of encapsulant sheets for solar cell modules>
The raw materials for the encapsulant composition described below were mixed in the proportions (parts by mass) shown in Table 1 below, and the encapsulant compositions for the core layer and the skin layer of the encapsulant sheets of Examples and Comparative Examples were prepared, respectively. A sealing material composition was prepared. Each encapsulant composition was used for a core layer and a skin layer at an extrusion temperature of 210° C. and a take-up speed of 1.1 m/min using a φ30 mm extruder and a film forming machine having a 200 mm width T-die. Each resin sheet was produced, and these resin sheets were laminated to produce encapsulant sheets having a three-layer structure in Examples and Comparative Examples, each comprising a core layer and skin layers disposed on both outermost surfaces. The thickness of each encapsulant sheet in Examples and Comparative Examples was a total thickness of 450 μm. Regarding the thickness ratio of each layer of the three-layer structure encapsulant sheets of Examples and Comparative Examples, the skin layer:core layer:skin layer thickness ratio for each encapsulant sheet was 1:8: 1 (total thickness of the skin layer (total of two layers) is 1/4 of the total thickness of the sealing material sheet). In Comparative Example 5, a single-layer encapsulant sheet having a thickness of 450 μm was formed.

The following raw materials were used as resin materials for the encapsulant composition for molding each resin sheet for the encapsulant sheet.
Polyethylene resins 1 to 5 (in the table, each is written as "PE1 to 5")
: Both are metallocene-based linear low-density polyethylene resins (M-LLDPE). The density, melting point, and MFR at 190°C are as shown in Table 1.
Silane-modified polyethylene resin 1 (indicated as "PS1" in the table)
: ² parts by mass of vinyltrimethoxysilane and a radical generator (reactive A silane-modified polyethylene resin obtained by mixing with 0.15 parts by mass of dicumyl peroxide (as a catalyst), melting and kneading at 200°C. Density: 0.900 g/cm ³ , MFR: 1.0 g/10 min. Melting point: 90°C.
Silane-modified polyethylene resin 2 (indicated as "PS2" in the table)
: ² parts by mass of vinyltrimethoxysilane and a radical generator (reactive A silane-modified polyethylene resin obtained by mixing with 0.15 parts by mass of dicumyl peroxide (as a catalyst), melting and kneading at 200°C. Density: 0.880 g/cm ³ , MFR: 2.0 g/10 minutes. Melting point: 60°C.
Silane-modified polyethylene resin 3 (indicated as "PS3" in the table)
: 2 parts by mass ^of vinyltrimethoxysilane and a radical generator (reactive A silane-modified polyethylene resin obtained by mixing with 0.15 parts by mass of dicumyl peroxide (as a catalyst), melting and kneading at 200°C. Density: 0.885 g/cm ³ , MFR: 13.0 g/10 min. Melting point: 58°C.
: 2 parts by mass of vinyltrimethoxysilane and 0.15 parts by mass of dicumyl peroxide as a radical generator (reaction catalyst) are mixed with 100 parts by mass of base resin i, melted and kneaded at 200°C, A silane-modified polyethylene resin having a density of 0.885 g/cm ³ and an MFR of 13 g/10 minutes was obtained. Melting point: 58°C.

<Weight average molecular weight of skin layer>
The weight average molecular weight in terms of polystyrene of the silane-modified polyethylene resin contained in each skin layer of Examples 1 and 2 and Comparative Example 1 was measured by the measurement method using the above-mentioned GPC method. The results are shown in Table 2.

<Evaluation example 1: Molding characteristics>
A lead wire (250 μm diameter) was placed on the surface of a white tempered glass plate with a flat surface, and each sealing material sheet of the example and comparative example cut into 150 mm x 150 mm was laminated to cover the lead wire. The samples were subjected to vacuum heating laminator treatment at a set temperature of 150°C, evacuation for 3 minutes, and atmospheric pressure for 7 minutes to obtain samples for evaluation of solar cell modules for each of the examples and comparative examples. The resin temperature (achieved temperature) of the sealant sheet in the laminate during this heat treatment was 147°C. These solar cell module evaluation samples were visually observed and their molding characteristics were evaluated according to the following evaluation criteria.
(Evaluation Criteria) A: The encapsulant sheet completely follows the unevenness of the facing substrate surface. No void formation was observed.
B: Up to 5 bubbles within 2 mm ² were observed.
C: Part of the encapsulant sheet did not completely follow the unevenness of the facing base material surface, and some lamination defective parts (gaps) were formed near the lead wires.
The evaluation results are listed in Table 4 as "molding characteristics."

<Evaluation example 2: Heat resistance test>
A heat resistance creep test was conducted as a heat resistance test. The same glass plate as in Evaluation Example 1, cut out to 5 cm x 7.5 cm, was placed on top of the encapsulant sheets of Examples and Comparative Examples. They were stacked one on top of the other, and vacuum heating laminator treatment was performed under the same conditions as in Evaluation Example 1 to create an evaluation sample. Thereafter, the large size glass was placed vertically and left at 90° C. for 12 hours, and the moving distance (mm) of the 5 cm x 7.5 cm glass plate after being left was measured and evaluated. Evaluation was performed based on the following criteria.
(Evaluation criteria) A: 0.0mm
B: More than 0.0mm and less than 1.0mm
C: 1.0 mm or more The evaluation results are listed in Table 4 as "heat resistance".

<Evaluation example 3: Tensile shear adhesive strength>
We measured the tensile shear adhesive strength, which is an indicator of suitability for double-sided glass protection substrate type modules. The measurement was performed according to the test method according to JIS K7197. Using the same two glass plates as in Evaluation Example 1 above, the encapsulant sheets of Examples and Comparative Examples cut out to 2.5 cm x 1.27 cm were placed between the two glass plates, and vacuumed under the same conditions as Evaluation Example 1. A sample for evaluation was prepared by applying a heating laminator treatment to adhere the sample. Thereafter, the tensile shear adhesive strength was measured and evaluated by the above test method at a tensile rate of 1.27 mm/min. Evaluation was performed based on the following criteria.
(Evaluation criteria) A: 1000N or more
B: 500N or more but less than 1000N
C: Less than 500N The evaluation results are shown in Table 4 as "tensile shear adhesive strength".

From Tables 1 to 4, it can be seen that although the encapsulant sheet of the present invention is an encapsulant sheet using polyethylene resin, it does not require a crosslinking process, has high productivity, and has excellent heat resistance and molding properties. Furthermore, it can be seen that the encapsulant sheet for solar cell modules has a high level of tensile shear adhesive strength at room temperature.

1 Encapsulant sheet 11 Core layer 12 Skin layer 2 Transparent front substrate 3 Solar cell element 31 Metal electrode 32 Lead wire 4 Back protection substrate 10 Solar cell module

Claims (6)

An encapsulant sheet for a solar cell module,
The encapsulant sheet is a multilayer sheet that uses polyethylene resin as a base resin and includes a core layer and skin layers disposed on both outermost surfaces,
The core layer has a melting point of 70°C or more and 110°C or less ,
The skin layer has a melting point of 70°C or more and 90°C or less and contains a silane-modified polyethylene resin,
The average MFR of all layers is 3.0 g/10 min or more and less than 3.8 g/10 min.
Encapsulant sheet. The weight average molecular weight of the silane-modified polyethylene resin in terms of polystyrene is 70,000 or more and 120,000 or less, and the amount of polymerized silane in the total resin component of the skin layer is 300 ppm or more and 2,000 ppm or less.
The sealing material sheet according to claim 1. A solar cell module in which a transparent front substrate, a sealing material on the light-receiving surface side, a solar cell element, a sealing material on the non-light-receiving surface side, and a back protection substrate are sequentially laminated,
The encapsulant on the non-light receiving surface side is the encapsulant sheet according to claim 1 or 2.
solar cell module. The transparent front substrate and the back protection substrate are both glass protection substrates,
The solar cell module according to claim 3. It is a frameless module in which there is no protective frame that surrounds the side surface of the module laminate sandwiched between glass protective substrates to maintain the shape of the module laminate;
The solar cell module according to claim 4. On the surface of the solar cell element, there is a convex portion formed by protruding a part of the surface in a linear or dotted manner, and the convex portion is buried inside the encapsulant sheet laminated on the surface. Crowded,
The thickness of the convex portion is 50% or more and 90% or less of the thickness of the encapsulant sheet laminated on the surface of the solar cell element.
The solar cell module according to any one of claims 3 to 5.

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