JP2015198148A - Light shielding sheet, back surface protection sheet for solar battery module using light shielding sheet, and solar battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light shielding sheet in which a light shielding layer that is used to constitute one layer of a back surface protection sheet for a solar battery module as a laminate and has excellent adhesiveness to a base material is formed by coating, and to provide a back surface protection sheet for a solar battery module using the light shielding sheet.SOLUTION: A back surface protection sheet for a solar battery module has a close contact reinforcing layer 62 disposed at an outermost layer to reinforce the close contact with a sealing material, and a light shielding layer 61 formed of a coating layer or film laminated on the other surface of the close contact reinforcing layer 62. The close contact reinforcing layer 62 comprises: a core layer 621 containing polypropylene resin having melting point of 160°C which is 80 wt% or more with respect to the whole resin; and skin layers 622 which contain 50 wt% or more of polypropylene resin having a melting point of 120°C or more and 135°C or less containing ethylene unit and are exposed to the outermost layers, where the close contact reinforcing layer 62 is a three-layer co-extrusion film of the skin layer 622, the core layer 621 and the skin layer 622 which are laminated in this order.

Description

  The present invention relates to a light shielding sheet, and more particularly to a light shielding sheet used for constituting one layer of a back surface protection sheet for a solar cell module which is a laminate. Moreover, this invention relates to the back surface protection sheet for solar cell modules and solar cell module in which the said light shielding sheet was used.

  In recent years, solar cells as a clean energy source have attracted attention due to the growing awareness of environmental issues. Generally, the solar cell module which comprises a solar cell is a transparent front substrate, a surface side filler sheet, a solar cell, a back surface side filler material sheet, and a back surface protection sheet (it is also called a back surface protection sheet etc.) from the light-receiving surface side. These members are sequentially stacked, and have a function of generating power when sunlight enters the solar battery cell.

  Such a solar cell module is used outdoors. Therefore, each member constituting the solar cell module is required to have a characteristic that can withstand a harsh environment outdoors for a long period of time. In particular, since the back protective sheet is used outside the solar cell module among the above members, a high level of weather resistance, light resistance, and the like are required.

  As a member of such a back surface protection sheet, in Patent Document 1, a solar cell cover material comprising a three-layer laminate of a hydrolysis-resistant resin film, a metal oxide-coated resin film, and a white resin film Back surface protection sheets have been proposed. This white resin film is obtained by kneading a white pigment in a resin, and is used to reflect light incident on the back surface protection sheet and return it to the solar cell element to improve power conversion efficiency. Therefore, this white resin film is arrange | positioned in the place nearest to the light-incidence side in a back surface protection sheet.

  However, in the back surface protection sheet proposed in Patent Document 1, since the white resin film having a light shielding property is disposed at a position closest to the light incident side (side near the solar cell) in the back surface protection sheet, the back surface Of the protective sheet, the layer located on the outer side (the layer on the back surface side of the solar cell module) cannot be protected by the light shielding property of the white resin film. For this reason, in the layer which comprises the exterior side of a back surface protection sheet, low cost and excellent workability, such as polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), etc., but using materials with inferior light resistance should be used. I can't. From such a viewpoint, it is desirable that the layer for imparting light shielding properties to the back surface protective sheet is provided in the outermost layer of the back surface protective sheet. In addition, the layer for imparting light shielding properties to the back surface protective sheet is desirably provided by coating from the viewpoint of workability.

  Therefore, Patent Document 2 is a coating formed by applying a coating liquid containing a white pigment, a resin compound having a plurality of crosslinkable substituents, and a polyisocyanate compound to the surface of a substrate, and the coating liquid. When the light-shielding layer is formed on the surface of the substrate, the white pigment in the coating liquid is 70 parts by mass or more with respect to 100 parts by mass of the resin compound and the polyisocyanate compound, whereby the film and the base that are the light-shielding layer are formed. A solar cell back surface protective sheet having improved adhesion to a material has been proposed.

Japanese Patent Laid-Open No. 2002-100788 JP 2011-210835 A

  The back surface protection sheet, when used, has strong adhesion to the sealing material sheet, etc., and adhesion durability, assuming that it is used outdoors for a long time after integration as a solar cell module. Is required. However, on the other hand, in the manufacturing site of the solar cell module, the rear surface protection sheet after being integrated as a module in order to redo some processes and promote the reuse of some members such as solar cell elements. There has also been a demand for reworkability that allows the work to be peeled off without damaging the encapsulant sheet or the solar cell element disposed inside the encapsulant sheet or a part cut into an appropriate part. . In this specification, “reworkability” refers to the adaptability of the back surface protection sheet to such work, and “rework” refers to such work itself. .

  In recent years, the demand for low cost for solar cell modules has further increased. Patent Document 2 proposes a light-shielding sheet having high adhesion to a base material such as polyethylene terephthalate (PET), dispersibility of white pigments, light hiding properties and gas barrier properties. However, although PET is an inexpensive and highly versatile resin, it is a polyester-based resin, is easily hydrolyzed, and is inferior in light resistance. Moreover, in the invention which concerns on patent document 2, since it has several processes of the process of apply | coating the coating agent for forming a light shielding layer in a base material, and the process of joining a light shielding sheet to a sealing material with an adhesive agent etc., production There is a problem that the number of processes increases and the cost increases. In addition, the above-mentioned back protective sheet having reworkability has a low adhesion with polyethylene-based resins such as ethylene-vinyl acetate copolymer resin (EVA) at 130 ° C. to 150 ° C., and adhesion reinforcement. There is a need for a backside protective sheet that does not cohesively break within the layer. Therefore, there has been a strong demand for the development of a back surface protection sheet that has excellent light resistance, has few production processes, and has reworkability.

  The present invention has been made in view of the above situation, and is a back surface protection sheet that is used to constitute one layer of a back surface protection sheet for a solar cell module that is a laminate and has solvent resistance and reworkability. However, it aims at providing the back surface protection sheet for solar cell modules etc. with high productivity at low cost.

  As a result of intensive studies to solve the above problems, the present inventors have found that the adhesion between a polypropylene (PP) resin containing an ethylene unit having a predetermined melting point range and a light shielding layer is excellent. Therefore, the adhesion reinforcing layer is provided with a skin layer containing 50% by mass or more of a polypropylene resin containing an ethylene unit and having a melting point of 120 ° C. or higher and 135 ° C. or lower and exposed to the outermost layer, and the adhesion reinforcing layer is formed as a skin layer / core layer / It is a three-layer co-extruded film of skin layer, and a low-cost and high productivity by laminating a coating layer having a thickness of 1 μm to 30 μm or a film having a thickness of 10 μm to 100 μm on one surface of the skin layer Although it is a back surface protection sheet, it has been found that the back surface protection sheet has adhesion to the adhesion reinforcing layer, is excellent in light shielding properties, and is excellent in reworkability, and has completed the present invention.

  That is, the present invention provides (1) a back surface protection sheet for a solar cell module, provided with an adhesion reinforcing layer disposed on the outermost layer of the back surface protection sheet to reinforce adhesion with a sealing material, Is exposed to the outermost layer, containing a core layer containing a polypropylene resin having a melting point of 160 ° C. or higher in a total resin of 80% by mass or more and a polypropylene resin containing an ethylene unit having a melting point of 120 ° C. or higher and 135 ° C. or lower in an amount of 50% by mass or more. A coating layer having a thickness of 1 μm or more and 30 μm or less on one surface of the skin layer, wherein the adhesion reinforcing layer is a three-layer coextruded film of skin layer / core layer / skin layer Or the back surface protection sheet characterized by laminating | stacking the light shielding layer which consists of a film of thickness 10 micrometers or more and 100 micrometers or less.

  (2) The back surface protection sheet according to (1), wherein the light shielding layer is a fluorine-based film containing a white pigment, and is laminated on one surface of the skin layer by an adhesive via a dry lamination method.

  (3) The light shielding layer is a coating layer in which a white pigment is dispersed in a resin, and the resin includes a fluororesin having a plurality of crosslinkable substituents and a (meth) acrylic resin having a plurality of crosslinkable substituents. The mixture is crosslinked with a polyisocyanate compound, and the (meth) acrylic resin is 60% by mass or more and 90% by mass or less with respect to the total mass of the fluororesin and the (meth) acrylic resin. The back surface protection sheet according to (1).

  (4) The back surface protective sheet according to any one of (1) to (3), wherein the content of the ethylene unit in the skin layer is 5.0% by mass or more and 10.0% by mass or less.

  (5) The back surface protective sheet according to any one of (1) to (4), wherein the white pigment is 50 to 300 parts by mass with respect to 100 parts by mass of the resin.

  (1) The solar cell module using the back surface protection sheet in any one of (5).

  According to the present invention, a solar cell module having a sufficient adhesion, adhesion stability, and reworkability while having a low production cost, a low cost, and a high productivity back surface protection sheet for solar cell modules. A back protection sheet for battery modules and the like are provided.

It is a schematic diagram of the cross section which shows an example of the laminated constitution of the solar cell module of this invention. It is the partial expanded schematic diagram of the cross section which shows an example of the laminated constitution of the adhesion reinforcement layer of the back surface protection sheet for solar cell modules of this invention.

  A specific embodiment of the present invention will be described. This embodiment has a light-shielding layer, a light-shielding layer used for constituting one layer of a back protective sheet for a solar cell module that is a laminate, a light-shielding layer and a polypropylene resin-based adhesion reinforcing layer, a core layer And a multilayer structure including a skin layer, and particularly for the skin layer, a back surface protection sheet for a solar cell module composed of polypropylene (PP) containing ethylene units having a predetermined melting point range at a certain ratio, and It is a solar cell module in which the back surface protection sheet for solar cell modules is used.

<Basic configuration of solar cell module>
First, the basic structure of the solar cell module using the back surface protection sheet for solar cell modules of this invention is demonstrated using FIG. As shown in FIG. 1, the solar cell module 1 includes a transparent front substrate 2, a front sealing material layer 3, a solar cell element 4, a back sealing material layer 5, and a back surface protection according to the present invention from the light receiving surface side. The sheets 6 are sequentially stacked.

  The transparent front substrate 2 is generally a glass substrate. The transparent front substrate 2 may also be another member as long as it maintains the weather resistance, impact resistance, and durability of the solar cell module 1 and transmits sunlight with high transmittance. .

  The sealing material layer made up of the front sealing material layer 3 and the back sealing material layer 5 is arranged in the solar cell module 1 to fix the position of the solar cell element 4 and to reduce the impact from the outside. It is a layer made of a resin base material. As the resin substrate for forming the sealing material layer, a thermoplastic resin such as ethylene-vinyl acetate copolymer resin (EVA), ionomer, polyvinyl butyral (PVB), polyethylene resin such as polyethylene can be used as appropriate. However, in the present invention, EVA is preferably used from the viewpoint of the balance between adhesion and reworkability.

  In addition, the back surface protection sheet 6 of this invention is especially excellent in adhesiveness between resin which performed the crosslinking process. Of the above material resins, EVA is generally required to be subjected to a crosslinking treatment when modularized. As the polyethylene-based resin, a low-density polyethylene resin of a type in which an appropriate amount of a crosslinking agent is added and thermally crosslinked at the time of modularization can be preferably used.

  As the solar cell element 4, conventionally known solar cell elements can be widely used. FIG. 1 shows a case where the solar cell element 4 is a crystalline silicon solar cell manufactured using a single crystal silicon substrate or a polycrystalline silicon substrate. In addition, amorphous silicon or microcrystalline silicon is used as a transparent front substrate. 2 may be a thin film solar cell element formed by forming an extremely thin silicon film of about 1 μm or less on 2. The back surface protective sheet 6 of the present invention can also be preferably used for a solar cell module on which a thin film solar cell element is mounted.

  Since the back surface protective sheet 6 is disposed in the outermost layer of the solar cell module 1, it has high weather resistance and high adhesion with the back surface sealing material layer 5 described above at normal temperature. It is required to be a thing. The back surface protection sheet 6 has reworkability at high temperatures that can contribute to the improvement of productivity in the manufacturing stage of the solar module while satisfying the demands on the physical properties at the time of use as such a solar cell module. It has been made. Details of the back surface protection sheet 6 according to the present invention will be described later.

<Back protection sheet>
As shown in FIG. 2, the back surface protective sheet 6 of the present invention is a multilayer structure including at least a light shielding layer 61 and an adhesion reinforcing layer 62.

  The light shielding layer 61 is disposed on one surface of the adhesion enhancing layer 62. In the solar cell module 1, the back surface protective sheet 6 is disposed so that the adhesion reinforcing layer 62 and the back surface sealing material layer 5 are in close contact with each other.

[Shading layer]
The light shielding layer which is this embodiment is demonstrated. The back surface protection sheet for solar cell modules of this embodiment contains an adhesion reinforcement layer and a light shielding layer at least. The light shielding layer is formed by drying the coating agent or by laminating films. When drying the coating agent, the resin contained in the light shielding layer contains at least 60% by mass and 90% by mass of (meth) acrylic resin with respect to the total mass of at least the fluororesin and the (meth) acrylic resin. The glass transition temperature (Tg) of the (meth) acrylic resin is preferably 100 ° C. or lower, and more preferably 30 ° C. or lower and 60 ° C. or lower. The amount of the polyisocyanate compound that is the curing agent is preferably such that the NCO / OH ratio (the NCO value of the curing agent / the OH value of the main resin) is 1.0 or more and 2.0 or less. The resin contained in the light shielding layer is a reaction product of a resin compound having a plurality of crosslinkable substituents and a polyisocyanate compound, and the resin compound having a plurality of crosslinkable substituents contained in the coating liquid is crosslinked by the polyisocyanate compound. To be formed. In addition, the light shielding layer contains at least a resin and a white pigment, and it is desirable that the white pigment is dispersed in an amount of 50 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the resin in the light shielding layer. In the following description of the present specification, a resin compound having a plurality of crosslinkable substituents, that is, a resin compound before being cured by crosslinking with a polyisocyanate compound is referred to as “main resin” and is included in the light shielding layer. It is distinguished from the resin to be cured, that is, the resin cured to form the light shielding layer.

  The coating liquid for forming a light shielding layer on the surface of the back surface protection sheet for solar cell modules is demonstrated. The coating liquid contains a main resin having a plurality of crosslinkable substituents, a polyisocyanate compound, a white pigment, and a solvent, and various additives as necessary. The white pigment is dispersed in the coating liquid. Here, the main resin is cross-linked and polymerized by reacting with the polyisocyanate compound. For this reason, this coating liquid is preferably composed of a main component containing a main component resin and a white pigment and a curing agent containing a polyisocyanate compound, and is a two-component type in which these are mixed immediately before use. The polyisocyanate compound is a compound containing a plurality of isocyanate groups in one molecule. Hereinafter, each constituent material will be described.

<Main resin>
As the main resin, a fluororesin having a plurality of crosslinkable substituents for reacting with the polyisocyanate compound and a (meth) acrylic resin are used, and the resin is cured by being cross-linked by reacting with the polyisocyanate compound. A smooth coating is formed. Moreover, as for these, it is desirable that 60 to 90 mass% of (meth) acrylic resins are contained with respect to the total mass of a fluororesin and the said (meth) acrylic resin.

  The coating liquid contains an organic solvent for dissolving or dispersing the main resin. And after drying a solvent from the apply | coated coating liquid, the main ingredient resin contained in a coating liquid is bridge | crosslinked with a polyisocyanate compound, and the film which is a light shielding layer is formed. In order to volatilize the solvent, the applied coating liquid is preferably heated to 60 to 200 ° C., for example, for 1 to 5 minutes, and more preferably 100 to 150 ° C. Thereafter, as an aging period for sufficiently carrying out the crosslinking reaction, it is left at, for example, 40 to 50 ° C. for 3 to 4 days. The temperature and time for drying the solvent, and the temperature and time for aging are appropriately adjusted according to the type of the solvent used, the main resin, and the polyisocyanate compound.

  The light shielding layer is located on the outermost surface on the side opposite to the light receiving surface side (that is, the back surface side) in the solar cell module. That is, since the light shielding layer is exposed to a severe natural environment such as ultraviolet rays and wind and rain during a long period of use of the solar cell module, high light resistance and weather resistance are required. From such a viewpoint, a mixture of a fluororesin having a plurality of crosslinkable substituents and a (meth) acrylic resin having a plurality of crosslinkable substituents is used as the main resin used for forming the light shielding layer. .

(Fluorine resin)
First, the fluororesin will be described. The fluororesin is a so-called modified fluororesin, for example, a copolymer of a fluoroolefin and a monomer containing a crosslinkable substituent. As a monomer constituting this copolymer, another monomer having an ethylenically unsaturated bond may be used in combination. Such a fluororesin contains a fluorine atom that imparts light resistance and weather resistance, and imparts light resistance, weather resistance, and the like to the light shielding layer.

  Examples of such a fluororesin include a copolymer of tetrafluoroethylene and a hydroxyl group-containing vinyl ether, a copolymer of chlorotrifluoroethylene and a hydroxyl group-containing vinyl ether, and the like. Among these, a copolymer of chlorotrifluoroethylene and a hydroxyl group-containing vinyl ether is preferably used. An example of such a resin is a copolymer of chlorotrifluoroethylene, diethylene glycol monoallyl ether, and vinyl butyrate having a mass average molecular weight of 1000 to 30000 and a hydroxyl value of 5 to 200 mg / g.

((Meth) acrylic resin)
Next, a mixture of a fluororesin and a (meth) acrylic resin having a plurality of crosslinkable substituents will be described. This is a mixture of a fluororesin having a plurality of crosslinkable substituents and a (meth) acrylic resin having a plurality of crosslinkable substituents. Adhesiveness to the substrate by the resin can be imparted to the light shielding layer. As the fluororesin having a plurality of crosslinkable substituents, those described above can be used. As a (meth) acrylic resin having a plurality of crosslinkable substituents, one or two or more (meth) acrylic acid compounds and monomers having a crosslinkable substituent are copolymerized, or one or two or more kinds The thing which copolymerized the monomer which has a (meth) acrylic acid compound and a crosslinkable substituent, and 1 type, or 2 or more types of ethylenic monomers is used. Here, in addition to the above monomer, a monomer having a substituent for imparting light resistance to the (meth) acrylic acid resin may be used as a monomer used to obtain the (meth) acrylic acid resin. . In the present invention, the term “(meth) acryl” is used to mean “acryl and / or methacryl”.

  The glass transition temperature (Tg) of the (meth) acrylic resin is preferably 100 ° C. or lower, and more preferably 30 ° C. or higher and 60 ° C. or lower.

  Further, the (meth) acrylic resin contains 60% by mass to 90% by mass of the (meth) acrylic resin with respect to the total mass of the fluororesin and the (meth) acrylic resin, and the (meth) acrylic resin is the main resin. It is characterized by being rich with respect to the whole.

  Such (meth) acrylic resins include hydroxyl such as (meth) acrylic acid-2-hydroxyethyl, (meth) acrylic acid-2-hydroxypropyl, (meth) acrylic acid-2-hydroxy-3-phenoxypropyl, and the like. (Meth) acrylic compound having a group, and (meth) acrylic acid or alkyl group as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, It is a copolymer of an alkyl (meth) acrylate monomer having a 2-ethylhexyl group, a cyclohexyl group, etc., and preferably has a glass transition temperature (Tg) of 100 ° C. or lower, and 30 ° C. or higher. It is more preferable to use a thing of 60 degrees C or less. Moreover, as a monomer used for copolymerization, (meth) acrylamide, N-alkyl (meth) acrylamide, N, N-dialkyl (meth) acrylamide (the alkyl group includes a methyl group, an ethyl group, n -Propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group and the like), N-alkoxy (meth) acrylamide, N, N-di Alkoxy (meth) acrylamide (alkoxy groups include methoxy group, ethoxy group, butoxy group, isobutoxy group, etc.), amide group-containing monomers such as N-methylol (meth) acrylamide, N-phenyl (meth) acrylamide, Glycidides such as glycidyl (meth) acrylate and allyl glycidyl ether Group-containing monomer, styrene, α-methylstyrene, vinyl methyl ether, vinyl ethyl ether, maleic acid, alkyl maleic acid monoester, fumaric acid, alkyl fumaric acid monoester, itaconic acid, alkyl itaconic acid monoester, (meth) acrylonitrile Various compounds having an ethylenically unsaturated bond such as vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, and butadiene may be used. Among these, a copolymer of methyl (meth) acrylate and 2-ethylhexyl acrylate, a copolymer of methyl (meth) acrylate, 2-ethylhexyl acrylate, and hydroxyethyl acrylate, which has a glass transition temperature. It is preferable that (Tg) is 30 ° C. or higher and 60 ° C. or lower. Moreover, 1000-300,000 is mentioned as a preferable mass mean molecular weight of such resin.

  The mixing ratio of the fluororesin and the (meth) acrylic resin is preferably 60% by mass or more and 90% by mass or less, and more preferably 70% by mass or more and 80% by mass or less. When the amount of the (meth) acrylic resin exceeds 90% by mass, good light resistance, weather resistance and the like cannot be imparted to the light shielding layer. Moreover, when the amount of fluorine atoms in the resin is less than 60% by mass, the white pigment cannot have sufficient dispersibility, and sufficient functional groups for imparting solubility, reactivity, and the like to the resin are sufficient. It cannot be introduced.

  The OH value of the main resin is preferably 6.5 or more and 30 or less. If it is less than 6.5, crosslinking does not proceed sufficiently and the curability is lowered, so that a desirable light shielding layer cannot be formed. On the other hand, when it exceeds 30, adhesion with the skin layer in the adhesion reinforcing layer is lowered, which is not preferable.

(Other resins, etc.)
In addition, another resin or the like can be appropriately added as long as it is in the range of 30% by mass or less with respect to the total mass of the fluororesin and the (meth) acrylic resin. For example, a resin exemplified by an epoxy resin, a urethane resin, or an ionizing radiation curable resin may be added as necessary.

  The content of the main resin in the coating liquid is preferably 10 to 60% by mass, more preferably 30 to 50% by mass, and further preferably 40 to 50% by mass. When the content of the resin in the coating liquid is 10% by mass or more, the white pigment contained in the coating liquid can be favorably dispersed. Moreover, the applicability | paintability of a coating liquid becomes favorable because content of resin in a coating liquid is 60 mass% or less.

(Curing agent)
As the curing agent, a polyisocyanate compound having an NCO group is used. A polyisocyanate compound is a compound having two or more isocyanate groups in one molecule. As described above, the polyisocyanate compound crosslinks the main resin and cures (high molecular weight) to form a resin contained in the light shielding layer. At this time, a polyisocyanate compound becomes a part of resin contained in a light shielding layer with main ingredient resin. Examples of the polyisocyanate compound include aliphatic, alicyclic, aromatic, and aromatic-aliphatic compounds, but the light shielding layer is exposed to the external environment for a long period of time. From the viewpoint of suppressing coloring, an aliphatic or alicyclic polyisocyanate compound is preferably used.

  Specific examples of the polyisocyanate compound include aliphatic isocyanates having 3 to 12 carbon atoms such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; 1,4-cyclohexane diisocyanate, isophorone diisocyanate ( Alicyclic diisocyanates having 5 to 18 carbon atoms such as IPDI); modified products of these diisocyanates (burettes, isocyanurate modified products, etc.). These can be used alone or in combination of two or more.

  The amount of the polyisocyanate compound used is preferably such that the NCO / OH ratio (NCO number of the curing agent / OH ratio of the main resin) is 1.0 to 2.0, and 1.0 to 1.5. The amount is more preferred. When the NCO / OH ratio is in the above range, good adhesion, solvent resistance, flexibility, and adhesion with a propylene resin can be obtained. When the NCO / OH ratio is less than 1.0, the solvent resistance and curability deteriorate, and when it exceeds 2.0, the flexibility of the resin and the adhesion to the polypropylene resin deteriorate, which is not preferable. In addition, when using the solution containing a polyisocyanate compound as a hardening | curing agent and making it a 2 liquid type coating liquid, a well-known organic solvent is suitably selected and used for a hardening | curing agent. Such a solvent will be described later.

(White pigment)
Next, the white pigment will be described. The white pigment is added to impart light shielding properties and adhesion to a light shielding layer prepared by applying and curing a coating liquid.

  Examples of white pigments include titanium oxide, talc, silica, barium sulfate, and calcium hydroxide. Among these, titanium oxide is preferably used as the white pigment. There are two types of titanium oxide, rutile type and anatase type. However, some anatase type titanium oxides exhibit oxidation catalytic action. It is preferable to use it.

  The addition amount of the white pigment in the coating liquid is preferably 50 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the resin containing the main resin and the polyisocyanate compound. And the white pigment added to the coating liquid exists in the coating liquid in a dispersed state. Moreover, as already explained, the main resin and the polyisocyanate compound react and cure to become a resin contained in the light shielding layer. For these reasons, it is preferable that the light-shielding layer formed by applying and curing the coating liquid has a white pigment dispersed in an amount of 50 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the resin. More preferably, it is 250 parts by mass or more. When the white pigment is less than 50 parts by mass with respect to 100 parts by mass of the resin contained in the coating, the adhesion between the coating formed on the substrate and the substrate is reduced, and the concealability in visible light is also reduced. Therefore, it is not preferable. On the other hand, if the white pigment is 300 mass or more, the dispersibility and coatability of the white pigment are lowered, which is not preferable.

(solvent)
Next, the solvent used for the coating liquid will be described. The solvent is added to impart applicability to the substrate to the coating liquid and to disperse the white pigment in the coating liquid. After the coating solution is applied to the substrate, the solvent contained in the applied coating solution is volatilized, and a light-shielding layer is formed on the surface of the substrate by the subsequent curing reaction. Therefore, the ratio between the resin component and the white pigment in the light shielding layer is the same as the ratio between the resin component and the white pigment in the coating liquid.

  The solvent is not particularly limited as long as it can dissolve or disperse components such as the main resin and the polyisocyanate compound and does not react with the polyisocyanate compound contained in the coating liquid. Examples of such solvents include water-insoluble solvents such as toluene, xylene, butyl acetate, ethyl acetate, and ethylbenzene, and water-soluble solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. A solvent is suitably selected according to the resin component used for a coating liquid, and is used individually or in combination of 2 or more types. Further, a high boiling point solvent such as tripropylene glycol dimethyl ether may be added to adjust the drying rate during coating.

  Next, the additive used for a coating liquid is demonstrated. Additives are added as necessary to impart weather resistance, light resistance, heat resistance, moisture resistance, flame resistance, and the like to the light shielding layer. In addition, the additive is added as necessary to improve the stability, coating property, drying property, blocking property and the like of the coating solution.

  Examples of the additive include a dispersant, an antifoaming agent, a light stabilizer, an ultraviolet absorber, a heat stabilizer, and an antioxidant. Any known one can be used without particular limitation, and is appropriately selected according to the performance required for the coating liquid and the light shielding layer.

  The coating liquid is prepared by mixing a main resin, a white pigment, a solvent, and, if necessary, an additive and dispersing the white pigment. As a method for dispersing the white pigment in the coating liquid, a known method can be used without particular limitation. For example, a method of preparing a mixed solution by mixing a main resin, a white pigment, a solvent, and, if necessary, an additive, and then stirring the mixed solution using a stirrer. Of the components contained in the coating liquid, for the polyisocyanate compound, as described above, in order to avoid reacting with the main resin component during storage, a solution different from the main agent containing the main resin and white pigment is used. It is preferable to keep it as a curing agent. In this case, the main agent and the curing agent are mixed immediately before use to form a coating liquid.

  What is necessary is just to set the viscosity of a coating liquid suitably according to the coating method of a coating liquid. An example of the viscosity of the coating solution is preferably 10 to 100 cPs, more preferably 50 to 80 cPs. The viscosity of the coating solution may be adjusted by adjusting the amount of solvent added to the coating solution.

<Film>
A film may be used as the light shielding layer instead of the coating layer. As a specific example, a light shielding layer can be provided by dry laminating a white fluorine film or a white polyester film on one surface of the skin layer of the adhesion reinforcing layer using a urethane-based adhesive. In addition, this film shall be 10 micrometers or more and 100 micrometers or less. If it is less than 10 μm, it is not preferable in terms of light shielding properties and scratch resistance, and if it exceeds 100 μm, it is not preferable in terms of productivity.

[Adhesion strengthening layer]
The adhesion reinforcing layer 62 is a layer disposed on one outermost layer of the back surface protection sheet 6, and becomes a contact surface between the back surface sealing material layer 5 in the solar cell module 1, and the back surface protection sheet 6 and the back surface sealing layer. It is a layer having a function of improving the adhesion between the stopper layer 5. The adhesion reinforcing layer 62 is required to have high adhesion and adhesion stability between the back surface protective sheet 6 and the back surface sealing material layer 5. As the back surface sealing material layer 5 in the present invention, an ethylene-vinyl acetate alcohol copolymer resin (EVA resin) containing a crosslinking agent is preferably used, but is not limited thereto, and a polyolefin resin such as polyethylene is used. Also good. In this case, a cross-linked polyolefin resin using ionizing radiation, a polyolefin resin containing a small amount of an organic peroxide and completing the cross-linking at the end of film formation, and a cross-link after film formation containing an organic peroxide. A polyolefin-based resin that performs the above can be used.

  Furthermore, in the present invention, the adhesion enhancement layer 62 is adhered in order to satisfy the requirement for adhesion at room temperature, which is in use, and also has reworkability at a high temperature in the production process. By limiting the composition to a unique range, the back protection sheet 6 can be reworked at high temperatures.

  As shown in FIG. 2, the adhesion reinforcing layer 62 is a layer composed of two or more layers including a core layer 621 and a skin layer 622 that is laminated on the surface of the core layer 621 and exposed to the outermost layer. The core layer 621 and the skin layer 622 constituting the adhesion reinforcing layer 62 are mainly composed of a polypropylene (PP) resin. Thereby, appropriate rigidity can be provided to the back surface protection sheet 6.

  The thickness of the adhesion reinforcing layer 62 may be appropriately determined in consideration of the thickness required for the back surface protective sheet 6. As an example, the thickness of the adhesion reinforcing layer 62 is 3 to 200 μm, and is not particularly limited. When the thickness of the adhesion reinforcing layer 62 is 3 μm or more, sufficient adhesion between the back surface protective sheet 6 and the back surface sealing material layer 5 can be imparted.

  The adhesion reinforcing layer 62 has a multilayer structure formed by laminating the core layer 621 and the skin layer 622. For example, in order to impart appropriate rigidity to the back surface protection sheet, the adhesion reinforcing layer is a single PP resin having excellent rigidity. If constituted solely, the adhesion between the back surface protective sheet and the sealing material tends to decrease in inverse proportion to the increase in rigidity. Therefore, in the back surface protective sheet 6 of the present invention, the core layer 621 and the skin layer 622 constituting the adhesion reinforcing layer 62 are made of polypropylene (PP) resins having different ethylene contents as material resins and used for each layer. Optimized. Thereby, the back surface protection sheet 6 is improving both the adhesiveness and rework property which were in the relationship of the conventional trade-off to the preferable range.

  Moreover, it is preferable that the adhesion reinforcement layer 62 does not cause cohesive failure at 130 ° C. or higher and 150 ° C. or lower. Cohesive failure means that peeling occurs inside a layer when a tensile force is applied. If the adhesion strengthening layer 62 is torn or causes cohesive failure at 130 ° C. or more and 150 ° C. or less, it peels off in the adhesion reinforcing layer 62 at the time of rework, so that the material of the adhesion reinforcing layer adheres to the sealing material layer side. Since the material to which the adhesion reinforcing layer is adhered cannot be reused, the back surface protective sheet having the adhesion reinforcing layer that causes cohesive failure at 130 ° C. or more and 150 ° C. or less has no rework property. This is because the object of the present invention cannot be achieved.

  The core layer 621 is a layer having a function of suppressing the curl deformation of the back surface protective sheet 6 by imparting appropriate rigidity to the adhesion reinforcing layer 62 itself while maintaining the adhesion of the adhesion reinforcing layer 62. It is a layer comprising 80% by mass or more of a polypropylene (PP) resin having a temperature of 160 ° C. or higher. In order to suppress curl deformation, it is preferable to use a homopolypropylene (homo PP) resin in the core layer 621 in an amount of 80% by mass or more based on the total resin. Homo PP is a polymer composed only of polypropylene and has high crystallinity, and therefore has excellent rigidity. By using this for the core layer, curling deformation of the back surface protective sheet 6 can be significantly suppressed and its handling property can be enhanced.

  Moreover, cohesive failure in the core layer at 130 to 150 ° C. can be prevented by setting the melting point of the core layer to 160 ° C. or higher. For this reason, the core layer is not coherently broken during rework, so that it is possible to provide an adhesion reinforcing layer with excellent reworkability.

  The core layer 621 preferably further contains an inorganic filler. Thereby, the rigidity of the adhesion reinforcing layer 62 is further increased, and the occurrence of curl deformation in the back surface protective sheet 6 is sufficiently suppressed. Such inorganic fillers include talc (hydrous magnesium silicate) or titanium oxide, and others such as calcium carbonate, carbon black, titanium black, Cu—Mn based composite oxide, Cu—Cr—Mn based composite oxide, Alternatively, zinc oxide, aluminum oxide, iron oxide, silicon oxide, barium sulfate, calcium carbonate, titanium yellow, chrome green, ultramarine, aluminum powder, mica, barium carbonate, or the like can be used. Among them, talc and titanium oxide can be preferably used in order to sufficiently improve handling properties. The content of the inorganic filler in the resin film forming the core layer 621 is not essential, and the content may be in the range of 0% to 30%, but in order to obtain more preferable handling properties, the above content is included. The amount is preferably 5% by mass or more and 25% by mass or less.

  As the inorganic filler, talc can be particularly preferably used. However, when talc is added as the inorganic filler to be added, the content in the resin forming the core layer should be 2% by mass or more and 20% by mass or less. Is particularly preferred. This is thought to be because talc has a high aspect ratio and is aligned horizontally during extrusion molding, so the shrinkage rate in the extrusion direction is small.

  In addition, when it is calculated | required that a back surface protection sheet should have a colored external appearance, it is excellent in a weather resistance among said inorganic fillers, and it is easy to obtain including price that it is easy to paint. Therefore, the white pigment may further include titanium oxide or the like, and the black pigment may further include carbon black or the like. The inclusion of these colored pigments is preferable in that it can improve the power generation efficiency due to re-reflection of sunlight or meet the demands on the design. In particular, it has been found that titanium oxide also has an effect of improving the handleability like the above talc.

  An example of the thickness of the core layer 621 is 40 to 160 μm, and is not particularly limited. When the thickness of the core layer 621 is 40 μm or more, sufficient dimensional stability can be imparted, and when the thickness of the core layer 621 is 160 μm or less, film transportability at the time of lamination is imparted. be able to.

<Skin layer>
The skin layer 622 is a layer having a function of developing reworkability at a predetermined temperature as well as sufficient adhesion to the sealing material layer of the adhesion reinforcing layer 62. Therefore, the skin layer 622 contains 50% by mass or more of a polypropylene resin having a melting point of 120 ° C. or higher and 135 ° C. or lower. When the polypropylene resin having a melting point of 120 ° C. or more and 135 ° C. or less is less than 50% by mass, the adhesion at room temperature is insufficient.

  The ethylene unit is preferably more than 5.0% by mass and 10.0% by mass or less. Here, the ethylene unit may be contained as a copolymer component or may be contained as a finely dispersed component such as a rubber component. Polypropylene resin containing ethylene units has lower crystallinity and better flexibility than homo PP, but can be used for the encapsulant layer of the back protection sheet 6 by adjusting the ethylene unit content to a limited range. Adhesion to time can be sufficiently enhanced, and reworkability at a high temperature such as immediately after lamination at the time of production can be imparted.

  When the melting point in the polypropylene resin constituting the skin layer 622 is higher than 135 ° C. or the content of the ethylene unit is less than 5% by mass, the adhesion at room temperature is insufficient. Further, when the melting point is less than 120 ° C. or the content of the ethylene unit exceeds 10% by mass, rework becomes extremely difficult.

  As described above, the rework temperature is about 130 ° C. to 140 ° C., and at this temperature, part of the skin layer or the melting point is higher than the melting point, and it is considered that the rework property is improved.

  As described above, in order to make the content of ethylene units in the polypropylene resin constituting the skin layer 622 more than 5.0% by mass and 10.0% by mass or less, a certain amount of ethylene units are contained in the propylene chain. The incorporated elastomer polypropylene (elastomer PP) alone or a mixed system of the elastomer PP and random PP in which a certain amount of ethylene units are incorporated in the propylene chain may be used. Thus, the content of the ethylene unit in the polypropylene resin can be adjusted to an appropriate range by appropriately adjusting the blending ratio of the elastomer PP and the random PP. For example, an elastomer PP having an ethylene unit content of 5% or more and a random PP having an ethylene unit content of about 2.5% may be used in combination. As described above, the “content of the ethylene unit in the polypropylene resin” as used in the present specification means that even when the elastomer PP and the random PP are blended in the production process, the blending ratio thereof, etc. Regardless of the above, it refers to the content of the ethylene unit relative to the total amount in all the polypropylene resins constituting each layer.

  It should be noted that, rather than simply blending the ethylene component, the skin layer 622 contains a random PP copolymerized as described above, so that the skin layer is simply blended with PP and polyethylene resin. It is considered that there is a merit that the mechanical strength of 622 is easily maintained.

  The thickness of the skin layer 622 may be appropriately determined in consideration of the thickness required for the back surface protective sheet 6. As an example, the thickness of the skin layer 622 is 1 μm or more and 40 μm or less, and is not particularly limited. When the thickness of the skin layer 622 is 1 μm or more, sufficient adhesion between the back surface protective sheet 6 and the back surface sealing material layer 5 can be imparted, and the thickness of the skin layer 622 is 40 μm or less. By being, the film conveyance aptitude at the time of a lamination process can be provided. The thickness ratio between the core layer 621 and the skin layer 622 can be appropriately set within a range of, for example, 50: 1 to 4: 1. The skin layer is basically transparent without containing a colored pigment such as titanium oxide.

[Method of forming light shielding layer]
Next, a method for forming the light shielding layer by applying the coating liquid on the surface of the substrate will be described. The light-shielding layer forms the coating film by applying the coating liquid on the surface of the polypropylene resin, evaporates the solvent contained in the coating film, and then crosslinks the main resin and polyisocyanate compound contained in the coating film. It is formed by reacting and curing.

  As a method for applying the coating liquid to the surface of the substrate, a conventionally known method can be used without particular limitation. Examples of such a coating method include a printing method, a coating method using a gravure coater, a roll coating method, a spray coating method, a dip coating method, a solid coating method, and a brush coating method.

  As a method for evaporating the solvent contained in the coating film, a conventionally known method can be used without particular limitation. Examples of such an evaporation method include a heating method, a reduced pressure drying method, a hot air drying method, and a natural drying method, but are not particularly limited. The conditions for evaporating the solvent contained in the coating film may be appropriately set according to the solvent to be used, and examples include heating to 60 to 200 ° C. for 1 to 5 minutes. The coating film obtained by evaporating the solvent is subjected to aging for sufficiently carrying out the crosslinking reaction. The aging conditions may be appropriately set according to the types of the main resin and polyisocyanate compound used. For example, the aging condition may be left at 40 to 50 ° C. for 3 to 4 days.

  When the solvent is removed from the coating film by evaporation, the base resin, white pigment, polyisocyanate compound and additives added to the coating solution remain on the surface of the substrate to form a film. This film is cured to become a light shielding layer. The thickness of the light shielding layer is not particularly limited, and may be determined as appropriate according to the conditions to which the light shielding sheet is applied. As thickness of a light shielding layer, 1-30 micrometers is preferable and 10-20 micrometers is mentioned more preferably. When the thickness of the light shielding layer is less than 1 μm, it is not preferable because sufficient light shielding properties cannot be imparted and scratch resistance and solvent resistance are inferior. If the thickness of the light shielding layer exceeds 30 μm, the cost increases, which is not preferable from the viewpoint of productivity.

[Back side protection sheet for solar cell module]
Next, the back surface protection sheet for solar cell modules in which the light shielding sheet is used will be described. This back surface protection sheet for solar cell modules is a laminated body, and the said light shielding layer exists in the outermost layer. Thereby, when the back surface protection sheet for solar cell modules is applied to a solar cell module, a light shielding layer turns into the surface of the back surface side of a solar cell module.

[Solar cell module]
Next, the solar cell module in which the said back surface protection sheet for solar cell modules was used is demonstrated.

  The solar cell module is configured by laminating a solar cell module back surface protective sheet, a first sealing material, a solar cell element, a second sealing material, and a transparent front substrate in this order from the back surface side of the solar cell module. As for the back surface protection sheet for solar cell modules, the surface on the opposite side to the said light shielding layer is joined to a 1st sealing material. Therefore, the back surface of the solar cell module coincides with the surface on the light shielding layer side of the back surface protective sheet for solar cell module.

  For example, the solar cell module is formed by sequentially laminating the members forming the respective layers and then integrating them by vacuum suction or the like, and then thermocompression-bonding the respective layers as an integrally formed body by a molding method such as a lamination method. Can be manufactured.

  Further, the solar cell module is formed on the front side and the back side of the solar cell element by a molding method usually used in ordinary thermoplastic resins, for example, T-die extrusion molding. The stop material is melt-laminated, the solar cell element is sanded with the first encapsulant and the second encapsulant, and then the transparent front substrate and the back protection sheet for the solar cell module are sequentially laminated, and then these are vacuum-sealed. You may manufacture by the method of integrating by suction etc. and carrying out thermocompression bonding.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Ink dispersibility test]
Product name Zeffle GK-570 (hydroxyl value 90-100 mg / g) manufactured by Daikin Industries, Ltd. as a fluororesin having a plurality of crosslinkable substituents, and Shin-Nakamura as a (meth) acrylic resin having a plurality of crosslinkable substituents Made by Chemical Co., Ltd., product name Vanaresin UVA-5080 (OHV20) (mass average molecular weight 50,000, Tg 80 ° C., hydroxyl value 20 mg / g) as a white pigment, titanium oxide (manufactured by Sakai Chemical Industry Co., Ltd., product name R- 5N: average particle diameter of 0.25 μm, alumina treatment) was used in an amount of 200% by mass with respect to the total mass of the fluororesin and the (meth) acrylic resin, and a mixture of ethyl acetate: butyl acetate = 1: 1 was used as the solvent. . The main ingredients of each coating solution were prepared with the blending amounts (mass%) described in Table 1. The solid content concentration of the main agent was 43 to 45% by mass. In the preparation of each main agent, a mixture was prepared by combining the components and solvents described in Table 1, and the mixture was stirred for 60 minutes using a paint shaker. Thereafter, the ink dispersibility of the coating liquid was visually confirmed.

[Evaluation criteria]
○: Dispersibility is good △: Dispersibility is bad ×: Ink cannot be formed

  From Table 1, if the (meth) acrylic resin is contained in an amount of 60% by mass or more based on the total mass of the fluororesin and the (meth) acrylic resin, the ink dispersibility is good, so that the light shielding layer is formed. It can be seen that the coating liquid is good.

(Example 1)
<Manufacture of coating agent for light shielding layer>
In the coating liquid of Production Example 2, hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) were adjusted to the NCO / OH ratio as shown in Table 2, and this was used as a curing agent in each coating liquid. These main agent and curing agent were mixed so that the blending amount of the polyisocyanate compound was the amount described in Table 2 immediately before use (coating) to obtain a coating agent.

<Manufacture of adhesive resin sheet>
The following adhesive resin sheets were sequentially laminated and integrated by dry laminating to produce an adhesive resin sheet sample of Example 1.

Core layer: A resin composition in which the following homo PP resin is used for the core layer of the adhesive resin sheet, and the following titanium oxide as an inorganic filler is kneaded so that the content in the homo PP resin is 20% by mass. Was used as a composition for the core layer.
Homo PP: Mitsubishi Plastics Co., melting point 165 ° C
Titanium oxide: Ti-pure R105 (manufactured by Dupont), average particle size 0.2 to 0.25 μm
Skin layer: For the skin layer of the adhesive resin sheet, random PP resin containing ethylene (melting point 140 ° C., ethylene content 3% by mass) and elastomer PP resin (melting point 125 ° C., ethylene content 7% by mass) PP-based resin kneaded so that the ratio of the elastomer PP resin was 1: 1 and the ethylene unit amount was 5.0% by mass was used as the composition for the skin layer.
Random PP resin: melting point 140 ° C., ethylene unit content 2.5%.
Elastomer PP resin: melting point 125 ° C., ethylene unit content 7%.

  Each of the above compositions was formed as a multilayer film by coextrusion to obtain a resin sheet having a thickness of 60 μm (skin layer 3 μm / core layer 54 μm / skin layer 3 μm), and the adhesive resin sheets of Examples 1 to 3 and Comparative Example 4 (In addition, the adhesion reinforcement layer manufactured with this manufacturing method is hereafter called an adhesive resin sheet.).

<Preparation of back surface protection sheet for solar cell module>
Each coating solution prepared as described above was applied to the surface of the skin layer of the adhesive resin sheet with a bar coater, and the coated coating solution was dried at 110 ° C. for 2 minutes, and then at 40 ° C. for 3 days. A light shielding layer was formed by aging, and backside protective sheets of Examples 1 to 3 and Comparative Example 4 were produced.

(Comparative Examples 1-4)
<Manufacture of coating agent for light shielding layer>
In the coating solutions of Production Examples 1 and 2, hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) were adjusted to an NCO / OH ratio as shown in Table 2, and this was used as a curing agent in each coating solution. These main agent and curing agent were mixed so that the blending amount of the polyisocyanate compound was the amount described in Table 2 immediately before use (coating) to obtain a coating agent.

<Preparation of back surface protection sheet for solar cell module>
Using polyethylene (PE), homopolypropylene (homo PP), and polyethylene terephthalate (PET) as the adhesion reinforcing layer, each coating solution prepared as described above is applied to the surface with a bar coater, and the coating is applied. The liquid was dried at 110 ° C. for 2 minutes and then aged at 40 ° C. for 3 days to form a light-shielding layer, and backside protective sheets of Comparative Examples 1 to 4 were produced.

[Shading layer adhesion test]
About each of the back surface protection sheet for solar cell modules in which the light shielding sheet formed with the coating agent of an Example and a comparative example was used, according to ASTM D3359-09 and JIS5600, it is 100 squares with the light shielding sheet coating and a base material with a cutter. The remaining part after scratching the eyes (the total size of 100 squares is 10 mm × 10 mm), rubbing 12 mm wide cellophane tape (CT405AP-12 manufactured by Nichiban Co., Ltd.) The area was measured for durability adhesion according to the following evaluation criteria, and the results are shown in Table 2 as the evaluation results of substrate adhesion.

[Evaluation criteria]
5B: Coating film peeling rate 0%
4B: Coating film peeling rate 0 to 5%
3B: Coating film peeling rate of 5 to 15%
2B: Coating film peeling rate of 15 to 35%
1B: Coating film peeling rate of 35 to 65%
0B: 65% or higher coating film peeling rate

[Encapsulant adhesion test]
The adhesion was evaluated for the samples for adhesion evaluation using the samples of Examples and Comparative Examples. Evaluation was performed based on the numerical value measured by the following method.

<Creating a pseudo module>
About the back surface protection sheet sample, the following sealing material 1 or 2 cut into the same size as the sample is applied to the surface of the adhesion reinforcing layer (adhesive resin sheet side) at 140 ° C. to 155 ° C. for 15 minutes. Lamination was performed using a manufacturing vacuum laminator to obtain a sample for adhesion evaluation.
Sealing material sheet (indicated as “EVA” in Table 1): EVA cross-linking type, thickness 500 μm.

(Initial adhesion test: peel test)
For each sample for evaluation of adhesion, the adhesion strength was measured for adhesion by peeling strength (N) at 180 ° peeling with a width of 15 mm. For the measurement, using a peeling test apparatus (manufactured by “A & D Co., Ltd., trade name“ TENSILON RTG-1210 ”), measurement is performed at 23 ° C. under a peeling condition of 50 mm / min by 180 ° peeling. Performed and evaluated. The evaluation results are shown in Table 2 below as “sealing material adhesion”.
[Evaluation criteria]
○: 50 N / 15 mm or more ×: less than 50 N / 15 mm

[Moist heat test]
About each of the back surface protection sheet for solar cell modules in which the light-shielding sheet of an Example and a comparative example was used, 120 degreeC, 85% RH, and 1.65 atm environment in HASTEST (MODEL PC-R8D) by Hirayama Manufacturing Co., Ltd. Stored under 96 hours. Thereafter, the above [Substrate Adhesion Test] was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2 below as “wet heat adhesion”.

[Evaluation criteria]
5B: Coating film peeling rate 0%
4B: Coating film peeling rate 0 to 5%
3B: Coating film peeling rate of 5 to 15%
2B: Coating film peeling rate of 15 to 35%
1B: Coating film peeling rate of 35 to 65%
0B: 65% or higher coating film peeling rate

[Solvent resistance test]
The solvent resistance test according to ASTM D5402-06 was carried out on the surface of the backside protective sheet of Examples and Comparative Examples on the weatherproof coating layer side. A cotton soaked with acetone was used as the solvent, and the surface was rubbed 30 times at a speed of about once per second with a force of 1500 g, and the surface was observed and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2 below as “solvent resistance”.

[Evaluation criteria]
○: No peeling ×: There is peeling

[Weather resistance test]
About the back surface protection sheet of an Example and a comparative example, a MW (metal weather) test is performed on the following conditions, and each back surface protection sheet after the test is subjected to an adhesion test, and durability adhesion is evaluated according to the following evaluation criteria. The results are shown in Table 2 as the weather resistance evaluation results.

[MW test]
Metal halide lamp type testing machine JTM G 01 2000 Japan Testing Machine Industry Association Standard JTM STANDARD Metalhalide Lamp type appratus
Device name: Daipla Metal Weather (Daipla Wintes Co., Ltd.)
Model: KU-R5CI-A
Light source lamp: MW-60W
Filter: KF-1 (irradiation range 295 nm to 780 nm)
Illuminance: 60 ± 5 mW / cm2 (Ushio Electric Co., Ltd. illuminance meter used)
Test conditions: Lite (irradiation) 63 ° C. 50% RH 20 hours, Dew (condensation) 30 ° C. 98% RH 4 hours, Rest (rest): 30 ° C., 98% RH, 0.01 hour, 10 s shower before and after Dew 250 hours test conducted as one cycle.
In the shower, pure water having a conductivity of 2 μS / cm or less was used at 25 ° C.

[Evaluation criteria]
5B: Coating film peeling rate 0%
4B: Coating film peeling rate 0 to 5%
3B: Coating film peeling rate of 5 to 15%
2B: Coating film peeling rate of 15 to 35%
1B: Coating film peeling rate of 35 to 65%
0B: 65% or higher coating film peeling rate

[Reworkability evaluation]
About the said back surface protection sheet sample of each of an Example and a comparative example, the rework property was evaluated on the following references | standards. As for the evaluation method, the sample laminated in the module form was reheated at 145 ° C. for 20 minutes, and then peeled off using a cutter and pliers on a laminator, and its reworkability was confirmed.

[Evaluation criteria]
○: Reworkability is very good △: Reworkability is good ×: Reworkability is bad

※基材劣化のため測定不可

* Cannot be measured due to deterioration of the base material

  From Table 2, it can be seen that the back surface protective sheet of the present invention is excellent in the light shielding layer adhesion, sealing material adhesion, wet heat storage, solvent resistance, weather resistance, and reworkability, and is an excellent back surface protection sheet.

(Example 2)
As the light shielding layer, white polyvinyl fluoride resin (PVF) was used. Specifically, the light shielding layer was provided by dry-laminating the adhesive resin sheet using a urethane-based adhesive. Except for this point, a back protective sheet was prepared in the same manner as in Example 1.

(Example 3)
White polyvinylidene fluoride resin (PVDF) was used as the light shielding layer. Specifically, the light shielding layer was provided by dry-laminating the adhesive resin sheet using a urethane-based adhesive. Except for this point, a back protective sheet was prepared in the same manner as in Example 1.

(Comparative Examples 5-7)
As the light shielding layer, white polyvinyl fluoride resin (PVF) was used. Specifically, the light shielding layer was provided by dry-laminating the adhesion reinforcing layer shown in Table 3 using a urethane-based adhesive. Except for this point, a back protective sheet was prepared in the same manner as in Example 1.

  About the back surface protection sheets of Examples 2 and 3 and Comparative Examples 5 to 7, the sealing material adhesion, wet heat storage stability, solvent resistance, weather resistance, and reworkability were measured in the same manner as in Examples 1 and Comparative Examples 1 to 4. did. In addition, about the light shielding layer adhesiveness, it measured with the following method. The measurement results are shown in Table 3.

[Shading layer adhesion test]
About each of the back surface protection sheet for solar cell modules in which the light shielding sheet of the white polyvinyl fluoride resin (PVF) or the white polyvinylidene fluoride resin (PVDF) of the example and the comparative example is used, the peel strength (N) is 15 mm wide. The adhesion strength was measured for adhesion at 180 ° peeling. For the measurement, using a peeling test apparatus (manufactured by “A & D Co., Ltd., trade name“ TENSILON RTG-1210 ”), measurement is performed at 23 ° C. under a peeling condition of 50 mm / min by 180 ° peeling. Performed and evaluated. The evaluation results are shown in Table 3 below as “shading layer adhesion”.
[Evaluation criteria]
○: 4N / 15mm or more ×: Less than 4N / 15mm

  From Table 3, the back surface protective sheet of the present invention is excellent in light shielding layer adhesion, sealing material adhesion, wet heat storage, solvent resistance, weather resistance and reworkability, even when a resin film is used as the light shielding layer. It turns out that it is the outstanding back surface protection sheet.

DESCRIPTION OF SYMBOLS 1 Solar cell module 2 Transparent front substrate 3 Front sealing material layer 4 Solar cell element 5 Back surface sealing material layer 6 Back surface protection sheet 61 Light shielding layer 62 Adhesion reinforcement | strengthening layer 621 Core layer 622 Skin layer

Claims (6)

A back surface protection sheet for a solar cell module,
Providing an adhesion reinforcement layer that is arranged in the outermost layer of the back surface protection sheet and strengthens the adhesion with the sealing material,
The adhesion reinforcing layer includes a core layer containing a polypropylene resin having a melting point of 160 ° C. or higher in an amount of 80% by mass or more of the total resin,
A skin layer containing 50 mass% or more of a polypropylene resin containing an ethylene unit and having a melting point of 120 ° C or higher and 135 ° C or lower and exposed to the outermost layer,
The adhesion reinforcing layer is a three-layer coextruded film of skin layer / core layer / skin layer, and on one surface of the skin layer, a coating layer having a thickness of 1 μm to 30 μm or a thickness of 10 μm to 100 μm A back protective sheet, wherein a light shielding layer made of a film is laminated.   The back surface protection sheet according to claim 1, wherein the light shielding layer is a fluorine-based film containing a white pigment, and is laminated on one surface of the skin layer by an adhesive with a dry lamination method. The light shielding layer is a coating layer in which a white pigment is dispersed in a resin;
The resin is a mixture of a fluororesin having a plurality of crosslinkable substituents and a (meth) acrylic resin having a plurality of crosslinkable substituents, crosslinked with a polyisocyanate compound,
The back surface protection sheet according to claim 1, wherein the (meth) acrylic resin is 60% by mass or more and 90% by mass or less with respect to a total mass of the fluororesin and the (meth) acrylic resin.   The back surface protection sheet according to any one of claims 1 to 3, wherein the content of the ethylene unit in the skin layer is 5.0 mass% or more and 10.0 mass% or less.   The back protective sheet according to any one of claims 1 to 4, wherein the white pigment is 50 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the resin. The solar cell module using the back surface protection sheet in any one of Claim 1 to 5.

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