JP2016072540A - Rear surface protective sheet and solar cell module using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rear surface protective sheet for a solar cell module having high adhesion and adhesion durability which can sufficiently contribute to enhancement in a photovoltaic power generation conversion efficiency.SOLUTION: There is provided a rear surface protective sheet for a solar cell module in which a polypropylene resin-based adhesion-reinforcing layer formed on a base material layer of the rear surface protective sheet has a multilayer structure including a core layer and a skin layer, the skin layer uses polypropylene (PP) containing an ethylene unit having a predetermined melting point range at a constant rate, a content of the polypropylene resin having a melting point of 160°C or higher in the core layer is 80% or more, and a prism structure in which a plurality of fine projections are formed so as to be adjacent to each other is formed on a surface on a light-receiving surface side of the core layer.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a back surface protection sheet for a solar cell module and a solar cell module using the same. More specifically, the present invention relates to a back surface protection sheet that can contribute to an improvement in power generation efficiency of a solar cell module by having a prism structure on the surface.

  In recent years, solar cells as a clean energy source have attracted attention due to the growing awareness of environmental issues. In general, a solar cell module constituting a solar cell has a configuration in which a transparent front substrate, a front sealing material, a solar cell element, a back sealing material, and a back surface protection sheet are laminated in order from the light receiving surface side. It has a function of generating electricity by being incident on the solar cell element.

  The back surface protection sheet for a solar cell module is required to play a role of preventing moisture (water vapor) from entering the back surface sealing material as a member constituting the solar cell module. As such a back surface protection sheet for a solar cell module, for example, a polyethylene-based or fluorine-based resin film is used. Among them, a back surface protection sheet using a polyethylene terephthalate (PET) film is particularly widely used because it is inexpensive and excellent in processability and does not emit toxic gas when burned.

  Moreover, ethylene-vinyl acetate copolymer resin (EVA), polyolefin resin, etc. are used as a sealing material for solar cell modules. The back surface protection sheet for the solar cell module is required to have high adhesion with these sealing materials.

  As a back surface protection sheet with improved adhesion to the sealing material, a layer for improving the adhesion between the sealing material (hereinafter referred to as “adhesion”) on a base material layer made of PET or the like that is inexpensive and excellent in workability. As a “strengthening layer”, there is disclosed a back surface protective sheet (see Patent Documents 1 and 2) in which a polypropylene resin having excellent hydrolysis resistance and heat fusion properties is disposed in the outermost layer. The back surface protection sheet in which the adhesion reinforcing layer is made of a polypropylene resin can suppress curl deformation of the back surface protection sheet in a case where it is in a single wafer state in the work process, for example, which is preferable from the viewpoint of handling properties in the work process. Is.

  On the other hand, the back surface protection sheet which can raise the electric power generation efficiency of a solar cell module by giving light reflectivity to the surface is also developed. For example, a solar cell module has been proposed in which the back cover member has an uneven shape, white pigment is mixed, and the effect of reflecting incident light is enhanced to improve power generation efficiency (Patent Document 3).

  Here, in the case of the back surface protective sheet having a concavo-convex shape on the surface, heat resistance sufficient to hold the concavo-convex shape is also required during the thermocompression treatment in the integration step of the solar cell module.

  That is, the back surface protection sheet for solar cells is required to have both a light reflection function that can contribute to an improvement in power generation efficiency of the solar cell module and adhesion between the sealing material and the like. However, the present situation is that a back surface protection sheet for a solar cell module that satisfies such characteristics has not been developed yet.

JP 2007-150084 A JP 2007-19059 A Japanese Patent Laid-Open No. 10-284747

  The present invention has been made in order to solve the above-described problems, and the object thereof is to combine the light reflection function that can contribute to the improvement of power generation efficiency of the solar cell module and the adhesion between the sealing material and the like. It is providing the back surface protection sheet for solar cell modules.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, in the back surface protection sheet for the solar cell module, the polypropylene resin-based adhesion reinforcing layer formed on the base material layer of the back surface protection sheet has a multilayer structure including a core layer and a skin layer. By using polypropylene (PP) containing an ethylene unit in a predetermined melting point range at a constant rate, the core layer has a melting point of 160 ° C. or higher, and a prism structure is formed on the light receiving surface side of the core layer. The present inventors have found that the above problems can be solved and have completed the present invention. More specifically, the present invention provides the following.

(1) A back surface protective sheet for a solar cell module, comprising: a base material layer; and an adhesion reinforcing layer disposed on the outermost layer of the back surface protective sheet to reinforce adhesion with a sealing material, The adhesion reinforcing layer includes a skin layer exposed on the outermost surface of the back protective sheet and a core layer, and the skin layer contains 50% by mass or more of a polypropylene resin containing an ethylene unit, and the skin The content of the ethylene unit in the layer is 2.0% by mass or more and 10.0% by mass or less in the total polypropylene resin component of the skin layer, and the core layer is composed of a polypropylene resin having a melting point of 160 ° C. or higher and a white color. And a content of the polypropylene resin is 80% by mass or more in the total resin component of the core layer, and a plurality of fine convex portions are adjacent to the light receiving surface side surface of the core layer. Become Back protective sheet prism structure is formed.

(2) The back surface protective sheet according to (1), wherein the shape of the vertical cross section of the fine convex portion is a triangle, and the apex angle of the convex portion is an average of 90 ° or more.

(3) The back surface protection sheet according to (1) or (2), wherein the adhesion reinforcing layer has a second skin layer disposed between the core layer and the base material layer.

(4) A solar cell module in which the sealing material that adheres to the adhesion reinforcing layer is made of a heat-crosslinkable resin, using the back surface protective sheet according to any one of (1) to (3).

(5) In the integration step, including an integration step of laminating and integrating the back surface protection sheet according to any one of (1) to (3) and other solar cell module constituent members by thermocompression treatment. A method for producing a solar cell module, wherein the thermocompression treatment is performed at 110 ° C. or higher and 160 ° C. or lower.

  According to the present invention, the adhesion reinforcing layer formed on the base material layer of the back surface protective sheet for solar cell module has a multi-layer configuration, and the skin layer is molded with a polypropylene resin containing ethylene units having a predetermined melting point, By forming a prism structure on the light receiving surface side of the core layer, the solar cell module has a light reflection function that can contribute to an improvement in power generation efficiency of the solar cell module and an adhesive property between the sealing material and the like. A back surface protection sheet can be 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 a schematic diagram of the cross section which shows an example of the layer structure of 1st embodiment of the back surface protection sheet for solar cell modules of this invention. It is a schematic diagram of the cross section which shows an example of the layer structure of 2nd embodiment of the back surface protection sheet for solar cell modules of this invention.

  Hereinafter, the back surface protection sheet for the solar cell module of the present invention (hereinafter also simply referred to as “back surface protection sheet”) and the details of the solar cell module using the same will be described. The present invention is not limited to the embodiments described below.

<Basic configuration of solar cell module>
First, the basic structure of the solar cell module using the back surface protection sheet for the solar cell module of the present embodiment will be described with reference to FIG. In the solar cell module 1, 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 sheet 6 according to the present invention are laminated in this order from the light receiving surface side. It has a configuration.

  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 base material for forming the sealing material layer, ethylene-vinyl acetate copolymer resin (EVA), ionomer, polyvinyl butyral (PVB), polyolefin resin such as polyethylene, etc. can be used as appropriate. In the form, it is preferable to use a heat-crosslinkable resin. Here, the thermo-crosslinking resin refers to a resin that is cross-linked by heating, such as a thermosetting resin or a resin mixed with a cross-linking agent.

  In the present invention, the surface structure on the light-receiving surface side of the core layer in the adhesion reinforcing layer of the back surface protective sheet has a prism structure in which a plurality of fine convex portions are adjacent to each other. Therefore, by using a heat-crosslinkable resin as the resin for forming the sealing material layer, the sealing material is softened by heating in the process of stacking and integrating the solar cell modules by thermocompression treatment, and the core layer by pressure bonding. The sealing material is deformed into a fine convex shape following the fine convex portion. Thereafter, the sealing material deformed into a fine convex shape is cured by being cross-linked, so that the back sealing material layer 5 follows the structure of the surface on the light receiving surface side of the core layer, which is particularly preferable. Among the thermally crosslinkable resins, it is preferable to use an ethylene-vinyl acetate copolymer resin (EVA) that has excellent adhesion to the back surface protective sheet. In addition, the light-receiving surface side means the light-receiving surface side of a solar cell module when a back surface protection sheet is laminated | stacked as a solar cell module.

  In addition, the back surface protection sheet 6 is particularly excellent in adhesion between the resin subjected to the crosslinking treatment. Of the above material resins, EVA is generally required to be subjected to a crosslinking treatment when modularized. As the polyolefin-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 sealing material layer 5 described above. Is required. The back surface protection sheet 6 can contribute to the improvement of the power generation efficiency of the solar module while satisfying the requirements in terms of physical properties when used as a solar cell module. Details of the back surface protection sheet 6 will be described later.

<Back protection sheet>
As shown in FIG. 2, the back surface protection sheet 6 is a multilayer structure including at least a base material layer 61 and an adhesion reinforcing layer 62.

  The adhesion reinforcing layer 62 is disposed on one surface of the base material layer 61, and the weather resistant layer is disposed on the other surface of the base material layer 61 as necessary. 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.

[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. Generally, the back sealing material layer 5 is made of an ethylene-vinyl acetate alcohol copolymer resin (EVA), an ionomer, polyvinyl butyral (PVB), or a polyolefin resin such as polyethylene. The adhesion reinforcing layer 62 is provided with high adhesion between the back surface protective sheet 6 and the back surface sealing material layer 5 made of these resins.

  Furthermore, the back surface protection sheet 6 can diffusely reflect the light incident on the back surface protection sheet 6 while satisfying the adhesiveness requirement in the case of being integrated with the solar cell module. It is characterized by being. Since the incident angle of sunlight changes with time, the back surface protective sheet 6 having a prism structure capable of diffusely reflecting sunlight rather than the back surface protective sheet whose surface is mirror-like and specularly reflects sunlight. In this case, the change in power generation efficiency due to the change in the incident angle can be reduced, and for example, the total power generation amount per day under the same weather conditions can be increased.

  The back surface protective sheet 6 has a prism structure in which the entire surface on the light receiving surface side of the core layer containing 80% by mass of a polypropylene resin having a melting point of 160 ° C. or higher is formed by a plurality of fine convex portions adjacent to each other. As shown in FIG. 2, the core layer 621 containing 80% by mass of a polypropylene resin having a melting point of 160 ° C. or higher has a prism structure in which the surface on the light-receiving surface side has a plurality of fine convex portions adjacent to each other. 621 itself is hard to be softened by the laminate and can maintain the shape of the entire surface on the light receiving surface side. Therefore, a core containing a polypropylene resin having a melting point of 160 ° C. or higher by 80% by mass or more by setting the laminating temperature preferably in the range of 110 ° C. or higher and 160 ° C. or lower, more preferably in the range of 135 ° C. or higher and 155 ° C. or lower. The fine convex portion of the layer is preferable because the structure can be maintained before and after lamination.

  The skin layer exposed on the outermost surface of the back protective sheet preferably contains 50% by mass or more of a polypropylene resin having a melting point of 110 ° C. or higher and 150 ° C. or lower, preferably 120 ° C. or higher and 140 ° C. or lower. Therefore, the skin layer 622a is significantly softened as compared with the core layer 621 at the time of lamination during the thermocompression treatment. After the thermocompression treatment, as shown in FIG. 2, the light receiving surface side surface of the skin layer has a prism structure in which a plurality of fine convex portions are adjacent to the surface of the core layer on the light receiving surface side. .

  Since the structure of the entire surface on the light receiving surface side of the core layer 621 is a prism structure in which a plurality of fine convex portions 623 are adjacent to each other, the interface between the skin layer 622a and the back sealing material layer 5 is also the light receiving surface of the core layer 621. A prism structure can be formed as well as the shape of the entire surface on the side.

  When the reflective surface is a flat surface, the structure of the interface between the skin layer 622a exposed on the outermost surface of the back surface protective sheet and the back surface sealing material layer 5 is a prism structure in which a plurality of fine convex portions 623 are adjacent to each other. In comparison, the reflection angle can be more confused to diffusely reflect light. The core layer 621 includes a white pigment. By including the white pigment, it is possible to meet the demands on the design surface and to scatter the light of sunlight. Therefore, the back surface protection sheet of this embodiment is an excellent back surface protection sheet that has a small influence on power generation efficiency due to a change in incident angle. In addition, it is preferable that white pigment content shall be 20 to 30 mass% in all the components of a core layer. 20 mass% or more is preferable because light is sufficiently scattered, and 30 mass% or less has good extrudability when extruding the core layer. It is preferable because it improves.

  Here, in the back surface protection sheet 1, the shape of the vertical cross section of the fine convex portion 623 is a triangle, and the apex angle 624 is preferably 90 ° or more on average, and 110 ° or more on average. More preferred. By setting it to such an angle, preferable adhesiveness with the back sealing material layer 5 can be obtained. In addition, it is preferable that the entire surface on the light-receiving surface side of the core layer 621 has a prism structure in which a plurality of fine convex portions 623 are adjacent to each other in order to increase light scattering. Moreover, it is preferable from the viewpoint of productivity that the fine protrusions 623 having the same shape are formed on the entire surface.

  The surface on the light-receiving surface side of the core layer has a prismatic structure in which a plurality of fine convex portions having a triangular vertical cross section are adjacent to each other, for example, a fine convex portion having a quadrangular pyramid shape such as a pyramid structure. Even in the shape, the reflection angle can be confused and the light can be diffusely reflected as in the prism structure.

  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 not particularly limited, and may be 3 μm or more and 200 μm or less. 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.

  For example, as shown in FIG. 3, the adhesion reinforcing layer has a configuration such as an adhesion reinforcing layer 62 having a three-layer structure in which a skin layer 622a, a core layer 621, and a second skin layer 622b are sequentially laminated. Also good. Also by such a structure, it can be set as the back surface protection sheet 6 which fully improved adhesiveness with the sealing material. In addition, there exists a merit that the production efficiency of a back surface protection sheet can be improved by setting it as such a symmetrical layer structure, Moreover, the curl deformation | transformation in a manufacture process can be suppressed. In addition, a 2nd skin layer is a layer arrange | positioned between a core layer and a base material layer.

  The adhesion reinforcing layer 62 has a multilayer structure formed by laminating the core layer 621 and the skin layer 622, but in order to give appropriate rigidity to the back surface protective sheet, for example, the adhesion reinforcing layer is a single polypropylene 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 which had the relationship of the conventional tradeoff, and the rigidity suitable for the back surface protection sheet 6 to the preferable range.

<Core layer>
The core layer 621 is a layer having a function of suppressing the curl deformation of the back surface protective sheet 6 by providing an appropriate rigidity to the adhesion reinforcing layer 62 itself, in addition to the function of changing the reflection angle and scattering light. Yes, it is a layer comprising 80% by mass or more of polypropylene (PP) resin having a melting point of 160 ° C. or higher. In order to maintain the prism structure and suppress curl deformation, a homopolypropylene (homo PP) resin can be preferably used for the core layer 621. 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, the structure can be maintained before and after lamination, and curling deformation of the back surface protective sheet 6 can be significantly suppressed, and its handling property can be enhanced.

  The core layer 621 further includes a white pigment. Thereby, in addition to the function of scattering light, 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. As such a white pigment, talc (hydrous magnesium silicate) or titanium oxide, and as others, 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, or the like can be used. About content of a white pigment, it is preferable to make content in all the components into the range of 20 to 30 mass%. By setting it as such a range, while being able to fully improve handling property, it can be set as the back surface protection sheet which can scatter light with a white pigment.

  As an example, the thickness of the core layer 621 is 40 μm or more and 160 μm or less, 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.

  In addition, the core layer 621 is blended with various additives such as antioxidants, surfactants, thickeners, softeners, fillers, pigments, dyes and the like as long as they do not impair the object of the present invention. can do.

<Skin layer>
The skin layer 622 is a layer that is mainly exposed on the outermost surface of the back surface protection sheet and has a function of developing sufficient adhesion to the sealing material layer of the adhesion reinforcing layer 62. Therefore, the skin layer 622 contains 50 mass% or more, preferably 80 mass% or more of a polypropylene resin containing an ethylene unit and having a melting point of 110 ° C. or more and 150 ° C. or less, preferably 120 ° C. or more and 140 ° C. or less. When the polypropylene resin having a melting point containing an ethylene unit is less than 50% by mass, the adhesion to the sealing material and the core layer becomes insufficient.

  As an ethylene unit, it is 2.0 mass% or more and 10.0 mass% or less in all the polypropylene resin components of a skin layer. By using polypropylene containing an ethylene unit in the skin layer, the adhesion between the sealing material and the core layer can be achieved while adjusting the softening point and melting point of the skin layer to the optimum ranges. When the melting point in the polypropylene resin constituting the skin layer 622 is higher than 150 ° C. or the ethylene unit content is less than 2.0% by mass, the skin layer is sufficient in the integration step of stacking and integrating by thermocompression bonding. Cannot be softened, and the adhesiveness with the sealing material layer becomes insufficient. Further, when the melting point in the polypropylene resin constituting the skin layer 622 is less than 110 ° C. or the content of the ethylene unit exceeds 10.0% by mass, the adhesion with the core layer mainly composed of the polypropylene resin becomes insufficient. . 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.

  Further, the skin layer 622 contains various additives such as an antioxidant, a surfactant, a thickener, a softener, a filler, a pigment, and a dye as long as the object of the present invention is not impaired. can do. Polypropylene resin containing an ethylene unit is lower in crystallinity and superior in flexibility than homo-PP, but by adjusting the content of the ethylene unit to a limited range, it can be used for the sealing material layer of the back surface protective sheet 6. Adhesion to can be sufficiently enhanced.

  In order to set the content of the ethylene unit in the polypropylene resin constituting the skin layer 622 to 2.0% by mass or more and 10.0% by mass or less as described above, a certain amount of ethylene unit is incorporated into the propylene chain. Elastomer polypropylene (elastomer PP) alone may be used, or a mixed system of 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 7% 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 manufacturing process, the blending ratio thereof is, for example, Regardless, it refers to the ethylene unit content 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 may be 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.

[Base material layer]
The base material layer 61 is a layer arranged as a base material of the back surface protection sheet 6, and uses a resin sheet obtained by molding a resin material into a sheet shape. For example, polyethylene resin, cyclic polyolefin resin, polystyrene resin, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, polyvinyl chloride resin, poly (meth) acrylic resin, polycarbonate resin, polyethylene Polyester resins such as terephthalate (PET) and polyethylene naphthalate, polyamide resins such as various nylons, polyimide resins, polyamideimide resins, polyarylphthalate resins, silicone resins, polysulfone resins, polyphenylene sulfide resins Various resin sheets such as polyethersulfone resin, polyurethane resin, acetal resin, and cellulose resin can be used. Among these, polyethylene terephthalate (PET) can be preferably used from the viewpoints of physical properties such as insulation performance, mechanical strength, cost, transparency, and economy, and hydrolysis resistant PET is particularly preferably used from the viewpoint of maintaining mechanical strength. it can.

  The thickness of the base material layer 61 is not particularly limited, but may be appropriately determined in consideration of the thickness required for the back surface protective sheet 6. A typical example of the thickness of the back surface protective sheet 6 is a range of 10 μm to 500 μm. In accordance with this, the thickness of the base material layer 61 is preferably 38 μm or more and 250 μm or less. When the thickness of the base material layer 61 is 38 μm or more, preferable durability and weather resistance can be imparted to the back surface protective sheet 6, and when the thickness of the base material layer 61 is 250 μm or less, lamination processing is performed. It is possible to impart film transportability at the time.

  In a conventionally known general back surface protection sheet using PET as a base material layer, a PET resin film for forming the base material layer and other resin films for forming an adhesion layer are laminated and integrated with an adhesive or the like. At this time, there has been a problem that the back surface protection sheet frequently undergoes curl deformation. However, as will be described in detail later, in the back surface protection sheet 6 of the present invention, the back surface protection sheet 62 has a multi-layer structure having a configuration unique to the present invention, so that the back surface protection can be performed regardless of the type of the base material layer. Sheet curling can be sufficiently suppressed. For this reason, PET excellent in each of the above physical properties and economy can be preferably used as the resin constituting the base material layer.

[Weatherproof layer]
The back surface protection sheet of this embodiment can also laminate | stack a weathering layer as needed. A weathering layer can be located on the surface of the back surface side of a solar cell module, when the back surface protection sheet 6 is used for a solar cell module, for example (not shown). Therefore, the weather resistant layer is excellent in weather resistance, heat resistance, light resistance and the like. Such resin sheets include PCTFE (polychlorotrifluoroethylene), PFA (tetrafluoroethylene perfluoroalkyl vinyl ester copolymer), PTFE (polytetrafluoroethylene), ETFE (tetrafluoroethylene / ethylene copolymer). Polymer) and resin sheets such as fluorine resins such as PVDF (polyvinylidene fluoride) are preferably exemplified.

  In addition to resin sheets such as fluororesin, white PET in which polyethylene terephthalate (PET) includes a white pigment such as titanium oxide, transparent polyethylene terephthalate (PET), modified polyphenylene ether (m-PPE), etc. A resin sheet in which a weather resistant resin is further laminated on the surface by coating or laminating can also be preferably used. Here, polyethylene terephthalate (PET) includes hydrolysis-resistant polyethylene terephthalate (HR-PET). In addition, examples of the weather resistant resin to be further laminated include, for example, a fluororesin, an acrylic resin, or an ionizing radiation curable resin, but are not particularly limited.

  In particular, when it is necessary to impart gas barrier properties such as water vapor barrier properties to the back surface protective sheet 6, a transparent vapor deposition layer made of a metal oxide may be formed on the surface of the weather resistant layer. In this case, the kind of metal oxide to be deposited, the thickness of the deposited layer, and the like may be appropriately set in consideration of the performance required for the back surface protection sheet 6.

<Production method of back surface protection sheet>
The manufacturing method of the back surface protection sheet of this embodiment is demonstrated. The back surface protective sheet 6 includes a base resin sheet forming step for forming a base resin sheet for forming the base layer 61, an adhesive resin sheet forming step for forming an adhesive resin sheet for forming the adhesion reinforcing layer 62, and It can manufacture by passing through the integration process which laminates | stacks and integrates an adhesive resin sheet with a base resin sheet.

(Base resin sheet forming process)
The base resin sheet for forming the base layer 61 is made of the resin material such as PET described above by an extrusion method, a cast molding method, a T-die method, a cutting method, an inflation method, and other film forming methods. It can be formed by forming a film. The base resin sheet may contain other additives such as pigments in addition to the resin material as long as the effects of the present invention are not impaired.

(Adhesion strengthening layer forming process)
The adhesive resin sheet for forming the adhesion reinforcing layer 62 is a resin for skin layers comprising a resin composition for a core layer containing homo PP as a main component and containing a predetermined inorganic filler, and polypropylene containing a certain amount of polyethylene. The composition can be obtained by integral molding with a known coextrusion method. Since it becomes possible to integrally form the adhesion reinforcing layer by the co-extrusion method, it is preferable in terms of productivity. Each of the above resin assemblies includes other additives such as other resins and pigments as long as each of them contains polypropylene having a predetermined monomer sequence within the above-mentioned predetermined range. May be.

  Moreover, it is preferable that the adhesion reinforcement layer comprises 3 layers by arrange | positioning the 2nd skin layer between a core layer and a base material layer, and also it is preferable that it is 2 types and 3 layers. . By setting it as such a structure, while improving adhesiveness with a sealing material, adhesiveness with a base material layer can also be improved. Here, two types and three layers are composed of three layers of skin layer / core layer / skin layer, and the composition of each of the two skin layers is the same, and is composed of two types of composition of the core layer and the skin layer. It means what is being done.

  In order to form a prism structure on the light-receiving surface side surface of the core layer, for example, a method in which a mold is pressed and pressure-bonded while the resin sheet is heated, or a light or thermosetting resin is formed on the surface of the base material. A method in which a mold is pressed against the surface and the resin is cured by irradiation or heating with an active energy ray, and a method in which the resin previously filled in the concave portion of the mold is transferred onto the substrate Etc.

(Integration process)
The back surface protective sheet of the present invention is formed by laminating and further integrating the base resin sheet, the adhesive resin sheet described above, and a sheet for forming other layers formed by the same method as necessary. 6 can be obtained. The integration of the sheets can be performed by a conventionally known dry laminating method. Conventionally known laminating adhesives can be used and are not particularly limited. A two-component curable dry laminating adhesive composed of a main agent such as urethane or epoxy and a curing agent can be used as appropriate.

<Method for manufacturing solar cell module>
The solar cell module 1 is, for example, vacuum suction after sequentially laminating members composed of the transparent front substrate 2, the front sealing material layer 3, the solar cell element 4, the back sealing material layer 5, and the back surface protection sheet 6. Then, the above-mentioned members can be manufactured by thermocompression molding as an integrally molded body by a molding method such as a lamination method. For example, in the case of vacuum heat laminating, the laminating temperature is preferably in the range of 110 ° C. or higher and 160 ° C. or lower, and more preferably in the range of 145 ° C. or higher and 155 ° C. or lower. By setting it as such a range, the core layer containing 80 mass% or more of a polypropylene resin having a melting point of 160 ° C. or higher is not easily softened by the laminate itself, and the shape of the entire surface on the light receiving surface side can be maintained. The laminating time is preferably in the range of 5 to 20 minutes, particularly preferably in the range of 8 to 15 minutes. In this way, the solar cell module 1 can be manufactured by thermocompression-bonding each of the above layers as an integral molded body.

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

<Manufacture of adhesive resin sheet>
The following adhesive resin sheets were sequentially laminated and integrated by dry laminating to produce adhesive resin sheet samples of each example and comparative example.
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. For the core layers of Examples 1 and 2 and Comparative Examples 1, 2, and 5, a prismatic structure is formed on the surface of the core layer on the light-receiving surface side by press working with a plated plate provided with a prism shape using a hydraulic press. (Conditions: 135 ° C., 50 kg / cm ² , 2 minutes).

In the core layer and the skin layer, the following resins were kneaded so as to have the ratio shown in Table 1.
(resin)
Homo PP resin: manufactured by Mitsubishi Plastics Co., Ltd., melting point 165 ° C. (in Table 1, expressed as homo PP. Table 1 lists the mass% of homo PP resin in all resin components of the core layer).
Titanium oxide (white pigment): Ti-pure R105 (manufactured by Dupont), average particle size 0.20 to 0.25 μm In any of the comparative examples, the content was 25% by mass in all components.
Random PP resin: melting point 140 ° C., ethylene unit content 2.5%.
Elastomer PP resin: melting point 125 ° C., ethylene unit content 7.0%.
High density polyethylene resin: (indicated as “HDPE” in Table 1, density 0.91 to 0.92, MFR 5 to 10 g / 10 min (190 ° C.))
As for the skin layer, 100% random PP resin was used for Example 1 and Comparative Example 4, 100% elastomer PP resin was used for Example 2, and 100% high density polyethylene resin was used for Comparative Examples 2 and 3 for comparison. About Example 5, what mixed elastomer PP resin and high-density polyethylene resin so that it might become the amount of ethylene units of Table 1 was used.

  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 an adhesive resin sheet of each example and comparative example.

<Manufacture of backside protection sheet>
The adhesive resin sheets of the above Examples and Comparative Examples were laminated with a PET film (“Melinex S” manufactured by Teijin DuPont Co., Ltd.) having a thickness of 100 μm by a conventionally known dry laminating method to obtain a back surface protective sheet.

  About each said back surface protection sheet of Example 1, 2 and Comparative Examples 1-5, the following sealing material sheet cut to the same size as a sample on the surface of the said adhesion reinforcement layer (adhesion resin sheet side) is 145. Lamination was performed using a vacuum laminator for manufacturing a solar cell module at 15 ° C. for 15 minutes to obtain a sample for adhesion evaluation. As the sealing material sheet, an EVA high-speed crosslinking type, a thickness of 500 μm (manufactured by Bridgestone) was used.

<Crush confirmation test after lamination>
In the samples of Example 1 and Comparative Example 2, the cross section was confirmed with an optical microscope in order to verify the collapse after lamination by the dry laminating method. It was confirmed that the fine convex portion was adjacent to the prism structure, and the apex angle of the fine convex portion was 90 °, but in Comparative Example 2, the prism structure could not be confirmed. It was.

<Adhesion evaluation>
The adhesion was evaluated for the samples for adhesion evaluation using the samples of Examples 1 and 2 and Comparative Examples 1 to 8. Evaluation was performed based on the numerical value measured by the following method.
(Adhesion test: peel test)
For each sample for evaluation of adhesion, the initial adhesion strength (denoted as initial adhesion strength in Table 2) and the adhesion strength after the dump heat test with a peel strength (N) of 180 mm peel of 15 mm width. (In Table 2, expressed as DH1000 adhesion strength). For the measurement, using a peel test apparatus (manufactured by “A & D Co., Ltd., trade name“ TENSILON RTG-1210 ”), measurement is performed at 23 ° C. with a peel condition of 50 mm / min at 180 ° peel. The average value of four measurements was adopted. In addition, regarding the sealing material sheet / skin layer adhesion in Table 2, a sample having a measured value of 50 N / 15 mm or more was marked with ◯, and a sample with less than that was marked with ×. In addition, in the core layer / skin layer adhesion in Table 2, in the above peeling test, the case where peeling at the core layer / skin layer does not occur is indicated as ◯, and the peeling at the core layer / skin layer occurs. X.

  In addition, the dump heat test was based on JIS C8917, and the durability test of the sample was performed for 1000 hours on the conditions of 85 degreeC in a test tank, and 85% of humidity.

<Power generation comparison with solar simulator>
PV characteristics were evaluated for the samples using the samples of Examples 1 and 2 and Comparative Examples 2 to 4. Specifically, the solar cell module is prepared by laminating the sealing material sheet on the cell in a state where aluminum sealing is performed except for the cell part of the T-SEC single crystal cell (TSS63TN) to prevent light from wrapping around, Using a solar simulator (EWXS-300S-50 manufactured by Eiko Seiki Co., Ltd.), the conditions were a cell back surface temperature of 25 ° C. and an illuminance of 100 mW / cm ² (STC (Standard Test Cell conditions)). The Isc value of Comparative Example 4 was set to 100, and the ratio of the Isc values of Example 1 and Comparative Examples 2 to 4 was obtained. The evaluation results are shown in Table 2.

<Comparison of power generation by simulation>
The samples of Example 1 and Comparative Example 4 were used as single cell modules (cells 5 inches, 18-corner size), and the amount of light collected at each time was measured by optical simulation. Specifically, sunlight and single cell solar cell modules were reproduced on simulation software, and the amount of light incident on the cell at the solar altitude at each time on the day of the summer solstice was compared. Table 3 shows the rate of increase in the amount of light collected in Example 1 with respect to Comparative Example 4 at each time.

  From Table 2, it can be seen that the samples of Examples 1 and 2 are samples having excellent adhesion and adhesion durability. On the other hand, in Comparative Example 1 in which the content of the ethylene unit is less than 2.0% by mass in the total resin components of the skin layer, the adhesion at the DH1000 adhesion strength between the sealing material sheet / skin layer is reduced. It turns out that it is a sample with inferior endurance durability with a sealing material sheet. In Comparative Example 5 in which the content of the ethylene unit exceeds 10.0% by mass in the total resin components of the skin layer, the initial adhesion strength between the core layer / skin layer adhesion is reduced. It can be seen that this is a sample with poor adhesion.

  From Table 2 and Table 3, the back surface protection sheet (Examples 1 and 2) in which the prism structure in which a plurality of fine convex portions are adjacent to the surface on the light receiving surface side of the core layer is formed as a prism structure. Compared with the non-back side protective sheet (Comparative Examples 2, 3, 4), the Isc value in the outdoor condition (power generation test by simulation) and the amount of light collected in the STC condition (power generation comparison in the solar simulator) are higher. I understand that. From this, it turns out that the back surface protection sheet for solar cell modules of this invention is the outstanding back surface protection sheet which can fully contribute to the improvement of photovoltaic power generation conversion efficiency.

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 Base material layer 62 Adhesion reinforcement | strengthening layer 621 Core layer 622 Skin layer 623 Fine convex part 624 Vertical angle

Claims (5)

A back surface protection sheet for a solar cell module,
A base material layer, and 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 comprises a skin layer exposed on the outermost surface of the back protective sheet, and a core layer,
The skin layer contains 50% by mass or more of a polypropylene resin containing an ethylene unit,
The content of the ethylene unit in the skin layer is 2.0% by mass or more and 10.0% by mass or less in the total polypropylene resin component of the skin layer,
The core layer contains a polypropylene resin having a melting point of 160 ° C. or higher and a white pigment, and the content of the polypropylene resin is 80% by mass or more in the total resin components of the core layer,
The back surface protection sheet in which the prism structure which a some fine convex part adjoins is formed in the surface at the side of the light-receiving surface of the said core layer.   The back surface protective sheet according to claim 1, wherein the shape of the vertical cross section of the fine protrusions is a triangle, and the apex angle of the protrusions is an average of 90 ° or more.   The back adhesion protection sheet according to claim 1 or 2 in which said adhesion reinforcement layer has the 2nd skin layer arranged between said core layer and said base material layer.   The solar cell module which uses the back surface protection sheet in any one of Claim 1 to 3, and the sealing material closely_contact | adhered to the said contact | adherence reinforcement | strengthening layer consists of thermally crosslinkable resin. A backside protective sheet according to any one of claims 1 to 3 and other solar cell module constituent members are provided with an integration step of stacking and integrating by thermocompression bonding,
The manufacturing method of the solar cell module which performs the thermocompression-bonding process in the said integration process at 110 to 160 degreeC.

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