JP2023095919A - Transparent protective sheet for solar cell module - Google Patents

Abstract

To provide a transparent protective sheet for a solar cell module that has a polyester resin as a base material resin, the transparent protective sheet achieving both transparency and weatherability at a higher level than before, the protective sheet having, as for the transparency, specifically a light transmittance of 90.0% or more in a wavelength of 400 nm or more and 1200 nm or less.SOLUTION: A transparent protective sheet 6 for a solar cell module includes a base material layer 60 containing a polyester resin as a base resin, and a weather resistant layer 63 laminated on one face of the base material layer 60 with a weather resistant adhesive layer 66 therebetween. In the transparent protective sheet 6, the refractive index of the weather resistant layer 63 is smaller than the refractive index of the base material layer; the difference between the refractive index of the weather resistant adhesive layer 66 and the refractive index of the weather resistant layer 63, and the difference between the refractive index of the weather resistant adhesive layer 66 and the refractive index of the base material layer 60 are both 0.20 or less.SELECTED DRAWING: Figure 2

Description

The present invention relates to a transparent protective sheet for solar cell modules. More specifically, it relates to a transparent protective sheet that can be used as an outermost layer in a solar cell module.

2. Description of the Related Art In recent years, due to growing awareness of environmental issues, solar cells have attracted attention as a clean energy source. 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 rear sealing material and a protective sheet are laminated in this order from the light receiving surface side. It has a function of generating power by being incident on the solar cell element. The protective sheet is not only used as a back surface protective sheet, but may also be used as a front surface protective sheet in place of a transparent front substrate such as glass.

And the solar cell module is used outdoors for a long period of time. Therefore, each of the members constituting the solar cell module is required to have durability to withstand harsh outdoor environments for a long period of time. Above all, protective sheets are required to have particularly high weather resistance.

Conventionally, fluorine-based films have been widely used as protective sheets for solar cell modules that require such high weather resistance. However, as a response to the demand for manufacturing cost reduction and weight reduction, a coating type protective sheet with improved weather resistance using a polyester resin such as polyethylene terephthalate (PET) as a base sheet has been proposed (Patent document 1).

On the other hand, in recent years, as a protective sheet for use in a so-called see-through type or double-sided lighting type solar cell module, there is a demand for a protective sheet that maintains the weather resistance described above and also has transparency (Patent Document 2). reference).

Transparent protective sheets for solar cell modules are required to have high levels of weather resistance and transparency. In order to meet this demand, various transparent protective sheets having a multi-layer structure in which a weather-resistant layer for imparting high weather resistance is further laminated on a substrate layer formed of a transparent thermoplastic resin or the like have been developed. (See Patent Document 3).

However, when the transparent protective sheet has a multi-layer structure, light reflection at the interface caused by the difference in refractive index between the layers hinders improvement in transparency. At present, there is a certain structural limit to improving the transparency of a protective sheet. The refractive index of polyester-based resin is about 1.65 for general polyethylene terephthalate (PET) and about 1.77 for general polyethylene naphthalate (PEN). The upper limit of the light transmittance of a laminate obtained by laminating these resins at a wavelength of 400 nm or more and 1200 nm or less was about 80 to 85%.

The term “transparent” as used herein means that it is possible to “transmit light rays in the visible light region and the near infrared region”, and more specifically, the light transmittance at wavelengths of 400 nm to 1200 nm is at least 80% or more. shall mean that Conventional transparent protective sheets can be said to be transparent at this level, but the transparent protective sheet of the present invention has a high degree of transparency (light transmittance of 90.0% or more) that greatly exceeds this level. . In addition, unless otherwise specified, the term "light transmittance" as used herein refers to light transmittance at a wavelength of 400 nm or more and 1200 nm or less measured according to JIS-K-7105 or JIS-K-7136. shall be said.

Japanese translation of PCT publication No. 2010-519742 JP 2012-040842 A JP 2012-040842 A

The present invention has been made in view of the above circumstances, and is a protective sheet using a polyester resin as a base resin, which achieves both transparency and weather resistance at a higher level than before. Regarding transparent protective sheet and transparency, specifically, the object is to provide a transparent protective sheet for solar cell modules having a light transmittance of 90.0% or more at a wavelength of 400 nm or more and 1200 nm or less.

The inventors of the present invention have made intensive studies to solve the above problems, and have found that all layers including an adhesive layer interposed between each layer based on the refractive index of the base material layer of the transparent protective sheet. By optimizing the refractive index and arranging a resin layer with a relatively small refractive index as the weather-resistant layer that is the surface in contact with the outside air, the inventors have found that the above problems can be solved, and completed the present invention. came to. More specifically, the present invention provides the following.

(1) A transparent protective sheet for a solar cell module, comprising: a substrate layer made of a polyester-based resin having a refractive index of 1.50 or more and 1.60 or less; and a weather-resistant layer laminated via a weather-resistant adhesive layer, wherein the weather-resistant layer has a refractive index of 1.35 or more and 1.45 or less, and the refractive index of the weather-resistant adhesive layer and the weather-resistant layer and the difference between the refractive index of the weather-resistant adhesive layer and the refractive index of the base material layer bonded to the weather-resistant adhesive layer are both 0.20 or less. sheet.

(2) The base material layer is a laminate having a multilayer structure in which a plurality of base resin sheets made of the polyester resin are laminated via base material adhesive layers, and the base material adhesive layer The transparent protective sheet according to (1), wherein the difference between the refractive index and the refractive index of the base resin sheet facing the base adhesive layer is both 0.01 or less.

(3) The transparent protective sheet according to (2), wherein each of the base resin sheets is a hydrolysis-resistant polyethylene terephthalate resin.

(4) An easy-adhesion layer is formed on the other surface of the substrate layer, and the difference between the refractive index of the easy-adhesion layer and the refractive index of the substrate layer is 0.05 or less, ( The transparent protective sheet according to any one of 1) to (3).

(5) The transparent protective sheet according to any one of (1) to (4), which has a light transmittance of 90.5% or more at a wavelength of 400 nm or more and 1200 nm or less.

(6) A solar cell module comprising a solar cell element and an adhesive, wherein the transparent protective sheet according to any one of (1) to (5) is disposed as the outermost layer.

(7) A solar cell module comprising a solar cell element and an adhesive, wherein the transparent protective sheet according to (4) is disposed as an outermost layer, wherein the easily adhesive layer of the transparent protective sheet includes: A solar cell module in which the adhesive is laminated.

(8) The solar cell module according to (6) or (7), wherein the adhesive is polyethylene resin or ethylene-vinyl acetate copolymer resin.

According to the present invention, there is provided a protective sheet using a polyester-based resin as a base resin, which achieves both transparency and weather resistance at a higher level than ever before. A transparent protective sheet for a solar cell module having a light transmittance of 90.0% or more at a wavelength of 400 nm or more and 1200 nm or less can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an example of the layer structure of a solar cell module using the transparent protective sheet for solar cell modules of the present invention; 1 is a cross-sectional view showing an example of the layer structure of a transparent protective sheet for a solar cell module of the present invention; FIG.

Hereinafter, the transparent protective sheet for solar cell modules of the present invention will be described in detail. The invention is not limited to the embodiments described below.

<Basic configuration of solar cell module>
First, the basic configuration of a solar cell module using the transparent protective sheet of the present invention will be described. FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of a solar cell module 1 that is an embodiment of the present invention. As shown in FIG. 1, the solar cell module 1 has a configuration in which a transparent front substrate 2, a front sealing material 3, a solar cell element 4, a rear sealing material 5, and a transparent protective sheet 6 are laminated in this order from the light receiving surface side. be. In addition, the transparent protective sheet in the present invention is not necessarily limited to that arranged on the non-light-receiving surface side. It can also be used as a transparent protective sheet for

<Transparent protection sheet>
The transparent protective sheet 6 of the present invention will be explained with reference to FIG. The transparent protective sheet 6 is a protective sheet for solar cell modules, and is assumed to be arranged as one of the outermost layers of the solar cell module 1 . Therefore, it is required to have high weather resistance in addition to transparency.

The transparent protective sheet 6 is a multi-layered resin sheet, and includes at least a base layer 60 and a weather-resistant layer 63 laminated on one surface thereof with a weather-resistant adhesive layer 66 interposed therebetween. . Moreover, it is preferable that the other surface of the base material layer 60 is formed with an easy-adhesion layer 64 for improving adhesion to the adhesive material for the solar cell module such as the rear sealing material 5 .

The substrate layer 60 may be a single-layer substrate resin sheet, but as shown in FIG. It is more preferable that the laminated body has a multi-layer structure in which the layers are laminated with intervening layers. When the base material layer 60 has such a multilayer structure, for example, the first base material layer 61 arranged on the side of the weather resistant layer 63 has higher weather resistance than the second base material layer 62. A layered configuration can be given as an example of a more preferable layered configuration. Specifically, while the first base material layer 61 and the second base material layer 62 are made of the same kind of polyester-based resin, only the first base material layer 61 is made of an annealed resin. can be exemplified.

The transparent protective sheet 6 having the above basic structure has a light transmittance of 90.0% or more, preferably 90.5% or more, at a wavelength of 400 nm or more and 1200 nm or less. Further, the light transmittance of each layer constituting the transparent protective sheet 6 does not necessarily need to be 90.0% or more in all layers. As will be described in detail below, by optimizing the overall design so that the difference in refractive index between the resin layers that are in close contact with each other at the interface between each layer of the multilayer structure is within a predetermined range, the interface between the layers The layer structure of the transparent protective sheet 6 is characterized in that it suppresses the reflectance in the transparent protective sheet 6 and achieves a high degree of transparency as the entire transparent protective sheet, that is, the light transmittance described above. A specific description of the aspect in which "the difference in refractive index between the resin layers is within a predetermined range" will be described below together with the details of each layer.

In addition, when the transparent protective sheet 6 is integrated as the solar cell module 1 and used, the weather resistant layer 63 is exposed on the outermost layer side of the solar cell module 1 . In addition, when the easy-adhesion layer 64 is formed, the easy-adhesion layer 64 is used so as to form a contact surface with another resin base material such as the rear sealing material 5 or the like.

[Base material layer]
In order to provide the transparent protective sheet 6 with the high degree of transparency described above, the base material layer 60, which is the main component thereof, is naturally required to have high transparency. Specifically, it is preferable that the light transmittance at a wavelength of 400 nm or more and 1200 nm or less is 88% or more.

The base material layer 60 is required not only to have the above-described transparency, but also to have a refractive index within the unique range specified by the present application. Specifically, as the resin constituting the base material layer 60 of the transparent protective sheet 6, a resin having a refractive index in the range of 1.50 or more and 1.60 or less can be used. The "refractive index" is the value obtained by dividing the light velocity c in a vacuum by the light velocity v in the resin base material (medium) with respect to light with a wavelength of 589.3 nm (D line of sodium). To tell. Hydrolysis-resistant polyethylene terephthalate (HR-PET) is used in the transparent protective sheet 6 as a transparent resin that satisfies the requirements related to the refractive index and has excellent weather resistance. can be preferably used as a resin that constitutes the

Here, in a protective sheet for a solar cell module, a base material is generally used as a resin material that has transparency and also has the weather resistance required for a protective sheet in consideration of economic efficiency, workability, etc. Polyester-based resins such as polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) can be used as the layer-forming resin. However, many common polyester-based resins usually have a refractive index exceeding 1.60. The refractive index of general PET is about 1.65, and the refractive index of general PEN is about 1.77. Therefore, these general-purpose polyester-based resins are not suitable as resins constituting the base material layer 60 of the transparent protective sheet 6 . The transparent protective sheet 6 is based on a unique concept, focusing on the refractive index of each layer, which has been overlooked in conventional protective sheets for solar cell modules. A polyester-based resin having a specific refractive index (refractive index of 1.50 or more and 1.60 or less), a preferred specific example is substantially hydrolysis-resistant polyethylene terephthalate (HR) having a refractive index of about 1.58. -PET), there is a remarkable difference from the selection of resin materials in conventional general protective sheets. Needless to say, a transparent polyester resin that satisfies the above conditions of refractive index and is used in place of HR-PET is within the scope of the present invention.

In addition, as a resin material having the weather resistance required for the protective sheet for the solar cell module, a fluorine-based resin may also be selected. However, since the fluororesin is soft and stretchable, it tends to cause problems such as stretching during drying after coating with an adhesive or the like. In this respect, polyester-based resins are more advantageous as resins for forming base layers of protective sheets for solar cell modules.

When the substrate layer 60 has a multi-layer structure in which a first substrate layer 61 and a second substrate layer 62 are laminated via a substrate adhesive layer 65 as shown in FIG. As described above, both the first base material layer 61 and the second base material layer 62 use a transparent polyester-based resin, represented by HR-PET, having a refractive index in the range of 1.50 or more and 1.60 or less. be able to.

The base resin sheet that constitutes the base layer 60 is formed by using the above-described HR-PET or the like using an extrusion method, a cast molding method, a T-die method, a cutting method, an inflation method, or another film forming method. can be obtained by The thickness of the base material layer 60 is not particularly limited, but the total thickness is preferably 200 μm or more and 300 μm or less. If the total thickness of the base material layer 60 is less than 200 μm, it is not preferable in that the insulation is lowered. Further, if the thickness exceeds 300 μm, it is not preferable in terms of workability.

When the total thickness of the base material layer 60 is set to 200 μm or more for the reason described above, it may be composed of a single-layer base resin sheet having a thickness of 200 μm or more. It is more preferable to configure this by laminating material resin sheets. In general, when a base resin sheet using PET as a base resin becomes a thick sheet with a thickness of about 150 μm or more, the orientation of the molecules decreases due to a decrease in the draw ratio during film formation. is reduced, and the risk of insufficient hydrolysis resistance increases. In this case, curling may easily occur during production due to the difference in orientation between the surface layer and the central portion of the base resin sheet. Such a risk can be avoided by forming the substrate layer 60 as a multilayer sheet in which substrate resin sheets having a thickness of 100 μm or more and 150 μm or less and using PET as a base resin are laminated.

The base material layer 60 may contain components other than the above-described resins within a range that does not impair the effects of the present invention. Also, for example, processability, heat resistance, light resistance, weather resistance, mechanical properties, dimensional stability, antioxidant properties, slip properties, release properties, flame retardancy, anti-mold properties, electrical properties, etc. Various plastic compounding agents, additives, other resins, etc. can be added for the purpose of improvement and modification. The amount of these additives and the like to be added is not particularly limited, and can be arbitrarily added according to the purpose. Common additives include, for example, lubricants, cross-linking agents, antioxidants, ultraviolet absorbers, light stabilizers, fillers, lubricants, reinforcing fibers, reinforcing agents, antistatic agents, flame retardants, flame retardants, foaming agents, agents, antifungal agents, modifying resins, and the like.

(Base material adhesive layer)
When the substrate layer 60 has a multilayer structure as shown in FIG. 2, the substrate adhesive layer 65 that bonds the first substrate layer 61 and the second substrate layer 62 is also required to have transparency. In the transparent protective sheet 6, the substrate adhesive layer 65 has not only transparency but also a refractive index adjusted within a specific range in relation to each resin layer constituting the substrate layer 60. It is As a result, the transparent protective sheet 6 prevents light reflection at each interface between the substrate adhesive layer 65 and the first substrate layer 61 and the second substrate layer 62 when the substrate layer 60 has a multi-layer structure. By reducing the ratio, the high transparency of the transparent protective sheet 6 is maintained. Specifically, regarding the refractive index of the base adhesive layer 65, the refractive index of the base resin sheets constituting the first base layer 61 and the second base layer 62 facing the base adhesive layer 65 is The difference between is 0.01 or less.

The base material adhesive layer 65, the weather resistant adhesive layer 66 described later, and other adhesive layers constituting the transparent protective sheet 6, and the refractive index of each layer were determined according to JIS K7142 by an Abbe refractometer DR-M2 manufactured by Atago. can be measured using More specifically, for the measurement of the refractive index of the adhesive layer and the primer layer, it is coated on the release film with a miya bar, then dried, and further coated and dried repeatedly to obtain a thickness of about 200 μm. can be prepared and measured using Atago's Abbe refractometer DR-M2 in accordance with JISK7142 in the same manner as described above.

As an adhesive for forming the substrate adhesive layer 65 that is transparent and has a refractive index within the above range, for example, the "specific polyurethane diol and A two-liquid type laminate adhesive consisting of a main agent containing a mixture with an aliphatic polycarbonate diol and a curing agent can be used.

The main component of the adhesive is characterized by containing a mixture of polyurethane diol and aliphatic polycarbonate diol. Polyurethane diol and aliphatic polycarbonate diol constituting the base material are both polyols having hydroxyl groups, and can form the base adhesive layer 65 by reacting with a curing agent having isocyanate groups.

The polyurethane diol, which is the main component, is a polyurethane having a urethane structure as a repeating unit and having hydroxyl groups at both ends. The hydroxyl value of the polyurethane diol is preferably in the range of 10-50 mgKOH/g. Polyurethane diol is obtained by reacting aliphatic polycarbonate diol, 1,6 hexanediol, and isophorone diisocyanate as a main component of adhesives to improve its adhesiveness and weather resistance.

A commercially available aliphatic polycarbonate diol can also be used. In order to obtain an adhesive excellent in durability, weather resistance, heat resistance, and hydrolysis resistance, for example, aliphatic polycarbonate diol having a number average molecular weight of 1000 (manufactured by Asahi Kasei Chemicals, trade name "Duranol T5651"), number average molecular weight 2000 aliphatic polycarbonate diol (manufactured by Asahi Kasei Chemicals, trade name "Duranol T5662") can be preferably used.

As the solvent that can be used when the aliphatic polycarbonate diol, 1,6-hexanediol and isophorone diisocyanate are reacted, any solvent that can dissolve these compounds and does not react with the solvent can be used. Although not particularly limited, carboxylic acid ester solvents such as ethyl acetate can be used from the viewpoint of compatibility and workability during lamination.

The thickness of the adhesive layer may be appropriately changed according to the transparency, adhesive strength, etc. required for the transparent protective sheet 6, and is, for example, 1.0 μm or more and 10 μm or less.

[Weather resistant layer]
The weather-resistant layer 63 is a layer laminated on the outermost layer of the transparent protective sheet 6 to protect the base layer 60 . The weather-resistant layer 63 is formed by laminating a weather-resistant resin sheet (weather-resistant resin sheet) on one surface of the base material layer 60 with a weather-resistant adhesive layer 66 interposed therebetween. In order to maintain the transparency of the transparent protective sheet 6 , the weather resistant layer 63 is also required to have transparency equivalent to that of the base layer 60 . The resin constituting the weather resistant layer 63 of the transparent protective sheet 6 has a refractive index of 1.30 or more and 1.50 or less, preferably 1.35 or more and 1.45 or less.

As the resin constituting the weather resistant layer of the transparent protective sheet, a fluororesin having both transparency and excellent weather resistance is generally used. Specific examples of such fluorine-based resins include ETFE (tetrafluoroethylene/ethylene copolymer), PCTFE (polychlorotrifluoroethylene), PFA (tetrafluoroethylene perfluoroalkylvinyl ester copolymer), and PTFE. (polytetrafluoroethylene), PVDF (polyvinylidene fluoride) and the like can be exemplified. It can be preferably used as.

(weather resistant adhesive layer)
The weather-resistant adhesive layer 66 that adheres the weather-resistant layer 63 to the surface of the base material layer 60 is also required to have the same transparency as the above-described base material adhesive layer 65 . In the transparent protective sheet 6 , the weather resistant adhesive layer 66 is not only transparent, but also has a refractive index within a specific range relative to the refractive index of the weather resistant layer 63 . As a result, the transparent protective sheet 6 reduces the light reflectance at each interface between the weather resistant adhesive layer 66 and the base material layer 60 and the weather resistant layer 63, thereby maintaining high transparency of the transparent protective sheet 6. . Specifically, regarding the refractive index of the weather-resistant adhesive layer 66, the difference in refractive index between the base-material adhesive layer 65 and the weather-resistant layer 63 facing the base-material adhesive layer 65 and the base material bonded to the base-material adhesive layer 65 The difference in refractive index from the layer 60 should be 0.20 or less. In the case where the base material layer 60 is composed of the first base material layer 61 and the second base material layer 62 as shown in FIG. 66 and the first base layer 61 in contact with the refractive index difference.

As the adhesive for forming the weather-resistant adhesive layer 66 which is transparent and has a refractive index within the above range, the same adhesive as the adhesive constituting the substrate adhesive layer may be used. It is also possible to use an adhesive with excellent weather resistance, which is obtained by adding an ultraviolet absorber to a two-liquid type laminate adhesive consisting of a main agent containing a mixture of a specific polyurethane diol and an aliphatic polycarbonate diol and a curing agent. .

[Easy adhesion layer]
The easily bonding layer 64 is a so-called primer layer, and as shown in FIG. 2, it is formed on the other surface of the base material layer 60 of the transparent protective sheet 6 opposite to the surface on which the weather resistant layer 63 is laminated. . The easy-adhesion layer 64 is also required to have transparency equivalent to that of the base material layer 60 in order to maintain the transparency of the transparent protective sheet 6 . The easy-adhesion layer 64 of the transparent protective sheet 6 has a refractive index of 0.05 or less so that the difference between the refractive index of the easy-adhesion layer and the refractive index of the base material layer 60 is 0.05 or less. Form. As a primer composition that constitutes the easy-adhesion layer 64 having such a refractive index range, in the transparent protective sheet 6, a primer composition containing an olefin-based resin and having an aqueous medium as a main solvent can be particularly preferably used. . When the substrate layer 60 is composed of the first substrate layer 61 and the second substrate layer 62 as shown in FIG. means the difference in refractive index from the second base material layer 62 in contact with .

The olefin-based resin contained in the primer composition (hereinafter also simply referred to as "primer composition") used to form the easy-adhesion layer 64 is an acid resin containing an olefin component and an unsaturated carboxylic acid component. A modified polyolefin resin is preferred. In addition, the acid-modified polyolefin resin preferably has an MFR of 0.01 g/10 min or more and less than 100 g/10 min at 190° C. and a load of 2.16 kg, measured according to JIS K7210. As a result, it is possible to form an easy-adhesion layer 64 that maintains good dispersibility in an aqueous medium in the primer composition stage and that has excellent adhesion to the olefin-based resin that forms the back sealing material 5 . .

The easy-adhesion layer 64 of the present invention significantly improves the adhesion between the base material layer 60 made of, for example, a polyester-based resin and the rear sealing material 5 made of an olefin-based resin such as EVA or low-density polyethylene. It is clear from the description of JP-A-2013-74172, for example, that it can be increased to .

The olefin component, which is the main component of the acid-modified polyolefin resin contained in the primer composition, is not particularly limited. Alkenes having 2 to 6 carbon atoms such as ethylene, propylene, isobutylene, 2-butene, 1-butene, 1-pentene and 1-hexene are preferred, and mixtures thereof can also be used. Also, the acid-modified polyolefin resin contained in the primer composition is a polyolefin resin acid-modified with an unsaturated carboxylic acid component. Examples of unsaturated carboxylic acid components include acrylic acid and methacrylic acid.

The content of the unsaturated carboxylic acid component in the acid-modified polyolefin resin is 0.1% by mass or more and 10% by mass or less, preferably 0.2% by mass or more and 8% by mass or less. If the content of the unsaturated carboxylic acid component is less than 0.1% by mass, the dispersibility in the aqueous dispersion tends to be insufficient. On the other hand, when the content exceeds 10% by mass, there is a tendency that the adhesiveness to the olefinic resin forming the rear sealing material 5 and the water resistance tend to deteriorate.

The number average particle size of the acid-modified polyolefin resin in the aqueous dispersion containing the acid-modified polyolefin resin is preferably 0.5 μm or less from the viewpoint of adhesion and dispersion stability, and is in the range of 0.01 to 0.4 μm. is more preferable, and 0.02 to 0.3 μm is particularly preferable. The pH of the aqueous dispersion containing the acid-modified polyolefin resin is preferably in the range of pH 7-12, more preferably pH 8-11, from the viewpoint of dispersion stability.

Specific examples of acid-modified polyolefin resins include ethylene-(meth)acrylic acid esters such as ethylene-ethyl acrylate-(anhydrous) maleic acid copolymer and ethylene-butyl acrylate-(anhydrous) maleic acid copolymer. (anhydrous) maleic acid copolymer, ethylene-propylene-(meth)acrylic acid ester-(anhydrous) maleic acid copolymer, ethylene-butene-(meth)acrylic acid ester-(anhydrous) maleic acid copolymer, propylene -butene-(meth)acrylic acid ester-(anhydrous) maleic acid copolymer, ethylene-propylene-butene-(meth)acrylic acid ester-(anhydrous) maleic acid copolymer, ethylene-acrylic acid copolymer, ethylene - methacrylic acid copolymer, ethylene-maleic anhydride copolymer, ethylene-propylene-(anhydride) maleic acid copolymer, ethylene-butene-(anhydride) maleic acid copolymer, propylene-butene-(anhydride) maleic acid acid copolymers, ethylene-propylene-butene-(anhydride) maleic acid copolymers, and the like.

In the primer composition, the acid-modified polyolefin resin should be used as an aqueous dispersion. The acid-modified polyolefin resin can be processed into an aqueous dispersion by dispersing it in an aqueous medium. As a dispersing method, a known dispersing method such as a self-emulsification method or a forced emulsification method may be employed. The aqueous dispersion containing the acid-modified polyolefin resin may be an anionic aqueous dispersion obtained by neutralizing the unsaturated carboxylic acid component of the acid-modified polyolefin resin with a basic compound in an aqueous medium. It is preferable from the viewpoint of adhesiveness.

In the primer composition, the aqueous medium used as the main solvent for aqueous dispersion of the acid-modified polyolefin resin is water or a liquid containing water. Specifically, the solvent of the primer composition uses an aqueous medium as the main solvent, and the content of the aqueous medium with respect to 100 parts by mass of the solvent is more than 50 parts by mass and 100 parts by mass or less, preferably 70 parts by mass. part or more and 100 parts by mass or less.

In addition, the primer composition should contain an organic solvent having an SP value within a specific range as a co-solvent in the aqueous dispersion containing the acid-modified polyolefin resin within a range that does not inhibit the expression of the above effects of the present invention. can be done. Specifically, when the solvent of the primer composition contains an organic solvent as an auxiliary solvent, the content of the organic solvent with respect to 100 parts by mass of the solvent is 0 parts by mass or more and less than 50 parts by mass, preferably , 0 parts by mass or more and less than 30 parts by mass. In addition, the organic solvent may be appropriately selected from the viewpoint that it has an SP value that reduces the solubility of the resin according to the SP value of the main resin constituting the infrared-transmitting dark layer. is preferred. For example, when a polycarbonate polyurethane having an SP value of about 10 is used as the main resin of the infrared permeable dark layer, an organic solvent having an SP value of about 12 is used as an auxiliary solvent. can be used as needed. Typical examples of such organic solvents include isopropyl alcohol (SP value: 11.9), 1-propanol (SP value: 11.9), ethanol (SP value: 12.7), and the like.

In addition, as non-volatile dispersing aids for promoting aqueous dispersion of acid-modified polyolefin resins, for example, emulsifiers, compounds having protective colloid action, modified waxes, acid-modified compounds with a high acid value, water-soluble polymers etc. can be added as appropriate. In addition to the non-volatile dispersing aid, various additives and other additive resins that can make the physical properties of the primer composition more desirable by adding it to the primer composition, more specifically, the above patents In addition to the non-volatile dispersing aids disclosed in the literature (JP-A-2014-240174), various additives and the like can be appropriately and preferably used.

[Refractive index of each layer]
As described above, in the transparent protective sheet 6, the difference in refractive index between the resin layers is set within a predetermined range. Specifically, the refractive index of HR-PET used as the base material layer is about 1.58. By arranging a resin with an index of 1.45 or less, the theoretical reflectance calculated by the following formula 1 on the outermost surface is reduced, and the difference in refractive index at other interfaces is minimized to make the interface The reflectance at is minimized. As an example, the reflectance (%) at the interface between the air (refractive index: 1.00) and the weather resistant layer 63 (refractive index: 1.45) is {(1.00-1.45)/(1.00+1. 45)} ² × 100 = 3.4 (%). Further, by setting the difference in the refractive index between each adhesive layer and each resin substrate facing it within the range described above, the reflectance at each interface is set to less than 0.1%. can be done.

Reflectance (R) = ((n1-n2)/(n1+n2) ² )
(n1 and n2 are the refractive indices of the respective resin substrates in close contact on the interface) (Equation 1)

<Method for manufacturing solar cell module>
For example, the solar cell module 1 is formed by sequentially stacking members comprising the transparent front substrate 2, the front sealing material 3, the solar cell elements 4, the rear sealing material 5, and the transparent protective sheet 6, followed by vacuum suction or the like. It is possible to manufacture the above-mentioned members 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 lamination, the lamination temperature is preferably in the range of 130.degree. C. to 190.degree. Also, the lamination time is preferably in the range of 5 to 60 minutes, more preferably in the range of 8 to 40 minutes. In this way, the solar cell module 1 can be manufactured by thermocompression molding each of the above layers as an integrally molded body.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

<Production of transparent protective sheet>
Examples and Comparative Examples Transparent protective sheets were produced using the following resin sheets, material compositions, adhesives, and the like. The layer structure of each transparent protective sheet was as shown in Table 1. First, each resin sheet was bonded using the following adhesive to form a laminate, which was used as a transparent protective sheet of Example 1 and Comparative Example. However, in Example 2, a transparent protective sheet was produced by further forming an easy-adhesion layer on the laminate by the following method.

(Base material layer)
A hydrolysis-resistant polyethylene terephthalate (HR-PET) film (AP (manufactured by Teijin DuPont Films Ltd.)) having a thickness of 125 μm or 250 μm was used as the base resin sheet constituting the base layer. In Table 1, the film with a thickness of 125 μm is indicated as “PET125” and the film with a thickness of 250 μm as “PET250”. In addition, in Table 1, a polyethylene naphthalate (PEN) film (Q51 (manufactured by Teijin DuPont Films Co., Ltd.)) with a thickness of 250 μm was used only for the base resin sheet constituting the base layer of Comparative Example 3. PEN”.

(weather resistant layer)
A 25 μm-thick ETFE (tetrafluoroethylene/ethylene copolymer) film (AFLEX 25ND (manufactured by Asahi Glass Co., Ltd.)) was used as a weather-resistant resin sheet constituting the weather-resistant layer. This is described as "ETFE25" in Table 1.

(Easy adhesion layer)
The following primer composition was used as a material for forming an easy-adhesion layer on the substrate layer. The same primer composition was applied to the surface of the base material layer by gravure coating at a coating amount of 1.0 g/m ² , and the coating film was formed to form an easy adhesion layer having a thickness of 1.0 μm. This is described as "Pr1" in Table 1.
Primer composition: A primer composition comprising 59 parts by mass of water, 18 parts by mass of acid-modified polyolefin resin, less than 1 part by mass of acrylic resin, 18 parts by mass of IPA, less than 1 part by mass of triethylamine, and 3 parts by mass of wax.

(adhesive layer)
Adhesives for forming a substrate adhesive layer and a weather resistant adhesive layer were produced by the steps of the following methods (a) to (c). Bonding using the manufactured adhesive is performed by dissolving the adhesive in a solvent ethyl acetate, applying gravure coating so that the film thickness after curing is 5.0 μm, and curing by aging treatment at 30 to 50 ° C. for 70 to 200 hours. It was done by letting This is indicated as "AD" in Table 1.
(a) Production of main component Under a nitrogen atmosphere, 100 parts by mass of an aliphatic polycarbonate diol having a number average molecular weight of 1000 (manufactured by Asahi Kasei Chemicals, trade name "Duranol T5651") and 1,6-hexanediol are placed in a flask equipped with a stirrer. (5 parts by mass), isophorone diisocyanate (27.5 parts by mass), and ethyl acetate (132.5 parts by mass) are added, and heated under reflux until the absorption of isocyanate at 2270 cm ⁻¹ disappears in the infrared absorption spectrum, to form a polyurethane. A 50% solution of the diol was obtained.
Aliphatic polycarbonate diol (manufactured by Asahi Kasei Chemicals Co., Ltd., trade name "Duranol T5651") was prepared as an aliphatic polycarbonate diol that is a main component.
A main agent was prepared using the polyurethane diol and the aliphatic polycarbonate diol, which are the main agent components produced above. The main agent was prepared by blending 15 parts by mass of aliphatic polycarbonate diol with 100 parts by mass of polyurethane diol.
(b) Production of Curing Agent Nurate isophorone diisocyanate and hexamethylene diisocyanate bifunctional polyurethane diisocyanate ("Duranate D101" manufactured by Asahi Kasei Chemicals) were used as curing agent materials. The blending ratio (mass) was 40:60 for the nurate form of isophorone diisocyanate and the hexamethylene diisocyanate-based bifunctional polyurethane diisocyanate. The above blending ratio (mass) is a solid mass ratio not containing a solvent, but the solid content was adjusted to 50% during production.
(c) Mixing of Main Agent and Curing Agent Using the main agent and curing agent produced above, an adhesive was produced. Further, the main agent and the curing agent were mixed by dissolving the main agent and the curing agent in a solvent so that each of them was 50% by mass (ethyl acetate solution). 3-glycidoxypropyltrimethoxysilane was added to the curing agent as a silane coupling agent at a rate of 1.2% with respect to the entire adhesive.

<Evaluation of transparent protective sheet>
In order to evaluate the transparency of each transparent protective sheet of Examples and Comparative Examples, V670 manufactured by JASCO Corporation was used to measure light transmittance at a wavelength of 400 nm or more and 1200 nm or less according to JIS K7361-1:1997. Table 1 shows the results.

<Refractive index of each layer of transparent protective sheet and reflectance at interface between layers>
As a reference test for confirming the correlation between the configuration and effects of the present invention, the transparent protective sheet of Example 3 was measured for the refractive index of each layer by the measurement method described in <paragraph 0038>. The theoretical value of the reflectance at each interface between layers was calculated according to Equation 1 described above. Table 2 shows the measurement and calculation results. It is assumed that the weather resistant layer is in contact with the outside air (air), and the easily adhesive layer is in contact with the sealing material made of EVA resin to form an interface. Further, the refractive index of other resin sheets was also measured, and it was 1.77 for PEN.

As can be seen from Tables 1 and 2, the transparent protective sheet of the present invention has extremely high transparency while being a multi-layered protective sheet in which functional layers are laminated for enhancing weather resistance and preferably adhesion to substrates. It turns out that it is a thing.

REFERENCE SIGNS LIST 1 solar cell module 2 transparent front substrate 3 front sealing material 4 solar cell element 5 rear sealing material 6 transparent protective sheet 60 substrate layer 61 first substrate layer 62 second substrate layer 63 weather resistant layer 64 easy adhesion layer 65 Base material adhesive layer 66 Weather resistant adhesive layer

Claims (1)

A transparent protective sheet for a solar cell module,
A base material layer having a polyester-based resin as a base resin;
a weather-resistant layer laminated on one surface of the base material layer via a weather-resistant adhesive layer;
The refractive index of the weather resistant layer is smaller than the refractive index of the base material layer,
The difference between the refractive index of the weather-resistant adhesive layer and the refractive index of the weather-resistant layer, and the difference between the refractive index of the weather-resistant adhesive layer and the refractive index of the base material layer bonded to the weather-resistant adhesive layer. is 0.20 or less.

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