JP2015192109A - Backside protective sheet for solar batteries and solar battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backside protective sheet for solar batteries, which has an excellent resistance against dust, sand or the like; and a solar battery module capable of offering a stable power generation performance over a long period of time.SOLUTION: A backside protective sheet for solar batteries comprises: a base material; and an ultraviolet-absorbing layer including a binder including a (meth) acrylate resin and an ultraviolet absorbing pigment. An outermost surface of the base material on the side of the ultraviolet light-absorbing layer has an elastic recovery rate of 60% or more, and a Vickers hardness of 1.0×10-1.0×10Pa.

Description

  The present invention relates to a solar cell back surface protective sheet and a solar cell module.

  In recent years, various methods such as nuclear power generation, hydroelectric power generation, wind power generation, and solar power generation have been studied as alternative energy for fossil fuels such as oil and coal, and solar power generation that directly converts solar energy into electric energy. Is expected as a clean energy source.

  In this solar power generation, a solar cell element is sealed with a sealing material, and the sealed solar cell element is disposed on the back surface side with a surface protective material such as glass disposed on the side on which sunlight is incident. A solar cell module having a structure sandwiched between back surface protection materials to be used is used. Recently, a resin sheet such as a polyester sheet has been applied to the back surface protective material constituting the module.

  Since solar cell modules are generally installed outdoors and used continuously for a long period of several decades, a high level of durability is also required for the back surface protection material in order to stably maintain power generation performance. It is done. In terms of durability, in addition to UV resistance and heat resistance when exposed to sunlight, resistance to scratches caused by sand and dust flying with the wind and collision is also important. When the protective material is scratched, deterioration tends to be facilitated starting from the scratched portion.

  As a back surface protective material, a back surface of a solar cell in which a polyethylene terephthalate film as a base material is laminated with a white polyethylene film on one side and a resin layer containing a resin, a predetermined amount of a conductive material, and a color pigment on the other side. A sealing sheet is disclosed (see, for example, Patent Document 1). Further, as other examples of the back surface protective material, a back sheet for a solar cell module having a light shielding layer containing titanium oxide and a resin as an outermost layer on a polyester base material, a protective layer obtained by crosslinking and curing a resin composition, a polyurethane resin A primer layer in which a pigment such as titanium oxide is dispersed, a polyester resin layer, and a back surface protection sheet for a solar cell module in which a base material is laminated, and a hardened white layer containing a resin and a white pigment on the base material. A solar cell backsheet is disclosed (see, for example, Patent Documents 2 to 4).

International Publication No. 2011/066807 Pamphlet JP 2011-210835 A JP 2011-77320 A JP 2013-65803 A

  However, it is difficult to say that a conventionally known back surface protection material satisfies sufficient characteristics regardless of the environment as a resistance against a collision of sand, dust, and the like. In order to secure the more stable power generation performance by suppressing the influence of external stress more than before, it is required to improve the resistance against dust and the like.

  The present invention has been made in view of the above, and provides a back surface protection sheet for solar cells having excellent sand resistance against dust and the like, and a solar cell module capable of obtaining stable power generation performance over a long period of time. The purpose is to achieve this goal.

Specific means for achieving the above-described problems are as follows.
<1> It has a base material, a binder containing a (meth) acrylate resin, and an ultraviolet absorbing layer containing an ultraviolet absorbing pigment, and the outermost surface of the substrate having the ultraviolet absorbing layer has an elastic recovery rate of 60%. It is the above and the back surface protection sheet for solar cells whose Vickers hardness is 1.0 * 10 < ⁷ > Pa or more and 1.0 * 10 < ⁹ > Pa or less.

<2> The back protective sheet for solar cells according to <1>, wherein the (meth) acrylate resin is a urethane (meth) acrylate resin.
<3> The back protective sheet for solar cells according to <1> or <2>, wherein the ultraviolet absorbing layer further contains a polyrotaxane.
<4> The back surface protective sheet for solar cells according to any one of <1> to <3>, wherein the base material contains an ultraviolet absorbing pigment.
<5> The back surface protective sheet for a solar cell according to any one of <1> to <4>, wherein the surface roughness of the outermost surface is 0.01 μm or more and 0.20 μm or less.
<6> The back surface protection for solar cells according to any one of <1> to <5>, wherein the layer including the outermost surface has a ratio of the particle diameter of the ultraviolet absorbing pigment to the thickness of 0.01 to 0.15. Sheet.
<7> The sun according to any one of <1> to <6>, wherein the surface specific resistance value of the outermost surface is 1.0 × 10 ¹¹ Ω / □ or more and 1.0 × 10 ¹⁴ Ω / □ or less. Battery back protection sheet.
<8> The back surface protection for solar cells according to any one of <1> to <7>, wherein the content ratio of fluorine atoms to carbon atoms on the outermost surface is 0.1 or more and 0.7 or less in terms of atomic ratio. Sheet.

<9> A solar cell module comprising the solar cell back surface protective sheet according to any one of <1> to <8>.
<10> A transparent base material on which sunlight is incident, an element structure portion provided on the base material and having a solar cell element and a sealing material for sealing the solar cell element, and a base material for the element structure portion. The solar cell module provided with the back surface protection sheet for solar cells as described in any one of <1>-<8> arrange | positioned on the opposite side to the side located.

  ADVANTAGE OF THE INVENTION According to this invention, the back surface protection sheet for solar cells which has the outstanding sand resistance with respect to dust etc. is provided. Moreover, according to this invention, the solar cell module from which stable electric power generation performance is obtained over a long term is provided.

  Hereinafter, the back surface protection sheet for solar cells of this invention and a solar cell module provided with the same are demonstrated in detail.

In this specification, (meth) acrylate indicates that both acrylate and methacrylate are included, and (meth) acryl indicates that both acrylic and methacryl are included.
In the present specification, a numerical range using the notation “to” means a range including numerical values described before and after “to” as a lower limit value or an upper limit value, respectively.

<Back side protection sheet for solar cells>
The back surface protection sheet for solar cells of the present invention has at least a base material, a binder containing a (meth) acrylate resin, and an ultraviolet absorbing layer containing an ultraviolet absorbing pigment. The outermost surface is configured as a range having an elastic recovery rate of 60% or more and a Vickers hardness of 1.0 × 10 ⁷ Pa or more and 1.0 × 10 ⁹ Pa or less.

In the present invention, when used in a solar cell module, the elastic recovery rate is adjusted to 60% or more on the side having the ultraviolet absorbing layer as viewed from the substrate, that is, the exposed surface, and the value of Vickers hardness is adjusted to a specific region. Thus, the force of repairing works against deformation caused by dust and the like colliding with the back surface protection sheet of the solar cell, and scratches are less likely to remain.
Thereby, the damage | wound etc. which sand adheres to a back surface protection sheet reduce, and the fall of durability accelerated | stimulated from a damage | wound etc. can be prevented, and also the fall of the power generation performance of a solar cell module can be prevented.

  The protective sheet for a solar cell of the present invention preferably has a layer containing a polyolefin resin and a color pigment on the surface opposite to the side having the ultraviolet absorbing layer of the substrate.

-Elastic recovery rate of outermost surface-
The elastic recovery rate in this specification is measured by a nanoindentation method based on ISO 14577-1 (instrumentation indentation hardness) at a load speed of 0.14 mN / sec and a maximum load of 1 mN. Specifically, “maximum indentation depth (hmax)” and “indentation depth after unloading (hf)” are measured and calculated from (hmax−hf) / (hmax).
The maximum indentation depth (hmax) is the indentation depth when the maximum load is held.
The indentation depth (hf) after removing the load is the indentation depth when the load is completely removed.
For example, it can be measured using an ultra micro hardness meter (DUH-201S, manufactured by Shimadzu Corporation).

In the back surface protective sheet for solar cells of the present invention, the elastic recovery rate of the outermost surface on the side having the ultraviolet absorbing layer of the substrate is 60% or more.
When the elastic recovery rate is 60% or more, even if deformation of the sheet (dentation on the surface) occurs due to collision with sand or the like, the sheet will return to its original shape after a certain period of time. It is advantageous to sex.
The elastic recovery rate is preferably 62% or more, more preferably 70% or more and 100% or less, and further preferably 80% or more and 100% or less.

  The elastic recovery rate of the outermost surface can be adjusted by selecting the material used for the layer forming the outermost surface. Specifically, the type and content ratio of the resin in the ultraviolet absorbing layer, the type and degree of crosslinking of the crosslinking agent, the content and size of inorganic particles, the shape, the photocuring composition, the photocuring degree, etc. are appropriately selected. Can be adjusted. Specific methods and components for adjusting the elastic recovery rate will be described later.

−Vickers hardness on the outermost surface−
Back protective sheet for a solar cell, the Vickers hardness at the outermost surface of the side having the ultraviolet absorbing layer of the substrate, and the range of 1.0 × ¹⁰ 7 Pa or more 1.0 × ¹⁰ 9 Pa. That is, when a solar cell module is manufactured, the outermost surface of the solar cell back surface protective sheet is formed, and by adjusting the Vickers hardness of the outermost surface to a predetermined range, resistance to withstand sand collision can be obtained. .
When the Vickers hardness is 1.0 × 10 ⁷ Pa or more, the scratch resistance when external force is applied is improved, and when the sand collides, scratches that are the starting point of durability deterioration are less likely to be attached. Further, when the Vickers hardness is 1.0 × 10 ⁹ Pa or less, the impact energy of the sand can be absorbed by the deformation of the surface, so that it becomes difficult to be damaged by plastic deformation.
The Vickers hardness is preferably 1.0 × 10 ⁷ Pa to 5.0 × 10 ⁸ Pa, more preferably 5.0 × 10 ⁷ Pa to 1.0 × 10 ⁸ for the above reasons.

  The Vickers hardness (unit: Pa) is measured with a Triangular indenter using an ultra-micro hardness meter (DUH-201S, manufactured by Shimadzu Corporation), and is calculated from the depth after load removal in the load-removal mode.

  The Vickers hardness on the outermost surface can be adjusted by controlling the hardness of the layer forming the outermost surface. Specifically, the type and content ratio of the resin in the ultraviolet absorbing layer, the type and degree of crosslinking of the crosslinking agent, the content and size of inorganic particles, the shape, the photocuring composition, the photocuring degree, etc. are appropriately selected. Can be adjusted. Specific methods and components for adjusting the elastic recovery rate will be described later.

(UV absorbing layer)
The ultraviolet absorbing layer constituting the back protective sheet for solar cells of the present invention contains at least a binder containing a (meth) acrylate resin and an ultraviolet absorbing pigment, and when the outermost surface is used, the elastic recovery rate is 60%. The Vickers altitude is 1.0 × 10 ⁷ Pa or more and 1.0 × 10 ⁹ Pa or less.

-Binder-
The ultraviolet absorbing layer contains at least one kind of binder, and contains (meth) acrylate resin as one of the binders. The (meth) acrylate resin is a relatively hard resin among resin materials, and the surface hardness of the outermost surface is increased by including at least the (meth) acrylate resin.

(Meth) acrylate resin is a resin in which (meth) acrylic acid ester is homopolymerized or copolymerized with other monomer components. Methyl methacrylate, methyl acrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate , (Meth) acrylic esters such as isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate, t-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate It is obtained by polymerizing an ester monomer selected from:
Other monomer components include unsaturated carboxylic acids (eg, acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid, fumaric acid, etc.), unsaturated hydrocarbons (eg, butadiene, ethylene, etc.), and vinyl esters. And a monomer selected from the group consisting of (for example, vinyl acetate).

  The (meth) acrylate resin may be introduced as an acrylic polyol-based resin by introducing a hydroxyl group serving as a base point (crosslinking point) of the crosslinked structure. As a polymerization monomer for giving a hydroxyl group to a (meth) acrylate resin to form a (meth) acryl polyol resin, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate , Monomers of unsaturated compounds such as 2-hydroxybutyl acrylate, 2-hydroxybutyl methacrylate, 2-hydroxy vinyl ether, polyethylene glycol methacrylate, polypropylene glycol monoacrylate, and polypropylene glycol monomethacrylate.

As the (meth) acrylate resin, a resin in which a (meth) acryl polyol resin and an ultraviolet absorber are copolymerized or a resin in which a (meth) acryl polyol resin and a light stabilizer are copolymerized may be used.
The details of paragraphs 0019 to 0039 of JP-A-2002-90515 can be referred to for details such as a method for producing a resin in which a (meth) acryl polyol and a light stabilizer or ultraviolet absorber are copolymerized. .
Among them, a copolymer obtained by copolymerizing an acrylic monomer, an ultraviolet absorber, and a light stabilizer is preferable, and a Hals hybrid polymer (registered trademark) [manufactured by Nippon Shokubai Co., Ltd.] containing this copolymer as an active ingredient is preferable. Can be used.
In addition, about the detail of a ultraviolet absorber and a light stabilizer, the description of the paragraphs 0027-0028 of the international publication 2011/0668067 pamphlet can be referred.

  A mode in which the (meth) acrylate resin has a crosslinking point and the (meth) acrylate resin is crosslinked with a crosslinking agent at the crosslinking point is preferable. Thereby, the Vickers hardness of the outermost surface can be adjusted. Details of the crosslinking agent will be described later.

-Crosslinking agent-
The ultraviolet absorbing layer can contain at least one crosslinking agent that crosslinks the (meth) acrylate resin. The crosslinking agent reacts with, for example, a hydroxyl group serving as a crosslinking point in the (meth) acrylate resin to cure the ultraviolet absorbing layer by crosslinking, thereby adjusting the Vickers hardness of the outermost surface.

The crosslinking agent is preferably a polyisocyanate-based resin, and preferably has a formulation that promotes the formation of urethane bonds (crosslinked structure).
Examples of the polyisocyanate resin used as the crosslinking agent include aromatic polyisocyanates, araliphatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates. These are resins made from the following diisocyanate compounds.

  Examples of the diisocyanate used as a raw material for the aromatic polyisocyanate include m- or p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate (NDI), 4,4′-, 2,4 ′. -Or 2,2'-diphenylmethane diisocyanate (MDI), 2,4- or 2,6-tolylene diisocyanate (TDI), 4,4'-diphenyl ether diisocyanate and the like.

  Examples of the diisocyanate used as a raw material for the araliphatic polyisocyanate include 1,3- or 1,4-xylylene diisocyanate (XDI), 1,3- or 1,4-tetramethylxylylene diisocyanate (TMXDI), and the like. Is mentioned.

  Examples of the diisocyanate used as a raw material for the alicyclic polyisocyanate include 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate; IPDI), 4,4′-, 2,4′- or 2,2′-dicyclohexylmethane diisocyanate (hydrogenated MDI), methyl-2,4-cyclohexanediisocyanate, methyl-2,6-cyclohexanediisocyanate, and 1,3-or Examples include 1,4-bis (isocyanatomethyl) cyclohexane (hydrogenated XDI).

  Examples of the diisocyanate used as a raw material for the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-, 2,3- or Examples include 1,3-butylene diisocyanate and 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate.

As a raw material of polyisocyanate, these diisocyanates can be used in combination, or can be used as a modified body such as a burette modified body or a nurate modified body. Among them, as a raw material for polyisocyanate, a resin containing an aromatic ring having a light absorption band in the ultraviolet region in the resin skeleton easily yellows upon irradiation with ultraviolet rays. It is preferable to use a curing agent mainly composed of a group polyisocyanate.
Furthermore, from the viewpoint of solvent resistance, it is preferable to use an alicyclic polyisocyanate having an excellent curability for the ultraviolet absorbing layer.
Moreover, the nurate modified body of hexamethylene diisocyanate is preferable from the viewpoint of easy progress of the crosslinking reaction with the acrylic polyol-based resin, the degree of crosslinking, heat resistance, ultraviolet resistance and the like.

  Commercially available products may be used as the cross-linking agent, and examples of commercially available products include Desmodule (registered trademark) series (for example, Desmodule N3300) manufactured by Sumika Bayer.

-Elastic recovery resin-
The ultraviolet absorption layer has an elastic recovery rate of 60% or more on the outermost surface and a surface Vickers hardness of 1.0 × 10 ⁷ Pa or more and 1.0 so that it can be self-repaired when sand or dust collides. It is comprised in the layer which is x10 < ⁹ > Pa or less.
The ultraviolet absorbing layer contains an elastic recovering resin in order to adjust the elastic recovery rate and the Vickers hardness to the above ranges.

  In order to make the ultraviolet absorbing layer a layer having the above elastic recovery rate and Vickers hardness, for example, a photocurable resin (for example, urethane (meth) acrylate resin, polyester (meth) acrylate resin, silicone (meth) acrylate resin) , Epoxy (meth) acrylate resin, etc.), thermosetting resin (for example, urethane resin, phenol resin, urea resin (urea resin), phenoxy resin, silicone resin, polyimide resin, diallyl phthalate resin, furan resin, bismaleimide resin, A cyanate resin or the like).

  Among these, a photocurable resin is preferable, and a urethane (meth) acrylate resin is preferable from the viewpoint of easily adjusting the elastic recovery rate and hardness.

-Urethane (meth) acrylate-
Urethane (meth) acrylate resin, for example, after reacting polyester polyol (A) and polyisocyanate (B) to synthesize an isocyanate group-terminated urethane prepolymer, reacts with a hydroxyl group-containing (meth) acrylate compound (C). Preferred examples thereof include a product obtained from the above, a polymer of an acrylic resin having a hydroxyl group and an isocyanate, and the like.

The polyester polyol (A) is obtained by reacting a polybasic acid and a polyhydric alcohol. Specific examples thereof include polytetramethylene glycol (PTMG), polyoxypropylene diol (PPG), and polyoxyethylene diol. Etc.
The polyisocyanate (B) is not particularly limited as long as it has two or more isocyanate groups in the molecule. Specific examples thereof include 2,4-tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), Examples include hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and xylylene diisocyanate (XDI).
Examples of the hydroxyl group-containing (meth) acrylate compound (C) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, glycidol di (meth) acrylate, penta Examples include erythritol triacrylate.

  A commercially available product may be used as the urethane (meth) acrylate resin synthesized using the above-described polyester polyol (A), polyisocyanate (B), and hydroxyl group-containing (meth) acrylate compound (C). Examples of commercially available products include UV curable urethane acrylate resins (for example, UV1700B, UV6300B, UV7600B, etc.) manufactured by Nippon Gosei Co., Ltd.

  Further, a polymer of an acrylic resin having a hydroxyl group and an isocyanate should be prepared by the method described in “Claim 2” and “Claim 3” and paragraphs 0142 to 0148 of JP 2012-25821 A. Can do.

The outermost layer preferably has a fluorine atom in terms of antifouling properties on the surface and reduction in friction coefficient (slipperiness).
Examples of the method of containing a fluorine atom include a method of using a fluorine-containing acrylate monomer together with the above-mentioned hydroxyl group-containing (meth) acrylate compound (C), and fluorine described in paragraph 0124 of JP2011-158751A. It can be contained by the chemical treatment.

-Polyrotaxane-
Since the ultraviolet absorbing layer is a layer having the elastic recovery rate and the Vickers hardness as described above, as another preferred embodiment of the ultraviolet absorbing layer, for example, a layer containing polyrotaxane can be used.

The polyrotaxane has an opening portion of a cyclic molecule pierced by a linear molecule, and a plurality of cyclic molecules include the linear molecule at both ends (both ends of the linear molecule). It is a molecular complex in which blocking groups are arranged so that cyclic molecules are not released.
Polyrotaxane is a concept that includes, in addition to a molecular complex, a cross-linked product in which molecular complexes are cross-linked at a cyclic molecular part, and a polymer in which the molecular complex is polymerized with another monomer or polymer.

~ Linear molecule ~
The linear molecule constituting the polyrotaxane is not particularly limited as long as it is a molecule or substance that is included in a cyclic molecule and can be integrated non-covalently and is linear.
The “linear molecule” refers to a molecule including a polymer and all other substances satisfying the above requirements.
Further, “linear” of “linear molecule” means substantially “linear”. That is, the linear molecule may have a branched chain as long as the cyclic molecule as a rotor is rotatable or the cyclic molecule is slidable on the linear molecule. Further, the length of the “straight chain” is not particularly limited as long as the cyclic molecule can slide or move on the linear molecule.

  Examples of linear molecules include hydrophilic polymers (for example, polyvinyl alcohol and polyvinylpyrrolidone, poly (meth) acrylic acid, cellulose resins (carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), polyacrylamide, polyalkylene oxide (for example, Polyethylene glycol), polyvinyl acetal resin, polyvinyl methyl ether, polyamine, polyethyleneimine, casein, gelatin, starch, and / or copolymers thereof, hydrophobic polymers (eg, polyethylene, polypropylene, and other olefins) Polyolefin resins such as copolymer resins with monomers, polyester resins, polyvinyl chloride resins, polystyrene, acrylonitrile-styrene copolymer resins, etc. Acrylic resins such as styrene resin, polymethyl methacrylate, (meth) acrylic acid ester copolymer, acrylonitrile-methyl acrylate copolymer resin, polycarbonate resin, polyurethane resin, vinyl chloride-vinyl acetate copolymer resin, polyvinyl butyral resin, etc. And derivatives or modified products thereof).

  Among these, the linear molecule is preferably a hydrophilic polymer in terms of higher haze value and reflectance maintenance ratio, polyethylene glycol, polypropylene glycol, a copolymer of polyethylene glycol and polypropylene glycol, More preferably, it is polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polydimethylsiloxane, polyethylene, or polypropylene, more preferably polyethylene glycol, polyethylene glycol, and a copolymer of polyethylene glycol and polypropylene glycol, polyethylene glycol It is particularly preferred that

  The linear molecule preferably has a high breaking strength. The breaking strength of the polyrotaxane-containing layer depends on other factors such as the bond strength between the blocking group and the linear molecule, the bond strength between the cyclic molecule and other components of the surface coating layer, and the bond strength between the cyclic molecules. However, if the linear molecule itself has a high breaking strength, a higher breaking strength can be obtained.

The molecular weight of the linear molecule is preferably 1,000 or more (for example, 1,000 to 1,000,000), more preferably 5,000 or more (for example, 5,000 to 1,000,000 or 5,000 to 5,000). 500,000), more preferably 10,000 or more (for example, 10,000 to 1,000,000, 10,000 to 500,000, or 10,000 to 300,000).
Moreover, it is preferable that a linear molecule is a biodegradable molecule | numerator from a viewpoint of the influence on an environment.

  The linear molecule preferably has reactive groups at both ends. By having a reactive group, it can react easily with a blocking group. Although a reactive group is dependent on the block group to be used, a hydroxyl group, an amino group, a carboxyl group, a thiol group, an aldehyde group etc. can be mentioned, for example.

~ Cyclic molecule ~
The cyclic molecule constituting the polyrotaxane may be any cyclic molecule as long as it is a cyclic molecule that can be included in a linear molecule.
The “cyclic molecule” refers to various cyclic substances including cyclic molecules, and refers to molecules or substances that are substantially cyclic. Here, “substantially annular” means that the letter “C” is not completely closed, such as the letter “C”, and one end and multiple ends of the letter “C” are not connected. It is also intended to include those having overlapping spiral structures.

  Examples of the cyclic molecule include various cyclodextrins (for example, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, dimethylcyclodextrin and glucosylcyclodextrin, derivatives or modified products thereof), crown ethers, benzo Examples include crowns, dibenzocrowns, dicyclohexanocrowns, and derivatives or modified products thereof.

  Cyclodextrins and crown ethers differ in the size of the opening of the cyclic molecule depending on the type. Therefore, when the type of linear molecule, specifically, the linear molecule to be used is regarded as a cylinder, the cyclic molecule to be used is determined by the diameter of the cross section of the cylinder, the hydrophobicity or hydrophilicity of the linear molecule, etc. You can choose. When a cyclic molecule having a relatively large opening and a cylindrical linear molecule having a relatively small diameter are used, two or more linear molecules can be included in the opening of the cyclic molecule. . Of these, cyclodextrins (particularly α-cyclodextrin) are preferable from the viewpoint of environmental influences and the like.

  When the cyclic molecule is cyclodextrin, the number of cyclic molecules included in the linear molecule (inclusion amount) is preferably 0.05 to 0.60, with the maximum inclusion amount being 1. 10 to 0.50 is more preferable, and 0.20 to 0.40 is more preferable.

When the cyclic molecule is a cyclodextrin compound such as α-cyclodextrin, the cyclodextrin compound is preferably one in which at least one hydroxyl group is substituted (modified) with a hydrophobic group in terms of excellent antifouling properties.
Specific examples of hydrophobic groups include alkyl groups, benzyl groups, benzene derivative-containing groups, acyl groups, silyl groups, trityl groups, nitrate ester groups, tosyl groups, fluorine atom-containing organic groups, unsaturated double bond groups, and the like. Can be mentioned. Among them, an acyl group (particularly an acetyl group) or a fluorine atom-containing organic group is preferable because it is more excellent in antifouling properties. Specific examples of the unsaturated double bond group are the same as the unsaturated double bond group described later.

The fluorine atom-containing organic group is not particularly limited as long as it is a monovalent organic group containing a fluorine atom. The fluorine atom-containing organic group may contain a hetero atom (for example, an oxygen atom) other than the fluorine atom.
The monovalent organic group is not particularly limited, and specific examples thereof include aliphatic hydrocarbon groups (for example, alkyl groups, alkenyl groups, alkynyl groups, etc.), aromatic hydrocarbon groups (for example, aryl groups), heterocyclic rings. Group (for example, azole group, pyridyl group) and the like.

  The fluorine atom-containing organic group is preferably a group represented by the following formula (1) from the viewpoint of better antifouling properties.

In the formula (1), R ₁₁ represents an alkyl group having a fluorine atom, and specific examples thereof include a fluoromethyl group, a difluoromethyl group, and a trifluoromethyl group.
R ₁₂ represents a monovalent hydrocarbon group which may be branched, and specific examples thereof include an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 1 to 30 carbon atoms, and an alkynyl group having 1 to 30 carbon atoms. Group etc. are mentioned, Among these, a C1-C10 alkyl group is preferable.
L ₁₁ and L ₁₂ each independently represents a single bond or a divalent linking group. As the divalent linking group, a substituted or unsubstituted divalent aliphatic hydrocarbon group (preferably having 1 to 8 carbon atoms, for example, an alkylene group such as a methylene group, an ethylene group or a propylene group), substituted or unsubstituted divalent aromatic hydrocarbon groups (. preferably arylene group, such as 6 to 12 such as a phenylene group having a carbon number), - O -, - S -, - SO 2 -, - N (R) - (R: Alkyl group), —CO—, —NH—, —COO—, —CONH—, or a combination thereof (for example, an alkyleneoxy group, an alkyleneoxycarbonyl group, an alkylenecarbonyloxy group, and the like). L ₁₁ is preferably an alkylene group. L ₁₂ is preferably a group represented by the following formula (2). “*” In the formula (1) represents a bonding position.

In Formula (2), _Xa and _Xb each independently represent an oxygen atom or a sulfur atom. Further, “*” in the formula (2) represents a bonding position.

The degree of modification with a hydrophobic group is preferably 0.02 or more (preferably 1 or less), more preferably 0.04 or more, assuming that the maximum number of cyclodextrin hydroxyl groups that can be modified is 1. More preferably, it is 0.06 or more.
Here, the maximum number that the hydroxyl groups of cyclodextrin can be modified is, in other words, the total number of hydroxyl groups that cyclodextrin had before modification. In other words, the degree of modification is the ratio of the number of modified hydroxyl groups to the total number of hydroxyl groups.

~ Block group ~
As the blocking group constituting the polyrotaxane, any group may be used as long as the cyclic molecule maintains a form in which the cyclic molecule is skewered with a linear molecule. Examples of such a group include a group having “bulkiness” and / or a group having “ionicity”. Here, the “group” means various groups including a molecular group and a polymer group. In addition, the “ionicity” of the group having “ionicity” and the “ionicity” of the cyclic molecule influence each other, for example, by repulsion, the cyclic molecule is skewered by linear molecules. It is possible to retain the form.

  Further, as described above, the blocking group may be a polymer main chain or a side chain as long as it retains the skewered form. When the blocking group is the polymer A, the matrix may be a polymer A and a part thereof may include a polyrotaxane, or conversely, the matrix may include a polyrotaxane and a part thereof includes the polymer A. Form may be sufficient. Thus, by combining with the polymer A having various characteristics, a composite material having a combination of the characteristics of the polyrotaxane and the characteristics of the polymer A can be formed.

Specific examples of the blocking group include dinitrophenyl such as 2,4-dinitrophenyl group and 3,5-dinitrophenyl group, cyclodextrin, adamantane, trityl, fluorescein and pyrene, and groups derived from derivatives or modified products thereof. Can be mentioned.
The blocking group may be substituted (modified) with the hydrophobic group.

-Polyrotaxane synthesis method-
The method for synthesizing the polyrotaxane is not particularly limited. For example, the polyrotaxane can be synthesized by the methods described in Japanese Patent No. 2810264 and Japanese Patent No. 3475252.
Specifically, α-cyclodextrin as a cyclic molecule, polyethylene glycol as a linear molecule, 2,4-dinitrophenyl group as a blocking group, acetyl group as a hydrophobic group, and acryloyl group as an unsaturated double bond group are used. For example, it can be synthesized as follows.

  First, in order to introduce a blocking group later, both ends of polyethylene glycol are modified with amino groups to obtain a polyethylene glycol derivative. A pseudo polyrotaxane is prepared by mixing α-cyclodextrin and a polyethylene glycol derivative. In the preparation, when the maximum inclusion amount is 1, for example, the mixing time is 1 hour to 48 hours and the mixing temperature is 0 ° C. so that the inclusion amount is 0.001 to 0.6 with respect to 1. It can be set to -100 degreeC.

  Generally, up to 230 α-cyclodextrins can be packaged with respect to an average molecular weight of 20,000 of polyethylene glycol. Therefore, this value is the maximum inclusion amount. The above conditions are such that the average molecular weight of polyethylene glycol is 20,000, and α-cyclodextrin has an average of 60 to 65 (63), that is, a maximum inclusion amount of 0.26 to 0.29 (0.28). This is a condition for inclusion by value. The inclusion amount of α-cyclodextrin can be confirmed by NMR, light absorption, elemental analysis and the like.

  The obtained pseudo polyrotaxane is reacted with 2,4-dinitrofluorobenzene dissolved in DMF to obtain a polyrotaxane introduced with a blocking group.

The above-mentioned modification of the cyclodextrins with a hydrophobic group may be performed on the synthesized polyrotaxane or may be performed on the cyclodextrins in advance before synthesizing the polyrotaxane.
Examples of the method of modifying with a acetyl group as a hydrophobic group include a method of modifying a hydroxyl group of cyclodextrin with acetic anhydride.

-Preferable embodiment of polyrotaxane-
The polyrotaxane is preferably one having at least one group selected from the group consisting of an acyl group (particularly an acetyl group) and a fluorine atom-containing organic group in the cyclic molecule in terms of excellent antifouling properties. More preferred are those having an acyl group (particularly an acetyl group) and a fluorine atom-containing organic group.

The content of the polyrotaxane in the ultraviolet absorbing layer is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 20% by mass or more, in that the haze value and the maintenance factor of the reflectance are higher. More preferably, it is more preferably 50% by mass or more.
Further, the content of the polyrotaxane having a fluorine atom-containing organic group in the ultraviolet absorbing layer is preferably 0.1% by mass to 50% by mass in terms of higher haze value and reflectance maintenance rate. 5 mass% or more and less than 30 mass% is more preferable, 1 mass%-20 mass% are further more preferable, and 10 mass%-20 mass% are especially preferable.
The content of the polyrotaxane can be determined by an NMR method (solution NMR method, solid NMR method), an X-ray diffraction method described in JP 2010-261134 A, or the like.

  In addition, when forming the ultraviolet absorption layer hardened | cured using the composition for layer formation containing the polyrotaxane which has at least one of a reactive group and a polymeric group in the cyclic molecule mentioned later, content of the polyrotaxane in an ultraviolet absorption layer Means the content (% by mass) of the polyrotaxane relative to the total solid content in the layer forming composition. Similarly, in the case where a cured UV absorbing layer is formed using a layer-forming composition containing a polyrotaxane having at least one of a reactive group and a polymerizable group in a cyclic molecule described later, the fluorine atom contained in the UV absorbing layer The content of the polyrotaxane having an organic group refers to the content (% by mass) of the polyrotaxane having a fluorine atom-containing organic group with respect to the total solid content in the layer forming composition.

-Method of forming ultraviolet absorbing layer containing polyrotaxane-
A method for forming an ultraviolet absorbing layer containing a polyrotaxane is not particularly limited. For example, a layer forming composition containing a polyrotaxane having a reactive group in a cyclic molecule and a solvent is formed on a substrate. Examples thereof include a method of forming an ultraviolet absorbing layer by applying and curing at least one of heat treatment and light irradiation treatment on the applied layer-forming composition.
Note that after the heat treatment or light irradiation treatment, unreacted components may be appropriately removed from the composition after the heat treatment or light irradiation treatment using a solvent.

Specific examples of the reactive group are the same as the reactive group of the linear molecule described above. Among these, the reactive group is preferably a hydroxyl group (particularly a polycaprolactone group) or a polymerizable group, and more preferably a polymerizable group. Here, the polycaprolactone group is a group represented by * — (CO—C ₅ H ₁₀ O) _n —H (*: bond position, n: integer). A specific example of the polymerizable group is preferably an unsaturated double bond group, and more preferably an acryloyl group or a methacryloyl group.

As a preferable polyrotaxane, a polyrotaxane having an unsaturated double bond group in a cyclic molecule can be exemplified.
Examples of the method for introducing an unsaturated double bond group into a cyclic molecule include the following methods. That is, a method by carbamate bond formation with isocyanate compounds, etc .; a method by ester bond formation with carboxylic acid compounds, acid chloride compounds or acid anhydrides; a method by silyl ether bond formation with silane compounds, etc .; a carbonate bond formation with chlorocarbonic acid compounds, etc. By the method;

  When a (meth) acryloyl group is introduced as an unsaturated double bond group via a carbamoyl bond, the polyrotaxane is dissolved in a dehydrating solvent such as DMSO or DMF, and a (meth) acryloylating agent having an isocyanate group is added. Do. In addition, when it introduce | transduces via an ether bond or an ester bond, the (meth) acrylating agent which has active groups, such as a glycidyl group and an acid chloride, can also be used.

  The step of substituting the hydroxyl group of the cyclic molecule with an unsaturated double bond group may be before the step of preparing the pseudopolyrotaxane, between the steps, or after the step. Further, it may be before the step of preparing the polyrotaxane by introducing a blocking group into the pseudopolyrotaxane, between the steps, or after the step. Furthermore, when the polyrotaxane is a polyrotaxane having a reactive group in the cyclic molecule, it may be before the process of reacting the polyrotaxanes with each other or between the processes. It can also be provided at these two or more times. The substitution step is preferably performed after the polyrotaxane is prepared by introducing a blocking group into the pseudopolyrotaxane and before the polyrotaxane is reacted with each other. The conditions used in the substitution step depend on the unsaturated double bond group to be substituted, but are not particularly limited, and various reaction methods and reaction conditions can be used.

-UV absorbing pigment-
The ultraviolet absorbing layer contains at least one ultraviolet absorbing pigment. The ultraviolet absorbing pigment is a pigment having absorption in the ultraviolet region, and specifically includes a pigment having absorption in a wavelength region of 250 nm to 450 nm. The ultraviolet absorbing pigment may be either an inorganic pigment or an organic pigment, but a white pigment or a black pigment is preferable from the viewpoint of ultraviolet resistance and design properties.
As the white pigment, titanium oxide is preferable, and from the viewpoint of color development, titanium oxide having a number average particle size of 0.1 μm to 1.0 μm is particularly preferable. Furthermore, titanium oxide having a number average particle diameter of 0.2 μm to 0.5 μm is more preferable in terms of dispersibility and cost with respect to the (meth) acrylate resin (particularly acrylic polyol resin).
Further, as the black pigment, carbon black is preferable, and carbon black having a number average particle diameter of 0.01 μm to 0.5 μm is preferable. Furthermore, carbon black having a number average particle size of 0.02 μm to 0.1 μm is more preferable from the viewpoint of dispersibility and cost with respect to the (meth) acrylate resin (particularly acrylic polyol resin).

  The content of the ultraviolet absorbing pigment is preferably 40% by mass to 70% by mass, and more preferably 45% by mass to 55% by mass with respect to the entire ultraviolet absorbing layer. When the content of the ultraviolet absorbing pigment is 40% by mass or more, the light shielding performance against ultraviolet rays and / or visible light is good, and even when exposed to the outdoors for a long time, the base film is prevented from being deteriorated and yellowed. it can. Generation | occurrence | production of the chalking (Chalking) in the layer surface is prevented as content of an ultraviolet-absorbing pigment is 70 mass% or less.

-Inorganic fine particles-
The ultraviolet absorbing layer may contain at least one kind of inorganic fine particles from the viewpoint of adjusting the Vickers hardness of the layer. By containing inorganic fine particles, the hardness and refractive index of the film can be adjusted by contributing to the hardness of the inorganic fine particles. When fine particles modified with a hydrophilic / hydrophobic group are selected as the inorganic fine particles, the wettability of the surface of the ultraviolet absorbing layer and the interlayer adhesion with the layer formed on the ultraviolet absorbing layer can be controlled.

  The average particle size of the inorganic fine particles is preferably in the range of 2 nm to 200 nm, more preferably in the range of 10 nm to 150 nm, particularly in terms of further increasing the hardness of the ultraviolet absorbing layer. The average particle diameter is determined from a photograph obtained by observing dispersed particles with a transmission electron microscope. Specifically, the projected area of the particles is obtained, the equivalent circle diameter is obtained from the projected area, and the average particle diameter (average primary particle diameter) is obtained. The average particle diameter is a value calculated by measuring the projected area of 300 or more particles and obtaining the equivalent circle diameter.

  Examples of the inorganic fine particles include inorganic particles such as inorganic oxide particles. As the inorganic oxide particles, inorganic oxide particles having an element selected from Si, Al, and Zr are preferable, and examples thereof include silicon dioxide (silica), titanium dioxide (titania), zirconium oxide, and aluminum oxide (alumina). Particles. Among these, silicon dioxide particles and aluminum oxide particles are more preferable from the viewpoint of dispersibility, and alumina particles are more preferable from the viewpoint that the aspect ratio can be controlled.

The aspect ratio of the inorganic oxide particles is preferably in the range of 300 to 800. That is, the inorganic oxide particles are preferably particles having an elongated shape such as a fiber shape, a rod shape, or a needle shape, from the viewpoint of preventing cracking of the layer and obtaining an effect of preventing the occurrence of cracking even when the layer thickness is increased.
Specifically, alumina hydrate particles or alumina particles having a fibrous or needle-like shape are particularly suitable.
As the aspect ratio, the aspect ratio is obtained as a ratio of the major axis length to the measured minor axis length by observing the particles with an electron microscope, measuring the minor axis length and the major axis length of each particle.

  As the silica particles, dry powdery silica produced by combustion of silicon tetrachloride can be used, but colloidal silica in which silicon dioxide is dispersed in a solvent is more preferable. Specifically, as an example of silica particles, the Snowtex series (for example, Snowtex MEK-ST, same MEK-ST-L, same MEK-ST-XL, same OL) manufactured by Nissan Chemical Industries, Examples thereof include Sun Square H-121-ET manufactured by AGC.

  Examples of the zirconium oxide particles include nano-use series (for example, nano-use ZR) manufactured by Nissan Chemical Industries, Ltd.

The alumina hydrate particles are preferably at least one selected from amorphous, boehmite, and pseudoboehmite, and more preferably boehmite or pseudoboehmite.
Here, boehmite is a crystal of alumina hydrate represented by Al ₂ O ₃ .nH ₂ O (n = 1 to 1.5). Pseudo boehmite refers to a colloidal aggregate of boehmite.
The crystal system of alumina particles that can be used as inorganic oxide particles is preferably at least one selected from γ, θ, and α, and more preferably γ or θ.
Examples of commercially available products include boehmite sol manufactured by Kawaken Fine Chemical Co., Ltd., alumina sol A-2 manufactured by Kawaken Fine Chemical Co., Ltd., AS-520 manufactured by Nissan Chemical Co., Ltd., Quartron manufactured by Fuso Chemical Co., Ltd., and manufactured by Sumitomo Chemical Co., Ltd. Examples include the AKP series. Examples of particles having a relatively large aspect ratio (major axis length / minor axis length = 300 to 800) include aluminum oxide (alumina sol F-1000 (aspect ratio: 350), alumina sol F manufactured by Kawaken Fine Chemical Co., Ltd. -3000 (aspect ratio 750) and the like.

The alumina hydrate particles or alumina particles are preferably dispersed in an aqueous solution. Alumina hydrate particles or an aqueous solution in which alumina particles are dispersed is called an aqueous alumina sol, and this aqueous alumina sol can be produced by hydrolyzing a hydrolyzable aluminum compound to form a colloid under acidic conditions. . The hydrolyzable aluminum compound includes various inorganic aluminum compounds and aluminum compounds having an organic group. Examples of the inorganic aluminum compound include salts of inorganic acids such as aluminum chloride, aluminum sulfate, and aluminum nitrate, aluminates such as sodium aluminate, and aluminum hydroxide.
Examples of the aluminum compound having an organic group include carboxylates such as aluminum acetate, aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide, aluminum sec-butoxide, and other aluminum alkoxides, cyclic aluminum oligomers, Illustrative are aluminum chelates such as propoxy (ethylacetoacetate) aluminum and tris (ethylacetoacetate) aluminum, and organoaluminum compounds such as alkylaluminum.

Among these compounds, aluminum alkoxides are preferable and those having an alkoxyl group having 2 to 5 carbon atoms are particularly preferable because they have moderate hydrolyzability and easy removal of by-products.
As the acid used for the hydrolysis, monovalent acids such as hydrochloric acid, nitric acid, formic acid, acetic acid, propionic acid and butyric acid are preferable, and acetic acid is particularly preferable in terms of operability and economy. The usage-amount of an acid is 0.2 mol times-2.0 mol times with respect to aluminum alkoxide, Preferably it is 0.3 mol times-1.8 mol times. By making the usage-amount of the acid used for a hydrolysis into the said range, the average aspect-ratio of the particle | grains obtained can be made into a desired range, and stability with time can be improved.
In addition, it is preferable to perform a hydrolysis for 0.1 hour-3 hours at 100 degrees C or less.

The solid content concentration of the acid solution of the aluminum alkoxide to be hydrolyzed is preferably 2% by mass to 15% by mass, and preferably 3% by mass to 10% by mass. By setting the solid content concentration within the above range, the average aspect ratio of the obtained particles can be set to a desired range, and the stirrability of the reaction liquid can be enhanced.
After the alcohol produced by hydrolysis is distilled off, peptization is performed. The peptization treatment is preferably performed by heating at 100 ° C. to 200 ° C. for 0.1 hour to 10 hours, more preferably 110 to 180 ° C. for 0.5 hour to 5 hours.
In this way, inorganic oxide particles having a desired average aspect ratio are obtained.

  The volume ratio of the inorganic oxide particles to the binder and the inorganic oxide particles in the ultraviolet absorbing layer is preferably 15% by volume or more and 40% by volume or less. When the volume ratio of the inorganic oxide particles is in the above range, the Vickers hardness of the surface of the ultraviolet absorbing layer can be adjusted to a predetermined range.

-Surfactant-
Various surfactants may be added to the ultraviolet absorbing layer from the viewpoint of further improving the coatability. As the surfactant, various surfactants such as a fluorine-based surfactant, a nonionic surfactant, a cationic surfactant, an anionic surfactant, and a silicone-based surfactant can be contained.

Examples of the fluorosurfactant include Megafac F171, F172, F173, F176, F176, F177, F141, F142, F143, F144, R30, F437, F475, F479, F482, F554, F780, F780, F781 (above DIC Corporation), Florard FC430, FC431, FC171 (above, Sumitomo 3M Limited), Surflon S-382, SC-101, Same SC-103, Same SC-104, Same SC-105, Same SC1068, Same SC-381, Same SC-383, Same S393, Same KH-40 (manufactured by Asahi Glass Co., Ltd.), PF636, PF656, PF6320 PF6520, PF7002 (manufactured by OMNOVA), and the like.
Nonionic surfactants include, for example, glycerol, trimethylolpropane, trimethylolethane and their ethoxylates and propoxylates (eg, glycerol propoxylate, glycerin ethoxylate, etc.), polyoxyethylene lauryl ether, polyoxyethylene stearyl. Ether, polyoxyethylene oleyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, polyethylene glycol dilaurate, polyethylene glycol distearate, sorbitan fatty acid ester (Pluronic L10, L31, L61, L62, 10R5 manufactured by BASF) , 17R2, 25R2, Tetronic 304, 701, 704, 901, 904, 150R1, Pi Nin D-6512, D-6414, D-6112, D-6115, D-6120, D-6131, D-6108-W, D-6112-W, D-6115-W, D-6115-X, D -6120-X (manufactured by Takemoto Yushi Co., Ltd.), Solsperse 20000 (manufactured by Nippon Lubrizol Co., Ltd.), NAROACTY CL-95, HN-100 (manufactured by Sanyo Chemical Industries, Ltd.) and the like.
Examples of the cationic surfactant include phthalocyanine derivatives (trade name: EFKA-745, manufactured by Morishita Sangyo Co., Ltd.), organosiloxane polymer KP341 (manufactured by Shin-Etsu Chemical Co., Ltd.), (meth) acrylic acid (co ) Polymer Polyflow No. 75, no. 90, no. 95 (manufactured by Kyoeisha Chemical Co., Ltd.), W001 (manufactured by Yusho Co., Ltd.) and the like.
Examples of the anionic surfactant include W004, W005, W017 (manufactured by Yusho Co., Ltd.), sanded BL (manufactured by Sanyo Chemical Industries, Ltd.), and the like.
Examples of the silicone surfactant include “Toray Silicone DC3PA”, “Toray Silicone SH7PA”, “Toray Silicone DC11PA”, “Tore Silicone SH21PA”, “Tore Silicone SH28PA”, “Toray Silicone” manufactured by Toray Dow Corning Co., Ltd. “Silicone SH29PA”, “Toresilicone SH30PA”, “Toresilicone SH8400”, “TSF-4440”, “TSF-4300”, “TSF-4445”, “TSF-4460”, “TSF-4460”, “Momentive-Formance Materials, Inc.” Examples thereof include “TSF-4442”, “KP341”, “KF6001”, “KF6002” manufactured by Shin-Etsu Chemical Co., Ltd., “BYK307”, “BYK323”, “BYK330” manufactured by BYK Chemie.
Only one type of surfactant may be used, or two or more types may be combined.
The addition amount of the surfactant is preferably 0.001% by mass to 2.0% by mass, and more preferably 0.005% by mass to 1.0% by mass with respect to the total mass of the aqueous composition.

The ultraviolet absorbing layer can be formed by coating. For example, the method etc. which prepare the curable composition containing curable resin, apply | coat this composition as a coating liquid, and make it harden | cure by ultraviolet irradiation are mentioned.
The coating can be performed by a coating method using a known coating apparatus such as a gravure coater, a reverse coater, a die coater, a blade coater, a roll coater, an air knife coater, a screen coater, a bar coater, or a curtain coater.

The composition for forming the ultraviolet absorbing layer may contain a solvent and various additives in addition to the components described above.
Examples of the solvent include hydrocarbons, hydrogen halides, ethers, esters, ketones and the like, and specifically, xylene, dibutyl ether and the like are preferable.
Examples of additives include photopolymerization initiators, antistatic agents, leveling agents, ultraviolet absorbers, light stabilizers, antioxidants, antifoaming agents, thickeners, antisettling agents, pigments, dispersants, silane cups. A ring etc. are mentioned.

The form of the ultraviolet absorbing layer may be configured as either a single layer structure or a multilayer structure. When the ultraviolet absorbing layer is formed in a multilayer structure, it is preferable that the inner (base material side) layer contains an ultraviolet absorbing pigment and the outer layer (surface side of the ultraviolet absorbing layer) does not contain an ultraviolet absorbing pigment.
When the ultraviolet absorbing layer is formed in a multilayer structure, the elastic recovery rate of the surface of the outermost layer is 60% or more, and the Vickers hardness of the surface of the outermost layer is 1.0 × 10 ⁷ Pa or more and 1.0 × 10 ⁹ Pa. The following is sufficient.

  The thickness of the ultraviolet absorbing layer (in the case of a multilayer structure, the total thickness of each layer) may be appropriately selected depending on the application and the like, but is preferably 0.2 μm to 10 μm, more preferably 0.5 μm to 7 μm. The thickness of the ultraviolet absorbing layer can be controlled by adjusting the coating amount of the coating liquid for coating and forming the ultraviolet absorbing layer.

Furthermore, it is preferable that the back surface protection sheet for solar cells of this invention has the following properties.
Sand resistance can be improved more effectively because the outermost surface of the substrate having the ultraviolet absorbing layer has the following properties.

(1) Surface roughness In the back surface protection sheet for solar cells of the present invention, the surface roughness of the outermost surface on the side having the ultraviolet absorbing layer of the substrate is preferably in the range of 0.01 μm or more and 0.20 μm or less. . As described above, the surface roughness of the outermost surface of the substrate having the ultraviolet absorbing layer can be adjusted to the above range by selecting the material of the ultraviolet absorbing layer.
When the surface roughness is 0.01 μm or more, it is advantageous in that the solar cell back surface protective sheet has improved slipperiness and can be easily handled. Further, when the surface roughness is 0.20 μm or less, it is advantageous in that it is difficult to be scraped when sand or the like collides, and generation of scratches or the like can be prevented.
The surface roughness is preferably 0.05 μm or more and 0.20 μm or less, and more preferably 0.1 μm or more and 0.15 μm or less.
The surface roughness here is a value obtained by calculating as the surface roughness in a region of 0.3 mm × 0.3 mm using a three-dimensional optical profiler (Zigo, manufactured by Canon Inc.).

  Said surface roughness can be adjusted to the said range by adjusting the size (particle diameter) and content of the ultraviolet absorption pigment contained in an ultraviolet absorption layer, and the thickness of a layer. For example, in the ultraviolet absorbing layer, the ratio of the particle size (μm) of the ultraviolet absorbing pigment contained in the layer to the layer thickness (μm) (= particle size / layer thickness) is adjusted to a range of 0.01 to 0.15. By doing so, the above range can be obtained. The ratio of the particle size of the ultraviolet absorbing pigment to the layer thickness is preferably adjusted to a range of 0.07 to 0.15.

(2) Surface specific resistance value In the back surface protection sheet for solar cells of the present invention, the surface specific resistance value of the outermost surface on the side having the ultraviolet absorbing layer of the substrate is 1.0 × 10 ¹¹ Ω / □ or more and 1.0. It is preferable to be in the range of × 10 ¹⁴ Ω / □ or less. When the surface specific resistance value of the outermost surface is within the above range, it is difficult for sand and dust to adhere, and the destruction mode in which scratches etc. occur when another sand collides with the adhered sand is suppressed, and the resistance It becomes better due to sandiness.
The surface specific resistance value on the outermost surface is more preferably in the range of 1.0 × 10 ¹² Ω / □ to 1.0 × 10 ¹³ Ω / □.
Adjustment of the surface specific resistance value of the outermost surface on the side having the ultraviolet absorbing layer of the substrate may be performed by any method as long as the surface staticity is lowered. The method of containing in an absorption layer is mentioned. As the antistatic agent, the description in paragraphs 0034 to 0048 of the pamphlet of International Publication No. 2011/066807 can be referred to. Specific examples of the conductive polymer include a polyacetylene polymer, a polypyrrole polymer, a polythiophene polymer, a polyaniline polymer, and the like. As an example of a commercially available product, a conductive polymer Baytron manufactured by Bayer can be used. Furthermore, examples of the conductive oxide include indium oxide, zinc oxide, tin oxide, potassium titanate, titanium oxide, tin-antimony oxide, indium-tin oxide, and antimony-tin oxide. As an example of a commercially available product, a conductive oxide ATO-T-1 manufactured by Mitsubishi Materials Electronics Chemical Co., Ltd. can be used.
In addition to the above, an anionic antistatic agent, a nonionic antistatic agent, or the like may be used. The conductive material may be used in a range where the surface specific resistance value satisfies the above range.
The surface specific resistance value is measured using a high resistance-resistivity meter (Hiresta, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

(3) Content ratio of fluorine atom to carbon atom (F / C)
In the solar cell back surface protective sheet of the present invention, the ratio of fluorine atoms to carbon atoms (F / C; atomic ratio) on the outermost surface of the substrate having the ultraviolet absorbing layer is 0.1 or more and 0.7 or less. It is preferable that it is the range of these. The presence of fluorine atoms on the outermost surface of the substrate that has the UV-absorbing layer makes it difficult for sand and dust to adhere to it, and scratches and the like occur when other sand collides with the attached sand. The failure mode is suppressed, and the sand resistance is excellent.
The F / C value of the outermost surface on the side having the ultraviolet absorbing layer of the substrate is more preferably in the range of 0.5 to 0.7.
Adjustment of the F / C value of the outermost surface on the side having the ultraviolet absorbing layer of the base material may be any method as long as the surface slipperiness is improved and sand dust is less likely to adhere. For example, the method etc. which contain a fluorine-type compound etc. in an ultraviolet absorption layer are mentioned.
Examples of fluorine compounds include fluorine-containing acrylate, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene / ethylene copolymer, tetrafluoroethylene / perfluoroalkyl, and the like. Examples thereof include vinyl ether copolymers. The fluorine compound may be used in a range where the F / C value satisfies the above range.
The F / C value is a value calculated by measuring the amount of elements on the outermost surface of the substrate having the ultraviolet absorbing layer using an X-ray photoelectron spectrometer (Quantum 2000, manufactured by PHI).

(Base material)
The back surface protection sheet for solar cells of this invention is comprised using the base material.
The substrate may be in the form of a sheet or film, and may be a single layer or a multilayer film obtained by bonding a plurality of sheets or films.

Base materials include polyester films such as polyethylene terephthalate (PET) film and polyethylene naphthalate (PEN) film, polyolefin films such as polyethylene film and polypropylene film, polystyrene film, polyamide film, polyvinyl chloride film, polycarbonate film, polyacrylic A nitrile film, a polyimide film, a fluorine resin film, etc. are mentioned.
Among these, a PET film or a PEN film is preferable from the viewpoint of mechanical strength, heat resistance, and economy. From the viewpoint of maintaining long-term properties, a hydrolysis-resistant polyethylene terephthalate film (hydrolysis-resistant PET film) or a hydrolysis-resistant polyethylene naphthalate film (hydrolysis-resistant PEN film) is more preferable.
In addition, the substrate is preferably a fluororesin film in terms of weather resistance, and a film in which a polyester film and a fluororesin film are laminated is also suitable.

The hydrolysis resistant PET film refers to a film whose tensile elongation after storage for 10 hours under high-pressure steam at 140 ° C. is maintained at 60% or more with respect to the tensile elongation before storage.
By using such a hydrolysis-resistant PET film, the weather resistance of the back protective sheet for solar cell module can be improved, and the power generation performance of the solar cell module can be more stably maintained over a long period of time.

The hydrolysis-resistant PET film uses terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component, and has an intrinsic viscosity [η] of 0.70 to 1.20 (more preferably 0.75 to 1.00). The PET can be obtained by biaxial stretching.
Intrinsic viscosity [η] is a value measured at a temperature of 25 ° C. by dissolving PET using o-chlorophenol as a solvent. When the intrinsic viscosity is 0.70 or more, the hydrolysis resistance and heat resistance are good, and when the intrinsic viscosity is 1.20 or less, the film forming property is excellent.

The PET may be homo-PET that is a homopolymer, or copolymer PET obtained by copolymerizing copolymer components. Examples of the copolymer component include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, and the like. A dicarboxylic acid component is mentioned.
In addition, in PET, additives (for example, heat stabilizer, oxidation stabilizer, ultraviolet absorber, anti-glare stabilizer, organic lubricant, organic type) are added to PET as necessary. Fine particles, fillers, antistatic agents, nucleating agents, dyes, dispersants, coupling agents, etc.) may be blended.

  Specific examples of the hydrolysis-resistant PET film include “Lumirror” (registered trademark) X10S manufactured by Toray Industries, Inc.

  A PEN film is obtained by biaxially stretching a resin polymerized by a known method using 2,6-naphthol dicarboxylic acid as a dicarboxylic acid component and ethylene glycol as a diol component.

The thickness of the hydrolysis-resistant PET film or PEN film is preferably 38 μm to 300 μm, and more preferably 50 μm to 250 μm in terms of film stiffness, voltage resistance, cost, and processability.
In order to meet the HAI (High Current Arc Ignition) test in UL746A which is a flame retardant standard, the thickness of the hydrolysis-resistant PET film and PEN film is preferably 200 μm to 250 μm.

  The fluororesin film is obtained as a film having a desired thickness by melting the fluororesin, extruding it from the die into a sheet shape, and cooling it on a rotary cooling drum.

  Fluorine-based resins include polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer, tetrafluoroethylene / propylene copolymer, tetrafluoroethylene / hexafluoropropylene / propylene copolymer , Ethylene / tetrafluoroethylene copolymer (ETFE), hexafluoropropylene / tetrafluoroethylene copolymer (FEP), or perfluoro (alkyl vinyl ether) / tetrafluoroethylene copolymer, polychlorotrifluoroethylene resin, etc. It is done. Among these, in terms of melt extrusion moldability, in particular, polyvinyl fluoride, ethylene / tetrafluoroethylene copolymer (ETFE), hexafluoropropylene / tetrafluoroethylene copolymer (FEP), perfluoro (alkyl vinyl ether) / tetra. A fluoroethylene copolymer and a polychlorotrifluoroethylene polymer are preferred.

  The substrate may be subjected to surface treatment such as corona discharge treatment, plasma treatment, flame treatment, chemical treatment, etc. on the surface. By performing the surface treatment to activate the substrate surface, the adhesion of the adjacent layer can be enhanced.

-UV absorbing pigment-
The substrate itself preferably contains an ultraviolet absorbing pigment.
By including the ultraviolet absorbing pigment in the base material, it becomes possible to reduce the ratio of the ultraviolet absorbing pigment contained in the aforementioned ultraviolet absorbing layer while satisfying the amount of the ultraviolet absorbing pigment required as the total amount in the sheet. . Thereby, in the ultraviolet absorption layer, the content ratio of the inorganic oxide particles can be easily increased, and the Vickers hardness on the outermost surface can be more easily adjusted.

  The ultraviolet absorbing pigment contained in the substrate is the same as the ultraviolet absorbing pigment that can be used in the aforementioned ultraviolet absorbing layer, and the preferred embodiment is also the same.

  When the substrate contains an ultraviolet light absorbing pigment, the content of the ultraviolet light absorbing pigment in the substrate is preferably 1% by mass to 20% by mass with respect to the resin constituting the substrate, and 3% by mass to 10% by mass. % Is more preferred. When the content of the ultraviolet light absorbing pigment in the substrate is 1% by mass or more, the amount of the ultraviolet light absorbing pigment contained in the second layer is reduced, and it becomes easy to add a desired amount of inorganic oxide particles. Moreover, it is advantageous at the point of embrittlement prevention of a base material as content of an ultraviolet light absorption pigment is 20 mass% or less.

(Colored layer)
It is preferable that the back surface protection sheet for solar cells of this invention has a layer (colored layer) containing at least polyolefin resin and a color pigment.
The colored layer is preferably formed on the surface of the substrate opposite to the side having the ultraviolet absorbing layer.

-Color pigment-
The colored layer preferably contains at least one kind of colored pigment. The colored pigment is used for the purposes of (1) coloring the resin layer, (2) maintaining the color tone (not fading), (3) shielding ultraviolet rays and / or visible light, and (4) preventing the surface resistance from decreasing.
The coloring pigment may be either an inorganic pigment or an organic pigment, and may be appropriately selected according to the purpose. A white pigment or a black pigment is preferable from the viewpoint of improving power generation efficiency and design. As the white pigment, white fine particles are preferable. Examples of the white fine particles are preferably inorganic fine particles such as calcium carbonate, silica, alumina, magnesium hydroxide, zinc oxide, talc, kaolin clay, titanium oxide, and barium sulfate, and more preferably titanium oxide particles.
The crystal structure of the particles is known to be rutile, anatase, brookite, etc., but it is colored rutile because of its excellent whiteness, weather resistance, and light reflectivity. Pigments are preferred.

As for titanium oxide, it is preferable that the particle | grain surface is surface-coated by the surface coating agent. The composition of the surface coating agent is not limited, but inorganic oxides such as silicon oxide, alumina, or zinc oxide are preferable. There is no restriction | limiting in particular in the coating method by a surface coating agent, The titanium oxide particle surface-coated by the well-known method can be used.
Furthermore, in terms of stabilizing the titanium oxide particles, a light stabilizer such as a hindered amine can be added to the resin.

  The average particle diameter of the color pigment (particularly white fine particles) is preferably 0.2 μm to 0.7 μm, and more preferably 0.25 μm to 0.35 μm from the viewpoint of further increasing the reflectance of visible light.

The content of the coloring pigment in the colored layer, the area of the colored layer ^is preferably in the range of ^{1g / m 2 ~30g / m 2} , the range of ^5g / ^{m 2 ~2} / m 2 is more preferable. As will be described later, when the colored layer is formed in a laminated structure, the thickness of the colored layer having, for example, a three-layer structure is preferably in the range of 50 μm to 300 μm.

-Polyolefin resin-
Polyolefin resins include polyethylene resins, polypropylene resins, and mixed resins thereof.

  Examples of the polyethylene resin include high-pressure low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and mixed resins thereof.

The linear low density polyethylene is a copolymer of ethylene and α-olefin (hereinafter sometimes abbreviated as LLDPE), and is a copolymer of α-olefin having 4 to 20 carbon atoms (preferably 4 to 8). A polymer is preferred. Specific examples of linear low density polyethylene include butene-1, pentene-1, 4-methyl-1-pentene, hexene-1, heptene-1, octene-1, nonene-1, decene-1, and the like. A copolymer is mentioned.
These α-olefins can be used alone or in combination.
In particular, butene-1, hexene-1, octene-1 and the like are preferable from the viewpoint of polymerization productivity.

  Examples of the polypropylene resin include homopolypropylene, ethylene / propylene random copolymer, and ethylene / propylene block copolymer.

  The copolymer of ethylene and propylene preferably has an ethylene content in the range of 1 mol% to 15 mol%. When the ethylene content is 1 mol% or more, the dispersibility in LLDPE or LDPE or a mixed resin thereof is improved, and the resin does not easily fall off when scraping occurs between a metal roll and a rubber roll. Occurrence can be suppressed. In addition, the adhesion with EVA is increased. On the other hand, when the ethylene content is 15 mol% or less, the sheet thickness is not reduced and the concealing property of the bus bar or the like can be improved when thermocompression bonding with EVA is performed.

  The MFR at 230 ° C. of the polypropylene resin is preferably in the range of 1.0 g / 10 min to 15 g / 10 min. When the MFR is 1.0 g / 10 min or more, the film width is less likely to decrease (neck down) than the discharge width of the die in the film forming process, and stable production of the film is facilitated. Moreover, it is preferable for MFR to be 15 g / 10 min or less because the crystallization rate is reduced and the film does not become brittle.

  The melting point of the polypropylene resin is preferably in the range of 140 ° C. to 170 ° C. in terms of heat resistance, slipperiness, film handling properties, curl resistance, and thermal adhesiveness with EVA. When the melting point is 140 ° C. or higher, the first layer (or the A layer having a three-layer laminated structure described later) has excellent heat resistance, and the sheet thickness when thermally bonded to EVA as a back surface protective sheet for a solar cell module The decrease is suppressed, and the withstand voltage characteristic is also secured. Moreover, it becomes what was excellent in adhesiveness with EVA because melting | fusing point is 170 degrees C or less.

Here, the form of the colored layer will be described.
There is no restriction | limiting in particular as a form of a colored layer, You may be comprised in any of a single layer structure or a multilayer structure. When the colored layer is formed in a multilayer structure, it may be any of a two-layer structure, a three-layer structure, a four-layer structure, etc., for example, a structure in which three layers “A layer / B layer / C layer” are laminated It may be configured as a polyolefin resin multilayer film.

  The A layer is preferably a resin composition in which a polyethylene resin and a polypropylene resin are mixed. By mixing the polypropylene resin with the polyethylene resin, the heat resistance is improved and the adhesion with the B layer is further improved. In this case, the polyethylene resin used for the A layer is preferably a high pressure process low density polyethylene, a linear low density polyethylene, a high density polyethylene, or a mixed resin thereof.

  As melting | fusing point of LLDPE used for A layer, the range of 110 to 130 degreeC is preferable. When the melting point is 130 ° C. or lower, the thermal adhesiveness with the ethylene-vinyl acetate copolymer resin (EVA) used as the sealing material is excellent. Moreover, when the melting point is 110 ° C. or higher, the thickness of the sheet is not reduced when thermocompression bonding with EVA, and the withstand voltage characteristic can be ensured.

Moreover, the density of LLDPE is preferably 0.90 g / cm ³ or more. The upper limit of the density is preferably 0.94 g / cm ³ . When the density is 0.94 g / cm ³ or less, the dispersibility is improved when a polypropylene resin is used in combination, and even when scratching occurs between the metal roll and the rubber roll, the resin does not easily fall off. Occurrence is also suppressed.

The content of α-olefin in LLDPE is preferably 0.5 mol% to 10 mol%, more preferably 2.0 mol% to 8.0 mol%. When the α-olefin content is 0.5 mol% to 10 mol%, the density of LLDPE can be adjusted to a range of 0.90 g / cm ³ or more and 0.94 g / cm ³ or less.

  The melt index (melt flow rate; hereinafter abbreviated as “MFR”) of LLDPE in layer A at 190 ° C. is preferably 0.5 g / 10 min to 10.0 g / 10 min, more preferably It is 1.0 g / 10 minutes to 5.0 g / 10 minutes. When the MFR is 0.5 g / 10 min or more, lamination unevenness with other layers hardly occurs during film formation. Further, when the MFR is 10.0 g / 10 min or less, the handling property at the time of casting hardly occurs, and the embrittlement due to the increase in crystallinity hardly occurs.

High-pressure low-density polyethylene used in the A layer (hereinafter abbreviated as "LDPE") The density of ^the range of 0.90g / cm ³ ~0.93g / cm 3 are preferred. When the density is 0.90 g / cm ³ or more, the slipping property of the film is excellent, and the handling property of the film during processing is also improved. On the other hand, when the density is 0.93 g / cm ³ or less, the effect of improving the dispersibility of the polyethylene resin and the polypropylene resin is easily exhibited.

The A layer, density 0.94g ^/ cm ³ ~0.97g ^/ cm 3 density polyethylene (hereinafter abbreviated as "HDPE") is used, although excellent in the waist and anti-curl of the film, during processing Since HDPE falls off due to roll friction and white powder is generated, problems such as film stains and scratches may occur. Since the melting point is higher than that of LLDPE and LDPE, the heating temperature for thermal bonding with EVA is reduced. Care must be taken such as setting it higher, and depending on the thermal bonding conditions, there is a concern that the adhesion strength with EVA will be lower.

  The surface average roughness Ra of the A layer is preferably 0.10 μm to 0.30 μm from the viewpoint of satisfying the film handling function during processing.

The B layer preferably contains white fine particles and a polypropylene resin composition.
Polypropylene resin composition includes, in terms of heat resistance, homopolypropylene, a resin selected from a random or block copolymer of ethylene and propylene, or a mixed resin of these resins and polyethylene, and a polyethylene content Is preferably less than 30% by mass of the total resin component.

  When the polypropylene resin is a copolymer of ethylene and propylene, the ethylene content is preferably 15 mol% or less from the viewpoint of heat resistance.

  The MFR at 230 ° C. of the polypropylene-based resin is preferably in the range of 1.0 g / 10 min to 15 g / 10 min from the viewpoint of excellent lamination properties when coextruded with the A layer and the C layer described later. When the MFR is 1.0 g / 10 min or more, the film melt-extruded from the die in the film forming process is not easily necked down, and the stable film formation is facilitated, for example, the flatness in the width direction of the film does not deteriorate. On the other hand, if the MFR is 15 g / 10 min or less, the crystallization speed decreases and the film is difficult to become brittle.

  The B layer preferably contains white fine particles. The white fine particles can be selected from the aforementioned white fine particles that can be contained in the colored layer.

  The content of the white fine particles in the B layer is preferably in the range of 5% by mass to 50% by mass with respect to the polyolefin resin (particularly polypropylene resin), although it depends on the specific gravity. Especially, the range of 10 mass%-30 mass% is more preferable with respect to polyolefin resin (especially polypropylene resin). When the content is 5% by mass or more, whitening and light reflection effect are good, and wiring material such as a bus bar is not transparent and has excellent design. Further, when the content is 50% by mass or less, white fine particles hardly aggregate at the time of film formation and can be stably formed.

The C layer can be configured using a polypropylene resin composition.
The C layer, like the B layer, is mainly composed of at least one resin selected from polypropylene resins such as homopolypropylene, a random or block copolymer of ethylene and propylene in terms of heat resistance. It is preferable that 70 mass% or more is contained.
The polypropylene resin is more preferably a block copolymer in terms of heat resistance, slipperiness, film handling, scratch resistance, and curl resistance.

  Although the thickness of the polyolefin resin multilayer film depends on the structure of the solar cell, the range of 10 μm to 250 μm is preferable, and the range of 20 μm to 200 μm is more preferable in terms of film production and lamination with other substrates. preferable. When the thickness is 250 μm or less, the economy is excellent and the handleability is excellent. Furthermore, the polyolefin-based resin multi-layer is excellent in that the back surface protection sheet is deformed thinly due to the influence of the wiring member, so that the solar power generation element, the interconnector, and the bus bar are excellent in heat resistance and concealment. The thickness of the film is preferably 50 μm to 200 μm, more preferably 130 μm to 200 μm.

The lamination ratio of the A layer / B layer / C layer constituting the polyolefin resin multilayer film is not particularly limited, but when the total thickness of the polyolefin resin multilayer film is 100%, the A layer and the C layer are respectively A case where the content is 5% to 20% and the B layer is 90% to 60% is preferable.
In addition, the B layer containing white fine particles is sandwiched between the A layer and the C layer by arranging the layers in the order of layer A / layer B / layer C, and a large amount of particles are produced in the die at the time of manufacture. It is possible to more effectively avoid the occurrence of process contamination and film scratches due to the decomposition of the resin degradation product being contained and the degradation product falling off.

The polyolefin-based resin multilayer film having a structure in which the above three layers “A layer / B layer / C layer” are laminated can be produced as follows. That is,
The resin for forming each layer is supplied to a single-screw melt extruder and melted in the range of 220 ° C. to 280 ° C., respectively. After removing foreign substances and coarse inorganic particles through a filter installed in the middle of the polymer tube, the multi-manifold type T die or the feed block installed on the top of the T die is used for the A layer / B layer / C layer. Three-type three-layer lamination is performed, and discharged from a T die onto a rotating metal roll with the C layer side set to the metal roll surface side to obtain an unstretched film. At this time, the surface temperature of the rotating metal roll is preferably controlled to 20 ° C. to 60 ° C. in that the crystallinity is enhanced without causing adhesion of the C layer to the metal roll. Moreover, in order to make a molten polymer contact | adhere to a metal roll, it is preferable to use the method of spraying air from a nonmetallic roll side, or a nip roll.

<Solar cell module>
The solar cell module of the present invention is configured by providing the above-described solar cell back surface protective sheet of the present invention. Specifically, the solar cell module of the present invention is provided on a transparent base material (a front base material such as a glass substrate) on which sunlight enters and the base material, and seals the solar cell element and the solar cell element. An element structure portion having a sealing material to be stopped, and a solar cell backsheet (including a back surface protection sheet for solar cells of the present invention) disposed on the side opposite to the side where the substrate of the element structure portion is located. And has a laminated structure of “transparent front substrate / element structure portion / back sheet”.
A transparent front substrate disposed on the side on which sunlight directly enters an element structure portion on which a solar cell element that converts light energy of sunlight into electric energy is disposed, and the solar cell backsheet of the present invention Between the front base material and the back sheet, using an encapsulant such as an ethylene-vinyl acetate (EVA) system for the element structure part (for example, solar battery cell) including the solar battery element. The structure is sealed and bonded.

  The members other than the solar cell module, the solar cell, and the back sheet are described in detail in, for example, “Photovoltaic power generation system constituent material” (supervised by Eiichi Sugimoto, Kogyo Kenkyukai, published in 2008).

  The transparent base material should just have the light transmittance which sunlight can permeate | transmit, and can be suitably selected from the base materials which permeate | transmit light. From the viewpoint of power generation efficiency, the higher the light transmittance, the better. For such a substrate, for example, a glass substrate, a transparent resin such as an acrylic resin, or the like can be suitably used.

  Examples of solar cell elements include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, and group III-V such as copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, and gallium-arsenic. Various known solar cell elements such as II-VI group compound semiconductor systems can be applied. A space between the substrate and the polyester film can be configured by sealing with a resin (so-called sealing material) such as an ethylene-vinyl acetate copolymer.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” and “%” are based on mass.

(Example 1)
[Base film]
A hydrolysis-resistant white polyethylene terephthalate film (trade name; Lumirror (registered trademark) X10S (125 μm)) manufactured by Toray Industries, Inc. was prepared as a base film.

[Colored layer]
As a film constituting the colored layer, a polyolefin-based resin multilayer film having a structure of A layer / B layer / C layer was prepared by the following procedure.

First, an average particle diameter of 200 nm surface-treated with 40% homopolypropylene having a melting point of 162 ° C. and a density of 0.900 g / cm ³ and an inorganic oxide (main component = one or more selected from silicon, aluminum, and zinc). 60% of rutile type titanium oxide (manufactured by Sakai Chemical Industry Co., Ltd., FTR-700) was melt kneaded at 240 ° C. with a twin screw extruder. Thereafter, the strand was cut to produce a titanium oxide master batch A.

As a resin used for the A layer, a linear low density polyethylene (LLDPE; hereinafter referred to as linear) having a melting point of 127 ° C., a density of 0.940 g / cm ³ and a melt flow rate (MFR; the same shall apply hereinafter) of 5.0 g / 10 min. 80 parts of low-density polyethylene (referred to as “LLDPE”), and a low-density polyethylene (LDPE; hereinafter referred to as “LDPE”) 20 at a melting point of 112 ° C., a density of 0.912 g / cm ³ , and an MFR of 4.0 g / 10 minutes. Parts (total 100 parts of polyethylene resin), melting point 150 ° C., density 0.900 g / cm ³ , MFR 7 g / 10 min ethylene / propylene random copolymer (ethylene content: 4 mol%; polypropylene resin) ) 100 parts of mixed resin was prepared.

As a resin used for the B layer, a mixed resin was prepared by mixing 100 parts of homopolypropylene having a melting point of 160 ° C., a density of 0.900 g / cm ³ , and an MFR of 7 g / 10 minutes, and 30 parts of titanium oxide master batch A. The content of titanium oxide as a coloring agent is 13.8%.

As a resin used for the C layer, an ethylene / propylene block copolymer (ethylene content: 7 mol%) having a melting point of 160 ° C., a density of 0.900 g / cm ³ , and an MFR of 4.0 g / 10 min was prepared.

  Each resin for forming each layer of the A layer, the B layer, or the C layer prepared as described above was supplied to a single-screw melt extruder and melted at 260 ° C., respectively. And it led to the multi-manifold type T-die so that it might become the lamination | stacking order of A layer / B layer / C layer, and it extruded on the casting drum kept at 30 degreeC. A polyolefin resin having a thickness of 150 μm in which the ratio of the thickness of each layer (A layer / B layer / C layer) is 10% / 80% / 10% by blowing cold air of 25 ° C. from the non-drum surface side. A multilayer film was obtained.

[Bonding of base film and polyolefin resin multilayer film]
Add 1 part of curing agent (KR-90, manufactured by DIC Corporation) to 10 parts of adhesive (LX-703VL, manufactured by DIC Corporation) and dilute with ethyl acetate to a solid content concentration of 30% A prepared adhesive ink was prepared. This adhesive ink was coated on Lumirror (registered trademark) X10S using a film coater (Okazaki Machinery Co., Ltd.) so that the thickness after drying at a drying temperature of 120 ° C. was 5.0 μm. Then, an adhesive layer was formed.
The polyolefin resin multilayer film is laminated in contact with this adhesive layer, Lumirror (registered trademark) X10S and the polyolefin resin multilayer film are bonded, and the first layer (polyolefin resin multilayer film) is formed on the base film. ) Was formed.

[Formation of UV absorbing layer]
The component in the following composition was mixed and the coating composition for forming an ultraviolet absorption layer was obtained.
<Composition>
-(Meth) acrylate resin ... 30 parts (Huls hybrid polymer (registered trademark) BK1, manufactured by Nippon Shokubai Co., Ltd.) in which an ultraviolet light absorber and a light stabilizer (HALS) are crosslinked to an acrylic polyol resin
-Cross-linking agent 15 parts (Nurate type hexamethylene diisocyanate resin, Desmodur (registered trademark) N3300 (solid content concentration: 100%), manufactured by Sumika Bayer)
・ Elastic recovery resin ・ ・ ・ 5 parts (urethane (meth) acrylate, self-healing clear (registered trademark), manufactured by NATCO)
・ Titanium oxide (ultraviolet absorbing pigment) 50 parts (D-918 (particle size 0.26 μm), manufactured by Sakai Chemical Co., Ltd.)
・ Methyl ethyl ketone (solvent) ・ ・ ・ 180 parts

After applying corona treatment to the surface of the base film (Lumirror (registered trademark) X10S) on which the polyolefin-based resin multilayer film is not laminated, the coating composition is applied so that the thickness after drying is 2.0 μm. Was applied to form an ultraviolet absorbing layer.
As described above, the protective sheet for the back surface of the solar cell of the present invention was produced.

(Comparative Example 1)
In Example 1, as shown in Table 1 below, the amount of (meth) acrylate resin in the coating composition for forming the ultraviolet absorbing layer was changed, and the elastic recovery resin was not used, and ultraviolet irradiation was performed. A back protective sheet for a solar cell of Comparative Example 1 was produced in the same manner as Example 1 except that it was not present.

(Example 2 to Example 5)
In Example 1, as shown in Table 1 below, the same as Example 1 except that the amount of (meth) acrylate resin and the amount of elastic recovering resin in the coating composition for forming the ultraviolet absorbing layer were changed. Thus, protective sheets for the back surface for solar cells of Examples 2 to 5 were produced.

(Example 6)
In Example 1, as shown in Table 1 below, polyrotaxane A synthesized by the following method was used in place of self-healing clear (registered trademark) as the elastic recovery resin in the coating composition for forming the ultraviolet absorbing layer. A back protective sheet for a solar cell of Example 6 was prepared in the same manner as in Example 1 except that the amount of (meth) acrylate resin and the amount of elastic recovery resin were changed.

(Synthesis Example 1: Crosslinkable polyrotaxane A)
In a 100 ml Erlenmeyer flask, 4 g of polyethylene glycol (average molecular weight 20,000) and 20 ml of dry methylene chloride were added to dissolve polyethylene glycol. This solution was placed under an argon atmosphere, 0.8 g of 1,1′-carbonyldiimidazole was added, and the mixture was stirred and reacted at room temperature (20 ° C.) for 6 hours under an argon atmosphere.
The reaction product obtained above was poured into 300 ml of diethyl ether stirred at high speed. After leaving still for 10 minutes, the liquid which has a deposit was centrifuged at 10,000 rpm for 5 minutes. The precipitate was taken out and dried in vacuum at 40 ° C. for 3 hours.
The resulting product was dissolved in 20 ml of methylene chloride. This solution was added dropwise to 10 ml of ethylenediamine over 3 hours, followed by stirring for 40 minutes. The obtained reaction product was subjected to a rotary evaporator to remove methylene chloride. Then, it melt | dissolved in 50 ml of water, put into the dialysis tube (fraction molecular weight 8,000), and dialyzed in water for 3 days. The obtained dialyzate was dried with a rotary evaporator. Further, this dried product was dissolved in 20 ml of methylene chloride and reprecipitated with 180 ml of diethyl ether. The liquid having a precipitate was centrifuged at 100,000 rpm for 5 minutes and vacuum dried at 40 ° C. for 2 hours to obtain 2.83 g of polyethylene glycol bisamine (number average molecular weight 20,000).
4.5 g of the obtained polyethylene glycol bisamine and 18.0 g of α-cyclodextrin were added to 150 mL of water and heated to 80 ° C. to dissolve. The solution was cooled and allowed to stand at 5 ° C. for 16 hours. The produced white paste-like precipitate was collected and dried.
The dried product was added to a mixed solution of 12.0 g of 2,4-dinitrofluorobenzene and 50 g of dimethylformamide and stirred at room temperature for 5 hours. The reaction mixture was dissolved by adding 200 mL of dimethyl sulfoxide (DMSO), and then poured into 3750 mL of water to separate a precipitate. The precipitate was redissolved in 250 mL of DMSO and then poured again into 3500 mL of 0.1% saline to separate the precipitate. The precipitate was washed with water and methanol three times each, and then vacuum-dried at 50 ° C. for 12 hours, whereby polyethylene glycol bisamine was included in α-cyclodextrin in a skewered manner, and both terminal amino groups were formed. 2.0 g of a polyrotaxane having a 2,4-dinitrophenyl group bonded thereto was obtained. The obtained polyrotaxane is referred to as “polyrotaxane a1”.

When the obtained polyrotaxane a1 was subjected to ultraviolet absorption measurement and ¹ H-NMR measurement to calculate the inclusion amount of α-cyclodextrin, the inclusion amount was 72.
Specifically, in the ultraviolet absorption measurement, the inclusion amount of cyclodextrin was calculated by measuring the molar extinction coefficient at 360 nm of each of the synthesized inclusion compound and 2,4-dinitroaniline. Moreover, in < ¹ > H-NMR measurement, it computed from the integral ratio of the hydrogen atom of a polyethyleneglycol part, and the hydrogen atom of a cyclodextrin part.

Polyrotaxane a1 (1 g) was dissolved in 50 g of a lithium chloride / N, N-dimethylacetamide 8% solution. To this solution were added 6.7 g of acetic anhydride, 5.2 g of pyridine, and 100 mg of N, N-dimethylaminopyridine, and the mixture was stirred overnight at room temperature. The reaction solution was poured into methanol, and the precipitated solid was separated by centrifugation. The separated solid was dried and then dissolved in acetone. The solution was poured into water, and the precipitated solid was separated by centrifugation and dried to obtain polyrotaxane (1.2 g) in which a part of the hydroxyl groups of cyclodextrin was modified with acetyl groups. The obtained polyrotaxane is referred to as “polyrotaxane a2”.
The ¹ H-NMR measurement of polyrotaxane a2 was performed, and the amount of acetyl group introduced (modification degree) was calculated and found to be 75%.

Polyrotaxane a2 (1 g) was dissolved in 50 g of a lithium chloride / N, N-dimethylacetamide 8% solution. To this solution, 5.9 g of acrylic acid chloride, 5.2 g of pyridine, and 100 mg of N, N-dimethylaminopyridine were added, and the mixture was stirred overnight at room temperature. The reaction solution was poured into methanol, and the precipitated solid was separated by centrifugation. The separated solid was dried and then dissolved in acetone. The solution was poured into water, and the precipitated solid was separated by centrifugation and dried to obtain a polyrotaxane (0.8 g) in which the hydroxyl group of cyclodextrin was modified with an acryloyl group and an acetyl group. The obtained polyrotaxane is referred to as “crosslinkable polyrotaxane A”.
When ¹ H-NMR measurement of the crosslinkable polyrotaxane A was performed and the introduction amount (modification degree) of acryloyl group and acetyl group was calculated, it was 87%. That is, the introduction amount (modification degree) of the acryloyl group is 12%.

(Example 7 and Comparative Example 2)
In Example 1, as shown in Table 1 below, urethane (meth) acrylate (self-reacting resin) was used as an elastic recovering resin without using Halshybrid polymer (as (meth) acrylate resin of the coating composition for forming the ultraviolet absorbing layer). A back protective sheet for solar cell of Example 7 and Comparative Example 2 was prepared in the same manner as in Example 1 except that Healing Clear (registered trademark) and Polyrotaxane A were used in the mixing ratio shown in Table 1. .

(Example 8 and Example 9)
In Example 3, as shown in Table 1, solar cell back surface protective sheets of Examples 8 and 9 were prepared in the same manner as in Example 3 except that the film thickness of the ultraviolet absorbing layer was changed.

(Example 10)
The following composition was further applied to the ultraviolet absorbing layer formed in Example 3, dried at 90 ° C. for 2 minutes, and then cured by irradiating with ultraviolet rays, so that the total amount of the ultraviolet absorbing layer after drying was increased. An ultraviolet absorbing layer was formed so that the coating layer thickness was 4.0 μm, and a back protective sheet for a solar cell of Example 10 was produced.

<Composition>
-(Meth) acrylate resin ... 30 parts (Huls hybrid polymer (registered trademark) BK1, manufactured by Nippon Shokubai Co., Ltd.) in which an ultraviolet light absorber and a light stabilizer (HALS) are crosslinked to an acrylic polyol resin
-Cross-linking agent 15 parts (Nurate type hexamethylene diisocyanate resin, Desmodur (registered trademark) N3300 (solid content concentration: 100%), manufactured by Sumika Bayer)
・ Elastic recovery resin ・ ・ ・ 5 parts (urethane (meth) acrylate, self-healing clear (registered trademark), manufactured by NATCO)
・ Methyl ethyl ketone (solvent) ・ ・ ・ 100 parts

(Example 11)
In Example 3, as shown in Table 1 below, Example 1 except that the presence or absence of the ultraviolet absorbing pigment in the substrate and the amount of the ultraviolet absorbing pigment in the coating composition forming the ultraviolet absorbing layer were changed. Similarly, a solar cell back protective sheet of Example 11 was produced. In Example 11, a transparent polyethylene terephthalate film Toyobo Co., Ltd. Cosmo Shine 4100 was used as the substrate.

(Example 12 and Example 13)
In Example 3, as shown in Table 1, Example 12 and Example 13 were the same as Example 1 except that other additives were added to the coating composition for forming the ultraviolet absorbing layer. A back protective sheet for solar cells was produced.
In Example 12, 0.1 part by mass of a conductive polymer Baytron (polythiophene-based conductive polymer aqueous dispersion, manufactured by Bayer) was added.
In Example 17, 0.13 parts by weight of conductive oxide ATO-T-1 (manufactured by Mitsubishi Materials Electronics Chemical Co., Ltd.) was added.

(Examples 14 to 16)
In Example 3, as shown in Table 1, Example 14 to Example were carried out in the same manner as in Example 3 except that the type and amount of (meth) acrylate resin in the coating composition for forming the ultraviolet absorbing layer were changed. The back surface protection sheet for solar cells of Example 16 was produced.
As the fluorine-containing acrylic monomer, Ftop EF-PA2 manufactured by Mitsubishi Materials Electronics Chemical Co., Ltd. was used in Examples 14 to 16.

(Evaluation)
About the protection sheet for solar cell back surfaces produced by said Example and comparative example, it evaluated by the following method. The evaluation results are shown in Tables 1 and 2 below.

-1. Vickers hardness and elastic recovery rate
The Vickers hardness on the outermost surface was measured using a Triangular indenter with an ultra micro hardness tester (DUH-201S, manufactured by Shimadzu Corporation), and calculated by the depth after load removal in the load-removal mode.

-2. Surface roughness
The surface roughness was calculated as the surface roughness in a region of 0.3 mm × 0.3 mm using a three-dimensional optical profiler (Zigo, manufactured by Canon Inc.).

-3. Surface specific resistance
The surface specific resistance was measured using a high resistance-resistivity meter (Hiresta, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

-4. Content ratio of fluorine atom to carbon atom (F / C) −
F / C was calculated by measuring the amount of elements on the film surface using an X-ray photoelectron spectrometer (Quantum 2000, manufactured by PHI). Specifically, X-ray photoelectron spectroscopy measurement was performed under the following measurement conditions, and the elemental composition (at%) was calculated from the intensity of each narrow spectrum of F, C, O, and N obtained by the measurement. And F / C was calculated | required from the calculated elemental composition of F, C, N, and O. The measurement conditions are as follows.
<Measurement conditions>
X-ray source: monochromatic Al-Ka, output 16 kV-34W1 (X-ray generation area 170 μmφ)
・ Charge neutralization: Combined use of electron gun (2μA) and ion gun (1V) ・ Spectroscopic system: Path energy
187.85 eV (wide spectrum)
58.70 eV (Narrow spectrum, N1s)
29.35 eV (narrow spectrum, C1s, O1s, F1s)
11.75 eV (narrow spectrum, C1s)
・ Extraction angle: 45 ° (from the surface)

-5. Sandfall test-
A sand fall test was performed using silicon carbide powder under conditions according to ASTM D968-05, Method B. A value obtained by dividing the amount of sand fall (kg) at the time when the sand fall was performed and the base material was exposed by the film thickness (μm) shaved by the sand was used as an evaluation value.

  As shown in Table 1, it can be seen that good results were obtained for the evaluation of sand resistance in the Examples.

Claims (10)

A substrate;
A binder containing a (meth) acrylate resin and an ultraviolet absorbing layer containing an ultraviolet absorbing pigment,
The outermost surface of the substrate having the ultraviolet absorbing layer has an elastic recovery rate of 60% or more and a Vickers hardness of 1.0 × 10 ⁷ Pa to 1.0 × 10 ⁹ Pa for solar cells. Back protection sheet.   The back protective sheet for a solar cell according to claim 1, wherein the (meth) acrylate resin is a urethane (meth) acrylate resin.   The back surface protection sheet for solar cells of Claim 1 or Claim 2 in which the said ultraviolet absorption layer further contains a polyrotaxane.   The back surface protection sheet for solar cells of any one of Claims 1-3 in which the said base material contains a ultraviolet absorption pigment.   The back surface protection sheet for solar cells according to any one of claims 1 to 4, wherein the outermost surface has a surface roughness of 0.01 µm or more and 0.20 µm or less.   The back surface protection sheet for solar cells according to any one of claims 1 to 5, wherein the layer including the outermost surface has a ratio of a particle diameter of the ultraviolet absorbing pigment to a thickness of 0.01 to 0.15. . The surface specific resistance value of the outermost surface is 1.0 × 10 ¹¹ Ω / □ or more and 1.0 × 10 ¹⁴ Ω / □ or less. 7. The solar cell according to claim 1. Back protection sheet.   The back surface protection sheet for solar cells according to any one of claims 1 to 7, wherein a content ratio of fluorine atoms to carbon atoms on the outermost surface is 0.1 or more and 0.7 or less in terms of atomic ratio.   The solar cell module provided with the back surface protection sheet for solar cells of any one of Claims 1-8.   A transparent base material on which sunlight is incident, an element structure portion provided on the base material and having a solar cell element and a sealing material for sealing the solar cell element, and the base material of the element structure portion The solar cell module provided with the back surface protection sheet for solar cells of any one of Claims 1-8 arrange | positioned on the opposite side to the side in which this is located.