JP6071937B2 - Solar cell back surface protection sheet and solar cell module - Google Patents

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 ultraviolet light resistance and heat resistance when exposed to sunlight, resistance to scratches caused by sand and dust flying and colliding with the wind 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 has a back surface protection sheet for solar cells that has excellent sand resistance against collisions with dust and the like and is less prone to cracking, and stable power generation performance over a long period of time. It aims at providing the solar cell module which can be obtained, and makes it a subject to achieve this objective.

Specific means for achieving the above-described problems are as follows.
<1> A first layer containing a polyolefin resin and a color pigment, a base material, a binder containing a (meth) acrylate resin, and a second layer containing an ultraviolet absorbing pigment in this order, It is the back surface protection sheet for solar cells whose Vickers hardness of the outermost surface in the 2nd layer side is 5.0 * 10 < ⁹ > Pa or more and 1.0 * 10 < ¹¹ > Pa or less.
<2> The back surface protective sheet for solar cell according to <1>, wherein the second layer or the third layer having the outermost surface further includes inorganic oxide particles having an element selected from Si, Al, and Zr. It is.
<3> The back surface protective sheet for solar cells according to <2>, wherein the volume ratio of the inorganic oxide particles to the binder and the inorganic oxide particles is 15% by volume or more and 40% by volume or less.
<4> The solar cell back surface protective sheet according to <2> or <3>, wherein the inorganic oxide particles have an aspect ratio of 300 or more and 800 or less.
<5> The (meth) acrylate resin contained in the second layer has a crosslinking point, and the (meth) acrylate resin is crosslinked with a crosslinking agent according to any one of <1> to <4>. It is a back surface protection sheet for solar cells.
<6> A third layer containing a binder is provided on the side opposite to the base material of the second layer, and the outermost surface is a surface opposite to the side of the third layer having the second layer <1. It is the back surface protection sheet for solar cells as described in any one of>-<5>.
The binder contained in the <7> 3rd layer is a back surface protection sheet for solar cells as described in <6> containing the polymer of an alkoxysilane.
<8> The solar cell back surface protective sheet according to <6> or <7>, wherein the thickness of the third layer is 0.5 μm or more and 3 μm or less.

A <9> 2nd layer is a back surface protection sheet for solar cells as described in any one of <1>-<8> containing urethane (meth) acrylate resin as said (meth) acrylate resin.
A <10> 2nd layer is a back surface protection sheet for solar cells as described in any one of <1>-<9> which contains a polyrotaxane further as a binder.
<11> The back surface protective sheet for solar cell according to any one of <1> to <10>, wherein the base material contains an ultraviolet absorbing pigment.
<12> The solar cell back surface protective sheet according to any one of <1> to <11>, wherein the outermost surface has a surface roughness of 0.01 μm or more and 0.20 μm or less.
<13> The layer including the outermost surface has a ratio of the particle size [μm] of the ultraviolet absorbing pigment contained in the layer to the layer thickness [μm] of 0.01 to 0.15 <1> to <12> It is a back surface protection sheet for solar cells as described in any one of these.
<14> The sun according to any one of <1> to <13>, 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. It is a back surface protection sheet for batteries.
<15> The back surface protection for solar cells according to any one of <1> to <14>, 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. It is a sheet.
<16> A solar cell module comprising the solar cell back surface protective sheet according to any one of <1> to <15>.
<17> 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. It is a solar cell module provided with the back surface protection sheet for solar cells as described in any one of <1>-<15> arrange | positioned on the opposite side to the located side.

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 collisions, such as dust, and is hard to produce a crack is provided. Also,
ADVANTAGE OF THE INVENTION According to this invention, the solar cell module which can obtain the stable electric power generation performance 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 protective sheet for solar cell of the present invention includes at least a first layer containing a polyolefin resin and a color pigment, a base material, a second layer containing a binder containing a (meth) acrylate resin and an ultraviolet absorbing pigment, In this order, and the Vickers hardness of the outermost surface on the second layer side of the substrate is in the range of 5.0 × 10 ⁹ Pa to 1.0 × 10 ¹¹ Pa.

In the present invention, when a solar cell module is produced using a back surface protection sheet for solar cells, the surface of the outermost layer is not simply hardened, but Vickers hardness is used as an index, and the value of Vickers hardness is By adjusting to a specific region, it is possible to achieve a good balance between improvement in sand resistance, which is a contradictory property, and prevention of cracking.
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.

In the back surface protection sheet for solar cells of the present invention, it is only necessary that the Vickers hardness on the outermost surface on the side having the second layer as viewed from the substrate satisfies a predetermined range.
Therefore, when the back surface protection sheet for solar cells of the present invention is an aspect in which, for example, the first layer, the base material, and the second layer are laminated in this order (hereinafter referred to as the first aspect), Therefore, the Vickers hardness of the surface of the second layer is adjusted to the above range.
Moreover, the back surface protection sheet for solar cells of this invention is the aspect (henceforth, 2nd aspect) which laminated | stacked four of the 1st layer, the base material, the 2nd layer, and the 3rd layer in this order, for example. In some cases, since the surface of the third layer is the outermost surface, the Vickers hardness of the surface of the third layer is adjusted to the above range.
Thus, when the back surface protection sheet for solar cells of this invention is the aspect which laminated | stacked the 1st layer, the base material, the 2nd layer, and the nth layer (n> = 3) sequentially, nth The surface of the layer may be the outermost surface, and the Vickers hardness of the surface of the nth layer may be adjusted to the above range.

~ Vickers hardness of outermost surface ~
The back surface protective sheet for solar cells has a Vickers hardness of 5.0 × 10 ⁹ Pa or more and 1.0 × 10 ¹¹ Pa or less on the outermost surface on the side having the second layer of the base material. That is, when producing a solar cell module, the second layer side seen from the substrate in the solar cell back surface protective sheet will be the outermost surface, by adjusting the Vickers hardness of this outermost surface to a predetermined range, It can withstand the impact of sand.
When the Vickers hardness is 5.0 × 10 ⁹ Pa or more, scratch resistance when external force is applied is improved, resistance when sand collides is improved, and scratches and dents that are the starting point of durability decrease It becomes difficult to follow. Further, when the Vickers hardness is 1.0 × 10 ¹¹ Pa or less, the layer does not become too hard and cracks are hardly generated in the layer.
The Vickers hardness is preferably 1.0 × 10 ¹⁰ Pa or more and 1.0 × 10 ¹¹ Pa or less, more preferably 5.0 × 10 ¹⁰ Pa or more and 8.0 × 10 ¹⁰ Pa or less for the same reason as above. .

  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 of the outermost surface can be adjusted by controlling the hardness of each layer laminated on the side having the second layer of the base material. Specifically, in the outermost layer forming the outermost surface or the outermost layer and its adjacent layers, the type and content ratio of resin in each layer, the type and degree of crosslinking of the crosslinking agent, the content and size of inorganic particles , Shape, or photocuring composition, photocuring degree, and the like can be adjusted by appropriate selection. Specific methods and components for adjusting the Vickers hardness will be described in detail in the second layer described later.

-First embodiment-
The back surface protection sheet for solar cells according to the first aspect of the present invention is configured by laminating a first layer, a base material, and a second layer in this order. Hereinafter, each layer and the substrate will be described in detail.

(First layer)
The 1st layer which comprises the back surface protection sheet for solar cells of this invention contains polyolefin resin and a coloring pigment at least. The first layer can be further formed using inorganic particles, other additives, and the like.

-Color pigment-
The first layer contains at least one color pigment. The coloring 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 decrease in surface resistance.
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 first layer in, the area of the first ^layer, the range of 1g / ^{m 2} ~30g / m 2 is preferably in the range of ^5g / ^{m 2 ~2} / m 2 More preferred.
Further, as will be described later, when the first layer is formed in a laminated structure, the thickness of the first 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. Moreover, the adhesive force with EVA becomes high. 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 melt flow rate (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 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 first layer will be described.
There is no restriction | limiting in particular as a form of a 1st layer, You may be comprised in any of a single layer structure or a multilayer structure. When the first 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 of “A layer / B layer / C layer” are laminated It may be configured as a polyolefin resin multilayer film having

  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 in terms of excellent laminating properties when the B layer is 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 first 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.

(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 stabilizers, oxidation stabilizers, ultraviolet light absorbers, anti-wrinkle stabilizers, organic lubricants, organic lubricants, and the like) as long as the effects of the present invention are not impaired. System fine particles, fillers, antistatic agents, nucleating agents, dyes, dispersing agents, 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-naphthalenedicarboxylic 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.
Moreover, 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 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 and solidifying 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 second layer described later while satisfying the amount of the ultraviolet absorbing pigment required as the total amount in the sheet. . Thereby, in the second layer, the content ratio of the inorganic oxide particles can be easily increased, and the surface Vickers hardness 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 second layer described later, and the preferred embodiment is also the same.

  When the substrate contains an ultraviolet absorbing pigment, the content of the ultraviolet absorbing pigment in the substrate is preferably 1% by mass to 20% by mass and 3% by mass to 10% by mass with respect to the resin constituting the substrate. More preferred. When the content of the ultraviolet absorbing pigment in the substrate is 1% by mass or more, the amount of the ultraviolet absorbing pigment contained in the second layer is reduced, and it becomes easy to add a desired amount of inorganic oxide particles. Further, when the content of the ultraviolet absorbing pigment is 20% by mass or less, it is advantageous in terms of preventing embrittlement of the substrate.

(Second layer)
The 2nd layer which comprises the back surface protection sheet for solar cells of this invention contains the binder containing a (meth) acrylate resin and an ultraviolet absorption pigment at least. In the first aspect, the surface of the second layer has Vickers hardness in the above range and is excellent in sand resistance.

-UV absorbing pigment-
The second 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 size of 0.2 μm to 0.5 μm is more preferable from the viewpoint of dispersibility and cost with respect to a (meth) acrylate resin (particularly acrylic polyol-based resin) described later.
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 a (meth) acrylate resin (particularly acrylic polyol resin) described later.

The content of the ultraviolet absorbing pigment in the second layer is preferably in the range of 10% by mass to 60% by mass and more preferably in the range of 30% by mass to 50% by mass with respect to the total mass of the layer.
When the content of the ultraviolet absorbing pigment is 10% by mass or more, the ultraviolet absorbing performance is good, and it is advantageous in terms of preventing embrittlement of the base material and the second layer even when exposed to the outdoors for a long time. , 60 mass% or less is advantageous in that the surface roughness of the second layer can be reduced.

-Binder-
The second 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 the resin materials, and the surface hardness of the second layer 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 light absorber, and a light stabilizer is preferable, and Hals hybrid polymer (registered trademark) (manufactured by Nippon Shokubai Co., Ltd.) containing this copolymer as an active ingredient is preferable. It can be used suitably.
In addition, about the detail of an ultraviolet light absorber and a light stabilizer, the description of 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 surface hardness of the second layer is further increased. Details of the crosslinking agent will be described later.

-Crosslinking agent-
The second layer can contain at least one crosslinking agent that crosslinks the (meth) acrylate resin. The crosslinking agent can react with, for example, a hydroxyl group serving as a crosslinking point in the (meth) acrylate resin to crosslink and cure the second layer, thereby further increasing the surface hardness of the second layer.

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 excellent curability for the second 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.

-Curable resin-
A 2nd layer can be comprised in the layer (hard coat layer) hardened | cured by UV light or a heat | fever including the resin hardened | cured by provision of ultraviolet (UV) light or a heat | fever with (meth) acrylate resin. Thereby, the surface hardness of the second layer can be further increased.

The second layer may contain a radiation curable resin that is a resin curable by ultraviolet light.
Examples of the radiation curable resin include a compound having a reactive group such as one or two or more unsaturated bonds, and specific examples include a compound having an acrylate functional group. Among these, a compound containing a (meth) acrylate structure is preferable.
Examples of the compound having one unsaturated bond include ethyl (meth) acrylate, ethylhexyl (meth) acrylate, styrene, methylstyrene, N-vinylpyrrolidone and the like. Examples of the compound having two or more unsaturated bonds include polymethylolpropane tri (meth) acrylate, tripropylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, penta Erythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dipentaerythritol penta (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and the like A polyfunctional compound modified with ethylene oxide (EO) or the like, or a reaction product of the above polyfunctional compound and (meth) acrylate (eg poly (meth) acrylate ester of polyhydric alcohol) It can be mentioned.
A preferred compound as the (meth) acrylate is a compound having three or more unsaturated bonds. When a compound having three or more unsaturated bonds is used, the crosslinking density of the layer is improved and the hardness is improved. Specifically, as the compound having three or more unsaturated bonds, pentaerythritol triacrylate, pentaerythritol tetraacrylate, polyester polyfunctional acrylate oligomer (trifunctional to 15 functional), urethane polyfunctional acrylate oligomer (trifunctional to 15). As a commercially available product, for example, A-DPH, A-TMMT (both manufactured by Shin-Nakamura Chemical Co., Ltd.) and the like can be mentioned.

As the radiation curable resin, in addition to the above compounds, a polyester resin having a relatively low molecular weight (number average molecular weight 300 to 80,000, preferably 400 to 5000) having a reactive group such as an unsaturated double bond, poly Ether resins, acrylic resins, epoxy resins, urethane resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiol polyene resins, and the like can also be used.
Here, the resin includes all dimers, oligomers, and polymers other than monomers.

  Radiation curable resins can also be used in combination with solvent-drying resins (such as thermoplastic resins, which can be used as a coating only by drying the solvent added to adjust the solid content during coating). it can. By using the solvent-drying resin in combination, film defects on the coated surface can be effectively prevented. The solvent-drying resin that can be used in combination with the radiation curable resin is not particularly limited, and generally a thermoplastic resin can be used.

The thermoplastic resin is not particularly limited. For example, a styrene resin, a (meth) acrylic resin, a vinyl acetate resin, a vinyl ether resin, a halogen-containing resin, an alicyclic olefin resin, a polycarbonate resin, or a polyester resin. Examples thereof include resins, polyamide-based resins, cellulose derivatives, silicone-based resins, rubbers, and elastomers. The thermoplastic resin is preferably amorphous and soluble in an organic solvent (in particular, a common solvent capable of dissolving a plurality of polymers and curable compounds). In particular, from the viewpoints of film forming properties, transparency, and weather resistance, styrene resins, (meth) acrylic resins, alicyclic olefin resins, polyester resins, cellulose derivatives (cellulose esters, etc.) and the like are preferable.
As a commercial item, acrylic base MH-101-5 (made by Fujikura Kasei Co., Ltd.) etc. are mentioned, for example.

The second layer may contain a thermosetting resin.
The thermosetting resin is not particularly limited. For example, phenol resin, urea resin, diallyl phthalate resin, melamine resin, guanamine resin, unsaturated polyester resin, polyurethane resin, epoxy resin, aminoalkyd resin, melamine-urea cocondensation resin , Silicon resin, polysiloxane resin, and the like.

When the second layer is formed into a photocured layer, it preferably contains a photopolymerization initiator.
There is no restriction | limiting in particular as a photoinitiator, What is necessary is just to select from a well-known thing. Examples of the photopolymerization initiator include acetophenone compounds, benzophenone compounds, Michler benzoyl benzoate, α-amyloxime esters, thioxanthone compounds, propiophenone compounds, benzyl compounds, benzoin compounds, and acylphosphine oxide compounds. Compounds.
Moreover, it is preferable to mix and contain a photosensitizer, and specific examples of the photosensitizer include n-butylamine, triethylamine, poly-n-butylphosphine, and the like.

  As the photopolymerization initiator, when the radiation curable resin is a resin system having a radically polymerizable unsaturated group, an acetophenone compound, a benzophenone compound, a thioxanthone compound, benzoin, benzoin methyl ether, etc. may be used alone or in combination. It is preferable to use a mixture of seeds. Further, when the radiation curable resin is a resin system having a cationic polymerizable functional group, examples of the photopolymerization initiator include aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, metallocene compounds, benzoin sulfonic acid esters, etc. Are preferably used alone or as a mixture of two or more.

  As a photopolymerization initiator, in the case of a radiation curable resin having a radical polymerizable unsaturated group, IRGACURE 184 (manufactured by BASF) is commercially available because it has good compatibility with the radiation curable resin and little yellowing. 1-hydroxy-cyclohexyl-phenyl-ketone is preferred.

The content of the photopolymerization initiator in the second layer is preferably 1 part by mass to 10 parts by mass with respect to 100 parts by mass of the radiation curable resin. A 2nd layer can be made into desired hardness because content of a photoinitiator is 1 mass part or more. In addition, when the content of the photopolymerization initiator is 10 parts by mass or less, ionizing radiation reaches the deep part of the coated film, and internal curing is promoted.
As content of a photoinitiator, a more preferable minimum is 2 mass parts, and a more preferable upper limit is 8 mass parts. When the content of the photopolymerization initiator is in this range, a hardness distribution does not occur in the film thickness direction, and uniform hardness is likely to occur.

-Inorganic fine particles-
The second layer preferably contains at least one kind of inorganic fine particles as a curing agent for curing 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 second layer and the interlayer adhesion with the layer formed on the second 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 second 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. By including inorganic oxide particles with an aspect ratio of 300 or more and 800 or less, it is possible to increase the thickness of the layer, and even if it is thick, it is difficult to break, and the hardness of the layer itself also increases, so sand resistance is also improved. To do.
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 second layer is preferably 15% by volume or more and 40% by volume or less. When the volume ratio of the inorganic oxide particles is 15% by volume or more, the particle content does not decrease too much, and the Vickers hardness of the surface of the second layer can be maintained higher. Further, when the volume ratio of the inorganic oxide particles is 40% by volume or less, the relative amount of the particles with respect to the binder does not increase excessively, so that the effect of preventing generation of cracks in the layer is high.

-Surfactant-
Various surfactants may be added to the second layer from the viewpoint of further improving 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” manufactured by Momentive Performance Materials, Inc. -4552 "," KP341 "," KF6001 "," KF6002 "manufactured by Shin-Etsu Silicone Co., Ltd.," BYK307 "," BYK323 "," BYK330 "manufactured by Big 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 second 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 second 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 thickness of the second layer may be appropriately selected depending on the use and the like, but is preferably 0.2 μm to 10 μm, more preferably 0.5 μm to 7 μm. The thickness of the second layer can be controlled by adjusting the coating amount of the coating liquid for coating and forming the second layer.

-Second embodiment-
The back surface protection sheet for solar cells according to the second aspect of the present invention includes a third layer on the second layer in addition to the first layer, the base material, and the second layer laminated in the first aspect. This layer is provided. By having the third layer in addition to the second layer, it is possible to separate the functions between the layers, and as a result, there is an advantage that the hardness of the outermost surface can be easily increased and smoothed.

The details of the first layer and the substrate in the second embodiment are the same as in the first embodiment, and the preferred embodiments are also the same.
In addition, the second layer in the second embodiment can be configured in the same manner as in the first embodiment, and the preferred embodiment is also the same, but it can also be configured to include an elastic recovering resin described later. This is a preferred embodiment.

-Elastic recovery resin-
When the second layer has the third layer thereon, the second layer may be formed into a layer having an elastic recovery function that is self-repaired when sand or dust collides. Specifically, the second layer may be configured as a layer having a Vickers hardness of 1.0 × 10 ⁹ Pa or less and an elastic recovery rate of 60% or more.
By having a second layer containing an elastic recovering resin under the third layer, it is possible to absorb the impact when sand or dust collides with the third layer, thereby improving sand resistance. Can do.

  When the second layer is provided as a layer having the above-described hardness and elastic recovery rate, 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 (eg, urethane resin, phenol resin, urea resin (urea resin), phenoxy resin, silicone resin, polyimide resin, diallyl phthalate resin, furan resin, bismaleimide resin , Cyanate resin, etc.).

Among these, a photocurable resin is preferable, and a urethane (meth) acrylate resin is preferable from the viewpoint of easy adjustment of hardness.
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 aspect in which the second layer contains a fluorine atom is preferable in terms of surface antifouling property and the like.
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-
When providing a 2nd layer as a layer which has the above hardness and an elastic recovery factor, as a suitable other aspect of a 2nd layer, it can comprise, for example as a layer containing a polyrotaxane.

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 linear molecule preferably has a molecular weight of 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. At the time of preparation, when the maximum inclusion amount is 1, for example, the mixing time is 1 to 48 hours so that the inclusion amount is 0.001 to 0.6 with respect to 1, and the mixing temperature is 0 ° C. to It can be 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 N, N-dimethylformamide (DMF) to obtain a polyrotaxane having a blocking group introduced therein.

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 second layer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more in terms of higher haze value and reflectivity maintenance rate. 30 mass% or more is still more preferable, and 50 mass% or more is especially preferable.
In addition, the content of the polyrotaxane having a fluorine atom-containing organic group in the second layer is preferably 0.1% by mass to 50% by mass in terms of higher haze value and reflectivity maintenance rate. More preferably, the content is more than 5% by mass and less than 30% by mass, more preferably 1% by mass to 20% by mass, and particularly preferably 10% by mass to 20% by mass.
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 2nd 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, of the polyrotaxane in a 2nd layer The content refers to the content (% by mass) of the polyrotaxane relative to the total solid content in the layer forming composition. Similarly, when forming a cured second layer 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, fluorine in the second layer The content of the polyrotaxane having an atom-containing 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 for forming second layer containing polyrotaxane-
The method for forming the second layer containing the 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 the substrate. And a method of forming the second layer by applying at least one of heat treatment and light irradiation treatment to the composition for forming a layer formed by coating.
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, a polymethrotaxane is dissolved in a dehydrating solvent such as dimethyl sulfoxide (DMSO) or DMF, and a (meth) acryloylating agent having an isocyanate group It is done by adding. 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.

(Third layer)
The 3rd layer which comprises the back surface protection sheet for solar cells which concerns on the 2nd aspect of this invention contains the binder containing a (meth) acrylate resin and an ultraviolet absorption pigment at least.

-Binder-
The third layer contains at least one binder and contains a (meth) acrylate resin as one of the binders. The (meth) acrylate resin is a relatively hard resin among the resin materials, and the surface hardness of the third layer is increased by including at least the (meth) acrylate resin.
The (meth) acrylate resin in the third layer is a resin in which (meth) acrylic acid ester is homopolymerized or copolymerized with other monomer components, and is the same as the (meth) acrylate resin in the second layer, which is preferable. The aspect is also the same.

-Curable resin-
The third layer is a layer (hard coat) that contains a (meth) acrylate resin and a curable resin, specifically, an epoxy group-containing alkoxysilane, an epoxy group-free alkoxysilane, and a metal complex. Layer). Thereby, the surface hardness of the third layer can be further increased, and the alkali resistance is also high. Since it has high alkali resistance, the haze of the layer is kept low and the optical properties are excellent.

  The epoxy group-containing alkoxysilane and the epoxy group-free alkoxysilane are preferably water-soluble or water-dispersible alkoxysilanes. Water solubility or water dispersibility is preferable in terms of reducing environmental pollution caused by VOC (volatile organic compounds).

  Each of the epoxy group-containing alkoxysilane and the epoxy group-free alkoxysilane preferably has a hydrolyzable group. Silanol is produced | generated when a hydrolysable group is hydrolyzed in acidic aqueous solution, and an oligomer is produced | generated when silanols condense.

  The content ratio of the epoxy group-containing alkoxysilane to the total amount of the alkoxysilane composed of the epoxy group-containing alkoxysilane and the epoxy group-free alkoxysilane is preferably 20% by mass to 85% by mass. About the minimum of the content rate of an epoxy-group-containing alkoxysilane, 25 mass% or more is preferable and 30 mass% or more is more preferable. Moreover, about an upper limit, 80 mass% or less is preferable, and 75 mass% or less is more preferable. When the content ratio of the epoxy group-containing alkoxysilane with respect to the total amount of the alkoxysilane is within the above range, it is advantageous for improving the stability of the composition when the composition for forming the third layer is prepared, and is resistant to alkali. It becomes easy to form a strong third layer.

  The epoxy group-containing alkoxysilane is an alkoxysilane having an epoxy group. Any epoxy group-containing alkoxysilane may be used as long as it has one or more epoxy groups in one molecule, and the number of epoxy groups is not particularly limited. In addition to the epoxy group, the epoxy group-containing alkoxysilane may further have a group such as an alkyl group, an amide group, a urethane group, a urea group, an ester group, a hydroxy group, or a carboxyl group.

  As the epoxy group-containing alkoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltri Ethoxysilane, 2- (3,4-epoxycyclohexyl) ethylmethyldimethoxysilane, 2- (3,4-epoxycyclohexyl) ethylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyl A triethoxysilane etc. can be mentioned. Examples of commercially available products include KBE-403 (manufactured by Shin-Etsu Chemical Co., Ltd.).

  The epoxy group-free alkoxysilane is an alkoxysilane having no epoxy group. The epoxy group-free alkoxysilane may be an alkoxysilane having no epoxy group, and may have a group such as an alkyl group, an amide group, a urethane group, a urea group, an ester group, a hydroxy group, or a carboxyl group. Good.

  The epoxy group-free alkoxysilane is preferably a tetraalkoxysilane or trialkoxysilane, or a mixture thereof. It is preferably a mixture of tetraalkoxysilane or trialkoxysilane, and by containing a mixture of tetraalkoxysilane and trialkoxysilane, while having an appropriate flexibility when the third layer is formed, Sufficient hardness can be obtained.

  When the epoxy group-free alkoxysilane is a mixture of tetraalkoxysilane and trialkoxysilane, the molar ratio of tetraalkoxysilane and trialkoxysilane is preferably 25:75 to 85:15, and 30:70 to 80:20 is more preferable, and 30:70 to 65:35 is even more preferable. By setting the molar ratio within the above range, it becomes easy to control the degree of polymerization of the alkoxysilane within a desired range and to control the hydrolysis rate and the solubility of the aluminum chelate.

Tetraalkoxysilane is a tetrafunctional alkoxysilane, more preferably having 1 to 4 carbon atoms in each alkoxy group. Of these, tetramethoxysilane and tetraethoxysilane are particularly preferably used. By setting the number of carbon atoms to 4 or less, the hydrolysis rate of tetraalkoxysilane when mixed with acidic water does not become too slow, and the time required for dissolution until a uniform aqueous solution is shortened. Thereby, the manufacturing efficiency at the time of manufacturing a 3rd layer can be improved.
Examples of commercially available products include KBE-04 (manufactured by Shin-Etsu Chemical Co., Ltd.).

The trialkoxysilane is a trifunctional alkoxysilane represented by the following general formula (A).
RSi (OR ¹ ) ₃ (A)
In General Formula (A), R represents an organic group having 1 to 15 carbon atoms that does not include an amino group, and R ¹ represents an alkyl group having 4 or less carbon atoms (for example, a methyl group, an ethyl group, or the like).

  The trifunctional alkoxysilane represented by the general formula (A) does not contain an amino group as a functional group. That is, this trifunctional alkoxysilane has an organic group R having no amino group. When R has an amino group, if it is mixed with a tetrafunctional alkoxysilane and hydrolyzed, dehydration condensation is promoted between the produced silanols. For this reason, an aqueous composition becomes unstable and is not preferable.

  R in the general formula (A) may be an organic group having a molecular chain length in the range of 1 to 15 carbon atoms. By setting the number of carbon atoms to 15 or less, the flexibility when the third layer is formed is not excessively large, and sufficient hardness can be obtained. By setting the carbon number of R within the above range, a third layer with improved brittleness can be obtained. Moreover, the adhesiveness of other films, such as a support body, and a 3rd layer can be improved.

  Furthermore, the organic group represented by R may have a hetero atom such as oxygen, nitrogen, sulfur and the like. Adhesiveness with other films can be further improved because the organic group has a hetero atom.

  As trialkoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, propyltrimethoxysilane, Phenyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltriethoxysilane, 3-chloropropyltriethoxysilane, 3-ureidopropyltriethoxysilane, methyltriethoxysilane, methyl Trimethoxysilane, ethyltriethoxysilane, ethyltrimethoxysilane, propyltriethoxysilane, propyltrimethoxysilane, phenyltriethoxysilane, phenol It can be exemplified Le trimethoxysilane. Of these, methyltriethoxysilane and methyltrimethoxysilane are particularly preferably used. Examples of commercially available products include KBE-13 (manufactured by Shin-Etsu Chemical Co., Ltd.).

  The third layer can include a metal complex (curing agent). As the metal complex, a metal complex containing a metal selected from Al, Mg, Mn, Ti, Cu, Co, Zn, Hf, and Zr is preferable. A plurality of metal complexes can also be used in combination.

  A metal complex can be easily obtained by reacting a metal alkoxide with a chelating agent. Examples of chelating agents include β-diketones such as acetylacetone, benzoylacetone and dibenzoylmethane, β-keto acid esters such as ethyl acetoacetate and ethyl benzoylacetate.

Preferred examples of the metal complex include ethyl acetoacetate aluminum diisopropylate, aluminum tris (ethyl acetoacetate), alkyl acetoacetate aluminum diisopropylate, aluminum monoacetyl acetate bis (ethyl acetoacetate), aluminum tris (acetylacetonate) Aluminum chelate compounds such as ethyl acetoacetate magnesium monoisopropylate, magnesium bis (ethyl acetoacetate), magnesium acetoacetate magnesium monoisopropylate, magnesium bis (acetylacetonate), etc., zirconium tetraacetylacetonate, zirconium Tributoxyacetylacetonate, zirconium acetylacetate Natobisu (ethylacetoacetate), manganese acetylacetonate, cobalt acetylacetonate, copper acetylacetonate, titanium acetylacetonate, titanium oxy acetylacetonate, chelate compounds and the like. Of these, aluminum tris (acetylacetonate), aluminum tris (ethylacetoacetate), magnesium bis (acetylacetonate), magnesium bis (ethylacetoacetate), and zirconium tetraacetylacetonate are preferred, and storage stability Considering availability, aluminum tris (acetylacetonate) and aluminum tris (ethylacetoacetate), which are aluminum chelate complexes, are particularly preferable.
Examples of commercially available products include aluminum chelate A (W), aluminum chelate D, aluminum chelate M (manufactured by Kawaken Fine Chemical Co., Ltd.), and the like.

The content ratio of the metal complex is preferably 17 mol% to 70 mol% with respect to the epoxy group-containing alkoxysilane. The content ratio of the metal complex is more preferably 20 mol% or more. The metal complex content is preferably 65 mol% or less, and more preferably 60 mol% or less.
When the content ratio of the metal complex is not less than the lower limit value, excellent alkali resistance is exhibited when the third layer is formed, and when the content ratio of the metal complex is not more than the upper limit value, the dispersibility in the aqueous solution is good. And the manufacturing cost can be reduced.

-Inorganic fine particles-
The third layer preferably further contains inorganic fine particles.
Examples of the inorganic fine particles include inorganic oxide particles. As examples of the inorganic metal oxide particles, metal oxide particles such as silica particles, alumina particles, zirconia particles, and titanium particles are preferable, and silica particles are particularly preferable from the viewpoint of crosslinking with alkoxysilane.

As the silica particles, dry powdery silica produced by combustion of silicon tetrachloride can be used, but colloidal silica in which silicon dioxide or a hydrate thereof is dispersed in water is more preferably used. Examples of the silica particles include Snowtex series (Snowtex 033, Snowtex OL, etc.) manufactured by Nissan Chemical Industries.
In addition, as for colloidal silica, it is more preferable that pH at the time of adding in an aqueous composition is adjusted to the range of 2-7. When the pH is 2 to 7, the stability of silanol, which is a hydrolyzate of alkoxysilane, is better than when the pH is less than 2 or greater than 7, and the dehydration condensation reaction of the silanol proceeds faster. The increase in the viscosity of the coating liquid due to this can be suppressed.

The average particle diameter of the inorganic fine particles is preferably in the range of 2 nm to 200 nm, and more preferably in the range of 10 nm to 150 nm. The range of is more preferable.
The average particle size is determined in the same manner as the method for calculating the average particle size of the inorganic fine particles that can be contained in the second layer.

  In the third layer, the same surfactant as in the second layer may be added for the purpose of improving the smoothness of the third layer and reducing the friction on the coating film surface. By containing the surfactant, it becomes difficult for dust to adhere to the surface, and the effect of improving sand resistance can be further enhanced.

Further, the third layer may be colored by dispersing pigments, dyes, and other fine particles.
Furthermore, an ultraviolet light absorber or an antioxidant may be added to improve the weather resistance. Further, an acid (a 1% by mass aqueous solution of industrial acetic acid (manufactured by Daicel Chemical Industries)) or the like may be added.

The thickness of the third layer may be appropriately selected depending on the use and the like, but is preferably 0.2 μm to 10 μm, more preferably 0.5 μm to 3 μm, and further preferably 2 μm to 3 μm. When the thickness of the third layer is 0.2 μm or more, and further 0.5 μm or more, it is easy to obtain the outermost surface that is hard and has high smoothness. Further, if the thickness of the third layer is 10 μm or less, and further 3 μm or less, cracks are unlikely to occur.
The thickness of the third layer can be controlled by adjusting the coating amount of the coating liquid for coating and forming the third 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 second 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 second layer of the substrate may be in the range of 0.01 µm to 0.20 µm. preferable. As described in the third layer, the surface roughness of the outermost surface should be composed of a hardened layer containing an epoxy group-containing alkoxysilane, an epoxy group-free alkoxysilane and a metal complex. To adjust to the above range.
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 absorbing pigment contained in the layer forming the outermost surface and the thickness of the layer. . For example, in the layer forming the outermost surface, the ratio (= particle diameter / layer thickness) of the particle diameter (μm) of the ultraviolet absorbing pigment contained in the layer to the layer thickness (μm) is 0.01 to 0.00. The above range can be obtained by adjusting the range to 15. 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 protective sheet for solar cells of the present invention, the surface specific resistance value on the outermost surface on the side having the second layer of the substrate is 1.0 × 10 ¹¹ Ω / □ or more. It is preferably in the range of 0 × 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 / □.
The surface specific resistance value of the outermost surface may be adjusted by any method as long as the surface staticity is lowered. For example, a method of containing a conductive material such as an antistatic agent in the layer forming the outermost surface. Can be 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 back surface protection sheet for solar cells of the present invention, the ratio of fluorine atoms to carbon atoms (F / C; atomic ratio) on the outermost surface on the side having the second layer of the substrate is 0.1 or more and 0.7. The following range is preferable. The presence of fluorine atoms on the outermost surface makes it difficult for sand, dust, etc. to adhere to it. It will be excellent.
The F / C value on the outermost surface is more preferably in the range of 0.5 to 0.7.
The F / C value of the outermost surface can be adjusted by any method as long as the surface slipperiness is improved and the dust is less likely to adhere. For example, the method etc. which contain a fluorine-type compound etc. in the layer which forms the outermost surface 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 element amount on the film surface using an X-ray photoelectron spectrometer (Quantum 2000, manufactured by PHI).

  The third 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 method is the same as in the second layer.

  The composition for forming the third layer may contain a solvent and various additives in addition to the components described above. About the detail of a solvent and an additive, it is the same as that of the solvent and additive which can be contained in a 2nd layer.

<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 only needs to have a light-transmitting property through which sunlight can pass, and can be appropriately selected from base materials that 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.

[First aspect]
First, the Example of the back surface protection sheet for solar cells which concerns on the 1st aspect of this invention is shown.

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.

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

First, an average particle diameter 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). 200% rutile type titanium oxide (manufactured by Sakai Chemical Industry Co., Ltd., FTR-700) 60% 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]
One part of curing agent (KR-90, manufactured by Dainippon Ink & Chemicals, Inc.) is added to 10 parts of adhesive (LX-703VL, manufactured by Dainippon Ink & Chemicals, Inc.), and the solid content concentration is 30%. An adhesive ink diluted with ethyl acetate 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.
A polyolefin resin multilayer film is stacked in contact with the adhesive layer, Lumirror (registered trademark) X10S and a polyolefin resin multilayer film are bonded together, and a first layer (polyolefin resin multilayer film) is formed on the base film. Formed.

[Formation of second layer]
The component in the following composition was mixed and the coating composition for forming a 2nd layer was obtained.
<Composition>
・ (Meth) acrylate resin: 35 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)
Titanium oxide (ultraviolet absorbing pigment) 40 parts (D-918 (particle size 0.26 μm), manufactured by Sakai Chemical Co., Ltd.)
Silica particles (inorganic oxide particles) ... 10 parts (Sunsphere H-121-ET, manufactured by AGC)
・ 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 a second 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, it was the same as Example 1 except that the amount of the ultraviolet absorbing pigment in the coating composition forming the second layer was changed and no inorganic oxide particles were used. Thus, a protective sheet for the back surface of a solar cell for comparison was produced.

(Example 2)
In Example 1, the solar cell back surface protective sheet of the present invention was produced in the same manner as in Example 1 except that the second layer was formed as follows.
~ Formation of the second layer ~
The component in the following composition was mixed and the coating composition for forming a 2nd layer was obtained.
・ (Meth) acrylate resin 30 parts (Acrybase MH-101-5, manufactured by Fujikura Kasei Co., Ltd.)
・ Photo curable monomer (A-DPH, Shin-Nakamura Chemical Co., Ltd.) 15 parts ・ Photopolymerization initiator (IRGACURE 184, BASF Co.) 5 parts
(50 parts as resin)
・ 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 the corona treatment was performed on the surface of the base film (Lumirror (registered trademark) X10S) on which the polyolefin resin multilayer film was not laminated, the above coating composition was applied and dried at 90 ° C. for 2 minutes. . Thereafter, using a 160 W / cm air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.) with respect to the coating layer after drying in a nitrogen atmosphere having an oxygen concentration of 1.0% or less, the irradiation dose is 100 mJ / cm ² . Irradiated with ultraviolet light (UV; hereinafter the same) with a light amount. Thus, the 2nd layer whose thickness after drying is 2.0 micrometers was formed, and the solar cell back surface protection sheet of this invention was produced.

(Examples 3 to 5)
In Example 1, as shown in Table 1, in the same manner as in Example 1 except that the kind of inorganic oxide particles used for forming the second layer and the thickness of the second layer were changed, A protective sheet for the back surface of the solar cell of the invention was produced.
As the inorganic oxide particles, in Examples 3 and 4, aluminum oxide (alumina sol A-2, average particle diameter of 10 to 20 nm) manufactured by Kawaken Fine Chemical Co., Ltd. was used. In Example 5, Nissan Chemical Industries (Inc. Zirconium oxide (nanouse ZR, average particle diameter 10 nm to 30 nm) was used.

(Examples 6 to 9, Comparative Example 2)
In Example 1, as described in Table 1, except that the amount of the inorganic oxide particles used for forming the second layer was changed, in the same manner as in Example 1, for the back surface of the solar cell of the present invention A protective sheet and a protective sheet for the back side of a solar cell for comparison were prepared.

(Examples 10 to 13)
In Example 1, as shown in Table 1, in the same manner as in Example 1 except that the kind of inorganic oxide particles used for forming the second layer and the thickness of the second layer were changed, A protective sheet for the back surface of the solar cell of the invention was produced.
As the inorganic oxide particles, in Examples 10 and 11, aluminum oxide (Alumina Sol F-1000, average major axis 1400 nm, average minor axis 4 nm, aspect ratio 350) manufactured by Kawaken Fine Chemical Co., Ltd. was used. In No. 13, aluminum oxide (alumina sol F-3000, average major axis 3000 nm, average minor axis 4 nm, aspect ratio 750) manufactured by Kawaken Fine Chemical Co., Ltd. was used.

(Example 14)
In Example 1, as shown in Table 1, the amount of the (meth) acrylate resin used for forming the second layer was changed, and the same procedure as in Example 1 was performed except that the crosslinking agent was not used. The protective sheet for solar cell back surface of this invention was produced.

(Example 15)
In Example 1, as shown in Table 1, the same procedure as in Example 1 was conducted except that the ultraviolet absorbing pigment was not included in the base film and the amount of the ultraviolet absorbing pigment used for forming the second layer was changed. Thus, a protective sheet for the back surface of the solar cell of the present invention was produced.
Here, instead of Lumirror (registered trademark) X10S, a transparent polyethylene terephthalate film (Cosmo Shine 4100, manufactured by Toyobo Co., Ltd.) was used as the substrate.

(Examples 16 to 17)
In Example 1, as shown in Table 1, the solar cell back surface of the present invention was used in the same manner as in Example 1 except that an additive was added to the coating composition for forming the second layer. A protective sheet was prepared.
In Example 16, 0.1 part of a conductive polymer Baytron (polythiophene-based conductive polymer aqueous dispersion, manufactured by Bayer) was added as an additive. In Example 17, 0.1 part of conductive oxide ATO-T-1 (manufactured by Mitsubishi Materials Electronics Chemical Co., Ltd.) was added.

(Examples 18 to 20)
In Example 1, as shown in Table 1, the procedure was the same as in Example 1 except that the type and amount of the (meth) acrylate resin used in the coating composition for forming the second layer were changed. The protective sheet for solar cell back surface of this invention was produced.
As the fluorine-containing acrylic monomer, Ftop EF-PA2 manufactured by Mitsubishi Materials Electronics Chemical Co., Ltd. was used.

[Second embodiment]
Next, the Example of the back surface protection sheet for solar cells which concerns on the 2nd aspect of this invention is shown.

(Example 101)
[Base film / first layer]
In the same manner as in Example 1, a base film and a polyolefin-based resin multilayer film constituting the first layer were prepared and bonded.

[Second layer]
The component in the following composition was mixed and the coating composition for forming a 2nd layer was obtained.
・ (Meth) acrylate resin: 35 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)
Titanium oxide (ultraviolet absorbing pigment) 40 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 a second layer.

[Third layer]
The component in the following composition was mixed and the coating composition for forming a 3rd layer was obtained.
・ (Meth) acrylate resin 30 parts (Acrybase MH-101-5, manufactured by Fujikura Kasei Co., Ltd.)
Photocurable monomer (A-DPH, Shin-Nakamura Chemical Co., Ltd.) 15 parts Photopolymerization initiator (IRGACURE 184, BASF Co.) 5 parts (more than 50 parts as resin)
・ Methyl ethyl ketone (solvent) ・ ・ ・ 180 parts

After the corona treatment is applied to the surface of the second layer, the above coating composition is applied, and an air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.) of 160 W / cm in a nitrogen atmosphere with an oxygen concentration of 1.0% or less. Was used for UV irradiation with a light amount of 100 mJ / cm ² . Thus, the 3rd layer whose thickness after drying is 1.0 micrometer was formed.
As described above, the protective sheet for the back surface of the solar cell of the present invention was produced.

(Example 102)
In Example 101, the solar cell back surface protective sheet of the present invention was produced in the same manner as in Example 1 except that an alkoxysilane-based third layer was formed as described below.
~ Formation of the third layer ~
・ Alkoxysilane 1 (KBE-403, manufactured by Shin-Etsu Chemical Co., Ltd.) 30 parts ・ Alkoxysilane 2 (KBE-04, manufactured by Shin-Etsu Chemical Co., Ltd.) 10 parts ・ Acid (1% industrial acetic acid aqueous solution, Daicel Chemical Industries, Ltd.) ... 100 parts / Chelate Complex (Aluminum Chelate D, Kawaken Fine Chemicals Co., Ltd.) ... 10 parts / Silica Fine Particles (Snowtex OL, Nissan Chemical Industries, Ltd.) ... 5 Part / Surfactant (Sanded BL, Sanyo Chemical Industries, 1% aqueous solution) ... 10 parts / Surfactant ... 10 parts (Naroacty CL-95, Sanyo Chemical Industries, 1% aqueous solution)

  After performing the corona treatment on the surface of the second layer, the above coating composition was applied and heated at 90 ° C. for 2 minutes. Thereafter, it was further dried at 150 ° C. for 2 minutes to form a third layer having a thickness after drying of 1.0 μm.

(Examples 103 to 106)
In Example 101, as shown in Table 2, the solar cell back surface protective sheet of the present invention was the same as Example 101 except that inorganic oxide particles were added to the third layer and the film thickness was changed. Was made.
In Example 103, silica particles (Sunsphere H-121-ET) manufactured by AGC were used as the inorganic oxide particles. In Examples 104 and 105, aluminum oxide (alumina sol A- manufactured by Kawaken Fine Chemical Co., Ltd.) was used. In Example 106, zirconium oxide (nanouse ZR) manufactured by Nissan Chemical Industries, Ltd. was used.

(Examples 107 to 110, Comparative Example 3)
In Example 101, as shown in Table 2, the solar cell back surface protection of the present invention was performed in the same manner as in Example 101 except that the amount of the inorganic oxide particles used for forming the third layer was changed. A protective sheet for the back surface of a sheet and a solar cell for comparison was prepared.

(Examples 111 to 114)
In Example 101, as shown in Table 2, except that the kind of inorganic oxide particles used for forming the third layer and the thickness of the third layer were changed, A protective sheet for the back surface of the solar cell of the invention was produced.
In Examples 101 and 111, aluminum oxide (Alumina Sol F-1000, average major axis 1400 nm, average minor axis 4 nm, aspect ratio 350) manufactured by Kawaken Fine Chemical Co., Ltd. was used as the inorganic oxide particles. Examples 112 and 113 Then, aluminum oxide (alumina sol F-3000, average major axis 3000 nm, average minor axis 4 nm, aspect ratio 750) manufactured by Kawaken Fine Chemical Co., Ltd. was used.

(Examples 115-119)
In Example 101, as shown in Table 2, the solar cell back surface protective sheet of the present invention was produced in the same manner as in Example 101 except that the thickness of the third layer was changed.

(Examples 120 and 121)
In Example 101, as shown in Table 2, the resin composition of the second layer was changed, and the second layer was formed as follows. A protective sheet for the back surface of the solar cell was produced.
As a resin composition, in Example 120, urethane (meth) acrylate (self-healing clear (registered trademark), manufactured by NATCO Corporation) was used, and in Example 121, polyrotaxane A synthesized as described below was used.

~ Formation of the second layer ~
After corona treatment was performed on the surface on which the polyolefin resin multilayer film of Lumirror (registered trademark) X10S was not laminated, a coating composition having the composition shown in Table 2 was applied and dried at 90 ° C. for 2 minutes. Thereafter, UV irradiation was performed at a light amount of 00 mJ / cm ² using a 160 W / cm air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.) in a nitrogen atmosphere with an oxygen concentration of 1.0% or less. In this way, a second layer was formed.

~ Synthesis of 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 light absorption measurement and ¹ H-NMR measurement to calculate the inclusion amount of α-cyclodextrin, the inclusion amount was 72.
Specifically, in the ultraviolet light 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 122)
In Example 101, as shown in Table 2, the present invention was carried out in the same manner as in Example 101 except that the ultraviolet absorbing pigment was not included in the substrate and the amount of the ultraviolet absorbing pigment in the second layer was changed. A protective sheet for the back surface of a solar cell was prepared.
Here, instead of Lumirror (registered trademark) X10S, a transparent polyethylene terephthalate film (Cosmo Shine 4100, manufactured by Toyobo Co., Ltd.) was used as the substrate.

(Examples 123 and 124)
In Example 101, as shown in Table 2, the solar cell back surface protection of the present invention was performed in the same manner as in Example 101 except that an additive was added to the coating composition for forming the third layer. A sheet was produced.
In Example 123, 0.1 part of a conductive polymer Baytron (polythiophene-based conductive polymer aqueous dispersion, manufactured by Bayer) was added as an additive. In Example 124, 0.1 part of conductive oxide ATO-T-1 (manufactured by Mitsubishi Materials Electronic Chemicals) was added.

(Examples 125-127)
In Example 101, as shown in Table 2, the solar cell back surface protection of the present invention was the same as Example 101 except that the type and amount of the resin used for forming the third layer were changed. A sheet was produced.
As the fluorine-containing acrylic monomer, Ftop EF-PA2 manufactured by Mitsubishi Materials Electronics Chemical Co., Ltd. was used.

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

-1. Vickers hardness
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 the content ratio (F / C; atomic ratio) of the fluorine atom with respect to a carbon atom 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 sand removal was performed and the base material was exposed by the film thickness (μm) shaved by sand was used as an evaluation value for evaluating sand resistance.

-6. Cracking
The surface of the solar cell back sheet was visually inspected, and the degree of cracking was evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: The occurrence of cracks was not detected at all.
B: Although a slight crack was detected, there is no practical problem.
C: Cracks to the extent that causes a practical problem were detected.

  As shown in Tables 1 and 2, in the examples in which the Vickers hardness on the outermost surface was adjusted within a predetermined range, a protective sheet for the back surface of a solar cell excellent in sand resistance was obtained while preventing the occurrence of cracks. By adjusting the Vickers hardness to a specified range, the outermost layer that forms the outermost surface can be cracked and sand-resistant, regardless of whether it is a hard-coated type or an elastic-coated type with elastic recovery. It was effective in coexistence with.

Claims (17)

A first layer comprising a polyolefin resin and a colored pigment;
A substrate;
A second layer comprising a binder comprising a (meth) acrylate resin and an ultraviolet absorbing pigment;
In this order, and the Vickers hardness of the outermost surface on the second layer side of the substrate is 5.0 × 10 ⁹ Pa or more and 1.0 × 10 ¹¹ Pa or less.   The back surface protective sheet for a solar cell according to claim 1, wherein the layer including the outermost surface further includes inorganic oxide particles having an element selected from Si, Al, and Zr.   The back surface protective sheet for a solar cell according to claim 2, wherein the layer including the outermost surface has a volume ratio of the inorganic oxide particles to the binder and the inorganic oxide particles of 15 vol% to 40 vol%.   The back surface protection sheet for solar cells according to claim 2 or 3, wherein the aspect ratio of the inorganic oxide particles is 300 or more and 800 or less.   The solar cell according to any one of claims 1 to 4, wherein the (meth) acrylate resin contained in the second layer has a crosslinking point, and the (meth) acrylate resin is crosslinked with a crosslinking agent. Back surface protection sheet.   A third layer containing a binder is provided on the side of the second layer opposite to the substrate, and the outermost surface is a surface opposite to the side of the third layer having the second layer. The back surface protection sheet for solar cells of any one of Claims 1-5.   The back surface protection sheet for solar cells according to claim 6, wherein the binder contained in the third layer contains an alkoxysilane polymer.   The back surface protection sheet for solar cells according to claim 6 or 7, wherein the thickness of the third layer is 0.5 µm or more and 3 µm or less.   The solar cell back surface protection sheet according to any one of claims 1 to 8, wherein the second layer includes a urethane (meth) acrylate resin as the (meth) acrylate resin.   The back protective sheet for a solar cell according to any one of claims 1 to 9, wherein the second layer further contains a polyrotaxane as the binder.   The back surface protection sheet for solar cells of any one of Claims 1-10 in which the said base material contains a ultraviolet absorption pigment.   The solar cell back surface protection sheet according to any one of claims 1 to 11, wherein the outermost surface has a surface roughness of 0.01 µm or more and 0.20 µm or less.   The layer including the outermost surface has a ratio of the particle diameter of the ultraviolet absorbing pigment contained in the layer to the layer thickness of 0.01 to 0.15. 13. Back surface protection sheet for solar cells. ^14. The solar cell according to claim 1, wherein a surface specific resistance value of the outermost surface is 1.0 × 10 ¹¹ Ω / □ or more and 1.0 × 10 ¹⁴ Ω / □ or less. Back protection sheet.   The back surface protection sheet for solar cells according to any one of claims 1 to 14, 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 1-15.   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 1-15 arrange | positioned on the opposite side to the side in which this is located.