JP2012222227A - Back sheet for solar cells, laminated body for the solar cells, solar cell module, and manufacturing methods of the back sheet, the laminated body, and the solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back sheet for solar cells which achieves good adhesion with a sealing material.SOLUTION: A back sheet for solar cells includes: a base film; and a while layer disposed on at least one surface of the base film and containing while pigments and a binder. The binder contains a polymeric resin and a tackifier.

Description

  The present invention relates to a solar cell backsheet, a solar cell laminate, a solar cell module, and a method for producing them.

Solar cells are a power generation system that emits no carbon dioxide during power generation and has a low environmental load, and have been rapidly spreading in recent years.
The solar cell module is usually a front side glass on which sunlight is incident and a so-called back sheet (also referred to as a back protective sheet) arranged on the side opposite to the side on which sunlight is incident (back side). Between the front surface glass and the solar battery cell, and between the solar battery cell and the back sheet, respectively, EVA (ethylene-vinyl acetate) resin. It is sealed with a sealing material such as.

  Since the solar cell module is used for a long time in harsh environments such as outdoors, high reliability is required in terms of moisture and heat resistance and weather resistance. The back sheet has a function of preventing moisture from entering from the back surface of the solar cell module, and conventionally glass or fluororesin has been used, but in recent years, a polyester sheet seems to be used from the viewpoint of cost. It is becoming. The back sheet is not a polymer sheet consisting of a simple single-layer polyester sheet, but a single-layer or multi-layer polymer sheet having various functions as shown below using a polyester sheet as a base film. There is a case.

  As the function, in particular, the back sheet is required to have light reflection performance by adding inorganic fine particles which are white pigments such as titanium oxide to the back sheet. This is to increase power generation efficiency by irregularly reflecting light that has passed through the cell out of sunlight incident from the front side of the module and returning it to the cell. About this point, the example of the white polyethylene terephthalate film to which the white inorganic fine particle was added is disclosed (for example, refer patent documents 1 and 2). Moreover, the example of the back surface protection sheet which has a white ink layer containing a white pigment is also disclosed (for example, refer patent document 3). Moreover, the example which provides the weather resistant layer which provides functions, such as water-resistant decomposition property, to a back seat | sheet is also known (refer patent document 2 and 3).

  However, the backsheets of these polymer sheets have insufficient adhesion with a sealing material such as EVA, and the backsheet peels off from the sealing material when operated for a long period of time. There is a known problem of intrusion (see Patent Document 1). If peeling of the back sheet from the sealing material occurs, even if a weather resistant layer is laminated on the back sheet, the performance cannot be exhibited in the first place, so in the field of the back sheet which is a polymer sheet, the weather resistant layer itself From the viewpoint of weather resistance, the first requirement is to maintain a strong adhesion between the backsheet and the EVA sealing material as a result rather than performance.

  In order to solve this problem, in order to obtain strong adhesion between the back sheet and the EVA sealing material, a method of providing an easy-adhesive layer on the outermost layer of the back sheet is known. For example, Patent Document 1 describes a technique in which a thermal adhesive layer (also referred to as an easy-adhesion layer) formed by diluting a styrene / olefin copolymer resin in an organic solvent on a white polyethylene terephthalate film is described. ing.

Japanese Patent Laid-Open No. 2003-060218 Japanese Patent Laid-Open No. 2002-100788 JP 2006-210557 A

When the present inventors examined the adhesive strength with the EVA sheet used as the sealing material for the solar cell backsheets described in Patent Documents 1 to 3, it was found that the adhesive strength was insufficient in the first place.
The problem to be solved by the invention is to provide a protective sheet for a solar cell that has good adhesion to a sealing material.

Conventionally, when a low molecular weight compound is added to a back sheet, it has been generally considered that when a back sheet for a solar cell is attached to a solar cell module, the durability is negatively affected. Therefore, it has been generally studied to reduce the content of the low molecular compound in the outermost layer of the backsheet.
On the other hand, as a result of intensive studies by the present inventors for the purpose of solving the above-mentioned problems, an easy adhesion layer is not separately provided between the white layer and the sealing material, and the white layer containing the white pigment has a low molecular weight. By adding the tackifier which is a compound, it came to discover that the adhesive force of sealing materials, such as EVA, and the white layer which is the outermost layer of a backsheet becomes favorable.
That is, the configuration of the present invention, which is a specific means for solving the above problems, is as follows.

[1] It has a base film and a white layer containing a white pigment and a binder disposed on at least one surface side of the base film, and the binder contains a polymer resin and a tackifier. A solar cell backsheet.
[2] The solar cell backsheet according to [1], wherein the white pigment is titanium oxide fine particles.
[3] The solar cell according to [1] or [2], wherein a volume fraction of the white pigment and the binder in the white layer is in a range of 30:70 to 80:20. Back sheet.
[4] The solar cell as described in any one of [1] to [3], wherein the content of the tackifier with respect to the polymer resin is 1 to 30% by mass in the binder. Back sheet.
[5] The solar cell backsheet according to any one of [1] to [4], wherein the polymer resin in the binder is a polyolefin resin.
[6] The solar cell backsheet according to any one of [1] to [5], wherein a minimum film-forming temperature of the polymer resin in the binder is 25 ° C. or higher.
[7] The solar cell backsheet according to any one of [1] to [6], wherein the tackifier is made of a rosin derivative.
[8] The solar cell backsheet according to any one of [1] to [7], wherein the tackifier has a molecular weight of 200 to 1000.
[9] A step of laminating a white layer forming composition containing a white pigment and a binder on at least one surface side on the base film to form a white layer, and the binder of the white layer forming composition Contains a polymer resin and a tackifier, and a method for producing a solar cell backsheet.
[10] The white layer forming composition is a white layer coating liquid that is a water-based paint of a resin emulsion containing a white pigment and a binder, and the white layer coating liquid is optionally formed on the base film or the base film. The manufacturing method of the solar cell backsheet as described in [9] including the process apply | coated on the other layer which may be provided in.
[11] The method for producing a solar cell backsheet according to [9] or [10], wherein a minimum film-forming temperature of the polymer resin in the binder is 25 ° C. or higher.
[12] A solar cell backsheet produced by the method for producing a solar cell backsheet according to any one of [9] to [11].
[13] The back sheet for solar cells according to any one of [1] to [8] and [12], and is directly adhered to at least the white layer side surface of the solar cell protective sheet, And a polymer layer containing an ethylene-vinyl acetate copolymer.
[14] A transparent front substrate on the side on which sunlight is incident, a solar cell element, a sealing material that seals the solar cell element, and a side of the sealing material that is opposite to the front substrate. The solar cell backsheet according to any one of [1] to [8] and [12], wherein the solar cell backsheet is bonded to the sealing material. And a solar cell module, wherein the white layer of the solar cell backsheet is directly bonded to the sealing material.
[15] A solar cell element, a step of sealing the solar cell element with a sealing material, a step of adhering a transparent front substrate on the side where sunlight is incident on one surface of the sealing material, It has the process of adhere | attaching the solar cell backsheet as described in any one of [1]-[8] and [12] on the opposite side to the said front substrate of the said sealing material, The said solar cell back The manufacturing method of the solar cell module characterized by including the process of making the said white layer of a sheet | seat and the said sealing material contact directly, and making it adhere | attach at the temperature of 180 degrees C or less.

  ADVANTAGE OF THE INVENTION According to this invention, the solar cell backsheet with favorable adhesive force with a sealing material is provided.

It is a section schematic diagram showing roughly an example of composition of a solar cell module of the present invention. It is a section schematic diagram showing roughly an example of composition of a back sheet for solar cells of the present invention. It is a section schematic diagram showing roughly other examples of composition of a back sheet for solar cells of the present invention. It is a section schematic diagram showing roughly other examples of composition of a back sheet for solar cells of the present invention.

In the following, the solar cell backsheet of the present invention and materials used therefor will be described in detail.
The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Back sheet for solar cells]
The solar cell backsheet of the present invention has a base film, and a white layer containing a white pigment and a binder disposed on at least one surface side of the base film, and the binder is a polymer resin. A tackifier is included.
Hereinafter, the details of preferred embodiments of the configuration, each component, the production method, etc. of the solar cell backsheet of the present invention will be described.

<Configuration of solar cell backsheet>
2 to 4 show an example of the configuration of the solar cell backsheet of the present invention, and FIG. 1 shows an example of the configuration of a solar cell module using the solar cell backsheet. In the solar cell backsheet 20 of FIG. 2, the white layer 16 is provided on one surface of the base film 18. When using the solar cell backsheet of this invention as an aspect without such a weather-resistant layer, it may be called a solar cell backsheet member. Furthermore, the undercoat layer 14 may be provided as another layer between the base film 18 and the white layer 16 as shown in FIG.
In the solar cell backsheet of the present invention, it is preferable that a weather-resistant layer is provided on the other surface of the base film 18 as shown in FIG. The base film 18 is preferably provided with two weathering layers, a weathering layer first layer 11 and a weathering layer second layer 12.
In FIG. 1, the preferable arrangement | positioning position of the solar cell backsheet of this invention in a solar cell module is shown. The solar cell backsheet 20 of the present invention has good adhesion between the white layer 16 and the sealing material 22 that seals the solar cell element 20 of the solar cell module 10. Therefore, it is not necessary to provide an adhesive layer between the white layer 16 of the solar cell backsheet 20 of the present invention and the sealing material 22 of the solar cell module 10 from the viewpoint of adhesion. In the solar cell module 10 of the present invention, a transparent front substrate 26 is preferably disposed on the side of the sealing material 22 opposite to the solar cell backsheet of the present invention.

<Each component of back sheet for solar cell>
Hereinafter, a preferable aspect is demonstrated about each structural member which comprises the solar cell backsheet of this invention.

(Base film)
The solar cell backsheet of the present invention has a base film.
The material of the base film is not particularly limited, and for example, polyester, polyolefin such as polypropylene or polyethylene, or fluorine-based polymer such as polyvinyl fluoride is used.
Among these, the material of the base film is preferably polyester from the viewpoints of cost and mechanical strength.

The polyester is preferably a linear saturated polyester synthesized from an aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof.
Specific examples of such linear saturated polyesters include polyethylene terephthalate (PET), polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylenedimethylene terephthalate), and polyethylene-2,6-naphthalate.
Among these, polyethylene terephthalate or polyethylene-2,6-naphthalate is particularly preferable from the viewpoint of the balance between mechanical properties and cost.

  The polyester may be a homopolymer or a copolymer. Further, the polyester may be blended with a small amount of another type of resin such as polyimide.

The carboxyl group content in the polyester is preferably 50 equivalents / t or less, more preferably 35 equivalents / t or less with respect to the polyester. When the carboxyl group content is 50 equivalents / t or less, hydrolysis resistance can be maintained, and a decrease in strength when subjected to wet heat aging can be suppressed to be small. The lower limit of the carboxyl group content is preferably 2 equivalents / t in terms of maintaining adhesiveness with a layer formed on the polyester (for example, a white layer).
The carboxyl group content in the polyester can be adjusted by polymerization catalyst species and film forming conditions (film forming temperature and time).

  As the polymerization catalyst for polymerizing the polyester, Sb-based, Ge-based, and Ti-based compounds are preferably used from the viewpoint of suppressing the carboxyl group content to a predetermined range or less, and Ti-based compounds are particularly preferable. In the case of using a Ti-based compound, an embodiment in which polymerization is performed by using the Ti-based compound as a catalyst in a range of 1 ppm to 30 ppm, more preferably 3 ppm to 15 ppm is preferable. When the proportion of the Ti-based compound is within the above range, the terminal carboxyl group can be adjusted to the following range, and the hydrolysis resistance of the polymer substrate can be kept low.

  Examples of the synthesis of polyester using a Ti compound include Japanese Patent Publication No. 8-301198, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 3997756, Japanese Patent No. 3996226, Japanese Patent No. 3997866, Japanese Patent No. 39968671, The methods described in Japanese Patent No. 40000867, Japanese Patent No. 4053837, Japanese Patent No. 4127119, Japanese Patent No. 4134710, Japanese Patent No. 4159154, Japanese Patent No. 4269704, Japanese Patent No. 431538, and the like can be applied.

  The polyester is preferably solid-phase polymerized after polymerization. Thereby, a preferable carboxyl group content can be achieved. The solid-phase polymerization may be a continuous method (a method in which a tower is filled with a resin, and this is slowly heated for a predetermined time and then sent out), or a batch method (a resin is charged into a container). And a method of heating for a predetermined time). Specifically, solid-phase polymerization is described in Japanese Patent No. 2621563, Japanese Patent No. 3121876, Japanese Patent No. 3136774, Japanese Patent No. 3603585, Japanese Patent No. 3616522, Japanese Patent No. 3617340, Japanese Patent No. 3680523, Japanese Patent No. 3717392, Japanese Patent No. 4167159, etc. The method can be applied.

  The temperature of the solid phase polymerization is preferably 170 ° C. or higher and 240 ° C. or lower, more preferably 180 ° C. or higher and 230 ° C. or lower, and further preferably 190 ° C. or higher and 220 ° C. or lower. The solid phase polymerization time is preferably 5 hours to 100 hours, more preferably 10 hours to 75 hours, and still more preferably 15 hours to 50 hours. The solid phase polymerization is preferably performed in a vacuum or in a nitrogen atmosphere.

For example, the base film is obtained by melt-extruding the above polyester into a film shape and cooling and solidifying it with a casting drum to form an unstretched film. In the width direction (also referred to as the transverse direction) at a temperature of Tg ° C. to (Tg + 60) ° C. A biaxially stretched film stretched so as to be doubled is preferable.
Further, heat treatment may be performed at 180 ° C. to 230 ° C. for 1 second to 60 seconds as necessary.

The thickness of the base film is preferably 25 μm to 300 μm, and more preferably 120 μm to 300 μm. When the thickness is 25 μm or more, sufficient mechanical strength is obtained, and when the thickness is 300 μm or less, it is advantageous in terms of cost.
In particular, the polyester base material tends to withstand hydrolysis for a long period of time in a wet and heat environment, and in the present invention, the base film has a thickness of 120 μm or more and 300 μm or less, and is in the polyester. When the carboxyl group content is 2 to 50 equivalent / t, the effect of improving the wet heat durability is further exhibited.

(White layer)
The solar cell backsheet of the present invention has a white pigment and a white layer containing a binder disposed on at least one surface side of the substrate film, and the binder contains a polymer resin and a tackifier. It is characterized by.
Hereinafter, the components contained in the white layer and the method for forming the white layer will be described in order.

(1) Component contained in white layer Examples of the component contained in the white layer include a white pigment, a binder (including at least a polymer resin and a tackifier in the binder), and other additives.

-White pigment-
The first function of the white layer is to increase the power generation efficiency of the solar cell module by reflecting the light that reaches the back sheet without being used for power generation by the solar cell in the incident light and returning it to the solar cell. is there. The second function is to improve the decorativeness of the appearance when the solar cell module is viewed from the surface side. In general, when the solar cell module is viewed from the surface side, the back sheet can be seen around the solar cell, and by providing a white layer on the back sheet, the decorativeness can be improved and the appearance can be improved.

The white pigment used in the white layer is not particularly limited, and may be selected according to required reflectivity, design, etc., and may be an inorganic pigment or an organic pigment, but is preferably an inorganic pigment, and inorganic fine particles It is more preferable that
Examples of the white pigment include titanium oxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, and talc. Titanium oxide fine particles are preferable from the viewpoint of reflectivity and cost.

The white layer has a function of increasing power generation efficiency by irregularly reflecting light passing through the cell out of sunlight incident from the front surface of the solar cell module and returning it to the cell.
The light reflectance at a wavelength of 550 nm of the surface (outermost surface) on which the white layer is disposed of the base film is to control the content and layer thickness of the white pigment in the white layer within the numerical range described above or below. Thus, the reflectance can be adjusted in the direction of increasing.

The volume average particle size of the white pigment is preferably 0.03 μm to 0.8 μm, more preferably 0.15 μm to 0.5 μm. By setting the volume average particle diameter of the white pigment within this range, it is possible to suppress a decrease in light reflection efficiency.
The volume average particle diameter of the white pigment is a value measured by Microtrac FRA manufactured by Honeywell.

The preferred content of the white pigment in the white layer varies depending on the type and average particle size of the white pigment used, but if the content of the white pigment in the white layer is not too small, the reflectivity and design can be sufficiently exhibited. If not too much, it is preferable from the viewpoint of adhesiveness with the sealing material. From the viewpoint of sufficiently exerting these functions, in the solar cell backsheet of the present invention, the content of the white pigment in the white layer is preferably 3 g / m ^{2 to} 20 g / m ² , more preferably 5 g / m ^2. ˜17 g / m ² .

  In the solar cell backsheet of the present invention, from the same viewpoint, the volume fraction of the white pigment and the binder in the white layer is preferably in the range of 30:70 to 80:20, and 30: More preferably, it is in the range of 70 to 70:30, and particularly preferably in the range of 40:60 to 60:40.

-Binder-
In the present invention, the binder of the white layer includes a polymer resin and a tackifier. Hereinafter, the polymer resin and the tackifier contained in the binder will be described.

(Polymer resin)
The polymer resin in the binder is not particularly limited as long as it is not contrary to the gist of the present invention.

  Further, the minimum film forming temperature of the binder used in the present invention is preferably 25 ° C. or more, more preferably 25 to 120 ° C., and particularly preferably 30 to 100 ° C. In this specification, the minimum temperature required for the emulsion particles to fuse to form a film is referred to as the minimum film forming temperature. MFT is closely related to the glass transition temperature and the particle size of the emulsion.

The shape and usage of the polymer resin are not particularly limited as long as a polymer layer can be formed. For example, a water-dispersible polymer resin or a meltable polymer resin may be used. Further, it may be a crystalline polymer resin or an amorphous polymer resin.
Among them, in the present invention, it is preferable to use a polymer resin dispersible in a solvent from the viewpoint of being able to form the white layer by coating and further improving the adhesiveness after aging with wet heat. More preferably, the polymer resin is dispersible in water.

  The polymer resin used as the binder for the white layer may be used alone, or a plurality of the polymer resins may be mixed and used.

  Examples of the polymer resin used as the binder of the white layer include a polyolefin resin, a polyester resin, and an acrylic resin. Among these, in the present invention, it is preferable to use a polyolefin resin.

  Examples of the main chain skeleton of the polyolefin resin include an ethylene-acrylic acid ester-maleic anhydride (and / or acrylic acid) copolymer and an ethylene-propylene-maleic anhydride (and / or acrylic acid) copolymer. , Ethylene-butene-maleic anhydride (and / or acrylic acid) copolymer, propylene-butene-maleic anhydride (and / or acrylic acid) copolymer, ethylene-propylene-butene-maleic anhydride copolymer, Ethylene-propylene-acrylic ester-maleic anhydride (and / or acrylic acid) copolymer, ethylene-butene-acrylic ester-maleic anhydride (and / or acrylic acid) copolymer, propylene-butene-acrylic acid Ester-maleic anhydride (and / or acrylic ) Copolymers, ethylene - propylene - butene - acrylic ester - maleic anhydride (and / or acrylic acid) copolymers, and the like.

  The elastic modulus of the polyolefin resin used in the present invention is preferably 320 MPa, the elastic modulus of the polyolefin resin is more preferably from 10 to 250 MPa, particularly preferably from 20 to 150 MPa, and from 30 to 100 MPa. More particularly preferred.

  The method for obtaining the polyolefin resin is not particularly limited, and may be obtained commercially or synthesized. Further, an additive may be added to control the range of the elastic modulus of the polyolefin resin.

  Examples of the polyolefin resin used in the present invention that are commercially available include Arrow Base SE-1010, manufactured by Unitika Ltd., SE-1013N, SD-1010, TC-4010, TD-4010, Hitech S3148, S3121, S8512 (manufactured by Toho Chemical Co., Ltd.), Chemipearl S-120, S-75N, V100, EV210H (both manufactured by Mitsui Chemicals, Inc.) and the like can be mentioned. Among them, in the present invention, it is preferable to use Arrow Base SE-1013N manufactured by Unitika Ltd.

The binder of the white layer may contain other binders other than the polyolefin resin as long as it does not contradict the gist of the present invention.
Examples of the other binder include a polyurethane-based binder. Examples of the polyurethane binder include Superflex 110 and 460, both of which are manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
The ratio (mass ratio) of the polyolefin resin and the other binder is preferably 50:50 to 100: 0, and more preferably 80:20 to 100: 0.

-Tackfire-
The tackifier is not particularly limited as long as it can impart adhesiveness to the polymer resin used for the binder.

  The softening point of the tackifier used in the present invention is preferably 50 to 180 ° C, more preferably 60 to 170 ° C, and particularly preferably 80 to 150 ° C. Here, in the present specification, the softening point of the tackifier refers to a temperature at which thermal deformation occurs with respect to a load.

  The molecular weight of the tackifier used in the present invention is preferably 200 to 1000 from the viewpoint of adhesion to the sealing material, more preferably 200 to 800, and particularly preferably 300 to 700.

  In the binder, the content of the tackifier with respect to the polymer resin is preferably 1 to 30% by mass, more preferably 5 to 25% by mass, and particularly preferably 10 to 20% by mass. preferable. In particular, it is preferable that the content of the tackifier with respect to the polymer resin is equal to or more than the lower limit value from the viewpoint of sufficiently imparting the tackiness effect to the white layer.

  The said tack fire used for the binder of the said white layer may be used independently, and may mix and use the said several tack fire.

As preferable examples of the tackifier used in the back sheet of the present invention, rosin derivatives and petroleum resins can be used. Examples of the rosin derivative include rosin ester, polymerized rosin ester, disproportionated rosin ester, hydrogenated rosin ester, and rosin phenol. Moreover, the said petroleum resin can also be used and a hydrogenated petroleum resin can also be used.
In the present invention, the tackifier is preferably a rosin derivative.

  There is no restriction | limiting in particular also about the acquisition method of the said tack fire, You may obtain commercially and may synthesize | combine.

  Commercially available tackifiers used in the present invention include, for example, Harrier Star SK-385NS, Harrier Star SK-816E (both rosin ester, manufactured by Harima Chemical Co., Ltd.), super ester E-720 ( Rosin ester, manufactured by Arakawa Chemical Industries, Ltd.), emulsion AP-1100-NT (petroleum resin, manufactured by Arakawa Chemical Industries, Ltd.), and the like. Among them, it is preferable to use Harrier Star SK-816E in the present invention.

-Other additives-
The white layer may further contain various additives such as a surfactant, fine particles other than the white pigment, an ultraviolet absorber, an antioxidant, and the like. In particular, white layer formation for forming a white layer is possible. The composition for use is preferably prepared using a surfactant for the dispersion stability of the color pigment.

  As the surfactant, for example, known surfactants such as anionic, cationic, and nonionic surfactants can be used. Specifically, Demole EP (manufactured by Kao Corporation), NAROACTY CL95 [ Sanyo Chemical Industries, Ltd.]. The surfactant may be a single species or a plurality of species.

Examples of the fine particles other than the white pigment include inorganic oxide fillers such as silica, magnesium oxide, and tin oxide. Among these, tin oxide or silica is preferable because the decrease in adhesiveness when exposed to a humid heat atmosphere is small.
The volume average particle size of the inorganic oxide filler is preferably 10 nm to 700 nm, and more preferably 20 nm to 300 nm. By using an inorganic oxide filler having an average particle size within this range, good easy adhesion between the white layer and the adjacent layer is obtained, and particularly in a wet heat environment (for example, 85 ° C., relative humidity 85%). Adhesiveness with an adjacent layer (more preferably, a sealing material of a solar cell module, for example, a sealing material layer containing EVA) can be expressed. In addition, the volume average particle diameter of the inorganic oxide filler is a value measured by a Honeywell Microtrac FRA.
The shape of the fine particles other than the white pigment is not particularly limited, and a spherical shape, an indefinite shape, a needle shape, or the like can be used.

The content of the fine particles other than the white pigment in the white layer is preferably 5% by mass to 400% by mass, and 50% by mass to 300% by mass with respect to the total mass of the binder resin in the white layer. Is more preferable. When the content of the fine particles is 5% by mass or more, the adhesiveness when exposed to a humid heat atmosphere and the adhesion with the solar cell module sealing material when aged in a humid heat environment are good, When the content is 400% by mass or less, deterioration of the surface state of the white layer can be prevented.
In addition, as fine particles other than the inorganic oxide filler, for example, calcium carbonate, magnesium carbonate, or the like may be included.

(2) Method for forming white layer The method for producing a back sheet for a solar cell of the present invention is a method in which a white layer-forming composition containing a white pigment and a binder is laminated on at least one surface side on a base film. Including a step of forming a layer, wherein the binder of the composition for forming a white layer contains a polymer resin and a tackifier.
The white layer can be formed by a known method and is not particularly limited. For example, the substrate film may be used as a support to form a solution film or a melt film, and the white layer may be formed into a solution film or a melt film on another support in advance. You may laminate | stack the said base film through an adhesive agent etc.
Moreover, there is no restriction | limiting in particular also about the film thickness of the laminated | stacked white layer, However, It is preferable that it is 1-20 micrometers, It is more preferable that it is 2-18 micrometers, It is especially preferable that it is 3-15 micrometers.

Among them, the solar cell backsheet of the present invention is preferably formed into a solution using the base film as a support. The solution film forming method is not particularly limited and may be cast film formation or coating, but in the solar cell backsheet of the present invention, the white layer is formed by coating. It is preferable to become.
The white layer may be provided not only on one side of the base film but also on both sides. In this case, it is preferable to apply the white layer on both sides of the base film.
Moreover, when the said white layer has the other layer mentioned later between the said base film, it forms by apply | coating the said white layer directly on a base film, or on the said other layer. Can do.

  Furthermore, in the present invention, the white layer forming composition is a white layer coating liquid that is a water-based paint of a resin emulsion containing a white pigment and a binder, and the white layer coating liquid is a base film or the base film. It is more preferable to include a step of coating on another layer which may optionally be provided on the top.

Application | coating on the base film of the said composition for white layer formation can utilize well-known methods, such as a gravure coater and a bar coater, for example.
The white layer forming composition preferably has a volume ratio of white pigment to the binder resin of 30:70 to 80:20 from the viewpoint of reflection performance and film strength. Moreover, it is preferable to apply | coat this composition for white layer formation from the same viewpoint so that the coating thickness after drying may be set to 1-20 micrometers or less on the said base film. Further, it is preferable that the coating amount of the white pigment is coated to a ^{3g / m 2 ~20g / m 2} .

  Hereinafter, components that are preferably contained in the white layer forming composition when forming the white layer will be described with respect to components other than those described above as components contained in the white layer.

-Solvent-
When the white layer forming composition is a white layer coating solution, the coating solvent is not particularly limited as long as each component constituting the white layer is dispersed or dissolved and can be removed after coating. Water is preferably used, and 60% by mass or more of the solvent contained in the white layer forming composition is preferably water. Such an aqueous composition is preferable in that it is difficult to place a load on the environment, and the ratio of water is 60% by mass or more, which is advantageous in terms of explosion-proof property and safety. The proportion of water in the white layer forming composition is preferably larger from the viewpoint of environmental burden, and more preferably 70% by mass or more of water in the total solvent.

-Crosslinking agent-
The white layer forming composition preferably contains a crosslinking agent.
It is preferable that the white layer forming composition contains a crosslinking agent, whereby the binder contained in the white layer forming composition can be crosslinked to form a colored layer having adhesiveness and strength.
Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, an oxazoline-based cross-linking agent is particularly preferable from the viewpoint of ensuring adhesion after aging with wet heat with the sealing material of the solar cell module.

Specific examples of the oxazoline-based crosslinking agent include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2- Oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2'-bis- (2-oxazoline), 2,2'-methylene-bis- (2-oxazoline), 2,2′-ethylene-bis- (2-oxazoline), 2,2′-trimethylene-bis- (2-oxazoline), 2,2′-tetramethylene-bis- (2-oxazoline) ), 2,2′-hexamethylene-bis- (2-oxazoline), 2,2′-octamethylene-bis- (2-oxazoline), 2,2′-ethylene-bis- (4,4 ′) Dimethyl-2-oxazoline), 2,2'-p-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene- There are bis- (4,4′-dimethyl-2-oxazoline), bis- (2-oxazolinylcyclohexane) sulfide, bis- (2-oxazolinyl norbornane) sulfide, and the like. Furthermore, (co) polymers of these compounds can also be preferably used.
A commercially available product may be used as the oxazoline-based crosslinking agent, and for example, Epocros K2010E, K2020E, K2030E, WS500, WS700 [all manufactured by Nippon Shokubai Chemical Co., Ltd.] and the like can be used.

  The content of the crosslinking agent relative to the total solid mass of the white layer forming composition is preferably 5% by mass to 50% by mass, and preferably 20% by mass to 40% by mass with respect to the total mass of the aqueous binder. More preferred. When the content of the cross-linking agent is 5% by mass or more, a sufficient cross-linking effect can be obtained, and a decrease in strength and poor adhesion of the white layer can be suppressed. On the other hand, the pot life fall of the said composition for white layer formation can be prevented because it is 50 mass% or less.

(Other layers)
The solar cell backsheet of the present invention has the white layer on at least one surface side of the base film, but may include at least one other layer between the white layer and the base film. .
On the other hand, an embodiment in which the white layer and the base film are in direct contact is also preferable from the viewpoint of reducing the manufacturing cost and from the viewpoint of further reducing the thickness.
By having the said other layer between the said base film and the said white layer, the adhesiveness between a base film and the said white layer can be improved more.
In the solar cell backsheet of the present invention, the other layer is preferably an undercoat layer, that is, the other layer is preferably formed by coating.
On the other hand, in the solar cell backsheet of this invention, the aspect in which the said other layer is only a layer which consists of inorganic substances or organic substances other than an inorganic oxide is also preferable. That is, an embodiment in which the other layer does not contain an inorganic oxide is also preferable. For example, the other layers are preferably formed by a method other than vapor deposition of inorganic oxide, for example, coating. Moreover, when forming the said other layer by application | coating, the aspect which does not contain inorganic oxide microparticles | fine-particles etc. is also preferable.
Hereinafter, the case where the solar cell backsheet of the present invention, which is a preferred embodiment of the other layers, includes an undercoat layer will be described.

The undercoat layer can be formed by applying an undercoat layer forming composition on a base film.
The undercoat layer forming composition preferably contains at least an aqueous binder.
As the aqueous binder, polyester, polyurethane, acrylic resin, polyolefin and the like can be used. In the solar cell backsheet of the present invention, the main component of the other layer is preferably a polyester resin.
Furthermore, in addition to the water-based binder, it may contain an epoxy-based, isocyanate-based, melamine-based, carbodiimide-based or oxazoline-based crosslinking agent, anionic or nonionic surfactant, silica filler or the like. The preferred ranges of these additives and the like are the same as the preferred ranges of these additives and the like in the white layer.
The content of the aqueous binder relative to the total solid mass of the undercoat layer forming composition is preferably 50% by mass to 100% by mass, and more preferably 70% by mass to 100% by mass.

  The undercoat layer may contain various additives such as inorganic oxide filler and fine particles other than the inorganic oxide filler described later, an ultraviolet absorber, an antioxidant, and a surfactant.

The method for applying the undercoat layer-forming aqueous composition is not particularly limited.
As a coating method, for example, a gravure coater or a bar coater can be used.
The coating amount of the undercoat layer-forming aqueous composition is preferably less than 10 μm, more preferably 0.05 μm to 2 μm, and particularly preferably 0.1 μm to 1 in terms of the layer thickness after drying, from the viewpoints of adhesiveness and planarity. It is preferable to apply to the base film so as to be 5 μm.

Water is preferably used as a coating solvent for the undercoat layer-forming aqueous composition, and 60% by mass or more of the solvent contained in the undercoat layer-forming aqueous composition is preferably water. The aqueous composition is preferable in that it is difficult to load the environment, and the ratio of water is 60% by mass or more, which is advantageous in terms of explosion-proof property and safety.
The proportion of water in the undercoat layer-forming aqueous composition is preferably larger from the viewpoint of environmental load, and more preferably 70% by mass or more of water based on the total solvent.

(Weather-resistant layer)
The back sheet for a solar cell of the present invention further contains at least one of a fluorine-based resin and a silicone-acrylic composite resin on the surface of the base film opposite to the surface on which the white layer is disposed. It is preferable to have a weather-resistant layer.

  Examples of the fluorine resin contained in the composition for forming a weather resistant layer for forming the weather resistant layer include chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chloroethylene, and the like. Examples thereof include a trifluoroethylene / ethylene copolymer and a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer. Among these, from the viewpoints of solubility and weather resistance, a chlorotrifluoroethylene / vinyl ether copolymer copolymerized with a vinyl compound is preferable.

Examples of the fluorine-based resin contained in the composition for forming a weather-resistant layer include Obligato SW0011F (manufactured by AGC Co-Tech Co., Ltd.).
From the viewpoint of weather resistance and film strength, the content of the fluororesin with respect to the total solid mass of the weather resistant layer forming composition is preferably 40% by mass to 90% by mass, and 50% by mass to 80% by mass. % Is more preferable.

Examples of the silicone-acrylic composite resin contained in the weather resistant layer forming composition include Ceranate WSA1060, WSA1070 (both manufactured by DIC Corporation) and H7620, H7630, H7650 (both manufactured by Asahi Kasei Chemicals Corporation).
The content of the silicone-acrylic composite resin with respect to the total solid content mass of the weather resistant layer forming composition is preferably 40% by mass to 90% by mass, and 50% by mass to 80% by mass from the viewpoint of weather resistance and film strength. More preferably, it is mass%.

The coating amount of the weather-resistant layer forming composition from adhesion standpoint of weatherability and the base film, it is preferable that the ^{0.5g / m 2 ~15g / m 2} , 3g / m 2 ~7g / M ² is more preferable.

Although there is no restriction | limiting in particular in the method for forming the said composition for weather-resistant layer formation, It is preferable to form by application | coating.
As a coating method, for example, a gravure coater or a bar coater can be used.
Water is preferably used as a coating solvent for the weatherable layer forming composition, and 60% by mass or more of the solvent contained in the weatherable layer forming composition is preferably water. The aqueous composition is preferable in that it is difficult to load the environment, and the ratio of water is 60% by mass or more, which is advantageous in terms of explosion-proof property and safety.
The proportion of water in the composition for forming a weather-resistant layer is preferably larger from the viewpoint of environmental burden, and more preferably 70% by mass or more of water in the total solvent.

  The weather-resistant layer may contain various additives such as the inorganic oxide filler and fine particles other than the inorganic oxide filler, an ultraviolet absorber, an antioxidant, and a surfactant.

The layer thickness of the weather resistant layer is preferably 0.5 μm to 15 μm, and more preferably 3 μm to 7 μm. By setting the film thickness to 0.5 μm or more, weather resistance can be sufficiently exhibited, and by setting the film thickness to 15 μm or less, it is possible to suppress deterioration of the surface condition.
The weather-resistant layer may be a single layer or a structure in which two or more layers are laminated. The solar cell backsheet of the present invention preferably has a structure in which two weathering layers are laminated.

<Characteristics of solar cell backsheet>
(Light reflectance)
The surface (outermost surface) on which the white layer of the solar cell backsheet of the present invention is disposed preferably has a light reflectance of 70% or more at a wavelength of 550 nm. When the light reflectance is 70% or more, the light passing through the cells of the solar battery can be sufficiently returned to the cells, which is preferable in increasing the power generation efficiency. The light reflectance is more preferably 75% or more, and particularly preferably 80% or more.

[Laminated body for solar cell]
The laminate for a solar cell of the present invention is directly bonded to at least the white layer side surface of the back sheet for a solar cell of the present invention and the protective sheet for the solar cell, and an ethylene-vinyl acetate copolymer. And a polymer layer containing.
The protective sheet for a solar cell of the present invention has an adhesive layer and the like because the surface on the white layer side has good adhesion to a sealing material (eg, EVA, PVB, especially EVA) used in a solar cell module. It can be attached to both without intervention. Further, the solar cell laminate in which a sealing material such as a styrene-vinyl acetate copolymer is directly bonded to at least the white layer side surface of such a solar cell protective sheet is aged in a humid heat environment. However, the adhesion between the two is good over a long period of time.
Such a solar cell laminate may be used as it is as a sealing material itself for sealing a solar cell element, or may be used as a part of a sealing material for a solar cell module.

[Solar cell module]
The solar cell protective sheet of the present invention is suitable for the production of a solar cell module.
In the solar cell module, for example, a solar cell element that converts sunlight light energy into electric energy is disposed between the transparent substrate on which sunlight is incident and the solar cell backsheet of the present invention described above. The substrate and the backsheet are sealed with a sealing material such as an ethylene-vinyl acetate copolymer.

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 solar cell module of the present invention includes a transparent front substrate on the side on which sunlight is incident, a solar cell element, a sealing material that seals the solar cell element, and the front substrate of the sealing material. A solar cell backsheet that is disposed on the opposite side and adheres to the sealing material, the solar cell backsheet includes the solar cell backsheet of the present invention, and the solar cell backsheet The white layer is directly bonded to the sealing material.
On the other hand, in the case of using the laminate of the present invention, the solar cell module includes a transparent front substrate on which sunlight is incident, a solar cell element, a sealing material that seals the solar cell element, A solar cell backsheet that is disposed on the opposite side of the sealing material from the front substrate and adheres to the sealing material, and that is used as the solar cell backsheet and the solar cell of the present invention as the sealing material. It is preferable that a laminated body is included.
Preferably, the solar cell element, the sealing material that seals the solar cell element, the surface protective member that adheres to the sealing material and protects the light-receiving surface side, and the sealing material that adheres to the light-receiving surface are opposite to each other A back surface protection member that protects the side, the sealing material includes an ethylene-vinyl acetate copolymer (EVA), and the back surface protection member is the back sheet for a solar cell of the present invention, the back surface for the solar cell It can be set as the structure which the coloring layer of the sheet | seat adhered directly with the sealing material. If it is such a solar cell module, even if the solar cell backsheet is in a wet heat environment with EVA, it can be in close contact over a long period of time, and a long-life solar cell module can be obtained.

  The transparent front substrate may be appropriately selected from base materials that transmit light as long as the transparent front substrate has light transmittance through which sunlight can pass. 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 the solar cell element 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.

[Method for manufacturing solar cell module]
The method for producing a solar cell module of the present invention includes a solar cell element, a step of sealing the solar cell element with a sealing material, and transparency on the side where sunlight enters one surface of the sealing material. A step of adhering a front substrate; and a step of adhering the back sheet for a solar cell of the present invention to the side of the sealing material opposite to the front substrate, The method includes a step of directly contacting the fixing material and bonding the material at a temperature of 180 ° C. or lower.
The solar cell backsheet of the present invention has good adhesion between the backsheet and the encapsulant without providing a so-called easy-adhesion layer that improves the adhesion with a conventionally known EVA encapsulant. Here, the conventionally known easy-adhesion layer has to be laminated at a high temperature when sealing with the EVA sealing material. On the other hand, in the preferable aspect of the solar cell backsheet of this invention, the white layer and sealing material of a backsheet can be adhere | attached at the temperature of the said range, and manufacturing cost can be reduced.

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” is based on mass.
The volume average particle size was measured using a laser analysis / scattering particle size distribution measuring apparatus LA950 (manufactured by Horiba, Ltd.).

[Example 1]
<Preparation of base film>
-Synthesis of polyester-
A slurry of 100 kg of high-purity terephthalic acid (manufactured by Mitsui Chemicals) and 45 kg of ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) is charged with about 123 kg of bis (hydroxyethyl) terephthalate in advance, at a temperature of 250 ° C. and a pressure of 1.2 The esterification reaction tank maintained at × 10 ⁵ Pa was sequentially supplied over 4 hours, and the esterification reaction was further performed over 1 hour after the completion of the supply. Thereafter, 123 kg of the obtained esterification reaction product was transferred to a polycondensation reaction tank.

  Subsequently, 0.3% by mass of ethylene glycol was added to the polycondensation reaction tank to which the esterification reaction product had been transferred, based on the resulting polymer. After stirring for 5 minutes, an ethylene glycol solution of cobalt acetate and manganese acetate was added to 30 ppm and 15 ppm, respectively, with respect to the resulting polymer. After further stirring for 5 minutes, a 2% by mass ethylene glycol solution of a titanium alkoxide compound was added to 5 ppm with respect to the resulting polymer. Five minutes later, a 10% by mass ethylene glycol solution of ethyl diethylphosphonoacetate was added so as to be 5 ppm with respect to the resulting polymer. Thereafter, while stirring the low polymer at 30 rpm, the reaction system was gradually heated from 250 ° C. to 285 ° C. and the pressure was reduced to 40 Pa. The time to reach the final temperature and final pressure was both 60 minutes. When the predetermined stirring torque was reached, the reaction system was purged with nitrogen, returned to normal pressure, and the polycondensation reaction was stopped. And it discharged to cold water in the shape of a strand, and it cut immediately, and produced the polymer pellet (about 3 mm in diameter, about 7 mm in length). The time from the start of decompression to the arrival of the predetermined stirring torque was 3 hours.

  However, the titanium alkoxide compound used was the titanium alkoxide compound (Ti content = 4.44% by mass) synthesized in Example 1 of paragraph No. [0083] of JP-A-2005-340616.

-Solid state polymerization-
The pellets obtained above were held in a vacuum vessel maintained at 40 Pa at a temperature of 220 ° C. for 30 hours for solid phase polymerization.

-Base formation-
The pellets after undergoing solid phase polymerization as described above were melted at 280 ° C. and cast onto a metal drum to prepare an unstretched base having a thickness of about 3 mm. Thereafter, the film was stretched 3 times in the longitudinal direction at 90 ° C., and further stretched 3.3 times in the transverse direction at 120 ° C. Thus, a biaxially stretched polyethylene terephthalate support (hereinafter referred to as “PET support”) having a thickness of 250 μm was obtained. The carboxyl group content in the polyester of the PET support was 14 equivalents / t relative to the polyester.

<Formation of undercoat layer and white layer>
-Preparation of coating solution for undercoat layer-
Components in the following composition were mixed to prepare an undercoat layer coating solution.
<Composition of coating solution for undercoat layer>
・ 48 parts by weight of polyester resin aqueous dispersion
[Byronal 1245, manufactured by Toyobo Co., Ltd., solid content: 30% by mass; binder]
・ PMMA resin fine particles 0.5 double both parts
[MP-1000, manufactured by Soken Chemical Co., Ltd., solid content: 100% by mass; mat material]
・ Oxazoline compound 3 parts by mass
[Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass; cross-linking agent]
-17 parts by mass of carbodiimide compound
[Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 40% by mass; crosslinking agent]
・ Polyoxyalkylene alkyl ether 0.15 parts by mass
[Naroacty CL-95, manufactured by Sanyo Chemical Industries, solid content: 100% by mass]

-Preparation of white inorganic fine particle dispersion 1-
Components in the following composition were mixed, and the mixture was subjected to a dispersion treatment for 1 hour by a dynomill type disperser.
<Composition of white inorganic fine particle dispersion 1>
・ Titanium dioxide (volume average particle size = 0.42 μm) 36.3 parts by mass
[Taipeke R-780-2, manufactured by Ishihara Sangyo Co., Ltd., solid content: 100% by mass; white pigment]
・ 1.81 parts by mass of polyvinyl alcohol
[PVA-105, manufactured by Kuraray Co., Ltd., solid content: 100% by mass; dispersion resin]
・ Surfactant 0.114 parts by mass
[Demol EP, manufactured by Kao Corporation, solid content: 100% by mass; dispersant]
・ 46.8 parts by weight of distilled water

-Preparation of white layer coating solution-
Components in the following composition were mixed to prepare a white layer coating solution.
<Composition of white layer coating solution>
-635 parts by mass of white inorganic fine particle dispersion 1 obtained above-127 parts by mass of aqueous polyolefin resin dispersion
[Chemipearl S120, manufactured by Mitsui Chemicals, solid content: 27% by mass; polymer resin]
・ Rosin ester 10.2 parts by mass
[Harry Star SK-385NS, manufactured by Harima Kasei Co., Ltd., solid content: 50.6% by mass; tackfire]
・ Polyoxyalkylene alkyl ether 0.22 parts by mass
[Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 100% by mass; coating aid]
・ Oxazoline compound 30 parts by mass
[Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass; cross-linking agent]
・ 1.8 parts by mass of silica fine particles
[Aerosil OX-50, manufactured by Nippon Aerosil Co., Ltd., solid content: 100% by mass; additive]
・ Distilled water 163.4 parts by mass

-Formation of undercoat layer and white layer-
One side of the PET support is transported at a transport speed of 80 m / min, and after corona discharge treatment is performed at 730 J / m ² , the dry weight of the undercoat layer coating solution is 124 mg / m ² by the bar coating method. It was applied as follows. And this was dried at 180 degreeC for 1 minute, and the undercoat layer was formed. Subsequently, the white layer coating solution was applied on the undercoat layer by a bar coating method so that the dry weight was 10.5 g / m ^2, and then dried at 170 ° C. for 1 minute, whereby one side of the PET support was obtained. A white PET film in which an undercoat layer and a white layer were laminated was obtained.

<Formation of weather-resistant layer>
The following weather-resistant layer first layer and weather-resistant layer second layer were formed on the surface opposite to the surface on which the white layer of the white PET film was applied.
-Preparation of white inorganic fine particle dispersion 2-
Each component shown in the composition of the following white inorganic fine particle dispersion 2 was mixed, and the mixture was subjected to a dispersion treatment for 1 hour by a dynomill type disperser.

<Composition of white inorganic fine particle dispersion 2>
Titanium dioxide (white pigment, volume average particle size 0.42 μm) 40 parts by mass [Taipek R-780-2, manufactured by Ishihara Sangyo Co., Ltd., solid content 100%]
Polyvinyl alcohol aqueous solution 8.0 parts by mass [PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10%]
・ Surfactant [Demol EP, manufactured by Kao Corporation, solid content: 25%] 0.5 parts by mass ・ 51.5 parts by mass of distilled water

-Preparation of coating solution for forming weather resistant layer first layer-
Each component shown in the composition of the following weathering layer first layer forming coating solution was mixed to prepare a weathering layer first layer forming coating solution.

<Composition of the coating solution for forming the weather resistant layer first layer>
Acrylic / silicone binder (silicone resin, P-1) 362.3 parts by mass [Ceranate WSA-1070, manufactured by DIC, solid content: 40%]
-Carbodiimide compound (crosslinking agent, A-1) 48.3 parts by mass [Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 40%]
Surfactant 9.7 parts by mass [Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1%]
-White inorganic fine particle dispersion 2 obtained above 157.0 parts by mass-Distilled water 422.7 parts by mass

-Formation of weather resistant layer first layer-
The surface opposite to the surface on which the white layer of the white PET film is applied is conveyed at a conveyance speed of 80 m / min and subjected to corona discharge treatment under the condition of 730 J / m ² , and then the first weathering layer is formed. The coating liquid for coating was applied so that the amount of the silicone resin (P-1) was 3.0 g / m ² in terms of the coating amount, dried at 180 ° C. for 1 minute, and the dry weathering layer having a dry thickness of 3 μm. One layer was formed.

-Preparation of coating solution for forming second layer of weathering layer-
Each component shown in the composition of the coating solution for forming the weather resistant layer second layer was mixed to prepare a coating solution for forming the weather resistant layer second layer.

<Composition of the coating solution for forming the second layer of the weather resistant layer>
Acrylic / silicone binder (silicone resin, P-1) 362.3 parts by mass [Ceranate WSA-1070, manufactured by DIC, solid content: 40%]
Carbodiimide compound (crosslinking agent, A-1) 24.2 parts by mass [Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 40%]
-Surfactant 24.2 parts by mass [Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1%]
・ 703.8 parts by weight of distilled water

-Formation of second layer of weather resistant layer-
The obtained coating solution for forming the second weathering layer was applied on the first weathering layer so that the amount of the silicone resin (P-1) was 2.0 g / m ² in terms of the coating amount. And dried at 180 ° C. for 1 minute to form a second weathering layer having a dry thickness of 2.5 μm.

  In this way, a back sheet for a solar cell of Example 1 was prepared in which an undercoat layer and a white layer were provided on one side of a PET support, and one weathering layer and two weathering layers were provided on the opposite side.

  For the back sheet for solar cell of Example 1, evaluation of break elongation retention, adhesion, adhesion after wet heat aging (adhesion durability), and reflectance were performed by the following methods. Moreover, the evaluation of the shear agglomeration test related to the production suitability of the solar cell backsheet of Example 1 was performed by the method shown below. The results are shown in Table 1 below.

<Evaluation>
-1. Breaking elongation retention rate-
For the solar cell backsheet produced as described above, the elongation at break (%) represented by the following formula was calculated based on the measured values L0 and L1 of the elongation at break obtained by the following measurement method. . Those practically acceptable have a breaking elongation retention of 50% or more.
Elongation at break (%) = L1 / L0 × 100%

<Method for measuring elongation at break>
The polymer sheet is cut into a width of 10 mm and a length of 200 mm to prepare a sample A and a sample B for measurement.
The sample A is conditioned for 24 hours in an atmosphere of 25 ° C. and a relative humidity of 60%, and then a tensile test is performed with Tensilon (RTC-1210A manufactured by ORIENTEC). The length of the sample to be stretched is 10 cm, and the pulling speed is 20 mm / min. The breaking elongation of the sample A obtained by this evaluation is defined as L0.
Separately, the sample B is wet-heat treated for 50 hours in an atmosphere of 120 ° C. and a relative humidity of 100%, and then a tensile test is performed in the same manner as the sample A. The breaking elongation of Sample B at this time is L1.

-2. Adhesion before wet heat aging
The solar cell backsheet produced as described above was cut into a width of 20 mm × 150 mm to prepare two sample pieces. These two sample pieces are arranged so that the white layers face each other, and an EVA sheet (EVA sheet: SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.) cut into 20 mm width × 100 mm length is sandwiched therebetween, and a vacuum laminator It was made to adhere to EVA by hot pressing using (Nisshinbo Co., Ltd. vacuum laminating machine). The bonding conditions at this time were as follows.
Using a vacuum laminator, evacuation was performed at 128 ° C. for 3 minutes, and then pressure was applied for 2 minutes to temporarily bond. Thereafter, the main adhesion treatment was performed in a dry oven at 150 ° C. for 30 minutes. In this way, a sample for adhesion evaluation was obtained in which the 20 mm portion from one end of the two sample pieces adhered to each other was not bonded to EVA, and the EVA sheet was bonded to the remaining 100 mm portion.

The EVA non-adhered part (part of 20 mm from one end of the sample piece) of the obtained adhesion evaluation sample is sandwiched between upper and lower clips with Tensilon (RTC-1210A manufactured by ORIENTEC), with a peeling angle of 180 ° and a pulling speed of 300 mm / min. A tensile test was performed to measure the adhesive strength.
Based on the measured adhesive strength, ranking was performed according to the following evaluation criteria. Among these, ranks 4 and 5 are practically acceptable ranges.
<Evaluation criteria>
5: Adhesion was very good (60 N / 20 mm or more)
4: Adhesion was good (30N / 20mm or more and less than 60N / 20mm)
3: Adhesion was slightly poor (20N / 20mm or more and less than 30N / 20mm)
2: Adhesion failure occurred (10N / 20mm or more and less than 20N / 20mm)
1: Adhesion failure was remarkable (less than 10N / 20mm)

-3. Adhesion after wet heat aging
After the solar cell backsheet is held for 48 hours (wet heat aging) under environmental conditions of 120 ° C. and relative humidity of 100%, the above-mentioned -2. Adhesive strength was measured by the same method as in the adhesion before wet heat aging, and ranked according to the same evaluation criteria. In addition, about the adhesiveness after wet heat aging, rank 3 or more is a practically permissible range, and ranks 4 and 5 are practically more preferable ranges.

-4. Reflectance-
About the solar cell backsheet produced as described above, the reflectance for light of 550 nm using a spectrophotometer UV-2450 (manufactured by Shimadzu Corporation) with an integrating sphere attachment device ISR-2200 attached. Was measured. However, the reflectance of the barium sulfate standard plate was measured as a reference, and the reflectance of the solar cell backsheet was calculated using this as 100%.

-5. Shear aggregation test
In order to investigate the shear cohesiveness of the white layer coating liquid used for the production of the solar cell backsheet as described above, a weight of 10 kg was applied to 1 kg of the white layer coating liquid using a Marlon tester (manufactured by Kumagaya Riki Kogyo). After applying a shear load at 1200 rpm and a liquid temperature of 25 ° C. for 10 minutes, the aggregate in the white layer coating liquid was filtered through a filter, and its weight was measured.
<Evaluation criteria>
Aggregate weight of 2 mg or less: Production suitability is very good.
Aggregate weight exceeds 2 mg and 3 mg or less: Good production suitability.
Aggregate weight exceeds 3 mg and 10 mg or less: suitable for production.
Aggregate weight over 10 mg: no suitability for production.

[Examples 2 to 9, Comparative Examples 1 to 4]
In Example 1, the types of the polymer resin and the tackifier in the binder of the white layer, and the ratio of the tackifier to the polymer resin are as shown in Table 1 below so that the solid content of the polymer resin is the same. Except having each changed, it carried out similarly to Example 1, and produced the solar cell backsheet of Examples 2-9, and the solar cell backsheet of Comparative Examples 1-4.

The binders used in the examples and comparative examples are as follows.
P1: Chemipearl S120 (polyolefin resin, manufactured by Mitsui Chemicals, solid content concentration 27% by mass)
P2: Chemipearl S75N (polyolefin resin, Mitsui Chemicals, solid content concentration 24 mass%)
P3: Arrow base SE1013N (polyolefin resin, Chisso Corporation, solid content concentration 20% by mass)
P4: Vylonal MD1245 (polyester resin, Toyobo Co., Ltd., solid content concentration 30% by mass)
The tackifier used in each example and comparative example is as follows.
T1: Harrier Star SK-385NS (Rosin ester, Harima Kasei Co., Ltd., solid content concentration 50.6% by mass)
T2: Super ester E-720 (rosin ester, Arakawa Chemical Industries, solid content concentration 50.9% by mass)
T3: Harrier Star SK-816E (rosin ester, Harima Kasei Co., Ltd., solid content 54 mass%)
T4: Emulsion AP-1100-NT (petroleum resin, Arakawa Chemical Co., Ltd., solid content concentration 50.8% by mass)

  The solar cell backsheets of the obtained Examples and Comparative Examples were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1 below.

From the said Table 1, it turned out that the solar cell backsheet of each Example has favorable adhesiveness with a sealing material. Moreover, it turned out that the adhesiveness with a sealing material is also favorable after wet heat aging, On the other hand, Comparative Examples 1-4 are all aspects which do not add a tack fire, and all are adhesiveness before wet heat aging. Was bad. Moreover, about Comparative Examples 1 and 4, the adhesiveness after wet heat aging was also bad.
Moreover, according to the manufacturing method of this invention, it turned out that the solar cell backsheet of each Example can be manufactured with sufficient manufacture aptitude.

[Examples 10 to 18]
<Preparation of modules for solar cells>
3 mm thick tempered glass, EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), crystalline solar cell, EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), Examples 1-9 The back sheet for solar cell obtained in the above was superposed in this order, and the back sheet and the EVA sheet were adhered by hot pressing using a vacuum laminator (manufactured by Nisshinbo Co., Ltd., vacuum laminating machine).
At this time, the back sheet was disposed such that the surface provided with the white layer (the surface provided with no weathering layer) was in contact with the EVA sheet. Moreover, the adhesion conditions of EVA are as follows.
Using a vacuum laminator, evacuation was performed at 128 ° C. for 3 minutes, and then pressure was applied for 2 minutes to temporarily bond. Thereafter, the main adhesion treatment was performed in a dry oven at 150 ° C. for 30 minutes.
Thus, the solar cell module of Examples 10-18 which is a crystalline solar cell module each provided with the solar cell backsheet obtained in Examples 1-9 was produced.
When the power generation operation was performed using the produced solar cell modules of Examples 10 to 18, all the solar cell modules exhibited good power generation performance as solar cells.
Moreover, even after the solar cell modules of Examples 10 to 18 were held in an atmosphere of 120 ° C. and relative humidity of 100% for 48 hours, the backsheet was not peeled off and the good appearance was maintained.

DESCRIPTION OF SYMBOLS 10 Solar cell module 11 Weather resistant layer 1st layer 12 Weather resistant layer 2nd layer 14 Undercoat layer 16 White layer 18 Base film 20 Back sheet 22 for solar cells Solar cell element 24 Sealant 26 Transparent substrate

Claims (15)

A base film;
A white layer containing a white pigment and a binder disposed on at least one surface of the base film;
The back sheet for solar cells, wherein the binder contains a polymer resin and a tackifier.   The solar cell backsheet according to claim 1, wherein the white pigment is titanium oxide fine particles.   The solar cell backsheet according to claim 1 or 2, wherein a volume fraction of the white pigment and the binder in the white layer is in the range of 30:70 to 80:20.   The backsheet for a solar cell according to any one of claims 1 to 3, wherein a content of the tackifier with respect to the polymer resin is 1 to 30% by mass in the binder.   The solar cell backsheet according to any one of claims 1 to 4, wherein the polymer resin in the binder is a polyolefin resin.   The solar cell backsheet according to any one of claims 1 to 5, wherein a minimum film-forming temperature of the polymer resin in the binder is 25 ° C or higher.   The said tackifier consists of rosin derivatives, The solar cell backsheet as described in any one of Claims 1-6 characterized by the above-mentioned.   The backsheet for solar cell according to any one of claims 1 to 7, wherein the tackifier has a molecular weight of 200 to 1,000. Including a step of laminating a white layer forming composition containing a white pigment and a binder on at least one surface side of the base film to form a white layer,
The method for producing a back sheet for a solar cell, wherein the binder of the white layer forming composition contains a polymer resin and a tackifier. The white layer forming composition is a white layer coating liquid which is an aqueous paint of a resin emulsion containing a white pigment and a binder,
The back | bag for solar cells of Claim 9 including the process of apply | coating this coating liquid for white layers on the base film or the other layer optionally provided on this base film. Sheet manufacturing method.   The method for producing a back sheet for a solar cell according to claim 9 or 10, wherein the minimum film-forming temperature of the polymer resin in the binder is 25 ° C or higher.   It manufactured with the manufacturing method of the solar cell backsheet as described in any one of Claims 9-11, The solar cell backsheet characterized by the above-mentioned. The solar cell backsheet according to any one of claims 1 to 8 and 12,
A solar cell laminate, comprising: a polymer layer that is directly bonded to at least the white layer side surface of the solar cell protective sheet and that includes an ethylene-vinyl acetate copolymer. A transparent front substrate on the side where sunlight enters,
A solar cell element;
A sealing material for sealing the solar cell element;
A solar cell backsheet that is disposed on the side opposite to the front substrate of the sealing material and adheres to the sealing material;
The back sheet for solar cells includes the back sheet for solar cells according to any one of claims 1 to 8, and the white layer of the back sheet for solar cells is directly bonded to the sealing material. A solar cell module characterized by A step of sealing the solar cell element and the solar cell element with a sealing material;
Bonding a transparent front substrate on the side on which sunlight is incident on one surface of the sealing material;
A step of bonding the solar cell backsheet according to any one of claims 1 to 8 and 12 to the side of the sealing material opposite to the front substrate,
The manufacturing method of the solar cell module characterized by including the process of making the said white layer of the said solar cell backsheet and the said sealing material contact directly, and making it adhere | attach at the temperature of 180 degrees C or less.