JP5599339B2 - Solar cell back surface protective sheet, method for producing the same, and solar cell module - Google Patents

Description

  The present invention relates to a solar cell back surface protective sheet and a solar cell module provided on the side opposite to the sunlight incident side of a solar cell element.

  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 surface glass on the side on which sunlight is incident and a solar cell back surface protection sheet (hereinafter also referred to as a back sheet) disposed on the side opposite to the side on which sunlight is incident (back surface side). ) Between the front face glass and the solar battery cell and between the solar battery cell and the back sheet, respectively (EVA (ethylene-vinyl acetate). ) Sealed with resin.

  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, polyester has been used from the viewpoint of cost. It has become to. And a back sheet is not a mere polymer sheet, but may have various functions as shown below.

  As the function, for example, a white sheet such as titanium oxide added to the back sheet to have a reflective performance may be required. 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. As such a white film, a white resin film such as a method of applying a coating liquid or a white paint containing a white pigment on a stretched polyester film, a white polyester film containing a white pigment or forming a void by foaming or stretching The method of laminating is mentioned. Among these, since the material cost is low and it is easy to obtain a high reflectance, a titanium oxide kneaded type white polyester film is widely used (see Patent Document 1). The titanium oxide wrought type white resin film used in this document has a thickness of 50 μm, and is used by being laminated on another polyester substrate (weather-resistant polyester film) having a thickness of 188 μm. The reason for increasing the film thickness as such a base film is to achieve various physical properties required as a solar cell back surface protection sheet, and generally has some high physical properties such as weather resistance, voltage resistance and strength. Necessary.

  In recent years, it has been demanded to further increase the solar cell reflectivity by the solar cell back surface protection sheet to increase the power generation efficiency of the solar cell. However, conventionally, there is no known example of a solar cell back surface protective sheet in which the thickness of a white resin kneaded type white resin film including Patent Document 1 is increased, and white relative to the total of the binder and the white pigment is not known. An example of a solar cell back surface protection sheet of a type in which a white resin film having an increased pigment ratio (hereinafter also referred to as a P / P + B ratio) is laminated with a base film has not been known. Also, when a coating liquid containing a white pigment is applied on a stretched polyester film substrate, there has been no known example of a solar cell back surface protective sheet in which the P / P + B ratio is increased to increase the reflectance. .

  On the other hand, the example which raised the reflectance using the white pigment in fields other than a solar cell back surface protection sheet is also known. For example, Claim 2 of Patent Document 2 describes that a layer having an increased ratio of a white pigment to a binder is provided to increase the diffuse reflectance of the coating substrate for the reflector. Claim 1 of Patent Document 3 Suggests a mode in which a glossy unevenness of the electrophotographic transfer sheet is improved by providing a layer in which the ratio of the white pigment to the binder is increased. However, for example, Patent Document 3 discloses that the coating layer becomes brittle when the solid content volume concentration of the white pigment is increased, and it cannot be immediately converted to the solar cell back surface protection sheet field where improvement in film strength is also required. There wasn't.

JP 2008-130642 A JP 2009-276634 A JP 2007-290294 A JP 2007-248924 A

The present inventors examined a method of increasing the reflectance by increasing the thickness of a white pigment kneaded type white resin film, and found that the thickness needs to be about 300 μm. However, when the thickness of such a white pigment kneaded type white resin film is increased, it is necessary to add a large amount of white pigment in order to maintain the reflectance, which is not preferable from the viewpoint of material cost.
On the other hand, when the present inventors examined a sheet having an increased reflectance by increasing the P / P + B ratio when applying a coating liquid containing a white pigment onto a stretched polyester film substrate, It has been found that there is a problem that the adhesion between the pigments is low, particularly the adhesion deteriorates after elapse of time under wet heat conditions, and the film strength of the white pigment coating film itself is also low.

  The present invention has been made in view of the above, and the problem to be solved by the present invention is to provide a solar cell back surface protective sheet having good adhesiveness, film strength, planarity, and reflectance after wet heat aging. It is to provide.

  Here, Patent Document 4 discloses an example in which an image receiving layer having a white pigment is formed on a support through a conductive undercoat layer of 0.01 to 1 μm in the field of electrophotographic image receiving sheets. ing. This document discloses improving the elongation at break and the surface electrical resistance of the conductive undercoat layer itself, but does not mention anything about the relationship between the thickness of the conductive undercoat layer and the image-receiving layer having a white pigment. There wasn't. On the other hand, in Patent Document 3 which discloses an embodiment in which the ratio of white pigment is actually increased, a specific primer layer of 3 μm or more is provided from the viewpoint of enhancing the adhesion between the high pigment concentration layer and other layers. It has been disclosed that it is preferably provided in the meantime, and it has been suggested that there is a tendency to increase the thickness of the primer layer.

  On the other hand, the present inventors formed a primer layer having a reduced thickness against a polymer substrate having a specific range of thickness, contrary to conventional knowledge, and a binder and a white color were formed on the primer layer. By forming a white pigment layer in which the ratio of the white pigment to the total pigment is controlled within a specific high range, it has been found that the adhesion, film strength and reflectance of the white pigment layer after wet heat aging can be increased. .

  At the same time, the solar cell back surface protection sheet with this configuration has achieved high reflectivity regardless of the thickness of the white pigment layer, and it has been necessary to increase the white pigment content in order to increase the reflectivity. Compared with the white type resin sheet, the problem of the material cost that occurred when the thickness of the white pigment layer increased was also improved. That is, the inventors have found that the above-described problem can be achieved with the following configuration, and have completed the present invention.

Specific means for solving the above problems are as follows.
[1] A polymer base material having a thickness of 120 to 350 μm, an undercoat layer having a thickness of 2 μm or less, a binder and a white pigment, and the ratio of the white pigment to the total of the binder and the white pigment is 80 to 95% by mass And a white pigment layer in this order.
[2] The solar cell back surface protective sheet according to [1], wherein at least one of the white pigment layer and the undercoat layer contains 5 to 50% by mass of a crosslinking agent with respect to the binder.
[3] The solar cell back surface protective sheet according to [2], wherein the crosslinking agent is a crosslinking agent having a carbodiimide group or an oxazoline group.
[4] The undercoat layer includes at least one resin selected from the group consisting of a polyolefin resin, a polyurethane resin, a polyvinyl alcohol resin, a polyacrylic resin, and a polyester resin [1] to [3] The solar cell back surface protection sheet of any one of these.
[5] The solar cell back surface protective sheet according to any one of [1] to [4], wherein the undercoat layer contains an inorganic oxide filler.
[6] The surface of the polymer substrate is subjected to surface treatment by at least one method of corona treatment, atmospheric pressure plasma treatment, flame treatment, and flame treatment using a silane compound-introduced flame. The solar cell back surface protective sheet according to any one of [5].
[7] The solar cell according to any one of [1] to [6], wherein the polymer base material has a thermal shrinkage of 0 to 0.5% at about 150 ° C. for 30 minutes. Back protection sheet.
[8] The solar cell back surface protective sheet according to any one of [1] to [7], wherein the polymer base material is a polyester having a carboxyl group content of 35 equivalents / ton or less.
[9] The solar cell back surface protective sheet according to any one of [1] to [8], wherein a reflectance with respect to light having a wavelength of 550 nm is 75% or more.
[10] The solar cell back surface protective sheet according to any one of [1] to [9], wherein both the undercoat layer and the white pigment layer are formed by coating.
[11] A solar cell module comprising a transparent substrate on which sunlight is incident, a solar cell element, and the solar cell back surface protective sheet according to any one of [1] to [10]. .

  According to the present invention, it is possible to provide a solar cell back surface protective sheet having good adhesion, film strength, surface condition and reflectance after wet heat aging. Moreover, according to this invention, the cheap solar cell module which has the stable electric power generation efficiency can be provided.

It is the schematic which shows the cross section of the structure of the solar cell back surface protection sheet of this invention. It is the schematic which shows the cross section of the solar cell back surface protection sheet of the white pigment kneading type used by the comparative example.

Hereinafter, the solar cell back surface protective sheet and solar cell module of the present invention 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.

[Solar cell protection sheet]
The solar cell back surface protective sheet of the present invention (hereinafter also referred to as the sheet of the present invention) comprises a polymer substrate having a thickness of 120 to 350 μm, an undercoat layer having a thickness of 2 μm or less, a binder and a white pigment, and the binder. It has the white pigment layer whose ratio of the said white pigment with respect to the sum total of the said white pigment is 80-95 mass% in this order, It is characterized by the above-mentioned.
With such a configuration, the sheet of the present invention has good adhesiveness, film strength, planarity, and reflectance after wet heat aging. In addition, due to the above characteristics of the sheet of the present invention, the solar cell module using the sheet of the present invention is excellent in power generation performance due to the good surface shape and high light reflectivity of the sheet of the present invention. It is possible to stably maintain power generation performance over a long period of time without causing peeling or the like over time.
Hereinafter, the solar cell protective sheet of the present invention will be described.

<Configuration>
In FIG. 1, the structure of the solar cell protection sheet of this invention is shown. In the solar cell back surface protective sheet of the present invention, an undercoat layer 2 is laminated on a polymer substrate 1, and a white pigment layer is further laminated on the undercoat layer 2. FIG. 1 is not intended to limit the present invention. In particular, the thickness ratio of each layer in FIG. 1 is different from the actual ratio for convenience.

<Polymer substrate>
The sheet | seat of this invention contains the polymer base material of thickness 120-300 micrometers. When the thickness is 300 μm or less, particularly in the case of a polyester base material, the hydrolysis resistance is good, the effect of improving the wet heat durability is exhibited, and it can withstand long-term use. On the other hand, the thickness of 120 μm or more is essential in the present invention from the viewpoint of the withstand voltage performance of the solar cell module. However, it is preferably 300 μm or less from the viewpoint of sheet productivity.
In the present invention, when the thickness is 120 μm or more and 300 μm or less, and the carboxyl group content in the polyester described below is 35 equivalents / ton or less, the effect of improving wet heat durability is further exhibited.
The thickness of the polymer substrate is more preferably 120 to 300 μm, and particularly preferably 200 to 300 μm.

  Examples of the polymer substrate include polyesters, polyolefins such as polypropylene and polyethylene, and fluorine-based polymers such as polyvinyl fluoride. Among these, polyester is preferable from the viewpoint of cost and mechanical strength.

  The polyester used as the polymer substrate (support) in the present invention is 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 polyester include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylenedimethylene terephthalate), polyethylene-2,6-naphthalate and the like. Among these, polyethylene terephthalate or polyethylene-2,6-naphthalate is particularly preferable from the viewpoint of 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.

  When the polyester in the present invention is polymerized, it is preferable to use an Sb-based, Ge-based, or Ti-based compound as a catalyst from the viewpoint of keeping the carboxyl group content within a predetermined range, and among these, a Ti-based compound is 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.

In the present invention, the carboxyl group content in the polyester is preferably 50 equivalent / ton or less, more preferably 35 equivalent / ton or less. When the carboxyl group content is 35 equivalents / ton or less, hydrolysis resistance can be maintained, and a decrease in adhesiveness when subjected to wet heat aging can be suppressed. The lower limit of the carboxyl group content is desirably 2 equivalents / ton or more from the viewpoint of maintaining the adhesion between the layer formed on the polyester (for example, a white pigment layer).
The carboxyl group content in the polyester can be adjusted by polymerization catalyst species and film forming conditions (film forming temperature and time).

The polymer substrate is preferably surface-treated by at least one method of corona treatment, atmospheric pressure plasma treatment, flame treatment, and flame treatment using a flame introduced with a silane compound. The surface treatment may be applied to only one surface of the base material, or the surface treatment may be applied to both surfaces of the base material. When the functional layer is formed by coating, the surface treatment is preferably performed on both surfaces. Among these, it is preferable to use a corona treatment in the present invention. A preferred embodiment of the corona treatment is a corona treatment with a treatment strength range of 150 to 500 J / m ² at an output of 0.1 to 3.0 kw / electrode 1 m (representing an output per 1 m of electrode) with respect to the polymer substrate. This is a mode in which processing is performed.
In the corona treatment, the output is more preferably 0.5 to 2.5 kw / electrode 1 m, and particularly preferably 0.7 to 1.7 kw / electrode 1 m. More preferably treated intensity range is 160~450J / m ^2, and particularly preferably 170~360J / m ^2.

It is preferable that the heat shrinkage rate of the polymer substrate before and after 30 minutes at 150 ° C. is 0 to 0.5%, and more preferable heat shrinkage is 0.05% to 0.5%, and more preferably. It is 0.1 to 0.45%, more preferably 0.15% to 0.4%. The amount of heat shrinkage here refers to the average value of MD (film transport direction) and TD (direction orthogonal to the film transport direction) of measured values before and after storage at 150 ° C. for 30 minutes.
When the heat shrinkage is not more than the upper limit value of the above preferred range, peeling between layers of the solar cell protective sheet of the present invention hardly occurs due to the shrinkage. On the other hand, when the amount of heat shrinkage is 0.05% or more, it is preferable from the viewpoint that wrinkles due to dimensional change (sag) due to thermal expansion during heat treatment are less likely to occur.

<Undercoat layer>
The solar cell back surface protective sheet of the present invention is characterized in that an undercoat layer having a thickness of 2 μm or less is provided between the polymer substrate (support) and the white pigment layer. In the sheet of the present invention, by providing such a thin subbing layer, the adhesiveness after wet heat aging, film strength, and the surface state of the white pigment layer, despite the high proportion of the white pigment in the white pigment layer, Can be improved at the same time. In particular, when the thickness of the undercoat layer is 2 μm or less, the present invention has found that when the white pigment content in the white pigment layer is increased, coating repelling defects and white pigment unevenness are less likely to occur. It is.
The thickness of the undercoat layer is preferably 0.05 μm to 2 μm, more preferably 0.1 μm to 1.5 μm. When the thickness is 0.05 μm or more, it is easy to ensure necessary adhesiveness.

(Binder for undercoat layer)
The undercoat layer can contain a binder. In the present invention, as the binder, the undercoat layer preferably contains at least one resin selected from the group consisting of polyolefin resin, polyurethane resin, polyvinyl alcohol resin, polyacrylic resin and polyester resin. It is more preferable to use resin, polyolefin or the like. These binders may be used alone or in combination of two or more.

(Undercoat layer additive)
The undercoat layer may contain various additives, and preferably contains a crosslinking agent, an inorganic oxide filler, and a surfactant.
Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, it is preferable to use a carbodiimide-based crosslinking agent or an oxazoline-based crosslinking agent from the viewpoint of securing adhesiveness after wet heat aging. That is, in the present invention, the undercoat layer preferably includes a crosslinked structure derived from at least one of a carbodiimide compound-based crosslinking agent and an oxazoline compound-based crosslinking agent.

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′- Methyl-2-oxazoline), 2,2'-p-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene- Bis- (4,4′-dimethyl-2-oxazoline), bis- (2-oxazolinylcyclohexane) sulfide, bis- (2-oxazolinylnorbornane) sulfide and the like can be mentioned. Furthermore, (co) polymers of these compounds can also be preferably used.
As the oxazoline-based crosslinking agent, Epocros K2010E, K2020E, K2030E, WS500, WS700 (all manufactured by Nippon Shokubai Chemical Co., Ltd.) and the like can be used.

  Specific examples of the carbodiimide-based crosslinking agent include carbodilite V-02-L2 (manufactured by Nisshinbo Chemical Co., Ltd.) and the following compounds. Carbodilite SV-02 (Nisshinbo Chemical Co., Ltd.), Carbodilite E-01 (Nisshinbo Chemical Co., Ltd.).

  In the sheet of the present invention, the undercoat layer preferably contains 5 to 50% by mass of a crosslinking agent, more preferably 10 to 40% by mass of the crosslinking agent, and more preferably 20 to 40%. It is particularly preferable to contain a mass% crosslinking agent.

The undercoat layer preferably contains an inorganic oxide filler.
Examples of the inorganic oxide filler include silica, calcium carbonate, magnesium oxide, magnesium carbonate, and tin oxide. Among these, tin oxide and silica fine particles are preferable, and silica is more preferable in that the decrease in adhesiveness when exposed to a humid heat atmosphere is small.

  The inorganic oxide filler has a volume average particle size of preferably about 10 to 700 nm, more preferably about 20 to 300 nm. When the particle size is within this range, better easy adhesion can be obtained. The particle size is a value measured by a laser analysis / scattering particle size distribution measuring apparatus LA950 (manufactured by Horiba, Ltd.).

  There is no restriction | limiting in particular in the shape of the said inorganic oxide filler, Any things, such as a spherical form, an indeterminate form, and a needle shape, can be used.

The content of the inorganic oxide filler is preferably in the range of 5 to 400% by mass with respect to the binder in the undercoat layer. If the content of the inorganic fine particles is 5% by mass or more, good adhesiveness can be maintained when exposed to a humid heat atmosphere, and if it is 400% by mass or less, the surface of the white content layer laminated on the undercoat layer. The condition becomes difficult to deteriorate.
Among these, the content of the inorganic oxide filler is more preferably in the range of 50 to 300% by mass.

<White pigment layer>
The white pigment layer in the present invention contains a binder and a white pigment, and the ratio of the white pigment to the total of the binder and the white pigment (P / P + B ratio) is 80 to 95% by mass. The white pigment layer may further include other components such as various additives as necessary.

  The function of the white pigment layer in the present invention is to generate power of the solar cell module by reflecting the light that has passed through the solar cell and has reached the back sheet without being used for power generation, and returns it to the solar cell. It is to increase efficiency.

(White pigment)
The white pigment layer contains at least one kind of white pigment.
Examples of the white pigment include inorganic pigments such as titanium oxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, ultramarine blue, bitumen, and carbon black, and organic pigments such as phthalocyanine blue and phthalocyanine green. Can be appropriately selected and contained.

The white pigment layer in the present invention preferably contains the white pigment in the range of 2.5~8.5g / m ^2. When the content of the white pigment in the white pigment layer is 2.5 g / m ² or more, the light reflectance tends to be improved. If the content of the white pigment in the white pigment layer is 8.5 g / m ² or less, the surface shape of the white pigment layer tends to be good, and the film strength tends to be improved.
Among these, a more preferable content of the white pigment is in the range of 4.5 to 8.0 g / m ² .

  The average particle diameter of the white pigment is preferably 0.03 to 0.8 μm, more preferably about 0.15 to 0.5 μm in volume average particle diameter. When the average particle size is within the above range, the light reflection efficiency is high. The average particle diameter is a value measured by a laser analysis / scattering particle size distribution measuring apparatus LA950 (manufactured by Horiba, Ltd.).

(Binder for white pigment layer)
The white pigment layer contains at least one binder.
The content of the binder is such that the ratio of the white pigment to the total of the binder and the white pigment (P / P + B ratio) is 80 to 95% by mass, more preferably 82 to 93% by mass, and 84 to 90%. It is particularly preferable that the content is mass%. There is no known example in which the white pigment layer added with the white pigment at such a high concentration is used in the solar cell back surface protection sheet field, and the other properties of the white pigment layer have been improved by the configuration of the present invention. Thus, such a composition can be achieved. Moreover, the solar cell back surface protection sheet of this invention has a high light reflectance by setting it as such high concentration.

  Binders suitable for the white pigment layer are polyester, polyurethane, acrylic resin, polyolefin and the like, and acrylic resin and polyolefin are preferable from the viewpoint of durability. As the acrylic resin, a composite resin of acrylic and silicone is also preferable. Examples of preferred binders include Chemipearl S-120 and S-75N (both manufactured by Mitsui Chemicals, Inc.) as polyolefins, and Julimer ET-410 and SEK-301 (both Nippon Pure Chemical Industries, Ltd.) as examples of acrylic resins. Examples of composite resins of acrylic and silicone include Ceranate WSA1060, WSA1070 (both manufactured by DIC Corporation), H7620, H7630, H7650 (both manufactured by Asahi Kasei Chemicals Corporation), and the like.

(Additive for white pigment layer)
In addition to the binder and the pigment, additives such as a cross-linking agent, a surfactant, and a filler may be further added to the white pigment layer in the present invention as necessary.

Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, an oxazoline-based crosslinking agent is preferable, and specifically, an oxazoline-based crosslinking agent that can be used for an easily-adhesive layer described later can be suitably used.
When adding a crosslinking agent, as the addition amount, 5-50 mass% is preferable with respect to the binder in a white pigment layer, More preferably, it is 10-40 mass%. When the addition amount of the crosslinking agent is 5% by mass or more, a sufficient crosslinking effect is obtained while maintaining the strength and adhesiveness of the white pigment layer, and when it is 50% by mass or less, the pot life of the coating liquid is prolonged. I can keep it.

Examples of the surfactant include known surfactants such as anionic and nonionic surfactants. When adding a surfactant, the addition amount is preferably 0.1 to 15 mg / m ² , more preferably 0.5 to 5 mg / m ² . When the addition amount of the surfactant is 0.1 mg / m ² or more, generation of repellency can be suppressed and good layer formation can be obtained, and when it is 15 mg / m ² or less, adhesion can be performed satisfactorily. .

  In addition to the above pigment, an inorganic oxide filler such as silica may be further added to the white pigment layer in the present invention. When adding an inorganic oxide filler, the addition amount is preferably 20% by mass or less, more preferably 15% by mass or less, with respect to the binder in the white pigment layer. When the added amount of the inorganic oxide filler is 20% by mass or less, a necessary reflectance can be obtained while suppressing a decrease in the ratio of the pigment.

(Physical properties of white pigment layer)
In the sheet of the present invention, when a white pigment is added as a pigment to the white pigment layer to form a reflective layer, the light reflectance at 550 nm on the surface on which the white pigment layer is provided is 75% or more. preferable.
The light reflectance is the ratio of the amount of light incident from the surface of the white pigment layer of the sheet of the present invention to the amount of incident light reflected from the reflective layer and emitted from the easy-adhesive layer again.
When the light reflectance is 75% or more, the light that passes through the cell and enters the cell can be effectively returned to the cell, and the effect of improving the power generation efficiency is great. By controlling the content of the colorant in the range of 2.5 to 8.5 g / m ² , the light reflectance can be easily adjusted to 75% or more.

  When the white pigment layer is configured as a reflective layer, the thickness of the reflective layer is preferably 1 to 20 μm, more preferably 1 to 10 μm, particularly preferably 1 to 5 μm, and more particularly preferably about 1 to 2 μm. is there. When this thickness is 1 μm or more, necessary decorative properties and reflectance can be obtained, and when it is 20 μm or less, the surface shape can be kept good.

<Other functional layers>
The sheet of the present invention may have other functional layers.
Examples of the other functional layers include an easily adhesive layer and a back layer.

<Method for producing solar cell back surface protection sheet>
The solar cell back surface protective sheet of the present invention is produced by any method as long as it can form the undercoat layer and the white pigment layer in the present invention sequentially on the polymer substrate as described above. May be. In the present invention, a method of applying a coating process for applying a coating solution for an undercoat layer and a coating solution for a white pigment layer in order from the polymer support side on the polymer substrate (the sun of the present invention). The method for producing the battery back surface protective sheet) can be suitably produced.

<Manufacture of polymer substrate>
(Adjustment of polymer base resin)
The sheet | seat of this invention can use the above-mentioned resin as a polymer base material. Such polymer substrates may be obtained synthetically or commercially. When polyester is used as the polymer substrate, it is preferably obtained by synthesis. Hereinafter, a method for producing a polyester film as a polymer substrate, and more preferable polyethylene terephthalate (hereinafter, also referred to as PET) will be described.

-Esterification process-
In this invention, the esterification process which provides an esterification reaction and a polycondensation reaction and produces | generates polyester can be provided. In this esterification step, (a) an esterification reaction and (b) a polycondensation reaction in which an esterification reaction product produced by the esterification reaction is subjected to a polycondensation reaction can be provided.

(A) Esterification reaction The amount of the aliphatic diol (preferably ethylene glycol) used is 1.015 to 1.0.1 per mol of the aromatic dicarboxylic acid (preferably terephthalic acid) and, if necessary, its ester derivative. A range of 50 moles is preferred. The amount used is more preferably in the range of 1.02 to 1.30 mol, and still more preferably in the range of 1.025 to 1.10 mol. If the amount used is in the range of 1.015 or more, the esterification reaction proceeds favorably, and if it is in the range of 1.50 mol or less, for example, by-production of diethylene glycol due to dimerization of ethylene glycol is suppressed, Many characteristics such as melting point, glass transition temperature, crystallinity, heat resistance, hydrolysis resistance, and weather resistance can be kept good.

PET preferably contains 90% by mole or more of terephthalic acid and ethylene glycol, more preferably 95% by mole or more, and still more preferably 98% by mole or more.
The PET may have different properties depending on the catalyst described later, and one or more selected from a germanium (Ge) catalyst, an antimony (Sb) catalyst, an aluminum (Al) catalyst, and a titanium (Ti) catalyst. PET that is polymerized using two or more types is preferred, and more preferably, a Ti-based catalyst is used.

  Conventionally known reaction catalysts can be used for the esterification reaction and / or the transesterification reaction. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Usually, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst at an arbitrary stage before the polyester production method is completed. As such a method, for example, when a germanium compound is taken as an example, it is preferable to add the germanium compound powder as it is.

It is preferable that the manufacturing method of the sheet | seat of this invention includes the process of preparing the said polyester resin with which it uses for melt film formation by esterification reaction using a Ti-type catalyst.
A film containing a polyester resin esterified using the Ti-based catalyst is preferable because weather resistance is hardly lowered. Although not bound by any theory, it is presumed that the reason is as follows. The decrease in weather resistance of the weather resistant polyester film depends to some extent on the hydrolysis of the polyester. The esterification reaction catalyst also promotes a hydrolysis reaction that is a reverse reaction of esterification, but a Ti catalyst has a low effect of the hydrolysis reaction that is a reverse reaction. Therefore, even if the esterification reaction catalyst remains in the film after film formation to some extent, the polyester resin esterified using the Ti-based catalyst is more than the polyester resin esterified using another catalyst. Also, the weather resistance can be made relatively high.

Examples of the Ti-based catalyst include oxides, hydroxides, alkoxides, carboxylates, carbonates, oxalates, organic chelate titanium complexes, and halides. The Ti-based catalyst may be used in combination of two or more titanium compounds as long as the effects of the present invention are not impaired.
Examples of Ti-based catalysts include tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, tetra-t-butyl titanate, tetracyclohexyl titanate, tetraphenyl Titanium alkoxide such as titanate and tetrabenzyl titanate, titanium oxide obtained by hydrolysis of titanium alkoxide, titanium-silicon or zirconium composite oxide obtained by hydrolysis of a mixture of titanium alkoxide and silicon alkoxide or zirconium alkoxide, titanium acetate , Titanium oxalate, potassium potassium oxalate, sodium oxalate, potassium titanate, sodium titanate, titanium titanate-aluminum hydroxide mixture, titanium chloride, titanium chloride-aluminum chloride Miniumu mixture, titanium acetylacetonate, an organic chelate titanium complex having an organic acid as a ligand, and the like.

  Among the Ti-based catalysts, at least one of organic chelate titanium complexes having an organic acid as a ligand can be suitably used. Examples of the organic acid include citric acid, lactic acid, trimellitic acid, malic acid and the like. Among them, an organic chelate complex having citric acid or citrate as a ligand is preferable.

For example, when a chelate titanium complex having citric acid as a ligand is used, there is little generation of foreign matters such as fine particles, and a polyester resin having better polymerization activity and color tone than other titanium compounds can be obtained. Furthermore, even when using a citric acid chelate titanium complex, by adding it at the stage of the esterification reaction, a polyester resin having better polymerization activity and color tone and less terminal carboxyl groups can be obtained compared to the case where it is added after the esterification reaction. It is done. In this regard, the titanium catalyst also has a catalytic effect of the esterification reaction. By adding it at the esterification stage, the oligomer acid value at the end of the esterification reaction is lowered, and the subsequent polycondensation reaction is performed more efficiently. In addition, complexes with citric acid as a ligand are more resistant to hydrolysis than titanium alkoxides, etc., and do not hydrolyze in the esterification reaction process, while maintaining the original activity and catalyzing the esterification and polycondensation reactions It is estimated to function effectively as
In general, it is known that the greater the amount of terminal carboxyl groups, the worse the hydrolysis resistance. By reducing the amount of terminal carboxyl groups by the addition method of the present invention, improvement in hydrolysis resistance is expected. The
Examples of the citric acid chelate titanium complex are readily available as commercial products such as VERTEC AC-420 manufactured by Johnson Matthey.

  For the synthesis of Ti-based polyester using such a Ti compound, for example, Japanese Patent Publication No. 8-30119, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 397756, and Japanese Patent No. 396226 are disclosed. Japanese Patent No. 3997866, Japanese Patent No. 3996687, Japanese Patent No. 40000867, Japanese Patent No. 4053837, Japanese Patent No. 4127119, Japanese Patent No. 4134710, Japanese Patent No. 4159154, Japanese Patent No. 4269538, Japanese Patent No. The methods described in JP 2005-340616 A, JP 2005-239940 A, JP 2004-319444 A, JP 2007-204538 A, Japanese Patent No. 3436268, Japanese Patent No. 3780137, and the like can be applied.

  In the present invention, an aromatic dicarboxylic acid and an aliphatic diol are polymerized in the presence of a catalyst containing a titanium compound, and at least one of the titanium compounds is an organic chelate titanium complex having an organic acid as a ligand. It is preferable that an esterification reaction process including at least a process of adding an organic chelate titanium complex, a magnesium compound, and a pentavalent phosphate ester having no aromatic ring as a substituent in this order is provided. In this case, in addition to this esterification reaction step, production of a polyester resin comprising a polycondensation step in which a polycondensation product is produced by polycondensation reaction of the esterification reaction product produced in the esterification reaction step The aspect which produces a film with a method is more preferable. The polycondensation step will be described later.

In this case, in the course of the esterification reaction, the addition of a magnesium compound to the presence of an organic chelate titanium complex as a titanium compound, followed by the addition order of adding a specific pentavalent phosphorus compound, thereby providing a titanium catalyst. As the result, the coloring reaction is less and the electrostatic application property is high. At the same time, a polyester resin with improved yellowing when exposed to high temperatures is obtained.
As a result, coloring during polymerization and subsequent coloring during melt film formation are reduced, and yellowishness is reduced compared to conventional antimony (Sb) catalyst-based polyester resins, and germanium catalysts having a relatively high transparency are also obtained. It is possible to provide a polyester resin having a color tone and transparency comparable to a polyester resin and having excellent heat resistance. Moreover, PET resin which has high transparency and few yellowishness is obtained, without using color tone adjusting materials, such as a cobalt compound and a pigment | dye.

  This polyester resin can be used for applications requiring high transparency (for example, optical film, industrial squirrel, etc.), and it is not necessary to use an expensive germanium-based catalyst, so that the cost can be greatly reduced. In addition, since foreign matters caused by the catalyst that are likely to occur in the Sb catalyst system are also avoided, the occurrence of failures and quality defects in the film forming process can be reduced, and the cost can be reduced by improving the yield.

  In the above, when the aromatic dicarboxylic acid and the aliphatic diol are mixed with a catalyst containing an organic chelate titanium complex that is a titanium compound prior to the addition of the magnesium compound and the phosphorus compound, the organic chelate titanium complex or the like is subjected to an esterification reaction. Therefore, the esterification reaction can be carried out satisfactorily. At this time, you may add a titanium compound in mixing the dicarboxylic acid component and the diol component. Moreover, after mixing a dicarboxylic acid component (or diol component) and a titanium compound, you may mix a diol component (or dicarboxylic acid component). Further, the dicarboxylic acid component, the diol component, and the titanium compound may be mixed at the same time. The mixing is not particularly limited, and can be performed by a conventionally known method.

  In the esterification reaction, it is preferable to provide a process in which an organic chelate titanium complex which is a titanium compound and a magnesium compound and a pentavalent phosphorus compound as additives are added in this order. At this time, the esterification reaction proceeds in the presence of the organic chelate titanium complex, and thereafter, the addition of the magnesium compound is started before the addition of the phosphorus compound.

  As the pentavalent phosphorus compound, at least one pentavalent phosphate having no aromatic ring as a substituent is used. Examples of the pentavalent phosphate ester include trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, tris phosphate (triethylene glycol), methyl acid phosphate, and ethyl acid phosphate. Isopropyl acid phosphate, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate, triethylene glycol acid phosphate and the like.

Among pentavalent phosphate esters, phosphate esters having a lower alkyl group having 2 or less carbon atoms as a substituent [(OR) ₃ —P═O; R = alkyl group having 1 or 2 carbon atoms] are preferable, Specifically, trimethyl phosphate and triethyl phosphate are particularly preferable.

  In particular, when a chelate titanium complex coordinated with citric acid or a salt thereof is used as the catalyst as the titanium compound, the pentavalent phosphate ester has better polymerization activity and color tone than the trivalent phosphate ester. Furthermore, in the case of adding a pentavalent phosphate having 2 or less carbon atoms, the balance of polymerization activity, color tone, and heat resistance can be particularly improved.

  Inclusion of the magnesium compound improves electrostatic applicability. In this case, although it is easy to color, in this invention, coloring is suppressed and the outstanding color tone and heat resistance are obtained.

  Examples of the magnesium compound include magnesium salts such as magnesium oxide, magnesium hydroxide, magnesium alkoxide, magnesium acetate, and magnesium carbonate. Among these, magnesium acetate is most preferable from the viewpoint of solubility in ethylene glycol.

  As a preferred embodiment, before the esterification reaction is completed, after adding a chelate titanium complex having 1 ppm to 30 ppm of citric acid or citrate as a ligand to the aromatic dicarboxylic acid and the aliphatic diol, the chelate titanium complex 60 ppm to 90 ppm (more preferably 70 ppm to 80 ppm) of a weak acid magnesium salt is added, and after the addition, 60 ppm to 80 ppm (more preferably 65 ppm to 75 ppm) of an aromatic ring as a substituent. The aspect which adds the pentavalent phosphate which is not performed is mentioned.

  The esterification reaction may be carried out using a multistage apparatus in which at least two reactors are connected in series under conditions where ethylene glycol is refluxed while removing water or alcohol produced by the reaction from the system. it can.

  The dicarboxylic acid and the diol can be introduced by preparing a slurry containing them and continuously supplying it to the esterification reaction step.

  The esterification reaction described above may be performed in one stage or may be performed in multiple stages.

(B) Polycondensation In polycondensation, an esterification reaction product generated by an esterification reaction is subjected to a polycondensation reaction to generate a polycondensation product. The polycondensation reaction may be performed in one stage or may be performed in multiple stages.

  The esterification reaction product such as an oligomer generated by the esterification reaction is subsequently subjected to a polycondensation reaction. This polycondensation reaction can be suitably performed by supplying it to a multistage polycondensation reaction tank.

For example, the polycondensation reaction conditions in the case of performing in a three-stage reaction tank are as follows: the first reaction tank has a reaction temperature of 255 to 280 ° C, more preferably 265 to 275 ° C, and a pressure of 13.3 × 10 ^-3. -1.3 x 10 ^-3 MPa (100 to 10 torr), more preferably 6.67 x 10 ^{-3 to} 2.67 x 10 ^-3 MPa (50 to 20 torr). The temperature is 265 to 285 ° C., more preferably 270 to 280 ° C., and the pressure is 2.67 × 10 ^{−3 to} 1.33 × 10 ⁻⁴ MPa (20 to 1 torr), more preferably 1.33 × 10 ^{−. 3 to} 4.0 × 10 ⁻⁴ MPa (10 to ³ torr), and the third reaction tank in the final reaction tank has a reaction temperature of 270 to 290 ° C., more preferably 275 to 285 ° C., and a pressure of ^{1.33 × 10 -3 ~1.33 × 10 -5} MPa 10~0.1torr), embodiments are preferred and more preferably ^{6.67 × 10 -4 ~6.67 × 10 -5} MPa (5~0.5torr).

  Measurement of each element of Ti, Mg, and P is obtained by quantifying each element in PET using high-resolution high-frequency inductively coupled plasma-mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology). It can carry out by calculating content [ppm] from the obtained result.

-Solid phase polymerization process-
The polyester constituting the substrate may be solid-phase polymerized after polymerization. Thereby, preferable carboxyl group content can be achieved. Solid phase polymerization is a technique in which the degree of polymerization is increased by heating the polymerized polyester in a vacuum or nitrogen gas at a temperature of about 170 ° C. to 240 ° C. for about 5 to 100 hours. Specifically, for solid phase polymerization, 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 are disclosed. The method described in Japanese Patent No. 4167159 can be applied.
The solid-phase polymerization can be suitably performed using the polyester polymerized by the esterification reaction described above or a commercially available polyester in the form of small pieces such as pellets.

A preferable solid-state polymerization temperature is 190 to 230 ° C, more preferably 200 to 220 ° C, and further preferably 205 to 215 ° C.
The preferred solid phase polymerization temperature is 10 hours to 80 hours, more preferably 15 hours to 50 hours, and even more preferably 20 hours to 30 hours.
Such heat treatment is preferably performed in a low oxygen atmosphere, for example, in a nitrogen atmosphere or in a vacuum. Furthermore, you may mix polyhydric alcohol (ethylene glycol etc.) 1ppm-1%.

  Solid-phase polymerization may be carried out in a batch mode (a method in which a resin is placed in a container and stirred while applying heat for a predetermined time), or a continuous mode (a resin is placed in a heated cylinder and this is stirred). It may be carried out by a system in which the gas is passed through the cylinder while being kept flowing for a predetermined time while being heated, and sequentially fed out.

  In the production method of the present invention, the PET film is preferably formed by melt-kneading the polyester after the solid-phase polymerization step and extruding it from a die (extrusion die).

In the production method of the present invention, the PET resin can be melted using an extruder. The melting temperature is preferably 250 ° C to 320 ° C, more preferably 260 ° C to 310 ° C, and further preferably 270 ° C to 300 ° C.
The extruder may be uniaxial or multi-axial. More preferably, the inside of the extruder is replaced with nitrogen from the viewpoint that generation of terminal COOH due to thermal decomposition can be further suppressed.

  The molten resin (melt) of the PET resin is preferably extruded from an extrusion die through a gear pump, a filter or the like. At this time, it may be extruded as a single layer or may be extruded as a multilayer.

The melt-extruded melt is preferably cooled on a support, solidified and formed into a film.
There is no restriction | limiting in particular as said support body, The cooling roll used for normal melt film forming can be used.

  The temperature of the cooling roll itself is preferably 10 ° C to 80 ° C, more preferably 15 ° C to 70 ° C, and still more preferably 20 ° C to 60 ° C. Further, from the viewpoint of improving the adhesion between the molten resin (melt) and the cooling roll and increasing the cooling efficiency, it is preferable to apply static electricity before the melt contacts the cooling roll.

  The thickness of the molten resin (melt) discharged in a band after solidification (before stretching) is in the range of 2600 μm to 6000 μm, and a polyester film having a thickness of 260 μm to 400 μm can be obtained through subsequent stretching. The thickness of the melt after solidification is preferably in the range of 3100 μm to 6000 μm, more preferably 3300 μm to 5000 μm, and even more preferably in the range of 3500 μm to 4500 μm. When the thickness after solidification and before stretching is 6000 μm or less, wrinkles are unlikely to occur during melt extrusion, and unevenness is suppressed. Moreover, it is preferable that the thickness before stretching after solidification is 2600 μm or more suppresses uneven adhesion to the chill roll (cooling roll for solidification) generated due to weak melt, and is preferable from the viewpoint of reducing unevenness of the film.

(Stretching process)
In the manufacturing method of this invention, the process of extending | stretching the produced extruded film (unstretched film) may be included after the said film forming process. In the production method of the present invention, the substrate is preferably biaxially stretched from the viewpoint of mechanical strength.

(surface treatment)
In the production method of the present invention, the polymer substrate is preferably surface-treated by at least one of corona treatment, atmospheric pressure plasma treatment, flame treatment, and flame treatment using a silane compound-introduced flame.

<Formation of undercoat layer>
It is preferable to apply an undercoat layer coating solution to the polymer substrate.
There is no particular limitation on the method for applying the undercoat layer and the solvent of the coating solution used.
As a coating method, for example, a gravure coater or a bar coater can be used.
The solvent used for the coating solution may be water or an organic solvent such as toluene or methyl ethyl ketone. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.
The coating may be performed on the polymer substrate after biaxial stretching, or may be performed by stretching in a direction different from the initial stretching after coating on the polymer substrate after uniaxial stretching. Furthermore, you may extend | stretch in 2 directions, after apply | coating to the base material before extending | stretching.
The coating amount of the undercoat layer coating liquid is preferably varied according to the thickness of the subbing layer to determine, is preferably 2 g / m ² or less, more preferably 0.05g / m ² ~2g / m ^2, more preferably from ^{0.1g / m 2 ~1.5g / m 2} .
If the undercoat layer contains the inorganic oxide filler, preferably has a coating weight is 0.005~0.05g / m ^2, more preferably from 0.005~0.03g / m ² 0.005 to 0.02 g / m ² is particularly preferable.

<Formation of white pigment layer>
The white pigment layer can be formed by a method in which a polymer sheet containing a pigment is bonded to a substrate, a method in which the white pigment layer is coextruded when forming the substrate, a method by coating, or the like. Specifically, a white pigment layer can be formed by laminating, co-extrusion, coating or the like directly on the surface of the polymer substrate or through an undercoat layer having a thickness of 2 μm or less. The formed white pigment layer may be in a state of being in direct contact with the surface of the polymer substrate, or may be in a state of being laminated through an undercoat layer.
Among the methods described above, the method by coating is preferable because it is simple and can be formed in a thin film with uniformity.

In the case of coating, as a coating method, for example, a known coating method such as a gravure coater or a bar coater can be used.
The coating solution may be an aqueous system using water as an application solvent, or a solvent system using an organic solvent such as toluene or methyl ethyl ketone. Among these, from the viewpoint of environmental burden, it is preferable to use water as a solvent. A coating solvent may be used individually by 1 type, and may mix and use 2 or more types.
It is preferable to apply the white pigment layer coating solution onto the undercoat layer.
The coating amount of the white pigment coating solution is preferably changed according to the desired thickness of the white pigment layer, but in the present invention, the surface state of the white pigment layer is found to be disturbed due to the thickness of the undercoat layer. . Therefore, for the purpose of changing the reflectance and other physical properties of the white pigment layer, it is not necessary to change the coating amount, and it is preferable to adjust the amount of the white pigment contained in the white pigment layer. The coating amount of the white pigment coating solution is preferably from the viewpoint of reflectivity and adhesion maintained it is 5.0~10.0g / m ^2, more preferably be 6.0~9.0g / m ² , more preferably from ^{7g / m 2 ~9g / m 2} .

[Solar cell module]
The solar cell module of the present invention includes a transparent substrate on which sunlight is incident, a solar cell element, and the solar cell back surface protective sheet of the present invention. In the solar cell module of the present invention, a solar cell element that converts light energy of sunlight into electric energy is disposed between the transparent substrate on which sunlight is incident and the solar cell back surface protective sheet of the present invention described above. In addition, it is preferable that the substrate and the back sheet are sealed with an ethylene-vinyl acetate sealing material.

  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 substrate 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, gallium-arsenide, and II. Various known solar cell elements such as a group VI compound semiconductor can be applied.

The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the examples shown below. 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]
<Production of polymer substrate>
-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 substrate (hereinafter referred to as “biaxially stretched PET”) having a thickness of 300 μm was obtained.
The base thickness of the biaxially stretched PET substrate is shown in Table 1 below.

-Carboxyl group content of biaxially stretched PET substrate-
A weight w [g] of about 0.1 g of biaxially stretched PET was measured, put into a round bottom flask containing 5 mL of benzyl alcohol, and kept at a temperature of 205 ° C. for 24 hours in a stoppered state. The contents were then added to 15 mL of chloroform. A solution obtained by adding a small amount of phenol red indicator to this solution was titrated with a benzyl alcohol solution of potassium hydroxide having a concentration of 0.01 N / L. The amount of potassium hydroxide solution required for the titration was set to x mL, and the carboxyl group amount (COOH group amount) of biaxially stretched PET was determined by the following formula.
Carboxyl group content (equivalent / t) = 0.01 × (x / w)
The obtained results are shown in Table 1 below.

-Thermal contraction rate of biaxially stretched PET substrate-
A biaxially stretched PET film was sampled into a 5 cm × 15 cm rectangle, and a 15 cm side cut out parallel to MD (film transport direction) was an MD sample, 15 cm parallel to TD (direction perpendicular to the film transport direction) The side cut out was used as a TD sample, and three pieces each were cut out. These samples were cut out at the points where the film forming width was divided into five equal parts, and a total of 15 MD samples and 15 TD samples were prepared.
Each sample was conditioned at 25 ° C. and a relative humidity of 60% for 3 hours or longer. A pair of 10 cm-basic holes was made in this sample, and the distance between the holes was measured with a pin gauge (L1).
Each sample was heat-treated in an air thermostat at 150 ° C. for 30 minutes under no tension. Thereafter, each sample was conditioned at 25 ° C. and a relative humidity of 60% for 3 hours or more, and the distance between the holes was measured with a pin gauge (L2).
100 × (L1-L2) / L1 was defined as the thermal shrinkage (%) of each sample.
As a result of obtaining the average values of all the MD and TD samples, they are shown as “heat shrinkage” in Table 1.

<Preparation of coating solution for undercoat layer>
-Preparation of undercoat layer-
Components in the following composition were mixed to prepare an undercoat layer coating solution.
<Composition of coating solution for undercoat layer>
・ Polyester resin: 1.7% by mass
(Byronal MD-1200, manufactured by Toyobo Co., Ltd., solid content: 17% by mass)
・ Polyester resin: 3.8% by mass
(Pesresin A-520, manufactured by Takamatsu Yushi Co., Ltd., solid content: 30% by mass)
・ Polyoxyalkylene alkyl ether: 1.5% by mass
(Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Inorganic oxide filler: 1.6% by mass
(Snowtex C, manufactured by Nissan Chemical Co., Ltd., solid content: 20% by mass)
・ Carbodiimide compound: 4.3% by mass
(Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass, crosslinking agent)
・ Distilled water: 87.1% by mass
In addition, the ratio of the crosslinking agent addition amount (4.3 mass%) to the binder addition amount (total 5.5 mass% of the following two kinds of polyester resins) in the composition of the coating solution for the undercoat layer was calculated as a percentage. However, it was 30% (mass ratio). The results are shown in Table 1 below.

<Preparation of white pigment layer coating solution>
-Preparation of white pigment dispersion-
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 pigment dispersion>
・ Titanium dioxide (volume average particle size = 0.42 μm) 44.9% by mass
(Taipeke R-780-2, manufactured by Ishihara Sangyo Co., Ltd., solid content 100% by mass)
・ Polyvinyl alcohol: 8.0% by mass
(PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10% by mass)
・ Surfactant (Demol EP, manufactured by Kao Corporation, solid content: 25% by mass): 0.5% by mass
・ Distilled water: 46.6% by mass

-Preparation of coating solution for white pigment layer-
Components in the following composition were mixed to prepare a white pigment layer coating solution.
<Composition of coating solution for white pigment layer>
・ The above pigment dispersion: 70.9 mass%
-Polyacrylic resin aqueous dispersion ... 19.2 mass%
(Binder: Jurimer ET410, manufactured by Nippon Pure Chemical Industries, Ltd., solid content: 30% by mass)
・ Polyoxyalkylene alkyl ether: 3.0% by mass
(Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Oxazoline compound: 6.9% by mass
(Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass, crosslinking agent)
In addition, when the ratio of the crosslinking agent addition amount (6.9% by mass) to the binder addition amount (the solid content of the following polyacrylic resin 5.76% by mass) in the composition of the white pigment layer coating liquid was calculated as a percentage. 30% (mass ratio). The results are shown in Table 1 below.

<Preparation of solar cell back surface protection sheet>
The undercoat layer coating solution was applied onto the biaxially stretched PET prepared above. Then, it was dried at 180 ° C. for 1 minute to form an undercoat layer (thickness: 0.1 μm) having a coating amount of 0.1 g / m ² .
Further, the white pigment layer coating solution was applied onto the dried undercoat layer so that the amount of titanium dioxide was 6.5 g / m ² (P / P + B ratio 84.4% by mass), and 180 ° C. And dried for 1 minute to form a white pigment layer (reflection layer) (thickness: 1.4 μm).

  As described above, the back protective sheet for solar cells of Example 1 (hereinafter referred to as “sample sheet”) was produced. About this sample sheet, the adhesiveness before and behind wet heat aging, film | membrane intensity | strength, surface shape, and evaluation of the reflectance were performed by the method shown below. The results are shown in Table 1 below.

<Evaluation>
-1. Adhesiveness
[A] Adhesiveness before wet heat aging The sample sheet 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 pigment layer side is inside, and an EVA sheet (EVA sheet: SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.) cut into 20 mm width × 100 mm length is sandwiched between them. By hot pressing using a vacuum laminator (vacuum laminator manufactured by Nisshinbo Co., Ltd.), it was bonded to EVA. 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 at 150 ° C. for 30 minutes using a dry oven. 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-bonded portion of the obtained sample for adhesion evaluation was sandwiched between upper and lower clips with Tensilon (RTC-1210A manufactured by ORIENTEC), a tensile test was performed at a peeling angle of 180 ° and a pulling speed of 300 mm / min, and the adhesive strength was measured. .
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)

[B] Adhesiveness after wet heat aging The obtained sample for adhesion evaluation was held for 48 hours (wet heat aging) at 120 ° C. and 100% relative humidity, and then the same method as in [A] above. The adhesive force was measured. Moreover, based on the measured adhesive strength after wet heat aging, the adhesive strength was evaluated by the same method as in the above [A].

[C] Amount of change in adhesiveness before and after wet heat aging The ratio of the same adhesion evaluation sample to the adhesive force before [A] wet heat aging of the same adhesion evaluation sample [%; = adhesive force after wet heat aging / [A] Adhesive strength before wet heat aging × 100] was calculated.

-2. Film strength
The sample sheet prepared as described above is stored for 2 hours in an atmosphere of 25 ° C. and 65% relative humidity, and then a rubbing test is performed in which the sheet is rubbed at a speed of 2460 mm / min with black paper loaded with a 1 kg / cm width. did. The degree of powder fall of the coating layer adhering on the black paper after the rubbing test was visually observed, and evaluated according to the following evaluation criteria using the degree of powder fall as an index. Among these, ranks 4 and 5 are practically acceptable ranges.
<Evaluation criteria>
5: There was no powder falling off.
4: Slightly falling off was observed.
3: Powder fall was seen.
2: Strong powder fall was seen.
1: Powder fall was observed on almost the entire surface of the black paper.

-3. Plane-
The surface state of the sample sheet produced as described above was visually observed and evaluated according to the following evaluation criteria. Among these, ranks 4 and 5 are practically acceptable ranges.
<Evaluation criteria>
5: No unevenness or repellency was observed.
4: Slight unevenness was observed, but no repelling was observed.
3: Unevenness was observed, but no repelling was observed.
2: Unevenness was clearly confirmed, and repelling was observed in part (less than 10 pieces / m ² ).
1: Unevenness was clearly confirmed, and repelling was observed at 10 pieces / m ² or more.

-4. Reflectance-
Using a spectrophotometer UV-2450 (manufactured by Shimadzu Corporation) with an integrating sphere attachment device ISR-2200 attached, the reflectance of the sample sheet on the reflective layer with respect to 550 nm light was measured. However, the reflectance of the barium sulfate standard plate was measured as a reference, and the reflectance of the sample sheet was calculated using this as 100%.

[Examples 2 to 16, Comparative Examples 1 to 8]
In Example 1, base thickness and surface treatment of biaxially stretched PET substrate; thickness after drying of undercoat layer, binder coating amount, inorganic fine particle coating amount and crosslinking agent amount; white pigment layer titanium oxide pigment coating amount, A solar cell back surface protective sheet (sample sheet) was produced in the same manner as in Example 1 except that the binder coating amount and the crosslinking agent amount were changed as shown in Table 1. However, in Example 9, a treatment of 500 J / m ² with an output of 1.3 kW / electrode 1 m (representing an output per 1 m of electrode) with respect to the biaxially stretched PET base material before applying the undercoat layer. A strong corona treatment was applied.
Moreover, in the comparative example 2, the titanium oxide kneading base material (white film) of the structure of FIG. 2 for expressing the reflectance equivalent to Example 1 was created. In Comparative Examples 3 and 5, an undercoat layer was not provided. In Comparative Examples 6 to 8, the base thickness when producing a white film kneaded with titanium oxide in Comparative Example 2 was changed.
The obtained films of each Example and Comparative Example were evaluated in the same manner as Example 1. The results are shown in Table 1 below. In addition, regarding Comparative Examples 2 and 6 to 8 using a titanium oxide kneaded type base material, data on adhesiveness and film strength could not be measured. Further, the thickness of the white pigment layer in each Example and Comparative Example was 1.4 μm as in Example 1.

From the said Table 1, it turned out that all the solar cell back surface protection sheets of an Example have favorable adhesiveness, film | membrane intensity | strength, planar shape, and reflectance after wet heat aging.
On the other hand, the comparative example 1 made the ratio of the white pigment with respect to the sum total of a binder and a white pigment less than the lower limit of this invention, and the obtained sheet | seat had a bad reflectance. Comparative Example 2 is a white pigment kneaded type sheet prepared so as to have the same base thickness and reflectivity as Example 1, and the obtained sheet needs 50 g / m ² of white pigment. In other words, it was found that a larger amount of pigment was required than in the coating method (6.5 g / m ² ). In Comparative Example 3, no undercoat layer was provided, and the resulting sheet had poor adhesion and film strength after wet heat aging. In Comparative Example 4, the thickness of the undercoat layer was set to exceed the upper limit of the present invention, and the obtained sheet had a poor surface shape. In Comparative Example 5, no undercoat layer was provided, and the ratio of the white pigment to the total of the binder and the white pigment was less than the lower limit of the present invention. The intensity was poor and the reflectance was less than 75%. In Comparative Examples 6 to 8, the thickness of the white pigment kneaded sheet was made thinner in order than that of Comparative Example 2, and it was found that the reflectance decreased.

(Example 101)
A tempered glass having a thickness of 3 mm, an EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), a crystalline solar cell, an EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), and the sample of Example 1 The sheet (the solar cell back surface protection sheet of the present invention) was superposed in this order, and hot-pressed using a vacuum laminator (manufactured by Nisshinbo Co., Ltd., vacuum laminating machine) to adhere to EVA. At this time, the sample sheet was arrange | positioned so that the easily bonding layer might contact with an EVA sheet | seat. 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.
In this way, a crystalline solar cell module was produced. When the generated solar cell module was used for power generation operation, it showed good power generation performance as a solar cell.

DESCRIPTION OF SYMBOLS 1 Polymer base material 2 Undercoat layer 3 White pigment layer 4 White pigment kneading type polymer base material

Claims (11)

A polymer substrate having a thickness of 120 to 350 μm;
An undercoat layer having a thickness of 2 μm or less;
A white pigment layer containing a binder and a white pigment, and the ratio of the white pigment to the total of the binder and the white pigment is 84 to 95% by mass,
A solar cell back surface protective sheet characterized by having in this order.   The solar cell back surface protective sheet according to claim 1, wherein at least one of the white pigment layer and the undercoat layer contains 5 to 50% by mass of a crosslinking agent with respect to the binder.   The solar cell back surface protective sheet according to claim 2, wherein the crosslinking agent is a crosslinking agent having a carbodiimide group or an oxazoline group.   The undercoat layer includes at least one resin selected from the group consisting of polyolefin resin, polyurethane resin, polyvinyl alcohol resin, polyacrylic resin, and polyester resin. The solar cell back surface protection sheet of description.   The solar cell back surface protective sheet according to any one of claims 1 to 4, wherein the undercoat layer contains an inorganic oxide filler.   6. The polymer substrate according to claim 1, wherein the polymer substrate is surface-treated by at least one method of corona treatment, atmospheric pressure plasma treatment, flame treatment, and flame treatment using a flame introduced with a silane compound. The solar cell back surface protection sheet of Claim 1.   The solar cell back surface protective sheet according to any one of claims 1 to 6, wherein the polymer base material has a heat shrinkage ratio of about 0 to 0.5% at about 150 ° C for 30 minutes.   The solar cell back surface protective sheet according to any one of claims 1 to 7, wherein the polymer base material is a polyester having a carboxyl group content of 35 equivalents / ton or less.   The solar cell back surface protective sheet according to any one of claims 1 to 8, wherein a reflectance with respect to light having a wavelength of 550 nm is 75% or more.   The solar cell back surface protective sheet according to any one of claims 1 to 9, wherein both the undercoat layer and the white pigment layer are formed by coating.   The solar cell module characterized by including the transparent board | substrate with which sunlight injects, a solar cell element, and the solar cell back surface protection sheet of any one of Claims 1-10.

Images