JP2015037171A - Protective sheet for solar cell and back sheet for solar cell, and solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective sheet for a solar cell and a back sheet for a solar cell, having scratch resistance, hardly be contaminated in a production process, and to provide a solar cell module capable of generating power for a long period of time.SOLUTION: There are provided: a protective sheet 31 for a solar cell having a substrate film 16 and a polymer layer 12, disposed as an outermost layer on one surface of the substrate film, containing a fluororesin and an olefinic lubricant whose ring and ball softening point is equal to or higher than 120°C; a back sheet 32 for a solar cell equipped with the same; and a solar cell module 10.

Description

  The present invention relates to a solar cell protective sheet, a solar cell backsheet, and a solar cell module.

  A solar cell module using crystalline silicon, amorphous silicon, or the like as a solar cell element is generally a transparent front substrate on which sunlight is incident, and a solar cell element as a photovoltaic element is sealed with a sealing material. The battery side substrate and the back surface protection sheet layer (solar cell backsheet) are laminated in this order, and are manufactured using a lamination method or the like in which vacuum suction is applied to perform thermocompression bonding. Since solar cells are placed in an environment where sunlight shines on the roof, etc., and is exposed to rain, the layers that make up the solar cell module have various functionalities that are representative of durability under humid heat environments. Is required.

Conventionally, glass has often been used as a transparent front substrate or solar cell backsheet, but various functionalities can be added by stacking functional layers, reducing the weight and cost of solar cell modules. From the viewpoint of achieving this, in recent years, it is required to use a protective sheet for a solar cell using a base material mainly composed of a resin film as a front substrate or a back sheet for a solar cell.
Such a protective sheet for a solar cell is often a laminate of various functional layers as described above. As a typical functional layer, an adhesive layer for closely adhering to the sealing material and a function of reflecting sunlight transmitted through the transparent front substrate and the battery side substrate are given to increase the expression efficiency of the solar cell element. And a weather-resistant layer that is preferably installed on the outermost layer of the solar cell protective sheet.

  For example, in Patent Document 1, a liquid crystal polymer film, a polyvinyl fluoride resin layer having a thickness of 0.5 to 100 μm formed by casting on one side of the liquid crystal polymer film, and the other side of the liquid crystal polymer film, There is disclosed a back protective sheet having an insulating resin layer that has an insulating property and can be strongly bonded to a filling layer, and an adhesive layer that bonds the liquid crystal polymer film and the adhesive resin layer.

Patent Document 2 includes a polymer base material, a polymer layer that is an outermost layer disposed on one surface of the polymer base material, and a polymer having a structure in which the polymer layer includes a siloxane bond, and a lubricant. The polymer content in the polymer layer is more than 0.2 g and less than 15 g per 1 m ^{2 of the} polymer layer, and the lubricant content in the polymer layer is 0.2 mg or more and 200 mg or less per 1 m ^{2 of the} polymer layer A protective sheet is disclosed.

  When manufacturing a protective sheet for a solar cell in which a functional layer is laminated on a base film, for example, while transporting the base film with a transport roll, a coating liquid is applied according to the functional layer formed on the base film, A functional layer is laminated | stacked by performing the process of drying sequentially.

JP 2012-195583 A JP 2010-165872 A

When forming a functional layer on a base film, when heat treatment is performed in a drying process or the like, the components constituting the functional layer melt and adhere to the transport roll, and transfer to another sheet and become dirty. There is a case. In order to prevent such retransfer, it is necessary to periodically clean the roll, which leads to a decrease in production efficiency.
For example, if the temperature of the sheet in the manufacturing process is kept low, melting of components contained in the functional layer is suppressed. However, if the sheet is produced at a low temperature, the heat shrinkage rate of the sheet does not decrease, and there is a difference in the heat shrinkage rate with other members when laminated on other members by heating and pressing. In this case, “warping” or the like occurs, which tends to cause a laminate failure.

  An object of the present invention is to provide a solar cell protective sheet and a solar cell backsheet that are scratch-resistant and hardly contaminated in the production process, and a solar cell module that can generate power over a long period of time.

In order to achieve the above object, the following invention is provided.
<1> A sun having a base film, and a polymer layer that is disposed as an outermost layer on one surface of the base film and includes a fluororesin and an olefin-based lubricant having a ring and ball softening point of 120 ° C. or higher. Battery protection sheet.
<2> The solar cell protective sheet according to <1>, wherein the olefin-based lubricant includes an olefin resin having at least one of an ethylene unit and a propylene unit.
<3> The solar cell protective sheet according to <1> or <2>, wherein the olefinic lubricant has a median diameter of 2 μm or less.
<4> The solar cell protective sheet according to any one of <1> to <3>, wherein the base film contains a resin selected from the group consisting of polyester, polyolefin, polyamide, and polyphenylene ether.
<5> The solar cell protective sheet according to any one of <1> to <4>, wherein the olefin resin contained in the olefin-based lubricant has a number average molecular weight (Mn) of 3000 or more and 10,000 or less.
<6> The solar cell protective sheet according to any one of <1> to <5>, wherein the fluorine-based resin includes a chlorotrifluoroethylene unit.
<7> The solar cell protective sheet according to any one of <1> to <6>, wherein the polymer layer has a crosslinked structure.
<8> The solar cell protective sheet according to <7>, wherein the crosslinked structure is derived from a crosslinking agent selected from the group consisting of a carbodiimide crosslinking agent, an oxazoline crosslinking agent, an isocyanate crosslinking agent, and an epoxy crosslinking agent.
<9> The solar cell protective sheet according to <8>, wherein the crosslinking agent is water-soluble.
<10> The solar cell protective sheet according to any one of <1> to <9>, wherein the polymer layer contains 6 to 30 parts by mass of an olefin-based lubricant with respect to 100 parts by mass of the fluororesin.
<11> The solar cell according to any one of <1> to <10>, having an intermediate layer containing a resin containing at least one of a fluorine atom and a silicone-acryl unit between the base film and the polymer layer. Protective sheet.
<12> A solar cell backsheet comprising the solar cell protective sheet according to any one of <1> to <11>.
<13> A transparent front substrate on which sunlight is incident, and a solar cell element and a sealing material that seals the solar cell element, disposed on the opposite side of the front substrate from the side on which sunlight is incident And a solar cell backsheet according to <12>, which is disposed on the opposite side of the element structure portion from the side on which the front substrate is located.

  ADVANTAGE OF THE INVENTION According to this invention, the solar cell module which can generate electric power over a long period of time and the solar cell protective sheet and solar cell backsheet which have scratch resistance and are hard to generate | occur | produce the stain | pollution | contamination in a manufacturing process are provided.

It is sectional drawing which shows roughly an example of a structure of the solar cell module containing the protection sheet for solar cells of this invention.

Hereinafter, the solar cell protective sheet 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.

The inventors have added the lubricant added to prevent the outermost layer of the protective sheet for solar cells from being scratched and melted in the drying process and adhere to the transport roll, and then part of the sheet transported later It was found that it was retransferred and soiled. In order to prevent contamination due to such re-transfer of the lubricant via the roll, the present inventors have conducted extensive research and as a result, the outermost layer contains a fluorine-based resin and an olefin-based lubricant having a ring and ball softening point of 120 ° C. or more. It has been found that the formation of the polymer layer suppresses the lubricant from melting and adhering to the roll in the manufacturing process, reducing the frequency of cleaning the roll, and consequently, reducing the production efficiency. It was. Furthermore, it has been found that there is no need to lower the heating temperature in the drying step in order to prevent the lubricant from melting, and a solar cell protective sheet having a low heat shrinkage during lamination can be obtained.
Hereinafter, the protective sheet for solar cells of the present invention will be specifically described.

[Protective sheet for solar cell]
The protective sheet for solar cell of the present invention is disposed as a base film and an outermost layer on one surface of the base film, and includes a fluorine-based resin and an olefin-based lubricant having a ring and ball softening point of 120 ° C. or higher. And a polymer layer.

In FIG. 1, an example of a structure of the solar cell module which used the protection sheet for solar cells of this invention as a back sheet for solar cells is shown. In the solar cell protective sheet 31, the polymer layer 12 is provided on one surface of the base film 16. The solar cell protective sheet or solar cell backsheet of the present invention is between the base film 16 and the polymer layer 12 or on the opposite side of the base film 16 from which the polymer layer is provided. Other layers may be provided. For example, the intermediate layer 14 is provided between the base film 16 and the polymer layer 12 in the solar cell protective sheet 31 shown in FIG. Further, an easy-adhesion layer 18 is provided on the surface opposite to the base film 16 to increase the adhesive force between the undercoat layer 17 and the sealing material 22 that seals the solar cell element 20, and the solar cell backsheet 32. Is configured.
In the solar cell module 10 of the present invention, a transparent front substrate 24 is preferably disposed on the side of the sealing material 22 opposite to the solar cell protective sheet of the present invention.
Hereinafter, the configuration of the protective sheet for solar cell of the present invention will be specifically described.

(Base film)
A base film functions as a support body in the protection sheet for solar cells of this invention. As a material constituting the base film, polyester, polystyrene, polyolefin, polyamide, polyphenylene ether, polyphenylene sulfide and the like can be used. Polyester, polyolefin, polyphenylene ether, or polyamide is preferable from the viewpoint of cost, mechanical stability, and durability, and polyester is particularly preferable.
Examples of the polyester that can be preferably used for the base film include 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. Of these, polyethylene terephthalate, polyethylene-2,6-naphthalate, and poly (1,4-cyclohexylenedimethylene terephthalate) are particularly preferable from the viewpoint of balance between mechanical properties and cost.

  The polyester constituting the base film may be a homopolymer or a copolymer. Further, polyester may be blended with a small amount of other types of resins such as polyimide.

A polyester base film (hereinafter sometimes referred to as a polyester base film) preferably has high hydrolysis resistance. For this reason, the carboxyl group content in the polyester is preferably 50 equivalents / ton or less, more preferably 35 equivalents / ton or less, and still more preferably 20 equivalents / ton or less. When the carboxyl group content is 50 equivalents / ton or less, hydrolysis resistance can be maintained, and a decrease in strength when subjected to wet heat aging can be suppressed. The lower limit of the carboxyl group content is 2 equivalents / ton, more preferably 3 equivalents / ton, more preferably 3 equivalents / ton in that the adhesion between the functional layer formed on the surface of the polyester base film is maintained. T is desirable.
The carboxyl group content in the polyester can be adjusted by polymerization catalyst species, film forming conditions (film forming temperature and time), solid phase polymerization, and additives (end-capping agent, etc.).

  When polymerizing polyester, it is preferable to use an Sb-based, Ge-based, Ti-based, or Al-based compound as a catalyst from the viewpoint of keeping the carboxyl group content below 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 ratio of the Ti-based compound is within the above range, the terminal carboxyl group content can be adjusted to the above range, and the hydrolysis resistance of the base film can be kept low. Further, it is preferable to add a phosphate ester compound for stabilization during polymerization, and the addition amount is preferably 10 ppm to 100 ppm, more preferably 30 ppm to 90 ppm, and even more preferably 50 ppm to 80 ppm as the elemental amount of P. It is as follows. As a specific compound of the phosphate ester compound, at least one of pentavalent phosphate esters having no aromatic ring as a substituent is preferably used. Examples of the pentavalent phosphate ester in the present invention include trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, tris phosphate (triethylene glycol), methyl acid phosphate, and phosphoric acid. Examples include ethyl acid, isopropyl acid phosphate, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate, and triethylene glycol acid phosphate.

  For the synthesis of polyester using a Ti-based compound, for example, Japanese Patent Publication No. 8-301198, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 397756, Japanese Patent No. 39622626, Japanese Patent No. 39786666 No. 3, Patent No. 3,996,871, Patent No. 4000086, Patent No. 4053837, Patent No. 4,127,119, Patent No. 4,134,710, Patent No. 4,159,154, Patent No. 4,269,704, Patent No. 4,313,538 and the like can be applied.

  The polyester forming the base film is preferably solid-phase polymerized after polymerization. Thereby, it is easy to achieve a preferable carboxyl group content. Solid-phase polymerization may be a continuous method (a method in which a tower is filled with a resin, which is slowly heated for a predetermined time and then sent out), or a batch method (a resin is charged into a container). , A method of heating for a predetermined time). 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 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.

In the present invention, it is also preferable to seal the terminal carboxylic acid in order to improve the weather resistance. The terminal blocking agent contains 0.1 to 10% by mass of the terminal blocking agent with respect to the polyester, and the amount of the terminal blocking agent added is more preferably 0.2 to 5% by mass, and still more preferably 0.3 to 2% by mass.
Examples of the terminal blocking agent include an epoxy compound, a carbodiimide compound, an oxazoline compound, a carbonate compound, and the like, and carbodiimide having high affinity with polyethylene terephthalate (PET) is preferable.

  The end-capping agent is preferably a high molecular weight from the viewpoint of preventing volatilization during film formation. Specifically, JP2011-136550, JP2002-26354, JP2003-60218, JP2007-136911, JP2007-204535, JP2008027070, JP2008-130642, JP2008-166338. JP2008-31680, WO2007 / 40039, WO2007 / 105306, WO2008 / 69024, JP2010-141291, JP2010-163613, JP2010-189558, JP2010-192743, JP2010-202837, Special JP 2010-212272, JP 2010-229240, JP 2010-235824, JP 2010-260903, JP 2010-280189, JP 2011-6659, JP 2011-21180, JP 2011-80057, JP 2011-97014, JP 201116938, JP 2011-119651, JP 2011-140529, JP 2011-140530, JP 2011-144282, WO 09/125701, JP 2011-155109, Special JP 2011-155110, JP 2011-171399, JP 2011-192789, JP 2011-204842, JP 2011-231211, JP 2011-243761, JP 2011-249756, JP 2012-33967, etc. Can do. Moreover, the carbodiimide which has the cyclic structure of Unexamined-Japanese-Patent No. 2011-153209 is preferable from a viewpoint of volatilization prevention.

  The base film is obtained by, for example, melt-extruding the above polyester into a film and cooling and solidifying it with a casting drum to form an unstretched film. The unstretched film is Tg (glass transition temperature) to (Tg + 60) ° C. Biaxial stretching that is stretched once or twice or more in the longitudinal direction so that the total magnification is 3 to 6 times, and then stretched so that the magnification is 3 to 5 times in the width direction at Tg to (Tg + 60) ° C. A film is preferred. Furthermore, what was heat-processed for 1 to 60 second at 180-230 degreeC as needed may be used.

  The thickness of the base film is preferably 30 μm or more and 350 μm or less, but is preferably 160 μm or more and 300 μm or less, more preferably 180 μm or more and 280 μm or less from the viewpoint of withstand voltage.

  The base film preferably has a breaking elongation after storage for 50 hours at 120 ° C. and a relative humidity of 100% of 50% or more with respect to the breaking elongation before storage (hereinafter, wet-heat treated under the above conditions). (The retention of elongation at break before and after the treatment of the base film is also simply referred to as “break elongation retention”). When the elongation at break is 50% or more, the change accompanying hydrolysis is suppressed, and the adhesive state at the adhesive interface with the coating layer is stably maintained during long-term use. Separation is prevented. Thereby, even when the back sheet for solar cells (hereinafter sometimes simply referred to as a back sheet) is placed over a long period of time, for example, outdoors or in a high temperature, high humidity environment or exposure, high durability performance is exhibited. More preferably, the time to reach 50% is preferably 75 hours or more and 200 hours or less, more preferably 100 hours or more and 180 hours or less.

  The base film preferably has a breaking strength after heat treatment at 180 ° C. for 50 hours is 50% or more of the breaking strength before the heat treatment. More preferably, the breaking strength after heat treatment at 180 ° C. for 80 hours is 50% or more of the breaking strength before heat treatment, and more preferably, the breaking strength after heat treatment at 180 ° C. for 100 hours is 50% of the breaking strength before heat treatment. That's it. Thereby, the heat resistance when exposed to high temperatures can be improved.

  The base film is preferably 1% or less, more preferably 0.5% or less, in both MD (Machine Direction) and TD (Transverse Direction) when heat-treated at 150 ° C. for 30 minutes. By maintaining the heat shrinkage at 1% or less, it is possible to prevent warping when the solar cell module is formed.

The base film may be subjected to surface treatment such as corona treatment, flame treatment, and glow discharge treatment as necessary. Of these, corona treatment is a preferred surface treatment method that can be performed at low cost.
Corona discharge treatment is usually performed by applying high frequency and high voltage between a metal roll (dielectric roll) coated with a derivative and an insulated electrode to cause dielectric breakdown of the air between the electrodes. Is ionized to generate a corona discharge between the electrodes. And it performs by passing a base film between this corona discharge. The preferable processing conditions used in the present invention are preferably a gap clearance of 1 to 3 mm between the electrode and the dielectric roll, a frequency of 1 to 100 kHz, and an applied energy of about 0.2 to 5 kV · A · min / m ² .

The glow discharge treatment is a method called vacuum plasma treatment or glow discharge treatment, in which plasma is generated by discharge in a gas (plasma gas) in a low-pressure atmosphere to treat the substrate surface. The low-pressure plasma used in the process of the present invention is a non-equilibrium plasma generated under conditions where the plasma gas pressure is low. The treatment of the present invention is performed by placing a film to be treated in this low-pressure plasma atmosphere.
In the glow discharge treatment, methods such as direct current glow discharge, high frequency discharge, and microwave discharge can be used as a method for generating plasma. The power source used for discharging may be direct current or alternating current. When alternating current is used, a range of about 30 Hz to 20 MHz is preferable. When alternating current is used, a commercial frequency of 50 or 60 Hz may be used, or a high frequency of about 10 to 50 kHz may be used. A method using a high frequency of 13.56 MHz is also preferable.

  As the plasma gas used in the glow discharge treatment, an inorganic gas such as oxygen gas, nitrogen gas, water vapor gas, argon gas, and helium gas can be used. In particular, oxygen gas or a mixed gas of oxygen gas and argon gas can be used. Is preferred. Specifically, it is desirable to use a mixed gas of oxygen gas and argon gas. When oxygen gas and argon gas are used, the ratio between the two is preferably a partial pressure ratio of oxygen gas: argon gas = 100: 0 to 30:70, more preferably 90:10 to 70:30. In addition, a method in which a gas such as water entering the processing container due to a leak or water vapor coming out of the object to be processed is used as the plasma gas without introducing a gas into the processing container.

As the pressure of the plasma gas, a low pressure at which non-equilibrium plasma conditions are achieved is necessary. The specific plasma gas pressure is preferably in the range of about 0.005 to 10 Torr, more preferably about 0.008 to 3 Torr. When the pressure of the plasma gas is less than 0.005 Torr, the effect of improving adhesiveness may be insufficient. Conversely, when the pressure exceeds 10 Torr, the current may increase and the discharge may become unstable.
The plasma output cannot be generally specified depending on the shape and size of the processing vessel, the shape of the electrode, and the like, but is preferably about 100 to 2500 W, more preferably about 500 to 1500 W. The treatment time of the glow discharge treatment is 0.05 to 100 seconds, more preferably about 0.5 to 30 seconds. If the treatment time is less than 0.05, the adhesion improving effect may be insufficient. Conversely, if the treatment time exceeds 100 seconds, problems such as deformation and coloring of the film to be treated may occur.
Discharge treatment intensity of the glow discharge treatment depends on the plasma power and treatment time, preferably in the range of 0.01~10kV · A · min / m ^2, 0.1~7kV · A · min / m ² is more preferable. Discharge treatment intensity that is sufficient adhesion improving effect of the 0.01 kV · A · min / m ² or more is obtained, and such deformation and coloration of the processed film by a 10 kV · A · min / m ² or less You can avoid problems.
In the glow discharge treatment, it is also preferable to preheat a film to be treated (film to be treated). By this method, better adhesiveness can be obtained in a shorter time than when heating is not performed. The heating temperature is preferably in the range of 40 ° C. to the softening temperature of the film to be processed + 20 ° C., more preferably in the range of 70 ° C. to the softening temperature of the film to be processed. By setting the heating temperature to 40 ° C. or higher, a sufficient adhesive improvement effect can be obtained. Moreover, the handleability of a favorable film can be ensured during a process by making heating temperature below into the softening temperature of a to-be-processed film.
Specific methods for raising the temperature of the film to be treated in vacuum include heating with an infrared heater, heating by contacting with a hot roll, and the like.

(Polymer layer)
The polymer layer is disposed as an outermost layer on one surface of the base film, and includes a fluorinated resin and an olefin-based lubricant having a ring and ball softening point of 120 ° C. or higher. The polymer layer is composed of a fluororesin and an olefin-based lubricant having a ring and ball softening point of 120 ° C. or higher (hereinafter sometimes referred to as “high softening point olefin-based lubricant”), so that it is difficult to be scratched. Moreover, even if the film surface temperature is heat-treated at 120 ° C. or higher, for example, in the drying process during the manufacturing process, the lubricant is difficult to melt and adhesion to the transport roll is suppressed. Moreover, since it is not necessary to lower the heat treatment temperature in the manufacturing process, thermal shrinkage can be kept small even when heated in a laminating process with a sealing material or the like.

-Fluorine resin-
The fluororesin contained in the polymer layer forming composition for forming the polymer layer is not particularly limited as long as it is a polymer having a repeating unit represented by-(CFX ¹ -CX ² X ³ )-. (Wherein X ¹ , X ² and X ³ each independently represent a hydrogen atom, a fluorine atom, a chlorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms).
Specific examples of the fluororesin include polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), polyvinyl fluoride (hereinafter sometimes referred to as PVF), and polyvinylidene fluoride (hereinafter referred to as PVDF). Polychlorinated ethylene fluoride (hereinafter sometimes referred to as PCTFE), polytetrafluoropropylene (hereinafter sometimes referred to as HFP), and the like.

The fluororesin may be a homopolymer obtained by polymerizing a single monomer, or may be a copolymer obtained by copolymerizing two or more kinds. Examples thereof include a copolymer of tetrafluoroethylene and tetrafluoropropylene (abbreviated as P (TFE / HFP)), a copolymer of tetrafluoroethylene and vinylidene fluoride (abbreviated as P (TFE / VDF)), etc. Can be mentioned.
Further, the fluorine resin used for the polymer layer may be a polymer obtained by copolymerizing a fluorine-based structural unit represented by-(CFX ¹ -CX ² X ³ )-and other structural units. Examples of these are copolymers of tetrafluoroethylene and ethylene (hereinafter abbreviated as P (TFE / E)), copolymers of tetrafluoroethylene and propylene (abbreviated as P (TFE / P)), tetrafluoroethylene and Copolymer of vinyl ether (abbreviated as P (TFE / VE)), copolymer of tetrafluoroethylene and perfluorovinyl ether (abbreviated as P (TFE / FVE)), copolymer of chlorotrifluoroethylene and vinyl ether (P (Abbreviated as CTFE / VE)), a copolymer of chlorotrifluoroethylene and perfluorovinyl ether (abbreviated as P (CTFE / FVE)), and the like.
Especially, it is preferable that the polymer layer used as an outermost layer contains a chlorotrifluoroethylene unit from a viewpoint of solubility and a weather resistance.

  The fluororesin used for the polymer layer may be one used by dissolving a polymer in an organic solvent, or one obtained by dispersing polymer fine particles in water. The latter is preferred because of its low environmental impact. The aqueous dispersions of fluororesins are described in, for example, Japanese Patent Application Laid-Open Nos. 2003-231722, 2002-20409, 9-194538, and the like. Applicable to

  As the binder for the polymer layer, the above fluororesins may be used alone or in combination of two or more. Moreover, you may use together resins other than fluororesins, such as an acrylic resin, a polyester resin, a polyurethane resin, a polyolefin resin, and a silicone resin, in the range which does not exceed 50 mass% of all the binders. However, if the resin other than the fluororesin exceeds 50% by mass, the intended effect of improving weather resistance may not be obtained.

  Commercially available fluororesins contained in the polymer layer forming composition include Obligato SW0011F (manufactured by AGC Co-Tech), Lumiflon LF200 (manufactured by Asahi Glass Co., Ltd.), Zeffle GK570 (manufactured by Daikin Industries, Ltd., SIFCLEAR). F101, F102 (manufactured by JSR Corporation)) and the like.

  These fluororesins may be used by dissolving a polymer in an organic solvent, or may be used by dispersing polymer fine particles in water. The latter is preferred because of its low environmental impact. For example, JP-A-2003-231722, JP-A-2002-20409, JP-A-9-194538, etc. describe the aqueous dispersions of fluorine-based resins, and the polymers described therein are applied to the present invention. Yes.

  From the viewpoint of weather resistance and film strength, the content of the fluororesin relative to the total solid mass of the polymer layer forming composition is preferably 40% by mass to 90% by mass, and 50% by mass to 80% by mass. More preferably.

-Olefin lubricant-
The polymer layer contains an olefinic lubricant (high softening point olefinic lubricant) having a ring and ball softening point of 120 ° C. or higher as a lubricant. Here, the ring-and-ball softening point is a value measured by the ring-and-ball method in accordance with JIS K2207. Specifically, the ring-and-ball softening point is a value measured by a ring and ball automatic softening point tester ASP-MG2 manufactured by Meitec. is there.

  Since the polymer layer (outermost layer) contains a high softening point olefinic lubricant, a decrease in slipperiness (that is, an increase in the dynamic friction coefficient) that tends to occur when a fluororesin is used can be suppressed. The susceptibility to scratches caused by external forces such as collisions is drastically reduced. Further, it is possible to improve the surface repellency of the coating liquid that is likely to occur when a fluorine-based resin is used, and it is possible to form a weather resistant layer containing a fluorine-based resin having a good surface shape.

  The high softening point olefin-based lubricant preferably contains at least one of an ethylene unit and a propylene unit. Examples thereof include polyolefin waxes such as polyethylene wax and polypropylene wax having a ring and ball softening point of 120 ° C. or higher.

  The high softening point olefin-based lubricant preferably contains an acid-modified olefin resin as the olefin resin. Examples of the high softening point olefin-based lubricant containing an acid-modified olefin resin include Chemipearl (registered trademark) series (for example, Chemipearl (registered trademark) W300, W700, W900, WP100, etc.), high wax (registered trademark) manufactured by Mitsui Chemicals, Inc. Trademark) series (for example, High Wax (registered trademark) NP50605A, NP0555A) and the like.

  The size of the high softening point olefin-based lubricant is preferably 2 μm or less, more preferably 1 μm or less, from the viewpoint of scratch resistance. The median diameter of the high softening point olefin-based lubricant is a value measured by a laser analysis / scattering particle size distribution measuring device MT3300EX2 [manufactured by Nikkiso Co., Ltd.].

  The ring-and-ball softening point of the high softening point olefinic lubricant contained in the polymer layer is preferably 130 ° C. or higher from the viewpoint of preventing melting in the drying step.

  From the viewpoint of scratch resistance, the number average molecular weight (Mn) of the olefin resin contained in the high softening point olefin-based lubricant is preferably 3000 or more and 10,000 or less, and more preferably 3000 or more and 8000 or less. The number average molecular weight (Mn) of the olefin resin contained in the high softening point olefin-based lubricant is the number average molecular weight in terms of polystyrene measured by gel permeation chromatography and is measured by a molecular weight distribution measurement system manufactured by Shimadzu Corporation. Value.

  A commercially available product may be used as the high softening point olefin-based lubricant contained in the polymer layer. Chemipearl (registered trademark) series (for example, Chemipearl (registered trademark) W300, W700, W900, WP100, etc.) manufactured by Mitsui Chemicals, Inc., high wax (registered trademark) series (for example, high wax (registered trademark) NP50605A, NP0555A) And Polylon P-502, Hydrin L-536 (all trade names) manufactured by Chukyo Yushi Co., Ltd., and the like.

  The content of the high softening point olefin-based lubricant in the polymer layer is preferably 4 to 30 parts by mass of the high softening point olefin-based lubricant with respect to 100 parts by mass of the fluororesin from the viewpoint of process contamination. More preferably, it is 6 parts by mass or more and 15 parts by mass or less. If 4 parts by mass or more of the high softening point olefin-based lubricant is included with respect to 100 parts by mass of the fluororesin, the effect of reducing the dynamic friction coefficient by containing the lubricant is surely obtained, and if it is 30 parts by mass or less, the polymer layer is applied. When forming, uneven coating and aggregates are generated, and repelling failures are less likely to occur.

-Crosslinking agent-
The polymer layer preferably contains a fluorine-based resin and a high softening point olefin-based lubricant, and further has a crosslinked structure derived from a crosslinking agent.
When the composition for forming a polymer layer contains a crosslinking agent, the fluororesin contained in the composition for forming a polymer layer can be crosslinked to form an outermost layer having adhesiveness and strength.
Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. From the viewpoint of ensuring adhesion with a base film after wet heat aging, a crosslinking agent selected from a carbodiimide crosslinking agent, an oxazoline crosslinking agent, an isocyanate crosslinking agent, and an epoxy crosslinking agent is preferred, and in particular, an oxazoline crosslinking agent. (Compound having an oxazoline group) is preferred.

  The oxazoline-based crosslinking agent has two or more oxazoline groups in the molecule and may be a low molecular compound or a polymer, but the polymer has better adhesion. preferable.

Specific examples of the oxazoline-based crosslinking agent include low-molecular-weight oxazoline-based crosslinking agents such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, and 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-o Xazoline), 2,2′-ethylenebis- (4,4′-dimethyl-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), 2,2 '(1,3-phenylene) -bis- (2-oxazoline) Bis- (2-oxazolinylcyclohexane) sulfide, bis- (2-oxazolinylnorbornane) sulfide, and the like. Furthermore, (co) polymers of these compounds can also be preferably used.
These may be used alone or in combination of two or more.

The polymer oxazoline-based crosslinking agent can be obtained by polymerizing a monomer component containing an addition-polymerizable oxazoline as a constituent component and a monomer copolymerizable with the addition-polymerizable oxazoline.
Examples of addition polymerizable oxazolines include 2-vinyl-2-oxazoline, 2-vinyl-4methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-iso Propenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, and the like are preferable, and these may be used alone or in combination of two or more. May be used. Among these, 2-isopropenyl-2-oxazoline is preferable for easy availability and good adhesion. The amount of these addition polymerizable oxazolines used is not particularly limited, but is preferably 5% by mass or more in the monomer component, more preferably 5 to 90% by mass, further preferably 10 to 60% by mass, and 30 to 60% by mass. % Is particularly preferred.
The monomer copolymerizable with the addition-polymerizable oxazoline is preferably selected from those that do not react with the oxazoline group. For example, methyl (meth) acrylate, ethyl (meth) acrylate, n- (meth) acrylate Butyl, isobutyl (meth) acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, lauryl (meth) acrylate , Stearyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, monoesterified product of (meth) acrylic acid and polyethylene glycol, (meth) acrylic acid- 2-Aminoethyl and its salts, caprola of (meth) acrylic acid (Meth) acrylic acid esters such as (meth) acrylic acid-2,2,6,6-tetramethylpiperidine and (meth) acrylic acid-1,2,2,6,6-pentamethylpiperidine; (Meth) acrylates such as sodium (meth) acrylate, potassium (meth) acrylate and ammonium (meth) acrylate; unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth) acrylamide, N-methylol (meta ) Unsaturated amides such as acrylamide and N- (2-hydroxyethyl) (meth) acrylamide; Vinyl esters such as vinyl acetate and vinyl propionate; Vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; Vinyl chloride, vinyl chloride Α, β-unsaturated aliphatic hydrocarbons containing halogen such as redene and vinyl fluoride; α, β-unsaturated aromatic hydrocarbons such as styrene, α-methylstyrene and sodium styrenesulfonate; These may be used alone or in combination of two or more.
The solar cell protective sheet of the present invention is preferably an oxazoline-based crosslinking agent, that is, a copolymer in which the compound having an oxazoline group includes a (meth) acrylic acid ester unit.

The oxazoline-based crosslinking agent is preferably aqueous such as water-soluble and / or water-dispersible from the viewpoint of excellent mixing stability with the aqueous dispersion of acid-modified polyolefin resin, and more preferably water-soluble. Here, “water-soluble” means that it can be dissolved in water at a certain concentration or more.
The polymerization method of the polymer oxazoline-based crosslinking agent is not particularly limited, and a known method can be employed. For example, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, a bulk polymerization method, or the like in an aqueous medium can be used. By these methods, an aqueous solution or an aqueous dispersion can be obtained. It is preferable that the oxazoline-based cross-linking agent of these polymers does not substantially contain a non-volatile aqueous additive to improve adhesion and weather resistance.

  The molecular weight of the polymer oxazoline-based crosslinking agent is preferably 1000 to 80000 in terms of number average molecular weight, more preferably 3000 to 60000, still more preferably 5000 to 40000, particularly preferably 8000 to 30000, most preferably 10,000 to 20000. preferable. When the number average molecular weight is less than 1000, the adhesiveness and weather resistance tend to decrease. When the number average molecular weight exceeds 80000, it is difficult to produce a polymer.

  As the oxazoline-based crosslinking agent, commercially available products may be used. For example, aqueous dispersion type Epocross “K-1010E”, “K-1020E”, “K-1030E”, K2010E, K2020E, K2030E, aqueous solution type WS500, WS700 [Epocross Series manufactured by Nippon Shokubai Co., Ltd.] and the like can be used.

  The content of the crosslinking agent with respect to the total solid content of the composition for forming a polymer layer is preferably 10% by mass to 75% by mass, more preferably 15% by mass to 60% by mass, and 20% by mass. A range of ˜50 mass% is particularly preferred. When the content of the cross-linking agent is 5% by mass or more, a sufficient cross-linking effect is obtained, and a decrease in strength of the polymer layer and poor adhesion can be suppressed. On the other hand, the pot life fall of the composition for polymer layer formation can be prevented because it is 50 mass% or less.

The coating amount of the polymer layer forming composition, the adhesiveness viewpoint of the weatherability and the base film, it is preferable that the ^{0.5g / m 2 ~20g / m 2} , 3g / m 2 ~15g / m ² is more preferable.

The layer thickness of the polymer layer is preferably 0.5 μm to 15 μm, and more preferably 3 μm to 10 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.
Note that the polymer layer may be a single layer or a structure in which two or more layers are laminated. The solar cell protective sheet of the present invention preferably has a structure in which two polymer layers are laminated.

-Other ingredients-
The polymer layer may contain components (additives) other than the fluorine-based resin, the high softening point olefin-based lubricant, and the crosslinking agent as long as the effects of the present invention are not impaired. Examples of the additive include a surfactant, colloidal silica, a silane coupling agent, a color pigment, an ultraviolet absorber, and an antioxidant.

-Formation of polymer layer-
Although there is no restriction | limiting in particular in the formation method of a polymer layer, It dries, after apply | coating the composition (coating liquid) for polymer layer formation to the surface of a base film directly or the other layer arrange | positioned on a base film. It can form suitably.

〔solvent〕
The coating solvent is not particularly limited as long as each component constituting the polymer layer can be dispersed or dissolved and can be removed after coating, but water is preferably used in the solvent contained in the polymer layer forming composition. It is preferable that 60 mass% or more of is 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 polymer layer forming composition is preferably larger from the viewpoint of environmental load, and more preferably 70% by mass or more of water is contained in the total solvent. In the protective sheet for solar cell of the present invention, the solvent residual ratio in the polymer layer is preferably 0.05% by mass or less, and 0.025% by mass or less with respect to the mass of the polymer layer (mass of the coating film). More preferably, it is particularly preferably 0.01% by mass or less.

For the application of the polymer layer forming composition onto the base film, a known coating method such as a gravure coater or a bar coater can be used.

  After the composition for forming a polymer layer is applied directly on the base film or on another layer, the polymer layer is formed by drying. The atmospheric temperature in the drying zone is preferably 145 ° C. or higher and 200 ° C. or lower, more preferably 160 ° C. or higher and 185 ° C. or lower, from the viewpoint of volatilizing the solvent and reducing the melting and heat shrinkage of the lubricant.

(Middle layer)
The protective sheet for solar cell of the present invention may have a layer other than the polymer layer on the base film. For example, an intermediate layer can be provided between the base film and the polymer layer.

  The intermediate layer includes at least a binder, and may have a single layer structure or a laminated structure including a plurality of layers.

-Binder-
The binder used for the intermediate layer may be an organic polymer, an inorganic polymer, or a binder made of an organic / inorganic composite polymer. By including the polymer, adhesion to the base film and adhesion to the polymer layer can be achieved. It is improved and resistance to deterioration in a humid heat environment is obtained.
There is no restriction | limiting in particular as an inorganic polymer, A well-known inorganic polymer can be used. The organic polymer or organic / inorganic composite polymer is not particularly limited, but preferably contains at least one of a fluorine atom and a silicone-acrylic unit, and includes at least one of a fluorine-based organic polymer and a silicone-acrylic organic / inorganic composite resin. It is more preferable to include a silicone-acrylic organic / inorganic composite resin.

  The intermediate layer may contain a colorant, scattering particles, a crosslinking agent, a surfactant, a filler, and the like as necessary. Among these, it is preferable from the viewpoint of further improving the strength and durability of the intermediate layer by adding a crosslinking agent to the binder (binder resin) to form a crosslinked structure derived from the crosslinking agent in the intermediate layer.

-Colorant-
There is no restriction | limiting in particular as a coloring agent, A well-known dye, a well-known pigment, etc. can be used. However, the colorant in the present specification excludes scattering particles. In the present invention, the colorant is preferably a black colorant, a green colorant, a blue colorant, or a red colorant.

The coloring pigment used in the intermediate layer is not particularly limited except that it preferably contains at least one selected from carbon black, titanium black, black composite metal oxide, cyanine color and quinacridone color. May be selected according to the color and optical density.
Here, as the black composite metal oxide, a composite metal oxide containing at least one of iron, manganese, cobalt, chromium, copper, and nickel is preferable, and among cobalt, chromium, iron, manganese, copper, and nickel It is more preferable to include two or more types, and at least one pigment selected from PBk26, PBk27, PBk28, and PBr34 is more particularly preferable. The PBk26 pigment is a complex oxide of iron, manganese and copper, the PBk27 pigment is a complex oxide of iron, cobalt and chromium, and the PBk-28 is a complex oxide of copper, chromium and manganese. PBr34 is a composite oxide of nickel and iron. Examples of the cyanine color and quinacridone color include cyanine green, cyanine blue, quinacridone red, phthalocyanine blue, and phthalocyanine green.

Among these, it is preferable to use carbon black as a colorant from the viewpoint of easily controlling the optical density within the above-mentioned preferable range and from the viewpoint of controlling the optical density with a small amount. For example, a black or gray colored layer may be formed by adding carbon black to the intermediate layer.
The carbon black is preferably carbon black fine particles having a particle diameter of 0.1 to 0.8 μm. Furthermore, it is preferable to use the carbon black fine particles dispersed in water together with a dispersant. Carbon black that can be obtained commercially can be used, for example, MF-5630 black (manufactured by Dainichi Seika Co., Ltd. or described in paragraph [0035] of JP 2009-132877 A Can be used.

-Scattered particles-
The scattering particles that can be included in the intermediate layer are not particularly limited, and known scattering particles can be used. In the present specification, the scattering particle means a particle that hardly absorbs light and does not contain a colorant. In the present invention, it is preferable to use a white pigment as the scattering particles.
Examples of white pigments that can be used as scattering particles include inorganic pigments such as titanium dioxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, and colloidal silica, and organic pigments such as hollow particles. Of these, titanium dioxide is preferable.
There are rutile type, anatase type, and brookite type in the crystal system of titanium dioxide. Of the titanium dioxide used in the present invention, the rutile type is preferred. The titanium dioxide used in the present invention may be surface-treated with aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), alkanolamine compound, silicon compound or the like, if necessary.
In particular, by using titanium dioxide having a bulk specific gravity of 0.50 g / cm ³ or more, titanium dioxide is densely packed and the weather-resistant layer becomes tough. On the other hand, when titanium dioxide having a bulk specific gravity exceeding 0.85 g / cm ³ is used, the dispersibility of titanium dioxide is deteriorated and the surface state of the coating layer is deteriorated. By setting the bulk specific gravity to 0.50 g / cm ³ or more and 0.85 g / cm ³ or less, titanium dioxide is tightly packed and the coating film becomes tough, so that even if the mass ratio of titanium dioxide is set high, it adheres Sex can be maintained high. The bulk specific gravity of titanium dioxide used for the weather resistant layer is particularly preferably 0.60 g / cm ³ or more and 0.80 g / cm ³ or less.

The bulk specific gravity of the white pigment in the present specification is a value measured by the following method. (1) The pigment is passed through a sieve having an aperture of 1.0 mm. (2) About the above-mentioned pigment, about 100 g of pigment is weighed (m) and gently put into a 250 mL graduated cylinder. If necessary, the top surface of the pigment layer is carefully leveled without compaction and the volume (V) is measured. (3) The bulk specific gravity is obtained according to the following formula. Bulk specific gravity = m / V (unit: g / cm ³ )

In addition to the base polymer such as silicone or fluorine resin, the intermediate layer can contain a white pigment as scattering particles to increase the reflectivity of the intermediate layer. Long-term high-temperature high-humidity test (85 ° C, relative humidity 85% In 2000 to 3000 hours) and a UV irradiation test (according to the UV test of IEC61215, the total irradiation amount is 45 Kwh / m ² ). Furthermore, by adding a white pigment such as scattering particles to the intermediate layer, the adhesion with other adjacent layers is further improved.
The content of the case of using the scattering particles in the intermediate layer is preferably an intermediate layer per layer ^{1.0g / m 2 ~15g / m 2} . When the content of the scattering particles, preferably the white pigment is 1.0 g / m ² or more, reflectance and UV resistance (light resistance) can be effectively provided. Further, when the content of the white pigment in the intermediate layer is 15 g / m ² or less, it is easy to maintain a good surface shape and the film strength is more excellent. Among them, more preferably the content of the scattering particles contained in the intermediate layer is in the range of ^{2.5g / m 2 ~12g / m 2} , the range of 4.5g / ^{m 2} ~10g / m 2 is particularly preferable.
The average particle size of the white pigment as the scattering particles is preferably 0.03 μm to 0.8 μm, more preferably about 0.15 μm to 0.5 μm in volume average particle size. When the average particle size is within the above range, the light reflection efficiency is high. The average particle size is a value measured by a laser analysis / scattering particle size distribution measuring apparatus Microtrac MT3300EXII [manufactured by Nikkiso Co., Ltd.].

  The content of the binder component in the intermediate layer is preferably in the range of 15 parts by mass to 200 parts by mass and more preferably in the range of 17 to 100 parts by mass with respect to 100 parts by mass of the white pigment that is the scattering particles. When the content of the binder is 15 parts by mass or more, the strength of the intermediate layer is sufficiently obtained, and when it is 200 parts by mass or less, the reflectance and the decorativeness can be kept good.

-Crosslinking agent-
Examples of the crosslinking agent that can be included in the intermediate layer include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, at least one kind of crosslinking agent selected from carbodiimide crosslinking agents, oxazoline crosslinking agents, and isocyanate crosslinking agents is preferable.
As the crosslinking agent, those described for the polymer layer are similarly applied to the intermediate layer, and preferred examples are also the same.

  The addition amount in the case of using a crosslinking agent for the intermediate layer is preferably 0.5 to 30 parts by mass, more preferably 3 parts by mass or more and less than 15 parts by mass with respect to 100 parts by mass of the binder contained in the intermediate layer. . When the addition amount of the crosslinking agent is 0.5 parts by mass or more, a sufficient crosslinking effect is obtained while maintaining the strength and adhesiveness of the polymer layer, and when it is 30 parts by mass or less, the pot life of the coating liquid is reduced. If the length is less than 15 parts by mass, the coated surface can be improved.

Examples of the surfactant that can be used for the intermediate layer include known surfactants such as anionic and nonionic surfactants. If a surfactant is added, the addition amount thereof is preferably from ^{0.1mg / m 2 ~10mg / m 2} , more preferably ^{0.5mg / m 2 ~3mg / m 2} . When the addition amount of the surfactant is 0.1 mg / m ² or more, the generation of repellency is suppressed and good layer formation is obtained, and when the addition amount is 10 mg / m ² or less, adhesion to the substrate film or the like is achieved. It can be performed well.
A filler may be added to the intermediate layer. A known filler such as colloidal silica can be used as the filler.

An intermediate | middle layer can be formed by apply | coating the coating liquid containing a binder etc. to the surface of the back surface side of a base film, and drying it.
In the solar cell protective sheet of the present invention, the intermediate layer is preferably a coating layer formed by applying an aqueous composition for forming an intermediate layer containing at least one of a fluororesin and a silicone-acrylic polymer.
In the method for producing a protective sheet for a solar cell of the present invention, an aqueous dispersion in which these silicone-acrylic resin or fluorine-based resin and other components used in combination are dispersed and contained in water is prepared. An embodiment in which the dispersion is applied as a water-based coating liquid on a desired substrate film is preferable.
There is no restriction | limiting in particular in the coating method and the solvent of the coating liquid to be 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. From the viewpoint of environmental burden, it is preferable to prepare an aqueous coating solution using water as a coating solvent.
A coating solvent may be used individually by 1 type, and may mix and use 2 or more types. A method in which an aqueous coating solution in which a binder is dispersed in water is formed and applied is preferable. In this case, the proportion of water in the solvent is preferably 60% by mass or more, and more preferably 80% by mass or more.

  After the application, a drying process for drying the coating film under desired conditions may be provided. What is necessary is just to select suitably about the drying temperature at the time of drying according to cases, such as a composition of a coating liquid, a coating amount. Moreover, when a base film is a biaxially stretched film, after apply | coating a coating liquid to the base film after biaxial stretching, you may dry a coating film, and the base film after uniaxial stretching Alternatively, the coating liquid may be applied to the film and the coating film may be dried, followed by stretching in a direction different from the initial stretching. Furthermore, you may extend | stretch to 2 directions, after apply | coating a coating liquid to the base film before extending | stretching and drying a coating film.

-Thickness-
The thickness of the intermediate layer is usually preferably 0.3 μm to 22 μm, more preferably 0.5 μm to 15 μm, still more preferably 0.8 μm to 12 μm, particularly preferably 1.0 μm to 8 μm, and 2 to 6 μm. The range of is most preferable. When the thickness is in the above range, moisture is difficult to penetrate from the surface of the intermediate layer to the inside when exposed to a moist heat environment, and it is difficult for moisture to reach the interface between the intermediate layer and the substrate film, so that adhesiveness is remarkable. In addition, the film strength of the intermediate layer itself is maintained well, and the weather resistance layer is less likely to break when exposed to a moist heat environment, thereby improving the adhesion.

[Back sheet for solar cells]
The solar cell backsheet of the present invention comprises the solar cell protective sheet of the present invention. The solar cell protective sheet of the present invention may be used as it is as the solar cell backsheet of the present invention, or, as shown in FIG. 1, other layers such as an undercoat layer 17 and an easy-adhesion layer 18 are provided. It may be a back sheet for use.

[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 light energy of sunlight into electric energy is disposed between the transparent front substrate on which sunlight is incident and the solar cell backsheet of the present invention described above. The space between the front substrate and the back sheet is 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 is disposed on a transparent front substrate on which sunlight is incident and on the side of the front substrate opposite to the side on which sunlight is incident, and seals the solar cell element and the solar cell element. It has the element structure part containing the sealing material which stops, and the solar cell backsheet of this invention arrange | positioned on the opposite side to the side in which the front base material of the element structure part is located.

  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.

  Solar cell elements include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, III-V groups such as copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, gallium-arsenide, and II Various known solar cell elements such as -VI group compound semiconductor systems can be applied.

Hereinafter, the present invention will be described more specifically with reference to 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 should not be construed as being limited by the specific examples shown below.
Unless otherwise specified, “part” is based on mass.

[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 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 3.4 times in the longitudinal direction at 90 ° C., and then the coating solution for forming the undercoat layer was applied to the corona-treated surface of the polyethylene terephthalate base film so that the coating amount was 5.1 ml / m ^2. After MD stretching, coating was performed by an in-line coating method before TD stretching to form an undercoat layer having a thickness of 0.1 μm. The TD stretching temperature is 105 ° C., stretched 4.5 times in the TD direction, and heat treatment is performed at 200 ° C. for 15 seconds. The MD relaxation rate is 5% at 190 ° C., and the MD relaxation rate is 11%. Then, heat relaxation was performed in the TD direction to obtain a biaxially stretched polyethylene terephthalate base film (hereinafter referred to as “PET base film”) having a thickness of 250 μm.

<Formation of weather-resistant layer>
As the weather resistant layer, the intermediate layer forming composition and the polymer layer forming composition having the compositions shown in Table 1 and Table 2 below are respectively used, and the intermediate layer and the polymer layer (outermost layer) are formed in this order on the base film. Thus, a solar cell protective sheet (back sheet) was obtained.

-Formation of intermediate layer-
1. Preparation of Titanium Dioxide Dispersion Using a dynomill disperser, a titanium dioxide dispersion was prepared by dispersing the titanium dioxide so that the average particle size of titanium dioxide was 0.42 μm. In addition, the average particle diameter of titanium dioxide was measured using Nikkiso Co., Ltd. and Microtrac MT3300EXII.

(Composition of titanium dioxide dispersion)
・ Titanium dioxide: 455.8 parts by mass
(Taipeke CR-95, manufactured by Ishihara Sangyo Co., Ltd., powder)
-PVA (polyvinyl alcohol) aqueous solution: 227.9 parts by mass
(PVA-105, manufactured by Kuraray Co., Ltd., concentration 10% by mass)
・ Dispersant: 5.5 parts by mass
(Demol EP, manufactured by Kao Corporation, concentration 25% by mass)
・ Distilled water: 310.8 parts by mass

2. Preparation of Composition for Forming Intermediate Layer Each component described in Table 1 below was mixed to prepare compositions D-1 to D-3 for forming an intermediate layer.

3. Formation of Intermediate Layer The obtained composition for forming an intermediate layer was coated on one side of the base film with a titanium dioxide coating amount of 10 g / m ² for D-1 and D-3 and 5 g / m ² for D- ^2. And then dried at 170 ° C. for 2 minutes to form intermediate layers (white layer, black layer) having a thickness of 9 μm (D-1, D-3) and 6 μm (D-2).

-Formation of polymer layer-
Polymer layer forming composition E-1 having the composition shown in Table 2 below was prepared.
The polymer layer-forming composition E-1 is applied on the intermediate layer so that the amount of the fluorine-based polymer applied is 1.0 g / m ² , dried at 170 ° C. for 2 minutes, and the outermost layer has a thickness of 0.8 μm. The polymer layer was formed.

[Example 2-18, Comparative Examples 1 and 2]
The drying temperature of the base film, outermost layer, intermediate layer, and outermost layer was changed to the materials and conditions shown in Table 3 below. The solar cell protective sheet was prepared in the same manner as in Example 1 except that the constituents of each layer were changed so that the solid content was the same amount (however, the cross-linking agent had the same equivalent number of reactive substituents). did.
The meanings of the abbreviations in Table 3 are as follows. Moreover, in Table 3, the addition amount (mass%) of the lubricant in the outermost layer is a value calculated with respect to 100 parts by mass of the fluororesin.

(Base film)
Polyester: PET base film prepared as described above Polyolefin: In the presence of hydrogen using a catalyst comprising diphenylmethylene (cyclopentadienyl) fluorenylzirconium dichloride and methylaluminoxane according to JP-A-2-274863 Syndiotactic polypropylene {by the bulk polymerization method of propylene {(Intrinsic viscosity measured in tetralin solution at 135 ° C. is 1.39 dl / g, melt flow index is 3.2 g / 10 min, crystallization measured by differential scanning calorimetry The peak temperature of the temperature was 74.6 ° C., and the syndiotactic pentad fraction measured by ¹³ C-NMR was 78.7%) (H-SPP)}. 80 parts by mass of the syndiotactic polypropylene obtained above and 20 parts by mass of isotactic homopolypropylene (manufactured by Mitsui Toatsu Chemical Co., Ltd., JHH-G: MFI 8 g / 10 min) were blended, and the T- A syndiotactic polypropylene film having a thickness of 240 μm was obtained by forming a film at an extruder temperature of 210 ° C. and a cooling roll temperature of 30 ° C. using an extruder with a die.
Polyamide: 98% by weight of polycaprolactam and 2% by weight of polycaprolactone having a molecular weight of 10,000 were mixed, melt-kneaded by an extruder set at 250 ° C., and pelletized. Subsequently, this pellet was melt-extruded from a T die at 270 ° C. and cooled on a drum at 30 ° C. to obtain an unstretched film. Subsequently, this film was simultaneously biaxially stretched at 80 ° C. to obtain a biaxially stretched polyamide film having a thickness of 240 μm.
Using a polyphenylene ether: polyphenylene ether: polyphenylene ether resin composition (SABIC Innovation Plastics Co., Ltd., “Noryl N300”), a 240 μm film was prepared by extrusion casting (cylinder temperature of 270 to 300 ° C.). Then, using a tenter device, the sheet was heat-treated in a dryer (internal temperature 180 ° C.). Thus, a polyphenylene ether film was obtained.

(Outermost layer)
A-1: Obligato SW0011F (manufactured by AGC Co-Tech, fluorinated resin)
A-2: SIFCLEAR F101 (manufactured by JSR Corporation, fluorine resin)
CTFE: containing chlorotrifluoroethylene unit VF2: containing vinylidene fluoride unit W900: Chemipearl (registered trademark) W900 (manufactured by Mitsui Chemicals, olefinic wax, ring-ball softening point: 132 ° C.) Molecular weight 4000
W300: Chemipearl (registered trademark) W300 (manufactured by Mitsui Chemicals, olefin wax, ring-ball softening point: 132 ° C.)
W700: Chemipearl (registered trademark) W700 (manufactured by Mitsui Chemicals, olefin wax, ring-ball softening point: 132 ° C.)
W950: Chemipearl (registered trademark) W950 (manufactured by Mitsui Chemicals, olefin-based wax, ring ball softening point: 113 ° C.) molecular weight 2000
WP100: Chemipearl (registered trademark) WP100 (manufactured by Mitsui Chemicals, Inc., olefin wax, ring ball softening point: 148 ° C.) molecular weight 7000
NP0555A: High wax NP0555A (Mitsui Chemicals, olefin wax, ring ball softening point: 143 ° C., molecular weight 18000) dispersed in water by the following method.
It is supplied at a rate of 3000 g / hr from the hopper of a twin screw extruder (Ikegai Iron Works, PCM-30, L / D = 40), and potassium hydroxide is supplied from the supply port provided in the vent portion of the extruder. 20% aqueous solution was continuously supplied at a rate of 90 g / hour and continuously extruded at a heating temperature of 210 ° C. The extruded resin mixture was cooled to 110 ° C. with a jacketed static mixer installed at the extruder port, and further poured into warm water at 80 ° C. to obtain an aqueous dispersion. The average particle size of the obtained water dispersion was 3.0 μm.
Oxazoline (water-soluble): Epocross WS700 (manufactured by Nippon Shokubai Co., Ltd., oxazoline-based crosslinking agent)
Oxazoline (latex): Epocross K-2030E (manufactured by Nippon Shokubai Co., Ltd., oxazoline-based crosslinking agent)
Epoxy: Denacol EX-614B (manufactured by Nagase ChemteX Corporation, epoxy-based crosslinking agent)
Isocyanate: TRIXENE DP9C / 214 (manufactured by BAXENDENE CHEMICAL, blocked isocyanate-based crosslinking agent)
Carbodiimide: Carbodilite V-02-L2 (Nisshinbo Co., Ltd., carbodiimide-based crosslinking agent)

<Evaluation of solar cell protective sheet>
The following evaluation was performed about the backsheet produced by the Example and the comparative example. The evaluation results are shown in Table 4 below.

−Scratch resistance−
The back sheet was conditioned for 24 hours in an atmosphere of 25 ° C. and 60% RH, and then the surface of the sheet was scratched with a sapphire needle having a tip diameter of 0.1 mm while changing the load at a speed of 1 cm / second. The surface of the sheet after scratching was observed with an optical microscope, and the lowest load at which scratches were observed was taken as a measure of scratch resistance. Larger values indicate better scratch resistance, and practically acceptable is 30 g or more.
A: 50 g or more B: 40 g or more C: 30 g or more D: less than 30 g

-Thermal shrinkage-
The back sheet was cut into a sample size of 120 mm in MD direction × 30 mm in TD direction, and heated in an oven at 150 ° C. for 30 minutes. Then, after adjusting the humidity for 30 minutes at room temperature, the length in the MD direction was measured, and the thermal shrinkage rate was measured. The thermal shrinkage rate was measured as described above for three samples cut out from each backsheet, and the average value was taken as the thermal shrinkage rate.

-Process dirt-
The polymer sheet (back sheet) was heated with a heating roll, and then passed through a non-heating type pass roll to evaluate the transfer property of the sliding agent to the non-heating type pass roll.
As the heating roll, a jacket roller manufactured by Tokuden Corporation was used. Tension could be applied to the polymer sheet in the transport line, and the evaluation result did not change particularly in the tension range of 10 to 40 kg / m. As for the holding angle to the heating type roll and the non-heating type pass roll in the conveying apparatus, the evaluation result did not change in the range of 0 to 140 degrees.
experimental method:
The polymer sheets were joined together in a transport line having a heated roll, a non-heated roll, and a suction drum, and were continuously transported at a transport speed of 5 m / min. At this time, the total length of the polymer sheet was 5 m.
After the test starts, the heated roll is gradually heated, and after the heated roll reaches the target temperature, it is transported for 60 minutes, then cooled to 50 ° C. or lower over 90 minutes, and the polymer sheet is removed from the transport line and visually observed. Evaluation was performed.
A: No transfer B: Slight transfer (transfer area to roll is 5% or less of roll surface area)
C: Transfer (transfer to entire roll surface)

  The evaluation results are shown in Table 4.

[Example 100]
<Production and evaluation of solar cell module>
3 mm thick tempered glass, EVA sheet (RC02B manufactured by Mitsui Chemicals Fabro Co., Ltd.), crystalline solar cell, EVA sheet (RC02B manufactured by Mitsui Chemicals Fabro Co., Ltd.), and each example The thus-prepared solar cell protective sheets were superposed in this order and hot-pressed using a vacuum laminator (Nisshinbo Co., Ltd., vacuum laminating machine) to bond the EVA and each member. At this time, the protective sheet for solar cell of each Example was arrange | positioned so that the surface on the opposite side to the side in which the polymer layer is provided may contact with an EVA sheet | seat. Moreover, the adhesion method is as follows.
Using a vacuum laminator, vacuum was applied at 150 ° C. for 3 minutes, and then pressure was applied for 10 minutes for adhesion.

  In this way, a crystalline solar cell module was produced. When the power generation operation was performed using the obtained solar cell module, all showed good power generation performance as a solar cell, and stable operation was performed over a long period of time.

DESCRIPTION OF SYMBOLS 10 Solar cell module 12 Polymer layer 14 Intermediate | middle layer 16 Base film 17 Undercoat layer 18 Easy-adhesion layer 20 Solar cell element 22 Sealing material 24 Transparent front substrate 31 Solar cell protective sheet 32 Solar cell back sheet

Claims (13)

  A solar cell comprising: a base film; and a polymer layer that is disposed as an outermost layer on one surface of the base film and includes a fluororesin and an olefin-based lubricant having a ring and ball softening point of 120 ° C. or higher. Protective sheet.   The protective sheet for solar cells according to claim 1, wherein the olefin-based lubricant contains an olefin resin having at least one of an ethylene unit and a propylene unit.   The protective sheet for solar cells according to claim 1 or 2, wherein the olefinic lubricant has a median diameter of 2 µm or less.   The solar cell protective sheet according to any one of claims 1 to 3, wherein the base film contains a resin selected from the group consisting of polyester, polyolefin, polyamide, and polyphenylene ether.   The solar cell protective sheet according to any one of claims 1 to 4, wherein the olefin resin contained in the olefin-based lubricant has a number average molecular weight (Mn) of 3000 or more and 10,000 or less.   The solar cell protective sheet according to any one of claims 1 to 5, wherein the fluororesin comprises a chlorotrifluoroethylene unit.   The solar cell protective sheet according to any one of claims 1 to 6, wherein the polymer layer has a crosslinked structure.   The protective sheet for solar cells according to claim 7, wherein the crosslinked structure is derived from a crosslinking agent selected from the group consisting of a carbodiimide crosslinking agent, an oxazoline crosslinking agent, an isocyanate crosslinking agent, and an epoxy crosslinking agent.   The solar cell protective sheet according to claim 8, wherein the crosslinking agent is water-soluble.   The said polymer layer is a protective sheet for solar cells as described in any one of Claims 1-9 which contains 6 to 30 mass parts of olefin type lubricants with respect to 100 mass parts of fluororesins.   11. The solar cell according to claim 1, comprising an intermediate layer containing a resin containing at least one of a fluorine atom and a silicone-acryl unit between the base film and the polymer layer. Protective sheet.   The solar cell backsheet containing the protective sheet for solar cells as described in any one of Claims 1-11. A transparent front substrate on which sunlight is incident;
An element structure portion including a solar cell element and a sealing material for sealing the solar cell element, disposed on the opposite side of the front base material from which sunlight is incident;
The solar cell backsheet according to claim 12, which is disposed on the opposite side of the element structure portion from the side on which the front substrate is located.
Including solar cell module.