WO2015133399A1

WO2015133399A1 - Fluorine resin film, method for producing same, laminate, and back sheet for solar cell module

Info

Publication number: WO2015133399A1
Application number: PCT/JP2015/055856
Authority: WO
Inventors: 透大杉; 理子菊池; 赤津　正道; 哲也小松崎
Original assignee: 株式会社クレハ
Priority date: 2014-03-04
Filing date: 2015-02-27
Publication date: 2015-09-11
Also published as: JP2015166427A

Abstract

Provided are: a fluorine resin, preferably polyvinylidene fluoride resin, film that contains titanium oxide within a range of 15-50 mass%, wherein on at least one surface of the film, the total proportion of the area of titanium oxide exposed by the surface in relation to the area of the film is 3.2% or less, and a method for producing said film; and a laminate provided with a layer comprising said film, and a back sheet for a solar cell module.

Description

Fluororesin film, method for producing the same, laminate, and solar cell module back sheet

The present invention relates to a fluororesin film, preferably a polyvinylidene fluoride resin film, a method for producing the same, a laminate including a layer made of the resin film, and a back sheet for a solar cell module.

Fluoropolymers such as polyvinylidene fluoride resin (hereinafter sometimes referred to as “PVDF”) have excellent weather resistance, heat resistance, stain resistance, chemical resistance, solvent resistance, mechanical properties, Widely used in fields that require long-term durability by utilizing secondary processability. In particular, fluororesin films such as films made of PVDF (hereinafter sometimes referred to as “PVDF films”) utilize the cost merit of thinning, and are used as protective materials for various surfaces as members for interior and exterior of buildings. It is widely used as a surface material for molded products that require chemical resistance and solvent resistance, as well as a surface protection material or back surface protection material for solar cell modules in which long-term reliability is important, and a fuel cell member.

In recent years, clean energy has been actively developed for the promotion of global warming countermeasures. In particular, solar power generation using sunlight has been greatly expanded mainly in Europe and the United States, and the spread of solar cells is progressing. PVDF with excellent weather resistance, heat resistance, stain resistance, chemical resistance, solvent resistance, mechanical properties, and secondary workability is a single layer or as a laminate with other thermoplastic resin layers. , It has come to be used as a surface protective material or a back surface protective material for solar cell modules used for solar power generation.

A solar cell is a power generator that directly converts sunlight into electrical energy. Solar cells are broadly classified into those using silicon semiconductors and those using compound semiconductors. Silicon semiconductor solar cells include single crystal silicon solar cells, polycrystalline silicon solar cells, and amorphous silicon solar cells.

A typical structure of a solar cell is composed of a surface protective material, a sealing material, a solar battery cell, a back surface protective material, and a frame. As shown in FIG. 1, the main components of the solar cell are a surface protective material 1, a sealing material 2, a solar cell 3, and a back surface protective material 4, and a plurality of solar cells 3 are wired (not shown). To make a solar cell module. That is, a solar cell module in which a plurality of solar cells are arranged and connected and packaged using a surface protective material, a sealing material, and a back surface protective material (hereinafter sometimes referred to as “back sheet”). That's it. Usually, a frame (not shown) made of metal such as aluminum is arranged at the end or peripheral edge of the solar cell module.

As the surface protective material 1, for example, a tempered glass plate, a transparent plastic plate, or a transparent plastic film is used. As the sealing material 2, an ethylene-vinyl acetate copolymer is widely used. As the back surface protective material 4, for example, a single-layer or multilayer plastic film, a plastic plate, a tempered glass plate, a metal plate (aluminum plate, painted steel plate, etc.) or the like is used. As the frame, for example, aluminum that is lightweight and excellent in environmental resistance is widely used.

The solar cell module is generally installed outdoors, and then the operation state is maintained for a long time. In order for the solar cell module to operate satisfactorily outdoors over a long period of time, it is necessary to have excellent durability in a harsh environment. For this reason, the surface protection material, the sealing material, and the back surface protection material of the solar cell module are required to have a function of protecting the solar cells over a long period of time in a harsh natural environment surrounding the solar cell module. ing.

The surface (outermost surface) far from the solar battery cell of the back sheet for the solar battery module is directly exposed to the outdoors. The surface close to the solar battery cell (adjacent surface with the sealing material) of the solar cell module backsheet is exposed to sunlight through the gaps between the solar battery cells. For this reason, the back sheet for solar cell modules has light resistance, weather resistance, heat resistance, moisture resistance, oxygen or water vapor barrier properties, electrical insulation, voltage resistance, mechanical properties, chemical resistance, salt resistance, anti-resistance It is required to be excellent in various properties such as dirtiness and adhesion to a sealing material.

In addition to being excellent in the above characteristics, the solar cell module backsheet has a beautiful appearance on the surface of the solar battery cell, and also efficiently reflects sunlight incident on the backsheet. It is required to have a function to If the incident light transmitted through the gaps between the solar cells can be efficiently reflected by the back sheet, the power conversion efficiency of the solar cells is improved by the reflected light. For this reason, a back sheet containing a colorant such as titanium oxide is known.

As a plastic film used as a back sheet for a solar cell module, from the viewpoint of satisfying various properties required for the back sheet for a solar cell module, there may be a fluororesin film, polyethylene terephthalate (hereinafter referred to as “PET”). ) Films, and composite films of these have been preferably used. Among these, from the viewpoints of light resistance, weather resistance, heat resistance, antifouling properties, etc., fluorine resin films or composite films of fluorine resin films have been more preferably used (Patent Documents 1 to 3).

As the fluorine resin film for the back sheet for the solar cell module, an ethylene-tetrafluoroethylene copolymer (ETFE) film, a polytetrafluoroethylene resin (PTFE) film, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) ) Film, polyvinyl fluoride resin (PVF) film, PVDF film, and the like. PVDF films are widely used because of their superior light resistance, weather resistance, antifouling properties, heat resistance, and the like.

In addition, a back sheet for a solar cell module made of a composite film including a fluororesin film is known as having weather resistance, antifouling properties, heat resistance, mechanical properties, and the like. For example, a PVDF layer and PET A back sheet for a solar cell module including a layer is known (Patent Document 3).

As for the back sheet for solar cell module, the demand for long-term reliability is becoming stricter, and since it is required to be used under severe conditions and to have a long life as a fluorine-based resin film, further excellent weather resistance, Heat resistance, mechanical properties, and the like are required, and a fluorine-based resin film containing titanium oxide has attracted attention (Patent Documents 4 and 5).

With the widespread use of solar cells, the number of solar cell module backsheets to be handled has increased dramatically, and various complex forms and types of roofs on which solar cells are installed have increased. Solar cell module backsheets and laminates having a layer made of a fluorine-based resin film containing titanium oxide are used in transportation work, installation work and incidental work, for example, solar cell module frames, electric wires, mounting brackets, etc. There are cases in which contact with metal, such as touching, bumping, and rubbing, occurs due to accidental or necessary work. When the fluorine-based resin film containing titanium oxide comes into contact with the metal, metal powder or metal pieces may adhere to the surface of the fluorine-containing resin film containing titanium oxide like a scratch. Even in the formation of a laminate including a layer made of a fluorine-based resin film or the assembling work of a solar cell module, metal powder or metal pieces may adhere to the surface of the film like a scratch. Metal powder and metal pieces adhering to the surface of a fluorine resin film or solar cell module backsheet like scratches can be removed by just stroking lightly, so the fluorine resin after removing metal powder and metal pieces It does not remain as a rubbing trace on the surface of the film or the back sheet for the solar cell module, and there is no problem in the function of the fluororesin film or the back sheet for the solar cell module. However, if metal powder or metal pieces adhere to the surface like scratches, the appearance of the fluororesin film or the back sheet for solar cell module is impaired, so it is considered as a defective product or product. It can also be a cause. Therefore, it has excellent weather resistance and mechanical properties, and it is difficult to form an adhesion such as an abrasion mark due to adhesion of metal powder or metal pieces caused by contact with metal (hereinafter referred to as “metal abrasion resistance”). There has been a strong demand for a fluororesin film including PVDF suitable for a solar cell module backsheet, and a laminate including a layer made of the fluororesin film and a solar cell module backsheet. .

JP 2002-134768 A JP 2003-347570 A JP 2003-251765 A JP 2009-78559 A Special table 2010-530140 gazette

An object of the present invention is excellent in weather resistance, mechanical properties, etc., and is adhered like a scratch due to adhesion of metal powder or metal pieces generated by contact with metal (hereinafter, simply referred to as “scratch trace”). The present invention provides a fluorine resin film including PVDF, a laminate including a layer made of the fluorine resin film, and a solar cell module backsheet.

The inventors of the present invention have made extensive studies to solve the above-mentioned problems. As a result, titanium oxide contained in a fluorine-based resin film including PVDF in order to improve weather resistance, heat resistance, mechanical properties, and the like. The Mohs hardness is about 5.5 to 6, and is harder than metals such as aluminum with a Mohs hardness of about 2 to 2.9 and copper with a Mohs hardness of about 2.5 to 3. In addition, when a fluorine resin film containing titanium oxide and a metal come into contact with each other, a phenomenon was found in which the metal which is the other party of the contact was scraped off. As a result of this phenomenon, the present inventors can easily remove the surface of the fluororesin film, but the rubbing trace in a state where the metal powder or metal pieces generated by scraping is temporarily attached is temporarily removed. I found a mechanism to be formed.

As a result of intensive research to further solve the above problems, the present inventors have controlled weatherability, heat resistance, mechanical properties by controlling the composition and surface properties of the fluorine-based resin film containing titanium oxide. It was found that a fluorine-based resin film (metal scratch resistance) that is not easily formed due to the adhesion of metal powder or metal pieces and that is excellent at the same time can be provided.

That is, according to the present invention, there is provided a fluororesin film containing 15 to 50% by mass of titanium oxide, and at least one surface of the film is a total of the area of the titanium oxide from which the surface is exposed to the area of the film. A ratio is 3.2% or less, The said fluorine-type resin film characterized by the above-mentioned is provided.

As embodiments of the present invention, the following fluororesin films (1) to (5) are provided.
(1) The said fluororesin film whose fluororesin which forms a fluororesin film is PVDF.
(2) The above fluorine, wherein the fluororesin is at least one resin selected from the group consisting of a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer having a comonomer copolymerization ratio of 15 mol% or less Resin film.
(3) The said fluororesin film whose titanium oxide is a titanium oxide which has a rutile type crystal form.
(4) The said fluororesin film which further contains another thermoplastic resin in the ratio of 25 mass% or less.
(5) The said fluororesin film whose other thermoplastic resin is polymethyl methacrylate.

Further, according to the present invention, the fluororesin film production method described above, wherein a fluororesin containing 15 to 50% by mass of titanium oxide is embossed after the film is produced by extrusion molding, or the film is obtained by extrusion molding. A process for producing the above-mentioned fluororesin film, which is subjected to surface processing at the same time as the production of the resin, is provided.

Furthermore, according to the present invention, there is provided a laminate comprising a layer made of the above-mentioned fluororesin film. Furthermore, according to this invention, the solar cell module backsheet provided with the layer which consists of said fluororesin film is provided.

According to the present invention, there is provided a fluororesin film containing 15 to 50% by mass of titanium oxide, and at least one surface of the film has a total ratio of the area of titanium oxide where the surface is exposed to the area of the film. 3.2% or less The above-mentioned fluorine-based resin film is excellent in weather resistance, mechanical properties, gloss, etc., and adheres to metal powder or metal fragments that are caused by contact with metal. There is an effect that a fluorine-based resin film in which a rubbing trace due to is hardly formed is obtained. Moreover, since it is a laminated body provided with the layer which consists of this fluororesin film, or a solar cell module backsheet, the laminated body suitable for a solar cell module backsheet etc., and a solar cell module which is rich in long-term reliability There is an effect that a back sheet for use is obtained.

FIG. 1 is a schematic cross-sectional view of an example of a solar cell module.

1. Fluorine-based resin Examples of the fluorine-based resin used for forming the fluorine-based resin film of the present invention include fluorine-based resins that have been conventionally used for applications such as a back sheet for a solar cell module. Specifically, for example, a homopolymer or copolymer of tetrafluoroethylene (ETFE, PTFE, PFA, etc.), a homopolymer or copolymer of vinyl fluoride, a homopolymer or copolymer of vinylidene fluoride Since the light resistance, weather resistance, antifouling property, heat resistance and the like are more excellent, a vinylidene fluoride homopolymer or copolymer can be preferably used. These fluororesins can be prepared by a conventional method. As the fluorine resin, one kind of fluorine resin may be used alone, or two or more kinds of fluorine resins may be combined (blended) and used.

2. Polyvinylidene fluoride resin (PVDF)
What is preferably used for forming the fluororesin film of the present invention is PVDF (polyvinylidene fluoride resin), that is, a homopolymer or copolymer of vinylidene fluoride. It means a homopolymer of vinylidene and a vinylidene fluoride copolymer mainly composed of vinylidene fluoride.

Examples of the vinylidene fluoride copolymer include, for example, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-chlorotrifluoroethylene mainly composed of vinylidene fluoride. Copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene terpolymer, And a mixture of two or more of these.

In these vinylidene fluoride copolymers, the copolymerization ratio of the comonomer copolymerized with vinylidene fluoride is preferably 15 mol% or less, more preferably 10 mol% or less, and particularly preferably 5 mol% or less. When the copolymerization ratio of the comonomer is 15 mol% or less, the vinylidene fluoride copolymer becomes a thermoplastic resin having crystallinity. The lower limit of the comonomer copolymerization ratio is preferably 1 mol%. If the comonomer ratio becomes too high, the vinylidene fluoride copolymer loses crystallinity and becomes an elastomer. The vinylidene fluoride copolymer that loses crystallinity and becomes an elastomer is a PVDF film that forms a PVDF film that is preferable as the fluororesin film of the present invention (hereinafter sometimes simply referred to as “the PVDF film of the present invention”). Absent.

Therefore, as the fluororesin film of the present invention, the fluororesin is selected from the group consisting of a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer having a comonomer copolymerization ratio of 15 mol% or less. More preferably, it is at least one. Among these fluororesins (PVDF), vinylidene fluoride homopolymers and vinylidene fluoride-hexafluoropropylene copolymers containing hexafluoropropylene units in a ratio of 15 mol% or less are heat resistant and melted. From the viewpoints of moldability, mechanical properties, antifouling properties, solvent resistance, secondary workability and the like, it is particularly preferable.

PVDF can be produced by suspension polymerization or emulsion polymerization. In the emulsion polymerization method, a chemically stable fluorine-based emulsifier is used to emulsify vinylidene fluoride alone or vinylidene fluoride and a comonomer such as hexafluoropropylene in an aqueous medium. Subsequently, it superposes | polymerizes using an inorganic peroxide, an organic peroxide, an organic percarbonate compound etc. as a polymerization initiator. After emulsion polymerization, a fine latex of submicron units is precipitated by an aggregating agent and aggregated, whereby PVDF can be recovered as particles of an appropriate size.

In the suspension polymerization method, a vinylidene fluoride or the vinylidene fluoride and a comonomer are suspended in an aqueous medium using a suspending agent such as methylcellulose. For example, an organic percarbonate (eg, di-n-propyl peroxydicarbonate) that exhibits activity at a low temperature is used as a polymerization initiator, and the critical temperature of vinylidene fluoride is 30.1 ° C. or lower, preferably 10 to 30 Polymerization is started at 0 ° C., more preferably 20 to 28 ° C. to produce primary polymer particles, and the temperature is raised to 30 to 90 ° C., preferably 40 to 80 ° C. as necessary, and the polymerization reaction is continued. To produce secondary polymer particles.

The intrinsic viscosity of PVDF is preferably in the range of 0.70 to 1.50 dl / g, more preferably 0.80 to 1.30 dl / g. The intrinsic viscosity of PVDF is a logarithmic viscosity at 30 ° C. measured using a Ubbelohde viscometer for a solution in which 4 g of PVDF is dissolved in 1 liter of N, N-dimethylformamide.

* The melting point of PVDF is usually in the range of 130 to 177 ° C, and in many cases 150 to 177 ° C. Here, the melting point of PVDF is a value measured by a differential scanning calorimeter (DSC). PVDF generates HF gas and decomposes when heated to a temperature of 350 ° C. or higher. PVDF has a wide processing temperature range from the melting point to the decomposition point. The melt processing temperature of PVDF is usually in the range of 200 to 250 ° C., preferably 210 to 240 ° C.

The PVDF in the PVDF film of the present invention is usually in the range of 30 to 85% by mass. In addition, in the PVDF film of this invention, the total amount of compounding ratios, such as PVDF, the titanium oxide mentioned later, another thermoplastic resin, and another additive, shall be 100 mass%. That is, the fluororesin in the fluororesin film of the present invention is usually 30 to 85% by mass, preferably 40 to 80% by mass, more preferably 45 to 75% by mass.

3. Titanium oxide The fluorine-based resin film of the present invention contains titanium oxide in a range of 15 to 50% by mass in addition to the fluorine-based resin such as PVDF. In particular, when the fluorine-based resin film of the present invention is used for a solar cell module backsheet, by containing titanium oxide, improvement in concealability and reflection efficiency can be realized.

Titanium oxide is widely used in two crystal forms, anatase and rutile. In the present invention, these two crystal forms can be used. Among these, rutile is excellent in dispersibility in fluorine-based resins such as PVDF at high temperatures and has extremely low volatility. Titanium oxide having a type crystal form is preferred.

As the titanium oxide, pigment grades can be preferably used. The average particle diameter (average primary particle diameter) of titanium oxide by image analysis of transmission electron microscope images is usually in the range of 150 to 1000 nm, preferably 180 to 700 nm, more preferably 200 to 400 nm. When the average particle diameter of titanium oxide is too small, the hiding power is reduced. Since the average particle diameter of titanium oxide is within the above range, the refractive index is large and the light scattering property is strong, so that the hiding power as a white pigment is increased. Titanium oxide is generally present in the form of secondary particles in which primary particles are aggregated. The specific surface area of titanium oxide by the BET method is usually in the range of 1 to 15, and in many cases 5 to 15.

Titanium oxide can be improved in properties such as dispersibility, concealability, and weather resistance by surface treatment with a surface treatment agent. Examples of the surface treatment agent include metal oxides such as aluminum, silicon, zirconium, tin, cerium, and bismuth; hydrated metal oxides such as zinc oxide; organometallic compounds such as organoaluminum compounds, organotitanium compounds, and organozirconium compounds; Examples thereof include organosilicon compounds such as silane coupling agents and polysiloxanes; phosphorus compounds such as aluminum phosphates and organophosphates; amine compounds.

By coating titanium oxide with a surface treatment agent, the reaction between the titanium oxide surface and the surrounding environment can be suppressed. The surface-treated titanium oxide is excellent in dispersibility in a fluororesin. The surface-treated titanium oxide can be dispersed in the fluororesin at a high concentration. In the case of using titanium oxide surface-treated with the same substance as used as a heat stabilizer described later, the amount of the surface treatment agent attached is extremely small. It does not have to be included in the quantity.

The content ratio of titanium oxide in the fluororesin film of the present invention is preferably 18 to 45% by mass, more preferably 20 to 40% by mass, and still more preferably 25 to 35% by mass. When the content ratio of titanium oxide is too small, for example, it may be difficult to obtain a fluorine-based resin film having whiteness, hiding power, and reflection efficiency that are preferable as a back sheet for a solar cell module. If the content ratio of titanium oxide is too large, it becomes difficult to produce a fluororesin film by extrusion, the mechanical properties of the fluororesin film deteriorate, and the smoothness of the fluororesin film surface is controlled. May become difficult and the formation of metal scratches may increase.

4). Other Thermoplastic Resins The fluororesin film of the present invention contains only a fluororesin (including one or more fluororesins) such as PVDF as a resin component. Although desirable, other thermoplastic resins may be included as desired to improve properties such as processability, impact resistance, adhesion, and heat resistance.

Other thermoplastic resins include polyolefins such as polyethylene and polypropylene; polyamides such as nylon 6 and nylon 66; polyesters such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate; acrylic resins such as polymethyl methacrylate; polystyrene, poly Examples include acrylonitrile, polyvinyl chloride, polyoxymethylene, polycarbonate, polyphenylene oxide, polyester urethane, poly m-phenylene isophthalamide, and poly p-phenylene terephthalamide.

As the other thermoplastic resin, a fluorine-based resin, for example, polymethyl methacrylate (hereinafter sometimes referred to as “PMMA”) compatible with PVDF is particularly preferable. PMMA not only has excellent compatibility with the fluorine-based resin, but also improves the adhesion of the fluorine-based resin film to other members, for example, other thermoplastic resin films. PMMA is, in addition to a methyl methacrylate homopolymer, a copolymer containing 50 mol% or less of a methacrylate unit and a methacrylic acid ester other than methyl methacrylate with a methyl methacrylate monomer as a structural unit, Furthermore, the mixture of 2 or more types of these polymers can be illustrated. Examples of the acrylate ester include methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate, and examples of methacrylic acid esters other than methyl methacrylate include ethyl methacrylate and propyl methacrylate. it can.

The other thermoplastic resin is preferably 25% by mass or less, more preferably 0 to 22% by mass, and further preferably 3 to 20% by mass in the fluororesin film containing titanium oxide. Can be contained.

5. Other Additives The fluororesin film of the present invention is further desired in addition to fluororesins such as titanium oxide and PVDF, and other thermoplastic resins blended as desired as described above. According to the present invention, other additives such as pigments or dyes, pigment dispersants, ultraviolet absorbers, heat stabilizers, light stabilizers, matting agents, lubricants, crystal nucleating agents, and mechanical property improving agents can be contained.

For example, the fluororesin film of the present invention may contain a mechanical property improver. The mechanical property improver can improve mechanical properties such as impact resistance, tensile strength, and elongation of the obtained fluororesin film such as PVDF film. For example, a core-shell type impact resistance modifier And copolymerized acrylic flow modifiers are known. As commercial products, Kaneace (registered trademark) manufactured by Kaneka Co., Ltd., Metabrene (registered trademark) manufactured by Mitsubishi Rayon Co., Ltd., Paraloid (registered trademark) manufactured by Rohm and Haas, etc. can be selected. . The mechanical property improvers can be used alone or in combination of two or more.

Further, the fluororesin film of the present invention can contain a heat stabilizer. Examples of heat stabilizers include polyhydroxymonocarboxylic acid calcium salts such as calcium gluconate; aliphatic carboxylic acid calcium salts having 5 to 30 carbon atoms such as calcium stearate and calcium oleate; inorganic calcium such as calcium carbonate and calcium hydroxide. Compound: Metal oxides such as zinc oxide and magnesium oxide are listed. A heat stabilizer can be used individually or in combination of 2 types or more, respectively. The heat stabilizer is usually in the form of powder from the viewpoint of dispersibility in the fluororesin. For example, an inorganic calcium compound such as calcium carbonate and a metal oxide such as zinc oxide have an average particle diameter (average primary particle diameter) in the range of 0.05 to 2 μm by image analysis of a transmission electron microscope image. Preferably there is. As the average particle size decreases, the effect of improving the thermal decomposition temperature of a fluorine-based resin such as PVDF can be exhibited. In order to efficiently enhance the heat stabilization effect by the heat stabilizer, it is preferable to adjust the content ratio of the heat stabilizer according to the content ratio of titanium oxide in the fluorine-based resin film such as a PVDF film. The content ratio of the heat stabilizer is usually smaller than the content ratio of titanium oxide. The mass ratio of titanium oxide to heat stabilizer is usually in the range of 100: 1 to 3: 1, preferably 80: 1 to 4: 1, more preferably 50: 1 to 5: 1.

These other additives are used in proportions suitable for each, and when other additives are contained, they are each independently usually 0.01 to 10% by mass, preferably in the fluororesin film. It is in the range of 0.1 to 8% by mass, more preferably 0.5 to 5% by mass. In particular, when the other additive is a heat stabilizer, if the content ratio of the heat stabilizer is too small, the heat stabilization effect is reduced, and the thermal decomposition temperature of the fluorine resin component in the resulting fluorine resin film is reduced. It becomes difficult to sufficiently suppress the decrease. When the content ratio of the heat stabilizer is too large, the hiding power, color tone, mechanical properties, etc. of the fluororesin film may be adversely affected.

6). Fluorine-based resin film The fluorine-based resin film of the present invention, preferably a PVDF film, is a fluorine-based resin film containing 15 to 50% by mass of titanium oxide, and at least one surface of the film is in relation to the area of the film, The fluorine resin film is characterized in that the total proportion of the area of titanium oxide whose surface is exposed is 3.2% or less. In the present invention, the surface-exposed titanium oxide means titanium oxide present on the surface of a fluororesin film containing 15 to 50% by mass of titanium oxide, that is, the outer surface from the plane serving as a reference for the fluororesin film. This means that the surface of the titanium oxide is exposed to the surface, and the surface of the titanium oxide is not coated with a resin, specifically, a fluororesin, and the surface thereof is exposed. The fluororesin film of the present invention is characterized in that the total ratio of the area of titanium oxide whose surface is exposed to the area of the film is 3.2% or less. The fluorine-based resin film of the present invention is a resin as a titanium oxide present on the surface of the fluorine-based resin film, specifically, a titanium oxide whose surface is covered with a fluorine-based resin and the surface is not exposed, and a resin, Specifically, the surface is not covered with a fluorine-based resin, and the surface thereof is exposed titanium oxide. The surface of the fluororesin film of the present invention is not covered with the latter resin, and the total area of the titanium oxide whose surface is exposed is 3.2% with respect to the area of the fluororesin film. The ratio is as follows.

[Total ratio of the area of titanium oxide whose surface is exposed]
Of the titanium oxide present on the surface of the film, the surface exposed titanium oxide is taken using a scanning electron microscope (SEM) to capture the surface images of fluororesin films, including PVDF films containing titanium oxide. It can confirm with the SEM image obtained. For the titanium oxide exposed on the surface confirmed by the SEM image, the total ratio of the area of the titanium oxide where the surface is exposed to the area of the film can be determined by “by binarizing the SEM image by the following method. It can obtain | require as "the surface exposure rate obtained." That is, using a scanning electron microscope (SEM), a predetermined region of the fluororesin film containing titanium oxide (selected from a range separated from both ends of the film in the width direction by 1/4 or more of the film width). The surface image is taken (pretreatment with platinum coating, acceleration voltage 5 kV, secondary electron image photographing mode, magnification 8000 times). Using the image editing processing software, the obtained SEM image jpeg file is a portion of the titanium oxide present on the film surface in a predetermined region, where the surface of the titanium oxide is exposed (hereinafter referred to as “TiO ₂ exposed portion”). ”And other parts (such as buried TiO ₂ ) are binarized. The total ratio of the area of titanium oxide whose surface is exposed to the area of the film [hereinafter referred to as “TiO ₂ exposure rate (%)”. ] Can be calculated as a calculation formula: (number of pixels of the exposed portion of TiO ₂ / number of pixels of the entire image) × 100. Note that the number of pixels in the entire image corresponds to the area of the film in the predetermined area.

The fluororesin film including the PVDF film of the present invention is a fluororesin film containing 15 to 50% by mass of titanium oxide, and at least one surface of the film is exposed to the area of the film. When the total proportion of the area of titanium oxide to be exposed [TiO ₂ exposure rate (%)] is 3.2% or less, the metal scratch resistance can be obtained without impairing the weather resistance and mechanical properties. The total ratio of the area of titanium oxide whose surface is exposed to the area of the film [TiO ₂ exposure rate (%)] is preferably 3.1% or less, more preferably 3.0% or less, and still more preferably 2. It is 8% or less, particularly preferably 2.5% or less. The lower limit of the total ratio of the area of titanium oxide that exposes the surface to the area of the film [TiO ₂ exposure rate (%)] is 0%, but in many cases it is about 0.3%. Depending on the composition and thickness of the film, even if the above ratio is 0.5% or more, a fluororesin film having metal scratch resistance can be obtained. In the fluororesin film of the present invention, at least one surface of the fluororesin film has a total ratio of the area of titanium oxide where the surface is exposed to the area of the film [TiO ₂ exposure rate (%)] is 3. If it is 2% or less, it can be said that it is a fluorine resin film provided with the surface which has metal abrasion resistance. Furthermore, depending on the use of the fluororesin film, both surfaces of the fluororesin film have a total ratio of the titanium oxide area where the surface is exposed to the area of the film being 3.2% or less, Both surfaces of the fluororesin film can have metal scratch resistance.

[Metal scratch resistance]
The fluororesin film of the present invention is a film having metal scratch resistance. The metal scratch resistance of the fluororesin film can be evaluated by measuring the color of the film surface before and after the friction test and obtaining the color difference (ΔE) by a method involving the following friction test. That is, it corresponds to the Gakushin type friction tester [Friction tester type II (Gakushin type) specified in JIS L0849 “Testing method for fastness to dyeing against friction”]. ], A fluorine resin film is attached to a 20 mm long × 21 mm wide friction element (head portion), and a distance of 10 cm is applied to an aluminum tape having a width of 40 mm attached to a test piece base with a load of 600 g. After reciprocating 30 times, the fluororesin film attached to the friction element is removed. Next, the color difference (ΔE) of the film surface before and after the friction test is obtained. The color difference (ΔE) is measured on the surface of the film before and after the friction test in accordance with JIS Z8722 using a spectroscopic color difference meter (reflection measurement diameter 30 mm, C light source, 2 ° field of view, L ^* a ^* b ^* color system). The color difference (ΔE) on the film surface before and after the friction test is based on the difference in colorimetric values (ΔL ^* , Δa ^* and Δb ^* ) on the film surface.
(Equation) ΔE = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ] ^1/2
(The value is one digit after the decimal point.)

If the color difference (ΔE) on the film surface before and after the friction test is 3.2 or less, it can be said that the metal-rubbing resistance of the fluororesin film is good, and if it is 1.5 or less, the metal-rubbing resistance is good. It can be said that it is excellent. That is, the evaluation criteria for metal scratch resistance based on the color difference (ΔE) on the film surface before and after the friction test are as follows.
<Evaluation criteria>
ΔE Evaluation symbol 0 to 1.5 Excellent metal scratch resistance S
1.6 to 3.2 Good metal scratch resistance A
3.3-7 Metal abrasion resistance is slightly inferior B
7 ~ Poor metal scratch resistance C

Fluorine resin film having metal scratch resistance, and a back sheet or laminate for a solar cell module comprising a layer made of the fluorine resin film such as PVDF film, for example, in carrying work, installation work or incidental work, Contact with metal such as solar cell module frames, electric wires, mounting brackets, etc. may occur due to accidental or work-related contact, bumping, or rubbing. However, the generated metal powder or metal piece does not adhere to the back sheet or laminate of the solar cell module including a layer made of the fluororesin film and the fluororesin film as in the case of scratches. Further, even in the formation of a laminate including a layer made of a fluororesin film and the assembly operation of the solar cell module, the metal powder and the metal piece do not adhere to the surface of the film like a scratch. Of course, the metal powder and metal pieces adhering to the surface of the fluorine resin film and the back sheet for the solar cell module can be removed by simply stroking, so the fluorine resin film and the back sheet for the solar cell module after the removal are removed. It does not remain as a rubbing trace on the surface, and there is no problem in the function of the fluorine resin film or the back sheet for the solar cell module. The fluororesin film of the present invention, as well as the back sheet and laminate for solar cell modules, do not attach metal powder or metal pieces as in the case of scratches. There is no concern. Furthermore, the fluororesin film of the present invention, and the back sheet and laminate for a solar cell module are designed so that metal powder and metal pieces do not adhere in various operations, or the attached metal powder and metal pieces are removed. This eliminates the need for work to be carried out, thus greatly reducing transportation and work costs.

〔Weatherability〕
In the fluororesin film of the present invention, at least one surface of the film has a metal scraping resistance by a total ratio of the area of titanium oxide with the surface exposed to the film area being 3.2% or less. And a film having excellent weather resistance by containing 15 to 50% by mass of titanium oxide. The weather resistance of the fluororesin film is as follows: in an atmosphere at a temperature of 63 ° C. and 63% RH, using a metal halide lamp as a light source, an illuminance of 1000 W / m ² and an irradiation time of 100 hours (total irradiation amount of 100 hours 360 MJ / m ² ). A weather resistance test is performed, and the color difference (ΔE) on the film surface before and after irradiation is measured and evaluated. If the color difference (ΔE) on the film surface before and after irradiation is 1.5 or less, it can be evaluated that there is weather resistance, and if it is 1 or less, it can be said that the weather resistance is excellent. Since the fluororesin film of the present invention has excellent weather resistance, the laminate and the solar cell module backsheet having a layer made of this fluororesin film can be used even if they are exposed to the external environment for a long time. Will not be lost.

(Mechanical properties)
In the fluororesin film of the present invention, at least one surface of the film has a metal scraping resistance by a total ratio of the area of titanium oxide with the surface exposed to the film area being 3.2% or less. A film having excellent mechanical properties by containing 15 to 50% by mass of titanium oxide. Specifically, the excellent mechanical characteristics of the fluororesin film are such that the breaking strength (maximum point stress) of the film at a temperature of 23 ° C. is 20 MPa or more, preferably 25 MPa or more, more preferably 30 MPa or more. The breaking strength (maximum point stress) of the film at a temperature of 23 ° C. is in accordance with JIS K7127, from the fluororesin film in the longitudinal direction (extrusion direction in the case of an extruded film, that is, MD direction) and in the lateral direction (in the case of an extruded film). Is a strip-like film having a length of 50 mm and a width of 10 mm cut out in parallel to the direction orthogonal to the extrusion direction, that is, the TD direction, and measured at a temperature of 23 ° C. (normal temperature) and a pulling speed of 200 mm / min. .

[Gloss (matte)]
In the fluororesin film of the present invention, at least one surface of the film has a metal scraping resistance by a total ratio of the area of titanium oxide with the surface exposed to the film area being 3.2% or less. At the same time, the surface of the film can have a matte glossiness. That is, the fluorine-based resin film of the present invention is not limited in glossiness, so-called matte or may have high gloss, but conventionally, for example, as a back sheet for a solar cell module, In some cases, a high-quality film is desired by having a matte gloss without gloss. In that case, according to the present invention, the gloss of the surface of the film whose total area of the titanium oxide area where the surface is exposed to the area of the film is 3.2% or less is 35% or less, preferably 32% or less, More preferably, it can be 28% or less. The glossiness of the film surface can be measured using a gloss meter in accordance with JIS Z8741. The method of making the fluororesin film of the present invention have a matte gloss without gloss is not particularly limited. For example, after the film is produced, post-treatment such as so-called mat processing is performed on the surface of the film. By performing machining, a film having a desired matte glossiness can be obtained by a method of making the matte or the like.

The fluororesin film of the present invention may be an unstretched film or a stretched film. However, when stretching is performed, additional equipment such as a stretching apparatus (longitudinal and lateral directions) and a heat treatment apparatus are necessary, Since it is difficult to produce a thick film, an unstretched film is preferable.

The thickness of the fluororesin film of the present invention is usually 2 to 500 μm, preferably 3 to 400 μm, more preferably 5 to 300 μm, still more preferably 8 to 250 μm, and particularly preferably 10 to 200 μm. When the fluororesin film of the present invention is used as a laminate having a layer composed of the fluororesin film or a back sheet for a solar cell module, the thickness of the fluororesin film is preferably 2 to 100 μm, more preferably It is 3 to 80 μm, more preferably 4 to 60 μm, particularly preferably 10 to 50 μm. If the thickness of the fluororesin film is less than 2 μm, the strength of the film is insufficient and the required mechanical properties cannot be obtained. As a result, for example, in the process of producing a laminate, heat is applied during heat lamination to other layers. Wrinkles may occur, and when used as a back sheet for a solar cell module, it is difficult to obtain required properties such as concealment and strength. When the thickness of the fluororesin film exceeds 500 μm, the flexibility of the film may be insufficient or the anisotropy may be increased, and the weight and thickness cannot be reduced.

7). Method for Producing Fluoropolymer Film The method for producing a fluororesin film of the present invention is a fluororesin film containing 15 to 50% by mass of titanium oxide, preferably a PVDF film, wherein at least one surface of the film is There is no particular limitation as long as a fluorine resin film in which the total ratio of the area of titanium oxide whose surface is exposed to the area of the film is 3.2% or less can be obtained. Fluorine resin containing the required amount of titanium oxide and, if necessary, other thermoplastic resin and other additives is melt-kneaded at a temperature above the melting point and then rolled (pressed) between rolls or in a mold. Then, the film is sandwiched by a polytetrafluoroethylene sheet having a predetermined surface roughness (Ra) (which may have an embossed pattern) placed in a metal press die. It can manufacture by the method of rolling. In addition, after melt-kneading a fluorine-based resin, for example PVDF, at a temperature equal to or higher than the melting point, it is extruded into a film from a T die or an inflation die, and can be manufactured by a method of embossing or surface processing as necessary. it can. Furthermore, the fluororesin film of the present invention can also be produced by a coating method using a known solvent or aqueous coating. From the viewpoint of productivity and quality uniformity, it is preferable to form a fluorine resin film by extrusion molding. Specifically, a fluorine resin containing 15 to 50% by mass of titanium oxide, such as PVDF, is extrusion molded. The fluororesin film can be produced by a method of embossing after producing a film by the method, or a method of producing a film by extrusion and simultaneously surface-treating it. Hereinafter, a method for producing a fluororesin film by extrusion will be further described.

After mixing a predetermined amount of fluorine resin, such as PVDF, titanium oxide, and optionally other thermoplastic resin and other additives, a material containing the fluorine resin is supplied to an extrusion molding machine, and the fluorine resin For example, after being melted and kneaded by heating to a melting point of PVDF or more, the melt is extruded into a film (also referred to as a sheet) from a T-die disposed at the tip of the extruder, and then a cooling roll (cast roll), Use a combination of elastic rolls (such as metal or rubber), mirror rolls (such as metal or rubber) and embossing rolls (such as metal or rubber), preferably while applying pressure, and below the melting point By cooling to this temperature, a fluororesin extruded film can be produced. For example, when obtaining a PVDF film, the melt kneading temperature in the extruder is usually in the range of 200 to 250 ° C., preferably 205 to 245 ° C., more preferably 210 to 240 ° C. The extrusion temperature from the T die is Usually, it is in the range of 195 to 235 ° C., preferably 200 to 230 ° C., more preferably 205 to 225 ° C.

More specifically, i) A fluororesin discharged from a T die in a film state in a molten state is placed directly under the T die and brought into contact with a metal cooling roll (cast roll) whose temperature is adjusted to a predetermined temperature. The film is produced by cooling to a predetermined temperature below the melting point, and then, if necessary, after passing between a mirror roll and an elastic roll whose temperature is adjusted to the predetermined temperature, the temperature is adjusted to the predetermined temperature. Embossing by passing between the embossed roll and the elastic roll, and ii) fluorinated resin discharged in a film from the T die in a molten state is placed directly under the T die and brought to a predetermined temperature. Depending on the method of surface processing at the same time as film production by sandwiching between temperature-controlled metal cooling roll (cast roll) and elastic roll (nip roll), etc. Fluorine-based resin film having a surface texture can be obtained.

An embossing roll having a surface roughness Ra (arithmetic mean roughness) of usually 0.2 to 15 μm, preferably 0.4 to 12 μm, more preferably 0.7 to 10 μm may be used. desirable. The embossing roll can form a desired roughness or pattern on the film surface by sandblasting, engraving, electrolytic polishing, or the like. It is desirable to use a mirror roll having a surface roughness of Ra (arithmetic mean roughness) of usually 0.1 μm or less, preferably 0.07 μm or less, more preferably 0.05 μm or less.

If desired, instead of using the mirror roll and the emboss roll in combination, the mirror roll and the mirror roll can be used in combination, or the emboss roll and the emboss roll can be used in combination. Furthermore, as described above, a backup roll made of metal, resin, rubber, or the like can be used while facing a cooling roll (cast roll), an embossing roll, or a mirror surface roll. The upper limit of the surface roughness of the embossing roll is appropriately determined depending on the type of the opposing roll and the surface roughness, but is usually 50 μm and in many cases 30 μm.

By adjusting the surface roughness, hardness, temperature, pressing force (surface pressure and / or linear pressure), film forming speed of the embossing roll, mirror surface roll, elastic roll, cooling roll and / or backup roll, etc. The surface roughness of the obtained fluororesin film can be adjusted.

The temperature of the embossing roll or mirror roll varies depending on the temperature of the discharged fluororesin and the film forming speed, but is usually in the range of 50 to 160 ° C., preferably 60 to 155 ° C., more preferably 70 to 150 ° C. If the temperature of the embossing roll or mirror roll is less than 50 ° C., the fluidity of the fluororesin, for example PVDF, is insufficient, and it is difficult to completely cover the surface of titanium oxide with the fluororesin. The total proportion of the area of titanium oxide whose surface is exposed may not be 3.2% or less. When the temperature of the embossing roll or mirror surface roll exceeds 160 ° C., a coarse fluorine resin crystal, for example, PVDF crystal is generated in the resulting fluorine resin film, and the above ratio becomes too large. Metal scratch resistance may not be obtained.

The embossing roll, mirror roll, elastic roll, cooling roll, and / or backup roll can be adjusted by a known method such as heating / cooling with a fluid such as water or oil, heating / cooling with an electric heater, heating / cooling with a piezoelectric element. Adopt and control. The temperature of the embossing roll and / or mirror surface roll may be different, but is preferably the same temperature.

The fluororesin film-like material containing titanium oxide adjusted so as to have a predetermined surface state between the embossing roll and / or the mirror-finished roll is subsequently guided to a predetermined temperature as required. By passing the roll group, the surface roughness (Ra) and mechanical properties of the film can be finely adjusted. The number of rolls of the guide roll group can be increased or decreased as necessary, and may be before the embossing roll and / or mirror roll (on the extruder side) or after (on the opposite side of the extruder side). Also, by adjusting the rotation speed of the rolls of the guide roll group, the surface roughness (Ra) of the resulting fluororesin film, the orientation state of MD (machine direction) and TD (orthogonal direction) and residual strain, The mechanical properties can be fine-tuned. The temperature of the rolls of the guide roll group can be selected as appropriate, and may be the same temperature, may be different temperatures, or may be room temperature without special temperature adjustment. It is good also as temperature higher than the temperature of an embossing roll and / or a mirror surface roll. As described above, the temperature adjustment of the rolls of the guide roll group can be controlled by employing a means known per se.

In order to produce the fluorine resin film of the present invention, for example, a PVDF film, a pinch roll comprising a pair of rolls may be used. In addition to the guide roll group, the surface roughness (Ra), mechanical properties, etc. of the obtained fluororesin film can be obtained by using a pinch roll and carrying it while sandwiching the fluororesin film. Further fine adjustment is possible. The surface roughness, temperature, surface pressure, and rotation speed of the pinch roll can be adjusted as appropriate.

As described above, the fluororesin film of the present invention is preferably an unstretched film. However, when producing a stretched film as necessary, the rotation speed of the rolls and pinch rolls of the guide roll group is sequentially set. By changing, the film-like material of fluororesin can be stretched in the longitudinal direction. In the case of stretching in the transverse direction, a known stretching means such as a tenter may be further provided. However, when producing a stretched film, the surface of the fluororesin film may crystallize, and it may be difficult to control the surface roughness (Ra). Therefore, the fluororesin film of the present invention is an unstretched film. preferable.

8). Laminate The fluororesin film of the present invention can be used as a single-layer film, but by laminating other thermoplastic resin films into a laminate comprising a layer made of a fluororesin film, for example, It can be used in fields where further improvement in mechanical strength such as impact resistance and flexibility is required.

Other thermoplastic resin films used to form a laminate comprising a layer made of a fluororesin film include polyolefins such as polyethylene and polypropylene; polyamides such as nylon 6 and nylon 66; polyethylene terephthalate, polybutylene terephthalate, polyethylene Polyester such as naphthalate (hereinafter sometimes referred to as “PEN”); acrylic resin such as polymethyl methacrylate; polystyrene, polyacrylonitrile, polyvinyl chloride, polyoxymethylene, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyether Examples include films of ether ketone, polyester urethane, poly m-phenylene isophthalamide, poly p-phenylene terephthalamide, and the required mechanical strength. , Heat resistance, weather resistance, in consideration of light resistance, may be selected one or more of these. If desired, a laminate including a layer made of the same kind or different kind of fluororesin film may be used. For example, the laminated body provided with the layer which consists of a PVDF film, and the layer which consists of fluorine-type resins, such as PTFE or PVF, etc. are mentioned.

When using a laminate comprising a layer made of a fluororesin film as a back sheet for a solar cell module, mechanical strength such as impact resistance and flexibility, weather resistance, concealment, adhesion to a sealing material, etc. From the viewpoint of the characteristics required for the back sheet, as other thermoplastic resin films, polyesters such as PET and PEN; films such as acrylic resins such as polycarbonate and PMMA are preferably used. In particular, a polyester film such as PET or PEN is preferable, and a PET film is most preferably used. Among them, a biaxially stretched PET film is preferable.

These other thermoplastic resin films may further contain other thermoplastic resins and other commonly used additives such as stabilizers, ultraviolet absorbers, pigments or dyes, if necessary. In particular, when using a laminate including a layer made of a fluorine-based resin film containing titanium oxide as a back sheet for a solar cell module, a pigment such as titanium oxide or carbon black to be added for improving the concealability is used. You may make it contain in a thermoplastic resin film. Since the fluorine-based resin film of the present invention has a high titanium oxide content of 15 to 50% by mass, the content of titanium oxide contained in these other thermoplastic resin films can be reduced.

The thickness of the laminate is not particularly limited, but is usually 3 to 800 μm, preferably 7 to 500 μm, more preferably 10 to 400 μm, and still more preferably 20 to 300 μm. If the thickness of the laminate is less than 3 μm, the strength of the laminate may be insufficient and required mechanical properties may not be obtained. For example, when used as a back sheet for a solar cell module, the required concealability and strength It becomes difficult to obtain characteristics such as. When the thickness exceeds 800 μm, the flexibility of the laminate may be insufficient, and weight reduction and thinning cannot be achieved. The thickness ratio of the fluororesin film containing titanium oxide and the other thermoplastic resin film in the laminate is not particularly limited, but is preferably 1/99 to 90/10, more preferably 5/95 to 70. / 30, more preferably 10/90 to 50/50, and particularly preferably 15/85 to 40/60.

9. Method for producing a laminate comprising a layer comprising a fluorine resin film A laminate comprising a layer comprising a fluorine resin film containing titanium oxide is a method for producing a laminate comprising a layer comprising a fluorine resin film known per se. Can be manufactured by. That is, a co-extrusion method, an extrusion lamination method, a heat welding method, an adhesion lamination method, a coating method, and the like can be adopted, but it is preferable to produce a laminate by a simple adhesion lamination method.

The lamination may be performed by joining a fluorine-containing resin film containing titanium oxide formed in advance and another thermoplastic resin film without using an adhesive or preferably through an adhesive layer. Known adhesives such as urethane adhesives and epoxy adhesives, and hot-melt adhesives can be used as adhesives for adhesive lamination, but two-component urethane adhesives are the most. preferable. In order to perform adhesion with an adhesive, after performing surface activation treatment on one or both of a fluorine-based resin film or other thermoplastic resin film containing titanium oxide as desired, an adhesive is applied, After heating and drying to form an adhesive layer with a predetermined thickness, bonding is performed by pressing the fluororesin film and another thermoplastic resin film while pressing them with a roll or the like, further heating as desired. Let

10. Solar cell module and back sheet for solar cell module The laminate comprising the fluororesin film of the present invention or a layer made of a fluororesin film is suitable for use as a back sheet for a solar cell module.

As the solar cell module, the one having the cross-sectional structure shown in FIG. That is, as shown in FIG. 1, the solar cell module includes a surface protective material 1, a sealing material 2, a solar battery cell 3, and a back surface protective material (back sheet) 4. A plurality of solar cells 3 are connected in series by wiring (not shown) to constitute a solar cell module. A frame (not shown) is disposed at the end or peripheral edge of the solar cell module.

Examples of the surface protective material 1 include, but are not limited to, a tempered glass plate, a transparent plastic plate, a single-layer or multilayer transparent plastic film, or a composite material obtained by combining these.

As the sealing material 2, transparent resin such as ethylene-vinyl acetate copolymer (EVA), butyral resin, silicon resin, epoxy resin, and fluorinated polyimide resin is used, but is not limited thereto. Among these sealing materials, EVA is preferable. Although the structure of the solar battery cell 3 varies depending on the type of the solar battery, various solar battery cells can be used. When EVA is used as the sealing material 2, EVA is supplied as a sheet. The solar battery cell 3 can also be sealed with EVA by sandwiching the solar battery cell 3 between the two EVA sheets and heating and pressing. Moreover, when using an EVA sheet | seat as the sealing material 2, it can compound and supply beforehand with the PVDF single layer film and laminated body by this invention.

As the back surface protective material (back sheet) 4, a fluorine resin single layer film containing titanium oxide according to the present invention, a fluorine resin film containing titanium oxide, and other thermoplastic resin films (for example, PET film) It is possible to use a laminate including a layer made of a fluorine-based resin film containing titanium oxide obtained by compounding. When using the laminated body provided with the layer which consists of a fluorine resin film containing a titanium oxide as the back sheet 4 for solar cell modules of this invention, since a fluorine resin film is excellent in a mechanical characteristic and a weather resistance, it is solar. It is preferable that the battery module is disposed on the rearmost surface side, that is, at a position far from the solar battery cell 3.

The solar cell module backsheet 4 of the present invention may be a laminate further provided with a barrier layer, or a composite material further provided with a tempered glass plate, a metal plate or a metal foil. In these laminates and composite materials, an adhesive layer can be disposed between the respective layers. Examples of the barrier layer include a vapor deposition layer of an inorganic oxide such as silicon oxide or aluminum oxide or a vapor deposition layer of a metal such as aluminum. These vapor deposition layers may be used in the form of an inorganic oxide vapor deposition film such as silicon oxide or aluminum oxide or a metal vapor deposition film such as aluminum formed on one side of the base film. Needless to say, the tempered glass plate, metal plate or metal foil functions as a barrier layer. Formation of a vapor deposition layer and formation of a barrier layer by sticking a metal foil can be appropriately performed by a known method. Adhesives used for bonding need to have a barrier layer, especially a vapor-deposited layer whose adhesive strength deteriorates when used outdoors for a long period of time, does not cause peeling, etc., and that the adhesive does not turn yellow. An adhesive or the like can be preferably used.

Therefore, as a solar cell module backsheet comprising a layer made of the fluorine resin film of the present invention, a laminate in which the fluorine resin film of the present invention and another resin film (for example, PET film) are combined, A laminate in which a fluorine resin film and a moisture-proof film are combined, a composite material in which the fluorine resin film and a tempered glass plate are combined, a composite material in which the fluorine resin film and a metal plate are combined, the fluorine The composite material etc. which compounded 2 or more types, such as a resin resin film, another resin film, a moisture-proof film, and a tempered glass board, are used. In a laminate or a composite material having a layer made of a fluororesin film, an adhesive layer can be disposed between each layer. Examples of the moisture-proof film include a composite film in which a deposited film of an inorganic oxide such as silicon oxide or aluminum oxide is formed on one surface of a base film. Examples of commercially available moisture-proof films include CELLEL (registered trademark) T030 manufactured by Kureha Corporation.

As a preferable layer configuration of the solar cell module backsheet of the present invention, for example, the following can be exemplified, but the invention is not limited thereto. The back sheet having a multi-layer structure shows the surface on the side in contact with the solar cell module as the right end.

(1) Fluorine resin film / adhesive / EVA of the present invention
(2) Fluorine resin film of the present invention / other resin film (3) Other resin film / fluorine resin film of the present invention (4) Fluorine resin film / adhesive / other resin film of the present invention (5 ) Other resin film / adhesive / fluorine resin film of the present invention (6) Fluorine resin film of the present invention / other resin film / adhesive / EVA
(7) Other resin film / fluorine resin film of the present invention / adhesive / EVA
(8) Fluorine resin film / adhesive / other resin film / adhesive / EVA of the present invention
(9) Other resin film / adhesive / fluorinated resin film / adhesive / EVA of the present invention
(10) Fluorine resin film / adhesive / other resin film / adhesive / fluorine resin film of the present invention (11) Glass plate / adhesive / fluorine resin film of the present invention (12) glass plate / Adhesive / Fluoropolymer film of the present invention / Adhesive / EVA
(13) Metal plate / adhesive / fluorine resin film of the present invention (14) Metal plate / adhesive / fluorine resin film of the present invention / adhesive / EVA
(15) Layer structure in which a moisture-proof film is added to the above layer structure

Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the examples. Evaluation methods for physical properties or characteristics in Examples and Comparative Examples are as follows.

[Total ratio of the area of titanium oxide whose surface is exposed]
The total ratio of the area of titanium oxide whose surface is exposed to the area of the film was determined by the following method. That is, using a scanning electron microscope (SEM, SU8020 manufactured by Hitachi High-Technologies Corporation), a surface image of a fluororesin film containing titanium oxide was taken (pretreatment with platinum coating, acceleration voltage 5 kV, 2 The following electronic image shooting mode, the magnification was set to 8000 times.) The jpeg file of the SEM image (1,228,800 pixels) of the film in a predetermined area was converted into titanium oxide using image editing software Adobe Photoshop (registered trademark). The portion where the surface of the substrate was exposed (hereinafter sometimes referred to as “TiO ₂ exposed portion”) and the other portions were binarized. The total ratio of the area of titanium oxide whose surface is exposed to the area of the film [hereinafter referred to as “TiO ₂ exposure rate (%)”. ] Was calculated from the calculation formula: (number of pixels of the exposed portion of TiO ₂ / number of pixels of the entire image) × 100.

[Metal scratch resistance]
The metal scratch resistance of the fluororesin film was evaluated by measuring the color of the film surface before and after the friction test and obtaining the color difference (ΔE) by a method involving the following friction test. That is, using a Gakushin friction tester (Gakushin friction tester II type AB-301 manufactured by Tester Sangyo Co., Ltd.), a fluorine resin film is applied to a 20 mm long x 21 mm wide friction element (head portion). Was attached to the aluminum tape having a width of 40 mm attached to the test piece base and brought into contact with a load of 600 g and reciprocated 30 times within a distance of 10 cm, and then the fluororesin film attached to the friction element was removed. Next, the color difference (ΔE) on the film surface before and after the friction test was determined. Color difference (ΔE) is measured on the film surface using a spectroscopic color difference meter (spectral color difference meter SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS Z8722 for the film before and after the friction test. Reflection measurement diameter 30 mm, C light source, 2 ° field of view, L ^* a ^* b ^* color system). The color difference (ΔE) on the film surface before and after the friction test is based on the difference in colorimetric values (ΔL ^* , Δa ^* and Δb ^* ) on the film surface.
(Equation) ΔE = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ] ^1/2
(The value was set to one digit after the decimal point.) The evaluation criteria for metal scratch resistance based on the color difference (ΔE) on the film surface before and after the friction test were as follows.
<Evaluation criteria>
ΔE Evaluation symbol 0 to 1.5 Excellent metal scratch resistance S
1.6 to 3.2 Good metal scratch resistance A
3.3-7 Metal abrasion resistance is slightly inferior B
7 ~ Poor metal scratch resistance C

〔Weatherability〕
The weather resistance of the fluorine-based resin film is as follows: Super UV tester SUV-W161 manufactured by Iwasaki Electric Co., Ltd., using a metal halide lamp with a wavelength of 295 to 450 nm as a light source in an atmosphere of 63 ° C. and 63% RH, and an illumination intensity of 1000 W The weather resistance test was conducted at / m ² and an irradiation time of 100 hours (total irradiation amount of 360 MJ / m ^{2 for} 100 hours), and the color difference (ΔE) on the film surface before and after irradiation was measured.

[Mechanical properties (breaking strength of film at a temperature of 23 ° C.)]
The mechanical properties (breaking strength of the film at a temperature of 23 ° C.) of the fluororesin film are in accordance with JIS K7127, and are longitudinal (extrusion direction, that is, MD direction) and transverse direction (extrusion direction orthogonal to) from the fluororesin film. Direction, that is, TD direction), a strip-shaped film with a length of 50 mm and a width of 10 mm is used as a test piece, and Tensilon RTM-100 made by Orientec Co., Ltd. The measurement was performed at a speed of 200 mm / min.

[Glossiness]
The glossiness of the surface of the fluororesin film was measured using a gloss meter (VG2000 manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS Z8741.

[Example 1]
PVDF [Kureha Co., Ltd. KF (registered trademark) # 850] 54 parts by mass, titanium oxide [Dyupon TI-PURE (registered trademark) R101; rutile titanium oxide, average particle size 0.29 μm, surface treatment Product] 30 parts by mass, PMMA [Dell Powder (registered trademark) 70H manufactured by Asahi Kasei Chemicals Co., Ltd.] 12.65 parts by mass, acrylic elastomer [Rohm & Haas Paraloid (registered trademark) EXL-2315] 1.35 mass Part, 1.5 parts by mass of calcium carbonate (SL2500 manufactured by Takehara Chemical Industry Co., Ltd.) and 0.5 parts by mass of calcium stearate (manufactured by Nitto Kasei Co., Ltd.) are supplied to a twin screw extruder and melted at a temperature of 220 ° C. It knead | mixed, melt-extruded from the die | dye to the strand form, and after cooling, it cut and obtained the pellet for film forming. The content of titanium oxide is 30% by mass.

The obtained pellets are supplied to a single screw extruder to be in a molten state, the molten resin is discharged from the T-shaped die downward into a film shape, and the molten resin is contact-solidified with a cast roll whose temperature is adjusted to 110 ° C. The film was formed into a film having a thickness of 20 μm and wound up. Then, No. of Table 1 which adjusted the temperature of the wound film to the surface temperature of 140 degreeC. No. 1 in Table 1 with a surface roughness Ra of 0.03 μm and a surface roughness Ra of 0.03 μm. 7 was passed between the elastic rolls shown in No. 7 at a pressing force of 30 N / mm and a speed of 2 m / min. Subsequently, No. of Table 1 which adjusted the surface temperature to 140 degreeC. No. 2 in Table 1 and an embossing roll having a surface roughness Ra of 0.89 μm (formed by sandblasting) of φ10 cm shown in FIG. A PVDF film containing titanium oxide having a thickness of 20 μm was produced by winding between an elastic roll shown in FIG. 7 at a pressing force of 30 N / mm and a speed of 2 m / min, and wound around a paper tube. During winding, the PVDF film was not disturbed or collapsed. About the PVDF film containing the obtained titanium oxide, the total ratio of the area of the titanium oxide where the surface is exposed to the area of the film with respect to the surface of the film on the side brought into contact with the embossing roll [TiO ₂ exposure rate (%) ], Color difference (ΔE) on the film surface before and after the friction test [hereinafter, referred to as “friction test color difference (ΔE)”. ], Evaluation results of metal scratch resistance (hereinafter sometimes referred to as “metal scratch resistance”), weather resistance [hereinafter also referred to as “weather resistance color difference (ΔE)”. ], Mechanical properties (breaking strength of the film at a temperature of 23 ° C .; hereinafter, simply referred to as “breaking strength”) and results of measurement of gloss [hereinafter, these are collectively referred to as “characteristics”. There is. ] Are shown in Table 2 together with a combination of rolls (displayed with respect to a mirror surface roll and an embossing roll. The same applies hereinafter).

[Example 2]
The embossing roll is designated as No. 1 in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 1 except that the embossing roll had a surface roughness Ra of 2.11 μm shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Example 3]
No. in Table 1 No. 1 in Table 1 and the mirror surface roll shown in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 2 except that it did not pass between the elastic rolls shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Example 4]
The embossing roll is designated as No. 1 in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 1 except that the embossing roll had a surface roughness Ra of 4.22 μm shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Example 5]
No. in Table 1 No. 1 in Table 1 and the mirror surface roll shown in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 4 except that it did not pass between the elastic rolls shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Example 6]
The embossing roll is designated as No. 1 in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 1 except that the embossing roll had a surface roughness Ra of 6.10 μm shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Example 7]
No. in Table 1 No. 1 in Table 1 and the mirror surface roll shown in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 6 except that it did not pass between the elastic rolls shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Example 8]
The embossing roll is designated as No. 1 in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 1 except that the embossing roll had a surface roughness Ra of 8.93 μm shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Example 9]
No. in Table 1 No. 1 in Table 1 and the mirror surface roll shown in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 8 except that it did not pass between the elastic rolls shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Example 10]
The pellet used in Example 1 is supplied to a single screw extruder to be in a molten state, a molten resin is discharged from the T-shaped die downward in a film form, and a cooling roll (cast roll) whose temperature is adjusted to a surface temperature of 110 ° C. A film having a thickness of 20 μm was formed at a speed of 6 m / min and wound up by subjecting the surface to a nip roll (made of silicone rubber) and subjecting the molten resin to contact solidification. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

[Comparative Example 1]
A PVDF film containing titanium oxide, discharged from a T-die and contacted and solidified with a cast roll, formed into a film and wound up, is unwound as it is without using a mirror roll and an emboss roll. Table 2 shows various properties of the PVDF film containing titanium oxide.

[Comparative Example 2]
No. in Table 1 No. 1 in the mirror surface roll shown in Table 1 and Table 1. After passing between the elastic rolls shown in FIG. No. 2 in Table 1 and the embossing roll shown in Table 1. A PVDF film containing titanium oxide was obtained in the same manner as in Example 1 except that it did not pass between the elastic rolls shown in FIG. Various characteristics of the obtained PVDF film containing titanium oxide are shown in Table 2 together with combinations of rolls.

From Table 2, it is a fluororesin film containing 15 to 50% by mass of titanium oxide, and at least one surface of the film has a total ratio of the area of titanium oxide with the surface exposed to the area of the film of 3. The fluororesin films of Examples 1 to 10 having an area ratio of 2% or less have a friction test color difference (ΔE) of 0.7 to 2.9, and thus the evaluation of metal scratch resistance is S (excellent). Or it turned out that it is A (good). Further, the fluorine resin films of Examples 1 to 10 have weather resistance and excellent mechanical properties, and the fluorine resin films of Examples 1 to 9 have a matte shape that may be desired. It was found to have a glossiness.

On the other hand, it is a fluororesin film containing 15 to 50% by mass of titanium oxide, and the surface of the film has a total ratio of 5.4% of the area of titanium oxide to which the surface is exposed to the area of the film. Since the fluororesin films of Comparative Example 1 and Comparative Example 2 having an area ratio of 3.3% (area ratio) have a friction test color difference (ΔE) of 14.1 or 5.7, they are resistant to metal abrasion. It was found that the evaluation of sex was C (bad) or B (slightly inferior).

According to the present invention, there is provided a fluororesin film containing 15 to 50% by mass of titanium oxide, and at least one surface of the film has a total ratio of the area of titanium oxide where the surface is exposed to the area of the film. 3.2% or less The above-mentioned fluororesin film is excellent in weather resistance, mechanical properties, and the like, and is abraded due to adhesion of metal powder or metal pieces generated by contact with metal. A fluorine resin film including a PVDF film suitable for a back sheet for a solar cell module, in which traces are hardly formed, a laminate including a layer made of the fluorine resin film, and a back sheet for a solar cell module Since it is provided, the industrial applicability is high.

1: Surface protective material 2: Sealing material 3: Solar cell 4: Back surface protective material (back sheet)

Claims

A fluorine-based resin film containing 15 to 50% by mass of titanium oxide,
At least one surface of the film is characterized in that the total proportion of the area of the titanium oxide from which the surface is exposed to the area of the film is 3.2% or less.
The fluororesin film according to claim 1, wherein the fluororesin forming the fluororesin film is a polyvinylidene fluoride resin.
The fluororesin is at least one resin selected from the group consisting of a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer having a comonomer copolymerization ratio of 15 mol% or less. Fluorine-based resin film.
The fluorine resin film according to any one of claims 1 to 3, wherein the titanium oxide is a titanium oxide having a rutile crystal form.
2. The fluororesin film according to claim 1, further comprising another thermoplastic resin in a proportion of 25% by mass or less.
6. The fluororesin film according to claim 5, wherein the other thermoplastic resin is polymethyl methacrylate.
The method for producing a fluororesin film according to any one of claims 1 to 6, wherein a fluororesin containing 15 to 50% by mass of titanium oxide is embossed after the film is produced by extrusion molding.
The method for producing a fluorine resin film according to any one of claims 1 to 6, wherein the fluorine resin containing 15 to 50% by mass of titanium oxide is subjected to surface treatment at the same time as the film is produced by extrusion molding.
A laminate comprising a layer made of the fluororesin film according to any one of claims 1 to 6.
A solar cell module backsheet comprising a layer made of the fluororesin film according to any one of claims 1 to 6.