JP6310858B2 - Fluorine resin film, method for producing the same, and solar cell module - Google Patents

Description

  The present invention relates to a novel fluororesin film, a method for producing the same, a solar cell back surface protection sheet formed using the fluororesin film, and a solar cell module including the solar cell back surface protection sheet.

  Fluorine-based resin films are widely used in fields that require long-term durability because of their excellent weather resistance, heat resistance, contamination resistance, chemical resistance, solvent resistance, and the like. In particular, a film mainly composed of vinylidene fluoride resin takes advantage of the cost benefits of thinning, and various surface protection materials such as materials for interior and exterior of buildings, container surface materials that have been required to have chemical resistance and organic solvent resistance, It is widely used for front and back materials of solar cells, fuel cell members and the like. Furthermore, in recent years, with a great increase in demand for solar cell modules, it has been widely used as a solar cell back surface protection sheet (Patent Documents 1 and 2).

  The demand for long-term durability for use as such a solar cell back surface protection sheet is becoming stricter, and the use under severe conditions and the extension of its life are required. Therefore, the present applicant has developed a technology for producing a vinylidene fluoride resin film in which the crystal form of the vinylidene fluoride resin is controlled to a specific crystal form, thereby suppressing heat resistance, particularly yellowing when heated. Developed (Patent Document 3). That is, by forming a film by extrusion and then reheating at a temperature of 100 ° C. or higher, the type I crystal structure (β crystal) and the type II crystal structure (α crystal) obtained from the absorbance of the infrared absorption spectrum in the film ) Was controlled so that the ratio of the type II crystal component was 90 to 100% when the total of 100 was 100, thereby obtaining a fluororesin film having a low degree of yellowing. However, it has been desired to obtain a fluororesin film having further improved long-term durability as the product has a longer life.

JP 2011-129672 A JP 2008-28294 A JP 2006-273980 A

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fluororesin film that further improves long-term durability, particularly yellowing resistance, compared to conventional films.
Another object of the present invention is to provide a method for producing the fluororesin film, a solar cell back surface protection sheet using the fluororesin film, and a solar cell module provided with the solar cell back surface protection sheet. To do.

  In Patent Document 3, the ratio of the α crystal obtained from the absorption intensity by the infrared absorption spectrum in the film is controlled to be high, but the value of the α crystal ratio obtained by such a method is somewhat high. As a result, it has been found that the difference in crystal structure may not be sufficiently reflected. Therefore, as a result of studying further indicators for the crystal structure of the resin, the present inventors found that a crystal structure difference that could not be distinguished from the absorption intensity by the infrared absorption spectrum was determined by a heat flux differential scanning calorimetry method. By analyzing the DSC curve, it was found that it could be clearly identified. And as a result of diligent research to obtain a fluorine-based resin film having a higher α crystal ratio than before, the present inventors set the cooling temperature in the extrusion molding to a range of 85 to 120 ° C. Then, it was unexpectedly found that a fluororesin film having further improved long-term durability, particularly yellowing resistance, can be obtained.

  That is, according to one aspect of the present invention, a fluororesin composition comprising a polyvinylidene fluoride resin as a main component is extruded and cooled at a cooling temperature set in the range of 85 to 120 ° C. In a DSC curve (first run) obtained by heating from room temperature to 200 ° C. at a heating rate of 10 ° C./min by a heat flux differential scanning calorimetry, polyfluorination in the range of 150 to 190 ° C. An endothermic peak (inherent peak) unique to vinylidene-based resins and one or more endothermic peaks on the low temperature side of the inherent peak are provided.

In the above, the extrusion molding method is not limited to a specific method as long as the cooling condition after the resin extrusion has a significant effect on the crystallization of the resin. The studied method is the T-die molding method, and therefore the T-die molding method is preferred. In the T-die molding method, the extruded resin is cooled by one or a plurality of cooling rolls. The temperature in the first cooling roll that first cools the extruded resin is the cooling in the present invention. The temperature is maintained at a constant temperature in the range of 85-120 ° C.
Thus, when the cooling temperature at the time of extrusion molding is set to 85 to 120 ° C. and a fluororesin composition comprising a polyvinylidene fluoride resin as a main component is extruded to form a film, In the DSC curve (first run) obtained by heat flux differential scanning calorimetry under a specific condition, there is an endothermic peak (inherent peak) inherent to the polyvinylidene fluoride resin in the range of 150 to 190 ° C. A novel film having one or more endothermic peaks on the low temperature side is obtained.
The film is also a film having an α crystal ratio of 80% or more determined by the following formula (1).

  Moreover, in the said fluororesin film, if the said fluororesin composition is a resin composition which contains a polyvinylidene fluoride resin as a main component, what kind of resin generally contained in a fluororesin, addition An agent or the like may be included. Here, “comprising polyvinylidene fluoride resin as a main component” means that the resin composition contains polyvinylidene fluoride resin as a resin component in an amount of 50% by mass or more, preferably 60% by mass or more. In addition, the case where only the polyvinylidene fluoride resin is used, that is, the case where the polyvinylidene fluoride resin is 100% by mass is also included. Therefore, in one embodiment of the present invention, the fluororesin composition contains only a polyvinylidene fluoride resin as a resin component. On the other hand, in another embodiment of the present invention, a polymethyl methacrylate resin excellent in compatibility with the polyvinylidene fluoride resin is blended, mixed, and extruded. For example, the resin composition to be extruded is a polyvinylidene fluoride resin 50 to 95% by mass, preferably 60 to 95% by mass, and a polymethyl methacrylate resin 5 to 50% by mass, preferably 5 to 40% by mass. Containing.

Further, in the fluorine resin film, the fluorine resin composition may contain various additives in addition to the resin component, but it is preferable to contain titanium oxide or an ultraviolet absorber for the purpose of shielding ultraviolet rays. Here, 5 to 40 parts by mass of titanium oxide is added to 100 parts by mass of the resin composition, and the ultraviolet absorber is 0.1 to 5 parts by mass, preferably 0.3 to 100 parts by mass of the resin composition. ~ 5 parts by weight are added.
Moreover, it is preferable that the said fluorine-type resin film is a thing in the range whose film thickness is 10-50 micrometers.

According to another aspect of the present invention, a step of extruding a molten resin comprising a fluororesin composition comprising a polyvinylidene fluoride resin as a main component into a film, and 85 to 120 of the extruded film resin. At a cooling temperature in the range of ° C., preferably by a cooling roll set at such a cooling temperature, and from a room temperature at a temperature rising rate of 10 ° C./min by a heat flux differential scanning calorimetry. In the DSC curve (first run) obtained when heated to 200 ° C., an endothermic peak (inherent peak) unique to the polyvinylidene fluoride resin in the range of 150 to 190 ° C. and one on the low temperature side of the intrinsic peak A method for producing a fluororesin film having the above endothermic peak is provided.
Also in this production method, the produced fluororesin film has an α crystal ratio determined by the formula (1) of 80% or more. In a preferred embodiment, the fluororesin composition has a polyvinylidene fluoride resin of 50 to 95% by mass, preferably 60 to 95% by mass, and a polymethyl methacrylate resin of 5 to 50% by mass, preferably 5 to 5% by mass. 40% by mass. Furthermore, the fluorine-based resin composition preferably contains 5 to 40 parts by mass of titanium oxide or 0.1 to 5 parts by mass of an ultraviolet absorber with respect to 100 parts by mass of the total resin components. Moreover, it is preferable that the said fluororesin film shall be in the range of 10-50 micrometers in film thickness.

  According to still another aspect of the present invention, there are provided a solar cell back surface protective sheet formed of the fluororesin film, and a solar cell module formed using the solar cell back surface protective sheet.

  Since the fluororesin film according to the present invention is formed from a fluororesin comprising a vinylidene fluoride resin as a main component, it has excellent weather resistance, heat resistance, contamination resistance, chemical resistance, and solvent resistance. Since the resin film has mechanical properties and secondary workability and has a specific peak pattern in the heat flux differential scanning calorimetry, it is excellent in long-term durability, particularly yellowing resistance. Moreover, the protection sheet for solar cell back surface and solar cell module formed using the fluorine resin film according to the present invention are also excellent in long-term durability, particularly yellowing resistance.

Heat flux differential performed on the fluororesin film formed in Example 1 (cooling roll temperature: 85 ° C), Example 2 (cooling roll temperature: 100 ° C) and Example 3 (cooling roll temperature: 120 ° C). It is a graph which shows the DSC curve obtained by scanning calorimetry. A graph in which the α crystal ratio obtained by infrared absorption spectrum analysis and the Δb value obtained by the moist heat resistance test are plotted with respect to the cooling temperature of the cooling roll in T-die molding, and the influence of the cooling temperature on the yellowing phenomenon of the film is represented. . The films produced by changing the cooling temperature between 45-75 ° C are Comparative Examples 3-6, and the films produced by changing the cooling temperature between 85-120 ° C are Examples 11-14. It is a spectrum figure which shows the result of the infrared absorption spectrum analysis performed with respect to the film produced from the fluororesin containing polymethyl methacrylate resin with various content. Films produced by changing the proportion of the polymethyl methacrylate resin in the resin composition between 0 to 50% by mass are Examples 15 to 19 and produced by changing the proportion to 60 to 70% by mass. The film which was made is Comparative Examples 7-8. It is a graph which shows the result of the X-ray diffraction implemented about the film which concerns on Examples 15-19 and Comparative Examples 7-8. It is a graph which shows the result of the DSC analysis implemented about the film which concerns on Examples 15-19 and Comparative Examples 7-8.

  Hereinafter, embodiments of the present invention will be described in detail.

  A fluororesin film according to an embodiment of the present invention is formed by extrusion molding from a fluororesin composition comprising a polyvinylidene fluoride resin as a main component.

<Fluorine resin composition>
As long as the fluororesin composition is a resin composition comprising a polyvinylidene fluoride resin as a main component, it may contain any resin, additive, etc. that are generally contained in a fluororesin. Here, “comprising polyvinylidene fluoride resin as a main component” means that the resin composition contains polyvinylidene fluoride resin as a resin component in an amount of 50% by mass or more, preferably 60% by mass or more. In addition, the case where only the polyvinylidene fluoride resin is used, that is, the case where the polyvinylidene fluoride resin is 100% by mass is also included.
“Polyvinylidene fluoride-based resin” is a crystalline resin having a vinylidene fluoride monomer as a main component and having various crystal structures such as α-type, β-type, and γ-type. A polymer or a copolymer of a monomer copolymerizable with vinylidene fluoride. Examples of the copolymer include a vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer and a vinylidene fluoride-hexafluoropropylene copolymer. Preferably, a homopolymer of vinylidene fluoride is used.

  The fluororesin composition may contain a resin component other than the polyvinylidene fluoride resin, but the resin component is excellent in compatibility with the vinylidene fluoride resin and has an extrusion temperature during film extrusion molding. A methacrylic ester resin is preferable because it can improve the workability by lowering, and can improve the adhesion when laminated with other materials. Here, the methacrylic ester resin includes a methyl methacrylate homopolymer (polymethyl methacrylate), a predetermined amount (for example, 50 mol% or more) of a methyl methacrylate monomer as a constituent unit, and an acrylic ester or methacrylic ester. Examples thereof include a copolymer containing a predetermined amount of methacrylic acid ester other than methyl acid, for example, less than 50 mol%, and a mixture of two or more of these polymers. 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 copolymer is not limited to a random copolymer. For example, a graft copolymer or the like is used, and a copolymer obtained by graft polymerization of a monomer mainly composed of methyl methacrylate on an acrylic saturated crosslinked rubber is also preferably used. A particularly preferred methacrylic ester resin is a polymethyl methacrylate resin.

  Therefore, in one example, the fluororesin composition contains only a polyvinylidene fluoride resin as a resin component. In another example, the fluororesin composition contains a polyvinylidene fluoride resin and a polymethyl methacrylate resin as resin components. In the latter case, as long as the polyvinylidene fluoride resin is the main component, the content of the polymethyl methacrylate resin is arbitrary, but in a preferred embodiment, the fluorine resin composition is a polyvinylidene fluoride resin 50-95. It contains 5% by mass, preferably 60-95% by mass, and 5-50% by mass, preferably 5-40% by mass, of polymethyl methacrylate resin.

  Furthermore, it is preferable that the fluororesin composition contains at least one of a pigment and an ultraviolet absorber in order to impart an ultraviolet shielding effect. For example, when the film is intended to protect the base substrate, there may be a case where a pigment is not added, but even in that case, an ultraviolet absorber is added. Although the weather resistance of the film itself is good, in the case where it is used without adding a pigment, various base materials such as ultraviolet rays reach various base materials and the vinylidene fluoride resin film does not deteriorate. This is because the adhesive or the like used for laminating with the base material is deteriorated and may cause a problem of peeling from the polyvinylidene fluoride resin film.

  The pigment to be used is not particularly limited and may be any inorganic pigment, organic pigment, pearl pigment, etc., but from the viewpoint of weather resistance, oxides and complex oxide inorganic pigments are preferably used. In particular, titanium oxide is preferable. The addition amount of the pigment, particularly titanium oxide, is 5 to 40 parts by mass, preferably 10 to 30 parts by mass with respect to 100 parts by mass of the resin. When the addition amount is less than 5 parts by mass, it cannot be uniformly dispersed in the film, and partial color unevenness may occur. On the other hand, when it exceeds 40 mass parts, the dispersibility to a fluororesin will fall remarkably and an external appearance defect may be caused.

  The ultraviolet absorber is not particularly limited as long as it is compatible with the vinylidene fluoride resin. For example, benzotriazole, oxalic acid, benzophenone, hindered amine, and many other types can be used. Preferably, a high molecular weight type ultraviolet absorber having a molecular weight of 300 or more is suitably used in order to minimize volatilization when used as a manufacturing process or film. The addition amount of a ultraviolet absorber is 0.1-5 mass parts with respect to 100 mass parts of resin, Preferably it is 0.3-5 mass parts.

  In addition to pigments or ultraviolet absorbers, the film of the present invention includes stabilizers, dispersants, antioxidants, matting agents, surfactants, antistatic agents, silica, alumina, etc., depending on the application used. It is also possible to add various additives such as fillers, fluorine-based surface modifiers and processing aids as long as their dispersibility is not impaired.

  As a method of mixing a pigment, an ultraviolet absorber and other various additives into the film of the present invention, a resin and an additive are mixed in advance and melt-kneaded using a commonly used single-screw extruder. The method can be adopted. In addition, by using a high-kneading type twin-screw extruder or by premixing at a high temperature using a high-speed rotary mixer and then melt-kneading with a single-screw extruder, A film having a good dispersion state and excellent appearance quality can be obtained.

  The film thickness of the fluororesin film of the present invention is preferably 50 μm or less, more preferably 10 to 30 μm. If it is less than 10 μm, the handling property is remarkably lowered, and sufficient durability performance may not be obtained. On the other hand, when it exceeds 50 μm, it is disadvantageous in terms of cost such as an increase in raw material cost. The film of the present invention may be used as a surface layer, and an acrylic resin layer or a blend of a vinylidene fluoride resin and an acrylic resin may be laminated as a back layer to form a film having two or more layers.

<Manufacture of fluororesin film>
In general, the fluororesin film can be extrusion-molded by a method of forming a film using a T-type die or a method of forming a film using an inflation die, but in the present invention, it is manufactured using a T-type die. A film forming method is preferably employed. Extrusion conditions are not particularly limited, and conditions conventionally used for forming a vinylidene fluoride resin film can be used. In the present invention, the cooling temperature after extrusion is 85 to 120 ° C. It is necessary to set in the range of preferably 90 to 120 ° C, more preferably 100 to 120 ° C. That is, when forming a film using a T-die molding machine, the high-temperature resin extruded from the T-shaped die is cooled and solidified by a metal cooling roll disposed under the T-shaped die, and the metal The temperature of a cooling roll is set to 85-120 degreeC, Preferably it is 90-120 degreeC, More preferably, it is set to the range of 100-120 degreeC. In addition, when the some cooling roll is arrange | positioned at the extruder, the temperature of the 1st cooling roll (1st cooling roll) is 85-120 degreeC, Preferably it is 90-120 degreeC, More preferably, it is 100-120. It is set in the range of ° C. In addition, a metal cooling roll and a rubber roll are usually arranged in pairs under the T-die, but the presence or absence of the rubber roll and the set temperature of the rubber roll are arbitrary. When the cooling temperature is set to less than 85 ° C., a film having desired long-term durability, particularly yellowing resistance cannot be obtained. On the other hand, when the cooling temperature is set higher than 120 ° C., the film cannot be successfully formed due to poor peeling from the roll.

  The raw material may be supplied by using a resin composition prepared by previously melting and kneading each raw material, but each raw material is directly supplied to a single-screw or twin-screw extruder, and usually 150 to 260 ° C. The film can be formed by melting at a temperature of 1 mm and extruding through a T-die for film.

<Fluorine resin film>
The fluororesin film obtained by extruding the fluororesin composition described above under the above-described conditions becomes a film having an α crystal ratio of 80% or more determined by the formula (1), but is determined by the formula (1). When the crystal ratio exceeds a certain value, it becomes saturated and does not reflect the change in the crystal structure of the film. However, such state change can be grasped by analysis using a heat flux differential scanning calorimetry. That is, in the fluororesin film, regardless of whether or not the cooling temperature is set in the range of 85 to 120 ° C., it is heated from room temperature to 200 ° C. at a heating rate of 10 ° C./min by the heat flux differential scanning calorimetry. In the DSC curve (first run) obtained at this time, an endothermic peak unique to the polyvinylidene fluoride resin is observed at around 170 ° C. However, the fluororesin film according to the present invention formed by setting the cooling temperature in the range of 85 to 120 ° C. includes one or more α crystals on the low temperature side of the endothermic peak inherent in the polyvinylidene fluoride resin. An endothermic peak temperature derived from is observed. As the endothermic peak on the low temperature side becomes more prominent, the proportion of α crystals increases and the long-term durability of the film, particularly yellowing resistance, is improved. For example, in the fluororesin film according to the present invention, the hue b value immediately after film production is about −2.5 to −0.5, but it can be significantly yellowed even after the moisture and heat resistance test described later. The Δb value before and after the test is suppressed to 2 or less.
In the fluororesin film formed under the conditions of the present invention, the endothermic peak seen on the low temperature side of the endothermic peak inherent to the polyvinylidene fluoride resin is always derived from the α crystal. When a film is formed under conditions other than the conditions of the present invention, such as a temperature range other than the temperature range, an endothermic peak may be seen on the low temperature side of the endothermic peak inherent to the polyvinylidene fluoride resin. However, this endothermic peak is not an endothermic peak derived from the α crystal but an endothermic peak derived from the β crystal, and this can be confirmed by, for example, an X-ray diffraction method. Therefore, the fluororesin film showing a desired DSC curve formed under the conditions within the scope of the present invention has superior weather resistance compared to the fluororesin film formed under conditions outside the scope of the present invention. In particular, it has yellowing resistance.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, the raw material used in the Example and the evaluation method of the characteristic of each sample of the produced film are as follows.

<Raw materials>
-Vinylidene fluoride resin: Kyner K720 (manufactured by Arkema), a crystalline polymer with a fluorine content of about 59% and a melting point of about 170 ° C, a polyvinylidene fluoride resin, MFR (conditions: 230 ° C, 3.8 kg load) 5 29 (g / 10min)
Methacrylic ester resin: Acrypet IR-S404 (Mitsubishi Rayon Co., Ltd.), methacrylic ester resin containing rubber components of butyl acrylate (n-BA) and butyl methacrylate (BMA), MFR (condition: 230 ° C, 37.3 N) 7.8 (g / 10 min)
Titanium oxide: Taipure R960 (manufactured by DuPont), (particle size: about 0.35 μm, pure titanium content: about 89%)

（２）耐湿熱性試験後の色相
耐湿熱性試験は、試験機としてプレッシャークッカーＳＰＹ−４０１６（アルプ社製）を用いて行った。ＥＶＡと貼り合せたフィルムサンプルを、日本電色工業社製の測色色差計ＺＥ−２０００を使用してそのＥＶＡとの貼り合せ面の色差測定を行なった後、試験機に投入し、下記条件で耐久試験を実施した。
温度：１２５℃
湿度：１００％
圧力：２．３ａｔｍ
時間：５０ｈｒ
試験後、フィルムのＥＶＡとの貼り合せ面の色差測定を再び行ない、試験前後のΔｂ値を算出した。評価基準は、Δｂ値が２以下で黄変が少ないと判断した。
（３）ＵＶ透過率
日立分光光度計Ｕ−３３１０（日立ハイテクフィールディング株式会社製）を用いてフィルムの波長３４０ｎｍにおけるＵＶ透過率を測定した。
（４）熱流束示差走査熱量測定
示差走査熱量測定装置ＤＳＣ３１００ＳＡ（ブルカー・エイエックスエス社製）を用いて下記条件下で測定を行った。
温度：室温→２００℃
昇温速度：１０℃／分
サンプル質量：１．５ｍｇ
（５）Ｘ線回折
Ｘ線回折装置Ｕｌｔｉｍａ ＩＶ（リガク社）を用いて下記条件下で測定を行った。
Ｘ線源：Ｃｕ封入管
印加電圧／電流：４０ｋＶ／４０ｍＡ
検出器：高速検出器Ｄ／ｔｅＸ Ｕｌｔｒａ<Evaluation method>
(1) α crystal ratio The infrared absorption spectrum was measured by NICOLET380 FT-IR (manufactured by Thermo Fisher Scientific). In the infrared absorption spectrum, the characteristic absorption of the β-type crystal of the polyvinylidene fluoride resin is at a wave number of 840 cm ⁻¹ , and the characteristic absorption of the α-type crystal is at the wave number of 765 cm ⁻¹ . The α crystal ratio was calculated from each peak intensity using the following formula (1) (Tatsumi Hanada, Satoshi Ando, crystallization of polyvinylidene fluoride in a polyvinylidene fluoride / polyvinyl acetate / polyethyl methacrylate blend system), Tokyo Kasei (See Gakuin University Bulletin, July 1992, No. 32, pages 5-12).

(2) Hue after heat and humidity resistance test The moisture and heat resistance test was performed using a pressure cooker SPY-4016 (manufactured by Alp) as a testing machine. The film sample bonded with EVA was subjected to color difference measurement on the bonding surface with EVA using a colorimetric color difference meter ZE-2000 manufactured by Nippon Denshoku Industries Co., Ltd. The endurance test was carried out.
Temperature: 125 ° C
Humidity: 100%
Pressure: 2.3 atm
Time: 50hr
After the test, the color difference measurement of the bonding surface of the film with EVA was performed again, and Δb values before and after the test were calculated. The evaluation criterion was that the Δb value was 2 or less and yellowing was small.
(3) UV transmittance The UV transmittance at a wavelength of 340 nm of the film was measured using a Hitachi spectrophotometer U-3310 (manufactured by Hitachi High-Tech Fielding Co., Ltd.).
(4) Heat flux differential scanning calorimetry Measurement was performed under the following conditions using a differential scanning calorimeter DSC3100SA (manufactured by Bruker AXS).
Temperature: Room temperature → 200 ° C
Rate of temperature increase: 10 ° C./min Sample mass: 1.5 mg
(5) X-ray diffraction Measurement was performed under the following conditions using an X-ray diffractometer Ultima IV (Rigaku).
X-ray source: Cu sealed tube Applied voltage / current: 40 kV / 40 mA
Detector: High-speed detector D / teX Ultra

<Examples 1-10 and Comparative Examples 1-2>
The PMMA ratio shown in Table 1 for vinylidene fluoride resin, polymethyl methacrylate resin, and titanium oxide (mass% of polymethyl methacrylate resin relative to 100 mass% in total of vinylidene fluoride resin and polymethyl methacrylate resin) And the amount of titanium oxide (mass part of titanium oxide with respect to 100 parts by mass of resin), put into a φ65 mm single screw extruder, kneaded, and then extruded from the extruder through a T-die at an extrusion temperature of 240 ° C. Through the first cooling roll set to the cooling temperature shown in 1, it was cooled and solidified to form a film, and the films according to Examples 1 to 10 and Comparative Examples 1 and 2 having the thicknesses shown in Table 1 were obtained.
About the produced film, according to the above-mentioned evaluation method, the alpha crystal ratio, the hue after the heat and humidity resistance test, the UV transmittance, and the heat flux differential scanning calorie were evaluated. The results are also shown in Table 1. Moreover, about the film which concerns on typical Examples 1-3, the DSC curve obtained by heat flux differential scanning calorimetry is shown in FIG. In Comparative Example 2, the film did not peel smoothly from the cooling roll, and a film that could be used for property evaluation could not be produced.

  From the results in Table 1, the films according to Examples 1 to 10 have an endothermic peak on the low temperature side of the intrinsic peak in addition to the high α crystal ratio, and the color difference Δb after the moist heat resistance test is a sufficiently small value. Thus, it is understood that the yellowing resistance is excellent. On the other hand, in Comparative Example 1, it can be seen that the α crystal ratio is low and the yellowing resistance is deteriorated. In addition, although the endothermic peak is seen also in the comparative example 1, it turned out that this peak is a peak derived from (beta) crystal | crystallization by X-ray diffraction. Moreover, from the result of FIG. 1, in the fluororesin films according to Examples 1 to 3, an endothermic peak is observed on the low temperature side of the intrinsic peak of the polyvinylidene fluoride resin, and the endotherm increases as the cooling roll temperature becomes higher. The peak was found to be prominent.

<Examples 11-14, Comparative Examples 3-6>
In order to investigate the influence of the setting temperature of the metal cooling roll on the yellowing phenomenon of the film, the PMMA ratio is 25%, the titanium oxide amount is 22 parts by mass, and the setting cooling temperature of the metal cooling roll is 45 ° C, 55 ° C, 65 ° C, The fluororesin films according to Comparative Examples 3 to 6 and Examples 11 to 14 were produced by changing the temperature to 75 ° C, 85 ° C, 100 ° C, 110 ° C, and 120 ° C. The α crystal ratio of the obtained film was determined and the Δb value was measured. The results are shown in FIG.
From FIG. 2, the α crystal ratio is low when the cooling temperature is low, and as a result, the yellowing phenomenon becomes remarkable. However, the α crystal ratio increases as the cooling temperature increases until the cooling temperature reaches 80 ° C. It can be seen that although the phenomenon is not sufficiently reduced, it is gradually reduced. However, it can be seen that when the cooling temperature reaches about 85 ° C., the α crystal ratio reaches a saturated state and does not increase any more, but the yellowing phenomenon is still gradually reduced. That is, it can be understood from this experimental result that there is a limit to the method for reducing the yellowing phenomenon based on the analysis by the α crystal ratio based on the infrared absorption spectrum analysis.

<Examples 15 to 19 and Comparative Examples 7 to 8>
In order to investigate the influence of the PMMA ratio on the crystal structure of the fluororesin film, the set temperature of the metal cooling roll is 85 ° C., the amount of titanium oxide is 22 parts by mass, and the PMMA ratio is 0% by mass to 10% by mass, 20% by mass. , 30% by mass, 40% by mass, 50% by mass, 60% by mass, and 70% by mass to produce fluorine-based resin films according to Examples 15 to 19 and Comparative Examples 7 to 8. The crystal structure of the obtained fluororesin film was analyzed by infrared absorption spectrum method, X-ray diffraction method, and heat flux differential scanning calorimetry. The results are shown in FIGS. From the analysis result by the infrared absorption spectrum method of FIG. 3, it can be seen that the peaks derived from the α crystal and the β crystal become smaller as the PMMA ratio increases. Moreover, from the analysis result by the X-ray diffraction method of FIG. 4, when the PMMA ratio exceeds 50 mass%, it is understood that crystallization of PVDF is suppressed. Furthermore, from the result of the analysis by the heat flux differential scanning calorimetry method of FIG. 5, it can be seen that the melting point Tm gradually decreases from about 170 ° C. (PMMA ratio: 0 mass%) as the PMMA ratio increases. Further, when the PMMA ratio exceeds 50% by mass, the inherent endothermic peak intensity becomes weak, and it is understood that PVDF and PMMA are compatible.

Claims (8)

Fluorine resin composition comprising a resin component mainly composed of polyvinylidene fluoride resin is formed by extrusion molding, cooled at a cooling temperature set in the range of 100 to 120 ° C., and heat flux differential scanning In the DSC curve (first run) obtained by heating from room temperature to 200 ° C. at a rate of temperature increase of 10 ° C./min by calorimetry, the endothermic characteristic of polyvinylidene fluoride resin in the range of 150 to 190 ° C. peak and (intrinsic peak), possess one or more endothermic peaks on the low temperature side of said intrinsic peaks,
The fluorine-based resin composition contains 5 to 40 parts by mass of titanium oxide with respect to 100 parts by mass of the resin component .

The fluorine resin film according to claim 1, wherein the α crystal ratio determined by is 80% or more. Resin component contains 50 to 95 wt% of a polyvinylidene fluoride resin, from 5 to 50 mass% of polymethyl methacrylate resin, a fluorine resin film according to claim 1 or 2. Fluorine-based resin composition, fluorine-based resin film according to claim 3, the resin component 100 parts by weight of the total, the ultraviolet absorbent containing 0.1 to 5 parts by weight.   The fluororesin film according to any one of claims 1 to 4, wherein the film thickness is within a range of 10 to 50 µm. A step of extruding a molten resin comprising a fluororesin composition comprising a resin component comprising a polyvinylidene fluoride resin as a main component into a film, and a cooling temperature of the extruded film resin within a range of 100 to 120 ° C. In a DSC curve (first run) obtained by heating from room temperature to 200 ° C. at a rate of temperature increase of 10 ° C./min by a heat flux differential scanning calorimetry method. possess the polyvinylidene fluoride resin in the range and specific endothermic peak (intrinsic peak), one or more endothermic peaks on the low temperature side of said intrinsic peaks,
A method for producing a fluororesin film in which the fluororesin composition contains 5 to 40 parts by mass of titanium oxide with respect to 100 parts by mass of the resin component .   The protection sheet for solar cell back surfaces formed with the fluorine resin film as described in any one of Claims 1-5.   A solar cell module formed using the solar cell back surface protective sheet according to claim 7.

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