JP2018120943A - Backside protection sheet for solar battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backside protection sheet superior in light resistance, high in partial discharge voltage per unit thickness and superior in flame retardancy and long-term reliability in manufacturing a solar battery module.SOLUTION: A backside protection sheet for a solar battery module has a light resistant film (A layer), a polyester film (B layer) and an easily adhesive resin layer (C layer) in this order. The B layer includes at least one polyester resin layer (B1 layer) containing cavities of 10-50% therein. The C layer has a sealant for holding and fixing a solar battery element, and an adhesion strength of 40 N/cm or more. The backside protection sheet is 60% or more in retention of elongation after exposed to UV light of 300 kWh/min cumulative amount from the side of the A layer, and has a thickness of 100 μm or more and less than 180 μm, and a partial discharge voltage of 600 V or more and less than 1000 V.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a back surface protection sheet for a solar cell module.

  Photovoltaic power generation is being put into practical use as a new energy source that is inexhaustible and non-polluting. As a solar cell module for this purpose, a surface protection sheet, a sealing material sheet 1, a solar power generation element provided with wiring, a sealing element A laminate in which the stop sheet 2 and the back surface protection sheet are laminated and integrated is widely known.

  The demand for long-term durability is increasing year by year, for example, the back surface protection sheet is incorporated in a solar cell module, and long-term quality assurance is required for 20 to 30 years after installation. Adhesion with the sheet is a very important required characteristic from the viewpoint of protecting the photovoltaic power generation element and preventing deterioration.

  Furthermore, although the back surface protection sheet is not directly exposed to sunlight, depending on the installation method, the back surface protection sheet is exposed to sunlight due to wraparound or reflection. Therefore, it is important to impart light resistance to the back surface protection sheet.

  Moreover, since a high voltage is applied for a long time when the solar cell system is operated, it is necessary to pay great attention to the electrical safety of the solar cell module, and it is desired that the back surface protection sheet has a high withstand voltage characteristic. . If the withstand voltage characteristic is inferior, a discharge of a minute charge inside the back surface protection sheet called partial discharge occurs during operation of the solar cell system, and if this continues for a long time, chemical deterioration of the resin constituting the back surface protection sheet proceeds. . When chemical degradation progresses due to partial discharge phenomenon, there is a possibility of causing dielectric breakdown in the back surface protection sheet when a high voltage is momentarily applied to the system due to lightning. Therefore, the back surface protection sheet is required to increase the voltage at which the occurrence of the partial discharge phenomenon starts (hereinafter referred to as “partial discharge voltage”) in order to suppress the occurrence of the partial discharge phenomenon as much as possible.

  The back surface protection sheet for increasing the partial discharge voltage includes at least one of a polypropylene resin and an inorganic filler or an organic filler, and has a base material layer in which pores are formed by stretching at least uniaxially. A sheet (see Patent Document 1) or a back surface protection sheet (see Patent Document 2) comprising a resin composition containing a polyester resin and an incompatible polymer, and comprising a reflective layer having a cavity inside and a diffusion layer containing inorganic particles. Proposed.

JP 2013-033959 A JP 2006-046512 A

  However, in the back surface protection sheet described in Patent Document 1, the melting point of the polypropylene resin is low, and in the thermocompression bonding process at the time of manufacturing the solar cell module, in particular, in the portion where the wiring portion of the solar cell module is raised in a convex shape, Are easily crushed and the polypropylene resin itself is easily swept away, resulting in problems of poor appearance such as a decrease in insulation performance due to film reduction, and the appearance of metallic colors and irregularities of electrical wiring on the back of the solar cell module.

  Moreover, in the back surface protection sheet described in Patent Document 2, it cannot be said that the flame-retardant property and long-term durability of the reflective layer having a cavity are sufficient, and improvement in practical use is required.

  The problem to be solved by the present invention is to provide a back protection sheet that has excellent light resistance, high partial discharge voltage per unit thickness, and excellent flame retardancy and long-term reliability in manufacturing a solar cell module. It is to be.

  In order to solve the above problems, the present invention has the following configuration.

1st invention has a light-resistant film (A layer), a polyester film (B layer), and an easily-adhesive resin layer (C layer) in this order, B layer contains a 10-50% cavity inside At least one polyester resin layer (B1 layer) is included, and the C layer has a sealing material for holding and fixing the solar cell element and an adhesive strength of 40 N / cm or more, and an ultraviolet ray having an integrated amount of 300 kWh / m ² from the A layer side. Is a back surface protection sheet for a solar cell module that has an elongation retention after irradiation of 60% or more, a thickness of 100 μm or more and less than 180 μm, and a partial discharge voltage of 600 V or more and less than 1000 V.

In the second invention, the light resistance film (A layer) has an average transmittance of 1% or less at a wavelength of 300 to 400 nm, and an elongation retention ratio of 50% or more after irradiation with ultraviolet rays having an integrated amount of 300 kWh / m ^2. It is characterized by being.

  A third invention is characterized in that the light-resistant film (A layer) is a light-resistant polyester film and includes at least one polyester resin layer to which a whitening agent is added.

  The fourth invention is characterized in that the light-resistant film (A layer) is a light-resistant fluorine film and includes at least one fluororesin layer to which a whitening agent is added.

  The fifth invention is characterized in that the light-resistant film (A layer) has a relative temperature index of 105 ° C. or higher.

  The sixth invention is characterized in that the light-resistant film (A layer) has flame retardancy of VTM-2 standard or higher, which indicates flame retardancy in safety standard UL94 for solar cell modules.

  The seventh invention is characterized in that an average relative reflectance at a wavelength of 400 nm to 1200 nm measured from the easily adhesive resin layer (C layer) side is 80% or more and 105% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the back surface protection sheet which is excellent in light resistance, has high partial discharge voltage per unit thickness, and was excellent in the flame retardance and long-term reliability can be provided.

It is the schematic sectional drawing which showed an example of the back surface protection sheet for solar cell modules of this invention. It is the schematic sectional drawing which showed an example of the back surface protection sheet for solar cell modules of this invention. It is the schematic sectional drawing which showed an example of the solar cell module using the back surface protection sheet for solar cell modules of this invention. It is the schematic sectional drawing which showed the sample preparation method for the adhesive strength measurement of the back surface protection sheet for solar cell modules of this invention, and a sealing material sheet.

The present invention has a light-resistant film (A layer), a polyester film (B layer), and an easily adhesive resin layer (C layer) in this order, and the B layer is a polyester containing 10 to 50% of voids inside. The layer C includes at least one resin layer (B1 layer), the layer C has an adhesive strength of 40 N / cm or more with a sealing material for holding and fixing the solar cell element, and an ultraviolet ray having an integrated amount of 300 kWh / m ² from the layer A side. Is a back surface protection sheet for a solar cell module that has an elongation retention after irradiation of 60% or more, a thickness of 100 μm or more and less than 180 μm, and a partial discharge voltage of 600 V or more and less than 1000 V.

  Hereinafter, embodiments of the back surface protective sheet for solar cell module of the present invention will be described in detail with reference to the drawings.

  1 and 2 are side cross-sectional views for explaining an example of one embodiment of a back surface protection sheet for a solar cell module of the present invention. In addition, what is shown to a figure is one Embodiment, It is not limited to this.

  The back surface protection sheet for solar cell modules of this invention has a light-resistant film (A layer), a polyester film (B layer), and an easily-adhesive resin layer (C layer) in this order.

  The polyester film (B layer) in the present invention needs to contain at least one polyester resin layer (B1 layer) containing 10 to 50%, preferably 20 to 40% voids inside the B1 layer. It is an important layer that imparts a high partial discharge voltage and high reflectivity when used as a protective sheet.

  The B1 layer is composed of, for example, a polyester resin composition containing a polyester resin and an incompatible polymer (relative to the polyester resin). Cavities are formed around the incompatible polymer by finely dispersing the incompatible polymer in the polyester resin and stretching it (for example, biaxial stretching). When the void ratio in the B1 layer is 10% or more, preferably 20% or more, sufficient void content can be obtained in the thickness direction of the polyester film (B layer), and the dielectric constant should be low in the film thickness direction. Even when a high voltage is applied, it is possible to suppress the concentration of the electric field on the portion with inferior insulation performance and to suppress the occurrence of the partial discharge phenomenon. Further, when the void ratio in the B1 layer is 50% or less, preferably 40% or less, the polyester film (B layer) containing the B1 layer is excellent in film formation stability and has good mechanical properties. Back surface protection when a shock is applied from the outside when the protective sheet is incorporated in a solar cell module (for example, when vibration is applied during transportation or when some load is applied during work during transportation or construction). Sheet breakage can be suppressed.

  In addition, due to the difference in refractive index between the polyester resin and the cavity in the B1 layer, it is possible to efficiently reflect sunlight that has entered the back surface protection sheet from the front of the solar cell module.

  Moreover, it is preferable that the average relative reflectance in wavelength 400-1200 nm measured from the C layer side of the back surface protection sheet for solar cell modules of this invention is 80% or more, More preferably, it is 90% or more. The average relative reflectance tends to increase as the void ratio of the B1 layer increases. However, the void ratio of the B1 layer has an upper limit as described above, and the average reflectance is preferably 105% or less.

  Generally, a part of sunlight received from the transparent substrate side on the light receiving surface side passes through the gap between the power generation element and the power generation element and enters the back surface protection sheet for the solar cell module. At this time, sunlight incident on the back surface protective sheet for solar cell module is reflected on the transparent substrate side and contributes to power generation. And the contribution to electric power generation becomes so large that the reflectance of the back surface protection sheet for solar cell modules is high.

  The polyester resin used in the present invention is a polymer obtained by condensation polymerization from a diol and a dicarboxylic acid, a hydroxycarboxylic acid, or a derivative thereof.

  Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, and sebacic acid. Examples of the diol include those represented by ethylene glycol, trimethylene glycol, tetramethylene glycol and cyclohexanedimethanol.

  Specific examples of the polyester resin include polyethylene terephthalate, polyethylene naphthalate, polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylenedimethylene terephthalate and polyethylene- Examples include 2,6-naphthalenedicarboxylate. These polyester resins may be a homopolyester or a copolyester, and examples of the copolymer component include diol components such as diethylene glycol, neopentyl glycol and polyalkylene glycol, and adipic acid, And dicarboxylic acid components such as sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and 5-sodiumsulfoisophthalic acid.

  Of the above, polyethylene terephthalate and polyethylene naphthalate are preferably used as the polyester resin, and polyethylene terephthalate is particularly preferable because it is excellent in water resistance, durability, chemical resistance, and the like. Here, polyethylene terephthalate contains 55 mol% or more and 100 mol% or less of ethylene glycol component in 100 mol% of all components such as diol, and 55 mol% or more of terephthalic acid component in 100 mol% of all components such as dicarboxylic acid. A homopolyester resin or copolyester resin containing 100 mol% or less. The component such as diol refers to a component derived from diol among the components incorporated into the polymer chain by condensation polymerization, and the component such as dicarboxylic acid refers to the component incorporated into the polymer chain by condensation polymerization. Those derived from dicarboxylic acids and the like.

  Examples of the incompatible polymer include poly-3-methylbutene-1, poly-4-methylpentene-1, polyvinyl t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, Polyvinylcyclohexane, polystyrene, polymethylstyrene, polydimethylstyrene, polyfluorostyrene, poly-2-methyl-4-fluorostyrene, polyvinyl tert-butyl ether, cellulose triacetate, cellulose tripropionate, polyvinyl fluoride, amorphous Examples thereof include polymers having a melting point of 180 ° C. or higher selected from polyolefins, cyclic olefin copolymer resins, polychlorotrifluoroethylene, and the like.

  Among these, polyolefins, particularly polymethylpentene and cyclic olefins are preferably used as incompatible polymers for polyester resins. The cyclic olefin copolymer resin is a copolymer composed of ethylene and at least one cyclic olefin selected from the group consisting of bicycloalkene and tricycloalkene.

  In the B1 layer, it is preferable that the polyester resin and the incompatible polymer each include a polyester resin composition containing 10 to 50 parts by mass of the incompatible polymer with respect to 100 parts by mass of the polyester resin. More preferably, it is 10 to 30 mass parts, More preferably, it is 10 to 25 mass parts. By setting the addition amount of the incompatible polymer to 10 parts by mass or more, it becomes possible to obtain a high porosity, a high partial discharge voltage, and a high reflectance, and by adding the addition amount to 50 parts by mass or less, the mechanical strength. Can be suppressed, and productivity during film formation can be improved.

  In order to disperse the incompatible polymer, it is effective to add a dispersion aid. The dispersion aid is a compound having an effect of promoting dispersion, and polyethylene glycol, a copolymer of polybutylene terephthalate and polytetramethylene glycol, and the like are preferably used. The total layer containing the polymer is 100% by mass, preferably 3% by mass to 40% by mass, and more preferably 3% by mass to 25% by mass.

  In addition, for example, an antistatic agent, an ultraviolet absorber, a stabilizer, an antioxidant, a plasticizer, a lubricant, a filler, and a coloring pigment are added to the polyester film (B layer) in the present invention as necessary. The resin film which added the agent within the range which does not impair the effect of this invention can also be used.

  Next, an example of a method for forming a polyester film (B layer) in the present invention, in particular, an example of a film consisting of only the B1 layer will be described in detail.

  Polymethylpentene is used as an incompatible polymer, polyethylene glycol is used as a dispersion aid, and polybutylene terephthalate and polytetramethylene glycol copolymer are mixed into polyethylene terephthalate, which is thoroughly mixed and dried. Feed to Extruder A heated to 270-300 ° C. In the T die die, the polymer from the extruder A is extruded to form a sheet. The sheet thus melted and laminated is closely cooled and solidified by electrostatic force on a drum whose drum surface temperature is cooled to 10 to 60 ° C. to form an unstretched film, and the obtained unstretched film is 80 to 120 It guide | induces to the roll group heated to the temperature of (degreeC), is longitudinally stretched by 2.0 to 5.0 time in the longitudinal direction, and then it cools with the roll group of the temperature of 20-50 degreeC. Subsequently, both ends of the longitudinally stretched film are guided to a tenter while being gripped by clips, and are stretched in a direction perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 90 to 140 ° C. The stretching ratio is 2.5 to 4.5 times in the longitudinal and lateral directions, and the area ratio (longitudinal stretching ratio x lateral stretching ratio) is preferably 9 to 16 times. If the area magnification is less than 9 times, the whiteness of the resulting film becomes poor. Conversely, if the area magnification exceeds 16 times, the film tends to be broken during stretching and the film-forming property tends to be poor. In order to give the flatness and dimensional stability of the biaxially stretched film in this manner, heat setting is performed at a temperature of 150 to 230 ° C. in the tenter, and after uniform cooling, the film is cooled to room temperature and wound. To obtain a polyester film (B layer).

  The thickness of the polyester film (B layer) in the back protective sheet for solar cell module of the present invention is preferably 75 μm or more and 150 μm or less, and more preferably 85 μm or more and 125 μm or less. The thickness ratio of the B1 layer in the polyester film (B layer) is preferably 50% or more. Therefore, the thickness of the B1 layer is preferably 37.5 μm or more and 150 μm or less. When the thickness of the B1 layer is 37.5 μm or more, a sufficient amount of cavities can be formed in the B1 layer, low dielectric properties can be obtained in the film thickness direction, and the thickness direction of the back surface protection sheet for solar cell modules When a high voltage is applied, the electric field received per unit volume in the thickness direction can be reduced to suppress the occurrence of a partial discharge phenomenon, which is preferable. On the other hand, there is no particular upper limit to the thickness of the B1 layer, but it is sufficient if a necessary partial discharge voltage can be achieved, and it is preferably 150 μm or less from the viewpoint of economy.

In this invention, a light-resistant film (A layer) is a layer which has a function which suppresses deterioration of the back surface protection sheet by the light irradiation from A layer side, after the back surface protection sheet of this invention is integrated in a solar cell module. is there. For this reason, it is preferable that the average transmittance at a wavelength of 300 to 400 nm is 1% or less, and the elongation retention after irradiation with ultraviolet rays having an integrated amount of 300 kWh / m ² is 60% or more. By setting the average transmittance at a wavelength of 300 to 400 nm to 1% or less, deterioration of the B layer and the C layer due to ultraviolet irradiation can be suppressed, and the A layer itself also has an elongation after irradiation with an integrated amount of 300 kWh / m ^2. It is preferable for the retention rate to be 50% or more because the protection function against ultraviolet rays can be retained for a long time.

  When the light-resistant film (A layer) includes at least one resin layer (A1 layer) to which a whitening agent has been added, a light-resistant film and an ultraviolet-resistant property can be preferably imparted when it is used as a back protective sheet.

  Examples of the whitening agent contained in the A1 layer include calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, alumina, mica, mica titanium, Talc, clay, kaolin, lithium fluoride, calcium fluoride, and the like can be used. Among these, it is preferable to use titanium oxide from the viewpoints of weather resistance and diffusibility.

  Examples of the titanium oxide include crystalline titanium oxides such as anatase titanium oxide and rutile titanium oxide. From the viewpoint of increasing the difference in refractive index from the polyester used, titanium oxide having a refractive index of 2.7 or more is preferable, and for example, rutile titanium oxide is particularly preferable.

  The light-resistant film (A layer) is preferably a light-resistant polyester film including at least one polyester resin layer to which the whitening agent is added. The polyester resin here is the same as that used for the B1 layer, and polyethylene terephthalate and polyethylene naphthalate are preferably used. In particular, polyethylene terephthalate is excellent in water resistance, durability, chemical resistance, etc. Preferably used.

  The light-resistant film (A layer) is also preferably a light-resistant fluorine film including at least one fluororesin layer to which the whitening agent is added. The fluororesin here refers to a resin containing 20 mol% or more of fluorine atoms in 100 mol% of all atoms forming the resin. For example, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene -Tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropolypropylene copolymer (FEP) etc. can be used individually or in mixture of multiple types. Especially, it is preferable to use polyvinyl fluoride and polyvinylidene fluoride from a viewpoint of long-term durability when it is set as a solar cell module.

  The relative temperature index (RTI) based on UL746B of the solar cell module back surface protection sheet is desirably certified at the highest temperature reached by the solar cell module during operation + 20 ° C. Conventionally, the maximum temperature reached about 80 ° C. However, in recent years, it is said that the maximum temperature reached by the solar cell module is around 100 ° C. as the efficiency of the solar cell module increases and the power generation amount increases. Therefore, it is preferable that RTI of the light-resistant film (A layer) in this invention is 105 degreeC or more, More preferably, it is 125 degreeC or more.

  Furthermore, it is preferable that the light-resistant film (A layer) in this invention is a film provided with the flame retardance, and the flame retardance more than the VTM-2 standard which shows the flame retardance in the safety standard UL94 for solar cell modules The solar cell element is protected by the back surface protection sheet by laminating the light-resistant film (A layer) on the back surface protection sheet for the solar cell module, and electric leakage ignition from the solar cell element or wiring In the event of a fire or fire, the spread of fire can be suppressed.

  The thickness of the light-resistant film (A layer) in the back surface protective sheet for solar cell module of the present invention is preferably 25 μm or more and 75 μm or less, more preferably 30 μm or more and 50 μm or less, whereby the back surface protection sheet can be used outdoors for a long time. Sufficient light resistance and ultraviolet resistance can be imparted.

  Specifically, the light-resistant film (A layer) in the present invention is a white hydrolysis-resistant biaxially stretched polyethylene formed by co-extrusion of a polyester resin layer and a polyester resin layer to which a whitening agent is added. A terephthalate film, “Lumirror” (registered trademark) MX11 (thickness 50 μm, 75 μm), MG13 (thickness 50 μm, 75 μm), MX70 (thickness 38 μm) manufactured by Toray Industries, Inc. can be used. Further, “Tedlar” (registered trademark) PV2001 (thickness 37.5 μm) or PV2111 (thickness 25 μm) manufactured by DuPont, which is a white polyvinyl fluoride (PVF) film, or Arkema, which is a white polyvinylidene fluoride (PVDF) film. “Kyner” (registered trademark) film (thickness 30 μm) manufactured by the company can be used.

By disposing a light-resistant film (A layer) in the present invention, the elongation retention after irradiation with ultraviolet rays with an integrated amount of 300 kWh / m ² from the A layer side of the back surface protective sheet for solar cell module of the present invention is 60. % Or more. If the elongation retention after irradiation with an integrated amount of 300 kWh / m ² of ultraviolet light is less than 60%, there may be a problem in the long-term durability of the solar cell module.

  In the present invention, the easy-adhesive resin layer (C layer) is formed by laminating a surface protective sheet, a sealing material sheet 1, a photovoltaic power generation element provided with wiring, a sealing material sheet 2, and a back surface protective sheet in this order. In the manufacturing process of the solar cell module integrated by thermocompression molding, the adhesive force between the back surface protection sheet and the sealing material sheet is determined.

  Examples of the sealing material sheet include ionomer resin, ethylene / vinyl acetate copolymer (EVA), polyvinyl butyral, silicone resin, polyurethane, and modified polyolefin. Among these, EVA is preferably used from the viewpoint of weather resistance, adhesion to other members, and member costs.

  In the present invention, it is important that the adhesion strength after thermocompression-molding with the easily adhesive resin layer (C layer) surface, the sealing material sheet is 40 N / cm or more. When the adhesion strength after thermocompression molding is less than 40 N / cm, the initial design specifications of the solar cell module cannot be satisfied. Moreover, it is necessary to maintain the adhesive strength for a long time even in an environment exposed outdoors, and the adhesive strength after thermocompression bonding with the sealing material sheet is 1000 hours after storage at 85 ° C. and 85% RH. And it is preferable that it is 40 N / cm or more.

  Furthermore, of the light incident from the front surface of the solar cell module, a resin is selected that exhibits resistance to light that does not cause a photodegradation reaction with respect to light that passes through the cells and passes through the sealing material sheet layer and reaches the back surface protection sheet. It is preferable to maintain the adhesion performance stably over a long period of time. Accordingly, the resin that forms the easy-adhesive resin layer (C layer) (hereinafter referred to as “easily-adhesive resin”) is preferably a light-resistant resin, and an acrylic resin or a fluorine-based resin that is further excellent in light resistance is used. It is preferable to use it.

  As the acrylic resin, an acrylic resin, an acrylic polyol copolymer, an acrylic / urethane copolymer, or the like is used. For example, “Acrynal” (manufactured by Toei Kasei Co., Ltd.), “Akrit” (manufactured by Taisei Fine Chemical Co., Ltd.), “Hitaroid” (manufactured by Hitachi Chemical Co., Ltd.), “Acridic” (manufactured by DIC Corporation), “Udouble” (manufactured by Nippon Shokubai Co., Ltd.), “Dianar” (manufactured by Mitsubishi Rayon Co., Ltd.), and the like. Examples of polyurethane resins include “Samprene” (manufactured by Sanyo Chemical Industries), “Takelac” (manufactured by Mitsui Chemicals), TA (manufactured by Hitachi Chemical Co., Ltd.), and “Seika Bond” (Ohnissei). Chemical Industry Co., Ltd.).

  Examples of the fluorine-based resin include perfluoroolefin-based resins mainly composed of perfluoroolefin units from the viewpoint of structural units. Specific examples include a tetrafluoroethylene homopolymer (PTFE), a copolymer of tetrafluoroethylene with hexafluoropropylene, perfluoro (alkyl vinyl ether) or the like, and other monomers copolymerizable therewith. And a copolymer with the body. Of these, a fluororesin mainly composed of tetrafluoroethylene is preferable in terms of excellent pigment dispersibility, weather resistance, copolymerization, and chemical resistance. For example, “Zeffle” GK manufactured by Daikin Industries, Ltd. Examples include series. Since these fluororesins are also excellent in flame retardancy, they also have the effect of improving the flame retardancy of the film for solar cell back surface protection sheet.

  Moreover, in order to improve adhesiveness with a polyester film (B layer) or the back surface protection sheet for solar cell modules of this invention is exposed to high temperature processing in a solar cell module manufacturing process, the heat resistance of a coating film. For the purpose of improving, it is preferable to form a crosslinked structure in these weather resistant resins.

  As for the thickness of the easily-adhesive resin layer (C layer) in this invention, 0.2-10 micrometers is preferable, More preferably, it is 1-5 micrometers. When this easy-adhesive resin layer (C layer) is formed by a coating method, if the thickness of the easy-adhesive resin layer (C layer) is less than 0.2 μm, phenomena such as repellency and film breakage occur during coating. Since it is easy and it is difficult to form a uniform coating film, the adhesion strength to the polyester film (B layer) and the sealing material sheet may not be sufficiently developed. On the other hand, when the thickness of the easy-adhesive resin layer (C layer) exceeds 10 μm, the adhesion strength is sufficiently developed, but the coating method is restricted, the production cost becomes high, the coating film adhesion to the transport roll, There is a concern that the coating film is liable to be peeled off.

  Examples of the solvent of the coating liquid for forming the easily adhesive resin layer (C layer) in the present invention by a coating method include, for example, toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dimethylformamide, Examples thereof include dimethylacetamide, methanol, ethanol and water. The properties of the coating liquid may be either an emulsion type or a dissolution type.

  The method for forming the easy-adhesive resin layer (C layer) on the polyester film (B layer) is not particularly limited, and a known coating method can be used. As a coating method, various methods can be applied. For example, a roll coating method, a dip coating method, a bar coating method, a die coating method, a gravure roll coating method, or a combination of these methods can be used. it can. Among these, the gravure roll coating method is generally preferable because it can stably form an easily adhesive resin layer (C layer).

  It is preferable to add an inorganic color pigment to the easily adhesive resin layer (C layer) of the present invention for the purpose of imparting light resistance. At present, white and black are mainly used for the appearance of the back surface protection sheet for solar cells, but for the purpose of the present invention, it is possible to add an inorganic white pigment to the easily adhesive resin layer (C layer). It is preferable for the purpose of imparting sex. In addition, there is an effect that a design pattern such as an electric wiring pattern in the solar cell module can be hidden.

  As the white pigment, titanium oxide having excellent light resistance is preferable. From the viewpoint of color development, the number average particle diameter is preferably 0.1 to 1.0 μm, and more preferably 0.2 to 0.5 μm from the viewpoint of dispersibility with respect to the easily adhesive resin layer (C layer) and cost. . The number average particle size can be measured by a laser diffraction / scattering method using a laser diffraction particle size distribution analyzer SALD-2300 manufactured by Shimadzu Corporation.

  The blending amount of the color pigment may be appropriately adjusted according to the design of the color tone to be developed. However, if the amount of pigment is too small, a color appearance with excellent design properties cannot be obtained, light resistance is insufficient, and conversely, if the amount is too large, the cost is high, resin There are concerns that the hardness of the layer is greatly improved, that the adhesion to the sealing material sheet is likely to be insufficient or reduced, and that the pigment bleeds out to the coating surface.

  For the above reason, the blending amount of the color pigment is preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass with respect to 100 parts by mass of the easily adhesive resin. If the color pigment is less than 20 parts by mass, suitable light resistance cannot be obtained, and if it is more than 80 parts by mass, the resin layer becomes brittle and it is difficult to obtain an appropriate strength, or poor dispersion of easily adhesive resin and colorant occurs. As a result, the light resistance tends to decrease.

  In addition, for the purpose of improving the heat resistance and mechanical properties of the easily adhesive resin layer (C layer) of the present invention, it is preferable to have a crosslinked structure as described above, and the hydroxyl group introduced into the easily adhesive resin layer (C layer) and You may mix | blend the crosslinking agent which has a functional group which can react. When a cross-linking agent is used in combination, the adhesion strength between the polyester film (B layer) and the easy-adhesive resin layer (C layer) is improved, or the easy-adhesive resin layer (C layer) is introduced with the introduction of a cross-linked structure. The effect of improving the heat resistance of is obtained. In the solar cell module manufacturing process, in the glass laminating process, the easy-adhesive resin layer (C layer) is exposed to a heat treatment of 30 minutes or longer at a high temperature of about 150 ° C. at maximum. In particular, heat resistance is required so that the resin layer (coating film) does not melt or flow. In this invention, the prescription which uses a polyisocyanate resin as a hardening | curing agent as a crosslinking agent which can react with a hydroxyl group as a hardening | curing agent, and promotes the production | generation of a urethane bond (crosslinked structure) is preferable. Examples of the polyisocyanate resin used as a crosslinking agent include aromatic polyisocyanates, araliphatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates. Among them, as a polyisocyanate raw material, a resin containing an aromatic ring having a light absorption band in the ultraviolet region in the resin skeleton easily yellows upon irradiation with ultraviolet rays. Therefore, an alicyclic polyisocyanate and an aliphatic polyisocyanate. It is preferable to use a curing agent containing as a main component, and a nurate-modified product of hexamethylene diisocyanate is preferable from the viewpoint of easy progress of crosslinking reaction, degree of crosslinking, heat resistance, ultraviolet resistance and the like.

  Furthermore, the easy-adhesive resin layer (C layer) of the present invention has a heat stabilizer, an antioxidant, a reinforcing agent, an anti-degradation agent, a weathering agent, a flame retardant, a plasticizer, a release agent, as long as the properties are not impaired. Molding agents, lubricants, crosslinking aids, pigment dispersants, antifoaming agents, leveling agents, UV absorbers, light stabilizers, thickeners, adhesion improvers, matting agents and the like may be added.

  Examples of heat stabilizers, antioxidants and deterioration inhibitors that can be used include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, alkali metal halides, and mixtures thereof.

  Examples of reinforcing agents that can be used include clay, talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, and oxidation. Examples include zinc, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate whisker, boron nitride, graphite, glass fiber, and carbon fiber.

  As the crosslinking aid that can be used, conventionally known tin-based, other metal-based, organic acid-based, and amino-based crosslinking aids can be used.

  Examples of the ultraviolet absorber that can be used include salicylic acid-based, benzophenone-based, benzotriazole-based, and cyanoacrylate-based ultraviolet absorbers.

  Examples of the light stabilizer that can be used include hindered amine light stabilizers.

  As a method of laminating the light-resistant film (A layer) or the polyester film (B layer) in the present invention and processing it into a sheet, a known dry laminating method can be used. Bonding of the resin film using the dry laminating method includes a main component such as a polyether polyurethane resin, a polyester polyurethane resin, a polyester resin, a polyepoxy resin, and a polyisocyanate curing agent. A known dry laminating adhesive can be used. However, the adhesive layer formed using these adhesives does not cause peeling due to deterioration of the adhesive strength due to long-term outdoor use, which leads to deterioration in appearance and light reflectance. It is necessary not to cause yellowing. Moreover, as thickness of an adhesive bond layer, Preferably it is the range of 1-10 micrometers. If it is less than 1 μm, it may be difficult to obtain sufficient adhesive strength. On the other hand, if it exceeds 10 μm, the speed of adhesive coating does not increase, and the amount of adhesive used increases, leading to an increase in production cost.

  The back surface protection sheet for solar cell modules of this invention needs that the partial discharge voltage in an air method is 600V or more, Preferably it is 650V or more. Although the method for measuring the partial discharge voltage in the air method will be described later, if this partial discharge voltage is high, even if a high voltage is applied to the back surface protection sheet for solar cell modules when the solar cell module is used, Partial discharge is less likely to occur. As a result, the electrical insulation of the back surface protection sheet for solar cell modules is easily secured. The partial discharge voltage in the air method can be increased by increasing the overall thickness of the back surface protection sheet for solar cell modules or by increasing the void ratio of the B1 layer. Further, the partial discharge voltage in the air method is not practically problematic as long as the required maximum allowable system voltage is satisfied. However, it is necessary to be less than 1000 V, preferably 800 V or less, from the viewpoint of economy.

  The thickness of the back surface protective sheet for a solar cell module of the present invention is appropriately selected from the preferred thickness ranges of the above light-resistant film (A layer), polyester film (B layer), and easy-adhesive resin layer (C layer). By adopting, it is necessary to be 100 μm or more, preferably 110 μm or more. By setting the thickness of the back surface protective sheet to 100 μm or more, a desired high partial discharge voltage can be achieved. On the other hand, the thickness of the back surface protection sheet for solar cell modules of the present invention needs to be less than 180 μm, more preferably 150 μm or less, from the viewpoint of processability and economy. By setting the thickness within these ranges, the partial discharge voltage per unit thickness is excellent, and can be set to 4.4 V / μm or more, preferably 4.5 V / μm or more. . The higher the partial discharge voltage per unit thickness, the higher the resource saving and the higher withstand voltage back protective sheet. However, the partial discharge voltage per unit thickness of 4.5 V / μm or more is A in the present invention. This is an important index for characterizing a back surface protective sheet that is balanced in various properties by the combination of the layer, the B layer, and the C layer.

  The back surface protection sheet for solar cell modules in this invention should just have a light-resistant film (A layer), a polyester film (B layer), and an easily-adhesive resin layer (C layer) in this order, A layer and Another plastic film may be laminated between the B layers or between the B layer and the C layer. Examples of the other plastic film include a white film, a barrier film having a metal oxide deposition layer, and an insulating film that prevents discharge from the photovoltaic power generation element to the outside. By laminating one or more of these, A back surface protective sheet for a solar cell module that satisfies various required characteristics can be obtained.

  When a white film is laminated, light reflectivity and concealment are improved, and when a film having a metal oxide vapor deposition layer is laminated, water vapor barrier properties are imparted, and when an insulating film is laminated, a back surface is provided. The thickness of the protective sheet is increased, and electrical characteristics such as dielectric breakdown voltage and partial discharge voltage can be improved. Moreover, the film laminated | stacked on the back surface protection sheet in this invention does not necessarily need to be one sheet, What is necessary is just to combine each member film suitably and to design a back surface protection sheet according to the characteristic to provide.

  An example of the white film is “Lumirror” E20 manufactured by Toray Industries, Inc., which is a white polyethylene terephthalate film. Examples of the film having a metal oxide deposition layer include “Barrier Rocks” (registered trademark) 1011HG manufactured by Toray Film Processing Co., Ltd., in which an aluminum oxide deposition layer is formed on a polyethylene terephthalate film substrate. An example of the insulating film is “Lumirror” S10 manufactured by Toray Industries, Inc., which is a polyethylene terephthalate film.

  Below, the method to manufacture a solar cell module using the back surface protection sheet for solar cell modules of this invention is demonstrated. As shown in FIG. 3, a surface protective sheet such as a glass plate, a sealing material sheet 1, a solar power generation element provided with wiring, a sealing material sheet 2, and a back surface protective sheet of the present invention are laminated in this order. A solar cell module is manufactured by using a conventional molding method such as a lamination method in which the layers are integrated by suction or the like and thermocompression-bonded, and the above-described layers are thermocompression-molded as an integrally molded body, and a frame is attached.

  The surface protective sheet constituting the solar cell module has physical or chemical strength such as sunlight permeability, insulation, weather resistance, heat resistance, light resistance, water resistance, moisture resistance, and antifouling property. It is preferable. Examples of the surface protective sheet include glass plates, polyamide resins (various nylons), polyester resins, cyclic polyolefin resins, polystyrene resins, (meth) acrylic resins, polycarbonate resins, and acetal resins. Various resin films or sheets such as others can be used.

The solar power generation element as a photovoltaic element constituting the solar cell module is a conventionally known solar power generation element, for example, a crystalline silicon solar power generation element such as a single crystal silicon type solar power generation element or a polycrystalline silicon type solar power generation element, a single junction Type or tandem structure type amorphous silicon solar power generation device, III-V compound semiconductor solar power generation device such as gallium arsenide (GaAs) or indium phosphorus (InP), cadmium tellurium (CdTe) or copper indium selenide (CuInSe ₂₎ II-VI group compound semiconductor solar power generation elements, organic solar power generation elements, etc. can be used. Furthermore, a thin film polycrystalline silicon solar power generation element, a thin film microcrystalline silicon solar power generation element, a hybrid element of a thin film crystal silicon solar power generation element and an amorphous silicon solar power generation element, or the like can also be used.

  Next, an Example is given and the back surface protection sheet for solar cell modules of this invention is demonstrated concretely.

[Characteristic evaluation method]
The characteristic evaluation method used in the present invention is as follows.

(1) Thickness of back surface protection sheet and thickness of each layer The thickness of the back surface protection sheet for solar cell modules was measured according to JIS C2151: 2006. Moreover, the back surface protection sheet was cut | disconnected in the thickness direction using the microtome, and the section | slice sample was obtained. Using a field emission scanning electron microscope (FE-SEM) S-800 manufactured by Hitachi, Ltd., three points were imaged at a magnification of 3000 times, and the average value of the layer thickness was obtained from the three points. Was measured, and the total thickness, which was the sum of the thickness of each layer and the thickness of each layer, was calculated.

(2) Cavity ratio The cavity ratio is obtained by cutting a polyester film (B layer) in the thickness direction using a microtome, and then obtaining a cross section of the obtained sample by using a field emission scanning electron microscope (FE-SEM) manufactured by Hitachi, Ltd. Using S-800, three points were imaged at a magnification of 3000 times, and the layer containing the most cavities among the layers constituting the film was specified as the B1 layer. Next, only the cavity portion in the B1 layer is traced on a transparent film, and the cavity area measured using an image analyzer (manufactured by Nireco Corporation: “Luzex” (registered trademark) IID) and the B1 layer in the observation image The ratio with the area of the corresponding part was calculated. The average value of the three measured values was defined as the void ratio of the B1 layer. Note that cavities whose area did not reach 0.1 μm ² were treated as not present.

(3) Partial discharge voltage The partial discharge voltage was measured for the back surface protection sheet for solar cell modules of 200 mm x 300 mm using the partial discharge tester "TPP5" by MPS. In a room adjusted to a temperature of 23 ± 2 ° C. and a humidity of 50 ± 5% RH, the voltage at which the applied voltage was increased from 0 V and the charge amount became 2 pC was used as the starting voltage. The applied voltage was raised to 1.1 times the starting voltage, and this voltage was applied for 10 seconds. Thereafter, the voltage at which the applied voltage was lowered and the electric charge disappeared (threshold value 1 pC) was defined as the partial discharge extinction voltage (V). Using the average, standard deviation, safety factor (1.25, 1.2) of the measurement result of the partial discharge extinction voltage at n = 10, and conversion from AC to DC, the calculation is performed according to the following formula. The value obtained was taken as the partial discharge voltage.

Partial discharge voltage (V) = (average value of partial discharge extinction voltage−standard deviation of partial discharge extinction voltage) × 1.414 ÷ (1.2 × 1.25)
(4) Adhesive strength (adhesiveness) when thermocompression bonded to the sealing material sheet
As the sealing material sheet, PV-45FR000 having a thickness of 450 μm manufactured by Sanvic Co., Ltd. made of ethylene / vinyl acetate copolymer (EVA) was used, and as shown in FIG. In the direction where the layer side faces the encapsulant sheet 2 and the release film, the back surface protection sheet for solar cell module / release film / encapsulant sheet 2 / encapsulant sheet 1 / glass plate is laminated in this order, ) After installation on a solar cell module laminator (LM-50 × 50-S) manufactured by NPC, thermocompression bonding was performed under the conditions of a vacuum time of 5 minutes, a control time of 1 minute, a press time of 9 minutes, and a temperature of 142 ° C. . After crimping, the module was cooled to room temperature to produce a pseudo module. Using the pseudo module, the adhesion strength between the back protective sheet for solar cell modules and the sealing material sheet was measured as follows.

  The back surface protection sheet for solar cell module / sealing material sheet 2 is peeled off between the back surface protection sheet side for solar cell module at 10 mm width, and using Tensilon PTM-50 manufactured by ORIENTEC Co., Ltd. under room temperature conditions, Peeling was performed at a peeling angle of 180 ° and a peeling speed of 100 mm / min, and the adhesion strength was measured.

(5) Average transmittance The light-resistant film (A layer) is a sample for evaluation of 50 mm square, and an ultraviolet-visible near-infrared spectrophotometer UV-3600Plus manufactured by Shimadzu Corporation is used based on JIS K 7105 (2006 version). Spectral spectra were measured by using, and the average transmittance was calculated by the arithmetic average of the transmittance in increments of 2 nm at wavelengths of 300 to 400 nm.

(6) Elongation retention after UV irradiation Using a Super Xenon Weather Meter SX2-75 manufactured by Suga Test Instruments Co., Ltd. for solar cell modules at an ultraviolet intensity of 180 W / m ² at a temperature of 63 ° C. and 50% RH. Ultraviolet irradiation (ultraviolet irradiation integrated amount 300 kWh / m ² ) was performed on the light-resistant film (A layer) side of the back protective sheet. The breaking elongation before and after that was measured by using Tensilon PTM-50 manufactured by Orientec Co., Ltd., at a pulling speed of 300 mm / min. A determination of 60% or more as a determination of the breaking elongation retention was regarded as acceptable.

In the same manner as described above, the light-resistant film (A layer) was irradiated with ultraviolet rays (ultraviolet irradiation cumulative amount 300 kWh / m ² ), and the elongation at break before and after the irradiation was measured. A determination of 50% or more as a determination of the elongation at break was taken as acceptable. In addition, when a light-resistant film (A layer) consists of two or more layers, an ultraviolet irradiation shall be performed from the resin layer (A1 layer) side to which the whitening agent was added.

(7) Flammability Using light-resistant film (A layer) as a sample for evaluation of length 200mm x width 50mm, safety standard for solar cell module, UL94 thin material vertical combustion test (when sample thickness is 250μm or less) Based on this, a combustion test was conducted. The sample for evaluation was allowed to stand at 23 ± 2 ° C. and 50 ± 5% RH for 48 hours, then wound in a cylindrical shape and attached vertically to a clamp. The flame retardancy was evaluated according to the evaluation criteria of VTM-0, VTM-1, and VTM-2.

(8) Average relative reflectance The back surface protective sheet was cut out at 5 cm x 5 cm. The average relative reflectance at 400 nm to 1200 nm was measured with a basic configuration using an integrating sphere attached to an ultraviolet-visible near-infrared spectrophotometer UV-3600Plus manufactured by Shimadzu Corporation. The measurement was based on a barium sulfate white plate attached to the apparatus, and the measurement conditions were a slit of 12 nm, a sampling pitch of 1 nm, and a high scanning speed. Further, the measurement was performed with the sample placed so that the incident surface of the measurement light was on the C layer side.

[Preparation of easy-adhesive resin layer (C layer) coating 1]
100 parts by weight of coating agent PRC-112W (solid content concentration: 30% by mass) manufactured by Toyo Ink SC Holdings Co., Ltd. containing an acrylic copolymer and a blocked isocyanate compound, and 20 parts by weight of n-butyl acetate as a diluent By stirring for 15 minutes, an easy-adhesive resin layer-forming coating material 1 (solid content concentration 25% by mass) was obtained.

[Preparation of paint 2 for forming an easily adhesive resin layer (C layer)]
100 parts by weight of a coating agent “Zeffle” GK570 white (solid content concentration: 65 mass%) manufactured by Daikin Industries, Ltd. containing a hydroxyl group-containing tetrafluoroethylene copolymer resin and titanium oxide blended as an inorganic pigment, nurate hexa Mixing 4 parts by weight of “Desmodur” N3300 (solid content concentration: 100% by mass) made by Sumika Bayer, which is a methylene diisocyanate resin, and 126 parts by weight of n-butyl acetate as a diluent, and stirring for 15 minutes The easily adhesive resin layer forming coating 2 (solid content concentration 30% by mass) was obtained.

Example 1
As the B1 layer of the polyester film (B layer), 55 parts by mass of polyethylene terephthalate and a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG, trade name: “Hytrel” (registered trademark) manufactured by Toray Du Pont Co., Ltd.) ) And 10 parts by mass of a polyethylene terephthalate copolymer (PET / I / PEG) obtained by copolymerizing 10 mol% of isophthalic acid in all dicarboxylic acid units or diol units and 5 mol% of polyethylene glycol having a molecular weight of 1000. Then, 30 parts by mass of polymethylpentene as an incompatible polymer was prepared and mixed, dried at a temperature of 180 ° C. for 3 hours, and then supplied to an extruder a heated to a temperature of 270 to 300 ° C.

  On the other hand, as a resin layer (B2 layer) that is co-extruded with the B1 layer, 70 parts by mass of a polyethylene terephthalate chip and 50% by mass of titanium dioxide having a number average secondary particle size of 0.25 μm are dispersed as a whitening agent. 30 parts by mass of polyethylene terephthalate master chips (containing 50% by mass of titanium dioxide based on the total amount of master chips) were vacuum-dried at a temperature of 180 ° C. for 3 hours and then supplied to an extruder b heated to a temperature of 280 ° C. Then, these polymers are laminated as a B2 layer / B1 layer / B2 layer through a laminating apparatus so that the thickness ratio of the film layer is 7.5: 70: 7.5, and formed into a sheet form from a T die. A film was obtained. Furthermore, this film was cooled and solidified with a cooling drum having a surface temperature of 25 ° C., and an unstretched film obtained by being led to a group of rolls heated to a temperature of 85 to 98 ° C. was 3.4 times longer in the longitudinal direction. It extended | stretched and cooled with the roll group of the temperature of 21 degreeC. Subsequently, both ends of the longitudinally stretched film thus obtained were guided to a tenter while being held with clips, and stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 120 ° C. . Then, heat setting at a temperature of 200 ° C. was performed in a tenter, and after uniform cooling, the solution was cooled to 25 ° C. to obtain a polyester film (B layer) having a winding thickness of 85 μm. The void ratio of the B1 layer was 35%.

  One side of the obtained polyester film (B layer) is coated with an easy-adhesive resin layer (C layer) forming coating 1 using a wire bar, dried at 150 ° C. for 30 seconds, and after drying, coating thickness Was provided with an easily adhesive resin layer (C layer) so as to be 2 μm.

  In addition, as a light-resistant film (A layer), a hydrolysis-resistant polyethylene terephthalate resin layer and a hydrolysis-resistant polyethylene terephthalate resin layer to which a whitening agent has been added are co-extruded and hydrolysis-resistant manufactured by Toray Industries, Inc. White polyethylene terephthalate film “Lumirror” MX70 (38 μm, RTI: 130 ° C., flame retardancy: VTM-2) was prepared.

  Next, a urethane adhesive layer (AD503 10 manufactured by Toyo Morton Co., Ltd.) is used on the surface of the polyester film (B layer) opposite to the surface on which the easily adhesive resin layer (C layer) is formed using a wire bar. A mixture of 1 part by weight of an isocyanate-based curing agent CAT-10 manufactured by the same company) and dried to give a coating thickness of 5 μm, and the MX70 hydrolysis-resistant polyethylene terephthalate resin layer side and 60 N / Lamination was performed with a nip pressure of cm. The laminated film was aged at a temperature of 40 ° C. for 72 hours to promote the curing reaction of the adhesive layer, thereby forming a back surface protection sheet for a solar cell module. The evaluation results are shown in Table 1.

(Example 2)
As the B1 layer of the polyester film (B layer), 62 parts by mass of polyethylene terephthalate and a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG, trade name: “Hytrel” (registered trademark) manufactured by Toray Du Pont Co., Ltd.) ) And 10 parts by mass of a polyethylene terephthalate copolymer (PET / I / PEG) obtained by copolymerizing 10 mol% of isophthalic acid in all dicarboxylic acid units or diol units and 5 mol% of polyethylene glycol having a molecular weight of 1000. , 23 parts by mass of polymethylpentene as an incompatible polymer, except that the film layer thickness ratio of B2 layer / B1 layer / B2 layer is 10: 100: 10, and the winding thickness is 120 μm Obtained a polyester film (B layer) in the same manner as in Example 1. The void ratio of the B1 layer was 25%. Furthermore, a light-resistant film (A layer) was co-extruded with a hydrolysis-resistant polyethylene terephthalate resin layer and a hydrolysis-resistant polyethylene terephthalate resin layer to which a whitening agent was added. The back protection for solar cell modules was the same as in Example 1 except that the hydrolysis-resistant white polyethylene terephthalate film “Lumirror” MX11 (50 μm, RTI: 125 ° C., flame retardancy: VTM-2) manufactured by Toray Industries, Inc. was used. A sheet was used. The evaluation results are shown in Table 1.

(Example 3)
As B1 layer of the polyester film (B layer), 45 parts by mass of polyethylene terephthalate, a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG, trade name: “Hytrel” (registered trademark) manufactured by Toray DuPont) 5 parts by mass, 10 parts by mass of a polyethylene terephthalate copolymer (PET / I / PEG) obtained by copolymerizing 10 mol% of isophthalic acid in all dicarboxylic acid units or diol units and 5 mol% of polyethylene glycol having a molecular weight of 1000 Except that polymethylpentene is 40 parts by mass as a soluble polymer, the film layer thickness ratio of B2 layer / B1 layer / B2 layer is 7.5: 60: 7.5, and the winding thickness is 75 μm Obtained a polyester film (B layer) in the same manner as in Example 1. The void ratio of the B1 layer was 45%. The paint 2 for forming an easily adhesive resin layer (C layer) was applied to one surface of the obtained polyester film (B layer) using a wire bar, and the temperature was 150 ° C. Was dried for 30 seconds, and an easy-adhesive resin layer (C layer) was provided so that the coating thickness after drying was 10 μm.

  Further, Example 1 except that the light-resistant film (A layer) was a white polyvinyl fluoride film “Tedlar” PV2111 (25 μm, RTI: 120 ° C., flammability: HB (according to UL94 horizontal combustion test)) manufactured by DuPont. Similarly, it was set as the back surface protection sheet for solar cell modules. The evaluation results are shown in Table 1.

Example 4
As the B1 layer of the polyester film (B layer), 72 parts by mass of polyethylene terephthalate and a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG, trade name: “Hytrel” (registered trademark) manufactured by Toray Du Pont Co., Ltd.) ) And 10 parts by mass of a polyethylene terephthalate copolymer (PET / I / PEG) obtained by copolymerizing 10 mol% of isophthalic acid in all dicarboxylic acid units or diol units and 5 mol% of polyethylene glycol having a molecular weight of 1000. A polyester film (B layer) having a winding thickness of 120 μm was obtained in the same manner as in Example 2 except that 13 parts by mass of polymethylpentene was used as the incompatible polymer. The void ratio of the B1 layer was 15%. Furthermore, it was set as the back surface protection sheet for solar cell modules in the procedure similar to Example 2. FIG. The evaluation results are shown in Table 1.

  Although the void ratio of the B1 layer was low and the reflectance measured from the C layer side as the back surface protective sheet was low, there was no practical problem.

(Example 5)
A light-resistant film (A layer) consisting of a hydrolysis-resistant polyethylene terephthalate resin layer to which a whitening agent is added, a hydrolysis-resistant white polyethylene terephthalate film “Lumirror” MG13 (50 μm, RTI: 105 ° C., manufactured by Toray Industries, Inc. Except having set it as flame retardancy: VTM-2), it was set as the back surface protection sheet for solar cell modules similarly to Example 2. FIG. The evaluation results are shown in Table 1.

  Since the average transmittance of the light-resistant film (A layer) is high and the elongation retention rate when irradiated with ultraviolet rays is low, as the back protection sheet, the elongation retention rate when irradiated with ultraviolet rays from the A layer side was low, There was no problem in practical use.

(Comparative Example 1)
Polyester film as in Example 1 except that the film layer thickness ratio of B2 layer / B1 layer / B2 layer in the polyester film (B layer) is 5: 40: 5 and the winding thickness is 50 μm. (B layer) was obtained. The void ratio of the B1 layer was 35%. Furthermore, it was set as the back surface protection sheet for solar cell modules in the procedure similar to Example 1. FIG. The evaluation results are shown in Table 1.

  The thickness of the back surface protection sheet for solar cell modules was 95 μm, and the partial discharge voltage was less than 600V.

(Comparative Example 2)
As B1 layer of the polyester film (B layer), 80 parts by mass of polyethylene terephthalate and a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG, trade name: “Hytrel” (registered trademark) manufactured by Toray DuPont Co., Ltd.) ) And 10 parts by mass of a polyethylene terephthalate copolymer (PET / I / PEG) obtained by copolymerizing 10 mol% of isophthalic acid in all dicarboxylic acid units or diol units and 5 mol% of polyethylene glycol having a molecular weight of 1000. A polyester film (B layer) having a winding thickness of 85 μm was obtained in the same manner as in Example 1 except that 5 parts by mass of polymethylpentene was used as the incompatible polymer. The void ratio of the B1 layer was 8%. Furthermore, it was set as the back surface protection sheet for solar cell modules in the procedure similar to Example 1. FIG. The evaluation results are shown in Table 1.

  Since the void ratio of the B1 layer was low, the partial discharge voltage per unit thickness was low, and the partial discharge voltage of the back surface protective sheet did not reach 600V.

(Comparative Example 3)
A back protective sheet for a solar cell module was prepared in the same procedure as in Example 2 except that the light-resistant film (A layer) was not laminated. The evaluation results are shown in Table 1.

  The polyester film (B layer) did not satisfy the VTM-2 standard in the flame retardancy test, and had a low degree of elongation retention when irradiated with ultraviolet rays from the B layer side of the back surface protective sheet, which had practical problems. .

  According to the back surface protection sheet for solar cell modules of the present invention, a back surface protection sheet for solar cell modules that exhibits a high partial discharge voltage and has sufficient insulation when used outdoors for a long period of time can be provided.

10: Back surface protection sheet for solar cell module 11: Light-resistant film (A layer)
12: Resin layer to which a whitening agent is added (A1 layer)
13: Resin layer coextruded with A1 layer (A2 layer)
14: Polyester film (B layer)
15: Polyester resin layer including a cavity (B1 layer)
16: Resin layer co-extruded with B1 layer (B2 layer)
17: Easy-adhesive resin layer (C layer)
18: Adhesive 22: Sealant sheet 1
23: Sealant sheet 2
24: Glass plate 25: Solar power generation element 32 as photovoltaic element provided with wiring: Sealing material sheet 1
33: Sealant sheet 2
34: Glass plate 35: Release film

Claims (7)

It has a light-resistant film (A layer), a polyester film (B layer), and an easily adhesive resin layer (C layer) in this order,
B layer contains at least one polyester resin layer (B1 layer) containing 10 to 50% of voids inside,
The C layer has a sealing material for holding and fixing the solar cell element and an adhesion strength of 40 N / cm or more,
The elongation retention after irradiation of ultraviolet rays with an integrated amount of 300 kWh / m ² from the A layer side is 60% or more,
A back protective sheet for a solar cell module having a thickness of 100 μm or more and less than 180 μm and a partial discharge voltage of 600 V or more and less than 1000 V. The average transmittance at a wavelength of 300 to 400 nm of the light-resistant film (A layer) is 1% or less, and the elongation retention after irradiation with ultraviolet rays having an integrated amount of 300 kWh / m ² is 50% or more. The back surface protection sheet for solar cell modules of description.   The back surface for a solar cell module according to claim 1 or 2, wherein the light-resistant film (A layer) is a light-resistant polyester film and includes at least one polyester resin layer to which a whitening agent is added. Protective sheet.   The back surface for a solar cell module according to claim 1 or 2, wherein the light-resistant film (A layer) is a light-resistant fluorine film and includes at least one fluorine resin layer to which a whitening agent is added. Protective sheet.   5. The back protective sheet for a solar cell module according to claim 1, wherein the light-resistant film (A layer) has a relative temperature index of 105 ° C. or higher.   The said light-resistant film (A layer) has the flame retardance more than the VTM-2 standard which shows the flame retardance in the safety standard UL94 for solar cell modules, The any one of Claims 1-5 characterized by the above-mentioned. Back protection sheet for solar cell modules.   The back surface for a solar cell module according to claim 1, wherein an average relative reflectance at a wavelength of 400 nm to 1200 nm measured from the easily adhesive resin layer (C layer) side is 80% or more and 105% or less. Protective sheet.