JP2008166338A - Solar cell module and sheet for sealing rear face of same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet for sealing the rear face of an inexpensive solar cell module that is superior in electric insulation and has UV resistance at its rear face, mechanical adhesive strength and environmental resistance, and to provide a solar cell module using the same. <P>SOLUTION: The sheet for sealing the rear face of a solar cell module is used for a solar cell module, which includes at least a sheet for sealing a rear face, a filler layer adjacent to the sheet for sealing a rear face and solar cell elements buried in the filler layer. The sheet for sealing a rear face is comprised of at least a resin film in contact with a filling agent and a hydrolysis-resistant white resin film as an outermost layer, and the partial discharge voltage of the sheet is ≥1,000 V. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solar cell module back surface sealing sheet and a solar cell module using the same. In particular, it relates to a sheet for sealing the back surface of a solar cell module having excellent electrical insulation, UV resistance on the back surface, mechanical adhesive strength, environmental resistance and low cost, and a solar cell module using the same. is there.

  In recent years, solar cells are rapidly spreading as clean energy. This solar cell module uses a solar cell element such as a crystalline silicon solar cell element, a surface protection sheet layer, a filler layer, a solar cell element as a photovoltaic element, an ethylene-vinyl acetate copolymer A filler layer typified by (hereinafter referred to as EVA), a back surface sealing sheet layer, and the like are laminated and manufactured using a vacuum suction heating lamination method or the like. Here, as the back surface sealing sheet constituting the solar cell module, a plastic sheet having a light weight and excellent strength is generally used. This backside sealing sheet has excellent mechanical strength, weather resistance, heat resistance, water resistance, light resistance, chemical resistance, light reflectivity, and gas barrier properties from the viewpoint of preventing intrusion of moisture, oxygen, etc. It is required to be excellent. As a typical configuration, there is a configuration in which polyester films excellent in weather resistance and gas barrier properties are laminated (Patent Documents 1 and 2).

On the other hand, with the spread of solar cells in recent years, great attention has been paid to the electrical safety of solar cells and the system voltage has been increased to improve the performance of the entire solar cell system. Since the request | requirement to set increased, the request | requirement of the electrical insulation performance with respect to the solar cell module back surface sealing sheet increased, and the proposal of the solar cell back surface sealing sheet corresponding to the solar cell system voltage 1000V is made. (Patent Document 3).
JP 2002-026354 A (paragraphs [0008] to [0010]) Japanese Patent Laid-Open No. 2002-100788 JP 2006-253264 A

  However, only by laminating the films as in Patent Documents 1 and 2, there is a drawback that the adhesive force with a filler typified by EVA is insufficient. Also, since electrical insulation is not particularly taken care of, it is difficult to cope with a system voltage of 1000V.

On the other hand, Patent Document 3 defines a solar cell back surface protection sheet satisfying 1000 V or more as a partial discharge voltage, which is a representative characteristic of electrical insulation capable of supporting a solar cell system voltage of 1000 V, and its configuration is weatherproof. The barrier film is sandwiched between the conductive polyester resin films. However, the weather resistance of the weather resistant polyester film used in this configuration, particularly hydrolysis resistance and UV resistance (UV) resistance of the back surface is not sufficient, using a polyester film with more excellent hydrolysis resistance, And the back surface protection sheet for solar cells which satisfy | fills the partial discharge voltage 1000V or more was calculated | required.
The present invention does not provide a solar cell module back surface sealing sheet having excellent electrical insulation, UV resistance on the back surface, mechanical adhesive strength, environmental resistance and low cost, and a solar cell module using the same. It is what.

  In order to solve the above problems, the present invention employs the following means. That is, the solar cell module back surface sealing sheet of the present invention includes at least a back surface sealing sheet, a filler layer adjacent to the back surface sealing sheet, and a solar cell element embedded in the filler layer. In the back surface sealing sheet used for the solar cell module, the back surface sealing sheet has at least a resin film in contact with the filler and a hydrolysis-resistant white resin film as an outermost layer, and the back surface sealing sheet The partial discharge voltage of the sheet is 1000 V or more.

  According to the present invention, it is possible to provide an inexpensive solar cell module backside sealing sheet that is excellent in electrical insulation and hydrolysis resistance, and that corresponds to a solar cell system voltage of 1000 V and has excellent durability. .

  The solar cell module back surface sealing sheet of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view illustrating an example of a solar cell module using the solar cell module back surface sealing sheet of the present invention. The solar cell module 1 includes a back surface sealing sheet 10, a filler layer 2 adjacent to the back surface sealing sheet, and a solar cell element 3 embedded in the filler layer 2, preferably a high light beam. A solar cell module surface sealing sheet 4 having a transmittance characteristic is provided. As the surface sealing sheet 4, for example, white plate glass or the like is used.

  Since the filler layer 2 is also used on the solar light incident side of the solar cell, it needs to have transparency, and is bonded to the front surface sealing sheet 4 and the rear surface sealing sheet 10. It is also necessary to have sex.

  Moreover, since the function which protects a solar cell element is also required, as this filler layer 2, there exist an ethylene-vinyl acetate copolymer, an ionomer resin, polyvinyl butyral resin, etc., but light resistance, heat resistance, water resistance In view of various characteristics such as, ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) is most often used and is also preferred in the present invention.

  FIG. 2 is an example of the solar cell module back surface sealing sheet of the present invention. The backside sealing sheet 10 in FIG. 2 has a resin film 11 on the side in contact with the filler layer 2 and a hydrolysis-resistant white resin film 12 on the outermost layer, which are laminated with an adhesive or the like. is there. Here, the resin film 11 and the hydrolysis-resistant white resin film 12 both have electrical insulation, and satisfy the partial discharge voltage of 1000 V as the entire back surface sealing sheet.

  FIG. 3 is a second example of the solar cell module back surface sealing sheet of the present invention. The back surface sealing sheet 20 in FIG. 3 includes another resin film 13 between the outermost hydrolysis-resistant white resin film 12 and the resin film 11 in contact with the filler layer 2. Thus, the structure which laminates | stacks a some resin film from the filler layer 2 side of the sheet | seat for back surface sealing, and arrange | positions a hydrolysis-resistant white resin film in the outermost layer may be taken.

  Thus, the solar cell module back surface sealing sheet (10, 20) of the present invention is formed by laminating two or more resin films including the hydrolysis-resistant white resin film. Is preferably 230 μm or more. In order to be able to cope with a high solar cell system voltage, specifically, a system voltage of 1000 V, a partial discharge voltage of 1000 V or more is required for the back surface sealing sheet. In order to satisfy this, in the present invention, it is preferable to set so that the total thickness of the resin films satisfies 230 μm or more. More preferably, the thickness is preferably set to 300 μm or more. If the total thickness is too thick, workability at the time of manufacturing the solar cell module is poor, the weight is increased, and the cost is increased. Therefore, the thickness is preferably 350 μm or less.

  FIG. 4 is a third example of the solar cell module back surface sealing sheet of the present invention. The backside sealing sheet 30 in FIG. 4 includes an electrically insulating water vapor barrier layer 31 in addition to the resin film 11 and the hydrolysis-resistant white resin film 12. Depending on the type of solar cell, the back surface sealing sheet may be required to have a high water vapor barrier property, which is suitable in that case.

The position of the electrically insulating water vapor barrier layer 31 may be configured in the order of resin film 11 / electrically insulating water vapor barrier layer 31 / hydrolysis resistant white resin film 12 as shown in FIG. Layer 31 / resin film 11 / hydrolysis resistant white resin film 12 may be configured,
When using the resin film 13 as described above,
Resin film 11 / Resin film 13 / Electrically insulating water vapor barrier layer 31 / Hydrolysis resistant white resin film 12
Resin film 11 / electrically insulating water vapor barrier layer 31 / resin film 13 / hydrolysis resistant white resin film 12
Electrically insulating water vapor barrier layer 31 / resin film 11 / resin film 13 / hydrolysis-resistant white resin film 12
Any of the positions may be used.

  An example of the electrically insulating water vapor barrier layer is a structure in which an inorganic oxide vapor deposition layer 33 is provided on an electrically insulating base film 32 as shown in FIG.

  As the electrical insulating base film 32, for example, a biaxially stretched polyethylene terephthalate (PET) film is preferably used, but a polyester film such as polyethylene naphthalate, a polyolefin film such as polyethylene or polypropylene, a polystyrene film, and a polyamide film. Polyvinyl chloride film, polycarbonate film, polyacrylonitrile film, polyimide film and the like may be used.

  Various well-known additives and stabilizers such as an antistatic agent, an ultraviolet ray preventing agent, a plasticizer, and a lubricant may be used on the surface of the electrically insulating base film 32.

  The thickness of the electrically insulating base film 32 is not particularly limited, but is preferably 6 to 30 μm in consideration of suitability as a packaging material and workability when forming the inorganic oxide vapor deposition layer 33. The thickness of the electrically insulating base film 32 may be added to the total thickness of the resin film.

  Specifically, the inorganic oxide vapor deposition layer 33 is formed by forming an inorganic oxide such as aluminum oxide or silicon oxide by a known physical vapor deposition method, chemical vapor deposition method, or the like. Moreover, after forming this inorganic oxide vapor deposition layer 33, you may provide the protective layer for improving water vapor | steam barrier property further, or protecting an inorganic oxide vapor deposition layer.

  As described above, the electrically insulating water vapor barrier layer 31 is formed on the resin film 11 or the hydrolysis-resistant white resin film 12 in addition to the structure in which the electrically insulating base film 32 includes the inorganic oxide vapor deposition layer 33. Alternatively, an inorganic oxide vapor deposition layer may be directly formed. However, in this case, the inorganic oxide vapor deposition layer should not be positioned on the outermost surface of the back surface sealing sheet or the surface in contact with the filler. If it is located on the outermost surface, the inorganic oxide vapor-deposited layer is easily cracked or scratched, and the water vapor barrier property may be deteriorated. Moreover, when it is located on the surface in contact with the filler layer, the adhesiveness to the filler may not be sufficient.

  FIG. 6 shows a fourth example of the solar cell module back surface sealing sheet of the present invention. The back surface sealing sheet 40 of FIG. 6 is provided with an adhesion improving layer 41 on the side of the resin film 11 in contact with the filler layer. Since the adhesiveness between the resin film 11 and the filler layer 2 is not always sufficient, the reliability of the solar cell module can be improved by providing the adhesion improving layer 41.

  As described above, since EVA is preferable for the filler layer 2, the adhesion improving layer 41 is required to have good adhesiveness. A first preferred adhesion improving layer 41 is composed of at least one resin selected from the group consisting of polyester resins and polyester polyurethane resins, and the crosslinking agent is at least selected from alkylated melamine and polyisocyanate. It consists of one kind of crosslinking agent.

  Here, “at least one resin selected from the group consisting of a polyester resin and a polyester polyurethane resin” refers to a case where one or more resins are selected from polyester resins, or a polyurethane resin. It means the case where one or more types of resins are selected, and the case where one or more types of resins are selected from among polyester resins and polyurethane resins. By selecting these resins as the resin for the adhesion improving layer, good adhesiveness with EVA and good preservability without blocking or sticking during storage can be obtained. In particular, polyester resins are preferred because they are less likely to cause blocking.

  In particular, higher adhesion strength can be obtained when the polyester resin or polyester polyurethane resin constituting the adhesion improving layer is crosslinked with at least one crosslinking agent selected from alkylated melamine and polyisocyanate. This is preferable. Furthermore, it is preferable that the resin constituting the adhesion improving layer is crosslinked with such a crosslinking agent because the water resistance and the adhesiveness can be further improved.

  As a method for forming such an adhesion improving layer, a well-known wet coating method such as a direct gravure coating method or a reverse gravure coating method is used.

  The thickness of the adhesion improving layer is preferably 0.5 to 3 μm because the adhesive strength is high, the cost of the strength coating agent is low, and the processing speed can be increased.

  As shown in FIG. 7, the second preferred adhesion improving layer 41 is composed of a laminate of a compatible resin layer 42 and an adhesive layer 43 that are compatible with the resin of the ethylene-vinyl acetate copolymer filler layer. is there. In FIG. 7, the adhesive layer 43 is coated on the resin film 11, and the compatible resin layer 42 is coated thereon and directly contacts the filler 2. The compatible resin layer 42 constituting the adhesion improving layer is compatible with the resin constituting the ethylene-vinyl acetate copolymer filler layer, and is the resin of the ethylene-vinyl acetate copolymer filler layer. What is necessary is just to produce compatibility above a softening point. Specifically, an ethylene-vinyl acetate copolymer or a copolymer obtained by copolymerizing a third component such as an acrylic or methacrylic monomer with the ethylene-vinyl acetate copolymer as a basic structure can be used. In particular, a paint resin obtained by emulsifying an ethylene-vinyl acetate copolymer is preferable because it can adopt a coating process with high productivity such as gravure coating, which has an advantage that the amount of resin used can be further reduced. .

  As the adhesive layer 43, a known dry laminating adhesive can be preferably used. Among these, urethane type adhesives such as ether type, polyester type and polyol type are preferably used since they have high adhesive strength and are excellent in constant temperature stability and long-term durability of the adhesive strength. Among them, polyester-based urethane adhesives are particularly preferably used since they have low tackiness immediately after coating and are easy to coat.

  As a method for forming the compatible resin layer 42 and the adhesive layer 43 constituting the adhesion improving layer 41, a well-known wet coating method such as a direct gravure coating method or a reverse gravure coating method is used.

  The thickness of the compatible resin layer 42 of the adhesion improving layer 41 is preferably 0.2 to 2 μm, more preferably 0.2 to 2 μm because the adhesive strength is high, the strength coating cost is low, and the processing speed can be increased. The film thickness should be controlled to 1 μm. The thickness of the compatible resin layer 42 is important from the standpoint of maintaining good storage stability that does not cause blocking or sticking during storage of the back surface sealing sheet. The thickness of the adhesive layer 43 is not particularly limited, but is preferably 0.1 μm or more and 1.5 μm or less. In view of easy coating, the thickness is more preferably 0.2 μm or more and 0.5 μm or less.

  The solar cell module back surface sealing sheet of the present invention preferably has a higher light reflectance when viewed from the solar cell element side. This is because the back surface sealing sheet reflects the light that has passed between the solar cell elements, and then returns it to the solar cell element again, and uses the light energy to increase the photoelectric conversion efficiency of the solar cell module. It is. In order to realize this, the resin film 11 in contact with the filler layer in the present invention is preferably white or highly transparent.

  That the resin film 11 is white means that the resin film 11 itself has diffuse reflectivity, and a method of applying a white paint on the resin film 11 or a method of using a white resin film such as a white polyester film. Can be mentioned. Since the material cost is low and high reflectivity is obtained, it is preferable to use a white polyester film, particularly a white polyethylene terephthalate film, as the resin film 11.

  On the other hand, when the resin film 11 is highly transparent, the light passing between the solar cell elements is also transmitted through the highly transparent resin film 11 and reflected by the hydrolysis-resistant white resin film 12. Since the hydrolysis-resistant white resin film 12 has a high reflectance as will be described later, a high reflectance can be obtained as the entire solar cell module back surface sealing sheet. For this purpose, the total light transmittance of the resin film 11 is preferably 85% or more. Since the material cost is low and high transparency can be obtained, a transparent polyester film, particularly a highly transparent polyethylene terephthalate film having a total light transmittance of 85% or more is preferably used as the resin film 11.

  As the adhesive layer, a known dry laminating adhesive can be used. In particular, ether-based, polyester-based, polyol-based and other urethane-based adhesives are preferably used because of their high adhesive strength and excellent thermostatic stability and long-term durability. Among them, polyester-based urethane adhesives are preferably used because they have low tackiness immediately after coating and are easy to coat.

  Finally, the hydrolysis-resistant white resin film 12 of the present invention will be described.

The hydrolysis-resistant white resin film 12 has a polyester resin layer using one or more layers having a number average molecular weight of 18500 to 40,000, and 5 to 40% by weight of titanium dioxide in the polyester resin layer. It is preferable that the polyester resin film having at least one layer containing the above-mentioned composition is formed into a shape satisfying the following four conditions by the polyester resin layer containing titanium dioxide.
1. Relative reflectance is 80% or more and 105% or less,
2. The apparent density is 1.37 to 1.65 g / cm ³ ,
3. The optical density is 0.55 to 3.50,
4). Optical density variation is within 20% of the center value.

  The polyester resin in the hydrolysis-resistant white resin film 12 of the present invention is a polycondensate of a dicarboxylic acid derivative and a diol derivative, such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, Poly 1,4-cyclohexane dimethylene terephthalate, 1,4-cyclohexane dimethanol copolymerized polyethylene terephthalate, or the like can be used. In particular, since polyethylene terephthalate is inexpensive, it can be preferably used for a wide variety of applications.

  In addition, these resins may be homo resins, and may be copolymers or blends. The melting point of the polyester preferably used is preferably 250 ° C. or higher in view of heat resistance, and preferably 300 ° C. or lower in terms of productivity. If it is in this range, other components may be copolymerized or blended. In addition, additives such as a slip agent, a colorant, an antistatic agent, and a low-density agent are added within a range of, for example, 60% by weight or less as long as they are within the range where there is no problem in terms of mechanical properties and productivity. Also good.

  The hydrolysis-resistant white resin film 12 of the present invention refers to a sheet obtained by subjecting an unstretched and non-oriented sheet obtained by melt molding the above polymer to biaxial stretching and heat treatment. The thickness of the sheet is preferably in the range of 20 to 350 microns from the viewpoint of appropriate waist strength, processability, and light weight of the solar cell.

  The polyester resin layer in the hydrolysis-resistant white resin film 12 of the present invention is a layer composed of a polyester resin having a number average molecular weight of 18500 to 40000, and may be a single layer or a plurality of layers. The hydrolysis-resistant white resin film 12 of the present invention refers to a multilayer or a single layer having the above-mentioned polyester resin layer and having other polyester layers as necessary.

  In the hydrolysis-resistant white resin film 12 of the present invention, the light transmittance at a wavelength of 300 nm to 350 nm is preferably 0.005 to 10%. The light transmittance at a wavelength of 300 nm to 350 nm in the present invention refers to the ratio of incident light having the wavelength incident on the film 12 and transmitted light on the opposite surface. In order to reduce UV degradation, the transmittance (hereinafter also referred to as UV transmittance) of the wavelength (300 to 350 nm) in the UV region of the hydrolysis-resistant white resin film 12 is preferably in the range of 0.005 to 10%. Needs to be in the range of 0.01-7%, more preferably 0.05-5%. The wavelength of incident light includes light in the UV region that degrades the hydrolysis-resistant white resin film 12. If the light can be shut out near the surface layer, the wavelength in the UV region toward the inner layer Is less penetrated, UV degradation of the inner layer is small, and weather resistance is excellent. When the UV transmittance exceeds 10%, the molecular chain is broken by the energy of the UV wavelength over time, and the mechanical properties are deteriorated. Moreover, it turns out that the color tone also changes to yellow and it has deteriorated from the appearance.

  As a method for controlling the light transmittance (UV transmittance) at a wavelength of 300 nm to 350 nm, it is possible to control by controlling the mixing ratio of the following titanium dioxide.

  As the mixing ratio of titanium dioxide increases, the concealability increases and the transmittance at a wavelength of 300 to 350 nm decreases remarkably. The UV transmittance of the thermoplastic resin sheet is preferably 0.005 to 10%, and this effect is manifested when the mixing ratio of titanium dioxide (content of titanium dioxide with respect to the layer containing titanium dioxide) is 5%. It is from the area exceeding%. Preferably, it is 7% by weight or more, more preferably 10% or more. As for the upper limit, the concentration of titanium dioxide is desirably 40% by weight or less from the viewpoint of productivity and sheet strength. By having the layer having the titanium dioxide content in the polyester resin layer, the light transmittance range of the wavelength of 300 to 350 nm of the present invention can be adjusted and achieved.

  In the present invention, the relative reflectance of the hydrolysis-resistant white resin film 12 is preferably 80% to 105%, more preferably 83% to 105%, and particularly preferably 85 to 105%. If it is less than 80%, the optical loss is large and hardly contributes to the conversion efficiency.

  Here, the relative reflectance referred to in the present invention is 100% reflectance (base value) when the reflectance is measured at a wavelength of 560 nm using alumina oxide as a standard white plate, and the measured value in the sample is It is converted as a numerical value for the base value. When the relative reflectance is within the range of the present invention, the light leaking from the gap between the solar battery modules can be diffusely reflected with respect to the incident light and delivered again to the solar battery cell. Since the illuminance can be improved, the conversion efficiency of the solar cell is improved.

In the present invention, the apparent density of the hydrolysis-resistant white resin film 12 is preferably 1.37 to 1.65 g / cm ³ .

Here, the apparent density refers to a numerical value calculated from the thickness, area, and weight of the entire sheet laminated in a multilayer or single layer. By adding inorganic particles having a high specific gravity, the refractive index difference is increased at the interface, contributing to the reflection performance. The lower limit of the apparent density contributing to the reflectance is from 1.37 g / cm ³ , and the upper limit is 1.65 g / cm ^{3 in} consideration of the lightness of the solar cell. The method for controlling the apparent density to 1.37 to 1.65 g / cm ³ can be achieved by controlling the type of polyester resin, the type of inorganic particles, and the mixing ratio of inorganic particles. As the inorganic particles, talc, magnesium oxide, titanium dioxide, zinc dioxide, calcium carbonate, barium sulfate, gypsum and the like are preferably used. In particular, when titanium dioxide is used, the wavelength in the UV region is diffusely reflected, and thus has a remarkable effect on UV resistance.

  In addition, it is effective to use a fluorescent brightening agent such as 4,4'-bis (2-benzoxazolyl) stilbene to increase the whiteness.

  In the hydrolysis-resistant white resin film 12 of the present invention, the optical density as measured with a Macbeth optical densitometer is preferably 0.55 or more, more preferably 0.60 or more. The upper limit is theoretically as high as possible, but is 3.5 or less, preferably 3.0 or less, and more preferably 2.5 or less from the viewpoint of productivity and sheet strength.

  Here, the optical density referred to in the present invention indicates that the higher the numerical value as a concealing index, the higher the concealing property. In the present invention, an optical densitometer (manufactured by Macbeth: TR-524). The value measured under the conditions described below. The hydrolysis-resistant white resin film 12 needs to be concealed by reflecting sunlight leaking from the gaps between the solar cell elements and converting the reflected light into electricity, thereby providing a function of improving the conversion efficiency. Because.

  In particular, the hydrolysis-resistant white resin film 12 disposed at the lowermost part of the solar cell module needs to prevent incident light leaking from the gap from leaking out of the solar cell. If the optical density is less than 0.55, the incident light is emitted outside the solar cell. In this case, since it cannot be used again for electrical conversion by a solar cell element, an improvement in conversion efficiency cannot be expected, which is not preferable. Increasing the mixing ratio of inorganic particles such as titanium dioxide increases the concealability and at the same time significantly lowers the transmittance.

  As described above, the optical density, which is an index of hiding properties, is preferably 0.55 to 3.5, and this effect is exhibited from a region where the mixing ratio of titanium dioxide exceeds 5% by weight. The titanium dioxide concentration is preferably 7% by weight or more, more preferably 10% by weight or more. As for the upper limit, the concentration of titanium dioxide is desirably 40% by weight or less from the viewpoint of productivity and sheet strength. The range of the optical density of the present invention can be obtained by providing the polyester resin layer with a layer having the titanium dioxide content relative to the layer containing titanium dioxide.

  In the present invention, it is preferable that the optical density variation when measured with a Macbeth optical densitometer is within 20% of the center value. The variation in optical density is expressed as (maximum value−minimum value) / center value. For example, when the center value of the optical density is 1.0, the variation in the optical density is in the range of 0.2, and the optical density is preferably in the range of 0.9 to 1.1. The optical density variation is preferably within 15% with respect to the center value, and particularly preferably within 10% with respect to the center value.

  Since the optical density variation is required to be uniform in the plane of the solar cell module, it is preferably satisfied within the range of 1.5 m length × 1 m width, which is currently a general-purpose size.

  Such optical density variation is sampled in a size of 1.5 m in the longitudinal direction and 1 m in the width direction every 100 m in the longitudinal direction from the center of the product roll, and further, four corners of the cut sample of 1.5 m × 1.0 m are 10 cm × 10 cm. And the optical density was measured three times using the 10 cm × 10 cm sample to obtain the optical density. For each product roll, the optical density variation was calculated from the maximum value, minimum value, and center value (the number of data was 20) of the optical density when measured 5 times, and was used as the optical density variation.

  If the optical density variation is out of the range of 20%, the variation in the UV transmittance, the variation in the total light transmittance, and the variation in the relative reflectance are affected, which is not preferable in terms of performance and quality.

In order to make such optical density variation within 20%, it is necessary to reduce the classification of the raw material chips. For example, when using raw material chips having different specific gravities, this can be achieved by changing the chip size. . The specific gravity of titanium dioxide is 3.9 to 4.2 g / cm ³ , and the specific gravity of polyester is 1.2 to 1.4 g / cm ³ . The specific gravity of the master chip containing 50% by weight of titanium dioxide is 2.5 to 2.8 g / cm ³ .

  Conventionally, the shape of the master chip has been a cylindrical shape having a length of 5.95 to 8.05 mm, a width of 3.20 to 4.80 mm, and a height of 1.70 to 2.30 mm.

  In the above chip shape, when diluting the titanium dioxide concentration to 5 to 40% by weight, the master chip of titanium dioxide and the polyester chip are classified in the hopper at the top of the extruder, and the master chip having a high specific gravity is discharged first. There was a problem. Therefore, the sheet discharged earlier contains a large amount of titanium dioxide, so that the optical density is high. In the sheet discharged later, the titanium dioxide density is low, the optical density is low, and the optical density variation is large. Therefore, by changing the shape of the titanium dioxide master chip into a cylindrical shape having the following length: 2.40 to 4.60 mm, width: 3.20 to 4.80 mm, and height: 1.70 to 2.30 mm, It becomes possible to make it the range of the optical density variation of the present invention.

  In the hydrolysis-resistant white resin film 12 of the present invention, in order to satisfy the hydrolysis resistance, it is preferable to use a polyester resin layer in which the polyester resin sheet has a number average molecular weight of 18500 or more. The upper limit of the number average molecular weight is preferably as high as possible. However, when the number average molecular weight exceeds 40,000, extrusion is substantially impossible, and the number average molecular weight is 35000 or less in view of melt moldability and biaxial stretchability. Is more preferable. That is, the number average molecular weight is preferably 18500 to 40000, more preferably 19000 to 35000, and particularly preferably 20000 to 30000.

  Here, the number average molecular weight referred to in the present invention is measured by sol permeation chromatography (GPC) described later, and the number average molecular weight is an index of the degree of polymerization. When the number average molecular weight is within the range of the present invention, even when the hydrolysis reaction of the polyester resin proceeds, the degree of polymerization at the reaction start point is high, so that deterioration over time is superior to the number average molecular weight lower than 18500. Can be reduced.

  In order to adjust the number average molecular weight within the scope of the present invention, in the polymerization of the thermoplastic resin, the temperature for high polymerization is changed, for example, 190 to 230 ° C., the polymerization time is changed for 10 to 23 hours, and different number average molecular weights. A polymer can be obtained.

  In the present invention, the total light transmittance of the hydrolysis-resistant white resin film 12 is preferably 0.005 to 25%.

  Here, a total light transmittance means the value measured based on JIS-K-7105 using Suga Test Instruments haze meter HGM-2DP. Such total light transmittance is an index of concealability, and in particular, by reducing the total light transmittance of wavelengths in the visible light region, solar light having a wavelength that contributes to power generation is transmitted and solar cells. It is possible to prevent escape to the outside.

  The effect of increasing the concealment is remarkable when 5 to 40% by weight of titanium dioxide is added. If it is less than 5% by weight, the concealability is lowered, and the target total light transmittance cannot be reduced. If it exceeds 40% by weight, it is not preferable because it causes clogging of the membrane-forming filter and the sheet itself is liable to break, resulting in deterioration of productivity. The titanium dioxide concentration is preferably 7% by weight or more, more preferably 10% or more. The range of the total light transmittance of this invention can be obtained by having in the polyester resin layer the layer which is content of the said titanium dioxide with respect to the layer containing titanium dioxide. As long as the titanium dioxide concentration satisfies the above range, a plurality of layers may be provided, or a high concentration layer may be provided for adjustment.

  In the hydrolysis-resistant white resin film 12 of the present invention, the thickness of the polyester resin layer having a number average molecular weight of 18500 or more is preferably 7 to 100% of the total thickness of the polyester resin sheet. Preferably, it is 10% or more. More preferably, it is 15% or more. That is, the entire hydrolysis-resistant white resin film 12 does not need to have a number average molecular weight of 18500 to 40,000, and a high molecular weight polyester resin having a thickness average of 7% or more in the thickness direction of the film has a number average molecular weight of 18500 to 40,000. It only has to be. As a layer having a thickness of 7% or more of the thickness of all layers, more preferably 10% or more, and a polyester resin layer having a number average molecular weight of 18500 to 40,000 as the hydrolysis-resistant white resin film 12 It is preferable to form the outermost outermost layer, that is, the outermost layer of the back protective sheet, in order to impart hydrolysis resistance. Even if it is a high molecular weight polyester resin layer having a number average molecular weight of 18500-40000 with a thickness of less than 7% in the layer thickness direction, it is inferior in hydrolysis resistance, resulting in a decrease in strong elongation retention and rapid deterioration. If it is laminated with a thickness of 7% or more, it is advantageous for delamination from the lamination interface.

  Moreover, in the hydrolysis-resistant white resin film 12 of the present invention, the polyester resin layer having a number average molecular weight of 18500 or more is composed of a plurality of layers, and the layer containing 5 to 40% by weight of titanium dioxide is the entire polyester resin layer. It is preferably 7 to 100% of the thickness. Preferably, it is 10% or more of the total thickness of the polyester resin layer. More preferably, it is 15% or more of the total thickness of the polyester resin layer. The content of titanium dioxide is more preferably 7 to 30% by weight, and still more preferably 10 to 20% by weight. In this polyester resin layer, by separating the layer having a high concentration of titanium dioxide from the other layers, both the film-forming property and the optical properties can be improved.

  Moreover, in order to effectively express the hydrolysis degradation prevention of the hydrolysis-resistant white resin film 12 of the present invention, it is more preferable that the polyester resin layers having an average molecular weight of 18500 to 40000 are laminated on both sides.

  The hydrolysis-resistant white resin film 12 of the present invention preferably has an elongation retention of 40 to 100% after aging for 3000 hours in an environment of a temperature of 85 ° C. and a humidity of 85%. Aging for 3000 hours in an environment of temperature 85 ° C. and humidity 85% is one of the tests for examining the hydrolyzability equivalent to 25 years in the outdoor exposure state as a thermoplastic resin sheet for solar cells. In order to satisfy the ratio, it is preferable to have a polyester resin layer having a number average molecular weight in the range of 18500 to 40,000, dispose this layer as the outermost layer, and make the layer thickness 7% or more of the total thickness of the sheet. When the film layer is less than 7%, deterioration proceeds from the outermost layer, and the elongation retention may be less than 40%.

  In the hydrolysis-resistant white resin film 12 of the present invention, the elongation retention after aging for 15 hours in an environment of 140 ° C. is preferably 40 to 100%. Solar cells are used outdoors and can be exposed to high temperatures such as in the desert or the tropics. Moreover, in the sealed area | region, it rises more than atmospheric temperature. Furthermore, since the solar cell module itself generates heat when generating electric power, heat resistance in an environment where the backsheet is used is also an important item. The accelerated test for heat resistance can be replaced by the above evaluation. In order to set the elongation retention after aging for 15 hours in an environment of a temperature of 140 ° C. to 40 to 100%, it has a polyester resin layer having a number average molecular weight in the range of 18500 to 40,000, and this layer is the outermost layer. It is preferable to arrange and make the layer thickness 7% or more of the total thickness of the sheet. If the polyester resin layer is less than 7%, the deterioration progresses from the outermost layer and the elongation retention may be less than 40%.

  First, the measurement method used in the present invention will be described.

(1) Measurement of film thickness The film thickness of the adhesion improving layer is obtained by scanning a film obtained by cutting a film provided with an adhesion improving layer or a sheet on which this film and another film are laminated with a cutter knife perpendicularly to the film surface. It was measured by observing the cross section with a scanning electron microscope.

(2) Measurement of adhesive strength with EVA Based on JIS K 6854, the adhesive strength with an ethylene-vinyl acetate copolymer (EVA) film was measured. The tested pseudo solar cell sample was obtained by stacking an EVA film on the adhesion improving layer surface of the solar cell back surface sealing sheet, and further overlaying a 0.3 mm thick semi-tempered glass on the surface, heating at 150 ° C., 3 kg / cm ² load Used for 30 minutes. As the EVA film, a 0.7 mm thick film manufactured by Mitsui Chemicals Fabro Co., Ltd. was used. The width of the test piece for the adhesive strength test was 10 mm. It can be judged that the adhesive strength is at a level of 2 kgw / 10 mm or more, which is practically acceptable.

(3) Measurement of blocking Two solar cell module back surface sealing sheets are stacked in a direction in which the adhesion improving layer surface does not face (that is, adhesion improving layer / base material layer // adhesion improving layer / base material layer), on a metal plate After placing the base material layer in contact with each other, a rectangular parallelepiped metal weight having a bottom surface of 3 × 4 cm is placed on the two sheets and left as it is in an environment at a temperature of 40 ° C. for 65 hours. Thereafter, the weight was removed, and the two pieces were pulled in the opposing direction along the plane (corresponding to the major axis direction of the bottom surface of the weight), and the shearing force was measured. When blocking does not occur, the shearing force is 0, and the higher the blocking, the higher the value. If the shearing force in this measuring method is 0.05 kgw or less, there is no practical problem.

(4) Measurement of partial discharge voltage About the sheet | seat for solar cell module back surface sealing, the partial discharge voltage was measured based on the following measuring method, and electric insulation was evaluated. 1000V or more was set as (circle) and less than 1000V was set as x.
(Measuring method)
Conformity standard: IEC60664 / A2: 2002 4.1.2.4
Test device: KPD2050 (manufactured by Kikusui Electronics)
Measurement pattern: Trapezoidal start voltage Charge threshold: 1.0 pC
Vanishing voltage charge threshold: 1.0 pC
Test time: 22.0 s.

<Preparation of hydrolysis-resistant white resin film>
First, the physical property regarding the hydrolysis-resistant white resin film, its evaluation method, and evaluation criteria will be described.

<Physical properties and evaluation methods, evaluation criteria>
(1) Number average molecular weight (Mn)
Using a 244 type gel permeation chromatograph GCP-244 (manufactured by WATERS) at room temperature (23 ° C.), two Shodex (R) K 80M (manufactured by Showa Denko KK) in the column, TSK-GEL-G2000Hxl ( One Tosoh Corporation) was used, and molecular weight calibration was performed using polystyrene (PS) (standard product) before measuring the hydrolysis-resistant white resin film. Using the elution volume (V) and molecular weight (M), the coefficient (A1) of the third-order approximation formula (i) is calculated and plotted.
Log (M) = A0 + A1V + A2V2 + A3V3 (i).

After proofreading and drawing, the sample of the hydrolysis-resistant white resin film was dissolved in orthochlorophenol / chloroform (1/4 volume ratio) in a solvent so as to be 0.2% (wt / vol). . The injection amount into the chromatograph was 0.400 ml, and the flow rate was 0.8 ml / min. The detector used was an R-401 differential refractive index (WATERS), and the number average molecular weight was calculated according to the following formula.
Number average molecular weight (Mn) = ΣNiMi / ΣNi
Molar fraction; Ni, molecular weight corresponding to each holding capacity (Vi) (Mi)
A composite or single film was sampled and measured. The composite film was sampled by polishing the film while observing under a microscope.

(2) Content of titanium dioxide Using the sheet as a sample, the elemental amount of titanium, which is an element peculiar to titanium dioxide, was determined by a fluorescent X-ray elemental analyzer (manufactured by Horiba, Ltd., MESA-500W type). The titanium dioxide content was converted from the titanium element amount.

(3) Optical density The transmitted light flux was measured with an optical densitometer (Macbeth: TR-524), and calculated according to the following formula.
Light source: Visible light spectral composition: Color temperature 3006 ° K tungsten bulb Measurement environment: Temperature 23 ° C ± 3 ° C, Humidity 65 ± 10% RH
Calculation formula: optical density = log 10 (F0 / F)
F: Sample transmitted light flux
F0: Transmitted light beam without sample.

(4) Optical density variation (%)
The variation in optical density was expressed as [(Fmax−Fmin) / Fave] × 100.
Fmax: Maximum value of 20 data, Fmin: Minimum value of 20 data, Fave: Average value of 20 data
The optical density measurement method was measured by the same method as in (3) above.
Optical density variation was sampled from the product roll at a central portion of 100 m in the longitudinal direction at a size of 1.5 m in the longitudinal direction and 1 m in the width direction, and four squares of 1.5 m × 1.0 m were cut into 10 cm × 10 cm. The optical density was measured three times using the sample, and the average value of the three times was defined as the optical density. For each product roll, the optical density variation was calculated from the maximum value, the minimum value, and the central value (the number of data is 20 at 5 locations × 4 samples) of the optical density when measured 5 times.

(5) Apparent density
Measurement was performed with an electromagnetic balance (SD-120L manufactured by Kensei Kogyo Co., Ltd.). N = 3 measurements were made and an average value was adopted.

(6) Hydrolysis resistance A ratio when the film was aged in an atmosphere of 85 ° C. to 85% RH, the breaking elongation of the sheet was measured by ASTM-D61T, and the breaking elongation without aging was 100% (retention ratio ) And judged according to the following criteria.
Aging time: 0 hr (100%), 3000 hr
A: Retention rate is 50% or more and less than 60% B: Retention rate is 50% or more and less than 60% Δ: Retention rate is 40% or more and less than 50% X: Retention rate is less than 40%

(7) UV resistance Using the accelerated tester iSuper UV Tester, the following cycle was repeated 5 times, the elongation retention was determined in the same manner as described above, and evaluated according to the same criteria as described above.
1 cycle: UV irradiation for 8 hours in an atmosphere of temperature 60 ° C. and humidity 50% RH, then aging for 4 hours in a condensation state (temperature 35 ° C., humidity 100 RH) UV irradiation intensity: 100 mW / cm ²
○: b value increase rate is 5 or less)
Δ: b value increase rate is greater than 5 and less than 25)
X: b value increase rate is 25 or more).

(8) Relative reflectance Using a spectrophotometer U-3310 manufactured by Hitachi, both the standard white plate opening and the test piece opening were 560 nm using alumina oxide as the standard white plate, and the inclination angle of the test piece opening was 10 °. Then, the diffuse reflectance was measured (T0), and the reflectance at that time was 100%. Thereafter, the opening of the test piece was replaced with a test piece, and the diffuse reflectance was measured at 560 nm. Then, it converted into relative reflectance (R) by the following formula.
・ R (%) = T1 / T0 × 100
T0: reflectance of standard white plate
T1: The reflectance of the test piece.

(9) UV (300 to 350 nm) light transmittance Using a Hitachi spectrophotometer U-3310, both the standard white plate opening and the test piece opening are 300 to 350 nm using alumina oxide as the standard white plate. The transmittance of the sample without a sample was measured with a tilt angle of 10 ° for the opening (A0), and the transmittance at that time was 100%. Then, this sample was arrange | positioned in front of incident light, the measured value of the transmittance | permeability (A1) of 300-350 nm was taken for every 5 nm wavelength, and the average value of the measured value was made into UV transmittance T (%).
・ T (%) = A1 / A0 × 100
A0: Transmittance without sample
A1: The transmittance of the test piece.

(10) Heat resistance Aging of the film in an atmosphere of 140 ° C. for 15 hours, measuring the breaking elongation of the film by ASTM-D61T, setting the breaking elongation without aging to 100%, and the ratio with the elongation after aging ( Retention rate) was calculated. And it determined on the following reference | standard.
◯: Retention ratio is 40% or more Δ: Retention ratio is 30% or more and less than 40% ×: Retention ratio is less than 30%

  Next, preparation of a hydrolysis-resistant white resin film will be described.

  100 parts of dimethyl terephthalate (parts by weight: hereinafter simply referred to as parts) is mixed with 64 parts of ethylene glycol, 0.1 parts of zinc acetate and 0.03 part of antimony trioxide are added as catalysts, and the reflux temperature of ethylene glycol is reached. Transesterification was performed.

To this was added 0.08 part of trimethyl phosphate, and the temperature was gradually raised and reduced, and polymerization was carried out at a temperature of 271 ° C. for 5 hours. The intrinsic viscosity of the obtained polyethylene terephthalate was 0.55. The polymer was cut into a chip having a length of 4 mm, and the chip shape of PET (polyethylene terephthalate) was a cylindrical shape. Length: 5.95 to 8.05 mm, width: 3.20 to 4.80 mm, high The height was 1.70-2.30 mm, and the specific gravity was 1.3 g / cm ³ . This PET was put into a rotary vacuum apparatus (rotary vacuum dryer) having a high polymerization temperature of 190 to 230 ° C. and a vacuum degree of 0.5 mmHg, and heated with stirring for 10 to 23 hours to obtain a PET polymer.

In the polymerization of PET used for the compound and the base, the high polymerization temperature is adjusted to 190 to 230 ° C., the high polymerization time is adjusted to 10 to 23 hours, and the intrinsic viscosity of the PET polymer is 0.71. Got. This PET polymer and titanium dioxide fine particles were compounded to obtain a master chip containing 50% by weight of titanium dioxide. Since this master chip had a specific gravity of 2.5 g / cm ³ , the chip shape of the master chip was length: 2.40 to 4.60 mm, width: 3.20 to 4.80 mm, and height: 1.70. It was made into the chip | tip shape where classification | category does not occur easily as a cylinder shape of-2.30 mm.

40% by weight of a titanium dioxide master chip was added to adjust the titanium dioxide concentration to 20% by weight with respect to the base polyester. These polymers were laminated through a laminating apparatus so as to be B layer / A layer / B layer, and formed into a sheet form from a T-die. The stacked configuration is a composite three-layer configuration. Here, a resin having an intrinsic viscosity of 0.71 and a number average molecular weight of 21,000 and no titanium dioxide was used for the A layer, and a resin having an intrinsic viscosity of 0.71 and a number average molecular weight of 21,000 and a titanium dioxide particle concentration of 20% by weight was used for the B layer. . An unstretched sheet obtained by cooling and solidifying the sheet-like molded product discharged from the T die with a cooling drum having a surface temperature of 25 ° C. is led to a roll group heated to 85 to 98 ° C., and stretched 3.3 times in the longitudinal direction. It cooled with the roll group of 25 degreeC. Subsequently, the film was stretched by 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 220 ° C. in a tenter, and after uniform cooling, the film was cooled to room temperature to obtain a film having a winding thickness of 125 μm. This hydrolysis-resistant white resin film is referred to as film A. This film A has an apparent density of 1.41 g / cm ³ , an optical density of 0.85, an optical density variation of 9.5%, a relative reflectance of 90%, a UV transmittance of 0.09%, and hydrolysis resistance. Was evaluated at 55%, and UV resistance was evaluated as b when the b value increase rate was 4, and heat resistance (elongation retention) was evaluated as 63%.

<Adhesion improvement layer A>
The adhesion improving layer A was coated with the following aqueous coating agent with a direct gravure coater and then dried under drying conditions of a temperature of 120 ° C. for 10 seconds to form an adhesion improving layer having a thickness of 1 μm.

Water-based paint:
(A): Polyester resin:
Acid component: terephthalic acid 28 mol% isophthalic acid 9 mol% trimellitic acid 10 mol%, sebacic acid 3 mol%
Glycol component: ethylene glycol 15 mol% neopentyl glycol 18 mol% 1,4-butanediol 17 mol%
An ammonium salt type aqueous dispersion of a polyester resin comprising the acid component and glycol component.

(B): 5 parts by weight of (B) is mixed in a solid content ratio with respect to 100 parts by weight of the solid content of the methylolated melamine resin (A), and 0.05 wt% of degussa OK412 is used as an antiblocking particle. Addition was made into a coating for an adhesion improving layer.

<Adhesion improvement layer B>
The adhesion improving layer B was formed by sequentially coating the following adhesive layer and compatible resin layer using a two-head tandem direct gravure coater under the following conditions.
・ Adhesive layer: Aromatic ester adhesive manufactured by Mitsui Chemicals Polyurethanes Co., Ltd.
Main agent: Takelac (registered trademark) A-310 12 parts (liquid)
Curing agent: Takenate (registered trademark) A-3 1 part (liquid)
Mix the above two liquids
Coating conditions: Solid content Thickness 0.3 μm Drying conditions 120 ° C. 4 seconds ・ Compatible resin layer: MC3800 (EVA emulsion) manufactured by Chuo Rika Kogyo Co., Ltd.
Coating conditions: Solid content Thickness 1 μm Drying conditions 125 ° C. 10 seconds.

(Example 1)
As the resin film 11, a highly transparent PET film (Lumilar (registered trademark) T60 manufactured by Toray Industries, Inc. (thickness: 188 μm, total light transmittance: 88.9%)) was used. The adhesion improving layer A is applied to one surface of the film, the above-mentioned film A (125 μm) is applied to the opposite surface, a commercially available polyester-based adhesive main agent LX703VL and a polyisocyanate curing agent KR90 (both Dainippon Ink and Chemicals, Inc. )) Was dry laminated with an adhesive (dry weight 4 g / m ² ) mixed at a weight ratio of 15: 1 to obtain a solar cell module back surface sealing sheet of the present invention. The evaluation results are shown in Table 1.

(Example 2)
Except having changed the adhesion improvement layer A of Example 1 into the adhesion improvement layer B, it carried out similarly to Example 1, and obtained the solar cell module back surface sealing sheet | seat of this invention. The evaluation results are shown in Table 1.

(Example 3)
The back surface of the solar cell module of the present invention is sealed in the same manner as in Example 2 except that the thickness of the highly transparent PET film Lumirror (registered trademark) T60 in Example 2 is changed from 188 μm to 125 μm (total light transmittance 89%). A stop sheet was obtained. The evaluation results are shown in Table 1.

Example 4
As the resin film 11, a white PET film (Lumirror (registered trademark) E20 (thickness: 50 μm) manufactured by Toray Industries, Inc.) was used, and the adhesion improving layer B was applied to this one side surface. On the opposite surface, Lumirror (registered trademark) S10 (thickness 125 μm) manufactured by Toray Industries, Inc. as a resin film 13 is dry-laminated with the adhesive described in Example 1, and the above-mentioned film A (125 μm) is further formed on S10. Was dry laminated with the adhesive described in Example 1 to obtain a sheet for sealing the back surface of the solar cell module of the present invention. The evaluation results are shown in Table 1.

(Example 5)
For sealing the back side of the solar cell module of the present invention in the same manner as in Example 4 except that the thickness of the film A which is a hydrolysis-resistant white resin film is 50 μm and the thickness of S10 as the resin film 13 is 188 μm. A sheet was obtained. The evaluation results are shown in Table 1.

(Example 6)
For sealing the back side of the solar cell module of the present invention in the same manner as in Example 4 except that the thickness of the film A which is a hydrolysis-resistant white resin film is 75 μm and the thickness of S10 as the resin film 13 is 125 μm. A sheet was obtained. The evaluation results are shown in Table 1.

(Example 7)
In the same manner as in Example 2, T60 having a thickness of 188 μm coated with the adhesion improving layer B / alumina transparent vapor-deposited film which is a dry laminate / gas barrier film with the adhesive of Example 1 (Barrier Rocks manufactured by Toray Film Processing Co., Ltd.) (Registered Trademark), 12 μm thickness) / laminate in the order of dry laminate / 125 μm thick film A with the adhesive of Example 1 to obtain a sheet for sealing the back surface of the solar cell module of the present invention. The evaluation results are shown in Table 1.

(Example 8)
In the same manner as in Examples 4 and 7, 50 μm thick E20 coated with adhesion improving layer B / dry laminate with the adhesive of Example 1 / S10 of 125 μm thickness / dry laminate with the adhesive of Example 1 / alumina The sheet for sealing the back surface of the solar cell module of the present invention was obtained by laminating in the order of transparent vapor-deposited film (12 μm thickness) / dry laminate / film A having a thickness of 125 μm with the adhesive of Example 1. The evaluation results are shown in Table 1.

(Comparative Example 1)
A solar cell module back surface sealing sheet was obtained in the same manner as in Example 7, except that the thickness of T60 of Example 7 was 50 μm and the thickness of film A, which is a hydrolysis-resistant white resin film, was 50 μm. The evaluation results are shown in Table 1.

(Comparative Example 2)
In Example 7, a solar cell module back surface sealing sheet was obtained in the same manner as in Example 7 except that the thickness of T60 was 75 μm and the thickness of the film A was 125 μm. The evaluation results are shown in Table 1.

(Comparative Example 3)
In Example 1, a solar cell module back surface sealing sheet was obtained in the same manner as in Example 7 except that instead of the film A, a fluorine-based film Tedlar (registered trademark) TWH20BS3 (50 μm) manufactured by DuPont was used. The evaluation results are shown in Table 1.

(Comparative Example 4)
In Example 1, instead of the film A, a sheet for sealing the back surface of the solar cell module was obtained in the same manner as in Example 7 except that a PET film (Lumirror (registered trademark) X10S manufactured by Toray Industries, Inc., thickness 125 μm) was used. Obtained. The evaluation results are shown in Table 1.

(Comparative Example 5)
In Example 1, a solar cell module back surface sealing sheet was obtained in the same manner as in Example 1 except that the adhesion improving layer was not provided. The evaluation results are shown in Table 1.

It is a cross-sectional schematic diagram of the solar cell which uses the sheet | seat for solar cell module back surface sealing of this invention. An example of the sheet | seat for solar cell module back surface sealing of this invention is shown. The 2nd example of the solar cell module back surface sealing sheet | seat of this invention is shown. The 3rd example of the sheet | seat for solar cell module back surface sealing of this invention is shown. An example of the water vapor | steam barrier film used for the solar cell module back surface sealing sheet | seat of FIG. 4 is shown. The 4th example of the sheet | seat for solar cell module back surface sealing of this invention is shown. An example of a structure of the adhesion | attachment improvement layer used for the solar cell module back surface sealing sheet | seat of FIG. 6 is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solar cell module 2 Filler 3 Solar cell element 4 Solar cell module surface sealing sheet 5 Lead wire 10, 20, 30, 40 Solar cell module back surface sealing sheet 11, 13 Resin film 12 Hydrolysis-resistant white resin Film 31 Electrically insulating water vapor barrier layer 32 Electrically insulating substrate film 33 Inorganic oxide vapor deposition layer 41 Adhesion improving layer 42 Compatible resin layer 43 Adhesive layer

Claims (11)

  In the back surface sealing sheet used for a solar cell module comprising at least a back surface sealing sheet, a filler layer adjacent to the back surface sealing sheet, and a solar cell element embedded in the filler layer, the back surface The back surface of the solar cell module in which the sealing sheet has at least a resin film in contact with the filler and a hydrolysis-resistant white resin film as the outermost layer, and the partial discharge voltage of the back surface sealing sheet is 1000 V or more Sealing sheet.   The sheet | seat for solar cell module back surface sealing of Claim 1 which has at least 1 layer of resin film between the resin film which touches the said filler, and the hydrolysis-resistant white resin film used as the said outermost layer.   The sheet for solar cell module back surface sealing according to claim 1 or 2, wherein the total thickness of the resin films constituting the back surface sealing sheet is 230 µm or more.   The solar cell module back surface sealing according to any one of claims 1 to 3, wherein the back surface sealing sheet has an electrically insulating water vapor barrier layer in addition to the resin film and the hydrolysis-resistant white resin film. Sheet.   The adhesive according to any one of claims 1 to 4, wherein the filler is an ethylene-vinyl acetate copolymer, and an adhesive improvement layer is provided on a surface on the filler layer side of the resin film in contact with the filler layer. The sheet | seat for solar cell module back surface sealing of description.   The solar cell module back surface sealing according to claim 5, wherein the adhesion improving layer is made of at least one resin selected from the group consisting of a polyester resin and a polyester polyurethane system, and has a thickness of 0.5 to 3 μm. Sheet.   The adhesion improving layer is composed of a laminate of a compatible resin layer compatible with the ethylene-vinyl acetate copolymer filler layer and an adhesive layer, and the resin so that the compatible resin layer is in contact with the filler layer. The sheet for sealing a back surface of a solar cell module according to claim 5, wherein the sheet is provided on the surface of a stretched polyester film, which is a film, and the film thickness of the compatible resin layer is 0.2 µm or more and 2 µm or less.   The sheet for sealing the back surface of a solar cell module according to any one of claims 1 to 7, wherein the resin film in contact with the filler layer is white. The sheet for sealing a back surface of a solar cell module according to any one of claims 1 to 6, wherein the resin film in contact with the filler layer is a resin film having a total light transmittance of 85% or more. The hydrolysis-resistant white resin film as the outermost layer has a polyester resin layer formed by using one or a plurality of layers having a number average molecular weight of 18500 to 40,000, and the polyester resin layer has 5 to 40 weights. % Of the polyester resin layer containing titanium dioxide, the relative reflectance is 80% to 105%, the apparent density is 1.37 to 1.65 g / cm ³ , and the optical density is 10. The solar cell according to claim 1, wherein the solar cell satisfies four conditions of 0.55 to 3.50 and optical density variation is within 20% of the center value. Module backside sealing sheet.   A solar cell formed by bonding and laminating an adhesion improving layer surface of the solar cell module back surface sealing sheet according to any one of claims 1 to 10 and a filler surface made of an ethylene-vinyl acetate copolymer of the solar cell module. module.

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