JP5330146B2 - PET film used for back sheet for solar cell module and back sheet for solar cell module using the same - Google Patents

Description

  The present invention relates to a solar cell module, and more particularly to a backsheet disposed on the back side of the solar cell module.

Solar cell modules have been applied to various electronic devices and the like since they were originally used in calculators. However, solar cell modules that supply clean energy have been attracting attention as a supply source for household and industrial power due to increased awareness of environmental problems.
A solar cell module mainly includes a solar cell element made of crystalline silicon and amorphous silicon, and more specifically, a surface protective layer called a front sheet, a filler layer, and a solar cell as a photovoltaic element. It is manufactured by a lamination method in which an element, a filler layer, and a back surface protective layer called a back sheet are laminated in this order, and for example, vacuum suction is used to perform thermocompression bonding. The material of the solar cell element and the laminated structure of the solar cell module are just examples. Moreover, let the surface irradiated with sunlight be the surface.

  In the solar cell module, on the assumption that the backsheet has electrical insulation, it is provided for the purpose of providing water vapor and other gas barrier properties and preventing deterioration of the solar cell element mounted inside. . Therefore, a laminated film in which a thick aluminum foil is laminated on an intermediate layer was used at the beginning. However, although the back sheet in which the aluminum foil is laminated on the intermediate layer is excellent in gas barrier properties, the cost is high, which hinders widespread use of solar cell modules. Moreover, since aluminum foil has electroconductivity, there exists a possibility that a short circuit (short circuit) may arise in a solar cell circuit by accident etc. during use. Therefore, various backsheets that do not use aluminum foil have been proposed (Patent Documents 1 to 3). For example, Patent Document 1 discloses a back sheet having a structure in which a base film having light reflectivity, an adhesive layer, a vapor deposition layer of an inorganic oxide, and a weather resistant resin film are sequentially laminated from the side arranged on the solar cell element side. Is described. Patent Document 1 describes that this back sheet can have excellent light reflectivity and gas barrier properties without using a metal foil such as an aluminum foil, and has long-term reliability such as performance and weather resistance. Has been.

JP 2000-114565 A JP 2002-26343 A JP 2006-253264 A

For example, PET (polyethylene terephthalate) is mainly used as the base film and the weather resistant resin film in the back sheet of Patent Document 1. However, this PET film is inferior in hydrolysis resistance as compared with a fluorine film or a PEN (polyethylene naphthalate) film. Therefore, if the PET film is used as it is, durability as a back sheet cannot be obtained sufficiently.
However, fluorine films and PEN films are expensive. Therefore, it is conceivable to improve the hydrolysis resistance by coating an epoxy resin on the PET film. However, the epoxy resin needs to be baked at 200 ° C. or higher, and this temperature exceeds the heat resistance temperature (about 180 ° C.) of the PET film. Therefore, when the epoxy resin is actually coated, the baking temperature is raised only to a temperature lower than the heat resistance temperature of the PET film. Therefore, the epoxy resin to be coated is not sufficiently cured, and the coating resin layer is whitened. Since this resin is easy to permeate | transmit a water | moisture content, it cannot improve the hydrolysis resistance of PET film.
The present invention has been made based on such a technical problem, and a PET film for a back sheet for a solar cell module, on which a sufficiently cured epoxy resin coating layer is formed, and a back sheet using the film. The purpose is to provide.

  For this purpose, the present inventors can print onto a PET film by adding an epoxy resin having a molecular weight of 40000-45000 g / mol to a commonly used epoxy resin agent having a molecular weight of 300-10000 g / mol. It was found that sufficient curing was obtained at a temperature of 180 ° C. or less, and that no whitening phenomenon occurred during the acceleration test. The PET film for a solar battery backsheet of the present invention based on this finding includes a PET film layer and a resin coating layer that is deposited on at least one surface of the PET film layer. In the present invention, the coating layer is composed of an epoxy resin having a molecular weight of 40000-45000 g / mol of 10-30% by mass, a melamine resin of 5-10% by mass, and the balance being an epoxy resin having a molecular weight of 300-10000 g / mol. The subsequent thickness is 3 to 10 μm.

  According to the present invention, by adding an epoxy resin having a molecular weight of 40000 to 45000 g / mol to the resin coating layer, baking can be performed at a temperature of 180 ° C. or less which is a heat resistant temperature of the PET film. Therefore, the present invention provides a resin film for a solar battery backsheet having excellent hydrolysis resistance without using an expensive fluorine film or PEN film.

It is a typical fragmentary sectional view which shows schematic structure of the solar cell module in this Embodiment. It is a typical fragmentary sectional view which shows schematic structure of the back seat | sheet in this Embodiment.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
The solar cell module 10 in which the backsheet according to the present invention is used includes a front sheet 1, a filler layer 2 made of a resin layer, a solar cell element 3 as a photovoltaic element, and a filling similar to that of the filler layer 2. The material layer 4 and the back sheet 5 are sequentially laminated. In addition, this structure is an example of a solar cell module to the last, Comprising: The object to which the back seat | sheet in this invention is applied is not limited.

<Front seat 1>
The front sheet 1 protects the solar cell element 3 as a photovoltaic element. In order for the irradiated sunlight to reach the solar cell element 3, the front sheet 1 needs to be excellent in light transmittance. Moreover, since it protects the solar cell element 3, it must be excellent in weather resistance, water vapor and other gas barrier properties. As the front sheet 1, a known material, typically glass, can be used.

<Filler layers 2, 4>
The filler layers 2 and 4 are provided so as to sandwich the solar cell element 3 in order to embed and stabilize the solar cell element 3 made of amorphous silicon, crystalline silicon, or the like. For the filler layers 2 and 4, resin compositions mainly composed of various thermoplastic resins excellent in thermal fluidity and thermal adhesiveness can be used. For example, a resin composition composed of one or more of a polyethylene resin, a polypropylene resin, a fluorine resin, a cyclic polyolefin resin, a poly (meth) acrylic resin, or a silicone resin is used. can do. All of these resins have transparency and transmit sunlight, and are excellent in scratch resistance and impact absorption. In addition, these resins have heat resistance that is unlikely to deteriorate or decompose due to the action of heat. The heat resistance is a heating action in a lamination method in which a vacuum suction is performed when the solar cell module 10 is manufactured, and a heating action by irradiation of sunlight while the solar cell module 10 is used. Is required.
The thickness of the filler layers 2 and 4 is preferably 200 to 1000 μm, and more preferably 350 to 600 μm.

<Solar cell element 3>
As the solar cell element 3 as a photovoltaic element constituting the solar cell module 10, a conventionally known single crystal silicon type solar cell element, a crystalline silicon solar electronic element represented by a polycrystalline silicon type solar cell element, Known devices such as an amorphous silicon solar cell element of a single junction type or a tandem structure type can be widely applied.

<Back sheet 5>
As shown in FIG. 2, the back sheet 5 has a three-layer structure except for the adhesive layer 54. That is, the first PET layer 51, the second PET layer 52, and the third PET layer 53 are laminated via the adhesive layer 54 from the solar cell element 3 (filler layer 4) side. However, this configuration is merely an example, and does not exclude application of the present invention to the backsheet 5 having another configuration.

  The first PET layer 51 mainly has a function of reflecting the light transmitted through the filler layers 2 and 4 toward the solar cell element 3 in the backsheet 5. The first PET layer 51 also has electrical insulation. The first PET layer 51 is composed of a PET film in which a white pigment such as titanium dioxide is kneaded to have light reflectivity.

  The second PET layer 52 has a gas barrier property that prevents water vapor and other gases from permeating the solar cell element 3 mainly in the back sheet 5. Therefore, the 2nd PET layer 52 forms the vapor deposition layer which consists of an inorganic compound in any one of the front and back of a PET film, Preferably both surfaces are formed. As the inorganic compound, aluminum oxide, silicon oxide, magnesium oxide, tin oxide, or a mixture thereof can be used. Among these, aluminum oxide is preferable. Although the thickness of a vapor deposition film is suitably set by the kind and structure of an inorganic compound to be used, it is normally selected from the range of 5-300 nm.

  The third PET layer 53 disposed as the outermost layer in the backsheet 5 bears weather resistance. Therefore, the third PET layer 53 is particularly improved in hydrolysis resistance. That is, the third PET layer 53 has a hydrolysis-resistant coating layer formed on either one of the front and back surfaces of the PET film, preferably on both surfaces. This coating layer consists of adding an epoxy resin having a molecular weight of 40,000 to 45,000 g / mol at 10 to 30% by mass to the resin constituting the coating layer. This coating layer can be baked at a temperature of 180 ° C. or less, which is the heat resistant temperature of the PET film.

When the molecular weight of the epoxy resin added to the coating layer is less than 40000 g / mol, whitening occurs during the accelerated test, and when it exceeds 45000 g / mol, the adhesion to the PET film is deteriorated. Therefore, in the present invention, the molecular weight of the epoxy resin added to the coating layer is set to 40000-45000 g / mol.
The epoxy resin having a molecular weight of 40000 to 45000 g / mol occupies 10 to 30% by mass of the resin constituting the coating layer. If it is less than 10% by mass, whitening occurs in the coating layer, and the effect of improving the hydrolysis resistance of the coating layer is insufficient. Therefore, there is a concern that the PET film constituting the third PET layer 53 is deteriorated in characteristics. Moreover, when it exceeds 30 mass%, coating layer itself will become hard and the adhesion defect to PET film will arise.

In the coating layer other than the epoxy resin having a molecular weight of 40000-45000 g / mol, an epoxy resin having a molecular weight other than 40000-45000 g / mol (molecular weight 300-10000 g / mol) can be used, and a resin such as melamine can be used. Can be used.
The melamine resin is necessary for crosslinking (hardening) the epoxy resin. The content is preferably 5 to 10% by mass. If it is less than 5%, crosslinking is reduced and an unreacted epoxy resin remains, so that hydrolysis (white turbidity) is likely to occur, and if it exceeds 10%, crosslinking is too much and the formed film becomes hard and water resistance decreases. To do.

  As the adhesive layer 54, known materials can be widely applied. For example, a two-component curable polyurethane adhesive and a heat-adhesive resin can be appropriately selected and used in accordance with the adhesion method.

After coating the epoxy resin-based coating agent shown in Table 1 with a solvent on both sides of a PET film substrate (Toray X10S (thickness: 50μ)), drying and curing at 150 ° C. for 30 seconds to form a coating layer PET films (test materials) were obtained on both front and back surfaces, and the thickness of the coating layer after curing was 7 μm.
An acceleration test was performed using the test material, and the time required for the breaking strength and elongation to drop to 50% of the original was measured. In the accelerated test (pressure cooker test), the specimen was placed in an environment of temperature: 105 ° C. and humidity: 100%, and the breaking strength and elongation were measured every 48 hours. A similar acceleration test was performed on a PET film base material on which no coating layer was formed. The results are shown in Table 2. In addition, it was visually observed whether a whitening phenomenon occurred in the coating layer after curing.

  An acceleration test was conducted in the same manner as in Example 1 except that the composition of the resin of the coating layer was changed as shown in Table 3. The results are also shown in Table 3.

  An accelerated test was conducted in the same manner as in Example 1 except that the coating thickness of the coating layer was changed as shown in Table 4. The results are also shown in Table 4.

DESCRIPTION OF SYMBOLS 1 ... Front sheet, 2, 4 ... Filler layer, 3 ... Solar cell element, 5 ... Back sheet,
10 ... Solar cell module

Claims (2)

A PET film layer;
A coating layer applied to at least one of the front and back surfaces of the PET film layer,
The coating layer is
The epoxy resin having a molecular weight of 40,000 to 45000 g / mol is composed of 10 to 30% by mass, the melamine resin is 5 to 10% by mass, and the balance is an epoxy resin having a molecular weight of 300 to 10,000 g / mol
A PET film for a back sheet for a solar cell module, wherein the thickness after curing is 3 to 10 μm.   The back sheet | seat for solar cell modules using the PET film of Claim 1.

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