Film for Solar Cell Rear Surface Sealing Sheet

Description

Title of the Invention: A solar battery backside sealing sheet film

Technical field

[0001]

The invention relates to a film for solar battery backside sealing sheets that has high light resistance and moist heat resistance to serve for long term use in a harsh outdoor environment. The present invention also relates to a solar battery backside sealing sheet and a solar battery module which comprise the solar battery backside sealing sheet film of the present invention.

Background art

[0002]
In recent years, there has been greater fear for the depletion of fossil fuels including oil and coal, and there is pressing need to develop alternative energy sources to these fossil fuels. Accordingly, various methods for nuclear power generation, hydraulic power generation, wind power generation, and photovoltaic power generation have been studied, and some have been in actual use. Photovoltaic power generation, which can convert the energy of sunlight directly into electric energy, has been put to practical use as a new, pollution-free energy source that can be used virtually permanently. Cost performance of photovoltaic power generation in practical use has been improved rapidly, making it a promising clean energy source.

[0003]
Solar batteries used for photovoltaic power generation, which convert the energy of sunlight directly into electric energy, serve as the core portion of photovoltaic power generation systems. Solar batteries comprise semiconductors of, for instance, silicon. In a solar battery, solar battery elements are arranged in series and/or in parallel and packaged in various ways into a unit to protect the elements for a long period of 20 years or so. This packaged unit is called a solar battery. A solar battery generally consists of a glass layer to cover the face that receives sunlight, a filler of thermoplastic resin to fill gaps, and a sealing sheet to protect the backside surface. For the filler, ethylene vinyl acetate copolymer resin (hereafter, EVA resin) is commonly used as they are high in transparency and moisture resistance. The backside sealing sheet, on the other hand, is required to have characteristics such as mechanical strength, weather resistance, heat resistance, water resistance, chemical resistance, light reflectivity, electrical insulating properties, moisture barrier properties, thermal adhesion properties for bonding to EVA resin and other filler materials, decorative properties, decorative characteristics, and adhesion strength to the outermost silicone resin layer for bonding to terminal boxes. In addition, backside sealing sheets need to have high light resistance because they are exposed to ultraviolet rays.

[0004]
The materials conventionally used for films for backside sealing sheets include white polyvinyl fluoride film (trade name: Tedlar (registered trademark), supplied by Du Pont Kabushiki Kaisha). Laminate-type backside sealing sheets consisting of a polyester film sandwiched between polyvinyl fluoride films have been widely used for solar batteries . A light resistant film produced by coating one or both surfaces of a polyester film with acrylic resin containing an ultraviolet absorber and photostabilization agent have also
been proposed and put to practical use (Patent document 1). A polyester film containing a kneaded ultraviolet absorber and photostabilization agent, etc.) have also been put to practical use (Patent document 2). White films produced from a layer produced by kneading white pigments such as titanium oxide into a polyester film have also been put to practical use (Patent document 3). Such White films are known to have light resistance from the viewpoint of little change in appearance caused by exposure to ultraviolet rays.

Prior art documents
Patent documents

[0005]
Patent document 1 : Japanese Unexamined Patent Publication (Kokai) No. 2005-015557
Patent document 2: Japanese Unexamined Patent Publication (Kokai) No. 2009-188105
Patent document 3: Japanese Unexamined Patent Publication (Kokai) No. HEI
11-291432

Summary of the invention

Problems to be solved by the invention

[0006]
However, though said polyvinyl fluoride films are highly weather resistant, they are low in mechanical strength, and can be softened by the heat of 140 to 150°C applied during hot pressing for producing a solar battery module to allow projections in the electrodes of solar battery elements to penetrate the filler layer. Being high in price, furthermore, it is difficult to produce low-price solar battery modules comprising these films. To produce a white or colored film to provide backside sealing sheets with good decorative
characteristics, it is necessary to use a relatively expensive colored film.

[0007]

Polyester films as proposed in Patent documents 1 and 2 can suffer bleed-out of the ultraviolet absorbers and photostabilizing agents to the surface of the coat or film when exposed to a high temperature, high humidify environment and ultraviolet rays. This not only leads to changes in the wettability and contact strength of the surface, but also the problem of losing the initially existing light resistance.

[0008]
The white films disclosed in Patent document 3, furthermore, can have some degree of ultraviolet light resistance because the pigments have some light absorptive capacity to prevent the film appearance from being affected by ultraviolet irradiation. However, the resin, which is the primary component, does not have light resistance and has the problem of being gradually degraded in its own film characteristics such as breaking strength and rupture elongation when irradiated with ultraviolet rays. As active efforts have been made to develop longer-life solar battery modules in recent years, solar battery modules are often installed obliquely from the ground in some areas including Europe. In such cases, they are exposed to ultraviolet rays reflected from the ground for a long period of time. Consequently, if the backside sealing sheet does not have a layer with a long-term stable light resistance to cover its outmost layer, it may be yellowed, causing deterioration in the appearance of the film, and in some cases, cracking may ake place in the sealing sheet, causing deterioration in various other characteristics including electrical insulating properties and moisture barrier properties required for the sheet.

Means of solving the problems

[0009]
The present invention adopts the following constitution to solve such problems given above. Specifically, the solar battery backside sealing sheet film according to the present
invention comprising a resin layer containing fluorine based resin, a color pigment, and
melamine cyanurate, which is laminated on at least one surface of a base film.

[0010]
In addition, the solar battery backside sealing sheet of the present invention comprises
the solar battery backside sealing sheet film of the present invention.

[0011]

Furthermore, the solar battery module of the present invention comprises the solar battery backside sealing sheet of the present invention and a cell filler layer, where the solar battery backside sealing sheet and the cell filler layer are bonded together.

Effect of the invention

[0012]

The present invention provides a solar battery backside sealing sheet film with high light resistance and moist heat resistance and also provides a solar battery backside sealing sheet produced thereof. A preferred embodiment of the invention further provides a solar battery backside sealing sheet film with high fire retardance and less blocking and chalking also provides a solar battery backside sealing sheet produced thereof. The solar battery backside sealing sheet according to the invention serves to produce as solar battery module with high durability. Description of embodiments

[0013]
The solar battery backside sealing sheet film according to the present invention comprises a resin layer containing fluorine based resin, a color pigment, and melamine cyanurate, which is laminated on at least one surface of a base film, thereby having higher light resistance and moist heat resistance than conventional films.

[0014] [Base Film]
Various resin films can be used as base film of the solar battery backside sealing sheet film. Specifically, the resin films include polyester resin films such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); resin films such as those of polycarbonate, polymethyl methacrylate, polyacrylate, polypropylene, and polyethylene; and resin films made of mixtures of these resins. Of these, the polyester resin film is preferred because of excellent strength, dimensional stability, and thermal stability. In terms of low cost, the polyester resins of PET, PEN, and the like are particularly preferred. Here, the polyester resin may be a copolymer, and examples of the copolymerization component to be used include diol components such as propylene glycol, diethylene glycol, neopentyl glycol, and cyclohexane dimethanol, and dicarboxylic acid components such as isophthalic acid, adipic acid, azelaic acid, sebacic acid, and ester-forming derivatives. Polyphenylene sulfide (PPS) having higher hydrolysis resistance, heat resistance, and flame resistance can also be used. Furthermore, it is also possible to use fluorine based films typified by polyvinyl fluoride conventionally used as film for backside sealing sheets.

[0015]
Since the solar battery backside sealing sheet film is excellent in light resistance, when used in a solar battery backside sealing sheet, the film can preferably serve as material for the outermost layer that is directly exposed to outside air (humidity and temperature), and ultraviolet rays reflected from the surface of the ground. From the viewpoint of its use for the outermost layer that is directly exposed to outside air, the base film is preferably a resin film having excellent hydrolysis resistance. Usually, a polyester resin
film is formed from, using as a raw material, a so-called polymer produced by condensation polymerization of monomers, and contains about 1.5 to 2 mass% of oligomers that has a structure between a monomer and a polymer. Oligomers are in many cases in the form of cyclic trimers, but films containing large amounts of such trimers suffer from a decrease in mechanical strength when being exposed to outdoor environment for a long period of time, and undergo cracks, material failure, and the like as a result of progression of hydrolysis caused by rainwater or the like. In contrast, the formation of a polyester film using, as a raw material, a polyester resin with containing 1.0% or less of cyclic trimers which are obtained by polymerization by a solid-phase polymerization process prevents the film from hydrolysis at high temperature and high humidity and serves to produce films with higher heat resistance and weather resistance .

The determination of the above cyclic trimer content can be performed using, for example, a solution prepared by dissolving 100 mg of polymer in 2 ml of ortho-chlorophenol and performing liquid chromatography to measure the content of the cyclic trimer (mass%) relative to the resin mass.

[0016] To the base film, if required, additives such as an antistatic agent, an ultraviolet absorbent, a stabilizer, an antioxidant, a plasticizer, a lubricant, a filler agent, and a coloring pigment may be added as long as the object of the present invention is not impaired.

[0017]
The thickness of the base film is, but not specifically limited to, in the range of 1 to 250
Hm in consideration of the voltage resistance, cost, and the like of the sealing sheet.
The lower limit of the thickness is preferably 25 um or more.

[0018]
To develop moisture barrier property, the base film to be used may be a moisture barrier film in which at least one inorganic oxide layer is formed by the vapor deposition method or the like. A moisture barrier film to be used for the present invention is a resin film having a moisture transmission rate of 5 g/(m2day) or less as measured by method B according to JIS K7129 (2000). Because of stability, cost, and the like during production of an inorganic oxide layer, the thickness of the above resin film is
preferably in the range of 1 to 100 urn, more preferably in the range of 5 to 50 um, and particularly preferably 10 to 30 um.

[0019]
The base film is preferably bi-axially extended so as to have good thermal dimensional stability. Furthermore, if required, the base film may be subjected to electric discharge treatment such as corona discharge or plasma discharge, or subjected to surface treatment such as an acid treatment.

[0020] [Resin layer]
The resin layer to be laminated on the base film of the present invention comprises (1) a fluorine based resin, (2) a color pigment, and (3) melamine cyanurate. Commonly, a resin layer with improved light resistance is produced by adding one or more organic ultraviolet absorbers and/or inorganic ultraviolet absorbers to the binder resin, along with a photostabilizing agent (HALS) with the aim of increasing the photostability through a mechanism for deactivating radicals that could be excited by light. A resin layer produced by adding, in a later step, ultraviolet absorbers and photostabilizing agents to a binder resin, however, can suffer bleed-out of the ultraviolet absorbers and photostabilizing agents from inside the coat film to the surface of the coat film when exposed to a high temperature, high humidify environment and ultraviolet rays. This not only leads to changes in the wettability and contact strength of the coat surface, but also can cause the problem of losing the initially existing ultraviolet screening capability. The present invention, on the other hand, uses, as a binder, fluorine based resin, which is extremely high in light resistance compared to polyester resins, olefin resins, and acrylic resins. Accordingly, it is not necessary to subsequently add an ultraviolet absorber and light stabilization agent to the binder resin, thereby eliminating the occurrence of such a problem as described above. Being high in fire retardance, the fluorine based resin also serves to improve the fire retardance of the solar battery backside sealing sheet film. To achieve improved contact with the base film and improved heat resistance of the resin layer, it is preferable to use fluorine based resin containing a curable functional group so that an appropriate crosslinked structure can be introduced in the resin layer. The solar battery backside sealing sheet produced from the solar battery backside sealing sheet film of the invention is exposed to high processing temperatures during the solar battery module production step, and accordingly, the resin layer is required to have high heat resistance.

[0021]
Examples of said functional group that makes fluorine based resin curable include, for instance, hydroxyl group, carboxyl group, amino group, glycidyl group, silyl group, cyanate group, and isocyanate group, from which of an appropriate one is selected from the viewpoint of easiness of resin production and curability. In particular, the hydroxyl group, cyano group, and silyl group are preferable because of their high curability, and in particular the hydroxyl group is highly preferable from the viewpoint of availability
of the resin and high reactivity. These curable functional groups are introduced fluorine based resin common by copolymerizing it with monomers containing a curable functional group.

[0022]

Usable hydroxyl-containing monomers include, for instance, hydroxyl-containing vinyl ethers such as 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 2-hydroxy-2-methyl propyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxy-2-methylbutyl vinyl ether, 5-hydroxypentyl vinyl ether, and 6-hydroxyhexyl vinyl ether; and hydroxyl-containing allyl ethers such as
2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, and glycerol monoallyl ether. Of these, hydroxyl-containing vinyl ethers, particularly 4-hydroxybutyl vinyl ether and 2-hydroxyethyl vinyl ether are preferable due to high polymerization reactivity and functional group's curability. Other useful hydroxyl-containing monomers include, for instance, hydroxyalkyl esters of (meth)acrylic acid, such as 2-Hydroxyethyl acrylate and 2-hydroxyethyl methacrylaye.

[0023]
From the viewpoint of constituent units, examples of fluorine based resin that contains a curable functional group include, for instance, perfiuoro olefin based resin composed mainly of perfiuoro olefin units. More specifically, they include homopolymer of tetrafluoroethylene (TFE), copolymers of TFE with hexafluoropropylene (HFP) or perfluoro-(alkyl vinyl ether) (PAVE) and the like, and copolymers of other monomers that can be copolymerized with the former.

[0024]
Said other copolymerizable monomers include, but not limited to, vinyl carboxylate esters such as vinyl acetate, vinyl propionate, vinyl butyrate, isovinyl butyrate, vinyl pivalate, vinyl caproate, vinyl versate, vinyl laurate, vinyl stearate, cyclohexyl vinyl carboxylate, vinyl benzoate, and para-t-butyl vinyl benzoate; alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, and cyclohexyl vinyl ether; alkyl
vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, and cyclohexyl vinyl ether; non-fluorine based olefins such as ethylene, propylene, n-butene, and isobutene; and fluorine based monomers such as vinylidene fluoride (VdF), chlorotrifluoro ethylene (CTFE), vinyl fluoride (VF), and fluorovinyl ether.

[0025]
Of these, TFE based resins composed mainly of TFE are preferable from the viewpoint of high pigment dispersibility, weather resistance, copolymerizability, and chemical resistance.

[0026]
Specific examples of perfluoro olefin based resin containing a curable functional group include, for instance, copolymers of TFE / isobutylene / hydroxybutyl vinyl ether / other monomers, copolymers of TFE / vinyl versate / hydroxybutyl vinyl ether / other monomers, and copolymers of TFE / VdF / hydroxybutyl vinyl ether / other monomers, of which copolymers of TFE / isobutylene / hydroxybutyl vinyl ether / other monomer, and copolymers of TFE / vinyl versate / hydroxybutyl vinyl ether / other monomers are preferable. TFE based curable resin paints include, for instance, Zeffle GK-Series supplied by Daikin Industries, Ltd.

[0027]
Said resin layer preferably has a thickness of 0.2 to 20 um. The lower limit of the thickness of said resin layer is preferably 5 um or more, more preferably 8 um or more.

The upper limit of the thickness of said resin layer is preferably 15 um or less, still more preferably 10 um or less. In the case where resin layer is formed by coating, troubles such as cissing and film breakage tend to occur during the coating step, making it difficult to produce a uniform coat film, if the thickness of the resin layer is less than 0.2 um. In such a case, good contact with the base film and particularly light resistance may not develop sufficiently. If the thickness of the resin layer is more than 20 um, on the
other hand, light resistance will develop adequately, but there may be problems such as limitations on the coating method to be used, increased production cost, sticking of coat film on conveyor rolls, and associated peeling of film.

[0028]
Solvent that can work effectively to prepare a coating liquid used to form a resin layer by coating include, for instance, toluene, xylene, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dimethyl formamide, dimethyl acetamide, methanol, ethanol, and water. With respect to the properties of said coating liquid, it may be either of an emulsion type or a dissolution type.

[0029]
There are no specific limitations on the method to be used to form a resin layer on a base film, and generally known coating methods may be used. There are various usable methods including, for instance, roll coating, dip coating, bar coating, die coating, gravure roll coating, and combinations thereof. Of these, gravure roll coating is preferable because the coat layer will have increased stability.

[0030]
[Color pigments]

Pigments used in the present invention should serve for the purposes of (1) coring the resin layer, (2) maintaining a color tone (preventing color fading), (3) blocking ultraviolet rays and/or visual light and (4) improving fire retardance. Among the various solar battery backside sealing sheets, white ones are dominant from the viewpoint of light reflectivity and decorative appearance, but recently, demands for black sheets have expanded on the ground that they appear better than white ones that form apparently white gaps between the electric generating elements. Moreover, as these pigments themselves absorb and/or reflect rays of specific wavelengths, coloring can serve to protect the base film from ultraviolet rays and/or visible light. They also serve for hiding design patterns such as electric wiring patterns in a solar battery module.

[0031]
The usable color pigments include inorganic, organic, and other various pigments. Of the color pigments currently in practical use, titanium oxide and carbon black are preferable as white and black pigments, respectively, from the viewpoint of general-purpose properties, price, color development performance, and ultraviolet resistance. In particular, titanium oxide pigments preferably have a number average particle diameter of 0.1-1.0 urn from the viewpoint of color development. It is more preferably 0.2-0.5 um from the viewpoint of dispersibility in fluorine based resin as well as cost Similarly, carbon black pigments preferably have a number average particle diameter of 0.01-0.5 um. It is more preferably 0.02-0.1 um from the viewpoint of dispersibility and cost

[0032]
The content of these color pigments may be adjusted appropriately to meet intended color designs. Here, if the content of pigments is too small, good decorative color appearance cannot be developed, or ultraviolet ray and/or visible light will not be blocked effectively. If exposed to outdoor light for a long term, furthermore, the base film can be degraded or yellowed. In addition, blocking may be caused as a result of an increased resin content. If the content of color pigments is too large, on the other hand, there may occur problems such as increased costs, easy deterioration in the contact between the base material and silicone resin used for bonding terminal boxes resulting from largely improved strength of the resin layer, and chalking in the resin layer surface. Because of a decreased resin content, furthermore, the contact between the resin layer and the base film may decrease. The invention uses a color pigment also for the purpose of improving fire retardance of the solar battery backside sealing sheet film, and therefore, its content is increased to some extent in order to develop fire retardance.

[0033]
For the above reason, it is preferable that the content of coloring pigments is preferably 30 to 80 mass% of the whole resin layer. The lower limit of the content is more preferably 50 mass% or more, still more preferably 65 mass% or more. The lower upper of the content is more preferably 75 mass% or less, still more preferably 70 mass% or less.

[0034]
[Melamine cyanurate]
For the present invention, the use of melamine cyanurate is intended to (1) improve the blocking resistance of resin layers and (2) improve their fire retardance. Melamine cyanurate is a halogen-free flame retarder and also serves as lubricant. For the invention, addition of melamine cyanurate to fluorine based resin works not only to improve the fire retardance of resin layers, but also to reduce the blocking caused by the use of fluorine based resin. The mechanism of the blocking reduction resulting from the
addition of melamine cyanurate to fluorine based resin is considered to be as follows.

When a resin layer formed on a base film by coating is dried by heating, melamine cyanurate and low-polarity fluorine based resin undergo phase separation resin layer, causing the melamine cyanurate, which is lower in molecular weight, to move towards the opposite side of the base film. Accordingly, the content of melamine cyanurate increases near the surface of the resin layer, thereby causing reduction in blocking.

[0035]
It is preferable that the content of coloring is preferably 1 to 30 mass% of the entire resin layer. The lower limit of the content is more preferably 3 mass% or more, still more preferably 5 mass% or more. The upper limit of the content is more preferably 20 mass% or less, still more preferably 10 mass% or less. If the content is less than 1 mass%, melamine cyanurate may fail to have an adequate effect. If the content is more than 30 mass%, to may lead to an increase in cost, bleed-out of melamine cyanurate to
the surface of the coat film, or a decrease in the solvent resistance required in the resin layer.

[0036]
[Crosslinking agent ]
As described above, a crosslinking agent having a functional group that can react with the functional group existing in the fluorine based resin may be added with the aim of improving characteristics of the resin layer.

When a crosslinking agent is used in combination, it can have effects such as an increase in contact strength between the base film and the resin layer, and an increase in the solvent resistance and heat resistance of the resin layer resulting from the introduction of a crosslinked structure. In particular, in the case of a solar battery backside sealing sheet that is designed to have a resin layer according to the invention located at the outermost position, the layer is required to have a particularly high heat resistance as it is subjected to heat treatment at a high temperature of up to 150°C for up to as long as 30 minutes or more during the solar battery module production process, or more specifically, during the glass lamination step (cell filling step). It is also required to have solvent resistance because it is subjected to cleaning steps including wiping with ethanol or other organic solvents after assembling of a module during the solar battery module production process. From the viewpoint of improvement in contact, solvent resistance, and heat resistance, it is preferable that to add a crosslinking agent.

[0037]
As described above, the functional group to be introduced in fluorine based resin is preferably a hydroxyl group, and accordingly, it is preferable that the crosslinking agent can react with that hydroxyl group. It is preferable that such a crosslinking agent is used in combination with a polyisocyanate based resin as curing agent to promote the formation of urethane bonds (crosslinked structure). Examples of said polyisocyanate based resin used as crosslinking agent include aromatic polyisocyanate, araliphatic
polyisocyanate, alicyclic polyisocyanate, and aliphatic polyisocyanate, which can be produced from diisocyanate compounds listed below as starting material. These may be used singly, or two or more thereof may be used in combination.

[0038]
Examples of diisocyanate that can serve as starting material to produce aromatic polyisocyanate include, for instance, m- or p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate (NDI), 4,4'-, 2,4'- or 2,2'-diphenyl methane diisocyanate (MDI), 2,4- or 2,6-tolylene diisocyanate (TDI), and 4,4'-diphenyl ether diisocyanate.

[0039]
Examples of diisocyanate that can serve as starting material to produce araliphatic polyisocyanate include, for instance, 1,3- or 1,4-xylylene diisocyanate (XDI) and 1,3- or 1,4-tetramethyl xylylene diisocyanate (TMXDI).

[0040]
Examples of diisocyanate that can serve as starting material to produce licyclic polyisocyanate include, for instance, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanate methyl-3,5,5-trimethyl cyclohexyl isocyanate (isophorone diisocyanate; IPDI), 4,4'-, 2,4'- or 2,2'-dicyclohexyl methane diisocyanate (hydrogenated MDI), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, and 1,3- or 1,4-bis(isocyanate methyl) cyclohexane (hydrogenated XDI).

[0041]
Examples of diisocyanate that can serve as starting material to produce aliphatic polyisocyanate include, for instance, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-, 2,3- or 1,3-butylene diisocyanate, and 2,4,4- or 2,2,4-trimethyl hexamethylene diisocyanate.

[0042]
To serve as starting material for production of polyisocyanate, two or more of these diisocyanate may be used in combination, or they may be in a modified form such as biuret-modified or nurate-modified form. Resins with a backbone containing an aromatic ring that absorbs light in the ultraviolet band tends to be yellowed when irradiated with ultraviolet ray, and therefore, it is preferable to use alicyclic
polyisocyanate and/or aliphatic polyisocyanate as curing agent. In addition, from the viewpoint of solvent resistance, it is preferable to use alicyclic polyisocyanate which works to cure the resin layer more rapidly. It is preferable, furthermore, to use a nurate-modified form of hexamethylene diisocyanate from the viewpoint of rapid progress of the crosslinked reaction, degree of crosslinking, heat resistance, and
ultraviolet resistance.

[0043]
[Other additives]
In addition, a thermal stabilizer, antioxidant, toughening agent, antidegradant, weathering agent, flame retardant, plasticizer, mold releasing agent, lubricant, crosslinked assistant, pigment dispersant, defoaming agent, leveling agent, ultraviolet absorber, photostabilizer, viscosity improver, contacted improving agent, and delustering agent may be added to a resin layer containing fluorine based resin unless they impair its characteristics.

[0044]
The usable thermal stabilizers, antioxidants, and antidegradants include, for instance, hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, halogenated alkali metals, and their mixtures.

[0045]
The usable toughening agents include, for instance, clay, talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, zinc oxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate whisker, boron nitride, graphite, glass fiber, and carbon fiber. The usable crosslinking assistants include, conventionally known tin based ones, other metal based ones, organic acid based ones, amino based ones.

[0046]

[Adhesive layer]
A solar battery backside sealing sheet can be produced by lamination of a solar battery backside sealing sheet film and other resin films. A known dry lamination process can be used as a technique for laminating these films and processing them into a sheet-like shape. To bond resin films using the dry lamination process, a known dry lamination adhesive can be used which consists of polyether polyurethane, polyester polyurethane, polyester, polyepoxy resin, or the like as base resin, and polyisocyanate resin as curing agent. The adhesive layer formed using any of these adhesives, however, should not suffer delamination as a result of deterioration in the adhesive strength attributed to long term outdoor use, or undergo yellowing that leads to a decrease in light reflectance. The adhesive layer preferably has a thickness in the range of 1 to 5 um. An adequate adhesive strength may not be achieved if it is less than 1 um. If it exceeds 5 um, on the other hand, there are possibilities that adhesive application speed will not be increased; a long aging time will be required for the purpose of developing an adhesive strength (to accelerate the cross-linking reaction between the base resin and the curing agent); and the amount of the adhesive will be increased.

[0047]
A known adhesive for dry lamination can be used as a material to be used to form an adhesive layer. A common adhesive for dry lamination is prepared by diluting two resins, namely a base resin and a cross-linking agent in a diluent solvent, and here, it is preferable that the cross-linking agent to be used is a polymer containing an isocyanate group, which may be high in reactivity with active hydroxyl groups and also high in reaction rate and can develop an initial contact strength quickly. In addition to these advantages, it serves to form an adhesive resin layer that is high in the adhesive strength to the base film, and shows stable adhesive strength at high temperatures and excellent long-term durability. Examples of said base resin to be used in combination with this polymer containing an isocyanate group include, for instance, a polyether-, polyester-, or polyol-based urethane resin and epoxy resin, and an appropriate one may be selected to meet detailed required characteristics and processing conditions. Furthermore, depending on the constitution of the solar battery backside sealing sheet, it is likely that ultraviolet rays can reach said adhesive layer to cause photo-degradation of the resin. From this viewpoint, the resin to be used to form the adhesive layer is preferably an aliphatic resin or an alicyclic resin in which aromatic rings do not exist or account for a very small part.

[0048]
[Solar battery backside sealing sheet]
The solar battery backside sealing sheet using a solar battery backside sealing sheet film will be described below. The solar battery backside sealing sheet is required to have various properties typified by, for example, moisture barrier, light reflectivity, long term moist heat resistance and light resistance, high adhesion to cell fillers, and electric insulation. To meet these required characteristics, a variety of efforts are being made in the industrial sector to provide various sheet designs (laminate designs) that combine different functional films with processing techniques such as deposition and wet coating, based on the concept of functional partition.

[0049]
Various solar battery Backside sealing sheets that meet different required properties can be produced by selecting one or more films from the group of a hydrolysis resistant film, a white film, a film with a deposited inorganic oxide layer, and a film that heat-bonds to EVA, which are different from the base film, and laminating them on the solar battery backside sealing sheet film of the present invention. In particular, it is preferable that the solar battery backside sealing sheet which forms the outermost face when built in a solar battery module comprises a hydrolysis resistant film as base film, and that a solar battery backside sealing sheet film is added on the base film. The use of a hydrolysis resistant film serves to prevent the inner layers (adhesive layer, film layer, etc.) which are located under the film, from being hydrolyzed. In addition, since a resin layer having ultraviolet and/or visible light shielding capability and fire retardance is located at the outermost position, the resin layer can serve to protect the inner layers from ultraviolet rays and/or visible light, and control fire spread in case of fire.

[0050]
On the other hand, it is preferable that one or more films selected from the group of a white film, a film with a deposited inorganic oxide, and a film that can heat-bonds to EVA is provided on the opposite side of the base film to the resin layer-laminated side. Light reflectivity develops when a white film is laminated, and moisture barrier property develops when a film with a deposited inorganic oxide layer is laminated. And adhesiveness to cell filler layers develops when a film that can heat-bonds to EVA is laminated. Examples of said film that can heat-bonds to EVA include olefin based films such as EVA film and polyethylene film. Said film to be added on the solar battery backside sealing sheet film of the present invention may not necessarily be a single film, but a solar battery backside sealing sheet may be designed by combining different component films depending on the intended characteristics.

[0051]
In its constitution, the solar battery backside sealing sheet may contain a deposited layer, sputtered layer, wet coating layer, and the like for the purpose of imparting functionalities, to coat any layer other than the resin layer of the invention.

[0052]
Described below are typical methods that can be used for manufacturing a solar battery backside sealing sheet film. As a base film, for example, a hydrolysis resistant polyethylene terephthalate film, such as Lumiror (registered trademark) XI OS manufactured by Toray Industries, Inc., is prepared. Then, a coating material is preparedby mixing a main resin consisting of a fluorine resin, a coloring pigment, and melamine cyanurate dispersed and mixed using a bead mill, together with a nurate type hexamethylene diisocyanate resin as a cross-linking agent, and a solvent. The base film is coated with the coating material by gravure coating to obtain a solar battery backside sealing sheet film. Furthermore, a solar battery backside sealing sheet can be produced by forming, by dry lamination, at least one film selected from the group of a white film, a film with a deposited inorganic oxide, and a film that can heat-bonds to EVA, on the opposite side to the resin layer-laminated side of the solar battery backside sealing sheet
film.

[0053]
If the solar battery backside sealing sheet according to the invention is used to produce a solar battery module, the resin layer of the solar battery backside sealing sheet film faces toward the outer side of the solar battery module, and incorporated in a solar battery module with the solar battery backside sealing sheet being bonded to the cell filler layer.

Examples

[0054]
Next, the solar battery backside sealing sheet film of the present invention and the solar battery backside sealing sheet formed thereof will be described concretely with reference to Examples.

[0055]

The methods used for characteristics evaluation for the invention are as described below.

[0056]

(1) Measurement of coating weitght for resin layer
A solar battery backside sealing sheet film was cut into test pieces with an area of 500 cm2 after resin layer formation, and the mass of each test piece, referred to as mass (1) [g], was measured. Next, from the test piece, the resin layer was dissolved and removed in methyl ethyl ketone, and the mass of the test piece, referred to as mass (2) [g], was measured again. Subsequently, the coating amount per unit area was calculated by the following equation. Coating amount measurements were made for three test pieces, and their average was determined to represent their coating amount. • Coating amount [g/m2] = {(mass (1)) - (mass (2))} x 20

[0057]
(2) Evaluation for solvent resistance
A sample was immersed in ethanol for 5 minutes, and subsequently rubbed 50 times with Kimwipe. -Then, the appearance of the coat film was visually observed and classified as follows.

A: No change found in the state of the coat film compared with untreated sample.

B: Peeling found between the base material and the coat film.

[0058]
(3) Evaluation for ultraviolet screening capability (spectroscopic measurement) Sspectroscopic measurement was carried out according to JIS K 7105 (2006). The measuring equipment used was a UV-3150 UV/VIS/NIR spectrophotometer supplied by Shimadzu Corporation. The ultraviolet screening capability of the solar battery backside sealing sheet film was evaluated based on transmittance measurements at a wavelength of 360 nm.

[0059]
(4) Evaluation for strength of contact between base film and resin layer To evaluate the strength of contact (coat layer contact strength) between the base film and the resin layer in the solar battery backside sealing sheet film prepared, test pieceswere subjected to crosscut test according to the method described in JIS K 5400 (1990).

Results were classified as flows.
AA: 100 out of 100 coat film squares remaining
A: 81 to 99 out of 100 coat film squares remaining
B: 80 or less out of 100 coat film squares remaining

[0060]
(5) Evaluation for ultraviolet resistance
Ultraviolet irradiation with a strength of 160 mW/cm2 was performed for 240 hours in a 60°C x 50% RH atmosphere. The measuring equipment used was Eye Super UV Tester SUV-W151 manufactured by Iwasaki Electric Co., Ltd. The b-value in the color system was measured before and after ultraviolet irradiation, and the value of Ab was calculated by the following equation.

■ Ab = (b-value after ultraviolet irradiation) - (b-value before ultraviolet irradiation)
Ultraviolet irradiation was performed similarly for "(3) evaluation of ultraviolet screening capability" and "(4) evaluation of adhesion strength between the base film and the resin layer" before and after the irradiation for the purpose of evaluating the ultraviolet resistance of these properties.

[0061]

(6) Evaluation for moist heat resistance
Test pieces of the solar battery backside sealing sheet film were heat-treated for 48 hours in an environment of 120°C and 100% RH. The test apparatus used was a TPS-211 pressure cooker manufactured by Espec Corp. Subsequently, the solar battery backside sealing sheet film was subjected to "(3) evaluation of ultraviolet screening capability" and "(4) evaluation of the adhesion strength between the base film and the resin layer" for the purpose of evaluating the moist heat resistance of these properties.

[0062]
(7) Evaluation for flame resistance
Horizontal burning (HB) test was performed according to UL94 and evaluations were made as follows.

A: acceptable in HB test
B: rejectable in HB test

[0063]
(8) Evaluation for blocking resistance
A resin layer was formed on a film, and 10 pieces of 5 cm x 5 cm were cut out from it.

They were stacked in such a way that the resin layer of each film piece faced the base film face of another film piece. Then, using a model DG-BT ink blocking tester supplied by DG Engineering K.K., they were aged at 40°C for three days under a load of 5 kg/cm . Subsequently, the adhesion between resin layers and base films was evaluated according to the following criteria.

A: inadequate adhesion between resin layers and base films
B: adequate adhesion between resin layers and base films

[0064]
(9) Evaluation for chalking resistance
A resin layer was formed on a film, which was then aged for three days in an environment at 40°C. After aging, the surface of the resin layer was observed and evaluated as follows.

A: free from chalking on the surface of the resin layer
B: chalking found on the surface of the resin layer

[0065]
(10) Measurement of strength of adhesion to filler (EVA adhesion strength)
An EVA sheet was put on the inner side surface of a solar battery backside sealing sheet (opposite side of the base film to the resin layer-laminated side), and a 3 mm thick semi-tempered glass plate is put on top of it. After vacuuming, a commercially available glass laminator was used to press them for 15 minutes under a load of 3 kgf/cm at an elevated temperature of 135°C to prepare a sample of a pseudo solar battery module. An EVA sheet with a thickness of 500 um supplied by Sanvic Inc. was used.
This sample of a pseudo solar battery module was used to measure the strength of adhesion to the EVA sheet according to JIS K 6854-2 (1999). Test pieces with a width of 10 mm were used for the adhesion strength test, and one measurement was made for each of two test pieces. The average of the two measurements was used to represent the adhesion strength. A test piece was assumed to be practically acceptable if the adhesive strength was 100 N/50 mm or more.

(11) Light reflectance
A sample of a pseudo solar battery module was prepared by the same procedures as in item (10). Light was applied to the glass side of the pseudo solar battery module sample, and the light reflectance of the inner side of the backside sealing sheet (opposite side to the resin layer-laminated surface of the base film) was measured. For reflectance determination, measurements made at a wavelength of 600 nm were used to represent the reflectance. The measuring apparatus used was a MPC-3100 spectrophotometer manufactured by Shimadzu Corporation.

[0067]
(12) Measurement of water vapor transmittance
Vapor transmittance was measured under the conditions of a temperature of 40°C and a humidity of 90%RH according to the B method (infrared sensing) specified in JIS K7129 (2000). The measuring equipment was a Permatran (registered trademark) W3/31 water vapor transmittance tester supplied by Mocon, Inc., U.S.A.). A measurement of water vapor transmittance was made for each of two test pieces, and their average was taken for evaluation.

[0068]

(Preparation of resin layer forming paint 1)
The fluorine based resin used here was Zeffle (registered trademark) GK570 (solid content: 65 mass%), which is a hydroxyl-containing TFE resin coating agent supplied by Daikin Industries, Ltd. The fluorine based resin was mixed with a color pigment, melamine cyanurate, and solvent into a mixture as specified in Table 1 and dispersed in a bead mill to provide a base paint with a solid content of 50 mass%. The color pigments used were as listed below.

■ White pigment: titanium oxide particles, JR-709 supplied by Tayca Corporation
■ Black pigment: carbon black particles, Special Black 4A supplied by Degussa AG The base paint was mixed with a nurate-type hexamethylene diisocyanate resin, Desmodur (registered trademark) N3300 (solid content: 100 mass%) supplied by Sumitomo Bayer Urethane Co., Ltd. to provide a micture with a mass ratio of base paint to nurate-type hexamethylene diisocyanate resin of 100/2. Furthermore, n-propyl acetate was added as diluent and stirred for 15 minutes to provide a paint having a solid content of 40 mass% (solid resin concentration). Thus, resin layer forming paint 1 with a solid content (solid resin concentration) of 40 mass% was prepared.

[0069]
(Preparation of resin layer forming paint 2)
Except that the initial mixture was prepared as specified in Table 1 with a color pigment
content of 80 mass% and a melamine cyanurate content of 1 mass% relative to the total
solid resin, the same procedure as for the preparation of resin layer forming paint 1 was
carried out to provide resin layer forming paint 2.

[0070]
(Preparation of resin layer forming paint 3)
Except that the initial mixture was prepared as specified in Table 1 with a color pigment content of 30 mass% and a melamine cyanurate content of 30 mass% relative to the total solid resin, the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 3.

[0071]
(Preparation of resin layer forming paint 4)
Except that the initial mixture was prepared as specified in Table 1 with a color pigment content of 85 mass% and a melamine cyanurate content of 1 mass% relative to the total solid resin, the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 4.

[0072]
(Preparation of resin layer forming paint 5)
Except that the initial mixture was prepared as specified in Table 1 with a color pigment content of 20 mass% and a melamine cyanurate content of 30 mass% relative to the total solid resin, the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 5.

[0073]
(Preparation of resin layer forming paint 6)
Except that the initial mixture was prepared as specified in Table 1 with a color pigment content of 30 mass% and a melamine cyanurate content of 40 mass% relative to the total solid resin, the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 6.

[0074]
(Preparation of resin layer forming paint 7)
Except that the initial mixture was prepared as specified in Table 1 with a color pigment content of 80 mass% and a melamine cyanurate content of 0.5 mass% relative to the total solid resin, the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 7.

[0075]
(Preparation of resin layer forming paint 8)
Except that Desmodur (registered trademark) N3200 (solid content: 100 mass%), a biuret type examethylene diisocyanate resin supplied by Sumika Bayer Urethane Co., Ltd., was used instead of a nurate type hexamethylene diisocyanate resin, the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 8.

[0076]
(Preparation of resin layer forming paint 9)
Except that a resin material (solid content: 40 mass%) prepared by adding an ultraviolet absorber and a light stabilization agent (HALS) to an acrylic resin produced from methyl methacrylic acid and 2-hydroxyethyl methacrylate was used instead of Zeffle (registered trademark) GK570 (solid content: 65 mass%), which is a hydroxyl-containing TFE resin coating agent supplied by Daikin Industries, Ltd., the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 9.

[0077]
(Preparation of resin layer forming paint 10)
Except that components were mixed as shown in Table 2 without using a color pigment, the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 10.

[0078]
(Preparation of resin layer forming paint 11)
Except that components were mixed as shown in Table 2 without using a melamine cyanurate, the same procedure as for the preparation of resin layer forming paint 1 was carried out to provide resin layer forming paint 11.

[0080]
(Preparation of adhesive for dry lamination)
A mixture of 16 parts of a dry lamination material (Dicdry (registered trademark)
LX-903 supplied by DIC Corporation), 2 parts by mass of a curing agent (KL-75 supplied by Dainippon Ink and Chemicals, Inc.), and 29.5 parts by mass of ethyl acetate was weighed out and stirred for 15 minutes. Thus, an adhesive for dry lamination with a solid content of 20 mass% was prepared.

[0081]
(Preparation of adhesive layer forming paint)
A mixture of 12 parts by mass of a dry lamination material (polyester polyurethane resin, Takelac (registered trademark) A-310 supplied by Mitsui Chemicals Polyurethanes, Inc.), 1 part by mass of an aromatic polyisocyanate resin (Takenate (registered trademark) A-3 supplied by Mitsui Chemicals Polyurethanes, Inc.), and 212 parts by mass of ethyl acetate was weighed out and stirred for 15 minutes. Thus, an adhesive layer forming paint with a solid content of 3 mass% was prepared.

[0082]
(Preparation of heat-bonding resin layer forming paint)
A mixture of 20 parts by mass of an aqueous emulsion paint containing EVA type ternary copolymer resin (Aquatex (registered trademark) MC-3800 supplied by CSC Co., Ltd.), 10.8 parts by mass of isopropyl alcohol, and 22.6 parts by mass of water was weighed out and stirred for 15 minutes. Thus, a heat-bonding resin layer forming paint with a solid content of 15 mass% was prepared.

[0083]
(Example 1)
The base film used was a hydrolysis resistant polyethylene terephthalate film with a cyclic trimer content of 1 wt% or less (Lumiror (registered trademark) XI OS (125 urn) supplied by Toray Industries, Inc.). Resin layer forming paint 1 was spread with a wire bar over one side of this base film and dried at 150°C for 60 seconds to form a resin layer which had a coating weight of 15.0 g/m2 after drying. Thus, solar battery backside sealing sheet film 1 was produced.

[0084]
(Example 2)
Except that resin layer forming paint 2 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside sealing sheet film 2.

[0085]
(Example 3)
Except that resin layer forming paint 3 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside sealing sheet film 3.

[0086]
(Example 4)
Except that resin layer forming paint 4 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside sealing sheet film 4.

[0087]
(Example 5)
Except that resin layer forming paint 5 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside sealing sheet film 5.

[0088]
(Example 6)
Except that resin layer forming paint 6 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside sealing sheet film 6.

[0089]
(Example 7)
Except that resin layer forming paint 7 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside
sealing sheet film 7.

[0090]
(Example 8)
Except that resin layer forming paint 8 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside sealing sheet film 8.

[0091]
(Comparative example 1)
Except that resin layer forming paint 9 was applied instead of resin layer forming paint
1, the same procedure as in Example 1 was carried out to produce solar battery backside
sealing sheet film 9.

[0092]

(Comparative example 2)
Except that resin layer forming paint 10 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside sealing sheet film 10.

[0093]
(Comparative example 3)
Except that resin layer forming paint 11 was applied instead of resin layer forming paint 1, the same procedure as in Example 1 was carried out to produce solar battery backside sealing sheet film 11.

[0094]
(Comparative example 4)
Lumiror (registered trademark) XIOS (supplied by Toray Industries, Inc., 125 um) was
used as solar battery backside sealing sheet film 15 without forming a resin layer.

[0095]
Characteristics of the solar battery backside sealing sheet films produced above in Examples 1 to 8 and Comparative examples 1 to 4 were evaluated by the evaluation methods described above. Results are shown in Tables 2 and 3.

[0098]
(Evaluation for Examples 1 to 8)
All solar battery backside sealing sheet films 1 to 8 produced in Example 1 to 8,
respectively, were high in ultraviolet resistance (Ab value), coat layer contact strength
after moist heat test and after ultraviolet ray irradiation, and ultraviolet screening
capability after moist heat test and after ultraviolet ray irradiation.

[0099]
(Evaluation for Examples 1-3)
In particular, solar battery backside sealing sheet films 1 to 3 produced in Example 1 to 3 had a color pigment content in the range of 30 to 80 mass% and a melamine cyanurate content in the range of 1 to 30 mass% in the resin layer, and were also good in fire retardance, blocking resistance, chalking resistance, and solvent resistance. Here, the coat layer contact strength after moist heat test tended to decrease as the color pigment content approached 80 mass%, due to a decrease in resin quantity and hardening of the coat layer. It was also seen that an increase in the Ab value due to a decrease in
ultraviolet screening capability, that is, an increase in the b-value after ultraviolet irradiation took place as the pigment content approached 30 mass%.

[0100]
(Evaluation for Examples 4 and 5)
Solar battery backside sealing sheet film 4 produced in Example 4, in which a color pigment accounted for 85 mass% of the resin layer, suffered from chalking on the resin layer surface due to the large color pigment content. In addition, the coat layer contact strength after moist heat test slightly decreased due to a smaller quantity of the resin component in the resin layer.

Solar battery backside sealing sheet film 5 produced in Example 5 was lower in fire retardance than the films produced in Examples 1 to 3, due to a smaller color pigment content of 20 mass% in the resin layer. In addition, blocking took place due to a large resin content of 50 mass% in the resin layer.

[0101]
(Evaluation for Examples 6 and 7)
Solar battery backside sealing sheet film 6 produced in Example 6, in which melamine cyanurate accounted for 40 mass% in the resin layer, was lower in solvent resistance than the films produced in Examples 1 to 3, due to the large melamine cyanurate content.

Solar battery backside sealing sheet film 7 produced in Example 7 suffered from blocking due to a small melamine cyanurate content of 0.5 mass% in the resin layer. In addition, the coat layer contact strength after moist heat test slightly decreased due to a smaller resin content in the resin layer.

[0102]
(Evaluation for Example 8)
For solar battery backside sealing sheet film 8 produced in Example 8, a biuret type hexamethylene diisocyanate resin was used as curing agent instead of a nurate type resin, resulting in insufficient curing of the coat layer and accordingly, a deterioration in solvent resistance.

[0103]
(Evaluation for Example 1)
Solar battery backside sealing sheet film 9 produced in Comparative example 1 comprised acrylic resin containing an ultraviolet absorber and a light stabilization agent (HALS), instead of fluorine based resin, to form resin layer. Accordingly, ultraviolet irradiation caused the ultraviolet absorber and light stabilization agent to bleed out from inside the resin layer to the resin layer surface, resulting in a decrease in ultraviolet screening capability and an increase in the Ab value of the base film. The fire retardance
was also poor.

[0104]

(Evaluation for Example 2)
Solar battery backside sealing sheet film 10 produced in Comparative example 2 did not contain a color pigment in the resin layer. Accordingly, it was low in ultraviolet screening capability, and the Ab value of the base film after ultraviolet irradiation increased, causing the film to be yellowed. The fire retardance was also poor because no color pigment was contained. In addition, blocking took place due to a large resin content in the resin layer.

[0105]
(Evaluation for Example 3)
Solar battery backside sealing sheet film 11 produced in Comparative example 3 did not contain melamine cyanurate in the resin layer. Accordingly, blocking took place. Coat layer contact strength after moist heat test also decreased slightly.

[0106]
(Evaluation for Example 4)
Solar battery backside sealing sheet film 12 used in Comparative example 4 (which was as-obtained Lumirror (registered trademark) XI OS film without a resin layer formed on it) did not have ultraviolet screening capability, and no color pigment layer for controlling the color tone of the film was formed. Accordingly, ultraviolet irradiation caused an increase in the Ab value of the base film, causing the film to be yellowed. This suggests that when it is used as the outermost layer of a solar battery backside
sealing sheet, cracks and pinhols can took place in the film in extreme cases, possibly leading not only to loss of characteristics required of a sealing sheet, such as electrical insulating properties and moisture barrier properties, but also to adverse influence on the operation of the solar battery module. Furthermore, no resin layer containing a color pigment was formed, resulting in inferior fire retardance.

[0107]
(Example 9)
Lumirror (registered trademark) E20F (50 urn) supplied by Toray Industries, Inc., which is a white polyethylene terephthalate film, was used as light reflectivity film. To provide a moisture barrier film, the opposite surface to the alumina deposition layer of an alumina deposition polyethylene terephthalate film (Barrier-Locks (registered trademark) 1031HGTS (12 um) supplied by Toray Advanced Film Co., Ltd.) was coated with a paint for adhesive layer formation and a paint for heat-bonding resin layer
formation applied in this order with a double-head tandem type direct gravure coater under the following conditions to produce a film.

• Adhesive layer coating conditions: target dried film thickness of 0.2 um, drier oven temperature setting of 120°C

• Heat-bonding resin layer coating conditions: target dried film thickness of 1.0 um,
drier oven temperature setting of 100°C

■ Coating speed: 100 m/min

• Aging: aging at 40°C for 2 days after coating and wind-up

[0108]
An adhesive for dry lamination was spread with a wire bar over the base film surface located opposite to the resin layer of solar battery backside sealing sheet film 1 produced as in Example 1, and dried at 80°C for 45 seconds to form an adhesive layer of 3.5 um. Then, a light reflective film was bonded to this adhesive layer using a hand roller. In addition, an adhesive for dry lamination was spread with a wire bar over the light reflectivity film surface located opposite to the resin layer of this laminate film, and dried at 80°C for 45 seconds to form an adhesive layer of 3.5 um. Subsequently, the alumina deposition layer surface of a moisture barrier film was bonded to this adhesive layer using a hand roller. Solar battery backside sealing sheet 1 was produced by aging a sheet composed of three films prepared in this way for three days in an oven heated at 40°C.

[0109]
(Example 10)
Solar battery backside sealing sheet 2 was produced by the same procedure as in Example 9, except that a white polyethylene film (150 um) supplied by Toray Advanced Film Co., Ltd., which has high adhesiveness to the EVA sheet, was used instead of E20F and a moisture barrier film.

[0110]
(Comparative example 5)
Except that solar battery backside sealing sheet film 10 produced in Comparative example 2 was used instead of solar battery backside sealing sheet film 1, the same procedure as in Example 9 was carried out to produce solar battery backside sealing Sheet 3.

[0111]
(Comparative example 6)
Except that solar battery backside sealing sheet film 12 produced in Comparative example 4 was used instead of solar battery backside sealing sheet film 1, the same procedure as in Example 9 was carried out to produce solar battery backside sealing sheet 4.


[0114]
(Evaluation for Examples 9 and 10)
Both solar battery backside sealing sheets 1 and 2 produced in Examples 9 and 10, respectively, were free from a decrease in contact strength between the base film and the resin layer attributable to ultraviolet ray applied to the resin layer located on the outermost side of the solar battery module. The resin layer and the base film were yellowed only slightly. The solar battery backside sealing sheets were also high in the strength of contact with fillers (EVA resin), which is an essential property required of
these sheets. Furthermore, sealing sheet 1, which comprised a water vapor barrier film, had good moisture barrier properties.

[0115]
(Evaluation for Example 5)
Being free from a color pigment in the outermost resin layer, solar battery backside sealing sheet 3 produced in Comparative example 5 did not have the advantage of hiding the wiring patterns and the like in the module and suffered from a change in color tone (increase in Ab value) in the sheet appearance. This suggests that long-term exposure to ultraviolet ray can cause degradation of the base film.

[0116]
(Evaluation for Example 6)
Solar battery backside sealing sheet 4 produced in Comparative example 6 had no resin layer formed on the outermost side. Thus, it had no resin layer to serve for blocking ultraviolet rays and accordingly, had no ultraviolet resistance. Therefore, it cannot be used for a solar battery module such as of field installation type that is expected to be installed in a location where it is exposed to ultraviolet rays reflected from the ground surface and the like.

[Industrial applicability]

[0117]
The solar battery backside sealing sheet film of the present invention is high in light resistance and moist heat resistance, and can be suitable for producing solar battery backside sealing sheets. Furthermore, a preferred embodiment of this invention of the solar battery backside sealing sheet film is high in fire retardance, and can be suitable for producing solar battery backside sealing sheets. These solar battery backside sealing sheets can be suitable for producing solar battery modules.

Claims
[Claim 1]

A solar battery backside sealing sheet film comprising a resin layer containing fluorine based resin, a color pigment, and melamine cyanurate, which is laminated on at least one surface of a base film.

[Claim 2]
A solar battery backside sealing sheet film as claimed in claim 1 wherein the resin layer contains a color pigment and melamine cyanurate that account for 30 to 80 mass% and 1 to 30 mass%, respectively, of the entire resin layer.

[Claim 3]
A solar battery backside sealing sheet film as claimed in either claim 1 or 2 wherein the resin layer contains at least one polyisocyanate resin selected from the group consisting of aromatic polyisocyanate resin, araliphatic polyisocyanate resin, alicyclic polyisocyanate resin, and aliphatic polyisocyanate resin.

[Claim 4]
A solar battery backside sealing sheet comprising a solar battery backside sealing sheet film as claimed in any of claims 1 to 3.

[Claim 5]
A solar battery backside sealing sheet wherein at least one film selected from the group consisting of a white film, a film with a deposited inorganic oxide layer, and a film that can heat-bonds to ethylene vinyl acetate copolymers, is laminated on the opposite side to the resin layer-laminated side of a solar battery backside sealing sheet film as claimed in any of claims 1 to 3.

[Claim 6]
A solar battery module comprising a solar battery backside sealing sheet as claimed in either Claim 4 or 5 and a cell filler layer wherein the solar battery backside sealing sheet and the cell filler layer are bonded together.