JP2012176608A - Surface protective material for solar cell, and solar cell module produced using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface protective material for a highly moisture-resistant solar cell, having a moisture-resistant film that has an inorganic thin film layer on one surface of a base material and that has a moisture vapor transmission rate of less than 0.1 g/m/day, wherein the surface protective material exhibits excellent moisture resistance that does not deteriorate for an extended period.SOLUTION: This surface protective material for a solar cell, having a moisture-resistant film that has an inorganic thin film layer on one surface of a base material and that has a moisture vapor transmission rate of less than 0.1 g/m/day, is characterized in having a weather-resistant film on the inorganic thin film layer side of the moisture-resistant film, and in having a back face film of a melting point of 130°C to 180°C inclusive, on the opposite side of the moisture-resistant film from the inorganic thin film layer, directly or via an adhesive layer.

Description

  The present invention relates to a highly moisture-proof surface protection material for solar cells having a moisture-proof film including an inorganic thin film layer, and uses the surface protection material for solar cells that does not deteriorate moisture resistance for a long time and the surface protection material for solar cells. The present invention relates to a highly durable solar cell module.

In recent years, solar cells that directly convert sunlight into electric energy have attracted attention and are being developed from the viewpoint of effective use of resources and prevention of environmental pollution. Solar cells consist of a structure in which cells for solar cells are sealed with a sealing material such as an ethylene-vinyl acetate copolymer, polyethylene, or polypropylene film between the upper protective material on the light receiving surface side and the upper protective material. The upper protective material, the sealing material, the power generation element (solar cell element), the sealing material and the lower protective material are laminated in this order, and are manufactured by bonding and integration by heating and melting.
Solar cell upper and lower protective materials (hereinafter sometimes referred to as “surface protective materials”) include durability against ultraviolet rays, deterioration of solar cell elements due to moisture or water permeation, internal conductors and electrodes It is a very important requirement to have excellent moisture resistance for preventing rusting.
In order to satisfy such requirements, as the surface protective material for solar cells, for example, from the exposed surface side, a weather-resistant film, a moisture-proof film having an inorganic thin film deposited surface on the exposed surface side, and adhesion such as a sealing material In addition, a laminated structure including a film having partial discharge resistance characteristics has been proposed.

For example, in the Example of patent document 1, the surface for solar cells obtained by providing a polyurethane adhesive layer on both sides of a moisture-proof film based on a biaxially stretched polyester film and laminating a weather-resistant polyester film on both sides thereof A protective material is disclosed.
Moreover, in the Example of patent document 2, the surface for solar cells which bonded the polyvinyl fluoride (PVF) film to the moisture-proof film which used the biaxially-stretched polyester film as a base material using the two-component curing type polyurethane-type adhesive agent similarly. A protective material is disclosed.
In Patent Document 3, a weather resistant resin layer having weather resistance is provided on the back surface, the weather resistant resin layer, a first vapor deposited resin layer having a metal oxide vapor deposited film on one surface, an intermediate resin layer, And a second vapor-deposited resin layer having a metal oxide vapor-deposited film on one surface, the back protective sheet for a solar cell module laminated by dry lamination, wherein the first vapor-deposited resin layer and the second vapor-deposited layer A back protective sheet for a solar cell module is disclosed in which a vapor deposition film of a resin layer is disposed on the intermediate resin layer side.
Furthermore, in Patent Document 4, there is provided a method for producing a back surface protection sheet for a solar cell module comprising a weather resistant resin layer having weather resistance on the back surface, wherein the weather resistant resin layer and a metal oxide vapor deposition film on one surface are provided. At least three vapor-deposited resin layers having a water vapor transmission rate are sequentially laminated by dry laminating, and each vapor-deposited resin layer has a water vapor permeability of 0.03 to 0.5 g / m ² · day at 40 ° C. and 90% RH, respectively. The manufacturing method of the back surface protection sheet for solar cell modules characterized by these is disclosed.

JP2009-188072 JP2009-49252 JP 2010-272761 JP 2010-272762 A

  When the surface protective material is incorporated into the solar cell, the surface protective material is laminated with another member and bonded and integrated by vacuum lamination, for example, under conditions of a temperature of 130 ° C. to 180 ° C. and a time of 10 minutes to 40 minutes. This lamination temperature is much higher than the acceleration test disclosed in the above-mentioned patent document of the conventional surface protective material, and serious damage is caused to the surface protective material. Consider the influence of this vacuum lamination process especially when using compound-based power generation element solar cell modules that require high moisture-proof performance and solar cell modules that do not use glass that requires flexibility as protective materials for solar cells. However, it is required to prevent deterioration of moisture resistance after the acceleration test.

However, in any of the above patent documents, a surface protective material using a high moisture-proof film having a water vapor transmission rate of less than 0.1 [g / m ² · day] is laminated and integrated with other members through a vacuum lamination process. Disclosed is a surface protective material for solar cells that does not assume deterioration of moisture-proof performance due to the above, and that maintains moisture-proof performance for a long period of time even after passing through high-temperature conditions such as a temperature of 130 ° C. to 180 ° C. and a time of 10 minutes to 40 minutes. It wasn't something to do.

In the example of Patent Document 1, only the 85 ° C., 85% humidity, 1000 hrs test was performed as the surface protective material for solar cells, and the results of evaluating the moisture resistance thereafter were shown. The rate is only 1 to 2 [g / m ² · day], and Patent Document 2 discloses a pressure cooker test (PCT: severe due to high temperature and pressure) as a surface protection material for solar cells. As a result of performing only an environmental test, 105 ° C., 92 hours) and evaluating the moisture resistance after that, only water vapor permeability after the test of 0.5 [g / m ² · day] is disclosed. .
Patent Documents 3 and 4 show the results of evaluating the initial moisture resistance as a solar cell surface protective material prepared by dry laminating, but the solar cell surface protective material has a temperature of 130. Even after a high temperature condition of from 10 to 180 ° C. and from 10 to 40 minutes, it did not have sufficient moisture-proof performance.

That is, the object of the present invention is to provide a highly moisture-proof solar cell surface using a highly moisture-proof film having an inorganic thin film layer on one surface of the substrate and having a water vapor transmission rate of less than 0.1 [g / m ² · day]. Providing an excellent surface protection material that does not deteriorate moisture resistance over a long period of time after high-temperature treatment such as vacuum lamination in a protective material, and a solar cell excellent in durability using the surface protection material for solar cells To provide a module.

As a result of intensive studies, the present inventors have determined that the structure of the solar cell surface protective material is an inorganic high moisture-proof film having an inorganic thin film layer and a water vapor transmission rate of less than 0.1 [g / m ² · day]. A film having a weather resistance film on the thin film layer side and having a specific melting point on the opposite side of the highly moisture-proof film to the inorganic thin film layer (hereinafter sometimes referred to as “rear surface”) It is found that long-term excellent moisture resistance and interlaminar strength can be satisfied at the same time, and durability of moisture resistance performance is realized by arranging the film to be combined (sometimes called "back film"), The present invention has been completed.

That is, the present invention
(1) A surface protection material for a solar cell having an inorganic thin film layer on one surface of a substrate and having a moisture-proof film having a water vapor transmission rate of less than 0.1 [g / m ² · day], Having a weather resistant film on the inorganic thin film layer side of the film, and having a back film having a melting point of 130 ° C. or higher and 180 ° C. or lower directly or via an adhesive layer on the opposite side of the moisture-proof film to the inorganic thin film layer A surface protection material for solar cells,
(2) The surface protective material for solar cells according to (1) above, wherein the moisture-proof film has a water vapor permeability of 0.05 [g / m ² · day] or less,
(3) The surface protective material for solar cells according to (1), wherein the moisture-proof film has a water vapor permeability of 0.01 [g / m ² · day] or less,

(4) The solar cell according to any one of (1) to (3), wherein the back film contains at least one resin selected from polypropylene, polylactic acid, polyvinyl fluoride, and polyvinylidene fluoride as a main component. Surface protection material,
(5) The surface protective material for a solar cell according to any one of (1) to (4), wherein the thickness of the back film is 25 μm or more and 300 μm or less,
(6) The solar cell surface protective material according to any one of (1) to (5), wherein the base material is a polyester-based resin film.
(7) The surface protective material for solar cells according to any one of the above (1) to (6), which has an adhesive layer between the moisture-proof film and the back film,
(8) The solar cell surface protective material according to any one of the above (1) to (7), which has the back film and the plastic film in this order on the opposite side of the moisture-proof film to the inorganic thin film layer,
(9) The surface protective material for a solar cell according to any one of (1) to (8), further including a sealing material,
(10) A solar cell module produced using the solar cell surface protective material according to any one of (1) to (9) above,
Exist.
In the present invention, “◯ or more and Δ or less” may be expressed as “O to Δ”.

  According to the present invention, in the surface protective material for high moisture-proof solar cells having a moisture-proof film having an inorganic thin film layer on one surface of the substrate and having a moisture-proof film having a moisture content of less than 0.1 [g / m 2 · day], Providing an excellent surface protection material that does not deteriorate moisture resistance over a long period of time after high-temperature treatment such as vacuum lamination, and also providing a solar cell module with excellent durability using the surface protection material for solar cells. be able to.

The present invention is described in further detail below.
Usually, the surface protection material for solar cells is produced through a lamination process by dry lamination. In dry lamination, an adhesive diluted with a solvent is applied to a weather resistant film to a predetermined thickness, and the solvent is evaporated by drying in the range of 100 ° C. to 140 ° C. to form an adhesive layer on the weather resistant film. The moisture-proof film is bonded with the inorganic thin film surface facing the adhesive. Thereafter, an adhesive diluted with a solvent in the same manner as described above was applied to the back surface of the moisture-proof film to a predetermined thickness, and the solvent was evaporated by drying in the range of 100 ° C. to 140 ° C. to form an adhesive layer on the moisture-proof film. Then, a film is further bonded and a surface protective material is created through curing at a predetermined temperature. Curing is usually carried out in the range of 30 ° C. to 80 ° C. for 1 day to 1 week. In this lamination process, heat and bonding tension act on each film, and residual strain is accumulated in the surface protective material.

Next, the surface protective material is heated and melted by vacuum lamination together with the solar cell element and the sealing material, and is integrated into the solar cell. This vacuum lamination process is performed in the range of 130 ° C to 180 ° C.
The residual strain accumulated in the above lamination process acts as a stress on each lamination interface when the solar cell is stored in a high temperature and high humidity environment. In particular, when residual strain accumulates on the back film, stress from the back surface acts on the inorganic thin film layer in a high-temperature and high-humidity environment, causing serious deterioration of the inorganic thin film layer.
In particular, in the case of a moisture-proof film having a high moisture-proof property with a water vapor excess rate of less than 0.1 [g / m ² · day] targeted by the present application, the deterioration of the moisture-proof performance due to stress from the back film is significant. This is because the stress from the back film has a significant effect on the inside of the inorganic thin film layer, and on each layer of the moisture-proof film substrate, anchor coat layer, and inorganic thin film layer, and the degree of deterioration of the moisture-proof performance that is impaired by this, This is because the higher the initial moisture-proof performance, the larger.

  From the above, the present inventors reduced the stress acting on the inorganic thin film layer of the moisture-proof film in a high-temperature and high-humidity environment by reducing the residual strain in the back film in the vacuum lamination process, and suppressed deterioration of moisture-proof performance. It came to find out to realize.

<Surface protective material>
The surface protective material for solar cells in the present invention is a surface protective material for solar cells having a highly moisture-proof film having an inorganic thin film layer on one surface of the substrate and having a water vapor transmission rate of less than 0.1 [g / m ² · day]. A material having a weather resistant film on the inorganic thin film layer side of the moisture-proof film, and 130 ° C. or higher and 180 ° C. directly or via an adhesive layer made of an adhesive on the back surface of the inorganic thin film layer of the moisture-proof film. It has a back film having the following melting point.

Hereinafter, each constituent layer will be described.
(Weather-resistant film)
The surface protection material for solar cells of the present invention has hydrolysis resistance and light resistance, and a weather resistant film is laminated on the inorganic thin film layer side of the moisture proof film in order to impart long-term durability. In addition, when a moisture-proof film has an inorganic thin film layer on both surfaces of a base material, a weather resistant film is laminated | stacked on the exposed surface side of a moisture-proof film.
The weather-resistant film is not particularly limited as long as it has weather resistance. For example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoro Fluorine resin films such as propylene copolymer (FEP), tetrafluoroethylene / ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), or A resin composition obtained by mixing an ultraviolet absorber with a resin such as acrylic, polycarbonate, polyethylene terephthalate (PET), or polyethylene naphthalate (PEN) is preferably used.

From the viewpoint of long-term durability, tetrafluoroethylene / ethylene copolymer (ETFE) and tetrafluoroethylene / hexafluoropropylene copolymer (FEP) are more preferably used as the resin.
A low-shrinkage weathering substrate such as polyethylene naphthalate is preferred because the change in characteristics is preferably small even in temperature / humidity changes during vacuum lamination and high temperature and high humidity. Further, in the case of a polyethylene terephthalate film or a fluorine-based film having a large shrinkage rate, it is preferable to use a film that has been subjected to low shrinkage or the like by prior heat treatment.

Considering both long-term weather resistance and film shrinkage, a film obtained by forming a resin composition in which an ultraviolet absorber is mixed with a polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) A film in which a layer containing an ultraviolet absorber is provided on a film obtained by forming a resin composition such as a polyester resin is preferably used.
Also, considering use in solar cell protective materials, it is desirable to be a weather-resistant film that is highly flexible and has excellent heat resistance, moisture resistance, and UV durability, and contains a fluorine-based film and UV absorber. A film in which a layer containing an ultraviolet absorber is provided on a hydrolysis-resistant polyester film or a hydrolysis-resistant polyester film is preferably used.

As the ultraviolet absorber to be used, various commercially available products can be applied, and examples thereof include various types such as benzophenone, benzotriazole, triazine, and salicylic acid ester. Examples of the benzophenone-based UV absorber include 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2′-carboxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-n. -Dodecyloxybenzophenone, 2-hydroxy-4-n-octadecyloxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, 2-hydroxy-5-chlorobenzophenone, 2, , 4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4, 4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, etc. But Kill.
The benzotriazole ultraviolet absorber is a hydroxyphenyl-substituted benzotriazole compound, for example, 2- (2-hydroxy-5-methylphenyl) benzotriazole, 2- (2-hydroxy-5-t-butylphenyl) Benzotriazole, 2- (2-hydroxy-3,5-dimethylphenyl) benzotriazole, 2- (2-methyl-4-hydroxyphenyl) benzotriazole, 2- (2-hydroxy-3-methyl-5-t- Butylphenyl) benzotriazole, 2- (2-hydroxy-3,5-di-t-amylphenyl) benzotriazole, 2- (2-hydroxy-3,5-di-t-butylphenyl) benzotriazole, etc. be able to. Examples of triazine ultraviolet absorbers include 2- [4,6-bis (2,4-dimethylphenyl) -1,3,5-triazin-2-yl] -5- (octyloxy) phenol, 2- ( And 4,6-diphenyl-1,3,5-triazin-2-yl) -5- (hexyloxy) phenol. Examples of salicylic acid esters include phenyl salicylate and p-octylphenyl salicylate.

The addition amount of the ultraviolet absorber is usually about 0.01 to 2.0% by mass and preferably 0.05 to 0.5% by mass in the weather resistant film.
A hindered amine light stabilizer is suitably used as a weather stabilizer that imparts weather resistance in addition to the above ultraviolet absorber. A hindered amine light stabilizer does not absorb ultraviolet rays like an ultraviolet absorber, but exhibits a remarkable synergistic effect when used together with an ultraviolet absorber.

  Examples of hindered amine light stabilizers include dimethyl succinate-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, poly [{6- (1,1 , 3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {{2, 2,6,6-tetramethyl-4-piperidyl} imino}], N, N′-bis (3-aminopropyl) ethylenediamine-2,4-bis [N-butyl-N- (1,2,2, 6,6-pentamethyl-4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate, bis (2,2,6,6-tetramethyl-4-piperidyl) separate, 2- (3 , 5-Di-tert-4- Mud alkoxybenzylacetic) -2-n-butyl malonic acid bis (1,2,2,6,6-pentamethyl-4-piperidyl) and the like. The addition amount of the hindered amine light stabilizer is usually about 0.01 to 0.5% by mass, preferably 0.05 to 0.3% by mass, in the weather resistant film.

  The thickness of the weather-resistant film is generally about 20 to 200 μm, preferably 20 to 100 μm, more preferably 20 to 50 μm from the viewpoint of film handling and cost.

(Dampproof film)
The moisture-proof film in the solar cell surface protective material of the present invention is a film having moisture-proof properties and having at least one inorganic thin film layer made of an inorganic oxide or the like on at least one surface of a substrate.
By this inorganic thin film layer, the inner surface side of the solar cell due to moisture permeation can be protected. Moreover, when an inorganic thin film layer has high transparency, when it uses as an upper protection material, the improvement of power generation efficiency can be achieved.

  The substrate having the inorganic thin film layer is preferably a resin film, and any material can be used as long as it is a resin that can be used for ordinary solar cell materials. Specifically, polyolefins such as homopolymers or copolymers such as ethylene, propylene and butene, amorphous polyolefins such as cyclic polyolefins, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), nylon 6 , Nylon 66, nylon 12, polyamide such as copolymer nylon, ethylene-vinyl acetate copolymer partial hydrolyzate (EVOH), polyimide, polyetherimide, polysulfone, polyethersulfone, polyetheretherketone, polycarbonate, polyvinyl Examples include butyral, polyarylate, fluororesin, acrylic resin, and biodegradable resin. In these, a thermoplastic resin is preferable and polyester, polyamide, and polyolefin are more preferable from points, such as a film physical property and cost. Among these, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are particularly preferable from the viewpoint of film properties. Further, when the base material is a film having a large shrinkage rate such as a polyethylene terephthalate film, the residual strain increases, so that the effect of the present invention becomes more remarkable.

The base material is a known additive, for example, an antistatic agent, an ultraviolet absorber, a plasticizer, a lubricant, a filler, a colorant, a stabilizer such as a weathering stabilizer, a lubricant, a crosslinking agent, an antiblocking agent, An antioxidant etc. can be contained. As the ultraviolet absorber and the weather resistance stabilizer, those mentioned in the description of the weather resistance film can be used.
The resin film as the substrate is formed by using the above raw materials, but when used as the substrate, it may be unstretched or stretched.
Further, one or more kinds of plastic films may be laminated.

  Such a substrate can be produced by a conventionally known method. For example, a raw material resin is melted by an extruder, extruded by an annular die or a T die, and rapidly cooled to be substantially amorphous and not oriented. An unstretched film can be manufactured. Further, by using a multilayer die, it is possible to produce a single layer film made of one kind of resin, a multilayer film made of one kind of resin, a multilayer film made of various kinds of resins, and the like.

  The unstretched film is subjected to a known method such as uniaxial stretching, tenter sequential biaxial stretching, tenter simultaneous biaxial stretching, tubular simultaneous biaxial stretching, or the like. A film stretched in a uniaxial direction or a biaxial direction can be produced by stretching in a direction (horizontal axis) perpendicular thereto. Although a draw ratio can be set arbitrarily, the heat shrinkage rate at 150 ° C. is preferably 0.01 to 5%, and more preferably 0.01 to 2%. Among these, from the viewpoint of film properties, biaxially stretched polyethylene naphthalate film, biaxially stretched polyethylene terephthalate film, coextruded biaxially stretched film of polyethylene terephthalate and polyethylene naphthalate, polyethylene terephthalate and / or polyethylene naphthalate and other plastics Extruded biaxially stretched films are preferred.

  In addition, it is preferable to provide an anchor coat layer by applying an anchor coating agent on the substrate in order to improve adhesion to the inorganic thin film. Examples of anchor coating agents include solvent-based or aqueous polyester resins, isocyanate resins, urethane resins, acrylic resins, modified vinyl resins, vinyl alcohol resins, and other alcoholic hydroxyl group-containing resins, vinyl butyral resins, nitrocellulose resins, and oxazoline group-containing resins. , Carbodiimide group-containing resins, methylene group-containing resins, epoxy group-containing resins, modified styrene resins, modified silicone resins, and the like. These can be used alone or in combination of two or more. Moreover, the anchor coat layer may contain a silane coupling agent, a titanium coupling agent, a UV absorber, a stabilizer such as a weathering stabilizer, a lubricant, an anti-blocking agent, an antioxidant, etc., if necessary. it can. As an ultraviolet absorber and a weather stabilizer, those mentioned in the description of the weather-resistant film can be used. It is also possible to use a polymer type in which the ultraviolet absorber and / or weathering stabilizer is copolymerized with the above-described resin.

As a method for forming the anchor coat layer, a known coating method is appropriately adopted. For example, any method such as a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, and a coating method using a spray can be used. Alternatively, the substrate may be immersed in a resin solution. After application, the solvent can be evaporated using a known drying method such as hot drying such as hot air drying or hot roll drying at a temperature of about 80 to 200 ° C., or infrared drying. Moreover, in order to improve water resistance and durability, the crosslinking process by electron beam irradiation can also be performed. Further, the formation of the anchor coat layer may be a method performed in the middle of the substrate production line (inline) or a method performed after the substrate is manufactured (offline).
The thickness of the anchor coat layer is preferably 10 to 200 nm, more preferably 10 to 100 nm, from the viewpoint of adhesion to the inorganic thin film layer.

  As the method for forming the inorganic thin film layer, any method such as a vapor deposition method and a coating method can be used, but the vapor deposition method is preferable in that a uniform thin film having a high gas barrier property can be obtained. This vapor deposition method includes methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). Examples of physical vapor deposition include vacuum deposition, ion plating, and sputtering. Examples of chemical vapor deposition include plasma CVD using plasma and a catalyst that thermally decomposes a material gas using a heated catalyst. Examples include chemical vapor deposition (Cat-CVD).

  Examples of the inorganic substance constituting the inorganic thin film layer include silicon, aluminum, magnesium, zinc, tin, nickel, titanium, hydrogenated carbon, and the like, or oxides, carbides, nitrides, or a mixture thereof. Is diamond-like carbon mainly composed of silicon oxide, aluminum oxide and hydrogenated carbon. In particular, silicon oxide, silicon nitride, silicon oxynitride, and aluminum oxide are preferable in that high gas barrier properties can be stably maintained.

The thickness of the inorganic thin film layer is preferably 10 to 1000 nm, more preferably 40 to 1000 nm, still more preferably 40 to 800 nm, and particularly preferably 50 to 600 nm from the viewpoint of stable moistureproof performance. preferable. The inorganic thin film layer may be a single layer or a multilayer.
Moreover, generally the thickness of the said base film is about 5-100 micrometers, 8-50 micrometers is preferable from the point of productivity or handleability, and 12-25 micrometers is still more preferable. Accordingly, the thickness of the moisture-proof film is generally about 5 to 100 μm, preferably 8 to 50 μm, more preferably 12 to 25 μm from the viewpoint of productivity and ease of handling.
In the moisture-proof film having high moisture-proof property, the moisture-proof performance in the present invention is remarkably exhibited because the moisture-proof performance is significantly deteriorated due to the stress from the back film. Therefore, in the present invention, the moisture-proof film has a water vapor transmission rate of less than 0.1 [g / m ² · day], preferably 0.05 [g / m ² · day] or less, more preferably 0.03 [g / m ² · day] or less, particularly preferably 0.01 [g / m ² · day] or less.

(Back film)
The back film in the present invention is a film that is provided directly or via an adhesive layer on the back side of the moisture-proof film, and is preferably a film that is bonded to the moisture-proof film via the adhesive layer. This reduces the stress due to shrinkage applied from the back side of the inorganic thin film layer at high temperature and high humidity. Therefore, specifically, a film having a melting point near the temperature at the time of vacuum lamination, that is, a film having a melting point of 130 ° C. or higher and 180 ° C. or lower is used, and the melting point falls within the above range between the back film and the moisture-proof film. It is preferred not to have other films that do not.
From the above viewpoint, the lower limit of the melting point is 130 ° C., preferably 140 ° C., and more preferably 150 ° C. The upper limit of the melting point is 180 ° C, preferably 175 ° C, and more preferably 170 ° C.

  By using a back film whose melting point is in the above temperature range, the molecular / crystal orientation in the film caused by the history of force and thermal history applied in the previous process is relaxed at the temperature during vacuum lamination. Residual strain can be reduced.

  In the vacuum lamination process, the back film flows easily with pressure, and it is difficult to maintain a film with a uniform thickness. However, in the present invention, the back film flows by using a back film having a melting point of 130 ° C. or higher. And the thickness can be maintained. Incidentally, if the melting point is less than 80 ° C., the solar cell module is heated to about 85 to 90 ° C. due to heat generated during power generation or radiant heat of sunlight regardless of the thickness. The function of protecting the original solar cell element during softening and operation is lost.

In addition, the said melting | fusing point is the value measured by the method as described in an Example.
From the above, the back film preferably has a melting point near the vacuum lamination temperature. For example, polypropylene (PP), polylactic acid (PLA), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), butyric acid. Although what formed resin compositions, such as a cellulose (CAB), into a film is used preferably, it is not limited to these. Further, a resin composition in which an ultraviolet absorber or a colorant is mixed may be formed.

  Considering the use of the back film as a solar cell surface protection material, it is desirable that it has high flexibility and is excellent in UV durability and humidification durability, and is mainly composed of polypropylene (PP), polylactic acid (PLA), and polyfluoride. Those containing one or more resins of vinyl fluoride (PVF) and polyvinylidene fluoride (PVDF) as a main component are preferable, and those resins containing 50% by weight or more are preferable. Here, the term “main component” is intended to allow other components to be included within a range that does not impede the effects of the present invention, and is not intended to limit the specific content. When the total component is 100 parts by mass, it means 50 parts by mass or more, preferably 65 parts by mass or more, more preferably 80 parts by mass or more and a component occupying a range of 100 parts by mass or less.

In addition, as said ultraviolet absorber, the thing similar to the ultraviolet absorber contained in the above-mentioned weather-resistant film can be used. Moreover, titanium oxide, calcium carbonate, etc. can be used as a coloring agent. As the resin, one of the above-listed resins can be used alone, or two or more of them can be used in combination.
As long as the back film is within the melting point range, the back film may be composed of only the components within the melting point range or may contain 50% by mass or more of the components.
The thickness of the back film is 25 μm or more from the viewpoint of ease of handling of the film, more preferably 50 μm or more, and it is desired that the thickness is further thicker from the viewpoint of ensuring partial discharge of the protective material, and more preferably 90 μm or more.

  Conventionally, as described above, it is desirable to increase the total thickness of the film disposed on the back side of the moisture-proof film in order to ensure a partial discharge voltage of the surface protective material. However, as the thickness increases, the residual strain accumulated in the manufacturing process of the surface protection material also increases, which limits the moisture-proof performance. In the present invention, as described above, the film having a melting point near the temperature at the time of vacuum lamination is used as the back film, so that the deterioration of the moisture-proof performance is suppressed even if the back film has a thickness of 90 μm or more, and the surface protection material. Can be used as Further, the total thickness of the back film is preferably 300 μm or less, more preferably 250 μm or less, and still more preferably 200 μm or less from the economical viewpoint.

(Plastic film)
The surface protective material for solar cell of the present invention further has a plastic film through the back film on the opposite side of the moisture-proof film to the inorganic thin film layer for the purpose of improving the withstand voltage performance and handling of the surface protective material. be able to. As the plastic film, the same film as the back film may be used, but other films may be used. From the viewpoint of adhesion to the sealing material and reflectance, polypropylene or polyethylene terephthalate (PET) is preferably used.

  In the present invention, in order to increase the elastic modulus / rigidity of the entire solar cell surface protective material, the plastic film is a laminated polyester film or fluorine film exemplified as the above-mentioned weather-resistant film. be able to.

  The plastic film has a thickness of preferably 10 μm or more, more preferably 20 μm or more from the viewpoints of little influence on moisture-proof deterioration and securing strength as an adhesion layer to the sealing material. Moreover, in order to make the residual distortion accumulate | stored in the manufacturing process of a surface protection material smaller, it is preferable that it is 100 micrometers or less, and it is more preferable that it is 50 micrometers or less.

(Surface protective material)
As described above, the surface protective material is not particularly limited as long as it has a weather-resistant film, a moisture-proof film, and a specific back film having a melting point of 130 ° C. or higher and 180 ° C. or lower. Furthermore, you may have. The back film needs to have a melting point within the above range, and the surface protective material has such a back film, thereby reducing stress due to shrinkage applied from the back to the inorganic thin film layer in a high temperature and high humidity environment. In addition, it is possible to maintain moisture-proof performance for a long time even after heat treatment such as vacuum lamination.
From the viewpoint of securing the interlaminar strength of the surface protective material, the weather-resistant film and moisture-proof film, the moisture-proof film and back film, or the plastic film provided therewith if necessary, are each laminated via an adhesive layer made of an adhesive It is preferable that
In particular, it is preferable that the moisture-proof film and the back film are bonded together via an adhesive layer.
As the adhesive, a polyurethane-based adhesive is preferably used, and specific examples of the main agent of the adhesive include a polycarbonate polyol, a polyether polyol, an acrylic polyol, a polyurethane polyol, or a composition containing a polyester polyol. From the viewpoint of stability, humidity stability, etc., those containing at least one of polycarbonate polyol, polyether polyol and polyurethane polyol are more preferred.

  Furthermore, the solar cell surface protective material of the present invention may be a sealing material / surface protective material integrated type formed by laminating a sealing material described later. Lamination of the lower protective sheet (back surface protective sheet), the sealing material, the solar cell element, the sealing material, and the upper protective sheet (front protective sheet) in the vacuum lamination process by laminating the sealing material in advance. And the efficiency of solar cell module manufacturing can be improved.

  The surface protective material for solar cells of the present invention further improves various physical properties (flexibility, heat resistance, transparency, adhesiveness, etc.), molding processability, economic efficiency, etc. without departing from the gist of the present invention. For example, various elastomers (olefin, styrene, etc.), resins modified with polar groups such as carboxyl groups, amino groups, imide groups, hydroxyl groups, epoxy groups, oxazoline groups, thiol groups, silanol groups, and tackifiers Resins and the like can be contained. The back film can contain the resin as long as it satisfies the melting point range.

  Examples of the tackifying resin include petroleum resins, terpene resins, coumarone-indene resins, logistic resins, and hydrogenated derivatives thereof. Specifically, the petroleum resin includes cyclopentadiene or an alicyclic petroleum resin derived from a dimer thereof and an aromatic petroleum resin derived from a C9 component, and the terpene resin includes a terpene resin derived from β-pinene and a terpene resin. Examples of the phenol resin and rosin resin include rosin resins such as gum rosin and wood rosin, and esterified rosin resins modified with glycerin and pentaerythritol. Further, the tackifying resin can be obtained mainly having various softening temperatures depending on the molecular weight, but a hydrogenated derivative of an alicyclic petroleum resin having a softening temperature of 100 to 150 ° C, preferably 120 to 140 ° C is particularly preferable. Usually, when the resin composition forming each film constituting the surface protective material is 100% by mass, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

  Moreover, various additives can be added to the surface protective material for solar cells, if necessary, in addition to the ultraviolet absorber and the weathering stabilizer described above. Examples of the additive include a silane coupling agent, an antioxidant, a light diffusing agent, a nucleating agent, a pigment (for example, a white pigment), a flame retardant, and a discoloration preventing agent. In the present invention, it is preferable that at least one additive selected from a silane coupling agent, an antioxidant, an ultraviolet absorber, and a weathering stabilizer is added. Moreover, when high heat resistance is requested | required, you may mix | blend a crosslinking agent and / or a crosslinking adjuvant.

  Examples of silane coupling agents include compounds having a hydrolyzable group such as an alkoxy group together with an unsaturated group such as a vinyl group, an acryloxy group or a methacryloxy group, an amino group or an epoxy group. . Specific examples of the silane coupling agent include N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, and γ-aminopropyltriethoxy. Examples include silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and the like. In the present invention, γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane are preferably used because of good adhesiveness and little discoloration such as yellowing. The addition amount of the silane coupling agent is usually about 0.1 to 5% by mass and preferably 0.2 to 3% by mass in each film constituting the surface protective material. In addition, a coupling agent such as an organic titanate compound can be used in the same manner as the silane coupling agent.

  As the antioxidant, various commercially available products can be applied, and various types such as monophenol type, bisphenol type, polymer type phenol type, sulfur type and phosphite type can be exemplified. Examples of monophenols include 2,6-di-tert-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-tert-butyl-4-ethylphenol, and the like. Examples of bisphenols include 2,2′-methylene-bis- (4-methyl-6-tert-butylphenol), 2,2′-methylene-bis- (4-ethyl-6-tert-butylphenol), 4,4 '-Thiobis- (3-methyl-6-tert-butylphenol), 4,4'-butylidene-bis- (3-methyl-6-tert-butylphenol), 3,9-bis [{1,1-dimethyl- 2- {β- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy} ethyl} 2,4,9,10-tetraoxaspiro] 5,5-undecane.

Examples of the high molecular phenolic group include 1,1,3-tris- (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3 , 5-di-tert-butyl-4-bidoxybenzyl) benzene, tetrakis- {methylene-3- (3 ', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate} methane, bis { (3,3'-bis-4'-hydroxy-3'-tert-butylphenyl) butyric acid} glycol ester, 1,3,5-tris (3 ', 5'-di-tert-butyl-4 '-Hydroxybenzyl) -s-triazine-2,4,6- (1H, 3H, 5H) trione, triphenol (vitamin E) and the like.
Examples of sulfur-based compounds include dilauryl thiodipropionate, dimyristyl thiodipropionate, and distearyl thiopropionate.

  Examples of the phosphite system include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl) phosphite, Crick neopentanetetrayl bis (octadecyl phosphite), tris (mono and / or di) phenyl phosphite, diisodecyl pentaerythritol diphosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10- Oxide, 10- (3,5-di-tert-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9,10 -Dihydro-9-oxa-10-fo Phaphenanthrene, cyclic neopentanetetraylbis (2,4-di-tert-butylphenyl) phosphite, cyclic neopentanetetraylbis (2,6-di-tert-methylphenyl) phosphite, 2 , 2-methylenebis (4,6-tert-butylphenyl) octyl phosphite.

  In the present invention, phenol-based and phosphite-based antioxidants are preferably used in view of the effect of the antioxidant, thermal stability, economy, and the like, and it is more preferable to use both in combination. The addition amount of the antioxidant is usually about 0.1 to 1% by mass and preferably 0.2 to 0.5% by mass in each film constituting the surface protection material for solar cell.

  As a method for forming each film constituting the surface protection material for solar cell used in the present invention, a known method, for example, a single-screw extruder, a multi-screw extruder, a Banbury mixer, a kneader or the like has melt mixing equipment. An extrusion cast method using a T die, a calendar method, or the like can be employed, and is not particularly limited. In the present invention, an extrusion casting method using a T die is preferably used from the viewpoints of handleability and productivity. The molding temperature in the extrusion casting method using a T die is appropriately adjusted depending on the flow characteristics and film-forming properties of the resin composition used, but is generally 130 to 350 ° C, preferably 250 to 300 ° C. Various additives may be supplied to the hopper after dry blending with the resin in advance, or may be supplied after melt-mixing all the materials in advance to produce pellets, or only the additive is pre-resined. It is also possible to prepare and supply a master batch concentrated in the above.

The surface protection material for solar cells of the present invention using the highly moisture-proof film having a water vapor permeability of less than 0.1 [g / m ² · day] thus obtained is a surface protection material for solar cells before heat treatment ( The moisture-proof performance of the laminated moisture-proof film) is preferably 0.1 [g / m ² · day] or less, more preferably 0.05 [g / m ² · day] or less in terms of water vapor transmission rate. It is. The surface protective material for solar cells of the present invention can be used as a surface protective material for electronic devices that require excellent moisture-proof performance, and more by using a laminated moisture-proof film that is excellent in initial moisture-proof performance. The effect of the present invention can be remarkably exhibited, which is preferable. Moreover, as for the moisture-proof performance, it is preferable that the deterioration degree after the pressure cooker test at 120 ° C., humidity 100%, and 32 hours is 20 or less, more preferably 15 or less with respect to the initial water vapor permeability of the laminated moisture-proof film. It is.

Furthermore, when a polyurethane adhesive is used as the adhesive, when the adhesive is thermally decomposed under high temperature and high humidity, carboxylic acid and hydroxyl groups are generated, and these functional groups form a chemical bond with the inorganic thin film layer. This is considered to cause deterioration of the inorganic thin film layer. Therefore, as the polyol contained in the main component of the polyurethane-based adhesive, polycarbonate polyol, polyether polyol, polyacryl polyol, polyurethane polyol and the like having excellent heat resistance are preferable to polyester polyol which is easily thermally decomposed.
In the present invention, the degree of deterioration of the moisture resistance (water vapor transmission rate) after the pressure cooker test is expressed as [(b−a) in the initial water vapor transmission rate (a) and the water vapor transmission rate (b) after the pressure cooker test. ) / A].

The initial moisture-proof performance of the solar cell surface protective material of the present invention refers to the moisture-proof performance before the member receives a high-temperature thermal history such as vacuum lameet conditions, and means a value before the moisture-proof performance is lowered due to heat. . Therefore, it includes changes over time from immediately after production to before heat treatment. For example, it means the value of moisture-proof performance in a state where heat treatment such as thermal lamination treatment performed at 130 to 180 ° C. for 10 to 40 minutes is not performed. To do. The initial water vapor transmission rate also has the same meaning as “above”.
The moisture-proof performance can be evaluated according to the conditions of JIS Z0222 “Method of testing moisture permeability of moisture-proof packaging container” and JIS Z0208 “Method of testing moisture permeability of moisture-proof packaging material (cup method)”.

The interlayer strength of the surface protective material of the present invention is preferably 4 N / 15 mm or more after a pressure cooker test of 120 ° C., 100% humidity and 32 hours. The interlayer strength is more preferably 7.0 mm or more, further preferably 7.3 mm or more, further preferably 7.5 N / 15 mm or more, and further preferably 8 N / 15 mm or more. In particular, even after a high temperature and high humidity treatment for producing a solar cell module, it is preferably 4 N / 15 mm or more, more preferably 7.0 mm or more, still more preferably 7.3 mm or more, and 7.5 N / 15 mm or more. It is particularly preferred.
The interlayer strength is a value measured by the method described in the examples.

(Production method of surface protection material)
The method for producing the surface protective material for solar cells of the present invention is not particularly limited. For example, each film formed as described above is dried at a temperature of 100 to 140 ° C. using a polyurethane-based adhesive. Can be produced by bonding together by dry lamination at a temperature of 0 to 80 ° C. In this case, it is preferable that the obtained laminated body is cured at a temperature of 30 to 80 ° C. for 1 to 7 days from the viewpoint of sufficiently bringing the adhesive to a saturation crosslinking degree. The surface protective material of the present invention thus obtained has excellent flexibility and moisture resistance that does not deteriorate the moisture resistance and interlayer strength even after the dry laminating process.

Moreover, it is preferable that the surface protection material for solar cells of the present invention has partial discharge resistance in addition to weather resistance and moisture resistance. Specifically, in the partial discharge resistance test for measuring the withstand voltage until the surface protection material reaches dielectric breakdown, it is preferable to have a withstand voltage of 700 to 1000 V as the solar cell protection material.
The thickness of the surface protective material is not particularly limited, but is usually about 100 to 400 μm, preferably about 100 to 300 μm, more preferably about 140 to 300 μm, and still more preferably about 180 to 260 μm. It is used in a sheet form.

  In order for the surface protective material to achieve the above-mentioned withstand voltage characteristics, although depending on the required withstand voltage, it is usually preferable that the thickness of the surface protective material is 180 to 230 μm. Therefore, although the thickness of each layer is arbitrary, for example, relatively expensive weather-resistant film and moisture-proof film are 10 to 50 μm, adhesive is 4 to 10 μm, back film is 50 to 100 μm, and plastic film is 50 to 50 μm. In addition, from the viewpoint of moisture-proof film productivity and dry lamination process productivity, the weather-resistant film and the moisture-proof film are 12 to 30 μm, the adhesive is 4 to 8 μm, and the back film is 50 to 100 μm. The plastic film has a configuration of 70 to 120 μm.

<Solar cell module, solar cell manufacturing method>
The surface protective material of the present invention can be used as a surface protective member for solar cells as it is or after being bonded to a glass plate or the like. In order to produce the solar cell module and / or the solar cell of the present invention using the surface protective material of the present invention, it may be produced by a known method.

  A solar cell module can be manufactured by using the surface protective material of the present invention for the layer structure of a surface protective member such as a solar cell upper protective material and a lower protective material, and fixing the solar cell element together with a sealing material. . Examples of such solar cell modules include various types. For example, an upper protective material (surface protective material of the present invention) / sealing material (sealing resin layer) / solar cell element / sealing material (sealing resin layer) / lower protective material, upper protective material / Formed on the inner peripheral surface of the lower protective material, having a configuration of sealing material (sealing resin layer) / solar cell element / sealing material (sealing resin layer) / lower protective material (surface protective material of the present invention) A structure in which a sealing material and an upper protective material (surface protective material of the present invention) are formed on the solar cell element formed, and formed on the inner peripheral surface of the upper protective material (surface protective material of the present invention) In addition, a solar cell element, for example, a structure in which a sealing material and a lower protective material are formed on an amorphous solar cell element formed on a fluororesin protective material by sputtering or the like can be used. It is optional to bond a glass plate to the outside of the surface protective material of the present invention as the upper protective material. In addition, when using the above-mentioned sealing material / surface protective material integrated surface protective material, the above-mentioned sealing material may not be used.

  As the solar cell element, for example, a single crystal silicon type, a polycrystalline silicon type, an amorphous silicon type, a gallium-arsenic, a copper-indium-selenium, a cadmium-tellurium, or the like III-V group or II-VI group compound semiconductor type, Examples include a dye sensitizing type and an organic thin film type.

  Although it does not specifically limit about each member which comprises the solar cell module produced using the surface protection material of this invention, As an sealing material, an ethylene-vinyl acetate copolymer is mentioned, for example. Can do. The upper protective member and the lower protective member other than the surface protective member of the present invention are single layer or multilayer sheets such as inorganic materials such as metals and various thermoplastic resin films, for example, metals such as tin, aluminum, and stainless steel. Examples thereof include inorganic materials such as glass, polyester, inorganic vapor-deposited polyester, fluorine-containing resins, and single-layer or multilayer protective materials such as polyolefin. The surface of the upper and / or lower protective material can be subjected to a known surface treatment such as a primer treatment or a corona treatment in order to improve the adhesion to the sealing material or other members.

  Configuration of an upper protective material (surface protective material of the present invention) / sealing material / solar cell element / sealing material / lower protective material described above for a solar cell module produced using the surface protective material of the present invention Will be described as an example. The surface protective material, sealing resin layer, solar cell element, sealing resin layer, and lower protective material of the present invention are laminated in order from the sunlight receiving side, and a junction box (solar cell) is further formed on the lower surface of the lower protective material. A terminal box for connecting wiring for taking out electricity generated from the element to the outside is bonded. The solar cell elements are connected by wiring in order to conduct the generated current to the outside. The wiring is taken out through a through hole provided in the backsheet and connected to the junction box.

  As a manufacturing method of the solar cell module, a known manufacturing method can be applied, and it is not particularly limited, but in general, an upper protective material, a sealing material, a solar cell element, a sealing material, a lower protective material. And a step of vacuum-sucking them and heat-pressing them. Also, batch type manufacturing equipment, roll-to-roll type manufacturing equipment, and the like can be applied. Specifically, an upper protective material, a sealing material, a solar cell element, a sealing material, and a lower protective material are vacuum laminator according to a conventional method, preferably 130 to 180 ° C., more preferably 130 to 150 ° C., deaeration It can be easily manufactured by heat-pressure bonding in a time of 2 to 15 minutes, a press pressure of 0.5 to 1 atm, and a press time of preferably 8 to 45 minutes, more preferably 10 to 40 minutes.

  The solar cell module produced using the surface protective material of the present invention is a small solar cell represented by a mobile device, a large solar cell installed on a roof or a roof, etc., depending on the type and module shape of the applied solar cell. It can be applied to various uses, both indoors and outdoors.

  EXAMPLES The present invention will be described more specifically with reference to examples. However, the present invention is not limited by these examples and comparative examples. Various physical properties were measured and evaluated as follows.

(Physical property measurement)
(1) Crystal melting peak temperature of the back film (melting point, Tm)
Using a differential scanning calorimeter Q20 manufactured by TA Instruments Inc., approximately 10 mg of the sample was heated from −40 ° C. to 200 ° C. at a heating rate of 10 ° C./min according to JIS K7121, and the melting peak After holding at 200 ° C. for 1 minute, the temperature was lowered to −40 ° C. at a cooling rate of 10 ° C./min, and again from the thermogram measured when the temperature was raised to 200 ° C. at a heating rate of 10 ° C./min. Among the peak temperatures, the maximum peak was defined as the (Tm) (° C.) melting point. When the melting point exceeded 200 ° C. and no melting peak was observed, such as polyester, the temperature rise upper limit temperature was set to 300 ° C., and then the same measurement was performed.

(2) Pressure Cooker Test Using a pressure cooker test LSK-500 manufactured by Tommy Seiko Co., Ltd., the test was performed at 120 ° C., 100% humidity and 32 hours.

(3) Moisture-proof Performance of Moisture-proof Film and Surface Protective Material The moisture-proof performance of the moisture-proof film was measured as the water vapor transmission rate after storage at 40 ° C. for one week after the creation of the moisture-proof film by the following method. For the surface protection material, the measured value of the surface protection material after pasting and curing each component film is the initial water vapor transmission rate, and after the curing, the glass, sealing material, surface protection material (of the moisture-proof film) The back side is the sealing material side), heat treatment is performed at 150 ° C. for 30 minutes, and then the water vapor transmission rate of the surface protective material after the pressure cooker test is performed is the moisture-proof property after the pressure cooker test. Value.
Specifically, in accordance with JIS Z 0222 “moisture-proof packaging container moisture permeability test method” and JIS Z 0208 “moisture-proof packaging material moisture permeability test method (cup method)”, the following methods were used for evaluation.
Using two samples each having a moisture permeable area of 10.0 cm × 10.0 cm square, a bag having about 20 g of anhydrous calcium chloride as a hygroscopic agent and sealed on all sides was produced. The bag was kept at a constant temperature of 40 ° C. and a relative humidity of 90%. Place in a humidity controller and measure the mass until about 200 days at intervals of 72 hours or more, and determine the water vapor transmission rate (g / m ² · day) from the slope of the regression line between the elapsed time after 4 days and the bag mass. Calculated. The degree of water vapor transmission rate deterioration was calculated by [(water vapor transmission rate after pressure cooker test−initial water vapor transmission rate) / initial water vapor transmission rate].

(4) Interlaminar strength measurement of surface protective material As described above, the surface protective material after curing is heat-treated at 150 ° C. for 30 minutes, cut into a strip shape with a measurement width of 15 mm after the pressure cooker test, and a tensile test The interlayer laminate strength (N / 15 mm) between the weather resistant film and the moisture-proof film was measured at 300 mm / min using STA-1150 manufactured by ORIENTIC.

(Structure film)
<Weather-resistant film>
A-1: Polyvinylidene fluoride (PVDF) film Kynar 302-PGM-TR (thickness: 30 μm) manufactured by Arkema was used.

<Dampproof film>
Moisture-proof film B-1
A 12 μm thick biaxially stretched polyethylene naphthalate film (manufactured by Teijin DuPont, “Q51C12”) was used as the base film, and the following coating solution was applied to the corona-treated surface and dried to a thickness of 0.1 μm. A layer was formed.
Next, SiO was heated and evaporated under a vacuum of 1.33 × 10 ⁻³ Pa (1 × 10 ⁻⁵ Torr) using a vacuum deposition apparatus, and SiOx (x = 1.5) having a thickness of 50 nm was formed on the coating layer. ) A moisture-proof film B-1 having an inorganic thin film layer was obtained. The moisture-proof performance of the produced moisture-proof film B-1 was 0.01 [g / m ² · day].

Coating solution “GOHSENOL” (degree of saponification: 97.0 to 98.8 mol%, degree of polymerization: 2400) manufactured by Nippon Gosei Co., Ltd. was added to 2810 g of ion-exchanged water and dissolved in warm solution at 20 ° C. With stirring at 645 g of 35% hydrochloric acid was added. Subsequently, 3.6 g of butyraldehyde was added with stirring at 10 ° C., and after 5 minutes, 143 g of acetaldehyde was added dropwise with stirring to precipitate resin fine particles. Subsequently, after hold | maintaining at 60 degreeC for 2 hours, the liquid was cooled, neutralized with sodium hydrogencarbonate, washed with water, and dried and the polyvinyl acetoacetal powder (acetalization degree 75 mol%) was obtained.
In addition, an isocyanate resin (“Sumijour N-3200” manufactured by Sumitomo Bayer Urethane Co., Ltd.) was used as a cross-linking agent, and mixing was performed so that the equivalent ratio of isocyanate groups to hydroxyl groups was 1: 2.

Moisture-proof film B-2
A tech barrier LX made by Mitsubishi Plastics, in which silica was deposited on a polyethylene terephthalate film having a thickness of 12 μm, was used. Further, the moisture resistance measured by the above-mentioned method was 0.2 [g / m ² · day].

<Adhesive and adhesive coating solution>
Adhesive coating liquid HD1013 manufactured by Rock Paint Co., Ltd. is used as a main component containing a polyurethane polyol component, and H62 manufactured by Rock Paint Co., Ltd. is used as a curing agent containing an aliphatic hexamethylene diisocyanate component, and the mass ratio is 10 The mixture was mixed so that the solid content concentration was 30% by mass, and diluted with ethyl acetate to prepare an adhesive coating solution.

<Back film>
The following back films C-1 to C-11 were prepared and subjected to corona discharge treatment on both sides according to a conventional method to form corona-treated surfaces.

Back film C-1 and C-2
To isotactic polypropylene, titanium oxide (8% by mass) as a whitening agent and ultrafine titanium oxide (particle diameter, 0.01 to 0.06 μm, 3% by mass) as an ultraviolet absorber are added and sufficiently To prepare a polypropylene resin composition, and the polypropylene resin composition is then extruded with an extruder to give an unstretched polypropylene (PP) resin film (C-1) having a thickness of 50 μm and a non-stretching film having a thickness of 90 μm. A stretched polypropylene (PP) resin film (C-2) was produced.

Back film C-3
Polyvinylidene fluoride (PVDF) film (Kynar 302-PGM-TR, thickness 30 μm) manufactured by Arkema Co. was used as C-3.
Back film C-4
A polylactic acid (PLA) resin film (Ecologe S, thickness 25 μm) manufactured by Mitsubishi Plastics, Inc. was used as C-4.

Back film C-5, C-6, C-7
A polyethylene terephthalate (PET) film (Diafoil T-100) manufactured by Mitsubishi Plastics Co., Ltd. was used with a thickness of 50 μm (C-5), a thickness of 100 μm (C-6), and a thickness of 188 μm (C-7).
Back film C-8
As the hydrolysis-resistant polyester film, a hydrolysis-resistant polyethylene terephthalate (PET) film (P100, thickness 50 μm) manufactured by Mitsubishi Resin Co., Ltd. was used as C-8.

Back film C-9
A polyamide (PA) 6 film (Santonyl SNR, thickness 25 μm) manufactured by Mitsubishi Plastics, Inc. was used as C-9.
Back film C-10
Asahi Glass Co., Ltd. ethylene-tetrafluoroethylene copolymer (ETFE) (Aflex 50N 1250NT, thickness 50 μm) was used as C-10.

Back film C-11
A biaxially stretched polyethylene naphthalate (PEN) film (Q51C25, thickness 25 μm) manufactured by Teijin DuPont Co., Ltd. was used as C-11.
The structure, thickness, and melting point values of C-1 to C-11 are summarized in Table 1 above.
<Plastic film>
As the plastic film, a polyethylene terephthalate (PET) film (Diafoil T-100) thickness 100 μm manufactured by Mitsubishi Plastics, Inc. was used.
<Encapsulant>
As an EVA sealing material, a product name: FIRSTEVA F806 (thickness: 500 μm) manufactured by Fuso Tokusha Co., Ltd. was used.

Example 1
The adhesive coating liquid 1 is applied and dried on the weather resistant film A-1 so that the solid content is 6 g / m ^2, and the inorganic thin film layer of the moisture-proof film B-1 is directed to the adhesive surface by a dry laminate with a tension of about 80 N / m. Pasted.
Thereafter, the adhesive coating liquid 1 is applied and dried on the side opposite to the inorganic thin film layer so as to have a solid content of 6 g / m ^2, and the corona-treated surface of the back film C-1 is bonded, followed by curing at 40 ° C. for 5 days, and the thickness. A surface protective material D-1 having a thickness of 104 μm was prepared. Laminated in the order of glass, sealing material, surface protective material D-1 (the sealing material side is the back film), vacuum laminated at 150 ° C. for 15 minutes, and then subjected to a pressure cooker test to obtain interlayer strength and moisture resistance. Sex was measured. The results are shown in Table 2.

Example 2
A surface protective material D-2 having a thickness of 144 μm was prepared in the same manner as in Example 1 except that the back film C-1 in Example 1 was changed to C-2, and after vacuum lamination, a pressure cooker test was performed. Strength and moisture resistance were measured. The results are shown in Table 2.

Example 3
A surface protective material D-3 having a thickness of 84 μm was prepared in the same manner as in Example 1 except that the back film C-1 in Example 1 was changed to C-3, and after vacuum lamination, a pressure cooker test was performed. Strength and moisture resistance were measured. The results are shown in Table 2.

Example 4
A surface protective material D-4 having a thickness of 79 μm was prepared in the same manner as in Example 1 except that the back film C-1 of Example 1 was changed to C-4, and after vacuum lamination, a pressure cooker test was performed. Strength and moisture resistance were measured. The results are shown in Table 2.

Example 5
A polyethylene terephthalate (PET) film (Diafoil T-100) manufactured by Mitsubishi Plastics Co., Ltd. is applied and dried on one side of a thickness of 100 μm to a solid content of 6 g / m ^2, and the back film C-2 One of the corona-treated surfaces was bonded to the adhesive surface by dry lamination.
The adhesive coating liquid 1 is applied and dried on the weather resistant film A-1 so that the solid content is 6 g / m ^2, and the inorganic thin film layer of the moisture-proof film B-1 is directed to the adhesive surface by a dry laminate with a tension of about 80 N / m. Pasted.
Next, the adhesive coating liquid 1 is applied and dried on the side opposite to the inorganic thin film layer so as to have a solid content of 6 g / m ^2, and the other corona-treated surface of the back film C-2 is bonded, and then 40 ° C. × 5 days. After curing, a surface protective material D-5 (weather-resistant film A-1 / moisture-proof film B-1 / back film C-2 / PET film) having a thickness of 250 μm was prepared. Laminated in the order of glass, sealing material, surface protective material D-5 (PET film on the sealing material side), vacuum laminated at 150 ° C. for 15 minutes, then pressure cooker test, interlayer strength, moisture proof Sex was measured. The results are shown in Table 2.

Comparative Example 1
A surface protective material D-6 having a thickness of 104 μm was prepared in the same manner as in Example 1 except that the back film C-1 in Example 1 was changed to C-5. After vacuum lamination, a pressure cooker test was conducted, and interlayer strength was measured. The moisture resistance was measured. The results are shown in Table 2.

Comparative Example 2
A surface protective material D-7 having a thickness of 154 μm was prepared in the same manner as in Example 1 except that the back film C-1 of Example 1 was changed to C-6, and after vacuum lamination, a pressure cooker test was conducted to obtain interlayer strength. The moisture resistance was measured. The results are shown in Table 2.

Comparative Example 3
A surface protective material D-8 having a thickness of 242 μm was prepared in the same manner as in Example 1 except that the back film C-1 in Example 1 was changed to C-7, and after vacuum lamination, a pressure cooker test was conducted to obtain an interlayer strength. The moisture resistance was measured. The results are shown in Table 2.

Comparative Example 4
A surface protective material D-9 having a thickness of 104 μm was prepared in the same manner as in Example 1 except that the back film C-1 in Example 1 was changed to C-8. After vacuum lamination, a pressure cooker test was conducted to measure the interlayer strength. The moisture resistance was measured. The results are shown in Table 2.

Comparative Example 5
A surface protective material D-10 having a thickness of 79 μm was prepared in the same manner as in Example 1 except that the back film C-1 in Example 1 was changed to C-9. After vacuum laminating, a pressure cooker test was performed to measure the interlayer strength. The moisture resistance was measured. The results are shown in Table 2.

Comparative Example 6
A surface protective material D-11 having a thickness of 104 μm was prepared in the same manner as in Example 1 except that the back film C-1 in Example 1 was changed to C-10. After vacuum laminating, a pressure cooker test was performed, and interlayer strength was measured. The moisture resistance was measured. The results are shown in Table 2.

Comparative Example 7
A surface protective material D-12 having a thickness of 79 μm was prepared in the same manner as in Example 1 except that the back film C-1 in Example 1 was changed to C-11. After vacuum laminating, a pressure cooker test was performed, and interlayer strength was measured. The moisture resistance was measured. The results are shown in Table 2.

Reference example 1
A surface protective material D-13 having a thickness of 104 μm was prepared in the same manner as in Example 1 except that the moisture-proof film B-1 in Example 1 was changed to B-2, and after vacuum lamination, a pressure cooker test was performed. Strength and moisture resistance were measured. The results are shown in Table 2.

Reference example 2
A surface protective material D-14 having a thickness of 154 μm was prepared in the same manner as in Comparative Example 2 except that the moisture-proof film B-1 in Comparative Example 2 was changed to B-2, and after vacuum lamination, a pressure cooker test was performed to measure the interlayer strength. The moisture resistance was measured. The results are shown in Table 2.

Thus, a highly moisture-proof surface protection material for solar cells having a moisture-proof film having an inorganic thin film layer on one surface of a substrate and having a moisture-proof film having a moisture permeability of less than 0.1 [g / m ² · day]. The surface protective material of Examples 1 to 5 having a back film having a melting point within a specific range on the side opposite to the inorganic thin film layer side of the moisture-proof film has long-term moisture-proof performance even after heat treatment in the vacuum lamination process. It was clarified from the evaluation by the pressure cooker test that it was retained. Moreover, it turned out that the surface protection material of Examples 1-5 has sufficient interlayer intensity | strength for a long term even if the said heat processing is made | formed. Especially about Example 5 which has a plastic film in addition to a back film, the moisture-proof performance after high heat processing was held more. Similarly, for Comparative Examples 1 to 7 in which a film having a melting point outside the above specified range was disposed on the back side of the moisture-proof film, it was revealed that the long-term moisture-proof performance after the heat treatment in the vacuum lamination process was significantly lowered. In addition, Reference Examples 1 and 2 having a low initial moisture-proof performance indicate that the degree of deterioration of the moisture-proof performance is small, and the degree of deterioration of the moisture-proof performance increases as the initial moisture-proof performance is higher, as compared with the Examples.
Thus, it became clear that the highly moisture-proof surface protection material for solar cells in the present invention has a remarkable effect of maintaining moisture resistance in a highly moisture-proof film that is particularly susceptible to deterioration in moisture-proof performance. Therefore, by using this for a solar cell module, it is possible to remarkably improve the durability of the solar cell module because moisture can reach the solar cell and deterioration of the surface protection material itself can be remarkably suppressed. It is.

Claims (10)

A surface protective material for a solar cell having a moisture-proof film having an inorganic thin film layer on one surface of a substrate and having a water vapor transmission rate of less than 0.1 [g / m ² · day],
It has a weather resistant film on the inorganic thin film layer side of the moisture proof film, and a back film having a melting point of 130 ° C. or higher and 180 ° C. or lower directly or via an adhesive layer on the opposite side of the moisture proof film to the inorganic thin film layer. A surface protective material for solar cells. The surface protective material for solar cells according to claim 1, wherein the moisture-proof film has a water vapor permeability of 0.05 [g / m ² · day] or less. The surface protective material for a solar cell according to claim 1, wherein the moisture-proof film has a water vapor permeability of 0.01 [g / m ² · day] or less.   The surface protection material for solar cells according to any one of claims 1 to 3, wherein the back film contains at least one resin selected from polypropylene, polylactic acid, polyvinyl fluoride, and polyvinylidene fluoride as a main component.   The thickness of the said back film is 25 micrometers or more and 300 micrometers or less, The surface protection material for solar cells in any one of Claims 1-4.   The solar cell surface protective material according to any one of claims 1 to 5, wherein the substrate is a polyester resin film.   The surface protective material for solar cells according to any one of claims 1 to 6, further comprising an adhesive layer between the moisture-proof film and the back film.   The surface protection material for solar cells according to any one of claims 1 to 7, comprising the back film and the plastic film in this order on the opposite side of the moisture-proof film to the inorganic thin film layer.   Furthermore, the surface protection material for solar cells in any one of Claims 1-8 which have a sealing material laminated | stacked.   The solar cell module produced using the surface protection material for solar cells in any one of Claims 1-9.