JP5982150B2 - Solar cell backsheet - Google Patents

Description

  The present invention relates to a solar cell backsheet having a specific polyvinyl acetal layer, a method for manufacturing the solar cell backsheet, a solar cell module using the backsheet, and a method for manufacturing the solar cell module. Furthermore, this invention relates to the polyvinyl acetal film for solar cell backsheet manufacture.

  A solar cell module usually has a photoelectric semiconductor layer (hereinafter referred to as a solar cell) having a transparent cover in order to protect it from external influences. The solar battery cell is often provided between a glass plate and a hard cover plate such as glass or a back sheet, and is sealed with an adhesive solar cell sealing material.

  Since solar cells are extremely fragile, for example, as disclosed in Patent Document 1 or Patent Document 2, polyethylene vinyl acetate (hereinafter sometimes abbreviated as “EVA”) or curing is often used as a sealing material. Crosslinkable compounds based on ionic casting resins are used. When these sealing materials are not cured, they can be adjusted to a low viscosity so as to surround solar cells without containing bubbles. Moreover, the sealing material which shows the mechanical strength more than a certain level is obtained after the crosslinking reaction by a hardening | curing agent or a crosslinking agent. As a problem of a solar cell module using EVA, there is corrosion of metal components caused by acetic acid generated by hydrolysis or thermal decomposition of EVA. Another problem when using EVA is that it is necessary to laminate while proceeding with the crosslinking reaction, and it is difficult to achieve a reduction in the time required for the manufacturing process in recent years. In addition, in the manufacture of solar cell modules using curable casting resins, it is difficult to control the embedding and curing of solar cells, and practically they are not employed. In addition, some casting resins tend to form or exfoliate after a few years.

  Further, as described in Patent Document 3 and the like, a film based on polyvinyl butyral (hereinafter, may be abbreviated as “PVB”) which is a thermoplastic resin is also used as a sealing material. PVB has only a small amount of acetic acid units that cause acid components, and has the advantage that corrosion of metal components is less likely to occur than EVA. Moreover, since PVB is a thermoplastic resin, it has a high viscosity at the flow start temperature, and there is little concern that PVB will flow out of the glass end and stain the device and the glass surface. Also, from a mechanical point of view, a film made of PVB has excellent adhesion to glass and penetration resistance, and can be used as an intermediate film for automotive windshields and architectural safety laminated glass. Moreover, since it does not include a crosslinking step, it is advantageous for manufacturing a solar cell module by a roll-to-roll process.

  Polyvinyl acetal such as PVB is more advantageous than EVA in that it is less likely to cause corrosion of metal components when used as a solar cell sealing material, so that it is possible to produce a solar cell module having long-term durability. Many solar cell modules of double-sided glass that make the most of the characteristics are produced. However, solar cell modules that use polyvinyl acetal as a sealing material are also required today for solar cell modules of the type that use a back sheet, and development of an inexpensive back sheet that can be adapted to this sealing material Is required.

  That is, since polyvinyl acetal has a different adhesion mechanism from EVA, even if a backsheet optimized for existing EVA is used, sufficient adhesion may not be obtained. Therefore, development of a back sheet that can be used for a solar cell module using polyvinyl acetal as a sealing material is desired. In addition, the solar cell backsheet is normally disposed on the back side of the solar cell without contacting the solar cell, and is different from the solar cell sealing material.

  Under such circumstances, for example, Patent Document 4 discloses a solar cell laminate including a solar cell layer including solar cells and a layer / (metal layer or polymer film layer) including PVB. The containing layer is used as a solar cell backsheet. However, it is described that the composition constituting the layer containing PVB contains about 15 to 60% of a plasticizer with respect to the total weight of the composition, and sufficient blocking resistance and insulation can be obtained. There may not be.

  Patent Document 5 discloses a laminate having a polyvinyl acetal layer and a layer made of other resin, and this laminate can be applied as a sealing material because of its weather resistance and high flexibility. Is described. However, Patent Document 5 describes that a polyvinyl acetal layer to which a plasticizer is not added is laminated with a surface-treated PET film, but a polyvinyl acetal layer as a sealing material is further added to a polyvinyl acetal layer. There is no disclosure of laminating, and there are cases where sufficient adhesive strength cannot be obtained.

  Furthermore, Patent Document 6 discloses a solar cell module including a substrate / thin film photovoltaic device / polyvinyl butyral layer / protective substrate. However, Patent Document 6 does not disclose that a polyvinyl acetal layer is further laminated on the polyvinyl butyral layer that seals the thin-film photovoltaic device, and as in Patent Document 5, sufficient adhesive strength is obtained. There was no case.

JP 58-023870 A Japanese Patent Laid-Open No. 6-177412 JP 2006-013505 A Special table 2010-512027 International Publication No. 2010/041391 Special table 2011-522419 gazette

  The subject of this invention is providing the solar cell backsheet which can be used also for the solar cell module which used the polyvinyl acetal as a solar cell sealing material, and the solar using this solar cell backsheet It is to provide a battery module.

  As a result of examining such problems, the present inventors have a multi-layer structure having a base material layer and a polyvinyl acetal layer, and a back sheet for a solar cell with a small plasticizer content in the polyvinyl acetal layer is provided. It has been found that the above problems can be solved. Furthermore, the present inventors have made extensive studies based on this finding and have completed the present invention.

  That is, the present invention comprises a multilayer structure having a base material layer and a polyvinyl acetal layer, and the content of the plasticizer in the polyvinyl acetal layer is less than 15 parts by mass with respect to 100 parts by mass of the polyvinyl acetal. It is a back sheet for.

  In the present invention, it is preferable that the multilayer structure further includes an adhesive layer between the base material layer and the polyvinyl acetal layer.

  Moreover, in this invention, it is preferable that the viscosity average polymerization degree of the polyvinyl acetal contained in the said polyvinyl acetal layer is 400-3000.

  Moreover, in this invention, it is preferable that the thickness of the said polyvinyl acetal layer is 0.001-0.24 mm.

  Moreover, in this invention, it is preferable that the content rate of the white pigment in the said polyvinyl acetal layer is 5-30 mass%.

  The present invention is also a solar cell module having the solar cell backsheet. Here, it is preferable to laminate | stack so that the said polyvinyl acetal layer in the said solar cell backsheet and the photovoltaic cell sealing material layer containing polyvinyl acetal may contact | connect.

  This invention is also the manufacturing method of a solar cell module including the process laminated | stacked so that the said polyvinyl acetal layer in the said solar cell backsheet and the photovoltaic cell sealing material layer containing polyvinyl acetal may contact | connect.

  This invention is also a polyvinyl acetal film for solar cell backsheet manufacture whose content of a plasticizer is less than 15 mass parts with respect to 100 mass parts of polyvinyl acetals.

  This invention is a manufacturing method of the solar cell backsheet further including the process of laminating | stacking the base material and the said polyvinyl acetal film for solar cell backsheet manufacture.

  The solar cell backsheet of the present invention is excellent in adhesiveness with a solar battery cell sealing material, and is further excellent in blocking resistance and electrical insulation. Therefore, according to the solar cell backsheet of the present invention, a solar cell module having excellent mechanical strength and a long life can be provided.

  The solar cell backsheet of the present invention comprises a multilayer structure having a base material layer and a polyvinyl acetal layer, and the content of the plasticizer in the polyvinyl acetal layer is less than 15 parts by mass with respect to 100 parts by mass of the polyvinyl acetal. is there. The multilayer structure may further include other layers such as an adhesive layer in addition to the base material layer and the polyvinyl acetal layer. Embodiments of the present invention will be described below. In the following description, specific materials may be exemplified as those that exhibit a specific function, but the present invention is not limited to this. Moreover, as long as there is no description in particular, the material illustrated may be used individually by 1 type, and may use 2 or more types together.

<Base material layer>
The base material layer which the multilayer structure in the solar cell backsheet of this invention has is not specifically limited, A various resin film can be used as a base material. Examples of such resins include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polycarbonate; polymethyl methacrylate; polyacrylate; polyolefin resins such as polypropylene and polyethylene; polyphenylene sulfide (PPS); And fluorine-containing resins such as vinyl fluoride and ethylene-tetrafluoroethylene copolymer (ETFE). These resins may be used alone or in combination of two or more. Among them, a polyester resin is preferable because it is excellent in strength, dimensional stability, and thermal stability, and PET and PEN are more preferable because they are inexpensive. The polyester resin may be a copolymer. Examples of the copolymer component include diol components such as propylene glycol, diethylene glycol, neopentyl glycol, and cyclohexanedimethanol; isophthalic acid, adipic acid, azelaic acid, and sebacic acid. And dicarboxylic acid components such as ester-forming derivatives thereof. On the other hand, ETFE is preferable in terms of optical properties and weather resistance.

  Although the thickness of the said base material layer is not specifically limited, 1-500 micrometers is preferable and 20-300 micrometers is more preferable. When the thickness of the base material layer is in the above range, a solar cell module having a good balance between cost and electrical insulation can be obtained.

<Polyvinyl acetal layer>
In the polyvinyl acetal layer used for the solar cell backsheet of the present invention, as described later, it is important that the content of the plasticizer is less than 15 parts by mass with respect to 100 parts by mass of the polyvinyl acetal. The polyvinyl acetal layer is preferably composed mainly of polyvinyl acetal. Specifically, the content is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 60% by mass or more. A mass% or more is particularly preferred. When the content of polyvinyl acetal is less than 40% by mass, the mechanical properties tend to be insufficient. Moreover, in the polyvinyl acetal layer used for the solar cell backsheet of this invention, unless it is contrary to the meaning of this invention, it is also possible to mix resin other than polyvinyl acetal. It is also possible to mix inorganic substances (titanium oxide, talc, etc.).

[Polyvinyl acetal]
As said polyvinyl acetal, a thing with an acetalization degree of 40-90 mol% is preferable. When the degree of acetalization is less than 40 mol%, the water absorption rate is increased, which is not preferable. On the other hand, if the degree of acetalization exceeds 90 mol%, a long time is required for the reaction for obtaining polyvinyl acetal, which may be undesirable in the reaction process. The degree of acetalization is more preferably 60 to 85 mol%, and further preferably 65 to 80 mol% from the viewpoint of water resistance. In addition, the said acetalization degree is based on the vinyl acetal unit in the polyvinyl acetal mentioned later.

  The polyvinyl acetal has a vinyl alcohol unit content in the polyvinyl acetal of preferably 8 to 55 mol%, more preferably 10 to 38 mol%, and even more preferably 12 to 34 mol%. . When the content of the vinyl alcohol unit is too high, the hygroscopicity of the obtained polyvinyl acetal layer increases, and the water absorbed by the polyvinyl acetal layer reduces the electrical insulation of the solar cell backsheet, or the base material layer. There is a risk of delamination between the polyvinyl acetal layer and the polyvinyl acetal layer. On the other hand, when the content rate of a vinyl alcohol unit is too low, there exists a possibility that the fall of the mechanical strength of the polyvinyl acetal layer obtained and delamination of a base material layer and a polyvinyl acetal layer may arise.

  In the polyvinyl acetal, the content of vinyl ester units in the polyvinyl acetal is preferably 5 mol% or less, more preferably 2 mol% or less, and even more preferably 1 mol% or less. Vinyl ester units generate acetic acid, which is a corrosive substance, by decomposition by heat and hydrolysis by moisture, and olefins are generated by elimination of acetic acid and tend to cause coloring.

  Polyvinyl acetal is usually composed of a vinyl acetal unit (having 2 carbon atoms in the main chain), a vinyl alcohol unit and a vinyl ester unit. The amount of each of these components is, for example, JIS K6728: 1977 “ It can be measured based on "polyvinyl butyral test method" or nuclear magnetic resonance (NMR).

  When the polyvinyl acetal contains units other than the vinyl acetal unit, the unit amount of vinyl alcohol and the unit amount of vinyl ester are usually measured and the remaining unit amount is subtracted from the total unit amount of polyvinyl acetal. The amount of vinyl acetal unit can be calculated.

  As a polyvinyl acetal used for the solar cell backsheet of this invention, what makes the below-mentioned aldehyde react with polyvinyl alcohol can be used. Such a polyvinyl acetal can be manufactured by a well-known method.

  Polyvinyl alcohol used as a raw material for polyvinyl acetal can be obtained, for example, by polymerizing a vinyl ester monomer and saponifying the resulting polymer. As a method for polymerizing the vinyl ester monomer, conventionally known methods such as a solution polymerization method, a bulk polymerization method, a suspension polymerization method, and an emulsion polymerization method can be employed. As the polymerization initiator, an azo initiator, a peroxide initiator, a redox initiator, or the like can be appropriately selected depending on the polymerization method. For the saponification reaction, a known alcoholysis or hydrolysis using an alkali catalyst or an acid catalyst can be applied. Among them, a saponification reaction using methanol as a solvent and a sodium hydroxide (NaOH) catalyst is simple and most preferable.

  The saponification degree of polyvinyl alcohol used as a raw material for polyvinyl acetal is not particularly limited, but it is preferable to set the content of the vinyl ester unit of the obtained polyvinyl acetal within the above range. The mol% or more is preferable, 98 mol% or more is more preferable, and 99 mol% or more is more preferable.

  Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, palmitic acid. Vinyl acid, vinyl stearate, vinyl oleate, vinyl benzoate and the like can be mentioned, with vinyl acetate being particularly preferred. Moreover, when superposing | polymerizing the said vinyl ester-type monomer, it can also be copolymerized with other monomers, such as an alpha olefin, in the range which does not impair the meaning of this invention. The other monomer units are usually used in a proportion of less than 10 mol% with respect to the vinyl ester monomer units of the resulting polyvinyl ester polymer.

  The polyvinyl alcohol used as the raw material for the polyvinyl acetal is preferably one having a viscosity average polymerization degree of 400 to 3000, more preferably 450 to 2000, still more preferably 500 to 1500, and particularly preferably 600 to 1000. . If the viscosity average polymerization degree of polyvinyl alcohol is too high, it becomes difficult to form a film of the resulting polyvinyl acetal. If the viscosity average polymerization degree is too low, the adhesion between the solar cell sealing material and the back sheet is poor. There is a possibility that problems such as lowering and a decrease in mechanical strength of the polyvinyl acetal layer may occur. Since the viscosity average polymerization degree of the polyvinyl acetal matches the viscosity average polymerization degree of the raw material polyvinyl alcohol, the preferred viscosity average polymerization degree of the polyvinyl alcohol matches the preferred viscosity average polymerization degree of the polyvinyl acetal.

  The viscosity average polymerization degree of polyvinyl alcohol can be measured based on, for example, JIS K6726 “Testing method for polyvinyl alcohol”.

  The solvent used for the production of the polyvinyl acetal is not particularly limited, but water is preferably used for industrial production in large quantities, and the polyvinyl alcohol is sufficiently water at a high temperature, for example, a temperature of 90 ° C. or higher in advance before the reaction. It is preferable to dissolve in the solution. Moreover, 5-40 mass% is preferable, as for the density | concentration of the aqueous solution which melt | dissolved polyvinyl alcohol, 6-20 mass% is more preferable, and 8-15 mass% is especially preferable. If the concentration of the aqueous solution of polyvinyl alcohol is too low, the productivity of polyvinyl acetal is not preferable. On the other hand, if the concentration of the aqueous polyvinyl alcohol solution is too high, stirring during the reaction becomes difficult, and gelation due to intermolecular hydrogen bonding of the polyvinyl alcohol occurs, resulting in uneven reaction.

  Polyvinyl acetal can be produced by adding an aldehyde to the aqueous solution of the polyvinyl alcohol and reacting it, but the catalyst used in that case is not particularly limited, and any acid catalyst of organic acid and inorganic acid Can also be used, and examples thereof include acetic acid, p-toluenesulfonic acid, nitric acid, sulfuric acid, hydrochloric acid, and carbonic acid. Of these, inorganic acids are preferable, and hydrochloric acid, sulfuric acid, and nitric acid are particularly preferable because a sufficient reaction rate can be obtained for the acetalization reaction and washing after the reaction is easy. The concentration of the acid used for the reaction depends on the type of acid used, but in the case of hydrochloric acid, sulfuric acid and nitric acid, it is preferably 0.01 to 5 mol / L, more preferably 0.1 to 2 mol / L. If the concentration of the catalyst is too low, the reaction rate is slow, and it takes time to obtain the desired degree of acetalization and the desired physical properties of polyvinyl acetal. On the other hand, if the concentration of the catalyst is too high, it is difficult to control the acetalization reaction, and it is not preferable because a trimer of aldehydes is easily generated.

  Here, as the aldehydes, for example, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, hexylaldehyde, benzaldehyde and the like are used. An aldehyde compound having 1 to 12 carbon atoms is preferable, a saturated alkyl aldehyde compound having 1 to 6 carbon atoms is more preferable, and a saturated alkyl aldehyde compound having 1 to 4 carbon atoms is particularly preferable. From the viewpoint of physical properties, butyraldehyde is preferable. Moreover, aldehydes may be acetalized using only 1 type and may be acetalized using 2 or more types together. Further, a small amount of polyfunctional aldehydes or aldehydes having other functional groups may be used in a range of 20% by mass or less of the total aldehydes.

  Examples of the procedure for reacting aldehydes with polyvinyl alcohol include known methods. For example, a method of adding aldehydes after adding the above catalyst to an aqueous solution of polyvinyl alcohol, a catalyst after adding aldehydes first. The method of adding is mentioned. In addition, aldehydes or catalysts to be added may be added all at once or sequentially, or added in portions, a method of adding a mixed solution of an aqueous solution of polyvinyl alcohol and an aldehyde to a solution containing the catalyst, or a solution of polyvinyl alcohol in a solution containing the aldehydes. Examples include a method of adding a mixed solution of an aqueous solution and a catalyst.

  The reaction temperature of the acetalization reaction is not particularly limited, but in order to improve the durability of the back sheet for solar cells, from the viewpoint of producing a porous polyvinyl acetal that can be easily washed after the reaction, The reaction is preferably performed at a relatively low temperature of 0 to 40 ° C. until the acetal particles are precipitated, and more preferably the reaction is performed at 5 to 20 ° C. When reaction temperature exceeds 40 degreeC, there exists a possibility that polyvinyl acetal will fuse | melt and it may become difficult to become porous. After carrying out the reaction at a relatively low temperature of 0 to 40 ° C., the reaction temperature is preferably 50 to 80 ° C., more preferably 65 to 75 ° C. in order to drive the reaction and increase the productivity.

  As a method for removing aldehydes and catalyst remaining after the acetalization reaction, known methods may be mentioned. The polyvinyl acetal obtained by the acetalization reaction using an acid catalyst is usually neutralized with an alkali compound, but it is preferable to remove aldehydes remaining in the polyvinyl acetal as much as possible before neutralization. Methods for removing aldehydes remaining in the polyvinyl acetal include a method of driving the reaction under conditions where the reaction rate of the aldehydes is high, a method of sufficiently washing with water, a water / alcohol mixed solvent, or the like, or a chemically aldehyde The method of processing is useful. Examples of the alkali compound used for neutralization include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide, and amine compounds such as ammonia, triethylamine, and pyridine. Among these, alkali metal hydroxides are particularly preferable.

  The polyvinyl acetal obtained by the above method is preferably adjusted so that the alkali titer value becomes a positive value so as not to be decomposed by an acid in the presence of water to generate aldehydes. The alkali titer value of the polyvinyl acetal after neutralization with the alkali compound is preferably from 0.1 to 30, more preferably from 1 to 20, and even more preferably from 1 to 10. If the alkali titer value is too low, the polyvinyl acetal may be easily hydrolyzed. Conversely, if the alkali titer value is too high, coloring may easily occur during the production of a polyvinyl acetal film (sheet). Here, the alkali titer value is an amount of 0.01 mol / L hydrochloric acid (mL) required for neutralizing and titrating an alkali component in 100 g of polyvinyl acetal.

  The amount of chloride ion, sulfate ion and nitrate ion derived from the acetalization catalyst contained in the polyvinyl acetal is preferably 100 ppm or less in total, more preferably 50 ppm or less, and 20 ppm or less. Further preferred. Since these ions cause corrosion of the metal component used in the solar cell module, a smaller amount is preferable.

[Plasticizer]
In the present invention, the content of the plasticizer in the polyvinyl acetal layer is very important. In the polyvinyl acetal layer of the multilayer structure in the solar cell backsheet of the present invention, it is important that the plasticizer content is less than 15 parts by mass with respect to 100 parts by mass of the polyvinyl acetal. Is preferably 8 parts by mass or less, more preferably 5 parts by mass or less, particularly preferably 2 parts by mass or less, and may be 0 parts by mass (that is, Does not need to contain a plasticizer). When the content of the plasticizer is 15 parts by mass or more, the blocking resistance and electrical insulation of the solar cell backsheet to be obtained are lowered.

  The plasticizer is not particularly limited, and examples thereof include triethylene glycol-di (2-ethylhexanoate) (3GO), tetraethylene glycol-di (2-ethylhexanoate), and di (2-butoxyethyl). ) -Adipic acid ester (DBEA), di (2-butoxyethyl) -sebacic acid ester (DBES), di (2-butoxyethyl) -azelaic acid ester, di (2-butoxyethyl) -glutaric acid ester, di ( 2-butoxyethyl) -phthalic acid ester, di (2-butoxyethoxyethyl) -adipic acid ester (DBEEA), di (2-butoxyethoxyethyl) -sebacic acid ester (DBEES), di (2-butoxyethoxyethyl) -Azelaic acid ester, di (2-butoxyethoxyethyl) -glutaric acid ester Di (2-butoxyethoxyethyl) -phthalic acid ester, di (2-hexoxyethyl) -adipic acid ester, di (2-hexoxyethyl) -sebacic acid ester, di (2-hexoxyethyl) -azeleic acid ester, di (2- Hexoxyethyl) -glutaric acid ester, di (2-hexoxyethoxyethyl) -adipic acid ester, di (2-hexoxyethoxyethyl) -sebacic acid ester, di (2-hexoxyethoxyethyl) -azeleic acid ester, di (2-hexoxyethoxyethyl) -glutaric acid ester, 1,2-cyclohexanedicarboxylic acid-diisononyl ester (DINCH) and the like. Among these, a plasticizer in which the sum of the number of carbon atoms and the number of oxygen atoms constituting the plasticizer molecule is larger than 28 is preferable. When the sum of the number of carbon atoms and the number of oxygen atoms constituting the plasticizer molecule is 28 or less, in particular, thermal decomposition and hydrolysis occur under high temperature and high humidity, resulting in an increased acid value. The acid concentration tends to increase. Examples of the plasticizer in which the sum of the number of carbon atoms and oxygen atoms constituting the plasticizer molecule is greater than 28 include, for example, triethylene glycol-di (2-ethylhexanoate) (3GO), tetraethylene glycol-di ( 2-ethylhexanoate), di (2-butoxyethoxyethyl) -adipate (DBEEA), di (2-butoxyethoxyethyl) -sebacate (DBEES), 1,2-cyclohexanedicarboxylic acid-diisononyl ester (DINCH) and the like. Among these, triethylene glycol di (2-ethylhexanoate) (3GO), 1,2- can be obtained in a small amount without deteriorating mechanical properties and optical properties. Cyclohexanedicarboxylic acid-diisononyl ester (DINCH) is preferred. Such plasticizers may be used alone or in combination of two or more.

[Other additives]
The polyvinyl acetal layer may further contain an antioxidant, an ultraviolet absorber, an adhesive strength modifier, an antiblocking agent, a dye, a functional inorganic compound, and the like.

  Examples of the antioxidant include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, etc. Among them, phenolic antioxidants are preferred, and alkyl-substituted phenolic antioxidants are preferred. Particularly preferred. These antioxidants can be used alone or in combination of two or more. Content of antioxidant is 0.001-5 mass parts with respect to 100 mass parts of polyvinyl acetals, Preferably it is 0.01-1 mass part.

  Known ultraviolet absorbers can be used, and examples thereof include benzotriazole ultraviolet absorbers, hindered amine ultraviolet absorbers, and benzoate ultraviolet absorbers. The content of the ultraviolet absorber is preferably 10 to 50,000 ppm, more preferably 100 to 10,000 ppm, based on mass with respect to polyvinyl acetal. Moreover, only one type of ultraviolet absorber may be used alone, or two or more types may be used in combination.

  Examples of the functional inorganic compound include a light reflecting material, a light absorbing material, a thermal conductivity improving material, an electrical property improving material, a gas barrier property improving material, a mechanical property improving material, and the like.

  Examples of the light reflecting material include white pigments. Among them, a white pigment having a refractive index exceeding 1.8 is preferable, and specific examples include titanium dioxide, lithopone, barium sulfate, zinc oxide, zinc sulfide, lead carbonate and the like. Among these, titanium dioxide is particularly preferable because of its high refractive index and excellent light reflectivity. Moreover, metals, such as aluminum, zinc, chromium, or titanium, can also be used as the light reflecting material. These light reflecting materials may be used alone or in combination of two or more.

  Although the content rate of the said white pigment is not specifically limited, It is preferable that it is 5-30 mass% with respect to a polyvinyl acetal layer, It is more preferable that it is 6-20 mass%, It is 7-16 mass% Is more preferable. When the content of the white pigment in the polyvinyl acetal layer is less than 5% by mass, light reflection is insufficient and the output of the solar cell tends to decrease. When the content of the white pigment exceeds 30% by mass, the mechanical properties are increased. Tend to decrease.

  The polyvinyl acetal layer in the solar cell backsheet of this invention can be formed using the polyvinyl acetal film which has the composition and structure similar to it. The present invention includes such a polyvinyl acetal film for producing a solar cell back sheet, that is, a polyvinyl acetal film for producing a solar cell back sheet having a plasticizer content in the above range. Moreover, this invention also includes the manufacturing method of the solar cell backsheet including the process of laminating | stacking the above-mentioned base material and the said polyvinyl acetal film for solar cell backsheet manufacture.

  As a method for producing the polyvinyl acetal film, a method using an extruder is suitably employed. The temperature of the polyvinyl acetal during extrusion by the extruder is preferably 150 to 250 ° C, and more preferably 180 to 230 ° C. If the temperature of the polyvinyl acetal becomes too high, the polyvinyl acetal will be decomposed and the content of volatile substances will increase. On the other hand, if the temperature of the polyvinyl acetal is too low, the content of volatile substances will increase. In order to efficiently remove the volatile substance, it is preferable to remove the volatile substance from the vent port of the extruder by reducing the pressure.

  The thickness of the polyvinyl acetal layer is preferably 0.001 to 0.24 mm, more preferably 0.01 to 0.20 mm, and still more preferably 0.05 to 0.15 mm. If the thickness of the polyvinyl acetal layer is thinner than 0.001 mm, the electrical insulation may be lowered, and if the thickness of the polyvinyl acetal layer is thicker than 0.24 mm, the cost of the polyvinyl acetal layer is increased. This is not preferable because the cost of the obtained solar cell backsheet increases.

  Further, the polyvinyl acetal layer has a deaeration property between the base material layer and the polyvinyl acetal layer in the solar cell backsheet of the present invention, or between the polyvinyl acetal layer and an adhesive layer described later. In order to increase, unevenness may be provided on the surface. As a method of providing unevenness on the surface of the polyvinyl acetal layer, a conventionally known method can be employed.For example, in the production of a polyvinyl acetal film, a method of providing a melt fracture structure by adjusting extrusion conditions, an extruded film A method of imparting an emboss structure is employed.

<Adhesive layer>
In addition to the base material layer and the polyvinyl acetal layer, the solar cell backsheet of the present invention may further have an adhesive layer. When it is judged that the adhesive strength between the base material layer and the polyvinyl acetal layer is not practically sufficient, a more stable adhesive strength can be obtained by providing an adhesive layer between the base material layer and the polyvinyl acetal layer. The adhesive for forming the adhesive layer is not particularly limited. For example, a compound containing an alkoxysilyl group and an amino group, a compound containing an alkoxysilyl group and an epoxy group; or a polyol such as a polyester polyol and the like Examples thereof include a mixture containing an isocyanate such as polyisocyanate. Among them, the compound containing the alkoxysilyl group and the amino group is 3-aminopropyltrimethoxysilane; the alkoxysilyl group and the epoxy group are contained in that an adhesive layer having more stable adhesive strength can be formed. 3-glycidyloxypropyltrimethoxysilane as the compound; a two-component curable urethane-based adhesive is preferable as the mixture containing the polyol and isocyanate.

  As a method of forming the adhesive layer, for example, an aqueous solution obtained by dissolving the adhesive as it is or by dissolving the adhesive in water as needed is applied to the surface of the base material layer or the polyvinyl acetal layer and dried. As a result, an adhesive layer is formed. The content of the adhesive in the aqueous solution is appropriately selected depending on the type of adhesive used and the thickness of the target adhesive layer, but is preferably 0.1 to 20 parts by mass with respect to 100 parts by mass of water. 0.5-10 mass parts is more preferable.

  Although the thickness of the said contact bonding layer is not specifically limited, 0.1-100 micrometers is preferable. When the thickness of the adhesive layer is less than 0.1 μm, film breakage may occur when the adhesive or an aqueous solution containing the adhesive is applied, or delamination may occur between the base material layer and the polyvinyl acetal layer. is there. On the other hand, when the thickness of the adhesive layer is larger than 100 μm, it is not preferable because the cost increases.

<Solar cell module>
The solar cell module of this invention can take a well-known structure as a structure of a solar cell module except having the solar cell backsheet of this invention. Further, the manufacturing method of the solar cell module is not particularly limited and is manufactured by a known method. From the viewpoint of further improving the adhesion between the solar cell sealing material layer and the back sheet, the sealing material is It is preferable to use polyvinyl acetal and to use the solar cell backsheet of the present invention as the backsheet.

  Furthermore, when manufacturing the solar cell module of this invention, it is preferable to include the process of laminating | stacking so that the said polyvinyl acetal layer in a solar cell backsheet and the photovoltaic cell sealing material layer containing polyvinyl acetal may contact | connect. The solar cell module obtained through such a process is laminated so that the polyvinyl acetal layer in the solar cell backsheet and the solar cell sealing material layer containing polyvinyl acetal are in contact with each other. This is preferable because the adhesiveness of the resin is further improved.

  As the solar cell module of the present invention, various types can be exemplified. For example, a configuration in which a solar cell is sandwiched between both sides by a sealing material, such as a surface-side transparent protective member / surface sealing material / solar battery cell / back surface sealing material / back sheet, surface-side transparent protection member / solar battery The thing of a structure like a cell / sealing material / back sheet (super straight structure) can be mentioned. In addition, the said back sheet means the back sheet for solar cells of this invention.

  Solar cells constituting the solar cell module include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, periodic table groups III-V and II-VI such as gallium / arsenic, CIGS, cadmium / tellurium, etc. Various types of solar cells such as compound semiconductors, dye sensitizers, and organic thin films such as organic thin films can be mentioned.

  Examples of the surface-side transparent protective member constituting the solar cell module include glass, acrylic resin, polycarbonate, polyester, and fluorine-containing resin.

  The glass used is not particularly limited, and examples thereof include float glass, tempered glass, netted glass, and organic glass. Although there is no restriction | limiting in particular in the thickness of glass, 1-10 mm is preferable and 2-6 mm is more preferable.

  The sealing material (solar cell sealing material) constituting the solar cell module is a polyvinyl acetal such as polyvinyl butyral from the viewpoint of further improving the adhesiveness with the solar cell backsheet of the present invention. preferable. Moreover, although the thickness of a sealing material is not specifically limited, 0.05-10.0 mm is preferable and 0.2-1.0 mm is more preferable.

  In addition, the solar cell module of the present invention can be combined with a known frame, junction box, sealing agent, mounting jig and mount, antireflection film, various facilities using solar heat, rain gutter structure, and the like.

  As a laminating method for obtaining a solar cell module, a known method can be adopted, for example, a method using a vacuum laminator device, a method using a vacuum bag, a method using a vacuum ring, a method using a nip roll, and the like. It is done. In addition, a method of adding to the autoclave process after temporary pressure bonding can be additionally performed.

  Among these, a method using a vacuum laminator is particularly suitable. For example, it is laminated using a known apparatus used for manufacturing a solar cell module under a reduced pressure of 0.01 to 300 mbar, usually at a temperature of 100 to 200 ° C., preferably 130 to 160 ° C. A method using a vacuum bag or a vacuum ring is described, for example, in EP 1 235 683, and is laminated at 130-145 ° C. under a pressure of about 200 mbar.

  The solar cell module of the present invention can be used as a member such as a window, a wall, a roof, a sunroom, a soundproof wall, a show window, a balcony, a handrail wall, or as a partition glass member for a conference room, etc. It can also be used as a part.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples.

  In the following examples and comparative examples, the polyvinyl butyral (PVB) used is the same viscosity average polymerization degree as the target viscosity average polymerization degree (viscosity measured based on JIS K6726 “Testing method for polyvinyl alcohol”). Polyvinyl alcohol having an average polymerization degree) acetalized with n-butyraldehyde under a nitric acid catalyst was used.

[Example 1]
1,2-cyclohexanedicarboxylic acid with respect to 100 parts by mass of PVB having a viscosity average polymerization degree of 1000, an acetalization degree of 78 mol%, a vinyl alcohol unit content of 21 mol% and a vinyl ester (vinyl acetate) unit content of 1 mol%. A composition obtained by mixing 10 parts by mass of acid-diisononyl ester was extruded with a single screw extruder (resin temperature 230 ° C.), and a PVB film having a thickness of 0.15 mm was formed at a winding speed of 3 m / min. Obtained. The PVB film and an ETFE film having a thickness of 100 μm (Asahi Kasei Co., Ltd .: Aflex 100N) were overlaid and subjected to hot pressing at 135 ° C., 12 kg / cm ² for 30 minutes to obtain a solar cell backsheet. .
Then, adhesiveness, blocking resistance, and electrical insulation were evaluated by the following method using the solar cell backsheet. The results are shown in Table 1.

(1) Adhesiveness: measurement of adhesive strength between solar cell encapsulant and solar cell backsheet In accordance with JIS K6854-2, solar cell encapsulant (Kuraray Co., Ltd .: TROSIFOL SOLAR R40, thickness 0) .76 mm) and the solar cell backsheet were measured. Specifically, first, the solar cell sealing material is stacked on a semi-tempered glass having a thickness of 3.2 mm so that the sealing material layer is in contact with the PVB layer of the solar battery backsheet. The back sheet was overlaid and laminated using a commercially available vacuum laminator device under the conditions of a hot plate set temperature of 155 ° C., evacuation for 11 minutes, pressure adjustment for 1 minute, and press for 15 minutes to prepare a measurement sample. .
The adhesive strength was measured using Tensilon RTG-1210 (manufactured by A & D Co., Ltd.) on three test pieces under the conditions of a measurement sample width of 10 mm and a peeling speed of 200 mm / min. And the average value of the measured result was made into adhesive strength. If the adhesive strength is 10 N / 10 mm or more, there is no practical problem. In Table 1, those having an adhesive strength of 10 N / 10 mm or more were judged as “◯”, those having an adhesive strength of 2 N / 10 mm or more and less than 10 N / 10 mm were judged as “Δ”, and those having an adhesion strength of less than 2 N / 10 mm were judged as “X”.

(2) Blocking resistance: measurement of shearing force Two samples (5 cm × 5 cm) for measurement of the solar cell backsheet are stacked in a direction in which the PVB layers do not face each other (that is, PVB layer / base material layer / PVB layer) / Overlayed in order of the base material layer), and the base material (ETFE film) layer was placed on the metal plate. Further, a 3 × 4 cm rectangular parallelepiped metal weight was placed on the two sheets and left in an environment with an air temperature of 40 ° C. for 65 hours. Thereafter, the weight was removed, and each of the two sheets was pulled in the opposing direction along the plane (the major axis direction of the bottom surface of the weight), and the shear force was measured. This measurement was performed on three sets of measurement samples, and the average value was taken as the shear force. When blocking does not occur, the shearing force is 0, and the greater the degree of occurrence of blocking, the higher the shearing force. If the shearing force in this measuring method is 0.05 kgf or less, there is no practical problem. In Table 1, those with 0.05 kgf or less were judged as “◯” and those with 0.05 kgw or more were judged as “x”.

(3) Electrical insulation: measurement of partial discharge voltage About the said solar cell backsheet, the partial discharge voltage was measured based on the following measuring method, and electrical insulation was evaluated.
Conformity standard: IEC60664 / A2: 2002 4.1.2.4
Test device: KPD2050 (manufactured by Kikusui Electronics Corporation)
Measurement pattern: trapezoidal start voltage charge threshold: 1.0 pC
Vanishing voltage charge threshold: 1.0 pC
Test time: 22.0 seconds In Table 1, those exceeding 1000 V were determined as “◯”, 950 V or more, less than 1000 V as “Δ”, and less than 950 V as “×”.

[Example 2]
A PVB film having a thickness of 0.15 mm was obtained in the same manner as in Example 1. Subsequently, on a 125 μm thick PET film (Toray Industries, Inc .: Lumirror X10S), Takelac A310 (Mitsui Chemicals) and Takelac A-3 (Mitsui Chemicals) are used as a two-component curable urethane adhesive. And a mixture of Takerak A310 / Takeratta A-3 (mass ratio) = 12/1 was applied to form an adhesive layer having a thickness of 30 μm. Then, the PVB film was placed on the surface of the adhesive layer that was not in contact with the PET film, dry laminated, and annealed at 60 ° C. for 7 days to obtain a solar cell backsheet.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 3]
A PVB film having a thickness of 0.15 mm was obtained in the same manner as in Example 1. Subsequently, an aqueous solution obtained by dissolving 0.5 parts by mass of 3-aminopropyltrimethoxysilane with respect to 100 parts by mass of deionized water on a 125 μm thick PET film (manufactured by Toray Industries, Inc .: Lumirror X10S). Was applied using an applicator to a thickness of 30 μm and dried at 80 ° C. to form a dried adhesive layer having a thickness of 0.3 μm. And the said PVB film was piled up on the surface which is not in contact with the PET film of the said contact bonding layer, and the solar cell backsheet was obtained by heat-pressing on conditions of 135 degreeC and 12 kg / cm < ² > for 30 minutes.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 4]
A solar cell backsheet was obtained in the same manner as in Example 2 except that the winding speed from the single screw extruder was changed to 4 m / min and a PVB film having a thickness of 0.1 mm was used.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 5]
A solar cell backsheet was obtained in the same manner as in Example 2 except that 1,2-cyclohexanedicarboxylic acid-diisononyl ester was not used.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 6]
The same as Example 2 except that PVB having a viscosity average polymerization degree of 1700, an acetalization degree of 78 mol%, a vinyl alcohol unit content of 21 mol% and a vinyl ester (vinyl acetate) unit content of 1 mol% was used. A solar cell backsheet was obtained by the method.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 7]
The same as in Example 4 except that PVB having a viscosity average polymerization degree of 1700, acetalization degree of 78 mol%, vinyl alcohol unit content of 21 mol% and vinyl ester (vinyl acetate) unit content of 1 mol% was used. A solar cell backsheet was obtained by the method.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 8]
To a composition comprising 100 parts by weight of PVB and 10 parts by weight of 1,2-cyclohexanedicarboxylic acid-diisononyl ester, titanium dioxide (manufactured by KRONOS: KRONOS 2220) was further added so that the content in the PVB film was 30% by weight. Except for this, a solar cell backsheet was obtained in the same manner as in Example 2.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 9]
A solar cell backsheet was obtained in the same manner as in Example 8 except that titanium dioxide was added so that the content of titanium dioxide TiO ₂ in the obtained PVB film was 15% by mass.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 10]
A solar cell backsheet was obtained in the same manner as in Example 8 except that titanium dioxide was added so that the content of titanium dioxide in the obtained PVB film was 5% by mass.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Example 11]
The same as Example 2 except that PVB having a viscosity average polymerization degree of 200, acetalization degree of 78 mol%, a vinyl alcohol unit content of 21 mol% and a vinyl ester (vinyl acetate) unit content of 1 mol% was used. A solar cell backsheet was obtained by the method.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. The results are shown in Table 1.

[Comparative Example 1]
A solar cell backsheet was obtained in the same manner as in Example 2 except that the amount of 1,2-cyclohexanedicarboxylic acid-diisononyl ester added was changed to 30 parts by mass.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. As a result, the resulting solar cell backsheet was particularly insufficient in blocking resistance and electrical insulation. The results are shown in Table 2.

[Comparative Example 2]
A solar cell backsheet was obtained in the same manner as in Example 2 except that the amount of 1,2-cyclohexanedicarboxylic acid-diisononyl ester added was changed to 20 parts by mass.
And about the back seat | sheet for this solar cell, by the method similar to Example 1, evaluation of adhesiveness, blocking resistance, and electrical insulation was implemented. As a result, the blocking resistance of the obtained solar cell backsheet was particularly insufficient. The results are shown in Table 2.

[Comparative Example 3]
A 125 μm thick PET film (Toray Industries, Inc .: Lumirror X10S) was used as it was as a solar cell backsheet, and the adhesion was evaluated in the same manner as in Example 1. As a result, the adhesion between the solar cell sealing material layer and the PET layer was insufficient. The results are shown in Table 2.

  In order to obtain a solar cell backsheet having excellent adhesion, blocking resistance and electrical insulation from the examples and comparative examples, the content of the plasticizer in the polyvinyl acetal layer constituting the backsheet may be reduced. It turns out to be important.

Claims (6)

A solar cell backsheet comprising a multilayer structure having a base material layer and a polyvinyl acetal layer, wherein the content of the plasticizer in the polyvinyl acetal layer is less than 15 parts by mass relative to 100 parts by mass of the polyvinyl acetal ,
The solar cell module laminated | stacked so that the said polyvinyl acetal layer in the said solar cell backsheet and the photovoltaic cell sealing material layer containing polyvinyl acetal may contact | connect. The solar cell module according to claim 1, wherein the multilayer structure further includes an adhesive layer between the base material layer and the polyvinyl acetal layer. The solar cell module of Claim 1 or 2 whose viscosity average polymerization degree of the polyvinyl acetal contained in the said polyvinyl acetal layer is 400-3000. The solar cell module of any one of Claims 1-3 whose thickness of the said polyvinyl acetal layer is 0.001-0.24 mm. The solar cell module of any one of Claims 1-4 whose content rate of the white pigment in the said polyvinyl acetal layer is 5-30 mass%. It is a manufacturing method of the solar cell module of any one of Claims 1-5, Comprising: The said polyvinyl acetal layer in the said solar cell backsheet, and the photovoltaic cell sealing material layer containing polyvinyl acetal contact | connect. The manufacturing method of a solar cell module including the process of laminating | stacking.