JP2013258366A - Protective sheet for protecting solar cell and method for manufacturing the same, and solar cell including the protective sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel protective sheet having high weather resistance and high steam barrier properties, and a method for easily manufacturing the protective sheet.SOLUTION: A manufacturing method disclosed is a method for manufacturing a protective sheet for protecting a surface of a solar cell. The manufacturing method includes the steps of: (i) forming a laminated film comprising a methacrylic resin layer and a polyvinyl acetal layer by a co-extrusion method; and (ii) laminating the laminated film and a steam barrier film so that the steam barrier film, the polyvinyl acetal layer, and the methacrylate resin layer are laminated in the order. A carbon number of an acetal part per 100 carbon atoms is in the range of 30-70, the acetal part constituting a main chain of polyvinyl acetal used in the polyvinyl acetal layer, and an average degree of polymerization of the polyvinyl acetal is in the range of 500-2,000.

Description

  The present invention relates to a protective sheet for protecting a solar cell, a method for producing the same, and a solar cell using the same.

  A flexible solar cell using a flexible substrate is expected to have a wide range of applications. A solar cell usually requires a translucent protective member that protects the light incident surface. In order to take advantage of the characteristics of a flexible solar cell, it is necessary to use a flexible protective member. As such a protective member, a flexible protective member for a solar cell has been conventionally proposed (Patent Documents 1 and 2). Patent Document 1 discloses a protective film in which a silicon oxide vapor deposition film formed by a CVD method and a silicon oxide vapor deposition film formed by a reactive ion cluster beam method are laminated on a fluorine resin film. It is disclosed. Patent Document 2 discloses a protective sheet including a plastic film and a first inorganic layer, an organic layer, and a second inorganic layer laminated thereon.

  When protecting solar cells, the barrier property of water vapor is important. An example of a barrier layer having a water vapor barrier property is disclosed in Patent Document 3.

JP 2011-014559 A JP 2012-015294 A International Publication WO2011 / 122036

  The protective sheet for protecting the solar cell is required to have high weather resistance and high water vapor barrier properties. However, in order to realize both of them, it is necessary to stack a plurality of layers having different properties, and the manufacturing method tends to be complicated. Under such circumstances, one of the objects of the present invention is to provide a novel protective sheet having high weather resistance and high water vapor barrier properties, and a production method capable of easily producing the same.

  In order to achieve the above object, the production method of the present invention is a production method of a protective sheet for protecting the surface of a solar cell, and (i) a coextrusion method of a laminated film of a methacrylic resin layer and a polyvinyl acetal layer And (ii) laminating the laminated film and the water vapor barrier film so that the water vapor barrier film, the polyvinyl acetal layer, and the methacrylic resin layer are laminated in this order, The carbon number of the acetal part per 100 carbon atoms constituting the main chain of the polyvinyl acetal used for the polyvinyl acetal layer is in the range of 30 to 70, and the average degree of polymerization of the polyvinyl acetal is in the range of 500 to 2000.

  The protective sheet of the present invention is a protective sheet for protecting the surface of a solar cell, and includes a coextruded film in which a methacrylic resin layer and a polyvinyl acetal layer are laminated, and a water vapor barrier film, The barrier film, the polyvinyl acetal layer, and the methacrylic resin layer are laminated in this order.

  Moreover, the solar cell of the present invention is a solar cell comprising a protective sheet for protecting the surface, wherein the protective sheet is the protective sheet of the present invention, wherein the methacrylic resin layer is the water vapor barrier film. It is arranged outside.

  According to the present invention, a protective sheet having high weather resistance and high water vapor barrier properties can be obtained. By using this protective sheet, a highly durable solar cell can be obtained. Since the protective sheet of the present invention can be flexible, it can be suitably used as a protective sheet for protecting a flexible solar cell. According to the production method of the present invention, a protective sheet having high weather resistance and high water vapor barrier properties can be easily produced.

  Hereinafter, embodiments of the present invention will be described. In the following description, specific materials and numerical values may be exemplified, but the present invention is not limited to such materials and numerical values. 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. In this specification, “gas barrier property” means the ability to barrier a gas other than water vapor (for example, oxygen gas) unless otherwise specified. In this specification, the water vapor barrier property and the gas barrier property may be collectively referred to as “barrier property”.

[Protective sheet]
The protective sheet of the present invention is a protective sheet for protecting the surface of the solar cell. This protective sheet includes a coextruded film in which a methacrylic resin layer and a polyvinyl acetal layer are laminated, and a water vapor barrier film. The water vapor barrier film, the polyvinyl acetal layer, and the methacrylic resin layer are laminated in this order. Below, the said water vapor | steam barrier film may be called a water vapor | steam barrier film (F). The coextruded film and the water vapor barrier film (F) may be laminated by a heat laminating method.

  The water vapor barrier film (F) may be any film that can achieve the water vapor barrier property required for the protective sheet of the solar cell. The water vapor barrier property that can be achieved by the protective sheet containing the water vapor barrier film (F) will be described later.

  The water vapor barrier film (F) includes a base material and a water vapor barrier layer formed on the base material. Below, the said base material may be called "base material (X)." The water vapor barrier layer may be laminated only on one side of the substrate (X), or may be laminated on both sides of the substrate (X).

  The protective sheet of the present invention is typically a protective sheet having translucency. By forming the base material (X) and each layer constituting the protective sheet with a light-transmitting material, a light-transmitting protective sheet is obtained. Note that there are cases where even a layer made of a material having high light absorption can achieve sufficient light-transmitting properties by reducing the thickness of the layer.

  As a water vapor barrier layer, a coating film of a metal such as aluminum is known. However, a coating film of an insulating inorganic oxide such as silica or alumina is preferably used as the water vapor barrier layer when applied to a solar cell because there is no fear of leakage of current. More specifically, aluminum oxide, magnesium oxide, silicon nitride, silicon oxynitride, or the like is used. Known methods for forming such a coating film include vapor deposition methods (for example, physical vapor deposition (PVD) and chemical vapor deposition (CVD)) and wet coating methods. A method may be used.

  An inorganic vapor deposition layer may be formed on the coextruded film. In that case, the coextruded film on which the inorganic vapor deposition layer is formed and the substrate (X) are laminated.

  Further, the water vapor barrier layer may be a layer containing a reaction product (R) described later. Hereinafter, the water vapor barrier layer containing the reaction product (R) may be referred to as “layer (Y)”. Moreover, the water vapor | steam barrier film (F) containing the base material (X) and the layer (Y) laminated | stacked on the base material (X) may be called "multilayer structure." This multilayer structure will be described below.

[Multilayer structure (an example of a water vapor barrier film (F))]
The multilayer structure of the present invention has a substrate (X) and a layer (Y) laminated on the substrate (X). The layer (Y) includes a reaction product (R), and the reaction product (R) is a reaction product obtained by reacting at least the metal oxide (A) and the phosphorus compound (B), and 800 In the infrared absorption spectrum of the layer (Y) in the range of ˜1400 cm ^−1, the wave number (n ¹ ) at which the infrared absorption is maximum is in the range of 1,080 to 1,130 cm ⁻¹ . Hereinafter, the wave number (n ¹ ) may be referred to as “maximum absorption wave number (n ¹ )”. The metal oxide (A) usually reacts with the phosphorus compound (B) in the form of particles of the metal oxide (A).

  In the present invention, the metal atom (M) constituting the metal oxide (A) is substantially an aluminum atom. Here, “substantially an aluminum atom” is an amount such that the content of metal atoms other than aluminum can ignore the influence of the other metal atoms on the properties of the layer (Y). Means that. The proportion of aluminum metal atoms in the metal atoms (M) constituting the metal oxide (A) is usually 90 mol% or more, for example, 95 mol% or more, 98 mol% or more, 99 mol% or more, or 100 mol%. It is.

  The layer (Y) has a structure in which the metal oxide (A) particles are bonded to each other via a phosphorus atom derived from the phosphorus compound (B). The form bonded via a phosphorus atom includes the form bonded via an atomic group containing a phosphorus atom, for example, bonded via an atomic group containing a phosphorus atom and not containing a metal atom. Are included.

  In the layer (Y), the number of moles of metal atoms that are bonded to the metal oxide (A) particles and are not derived from the metal oxide (A) is the same as the metal oxide (A) particles. Is preferably in the range of 0 to 1 times the number of moles of phosphorus atoms to which is bonded (for example, in the range of 0 to 0.9 times). It may be 01 times or less, or 0 times.

  The layer (Y) of the multilayer structure of the present invention may partially contain a metal oxide (A) and / or a phosphorus compound (B) that is not involved in the reaction.

In general, a metal atom and a phosphorus compound react to react a metal atom (M) constituting the metal compound and a phosphorus atom (P) derived from the phosphorus compound bonded via an oxygen atom (O). When a bond represented by is generated, a characteristic peak occurs in the infrared absorption spectrum. Here, the characteristic peak shows an absorption peak at a specific wave number depending on the environment and structure around the bond. As disclosed in International Publication No. WO2011 / 122036, when the absorption peak based on the M—O—P bond is located in the range of 1080 to 1130 cm ⁻¹ , excellent barrier properties in the resulting multilayer structure Was found to be expressed. In particular, when the absorption peak appears as an absorption peak of the maximum absorption wave number in the region of 800 to 1400 cm ⁻¹ where absorption derived from bonds between various atoms and oxygen atoms is generally observed, in the obtained multilayer structure Furthermore, it turned out that the outstanding barrier property is expressed.

In addition, although this invention is not limited at all, the metal atom (A) particle | grains interpose the phosphorus atom derived from a phosphorus compound (B), and the metal atom which does not originate in a metal oxide (A). A bond represented by M-O-P in which the metal atom (M) and the phosphorus atom (P) constituting the metal oxide (A) are bonded via an oxygen atom (O). When generated, due to the relatively fixed environment of the surface of the metal oxide (A) particles, the infrared absorption spectrum of the layer (Y) has an absorption peak based on the M—O—P bond of 1,800 to 1,800. It is thought that it appears as an absorption peak of the maximum absorption wave number in the region of 800 to 1400 cm ^{−1 in} the range of 1130 cm ⁻¹ .

In contrast, when a metal compound not forming a metal oxide such as a metal alkoxide or metal salt and a phosphorus compound (B) are mixed in advance and then hydrolyzed and condensed, the metal atom derived from the metal compound and A complex in which phosphorus atoms derived from the phosphorus compound (B) are mixed almost uniformly and reacted is obtained, and in the infrared absorption spectrum, the maximum absorption wave number (n ¹ ) in the range of 800 to 1400 cm ⁻¹ is 1080 to 1130 cm ^−. Beyond the range of ¹ .

The maximum absorption wave number (n ¹ ) is preferably in the range of 1085 to 1120 cm ⁻¹ , and more preferably in the range of 1090 to 1110 cm ⁻¹ , because a multilayer structure having better barrier properties is obtained.

In the infrared absorption spectrum of the layer (Y), absorption of stretching vibrations of hydroxyl groups bonded to various atoms may be observed in the range of 2500 to 4000 cm ⁻¹ . Examples of hydroxyl groups that are absorbed in this range include hydroxyl groups that exist on the surface of the metal oxide (A) portion and have the form of M-OH, and are bonded to phosphorus atoms (P) derived from the phosphorus compound (B). And a hydroxyl group having a P—OH form, a hydroxyl group having a C—OH form derived from the polymer (C) described later, and the like. The amount of the hydroxyl group present in the layer (Y) can be correlated with the absorbance (A ² ) at the maximum absorption wave number (n ² ) based on the stretching vibration of the hydroxyl group in the range of 2500 to 4000 cm ⁻¹ . Here, the wave number (n ² ) is a wave number that maximizes infrared absorption based on hydroxyl group stretching vibration in the infrared absorption spectrum of the layer (Y) in the range of 2500 to 4000 cm ⁻¹ . Hereinafter, the wave number (n ² ) may be referred to as “maximum absorption wave number (n ² )”.

As the amount of the hydroxyl group present in the layer (Y) increases, the hydroxyl barrier becomes a permeation path for water molecules, and the water vapor barrier property tends to decrease. In the infrared absorption spectrum of the layer (Y), the ratio [absorbance (A ² ) / absorbance (A ¹ )] of the absorbance (A ¹ ) and the absorbance (A ² ) at the maximum absorption wave number (n ¹ ) is It is considered that the smaller the particle of the metal oxide (A), the more effectively the particles of the metal oxide (A) are bonded through the phosphorus atom derived from the phosphorus compound (B). Therefore, the ratio [absorbance (A ² ) / absorbance (A ¹ )] is preferably 0.2 or less from the viewpoint of highly expressing the gas barrier property and water vapor barrier property of the resulting multilayer structure. More preferably, it is 1 or less. The multilayer structure in which the layer (Y) has the above ratio [absorbance (A ² ) / absorbance (A ¹ )] is the number of moles of metal atoms (N _M ) constituting the metal oxide (A) described later. And the ratio of the number of moles of phosphorus atoms derived from the phosphorus compound (B) (N _P ), heat treatment conditions, and the like. Although not particularly limited, in the infrared absorption spectrum of the precursor layer for later layers (Y), maximum absorbance in the range 800～1400Cm ^-1 and (A ¹ '), 2500~4000cm ^-1 In some cases, the maximum absorbance (A ² ′) based on the stretching vibration of the hydroxyl group in the range satisfies the relationship of absorbance (A ² ′) / absorbance (A ¹ ′)> 0.2.

In the infrared absorption spectrum of the layer (Y), the half width of the absorption peak having a maximum in the maximum absorption wave number (n ¹ ) is 200 cm ⁻¹ or less from the viewpoint of gas barrier properties and water vapor barrier properties of the resulting multilayer structure. Is preferably 150 cm ⁻¹ or less, more preferably 130 cm ⁻¹ or less, more preferably 110 cm ⁻¹ or less, further preferably 100 cm ⁻¹ or less, and 50 cm ^−. Particularly preferably, it is ¹ or less. Although this invention is not limited at all, when the particles of the metal oxide (A) are bonded to each other via a phosphorus atom, the particles of the metal oxide (A) are phosphorous derived from the phosphorus compound (B). Metal atoms (M) and phosphorus atoms (P) constituting the metal oxide (A) are bonded with oxygen atoms (O) through atoms and without metal atoms not derived from the metal oxide (A). When the bond represented by M-O-P is formed through the metal oxide (A), the maximum absorption wave number (n ¹ ) is maximized due to the relatively fixed environment of the surface of the metal oxide (A) particles. It is considered that the half width of the absorption peak having a value falls within the above range. In this specification, the half width of the absorption peak of the maximum absorption wave number (n ¹ ) is the wave number of two points having an absorbance (absorbance (A ¹ ) / 2) that is half of the absorbance (A ¹ ) at the absorption peak. It can be obtained by calculating the difference.

  The infrared absorption spectrum of the above layer (Y) is measured by the ATR method (total reflection measurement method), or the layer (Y) is scraped from the multilayer structure and the infrared absorption spectrum is measured by the KBr method. Can be obtained.

  In one example, the layer (Y) is formed by bonding the metal oxide (A) particles through the phosphorus atom derived from the phosphorus compound (B) and not through the metal atom not derived from the metal oxide (A). The layer (Y) has the structure as described above. That is, the particles of the metal oxide (A) may be bonded to each other through a metal atom derived from the metal oxide (A), but have a structure in which the particles are bonded without any other metal atom. Here, “the structure bonded through the phosphorus atom derived from the phosphorus compound (B) and not through the metal atom not derived from the metal oxide (A)” means the metal oxide (A) to be bonded. Means that the main chain of the bond between the particles has a phosphorus atom derived from the phosphorus compound (B) and does not have a metal atom not derived from the metal oxide (A). A structure having a metal atom in the side chain is also included. However, the layer (Y) has a structure in which the particles of the metal oxide (A) are bonded to each other through both phosphorus atoms and metal atoms derived from the phosphorus compound (B) (bonded metal oxide (A ) May have a part of the main chain of the bond between particles having a structure including both a phosphorus atom and a metal atom derived from the phosphorus compound (B).

In the layer (Y), as the bonding form of each particle of the metal oxide (A) and the phosphorus atom, for example, the metal atom (M) and the phosphorus atom (P) constituting the metal oxide (A) are oxygen. The form couple | bonded through the atom (O) can be mentioned. The particles of the metal oxide (A) may be bonded to each other via a phosphorus atom (P) derived from one molecule of the phosphorus compound (B), but phosphorus derived from two or more molecules of the phosphorus compound (B). It may be bonded via an atom (P). As a specific form of bonding between two bonded metal oxide (A) particles, a metal atom constituting one bonded metal oxide (A) particle is represented as (Mα), When the metal atom constituting the other metal oxide (A) particle is represented by (Mβ), for example, (Mα) -OPO- (Mβ) bond form; (Mα) -OP— [O—P] _n —O— (Mβ) bond form; (Mα) —O—P—Z—P—O— (Mβ) bond form; (Mα) —O—P—Z—P— [ O—P—Z—P] _n —O— (Mβ) and the like. In the example of the bonding form, n represents an integer of 1 or more, and Z represents a constituent atomic group existing between two phosphorus atoms when the phosphorus compound (B) has two or more phosphorus atoms in the molecule. And the description of other substituents bonded to the phosphorus atom is omitted. In the layer (Y), one metal oxide (A) particle is preferably bonded to a plurality of other metal oxide (A) particles from the viewpoint of barrier properties of the resulting multilayer structure.

[Metal oxide (A)]
As described above, the metal atom (M) constituting the metal oxide (A) is substantially an aluminum atom. Examples of metal atoms (M) other than aluminum include metals of Group 2 of the periodic table such as magnesium and calcium; metals of Group 12 of the periodic table such as zinc; metals of Group 13 of the periodic table such as aluminum; silicon and the like A metal belonging to Group 14 of the periodic table; transition metals such as titanium and zirconium. Silicon may be classified as a semimetal, but in this specification, silicon is included in the metal. The metal atom (M) constituting the metal oxide (A) may be one type or two or more types. Among these, the metal atom (M) other than the aluminum atom is preferably at least one selected from the group consisting of titanium and zirconium.

  As the metal oxide (A), those produced by a liquid phase synthesis method, a gas phase synthesis method, a solid pulverization method or the like can be used. In view of the controllability of the thickness and production efficiency, those produced by the liquid phase synthesis method are preferred.

  In the liquid phase synthesis method, the compound (L) containing a metal atom (M) to which a hydrolyzable characteristic group is bonded is used as a raw material to hydrolyze and condense the compound (L). A metal oxide (A) can be synthesized as a product. That is, the metal oxide (A) may be a hydrolysis condensate of the compound (L). Moreover, when manufacturing the hydrolysis-condensation product of a compound (L) with a liquid phase synthesis method, the compound (L) which a partly hydrolyzed compound (L) other than the method of using the compound (L) itself as a raw material ( L) partial hydrolyzate, compound (L) completely hydrolyzed product obtained by completely hydrolyzing compound (L), compound (L) partially hydrolyzed and condensed part of compound (L) Metal oxidation can also be achieved by condensing or hydrolyzing a hydrolysis condensate, a product obtained by condensing a part of a complete hydrolyzate of compound (L), or a mixture of two or more of these as raw materials. A thing (A) can be manufactured. The metal oxide (A) thus obtained is also referred to as “hydrolysis condensate of compound (L)” in the present specification. There are no particular limitations on the type of the hydrolyzable characteristic group (functional group), and examples include halogen atoms (F, Cl, Br, I, etc.), alkoxy groups, acyloxy groups, diacylmethyl groups, nitro groups, and the like. However, a halogen atom or an alkoxy group is preferable, and an alkoxy group is more preferable because of excellent controllability of the reaction.

The compound (L) preferably contains at least one compound (L ¹ ) represented by the following formula (I) because the reaction is easily controlled and the resulting multilayer structure has excellent barrier properties.

AlX ¹ _m R ¹ _(3-m) (I)
[In Formula (I), X ¹ is selected from F, Cl, Br, I, R ² O—, R ³ C (═O) O—, (R ⁴ C (═O)) ₂ CH— and NO _3. Selected from the group of R ¹ , R ² , R ³ and R ⁴ are each selected from the group consisting of an alkyl group, an aralkyl group, an aryl group and an alkenyl group. In Formula (I), when a plurality of X ¹ are present, these X ¹ may be the same as or different from each other. In the formula (I), when a plurality of R ¹ are present, these R ¹ may be the same or different from each other. In the formula (I), when a plurality of R ² are present, these R ² may be the same or different from each other. In the formula (I), when a plurality of R ³ are present, these R ³ may be the same or different from each other. In the formula (I), when a plurality of R ⁴ are present, these R ⁴ may be the same as or different from each other. m represents an integer of 1 to 3. ]

Examples of the alkyl group represented by R ¹ , R ² , R ³ and R ⁴ include a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, a s-butyl group, a t-butyl group, and 2-ethylhexyl. Groups and the like. Examples of the aralkyl group represented by R ¹ , R ² , R ³ and R ⁴ include a benzyl group, a phenethyl group and a trityl group. Examples of the aryl group represented by R ¹ , R ² , R ³ and R ⁴ include a phenyl group, a naphthyl group, a tolyl group, a xylyl group, and a mesityl group. Examples of the alkenyl group represented by R ¹ , R ² , R ³ and R ⁴ include a vinyl group and an allyl group. For example, R ¹ is preferably an alkyl group having 1 to 10 carbon atoms, and more preferably an alkyl group having 1 to 4 carbon atoms. X ¹ is preferably F, Cl, Br, I, or R ² O—. In a preferred example of the compound (L ¹ ), X ¹ is a halogen atom (F, Cl, Br, I) or an alkoxy group having 1 to 4 carbon atoms (R ² O—), and m is 3. In one example of the compound (L ¹ ), X ¹ is a halogen atom (F, Cl, Br, I) or an alkoxy group having 1 to 4 carbon atoms (R ² O—), and m is 3.

Specific examples of the compound (L ¹ ) include, for example, aluminum chloride, aluminum triethoxide, aluminum trinormal propoxide, aluminum triisopropoxide, aluminum trinormal butoxide, aluminum tri-s-butoxide, aluminum tri-t-butoxide, Examples thereof include aluminum compounds such as aluminum triacetate, aluminum acetylacetonate, and aluminum nitrate. Among these, as the compound (L ¹ ), at least one compound selected from aluminum triisopropoxide and aluminum tris-butoxide is preferable. As the compound (L ¹ ), one type may be used alone, or two or more types may be used in combination.

Further, the compound (L) other than the compound (L ¹ ) is not particularly limited as long as the effects of the present invention can be obtained. However, for example, the above-mentioned water is added to metal atoms such as titanium, zirconium, magnesium, calcium, zinc, and silicon. Examples thereof include a compound having a decomposable characteristic group bonded thereto. Silicon may be classified as a semimetal, but in this specification, silicon is included in the metal. Among these, since the obtained multilayer structure is excellent in gas barrier properties, the compound (L) other than the compound (L ¹ ) is preferably a compound having titanium or zirconium as a metal atom. Specific examples of the compound (L) other than the compound (L ¹ ) include, for example, titanium tetraisopropoxide, titanium tetranormal butoxide, titanium tetra (2-ethylhexoxide), titanium tetramethoxide, titanium tetraethoxide. And titanium compounds such as titanium acetylacetonate; zirconium compounds such as zirconium tetranormal propoxide, zirconium tetrabutoxide and zirconium tetraacetylacetonate.

As long as the effect of the present invention is obtained, the ratio of the compound (L ¹ ) to the compound (L) is not particularly limited. The proportion of the compound other than the compound (L ¹ ) in the compound (L) is, for example, 20 mol% or less, 10 mol% or less, 5 mol% or less, or 0 mol%. In one example, the compound (L) consists only of the compound (L ¹ ).

  By hydrolyzing the compound (L), at least a part of the hydrolyzable characteristic group of the compound (L) is substituted with a hydroxyl group. Furthermore, the hydrolyzate condenses to form a compound in which the metal atom (M) is bonded through the oxygen atom (O). When this condensation is repeated, a compound that can be substantially regarded as a metal oxide is formed. In addition, a hydroxyl group usually exists on the surface of the metal oxide (A) thus formed. In this specification, the hydrolysis condensate of compound (L) may be referred to as “metal oxide (A)”. That is, in this specification, “metal compound (A)” can be read as “hydrolysis condensate of compound (L)”, and “hydrolysis condensate of compound (L)” is referred to as “metal oxide. (A) "can be read.

  In this specification, the oxygen atom (O) bonded to only the metal atom (M), such as the oxygen atom (O) in the structure represented by MOM, with respect to the number of moles of the metal atom (M). For example, the oxygen atom (O) in the structure represented by M—O—H is excluded, and the oxygen atom bonded to the metal atom (M) and the hydrogen atom (H) is excluded) ([[ A compound in which the number of moles of oxygen atoms (O) bonded only to metal atoms (M) / [number of moles of metal atoms (M)]) is 0.8 or more is included in the metal oxide (A) And The ratio of the metal oxide (A) is preferably 0.9 or more, more preferably 1.0 or more, and further preferably 1.1 or more. Although the upper limit of the said ratio is not specifically limited, When the valence of a metal atom (M) is set to n, it will normally be represented by n / 2.

  In order for the hydrolysis condensation to occur, it is important that the compound (L) has a hydrolyzable characteristic group (functional group). When these groups are not bonded, the hydrolysis condensation reaction does not occur or becomes extremely slow, making it difficult to prepare the target metal oxide (A).

  A hydrolysis condensate can be manufactured from a specific raw material by the method employ | adopted by the well-known sol-gel method, for example. The raw materials include compound (L), partial hydrolyzate of compound (L), complete hydrolyzate of compound (L), partial hydrolyzed condensate of compound (L), and complete hydrolysis of compound (L). It is possible to use at least one selected from the group consisting of a part of the product condensed (hereinafter sometimes referred to as “compound (L) component”). These raw materials may be produced by a known method, or commercially available ones may be used. Although there is no particular limitation, for example, a condensate obtained by hydrolytic condensation of about 2 to 10 compounds (L) can be used as a raw material. Specifically, for example, a product obtained by hydrolyzing and condensing aluminum triisopropoxide to form a 2- to 10-mer condensate can be used as a part of the raw material.

  The number of molecules condensed in the hydrolyzed condensate of compound (L) can be controlled by the conditions at the time of condensing or hydrolyzing the compound (L) component. For example, the number of molecules to be condensed can be controlled by the amount of water, the type and concentration of the catalyst, the temperature and time for condensation or hydrolysis condensation, and the like.

  As described above, the layer (Y) includes the reaction product (R), and the reaction product (R) is a reaction product obtained by reacting at least the metal oxide (A) and the phosphorus compound (B). It is a thing. Such a reaction product or structure can be formed by mixing and reacting the metal oxide (A) and the phosphorus compound (B). The metal oxide (A) used for mixing with the phosphorus compound (B) (immediately before mixing) may be the metal oxide (A) itself or a composition containing the metal oxide (A). It may be in the form of a thing. In a preferred example, the metal oxide (A) is mixed with the phosphorus compound (B) in the form of a liquid (solution or dispersion) obtained by dissolving or dispersing the metal oxide (A) in a solvent.

  As a method for producing the metal oxide (A) solution or dispersion, a method disclosed in International Publication No. WO2011 / 122036 can be applied. When the metal oxide (A) is aluminum oxide (alumina), a preferable alumina dispersion is hydrolyzed and condensed in an aqueous solution in which aluminum alkoxide is adjusted with an acid catalyst as necessary to obtain an alumina slurry. This can be obtained by peptization in the presence of a specific amount of acid.

[Phosphorus Compound (B)]
The phosphorus compound (B) contains a site capable of reacting with the metal oxide (A), and typically contains a plurality of such sites. In a preferred example, the phosphorus compound (B) contains 2 to 20 such sites (atomic groups or functional groups). Examples of such a part include a part capable of reacting with a functional group (for example, a hydroxyl group) present on the surface of the metal oxide (A). For example, examples of such a site include a halogen atom directly bonded to a phosphorus atom and an oxygen atom directly bonded to a phosphorus atom. Those halogen atoms and oxygen atoms can cause a condensation reaction (hydrolysis condensation reaction) with a hydroxyl group present on the surface of the metal oxide (A). The functional group (for example, hydroxyl group) present on the surface of the metal oxide (A) is usually bonded to the metal atom (M) constituting the metal oxide (A).

  As the phosphorus compound (B), for example, a compound having a structure in which a halogen atom or an oxygen atom is directly bonded to a phosphorus atom can be used. By using such a phosphorus compound (B), a metal oxide (A) can be used. It can be combined by condensation (hydrolysis) with a hydroxyl group present on the surface. The phosphorus compound (B) may have one phosphorus atom, or may have two or more phosphorus atoms.

The phosphorus compound (B) may be at least one compound selected from the group consisting of phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof. Specific examples of polyphosphoric acid include pyrophosphoric acid, triphosphoric acid, polyphosphoric acid condensed with four or more phosphoric acids, and the like. Examples of the above derivatives include salts of phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, (partial) ester compounds, halides (chlorides, etc.), dehydrates (niline pentoxide, etc.) and the like. . In addition, examples of phosphonic acid derivatives include a hydrogen atom directly bonded to a phosphorus atom of phosphonic acid (HP (═O) (OH) ₂ ), which may have various functional groups. Substituted compounds (eg, nitrilotris (methylenephosphonic acid), N, N, N ′, N′-ethylenediaminetetrakis (methylenephosphonic acid), etc.), salts thereof, (partial) ester compounds, halides and dehydration Things are also included. Furthermore, organic polymers having a phosphorus atom such as phosphorylated starch can also be used as the phosphorus compound (B). These phosphorus compounds (B) may be used alone or in combination of two or more. Among these phosphorus compounds (B), the stability of the coating liquid (U) and the barrier properties of the resulting multilayer structure are better when the layer (Y) is formed using the coating liquid (U) described later. Therefore, it is preferable to use phosphoric acid alone or to use phosphoric acid and other phosphorus compounds in combination.

  As described above, the layer (Y) includes the reaction product (R), and the reaction product (R) is a reaction product obtained by reacting at least the metal oxide (A) and the phosphorus compound (B). It is a thing. Such a reaction product or structure can be formed by mixing and reacting the metal oxide (A) and the phosphorus compound (B). The phosphorus compound (B) used for mixing with the metal oxide (A) (immediately before mixing) may be the phosphorus compound (B) itself or a form of a composition containing the phosphorus compound (B). The form of the composition containing the phosphorus compound (B) is preferable. In a preferred example, the phosphorus compound (B) is mixed with the metal oxide (A) in the form of a solution obtained by dissolving the phosphorus compound (B) in a solvent. Although any solvent can be used at that time, water or a mixed solvent containing water is a preferable solvent.

[Reaction product (R)]
The reaction product (R) includes a reaction product produced by reacting only the metal oxide (A) and the phosphorus compound (B). The reaction product (R) also includes a reaction product produced by reacting the metal oxide (A), the phosphorus compound (B), and another compound. The reaction product (R) can be formed by the method described in the production method described later.

[Ratio of metal oxide (A) and phosphorus compound (B)]
In the layer (Y), the ratio between the number of moles of metal atoms (M) constituting the metal oxide (A) (N _M ) and the number of moles of phosphorus atoms derived from the phosphorus compound (B) (N _P ) It is preferable to satisfy the relationship 0.8 ≦ number of moles (N _M ) / number of moles (N _P ) ≦ 4.5, and 1.0 ≦ number of moles (N _M ) / number of moles (N _P ) ≦ 3.6. It is more preferable to satisfy the relationship of 1.1 ≦ number of moles (N _M ) / number of moles (N _P ) ≦ 3.0. When the value of the number of moles (N _M ) / number of moles (N _P ) exceeds 4.5, the metal oxide (A) becomes excessive with respect to the phosphorus compound (B), and the particles of the metal oxide (A) Insufficient bonding, and the amount of hydroxyl groups present on the surface of the metal oxide (A) increases, so that the barrier property and its reliability tend to decrease. On the other hand, when the value of the number of moles (N _M ) / number of moles (N _P ) is less than 0.8, the phosphorus compound (B) becomes excessive with respect to the metal oxide (A), and the metal oxide (A) The excess phosphorus compound (B) which does not participate in the bond with the compound increases, and the amount of the hydroxyl group derived from the phosphorus compound (B) tends to increase, and the barrier property and its reliability also tend to be lowered.

In addition, the said ratio can be adjusted with ratio of the quantity of a metal oxide (A) and the quantity of a phosphorus compound (B) in the coating liquid for forming a layer (Y). The ratio between the number of moles (N _M ) and the number of moles (N _P ) in the layer (Y) is usually the ratio in the coating solution, and the number of moles of metal atoms constituting the metal oxide (A) and the phosphorus compound ( It is the same as the ratio to the number of moles of phosphorus atoms constituting B).

[Polymer (C)]
The layer (Y) may further contain a specific polymer (C). The polymer (C) is a polymer having at least one functional group (f) selected from the group consisting of a hydroxyl group, a carboxyl group, a carboxylic anhydride group, and a carboxyl group salt. In the present specification, a polymer that satisfies the requirements as the phosphorus compound (B) and includes the functional group (f) is not included in the polymer (C) but is treated as the phosphorus compound (B). .

  Specific examples of the polymer (C) having a hydroxyl group include polyvinyl alcohol, partially saponified products of polyvinyl acetate, polysaccharides such as polyethylene glycol, polyhydroxyethyl (meth) acrylate, starch, and polysaccharides derived from polysaccharides. Derivatives and the like. Specific examples of the polymer (C) having a carboxyl group, a carboxylic anhydride group or a carboxyl group salt include polyacrylic acid, polymethacrylic acid, poly (acrylic acid / methacrylic acid), and salts thereof. Can do. Specific examples of the polymer (C) containing a structural unit not containing the functional group (f) include an ethylene-vinyl alcohol copolymer, an ethylene-maleic anhydride copolymer, and a styrene-maleic anhydride copolymer. , Saponified products of isobutylene-maleic anhydride alternating copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, and the like. In order to obtain a multilayer structure having better barrier properties and hot water resistance, the polymer (C) is composed of polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polysaccharide, polyacrylic acid, polyacrylic acid salt, poly It is preferably at least one polymer selected from the group consisting of methacrylic acid and polymethacrylic acid salts.

  There is no restriction | limiting in particular in the molecular weight of a polymer (C). In order to obtain a multilayer structure having more excellent barrier properties and mechanical properties (drop impact strength, etc.), the number average molecular weight of the polymer (C) is preferably 5,000 or more, and 8,000. More preferably, it is more preferably 10,000 or more. The upper limit of the number average molecular weight of the polymer (C) is not particularly limited, and is, for example, 1,500,000 or less.

  In order to further improve the barrier properties, the content of the polymer (C) in the layer (Y) is preferably 50% by mass or less, based on the mass of the layer (Y) (100% by mass). It is more preferably at most mass%, more preferably at most 30 mass%, and may be at most 20 mass%. The polymer (C) may or may not react with the other components in the layer (Y). In the present specification, the case where the polymer (C) reacts with other components is also expressed as the polymer (C). For example, when the polymer (C) is bonded to a phosphorus atom derived from the metal oxide (A) and / or the phosphorus compound (B), it is also expressed as the polymer (C). In this case, the content of the polymer (C) is calculated by dividing the mass of the polymer (C) before bonding with the metal oxide (A) and / or the phosphorus atom by the mass of the layer (Y). To do.

  The layer (Y) is composed only of a reaction product (R) (including one having a polymer (C) portion) formed by reacting at least the metal oxide (A) and the phosphorus compound (B). It may be composed only of the reaction product (R) and the unreacted polymer (C), but may further contain other components.

  Examples of other components include inorganic acid metal salts such as carbonates, hydrochlorides, nitrates, hydrogen carbonates, sulfates, hydrogen sulfates, borates, and aluminates; oxalates, acetates, Organic acid metal salts such as tartrate and stearate; Metal complexes such as acetylacetonate metal complexes (such as aluminum acetylacetonate), cyclopentadienyl metal complexes (such as titanocene), cyano metal complexes; layered clay compounds; Agents; polymer compounds other than the polymer (C); plasticizers; antioxidants; ultraviolet absorbers; flame retardants and the like.

  The content of the other components in the layer (Y) is preferably 50% by mass or less, more preferably 20% by mass or less, further preferably 10% by mass or less, and more preferably 5% by mass. The following is particularly preferable, and may be 0% by mass (excluding other components).

[Thickness of layer (Y)]
The thickness of the layer (Y) of the multilayer structure of the present invention (when the multilayer structure has two or more layers (Y), the total thickness of each layer (Y)) is 4.0 μm or less. Preferably, it is 2.0 μm or less, more preferably 1.0 μm or less, and particularly preferably 0.9 μm or less. By thinning the layer (Y), the dimensional change of the multilayer structure during processing such as printing and laminating can be kept low, and the flexibility of the multilayer structure is further increased. It can be close to the mechanical characteristics of.

  The thickness of the layer (Y) (when the multilayer structure has two or more layers (Y), the total thickness of each layer (Y)) is 0.1 μm or more (for example, 0.2 μm or more). It is preferable. The thickness per layer (Y) is preferably 0.05 μm or more (for example, 0.15 μm or more) from the viewpoint of improving the barrier property of the multilayer structure of the present invention. The thickness of the layer (Y) can be controlled by the concentration of a coating liquid (U) described later used for forming the layer (Y) and the coating method.

By using the multilayer structure, it is possible to improve the water vapor barrier property of the protective sheet. The multilayer structure can particularly enhance the water vapor barrier property of the protective sheet by using the base material (X) having a tension at 3% strain of 2000 N / m or more. Specifically, 40 ° C., a moisture permeability under conditions of 90/0% RH, 0.05g / (m 2 · day) or less and 0.01g / (m ² · day) or less and 0.005 g / ( m ² · day) or less. When used as a protective sheet for a solar cell, it is preferable that the moisture permeability in the above conditions is 0.05g / (m ² · day) or less, more preferably 0.001g / (m ² · day) or less . Here, “90/0% RH” means that relative humidity on one side of the multilayer structure is 90% and relative humidity on the other side is 0%.

[Substrate (X)]
The substrate (X) is a layered substrate such as a film. There is no restriction | limiting in particular in the material of base material (X), The base material which consists of various materials can be used. Examples of the material of the substrate (X) include a thermoplastic resin having translucency, and specifically, polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate, polystyrene, polymeta Methyl acrylate / styrene copolymer, syndiotactic polystyrene, cyclic polyolefin, cyclic olefin copolymer (COC), polyacetyl cellulose, polyimide, polypropylene, polyethylene, polyethylene naphthalate, polyvinyl acetal, polyvinyl butyral, polyvinyl alcohol, poly Vinyl chloride, polymethylpentene, etc. are included. Among these, polyethylene terephthalate (PET), polycarbonate (PC), and cyclic olefin copolymer (COC) are preferable in that they have high transparency and excellent heat resistance. The substrate (X) may be composed of a plurality of resins. The substrate (X) may be a multilayer film composed of a plurality of layers.

  The thermoplastic resin film may be a stretched film or an unstretched film. A stretched film, particularly a biaxially stretched film is preferred because the processability (printing, laminating, etc.) of the resulting multilayer structure is excellent. The biaxially stretched film may be a biaxially stretched film produced by any one of a simultaneous biaxial stretching method, a sequential biaxial stretching method, and a tubular stretching method.

  The thickness of the substrate (X) is not limited, and may be, for example, in the range of 10 μm to 300 μm or in the range of 20 μm to 200 μm. However, if the base material (X) is thick, the light absorption by the base material (X) increases, and the flexibility of the multilayer structure decreases, so the thickness of the base material (X) is usually 150 μm. The following is preferable.

[Configuration of multilayer structure]
The multilayer structure (laminate) of the present invention may be constituted only by the base material (X) and the layer (Y), or only by the base material (X), the layer (Y) and the adhesive layer (H). It may be configured. The multilayer structure of the present invention may include a plurality of layers (Y). In addition, the multilayer structure of the present invention has a layer other than the substrate (X), the layer (Y), and the adhesive layer (H) (for example, other layers such as a thermoplastic resin film layer and an inorganic vapor deposition layer). May further be included. The multilayer structure of the present invention having such other members (such as other layers) is further obtained by laminating the layer (Y) directly on the substrate (X) or via the adhesive layer (H). It can be produced by bonding or forming the other member (other layer, etc.) directly or via an adhesive layer. By including such other members (such as other layers) in the multilayer structure, the characteristics of the multilayer structure can be improved or new characteristics can be imparted. For example, heat-sealability can be imparted to the multilayer structure of the present invention, and barrier properties and mechanical properties can be further improved.

  The multilayer structure used in the present invention may include two or more layers (Y), and the layer (Y) is laminated on each of the one principal surface side and the other principal surface side of the base material (X). May be.

[Coextruded film]
As described above, the protective sheet of the present invention includes a coextruded film in which a methacrylic resin layer and a polyvinyl acetal layer are laminated. A method for producing the coextruded film will be described later.

  The thickness of the methacrylic resin layer may be in the range of 25 μm to 500 μm, for example, in the range of 30 μm to 300 μm or 40 μm to 200 μm. The thickness of the polyvinyl acetal layer may be in the range of 1 μm to 100 μm, for example, in the range of 2 μm to 50 μm or 5 μm to 30 μm. Below, the methacryl resin and polyvinyl acetal used for a coextruded film are demonstrated.

  The methacrylic resin layer contains a methacrylic resin. Hereinafter, the methacrylic resin contained in the methacrylic resin layer may be referred to as “methacrylic resin (A)”. The methacrylic resin (A) used in the present invention is obtained by polymerizing a monomer mixture containing an alkyl methacrylate.

  As alkyl methacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, myristyl Examples include methacrylate, palmityl methacrylate, stearyl methacrylate, behenyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, and benzyl methacrylate. These alkyl metallates may be used alone or in combination of two or more. Of these, alkyl methacrylates having 1 to 4 carbon atoms in the alkyl group are preferred, and methyl methacrylate is particularly preferred.

  The monomer mixture may contain an alkyl acrylate in addition to the alkyl methacrylate. As alkyl acrylates, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, myristyl Examples include acrylate, palmityl acrylate, stearyl acrylate, behenyl acrylate, cyclohexyl acrylate, phenyl acrylate, and benzyl acrylate. Of these, alkyl acrylates having 1 to 8 carbon atoms in the alkyl group are preferred. These alkyl acrylates may be used alone or in combination of two or more.

  The monomer mixture may contain other ethylenically unsaturated monomers copolymerizable with alkyl methacrylate and alkyl acrylate.

  Examples of the ethylenically unsaturated monomer copolymerizable with alkyl methacrylate and alkyl acrylate include diene compounds such as 1,3-butadiene and isoprene; styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, Styrene substituted with halogen, 1-vinylnaphthalene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4- (phenylbutyl) styrene, etc. Vinyl aromatic compounds; ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile; acrylic acid, methacrylic acid, acrylamide, methacrylamide, maleic anhydride, maleic imide, monomethyl maleate, dimethyl maleate, etc. It is possible. These ethylenically unsaturated monomers may be used alone or in combination of two or more.

  In the methacrylic resin (A) used in the present invention, the proportion of the alkyl methacrylate unit is preferably 50 to 100% by mass, and more preferably 80 to 99.9% by mass from the viewpoint of weather resistance. Moreover, it is preferable to contain an alkyl acrylate unit in 0.1-20 mass% from a heat resistant viewpoint.

  The methacrylic resin (A) used in the present invention has a weight average molecular weight (denoted as Mw, the same shall apply hereinafter) in terms of strength characteristics and meltability, preferably 40,000 or more, more preferably 40,000 to 10,000. 000,000, particularly preferably 80,000 to 1,000,000.

  The methacrylic resin (A) used in the present invention may be one in which monomers are linearly bonded, may have a branch, or may have a cyclic structure. .

  The methacrylic resin (A) used in the present invention is not particularly limited by its production method as long as it is a method capable of polymerizing an α, β-unsaturated compound, but is preferably produced by radical polymerization. Examples of the polymerization method include bulk polymerization, suspension polymerization, solution polymerization, and emulsion polymerization.

  Examples of radical polymerization initiators used during polymerization include azo compounds such as azobisisobutyronitrile and azobisγ-dimethylvaleronitrile; benzoyl peroxide, cumyl peroxide, oxyneodecanoate, diisopropyl peroxydicarbonate, t Examples thereof include peroxides such as -butyl cumyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, cyclohexanone peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, and lauroyl peroxide. The polymerization initiator is generally used in an amount of 0.05 to 0.5 parts by mass with respect to 100 parts by mass of all monomers. The polymerization is usually performed at a temperature of 50 to 140 ° C. for 2 to 20 hours.

  In order to control the molecular weight of the methacrylic resin (A), a chain transfer agent can be used. Examples of chain transfer agents include methyl mercaptan, ethyl mercaptan, isopropyl mercaptan, n-butyl mercaptan, t-butyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, ethylthioglycoate, mercaptoethanol, thio- β-naphthol, thiophenol and the like can be mentioned. A chain transfer agent is normally used in 0.005-0.5 mass% with respect to all the monomers.

  The methacrylic resin (A) used in the present invention is various additives such as an antioxidant, a stabilizer, an ultraviolet absorber, a lubricant, and a processing aid as required, as long as the performance such as optical properties is not impaired. Further, an antistatic agent, a colorant, an impact resistance aid, a foaming agent, a filler, a matting agent, and the like may be blended. In addition, it is preferable that a softener and a plasticizer are not included in a large amount from the viewpoints of mechanical properties and surface hardness maintenance of a molded body made of the thermoplastic resin composition. On the other hand, in order to ensure stability during film formation, a known rubber such as a soft rubber whose main component is butyl acrylate having a refractive index adjusted may be added.

  In order to increase the durability of the methacrylic resin layer, various additives (for example, an ultraviolet absorber) may be added to the methacrylic resin layer. A preferred example of the methacrylic resin layer having high weather resistance is a methacrylic resin layer to which an ultraviolet absorber is added. Examples of the ultraviolet absorber include known ultraviolet absorbers such as benzotriazole, benzophenone, salicylate, cyanoacrylate, nickel, and triazine ultraviolet absorbers. Furthermore, other stabilizers, light stabilizers, antioxidants and the like may be used in combination.

  The degree of acetalization of the polyvinyl acetal used for the polyvinyl acetal layer is preferably in the range of 55 to 85 mol%, and may be in the range of 60 to 80 mol% or 62 to 78 mol%.

  Polyvinyl acetal can be synthesized by reacting a polyvinyl alcohol resin and an aldehyde by a known method. Examples of the aldehyde to be reacted with the polyvinyl alcohol resin include aldehydes having 2 to 6 carbon atoms, and specifically include acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde and the like. Among these, it is preferable to use at least one selected from the group consisting of acetaldehyde and n-butyraldehyde.

  When the polyvinyl acetal is acetalized with acetaldehyde and / or n-butyraldehyde, the number of moles of the portion acetalized by acetaldehyde (AA) and the number of moles of the portion acetalized by n-butyraldehyde ( The ratio (molar ratio) to BA) may be in the range of AA / BA = 10/90 to 90/10, such as AA / BA = 20/80 to 80/20 or AA / BA = 25 / It may be in the range of 75 to 75/25.

  From the viewpoint of increasing compatibility with the methacrylic resin (A) and facilitating coextrusion, the polyvinyl acetal has a carbon number of 30 to 70 in the acetal part per 100 carbon atoms constituting the main chain of the polyvinyl acetal. Satisfy certain requirements. Here, “the number of carbon atoms in the acetal part is 30” means, for example, that when acetalization is performed with butyraldehyde having 4 carbon atoms to a degree of acetalization of 30 mol% or acetalization degree with 2 carbon atoms is 60 mol%. This corresponds to the case of acetalization or the case of acetalization with an average carbon number of 3 and AA / BA = 50/50 to an acetalization degree of 45 mol%. Further, “the carbon number of the acetal part is 70” corresponds to, for example, the case where the acetalization degree is 70 mol% with butyraldehyde having 4 carbon atoms. The above is a calculation example in which it is assumed that polyvinyl alcohol before acetalization has no residual acetic acid group or copolymer monomer and the number of hydroxyl groups per 100 carbon atoms constituting the main chain is 50.

  The average degree of polymerization of the polyvinyl acetal is in the range of 500 to 2000, preferably in the range of 700 to 1700, preferably in the range of 800 to 1500, using the viscosity average degree of polymerization based on the polyvinyl alcohol before acetalization. More preferably.

  A well-known thing can be used for the polyvinyl alcohol resin which can be used for the synthesis | combination of a polyvinyl acetal. For example, a polyvinyl alcohol resin synthesized by saponifying a polymer of a vinyl ester monomer can be used. Vinyl acetate is used as the vinyl ester monomer, but vinyl ester monomers other than vinyl acetate may be used in addition to vinyl acetate. Examples of vinyl ester monomers other than vinyl acetate include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, lauric acid Vinyl, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate and the like are included.

  In the polyvinyl acetal, the proportion of the structural unit containing the residual acetic acid group in all the structural units is preferably 5 mol% or less, and may be 3 mol% or less or 2 mol% or less.

The preferable example of a structure of the protection sheet of this invention is shown below.
(1) Substrate / water vapor barrier layer / polyvinyl acetal layer / methacrylic resin layer (2) Water vapor barrier layer / substrate / water vapor barrier layer / polyvinyl acetal layer / methacrylic resin layer (3) Water vapor barrier layer / polyvinyl acetal layer / methacrylic layer Resin layer

[Solar cell and manufacturing method thereof]
The solar cell of the present invention includes the protective sheet of the present invention (typically a translucent protective sheet). In the protective sheet, the methacrylic resin layer is disposed outside the water vapor barrier film (F). That is, the solar cell element and the protective sheet are arranged in the order of solar cell element / water vapor barrier film / polyvinyl acetal layer / methacrylic resin layer. The methacrylic resin layer functions as a protective layer that protects the surface of the solar cell. In addition, there is no limitation in the structure of parts other than a protection sheet, The structure of a well-known solar cell is applicable.

  The protective sheet of the present invention is excellent in both gas barrier properties and water vapor barrier properties. Moreover, according to this invention, the protective sheet excellent in translucency can be obtained. Therefore, the protective sheet of the present invention can be preferably used as a protective sheet for solar cells, and can be particularly preferably used as a protective sheet for the light incident surface of solar cells. Moreover, since the protective sheet of the present invention can be made flexible, it can be particularly preferably used as a protective sheet for flexible solar cells. In this specification, examples of the “flexible object” include a flexible object that can be wound around a curved surface of a cylinder having a diameter of 30 cm without any problem. For example, a cylinder having a diameter of 15 cm A flexible object that can be wound around a curved surface without any problem is included.

  The protective sheet of this invention can be used instead of the glass which protects the surface of a solar cell. That is, by using the protective sheet of the present invention, it is possible to avoid the use of a thick glass substrate that does not substantially have flexibility. However, you may use the protection sheet of this invention for the solar cell containing a thick glass substrate.

  The solar cell of the present invention is obtained by fixing the protective sheet of the present invention to a predetermined surface of the solar cell. There is no particular limitation on the method for fixing the protective sheet. The protective sheet may be fixed by a known method, and may be fixed (adhered) using an adhesive layer such as OCA (OPTICAL CLEAR ADHESIVE). Specifically, it may be laminated using an adhesive layer different from the protective sheet, or may be laminated using a protective sheet including the adhesive layer. There is no limitation in particular in an adhesive layer, You may use a well-known adhesive layer and the adhesive layer mentioned above. Examples of the adhesive layer include a film that functions as an adhesive layer.

  There is no limitation in particular in the solar cell in which the protection sheet of this invention is used. Examples of solar cells include silicon-based solar cells, compound semiconductor solar cells, and organic solar cells. Examples of silicon-based solar cells include single crystal silicon solar cells, polycrystalline silicon solar cells, amorphous silicon solar cells, and the like. Examples of compound solar cells include III-V group compound semiconductor solar cells, II-VI group compound semiconductor solar cells, and I-III-VI group compound semiconductor solar cells. The solar cell may be an integrated solar cell in which a plurality of unit cells are connected in series, or may not be an integrated solar cell.

  Some solar cells can be formed by a so-called roll-to-roll method. In the roll-to-roll method, a flexible substrate (for example, a stainless steel substrate or a resin substrate) wound around a feeding roll is fed out, a solar cell element is formed on the substrate, and then the substrate on which the solar cell element is formed is Take up with a take-up roll. Since the protective sheet of the present invention can be formed in the form of a flexible long sheet, it can be suitably used as a protective sheet for solar cells formed by a roll-to-roll method. For example, the protective sheet of the present invention may be wound on a roll, the solar cell element may be formed by a roll-to-roll method, and then the protective sheet may be laminated on the solar cell element before being wound on a take-up roll. . Moreover, you may laminate | stack both using the solar cell formed by the roll-to-roll system, and being wound by the roll, and the protective sheet wound by the roll.

[Protective sheet manufacturing method]
The method of the present invention for producing a protective sheet will be described below. In addition, since the matter demonstrated about the protection sheet of this invention is applicable to the manufacturing method of this invention, the overlapping description may be abbreviate | omitted. Moreover, the matter demonstrated about the manufacturing method of this invention is applicable to the protection sheet of this invention. The production method of the present invention includes the following steps (i) and (ii).

  In step (i), a laminated film of a methacrylic resin layer and a polyvinyl acetal layer is formed by a coextrusion method. This laminated film can be manufactured by, for example, T-die molding having a multilayer die. The molding temperature at this time is appropriately adjusted depending on the flow characteristics and film-forming properties of the resin used, but is generally 150 to 270 ° C, preferably 180 ° C to 250 ° C. Various additives such as antioxidants, UV absorbers, and weather stabilizers may be supplied to the popper after dry blending with the resin in advance, or supplied after preparing all the materials by melting and mixing them in advance. Alternatively, a master batch in which only the additive is previously concentrated in the resin may be prepared and supplied.

  In step (ii), the laminated film formed in step (i) and the water vapor barrier film (F) are laminated so that the water vapor barrier film (F), the polyvinyl acetal layer, and the methacrylic resin layer are laminated in this order. To do.

  In step (ii), lamination of the laminated film formed in step (i) and the water vapor barrier film (F) may be performed by any known method such as a thermal lamination method or a dry lamination method. It is preferable to laminate by a thermal laminating method. In this case, since the polyvinyl acetal layer functions as an adhesive layer, the protective sheet of the present invention can be easily formed by using a thermal laminating method. In addition, although it is also possible to laminate | stack a laminated film and a water vapor | steam barrier film using the contact bonding layer which does not depend on heat sealing, in that case, a process will become complicated.

  Thermal lamination can be performed by, for example, a vacuum lamination method. The conditions for vacuum lamination are appropriately adjusted depending on the thermal characteristics of the film to be used. For example, the conditions can be 160 ° C., 0.03 MPa, and 9 minutes.

  When the water vapor barrier layer is an inorganic vapor deposition layer, as described above, the water vapor barrier film (F) can be formed by vapor-depositing the inorganic vapor deposition layer on the substrate (X).

[Method for producing multilayer structure]
Hereinafter, an example of a method for producing the multilayer structure of the present invention will be described. According to this method, the multilayer structure of the present invention can be easily produced. The materials used in the method for producing a multilayer structure of the present invention, the configuration of the multilayer structure, and the like are the same as those described above, and therefore, description of overlapping portions may be omitted. For example, the description in the description of the multilayer structure of the present invention can be applied to the metal oxide (A), the phosphorus compound (B), and the polymer (C). In addition, the matter which demonstrated this manufacturing method is applicable to the multilayer structure of this invention. The matters described for the multilayer structure of the present invention can be applied to the production method of the present invention. In addition, about the formation method of a layer (Y), it is possible to apply the method currently disclosed by international publication WO2011 / 122036.

  This example method includes steps (I), (II) and (III). In the step (I), by mixing the metal oxide (A), at least one compound containing a site capable of reacting with the metal oxide (A), and a solvent, the metal oxide (A), A coating liquid (U) containing the at least one compound and the solvent is prepared. In the step (II), the coating liquid (U) is applied on the base material (X) to form a precursor layer of the layer (Y) on the base material (X). In step (III), the precursor layer is processed to form a layer (Y) on the substrate (X).

[Step (I)]
The at least one compound containing a site capable of reacting with the metal oxide (A) used in the step (I) includes a phosphorus compound (B). The number of moles of metal atoms contained in the at least one compound is preferably in the range of 0 to 1 times the number of moles of phosphorus atoms contained in the phosphorus compound (B). The ratio of (number of moles of metal atoms contained in the at least one compound) / (number of moles of phosphorus atoms contained in the phosphorus compound (B)) is in the range of 0 to 1 (for example, in the range of 0 to 0.9). By doing so, a multilayer structure having better barrier properties can be obtained. This ratio is preferably 0.3 or less, more preferably 0.05 or less, further preferably 0.01 or less, in order to further improve the barrier properties of the multilayer structure. It may be. Typically, the at least one compound consists only of the phosphorus compound (B).

The step (I) preferably includes the following steps (Ia) to (Ic).
Step (Ia): A step of preparing a liquid (S) containing the metal oxide (A).
Step (Ib): A step of preparing a solution (T) containing the phosphorus compound (B).
Step (Ic): A step of mixing the liquid (S) obtained in the above steps (Ia) and (Ib) and the solution (T).

  Step (Ib) may be performed prior to step (Ia), may be performed simultaneously with step (Ia), or may be performed after step (Ia). Hereinafter, each step will be described more specifically.

  In step (Ia), a liquid (S) containing a metal oxide (A) is prepared. The liquid (S) is a solution or a dispersion. The liquid (S) can be prepared, for example, by a technique adopted in a known sol-gel method. For example, the above-mentioned compound (L) component, water, and an acid catalyst or an organic solvent as necessary are mixed, and the compound (L) component is condensed or hydrolyzed by a method employed in a known sol-gel method. Can be prepared. The dispersion of the metal oxide (A) obtained by condensing or hydrolyzing the compound (L) component can be used as it is as the liquid (S) containing the metal oxide (A). However, a specific treatment (such as peptization or addition or subtraction of a solvent for concentration control) may be performed on the dispersion as necessary.

  The content of the metal oxide (A) in the liquid (S) is preferably in the range of 0.1 to 30% by mass, more preferably in the range of 1 to 20% by mass, More preferably, it is within the range of 15% by mass.

  In step (Ib), a solution (T) containing the phosphorus compound (B) is prepared. The solution (T) can be prepared by dissolving the phosphorus compound (B) in a solvent. When the solubility of the phosphorus compound (B) is low, dissolution may be promoted by heat treatment or ultrasonic treatment.

  The content of the phosphorus compound (B) in the solution (T) is preferably in the range of 0.1 to 99% by mass, more preferably in the range of 0.1 to 95% by mass, More preferably, it is in the range of 1 to 90% by mass. The content of the phosphorus compound (B) in the solution (T) may be in the range of 0.1 to 50% by mass, in the range of 1 to 40% by mass, It may be in the range of 30% by mass.

  In the step (Ic), the liquid (S) and the solution (T) are mixed. At the time of mixing the liquid (S) and the solution (T), in order to suppress a local reaction, it is preferable to mix while suppressing the addition rate and vigorously stirring. At this time, the solution (T) may be added to the stirring liquid (S), or the liquid (S) may be added to the stirring solution (T). Moreover, the coating liquid (U) excellent in storage stability may be obtained by maintaining the temperature at the time of mixing at 30 degrees C or less (for example, 20 degrees C or less). Furthermore, the coating liquid (U) excellent in storage stability may be obtained by continuing stirring for about 30 minutes after the completion of mixing.

  The coating liquid (U) may contain at least one acid compound selected from acetic acid, hydrochloric acid, nitric acid, trifluoroacetic acid, and trichloroacetic acid, if necessary. When the coating liquid (U) contains the acid compound, the liquid oxide (A) and the phosphorus compound (B) are mixed when the liquid (S) and the solution (T) are mixed in the step (Ic). The reaction rate is moderated, and as a result, a coating liquid (U) having excellent temporal stability may be obtained.

  The content of the acid compound in the coating liquid (U) is preferably in the range of 0.1 to 5.0% by mass, and more preferably in the range of 0.5 to 2.0% by mass. . In these ranges, the effect of the addition of the acid compound can be obtained, and the acid compound can be easily removed. When the acid component remains in the liquid (S), the amount of the acid compound added may be determined in consideration of the residual amount.

  The liquid obtained by mixing in the step (Ic) can be used as it is as the coating liquid (U). In this case, the solvent contained in the liquid (S) or solution (T) is usually the solvent for the coating liquid (U). Alternatively, the coating liquid (U) may be prepared by treating the liquid obtained by mixing in the step (Ic). For example, treatments such as addition of an organic solvent, pH adjustment, viscosity adjustment, and additive addition may be performed.

  As long as the effects of the present invention can be obtained, the coating liquid (U) may contain other substances than the substances described above. For example, the coating liquid (U) is an inorganic metal salt such as carbonate, hydrochloride, nitrate, hydrogen carbonate, sulfate, hydrogen sulfate, borate, aluminate; oxalate, acetate, tartrate Organic acid metal salts such as stearates; metal complexes such as acetylacetonate metal complexes (such as aluminum acetylacetonate), cyclopentadienyl metal complexes (such as titanocene), cyano metal complexes; layered clay compounds; It may contain a polymer compound other than the polymer (C); a plasticizer; an antioxidant; an ultraviolet absorber;

[Step (II)]
In the step (II), the coating liquid (U) is applied on the base material (X) to form a precursor layer of the layer (Y) on the base material (X). The coating liquid (U) may be applied directly on at least one surface of the substrate (X). Also, before applying the coating liquid (U), the surface of the substrate (X) is treated with a known anchor coating agent, or a known adhesive is applied to the surface of the substrate (X). Then, the adhesive layer (H) may be formed on the surface of the substrate (X).

  The method for applying the coating liquid (U) on the substrate (X) is not particularly limited, and a known method can be employed. Preferred methods include, for example, a casting method, a dipping method, a roll coating method, a gravure coating method, a screen printing method, a reverse coating method, a spray coating method, a kiss coating method, a die coating method, a metering bar coating method, and a chamber doctor combined coating method. And curtain coating method.

  Usually, in the step (II), the precursor layer of the layer (Y) is formed by removing the solvent in the coating liquid (U). There is no restriction | limiting in particular in the removal method of a solvent, A well-known drying method is applicable. Specifically, drying methods such as a hot air drying method, a hot roll contact method, an infrared heating method, and a microwave heating method can be applied alone or in combination. The drying temperature is preferably 0 to 15 ° C. or lower than the flow start temperature of the substrate (X). When the coating liquid (U) contains the polymer (C), the drying temperature is preferably 15 to 20 ° C. lower than the thermal decomposition start temperature of the polymer (C). The drying temperature is preferably in the range of 70 to 200 ° C, more preferably in the range of 80 to 180 ° C, and further preferably in the range of 90 to 160 ° C. The removal of the solvent may be carried out under normal pressure or reduced pressure. Further, the solvent may be removed by a heat treatment in step (III) described later.

  When laminating the layer (Y) on both surfaces of the layered substrate (X), the coating liquid (U) is applied to one surface of the substrate (X), and then the first layer ( First layer (Y) precursor layer) and then applying the coating liquid (U) to the other surface of the substrate (X), and then removing the solvent to remove the second layer (first layer). A precursor layer of two layers (Y) may be formed. The composition of the coating liquid (U) applied to each surface may be the same or different.

[Step (III)]
In step (III), the layer (Y) is formed by processing the precursor layer (precursor layer of layer (Y)) formed in step (II). Examples of the method for treating the precursor layer include heat treatment and irradiation with electromagnetic waves such as ultraviolet rays. The treatment performed in step (III) may be a treatment of reacting the metal oxide (A) with the phosphorus compound (B). For example, in the treatment performed in the step (III), the metal oxide (A) is reacted with the phosphorus compound (B) to react the metal oxide (A) via the phosphorus atom derived from the phosphorus compound (B). The process which couple | bonds these particle | grains may be sufficient. Usually, step (III) is a step of heat-treating the precursor layer at a temperature of 110 ° C. or higher. Although not particularly limited, in the infrared absorption spectrum of the precursor layer has a maximum absorbance at a range of 800～1400Cm ^-1 and (A ¹ '), the expansion and contraction of the hydroxyl groups in the range of 2500～4000Cm ^-1 In some cases, the maximum absorbance (A ² ′) based on vibration satisfies the relationship of absorbance (A ² ′) / absorbance (A ¹ ′)> 0.2.

  In step (III), a reaction in which the metal oxide (A) particles are bonded via phosphorus atoms (phosphorus atoms derived from the phosphorus compound (B)) proceeds. In another aspect, in the step (III), a reaction for generating the reaction product (R) proceeds. In order to allow the reaction to proceed sufficiently, the temperature of the heat treatment is 110 ° C. or higher, preferably 120 ° C. or higher, more preferably 140 ° C. or higher, and even more preferably 170 ° C. or higher. If the heat treatment temperature is low, it takes a long time to obtain a sufficient degree of reactivity, which causes a decrease in productivity. The preferable upper limit of the temperature of heat processing changes with kinds etc. of base material (X). For example, when a thermoplastic resin film made of polyamide resin is used as the base material (X), the heat treatment temperature is preferably 190 ° C. or lower. Moreover, when using the thermoplastic resin film which consists of polyester resins as a base material (X), it is preferable that the temperature of heat processing is 220 degrees C or less. The heat treatment can be performed in air, a nitrogen atmosphere, an argon atmosphere, or the like.

  The heat treatment time is preferably in the range of 0.1 second to 1 hour, more preferably in the range of 1 second to 15 minutes, and still more preferably in the range of 5 to 300 seconds. An example of the heat treatment is performed in the range of 110 to 220 ° C. for 0.1 second to 1 hour. In another example of the heat treatment, the heat treatment is performed in the range of 120 to 200 ° C. for 5 to 300 seconds (for example, 60 to 300 seconds).

  In order to dispose the adhesive layer (H) between the substrate (X) and the layer (Y), the surface of the substrate (X) is coated with a known anchor coating agent before applying the coating liquid (U). It is preferable to perform an aging treatment in the case where the treatment is carried out with or a known adhesive is applied to the surface of the substrate (X). Specifically, after applying the coating liquid (U) and before the heat treatment step (III), the base material (X) to which the coating liquid (U) is applied is kept at a relatively low temperature for a long time. It is preferable to leave. The temperature of the aging treatment is preferably less than 110 ° C, more preferably 100 ° C or less, and further preferably 90 ° C or less. The temperature of the aging treatment is preferably 10 ° C or higher, more preferably 20 ° C or higher, and further preferably 30 ° C or higher. The aging time is preferably in the range of 0.5 to 10 days, more preferably in the range of 1 to 7 days, and still more preferably in the range of 1 to 5 days. By performing such an aging treatment, the adhesive force between the substrate (X) and the layer (Y) becomes stronger.

  The water vapor barrier film (F) containing the base material (X) and the layer (Y) is obtained by the above process. When the multilayer structure used in the present invention includes other layers other than the water vapor barrier film (F), the water vapor barrier film and other layers are laminated. There is no limitation on those lamination methods, and a dry lamination method using an adhesive layer or a method using a thermal lamination method may be used.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples. In addition, the measurement and evaluation in an Example and a comparative example were implemented with the following method.

(1) Tension at 3% strain of base material A roll-shaped base material was cut into a strip shape having a width of 1.5 cm and a length of 15 cm so that the transport direction (MD direction) was a long side, thereby preparing a test piece. . About this test piece, using an autograph (“AGS-H” manufactured by Shimadzu Corporation), the tension when stretched 3% in the long side direction under the condition of 23 ° C. and 50% RH in accordance with JIS K7127 was measured. 3% strain tension (N / m) was calculated by converting the width direction into unit length (1 m).

(2) Moisture permeability The moisture permeability (water vapor permeability; WVTR) was measured using a vapor permeation measuring device ("GTR-WV" manufactured by GTR Tech Co.) according to the gas chromatography method (JIS-K7129-C). Specifically, the moisture permeability (unit: g / (m ² · day)) was measured under the conditions of a temperature of 40 ° C., a humidity on the water vapor supply side of 90% RH, and a humidity on the carrier gas side of 0% RH. .

  The moisture permeability was measured by collecting samples from 10 locations (such as the initial stage of winding, the end of winding, and the midpoint between them) of the manufactured roll-shaped multilayer structure. And the average value of the water vapor transmission rate was computed from the measured value of 10 places.

(Production of polyvinyl acetal)
The polyvinyl acetal used by the manufacture example mentioned later was manufactured with the following method. First, polyvinyl acetal was precipitated by adding a predetermined amount of aldehyde (acetaldehyde and / or n-butyraldehyde) and hydrochloric acid to an aqueous solution of polyvinyl alcohol (PVA) and stirring to acetalize. The precipitated polyvinyl acetal was used after washing and drying. About 9 types of produced polyvinyl acetals (PA1)-(PA9), the molar ratio of acetaldehyde and n-butyraldehyde in the aldehyde used for acetalization, the acetalization degree of the obtained polyvinyl acetal, and polyvinyl alcohol (PVA) Table 1 shows the degree of polymerization based on Polyvinyl acetal (PA2) and (PA3) are polyvinyl butyral.

(Manufacture of water vapor barrier film (F1))
The water vapor barrier film (F1) used in Production Example 1 and the like was produced by the following method. First, it heated up at 70 degreeC, stirring 230 mass parts of distilled water. In the distilled water, 88 parts by mass of aluminum isopropoxide was added dropwise over 1 hour, the liquid temperature was gradually raised to 95 ° C., and the generated isopropanol was distilled off to carry out hydrolysis and condensation. Next, 4.0 parts by mass of a 60% by mass nitric acid aqueous solution was added, and the mixture of the hydrolyzed condensate particles was peptized by stirring at 95 ° C. for 3 hours. The dispersion thus obtained was concentrated so that the solid content concentration was 10% by mass in terms of alumina to obtain a dispersion (S1).

  Further, 42.85 parts by weight of distilled water, 19.00 parts by weight of methanol and 1.39 parts by weight of trifluoroacetic acid are added to 1.76 parts by weight of 85% by weight phosphoric acid aqueous solution, and the mixture is stirred uniformly. As a result, a solution (T1) was obtained. Subsequently, with the solution (T1) being stirred, 35.00 parts by weight of the dispersion liquid (S1) was dropped, and stirring was further continued for 30 minutes after completion of the dropping to obtain a coating liquid (U1).

  Next, a roll-shaped biaxially stretched polyethylene terephthalate film (hereinafter sometimes abbreviated as “PET”) was prepared as a substrate. A substrate having a thickness of 25 μm and a tension at 3% strain in the MD direction of 3600 N / m was used as the substrate. On one surface of the substrate, the coating liquid (U1) was continuously coated by a gravure coating method so that the thickness after drying was 0.5 μm, and dried in a hot air drying oven at 100 ° C. Next, the coating liquid (U1) was continuously coated on the other surface of the base material by a gravure coating method so that the thickness after drying was 0.5 μm, and dried in a hot air drying oven at 100 ° C. After that, it was wound into a roll. Thus, the precursor layer of the layer (Y) was formed.

  “Tension at 3% strain” means that a base material whose unit length (1 m) in a certain direction measured at 23 ° C. and 50% RH is 3% in a direction perpendicular to the direction. It means the tension when stretched.

The obtained precursor layer was subjected to heat treatment at 200 ° C. for 1 minute by passing through a hot-air drying furnace, and layer (Y) (0.5 μm) / PET (25 μm) / layer (Y) (0. A water vapor barrier film (F1) having a structure of 5 μm) was obtained. About the obtained water vapor | steam barrier film (F1), it evaluated by the method mentioned above. The water vapor transmission rate was 0.0013 g / (m ² · day).

(Manufacture of water vapor barrier film (F2))
The water vapor barrier film (F2) used in Production Example 3 was produced by the following method. A film having excellent water vapor barrier properties was obtained by subjecting stretched PET of 25 μm to vacuum deposition. The conditions for vacuum deposition were vapor deposition material: silicon oxide, reaction gas: oxygen gas, and a degree of vacuum of 4.5 × 10 ⁻² Pa.

Example 1
First, the UV inhibitor ADK STAB LA-31 (manufactured by Adeka) 2.0 mass with respect to 100 parts by mass of a methacrylic resin composed of methyl methacrylate units (97.8 mass%) and methyl acrylate units (2.2 mass%). A methacrylic resin (A1) added with parts was prepared. Next, by using this methacrylic resin and polyvinyl acetal (PA1) obtained by adding 2.0 parts by mass of Adeka Stub LA-31 (manufactured by Adeka) as an ultraviolet inhibitor to the above-mentioned polyvinyl acetal, a methacrylic resin (PA1) is obtained by a coextrusion method. A laminated film (1) having a configuration of A1) layer / polyvinyl acetal (PA1) layer was formed. The coextrudability at this time was good. Coextrusion was performed at a temperature of 230 ° C. (the same applies to the following examples and comparative examples).

  Next, the laminated film (1) and the above-described water vapor barrier film (F1) were thermally laminated at 170 ° C. Thus, the protective sheet (1) of Example 1 having a configuration of methacrylic resin (A1) layer / polyvinyl acetal (PA1) layer / water vapor barrier film (F1) was produced. In this protective sheet (1), the adhesion between the laminated film (1) and the water vapor barrier film (F1) was good. For adhesion, put a Teflon (registered trademark) film between the laminated film (1) and the water vapor barrier film (F1), and perform a 180 degree peel test using that part. When the adhesive strength was 10 N / 25 mm or more, it was judged that the adhesiveness was good.

(Example 2)
First, 76 parts by mass of the methacrylic resin (A1) described in Example 1 and 24 parts by mass of elastic fine particles (rubber fine particles) were melted and kneaded to produce methacrylic resin (A1 ′) pellets containing elastic fine particles. did. The elastic fine particles have an average particle size of about 300 nm, the innermost layer is a methyl methacrylate cross-linked polymer, the intermediate layer is a soft rubber elastic body mainly composed of butyl acrylate, and the outermost layer is an acrylic polymer consisting of a methyl methacrylate polymer. Fine particles made of a polymer were used. Then, using the methacrylic resin (A1 ′) and the polyvinyl acetal (PA1) described above, a laminated film (2) having a configuration of methacrylic resin (A1 ′) layer / polyvinyl acetal (PA1) layer is obtained by a coextrusion method. Formed. The coextrudability at this time was good.

  Next, the laminated film (2) and the water vapor barrier film (F1) described above were heat-laminated at 170 ° C. In this way, the protective sheet (2) of Example 2 having the structure of methacrylic resin (A1 ′) layer / polyvinyl acetal (PA2) layer / water vapor barrier film (F1) was produced. In this protective sheet (2), the adhesion between the laminated film (2) and the water vapor barrier film (F1) was good.

(Examples 3 to 7)
Using a methacrylic resin (A1 ′) and the polyvinyl acetal (PA2-6) shown in Table 2, a laminated film having a configuration of methacrylic resin layer / polyvinyl acetal layer was formed by a coextrusion method. The coextrudability at this time was good.

  Next, the obtained laminated film and the water vapor barrier film (F1 or F2) shown in Table 2 were heat-laminated at 170 ° C. In this way, a protective sheet having a configuration of methacrylic resin layer / polyvinyl acetal layer / water vapor barrier film was produced. In this protective sheet, the adhesion between the laminated film and the water vapor barrier film was good.

(Comparative Examples 1-3)
Using a methacrylic resin (A1 ′) and the polyvinyl acetal (PA7-9) shown in Table 2, a laminated film having a configuration of a methacrylic resin (A1 ′) layer / polyvinyl acetal (PA3) layer by a coextrusion method. Attempted formation. However, the coextrudability was poor and a laminated film could not be formed.

(Comparative Example 4)
An attempt was made to produce a protective sheet by thermally laminating a film of methacrylic resin (A1 ′) and the above-described water vapor barrier film (F1) at 170 ° C. However, it was not possible to bond both with a thermal laminate, and a protective sheet could not be produced.

  The results are shown in Table 2.

  As shown in Table 2, the methacrylic resin layer and the water vapor barrier layer could be easily heat-laminated by selecting a predetermined adhesive layer.

  About the protective sheet formed in Examples 1-7, evaluation as a protective sheet of a solar cell was performed. Specifically, the durability test is 2000 hours under the conditions of a high temperature and high humidity test 85 ° C. and 85% RH, and the weather resistance test is 3000 hours with a xenon weather meter (illuminance 168 kWh, temperature 89 ° C. black panel, humidity 50%). The total light transmittance, the water vapor barrier property, the light resistance, and the adhesion were evaluated before and after the test, but the changes were slight, and the protective sheet formed in Examples 1 to 7 was used as a protective sheet for solar cells. It was found to have sufficient properties.

  The present invention can be used for a protective sheet for a solar cell and a solar cell using the same.

Claims (9)

A method for producing a protective sheet for protecting the surface of a solar cell, comprising:
(I) forming a laminated film of a methacrylic resin layer and a polyvinyl acetal layer by a coextrusion method;
(Ii) laminating the laminated film and the water vapor barrier film so that the water vapor barrier film, the polyvinyl acetal layer, and the methacrylic resin layer are laminated in this order,
The carbon number of the acetal part per 100 carbon atoms constituting the main chain of the polyvinyl acetal used for the polyvinyl acetal layer is in the range of 30 to 70,
The method for producing a protective sheet, wherein the average degree of polymerization of the polyvinyl acetal is in the range of 500 to 2,000.   The manufacturing method according to claim 1, wherein in the step (ii), the laminated film and the water vapor barrier film are laminated by a thermal laminating method.   The manufacturing method of Claim 1 or 2 whose ratio of the structural unit containing the residual acetic acid group which occupies for all the structural units in the said polyvinyl acetal is 5 mol% or less.   The production method according to any one of claims 1 to 3, wherein the degree of acetalization of the polyvinyl acetal is in the range of 55 to 85 mol%.   The manufacturing method of any one of Claims 1-4 in which the said polyvinyl acetal layer consists of polyvinyl butyral. A protective sheet for protecting the surface of the solar cell,
A coextruded film in which a methacrylic resin layer and a polyvinyl acetal layer are laminated, and a water vapor barrier film,
The protective sheet in which the water vapor barrier film, the polyvinyl acetal layer, and the methacrylic resin layer are laminated in this order.   The protective sheet according to claim 6, wherein the coextruded film and the water vapor barrier film are laminated by a thermal laminating method. The water vapor barrier film includes a base material, and a water vapor barrier layer laminated on the base material,
The water vapor barrier layer contains a reaction product (R),
The reaction product (R) is a reaction product obtained by reacting at least the metal oxide (A) and the phosphorus compound (B),
In the infrared absorption spectrum of the water vapor barrier layer in the range of 800 to 1400 cm ^−1, the wave number (n ¹ ) at which infrared absorption is maximum is in the range of 1080 to 1130 cm ⁻¹ ,
The protective sheet according to claim 6 or 7, wherein the metal atom constituting the metal oxide (A) is substantially an aluminum atom. A solar cell comprising a protective sheet for protecting the surface,
The protective sheet is the protective sheet according to any one of claims 6 to 8,
In the protective sheet, the methacrylic resin layer is disposed outside the water vapor barrier film.