Transparent protection sheet and solar cell module

Abstract

A transparent protection sheet (5) according to the present disclosure comprises a vinylidene fluoride-based film and is used for a double-sided light-reception-type solar cell module (10). The vinylidene fluoride-based film includes at least a layer comprising a resin composition (C) containing 60-85 mass % of a vinylidene fluoride-based resin (F) and 15-40 mass % of a (meth) acrylic resin (A). The (meth) acrylic resin (A) includes a multilayer structure polymer (a) and may include a non-multilayer structure polymer (b). The multilayer structure polymer (a) is 60-100 mass % and the non-multilayer structure polymer (b) is 0-40 mass % in 100 mass % of the (meth) acrylic resin (A).

Description

Transparent protective sheet and solar cell module

[0001] The present disclosure relates to a transparent protective sheet and a solar cell module having the transparent protective sheet.

[0002] To combat global warming and reduce carbon dioxide emissions, it is important to promote the use of renewable natural energy instead of fossil fuels. Among these, photovoltaic power generation, which directly converts solar light energy into electricity, is attracting attention. A typical solar cell module has a structure in which solar cells are encapsulated with ethylene-vinyl acetate copolymer (EVA) resin or the like, the surface exposed to sunlight is covered with glass, and the backside is protected with a backsheet.

[0003] In the backsheets of conventional single-sided light-receiving solar cells, opaque resins such as white resins are often used to reflect light that has passed through the solar cell and thereby increase the conversion efficiency. For example, Patent Document 1 discloses a backsheet for a solar cell module that includes a layer made of a white resin film containing vinylidene fluoride resin and titanium oxide.

[0004] On the other hand, as a transparent backsheet, for example, Patent Document 2 discloses a sheet obtained by laminating together a transparent, highly moisture-proof film (a polyethylene terephthalate film coated with an inorganic oxide) and a transparent, highly light-resistant film (a fluororesin film) having excellent ultraviolet resistance.

[0005] International Publication No. 2010 / 122936 Japanese Patent Application Laid-Open No. 2000-174296

[0006] For backsheets of see-through or bifacial solar cell modules that have been developed in recent years, there is a market demand for sheets with excellent transparency to enhance photoelectric conversion efficiency, in addition to mechanical strength and weather resistance that can withstand long-term outdoor use. Furthermore, there is a demand for backsheets with excellent flexibility from the viewpoints of transportability, ease of installation, storability, etc.

[0007] Although the problems with the backsheet have been described, similar problems can arise with the frontsheet used on the front surface of the solar cell module.

[0008] The present disclosure has been made in consideration of the above background, and aims to provide a transparent protective sheet that combines transparency and light resistance with excellent flexibility, and a bifacial solar cell module having the transparent protective sheet.

[0009] The present disclosure provides the following thermoplastic resin film and laminate film: [1]: A transparent protective sheet for a bifacial solar cell module, having a vinylidene fluoride film, wherein the vinylidene fluoride film includes at least a layer made of a resin composition (C) containing 60 to 85 mass% of a vinylidene fluoride resin (F) and 15 to 40 mass% of a (meth)acrylic resin (A), wherein the (meth)acrylic resin (A) includes a multilayer polymer (a) and optionally a non-multilayer polymer (b), and wherein the multilayer polymer (a) accounts for 60 to 100 mass% and the non-multilayer polymer (b) accounts for 0 to 40 mass% of 100 mass% of the (meth)acrylic resin (A). [2]: The transparent protective sheet according to [1], wherein the multilayer-structured polymer (a) is a particle and comprises a shell layer constituting the outermost layer and a core layer constituting the inner side thereof, the shell layer comprises a hard polymer layer, the core layer comprises one or more soft polymer layers, and the soft polymer layer (when there are multiple soft polymer layers, the soft polymer layer formed on the outer side) has an average particle size of 0.05 to 0.16 μm. [3]: The transparent protective sheet according to [1] or [2], wherein the multilayer structure polymer (a) comprises an acetone soluble component and an acetone insoluble component, the acetone soluble component contains 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 20% by mass of structural units derived from an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and has a glass transition temperature of 80 to 100°C, and the acetone insoluble component contains 20 to 60% by mass of structural units derived from methyl methacrylate and 40 to 80% by mass of structural units derived from an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and has a glass transition temperature of 0°C or lower.[4]: The multilayer structure polymer (a) is a particle, and is composed of a shell layer constituting the outermost layer and a core layer constituting the inside thereof, and the core layer further has an intermediate layer and an innermost layer located therein, the innermost layer being a hard polymer layer containing 80 to 99 mass% of structural units derived from methyl methacrylate and 1 to 20 mass% of structural units derived from alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, the intermediate layer being a soft polymer layer containing 70 to 100 mass% of structural units derived from alkyl acrylate having an alkyl group with 1 to 8 carbon atoms and 0 to 30 mass% of structural units derived from methyl methacrylate, and the shell layer being a hard polymer layer containing 80 to 99 mass% of structural units derived from methyl methacrylate and 1 to 20 mass% of structural units derived from alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, The transparent protective sheet according to any one of [1] to [3], wherein the multilayer structure polymer (a) contains 5 to 30 mass% of the hard polymer in the innermost layer, 20 to 45 mass% of the soft polymer in the intermediate layer, and 50 to 75 mass% of the hard polymer in the outermost layer, based on 100 mass% of the multilayer structure polymer (a). [5]: The transparent protective sheet according to any one of [1] to [4], which has a haze of 5.0% or less. [6]: The transparent protective sheet according to any one of [1] to [5], which has a thickness of 10 to 50 μm. [7]: A bifacial solar cell module having the transparent protective sheet according to any one of [1] to [6].

[0010] The present disclosure has the excellent effect of providing a transparent protective sheet and a bifacial solar cell module that are both transparent and light-resistant, and also have excellent flexibility.

[0011] FIG. 1 is a schematic cross-sectional view showing an example of a solar cell module.

[0012] An example of an embodiment to which the present disclosure is applied will be described below. The present disclosure is not limited to this embodiment, and other embodiments may also fall within the scope of the present disclosure as long as they conform to the spirit of the present disclosure. Furthermore, the numerical values ​​"A to B" specified in this specification include numerical values ​​A and B. The numerical values ​​specified in this specification are values ​​obtained by the methods disclosed in the embodiments or examples. Furthermore, the terms "sheet" and "film" in this specification have the same meaning. Unless otherwise noted, the various components appearing in this specification may each be used independently, either alone or in combination of two or more types. (Meth)acrylic is a general term for acrylic and methacrylic. Unless otherwise specified in this specification, a "unit" contained in a polymer is a repeating unit contained in the polymer, and is a monomer unit derived from a raw material monomer or a derived unit derived from one or more monomer units.

[0013] 1. Solar Cell Module FIG. 1 shows a schematic cross-sectional view of a solar cell module according to this embodiment. The solar cell module 10 has a configuration in which a transparent protective substrate 1, a first sealing material 2, a solar cell 3, a second sealing material 4, and a transparent protective sheet 5 are formed in this order. The solar cell module 10 has a configuration in which the solar cell 3 is sandwiched between the transparent protective substrate 1 and the transparent protective sheet 5 and sealed with the first sealing material 2 and the second sealing material 4. Because the solar cell module 10 uses the transparent protective substrate 1 and the transparent protective sheet 5, it is particularly suitable for bifacial applications. Below, an application to a bifacial solar cell module will be described. Note that instead of the transparent protective substrate 1, the transparent protective sheet 5 may be provided as the outermost layer on both main surfaces of the solar cell module 10.

[0014] The transparent protective substrate 1 is located on the front side and serves to protect the solar cell 3. A highly transparent material is selected as the material for the transparent protective substrate 1, allowing the solar cell 3 to receive sunlight. As used herein, "transparent" refers to a transmittance of 80% or more in the wavelength band used for photoelectric conversion of the solar cell 3. The transmittance is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more. The transparent protective substrate 1 is preferably glass when mechanical strength and moisture resistance are required, and preferably a resin film when flexibility is required. These may be single-layer or multi-layer. A laminate of different materials, such as glass, a resin film, or a transparent film coated with an inorganic oxide such as silica or alumina, may also be used. When a multi-layer or laminate is used, bonding may be performed via an adhesive layer or the like, as necessary.

[0015] The first sealing material 2 and the second sealing material 4 serve to seal the solar cell 3, and may be, for example, a film formed from an ethylene-vinyl acetate copolymer (EVA) resin composition. The first sealing material 2 and the second sealing material 4 each have a thickness of, for example, 30 to 2000 μm. The solar cell 3 is a photoelectric conversion element, and any known power generation element such as silicon may be used without limitation.

[0016] The transparent protective sheet 5 is disposed as the outermost layer on the back side of the solar cell module 10, and serves to protect the solar cell 3. A bifacial solar cell module can receive light and generate power from the back side, which is expected to improve power generation efficiency. The transparent protective sheet will be described in detail below.

[0017] 2. Transparent Protective Sheet The transparent protective sheet includes at least a vinylidene fluoride film. That is, the transparent protective sheet may be composed solely of a single-layer or multi-layer vinylidene fluoride film, or may be a laminate of a vinylidene fluoride film and one or more other layers within the scope of the present disclosure. Examples of other layers include a substrate layer and a moisture-proof layer. From the standpoints of processability and cost, the substrate layer is preferably a (meth)acrylic resin (A) and a polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN). When forming a laminate, the layers may be bonded via an adhesive layer as needed. In the case of a multi-layer structure, it is preferable to position the layer with higher light resistance on the outer side to enhance durability. From the standpoint of enhancing transparency and light resistance, the transparent protective sheet is preferably a single-layer vinylidene fluoride film.

[0018] The transparent protective sheet is a sheet having a transmittance of 80% or more in the wavelength band used for photoelectric conversion of the solar cell 3. Typically, this is met if the light transmittance is 80% or more in the wavelength range of 400 to 1100 nm. If the transparent protective sheet is a multi-layer or laminated body, it is not necessary for each layer to satisfy the above, and it is sufficient that the transparent protective sheet as a whole has a transmittance of 80% or more in the wavelength range used for photoelectric conversion of the solar cell 3.

[0019] From the viewpoint of achieving superior transparency, the haze of the present transparent protective sheet is preferably 5.0% or less, more preferably 4.0% or less, and even more preferably 3.0% or less. The lower the haze, the better, and although there is no lower limit, it is typically about 1.0%.

[0020] The thickness of the transparent protective sheet can be designed as desired, but from the viewpoint of achieving both flexibility and mechanical strength, it is preferably 10 to 50 μm. The lower limit is more preferably 12 μm, and even more preferably 15 μm. The upper limit is more preferably 45 μm, and even more preferably 40 μm.

[0021] The transparent protective sheet has excellent weather resistance and transparency, making it particularly suitable as a back sheet for bifacial solar cell modules. The transparent protective sheet of the present disclosure is also suitable as a front sheet and / or back sheet for monofacial solar cell modules or see-through solar cell modules, which require lightweight and flexibility. It is also suitable as a front sheet for various solar cell modules.

[0022] 2-1. Vinylidene fluoride film The vinylidene fluoride film has one or more layers made of a resin composition (C) containing 60 to 85 mass% of a vinylidene fluoride resin (F) and 15 to 40 mass% of a (meth)acrylic resin (A). A layer made of a vinylidene fluoride resin composition other than the resin composition (C) may be laminated within a range not departing from the spirit of the present disclosure. The vinylidene fluoride film may contain components other than the vinylidene fluoride resin (F) and the (meth)acrylic resin (A) within a range not departing from the spirit of the present disclosure.

[0023] The (meth)acrylic resin (A) contains a multilayer structure polymer (a) (hereinafter also referred to as polymer (a)). The (meth)acrylic resin (A) may contain a non-multilayer structure polymer (b) (hereinafter also referred to as polymer (b)). In 100% by mass of the (meth)acrylic resin (A), the polymer (a) accounts for 60 to 100% by mass and the polymer (b) accounts for 0 to 40% by mass. By using the above-mentioned configuration, a vinylidene fluoride film having excellent transparency, light resistance, and flexibility can be obtained.

[0024] 2-1a. Vinylidene fluoride resin (F) The vinylidene fluoride resin (F) is a polymer primarily composed of vinylidene fluoride units (structural units derived from vinylidene fluoride). The vinylidene fluoride resin (F) may contain structural units derived from fluorine-containing monomers in addition to the structural units derived from vinylidene fluoride. The structural units derived from fluorine-containing monomers may be of one type or two or more types. The content of vinylidene fluoride units is preferably 50% by mass or more, more preferably 75% by mass or more, and even more preferably 85% by mass or more, based on 100% by mass of the vinylidene fluoride resin (F), and may be a 100% by mass homopolymer (PVDF).

[0025] Examples of the fluorine-containing monomer include hexafluoropropylene (HFP), trifluoroethylene, chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), and perfluoroalkyl vinyl ether. Among these, hexafluoropropylene, chlorotrifluoroethylene, and tetrafluoroethylene are preferred from the viewpoint of transparency, and hexafluoropropylene is more preferred.

[0026] The content of the structural unit derived from the fluorine-containing monomer in the vinylidene fluoride resin (F) is preferably 2 to 25% by mass from the viewpoints of transparency and high crystallinity. The lower limit is more preferably 4% by mass, and even more preferably 6% by mass. The upper limit is more preferably 20% by mass, and even more preferably 15% by mass. By setting the content within the above range, the crystallinity of the vinylidene fluoride resin (F) is improved, and therefore, the physical properties of the film can be expected to be improved.

[0027] The vinylidene fluoride resin (F) may further contain other structural units in addition to the structural units derived from vinylidene fluoride and the structural units derived from the fluorine-containing monomer, as long as the effects of the present disclosure are achieved. Such other structural units may be one or more types. Examples of such other structural units include ethylene, unsaturated dibasic acid derivatives (e.g., monomethyl maleate, dimethyl maleate), and vinyl acetate.

[0028] The weight average molecular weight (hereinafter also referred to as Mw) of the vinylidene fluoride resin (F) is preferably 100,000 to 450,000, more preferably 150,000 to 450,000, and even more preferably 170,000 to 400,000, from the viewpoint of achieving both mechanical strength and a melt viscosity suitable for molding.

[0029] The polymerization of the vinylidene fluoride resin (F) can be performed using known polymerization methods such as suspension polymerization and emulsion polymerization. In emulsion polymerization, vinylidene fluoride alone or vinylidene fluoride and a comonomer such as hexafluoropropylene are emulsified in an aqueous medium using a chemically stable fluorine-based emulsifier. Polymerization is then carried out using a polymerization initiator such as an inorganic peroxide, an organic peroxide, or an organic percarbonate compound. After emulsion polymerization, the submicron-sized latex is precipitated and agglomerated using a flocculant, allowing vinylidene fluoride resin particles of an appropriate size to be recovered. In suspension polymerization, vinylidene fluoride alone or vinylidene fluoride and a comonomer are suspended in an aqueous medium using a suspending agent such as methyl cellulose. Using, for example, an organic percarbonate active at low temperatures as a polymerization initiator, polymerization is initiated at a temperature below the critical temperature of vinylidene fluoride to produce primary polymer particles. If necessary, the temperature is increased to continue the polymerization reaction and produce secondary polymer particles.

[0030] The vinylidene fluoride resin (F) may be used alone or in combination of two or more. From the viewpoint of ease of crystallization, it is preferable to use a vinylidene fluoride homopolymer (PVDF) alone as the vinylidene fluoride resin (F).

[0031] Examples of commercially available vinylidene fluoride resins (F) include "Kynar 720 (trade name)" and "Kynar 710 (trade name)" manufactured by Arkema K.K., "KF#850 (trade name)" and "KF#1100 (trade name)" manufactured by Kureha Corporation, and "Solef 1006 (trade name)" and "Solef 1008 (trade name)" manufactured by Solvay Specialty Polymers Japan, Ltd.

[0032] 2-1b. (Meth)acrylic Resin (A) The (meth)acrylic resin (A) refers to a methacrylic resin or an acrylic resin, and includes a multilayer polymer (a). The (meth)acrylic resin (A) may also contain a non-multilayer polymer (b) as an optional component. The multilayer polymer (a) may have two or more layers, and may have three, four, or more layers. The non-multilayer polymer (b) refers to all (meth)acrylic resins excluding the multilayer polymer (a). Whether or not the (meth)acrylic resin (A) falls under the category of a multilayer polymer can be confirmed by electronically staining a film with a 10% aqueous solution of phosphotungstic acid and observing the shape (morphology) of the stained portion with a transmission electron microscope.

[0033] In 100% by mass of the (meth)acrylic resin (A), the multilayer structure polymer (a) is 60 to 100% by mass, and the non-multilayer structure polymer (b) is 0 to 40% by mass. The lower limit of the multilayer structure polymer (a) is more preferably 65% ​​by mass, and even more preferably 80% by mass. The upper limit of the non-multilayer structure polymer (b) is more preferably 35% by mass, and even more preferably 20% by mass.

[0034] 2-1b-1. Multilayered Polymer (a) The multilayered polymer (a) (polymer (a)) is usually in the form of particles. From the viewpoint of improving impact resistance, the multilayered polymer (a) preferably has a shell layer constituting the outermost layer and a core layer constituting the inner side thereof, the shell layer being made of a hard polymer layer, and the core layer being particles containing one or more soft polymer layers. From the viewpoint of improving impact resistance, the average particle size of the soft polymer layer (when there are multiple soft polymer layers, the soft polymer layer formed on the outer side) is preferably 0.05 to 0.30 μm, more preferably 0.05 to 0.16 μm. The lower limit of this average particle size is more preferably 0.06 μm. The upper limit of this average particle size is more preferably 0.15 μm, more preferably 0.14 μm, and even more preferably 0.11 μm.

[0035] A soft polymer refers to a polymer having a glass transition temperature (hereinafter also referred to as Tg) of 25°C or less. In the case of a polymer having multiple Tg's or a polymer having a Tg and a melting point (Tm), if the lowest Tg is 25°C or less, it is included in the soft polymer category. A hard polymer layer refers to a polymer having a Tg of 50°C or more. In the case of a polymer having multiple Tg's or a polymer having a Tg and a melting point (Tm), if the lowest Tg is 50°C or more, it is included in the hard polymer category. A soft polymer layer refers to one containing 70% by mass or more of a soft polymer, and a hard polymer layer refers to one containing 70% by mass or more of a hard polymer. In the soft polymer layer, the soft polymer is preferably 80% by mass or more, more preferably 90% by mass, even more preferably 95% by mass, or even 100% by mass. In the hard polymer layer, the hard polymer is preferably 80% by mass or more, more preferably 90% by mass, even more preferably 95% by mass, or even 100% by mass.

[0036] The soft polymer layer preferably has a crosslinked structure. On the other hand, the hard polymer layer preferably has a non-crosslinked structure. In the multilayer structure polymer (a) in which the outermost layer is a hard polymer layer having a non-crosslinked structure, the outermost layer polymer that has not graft reacted with the soft polymer layer becomes acetone soluble. On the other hand, the outermost layer that has graft reacted with the soft polymer layer, the soft polymer layer which is a rubber component layer having a crosslinked structure, and the inner layer become acetone insoluble.

[0037] From the viewpoint of improving moldability, the acetone soluble matter preferably contains 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 20% by mass of structural units derived from alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, and further preferably has a Tg of 80 to 100°C from the viewpoint of heat resistance.

[0038] On the other hand, from the viewpoint of impact resistance, the acetone insoluble matter preferably contains 20 to 60% by mass of structural units derived from methyl methacrylate and 40 to 80% by mass of structural units derived from alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, and furthermore, from the viewpoint of enhancing impact resistance, it is preferable that the Tg is 0° C. or lower. Note that the acetone soluble matter and acetone insoluble matter in this specification are defined by the method in the Examples described later.

[0039] Suitable examples of the multilayer polymer (a) include those in which the shell layer is composed of a hard polymer layer and the core layer has, for example, the following configuration. That is, the core layer may be (i) a single layer of a soft polymer layer (two layers: shell layer and core layer), (ii) a two-layer structure consisting of a soft polymer layer (intermediate layer) and a hard polymer layer (innermost layer) (three layers: shell layer and core layer), (iii) a two-layer structure consisting of a hard polymer layer (intermediate layer) and a soft polymer layer (innermost layer) (three layers: shell layer and core layer), (iv) a two-layer structure consisting of a soft polymer layer (intermediate layer) and a soft polymer layer (innermost layer) (three layers: shell layer and core layer), or (v) a three-layer structure consisting of a soft polymer layer (first intermediate layer), a hard polymer layer (second intermediate layer), and a soft polymer layer (innermost layer) from the outside of the core layer (four layers: shell layer and core layer). Each layer is formed from one or more resins. The hard polymer layer and the soft polymer layer can be distinguished and confirmed by subjecting the film to electron staining with a 10% aqueous solution of phosphotungstic acid and observing the shape (morphology) of the stained portion with a transmission electron microscope.

[0040] From the viewpoint of dispersibility of the multilayer structure polymer (a), it is preferable that the shell layer is constituted by a hard polymer layer. From the viewpoint of improving impact resistance, it is preferable that the core layer is constituted by two or more layers (three or more layers in total including the shell layer and the core layer) having one or more intermediate layers including a soft polymer layer and an innermost layer made of a hard polymer layer. Among these, the following configurations are more preferable.

[0041] The innermost layer of the core layers is preferably a hard polymer layer containing 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 20% by mass of structural units derived from alkyl acrylate having an alkyl group with a carbon number of 1 to 8. By forming the innermost layer from a hard polymer layer of the above structural units, the layer will have excellent impact strength.

[0042] The intermediate layer of the core layer is preferably a soft polymer layer containing 70 to 100% by mass of structural units derived from alkyl acrylates in which the alkyl group has 1 to 8 carbon atoms and 0 to 30% by mass of structural units derived from methyl methacrylate. By making the structural units derived from alkyl acrylates in which the alkyl group has 1 to 8 carbon atoms 70% by mass or more in the soft polymer layer in the intermediate layer, excellent impact strength can be achieved.

[0043] The shell layer (outermost layer) is preferably a hard polymer layer containing 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 20% by mass of structural units derived from alkyl acrylate in which the alkyl group has 1 to 8 carbon atoms. By containing 80 to 99% by mass of structural units derived from methyl methacrylate, excellent light resistance is achieved.

[0044] The polymer (a) of (ii) above is more preferred, which is a combination of an innermost layer, an intermediate layer, and an outermost layer each having the structural unit. Furthermore, it is even more preferred that, based on 100% by mass of the multilayer structure polymer (a), the hard polymer of the innermost layer accounts for 5 to 30% by mass, the soft polymer of the intermediate layer accounts for 20 to 45% by mass, and the hard polymer of the shell layer (outermost layer) accounts for 50 to 75% by mass.

[0045] The innermost layer, intermediate layer, and outermost layer may each independently have a structural unit derived from a monomer other than a methyl methacrylate unit and an alkyl acrylate unit having an alkyl group with a carbon number of 1 to 8, within the scope of the present disclosure. The other monomer may be a monofunctional monomer or a polyfunctional monomer.

[0046] Examples of alkyl acrylates in which the alkyl group has 1 to 8 carbon atoms include methyl acrylate (MA), ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate (BA), isobutyl acrylate, s-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate.

[0047] Other monofunctional monomers include esters of (meth)acrylic acid and saturated aliphatic alcohols (saturated aliphatic alcohols having 9 to 22 carbon atoms), such as ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, pentyl methacrylate, hexyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate, or esters of methacrylic acid and saturated aliphatic alcohols having 1 to 8 carbon atoms; cyclohexyl (meth)acrylate, Examples of the other monofunctional monomers include esters of (meth)acrylic acid and C5 or C6 alicyclic alcohols such as acrylate; (meth)acrylic acid esters such as esters of (meth)acrylic acid and phenols such as phenyl (meth)acrylate, and esters of (meth)acrylic acid and aromatic alcohols such as benzyl (meth)acrylate; aromatic vinyl monomers such as styrene (St), α-methylstyrene, 1-vinylnaphthalene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, and halogenated styrenes; and vinyl cyanide monomers such as acrylonitrile and methacrylonitrile. One or more types of other monofunctional monomers may be used.

[0048] Other polyfunctional monomers are monomers having two or more carbon-carbon double bonds in the molecule. Examples of polyfunctional monomers include esters of unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and cinnamic acid with unsaturated alcohols such as allyl alcohol and methallyl alcohol; diesters of the above unsaturated monocarboxylic acids with glycols such as ethylene glycol, butanediol, and hexanediol; and diesters of dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, and maleic acid with the above unsaturated alcohols. Specific examples include allyl acrylate, methallyl acrylate, allyl methacrylate (ALMA), methallyl methacrylate, allyl cinnamate, methallyl cinnamate, diallyl maleate, diallyl phthalate, diallyl terephthalate, diallyl isophthalate, divinylbenzene, ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, and hexanediol di(meth)acrylate. Among these, allyl methacrylate (ALMA) is preferred. The polyfunctional monomers may be used alone or in combination of two or more.

[0049] In the multilayer structure polymer (a), the Mw of the constituent copolymer of the outermost layer, as measured by GPC, is preferably 40,000 to 200,000, more preferably 50,000 to 150,000, and even more preferably 60,000 to 120,000. By setting the Mw to 40,000 to 200,000, it is possible to achieve both good impact strength and good processability.

[0050] The average particle size of the soft polymer layer of the core layer (when there are multiple soft polymer layers, the outermost soft polymer layer) is preferably 0.05 to 0.30 μm, more preferably 0.05 to 0.16 μm. By having an average particle size within this range, the occurrence of internal voids is suppressed, while the multilayer structure polymer (a) improves the stress relaxation of the vinylidene fluoride film, thereby increasing the impact strength of the molded product. Note that voids refer to fractures that occur inside the particles, and since the amount of energy absorbed is very small, they do not contribute much to the development of impact resistance. The lower limit of the average particle size of the soft polymer layer of the core layer is more preferably 0.06 μm, and even more preferably 0.07 μm. The upper limit is more preferably 0.150 μm, and even more preferably 0.11 μm.

[0051] The average particle size of the multilayer structure polymer (a) can be measured using an electron microscope or by measuring latex using a light scattering method, and the average particle size described in this example is a value obtained by the method in the example. In the electron microscope method, the resin composition is electronically stained with a phosphotungstic acid solution, and the average particle size is the average value of the major axis diameter and minor axis diameter of the outermost diameter in the soft polymer layer of the dyed polymer (a) observed with a transmission electron microscope. In the light scattering method, during polymerization of the multilayer structure polymer particles, the latex polymerized up to the rubber component layer is sampled and measured using a laser diffraction / scattering particle size distribution analyzer LA-950V2 manufactured by Horiba, Ltd.

[0052] The method for producing the multilayer polymer (a) of the present disclosure is not particularly limited. For example, three-layer polymer (a) particles can be produced by emulsion polymerizing a monomer for obtaining a polymer constituting the innermost layer to obtain seed particles, then seed emulsion polymerizing a monomer for obtaining a polymer for the intermediate layer in the presence of the seed particles to obtain intermediate particles, and then seed emulsion polymerizing a monomer for obtaining a polymer for the outermost layer in the presence of the intermediate particles to obtain polymer (a) particles. Multilayer polymers (a) having two layers or four or more layers can be easily produced by those skilled in the art by referring to the above-mentioned method for producing a three-layer multilayer polymer (a). Emulsion polymerization or seed emulsion polymerization is a well-known technique in the art for obtaining general multilayer polymer particles, and can be produced by referring to other literature.

[0053] In the polymerization reaction step, polymerization conditions are adjusted to obtain the desired Mw. The polymerization conditions can be adjusted mainly by the amount of a molecular weight modifier such as alkyl mercaptan. The average particle size of the multilayer structure polymer (a) is preferably about 0.09 to 0.25 μm from the viewpoint of impact resistance. The average particle size at this time can be measured by a light scattering method using a laser diffraction / scattering particle size distribution analyzer LA-950V2 manufactured by Horiba, Ltd., by sampling the polymerized latex during particle polymerization of the multilayer structure polymer (a).

[0054] 2-1b-2. Non-multilayer structure polymer (b) The non-multilayer structure polymer (b) (hereinafter also referred to as polymer (b)) refers to a (meth)acrylic resin (A) that does not have a multilayer structure. From the viewpoint of compatibility with polymer (a), a homopolymer of a methacrylic acid ester polymer, a methacrylic acid ester-acrylic acid alkyl ester copolymer, or a block copolymer having a methacrylic acid ester polymer block and an acrylic acid ester polymer block is preferred.

[0055] The polymer (b) preferably has structural units derived from alkyl methacrylate, more preferably structural units derived from methyl methacrylate. Preferably, the proportion of structural units derived from methyl methacrylate is 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may even be 100% by mass. In other words, the proportion of structural units derived from monomers other than methyl methacrylate is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. Examples of methacrylic acid esters include methyl methacrylate (MMA), ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, pentadecyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, phenoxyethyl methacrylate, 2-hydroxyethyl methacrylate, 2-methoxyethyl methacrylate, glycidyl methacrylate, and allyl methacrylate (ALMA). Among these, from the viewpoint of improving the transparency and heat resistance of the resin composition (C) according to the present disclosure, methyl methacrylate (MMA), ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, etc. are preferred, and methyl methacrylate (MMA) is particularly preferred. One or more types of methacrylic acid esters can be used.

[0056] Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate (BA), isobutyl acrylate, s-butyl acrylate, t-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, isobornyl acrylate, phenyl acrylate, benzyl acrylate, phenoxyethyl acrylate, 2-hydroxyethyl acrylate, 2-methoxyethyl acrylate, glycidyl acrylate, and allyl acrylate. One or more types of acrylic acid esters can be used.

[0057] The polymer (b) may be a commercially available product, such as "PARAPET H1000B" (MFR: 22 g / 10 min (230°C, 37.3 N)), "PARAPET GF" (MFR: 15 g / 10 min (230°C, 37.3 N)), "PARAPET EH" (MFR: 1.3 g / 10 min (230°C, 37.3 N)), "PARAPET HRL" (MFR: 2.0 g / 10 min (230°C, 37.3 N)), or "PARAPET G" (MFR: 8.0 g / 10 min (230°C, 37.3 N)) [all trade names, manufactured by Kuraray Co., Ltd.].

[0058] The Mw of the polymer (b) is preferably from 30,000 to 1,000,000, more preferably from 40,000 to 500,000, and even more preferably from 50,000 to 200,000, from the viewpoint of the balance between impact resistance, toughness, moldability, and fluidity during processing.

[0059] From the viewpoint of heat resistance of the film, the Tg of the polymer (b) is preferably 80 to 130° C. The upper limit of the Tg is more preferably 125° C., and even more preferably 120° C. The lower limit of the Tg is more preferably 90° C., and even more preferably 100° C.

[0060] 2-2. Resin Composition for Producing Vinylidene Fluoride Films Polymer (a) and, if necessary, polymer (b) are kneaded and mixed to obtain a (meth)acrylic resin (A). Next, the (meth)acrylic resin (A) and vinylidene fluoride resin (F) are kneaded and mixed. Alternatively, polymer (a), polymer (b), and vinylidene fluoride resin (F) may be kneaded simultaneously. Kneading can be performed by known methods, such as using a batch kneader such as a Banbury mixer, a pressure kneader, or a Prabender Plastograph, or a continuous kneader such as a single-screw, twin-screw, or multi-screw extruder. Alternatively, high-concentration master pellets may be prepared by the above method, and then diluted and melt-kneaded. From the viewpoint of productivity, a single-screw or twin-screw system is preferred.

[0061] The resin composition for producing the vinylidene fluoride film of the present disclosure may contain other polymers as needed in addition to the vinylidene fluoride resin (F) and the (meth)acrylic resin (A), provided that the effects of the present disclosure are not impaired. Examples of other polymers include olefin resins such as polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, and polynorbornene; ethylene ionomers; styrene resins such as polystyrene, styrene-maleic anhydride copolymer, high-impact polystyrene, AS resin, ABS resin, AES resin, AAS resin, ACS resin, and MBS resin; methyl methacrylate-styrene copolymers; ester resins such as polyethylene terephthalate and polybutylene terephthalate; amide resins such as nylon 6, nylon 66, and polyamide elastomer; polyphenylene sulfide, polyether ether ketone, Examples of the other polymers include other thermoplastic resins such as polysulfone, polyphenylene oxide, polyimide, polyetherimide, polycarbonate, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyacetal, and phenoxy resins; thermosetting resins such as phenolic resins, melamine resins, silicone resins, and epoxy resins; polyurethane; modified polyphenylene ether; silicone-modified resins; acrylic rubber, silicone rubber; styrene-based thermoplastic elastomers such as SEPS, SEBS, and SIS; and olefin-based rubbers such as IR, EPR, and EPDM. One or more of the other polymers can be used.

[0062] The resin composition for forming the vinylidene fluoride film of the present disclosure may contain various additives as needed. Examples include antioxidants, heat degradation inhibitors, UV absorbers, light stabilizers, lubricants, release agents, polymer processing aids, antistatic agents, flame retardants, dyes / pigments, light diffusers, matting agents, anti-sticking agents, impact resistance modifiers, and phosphors. The content of these additives can be appropriately set within a range that does not impair the effects of the present disclosure. For example, the content of the antioxidant is 0.01 to 1 part by weight, the content of the UV absorber is 0.01 to 3 parts by weight, the content of the light stabilizer is 0.01 to 3 parts by weight, the content of the lubricant is 0.01 to 3 parts by weight, the content of the dye / pigment is 0.01 to 3 parts by weight, and the content of the anti-sticking agent is 0.001 to 1 part by weight, per 100 parts by weight of the resin composition.

[0063] The antioxidant is effective in preventing oxidative degradation of the resin by itself in the presence of oxygen. Examples include phosphorus-based antioxidants, phenol-based antioxidants, sulfur-based antioxidants, and amine-based antioxidants. Among these, from the viewpoint of the effect of preventing degradation of optical properties due to coloring, phosphorus-based antioxidants and phenol-based antioxidants are preferred, and the use of a phenol-based antioxidant alone or a combination of a phosphorus-based antioxidant and a phenol-based antioxidant is more preferred. When a phosphorus-based antioxidant and a phenol-based antioxidant are used in combination, the phosphorus-based antioxidant / phenol-based antioxidant mass ratio is preferably 0.2 / 1 to 2 / 1, and more preferably 0.5 / 1 to 1 / 1.

[0064] Preferred examples of the phosphorus-based antioxidant include 2,2-methylenebis(4,6-di-t-butylphenyl)octyl phosphite ("ADK STAB HP-10" manufactured by ADEKA Corporation), tris(2,4-di-t-butylphenyl)phosphite ("IRGAFOS168" manufactured by BASF Japan Ltd.), and 3,9-bis(2,6-di-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane ("ADK STAB PEP-36" manufactured by ADEKA Corporation).

[0065] Preferred phenolic antioxidants include pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] ("IRGANOX 1010" manufactured by BASF Japan Ltd.) and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate ("IRGANOX 1076" manufactured by BASF Japan Ltd.).

[0066] Preferred sulfur-based antioxidants include dilauryl 3,3'-thiodipropionate, distearyl 3,3'-thiodipropionate, and pentaerythritol tetrakis(3-laurylthiopropionate).

[0067] As the amine-based antioxidant, octylated diphenylamine and the like are preferred.

[0068] The thermal degradation inhibitor can prevent thermal degradation of resins by capturing polymer radicals generated when the resin is exposed to high temperatures under substantially oxygen-free conditions. Preferred examples of the thermal degradation inhibitor include 2-t-butyl-6-(3'-t-butyl-5'-methyl-hydroxybenzyl)-4-methylphenyl acrylate (Sumitomo Chemical Co., Ltd.'s "Sumilizer GM") and 2,4-di-t-amyl-6-(3',5'-di-t-amyl-2'-hydroxy-α-methylbenzyl)phenyl acrylate (Sumitomo Chemical Co., Ltd.'s "Sumilizer GS").

[0069] UV absorbers are compounds that have UV absorption ability and are said to have the function of converting light energy into heat energy. Examples of UV absorbers include benzophenones, benzotriazoles, triazines, benzoates, salicylates, cyanoacrylates, oxalic acid anilides, malonic acid esters, and formamidines. Among these, benzotriazoles and triazines are preferred. One or more types of UV absorbers can be used.

[0070] Benzotriazoles are highly effective in suppressing deterioration of optical properties such as coloration due to exposure to ultraviolet light, and are therefore suitable when the thermoplastic resin composition of the present disclosure is applied to optical applications. Preferred benzotriazoles include 4-methyl-2-(2H-benzotriazol-2-yl)phenol (manufactured by Johoku Chemical Industry Co., Ltd. under the trade name JF-77), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (manufactured by BASF Japan Ltd. under the trade name TINUVIN 329), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (manufactured by BASF Japan Ltd. under the trade name TINUVIN 234), and 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-t-octylphenol] (manufactured by ADEKA Corporation under the trade name Adekastab LA-31).

[0071] Furthermore, when efficient absorption of wavelengths around 380 nm is desired, triazine ultraviolet absorbers are preferably used, such as 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine ("ADEKA STAB LA-F70" manufactured by ADEKA Corporation) and its analogous hydroxyphenyltriazine ultraviolet absorbers ("TINUVIN 477" and "TINUVIN 460" manufactured by BASF Japan Ltd.).

[0072] Light stabilizers are compounds that are said to have the function of capturing radicals generated primarily by oxidation due to light. Suitable light stabilizers include hindered amines such as compounds having a 2,2,6,6-tetraalkylpiperidine skeleton. For example, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate ("ADEKA STAB LA-77Y" manufactured by ADEKA Corporation) can be mentioned.

[0073] Examples of the antistatic agent include alkyl sulfonates such as sodium heptyl sulfonate, sodium octyl sulfonate, sodium nonyl sulfonate, sodium decyl sulfonate, sodium dodecyl sulfonate, sodium cetyl sulfonate, sodium octadecyl sulfonate, sodium diheptyl sulfonate, potassium heptyl sulfonate, potassium octyl sulfonate, potassium nonyl sulfonate, potassium decyl sulfonate, potassium dodecyl sulfonate, potassium cetyl sulfonate, potassium octadecyl sulfonate, potassium diheptyl sulfonate, lithium heptyl sulfonate, lithium octyl sulfonate, lithium nonyl sulfonate, lithium decyl sulfonate, lithium dodecyl sulfonate, lithium cetyl sulfonate, lithium octadecyl sulfonate, and lithium diheptyl sulfonate.

[0074] Examples of the flame retardant include metal hydrates having a hydroxyl group or crystal water, such as magnesium hydroxide, aluminum hydroxide, hydrated aluminum silicate, hydrated magnesium silicate, and hydrotalcite; phosphate compounds, such as polyamine phosphate and phosphate esters; and silicon compounds. Of these, preferred are phosphate ester-based flame retardants, such as trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, tricyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, dimethylethyl phosphate, methyldibutyl phosphate, ethyldipropyl phosphate, and hydroxyphenyldiphenyl phosphate.

[0075] The transparent protective sheet of the present disclosure can be molded using commonly used molding methods and molding devices. For example, the sheet can be produced by molding methods involving heat melting, such as injection molding, extrusion molding, compression molding, blow molding, calendar molding, and vacuum molding, as well as solution casting methods. It can also be processed well by common melt extrusion methods such as inflation and T-die extrusion, or calendaring, and even solution casting. If necessary, it is also possible to obtain a sheet with better surface properties by simultaneously contacting both sides of the sheet with rolls or metal belts, particularly by simultaneously contacting rolls or metal belts heated to a temperature above Tg. Furthermore, depending on the purpose, it is also possible to modify the sheet by lamination molding or biaxial stretching.

[0076] Examples and comparative examples according to the present disclosure will be described. [Evaluation Items and Evaluation Method] The evaluation items and evaluation method are as follows.

[0077] (Weight-average molecular weight (Mw)) A sample solution was prepared by dissolving 4 mg of the resin to be measured in 5 mL of tetrahydrofuran. The column oven temperature was set to 40°C, and 20 μL of the sample solution was injected into the apparatus at an eluent flow rate of 0.35 mL / min, and a chromatogram was measured. Ten standard polystyrenes with molecular weights in the range of 400 to 5,000,000 were measured by GPC (gel permeation chromatography), and a calibration curve showing the relationship between retention time and molecular weight was created. The Mw of the resin to be measured was determined based on this calibration curve. From the chromatogram measured by GPC, the value corresponding to the molecular weight of the standard polystyrene was taken as the molecular weight of the copolymer. Apparatus: GPC apparatus HLC-8320 manufactured by Tosoh Corporation Separation column: TSKguard column Super HZ-H, TSKgel HZM-M, and TSKgel Super HZ4000 manufactured by Tosoh Corporation connected in series Eluent: tetrahydrofuran Eluent flow rate: 0.35 mL / min Column temperature: 40°C Detection method: differential refractive index (RI)

[0078] (Glass Transition Temperature (Tg)) In accordance with JIS K7121, a DSC curve was measured using a differential scanning calorimeter (Shimadzu Corporation, DSC-50) under conditions of once heating to 250° C., then cooling to room temperature, and then heating from room temperature to 230° C. at a rate of 20° C. / min. The midpoint glass transition temperature determined from this DSC curve was taken as Tg in the present disclosure.

[0079] (Average Particle Diameter (Second Layer) of Multilayer Structure Polymer (a)) Using the films produced in the Examples and Comparative Examples, cross-sectional sections parallel to the extrusion direction were prepared to a thickness of 50 nm using an ultramicrotome (Leica EM UC7rt, manufactured by JEOL Ltd.). The prepared sections were electron-stained with a 10% aqueous solution of phosphotungstic acid, and the shape (morphology) of the stained sections was observed using an electron microscope (manufactured by JEOL Ltd., main body: JSM-7600F, detector: SM-74240RTED). For the observed spherical stained sections, the particle diameters of 30 stained sections (if the stained sections were elliptical, the average value of the major and minor axes) were measured, and the number-based average diameter was used as the average particle diameter up to the second layer of the multilayer structure polymer (a).

[0080] (Average Particle Diameter of Multilayer Structure Polymer (a) (Third Layer)) A latex of the multilayer structure polymer (a) was sampled, and the average value (volume average particle diameter) in the volume-based particle size distribution measured by a light scattering method was determined using a laser diffraction / scattering particle size distribution analyzer LA-910 manufactured by Horiba, Ltd.

[0081] (Weight-average molecular weight (Mw) of the outermost layer of multilayer polymer (a)) 2 g of multilayer polymer (a) (mass of solid content before separation) was added to 50 mL of acetone and stirred at room temperature for 24 hours. The entire resulting liquid was centrifuged using a centrifuge (CR20GIII, manufactured by Hitachi Koki Co., Ltd.) at a rotation speed of 20,000 rpm, a temperature of 0°C, and for 180 minutes. The supernatant and precipitate were separated and dried under vacuum at 50°C for 8 hours to obtain an acetone-soluble fraction and an acetone-insoluble fraction. 4 mg of the resulting acetone-soluble fraction was used as the resin to be measured to determine the Mw.

[0082] (Transparency) For the transparent protective sheets (vinylidene fluoride films) obtained in the examples and comparative examples, the haze was measured in accordance with JIS K7361-1 and the transparency was evaluated according to the following criteria: A: Haze less than 5%. B: Haze 5% or more but less than 10%. C: Haze 10% or more.

[0083] (Weather Resistance) For the transparent protective sheets (vinylidene fluoride films) obtained in the Examples and Comparative Examples, the total light transmittance was measured in accordance with JIS K7361-1 at an output equivalent to CIE standard illuminant D65. A weather resistance test was performed using a Sunshine Weatherometer (manufactured by Suga Test Instruments Co., Ltd.) under the conditions of a black panel at 63°C and spraying for 12 minutes per hour for 3,000 hours. The sample was then removed and the total light transmittance was measured again. Weather resistance was evaluated based on the change in total light transmittance before and after the weather resistance test [(total light transmittance before test - total light transmittance after test) / total light transmittance before test) x 100] according to the following criteria: A: Change in total light transmittance less than 10%; B: Change in total light transmittance 10% or more but less than 20%; C: Change in total light transmittance 20% or more.

[0084] (Flexibility) The films obtained in the Examples and Comparative Examples were conditioned for 24 hours in an environment of 23°C and 55% RH, and then cut into 100 mm (length) x 10 mm (width) under the same conditions. The films were checked for their ability to be folded twice, once in a mountain fold and once in a valley fold, at the center of the lengthwise direction, with a radius of curvature of 0 mm and a bending angle of 180°, so that the film overlapped perfectly. The evaluation criteria were as follows: A: Able to bend 180°; B: Able to bend 180° but broke; C: Cannot bend 180°.

[0085] <Examples of Various Materials> In the following examples and comparative examples, the following vinylidene fluoride resin (F) and non-multilayer structure polymer (b) were used. Vinylidene fluoride resin (F): KF Polymer #1100 (trade name, manufactured by Kureha Corporation), 100% by mass of vinylidene fluoride units (homopolymer of vinylidene fluoride), Mw = 280,000, Tg = -35°C. Non-multilayer structure polymer (b): MMA-MA copolymer, MMA copolymerization ratio = 94%, MA copolymerization ratio = 6%, Mw = 130,000, Tg = 105°C.

[0086] Reference Example 1: Multilayer Structure Polymer (a-1) Under a nitrogen atmosphere, 200 parts by mass of distilled water, 1.3 parts by mass of an emulsifier ("Neopelex G-15" manufactured by Kao Corporation), and 0.05 parts by mass of sodium carbonate were placed in a polymerization vessel equipped with a stirring blade, a condenser, and a dropping funnel, and the mixture was heated to 80°C to uniformly dissolve. Next, at the same temperature, 0.01 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added, and then a mixture consisting of 2.52 parts by mass of n-butyl acrylate (BA), 2.52 parts by mass of methyl methacrylate (MMA), and 0.01 parts by mass of allyl methacrylate (ALMA) was added dropwise from the dropping funnel over 30 minutes to form a first layer. After completion of the dropwise addition, the reaction was continued for an additional 30 minutes at 80°C, and it was confirmed by gas chromatography that at least 99% of each monomer had been consumed.

[0087] Next, 0.09 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added to the obtained copolymer latex, and then a mixture consisting of 28.50 parts by mass of n-butyl acrylate (BA), 1.52 parts by mass of methyl methacrylate (MMA), and 0.9 parts by mass of allyl methacrylate (ALMA) was added dropwise from a dropping funnel over 50 minutes to form a second layer. After completion of the dropping, the reaction was continued at 80°C for another 30 minutes, and it was confirmed by gas chromatography that 99% or more of each monomer had been consumed.

[0088] Next, a mixture consisting of 56.82 parts by mass of methyl methacrylate (MMA), 8.12 parts by mass of n-butyl acrylate (BA), and 0.19 parts by mass of n-octyl mercaptan was added dropwise from the dropping funnel over 100 minutes to form a third layer. After completion of the dropwise addition, the reaction was continued at 80°C for another hour, and polymerization was terminated when it was confirmed by gas chromatography that 99.9% or more of each monomer had been consumed. The average particle size of the particles in the obtained latex was 0.09 μm as measured by a light scattering method.

[0089] The latex was cooled at -30°C for 24 hours to freeze and aggregate, and then the aggregate was melted and removed. It was dried under reduced pressure at 50°C for 2 days to obtain a powdery three-layer multilayer polymer (a-1). The Mw of the polymer component constituting the outermost layer was 80,000. The analytical results are shown in Table 1.

[0090] Reference Example 2: Multilayer Structure Polymer (a-2) Under a nitrogen atmosphere, 150 parts by mass of distilled water, 1.00 parts by mass of an emulsifier ("Neopelex G-15" manufactured by Kao Corporation), and 0.05 parts by mass of sodium carbonate were placed in a polymerization vessel equipped with a stirring blade, a condenser, and a dropping funnel, and the mixture was heated to 80°C to uniformly dissolve. Next, at the same temperature, 0.02 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added, and then a mixture consisting of 0.61 parts by mass of methyl acrylate (MA), 9.39 parts by mass of methyl methacrylate (MMA), and 0.02 parts by mass of allyl methacrylate (ALMA) was added dropwise from the dropping funnel over 20 minutes to form a first layer. After completion of the dropwise addition, the reaction was continued for an additional 30 minutes at 80°C, and it was confirmed by gas chromatography that at least 99% of each monomer had been consumed.

[0091] Next, 0.07 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added to the obtained copolymer latex, and then a mixture consisting of 41.11 parts by mass of n-butyl acrylate (BA), 8.89 parts by mass of styrene (St), and 2.00 parts by mass of allyl methacrylate (ALMA) was added dropwise from the dropping funnel over 80 minutes to form a second layer. After completion of the dropping, the reaction was continued at 80°C for an additional 60 minutes, and gas chromatography confirmed that at least 99% of each monomer had been consumed.

[0092] Next, a mixture consisting of 37.61 parts by mass of methyl methacrylate (MMA), 2.39 parts by mass of methyl acrylate (MA), and 0.12 parts by mass of n-octyl mercaptan was added dropwise to the obtained copolymer latex from the dropping funnel over 60 minutes to form a third layer. After completion of the dropwise addition, the reaction was continued at 80°C for an additional 60 minutes, and the polymerization was terminated when it was confirmed by gas chromatography that 99.9% or more of each monomer had been consumed. The average particle size of the particles in the obtained latex was 0.11 μm as measured by a light scattering method.

[0093] The latex was cooled at -30°C for 24 hours to freeze and aggregate, and then the aggregate was melted and removed. It was dried under reduced pressure at 50°C for 2 days to obtain a powdery three-layer multilayer polymer (a-2). The Mw of the polymer component constituting the outermost layer was 63,000. The analytical results are shown in Table 1.

[0094] Reference Example 3 Multilayer Structure Polymer (a-3) In a nitrogen atmosphere, 100 parts by mass of distilled water, 0.019 parts by mass of a surfactant (polyoxyethylene alkyl ether sodium acetate (NIKKOL-ECT-3NEX)), and 0.10 parts by mass of sodium carbonate were placed in a polymerization vessel equipped with a stirring blade, a cooling tube, and a dropping funnel, and the mixture was heated to 80°C to uniformly dissolve. Next, at the same temperature, 0.04 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added, and then a mixture of 2.11 parts by mass of methyl acrylate (MA), 32.89 parts by mass of methyl methacrylate (MMA), 0.07 parts by mass of allyl methacrylate (ALMA), and 0.25 parts by mass of a surfactant (polyoxyethylene alkyl ether sodium acetate (NIKKOL-ECT-3NEX)) was added dropwise from the dropping funnel over 60 minutes to form a first layer. After the dropwise addition was completed, the reaction was continued for another 30 minutes at 80° C., and it was confirmed by gas chromatography that 99% or more of each monomer had been consumed.

[0095] Next, 0.05 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added to the resulting copolymer latex, and then a mixture consisting of 37.00 parts by mass of n-butyl acrylate (BA), 8.00 parts by mass of styrene (St), 0.90 parts by mass of allyl methacrylate (ALMA), and 0.012 parts of a surfactant (sodium polyoxyethylene alkyl ether acetate (NIKKOL-ECT-3NEX)) was added dropwise from the dropping funnel over 60 minutes to form a second layer. After completion of the dropwise addition, the reaction was continued for an additional 30 minutes at 80°C, and it was confirmed by gas chromatography that at least 99% of each monomer had been consumed.

[0096] Next, 0.02 parts by weight of a 3% aqueous solution of potassium peroxodisulfate was added to the resulting copolymer latex, and a mixture consisting of 18.80 parts by weight of methyl methacrylate (MMA), 1.20 parts by weight of methyl acrylate (MA), and 0.04 parts by weight of n-octyl mercaptan was added dropwise from the dropping funnel over 30 minutes to form a third layer. After completion of the dropwise addition, the reaction was continued at 80°C for an additional 60 minutes, and polymerization was terminated when it was confirmed by gas chromatography that at least 99.9% of each monomer had been consumed. The average particle size of the particles in the resulting latex was 0.23 μm as measured by light scattering.

[0097] The latex was cooled at -30°C for 24 hours to freeze and aggregate, and then the aggregate was melted and removed. It was dried under reduced pressure at 50°C for 2 days to obtain a powdery three-layer multilayer polymer (a-3). The Mw of the polymer component constituting the outermost layer was 60,000. The analytical results are shown in Table 1.

[0098]

[0099] (Production Examples 1 to 3: (Meth)acrylic resins (A-1) to (A-3)) As shown in Table 2, the multilayer structure polymers (a-1) to (a-3) of Reference Examples 1 to 3 were used as acrylic resins (A-1) to (A-3).

[0100] (Production Examples 4 to 6: (Meth)acrylic Resins (A-4) to (A-6)) The multilayer structure polymer (a-1) of Reference Example 1 and the non-multilayer structure polymer (b) were melt-kneaded in the ratios shown in Table 2 using a 20 mmφ vented twin-screw extruder at a maximum temperature of 250°C, and the melt-kneaded mixture was extruded to obtain pellets of acrylic resins (A-4) to (A-6).

[0101]

[0102] Example 1: Vinylidene fluoride film made of resin composition (C-1) 80 parts by mass of vinylidene fluoride resin (F) and 20 parts by mass of the acrylic resin (A-1) prepared in Production Example 1 were pre-dried overnight at 80°C, then dry-blended, and then melt-kneaded in a 20 mmφ vented twin-screw extruder at a maximum temperature of 240°C. The melt-kneaded mixture was then extruded to obtain a pellet-shaped resin composition (C-1). The obtained resin composition (C-1) pellets were pre-dried overnight at 80 ° C., and then extruded in a 30 mm diameter vented single-screw extruder equipped with a 150 mm wide T-die. The cylinder temperature was set to increase stepwise from 180 ° C. to 240 ° C. from the upstream of the extruder (feed section) to the downstream of the extruder (final metering section). The T-die temperature was 240 ° C., the T-die lip opening was 0.6 mm, and the extruder was cast onto a single 40 ° C. cooling roll to obtain a vinylidene fluoride film with a thickness of 25 μm. The evaluation results of the obtained film are shown in Table 3.

[0103] (Examples 2 to 6, Comparative Examples 1 to 3) Vinylidene fluoride films were obtained in the same manner as in Example 1, except that the contents of the vinylidene fluoride resin (F) and the acrylic resins (A-1) to (A-6) were set as shown in Table 3. The evaluation results of the obtained films are shown in Table 3.

[0104]

[0105] As shown in Comparative Example 1, it was confirmed that a vinylidene fluoride film made of vinylidene fluoride resin (F) had high haze and poor transparency due to crystallization of the vinylidene fluoride resin. The vinylidene fluoride film of Comparative Example 2, which did not satisfy the requirements of 60 to 85 mass% vinylidene fluoride resin (F) and 15 to 40 mass% (meth)acrylic resin (A), had poor weather resistance. This is thought to be due to deterioration of the multilayer structure polymer (a) in the (meth)acrylic resin (A). Furthermore, Comparative Example 3, which satisfied the requirements of 60 to 85 mass% vinylidene fluoride resin (F) and 15 to 40 mass% (meth)acrylic resin (A), but did not satisfy the requirement of 60 to 100 mass% of the multilayer structure polymer (a) per 100 mass% of (meth)acrylic resin (A), and thus had a low content of the multilayer structure polymer (a), was confirmed to have reduced mechanical properties and poor evaluation results for flexibility. On the other hand, a transparent protective sheet having a vinylidene fluoride film including a layer made of a resin composition (C) containing 60 to 85 mass% of a vinylidene fluoride resin (F) and 15 to 40 mass% of a (meth)acrylic resin (A), wherein the (meth)acrylic resin (A) contains a multilayer polymer (a) and optionally a non-multilayer polymer (b), and wherein the multilayer polymer (a) accounts for 60 to 100 mass% and the non-multilayer polymer (b) accounts for 0 to 40 mass% of 100 mass% of the (meth)acrylic resin (A), was confirmed to have both transparency and weather resistance and also excellent flexibility, as shown in Examples 1 to 6.

[0106] This application claims priority based on Japanese Patent Application No. 2023-133185, filed on August 18, 2023, the disclosure of which is incorporated herein in its entirety by reference.

[0107] 1: Transparent protective substrate 2: First sealing material 3: Solar cell 4: Second sealing material 5: Transparent protective sheet 10: Solar cell module

Claims

1. A transparent protective sheet for a double-sided light-receiving solar cell module having a vinylidene fluoride film, wherein the vinylidene fluoride film comprises at least a layer made of a resin composition (C) containing 60 to 85 mass% of a vinylidene fluoride resin (F) and 15 to 40 mass% of a (meth)acrylic resin (A), wherein the (meth)acrylic resin (A) contains a multilayer structure polymer (a) and optionally a non-multilayer structure polymer (b), and wherein, in 100 mass% of the (meth)acrylic resin (A), the multilayer structure polymer (a) accounts for 60 to 100 mass% and the non-multilayer structure polymer (b) accounts for 0 to 40 mass%.

2. The transparent protective sheet according to claim 1, wherein the multilayered polymer (a) is a particle and comprises a shell layer constituting the outermost layer and a core layer constituting the inner side thereof, the shell layer is composed of a hard polymer layer, the core layer contains one or more soft polymer layers, and the soft polymer layer (when there are multiple soft polymer layers, the soft polymer layer formed on the outside) has an average particle size of 0.05 to 0.16 μm.

3. The transparent protective sheet according to claim 1, wherein the multilayer structure polymer (a) is composed of an acetone soluble portion and an acetone insoluble portion, the acetone soluble portion contains 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 20% by mass of structural units derived from an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and has a glass transition temperature of 80 to 100°C, and the acetone insoluble portion contains 20 to 60% by mass of structural units derived from methyl methacrylate and 40 to 80% by mass of structural units derived from an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and has a glass transition temperature of 0°C or lower.

4. The transparent protective sheet according to claim 2, wherein the core layer further comprises an intermediate layer and an innermost layer located thereon, the innermost layer being a hard polymer layer containing 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 20% by mass of structural units derived from an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, the intermediate layer being a soft polymer layer containing 70 to 100% by mass of structural units derived from an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms and 0 to 30% by mass of structural units derived from methyl methacrylate, and the shell layer being a hard polymer layer containing 80 to 99% by mass of structural units derived from methyl methacrylate and 1 to 20% by mass of structural units derived from an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, and wherein the multilayer structure polymer (a) is 100% by mass, and the hard polymer of the innermost layer is 5 to 30% by mass, the soft polymer of the intermediate layer is 20 to 45% by mass, and the hard polymer of the outermost layer is 50 to 75% by mass.

5. The transparent protective sheet according to claim 1, which has a haze of 5.0% or less.

6. The transparent protective sheet according to claim 1, which has a thickness of 10 to 50 μm.

7. A bifacial solar cell module having the transparent protective sheet according to any one of claims 1 to 6.

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