JP2019196422A - Polyvinyl alcohol film and method for producing the same - Google Patents

Abstract

To provide a polyvinyl alcohol film that has transparency and has a small stress in a tensile test and to provide a method for producing the polyvinyl alcohol film.SOLUTION: The polyvinyl alcohol film includes a polyvinyl alcohol and resin particles having a core-shell structure in which a resin constituting a shell in the resin particle has a glass transition temperature (Tg1) of 100°C or higher and a resin constituting a core has a glass transition temperature (Tg2) of 10°C or lower. Preferably, the resin particle has an average particle size of 150 nm or less.SELECTED DRAWING: None

Description

  The present invention relates to a polyvinyl alcohol film and a method for producing the same.

  Polyvinyl alcohol films (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”) are used in a wide range of application fields such as packaging films, water-soluble films, agricultural films, release films, polarizing films, etc. Has been.

  The PVA film is usually given flexibility by adding a plasticizer. However, such a PVA film has the disadvantage that the plasticizer decreases with time and the flexibility decreases. So far, as a technique for imparting flexibility other than the addition of a plasticizer, for example, in the case of PVA fibers, a technique of adding an aqueous resin emulsion (resin particles) to a spinning dope has been proposed (see Patent Document 1). .

Japanese Patent Publication No. 47-42050

  When the aqueous resin emulsion is added to the spinning dope, since the spinning dope is at a high temperature, the aqueous resin emulsion agglomerates, resulting in a phenomenon that the transparency of the obtained PVA fiber is lowered. On the other hand, in the case of a PVA film, there are many uses that require transparency. For this reason, when a well-known aqueous resin emulsion is added to a film-forming stock solution, the problem that the transparency of the obtained PVA film falls arises.

  Regarding the above flexibility, the stress value at the time of the tensile test is important in the PVA film. That is, a small stress value at the time of the tensile test of the PVA film is an index indicating that the film is difficult to tear and has excellent flexibility.

  This invention is made | formed based on the above situations, The objective is to provide the polyvinyl alcohol film which has transparency, and the stress at the time of a tensile test is small, and its manufacturing method.

The present invention made to solve the above problems is as follows.
[1] A glass transition temperature (Tg2) of a resin that includes polyvinyl alcohol and resin particles having a core-shell structure, the resin constituting the shell in the resin particles has a glass transition temperature (Tg1) of 100 ° C. or higher, and a core that constitutes the core. ) Is 10 ° C. or less.
[2] The polyvinyl alcohol film of [1], wherein the resin particles have an average particle size of 150 nm or less.
[3] The polyvinyl alcohol film of [1] or [2], wherein the content of the resin particles with respect to 100 parts by mass of the polyvinyl alcohol is 1 part by mass or more and 50 parts by mass or less.
[4] A step of forming a film using a film-forming stock solution, wherein the film-forming stock solution includes polyvinyl alcohol and resin particles having a core-shell structure, and a glass transition temperature (Tg1) of a resin constituting a shell in the resin particles. ) Is 100 ° C. or higher, and the glass transition temperature (Tg2) of the resin constituting the core is 10 ° C. or lower.

  ADVANTAGE OF THE INVENTION According to this invention, it has transparency and can provide the polyvinyl alcohol film with a small stress at the time of a tensile test, and its manufacturing method.

  Hereinafter, embodiments of the PVA film of the present invention and the production method thereof will be described in detail. In the present specification, “(meth) acryl” means a generic name of “methacryl” and “acryl”.

<PVA film>
The PVA film according to an embodiment of the present invention includes PVA and resin particles.

(PVA)
PVA is a polymer having a vinyl alcohol unit (—CH ₂ —CH (OH) —) as a main structural unit. PVA may have a vinyl ester unit and other units in addition to the vinyl alcohol unit.

As PVA, what is obtained by saponifying the polyvinyl ester obtained by superposing | polymerizing 1 type (s) or 2 or more types of vinyl ester can be used. Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, and isopropenyl acetate. Among vinyl esters, a compound having a vinyloxycarbonyl group (H ₂ C═CH—O—CO—) in the molecule is preferable from the viewpoint of ease of production, availability, cost and the like, and vinyl acetate is more preferable. preferable.

  The polyvinyl ester is preferably obtained using only one or two or more types of vinyl esters as monomers, and more preferably polyvinyl ester obtained using only one type of vinyl esters as monomers. As long as the effect of the present invention is not significantly impaired, a copolymer resin of one or more vinyl esters and other monomers copolymerizable therewith may be used.

  The upper limit of the proportion of structural units derived from other copolymerizable monomers is preferably 15 mol%, more preferably 10 mol%, based on the number of moles of all structural units constituting the copolymer resin. Mole% is more preferable, and 1 mol% is still more preferable.

  Other monomers copolymerizable with the vinyl ester include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; (meth) acrylic Methyl methacrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, (meth) acrylic (Meth) acrylic acid esters such as t-butyl acid, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide; N-methyl (meth) acrylamide N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, ( T) Acrylamide propane sulfonic acid or a salt thereof, (Meth) acrylamide propyl dimethylamine or a salt thereof, N-methylol (meth) acrylamide or a derivative thereof (meth) acrylamide derivative; N-vinylformamide, N-vinylacetamide, N N-vinyl amides such as vinyl pyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; Vinyl cyanides such as (meth) acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl acetate, vinyl chloride Allyl compounds such as ril; maleic acid or salts, esters or acid anhydrides thereof; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids or salts thereof Can be mentioned.

  The polyvinyl ester can have a structural unit derived from one or more of the above monomers.

  As PVA, those not graft-copolymerized can be preferably used. However, the PVA may be modified with one or two or more types of graft copolymerizable monomers as long as the effects of the present invention are not significantly impaired. The graft copolymerization can be performed on at least one of the polyvinyl ester and the PVA obtained by saponifying the polyvinyl ester. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA.

  A part of the hydroxy group of PVA may be cross-linked or may not be cross-linked. Moreover, PVA may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure.

  The lower limit of the degree of polymerization of PVA is preferably 1,000, more preferably 1,500, and even more preferably 1,700. When the degree of polymerization of PVA is not less than the above lower limit, the flexibility of the PVA film can be improved. On the other hand, the upper limit of the degree of polymerization is preferably 10,000, more preferably 8,000, and further preferably 5,000. When the degree of polymerization of PVA is not more than the above upper limit, it is possible to suppress an increase in production cost of PVA and occurrence of defects during film formation. In addition, the polymerization degree of PVA means the average polymerization degree measured according to description of JIS K6726-1994.

  The range of the degree of saponification of PVA varies depending on the application, but generally the degree of saponification is preferably 82 mol% or more and 100 mol% or less. In applications other than the water-soluble film, 95 mol% or more and 100 mol% or less may be more preferable. The degree of saponification of PVA is the ratio of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted to vinyl alcohol units by saponification (mol%). ). The saponification degree can be measured according to the description of JIS K6726-1994.

  As a minimum of content of PVA in the PVA film concerned, 50 mass% is preferred, 70 mass% is more preferred, and 80 mass% is still more preferred. By making content of PVA more than the said minimum, the characteristic of PVA is fully exhibited and transparency can be improved. On the other hand, as an upper limit of this content, 95 mass% is preferable, 90 mass% is more preferable, 85 mass% is further more preferable. By setting the content of PVA to the above upper limit or less, flexibility can be increased.

(Resin particles)
The resin particles have a core-shell structure including a core and a shell covering at least a part of the core.

  The glass transition temperature (Tg1) of the resin constituting the shell of the resin particles is 100 ° C. or higher. As a result, the surface of the resin particles is prevented from fusing and agglomerating in a state where the film-forming stock solution is at a high temperature, and as a result, the resulting PVA film can have transparency. 110 degreeC is preferable and, as for the minimum of the glass transition temperature (Tg1) of resin which comprises a shell, 120 degreeC is more preferable. On the other hand, the upper limit of the glass transition temperature (Tg1) of the resin constituting the shell is, for example, 200 ° C., and preferably 180 ° C. By setting the glass transition temperature (Tg1) to be equal to or lower than the above upper limit, flexibility can be further increased.

  The glass transition temperature (Tg2) of the resin constituting the core of the resin particles is 10 ° C. or lower. Thereby, the said PVA film has a small stress at the time of a tensile test, and can exhibit favorable softness | flexibility. The upper limit of the glass transition temperature (Tg2) of the resin constituting the core is preferably 5 ° C, more preferably 0 ° C, even more preferably -5 ° C, even more preferably -20 ° C, and more preferably -40 ° C. It may be more preferable. On the other hand, the lower limit of the glass transition temperature (Tg2) of the resin constituting the core is not particularly limited, and may be, for example, -100 ° C, -80 ° C, or -60 ° C.

  Here, the glass transition temperature (Tg1) and the glass transition temperature (Tg2) are formed using resin particles, and are measured values by dynamic viscoelasticity measurement performed on the obtained resin film. According to the measurement for such a resin film, two glass transition temperatures are observed. The glass transition temperature on the high temperature side is the glass transition temperature (Tg1) of the resin constituting the shell, and the glass transition temperature on the low temperature side. Is the glass transition temperature (Tg2) of the resin constituting the core.

  The upper limit of the average particle diameter of the resin particles in the PVA film is preferably 150 nm, more preferably 120 nm, still more preferably 115 nm, and still more preferably 105 nm. By setting the average particle diameter of the resin particles to the upper limit or less, the transparency and flexibility of the PVA film can be increased. Further, since it is difficult to make resin particles that are too small, the lower limit of the average particle diameter is, for example, 10 nm, and may be 30 nm. In addition, this average particle diameter is the value which melt | dissolved PVA of the said PVA film, took out the resin particle, and measured with the dynamic light scattering method with respect to this resin particle. The specific measuring method shall be based on the method described in the Example mentioned later.

  The lower limit of the content of the resin particles in the PVA film is preferably 1 part by weight, more preferably 3 parts by weight, still more preferably 5 parts by weight, and even more preferably 7 parts by weight with respect to 100 parts by weight of PVA. Part is more preferable, and 15 parts by mass is even more preferable. By setting the content of the resin particles to the above lower limit or more, the flexibility of the PVA film can be improved more easily. On the other hand, the upper limit of the content of the resin particles is preferably 50 parts by mass, more preferably 40 parts by mass, further preferably 30 parts by mass, still more preferably 25 parts by mass, and particularly preferably 20 parts by mass. By making the content of the resin particles not more than the above upper limit, the transparency of the PVA film can be improved.

  Hereinafter, the resin particles will be described in more detail.

(core)
The core is made of a resin having a glass transition temperature (Tg2) of 10 ° C. or lower. In addition, although a core can be comprised only from this resin substantially, you may further contain the other component in the range which does not affect the effect of this invention.

  The monomer of the resin constituting the core is not particularly limited, but preferably has radical polymerizability and has a solubility in water of less than 10% by mass. The resin particles having a core-shell structure are usually produced by emulsion polymerization. When the solubility of the monomer in water is 10% by mass or more, since polymerization in the aqueous phase occurs, emulsion polymerization becomes difficult, which is not preferable.

  Specific examples of the resin monomer constituting the core include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, and (meth) acrylic. N-butyl acid, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecyl (meth) acrylate, (meth) acrylic Lauryl acid, dodecyl (meth) acrylate, trimethoxysilylpropyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, (meth) acrylic acid 2-methoxyethyl, phenyl (meth) acrylate, naphthyl (meth) acrylate, (meth) (Meth) acrylic acid esters such as 2- (trimethylsilyloxy) ethyl crylate and 3- (trimethylsilyloxy) propyl (meth) acrylate; styrene, indene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, aromatic vinyl compounds such as p-tert-butoxystyrene, p-chloromethylstyrene, p-acetoxystyrene, divinylbenzene; vinyl acetate; vinyl halide compounds such as vinyl chloride; conjugated diene compounds such as butadiene and isoprene; acrylonitrile, etc. Other vinyl compounds; and the like. These monomers may be used alone or in combination of two or more.

  Among the monomers, (meth) acrylic acid alkyl ester is preferable. The lower limit of the carbon number of the alkyl group of the (meth) acrylic acid alkyl ester is 1, but 2 is preferable, 3 is more preferable, and 4 is more preferable. On the other hand, the upper limit of the carbon number of this alkyl group is, for example, 10, preferably 8, more preferably 6, and further preferably 4. Moreover, it is also preferable that it is an acrylic acid alkylester. That is, butyl acrylate is most preferable among (meth) acrylic acid alkyl esters. Resin particles using such a (meth) acrylic acid alkyl ester as a monomer for the resin constituting the core have a low glass transition point and can exhibit particularly good flexibility.

  For the synthesis of the resin constituting the core, a crosslinking agent may be added and copolymerized. By appropriately cross-linking, the mechanical properties of the resin particles can be improved. As the cross-linking agent, usually a bifunctional monomer having two polymerizable groups is preferably used, but a trifunctional or higher polyfunctional monomer is used to adjust the cross-linking density of the resin forming the core. It is also possible to do. In addition, it is preferable that the several polymeric group which a crosslinking agent has is the same polymeric group. When a diene monomer such as butadiene or isoprene is used as a part or all of the resin monomer constituting the core, an unsaturated double bond remains after polymerization. It can be.

  Specific examples of the crosslinking agent include, for example, ethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neo Pentyl glycol diacrylate, tripropylene glycol diacrylate, bisphenol A diglycidyl ether both-end acrylic acid adduct, pentaerythritol triacrylate, pentaerythritol tetraacrylate, polyester diacrylate, tris (2-hydroxyethyl) isocyanurate triacrylate, Tris (2- (2,3-dihydroxypropoxy) ethyl) isocyanurate triacrylate, tris (2 Hydroxyethyl) isocyanurate diacrylate, cyclohexane dimethanol diacrylate, tricyclodecane dimethanol diacrylate, diacrylate of diol which is an adduct of bisphenol A ethylene oxide or propylene oxide, ethylene oxide or propylene oxide of hydrogenated bisphenol A Examples include diacrylates of diols, trimethylolpropane triacrylate, trimethylolpropane trioxyethyl acrylate, and pentaerythritol triacrylate.

  Furthermore, you may add a grafting agent to the synthesis | combination of resin which comprises a core. The grafting agent is, for example, a compound having a plurality of polymerizable groups (for example, a vinyl group and a (meth) acryloyl group) having different reactivities. By adding the grafting agent, it is possible to chemically bond the core and the shell, and the breakage of the resin particles can be suppressed even in the processing steps of the PVA film under various conditions. When diene monomers such as butadiene and isoprene are used for some or all of the resin monomers constituting the core, the unsaturated double bond remaining after polymerization is regarded as a substitute for the grafting agent. In many cases, it is not necessary to add a grafting agent.

  Specific examples of the grafting agent include methacrylic acid esters such as allyl methacrylate, dicyclopentenyl methacrylate, and dicyclopentenyloxyethyl methacrylate, and acrylic acid esters such as allyl acrylate, dicyclopentenyl acrylate, and dicyclopentenyloxyethyl acrylate. Can be mentioned.

(shell)
The shell is made of a resin having a glass transition temperature (Tg1) of 100 ° C. or higher. In addition, although the shell can be comprised only from this resin substantially, you may further contain the other component in the range which does not affect the effect of this invention.

  Although the monomer of the resin constituting the shell is not particularly limited, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, (meth) acrylic N-butyl acid, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecyl (meth) acrylate, (meth) acrylic Lauryl acid, dodecyl (meth) acrylate, trimethoxysilylpropyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, (meth) acrylic acid 2-methoxyethyl, phenyl (meth) acrylate, naphthyl (meth) acrylate, ( And (meth) acrylic acid esters such as 2- (trimethylsilyloxy) ethyl acrylate and 3- (trimethylsilyloxy) propyl (meth) acrylate; styrene, indene, p-methylstyrene, α-methylstyrene, p-methoxy Aromatic vinyl compounds such as styrene, p-tert-butoxystyrene, p-chloromethylstyrene, p-acetoxystyrene and divinylbenzene; vinyl acetate; vinyl halide compounds such as vinyl chloride; conjugated diene compounds such as butadiene and isoprene; And other vinyl compounds such as acrylonitrile. These monomers may be used alone or in combination of two or more.

  As the resin constituting the shell, it is preferable to use a monomer having a high affinity with PVA in order to suppress fusion in a state where the film-forming stock solution is at a high temperature. Specifically, (meth) acrylic acid esters are preferable, (meth) acrylic acid alkyl esters such as methyl (meth) acrylate, and (meth) acrylic acid cycloalkyl esters such as (meth) acrylic acid tricyclodecyl. More preferred.

  A chain transfer agent can be added as necessary to the synthesis of the resin constituting the shell. By adding a chain transfer agent, the molecular weight can be adjusted. Furthermore, the affinity with PVA can be controlled.

  Specific examples of the chain transfer agent include 2-mercaptoethanol, 3-mercapto-1,3-propanediol, mercaptoacetic acid, methyl mercaptoacetate, ethyl mercaptoacetate, 2-ethylhexyl mercaptoacetate, 3-mercaptopropionic acid, 3 -Methyl mercaptopropionate, n-hexyl 3-mercaptopropionate, cyclohexyl 3-mercaptopropionate, 2-ethylhexyl 3-mercaptopropionate, n-octyl 3-mercaptopropionate, n-dodecyl 3-mercaptopropionate, 3-mercaptopropion N-tridecyl acid, mercaptosuccinic acid, butanethiol, octanethiol, n-dodecanethiol, t-dodecanethiol, hexadodecanethiol, octadodecanethiol, cyclohexanethio Thiols such as thiophenol and thiophenol; xanthogen disulfide compounds such as dimethylxanthogen disulfide, diethylxanthogen disulfide and diisopropylxanthogen disulfide; thiuram disulfide compounds such as tetramethylthiuram disulfide and tetraethylthiuram disulfide; halogenated hydrocarbon compounds such as carbon tetrachloride An aromatic compound such as 2,4-diphenyl-4-methyl-1-pentene;

  In the case of emulsion polymerization, the chain transfer reaction occurs in a micelle as a polymerization site, and the molecular weight is determined by the ratio of the monomer to the chain transfer agent. For this reason, it is desirable to reach the micelle as much as the monomer. That is, it is preferable to select a chain transfer agent having the same degree of hydrophilicity or hydrophobicity as the monomer to be used.

  The mass ratio of the core and the shell in the resin particle is not particularly limited. For example, the total mass of the core and the shell, that is, the ratio of the mass of the shell to the mass of the resin particles can be 1% by mass or more and 90% by mass or less.

(Method for producing resin particles)
Although the manufacturing method of the resin particle is not particularly limited, for example, an emulsion polymerization method can be adopted. Specifically, the resin monomer constituting the core is first polymerized to synthesize the core particles, and then the resin monomer constituting the shell is continuously or intermittently added to the core particles. By forming a shell, resin particles having a core-shell structure can be obtained.

  The amount of water used in the emulsion polymerization method is advantageous from the viewpoint of productivity, but if the concentration of the resin particles is too high, problems such as viscosity and stability of the liquid and heat removal from the polymerization heat tend to occur. From these viewpoints, the amount of water is preferably in the range of 1 to 10 parts by mass, and in the range of 1.2 to 6 parts by mass with respect to 1 part by mass of all monomers including the core and the shell. It is more preferable that the range is 1.5 to 3 parts by mass.

  Examples of the emulsifier used in the emulsion polymerization method include general ones such as anionic, nonionic, and nonionic-anionic. However, since the nonionic emulsifier has a cloud point at a high temperature, aggregation is likely to occur in a state in which the film-forming stock solution is at a high temperature. From such a viewpoint, it is preferable to use an anionic or nonionic-anionic emulsifier.

  Specific examples of emulsifiers include anionic emulsifiers such as sodium, potassium or ammonium salts of aliphatic carboxylic acids such as laurate, myristate, palmitate, stearate and alkenyl succinate; Examples include sodium salt, potassium salt or ammonium salt of rosin disproportionation or hydrogenated product; sodium salt, potassium salt or ammonium salt of aliphatic sulfate compound such as lauryl sulfate. Examples of nonionic-anionic emulsifiers include polyoxyethylene octyl phenyl ether sulfonate, polyoxyethylene octyl phenyl ether sulfate, and polyoxyethylene alkyl ether sulfate. The counter cation of these salts includes sodium, potassium or ammonium.

When the solubility of the monomer in water is about 1% or less, the following relationship is known between the emulsifier concentration and the obtained resin particle concentration.
Resin particle concentration = k × (emulsifier concentration) 3/5
Here, k is a constant that varies depending on the type of emulsifier. Therefore, the target particle concentration may be calculated from the target average particle size, the amount of monomer, and the amount of water, and an emulsifier amount corresponding to the target particle concentration may be added.

  Usually, the emulsifier is generally dissolved in water from the beginning of the polymerization, but it can also be added later, and the emulsifier may be added sequentially with the monomer.

  In the emulsion polymerization method, a material for forming a protective colloid may be added. By adding such a material, it becomes possible to adjust the storage stability of the particles and the affinity with PVA. Specific examples of the material include nonionic emulsifiers such as polyoxyethylene octyl phenyl ether and polyoxyethylene nonyl phenyl ether, and PVA.

  The polymerization initiator to be used is generally a water-soluble azo-based or peroxide-based initiator. If necessary, an oil-soluble polymerization initiator may be used.

  Specific examples of the polymerization initiator include 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride and 2,2′-azobis [2- (2-imidazolin-2-yl). ) Propane] disulfate dihydrate, 2,2′-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate 2,2′-azobis [2- (2-imidazolin-2-yl) propane, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 4,4′-azobis (4-cyanovalic acid), azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2 An azo compound such as azobis (4-methoxy-2,4-dimethylvaleronitrile); an inorganic peroxide such as sodium persulfate, potassium persulfate, hydrogen peroxide; t-butyl hydroperoxide, cumene hydroperoxide, Examples thereof include organic peroxides such as p-mentane tank men hydroperoxide. These may be used alone or in combination of two or more.

  In addition to the polymerization initiator, a redox initiator system in which an organic peroxide or hydrogen peroxide and a transition metal salt are mixed to generate radicals by an oxidation-reduction reaction may be used.

  Examples of the transition metal salt include iron (II) sulfate, iron (II) thiosulfate, iron (II) carbonate, iron (II) chloride, iron (II) bromide, iron (II) iodide, iron hydroxide ( II), iron oxide (II), copper sulfate (I), copper thiosulfate (I), copper carbonate (I), copper chloride (I), copper bromide (I), copper iodide (I), hydroxide Examples thereof include copper (I), copper (I) oxide, and hydrates thereof.

  Further, in the redox initiator system, a reducing agent, a metal ion chelating agent, an electrolyte and the like may be added as necessary. Specific examples include reducing agents such as sodium hydroxymethanesulfinate and sodium ascorbate, metal ion chelating agents such as disodium ethylenediaminetetraacetate, electrolytes such as sodium chloride, sodium sulfate, and trisodium phosphate. .

  The polymerization initiator or redox initiator system may be added to water from the beginning of polymerization, or may be added continuously or intermittently.

  When producing resin particles by the emulsion polymerization method, various additives may be added as necessary. Examples of the additive include an antioxidant, a light stabilizer, and a preservative. Specific examples include hindered phenol compounds such as 2,6-di-t-butyl-4-methylphenol, and hindered amine compounds such as diphenyl-p-phenylenediamine. These may be used individually by 1 type, or may use 2 or more types together. These addition amounts are 0.05 mass part or more and 5 mass parts or less with respect to 100 mass parts of used monomers, for example. These additions are generally added to the emulsion after completion of emulsion polymerization, but can be added from the initial stage of polymerization as long as they do not affect the polymerization reaction.

(Plasticizer)
The PVA film can further include a plasticizer. When the PVA film contains a plasticizer, it is possible to improve handling properties and stretchability. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. These plasticizers can be used alone or in combination of two or more. Among these, glycerin is preferable in terms of the effect of improving stretchability.

  As a minimum of content of a plasticizer in the PVA film, 2 mass parts are preferred to 3 mass parts of PVA, 3 mass parts are more preferred, 4 mass parts are still more preferred, and 6 mass parts are still more preferred. By setting the content of the plasticizer to be at least the above lower limit, the stretchability is further improved. On the other hand, as an upper limit of this content, 20 mass parts is preferable, 17 mass parts is more preferable, and 14 mass parts is further more preferable. By making content of a plasticizer below the said upper limit, it can suppress that a PVA film becomes too flexible or a plasticizer bleeds out on the surface, and handleability falls.

(Other additives)
The PVA film further includes a filler, a processing stabilizer such as a copper compound, a weather resistance stabilizer, a colorant, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, and other thermoplastic resins. Other additives such as lubricants, fragrances, defoamers, deodorants, extenders, release agents, mold release agents, reinforcing agents, crosslinking agents, fungicides, preservatives, crystallization rate retarders, It can mix | blend suitably as needed.

  However, the upper limit of the content of other additives other than PVA and resin particles in the PVA film may be preferably 10% by mass, more preferably 1% by mass, and more preferably 0.2% by mass. It may be preferable. When content of another additive exceeds the said upper limit, the softness | flexibility and transparency of a PVA film may be affected.

(Shape, etc.)
Although there is no restriction | limiting in particular in the shape of the said PVA film, Since it can manufacture continuously with sufficient productivity, it is preferable that it is a long film. The length of the long PVA film is not particularly limited, and can be set as appropriate depending on the application. For example, the length can be in the range of 5 m or more and 20,000 m or less. There is no restriction | limiting in particular in the width | variety of the said PVA film, For example, in the case of a water-soluble film, a minimum can be 1 cm. In applications other than water-soluble films, a wide PVA film has recently been demanded, so the lower limit is preferably 1 m, more preferably 2 m, and even more preferably 4 m. Although there is no restriction | limiting in particular in the upper limit of the width | variety of the said PVA film, For example, it can be 7 m. If the width is too wide, it tends to be difficult to produce uniformly when a PVA film is produced with an apparatus in practical use.

  The PVA film may be a single layer film or a multilayer film (laminate). However, a single layer film is preferred from the standpoint that the effects of the present invention are more remarkably exhibited.

  The upper limit of the average thickness of the PVA film is not particularly limited, but is, for example, 100 μm, preferably 80 μm, more preferably 60 μm, and further preferably 40 μm. On the other hand, the lower limit of the average thickness is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. Handling property etc. can be improved because the average thickness of a PVA film is the said range.

The PVA film has transparency, has low stress during a tensile test, and is excellent in flexibility. The upper limit of the stress at 200% strain at the tensile test of the PVA film is preferably 65N / mm ^2, more preferably 60N / mm ^2, more preferably 55N / mm ^2. When the stress at the time of the tensile test of the PVA film is too small, the handleability becomes poor. Therefore, the lower limit of the stress at a strain of 200% at the time of the tensile test of the PVA film is preferably 30 N / mm ² and 35 N / mm ² is More preferred is 40 N / mm ² .

(Use)
The said PVA film can be used for the same various uses as the conventional PVA film, such as a packaging film, a water-soluble film, an agricultural film, a release film, and a polarizing film. The PVA film has transparency, has low stress during a tensile test, and is excellent in flexibility. Therefore, the said PVA film is suitable as a raw film used as the material of stretched optical films, such as a polarizing film and retardation film. That is, a stretched optical film can be obtained by stretching the PVA film. The PVA film is particularly suitable as an original film of a polarizing film that requires high transparency among stretched optical films.

(Method for producing PVA film)
The manufacturing method of the said PVA film is not specifically limited, The manufacturing method from which the thickness and width | variety of the PVA film after film forming become more uniform can be employ | adopted preferably. For example, PVA and resin particles constituting the PVA film, and, if necessary, one or more of plasticizers, other additives, and surfactants described later are dissolved in a liquid medium. It can be obtained by forming a film using a membrane stock solution. Moreover, it can manufacture also using the film-forming stock solution which melt | dissolved PVA as needed.

  That is, the method for producing a PVA film according to an embodiment of the present invention includes a step of forming a film using a film-forming stock solution, and the film-forming stock solution includes polyvinyl alcohol and resin particles having a core-shell structure, The glass transition temperature (Tg1) of the resin constituting the shell in the resin particles is 100 ° C. or higher, and the glass transition temperature (Tg2) of the resin constituting the core is 10 ° C. or lower. According to the production method, since the resin particles hardly aggregate in the film-forming stock solution, it is possible to obtain a PVA film having transparency, low stress during a tensile test, and excellent flexibility.

  In the film-forming stock solution, the resin particles are preferably mixed uniformly. In addition, the preferable average particle diameter of the resin particle in the film-forming undiluted | stock solution is the same as the average particle diameter in the PVA film mentioned above. The average particle diameter is a value measured by a dynamic light scattering method. Moreover, when the film-forming stock solution contains at least one of a plasticizer, other additives, and a surfactant, it is preferable that these components are uniformly mixed.

  Examples of the liquid medium include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine. Can be mentioned. These liquid media can use 1 type (s) or 2 or more types. Among these, water is preferable from the viewpoint of low environmental load and recoverability.

  The volatile fraction of the film-forming stock solution (the content of volatile components such as liquid media removed by volatilization or evaporation during film-forming in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc. Generally, the lower limit is preferably 50% by mass, more preferably 55% by mass, and even more preferably 60% by mass. When the volatile fraction of the film-forming stock solution is equal to or more than the above lower limit, the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming are smoothly performed during preparation of the film-forming stock solution, and there are few foreign matters and defects. Film production is facilitated. On the other hand, the upper limit of the volatile fraction is preferably 95% by mass, more preferably 90% by mass, and still more preferably 85% by mass. When the volatile fraction of the film-forming stock solution is not more than the above upper limit, the concentration of the film-forming stock solution does not become too low, and the production of an industrial PVA film becomes easy.

  The film-forming stock solution preferably contains a surfactant. By including the surfactant, the occurrence of uneven thickness of the PVA film can be suppressed, or the film can be easily peeled off from the metal roll or belt used for film formation. The type of the surfactant is not particularly limited, but anionic surfactants and nonionic surfactants are preferable from the viewpoint of peelability from a metal roll or belt.

  As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfuric acid ester type such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate are preferable.

  Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octyl phenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene lauryl amino ether Alkylamine type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxyalkylene An allyl phenyl ether type such as allyl phenyl ether is preferred.

  These surfactants can be used alone or in combination of two or more.

  When the film-forming stock solution contains a surfactant, the lower limit of the content is preferably 0.01 parts by mass and more preferably 0.02 parts by mass with respect to 100 parts by mass of PVA. When the content of the surfactant is not less than the above lower limit, the peelability is further improved. On the other hand, as an upper limit of this content, 0.5 mass part is preferable, 0.3 mass part is more preferable, and 0.1 mass part is further more preferable. When the content of the surfactant is not more than the above upper limit, it is possible to suppress the surfactant from bleeding out on the surface of the PVA film, the films being in close contact with each other, and the handleability being lowered.

  As a film forming method for forming a PVA film using the above film forming stock solution, a conventionally known method is used. For example, a cast film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method and the like may be mentioned. These film forming methods may be used alone or in combination of two or more. . Among these film forming methods, the cast film forming method and the extrusion film forming method are preferable because a PVA film having uniform thickness and width and good physical properties can be obtained.

  In addition, as a minimum of the temperature of the film-forming stock solution at the time of film-forming or when preparing and storing the film-forming stock solution, 40 ° C is preferable, and 50 ° C is more preferable. On the other hand, the upper limit of the temperature of this film-forming stock solution is preferably 100 ° C.

  The formed PVA film can be heat-treated as necessary. There is no restriction | limiting in particular in heat processing temperature, What is necessary is just to adjust suitably. If the heat treatment temperature is too high, discoloration or deterioration of the PVA film is observed. Accordingly, the upper limit of the heat treatment temperature is preferably 210 ° C, more preferably 180 ° C, and even more preferably 150 ° C. On the other hand, as a minimum of heat processing temperature, it is 60 degreeC, for example, and 90 degreeC is preferable.

  There is no restriction | limiting in particular in heat processing time, What is necessary is just to adjust suitably, From a viewpoint of manufacturing a PVA film efficiently, as an upper limit, 30 minutes are preferable and 15 minutes are more preferable. On the other hand, the lower limit is preferably 1 second, for example, and more preferably 5 seconds.

  The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples. In addition, each evaluation method employ | adopted in the following examples and comparative examples is shown below.

[Average Particle Size of Resin Particles After Synthesis (Before Preparation to Film Formation Stock Solution)]
The synthesized dispersion of resin particles was cooled to 25. Using a zeta potential / particle size measurement system “ELS-Z2” manufactured by Otsuka Electronics Co., Ltd., the dynamic light scattering of the dispersion was measured, and cumulant analysis was performed to determine the average particle size. In addition, the refractive index of water, the refractive index of water 1.33 cP, and the relative dielectric constant of water 78.3 were used as the value of the refractive index, viscosity, and relative dielectric constant of the measurement solvent. The noise cut level was set to 0.3%, the number of integrations was set to 70 times, and the pinhole was set to 50 μm.

[Glass transition temperature of resin particles]
The resin particles were dried, and the resin particles were heat-treated at 110 ° C. for 10 minutes, thereby collecting a resin film formed only from the resin particles. The glass transition temperature was calculated | required using the dynamic viscoelasticity measuring apparatus ("Rheogel-E4000" of UBM company).

[High temperature test]
The stock solution was kept at a high temperature of 93 ° C. for 4 hours and then cooled to 25 ° C. Then, the presence or absence of aggregates was confirmed visually. Furthermore, using a zeta potential / particle size measurement system “ELS-Z2” manufactured by Otsuka Electronics Co., Ltd., dynamic light scattering was measured, and cumulant analysis was performed to determine the average particle size. The refractive index of water, the viscosity, and the relative dielectric constant of the measurement solvent were water refractive index of 1.33, water viscosity of 0.89 cP, and water relative dielectric constant of 78.3. The noise cut level was set to 0.3%, the number of integrations was set to 70 times, and the pinhole was set to 50 μm.

[Average particle diameter of resin particles in PVA film]
The PVA film was placed in hot water and stirred for 4 hours, and then cooled to 25 ° C. to prepare a dispersion of resin particles. Using a zeta potential / particle size measurement system “ELS-Z2” manufactured by Otsuka Electronics Co., Ltd., the dynamic light scattering of the dispersion was measured, and cumulant analysis was performed to determine the average particle size. In addition, the refractive index of water, the refractive index of water 1.33 cP, and the relative dielectric constant of water 78.3 were used as the value of the refractive index, viscosity, and relative dielectric constant of the measurement solvent. The noise cut level was set to 0.3%, the number of integrations was set to 70 times, and the pinhole was set to 50 μm.

[transparency]
The transparency of the PVA film was judged visually.

[Tensile test]
The PVA film was vacuum-dried at 23 ° C. for 24 hours, and a film piece of 30 mm in the length direction and 10 mm in the width direction was cut out from the PVA film. Then, this PVA film piece was attached to a tensile test apparatus (“Autograph AGS-H” manufactured by Shimadzu Corporation) with a chuck distance of 10 mm, and a tensile test was performed at a speed of 50 mm / min. And the stress in 200% of distortion was calculated | required. When the stress is small, it can be regarded as excellent in flexibility.

[Synthesis Example 1] (Resin Particle 1)
300 parts by mass of ion-exchanged water was charged into a reaction vessel equipped with a reflux tube, and 35.71 parts by mass of Latemul ASK (emulsifier, dipotassium alkenyl succinate, manufactured by Kao Corporation) and 0.2 parts by mass of potassium persulfate were added. After performing nitrogen substitution at room temperature for about 30 minutes, the temperature is raised to 60 ° C. and held at that temperature for 15 minutes. A mixture of 0.5 parts by weight of trimethylolpropane trimethacrylate and 1.0 part by weight of allyl methacrylate as a grafting agent was continuously added over about 1 hour. After completion of the addition, the reaction was continued for 1 hour, and then 12.5 parts of tricyclodecane methacrylate, which is a monomer of the resin constituting the shell that had been separately substituted with nitrogen, was continuously added over about 10 minutes. After completion of the addition, the mixture was held for 1 hour, further heated to 100 ° C. and heated for 1 hour, to obtain resin particles 1. The average particle diameter of the obtained resin particles 1 measured by a dynamic light scattering method was 58 nm. Moreover, the glass transition temperature (Tg1) of resin which comprises a shell was 175 degreeC, and the glass transition temperature (Tg2) of resin which comprises a core was -51 degreeC.

[Synthesis Example 2] (Resin Particle 2)
Resin particles 2 were obtained in the same manner as in Synthesis Example 1, except that Latemul E-108MB (sodium polyoxyethylene alkyl ether sulfate, manufactured by Kao Corporation) was used as the emulsifier in Synthesis Example 1. The average particle diameter of the obtained resin particles 2 measured by a dynamic light scattering method was 61 nm. Moreover, the glass transition temperature (Tg1) of resin which comprises a shell was 175 degreeC, and the glass transition temperature (Tg2) of resin which comprises a core was -51 degreeC.

[Synthesis Example 3] (Resin Particle 3)
In Synthesis Example 1, resin particles 3 were obtained in the same manner as in Synthesis Example 1 except that the monomer of the resin constituting the shell was changed to methyl methacrylate. The average particle diameter of the obtained resin particles 3 measured by a dynamic light scattering method was 60 nm. Moreover, the glass transition temperature (Tg1) of resin which comprises a shell was 120 degreeC, and the glass transition temperature (Tg2) of resin which comprises a core was -51 degreeC.

[Synthesis Example 4] (Resin particles 4: resin particles not having a core-shell structure)
300 parts by mass of ion-exchanged water was charged into a reaction vessel equipped with a reflux tube, and 35.71 parts by mass of Latemul ASK (emulsifier, dipotassium alkenyl succinate, manufactured by Kao Corporation) and 0.2 parts by mass of potassium persulfate were added. After performing nitrogen substitution at room temperature for about 30 minutes, the temperature is raised to 60 ° C. and held at that temperature for 15 minutes. A mixture of 0.5 parts by weight of trimethylolpropane trimethacrylate and 1.0 part by weight of allyl methacrylate as a grafting agent was continuously added over about 1 hour. After completion of the addition, the mixture was held for 1 hour, further heated to 100 ° C. and heated for 1 hour to obtain resin particles 4. The average particle diameter of the obtained resin particles 4 measured by a dynamic light scattering method was 52 nm. Moreover, the glass transition temperature of resin which comprises the resin particle 4 was -51 degreeC.

[Synthesis Example 5] (Resin particles 5: resin particles having no core-shell structure)
300 parts by mass of ion-exchanged water was charged into a reaction vessel equipped with a reflux tube, and 35.71 parts by mass of Latemul ASK (emulsifier, dipotassium alkenyl succinate, manufactured by Kao Corporation) and 0.2 parts by mass of potassium persulfate were added. After performing nitrogen substitution at room temperature for about 30 minutes, the temperature was raised to 60 ° C. and maintained at that temperature for 15 minutes, and then 12.5 parts of tricyclodecane methacrylate, which is a monomer of the resin constituting the shell, was added. It was continuously added over 10 minutes. After completion of the addition, the mixture was held for 1 hour, further heated to 100 ° C. and heated for 1 hour, to obtain resin particles 5. The average particle diameter of the obtained resin particles 5 measured by a dynamic light scattering method was 65 nm. Further, the glass transition temperature of the resin constituting the resin particle 5 was 175 ° C.

[Example 1]
A 10% aqueous solution of PVA having a polymerization degree of 2400 and a saponification degree of 98% and the resin particles 1 are mixed so that the resin particles 1 are 20 parts by mass with respect to 100 parts by mass of PVA in terms of solid content to obtain a film forming stock solution It was. When a high temperature test was performed on this film-forming stock solution, no formation of aggregates was observed. The average particle diameter of the resin particles 1 after the high temperature test measured by the dynamic light scattering method was 100 nm.
A glass plate was placed on the hot plate, and a PET film (Lumirror, manufactured by Toray Industries, Inc.) was spread and heated to 60 ° C. Subsequently, the film-forming stock solution after the high-temperature test was performed was fluted with a wire bar. Then, the coating film of the film forming stock solution was dried and further heat-treated at 110 ° C. for 10 minutes to obtain a PVA film having an average thickness of 30 μm. It was 100 nm when the average particle diameter of the resin particle in a PVA film was calculated | required.
The obtained PVA film was transparent, and when a tensile test was performed, the stress at a strain of 200% was 53 N / mm ² .

[Example 2]
A film-forming stock solution was obtained in the same manner as in Example 1 except that the resin particles 2 were used. When a high temperature test was performed on this film-forming stock solution, no formation of aggregates was observed. The average particle diameter of the resin particles 2 after the high temperature test measured by the dynamic light scattering method was 110 nm.
A glass plate was placed on the hot plate, and a PET film (Lumirror, manufactured by Toray Industries, Inc.) was spread and heated to 60 ° C. Subsequently, the film-forming stock solution after the high-temperature test was performed was fluted with a wire bar. Then, the coating film of the film forming stock solution was dried and further heat-treated at 110 ° C. for 10 minutes to obtain a PVA film having an average thickness of 30 μm. It was 110 nm when the average particle diameter of the resin particle in a PVA film was calculated | required.
The obtained PVA film was transparent, and when a tensile test was performed, the stress at a strain of 200% was 55 N / mm ² .

[Example 3]
A film-forming stock solution was obtained in the same manner as in Example 1 except that the resin particles 3 were used. When a high temperature test was performed on this film-forming stock solution, no formation of aggregates was observed. The average particle diameter measured by the dynamic light scattering method of the resin particles 3 after the high temperature test was 120 nm.
A glass plate was placed on the hot plate, and a PET film (Lumirror, manufactured by Toray Industries, Inc.) was spread and heated to 60 ° C. Subsequently, the film-forming stock solution after the high-temperature test was performed was fluted with a wire bar. Then, the coating film of the film forming stock solution was dried and further heat-treated at 110 ° C. for 10 minutes to obtain a PVA film having an average thickness of 30 μm. It was 120 nm when the average particle diameter of the resin particle in a PVA film was calculated | required.
The obtained PVA film was transparent, and when a tensile test was performed, the stress at a strain of 200% was 58 N / mm ² .

[Example 4]
A 10% aqueous solution of polyvinyl alcohol having a polymerization degree of 2400 and a saponification degree of 88% and the resin particles 1 are mixed so that the resin particles 1 are 20 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol in terms of solid content. Got. When a high temperature test was performed on this film-forming stock solution, no formation of aggregates was observed. The average particle diameter of the resin particles 1 after the high temperature test measured by the dynamic light scattering method was 100 nm.
A glass plate was placed on the hot plate, and a PET film (Lumirror, manufactured by Toray Industries, Inc.) was spread and heated to 60 ° C. Subsequently, the film-forming stock solution after the high-temperature test was performed was fluted with a wire bar. Then, the coating film of the film forming stock solution was dried and further heat-treated at 110 ° C. for 10 minutes to obtain a PVA film having an average thickness of 30 μm. It was 100 nm when the average particle diameter of the resin particle in a PVA film was calculated | required.
The obtained PVA film was transparent, and when a tensile test was performed, the stress at a strain of 200% was 52 N / mm ² .

[Comparative Example 1]
A film-forming stock solution was obtained in the same manner as in Example 1 except that the resin particles 4 were used. When this film-forming stock solution was subjected to a high-temperature test, the film-forming stock solution became cloudy and the formation of aggregates having a size of 1 mm or more could be visually confirmed. It was judged that measurement by the dynamic light scattering method was impossible due to remarkable aggregation. Moreover, since aggregation was remarkable, it was judged that production of a transparent PVA film was impossible.

[Comparative Example 2]
A glass plate was placed on the hot plate, and a PET film (Lumirror, manufactured by Toray Industries, Inc.) was spread and heated to 60 ° C. Next, a 10% aqueous solution of PVA having a polymerization degree of 2400 and a saponification degree of 98% was poured with a wire bar. Then, the coating film of the film forming stock solution was dried and further heat-treated at 110 ° C. for 10 minutes to obtain a PVA film having an average thickness of 30 μm.
The obtained PVA film was transparent, but when a tensile test was performed, the stress at a strain of 200% was 72 N / mm ² .

[Comparative Example 3]
A film-forming stock solution was obtained in the same manner as in Example 1 except that the resin particles 5 were used. When a high temperature test was performed on this film-forming stock solution, no formation of aggregates was observed. The average particle diameter of the resin particles 5 after the high temperature test measured by the dynamic light scattering method was 80 nm.
A glass plate was placed on the hot plate, and a PET film (Lumirror, manufactured by Toray Industries, Inc.) was spread and heated to 60 ° C. Subsequently, the film-forming stock solution after the high-temperature test was performed was fluted with a wire bar. Then, the coating film of the film forming stock solution was dried and further heat-treated at 110 ° C. for 10 minutes to obtain a PVA film having an average thickness of 30 μm. It was 90 nm when the average particle diameter of the resin particle in a PVA film was calculated | required.
The obtained PVA film was transparent, but when a tensile test was performed, the stress at a strain of 200% was 75 N / mm ² .

(Discussion)
As described above, the resin particles 1 to 1 having a core-shell structure in which the glass transition temperature (Tg1) of the resin constituting the shell is 100 ° C. or higher and the glass transition temperature (Tg2) of the resin constituting the core is 10 ° C. or lower. The PVA films of Examples 1 to 4 using 3 were transparent, and the stress during the tensile test was shown to be small. These PVA films were confirmed to be excellent flexibility films.

  On the other hand, in Comparative Example 1 using resin particles 4 which are resin particles 4 having no core-shell structure and a low Tg of −51 ° C., aggregation of the resin particles occurs in the high temperature test, and a transparent PVA film is formed. I couldn't. In Comparative Example 2 in which no resin particles were used and in Comparative Example 3 in which resin particles 5 having no core-shell structure and high Tg of 175 ° C. were used, the stress during the tensile test was small. A PVA film could not be obtained.

  The PVA film of the present invention is used for packaging films, water-soluble films, agricultural films, release films, polarizing films and the like.

Claims (4)

Including polyvinyl alcohol and resin particles having a core-shell structure,
The polyvinyl alcohol film whose glass transition temperature (Tg1) of resin which comprises the shell in the said resin particle is 100 degreeC or more, and whose glass transition temperature (Tg2) of resin which comprises a core is 10 degrees C or less.   The polyvinyl alcohol film according to claim 1, wherein an average particle diameter of the resin particles is 150 nm or less.   The polyvinyl alcohol film according to claim 1 or 2, wherein a content of the resin particles with respect to 100 parts by mass of the polyvinyl alcohol is 1 part by mass or more and 50 parts by mass or less. Comprising the step of forming a film using a film-forming stock solution,
The film-forming stock solution contains polyvinyl alcohol and resin particles having a core-shell structure,
The manufacturing method of the polyvinyl alcohol film whose glass transition temperature (Tg1) of resin which comprises the shell in the said resin particle is 100 degreeC or more, and whose glass transition temperature (Tg2) of resin which comprises a core is 10 degrees C or less.