TW202006055A - Poly(vinyl alcohol) film, stretched film, polarizing film, and method for producing poly(vinyl alcohol) film - Google Patents

Abstract

Provided are: a poly(vinyl alcohol) (PVA) film having excellent stretchability; a stretched film obtained from the PVA film; and a polarizing film having excellent shapability. The poly(vinyl alcohol) film of the present invention comprises poly(vinyl alcohol) (A) and polyisoprene rubber particles (B), wherein the content of the polyisoprene rubber particles (B) is higher than 35 parts by mass but not higher than 60 parts by mass per 100 parts by mass of the poly(vinyl alcohol) (A).

Description

Method for manufacturing polyvinyl alcohol film, stretch film, polarizing film, and polyvinyl alcohol film

The invention relates to a method for manufacturing polyvinyl alcohol film, stretch film, polarizing film, and polyvinyl alcohol film.

Polyvinyl alcohol film (hereinafter referred to as "PVA" may be abbreviated as "PVA") is used in a wide range of applications such as packaging films, water-soluble films, agricultural films, release films, and optical films.

The PVA film is harder than other plastic films in the state of not containing a plasticizer, and there are cases where mechanical properties such as impact strength and step passability during secondary processing such as elongation are problems. In order to prevent such problems, those who add plasticizers to PVA films are often used to improve flexibility. In particular, when a PVA film is used as a raw material of a polarizing film, since high elongation is required when applying elongation processing, those using plasticizers to improve elongation performance are used. However, such a PVA film containing a plasticizer has a problem that the plasticizer decreases with time and the elongation processability decreases.

For this problem, as a method of imparting good elongation processability by a method other than the addition of a plasticizer, in the case of PVA fiber, a method of adding an emulsified dispersion of an ethylene vinyl acetate copolymer to a spinning dope is proposed (Refer to Patent Document 1).

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 47-42050

On the other hand, as the application of the PVA film, there is a PVA film that has been subjected to various stretching treatments. In such applications, it is important to reduce the residual stress, which is a cause of problems such as deformation after processing, while requiring high extensibility for PVA films, and low tensile stress.

However, in the conventional method as described above, it is difficult to provide high elongation to the PVA film while reducing the tensile stress, and the elongation processability of the PVA film is insufficient. In addition, as the deformation speed of the PVA film becomes larger, the tensile stress of the PVA film tends to become larger. Therefore, even if the deformation speed is large, the PVA film has a small tensile stress.

In addition, the polarizing film obtained by stretching the PVA film is used for optical purposes, and is mainly used for polarizing plates and sunglasses for liquid crystal displays. However, it has been known that the polarizing film is cracked parallel to the extending direction in applications such as folding displays, highly designed sunglasses, etc. in which the polarizing film is further deformed in recent years. The greater the deformation speed of the polarizing film, the more pronounced this problem becomes. Therefore, a polarizing film with excellent formability that does not cause problems such as cracking even when deformed under a condition of a high deformation speed is required.

Therefore, the first object of the present invention is to provide a PVA film excellent in stretch processability and a stretch film obtained from the PVA film. Furthermore, the second object of the present invention is to provide a polarizing film excellent in formability.

According to the present invention, the above object can be achieved by providing the following:

[1] A PVA film comprising PVA (A) and polyisoprene rubber particles (B), and the content of the polyisoprene rubber particles (B) is relative to 100 parts by mass of the PVA (A ) In terms of more than 35 parts by mass and less than 60 parts by mass;

[2] The PVA film described in [1], wherein the degree of polymerization of PVA (A) is 1,000 or more and 10,000 or less, and the degree of saponification is 95 mol% or more;

[3] The PVA film as described in [1] or [2], wherein the weight average molecular weight of the polyisoprene rubber constituting the polyisoprene rubber particles (B) is 5,000 or more and 80,000 or less;

[4] The PVA film as described in any one of [1] to [3], wherein the thickness is 1 μm or more and 60 μm or less;

[5] The PVA film as described in any one of [1] to [4], which is a raw film for optical films;

[6] A stretched film obtained from the PVA film as described in any one of [1] to [5];

[7] A polarizing film obtained from the PVA film or stretched film as described in any one of [1] to [6];

[8] A method for producing a polyvinyl alcohol film, comprising a step of forming a film using a film-forming stock solution mixed with polyvinyl alcohol (A) and a dispersion liquid containing polyisoprene rubber particles (B), The content of the polyisoprene rubber particles (B) in the film-forming stock solution is more than 35 parts by mass and 60 parts by mass or less relative to 100 parts by mass of the polyvinyl alcohol (A).

According to the present invention, a PVA film excellent in stretch processability and a stretch film obtained from the PVA film can be provided. In addition, by subjecting the PVA film or the stretched film to dyeing processing or the like, a polarizing film excellent in formability can be provided.

[Form for carrying out the invention]

Hereinafter, embodiments of the PVA film of the present invention, its manufacturing method, stretched film, and polarizing film will be described in detail.

<PVA film>

A PVA film according to an embodiment of the present invention includes PVA (A) and polyisoprene rubber particles (B). The PVA film is usually an unstretched film (non-stretched film). As described in detail below, by stretching the PVA film, a stretched film can be obtained. In addition, by subjecting the PVA film or the stretched film to dyeing processing or the like, a polarized film can be obtained.

(PVA)

PVA (polyvinyl alcohol) usually becomes the main component of the PVA film. PVA is a polymer having vinyl alcohol units (-CH ₂ -CH(OH)-) as the main structural unit. In addition, the main structural unit refers to the structural unit that accounts for the largest proportion of all structural units, and the proportion of the total structural unit is preferably 50 mol% or more (hereinafter referred to as "main structural unit" The same is true). PVA may have vinyl ester units and other units in addition to vinyl alcohol units.

As the PVA, it is possible to use one obtained by saponifying a polyvinyl ester obtained by polymerizing one kind or two or more kinds of vinyl esters. Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl versatate, vinyl versatate, and vinyl laurate. Vinyl fatty acid ester, vinyl benzoate, isopropylene acetate, etc. Among vinyl esters, compounds with vinyloxycarbonyl groups (H ₂ C=CH-O-CO-) in the molecule are preferred from the standpoint of ease of manufacturing, availability, and cost. Preferably, vinyl acetate is more preferred.

The polyvinyl ester is preferably obtained by using only one kind or two or more kinds of vinyl esters as monomers, and more preferably obtained by using only one kind of vinyl esters as monomers. As long as it does not significantly impair the effects of the present invention, it may be a copolymerized resin of one or more vinyl esters and other monomers copolymerizable therewith.

The upper limit of the proportion of structural units derived from other monomers that can be copolymerized is based on the number of moles of all structural units constituting the copolymerized resin, preferably 15 mole%, more preferably 10 mole% , 5 mol% is further preferred, 1 mol% is further preferred. That is, in the PVA obtained by saponifying polyvinyl esters, the lower limit of the proportion of vinyl alcohol units in the total structural units is preferably 85 mol%, 90 mol% is better, and 95 mol% is Further preferred, 99 mole% is even further preferred.

Examples of other monomers that can be copolymerized with vinyl esters include: α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; (meth)acrylic acid or its salts; (methyl) Methyl acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, (A (Meth) acrylate, tertiary butyl acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, etc. (meth) acrylate; (meth) acrylic Acetamide; N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, diacetone (meth)acrylamide Amine, (meth)acrylamide propanesulfonic acid or its salt, (meth)acrylamide propyl dimethylamine or its salt, N-hydroxymethyl(meth)acrylamide or its derivative, etc. ( Methyl) acrylamide derivatives; N-vinyl amide, N-vinyl acetamide, N-vinyl pyrrolidone and other N-vinyl amides; methyl vinyl ether, ethyl vinyl ether, Vinyl ethers such as n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; (methyl) Vinyl cyanide such as acrylonitrile; halogenated vinyl groups such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl compounds such as allyl acetate and propylene chloride; maleic acid or its salts , Esters or anhydrides; itaconic acid, or its salts, esters or anhydrides; vinylsilyl compounds such as vinyl trimethoxysilane; unsaturated sulfonic acid or its salts, etc.

The polyvinyl ester may have one kind or two or more kinds of structural units derived from the above monomers.

As PVA, those without graft copolymerization can be preferably used. However, as long as it does not significantly impair the effects of the present invention, PVA may be modified by one or two or more monomers that can be graft-copolymerized. The graft copolymerization can be performed on at least one of polyvinyl ester and PVA that can be obtained by saponification. Examples of the graft copolymerizable monomer include: unsaturated carboxylic acid or its derivative; unsaturated sulfonic acid or its derivative; α-olefin having 2 to 30 carbon atoms. The proportion of structural units derived from monomers that can be graft-copolymerized in polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles constituting the entire structural unit of polyvinyl ester or PVA .

In PVA, a part of its hydroxyl group may be cross-linked or uncross-linked. In addition, a part of the hydroxyl group of the PVA system can react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure.

The lower limit of the polymerization degree of PVA is preferably 1,000, more preferably 1,500, and further preferably 1,700. When the degree of polymerization of PVA is at least the above lower limit, the toughness of the PVA film and the resulting stretched film can be improved. On the other hand, the upper limit of the polymerization degree is preferably 10,000, more preferably 8,000, and even more preferably 5,000. When the degree of polymerization of PVA is equal to or lower than the above upper limit, it is possible to suppress the increase in the manufacturing cost of PVA and the occurrence of defects during film formation. In addition, the degree of polymerization of PVA means the average degree of polymerization measured according to the description of JIS K6726-1994.

The lower limit of the saponification degree of PVA may be, for example, 80 mol%, preferably 95 mol%, more preferably 98 mol%, and further preferably 99 mol%. When the degree of saponification is at least the above lower limit, the effect of the present invention can be more fully exhibited. In addition, in the case of the use of the water-soluble film, PVA with a low degree of saponification can be used. On the other hand, the upper limit of the degree of saponification may be 100 mol%. In addition, the degree of saponification of PVA refers to the ratio of the molar number of vinyl alcohol units to the total molar number of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification and vinyl alcohol units (Mohr%). The degree of saponification can be measured according to the description of JIS K6726-1994.

The lower limit of the PVA content in the PVA film is preferably 60% by mass, more preferably 62.5% by mass, and further preferably 64% by mass. By setting the content of PVA to the above lower limit or more, the characteristics of PVA can be fully utilized, and the transparency and smoothness of the resulting stretched film can be improved. On the other hand, the upper limit of this content is preferably 74% by mass, more preferably 72% by mass, and further preferably 70% by mass. By setting the content of PVA to be equal to or lower than the above upper limit, the stretch workability and the like can be improved.

(Polyisoprene rubber particles)

Polyisoprene rubber particles are particles of polyisoprene rubber. The polyisoprene rubber particles may contain components other than polyisoprene rubber. That is, the polyisoprene rubber is composed of polyisoprene rubber as a main component and other arbitrary components. However, the lower limit of the content of polyisoprene rubber in the polyisoprene rubber particles is, for example, 80% by mass, may be 90% by mass, or may be 95% by mass. Examples of other components that the polyisoprene rubber particles may contain include emulsifiers adhering to the surface and additives other than these.

The polyisoprene rubber particles generally exist uniformly dispersed with respect to the PVA as a base material. By containing a specified amount of polyisoprene rubber particles, the PVA film can obtain a stretched film excellent in stretchability from the PVA film.

The polyisoprene rubber is a polymer rubber having a structural unit derived from isoprene as a main structural unit. The lower limit of the content ratio of the isoprene units in the total structural units constituting the polyisoprene rubber is, for example, 50 mol%, preferably 70 mol%, more preferably 90 mol% There are also 95 mol% for a further better situation. The polyisoprene rubber may be substantially a homopolymer of isoprene. In addition, polyisoprene has isomers, but polyisoprene rubber is usually cis 1,4-polyisoprene. When the polyisoprene rubber is a copolymer, examples of monomers other than isoprene include the monomers mentioned as "other monomers copolymerizable with vinyl esters". Diene compounds such as butadiene, styrene, etc.

Polyisoprene rubber can be modified. For example, it can be modified by using modifiers such as tin tetrachloride, silicon tetrachloride, alkoxysilane having an epoxy group in the molecule, and alkoxysilane containing an amine group, and has a branched structure Or functional group of polyisoprene rubber, but not limited to these.

The lower limit of the weight average molecular weight of the polyisoprene rubber is, for example, preferably 5,000, more preferably 10,000, and further preferably 15,000. On the other hand, the upper limit of the weight average molecular weight is preferably 80,000, more preferably 60,000, and further preferably 40,000. By using a polyisoprene rubber having a weight average molecular weight within the above range, the stretch processability and various characteristics of the stretch film obtained can be further improved.

The content of the polyisoprene rubber particles in the PVA film is greater than 35 parts by mass relative to 100 parts by mass of PVA, preferably 40 parts by mass or more, and more preferably 45 parts by mass or more. By setting the content of the polyisoprene rubber particles to be greater than the above lower limit or to be above the above lower limit, the stretch processability of the PVA film is improved. On the other hand, the upper limit of the content of polyisoprene rubber particles is 60 parts by mass, preferably 50 parts by mass. By setting the content of the polyisoprene rubber particles to the above upper limit or less, the PVA film can be set to a good surface state.

(Manufacturing method of polyisoprene rubber particles)

Polyisoprene rubber particles can be produced as a dispersion of polyisoprene rubber particles. The production method of the dispersion liquid of polyisoprene rubber particles is not particularly limited, and for example, well-known methods such as anionic polymerization method and post-emulsion method can be used. Specifically, for example, after first synthesizing polyisoprene rubber, an emulsifier and water are added to the polyisoprene rubber, and vigorously stirred by an emulsifier or the like, whereby polyisoprene rubber particles can be obtained Dispersions. At this time, the average particle size of the polyisoprene rubber particles can be adjusted by adjusting the intensity of stirring, the stirring time, etc., and selecting an emulsifier. In addition, a dispersion liquid of polyisoprene rubber particles can be produced by a well-known emulsion polymerization method.

When dispersing polyisoprene rubber in water and using it as an oil-drop dispersion in water, it is preferable to prepare the dispersion in advance by a mechanical method or a chemical method, and use it at a specified concentration by dilution or the like . Examples of the mechanical method include a homogenizer, a homomixer, a disperser mixer, a colloid mill, a pipe line mixer, a high-pressure homogenizer, and an ultrasonic emulsifier. Etc. can be used alone or in combination. As the chemical method, various methods such as reverse phase emulsification method, D phase emulsification method, HLB temperature emulsification method, gel emulsification method, and liquid crystal emulsification method can be cited. From the viewpoint of easily obtaining a dispersion liquid with fine particle size, the system The inverse emulsification method is preferred. In addition, in order to obtain a dispersion liquid with a fine particle size, it is also preferable to perform the above-mentioned operation while heating at an appropriate temperature (for example, 30 to 80° C.) for the purpose of reducing the viscosity of the polyisoprene rubber. From the viewpoint of improving the stability of the dispersion, it is better to prepare the dispersion with a solid content concentration of 20 to 80% by mass, and more preferably 30 to 70% by mass.

As a catalyst when polymerizing polyisoprene rubber, for example, titanium tetrahalide-trialkyl aluminum series, diethyl aluminum-cobalt series, trialkyl aluminum-boron trifluoride-nickel series, Diethylaluminum chloride-nickel series and other Ziegler series catalysts; triethylaluminum-organic acid neodymium-Lewis acid series and other lanthanide rare earth metal catalysts, or organic alkali metals used in the same way as S-SBR Compounds etc.

The emulsifier used in the production of polyisoprene rubber particles is not particularly limited, and examples thereof include common ones such as anionic, nonionic, and nonionic-anionic.

Specific examples of emulsifiers include anionic emulsifiers such as sodium salts of aliphatic carboxylic acids such as laurate, myristate, palmitate, stearate, and alkenyl succinate. , Potassium salt or ammonium salt; sodium salt, potassium salt or ammonium salt of natural rosin heterogeneity or hydride; sodium salt, potassium salt or ammonium salt of aliphatic sulfuric acid compounds such as lauryl sulfate. In addition, examples of the nonionic-anionic emulsifier include polyoxyethylene octyl phenyl ether sulfonate, polyoxyethylene octyl phenyl ether sulfate, polyoxyethylene alkyl ether sulfate, etc. Anionic soaps such as phosphate soaps such as ester soaps, cetyl phosphates, polyoxyethylene lauryl ether phosphates, polyoxyethylene tridecyl ether phosphates, polyoxyethylene nonylphenyl phosphates, etc. Examples of relative cations of these salts include sodium, potassium, and ammonium.

The amount of emulsifier used is preferably 0.5 to 15 parts by mass, and more preferably 1 to 10 parts by mass relative to 100 parts by mass of polyisoprene rubber. If the amount of the emulsifier used is below the upper limit, the stability of the polyisoprene rubber particles will not be affected, and the use of excess emulsifier can be suppressed, which is economically advantageous. In addition, if the amount of the emulsifier used is more than the above lower limit, the increase in the particle size of the polyisoprene rubber particles can be suppressed, and the occurrence of creaming and separation phenomena can be suppressed. For the purpose of improving the stability of the polyisoprene rubber particles, alkaline substances such as sodium hydroxide, potassium hydroxide, and amines can be added as needed to adjust the pH before use.

In addition, commercially available products can also be used as the dispersion liquid of polyisoprene rubber or polyisoprene rubber particles.

(Plasticizer)

The PVA film may further contain a plasticizer. By including a plasticizer, this PVA film can improve stretch processability, handleability, and roll quality. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trihydroxy. Methyl propane and so on. One or more of these plasticizers can be used. From the standpoint of elongation processability and roll quality improvement effect, glycerin is preferred among these.

The lower limit of the content of the plasticizer in the PVA film is preferably 1 part by mass relative to 100 parts by mass of PVA, and more preferably 5 parts by mass. By setting the content of the plasticizer to the above lower limit or more, the processing extensibility and the like are further improved. On the other hand, the upper limit of this content is preferably 20 parts by mass, more preferably 15 parts by mass. By setting the content of the plasticizer to the above upper limit or less, it can be suppressed that the PVA film becomes too soft or the plasticizer bleeds out to the surface, thereby reducing handleability.

(Other additives, etc.)

The PVA film can be further appropriately blended according to needs: processing stabilizers such as fillers, copper compounds, weather resistance stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, other Thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, stripping agents, mold release agents, reinforcing agents, cross-linking agents, mold inhibitors, preservatives, crystallization rate retarders, surfactants And other additives.

From the viewpoint of film forming properties, it is preferable to include a surfactant among other additives. By including a surfactant, it is possible to suppress the occurrence of uneven thickness of the PVA film, and it becomes easy to make metal rolls and stripped films used for self-made films. The type of the above-mentioned surfactant is not particularly limited, but from the standpoint of peelability from metal rolls and belts, anionic surfactants and nonionic surfactants are preferred.

As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate type such as polyoxyethylene lauryl ether sulfate and octyl sulfate; a sulfonic acid type such as dodecylbenzenesulfonate and the like are preferred.

As the nonionic surfactant, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octyl phenyl ether; and alkyl esters such as polyoxyethylene laurate are preferred Type; alkyl amine type such as polyoxyethylene lauryl amino ether; alkyl amide type such as polyoxyethylene lauryl amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; lauric acid diethanolamide, Alkanolamide type such as oleic diethanolamide; allylphenyl ether type such as polyoxyallyl allyl phenyl ether.

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

When the PVA film contains a surfactant, the lower limit of the content is preferably 0.01 parts by mass relative to 100 parts by mass of PVA, and more preferably 0.03 parts by mass. When the content of the surfactant is at least the above lower limit, the releasability and film-forming properties are further improved. On the other hand, the upper limit of this content is preferably 0.5 parts by mass, more preferably 0.3 parts by mass. When the content of the surfactant is equal to or less than the above upper limit, it can be suppressed that the surfactant bleeds out to the surface of the PVA film, the films are in close contact with each other, and the handling property is reduced.

The upper limit of the content of other additives other than PVA, polyisoprene rubber particles, plasticizer, and surfactant in the PVA film is preferably 10% by mass, and more preferably 5% by mass In some cases, 1% by mass is better, and 0.2% by mass is even better. When the content of other additives is greater than the above upper limit, it may affect the processing extensibility of the PVA film and the transparency of the resulting extended film.

(Shape)

The shape of the PVA film is not particularly limited, but from the viewpoint of good productivity and continuous production, a long film is preferred. The length of the elongated PVA film is not particularly limited, and can be appropriately set according to the application and the like. For example, the length can be set within a range of 5 m or more and 20,000 m or less. The width of the PVA film is not particularly limited. For example, in the case of a water-soluble film, the lower limit can be set to 1 cm. In addition, since various applications require wide-width PVA films in recent years, the lower limit is preferably 1 m, 2 m is more preferable, and 4 m is even more preferable. The upper limit of the width of the PVA film is not particularly limited, but it can be set to 7 m, for example. If the width is too wide, when a PVA film is manufactured with a practical device, it tends to become difficult to produce uniformly.

The PVA film may be a single-layer film or a multilayer film (laminate).

The upper limit of the thickness (average thickness) of the PVA film is not particularly limited, but is, for example, 100 μm, preferably 60 μm, and more preferably 40 μm. On the other hand, the lower limit of this thickness is preferably 1 μm, more preferably 5 μm, and even more preferably 10 μm. When the thickness of the PVA film is within the above-mentioned range, the handleability and stretch processability can be improved. In addition, the thickness (average thickness) is set to the average of the values measured at any five locations. The following also applies to the thickness (average thickness).

(Use)

This PVA film can be used for various purposes similar to conventional PVA films, such as packaging films, water-soluble films, agricultural films, release films, and optical films. In addition, the PVA film is suitable as a raw film of a stretched film. In particular, since this PVA film can obtain a stretched film excellent in stretchability, it is suitable as a raw material film used as a material of an optical film. That is, by stretching the PVA film, an optical film can be preferably obtained. In addition, the raw material film refers to a film used as a material, and is not limited to a rolled film.

Optical film refers to a light-transmitting film used in optical devices. As the optical device, a display device such as a liquid crystal display device or an organic EL display can be exemplified. Examples of the optical film include a polarizing film, a polarizer protective film, a color compensation film, a brightness enhancement film, a viewing angle widening film, and a retardation film. In addition, the PVA film can make use of its excellent transparency and gas barrier properties. As examples other than optical films, gas barrier films such as organic EL displays can also be used.

In addition, the PVA film is as described above, and it can be preferably used as a raw material film as a stretched film, and can also be used for various applications without stretching.

[0053] <Manufacturing method of PVA film>

The manufacturing method of the PVA thin film is not particularly limited, and a manufacturing method in which the thickness and width of the PVA thin film after film formation becomes more uniform can be preferably used. For example, it can be obtained by using a film-forming stock solution in which PVA and polyisoprene rubber particles constituting a PVA film are dissolved in a liquid medium, and further dissolving other components such as a plasticizer as needed. In addition, it can be manufactured even if a film-forming stock solution obtained by melting PVA is used as required.

That is, a method of manufacturing a PVA film according to an embodiment of the present invention is prepared by using a film-forming stock solution mixed with polyvinyl alcohol (A) and a dispersion liquid containing polyisoprene rubber particles (B) In the film formation step, the content of the polyisoprene rubber particles (B) in the film-forming stock solution is more than 35 parts by mass and 60 parts by mass or less relative to 100 parts by mass of the polyvinyl alcohol (A).

According to this manufacturing method, a PVA film excellent in stretch processability can be manufactured.

In the film-forming stock solution, the polyisoprene rubber particles are preferably uniformly mixed. In addition, by mixing the dispersion liquid of polyisoprene rubber particles with a liquid medium, PVA, and other additives, a film-forming stock solution in which the polyisoprene rubber particles are uniformly mixed can be effectively obtained. In addition, when the film-forming stock solution contains a plasticizer, other additives, etc., it is preferable that these components are uniformly mixed.

Examples of the liquid medium include water, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, and diethylene glycol. Alcohol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. One or more of these liquid media can be used. From the point of view of low environmental load and recyclability, water is preferred among these.

The volatile fraction of the film-forming stock solution (in the film-forming stock solution, the content ratio of the volatile components such as the liquid medium removed due to volatilization and evaporation during film-making) varies depending on the film-forming method, film-forming conditions, etc. The lower limit is preferably 50% by mass, more preferably 55% by mass, and further preferably 60% by mass. With the volatile fraction of the membrane-forming stock solution above the lower limit, the viscosity of the membrane-forming stock solution will not become too high, and the filtration and defoaming during the preparation of the membrane-forming stock solution can be smoothly performed, making it easier to produce less foreign matter and disadvantages PVA film. On the other hand, the upper limit of this volatile fraction is preferably 95% by mass, more preferably 90% by mass. The volatile fraction of the film-forming stock solution is below the upper limit, and the concentration of the film-forming stock solution does not become too low, and industrial PVA thin film production becomes easy.

As a film-forming method when manufacturing a PVA thin film using a film-forming stock solution, a conventionally known method can be used. As a film forming method, a method of applying a film forming solution to a substrate and manufacturing a PVA thin film on the substrate; or a method of directly manufacturing a single-layer PVA thin film. Examples of the film forming method include a casting film forming method, an extrusion film forming method, a wet film forming method, and a gel film forming method. These film forming methods may use only one type, or a combination of two or more types. use. Among these film-forming methods, the casting film-forming method and the extrusion film-forming method are preferred because PVA thin films with uniform thickness and width and good physical properties can be obtained.

For the PVA film produced by the film, heat treatment can be carried out as required. The heat treatment temperature is not particularly limited as long as it is adjusted appropriately. If the heat treatment temperature is too high, discoloration and deterioration of the PVA film can be observed. Therefore, the upper limit of the heat treatment temperature is preferably 210°C, more preferably 180°C, and further preferably 150°C. On the other hand, the lower limit of the heat treatment temperature is, for example, 60°C, and preferably 90°C.

The heat treatment time is not particularly limited as long as it is appropriately adjusted, and from the viewpoint of efficiently manufacturing the PVA film, the upper limit is preferably 30 minutes, and more preferably 15 minutes. On the other hand, as this lower limit, for example, 10 seconds is preferable, and 1 minute is more preferable.

<Stretch Film>

The stretched film of one embodiment of the present invention is a stretched film obtained by stretching the PVA film of one embodiment of the present invention. The stretched film is usually oriented with the PVA in a specified direction (stretching direction). The stretched film may be stretched uniaxially or biaxially, but it is preferably uniaxially stretched. The stretched film stretched uniaxially can be preferably used as an optical film such as a polarizing film. The stretched film may be a single-layer film or a multilayer film, and a single-layer film is preferred.

The upper limit of the thickness (average thickness) of the stretched film is, for example, 30 μm, and preferably 16 μm. When the thickness of the stretched film is equal to or less than the above upper limit, sufficient thinning can be achieved. On the other hand, the lower limit of this thickness is preferably 5 μm, and more preferably 8 μm. When the thickness of the stretched film is equal to or greater than the above lower limit, it becomes less likely to be broken, and handling properties can be improved.

The stretched film can be used as a packaging film, a water-soluble film, an agricultural film, a release film, an optical film, and the like, and it is preferably used as an optical film.

Examples of the optical film include a polarizing film, a polarizer protective film, a color compensation film, and a brightness enhancement film. Among them, the polarizing film is more preferable.

<Manufacturing method of stretched film>

The stretched film can be obtained by the above-mentioned manufacturing method including the step of stretching the PVA film. That is, in the manufacturing process of this stretched film, the stretching process is optional except that the PVA film described above can be used by the same method as in the past. Therefore, the manufacturing process of the stretched film may not include processes other than the stretching process (dyeing process, fixing process, etc.) in the manufacturing process of the polarizing film described below. That is, according to this manufacturing method, the stretched film can be obtained relatively easily without going through special steps.

By subjecting the PVA film or the stretched film to dyeing processing or the like, a polarizing film excellent in formability can be provided.

<polarizing film>

The polarizing film according to one embodiment of the present invention is a polarizing film obtained by dyeing the PVA film or stretched film according to one embodiment of the present invention described above. The polarizing film is attached to the PVA film or the stretched film to adsorb dichroic dye and boric acid. Since the polarizing film contains a specified amount of polyisoprene rubber particles, problems such as cracking due to deformation are less likely to occur, so it is suitable for folding displays and highly designed sunglasses.

The polarizing film can also be used as a polarizing plate by bonding a protective film that is optically transparent and has mechanical strength on both sides or one side. As the protective film, cellulose triacetate (TAC) film, cellulose acetate butyrate (CAB) film, acrylic film, polyester film, etc. can be used. In addition, examples of the adhesive used for bonding include PVA-based adhesives and ultraviolet-curable adhesives. PVA-based adhesives are preferred.

The polarizing plate obtained as described above can be further laminated with optical films such as retardation films, viewing angle enhancing films, and brightness enhancing films. In addition, as the above-mentioned viewing angle enhancement film and the like, a stretched film according to an embodiment of the present invention can also be used. The polarizing plate can be used as a component of a liquid crystal display device after being coated with an adhesive such as acrylic and then bonded to a glass substrate.

<Manufacturing method of polarizing film>

Specific methods for manufacturing the polarizing film include swelling treatment, dyeing treatment, uniaxial stretching treatment, and further cross-linking treatment, fixing treatment, washing treatment, drying treatment, if necessary Methods such as heat treatment. At this time, the order of each treatment such as swelling treatment, dyeing treatment, cross-linking treatment, uniaxial stretching, and fixing treatment is not particularly limited, and two or more treatments may be performed simultaneously. In addition, one or more of each process may be performed twice or more than once.

In addition, as another method for manufacturing the polarizing film, a method of applying treatment other than swelling treatment to the stretched film may be mentioned. That is, the polarizing film can also be obtained by applying dyeing treatment, uniaxial stretching treatment, and further applying cross-linking treatment, fixing treatment, washing treatment, drying treatment, heat treatment, etc. as needed. At this time, the order of each treatment such as dyeing treatment, cross-linking treatment, uniaxial stretching, and fixing treatment is not particularly limited, and two or more treatments may be performed simultaneously. In addition, one or more of each process may be performed twice or more than once.

Among the manufacturing methods of the polarizing film, it is particularly preferable to apply swelling treatment, dyeing treatment, uniaxial stretching treatment, and further applying cross-linking treatment, fixing treatment, washing treatment, drying treatment, if necessary After heat treatment or the like, there is further provided a method of performing uniaxial stretching by the dry stretching method.

The following describes the case where the polarizing film is manufactured using the PVA film, and the conditions of each treatment such as the dyeing process described later are the same as the case where the stretched film is used for manufacturing.

The swelling treatment can be performed by immersing the PVA film in water. The lower limit of the temperature of the water when immersed in water is preferably 20°C, more preferably 22°C, and even more preferably 25°C. On the other hand, the upper limit of this temperature is preferably 50°C, more preferably 38°C, and further preferably 35°C. In addition, the lower limit of the time for immersion in water is preferably 0.1 minutes, and more preferably 0.5 minutes. On the other hand, the upper limit of this time is preferably 5 minutes, more preferably 3 minutes. In addition, the water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

The dyeing treatment can be performed by bringing the dichroic pigment into contact with the PVA film. As the dichroic dye, an iodine-based dye or a dichroic dye is generally used.

In the case of the iodine-based pigment, the period of the dyeing treatment may be any stage before the uniaxial stretching process, during the uniaxial stretching process, and after the uniaxial stretching process. The dyeing treatment is usually performed by immersing the PVA film in a solution (especially aqueous solution) containing iodine-potassium iodide as a dyeing bath. The concentration of iodine in the dyeing bath is preferably 0.01% by mass or more and 0.5% by mass or less, and the concentration of potassium iodide is preferably 0.01% by mass or more and 10% by mass or less. In addition, the lower limit of the temperature of the dyeing bath is preferably 20°C, and more preferably 25°C. On the other hand, the upper limit of this temperature is preferably 50°C, and more preferably 40°C.

In the case of dichroic dyes, as the time of the dyeing process, it may be any stage of making a PVA film, before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. In the dyeing process, a dichroic dye such as an azo compound is adsorbed and impregnated into a person who swells the PVA film. When the swelling treatment is omitted, the swelling treatment can be performed simultaneously in the dyeing treatment.

In addition to the use of the azo compound in the form of a free acid, a salt of the compound can be used. Such salts are, for example, alkali metal salts such as lithium salts, sodium salts, and potassium salts, or organic salts such as ammonium salts and alkylamine salts, preferably sodium salts.

The dyeing treatment is usually performed by immersing the PVA film in a solution (especially an aqueous solution) containing an azo compound as a dyeing bath. The concentration of each azo compound in the dyeing bath is preferably 0.00001% by mass or more and 10% by mass or less. In addition, the temperature of the dyeing bath is preferably 5 to 60°C, more preferably 20 to 50°C, and particularly preferably 35 to 50°C. The time of immersion in the solution can be adjusted moderately, and it is better to adjust from 30 seconds to 20 minutes, more preferably from 1 to 10 minutes.

As the dyeing solution, in addition to the azo compound, a dyeing aid may be further contained as needed. Examples of the dyeing aid include sodium carbonate, sodium bicarbonate, sodium chloride, sodium sulfate, anhydrous sodium sulfate, and sodium tripolyphosphate. The content of the dyeing aid can be adjusted at any concentration according to the time and temperature of the dyeing property. As separate contents, 0.01 to 5 mass% is preferable in the dyeing solution, and 0.1 to 2 mass% For better.

By applying a cross-linking treatment to the PVA film, it is possible to effectively prevent the PVA from dissolving into water when wet stretching is performed at a high temperature. From this point of view, it is preferable to perform the cross-linking treatment before the uniaxial stretching treatment. The cross-linking treatment can be performed by immersing the PVA film in an aqueous solution containing a cross-linking agent. As the crosslinking agent, one or more boron inorganic compounds such as boric acid such as boric acid and borax can be used. The lower limit of the concentration of the cross-linking agent in the aqueous solution containing the cross-linking agent is preferably 1% by mass, more preferably 2% by mass, and further preferably 3% by mass. On the other hand, the upper limit of this concentration is preferably 15% by mass, 7% by mass is more preferable, and 6% by mass is even more preferable. When the concentration of the crosslinking agent is within the above range, sufficient extensibility can be maintained. When an iodine-based pigment is used in an aqueous solution containing a cross-linking agent, an auxiliary agent such as potassium iodide may be contained. The lower limit of the temperature of the aqueous solution containing the crosslinking agent is preferably 20°C, more preferably 25°C. On the other hand, the upper limit of this temperature is preferably 50°C, and more preferably 40°C. By setting the temperature within the above range, crosslinking can be performed efficiently.

The uniaxial stretching process can be performed by any of the wet stretching method and the dry stretching method. In the case of the wet stretching method, it may be carried out in an aqueous solution of boric acid, or it may be carried out in the above-mentioned dyeing bath or a fixing treatment bath described later. In the case of the dry stretching method, the uniaxial stretching process can be maintained at room temperature, the uniaxial stretching process can be performed while heating, or the uniaxial stretching process can be performed in the air using a water-absorbing PVA film. Among these, the wet stretching method is more preferable, and uniaxial stretching treatment in a boric acid aqueous solution is more preferable. The lower limit of the boric acid concentration of the aqueous solution of boric acid is preferably 0.5% by mass, more preferably 1.0% by mass, and further preferably 1.5% by mass. On the other hand, the upper limit of the boric acid concentration is preferably 6% by mass, more preferably 5% by mass. In addition, the boric acid aqueous solution may contain potassium iodide in the case of an iodine-based dye, and its concentration is preferably 0.01% by mass or more and 10% by mass or less.

From the viewpoint of the polarization performance of the obtained polarizing film, the lower limit of the stretching magnification in the uniaxial stretching process is preferably 4 times, and more preferably 5 times. The upper limit of the extension magnification is not particularly limited, but for example, 10 times is better, and 8 times is better.

When manufacturing a polarizing film, in order to enhance the adsorption of the dichroic dye (iodine-based dye, etc.) to the PVA film, it is preferable to perform a fixing treatment after uniaxial stretching treatment. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more kinds of boron inorganic compounds such as boric acid and borax can be used. In addition, iodine compounds and metal compounds may be added to the fixed treatment bath as needed. The lower limit of the concentration of the boron inorganic compound in the fixing treatment bath is preferably 0.5% by mass, more preferably 1% by mass. On the other hand, the upper limit of this concentration is preferably 15% by mass, more preferably 10% by mass. By setting the concentration within the above range, the absorption of the dichroic pigment can be further enhanced. The lower limit of the temperature of the fixed treatment bath is preferably 15°C. On the other hand, the upper limit of this temperature is preferably 60°C, and more preferably 40°C.

The washing treatment is usually performed by immersing the PVA film in water or the like. In the case of iodine-based pigments, from the viewpoint of improving the polarizing performance, it is preferable that the water used in the washing treatment contains an auxiliary agent such as potassium iodide. In this case, the concentration of iodide such as potassium iodide is preferably 0.5% by mass or more and 10% by mass or less. In addition, the lower limit of the temperature of water and the like used in the washing treatment is usually 5°C, preferably 10°C, and more preferably 15°C. On the other hand, the upper limit of this temperature is usually 50°C, preferably 45°C, and more preferably 40°C. From an economic point of view, it is not good if the temperature of water or the like is too low. On the other hand, if the temperature of water or the like is too high, the polarization performance may be reduced.

The conditions of the drying process are not particularly limited, and the lower limit of the drying temperature is preferably 30°C, and more preferably 50°C. On the other hand, the upper limit of the drying temperature is preferably 150°C, and more preferably 130°C. By drying at a temperature within the above range, a polarizing film excellent in size stability can be easily obtained.

By performing heat treatment after the drying process, a polarizing film excellent in dimensional stability can be obtained. Here, the heat treatment is a process of further heating the polarizing film with a moisture content of 5% or less after the drying process to improve the size stability of the polarizing film. The conditions of the heat treatment are not particularly limited, but it is preferable to perform the heat treatment within the range of 60°C or more and 150°C or less. If the heat treatment is performed at a temperature lower than 60°C, the size stabilization effect by the heat treatment is insufficient. On the other hand, if the heat treatment is performed at a temperature higher than 150°C, the polarizing film may yellowish violently.

The polarizing film is not limited to those having a two-dimensional shape (planar shape), but includes those processed into a three-dimensional shape. That is, the polarizing film may be formed by applying stretching or the like after dyeing. As a method for stretching the dyed film, there are various methods such as wet stretching, vacuum forming, and thermoforming, and it is not limited thereto. As the stretching ratio, from the viewpoint of maintaining performance, it is better to stretch by 1.2 to 2 times, and more preferably by 1.3 to 1.5 times. As the elongation speed, from the viewpoint of productivity, 100 to 10000%/min is preferable, and 500 to 5000%/min is more preferable. The stretching temperature is preferably 100° C. or lower when using an iodine-based dye, and 160° C. or lower when using a dichroic dye. In the case of an iodine-based pigment, molding at a temperature higher than 100°C may cause discoloration and decrease in performance, and at the same time, stretching at a low temperature may cause breakage.

[Example]

The present invention will be specifically described by the following examples, but the present invention is not limited by these examples at all. In addition, each evaluation method used in the following examples and comparative examples is shown below.

[Measurement method of weight average molecular weight of liquid rubber (polyisoprene rubber)]

The weight average molecular weight of the liquid rubber is determined by GPC (gel permeation chromatography) in terms of molecular weight in terms of standard polystyrene.

The measurement equipment and conditions are as follows.

Device: GPC device "GPC8020" manufactured by Tosoh Corporation

Separation column: "TSKgelG4000HXL" manufactured by Tosoh Corporation

Detector: "RI-8020" manufactured by Tosoh Corporation

Eluent: Tetrahydrofuran

Flow rate of eluent: 1.0ml/min

Sample concentration: 5mg/10ml

Column temperature: 40℃

[Stretchability of PVA film (tensile stress)]

The PVA film was conditioned at 23° C. and 50% RH for 24 hours, from which the PVA film was cut into a film sheet having a length of 30 mm and a width of 10 mm. After that, the PVA film sheet was mounted on the tensile tester ("single column desktop tester: 5952") made by Instron so that the initial chuck interval became 10 mm, at 100 [mm/ Min] speed tensile test. The value of the test force [N] when the chuck interval at this time becomes 30 mm divided by the cross-sectional area [mm ² ] of the blank before stretching is taken as the tensile stress [N/mm ² ]. At this time, the same measurement was repeated 10 times for one sample, and the average value was used as data. When the tensile stress is less than 45 N/mm ² , it is judged that it is easy to stretch and the stretch workability is good.

[Formability of polarizing film (TD fracture strain)]

The polarizing film was humidified at 23° C. and 50% RH for 24 hours or more, whereby the polarizing film was cut into a film sheet having a length (MD) of 10 mm and a width (TD) of 30 mm. After that, the polarizing film sheet was mounted on a tensile testing device manufactured by Shimadzu Corporation ("Autograph(AGS-H) so that the initial chuck interval became 10 mm and the stretching direction was consistent with the TD of the polarizing film. "), under a heating environment of 140°C, a tensile test was carried out at a speed of 100 [mm/min]. At this time, the same measurement was repeated 10 times for one sample, and the one with the largest TD fracture strain was used as the data. When the TD fracture strain is 40% or more, it is judged that it is easy to form and the formability is good. Here, the TD fracture strain is the time when the polarizing film is extended Xmm from the initial inter-chuck distance (10mm) and fractured in the above tensile test.

(X/10)×100(%) value.

[Synthesis Example 1] Synthesis of rubber particles

(1) Synthesis of liquid rubber

A fully dried 5L autoclave was replaced with nitrogen, 1200 g of hexane and 112 g of secondary butyllithium (10.5% by mass hexane solution) were added, and the temperature was raised to 50°C. Thereafter, 1200 g of isoprene was sequentially added while controlling the polymerization temperature so as to be 50° C. under stirring conditions, and polymerization was carried out for 1 hour. After that, methanol was added to stop the polymerization reaction to obtain a polymer solution. Water was added to the obtained polymer solution and stirred, and the polymer solution was washed with water. After the stirring was completed, it was confirmed that the polymer solution phase was separated from the water phase, and then the water was discharged. The polymer solution after washing was vacuum dried at 70° C. for 24 hours to obtain liquid polyisoprene (liquid rubber). The weight average molecular weight of the obtained liquid rubber was measured and found to be 10,000.

(2) Preparation of rubber particle water dispersion

15 g of anionic emulsifier ("Phosphanol RS-710" of Toho Chemical Industry Co., Ltd.) was added to 250 g of the above-mentioned liquid rubber and stirred for 20 minutes. Next, while stirring, a small amount of 177 g of water was sequentially added. After adding a specified amount of water, it was stirred for 20 minutes, thereby obtaining an aqueous dispersion of rubber particles (polyisoprene rubber particles).

[Example 1]

(Production of PVA film)

100 parts by mass of PVA (a saponified product of a homopolymer of vinyl acetate, a degree of polymerization of 2,400, and a degree of saponification of 99.5 mol %), 45 parts by mass of rubber particles, 10 parts by mass of glycerin as a plasticizer, 0.1 parts by mass Parts of sodium polyoxyethylene lauryl ether sulfate as a surfactant and water are used to prepare a film-forming stock solution with a volatile content of 85% by mass. In addition, the rubber particles are mixed with other components in the state of the aqueous dispersion obtained in Synthesis Example 1 above. The above film-forming stock solution was cast on a metal drum with a surface temperature of 80° C., and dried until the volatile fraction (water content) became 5 mass% to obtain a long PVA film (thickness before heat treatment) with a thickness of 30 μm, a length of 1.5 m, and a width of 30 cm. PVA film). This PVA film was heat-treated at a temperature of 110°C for 10 minutes to obtain the PVA film of Example 1.

[Comparative Example 1]

A PVA film was obtained in the same manner except that no rubber particles were added in the preparation of the PVA film of Example 1.

[Comparative Example 2]

A PVA film was obtained in the same manner except that 10 parts by mass of rubber particles were added to the preparation of the PVA film of Example 1.

[Example 2]

(Production of polarizing film)

From the central portion in the width direction of the PVA film obtained in Example 1, a sample having a width of 5 cm×a length of 10 cm was cut so as to uniaxially extend a width of 5 cm×a length of 5 cm. While immersing this sample in pure water at 40°C for 120 seconds, it was uniaxially extended 1.3 times in the longitudinal direction to perform swelling treatment (uniaxial extension in the first stage). Next, it was immersed in a dyeing bath (temperature 48°C) containing an aqueous solution containing 0.00002% by mass of Direct blue 15 dye, 0.1% by mass of sodium tripolyphosphate and 0.1% by mass of sodium sulfate for 300 seconds. At the same time, the whole length is uniaxially extended 2.4 times in the longitudinal direction to adsorb the dye (uniaxial extension in the second stage). Further, while immersed in a cross-linking treatment bath (temperature 40°C) containing an aqueous solution containing 2% by mass of boric acid for 60 seconds, the whole length was uniaxially extended 2.7 times in the longitudinal direction to adsorb boric acid (the third stage) Uniaxial extension). Then, while immersed in a stretching treatment bath (temperature 58° C.) containing an aqueous solution containing 3.9% by mass of boric acid, it was uniaxially stretched and aligned in the longitudinal direction so that the length of the initial film became 4.0 times. Uniaxial extension of the fourth stage). Immediately after the extension, it was immersed in a water tank (temperature 25°C) as a washing tank for 5 seconds. Finally, it was dried at 70°C for 3 minutes to produce a polarizing film.

[Comparative Example 3]

A polarizing film was obtained in the same manner except that the PVA film of Comparative Example 1 to which no rubber particles were added was used instead of the PVA film obtained in Example 1 in the preparation of the polarizing film of Example 2.

[Comparative Example 4]

The PVA film added with 70 parts by mass of rubber particles was used instead of the PVA film obtained in Example 1 in the preparation of the polarizing film of Example 2. At this time, since the PVA film was broken during the uniaxial stretching process in the first stage, the production of the polarizing film was suspended. It is speculated that this is because the dispersibility of the liquid rubber in the PVA film is poor, and a large number of defects due to the shrinkage of the liquid rubber occur on the surface of the PVA film, so uneven thickness occurs, and the PVA film breaks at this starting point.

[Evaluation]

With respect to each PVA film obtained in Example 1 and Comparative Examples 1 and 2, the stretchability was evaluated by the aforementioned method. Table 1 shows the evaluation results.

In addition, for each polarizing film obtained in Example 2 and Comparative Example 3, the TD fracture strain was measured by the aforementioned method. Table 2 shows the evaluation results.

[Table 1]

[Table 2]

[Explanation of evaluation results] <Example 1>

The PVA film contains a specified amount of rubber particles (polyisoprene rubber particles), the tensile stress is less than 45 N/mm ² , and the stretchability is good.

Surprisingly, even under the condition that the deformation speed of the PVA film is large, that is, the tensile test is carried out at a speed of 100 [mm/min], the tensile stress is less than 45 N/mm ² .

<Comparative Example 1, 2>

This is a comparative example in which the content of rubber particles in the PVA film is small.

At this time, the tensile stress is 45 N/mm ² or more, and the stretch workability is insufficient.

<Example 2>

By using a PVA film containing a specified amount of rubber particles as the raw material film of the polarizing film, the TD fracture strain is 40% or more, and the formability is good.

Surprisingly, even under the condition that the deformation speed of the polarizing film is large, that is, the tensile test is carried out at a speed of 100 [mm/min], the TD strain at break is more than 40%.

<Comparative Example 3>

It is a comparative example using a PVA film containing no rubber particles as a raw material film of a polarizing film.

At this time, the TD fracture strain is 40% or less, and the formability is insufficient.

Claims (8)

A polyvinyl alcohol film comprising polyvinyl alcohol (A) and polyisoprene rubber particles (B), the content of the polyisoprene rubber particles (B) is relative to 100 parts by mass of the polyethylene The alcohol (A) is more than 35 parts by mass and 60 parts by mass or less. The polyvinyl alcohol film according to claim 1, wherein the degree of polymerization of polyvinyl alcohol (A) is 1,000 or more and 10,000 or less, and the degree of saponification is 95 mol% or more. The polyvinyl alcohol film according to claim 1 or 2, wherein the weight average molecular weight of the polyisoprene rubber constituting the polyisoprene rubber particles (B) is 5,000 or more and 80,000 or less. The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the thickness is 1 μm or more and 60 μm or less. The polyvinyl alcohol film according to any one of claims 1 to 4, which is a raw film for optical films. An extended film obtained from the polyvinyl alcohol film according to any one of claims 1 to 5. A polarizing film obtained from the polyvinyl alcohol film or stretched film according to any one of claims 1 to 6. A method for manufacturing a polyvinyl alcohol film, comprising the step of forming a film using a film-forming stock solution mixed with polyvinyl alcohol (A) and a dispersion liquid containing polyisoprene rubber particles (B), The content of the polyisoprene rubber particles (B) in the film-forming stock solution is more than 35 parts by mass and 60 parts by mass or less relative to 100 parts by mass of the polyvinyl alcohol (A).