CN114051513A

CN114051513A - Polyvinyl alcohol film, stretched film, polarizing film, and method for producing polyvinyl alcohol film

Info

Publication number: CN114051513A
Application number: CN202080050406.4A
Authority: CN
Inventors: 田边裕史; 矶崎孝徳; 鸟越信一; 大园达也; 香田大辅
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 2019-07-11
Filing date: 2020-07-10
Publication date: 2022-02-15
Anticipated expiration: 2040-07-10
Also published as: JPWO2021006329A1; WO2021006329A1; CN114051513B; TW202110969A; JP7496355B2; KR20220035023A

Abstract

Provided are a PVA film which is excellent in stretch processability and productivity and which enables to obtain a stretched film and a polarizing film excellent in moldability, a stretched film and a polarizing film produced from the PVA film, and a method for producing the PVA film. A polyvinyl alcohol film comprising a polyvinyl alcohol (A) and a modified conjugated diene polymer (B) having a hydrophilic group.

Description

Polyvinyl alcohol film, stretched film, polarizing film, and method for producing polyvinyl alcohol film

Technical Field

The present invention relates to a polyvinyl alcohol film, a stretched film, a polarizing film, and a method for producing a polyvinyl alcohol film.

Background

Polyvinyl alcohol films (hereinafter, polyvinyl alcohol may be abbreviated as "PVA") are used in a wide range of fields of use, such as packaging films, water-soluble films, agricultural films, release films, and optical films.

The PVA film is rigid in comparison with other plastic films in a state where it does not contain a plasticizer, and may have problems in mechanical properties such as impact strength, process acceptability in secondary processing such as stretching, and the like. In order to prevent these problems, a product having improved flexibility by adding a plasticizer to a PVA film is generally used in many cases. In particular, when a PVA film is used as a raw material for a polarizing film, high stretchability is required in the case of performing stretching processing, and therefore, a product having improved stretch processability by adding a plasticizer is used. However, PVA films containing such a plasticizer have a problem that the plasticizer decreases with time and the stretch processability decreases.

In order to solve this problem, as a method for imparting good drawing processability by a method other than adding a plasticizer, a method of adding an emulsified dispersion of an ethylene-vinyl acetate copolymer to a spinning dope in the case of PVA fibers has been proposed (see patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese examined patent publication No. 47-42050.

Disclosure of Invention

Problems to be solved by the invention

On the other hand, as applications of the PVA film, there are applications of PVA films subjected to various stretching treatments. In such applications, high stretchability is required for the PVA film, and it is important to reduce the tensile stress in order to reduce the residual stress that causes problems such as deformation after processing.

However, in the method of adding the above-mentioned emulsified dispersion liquid of ethylene-vinyl acetate copolymer, it is difficult to impart high stretchability to the PVA film and to reduce the tensile stress thereof, and the stretch processability of the PVA film is insufficient. Further, since the tensile stress of the PVA film tends to be larger as the deformation speed of the PVA film is larger, a PVA film having a small tensile stress even if the deformation speed is larger is demanded.

The polarizing film obtained by stretching the PVA film is used for optical applications, mainly polarizing plates for liquid crystal displays and sunglasses. However, it is known that: in recent years, in applications where a polarizing film is further deformed, such as a folding display and a sunglass having high design properties, the polarizing film may be broken parallel to the stretching direction. The problem becomes more pronounced the greater the deformation speed of the polarizing film. Therefore, a polarizing film excellent in moldability is desired which does not suffer from chipping or the like even when deformed at a high deformation rate.

Here, the present inventors found that: by adding a rubber component to PVA, the resulting PVA film is improved in stretch processability, and moldability into a stretched film and a polarizing film. However, when a PVA film is produced by casting a film-forming dope on the surface of a base material such as a metal drum in the case of adding a rubber component, there is a new problem that the rubber component adheres to the base material such as the metal drum. When the amount of adhesion of the rubber component to a base material such as a metal drum increases, the rubber component may become dirt and adhere to the PVA film. Therefore, it is necessary to remove the rubber component adhering to the base material such as the metal drum by cleaning or the like as needed. However, when isoprene rubber or the like is used as the rubber component, it may be difficult to sufficiently remove the isoprene rubber by washing with water or the like. As described above, the rubber component (deposit) adhering to the base material such as the metal drum is not preferable because it is sometimes difficult to remove even by washing or the like, and productivity is sometimes lowered by washing or the like.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a PVA film that is excellent in stretch processability and productivity and can obtain a stretched film and a polarizing film excellent in moldability, a stretched film and a polarizing film produced from the PVA film, and a method for producing the PVA film.

Means for solving the problems

The above object is achieved by providing the following technical solutions:

[1] a polyvinyl alcohol film comprising a polyvinyl alcohol (A) and a modified conjugated diene polymer (B) having a hydrophilic group;

[2] the polyvinyl alcohol film according to [1], wherein the content of the modified conjugated diene polymer (B) is 10 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol (A);

[3] the polyvinyl alcohol film according to [1] or [2], wherein the polyvinyl alcohol (A) has a polymerization degree of 1,000 or more and 10,000 or less and a saponification degree of 95 mol% or more;

[4] the polyvinyl alcohol film according to any one of [1] to [3], wherein the modified conjugated diene polymer (B) has a weight-average molecular weight of 5,000 to 80,000;

[5] the polyvinyl alcohol film according to any one of [1] to [4], wherein the hydrophilic group is a graft chain having a repeating structure containing a nonionic polar group;

[6] a stretched film obtained from the polyvinyl alcohol film according to any one of [1] to [5 ];

[7] a polarizing film obtained from the polyvinyl alcohol film of any one of [1] to [5] or the stretched film of [6 ];

[8] a method for producing a polyvinyl alcohol film, comprising a step of forming a film using a film-forming stock solution obtained by mixing polyvinyl alcohol (a) and a dispersion liquid containing a modified conjugated diene polymer (B) having a hydrophilic group;

[9] the method for producing a polyvinyl alcohol film according to [8], wherein a content of the modified conjugated diene polymer (B) in the film-forming stock solution is 10 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol (A);

[10] the method for producing a polyvinyl alcohol film according to [8] or [9], wherein the hydrophilic group is a graft chain having a repeating structure containing a nonionic polar group.

Effects of the invention

According to the present invention, a PVA film excellent in stretch processability and productivity and capable of obtaining a stretched film and a polarizing film excellent in moldability, a stretched film and a polarizing film produced from the PVA film, and a method for producing the PVA film can be provided.

Detailed Description

The following will describe in detail embodiments of the PVA film, the method for producing the same, the stretched film, and the polarizing film of the present invention.

< PVA film >

A PVA film according to one embodiment of the present invention includes PVA (a) and a modified conjugated diene polymer (B) having a hydrophilic group. The PVA film is usually a film that has not been subjected to stretching (non-stretched film). As described in detail later, the PVA film is stretched to obtain a stretched film. The polarizing film is obtained by subjecting the PVA film or the stretched film to dyeing or the like.

The PVA film contains the modified conjugated diene polymer (B), and thus has excellent stretch processability, and can provide a stretched film and a polarizing film having excellent moldability. Further, by providing the modified conjugated diene polymer (B) contained in the PVA film with a hydrophilic group, even when the modified conjugated diene polymer (B) adheres to a substrate such as a metal drum, the adhered matter can be easily removed with water or the like. Therefore, the PVA film is also excellent in productivity.

[PVA(A)]

PVA (polyvinyl alcohol) (a) generally becomes the main component of the PVA film. PVA (A) is a polymer having a vinyl alcohol unit (-CH)₂-CH (OH) -) as the main structural unit. The main structural unit is a structural unit having the largest proportion of all structural units, and the proportion of all structural units is preferably 50 mol% or more (c:)Hereinafter, the same applies to the "main structural unit"). The PVA (A) may have a vinyl ester unit or other units in addition to the vinyl alcohol unit.

As the PVA (a), PVA obtained by saponifying polyvinyl ester obtained by polymerizing 1 kind, or 2 or more kinds of vinyl esters can be used. Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, and isopropenyl acetate. Among the vinyl esters, those having an ethyleneoxycarbonyl group (H) in the molecule are preferable from the viewpoints of ease of production, ease of acquisition, cost, and the like₂C = CH-O-CO —), more preferably vinyl acetate.

The polyvinyl ester is preferably a polyvinyl ester obtained by using only 1 or 2 or more vinyl esters as monomers, and more preferably a polyvinyl ester obtained by using only 1 vinyl ester as a monomer. The copolymer resin may be a copolymer resin of 1 or 2 or more kinds of vinyl esters and other monomers copolymerizable therewith, within a range not significantly impairing the effects of the present invention.

The upper limit of the proportion of the structural unit derived from another monomer copolymerizable therewith is preferably 15 mol%, more preferably 10 mol%, further preferably 5 mol%, and further preferably 1 mol%, based on the number of moles of the whole structural units constituting the copolymer resin. The lower limit of the proportion of the vinyl alcohol unit in the pva (a) obtained by saponifying a polyvinyl ester in the whole structural units is preferably 85 mol%, more preferably 90 mol%, still more preferably 95 mol%, and yet more preferably 99 mol%.

Examples of the other monomer copolymerizable with the vinyl ester include α -olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutylene; (meth) acrylic acid or a salt thereof; (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, and octadecyl (meth) acrylate; (meth) acrylamide; (meth) acrylamide derivatives such as N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamidopropanesulfonic acid or a salt thereof, (meth) acrylamidopropyldimethylamine or a salt thereof, and N-methylol (meth) acrylamide or a derivative thereof; n-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; ethylene cyanide such as (meth) acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester or anhydride thereof; itaconic acid or a salt, ester or anhydride thereof; vinyl silyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids or salts thereof, and the like.

The polyvinyl ester may have structural units derived from 1 or 2 or more of the above monomers.

As PVA (A), PVA that has not been subjected to graft copolymerization may be preferably used. The PVA (A) may be modified with 1 or 2 or more kinds of graft-copolymerizable monomers within a range not significantly impairing the effects of the present invention. At least one of polyvinyl ester and PVA obtained by saponifying the same may be graft-copolymerized. Examples of the graft-copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; an unsaturated sulfonic acid or a derivative thereof; alpha-olefins having 2 to 30 carbon atoms, and the like. The proportion of the structural unit derived from a graft-copolymerizable monomer in the polyvinyl ester or pva (a) is preferably 5 mol% or less, depending on the number of moles of the whole structural units constituting the polyvinyl ester or pva (a).

A part of the hydroxyl groups in PVA (A) may or may not be crosslinked. In addition, a part of the hydroxyl groups in pva (a) may react with aldehyde compounds such as acetaldehyde and butylaldehyde to form an acetal structure.

The lower limit of the degree of polymerization of pva (a) is preferably 1,000, more preferably 1,500, and still more preferably 1,700. When the polymerization degree of PVA (a) is not less than the lower limit, toughness and the like of the PVA film, the obtained stretched film, and the polarizing film can be improved. On the other hand, the upper limit of the polymerization degree is preferably 10,000, more preferably 8,000, and still more preferably 5,000. When the polymerization degree of pva (a) is not more than the upper limit, an increase in production cost of pva (a) and the occurrence of defects during film formation can be suppressed. The polymerization degree of PVA (A) is an average polymerization degree measured according to JIS K6726-1994.

The lower limit of the saponification degree of the pva (a) may be, for example, 80 mol%, preferably 95 mol%, more preferably 98 mol%, and still more preferably 99 mol%. The effects of the present invention are more fully exhibited by setting the saponification degree to the lower limit or more. In the case of the use as a water-soluble film, PVA having a low saponification degree may be used. On the other hand, the upper limit of the saponification degree may be 100 mol%. The degree of saponification of PVA (A) means: the proportion (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles of the structural unit (typically, vinyl ester unit) that can be converted into the vinyl alcohol unit by saponification and the vinyl alcohol unit. The degree of saponification can be measured according to JIS K6726-1994.

The lower limit of the content of PVA (a) in the PVA film may be preferably 60 mass%, more preferably 65 mass%, and still more preferably 70 mass%, 75 mass%, 80 mass%, or 85 mass%. When the content of pva (a) is not less than the above lower limit, the properties of pva (a) can be sufficiently exhibited, and the transparency, smoothness and the like of the obtained stretched film, polarizing film and the like can be improved. On the other hand, the upper limit of the content may be preferably 99% by mass, more preferably 95% by mass, still more preferably 90% by mass, and still more preferably 85% by mass, 80% by mass, 75% by mass, or 70% by mass. When the content of pva (a) is not more than the upper limit, the stretch processability, the moldability of the obtained stretched film, polarizing film, and the like can be improved.

[ modified conjugated diene Polymer (B) ]

The modified conjugated diene polymer (B) is a conjugated diene polymer having a hydrophilic group. The modified conjugated diene polymer (B) may be a conjugated diene rubber having a hydrophilic group. For example, the modified conjugated diene polymer (B) is a polymer obtained by modifying an unmodified conjugated diene polymer (B') (unmodified conjugated diene rubber) to introduce a hydrophilic group.

The modified conjugated diene polymer (B) contains a conjugated diene unit as a monomer unit constituting the polymer (usually, the main chain of the polymer). That is, the modified conjugated diene polymer (B) is a polymer using a conjugated diene as a monomer. Examples of the conjugated diene include butadiene, isoprene, 2, 3-dimethylbutadiene, 2-phenylbutadiene, 1, 3-pentadiene, 2-methyl-1, 3-pentadiene, 1, 3-hexadiene, 1, 3-octadiene, 1, 3-cyclohexadiene, 2-methyl-1, 3-octadiene, 1,3, 7-octatriene, myrcene, α -farnesene, β -farnesene, and chloroprene. Among these, butadiene and isoprene are preferable, and isoprene is more preferable. The main chain of the modified conjugated diene polymer (B) may have a suitable structure (e.g., a structure of a monomer unit) as an unmodified conjugated diene polymer (B') described below.

The hydrophilic group of the modified conjugated diene polymer (B) may be, for example, a group containing at least one of an oxygen atom and a nitrogen atom, and examples thereof include a hydroxyl group, a carboxyl group, an ester group (-COO-), an ether group (-O-), an amide group, a sulfonic group, an acid anhydride group, and a group containing 1 or 2 or more of these groups.

The hydrophilic group is preferably a graft chain having a repeating structure including a nonionic polar group. Examples of the nonionic polar group include a hydroxyl group, an ester group, an ether group, an amide group, and an acid anhydride group, and an ether group is preferable. The graft chain means a chain linked to the main chain directly or via other groups, but its synthetic method is not particularly limited.

Examples of the repeating structure containing a nonionic polar group include:

-(CR²R³-CR⁴R⁵poly (O) — orAn alkylene glycol structure,

-(CH₂-CR⁷COOR⁸) A poly (meth) acrylate structure shown, and the like,

preferably a polyalkylene glycol structure.

R is as defined above²、R³、R⁴And R⁵Each independently represents a hydrogen atom or a 1-valent hydrocarbon group having 1 to 6 carbon atoms. R is as defined above⁷Is a hydrogen atom or a methyl group. R is as defined above⁸Is a C1-6 hydrocarbon group. R⁸Some or all of the hydrogen atoms of the hydrocarbon groups shown are optionally substituted with hydrophilic groups.

As the above-mentioned R²、R³、R⁴、R⁵And R⁸Examples of the 1-valent hydrocarbon group having 1 to 6 carbon atoms include aliphatic hydrocarbon groups such as alkyl groups such as methyl group, ethyl group and propyl group, and alkenyl groups such as vinyl group; alicyclic groups such as cyclohexyl; aromatic hydrocarbon groups such as phenyl groups. Among these, aliphatic hydrocarbon groups are preferable, and alkyl groups are more preferable. R is as defined above²、R³、R⁴And R⁵Each is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom.

The graft chain having a polyalkylene glycol structure is a hydrophilic group having a plurality of ether groups. The graft chain having a polyalkylene glycol structure can be represented by, for example, the following formula (a).

-(CR²R³-CR⁴R⁵-O)_n-R⁶・・・(A)

In the formula (A), R²、R³、R⁴And R⁵Each independently represents a hydrogen atom or a 1-valent hydrocarbon group having 1 to 6 carbon atoms. R⁶Is a hydrogen atom, a C1-6 hydrocarbon group or a C1-6 acyl group. n is an integer of 3 to 600.

R is as defined above²、R³、R⁴And R⁵Each is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. R is as defined above⁶The alkyl group is preferably a 1-valent hydrocarbon group, more preferably an alkyl group, still more preferably a methyl group and an ethyl group, and yet more preferably a methyl group. The lower limit of n is preferably 5, and more preferably 7. The upper limit of n is preferably 200, more preferably 200Preferably 100, and more preferably 40.

The graft chain having a poly (meth) acrylate structure can be represented by, for example, the following formula (B).

-(CH₂-CR⁷COOR⁸)_m-R⁹・・・(B)

In the formula (B), R⁷Is a hydrogen atom or a methyl group. R⁸Is a C1-6 hydrocarbon group. R⁸Some or all of the hydrogen atoms of the hydrocarbon groups shown are optionally substituted with hydrophilic groups. R⁹Is a hydrogen atom or a 1-valent organic group. m is an integer of 3 to 600. The organic group means a group containing a carbon atom, and examples thereof include a hydrocarbon group, an alkoxy group, an acyl group, a carboxyl group, and a combination thereof.

Among the graft chains having a repeating structure containing a nonionic polar group, a graft chain having a polyalkylene glycol structure is more preferable.

The number of the average hydrophilic groups per molecule of the modified conjugated diene polymer (B) is preferably 1 to 30, more preferably 1 to 25, and still more preferably 1 to 20. When the amount is within the above range, the cleaning property of removing the deposits from the PVA film, that is, the productivity is further improved.

The average number of hydrophilic groups per molecule of the modified conjugated diene polymer (B) can be determined from the equivalent weight of the hydrophilic groups of the modified conjugated diene polymer (B) (g/hydrophilic group-mol) and the number average molecular weight Mn in terms of polystyrene by the following formula.

(number of average hydrophilic groups per molecule) = [ (number average molecular weight Mn)/(molecular weight of styrene unit) × (average molecular weight of conjugated diene and other monomer units other than conjugated diene contained as necessary) ]/(equivalent of hydrophilic group)

The equivalent weight of the hydrophilic group of the modified conjugated diene polymer (B) means the mass of isoprene, butadiene and other monomers contained as needed per 1 mole of the hydrophilic group. The equivalent of the hydrophilic group can be used¹H-NMR or¹³C-NMR and based on peaks originating from hydrophilic groups and from the polymer backboneThe area ratio of the peaks was calculated.

In the modified conjugated diene polymer (B), the position to be introduced with the hydrophilic group may be a polymerization terminal or a side chain of the polymer chain, and the side chain of the polymer chain is preferable from the viewpoint of easily introducing a plurality of hydrophilic groups. The hydrophilic group may be contained in 1 kind alone or 2 or more kinds. That is, the modified conjugated diene polymer (B) may be modified with 1 type of modifying compound, or may be modified with 2 or more types of modifying compounds.

The melt viscosity of the modified conjugated diene polymer (B) measured at 38 ℃ is preferably 0.1 to 4,000Pa, more preferably 1 to 3,500Pa, and further preferably 1 to 3,000 Pa. When the melt viscosity of the modified conjugated diene polymer (B) is in the above range, the resulting PVA film is improved in the stretch processability, the moldability into a stretched film and a polarizing film, and the like. The melt viscosity of the modified conjugated diene polymer (B) was measured at 38 ℃ with a Brookfield type viscometer.

The weight average molecular weight (Mw) of the modified conjugated diene polymer (B) is preferably 5,000 or more and 80,000 or less, more preferably 6,000 or more and 50,000 or less, and further preferably 7,000 or more and 30,000 or less. The Mw of the modified conjugated diene polymer (B) is a polystyrene-equivalent weight average molecular weight determined by Gel Permeation Chromatography (GPC) measurement. When the Mw of the modified conjugated diene polymer (B) is within the above range, the process yield during production is excellent and the economy is good. Further, the PVA film is improved in stretch processability, moldability into a stretched film and a polarizing film, and the like. In addition, 2 or more kinds of modified conjugated diene polymers (B) having different Mw may be used in combination.

The molecular weight distribution (Mw/Mn) of the modified conjugated diene polymer (B) is preferably 1.0 to 20.0, more preferably 1.0 to 15.0, and still more preferably 1.0 to 10.0. When the Mw/Mn is within the above range, the viscosity variation of the modified conjugated diene polymer (B) is reduced, which is preferable. The molecular weight distribution (Mw/Mn) is a ratio of weight average molecular weight (Mw)/number average molecular weight (Mn) in terms of standard polystyrene determined by GPC measurement.

The vinyl group content of the modified conjugated diene polymer (B) is 0 mol% or more and less than 100 mol%, preferably 1 mol% or more and less than 70 mol%, and more preferably 3 mol% or more and less than 50 mol%. "vinyl content" means: the modified liquid diene polymer (B) contains 100 mol% of the total of conjugated diene units, based on the total of conjugated diene units, of the modified liquid diene polymer (B), and the total mol% of conjugated diene units bonded by 1, 2-bonds or 3, 4-bonds (conjugated diene units bonded other than 1, 4-bonds). The vinyl content can be used¹H-NMR was calculated from the area ratio of the peak derived from the conjugated diene unit bonded with the 1, 2-bond or 3, 4-bond to the peak derived from the conjugated diene unit bonded with the 1, 4-bond. The vinyl group content of the modified conjugated diene polymer (B) can be set to a desired value by, for example, controlling the kind of solvent used in producing the unmodified conjugated diene polymer (B'), the polar compound used as needed, the polymerization temperature, and the like.

The glass transition temperature (Tg) of the modified conjugated diene polymer (B) is preferably-150 to 50 ℃, more preferably-130 to 50 ℃, and still more preferably-130 to 30 ℃. When the Tg is in the above range, the stretching processability of the PVA film, the moldability of the stretched film, and the like are further improved.

The modified conjugated diene polymer (B) may be used alone in 1 kind or in combination of 2 or more kinds.

The lower limit of the content of the modified conjugated diene polymer (B) in the PVA film may be, for example, 5 parts by mass, preferably 10 parts by mass, more preferably 15 parts by mass, and further preferably 20 parts by mass, 25 parts by mass, 30 parts by mass, or 35 parts by mass, based on 100 parts by mass of the PVA (a). When the content of the modified conjugated diene polymer (B) is not less than the lower limit, the stretching processability of the PVA film, the moldability of the stretched film and the polarizing film, and the like are further improved.

The upper limit of the content of the modified conjugated diene polymer (B) in the PVA film may be, for example, 100 parts by mass, preferably 80 parts by mass, more preferably 60 parts by mass, and still more preferably 40 parts by mass, 30 parts by mass, or 20 parts by mass, based on 100 parts by mass of PVA. When the content of the modified conjugated diene polymer (B) is not more than the upper limit, the PVA film is more suitable for stretch processability and the like. Further, by setting the content of the modified conjugated diene polymer (B) to the upper limit or less, transparency, other optical properties, surface properties, and the like can be improved.

(method for synthesizing modified conjugated diene Polymer (B))

The method for synthesizing the modified conjugated diene polymer (B) is not particularly limited, and for example, the modified conjugated diene polymer (B ') can be obtained by acid modification of an unmodified conjugated diene polymer (B') and, if necessary, grafting with a compound (X) described later.

In the unmodified conjugated diene polymer (B') used as a raw material, it is one preferable embodiment that 50% by mass or more of all monomer units constituting the polymer are butadiene and/or isoprene. The total content of the butadiene unit and the isoprene unit is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, based on the total monomer units of the unmodified conjugated diene polymer (B').

Examples of the monomer units other than the butadiene unit and the isoprene unit that the unmodified conjugated diene polymer (B') may contain include a conjugated diene unit other than the butadiene and the isoprene described above, an aromatic vinyl compound unit, and the like.

Examples of the aromatic vinyl compound providing the aromatic vinyl compound unit include styrene, α -methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-tert-butylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2, 4-dimethylstyrene, 2, 4-diisopropylstyrene, 2,4, 6-trimethylstyrene, 2-ethyl-4-benzylstyrene, 4- (phenylbutyl) styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, vinylanthracene, N-diethyl-4-aminoethylstyrene, vinylpyridine, 4-methoxystyrene, 4-dodecylstyrene, 4-dimethylstyrene, 2, 4-diisopropylstyrene, 2, 4-trimethylstyrene, 2-ethyl-4-benzylstyrene, 4- (phenylbutyl) styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, vinylanthracene, N-diethyl-4-aminoethylstyrene, vinylpyridine, 4-methoxystyrene, and, Monochlorostyrene, dichlorostyrene, divinylbenzene, and the like. Among these, styrene, α -methylstyrene and 4-methylstyrene are preferred.

The content of the monomer units other than the butadiene unit and the isoprene unit in the unmodified conjugated diene polymer (B') is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less. For example, when the vinyl aromatic compound unit is in the above range or less, the stretching processability of the PVA film, the moldability of the stretched film and the polarizing film, and the like tend to be improved.

The unmodified conjugated diene polymer (B') is preferably a polymer obtained by polymerizing a conjugated diene and, if necessary, other monomers other than the conjugated diene by, for example, emulsion polymerization, solution polymerization, or the like.

As the emulsion polymerization method, a known method or a method based on a known method can be applied. For example, a predetermined amount of a conjugated diene-containing monomer is dispersed by emulsification in the presence of an emulsifier, and emulsion polymerization is performed using a radical polymerization initiator.

Examples of the emulsifier include long-chain fatty acid salts having 10 or more carbon atoms and rosin acid salts. Examples of the long-chain fatty acid salt include potassium salts and sodium salts of fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid.

As the dispersion medium, water is usually used, and a water-soluble organic solvent such as methanol or ethanol may be contained within a range not impairing the stability at the time of polymerization.

Examples of the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate; organic peroxides, hydrogen peroxide, and the like.

In order to adjust the molecular weight of the obtained unmodified conjugated diene polymer (B'), a chain transfer agent may be used. Examples of the chain transfer agent include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan; carbon tetrachloride, thioglycolic acid, diterpenes, terpinolene, gamma-terpinene, alpha-methylstyrene dimer, and the like.

The temperature of the emulsion polymerization may be suitably set depending on the kind of the radical polymerization initiator used, and is usually in the range of 0 to 100 ℃ and preferably in the range of 0 to 60 ℃. The polymerization method is either continuous polymerization or batch polymerization.

The polymerization reaction can be stopped by adding a polymerization inhibitor. Examples of the polymerization inhibitor include amine compounds such as isopropylhydroxylamine, diethylhydroxylamine and hydroxylamine; quinone compounds such as hydroquinone and benzoquinone; sodium nitrite, and the like.

After the polymerization reaction is stopped, an antioxidant may be added as needed. After the polymerization reaction is stopped, unreacted monomers are removed from the resulting latex as needed. Next, the unmodified conjugated diene polymer (B') is coagulated while adjusting the pH of the coagulation system to a predetermined value by using a salt such as sodium chloride, calcium chloride, or potassium chloride as a coagulant and adding an acid such as nitric acid or sulfuric acid as necessary. Thereafter, the polymer is recovered by separating the dispersion medium. Subsequently, the polymer (B ') was washed with water and dehydrated, and then dried to obtain an unmodified conjugated diene polymer (B'). In the coagulation, the latex and the extension oil as an emulsified dispersion are mixed in advance as necessary, and the mixture is recovered as an unmodified conjugated diene polymer (B') extended with oil.

As the solution polymerization method, a known method or a method based on the known method can be applied. For example, a monomer containing a conjugated diene is polymerized in a solvent using a ziegler-based catalyst, a metallocene-based catalyst, an anionically polymerizable active metal or an active metal compound in the presence of a polar compound as required.

Examples of the solvent include aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane, and isooctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; aromatic hydrocarbons such as benzene, toluene, and xylene.

Examples of the active metal capable of anionic polymerization include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanoid rare earth metals such as lanthanum and neodymium. Among the anionically polymerizable active metals, alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred.

The anionically polymerizable active metal compound is preferably an organic alkali metal compound. Examples of the organic alkali metal compound include organic monolithium compounds such as methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, hexyllithium, phenyllithium, and lithium stilbene; polyfunctional organic lithium compounds such as dilithiomethane, dilithinonaphthalene, 1, 4-dilithiobutane, 1, 4-dilithio-2-ethylcyclohexane, and 1,3, 5-trilithiobenzene; sodium naphthalene, potassium naphthalene, and the like. Among the organic alkali metal compounds, an organic lithium compound is preferable, and an organic monolithium compound is more preferable.

The amount of the organic alkali metal compound to be used may be appropriately set depending on the melt viscosity, molecular weight, and the like of the target unmodified conjugated diene polymer (B') and modified conjugated diene polymer (B), and is usually 0.01 to 3 parts by mass per 100 parts by mass of the total monomers including the conjugated diene.

The organic alkali metal compound may be used in the form of an organic alkali metal amide by reacting it with a secondary amine such as dibutylamine, dihexylamine, dibenzylamine, or the like.

The polar compound is generally used for adjusting the microstructure of the conjugated diene site without deactivating the reaction in anionic polymerization. Examples of the polar compound include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as tetramethylethylenediamine and trimethylamine; alkali metal alkoxides, phosphine compounds, and the like. The polar compound is usually used in an amount of 0.01 to 1000 mol based on the organic alkali metal compound.

The temperature of the solution polymerization is usually in the range of-80 to 150 ℃, preferably 0 to 100 ℃, and more preferably 10 to 90 ℃. The polymerization system may be either a batch system or a continuous system.

The polymerization reaction can be stopped by adding a polymerization inhibitor. Examples of the polymerization inhibitor include alcohols such as methanol and isopropanol. The obtained polymerization reaction liquid is poured into a poor solvent such as methanol to precipitate the unmodified conjugated diene polymer (B '), or the polymerization reaction liquid is washed with water and separated, and then dried, whereby the unmodified conjugated diene polymer (B') can be separated.

Among the above methods, the solution polymerization method is preferable as the method for producing the unmodified conjugated diene polymer (B').

The acid modification of the unmodified conjugated diene polymer (B ') can be carried out by a conventionally known method, and a method of adding an unsaturated carboxylic acid or an unsaturated carboxylic acid derivative to the unmodified conjugated diene polymer (B') is preferable.

Examples of the unsaturated carboxylic acid include maleic acid, fumaric acid, itaconic acid, and (meth) acrylic acid. Examples of the unsaturated carboxylic acid derivative include anhydrides, esters, amides, and imides of unsaturated carboxylic acids.

Among the unsaturated carboxylic acids and unsaturated carboxylic acid derivatives, maleic acid and derivatives thereof are preferable, and maleic anhydride is more preferable. That is, the acid-modified conjugated diene polymer is preferably a maleic anhydride-modified conjugated diene polymer. The acid-modified conjugated diene polymer itself is also a modified conjugated diene polymer (B) having a hydrophilic group such as a carboxyl group or an acid anhydride group.

The method for adding the unsaturated carboxylic acid or the unsaturated carboxylic acid derivative to the unmodified conjugated diene polymer (B ') is not particularly limited, and for example, a method of adding the unsaturated carboxylic acid or the unsaturated carboxylic acid derivative and, if necessary, a radical catalyst to the unmodified conjugated diene polymer (B') and heating the mixture in the presence or absence of an organic solvent can be employed. The acid-modified conjugated diene polymer may be modified with the compound (X) described below as it is, or may be modified after hydrogenation.

Examples of the compound (X) that reacts with the acid-modified conjugated diene polymer include compounds (alcohols or amines) having at least 1 hydroxyl group or amino group. By reacting the acid-modified conjugated diene polymer with such a compound (X), an ester group or an amide group is formed as a hydrophilic group in the conjugated diene polymer. The compound (X) is preferably a compound having 1 hydroxyl group or amino group and a hydrophilic group. Such suitable compounds also include compounds having more than 2 hydroxyl or amino groups. By reacting the acid-modified conjugated diene polymer with such a compound (X), an ester group or an amide group is formed as a hydrophilic group in the conjugated diene polymer, and a hydrophilic group further possessed by the compound (X) is introduced into the conjugated diene polymer.

The compound (X) is more preferably a compound having at least 1 hydroxyl group or amino group and having a repeating structure containing a nonionic polar group. More preferable compound (X) is a compound represented by the following formula (1). By using the compound represented by the following formula (1), a graft chain having a polyalkylene glycol structure, which is one form of a graft chain having a repeating structure containing a nonionic polar group as a hydrophilic group, can be introduced into the conjugated diene polymer.

[ solution 1]

In the formula (1), R¹Is hydroxyl or amino. R²、R³、R⁴And R⁵Each independently represents hydrogen or a hydrocarbon group having 1 to 6 carbon atoms. R⁶Is a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms or an acyl group having 1 to 6 carbon atoms. n is an integer of 3 to 600.

As R¹Preferably a hydroxyl group. R in the formula (1)²~R⁶And n may be suitably in the form of R in the above formula (A)²~R⁶And n are suitably in the same form.

Examples of the compound represented by the formula (1) include triethylene glycol, triethylene glycol monomethyl ether, polyethylene glycol monoalkyl ether, polyethylene glycol monoalkyl alkyl ether, polyethylene glycol monoalkyl alkenyl ether, polyethylene glycol monoalkyl ester, propylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether, methoxypolyethyleneglycol amine, and monoalkyl ether of a copolymer of propylene oxide and ethylene oxide.

The lower limit of the weight average molecular weight of the compound represented by formula (1) is, for example, 100, preferably 200, and more preferably 300. On the other hand, the upper limit of the weight average molecular weight is, for example, 10,000, more preferably 8,000, 6,000, 4,000, 2,000 or 1,000. The compound represented by the formula (1) may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The method for adding the compound (X) to the acid-modified conjugated diene polymer is not particularly limited, and the following method can be employed: the compound (X) is added to the acid-modified conjugated diene polymer, and if necessary, an amine catalyst is added, and heating is performed in the presence or absence of an organic solvent.

Examples of the amine catalyst include tertiary amines such as tetramethylethylenediamine, trimethylamine, and dimethylbenzylamine.

Examples of the organic solvent used in the above method generally include hydrocarbon solvents, halogenated hydrocarbon solvents, and the like. Among these organic solvents, hydrocarbon solvents such as n-butane, n-hexane, n-heptane, cyclohexane, benzene, toluene, and xylene are preferable.

When the reaction of the addition compound (X) is carried out by the above-mentioned method, an antioxidant may be added from the viewpoint of suppressing side reactions.

Examples of the antioxidant include 2, 6-di-tert-butyl-4-methylphenol (BHT), 2 ' -methylenebis (4-methyl-6-tert-butylphenol), 4 ' -thiobis (3-methyl-6-tert-butylphenol), 4 ' -butylidenebis (3-methyl-6-tert-butylphenol) (AO-40), 3, 9-bis [1, 1-dimethyl-2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy ] ethyl ] -2,4,8, 10-tetraoxaspiro [5.5] undecane (AO-80), 2, 4-bis [ (octylthio) methyl ] -6-methylphenol (Irganox1520L), 2, 4-bis [ (dodecylthio) methyl ] -6-methylphenol (Irganox1726), 2- [1- (2-hydroxy-3, 5-di-tert-pentylphenyl) ethyl ] -4, 6-di-tert-pentylphenyl acrylate (Sumilizer GS), 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenylacrylate (Sumilizer GM), 6-tert-butyl-4- [3- (2,4,8, 10-tetra-tert-butyldibenzo [ d, f ] [1,3,2] dioxaphosphepin-6-yloxy) propyl ] -2-methylphenol (Sumilizer GP), tris (2, 4-di-tert-butylphenyl) phosphite (Irgafos168), Dioctadecyl 3,3 '-dithiodipropionate, hydroquinone, p-methoxyphenol, N-phenyl-N' - (1, 3-dimethylbutyl) p-phenylenediamine (ノクラック 6C), bis (2,2,6, 6-tetramethyl-4-piperidyl) sebacate (LA-77Y), N-dioctadecylhydroxylamine (Irgastab FS 042), bis (4-tert-octylphenyl) amine (Irganox5057), and the like. The antioxidant can be used alone in 1 kind, or in combination with 2 or more kinds.

The amount of the antioxidant to be added is preferably 0 to 10 parts by mass, more preferably 0 to 5 parts by mass, based on 100 parts by mass of the unmodified conjugated diene polymer (B').

The reaction conditions of the acid-modified conjugated diene polymer and the compound (X) are not particularly limited, and the reaction temperature is, for example, preferably 10 to 200 ℃ and more preferably 30 to 180 ℃. In addition, the reaction time is preferably 1 to 200 hours, more preferably 1 to 100 hours, and further preferably 1 to 50 hours.

The total amount of the unsaturated carboxylic acid, the unsaturated carboxylic acid derivative and the compound (X) added in the modified conjugated diene polymer (B) is preferably 1 to 400 parts by mass, more preferably 20 to 300 parts by mass, and still more preferably 50 to 250 parts by mass, based on 100 parts by mass of the unmodified conjugated diene polymer (B'). The amount of addition can be determined using various analytical instruments such as nuclear magnetic resonance spectroscopy.

The modified conjugated diene polymer (B) can be synthesized, for example, by a method described in international publication No. 2010/038835, japanese patent application laid-open No. 2015-086283, and the like, in addition to the above-described synthesis method.

[ plasticizer ]

The PVA film may further comprise a plasticizer. By including a plasticizer in the PVA film, the stretch processability, handling properties, roll quality, and the like can be improved. Examples of the preferred plasticizer include polyhydric alcohols, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. These plasticizers may be used in an amount of 1 or 2 or more. Among these, glycerin is preferable from the viewpoint of the effect of improving the stretch processability and the roll quality.

The lower limit of the content of the plasticizer in the PVA film is preferably 1 part by mass, and more preferably 5 parts by mass, based on 100 parts by mass of PVA (a). When the content of the plasticizer is not less than the lower limit, the processing stretchability and the like are further improved. On the other hand, the upper limit of the content is preferably 20 parts by mass, and more preferably 15 parts by mass. When the content of the plasticizer is not more than the upper limit, it is possible to suppress deterioration of handleability due to excessive softening of the PVA film or bleeding of the plasticizer to the surface.

[ other additives, etc. ]

The PVA film may further contain, as necessary, other additives such as a filler, a processing stabilizer such as a copper compound, a weather resistance stabilizer, a coloring agent, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, another thermoplastic resin, a lubricant, a fragrance, an antifoaming agent, a deodorizing agent, an extender, a releasing agent, a reinforcing agent, a crosslinking agent, a mold inhibitor, a preservative, a crystallization rate retarder, and a surfactant.

Among other additives, a surfactant is preferably contained from the viewpoint of film-forming properties and the like. By including the surfactant, the PVA film is prevented from being uneven in thickness, or the film is easily peeled from a substrate such as a metal roll or a belt used for film formation. The type of the surfactant is not particularly limited, but from the viewpoint of releasability from a metal roll or a belt, an anionic surfactant and a nonionic surfactant are preferable.

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

The nonionic surfactant is preferably an alkyl ether type such as polyoxyethylene oleyl ether; alkylphenyl ether type such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkylamine type such as polyoxyethylene lauryl amino ether; alkylamide types such as polyoxyethylene laurylamide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; and an allylphenyl ether type such as polyoxyalkylene allylphenyl ether.

These surfactants may be used alone in 1 kind, or in combination of 2 or more kinds.

When the PVA film contains a surfactant, the lower limit of the content thereof is preferably 0.01 part by mass, and more preferably 0.03 part by mass, based on 100 parts by mass of PVA (a). When the content of the surfactant is not less than the lower limit, the releasability, film-forming property, and the like are further improved. On the other hand, the upper limit of the content is preferably 0.5 parts by mass, and more preferably 0.3 parts by mass. When the content of the surfactant is not more than the upper limit, the surfactant can be prevented from bleeding out to the surface of the PVA film, the films can be closely adhered to each other, and the handleability can be prevented from being lowered.

The upper limit of the content of the other additives other than PVA (a), the modified conjugated diene polymer (B), the plasticizer, and the surfactant in the PVA film may be preferably 10% by mass, more preferably 5% by mass, still more preferably 1% by mass, and still more preferably 0.2% by mass. When the content of the other additives exceeds the above upper limit, the processing stretchability of the PVA film, the moldability and transparency of the resulting stretched film and polarizing film, and the like may be affected.

[ shape, etc. ]

The shape of the PVA film is not particularly limited, and a long film is preferable because continuous production can be performed with good productivity. The length of the long PVA film is not particularly limited, and may be appropriately set according to the application and the like. For example, the length may be set to be in the range of 5m or more and 20,000m or less. The width of the PVA film is not particularly limited, and for example, in the case of a water-soluble film, the lower limit may be 1 cm. In addition, in various applications, since a wide PVA film is demanded in recent years, the lower limit is preferably 1m, more preferably 2m, and still more preferably 4 m. The upper limit of the width of the PVA film is not particularly limited, and may be 7m, for example. If the width is too wide, uniform production tends to be difficult when a PVA film is produced by a practical apparatus.

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, and is, for example, 100. mu.m, preferably 60 μm, and more preferably 40 μm. On the other hand, the lower limit of the thickness is preferably 1 μm, more preferably 5 μm, and still more preferably 10 μm. By setting the thickness of the PVA film to the above range, handleability, stretch processability, and the like can be improved. The thickness (average thickness) is an average of measured values at arbitrary 5 points.

[ use ]

The PVA film can be used for various applications similar to conventional PVA films, such as packaging films, water-soluble films, agricultural films, release films, and optical films. Further, the PVA film is suitable as a raw material film for a stretched film and a polarizing film. In particular, the PVA film is excellent in stretch processability and can give a stretched film and a polarizing film excellent in moldability, and therefore, is suitable as a material film to be used as an optical film material. That is, an optical film can be suitably obtained by stretching the PVA film. The PVA film according to one embodiment of the present invention may be a packaging film, a water-soluble film, an agricultural film, a release film, a stretch film, an optical film, or a polarizing film.

The optical film is a film having light transmittance used in an optical device. As a typical example of the optical device, a liquid crystal display device, a display device such as an organic EL display, or the like is given. Examples of the optical film include a polarizing film, a polarizer protective film, a color compensation film, a brightness enhancement film, a viewing angle expansion film, and a retardation film. In addition, the PVA film utilizes its excellent transparency and gas barrier property, and can be used as a gas barrier film for an organic EL display or the like as another example of an optical film.

The PVA film can be suitably used as a raw material film for a stretched film and a polarizing film as described above, or can be used for various applications without being stretched.

< method for producing PVA film >

The method for producing the PVA film is not particularly limited, and a production method in which the thickness and width of the PVA film after film formation are more uniform can be preferably employed. For example, the PVA (a) and the modified conjugated diene polymer (B) constituting the PVA film, and other components such as a plasticizer, which are further contained as necessary, are dissolved in a liquid medium to form a film, thereby obtaining a film. Further, if necessary, the film can be produced using a film-forming stock solution in which pva (a) or the like is melted.

A method for manufacturing a PVA film according to an embodiment of the present invention includes: and a step of forming a film using a film-forming dope obtained by mixing PVA (A) with a dispersion liquid containing a modified conjugated diene polymer (B) having a hydrophilic group. According to this production method, a PVA film excellent in stretch processability and productivity can be produced, and a stretched film and a polarizing film excellent in moldability can be obtained from the PVA film.

The specific forms and suitable forms of the PVA (a) and the modified conjugated diene polymer (B) used in this production method are the same as those of the PVA (a) and the modified conjugated diene polymer (B) which are components of the PVA film according to one embodiment of the present invention.

The lower limit of the content of the modified conjugated diene polymer (B) in the film-forming stock solution may be, for example, 5 parts by mass, preferably 10 parts by mass, more preferably 15 parts by mass, and still more preferably 20 parts by mass, 25 parts by mass, 30 parts by mass, or 35 parts by mass, based on 100 parts by mass of the pva (a). On the other hand, the upper limit of the content may be, for example, 100 parts by mass, and may be preferably 80 parts by mass, more preferably 60 parts by mass, and further preferably 40 parts by mass, 30 parts by mass or 20 parts by mass.

In the film-forming dope, the modified conjugated diene polymer (B) is preferably uniformly mixed. By mixing the dispersion of the modified conjugated diene polymer (B) with a liquid medium, pva (a), other additives, and the like, a film-forming raw solution in which the modified conjugated diene polymer (B) is uniformly mixed can be efficiently obtained. Further, when the film-forming raw solution contains a plasticizer, other additives, and the like, it is preferable that these components are uniformly mixed.

The method for producing the dispersion of the modified conjugated diene polymer (B) is not particularly limited, and can be obtained, for example, by synthesizing the modified conjugated diene polymer (B), adding water, and stirring with an emulsifier, a stirrer, or the like. In this case, the average particle diameter of the modified conjugated diene polymer (B) can be adjusted by adjusting the stirring intensity, the stirring time, the pH by an acid or a base, or selecting an emulsifier.

The acid or base used for producing the dispersion liquid of the modified conjugated diene polymer (B) is not particularly limited, and examples of the acid include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, citric acid, carbonic acid, and acetic acid, and examples of the base include sodium hydroxide, potassium hydroxide, and ammonia.

The emulsifier used in the production of the dispersion of the modified conjugated diene polymer (B) is not particularly limited, and any conventional emulsifier such as an anionic emulsifier, a nonionic emulsifier, and a nonionic-anionic emulsifier can be used. Specific examples of the emulsifier include anionic emulsifiers such as sodium salt, potassium salt or ammonium salt of aliphatic carboxylic acid such as laurate, myristate, palmitate, stearate and alkenylsuccinate; sodium salt, potassium salt or ammonium salt of disproportionated or hydrogenated natural rosin; sodium salt, potassium salt, ammonium salt of aliphatic sulfate compound such as lauryl sulfate, etc. Examples of the nonionic-anionic emulsifier include polyoxyethylene octylphenyl ether sulfonate, polyoxyethylene octylphenyl ether sulfate, and polyoxyethylene alkyl ether sulfate. Examples of the counter cation of these salts include sodium, potassium, and ammonium.

Examples of the liquid medium used in the film-forming solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine. These liquid media may be used in 1 kind or 2 or more kinds. Among these, water is preferable from the viewpoint of a small load on the environment and recyclability.

The evaporation fraction of the film-forming dope (the content ratio of volatile components such as a liquid medium that are removed by evaporation or evaporation during film formation) varies depending on the film-forming method, the film-forming conditions, and the like, and generally, the lower limit is preferably 50 mass%, more preferably 55 mass%, and still more preferably 60 mass%. By setting the volatility fraction of the film-forming dope to the above lower limit or more, the viscosity of the film-forming dope is not excessively high, filtration and deaeration in the preparation of the film-forming dope can be smoothly performed, and a PVA film having few foreign matters and defects can be easily produced. On the other hand, the upper limit of the volatile fraction is preferably 95% by mass, and more preferably 90% by mass. By setting the volatile fraction of the film-forming dope to the upper limit or less, the concentration of the film-forming dope is not excessively low, and thus the PVA film can be easily industrially produced.

As a film forming method in the case of producing a PVA film using the film forming dope, a conventionally known method can be used. As the film forming method, a method of coating a film forming dope on a substrate such as a metal drum to produce a PVA film on the substrate, or a method of directly producing a single layer PVA film may be used. Examples of the film-forming method include a casting film-forming method, an extrusion film-forming method, a wet film-forming method, a gel film-forming method, and the like, and only 1 kind of these film-forming methods may be used, or 2 or more kinds may be used in combination. Among these film forming methods, a casting film forming method and an extrusion film forming method are preferable in that a PVA film having a uniform thickness and width and excellent physical properties can be obtained.

Here, according to the method for producing a PVA film of one embodiment of the present invention, since the modified conjugated diene polymer (B) added to the film formation stock solution has a hydrophilic group, the modified conjugated diene polymer (B) is less likely to adhere to a substrate such as a metal drum. In addition, even when the adhesive has adhered to the surface, the adhesive can be easily washed away with water or the like. Therefore, according to this production method, a PVA film having high productivity and excellent stretch processability can be produced.

The PVA film produced may be heat-treated as necessary. The heat treatment temperature is not particularly limited as long as it is appropriately adjusted. When the heat treatment temperature is too high, the PVA film is discolored and deteriorated. Therefore, the upper limit of the heat treatment temperature is preferably 210 ℃, more preferably 180 ℃, and still more preferably 150 ℃. On the other hand, the lower limit of the heat treatment temperature is, for example, 60 ℃ and preferably 90 ℃.

The heat treatment time is not particularly limited, and may be appropriately adjusted, and from the viewpoint of efficiently producing a PVA film, the upper limit is preferably 30 minutes, and more preferably 15 minutes. On the other hand, the lower limit thereof is, for example, preferably 10 seconds, and more preferably 1 minute.

< stretched film >

The stretched film according to an embodiment of the present invention is a stretched film obtained by stretching the PVA film according to the above-described embodiment of the present invention. In this stretched film, PVA is generally oriented in a predetermined direction (stretching direction). The stretched film may be uniaxially stretched or biaxially stretched, preferably uniaxially stretched. The stretched film uniaxially stretched can be suitably used as an optical film such as a polarizing film. The stretched film may be a single-layer film or a multilayer film, and is preferably a single-layer film. The stretched film is less likely to cause problems such as chipping due to deformation by containing the modified conjugated diene polymer (B), and therefore, is suitable for a foldable display, a sunglass with high design, and the like.

The upper limit of the thickness (average thickness) of the stretched film is, for example, 30 μm, and preferably 16 μm. By setting the thickness of the stretched film to the upper limit or less, sufficient thinning can be achieved. On the other hand, the lower limit of the thickness is preferably 5 μm, and more preferably 8 μm. When the thickness of the stretched film is not less than the lower limit, the film is less likely to be broken, and the handling property and the like 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, etc., and is preferably used as an optical film.

The optical film includes a polarizing film, a polarizer protective film, a color compensation film, a brightness enhancement film, and the like, and among these, a polarizing film is preferable.

< method for producing stretched film >

The stretched film can be obtained by the above-described production method including the step of stretching the PVA film. That is, the stretched film can be produced by the same method as the conventional method except that the PVA film is used, and the stretched film is optionally produced except that the PVA film is used. Therefore, the stretched film may not include a treatment (dyeing treatment, fixing treatment, or the like) other than the stretching treatment in the polarizing film production step described later. That is, according to this production method, a stretched film can be relatively easily obtained without going through a special step.

The PVA film or the stretched film is subjected to dyeing processing or the like, thereby providing a polarizing film having excellent moldability.

< polarizing film >

The polarizing film according to an embodiment of the present invention is obtained by dyeing or the like the PVA film or the stretched film according to the above-described embodiment of the present invention. In the polarizing film, a dichroic dye or boric acid is adsorbed on the PVA film or the stretched film. Since the polarizing film is less likely to cause problems such as chipping due to deformation by containing the modified conjugated diene polymer (B), the polarizing film is suitable for a foldable display, a sunglass having high design properties, and the like.

The polarizing film may be used by laminating an optically transparent protective film having mechanical strength on both or one side thereof to form a polarizing plate. As the protective film, a cellulose Triacetate (TAC) film, a Cellulose Acetate Butyrate (CAB) film, an acrylic film, a polyester film, or the like can be used. The adhesive used for bonding may be a PVA adhesive, an ultraviolet-curable adhesive, or the like, and is preferably a PVA adhesive.

The polarizing plate obtained in the above manner may further be bonded with an optical film such as a retardation film, a viewing angle improving film, or a brightness enhancing film. The stretched film according to an embodiment of the present invention may be used as the viewing angle improving film. The polarizing plate may be used as a member of a liquid crystal display device by coating an adhesive such as an acrylic adhesive and then bonding the resultant to a glass substrate.

< method for producing polarizing film >

Specific methods for producing the polarizing film include: the PVA film is subjected to swelling treatment, dyeing treatment, uniaxial stretching treatment, and further subjected to crosslinking treatment, fixing treatment, washing treatment, drying treatment, heat treatment, and the like as necessary. In this case, the order of the respective treatments such as the swelling treatment, the dyeing treatment, the crosslinking treatment, the uniaxial stretching, and the fixing treatment is not particularly limited, and two or more kinds of treatments may be simultaneously performed. Further, 1 or 2 or more of each treatment may be performed 2 times or 2 or more times.

In addition, as another method for producing the polarizing film, a method of subjecting the stretched film to various treatments other than the swelling treatment may be mentioned. That is, the polarizing film can also be obtained by subjecting the stretched film to dyeing treatment, uniaxial stretching treatment, and further, if necessary, crosslinking treatment, fixing treatment, washing treatment, drying treatment, heat treatment, and the like. In this case, the order of the respective treatments such as dyeing treatment, crosslinking treatment, uniaxial stretching, fixing treatment and the like is not particularly limited, and two or more kinds of treatments may be simultaneously performed. Further, 1 or 2 or more of each treatment may be performed 2 times or 2 or more times.

Among these methods for producing a polarizing film, a method having the following steps is particularly preferred: the PVA film is subjected to swelling treatment, dyeing treatment, uniaxial stretching treatment, and further subjected to crosslinking treatment, fixing treatment, washing treatment, drying treatment, heat treatment, and the like as necessary, and then uniaxially stretched by a dry stretching method.

Hereinafter, the polarizing film is produced using the PVA film in detail, but the conditions of the respective processes such as the dyeing process described later are also the same in the case of the production using the stretched film.

The swelling treatment may be performed by immersing the PVA film in water. The lower limit of the water temperature when immersed in water is preferably 20 ℃, more preferably 22 ℃, and still more preferably 25 ℃. On the other hand, the upper limit of the temperature is preferably 55 ℃, more preferably 40 ℃, and still more preferably 35 ℃. The lower limit of the time for immersing in water is preferably 0.1 minute, and more preferably 0.5 minute. On the other hand, the upper limit of the time is preferably 5 minutes, and more preferably 3 minutes. The water to be immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

The dyeing treatment may be performed by contacting a dichroic dye with the PVA film. As the dichroic dye, an iodine-based dye or a dichroic dye is generally used.

In the case of an iodine-based dye, the dyeing treatment may be performed at any stage of before the uniaxial stretching treatment, during the uniaxial stretching treatment, or after the uniaxial stretching treatment. The dyeing treatment is generally performed by immersing the PVA film in a solution (particularly, an aqueous solution) containing iodine-potassium iodide as a dyeing bath. The iodine concentration in the dyeing bath is preferably 0.01 mass% or more and 0.5 mass% or less, and the potassium iodide concentration is preferably 0.01 mass% or more and 10 mass% or less. Further, the lower limit of the temperature of the dyeing bath is preferably 20 ℃, more preferably 25 ℃. On the other hand, the upper limit of the temperature is preferably 50 ℃ and more preferably 40 ℃.

In the case of the dichroic dye, the dyeing process may be performed at any stage of the PVA film production, before the uniaxial stretching process, during the uniaxial stretching process, or after the uniaxial stretching process. In the dyeing treatment, a dichroic dye, such as an azo compound, is adsorbed and impregnated to a product obtained by subjecting a PVA film to a swelling treatment. When the swelling treatment is omitted, the swelling treatment may be performed simultaneously in the dyeing treatment.

The azo compound may be used in the form of a free acid, or a salt thereof. Examples of such salts include alkali metal salts such as lithium salts, sodium salts and potassium salts, and organic salts such as ammonium salts and alkylamine salts, and sodium salts are preferred.

The dyeing treatment is generally performed by immersing the PVA film in a solution (particularly, 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 mass% or more and 10 mass% or less. In addition, the temperature of the dyeing bath is preferably 5-60 ℃, more preferably 20-50 ℃, and particularly preferably 35-50 ℃. The time for immersing in the solution can be suitably adjusted, preferably to 30 seconds to 20 minutes, and more preferably to 1 to 10 minutes.

The dyeing solution may contain a dyeing assistant in addition to the azo compound, if necessary. Examples of the dyeing assistant include sodium carbonate, sodium bicarbonate, sodium chloride, sodium sulfate, anhydrous sodium sulfate, and sodium tripolyphosphate. The content of the dyeing auxiliary can be adjusted at any concentration according to the time and temperature based on the dyeing property of the dye, and the respective content is preferably 0.01 to 5% by mass, more preferably 0.1 to 2% by mass in the dyeing solution.

The PVA film is crosslinked, whereby dissolution of PVA into water during wet stretching at high temperature can be effectively prevented. From this viewpoint, it is preferable to perform the crosslinking treatment before the uniaxial stretching treatment. The crosslinking treatment may be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent. As the crosslinking agent, 1 or 2 or more kinds of boron inorganic compounds such as boric acid and boric acid salt such as borax can be used. The lower limit of the concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably 1% by mass, more preferably 2% by mass, and still more preferably 3% by mass. On the other hand, the upper limit of the concentration is preferably 15% by mass, more preferably 7% by mass, and still more preferably 6% by mass. By setting the concentration of the crosslinking agent within the above range, sufficient stretchability can be maintained. When an iodine-based dye is used, the aqueous solution containing the crosslinking agent may contain an auxiliary agent such as potassium iodide. The lower temperature limit of the aqueous solution containing the crosslinking agent is preferably 20 ℃ and more preferably 25 ℃. On the other hand, the upper limit of the temperature is preferably 50 ℃ and more preferably 40 ℃. When the temperature is within the above range, crosslinking can be efficiently performed.

The uniaxial stretching treatment may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, the stretching may be performed in an aqueous boric acid solution, or may be performed in the above-mentioned dyeing bath or in a fixing treatment bath described later. In the case of the dry stretching method, the uniaxial stretching treatment may be performed directly at room temperature, or may be performed while heating, or may be performed in air using a PVA film after water absorption. Among these, wet stretching is preferable, and uniaxial stretching treatment in an aqueous solution of boric acid is more preferable. The lower limit of the boric acid concentration of the aqueous boric acid solution is preferably 0.5% by mass, more preferably 1.0% by mass, and still more preferably 1.5% by mass. On the other hand, the upper limit of the boric acid concentration is preferably 6 mass%, more preferably 5 mass%. When the aqueous boric acid solution is an iodine-based dye, potassium iodide may be contained, and the concentration thereof is preferably 0.01 mass% or more and 10 mass% or less.

The lower limit of the stretching ratio in the uniaxial stretching treatment is preferably 3 times, more preferably 5 times, from the viewpoint of the polarizing performance of the obtained polarizing film. The upper limit of the stretch ratio is not particularly limited, and for example, it may be 10 times, more preferably 8 times.

In order to strongly adsorb a dichroic dye (iodine dye or the like) to a PVA film in the production of a polarizing film, it is preferable to perform a fixing treatment after a uniaxial stretching treatment. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing 1 or 2 or more kinds of boron inorganic compounds such as boric acid and borax may be used. Further, an iodine compound or a metal compound may be added to the fixing treatment bath as needed. The lower limit of the concentration of the boron inorganic compound in the fixing treatment bath is preferably 0.5 mass%, and more preferably 1 mass%. On the other hand, the upper limit of the concentration is preferably 15% by mass, and more preferably 10% by mass. When the concentration is within the above range, the dichroic dye can be more strongly adsorbed. The lower limit of the temperature of the fixed treatment bath is preferably 15 ℃. On the other hand, the upper limit of the temperature is preferably 60 ℃ and more preferably 40 ℃.

The cleaning treatment is generally performed by immersing the PVA film in water or the like. In the case of an iodine-based dye, water or the like used in the cleaning treatment preferably contains an auxiliary agent such as potassium iodide from the viewpoint of improving the polarization performance. In this case, the concentration of an iodide such as potassium iodide is preferably 0.5 mass% or more and 10 mass% or less. The lower limit of the temperature of water or the like used in the cleaning treatment is generally 5 ℃, preferably 10 ℃, and more preferably 15 ℃. On the other hand, the upper limit of the temperature is generally 50 ℃, preferably 45 ℃, and more preferably 40 ℃. From the viewpoint of economy, it is not preferable that 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 degraded.

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

By performing the heat treatment after the drying treatment, a polarizing film having excellent dimensional stability can be obtained. Here, the heat treatment means: and (3) a process of further heating the polarizing film having a moisture content of 5% or less after the drying process to improve the dimensional stability of the polarizing film. The heat treatment conditions are not particularly limited, but heat treatment is preferably performed in the range of 60 ℃ to 150 ℃. By performing the heat treatment at 60 ℃ or higher, the effect of the dimensional stabilization by the heat treatment can be improved. On the other hand, yellowing of the polarizing film can be suppressed by performing heat treatment at 150 ℃ or lower.

The polarizing film is not limited to a two-dimensional shape (planar shape), and includes a polarizing film processed into a three-dimensional shape. That is, the polarizing film may be subjected to shaping such as stretching after dyeing. As a method for stretching the dyed film, various methods such as wet stretching, vacuum forming, and thermoforming may be used, but the method is not limited thereto. The stretch ratio is preferably 1.2 to 2 times, and more preferably 1.3 to 1.5 times, from the viewpoint of maintaining the performance. The stretching speed is preferably 100 to 10000%/minute, and more preferably 500 to 5000%/minute, from the viewpoint of productivity. The stretching temperature is preferably 100 ℃ or lower when an iodine-based dye is used, and preferably 160 ℃ or lower when a dichroic dye is used. In the case of iodine-based dyes, the molding at 100 ℃ or lower can suppress discoloration and breakage during stretching.

Examples

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples at all. The evaluation methods used in the following examples and comparative examples are as follows.

[ method for measuring weight average molecular weight of modified conjugated diene Polymer ]

The weight average molecular weight of the modified conjugated diene polymer was determined by GPC (gel permeation chromatography) using a molecular weight equivalent to standard polystyrene.

The measurement apparatus and conditions are as follows.

The device comprises the following steps: GPC apparatus "GPC 8020" manufactured by Tosoh corporation "

Separating the column: "TSKgelG 4000 HXL" manufactured by Tosoh corporation "

A detector: RI-8020 manufactured by Tosoh corporation "

Eluent: tetrahydrofuran (THF)

Eluent flow rate: 1.0 ml/min

Sample concentration: 5mg/10ml

Column temperature: at 40 ℃.

[ stretch processability (tensile stress) of PVA film ]

A PVA film was subjected to humidity conditioning at 23 ℃ and 50% RH for 24 hours, and a sheet having a length direction of 30mm and a width direction of 10mm was cut out from the PVA film. Thereafter, the PVA film was mounted on a tensile testing apparatus (model: 5952) manufactured by インストロン so that the initial jig interval became 10mm, and the film thickness was 100 mm/min]The tensile test was carried out at a speed of (1). Test force N when the distance between the clamps at this time reached 30mm]Divided by the cross-sectional area of the material before drawing [ mm ]²]The value obtained was taken as the tensile stress [ N/mm ]²]. At this time, the same measurement was repeated 10 times for 1 sample, and the average value was used as data. Tensile stress of less than 50N/mm²In the case of the above, it was judged that the stretching was easy and the stretch processability was good.

[ cleaning Properties (productivity) of conjugated diene Polymer adhered to Metal Drum when producing PVA film ]

In the production of the PVA film, the cleaning property test was performed because the conjugated diene polymer present on the surface of the PVA film adheres to the metal drum. Specifically, after the PVA film was produced, the metal drum was wiped with cotton cloth wetted with water. Thereafter, it was visually checked whether or not the conjugated diene polymer remained on the surface of the metal drum, and when it remained, it was denoted as B, and when it remained, it was denoted as A.

[ formability of polarizing film (TD fracture deformation) ]

A polarizing film was subjected to humidity conditioning at 23 ℃ and 50% RH for 24 hours or more, and a film piece having a longitudinal direction (MD) of 10mm and a width direction (TD) of 30mm was cut out from the polarizing film. Thereafter, the polarizing film sheet was mounted on a tensile test apparatus ("オートグラフ (AGS-H)") manufactured by shimadzu so that the initial jig interval was 10mm and the tensile direction was consistent with the TD of the polarizing film, and a tensile test was performed at a speed of 100[ mm/min ] (1000%/min) in a heating environment at 140 ℃. At this time, the same measurement was repeated 10 times for 1 sample, and the value having the largest TD fracture deformation was used as data. When the TD fracture deformation was 40% or more, it was judged that the molding was easy and the moldability was good. Here, TD fracture set means: in the above tensile test, the value of (X/10) × 100(%) at which the polarizing film elongates by Xmm from the initial inter-jig distance (10mm) and breaks occurs.

Production example 1

(1) Synthesis of conjugated diene Polymer (B' -1)

A sufficiently dried 5L autoclave was purged with nitrogen, 1200g of hexane and 112g of sec-butyllithium (10.5 mass% hexane solution) were charged, and the temperature was raised to 50 ℃. Then, 1200g of isoprene was gradually added while controlling the polymerization temperature to 50 ℃ under stirring, and polymerization was carried out for 1 hour. Thereafter, methanol was added to stop the polymerization reaction, thereby obtaining a polymer solution. To the resulting polymer solution was added water, followed by stirring, and washing the polymer solution with water. After completion of the stirring, it was confirmed that the polymer solution phase and the aqueous phase had separated, and water was drained. The polymer solution after completion of the washing was dried under vacuum at 70 ℃ for 24 hours to obtain a conjugated diene polymer (B' -1).

(2) Synthesis of aqueous Dispersion of conjugated diene Polymer (B' -1)

15g of an emulsifier (フォスファノール RS-710, manufactured by Toho chemical industries Co., Ltd.) was added to 250g of the conjugated diene polymer (B' -1), and the mixture was stirred for 20 minutes. Next, 177g of water was added little by little with stirring. After a predetermined amount of water was added, the mixture was stirred for 20 minutes to obtain an aqueous dispersion of the conjugated diene polymer (B' -1).

Production example 2

(1) Synthesis of modified conjugated diene Polymer (B-1) having hydrophilic group

200g of the conjugated diene polymer (B' -1) obtained in production example 1 and 40g of maleic anhydride were charged into a reaction vessel, and the mixture was reacted at 170 ℃ for 24 hours. Further, 408g of polyethylene glycol monomethyl ether (polyethylene glycol monomethyl ether 1000, average molecular weight: 1,000, average number of polyoxyethylene units: 22, manufactured by Tokyo chemical industry Co., Ltd.) and 0.7g of N, N-dimethylbenzylamine were charged and reacted for 6 hours to obtain a modified conjugated diene polymer (B-1) having a hydrophilic group. The weight-average molecular weight of the modified conjugated diene polymer (B-1) was 27,000.

(2) Synthesis of aqueous Dispersion of modified conjugated diene Polymer (B-1)

To 250g of the modified conjugated diene polymer (B-1), 13g of an aqueous sodium hydroxide solution (sodium hydroxide concentration: 50% by mass) was added, and the mixture was stirred at 50 ℃ for 60 minutes, followed by adding 451g of water little by little while stirring, thereby obtaining an aqueous dispersion of the modified conjugated diene polymer (B-1).

Production example 3

(1) Synthesis of modified conjugated diene Polymer (B-2) having hydrophilic group

250g of the conjugated diene polymer (B' -1) obtained in production example 1 and 50g of maleic anhydride were charged into a reaction vessel, and the mixture was reacted at 170 ℃ for 24 hours. Further, 204g of polyethylene glycol monomethyl ether (polyethylene glycol monomethyl ether 400, average molecular weight: 400, average number of polyoxyethylene units: 8, manufactured by Tokyo chemical industry Co., Ltd.) and 0.9g of N, N-dimethylbenzylamine were charged and reacted for 6 hours to obtain a modified liquid diene polymer (B-2) having a hydrophilic group. The weight-average molecular weight of the modified conjugated diene polymer (B-2) was 18,000.

(2) Preparation of aqueous Dispersion of modified conjugated diene Polymer (B-2)

To 250g of the modified conjugated diene polymer (B-2) was added 20g of an aqueous sodium hydroxide solution (sodium hydroxide concentration: 50% by mass), followed by stirring at 50 ℃ for 60 minutes and then adding 443g of water little by little while stirring to obtain an aqueous dispersion of the modified conjugated diene polymer (B-2).

[ example 1]

(preparation of PVA film)

100 parts by mass of PVA (saponified product of vinyl acetate homopolymer, having a polymerization degree of 2,400 and a saponification degree of 99.5 mol%), 15 parts by mass of modified conjugated diene polymer (B-1), 10 parts by mass of glycerin as a plasticizer, 0.1 part by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and water were mixed to prepare a film-forming dope having a volatile fraction of 85 mass%. The modified conjugated diene polymer (B-1) was obtained by mixing the aqueous dispersion obtained in production example 2 with other components. The film-forming dope was cast on a metal drum having a surface temperature of 80 ℃ and dried until the volatile fraction (water content) reached 5 mass%, to obtain a long PVA film (PVA film before heat treatment) having a thickness of 30 μm, a length of 1.5m and a width of 30 cm. The PVA film was subjected to a heat treatment at a temperature of 110 ℃ for 10 minutes to obtain a PVA film of example 1.

(preparation of polarizing film)

A sample having a width of 5cm × a length of 10cm was cut out from the widthwise central portion of the obtained PVA film so as to be uniaxially stretched in a range of 5cm × 5 cm. The sample was immersed in pure water at 40 ℃ for 120 seconds while uniaxially stretched 1.3 times in the longitudinal direction, and subjected to a swelling treatment (first stage uniaxial stretching). Subsequently, the resultant was immersed in a dyeing treatment bath (temperature 48 ℃) containing an aqueous solution containing 0.00002 mass% of Direct blue15 dye, 0.1 mass% of sodium tripolyphosphate, and 0.1 mass% of sodium sulfate for 300 seconds, and the whole was uniaxially stretched 2.4 times in the longitudinal direction to adsorb the dye (uniaxial stretching in the second stage). Further, the whole was immersed in a crosslinking treatment bath (temperature 40 ℃) containing an aqueous solution containing 2 mass% of boric acid for 60 seconds, and uniaxially stretched 2.7 times in the longitudinal direction to adsorb boric acid (uniaxial stretching in the third stage). Then, the film was immersed in a stretching treatment bath (temperature 58 ℃) containing an aqueous solution containing 3.9 mass% of boric acid, and was uniaxially stretched in the longitudinal direction to 4.0 times the length of the original film to be oriented (uniaxial stretching in the fourth stage). Immediately after stretching, the sheet was immersed in a water bath (temperature 25 ℃ C.) as a cleaning bath for 5 seconds. Finally, it was dried at 70 ℃ for 3 minutes to obtain a polarizing film of example 1.

[ example 2]

A PVA film and a polarizing film were obtained in the same manner as in example 1 except that 30 parts by mass of the modified conjugated diene polymer (B-1) was added to the PVA film.

[ example 3]

A PVA film and a polarizing film were obtained in the same manner as in example 1, except that 45 parts by mass of the modified conjugated diene polymer (B-1) was added to the PVA film.

[ example 4]

A PVA film and a polarizing film were obtained in the same manner as in example 3, except that the modified conjugated diene polymer (B-1) was changed to the modified conjugated diene polymer (B-2) in the production of the PVA film.

Comparative example 1

A PVA film and a polarizing film were obtained in the same manner as in example 1, except that the modified conjugated diene polymer (B-1) was not added to the PVA film.

Comparative example 2

A PVA film and a polarizing film were obtained in the same manner as in example 1 except that the modified conjugated diene polymer (B-1) was changed to the unmodified conjugated diene polymer (B' -1) in the production of the PVA film.

The PVA films obtained in the examples and comparative examples were evaluated for their stretch processability, the cleaning property (productivity) of a metal drum adhered to the PVA film during production thereof, and the formability of a polarizing film by the above methods. The evaluation results are shown in table 1. In comparative example 1, since the conjugated diene polymer was not added to the film forming stock solution of the PVA film, the cleaning property (productivity) was not evaluated. In comparative example 2, the evaluation of the cleaning property (productivity) was not carried out because the conjugated diene polymer remained in the metal bowl.

As shown in Table 1, the PVA films obtained in examples 1 to 4 had low tensile stress and excellent stretch processability. In examples 1 to 4, the conjugated diene polymer adhered to the metal drum during production of the PVA film was easily removed by washing, and the washing property was excellent. That is, it can be said that: the PVA films of examples 1 to 4 can shorten the cleaning time of the metal drum and are excellent in productivity. Further, the polarizing films obtained in examples 1 to 4 had a large TD fracture shape, and were less likely to be broken during molding. That is, the polarizing films obtained in examples 1 to 4 were excellent in moldability.

On the other hand, in comparative example 1 in which no conjugated diene polymer was added, the obtained PVA film had low stretch processability and the obtained polarizing film had poor moldability. In comparative example 2 in which an unmodified conjugated diene polymer was added, the conjugated diene polymer adhering to the metal drum during production of the PVA film could not be easily removed by washing, and the washing performance was poor. That is, it can be said that: the PVA film of comparative example 2 takes time in cleaning the metal drum, and thus productivity is low.

Industrial applicability

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

Claims

1. A polyvinyl alcohol film comprising polyvinyl alcohol (A) and a modified conjugated diene-based polymer (B) having a hydrophilic group.

2 . The polyvinyl alcohol film according to claim 1 , wherein the content of the modified conjugated diene-based polymer (B) is 10 parts by mass or more and 80 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A). 3 . the following.

The polyvinyl alcohol film according to claim 1 or 2, wherein the polyvinyl alcohol (A) has a degree of polymerization of 1,000 or more and 10,000 or less, and a degree of saponification of 95 mol % or more.

4 . The polyvinyl alcohol film according to claim 1 , wherein the weight average molecular weight of the modified conjugated diene-based polymer (B) is 5,000 or more and 80,000 or less. 5 .

5 . The polyvinyl alcohol film according to claim 1 , wherein the hydrophilic group is a graft chain having a repeating structure including a nonionic polar group. 6 .

6. A stretched film obtained from the polyvinyl alcohol film according to any one of claims 1 to 5.

7 . A polarizing film obtained from the polyvinyl alcohol film according to any one of claims 1 to 5 or the stretched film according to claim 6 . 8 .

8. A method for producing a polyvinyl alcohol film, comprising a step of forming a film using a film-forming stock solution comprising a mixture of polyvinyl alcohol (A) and a modified conjugated diene having a hydrophilic group It is obtained by mixing the dispersion liquid of the polymer (B).

9 . The method for producing a polyvinyl alcohol film according to claim 8 , wherein the content of the modified conjugated diene-based polymer (B) in the film-forming stock solution is 100 mass per polyvinyl alcohol (A). 10 . The part is 10 parts by mass or more and 80 parts by mass or less.

The method for producing a polyvinyl alcohol film according to claim 8 or 9, wherein the hydrophilic group is a graft chain having a repeating structure including a nonionic polar group.