阅读说明：本技术 聚乙烯醇膜和使用其的偏振膜的制造方法 (Polyvinyl alcohol film and method for producing polarizing film using same ) 是由 鹰取洋平 中井慎二 于 2019-09-27 设计创作，主要内容包括：PVA,其特征在于,其含有PVA(A)、选自下述式(I)或(II)所示的苯乙烯基醚型表面活性剂中的至少1种表面活性剂(B)、以及选自硫酸酯盐型或磺酸盐型中的至少1种表面活性剂(C),表面活性剂(B)的含量相对于PVA(A)100质量份为0.04～0.4质量份,表面活性剂(C)的含量相对于PVA(A)100质量份为0.04～0.4质量份。该PVA膜的活性剂凝聚物数量少,剥离性和膜面品质良好。因此,通过将该PVA膜用作原材,能够获得光学性能良好的偏振膜。[式(I)中,苯乙烯单元数(m)为2～3,聚氧亚乙基链数(n)为12～30]。[式(II)中,苯乙烯单元数(m)为2～3,聚氧亚乙基链数(n)和聚氧亚丙基链数(l)的合计(n+l)为12～30]。(The PVA is characterized by comprising PVA (A), at least 1 surfactant (B) selected from styryl ether surfactants shown in the formula (I) or (II) and at least 1 surfactant (C) selected from sulfate salt type or sulfonate salt type, wherein the content of the surfactant (B) is 0.04-0.4 part by mass relative to 100 parts by mass of the PVA (A), and the content of the surfactant (C) is 0.04-0.4 part by mass relative to 100 parts by mass of the PVA (A). The PVA film has a small amount of active agent aggregatesThe peeling property and film surface quality were good. Therefore, by using this PVA film as a raw material, a polarizing film having excellent optical properties can be obtained. [ in the formula (I), the number of styrene units (m) is 2 to 3, and the number of polyoxyethylene chains (n) is 12 to 30]. [ in the formula (II), the number of styrene units (m) is 2 to 3, and the total (n + l) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) is 12 to 30]。)

1. A polyvinyl alcohol film comprising polyvinyl alcohol (A), at least 1 surfactant (B) selected from styryl ether surfactants represented by the following formula (I) or (II), and at least 1 surfactant (C) selected from sulfate or sulfonate,

the content of the surfactant (B) is 0.04-0.4 parts by mass per 100 parts by mass of the polyvinyl alcohol (A),

the content of the surfactant (C) is 0.04-0.4 parts by mass per 100 parts by mass of the polyvinyl alcohol (A),

[ chemical formula 1]

In the formula (I), the number of styrene units (m) is 2-3, and the number of polyoxyethylene chains (n) is 12-30;

[ chemical formula 2]

In the formula (II), the number of styrene units (m) is 2 to 3, and the total (n + l) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) is 12 to 30.

2. The polyvinyl alcohol film according to claim 1, wherein the mass ratio (B: C) of the surfactant (B) to the surfactant (C) is 1:0.2 to 1: 10.

3. The polyvinyl alcohol film according to claim 1 or 2, wherein the width of the film is 1.5m or more.

4. The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the length of the film is 3000m or more.

5. The polyvinyl alcohol film according to any one of claims 1 to 4, wherein the film has a thickness of 10 to 70 μm.

6. A method for producing a polarizing film, comprising a step of dyeing the polyvinyl alcohol film according to any one of claims 1 to 5 and a step of stretching the film.

Technical Field

The present invention relates to a polyvinyl alcohol film (hereinafter, polyvinyl alcohol may be abbreviated as "PVA") having a small amount of active agent aggregates and excellent in releasability and film surface quality, and a method for producing a polarizing film using the same.

Background

PVA films are used in various applications by utilizing unique properties related to transparency, optical characteristics, mechanical strength, water solubility, and the like. In particular, due to its excellent optical properties, PVA films are used as a raw material (raw material film) for producing polarizing films of polarizing plates, which are basic components of Liquid Crystal Displays (LCDs), and their applications are expanding. Polarizing plates for LCDs are required to have high optical performance, and polarizing films as their constituent elements are also required to have high optical performance.

Polarizing plates are generally manufactured by subjecting a PVA film as a raw material to dyeing, uniaxial stretching, fixing treatment with a boron compound or the like as necessary, and the like to manufacture a polarizing film, and then attaching a protective film such as a cellulose Triacetate (TAC) film to the surface of the polarizing film. The PVA film as a raw material is generally produced by a method of drying a film-forming raw solution containing PVA, such as a casting film-forming method.

Various technologies related to PVA films or methods for producing the same have been known so far. Patent document 1 describes: a PVA film having a moisture content of 5 wt% or less is obtained by preparing an aqueous PVA resin solution containing polyoxyethylene laurylamine having a polyoxyethylene chain number of 2 as a surfactant, bringing the aqueous PVA resin solution into contact with a drum roll for 30 to 120 seconds, forming a film by a casting method, and setting the evaporation rate of water in the aqueous PVA solution to 15 to 30 wt%/min. It is said that a PVA film having excellent carrying properties and no optical defects can be obtained.

Patent document 2 describes a PVA film containing: a PVA resin, sodium lauryl sulfate as a sulfate ester salt type anionic surfactant (a), polyoxyethylene lauryl ether as an ether type nonionic surfactant (b), and lauric acid diethanolamide as a nitrogen-containing type nonionic surfactant (c). It is said that the composition has excellent optical characteristics such as no optical streaks and optical color unevenness, and can exhibit an excellent effect of blocking resistance.

Further, patent document 3 describes a PVA film containing: a PVA resin, polyoxyethylene lauryl ether as the ether-type nonionic surfactant (a), and two of polyoxyethylene dodecylamine and lauric diethanolamide as the nitrogen-containing nonionic surfactant (b). It is said that the composition has excellent optical characteristics such as no optical streaks and exhibits an excellent effect of blocking resistance. However, the PVA films obtained in patent documents 1 to 3 are improved by forming active agent aggregates.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2011-2458872

Patent document 2: japanese patent laid-open publication No. 2005-206809

Patent document 3: japanese patent laid-open No. 2005-206810.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above problems, and an object thereof is to provide a PVA film having a small number of active agent aggregates and excellent in peelability and film surface quality, and a method for producing a polarizing film using the PVA film.

Means for solving the problems

As a result of intensive studies made by the present inventors to achieve the above object, it has been found that a PVA film having a small amount of aggregates of an active agent and having good releasability and film surface quality can be obtained even when an aqueous PVA solution before film formation is cloudy, by containing a specific amount of polyvinyl alcohol (a) (hereinafter sometimes referred to as "PVA (a)"), at least 1 surfactant (B) (hereinafter sometimes referred to as "surfactant (B)") selected from among styryl ether surfactants represented by the following formulae (I) and (II), and at least 1 surfactant (C) (hereinafter sometimes referred to as "surfactant (C)") selected from among sulfate ester surfactants and sulfonate ester surfactants in which a styryl ether surfactant is dispersed, and the present invention has been completed.

Namely, the present invention relates to:

[1] a polyvinyl alcohol film comprising polyvinyl alcohol (A), at least 1 surfactant (B) selected from among styryl ether surfactants represented by the following formula (I) or (II), and at least 1 surfactant (C) selected from among sulfate or sulfonate surfactants, wherein the content of the surfactant (B) is 0.04 to 0.4 part by mass per 100 parts by mass of the polyvinyl alcohol (A), the content of the surfactant (C) is 0.04 to 0.4 part by mass per 100 parts by mass of the polyvinyl alcohol (A),

[ chemical formula 1]

[ in the formula (I), the number of styrene units (m) is 2 to 3, and the number of polyoxyethylene chains (n) is 12 to 30. ]

[ chemical formula 2]

[ in the formula (II), the number of styrene units (m) is 2 to 3, and the total (n + l) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) is 12 to 30. ]

[2] The polyvinyl alcohol film according to [1], wherein the mass ratio (B: C) of the surfactant (B) to the surfactant (C) is 1:0.2 to 1: 10;

[3] the polyvinyl alcohol film according to [1] or [2], wherein the width of the film is 1.5m or more;

[4] the polyvinyl alcohol film according to any one of [1] to [3], wherein the length of the film is 3000m or more;

[5] the polyvinyl alcohol film according to any one of [1] to [4], wherein the film has a thickness of 10 to 70 μm;

[6] a method for producing a polarizing film, comprising a step of dyeing the polyvinyl alcohol film according to any one of [1] to [5] and a step of stretching the film.

Effects of the invention

The PVA film of the present invention has a small number of aggregates of the active agent, and is excellent in peelability and film surface quality. Therefore, by using this PVA film as a raw material, a polarizing film having excellent optical properties can be obtained.

Detailed Description

The PVA film of the present invention contains PVA (A), at least 1 surfactant (B) selected from the styryl ether surfactants represented by the following formula (I) or (II), and at least 1 surfactant (C) selected from the sulfate salt type or the sulfonate salt type.

[ chemical formula 3]

[ in the formula (I), the number of styrene units (m) is 2 to 3, and the number of polyoxyethylene chains (n) is 12 to 30 ].

[ chemical formula 4]

[ in the formula (II), the number of styrene units (m) is 2 to 3, and the total (n + l) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) is 12 to 30 ].

In the PVA film of the present invention, it is important to use at least 1 surfactant (B) selected from the styryl ether type surfactants represented by the above formula (I) or (II) and at least 1 surfactant (C) selected from the sulfate type or the sulfonate type in combination at a specific content relative to PVA (a). The present inventors have confirmed that: when the surfactant (B) is used alone for PVA (a), the film surface quality of the PVA film obtained is deteriorated. Further, the present inventors have confirmed that: when the surfactant (C) is used alone for PVA (a), the obtained PVA film is deteriorated in releasability and film surface quality.

In contrast, in the present invention, by using the surfactant (B) and the surfactant (C) in combination at a specific content relative to the PVA (a), a PVA film having a small number of aggregates of the active agent and excellent in releasability and film surface quality can be obtained. As shown in the turbidity evaluation in the examples described below, the present inventors have confirmed that, when a film-forming raw solution for producing a PVA film is prepared, white turbidity, which is considered to be caused by aggregation of an active agent, is present in the film-forming raw solution. The inventor and the like clearly understand through research: even when a PVA film is produced using the cloudy film-forming stock solution, a PVA film having a small amount of active agent aggregates and having good peelability and film surface quality can be obtained. This is surprising.

[PVA(A)]

As the PVA (a), PVA produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester can be used. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. These can be used alone in 1 kind, also can be combined with 2 or more, preferably the former. From the viewpoints of availability, cost, and productivity of pva (a), vinyl acetate is preferable as the vinyl ester.

Examples of the other monomer copolymerizable with the vinyl ester include ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or a salt thereof; acrylic esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or a salt thereof; methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamide derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, and N-methylolacrylamide or a derivative thereof; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid or a salt thereof, methacrylamidopropyldimethylamine or a salt thereof, and N-methylolmethacrylamide 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; vinyl cyanide such as acrylonitrile and methacrylonitrile; 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; isopropenyl acetate, and the like. These other monomers may be used alone in 1 kind, or may be used in combination in 2 or more kinds. Among these, ethylene and an olefin having 3 to 30 carbon atoms are preferable as the other monomer, and ethylene is more preferable.

The proportion of the structural unit derived from the other monomer in the vinyl ester polymer is not particularly limited, and is preferably 15 mol% or less, more preferably 5 mol% or less, based on the number of moles of the entire structural units constituting the vinyl ester polymer.

The polymerization degree of pva (a) is not necessarily limited, but the film strength tends to decrease as the polymerization degree decreases, and therefore, it is preferably 200 or more, more preferably 300 or more, still more preferably 400 or more, and particularly preferably 500 or more. Further, if the polymerization degree is too high, the viscosity of the aqueous solution of pva (a) or the molten pva (a) tends to be high, and film formation tends to be difficult, and therefore, 10000 or less is preferable, 9000 or less is more preferable, 8000 or less is further preferable, and 7000 or less is particularly preferable. The polymerization degree of PVA (A) is an average polymerization degree measured according to JIS K6726-1994, and is determined by the following equation based on the intrinsic viscosity [ eta ] (unit: deciliter/g) measured in water at 30 ℃ after re-saponification and purification of PVA (A).

Degree of polymerization ([ η ])]×10⁴/8.29)^(1/0.62)

The saponification degree of pva (a) is not particularly limited, and for example, 60 mol% or more of pva (a) may be used, but from the viewpoint of use as a raw material film for producing an optical film such as a polarizing film, the saponification degree of pva (a) is preferably 95 mol% or more, more preferably 98 mol% or more, and still more preferably 99 mol% or more. Here, the saponification degree of PVA (A) means: the ratio (% by mole) of the number of moles of the vinyl alcohol unit to the total number of moles of the structural unit (typically, vinyl ester monomer unit) that is converted into a vinyl alcohol unit by saponification and the vinyl alcohol unit of pva (a) is expressed as a percentage. The degree of saponification of PVA (A) can be measured according to JIS K6726-1994.

PVA (A) may be 1 type of PVA alone, or 2 or more types of PVA differing in polymerization degree, saponification degree, modification degree, etc. may be used in combination. Wherein, the PVA film contains PVA with acid functional groups such as carboxyl and sulfonic acid group; PVA having an acid anhydride group; PVA having a basic functional group such as an amino group; when the PVA having a functional group which promotes a crosslinking reaction, such as a neutralized product thereof, is used, the secondary processability of the PVA film may be lowered by the crosslinking reaction between PVA molecules. Therefore, when excellent secondary processability is required as in the case of a raw material film for producing an optical film, the content of each of the PVA having an acidic functional group, the PVA having an acid anhydride group, the PVA having a basic functional group and the neutralized product thereof in PVA (a) is preferably 0.1% by mass or less, and more preferably none.

The content of the PVA (a) in the PVA film is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 85% by mass or more.

[ styryl ether type surfactant (B) ]

The styryl ether type surfactant (B) used in the present invention is represented by the following formula (I) or (II).

[ chemical formula 5]

[ in the formula (I), the number of styrene units (m) is 2 to 3, and the number of polyoxyethylene chains (n) is 12 to 30 ].

[ chemical formula 6]

[ in the formula (II), the number of styrene units (m) is 2 to 3, and the total (n + l) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) is 12 to 30 ].

In the above formulae (I) and (II), the number of styrene units (m) is 2 to 3. When the number of styrene units (m) is less than 2, the surfactant does not sufficiently ooze out to the interface between the PVA film and the drum when the PVA aqueous solution is ejected from the die and dried on the surface of the drum. As a result, the surfactant remaining in the PVA film was observed as the number of aggregates. Further, the PVA film is deteriorated in releasability and film surface quality. On the other hand, when the number (m) of styrene units exceeds 3, the ability to lower the surface tension is insufficient, and the film surface quality is deteriorated.

In the formula (I), the number of polyoxyethylene chains (n) is 12 to 30, and in the formula (II), the total (n + l) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) is 12 to 30. When the number of (n) and the number of (n + l) are within these ranges, a PVA film having a small number of active agent aggregates and excellent releasability and film surface quality can be obtained when used in combination with the surfactant (C) described later.

When the number of polyoxyethylene chains (n) in the formula (I) is less than 12, or when the total (n + l) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) in the formula (II) is less than 12, the ability to reduce the surface tension is insufficient, and the quality of the film surface is deteriorated.

On the other hand, when the number (n) of polyoxyethylene chains exceeds 30 in the formula (I), or when the total (n + l) of the number (n) of polyoxyethylene chains and the number (l) of polyoxypropylene chains exceeds 30 in the formula (II), the hydrophilicity of the surfactant becomes too high, and the surfactant is stabilized in the PVA aqueous solution, and therefore, when the film is formed on the surface of the drum, the surfactant is less likely to bleed out to the interface between the PVA film and the drum. As a result, the peeling property and the film surface quality are deteriorated. In the formula (I), the number of polyoxyethylene chains (n) is preferably 25 or less, more preferably 20 or less. In the formula (II), the total (n + l) of the number (n) of polyoxyethylene chains and the number (l) of polyoxypropylene chains is preferably 25 or less, more preferably 20 or less.

The content of the styryl ether surfactant (B) used in the present invention is 0.04 to 0.4 part by mass with respect to 100 parts by mass of the PVA (A). When the content of the styryl ether type surfactant (B) is less than 0.04 parts by mass, the peeling property and film surface quality of the PVA film obtained are deteriorated. The content of the styryl ether type surfactant (B) is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more. On the other hand, when the content of the styryl ether type surfactant (B) exceeds 0.4 parts by mass, the film surface quality of the PVA film obtained deteriorates. The content of the styryl ether type surfactant (B) is preferably 0.38 parts by mass or less, and more preferably 0.3 parts by mass or less. The styryl ether surfactant (B) used in the present invention may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

[ surfactant (C) ]

The surfactant (C) used in the present invention is at least 1 surfactant selected from a sulfate type or a sulfonate type. The content of the surfactant (C) used in the present invention is 0.04 to 0.4 part by mass per 100 parts by mass of the PVA (A). When the content of the surfactant (C) is less than 0.04 parts by mass, the film surface quality of the PVA film obtained deteriorates. The content of the surfactant (C) is preferably 0.05 parts by mass or more, and more preferably 0.06 parts by mass or more. On the other hand, when the content of the surfactant (C) exceeds 0.4 parts by mass, thermal decomposition products of the surfactant (C) are observed as aggregates in the PVA film. Further, the film surface quality of the PVA film obtained is deteriorated. The content of the surfactant (C) is preferably 0.3 parts by mass or less, more preferably 0.2 parts by mass or less, and further preferably 0.1 parts by mass or less.

In the present invention, the mass ratio (B: C) of the styryl ether surfactant (B) to the surfactant (C) is preferably 1:0.2 to 1: 10. When the mass ratio (B: C) is less than 1:0.2, the film surface quality of the PVA film to be obtained may deteriorate. The mass ratio (B: C) is more preferably 1:0.25 or more, and still more preferably 1:0.3 or more. On the other hand, when the mass ratio (B: C) exceeds 1:10, the film surface quality may deteriorate. The mass ratio (B: C) is preferably 1:8 or less, more preferably 1:6 or less, still more preferably 1:4 or less, and particularly preferably 1:2 or less.

Examples of the sulfate salt type include sodium alkylsulfate, potassium alkylsulfate, ammonium alkylsulfate, triethanolamine alkylsulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxypropylene alkyl ether sulfate, and sodium polyoxyethylene alkylphenyl ether sulfate. The alkyl group is preferably an alkyl group having 8 to 20 carbon atoms, and a lauryl group is more preferred.

Examples of the sulfonate type include sodium alkylsulfonate, potassium alkylsulfonate, ammonium alkylsulfonate, triethanolamine alkylsulfonate, sodium alkylbenzenesulfonate, disodium dodecyldiphenylether disulfonate, sodium alkylnaphthalenesulfonate, disodium alkylsulfosuccinate, and disodium polyoxyethylene alkylsulfosuccinate. The alkyl group is preferably an alkyl group having 8 to 20 carbon atoms, and among them, a dodecyl group is more preferable. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

Among them, the surfactant (C) is preferably a sulfate salt type from the viewpoint of reducing the amount of the active agent aggregates of the PVA film to be obtained as much as possible.

[ PVA film ]

The PVA film of the present invention preferably contains a plasticizer from the viewpoint of imparting flexibility to the PVA film. Examples of the preferable plasticizer include polyhydric alcohols, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Among them, only 1 kind of plasticizer may be used, or 2 or more kinds of plasticizers may be used in combination. Among them, ethylene glycol or glycerin is preferable from the viewpoint of compatibility with pva (a), acquisition properties, and the like.

The content of the plasticizer is preferably in the range of 1 to 30 parts by mass based on 100 parts by mass of the PVA (A). When the content of the plasticizer is 1 part by mass or more, problems are less likely to occur in mechanical properties such as impact strength and in process passability during secondary processing. On the other hand, when the content of the plasticizer is 30 parts by mass or less, the film becomes appropriately soft, and the handling property is improved.

The PVA film of the present invention may further contain other components than PVA, a surfactant and a plasticizer, as necessary. Examples of such other components include water, antioxidants, ultraviolet absorbers, lubricants, colorants, fillers (inorganic particles, seeds, etc.), preservatives, antifungal agents, and other polymer compounds than the above components. The content of other components in the resin composition is preferably 10% by mass or less.

The width of the PVA film of the present invention is not particularly limited, and is preferably 1.5m or more, more preferably 3m or more, further preferably 4.5m or more, particularly preferably 5.0m or more, and most preferably 5.5m or more, from the viewpoint of recent demand for polarizing films having a wide width. On the other hand, if the width of the PVA film is too wide, the manufacturing cost of a film forming apparatus for manufacturing the PVA film may be increased, or it may be difficult to uniformly stretch the PVA film when manufacturing an optical film by using a manufacturing apparatus already put into practical use, and therefore, the width of the PVA film is preferably 7.5m or less, more preferably 7.0m or less, and still more preferably 6.5m or less.

The shape of the PVA film of the present invention is not particularly limited, and a long film is preferable from the viewpoint of enabling continuous and smooth production of a more uniform PVA film, from the viewpoint of continuous use in the production of an optical film or the like, and the like. The length of the long film (length in the flow direction) is not particularly limited and may be set as appropriate. The length of the film is preferably 3000m or more. On the other hand, the length of the film is preferably 30000m or less. The long film is preferably wound around a core or the like to form a film roll.

The thickness of the PVA film of the present invention is not particularly limited, and may be appropriately set. From the viewpoint of use as a raw material film for producing an optical film such as a polarizing film, the film thickness is preferably 10 to 70 μm. The thickness of the PVA film may be determined as an average value of values measured at arbitrary 10 points.

The amount of the active agent aggregates in the PVA film of the present invention is measured by the method described in the following examples. The number of the active agent aggregates is preferably 3 or less, more preferably 2 or less, and still more preferably 1 or less.

The method for producing the PVA film of the present invention is not particularly limited, and for example, the PVA film can be produced by a known method such as a casting film-forming method or a melt extrusion film-forming method using a film-forming stock solution containing PVA (a), a styryl ether type surfactant (B), a surfactant (C), a liquid medium, and the plasticizer and other components, which are further contained as necessary. The film-forming stock solution may be a solution in which pva (a) is dissolved in a liquid medium, or a solution in which pva (a) is melted.

Examples of the liquid medium 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, and 1 or 2 or more of these can be used. Among them, water is preferable from the viewpoint of a small load on the environment and recyclability.

The evaporation fraction of the film-forming stock solution (the content of volatile components such as a liquid medium removed by evaporation or evaporation during film formation in the film-forming stock solution) varies depending on the film-forming method, the film-forming conditions, and the like, and is preferably within a range of 50 to 90 mass%, and more preferably within a range of 55 to 80 mass%. By setting the volatilization fraction of the film-forming dope to 50 mass% or more, the film can be easily formed without excessively increasing the viscosity of the film-forming dope. On the other hand, when the evaporation fraction of the film-forming dope is 90 mass% or less, the viscosity of the film-forming dope is not excessively low, and the thickness uniformity of the PVA film obtained is improved.

The PVA film of the present invention can be produced by a casting film-forming method or a melt extrusion film-forming method using the film-forming dope, and can be obtained by, for example, casting or discharging the film-forming dope in a film form on a support such as a drum or a belt, and drying the film-forming dope on the support. The obtained film may be further dried by a drying roll or a hot air drying device, subjected to heat treatment by a heat treatment device, or subjected to humidity control by a humidity control device, as necessary. The PVA film produced is preferably wound around a core or the like to produce a film roll. In addition, both ends of the manufactured PVA film in the width direction may be cut.

The PVA film of the present invention can be suitably used as a raw material film for producing a polarizing film, a phase difference film, a special light collecting film, and the like. According to the present invention, a PVA film having high light transmittance and high quality can be obtained. Therefore, the PVA film for optical use is a suitable embodiment of the present invention.

A method for producing a polarizing film having a step of dyeing the PVA film and a step of stretching the PVA film is a suitable embodiment of the present invention. The manufacturing method may further include a fixing treatment step, a drying treatment step, a heat treatment step, and the like. The order of dyeing and stretching is not particularly limited, and the dyeing treatment may be performed before the stretching treatment, simultaneously with the stretching treatment, or after the stretching treatment. The steps such as stretching and dyeing may be repeated a plurality of times. In particular, it is preferable to divide the stretching into two or more stages because uniform stretching is easily performed.

Examples of the dye used for dyeing the PVA film include iodine and dichroic organic dyes (e.g., dyes such as DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; DirectBlue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1, 85; DirectYellow 8, 12, 44, 86, 87; and dichroic dyes such as direcorange 26, 39, 106, 107). These dyes may be used alone in 1 kind or in combination of 2 or more kinds. The dyeing can be usually carried out by immersing the PVA film in a solution containing the above dye, and the treatment conditions and the treatment method are not particularly limited.

The PVA film may be stretched by a uniaxial stretching method or a biaxial stretching method, and the former is preferable. The uniaxial stretching of the PVA film in the flow direction (MD) or the like may be performed by either a wet stretching method or a dry heat stretching method, and the wet stretching method is preferable from the viewpoint of stability of the performance and quality of the obtained polarizing film. As the wet stretching method, there is a method of stretching a PVA film in pure water, an aqueous solution containing various components such as an additive and a water-soluble organic solvent, or an aqueous dispersion in which various components are dispersed. Specific examples of the uniaxial stretching method by the wet stretching method include a method of performing uniaxial stretching in warm water containing boric acid, a method of performing uniaxial stretching in a solution containing the dye or in a fixing treatment bath described later, and the like. The PVA film after water absorption may be uniaxially stretched in air, or may be uniaxially stretched by other methods.

The stretching temperature in the uniaxial stretching is not particularly limited, and when the wet stretching is performed, the temperature is preferably in the range of 20 to 90 ℃, more preferably 25 to 70 ℃, and further preferably 30 to 65 ℃, and when the dry stretching is performed, the temperature is preferably in the range of 50 to 180 ℃.

From the viewpoint of polarization performance, the stretching ratio of the uniaxial stretching treatment (total stretching ratio in the case of uniaxial stretching in multiple stages) is preferably as high as possible until just before the film breaks, and is more preferably 4 times or more, more preferably 5 times or more, and still more preferably 5.5 times or more. The upper limit of the stretch ratio is not particularly limited as long as the film does not break, and is preferably 8.0 times or less in order to perform uniform stretching.

In the production of the polarizing film, it is preferable to perform a fixing treatment in order to make the dye strongly adsorbed to the uniaxially stretched PVA film. As the fixing treatment, a method of immersing the PVA film in a treatment bath to which boric acid and/or a boron compound are added, or the like, which is generally used. At this time, an iodine compound may be added to the treatment bath as needed.

The PVA film subjected to the uniaxial stretching treatment or the uniaxial stretching treatment and the fixing treatment is preferably subjected to a subsequent drying treatment and a heat treatment. The temperature of the drying treatment and the heat treatment is preferably 30 to 150 ℃, and particularly preferably 50 to 140 ℃. If the temperature is too low, the dimensional stability of the polarizing film obtained tends to be low. On the other hand, if the temperature is too high, the polarization performance is likely to be lowered due to decomposition of the dye.

The polarizing plate can be produced by laminating optically transparent protective films having mechanical strength on both sides or one side of the polarizing film obtained in the above manner. As the protective film at this time, a cellulose Triacetate (TAC) film, a Cellulose Acetate Butyrate (CAB) film, an acrylic film, a polyester film, or the like can be used. As the adhesive for attaching the protective film, a PVA adhesive, a urethane adhesive, or the like is generally used, and among them, a PVA adhesive is preferably used.

The polarizing plate obtained in the above manner can be used as a member of a liquid crystal display device by covering it with an adhesive such as an acrylic adhesive and then bonding it to a glass substrate. When the polarizing plate is bonded to the glass substrate, a retardation film, a viewing angle improving film, a brightness enhancing film, and the like may be simultaneously bonded.

Examples

The present invention will be specifically described below with reference to examples and the like, but the present invention is not limited to these examples at all.

[ amount of aggregate of active agent ]

A10 m region was cut out from the surface layer side of the PVA film roll to be measured, and a square sample having a width direction of 1.5cm, a length direction of 1.5cm and a thickness of 60 μm was cut out. Thereafter, an image of the center portion in the film thickness direction was taken at 1000 magnifications using a differential interference difference microscope. The picked-up image was analyzed by using image analysis software "ImagePro" manufactured by ローパー of Japan, and the number of active agent aggregates in a 135. mu. m.times.100. mu.m region was measured.

[ peelability ]

In the case of the long film having a thickness of 4000m or more, the film was peeled from the casting drum, and the film was evaluated as "adhered to the drum and could not be peeled off" x ", and the film could be peeled off without any problem" o ".

[ film surface quality ]

The cut PVA film was disposed between a white screen and a projector in a dark room, and the shadow mapped on the screen was observed. When the discontinuous depth and the striped depth were observed, they were marked as "x", and when the depth was not observed but was uniform, they were marked as "o". In the observation, the distance between the screen and the projector was 360cm, and the distance between the screen and the PVA film was 10 cm.

[ evaluation of turbidity ]

The film-forming stock solution was taken out from the discharge port at the outlet of the twin-screw extruder, and the degree of cloudiness of the solution was visually evaluated. The liquid was rated as "good" if it was clear, rated as "Δ" if it was slightly cloudy, and rated as "x" if it was clearly cloudy.

Example 1

100 parts by mass of PVA chips having a polymerization degree of 2400 and a saponification degree of 99.9 mol% were immersed in 2500 parts by mass of distilled water at 35 ℃ for 24 hours, and then centrifuged to obtain PVA-containing chips having a volatilization fraction of 70 mass%. To 333 parts by mass of the PVA-containing small pieces (100 parts by mass of dried PVA) were mixed 10 parts by mass of glycerin, 0.27 part by mass of an active agent having a styrene unit number (m) of 2 and a polyoxyethylene chain number (n) of 13 as the styrene ether type surfactant (B), and 0.08 part by mass of sodium polyoxyethylene lauryl ether sulfate as the surfactant (C), and the mixture thus obtained was heated and melted by a twin-screw extruder having a vent hole (maximum temperature of 130 ℃ C.) to prepare a film-forming stock solution.

The dope was cooled to 100 ℃ by a heat exchanger, extruded from a 180cm wide coat hanger die onto a drum having a surface temperature of 90 ℃ to form a film, and dried by a hot air drying apparatus, and both ends of the film thickened by necking at the time of film formation were cut off, thereby continuously producing a PVA film having a film thickness of 60 μm and a width of 165 cm. The PVA film was wound around a cylindrical core in an amount of 4000m in length to produce a film roll. The PVA film thus obtained was evaluated for the number of aggregates of the active agent, peeling property, film surface quality, and turbidity of the film-forming stock solution by the methods described above. The results are shown in Table 1.

Examples 2 to 5 and comparative examples 1 to 9

PVA films were produced and evaluated in the same manner as in example 1, except that the kinds and amounts of the styryl ether type surfactant (B) and the surfactant (C) were changed as shown in table 1. The results are shown in Table 1.

As shown in table 1, in the PVA films of examples 1 to 5, the number of active agent aggregates in the obtained PVA film was 3 or less, and the peeling property and the film surface quality were also good, although the PVA aqueous solution (film-forming stock solution) was clouded.

On the other hand, in comparative example 1 in which the surfactant (C) was not used, the film surface quality of the PVA film obtained was not good. In comparative example 2 in which the surfactant (B) was not used, the obtained PVA film was inferior in releasability and film surface quality. In comparative example 3 in which the content of the surfactant (B) exceeded 0.4 parts by mass, the film surface quality of the PVA film obtained was not good. In comparative example 4 in which the content of the surfactant (B) was less than 0.04, the PVA film obtained was inferior in releasability and film surface quality. In comparative example 5 using the surfactant (B) having a styrene unit number (m) of 1, the PVA film obtained had a large number of active agent aggregates, and was inferior in releasability and film surface quality. In comparative example 6 using the surfactant (B) in which the total (n + l) of the polyoxyethylene chain number (n) and the polyoxypropylene chain number (l) was 5, the film surface quality of the PVA film obtained was poor. In comparative example 7 using the surfactant (B) having a polyoxyethylene chain number (n) of 31, the PVA film obtained was inferior in releasability and film surface quality. In comparative example 8 in which the content of the surfactant (C) exceeded 0.4 parts by mass, the PVA film obtained exhibited a large amount of aggregates of the active agent, and the film surface quality was not good. In comparative example 9 in which the content of the surfactant (C) was less than 0.04 parts by mass, the film surface quality of the PVA film obtained was not good.