WO2020067489A1

WO2020067489A1 - Polyvinyl alcohol film and method for manufacturing polarizing film using same

Info

Publication number: WO2020067489A1
Application number: PCT/JP2019/038315
Authority: WO
Inventors: 洋平鷹取; 慎二中井
Original assignee: 株式会社クラレ
Priority date: 2018-09-28
Filing date: 2019-09-27
Publication date: 2020-04-02
Also published as: JPWO2020067489A1; KR20210069645A; CN112740085B; TW202026351A; CN112740085A; TWI805849B; JP7199445B2

Abstract

A PVA containing PVA (A), at least one type of surfactant (B) selected from styryl-ether-type surfactants represented by formula (I) or (II), and at least one type of surfactant (C) selected from sulfuric ester salts or sulfonic ester salts, the PVA being characterized in that the content of the surfactant (B) is 0.04-0.4 part by mass with respect to 100 parts by mass of the PVA (A), and the content of the surfactant (C) is 0.04-0.4 part by mass with respect to 100 parts by mass of the PVA (A). This PVA film has a low number of activator aggregates, and good release properties and film surface quality. Consequently, a polarizing film having good optical performance is obtained when the above PVA film is used as a raw roll. [In formula (I), the number (m) of styrene units is 2-3, and the number (n) of polyoxyethylene chains is 12-30.] [In formula (II), the number (m) of styrene units is 2-3, and the total (n + l) of the number (n) of polyoxyethylene chains and the number (l) of polyoxypropylene chains is 12-30.]

Description

Polyvinyl alcohol film and method for producing polarizing film using the same

The present invention relates to a polyvinyl alcohol film having a small number of activator aggregates, good releasability and film surface quality (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA"), and a polarizing film using the same. It relates to a manufacturing method.

(4) PVA films are used in various applications by utilizing unique properties regarding transparency, optical properties, mechanical strength, water solubility, and the like. In particular, a PVA film is used as a raw material (raw film) of a polarizing film constituting a polarizing plate which is a basic component of a liquid crystal display (LCD) by utilizing its excellent optical properties. Applications are expanding. High optical performance is required for a polarizing plate for an LCD, and high optical performance is also required for a polarizing film as a constituent element thereof.

A polarizing plate is generally manufactured by dyeing, uniaxially stretching, and, if necessary, fixing a raw PVA film with a boron compound or the like to produce a polarizing film, and then forming cellulose triacetate on the surface of the polarizing film. It is manufactured by attaching a protective film such as a (TAC) film. The raw PVA film is generally manufactured by a method of drying a film forming stock solution containing PVA, such as a cast film forming method.

技術 Many techniques related to the PVA film and its manufacturing method have been known. Patent Document 1 discloses that a PVA resin aqueous solution containing a polyoxyethylene laurylamine having 2 polyoxyethylene chains as a surfactant is prepared, and the PVA resin aqueous solution is contacted with a drum-type roll for a contact time of 30 to 120 seconds. It is described that a PVA film having a water content of 5% by weight or less was obtained by forming a film by a casting method and adjusting the evaporation rate of water in the PVA aqueous solution to 15 to 30% by weight / minute. According to this, it is said that a PVA film excellent in transport performance and free from optical defects can be obtained.

Patent Document 2 discloses a PVA resin, sodium dodecyl sulfate as a sulfate ester type anionic surfactant (a), polyoxyethylene dodecyl ether as an ether type nonionic surfactant (b), and a nitrogen-containing nonionic surfactant. A PVA film containing lauric acid diethanolamide as the system surfactant (c) is described. According to this, it is said that it has excellent optical characteristics without optical stripes or optical color unevenness, and can exhibit an effect excellent in blocking resistance.

Further, Patent Document 3 discloses a PVA resin, a polyoxyethylene dodecyl ether as an ether type nonionic surfactant (a), and a polyoxyethylene dodecylamine as two types of nitrogen-containing nonionic surfactants (b). PVA films containing lauric acid diethanolamide are described. According to this, it is said that it has excellent optical characteristics without optical stripes and the like, and can exhibit an effect with excellent blocking resistance. However, in the PVA films obtained in Patent Documents 1 to 3, an activator aggregate is formed, and improvement has been demanded.

JP 2011-245873 A JP 2005-206809 A JP 2005-206810 A

The present invention has been made in order to solve the above problems, and provides a PVA film having a small number of activator agglomerates, good peelability and good film surface quality, and a method for producing a polarizing film using the same. With the goal.

The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that polyvinyl alcohol (A) (hereinafter sometimes referred to as “PVA (A)”), the following formula (I) or (II) At least one surfactant (B) selected from styryl ether surfactants represented by the following formula (hereinafter sometimes referred to as “surfactant (B)”), and a styryl ether surfactant. A predetermined amount of at least one surfactant (C) (hereinafter, may be referred to as “surfactant (C)”) selected from a sulfate ester type or a sulfonate type. The present inventors have found that despite the fact that the PVA aqueous solution before film formation is cloudy, it is possible to obtain a PVA film with a small number of activator agglomerates and excellent peelability and film surface quality, and completed the present invention.

That is, the present invention
[1] Polyvinyl alcohol (A), at least one surfactant (B) selected from styryl ether surfactants represented by the following formula (I) or (II), and sulfate ester salt or sulfone A polyvinyl alcohol film containing at least one surfactant (C) selected from the acid salt type, wherein the content of the surfactant (B) is 0 with respect to 100 parts by mass of the polyvinyl alcohol (A). 0.04 to 0.4 parts by mass, and the content of the surfactant (C) is 0.04 to 0.4 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A).

[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 + 1) 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) and 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 1.5 m or more,
[4] The polyvinyl alcohol film according to any one of [1] to [3], wherein the length of the film is 3000 m or more,
[5] The polyvinyl alcohol film according to any 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.

ＰＶ The PVA film of the present invention has a small number of activator aggregates, and has good releasability and film surface quality. Therefore, by using the PVA film as a raw material, a polarizing film having good optical performance can be obtained.

The PVA film of the present invention comprises PVA (A), at least one surfactant (B) selected from styryl ether surfactants represented by the following formula (I) or (II), and a sulfate ester salt: Or at least one surfactant (C) selected from the group consisting of sulfonic acid and sulfonic acid.

[In the formula (II), the number of styrene units (m) is 2 to 3, and the total (n + 1) 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, at least one surfactant (B) selected from styryl ether surfactants represented by the above formula (I) or (II) with respect to PVA (A); It is important to use at least one surfactant (C) selected from a sulfate ester type or a sulfonate type in a predetermined content. The present inventors have confirmed that when the surfactant (B) is used alone with respect to the PVA (A), the film surface quality of the obtained PVA film is deteriorated. In addition, the present inventors have confirmed that when the surfactant (C) is used alone with respect to the PVA (A), the peelability and film surface quality of the obtained PVA film are deteriorated.

On the other hand, in the present invention, the surfactant (B) and the surfactant (C) are used together in a predetermined content with respect to PVA (A), so that the number of activator aggregates is small, and A PVA film having good properties and film surface quality can be obtained. Here, as shown in the turbidity evaluation in the examples described below, the present inventors prepared a film-forming stock solution used for the production of PVA film, due to aggregation of the active agent in the film-forming stock solution. A possible cloudiness has been confirmed. The present inventors have studied and found that even when a PVA film was produced using this cloudy film-forming stock solution, a PVA film having a small number of activator aggregates and having good releasability and film surface quality was obtained. It became clear that it could be done. This is surprising.

[PVA (A)]
As the PVA (A), those produced by saponifying a vinyl ester-based 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. One of these may be used alone or two or more of them may be used in combination, but the former is preferred. Vinyl acetate is preferred as a vinyl ester from the viewpoints of availability, cost, and productivity of PVA (A).

Other monomers copolymerizable with vinyl esters include, for example, ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene; acrylic acid or a salt thereof; methyl acrylate, ethyl acrylate, acrylic acid acrylates such as n-propyl, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid Acid or salt thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate , Dodecyl methacrylate, octyl methacrylate Methacrylic acid esters such as decyl; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, N-methylolacrylamide Or an acrylamide derivative such as a derivative thereof; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamide propanesulfonic acid or a salt thereof, methacrylamidopropyldimethylamine or a salt thereof, N-methylol methacrylamide or a derivative thereof, and the like. Methacrylamide derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; Vinyl ether such as vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether 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 its salts, esters or acid anhydrides; itaconic acid or its salts, esters or Acid anhydride; vinylsilyl compound such as vinyltrimethoxysilane; isopropenyl acetate; One of these other monomers may be used alone, or two or more thereof may be used in combination. Among them, as the other monomer, ethylene and an olefin having 3 to 30 carbon atoms are preferable, and ethylene is more preferable.

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

The degree of polymerization of PVA (A) is not necessarily limited, but is preferably 200 or more, more preferably 300 or more, and still more preferably 400 or more because the film strength tends to decrease as the degree of polymerization decreases. And particularly preferably 500 or more. When the degree of polymerization is too high, the viscosity of the aqueous solution of PVA (A) or the melted PVA (A) becomes high, and the film formation tends to be difficult. Therefore, it is preferably 10,000 or less, more preferably. Is 9,000 or less, more preferably 8,000 or less, and particularly preferably 7,000 or less. Here, the degree of polymerization of PVA (A) means the average degree of polymerization measured according to the description of JIS K6726-1994. The intrinsic viscosity [η] (unit: deciliter / g) is determined by the following equation.
Degree of polymerization = ([η] × 10 ⁴ /8.29) ^{(1 / 0.62)}

The saponification degree of PVA (A) is not particularly limited, and for example, PVA (A) of 60 mol% or more can be used. However, from the viewpoint of use as a raw film for producing an optical film such as a polarizing film, PVA (A) is used. The degree of saponification of (A) is preferably at least 95 mol%, more preferably at least 98 mol%, even more preferably at least 99 mol%. Here, the saponification degree of PVA (A) means the total number of moles of a structural unit (typically, a vinyl ester monomer unit) and a vinyl alcohol unit which PVA (A) can be converted into a vinyl alcohol unit by saponification. Means the ratio (mol%) occupied by the number of moles of the vinyl alcohol unit. The degree of saponification of PVA (A) can be measured according to the description of JIS K6726-1994.

As PVA (A), one kind of PVA may be used alone, or two or more kinds of PVA having different degrees of polymerization, saponification, modification, etc. may be used in combination. However, the PVA film is a PVA having an acidic functional group such as a carboxyl group or a sulfonic acid group; a PVA having an acid anhydride group; a PVA having a basic functional group such as an amino group; Contains a PVA having a functional group that promotes the PVA film, the secondary processing property of the PVA film may be reduced by a crosslinking reaction between PVA molecules. Therefore, when excellent secondary workability is required, such as a raw film for producing an optical film, in PVA (A), PVA having an acidic functional group, PVA having an acid anhydride group, basic PVA, The content of PVA having a functional group and the neutralized product thereof is preferably 0.1% by mass or less, and more preferably none of them.

ＰＶThe content of PVA (A) in the PVA film is preferably 50% by mass or more, more preferably 70% by mass or more, and even 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).

中 In the above formulas (I) and (II), the number of styrene units (m) is 2-3. If the number of styrene units (m) is less than 2, the surfactant does not sufficiently bleed out at the interface between the PVA film and the drum when the PVA aqueous solution is discharged from the die and dried on the drum surface. As a result, the surfactant remaining in the PVA film is observed as the number of aggregates. In addition, the peelability and film surface quality of the PVA film deteriorate. On the other hand, when the number of styrene units (m) exceeds 3, there is a problem that the ability to lower the surface tension is insufficient and the film surface quality is deteriorated.

In the above formula (I), the number of polyoxyethylene chains (n) is 12 to 30, and in the above formula (II), the total (n + 1) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) ) Is 12 to 30. By setting the number of (n) and the number of (n + 1) in this range, when used together with the surfactant (C) described below, the number of activator aggregates is small, and the releasability and film surface quality are good. A PVA film can be obtained.

In the above formula (I), when the number of polyoxyethylene chains (n) is less than 12, or in the above formula (II), the total (n + 1) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) ) Is less than 12, there is a problem that the ability to lower the surface tension is insufficient and the film surface quality is deteriorated.

On the other hand, in the above formula (I), when the number of polyoxyethylene chains (n) exceeds 30, or in the above formula (II), the sum of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) When (n + 1) exceeds 30, the hydrophilicity of the surfactant becomes too high, and the surfactant is stabilized in the PVA aqueous solution. Therefore, when the surfactant is formed on the drum surface, the surfactant becomes a PVA film. Bleeding out to the interface with the drum becomes difficult. As a result, there arises a problem that the releasability and film surface quality deteriorate. In the above formula (I), the number of polyoxyethylene chains (n) is preferably 25 or less, more preferably 20 or less. In the above formula (II), the total (n + 1) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) is preferably 25 or less, more preferably 20 or less.

含有 The content of the styryl ether type surfactant (B) used in the present invention is 0.04 to 0.4 parts by mass based on 100 parts by mass of PVA (A). When the content of the styryl ether type surfactant (B) is less than 0.04 parts by mass, the peelability and film surface quality of the obtained PVA film are deteriorated. The content of the styryl ether surfactant (B) is preferably at least 0.1 part by mass, more preferably at least 0.2 part by mass. 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 obtained PVA film deteriorates. The content of the styryl ether surfactant (B) is preferably 0.38 parts by mass or less, more preferably 0.3 parts by mass or less. As the styryl ether type surfactant (B) used in the present invention, one type may be used alone, or two or more types may be used in combination.

[Surfactant (C)]
The surfactant (C) used in the present invention is at least one surfactant selected from a sulfate ester type and a sulfonate type. The content of the surfactant (C) used in the present invention is 0.04 to 0.4 parts by mass based on 100 parts by mass of PVA (A). When the content of the surfactant (C) is less than 0.04 parts by mass, the film surface quality of the obtained PVA film deteriorates. The content of the surfactant (C) is preferably at least 0.05 part by mass, more preferably at least 0.06 part by mass. On the other hand, when the content of the surfactant (C) exceeds 0.4 parts by mass, a thermally decomposed product of the surfactant (C) is observed as an aggregate in the PVA film. Further, the film surface quality of the obtained PVA film 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.

において In the present invention, the mass ratio (B: C) of the styryl ether type surfactant (B) to the surfactant (C) is preferably from 1: 0.2 to 1:10. When the mass ratio (B: C) is less than 1: 0.2, the film surface quality of the obtained PVA film may be deteriorated. The mass ratio (B: C) is more preferably 1: 0.25 or more, and even 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 be deteriorated. 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 type include sodium alkyl sulfate, potassium alkyl sulfate, ammonium alkyl sulfate, triethanolamine alkyl sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxypropylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, and the like. Is mentioned. As the alkyl, alkyl having 8 to 20 carbon atoms is preferable, and lauryl is more preferable.

Examples of the sulfonate type include sodium alkyl sulfonate, potassium alkyl sulfonate, ammonium alkyl sulfonate, triethanolamine alkyl sulfonate, sodium alkylbenzene sulfonate, disodium dodecyl diphenyl ether disulfonate, sodium alkyl naphthalene sulfonate, and alkyl sulfo succinate. And disodium polyoxyethylene alkyl sulfosuccinate. The alkyl is preferably an alkyl having 8 to 20 carbon atoms, and more preferably dodecyl. These may be used alone or in combination of two or more.

Among them, from the viewpoint of minimizing the number of activator aggregates in the obtained PVA film, it is preferable that the surfactant (C) is of a sulfate type.

[PVA film]
From the viewpoint that the flexibility can be imparted to the PVA film, the PVA film of the present invention preferably contains a plasticizer. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. These may use only one kind of plasticizer, or may use two or more kinds of plasticizers in combination. Among them, ethylene glycol or glycerin is preferable from the viewpoint of compatibility with PVA (A) and availability.

含有 The content of the plasticizer is preferably in the range of 1 to 30 parts by mass with respect to 100 parts by mass of PVA (A). If the content of the plasticizer is 1 part by mass or more, problems are unlikely to occur in mechanical properties such as impact strength and in processability during secondary processing. On the other hand, when the content of the plasticizer is 30 parts by mass or less, the film becomes moderately flexible, and handleability is improved.

ＰＶ The PVA film of the present invention may further contain components other than PVA, a surfactant, and a plasticizer, if necessary. Such other components include, for example, moisture, antioxidants, ultraviolet absorbers, lubricants, coloring agents, fillers (inorganic particles, starch, etc.), preservatives, fungicides, and other components other than those described above. Polymer compounds and the like can be mentioned. The content of other components in the resin composition is preferably 10% by mass or less.

Although the width of the PVA film of the present invention is not particularly limited, since a wide polarizing film has recently been required, the width is preferably 1.5 m or more, more preferably 3 m or more, and 4 m or more. It is more preferably at least 5.5 m, particularly preferably at least 5.0 m, most preferably at least 5.5 m. On the other hand, if the width of the PVA film is too wide, the manufacturing cost of a film forming apparatus for forming the PVA film increases, and furthermore, the uniformity of the production of an optical film with a practically used manufacturing apparatus. Since it may be difficult to stretch the PVA film, the width of the PVA film is preferably 7.5 m or less, more preferably 7.0 m or less, and more preferably 6.5 m or less. More preferred.

Although the shape of the PVA film of the present invention is not particularly limited, it is long in view of the fact that a more uniform PVA film can be continuously and smoothly produced, and that it can be used continuously when producing an optical film and the like. It is preferably a film having a length. The length of the long film (length in the flow direction) is not particularly limited, and can be appropriately set. The length of the film is preferably 3000 m or more. On the other hand, the length of the film is preferably 30,000 m or less. It is preferable that the long film is wound into a core to form a film roll.

厚み The thickness of the PVA film of the present invention is not particularly limited and can be appropriately set. From the viewpoint of use as a raw film for producing an optical film such as a polarizing film, the thickness of the film is preferably from 10 to 70 μm. In addition, the thickness of a PVA film can be calculated | required as an average value of the value measured in arbitrary 10 places.

The number of activator aggregates in the PVA film of the present invention is measured by the method described in the following example. The number of such activator aggregates is preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less.

The method for producing the PVA film of the present invention is not particularly limited. For example, PVA (A), styryl ether type surfactant (B), surfactant (C), liquid medium, and if necessary, the above-mentioned plastic It 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 an agent and other components. The stock solution may be a solution obtained by dissolving PVA (A) in a liquid medium, or may be a solution obtained by melting PVA (A).

Examples of the liquid medium in the film-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, Ethylenediamine, diethylenetriamine and the like can be mentioned, and one or more of these can be used. Among them, water is preferable from the viewpoint of a small load on the environment and recoverability.

The volatile content of the stock solution for film formation (the content ratio of volatile components such as a liquid medium which is removed by volatilization and evaporation during film formation in the stock solution for film formation) varies depending on the film forming method, film forming conditions, and the like. It is preferably in the range of 90% by mass, more preferably in the range of 55 to 80% by mass. When the volatile content of the film forming solution is 50% by mass or more, the viscosity of the film forming solution does not become too high, and the film is easily formed. On the other hand, when the volatile matter content of the film-forming stock solution is 90% by mass or less, the viscosity of the film-forming stock solution does not become too low, and the thickness uniformity of the obtained PVA film is improved.

There is no particular limitation on the specific production method when the PVA film of the present invention is produced by the casting film forming method or the melt extrusion film forming method using the above film forming stock solution. It can be obtained by casting or discharging in the form of a film on a support such as a belt or a belt, and drying on the support. If necessary, the obtained film may be further dried by a drying roll or a hot air drying device, may be subjected to heat treatment by a heat treatment device, or may be subjected to humidity control by a humidity control device. The manufactured PVA film is preferably wound into a core to form a film roll. Further, both ends in the width direction of the manufactured PVA film may be cut off.

ＰＶ The PVA film of the present invention can be suitably used as a raw film for producing a polarizing film, a retardation film, a special light-condensing film and the like. According to the present invention, a PVA film having high light transmittance and high quality can be obtained. Therefore, a preferred embodiment of the present invention is an optical PVA film.

偏光 A preferred embodiment of the present invention is a method for producing a polarizing film, comprising a step of dyeing the PVA film and a step of stretching. The manufacturing method may further include a fixing step, a drying 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, the dyeing treatment may be performed simultaneously with the stretching treatment, or the dyeing treatment may be performed after the stretching treatment. . Further, 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 steps because uniform stretching can be easily performed.

As a dye used for dyeing the PVA film, iodine or a dichroic organic dye (for example, DirectBlack # 17, 19, 154; DirectBrown # 44, 106, 195, 210, 223; DirectRed # 2, 23, 28, 31, 37, 39) DirectBlue {1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1, 85; Direct Yellow # 8, 12, 44, 86, 87; dichroic dyes such as Direct Orange # 26, 39, 106, 107) can be used. These dyes can be used alone or in combination of two or more. Dyeing can usually be performed by immersing the PVA film in a solution containing the dye, but the processing conditions and processing method are not particularly limited.

方法 As a method of stretching the PVA film, a uniaxial stretching method and a biaxial stretching method are mentioned, and the former is preferable. The uniaxial stretching for stretching 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, but from the viewpoint of the stability of the performance and quality of the obtained polarizing film, the wet stretching method is used. Is preferred. Examples of the wet stretching method include a method of stretching a PVA film in pure water, an aqueous solution containing various components such as additives 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 uniaxially stretching in warm water containing boric acid, and a method of uniaxially stretching in a solution containing the dye or in a fixing bath described later. Further, the film may be uniaxially stretched in air using a PVA film after water absorption, or may be uniaxially stretched by another method.

The stretching temperature at the time of uniaxial stretching is not particularly limited. In the case of wet stretching, a temperature in the range of preferably 20 to 90 ° C., more preferably 25 to 70 ° C., and still more preferably 30 to 65 ° C. is employed. In the case of hot stretching, a temperature in the range of 50 to 180 ° C. is preferably employed.

The stretching ratio of the uniaxial stretching treatment (total stretching ratio in the case of performing uniaxial stretching in multiple stages) is preferably as much as possible until immediately before the film is cut from the point of polarizing performance, and specifically, is 4 times or more. Is preferably 5 times or more, and more preferably 5.5 times or more. The upper limit of the stretching ratio is not particularly limited as long as the film is not broken, but 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 strengthen the adsorption of the dye to the uniaxially stretched PVA film. As the fixing treatment, a method of immersing the PVA film in a treatment bath to which a common boric acid and / or boron compound is added or the like can be adopted. At that time, an iodine compound may be added to the treatment bath as needed.

ＰＶ It is preferable that the PVA film subjected to the uniaxial stretching treatment or the uniaxial stretching treatment and the fixing treatment is then subjected to a drying treatment or a heat treatment. The temperature for the drying treatment or the heat treatment is preferably from 30 to 150 ° C., particularly preferably from 50 to 140 ° C. If the temperature is too low, the dimensional stability of the obtained polarizing film tends to decrease. On the other hand, if the temperature is too high, the polarization performance tends to decrease due to the decomposition of the dye.

保護 An optically transparent protective film having mechanical strength can be attached to both sides or one side of the polarizing film obtained as described above to form a polarizing plate. As the protective film in that case, a cellulose triacetate (TAC) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Further, as an adhesive for bonding the protective film, a PVA-based adhesive or a urethane-based adhesive is generally used, and among them, a PVA-based adhesive is preferably used.

(4) The polarizing plate obtained as described above can be used as a component of a liquid crystal display device by coating it with an adhesive such as an acrylic resin and 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 improving film, and the like may be simultaneously bonded.

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.

[Number of activator aggregates]
A 10 m area was cut out from the surface layer side of the PVA film roll to be measured, and a square sample having a width of 1.5 cm, a length direction of 1.5 cm, and a thickness of 60 μm was cut out. Thereafter, an image of the central part in the film thickness direction was photographed at a magnification of 1000 using a differential interference microscope. The photographed image was analyzed using image analysis software “ImagePro” manufactured by Nippon Roper Co., Ltd., and the number of activator aggregates in an area of 135 μm × 100 μm was measured.

[Releasability]
In the production of a long film of 4000 m or more, when the film was peeled off from the cast drum, those that could not be peeled off due to adhesion to the drum were evaluated as x, and those that could be peeled off without any problem were evaluated as o.

[Film surface quality]
The cut PVA film was placed in a dark room between a white screen and a projector, and the shadows reflected on the screen were observed. When discontinuous shading or streak-like shading could be confirmed, it was evaluated as x, and when the shading was not observed and uniform, it was evaluated as o. At the time of observation, the distance between the screen and the projector was 360 cm, and the distance between the screen and the PVA film was 10 cm.

[Turbidity evaluation]
The film forming stock solution was withdrawn from the outlet of the twin-screw extruder outlet, and the turbidity of the solution was visually evaluated. When the liquid was transparent, it was evaluated as ○, when it was slightly clouded, and when it was strongly clouded, it was marked X.

Example 1
After 100 parts by mass of a PVA chip having a polymerization degree of 2400 and a saponification degree of 99.9 mol% was immersed in 2500 parts by mass of distilled water at 35 ° C. for 24 hours, centrifugal dehydration was performed to obtain a PVA-containing chip having a volatile content of 70% by mass. Obtained. For 333 parts by mass of the PVA-containing chip (100 parts by mass of dry PVA), 10 parts by mass of glycerin, the number of styrene units (m) as styryl ether type surfactant (B) is 2, and the number of polyoxyethylene chains After mixing 0.27 parts by mass of an activator (n) of 13 and 0.08 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant (C), the resulting mixture is twin-screw extruded with a vent. The mixture was heated and melted (maximum temperature 130 ° C.) with a machine to obtain a film forming stock solution.

After cooling this film-forming stock solution to 100 ° C. with a heat exchanger, the film was extruded from a coat hanger die having a width of 180 cm onto a drum having a surface temperature of 90 ° C., and further dried using a hot-air drying device. A PVA film having a thickness of 60 μm and a width of 165 cm was continuously produced by cutting off both ends of the film which was thickened by neck-in during film formation. A length of 4000 m of the PVA film was wound around a cylindrical core to form a film roll. The obtained PVA film was evaluated for the number of activator aggregates, the releasability, the film surface quality, and the turbidity of the stock solution by the methods described above. Table 1 shows the results.

Examples 2 to 5, Comparative Examples 1 to 9
The production and evaluation of the PVA film were performed in the same manner as in Example 1 except that the types and amounts of the styryl ether type surfactant (B) and the surfactant (C) were changed as shown in Table 1. went. Table 1 shows the results.

As shown in Table 1, in the PVA films of Examples 1 to 5, the number of activator aggregates was 3 or less in the obtained PVA film even though the PVA aqueous solution (stock solution) was cloudy. , Peelability and film surface quality were also good.

On the other hand, in Comparative Example 1 in which the surfactant (C) was not used, the film surface quality of the obtained PVA film was not good. In Comparative Example 2 in which the surfactant (B) was not used, the obtained PVA film was not good in peelability and film surface quality. In Comparative Example 3 in which the content of the surfactant (B) exceeds 0.4 parts by mass, the film surface quality of the obtained PVA film was not good. In Comparative Example 4 in which the content of the surfactant (B) was less than 0.04, the obtained PVA film was not good in peelability and film surface quality. In Comparative Example 5 in which the surfactant (B) having a styrene unit number (m) of 1 was used, the obtained PVA film had a large number of activator aggregates, and the peelability and film surface quality were not good. In Comparative Example 6 using the surfactant (B) in which the total (n + 1) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) was 5, the obtained PVA film had poor film surface quality. Did not. In Comparative Example 7, in which the surfactant (B) having a polyoxyethylene chain number (n) of 31 was used, the obtained PVA film was not good in the peelability and film surface quality. In Comparative Example 8 in which the content of the surfactant (C) was more than 0.4 parts by mass, the obtained PVA film had a large number of activator aggregates, 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 obtained PVA film was not good.

Claims

Polyvinyl alcohol (A), at least one surfactant (B) selected from styryl ether surfactants represented by the following formulas (I) or (II), and sulfate ester type or sulfonate type A polyvinyl alcohol film containing at least one surfactant (C) selected from the group consisting of:
The content of the surfactant (B) is 0.04 to 0.4 parts by mass based on 100 parts by mass of the polyvinyl alcohol (A);
A polyvinyl alcohol film having a surfactant (C) content of 0.04 to 0.4 parts by mass based on 100 parts by mass of the polyvinyl alcohol (A).

[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 + 1) of the number of polyoxyethylene chains (n) and the number of polyoxypropylene chains (l) is 12 to 30. ]
The polyvinyl alcohol film according to claim 1, wherein the mass ratio (B: C) of the surfactant (B) and the surfactant (C) is 1: 0.2 to 1:10.
The polyvinyl alcohol film according to claim 1 or 2, wherein the film has a width of 1.5 m or more.
(4) The polyvinyl alcohol film according to any one of (1) to (3), wherein the length of the film is 3000 m 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.
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.