JP7282100B2 - Polyvinyl alcohol film and method for producing polarizing film using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyvinyl alcohol film containing polyvinyl alcohol (A), a nonionic surfactant (B) and an anionic surfactant (C), and a method for producing a polarizing film using the same.

Polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) films are used in various applications by utilizing their unique properties such as transparency, optical properties, mechanical strength and water solubility. In particular, by utilizing its excellent optical properties, PVA film is used as a raw material (original film) for manufacturing polarizing films that constitute polarizing plates, which are the basic components of liquid crystal displays (LCDs). Applications are expanding. A polarizing plate for LCD is required to have high optical performance, and a polarizing film, which is a component thereof, is also required to have high optical performance.

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

Many techniques related to PVA films and their manufacturing methods have been known so far. In Patent Document 1, a PVA resin aqueous solution containing polyoxyethylene laurylamine having a chain number of 2 as a surfactant is prepared, and the PVA resin aqueous solution is brought into contact with a drum type roll for a contact time of 30 to 120 seconds to cast. It is described that a PVA film having a moisture content of 5% by weight or less was obtained by forming a film according to the method and setting the evaporation rate of water in the PVA aqueous solution to 15 to 30% by weight per minute. According to this document, it is possible to obtain a PVA film having excellent transport performance and no optical defects.

Further, in Patent Document 2, PVA resin, sodium dodecyl sulfate as a sulfate ester salt type anionic surfactant (a), polyoxyethylene dodecyl ether as an ether type nonionic surfactant (b), and a nitrogen-containing nonion PVA films containing lauric acid diethanolamide as system surfactant (c) are described. According to this, it is said that it has excellent optical properties free from optical streaks, optical color unevenness, etc., and can exhibit an excellent effect of anti-blocking property.

Furthermore, in Patent Document 3, PVA resin, polyoxyethylene dodecyl ether as an ether-type nonionic surfactant (a), and polyoxyethylene dodecylamine as two types of nitrogen-containing nonionic surfactants (b) A PVA film containing lauric acid diethanolamide is described. According to this, it has excellent optical properties free from optical streaks, etc., and exhibits excellent blocking resistance.

JP 2011-245872 A Japanese Patent Application Laid-Open No. 2005-206809 Japanese Patent Application Laid-Open No. 2005-206810

However, in the PVA films obtained in Patent Documents 1 to 3, active agent aggregates are formed, resulting in deterioration of haze, and improvement has been desired. In addition, as in Patent Documents 2 and 3, when a tertiary amide-type lauric acid diethanolamide is used as a nonionic surfactant, its hydrolysis resistance (heat resistance) is low, so the blending amount is large. There is room for improvement from the economic point of view. In addition, when a large amount of tertiary amide type nonionic surfactant is blended, its decomposition products are likely to stay and stains are likely to occur during the film forming process, and there is room for improvement from the viewpoint of productivity.

Accordingly, the inventors of the present application conducted extensive studies, and found that secondary amide nonionic surfactants are superior in heat resistance to tertiary amide nonionic surfactants. In other words, it is preferable to use a secondary amide type nonionic surfactant from the viewpoint of economy and productivity in producing a PVA film. However, when a secondary amide type nonionic surfactant is used alone, the obtained PVA film has a large number of active agent aggregates, a high haze value, and optical defects. The inventors have confirmed. Therefore, even when a secondary amide type nonionic surfactant with high heat resistance is used, the present invention has a small number of activator aggregates, a low haze value, few optical defects, and a stretchable surfactant. It is an object of the present invention to provide a PVA film having a high magnification and good polarizing performance when processed into a polarizing film, and a method for producing a polarizing film using the PVA film.

The subject is a polyvinyl alcohol film containing polyvinyl alcohol (A), a nonionic surfactant (B) and an anionic surfactant (C),
Nonionic surfactant (B) is a secondary amide type aliphatic alkanolamide represented by the following formula (I),
The content of the nonionic surfactant (B) is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A),
The problem is solved by providing a polyvinyl alcohol film in which the content of the anionic surfactant (C) is 0.01 to 0.24 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A).

［式（Ｉ）中、Ｒは炭素数８～１８のアルキル基であり、ポリオキシエチレン鎖数（ｎ）が２～１０である。］

[In formula (I), R is an alkyl group having 8 to 18 carbon atoms, and the number of polyoxyethylene chains (n) is 2 to 10. ]

At this time, the total content (B + C) of the nonionic surfactant (B) and the anionic surfactant (C) is 0.05 to 0.24 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A). is preferred.

Further, the content ratio (B:C) of the nonionic surfactant (B) and the anionic surfactant (C) is preferably 20:80 to 80:20.

It is preferable that the film width is 1.5 m or more. It is also preferred that the length of the film is 3000 m or more. It is also preferred that the film thickness is 10 to 70 μm.

The above problem is also solved by providing a method for producing a polarizing film, which comprises the steps of dyeing and stretching the polyvinyl alcohol film.

The above problem is a method for producing a polyvinyl alcohol film containing polyvinyl alcohol (A), a nonionic surfactant (B) and an anionic surfactant (C),
A step of blending polyvinyl alcohol (A), a nonionic surfactant (B) and an anionic surfactant (C) to prepare a membrane-forming stock solution;
a step of forming a film using the film-forming stock solution,
Nonionic surfactant (B) is a secondary amide type aliphatic alkanolamide represented by the following formula (I),
The amount of the nonionic surfactant (B) in the film forming stock solution is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A),
It is also solved by providing a production method in which the amount of the anionic surfactant (C) blended in the film-forming stock solution is 0.01 to 0.24 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A). be.

［式（Ｉ）中、Ｒは炭素数８～１８のアルキル基であり、ポリオキシエチレン鎖数（ｎ）が２～１０である。］

[In formula (I), R is an alkyl group having 8 to 18 carbon atoms, and the number of polyoxyethylene chains (n) is 2 to 10. ]

The PVA films of the present invention have a low number of active agent agglomerates, low haze values, low optical defects, and high draw ratios. Therefore, by using the PVA film as a raw film, a polarizing film having good optical performance can be obtained. In addition, since the nonionic surfactant (B) is a highly heat-resistant secondary amide type, the economic efficiency and productivity in producing a PVA film are excellent.

The PVA film of the present invention comprises polyvinyl alcohol (A) (hereinafter sometimes abbreviated as PVA (A)), a nonionic surfactant (B) represented by the following formula (I), and an anionic surfactant ( C).

［式（Ｉ）中、Ｒは炭素数８～１８のアルキル基であり、ポリオキシエチレン鎖数（ｎ）が２～１０である。］

[In formula (I), R is an alkyl group having 8 to 18 carbon atoms, and the number of polyoxyethylene chains (n) is 2 to 10. ]

In the PVA film of the present invention, the nonionic surfactant (B) represented by the above formula (I) and the anionic surfactant (C) are used together in a predetermined content with respect to PVA (A). is important. The present inventors have found that when the nonionic surfactant (B) represented by the above formula (I) is used alone for PVA (A), the number of active agent aggregates is large and the haze value is high. , confirms that optical defects occur. In addition, the present inventors have found that when the anionic surfactant (C) is used alone for PVA (A), the ability to reduce the surface tension is insufficient and the processability is deteriorated, and the PVA film It has been confirmed that optical defects occur in

In the present invention, the nonionic surfactant (B) represented by the above formula (I) and the anionic surfactant (C) are used in combination in predetermined contents with respect to PVA (A) to obtain an active agent It is possible to obtain a PVA film with a small number of aggregates, a low haze value, few optical defects, a high draw ratio, and good polarizing performance when processed into a polarizing film. In addition, since the nonionic surfactant (B) is a highly heat-resistant secondary amide type, the economic efficiency and productivity in producing a PVA film are excellent.

The nonionic surfactant (B) used in the present invention is a secondary amide type aliphatic alkanolamide represented by the above formula (I). As a result of investigation by the present inventors, it was found that the secondary amide type aliphatic alkanolamide has excellent heat resistance. Therefore, by using a secondary amide-type aliphatic alkanolamide as the nonionic surfactant (B), PVA films with a small number of active agent aggregates, a low haze value, and a high film surface quality can be continuously produced. can do. From this point of view, it is highly advantageous to use the secondary amide type aliphatic alkanolamide represented by the above formula (I) as the nonionic surfactant (B).

[PVA (A)]
As the PVA (A), one produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester can be used. Examples of vinyl esters 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 the vinyl ester from the viewpoints of availability, cost, productivity of PVA (A), and the like.

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 salts thereof; methyl acrylate, ethyl acrylate, acrylic acid Acrylic esters such as n-propyl, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacryl Acids or salts 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, octadecyl methacrylate, and other methacrylic acid esters; salts thereof, acrylamide derivatives such as N-methylolacrylamide or derivatives thereof; Methacrylamide derivatives such as methylol methacrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide and N-vinylpyrrolidone; Methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n- Vinyl ethers such as butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; halogenated compounds such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride vinyl; 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 anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; can be mentioned. These other monomers may be used singly or in combination of two or more. Among others, ethylene and olefins having 3 to 30 carbon atoms are preferred, and ethylene is more preferred as the other monomer.

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

The degree of polymerization of PVA (A) is not necessarily limited, but since the film strength tends to decrease as the degree of polymerization decreases, it is preferably 200 or more, more preferably 300 or more, and even more preferably 400 or more. , particularly preferably 500 or more. In addition, if the degree of polymerization is too high, the viscosity of the aqueous solution of PVA (A) or the molten PVA (A) tends to be high, which tends to make film formation difficult. 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, which is measured in water at 30°C after resaponification and purification of PVA (A). It is obtained by the following formula from the intrinsic viscosity [η] (unit: deciliter/g).
Degree of polymerization = ([η] × 10 ⁴ /8.29) ^(1/0.62)

The degree of saponification of PVA (A) is not particularly limited, and for example, PVA (A) of 60 mol% or more can be used. The degree of saponification of (A) is preferably 95 mol% or more, more preferably 98 mol% or more, even more preferably 99 mol% or more. Here, the degree of saponification of PVA (A) is the total number of moles of structural units (typically vinyl ester-based monomer units) that can be converted to vinyl alcohol units by saponification and vinyl alcohol units possessed by PVA (A). means the ratio (mol%) of the number of moles of the vinyl alcohol unit to the The degree of saponification of PVA (A) can be measured according to the description of JIS K6726-1994.

As the PVA (A), one type of PVA may be used alone, or two or more types of PVA having different degrees of polymerization, saponification, and modification may be used in combination. However, the PVA film may be 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; If PVA having a functional group that promotes is contained, the secondary workability of the PVA film may be lowered due to the cross-linking reaction between PVA molecules. Therefore, in the case where excellent secondary workability is required, such as a raw film for optical film production, PVA (A) having an acidic functional group, PVA having an acid anhydride group, basic The content of PVA having a functional group and the content of neutralized products thereof is preferably 0.1% by mass or less, and more preferably none of them is contained.

The 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.

[Nonionic surfactant (B)]
In the present invention, it is important that the nonionic surfactant (B) is a secondary amide type aliphatic alkanolamide represented by the following formula (I).

［式（Ｉ）中、Ｒは炭素数８～１８のアルキル基であり、ポリオキシエチレン鎖数（ｎ）が２～１０である。］

[In formula (I), R is an alkyl group having 8 to 18 carbon atoms, and the number of polyoxyethylene chains (n) is 2 to 10. ]

In formula (I) above, R is an alkyl group having 8 to 18 carbon atoms. The alkyl group may be linear or branched, but preferably linear. When the number of carbon atoms (alkyl chain length) of R is less than 8, many optical defects occur in the PVA film. The carbon number (alkyl chain length) of R is preferably 9 or more, more preferably 10 or more. On the other hand, when the number of carbon atoms (alkyl chain length) of R exceeds 18, problems arise in that the number of activator aggregates increases in the PVA film and the haze value increases. The carbon number (alkyl chain length) of R is preferably 15 or less, more preferably 13 or less.

In the above formula (I), the polyoxyethylene chain number (n) is 2-10. By setting the polyoxyethylene chain number (n) within this range, the formation of active agent aggregates in the PVA film is suppressed when used in combination with the anionic surfactant (C) described later. If the number of polyoxyethylene chains (n) is less than 2, problems arise in that the number of active agent aggregates increases in the PVA film and the haze value increases. The polyoxyethylene chain number (n) is preferably 4 or more. On the other hand, when the polyoxyethylene chain number (n) exceeds 10, many optical defects occur in the PVA film. The polyoxyethylene chain number (n) is preferably 8 or less.

The content of the nonionic surfactant (B) represented by the above formula (I) is 0.01 to 0.12 parts by weight per 100 parts by weight of PVA (A). If the content of the nonionic surfactant (B) is less than 0.01 parts by mass, the ability to reduce the surface tension is insufficient, resulting in poor processability and many optical defects in the PVA film. The content of the nonionic surfactant (B) is preferably 0.02 parts by mass or more. On the other hand, when the content of the nonionic surfactant (B) exceeds 0.12 parts by mass, problems arise in that the number of active agent aggregates increases in the PVA film and the haze value increases. The content of the nonionic surfactant (B) is preferably 0.1 parts by mass or less, more preferably 0.08 parts by mass or less, and even more preferably 0.06 parts by mass or less. . The nonionic surfactant (B) used in the present invention may be used alone or in combination of two or more.

The content of the anionic surfactant (C) is 0.01 to 0.24 parts by mass with respect to 100 parts by mass of PVA (A). If the content of the anionic surfactant (C) is less than 0.01 part by mass, problems arise such as an increase in the number of active agent aggregates and a high haze value. Also, the limit draw ratio is lowered. The content of the anionic surfactant (C) is preferably 0.02 parts by mass or more, more preferably 0.03 parts by mass or more. On the other hand, when the content of the anionic surfactant (C) exceeds 0.24 parts by mass, not only the number of aggregates of the active agent increases, but also the problem of inclusion of air bubbles in the PVA film may occur. be. The content of the anionic surfactant (C) is preferably 0.18 parts by mass or less, more preferably 0.16 parts by mass or less, and even more preferably 0.14 parts by mass or less. , 0.12 parts by mass or less.

Although the anionic surfactant (C) is not particularly limited, it is preferably at least one selected from the group consisting of sulfate type and sulfonate type.

Examples of the sulfate salt type include sodium alkyl sulfate, potassium alkyl sulfate, ammonium alkyl sulfate, triethanolamine alkyl sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxypropylene alkyl ether sulfate, and sodium polyoxyethylene alkylphenyl ether sulfate. is mentioned. The alkyl is preferably alkyl having 8 to 20 carbon atoms, more preferably alkyl having 10 to 16 carbon atoms.

Examples of the sulfonate type include sodium alkylsulfonate, potassium alkylsulfonate, ammonium alkylsulfonate, triethanolamine alkylsulfonate, sodium alkylbenzenesulfonate, disodium dodecyldiphenyl ether disulfonate, sodium alkylnaphthalenesulfonate, and alkylsulfosuccinate. disodium salt, disodium polyoxyethylene alkyl sulfosuccinate, and the like. The alkyl is preferably alkyl having 8 to 20 carbon atoms, more preferably alkyl having 10 to 16 carbon atoms.

The above surfactants may be used alone or in combination of two or more. Among them, the anionic surfactant (C) is preferably of the sulfate type from the viewpoint of the ability to reduce surface tension and processability.

In the present invention, the total content (B + C) of the nonionic surfactant (B) represented by the formula (I) and the anionic surfactant (C) is, with respect to 100 parts by mass of PVA (A), It is preferably 0.05 to 0.24 parts by mass. If the total content (B+C) is less than 0.05 part by mass, the ability to reduce the surface tension is insufficient, resulting in poor process passability and the possibility of many optical defects occurring in the PVA film. More preferably, the total content (B+C) is 0.06 parts by mass or more. On the other hand, if the total content (B+C) exceeds 0.24 parts by mass, problems may arise such as the number of activator aggregates in the PVA film increasing and the haze value increasing. The total content (B+C) is more preferably 0.22 parts by mass or less, still more preferably 0.2 parts by mass or less, and particularly preferably 0.15 parts by mass or less.

In the present invention, the content mass ratio (B:C) of the nonionic surfactant (B) represented by the formula (I) and the anionic surfactant (C) is 20:80 to 80:20. is preferred. If the content mass ratio (B:C) is less than 20:80, the PVA film may have many optical defects. The content mass ratio (B:C) is more preferably 25:75 or more, and even more preferably 30:70 or more. On the other hand, if the content mass ratio (B:C) exceeds 80:20, problems may arise such as the number of activator aggregates in the PVA film increasing and the haze value increasing. Moreover, there exists a possibility that the limit draw ratio may fall. The content mass ratio (B:C) is more preferably 75:25 or less, even more preferably 70:30 or less.

[PVA film]
From the viewpoint of being able to impart flexibility 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, trimethylolpropane and the like. These may use only 1 type of plasticizers, and may use 2 or more types of plasticizers together. Among them, ethylene glycol or glycerin is preferable from the viewpoint of compatibility with PVA (A) and availability.

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). When the content of the plasticizer is 1 part by mass or more, problems with mechanical properties such as impact strength and process passability during secondary processing are less likely to occur. On the other hand, when the content of the plasticizer is 30 parts by mass or less, the film becomes moderately flexible and the handleability is improved.

The PVA film of the present invention may further contain components other than PVA, surfactants and plasticizers, if necessary. Such other components include, for example, moisture, antioxidants, ultraviolet absorbers, lubricants, coloring agents, fillers (inorganic particles, starch, etc.), preservatives, antifungal agents, and other components other than those mentioned above. A high molecular compound etc. are mentioned. The content of other components in the PVA film is preferably 10% by mass or less.

There is no particular limitation on the width of the PVA film of the present invention. The width is preferably 1.5 m or more because wide polarizing films have been demanded in recent years. In addition, if the width of the PVA film is too wide, the manufacturing cost of the film forming apparatus for forming the PVA film increases, and furthermore, when the optical film is produced by a practical production apparatus, the uniformity is reduced. The width of the PVA film is usually 7.5 m or less because it may be difficult to stretch the film to a large thickness.

The shape of the PVA film of the present invention is not particularly limited. A shaku film is preferred. The length of the long film (the length in the machine direction) is not particularly limited and can 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. A long film is preferably wound around a core to form a film roll.

The thickness of the PVA film of the present invention is not particularly limited and can be set as appropriate. The thickness of the film is preferably 10 to 70 μm from the viewpoint of using it as a raw film for producing an optical film such as a polarizing film. In addition, the thickness of the PVA film can be obtained as an average value of values measured at arbitrary 10 points.

The haze and number of active agent agglomerates of the PVA films of the present invention are measured by the methods described in the Examples below. The haze value is preferably 0.5 or less, more preferably 0.4 or less. The number of such active agent aggregates is preferably 550 or less, more preferably 420 or less, and even more preferably 300 or less.

The method for producing the PVA film of the present invention is not particularly limited, but a suitable production method is polyvinyl alcohol film containing polyvinyl alcohol (A), nonionic surfactant (B) and anionic surfactant (C). A production method comprising a step of blending polyvinyl alcohol (A), a nonionic surfactant (B) and an anionic surfactant (C) to prepare a membrane-forming stock solution, and a step of producing using the membrane-forming stock solution. forming a film, wherein the nonionic surfactant (B) is a secondary amide type aliphatic alkanolamide represented by the above formula (I), and the nonionic surfactant (B) in the film-forming stock solution is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A), and the amount of the anionic surfactant (C) in the membrane-forming stock solution is the polyvinyl alcohol (A ) is 0.01 to 0.24 parts by mass per 100 parts by mass.

A liquid medium may be further added in the step of preparing the membrane-forming stock solution. Examples of the liquid medium at this time include water, dimethylsulfoxide, 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 point of view of less load on the environment and recoverability.

In the method for producing a PVA film of the present invention, for example, PVA (A), a nonionic surfactant (B) represented by the above formula (I), an anionic surfactant (C), a liquid medium, and if necessary Further, known methods such as casting film-forming method and melt-extrusion film-forming method can be employed using the film-forming stock solution containing the plasticizer and other components described above. The membrane-forming stock solution may be obtained by dissolving PVA (A) in a liquid medium, or may be obtained by melting PVA (A).

The volatile fraction of the film-forming stock solution (the content of volatile components such as liquid media removed by volatilization or evaporation during film-forming in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc., but is 50 to 50%. It is preferably in the range of 90 mass %, more preferably in the range of 55 to 80 mass %. When the volatile content of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, and film formation is facilitated. On the other hand, when the volatile content of the membrane-forming stock solution is 90% by mass or less, the thickness uniformity of the obtained PVA film is improved without the viscosity of the membrane-forming stock solution becoming too low.

The amount of the nonionic surfactant (B) blended in the film-forming solution is preferably 0.01 to 0.12 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A). If the amount of the nonionic surfactant (B) is less than 0.01 parts by mass, the ability to reduce the surface tension is insufficient, resulting in poor processability and many optical defects in the resulting PVA film. . More preferably, the amount of the nonionic surfactant (B) to be blended is 0.02 parts by mass or more. On the other hand, when the amount of the nonionic surfactant (B) exceeds 0.12 parts by mass, problems arise in that the resulting PVA film has a large number of active agent aggregates and a high haze value. . The amount of the nonionic surfactant (B) is more preferably 0.1 parts by mass or less, further preferably 0.08 parts by mass or less, and particularly preferably 0.06 parts by mass or less. preferable. The nonionic surfactant (B) used in the present invention may be used alone or in combination of two or more.

The amount of the anionic surfactant (C) blended in the film forming stock solution is preferably 0.01 to 0.24 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A). If the amount of the anionic surfactant (C) is less than 0.01 part by mass, the resulting PVA film will have a large number of active agent aggregates and a high haze value. In addition, the limit draw ratio of the obtained PVA film is lowered. The content of the anionic surfactant (C) is more preferably 0.02 parts by mass or more, and even more preferably 0.03 parts by mass or more. On the other hand, when the amount of the anionic surfactant (C) exceeds 0.24 parts by mass, not only the number of active agent aggregates increases in the obtained PVA film, but also the problem that air bubbles are mixed in the PVA film. may occur. The amount of the anionic surfactant (C) is more preferably 0.18 parts by mass or less, further preferably 0.16 parts by mass or less, and particularly preferably 0.14 parts by mass or less. It is preferably 0.12 parts by mass or less, and most preferably 0.12 parts by mass or less.

Next, the process of forming a film will be described. The PVA film of the present invention is suitably produced by a casting film-forming method or a melt-extrusion film-forming method using the film-forming stock solution. There is no particular limitation on the specific manufacturing method at this time, and for example, the film-forming liquid may be obtained by casting or discharging the film-forming stock solution onto a support such as a drum or belt and drying it on the support. can be done. If necessary, the obtained film may be further dried with a drying roll or a hot air dryer, heat-treated with a heat treatment device, or humidity-controlled with a humidity control device. The produced PVA film is preferably wound around a core to form a film roll. In addition, both ends in the width direction of the manufactured PVA film may be cut off.

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 trapping film, and the like. According to the present invention, a PVA film having high light transmittance and high quality can be obtained. Therefore, it is a preferred embodiment of the present invention that it is an optical PVA film.

A preferred embodiment of the present invention is a method for producing a polarizing film comprising the steps of dyeing and stretching the PVA film. 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, the dyeing treatment may be performed simultaneously with the stretching treatment, or the dyeing treatment may be performed after the stretching treatment. . Further, the steps such as stretching and dyeing may be repeated multiple times. In particular, it is preferable to divide the stretching into two or more stages because it facilitates uniform stretching.

Dyes used for dyeing PVA films include iodine or dichroic organic dyes (e.g., 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; Dichroic dyes such as DirectYellow 8, 12, 44, 86, 87; DirectOrange 26, 39, 106, 107) can be used. These dyes can be used individually by 1 type or in combination of 2 or more types. Dyeing can usually be carried out by immersing the PVA film in a solution containing the above dyes, but the treatment conditions and treatment method are not particularly limited.

The method for stretching the PVA film includes a uniaxial stretching method and a biaxial stretching method, the former being preferred. Uniaxial stretching, in which the PVA film is stretched in the machine direction (MD) or the like, may be carried out by either a wet stretching method or a dry heat stretching method. is preferred. The wet stretching method includes stretching a PVA film in pure water, an aqueous solution containing various components such as additives and water-soluble organic solvents, or a water dispersion in which various components are dispersed. Specific examples of the uniaxial stretching method by wet stretching include a method of uniaxial stretching in hot water containing boric acid, a method of uniaxial stretching in a solution containing the dye or a fixing treatment bath described later, and the like. Moreover, the PVA film after absorbing water may be uniaxially stretched in the air, or may be uniaxially stretched by another method.

The stretching temperature during uniaxial stretching is not particularly limited, but 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. A temperature in the range of 50 to 180° C. is preferably employed in the case of hot drawing.

The stretch ratio of the uniaxial stretching treatment (the total stretch ratio when uniaxial stretching is performed in multiple stages) is preferably 4 times or more, and is preferably 4 times or more, from the viewpoint of polarizing performance, until the film is cut as much as possible. is preferred, 5 times or more is more preferred, and 5.5 times or more is even more preferred. The upper limit of the draw ratio is not particularly limited as long as the film is not broken, but it is preferably 8.0 times or less for uniform drawing.

In the production of the polarizing film, it is preferable to carry out 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 general treatment bath containing boric acid and/or a boron compound can be employed. At that time, if necessary, an iodine compound may be added to the treatment bath.

The PVA film that has been uniaxially stretched or uniaxially stretched and fixed is preferably then dried or heat treated. The temperature for the drying treatment or heat treatment is preferably 30 to 150°C, particularly preferably 50 to 140°C. If the temperature is too low, the dimensional stability of the resulting polarizing film tends to deteriorate. On the other hand, if the temperature is too high, the polarizing performance tends to deteriorate due to the decomposition of the dye.

A protective film that is optically transparent and has mechanical strength can be adhered to one or both sides of the polarizing film obtained as described above to form a polarizing plate. As a 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. In addition, PVA-based adhesives, urethane-based adhesives, and the like are generally used as adhesives for bonding the protective film, and among them, PVA-based adhesives are preferably used.

The polarizing plate obtained as described above can be used as a component of a liquid crystal display device by being coated with an adhesive such as an acrylic adhesive and then pasted onto a glass substrate. When the polarizing plate is attached to the glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, etc. may be attached at the same time.

EXAMPLES The present invention will be specifically described below with reference to Examples, etc., but the present invention is not limited to these Examples.

[Heat resistance of nonionic surfactant (B)]
A 10-m area was cut out from the surface layer side of the PVA film roll to be measured, and a sample piece of MD 100 mm×TD 100 mm (thickness 60 μm) was taken from an arbitrary position. The collected samples were pretreated under the following conditions.

(Pretreatment conditions)
1. Accurately weigh 0.3 g of sample into a 50 ml sample tube.
2. Add 15 ml of HFIP (hexafluoroisopropanol) and stir to dissolve at 50°C.
3. After dissolution, the solution is cooled to room temperature and added dropwise to 60 ml of methanol (room temperature, under stirring) for reprecipitation.
4. Filter through a cotton plug to remove precipitate.
5. The filtrate is concentrated with an evaporator (40° C.).
6. After concentration, the solution was made up to 2 ml with methanol and used as an analysis sample.

(Quantification of nonionic surfactant)
The pretreated sample was quantified by HPLC, and the retention rate of nonionic surfactant (B) (content of nonionic surfactant in film/blended amount of nonionic surfactant blended during film production) was obtained. rice field. HPLC was performed under the following conditions.

・流量：１ｍｌ／ｍｉｎ
・カラム：ＴＳＫｇｅｌ ＯＤＳ－８０Ｔｓ(４．６×１５０ｍｍ、５μｍ、東ソー）
・温度：４０℃
・注入量：２０μＬ
・検出器：ＥＬＳＤ(Ｇａｉｎ５０、Ｇａｓ４０、Ｎｅｂ３６℃、Ｄ.Ｔｕｂｅ４５℃）(HPLC measurement conditions for nonionic surfactant)
・ Apparatus: LC-20A1 (manufactured by Shimadzu Corporation)
- Mobile phase: a mixture of 0.1% formic acid aqueous solution and methanol - Gradient time and mobile phase methanol concentration:

・Flow rate: 1ml/min
・ Column: TSKgel ODS-80Ts (4.6 × 150 mm, 5 μm, Tosoh)
・Temperature: 40℃
・Injection volume: 20 μL
・Detector: ELSD (Gain 50, Gas 40, Neb 36°C, D.Tube 45°C)

・流量：1ｍｌ/ｍｉｎ
・カラム：ＴＳＫｇｅｌ ＯＤＳ－80－Ｔｓ（4.6×150ｍｍ、5μｍ、東ソー）
・温度：４０℃
・注入量：２０μＬ
・検出器：ＥＬＳＤ（Ｇａｉｎ１００、ｇａｓ４０、Ｎｅｂ１２℃、Ｄ.Ｔｕｂｅ４５℃）(HPLC measurement conditions for sodium polyoxyethylene lauryl ether sulfate)
・Apparatus: AQUITY UPLC (Waters)
・Mobile phase: mixture of 5mM IPC-DBAA aqueous solution and methanol ・Duration of gradient and concentration of methanol in mobile phase:

・Flow rate: 1ml/min
・Column: TSKgel ODS-80-Ts (4.6×150mm, 5μm, Tosoh)
・Temperature: 40℃
・Injection volume: 20 μL
・Detector: ELSD (Gain 100, gas 40, Neb 12°C, D.Tube 45°C)

(HPLC measurement conditions for sodium alkylsulfonate)
・Apparatus: AQUITY UPLC (Waters)
- Mobile phase: a mixture of 100 mM ammonium acetate aqueous solution and acetonitrile, 20:80
・Flow rate: 1ml/min
・Column: Acclaim Surfactant Plus (4.6×150 mm, 5 μm, Thermo)
・Temperature: 30℃
・Injection volume: 20 μL
・Detector: ELSD (Gain 100, gas 40, Neb 12°C, D.Tube 45°C)

[Quality of PVA film]
(Method for measuring haze)
A 10-m region was cut out from the surface layer side of the PVA film roll to be measured, and three sample pieces of a square of MD50 mm×TD50 mm (thickness: 60 μm) were taken from arbitrary positions. Using a haze meter "HZ-2" manufactured by Suga Test Instruments Co., Ltd., the haze of the central portion of the PVA film was measured three times each according to JIS K7136, and the average value was obtained.

(Method for measuring the 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 sample piece of MD50 mm×TD50 mm (thickness 60 μm) was further taken from an arbitrary position. Using a microscope VHX6000 (magnification: 1000 times) manufactured by Keyence Corporation, images of the collected samples were taken at positions spaced about 1 μm apart in the thickness direction of the film, and the number of activator aggregates appearing in the captured images was counted. .

(Evaluation method for optical defects)
The streak-like defects and shark-skin-like defects existing parallel to the flow direction (MD direction) during film formation on the PVA film were visually observed and evaluated. Specifically, a sample piece cut out from the PVA film obtained in the following examples and comparative examples was hung so that the MD direction was vertical, and a 30 W straight tubular fluorescent lamp was placed vertically behind it and turned on. , streaky defects were evaluated according to the following criteria.
A: The most suitable level for products with no streak-like or shark-skin-like defects.
B: There are some streak-like or shark-skin-like defects, but the level is usable as a product.
C: Many streak-like or shark-skin-like defects, unsuitable for products.

(Measurement of limit draw ratio)
A sample having a size of 100 mm MD×50 mm TD was taken from the PVA film roll to be measured, and a marked line with a length of 50 mm was drawn in the center of the sample. Four samples with marked lines were attached to a stretching jig, and the sample was immersed in water at a temperature of 30 ° C. for 1 minute. It was drawn (first stage drawing). The sample is then immersed for 2 minutes in a dyeing bath containing 0.02-0.05% by weight of iodine and 1.0% by weight of potassium iodide at a temperature of 32° C. The film was uniaxially stretched (second-stage stretching) in the machine direction (MD) up to 2.5 times.

The sample was then stretched lengthwise (MD) to 3.6 times its original length while immersed in a crosslinking bath containing boric acid at a concentration of 2.6% by weight at a temperature of 32°C for 2 minutes. It was uniaxially stretched (third stage stretching). Further, the sample was uniaxially stretched (fourth stage stretching) while being immersed in a stretching bath containing 2.8% by mass of boric acid and 5.0% by mass of potassium iodide at a temperature of 57°C. , was removed from the draw bath when 2 out of 4 were cut. The length of the distance between the gauge marks of two uncut samples was measured, and the length of the distance between the gauge marks after stretching was divided by the length of the distance between the gauge lines before stretching (50 mm). It was defined as the limit draw ratio at °C.

[Polarization performance of polarizing film]
(a) Preparation of polarizing film The PVA films obtained in Examples and Comparative Examples were stretched to the limit draw ratio in the same manner as in "Measurement of limit draw ratio" above, and two uncut samples were cut at 60 °C. and dried for 1 minute to obtain a polarizing film. At this time, the iodine concentration of the dyeing bath is changed in the range of 0.02 to 0.05%, 10 polarizing films with different iodine amounts are produced, and the light transmittance Ts and the degree of polarization V are obtained by the following method. rice field.
(b) Measurement of transmittance Ts Two square samples of MD 20 mm × TD 20 mm were taken from the polarizing film produced using the PVA film obtained in the example or comparative example, and a spectrophotometer with an integrating sphere (Jasco "V7100" manufactured by K.K. The light transmittance when tilted at 45° and the light transmittance when tilted at −45° with respect to the vertical direction were measured, and an average value Ts1 (%) of them was obtained. Similarly, the light transmittance when tilted at 45° and the light transmittance when tilted at −45° were measured for the other sample, and an average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged according to the following formula (1) to obtain the transmittance Ts (%) of the polarizing film.
Ts=(Ts1+Ts2)/2 (1)
(c) Measurement of the degree of polarization V The light transmittance T∥(%) when the two samples taken in the measurement of the transmittance Ts are superimposed so that their length directions are parallel, and the length The transmittance T ⊥ (%) of light when superimposed so that the vertical direction is orthogonal is measured in the same manner as in the above “(b) Measurement of transmittance Ts”, and the degree of polarization is obtained by the following formula (2). V (%) was obtained.
V = {(T∥-T⊥)/(T∥+T⊥)} ^1/2 × 100 (2)
(d) Calculation of Light Transmittance An approximate expression was obtained by plotting the value of the degree of polarization V against the value of the transmittance Ts of the produced polarizing film. Then, the transmittance Ts when the degree of polarization V is 99.995% was calculated from an approximate expression and used as an index of light transmittance.

Example 1
As PVA (A), chips of PVA (saponified vinyl acetate homopolymer) having a degree of polymerization of 2400 and a degree of saponification of 99.9 mol % were used. After immersing 100 parts by mass of the PVA chip in 2500 parts by mass of distilled water at 35° C., centrifugal dehydration was performed to obtain PVA water-containing chips with a volatile content of 60% by mass.

With respect to 250 parts by mass of the PVA hydrous chip (100 parts by mass of PVA), 25 parts by mass of distilled water, 12 parts by mass of glycerin, 0.03 parts by mass of nonionic surfactant (B), anionic surfactant (C ) was mixed with 0.04 parts by mass, and the resulting mixture was heated and melted (maximum temperature: 130°C) with a twin-screw extruder to obtain a membrane-forming stock solution. The nonionic surfactant (B) used at this time has 12 carbon atoms in R (alkyl group) in the above formula (I), and the polyoxyethylene chain number (n) in the above formula (I) is 6. It was a certain secondary amide type aliphatic alkanolamide. The anionic surfactant (C) was sodium polyoxyethylene alkyl ether sulfate (polyoxyethylene chain number: 3, alkyl chain: carbon number: 12).

After cooling this film-forming stock solution to 100° C. with a heat exchanger, it is extruded from a coat hanger die of 180 cm width onto a drum with a surface temperature of 90° C., dried using a hot air dryer, and then dried. A PVA film having a film thickness of 60 μm and a width of 165 cm was continuously produced by cutting off both ends of the film which had become thick due to neck-in during film production. A length of 4000 m of the produced PVA film was wound around a cylindrical core to form a film roll. The obtained PVA film was evaluated for heat resistance, optical defect, haze, number of active agent aggregates, critical draw ratio, and polarizing performance of the polarizing film by the methods described above. Table 3 shows the results.

Examples 2-9, Comparative Examples 1-5
A PVA film was produced in the same manner as in Example 1 except that the types and amounts of the nonionic surfactant (B) and the anionic surfactant (C) were changed as shown in Table 3. evaluated. In Examples 8 and 9, sodium alkylsulfonate having 15 carbon atoms in the alkyl chain was used as the anionic surfactant (C). In Comparative Example 5, a tertiary amide type lauric acid diethanolamide was used as the nonionic surfactant (B). Table 3 shows the results.

As shown in Table 3, the PVA films of Examples 1-9 had low numbers of active agent aggregates and low haze values. Although the PVA films of Examples 7 and 8 had optical defects in some places, they were at a level at which they could be used as products. In addition, the PVA films of Examples 1 to 9 had a high critical draw ratio, and thus were difficult to tear and had excellent polarizing performance. On the other hand, the PVA film of Comparative Example 1, in which the nonionic surfactant (B) represented by formula (I) was not used, had many optical defects. The PVA film of Comparative Example 2 in which the anionic surfactant (C) was not used, the PVA film of Comparative Example 3 in which the content of the nonionic surfactant (B) represented by the above formula (I) was high, and the anion The PVA film of Comparative Example 4, in which the added amount of the system surfactant (C) was large, had a large number of active agent aggregates and a high haze value. In addition, the PVA films of Comparative Examples 2 to 4 had a low limit draw ratio and were easy to cut, and the polarizing performance was not good. In Comparative Example 5 in which lauric acid diethanolamide was used as the nonionic surfactant, the heat resistance of the nonionic surfactant was low, the number of active agent aggregates was large, and the haze value was high. In addition, the PVA film of Comparative Example 5 had a low critical draw ratio, was easily torn, and had poor polarizing performance.

Claims (8)

A polyvinyl alcohol film containing polyvinyl alcohol (A), a nonionic surfactant (B) and an anionic surfactant (C),
Nonionic surfactant (B) is a secondary amide type aliphatic alkanolamide represented by the following formula (I),
The content of the nonionic surfactant (B) is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A),
A polyvinyl alcohol film in which the content of the anionic surfactant (C) is 0.01 to 0.24 parts by mass based on 100 parts by mass of the polyvinyl alcohol (A).

[In formula (I), R is an alkyl group having 8 to 18 carbon atoms, and the number of polyoxyethylene chains (n) is 2 to 10. ] The total content (B + C) of the nonionic surfactant (B) and the anionic surfactant (C) is 0.05 to 0.24 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A). The polyvinyl alcohol film according to claim 1. The polyvinyl alcohol film according to claim 1 or 2, wherein the content ratio (B:C) of the nonionic surfactant (B) and the anionic surfactant (C) is 20:80 to 80:20. The polyvinyl alcohol film according to any one of claims 1 to 3, having a width of 1.5 m or more. The polyvinyl alcohol film according to any one of claims 1 to 4, which has a length of 3000 m or more. The polyvinyl alcohol film according to any one of claims 1 to 5, which has a thickness of 10 to 70 µm. A method for producing a polarizing film, comprising the steps of dyeing and stretching the polyvinyl alcohol film according to any one of claims 1 to 6. A method for producing a polyvinyl alcohol film containing polyvinyl alcohol (A), a nonionic surfactant (B) and an anionic surfactant (C),
A step of blending polyvinyl alcohol (A), a nonionic surfactant (B) and an anionic surfactant (C) to prepare a membrane-forming stock solution;
a step of forming a film using the film-forming stock solution,
Nonionic surfactant (B) is a secondary amide type aliphatic alkanolamide represented by the following formula (I),
The amount of the nonionic surfactant (B) in the film forming stock solution is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A),
The manufacturing method, wherein the amount of the anionic surfactant (C) in the film forming stock solution is 0.01 to 0.24 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A).

[In formula (I), R is an alkyl group having 8 to 18 carbon atoms, and the number of polyoxyethylene chains (n) is 2 to 10. ]