KR20230098570A - Film for manufacturing optical film, method for manufacturing optical film, and optical film - Google Patents

Abstract

When an optical film having the same degree of shrinkage stress is manufactured, an increase in the stretching temperature can be suppressed and an optical film having excellent optical performance can be obtained, and a method for manufacturing an optical film using such a film for optical film production and an optical film. The present invention includes polyvinyl alcohol having a silicon-containing group and an ethylene unit, wherein the silicon-containing group is a silanol group or a group that can be converted to a silanol group in the presence of water, and all structural units in the polyvinyl alcohol It is a film for optical film production whose content of the said silicon-containing group is 0.01 mol% or more and 1.0 mol% or less with respect to, and content of the said ethylene unit is 0.5 mol% or more and 10 mol% or less.

Description

Film for manufacturing optical film, method for manufacturing optical film, and optical film

The present invention relates to a film for producing an optical film, a method for manufacturing an optical film, and an optical film.

BACKGROUND OF THE INVENTION A polarizing plate having functions of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Most polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of the polarizing film. As a polarizing film, an iodine-based dye (I ₃ ^- or I _5- ^, etc.) and dichroic dyes such as dichroic organic dyes are mainly adsorbed.

LCDs are widely used, such as small devices such as electronic desk calculators and wristwatches, smartphones, notebook computers, LCD monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring instruments used indoors and outdoors. Corresponding to the recent high performance of LCD, high performance is requested|required also of the polarizing plate which is a component of LCD. Specifically, a polarizing plate having superior optical performance and excellent dimensional stability even at high temperatures is required. Therefore, also about the polarizing film used for a polarizing plate, it is requested|required that it has more superior optical performance (polarization performance) and that shrinkage stress in high temperature is small.

However, in a polarizing film, it is not easy to reduce shrinkage stress under high temperature while improving optical performance (polarization performance). This is because, in general, a trade-off relationship exists between the polarization performance and shrinkage stress of a polarizing film. That is, when trying to increase the polarization performance of a polarizing film, the shrinkage stress increases, and when trying to reduce the shrinkage stress, the polarization performance decreases.

Patent Literature 1 discloses a polarizing film in which PVA having a degree of polymerization of at least 2500 is used as a polarizing film having improved optical performance, heat-and-moisture resistance, and the like. In Patent Literature 1, film formation is performed using a PVA film forming solution in which PVA having a high degree of polymerization having a degree of polymerization of 4980 or the like is dissolved in a solvent containing dimethyl sulfoxide as a main component.

Japanese Unexamined Patent Publication No. 1-105204

In production of an industrial PVA film, it is common to use a PVA aqueous solution in which water is used as a solvent as a film forming solution in consideration of environmental aspects, economic efficiency, and the like. However, when PVA with a high degree of polymerization is used as in Patent Literature 1, since the viscosity of the PVA aqueous solution increases, the film forming property of the PVA film is poor, which is not preferable for industrial production. Therefore, a method of increasing the optical performance of an optical film other than a method of increasing the degree of polymerization of PVA is desired. Moreover, when the manufacturing conditions (stretching conditions) of an optical film are made the same, the optical film obtained from the PVA film which has PVA of high polymerization degree has shrinkage stress becoming high compared with the PVA film which has PVA of low polymerization degree. Therefore, when a PVA film having PVA having a high polymerization degree is used, in order to obtain an optical film having excellent optical performance and a small shrinkage stress, it is necessary to raise the stretching temperature at the time of manufacturing the optical film, industrial production not desirable Therefore, even when the PVA film which has PVA of high polymerization degree is used, the technique of obtaining the optical film excellent in optical performance is desired, without raising the stretching temperature at the time of manufacturing an optical film to a high temperature.

The present inventors found that the optical performance of the optical film obtained could be improved significantly, suppressing the viscosity raise of PVA aqueous solution, if the PVA film containing PVA which has a silicon-containing group was used. However, even in the case of using a PVA film containing PVA having a silicon-containing group, it was still necessary to raise the stretching temperature at the time of manufacturing the optical film.

The present invention has been made based on the above circumstances, and an object thereof is to suppress the increase in the stretching temperature and to obtain an optical film having excellent optical performance when an optical film having the same shrinkage stress is manufactured. It aims at providing the film for film manufacture, the manufacturing method of the optical film using such a film for optical film manufacture, and an optical film.

The purpose of the above is

[1] A PVA containing a silicon-containing group and an ethylene unit, wherein the silicon-containing group is a silanol group or a group that can be converted to a silanol group in the presence of water, and the silicon-containing group for all structural units in the PVA Film for optical film manufacture whose content of group is 0.01 mol% or more and 1.0 mol% or less, and content of the said ethylene unit is 0.5 mol% or more and 10 mol% or less;

[2] The film for producing an optical film according to [1], wherein the PVA has a viscosity average polymerization degree of 1,000 or more and 6,000 or less, and a saponification degree of 98.7 mol% or more;

[3] The film for producing an optical film according to [2], wherein the product of the viscosity average degree of polymerization and the content of the silicon-containing group is 100 mol% or more and 2,000 mol% or less;

[4] The film for producing an optical film according to any one of [1] to [3] having an average thickness of 1 μm or more and 75 μm or less;

[5] The film for producing an optical film according to any one of [1] to [4], wherein the degree of swelling is 140% or more and 400% or less;

[6] The film for producing an optical film according to any one of [1] to [5], wherein the optical film is a polarizing film;

[7] The film for producing an optical film according to any one of [1] to [6], which is an unstretched film;

[8] A method for producing an optical film comprising a step of uniaxially stretching the film for optical film production according to any one of [1] to [7];

[9] The method for producing an optical film according to [8], wherein the optical film is a polarizing film;

[10] PVA containing a silicon-containing group and an ethylene unit, wherein the silicon-containing group is a silanol group or a group that can be converted to a silanol group in the presence of water, and the silicon-containing group for all structural units in the PVA An optical film having a group content of 0.01 mol% or more and 1.0 mol% or less, and an ethylene unit content of 0.5 mol% or more and 10 mol% or less;

[11] The optical film according to [10], wherein the shrinkage stress is 100 N/m 2 or less;

[12] The optical film of [10] or [11], which is a polarizing film; and

[13] The optical film according to any one of [10] to [12], which is a single layer film;

This is achieved by providing any of

ADVANTAGE OF THE INVENTION According to the present invention, when an optical film having the same degree of shrinkage stress is manufactured, an increase in the stretching temperature can be suppressed and an optical film having excellent optical performance can be obtained, and a film using such a film for optical film production can be obtained. A method for manufacturing an optical film and an optical film can be provided. In other words, according to the film for manufacturing an optical film and the manufacturing method of the optical film of the present invention, increase in shrinkage stress and increase in temperature of the stretching temperature can be suppressed while improving the optical performance of the obtained optical film.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph plotting the stretching temperature when the shrinkage stress of each polarizing film obtained in Examples 1 to 3 and Comparative Examples 1 to 5 becomes 75 N/mm 2 with respect to the dichroism ratio at that time.
2 is a graph plotting the stretching temperature when the shrinkage stress of each polarizing film obtained in Example 3 and Comparative Examples 1, 4, and 5 becomes 75 N/mm 2 with respect to the dichroism ratio at that time.

<Film for optical film production>

The film for optical film manufacture of this invention contains polyvinyl alcohol (Hereinafter, it may call "modified PVA.") which has a silicon-containing group and an ethylene unit.

(modified PVA)

Modified PVA is a polymer having a vinyl alcohol unit (-CH ₂ -CH(OH)-) as a structural unit, and also has a silicon-containing group and an ethylene unit. Modified PVA may further have vinyl ester units, such as a vinyl acetate unit, and other structural units.

1,000 is preferable, as for the lower limit of the viscosity average degree of polymerization of modified PVA, 2,000 is more preferable, and 2,500 is still more preferable. When the viscosity average polymerization degree of modified PVA is more than the said lower limit, the film for optical film manufacture of this invention becomes what is excellent in extending|stretching processability, and can obtain the optical film which has higher optical performance and favorable heat-and-moisture resistance. On the other hand, as for the upper limit of the said viscosity average degree of polymerization, 6,000 are preferable, 5,000 are more preferable, and 4,000 are still more preferable. When the viscosity average degree of polymerization of the modified PVA is equal to or less than the above upper limit, good water solubility is exhibited and an increase in the viscosity of the aqueous solution is suppressed. Moreover, when the viscosity average polymerization degree of modified PVA is below the said upper limit, the temperature increase of extending|stretching temperature is suppressed more. For this reason, when the viscosity average polymerization degree of modified PVA is below the said upper limit, favorable film forming property is exhibited and productivity of the film for optical film manufacture of this invention can be improved. Moreover, when the viscosity average polymerization degree of modified PVA is below the said upper limit, the optical film in which the increase of shrinkage stress was suppressed becomes easy to be obtained from the film for optical film manufacture of this invention.

The viscosity average degree of polymerization means an average degree of polymerization measured according to the description of JIS K6726-1994. That is, in the present specification, the viscosity average degree of polymerization is determined by re-saponifying and refining the residual vinyl ester groups of PVA, and then measuring the intrinsic viscosity [η] (unit: deciliter/g) in water at 30°C, according to the following formula can be obtained by

Viscosity average degree of polymerization Po = ([η] × 10 ⁴ /8.29) ^(1/0.62)

The lower limit of the degree of saponification of the modified PVA is preferably 98.7 mol%, more preferably 99.0 mol%, still more preferably 99.5 mol%, still more preferably 99.8 mol%, and particularly preferably 99.9 mol%. When the degree of saponification is equal to or greater than the lower limit, an optical film superior in optical performance and heat-and-moisture resistance is obtained. On the other hand, although there is no particular restriction on the upper limit of the degree of saponification, from the viewpoint of productivity of modified PVA, 99.99 mol% or less is preferable.

The degree of saponification of PVA is the ratio of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification in PVA (mol %) says The degree of saponification of PVA can be measured according to the description of JIS K6726-1994.

Modified PVA has a silicon-containing group. This silicon-containing group is a silanol group or a group that can be converted to a silanol group in the presence of water. The silanol group refers to a group having a silicon atom and at least one hydroxyl group bonded to the silicon atom. The number of hydroxyl groups that the silanol group has is usually one of 1 to 3, and it is preferable that it is 3. The hydroxyl group of the silanol group may be present in the state of a salt (eg, -ONa, -OK, etc.).

The group that can be converted to a silanol group in the presence of water means a group that can be converted to a silanol group when PVA is heated in water under conditions of a reaction time of 2 hours and a reaction temperature of 150°C. Conversion to this silanol group may occur by hydrolysis. Examples of groups that can be converted into silanol groups in the presence of water include groups in which at least one alkoxy group or acyloxy group is bonded to a silicon atom, and specifically, trimethoxysilyl group, triethoxysilyl group, triiso Propoxysilyl group, dimethoxymethylsilyl group, diethoxymethylsilyl group, methoxydimethylsilyl group, ethoxydimethylsilyl group, triacetoxysilyl group, etc. are mentioned.

Examples of the silicon-containing group, that is, a silanol group or a group that can be converted into a silanol group in the presence of water, include groups represented by any of the following formulas (1) to (3). Among these, the group represented by following formula (1) is preferable.

[Formula 1]

In Formulas (1) to (3), R ¹ is each independently a hydrogen atom, a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms, or a substituted or unsubstituted acyl group having 1 to 20 carbon atoms. R ² is each independently a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms.

Examples of hydrocarbon groups having 1 to 20 carbon atoms represented by R ¹ and R ² include aliphatic hydrocarbon groups, alicyclic hydrocarbon groups (such as cyclohexyl groups), aromatic hydrocarbon groups (such as phenyl groups), and preferred aliphatic hydrocarbon groups. Examples of the aliphatic hydrocarbon group include alkyl groups such as methyl, ethyl and propyl groups, alkenyl groups such as vinyl, and alkynyl groups such as ethynyl, and an alkyl group is preferable. As carbon number of the hydrocarbon group represented by ^R1 and ^R2 , 1-6 are preferable and 1-3 are more preferable. At least a part of the hydrogen atoms of the hydrocarbon group represented by R ¹ and R ² may be substituted with a halogen atom, a carboxy group, an alkoxy group (methoxy group, ethoxy group, etc.) or the like.

Examples of the acyl group of 1 to 20 carbon atoms represented by R ¹ include a hydrogen atom or a group in which a carbonyl group (-CO-) is bonded to a hydrocarbon group of 1 to 19 carbon atoms. As a hydrocarbon group of 1-19 carbon atoms, an aliphatic hydrocarbon group is preferable and an alkyl group is more preferable. As an acyl group, a formyl group, an acetyl group, a propionyl group, a benzoyl group etc. are mentioned specifically,. As carbon number of the acyl group represented by R ^<1> , 1-6 are preferable and 1-3 are more preferable. At least a part of the hydrogen atoms of the acyl group represented by R ¹ may be substituted with a halogen atom, a carboxy group, an alkoxy group (such as a methoxy group), or the like.

In the group represented by any of the formulas (1) to (3), when at least one of R ¹ is a hydrogen atom, the group is a silanol group. In addition, in the group represented by any one of the formulas (1) to (3), when all R ¹ are not hydrogen atoms, this group is a group that can be converted to a silanol group in the presence of water. As R ¹ , it is preferably a hydrogen atom or a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms.

From the viewpoint of the optical performance of the resulting optical film, etc., the silicon-containing group is preferably directly bonded to a carbon atom in the polymer main chain via a silicon-carbon bond.

The content of silicon-containing groups relative to all structural units in the modified PVA is 0.01 mol% or more and 1.0 mol% or less. Thus, the optical performance of the optical film obtained is improved by using the modified PVA which has a predetermined amount of silicon-containing groups. The lower limit of the silicon-containing group content of the modified PVA is 0.01 mol%, preferably 0.05 mol%, more preferably 0.1 mol%, and even more preferably 0.15 mol% in some cases. By making content of a silicon-containing group more than the said minimum, the optical performance of the optical film obtained can fully be improved. On the other hand, the upper limit of the content of silicon-containing groups relative to all structural units in the modified PVA is 1.0 mol%, preferably 0.8 mol%, more preferably 0.6 mol%, still more preferably 0.4 mol%. By setting the content of the silicon-containing group below the above upper limit, the water solubility of the modified PVA and the viscosity stability of the aqueous solution become good, and the film productivity (film forming property) can be improved. Moreover, it is also possible to suppress the temperature increase of extending|stretching temperature etc. by making content of a silicon-containing group below the said upper limit.

In the modified PVA, the silicon-containing group content (mol%) can be determined, for example, from proton NMR of the vinyl ester polymer before saponification. Here, when measuring the proton NMR of the vinyl ester polymer before saponification, the vinyl ester polymer is re-precipitated and purified with hexane-acetone to completely remove unreacted monomers from the polymer, followed by drying at 90 ° C. under reduced pressure for 2 days. , dissolved in CDCl ₃ solvent, and used for analysis.

The lower limit of the product of the viscosity average degree of polymerization of the modified PVA and the silicon-containing group content is preferably 100 mol%, more preferably 200 mol%, still more preferably 300 mol%, even more preferably 400 mol%. there is. When the product is equal to or greater than the lower limit, the resulting optical film has more excellent optical performance. On the other hand, the upper limit of the product is preferably 2,000 mol%, more preferably 1,500 mol%, still more preferably 1,200 mol%, and particularly preferably 800 mol%. Since the water solubility of modified PVA becomes higher and the temperature increase of extending|stretching temperature is suppressed more because the said product is below the said upper limit, it is possible to improve productivity of the said film for optical film manufacture more, etc.

Modified PVA preferably has a structural unit having a silicon-containing group. As a structural unit which has a silicon-containing group, the structural unit represented by following formula (4) is mentioned.

[Formula 2]

In Formula (4), R ³ is a hydrogen atom or a methyl group. R ⁴ is a single bond or a divalent linking group. R ⁵ is a silicon-containing group.

As R ³ , a hydrogen atom is preferable.

As a divalent linking group represented by R ⁴ , -(CH ₂ ) _n - (n is an integer of 1 to 5) or -CONR ⁶ -R ⁷ - (R ⁶ is a hydrogen atom or 1 to 5 carbon atoms) An alkyl group, R ⁷ is a group represented by -(CH ₂ ) _n - or a divalent hydrocarbon group containing at least one of an oxygen atom and a nitrogen atom).

Examples of the divalent hydrocarbon group containing at least one of an oxygen atom and a nitrogen atom include -CH ₂ CH ₂ NHCH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ NHCH ₂ CH ₂ -, -CH ₂ CH ₂ NHCH ₂ -, -CH ₂ CH ₂ N(CH ₃ )CH ₂ CH ₂ -, -CH ₂ CH ₂ N(CH ₃ )CH ₂ -, -CH ₂ CH ₂ OCH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ OCH ₂ CH ₂ -, -CH ₂ CH ₂ OCH ₂ -, and the like. The number of carbon atoms in the divalent hydrocarbon group containing at least one of an oxygen atom and a nitrogen atom can be, for example, 2 or more and 6 or less.

R ⁴ is preferably a single bond.

Specific examples of the silicon-containing group represented by R ⁵ are as described above, and include groups represented by any of the formulas (1) to (3), and the group represented by the formula (1) is preferable.

The number of silicon-containing groups included in the structural unit having silicon-containing groups is not particularly limited, but may be one. The range of content of the structural unit which has a silicon-containing group with respect to all the structural units in modified PVA may be the range of content of the silicon-containing group mentioned above. In addition, the range of the product of the viscosity average degree of polymerization of modified PVA and the content of the structural unit having a silicon-containing group may be the range of the product of the aforementioned viscosity average degree of polymerization and the content of the silicon-containing group.

Modified PVA has an ethylene unit (-CH ₂ -CH ₂ -) further. The content of ethylene units relative to all structural units in the modified PVA is 0.5 mol% or more and 10 mol% or less. In this way, by using the modified PVA having a predetermined amount of ethylene units, an optical film excellent in optical performance can be obtained while suppressing an increase in the stretching temperature. 1.0 mol% is preferable and, as for the minimum of content of an ethylene unit, 2.0 mol% is more preferable. By making content of an ethylene unit more than the said minimum, the temperature increase of extending|stretching temperature can be suppressed more. On the other hand, the upper limit of the content of the ethylene unit is preferably 6 mol%, more preferably 5 mol%, still more preferably 4.5 mol%. By making content of an ethylene unit below the said upper limit, it is possible to improve the water solubility of modified PVA, etc.

The content of the ethylene unit in the modified PVA can be obtained, for example, using proton NMR. For example, similar to the content of the silicon-containing group described above, the modified vinyl ester polymer that is a precursor of the modified PVA is obtained by proton NMR. By measuring with , it is possible to obtain the ethylene unit content of the modified PVA.

Modified PVA may have structural units other than a vinyl alcohol unit, a vinyl ester unit, a structural unit having a silicon-containing group, and an ethylene unit. However, the content of the other structural units relative to all structural units of the modified PVA is preferably 15 mol% or less, more preferably 5 mol% or less, still more preferably 1 mol% or less, and 0.1 mol% or less. In some cases, it is even more desirable. When the modified PVA is substantially composed of a structural unit having a vinyl alcohol unit, a vinyl ester unit, a silicon-containing group, and a structural unit having an ethylene unit, the effects of the present invention may be more sufficiently exhibited in some cases.

The film for optical film production may contain one type of modified PVA alone, or may contain two or more types of modified PVA from which the degree of polymerization, degree of saponification, silicon-containing group content, and ethylene unit content differ from each other.

Although the lower limit of content of the modified PVA in the said film for optical film manufacture is not specifically limited, 50 mass % is preferable, 80 mass % is more preferable, and 85 mass % is still more preferable. By making content of modified PVA more than the said minimum, the effect of this invention can be further heightened. In addition, the upper limit of this content is not specifically limited, It may be 100 mass %, 99 mass % is preferable, and 95 mass % is more preferable. In addition, content (mass %) of each component in the film for optical film manufacture is a dry state, ie, a value based on the total content of all components other than water.

(Method for producing modified PVA)

The manufacturing method of modified PVA is not specifically limited. For example, it can manufacture by copolymerizing a vinyl ester monomer, the monomer which has a silicon-containing group, and ethylene, and saponifying the obtained vinyl ester polymer.

Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerianate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. can Among these, vinyl acetate is preferable.

Examples of the monomer having a silicon-containing group include vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, allyltrimethoxysilane, Allylmethyldimethoxysilane, allyldimethylmethoxysilane, allyltriethoxysilane, allylmethyldiethoxysilane, allyldimethylethoxysilane, vinyltris(β-methoxyethoxy)silane, vinylisobutyldimethoxysilane, vinyl Ethyldimethoxysilane, Vinylmethoxydibutoxysilane, Vinyldimethoxybutoxysilane, Vinyltributoxysilane, Vinylmethoxydihexyloxysilane, Vinyldimethoxyhexyloxysilane, Vinyltrihexyloxysilane, Vinylmethoxydioctyloxy Silane, vinyldimethoxyoctyloxysilane, vinyltrioctyloxysilane, vinylmethoxydilauryloxysilane, vinyldimethoxylauryloxysilane, vinylmethoxydioleyloxysilane, vinyldimethoxyoleyloxysilane, 3-( Meth)acrylamide-propyltrimethoxysilane, 3-(meth)acrylamide-propyltriethoxysilane, 3-(meth)acrylamide-propyltri(β-methoxyethoxy)silane, 2-(meth) Acrylamide-ethyltrimethoxysilane, 1-(meth)acrylamide-methyltrimethoxysilane, 2-(meth)acrylamide-2-methylpropyltrimethoxysilane, 2-(meth)acrylamide-isopropyl Trimethoxysilane, N-(2-(meth)acrylamide-ethyl)-aminopropyltrimethoxysilane, (3-(meth)acrylamide-propyl)-oxypropyltrimethoxysilane, 3-(meth) Acrylamide-propyltriacetoxysilane, 2-(meth)acrylamide-ethyltriacetoxysilane, 4-(meth)acrylamide-butyltriacetoxysilane, 3-(meth)acrylamide-propyltripropionyloxy Silane, 2-(meth)acrylamide-2-methylpropyltriacetoxysilane, N-(2-(meth)acrylamide-ethyl)-aminopropyltriacetoxysilane, 3-(meth)acrylamide-propyliso Butyldimethoxysilane, 2-(meth)acrylamide-ethyldimethylmethoxysilane, 3-(meth)acrylamide-propylmethyldiacetoxysilane, 2-(meth)acrylamide-2-methylpropylhydrogendimethoxy Silane, 3-(N-methyl-(meth)acrylamide)-propyltrimethoxysilane, 2-(N-ethyl-(meth)acrylamide)-ethyltriacetoxysilane, etc. are mentioned.

The method for copolymerizing a vinyl ester monomer, a monomer having a silicon-containing group, and ethylene is not particularly limited, and publicly known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization may be used. Among these methods, a bulk polymerization method performed without a solvent and a solution polymerization method performed using a solvent such as alcohol are preferable. As a solvent used as a solvent at the time of solution polymerization, Ester, such as methyl acetate and ethyl acetate; Aromatic hydrocarbons, such as benzene and toluene; Lower alcohols, such as methanol and ethanol, etc. are mentioned.

As the initiator used in the copolymerization reaction, conventionally known azo-based initiators, peroxide-based initiators, redox-based initiators and the like are appropriately selected. As the azo initiator, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2 ,4-dimethylvaleronitrile) and the like. Examples of the peroxide initiator include percarbonate compounds such as dinormal propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butylperoxyneodecanate, α-cumylperoxyneodecanate, and t-butylperoxyneodecanate; Acetyl cyclohexyl sulfonyl peroxide, diisobutyryl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate etc. are mentioned. Furthermore, it is possible to make an initiator by combining potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like with the above-mentioned peroxide-based initiator. Examples of the redox initiator include a combination of the above peroxide and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, or rongalite.

The polymerization temperature during the copolymerization reaction is not particularly limited, but is preferably 0°C or higher and 180°C or lower, more preferably 20°C or higher and 160°C or lower, and still more preferably 30°C or higher and 150°C or lower.

As a method for producing the vinyl ester polymer, it is preferable to copolymerize the vinyl ester monomer and the monomer having a silicon-containing group while pressurizing ethylene. The ethylene pressure in the polymerization reactor at that time is not particularly limited, but is preferably 0.01 to 2.0 MPa, more preferably 0.05 to 1.0 MPa, and even more preferably 0.1 to 0.65 MPa in some cases. The polymerization rate of the vinyl ester monomer at the outlet of the polymerization reactor is not particularly limited, but is preferably 5 to 90% and more preferably 15 to 85% in some cases.

When copolymerizing a vinyl ester monomer, a monomer having a silicon-containing group, and ethylene, other copolymerizable monomers may be copolymerized as necessary as long as the effect of the present invention is not impaired. As this other monomer, For example, C3-C30 olefins, such as propylene, 1-butene, and isobutene; acrylic acid or its salt; Acrylic acid esters, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or its salt; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-methacrylate methacrylic acid esters such as ethylhexyl, dodecyl methacrylate, and octadecyl methacrylate; Acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid or its salts, acrylamidepropyldimethylamine or its salts, N-methylolacrylamide Acrylamide derivatives, such as an amide or its derivative(s); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid or its salts, methacrylamidepropyldimethylamine or its salts, N-methylolmethacrylamide or its derivatives, etc. krylamide derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; Vinyl such as methyl 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 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 salt, ester or acid anhydride; itaconic acid or its salt, ester or acid anhydride; Isopropenyl acetate etc. are mentioned. The vinyl ester polymer may have a structural unit derived from one or two or more of the above-mentioned other monomers.

The ratio of the structural units derived from the other monomers (vinyl ester monomer, monomer having a silicon-containing group, and monomer other than ethylene) in the vinyl ester polymer is not necessarily limited as long as the effect of the present invention is not impaired, but the vinyl ester Based on the number of moles of all structural units constituting the polymer, the amount is preferably 15 mol% or less, more preferably 5 mol% or less, even more preferably 1 mol% or less, and even more preferably 0.1 mol% or less in some cases. .

The vinyl ester polymer is then saponified in a solvent in accordance with a known method, leading to a modified PVA. As a solvent used for the saponification reaction, alcohol is preferable. Examples of the alcohol include lower alcohols such as methanol and ethanol, and methanol is particularly preferably used. The solvent used for the saponification reaction may further contain, in addition to alcohol, an organic solvent such as acetone, esters such as methyl acetate and ethyl acetate, and toluene. Examples of the catalyst used in the saponification reaction include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, alkali catalysts such as sodium methylate, acid catalysts such as mineral acids, and the like. The temperature of the saponification reaction can be, for example, 20°C or higher and 60°C or lower. When a gel-like product precipitates out as the saponification reaction proceeds, modified PVA is obtained by pulverizing the product at that point and drying it after washing.

(plasticizer)

It is preferable that the film for optical film manufacture of this invention contains a plasticizer. When the film for optical film manufacture contains a plasticizer, it is possible to improve ductility. As the plasticizer, a polyhydric alcohol is preferred. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Among these, glycerin is preferable from the viewpoint of the effect of improving the stretchability. 1 type or 2 or more types can be used for a plasticizer.

As a lower limit of content of the plasticizer in the film for optical film manufacture of this invention, 1 mass part is preferable with respect to 100 mass parts of modified PVA, 3 mass parts is more preferable, and 5 mass parts is still more preferable. When content of a plasticizer is more than the said lower limit, the ductility of a film improves and it is possible to further improve the optical performance of the optical film obtained. On the other hand, the upper limit of the content of the plasticizer is preferably 20 parts by mass, more preferably 17 parts by mass, and still more preferably 15 parts by mass with respect to 100 parts by mass of the modified PVA. When the content of the plasticizer is equal to or less than the above upper limit, it is possible to suppress excessive softening of the film and deterioration in handleability.

(Surfactants)

It is preferable that the said film for optical film manufacture contains surfactant. By forming a film using a film forming undiluted solution containing a surfactant, the film forming property is improved, the occurrence of uneven film thickness is suppressed, and the film is easily separated from the metal roll or belt used for film forming. In the case where a film for optical film production is produced from a film forming stock solution containing a surfactant, the resulting film may contain a surfactant.

Although the kind of surfactant is not specifically limited, From a viewpoint of peelability from a metal roll or belt, anionic surfactant and nonionic surfactant are preferable.

Examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfuric acid ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzenesulfonate.

Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; Alkyl phenyl ether types, such as polyoxyethylene octyl phenyl ether; Alkyl ester types, such as polyoxyethylene laurate; Alkylamine types, such as polyoxyethylene laurylamino ether; Alkyl amide types, such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; Allyl phenyl ether types, such as polyoxyalkylene allyl phenyl ether, etc. are mentioned.

Surfactant can be used individually by 1 type or in combination of 2 or more types.

When the film for optical film production contains a surfactant, the lower limit of the content is preferably 0.01 part by mass, more preferably 0.02 part by mass, and still more preferably 0.05 part by mass with respect to 100 parts by mass of modified PVA. By making content of surfactant more than the said lower limit, film forming property and peelability improve more. On the other hand, the upper limit of this content is preferably 0.5 parts by mass, more preferably 0.3 parts by mass, and still more preferably 0.1 parts by mass, based on 100 parts by mass of modified PVA. By making content of surfactant below the said upper limit, it can suppress that a surfactant bleeds out on the surface of a film, blocking arises, and handling property falls.

(other additives, etc.)

In the film for producing an optical film of the present invention, further, fillers, processing stabilizers such as copper compounds, weather resistance stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, other thermoplastic resins, lubricants, fragrances, antifoaming agents, Additives such as a deodorant, an extender, a release agent, a release agent, a reinforcing agent, a crosslinking agent, an antifungal agent, an antiseptic agent, and a crystallization rate retardant may be appropriately contained as necessary.

PVA other than the above-mentioned modified PVA may be contained in the film for optical film manufacture of this invention. 80 mass % or more is preferable, as for the total content of all PVA containing modified PVA, a plasticizer, and surfactant in the film for optical film manufacture of this invention, 90 mass % or more is more preferable, and 95 mass % or more is More preferably, 99% by mass or more is even more preferable in some cases. The effect of this invention can be exhibited more fully because the film for optical film manufacture of this invention is comprised substantially from PVA, a plasticizer, and surfactant.

As content of the above-mentioned modified PVA with respect to all the PVA contained in the film for optical film manufacture of this invention, 50 mass % or more is preferable, 80 mass % or more is more preferable, 90 mass % or more is more preferable, 95 mass % or more is more preferable, and 99 mass % or more is still more preferable. The film for optical film manufacture of this invention WHEREIN: The effect of this invention can be exhibited more fully by mainly using modified PVA as PVA.

80 mass % or more is preferable, as for the total content of modified PVA in the film for optical film manufacture of this invention, a plasticizer, and surfactant, 90 mass % or more is more preferable, 95 mass % or more is still more preferable, and 99 In some cases, mass % or more is more preferable. The effect of this invention can be exhibited more fully because the film for optical film manufacture of this invention is comprised substantially from modified PVA, a plasticizer, and surfactant.

(shape, physical properties, etc.)

The film for optical film manufacture of this invention is what is called a raw film used as a material of an optical film. However, the film for optical film manufacture of this invention is not limited to what is roll shape.

Although the average thickness of the film for optical film production of this invention is not specifically limited, 1 micrometer is preferable as a lower limit, 5 micrometers are more preferable, and 10 micrometers are still more preferable. When average thickness is more than the said lower limit, the break at the time of the uniaxial stretching process at the time of manufacturing an optical film can be suppressed. Moreover, as an upper limit of this average thickness, 75 micrometers are preferable, 60 micrometers are more preferable, 45 micrometers are still more preferable, and 35 micrometers are still more preferable. When the average thickness is equal to or less than the above upper limit, the stretching nonuniformity at the time of the uniaxial stretching treatment can be suppressed. In addition, "average thickness" refers to the average value of the thickness measured at arbitrary 5 points (the same applies to the average thickness hereinafter).

The film for optical film production of the present invention may be a single-layer film composed of a single PVA layer (a layer containing modified PVA) or a multilayer film composed of a single PVA layer. However, when using for manufacture of a polarizing film, etc., it is preferable that it is a single-layer film. As a lower limit of the average thickness of the PVA layer of the film for optical film manufacture of this invention, 1 micrometer is preferable, 5 micrometers are more preferable, and 10 micrometers are still more preferable. When average thickness is more than the said lower limit, the break at the time of the uniaxial stretching process at the time of manufacturing an optical film can be suppressed. Moreover, as an upper limit of this average thickness, 75 micrometers are preferable, 60 micrometers are more preferable, 45 micrometers are still more preferable, and 35 micrometers are still more preferable. When the average thickness is equal to or less than the above upper limit, the stretching nonuniformity at the time of the uniaxial stretching treatment can be suppressed.

The specific composition and preferable composition of the PVA layer in the film for optical film manufacture can refer to the specific composition of the above-mentioned film itself for optical film manufacture and description of a preferable composition.

When the film for producing an optical film of the present invention is a single-layer film, the average thickness is preferably 20 μm or more, and more preferably 30 μm or more, in order to ensure handling properties. On the other hand, when the film for manufacturing an optical film of the present invention is a multilayer film, the average thickness of the PVA layer may be 20 µm or less, or 15 µm or less.

A multilayer film refers to a film having two or more layers. The number of layers of the multilayer film may be 5 or less, or 3 or less. As a multilayer film, the film for optical film manufacture which has a laminated structure of a base material resin layer and a PVA layer is mentioned. The average thickness of the base resin layer is 20 μm or more and 500 μm or less, for example. It is preferable that the base material resin layer in the multilayer film can be uniaxially stretched together with the PVA layer. As the resin constituting the base resin layer, polyester, polyolefin, or the like can be used. Among them, an amorphous polyester resin is preferable, and an amorphous polyester resin obtained by copolymerizing polyethylene terephthalate and polyethylene terephthalate with copolymerization components such as isophthalic acid and 1,4-cyclohexanedimethanol is preferably used. An adhesive layer may be formed between the base material resin layer and the PVA layer.

The width of the film for producing an optical film of the present invention is not particularly limited and can be determined according to its use and the like. For example, as for the lower limit of the width|variety of the film for optical film manufacture, 3 m is preferable. In recent years, when the width|variety of the film for optical film manufacture is made into 3 m or more at the point where the screen size of a liquid crystal television or liquid crystal monitor is advancing, it is suitable for the use which uses these as a final product. On the other hand, as for the upper limit of the width|variety of the film for optical film manufacture, 7 m is preferable. By setting the width to 7 m or less, it is possible to efficiently perform a uniaxial stretching process when manufacturing an optical film with a device that is put into practical use.

It is preferable that swelling degree of the film for optical film manufacture of this invention exists in the range of 140 % or more and 400 % or less from a viewpoint of productivity or optical performance of an optical film. 180% is more preferable, and, as for the minimum of this swelling degree, 190% is still more preferable. Moreover, as for the upper limit of swelling degree, 220 % is more preferable, and 210 % is still more preferable. The degree of swelling of the film can be adjusted to a smaller value by, for example, strengthening the heat treatment conditions.

Here, "swelling degree of a film" means the value calculated|required by the following formula.

Degree of swelling (%) = 100 × N/M

In the formula, N represents the mass (g) of the sample obtained after immersing the sample extracted from the film in distilled water at 30°C for 30 minutes and removing surface water. M represents the mass (g) of the sample after drying the sample in a dryer at 105°C for 16 hours.

The film for optical film manufacture of this invention is a film (non-stretched film, unstretched film) which is not substantially extended normally. The in-plane retardation of the film for optical film production is preferably 100 nm or less, more preferably 50 nm or less. Usually, an optical film can be obtained by carrying out the stretching process (uniaxial stretching process or biaxial stretching process) of the film for optical film manufacture of this invention.

ADVANTAGE OF THE INVENTION According to the film for optical film manufacture of this invention, when manufacturing an optical film with the same degree of shrinkage stress, the high temperature of a drawing temperature is suppressed, and the optical film excellent in optical performance can be obtained. Moreover, with optical performance, light transmittance, polarization property, etc. are mentioned. A polarizing film, retardation film, a viewing angle improvement film, a brightness improvement film etc. are mentioned as an optical film which can be manufactured with the said film for optical film manufacture, It is preferable that it is a polarizing film.

<Manufacturing method of film for optical film manufacture>

Although the manufacturing method of the film for optical film manufacture of this invention is not specifically limited, The manufacturing method in which the thickness and width|variety of the film after film formation become more uniform is employable preferably. For example, it can be produced using a film forming stock solution in which modified PVA and, if necessary, one or more of plasticizers, surfactants, and other additives are dissolved in a liquid medium. When the film forming dope contains at least one of a plasticizer, a surfactant and other additives, it is preferable that these components are mixed uniformly.

Examples of the liquid medium used for preparation of the film forming stock solution include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, and triethylene. Glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. are mentioned, One type or two or more types of these can be used. Among these, water is preferable from the viewpoint of load on the environment and recovery. Moreover, the above-mentioned modified PVA has good water solubility, and the viscosity increase at the time of setting it as a comparatively high temperature (eg 80 degreeC) aqueous solution is also suppressed. Also in this respect, water can be preferably used as the liquid medium.

The volatile matter ratio of the film-forming dope (the ratio of content of volatile components such as liquid media removed by volatilization or evaporation in the film-forming dope in the film-forming dope) is, for example, preferably 50% by mass or more and 95% by mass or less, and 55% by mass % or more and 90 mass % or less are more preferable, and 60 mass % or more and 85 mass % or less are still more preferable. When the volatile content of the membrane-forming stock solution is 50% by mass or more, the viscosity of the membrane-forming stock solution does not increase too much, filtration and defoaming are smoothly performed during preparation of the membrane-forming stock solution, and production of a film with fewer foreign substances or defects is facilitated. On the other hand, when the volatile content of the film-forming dope is 95% by mass or less, the concentration of the film-forming dope does not become too low, and industrial film production becomes easy.

The temperature of the membrane forming undiluted solution at the time of film forming can be, for example, 60°C or more and 150°C or less, and is preferably 70°C or more and 130°C or less. By using modified PVA and carrying out film formation at such a relatively high temperature, the viscosity of the film-forming stock solution can be kept relatively low, and film-forming properties can be improved.

Examples of the film forming method when forming a film using a film forming undiluted solution include a cast film forming method, an extrusion film forming method, a wet film forming method, and a gel film forming method. These film forming methods may be employed singly or in combination of two or more. Among these film forming methods, the cast film forming method and the extrusion film forming method are preferable in terms of obtaining a film having uniform thickness and width and good physical properties. Drying or heat treatment can be given to the film formed into a film as needed.

As an example of the specific manufacturing method of the film for optical film manufacture of this invention, the following examples are mentioned, for example. Using a T-shaped slit die, hopper plate, I-die, lip coater die, etc., the film forming undiluted solution is uniformly discharged or softened on the circumferential surface of a rotating heated first roll (or belt) located on the upstream side . Volatile components are evaporated from one surface of the film discharged or cast on the circumferential surface of this first roll (or belt) and dried. Subsequently, further drying is performed on the circumferential surface of one or a plurality of rotating heated rolls disposed downstream thereof, or further drying is performed by passing through a hot air drying device. After that, the film is wound up by a winding device. Drying with a heated roll and drying with a hot air drying device may be appropriately combined and performed.

In addition, when the film for optical film manufacture of this invention is a multilayer film, a multilayer film can be manufactured, for example by apply|coating a film forming undiluted solution on a base resin film (base resin layer). At this time, in order to improve the adhesiveness between the PVA layer and the base resin layer, the surface of the base resin film may be modified or an adhesive may be applied to the surface of the base resin film.

<Manufacturing method of optical film>

The manufacturing method of the optical film of this invention is equipped with the process of uniaxially stretching the film for optical film manufacture mentioned above. Below, as an example of the manufacturing method of an optical film, the manufacturing method of a polarizing film is mentioned and demonstrated concretely.

As a manufacturing method of a polarizing film, the film for optical film manufacture (henceforth, it is also called "PVA film".) Each dyeing process of dyeing|staining, the extending|stretching process of carrying out uniaxial stretching, and the swelling process which further swells as needed, A method comprising a crosslinking step of crosslinking, a fixation treatment step of fixation treatment, a washing step of washing, a drying step of drying, a heat treatment step of heat treatment, and the like can be mentioned. In this case, although the order of each process is not specifically limited, For example, it can carry out in order, such as a swelling process, a dyeing process, a bridge|crosslinking process, an extending|stretching process, and a fixation process. Moreover, one or two or more steps may be performed simultaneously, and each step may be performed twice or more.

A swelling process can be performed by immersing a PVA film in water. The water temperature at the time of immersion in water is preferably 20°C or more and 55°C or less, more preferably 22°C or more and 50°C or less, and still more preferably 25°C or more and 45°C or less. Moreover, as time to immerse in water, 0.1 minute or more and 5 minutes or less are preferable, for example, and 0.5 minute or more and 3 minutes or less are more preferable. In addition, water at the time of immersion in water is not limited to pure water, An aqueous solution in which various components were dissolved may be sufficient, and a mixture of water and an aqueous medium may be sufficient as it.

A dyeing process can be performed by making a dichroic dye contact with respect to a PVA film. As the dichroic dye, it is common to use an iodine-based dye. As the timing of dyeing, any stage of before uniaxial stretching, at the time of uniaxial stretching, and after uniaxial stretching may be used. For dyeing, a method in which a PVA film is immersed in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath is preferably employed. The concentration of iodine in the dyeing bath is preferably 0.01% by mass or more and 0.5% by mass or less, and the concentration of potassium iodide is preferably 0.01% by mass or more and 10% by mass or less. In addition, the temperature of the dyeing bath is preferably 20°C or more and 50°C or less, particularly 25°C or more and 40°C or less. A preferable dyeing time is 0.2 minutes or more and 5 minutes or less.

By performing the crosslinking step of crosslinking the modified PVA in the PVA film, elution of the modified PVA into water during wet stretching at high temperature can be effectively suppressed. From this point of view, it is preferable to carry out the crosslinking step after the dyeing step and before the stretching step. A crosslinking process can be performed by immersing a PVA film in the aqueous solution containing a crosslinking agent. As a crosslinking agent, 1 type(s) or 2 or more types of boron compounds, such as borates, such as boric acid and borax, can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 7% by mass or less, and more preferably 2% by mass or more and 6% by mass or less. Sufficient stretchability can be maintained when the concentration of the crosslinking agent is within the above range. The aqueous solution containing a crosslinking agent may contain potassium iodide etc. The temperature of the aqueous solution containing the crosslinking agent is preferably 20°C or more and 60°C or less, particularly 25°C or more and 55°C or less. Efficient crosslinking can be achieved by setting the temperature within the above range.

The stretching step of uniaxially stretching the PVA film may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it may be carried out in an aqueous solution containing boric acid, or in the dyeing bath described above or in a fixing treatment bath described later. In addition, in the case of the dry stretching method, stretching may be carried out at room temperature, stretching may be carried out while heating, or it may be carried out in air using a PVA film after water absorption. Among these, the wet stretching method is preferable from the viewpoint of being capable of stretching with high uniformity in the width direction, and uniaxial stretching in an aqueous solution containing boric acid is more preferable. The concentration of boric acid in the aqueous solution of boric acid is preferably 0.5% by mass or more and 6.0% by mass or less, more preferably 1.0% by mass or more and 5.0% by mass or less, and particularly preferably 1.5% by mass or more and 4.0% by mass or less. Moreover, boric acid aqueous solution may contain potassium iodide, and, as for the density|concentration of potassium iodide, 0.01 mass % or more and 10 mass % or less are preferable. The stretching temperature in uniaxial stretching is preferably 30°C or higher and 90°C or lower, more preferably 40°C or higher and 80°C or lower, still more preferably 50°C or higher and 75°C or lower, and particularly 55°C or higher and 68°C or lower. desirable.

It is preferable that it is 5 times or more at the point of the polarization performance of the polarizing film obtained, and, as for the draw ratio (total draw ratio from the non-stretched PVA film) in uniaxial stretching, it is more preferable that it is 5.5 times or more. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

The direction of uniaxial stretching in the case of uniaxially stretching a long PVA film is not particularly limited, and uniaxial stretching in the direction of a long picture or transverse uniaxial stretching can be employed. From the viewpoint of obtaining a polarizing film with excellent polarization performance, uniaxial stretching in the direction of a long picture is preferable. Uniaxial stretching in the direction of a long picture can be performed by changing the circumferential speed between each roll using a stretching apparatus provided with a plurality of mutually parallel rolls. On the other hand, transverse uniaxial stretching can be performed using a tenter type stretching machine.

It is preferable that the maximum stretching stress in the stretching step is 30 N/mm 2 or less. Here, the maximum stretching stress is a value obtained by dividing the maximum tensile force applied to the PVA film by the cross-sectional area of the PVA film as a raw material. By making the maximum stretching stress small, a polarizing film having a small shrinkage stress can be obtained. The maximum stretching stress is more preferably 25 N/mm 2 or less. Moreover, usually, the maximum stretching stress is 1 N/mm 2 or more. The maximum stretching stress in the stretching step can be lowered by increasing the stretching temperature.

In manufacture of a polarizing film, in order to make adsorption|suction of a dichroic dye (iodine type dye etc.) to a PVA film strong, a fixation process can be implemented after an extending process. As a fixation treatment bath used for fixation treatment, the aqueous solution containing 1 type(s) or 2 or more types of boron compounds, such as boric acid and borax, can be used. Moreover, you may add an iodine compound or a metal compound in the fixation treatment bath as needed. The concentration of the boron compound in the fixation treatment bath is preferably 2% by mass or more and 15% by mass or less, particularly 3% by mass or more and 10% by mass or less. Adsorption of the dichroic dye can be made more robust by setting the concentration of the boron compound within the above range. The temperature of the fixed treatment bath is preferably 15°C or more and 60°C or less, particularly 25°C or more and 40°C or less.

The cleaning step is generally performed by immersing the film in distilled water, pure water, aqueous solution, or the like. At this time, it is preferable to use an aqueous solution containing an iodide such as potassium iodide as an auxiliary agent from the viewpoint of improving the polarization performance, and the iodide concentration is preferably 0.5% by mass or more and 10% by mass or less. The temperature of the aqueous solution in the washing treatment is generally 5°C or more and 50°C or less, preferably 10°C or more and 45°C or less, and more preferably 15°C or more and 40°C or less. By setting the temperature of the aqueous solution within the above range, it is possible to further enhance the polarization performance and the like.

The conditions for the drying step are not particularly limited, but it is preferable to dry the PVA film at a temperature of 30°C or more and 150°C or less, particularly 50°C or more and 130°C or less. A polarizing film excellent in dimensional stability is easily obtained by drying at a temperature within the above range.

Moreover, optical films other than polarizing films, such as retardation film, can also be manufactured by the method provided with the process of uniaxially stretching the film for optical film manufacture of this invention. A conventionally well-known method can be employ|adopted as a specific manufacturing method except using the film for optical film manufacture of this invention.

<optical film>

The optical film of the present invention includes PVA (modified PVA) having a silicon-containing group and an ethylene unit, the silicon-containing group being a silanol group or a group that can be converted into a silanol group in the presence of water, and in the modified PVA It is an optical film in which the content of the silicon-containing groups relative to all structural units of is 0.01 mol% or more and 1.0 mol% or less, and the content of the ethylene units is 0.5 mol% or more and 10 mol% or less.

The optical film of this invention obtained by the manufacturing method mentioned above using the film for optical film manufacture of this invention may be sufficient as it. The details, such as the specific structure and content of modified PVA contained in the optical film of this invention, are the same as the modified PVA contained in the film for optical film manufacture of this invention. Moreover, the other component similar to the film for optical film manufacture of this invention may be contained in the optical film of this invention.

The optical film of the present invention may be a polarizing film, a retardation film, a viewing angle improving film, a luminance enhancing film, or the like, and is preferably a polarizing film. In this case, the dichroic dye is normally contained in the polarizing film, and modified PVA may be crosslinked.

It is preferable that it is a stretched film, and, as for the optical film of this invention, it is more preferable that it is a uniaxially stretched film. Further, the optical film of the present invention may be a single layer film or a multilayer film, but is preferably a single layer film. In the case of such a film, the optical film of the present invention can be more preferably used as a polarizing film or the like.

It is preferable that the shrinkage stress of the optical film of this invention is 100 N/mm<2> or less. When the shrinkage stress is small, the dimensional stability becomes excellent even when used at a high temperature. The shrinkage stress is more preferably 80 N/mm 2 or less. The lower limit of the shrinkage stress of the optical film of the present invention may be, for example, 10 N/mm 2 , 20 N/mm 2 or 40 N/mm 2 . Here, the shrinkage stress is a value obtained by dividing the tension obtained by fixing both ends of a polarizing film serving as a sample in the stretching direction and maintaining the temperature at 80°C for 4 hours by the cross-sectional area of the sample, specifically, in Examples described later. It refers to the value obtained by the method described in

When the optical film of the present invention is a polarizing film, it is preferable that the dichroic ratio (R) of the polarizing film is 100 or more. By including the above-mentioned modified PVA, a polarizing film having such a high dichroic ratio (R) can be manufactured with good productivity. The dichroism ratio (R) is more preferably 150 or more, still more preferably 190 or more, and particularly preferably 200 or more. As an upper limit of this dichroism ratio (R), 350 may be sufficient as it, 300 or 250 may be sufficient as it, for example.

The calculation method of the dichroism ratio (R) of a polarizing film is as follows. First, the relationship between the transmittance (T') excluding surface reflection and the single transmittance (T) is expressed by formula (a). At this time, the refractive index of the polarizing film is assumed to be 1.5, and the reflectance on the surface is assumed to be 4%. The relationship between transmittance (T'), degree of polarization (V) and dichroic ratio (R) is represented by formula (b). Therefore, after measuring the single transmittance (T) and polarization degree (V), the dichroic ratio (R) of the polarizing film can be calculated by solving equations (a) and (b) using these values.

T' = T/(1 - 0.04) ² ... (a)

R = {-ln[T'(1-V)]}/{-ln[T'(1+V)]}... (b)

A polarizing film is usually used as a polarizing plate by bonding a protective film that is optically transparent and has mechanical strength to both surfaces or one side thereof. As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate-butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Moreover, as an adhesive agent for bonding, a PVA-type adhesive agent, a urethane-type adhesive agent, an acrylate-type ultraviolet curable adhesive agent, etc. are mentioned. That is, a polarizing plate has a polarizing film and a protective film laminated directly on one or both surfaces of the polarizing film through an adhesive layer.

A polarizing plate can be bonded together to a glass substrate, and can be used as a component of LCD, after coating adhesives, such as an acrylic type, for example. Moreover, a retardation film, a viewing angle improvement film, a brightness improvement film, etc. may be bonded to the polarizing plate further.

Example

Hereinafter, the present invention will be described in more detail by examples, but the present invention is not limited at all by these examples. The method of each measurement and evaluation is as follows.

[Polymerization degree of PVA (viscosity average degree of polymerization)]

For each PVA synthesized in the following Synthesis Example, the viscosity average degree of polymerization was measured according to the description of JIS K6726-1994.

[Degree of Saponification of PVA]

About each PVA synthesized in the following synthesis example, the saponification degree was measured according to the description of JISK6726-1994.

[Content of Silicon-Containing Groups and Ethylene Units in PVA]

For each PVA synthesized in the following Synthesis Examples, the content of silicon-containing groups and ethylene units was measured from proton NMR of the vinyl ester polymer before saponification. When measuring the proton NMR of the vinyl ester polymer before saponification, the vinyl ester polymer is re-precipitated and purified with hexane-acetone to completely remove unreacted monomers from the polymer, and then dried under reduced pressure at 90 ° C. for 2 days, then CDCl ₃ was dissolved in a solvent and used for analysis.

[Film swelling degree]

Each film (film for optical film manufacture) obtained by the following Examples and Comparative Examples was cut so as to be 1.5 g, and was immersed in 1000 g of 30°C distilled water for 30 minutes. After being immersed for 30 minutes, the film was taken out, and after absorbing water on the surface with filter paper, the mass (N) was measured. Then, after drying the film with a dryer at 105°C for 16 hours, the mass (M) after drying was measured. From the obtained mass (N) and mass (M), the degree of swelling of the film was determined by the following formula.

Degree of swelling (%) = 100 × N/M

[Dichroic ratio of polarizing film (optical performance)]

A 4 cm rectangular sample was collected in the longitudinal direction of the polarizing film from the central portion in the width direction of each polarizing film obtained in the following Examples and Comparative Examples. For this sample, a spectrophotometer with an integrating sphere (“V7100” manufactured by Nippon Spectroscopy Co., Ltd.) was used to correct the visibility in the visible light region with a C light source and a 2° field of view in accordance with JIS Z8722 (object color measurement method). After implementation, single transmittance (T) and polarization degree (V) were measured.

The dichroic ratio (R) of the polarizing film was calculated by solving the following formulas (a) and (b) from the values of the obtained single transmittance (T) and polarization degree (V). Here, the refractive index of the polarizing film was assumed to be 1.5, and the reflectance on the surface was assumed to be 4%. In this way, the dichroic ratio (R) of the polarizing film produced under the temperature conditions of the uniaxial stretching treatment bath in Examples and Comparative Examples was set to R ₀ .

T' = T/(1 - 0.04) ² ... (a)

R = {-ln[T'(1-V)]}/{-ln[T'(1+V)]}... (b)

[Shrinkage stress of polarizing film]

The shrinkage stress of each polarizing film obtained in the following Examples and Comparative Examples was measured using an autograph "AG-X" equipped with a thermostat manufactured by Shimadzu Corporation and a video extensometer "TR ViewX120S". The polarizing film which controlled humidity at 20 degreeC/20 %RH for 18 hours was used for the measurement. After setting the thermostat of Autograph “AG-X” to 20°C, attaching the polarizing film (lengthwise direction 15cm, width direction 1.5cm) to the chuck (chuck spacing 5cm), and at the same time as the start of tension, the thermostat was heated to 80°C. The temperature increase was initiated. In addition, the stretching direction of the polarizing film was set to the longitudinal direction, and it was made to stretch in this direction. The polarizing film was stretched at a rate of 1 mm/min, the tension was stopped when the tension reached 2 N, and the tension was measured from that state until 4 hours later. At this time, since the distance between the chucks changes due to thermal expansion, the distance between the chucks can be corrected as much as the gauge seal attached to the chuck moves by attaching a gauge line seal to the chuck and using the video extensometer "TR ViewX120S". The measurement was carried out in such a way that In addition, the value obtained by subtracting the initial tension of 2 N from the measured value of the tension after 4 hours was used as the shrinkage force of the polarizing film, and the value obtained by dividing this shrinkage force by the cross-sectional area of the sample was used as the shrinkage stress (N/mm 2 ). Moreover, in this way, the shrinkage stress (SF) of the polarizing film manufactured under the temperature conditions of the uniaxial stretching treatment bath of Examples and Comparative Examples was SF ₀ .

[Dichroic Ratio and Stretching Temperature at 75 N/mm2 of Shrinkage Stress of Polarizing Film]

In the following Examples and Comparative Examples, the temperature of the uniaxial stretching treatment bath was set to a lower temperature by 2 ° C. or 4 ° C., and the iodine concentration of the dyeing treatment bath was changed so that the transmittance of the polarizing film obtained was 44.0%. With the method, polarizing films having different uniaxial stretching treatment bath temperatures were obtained. The single transmittance (T) and polarization degree (V) of each obtained polarizing film were measured, and the dichroic ratio (R) was determined by the method described above. Here, the dichroic ratio (R) of the polarizing film obtained under the condition that the temperature of the uniaxial stretching treatment bath is 2 ° C. lower is R _-2 , and the dichroic ratio (R ) was set to R _-4 . In addition, the shrinkage stress of each polarizing film was measured by the method described above. Here, the shrinkage force (SF) of the polarizing film obtained under the condition that the temperature of the uniaxial stretching treatment bath is 2 ° C. lower is SF _-2 , and the shrinkage force (SF) of the polarizing film obtained under the condition that the temperature of the uniaxial stretching treatment bath is lower than 4 ° C. SF _-4 was used.

Values of dichroic ratios (R ₀ , R _-2 , R _-4 ) and shrinkage stresses (SF ₀ , SF _-2 , SF _-4 ) of the three types of polarizing films having different temperatures in the uniaxial stretching treatment bath obtained in this way From this, the relationship between the dichroism ratio and the shrinkage stress was plotted, and the dichroism ratio in the shrinkage stress of 75 N/mm 2 was calculated by linear approximation. Further, the relationship between the shrinkage stress and the temperature of the uniaxial stretching treatment bath was plotted, and the stretching temperature at a shrinkage stress of 75 N/mm 2 was calculated by linear approximation.

[Synthesis Example 1] Synthesis of PVA-1

3000 g of vinyl acetate and 3.6 g of vinyltrimethoxysilane as a monomer having a silicon-containing group were introduced into a 5 L pressurized reaction vessel equipped with an agitator, nitrogen inlet, ethylene inlet, initiator addition port and delay solution addition port, and 60 ° C. After raising the temperature by , the system was purged with nitrogen by nitrogen bubbling for 30 minutes. Subsequently, ethylene was introduced so that the pressure in the reactor was 0.26 MPa. After adjusting the temperature inside the polymerization tank to 60°C, 1.0 g of 2,2'-azobisisobutyronitrile (AIBN) was injected to initiate polymerization. During the polymerization, ethylene was introduced while a 2% by mass methanol solution of vinyltrimethoxysilane was injected, the reactor pressure was maintained at 0.26 MPa, and the polymerization temperature was maintained at 60°C. After 3 hours, when the polymerization rate reached 20%, cooling was performed. polymerization was stopped. The methanol solution of vinyltrimethoxysilane added to the end of the polymerization was 84 ml. Then, unreacted vinyl acetate was removed under reduced pressure to obtain a methanol solution of modified polyvinyl acetate (hereinafter sometimes abbreviated as modified PVAc). The concentration of the methanol solution of the obtained modified PVAc was adjusted to 23.5% by mass, and a NaOH methanol solution (10% by mass) was added so that the alkali molar ratio (number of moles of NaOH/number of moles of vinyl ester units in the modified PVAc) was 0.04, followed by saponification. did The obtained polyvinyl alcohol was washed with methanol. The polymerization degree (viscosity average degree of polymerization) of PVA-1 obtained by the above operation was 3,300, the saponification degree was 99.9 mol%, the silicon-containing group content was 0.2 mol%, and the ethylene unit content was 2.5 mol%.

[Synthesis Examples 2 to 9] Synthesis of PVA-2 to PVA-9

PVA-2 having the viscosity average degree of polymerization, degree of saponification, content of silicon-containing groups, and content of ethylene units described in Table 1 according to Synthesis Example 1, and further adjusting the proportion of monomers used, polymerization conditions and saponification conditions appropriately ~PVA-9 was obtained.

[Example 1]

An aqueous solution containing 100 parts by mass of PVA-1, 10 parts by mass of glycerin as a plasticizer, and 0.1 part by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant and having a PVA content of 9.5% by mass was prepared as a film forming stock solution. This film forming undiluted solution was dried on a metal roll at 80 ° C., and the obtained film was subjected to heat treatment in a hot air dryer at a temperature of 105 ° C. for 10 minutes to adjust the swelling degree to 200%, and obtain a PVA film having an average thickness of 30 μm (for optical film production). film) was prepared.

A sample of 5 cm in width x 9 cm in length was cut so that a range of 5 cm in width x 5 cm in length could be uniaxially stretched from the central portion in the width direction of the obtained PVA film. This sample was uniaxially stretched 2.0 times in the longitudinal direction while being immersed in 30°C pure water for 60 seconds, and subjected to a swelling treatment. Subsequently, while immersed in an aqueous solution containing 0.05% by mass of iodine and 1.15% by mass of potassium iodide (dyeing treatment bath: temperature: 32°C) for 120 seconds, 1.2 times (2.4 times as a whole) was uniaxially stretched in the longitudinal direction to adsorb iodine. . Subsequently, it was uniaxially stretched in the longitudinal direction at 1.25 times (3.0 times as a whole) while being immersed in an aqueous solution containing 2.6% by mass of boric acid (boric acid crosslinking treatment bath: temperature: 32°C) for 120 seconds. Further, it was uniaxially stretched in the longitudinal direction up to 6.0 times as a whole while being immersed in a 69°C aqueous solution (uniaxial stretching treatment bath) containing 2.8% by mass of boric acid and 5% by mass of potassium iodide. Then, the film was washed by immersing for 5 seconds in a potassium iodide aqueous solution (washing bath) at a temperature of 22°C containing boric acid at a concentration of 1.5% by mass and potassium iodide at a concentration of 3.5% by mass. Finally, it dried at 80 degreeC for 4 minutes and obtained the polarizing film.

The dichroism ratio in the shrinkage stress of 75 N/mm<2> of the polarizing film was calculated|required by the method mentioned above using the obtained polarizing film. Moreover, the stretching temperature in the shrinkage stress of 75 N/mm<2> of the polarizing film was calculated|required by the method mentioned above. The results are shown in Table 1 and FIG. 1 .

[Examples 2 to 3 and Comparative Examples 1 to 5]

Examples except that the PVA content of the film forming stock solution and the heat treatment temperature were adjusted so that the average thickness of the PVA film was 30 μm and the degree of swelling was 200% using the PVA (PVA-2 to PVA-8) shown in Table 1. Production and evaluation of the PVA film were performed in the same manner as in 1. Example 1 except that the temperature of the uniaxial stretching treatment bath and the iodine concentration of the dyeing treatment bath were changed using the obtained PVA film so that the polarizing film obtained had a shrinkage stress of around 75 N/mm 2 and a single transmittance of 44.0%. In the same manner, production and evaluation of the polarizing film were performed. A result is shown in Table 1 and FIGS. 1 and 2.

[Comparative Example 6]

An attempt was made to prepare a film forming stock solution using PVA-9 as the PVA, but the film forming stock solution could not be prepared because PVA did not dissolve. Therefore, a PVA film and a polarizing film could not be manufactured, and the dichroism ratio and stretching temperature in the shrinkage stress of 75 N/mm<2> of a polarizing film could not be measured either.

As shown in Table 1 and FIG. 1, according to the film for optical film production (PVA film) of Examples 1 to 3, when producing an optical film having a shrinkage stress of 75 N/mm 2 , at a stretching temperature of 68° C. or lower , an optical film having a dichroism ratio of 200 or more can be obtained. That is, according to the manufactured films for optical films of Examples 1 to 3, when an optical film having the same degree of shrinkage stress is manufactured, an increase in the stretching temperature is suppressed, and an optical film having excellent optical performance can be obtained. In other words, according to the manufactured films for optical films of Examples 1 to 3, the increase in shrinkage stress and the increase in the stretching temperature can be suppressed while improving the optical performance of the obtained optical film.

As shown in FIG. 2, when the film for optical film manufacture using PVA of the same degree of polymerization (PVA film) is compared, the following things can be seen. Compared to Comparative Example 1 using unmodified PVA having a polymerization degree of 2400, Comparative Examples 4 and 5 using modified PVA having a polymerization degree of 2400 and a content of 0.2 mol% or 0.4 mol% of silicon-containing groups at a shrinkage stress of 75 N/mm 2 Although the dichroic ratio (optical performance) is markedly high, the stretching temperature is also markedly increased. That is, compared to the case where unmodified PVA is used, according to the PVA film using the PVA containing only silicon, the optical performance of the obtained optical film can be significantly improved, but it is found that the increase in the stretching temperature cannot be suppressed. there is. On the other hand, in Example 3 using modified PVA having a degree of polymerization of 2400, a silicon-containing group content of 0.2 mol% and an ethylene unit content of 4.5 mol%, the dichroism ratio (optical performance) at a shrinkage stress of 75 N/mm 2 was compared to Comparative Example 4 While higher, the stretching temperature was substantially equal, and the increase in temperature of the stretching temperature could be suppressed. That is, according to the film for producing an optical film (PVA film) using PVA having a silicon-containing group and an ethylene unit compared to the case of using a PVA having only a silicon-containing group, when producing an optical film having the same degree of shrinkage stress, An increase in the stretching temperature can be suppressed, and an optical film having excellent optical performance can be obtained. In other words, the increase in shrinkage stress and the increase in the stretching temperature can be suppressed while improving the optical performance of the obtained optical film.

The film for optical film manufacture of this invention can be used suitably as materials, such as a polarizing film which is a constituent material of LCD.

Claims (13)

It contains polyvinyl alcohol having a silicon-containing group and an ethylene unit,
The silicon-containing group is a silanol group or a group that can be converted to a silanol group in the presence of water;
The film for optical film production whose content of the said silicon-containing group with respect to all the structural units in the said polyvinyl alcohol is 0.01 mol% or more and 1.0 mol% or less, and content of the said ethylene unit is 0.5 mol% or more and 10 mol% or less. According to claim 1,
The film for optical film production whose viscosity average degree of polymerization of the said polyvinyl alcohol is 1,000 or more and 6,000 or less, and whose saponification degree is 98.7 mol% or more. According to claim 2,
The film for optical film manufacture whose product of the said viscosity average degree of polymerization and content of the said silicon-containing group is 100 mol% or more and 2,000 mol% or less. According to any one of claims 1 to 3,
An average thickness of 1 μm or more and 75 μm or less, a film for producing an optical film. According to any one of claims 1 to 4,
The film for optical film manufacture whose degree of swelling is 140 % or more and 400 % or less. According to any one of claims 1 to 5,
The film for optical film manufacture whose said optical film is a polarizing film. According to any one of claims 1 to 6,
A film for manufacturing an optical film, which is a non-stretched film. The manufacturing method of the optical film provided with the process of uniaxially stretching the film for optical film manufacture in any one of Claims 1-7. According to claim 8,
The method for producing an optical film, wherein the optical film is a polarizing film. It contains polyvinyl alcohol having a silicon-containing group and an ethylene unit,
The silicon-containing group is a silanol group or a group that can be converted to a silanol group in the presence of water;
The optical film in which the content of the silicon-containing groups relative to all structural units in the polyvinyl alcohol is 0.01 mol% or more and 1.0 mol% or less, and the content of the ethylene units is 0.5 mol% or more and 10 mol% or less. According to claim 10,
An optical film having a shrinkage stress of 100 N/m 2 or less. According to claim 10 or 11,
An optical film, which is a polarizing film. According to any one of claims 10 to 12,
An optical film, which is a monolayer film.

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