JP7604516B2 - Film for manufacturing optical film and method for manufacturing optical film - Google Patents

Description

The present invention relates to a film for producing optical films and a method for producing optical films.

Polarizing plates, which have the function of transmitting and blocking light, are basic components of liquid crystal displays (LCDs) along with liquid crystals, which change the polarization state of light. Many polarizing plates have a structure in which a protective film, such as a triacetate cellulose (TAC) film, is laminated to the surface of a polarizing film. The mainstream polarizing film is one in which a dichroic dye, such as an iodine-based dye (I ₃ ^- , I ₅ ^- , etc.) or a dichroic organic dye, is adsorbed onto a matrix (stretched film) made by uniaxially stretching a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA").

LCDs are used in a wide range of applications, including small devices such as calculators and watches, smartphones, laptops, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and measuring instruments used both indoors and outdoors. In recent years, there has been a demand for improved display quality in these devices. Accordingly, there is a demand for higher performance polarizing films; specifically, polarizing films with excellent optical properties such as the degree of polarization and transmittance are in demand.

A polarizing film using PVA with a high degree of polymerization is known as a polarizing film with improved optical properties (Patent Document 1). In this patent document 1, a film is formed using a PVA film-forming solution in which PVA with a high degree of polymerization is dissolved in a solvent mainly composed of dimethyl sulfoxide.

Japanese Unexamined Patent Publication No. 1-105204

In industrial PVA film production, it is common to use an aqueous PVA solution in which water is used as a solvent as a film-forming solution, taking into consideration environmental and economic considerations. However, as in Patent Document 1, PVA with a high degree of polymerization increases the viscosity of the aqueous solution, making it poorly film-forming and undesirable for industrial production. Therefore, a method is desired to improve the optical performance of optical films while preventing a deterioration in productivity.

The present invention has been made based on the above circumstances, and its object is to provide a film for producing optical films which has good productivity and can produce optical films with excellent optical performance, and a method for producing optical films using such a film for producing optical films.

The above objectives are:
[1] A film for optical film production containing PVA, wherein in a dynamic viscosity measurement of an aqueous solution in which the film for optical film production is dissolved so that the concentration of the PVA is 12% by mass, the ratio Rt(η ^* ₁ (30)/η ^* ₁ (80)) of complex viscosity η ^* ₁ (30) to complex viscosity η ^* ₁ (80) is 4.5 or more and 50 or less;
[The complex viscosity η ^* ₁ (30) is a complex viscosity at an angular frequency of 1 rad/sec obtained from dynamic viscoelasticity measurement of the aqueous solution at 30° C. The complex viscosity η ^* ₁ (80) is a complex viscosity at an angular frequency of 1 rad/sec obtained from dynamic viscoelasticity measurement of the aqueous solution at 80° C.]
[2] The film for producing an optical film according to ^[ ₁ ], wherein the ratio _Rω (30) of the complex viscosity η*1( ₃₀ ) to the complex viscosity η ^* 500(30) ( ^η * ₁ (30)/η ^* ₅₀₀ (30)) is 5 or more and 150 or less;
[The complex viscosity η ^* ₅₀₀ (30) is the complex viscosity at an angular frequency of 500 rad/sec obtained by dynamic viscoelasticity measurement of the aqueous solution at 30° C.]
[3] The film for producing an optical film according to [1] or [2], wherein the PVA contains a modified PVA having a silicon-containing group;
[4] The film for producing an optical film according to [3], wherein the content of the silicon-containing group relative to all structural units in the modified PVA is 0.01 mol % or more and 2 mol % or less;
[5] The film for producing an optical film according to any one of [1] to [4], wherein the optical film is a polarizing film;
[6] 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 [5];
[7] The method for producing an optical film according to [6], wherein the optical film is a polarizing film;
This is achieved by providing either

According to the present invention, it is possible to provide a film for producing optical films, which has good productivity and can produce optical films with excellent optical performance, and a method for producing optical films using such a film for producing optical films.

1 is a flow curve of complex viscosity obtained by measuring the dynamic viscoelasticity of an aqueous PVA solution at 30° C. in which the film for producing an optical film (PVA film) of Example 1 was dissolved so that the PVA concentration was 12% by mass.

<Film for optical film manufacturing>
The film for optical film production of the present invention is a film for optical film production containing PVA, and in a dynamic viscosity measurement of an aqueous solution in which the film for optical film production is dissolved so that the concentration of the PVA is 12 mass %, the ratio Rt(η ^* ₁ ( ₃₀ )/η ^* 1(80)) of complex viscosity η ^* ₁ (30) to complex viscosity η ^* ₁ (80) is 4.5 or more and 50 or less.

The complex viscosity η ^* ₁ (30) is the complex viscosity at an angular frequency of 1 rad/sec obtained from dynamic viscoelasticity measurement of the aqueous solution at 30° C. The complex viscosity η ^* ₁ (80) is the complex viscosity at an angular frequency of 1 rad/sec obtained from dynamic viscoelasticity measurement of the aqueous solution at 80° C. That is, the complex viscosity η ^* ₁ (30) is the complex viscosity at an angular frequency of 1 rad/sec obtained from dynamic viscoelasticity measurement of an aqueous solution at 30° C. in which the optical film manufacturing film is dissolved so that the PVA concentration is 12% by mass. The complex viscosity η ^* ₁ (80) is the complex viscosity at an angular frequency of 1 rad/sec obtained from dynamic viscoelasticity measurement of an aqueous solution at 80° C. in which the optical film manufacturing film is dissolved so that the PVA concentration is 12% by mass.

(Dynamic viscoelasticity measurement)
Dynamic viscoelasticity measurement is a method for measuring the mechanical properties of a sample by applying a time-varying (oscillating) strain or stress to the sample and measuring the resulting stress or strain. Dynamic viscoelasticity can be measured using a dynamic viscoelasticity measuring device (rheometer).

In the present invention, dynamic viscoelasticity measurements are performed using an "ARES-G2" manufactured by TA instruments under the following conditions:

Geometry: Cone plate and disc-shaped plate with a cone angle of 0.02 rad Plate diameter: 40 mm
Strain: 1%
Angular frequency range: 1 to 500 rad/sec Measurement temperature (temperature of aqueous solution): 30°C or 80°C

In the present invention, the dynamic viscoelasticity measurement is performed using a PVA aqueous solution so that the PVA concentration of the optical film manufacturing film is 12% by mass. This PVA aqueous solution can be prepared by weighing the optical film manufacturing film and distilled water in a container, and then heating and dissolving at 95 ° C for 4 hours while stirring. When the optical film manufacturing film contains substances other than PVA, the PVA content is determined in advance before dissolving. For example, when the optical film manufacturing film contains water-soluble substances such as moisture and plasticizers, the optical film manufacturing film is swollen with water and washed to dissolve these substances, and then dried in a dryer at 105 ° C for 17 hours or more and weighed, so that the PVA content in the optical film manufacturing film can be determined. However, even when the optical film manufacturing film contains substances other than PVA, the aqueous solution used for the dynamic viscoelasticity measurement is prepared by dissolving the optical film manufacturing film containing substances other than PVA in water. The dynamic viscoelasticity measurement is performed using an aqueous solution of PVA having a concentration of 12% by mass at a temperature of 30° C. or 80° C.

(Complex Viscosity)
In the film for optical film production of the present invention, the ratio Rt ( ^{η* 1} ₍ 30)/η ^* ₁ (80)) of the complex viscosity η ^* ₁ (30) to the complex viscosity η* ₁ (80) must be 4.5 or more and 50 or less. When Rt is less than 4.5, the complex viscosity η ^* ₁ (30) is too low or the complex viscosity η ^* ₁ (80) is too high. When the complex viscosity η ^* ₁ (30) is too low, it means that the interaction due to crosslinking of PVA in the film for optical film production is insufficient, and even if the film for optical film production is stretched, sufficient orientation does not occur, and an optical film with excellent optical performance cannot be obtained. On the other hand, when the complex viscosity η ^* ₁ (80) is too high, it means that the viscosity does not decrease sufficiently even if the film-forming solution of the film for optical film production is heated to a high temperature, and good productivity cannot be achieved. From this point of view, it is preferable that the complex viscosity η ^* ₁ (30) is 15 Pa·s or more, and the complex viscosity η ^* ₁ (80) is 15 Pa·s or less. In addition, a film for optical film production having an Rt of more than 50 is not easy to produce. By setting Rt in the above range, an optical film having excellent optical performance can be obtained while maintaining good productivity. Rt is preferably 5 or more, and more preferably 7 or more. On the other hand, the upper limit of Rt is preferably 40.

In the film for optical film production of the present invention, the lower limit of the complex viscosity η ^* ₁ (30) is preferably 15 Pa·s, more preferably 30 Pa·s. When the complex viscosity η ^* ₁ (30) is equal to or greater than the lower limit, the interaction due to crosslinking or the like of the PVA in the film for optical film production is in a particularly sufficient state, so that the stretching causes particularly sufficient orientation, and the optical performance of the obtained optical film can be further improved. The upper limit of the complex viscosity η ^* ₁ (30) is preferably 500 Pa·s, more preferably 400 Pa·s. When the complex viscosity η ^* ₁ (30) is equal to or less than the upper limit, the viscosity increase in the film-forming solution for the film for optical film production is suppressed even when the temperature of the film-forming solution is low (30°C), and better productivity can be achieved.

In the film for optical film production of the present invention, the complex viscosity η ^* ₁ (80) is preferably 3 Pa·s or more and 15 Pa·s or less. The upper limit of the complex viscosity η ^* ₁ (80) is more preferably 12 Pa·s, and in some cases, 10 Pa·s or 5 Pa·s is even more preferable. When the complex viscosity η ^* ₁ (80) is equal to or less than the upper limit, the increase in viscosity of the film-forming solution for optical film production, particularly when the temperature of the film-forming solution is high (80° C.), is more suppressed, and better productivity can be achieved.

In the film for optical film production of the present invention, the ^lower limit of the ratio _Rω (30) (η ^* ₁ (30)/η ^* ₅₀₀ (30)) of the complex viscosity η ^* ₁ (30) to the complex viscosity η* ₅₀₀ (30) may be, for example, 3, but is preferably 5, and more preferably 10. When _Rω (30) is equal to or greater than the lower limit, the viscosity of the film-forming solution for optical film production is significantly reduced with respect to the shear rate, and therefore better productivity can be achieved. On the other hand, the upper limit of the ratio _Rω (30) is preferably 150, and more preferably 100.

In the film for producing an optical film of the present invention, the complex viscosity η ^* ₅₀₀ (30) is preferably 1 Pa·s or more and 12 Pa·s or less. The upper limit of the complex viscosity η ^* ₅₀₀ (30) is more preferably 10 Pa·s, even more preferably 5 Pa·s, and particularly preferably 4.5 Pa·s. When the complex viscosity η ^* ₅₀₀ (30) is equal to or less than the upper limit, the viscosity of the film-forming solution for producing an optical film at a high shear rate is sufficiently low, and therefore better productivity can be achieved.

Here, the complex viscosity η ^* ₅₀₀ (30) is the complex viscosity at an angular frequency of 500 rad/sec obtained from dynamic viscoelasticity measurement of the aqueous solution at 30° C. In other words, the complex viscosity η ^* ₅₀₀ (30) is the complex viscosity at an angular frequency of 500 rad/sec obtained from dynamic viscoelasticity measurement of an aqueous solution at 30° C. in which the optical film-producing film is dissolved so that the PVA concentration is 12% by mass.

(PVA)
In the film for optical film production of the present invention, PVA is usually the main component. The main component refers to the component with the highest content by mass. The lower limit of the content of PVA in the film for optical film production of the present invention is preferably 60 mass%, more preferably 80 mass%, and even more preferably 85 mass%. By making the content of PVA equal to or higher than the lower limit, the effect of the present invention can be further enhanced. On the other hand, the upper limit of the content is not particularly limited, and may be 100 mass%, preferably 99 mass%, and more preferably 95 mass%. PVA may be only one type, or may contain two or more types. The content (mass%) of each component in the film for optical film production is based on the dry state, that is, the total content of all components other than water.

PVA is a polymer having a vinyl alcohol unit (-CH ₂ -CH(OH)-) as a structural unit. The PVA may have a vinyl ester unit and further other structural units in addition to the vinyl alcohol unit.

The lower limit of the viscosity average polymerization degree of PVA is preferably 1,000, more preferably 1,500, even more preferably 2,000, and particularly preferably 2,200. By having the viscosity average polymerization degree of PVA be equal to or greater than the lower limit, the film for optical film production of the present invention has excellent stretching processability, and an optical film with better optical performance can be produced. On the other hand, the upper limit of the viscosity average polymerization degree is preferably 5,000, more preferably 4,000, even more preferably 3,000, and particularly preferably 2,700. By having the viscosity average polymerization degree of PVA be equal to or less than the upper limit, good water solubility is exhibited, and an increase in the viscosity of the aqueous solution is suppressed. Therefore, by having the viscosity average polymerization degree of PVA be equal to or less than the upper limit, film formability is improved, and the productivity of the film for optical film production of the present invention can be increased.

The viscosity average degree of polymerization means the average degree of polymerization measured in accordance with the description of JIS K6726-1994. That is, in this specification, the viscosity average degree of polymerization is calculated from the intrinsic viscosity [η] (unit: deciliter/g) measured in water at 30° C. after resaponifying the remaining vinyl ester groups of PVA and purifying it, according to the following formula:
Viscosity average degree of polymerization Po=([η]×10 ⁴ /8.29) ^(1/0.62)

The lower limit of the saponification degree of PVA is preferably 98.7 mol%, more preferably 99.0 mol%, even more preferably 99.5 mol%, even more preferably 99.8 mol%, and particularly preferably 99.9 mol%. By having a saponification degree equal to or greater than the lower limit, an optical film having superior optical performance and moist heat resistance can be obtained. On the other hand, there is no particular limit to the upper limit of the saponification degree, but from the viewpoint of PVA productivity, 99.99 mol% or less is preferable.

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

(Modified PVA)
The PVA preferably contains a modified PVA having a silicon-containing group (hereinafter, the modified PVA having a silicon-containing group may be referred to as "modified PVA"). By containing the modified PVA, the dynamic viscoelasticity parameters according to the present invention are easily satisfied.

The modified PVA is a polymer having a vinyl alcohol unit (-CH ₂ -CH(OH)-) as a structural unit and having a silicon-containing group. The modified PVA may contain a structural unit containing a silicon-containing group, and may further contain a vinyl ester unit such as a vinyl acetate unit or other structural unit.

The silicon-containing group of the modified PVA is not particularly limited as long as it is a group containing a silicon atom, but is preferably a silanol group or a group that can be converted to a silanol group in the presence of water. A silanol group is a group having a silicon atom and at least one hydroxyl group bonded to the silicon atom. The number of hydroxyl groups in the silanol group is usually 1 to 3, and is preferably 3. The hydroxyl group in the silanol group may be present in the form of a salt (e.g., -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. This conversion to a silanol group may occur by hydrolysis. Examples of groups that can be converted to a silanol group in the presence of water include groups in which at least one alkoxy group or acyloxy group is bonded to a silicon atom, and specific examples include trimethoxysilyl groups, triethoxysilyl groups, triisopropoxysilyl groups, dimethoxymethylsilyl groups, diethoxymethylsilyl groups, methoxydimethylsilyl groups, ethoxydimethylsilyl groups, and triacetoxysilyl groups.

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

In formulas (1) to (3), each R ¹ is 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. Each R ² is independently a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms.

Examples of the hydrocarbon group having 1 to 20 carbon atoms represented by ^R1 and ^R2 include aliphatic hydrocarbon groups, alicyclic hydrocarbon groups (cyclohexyl group, etc.), and aromatic hydrocarbon groups (phenyl group, etc.), with aliphatic hydrocarbon groups being preferred. Examples of the aliphatic hydrocarbon group include alkyl groups such as methyl, ethyl, and propyl groups, alkenyl groups such as vinyl groups, and alkynyl groups such as ethynyl groups, with alkyl groups being preferred. The number of carbon atoms in the hydrocarbon group represented by ^R1 and ^R2 is preferably 1 to 6, and more preferably 1 to 3. At least a portion of the hydrogen atoms in the hydrocarbon group represented by ^R1 and ^R2 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 having 1 to 20 carbon atoms represented by ^R1 include a hydrogen atom or a group in which a carbonyl group (-CO-) is bonded to a hydrocarbon group having 1 to 19 carbon atoms. The hydrocarbon group having 1 to 19 carbon atoms is preferably an aliphatic hydrocarbon group, and more preferably an alkyl group. Specific examples of the acyl group include a formyl group, an acetyl group, a propionyl group, and a benzoyl group. The number of carbon atoms in the acyl group represented by ^R1 is preferably 1 to 6, and more preferably 1 to 3. At least a portion of the hydrogen atoms in the acyl group represented by ^R1 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 one of the formulas (1) to (3), when at least one 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, the group is a group that can be converted to a silanol group in the presence of water. R ¹ 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, it is preferable that the silicon-containing group is directly bonded to a carbon atom in the polymer main chain via a silicon-carbon bond.

The lower limit of the content of silicon-containing groups relative to the total structural units of the modified PVA is preferably 0.01 mol%, more preferably 0.05 mol%, even more preferably 0.1 mol%, and even more preferably 0.2 mol%. By making the content of silicon-containing groups equal to or greater than the lower limit, the complex viscosity η ^* ₁ (30) is sufficiently high, and the optical performance obtained can be further improved. On the other hand, the upper limit of the content of silicon-containing groups relative to the total structural units of the modified PVA is preferably 2.0 mol%, more preferably 0.8 mol%, and more preferably 0.6 mol%. By making the content of silicon-containing groups equal to or less than the upper limit, the water solubility of the modified PVA is increased, and the productivity (film formability) can be improved.

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

The preferred range of the viscosity average polymerization degree of the modified PVA is the same as the preferred range of the viscosity average polymerization degree of the PVA described above. The preferred range of the saponification degree of the modified PVA is the same as the preferred range of the saponification degree of the PVA described above.

The lower limit of the product of the viscosity average polymerization degree of the modified PVA and the content of silicon-containing groups is preferably 100 mol%, more preferably 300 mol%, even more preferably 500 mol%, and particularly preferably 700 mol%. When the product is equal to or greater than the lower limit, the optical performance of the resulting optical film is more excellent. On the other hand, the upper limit of the product is preferably 2,000 mol%, more preferably 1,500, and even more preferably 1,200. When the product is equal to or less than the upper limit, the water solubility of the modified PVA can be further increased, and the productivity of the film for producing the optical film can be further increased.

The modified PVA preferably has a structural unit having a silicon-containing group. An example of the structural unit having a silicon-containing group is a structural unit represented by the following formula (4).

In formula (4), ^R3 is a hydrogen atom or a methyl group, ^R4 is a single bond or a divalent linking group, and ^R5 is a silicon-containing group.

^R3 is preferably a hydrogen atom.

Examples of the divalent linking group represented by ^R4 include groups represented by -( _CH2 ) _n- (n is an integer of 1 to 5) or ^-CONR6 - ^R7- ( ^R6 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and ^R7 is the group represented by -( _CH2 ) _n- or a divalent hydrocarbon group containing at least one of an oxygen atom and a nitrogen atom).

Examples _of divalent hydrocarbon groups containing at _least one of _an oxygen atom and a nitrogen atom include _{-CH2CH2NHCH2CH2CH2- , -CH2CH2NHCH2CH2-} , _{-CH2CH2NHCH2CH2-} , -CH2CH2NHCH2-, _{-CH2CH2N ( CH3} ) _CH2CH2- , _{-CH2CH2N (} CH3 _{) CH2- , -CH2CH2OCH2CH2CH2- , -CH2CH2OCH2CH2-} , -CH2CH2OCH2CH2-, _{etc. 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 _{to 6} .

^R4 is preferably a single bond.

Specific examples of the silicon-containing group represented by ^R5 are as described above, and include the groups represented by any one of the formulas (1) to (3), with the group represented by the formula (1) being preferred.

The number of silicon-containing groups contained in the structural unit having a silicon-containing group is not particularly limited, but may be 1. The range of the content of the structural unit having a silicon-containing group relative to all structural units of the modified PVA may be the range of the content of the silicon-containing group relative to all structural units described above. In addition, the range of the product of the viscosity average degree of polymerization of the modified PVA and the content of the structural unit having a silicon-containing group may be the range of the product of the viscosity average degree of polymerization and the content of the silicon-containing group described above.

The modified PVA may have structural units other than the vinyl alcohol unit, the vinyl ester unit, and the structural unit having a silicon-containing group. However, the content of the other structural units relative to the total structural units of the modified PVA 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. When the modified PVA is substantially composed of a structural unit having a vinyl alcohol unit, a vinyl ester unit, and a silicon-containing group, the effects of the present invention may be more fully achieved.

The film for producing optical films may contain one type of modified PVA alone, or may contain two or more types of modified PVA that differ from each other in terms of degree of polymerization, degree of saponification, content of silicon-containing groups, etc.

The lower limit of the content of modified PVA in the film for optical film production is not particularly limited, but is preferably 60% by mass, more preferably 80% by mass, and even more preferably 85% by mass. By making the content of modified PVA equal to or greater than the lower limit, the effect of the present invention can be further enhanced. On the other hand, the upper limit of this content is not particularly limited, and may be 100% by mass, preferably 99% by mass, and more preferably 95% by mass.

In addition, the content of modified PVA relative to all PVA contained in the film for optical film production of the present invention is preferably 60% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more. By mainly using modified PVA as the PVA in the film for optical film production of the present invention, the effects of the present invention can be more fully exhibited. The upper limit of this content is not particularly limited and may be 100% by mass.

(Method for producing modified PVA)
The method for producing the modified PVA having a silicon-containing group is not particularly limited. For example, the modified PVA can be produced by copolymerizing a vinyl ester monomer with a monomer having a silicon-containing group, and saponifying the resulting vinyl ester polymer.

Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Of these, vinyl acetate is preferred.

Monomers having silicon-containing groups include vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, allyltrimethoxysilane, allylmethyldimethoxysilane, allyldimethylmethoxysilane, allyltriethoxysilane, allylmethyldiethoxysilane, allyldimethylethoxysilane, vinyltris(β-methoxyethoxy)silane, vinylisobutyldimethoxysilane, vinylethyldimethoxysilane, vinylmethoxydibutoxysilane, vinyldimethoxybutoxysilane, and vinyltributoxysilane. , vinyl methoxydihexyloxysilane, vinyl dimethoxyhexyloxysilane, vinyl trihexyloxysilane, vinyl methoxydioctyloxysilane, vinyl dimethoxyoctyloxysilane, vinyl trioctyloxysilane, vinyl methoxydilauryloxysilane, vinyl dimethoxylauryloxysilane, vinyl methoxydioleyloxysilane, vinyl dimethoxyoleyloxysilane, 3-(meth)acrylamide-propyl trimethoxysilane, 3-(meth)acrylamide-propyl triethoxysilane, 3-(meth)acrylamide-propyl tri(β-methoxyethoxy)silane, 2-(meth)acrylamide-ethyl trimethoxysilane Silane, 1-(meth)acrylamide-methyltrimethoxysilane, 2-(meth)acrylamide-2-methylpropyltrimethoxysilane, 2-(meth)acrylamide-isopropyltrimethoxysilane, 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-propyltripropionyloxysilane , 2-(meth)acrylamide-2-methylpropyltriacetoxysilane, N-(2-(meth)acrylamide-ethyl)-aminopropyltriacetoxysilane, 3-(meth)acrylamide-propylisobutyldimethoxysilane, 2-(meth)acrylamide-ethyldimethylmethoxysilane, 3-(meth)acrylamide-propylmethyldiacetoxysilane, 2-(meth)acrylamide-2-methylpropylhydrogendimethoxysilane, 3-(N-methyl-(meth)acrylamide)-propyltrimethoxysilane, 2-(N-ethyl-(meth)acrylamide)-ethyltriacetoxysilane, and the like.

The method for copolymerizing the vinyl ester monomer and the monomer having a silicon-containing group is not particularly limited, and includes known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these methods, bulk polymerization carried out without a solvent and solution polymerization carried out using a solvent such as alcohol are preferred. Solvents used as solvents during solution polymerization include esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as benzene and toluene; and lower alcohols such as methanol and ethanol.

The initiator used in the copolymerization reaction is appropriately selected from conventionally known azo initiators, peroxide initiators, redox initiators, etc. Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), etc. Examples of the peroxide initiator include percarbonate compounds such as di-normal propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and t-butyl peroxyneodecanate; acetylcyclohexylsulfonyl peroxide, diisobutyryl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Furthermore, the above-listed peroxide initiators can be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, and the like to form an initiator. Examples of the redox initiator include combinations of the above-listed peroxides with reducing agents such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and Rongalite.

There are no particular restrictions on the polymerization temperature when carrying out the copolymerization reaction, but a temperature of 0°C or higher and 180°C or lower is preferred, a temperature of 20°C or higher and 160°C or lower is more preferred, and a temperature of 30°C or higher and 150°C or lower is even more preferred.

When copolymerizing a vinyl ester monomer with a monomer having a silicon-containing group, other copolymerizable monomers can be copolymerized as necessary, as long as the effects of the present invention are not impaired. Examples of such other monomers include ethylene; olefins having 2 to 30 carbon atoms, such as propylene, 1-butene, and isobutene; acrylic acid or its salts; 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 salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and t-butyl acrylate; methacrylic acid esters such as propyl, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, N-methylolacrylamide, methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid or a salt thereof, methacrylamide propyl dimethylamine or a salt thereof, N-methylol methacrylamide or a derivative thereof; N-vinyl amides such as N-vinyl formamide, N-vinyl acetamide, and N-vinyl pyrrolidone; vinyl ethers 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; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester, or acid anhydride thereof; itaconic acid or a salt, ester, or acid anhydride thereof; and isopropenyl acetate. The vinyl ester polymer may have structural units derived from one or more of the other monomers mentioned above.

The proportion of structural units derived from the other monomers (monomers other than vinyl ester monomers and monomers having a silicon-containing group) in the vinyl ester polymer is not necessarily limited as long as it does not interfere with the effects of the present invention, but may be 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, based on the number of moles of all structural units constituting the vinyl ester polymer.

The vinyl ester polymer is then saponified in a solvent according to a known method to produce a modified PVA. The solvent used in the saponification reaction is preferably an alcohol. Examples of alcohol include lower alcohols such as methanol and ethanol, with methanol being particularly preferred. The solvent used in the saponification reaction may further contain, in addition to alcohol, acetone, esters such as methyl acetate and ethyl acetate, and organic solvents such as toluene. Examples of catalysts used in the saponification reaction include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, alkali catalysts such as sodium methylate, and acid catalysts such as mineral acids. The temperature of the saponification reaction can be, for example, 20°C or higher and 60°C or lower. If a gel-like product precipitates as the saponification reaction proceeds, the product is crushed at that point, washed, and then dried to obtain a modified PVA.

In addition, the modified PVA having a silicon-containing group may be a modified PVA in which a silicon-containing group is introduced into unmodified PVA by a silylating agent, or a modified PVA in which a structural unit having a silicon-containing group is introduced by graft copolymerization. Examples of the silylating agent include reactive silane compounds that can react with the hydroxyl group of PVA, such as triethoxychlorosilane and methyltrichlorosilane. In addition, the film for optical film production of the present invention can be easily obtained by using a PVA crosslinked with a crosslinking agent as a PVA other than the modified PVA having a silicon-containing group.

(Plasticizer)
The film for optical film production of the present invention preferably contains a plasticizer. When the film for optical film production contains a plasticizer, it is possible to improve the stretchability. The plasticizer is preferably a polyhydric alcohol. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Among these, glycerin is preferred from the viewpoint of improving the stretchability. One or more kinds of plasticizers can be used.

The lower limit of the content of the plasticizer in the film for optical film production of the present invention is preferably 1 part by mass, more preferably 3 parts by mass, and even more preferably 5 parts by mass, relative to 100 parts by mass of PVA. By having the content of the plasticizer be equal to or greater than the lower limit, the stretchability of the film is improved, and the optical performance of the obtained optical film can be further improved. 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 even more preferably 15 parts by mass, relative to 100 parts by mass of PVA. By having the content of the plasticizer be equal to or less than the upper limit, it is possible to prevent the film from becoming too flexible and reducing the handleability.

(Surfactant)
The optical film-producing film preferably contains a surfactant. By forming a film using a film-forming solution containing a surfactant, the film-forming properties are improved, the occurrence of unevenness in the film thickness is suppressed, and the film is easily peeled off from a metal roll or belt used in film formation. When a film for optical film production is produced from a film-forming solution containing a surfactant, the resulting film may contain a surfactant.

The type of surfactant is not particularly limited, but anionic surfactants and nonionic surfactants are preferred from the standpoint of releasability from metal rolls and belts.

Examples of anionic surfactants include carboxylic acid types such as potassium laurate; sulfate 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 octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkyl amine types such as polyoxyethylene lauryl amino 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; and allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether.

Surfactants may be used alone or in combination of two or more.

When the optical film manufacturing film contains a surfactant, the lower limit of the content is preferably 0.01 parts by mass, more preferably 0.02 parts by mass, and even more preferably 0.05 parts by mass, relative to 100 parts by mass of PVA. By making the content of the surfactant equal to or greater than the lower limit, the film-forming property and peelability are further improved. On the other hand, the upper limit of the content is preferably 0.5 parts by mass, more preferably 0.3 parts by mass, and even more preferably 0.1 parts by mass, relative to 100 parts by mass of PVA. By making the content of the surfactant equal to or less than the upper limit, it is possible to prevent the surfactant from bleeding out onto the surface of the film, causing blocking and reducing handleability.

(Other additives, etc.)
The film for producing an optical film of the present invention may further contain additives, such as a filler, a processing stabilizer such as a copper compound, a weather resistance stabilizer, a colorant, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, other thermoplastic resins, a lubricant, a fragrance, an antifoaming agent, a deodorant, an extender, a peeling agent, a releasing agent, a reinforcing agent, a crosslinking agent, a mildew inhibitor, a preservative, and a crystallization rate retarder, as necessary.

The total content of PVA, plasticizer, and surfactant in the film for optical film production of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and in some cases even more preferably 99% by mass or more. When the film for optical film production of the present invention is substantially composed of PVA, plasticizer, and surfactant, the effects of the present invention can be more fully exhibited.

In addition, the total content of the modified PVA having a silicon-containing group, the plasticizer, and the surfactant in the film for producing an optical film of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and in some cases even more preferably 99% by mass or more. When the film for producing an optical film of the present invention is substantially composed of the modified PVA having a silicon-containing group, the plasticizer, and the surfactant, the effects of the present invention can be more fully exhibited.

(shape, physical properties, etc.)
The film for producing an optical film of the present invention is a so-called original film used as a material for an optical film. However, the film for producing an optical film of the present invention is not limited to a roll-shaped film.

The average thickness of the film for optical film production of the present invention is not particularly limited, but the lower limit is preferably 1 μm, more preferably 5 μm, and even more preferably 10 μm. By having an average thickness equal to or greater than the lower limit, it is possible to suppress breakage during the uniaxial stretching process when producing the optical film. Furthermore, the upper limit of this average thickness is preferably 75 μm, more preferably 60 μm, even more preferably 45 μm, and even more preferably 35 μm. By having an average thickness equal to or less than the upper limit, it is possible to suppress stretching unevenness during the uniaxial stretching process. Note that the "average thickness" refers to the average value of thicknesses measured at any five points (the same applies to the average thickness below).

The film for optical film production of the present invention may be a single layer film consisting of one PVA layer (layer containing PVA), or may be a multilayer film containing one PVA layer. However, when used for manufacturing a polarizing film, it is preferable to use a single layer film. The lower limit of the average thickness of the PVA layer of the film for optical film production of the present invention is preferably 1 μm, more preferably 5 μm, and even more preferably 10 μm. By having the average thickness be equal to or greater than the lower limit, it is possible to suppress breakage during the uniaxial stretching process when manufacturing the optical film. In addition, the upper limit of this average thickness is preferably 75 μm, more preferably 60 μm, even more preferably 45 μm, and even more preferably 35 μm. By having the average thickness be equal to or less than the upper limit, it is possible to suppress stretching unevenness during the uniaxial stretching process.

The specific composition and preferred composition of the PVA layer in the film for producing optical films can be referenced from the description of the specific composition and preferred composition of the film for producing optical films itself described above.

When the film for optical film production of the present invention is a single layer film, the average thickness is preferably 20 μm or more, more preferably 30 μm or more, in order to ensure handling properties. On the other hand, when the film for optical film production of the present invention is a multilayer film, the average thickness of the PVA layer can 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 a multilayer film may be five or less, or three or less. An example of a multilayer film is a film for manufacturing an optical film having a laminated structure of a base resin layer and a PVA layer. The average thickness of the base resin layer is, for example, 20 μm or more and 500 μm or less. It is preferable that the base 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, etc. can be used. Among them, amorphous polyester resin is preferable, and amorphous polyester resin obtained by copolymerizing polyethylene terephthalate with a copolymerization component such as isophthalic acid or 1,4-cyclohexanedimethanol is preferably used. An adhesive layer may be provided between the base resin layer and the PVA layer.

The width of the film for optical film production of the present invention is not particularly limited and can be determined depending on the application. For example, the lower limit of the width of the film for optical film production is preferably 3 m. In recent years, the screen size of liquid crystal televisions and liquid crystal monitors has been increasing, so if the width of the film for optical film production is 3 m or more, it is suitable for applications in which these are used as final products. On the other hand, the upper limit of the width of the film for optical film production is preferably 7 m. By setting the width to 7 m or less, when producing optical films using practical equipment, it is possible to efficiently perform uniaxial stretching processing.

From the viewpoint of the productivity and optical performance of the optical film, the swelling degree of the film for optical film production of the present invention is preferably in the range of 140% or more and 400% or less. The lower limit of the swelling degree is more preferably 180%, and even more preferably 190%. The upper limit of the swelling degree is more preferably 220%, and even more preferably 210%. The swelling degree of the film can be adjusted to a smaller value, for example, by strengthening the heat treatment conditions.

The "degree of swelling of the film" as used herein refers to a value calculated according to the following formula.
Swelling degree (%) = 100 x N/M
In the formula, N represents the mass (g) of a sample taken from the film after immersing the sample in distilled water at 30° C. for 30 minutes and removing the surface water, and 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 production of the present invention is usually a film that is not substantially stretched (non-stretched film, unstretched film). 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 subjecting the film for optical film production of the present invention to a stretching process (uniaxial stretching process or biaxial stretching process).

The film for optical film production of the present invention can provide an optical film with good productivity and excellent optical performance. The optical performance includes light transmittance, polarization, etc. Examples of optical films that can be produced using the film for optical film production include polarizing films, retardation films, viewing angle improving films, brightness improving films, etc., and polarizing films are preferred.

<Method of manufacturing film for producing optical film>
The method for producing the film for optical film production of the present invention is not particularly limited, but a method that makes the thickness and width of the film more uniform after film production can be preferably adopted. For example, it can be produced using a film-forming solution in which PVA and, if necessary, one or more of a plasticizer, a surfactant, and other additives are dissolved in a liquid medium. When the film-forming solution contains at least one of a plasticizer, a surfactant, and other additives, it is preferable that these components are uniformly mixed.

Examples of liquid media used in the preparation of the film-forming solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine, and one or more of these can be used. Among these, water is preferred in terms of environmental load and recyclability. In addition, when the modified PVA having the above-mentioned silicon-containing group is used as the PVA, this modified PVA has good water solubility and also suppresses the increase in viscosity when it is made into an aqueous solution at a relatively high temperature (e.g., 80°C). From this point of view, water can be preferably used as the liquid medium.

The volatile fraction of the film-forming solution (the content in the film-forming solution of volatile components such as liquid media that are removed by volatilization or evaporation during film formation) is, for example, preferably 50% by mass or more and 95% by mass or less, more preferably 55% by mass or more and 90% by mass or less, and even more preferably 60% by mass or more and 85% by mass or less. When the volatile fraction of the film-forming solution is 50% by mass or more, the viscosity of the film-forming solution does not become too high, and filtration and degassing during the preparation of the film-forming solution are performed smoothly, making it easy to produce a film with few foreign matter and defects. On the other hand, when the volatile fraction of the film-forming solution is 95% by mass or less, the concentration of the film-forming solution does not become too low, making it easy to produce a film industrially.

The temperature of the film-forming solution during film production can be, for example, 70°C or higher and 100°C or lower. By producing the film at such a relatively high temperature, the viscosity of the film-forming solution can be kept relatively low, improving film-forming properties.

Examples of methods for producing a film using a film-forming solution include cast film-forming, extrusion film-forming, wet film-forming, and gel film-forming. These film-forming methods may be used alone or in combination of two or more. Among these film-forming methods, cast film-forming and extrusion film-forming are preferred because they can produce a film with uniform thickness and width and good physical properties. The produced film can be dried or heat-treated as necessary.

Specific examples of the manufacturing method of the film for optical film manufacturing of the present invention include the following. Using a T-type slit die, a hopper plate, an I-die, a lip coater die, or the like, the film-forming solution is uniformly discharged or cast onto the peripheral surface of a rotating heated first roll (or belt) located on the most upstream side. The volatile components are evaporated from one side of the film discharged or cast onto the peripheral surface of the first roll (or belt) to dry it. The film is then further dried on the peripheral surface of one or more rotating heated rolls arranged downstream, or further dried by passing through a hot air dryer. The film is then wound up by a winding device. Drying by a heated roll and drying by a hot air dryer may be performed in an appropriate combination.

When the film for optical film production of the present invention is a multilayer film, the multilayer film can be produced, for example, by applying a film-forming solution onto a base resin film (base resin layer). At this time, in order to improve the adhesion 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.

<Method of Manufacturing Optical Film>
The method for producing an optical film of the present invention includes a step of uniaxially stretching the above-mentioned film for producing an optical film. Hereinafter, a method for producing a polarizing film will be specifically described as an example of the method for producing an optical film.

Examples of methods for manufacturing polarizing films include a dyeing process for dyeing a film for manufacturing optical films (hereinafter also referred to as "PVA film"), a stretching process for uniaxial stretching, and, if necessary, a swelling process for swelling, a crosslinking process for crosslinking, a fixing process for fixing, a cleaning process for washing, a drying process for drying, a heat treatment process for heat treatment, etc. In this case, the order of each process is not particularly limited, but can be, for example, the swelling process, dyeing process, crosslinking process, stretching process, and fixing process. In addition, one or more processes can be performed simultaneously, and each process can be performed twice or more times.

The swelling process can be carried out by immersing the PVA film in water. The temperature of the water during immersion is preferably 20°C or more and 55°C or less, more preferably 22°C or more and 50°C or less, and even more preferably 25°C or more and 45°C or less. The time for immersion in water is preferably, for example, 0.1 minutes or more and 5 minutes or less, and more preferably 0.5 minutes or more and 3 minutes or less. The water used for immersion in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

The dyeing process can be carried out by contacting the PVA film with a dichroic dye. Iodine-based dyes are generally used as the dichroic dye. The timing of dyeing may be any stage before, during, or after uniaxial stretching. A method of dyeing by immersing the PVA film in a dye bath containing iodine and potassium iodide (particularly an aqueous solution) is preferably used. The concentration of iodine in the dye bath is preferably 0.01% by mass to 0.5% by mass, and the concentration of potassium iodide is preferably 0.01% by mass to 10% by mass. The temperature of the dye bath is preferably 20°C to 50°C, particularly 25°C to 40°C. The preferred dyeing time is 0.2 minutes to 5 minutes.

By carrying out a crosslinking process to crosslink the PVA in the PVA film, it is possible to effectively prevent the PVA from dissolving into water during wet stretching at high temperatures. From this viewpoint, it is preferable to carry out the crosslinking process after the dyeing process and before the stretching process. The crosslinking process can be carried out by immersing the PVA film in an aqueous solution containing a crosslinking agent. As the crosslinking agent, one or more boron compounds such as boric acid and borax and other borates 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 even more preferably 2% by mass or more and 6% by mass or less. By having the concentration of the crosslinking agent within the above range, sufficient stretchability can be maintained. The aqueous solution containing the 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. By setting the temperature within the above range, crosslinking can be carried out efficiently.

The stretching process for 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 performed in an aqueous solution containing boric acid, or in the dyeing bath described above or in a fixing treatment bath described below. In the case of the dry stretching method, the stretching may be performed at room temperature, or may be performed while heating, or may be performed in air using the PVA film after absorbing water. Among these, the wet stretching method is preferred because it can be stretched with high uniformity in the width direction, and uniaxial stretching in an aqueous solution containing boric acid is more preferred. 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. In addition, the aqueous solution of boric acid may contain potassium iodide, and the concentration of potassium iodide is preferably 0.01% by mass or more and 10% by mass or less. The stretching temperature in the uniaxial stretching is preferably 30°C or higher and 90°C or lower, more preferably 40°C or higher and 80°C or lower, and particularly preferably 50°C or higher and 75°C or lower.

The stretching ratio in uniaxial stretching (total stretching ratio from the unstretched PVA film) is preferably 5 times or more, more preferably 5.5 times or more, from the viewpoint of the polarizing performance of the resulting polarizing film. There is no particular upper limit to the stretching ratio, but the stretching ratio is preferably 8 times or less.

There is no particular restriction on the direction of uniaxial stretching when uniaxially stretching a long PVA film, and uniaxial stretching in the long direction or uniaxial stretching in the transverse direction can be used. Uniaxial stretching in the long direction is preferred because it results in a polarizing film with excellent polarization performance. Uniaxial stretching in the long direction can be performed by using a stretching device equipped with multiple rolls parallel to each other and changing the peripheral speed between each roll. On the other hand, uniaxial stretching in the transverse direction can be performed using a tenter-type stretching machine.

In the manufacture of polarizing films, a fixing process can be performed after the stretching process in order to strengthen the adsorption of the dichroic dye (iodine-based dye, etc.) to the PVA film. The fixing bath used for the fixing process can be an aqueous solution containing one or more boron compounds such as boric acid and borax. If necessary, an iodine compound or a metal compound may be added to the fixing bath. The concentration of the boron compound in the fixing 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. By setting the concentration of the boron compound within the above range, the adsorption of the dichroic dye can be made stronger. The temperature of the fixing bath is preferably 15°C or more and 60°C or less, particularly 25°C or more and 40°C or less.

The cleaning process is generally performed by immersing the film in distilled water, pure water, an aqueous solution, or the like. In this case, 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 concentration of the iodide is preferably 0.5% by mass to 10% by mass. In addition, the temperature of the aqueous solution in the cleaning process is generally 5°C to 50°C, preferably 10°C to 45°C, and more preferably 15°C to 40°C. By setting the temperature of the aqueous solution within the above range, it is possible to further improve the polarization performance.

There are no particular limitations on the conditions for the drying process, but it is preferable to dry the PVA film at a temperature of 30°C or higher and 150°C or lower, and particularly 50°C or higher and 130°C or lower. Drying at a temperature within the above range makes it easier to obtain a polarizing film with excellent dimensional stability.

In addition, optical films other than polarizing films, such as retardation films, can also be manufactured by a method that includes a step of uniaxially stretching the film for manufacturing an optical film of the present invention. As for the specific manufacturing method, a conventionally known method can be adopted, except that the film for manufacturing an optical film of the present invention is used.

<Optical film>
An optical film can be obtained by the above-mentioned production method using the film for producing an optical film of the present invention.

The optical film may be a polarizing film, a retardation film, a viewing angle improving film, a brightness improving film, etc., and is preferably a polarizing film. In this case, the polarizing film usually contains a dichroic dye, and the PVA may be crosslinked.

The optical film is preferably a stretched film, more preferably a uniaxially stretched film. The optical film may be a single-layer film or a multi-layer film, but is preferably a single-layer film. In the case of such a film, the optical film can be more suitably used as a polarizing film, etc.

When the optical film is a polarizing film, it is preferable that the dichroic ratio (R) of the polarizing film is 100 or more. By using a PVA film that satisfies the above-mentioned dynamic viscoelasticity parameters, a polarizing film having such a high dichroic ratio (R) can be produced with good productivity. The dichroic ratio (R) is more preferably 150 or more, and even more preferably 190 or more. The upper limit of this dichroic ratio (R) is, for example, 350, and may be 300 or 260.

The method for calculating the dichroic 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 shown by formula (a). In this case, the refractive index of the polarizing film is assumed to be 1.5, and the reflectance at the surface is assumed to be 4%. The relationship between the transmittance (T'), the degree of polarization (V), and the dichroic ratio (R) is shown by formula (b). Therefore, the single transmittance (T) and the degree of polarization (V) are measured, and then the dichroic ratio (R) of the polarizing film can be calculated by solving formulas (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 laminating an optically transparent and mechanically strong protective film on one or both sides of the polarizing film. Examples of protective films that can be used include cellulose triacetate (TAC) film, cycloolefin polymer (COP) film, cellulose acetate butyrate (CAB) film, acrylic film, and polyester film. Examples of adhesives used for lamination include PVA adhesives, urethane adhesives, and acrylate UV-curable adhesives. In other words, a polarizing plate has a polarizing film and a protective film laminated directly or via an adhesive layer on one or both sides of the polarizing film.

The polarizing plate can be used as a part of an LCD by, for example, coating it with an acrylic or other adhesive and then bonding it to a glass substrate. In addition, the polarizing plate may also be bonded with a retardation film, a viewing angle improving film, a brightness improving film, etc.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods of measurement and evaluation are as follows.

[Polymerization degree of PVA (viscosity average polymerization degree)]
The viscosity average degree of polymerization of the PVA synthesized in the following synthesis examples was measured in accordance with the description of JIS K6726-1994.

[Degree of saponification of PVA]
For the PVA synthesized in the following synthesis examples, the degree of saponification was measured according to the description of JIS K6726-1994.

[Silicon-containing group content in PVA]
For the PVA synthesized in the following synthesis examples, the content of silicon-containing groups relative to all structural units was measured from the 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 was purified by reprecipitation with hexane-acetone to completely remove unreacted monomers from the polymer, and then dried at 90°C under reduced pressure for 2 days, and then dissolved in _CDCl3 solvent for analysis.

[Film swelling degree]
The films (films for optical film production) obtained in the following Examples or Comparative Examples were cut to 1.5 g and immersed in 1000 g of distilled water at 30° C. for 30 minutes. After immersion for 30 minutes, the films were taken out, the water on the surface was absorbed with filter paper, and the mass (N) was measured. The films were then dried in a dryer at 105° C. for 16 hours, and the mass (M) after drying was measured. The swelling degree of the film was calculated from the obtained mass (N) and mass (M) according to the following formula.
Swelling degree (%) = 100 x N/M

[Dichroic ratio of polarizing film (optical performance)]
A rectangular sample of 4 cm in the length direction of the polarizing film obtained in the following Examples or Comparative Examples was taken from the center in the width direction of the polarizing film. The single transmittance (T) and polarization degree (V) of this sample were measured using an integrating sphere spectrophotometer ("V7100" manufactured by JASCO Corporation) in accordance with JIS Z8722 (measurement method for object color) after luminosity correction in the visible light region with a C light source and a 2° visual field.
The dichroic ratio (R) of the polarizing film was calculated by solving the following formulas (a) and (b) from the obtained single transmittance (T) and polarization degree (V). Here, the refractive index of the polarizing film was set to 1.5, and the reflectance at the surface was set to 4%. The dichroic ratio (R) of the polarizing film produced in this manner under the temperature conditions of the uniaxial stretching treatment bath in the 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)

[Contraction force of polarizing film]
The polarizing film obtained in the following Examples or Comparative Examples was used to measure the shrinkage force of the polarizing film using Shimadzu Corporation's thermostatic chamber equipped autograph "AG-X" and video extensometer "TR ViewX120S". For the measurement, a polarizing film that had been conditioned at 20°C/20% RH for 18 hours was used. After the thermostatic chamber of the autograph "AG-X" was set to 20°C, the polarizing film (15 cm in length, 1.5 cm in width) was attached to a chuck (chuck interval 5 cm), and the temperature of the thermostatic chamber was raised to 80°C at the same time as the tension started. The polarizing film was pulled at a speed of 1 mm/min, and the tension was stopped when the tension reached 2N, and the tension was measured in this state for up to 4 hours. At this time, since the distance between the chucks changes due to thermal expansion, a marking seal was attached to the chuck, and the measurement was performed using a video extensometer "TR ViewX120S" so that the distance between the chucks could be corrected by the amount of movement of the marking seal attached to the chuck. The shrinkage force of the polarizing film was determined by subtracting the initial tension of 2 N from the measured tension after 4 hours. The shrinkage force (SF) of the polarizing film thus produced under the temperature conditions of the uniaxial stretching treatment bath in the Examples and Comparative Examples was determined to be SF ₀ .

[Dichroic ratio of polarizing film at shrinkage force of 15 N]
In the following examples and comparative examples, polarizing films with different temperatures of the uniaxial stretching bath were obtained in the same manner, except that the temperature of the uniaxial stretching bath was set to a temperature 2°C or 4°C lower, and the iodine concentration of the dyeing bath was changed so that the transmittance of the obtained polarizing film was 44.0%. The single transmittance (T) and polarization degree (V) of each obtained polarizing film were measured, and the dichroic ratio (R) was obtained by the above-mentioned method. Here, the dichroic ratio (R) of the polarizing film obtained under the condition of a uniaxial stretching bath temperature 2°C lower was R _-2 , and the dichroic ratio (R) of the polarizing film obtained under the condition of a uniaxial stretching bath temperature 4°C lower was R _-4 . In addition, the contraction force of each polarizing film was measured by the above-mentioned method. Here, the contraction force (SF) of the polarizing film obtained under the condition of a uniaxial stretching bath temperature 2°C lower was SF _-2 , and the contraction force (SF) of the polarizing film obtained under the condition of a uniaxial stretching bath temperature 4°C lower was SF _-4 .

The dichroic ratio (R ₀ , R _-2 , R _-4 ) and shrinkage force (SF ₀ , SF _-2 , SF _-4 ) values of the three types of polarizing films thus obtained, each having a different temperature in the uniaxial stretching treatment bath, were used to plot the relationship between the dichroic ratio and the shrinkage force, and the dichroic ratio of the polarizing film at a shrinkage force of 15 N was calculated by linear approximation.

[Complex Viscosity of PVA Aqueous Solution by Dynamic Viscosity Measurement]
(Preparation of PVA aqueous solution)
A PVA aqueous solution for dynamic viscoelasticity measurement was prepared using the PVA film produced in the following Examples or Comparative Examples. Specifically, the PVA film and distilled water were weighed in a container so that the PVA concentration was 12% by mass, and then the PVA aqueous solution was prepared by heating and dissolving at 95°C for 4 hours while stirring. In the preparation, the PVA film was first swollen with water and washed to elute substances other than PVA contained in the PVA film (water, plasticizer, surfactant), and then the film was dried in a dryer at 105°C for 17 hours or more and weighed to determine the PVA content in the PVA film. Then, based on the determined PVA content, the PVA film from which substances other than PVA were not eluted was weighed and dissolved so that the PVA concentration was 12% by mass.

(Dynamic Viscosity Measurement)
Dynamic viscoelasticity measurements were performed using a dynamic viscoelasticity measuring device (TA instruments, "ARES-G2") under the following measurement conditions, with the temperature of each PVA aqueous solution set to 30°C or 80°C.

(Measurement conditions for dynamic viscoelasticity measurement)
Geometry: Cone plate with a cone angle of 0.02 rad and disc-shaped plate Plate diameter: 40 mm
Strain: 1%
Angular frequency range: 1 to 500 rad/sec Measurement temperature (temperature of PVA aqueous solution): 30°C or 80°C

Here, the temperature of the PVA aqueous solution was set to 30°C or 80°C in the following manner. First, about 1 mL of the PVA aqueous solution to be measured was applied onto a plate heated to 30°C or 80°C. Then, after adjusting the gap between the cone plate and the disk-shaped plate to a specified value, the PVA aqueous solution that protruded from the plate was removed with a cotton swab, and dynamic viscoelasticity measurement was performed. When the temperature of the PVA aqueous solution was set to 80°C and dynamic viscoelasticity measurement was performed, a small amount of bis(2-ethylhexyl) phthalate was applied along the cone plate after removing the sample that protruded from the plate in order to prevent the aqueous solution from evaporating during measurement. In addition, a solvent trap cover was used to perform the measurement.

(Complex Viscosity of PVA Aqueous Solution)
From the flow curve of the complex viscosity obtained by dynamic viscoelasticity measurement of the PVA aqueous solution at a temperature of 30° C., the complex viscosity η ^* ₁ (30) at an angular frequency of 1 rad/sec and the complex viscosity η ^* ₅₀₀ (30) at an angular frequency of 500 rad/sec were obtained. In addition, the ratio (η ^* ₁ (30)/η ^* ₅₀₀ (30)) was calculated and taken as _Rω (30). On the other hand, from the flow curve of the complex viscosity obtained by dynamic viscoelasticity measurement of the PVA aqueous solution at a temperature of 80° C., the complex viscosity η ^* ₁ (80) at an angular frequency of 1 rad/sec and the complex viscosity η ^* ₅₀₀ (80) at an angular frequency of 500 rad/sec were similarly obtained. In addition, the ratio (η ^* ₁ (80)/η ^* ₅₀₀ (80)) was calculated and taken as _Rω (80). Furthermore, the ratio (η ^* ₁ (30)/η ^* ₁ (80)) of the complex viscosity η ^* ₁ (30) and the complex viscosity η ^* ₁ (80) determined above was calculated and designated as Rt. The dynamic viscosity measurement was performed three times for each of the PVA aqueous solutions prepared from the PVA films of the Examples and Comparative Examples, and the complex viscosities η ^* ₁ (30), η ^* ₅₀₀ (30), η ^* ₁ (80) and η ^* ₅₀₀ (80) of the PVA aqueous solutions were determined using the average data of these three measurements.

[Synthesis Example 1] Synthesis of PVA-1 2550g of vinyl acetate, 450g of methanol, and 116.8ml of a 5% by mass vinyltrimethoxysilane methanol solution were charged into a 6L reaction vessel equipped with a stirrer, a nitrogen inlet, an additive inlet, and an initiator inlet, and the temperature was raised to 60°C, and the system was replaced with nitrogen by nitrogen bubbling for 30 minutes. The temperature in the reaction vessel was adjusted to 60°C, and 0.3g of 2,2'-azobis(isobutyronitrile) was added to start polymerization. From the start of polymerization, 53ml of methanol containing 5% by mass of vinylmethoxysilane was added to the system while carrying out the polymerization reaction for 3 hours, at which point the polymerization was stopped. The polymerization rate at the time the polymerization reaction was stopped was 25.0%. The polymerization temperature was maintained at 60°C during polymerization. Next, unreacted vinyl acetate was removed under reduced pressure to obtain a methanol solution of polyvinyl acetate (hereinafter sometimes abbreviated as PVAc).

The concentration of the resulting PVAc in methanol was adjusted to 23.5% by mass, and a NaOH methanol solution (10% by mass concentration) was added so that the alkali molar ratio (moles of NaOH/moles of vinyl ester units in PVAc) was 0.04, followed by saponification. The resulting polyvinyl alcohol was washed with methanol.

The degree of polymerization (viscosity average degree of polymerization) of PVA-1 obtained by the above operations was 2,400, the degree of saponification was 99.9 mol%, and the content of silicon-containing groups was 0.3 mol%.

Synthesis Examples 2 to 5: Synthesis of PVA-2 to PVA-5 According to Synthesis Example 1, the ratio of monomers used, polymerization conditions, and saponification conditions were appropriately adjusted to obtain PVA-2 to PVA-5 having the viscosity average degree of polymerization, degree of saponification, and content of silicon-containing group shown in Table 1.

[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 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and having a PVA content of 7.5% by mass, was prepared as a film-forming stock solution. This film-forming stock solution was dried on a metal roll at 80° C., and the resulting film was heat-treated in a hot air dryer at a temperature of 127° C. for 10 minutes to adjust the swelling degree to 200%, thereby producing a PVA film (film for producing an optical film) with an average thickness of 30 μm.

A sample of 5 cm wide x 9 cm long was cut from the center of the width direction of the obtained PVA film so that a range of 5 cm wide x 5 cm long could be uniaxially stretched. This sample was immersed in pure water at 30 ° C for 60 seconds and uniaxially stretched to 2 times in the length direction for swelling treatment. Next, it was immersed in an aqueous solution containing 0.075 mass % iodine and 2 mass % potassium iodide (dyeing treatment bath: temperature 32 ° C) for 120 seconds and uniaxially stretched to 1.2 times (total 2.4 times) in the length direction to adsorb iodine. Next, it was immersed in an aqueous solution containing 2.6 mass % boric acid (boric acid crosslinking treatment bath: temperature 32 ° C) for 120 seconds and uniaxially stretched to 1.25 times (total 3.0 times) in the length direction. The film was then immersed in an aqueous solution containing 2.8% by mass of boric acid and 5% by mass of potassium iodide (uniaxial stretching bath: temperature 69° C.) and uniaxially stretched to a total of 6.0 times in the length direction. The film was then washed by immersing it in an aqueous solution containing 1.5% by mass of boric acid and 2.5% by mass of potassium iodide (washing bath: temperature 22° C.) for 5 seconds. Finally, the film was dried at 80° C. for 4 minutes to obtain a polarizing film.

The single transmittance (T) and polarization degree (V) of the obtained polarizing film were measured by the above-mentioned method, and the dichroic ratio (R ₀ ) was calculated. The single transmittance (T) was 44.12%, the polarization degree (V) was 99.9738%, and the dichroic ratio (R ₀ ) was 203. The contraction force (SF ₀ ) of the polarizing film was measured by the above-mentioned method and was found to be 13.6 N. The dichroic ratio of the polarizing film at a contraction force of 15 N was calculated by the above-mentioned method and was found to be 206.

Using the obtained PVA film, a PVA aqueous solution was prepared by the method described above, and dynamic viscoelasticity measurements were performed. At this time, 21.3 g of the PVA film (PVA content: 18 g) and 128.7 g of distilled water were weighed to obtain a 12% by mass PVA aqueous solution. Figure 1 shows the flow curve of the complex viscosity obtained from the dynamic viscoelasticity measurement (angular frequency: 1 to 500 rad/sec) of the aqueous solution at 30°C.

[Examples 2 to 3 and Comparative Examples 1 to 2]
Using the PVAs (PVA-2 to PVA-5) shown in Table 1, PVA films were produced and evaluated in the same manner as in Example 1, except that the PVA content in the film-forming solution and the heat treatment temperature were adjusted so that the average thickness of the PVA film was 30 μm and the swelling degree was 200%. In addition, using the obtained PVA films, polarized films were produced and evaluated in the same manner as in Example 1, except that the temperature of the uniaxial stretching treatment bath and the iodine concentration of the dyeing treatment bath were changed so that the shrinkage force of the obtained polarized film was about 15 N and the single-piece transmittance was 44.0%. The evaluation results are shown in Table 1.

As shown in Table 1, Comparative Example 1 using unmodified PVA-4 with a degree of polymerization of 2400 has a small complex viscosity ratio Rt of 3.1, and the viscosity at 30 ° C. is particularly low. In Comparative Example 1, the crosslinking between PVAs is insufficient due to such a low viscosity, and a polarizing film with a high dichroic ratio is not obtained. On the other hand, Comparative Example 2 using unmodified PVA-5 with a degree of polymerization of 4000 has a small complex viscosity ratio Rt of 4.1, and the viscosity at 80 ° C. is relatively high. Therefore, although a polarizing film with a high dichroic ratio is obtained in Comparative Example 2, the viscosity of the film-forming solution is high, and the productivity (film-forming ability) is low. In contrast to these, Examples 1 to 3 all have a complex viscosity ratio Rt of 4.5 or more, and the viscosity of the aqueous solution at 30 ° C. is relatively high and the viscosity of the aqueous solution at 80 ° C. is relatively low. Therefore, it can be said that the PVA films (films for producing optical films) of Examples 1 to 3 can improve the optical performance of the optical film while maintaining good film-forming properties (productivity).

Claims (7)

A film for producing an optical film, comprising polyvinyl alcohol,
In a dynamic viscosity measurement of an aqueous solution in which the film for producing an optical film was dissolved so that the concentration of the polyvinyl alcohol was 12% by mass,
The ratio Rt( ^{η* 1} ₍ 30)/η ^* ₁ (80)) of the complex viscosity η ^* ₁ (30) to the complex viscosity η _*1 (80) is 4.5 or more and 50 or less,
The film for producing an optical film, wherein the polyvinyl alcohol has a degree of saponification of 99.0 mol % or more .
[The complex viscosity η ^* ₁ (30) is a complex viscosity at an angular frequency of 1 rad/sec obtained from dynamic viscoelasticity measurement of the aqueous solution at 30° C. The complex viscosity η ^* ₁ (80) is a complex viscosity at an angular frequency of 1 rad/sec obtained from dynamic viscoelasticity measurement of the aqueous solution at 80° C.] 2. The film for producing an optical ^film according to claim 1, wherein a ratio _Rω (30) (η ^* ₁ (30)/η ^* 500(30)) of the complex viscosity η* ₁ (30) to the _complex viscosity ^η * ₅₀₀ (30) is 5 or more and 150 or less.
[The complex viscosity η ^* ₅₀₀ (30) is the complex viscosity at an angular frequency of 500 rad/sec obtained by dynamic viscoelasticity measurement of the aqueous solution at 30° C.] The film for optical film production according to claim 1 or 2, wherein the polyvinyl alcohol comprises a modified polyvinyl alcohol having a silicon-containing group. The film for optical film production according to claim 3, wherein the content of the silicon-containing group relative to all structural units in the modified polyvinyl alcohol is 0.01 mol % or more and 2 mol % or less. The film for producing an optical film according to any one of claims 1 to 4, wherein the optical film is a polarizing film. A method for producing an optical film, comprising a step of uniaxially stretching a film for producing an optical film according to any one of claims 1 to 5. The method for producing an optical film according to claim 6, wherein the optical film is a polarizing film.

Images