Film for optical film production and method for producing optical film

Abstract

This invention provides an optical film for manufacturing optical films with good productivity and excellent optical performance, as well as a method for manufacturing optical films using this optical film. The invention relates to an optical film for manufacturing optical films, specifically an optical film containing polyvinyl alcohol. In a dynamic viscosity measurement of an aqueous solution in which the aforementioned optical film for manufacturing optical films is dissolved at a polyvinyl alcohol concentration of 12% by mass, the complex viscosity η... * 1(30) and complex viscosity η * The ratio of 1(80) to Rt(η) * 1(30) / η * 1(80)) is 4.5 or higher and 50 or lower. [Complex viscosity η] * 1(30) is the complex viscosity of the aforementioned aqueous solution at 30°C with an angular frequency of 1 rad / s, obtained from dynamic viscoelasticity measurements. The complex viscosity η * 1(80) is the complex viscosity of the aforementioned aqueous solution at 80°C with an angular frequency of 1 rad / s, obtained by dynamic viscoelasticity determination.

Description

Technical Field

[0001] This invention relates to a film for manufacturing optical films and a method for manufacturing optical films. Background Technology

[0002] Polarizing plates, which have both light-transmitting and light-blocking functions, and liquid crystals, which change the polarization state of light, are both fundamental components of liquid crystal displays (LCDs). Many polarizing plates have a structure in which a protective film, such as a triacetate cellulose (TAC) film, is laminated onto the surface of the polarizing film. As the polarizing film, an iodine-based pigment (I3) is adsorbed onto a substrate (stretched film) formed by uniaxially stretching a polyvinyl alcohol film (hereinafter sometimes abbreviated as "PVA"). - I5 - Polarizing films obtained from dichroic pigments such as dichroic organic dyes have become the mainstream.

[0003] LCDs are widely used in a wide range of applications, including small instruments such as calculators and watches, smartphones, laptops, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and indoor and outdoor measuring equipment. In recent years, there has been a growing demand for improved display quality in these devices. Consequently, there is a growing need for high-performance polarizing films, specifically polarizing films with excellent optical properties such as polarization degree and transmittance.

[0004] As a polarizing film that improves optical properties, a known polarizing film is one obtained using PVA with a high degree of polymerization (Patent Document 1). In Patent Document 1, a PVA film-forming solution obtained by dissolving highly polymerized PVA in a solvent with dimethyl sulfoxide as the main component is used to form a film.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 1-105204 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] In the industrial manufacturing of PVA films, considering environmental and economic factors, PVA aqueous solutions using water as a solvent are typically used as the film-forming solution. However, as shown in Patent Document 1, PVA with a high degree of polymerization exhibits poor film-forming properties due to the increased viscosity of its aqueous solution, making it less desirable for industrial production. Therefore, a method is desired that improves the optical performance of optical films while preventing productivity degradation.

[0010] The present invention is made based on the above-described circumstances, and its object is to provide an optical film for manufacturing optical films with good productivity and excellent optical performance, and a method for manufacturing optical films using such an optical film for manufacturing optical films.

[0011] means for solving problems

[0012] The aforementioned objective is achieved by providing any of the following technical solutions.

[0013] [1] An optical film manufacturing membrane, which is an optical film manufacturing membrane containing PVA, wherein the complex viscosity η is determined in a dynamic viscosity measurement of an aqueous solution in which the aforementioned optical film manufacturing membrane is dissolved at a concentration of 12% by mass of the aforementioned PVA. * 1(30) and complex viscosity η * The ratio of 1(80) to Rt(η) * 1(30) / η * 1(80)) is 4.5 or higher and 50 or lower;

[0014] [The aforementioned complex viscosity η] * 1(30) is the complex viscosity of the aforementioned aqueous solution at 30°C with an angular frequency of 1 rad / s, obtained from dynamic viscoelasticity measurements. The aforementioned complex viscosity η * 1(80) is the complex viscosity of the aforementioned aqueous solution at 80°C, obtained from dynamic viscoelasticity measurements at an angular frequency of 1 rad / s.

[0015] [2] The film for manufacturing optical films according to [1], wherein the aforementioned complex viscosity η * 1(30) and complex viscosity η * 500 (30) ratio R ω (30)(η * 1(30) / η * 500 (30) is 5 or more and 150 or less;

[0016] [The aforementioned complex viscosity η] * 500 (30) is the complex viscosity of the aforementioned aqueous solution at 30°C, obtained from dynamic viscoelasticity measurements at an angular frequency of 500 rad / s.

[0017] [3] A film for manufacturing an optical film according to [1] or [2], wherein the aforementioned PVA comprises a modified PVA having silicon-containing groups;

[0018] [4] The film for manufacturing optical films according to [3], wherein the content of the aforementioned silicon-containing groups in the aforementioned modified PVA relative to all structural units is 0.01 mol% or more and 2 mol% or less;

[0019] [5] A film for manufacturing an optical film according to any one of [1] to [4], wherein the aforementioned optical film is a polarizing film;

[0020] [6] A method for manufacturing an optical film, comprising a step of uniaxially stretching the optical film manufacturing film of any one of [1] to [5];

[0021] [7] The method for manufacturing an optical film according to [6], wherein the aforementioned optical film is a polarizing film.

[0022] Invention Effects

[0023] According to the present invention, an optical film manufacturing film with good productivity and capable of producing optical films with excellent optical properties, and a method for manufacturing an optical film using such an optical film manufacturing film are provided. Attached Figure Description

[0024] Figure 1 The flow curve of the complex viscosity obtained by dynamic viscoelasticity measurement is obtained by dissolving the optical film (PVA film) of Example 1 at a concentration of 12% by mass to obtain a PVA aqueous solution at 30°C. Detailed Implementation

[0025] <Membranes for Optical Film Manufacturing>

[0026] The optical film manufacturing membrane of the present invention is an optical film manufacturing membrane containing PVA. In the dynamic viscosity measurement of an aqueous solution in which the aforementioned optical film manufacturing membrane is dissolved at a PVA concentration of 12% by mass, the complex viscosity η... * 1(30) and complex viscosity η * The ratio of 1(80) to Rt(η) * 1(30) / η * 1(80)) is 4.5 or higher and 50 or lower.

[0027] Complex viscosity η * 1(30) is the complex viscosity of the aforementioned aqueous solution at 30°C with an angular frequency of 1 rad / s, obtained from dynamic viscoelasticity measurements. Complex viscosity η * 1(80) is the complex viscosity of the aforementioned aqueous solution at 80°C with an angular frequency of 1 rad / s, obtained from dynamic viscoelasticity measurements. That is, the complex viscosity η * 1(30) is the complex viscosity at an angular frequency of 1 rad / s, obtained by dynamic viscoelasticity determination, of an aqueous solution at 30°C containing the optical film manufacturing film dissolved in PVA at a concentration of 12% by mass. Complex viscosity η *1(80) is the complex viscosity at an angular frequency of 1 rad / s obtained by dynamic viscoelasticity determination of an aqueous solution of the film for manufacturing optical film at 80°C in which the concentration of PVA is 12% by mass.

[0028] (Dynamic viscoelasticity measurement)

[0029] Dynamic viscoelasticity determination refers to the method of applying strain or stress to a sample that changes over time (vibration) and measuring the resulting stress or strain to determine the mechanical properties of the sample. Dynamic viscoelasticity can be measured using a dynamic viscoelasticity measuring device (rheometer).

[0030] In this invention, the dynamic viscoelasticity is measured using the "ARES-G2" instrument manufactured by TA Instruments, and the values ​​are obtained under the following conditions.

[0031] Geometry: Conical plates and disk-shaped plates with a cone angle of 0.02 rad.

[0032] Plate diameter: 40mm

[0033] Strain: 1%

[0034] Angular frequency range: 1~500 rad / s

[0035] Temperature measurement (temperature of aqueous solution): 30℃ or 80℃

[0036] In this invention, the dynamic viscoelasticity determination is performed using a PVA aqueous solution obtained by dissolving an optical film manufacturing membrane at a PVA concentration of 12% by mass. This PVA aqueous solution is prepared by weighing the optical film manufacturing membrane and distilled water into a container, then heating and dissolving it at 95°C for 4 hours while stirring. If the optical film manufacturing membrane contains substances other than PVA, the PVA content is determined before dissolution. For example, if the optical film manufacturing membrane contains water, plasticizers, or other water-soluble substances, these substances are dissolved by swelling the membrane with water and washing it. Then, the membrane is dried in a dryer at 105°C for at least 17 hours and weighed to determine the PVA content. In cases where the optical film manufacturing membrane contains substances other than PVA, the aqueous solution for the dynamic viscoelasticity determination is also prepared by dissolving the optical film manufacturing membrane containing substances other than PVA in water. In addition, when performing dynamic viscoelasticity measurements, the aqueous solution of PVA with a concentration of 12% by mass was set to 30°C or 80°C.

[0037] (Complex viscosity)

[0038] In the optical film manufacturing film of the present invention, the complex viscosity η * 1(30) and complex viscosity η * The ratio of 1(80) to Rt(η) * 1(30) / η * 1(80)) must be above 4.5 and below 50. When Rt is less than 4.5, the complex viscosity η * 1(30) Too low or complex viscosity η * 1(80) is too high. Complex viscosity η * A viscosity 1(30) that is too low means that the interaction achieved by the crosslinking of PVA in the film used for manufacturing the optical film is insufficient. Even if the film is stretched, sufficient orientation will not occur, and an optical film with excellent optical properties cannot be obtained. On the other hand, at complex viscosity η * If the viscosity η is too high (1(80)), it means that even if the film-forming solution for the optical film is set to a high temperature, the viscosity will not decrease sufficiently, and good productivity cannot be achieved. From this point of view, the preferred viscosity is: complex viscosity η * 1(30) is 15 Pa·s or higher, and the aforementioned complex viscosity η * 1(80) is 15 Pa·s or less. Furthermore, films for optical film manufacturing with an Rt exceeding 50 are difficult to manufacture. In this way, by setting Rt to the aforementioned range, it is possible to obtain optical films with excellent optical performance while maintaining good productivity. Rt is preferably 5 or more, more preferably 7 or more. On the other hand, the upper limit of Rt is preferably 40.

[0039] In the optical film manufacturing film of the present invention, the complex viscosity η * The lower limit of 1(30) is preferably 15 Pa·s, more preferably 30 Pa·s. At complex viscosity η * When 1(30) is above the aforementioned lower limit, the interactions achieved by the cross-linking of PVA in the film used for manufacturing the optical film are particularly sufficient. Therefore, by stretching, particularly sufficient orientation occurs, and the optical properties of the resulting optical film can be further improved. Complex viscosity η * The upper limit of 1(30) is preferably 500 Pa·s, more preferably 400 Pa·s. In complex viscosity η * When 1(30) is below the aforementioned upper limit, even when the temperature of the film-forming solution for the optical film manufacturing is low (30°C), the viscosity increase can be suppressed, and better productivity can be achieved.

[0040] In the optical film manufacturing film of the present invention, the complex viscosity η * 1(80) is preferably 3 Pa·s or more and 15 Pa·s or less. Complex viscosity η *The upper limit of 1(80) is sometimes more preferably 12 Pa·s, and even more preferably 10 Pa·s or 5 Pa·s. In complex viscosity η * When 1(80) is below the aforementioned upper limit, the viscosity increase in the film-forming solution for optical film manufacturing, especially when the temperature of the film-forming solution is high (80°C), is further suppressed, resulting in better productivity.

[0041] In the optical film manufacturing film of the present invention, the complex viscosity η * 1(30) and complex viscosity η * 500 (30) ratio R ω (30)(η * 1(30) / η * 500 The lower limit of (30) can be, for example, 3, preferably 5, and more preferably 10. In R ω (30) When the viscosity is above the aforementioned lower limit, the viscosity of the film-forming solution in the film-forming solution for optical film manufacturing is significantly reduced relative to the shear rate, thus achieving better productivity. On the other hand, the aforementioned R... ω The upper limit of (30) is preferably 150, more preferably 100.

[0042] In the optical film manufacturing film of the present invention, the complex viscosity η * 500 (30) Preferably, it is 1 Pa·s or more and 12 Pa·s or less. Complex viscosity η * 500 (30) The upper limit is more preferably 10 Pa·s, further preferably 5 Pa·s, and particularly preferably 4.5 Pa·s. At complex viscosity η * 500 (30) When the viscosity of the film-forming solution for the film used in optical film manufacturing is low at the shear rate, the viscosity of the film-forming solution is sufficiently low, thus enabling better productivity.

[0043] Here, the complex viscosity η * 500 (30) is the complex viscosity of the aforementioned aqueous solution at 30°C with an angular frequency of 500 rad / s, obtained from dynamic viscoelasticity measurements. That is, the complex viscosity η * 500 (30) is the complex viscosity at an angular frequency of 500 rad / s, obtained by dynamic viscoelasticity determination, in an aqueous solution of the film for manufacturing optical film at 30°C in which the concentration of PVA is 12% by mass.

[0044] (PVA)

[0045] In the optical film manufacturing membrane of the present invention, PVA is typically the main component. The main component refers to the component with the highest content based on mass. The lower limit for the PVA content in the optical film manufacturing membrane of the present invention is preferably 60% by mass, more preferably 80% by mass, and even more preferably 85% by mass. By setting the PVA content to the aforementioned lower limit or above, the effects of the present invention can be further improved. On the other hand, the upper limit of this content is not particularly limited and can be 100% by mass, preferably 99% by mass, and even more preferably 95% by mass. PVA may be only one type or may include two or more types. It should be noted that the content (by mass%) of each component in the optical film manufacturing membrane is based on the total content of all components except water in a dry state.

[0046] PVA is a polymer having a vinyl alcohol unit (-CH2-CH(OH)-) as a structural unit. In addition to vinyl alcohol units, PVA may also have vinyl ester units and other further structural units.

[0047] The lower limit of the viscosity-uniform polymerization degree of PVA is preferably 1,000, more preferably 1,500, further preferably 2,000, and particularly preferably 2,200. By setting the viscosity-uniform polymerization degree of PVA to the aforementioned lower limit or above, the stretch processability of the film for manufacturing optical films of the present invention becomes excellent, and optical films with superior optical properties can be manufactured. On the other hand, the upper limit of the aforementioned viscosity-uniform polymerization degree is preferably 5,000, more preferably 4,000, further preferably 3,000, and particularly preferably 2,700. By setting the viscosity-uniform polymerization degree of PVA to the aforementioned upper limit or below, good water solubility is achieved, and the increase in viscosity of the aqueous solution is suppressed. Therefore, by setting the viscosity-uniform polymerization degree of PVA to the aforementioned upper limit or below, film-forming properties are improved, and the productivity of the film for manufacturing optical films of the present invention can be improved.

[0048] The viscosity-average degree of polymerization refers to the average degree of polymerization measured according to JIS K6726-1994. That is, in this specification, the viscosity-average degree of polymerization is determined as follows: after resaponification and purification of the residual vinyl groups of PVA, the measurement is performed in water at 30°C, and the intrinsic viscosity [η] (unit: deciliters / g) obtained therefrom is calculated using the following formula.

[0049] Viscosity-uniform degree of polymerization Po=([η]×10 4 / 8.29) (1 / 0.62)

[0050] The lower limit of the degree of saponification 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 making the degree of saponification above the aforementioned lower limit, an optical film with superior optical properties and resistance to damp heat can be obtained. On the other hand, the upper limit of the degree of saponification is not particularly limited, but from the viewpoint of PVA productivity, it is preferably 99.99 mol% or less.

[0051] The degree of saponification of PVA refers to the ratio (mol%) of the number of moles of vinyl alcohol units in PVA to the total number of moles of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units through saponification. The degree of saponification of PVA can be determined according to the description in JIS K6726-1994.

[0052] (Modified PVA)

[0053] The PVA preferably comprises modified PVA having silicon-containing groups (hereinafter, modified PVA having silicon-containing groups is sometimes referred to as "modified PVA"). By including the aforementioned modified PVA, the dynamic viscoelastic parameters described in this invention are easily satisfied.

[0054] Modified PVA is a polymer with vinyl alcohol units (-CH2-CH(OH)-) as structural units and silicon-containing groups. Modified PVA may contain structural units containing silicon-containing groups, and may further contain vinyl ester units such as vinyl acetate units, or other structural units.

[0055] The silicon-containing groups in the modified PVA are not particularly limited as long as they contain silicon atoms, but are preferably silanol groups or groups that can be converted into silanol groups in the presence of water. A silanol group refers to a group having a silicon atom and at least one hydroxyl group bonded to that silicon atom. The number of hydroxyl groups in the silanol group is usually any one to three, preferably three. The hydroxyl groups in the silanol group can exist in the form of salts (e.g., -ONa, -OK, etc.).

[0056] A group capable of being converted to a silanol group in the presence of water refers to a group that can be converted to a silanol group when PVA is heated in water for 2 hours at a temperature of 150°C. This conversion to a silanol group can occur through hydrolysis. Examples of groups capable of being converted to a silanol group in the presence of water include groups with at least one alkoxy or acyloxy bonded to a silicon atom, specifically trimethoxysilyl, triethoxysilyl, triisopropoxysilyl, dimethoxymethylsilyl, diethoxymethylsilyl, methoxydimethylsilyl, ethoxydimethylsilyl, and triacetoxysilyl.

[0057] As a silanol group or a group that can be converted into a silanol group in the presence of water, groups represented by any of the following formulas (1) to (3) can be listed. Among these, the group represented by the following formula (1) is preferred.

[0058] [Chemistry 1]

[0059]

[0060] In equations (1) to (3), R 1 Each 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. R 2 Each is an independent hydrocarbon group consisting of 1 to 20 substituted or unsubstituted carbon atoms.

[0061] As R 1 and R 2 The hydrocarbon groups with 1 to 20 carbon atoms shown can include aliphatic hydrocarbon groups, alicyclic hydrocarbon groups (cyclohexyl, etc.), aromatic hydrocarbon groups (phenyl, etc.), etc., with aliphatic hydrocarbon groups being preferred. Examples of aliphatic hydrocarbon groups include alkyl groups such as methyl, ethyl, and propyl; alkenyl groups such as vinyl; and alkynyl groups such as ethynyl, etc., with alkyl groups being preferred. As R 1 and R 2 The number of carbon atoms in the hydrocarbon group shown is preferably 1 to 6, more preferably 1 to 3. R 1 and R 2 At least some of the hydrogen atoms in the hydrocarbon group shown may be optionally replaced by halogen atoms, carboxyl groups, alkoxy groups (methoxy, ethoxy, etc.).

[0062] As R 1 The acyl group with 1 to 20 carbon atoms shown can be a hydrogen atom or a group with a carbonyl (-CO-) bonded to a hydrocarbon group with 1 to 19 carbon atoms. As a hydrocarbon group with 1 to 19 carbon atoms, an aliphatic hydrocarbon group is preferred, and an alkyl group is more preferred. Specifically, as an acyl group, formyl, acetyl, propionyl, benzoyl, etc., can be listed. As R 1 The number of carbon atoms in the acyl group shown is preferably 1 to 6, more preferably 1 to 3. R 1 At least some of the hydrogen atoms in the acyl group shown may be optionally replaced by halogen atoms, carboxyl groups, alkoxy groups (methoxy groups, etc.).

[0063] In any of the groups represented by formulas (1) to (3) above, at least one R 1 When the atom is hydrogen, the group is a silanol group. Furthermore, in any of the groups represented by formulas (1) to (3) above, all R... 1When neither of the atoms is hydrogen, this group is capable of being converted into a silanol group in the presence of water. As R 1 Preferably, it is a hydrogen atom or a hydrocarbon group with 1 to 20 substituted or unsubstituted carbon atoms.

[0064] From the viewpoint of the optical properties of the resulting optical film, it is preferable that the silicon-containing groups are directly bonded to the carbon atoms in the polymer backbone via silicon-carbon bonds.

[0065] The lower limit for the content of silicon-containing groups in modified PVA relative to all structural units is preferably 0.01 mol%, more preferably 0.05 mol%, even more preferably 0.1 mol%, and still more preferably 0.2 mol%. By setting the content of silicon-containing groups to the aforementioned lower limit or above, the aforementioned complex viscosity η is achieved. * 1(30) By sufficiently increasing the content of silicon-containing groups in the modified PVA, the optical properties can be further improved. On the other hand, the upper limit of the content of silicon-containing groups in the modified PVA relative to all structural units is preferably 2.0 mol%, preferably 0.8 mol%, and more preferably 0.6 mol%. By setting the content of silicon-containing groups below the aforementioned upper limit, the water solubility of the modified PVA is improved, thereby improving productivity (film-forming properties).

[0066] In modified PVA, the content (mol%) of silicon groups is determined, for example, by proton NMR of the vinyl ester polymer before saponification. Here, when determining 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, it is dried under reduced pressure at 90°C for 2 days, dissolved in CDCl3 solvent, and used for analysis.

[0067] The suitable range for the viscosity-uniform degree of polymerization of modified PVA is the same as the suitable range for the viscosity-uniform degree of polymerization of the aforementioned PVA. Furthermore, the suitable range for the degree of saponification of modified PVA is the same as the suitable range for the degree of saponification of the aforementioned PVA.

[0068] The lower limit of the product of the viscosity-uniform polymerization degree of 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%. By making the aforementioned product above the aforementioned lower limit, the optical properties of the obtained optical film are superior. On the other hand, the upper limit of the aforementioned product is preferably 2,000 mol%, more preferably 1,500, and even more preferably 1,200. By making the aforementioned product below the aforementioned upper limit, the water solubility of the modified PVA can be further improved, and the productivity of the film for manufacturing the optical film can be further improved.

[0069] The modified PVA preferably contains structural units having silicon-containing groups. As structural units having silicon-containing groups, the structural unit shown in the following formula (4) can be listed.

[0070] [Chemistry 2]

[0071]

[0072] In equation (4), R 3 It can be a hydrogen atom or a methyl group. R 4 It is a single bond or a divalent linker. R 5 It contains silicon groups.

[0073] As R 3 Preferably, it contains hydrogen atoms.

[0074] As R 4 The divalent linking groups shown include -(CH2). n -(n is an integer from 1 to 5) or -CONR 6 -R 7 -(R 6 It is an alkyl group having 1 to 5 hydrogen atoms or carbon atoms. R 7 For the aforementioned -(CH2) n -The group shown is a group that contains at least one of oxygen and nitrogen atoms (or a divalent hydrocarbon group).

[0075] Examples of divalent hydrocarbon groups containing at least one of oxygen and nitrogen atoms include -CH2CH2NHCH2CH2CH2-, -CH2CH2NHCH2CH2-, -CH2CH2NHCH2-, -CH2CH2N(CH3)CH2CH2-, -CH2CH2N(CH3)CH2-, -CH2CH2OCH2CH2CH2-, -CH2CH2OCH2CH2-, and -CH2CH2OCH2-. The number of carbon atoms in a divalent hydrocarbon group containing at least one of oxygen and nitrogen atoms can be, for example, 2 or more and 6 or less.

[0076] R 4 Single bonds are preferred.

[0077] As R 5 Specific examples of silicon-containing groups shown are, as described above, groups represented by any of the aforementioned formulas (1) to (3), preferably groups represented by the aforementioned formula (1).

[0078] The number of silicon-containing groups in the structural unit containing silicon groups is not particularly limited and can be 1. The content range of silicon-containing structural units in modified PVA relative to all structural units can be the same as the content range of silicon-containing groups relative to all structural units. Furthermore, the product of the viscosity-average degree of polymerization of modified PVA and the content of silicon-containing structural units can be the same as the product of the viscosity-average degree of polymerization and the content of silicon-containing groups.

[0079] Modified PVA may have structural units other than vinyl alcohol units, vinyl ester units, and structural units with silicon-containing groups. The content of these other structural units relative to the total structural units is sometimes preferably 15 mol% or less, more preferably 5 mol% or less, further preferably 1 mol% or less, and even more preferably 0.1 mol% or less. By substantially consisting of vinyl alcohol units, vinyl ester units, and structural units with silicon-containing groups, the effects of the present invention are sometimes more fully realized.

[0080] The film used for manufacturing this optical film can contain only one type of modified PVA, or it can contain two or more types of modified PVA with different degrees of polymerization, saponification, and silicon group content.

[0081] The lower limit of the modified PVA content in the film used for manufacturing the optical film is not particularly limited, but it is preferably 60% by mass, more preferably 80% by mass, and even more preferably 85% by mass. By setting the modified PVA content to the aforementioned lower limit or above, the effect of the present invention can be further improved. On the other hand, the upper limit of this content is not particularly limited, and it can be 100% by mass, preferably 99% by mass, and more preferably 95% by mass.

[0082] Furthermore, the content of modified PVA in the film for manufacturing the optical film of the present invention, relative to the total PVA, is preferably 60% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and even more preferably 99% by mass or more. In the film for manufacturing the optical film of the present invention, by primarily using modified PVA as the PVA, the effects of the present invention can be more fully realized. There is no particular upper limit to this content, and it can be 100% by mass.

[0083] (Manufacturing method of modified PVA)

[0084] There are no particular limitations on the method for manufacturing modified PVA with silicon-containing groups. It can be manufactured, for example, by copolymerizing a vinyl ester monomer with a monomer having silicon-containing groups and then saponifying the resulting vinyl ester polymer.

[0085] Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl neopentanoate, and vinyl tert-carbonate. Among these, vinyl acetate is preferred.

[0086] Examples of monomers containing silicon groups include vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, allyltrimethoxysilane, allylmethyldimethoxysilane, allyldimethylmethoxysilane, allyltriethoxysilane, allylmethyldiethoxysilane, allyldimethylethoxysilane, vinyltri(β-methoxyethoxy)silane, vinylisobutyldimethoxysilane, vinylethyldimethoxysilane, vinylmethoxydibutoxysilane, and vinyldimethoxysilane. Vinyl butoxysilane, vinyl tributoxysilane, vinyl methoxy dihexyloxysilane, vinyl dimethoxy hexyloxysilane, vinyl trihexyloxysilane, vinyl methoxy dioctyloxysilane, vinyl dimethoxy octyloxysilane, vinyl trioctyloxysilane, vinyl methoxy dilauryloxysilane, vinyl dimethoxy lauryloxysilane, vinyl dimethoxy dioleoxysilane, vinyl dimethoxy oleoxysilane, 3-(methyl)acrylamide-propyltrimethoxysilane, 3-(methyl)acrylamide-propyltriethoxysilane, 3-(methyl)acrylamide-propyltri(β-methoxyethoxy)silane, 2-( (Methyl)acrylamide-ethyltrimethoxysilane, 1-(methyl)acrylamide-methyltrimethoxysilane, 2-(methyl)acrylamide-2-methylpropyltrimethoxysilane, 2-(methyl)acrylamide-isopropyltrimethoxysilane, N-(2-(methyl)acrylamide-ethyl)-aminopropyltrimethoxysilane, (3-(methyl)acrylamide-propyl)-oxypropyltrimethoxysilane, 3-(methyl)acrylamide-propyltriacetoxysilane, 2-(methyl)acrylamide-ethyltriacetoxysilane, 4-(methyl)acrylamide-butyltriacetoxysilane, 3-(methyl)acrylamide-propyl Examples of silanes include tripropionyloxysilane, 2-(methyl)acrylamide-2-methylpropyltriacetoxysilane, N-(2-(methyl)acrylamide-ethyl)-aminopropyltriacetoxysilane, 3-(methyl)acrylamide-propylisobutyldimethoxysilane, 2-(methyl)acrylamide-ethyldimethylmethoxysilane, 3-(methyl)acrylamide-propylmethyldiacetoxysilane, 2-(methyl)acrylamide-2-methylpropylhydrogen-containing dimethoxysilane, 3-(N-methyl-(methyl)acrylamide)-propyltrimethoxysilane, and 2-(N-ethyl-(methyl)acrylamide)-ethyltriacetoxysilane.

[0087] There are no particular limitations on the method for copolymerizing vinyl ester monomers with monomers containing silicon groups, and known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be cited. Among these methods, bulk polymerization carried out under solvent-free conditions and solution polymerization using solvents such as alcohols are preferred. Examples of solvents used in 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.

[0088] As initiators used in copolymerization reactions, existing well-known azo initiators, peroxide initiators, and redox initiators can be appropriately selected. Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylpentanonitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylpentanonitrile). Examples of peroxide initiators include percarbonate compounds such as di-n-propyl peroxide, diisopropyl peroxide, di(2-ethylhexyl) peroxide, and di(ethoxyethyl) peroxide; perester compounds such as tert-butyl peroxyneodecanate, α-isopropylphenyl peroxyneodecanate, and tert-butyl peroxyneodecanate; acetylcyclohexylsulfonyl peroxide and diisobutyryl peroxide; and phenoxyacetic acid 2,4,4-trimethylpentyl-2-peroxy ester. Furthermore, the aforementioned peroxide-based initiators can be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, etc., to form initiators. As redox initiators, examples include initiators obtained by combining the aforementioned peroxides with reducing agents such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, and sodium silicate.

[0089] There is no particular limitation on the polymerization temperature during the copolymerization reaction, but it is preferably above 0°C and below 180°C, more preferably above 20°C and below 160°C, and even more preferably above 30°C and below 150°C.

[0090] When copolymerizing vinyl ester monomers with monomers containing silicon groups, copolymerization can be performed with other copolymerizable monomers as needed, provided it does not impair the effects of the present invention. Examples of such other monomers include, for instance, ethylene; olefins with 2 to 30 carbon atoms such as propylene, 1-butene, and isobutene; acrylic acid or its salts; acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or its salts; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamide propanesulfonic acid or its salts, acrylamide propyl dimethylamine or its salts, N... Acrylamide derivatives such as hydroxymethylacrylamide or its derivatives; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamide propanesulfonic acid or its salts, methacrylamide propyl dimethylamine or its salts, N-hydroxymethylmethacrylamide or its derivatives; N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone or other N-vinylamides; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether or other vinyl ethers; cyanoethylene such as acrylonitrile and methacrylonitrile; halogenated vinyl ethers such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride or other halogenated vinyl ethers; allyl acetate, allyl chloride or other allyl compounds; maleic acid or its salts, esters or anhydrides; itaconic acid or its salts, esters or anhydrides; isopropyl acetate, etc. Vinyl ester polymers may have structural units derived from one or more of the other monomers mentioned above.

[0091] The proportion of structural units derived from the other monomers mentioned above (monomers other than vinyl ester monomers and monomers having silicon-containing groups) in the vinyl ester polymer is not limited as long as it does not impair the effect of the present invention. Depending on the total number of moles of all structural units constituting the vinyl ester polymer, it is sometimes preferred to be 15 mol% or less, more preferably 5 mol% or less, further preferably 1 mol% or less, and even more preferably 0.1 mol% or less.

[0092] The vinyl ester polymer is then saponified in a solvent according to a known method and directed towards modified PVA. An alcohol is preferably used as the solvent in the saponification reaction. Examples of alcohols include lower alcohols such as methanol and ethanol, with methanol being particularly suitable. In addition to alcohols, the solvent used in the saponification reaction may further contain esters such as acetone, methyl acetate, and ethyl acetate, or organic solvents such as toluene. Examples of catalysts used in the saponification reaction include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; alkaline catalysts such as sodium methoxide; and acid catalysts such as inorganic acids. The temperature of the saponification reaction can be set, for example, above 20°C and below 60°C. When a gel-like product gradually precipitates as the saponification reaction proceeds, the product is pulverized and washed at this point, and then dried to obtain modified PVA.

[0093] Furthermore, as modified PVA containing silicon groups, it can be a modified PVA obtained by introducing silicon groups into unmodified PVA or the like using a silylating agent; or a modified PVA obtained by introducing structural units containing silicon groups through graft copolymerization. Examples of the aforementioned silylating agents include reactive silane compounds such as triethoxychlorosilane and methyltrichlorosilane, which can react with the hydroxyl groups of PVA. Additionally, as PVA other than modified PVA containing silicon groups, the film for manufacturing the optical film of the present invention can also be easily obtained by using PVA that has been cross-linked using a cross-linking agent or the like.

[0094] (Plasticizer)

[0095] The optical film for manufacturing the present invention preferably contains a plasticizer. By including a plasticizer in the optical film for manufacturing, tensile properties and the like can be improved. Polyols are preferably used as plasticizers. Examples of polyols include ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Among these, glycerol is preferred from the viewpoint of improving tensile properties. One or more plasticizers can be used.

[0096] The lower limit for the content of the plasticizer in the film for manufacturing the optical film of the present invention is preferably 1 part by weight, more preferably 3 parts by weight, and even more preferably 5 parts by weight, relative to 100 parts by weight of PVA. By making the content of the plasticizer at or above the aforementioned lower limit, the tensile strength of the film is improved, and the optical performance of the resulting optical film can be further improved. On the other hand, the upper limit for the content of the plasticizer is preferably 20 parts by weight, more preferably 17 parts by weight, and even more preferably 15 parts by weight, relative to 100 parts by weight of PVA. By making the content of the plasticizer below or below the aforementioned upper limit, it is possible to prevent the film from becoming too soft, which would lead to a decrease in processability.

[0097] (surfactant)

[0098] The film for manufacturing optical films preferably contains a surfactant. By using a film-forming solution containing a surfactant, film-forming properties are improved, uneven film thickness is suppressed, and the film is easily peeled off from the metal rollers or belts used for film formation. When manufacturing a film for optical film production from a film-forming solution containing a surfactant, the resulting film may contain the surfactant.

[0099] There is no particular limitation on the type of surfactant, but from the viewpoint of peelability that can be peeled off from metal rollers and belts, anionic surfactants and nonionic surfactants are preferred.

[0100] Examples of anionic surfactants include carboxylic acid types such as potassium lauryl ether sulfate; sulfate types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzene sulfonate.

[0101] As nonionic surfactants, examples include alkyl ethers such as polyoxyethylene oleyl ether; alkyl phenyl ethers such as polyoxyethylene octylphenyl ether; alkyl esters such as polyoxyethylene laurate; alkylamines such as polyoxyethylene lauryl amino ether; alkylamides such as polyoxyethylene laurylamide; polypropylene glycol ethers such as polyoxyethylene polyoxypropylene ether; alkanolamides such as lauric acid diethanolamide and oleic acid diethanolamide; and allyl phenyl ethers such as polyoxyalkylene allylphenyl ether.

[0102] Surfactants can be used alone or in combination of two or more.

[0103] When the film used for manufacturing this optical film contains a surfactant, the lower limit of its content relative to 100 parts by weight of PVA is preferably 0.01 parts by weight, more preferably 0.02 parts by weight, and even more preferably 0.05 parts by weight. By setting the surfactant content to the aforementioned lower limit or above, the film-forming properties and peelability are further improved. On the other hand, the upper limit of this content relative to 100 parts by weight of PVA is preferably 0.5 parts by weight, more preferably 0.3 parts by weight, and even more preferably 0.1 parts by weight. By setting the surfactant content to the aforementioned upper limit or below, it is possible to suppress the surfactant from seeping to the surface of the film and causing adhesion, thereby suppressing the reduction in processability.

[0104] (Other additives, etc.)

[0105] The optical film for manufacturing the present invention may further contain, as needed, appropriate additives such as fillers, processing stabilizers such as copper compounds, weather stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, other thermoplastic resins, lubricants, fragrances, defoamers, deodorizers, expanders, release agents, mold release agents, reinforcing agents, crosslinking agents, mildew inhibitors, preservatives, and crystallization rate delayers.

[0106] In the optical film manufacturing process of the present invention, the total content of PVA, plasticizer, and surfactant is sometimes preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and even more preferably 99% by mass or more. Because the optical film manufacturing process of the present invention is substantially composed of PVA, plasticizer, and surfactant, the effects of the present invention can be more fully realized.

[0107] Furthermore, the total content of modified PVA having silicon-containing groups, plasticizer, and surfactant in the optical film of the present invention is sometimes preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and even more preferably 99% by mass or more. The optical film of the present invention, by being substantially composed of modified PVA having silicon-containing groups, plasticizer, and surfactant, can more fully exert the effects of the present invention.

[0108] (shape / properties, etc.)

[0109] The optical film for manufacturing the present invention is a so-called raw material film used as a material for optical films. However, the optical film for manufacturing the present invention is not limited to being in roll form.

[0110] The average thickness of the film used in manufacturing the optical film of the present invention is not particularly limited, but a lower limit is preferably 1 μm, more preferably 5 μm, and even more preferably 10 μm. By making the average thickness above the aforementioned lower limit, breakage during uniaxial stretching processing in the manufacturing of the optical film can be suppressed. Furthermore, an upper limit for this average thickness is preferably 75 μm, more preferably 60 μm, even more preferably 45 μm, and even more preferably 35 μm. By making the average thickness below the aforementioned upper limit, uneven stretching during uniaxial stretching processing can be suppressed. It should be noted that "average thickness" refers to the average value of the thickness measured at any 5 points (hereinafter, the same applies to average thickness).

[0111] The optical film manufacturing film of the present invention can be a single-layer film consisting of a single PVA layer (a layer containing PVA) or a multilayer film containing a single PVA layer. When used for manufacturing polarizing films, a single-layer film is preferred. The lower limit of the average thickness of the PVA layer in the optical film manufacturing film of the present invention is preferably 1 μm, more preferably 5 μm, and even more preferably 10 μm. By making the average thickness above or above the aforementioned lower limit, breakage during uniaxial stretching processing in the manufacture of the optical film can be suppressed. 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 making the average thickness below or below the aforementioned upper limit, uneven stretching during uniaxial stretching processing can be suppressed.

[0112] The specific composition and suitable composition of the PVA layer in the film for manufacturing optical films can be found in the above description of the specific composition and suitable composition of the film itself for manufacturing optical films.

[0113] When the film for manufacturing the optical film of the present invention is a single-layer film, in order to ensure operability, the average thickness is preferably 20 μm or more, and more preferably 30 μm or more. On the other hand, when the film for manufacturing the optical film of the present invention is a multilayer film, the average thickness of the PVA layer can be set to 20 μm or less, or it can be set to 15 μm or less.

[0114] A multilayer film refers to a film having two or more layers. The number of layers in a multilayer film can be five or fewer, or three or fewer. Examples of multilayer films include those for manufacturing optical films with a laminated structure of a substrate resin layer and a PVA layer. The average thickness of the substrate resin layer is, for example, 20 μm or more and 500 μm or less. Preferably, the substrate resin layer in the multilayer film can be uniaxially stretched together with the PVA layer. Polyesters, polyolefins, etc., can be used as the resin constituting the substrate resin layer. Among these, amorphous polyester resins are preferred, such as polyethylene terephthalate (PET) and amorphous polyester resins obtained by copolymerizing PET with isophthalic acid, 1,4-cyclohexanediol, etc. An adhesive layer can be provided between the substrate resin layer and the PVA layer.

[0115] The width of the film used for manufacturing optical films according to the present invention is not particularly limited and can be determined according to its application, etc. For example, the lower limit of the width of the film used for manufacturing optical films is preferably 3m. In recent years, from the viewpoint that LCD TVs and LCD monitors are gradually becoming larger, if the width of the film used for manufacturing optical films is set to 3m or more in advance, it is suitable for use as a final product. On the other hand, the upper limit of the width of the film used for manufacturing optical films is preferably 7m. By setting the width to 7m or less, when manufacturing optical films using already practical devices, uniaxial stretching and the like can be performed effectively.

[0116] From the viewpoints of optical film productivity and optical performance, the degree of swelling of the film for manufacturing the optical film of the present invention is preferably in the range of 140% or more and 400% or less. The lower limit of this degree of swelling is more preferably 180%, and even more preferably 190%. Furthermore, the upper limit of the degree of swelling is more preferably 220%, and even more preferably 210%. The degree of swelling of the film can be adjusted to a smaller value, for example, by strengthening the heat treatment conditions.

[0117] Here, "the degree of swelling of the membrane" refers to the value obtained using the following formula.

[0118] Swelling degree (%) = 100 × N / M

[0119] In the formula, N represents the mass (g) of the sample after immersing it in distilled water at 30°C for 30 minutes and removing the surface water. M represents the mass (g) of the sample after drying it in a desiccator at 105°C for 16 hours.

[0120] The optical film for manufacturing the present invention is typically a substantially unstretched film (unstretched film, non-stretched film). The in-plane phase difference of this optical film for manufacturing is preferably 100 nm or less, more preferably 50 nm or less. Generally, the optical film can be obtained by stretching the optical film for manufacturing the present invention (uniaxial stretching or biaxial stretching).

[0121] The optical film for manufacturing according to the present invention has good productivity and can produce optical films with excellent optical properties. It should be noted that optical properties include, for example, light transmittance and polarization. Examples of optical films that can be manufactured using this optical film for manufacturing include polarizing films, phase reversal films, field-angle improvement films, and brightness enhancement films; polarizing films are preferred.

[0122] <Method for manufacturing films for optical film manufacturing>

[0123] The manufacturing method of the optical film of the present invention is not particularly limited, but a manufacturing method that results in a more uniform film thickness and width after film formation is preferred. For example, a film-forming stock solution obtained by dissolving one or more of PVA, and, if necessary, plasticizers, surfactants, and other additives in a liquid medium can be used. When the film-forming stock solution contains at least one of plasticizers, surfactants, and other additives, these components are preferably uniformly mixed.

[0124] Examples of liquid media used for preparing film-forming solutions include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine. One or more of these can be used. Among these, water is preferred from the viewpoint of environmental impact and recyclability. Furthermore, when using the aforementioned modified PVA with silicon-containing groups as the PVA, the modified PVA exhibits good water solubility, and the viscosity increase when preparing aqueous solutions at higher temperatures (e.g., 80°C) is suppressed. Therefore, water can also be suitably used as the liquid medium.

[0125] The volatile content (the proportion of volatile components such as liquid media removed by evaporation or volatilization during membrane formation) of the membrane-forming stock solution is 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. By ensuring that the volatile content of the membrane-forming stock solution is 50% by mass or more, the viscosity of the membrane-forming stock solution will not become too high, allowing for smooth filtration and degassing during the preparation of the membrane-forming stock solution, and facilitating the manufacture of membranes with fewer foreign matter and defects. On the other hand, by ensuring that the volatile content of the membrane-forming stock solution is 95% by mass or less, the concentration of the membrane-forming stock solution will not become too low, making it easier to manufacture membranes industrially.

[0126] The temperature of the film-forming stock solution used in film formation can be set, for example, above 70°C and below 100°C. By performing film formation at this higher temperature, the viscosity of the film-forming stock solution can be reduced, thereby improving film-forming properties.

[0127] Examples of film-forming methods using film-forming solutions include casting, extrusion, wet film-forming, and gel film-forming. One or more of these methods can be used. Among these methods, casting and extrusion are preferred as they produce films with uniform thickness and width and good physical properties. The manufactured film can be dried or heat-treated as needed.

[0128] Examples of a specific manufacturing method for the film used in the optical film manufacturing of the present invention can be cited as follows: Using a T-slit die, hopper plate, I-die, lip coating machine die, etc., the film-forming solution is uniformly sprayed or cast onto the circumferential surface of a rotating and heated first roller (or belt) located at the upstream side. The volatile components evaporate from one side of the film sprayed or cast onto the circumferential surface of the first roller (or belt), thus drying the film. Next, it is further dried on the circumferential surface of one or more rotating and heated rollers located downstream, or further dried by passing it through a hot air drying apparatus. Thereafter, the film is wound up using a winding device. Drying based on heated rollers and drying based on a hot air drying apparatus can be appropriately combined.

[0129] It should be noted that when the optical film for manufacturing according to the present invention is a multilayer film, the multilayer film can be manufactured, for example, by coating a film-forming solution onto a substrate resin film (substrate resin layer). In this case, in order to improve the adhesion between the PVA layer and the substrate resin layer, the surface of the substrate resin film can be modified or an adhesive can be coated onto the surface of the substrate resin film.

[0130] <Methods for manufacturing optical films>

[0131] The method for manufacturing the optical film of the present invention includes a step of uniaxially stretching the film for manufacturing the aforementioned optical film. Hereinafter, as an example of the method for manufacturing an optical film, a method for manufacturing a polarizing film will be specifically described.

[0132] Methods for manufacturing polarizing films include dyeing processes for dyeing optical film manufacturing films (hereinafter also referred to as "PVA films"), stretching processes for uniaxial stretching, swelling processes for further swelling as needed, crosslinking processes for crosslinking, fixing processes for fixing, cleaning processes for cleaning, drying processes for drying, and heat treatment processes for heat treatment. In this case, the order of the processes is not particularly limited, and can be performed in, for example, the swelling process, dyeing process, crosslinking process, stretching process, and fixing process. Furthermore, one or more processes can be performed simultaneously, or each process can be performed two or more times.

[0133] The swelling process can be performed by immersing the PVA film in water. The water temperature for immersion is preferably 20°C or higher and 55°C or lower, more preferably 22°C or higher and 50°C or lower, and even more preferably 25°C or higher and 45°C or lower. Furthermore, the immersion time is preferably, for example, 0.1 minutes or higher and 5 minutes or lower, more preferably 0.5 minutes or higher and 3 minutes or lower. It should be noted that the water used for immersion is not limited to pure water; it can be an aqueous solution containing various dissolved components, or a mixture of water and an aqueous medium.

[0134] The dyeing process can be performed by contacting a dichroic dye with the PVA film. Iodine-based dyes are typically used as dichroic dyes. The dyeing can be performed at any stage, before, during, or after uniaxial stretching. A suitable method is to immerse the PVA film in a solution (especially an aqueous solution) containing iodine and potassium iodide as a dyeing bath. The iodine concentration in the dyeing bath is preferably 0.01% by mass or more and 0.5% by mass or less, and the potassium iodide concentration is preferably 0.01% by mass or more and 10% by mass or less. Furthermore, the temperature of the dyeing bath is preferably set to 20°C or more and 50°C or less, and particularly preferably 25°C or more and 40°C or less. A suitable dyeing time is 0.2 minutes or more and 5 minutes or less.

[0135] By performing a crosslinking process that crosslinks the PVA in the PVA film, the leaching of PVA into water during wet stretching at high temperatures can be effectively suppressed. From this perspective, the crosslinking process is preferably performed after the dyeing process and before the stretching process. The crosslinking process can be performed 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 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 keeping the concentration of the crosslinking agent within the aforementioned range, sufficient stretchability can be maintained. The aqueous solution containing the crosslinking agent may contain potassium iodide or the like. The temperature of the aqueous solution containing the crosslinking agent is preferably set to 20°C or more and 60°C or less, particularly preferably 25°C or more and 55°C or less. By setting the temperature within the aforementioned range, efficient crosslinking can be achieved.

[0136] The uniaxial stretching process of the PVA film can be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, or in the aforementioned dyeing bath or the fixation bath described later. Furthermore, in the case of the dry stretching method, stretching can be performed directly at room temperature, or while heating, or using a water-absorbing PVA film in air. Among these, the wet stretching method is preferred from the perspective of achieving high uniformity in the width direction of stretching, and uniaxial stretching in an aqueous solution containing boric acid is more preferred. The concentration of boric acid in the aqueous solution 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. Furthermore, 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 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.

[0137] From the viewpoint of the polarization properties of the resulting polarized film, the stretching ratio (total stretching ratio compared to the unstretched PVA film) during uniaxial stretching is preferably 5 times or more, more preferably 5.5 times or more. There is no particular upper limit to the stretching ratio, but it is preferably 8 times or less.

[0138] When uniaxially stretching long strips of PVA film, the uniaxial stretching direction is not particularly limited; uniaxial stretching along the length direction or transverse uniaxial stretching can be performed. From the perspective of obtaining a polarizing film with excellent polarization properties, uniaxial stretching along the length direction is preferred. Uniaxial stretching along the length direction can be performed using a stretching device with multiple parallel rollers and varying the circumferential speed between each roller. On the other hand, transverse uniaxial stretching can be performed using a tenter frame type stretching machine.

[0139] In manufacturing polarizing films, a fixation process can be performed after the stretching process to ensure that dichroic pigments (such as iodine-based pigments) are firmly adsorbed onto the PVA film. The fixation bath used in this process can be an aqueous solution containing one or more boron compounds such as boric acid and borax. Furthermore, iodine compounds or metal compounds can be added to the fixation bath as needed. The concentration of the boron compound in the fixation bath is preferably 2% by mass or more and 15% by mass or less, particularly preferably 3% by mass or more and 10% by mass or less. By setting the concentration of the boron compound within the aforementioned range, the adsorption of the dichroic pigments can be made more robust. The temperature of the fixation bath is preferably 15°C or more and 60°C or less, particularly preferably 25°C or more and 40°C or less.

[0140] The cleaning process is generally performed by immersing the membrane in distilled water, pure water, or an aqueous solution. From the viewpoint of improving polarization performance, it is preferable to use an aqueous solution containing iodides such as potassium iodide as an additive, with the concentration of the iodide preferably set to 0.5% by mass or more and 10% by mass or less. Furthermore, the temperature of the aqueous solution during the cleaning process is typically 5°C or higher and 50°C or lower, preferably 10°C or higher and 45°C or lower, and more preferably 15°C or higher and 40°C or lower. By setting the temperature of the aqueous solution within the aforementioned range, polarization performance can be further improved.

[0141] The drying conditions are not particularly limited, but it is preferable to dry the PVA film at a temperature above 30°C and below 150°C, and particularly preferably above 50°C and below 130°C. By drying at a temperature within the aforementioned range, polarizing films with excellent dimensional stability can be easily obtained.

[0142] It should be noted that optical films other than polarizing films, such as phase retardation films, can also be manufactured by a method that includes a uniaxial stretching process for the optical film manufacturing film of the present invention. Specifically, in addition to using the optical film manufacturing film of the present invention, existing known methods can be employed in the manufacturing process.

[0143] <Optical film>

[0144] Using the optical film manufacturing method of the present invention, an optical film can be obtained.

[0145] The aforementioned optical film can be a polarizing film, a phase retardation film, a field-angle improvement film, a brightness enhancement film, etc., preferably a polarizing film. In this case, the polarizing film typically contains dichroic pigments, and the PVA may be cross-linked.

[0146] The aforementioned optical film is preferably a stretched film, and more preferably a uniaxial stretched film. Furthermore, the optical film can be a single-layer film or a multi-layer film, but a single-layer film is preferred. When it is such a film, the optical film is more suitable for use as a polarizing film, etc.

[0147] When the aforementioned optical film is a polarizing film, the dichroism ratio (R) of the polarizing film is preferably 100 or higher. By using a PVA film that satisfies the above-mentioned dynamic viscoelastic parameters, it is possible to manufacture a polarizing film with such a high dichroism ratio (R) with good productivity. The dichroism ratio (R) is more preferably 150 or higher, and even more preferably 190 or higher. As an upper limit for this dichroism ratio (R), for example, it is 350, but it can be 300 or 260.

[0148] The method for calculating the dichroism ratio (R) of a polarizing film is as follows. First, the relationship between the transmittance (T') after excluding surface reflection and the transmittance of a single element (T) is shown in equation (a). Here, the refractive index of the polarizing film is set to 1.5, and the surface reflectance is set to 4%. The relationship between transmittance (T'), degree of polarization (V), and dichroism ratio (R) is shown in equation (b). Therefore, based on the measured transmittance (T) and degree of polarization (V), equations (a) and (b) are solved using these values, thereby allowing the calculation of the dichroism ratio (R) of the polarizing film.

[0149] T' = T / (1-0.04) 2 ...(a)

[0150] R={-ln[T'(1-V)]} / {-ln[T'(1+V)]} ...(b)

[0151] Polarizing films are typically made by laminating an optically transparent and mechanically strong protective film onto one or both sides of the polarizing film to create a polarizing plate. Protective films can be made of cellulose triacetate (TAC), cyclic olefin polymer (COP), cellulose acetate butyrate (CAB), acrylic, or polyester materials. Adhesives used for lamination include PVA, urethane, and UV-curable acrylic adhesives. In other words, the polarizing plate has a polarizing film and a protective film directly laminated to one or both sides of the polarizing film, or laminated thereon with the aid of an adhesive layer.

[0152] Polarizing plates can be used as components of LCDs by being bonded to a glass substrate after being coated with an acrylic adhesive, for example. It should be noted that polarizing plates can be further bonded with phase retardation films, field-angle improvement films, brightness enhancement films, etc.

[0153] Example

[0154] The present invention will now be described in more detail by way of examples, but the invention is not limited to these examples in any way. The methods for each determination and evaluation are as follows.

[0155] [Degree of polymerization of PVA (viscosity-average degree of polymerization)]

[0156] For the PVA synthesized in the following synthesis examples, the viscosity-uniform degree of polymerization was determined according to JIS K6726-1994.

[0157] [Degree of saponification of PVA]

[0158] For the PVA synthesized in the following examples, the degree of saponification was determined according to JIS K6726-1994.

[0159] [Silicon group content in PVA]

[0160] For the PVA synthesized in the following synthetic examples, the content of silicon-containing groups relative to all structural units was determined by proton NMR of the vinyl ester polymer before saponification. To determine the proton NMR of the vinyl ester polymer before saponification, the polymer was purified by hexane-acetone reprecipitation to completely remove unreacted monomers. Following this, it was dried under reduced pressure at 90°C for two days, dissolved in CDCl3 solvent, and then used for analysis.

[0161] [Membrane swelling degree]

[0162] The membrane (for manufacturing optical films) obtained in the following examples or comparative examples was cut into 1.5g pieces and immersed in 1000g of distilled water at 30°C for 30 minutes. After immersion for 30 minutes, the membrane was removed, the surface water was absorbed with filter paper, and its mass (N) was measured. Next, the membrane was dried in a dryer at 105°C for 16 hours, and the mass (M) after drying was measured. The degree of swelling of the membrane was calculated from the obtained mass (N) and mass (M) using the following formula.

[0163] Swelling degree (%) = 100 × N / M

[0164] [Dichroism ratio (optical performance) of polarizing films]

[0165] A rectangular sample with a length of 4 cm was taken from the central portion of the polarizing film in the width direction obtained in the following examples or comparative examples. For this sample, a spectrophotometer with an integrating sphere ("V7100" manufactured by Japan Spectrophotometer Co., Ltd.) was used to perform visibility correction in the visible light region with a C light source and a 2° field of view, according to JIS Z8722 (Method for Determination of Object Color). Based on this, the single-cell transmittance (T) and polarization degree (V) were measured.

[0166] The dichroism ratio (R) of the polarizing film is calculated by solving equations (a) and (b) below using the values ​​of the obtained monomer transmittance (T) and degree of polarization (V). Here, the refractive index of the polarizing film is set to 1.5, and the surface reflectance is set to 4%. Furthermore, by operating in this way, the dichroism ratio (R) of the polarizing film manufactured under the temperature conditions of the uniaxial stretching treatment bath in the examples and comparative examples is set to R0.

[0167] T' = T / (1-0.04) 2 ...(a)

[0168] R={-ln[T'(1-V)]} / {-ln[T'(1+V)]} ...(b)

[0169] [Contraction force of polarizing film]

[0170] Using the polarizing film obtained in the following examples or comparative examples, the shrinkage force of the polarizing film was measured using an automatic plotter with a thermostat "AG-X" manufactured by Shimadzu Corporation and a camera-type elongation meter "TRViewX120S". The polarizing film was conditioned for 18 hours at 20°C / 20% RH. After setting the thermostat of the automatic plotter "AG-X" to 20°C, the polarizing film (15 cm in length and 1.5 cm in width) was mounted on a chuck (chuck spacing 5 cm). Simultaneously with the start of stretching, the thermostat was heated to 80°C. The polarizing film was stretched at a speed of 1 mm / min, and stretching was stopped when the tension reached 2 N. The tension was measured after maintaining this state for 4 hours. At this time, the chuck spacing changed due to thermal expansion. Therefore, a marking seal was affixed to the chuck, and the camera-type elongation meter "TRViewX120S" was used to measure the amount of movement of the marking seal affixed to the chuck, correcting for the chuck spacing. It should be noted that the shrinkage force of the polarizing film is obtained by subtracting the initial tension of 2N from the tension measured after 4 hours. Furthermore, the shrinkage force (SF) of the polarizing film manufactured using the temperature conditions of the uniaxial stretching treatment bath in the examples and comparative examples is taken as SF0.

[0171] [Dichroism ratio of the polarizing film when the contraction force is 15N]

[0172] In the following examples or comparative examples, the temperature of the uniaxial stretching treatment bath was set to be 2°C or 4°C lower, and the iodine concentration of the dyeing treatment bath was varied so that the transmittance of the resulting polarized film was 44.0%. Otherwise, polarized films with different uniaxial stretching treatment bath temperatures were obtained using the same method. The monomer transmittance (T) and degree of polarization (V) of each obtained polarized film were measured, and the dichroism ratio (R) was determined using the aforementioned method. Here, the dichroism ratio (R) of the polarized film obtained under the condition of a uniaxial stretching treatment bath temperature 2°C lower is denoted as R0. -2 The dichroism ratio (R) of the polarization film obtained under a uniaxial stretching bath temperature 4°C lower than the specified temperature is denoted as R. -4 Furthermore, the shrinkage force of each polarizing film was measured using the aforementioned method. Here, the shrinkage force (SF) of the polarizing film obtained under conditions where the temperature of the uniaxial stretching treatment bath is below 2°C is denoted as SF. -2 The shrinkage force (SF) of the polarization film obtained under conditions where the temperature of the uniaxial stretching bath is below 4°C is denoted as SF. -4 .

[0173] Based on this operation, the dichroism ratios (R0, R1, R2) of three polarization films with different temperatures in the uniaxial stretching bath were determined. -2 R -4 ) and contractile force (SF0, SF) -2 SF -4 The value of ) was used to plot the relationship between the dichroism ratio and the shrinkage force, and a linear fit was performed to calculate the dichroism ratio when the shrinkage force of the polarizing film is 15N.

[0174] [Complex viscosity of PVA aqueous solution based on dynamic viscosity measurement]

[0175] (Preparation of PVA aqueous solution)

[0176] Using the PVA membrane manufactured in the following examples or comparative examples, a PVA aqueous solution for dynamic viscoelasticity determination was prepared. Specifically, a PVA membrane and distilled water were weighed into a container to achieve a PVA concentration of 12% by mass, and then heated at 95°C for 4 hours with stirring to dissolve the mixture, thereby preparing a PVA aqueous solution. During preparation, the PVA membrane was first swollen with water and then washed to dissolve substances other than PVA (water, plasticizer, surfactant) contained in the PVA membrane. The membrane was then dried in a dryer at 105°C for at least 17 hours and weighed to determine the PVA content in the PVA membrane. Furthermore, based on the determined PVA content, a PVA membrane was weighed to achieve a PVA concentration of 12% by mass without dissolving substances other than PVA, and then dissolved.

[0177] (Dynamic viscosity measurement)

[0178] Using a dynamic viscoelasticity measuring device (TA Instruments' "ARES-G2"), the temperature of each PVA aqueous solution was set to 30°C or 80°C under the following test conditions to perform dynamic viscoelasticity measurements.

[0179] (Determination conditions for dynamic viscoelasticity)

[0180] Geometry: Conical plates and disk-shaped plates with a cone angle of 0.02 rad.

[0181] Plate diameter: 40mm

[0182] Strain: 1%

[0183] Angular frequency range: 1~500 rad / s

[0184] Temperature to be measured (temperature of PVA aqueous solution): 30℃ or 80℃

[0185] Here, the temperature of the PVA aqueous solution is set to 30°C or 80°C in the following steps. First, approximately 1 mL of the PVA aqueous solution to be measured is applied to a plate heated to 30°C or 80°C. Then, the conical plate and the disc plate are joined together with a predetermined gap between them. The excess PVA aqueous solution overflowing from the plate is removed with a cotton swab, and the dynamic viscoelasticity measurement is performed. It should be noted that when the PVA aqueous solution temperature is set to 80°C for the dynamic viscoelasticity measurement, to prevent evaporation of the aqueous solution during the measurement, a small amount of bis(2-ethylhexyl) phthalate is applied along the conical plate after removing the sample overflowing from the plate. Additionally, a solvent trap cover is used for the measurement.

[0186] (Complex viscosity of PVA aqueous solution)

[0187] Based on the flow curve of complex viscosity obtained by dynamic viscoelasticity measurement of PVA aqueous solution at a temperature set to 30℃, the complex viscosity η at an angular frequency of 1 rad / s is calculated. * 1(30) and complex viscosity η at an angular frequency of 500 rad / s * 500 (30). Additionally, calculate their ratio (η). * 1(30) / η * 500 (30)), as R ω (30). On the other hand, the complex viscosity η at an angular frequency of 1 rad / s was also determined from the flow curve of the PVA aqueous solution obtained by dynamic viscoelasticity measurement with the temperature set at 80°C. * 1(80) and the complex viscosity η at an angular frequency of 500 rad / s *500 (80). Additionally, calculate their ratio (η). * 1(80) / η * 500 (80)), as R ω (80). Then, the complex viscosity η obtained above is calculated. * 1(30) and complex viscosity η * The ratio of 1(80) to (η) * 1(30) / η * 1(80)), as Rt. It should be noted that the dynamic viscosity measurement was performed three times for each PVA aqueous solution prepared from the PVA film of the examples or comparative examples, and the complex viscosity η of the PVA aqueous solution was calculated by averaging the data from the three measurements. * 1(30), η * 500 (30), η * 1(80) and η * 500 (80).

[0188] [Synthesis Example 1] Synthesis of PVA-1

[0189] 2550 g of vinyl acetate, 450 g of methanol, and 116.8 ml of a 5% (w / w) vinyltrimethoxysilane methanol solution were added to a 6 L reactor equipped with a stirrer, nitrogen inlet, additive inlet, and initiator inlet. After heating to 60 °C, the system was purged with nitrogen by bubbling for 30 minutes. The temperature in the reactor was adjusted to 60 °C, and 0.3 g of 2,2'-azobis(isobutyronitrile) was added to initiate polymerization. From the start of polymerization, 53 ml of methanol containing 5% (w / w) vinyltrimethoxysilane was added to the system while the polymerization reaction proceeded for 3 hours, at which point polymerization was stopped. The polymerization rate at the point of stopping the reaction was 25.0%. It should be noted that 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).

[0190] The concentration of the methanol solution of the obtained PVAc was adjusted to 23.5% by mass, and a 10% by mass NaOH methanol solution was added to achieve an alkali molar ratio (moles of NaOH / moles of vinyl ester units in PVAc) of 0.04 for saponification. The resulting polyvinyl alcohol was then washed with methanol.

[0191] The PVA-1 obtained through the above operations has a degree of polymerization (viscosity-average degree of polymerization) of 2,400, a degree of saponification of 99.9 mol%, and a silicon content of 0.3 mol%.

[0192] [Synthetic Examples 2-5] Synthesis of PVA-2 to PVA-5

[0193] Following Synthesis Example 1, by appropriately adjusting the proportion of monomers used, polymerization conditions, and saponification conditions, PVA-2 to PVA-5 with the viscosity-uniform polymerization degree, saponification degree, and silicon group content recorded in Table 1 were obtained.

[0194] [Example 1]

[0195] An aqueous solution containing 1100 parts by weight of PVA-1, 10 parts by weight of glycerol as a plasticizer, and 0.1 parts by weight of sodium polyoxyethylene lauryl ether sulfate as a surfactant, with a PVA content of 7.5% by weight, was prepared as a film-forming stock solution. This film-forming stock solution was dried on a metal roller at 80°C, and the resulting film was heat-treated in a hot air dryer at 127°C for 10 minutes to adjust the swelling degree to 200%, thereby producing a PVA film (for optical film manufacturing) with an average thickness of 30 μm.

[0196] A sample measuring 5cm wide and 9cm long was cut from the center of the obtained PVA film, allowing for uniaxial stretching within a 5cm width × 5cm length range. This sample was then immersed in pure water at 30°C for 60 seconds, simultaneously uniaxially stretched to twice its original length for swelling treatment. Next, it was immersed in an aqueous solution containing 0.075% by mass of iodine and 2% by mass of potassium iodide (staining bath: temperature 32°C) for 120 seconds, simultaneously uniaxially stretched to 1.2 times its original length (2.4 times overall) to allow iodine adsorption. Finally, it was immersed in an aqueous solution containing 2.6% by mass of boric acid (boric acid crosslinking bath: temperature 32°C) for 120 seconds, simultaneously uniaxially stretched to 1.25 times its original length (3.0 times overall). Next, the membrane was immersed in an aqueous solution containing 2.8% by mass boric acid and 5% by mass potassium iodide (uniaxial stretching treatment bath: temperature 69°C), while being uniaxially stretched along its length to a total length of 6.0 times. Subsequently, the membrane was cleaned by immersing it in an aqueous solution containing 1.5% by mass boric acid and 2.5% by mass potassium iodide (washing bath: temperature 22°C) for 5 seconds. Finally, the membrane was dried at 80°C for 4 minutes to obtain the polarizing film.

[0197] Using the obtained polarizing film and the aforementioned method, the monomer transmittance (T) and degree of polarization (V) were measured, and the dichroism ratio (R0) was calculated. The monomer transmittance (T) was 44.12%, the degree of polarization (V) was 99.9738%, and the dichroism ratio (R0) was 203. Furthermore, the shrinkage force (SF0) of the polarizing film, measured using the aforementioned method, was 13.6 N. Moreover, the dichroism ratio when the shrinkage force of the polarizing film was 15 N was calculated using the aforementioned method, and the result was 206.

[0198] Furthermore, using the obtained PVA film, a PVA aqueous solution was prepared using the aforementioned method, and dynamic viscoelasticity was measured. At this time, a 12% by mass PVA aqueous solution was obtained by weighing 21.3 g of PVA film (PVA content 18 g) and 128.7 g of distilled water. The flow curve of the complex viscosity of the aqueous solution at 30°C, obtained by dynamic viscoelasticity measurement (angular frequency: 1–500 rad / s), is shown below. Figure 1 .

[0199] [Examples 2-3 and Comparative Examples 1-2]

[0200] Using the PVA (PVA-2 to PVA-5) listed in Table 1, the PVA content of the film-forming solution and the heat treatment temperature were adjusted to achieve an average PVA film thickness of 30 μm and a swelling degree of 200%. Otherwise, the PVA film was prepared and evaluated in the same manner as in Example 1. Furthermore, using the obtained PVA film, the temperature of the uniaxial stretching treatment bath and the iodine concentration of the dyeing treatment bath were varied to achieve a polarizing film shrinkage force of approximately 15 N and a monomer transmittance of 44.0%. Otherwise, the polarizing film was prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0201] [Table 1]

[0202]

[0203] As shown in Table 1, in Comparative Example 1, which uses unmodified PVA-4 with a degree of polymerization of 2400, the complex viscosity ratio Rt is as low as 3.1, especially the viscosity at 30°C. In Comparative Example 1, due to such low viscosity, it can be said that the cross-linking between PVAs is insufficient, and a polarizing film with a high dichroism ratio cannot be obtained. On the other hand, in Comparative Example 2, which uses unmodified PVA-5 with a degree of polymerization of 4000, the complex viscosity ratio Rt is as low as 4.1, especially the viscosity at 80°C. Therefore, in Comparative Example 2, although a polarizing film with a high dichroism ratio can be obtained, the viscosity of the film-forming solution is high, resulting in low (film-forming) productivity. In contrast, in Examples 1 to 3, the complex viscosity ratio Rt is all above 4.5, the viscosity of the aqueous solution at 30°C is high, and the viscosity of the aqueous solution at 80°C is low. Therefore, according to Examples 1 to 3, the PVA films (films for optical film manufacturing) can be said to improve the optical performance of optical films while maintaining good film-forming properties (productivity).

Claims

1. A film for manufacturing optical films, wherein the film comprises polyvinyl alcohol. In the dynamic viscosity determination of an aqueous solution containing the optical film manufacturing membrane dissolved at a polyvinyl alcohol concentration of 12% by mass, Complex viscosity η * 1 (30) to complex viscosity η * 1 (80) ratio Rt(η * 1 (30) / η * 1 (80) ) is 4.5 or more and 50 or less, The aforementioned polyvinyl alcohol has a saponification degree of 99.0 mol% or higher. the complex viscosity η * 1(30) is the complex viscosity at an angular frequency of 1 rad / sec of the aqueous solution at 30°C, obtained from dynamic viscoelasticity measurement, the complex viscosity η * 1(80) is the complex viscosity at an angular frequency of 1 rad / sec of the aqueous solution at 80°C, obtained from dynamic viscoelasticity measurement.

2. The film for manufacturing optical films according to claim 1, wherein, The complex viscosity η * 1 (30) to the complex viscosity η * 500 The ratio R of the complex viscosity η ω (η * 1 (30) / η * 500 (30) is 5 or more and 150 or less, The complex viscosity η * 500 (30) is the complex viscosity of the aqueous solution at 30°C with an angular frequency of 500 rad / s, obtained by dynamic viscoelasticity determination.

3. The film for manufacturing optical films according to claim 1 or 2, wherein, The polyvinyl alcohol comprises a modified polyvinyl alcohol having silicon-containing groups.

4. The film for manufacturing optical films according to claim 3, wherein, The content of the silicon-containing groups in the modified polyvinyl alcohol is more than 0.01 mol% and less than 2 mol% relative to all structural units.

5. The film for manufacturing optical films according to claim 1 or 2, wherein, The optical film is a polarizing film.

6. A method for manufacturing an optical film, comprising a step of uniaxially stretching the film for manufacturing an optical film according to any one of claims 1 to 5.

7. The method for manufacturing an optical film according to claim 6, wherein, The optical film is a polarizing film.

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