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

Abstract

Provided are an optical film manufacturing film in which the increase in the stretching temperature when manufacturing an optical film having the same degree of shrinkage stress is suppressed and an optical film having excellent optical properties can be obtained, a method for manufacturing an optical film using the optical film manufacturing film, and an optical film. The present invention is an optical film manufacturing film comprising a polyvinyl alcohol having a silicon-containing group and an ethylene unit, the silicon-containing group being a silanol group or a group capable of being converted into a silanol group in the presence of water, the content of the silicon-containing group in the polyvinyl alcohol being 0.01 mol% or more and 1.0 mol% or less with respect to the total structural units, and the content of the ethylene unit being 0.5 mol% or more and 10 mol% or less.

Description

Technical Field

[0001] This invention relates to a film for manufacturing optical films, a method for manufacturing optical films, and an optical film. 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 used in a wide range of applications, including small instruments such as calculators and watches, smartphones, laptops, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, mobile phones, and indoor and outdoor measuring devices. In response to the increasing performance of LCDs in recent years, there is also a demand for high-performance polarizing plates, a key component of LCDs. Specifically, there is a need for polarizing plates with superior optical performance and excellent dimensional stability even at high temperatures. Therefore, the polarizing film used in polarizing plates also requires superior optical performance (polarization performance) and low shrinkage stress at high temperatures.

[0004] However, for polarizing films, it is not easy to reduce shrinkage stress at high temperatures while improving optical performance (polarization performance). This is because the polarization performance of a polarizing film and its shrinkage stress are usually inversely related. That is, if you want to improve the polarization performance of the polarizing film, the shrinkage stress will increase, and if you want to reduce the shrinkage stress, the polarization performance will decrease.

[0005] Patent Document 1 discloses a polarizing film obtained using PVA with a degree of polymerization of at least 2500, which improves optical performance and resistance to damp heat. In this Patent Document 1, a PVA film-forming solution obtained by dissolving PVA with a high degree of polymerization of 4980 or similar in a solvent with dimethyl sulfoxide as the main component is used to form the film.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 1-105204 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] 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, when using PVA with a high degree of polymerization, as in Patent Document 1, the viscosity of the PVA aqueous solution increases, resulting in poor film-forming properties and making it undesirable for industrial production. Therefore, a method is desired to improve the optical properties of optical films through methods other than increasing the degree of polymerization of PVA. Furthermore, when the manufacturing conditions (stretching conditions) of the optical film are the same, the optical film obtained from a PVA film with a high degree of polymerization exhibits higher shrinkage stress compared to a PVA film with a low degree of polymerization. Therefore, when using a PVA film with a high degree of polymerization, to obtain an optical film with excellent optical properties and low shrinkage stress, it is necessary to increase the stretching temperature during the manufacturing of the optical film, which is not preferred for industrial production. Therefore, a method is desired to obtain an optical film with excellent optical properties even when using a PVA film with a high degree of polymerization without increasing the stretching temperature during the manufacturing of the optical film.

[0011] The inventors have discovered that by using a PVA film containing PVA with silicon-containing groups, the optical performance of the resulting optical film can be significantly improved while suppressing the increase in viscosity of the PVA aqueous solution. However, even when using a PVA film containing PVA with silicon-containing groups, it is still necessary to increase the stretching temperature during the manufacture of the optical film.

[0012] The present invention is made based on the above-mentioned circumstances, and its object is to provide an optical film for manufacturing an optical film in which the high temperature of the stretching temperature is suppressed when manufacturing an optical film with the same shrinkage stress and an optical film with excellent optical performance is obtained, a method for manufacturing an optical film using such an optical film for manufacturing an optical film, and an optical film.

[0013] means for solving problems

[0014] The aforementioned objective is achieved by providing any of the following technical solutions.

[0015] [1] A film for manufacturing optical films, comprising PVA having silicon-containing groups and ethylene units, wherein the silicon-containing groups are silanol groups or groups that can be converted into silanol groups in the presence of water, wherein the content of the silicon-containing groups in the PVA is 0.01 mol% or more and 1.0 mol% or less relative to all structural units, and the content of the ethylene units is 0.5 mol% or more and 10 mol% or less;

[0016] [2] The film for manufacturing optical films according to [1], wherein the viscosity-average degree of polymerization of the aforementioned PVA is 1,000 or more and 6,000 or less, and the degree of saponification is 98.7 mol% or more;

[0017] [3] The film for manufacturing optical films according to [2], wherein the product of the aforementioned viscosity-uniform polymerization degree and the aforementioned content of silicon-containing groups is 100 mol% or more and 2,000 mol% or less;

[0018] [4] The film for manufacturing optical films according to any one of [1] to [3] has an average thickness of 1 μm or more and 75 μm or less;

[0019] [5] The film for manufacturing optical films according to any one of [1] to [4] has a swelling degree of 140% or more and 400% or less;

[0020] [6] A film for manufacturing an optical film according to any one of [1] to [5], wherein the aforementioned optical film is a polarizing film;

[0021] [7] The film for manufacturing optical films according to any one of [1] to [6] is an unstretched film;

[0022] [8] A method for manufacturing an optical film, comprising a step of uniaxially stretching a film for manufacturing an optical film according to any one of [1] to [7];

[0023] [9] The method for manufacturing an optical film according to [8], wherein the aforementioned optical film is a polarizing film;

[0024]

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

[0025]

[11] According to the optical film of

[10] , its shrinkage stress is 100 N / m. 2 the following;

[0026]

[12] According to the optical film of

[10] or

[11] , it is a polarizing film; and

[0027]

[13] The optical film according to any one of

[10] to

[12] is a single-layer film.

[0028] Invention Effects

[0029] According to the present invention, an optical film for manufacturing an optical film is provided, which suppresses the increase in high stretching temperature when manufacturing an optical film with the same level of shrinkage stress and enables the production of an optical film with excellent optical properties; a method for manufacturing an optical film using such an optical film for manufacturing an optical film is provided; and an optical film is provided. In other words, the optical film for manufacturing an optical film and the method for manufacturing an optical film according to the present invention can improve the optical properties of the obtained optical film while suppressing the increase in shrinkage stress and the increase in high stretching temperature. Attached Figure Description

[0030] Figure 1 The shrinkage stress of each polarizing film obtained in Examples 1-3 and Comparative Examples 1-5 is 75 N / mm. 2 The graph is obtained by plotting the stretching temperature at that time relative to the dichroism ratio at that time.

[0031] Figure 2 The shrinkage stress of each polarizing film obtained in Example 3 and Comparative Examples 1, 4, and 5 is 75 N / mm. 2 The graph is obtained by plotting the stretching temperature at that time relative to the dichroism ratio at that time. Detailed Implementation

[0032] <Membranes for Optical Film Manufacturing>

[0033] The film for manufacturing optical films of the present invention comprises polyvinyl alcohol (hereinafter sometimes referred to as "modified PVA") having silicon-containing groups and ethylene units.

[0034] (Modified PVA)

[0035] Modified PVA is a polymer having vinyl alcohol units (-CH2-CH(OH)-) as structural units, and also having silicon-containing groups and ethylene units. The modified PVA may optionally further contain vinyl ester units such as vinyl acetate units, or other structural units.

[0036] The lower limit of the viscosity-uniform polymerization degree of the modified PVA is preferably 1,000, more preferably 2,000, and even more preferably 2,500. By setting the viscosity-uniform polymerization degree of the modified PVA to the aforementioned lower limit or above, the stretching processability of the film for manufacturing the optical film of the present invention becomes excellent, and an optical film with higher optical performance and good resistance to damp heat can be obtained. On the other hand, the upper limit of the aforementioned viscosity-uniform polymerization degree is preferably 6,000, more preferably 5,000, and even more preferably 4,000. By setting the viscosity-uniform polymerization degree of the modified PVA to the aforementioned upper limit or below, good water solubility is achieved, and the increase in viscosity of the aqueous solution is suppressed. In addition, by setting the viscosity-uniform polymerization degree of the modified PVA to the aforementioned upper limit or below, the high temperature of the stretching temperature is further suppressed. Therefore, by setting the viscosity-uniform polymerization degree of the modified PVA to the aforementioned upper limit or below, good film-forming properties are achieved, and the productivity of the film for manufacturing the optical film of the present invention can be improved. Furthermore, when the viscosity-uniform polymerization degree of the modified PVA is below the aforementioned upper limit, it is easy to obtain an optical film with suppressed increase in shrinkage stress from the optical film manufacturing film of the present invention.

[0037] 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.

[0038] Viscosity-uniform degree of polymerization Po=([η]×10 4 / 8.29) (1 / 0.62)

[0039] The lower limit of the degree of saponification of modified 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 achieving a saponification degree above the aforementioned lower limit, an optical film with superior optical properties and resistance to damp heat is obtained. On the other hand, the upper limit of the degree of saponification is not particularly limited, but from the viewpoint of the productivity of modified PVA, it is preferably 99.99 mol% or less.

[0040] 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.

[0041] The modified PVA has a silicon-containing group. This silicon-containing group is a silanol group or a group that can be converted to a silanol group in the presence of water. A silanol group is 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 typically 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.).

[0042] 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.

[0043] As a silicon-containing group, i.e. a silanol group, or a group that can be converted into a silanol group in the presence of water, any of the groups shown in formulas (1) to (3) below can be listed. Among these, the group shown in formula (1) below is preferred.

[0044] [Chemistry 1]

[0045]

[0046] 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.

[0047] 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.).

[0048] 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.).

[0049] 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... 1 When neither of the atoms is hydrogen, this group is capable of being converted into a silanol group in the presence of water. As R 1Preferably, it is a hydrogen atom or a hydrocarbon group with 1 to 20 substituted or unsubstituted carbon atoms.

[0050] 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.

[0051] The content of silicon-containing groups in the modified PVA relative to all structural units is 0.01 mol% or more and 1.0 mol% or less. By using modified PVA with a specified amount of silicon-containing groups, the optical properties of the resulting optical film are improved. The lower limit of the silicon-containing group content in the modified PVA is 0.01 mol%, sometimes preferably 0.05 mol%, more preferably 0.1 mol%, and even more preferably 0.15 mol%. By setting the silicon-containing group content to the aforementioned lower limit or above, the optical properties of the resulting optical film can be sufficiently improved. On the other hand, the upper limit of the silicon-containing group content in the modified PVA relative to all structural units is 1.0 mol%, preferably 0.8 mol%, more preferably 0.6 mol%, and even more preferably 0.4 mol%. By setting the silicon-containing group content to the aforementioned upper limit or below, the water solubility and viscosity stability of the modified PVA in aqueous solutions become good, and film production efficiency (film-forming properties) can be improved. Furthermore, by setting the silicon-containing group content to the aforementioned upper limit or below, it is also possible to suppress the high temperature of the stretching temperature, etc.

[0052] 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.

[0053] The lower limit of the product of the viscosity-uniform polymerization degree of modified PVA and the content of silicon-containing groups is sometimes preferably 100 mol%, more preferably 200 mol%, even more preferably 300 mol%, and still more preferably 400 mol%. By making the aforementioned product above the aforementioned lower limit, the optical properties of the resulting optical film become more superior. On the other hand, the upper limit of the aforementioned product is preferably 2,000 mol%, more preferably 1,500 mol%, even more preferably 1,200 mol%, and particularly preferably 800 mol%. By making the aforementioned product below the aforementioned upper limit, the water solubility of modified PVA is further improved, and the high temperature of the stretching temperature is further suppressed. Therefore, the productivity of the film for manufacturing the optical film can be further improved.

[0054] 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.

[0055] [Chemistry 2]

[0056]

[0057] 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.

[0058] As R 3 Preferably, it contains hydrogen atoms.

[0059] 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).

[0060] 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.

[0061] R 4 Single bonds are preferred.

[0062] 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).

[0063] 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 the structural unit containing silicon groups in the modified PVA relative to all structural units can be the range of the silicon-containing group content mentioned above. In addition, the product of the viscosity-average degree of polymerization of the modified PVA and the content of the structural unit containing silicon groups can be the range of the product of the viscosity-average degree of polymerization and the content of silicon-containing groups mentioned above.

[0064] The modified PVA also contains ethylene units (-CH2-CH2-). The content of ethylene units in the modified PVA relative to all structural units is 0.5 mol% or more and 10 mol% or less. By using modified PVA with a specified amount of ethylene units, it is possible to obtain an optical film that exhibits excellent optical properties while suppressing the increase in stretching temperature. The lower limit of the ethylene unit content is preferably 1.0 mol%, more preferably 2.0 mol%. By setting the ethylene unit content to the aforementioned lower limit or above, it is possible to further suppress the increase in stretching temperature. On the other hand, the upper limit of the ethylene unit content is preferably 6 mol%, more preferably 5 mol%, and even more preferably 4.5 mol%. By setting the ethylene unit content to the aforementioned upper limit or below, it is possible to improve the water solubility, etc., of the modified PVA.

[0065] The content of ethylene units in modified PVA can be determined using, for example, proton NMR. For instance, the content of ethylene units in modified PVA can be determined by measuring the precursor of modified PVA, namely the modified vinyl ester polymer, using proton NMR in the same manner as the content of silicon-containing groups mentioned above.

[0066] Modified PVA may have structural units other than vinyl alcohol units, vinyl ester units, structural units having silicon-containing groups, and ethylene units. 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 making the modified PVA substantially composed of structural units of vinyl alcohol units, vinyl ester units, structural units having silicon-containing groups, and ethylene units, the effects of the present invention are sometimes more fully realized.

[0067] 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, degree of saponification, content of silicon groups, and content of ethylene units.

[0068] The lower limit of the modified PVA content in the film for manufacturing the optical film is not particularly limited, but is preferably 50% by mass, more preferably 80% by mass, and even more preferably 85% by mass. By setting the content of modified PVA 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 can be 100% by mass, preferably 99% by mass, and more preferably 95% by mass. It should be noted that the content (by mass%) of each component in the film for manufacturing the optical film is a value based on the total content of all components except water in a dry state.

[0069] (Manufacturing method of modified PVA)

[0070] There are no particular limitations on the manufacturing method of modified PVA. For example, it can be manufactured by copolymerizing vinyl ester monomers with monomers having silicon-containing groups and ethylene, and then saponifying the resulting vinyl ester polymer.

[0071] 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.

[0072] 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.

[0073] There are no particular limitations on the method for copolymerizing vinyl ester monomers with monomers containing silicon groups and ethylene, 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.

[0074] 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.

[0075] 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.

[0076] As a method for manufacturing vinyl ester polymers, copolymerization of ethylene under pressure is preferably carried out in the presence of vinyl ester monomers and monomers having silicon-containing groups. The ethylene pressure within the polymerization reactor is not particularly limited, but is sometimes preferably 0.01–2.0 MPa, more preferably 0.05–1.0 MPa, and even more preferably 0.1–0.65 MPa. The polymerization rate of the vinyl ester monomers at the outlet of the polymerization reactor is not particularly limited, but is sometimes preferably 5–90%, more preferably 15–85%.

[0077] When copolymerizing vinyl ester monomers with monomers containing silicon groups and ethylene, 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, olefins with 3 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, and N-hydroxy... Acrylamide derivatives such as methacrylamide 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-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; 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, and stearyl vinyl ether; cyanoethylene such as acrylonitrile and methacrylonitrile; halogenated vinyl ethers such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl acetate, allyl chloride, and 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.

[0078] The proportion of structural units derived from the aforementioned other monomers (excluding vinyl ester monomers, monomers having silicon-containing groups, and ethylene) 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.

[0079] 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.

[0080] (Plasticizer)

[0081] 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.

[0082] As the lower limit of the plasticizer content in the film for manufacturing the optical film of the present invention, it 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 modified PVA. By making the plasticizer content above the aforementioned lower limit, the tensile strength of the film is improved, and the optical performance of the obtained optical film can be further improved. On the other hand, as the upper limit of the plasticizer content, it 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 modified PVA. By making the plasticizer content below the aforementioned upper limit, it is possible to prevent the film from becoming too soft, which would lead to a decrease in processability.

[0083] (surfactant)

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] Surfactants can be used alone or in combination of two or more.

[0089] 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 modified 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 modified 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.

[0090] (Other additives, etc.)

[0091] 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.

[0092] The optical film for manufacturing the present invention may contain PVA other than the modified PVA described above. The total content of all PVA, including the modified PVA, plasticizer, and surfactant in the optical film for manufacturing the present invention is 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 for manufacturing the present invention is substantially composed of PVA, plasticizer, and surfactant, the effects of the present invention can be more fully realized.

[0093] The content of the modified PVA in the film for manufacturing the optical film of the present invention relative to the total PVA is preferably 50% 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.

[0094] The total content of modified PVA, plasticizer, and surfactant in the optical film manufacturing 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. By making the optical film manufacturing film of the present invention substantially composed of modified PVA, plasticizer, and surfactant, the effects of the present invention can be more fully realized.

[0095] (shape / physical properties, etc.)

[0096] 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.

[0097] 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).

[0098] The optical film manufacturing film of the present invention can be a single-layer film consisting of a single PVA layer (containing a layer of modified PVA) or a multilayer film containing a single PVA layer. When used in the manufacture of 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.

[0099] The specific composition and suitable composition of the PVA layer in the film for manufacturing optical films can be found in the description of the specific composition and suitable composition of the film itself for manufacturing optical films mentioned above.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] Here, "the degree of swelling of the membrane" refers to the value obtained using the following formula.

[0105] Swelling degree (%) = 100 × N / M

[0106] 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.

[0107] 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).

[0108] According to the optical film manufacturing film of the present invention, when manufacturing an optical film with the same level of shrinkage stress, the high temperature of the stretching temperature is suppressed, and an optical film with excellent optical properties can be obtained. 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 manufacturing film include polarizing films, retardation films, field-angle improvement films, and brightness enhancement films; a polarizing film is preferred.

[0109] <Method for manufacturing films for optical film production>

[0110] 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 modified 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.

[0111] Examples of liquid media used for preparing the film-forming solution 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, the modified PVA described above 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 a liquid medium.

[0112] 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.

[0113] The temperature of the film-forming stock solution used in film formation can be set, for example, above 60°C and below 150°C, preferably above 70°C and below 130°C. By using silanol-modified PVA and forming the film at this relatively high temperature, the viscosity of the film-forming stock solution can be kept low, thereby improving film-forming properties.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] <Methods for manufacturing optical films>

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] By performing a crosslinking process to crosslink the modified PVA in the PVA film, the leaching of the modified PVA into water during wet stretching at high temperatures can be effectively suppressed. From this viewpoint, 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.

[0123] 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 above 30°C and below 90°C, more preferably above 40°C and below 80°C, even more preferably above 50°C and below 75°C, and particularly preferably above 55°C and below 68°C.

[0124] 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.

[0125] 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.

[0126] The maximum tensile stress in the stretching process is preferably 30 N / mm. 2 Below. Here, maximum tensile stress refers to the value obtained by dividing the maximum tensile force borne by the PVA film by the cross-sectional area of ​​the PVA film in the raw material. By reducing the maximum tensile stress, a polarizing film with low shrinkage stress can be obtained. A maximum tensile stress of 25 N / mm is more suitable. 2 The following is a summary. Additionally, the maximum tensile stress is typically 1 N / mm². 2 The maximum tensile stress during the stretching process can be reduced by increasing the stretching temperature.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] <Optical film>

[0132] The optical film of the present invention is an optical film comprising PVA (modified PVA) having silicon-containing groups and ethylene units, wherein the silicon-containing groups are silanol groups or groups that can be converted into silanol groups in the presence of water, and 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 1.0 mol% or less, and the content of the aforementioned ethylene units is 0.5 mol% or more and 10 mol% or less.

[0133] The optical film of the present invention can be an optical film obtained by using the optical film manufacturing film of the present invention and the manufacturing method described above. The specific structure, content, and other details of the modified PVA contained in the optical film of the present invention are the same as those of the modified PVA contained in the optical film manufacturing film of the present invention. Furthermore, the optical film of the present invention may contain other components that are the same as those in the optical film manufacturing film of the present invention.

[0134] The optical film of the present invention can be a polarizing film, a phase difference film, a field-angle improvement film, a brightness enhancement film, etc., and is preferably a polarizing film. In this case, the polarizing film typically contains a dichroic pigment, and the modified PVA may be cross-linked.

[0135] The optical film of the present invention is preferably a stretched film, and more preferably a uniaxial stretched film. Furthermore, the optical film of the present invention can be a single-layer film or a multi-layer film, but is preferably a single-layer film. When it is such a film, the optical film of the present invention is more suitable for use as a polarizing film, etc.

[0136] The shrinkage stress of the optical film of the present invention is preferably 100 N / mm. 2 The following is an explanation of how low shrinkage stress results in excellent dimensional stability, even under high-temperature conditions. A shrinkage stress of 80 N / mm is ideally achieved. 2 The lower limit of the shrinkage stress of the optical film of the present invention can be, for example, 10 N / mm. 2 It can also be 20N / mm 2 or 40N / mm 2 Here, the shrinkage stress is the value obtained by dividing the tension at both ends of the polarization film of the sample, which is fixed in the tensile direction and maintained at 80°C for 4 hours, by the cross-sectional area of ​​the sample. Specifically, it refers to the value obtained by the method described in the following examples.

[0137] When the optical film of the present invention is a polarizing film, the dichroism ratio (R) of the polarizing film is preferably 100 or higher. By including the modified PVA described above, it is possible to manufacture a polarizing film having such a high dichroism ratio (R) with good productivity. The dichroism ratio (R) is more preferably 150 or higher, even more preferably 190 or higher, and particularly preferably 200 or higher. As an upper limit for this dichroism ratio (R), for example, it can be 350, 300, or 250.

[0138] 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.

[0139] T' = T / (1-0.04) 2 ...(a)

[0140] R={-ln[T'(1-V)]} / {-ln[T'(1+V)]} ...(b)

[0141] 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.

[0142] 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.

[0143] Example

[0144] 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.

[0145] [Degree of polymerization of PVA (viscosity-average degree of polymerization)]

[0146] For each PVA synthesized in the following synthesis examples, the viscosity-uniform degree of polymerization was determined according to JIS K6726-1994.

[0147] [Degree of saponification of PVA]

[0148] For each PVA synthesized in the following synthetic examples, the degree of saponification was determined according to JIS K6726-1994.

[0149] [Content of silicon-containing groups and ethylene units in PVA]

[0150] For each PVA synthesized in the following synthetic examples, the content of silicon-containing groups and ethylene units was determined based on the proton NMR of the vinyl ester polymer before saponification. For the proton NMR determination of the vinyl ester polymer before saponification, the vinyl ester polymer was purified by hexane-acetone reprecipitation to completely remove unreacted monomers from the polymer. Then, it was dried under reduced pressure at 90°C for two days, dissolved in CDCl3 solvent, and used for analysis.

[0151] [Membrane swelling degree]

[0152] The films (films for optical film manufacturing) obtained in the following examples and comparative examples were cut to a weight of 1.5g and immersed in 1000g of distilled water at 30°C for 30 minutes. After immersion for 30 minutes, the films were removed, the surface water was absorbed with filter paper, and their mass (N) was measured. Next, the films were dried in a dryer at 105°C for 16 hours, and the mass (M) after drying was measured. The degree of swelling of the film was calculated from the obtained mass (N) and mass (M) using the following formula.

[0153] Swelling degree (%) = 100 × N / M

[0154] [Dichroism ratio (optical performance) of polarizing films]

[0155] A rectangular sample with a length of 4 cm was taken from the central portion of each polarizing film obtained in the following examples and comparative examples, along the width direction. For this sample, a spectrophotometer with an integrating sphere ("V7100" manufactured by Nippon 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 degree of polarization (V) were measured.

[0156] 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.

[0157] T' = T / (1-0.04) 2 ...(a)

[0158] R={-ln[T'(1-V)]} / {-ln[T'(1+V)]} ...(b)

[0159] [Contraction stress of polarizing film]

[0160] The shrinkage stress of each polarizing film obtained in the following examples and comparative examples was measured using an automatic plotter with a thermostat, the "AG-X," manufactured by Shimadzu Corporation, and a camera-type elongation meter, the "TRViewX120S." The polarizing films were conditioned at 20°C / 20% RH for 18 hours. After setting the thermostat of the "AG-X" to 20°C, the polarizing film (15 cm in length and 1.5 cm in width) was mounted in a chuck (chuck spacing 5 cm). Simultaneously with the start of stretching, the thermostat was heated to 80°C. It should be noted that the stretching direction of the polarizing film was set to the length direction, and it was stretched in this direction. The polarizing film was stretched at a speed of 1 mm / min, and the stretching was stopped when the tension reached 2 N. The tension was measured after maintaining this state for 4 hours. At this point, the distance between the chucks changes due to thermal expansion. Therefore, a marking seal is affixed to the chucks, and a camera-type elongation meter "TRViewX120S" is used to measure the amount of movement of the marking seal affixed to the chucks, which can be corrected for the distance between the chucks. It should be noted that the tension measured after 4 hours is subtracted from the initial tension of 2N to obtain the shrinkage force of the polarizing film, and this shrinkage force is divided by the cross-sectional area of ​​the sample to obtain the shrinkage stress (N / mm²). 2 Furthermore, in this operation, the shrinkage stress (SF) of the polarization film manufactured using the temperature conditions of the uniaxial stretching treatment bath of the embodiments and comparative examples is taken as SF0.

[0161] The shrinkage stress of the polarizing film is 75 N / mm. 2 [Dichroism ratio and stretching temperature]

[0162] In the following examples and 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 R. -2The 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 stress of each polarizing film was determined 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 2°C lower is denoted as SF. -2 The shrinkage force (SF) of the polarization film obtained under a uniaxial stretching bath temperature 4°C lower than the specified temperature is denoted as SF. -4 .

[0163] 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 shrinkage stress (SF0, SF) -2 SF -4 The value of ) was used to plot the relationship between the dichroism ratio and shrinkage stress, and a linear fit was performed. From this, the shrinkage stress was calculated to be 75 N / mm². 2 The dichroism ratio at that time. Furthermore, by plotting the relationship between shrinkage stress and the temperature of the uniaxial tensile treatment bath and performing linear fitting, the shrinkage stress was calculated to be 75 N / mm². 2 The stretching temperature at that time.

[0164] [Synthetic Example 1] Synthesis of PVA-1

[0165] 3000g of vinyl acetate and 3.6g of vinyltrimethoxysilane (a monomer with silicon-containing groups) were added to a 5L pressurized reactor equipped with a stirrer, nitrogen inlet, ethylene inlet, initiator addition port, and delayed solution addition port. After heating to 60°C, the system was purged with nitrogen by bubbling for 30 minutes. Next, ethylene was introduced to a reactor pressure of 0.26MPa. After adjusting the internal temperature of the polymerization tank to 60°C, 1.0g of 2,2'-azobisisobutyronitrile (AIBN) was injected to initiate polymerization. During polymerization, ethylene was introduced while simultaneously injecting a 2% by mass methanol solution of vinyltrimethoxysilane, maintaining the reactor pressure at 0.26MPa and the polymerization temperature at 60°C. After 3 hours, when the polymerization rate reached 20%, cooling was performed to stop the polymerization. The total amount of vinyltrimethoxysilane methanol solution added until the polymerization was completed was 84ml. Next, unreacted vinyl acetate was removed under reduced pressure to obtain a methanol solution of modified polyvinyl acetate (hereinafter sometimes abbreviated as modified PVAc). The concentration of the obtained methanol solution of modified PVAc was adjusted to 23.5% by mass, and saponification was performed by adding NaOH methanol solution (concentration of 10% by mass) at an alkali molar ratio (moles of NaOH / moles of vinyl ester units in modified PVAc) of 0.04. The resulting polyvinyl alcohol was washed with methanol. The PVA-1 obtained through the above operations had a degree of polymerization (viscosity-average degree of polymerization) of 3,300, a degree of saponification of 99.9 mol%, a silicon group content of 0.2 mol%, and an ethylene unit content of 2.5 mol%.

[0166] [Synthetic Examples 2-9] Synthesis of PVA-2 to PVA-9

[0167] Following Synthesis Example 1, and by appropriately adjusting the proportions of the monomers used, the polymerization conditions, and the saponification conditions, PVA-2 to PVA-9 were obtained, possessing the viscosity-uniform polymerization degree, saponification degree, silicon group content, and ethylene unit content as described in Table 1.

[0168] [Example 1]

[0169] An aqueous solution containing 100 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 9.5% 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 105°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.

[0170] A sample measuring 5cm in width and 9cm in length 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 2.0 times along its length for swelling treatment. Next, it was immersed in an aqueous solution containing 0.05% by mass of iodine and 1.15% by mass of potassium iodide (staining bath: temperature 32°C) for 120 seconds, simultaneously uniaxially stretched 1.2 times (2.4 times overall) along its length, thereby allowing 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 1.25 times (3.0 times overall) along its length. Next, the membrane was immersed in a 69°C aqueous solution (uniaxial stretching treatment bath) containing 2.8% by mass boric acid and 5% by mass potassium iodide, while being uniaxially stretched along its length to a total length of 6.0 times. Subsequently, the membrane was cleaned by immersing it in a 22°C aqueous solution (washing bath) containing 1.5% by mass boric acid and 3.5% by mass potassium iodide. Finally, the membrane was dried at 80°C for 4 minutes to obtain the polarizing film.

[0171] Using the obtained polarizing film and the aforementioned method, the shrinkage stress of the polarizing film was determined to be 75 N / mm. 2 The dichroism ratio at that time. Furthermore, using the aforementioned method, the shrinkage stress of the polarizing film was determined to be 75 N / mm. 2 The tensile temperature at which the tensile strength was measured. The results are shown in Table 1 and... Figure 1 .

[0172] [Examples 2-3 and Comparative Examples 1-5]

[0173] Using the PVA (PVA-2 to PVA-8) listed in Table 1, the PVA content and heat treatment temperature of the film-forming solution were adjusted to achieve an average PVA film thickness of 30 μm and a swelling degree of 200%. Otherwise, the process was the same as in Example 1, for the fabrication and evaluation of the PVA film. Using the obtained PVA film, the shrinkage stress of the resulting polarizing film was set to 75 N / mm. 2 The temperature of the uniaxial stretching treatment bath and the iodine concentration of the dyeing treatment bath were varied to achieve a monomer transmittance of 44.0%. Otherwise, the polarization film was manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1 and... Figure 1 , 2 .

[0174] [Comparative Example 6]

[0175] An attempt was made to prepare the film-forming solution using PVA-9 as the PVA, but the PVA did not dissolve, making it impossible to prepare the film-forming solution. Therefore, it was impossible to manufacture PVA films and polarizing films, and it was also impossible to determine the shrinkage stress of the polarizing film to be 75 N / mm. 2 The dichroism ratio and stretching temperature at that time.

[0176] [Table 1]

[0177]

[0178] As shown in Table 1 and Figure 1 As shown, according to Examples 1-3, an attempt was made to manufacture a film (PVA film) for optical film production with a shrinkage stress of 75 N / mm. 2 When manufacturing optical films, optical films with a dichroism ratio of 200 or higher can be obtained at a stretching temperature of 68°C or lower. That is, according to the optical film manufacturing films of Examples 1-3, when manufacturing optical films with the same level of shrinkage stress, the high temperature of the stretching temperature is suppressed, and optical films with excellent optical properties can be obtained. In other words, the optical film manufacturing films of Examples 1-3 can improve the optical properties of the obtained optical films while suppressing the increase of shrinkage stress and the high temperature of the stretching temperature.

[0179] like Figure 2 As shown, by comparing optical film manufacturing films (PVA films) obtained using PVA with the same degree of polymerization, the following can be observed. Compared with Comparative Example 1 obtained using unmodified PVA with a degree of polymerization of 2400, Comparative Examples 4 and 5 obtained using modified PVA with a degree of polymerization of 2400 and a silicon group content of 0.2 mol% or 0.4 mol% exhibit a shrinkage stress of 75 N / mm. 2 The dichroism ratio (optical performance) is exceptionally high, but the stretching temperature also increases significantly. It can be seen that, compared to using unmodified PVA, the PVA film obtained using PVA containing only silicon groups significantly improves the optical performance of the resulting optical film, but cannot suppress the increase in stretching temperature. On the other hand, in Example 3, using modified PVA with a degree of polymerization of 2400, a silicon group content of 0.2 mol%, and an ethylene unit content of 4.5 mol%, the shrinkage stress was 75 N / mm. 2 The dichroism ratio (optical performance) of the film obtained using PVA containing only silicon groups is higher than that of Comparative Example 4, and the stretching temperature is approximately the same, thus suppressing the increase in stretching temperature. In other words, compared to using PVA with only silicon groups, the film for manufacturing optical films (PVA film) using PVA containing both silicon groups and ethylene units suppresses the increase in stretching temperature when manufacturing optical films with the same level of shrinkage stress, and an optical film with excellent optical performance can be obtained. In other words, it is possible to improve the optical performance of the obtained optical film while suppressing the increase in shrinkage stress and the increase in stretching temperature.

[0180] Industrial availability

[0181] The optical film manufacturing film of the present invention can be suitably used as a constituent material of LCDs, i.e., a material for polarizing films, etc.

Claims

1. A film for manufacturing polarizing films, comprising polyvinyl alcohol having silicon-containing groups and ethylene units, The silicon-containing group is a silanol group or a group that can be converted into a silanol group in the presence of water. The content of the silicon-containing groups in the polyvinyl alcohol is more than 0.01 mol% and less than 1.0 mol% relative to all structural units, and the content of the ethylene units is more than 0.5 mol% and less than 10 mol%.

2. The film for polarizing film production according to claim 1, wherein The polyvinyl alcohol has a viscosity-uniform polymerization degree of 1,000 or more and 6,000 or less, and a saponification degree of 98.7 mol% or more.

3. The film for polarizing film production according to claim 2, wherein The product of the viscosity-uniform polymerization degree and the content of the silicon-containing groups is more than 100 mol% and less than 2,000 mol%.

4. The film for manufacturing polarizing film according to any one of claims 1 to 3, wherein the average thickness is 1 μm or more and 75 μm or less.

5. The film for manufacturing polarizing film according to any one of claims 1 to 3, wherein the degree of swelling is 140% or more and 400% or less.

6. The film for manufacturing polarizing films according to any one of claims 1 to 3, wherein it is an unstretched film.

7. A method for manufacturing a polarizing film, comprising a step of uniaxially stretching a film for manufacturing a polarizing film according to any one of claims 1 to 6.

8. A polarizing film comprising polyvinyl alcohol having silicon-containing groups and ethylene units, The silicon-containing group is a silanol group or a group that can be converted into a silanol group in the presence of water. The content of the silicon-containing groups in the polyvinyl alcohol is more than 0.01 mol% and less than 1.0 mol% relative to all structural units, and the content of the ethylene units is more than 0.5 mol% and less than 10 mol%.

9. The polarizing film according to claim 8, which has a shrinkage stress of 100 N / m 2 The following.

10. The polarizing film according to claim 8 or 9, wherein it is a single-layer film.

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