Optical film, polarizing plate, and liquid crystal display device

Abstract

Provided is an optical film that can be molded with low stretching stress, that has appropriate retardation development, and that also has excellent durability under severe environmental conditions.　This optical film contains diacetyl cellulose and is characterized by: containing a nitrogen-containing heterocyclic compound; the nitrogen-containing heterocyclic compound having an aromatic ring containing 1-3 nitrogen atoms; a hydrogen atom being bonded to at least one of the nitrogen atoms contained in the aromatic ring; the acid dissociation constant when the hydrogen atom bonded to the nitrogen atom dissociates as a hydrogen ion being 14 or greater; and the nitrogen-containing heterocyclic compound being represented by general formula 1.

Description

Optical films, polarizing plates, and liquid crystal display devices

[0001] This disclosure relates to optical films, polarizing plates, and liquid crystal display devices. More specifically, this disclosure relates to optical films that can be molded with low stretch stress, have moderate phase difference characteristics, and exhibit excellent durability under harsh environmental conditions.

[0002] In recent years, with the expansion of liquid crystal display (LCD) applications, there has been a growing demand for large-scale, high-quality applications such as televisions. As a result, even higher quality is required for polarizing plates, phase difference films, and polarizing plate protective films.

[0003] Among these, films containing acetylcellulose have conventionally been known as phase difference films. However, acetylcellulose sometimes causes problems with the stability of its optical properties due to its ability to absorb water.

[0004] In response to this, cellulose acylate films containing additives that have a nucleic acid base skeleton are being investigated (see, for example, Patent Document 1). This aims to suppress the fluctuation of the phase difference of the optical film in response to changes in ambient humidity.

[0005] Furthermore, cellulose acylate films containing hydrogen-bonding compounds and specific hydrophobic agents are being investigated (see, for example, Patent Document 2). This aims to suppress fluctuations in the phase difference of the optical film in response to changes in ambient humidity. Moreover, this aims to suppress the degradation of the polarizer when it is bonded to a polarizing plate and subjected to high temperature and high humidity conditions over time.

[0006] Japanese Patent Publication No. 2011-241379 Japanese Patent Publication No. 2012-082235

[0007] The inventions described in Patent Documents 1 and 2 above aim to suppress the formation of hydrogen bonds between cellulose acylate and water by adding specific additives to the cellulose acylate film. Furthermore, the inventions described in Patent Documents 1 and 2 aim to suppress the deterioration of the optical film's performance.

[0008] On the other hand, in order to manufacture large-sized liquid crystal display devices, it is necessary to manufacture large-sized phase difference films. To form large-sized phase difference films, it is necessary to deform acetylcellulose significantly through a stretching operation. However, this large stretching operation, which involves greatly stretching the acetylcellulose, has the problem of applying large stretching stress to the acetylcellulose, resulting in excessively large phase differences. In addition, the large stretching operation on acetylcellulose generates large residual stress, and when a liquid crystal display device is manufactured using this acetylcellulose as a phase difference film, defects such as uneven display are likely to occur. The inventions described in the above-mentioned Patent Documents 1 and 2 were insufficient to address the above problems when forming such large-sized phase difference films.

[0009] This disclosure has been made in view of the above circumstances. The problem that this disclosure aims to solve is to provide an optical film that can be molded with low stretch stress, has appropriate phase difference characteristics, and exhibits excellent durability under harsh environmental conditions. Furthermore, another problem that this disclosure aims to solve is to provide a polarizing plate and a liquid crystal display device using the above optical film.

[0010] To solve the above-mentioned problems, this disclosure provides the following optical film, polarizing plate, and liquid crystal display device.

[0011] 1. An optical film containing diacetylcellulose, wherein it contains a nitrogen-containing heterocyclic compound, the nitrogen-containing heterocyclic compound having an aromatic ring containing one to three nitrogen atoms, at least one of the nitrogen atoms in the aromatic ring being bonded to a hydrogen atom, the acid dissociation constant when the hydrogen atom bonded to the nitrogen atom dissociates as a hydrogen ion being 14 or more, and the nitrogen-containing heterocyclic compound being a compound represented by the following general formula 1.

[0012]

[0013] (In general formula 1, W １ ~W ７(One to three of the atoms are nitrogen atoms, and at least one of the nitrogen atoms is bonded to a hydrogen atom; Z represents a hydrogen atom, a hydroxyl group, an alkoxy group, or an aryloxy group; L represents a linking group; and n is 1 or 2.)

[0014] 2. The optical film according to item 1, wherein the ClogP of the nitrogen-containing heterocyclic compound is 1 to 7.

[0015] 3. A polarizing plate containing the optical film described in paragraph 1.

[0016] 4. A liquid crystal display device including the polarizing plate described in paragraph 3.

[0017] The optical film of this disclosure contains diacetylcellulose. Therefore, it exhibits high phase difference characteristics and can be suitably used as a phase difference film (optical compensation film). The optical film of this disclosure contains a nitrogen-containing heterocyclic compound in which the acid dissociation constant when a hydrogen atom bonded to a specific nitrogen atom dissociates as a hydrogen ion is 14 or higher. Furthermore, the nitrogen-containing heterocyclic compound contained in the optical film of this disclosure is a compound represented by the above general formula 1. Therefore, it can be molded with low stretch stress, has appropriate phase difference characteristics, and exhibits excellent durability under harsh environmental conditions.

[0018] The mechanism of action or mechanism of the effects of this disclosure is not clearly defined, but it is presumed to be as follows.

[0019] Diacetylcellulose has low resin fluidity due to the strong hydrogen bonds formed between its molecules. Therefore, when diacetylcellulose is subjected to large stretching operations, it is thought that large stretching stresses are applied, the phase difference becomes too large, and large residual stresses remain.

[0020] In contrast, the optical film of the present disclosure contains a nitrogen-containing heterocyclic compound having an acid dissociation constant of 14 or more when a hydrogen atom bonded to a specific nitrogen atom dissociates as a hydrogen ion. Since the nitrogen-containing heterocyclic compound has a high acid dissociation constant, it becomes strongly basic and is easily protonated. Therefore, hydrogen bonds are more likely to form between diacetyl cellulose and the nitrogen-containing heterocyclic compound than between the intermolecular hydrogen bonds of diacetyl cellulose. Thus, it is presumed that the formation of intermolecular hydrogen bonds in diacetyl cellulose is suppressed. And it is presumed that by suppressing the formation of intermolecular hydrogen bonds in diacetyl cellulose, a large stretching operation can be performed with a small stretching stress. And it is presumed that by being able to perform a large stretching operation with a small stretching stress, the retardation does not become too large and an appropriate retardation can be achieved. Further, it is presumed that by being able to perform a large stretching operation with a small stretching stress, no large residual stress remains and defects are unlikely to occur when manufacturing a liquid crystal display device. <> <>

[0021] In addition, since the nitrogen-containing heterocyclic compound forms a hydrogen bond with diacetyl cellulose, the hydrogen bond between diacetyl cellulose and water is suppressed. Therefore, the optical film of the present disclosure containing the nitrogen-containing heterocyclic compound has high durability under high temperature and high humidity environmental conditions. <> <>

[0022] It is a schematic cross-sectional view schematically showing an embodiment of a polarizing plate of the present disclosure. It is a schematic cross-sectional view schematically showing an embodiment of a liquid crystal display device of the present disclosure. <> <>

[0023] Hereinafter, embodiments of the present disclosure will be specifically described. The present disclosure is not limited to the following embodiments, and it should be understood that those obtained by appropriately changing and improving the following embodiments based on ordinary knowledge of those skilled in the art without departing from the gist of the present disclosure also fall within the scope of the present disclosure. <> <>

[0024] One embodiment of the optical film of the present disclosure is an optical film containing diacetyl cellulose. And the optical film of this embodiment contains a nitrogen-containing heterocyclic compound, and the nitrogen-containing heterocyclic compound has an aromatic ring containing 1 to 3 nitrogen atoms. This aromatic ring can also be referred to as a nitrogen-containing aromatic heterocyclic ring, and hereinafter may also be referred to as a nitrogen-containing aromatic ring. In the optical film of this embodiment, at least one of the nitrogen atoms contained in the above nitrogen-containing aromatic ring is bonded to a hydrogen atom. And when the hydrogen atom bonded to the nitrogen atom dissociates as a hydrogen ion, the acid dissociation constant is 14 or more. Hereinafter, the acid dissociation constant may be referred to as "pKa". Further, the acid dissociation constant when the hydrogen atom bonded to the nitrogen atom dissociates as a hydrogen ion may be referred to as "the acid dissociation constant of the nitrogen-containing aromatic ring" or "the pKa of the nitrogen-containing aromatic ring". Furthermore, in the optical film of this embodiment, the above nitrogen-containing heterocyclic compound is a compound represented by the following general formula 1.

[0025]

[0026] In general formula 1, one to three of W １ to W ７ represent nitrogen atoms. At least one of the nitrogen atoms is bonded to a hydrogen atom. And in general formula 1, Z represents a hydrogen atom, a hydroxy group, an alkoxy group, an aryloxy group, and L represents a linking group. In general formula 1, n represents the number of groups represented by "ZL-", and is 1 or 2. Also, the condensed ring of the 5-membered ring and the 6-membered ring in general formula 1 constitutes the above nitrogen-containing aromatic ring.

[0027] Since the optical film of this embodiment contains diacetyl cellulose, it has high retardation expressivity and can be suitably used as a retardation film (optical compensation film). The optical film of this embodiment has the above acid dissociation constant of 14 or more and contains the nitrogen-containing heterocyclic compound represented by the above general formula 1, so it can be molded with low stretching stress, has appropriate retardation expressivity, and is also excellent in durability under severe environmental conditions.

[0028] (1) Optical film (1-1) Nitrogen-containing heterocyclic compound In the optical film of this embodiment, the nitrogen-containing heterocyclic compound has an aromatic ring containing one to three nitrogen atoms. That is, the nitrogen-containing heterocyclic compound has an aromatic heterocyclic ring containing a nitrogen atom as a heteroatom constituting the ring. The nitrogen-containing heterocyclic compound contains the compound represented by the above general formula 1. Therefore, the nitrogen-containing heterocyclic compound contained in the optical film of this embodiment has excellent durability under harsh environmental conditions. As a result, the optical film of this embodiment containing the nitrogen-containing heterocyclic compound exhibits small fluctuations in retardation values ​​during environmental changes.

[0029] In the nitrogen-containing heterogeneous compound represented by the general formula 1 above, W １ ~W ７ One to three of the atoms are nitrogen atoms. One of the nitrogen atoms is bonded to a hydrogen atom. In general formula 1, Z represents a hydrogen atom, a hydroxyl group, an alkoxy group, or an aryloxy group, and n is 1 or 2. In general formula 1, L represents a linking group. Examples of linking groups include atoms containing at least one of carbon atoms, nitrogen atoms, sulfur atoms, and oxygen atoms, or groups of atoms containing at least two of these. Specifically, for example, "-O-", "-S-", "-N(R)-", "-CO-", and "-SO ２ Examples of alkylene groups include "-O-", alkylene groups, arylene groups, or combinations thereof. Examples of alkylene groups include methylene, ethylene, propylene, 1,4-cyclohexylene, dodecylene, hexadecylene, 2-ethylhexylene, and 2-hexyldecylene. Examples of arylene groups include phenylene and naphthylene. R represents a hydrogen atom, an alkyl group, or a cycloalkyl group. Among these, "-O-", alkylene groups, and arylene groups are particularly preferred.

[0030] (1-1-1) Acid Dissociation Constant of Nitrogen-Containing Aromatic Ring The optical film of this embodiment has a pKa of the nitrogen-containing aromatic ring of 14 or more. Since the optical film of this embodiment has a pKa of the nitrogen-containing aromatic ring of 14 or more, it can be molded with low drawing stress, has appropriate retardation expressivity, and is also excellent in durability under severe environmental conditions. If the pKa is less than 14, it is not preferable because the effect of reducing the drawing stress is particularly small.

[0031] The pKa of the nitrogen-containing aromatic ring is a value obtained by theoretical calculation based on the structure of the nitrogen-containing aromatic ring. In the calculation of the theoretical value, Z and L in the general formula 1 above are not included in the calculation. The value of pKa can be calculated by calculation formula A "ΔG(aq) = pKa × RTln10". In calculation formula A, ΔG(aq) is the free energy change in the following reaction formula R in the solution due to proton dissociation. Reaction formula R is "[HA(aq) = H ＋ (aq) + A － (aq)" (in reaction formula R, "=" means that the reaction represented by reaction formula R is an equilibrium reaction, HA represents a nitrogen-containing aromatic ring, and H is hydrogen bonded to nitrogen). In calculation formula A, "R" is the gas constant, "T" is the absolute temperature, and "ln10" is the natural logarithm of 10. The value of ΔG can be obtained by performing structure optimization and free energy (ΔG) calculation for the nitrogen-containing aromatic ring (HA) and its deprotonated species (A － ) based on the density functional theory (DFT). B3LYP can be used for the functional, and aug-cc-pVDZ can be used for the basis function. The solvent effect can be considered by the solvation model density (SMD). In addition, the free energy of the proton can use literature values and the like.

[0032] (1-1-2) ClogP of Nitrogen-Containing Heterocyclic Compounds The optical film of this embodiment preferably has a ClogP of nitrogen-containing heterocyclic compound in the range of 1 to 7, and more preferably in the range of 2 to 5. Because the ClogP is in this range, the optical film of this embodiment has good solubility in solvents and compatibility with resins. If the ClogP is less than 1, the solubility in solvents may decrease. If the ClogP is greater than 7, the compatibility with resins may decrease. Here, logP is the "octanol / water partition coefficient". The "octanol / water partition coefficient" is the value obtained by dividing the mass of solute dissolved in octanol by the mass of solute dissolved in water after distributing the solute between two layers of octanol and water, and taking the logarithm. logP is an index of hydrophobicity, and a larger value indicates higher hydrophobicity. ClogP also means the estimated value of logP calculated using an estimation formula for estimating logP. ClogP can be calculated using "CHEMDRAW" (a registered trademark of LevitySignals Software, Inc.), a commercially available chemical structure drawing software.

[0033] Examples of compounds represented by general formula 1 include the following compounds:

[0034]

[0035] Among these compounds, the indole structure is preferred.

[0036] (1-1-3) Content of Nitrogen-Containing Heterocyclic Compounds The optical film of this embodiment preferably contains nitrogen-containing heterocyclic compounds in the range of 1 to 20% by mass. The optical film of this embodiment is more preferably containing nitrogen-containing heterocyclic compounds in the range of 3 to 7% by mass. Because the optical film of this embodiment contains nitrogen-containing heterocyclic compounds in this range, it can be molded with low stretch stress, has appropriate phase difference characteristics, and exhibits excellent durability under harsh environmental conditions. If the content of nitrogen-containing heterocyclic compounds is less than 1% by mass, the stretch stress will be high and the phase difference may be large. If the content of nitrogen-containing heterocyclic compounds is greater than 20% by mass, the haze of the optical film may be large.

[0037] (1-2) Diacetylcellulose Cellulose is a polymer in which β-glucose units are linked in a linear chain by β-1,4-glycosidic bonds. Cellulose esters are cellulose in which some or all of the hydrogen atoms of the hydroxyl groups (-OH) at positions 2, 3, and 6 in one glucose unit are replaced with acyl groups. Cellulose esters in which the acyl groups are acetyl groups are called "acetylcellulose". Acetylcellulose in which two of the hydrogen atoms of the hydroxyl groups in one glucose unit are replaced with acetyl groups is called "diacetylcellulose".

[0038] In the optical film of this embodiment, the diacetylcellulose is acetylcellulose in which the degree of substitution of acetyl groups is in the range of 2.0 to 2.6. In the optical film of this embodiment, it is preferable that the degree of substitution of acetyl groups of the diacetylcellulose is within the above range because it results in an appropriate phase difference value.

[0039] (1-2-1) Degree of substitution of acetyl groups The degree of substitution of acetyl groups represents the average number of acetyl groups per glucose unit. In other words, it represents how many of the hydrogen atoms in the hydroxyl groups at positions 2, 3, and 6 in one glucose unit are substituted with acetyl groups. Therefore, the maximum value of the degree of substitution of acetyl groups is 3.0, which means that all of the hydrogen atoms in the hydroxyl groups at positions 2, 3, and 6 are substituted with acetyl groups.

[0040] Acetyl groups may be evenly substituted at the 2nd, 3rd, and 6th positions of one glucose unit, or they may be substituted in a distributed manner. The degree of substitution of acetyl groups is determined by the method specified in ASTM-D817-96.

[0041] From the viewpoint of obtaining desired optical properties, acetylcelluloses with different degrees of substitution may be mixed and used as diacetylcellulose. The mixing ratio of acetylcelluloses with different degrees of substitution is not particularly limited.

[0042] (1-2-2) From the viewpoint of the molecular weight and mechanical strength of diacetylcellulose, the number average molecular weight (Mn) of diacetylcellulose is 2 × 10⁻⁶ ４ ~3 x 10５ It is preferable that it be within the range of 2 × 10 ４ ~1.2 x 10 ５ It is even more preferable that it be within the range of 4 × 10 ４ ~8 x 10 ４ It is particularly preferable that it be within the range.

[0043] From the standpoint of mechanical strength, the weight-average molecular weight (Mw) of diacetylcellulose is 2 × 10⁻⁶. ４ ~1 x 10 ６ It is preferable that it be within the range of 2 × 10 ４ ~1.2 x 10 ５ It is even more preferable that it be within the range of 4 × 10 ４ ~8 x 10 ４ It is particularly preferable that the molecular weight be within this range. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of acetylcellulose can be determined by measuring them using gel permeation chromatography under the following conditions.

[0044] <Gel Permeation Chromatography> Solvent: Methylene chloride Column: Three Shodex K806, K805, and K803G columns (all manufactured by Showa Denko) connected together were used. Column temperature: 25°C Sample concentration: 0.1% by mass Detector: RI Model 504 (manufactured by GL Sciences) Pump: L6000 (manufactured by Hitachi, Ltd.) Flow rate: 1.0 mL / min Calibration curve: A calibration curve was used with 13 samples of standard polystyrene STK (manufactured by Tosoh Corporation) in the range of Mw = 500 to 2,800,000. It is preferable to use the 13 samples at approximately equal intervals.

[0045] (1-2-3) Production of diacetylcellulose Diacetylcellulose can be synthesized by known methods.

[0046] The raw material cellulose for diacetylcellulose is not particularly limited, and examples include cotton linters, wood pulp, and kenaf. The raw material cellulose, acetic acid, acetic anhydride, and a catalyst (such as sulfuric acid) are mixed to esterify the cellulose. The reaction is continued until a triester of cellulose is formed. In the triester, all three hydrogen atoms of the hydroxyl groups in one glucose unit are replaced by acetyl groups.

[0047] Next, diacetylcellulose having the desired degree of acetyl substitution is obtained by hydrolyzing the triester of cellulose. Subsequently, acetylcellulose is finally obtained through processes such as filtration, precipitation, washing with water, dehydration, and drying. Specifically, it can be synthesized by referring to the method described in Japanese Patent Application Publication No. 10-45804.

[0048] Commercially available diacetylcellulose products include "LM80, L20, L30, L40, L50" ​​(manufactured by Daicel Corporation) and "Ca398-3, Ca398-6, Ca398-10, Ca398-30, Ca394-60S" (manufactured by Eastman Chemical Corporation).

[0049] (1-3) Other components The optical film of this embodiment may also contain other components such as plasticizers, ultraviolet absorbers, antioxidants, fine particles, phase difference adjusters, hydrolysis inhibitors, acid scavengers, etc.

[0050] (1-3-1) Plasticizer The optical film of this embodiment may contain, in addition to the nitrogen-containing heterocyclic compound and diacetylcellulose described above, a known plasticizer with a molecular weight of 10,000 or less, to the extent that it does not impair the effect. The plasticizer is not particularly limited, but examples include polycarboxylic acid ester plasticizers, glycolate plasticizers, phthalate ester plasticizers, fatty acid ester plasticizers, and polyhydric alcohol ester plasticizers. One of these may be contained in the optical film, or multiple of these may be contained in the optical film.

[0051] Polyhydric alcohol esters are esters (alcohol esters) of aliphatic polyhydric alcohols with a valency of 2 or more and a monocarboxylic acid, and are preferably aliphatic polyhydric alcohol esters with a valency of 2 to 20. Polyhydric alcohol esters preferably have an aromatic ring or a cycloalkyl ring in their molecule.

[0052] Preferred examples of aliphatic polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, trimethylolpropane, pentaerythritol, trimethylolethane, and xylitol. Among these, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are particularly preferred.

[0053] The monocarboxylic acid is not particularly limited and may be an aliphatic monocarboxylic acid, an alicyclic monocarboxylic acid, or an aromatic monocarboxylic acid. To improve the moisture permeability of the film and reduce volatility, an alicyclic monocarboxylic acid or an aromatic monocarboxylic acid is preferred. The monocarboxylic acid may be a single type or a mixture of two or more types. Furthermore, all of the OH groups contained in the aliphatic polyhydric alcohol may be esterified, or some of the OH groups may be left as they are.

[0054] Aliphatic monocarboxylic acids are preferably fatty acids having a linear or side chain with 1 to 32 carbon atoms. More preferably, the number of carbon atoms in the aliphatic monocarboxylic acid is 1 to 20, and even more preferably 1 to 10. Examples of aliphatic monocarboxylic acids include saturated fatty acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethylhexanoic acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, heptacosanic acid, montanic acid, melissic acid, and laxeric acid; and unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid. In particular, acetic acid, or a mixture of acetic acid and other monocarboxylic acids, is preferred to enhance compatibility with cellulose acetate.

[0055] Examples of alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, and cyclooctanecarboxylic acid.

[0056] Examples of aromatic monocarboxylic acids include benzoic acid; benzoic acid with 1 to 3 alkyl or alkoxy groups introduced to the benzene ring; and aromatic monocarboxylic acids having 2 or more benzene rings, with benzoic acid being preferred. Examples of the alkoxy groups include methoxy groups and ethoxy groups. Examples of benzoic acid with 1 to 3 alkyl or alkoxy groups introduced to the benzene ring include toluic acid. Examples of aromatic monocarboxylic acids having 2 or more benzene rings include biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralinecarboxylic acid.

[0057] Polycarboxylic acid esters are esters of a polycarboxylic acid with a valency of 2 or more, preferably 2 to 20, and an alcohol. The polycarboxylic acid is preferably a 2 to 20 aliphatic polycarboxylic acid, a 3 to 20 aromatic polycarboxylic acid, or a 3 to 20 alicyclic polycarboxylic acid.

[0058] Examples of polycarboxylic acids include trivalent or higher aromatic polycarboxylic acids or their derivatives such as trimellitic acid, trimesic acid, and pyromellitic acid; aliphatic polycarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, and tetrahydrophthalic acid; and oxypolycarboxylic acids such as tartaric acid, tartonic acid, malic acid, and citric acid. Oxypolycarboxylic acids are preferred to suppress volatilization from the film.

[0059] Examples of alcohols include aliphatic saturated alcohols having a straight chain or side chains, aliphatic unsaturated alcohols having a straight chain or side chains, alicyclic alcohols, and aromatic alcohols. The number of carbon atoms in aliphatic saturated alcohols or aliphatic unsaturated alcohols is preferably 1 to 32, more preferably 1 to 20, and even more preferably 1 to 10. Examples of alicyclic alcohols include cyclopentanol and cyclohexanol. Examples of aromatic alcohols include benzyl alcohol and cinnamyl alcohol.

[0060] The molecular weight of the polycarboxylic acid ester is not particularly limited, but it is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. From the viewpoint of suppressing bleed-out, a higher molecular weight of the polycarboxylic acid ester plasticizer is preferable. On the other hand, from the viewpoint of water permeability and compatibility with diacetylcellulose, a lower molecular weight of the polycarboxylic acid ester plasticizer is preferable.

[0061] Examples of polycarboxylic acid esters include triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl trimenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, tributyl trimellitate, and tetrabutyl pyromellitate.

[0062] The polycarboxylic acid ester may also be a phthalate ester. Examples of phthalate esters include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

[0063] Examples of glycolates include alkylphthalylalkyl glycolates. Examples of alkylphthalylalkyl glycolates include methylphthalylmethyl glycolate, ethylphthalylethyl glycolate, propylphthalylpropyl glycolate, butylphthalylbutyl glycolate, octylphthalyloctyl glycolate, methylphthalylethyl glycolate, ethylphthalylmethyl glycolate, ethylphthalylpropyl glycolate, methylphthalylbutyl glycolate, ethylphthalylbutyl glycolate, butylphthalylmethyl glycolate, butylphthalylethyl glycolate, propylphthalylbutyl glycolate, butylphthalylpropyl glycolate, methylphthalyloctyl glycolate, ethylphthalyloctyl glycolate, octylphthalylmethyl glycolate, octylphthalylethyl glycolate, and ethylphthalylethyl glycolate, with ethylphthalylethyl glycolate being preferred.

[0064] Ester-based plasticizers include fatty acid esters, citrate esters, and phosphate esters.

[0065] Examples of fatty acid esters include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate. Examples of citrate esters include acetyltrimethyl citrate, acetyltriethyl citrate, and acetyltributyl citrate. Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, biphenyl diphenyl phosphate, trioctyl phosphate, and tributyl phosphate, with triphenyl phosphate being preferred.

[0066] The plasticizer content is preferably in the range of 1 to 20 parts by mass, and more preferably in the range of 1.5 to 15 parts by mass, per 100 parts by mass of diacetylcellulose. When the plasticizer content is within the above range, the plasticity-imparting effect can be achieved, and the resistance to plasticizer leaching from the optical film is also excellent.

[0067] (1-3-2) UV absorber When the optical film of this embodiment is used as an optical film to be placed on the surface side (viewing side) of a liquid crystal display device, it is preferable to contain a UV absorber. This can improve light resistance. The purpose of the UV absorber is to improve light resistance by absorbing ultraviolet light of 400 nm or less. The UV absorber preferably has a transmittance of 10% or less, more preferably 5% or less, and particularly preferably 2% or less at a wavelength of 370 nm.

[0068] In the optical film of this embodiment, the ultraviolet absorbers that are preferably used are benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and triazine-based ultraviolet absorbers, with benzotriazole-based ultraviolet absorbers and benzophenone-based ultraviolet absorbers being particularly preferred.

[0069] Examples of UV absorbers include 5-chloro-2-(3,5-di-sec-butyl-2-hydroxylphenyl)-2H-benzotriazole, (2-2H-benzotriazole-2-yl)-6-(linear and side-chain dodecyl)-4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, and 2,4-benzyloxybenzophenone. Other examples of UV absorbers include tinubines such as tinubine 109, tinubine 171, tinubine 234, tinubine 326, tinubine 327, tinubine 328, and tinubine 928. All of the above UV absorbers are commercially available products manufactured by BASF Japan and are preferably used. Among these, halogen-free types are preferred.

[0070] In addition, disc-shaped compounds such as compounds having a 1,3,5-triazine ring are also preferably used as ultraviolet absorbers.

[0071] The optical film of this embodiment preferably contains two or more types of ultraviolet absorbers.

[0072] Furthermore, polymer ultraviolet absorbers can also be preferably used as ultraviolet absorbers, and in particular, the polymer-type ultraviolet absorber described in Japanese Patent Publication No. 6-148430 is preferably used.

[0073] One method for adding UV absorbers is to dissolve them in an organic solvent and add them to the dope. Examples of organic solvents include alcohols such as methanol, ethanol, and butanol, as well as methylene chloride, methyl acetate, acetone, and dioxolane. Alternatively, these organic solvents may be mixed and used as a mixed solvent. In addition, the UV absorber may be added directly to the dope composition.

[0074] For inorganic powders that do not dissolve in organic solvents, a dissolver or sand mill may be added to the organic solvent, dispersed, and then added to the dope.

[0075] The optimal amount of UV absorber to use varies depending on the type of UV absorber, the usage conditions, etc. For example, when the dry film thickness of the optical film is 15 to 50 μm, a range of 0.5 to 10% by mass relative to the optical film is preferred, and a range of 0.6 to 4% by mass is more preferred.

[0076] (1-3-3) Antioxidants Antioxidants are also called degradation inhibitors. When liquid crystal display devices are placed in high humidity and high temperature conditions, degradation of the optical film may occur. Antioxidants, when included in the optical film, suppress such degradation of the optical film. For example, antioxidants can delay or prevent the decomposition of the optical film by the amount of halogens in the residual solvent in the optical film or phosphoric acid in phosphoric acid-based plasticizers.

[0077] Hindered phenol compounds are preferably used as such antioxidants. Examples of antioxidants include 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-to Examples include lyazine, 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxyhydrocinnamamide), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, and tris-(3,5-di-t-butyl-4-hydroxybenzyl)-isocyanurate.

[0078] Particularly preferred antioxidants are 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate]. In addition, hydrazine-based metal deactivators such as N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine and phosphorus-based processing stabilizers such as tris(2,4-di-t-butylphenyl)phosphite may be used in combination.

[0079] The amount of antioxidant added is preferably in the range of 0.1 to 10.0 parts by mass, and more preferably in the range of 1 to 5 parts by mass, per 100 parts by mass of diacetylcellulose.

[0080] (1-3-4) Fine particles The optical film of this embodiment may further contain fine particles (matting agent) as needed to enhance the surface slipperiness.

[0081] The fine particles may be inorganic or organic. Examples of inorganic fine particles include silicon dioxide (silica), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Among these, silicon dioxide and zirconium oxide are preferred as inorganic fine particles, with silicon dioxide being even more preferred. By using silicon dioxide as the inorganic fine particle, the increase in haze of the resulting optical film can be reduced. Examples of organic fine particles include fine particles containing silicone resin, fluororesin, acrylic resin, etc. Among these, fine particles containing silicone resin are preferred as organic fine particles, and fine particles containing silicone resin having a three-dimensional network structure are particularly preferred.

[0082] Examples of commercially available silicone resin microparticles include Tospar® 103, 105, 108, 120, 145, 3120, and 240 (all manufactured by Toshiba Silicone Co., Ltd.).

[0083] Examples of inorganic silicon dioxide nanoparticles include Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600, NAX50 (all manufactured by Nippon Aerosil Co., Ltd.), and Seahostar KE-P10, KE-P30, KE-P50, KE-P100 (all manufactured by Nippon Shokubai Co., Ltd.). Among these, Aerosil R972V, NAX50, and Seahostar KE-P30 are particularly preferred. These silicon dioxide nanoparticles make it possible to reduce the coefficient of friction while keeping the turbidity of the resulting optical film low.

[0084] The primary particle size of the fine particles is preferably in the range of 5 to 50 nm, and more preferably in the range of 7 to 20 nm. A larger primary particle size has a greater effect on improving the slipperiness of the resulting optical film, but it tends to reduce transparency. Therefore, the fine particles may be contained in the optical film as secondary aggregates with a particle size in the range of 0.05 to 0.3 μm. The size of the primary particles or their secondary aggregates can be determined by observing them with a transmission electron microscope and taking the average particle size of 100 primary particles or secondary aggregates. Observation of primary particles or secondary aggregates with a transmission electron microscope can be performed at a magnification of 50 to 2,000,000 times.

[0085] The content of fine particles is preferably in the range of 0.05 to 10 parts by mass, and more preferably in the range of 0.1 to 5 parts by mass, per 100 parts by mass of diacetylcellulose.

[0086] (1-3-5) Phase difference adjusting agent The optical film of this embodiment may contain a phase difference adjusting agent in addition to the nitrogen-containing heterocyclic compound and diacetylcellulose described above, to the extent that it does not impair the effect.

[0087] (1-3-6) Hydrolysis inhibitors The optical film of this embodiment may contain hydrolysis inhibitors in addition to the nitrogen-containing heterocyclic compounds and diacetylcellulose described above, to the extent that they do not inhibit the effect.

[0088] (1-3-7) Acid scavengers The optical film of this embodiment may contain an acid scavenger in addition to the nitrogen-containing heterocyclic compound and diacetylcellulose described above, to the extent that it does not impair the effect.

[0089] (1-4) Physical properties of the optical film (thickness) The thickness of the optical film in this embodiment is preferably in the range of 10 to 200 μm. The thickness of the optical film is more preferably in the range of 10 to 100 μm, and particularly preferably in the range of 20 to 60 μm.

[0090] (Width) The width of the optical film in this embodiment is preferably in the range of 1 to 4 m. The width of the optical film in this embodiment is more preferably in the range of 1.4 to 4 m, and particularly preferably in the range of 1.6 to 3 m. The optical film in this embodiment is easier to transport when its width is 4 m or less.

[0091] (Orientation Angle) When the slow axis or fast axis of the optical film of this embodiment is located within the film plane, the angle θ1 is the angle it makes with the film formation direction (longitudinal direction). Preferably, θ1 is in the range of -1 to 1°. More preferably, θ1 is in the range of -0.5 to 0.5°, and particularly preferably, in the range of -0.1 to 0.1°.

[0092] This θ1 can be defined as the orientation angle, and θ1 can be measured using the automatic birefringence meter "KOBRA®-21ADH" (manufactured by Oji Instruments Co., Ltd.). When θ1 is within the above range, high brightness can be obtained in the displayed image. In addition, light leakage can be suppressed or prevented, and colors can be faithfully reproduced in the display device.

[0093] (Moisture Permeability) The moisture permeability of the optical film of this embodiment is 300 to 1800 g / m² at 40°C and 90% RH. ２ - Preferably within a range of 24 hours. The moisture permeability of the optical film of this embodiment is 400 to 1500 g / m². ２ It is even more preferable that the amount be within the range of 24 hours, specifically 40 to 1300 g / m². ２ - It is particularly preferable that the range be within 24 hours. The moisture permeability can be measured in accordance with the method described in JIS Z 0208.

[0094] (Elongation at Break) The elongation at break of the optical film of this embodiment is preferably in the range of 5 to 80%, and more preferably in the range of 10 to 50%.

[0095] (Visible light transmittance) The visible light transmittance of the optical film of this embodiment is preferably 90% or more, and more preferably 93% or more.

[0096] (Phase difference value) By applying a liquid crystal layer to the optical film of this embodiment, a retardation value (phase difference value) over an even wider range can be obtained.

[0097] In this embodiment, the in-plane retardation value (Ro) and the retardation value (Rth) in the thickness direction of the optical film preferably satisfy 0 ≤ Ro and Rth ≤ 70 nm as a polarizing plate protective film. It is even more preferable that 0 ≤ Ro ≤ 30 nm and 0 ≤ Rth ≤ 50 nm are satisfied, and it is particularly preferable that 0 ≤ Ro ≤ 10 nm and 0 ≤ Rth ≤ 30 nm are satisfied.

[0098] The optical film of this embodiment is preferably used as a phase difference film. In that case, it is preferable that 30 ≤ Ro ≤ 100 nm and 70 ≤ Rth ≤ 400 nm are satisfied. It is even more preferable that the optical film of this embodiment satisfies 35 ≤ Ro ≤ 65 nm and 90 ≤ Rth ≤ 180 nm. Furthermore, the range of variation and distribution of Rth is preferably less than ±50%, more preferably less than ±30%, and even more preferably less than ±20%. Moreover, the range of variation and distribution of Rth is even more preferably less than ±15%, even more preferably less than ±10%, even more preferably less than ±5%, and particularly preferably less than ±1%. Most preferably, there is no variation in Rth.

[0099] The retardation values ​​Ro and Rth are calculated using the following formulas.

[0100] Ro = (n ｘ -n ｙ )×d Rth=((n ｘ +n ｙ ) / 2-n ｚ ) × d where d represents the film thickness [nm]. ｘ n represents the maximum refractive index within the plane of the film, and is also called the refractive index in the slow axis direction. ｙ n represents the refractive index in the direction perpendicular to the slow axis within the film plane. ｚ This represents the refractive index of the film in the thickness direction.

[0101] The retardation values ​​Ro and Rth can be measured using an automated birefringence meter. For example, they can be measured at a wavelength of 590 nm under conditions of 23°C and 55% RH using the "KOBRA®-21ADH" (manufactured by Oji Instruments Co., Ltd.).

[0102] (2) Method for manufacturing optical film The optical film of this embodiment may be manufactured by solution casting or by molten casting. A manufacturing method by solution casting will be described below as an example, but the disclosure is not limited thereto.

[0103] The solution casting method comprises the steps of: preparing a dope by dissolving a material such as diacetylcellulose in a solvent; casting the dope onto a wide belt; drying the cast dope as a web; and peeling the web from the wide belt. In this disclosure, "dope" refers to a film material dissolved in a solvent. "Web" refers to a cast film on a wide belt formed by casting the dope onto the wide belt. "Film" refers to a web with an adjusted amount of residual solvent immediately before or after peeling from the wide belt.

[0104] (2-1) Dope preparation step Dope can be prepared by blending diacetylcellulose, nitrogen-containing heterocyclic compounds, and other additives in a solvent (dope preparation step). Diacetylcellulose is the diacetylcellulose contained in the optical film of this embodiment. Nitrogen-containing heterocyclic compounds are nitrogen-containing heterocyclic compounds contained in the optical film of this embodiment. Other additives are other components contained in the optical film of this embodiment.

[0105] The content of nitrogen-containing heterocyclic compounds in the dope is preferably 1 to 20% by mass, and more preferably 3 to 7% by mass, relative to the total dope. By setting the content of nitrogen-containing heterocyclic compounds within this range, it is possible to obtain an optical film that can be molded with low stretch stress and exhibits appropriate phase difference. If the content of nitrogen-containing heterocyclic compounds is less than 1% by mass, the stretch stress will be high, and the phase difference of the resulting optical film may be large. If the content of nitrogen-containing heterocyclic compounds is greater than 20% by mass, the haze of the optical film may be large.

[0106] A higher diacetylcellulose content in the dope is preferable because it reduces the drying load after casting onto a wide belt. However, if the diacetylcellulose content is too high, the load during dope filtration increases, resulting in poor filtration accuracy. From the viewpoint of achieving both of these, the diacetylcellulose content is preferably in the range of 10 to 35% by mass of the total mass of the dope. Furthermore, the diacetylcellulose content is more preferably in the range of 15 to 25% by mass of the total mass of the dope.

[0107] Other additives that may be added to the dope include plasticizers, UV absorbers, antioxidants, fine particles, phase difference adjusters, hydrolysis inhibitors, and acid scavengers. The amount of each additive can be appropriately determined so that the optical film of this embodiment is present in the preferred amounts described above.

[0108] The solvent may be contained as a single type or as two or more types. From the viewpoint of production efficiency, it is preferable that the good solvent and the poor solvent for diacetylcellulose be contained as a mixture. Furthermore, from the viewpoint of the solubility of diacetylcellulose, it is preferable that the good solvent be contained in greater quantities than the poor solvent.

[0109] The mixing ratio of the good solvent to the poor solvent is preferably in the range of 70 to 98% by mass for the good solvent and in the range of 2 to 30% by mass for the poor solvent. Here, "good solvent" refers to a solvent that dissolves diacetylcellulose on its own. "Poor solvent" refers to a solvent that swells acetylcellulose on its own or does not dissolve it at all.

[0110] Suitable solvents are not particularly limited and include, for example, organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Among these, methylene chloride or methyl acetate are preferred as suitable solvents.

[0111] The poor solvent is not particularly limited and includes, for example, methanol, ethanol, n-butanol, cyclohexane, and cyclohexanone. Furthermore, it is preferable that the dope contains water in the range of 0.01 to 2% by mass.

[0112] The solvent used to dissolve diacetylcellulose may be recovered from the film after drying the web (as described later) and reused. The recovered solvent may contain trace amounts of additives such as plasticizers, UV absorbers, polymers, and monomer components. Even if these additives are present, the recovered solvent can preferably be reused. If necessary, the recovered solvent may be purified.

[0113] The dissolution of diacetylcellulose can be carried out using known methods. By combining heating and pressurization, the solvent can be heated above its boiling point at atmospheric pressure. It is preferable to dissolve the acetylcellulose by stirring while heating the solvent at a temperature higher than the boiling point of the solvent at atmospheric pressure, and at a temperature at which the solvent does not boil under pressurization. This prevents the formation of gels or lumpy undissolved material called "mamako". Alternatively, the acetylcellulose may be mixed with a poor solvent to wet or swell it, and then dissolved by adding a better solvent.

[0114] Pressurization may be carried out by injecting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent through heating. Heating is preferably done from an external source, and for example, using a jacket-type container is preferable as it allows for easy temperature control.

[0115] The heating temperature of the solvent is preferably in the range of 45 to 120°C, more preferably in the range of 60 to 110°C, and even more preferably in the range of 70 to 105°C. The pressure is adjusted so that the solvent does not boil at the set temperature. By keeping the heating temperature within the above range, diacetylcellulose can be sufficiently dissolved while keeping the degree of pressurization low, thereby improving productivity.

[0116] Diacetylcellulose may be dissolved using a cooling method. By using the cooling method, diacetylcellulose can be dissolved in a solvent such as methyl acetate.

[0117] A diacetylcellulose solution, obtained by dissolving diacetylcellulose in a solvent, is filtered using a suitable filter material such as filter paper. The absolute filtration accuracy of the filter material is preferably 0.008 mm or less. More preferably, the absolute filtration accuracy of the filter material is in the range of 0.001 to 0.008 mm, and particularly preferably in the range of 0.003 to 0.006 mm. An absolute filtration accuracy of 0.008 mm or less allows for sufficient removal of insoluble matter. Furthermore, an absolute filtration accuracy of 0.001 mm or more helps to suppress clogging of the filter material.

[0118] The material of the filter media is not particularly limited, and known filter media can be used. From the viewpoint of preventing fiber shedding, for example, plastic filter media such as polypropylene and Teflon (registered trademark), or metal filter media such as stainless steel are recommended.

[0119] It is preferable to remove or reduce impurities, particularly bright spot foreign matter, contained in the raw material diacetylcellulose by filtration. "Bright spot foreign matter" refers to foreign matter produced by the following operation. Specifically, two polarizing plates are placed in a crossed nicol state, and a diacetylcellulose film or the like is placed between them. When light is shone from the side of one polarizing plate and observed from the side of the other polarizing plate, the bright spot foreign matter refers to the point (foreign matter) that is visible when light leaks from the opposite side. The number of bright spots with a diameter of 0.01 mm or more is 200 per cm. ２ Preferably, the following: 100 pieces / cm ２ It is even more preferable that the following rate is 50 pieces / m ２The following is particularly preferable: 10 pieces / cm ２ The following is most preferable. Furthermore, it is preferable to have fewer bright spots with a diameter of 0.01 mm or less.

[0120] The dope can be filtered using known methods. It is preferable to filter the dope while heating it at a temperature higher than the boiling point of the solvent under normal pressure, but at a temperature at which the solvent does not boil under pressure. This reduces the increase in the difference in filtration pressure (differential pressure) before and after filtration.

[0121] The dope heating temperature is preferably in the range of 45 to 120°C, more preferably in the range of 45 to 70°C, and particularly preferably in the range of 45 to 55°C. A low filtration pressure is preferable. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and particularly preferably 1.0 MPa or less.

[0122] (2-2) Dope casting process: The prepared dope is passed through a liquid delivery pump and delivered to a pressure die. The dope is then cast from the slits of the pressure die to the casting positions on the belt (dope casting process).

[0123] The die is preferably a pressure die, as it allows for adjustment of the slit shape in the die's mouthpiece and facilitates uniform film thickness. Examples of pressure dies include coat hanger dies and T-dies. From the viewpoint of increasing the film formation speed, two or more pressure dies may be provided on the belt, and the dope amount may be divided and laminated.

[0124] The width of the casting is preferably in the range of 1 to 4 m, more preferably in the range of 1.3 to 3 m, and particularly preferably in the range of 1.5 to 2.8 m, depending on the width of the belt.

[0125] In the casting process, the surface temperature of the belt is preferably within the range of -50°C or higher and below the boiling point of the solvent. Increasing the surface temperature can speed up the drying rate of the cast film (web). In addition, by not raising the surface temperature too high, foaming and deterioration of the flatness of the web can be suppressed.

[0126] The surface temperature of the belt is preferably in the range of 0 to 55°C, and more preferably in the range of 25 to 50°C. Alternatively, the web may be gelled by cooling the surface of the belt, and the web may be peeled off the drum while it contains a large amount of residual solvent.

[0127] The method for controlling the belt temperature is not particularly limited and includes methods such as blowing hot or cold air onto the belt, or bringing hot water into contact with the underside of the wide belt. The method using hot water is preferable because heat transfer is efficient, resulting in a shorter time until the belt temperature stabilizes. The method using hot air requires using air at a temperature higher than the target wide belt temperature.

[0128] (2-3) Web drying process: The web is dried on a belt to remove the solvent. Then, the amount of residual solvent (solvent) at the time of peeling is adjusted (web drying process).

[0129] Drying methods include blowing air from the web side, transferring heat from the back of the wide belt using a liquid, and transferring heat from both sides using radiant heat. Of these, the method of transferring heat from the back of the belt using a liquid is preferred from the viewpoint of drying efficiency. These drying methods may also be combined.

[0130] It is preferable to dry the cast web on a belt in an atmosphere within the range of 30 to 100°C. To maintain the atmosphere within the range of 30 to 100°C, it is preferable to apply hot air to the top surface of the web or heat it by means of infrared radiation or the like.

[0131] (2-4) Film peeling process: The web is dried to form a film, which is then peeled off at the peeling position (film peeling process).

[0132] The peeling temperature at the peeling position on the belt is preferably in the range of 10 to 40°C, and more preferably in the range of 11 to 30°C. The peeling tension when peeling the film from the belt is, for example, in the range of 196 to 245 N / m. However, if wrinkles are likely to form during peeling, peeling may be done with a peeling tension of 190 N / m or less. The film may also be stretched by applying peeling tension.

[0133] From the viewpoint of flatness, the amount of residual solvent in the web when the web is peeled from the belt is preferably in the range of 10 to 150% by mass. Furthermore, the amount of residual solvent in the web is more preferably in the range of 20 to 40% by mass or 60 to 130% by mass, and particularly preferably in the range of 20 to 30% by mass or 70 to 120% by mass.

[0134] In this disclosure, the amount of residual solvent is defined by the following formula.

[0135] Residual solvent amount (mass%) = {(M - N) / N} × 100, where M is the mass of the web or film sample, and N is the mass of the web or film sample after heating at 115°C for 1 hour. The web or film sample can be taken at any point during or after manufacturing.

[0136] Hereafter, the film that has been peeled from the belt and is not stretched using the tenter method with clips will be referred to as the "pre-stretched film."

[0137] (2-5) Stretching process In the stretching process, the film is stretched after being peeled off the belt. The film before stretching may be subjected to film processing other than stretching using the tenter method with clips before the stretching process.

[0138] There are no particular restrictions on the film processing, and examples include drying the film. In addition, stretching may be performed by methods other than the tenter method. In this case, there are no particular restrictions on the stretching direction, and the film may be stretched in the width direction or the length direction.

[0139] The thickness of the pre-stretching film immediately before the stretching process is preferably in the range of 10 to 200 μm, and more preferably in the range of 20 to 100 μm. Furthermore, the thickness variation in the longitudinal direction (conveying direction) of the pre-stretching film is preferably 0.30 μm or less, more preferably 0.25 μm or less, and particularly preferably 0.20 μm or less. By being within the above range, variations in optical properties such as retardation and orientation angle of the final obtained film can be suppressed.

[0140] The width of the pre-stretching film immediately before the stretching process is not particularly limited, but is preferably in the range of 600 to 2500 mm, and more preferably in the range of 800 to 2200 mm.

[0141] The modulus of elasticity of the film before stretching at the stretching temperature is preferably in the range of 0.01 to 5000 MPa, and more preferably in the range of 0.1 to 500 MPa. A modulus of elasticity of 0.01 MPa or higher allows for a certain degree of shrinkage during and after stretching, resulting in less wrinkle retention. Furthermore, a modulus of elasticity of 5000 MPa or lower suppresses the tension applied during stretching, thereby reducing the load on the tenter.

[0142] The pre-stretched film may be unoriented, or it may have a pre-existing orientation in the longitudinal or transverse direction. Furthermore, if necessary, the widthwise distribution of the orientation of the pre-stretched film may form a bowed shape, or so-called bowing. In other words, by appropriately adjusting the orientation of the pre-stretched film, the orientation of the final obtained film can be adjusted.

[0143] The amount of residual solvent in the pre-stretching film immediately before the stretching process is preferably 20% by mass or less, and more preferably 15% by mass or less. The amount of residual solvent in the pre-stretching film can be adjusted by drying. The drying method is not particularly limited and includes, for example, hot air, infrared rays, heated rolls, microwaves, etc. Among these drying methods, hot air is preferred from the viewpoint of simplicity. The drying temperature is preferably in the range of 40 to 200°C, and is preferably increased in stages.

[0144] Furthermore, stretching other than the tenter method may be performed simultaneously with the drying of the film. An example of stretching other than the tenter method is the roll drying method, in which the unstretched film is alternately passed through a number of rolls arranged vertically, and stretched while drying.

[0145] In the stretching process, the ends in the width direction are clamped with clips and stretched.

[0146] In the tenter method using clips, first, both ends of the film in the width direction are fixed with clips. Then, the clips are spread apart horizontally to stretch the film horizontally. Alternatively, the clips may be spread apart in the direction of travel to stretch the film vertically. Alternatively, the clips may be spread both vertically and horizontally simultaneously to stretch the film in both directions.

[0147] It is preferable to drive the clip during stretching using a linear drive system with an electric motor without a shaft. This allows the clip to move smoothly and reduces losses such as breakage.

[0148] In the stretching process, the film may be stretched biaxially or uniaxially sequentially or simultaneously in the longitudinal direction and in the direction perpendicular to the longitudinal direction within the film surface, i.e., the width direction.

[0149] In the stretching process, the stretching ratio in the width direction is preferably in the range of 1.1 to 2.5 times, and more preferably in the range of 1.1 to 2.0 times. Furthermore, the stretching ratio in the longitudinal direction is preferably in the range of 1.1 to 2.0 times, and more preferably in the range of 1.1 to 1.8 times.

[0150] In the stretching process, the stretching stress in the width direction is preferably in the range of 3 to 15 [MPa], more preferably in the range of 3 to 10 [MPa], and particularly preferably in the range of 3 to 6 [MPa]. If the stretching stress in the width direction is greater than 15 [MPa], the phase difference of the resulting optical film may become too large, or the film may break. By keeping the stretching stress in the width direction within the above range, the resulting optical film can exhibit an appropriate phase difference.

[0151] The stretching temperature is preferably in the range of 120 to 250°C, more preferably in the range of 150 to 240°C, and even more preferably in the range of 180 to 220°C.

[0152] (2-6) Winding Process In the winding process, the film stretched in the stretching process is wound into a roll to obtain the optical film of this embodiment. Thus, the optical film of this embodiment can be obtained as a roll of optical film. The method for winding the film into a roll in the winding process is not particularly limited, and known methods can be used. Also, the winding device is not particularly limited, and known devices can be used.

[0153] (3) Polarizing plates (3-1) Polarizing plates One embodiment of the polarizing plate of this disclosure is a polarizing plate including the optical film of this embodiment. Because the polarizing plate of this embodiment includes the optical film of this embodiment, the phase difference is compensated and the polarizing plate is also excellent in durability under harsh environmental conditions.

[0154] The polarizing plate of this embodiment preferably comprises a polarizer and an optical film of this embodiment disposed on at least one surface of the polarizer. As shown in Figure 1, the polarizing plate 1 of this embodiment has optical films (first optical film 2, second optical film 5) attached to both surfaces of the polarizer 4 via an ultraviolet-curing adhesive. In Figure 1, the layer of cured product of the ultraviolet-curing adhesive is omitted. Figure 1 is a schematic cross-sectional view illustrating one embodiment of the polarizing plate of this disclosure.

[0155] (3-2) Method for Manufacturing Polarizing Plates The method for manufacturing polarizing plates according to this embodiment is as follows. First, in the pretreatment step, the optical film and polarizer are pretreated, and then in the coating step, an ultraviolet-curable adhesive is applied. Next, in the bonding step, the optical film and polarizer are bonded together via the ultraviolet-curable adhesive. Then, in the curing step, the ultraviolet-curable adhesive is cured.

[0156] (3-2-1) Pretreatment Process In the pretreatment process, an easy-adhesion treatment is applied to the bonding surface between the optical film and the polarizer. Examples of easy-adhesion treatments include corona treatment and plasma treatment.

[0157] (3-2-2) Coating Process In the coating process, the UV-curable adhesive is applied to at least one of the bonding surfaces between the optical film and the polarizer. When the UV-curable adhesive is applied directly to the surface of the optical film or the polarizer, the coating method is not limited. Examples of coating methods include doctor blades, wire bars, die coaters, comma coaters, gravure coaters, etc., and various wet coating methods can be used. Alternatively, after applying the UV-curable adhesive between the optical film and the polarizer, pressure may be applied with a roller or the like to evenly spread the UV-curable adhesive.

[0158] (3-2-3) Lamination Process In the lamination process, if an ultraviolet-curing adhesive is applied to the surface of the polarizer in the coating process described above, the optical film is placed on top of the ultraviolet-curing adhesive. If an ultraviolet-curing adhesive is applied to the surface of the optical film, the polarizer is placed on top of the ultraviolet-curing adhesive.

[0159] When a UV-curing adhesive is cast between an optical film and a polarizer, the optical film and polarizer are superimposed in that state. Typically, in this state, pressure is applied by sandwiching them from both sides of the optical film using pressure rollers or the like. Examples of materials for the pressure rollers include metal and rubber. The pressure rollers placed on both sides may be made of the same material or different materials.

[0160] (3-2-4) Curing Process In the curing process, ultraviolet light is irradiated onto the applied ultraviolet-curable adhesive. The ultraviolet-curable adhesive is then cured, and the optical film and polarizer that are superimposed via the ultraviolet-curable adhesive are bonded together. In the polarizing plate of this embodiment, a light-transmitting optical film is superimposed on both sides of the polarizer via an ultraviolet-curable adhesive. In this state, it is preferable to irradiate with ultraviolet light to cure the ultraviolet-curable adhesive on both sides simultaneously.

[0161] The ultraviolet irradiation conditions are not particularly limited, as long as they are suitable for curing UV-curing adhesives. The ultraviolet irradiation dose should be 50 to 1500 mJ / cm² in terms of cumulative light intensity. ２ Preferably, it is within the range of 100 to 500 mJ / cm². ２It is more preferable that the range is within this range. In the polarizing plate of this embodiment, it is preferable from the viewpoint of improving yield to irradiate ultraviolet light from the second optical film side.

[0162] When manufacturing polarizing plates on a continuous line, the line speed is preferably in the range of 1 to 500 m / min. More preferably, the line speed is in the range of 5 to 300 m / min, and particularly preferably in the range of 10 to 100 m / min. A line speed of 1 m / min or higher ensures productivity. Furthermore, damage to the optical film is suppressed, resulting in a polarizing plate with excellent durability. A line speed of 500 m / min or lower allows for sufficient curing of the UV-curable adhesive. This enables the formation of an adhesive layer with the desired hardness and excellent adhesion. It is preferable to adjust the line speed considering the curing time of the adhesive.

[0163] (4) Liquid Crystal Display Device One embodiment of the liquid crystal display device of this disclosure is a liquid crystal display device including the polarizing plate of this embodiment. Because the liquid crystal display device of this embodiment includes the polarizing plate of this embodiment, even in large sizes (110 inches or more), defects such as color unevenness are less likely to occur, and the liquid crystal display device is also excellent in durability under harsh environmental conditions.

[0164] In this embodiment, it is preferable that the modified plate of this embodiment is attached to at least one side of the liquid crystal layer. The polarizing plate of this embodiment can be used in liquid crystal display devices of various driving methods such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, and OCB. In particular, it is preferable to use it in a VA type liquid crystal display device.

[0165] In this embodiment, it is preferable to use two polarizing plates in the liquid crystal display device: a polarizing plate on the viewing side and a polarizing plate on the backlight (BL) side. The polarizing plates in this embodiment may be used as both polarizing plates or as one polarizing plate.

[0166] The liquid crystal cell used in the liquid crystal display device of this embodiment preferably comprises a liquid crystal layer and a pair of substrates that sandwich the liquid crystal layer. From the viewpoint of making the liquid crystal display device thinner and lighter, the pair of substrates are preferably glass substrates with a thickness in the range of 0.3 to 0.7 mm.

[0167] Figure 2 is a schematic cross-sectional view illustrating an example of the configuration of a liquid crystal display device (100) according to this embodiment, in which polarizing plates (101A and 101B) are arranged on both sides of a liquid crystal cell (101C).

[0168] As shown in Figure 2, a liquid crystal cell (101C) is constructed by sandwiching both sides of a liquid crystal layer (107) between transparent glass substrates (108A and 108B). Polarizing plates (101A and 101B) are placed on the respective surfaces of each glass substrate (108A and 108B) via an adhesive layer (106), thereby constructing a liquid crystal display device (100). In Figure 2, BL indicates the backlight.

[0169] A polarizing plate (101A) is constructed by laminating a first optical film (102A) to one surface of a polarizer (104A) and laminating a second optical film (105A) to the other surface of the polarizer (104A). The first optical film (102A) is disposed on one surface of the polarizer (104A) via an ultraviolet-curing adhesive (103A). The second optical film (105A) is disposed on the other surface of the polarizer (104A) via an ultraviolet-curing adhesive (103B). Furthermore, a polarizing plate (101B) is constructed by laminating a first optical film (102B) to one surface of a polarizer (104B) and laminating a second optical film (105B) to the other surface of the polarizer (104B). The first optical film (102B) is disposed on one side of the polarizer (104B) via an ultraviolet-curable adhesive (103C). The second optical film (105B) is disposed on the other side of the polarizer (104B) via an ultraviolet-curable adhesive (103D).

[0170] The liquid crystal cell (101C) comprises an alignment film, a transparent electrode, and a glass substrate (108A and 108B) on both sides of the liquid crystal material. Examples of materials for the glass substrate include soda-lime glass and silicate glass. Among these, silicate glass is preferred, and more specifically, silica glass or borosilicate glass is more preferred.

[0171] The glass constituting the glass substrate is preferably alkali-free glass that substantially does not contain alkaline components. Specifically, it is preferable that the alkaline component content in the glass substrate is 1000 ppm or less. More preferably, the alkaline component content in the glass substrate is 500 ppm or less, and even more preferably 300 ppm or less. By using alkali-free glass that substantially does not contain alkaline components, soda blowing caused by cation substitution on the optical film surface can be suppressed. This suppresses a decrease in density on the optical film surface and prevents damage to the glass substrate.

[0172] Glass substrates can be manufactured by known methods, such as the float method, down-draw method, and overflow down-draw method. Among these, the overflow down-draw method is preferred because, during molding, the surface of the glass substrate does not come into contact with the molding member, and the surface of the resulting glass substrate is less likely to be scratched.

[0173] The glass substrate may be a commercially available product. Examples of commercially available glass substrates include "AN100" (thickness 500 μm, manufactured by Asahi Glass Co., Ltd.), "EAGLE XG(r) Slim" (thickness 300 μm, 400 μm, etc., manufactured by Corning), and glass substrate (thickness in the range of 100 to 200 μm, manufactured by Nippon Electric Glass Co., Ltd.).

[0174] As shown in Figure 2, the polarizing plates (101A, 101B) and the liquid crystal cell (101C) are bonded together via an adhesive layer (106). The adhesive layer can be formed using double-sided tape, an ultraviolet-curing adhesive, or the like. An example of double-sided tape is the substrate-less tape "MO-3005C" (thickness 25 μm, manufactured by Lintec Corporation). The bonding method is not particularly limited, and known methods can be used.

[0175] The present disclosure will be specifically described below with reference to examples. The present disclosure is not limited to these examples. In the following examples, unless otherwise specified, the operations were carried out at room temperature (25°C). In the following examples, unless otherwise specified, "%" and "parts" mean "mass%" and "parts by mass," respectively.

[0176] 1. Preparation of Optical Film 1 (Example 1) Optical film 1 was prepared according to the following method.

[0177] (1) Preparation of Dope 1 <Fine particle dispersion> The following components were stirred and mixed in a dissolver for 50 minutes, and then dispersed in a manton-golin to obtain a fine particle dispersion. Fine particles "Aerosil (registered trademark) R812" (manufactured by Nippon Aerosil Co., Ltd.) 11 parts by mass Ethanol 89 parts by mass

[0178] <Fine Particle Additive Solution> Diacetylcellulose with a degree of substitution of 2.40 was added to a dissolution tank containing methylene chloride and heated until completely dissolved. This solution was then filtered using "Asaka Filter Paper No. 244" (manufactured by Asaka Filter Paper Co., Ltd.). While thoroughly stirring the filtered diacetylcellulose solution, the above fine particle dispersion was slowly added. The mixture was then dispersed using an attritor. The resulting dispersion was filtered using "Finemet NF" (manufactured by Nippon Seisen Co., Ltd.) to prepare the fine particle additive solution. Methylene chloride: 99.0 parts by mass; Diacetylcellulose: 4.0 parts by mass; Fine particle dispersion: 11.0 parts by mass

[0179] Next, a main dope solution with the following composition was prepared.

[0180] First, methylene chloride and ethanol were added to a pressurized dissolution tank. Diacetylcellulose with a degree of substitution of 2.40 was added to the pressurized dissolution tank containing the solvent while stirring. This was heated and stirred until completely dissolved. Nitrogen-containing heterocyclic compound 1 (compound 1) was further added to the solution as an additive and dissolved. The solution was filtered using "Asaka Filter Paper No. 244" (manufactured by Asaka Filter Paper Co., Ltd.) to prepare the main dope solution. Compound 1 is "compound 1" in the "Examples of compounds represented by general formula 1" above. The pKa of the nitrogen-containing aromatic ring of compound 1 was 14.4. The ClogP of compound 1 was 3.0. When referring to the pKa of the nitrogen-containing aromatic ring of compound 1, it means the acid dissociation constant when the hydrogen atom bonded to the nitrogen atom of the nitrogen-containing aromatic ring of compound 1 dissociates as a hydrogen ion.

[0181] <Composition of main dope solution> Methylene chloride 300.0 parts by mass Ethanol 30.0 parts by mass Diacetylcellulose 100.0 parts by mass Compound 1 5.0 parts by mass

[0182] Dope 1 was prepared by adding 2 parts by mass of fine particle additive solution to 100 parts by mass of the main dope solution and thoroughly mixing it using an in-line mixer (Toray stationary pipe mixer) "Hi-Mixer, SWJ" (manufactured by Toray Engineering Co., Ltd.).

[0183] (2) Formation of the pre-stretched film 1 Next, using a belt casting apparatus, the dope 1 was uniformly cast onto a stainless steel belt. The casting temperature was 22°C, and the width of the cast dope was 2 m. The thickness of the cast film (web) was 305 μm.

[0184] The web on the belt was evaporated until the residual solvent content was less than 100% by mass, and then peeled off the belt under a tension of 160 N / m to obtain a film. The film was dried by evaporating the solvent at 35°C while being transported to obtain pre-stretched film 1.

[0185] (3) Stretching process The pre-stretching film 1 was stretched in a tenter stretcher set to 210°C with a stretching stress of 6.5 MPa in the width-to-width (TD) direction. The stretching ratio in the width-to-width (TD) direction was 1.8 times. At the start of stretching, the residual solvent in the film was 3 to 15% by mass.

[0186] Subsequently, the film was dried in drying zones at 120°C and 140°C while being transported by numerous rollers. Then, the film was slit into 2500 mm widths to obtain optical film 1 with a thickness of 35 μm and a roll length of 3900 m.

[0187] Compound 1 described above was prepared by the following method.

[0188] 16.5 mL (160 mmol) of benzyl alcohol was mixed with 5.60 g (140 mmol) of sodium hydride, and 6.14 g (40.0 mmol) of 4-chloro-1H-pyrazolo[3,4-b]pyridine was added. The mixture was stirred at 100°C for 15 hours. The reaction mixture was cooled to room temperature, and 2 mL of pure water was added dropwise. Pure water and ethyl acetate were added to the mixture and separated, and the organic layer was washed with pure water. The organic layer was dried over magnesium sulfate, and the solvent was removed by distillation under reduced pressure. The resulting crude crystals were washed with ethyl acetate and air-dried at room temperature to obtain 6.94 g of compound 1. The yield was 77 mol% based on 4-chloro-1H-pyrazolo[3,4-b]pyridine. The obtained compound was: １ Compound 1 was confirmed by 1H-NMR spectroscopy. Benzyl alcohol B2378, manufactured by Tokyo Chemical Industry Co., Ltd., was used. 4-chloro-1H-pyrazolo[3,4-b]pyridine OR301233, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., was used.

[0189] 2. Preparation of Optical Films 2 to 16 (Examples 2 to 12, Comparative Examples 1 to 4) Optical films 2 to 16 were obtained in the same manner as optical film 1, except that at least some of the additives, stretching temperature, and stretching stress were changed as shown in Table I. In Table I, compounds 2 to 12 are "compounds 2 to 12" in the "Examples of compounds represented by general formula 1" above. Compounds 13, 14, and 15 are the following compounds.

[0190]

[0191] Compounds 2-5, 7-9, and 11-15 were prepared by conventionally known methods.

[0192] Compound 6 was prepared by the following method.

[0193] 4.32 g (40.0 mmol) of 1,2-diaminobenzene and 2.90 g (50.0 mmol) of propionaldehyde were added to 200 mL of ethanol, and the mixture was stirred at 80°C in air for 12 hours. The reaction mixture was concentrated under reduced pressure. The concentrate was washed with acetone, and the solvent was removed by distillation under reduced pressure. The resulting crude crystals were purified by silica gel chromatography (acetone / heptane) to obtain 5.2 g of compound 6. The yield was 90 mol% based on 1,2-diaminobenzene. The obtained compound was: １ Compound 6 was confirmed by 1H-NMR spectroscopy.

[0194] Compound 10 was prepared by the following method.

[0195] 2.77 g (10.0 mmol) of 2-bromoindole, 1.83 g (15.0 mmol) of phenylboronic acid, and 11.5 g (50.0 mmol) of tripotassium phosphate were mixed with 23.0 mg (0.10 mmol) of palladium(II) acetate, 82.0 mg (0.20 mmol) of SPhos, and 50 mL of toluene. The mixture was stirred at 90°C for 6 hours under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was separated by adding pure water and ethyl ether, and the organic layer was washed with pure water. The organic layer was dried over magnesium sulfate, and the solvent was removed by vacuum distillation. The resulting crude crystals were purified by silica gel chromatography (ethyl acetate / heptane) to obtain 16.3 g of compound 10. The yield was 84 mol% based on 2-bromoindole. The obtained compound was: １ Compound 6 was confirmed by 1H-NMR spectroscopy.

[0196] For the additive compounds 1 to 15, the pKa and ClgP of the nitrogen-containing aromatic rings were determined by the following method.

[0197] (pKa) The pKa of the nitrogen-containing aromatic ring was determined by theoretical calculations based on the structure of the nitrogen-containing aromatic ring. The value of pKa was calculated using formula A, "ΔG(aq) = pKa × RTln10". In formula A, ΔG(aq) is the change in free energy in the following reaction equation R in solution due to proton dissociation. The reaction equation R is "HA(aq) = H ＋ (aq) + A － (aq)" (In reaction equation R, "=" means an equilibrium reaction, HA represents a nitrogen-containing aromatic ring, and H is hydrogen bonded to nitrogen). In calculation formula A, "R" is the gas constant, "T" is the absolute temperature, and "ln10" is the natural logarithm of 10. The value of ΔG is calculated based on density functional theory (DFT) for the nitrogen-containing aromatic ring (HA) and its deprotonated species (A). － The values ​​were obtained by performing structural optimization and free energy (ΔG) calculations for the material. The B3LYP functional was used, and the aug-cc-pVDZ basis set was used. Solvent effects were considered using the solvent model density (SMD). The proton free energy used was the value (26.255 kJ / mol) described in the following literature: Reference: Z. Markovic' et al., Revisiting the solvent enthalpies and free energies of the proton and electron in various solutions, Comput. Theore et. Chem. (2015)

[0198] (ClogP) ClogP was calculated using CHEMDRAW (a registered trademark of LevitySignals Software, Inc.), a commercially available chemical structure drawing software.

[0199] 3. The optical films 1 to 16 obtained were evaluated for their retardation value in the thickness direction (Rth), Rth fluctuation suppression effect, and precipitation properties, as shown below. The results are shown in Table I.

[0200] (1) Thickness retardation value (Rth) Rth was measured using an automated birefringence meter. Specifically, it was measured at a wavelength of 590 nm under conditions of 23°C and 55% RH using "KOBRA®-21ADH" (manufactured by Oji Instruments Co., Ltd.).

[0201] (2) Rth fluctuation suppression effect The Rth fluctuation suppression effect is the effect of suppressing fluctuations in the retardation value (Rth) in the thickness direction of the optical film due to humidity fluctuations. In Table I, this Rth fluctuation suppression effect is referred to as "R value fluctuation". The cause of humidity fluctuation was assumed to be water immersion.

[0202] The retardation value fluctuation due to humidity changes was measured as described below. All of the following operations were performed under conditions of 23°C and 55% relative humidity.

[0203] An optical film was sandwiched between two glass slides, and the Rth was measured using the method described above; this was designated as Rth1. Then, another optical film was immersed in pure water for 24 hours, and the water-moistened optical film was sandwiched between two glass slides, and the Rth was measured; this was designated as Rth2. Care was taken to prevent air bubbles from entering between the glass slides and the film.

[0204] From the obtained Rth1 and Rth2, the change in the retardation value ΔRth of the optical film due to immersion in pure water at 23°C for 24 hours was calculated by applying the absolute value of the difference to the following formula (A).

[0205] Formula (A): ΔRth=|Rth1-Rth2|

[0206] Next, the retardation value fluctuation suppression effect was evaluated as the Rth fluctuation suppression rate (%), which can be calculated using the following formula (B).

[0207] Formula (B): Rth variation suppression rate (%) = ((ΔRth of reference film) - (ΔRth of each sample film)) / (ΔRth of reference film) × 100

[0208] The Rth fluctuation suppression rate was evaluated based on the following criteria. A and B indicate good results, while C and D indicate practical problems. A: Rth fluctuation suppression rate is 70% or higher for both B: Rth fluctuation suppression rate is 50% or higher but less than 70% for both C: Rth fluctuation suppression rate is 20% or higher but less than 50% for both D: Rth fluctuation suppression rate is less than 20% for both

[0209] (3) The precipitation-promoting optical film was left for 1000 hours in a high-temperature, high-humidity atmosphere of 60°C and 90% RH, and the presence or absence of bleed-out (crystal deposition) on the surface of the optical film was visually observed to evaluate its precipitation properties (durability).

[0210] Precipitation was evaluated based on the following criteria. A to C indicate good results, and D indicates a practical problem. A: No bleed-out observed on the polarizer protective film surface. B: Slight partial bleed-out observed on the polarizer protective film surface. C: Slight bleed-out observed across the entire surface of the polarizer protective film. D: Clear bleed-out observed across the entire surface of the polarizer protective film.

[0211]

[0212] From the values ​​of tensile stress in the above examples and comparative examples, it can be seen that the optical film of this disclosure can be molded at low tensile stress. Furthermore, from the values ​​of Rth in the above examples and comparative examples, it can be seen that the optical film of this disclosure has appropriate phase difference expression properties. In addition, from the evaluation results of the retardation value fluctuation suppression effect (R value fluctuation) and precipitation properties in the above examples and comparative examples, it can be seen that the optical film of this disclosure has excellent durability under harsh environmental conditions. Among the nitrogen-containing heterocyclic compounds represented by compounds 1 to 12, indole-based compounds are preferred.

[0213] According to this disclosure, it is possible to provide an optical film that can be molded with low stretch stress, has appropriate phase difference characteristics, and exhibits excellent durability under harsh environmental conditions.

[0214] 1 Polarizing plate 2 First optical film 4 Polarizer 5 Second optical film 100 Liquid crystal display device 101A, 101B Polarizing plate 101C Liquid crystal cell 102A, 102B First optical film 103A, 103B, 103C, 103D UV-curing adhesive layer 104A, 104B Polarizer 105A, 105B Second optical film 106 Adhesive layer 107 Liquid crystal layer 108A, 108B Glass substrate

Claims

1. An optical film containing diacetylcellulose, wherein it contains a nitrogen-containing heterocyclic compound, the nitrogen-containing heterocyclic compound having an aromatic ring containing one to three nitrogen atoms, at least one of the nitrogen atoms in the aromatic ring being bonded to a hydrogen atom, the acid dissociation constant when the hydrogen atom bonded to the nitrogen atom dissociates as a hydrogen ion being 14 or more, and the nitrogen-containing heterocyclic compound being a compound represented by the following general formula 1. (In general formula 1, W １ ~W ７ (One to three of the atoms are nitrogen atoms, and at least one of the nitrogen atoms is bonded to a hydrogen atom, Z represents a hydrogen atom, a hydroxyl group, an alkoxy group, or an aryloxy group, L represents a linking group, and n is 1 or 2) 2. The optical film according to claim 1, wherein the ClogP of the nitrogen-containing heterocyclic compound is 1 to 7.

3. A polarizing plate comprising the optical film described in claim 1.

4. A liquid crystal display device comprising a polarizing plate as described in claim 3.

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