阅读说明：本技术 酯树脂、增塑剂、纤维素酯树脂组合物、光学薄膜和液晶显示装置 (Ester resin, plasticizer, cellulose ester resin composition, optical film, and liquid crystal display device ) 是由 尾崎知代 田尻裕辅 吉村洋志 于 2018-12-06 设计创作，主要内容包括：本发明的目的在于提供可以改善加工成薄膜状时的耐透湿性、且在湿热环境下保存稳定性也优异的、可以适合作为对于纤维素酯树脂的增塑剂使用的酯树脂、包含其的树脂组合物、以及使用该树脂组合物而得到的光学薄膜和包含其的液晶显示装置,提供：酯树脂、包含其的纤维素酯树脂组合物、包含该组合物的光学薄膜和液晶显示装置,所述酯树脂为式B-(A-G)<Sub>n</Sub>-A-B〔B为脂肪族一元醇残基,G为亚烷基二醇残基、氧亚烷基二醇残基或芳基二醇残基,A为亚烷基二羧酸残基(A1)或芳基二羧酸残基(A2),且(A1)与(A2)的总计(A1+A2)中的(A2)的含有率为70～100摩尔％,n为重复数。〕所示的酯树脂,所述酯树脂的数均分子量为350～1000。(The purpose of the present invention is to provide a cellulose ester resin composition which can improve moisture permeation resistance when processed into a film form, has excellent storage stability in a hot and humid environment, and can be suitably used as a cellulose ester resinAn ester resin for a plasticizer, a resin composition containing the ester resin, an optical film obtained by using the resin composition, and a liquid crystal display device containing the optical film, wherein: an ester resin, a cellulose ester resin composition comprising the same, an optical film and a liquid crystal display device comprising the composition, wherein the ester resin is represented by the formula B- (A-G) n -a-B [ B is an aliphatic monohydric alcohol residue, G is an alkylene glycol residue, an oxyalkylene glycol residue, or an aryl glycol residue, a is an alkylene dicarboxylic acid residue (a1) or an aryl dicarboxylic acid residue (a2), and the content of (a2) in the total (a1+ a2) of (a1) and (a2) is 70 to 100 mol%, and n is the number of repetitions. The ester resin has a number average molecular weight of 350 to 1000.)

1. An ester resin characterized by being an ester resin represented by the following general formula (1),

B-(A-G)_n-A-B (1)

in the formula (1), B is an aliphatic monohydric alcohol residue having 4 to 20 carbon atoms, G is an alkylene glycol residue, an oxyalkylene glycol residue or an aryl glycol residue, A is an alkylene dicarboxylic acid residue (A1) or an aryl dicarboxylic acid residue (A2), and the content of the aryl dicarboxylic acid residue (A2) in the total (A1+ A2) of the alkylene dicarboxylic acid residue (A1) and the aryl dicarboxylic acid residue (A2) is 70 to 100 mol%, n is the number of repetitions, G, A in each of the repeating units is optionally the same or different, and a plurality of A, B is optionally the same or different,

the number average molecular weight of the ester resin is 350-1000.

2. The ester resin according to claim 1, wherein B in the general formula (1) is an aliphatic monohydric alcohol residue having 6 to 12 carbon atoms, G is an alkylene glycol residue having 2 to 12 carbon atoms, an oxyalkylene glycol residue having 4 to 12 carbon atoms or an aryl glycol residue having 6 to 18 carbon atoms, the alkylene dicarboxylic acid residue (A1) in A is an alkylene dicarboxylic acid residue having 2 to 12 carbon atoms, the aryl dicarboxylic acid residue (A2) in A is an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and the average value of n is 0.2 to 3.

3. The ester resin according to claim 1 or 2, wherein B in the general formula (1) is a nonanol residue or an isononanol residue, G is 1 or more residues selected from the group consisting of ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 2-butanediol, 1, 3-butanediol, 2-methyl-1, 3-propanediol, and neopentyl glycol, a1 is 1 or more residues selected from the group consisting of succinic acid, adipic acid, and dicarboxycyclohexane, and a2 is 1 or more residues selected from the group consisting of phthalic acid, terephthalic acid, and isophthalic acid.

4. The ester resin according to any one of claims 1 to 3, wherein the content of the aryldicarboxylic acid residue (A2) in the total mole number (A1+ A2) of the alkylenedicarboxylic acid residue (A1) and the aryldicarboxylic acid residue (A2) in A in the general formula (1) is 75 to 100 mole%.

5. The ester resin according to any one of claims 1 to 4, which is a plasticizer for cellulose ester resins.

6. A cellulose ester resin composition characterized by comprising: the ester resin and cellulose ester resin according to any one of claims 1 to 4.

7. An optical film comprising the cellulose ester resin composition according to claim 6.

8. The optical film of claim 7 for polarizer plate protection.

9. A liquid crystal display device characterized by having the optical film according to claim 7 or 8.

Technical Field

The present invention relates to: an ester resin suitable as a plasticizer for a cellulose ester resin, a cellulose ester resin composition containing the same, an optical film obtained using the resin composition, and a liquid crystal display device using the same.

Background

In recent years, the liquid crystal display has been made thinner, and the polarizing plate protective film has been made thinner from 80 μm to 40 to 20 μm. In the protective film for a polarizing plate, triacetyl cellulose resin (hereinafter, TAC) is often used in the past from the viewpoint of easy adhesion to the polarizing plate.

However, TAC has high moisture permeability and easily causes dimensional change due to moisture absorption and hydrolysis under humid and hot conditions, and therefore it is necessary to provide various additives by suppressing moisture absorption with additives (for example, see patent documents 1 and 2).

However, particularly in the case of an ester-based additive, the additive itself is hydrolyzed, and further improvement is required in terms of storage stability of the resin composition or a film formed by molding the resin composition.

Disclosure of Invention

Problems to be solved by the invention

In view of the above circumstances, an object of the present invention is to provide: in particular, an ester resin which can improve moisture permeation resistance when processed into a film form, has excellent storage stability under a humid and hot environment, and can be suitably used as a plasticizer for a cellulose ester resin; a resin composition comprising the same; and an optical film obtained using the resin composition and a liquid crystal display device using the same.

Means for solving the problems

The present inventors have conducted intensive studies and, as a result, have found that: the present inventors have completed the present invention by solving the above problems by using specific raw material components in the ester resin.

Namely, the present invention provides an ester resin represented by the following general formula (1),

B-(A-G)_n-A-B (1)

[ in formula (1), B is an aliphatic monohydric alcohol residue having 4 to 20 carbon atoms, G is an alkylene glycol residue, an oxyalkylene glycol residue or an aryl glycol residue, A is an alkylene dicarboxylic acid residue (A1) or an aryl dicarboxylic acid residue (A2), the content of the aryl dicarboxylic acid residue (A2) in the total (A1+ A2) of the alkylene dicarboxylic acid residue (A1) and the aryl dicarboxylic acid residue (A2) is 70 to 100 mol%, n is the number of repetitions, G, A in each of the repeating units is optionally the same or different, and a plurality of A, B are optionally the same or different. Angle (c)

The number average molecular weight of the ester resin is 350-1000.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, there can be provided: an ester resin which can improve moisture permeation resistance when processed into a film form, has excellent storage stability under a humid and hot environment, and can be suitably used as a plasticizer for a cellulose ester resin; a resin composition comprising the same; and an optical film obtained using the resin composition and a liquid crystal display device using the same.

Detailed Description

The ester resin of the present invention is characterized by being an ester resin represented by the following general formula (1),

B-(A-G)_n-A-B (1)

[ in formula (1), B is an aliphatic monohydric alcohol residue having 4 to 20 carbon atoms, G is an alkylene glycol residue, an oxyalkylene glycol residue or an aryl glycol residue, A is an alkylene dicarboxylic acid residue (A1) or an aryl dicarboxylic acid residue (A2), the content of the aryl dicarboxylic acid residue (A2) in the total (A1+ A2) of the alkylene dicarboxylic acid residue (A1) and the aryl dicarboxylic acid residue (A2) is 70 to 100 mol%, n is the number of repetitions, G, A in each of the repeating units is optionally the same or different, and a plurality of A, B are optionally the same or different. Angle (c)

The number average molecular weight of the ester resin is 350-1000.

In the general formula (1), B is an aliphatic monohydric alcohol residue having 4-20 carbon atoms. Here, the monohydric alcohol residue refers to a group obtained by removing a hydrogen atom from a hydroxyl group. The aliphatic group may have a branched structure or may be linear, and examples thereof include: the residue of 1-butanol, 2-butanol, isobutanol, t-butanol, 1-pentanol, isopentanol, t-pentanol, cyclopentanol, 1-hexanol, cyclohexanol, 1-heptanol, 1-octanol, 2-ethyl-1-hexanol, isononanol, 1-nonanol, t-nonanol, decanol, dodecanol, octadecanol (dodecahexanonol), eicosanol (dodecaoxonol), allyl alcohol, oleyl alcohol, etc. may be a resin formed of the same species as B in the general formula (1), or may be a mixture of different species.

Among them, from the viewpoint of good compatibility with the cellulose ester resin, excellent storage stability as a resin composition, and further excellent storage stability as a film, an aliphatic monohydric alcohol residue having 6 to 12 carbon atoms is preferable, an aliphatic monohydric alcohol residue having 9 to 12 carbon atoms is more preferable, and a nonanol residue or an isononanol residue is particularly preferable.

G in the aforementioned general formula (1) is an alkylene glycol residue, an oxyalkylene glycol residue or an aryl glycol residue. The diol residue is a group obtained by removing a hydrogen atom from a hydroxyl group.

The alkylene glycol residue is preferably an alkylene glycol residue having 2 to 12 carbon atoms from the viewpoint of more easily exhibiting the effect of the present invention, and examples thereof include: ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 2-butanediol, 1, 3-butanediol, 2-methyl-1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol, 2-dimethyl-1, 3-propanediol (neopentyl glycol), 2-diethyl-1, 3-propanediol (3, 3-dimethylolpentane), 2-n-butyl-2-ethyl-1, 3-propanediol (3, 3-dimethylolheptane), 3-methyl-1, 5-pentanediol, 1, 6-hexanediol, 2, 4-trimethyl-1, 3-pentanediol, 2-ethyl-1, 3-hexanediol, 1, 2-hexanediol, 2-methyl-1, 3-pentanediol, 1, 3-butanediol, 1, 2-methyl-1, 3-pentanediol, 2-methyl-1, 3-hexanediol, 2-methyl-1, 3-pentanediol, 2-methyl-, 2-methyl-1, 8-octanediol, 1, 9-nonanediol, 1, 10-decanediol, 1, 12-dodecanediol, and the like, and may be used alone or in combination of 2 or more. Among them, from the viewpoint of an ester resin having more excellent compatibility when mixed with a cellulose ester resin described later, the number of carbon atoms having no branch between OH groups is preferably 3 or less, and among them, residues of ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 2-butanediol, 1, 3-butanediol, 2-methyl-1, 3-propanediol, and neopentyl glycol are preferable, and residues of ethylene glycol and 1, 2-propanediol are more preferable.

The oxyalkylene glycol residue is preferably an oxyalkylene glycol residue having 4 to 12 carbon atoms from the viewpoint of more easily exhibiting the effect of the present invention, and examples thereof include: residues of diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, and the like may be used alone or in combination of 2 or more.

The aryl diol residue is preferably an aryl diol residue having 6 to 18 carbon atoms from the viewpoint of more easily exhibiting the effects of the present invention, and examples thereof include: residues of hydroquinone, resorcinol, bisphenol a, alkylene oxide adducts of bisphenol a, bisphenol F, alkylene oxide adducts of bisphenol F, biphenol, alkylene oxide adducts of biphenol, and the like may be used alone, or 2 or more thereof may be used in combination.

Further, a in the general formula (1) is an alkylene dicarboxylic acid residue (a1) or an aryl dicarboxylic acid residue (a 2). Here, the dicarboxylic acid residue means a group other than-OH in the carboxyl group.

The alkylene dicarboxylic acid residue (a1) is preferably an alkylene dicarboxylic acid residue having 2 to 12 carbon atoms, from the viewpoint of more easily exhibiting the effects of the present invention, and examples thereof include: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, 1, 2-dicarboxycyclohexane, 1, 2-dicarboxycyclohexene and other residues, can be used alone, can also be used in combination of 2 or more. Among them, from the viewpoint of obtaining an optical film having more excellent moisture permeation resistance, the residue of succinic acid, adipic acid, and 1, 2-dicarboxycyclohexane is preferable, and the residue of adipic acid is most preferable.

Examples of the aryldicarboxylic acid residue (a2) include: residues of phthalic acid, terephthalic acid, isophthalic acid, 1, 4-naphthalenedicarboxylic acid, 2, 3-naphthalenedicarboxylic acid, 2, 6-naphthalenedicarboxylic acid, 2, 7-naphthalenedicarboxylic acid, 1, 8-naphthalenedicarboxylic acid and the like may be used alone or in combination of 2 or more. Among them, from the viewpoint of obtaining an optical film having higher strength, the residue of phthalic acid, terephthalic acid, and isophthalic acid is preferable, and the residue of phthalic acid is most preferable.

In order to achieve both moisture permeation resistance and storage stability, which are the effects of the present invention, the content of the aryldicarboxylic acid residue (a2) in the total number of moles (a1+ a2) of the alkylenedicarboxylic acid residue (a1) and the aryldicarboxylic acid residue (a2) in a in the general formula (1) must be 70 to 100 mol%, preferably 75 to 100 mol%, and most preferably 90 to 100 mol%.

In the present invention, the ester resin represented by the above general formula (1) may be a mixture of compounds in which B, G, A are formed of the same compound and n is different from each other in repetition number, or may be a mixture of compounds in which B, G, A and n in the general formula (1) are different from each other.

The GPC measurement in the present invention is performed under the following conditions.

[ GPC measurement conditions ]

Measurement apparatus, high-efficiency GPC apparatus "H L C-8320 GPC", manufactured by Tosoh corporation "

Column "TSKGURDCO L UMNSuperHZ-L" manufactured by Tosoh corporation "+ TSKgelSuperHZM-M" manufactured by Tosoh corporation "+ TSKgelSuperHZ-2000" manufactured by Tosoh corporation "

A detector: RI (differential refractometer)

Data processing: EcoSedcata analysis 1.07, manufactured by Tosoh corporation "

Column temperature: 40 deg.C

Developing solvent: tetrahydrofuran (THF)

Flow rate 0.35m L/min

Measurement of the sample: 7.5mg of the sample was dissolved in 10ml of tetrahydrofuran, and the resulting solution was filtered through a microfilter to obtain a measurement sample.

Sample injection amount: 20 μ l

Standard sample the following monodisperse polystyrene having a known molecular weight was used according to the manual for measurement of "H L C-8320 GPC" described above.

(monodisperse polystyrene)

"A-300" made by Tosoh corporation "

"A-500" made by Tosoh corporation "

"A-1000" made by Tosoh corporation "

"A-2500" made by Tosoh corporation "

"A-5000" manufactured by Tosoh corporation "

"F-1" made by Tosoh corporation "

"F-2" made by Tosoh corporation "

"F-4" made by Tosoh corporation "

"F-10" made by Tosoh corporation "

"F-20" made by Tosoh corporation "

"F-40" made by Tosoh corporation "

"F-80" made by Tosoh corporation "

"F-128" made by Tosoh corporation "

F-288, Tosoh corporation "

From the viewpoint of further exhibiting the effect of the present invention, in the general formula (1), it is preferable that: b is an aliphatic monohydric alcohol residue having 6 to 12 carbon atoms, G is an alkylene glycol residue having 2 to 12 carbon atoms, an oxyalkylene glycol residue having 4 to 12 carbon atoms, or an aryl glycol residue having 6 to 18 carbon atoms, the alkylene dicarboxylic acid residue (A1) in A is an alkylene dicarboxylic acid residue having 2 to 12 carbon atoms, the aryl dicarboxylic acid residue (A2) in A is an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and particularly preferred are: b is a nonanol residue or an isononanol residue, G is a residue of ethylene glycol, 1, 2-propanediol, A1 is an adipic acid residue, A2 is a residue of phthalic acid.

The ester resin of the present invention has a number average molecular weight in the range of 350 to 1000, preferably 400 to 800, from the viewpoint of compatibility and film properties. The average value of the number of repetitions n in the general formula (1) is preferably in the range of 0.2 to 3 from the viewpoint of compatibility and film properties. The average value of the number average molecular weight and n is also a value measured by the aforementioned GPC measurement.

Further, the acid value of the ester resin of the present invention is preferably 5 or less, more preferably 1 or less, from the viewpoint of better compatibility with the cellulose ester resin. From the same viewpoint, the hydroxyl value of the ester resin is preferably 50 or less, more preferably 20 or less.

The ester resin of the present invention can be produced, for example, as follows: if necessary, the raw materials are subjected to an esterification reaction in the presence of an esterification catalyst, for example, at a temperature of 180 to 250 ℃ for 10 to 25 hours. The conditions such as the temperature and time of the esterification reaction are not particularly limited and may be appropriately set. The dicarboxylic acid may be used as a raw material, such as an acid itself, or an esterified product thereof, an acid chloride, or an acid anhydride.

Examples of the esterification catalyst include: titanium catalysts such as tetraisopropyl titanate and tetrabutyl titanate; tin-based catalysts such as dibutyltin oxide; and organic sulfonic acid catalysts such as p-toluenesulfonic acid.

The amount of the esterification catalyst to be used may be suitably set, and is usually preferably in the range of 0.001 to 0.1 part by mass based on 100 parts by mass of the total amount of the raw materials.

The ester resin of the present invention varies depending on the molecular weight thereof, the combination of raw materials, and the like, and is usually in the form of a liquid, a solid, a paste, or the like at ordinary temperature.

More specific examples of the method for producing the ester resin include the following methods: the compound having a carboxyl group at the terminal is obtained by using the above-mentioned alkylene glycol, oxyalkylene glycol or aryl glycol and dicarboxylic acid, and the obtained compound having a carboxyl group at the terminal is reacted with aliphatic monohydric alcohol. Here, the alkylene glycol, oxyalkylene glycol or aryl glycol and the dicarboxylic acid and the monohydric alcohol may be simultaneously charged into the reaction system and reacted, or may be continuously reacted as follows: a compound having a carboxyl group at a terminal is obtained using an alkylene glycol, an oxyalkylene glycol or an aryl glycol and a dicarboxylic acid, and then a monohydric alcohol is further charged into the reaction system.

The ester resin obtained as described above may be used as it is as the ester resin of the present invention, or the content of the n-0 component and the content of the high molecular weight component may be adjusted by a method such as a distillation method using a thin film distillation apparatus, a column adsorption method, or a solvent separation and extraction method.

The ester resin of the present invention obtained by such a method or the like is blended with a cellulose ester resin, whereby the obtained film can be excellent in balance between moisture permeation resistance and storage stability, and can be used as a so-called plasticizer, and particularly can be suitably used as an optical film.

The amount of the ester resin of the present invention to be blended with the cellulose ester resin may be determined depending on the intended performance (moisture permeation resistance, storage stability, transparency, etc.), and is, for example, in the range of 0.1 to 50 parts by mass, preferably in the range of 1 to 30 parts by mass, and particularly preferably in the range of 5 to 20 parts by mass with respect to 100 parts by mass of the cellulose ester resin.

As the aforementioned cellulose ester resin, for example, there can be exemplified: and those obtained by esterifying a part or all of hydroxyl groups of cellulose obtained from cotton linters, wood pulp, kenaf, and the like.

Examples of the cellulose ester resin include cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose nitrate, and when used as a protective film for a polarizing plate, cellulose acetate is preferably used because a film having excellent mechanical properties and transparency can be obtained. These cellulose ester resins may be used alone or in combination of 2 or more.

The cellulose acetate preferably has a polymerization degree of 250 to 400, and an acetylation degree of 54.0 to 62.5 mass%, more preferably 58.0 to 62.5 mass%. When the degree of polymerization and the degree of acetylation of the cellulose acetate are within the above ranges, a film having excellent mechanical properties can be obtained. In the present invention, so-called cellulose triacetate is more preferably used. In the present invention, the acetylation degree refers to a mass ratio of acetic acid generated by saponifying the cellulose acetate to the total amount of the cellulose acetate.

The number average molecular weight of the cellulose acetate is preferably 70000 to 300000, more preferably 80000 to 200000. When the number average molecular weight of the cellulose acetate is in this range, a film having excellent mechanical properties can be easily obtained.

The optical film of the present invention is a cellulose ester resin composition comprising the ester resin of the present invention and a cellulose ester resin, and may be a resin composition containing various other additives as required.

In order to obtain the optical film of the present invention, for example, extrusion molding, cast molding, or the like can be used. Specifically, for example, an unstretched optical film is extruded and molded by using an extruder equipped with a T die, a circular die, or the like. When the optical film of the present invention is obtained by extrusion molding, the resin composition obtained by melt-kneading the ester resin, cellulose ester resin, other additives, and the like may be used, and melt-kneading may be performed at the time of extrusion molding, or extrusion molding may be performed as it is.

Examples of the additives include: other modifiers other than the ester resin of the present invention, thermoplastic resins, ultraviolet absorbers, matting agents, deterioration preventing agents (e.g., antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, etc.), dyes, etc.

As the aforementioned other modifiers, those which do not impair the effects of the present invention can be used: ester resins other than the ester resins defined in the present invention, phosphoric acid esters such as triphenyl phosphate (TPP), tricresyl phosphate, cresyldiphenyl phosphate, etc., phthalic acid esters such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, etc., ethyl isophthaloyl glycolate, butyl phthalimidoyl butyl glycolate, trimethylolpropane tribenzoate, pentaerythritol tetraacetate, acetyl tributyl citrate, etc.

The thermoplastic resin is not particularly limited, and examples thereof include: polyester resins other than the ester resins of the present invention, polyester ether resins, acrylic resins, polyurethane resins, epoxy resins, toluene sulfone amide resins, and the like.

The ultraviolet absorber is not particularly limited, and examples thereof include: oxybenzophenone compounds, benzotriazole compounds, salicylate compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex salt compounds, and the like. The ultraviolet absorber is preferably used in an amount of 0.01 to 2 parts by mass based on 100 parts by mass of the cellulose ester resin.

Examples of the matting agent include: silica, titanium oxide, alumina, calcium carbonate, calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, kaolin, talc, and the like. The matting agent is preferably used in an amount of 0.1 to 0.3 parts by mass based on 100 parts by mass of the cellulose ester resin.

The type, amount and the like of the dye are not particularly limited as long as the dye does not interfere with the object of the present invention.

In addition, the optical film may be obtained by, for example, the following method in addition to the molding method: the cellulose ester resin composition may be obtained by dissolving the cellulose ester resin composition in an organic solvent to obtain a resin solution, casting the obtained resin solution on a metal support, and then distilling off and drying the organic solvent to form the resin solution by a so-called solution casting method (solution casting method).

According to the solution casting method, since the orientation of the cellulose ester resin in the film during the molding can be suppressed, the obtained film can exhibit substantially optical isotropy. The film exhibiting optical isotropy can be used for optical materials such as liquid crystal displays, and is useful as a protective film for polarizing plates. Further, the film obtained by the above method is less likely to have irregularities on the surface thereof and is excellent in surface smoothness.

The foregoing solution casting method generally includes the following steps: a step 1 of dissolving the cellulose ester resin composition in an organic solvent and casting the resulting resin solution on a metal support; a2 nd step of distilling off the organic solvent contained in the resin solution after casting and drying the organic solvent to form a thin film; next, in step 3, the thin film formed on the metal support is peeled off from the metal support, and is heated and dried.

The metal support used in the step 1 may be a metal support in the shape of a ring or a drum, and may be made of stainless steel and mirror-finished on the surface thereof.

In the case of casting the resin solution on the metal support, the resin solution filtered by a filter is preferably used in order to prevent foreign matters from being mixed into the obtained film.

The drying method in the above-mentioned step 2 is not particularly limited, and examples thereof include the following methods: blowing air at a temperature of 30 to 50 ℃ to the upper surface and/or the lower surface of the metal support to evaporate 50 to 80 mass% of the organic solvent contained in the resin solution after casting, thereby forming a thin film on the metal support.

Next, the 3 rd step is a step of: the thin film formed in the step 2 is peeled off from the metal support, and is dried by heating under a temperature condition higher than that in the step 2. The heat drying method is preferably a method of raising the temperature stepwise at a temperature of 100 to 160 ℃ to obtain good dimensional stability. By heating and drying under the temperature condition, the organic solvent remaining in the thin film after the 2 nd step can be substantially completely removed.

In the above-mentioned 1 st to 3 rd steps, the organic solvent may be recovered and reused.

The organic solvent that can be used when the resin composition is mixed and dissolved in an organic solvent is not particularly limited as long as it can dissolve them, and for example, when cellulose acetate is used as the cellulose ester, an organic halogen compound such as methylene chloride, or dioxolane is preferably used as the good solvent.

In addition, when a poor solvent such as methanol, ethanol, 2-propanol, n-butanol, cyclohexane, cyclohexanone is used in combination with the good solvent, it is preferable in terms of improving the production efficiency of the film.

The mixing ratio of the good solvent and the poor solvent is preferably in the range of 75/25 to 95/5 by mass.

The concentration of the cellulose ester resin in the resin solution is preferably 10 to 50 mass%, more preferably 15 to 35 mass%.

In the present invention, for example, the optical film in an unstretched state obtained by the above-described method is uniaxially stretched in the machine direction and in the transverse direction, if necessary, in the machine flow direction, and the stretched optical film can be obtained. In addition, a biaxially stretched film can be obtained by stretching by a sequential biaxial stretching method of roll stretching and tenter stretching, a simultaneous biaxial stretching method of tenter stretching, a biaxial stretching method of tube stretching, or the like. The stretch ratio is preferably 0.1% or more and 1000% or less, more preferably 0.2% or more and 600% or less, and particularly preferably 0.3% or more and 300% or less in at least one direction. By designing in this range, a stretched optical film preferable in view of birefringence, heat resistance, and strength can be obtained.

The optical film of the present invention is excellent in moisture permeation resistance and transparency, and also excellent in storage stability, and therefore, can be used, for example, as an optical film for a liquid crystal display device. Examples of the optical film of the liquid crystal display device include: a protective film for polarizing plates, a retardation film, a reflective film, a viewing angle improving film, an antiglare film, a non-reflective film, an antistatic film, a color filter, and the like, and among them, can be preferably used as a protective film for polarizing plates.

The thickness of the optical film is preferably in the range of 20 to 120 μm, more preferably in the range of 25 to 100 μm, and particularly preferably in the range of 25 to 80 μm. When the optical film is used as a protective film for a polarizing plate, if the film thickness is in the range of 25 to 80 μm, it is preferable to reduce the thickness of a liquid crystal display device, and it is possible to maintain sufficient film strength, Rth stability, moisture permeation resistance, and other excellent performances.

The optical film of the present invention is characterized by having better storage stability than the optical film without the ester resin. It is generally known that hydrolysis of cellulose ester resins is carried out in a hot and humid environment. In order to suppress this, an additive for improving moisture permeability resistance is used, but in ester resins other than the ester resin of the present invention, the ester resin itself may be hydrolyzed, and thus generated carboxylic acid such as acetic acid may promote hydrolysis of the cellulose ester resin. Therefore, the hydrolysis resistance of the ester resin used as an additive is suppressed, and even the storage stability in the resulting cellulose ester film is improved.

Further, the optical film can be adjusted to a desired Rth without bleeding out at high temperature and humidity, and thus can be widely used in various liquid crystal display systems depending on the application.

Examples of the liquid crystal display mode include IPS (In-plane switching), TN (twisted nematic), VA (vertical alignment), OCB (Optically compensated Bend), and the like.

The optical film of the present invention is suitable as an optical material for a polarizing plate protective film used for displays such as liquid crystal displays, plasma displays, organic E L displays, field emission displays, rear projection color TV, retardation films such as 1/4 wave plates, 1/2 wave plates, viewing angle control films, liquid crystal optical compensation films, display front panels, and the like, and the resin composition of the present invention can be used for waveguides, lenses, optical fibers, optical fiber substrates, covering materials, L ED lenses, lens covers, and the like in the fields of optical communication systems, optical exchange systems, and optical measurement systems.