JP6237041B2 - Method for producing retardation film - Google Patents

Description

  The present invention relates to a production method capable of producing a retardation film having a reverse dispersion retardation at low cost, and a liquid crystal display device using the retardation film obtained by this production method.

  In recent years, the demand for liquid crystal displays (LCD) such as mobile devices such as mobile phones, tablet terminals, personal computer monitors, and liquid crystal televisions is increasing. An LCD is a device that displays light by controlling light transmission using the optical rotation of light and the birefringence of liquid crystal, and switching between light and dark. Optical films such as retardation films are used.

The retardation film is a film that exhibits anisotropy of refractive index by a process such as stretching, and has a role of converting the polarization state of the polarization of the LCD. The degree of anisotropy of the refractive index is represented by a retardation value. Retardation (Re) is the product of birefringence Δn and thickness d.
Retardation (Re) = Δn · d
(Here, Δn = Nx−Ny, Nx is the refractive index in the stretching direction and the horizontal direction, and Ny is the refractive index in the stretching direction and the vertical direction.)

  In recent years, LCDs capable of obtaining high-definition images have been demanded. In order to obtain a high-definition image, the wavelength dependence of the retardation produced by the retardation film is important. In particular, there is a demand for a reverse dispersive film having a property of increasing the phase difference as the wavelength becomes longer, among the wavelength dependencies.

  Until now, the film which expresses reverse wavelength dispersibility is manufactured using various resin, such as a polycarbonate resin, an acrylic resin, a cellulose ester resin, as a base resin, for example. For example, a laminate exhibiting reverse dispersion formed by using two or more of the above-mentioned various resin films in a combination with different Abbe numbers and laminating the two or more films while changing the angle of the slow axis A film is disclosed (for example, see Patent Document 1). However, there has been a problem that a slow axis shift occurs when two or more kinds of films are laminated, and as a result, sufficient reverse wavelength dispersion cannot be expressed. In addition, since the films are laminated, there is a problem of high cost.

  In addition, a method has been proposed in which reverse dispersibility is expressed with a single film by using a copolymer polycarbonate of a diol having a fluorene structure in the side chain and a specific aliphatic diol as a base resin of a retardation film ( For example, see Patent Document 2). However, since the diol having a fluorene structure is expensive, the film obtained in Patent Document 2 has a problem of high cost.

  Furthermore, a method has been proposed in which reverse dispersibility is expressed by a single film by using cellulose acetate obtained by mixing three types of cellulose acetates having different total substitution degrees of acyl groups under conditions satisfying the three formulas. (For example, refer to Patent Document 3). However, since it is necessary to mix cellulose acylates having different degrees of substitution so as to satisfy the three formulas, the film obtained in Patent Document 3 also has a problem of high cost. Therefore, an inexpensive reverse dispersion retardation film is required.

Japanese Patent Laid-Open No. 2-120804 JP 2012-260661 A JP 2010-217500 A

  The first problem to be solved by the present invention is to provide a production method capable of producing an inversely dispersive retardation film at low cost. A second problem is to provide a reverse dispersion retardation film. A third problem is to provide a liquid crystal display device having an inexpensive reverse dispersion retardation film obtained by the production method.

  As a result of intensive studies, the inventors have found that a triacetyl cellulose film obtained by pouring an inexpensive triacetyl cellulose resin and a resin solution containing an ester compound having a specific range of hydrophobicity is triacetyl cellulose and an ester compound. Are not completely compatible with each other, a region composed of a triacetyl cellulose resin and a region composed of an ester compound are interspersed, and the triacetyl cellulose film is immersed in a solvent to thereby esterify the triacetyl cellulose film. The compound was removed and the region where the ester compound was present became pores, and the triacetyl cellulose film having the pores could be used as a reverse dispersive retardation film, completing the present invention. It came to do.

That is, the present invention provides a film containing a triacetyl cellulose resin by pouring a resin solution containing a triacetyl cellulose resin (a1) and an ester compound (a2) having an octanol-water partition coefficient (log P value) of 6 to 9. A first step of obtaining A1),
A second step of stretching the film (A1) to obtain a stretched film (A2);
The stretched film (A2) is not dissolved in the triacetylcellulose resin (a1), but is immersed in a solvent (a3) that dissolves the ester compound (a2), and the ester compound (a2) is one from the film (A2). A third step of obtaining a film (A3) from which all or part of the film has been removed is provided, and a method for producing a retardation film is provided.

  Further, the present invention is a retardation film comprising a triacetyl cellulose resin (a1), the retardation in the in-plane direction (Re450 nm) of light having a wavelength of 450 nm and the in-plane direction of light having a wavelength of 550 nm. The retardation film (Re550 nm) ratio [(Re450 nm) / (Re550 nm)] is less than 1 to provide a retardation film.

  The present invention also provides a liquid crystal display device comprising a retardation film obtained by the above production method.

  The present invention also provides a liquid crystal display device comprising the retardation film.

  According to the present invention, an inversely dispersible film can be produced using an inexpensive triacetyl cellulose resin as a raw material and without going through complicated steps such as film lamination. This film can be suitably used as a retardation film incorporated in a liquid crystal display device.

FIG. 1 is an observation photograph of the retardation film (1) obtained in Example 1 at a magnification of 3500 using a scanning electron microscope (SEM).

  The triacetyl cellulose resin (a1) used in the production method of the present invention is a resin obtained by acetylating a cellulose resin such as pulp or linter.

  Cellulose resin is a polysaccharide in which D-glucose, which is a basic unit, is connected in a straight chain with β-1,4 bonds. The glucose unit constituting cellulose has three hydroxyl groups at positions 2, 3, and 6, and these hydroxyl groups can be esterified. The esterification of cellulose can be performed by a known method. For example, cellulose is treated with a strong caustic soda solution and then acylated with an acid anhydride. The degree of substitution of the obtained cellulose acylate is about 3. By hydrolyzing this, a cellulose acylate having the desired degree of substitution can be produced. The type and degree of substitution of the cellulose acylate substituent can be determined by ASTM-D817.

  In general, cellulose acylate resins having different degrees of substitution and cellulose acylate resins having different substituents require a hydrolysis step or a separate esterification step, and are expensive resins.

  The triacetyl cellulose resin (a1) used in the production method of the present invention is an acetylated product of all three hydroxy groups of the glucose unit in the cellulose resin, and is an inexpensive resin that does not require subsequent steps. The degree of substitution of the triacetyl cellulose resin (a1) used in the production method of the present invention is in the range of 2.8 to 3.0, and the film (A1) shape can be favorably maintained in the second step described later. it can.

  In the production method of the present invention, a reverse-dispersible film can be obtained even when the triacetyl cellulose resin (a1), which has conventionally been obtained only with a positive-dispersible film, is used as the base resin. In order to achieve the object of the present invention of providing a film at low cost, it is preferable to use only an inexpensive triacetyl cellulose resin (a1), but other cellulose ester resins are used in combination as long as the effects of the present invention are not impaired. You can also Examples of other cellulose ester resins include cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose nitrate. When using other cellulose ester resins, one type may be used, or two or more types may be used in combination.

  The triacetyl cellulose resin (a1) used in the present invention preferably has a polymerization degree of 250 to 400. If the degree of polymerization is within such a range, a retardation film having excellent mechanical properties can be obtained.

  The number average molecular weight (Mn) of the triacetyl cellulose resin (a1) is preferably in the range of 70,000 to 300,000, and more preferably in the range of 80,000 to 200,000. If (Mn) of the cellulose acetate is within such a range, a retardation film having excellent mechanical properties can be obtained.

  Here, the number average molecular weight (Mn) is a value in terms of polystyrene based on GPC measurement. In addition, the measurement conditions of GPC of a triacetyl cellulose resin are as follows.

[GPC measurement conditions]
Measuring device: “HLC-8220 GPC” manufactured by Tosoh Corporation
Column: Guard column “HHR-H” (6.0 mm ID × 4 cm) manufactured by Tosoh Corporation + “TSK-GEL GMHHR-N” (7.8 mm ID × 30 cm) + Tosoh Corporation manufactured by Tosoh Corporation “TSK-GEL GMHHR-N” (7.8 mm ID × 30 cm) manufactured by Tosoh Corporation “TSK-GEL GMHHR-N” (7.8 mm ID × 30 cm) + “TSK− manufactured by Tosoh Corporation” GEL GMHHR-N "(7.8 mm ID x 30 cm)
Detector: ELSD ("ELSD2000" manufactured by Oltec)
Data processing: “GPC-8020 Model II data analysis version 4.30” manufactured by Tosoh Corporation
Measurement conditions: Column temperature 40 ° C
Developing solvent Methylene chloride
Flow rate 1.0 ml / min Sample: A 1.0 mass% methylene chloride solution in terms of resin solid content filtered through a microfilter (5 μl).
Standard sample: The following monodisperse polystyrene having a known molecular weight was used in accordance with the measurement manual of “GPC-8020 Model II Data Analysis Version 4.30”.

(Monodispersed polystyrene)
“A-500” manufactured by Tosoh Corporation
"A-1000" manufactured by Tosoh Corporation
"A-2500" manufactured by Tosoh Corporation
"A-5000" manufactured by Tosoh Corporation
“F-1” manufactured by Tosoh Corporation
"F-2" manufactured by Tosoh Corporation
“F-4” manufactured by Tosoh Corporation
“F-10” manufactured by Tosoh Corporation
“F-20” manufactured by Tosoh Corporation
“F-40” manufactured by Tosoh Corporation
“F-80” manufactured by Tosoh Corporation
“F-128” manufactured by Tosoh Corporation
“F-288” manufactured by Tosoh Corporation
“F-550” manufactured by Tosoh Corporation

  The ester compound (a2) used in the present invention needs to have an octanol-water partition coefficient (log P value) of 6 to 9. When the log P value is less than 6, the ester compound becomes hydrophilic and compatibility with triacetyl cellulose becomes good. In this case, phase separation does not occur, and voids do not occur after immersion in the solvent, which is not preferable because it is difficult to obtain a film that exhibits reverse dispersibility. If the log P value is larger than 9, the ester compound becomes hydrophobic, the compatibility with the triacetyl cellulose resin (a1) deteriorates, and the transparency is impaired. As a result, it is difficult to obtain a film that can be suitably used as a retardation film. That is not preferable. The ester compound (a2) is more preferably an ester compound having a log P value of 6 to 8 because a reverse dispersive retardation film maintaining transparency can be easily obtained.

  Here, the octanol-water partition coefficient (Log P value) is an index representing the hydrophobicity (easiness to dissolve in lipid) of a chemical substance, and is determined by the flask immersion method described in JIS Z-7260-107 (2000). Can be implemented. Further, the octanol-water partition coefficient (log P value) can be estimated by a computational chemical method or an empirical method instead of the actual measurement.

  As a method for obtaining the LogP value, for example, the Crippen's fragmentation method (“J. Chem. Inf. Comput. Sci.”, 27, p21 (1987)), the Viswanadhan's fragmentation method (“J. Chem. Inf. Comput. Sci. ", 29, p163 (1989)), Broto's fragmentation method (" Eur. J. Med. Chem.-Chim. Theor. ", 19, p71 (1984)), The CLogP method (reference documents Leo, A., Jow, PYC, Silipo, C., Hansch, C., J. Med. Chem., 18, 865 1975) and the like are preferably used. In the present invention, the LogP value was determined according to the above Crippen's fragmentation method.

  Preferred examples of the ester compound (a2) used in the present invention include ester compounds represented by the following general formula (1) and general formula (2).

（式中、Ａは炭素原子数４〜１０のジカルボン酸残基を表し、Ｂは炭素原子数６〜１１のモノアルコール残基を表す。Ｃは炭素原子数２〜９のグリコール残基を表し、Ｄは炭素原子数６〜１２のモノカルボン酸残基を表す。）

(In the formula, A represents a dicarboxylic acid residue having 4 to 10 carbon atoms, B represents a monoalcohol residue having 6 to 11 carbon atoms, and C represents a glycol residue having 2 to 9 carbon atoms. D represents a monocarboxylic acid residue having 6 to 12 carbon atoms.)

  The ester compound represented by the general formula (1) can be obtained, for example, by esterifying a dicarboxylic acid having 4 to 10 carbon atoms and a monoalcohol having 6 to 11 carbon atoms. The ester compound represented by the general formula (2) can be obtained, for example, by esterifying a glycol having 2 to 9 carbon atoms and a monocarboxylic acid having 6 to 12 carbon atoms.

  Examples of the dicarboxylic acid having 4 to 10 carbon atoms include succinic acid, adipic acid, azelaic acid, sebacic acid, and phthalic acid.

  Examples of the monoalcohol having 6 to 11 carbon atoms include hexanol, heptanol, octanol, nonyl alcohol, decyl alcohol, undecanol, 2-ethylhexanol, isononyl alcohol, and isodecyl alcohol.

  Examples of the glycol having 2 to 9 carbon atoms include ethylene glycol, propylene glycol, 1,3-propanediol, neopentyl glycol, 2-methylpropanediol, 3-methylpentanediol, 1,4-butanediol, Examples include 1,6-hexanediol, 1,9-nonanediol, cyclohexanedimethanol, paraxylene glycol and the like.

  Examples of the monocarboxylic acid having 6 to 12 carbon atoms include hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, lauric acid, 2-ethylhexanoic acid, benzoic acid, toluic acid, and tarsia. And rubutylbenzoic acid.

  Among the ester compounds (a2) used in the present invention, the ester compound represented by the general formula (1) is a general-purpose product as a plasticizer for vinyl chloride resin, and is preferable because it is available at low cost. An ester compound having a group and 2-ethylhexanol residue [dioctyl adipate], an ester compound having an adipic acid residue and diisononyl alcohol residue [diisononyl adipate], phthalic acid and 2-ethylhexanol residue The ester compound [phthalic acid (bis-2-ethylhexyl) [dioctyl phthalate]] is more preferable.

  The ester compound represented by the general formula (1) is, for example, the dicarboxylic acid and monoalcohol in the presence of an esterification catalyst as necessary, for example, within a temperature range of 180 to 250 ° C. It can be produced by an esterification reaction for 25 hours. In addition, conditions, such as temperature of esterification reaction and time, are not specifically limited, You may set suitably.

  Moreover, also about the ester compound represented by the said General formula (2), for example, in the presence of an esterification catalyst as needed, for example, within the temperature range of 180-250 degreeC of the said diol and monocarboxylic acid. It can manufacture by making it esterify for 10 to 25 hours. In addition, conditions, such as temperature of esterification reaction and time, are not specifically limited, You may set suitably.

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

  Although the usage-amount of the said esterification catalyst should just be set suitably, it is preferable to use normally in 0.001-0.1 mass part with respect to 100 mass parts of whole quantity of a raw material.

  The number average molecular weight (Mn) of the ester compound (a2) used in the present invention is necessary for the triacetyl cellulose resin (a1) and the ester compound (a2) to be easily phase-separated and to exhibit reverse dispersibility. The range of 300 to 500 is preferable, and the range of 350 to 450 is more preferable.

  Here, the number average molecular weight (Mn) is a value in terms of polystyrene based on GPC measurement. The measurement conditions for GPC of the ester compound are as described above. In the measurement of the number average molecular weight (Mn) of the ester compound (a2), tetrahydrofuran was used as the developing solvent. As a measurement sample, 5 μl of a 1.0% by mass tetrahydrofuran solution filtered in terms of resin solid content was filtered.

  The first step of the present invention is a step of obtaining a film (A1) containing a triacetyl cellulose resin by pouring a resin solution containing the triacetyl cellulose resin (a1) and the ester compound (a2). Specifically, in this step, for example, the cellulose ester resin (a1) and the ester compound (a2) are dissolved in an organic solvent, and the obtained resin solution is cast on a metal support ( I), the step (II) of forming a film by distilling off and drying the organic solvent contained in the cast resin solution, and peeling the film formed on the metal support from the metal support And heating and drying step (III).

  As a usage-amount of the ester compound (a2) used when obtaining a film (A1), 3-20 mass parts with respect to 100 mass parts of triacetyl cellulose resin (a1) expresses reverse wavelength dispersion favorably, And it is preferable from the phase difference film which is excellent in transparency, 5-20 mass parts is more preferable, and 5-15 mass parts is more preferable.

  The resin solution can be obtained, for example, by adding and dissolving the triacetyl cellulose resin (a1) and the ester compound (a2) in an organic solvent. The organic solvent used here is not particularly limited as long as it can dissolve the triacetyl cellulose resin (a1) and the ester compound (a2) (good solvent). Examples of the good solvent include methylene chloride and the like. It is preferable to use an organic halogen compound or dioxolane.

  In addition, it is preferable to use a poor solvent together with the good solvent in order to improve the production efficiency of the film (A1). The poor solvent has an effect of facilitating peeling by swelling triacetyl cellulose to improve the solubility of a good solvent or promoting gelation during drying. As the poor solvent, for example, methanol, ethanol, 2-propanol, n-butanol, cyclohexane, cyclohexanone and the like can be used.

  The mixing ratio when the good solvent and the poor solvent are used in combination is preferably in the range of good solvent / poor solvent = 75/25 to 95/5 mass ratio.

  10-50 mass% is preferable and, as for the density | concentration of the cellulose ester resin (a1) in the said resin solution, 15-35 mass% is more preferable.

  In obtaining the resin solution, various additives can be added to the resin solution together with the triacetyl cellulose resin (a1) and the ester compound (a2).

  Examples of the additive include a modifier, a thermoplastic resin, an ultraviolet absorber, a matting agent, a deterioration preventing agent (for example, an antioxidant, a peroxide decomposing agent, a radical inhibitor, a metal deactivator, an acid Capture agents, etc.) and dyes.

  Examples of the modifier include phosphate esters such as triphenyl phosphate (TPP) and tricresyl phosphate, phthalate esters such as dimethyl phthalate, diethyl phthalate, and dibutyl phthalate, ethyl phthalyl ethyl glycolate, and butyl phthalyl. Examples include butyl glycolate.

  Although it does not specifically limit as said thermoplastic resin, For example, polyester resins other than ester compound (a2) used by this invention, a polyester ether resin, a polyurethane resin, an epoxy resin, toluenesulfonamide resin etc. are mentioned.

  The ultraviolet absorber is not particularly limited, and examples thereof include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. The ultraviolet absorber is preferably in the range of 0.01 to 2 parts by mass with respect to 100 parts by mass of the triacetyl cellulose resin (a1).

  Examples of the matting agent include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, kaolin, and talc. The matting agent is preferably in the range of 0.1 to 0.3 parts by mass with respect to 100 parts by mass of the triacetyl cellulose resin (a1).

  The dye is not particularly limited in terms of type and blending amount as long as the object of the present invention is not impaired.

  Examples of the metal support used in the step (I) include an endless belt-shaped or drum-shaped metal support. For example, it is possible to use a stainless steel mirror-finished surface. it can.

  When casting the resin solution on the metal support, it is preferable to use a resin solution filtered with a filter in order to prevent foreign matters from entering the film obtained.

  Although it does not specifically limit as the drying method of the said process (II), For example, the air of the temperature range of 30-50 degreeC is applied to the said resin solution cast | casted by applying to the upper surface and / or lower surface of the said metal support body. The method of evaporating 50-80 mass% of the organic solvent contained and forming a film on the said metal support body is mentioned.

  Next, the step (III) is a step in which the film formed in the step (II) is peeled off from the metal support and heat-dried under a temperature condition higher than that in the step (II). As the heat drying method, for example, a method in which the temperature is raised stepwise under a temperature condition of 100 to 160 ° C. is preferable because good dimensional stability can be obtained. The organic solvent remaining in the film after the step (II) can be almost completely removed by heating and drying under the temperature condition.

  In the step (I) to step (III), the organic solvent can be recovered and reused.

  The second step of the present invention is a step of stretching the film (A1) obtained in the first step to obtain a stretched film (A2). The stretching operation may be performed in multiple stages, and biaxial stretching is preferably performed in the casting direction and the width direction. Also, when biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise. In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible.

  Simultaneous biaxial stretching includes stretching in one direction and contracting the other tension by relaxing. The preferred draw ratio for simultaneous biaxial stretching is × 1.05 to × 1.5 times in the width direction and × 0.8 to × 1.3 times in the longitudinal direction, particularly × 1.1 to × 1 in the width direction. 0.5 times and preferably in the longitudinal direction x0.8 to x0.99. Particularly preferably, it is x1.1 to x1.4 times in the width direction and x0.9 to x0.99 times in the longitudinal direction.

  Further, the “stretch direction” in the present invention is usually used to mean a direction in which a stretching stress is directly applied when performing a stretching operation, but in the case of being biaxially stretched in multiple stages, In some cases, it is used in the sense of the one having a higher draw ratio (that is, the direction usually serving as the slow axis).

  The stretching operation in the second step is preferably performed under heating conditions because a retardation film having excellent dimensional stability under high temperature and high humidity conditions (for example, 80 ° C. and 90% RH conditions) can be obtained. As heating temperature, 40-220 degreeC is preferable and 100-210 degreeC is more preferable.

  The stretching time in the second step is preferably a short time in order to reduce the dimensional change rate under high-temperature and high-humidity conditions (for example, 80 ° C. and 90% RH conditions). However, the minimum required stretching time range is defined from the viewpoint of film uniformity. Specifically, the range is preferably 1 to 10 seconds, and more preferably 4 to 10 seconds.

  In the third step, the stretched film (A2) obtained in the second step is not dissolved in the triacetyl cellulose resin (a1), but is immersed in the solvent (a3) in which the ester compound (a2) is dissolved, In this step, a film (A3) is obtained by removing a part or all of the ester compound (a2) from the film (A2). Here, the determination of whether or not the solvent corresponds to the solvent (a3) is, for example, 7.2.1 of the 7.2 result determination (Interpretation of Results) of ASTM D3132-84 (Reapproved 1996). It can be performed using the determination method described in ˜7.2.1.3.

  Specifically, whether or not the triacetyl cellulose resin (a1) is dissolved in the solvent is determined by sealing 10 parts by weight of the triacetyl cellulose resin (a1) and 90 parts by weight of the organic solvent to the flask and sealing at 16 ° C. at 25 ° C. The dissolution state after shaking for a period of time was observed, and in the following judgment categories described in 7.2.1.1 to 7.2.1.3 of ASTM D3132-84, 1. 1. “Complete solution” or 2. “Boundary solution”; This can be done by determining which category is “insoluble”.

  Whether or not the ester compound (a2) is dissolved in a solvent is specifically determined by sealing 10 parts by weight of the ester compound (a2) and 90 parts by weight of an organic solvent in a flask and shaking at 25 ° C. for 16 hours. The dissolved state after observing was observed, and in the following judgment categories described in 7.2.1.1 to 7.2.1.3 of ASTM D3132-84, 1. 1. “Complete solution” or 2. “Boundary solution”; This can be done by determining which category is “insoluble”.

1. “Complete Solution”; A single, clear liquid phase with no distinct solid or particulates (A single, clear liquid phase with no distinct solid particles).
2. “Borderline Solution”; a clear or turbid but with distant phase separation without clear phase separation.
3. “Insoluble”; separation into two phases: a liquid containing a separated gel solid phase or a liquid separated into two phases (two phases: two phases with two separate phases or two separate liquids).

  The solvent used in the third step corresponds to “3” in the determination of whether or not the triacetyl cellulose resin (a1) is dissolved in the solvent, and the ester compound (a2) is dissolved in the solvent. In the determination of whether or not, it is a solvent corresponding to the “1”.

  The organic solvent (a3) used in the present invention varies depending on the triacetyl cellulose resin (a1) and the ester compound (a2) to be used, and examples thereof include ketone solvents, ester solvents, nitrogen-containing solvents, glycol solvents, ethers. Examples of such solvents include hydrocarbon solvents, hydrocarbon solvents, and alcohol solvents.

  Examples of the ketone solvent include acetone, methyl ethyl ketone, cyclohexanone, diacetone alcohol, and the like. Examples of the ester solvent include methyl formate, methyl acetate, ethyl acetate, and ethyl lactate. Examples of the nitrogen-containing solvent include acetonitrile, N-methylpyrrolidone, dimethylformamide, and the like. Examples of the glycol solvent include methyl glycol and methyl glycol acetate.

  Examples of the ether solvent include tetrahydrofuran, dioxane, dioxolane and the like. Examples of the hydrocarbon solvent include benzene, cyclohexane, toluene, xylene, methylene chloride, chloroform, tetrachloroethane and the like. Examples of the alcohol solvent include methanol, ethanol, isopropanol, cyclohexanol and the like. Further, dimethyl sulfoxide and propylene carbonate not classified above can also be used.

  Among the solvents (a3) used in the present invention, ketone solvents, ester solvents, nitrogen-containing solvents, ether solvents, hydrocarbon solvents, alcohol solvents are preferable. Among ketone solvents, acetone and methyl ethyl ketone are preferable. Of the ester solvents, ethyl acetate is preferable. Of the nitrogen-containing solvents, acetonitrile is preferable, and among the ether solvents, tetrahydrofuran is preferable. Among the hydrocarbon solvents, benzene, cyclohexane and toluene are preferable, and among the alcohol solvents, methanol, ethanol and isopropanol are preferable.

  Among the solvents (a3) used in the present invention, an alcohol-based solvent is more preferable because it does not dissolve triacetyl cellulose and is excellent in the property of easily removing the ester compound by swelling, and methanol is more preferable.

  The solvent (a3) used in the present invention can easily remove the solvent (a3) from the film (A3) when the organic solvent having a boiling point of 20 ° C to 120 ° C dries the film (A3) described later. The organic solvent having a boiling point of 30 ° C to 120 ° C is more preferable.

  The time for immersing the stretched film (A2) in the solvent (a3) varies depending on the solvent type, temperature, and ester compound type used, but is usually 0.1 to 20 hours, more preferably 2 to 15 hours. . Specifically, when the ester compound (as a2) is dioctyl adipate, methanol is used as the solvent (a3), and the temperature of the methanol is 25 ° C., the immersion time is usually about 8 hours.

  Although the temperature at which the stretched film (A2) is immersed in the solvent (a3) varies depending on the solvent used, the melting point of the solvent is preferably + 5 ° C. or higher and the boiling point is −5 ° C. or lower. In order to shorten the immersion time of the solvent and increase the production time, it is preferable that the temperature of the solvent is high.

  The production method of the present invention is characterized by using a triacetyl cellulose resin (a1) and an ester compound (a2) having an octanol-water partition coefficient (log P value) of 6 to 9. The ester compound (a2) having a log P value within the above range has a moderate compatibility with the triacetyl cellulose resin (a1). The stretched film using the triacetyl cellulose resin (a1) and the ester compound (a2) in a combination having a medium compatibility is obtained from the region of the triacetyl cellulose resin (a1) and the region of the ester compound (a2). Becomes a separated film. By immersing the film thus separated in the solvent (a3) for dissolving the ester compound (a2), the ester compound (a2) is extracted from the film into the solvent (a3), and the ester compound ( The region where a2) exists is a hole. The present inventors presume that since the pores have morphological anisotropy, they contribute to refractive index anisotropy and exhibit reverse dispersion.

  In the present invention, usually, after the third step of obtaining the film (A3), a fourth step of drying the film (A3) is included. The means for drying the film is not particularly limited, and can generally be performed with hot air, infrared rays, heating rolls, microwaves, etc., but it is preferable to use hot air because it is simpler.

  The drying temperature is usually in the range of 40 to 150 ° C. It may be dried at a constant temperature, or the temperature may be increased stepwise. Moreover, when drying, you may carry out under a normal pressure and may carry out under reduced pressure in order to shorten drying time.

  In the production method of the present invention, retardation films having various thicknesses can be produced. The retardation film that can be produced by the production method of the present invention is usually 20 to 200 μm.

  The retardation film of the present invention is a retardation film containing a triacetyl cellulose resin (a1). The retardation film has an in-plane retardation (Re450 nm) in light having a wavelength of 450 nm and in-plane in light having a wavelength of 550 nm. The ratio [(Re450 nm) / (Re550 nm)] to the direction retardation (Re550 nm) is less than 1. The retardation film of the present invention can be preferably produced, for example, by the above-described method for producing a retardation film of the present invention. Among the retardation films of the present invention, those having [(Re450 nm) / (Re550 nm)] of 0.4 to 0.9 are preferable.

  The retardation film obtained by the production method of the present invention and the retardation film of the present invention can be used for various optical applications. For example, it can be used for a polarizer protective film having a retardation function, a 1 / 4λ plate, a 1 / 2λ plate, or the like.

  In addition, the liquid crystal display device of the present invention is characterized by having the retardation film obtained by the production method of the present invention and the retardation film of the present invention. Examples of the liquid crystal display device include a tablet terminal, a personal computer monitor, and a liquid crystal television. By using the retardation film obtained by the production method of the present invention, a liquid crystal display device with little light leakage can be obtained.

  Hereinafter, the present invention will be described more specifically based on examples. Unless otherwise indicated, parts and% in the examples are based on mass.

Synthesis Example 1 [Synthesis of ester compound (a2)]
Into a 1-liter four-necked flask equipped with a thermometer, a stirrer and a reflux condenser, 292 g of adipic acid, 573 g of 2-ethylhexanol and 0.05 g of tetraisopropyl titanate as an esterification catalyst were charged. While stirring, the temperature was raised stepwise until it reached 220 ° C. and reacted for a total of 10 hours. After the reaction, unreacted 2-ethylhexanol was removed under reduced pressure at 200 ° C. to obtain an ester compound (a2-1) that was a room temperature liquid. The acid value of the ester compound (a2-1) was 0.12, the hydroxyl value was 8, and the number average molecular weight was 380), and the log P value of this compound was 6.51.

Synthesis example 2 (same as above)
A four-necked flask with an internal volume of 1 liter equipped with a thermometer, stirrer and reflux condenser was charged with 292 g of adipic acid, 635 g of isononyl alcohol and 0.06 g of tetraisopropyl titanate as an esterification catalyst, and stirred under a nitrogen stream. However, the temperature was raised stepwise until reaching 220 ° C., and the reaction was carried out for a total of 10 hours. After the reaction, the unreacted isononyl alcohol was removed under reduced pressure at 200 ° C. to obtain an ester compound (a2-2) that was a room temperature liquid. The acid value of the ester compound (a2-2) was 0.18, the hydroxyl value was 10, and the number average molecular weight was 410, and the log P value of this compound was 7.2.

Synthesis example 3 (same as above)
A four-necked flask with an internal volume of 1 liter equipped with a thermometer, stirrer and reflux condenser was charged with 296 g of phthalic anhydride, 573 g of 2-ethylhexanol and 0.05 g of tetraisopropyl titanate as an esterification catalyst under a nitrogen stream. The temperature was raised stepwise until the temperature reached 230 ° C. with stirring for a total of 12 hours. After the reaction, unreacted 2-ethylhexanol was removed under reduced pressure at 200 ° C. to obtain an ester compound (a2-3) which was a room temperature liquid. The acid value of the ester compound (a2-3) was 0.18, the hydroxyl value was 10, the number average molecular weight was 400, and the log P value of this compound was 7.46.

Comparative Synthesis Example 1 [Synthesis of Comparative Reference Ester Compound (a′2)]
A 1-liter four-necked flask equipped with a thermometer, stirrer and reflux condenser was charged with 292 g of adipic acid, 356 g of 1-butanol and 0.04 g of tetraisopropyl titanate as an esterification catalyst, and stirred under a nitrogen stream. However, the temperature was raised stepwise until it reached 220 ° C., and the reaction was carried out for a total of 12 hours. After the reaction, unreacted 1-butanol was removed under reduced pressure at 200 ° C. to obtain a comparative ester compound (a′2-1) which was a liquid at room temperature. The acid value of the ester compound for comparison (a′2-1) was 0.18, the hydroxyl value was 10, the number average molecular weight was 265, and the log P value of this compound was 3.21.

Comparative synthesis example 2 (same as above)
In a 1-liter four-necked flask equipped with a thermometer, stirrer and reflux condenser, 236 g of succinic acid, 356 g of 1-butanol and 0.04 g of tetraisopropyl titanate as an esterification catalyst were charged and stirred under a nitrogen stream. However, the temperature was raised stepwise until reaching 220 ° C., and the reaction was carried out for a total of 11 hours. After the reaction, unreacted 1-butanol was removed under reduced pressure at 200 ° C. to obtain a comparative ester compound (a′2-2) which is a liquid at normal temperature. The acid value of the comparative ester compound (a′2-2) was 0.08, the hydroxyl value was 7, the number average molecular weight was 240, and the logP value of this compound was 2.37.

Comparative synthesis example 3 (same as above)
A 4-liter flask with an internal volume of 1 liter equipped with a thermometer, stirrer and reflux condenser was charged with 488 g of benzoic acid, 184 g of propylene glycol and 0.04 g of tetraisopropyl titanate as an esterification catalyst and stirred under a nitrogen stream. However, the temperature was raised stepwise until reaching 230 ° C., and the reaction was carried out for a total of 15 hours. After the reaction, unreacted propylene glycol was removed under reduced pressure at 200 ° C. to obtain a comparative ester compound (a′2-3) which was a normal temperature liquid. The acid value of the ester compound for comparison (a′2-3) was 0.15, the hydroxyl value was 4, the number average molecular weight was 290, and the log P value of this compound was 3.78.

Example 1
To 100 parts of triacetylcellulose (product name LT-35, manufactured by Daicel Chemical Industries) and 10 parts of the ester compound (a2-1), 810 parts of methylene chloride and 90 parts by weight of methanol were added and dissolved to obtain a resin solution. . The resin solution was cast on a glass plate so as to have a thickness of about 1 mm, allowed to stand overnight at room temperature, and then dried at 50 ° C. for 30 minutes and 120 ° C. for 30 minutes to obtain a film having a thickness of 80 μm.

  Next, a stretched film was prepared by uniaxial stretching at 205 ° C. so as to be 1.3 times the initial length with a heat stretching machine (manufactured by Imoto Seisakusho). This stretched film was immersed in methanol adjusted to 25 ° C. for 8 hours. After the immersion, the film was dried at 40 ° C. and 1 torr to obtain a retardation film (1). The determination of the solubility of triacetyl cellulose and the ester compound (a2-1) in methanol is described in ASTM D3132-84 (Reapproved 1996) according to 7.2.1.1 to 7.2.1.3. The cellulose ester was “insoluble” and the ester compound (a2-1) was “complete solution” in the determination category of the determination method.

  The stretched film before being immersed in methanol and the retardation film (1) obtained by the production method of the present invention were evaluated for the birefringence Δn, the degree of reverse dispersion and haze (HAZE) according to the following methods. The evaluation results are shown in Table 1. FIG. 1 shows an observation photograph of the cross section of the retardation film (1) in the stretching direction by a scanning electron microscope (SEM) at 3500 times. From this observation photograph, it can be confirmed that the ester compound (a2-1) is removed from the stretched film with methanol, and pores (Nano Pore) are formed.

<Evaluation method of birefringence Δn>
By measuring the retardation value at 550 nm with a retardation measuring device KOBRA-WR (manufactured by Oji Scientific Instruments), and dividing the obtained retardation value by the thickness of the stretched film and the retardation film (1). The birefringence Δn of the optical film was obtained.

<Method for evaluating degree of inverse dispersion>
In-plane direction retardation (Re450 nm) for light with a wavelength of 450 nm and in-plane direction retardation (Re550 nm) for light with a wavelength of 550 nm are measured with a phase difference measuring device KOBRA-WR (manufactured by Oji Scientific Instruments). [(Re450nm) / (Re550nm)] was obtained. If [(Re450nm) / (Re550nm)] is smaller than 1, it indicates that the film is reversely dispersible.

<Evaluation method of haze>
It measured according to JISK7105 using turbidimeter NDH5000 (Nippon Denshoku Industries Co., Ltd.).

Example 2
To 100 parts of triacetylcellulose (product name LT-35, manufactured by Daicel Chemical Industries) and 10 parts of the ester compound (a2-1), 810 parts of methylene chloride and 90 parts by weight of methanol were added and dissolved to obtain a resin solution. . The resin solution was cast on a glass plate so as to have a thickness of about 1 mm, allowed to stand overnight at room temperature, and then dried at 50 ° C. for 30 minutes and 120 ° C. for 30 minutes to obtain a film having a thickness of 80 μm.

  Next, a stretched film was prepared by uniaxial stretching at 205 ° C. so as to be 1.5 times the initial length with a heat stretching machine (manufactured by Imoto Seisakusho). This stretched film was immersed in methanol adjusted to 25 ° C. for 8 hours. After the immersion, the film was dried at 40 ° C. and 1 torr to obtain a retardation film (2).

  The stretched film before immersion in methanol and the retardation film (2) obtained by the production method of the present invention were evaluated for the birefringence Δn, the degree of reverse dispersibility, and haze (HAZE) according to the following methods. The evaluation results are shown in Table 1.

Example 3
To 100 parts of triacetylcellulose (product name LT-35, manufactured by Daicel Chemical Industries) and 10 parts of the ester compound (a2-2), 810 parts of methylene chloride and 90 parts by weight of methanol were added and dissolved to obtain a resin solution. . The resin solution was cast on a glass plate so as to have a thickness of about 1 mm, allowed to stand overnight at room temperature, and then dried at 50 ° C. for 30 minutes and 120 ° C. for 30 minutes to obtain a film having a thickness of 80 μm.

  Next, a stretched film was prepared by uniaxial stretching at 208 ° C. so as to be 1.5 times the initial length with a heat stretching machine (manufactured by Imoto Seisakusho). This stretched film was immersed in methanol adjusted to 25 ° C. for 8 hours. After the immersion, the film was dried at 40 ° C. and 1 torr to obtain a retardation film (3). In addition, the determination of the solubility of triacetyl cellulose and the ester compound (a2-2) in methanol was determined according to ASTM D3132-84 (Reapproved 1996), 7.2.1.1 to 7.2.1.3. The cellulose ester was “insoluble” and the ester compound (a2-2) was “complete solution” in the determination category of the determination method.

  The stretched film before being immersed in methanol and the retardation film (3) obtained by the production method of the present invention were evaluated for the birefringence Δn, the degree of reverse dispersion and haze (HAZE) according to the following methods. The evaluation results are shown in Table 1.

Example 4
To 100 parts of triacetyl cellulose (product name LT-35, manufactured by Daicel Chemical Industries) and 15 parts of the ester compound (a2-2), 810 parts of methylene chloride and 90 parts by weight of methanol were added and dissolved to obtain a resin solution. . The resin solution was cast on a glass plate so as to have a thickness of about 1 mm, allowed to stand overnight at room temperature, and then dried at 50 ° C. for 30 minutes and 120 ° C. for 30 minutes to obtain a film having a thickness of 80 μm.

  Next, a stretched film was prepared by uniaxial stretching at 217 ° C. so as to be 1.5 times the initial length with a heat stretching machine (manufactured by Imoto Seisakusho). This stretched film was immersed in methanol adjusted to 25 ° C. for 8 hours. After the immersion, the film was dried at 40 ° C. and 1 torr to obtain a retardation film (4).

  The stretched film before being immersed in methanol and the retardation film (4) obtained by the production method of the present invention were evaluated for the birefringence Δn, the degree of reverse dispersion and haze (HAZE) according to the following methods. The evaluation results are shown in Table 1.

Example 5
To 100 parts of triacetylcellulose (product name LT-35, manufactured by Daicel Chemical Industries) and 10 parts of the ester compound (a2-3), 810 parts of methylene chloride and 90 parts by weight of methanol were added and dissolved to obtain a resin solution. . The resin solution was cast on a glass plate so as to have a thickness of about 1 mm, allowed to stand overnight at room temperature, and then dried at 50 ° C. for 30 minutes and 120 ° C. for 30 minutes to obtain a film having a thickness of 80 μm.

  Next, a stretched film was prepared by uniaxial stretching at 203 ° C. so as to be 1.5 times the initial length with a heat stretching machine (manufactured by Imoto Seisakusho). This stretched film was immersed in methanol adjusted to 25 ° C. for 8 hours. After the immersion, the film was dried at 40 ° C. and 1 torr to obtain a retardation film (5). In addition, the determination of the solubility of triacetyl cellulose and the ester compound (a2-3) in methanol was determined according to ASTM D3132-84 (Reapproved 1996), 7.2.1.1 to 7.2.1.3. The cellulose ester was “insoluble” and the ester compound (a2-3) was “complete solution” in the determination category of the determination method.

  The stretched film before being immersed in methanol and the retardation film (5) obtained by the production method of the present invention were evaluated for the birefringence Δn, the degree of reverse dispersion and haze (HAZE) according to the following methods. The evaluation results are shown in Table 1.

Example 6
To 100 parts of triacetyl cellulose (product name LT-35, manufactured by Daicel Chemical Industries) and 15 parts of the ester compound (a2-2), 810 parts of methylene chloride and 90 parts by weight of methanol were added and dissolved to obtain a resin solution. . The resin solution was cast on a glass plate so as to have a thickness of about 1 mm, allowed to stand overnight at room temperature, and then dried at 50 ° C. for 30 minutes and 120 ° C. for 30 minutes to obtain a film having a thickness of 80 μm.

  Next, a stretched film was prepared by uniaxial stretching at 206 ° C. so as to be 1.5 times the initial length with a heat stretching machine (manufactured by Imoto Seisakusho). This stretched film was immersed in methanol adjusted to 25 ° C. for 8 hours. After the immersion, the film was dried at 40 ° C. and 1 torr to obtain a retardation film (6).

  The stretched film before being immersed in methanol and the retardation film (6) obtained by the production method of the present invention were evaluated for the birefringence Δn, the degree of reverse dispersion and haze (HAZE) according to the following methods. The evaluation results are shown in Table 1.

Comparative Example 1
A comparative retardation film (1 ′) was obtained in the same manner as in Example 1 except that the ester compound (a2-1) was not used. The same evaluation as in Example 1 was performed, and the results are shown in Table 2.

Comparative Example 2
A comparative retardation film (2 ′) was obtained in the same manner as in Example 1 except that the comparative ester compound (a′2-1) was used instead of the ester compound (a2-1). The same evaluation as in Example 1 was performed, and the results are shown in Table 2. The determination of the solubility of the comparative ester compound (a′2-1) in methanol was described in ASTM D3132-84 (Reapproved 1996), 7.2.1.1 to 7.2.1.3. As a result of the determination method, the comparative ester compound (a′2-1) was a “complete solution” in the determination category of the determination method.

Comparative Example 3
A comparative retardation film (3 ′) was obtained in the same manner as in Example 1 except that the comparative ester compound (a′2-2) was used instead of the ester compound (a2-1). The same evaluation as in Example 1 was performed, and the results are shown in Table 2. In addition, the determination of the solubility of the ester compound for comparison (a′2-2) in methanol was described in ASTM D3132-84 (Reapproved 1996), 7.2.1.1 to 7.2.1.3. As a result of the determination method, the comparative ester compound (a′2-2) was “complete solution” in the determination category of the determination method.

Comparative Example 4
A comparative retardation film (4 ′) was obtained in the same manner as in Example 1 except that the comparative ester compound (a′2-3) was used instead of the ester compound (a2-1). The same evaluation as in Example 1 was performed, and the results are shown in Table 2. In addition, the determination of the solubility of the ester compound for comparison (a′2-3) in methanol was described in ASTM D3132-84 (Reapproved 1996), 7.2.1.1 to 7.2.1.3. When the determination method was used, the comparative ester compound (a′2-3) was a “complete solution” in the determination category of the determination method.

Comparative Example 5
A comparative retardation film (5 ′) was obtained in the same manner as in Example 1 except that triphenyl phosphate was used instead of the ester compound (a2-1). The same evaluation as in Example 1 was performed, and the results are shown in Table 2. The determination of the solubility of triphenyl phosphate in methanol was carried out using the determination method described in 7.2.1.1 to 7.2.1.3 of ASTM D3132-84 (Reapproved 1996). In the determination category of the determination method, triphenyl phosphate was “complete solution”.

Comparative Example 6
A comparative retardation film (6 ′) is obtained in the same manner as in Example 1 except that diethyl phthalate is used in place of the ester compound (a2-1) and the stretching temperature for film formation is 178 ° C. It was. The same evaluation as in Example 1 was performed, and the results are shown in Table 2. The determination of the solubility of triphenyl phosphate in methanol was carried out using the determination method described in 7.2.1.1 to 7.2.1.3 of ASTM D3132-84 (Reapproved 1996). In the judgment category of the judgment method, diethyl phthalate was “complete solution”.

In Example 1, when the ester compound (a2-1) was used, [Re (450 nm) / Re (550 nm)] of the stretched film before solvent extraction was 1.34, whereas after immersion in the solvent, [Re (450 nm) / Re (550 nm)] is 0.76, which indicates that the retardation film obtained by the production method of the present invention is a film having reverse dispersion. In Example 2 where the draw ratio is increased, the same tendency as in Example 1 is observed.
Moreover, also in Examples 3-6 using the ester compound whose LogP value is between 6-9, the tendency similar to Example 1 is seen, and it turns out that a reverse dispersible film is obtained.

  In Comparative Example 1, the additive was not added, but even after solvent extraction, [Re (450 nm) / Re (550 nm)] was 1.31, and the retardation film having reverse dispersion was not obtained. Comparative Examples 2 to 6 are examples using a comparative control ester compound having a LogP value smaller than 6 or triphenyl phosphate or diethyl phthalate, but did not become a reverse dispersible film even after immersion in a solvent. .

  According to the present invention, a stretched film using a specific ester compound is immersed in a solvent, and the ester compound is extracted into the solvent, so that a retardation having reverse dispersion can be obtained even if an inexpensive triacetyl cellulose resin is used. A film can be obtained and is industrially useful.

Claims (10)

Triacetyl cellulose resin (a1) and the following general formula (1) or general formula (2) having an octanol-water partition coefficient (log P value) of 6 to 9

(In the formula, A represents a dicarboxylic acid residue having 4 to 10 carbon atoms, B represents a monoalcohol residue having 6 to 11 carbon atoms, and C represents a glycol residue having 2 to 9 carbon atoms. D represents a monocarboxylic acid residue having 6 to 12 carbon atoms.)
A first step of obtaining a film (A1) containing a triacetyl cellulose resin by pouring a resin solution containing the ester compound (a2) represented by :
A second step of stretching the film (A1) to obtain a stretched film (A2);
The stretched film (A2) is not dissolved in the triacetylcellulose resin (a1), but is immersed in a solvent (a3) that dissolves the ester compound (a2), and the ester compound (a2) is one from the film (A2). A method for producing a retardation film, comprising a third step of obtaining a film (A3) from which parts or all have been removed.   The method for producing a retardation film according to claim 1, wherein the ester compound (a2) is a compound having an octanol-water partition coefficient (log P value) of 6 to 8.   The method for producing a retardation film according to claim 1, wherein the ester compound (a2) is one or more compounds selected from the group consisting of dioctyl adipate, diisononyl adipate and dioctyl phthalate. The method for producing a retardation film according to any one of claims 1 to 3 , wherein an amount of the ester compound (a2) used is 5 to 20 parts by mass with respect to 100 parts by mass of the triacetyl cellulose resin (a1). . The boiling point of the said solvent (a3) is 20-120 degreeC, The manufacturing method of the phase difference film of any one of Claims 1-4 . The said solvent (a3) is methanol, The manufacturing method of the phase difference film of any one of Claims 1-5 . Furthermore, the manufacturing method of the retardation film of any one of Claims 1-6 including the 4th process of drying a film (A3) after said 3rd process. A retardation film containing a triacetyl cellulose resin (a1), the retardation in the in-plane direction (Re450 nm) for light having a wavelength of 450 nm and the retardation in the in-plane direction for light having a wavelength of 550 nm (Re550 nm). The ratio [(Re450nm) / (Re550nm)] with a ratio of less than 1 is a method for producing a retardation film ,
Triacetyl cellulose resin (a1) and the following general formula (1) or general formula (2) having an octanol-water partition coefficient (log P value) of 6 to 9

(In the formula, A represents a dicarboxylic acid residue having 4 to 10 carbon atoms, B represents a monoalcohol residue having 6 to 11 carbon atoms, and C represents a glycol residue having 2 to 9 carbon atoms. D represents a monocarboxylic acid residue having 6 to 12 carbon atoms.)
A first step of obtaining a film (A1) containing a triacetyl cellulose resin by pouring a resin solution containing the ester compound (a2) represented by:
A second step of stretching the film (A1) to obtain a stretched film (A2);
The stretched film (A2) is not dissolved in the triacetylcellulose resin (a1), but is immersed in a solvent (a3) that dissolves the ester compound (a2), and the ester compound (a2) is one from the film (A2). A method for producing a retardation film, comprising a third step of obtaining a film (A3) from which parts or all have been removed . A film containing a triacetyl cellulose resin (a1) and having pores having morphological anisotropy. Retardation in the in-plane direction with light having a wavelength of 450 nm (Re450 nm) and in-plane direction with light having a wavelength of 550 nm A retardation film having a ratio [(Re450 nm) / (Re550 nm)] to a foundation (Re550 nm) of less than 1. A liquid crystal display device comprising the retardation film according to claim 9 .

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