JP2012108349A - Retardation film, production method of the same, polarizing plate, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retardation film and a method for producing the film, showing appropriate optical performances as a retardation film, having high stability to a saponification process and excellent transparency even when the film is made sufficiently thin to be applicable to a roll-to-panel production method, and to provide a polarizing plate and a liquid crystal display device improved in polarization irregularity preventing property, a viewing angle and display uniformity, by incorporating the retardation film into the polarizing plate or the display device.SOLUTION: The retardation film is produced by successively laminating a core layer containing a specified cellulose ester and a skin layer containing a specified cellulose ester, in an order of the skin layer, the core layer and the skin layer. The film has an in-plane orientation degree Sof 3.3×10or more and an in-plane retardation value Ro exhibiting reverse wavelength dispersibility.

Description

  The present invention relates to a retardation film, a production method thereof, a polarizing plate, and a liquid crystal display device.

  Liquid crystal display devices are widely used in monitors for personal computers and portable devices, and for television applications because of their various advantages, such as low voltage and low power consumption, enabling miniaturization and thinning. In particular, television-use liquid crystal display devices that are expected to be viewed from various angles on a large screen have strict requirements for viewing angle dependency, and recently, the performance requirements for liquid crystal display devices for monitor use are also increasing. Therefore, various modes in which the viewing angle dependency is reduced by devising the alignment state of the liquid crystal in the liquid crystal cell have been proposed. For example, IPS (In-Plane Switching) mode, OCB (Optically Compensatory Bend) mode, VA Various studies have been made on liquid crystal display devices such as (Vertically Aligned) mode.

  However, even in these liquid crystal display devices, the viewing angle characteristics cannot be said to be sufficient, and further improvement is required. Therefore, in order to further improve the viewing angle characteristics, the liquid crystal display device is a liquid crystal cell, A retardation film (also referred to as a “retardation plate”) for improving viewing angle characteristics and a polarizing plate are used.

  The retardation film is used for eliminating image coloring or expanding the viewing angle, and a film provided with birefringence by stretching a resin film is attached to a polarizing plate, etc. A technique for providing birefringence as a retardation layer by providing a liquid crystal layer in which liquid crystal molecules are aligned in an arbitrary direction on a protective film for a polarizing plate is known.

  However, these techniques require that a retardation film and a retardation layer be provided separately from the protective film for a polarizing plate, and there is a problem that the manufacturing method of the polarizing plate becomes complicated and costs increase.

  On the other hand, it is possible to produce a polarizing plate capable of improving viewing angle characteristics with a simple configuration by imparting a function as a retardation film to a cellulose ester film widely used as a protective film for a polarizing plate. A retardation film has been proposed (see, for example, Patent Document 1).

  Cellulose ester film is rich in moisture permeability compared to other polymer films, and has high adhesiveness with polarizers of polarizing plates in which PVA having high hydrophilicity is generally used, and has high optical isotropy. Therefore, since it is generally used as a protective film for polarizing plates used in various liquid crystal display devices, by adding a function as a retardation film to this, it has a simple configuration without increasing the number of parts. Visibility can be improved.

  Patent Document 1 describes a retardation film in which a desired retardation value is given by adding a retardation increasing agent to cellulose triacetate.

  On the other hand, it is preferable that the wavelength dispersion of the in-plane retardation (retardation) Ro of the retardation film exhibits a so-called reverse dispersion property that the wavelength becomes larger as the wavelength becomes longer in the visible light region. That is, it is preferable that Ro (450) <Ro (550) <Ro (630) is satisfied.

  The reason is that if the Ro of the retardation layer is inverse wavelength dispersive, the optical wavelength is optimized at the center wavelength of about 550 nm in the visible light region, and there is a tendency to be optimized over the entire visible light region. is there. Therefore, it is preferable that the retardation layer exhibits reverse wavelength dispersion because not only light leakage occurring in the oblique direction in the black state can be reduced, but also color shift occurring in the oblique direction can be reduced.

  However, when a retardation increasing agent is used to impart a function as a retardation film to the cellulose ester film as in Patent Document 1, it is obtained by adding a retardation increasing agent. Since the retardation value in the in-plane direction shows forward wavelength dispersion (R value is smaller for longer wavelengths) or flat wavelength dispersion (R value is constant regardless of wavelength), improvement is required. It is said.

  In the case of producing a retardation film by stretching a cellulose ester film, it is known that the in-plane retardation (retardation) value Ro derived from the cellulose ester itself exhibits reverse wavelength dispersion. Therefore, in order to make the retardation value Ro in the in-plane direction in the retardation film have reverse wavelength dispersion, the in-plane retardation value Ro derived from the cellulose ester itself in the retardation film is It is possible to increase the ratio.

  Cellulose esters are known to increase intrinsic birefringence (birefringence developability by stretching treatment) by lowering the degree of acyl group substitution, and phase difference is obtained by stretching treatment using cellulose esters having reduced substitution degree. By producing a film, it is possible to impart reverse wavelength dispersion to the retardation value Ro in the in-plane direction of the retardation film.

  On the other hand, in order to further simplify the manufacturing process of a liquid crystal display device in recent years, it is called a roll-to-panel in which a long polarizing plate wound in a roll shape is directly bonded to a liquid crystal cell to produce a liquid crystal panel. Manufacturing technology is under consideration. In order to make the polarizing plate into a roll shape, further thinning (for example, 35 μm or less) is required, and the retardation film that is a component of the polarizing plate needs to be further thinned. In order to obtain a retardation (retardation) value Rt in the thickness direction necessary for compensation, it is necessary to further increase the retardation development property (plane orientation degree) per thickness. As described above, in the case where the surface light distribution is increased by using a phase difference (retardation) increasing agent as described in Patent Document 1, the phase difference (retardation) value in the in-plane direction is inevitably increased. Since the reverse wavelength dispersibility is impaired, it is necessary to further reduce the acyl group substitution degree of the cellulose ester (for example, the acyl group substitution degree of 2.4 or less) to increase the retardation development.

  However, when the acyl group substitution degree of the cellulose ester is 2.4 or less, another problem occurs. Usually, when bonding a cellulose-ester film to a polarizer, in order to improve the adhesiveness, the cellulose-ester film is processed with the alkaline solution (it is called "saponification process"). However, since the cellulose ester film having a very low degree of acyl group substitution has high solubility in an alkaline solution, there arises a problem that the retardation (retardation) value varies due to elution or the flatness of the film is impaired.

  For these problems, low retardation cellulose ester with high retardation is used for the inner layer (core layer) of the retardation film, and the outer layer (skin layer) is resistant to alkaline solution. The application of a laminated retardation film provided with a high-substitution cellulose ester film was studied. It is known that such a laminated retardation film in which cellulose esters having different degrees of substitution are laminated is obtained by a method such as a co-casting method (see, for example, Patent Document 2).

  By combining such techniques, it was considered that a retardation film having high stability to saponification treatment could be obtained while having high retardation development as a whole retardation film.

  However, there is a limit to increase the retardation in the material surface when the retardation development per thickness is further increased without impairing thin film properties as the above-mentioned laminated retardation film, and the production process It was necessary to increase the retardation (retardation) expression. Specifically, a method for increasing the draw ratio can be mentioned.

  However, using the above-mentioned method, high-magnification stretching is performed with a laminated retardation film made of triacetyl cellulose (TAC) / diacetyl cellulose (DAC) / triacetyl cellulose (TAC), and saponification is performed with the produced laminated retardation film. When the treatment was performed to produce a polarizing plate and used in a liquid crystal display device, uneven polarization occurred.

  As a result of careful examination of this problem, the present inventors have found that the cause of polarization unevenness is caused by the occurrence of craze in the skin layer (TAC), not the core layer occupying most of the laminated film. There was found. Accordingly, as a result of further investigation, the DAC core layer was saponified by saponification due to the craze generated in the skin layer (TAC) having poor stretchability by stretching the laminated film, and the retardation value (retardation) value due to elution. However, it has been found that this is caused by variation or loss of flatness.

European Patent No. 0911656A2 JP 2008-89802 A

  The present invention has been made in view of the above problems and situations, and the solution to the problem is as a retardation film even when the film is sufficiently thinned to be applicable to a roll-to-panel manufacturing method. The present invention provides a retardation film that exhibits appropriate optical performance, has high stability to saponification treatment, and is excellent in transparency, and a method for producing the same. Another object of the present invention is to provide a polarizing plate and a liquid crystal display device that have improved polarization degree unevenness prevention, viewing angle, and display uniformity by being provided with the retardation film.

  The above-mentioned problem according to the present invention is solved by the following means.

1. A phase difference film in which a core layer containing a cellulose ester satisfying the following formula (1) and a skin layer containing a cellulose ester satisfying the following formula (2) are laminated and formed in the order of the skin layer, the core layer, and the skin layer. The plane orientation degree S _th represented by the following formula (3) is 3.3 × 10 ⁻³ or more, and the in-plane direction retardation value Ro represented by the following formula (4) is the reverse wavelength. A retardation film characterized by exhibiting dispersibility.
Formula (1): 2.0 <Z ₁ <2.4
(In the formula (1), Z ₁ represents an average acyl substitution degree of the cellulose ester of the core layer.)
Formula (2): 2.7 <Z ₂ <3.0; provided that Z ₂ = X + Y, X = 1 to 3
(In the formula, Z ₂ represents the average acyl group substitution degree of the cellulose ester of the skin layer. X represents the propionyl group substitution degree, and Y represents the acetyl group substitution degree.)
Formula (3): _Sth = ( _nx + _ny ) / 2- _nz
(Wherein, n _x is a refractive index in the slow axis x direction in the film plane, n _y is the film in-plane direction, refractive index in the y direction perpendicular to the x direction, n _z in the thickness direction of the film Represents the refractive index in a certain z direction.)
Equation _{(4): Ro = (n} x -n y) × d
_{(Wherein, n x,} n _y have the same meanings as _n x, _{n y} of formula (3), d represents the thickness of the retardation film.)
2. The core layer contains a compound represented by the following general formula (1) and having a total average substitution degree in the range of 3.0 to 6.0. Phase difference film.

(In the formula, R _{1 to} R ₈ each independently represents a substituted or unsubstituted alkylcarbonyl group or a substituted or unsubstituted arylcarbonyl group. R _{1 to} R ₈ are the same as each other. Or it may be different.)
3. A method for producing a retardation film according to the item 1 or 2, wherein a temperature during stretching is in a range of 130 to 170 ° C., and is at least a width uniaxial. A method for producing a retardation film, characterized by stretching 20% or more in the direction.

  4). The retardation film of said 1st term | claim or 2nd term | claim is comprised, The polarizing plate characterized by the above-mentioned.

  5). A liquid crystal display device comprising the retardation film according to the first or second item.

  Even when the film is sufficiently thinned to be applicable to the roll-to-panel manufacturing method by the above-described means of the present invention, it exhibits suitable optical performance as a retardation film and has high stability against saponification treatment. In addition, a retardation film excellent in transparency and a method for producing the same can be provided. In addition, by providing the retardation film, it is possible to provide a polarizing plate and a liquid crystal display device with improved polarization degree unevenness prevention, viewing angle, and display uniformity.

Co-casting die and a diagram showing a multi-layered web formed by casting

In the retardation film of the present invention, a core layer containing a cellulose ester satisfying the formula (1) and a skin layer containing a cellulose ester satisfying the formula (2) are in order of a skin layer, a core layer, and a skin layer. An in-plane direction represented by the formula (4), which is a retardation film formed by lamination, having a plane orientation degree S _th represented by the formula (3) of 3.3 × 10 ⁻³ or more. The phase difference (retardation) value Ro of the present invention exhibits reverse wavelength dispersion. This feature is a technical feature common to the inventions according to claims 1 to 5.

  As an embodiment of the present invention, the total average substitution degree represented by the general formula (1) is in the range of 3.0 to 6.0 in the core layer from the viewpoint of manifesting the effects of the present invention. It is preferable to contain a compound.

  As a method for producing a retardation film for producing the retardation film of the present invention, the temperature during stretching is in the range of 130 to 170 ° C., and at least 20% or more is stretched in the width uniaxial direction. A production method is preferred.

  The retardation film of the present invention can be suitably used for polarizing plates and liquid crystal display devices.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

  The following terms and symbols used in the present application are defined as follows.

(1) “n _x ” is the refractive index in the direction in which the in-plane refractive index is maximized (ie, the slow axis direction), and “n _y ” is the direction in the plane perpendicular to the slow axis (ie, the slow axis direction). , The fast axis direction), and “ _nz ” is the refractive index in the thickness direction.

Further, for example, _"n x = _{n y"} is, _{n x} and _{n y} are not only exactly equal, but also a case where _{n x} and _{n y} are substantially equal. By "substantially equal" in the present application, n _x and n _y in a range which does not give practical effect on the overall optical properties of the liquid crystal panel is a spirit encompasses vary.

(2) “In-plane direction retardation (retardation) Ro” refers to the in-plane retardation value measured with light having a wavelength of 590 nm at 23 ° C. and 55% RH. Ro, when each slow axis direction of the film (layer) at a wavelength of 590 nm, the refractive index of the fast axis _direction, and n x, _{n y,} and a thickness of d (nm) of the film (layer), the formula: ro ₌ determined by _{(n x -n y) × d} .

(3) “Thickness direction retardation (retardation) Rt” refers to a thickness direction retardation value measured with light having a wavelength of 590 nm at 23 ° C. and 55% RH. Rt is the slow axis direction of the film (layer) at a wavelength of 590 nm, a fast axis direction, refractive index in the thickness direction, _{respectively,} and _{n x, n y, n z} , d of (nm) of the film (layer) When the thickness is taken, it is obtained by the formula: Rt = {(n _x + n _y ) / 2−n _z )} × d.

  (4) The “plane orientation degree” is a value calculated from the following formula.

(Formula): _Sth = ( _nx + _ny ) / 2- _nz
In the above formulas, _nx , _ny , and _nz represent the same refractive index as described in the above (1) to (3).

  In the present application, the “core layer” refers to a layer on the inner side of the laminated layers when the cellulose ester laminated film is composed of three or more laminated layers. The layer thickness is preferably thicker than the skin layer on the outside. When the cellulose ester laminated film has a two-layer structure, the layer with the thickest layer is defined as a “core layer”.

  On the other hand, the “skin layer” refers to a layer on the outer surface side of the laminated layers when the cellulose ester laminated film is composed of three or more laminated layers. The layer thickness is preferably thinner than the core layer on the inner side.

(Cellulose ester resin layer)
In the retardation film of the present invention, a core layer containing a cellulose ester satisfying the following formula (1) and a skin layer containing a cellulose ester satisfying the following formula (2) are in the order of the skin layer, the core layer, and the skin layer. An in-plane direction represented by the following formula (4), which is a retardation film that is laminated and has a plane orientation degree S _th represented by the following formula (3) of 3.3 × 10 ⁻³ or more. The phase difference (retardation) value Ro of the present invention exhibits reverse wavelength dispersion.
Formula (1): 2.0 <Z ₁ <2.4
(In the formula (1), Z ₁ represents an average acyl substitution degree of the cellulose ester of the core layer.)
Formula (2): 2.7 <Z ₂ <3.0; provided that Z ₂ = X + Y, X = 1 to 3
(In the formula, Z ₂ represents the average acyl group substitution degree of the cellulose ester of the skin layer. X represents the propionyl group substitution degree, and Y represents the acetyl group substitution degree.)
Formula (3): _Sth = ( _nx + _ny ) / 2- _nz
(Wherein, n _x is a refractive index in the slow axis x direction in the film plane, n _y is the film in-plane direction, refractive index in the y direction perpendicular to the x direction, n _z in the thickness direction of the film Represents the refractive index in a certain z direction.)
Equation _{(4): Ro = (n} x -n y) × d
_{(Wherein, n x,} n _y have the same meanings as _n x, _{n y} of formula (3), d represents the thickness of the retardation film.)
Two “skin layers” of the above three layers may have different average acyl group substitution degrees and different weight average molecular weights within the range satisfying the above requirement of the average acyl group substitution degree.

  In addition, another layer may be provided between any of the layers as long as the condition that the layers are formed in the order of the skin layer, the core layer, and the skin layer is satisfied and the effect of the present invention is not impaired.

  In addition, the glucose unit which comprises cellulose with a β-1,4-glycoside bond has free hydroxyl groups (hydroxyl groups) at the 2nd, 3rd and 6th positions. The cellulose ester according to the present invention is a polymer (polymer) obtained by esterifying some or all of these hydroxyl groups (hydroxyl groups) with an acyl group.

  “Acyl group substitution degree” represents the total of the ratios of esterification of hydroxyl groups (hydroxyl groups) at the 2nd, 3rd and 6th positions of glucose as a repeating unit. Specifically, the degree of substitution is 1 when each of the hydroxyl groups (hydroxyl groups) at the 2nd, 3rd and 6th positions of cellulose is 100% esterified. Therefore, when all of the 2nd, 3rd and 6th positions of cellulose are 100% esterified, the degree of substitution is 3 at the maximum.

  In the present application, the “average acyl group substitution degree” refers to an acyl group substitution degree in which the acyl group substitution degree of a plurality of glucose units constituting the cellulose ester is expressed as an average value per unit.

  In addition, the measuring method of acyl group substitution degree can be measured according to ASTM-D817-96.

  Examples of the acyl group include acetyl group, propionyl group, butanoyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, and isobutanoyl. Group, tert-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like.

  Among these, an acetyl group, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a tert-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and an acetyl group is particularly preferable. A propionyl group and a butanoyl group (when the acyl group has 2 to 4 carbon atoms), more preferably an acetyl group.

  In the case of an aliphatic acyl group, the number of carbon atoms is preferably 2 to 6 and more preferably 2 to 4 from the viewpoint of cellulose synthesis productivity and cost. Moreover, it is preferable that the part which is not substituted by the acyl group exists normally as a hydroxyl group (hydroxyl group).

  Examples of the cellulose ester include cellulose acetate, cellulose propionate, cellulose butyrate, and cellulose pentanate. Further, mixed fatty acid esters such as cellulose acetate, cellulose acetate propionate, cellulose propionate, cellulose acetate butyrate, and cellulose acetate pentanate may be used as long as the above-mentioned side chain carbon number is satisfied.

  Among these, cellulose acetate, cellulose acetate propionate, and cellulose propionate are particularly preferable cellulose esters for use in retardation films.

  The cellulose ester according to the present invention preferably has a weight average molecular weight Mw of 50,000 to 500,000, more preferably 50,000 to 300,000, still more preferably 50,000 to 270,000. .

  Since the average molecular weight and molecular weight distribution of a cellulose ester can be measured using high performance liquid chromatography, the weight average molecular weight (Mw) and molecular weight distribution are calculated using this.

  The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation)
A calibration curve with 13 samples from Mw = 100000 to 500 was used. The 13 samples are preferably used at approximately equal intervals.

  The raw material cellulose of the cellulose ester resin according to the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  The cellulose ester resin according to the present invention can be produced by a known method. Generally, cellulose is esterified by mixing cellulose as a raw material, a predetermined organic acid (such as acetic acid or propionic acid), an acid anhydride (such as acetic anhydride or propionic anhydride), and a catalyst (such as sulfuric acid). The reaction proceeds until the triester is formed. In the triester, three hydroxyl groups (hydroxyl groups) of the glucose unit are substituted with an acyl acid of an organic acid. When two kinds of organic acids are used at the same time, a mixed ester type cellulose ester such as cellulose acetate propionate or cellulose acetate butyrate can be produced. Next, cellulose ester resin having a desired degree of acyl group substitution is synthesized by hydrolyzing cellulose triester. Thereafter, a cellulose ester resin is completed through steps such as filtration, precipitation, washing with water, dehydration, and drying.

  Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

  As an embodiment of the present invention, from the viewpoint of the effect of the present invention, the thickness of the skin layer is in the range of 1 to 3 μm, and the thickness of the core layer is thicker than the thickness of the cellulose ester resin A layer. Is preferred.

  The thickness of the core layer is preferably in the range of 1 to 59 μm.

  In addition, in this invention, it is preferable that the thickness of the whole retardation film exists in the range of 40-60 micrometers.

(Compound represented by the general formula (1))
In the present invention, the core layer preferably contains a compound represented by the general formula (1) and having a total average substitution degree in the range of 3.0 to 6.0.

In General Formula (1), R _{1 to} R ₈ represent a substituted or unsubstituted alkylcarbonyl group or a substituted or unsubstituted arylcarbonyl group, and R _{1 to} R ₈ may be the same. , May be different.

Preferable specific examples of the compound represented by the general formula (1) include compounds shown in Table 1. In addition, R described in the following table represents any one of R _{1 to} R ₈ . As the substituent for the alkylcarbonyl group and the arylcarbonyl group, substituents such as a phenyl group and an alkoxy group included in the alkylcarbonyl group and the arylcarbonyl group shown in the following table are preferable.

  Although the compound represented by the said General formula (1) and a reference compound are described below, it is not limited to these.

  (Synthesis Example: Synthesis of Compound According to the Present Invention)

A four-headed colben equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube was mixed with 34.2 g (0.1 mol) of sucrose, 180.8 g (0.8 mol) of benzoic anhydride, 379. 7 g (4.8 mol) was charged, the temperature was raised while bubbling nitrogen gas from a nitrogen gas introduction tube with stirring, and an esterification reaction was carried out at 70 ° C. for 5 hours. Next, the inside of the Kolben was depressurized to 4 × 10 ² Pa or less, and after excess pyridine was distilled off at 60 ° C., the inside of the Kolben was depressurized to 1.3 × 10 Pa or less and the temperature was raised to 120 ° C. Most of the acid and benzoic acid formed were distilled off. Then, 1 L of toluene and 300 g of a 0.5% by mass aqueous sodium carbonate solution were added, and the mixture was stirred at 50 ° C. for 30 minutes and then allowed to stand to separate a toluene layer. Finally, 100 g of water is added to the collected toluene layer, and after washing with water at room temperature for 30 minutes, the toluene layer is separated, and toluene is distilled off at 60 ° C. under reduced pressure (4 × 10 ² Pa or less). A mixture of A-1, A-2, A-3, A-4 and A-5 was obtained. When the obtained mixture was analyzed by HPLC and LC-MASS, A-1 was 7% by mass, A-2 was 58% by mass, A-3 was 23% by mass, A-4 was 9% by mass, A-5. Was 3% by mass. A part of the obtained mixture was purified by column chromatography using silica gel to obtain A-1, A-2, A-3, A-4 and A-5 having a purity of 100%, respectively. It was.

  The total average substitution degree of the compound represented by the general formula (1) added to the retardation film in the present invention is 3.0 to 7.5, and the range of the substitution degree is 3.0 to 6. 0 is preferred. The substitution degree distribution may be adjusted to the desired substitution degree by adjusting the esterification reaction time or mixing compounds having different substitution degrees.

(Phase difference adjusting agent)
In the present invention, for example, an ester compound represented by the following general formula (2) can be preferably used as the phase difference adjusting agent.

General formula (2): B- (GA) n-GB
(In the formula, B is a hydroxyl group or carboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms. A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (2), a hydroxyl group or carboxylic acid residue represented by B, an alkylene glycol residue or oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue represented by A or It is composed of an aryl dicarboxylic acid residue and can be obtained by the same reaction as that of a normal ester compound.

  Examples of the carboxylic acid component of the ester compound represented by the general formula (2) include acetic acid, propionic acid, butyric acid, benzoic acid, p-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, and dimethylbenzoic acid. , Ethyl benzoic acid, normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid, aliphatic acid and the like, and these can be used as one kind or a mixture of two or more kinds.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the ester compound represented by the general formula (2) include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, , 3-butanediol, 1,2-propanediol, 2-methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol ( Neopentyl glycol), 2,2-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, 2,2,4-trimethyl 1,3-pentanedioe , 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, and the like. It is used as one kind or a mixture of two or more kinds.

  In particular, an alkylene glycol having 2 to 12 carbon atoms is particularly preferable because of excellent compatibility with a cellulose ester.

  Examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the ester compound represented by the general formula (2) include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Yes, these glycols can be used as one or a mixture of two or more.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the ester compound represented by the general formula (2) include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecane. There exist dicarboxylic acid etc., and these are each used as a 1 type, or 2 or more types of mixture. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

  The ester compound represented by the general formula (2) has a number average molecular weight of preferably 300 to 1500, and more preferably 400 to 1000. The acid value is 0.5 mgKOH / g or less, the hydroxyl (hydroxyl) value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl (hydroxyl) value is 15 mgKOH / g or less. is there.

  Although the specific compound of the ester type compound represented by General formula (2) which can be used for this invention below is shown, this invention is not limited to this.

  The retardation film of the present invention preferably contains a retardation adjusting agent in an amount of 0.1 to 30% by mass of the retardation film, and particularly preferably 0.5 to 10% by mass.

  Although it does not specifically limit as a phase difference adjusting agent which can be used in this invention, In addition to said compound, the following polyester polyol can be used.

  The polyester polyol that can be used in the present invention is a polymer having a hydroxyl group (hydroxyl group) at the end that can be obtained by a condensation reaction between a dibasic acid or an ester-forming derivative thereof and glycol. The ester-forming derivatives referred to here are esterified products of dibasic acids, dibasic acid chlorides, and anhydrides of dibasic acids.

  The polyester polyol is obtained by dehydration condensation reaction of aromatic dibasic acid and glycol, addition of glycol to aromatic anhydride dibasic acid and dehydration condensation reaction, or by alcohol removal of esterified product of aromatic dibasic acid and glycol. It can be obtained by a condensation reaction.

  As the aromatic dibasic acid or an ester-forming derivative thereof, an aromatic dicarboxylic acid having 10 to 16 carbon atoms or an ester-forming derivative thereof can be used. For example, a benzene ring structure, a naphthalene ring structure, Dicarboxylic acids having an aromatic ring structure such as anthracene ring structure and ester-forming derivatives thereof can be used. For example, orthophthalic acid having a substituent, isophthalic acid having a substituent, terephthalic acid having a substituent, substituted Group-containing phthalic anhydride, 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,6 -Anthracene dicarboxylic acid and the like, esterified products thereof, acid chlorides, 1,8-naphtha Etc. can be mentioned acid anhydrides Njikarubon acid, they may have a substituent on the aromatic ring, it can be used in combination used or two or more of these alone. 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid and esterified products thereof, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and esterified products thereof are preferable, and 2,6-naphthalenedicarboxylic acid and esterified products thereof are particularly preferable.

  The average carbon number of the dibasic acid of the polyester polyol means the carbon number of the dibasic acid when the polyester polyol is polymerized using a single dibasic acid. When the polyester polyol is polymerized using, it means the sum of the products of the carbon number of each dibasic acid and the molar fraction of the dibasic acid.

  In the present invention, it is important that the average number of carbon atoms of the dibasic acid used as a raw material for the polyester polyol is in the range of 10 to 16. If the average carbon number of the dibasic acid is 10 or more, the retardation (retardation) is excellent, and if the average carbon number is 16 or less, the compatibility with the cellulose ester is remarkably excellent. As a dibasic acid, Preferably the average of carbon number is 10-14, More preferably, the average of carbon number is 10-12.

  If the average carbon number is 10 to 16, the aromatic dibasic acid having 10 to 16 carbon atoms and the other dibasic acid can be used in combination.

  The dibasic acid that can be used in combination is preferably a dicarboxylic acid having 4 to 9 carbon atoms or an ester-forming derivative thereof. For example, succinic acid, glutaric acid, adipic acid, maleic acid, succinic anhydride, maleic anhydride, orthophthalic acid Examples thereof include acids, isophthalic acid, terephthalic acid, phthalic anhydride and the like, esterified products, and acid chlorides thereof.

  Examples of the glycol include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 2-methyl 1,3-propanediol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,4-cyclohexanediol Etc. can be used alone or in combination of two or more, among which ethylene glycol, diethylene glycol, 1,2-propylene glycol, 2-methyl 1,3-propanediol are preferred, more preferably ethylene glycol, diethylene glycol, 1,2- Russia is propylene glycol.

  The polyester polyol according to the present invention comprises the dibasic acid or ester-forming derivative thereof and glycol, if necessary, in the presence of an esterification catalyst, for example, within a temperature range of 180 to 250 ° C., for 10 to 25 hours, It can be produced by an esterification reaction by a known and conventional method.

  In conducting the esterification reaction, a solvent such as toluene or xylene may be used, but a method using no solvent or glycol used as a raw material as a solvent is preferable.

  As the esterification catalyst, for example, tetraisopropyl titanate, tetrabutyl titanate, p-toluenesulfonic acid, dibutyltin oxide and the like can be used. The esterification catalyst is preferably used in an amount of 0.01 to 0.5 parts by mass with respect to 100 parts by mass of the total amount of dibasic acids or their ester-forming derivatives.

  The molar ratio in reacting the dibasic acid or their ester-forming derivative with glycol must be such that the terminal group of the polyester becomes a hydroxyl group (hydroxyl group), and therefore the dibasic acid or their ester formation. The glycol is 1.1 to 10 moles per mole of the functional derivative. Preferably, glycol is 1.5 to 7 moles with respect to 1 mole of dibasic acid or an ester-forming derivative thereof, and more preferably with respect to 1 mole of dibasic acid or an ester-forming derivative thereof. 2-5 moles of glycol.

  On the other hand, the carboxyl group terminal in the polyester polyol lowers the humidity stability, so the content is preferably low. Specifically, the acid value is preferably 5.0 or less, more preferably 1.0 or less, and particularly preferably 0.5 or less.

  The acid value as used herein refers to the number of milligrams of potassium hydroxide necessary to neutralize the acid (carboxyl group present in the sample) contained in 1 g of the sample. The acid value is measured according to JIS K0070.

  The polyester polyol preferably has a hydroxyl (hydroxyl) value (OHV) in the range of 35 mg / g to 220 mg / g. The hydroxyl (hydroxyl group) value as used herein refers to the number of milligrams of potassium hydroxide required to neutralize acetic acid bonded to a hydroxyl group (hydroxyl group) when OH groups contained in 1 g of a sample are acetylated. . Acetic anhydride is used to acetylate OH groups in the sample, and unused acetic acid is titrated with a potassium hydroxide solution, and obtained from the difference from the initial titration value of acetic anhydride.

  The polyester polyol preferably has a hydroxyl group (hydroxyl group) content of 70% or more. When the hydroxyl group (hydroxyl group) content is low, the compatibility between the polyester polyol and the cellulose ester is lowered. For this reason, the hydroxyl group (hydroxyl group) content is preferably 70% or more, more preferably 90% or more, and most preferably 99% or more.

  In the present invention, a compound having a hydroxyl group (hydroxyl group) content of 50% or less is not included in the polyester polyol because one of the end groups is substituted with a group other than the hydroxyl group (hydroxyl group).

The hydroxyl group (hydroxyl group) content can be determined by the following formula (A). Formula (A): Y / X × 100 = hydroxyl group (hydroxyl group) content (%)
X: Hydroxyl group (hydroxyl group) value (OHV) of the polyester polyol
Y: 1 / (number average molecular weight (Mn)) × 56 × 2 × 1000
The polyester polyol preferably has a number average molecular weight within a range of 300 to 3,000, and more preferably has a number average molecular weight of 350 to 2,000.

  Moreover, it is preferable that the dispersion degree of the molecular weight of the polyester polyol based on this invention is 1.0-3.0, and it is still more preferable that it is 1.0-2.0. If the degree of dispersion is within the above range, a polyester polyol having excellent compatibility with the cellulose ester can be obtained.

  The polyester polyol preferably contains 50% or more of a component having a molecular weight of 300 to 1800. By setting the number average molecular weight within the above range, the compatibility can be greatly improved.

  As a method for controlling the number average molecular weight, the degree of dispersion, and the component content within the above preferred range, 2 to 5 mol of glycol is used per 1 mol of dibasic acid or ester-forming derivative thereof, and unreacted glycol is used. A method of distilling off under reduced pressure is preferred. The temperature at which the solvent is distilled off under reduced pressure is preferably 100 to 200 ° C, more preferably 120 to 180 ° C, and particularly preferably 130 to 170 ° C. The degree of reduced pressure when the solvent is distilled off under reduced pressure is preferably 0.1 to 500 Torr, more preferably 0.5 to 200 Torr, and most preferably 1 to 100 Torr.

  The polyester polyol number average molecular weight (Mn) and dispersity can be measured using gel permeation chromatography (GPC).

  An example of measurement conditions is as follows, but is not limited to this, and an equivalent measurement method can be used.

Solvent: Tetrahydrofuran (THF)
Column: TSKgel G2000HXL (Tosoh Co., Ltd. uses two connected)
Column temperature: 40 ° C
Sample concentration: 0.1% by mass
Apparatus: HLC-8220 (manufactured by Tosoh Corporation)
Flow rate: 1.0ml / min
Calibration curve: A calibration curve by PStQuick F (manufactured by Tosoh Corporation) is used.

  In obtaining the effects of the present invention, the polyester polyol is preferably contained in the film in an amount of 5 to 30% by mass. More preferably, it is 5-20 mass%.

Specific examples of dibasic acids having 10 to 16 carbon atoms are shown below, but the present invention is not limited thereto.
(1) 2,6-naphthalenedicarboxylic acid (2) 2,3-naphthalenedicarboxylic acid (3) 2,6-anthracenedicarboxylic acid (4) 2,6-naphthalenedicarboxylic acid: succinic acid (75: 25-99: 1 molar ratio)
(5) 2,6-naphthalenedicarboxylic acid: terephthalic acid (50:50 to 99: 1 molar ratio)
(6) 2,3-naphthalenedicarboxylic acid: succinic acid (75:25 to 99: 1 molar ratio)
(7) 2,3-naphthalenedicarboxylic acid: terephthalic acid (50:50 to 99: 1 molar ratio)
(8) 2,6-anthracene dicarboxylic acid: succinic acid (50:50 to 99: 1 molar ratio)
(9) 2,6-anthracene dicarboxylic acid: terephthalic acid (25:75 to 99: 1 molar ratio)
(10) 2,6-naphthalenedicarboxylic acid: adipic acid (67:33 to 99: 1 molar ratio)
(11) 2,3-naphthalenedicarboxylic acid: adipic acid (67:33 to 99: 1 molar ratio)
(12) 2,6-anthracene dicarboxylic acid: adipic acid (40:60 to 99: 1 molar ratio)
As the phase difference adjusting agent (B) that can be used in the present invention, an octanol-water partition coefficient (logP (B)) is 0 or more and 7 from the viewpoint of water solubility and orientation of the compound, in addition to the polyester polyol. It is also preferred to use less than the compound.

(Sugar ester compound)
The retardation film of the present invention has, as a retardation adjusting agent, an ester compound having at least one pyranose structure or at least one furanose structure and esterifying all or part of the OH groups in the structure. It is also preferable to contain a “sugar ester compound”.

  The proportion of esterification is preferably 70% or more of the OH groups present in the pyranose structure or furanose structure.

  Examples of the ester compound according to the present invention include the following, but the present invention is not limited thereto.

  Glucose, galactose, mannose, fructose, xylose or arabinose, lactose, sucrose, nystose, 1F-fructosyl nystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose .

  In addition, gentiobiose, gentiotriose, gentiotetraose, xylotriose, galactosyl sucrose, and the like are also included.

  Among these compounds, compounds having both a pyranose structure and a furanose structure are particularly preferable.

  Examples include sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose, and more preferably sucrose.

  The monocarboxylic acid used for esterifying all or part of the OH groups in the pyranose structure or furanose structure of the present invention is not particularly limited, and known aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, An aromatic monocarboxylic acid or the like can be used. The carboxylic acid used may be one kind or a mixture of two or more kinds.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid , Saturated fatty acids such as tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, Examples include unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and octenoic acid.

  Examples of preferable alicyclic monocarboxylic acids include acetic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include aromatic monocarboxylic acids having an alkyl group or alkoxy group introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, cinnamic acid, benzylic acid, biphenylcarboxylic acid, and naphthalene. Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as carboxylic acid and tetralincarboxylic acid, or derivatives thereof. More specifically, xylyl acid, hemelic acid, mesitylene acid, prenylic acid, γ-isoduric acid, jurylic acid, mesitic acid, α-isoduric acid, cumic acid, α-toluic acid, hydroatropic acid, atropic acid, hydrocinnamic acid, salicylic acid, o-anisic acid, m-anisic acid, p-anisic acid , Creosote acid, o-homosalicylic acid, m-homosalicylic acid, p-homosalicylic acid, o-pyrocate Acid, β-resorcylic acid, vanillic acid, isovanillic acid, veratromic acid, o-veratrumic acid, gallic acid, asaronic acid, mandelic acid, homoanisic acid, homovanillic acid, homoveratrumic acid, o-homoveratrumic acid, phthalonic acid, p-coumaric Examples of the acid include benzoic acid.

  The oligosaccharide ester compound can be applied as a compound having 1 to 12 at least one of the pyranose structure or the furanose structure according to the present invention.

  Oligosaccharides are produced by allowing an enzyme such as amylase to act on starch, sucrose, etc. Examples of oligosaccharides that can be applied to the present invention include maltooligosaccharides, isomaltoligosaccharides, fructooligosaccharides, galactooligosaccharides, xylooligos. Sugar.

Moreover, the said ester compound is a compound which condensed 1 or more and 12 or less at least 1 type of the pyranose structure or furanose structure represented with the following general formula (A). However, R < ₁₁ > -R < ₁₅ >, R < ₂₁ > -R < ₂₅ > represents a C2-C22 acyl group or a hydrogen atom, m and n represent the integer of 0-12, respectively, and m + n represents the integer of 1-12.

R _{11 to} R ₁₅ and R _{21 to} R ₂₅ are preferably a benzoyl group or a hydrogen atom. Benzoyl group may further have a substituent R _{26 (p} is 0-5), for example, an alkyl group, an alkenyl group, an alkoxyl group and a phenyl group, further the alkyl group, an alkenyl group, a phenyl group May have a substituent. Oligosaccharides can also be produced in the same manner as the ester compound according to the present invention.

  Although the specific example of the ester compound which concerns on this invention is given to the following, this invention is not limited to this.

  The retardation film of the present invention contains the sugar ester compound according to the present invention in an amount of 0.5 to 30% by mass of the cellulose ester film in order to suppress the fluctuation of the retardation value and stabilize the display quality. In particular, 5 to 30% by mass is preferably included.

  The content of the aromatic terminal polyester compound and the sugar ester compound represented by the general formula (2) according to the present invention can be selected in a mass ratio of 99: 1 to 1:99, and the total amount of both compounds. Is preferably 1 to 40% by mass relative to the cellulose ester.

<Other additives>
(Plasticizer)
The retardation film of the present invention can contain a plasticizer as necessary to obtain the effects of the present invention.

  The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a glycolate plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or a polyester plasticizer. Agent, acrylic plasticizer and the like.

  Of these, when two or more plasticizers are used, at least one plasticizer is preferably a polyhydric alcohol ester plasticizer.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  The polyhydric alcohol preferably used in the present invention is represented by the following general formula (a).

Formula (a) R1- (OH) n
However, R1 represents an n-valent organic group, n represents a positive integer of 2 or more, and an OH group represents an alcoholic and / or phenolic hydroxyl group.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

  Adonitol, arabitol, 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, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like.

  In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanoic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which 1 to 3 alkoxy groups such as an alkyl group, a methoxy group or an ethoxy group are introduced into the benzene ring of benzoic acid such as benzoic acid or toluic acid, biphenylcarboxylic acid, Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as naphthalenecarboxylic acid and tetralincarboxylic acid, or derivatives thereof. Benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  Below, the specific compound of a polyhydric alcohol ester is illustrated.

  The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used.

  Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl Glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycol Butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalate Ethyl glycolate, and the like.

  Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

  Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

  Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate.

  Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like.

  The polyvalent carboxylic acid ester compound is composed of an ester of divalent or higher, preferably divalent to 20 valent polyvalent carboxylic acid and alcohol. The aliphatic polyvalent carboxylic acid is preferably 2 to 20 valent, and in the case of an aromatic polyvalent carboxylic acid or an alicyclic polyvalent carboxylic acid, it is preferably 3 to 20 valent.

  The polyvalent carboxylic acid is represented by the following general formula (b).

Formula (b) R2 (COOH) m (OH) n
(However, R2 is an (m + n) -valent organic group, m is a positive integer of 2 or more, n is an integer of 0 or more, COOH group is a carboxyl group, and OH group is an alcoholic or phenolic hydroxyl group)
Examples of preferred polyvalent carboxylic acids include the following, but the present invention is not limited to these.

  Trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid or derivatives thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, tetrahydrophthal An aliphatic polyvalent carboxylic acid such as an acid, an oxypolyvalent carboxylic acid such as tartaric acid, tartronic acid, malic acid and citric acid can be preferably used. In particular, it is preferable to use an oxypolycarboxylic acid from the viewpoint of improving retention.

  There is no restriction | limiting in particular as alcohol used for the polyhydric carboxylic acid ester compound which can be used for this invention, Well-known alcohol and phenols can be used.

  For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

  In addition, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can also be preferably used.

  When an oxypolycarboxylic acid is used as the polycarboxylic acid, the alcoholic or phenolic hydroxyl group of the oxypolycarboxylic acid may be esterified with a monocarboxylic acid. Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, and tetralin carboxylic acid. The aromatic monocarboxylic acid which has, or derivatives thereof can be mentioned. Particularly preferred are acetic acid, propionic acid, and benzoic acid.

  The molecular weight of the polyvalent carboxylic acid ester compound is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. The larger one is preferable in terms of improvement in retention, and the smaller one is preferable in terms of moisture permeability and compatibility with cellulose ester.

  The alcohol used for the polyvalent carboxylic acid ester that can be used in the present invention may be one kind or a mixture of two or more kinds.

  The acid value of the polyvalent carboxylic acid ester compound that can be used in the present invention is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. Setting the acid value in the above range is preferable because the environmental fluctuation of the retardation is also suppressed.

  In addition, an acid value means the milligram number of potassium hydroxide required in order to neutralize the acid (carboxyl group which exists in a sample) contained in 1g of samples. The acid value is measured according to JIS K0070.

  Examples of particularly preferred polyvalent carboxylic acid ester compounds are shown below, but the present invention is not limited thereto.

  For example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, Examples include tributyl trimellitic acid and tetrabutyl pyromellitic acid.

(UV absorber)
The cellulose ester film B according to the present invention can also contain an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, and further Preferably it is 2% or less.

  Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body.

  For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6- (linear and side Chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., and tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, tinuvin 328, etc. These are commercially available products made by BASF Japan and can be preferably used.

  The UV absorbers preferably used in the present invention are benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers, particularly preferably benzotriazole UV absorbers and benzophenone UV absorbers. .

  In addition, a discotic compound such as a compound having a 1,3,5 triazine ring is also preferably used as the ultraviolet absorber.

  It is preferable that the polarizing plate protective film concerning this invention contains 2 or more types of ultraviolet absorbers.

  As the UV absorber, a polymer UV absorber can also be preferably used, and in particular, a polymer type UV absorber described in JP-A-6-148430 is preferably used.

  The method of adding the UV absorber can be added to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as methylene chloride, methyl acetate, acetone or dioxolane or a mixed solvent thereof. Or you may add directly in dope composition.

  For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose ester to disperse and then added to the dope.

  The amount of the UV absorber used is not uniform depending on the type of UV absorber, the operating conditions, etc., but when the dry film thickness of the polarizing plate protective film is 30 to 200 μm, it is 0.5 with respect to the polarizing plate protective film. -10 mass% is preferable, and 0.6-4 mass% is still more preferable.

(Antioxidant)
Antioxidants are also referred to as deterioration inhibitors. When a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film may be deteriorated.

  The antioxidant has a role of delaying or preventing the cellulose ester film from being decomposed by, for example, a residual solvent amount of halogen in the cellulose ester film or phosphoric acid of a phosphoric acid plasticizer. It is preferable to make it contain in a film.

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 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], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

  In particular, 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] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

  The addition amount of these compounds is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose derivative.

(Fine particles)
The cellulose ester film according to the present invention preferably contains fine particles.

  As fine particles used in the present invention, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and hydrated silicic acid. Mention may be made of calcium, aluminum silicate, magnesium silicate and calcium phosphate. Further, fine particles of an organic compound can also be preferably used. Examples of organic compounds include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene resin, silicone resin, polycarbonate resin, benzoguanamine resin, melamine resin Also, pulverized and classified products of organic polymer compounds such as polyolefin-based powders, polyester-based resins, polyamide-based resins, polyimide-based resins, polyfluorinated ethylene-based resins, and starches. Alternatively, a polymer compound synthesized by a suspension polymerization method, a polymer compound made spherical by a spray drying method or a dispersion method, or an inorganic compound can be used.

  Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm.

  These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable.

  The content of these fine particles in the polarizing plate protective film is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass. In the case of a polarizing plate protective film having a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  Silicon dioxide fine particles are commercially available, for example, under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above Nippon Aerosil Co., Ltd.). it can.

  Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Examples of the polymer include silicone resin, fluororesin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the turbidity of the polarizing plate protective film low. In the polarizing plate protective film used in the present invention, the dynamic friction coefficient of at least one surface is preferably 0.2 to 1.0.

  Various additives may be batch-added to a dope that is a cellulose ester-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the fine particles in-line in order to reduce the load on the filter medium.

  When the additive solution is added in-line, it is preferable to dissolve a small amount of cellulose ester in order to improve mixing with the dope. The amount of the cellulose ester is preferably 1 to 10 parts by mass, more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In order to perform in-line addition and mixing in the present invention, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer) or the like is preferably used.

(Method for producing cellulose ester laminated film)
A method for producing a retardation film (cellulose ester laminated film) of the present invention (hereinafter also referred to as “manufacturing method according to the present invention”) includes a dope containing a cellulose ester satisfying the formula (2), and the formula ( A step of multilayerly casting a dope containing a cellulose ester satisfying 1) in this order simultaneously or sequentially on the support, a step of drying the multilayer cast dope and peeling it from the support, and after peeling And a step of adding a retardation adjusting agent to at least one of the core layer dope and the skin B layer dope.

(Preparation of dope)
In the production method according to the present invention, the film of the present invention is produced using a solution (dope) obtained by dissolving a cellulose ester in an organic solvent by a solvent cast method.

  The organic solvent is selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to include a solvent. The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group (hydroxyl group). In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

  Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.

  Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.

  Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.

  Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.

  The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms substituted by halogen in the halogenated hydrocarbon is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is most preferable that it is 40-60 mol%. Methylene chloride is a representative halogenated hydrocarbon.

  Two or more organic solvents may be mixed and used.

  A cellulose ester solution can be prepared by a general method. A general method means processing at a temperature of 0 ° C. or higher (ordinary temperature or high temperature). The solution can be prepared by using a dope preparation method and apparatus in a normal solvent cast method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly, methylene chloride) as the organic solvent.

  The quantity of a cellulose ester is adjusted so that it may be contained in 10-40 mass% in the solution obtained. The amount of the cellulose ester is more preferably 10 to 30% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent).

  The solution can be prepared by stirring the cellulose ester and the organic solvent at room temperature (0 to 40 ° C.). The high concentration solution may be stirred under pressure and heating conditions. Specifically, the cellulose ester and the organic solvent are placed in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., and more preferably 80 to 110 ° C.

  Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.

  When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid.

  It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall.

  Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in a container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.

  A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, the cellulose ester can be dissolved in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a cellulose ester with a normal melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly according to a cooling melt | dissolution method.

  In the cooling dissolution method, first, a cellulose ester is gradually added with stirring to an organic solvent at room temperature. The amount of the cellulose ester is preferably adjusted so that it is contained in the mixture in an amount of 10 to 40% by mass. The amount of the cellulose ester is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture.

  The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this manner, the mixture of cellulose ester and organic solvent solidifies.

  The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling to the final cooling temperature.

  Further, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), the cellulose ester is dissolved in the organic solvent. The temperature can be raised by simply leaving it at room temperature or in a warm bath. The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. .

  A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution with the naked eye.

  In the cooling dissolution method, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container.

(Co-casting)
A cellulose ester film can be produced from the prepared two or more kinds of cellulose ester solutions (dope) by a solvent cast method.

  The dope is cast on a drum or band and the solvent is evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35% by mass. The surface of the drum or band is preferably finished in a mirror state. For casting and drying methods in the solvent casting method, U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.

  The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum or band and further dried with high-temperature air whose temperature is successively changed from 100 ° C. to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

  In the present invention, the obtained cellulose ester solution (dope) is formed by casting the two or more kinds of cellulose ester solutions on a smooth band or drum as a support. There is no restriction | limiting in particular as a manufacturing method of the film of this invention other than the above, A well-known co-casting method can be used. For example, a film may be produced while casting and laminating a solution containing a cellulose ester from a plurality of casting openings provided at intervals in the traveling direction of the metal support. The methods described in JP-A Nos. 158414, 1-122419, and 11-198285 can be applied. Further, it may be formed into a film by casting a cellulose ester solution from two casting ports. For example, JP-B-60-27562, JP-A-61-94724, JP-A-61-947245, This can be carried out by the methods described in JP-A Nos. 61-104813, 61-158413, and 6-134933. Also, a cellulose ester film casting method in which a flow of a high-viscosity cellulose ester solution described in JP-A-56-162617 is wrapped with a low-viscosity cellulose ester solution, and the high- and low-viscosity cellulose ester solution is simultaneously extruded. Good. Furthermore, it is also a preferred embodiment that the outer solution described in JP-A-61-94724 and JP-A-61-94725 contains a larger amount of an alcohol component which is a poor solvent than the inner solution.

  Alternatively, by using two casting ports, the film cast on the metal support is peeled off by the first casting port, and the second casting is performed on the side that is in contact with the metal support surface. Further, a film may be prepared, for example, a method described in Japanese Patent Publication No. 44-20235. The cellulose ester solution to be cast may be the same solution or different cellulose ester solutions and is not particularly limited. In order to give a function to a plurality of cellulose ester layers, a cellulose ester solution corresponding to the function may be extruded from each casting port. Further, the cellulose ester solution according to the present invention can be cast simultaneously with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, a UV absorbing layer, a polarizing layer). As a method for producing the film of the present invention, it is preferred that the film formation is simultaneous or sequential multilayer casting film formation.

  In conventional single-layer liquids, it is necessary to extrude a high-concentration and high-viscosity cellulose ester solution to obtain the required film thickness. In this case, the stability of the cellulose ester solution is poor and solids are generated. In many cases, however, it becomes a problem due to a failure or poor flatness. As a solution to this, by casting multiple cellulose ester solutions from the casting port, a highly viscous solution can be extruded onto a metal support at the same time. In addition to being able to reduce the drying load by using a concentrated cellulose ester solution, the production speed of the film could be increased.

  In the case of co-casting, the inner and outer thicknesses are not particularly limited, but preferably the outer side is preferably 0.2 to 50% of the total film thickness, more preferably 2 to 30%. . Here, in the case of co-casting with three or more layers, the total thickness of the layer in contact with the metal support and the layer in contact with the air side is defined as the outer thickness.

  In the case of co-casting, a cellulose ester film having a laminated structure can be produced by co-casting cellulose ester solutions having different additive concentrations such as the above-mentioned plasticizer, ultraviolet absorber and matting agent. For example, a cellulose ester film having a structure of skin layer / core layer / skin layer can be produced. For example, the matting agent can be contained in the skin layer in a large amount or only in the skin layer. The plasticizer and the ultraviolet absorber can be contained in the core layer more than the skin layer, and may be contained only in the core layer. In addition, the type of plasticizer and ultraviolet absorber can be changed between the core layer and the skin layer. For example, the skin layer contains a low-volatile plasticizer and / or an ultraviolet absorber, and the core layer has excellent plasticity. It is also possible to add a plasticizer or an ultraviolet absorber excellent in ultraviolet absorption. Moreover, it is also a preferable aspect that a release agent is contained only in the skin layer on the metal support side. It is also preferable to add more alcohol, which is a poor solvent, to the skin layer than the core layer in order to cool the metal support by the cooling drum method to gel the solution. The Tg of the skin layer and the core layer may be different, and the Tg of the core layer is preferably lower than the Tg of the skin layer. Further, the viscosity of the solution containing the cellulose ester during casting may be different between the skin layer and the core layer, and the viscosity of the skin layer is preferably smaller than the viscosity of the core layer. It may be smaller than the viscosity.

  In the present invention, the multi-layer cast dope is dried and peeled from the support.

(Drying process)
A method for drying a web that has been dried on a drum or belt and peeled off will be described. The web peeled at the peeling position immediately before the drum or belt makes one round is conveyed by alternately passing through a group of rolls arranged in a staggered manner, or both ends of the peeled web are gripped by clips or the like. It is transported by a non-contact transport method. Drying is performed by a method of applying wind at a predetermined temperature to both sides of the web (film) being conveyed or a method using a heating means such as a microwave. Since rapid drying may impair the flatness of the film to be formed, it is preferable to dry at a temperature at which the solvent does not foam in the initial stage of drying, and to dry at a high temperature after the drying proceeds. In the drying process after peeling from the support, the film tends to shrink in the longitudinal direction or the width direction by evaporation of the solvent. Shrinkage increases with drying at higher temperatures. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the finished film. From this point, for example, as shown in Japanese Patent Laid-Open No. 62-46625, a method in which all or part of the drying process is performed while holding the width at both ends of the web with clips or pins in the width direction. (Tenter method) is preferable. It is preferable that the drying temperature in the said drying process is 100-145 degreeC. The drying temperature, the amount of drying air, and the drying time vary depending on the solvent to be used. In the production of the film of the present invention, the web (film) peeled from the support is preferably stretched when the amount of residual solvent in the web is less than 120% by mass.

  The residual solvent amount can be expressed by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at an arbitrary point in time, and N is the mass when the web of which M is measured is dried at 110 ° C. for 3 hours.

(Stretching)
The manufacturing method which concerns on this invention includes the process of extending | stretching the film after peeling after the process of drying the dope which carried out multilayer casting, and peeling from a support body.

In the present invention, the solution cast film can be stretched without being heated to a high temperature as long as the residual solvent amount is in a specific range, but it is preferable because drying and stretching can shorten the process. . That is, the stretching process may be performed in a state where the solvent remains, or the stretching process after drying may be performed. However, if the temperature of the web is too high, the plasticizer will volatilize, so a range of 120 to 180 ° C is preferred. In addition, stretching in the biaxial directions perpendicular to each other is an effective method for bringing the refractive indexes _nx , _ny , and _nz of the film into the scope of the present invention.

For example, when stretching in the casting direction, if the shrinkage in the width direction is too large, the value of _nz becomes too large. In this case, it can be improved by suppressing the width shrinkage of the film or stretching in the width direction. When stretching in the width direction, the refractive index may be distributed with a width. This is sometimes seen when using, for example, the tenter method, but it is a phenomenon that occurs when the film is stretched in the width direction and contraction force is generated at the center of the film and the end is fixed. It is thought to be called the bowing phenomenon. Even in this case, by stretching in the casting direction, it is possible to suppress the bowing phenomenon and to improve the distribution of the width retardation. Furthermore, the film thickness fluctuation | variation of the film obtained by extending | stretching in the biaxial direction orthogonal to each other can be reduced. If the film thickness variation of the retardation film is too large, the retardation will be uneven. The film thickness variation of the retardation film is preferably ± 3%, more preferably ± 1%. For the purposes as described above, a method of stretching in the biaxial directions orthogonal to each other is effective, and the stretching ratios in the biaxial directions orthogonal to each other are 1.2 to 2.0 times and 0.7 to 1.0, respectively. It is preferable that the range be doubled. Here, stretching to 1.2 to 2.0 times with respect to one direction and making the other perpendicular to 0.7 to 1.0 times means that the distance between the clip or pin supporting the film is This means that the distance is 0.7 to 1.0 times the interval before stretching.

  In general, when a biaxial stretching tenter is used to stretch in the width direction so as to have an interval of 1.2 to 2.0 times, a contracting force acts in the longitudinal direction that is the perpendicular direction.

  Therefore, if the force is applied in only one direction and the stretching is continued, the width in the perpendicular direction is reduced, but this means that the amount of shrinkage is suppressed with respect to the amount that shrinks without restricting the width. This means that the interval between the clip or pin whose width is restricted is restricted to a range of 0.7 to 1.0 times that before stretching. At this time, in the longitudinal direction, a force is exerted to shrink the film by stretching in the width direction. By taking the interval between the clips or pins in the longitudinal direction, an excessive tension is not applied in the longitudinal direction. There is no particular limitation on the method of stretching the web. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction, the both ends of the web are fixed with clips and pins, and the interval between the clips and pins is increased in the traveling direction. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions and stretching in both the vertical and horizontal directions. Of course, these methods may be used in combination. That is, the film may be stretched in the transverse direction, longitudinally, or in both directions with respect to the film forming direction, and when stretched in both directions, simultaneous stretching or sequential stretching may be used. May be. In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

  Moreover, it is preferable from viewpoints, such as expansion of an optical expression area, that the manufacturing method concerning this invention includes the process of extending | stretching the film after the said extending process again.

(Physical properties of retardation film)
In the retardation film of the present invention, the plane orientation degree S _th represented by the following formula (3) is 3.3 × 10 ⁻³ or more, and the in-plane direction retardation represented by the following formula (4) ( (Retardation) The value Ro shows reverse wavelength dispersion.
Formula (3): _Sth = ( _nx + _ny ) / 2- _nz
(Wherein, n _x is a refractive index in the slow axis x direction in the film plane, n _y is the film in-plane direction, refractive index in the y direction perpendicular to the x direction, n _z in the thickness direction of the film Represents the refractive index in a certain z direction.)
Equation _{(4): Ro = (n} x -n y) × d
_{(Wherein, n x,} n _y have the same meanings as _n x, _{n y} of formula (3), d represents the thickness of the retardation film.)
In the present application, the various refractive indexes and the like are measured with light having a wavelength of 590 nm at 23 ° C. and 55% RH.

  In the present invention, the retardation value can be adjusted by adjusting the acyl group substitution degree of the cellulose ester, adding a retardation adjusting agent, or the like.

  In the present application, “the retardation value Ro in the in-plane direction has a reverse wavelength dispersion” means that the in-plane retardation value of the retardation film Ro has a measured wavelength in the visible light range. Means that it becomes larger as the wavelength becomes longer.

The plane orientation degree S _th needs to be 3.3 × 10 ⁻³ or more, but is preferably 4.3 × 10 ⁻³ or less.

In the present invention, the method for adjusting the degree of plane orientation is not limited. However, in the film production process, for example, by adjusting the draw ratio, the temperature of the drying process, etc., the plane orientation degree _Sth of the film is within the above range. Can be adjusted.

<transparency>
A haze value (turbidity) is used as an index for judging the transparency of the retardation film of the present invention. In particular, in a liquid crystal display device used outdoors, it is required that sufficient brightness and high contrast are obtained even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably. Moreover, it is preferable that the total light transmittance is 90% or more, More preferably, it is 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

  According to the retardation film of the present invention, high transparency can be obtained, but when acrylic particles are used for the purpose of improving another physical property, the refraction between the resin and the acrylic particles constituting the retardation film. By reducing the rate difference, an increase in haze value can be prevented.

  In addition, the retardation film of the present invention preferably has a defect with a diameter of 5 μm or more in the film plane of 1 piece / 10 cm square or less. Further, it is preferably 0.5 pieces / 10 cm square or less, more preferably 0.1 pieces / 10 cm square or less.

  Here, the diameter of the defect indicates the diameter when the defect is circular, and when the defect is not circular, the range of the defect is determined by observing with a microscope by the following method, and the maximum diameter (diameter of circumscribed circle) is determined.

  The range of the defect is the size of the shadow when the defect is observed with the transmitted light of the differential interference microscope when the defect is a bubble or a foreign object. When the defect is a change in the surface shape, such as transfer of a roll flaw or an abrasion, the size is confirmed by observing the defect with the reflected light of a differential interference microscope.

  In addition, when observing with reflected light, if the size of the defect is unclear, aluminum or platinum is deposited on the surface for observation.

  In order to obtain a film having excellent quality expressed by such a defect frequency with high productivity, it is necessary to filter the polymer solution with high precision immediately before casting, to increase the cleanliness around the casting machine, It is effective to set drying conditions after rolling stepwise and to dry efficiently while suppressing foaming.

<Moisture permeability>
The “moisture permeability” according to the present invention refers to the moisture permeability when kept for 24 hours under environmental conditions of a temperature of 40 ° C. and a humidity of 90% RH based on the calcium chloride-cup method defined in JIS Z0208. .

The retardation film of the present invention is preferably adjusted so that the water vapor transmission rate is 300 g / m ² · 24 hr or more.

(Description of optical member)
[Polarizer]
Since the retardation film of the present invention has high optical expression, it is preferably used as a polarizer protective film. The polarizing plate is formed by laminating and laminating a protective film on at least one surface of the polarizer. A conventionally known polarizer can be used. For example, a hydrophilic polymer film such as a polyvinyl alcohol film is treated with a dichroic dye such as iodine and stretched. The bonding of the cellulose ester film and the polarizer is not particularly limited, but can be performed with an adhesive made of an aqueous solution of a water-soluble polymer. As this water-soluble polymer adhesive, a completely saponified polyvinyl alcohol aqueous solution is preferably used.

  In particular, the film of the present invention can provide a display device with excellent viewing angle and less visibility by being attached to a liquid crystal cell of TN type, VA type, OCB type or the like. . In particular, a polarizing plate using the polarizer protective film according to the present invention has little deterioration under high temperature and high humidity conditions, and can maintain stable performance for a long time.

[Liquid Crystal Display]
The polarizing plate using the retardation film of the present invention can be used for liquid crystal cells and liquid crystal display devices in various display modes. TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-Ferroelectric Liquid Nyst) Various display modes such as HAN (Hybrid Aligned Nematic) have been proposed.

  The OCB mode liquid crystal cell is a liquid crystal display device using a bend alignment mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned in a substantially opposite direction (symmetrically) between an upper portion and a lower portion of the liquid crystal cell. OCB mode liquid crystal cells are disclosed in US Pat. Nos. 4,583,825 and 5,410,422. Since the rod-like liquid crystal molecules are aligned symmetrically between the upper part and the lower part of the liquid crystal cell, the bend alignment mode liquid crystal cell has a self-optical compensation function. The bend alignment mode liquid crystal display device has an advantage of high response speed.

  In a VA mode liquid crystal cell, rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied.

  The VA mode liquid crystal cell includes (1) a narrowly defined VA mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied, and substantially horizontally when a voltage is applied (Japanese Patent Laid-Open No. Hei 2-). 176625 (in Japanese Patent Publication No. 176625), and (2) a liquid crystal cell (SID97, Digest of tech. Papers (Proceedings) 28 (1997) 845 in which the VA mode is converted into a multi-domain (for MVA mode) in order to enlarge the viewing angle. ), (3) a liquid crystal cell in a mode (n-ASM mode) in which rod-like liquid crystalline molecules are substantially vertically aligned when no voltage is applied and twisted multi-domain alignment is applied when a voltage is applied (Sharp Technical Report No. 80, page 11); (4) A SURVAVAL mode liquid crystal cell (Monthly Display May 14th page (1999)) is included.

  The VA mode liquid crystal display device includes a liquid crystal cell and two polarizing plates disposed on both sides thereof. The liquid crystal cell carries a liquid crystal between two electrode substrates. In one aspect of the transmission type liquid crystal display device of the present invention, the film of the present invention is disposed between the liquid crystal cell and one polarizing plate, or between the liquid crystal cell and both polarizing plates. Arrange two.

  In another aspect of the transmissive liquid crystal display device according to the present invention, an optical compensation sheet made of the film of the present invention is used as a transparent protective film for a polarizing plate disposed between a liquid crystal cell and a polarizer. The above optical compensation sheet may be used only for the protective film (between the liquid crystal cell and the polarizer) of one polarizing plate, or two (between the liquid crystal cell and the polarizer) of both polarizing plates. You may use said optical compensation sheet for a sheet of protective film. When the optical compensation sheet is used for only one polarizing plate, it is particularly preferable to use it as a protective film for the liquid crystal cell side of the backlight side polarizing plate of the liquid crystal cell. For the lamination to the liquid crystal cell, the film of the present invention is preferably on the VA cell side. The protective film may be a normal cellulose ester film, and is preferably thinner than the film of the present invention. For example, it is preferably 40 to 80 μm, and examples thereof include, but are not limited to, commercially available KC4UY (40 μm manufactured by Konica Minolta Opto), KC5UX (60 μm manufactured by Konica Minolta Opto), TD80 (80 μm manufactured by Fujifilm), and the like.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
<Preparation of retardation films 101-112>
(Preparation of retardation film 101)
(Fine particle dispersion)
Fine particles (Aerosil R812 manufactured by Nippon Aerosil Co., Ltd.) 11 parts by weight Ethanol 89 parts by weight The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

(Fine particle additive)
A cellulose ester (acetyl group substitution degree: 2.35) was added to a dissolution tank containing methylene chloride and heated to be completely dissolved, and then dissolved in an Azumi filter paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. Filtered using 244. The fine particle dispersion was slowly added thereto while sufficiently stirring the filtered cellulose ester solution. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle addition solution.

99 parts by mass of methylene chloride Cellulose ester (acetyl group substitution degree 2.3: Mw = 170,000, Mw / Mn =
3.2) 4 parts by mass Fine particle dispersion 11 parts by mass A dope solution having the following composition was prepared using cellulose ester.

  First, methylene chloride and ethanol were added to the pressure dissolution tank. The cellulose ester was added to the pressure dissolution tank containing the solvent while stirring. This is completely dissolved with heating and stirring. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

(Composition of core layer dope)
Methylene chloride 300 parts by mass Ethanol 30 parts by mass Cellulose ester (acetyl group substitution degree 2.3; Mw = 170,000, Mw / Mn =
3.2) 100 parts by mass Hydrolysis inhibitor (A): KMSB; Daiichi Kogyo Seiyaku Co., Ltd. 10 parts by mass Phase difference modifier (B): KMO103; DIC Corporation 2 parts by mass <For skin layer Composition of dope solution>
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Cellulose ester (acetyl group substitution degree 1.8, propionyl group substitution degree 1.0; Mw = 229,000, Mw / Mn = 2.9) 100 parts by mass Hydrolysis inhibitor ( A): KMSB; manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 10 parts by mass Each of the above materials was put into a sealed container and dissolved while stirring to prepare each dope solution. Next, using the co-casting die shown in FIG. 1, a phase difference film 101 having a three-layer structure was produced by a co-casting method using a core layer dope and a skin layer dope.

  Add 2 parts by mass of the fine particle additive to 100 parts by mass of the dope and mix thoroughly with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ). The film was uniformly cast on a stainless steel belt support at a temperature of 33 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled at 30 ° C.

  On the stainless steel belt support, the solvent was evaporated until the residual solvent amount in the cast (cast) film was 75%, and then peeled off from the stainless steel belt support with a peeling tension of 130 N / m.

  The peeled cellulose ester film was stretched in the 30% width direction using a tenter while applying heat at 160 ° C. The residual solvent at the start of stretching was 15%.

  Next, drying was terminated while the drying zone was conveyed by a number of rolls. The drying temperature was 130 ° C. and the transport tension was 100 N / m.

  As described above, a retardation film 101 having a dry film thickness of 50 μm was obtained.

  Table 1 shows the contents of the cellulose ester used above and the cellulose ester used in the following examples.

(Production of retardation films 102 to 112)
In the production of the retardation film 101, retardation films 102 to 112 were produced in the same manner except that the type of cellulose ester, the type and addition amount of the compound, the stretching temperature, and the stretching ratio were changed as shown in Table 1.

  The contents of each retardation film produced by the above method are shown in Tables 1 and 2.

<Preparation of polarizing plates 101-112>
A 120 μm-thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution at 68 ° C. consisting of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer.

  Next, according to the following steps 1 to 5, the retardation films 101 to 112 are bonded to the polarizer, and the Konica Minolta Opto Konica Minoltack KC8UY (hereinafter referred to as “8UY”) film is bonded to the back side. Thus, polarizing plates 101 to 112 were produced.

  Step 1: A cellulose ester film and 8UY were immersed in a 2 mol / L potassium hydroxide solution at 50 ° C. for 30 seconds, then washed with water and dried to obtain a film having a saponified surface.

  Step 2: The deflector was immersed in a polyvinyl alcohol adhesive bath having a solid content of 2% by mass for 1 to 2 seconds.

  Step 3: The excess adhesive adhered to the deflector in Step 2 was gently wiped off, placed on the cellulose ester film treated in Step 1, and further placed on the back side with 8UY on the deflector side. .

Step 4: Step 3 Cellulose ester film laminated with the polarizers and the backside film pressure 20-30 N / cm ^2, the conveyance speed was laminated at about 2m / min.

  Process 5: The sample which bonded the cellulose-ester film and back surface film produced at process 4 in the 60 degreeC dryer was dried for 2 minutes, and the polarizing plate was produced.

  According to said method, the polarizing plates 101-112 were obtained. These polarizing plates were evaluated as follows.

(Evaluation for preventing polarization unevenness)
For each of the produced polarizing plates, two 10 cm × 10 cm polarizing plates were cut out as test pieces, stored for 120 hours in a high temperature and high humidity atmosphere at a temperature of 60 ° C. and a relative humidity of 90% RH, and then on a light box with a color temperature of 5000 K. Specimens cut out from the same polarizing plate are placed in crossed Nicols, and the degree of polarization is measured in an environment of 23 ° C. and relative humidity 55%, and the degree of polarization unevenness (polarization degree variation) is visually observed according to the following criteria. evaluated. The evaluation results are shown in Table 3.
Standard:
A: Unevenness of polarization degree is not generated. ○: Unevenness of polarization degree cannot be recognized with naked eyes. Δ: Although it appears as uneven polarization degree, there is no problem in use. X: There is a problem in display quality.

<Production of liquid crystal display device>
A liquid crystal panel for measuring the viewing angle and the like was produced as follows, and the characteristics as a liquid crystal display device were evaluated.

  Remove the polarizing plates on both sides of the VA mode type liquid crystal display device (Sony BRAVIAV1, 40-inch type) in advance, and the cellulose ester films 101-112 side of the prepared polarizing plate is the glass surface of the liquid crystal cell. It was pasted on both sides.

  In that case, it performed so that an absorption axis might turn to the same direction as the polarizing plate previously bonded, and each liquid crystal display device was produced.

  As the polarizing plate, a polarizing plate stored for 120 hours in a high-temperature and high-humidity atmosphere at a temperature of 60 ° C. and a relative humidity of 90% RH was used in the same manner as in the evaluation of prevention of uneven polarization degree.

  The liquid crystal display device was evaluated as follows, and the results are shown in Table 3.

(Evaluation of viewing angle)
About each produced said liquid crystal display device, the average value of contrast ratio (white transmittance | permeability / black transmittance | permeability) was calculated | required in the up-down and left-right direction in the polar angle of 60 degrees using the measuring machine (EZ-Contrast160D, ELDIM company make). . This average value was evaluated based on the following criteria.
Standard:
◎: 40 or more ○: 30 or more and less than 40 Δ: 20 or more and less than 30 x: less than 20 (Display uniformity)
In an environment of 23 ° C. and 55% RH, the backlight was continuously turned on for 12 hours, and the entire black display state was visually observed in a dark room, and the display uniformity was evaluated according to the following criteria.
Standard:
◎: Black luminance unevenness cannot be confirmed by visual observation ○: Black luminance is almost the same △: Black unevenness is slightly observed ×: Large difference in black luminance is observed Absent.

  The above evaluation results are shown in Table 3.

  As is clear from the results shown in Table 3, the polarizing plate and the liquid crystal display device using the retardation film of the present invention have excellent performance in evaluating the degree of polarization unevenness prevention, viewing angle, and display uniformity. You can see that

  A polarizing plate with little variation in optical characteristics can be provided. In addition, a liquid crystal display device using the same can be provided.

DESCRIPTION OF SYMBOLS 10 Co-casting die 11 Base part 13, 15 Slit for surface layer 14 Slit for base layer 16 Metal support 17, 19 Dope for skin layer 18 Dope for core layer 20 Multi-layer structure web 21 Skin layer web 22 Core layer web 23 Skin layer web

Claims (5)

A phase difference film in which a core layer containing a cellulose ester satisfying the following formula (1) and a skin layer containing a cellulose ester satisfying the following formula (2) are laminated and formed in the order of the skin layer, the core layer, and the skin layer. The plane orientation degree S _th represented by the following formula (3) is 3.3 × 10 ⁻³ or more, and the in-plane direction retardation value Ro represented by the following formula (4) is the reverse wavelength. A retardation film characterized by exhibiting dispersibility.
Formula (1): 2.0 <Z ₁ <2.4
(In the formula (1), Z ₁ represents an average acyl substitution degree of the cellulose ester of the core layer.)
Formula (2): 2.7 <Z ₂ <3.0; provided that Z ₂ = X + Y, X = 1 to 3
(In the formula, Z ₂ represents the average acyl group substitution degree of the cellulose ester of the skin layer. X represents the propionyl group substitution degree, and Y represents the acetyl group substitution degree.)
Formula (3): _Sth = ( _nx + _ny ) / 2- _nz
(Wherein, n _x is a refractive index in the slow axis x direction in the film plane, n _y is the film in-plane direction, refractive index in the y direction perpendicular to the x direction, n _z in the thickness direction of the film Represents the refractive index in a certain z direction.)
Equation _{(4): Ro = (n} x -n y) × d
_{(Wherein, n x,} n _y have the same meanings as _n x, _{n y} of formula (3), d represents the thickness of the retardation film.) 2. The retardation according to claim 1, wherein the core layer contains a compound represented by the following general formula (1) and having a total average substitution degree within a range of 3.0 to 6.0. the film.

(In the formula, R _{1 to} R ₈ each independently represents a substituted or unsubstituted alkylcarbonyl group or a substituted or unsubstituted arylcarbonyl group. R _{1 to} R ₈ are the same as each other. Or it may be different.)   It is a manufacturing method of the retardation film which manufactures the retardation film of Claim 1 or Claim 2, Comprising: The temperature at the time of extending | stretching exists in the range of 130-170 degreeC, and at least width-uniaxial direction A method for producing a retardation film, wherein the film is stretched 20% or more.   A retardation film comprising the retardation film according to claim 1.   A liquid crystal display device comprising the retardation film according to claim 1.

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