KR20200006294A - Cellulose Ester phase difference film - Google Patents

Abstract

The present invention provides a method for producing a cellulose ester film. The cellulose ester film is an optical film produced by mixing a first dope comprising a first resin substituted with naphthoic acid or propionic acid in at least one of three substituents of cellulose ester, and a second dope comprising a second resin substituted with a material having 5 to 15 carbon atoms in at least one of three substituents of the cellulose ester. The cellulose ester film of the present invention has an effect of improving uniformity of phase difference and suppressing the deterioration of brittle properties of the film.

Description

Cellulose ester retardation film {Cellulose Ester phase difference film}

The present invention relates to a cellulose ester retardation film, and more particularly to a retardation film having a low retardation nonuniformity by blending and solvent casting a resin substituted with at least one of the three substituents of the cellulose ester.

Recently, displays are being developed based on liquid crystal displays and OLEDs. As a result, the protective film of the polarizing plate has been increasingly demanded for thinning and high performance. Since a liquid crystal display device shows a display by polarization control by liquid crystal, a polarizing plate is needed, and what extended | stretched the PVA film containing iodine is used as a polarizing plate normally. Since this polarizing plate is fragile, a polarizing plate protective film is used as a thing to protect this. Generally, a triacetyl cellulose film is widely used for a polarizing plate protective film. In addition to these polarizing plate protective films, in order to control the phase difference of polarization, the thing of retardation film is also used. The retardation film used for such a liquid crystal display device etc. is used in order to solve the problem of color compensation, viewing angle expansion, etc. by using it in combination with a polarizing plate, and the retardation film used by OLED device has an antireflection function.

The polarizing plate protective film is most preferable in the case where the manufacturing process of a polarizing plate is considered to use the film which consists of cellulose acetates in order to protect the polarizing plate which consists of PVA containing moisture, and protects the polarizing plate. On the other hand, materials other than cellulose acetate have been used as retardation film in order to express optical performance. That is, conventionally, as a material of retardation film, polycarbonate, polysulfone, polyether sulfone, amorphous polyolefin, etc. are mentioned, for example. These polymer films have the characteristics that the retardation becomes smaller as the wavelength is longer, and it is difficult to provide ideal retardation characteristics to all wavelengths in the visible light region.

In the case of converting linearly polarized light into circularly polarized light or converting circularly polarized light into linearly polarized light with respect to the wavelength of the visible light region, in order to obtain the above effect with one sheet of retardation film, the phase difference is lambda / in wavelength (λ) incident on the retardation film. It is preferable to become four. Such a retardation film, for example, can implement an antireflection function in an OLED image display device using only one retardation film having a phase difference of λ / 4 and a polarizer. In addition, by using the back electrode for a reflective liquid crystal display device having a configuration that also serves as a reflective electrode, a reflective display device excellent in image quality can be obtained. In addition, a circular polarization of a reflection type polarizing plate composed of a cholesteric liquid crystal or the like which uses this retardation film on the back side or reflects only one circular polarization on the back side with respect to the observer of the guest host type liquid crystal layer is converted into linearly polarized light. It is similarly used also as an element.

In addition, since the retardation film converts linearly polarized light into elliptical polarization or circularly polarized light, or converts linearly polarized light in a certain direction to another direction, the retardation film can improve the viewing angle, contrast, etc. of the liquid crystal display using the same. . Generally, the retardation film is attached to a pair of polarizing plates, respectively, and is used. At present, as a retardation film for VA mode liquid crystal display devices, N-TAC and the like of Konica Minolta Holdings, Inc. in Japan are generally used. The NTAC retardation film is a cellulose acetate propionate (CAP) film having an in-plane retardation (Retardation, R0, λ = 550 nm reference) of 50 nm, and a retardation (Rth, λ = 550 nm reference) of 130 nm in thickness direction. Is done.

In order to improve the viewing angle characteristic (black display state (black characteristic, etc.)) of a liquid crystal display device, wavelength dispersion and a control technique are needed. In general, the N-TAC film exhibits reverse wavelength dispersion characteristics in which the retardation value increases with increasing wavelength, and exhibits an excellent viewing angle characteristic improvement effect as compared with a retardation film having a constant wavelength dispersion characteristic in which the retardation value decreases with increasing wavelength. Moreover, for the improvement of a liquid crystal display device, the retardation film which has a specific retardation value, and its combination is used.

Conventional retardation films (PC, PSu, PA, etc.) have the characteristic that the retardation becomes smaller as the wavelength is longer, and it is difficult to impart ideal retardation characteristics to all wavelengths in the visible light region, and these retardation films are used for a wide band. The required performance is obtained by joining. In order to obtain such a performance in one retardation film, it is preferable that the in-plane retardation R0 becomes λ / 4 in the wavelength λ incident on the retardation film, but for that purpose, the wavelength opposite to the above characteristic is used. The longer this property, the greater the in-plane retardation R0 is required. In the film made of cellulose acetate, if such retardation characteristics can be imparted, the polarizing plate protective film and the retardation film can be used, the retardation film composed of a plurality of retardation films can be omitted, and the optical film in the liquid crystal display device can be omitted. It is useful because the total light transmittance can be improved.

In this regard, Japanese Patent Application Laid-Open No. 2000-137116 proposes to use an orientation film of cellulose acetate having a total substitution degree (acetylation degree) of 2.5 to 2.8 as a retardation film. According to this method, the longer the wavelength is, the larger the phase difference is, and ideal phase difference characteristics are obtained for all wavelengths in the visible light region. That is, the above-mentioned patent discloses a retardation plate in which the retardation becomes smaller as the measurement wavelength is shorter with one film. The longer the birefringence Δn at a wavelength of 400 to 700 nm is a retardation plate composed of a larger polymer oriented film, and the polymer oriented film is a retardation film of a polymer film having a larger average refractive index at the wavelength as the shorter wavelength. Providing a version makes a challenge. And as a means to solve this problem, the technique of orienting by extending | stretching the cellulose acetate which has an acetylation degree of 2.5-2.8 is disclosed.

In the examples of the above-mentioned patent, 100 parts by weight of cellulose triacetate having an intrinsic viscosity [η] of 1.335 and an acetylation degree of 2.917, obtained from Wako Junyaku Kogyo Co., Ltd. was dissolved in 500 parts by weight of methylene chloride, and this solution was dissolved in 96% acetic acid. By adding 1000 parts by weight and removing methylene chloride under reduced pressure, hydrolysis of cellulose triacetate with acetic acid and water for 100 minutes at 70 ° C., precipitated with excess water, washed and dried It is described that a cellulose acetate having an acetylation degree of 2.661 is obtained. And a film was produced by the solvent casting method from the solution which melt | dissolved 100 weight part of this polymer and 3 weight part of dibutyl phthalates which are a plasticizer, and 700 weight part of methylene chloride / methanol (weight ratio 9/1) mixed solvents, The thing uniaxially stretched 1.5 time at 170 degreeC is disclosed. That is, in Example 1 of the said patent, it is said that retardation film which has the same wavelength characteristic (wavelength dispersion characteristic) as said latter is obtained by extending | stretching. And it is disclosed that it can also be set as (lambda) / 4 or other retardation film by adjusting retardation value. In Example 4 of the said patent, the cellulose acetate of the acetylation degree 2.421 is obtained. When the retardation characteristic of the film using this was measured, when the film thickness is about 100 micrometers (50-150 micrometers), and a film thickness suitable as a freestanding film, retardation is inadequate. In addition, when the film thickness is as thick as 200 µm, a preferable retardation of about 80 to 150 nm is provided, and the thickness direction retardation Rth at that time is excessively greater than 350 nm, and when it functions as a lambda / 4 phase difference film, the viewing angle is enlarged. It did not function as a film and was not enough. In addition, it does not describe the molecular weight distribution of the obtained cellulose acetate, and it does not describe or suggest about controlling a phase difference characteristic by controlling molecular weight distribution.

On the other hand, the protective film of the polarizer PVA layer of the polarizing plate was manufactured using a material such as TAC, acrylic, etc., but the manufacturing cost of the retardation film is expensive to add to the raw material added to CAP, COP, TAC, the problem that the cost increases There was also.

On the other hand, the film based on the phase difference generated by the conventional negative birefringence as described above, the liquid crystal coating on the base film to a thickness of 1 to 3 micron, where the retardation uniformity due to the difference in the coating thickness of the phase difference R0, Rth is fine There was a problem of deterioration.

United States Patent No. 8,304,079 Korean Patent Publication No. 2011-0002091

The present invention has been made to solve the problems of the prior art as described above, the phase difference uniformity by producing a retardation film by blending a solvent substituted by one or more of the three substituents of the cellulose ester and solvent casting (solvent casting) It is an object to provide a cellulose-ester retardation film excellent in brittleness and being improved.

In order to achieve the object as described above, the present invention, the first resin in which one or two or more selected from R1 to R3 in the general formula (1) is substituted with Naphthoic acid or propionic acid (Propionic acid) First dope comprising a; And a second dope comprising a second resin in which one or two or more selected from R1 to R3 in Formula 1 is substituted with a hydrocarbon having 5 to 15 carbon atoms; It includes, wherein the mixing ratio of the first resin and the second resin provides a cellulose ester retardation film, characterized in that 1: 9 to 9: 1.

[Formula 1]

(R1 to R3 are each independently a hydrogen atom or a hydrocarbon having 1 to 15 carbon atoms, n is one or more, and the molecular weight distribution Mw / Mn value of the cellulose ester measured by gel permeation chromatography is (Mw is the weight average molecular weight, Mn is a number average molecular weight) in the range 2.0 to 4.5, preferably 2.0 to 3.0.The molecular weight affects the viscosity of the dope and the mechanical properties of the film to be produced. ) Is lowered, the viscosity is higher than 4.5, the problem of fairness occurs as the pressure rises when the dope is discharged to the die.

In the naphthoic acid (Naththoic acid) is generally a structure as shown in the formula (2), Propionic acid (Propionic acid) is a compound of the structure as shown in the formula (3).

[Formula 2]

(1-Naphthoic acid)

(1-Naphthoic acid)

[Formula 3]

(Propionic acid)

(Propionic acid)

The first resin is one or two or more selected from R1, R2 and R3 of the cellulose ester is limited to naphthoic acid or propionic acid and the second resin is specifically cellulose acetate, propionate, butylate and Preference is given to fatty acid esters of mixed cellulose, such as cellulose acetate propionate or cellulose acetate butyrate. Of the lower fatty acid esters of cellulose, cellulose triacetate is particularly preferred.

Here, the surface direction retardation value (R0) of the cellulose ester retardation film is 0 to 100nm, the thickness direction retardation value (Rth) is -150 to -30nm, the total film thickness is preferably 20 to 80㎛.

In addition, the first dope is a first resin is dissolved 15 to 90% by weight in a solvent, the second dope is preferably a second resin is dissolved 10 to 40% by weight in a solvent.

The present invention having the above-described configuration has an advantage in that retardation uniformity is improved, and the brittleness of the film is excellent, so that a durable retardation film having no cracking phenomenon can be produced, thereby enabling the production of a polarizing plate of excellent quality. .

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereto.

The cellulose ester retardation film according to the present invention comprises a first resin comprising one or two or more selected from R1 to R3 in the general formula (1) substituted with naphthoic acid or propionic acid 1 dope; And a second dope comprising a second resin in which one or two or more selected from R1 to R3 in Formula 1 is substituted with a hydrocarbon having 5 to 15 carbon atoms; It includes, wherein the mixing ratio of the first resin and the second resin provides a cellulose ester retardation film, characterized in that 1: 9 to 9: 1.

[Formula 1]

(R1 to R3 are each independently a hydrogen atom or a hydrocarbon having 1 to 15 carbon atoms, n is one or more, and the molecular weight distribution Mw / Mn value measured by gel permeation chromatography is (Mw is the weight average molecular weight, and Mn is the number). Average molecular weight) 2.0 to 4.5, preferably 2.0 to 3.0)

Here, the surface direction retardation value (R0) of the cellulose ester retardation film is 0 to 100nm, the thickness direction retardation value (Rth) is -150 to -30nm, the total film thickness is preferably 20 to 80㎛.

In addition, the first dope is a first resin is dissolved 15 to 90% by weight in a solvent, the second dope is preferably a second resin is dissolved 10 to 40% by weight in a solvent.

Generally used cellulose esters are preferably lower fatty acid esters of cellulose. Lower fatty acids used to prepare lower fatty acid esters of cellulose refer to fatty acids having 6 or less carbon atoms. Examples of lower fatty acid esters are cellulose acetate, cellulose propionate, cellulose butyrate and fatty acid esters of mixed cellulose such as cellulose acetate propionate or cellulose acetate butyrate. Of the lower fatty acid esters of cellulose, cellulose triacetate or cellulose acetate propionate is particularly preferred.

In the present invention, the cellulose ester is a hydrocarbon having 5 to 15 carbon atoms in at least one of three substituents of cellulose ester and a resin (first resin) in which naphthoic acid or propionic acid is substituted in at least one of three substituents of cellulose ester. It is characteristic to use substituted resin (2nd resin). The first resin has a negative refractive index anisotropy characteristic with a large Nz value, and the retardation film is prepared by blending and solvent casting the blended first and second resins.

Preferably, as the first resin, one or two or more selected from R1, R2, and R3 are substituted with naphthoic acid and propionic acid, and cellulose triacetate is used as the second resin.

The molecular weight range of the cellulose ester is not limited, but the weight average molecular weight is preferably in the range of 150,000 to 220,000. By making the said molecular weight more than a predetermined level, it can prevent effectively that the intensity | strength of a film falls. Moreover, by making molecular weight below a fixed level, the viscosity of a cellulose ester solution (main dope liquid) is kept below a fixed level, and film production by a solvent casting method becomes easy. The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) which is the molecular weight dispersion degree of a cellulose ester is 2.0-4.5, Preferably it is the range of 2.0-3.0. Molecular weight affects the viscosity of the dope and the mechanical properties of the film to be produced. When the molecular weight distribution value is less than 2.0, the mechanical properties (especially modulus) are lowered. When the molecular weight is higher than 4.5, the viscosity is too high to discharge the dope into the die. If the pressure rises, the problem of fairness occurs.

The liquid crystal cellulose ester retardation film according to the present invention may be prepared by solvent casting. In the solvent casting method, the cellulose ester is dissolved in an agitator using additives such as a plasticizer, a UV absorber, a mat agent, and a mixed solvent such as methylene chloride and methanol, to prepare a dope, and can be used by filtration using a filtration device.

When the film is produced by the solvent casting method, the solvent for producing the cellulose ester solution (main dope) is preferably an organic solvent. As the organic solvent, halogenated hydrocarbons are preferably used, and halogenated hydrocarbons include chlorinated hydrocarbons, methylene chloride and chloroform, and methylene chloride is most preferably used.

Moreover, you may mix and use organic solvents other than halogenated hydrocarbon as needed. Organic solvents other than halogenated hydrocarbons include esters, ketones, ethers, alcohols and hydrocarbons. As ester, methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acylate, ethyl acylate, pentyl acete and the like can be used. As ketone, acetone, methyl ethyl ketone, diethyl ketone, di Isobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone and the like can be used, and ethers include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxe Solan, tetrahydrofuran, anisole, phentol, and the like can be used, and alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol , 2-methyl-2-butanol, cyclohexanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol and the like are used.

More preferably, methylene chloride may be used as the main solvent, and alcohol may be used as the subsolvent. Specifically, methylene chloride and alcohol may be mixed and used in a weight ratio of 80:20 to 95: 5. Most preferably, methyl chloride and methanol are used in a mixing ratio of 9: 1.

In the present invention, 15 to 90% by weight of a first resin in which naphthoic acid or propionic acid is substituted in at least one of the three substituents of cellulose ester is dissolved in a solvent, and the first dope is preferably used. It is good to dissolve%.

In addition, the second resin in which a hydrocarbon having 5 to 15 carbon atoms is substituted in at least one of the three substituents of the cellulose ester is characterized in that 10 to 40% by weight of the solvent is used to dissolve the second dope. 20 wt%, more preferably 17 wt%.

When the first resin is dissolved in a solvent less than 15% by weight, or the second resin is dissolved in less than 10% by weight, the prepared cellulose ester film cannot obtain a high negative Rth value, which is insufficient to improve the viewing angle. If the first resin is dissolved in more than 90% by weight of the solvent, or more than 40% by weight of the second resin in the solvent, the problem of brittle and haze deepening during film production occurs.

In the production of the cellulose ester film of the present invention, various additives such as UV blockers, plasticizers, anti-degradants, fine particles, optical property modifiers, and the like can be added, and at the time of addition, each dope or main dope liquid preparation step You can add anything at. Moreover, you may add and implement the process of adding and preparing an additive to the last preparation process of each dope or main dope liquid preparation process.

Specifically, in the cellulose ester solution (main dope solution), the first dope or the second dope used in the solvent casting method, various additives according to the use in each preparation step, for example, a plasticizer, a deterioration inhibitor, a matte particle, a release agent Additives, such as wavelength dispersion regulators, such as an ultraviolet stabilizer, an ultraviolet absorber, and an infrared absorber, and an optically anisotropic regulator, can be added. Specific kinds of such additives may be used without limitation as long as it is conventionally used in the art, the content is preferably used in a range that does not lower the physical properties of the film. The timing of adding the additive is determined by the type of the additive. The step of adding an additive at the end of the cellulose ester solution (dope) preparation may be performed.

On the other hand, the cellulose ester film contains a plasticizer for improving mechanical strength, imparting good casting resistance and water absorption, reducing water permeability, and the like. The plasticizer can be used as long as it is conventionally used without limitation, and examples thereof include carboxylic acid esters selected from phosphate esters and phthalic acid esters or citric acid esters, and terminal asymmetric aromatic compounds and terminal symmetric aliphatic compounds can also be used. Do. It is also preferable to use a polyhydric alcohol ester plasticizer, a polyester plasticizer, and a polyhydric carboxylic acid plasticizer.

In the case where the plasticizer is contained, the content thereof is preferably about 2% by weight to about 15% by weight relative to the cellulose ester-based resin in consideration of dimensional stability and processability, and if the content of the plasticizer is too small, the film There is little effect of reducing the moisture permeability, and when a slit process or a punching process is performed, a smooth cut surface cannot be obtained and a generation | occurrence | production of cutting waste tends to increase. That is, the effect to contain a plasticizer cannot fully be exhibited. Moreover, when too much, the plasticizer bleeds out from a resin film and it exists in the tendency for the physical property of a film to deteriorate.

On the other hand, as a UV blocking agent which concerns on this invention, the benzotriazole type UV blocking agent and the triazine type UV blocking agent which are high in transparency and are excellent in the effect which prevents deterioration of a polarizing plate and a liquid crystal element are preferable, and a benzotriazole type with a more suitable spectral absorption spectrum is preferable. UV blockers are particularly preferred.

The conventionally well-known benzotriazole type UV blocking agent used especially preferably with the UV blocking agent which concerns on this invention may be a bismuth, For example, 6,6'- methylene bis (2- (2H-benzo [d ] [1,2,3] triazol-2-yl))-4- (2,4,4-trimethylpentan-2-yl) phenol, 6,6'- methylenebis (2- (2H-benzo [ d] [1,2,3] triazol-2-yl))-4- (2-hydroxyethyl) phenol and the like. In the present invention, it is preferable to add about 0.1% by mass to about 20% by mass of the UV blocking agent, and it is preferable to add about 0.5% by mass to about 10% by mass, and about 1% by mass to about 5% by mass. It is preferable to add. These may use 2 or more types together.

As for the cellulose ester film of this invention, the solvent casting method can produce the film excellent in physical properties, such as an optical property, compared with another manufacturing method. In the solvent casting method, a main dope liquid is prepared by first mixing various additives such as a cellulose ester, a UV absorber, a mat agent, a retardation control agent, and a plasticizer with a mixed solvent containing methyl chloride as the main solvent.

Specifically, in the present invention, the cellulose ester solution (main dope solution) obtained by mixing or blending the first dope containing the first resin and the second dope containing the second resin as described above on the support through a casting die. Casting forms a cellulose ester sheet.

Specifically, the first dope dissolves 15% to 90% by weight of the first resin in which naphthoic acid or propionic acid is substituted in one or more of the three substituents of the cellulose ester in a solvent, and preferably 25% by weight. It is good. In the second dope, the second resin in which the hydrocarbon having 5 to 15 carbon atoms is substituted in at least one of the three substituents of the cellulose ester is dissolved in an amount of 10 to 40% by weight with respect to the solvent, and preferably 15 to 20% by weight. good.

In addition, the first dope and the second dope is blended in a mixing ratio of 1: 9 to 9: 1 to prepare a cellulose ester main dope solution. When the first dope ratio is selected to less than 1 or more than 9, it is difficult to obtain a negative retardation value, and when the first resin is dissolved in a solvent of less than 15% by weight or the second resin is dissolved in less than 10% by weight, Cellulose ester film has a problem of improving the viewing angle due to a high negative Rth value is not obtained, and when the first resin is dissolved in more than 90% by weight of the solvent, or more than 40% by weight of the second resin in the solvent when the film is produced There is a concern that brittle and haze deepening are a concern.

Subsequently, the cellulose ester sheet formed by casting the main dope solution on the support from the casting die or the T-die is volatilized from the support and conveyed to the stretching step when the solvent is volatilized to obtain self-support. The stretching process is generally performed in the temperature range of Tg to Tg-50 ° C to Tg + 50 ° C and the elongation is in the range of 100 to 150% in the width or length direction. However, the higher the elongation, the more the phase difference value due to the nonuniformity of the edges and the central portion is non-uniform.

The cellulose ester film thus formed is dried in the Tg or less in the Dryer, which can simultaneously obtain the heat setting effect of the Dryer, to control the appearance of the wrinkles and the like of the film and to increase the dimensional stability such as thermal shrinkage and wet thermal expansion rate.

The cellulose ester film produced by the present invention has a film thickness of about 20 μm to about 80 μm. According to the present invention, the thickness of the cellulose ester film is preferably about 20 μm to about 80 μm. In particular, when less than about 20 ㎛ falls in physical properties, if it is more than about 80 ㎛ falls in industrial applicability.

In addition, the prepared film satisfies the + C, + B Plate characteristics of the phase difference, R0 is 0 to 150nm, Rth is characterized in that -150 ~ -30nm. R0 and Rth are surface direction phase difference values and thickness direction phase difference values, respectively, represented by the following equations (1) and (2).

Equation (1) Re = (Nx-Ny) × d

Equation (2) Rth = (Nx + Ny) / 2-Nz × d

+ C: Nz> Nx = Ny

+ B: Nz> Nx> Ny

(Where d is the thickness of the film (nm), Nx is the maximum refractive index in the plane of the film, Ny is the refractive index in the direction perpendicular to Nx in the film plane, and Nz is the refractive index of the film in the thickness direction)

In addition, the cellulose ester film of the present invention can be applied to a polarizing plate and a liquid crystal display device. The polarizing plate and the liquid crystal display device is characterized in that it comprises a cellulose ester film. The polarizing plate is obtained by pasting protective films on both sides of the polarizer, and at least one of the protective films is the cellulose ester film. The liquid crystal display device has a liquid crystal cell and two polarizing plates arranged on both sides of the liquid crystal cell, wherein the liquid crystal cell is in a vertical alignment mode.

Such a polarizing plate may be manufactured according to a conventional method. For example, the cellulose ester film of the present invention is alkali saponified, and the resulting film is immersed in a polyvinyl alcohol (PVA) film in an iodine solution, and the film is drawn to fully polyvinyl alcohol on both sides of the polarizing film produced. Bond using an aqueous solution. Alkali saponification refers to a treatment in which a cellulose ester film is immersed in a hot alkali solution to improve the wettability of the film to the aqueous adhesive and to provide good adhesion to the film.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereto.

Example 1

<Step 1> Cellulose Ester

As the cellulose ester, a resin in which R 1 was substituted with propionic acid in Chemical Formula 1 was used as the first resin, and TAC (Cellulose triacetate) was used as the second resin.

[Formula 1]

<Step 2> Preparation of cellulose ester dope

The first resin prepared in Step 1 was dissolved in 25% by weight in a mixed solvent of methylene chloride and methanol 9: 1 to prepare a first dope.

The second resin was dissolved 17% by weight in a mixed solvent of 9: 1 methylene chloride and methanol, and a second dope was prepared by dissolving 8% by weight of triphenylphosphate as a plasticizer.

<Step 3> Preparation of cellulose ester film

The cellulose-ester main dope liquid which blended the 1st dope and the 2nd dope prepared in the step 2 by 25:75 ratio was cast uniformly on the stainless band support of width 800mm using the belt casting apparatus. The solvent was evaporated on the stainless band support and peeled off from the stainless band support. Subsequently, it conveyed for 15 minutes in the drying section set to 110 degreeC, and dried to produce the cellulose-ester film with a film thickness of 40 micrometers.

Example 2

A cellulose ester film was prepared in the same manner as in Example 1 except that the ratio of the first dope and the second dope was changed to 84:16 and the thickness of the film was 20 μm.

Example 3

A cellulose ester film was prepared in the same manner as in Example 1 except that the ratio of the first dope and the second dope was changed to 26:74 and the thickness of the film was 80 μm.

Example 4

A cellulose ester film was prepared in the same manner as in Example 1 except that the ratio of the first dope and the second dope was changed to 22:78 and the thickness of the film was 20 μm.

Example 5

A cellulose ester film was prepared in the same manner as in Example 1 except that the ratio of the first dope and the second dope was changed to 10:90 and the thickness of the film was prepared at 80 μm.

Comparative Example 1

A cellulose ester film was prepared in the same manner as in Example 1 except that the ratio of the first dope and the second dope was changed to 5:95.

Comparative Example 2

A cellulose ester film was prepared in the same manner as in Example 1 except that the ratio of the first dope and the second dope was changed to 95: 5.

1. Phase difference measurement

Using Axoscan equipment, R0, which is a phase difference value in the in-plane direction and Rth, which is a phase difference value in the thickness direction, was measured at a wavelength of 550 nm under an environment of 55 ° C. and 55% RH.

2. Folding evaluation

Brittle properties were evaluated by the following soft fracture test. The optical film moistened for 24 hours in an air-conditioned room at 23 ° C. and 55% RH was cut out at 100 mm (length) × 10 mm (width) under conditions of 5 ° C. and 22% RH, and a curvature radius of 0 mm and a bending angle were formed at the center in the longitudinal direction. The film was bent once each in two by acid folding and bone folding so that the film was superimposed at 180 °, and this evaluation was measured 10 times and evaluated as follows. In addition, in the evaluation here, "broken" shows that it split and separated into two or more pieces.

Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Blending
ratio 1 resin 25 84 26 22 10 95 5 2 resin 75 16 74 78 90 5 95 Thickness [㎛] 40 20 80 20 80 40 40 Phase difference R0
(Deviation) One
(± 1) One
(± 1) One
(± 1) One
(± 1) One
(± 1) 1.5
(± 1.5) 5
(± 0.2) Rth
(Deviation) -80
(± 2) -150
(± 2) -150
(± 2) -30
(± 2) -30
(± 2) -340
(± 10) 6
(± 1) Brittle Castle Folding evaluation OK OK OK OK OK fracture OK

According to the Examples and Comparative Examples of the present invention, as the ratio of the first resin increases, the phase difference Rth value tends to increase in the negative direction. Uniformity was high.

In addition, there was no cracking phenomenon when the first resin and the second resin were used in the range of 9: 1 to 1: 9 through Brittle's folding evaluation.

Claims (3)

A first dope including a first resin in which one or two or more selected from R1 to R3 in Formula 1 is substituted with naphthoic acid or propionic acid; And
A second dope comprising a second resin substituted with one or two or more selected from R1 to R3 in a chemical formula 1 to a hydrocarbon having 5 to 15 carbon atoms; Including,
The mixing ratio of the first dope and the second dope is 1: 9 to 9: 1 cellulose ester retardation film, characterized in that.
[Formula 1]

(R1-R3 are each independently a hydrogen atom or a hydrocarbon having 1 to 15 carbon atoms, and n is 1 or more.)
The method of claim 1,
The surface direction retardation value R0 of the cellulose ester retardation film is 0 to 100 nm, the thickness retardation value Rth is -150 to -30 nm, and the total thickness of the film is 20 to 80 μm. film.
The method of claim 1,
The first dope is a cellulose ester retardation film, characterized in that the first resin is dissolved 15 to 90% by weight in a solvent, the second dope is 10 to 40% by weight dissolved in a solvent.