JP2002040244A - Optical film, method for manufacturing the same, polarizing plate and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film with excellent optical characteristics and flatness, with less curling and with excellent facility for handling. SOLUTION: The optical film is characterized by containing a cellulose ester with number-average molecular weight (Mn) and weight average molecular weight (Mw) satisfying inequalities 50,000<=Mn<=130,000 and 130,000<=Mw<=290,000.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical film (hereinafter, also simply referred to as a film), a method for producing the same, a polarizing plate for liquid crystal display, and a display device.

[0002]

2. Description of the Related Art A liquid crystal display device can be directly connected to an IC circuit with low voltage and low power consumption, and in particular, can be made thin, so that it can be used as a display device for a word processor or a personal computer. Widely adopted. This liquid crystal display device has a basic configuration in which, for example, polarizing plates are provided on both sides of a liquid crystal cell.

A polarizing plate generally has a structure in which a transparent resin layer is laminated on both front and back sides of a polarizing film made of a polyvinyl alcohol film or the like in which iodine or a dye is adsorbed and oriented, and the transparent resin layer is made of cellulose acetate. Protective films of cellulose esters such as cellulose acetate butyrate and cellulose acetate propionate are preferably used because of their high transparency, excellent dimensional stability, and low birefringence.

[0004] In recent years, liquid crystal displays and organic EL displays have been developed as monitors that can replace CRTs in order to increase the screen size and image quality. Accordingly, requirements for protective films for polarizing plates have become stricter. In particular, the optical characteristics are becoming more severe, and there is a demand for a film having excellent optical isotropy and having a uniform and lower retardation. Further, the film is required to be thinner from the viewpoints of productivity improvement and transparency when the liquid crystal display is mounted, but in the conventional method, the optical isotropy is deteriorated or the flatness is deteriorated. There is a problem that handling becomes difficult due to the occurrence of curling or the like.

[0005]

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide an optical film having excellent optical properties, good flatness, little curl, and excellent handling properties.

[0006]

As a result of intensive studies, the present invention has been achieved by the following constitutions. 1. Number average molecular weight (Mn) is 50,000 ≦ Mn ≦ 130
000, weight average molecular weight (Mw) is 130,000 ≦ Mw
1. An optical film comprising a cellulose ester satisfying ≦ 290000. Number average molecular weight (Mn) is 50,000 ≦ Mn ≦ 130
000, weight average molecular weight (Mw) is 130,000 ≦ Mw
≤290000, Z-average molecular weight (MZ) is 190000
2. An optical film containing a cellulose ester satisfying ≦ Mz ≦ 490000, In the relationship between the molecular weight of the cellulose ester and the weight fraction, the weight fraction has two or more maximum values, and the number average molecular weight (Mn) of the smallest molecular weight corresponding to the maximum value is 50,000 ≦ Mn ≦ 130,000. 3. an optical film containing a cellulose ester having a weight average molecular weight (Mw) of 130,000 ≦ Mw ≦ 290000, 4. An optical film comprising the cellulose ester, wherein the content of the alkaline earth metal in the cellulose ester is 30 ppm or less, 5. The optical film according to any one of 1 to 4, wherein the cellulose ester contains an alkaline earth metal content of 30 ppm or less in the cellulose ester. 6. The optical film according to any one of 1 to 5, wherein the cellulose ester contains an acyl group having 2 to 4 carbon atoms, and the total degree of substitution of the acyl group is 2.60 to 2.90. The cellulose ester has a degree of acetyl substitution of 2.60 to
7. The optical film according to any one of 1 to 5, which is 2.80 triacetyl cellulose; The cellulose ester has a degree of acetyl substitution of 1.8 to 2.
2. Cellulose acetate propionate having a degree of propionyl substitution of 0.6 to 1.0;
8. The optical film according to any one of the above, Number average molecular weight (Mn) is 50,000 ≦ Mn ≦ 130
000, weight average molecular weight (Mw) is 130,000 ≦ Mw
≤290000, Z-average molecular weight (Mz) is 190000
Using a cellulose ester having ≦ Mz ≦ 490,000, casting a dope having a solid content concentration of 17% by mass or more and 35% by mass or less on a support, followed by peeling and drying, and a method for producing an optical film, 10. Number average molecular weight (Mn) is 50,000 ≦ Mn ≦ 13
0000, weight average molecular weight (Mw) is 130,000 ≦ M
a cellulose ester of w ≦ 290000, wherein the amount of water contained in the cellulose ester is 0.1 to 2.0.
%. A method for producing an optical film, comprising: preparing a dope in a state of being in the form of a dope, casting the dope on a support, and peeling and drying the dope. Number average molecular weight (Mn) is 50,000 ≦ Mn ≦ 13
0000, weight average molecular weight (Mw) is 130,000 ≦ M
A method for producing an optical film, wherein the dope containing a cellulose ester having a w ≦ 290000 has a water content of 0.02 to 0.7%, and the dope is cast on a support, and then separated and dried. , 12. After casting a dope having a solids concentration of 22% by mass or more and a viscosity of 23 Pa or less by a rotational viscometer at 23 ° C. or less on a support, holding the dope on the support for 30 to 90 seconds, and then peeling the dope. 12. a method for producing an optical film, which is dried to form a film having a thickness of 20 to 65 μm; After casting a dope having a solids concentration of 22% by mass or more and a viscosity of 23 Pa or less by a rotational viscometer at 23 ° C. or less on a support, holding the dope on the support for 30 to 90 seconds, and then peeling the dope. 13. The method for producing an optical film according to any one of 9 to 11, wherein the film is dried to form a film having a thickness of 20 to 65 μm. 55. The method for producing an optical film according to any one of 9 to 13, wherein the content ratio of the poor solvent is 3 to 7% relative to the total amount of the organic solvent contained in the cellulose ester dope; 15. The method for producing an optical film according to any one of 9 to 14, wherein the film is stretched 1.01 to 2.5 times in the width direction in a drying step after the film is peeled off. Optical films characterized by being manufactured by the methods of 1 to 15; a polarizing plate characterized by using the optical films described in 17.1 to 8 and 16; and a polarizing plate characterized by using the polarizing plate described by 18.17. Display device.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The cellulose ester film of the present invention requires that the average molecular weight of the cellulose ester be in a specific range. Since the average molecular weight can be measured using high performance liquid chromatography, the number average molecular weight (Mn), the weight average molecular weight (Mw), and the Z average molecular weight (Mz) can be calculated using this.

The measurement conditions are as follows.

Solvent: methylene chloride Column: Shodex K806, K805, K8
03G (Used by connecting three Showa Denko KK) Column temperature: 25 ° C Sample temperature: 0.1% by mass Detector: RI Model 504 (GL Science) Pump: L6000 (Hitachi, Ltd. Flow rate: 1.0 ml / 1 min Calibration curve: Standard polystyrene STK standard
d Polystyrene (manufactured by Tosoh Corporation) Mw = 1000
A calibration curve with 13 samples from 000 to 500 was used. Preferably, 13 samples are obtained at approximately equal intervals.

In the present invention, the number average molecular weight (Mn)
Is 50000 ≦ Mn ≦ 130000, the weight average molecular weight (Mw) is 130000 ≦ Mw ≦ 290000, and the Z average molecular weight (Mz) is 190000 ≦ Mz ≦ 490000. When the average molecular weight is below these ranges, mechanical properties such as tear strength are degraded, and the film tends to be broken particularly at the time of forming a thin film. On the other hand, if it exceeds, the viscosity of the dope solution containing the cellulose ester increases, causing an increase in filtration pressure, liquid sending pressure, and casting pressure during film formation, which is not preferable in production suitability especially at the time of high-speed film formation. . The preferred molecular weight range is 60000 ≦ Mn ≦ 1200
00, 150,000 ≦ Mw ≦ 270,000, 22,000
0 ≦ Mz ≦ 450,000, more preferably 700
00 ≦ Mn ≦ 90000, 160000 ≦ Mw ≦ 250
000, 250,000 ≦ Mz ≦ 430000.

In the present invention, a plurality of types of cellulose esters having different average molecular weights can be contained. This not only dramatically improves the resistance to film breakage due to excessive tension applied to the film during high-speed film formation or thin film film formation, but also provides a film with better optical isotropy. it can.

Specifically, it is preferable that the weight fraction has two or more maximum values in relation to the molecular weight of the cellulose ester and the weight fraction. At least one of them has an average molecular weight of 60000 ≦ Mn ≦ 120,000, 15
0000 ≦ Mw ≦ 270000, 220,000 ≦ Mz ≦
450,000, at least one of which is 1200
00 <Mn ≦ 170,000, 270000 <Mw ≦ 38
0000, 450,000 <Mz ≦ 900,000 is preferred. More preferably, at least one is 70,000 ≦ Mn ≦ 90000, 160000 ≦ Mw ≦
250,000, 250,000 ≦ Mz ≦ 430000, at least one of which is 130,000 ≦ Mn ≦ 16
0000, 290000 ≦ Mw ≦ 350,000, 500
It is preferable to be in the range of 000 ≦ Mz ≦ 8000000. The mass ratio of the cellulose ester corresponding to the latter molecular weight is 3% with respect to the total mass of the cellulose ester.
Preferably, it is 50%. Further, the concentration of the solid content in the dope solution in which the cellulose ester is dissolved is more preferably 17 to 35% by mass.

The solid content concentration in the present invention refers to the weight ratio of cellulose ester to the total weight of the dope solution.
When this value is lower than 17% by mass, the amount of the organic solvent in the dope is excessive, so that the drying load at the time of film formation increases, and not only a desired film formation speed cannot be achieved, but also the flatness and curl characteristics are hindered. And causes an increase in retardation in the thickness direction. In addition, in the region higher than 35% by mass, poor dissolution of not only the cellulose ester but also additives such as a plasticizer occurs, which causes clogging of the filter at the time of liquid sending and foreign matter failure at the time of film formation. I will. The preferred solid content concentration is 18% by mass or more and 32% by mass or less, more preferably 20% by mass or more and 29% by mass or less.

In the present invention, the content of the alkaline earth metal in the cellulose ester is preferably 30 ppm or less because of excellent optical characteristics. If it exceeds this range, not only does the viscosity of the dope solution in which the cellulose ester is dissolved significantly increase, but also the dope solution becomes cloudy and the quality of the film surface deteriorates due to foreign matter. A more preferable range is 15 ppm or less, and it is most preferable not to contain it at all.

In the present invention, the content of the alkaline earth metal, that is, the metal component such as the content of calcium (Ca) and the content of magnesium (Mg) is determined by using a micro-digest wet cracking device to dry absolutely dried triacetyl cellulose. After pretreatment with alkali melting, I
It can be determined by performing analysis using CP-AES (inductively coupled plasma emission spectrometer).

It is preferable that the cellulose ester contains mannose and xylose contained in the neutral sugar component at a specific ratio in order to improve the releasability during film formation. That is, it is preferable that mannose / xylose (molar ratio) = 0.35 / 1 to 3/1.
More preferably, it is 35/1 to 2/1. More preferably, it is 0.7 / 1 to 1.3 / 1.

Further, the total content of mannose and xylose contained in the neutral constituent sugar component of the cellulose ester is preferably 1 to 5 mol%, more preferably 2 to 3.5 mol%.

On the other hand, the amount of water contained in the cellulose ester is preferably 0.1% to 2.0%. As a result, not only can the viscosity of the dope solution in which the cellulose ester is dissolved be kept low, but also a film having excellent optical isotropy can be obtained. A more preferred range is from 0.1% to
1.5%, and more preferably 0.1% to 1.0%.

For the same reason, the water content in the cellulose ester dope is preferably 0.02% to 0.7%. More preferably, it is 0.02% to 0.5%, and still more preferably 0.02% to 0.4%.

The viscosity of the dope solution in which the cellulose ester of the present invention is dissolved can be easily measured by using a rotational viscometer. For example, JIS-
A Brookfield viscometer described in K7117 can be used.

The thickness of the cellulose ester film of the present invention can be arbitrarily set.
It is preferable from the viewpoint of improving productivity and the viewpoint of being superior in transparency. More preferably, it is 30 to 55 μm.

In the present invention, one of the objects is to improve the optical isotropy. Specifically, it is necessary to keep the retardation of the film low. The retardation has a Ro value representing the in-plane optical anisotropy and an Rt value representing the optical anisotropy in the film thickness direction, each of which is represented by the following formula.

Ro value (nm) = (Nx−Ny) × d Rt value (nm) = ((Nx + Ny) / 2−Nz) × d (where Nx is the refractive index in the slow-moving direction in the film plane) , Ny represents the refractive index in the advancing direction, Nz represents the refractive index in the thickness direction, and d represents the thickness (nm) of the film.) To measure the retardation value, an automatic birefringence meter KOBR was used.
It can be obtained by performing three-dimensional refractive index measurement at a wavelength of 590 nm using A-21ADH (manufactured by Oji Scientific Instruments) to determine the refractive indexes Nx, Ny, and Nz.

The range of the retardation value is Ro ≦ 10,
It is preferable that Rt ≦ 60 because the optical anisotropy of the film is small and the discoloration and light leakage of the display portion when incorporated into a liquid crystal display device are small. More preferably Ro ≦ 5,
Rt ≦ 50, more preferably Ro = 0 and Rt ≦ 40.

In the present invention, the effect of the present invention can be more exhibited when the ratio of the poor solvent to the total amount of the organic solvent contained in the cellulose ester dope is 3 to 7%. That is, when the concentration exceeds this range, not only does the viscosity of the dope solution rise sharply, but also the reduction of cloudiness and poor dissolution occurs. A more preferred range is 4 to 7%, and an even more preferred range is 5 to 6.5%.

The poor solvent referred to in the present invention includes, for example, lower aliphatic alcohols, and specific examples thereof include, but are not limited to, methanol, ethanol, n-propanol, isopropanol, and n-butanol.

The cellulose as a raw material of the cellulose ester used in the film of the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Cellulose esters obtained therefrom can be mixed and used at an arbitrary ratio.

When the acylating agent is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), the cellulose ester of the present invention may be an organic solvent such as acetic acid or an organic solvent such as methylene chloride. And using a protic catalyst such as sulfuric acid. The acylating agent is an acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H
_In the case of ( ₇ COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized by the method described in JP-A-10-45804. The cellulose ester of the present invention is obtained by adjusting and mixing the amount of the above-mentioned acylating agent according to each degree of substitution. In the cellulose ester, these acyl groups react with the hydroxyl groups of the cellulose molecule. Cellulose molecules are composed of a large number of linked glucose units, and the glucose unit has three hydroxyl groups. The number of acyl groups derived from these three hydroxyl groups is called the degree of substitution (mol%).
For example, in the cellulose triacetate preferably used in the present invention, all three hydroxyl groups of the glucose unit are bonded to acetyl groups (actually, 2.6 to 3.
0). As other cellulose esters, cellulose acetate to which a propionate group or a butyrate group is bonded in addition to an acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, or cellulose acetate propionate butyrate is preferably used. In addition, propionate is iso- and s-in addition to n- in addition to n-.
ec- and tert- also include each. Cellulose acetate propionate having a large degree of substitution of propionate groups is particularly useful as a film for a liquid crystal image display device because of its excellent water resistance and high mechanical strength.

The method for measuring the degree of substitution of the acyl group is ASTM-
It can be measured according to D817-96. In the present invention, an acyl group having 2 to 4 carbon atoms is contained, and the total degree of substitution of the acyl group is preferably 2.60 to 2.90,
More preferably, it is 2.60 to 2.80. A particularly preferred range is 2.65 to 2.75.

When the cellulose ester used in the film of the present invention is cellulose acetate, it is necessary to pay attention to the degree of acetylation (the amount of acetic acid bond) as well as the total degree of substitution. The acetylation degree is represented by mass% of acetic acid in cellulose acetate, and if it is too high, the solubility of the dope deteriorates. Conversely, if the degree of acetylation is too low, the water content increases more than necessary, and the storage stability after film formation is significantly deteriorated.
When the cellulose ester of the present invention is triacetyl cellulose, the preferred range of acetylation degree is 58 to 60%,
More preferably, it is 58.5-59.5%.

Solvents for dissolving the film material of the present invention to form a dope include methylene chloride, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolan, 1,4-dioxolan, cyclohexanone, Examples thereof include 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, and 1,3-difluoro-2-propanol.

The film of the present invention preferably contains a plasticizer.

The plasticizer that can be used is not particularly limited, but in the case of a phosphate ester type, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate,
Phthalates such as diphenylbiphenyl phosphate, trioctyl phosphate and tributyl phosphate include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate,
In the glycolic acid ester system such as dibutyl phthalate and di-2-ethylhexyl phthalate, triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. It is preferable to use them alone or in combination.

It is preferable to use an ultraviolet absorber in the film of the present invention. The ultraviolet absorber has an excellent ability to absorb ultraviolet light having a wavelength of 380 nm or less from the viewpoint of preventing deterioration of the liquid crystal and has good liquid crystal display properties. It is preferable to use those having absorption of visible light having a wavelength of 400 nm or more as small as possible. In particular, the transmittance at a wavelength of 380 nm is preferably 10% or less, more preferably 5% or less, and further preferably 2% or less.

Examples of the ultraviolet absorber include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds,
Examples thereof include a cyanoacrylate compound and a nickel complex salt compound, but the present invention is not limited thereto.

In the present invention, one of these ultraviolet absorbers
It is preferable to use at least two kinds of UV absorbers, and two or more different UV absorbers may be contained.

The method of adding the ultraviolet absorber may be such that the ultraviolet absorber is dissolved in an organic solvent such as alcohol, methylene chloride or dioxolane and then added to the dope, or may be added directly to the dope composition. Those which do not dissolve in an organic solvent such as inorganic powders can be added to a dope after dispersing in an organic solvent and a cellulose ester using a dissolver or a sand mill.

The amount of the ultraviolet absorber preferably used in the present invention is 0.1% by mass based on the cellulose ester.
1 mass% to 2.5 mass%, preferably 0.5 mass% to
2.0 mass%, more preferably 0.8 mass% to 2.0 mass%.

Further, it is preferable to add fine particles such as silicon oxide as a matting agent to the film of the present invention for the purpose of improving slipperiness and preventing blocking after winding. Fine particles such as silicon oxide are preferably surface-treated with an organic substance because the haze of the film can be reduced. Preferred organic substances for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes and the like.

The larger the average particle size of the fine particles, the greater the matting effect, and the smaller the average particle size, the better the transparency. Therefore, the average primary particle size of the fine particles is preferably 5 to 50 n.
m, more preferably 7 to 14 nm.

As the fine particles of silicon oxide, AEROSIL 200, 200V, 300 manufactured by Aerosil Co., Ltd.
R972, R972V, R974, R202, R81
2, OX50, TT600, etc., preferably AEROSIL 200V, R972V, R972, R9
74, R202, R812 and the like. The cellulose ester film used for the optical film of the present invention is preferably produced by a solution casting method. The solution casting film forming method is, for example, a mixed solvent consisting of a good solvent and a poor solvent for cellulose ester, a dope in which the cellulose ester and a plasticizer are dissolved, and a precision gear pump that sends out a certain amount of dope per hour from a die. Cast on a continuously rotating endless support,
After evaporating the solvent on the support and solidifying the dope, the web is peeled off from the support, and the cellulose acetate film is obtained while maintaining the width using a drying device and / or a tenter that is dried while being conveyed by rolls. It is.

The solvent content in the film when peeled from the support is preferably from 40 to 120% by mass from the viewpoints of film releasability, load in the drying step and control of the retardation value. More preferably, it is 60 to 100% by mass.

The tenter is preferably used because the retardation fluctuation due to the tension applied in the film transport direction can be appropriately corrected, and can be arbitrarily selected from a pin tenter method or a clip tenter method. The stretching ratio is preferably 1.01 to 2.5 times, more preferably 1.03 to 1.5 times, and still more preferably 1.05 to 1.5 times.
It is 1.1 times.

In the case where the optical film of the present invention is used as a protective film for a polarizing plate for display, a conventionally known polarizer can be used for producing a polarizing plate for display. For example, a film made of a hydrophilic polymer such as polyvinyl alcohol is treated with a dichroic dye such as iodine and stretched, or a film obtained by treating a plastic film such as vinyl chloride and orienting a polyene is used. Can be used.

As the polarizing plate for display, one obtained by laminating the protective film for polarizing plate for display on at least one surface side of a polarizer is preferably used.

[0047]

EXAMPLES The present invention will now be described more specifically with reference to examples, but embodiments of the present invention are not limited thereto.

Example A dope solution 1 was prepared as follows using cellulose esters having the component amounts and characteristics shown in Table 1.

(Preparation of Dope Solution 1) Triacetyl cellulose TAC1 100 kg Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 0.3 kg Tinuvin 171 (manufactured by Ciba Specialty Chemicals) 0.5 kg Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 0. 5 kg Ethylphthalylethyl glycolate 2 kg Triphenyl phosphate 10 kg Aerosil 200 V (manufactured by Nippon Aerosil Co.) 0.07 kg Methylene chloride 320 kg Ethanol 20 kg At least, put in a closed container, and completely pressurize while keeping the temperature at 80 ° C under stirring and stirring. Dissolved.

(Preparation of dope solutions 2 to 9) Dope solutions 2 to 9 were prepared in the same manner except that the cellulose acetate and the preparation of the dope solution 1 were changed as shown in Table 1. The solid content concentration was adjusted so that the viscosity at 23 ° C. measured with a Brookfield-type rotational viscometer was equivalent to that of the dope solution 1.

[0051]

[Table 1]

(Preparation of Film Sample 1) Dope Solution 1
After filtration, the dope temperature was adjusted to 33 using a belt casting apparatus.
At ℃, it was cast on a stainless steel band support from a die. After being held on the support for 60 seconds, it was peeled off from the stainless belt and dried while being conveyed by a number of rolls. At this time, the amount of the solvent remaining after peeling was 80%. At this time, the film was dried while being stretched 1.07 times in the width direction using a clip tenter. After drying, the film was wound into a roll to obtain a triacetyl cellulose (TAC) film having a thickness of 40 μm.

(Preparation of Film Samples 2 to 12) Film samples 2 to 12 were prepared in the same manner except that the used dope solution and film forming conditions of the film sample 1 were changed as shown in Table 2.

[0054]

[Table 2]

Using the prepared film samples 1 to 12,
The following evaluation was performed. Table 3 shows the results.

<Measurement of retardation>
After humidifying for 2 hours under 5% RH, the in-plane retardation Ro and the retardation Rt in the thickness direction using the automatic birefringence meter KOBRA-21ADH described above under the environment.
Was measured and calculated. The Rt value per unit film thickness is referred to as a plane orientation degree P, and was calculated by the following equation.

P = ((Nx + Ny) / 2-Nz) <Measurement of tear strength> The tear load was measured according to the Elmendorf tearing method described in JIS-K7128.

<Measurement of Water Content> Regarding the water content in the cellulose ester, after weighing 10 g of the cellulose ester and heating it in an oven at 120 ° C. for 1 hour, the water content (%) = (%) (Mass before heating-mass after heating) / mass after heating × 100. The amount of water in the dope can be measured by a general method such as Karl Fischer titration.

<Measurement of Curl> The curl degree was measured by JI using a sample cut 35 mm in the width direction and 1 mm in the longitudinal direction.
It carried out according to method A of S-K7619-1988.

<Evaluation of flatness> The sample was cut into a square of 1 m, and under a fluorescent lamp and a green lamp, foreign matters, scratches, pressed traces, streaks, unevenness, etc. on the surface generated during film formation were observed. The ranking was performed.

Rank 1: No defect is observed at all, and very good. Rank 2: Slight defect is observed, but there is no hindrance to practical use. Rank 3: Defect is somewhat conspicuous, and hinders practical use depending on the use. 4: Defects are conspicuous and hinder practical use Rank 5: Defects are extremely large and are not suitable for practical use at all

[0062]

[Table 3]

From the above results, it can be seen that each of the samples of the present invention is an optical film having excellent optical properties, good flatness, little curl, and excellent handleability.

<Preparation of Polarizing Plate> A polyvinyl alcohol film having a thickness of 120 μm was treated with 1 kg of iodine and 4 k of boric acid.
g of an aqueous solution containing 100 g, and stretched 6 times at 50 ° C. to prepare a polarizing film. A cellulose ester film sample of the present invention having both surfaces of this polarizing film subjected to an alkali saponification treatment was bonded to each other using a 5% aqueous solution of a completely saponified polyvinyl alcohol as an adhesive to prepare a polarizing plate.

The saponification of the cellulose ester film was carried out in the order of water washing, neutralization and water washing under the following conditions, followed by drying at 80 ° C. Saponification process 2 mol / l-NaOH 40 ° C 90 seconds Water washing process Water 30 ° C 45 seconds Neutralization process 10% by mass HCl 30 ° C 45 seconds Water washing process Water 30 ° C 45 seconds <Evaluation of characteristics as liquid crystal display device> 15-inch TFT color liquid crystal The polarizing plate of the display LA-1529HM (manufactured by NEC) was peeled off, and the two polarizing plates prepared above were stuck so as to sandwich the liquid crystal cell, so that the polarizing axes of the polarizing plates did not change from the original, and were attached to each other. TFT color liquid crystal display was manufactured. As a result, when the characteristics of the cellulose ester film as a polarizing plate were evaluated, the polarizing plate of the present invention had high contrast and exhibited excellent display properties. Thereby, it was confirmed that it was excellent as a polarizing plate for an image display device such as a liquid crystal display.

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Claims (18)

[Claims] Claims: 1. A number average molecular weight (Mn) of 50,000.ltoreq.M
n ≦ 130000, weight average molecular weight (Mw) is 1300
An optical film containing a cellulose ester satisfying 00 ≦ Mw ≦ 290000. 2. The number average molecular weight (Mn) is 50,000 ≦ M.
n ≦ 130000, weight average molecular weight (Mw) is 1300
00 ≦ Mw ≦ 290000, Z average molecular weight (Mz) is 1
An optical film comprising a cellulose ester satisfying 90000 ≦ Mz ≦ 490000. 3. In the relationship between the molecular weight of the cellulose ester and the weight fraction, the weight fraction has two or more maximum values,
The number average molecular weight (Mn) of the smallest one among the molecular weights corresponding to the maximum value is 50,000 ≦ Mn ≦ 130,000,
Weight average molecular weight (Mw) is 130,000 ≦ Mw ≦ 290
An optical film comprising a cellulose ester of 000. 4. An optical film comprising a cellulose ester having an alkaline earth metal content of 30 ppm or less in the cellulose ester. 5. The optical film according to claim 1, wherein the content of the alkaline earth metal in the cellulose ester is 30 ppm or less. 6. The cellulose ester contains an acyl group having 2 to 4 carbon atoms, and the total degree of substitution of the acyl group is from 2.60 to 2.
The optical film according to any one of claims 1 to 5, wherein the optical film has a thickness of 90. 7. The optical film according to claim 1, wherein the cellulose ester is triacetyl cellulose having a degree of acetyl substitution of 2.60 to 2.80. 8. The cellulose ester propionate according to claim 1, wherein the cellulose ester is a cellulose acetate propionate having a degree of acetyl substitution of 1.8 to 2.2 and a degree of propionyl substitution of 0.6 to 1.0. Item 2. The optical film according to item 1. 9. The number average molecular weight (Mn) is 50,000 ≦ M
n ≦ 130000, weight average molecular weight (Mw) is 1300
00 ≦ Mw ≦ 290000, Z average molecular weight (Mz) is 1
A method for producing an optical film, comprising using a cellulose ester satisfying 90000 ≦ Mz ≦ 490000, casting a dope having a solid content concentration of 17% by mass or more and 35% by mass or less on a support, followed by peeling and drying. . 10. The number average molecular weight (Mn) is 50,000 ≦
Mn ≦ 130,000, weight average molecular weight (Mw) is 130
It is a cellulose ester of 000 ≦ Mw ≦ 290000, wherein the amount of water contained in the cellulose ester is 0.1.
A method for producing an optical film, comprising: preparing a dope in a state of 1% to 2.0%, casting the dope on a support, and peeling and drying the dope. 11. The number average molecular weight (Mn) is 50,000 ≦
Mn ≦ 130,000, weight average molecular weight (Mw) is 130
A dope containing a cellulose ester having a molecular weight of 000 ≦ Mw ≦ 290000 is 0.02 to 0.7%, and the dope is cast on a support, followed by peeling and drying. Production method. 12. A dope having a solid content of not less than 22% by mass and a viscosity of not more than 80 Pa · s at 23 ° C. measured by a rotational viscometer is cast on a support and then kept on the support for 30 to 90 seconds. And then peeling and drying to form a film having a thickness of 20 to 65 μm. 13. A dope having a solid content of not less than 22% by mass and a viscosity of not more than 80 Pa · s at 23 ° C. measured by a rotational viscometer is cast on a support and kept on the support for 30 to 90 seconds. 12. A film having a film thickness of 20 to 65 [mu] m after peeling and drying.
Item 13. The method for producing an optical film according to item 9. 14. The content ratio of the poor solvent is 3 to 7% with respect to the total amount of the organic solvent contained in the cellulose ester dope.
The method for producing an optical film according to any one of claims 9 to 13, wherein 15. The method according to claim 9, wherein the film is stretched 1.01 to 2.5 times in the width direction in a drying step after the film is peeled off. Manufacturing method of optical film. 16. An optical film produced by the method according to claim 9. Description: 17. A polarizing plate, comprising the optical film according to claim 1. Description: 18. A display device using the polarizing plate according to claim 17.