JP2002311240A - Retardation film, method for manufacturing the same and elliptical polarization plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a retardation film having positive wavelength dispersion characteristics and little irregularity in the angle in the direction of the slow phase axis. SOLUTION: In the method for manufacturing a retardation film by at least uniaxially stretching a cellulose ester film obtained by the solution flow-casting method, a cellulose ester dope containing the cellulose ester and an organic solvent is spread on a supporting body and the organic solvent is vaporized until the film can be released. Then the film is released from the supporting body and dried further. While the obtained cellulose ester film is carried in the direction opposite to the flow casting direction, the film is stretched in the longitudinal direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a retardation film, a method for producing the same, and an elliptically polarizing plate. In particular, the present invention relates to a method for producing an optically uniform retardation film having little retardation characteristics and unevenness of a slow axis.

[0002]

2. Description of the Related Art A twisted nematic liquid crystal display device or a super twisted nematic liquid crystal display device used for a display portion of various OA equipments has a drawback that a display screen is colored by a phase difference generated in a liquid crystal cell. To resolve this drawback, a retardation film is used. This retardation film is often used as an elliptically polarizing plate or a circularly polarizing plate by being bonded to a polarizing plate.

[0003] These display devices have been increasing in size with increasing definition year by year, and the retardation film used therein has a wide range of retardation in the in-plane direction, retardation in the thickness direction, and slow axis direction. It is required to be controlled uniformly.

[0004] Attention has also been paid to the wavelength dispersion characteristics of retardation films. That is, there is a demand for a material having a larger phase difference as the wavelength becomes longer. For example, taking the case where a retardation film is used as a quarter-wave plate as an example, it is preferable to show a quarter-wave retardation at any wavelength in the visible light wavelength range of 400 to 700 nm.

As the retardation film, generally, a film obtained by uniaxially stretching a polycarbonate resin having a large intrinsic birefringence in the longitudinal direction (the direction in which the film travels during production) is used. However, it was not possible to obtain the positive wavelength dispersion characteristics as described above by using a polycarbonate-based retardation film alone.

Further, there is a problem that a phenomenon in which the stretched line is bent in the width direction of the film occurs, and the angle of the slow axis increases toward both ends in the width direction of the film, resulting in uneven angle.

This is a phenomenon in which a straight line is drawn in the width direction of a film before stretching, and when the film is stretched by a stretching machine, the line is bent in a bow shape in the film after stretching. In the case of longitudinal stretching, the direction of the slow axis is the longitudinal direction at the center in the width direction of the film, but the angle from the longitudinal direction increases toward the both ends of the film. In the case of transverse stretching, the direction of the slow axis is the transverse direction at the center in the width direction of the film, but the angle from the transverse direction increases toward the both ends of the film.

[0008] At present, the retardation film having a large angle unevenness of the slow axis as described above has a problem that even if it is used for a liquid crystal display device, the display screen is extremely colored and cannot be put to practical use.

[0009] The bending phenomenon of the drawing line has been well studied with respect to biaxial drawing of a polyester film.
The phenomenon of bending of the drawn line is called a bowing phenomenon, and various improvement methods have been proposed. This bowing phenomenon has a stretched line that is concave with respect to the traveling direction of the film during transverse stretching. However, when a cellulose ester is used, the stretched line by transverse stretching has a convex shape with respect to the film advancing direction, and the phenomenon is different from the case of the polyester film. I can't expect to get it.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a retardation film having a positive wavelength dispersion characteristic and a small angle unevenness in a slow axis direction.

[0011]

The above object of the present invention has been attained by the following constitutions.

1. In a method for producing a retardation film in which a cellulose ester film obtained by a solution casting method is stretched in at least one axis direction, a cellulose ester dope containing a cellulose ester and an organic solvent is cast on a support and peeled off. After evaporating the organic solvent until possible, the web is peeled from the support, and the cellulose ester film obtained by drying is stretched in the longitudinal direction while being transported in the direction opposite to the casting direction. A method for producing a retardation film, comprising:

2. 2. The method for producing a retardation film as described in 1 above, wherein the cellulose ester film has a residual solvent amount of 2% by mass or less and is stretched 1.05 to 2.0 times in the machine direction.

3. In a method for producing a retardation film in which a cellulose ester film obtained by a solution casting method is stretched in at least one axis direction, a cellulose ester dope containing a cellulose ester and an organic solvent is cast on a support and peeled off. After evaporating the organic solvent until possible, the web is peeled from the support, and the cellulose ester film obtained by drying is stretched in the transverse direction while being transported in the direction opposite to the casting direction. A method for producing a retardation film, comprising:

4. 4. The method for producing a retardation film according to the above item 3, wherein the cellulose ester film is stretched 1.05 times to 2.0 times in the transverse direction when the residual solvent amount is 2% by mass or less.

5. After evaporating the organic solvent until the cellulose ester film is castable on a support and a cellulose ester dope containing a cellulose ester and an organic solvent is evaporated, the web is peeled from the support, and then the peeled web The retardation film according to any one of the above items 1 to 4, which is a cellulose ester film obtained by drying while keeping the width of the film or shrinking in the width direction of 0 to 10%. Production method.

6. After evaporating the organic solvent until the cellulose ester film is castable on a support and a cellulose ester dope containing a cellulose ester and an organic solvent is evaporated, the web is peeled from the support, and then the peeled web Is a cellulose ester film obtained by drying while transporting while being wound around a plurality of rolls in which the distance between the rolls is 20 to 300% of the width of the casting film. The method for producing a retardation film according to any one of the above items.

[7] Any one of the above 1 to 4, wherein the cellulose ester film has a convex stretched line.
13. The method for producing a retardation film according to item 10.

8. In a method for producing a retardation film, in which a cellulose ester film obtained by a solution casting film forming method is stretched in at least one axis direction, the cellulose ester film comprises a cellulose ester dope containing a cellulose ester and an organic solvent on a support. After evaporating the organic solvent until it can be peeled off, the web is peeled from the support, and the amount of residual solvent in the peeled web is 5%.
When it is in the range of 100% by mass to 100% by mass, the stretching ratio is 1.0
The cellulose ester film obtained by longitudinal stretching in the range of 1 to 1.5 times is re-stretched in the longitudinal direction by 1.04 to 1.99 times while being transported in the direction opposite to the casting direction. A method for producing a retardation film.

9. In a method for producing a retardation film, in which a cellulose ester film obtained by a solution casting film forming method is stretched in at least one axis direction, the cellulose ester film comprises a cellulose ester dope containing a cellulose ester and an organic solvent on a support. After evaporating the organic solvent until it can be peeled off, the web is peeled from the support, and the amount of residual solvent in the peeled web is 5%.
Stretching ratio of 1.0 in the width direction when in the range of
The cellulose ester film obtained by transverse stretching in the range of 1 to 1.5 times is re-stretched 1.04 to 1.99 times in the transverse direction while being transported in the direction opposite to the casting direction. A method for producing a retardation film.

10. The cellulose ester has the following formula (I)
10. The method for producing a retardation film according to any one of the above items 1 to 9, wherein the cellulose ester satisfies both (II) and (II).

(I) 2.3 ≦ X + Y ≦ 2.85 (II) 1.4 ≦ X ≦ 2.85 wherein X is the degree of substitution of an acetyl group, and Y is the degree of substitution of a propionyl group and / or a butyryl group. is there.

11. (1) The cellulose ester has an acetyl group substitution degree of 1.4 to 2.4.
0. The method for producing a retardation film according to 0.

12. The method for producing a retardation film according to the above item 10 or 11, wherein the number average molecular weight of the cellulose ester is from 60,000 to 300,000.

13. 13. A retardation film obtained by the method for producing a retardation film according to any one of 1 to 12.

14. 14. An elliptically polarizing plate, wherein the retardation film according to 13 is attached to at least one side of a polarizing film.

The present invention will be described in more detail. In the present invention, the cellulose ester solution is called a cellulose ester dope or simply a dope.

First, a method for forming a cellulose ester film by the solution casting method according to the present invention will be described.

Dissolution step: This step is a step of dissolving the flakes in an organic solvent mainly containing a good solvent for the cellulose ester flakes in a dissolving vessel with stirring to form a dope. The dissolution includes various dissolution methods such as a method of dissolving at normal pressure, a method of dissolving at a temperature below the boiling point of the main solvent, a method of dissolving under a pressure higher than the boiling point of the main solvent, a method of dissolving by cooling, and a method of dissolving under high pressure. After dissolution, the dope is filtered with a filter medium, defoamed, and sent to the next step by a pump.

Casting step: The dope is fed to a pressurized die through a pressurized metering gear pump and, at a casting position, an endless metal belt for infinitely transferring or a casting support for a rotating metal drum (hereinafter simply referred to as a casting support). This is a step of casting a dope from a pressure die onto a support. The surface of the casting support is a mirror surface. Other casting methods include a doctor blade method of adjusting the film thickness of the cast dope film with a blade, a method using a reverse roll coater that adjusts with a roll that rotates in reverse, and the like.
A pressure die that can adjust the slit shape of the base and can easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.
Place a pressure die on the casting support to increase the film forming speed.
It is also possible to provide more than a group, and to divide the doping amount to form an overlying layer.

Solvent evaporation step: The web (the web is referred to as a dope film after casting the dope on the casting support) is heated on the casting support, and the web can be peeled from the support. This is a step of evaporating the solvent until the temperature becomes. To evaporate the solvent, a method of blowing air from the web side and / or
Alternatively, there is a method in which heat is transferred from the back surface of the support with a liquid, a method in which heat is transferred from the front and back surfaces with radiant heat, and the like, and a method of transferring heat from the back surface is preferable because of good drying efficiency. A method of combining them is also preferable.

Peeling step: This is a step of peeling the web from which the solvent has evaporated on the support at the peeling position. The peeled web is sent to the next step. If the residual solvent amount (the following formula) of the web at the time of peeling is too large, the web is difficult to peel, or conversely, if the web is sufficiently dried on the support and then peeled, a part of the web is peeled off in the middle.

As a method of increasing the film forming speed (the film forming speed can be increased because the film is separated while the residual solvent amount is as large as possible), there is a gel casting method in which the film can be separated even if the residual solvent is large. . Examples of the method include a method in which a poor solvent for the cellulose ester is added to the dope, gelling is performed after casting the dope, and a method in which the temperature of the support is lowered to gelate. There is also a method of adding a metal salt to the dope. By gelling on the support and strengthening the film, peeling can be accelerated and the film forming speed can be increased. If the residual solvent amount is greater at the time of peeling, if the web is too soft, the flatness at the time of peeling will be impaired, or shear and vertical streaks will easily occur due to peel tension, and the amount of the residual solvent peeled will be reduced in consideration of economic speed and quality. I can decide.

Drying step: a step of drying the web using a drying device that alternately transports the web through rolls arranged in a staggered manner and / or a tenter device that transports the web by clipping both ends of the web with clips. In general, hot air is blown to both sides of the web as a drying means, but there is also a method of heating by applying a microwave instead of the wind. Too fast drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed when the residual solvent is about 8% by mass or less. Throughout, the drying temperature is usually 40 to 250 ° C, preferably 70 to 180 ° C. The drying temperature, the amount of drying air, and the drying time vary depending on the solvent used, and the drying conditions may be appropriately selected according to the type and combination of the solvents used.

In the drying step after peeling from the surface of the casting support, the web tends to shrink in the width direction due to evaporation of the solvent. The quicker it dries at higher temperatures, the greater the shrinkage. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the resulting film. From this viewpoint, for example, Japanese Patent Application Laid-Open No. 62-4662.
The method of drying all the steps or a part of the steps as described in Japanese Patent Publication No. 5 (tenter method) while holding both ends of the width of the web with a clip in the width direction is preferable.

Winding step: The web is reduced to a residual solvent amount of 2
In this step, the film is wound up as a film after the amount becomes less than mass%. By setting the amount of the residual solvent to 0.4% by mass or less, a film having good dimensional stability can be obtained. As the winding method, a generally used method may be used, and there are a constant torque method, a constant tension method, a taper tension method, a program tension control method with constant internal stress, and the like.

The amount of the residual solvent can be expressed by the following equation. Residual solvent amount (% by mass) = {(M−N) / N} × 100 where M is the mass of the web at any time, and N is M
The mass when dried at 0 ° C. for 3 hours.

Although the thickness of the cellulose ester film varies depending on the purpose of use, the finished film is usually preferably in the range of 30 to 200 μm, more preferably 35 to 15 μm.
A range of 0 μm is preferable, and a range of 40 to 120 μm is particularly preferable. If the film is too thin, the film may be too stiff and inferior in handleability. If the thickness is too large, the display device becomes thick, and for example, portability may be impaired. To adjust the film thickness, it is necessary to control the dope concentration, the amount of liquid supplied by the pump, the slit gap of the die cap, the extrusion pressure of the die, the speed of the casting support, etc. so that the desired thickness is obtained. Good. In addition, as means for making the film thickness uniform, it is preferable to use a film thickness detecting means to feed back and adjust the programmed feedback information to each of the above-described devices.

In the process from the step immediately after casting to the step of drying through the solution casting film forming method, the atmosphere in the drying apparatus may be air, but an inert gas such as nitrogen gas, carbon dioxide gas or argon gas may be used. It may be performed in an atmosphere. Of course, the danger of explosive limits of the evaporated solvent in a dry atmosphere must always be considered.

The method for producing a cellulose ester film of the present invention will be described in more detail.

The cellulose ester of the present invention has a total of the degree of substitution of an acetyl group and the degree of substitution of a propionyl group and / or a butyryl group of 2.3 or more and 2.85 or less, and
The degree of substitution of the acetyl group is preferably 1.4 or more and 2.85 or less. When the degree of substitution of the acyl group having 2 to 4 carbon atoms is lower than this range, the heat and humidity resistance of the retardation film is poor. On the other hand, if the total degree of substitution is too large, the wavelength dispersion characteristics may become negative or sufficient retardation may not be obtained.

The cellulose ester of the present invention may be a cellulose ester having a propionate group or a butyrate group bonded to an acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, or cellulose acetate propionate butyrate. preferable. Note that butyrate is i- in addition to n-.
So- is also included. Cellulose acetate propionate having a high degree of substitution of propionate groups has excellent water resistance.

The cellulose as a raw material of the cellulose ester used in 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.

In the cellulose ester of the present invention, when the acylating agent is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), an organic solvent such as acetic acid or an organic solvent such as methylene chloride is used. 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. In the cellulose ester, the acyl group reacts with the hydroxyl group 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. For example, in cellulose triacetate, all three hydroxyl groups of a glucose unit have acetyl groups bonded thereto.

The method for measuring the degree of substitution of the acyl group is ASTM-
It can be measured according to D817-96.

The number average molecular weight of the cellulose ester of the present invention is preferably in the range of 60,000 to 300,000 because the resulting film has high mechanical strength. 70,000 ~
200,000 is preferred.

A useful chlorine-based organic solvent for forming the dope includes methylene chloride. Non-chlorine organic solvents include methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolan,
4-dioxane, cyclohexanone, ethyl formate, 2,
2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2- Methyl-2-propanol, 1,1,
1,3,3,3-hexafluoro-2-propanol,
Examples thereof include 2,2,3,3,3-pentafluoro-1-propanol and nitroethane. Methyl acetate, ethyl acetate, acetone can be preferably used. Particularly, methyl acetate is preferable.

The cellulose ester dope of the present invention includes:
In addition to the above organic solvents, 1 to 40% by mass of carbon atoms
It is preferable to include the alcohol of No. 4. In these, the solvent starts to evaporate after the dope is cast on the casting support, and when the alcohol ratio increases, the web (casting film) gels, making the web strong and easy to peel off from the casting support. It is also used as a gelling solvent, or when the ratio is small, it also has a role to promote the dissolution of the cellulose ester of the non-chlorine organic solvent. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol and se.
Examples thereof include c-butanol and tert-butanol. Among them, ethanol is preferred because of its stability, the boiling point is relatively low, the drying property is good, and there is no toxicity.

The concentration of the cellulose ester in the dope is 1
The dope viscosity is preferably adjusted to 5 to 40% by mass and the dope viscosity is adjusted to 10 to 50 Pa · s in order to obtain good film surface quality.

In the dope, a plasticizer, an antioxidant, an ultraviolet ray inhibitor, a matting agent, a dye and the like are sometimes added.
These compounds may be added together with the cellulose ester and the solvent when preparing the cellulose ester solution, or may be added during or after the solution is prepared. For liquid crystal display devices, it is preferable to add a plasticizer, an antioxidant, an ultraviolet inhibitor, or the like that imparts heat and moisture resistance.

In the present invention, a compound known as a plasticizer is preferably added for the purpose of improving mechanical properties, imparting flexibility, imparting water absorption resistance, reducing water vapor transmission rate, adjusting retardation, and the like. And carboxylic acid esters are preferably used. Examples of the phosphate ester include triphenyl phosphate, tricresyl phosphate, phenyldiphenyl phosphate and the like. Examples of carboxylic acid esters include phthalic acid esters and citric acid esters, and examples of phthalic acid esters include dimethyl phthalate, diethyl phthalate, dioctyl phthalate, and diethylhexyl phthalate. Tributyl can be mentioned. Other examples include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and triacetin. Alkyl phthalyl alkyl glycolates are also preferably used for this purpose. The alkyl of the alkylphthalylalkyl glycolate is an alkyl group having 1 to 8 carbon atoms. Alkyl phthalyl alkyl glycolate as 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, propyl phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl Phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycol Cholate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate and the like can be mentioned, methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, Octyl phthalyl octyl glycolate is preferred, and ethyl phthalyl ethyl glycolate is particularly preferred. Further, two or more of these alkylphthalylalkyl glycolates may be used in combination.

The addition amount of these compounds is preferably 1 to 20% by mass based on the cellulose ester from the viewpoints of achieving the desired effects and suppressing bleed-out from the film.

As the antioxidant, hindered phenol compounds are preferably used, and 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-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-
4-hydroxyphenyl) propionate, N, N'-
Hexamethylene bis (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-hydroxybenzyl) -isocyanurate and the like. Particularly, 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, N, N'-bis [3- (3,5-di-t-butyl-
Hydrazine-based metal deactivators such as 4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-
A phosphorus-based processing stabilizer such as (t-butylphenyl) phosphite may be used in combination. The addition amount of these compounds is 1 ppm to 1.0% by mass relative to the cellulose ester.
% Is preferable, and 10 to 1000 ppm is more preferable.

As an ultraviolet absorber, it has an excellent ability to absorb ultraviolet light having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the polarizer and the liquid crystal, and has a wavelength of 4 from the viewpoint of liquid crystal display.
Those having little absorption of visible light of 00 nm or more are preferable.
Examples include oxybenzophenone-based compounds, benzotriazole-based compounds, salicylic acid ester-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, nickel complex-based compounds, and the like. Particularly preferred ultraviolet absorbers are benzotriazole-based compounds and benzophenone-based compounds. Above all, benzotriazole-based compounds are preferable because unnecessary coloring of the cellulose ester is small. The content of the ultraviolet absorber is 0.01
-5 mass%, especially 0.5 mass% or more and 3 mass% or less.

In addition, heat stabilizers such as inorganic fine particles such as kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide and alumina, and alkaline earth metal salts such as calcium and magnesium are added. Is also good. Further, an antistatic agent, a flame retardant, a lubricant, an oil agent and the like may be added in some cases.

The additive contained in the cellulose ester film of the present invention preferably has a vapor pressure at 200 ° C. of 1333 Pa or less from the viewpoint of suppressing volatilization.

In the present invention, a cellulose ester dope is cast on a casting support to form a web, and the temperature at the peeling position on the support is 10 to 40 ° C., preferably 11 to 40 ° C.
The web is preferably peeled off at 30 ° C. and when the residual solvent amount of the web at the peeling position is 10 to 120% by mass. In order to keep the amount of the residual solvent at the time of peeling the web within this range, the surface temperature of the casting support after casting is controlled, and the temperature range is set so that the organic solvent can be efficiently evaporated from the web. Is preferably used. In order to control the temperature of the support, a heat transfer method having good heat transfer efficiency is preferably used. For example, a backside heat transfer method using a liquid is preferable. In the belt (support) machine, the temperature of the belt where the belt to be transferred comes below can be controlled by gentle wind. The temperature of the support can be partially changed by dividing the heating means, and can be set to different temperatures such as a casting position, a drying section, and a peeling position of the casting support.

In the present invention, it is preferable to dry the web while keeping the width of the peeled web or shrinking the web in the width direction at a ratio of 0 to 10% in the solution casting film formation of the cellulose ester. The width can be held or shrunk by, for example, fixing the both ends of the web with clips or pins using a transverse stretching machine called a tenter, and carrying the web while keeping the width of both ends or narrowing it. By drying in this manner, a retardation film having a small angle unevenness of the slow axis when this film is subsequently uniaxially stretched is obtained.

Further, in the present invention, when the peeled web is dried while being wound around a plurality of rolls during the solution casting film formation of the cellulose ester, the distance between the rolls (the position at which the roll and the web come into contact with each other) is determined. Is preferably 30% to 300% of the width of the web with respect to the width of the web. By drying in this manner, a retardation film having a small angle unevenness of the slow axis can be obtained. A more preferable range of the distance between the rolls is 50% to 150%.

Further, in the present invention, the stretched line of the cellulose ester film is preferably convex. By doing so, a retardation film having a small angle unevenness of the slow axis can be obtained. Usually, the drawing line is a line drawn in the width direction of the film before drawing and refers to a line obtained after drawing.Here, the drawing line is drawn in the width direction of the web immediately before being peeled from the support. In addition, it means a line in a film finally obtained through peeling and drying. Of course, the drawn line does not need to be actually drawn on the film. In order to determine whether the stretched line of the cellulose ester film is concave or convex, the angle of the slow axis in the film width direction may be examined. In other words, when the film is cast with the casting direction facing upward, the slow axis is inclined counterclockwise on the right from the center of the film width, and if it is inclined clockwise on the left, the drawn line is convex. Means that At this time, the angle between the slow axis of the film and the longitudinal direction is preferably in the range of ± 15 degrees. When the angle range is within this range, a retardation film having a small angle unevenness of the slow axis can be obtained.

The cellulose ester film obtained as described above is characterized by having a convex stretched line shown in FIG. FIG. 1 is an explanatory view of a drawing line related to the solution casting of a film. The drawing line (on a support) 1 of a web 2 is shown.
Advances in the direction of the arrow, and becomes a stretched line (after film formation) 3 after film formation.

The cellulose ester film obtained as described above still has an in-plane retardation of 20 n.
m, it is necessary to further stretch at least uniaxially to obtain a retardation film.

The stretching is performed as follows. In this method, the cellulose ester film obtained by the solution casting method is stretched in at least one axial direction while being transported in the direction opposite to the casting direction at the time of film formation. The film can be conveyed in the opposite direction, for example, by once winding the solution-cast film-formed cellulose ester into a roll and then unwinding the film from the roll.

The method of longitudinal stretching is not particularly limited, but a method can be used in which a plurality of rolls are provided with a difference in peripheral speed, and a difference in peripheral speed between the rolls is used to perform longitudinal stretching. Also,
A simultaneous biaxial stretching machine can also be preferably used. That is, the film can be fixed by fixing both ends of the film with clips or pins, and increasing the interval between the clips or pins in the vertical direction (conveying direction). Driving the clip portion by the linear drive method is preferable because stretching can be performed smoothly and the risk of breakage can be reduced. The stretching ratio in the machine direction is preferably in the range of 1.05 times to 2.0 times. If the stretching ratio is too small, the retardation of the retardation film may be insufficient, and if the stretching ratio is too large, the film may become cloudy.
The refractive indices Nx, Ny, Nz of the film (vertical direction,
It is preferable to control the stretching ratio, the temperature, the width shrinkage in the transverse direction, and the like so that the refractive index in the transverse direction and the thickness direction is a desired value. When the cellulose ester film is stretched in this manner, the stretched line becomes convex as shown in FIG. FIG. 2 is an explanatory view of a drawing line related to the longitudinal drawing of the film. The drawing line (before drawing) 4 of the web 2 is drawn by a roll drawing machine 5 to become a drawing line (after drawing) 6. This stretched line is drawn in a straight line in the width direction of the cellulose ester film, and what happens after stretching is examined. The cellulose ester film is formed in advance so as to have a convex stretched line, and then stretched uniaxially longitudinally while being transported in the direction opposite to the transport direction during film formation, thereby canceling out the stretched line generated during stretching. That is, the angle unevenness of the slow axis of the film can be reduced.

The method of the transverse stretching is not particularly limited, but a transverse stretching machine called a tenter can be preferably used. That is, a method in which both ends of the web are fixed with clips or pins, the interval between the clips or pins is expanded in the horizontal direction, and the web is stretched in the horizontal direction. Depending on the application of the retardation film, there is a case where it is desired to make the refractive index close to the longitudinal direction and the refractive index in the thickness direction. In this case, by using a simultaneous biaxial stretching machine while shortening the interval in the transport direction of the clip or pin in the transport direction (vertical direction),
The refractive index in the vertical direction can be made closer to the refractive index in the thickness direction. As the driving method of the tenter clip, it is preferable to drive the clip portion by a linear drive method since the stretching can be performed smoothly and the risk of breakage can be reduced. The stretching ratio in the transverse direction is preferably in the range of 1.05 to 2.0 times. If the stretching ratio is too small, the retardation of the retardation film may be insufficient, and if the stretching ratio is too large, the film may become cloudy.
The refractive indices Nx, Ny, Nz of the film (vertical direction,
It is preferable to control the stretching ratio, the temperature, the contraction ratio in the vertical direction, and the like so that the refractive index in the horizontal direction and the thickness direction is a desired value. When the cellulose ester film is stretched in this manner, the stretch line becomes convex as shown in FIG. FIG. 3 is an explanatory view of a stretching line related to the transverse stretching of the film. The web 2 is stretched transversely by a tenter clip 8 in a tenter oven 7, and the stretching line 4 before stretching becomes a stretching line (after stretching) 6. . This stretched line is drawn in a straight line in the width direction of the cellulose ester film, and what happens after stretching is examined. The cellulose ester film is formed in advance so as to have a convex stretched line, and then is stretched in the uniaxial direction while being transported in a direction opposite to the transport direction at the time of film formation, thereby canceling out the stretched line generated at the time of stretching. That is, the angle unevenness of the slow axis of the film can be reduced.

In the present invention, the following method can also be preferably used. That is, in the method for producing a retardation film in which the cellulose ester film obtained by the solution casting method is stretched in at least one axis direction, the cellulose ester film comprises a cellulose ester dope containing a cellulose ester and an organic solvent. After casting the organic solvent to evaporate the organic solvent until the organic solvent can be peeled off, the web is peeled off from the support, and the amount of residual solvent in the peeled web is 5%.
When it is in the range of 100% by mass to 100% by mass, the stretching ratio is 1.0
The cellulose ester film obtained by longitudinal stretching in the range of 1 to 1.5 times is re-stretched in the longitudinal direction by 1.04 to 1.99 times while being transported in the direction opposite to the casting direction. In a method for producing a retardation film, wherein a cellulose ester film obtained by a method for producing a retardation film or a solution casting film-forming method is stretched in at least one axis direction, the cellulose ester film comprises a cellulose ester and an organic solvent. After casting the cellulose ester dope on a support and evaporating the organic solvent until the organic solvent can be peeled off, the web is peeled from the support, and then the residual solvent amount of the peeled web is in the range of 5 to 60% by mass. The cellulose ester film obtained by transverse stretching in the width direction at a stretching ratio of 1.01 to 1.5 times in the width direction is transported in the direction opposite to the casting direction. 1.04 times in the transverse direction while 1.9
This is a method for producing a retardation film, comprising re-stretching 9 times. By performing the first-stage stretching in advance in this way,
The redrawing magnification can be kept small. As a result, the convex shape of the drawn line can be reduced. Further, by setting the transport direction at the time of the first-stage stretching and the re-stretching to the opposite direction, the stretching line is canceled out, and the angle unevenness of the slow axis of the film can be extremely reduced.

If the amount of the residual solvent in the web is too large, a sufficient effect cannot be obtained. If the amount is too small, the stretching becomes extremely difficult, and the web may be broken. On the other hand, if the stretching ratio is too small, a sufficient effect cannot be obtained. If the stretching ratio is too large, stretching becomes difficult and breakage may occur. A more preferable range of the stretching ratio is 1.1 times to 1.times.
The range is four times.

In the method of the present invention, stretching can be performed without heating to a high temperature, but it is preferable to combine drying and stretching because the process can be shortened. However, if the temperature of the web is too high, the plasticizer volatilizes, so the range of room temperature (15 ° C) to 160 ° C or less is preferable.
When stretching and drying are performed as in this case, the amount of residual solvent at the end of stretching is preferably in the range of 5 to 60% by mass. Further, the content is preferably 10 to 30% by mass.

The method of stretching the web is not particularly limited, but a transverse stretching machine called a tenter can be preferably used. That is, a method in which both ends of the web are fixed with clips or pins, the interval between the clips or pins is expanded in the horizontal direction, and the web is stretched in the horizontal direction. Stretching or shrinking in the longitudinal direction can be performed by using a simultaneous biaxial stretching machine to increase or decrease the interval in the transport direction of the clip or pin in the transport direction (vertical direction). Driving the clip portion by the linear drive method is preferable because stretching can be performed smoothly and the risk of breakage can be reduced.

As a method of stretching in the longitudinal direction, a method in which a plurality of rolls are provided with a difference in peripheral speed, and a method of stretching in the longitudinal direction by utilizing the difference in peripheral speed between the rolls can be used. For the re-stretching, the above-described stretching method for a cellulose ester film can be used. The total of the stretching ratio during the production of the cellulose ester film and the stretching ratio for re-stretching is preferably in the range of 1.05 to 2.0 times.

In the retardation film obtained as described above, the direction of the slow axis of the film (the maximum direction of the refractive index in the film plane) is set in the winding direction or the direction perpendicular to the winding direction (the width direction of the film). On the other hand, it is preferably in the range of ± 15 degrees, more preferably in the range of ± 5 degrees, and particularly preferably in the range of ± 1 degree.

The retardation value of the film has a preferable range depending on the type of liquid crystal cell to be combined.
For example, when combined with a TN type liquid crystal cell, the in-plane retardation Ro is preferably from 20 nm to 200 nm, more preferably from 30 nm to 100 nm. The retardation Rt in the thickness direction is preferably from 0 nm to 400 nm,
Further, the thickness is preferably 50 nm to 200 nm. Also, Rt and R
The ratio Rt / Ro of o is preferably 1.0 to 5.0, and more preferably 1.4 to 3.0. By setting the retardation value of the film in this range, a retardation film having excellent viewing angle characteristics can be obtained. The retardation film of the present invention has a wavelength of 4
In the range of 00 to 700 nm, a longer wavelength indicates a larger phase difference. Such characteristics are particularly preferable when the retardation film is used particularly as a quarter-wave plate. When the phase differences at the wavelengths of 450 nm, 590 nm, and 650 nm are R450, R590, and R650, respectively, it may be in the range of 0.5 <R450 / R590 <1.0 1.0 <R650 / R590 <1.5. It is preferable because it has an excellent function of converting linearly polarized light into circularly polarized light.

When the retardation film of the present invention is used as a quarter-wave plate, R590 is 137.5 nm ± 2.
It is preferably 0 nm, and more preferably 137.5 nm ± 10 nm. With this range, a good function of a quarter-wave plate can be obtained.

In order to obtain the above-described optical characteristics, the refractive index Nx of the retardation film in the slow axis direction and the refractive index Ny in the fast axis direction (direction orthogonal to the slow axis in the film plane) are obtained. The difference needs to be 0.0005 or more and 0.0050 or less. A more preferred range is 0.0010 or more, 0.0
030 or less.

The refractive index N in the slow axis direction of the film
When x, refractive index Ny in the fast axis direction, and refractive index Nz in the thickness direction, (Nx−Ny) / 2−Nz is also effective to be 0.0005 or more and 0.0050 or less.

To make the refractive index of the film fall within the above range,
As described above, this can be achieved by appropriately controlling the stretching conditions of the film.

The photoelastic coefficient of the retardation film of the present invention is:
The absolute value is preferably 60 × 10 ⁻¹³ cm ² / dyne or less, more preferably 20 × 10 ⁻¹³ cm ² / dyne or less. The photoelastic coefficient is a value obtained with an ellipsometer.
Further, the glass transition temperature of the film is preferably 120 ° C. or higher, more preferably 140 ° C. or higher. The glass transition temperature was measured at a heating rate of 10 using a differential scanning calorimeter (DSC).
It is determined as the average value of the temperature at which the baseline due to the glass transition of the film starts to change when measured at ° C / min and the temperature at which the baseline returns to the baseline again. A retardation film is often used outdoors as a component of a display device such as a mobile terminal or a car navigation, and is required to have heat resistance. When the characteristics of the retardation film are in the above range, a favorable display device in which the viewing angle is not deteriorated and the display is not colored can be obtained.

In the retardation film of the present invention, a liquid crystal resin or another retardation film may be further laminated on at least one side. Thereby, the phase difference can be controlled to a high degree, and the viewing angle can be improved to a high degree.

The retardation film of the present invention can be made into an elliptically polarizing plate by adhering to at least one side of a polarizing film.

As the polarizing film, conventionally known polarizing films can be used. For example, a polarizing film is obtained by treating a hydrophilic polymer film such as a polyvinyl alcohol film with a dichroic dye such as iodine and stretching. Polarizing films by themselves are not sufficiently durable, so in general,
A cellulose triacetate film is adhered on both sides as a protective film.

In order to form an elliptically polarizing plate, it may be bonded to the polarizing film with the protective film, or may be directly bonded to the polarizing film also as the protective film. In particular, the surface of the retardation film of the present invention can be bonded to a polarizing film by saponifying the surface of the retardation film using an adhesive comprising an aqueous solution of a water-soluble polymer as conventionally used. As this water-soluble polymer adhesive, a completely saponified polyvinyl alcohol aqueous solution is preferably used.

The elliptically polarizing plate thus obtained can be used for various display devices. Examples of the display device include a liquid crystal display device, an organic electroluminescent device, a plasma display, and the like.For example, in the case of a single-polarizer reflective liquid crystal display device,
The configuration is, from the front side, a polarizing plate protective film / polarizer /
The retardation film / glass substrate / ITO transparent electrode / alignment film / TN type liquid crystal / alignment film / metal electrode / reflection film / glass substrate of the present invention. In the conventional case, a polarizing plate protective film / a polarizer / a polarizing plate protective film / a retardation plate / a glass substrate / I
It has a structure of TO transparent electrode / alignment film / TN type liquid crystal / alignment film / metal electrode / reflection film / glass substrate. In the conventional configuration,
Although coloring is observed due to insufficient retardation characteristics with respect to the wavelength of the retardation plate, a favorable liquid crystal display device without coloring can be obtained by using the retardation film of the present invention.

In the case of a reflective polarizing element comprising a cholesteric liquid crystal, it can be used in the configuration of backlight / cholesteric liquid crystal layer / retardation film / polarizer / polarizer protective film of the present invention.

Further, the retardation film of the present invention is used for
In the case of a polarizing plate used as a wavelength plate, it becomes a circularly polarizing plate that can convert natural polarized light into circularly polarized light. When it is installed on a front panel such as a plasma display or an organic EL display, it functions as an anti-reflection film or an anti-glare film, and can prevent coloring and deterioration in visibility. It can also be used to prevent reflection on touch panels.

The organic electroluminescent device is also called an organic EL device, and is introduced, for example, in Japanese Journal of Applied Physics, Vol. 25, Item 773 (1986). The configuration is, for example, transparent substrate / anode / organic light emitting layer / cathode, or transparent substrate / anode /
Hole injection transport layer / electron injection transport layer / cathode or transparent substrate / anode / hole injection transport layer / electron injection transport layer / cathode or transparent substrate / anode / hole injection transport layer / organic light emitting layer / electron The injection transport layer / cathode and the like are arranged in this order.
In this configuration, light from the outside enters from the transparent substrate side, and light reflected on the cathode surface is reflected, resulting in poor visibility. However, by providing a circularly polarizing plate on the surface of the transparent substrate, light reflected on the surface of the cathode can be blocked, resulting in a display with excellent visibility.

Hereinafter, the present invention will be described in detail with reference to examples, but embodiments of the present invention are not limited thereto.

[0087]

EXAMPLES Each measurement and evaluation method in the examples was carried out by the following methods. <Number average molecular weight of cellulose ester> It is measured under the following conditions by gel permeation chromatography (GPC). Solvent: acetone Column: MPW × 1 (manufactured by Tosoh Corporation) Sample concentration: 0.2 W / v% Flow rate: 1.0 ml / min Sample injection volume: 300 μl Standard sample: polymethyl methacrylate (Mw = 188, 2)
00) Temperature: 23 ° C.

<Angle of the slow axis of the film, refractive index Nx in the slow axis direction, refractive index Ny in the fast axis direction, refractive index Nz in the thickness direction, retardation Ro in the in-plane direction, and retardation Rt in the thickness direction> Samples for measurement were cut out at intervals of 50 mm in the width direction of the film, measured as follows, and expressed as an average value. Unevenness of each characteristic value was represented by a difference between maximum and minimum.

Automatic birefringence meter KOBRA-21ADH
The three-dimensional refractive index was measured at a wavelength of 590 nm in an atmosphere of 23 ° C. and 55% RH using an instrument (manufactured by Oji Scientific Instruments), and the angle formed with the transverse direction of the slow axis and the refraction in the slow axis direction were measured. The refractive index Nx, the refractive index Ny in the fast axis direction, and the refractive index Nz in the thickness direction are obtained. In-plane retardation (Ro)
And the retardation (Rt) in the thickness direction was calculated from the following equation. Here, d is the thickness (nm) of the film.

Rt = ((Nx + Ny) / 2−Nz) × d Ro = (Nx−Ny) × d <Wavelength dispersion characteristics of film R450 / R550, R65
0 / R550> Automatic birefringence index meter KOBRA-21ADH
The wavelength dispersion was measured by using (manufactured by Oji Scientific Instruments) in an atmosphere of 23 ° C. and 55% RH.

Example 1 100 parts by mass of cellulose acetate propionate having a degree of substitution of an acetyl group of 1.95, a degree of substitution of a propionyl group of 0.7, and a number average molecular weight of 75,000, 8 parts by mass of triphenyl phosphate, ethyl phthalylethyl Glycolate 3
Parts by mass, 300 parts by mass of methyl acetate, and 90 parts by mass of ethanol were put into a pressure-sealed container, heated to 80 ° C., the pressure in the container was set to 2 atm, and the cellulose ester was completely dissolved with stirring to obtain a dope. Was. Azumi Filter Paper No. No. manufactured by Azumi Filter Paper Co., Ltd. After filtration using 244 for film formation, the dope was cooled down to 50 ° C. and allowed to stand overnight to perform a defoaming operation.

The above dope was cast from a die onto a stainless steel belt. After contacting warm water from the back of the stainless steel belt for 1 minute on a stainless steel belt whose temperature is controlled to 55 ° C.,
After contact with cold water of 5 ° C. and holding for 10 seconds, the freshly dried film was peeled from the stainless steel belt. In addition, 70 degreeC warm air was flowed in parallel with the conveyance direction from the surface of the stainless steel belt. The residual solvent amount in the film at the time of peeling was 70% by mass.

Next, the peeled film was dried while being conveyed at 60 ° C. for 10 minutes while holding both ends with tenter clips. At this time, the width of the tenter clip was adjusted so that the film width shrank by 5%. The film was dried at 120 ° C. for 20 minutes while being conveyed on a roll to obtain a cellulose ester film having a thickness of 120 μm. The final film residual solvent amount was 0.2% by mass. The obtained cellulose ester film had a convex stretched line.

Next, the film is heated to 160 ° C. by a roll stretching machine composed of a plurality of rolls while transporting the film in a direction opposite to the direction of film formation, and the film is transported 1.5 times (longitudinal direction). Stretched. Cool to room temperature immediately after stretching
A 00 μm retardation film was obtained.

Example 2 A dope obtained in the same manner as in Example 1 was cast from a die onto a stainless steel belt. After contacting warm water from the back of the stainless steel belt for 1 minute on a stainless steel belt whose temperature is controlled at 55 ° C., further contacting cold water of 15 ° C. with the back of the stainless steel belt and holding for 10 seconds. The freshly dried film was peeled from. In addition, 70 degreeC warm air was flowed in parallel with the conveyance direction from the surface of the stainless steel belt. The residual solvent amount in the film at the time of peeling was 70% by mass.

Next, the peeled film is transported while being wound around a plurality of rolls and dried at 60 ° C. for 10 minutes.
Further dried at 120 ° C. for 20 minutes while being transported on a roll,
A cellulose ester film having a thickness of 120 μm was obtained.
In addition, the interval between the rolls was arranged so as to be 100% with respect to the film width. The final film residual solvent amount is 0.
It was 2% by mass. The obtained cellulose ester film had a convex drawn line.

Next, the film is heated to 160 ° C. by a roll stretching machine composed of a plurality of rolls while transporting the film in a direction opposite to the direction of film formation, and the film is transported 1.5 times (longitudinal direction). Stretched. Cool to room temperature immediately after stretching
A 00 μm retardation film was obtained.

Example 3 100 parts by mass of cellulose acetate propionate having a degree of substitution of an acetyl group of 1.95, a degree of substitution of a propionyl group of 0.7, and a number average molecular weight of 75,000, 8 parts by mass of triphenyl phosphate, ethyl phthalylethyl Glycolate 3
Parts by mass, 336 parts by mass of methylene chloride, and 64 parts by mass of ethanol were charged into a pressure-sealed container, heated to 70 ° C., the pressure in the container was set to 2 atm, and the cellulose ester was completely dissolved with stirring to obtain a dope. Was. Azumi Filter Paper No. No. manufactured by Azumi Filter Paper Co., Ltd. After filtration using 244 and subjecting to film formation, the dope was cooled to 35 ° C. and allowed to stand overnight to perform a defoaming operation.

The above dope was cast from a die onto a stainless steel belt. After contacting warm water from the back of the stainless steel belt for 1 minute on a stainless steel belt whose temperature is controlled to 35 ° C.,
After contact with cold water of 5 ° C. and holding for 10 seconds, the freshly dried film was peeled from the stainless steel belt. Note that hot air of 45 ° C. was flowed from the surface of the stainless steel belt in parallel with the transport direction. The amount of residual solvent in the film at the time of peeling is 100
% By mass.

Next, the peeled film was conveyed while being wound around a plurality of rolls and dried at 50 ° C. for 10 minutes.
Further dried at 120 ° C. for 20 minutes while being transported on a roll,
A cellulose ester film having a thickness of 100 μm was obtained.
The rolls were arranged so that the interval between the rolls was 50% of the film width. Final film residual solvent volume is 0.1
% By mass. The obtained cellulose ester film had a convex drawn line.

While the roll of the obtained cellulose ester was being unwound, transverse stretching was performed as follows (the transport direction during stretching was opposite to that during the formation of the cellulose ester film).

Both ends of the film were gripped by clips and introduced into a tenter to perform transverse stretching. The stretching temperature was 150 ° C. and the stretching ratio was 1.5 times. Cool to 25 ° C immediately after stretching
A 5 μm retardation film was obtained.

Comparative Example 1 The procedure was performed in the same manner as in Example 1 except that the transport direction during stretching was changed to the same direction as when forming the cellulose ester film.

Comparative Example 2 The same procedure was performed as in Example 2 except that the transport direction during stretching was changed to the same direction as when forming the cellulose ester film.

Comparative Example 3 The same procedure was performed as in Example 3 except that the transport direction during stretching was changed to the same direction as when forming the cellulose ester film.

Example 4 Degree of substitution of acetyl group 2.65, number average molecular weight 15,000
0 parts by mass of cellulose acetate, 10 parts by mass of triphenyl phosphate, 2 parts by mass of ethylphthalylethyl glycolate, 300 parts by mass of methylene chloride, and 50 parts by mass of ethanol are put into a pressure-closed container and heated to 70 ° C. The pressure in the vessel was set to 2 atm, and the cellulose ester was completely dissolved with stirring to obtain a dope. Azumi Filter Paper No. No. manufactured by Azumi Filter Paper Co., Ltd. After filtration using 244 and subjecting to film formation, the dope was cooled to 35 ° C. and allowed to stand overnight to perform a defoaming operation.

The above dope was cast from a die onto a stainless steel belt. After contacting warm water from the back of the stainless steel belt for 1 minute on a stainless steel belt whose temperature is controlled to 35 ° C.,
After contact with cold water of 0 ° C. and holding for 10 seconds, the freshly dried film was peeled from the stainless steel belt. The residual solvent amount in the film at the time of peeling was 50% by mass. Next, the peeled film was heated to 100 ° C. by a roll stretching machine composed of a plurality of rolls and stretched 1.2 times in the transport direction (longitudinal direction). Cool to room temperature immediately after stretching, 8
A 0 μm cellulose ester film was obtained. The amount of residual solvent in the film was 0.15% by mass. The obtained cellulose ester film had a convex stretched line.

Next, the film is heated to 170 ° C. by a roll stretching machine composed of a plurality of rolls while transporting the film in a direction opposite to the direction in which the film is formed, and the transport direction (longitudinal direction) is increased by a factor of 1.3. Stretched. Cool to room temperature immediately after stretching
A 0 μm retardation film was obtained.

Example 5 A dope obtained in the same manner as in Example 4 was cast from a die onto a stainless steel belt. After contacting warm water from the back of the stainless steel belt and drying it on a stainless steel belt whose temperature is controlled at 35 ° C. for 1 minute, contact the back of the stainless steel belt with cold water at 10 ° C. and hold for 10 seconds. The freshly dried film was peeled from. The residual solvent amount in the film at the time of peeling was 50% by mass. Next, the peeled film was laterally stretched 1.2 times at 100 ° C. while holding both ends of the film with a tenter clip. Further, the film was dried at 120 ° C. for 10 minutes while being conveyed by a roll to obtain a cellulose ester film having a thickness of 80 μm. The final amount of residual solvent in the film was 0.15% by mass. The obtained cellulose ester film had a convex drawn line.

Next, the film was transversely stretched 1.3 times at 170 ° C. while holding both ends of the film with tenter clips while transporting the film in a direction opposite to the direction of film formation. Immediately after stretching, the film was cooled to room temperature to obtain a 70 μm retardation film.

[0111]

[Table 1]

As is clear from Table 1, according to the present invention, it is possible to obtain a retardation film having a positive wavelength dispersion characteristic and further having a small angle unevenness of the slow axis.

Example 6 A polyvinyl alcohol film having a thickness of 120 μm was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched 4 times at 50 ° C. to form a polarizing film. An 80 μm saponified cellulose triacetate film (KONICATAC) was laminated on one side of this polarizing film using a completely saponified 5% aqueous solution of polyvinyl alcohol as an adhesive to prepare a polarizing film with a protective film.

Further, the retardation film obtained in Example 1 (60 ° C., immersed in a 2 mol / l sodium hydroxide aqueous solution for 2 minutes and washed with water) And then at 100 ° C for 10
After drying for 5 minutes and alkali saponification), a completely saponified polyvinyl alcohol 5% aqueous solution was used as an adhesive to prepare an elliptically polarizing plate. Note that the films were bonded so that the angle between the slow axis of the retardation film and the polarizing axis of the polarizing film was parallel.

<Evaluation of Optical Uniformity of Retardation Film>
The elliptically polarizing plate / commercial linear polarizing plate / backlight was configured so that the surface of the retardation film was on the inside, and the commercial linear polarizing plate was rotated and observed in a crossed Nicols state. If the retardation film has no retardation or unevenness of the slow axis, a uniform dark field can be obtained.

(Results) In the retardation film obtained in the present invention, a uniform dark field was obtained, and it was found that the retardation film had sufficient optical uniformity as the retardation film. Similarly, when the same evaluation was performed using the film of Comparative Example 1, a uniform dark field was not obtained, and the optical uniformity as a retardation film was insufficient.

[0117]

According to the present invention, a retardation film having a positive wavelength dispersion characteristic and a small angle unevenness in a slow axis direction, a method for producing the same, and an elliptically polarizing plate are obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a drawing line related to solution casting of a film.

FIG. 2 is an explanatory diagram of a drawing line related to longitudinal stretching of a film.

FIG. 3 is an explanatory diagram of a drawing line related to a horizontal stretching of a film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stretching line (on support) 2 Web 3 Stretching line (after film-forming) 4 Stretching line (before stretching) 5 Roll stretching machine 6 Stretching line (after stretching) 7 Tenter oven 8 Tenter clip

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // B29K 1:00 B29K 1:00 B29L 7:00 B29L 7:00 11:00 11:00 F term ( (Reference) 2H049 BA04 BA06 BA25 BB03 BB12 BB33 BB43 BB49 BB51 BB62 BC03 BC05 BC09 BC14 BC22 2H091 FA08X FA08Z FA11X FA11Z FB02 FC07 HA07 HA10 KA02 LA18 LA19 4F205 AA01 AD08 AG01 AH73 GA07 GB41 GF13 AGC13 GF01 AGC11 QD19 QG01

Claims (14)

[Claims] 1. A method for producing a retardation film in which a cellulose ester film obtained by a solution casting method is stretched in at least one axis direction, wherein a cellulose ester dope containing a cellulose ester and an organic solvent is provided on a support. After evaporating the organic solvent until it can be cast and peeled, the web is peeled from the support, and the cellulose ester film obtained by further drying is transported in the direction opposite to the casting direction, A method for producing a retardation film, comprising stretching in the longitudinal direction. 2. The method for producing a retardation film according to claim 1, wherein the cellulose ester film is stretched 1.05 to 2.0 times in the machine direction when the residual solvent amount is 2% by mass or less. . 3. A method for producing a retardation film in which a cellulose ester film obtained by a solution casting method is stretched in at least one axis direction, wherein a cellulose ester dope containing a cellulose ester and an organic solvent is provided on a support. After evaporating the organic solvent until it can be cast and peeled off, the web is peeled off from the support, and the cellulose ester film obtained by drying is transported in the direction opposite to the casting direction. A method for producing a retardation film, comprising stretching in the direction. 4. The method for producing a retardation film according to claim 3, wherein the cellulose ester film is stretched 1.05 to 2.0 times in the transverse direction when the residual solvent amount is 2% by mass or less. . 5. The cellulose ester dope containing a cellulose ester and an organic solvent is cast on a support, the organic solvent is evaporated until the cellulose ester dope can be peeled off, and the web is peeled off from the support. 5. A cellulose ester film obtained by drying the web while keeping the width of the peeled web or shrinking in the width direction of 0 to 10%. A method for producing the retardation film according to the above. 6. The cellulose ester dope containing a cellulose ester and an organic solvent is cast on a support and the organic solvent is evaporated until the cellulose ester dope can be peeled off. The peeled web is then separated by a distance between the rolls of 2 to the width of the casting film.
The production of a retardation film according to any one of claims 1 to 4, wherein the cellulose ester film is a cellulose ester film obtained by drying while being wound around a plurality of rolls of 0 to 300%. Method. 7. The cellulose ester film according to claim 1, wherein the cellulose ester film has a convex stretched line.
13. The method for producing a retardation film according to item 10. 8. A method for producing a retardation film in which a cellulose ester film obtained by a solution casting method is stretched in at least one axis direction, wherein the cellulose ester film comprises a cellulose ester containing a cellulose ester and an organic solvent. After evaporating the organic solvent until the dope is cast on the support and peelable, the web is peeled from the support, and then the residual solvent amount of the peeled web is 5 to 5.
In the range of 100% by mass, the draw ratio in the longitudinal direction is 1.01.
The cellulose ester film obtained by longitudinal stretching in the range of 1 to 1.5 times is re-stretched 1.04 to 1.99 times in the longitudinal direction while being transported in the direction opposite to the casting direction. Of producing a retardation film. 9. A method for producing a retardation film, in which a cellulose ester film obtained by a solution casting method is stretched in at least one axis direction, wherein the cellulose ester film comprises a cellulose ester containing a cellulose ester and an organic solvent. After evaporating the organic solvent until the dope is cast on the support and peelable, the web is peeled from the support, and then the residual solvent amount of the peeled web is 5 to 5.
In the range of 100% by mass, the stretching ratio in the width direction is 1.01.
The cellulose ester film obtained by transverse stretching in the range of 1 to 1.5 times is re-stretched 1.04 to 1.99 times in the transverse direction while being transported in the direction opposite to the casting direction. Of producing a retardation film. 10. The method for producing a retardation film according to claim 1, wherein the cellulose ester satisfies the following formulas (I) and (II) at the same time. (I) 2.3 ≦ X + Y ≦ 2.85 (II) 1.4 ≦ X ≦ 2.85 where X is the degree of substitution of an acetyl group, and Y is the degree of substitution of a propionyl group and / or a butyryl group. 11. The cellulose ester according to claim 1, wherein the degree of substitution of the acetyl group is from 1.4 to 2.4.
0. The method for producing a retardation film according to 0. 12. The method for producing a retardation film according to claim 10, wherein the number average molecular weight of the cellulose ester is from 60,000 to 300,000. 13. A retardation film obtained by the method for producing a retardation film according to claim 1. Description: 14. An elliptically polarizing plate, wherein the retardation film according to claim 13 is attached to at least one side of a polarizing film.