JP4608800B2 - Method for producing retardation film - Google Patents

Description

【０１１２】
表１から明らかなように、本発明に依れば正の波長分散特性があり、更に遅相軸の角度むらが少ない位相差フィルムが得られることが分かる。
【０１１３】
実施例６
厚さ１２０μｍのポリビニルアルコールフィルムを沃素１質量部、ホウ酸４質量部を含む水溶液１００質量部に浸漬し、５０℃で４倍に延伸して偏光フィルムを作った。この偏光フィルムの片面に鹸化処理した８０μｍのセルローストリアセテートフィルム（コニカタック）を完全鹸化型ポリビニルアルコール５％水溶液を接着剤として用いて貼り合わせ保護フィルム付の偏光フィルムを作製した。
【０１１４】
更に上記保護フィルム付の偏光フィルムの保護フィルムのない面に、実施例１で得られた位相差フィルム（６０℃、２ｍｏｌ／ｌの濃度の水酸化ナトリウム水溶液中に２分間浸漬し水洗した後、１００℃で１０分間乾燥し、アルカリ鹸化処理したもの）を完全鹸化型ポリビニルアルコール５％水溶液を接着剤として用いて貼り合わせ楕円偏光板を作製した。なお、位相差フィルムの遅相軸と偏光フィルムの偏光軸とのなす角度は、平行になるように貼り合わせた。
【０１１５】
〈位相差フィルムの光学的均一性の評価〉
位相差フィルムの面が内側になるようにして上記楕円偏光板／市販の直線偏光板／バックライトの構成とし、市販の直線偏光板を回転させ、クロスニコルの状態で観察した。位相差フィルムにレタデーションや遅相軸のむらがなければ均一な暗視野が得られることになる。
【０１１６】
（結果）
本発明で得られた位相差フィルムでは、均一な暗視野が得られ、位相差フィルムとして十分な光学的均一性があることが分かった。同様に比較例１のフィルムを用いて同様の評価をしたところ均一な暗視野が得られず位相差フィルムとしての光学的均一性に不十分であった。
【０１１７】
【発明の効果】
本発明により、正の波長分散特性があり、遅相軸方向の角度むらが少ない位相差フィルムとその製造方法及び楕円偏光板を得た。
【図面の簡単な説明】
【図１】フィルムの溶液流延製膜に係わる延伸線の説明図である。
【図２】フィルムの縦延伸に係わる延伸線の説明図である。
【図３】フィルムの横延伸に係わる延伸線の説明図である。
【符号の説明】
１ 延伸線（支持体上）
２ ウェブ
３ 延伸線（製膜後）
４ 延伸線（延伸前）
５ ロール延伸機
６ 延伸線（延伸後）
７ テンターオーブン
８ テンタークリップ[0001]
BACKGROUND OF THE INVENTION
The present invention is a retardation film. Of Manufacturing method To the law Related. In particular, the present invention relates to a method for producing an optically uniform retardation film having little retardation characteristics and slow axis angle unevenness.
[0002]
[Prior art]
Twisted nematic liquid crystal display devices and super twisted nematic liquid crystal display devices used for display parts of various OA devices have a drawback that the display screen is colored due to a phase difference generated in the liquid crystal cell, and this disadvantage is solved. Therefore, a retardation film is used. This retardation film is often bonded to a polarizing plate and used as an elliptical polarizing plate or a circular polarizing plate.
[0003]
These display devices are becoming larger and larger in size year by year, and the retardation film used for them is uniform in a wide range of retardation in the in-plane direction, retardation in the thickness direction, and even in the slow axis direction. It is required to be controlled.
[0004]
Further, attention has been paid to the wavelength dispersion characteristics of the retardation film. That is, there has been a demand for a material that exhibits a larger phase difference as the wavelength increases. For example, taking the case where a retardation film is used as a quarter-wave plate, for example, it is preferable that a quarter-wave phase difference is exhibited at any wavelength within a wavelength range of 400 to 700 nm of visible light.
[0005]
In general, a retardation film is obtained by uniaxially stretching a polycarbonate resin having a large intrinsic birefringence in the longitudinal direction (direction in which the film travels during production). However, the above-mentioned positive wavelength dispersion characteristic cannot be obtained with a polycarbonate retardation film alone.
[0006]
Furthermore, there has been a problem that a phenomenon occurs in which the stretched line bends in the width direction of the film and the angle of the slow axis increases in the width direction of the film toward the both ends.
[0007]
This is a phenomenon in which, when a line is drawn straight in the width direction of the film before stretching and the film is stretched by a stretching machine, the line is bent in an arc 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 becomes larger toward the both ends of the film. In the case of transverse stretching, the slow axis direction is the transverse direction at the center in the width direction of the film, but the angle from the transverse direction becomes larger toward the both ends of the film.
[0008]
A retardation film having a large retardation of the slow axis as described above is not practical enough even if it is used in a liquid crystal display device.
[0009]
As for the phenomenon of bending of the stretched line, the biaxial stretching of the polyester film has been well studied, and the phenomenon of bending of the stretched line is called the Boeing phenomenon and various improvements 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 cellulose ester is used, the stretched line by transverse stretching has a convex shape with respect to the film traveling direction, and the phenomenon is different from that of the polyester film. Even if the improved method is used as it is, the effect is not necessarily obtained. I can't expect to get it.
[0010]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for producing a retardation film that has positive wavelength dispersion characteristics and little angular unevenness in the slow axis direction.
[0011]
[Means for Solving the Problems]
The above object of the present invention has been achieved by the following constitutions.
[0012]
1. 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 axial 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 cellulose ester film obtained by peeling the web from the support and further drying is stretched in the machine direction while being conveyed in the direction opposite to the casting direction. A method for producing a retardation film.
[0013]
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 longitudinal direction.
[0014]
3. 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 axial 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 cellulose ester film obtained by peeling the web from the support and further drying is stretched in the transverse direction while being conveyed in the direction opposite to the casting direction. A method for producing a retardation film.
[0015]
4). 4. The method for producing a retardation film as described in 3 above, wherein the cellulose ester film has a residual solvent amount of 2% by mass or less and is stretched by 1.05 to 2.0 times in the transverse direction.
[0016]
5. After the cellulose ester film evaporates the organic solvent until the cellulose ester dope containing the cellulose ester and the organic solvent is cast on the support and becomes peelable, the web is peeled from the support, and then the peeled web The retardation film according to any one of 1 to 4 above, which is a cellulose ester film obtained by drying while shrinking in a width direction of 0 to 10%. Production method.
[0017]
6). After the cellulose ester film evaporates the organic solvent until the cellulose ester dope containing the cellulose ester and the organic solvent is cast on the support and becomes peelable, the web is peeled from the support, and then the peeled web The cellulose ester film obtained by drying the film while being wound around a plurality of rolls having a distance between the rolls of 20 to 300% of the width of the cast film. The manufacturing method of retardation film of any one of these.
[0018]
7). The method for producing a retardation film as described in any one of 1 to 4 above, wherein the cellulose ester film has a convex stretched line.
[0019]
8). In the 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 axial direction, the cellulose ester film has a cellulose ester dope containing a cellulose ester and an organic solvent on a support. The organic solvent is evaporated until it can be peeled and then peeled, and then the web is peeled from the support, and then when the amount of residual solvent of the peeled web is in the range of 5 to 100% by mass, the draw ratio in the longitudinal direction The cellulose ester film obtained by longitudinal stretching in the range of 1.01 to 1.5 times is restretched in the longitudinal direction by 1.04 times to 1.99 times while being conveyed in the direction opposite to the casting direction. A method for producing a retardation film.
[0020]
9. In the 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 axial direction, the cellulose ester film has a cellulose ester dope containing a cellulose ester and an organic solvent on a support. The organic solvent is evaporated until it can be peeled off, and then the web is peeled from the support, and then when the residual solvent amount of the peeled web is in the range of 5 to 100% by mass, the draw ratio in the width direction The cellulose ester film obtained by transverse stretching in the range of 1.01 times to 1.5 times is restretched in the transverse direction by 1.04 times to 1.99 times while being conveyed in the direction opposite to the casting direction. A method for producing a retardation film.
[0021]
10. 10. The method for producing a retardation film as described in any one of 1 to 9 above, wherein the cellulose ester is a cellulose ester that simultaneously satisfies the following formulas (I) and (II).
[0022]
(I) 2.3 ≦ X + Y ≦ 2.85
(II) 1.4 ≦ X ≦ 2.85
However, X is a substitution degree of an acetyl group, Y is a substitution degree of a propionyl group and / or a butyryl group.
[0023]
11. 11. The method for producing a retardation film as described in 10 above, wherein the cellulose ester has an acetyl group substitution degree of 1.4 to 2.4.
[0024]
12 The method for producing a retardation film as described in 10 or 11 above, wherein the cellulose ester has a number average molecular weight of 60,000 to 300,000.
[0027]
The present invention will be described in more detail.
In the present invention, the cellulose ester solution is referred to as cellulose ester dope or simply dope.
[0028]
First, a method for forming a cellulose ester film by the solution casting method according to the present invention will be described.
[0029]
{Circle around (1)} Dissolution step: This is a step of forming a dope by dissolving the flakes in an organic solvent mainly composed of a good solvent for cellulose ester flakes in a dissolution vessel while stirring. There are various dissolution methods such as a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, a method performed using a cooling dissolution method, and a method performed at high pressure. After dissolution, the dope is filtered with a filter medium, defoamed, and sent to the next process with a pump.
[0030]
(2) Casting step: The dope is fed to a pressurizing die through a pressurization type fixed gear pump, and an endless metal belt for infinite transfer or a support for casting a rotating metal drum at the casting position (hereinafter simply referred to as “casting”). 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 in which the film thickness of the cast dope film is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll, but the slit shape of the die part is prepared. A pressure die that is easy to make uniform in film thickness is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. In order to increase the film forming speed, two or more pressure dies may be provided on the casting support, and the dope amount may be divided and stacked.
[0031]
(3) Solvent evaporation process: The web can be peeled from the support by heating the web (referred to as the dope film after the dope is cast on the casting support). This is a step of evaporating the solvent until. In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. The drying efficiency is good and preferable. A method of combining them is also preferable.
[0032]
(4) Peeling step: This is a step of peeling the web where the solvent has evaporated on the support at the peeling position. The peeled web is sent to the next process. If the residual solvent amount (the following formula) of the web at the time of peeling is too large, peeling is difficult, or conversely, if it is peeled off after sufficiently drying on the support, part of the web is peeled off.
[0033]
As a method for increasing the film forming speed (the film forming speed can be increased because the film is peeled off while the residual solvent amount is as large as possible), there is a gel casting method (gel casting) in which even a large amount of residual solvent can be removed. For example, a poor solvent for the cellulose ester is added to the dope, and after the dope is cast, the gel is formed, and the temperature of the support is lowered to form a gel. There is also a method of adding a metal salt in the dope. By gelling on the support and strengthening the film, it is possible to speed up the peeling and increase the film forming speed. When peeling at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be damaged, or slippage and vertical stripes due to peeling tension will tend to occur, and the amount of residual solvent will be reduced in consideration of economic speed and quality. It is decided.
[0034]
(5) Drying step: A step of drying the web using a drying device that alternately conveys the web through rolls arranged in a staggered manner and / or a tenter device that clips and conveys both ends of the web with a clip. As a drying means, hot air is generally blown on both sides of the web, but there is also a means for heating by applying a microwave instead of the wind. Too much drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. 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 differ depending on the solvent used, and the drying conditions may be appropriately selected according to the type and combination of the solvents used.
[0035]
In the drying step after peeling from the casting support surface, the web tends to shrink in the width direction due to evaporation of the solvent. Shrinkage increases as the temperature rapidly dries. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the finished film. From this point of view, for example, a method of drying the entire drying process or a part of the process as shown in Japanese Patent Application Laid-Open No. 62-46625 while holding the width at both ends of the web with a clip in the width direction (tenter method) ) Is preferred.
[0036]
(6) Winding step: This is a step of winding the web as a film after the residual solvent amount becomes 2% by mass or less. By setting the residual solvent amount to 0.4% by mass or less, a film having good dimensional stability can be obtained. As a winding method, a generally used method may be used. There are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.
[0037]
The amount of residual solvent can be expressed by the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at any point, and N is the mass when M is dried at 110 ° C. for 3 hours.
[0038]
The film thickness of the cellulose ester film varies depending on the purpose of use, but the finished film is usually preferably in the range of 30 to 200 μm, more preferably in the range of 35 to 150 μm, and particularly preferably in the range of 40 to 120 μm. If it is too thin, the film may be weak and handleability may be poor. If it is too thick, 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 pumping amount of the pump, the slit gap of the die base, the extrusion pressure of the die, the speed of the casting support, etc. so as to obtain the desired thickness. Good. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.
[0039]
In the process from immediately after casting through the solution casting film forming method to drying, the atmosphere in the drying apparatus may be air, but in an inert gas atmosphere such as nitrogen gas, carbon dioxide gas or argon gas. May be. Of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be considered.
[0040]
The method for producing a cellulose ester film of the present invention will be described in more detail.
[0041]
In the cellulose ester of the present invention, the total of the substitution degree of the acetyl group and the substitution degree of the propionyl group and / or butyryl group is 2.3 or more and 2.85 or less, and the substitution degree of the acetyl group is 1.4 or more and 2 or less. .85 or less is preferable. When the substitution degree of an acyl group having 2 to 4 carbon atoms is lower than this range, the heat and humidity resistance as a retardation film is poor. On the other hand, if the total degree of substitution is too large, the wavelength dispersion characteristic may be negative, or sufficient retardation may not be obtained.
[0042]
The cellulose ester of the present invention is preferably a cellulose ester 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. Note that butyrate includes iso- in addition to n-. Cellulose acetate propionate having a large substitution degree of propionate group is excellent in water resistance.
[0043]
The cellulose used as a raw material for the cellulose ester used in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.
[0044]
In the cellulose ester of the present invention, when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), an organic acid such as acetic acid or an organic solvent such as methylene chloride is used. The reaction is carried out using a protic catalyst such as sulfuric acid. The acylating agent is acid chloride (CH _Three COCl, C ₂ H _Five COCl, C _Three H ₇ In the case of 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 many glucose units linked together, 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, cellulose triacetate has an acetyl group bonded to all three hydroxyl groups of the glucose unit.
[0045]
The measuring method of the substitution degree of an acyl group can be measured according to ASTM-D817-96.
[0046]
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 mechanical strength of the resulting film is strong. Furthermore, 70000-200000 are preferable.
[0047]
A chlorinated organic solvent useful for dope formation includes methylene chloride. Non-chlorine organic solvents include methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-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, Examples include 1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, and the like. Methyl acetate, ethyl acetate and acetone can be preferably used. Particularly preferred is methyl acetate.
[0048]
The cellulose ester dope of the present invention preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent. After casting the dope onto the casting support, the solvent begins to evaporate, 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, and when these have a small proportion, it also has a role of promoting 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, sec-butanol, and tert-butanol. Of these, ethanol is preferred because the dope has a relatively low boiling point, relatively low boiling point, good drying properties, and no toxicity.
[0049]
The concentration of the cellulose ester in the dope is preferably adjusted to 15 to 40% by mass, and the dope viscosity is preferably adjusted to a range of 10 to 50 Pa · s in order to obtain good film surface quality.
[0050]
In the dope, a plasticizer, an antioxidant, an ultraviolet light inhibitor, a matting agent, a dye, and the like may be added. These compounds may be added together with the cellulose ester or the solvent during the preparation of the cellulose ester solution, or may be added during or after the solution preparation. For a liquid crystal screen display device, it is preferable to add a plasticizer, an antioxidant, an ultraviolet ray inhibitor or the like that imparts heat and humidity resistance.
[0051]
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 permeability, adjusting retardation, and the like. Esters are preferably used. Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like. Examples of carboxylic acid esters include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate, diethyl phthalate, dioctyl phthalate, and diethyl hexyl phthalate. Tributyl can be mentioned. In addition, butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, triacetin, and the like are also included. Alkylphthalylalkyl glycolates are also preferably used for this purpose. The alkyl in the alkylphthalylalkyl glycolate is an alkyl group having 1 to 8 carbon atoms. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl glycolate, Ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, 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 Collate, 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 preferable, and ethyl phthalyl ethyl glycolate is particularly preferably used. These alkyl phthalyl alkyl glycolates may be used in combination of two or more.
[0052]
The addition amount of these compounds is preferably 1 to 20% by mass with respect to the cellulose ester from the viewpoint of expression of the desired effect and suppression of bleed out from the film.
[0053]
As the antioxidant, a hindered phenol compound is 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-tert-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 -Di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl -2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate, etc. Can be mentioned. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. The amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose ester.
[0054]
As an ultraviolet absorber, from the viewpoint of preventing deterioration of a polarizer and a liquid crystal, it is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, the absorption of visible light having a wavelength of 400 nm or more is small. Is preferred. Examples include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Particularly preferred ultraviolet absorbers are benzotriazole compounds and benzophenone compounds. Among these, a benzotriazole-based compound is preferable because unnecessary coloring with respect to the cellulose ester is small. Content of a ultraviolet absorber is 0.01-5 mass%, especially 0.5 mass% or more and 3 mass% or less.
[0055]
In addition, thermal 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 may be added. Furthermore, an antistatic agent, a flame retardant, a lubricant, an oil agent, etc. may be added.
[0056]
The additive contained in the cellulose ester film of the present invention preferably has a vapor pressure of 1333 Pa or less at 200 ° C. from the viewpoint of volatilization suppression.
[0057]
In the present invention, the 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 30 ° C., and at the peeling position. It is preferable to peel the web when the residual solvent amount of the web is 10 to 120% by mass. In order to keep the residual solvent amount at the time of peeling of the web within this range, the surface temperature of the casting support after casting is controlled so that the organic solvent can be efficiently evaporated from the web. Can be preferably used. In order to control the support temperature, it is preferable to use a heat transfer method with good heat transfer efficiency. For example, a back surface heat transfer method using a liquid is preferable. In the belt (support) machine, the belt temperature can be adjusted with a gentle wind to control the temperature at which the belt to be transferred has come to the lower side. 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 part, and a peeling position of the casting support.
[0058]
In the present invention, when the cellulose ester solution is cast by casting, it is preferable to keep the width of the peeled web, or to dry while shrinking in the width direction at a rate of 0 to 10%. As a method of holding the width or shrinking the width, for example, a web stretcher called a tenter can be used to fix the both ends of the web with clips or pins, and the web can be conveyed while holding or narrowing the width of both ends. By drying in this way, when this film is stretched uniaxially, a retardation film with small angle unevenness of the slow axis can be obtained.
[0059]
Further, in the present invention, when the cellulose ester solution casting film is dried while being conveyed while being wound around a plurality of rolls, the distance between the rolls (from the position where the roll and the web are in contact with each other) It is also preferable that the distance to the position where the roll and the web come into contact with each other is 30% to 300% of the web width. By drying in this way, 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%.
[0060]
Furthermore, in this invention, it is preferable that the extending | stretching line of the said cellulose-ester film is convex. By doing in this way, a retardation film with small angle unevenness of the slow axis can be obtained. Usually, the stretched line is drawn in the width direction of the film before stretching and refers to the line obtained after stretching. Here, the line is drawn in the width direction of the web just before peeling from the support. It means the line in the film finally obtained after peeling and drying. Of course, the stretched line need not actually be 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 may be examined in the film width direction. In other words, when the film is cast upward, the slow axis is inclined counterclockwise on the right side from the center of the film width, and if it is inclined clockwise on the left side, the stretch line is convex. It means that. At this time, the angle formed by the longitudinal direction of the slow axis of the film is preferably within a range of ± 15 degrees. When the angle range is within this range, a retardation film having a slow axis with little uneven angle can be obtained.
[0061]
The cellulose ester film obtained as described above is characterized by having a convex stretched line shown in FIG. FIG. 1 is an explanatory diagram of stretch lines relating to solution casting of a film, but the stretch line (on the support) 1 of the web 2 proceeds in the direction of the arrow, and after film formation, the stretch line (after film formation). 3
[0062]
Since the cellulose ester film obtained as described above still has a retardation in the in-plane direction as small as less than 20 nm, it needs to be stretched at least uniaxially to form a retardation film.
[0063]
The stretching method is performed as follows. In this way, the cellulose ester film obtained by the solution casting film forming method is stretched in at least one axial direction while being conveyed in the direction opposite to the casting direction at the time of film forming. In order to convey the film in the opposite direction, for example, the cellulose ester formed by solution casting can be once wound up into a roll and then fed out from the roll.
[0064]
The method of longitudinal stretching is not particularly limited, but it can be carried out by a method in which a difference in peripheral speed is applied to a plurality of rolls and the roll is stretched in the longitudinal direction using the difference in the peripheral speed of the roll. A simultaneous biaxial stretching machine can also be preferably used. In other words, both ends of the film can be fixed with clips and pins, and the intervals between the clips and pins can be increased in the vertical direction (conveying direction). Driving the clip portion by the linear drive method is preferable because it can be smoothly stretched and the risk of breakage and the like can be reduced. The draw ratio in the machine direction is preferably in the range of 1.05 to 2.0 times. If the stretch ratio is too small, retardation may be insufficient as a retardation film, and if the stretch ratio is too large, the film may become cloudy. The draw ratio, temperature, width shrinkage in the transverse direction, etc. can be controlled so that the refractive indices Nx, Ny, Nz of the film (respectively indicate the refractive indices in the longitudinal direction, the transverse direction, and the thickness direction) become desired values. preferable. When the cellulose ester film is stretched in this manner, the stretch line becomes convex as shown in FIG. FIG. 2 is an explanatory diagram of stretch lines relating to the longitudinal stretching of the film, but the stretch line 4 (before stretching) 4 of the web 2 is stretched by a roll stretching machine 5 to become a stretch line (after stretching) 6. This stretched line is a line drawn in the width direction of the cellulose ester film, and it was investigated what happens after stretching. The cellulose ester film is formed in advance so as to have a convex stretch line, and then stretched in the uniaxial direction while being transported in the direction opposite to the transport direction during film formation to cancel the stretch line generated during stretching. The angle unevenness of the slow axis of the film can be reduced.
[0065]
The method of transverse stretching is not particularly limited, but a transverse stretching machine called a tenter can be preferably used. That is, it is a method in which both ends of the web are fixed with clips and pins, and the interval between the clips and pins is extended in the horizontal direction and extended in the horizontal direction. Depending on the application of the retardation film, it may be desirable to make the refractive index in the longitudinal direction and the thickness direction closer. In this case, the refractive index in the vertical direction and the thickness direction can be made closer by using a simultaneous biaxial stretching machine while reducing the distance in the conveyance direction of the clips and pins in the conveyance direction (longitudinal direction). As the driving method of the tenter clip, it is preferable to drive the clip portion by a linear drive method because it can be smoothly stretched and the risk of breakage and the like can be reduced. The stretching ratio in the transverse direction is preferably in the range of 1.05 times to 2.0 times. If the stretch ratio is too small, retardation may be insufficient as a retardation film, and if the stretch ratio is too large, the film may become cloudy. It is preferable to control the draw ratio, temperature, shrinkage ratio in the longitudinal direction, etc. so that the refractive indices Nx, Ny, Nz of the film (respectively indicate the refractive indices in the longitudinal direction, the transverse direction, and the thickness direction) become desired values. . When the cellulose ester film is stretched in this manner, the stretch line becomes convex as shown in FIG. FIG. 3 is an explanatory diagram of stretch lines related to the transverse stretching of the film. The web 2 is stretched laterally by the tenter clip 8 in the tenter oven 7 and the stretched line 4 before stretching becomes a stretched line (after stretching) 6. . This stretched line is a line drawn in the width direction of the cellulose ester film, and it was investigated what happens after stretching. The cellulose ester film is formed in advance so as to have a convex stretch line, and then stretched in a uniaxial direction while being transported in the direction opposite to the transport direction during film formation to cancel the stretch line generated during stretching. The angle unevenness of the slow axis of the film can be reduced.
[0066]
In the present invention, the following method can also be preferably used. That is, 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 axial direction, the cellulose ester film is a cellulose ester dope containing a cellulose ester and an organic solvent. After casting and evaporating until the organic solvent can be peeled, the web is peeled off from the support, and then stretched in the longitudinal direction when the amount of residual solvent of the peeled web is in the range of 5 to 100% by mass. The cellulose ester film obtained by longitudinal stretching in the range of magnification 1.01 times to 1.5 times is restretched 1.04 times to 1.99 times in the longitudinal direction while being conveyed in the direction opposite to the casting direction. A cellulose ester film obtained by a method for producing a retardation film or a solution casting film-forming method is characterized by being stretched in at least one axial direction. In the method for producing a difference film, the cellulose ester film is obtained by casting a cellulose ester dope containing a cellulose ester and an organic solvent on a support and evaporating the organic solvent until the organic solvent can be peeled, and then removing the web from the support. A cellulose ester film obtained by transverse stretching in the range of 1.01 to 1.5 times the draw ratio in the width direction when the amount of residual solvent of the peeled and then peeled web is in the range of 5 to 60% by mass. It is a method for producing a retardation film, wherein the film is redrawn 1.04 times to 1.99 times in the transverse direction while being conveyed in the direction opposite to the casting direction. In this way, by performing the first-stage stretching in advance, the re-stretching ratio can be kept small. As a result, the convex shape of the drawn line can be reduced. Furthermore, by making the conveying direction during the first-stage stretching and re-stretching opposite directions, the stretched lines are offset and the angle unevenness of the slow axis of the film can be extremely reduced.
[0067]
If the amount of residual solvent in the web is too large, a sufficient effect cannot be obtained, and if it is too small, stretching becomes extremely difficult and the web may break. Further, if the draw ratio is too small, a sufficient effect cannot be obtained, and if it is too large, stretching may become difficult and breakage may occur. A more preferable range of the draw ratio is a range of 1.1 times to 1.4 times.
[0068]
The stretching temperature can be stretched without heating to a high temperature in the method of the present invention. However, it is preferable to combine drying and stretching because the process can be shortened. However, since the plasticizer volatilizes when the temperature of the web is too high, a range of room temperature (15 ° C) to 160 ° C or less is preferable. In addition, when extending | stretching and drying together like this case, it is preferable that the amount of residual solvents in the time of completion | finish of extending | stretching exists in the range of 5-60 mass%. Furthermore, 10-30 mass% is preferable.
[0069]
A method for stretching the web is not particularly limited, but a transverse stretching machine called a tenter can be preferably used. That is, it is a method in which both ends of the web are fixed with clips and pins, and the interval between the clips and pins is extended in the horizontal direction and extended in the horizontal direction. Stretching or shrinking in the longitudinal direction can be performed by widening or shrinking the interval in the transport direction of the clip or pin in the transport direction (longitudinal direction) using a simultaneous biaxial stretching machine. Driving the clip portion by the linear drive method is preferable because it can be smoothly stretched and the risk of breakage and the like can be reduced.
[0070]
Moreover, as a method of extending | stretching to a vertical direction, the method of giving a circumferential speed difference to several rolls, and extending | stretching to a vertical direction using a roll circumferential speed difference among them can also be used. For re-stretching, the cellulose ester film stretching method described above can be used. The total of the draw ratio during the production of the cellulose ester film and the redraw ratio is preferably in the range of 1.05 to 2.0 times.
[0071]
In the retardation film obtained as described above, the slow axis direction of the film (the maximum refractive index direction in the film plane) is ± with respect to the winding direction or the direction perpendicular thereto (the width direction of the film). 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.
[0072]
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 20 nm to 200 nm, and more preferably 30 nm to 100 nm. The retardation Rt in the thickness direction is preferably 0 nm to 400 nm, and more preferably 50 nm to 200 nm. The ratio Rt / Ro between Rt and Ro is preferably 1.0 to 5.0, more preferably 1.4 to 3.0. By setting the retardation value of the film within this range, a retardation film having excellent viewing angle characteristics can be obtained.
The present invention Pertaining to The retardation film exhibits a larger retardation as the wavelength increases in the wavelength range of 400 to 700 nm. Such characteristics are particularly preferable when the retardation film is used as a quarter-wave plate. When the phase differences at wavelengths of 450 nm, 590 nm, and 650 nm are R450, R590, and R650, respectively.
0.5 <R450 / R590 <1.0
1.0 <R650 / R590 <1.5
It is preferable to be in the range because it has an excellent function of converting linearly polarized light into circularly polarized light.
[0073]
The present invention Pertaining to When the retardation film is used as a quarter-wave plate, R590 is preferably 137.5 nm ± 20 nm, and more preferably 137.5 nm ± 10 nm. By setting it within this range, a good quarter-wave plate function can be obtained.
[0074]
In order to obtain the above optical characteristics, the difference between the refractive index Nx in the slow axis direction of the retardation film and the refractive index Ny in the fast axis direction (direction perpendicular to the slow axis in the film plane) is It is necessary to make it 0.0005 or more and 0.0050 or less. A more preferable range is 0.0010 or more and 0.0030 or less.
[0075]
Further, when the refractive index Nx in the slow axis direction, the refractive index Ny in the fast axis direction, and the refractive index Nz in the thickness direction of the film, (Nx−Ny) / 2−Nz is 0.0005 or more and 0.0050 or less. It is also effective.
[0076]
Setting the refractive index of the film within the above range can be achieved by appropriately controlling the stretching conditions of the film as described above.
[0077]
The present invention Pertaining to The photoelastic coefficient of the retardation film is an absolute value of 60 × 10 ^-13 cm ² / Dyne or less, more preferably 20 × 10 ^-13 cm ² / Dyne or less is preferable. The photoelastic coefficient is a value obtained with an ellipsometer. The glass transition temperature of the film is preferably 120 ° C. or higher, more preferably 140 ° C. or higher. The glass transition temperature is a temperature at which the base line derived from the glass transition of the film starts to change and a temperature at which it returns to the base line again when measured at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC). Is obtained as an average value of. Retardation films are often used outdoors as parts constituting display devices such as mobile terminals and car navigation systems, and heat resistance is required. When the properties of the retardation film are within the above range, a good display device in which the viewing angle is not deteriorated and the display is not colored can be obtained.
[0078]
The present invention Pertaining to The retardation film may be further laminated with a liquid crystal resin or another retardation film 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.
[0079]
The present invention Pertaining to The retardation film can be formed into an elliptically polarizing plate by being bonded to at least one surface of the polarizing film.
[0080]
Conventionally known polarizing films can be used. For example, a hydrophilic polymer film such as a polyvinyl alcohol film is treated with a dichroic dye such as iodine and stretched. Since the polarizing film itself is not sufficiently durable, a cellulose triacetate film is generally adhered to both sides as a protective film.
[0081]
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 serving as the protective film. In particular, the present invention Pertaining to The retardation film can be bonded to the polarizing film by saponifying the surface using an adhesive made of an aqueous solution of a water-soluble polymer as conventionally used. The water-soluble polymer adhesive is preferably a completely saponified polyvinyl alcohol aqueous solution.
[0082]
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 electroluminescence device, a plasma display, and the like. For example, in the case of a single polarizing plate reflection type liquid crystal display device, the configuration is from the front side, polarizing plate protective film / polarizer / book invention Pertaining to Retardation film / glass substrate / ITO transparent electrode / alignment film / TN type liquid crystal / alignment film / metal electrode / reflection film / glass substrate. In the conventional case, the structure is polarizing plate protective film / polarizer / polarizing plate protective film / retardation plate / glass substrate / ITO transparent electrode / alignment film / TN liquid crystal / alignment film / metal electrode / reflection film / glass substrate. . In the conventional configuration, coloring is seen because the phase difference characteristics with respect to the wavelength of the phase difference plate are insufficient. Pertaining to By using the retardation film, a good liquid crystal display device without coloring can be obtained.
[0083]
In the case of a reflective polarizing element made of cholesteric liquid crystal, backlight / cholesteric liquid crystal layer / present invention Pertaining to It can be used in the configuration of retardation film / polarizer / polarizing plate protective film.
[0084]
In addition, the present invention Pertaining to In the case of a polarizing plate using a retardation film as a quarter-wave plate, a circularly polarizing plate capable of converting natural polarized light into circularly polarized light is obtained. This works as an antireflection film or an antiglare film by being installed on a front plate such as a plasma display or an organic EL display, and can prevent coloring and deterioration of visibility. It can also be used to prevent touch panel reflection.
[0085]
The organic electroluminescence device is also called an organic EL device, and is introduced in, for example, Japanese Journal of Applied Physics Vol. 25, Item 773 (1986). The structure is, for example, transparent substrate / anode / organic light emitting layer / cathode, or transparent substrate / anode / hole injection transport layer / electron injection transport light emitting layer / cathode, or transparent substrate / anode / hole injection transport layer / electron. The injection / transport layer / cathode, or the transparent substrate / anode / hole injection / transport layer / organic light emitting layer / electron injection / transport layer / cathode are formed in this order. In this configuration, light from the outside enters from the transparent substrate side, and the 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, the reflected light on the cathode surface can be blocked, so that the display has excellent visibility.
[0086]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this.
[0087]
【Example】
Each measurement and evaluation method in an Example was performed with the following method.
<Number average molecular weight of cellulose ester>
It measures on 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 = 188,200)
Temperature: 23 ° C.
[0088]
<Angle of slow axis of film, refractive index Nx in slow axis direction, refractive index Ny in fast axis direction, refractive index Nz in thickness direction, retardation Ro in in-plane direction, retardation Rt in 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. The unevenness of each characteristic value is represented by the maximum and minimum difference.
[0089]
Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), a three-dimensional refractive index measurement is performed at a wavelength of 590 nm in an atmosphere of 23 ° C. and 55% RH. The refractive index Nx in the angle and slow axis direction, the refractive index Ny in the fast axis direction, and the refractive index Nz in the thickness direction are obtained. In-plane direction retardation (Ro) and thickness direction retardation (Rt) were calculated from the following formulas. In the formula, d is the thickness (nm) of the film.
[0090]
Rt = ((Nx + Ny) / 2−Nz) × d
Ro = (Nx−Ny) × d
<Wavelength dispersion characteristics R450 / R550, R650 / R550 of the film>
Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), wavelength dispersion measurement was performed in an atmosphere of 23 ° C. and 55% RH.
[0091]
Example 1
Acetyl group substitution degree 1.95, propionyl group substitution degree 0.7, number average molecular weight 75000 cellulose acetate propionate 100 parts by mass, triphenyl phosphate 8 parts by mass, ethylphthalylethyl glycolate 3 parts by mass, 300 parts by mass of methyl acetate and 90 parts by mass of ethanol were put into a pressurized airtight container, heated to 80 ° C., the pressure in the container was set to 2 atm, and the cellulose ester was completely dissolved while stirring to obtain a dope. The solution was Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. After being filtered using 244 and subjected to film formation, the dope was lowered to 50 ° C. and allowed to stand overnight to perform a defoaming operation.
[0092]
The above dope was cast from a die onto a stainless steel belt. After contacting the hot water from the back of the stainless steel belt and drying on the stainless steel belt controlled to 55 ° C. for 1 minute, the back of the stainless steel belt is further contacted with 15 ° C. cold water for 10 seconds, and then the stainless steel belt. The dried film was peeled off. In addition, 70 degreeC warm air was flowed in parallel with the conveyance direction from the surface of the stainless steel belt. The amount of residual solvent in the film at the time of peeling was 70% by mass.
[0093]
Next, the peeled film was dried while being conveyed at 60 ° C. for 10 minutes while holding both ends with a tenter clip. At this time, the tenter clip width was adjusted so that the film width shrunk by 5%. While being rolled, the film was dried at 120 ° C. for 20 minutes 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 stretch line.
[0094]
Next, the film was heated to 160 ° C. by a roll stretching machine composed of a plurality of rolls while being transported in the direction opposite to the film transport direction, and stretched 1.5 times in the transport direction (longitudinal direction). . Immediately after stretching, the film was cooled to room temperature to obtain a 100 μm retardation film.
[0095]
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 the hot water from the back of the stainless steel belt and drying on the stainless steel belt controlled to 55 ° C. for 1 minute, the back of the stainless steel belt is further contacted with 15 ° C. cold water for 10 seconds, and then the stainless steel belt. The dried film was peeled off. In addition, 70 degreeC warm air was flowed in parallel with the conveyance direction from the surface of the stainless steel belt. The amount of residual solvent in the film at the time of peeling was 70% by mass.
[0096]
Next, the peeled film was transported while being wound on a plurality of rolls and dried at 60 ° C. for 10 minutes, and further dried at 120 ° C. for 20 minutes while being transported on a roll to obtain a cellulose ester film having a thickness of 120 μm. In addition, it arrange | positioned so that the space | interval of a roll might be 100% with respect to the film width. The final film residual solvent amount was 0.2% by mass. The obtained cellulose ester film had a convex stretch line.
[0097]
Next, the film was heated to 160 ° C. by a roll stretching machine composed of a plurality of rolls while being transported in the direction opposite to the film transport direction, and stretched 1.5 times in the transport direction (longitudinal direction). . Immediately after stretching, the film was cooled to room temperature to obtain a 100 μm retardation film.
[0098]
Example 3
Acetyl group substitution degree 1.95, propionyl group substitution degree 0.7, number average molecular weight 75000 cellulose acetate propionate 100 parts by mass, triphenyl phosphate 8 parts by mass, ethylphthalylethyl glycolate 3 parts by mass, 336 parts by mass of methylene chloride and 64 parts by mass of ethanol were put into a pressurized sealed container, heated to 70 ° C., the pressure in the container was set to 2 atm, and the cellulose ester was completely dissolved while stirring to obtain a dope. The solution was Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. After filtration using 244 for film formation, the dope was lowered to 35 ° C. and allowed to stand overnight to perform a defoaming operation.
[0099]
The above dope was cast from a die onto a stainless steel belt. After contacting the hot water from the back of the stainless steel belt and drying on a stainless steel belt controlled to 35 ° C. for 1 minute, the back of the stainless steel belt is further contacted with 15 ° C. cold water and held for 10 seconds, and then the stainless steel belt. The dried film was peeled off. In addition, 45 degreeC warm air was flowed in parallel with the conveyance direction from the surface of the stainless steel belt. The amount of residual solvent in the film at the time of peeling was 100% by mass.
[0100]
Next, the peeled film was conveyed while being wound around a plurality of rolls and dried at 50 ° C. for 10 minutes, and further dried at 120 ° C. for 20 minutes while being conveyed by a roll to obtain a cellulose ester film having a thickness of 100 μm. In addition, it arrange | positioned so that the space | interval of a roll might be 50% with respect to a film width. The final film residual solvent amount was 0.1% by mass. The obtained cellulose ester film had a convex stretch line.
[0101]
While drawing the roll of the obtained cellulose ester, transverse stretching was performed as follows (the conveyance direction during stretching is the opposite direction to that during film formation of the cellulose ester film).
[0102]
Both ends of the film were gripped with clips and introduced into a tenter for transverse stretching. The stretching temperature was 150 ° C. and the stretching ratio was 1.5 times. Immediately after stretching, the film was cooled to 25 ° C. to obtain a 75 μm retardation film.
[0103]
Comparative Example 1
In Example 1, it carried out similarly except having changed the conveyance direction at the time of extending | stretching to the same direction as the time of film formation of a cellulose-ester film.
[0104]
Comparative Example 2
In Example 2, it carried out similarly except having changed the conveyance direction at the time of extending | stretching to the same direction as the time of film formation of a cellulose-ester film.
[0105]
Comparative Example 3
In Example 3, it carried out similarly except having changed the conveyance direction at the time of extending | stretching to the same direction as the time of film formation of a cellulose-ester film.
[0106]
Example 4
Add 100 parts by mass of cellulose acetate having an acetyl group substitution degree of 2.65 and a number average molecular weight of 150,000, 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. The dope was put into a pressure-sealed container, heated to 70 ° C. to set the pressure in the container to 2 atm, and the cellulose ester was completely dissolved while stirring. The solution was Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. After filtration using 244 for film formation, the dope was lowered to 35 ° C. and allowed to stand overnight to perform a defoaming operation.
[0107]
The above dope was cast from a die onto a stainless steel belt. After contacting with hot water from the back of the stainless steel belt and drying on a stainless steel belt controlled at 35 ° C. for 1 minute, and then holding 10 ° C. cold water on the back of the stainless steel belt for 10 seconds, The dried film was peeled off. The amount of residual solvent in the film at the time of peeling was 50% by mass. Next, the peeled film was stretched 1.2 times in the transport direction (longitudinal direction) by heating the film to 100 ° C. with a roll stretching machine composed of a plurality of rolls. Immediately after stretching, the film was cooled to room temperature to obtain an 80 μm cellulose ester film. The amount of residual solvent in the film was 0.15% by mass. The obtained cellulose ester film had a convex stretch line.
[0108]
Next, the film was heated to 170 ° C. by a roll stretching machine consisting of a plurality of rolls while being transported in the direction opposite to the film transport direction, and stretched 1.3 times in the transport direction (longitudinal direction). . Immediately after stretching, the film was cooled to room temperature to obtain a 70 μm retardation film.
[0109]
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 with hot water from the back of the stainless steel belt and drying on a stainless steel belt controlled at 35 ° C. for 1 minute, and then holding 10 ° C. cold water on the back of the stainless steel belt for 10 seconds, The dried film was peeled off. The amount of residual solvent in the film at the time of peeling was 50% by mass. Next, the peeled film was 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 film residual solvent amount was 0.15% by mass. The obtained cellulose ester film had a convex stretch line.
[0110]
Next, the film was stretched 1.3 times at 170 ° C. while gripping both ends of the film with a tenter clip while transporting the film in the direction opposite to that during film formation. Immediately after stretching, the film was cooled to room temperature to obtain a 70 μm retardation film.
[0111]
[Table 1]

[0112]
As is apparent from Table 1, according to the present invention, it can be seen that a retardation film having positive wavelength dispersion characteristics and further having little slow axis angle unevenness can be obtained.
[0113]
Example 6
A 120 μm thick polyvinyl alcohol film 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 produce a polarizing film. A polarizing film with a protective film was prepared by laminating a saponified 80 μm cellulose triacetate film (Konicatak) on one side of this polarizing film using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive.
[0114]
Furthermore, on the surface without the protective film of the polarizing film with the protective film, the retardation film obtained in Example 1 (60 ° C., immersed in an aqueous solution of sodium hydroxide having a concentration of 2 mol / l for 2 minutes, washed with water, An elliptically polarizing plate was prepared by laminating a saponified alkali saponified 5% aqueous solution as an adhesive, which was dried at 100 ° C. for 10 minutes and alkali saponified. In addition, it bonded together so that the angle which the slow axis of a phase difference film and the polarization axis of a polarizing film make may become parallel.
[0115]
<Evaluation of optical uniformity of retardation film>
The configuration was the above elliptical polarizing plate / commercial linear polarizing plate / backlight 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 Nicol state. If the retardation film has no retardation or unevenness of the slow axis, a uniform dark field can be obtained.
[0116]
(result)
In the retardation film obtained by this invention, a uniform dark field was obtained and it turned out that there exists sufficient optical uniformity as a retardation film. Similarly, when the same evaluation was made 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]
【The invention's effect】
According to the present invention, a retardation film having positive wavelength dispersion characteristics and little angle unevenness in the slow axis direction, a method for producing the same, and an elliptically polarizing plate were obtained.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram of stretched lines relating to solution casting of a film.
FIG. 2 is an explanatory diagram of stretching lines related to the longitudinal stretching of the film.
FIG. 3 is an explanatory diagram of stretching lines related to the lateral stretching of the film.
[Explanation of symbols]
1 Stretching line (on support)
2 Web
3 Drawing wire (after film formation)
4 Stretching line (before stretching)
5 roll drawing machine
6 Stretching line (after stretching)
7 Tenter oven
8 Tenter clip

Claims (12)

  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 axial 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 cellulose ester film obtained by peeling the web from the support and further drying is stretched in the machine direction while being conveyed in the direction opposite to the casting direction. A method for producing a retardation film.   2. The method for producing a retardation film according to claim 1, 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 longitudinal direction.   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 axial 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 cellulose ester film obtained by peeling the web from the support and further drying is stretched in the transverse direction while being conveyed in the direction opposite to the casting direction. A method for producing a retardation film.   The method for producing a retardation film according to claim 3, wherein the cellulose ester film has a residual solvent amount of 2% by mass or less and is stretched by 1.05 to 2.0 times in the transverse direction.   After the cellulose ester film evaporates the organic solvent until the cellulose ester dope containing the cellulose ester and the organic solvent is cast on the support and becomes peelable, the web is peeled from the support, and then the peeled web The retardation film according to any one of claims 1 to 4, which is a cellulose ester film obtained by drying while shrinking in a width direction of 0 to 10%. Manufacturing method.   After the cellulose ester film evaporates the organic solvent until the cellulose ester dope containing the cellulose ester and the organic solvent is cast on the support and becomes peelable, 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 having a distance between rolls of 20 to 300% of the width of the cast film. 5. The method for producing a retardation film according to any one of 4 above.   The method for producing a retardation film according to claim 1, wherein the cellulose ester film has a convex stretched line.   In the 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 axial direction, the cellulose ester film has a cellulose ester dope containing a cellulose ester and an organic solvent on a support. The organic solvent is evaporated until it can be peeled and then peeled, and then the web is peeled from the support, and then when the amount of residual solvent of the peeled web is in the range of 5 to 100% by mass, the draw ratio in the longitudinal direction The cellulose ester film obtained by longitudinal stretching in the range of 1.01 to 1.5 times is restretched in the longitudinal direction by 1.04 times to 1.99 times while being conveyed in the direction opposite to the casting direction. A method for producing a retardation film.   In the 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 axial direction, the cellulose ester film has a cellulose ester dope containing a cellulose ester and an organic solvent on a support. The organic solvent is evaporated until it can be peeled off, and then the web is peeled from the support, and then when the residual solvent amount of the peeled web is in the range of 5 to 100% by mass, the draw ratio in the width direction The cellulose ester film obtained by transverse stretching in the range of 1.01 times to 1.5 times is restretched in the transverse direction by 1.04 times to 1.99 times while being conveyed in the direction opposite to the casting direction. A method for producing a retardation film. The method for producing a retardation film according to claim 1, wherein the cellulose ester is a cellulose ester that simultaneously satisfies the following formulas (I) and (II).
(I) 2.3 ≦ X + Y ≦ 2.85
(II) 1.4 ≦ X ≦ 2.85
However, X is a substitution degree of an acetyl group, Y is a substitution degree of a propionyl group and / or a butyryl group.   The method for producing a retardation film according to claim 10, wherein the substitution degree of the acetyl group of the cellulose ester is 1.4 to 2.4.   The number average molecular weight of a cellulose ester is 60000-300000, The manufacturing method of the retardation film of Claim 10 or 11 characterized by the above-mentioned.

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