JP2005300978A - Retardation film and polarizing plate using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film which can increase display contrast of a liquid crystal display and comprises a cellulose ester film having a slow axis in the width direction of the film and excellent transparency, and to provide a polarizing plate using the film. <P>SOLUTION: The retardation film comprises a cellulose ester film produced by forming a cellulose ester resin sheet by a melt flow film forming method and stretching and orienting the resin sheet in the width direction, and has 20 to 100 μm thickness, 20 to 100 nm retardation (Ro) in the plane and 90 to 200 nm retardation (Rt) in the thickness direction. The polarizing plate is composed of a polarizing film and two protective films for a polarizing plate disposed on either side of the film. At least one of the two protective films for a polarizing plate comprises the above retardation film and layered with the slow phase axis of the retardation film substantially parallel to the transmission axis of the polarizing film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention can increase the display contrast of a liquid crystal display device, has a slow axis in the width direction of the film, and has a retardation film made of a cellulose ester film excellent in transparency, and polarized light using the same Regarding the board.

  A liquid crystal display device is widely used as a display device for computers, portable terminals, and the like because of features such as space saving and low power consumption compared to a conventional CRT display device.

  The liquid crystal display device has a drawback that a viewing angle is narrow when the screen is viewed from an oblique direction due to a phase difference generated in the liquid crystal cell, and the viewing angle is narrow, and the contrast is lowered. Therefore, a retardation film is generally used. As a retardation film, a polycarbonate resin film having a large intrinsic birefringence and uniaxially stretched in the longitudinal direction (direction in which the film travels during production) has been widely used. In this retardation film, the slow axis direction is the same longitudinal direction as the stretching direction. When laminating a retardation film to a polarizing film, the slow axis direction must be the width direction of the polarizing film (the direction perpendicular to the uniaxial stretching direction of the polarizing film), but the longitudinal direction In a conventional retardation film having a slow axis, the polarizing film cannot be laminated in the form of a long roll, the film must be cut, and the sheet must be laminated by rotating the direction 90 degrees, Productivity was remarkably inferior.

  A film having a slow axis in the width direction can be bonded to a polarizing film in the form of a long roll, and the productivity can be remarkably improved.

  As a method of stretching in the width direction, a method using a tenter type transverse stretching machine is common. However, in this method, by stretching in the width direction, molecular orientation proceeds in the width direction, and at the same time, a regulating force is generated in the longitudinal direction, a compressive force acts in the thickness direction, and the plane orientation of the molecules increases. Therefore, it was difficult to develop retardation in the in-plane direction. Therefore, in order to increase the retardation in the in-plane direction, it is necessary to further increase the stretching ratio, but if the stretching ratio is too high, there is a problem that the film becomes cloudy and the transparency deteriorates. The range of retardation obtained while maintaining good film transparency was limited.

  In recent years, liquid crystal display devices have become larger. Due to the increase in screen size, the conventional viewing angle has become insufficient, and the retardation characteristics required for retardation films have also diversified, and these solutions have been desired.

  The liquid crystal display device has a configuration in which there are polarizing plates on both sides of the liquid crystal cell, and a retardation film is disposed between both the polarizing plates and the liquid crystal cell. The polarizing plate has a configuration in which a protective film is bonded to both surfaces of a polarizing film (for example, a stretched polyvinyl alcohol film dyed with iodine). As this protective film, a cellulose triacetate film is used because it is transparent and has excellent adhesion to a polarizing film. If a retardation film is laminated instead of this protective film, the number of optical films to be used can be reduced. From the viewpoint of adhesiveness with a polarizing film, it is preferable to use a cellulose ester film as a retardation film, but a cellulose triacetate film conventionally used as a protective film has poor stretchability and is transparent when stretched forcibly. There was a problem that the property deteriorated.

Here, prior patent documents relating to cellulose ester films used as optical films include the following.
The invention described in Japanese Patent Application Laid-Open No. 2002-267846 is an optical system free from cloudiness constituted by a stretched cellulose ester film in which the elongation at break in the direction perpendicular to the stretch direction is in a specific range (break elongation is 40 to 110%). This is related to the compensation sheet. JP-A-2000-352620 discloses an optical film having a cellulose ester film formed by melt casting. In JP-A-2002-296422, in forming a cellulose ester film by a solution casting film-forming method, the web peeled from the metal support is separated from the central portion by 1 to 30 from the center of the web. A method of stretching in the transverse direction at a high temperature is proposed.

  However, in the cellulose ester film described in Patent Document 1, as can be seen from the description of the examples, the haze of the cellulose ester film is 1.5 to 2.0%, and the optical film has transparency. There was a problem that it was not enough. Moreover, although the said patent document 2 describes forming a cellulose-ester film by the melt casting film forming method, about the cellulose-ester film which can make the display contrast of a liquid crystal display device high, description is given. There wasn't. Further, Patent Document 3 describes a method of stretching a cellulose ester film in the transverse direction. However, since the film is produced by a solution casting film-forming method, There was a problem that the transparency deteriorated.

  The object of the present invention is to solve the above-mentioned problems of the prior art, increase the display contrast of the liquid crystal display device, have a slow axis in the width direction of the film, and have excellent transparency. And a polarizing plate using the same.

  In the present invention, a cellulose ester film formed by the melt casting method is stretched and oriented in the width direction, whereby a cellulose ester film excellent in transparency is obtained, and the productivity at the time of polarizing plate processing is excellent. The inventors have found that a polarizing plate excellent in viewing angle characteristics of a liquid crystal display device can be obtained, and have completed the present invention.

  In order to achieve the above object, the retardation film according to claim 1 of the present invention comprises a cellulose ester film obtained by stretching and orienting a cellulose ester resin sheet formed by a melt casting method in the width direction. The thickness is 20 to 100 μm, the in-plane retardation (Ro) defined by the following formula (a) is 20 to 100 nm, and the thickness direction retardation (Rt) defined by the following formula (b) is 90 to 200 nm. A retardation film characterized by.

Ro = (nx−ny) × d (a)
Rt = {(nx + ny) / 2−nz} × d (b)
(Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is the film thickness) And the unit is nm.)
The retardation film according to claim 2 of the present invention is characterized in that, in the retardation film according to claim 1, the haze of the cellulose ester film is 0.1 to 1.4%.

  The retardation film according to claim 3 of the present invention is characterized in that, in the retardation film according to claim 1 or 2, the resin constituting the cellulose ester film is cellulose acetate propionate.

  The retardation film according to claim 4 of the present invention is the retardation film according to claim 1 or 2, wherein the resin constituting the cellulose ester film is an aliphatic polyester graft side chain having lactic acid as a main repeating unit. It is characterized by being a cellulose acetate having

  The invention of the polarizing plate according to claim 5 of the present invention is a polarizing plate comprising a polarizing film and two polarizing plate protective films disposed on both sides thereof, and at least of the two polarizing plate protective films. Either one is constituted by the retardation film according to any one of claims 1 to 4, and the slow axis of the retardation film and the transmission axis of the polarizing film are substantially parallel to each other. It is characterized by being laminated.

The invention of the retardation film according to claim 1 of the present invention comprises a cellulose ester film obtained by stretching and orienting the cellulose ester resin sheet formed by the melt casting film forming method in the width direction as described above, and the thickness is 20 The in-plane retardation (Ro) defined by the following formula (a) is 20 to 100 nm, and the thickness direction retardation (Rt) defined by the following formula (b) is 90 to 200 nm. With
Ro = (nx−ny) × d (a)
Rt = {(nx + ny) / 2−nz} × d (b)
(Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is the film thickness) And the unit is nm.)
According to the retardation film of the present invention, the retardation film has a slow axis in the width direction of the film and is excellent in transparency. By utilizing the polarizing plate using the retardation film, the display of the liquid crystal display device is eventually obtained. There is an effect that the contrast can be increased. Moreover, when laminating | stacking the phase difference film of this invention on a polarizing film, since it can laminate | stack in a roll form, there exists an effect that productivity at the time of polarizing plate processing improves remarkably.

  The retardation film according to claim 2 of the present invention is characterized in that, in the retardation film according to claim 1, the haze of the cellulose ester film is 0.1 to 1.4%. The retardation film of the present invention has an effect that it has a slow axis in the width direction, has a small haze, and is excellent in transparency.

  The retardation film according to claim 3 of the present invention is the retardation film according to claim 1 or 2, wherein the resin constituting the cellulose ester film is cellulose acetate propionate. Thus, according to the retardation film of the present invention, it is possible to obtain good formability by the melt casting film forming method and to easily obtain a desired retardation value.

  The retardation film according to claim 4 of the present invention is the retardation film according to claim 1 or 2, wherein the resin constituting the cellulose ester film is an aliphatic polyester graft side chain having lactic acid as a main repeating unit. According to the retardation film of the present invention, good formability can be obtained by the melt casting film forming method, and a desired retardation value can be easily obtained. There is an effect that can be done.

  The polarizing plate according to claim 5 of the present invention is, as described above, a polarizing plate comprising a polarizing film and two polarizing plate protective films disposed on both sides thereof, and two polarizing plate protections. At least any one of the films is constituted by the retardation film according to any one of claims 1 to 4, and the slow axis of the retardation film and the transmission axis of the polarizing film are substantially the same. The polarizing plates of the present invention are excellent in viewing angle characteristics, so that the display contrast of a liquid crystal display device using the polarizing plates is increased. There is an effect that can be.

  Next, embodiments of the present invention will be described, but the present invention is not limited thereto.

  In the present invention, the cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with an acyl group or the like. Examples thereof include cellulose acylates such as cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain (graft polymer side chain). . Of these, cellulose acetate propionate and cellulose acetate having an aliphatic polyester graft side chain are preferred. Other substituents may be included as long as the effects of the present invention are not impaired.

  As an example of cellulose acetate propionate, the substitution degree of acyl group is preferably 2.0 or more and 3.0 or less, and the substitution degree of acetyl group is preferably 1.4 or more and 2.4 or less. Further, the substitution degree of the acyl group is preferably 2.5 or more and 2.8 or less, and the substitution degree of the acetyl group is preferably 1.5 or more and 2.0 or less. By setting the degree of substitution within this range, good moldability by the melt casting film forming method can be obtained, and desired retardation (Ro, Rt) can be easily obtained. If the substitution degree of the acetyl group is lower than this range, the heat resistance as a retardation film may be inferior, especially the dimensional stability under wet heat, and if the substitution degree is too large, the necessary retardation characteristics may not be exhibited. There is.

  When a propionyl group is introduced as a substituent, the plasticity of the cellulose ester is improved and the moldability is improved.

  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.

In the present invention, the cellulose ester uses an organic acid such as acetic acid or an organic solvent such as methylene chloride when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride). The reaction is carried out using a protic catalyst such as sulfuric acid. When the acylating agent is acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized by the method described in JP-A-10-45804.

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

  Examples of the cellulose acetate having an aliphatic polyester graft side chain include cellulose acetate having an aliphatic polyester graft side chain containing lactic acid as a main repeating unit. The degree of acetyl substitution of cellulose acetate having an aliphatic polyester graft side chain mainly composed of lactic acid is preferably 2.5 to 3.0 per glucose unit. A thermoplastic cellulose acetate having an aliphatic polyester graft side chain having an acetyl substitution degree within this range has a remarkable plasticizing effect, and the brittleness of the resulting polymer does not become a problem. When the degree of acetyl substitution is less than 2.5, hydrogen bonding is caused by residual hydroxyl groups in cellulose acetate, so that even if an aliphatic polyester is grafted on the side chain, the plasticizing effect is small and the moldability may be poor. The degree of acetyl substitution is preferably 2.7 to 3.0, and most preferably 2.7 to 2.9. Polylactic acid containing lactic acid as a main repeating unit has a feature that thermal stability is particularly high among aliphatic polyesters.

  In the present invention, the molecular weight of the aliphatic polyester graft side chain is preferably 1000 to 10,000. When the molecular weight is in the range of 1000 to 10,000, good moldability can be obtained. More preferably, it is 2000-9000, Most preferably, it is 3000-8000.

  In the present invention, in order to obtain cellulose acetate having an aliphatic polyester graft side chain, it can be synthesized by a known method such as a method of performing ring-opening graft polymerization onto cellulose acetate using lactide as a monomer. When performing the ring-opening graft reaction, a known ring-opening polymerization catalyst can be used. Examples thereof include metals such as tin, zinc, titanium, bismuth, zirconium, germanium, antimony, sodium, potassium, and aluminum, and derivatives thereof. Particularly, the derivatives are preferably metal organic compounds, carbonates, oxides, and halides. Specific examples include tin octoate, tin chloride, zinc chloride, alkoxy titanium, germanium oxide, zirconium oxide, antimony trioxide, and alkyl aluminum.

  In the present invention, the number average molecular weight of the cellulose ester is preferably in the range of 60000 to 300000, since the mechanical strength of the resulting film is strong. Furthermore, 70000-200000 are preferable.

  In the present invention, various additives can be added to the cellulose ester.

  In the present invention, it is preferable to add a so-called plasticizer in order to improve dimensional stability under wet heat. It has not been known so far that a plasticizer has an effect of improving dimensional stability under wet heat. As the plasticizer, conventionally known plasticizers for cellulose esters can be preferably used. In particular, those having excellent compatibility are preferred, and for example, phosphate esters and carboxylic acid esters are preferred. 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. Mention may be made of tributyl. 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, such as 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. A plasticizer having a large molecular weight is preferable because it can suppress volatilization during extrusion. Examples of these include aliphatic polyesters composed of glycol and dibasic acids such as polyethylene adipate, polybutylene adipate, polyethylene succinate and polybutylene succinate, and fats composed of oxycarboxylic acids such as polylactic acid and polyglycolic acid. Aliphatic polyesters composed of lactones such as aromatic polyesters, polycaprolactone, polypropiolactone and polyvalerolactone, and vinyl polymers such as polyvinylpyrrolidone. These plasticizers can be used alone or in combination.

  It is preferable to contain 1-30 weight% of content of the plasticizer mentioned above with respect to a cellulose ester. By containing the plasticizer in this range, the dimensional stability of the cellulose ester film under wet heat can be improved.

  Examples of ultraviolet absorbers that can be used in the present invention include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. A benzotriazole-based compound with little coloring is preferable. Further, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are preferably used. As an ultraviolet absorber, from the viewpoint of preventing the deterioration of polarizers and liquid crystals, it has an excellent ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, it has little absorption of visible light having a wavelength of 400 nm or more. Is preferred. Specific examples of useful UV absorbers in the present invention include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butyl). Phenyl) benzotriazole, 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydroxy 3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl -3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5 A mixture of-(5-chloro-2H-benzotriazol-2-yl) phenyl] propionate can be mentioned, but is not limited thereto. As commercially available products, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Specific examples of benzophenone compounds include 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy- 5-benzoylphenylmethane) and the like, but is not limited thereto.

  The blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by weight, more preferably 0.1 to 5% by weight, based on the cellulose ester. If the amount used is too small, the ultraviolet absorption effect may be insufficient, and if it is too large, the transparency of the film may deteriorate. The ultraviolet absorber is preferably one having high heat stability.

  When the substitution degree of the acetyl group of the cellulose ester is low, the heat resistance may be lowered. In this case, it is effective to add an antioxidant.

  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.

  In the present invention, it is preferable to add fine particles in order to impart slipperiness of the film. The fine particles used in the present invention may be either an inorganic compound or an organic compound as long as it has heat resistance during melting. For example, as the inorganic compound, a compound containing silicon, silicon dioxide, aluminum oxide, zirconium oxide, calcium carbonate, Talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate and the like are preferred, and silicon-containing inorganic compounds and zirconium oxide are more preferred. Among them, silicon dioxide is particularly preferably used because the turbidity of the cellulose ester laminated film can be reduced. As specific examples of silicon dioxide, commercially available products having trade names such as Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600 (above Nippon Aerosil Co., Ltd.) can be preferably used. .

  In the present invention, as the fine particles of zirconium oxide, for example, those commercially available under trade names such as Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) can be used.

  As the organic compound, for example, polymers such as silicone resin, fluorine resin and acrylic resin are preferable, and among them, silicone resin is preferably used.

  Among the above-described silicone resins, those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120 and 240 (above, manufactured by Toshiba Silicone Co., Ltd.) ) Etc. can be used.

  In the present invention, the cellulose ester film is produced by first forming a cellulose ester into a sheet and stretching and orienting the sheet.

  In the present invention, the sheet is formed by a melt forming method. Examples of the melt molding method include a method using a T die, a melt extrusion method such as an inflation method, a calendar method, a heat press method, and an injection molding method. Among them, a melt extrusion method using a T die that has a small thickness unevenness, can be easily processed to a thickness of about 50 to 500 μm, and can reduce the absolute value of retardation and its variation is preferable.

  The conditions of the melt molding method can be molded in the same manner as the conditions used for other thermoplastic resins. For example, dry cellulose ester is melted at an extrusion temperature of about 200 to 300 ° C. using a single-screw or twin-screw extruder, filtered through a leaf disk type filter, etc. to remove foreign matters, and then sheeted from a T die. And solidified on a cooling drum. When introducing from the supply hopper to the extruder, it is preferable to prevent oxidative decomposition or the like under reduced pressure or in an inert gas atmosphere. The temperature of the cooling drum is preferably below the glass transition temperature of the cellulose ester. In order to bring the resin into close contact with the cooling drum, it is preferable to use a method in which the resin is brought into contact by electrostatic application, a method in which the resin is brought into contact by wind pressure, a method in which the full width or the end is brought into contact with nip, a method in which the resin is brought into contact with reduced pressure. Further, in order to reduce surface defects such as die lines, it is preferable that the piping from the extruder to the die has a structure in which the staying portion is minimized. It is preferable to use a die that has as few scratches as possible inside the lip. Since the volatile component may be deposited from the resin around the die and cause a die line, it is preferable to suck the atmosphere containing the volatile component. Moreover, since it may also precipitate in apparatuses, such as electrostatic application, it is preferable to apply alternating current or to prevent precipitation with other heating means.

  Additives such as plasticizers may be mixed with the resin in advance, or may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer.

  There is no restriction | limiting in particular in the thickness of a sheet | seat, What is necessary is just to set so that it may become desired thickness after extending | stretching, and 50-500 micrometers is preferable. Of course, the smaller the thickness unevenness, the better. The entire surface is within ± 5%, preferably within ± 3%, and more preferably within ± 1%.

  Unlike the cellulose ester resin sheet formed by the solution casting film forming method, the cellulose ester resin sheet formed by such a melt casting film forming method has a feature that the thickness direction retardation (Rt) is small, It has been found that by stretching such a cellulose ester resin sheet, in-plane direction retardation (Ro) can be easily developed, and the present invention has been achieved. That is, according to the present invention, since it is not necessary to increase the draw ratio, a cellulose ester film having no transparency and excellent transparency can be obtained.

  Next, the obtained sheet is stretched in a uniaxial direction. The molecules are oriented by stretching. The stretching method is not particularly limited, but a known pin tenter or clip type tenter can be preferably used. The stretching direction can be the longitudinal direction, the width direction, or any direction (oblique direction). However, according to the present invention, the stretching direction can be set to the width direction so that the polarizing film can be laminated in a roll form. Therefore, it is preferable. By stretching in the width direction, the slow axis of the cellulose ester film becomes the width direction. On the other hand, the transmission axis of the polarizing film is also usually in the width direction. A good viewing angle can be obtained by incorporating in a liquid crystal display device a polarizing plate that is laminated so that the transmission axis of the polarizing film and the slow axis of the cellulose ester film are parallel to each other.

  As the stretching conditions, the temperature and magnification can be selected so that desired retardation characteristics can be obtained. Usually, the draw ratio is 1.1 to 2.0 times, preferably 1.2 to 1.5 times, and the drawing temperature is usually Tg to Tg + 50 ° C., preferably Tg to Tg + 40 ° C. of the resin constituting the sheet. In the temperature range. If the draw ratio is too small, the desired retardation may not be obtained, and if it is too large, it may break. If the stretching temperature is too low, it will break, and if it is too high, the desired retardation may not be obtained.

  When the retardation of the cellulose ester film produced by the above method is corrected to a desired value, the film may be stretched or shrunk in the longitudinal direction or the width direction. In order to shrink in the longitudinal direction, for example, there is a method in which the film is contracted by temporarily stretching out the width stretching and relaxing in the longitudinal direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine. The latter method can be performed by using a general simultaneous biaxial stretching machine and by using a pantograph method or a linear drive method to drive the clip portion in a smooth and gradually narrowing interval between adjacent clips in the longitudinal direction. it can.

  In the present invention, the film thickness range of the cellulose ester film is 20 to 100 μm, and the range of 30 to 80 μm is preferable for the recent thin tendency, and the range of 30 to 60 μm is particularly preferable. The film thickness can be adjusted by controlling the extrusion flow rate, the slit gap of the die base, the speed of the cooling drum, etc. so as to obtain a desired thickness. 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.

  Before winding, the end may be slit and cut to the width to be the product, and knurling (embossing) may be applied to both ends to prevent scratching and scratching during winding. In the knurling method, a metal ring having an uneven pattern on the side surface can be processed by heating and / or pressing. In addition, since the film has deform | transformed and cannot use as a product normally, the holding part of the clip of both ends of a film is cut out, and is reused as a raw material.

  The cellulose ester film stretched in the width direction obtained as described above has a fixed retardation with molecules oriented by stretching. In this invention, the in-plane retardation (Ro) of the cellulose-ester film which comprises a phase difference film is 20-100 nm, and thickness direction retardation (Rt) is 90-200 nm. The ratio Rt / Ro between Rt and Ro is preferably 0.5 to 2.5, particularly preferably 1.0 to 2.0.

In addition, when the refractive index nx in the slow axis direction of the film, the refractive index ny in the fast axis direction, the refractive index nz in the thickness direction, and the film thickness of the film are d (nm),
Ro = (nx−ny) × d
Rt = {(nx + ny) / 2−nz} × d
Represented as:

  The variation in retardation is preferably as small as possible, and is usually within ± 10 nm, preferably ± 5 nm or less, and more preferably ± 2 nm or less.

  The variation and thickness unevenness in the retardation plane can be reduced by using such a small pre-stretched sheet and by applying a uniform stress to the sheet during stretching. For that purpose, it is desirable to stretch in a controlled temperature environment under a uniform temperature distribution, preferably within ± 5 ° C., more preferably within ± 2 ° C., particularly preferably within ± 0.5 ° C.

  The uniformity in the slow axis direction is also important, and the angle is preferably −5 to + 5 ° with respect to the width direction of the film, more preferably in the range of −1 to + 1 °, particularly −0. It is preferable that it is in the range of 0.5 to + 0.5 °.

  In the present invention, since the retardation film has a slow axis in the width direction, it can be bonded between the polarizing film and long rolls without cutting, and the productivity of the polarizing plate is dramatically increased. improves.

  The haze of the cellulose ester film constituting the retardation film of the present invention is 0.1 to 1.4%, preferably 0.3 to 1.0%.

  Here, if the haze of the cellulose ester film constituting the retardation film is less than 0.1%, the handleability of the film is inferior, and when the film is processed into a polarizing plate, the film is wrinkled or easily scratched. This is not preferable. Further, if the haze exceeds 1.4%, the transparency of the film is inferior. Therefore, when a polarizing plate using this film is incorporated in a liquid crystal display device, the sharpness of the image may be lowered, which is not preferable. .

  The retardation film according to the present invention can be formed into an elliptically polarizing plate by being bonded to at least one surface of a polarizing film.

  The polarizing film is a film that has been conventionally stretched by treating with a dichroic dye such as iodine a stretchable film such as a polyvinyl alcohol film. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose triacetate film having no anisotropy as a protective film to both sides thereof.

  In the present invention, the polarizing plate may be produced by laminating the retardation film according to the present invention to the polarizing plate, or the retardation film according to the present invention also serves as a protective film, and is directly laminated with the polarizing film. It may be produced. The method of bonding is not particularly limited, but can be performed with an adhesive composed of an aqueous solution of a water-soluble polymer. The water-soluble polymer adhesive is preferably a completely saponified polyvinyl alcohol aqueous solution. Furthermore, as described above, a long polarizing plate can be obtained by laminating a long polarizing film stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film of the present invention. . A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides thereof via a pressure sensitive adhesive layer (for example, an acrylic pressure sensitive adhesive layer). Or the like can be easily attached).

  The polarizing plate according to the present invention thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal molecule in which liquid crystal molecules are substantially vertically aligned when no voltage is applied, or a TN mode liquid crystal cell in which liquid crystal molecules are substantially horizontal and twisted when no voltage is applied. Is preferred.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

Example 1
Cellulose acetate propionate 100 parts by weight (Temperature dried at 60 ° C. for 24 hours,
Acetyl group substitution degree 1.95, propionyl group substitution degree 0.7,
And a number average molecular weight of 75,000)
Triphenyl phosphate 10 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 109 0.5 part by weight Tinuvin 171 0.5 part by weight Tinuvin 326 0.3 part by weight Antioxidant 0.01 part by weight 2,6-di -T-butyl-p-cresol and pentaerythrityl-tetrakis [3- (3,5-di-
t-butyl-4-hydroxyphenyl) propionate]
The above materials were mixed, and the mixture was melt-mixed at 250 ° C. using a twin-screw extruder and pelletized. Using this pellet, a cellulose acetate propionate resin sheet was obtained from a T-die by melting and extruding into a sheet on a 30 ° C. cooling drum at a melting temperature of 250 ° C. and cooling and solidifying.

  The obtained resin sheet was stretched 1.5 times in the width direction at 160 ° C. in the width direction using a tenter. Subsequently, it was cooled to 30 ° C. while being held by the tenter clip, and then released from the clip to obtain a cellulose acetate propionate film as a retardation film having a film thickness of 100 μm.

  The obtained retardation film was measured for in-plane retardation (Ro), thickness direction retardation (Rt) and haze, and the obtained results are shown in Table 1 below.

(Measurement method of Ro and Rt)
Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), a three-dimensional refractive index measurement is performed at a wavelength of 590 nm under an atmosphere of a temperature of 23 ° C. and a humidity of 55% RH. A refractive index nx, a refractive index ny in the fast axis direction, and a refractive index nz in the thickness direction are obtained. The retardation in the thickness direction (Rt) and the retardation in the in-plane direction (Ro) are calculated from the above-described retardation formula.

(Evaluation of transparency)
Transparency was evaluated by measuring the haze of the film according to JIS-K6714. From the practicality of the optical film, it is preferably 1.5% or less.

Example 2
In a nitrogen atmosphere, 100 parts by weight of cellulose acetate (acetyl substitution degree: 2.8, number average molecular weight 120000) 100 parts by weight and 400 parts by weight of L-lactide (manufactured by Pulac) were vacuum-dried at 60 ° C. for 24 hours. The solution was stirred at a temperature of 140 ° C. for 60 minutes for dissolution. Thereafter, 0.5 part by weight of tin octoate was added as a ring-opening polymerization catalyst and reacted for 60 minutes. Then it was cooled and chloroform was added.

  Next, a chloroform solution of the obtained reaction product was added to a large excess of methanol to precipitate the reaction product, and after suction filtration, dried, a flaky reaction product was obtained.

  100 parts by weight of the obtained flaky reaction product resin and 0.01 parts by weight of triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] as an antioxidant The mixture of parts was pelletized in the same manner as in Example 1 to obtain a resin sheet, and the resin sheet was further stretched to obtain a retardation film having a thickness of 100 μm.

  About the obtained retardation film, in-plane retardation (Ro), thickness direction retardation (Rt), and haze were measured similarly to the case of the said Example 1, and the obtained result was match | combined with following Table 1 Indicated.

Comparative Example 1
For comparison, a cellulose acetate propionate film is produced by a conventional solution casting film forming method. The following materials were used.

Cellulose acetate propionate 100 parts by weight (acetyl group substitution degree 1.95, propionyl group substitution degree 0.7,
And a number average molecular weight of 75,000)
Triphenyl phosphate 10 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 109 0.5 part by weight Tinuvin 171 0.5 part by weight Tinuvin 326 0.3 part by weight Methyl acetate 300 parts by weight Ethanol 90 parts by weight Put into a pressure sealed container and completely dissolve the cellulose acetate propionate while stirring to obtain a cellulose acetate propionate solution (dope). This dope is a stainless steel rotating endless solution casting apparatus Cast on a belt (support), contact with warm water from the back of the support, and dry on the support controlled to 55 ° C. for 1 minute, and then add cold water of 15 ° C. to the back of the support. After making it contact and hold | maintain for 10 second, the film was peeled from the support body. Next, the film was stretched 1.5 times at 120 ° C. in the width direction using a tenter. The amount of residual solvent in the film at the time of stretching was 70% by weight. Subsequently, it was cooled to 30 ° C. while being held by the tenter clip, and then released from the clip. Furthermore, it dried at 120 degreeC for 30 minute (s), and obtained the cellulose acetate propionate film as a comparative phase difference film which has a film thickness of 100 micrometers.

For the obtained comparative retardation film, in-plane retardation (Ro), thickness direction retardation (Rt), and haze were measured in the same manner as in Example 1, and the obtained results are shown in Table 1 below. It was shown together.

  As is apparent from the results in Table 1 above, according to the cellulose acetate propionate films of Examples 1 and 2 of the present invention, the film has a slow axis in the width direction, and the haze of the film is 0 respectively. 5% and 0.8% are excellent in transparency, and it can be seen that the display contrast of the liquid crystal display device can be increased by using the polarizing plate using the retardation film.

  On the other hand, according to the cellulose acetate propionate film of Comparative Example 1, the haze of the film was as high as 3.5%, the film was clouded and the transparency was deteriorated.

Example 3
Next, a long polyvinyl alcohol film having a thickness of 120 μm is continuously immersed in 100 parts by weight of an aqueous solution containing 1 part by weight of iodine and 4 parts by weight of boric acid, and longitudinally stretched four times at 50 ° C. I made a polarizing film. On the other hand, a 80 μm long Konicatak (manufactured by Konica, cellulose triacetate film) as a protective film was continuously immersed in an aqueous solution of sodium hydroxide having a concentration of 2 mol / l at 60 ° C. for 2 minutes and washed with water at 100 ° C. The cellulose triacetate was dried for 10 minutes and subjected to alkali saponification treatment. An adhesive was continuously applied to one side of the long polarizing film with a 5% aqueous solution of a fully saponified polyvinyl alcohol, and the long cellulose triacetate was bonded to the surface to prepare a long polarizing film with a protective film. .

  On the other hand, a long cellulose acetate propionate film as a retardation film obtained in Example 1 of the present invention was saponified in the same manner as described above. Further, the above-mentioned saponified long cellulose acetate propionate film is continuously pasted on the surface of the long polarizing film with the protective film without using the protective film using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive. In addition, a long polarizing plate was produced. In addition, it bonded together so that the angle which the width direction of retardation film and the transmission axis (width direction) of a polarizing film make may become parallel. Viewing angle characteristics were evaluated by the following method using the obtained polarizing plate of the present invention.

(Viewing angle characteristics)
The vertical alignment type liquid crystal cell was visually evaluated as follows. That is, the polarizing plate of the liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell is peeled off, and instead, the polarizing plate produced in Example 3 is transmitted through the polarizing plate on the viewer side. Using a liquid crystal display device bonded with an adhesive so that the axis is in the vertical direction and the transmission axis of the polarizing plate on the backlight side is in the horizontal direction, the image is viewed from a direction inclined by 80 degrees with respect to the normal direction of the screen. Observed.

  As a result, a clear image was observed, and the polarizing plate of the present invention had good viewing angle characteristics.

Claims (5)

It consists of a cellulose ester film obtained by stretching and orienting a cellulose ester resin sheet formed by the melt casting film forming method in the width direction, and has a thickness of 20 to 100 μm and an in-plane retardation (Ro) defined by the following formula (a) of 20 A retardation film having a thickness direction retardation (Rt) defined by ˜100 nm and the following formula (b): 90˜200 nm.
Ro = (nx−ny) × d (a)
Rt = {(nx + ny) / 2−nz} × d (b)
(Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is the film thickness) And the unit is nm.)   The retardation film according to claim 1, wherein the haze of the cellulose ester film is 0.1 to 1.4%.   The retardation film according to claim 1 or 2, wherein the resin constituting the cellulose ester film is cellulose acetate propionate.   3. The retardation film according to claim 1, wherein the resin constituting the cellulose ester film is a cellulose acetate having an aliphatic polyester graft side chain containing lactic acid as a main repeating unit.   It is a polarizing plate which consists of a polarizing film and two polarizing plate protective films arrange | positioned at the both sides, Comprising: At least any one of two polarizing plate protective films is any one of Claims 1-4 A polarizing plate comprising the retardation film according to claim 1 and laminated so that a slow axis of the retardation film and a transmission axis of the polarizing film are substantially parallel to each other.