JP2007065065A - Optical film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film which can be utilized for a protection film for a polarizing plate, a phase difference film, a visual field angle enlarging film or the like used in a liquid crystal display (LCD) or the like, which is manufactured by a molten flow stretching method using no solvent in producing a film and which has little size change even under various conditions suitable for the phase difference film and has no occurrence of density unevenness called frame trouble, and further to provide its manufacturing method. <P>SOLUTION: The optical film is constituted by laminating at least two resin layers containing a cellulose ester resin and at least one resin layer contains inorganic micro-particles (a matting agent) of ≤1 wt.% water content. Two or more resin layers are extruded together from a flow stretching die and are solidified by cooling to form a laminated web and the laminated web is stretched and wound up. At least one resin layer among two or more resin layers containing the cellulose ester resin contains inorganic micro-particles of ≤1 wt.% water content. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used in various functional films such as a protective film for polarizing plates used for liquid crystal display devices (LCD), retardation films, viewing angle widening films, antireflection films used in plasma displays, and organic EL displays. The present invention relates to an optical film that can be used for various functional films, and a method for producing the same.

  A liquid crystal display device is widely used as a monitor because it saves space and energy compared to a conventional CRT display device. Furthermore, it is also spreading for TV. In such a liquid crystal display device, various optical films such as a polarizing film and a retardation film are used.

  By the way, the polarizing film of the polarizing plate used for a liquid crystal display device is a polarizing plate protective film generally composed of a cellulose ester resin on one or both sides of a polarizer made of a stretched polyvinyl alcohol film. Laminated for protection. In addition, the retardation film is used for the purpose of widening the viewing angle and improving the contrast. The retardation of the retardation film can be extended by stretching a film of a polycarbonate, a polymer having an alicyclic structure, a cellulose ester resin, or the like. And a liquid crystal layer coated on a transparent substrate. Sometimes called an optical compensation film.

  These optical films are required to have no optical defect and uniform retardation. In particular, the required quality is becoming stricter as monitors and TVs are becoming larger and higher definition.

  Optical film production methods are roughly classified into a solution casting film forming method and a melt casting film forming method. The former is a method in which a polymer is dissolved in a solvent, the solution is cast on a support, the solvent is evaporated, and further, if necessary, stretched to form a film. Although it has been widely adopted from the viewpoint of excellent film thickness uniformity, etc., since it is a film forming method using a halogen-based solvent, the cost required for solvent recovery has been a very heavy burden. The latter is a method in which a polymer is heated and melted, cast onto a support, cooled and solidified, and further stretched as necessary to form a film, and since the solvent does not need to be dried, the equipment can be made relatively compact. However, there is a problem that the uniformity of the film thickness is inferior and the retardation is not uniform.

Here, as a method of manufacturing an optical film using a melt casting film forming method that does not use a solvent, for example, the following Patent Document 1 proposes.
Japanese Patent Application Laid-Open No. 2000-352620 discloses a cellulose ester film formed by melt casting. The cellulose ester film is stretched in one direction and a direction orthogonal thereto, and the cellulose ester film is It is disclosed to contain a non-volatile plasticizer and to contain an ultraviolet absorber. And according to the cellulose-ester film of patent document 1, providing the optical film which was optically and physically excellent, especially excellent in dimensional stability, without using a solvent is described.

  However, the cellulose ester film described in Patent Document 1 has a problem that unevenness in density called a frame failure may occur because the dimensional change of the film under various conditions is not sufficiently small.

  The purpose of the present invention is for a phase difference produced by a melt casting method that does not use a solvent at the time of film formation, and has little dimensional change even under various conditions suitable for a phase difference film, and does not cause density unevenness called a frame failure. An object of the present invention is to provide an optical film useful as a film and a method for producing the same.

  In order to achieve the above object, in the invention of the optical film according to claim 1, two or more resin layers containing a cellulose ester-based resin are laminated, and at least one of the resin layers has a water content of 1 It is characterized by containing inorganic fine particles (mat agent) in an amount of not more than% by weight.

  The invention according to claim 2 is the optical film according to claim 1, wherein the cellulose ester-based resin is cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, It is characterized by being at least one compound selected from the group consisting of cellulose acetate phthalate and cellulose phthalate.

  The invention according to claim 3 is a non-stretched laminated web in which two or more resin layers containing a cellulose ester resin are coextruded from a casting die by a melt casting film forming method, and cooled and solidified to form an unstretched laminated web. An optical film manufacturing method for gripping both ends of a web and stretching in the width direction and winding up the obtained stretched laminated film, wherein at least one resin of two or more resin layers containing a cellulose ester-based resin The layer is characterized by containing inorganic fine particles (mat agent) having a water content of 1% by weight or less.

  Invention of Claim 4 is a manufacturing method of the optical film of said Claim 1, Comprising: Cellulose ester type resin is cellulose acetate, a cellulose propionate, a cellulose butyrate, a cellulose acetate propionate, a cellulose It is characterized by being at least one compound selected from the group consisting of acetate butyrate, cellulose acetate phthalate, and cellulose phthalate.

  The invention of the optical film according to claim 1 is characterized in that two or more resin layers containing a cellulose ester-based resin are laminated, and at least one of the resin layers has inorganic fine particles (mat agent) having a water content of 1% by weight or less. ), And the optical film of the present invention is suitable for a retardation film because there is little dimensional change even under various conditions, there is no density unevenness. In the liquid crystal display device using the retardation film made of the optical film of the present invention, there is an effect that it is possible to always obtain a stable display quality regardless of the conditions under the use environment.

  The invention according to claim 2 is the optical film according to claim 1, wherein the cellulose ester-based resin is cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, Cellulose acetate phthalate and at least one compound selected from the group consisting of cellulose phthalate. According to the present invention, these cellulose ester resins have a small photoelastic coefficient and excellent optical properties. The effect is that it is possible to obtain a cellulose ester resin film suitable for a retardation film with little dimensional change even under various conditions in the state of the film after film formation.

  The invention according to claim 3 is a non-stretched laminated web in which two or more resin layers containing a cellulose ester resin are coextruded from a casting die by a melt casting film forming method, and cooled and solidified to form an unstretched laminated web. An optical film manufacturing method for gripping both ends of a web and stretching in the width direction and winding up the obtained stretched laminated film, wherein at least one resin of two or more resin layers containing a cellulose ester-based resin The layer contains inorganic fine particles (mat agent) having a water content of 1% by weight or less, and according to the present invention, a retardation film produced by a melt casting film forming method that does not use a solvent during film formation. A cellulose ester-based resin film suitable for the above can be obtained. Furthermore, the obtained cellulose ester-based resin film can function as a film for retardation with little dimensional change even under various conditions in the state of the film after film formation, and a liquid crystal display using this retardation film The apparatus has an effect that a stable display quality can always be obtained regardless of the conditions under the usage environment.

  Invention of Claim 4 is a manufacturing method of the optical film of said Claim 3, Comprising: Cellulose ester type resin is cellulose acetate, a cellulose propionate, a cellulose butyrate, a cellulose acetate propionate, a cellulose It is at least one compound selected from the group consisting of acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. According to the present invention, these cellulose ester resins have a small photoelastic coefficient and are excellent. In addition, the cellulose ester-based resin film suitable for the retardation film having little dimensional change can be obtained even under various conditions in the state of the film after film formation.

  Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  In the optical film according to the present invention, two or more resin layers containing a cellulose ester-based resin are laminated, and at least one of the resin layers contains inorganic fine particles (mat agent) having a water content of 1% by weight or less. It is what.

  A cellulose ester resin is used as a raw material for the optical film of the present invention. In addition, the cellulose ester-type resin has the characteristics that it is excellent in adhesiveness with the stretched polyvinyl alcohol which is a polarizer.

  As the cellulose ester resin, at least one compound selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate Is preferred. The degree of substitution of the acetyl group of the cellulose ester resin is preferably at least 1.5 or more because the resulting film has excellent dimensional stability.

  The method for measuring the substitution degree of the acyl group of the cellulose ester resin can be carried out in accordance with ASTM D-817-91. The molecular weight of the cellulose ester resin is preferably 50,000 to 300,000, particularly 60,000 to 200,000 as the number average molecular weight because the mechanical strength of the resulting film can be increased.

  In the present invention, the cellulose ester resin, which is the main material of the optical film, includes a plasticizer, an ultraviolet absorber, an antioxidant, fine particles (matte agent), an antistatic agent, a flame retardant, a dye and an oil agent for various purposes. Etc. can be contained.

  Examples of the plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, trinaphthyl phosphate, trixyl phosphate, arylene bis (diaryl phosphate) Phosphate ester plasticizers such as esters, tricresyl phosphate, phthalate plasticizers such as diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate and di-2-ethylhexyl phthalate, triacetin, tributyrin, butyl Phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycol Glycolate ester plasticizers such as butyl phthalyl butyl glycolate, citric acid plasticizers such as tributyl acetyl citrate, dipropylene glycol benzoate, tripropylene glycol dibenzoate, 1,3-dibutylene glycol dibenzoate, Examples include polyhydric alcohol ester plasticizers such as tetraethylene glycol dibenzoate, trimethylolpropane triacetate, and trimethylolpropane tribenzoate, and trimellitic acid tris (2-ethylhexyl). If necessary, two or more kinds of plasticizers may be used in combination. These addition amounts are preferably 1 to 30% by weight with respect to the cellulose ester resin in view of the effect of the plasticizer and bleed out.

  Moreover, since blending polyester ether, polyester-urethane, polyester, etc. can improve plasticity, it can be preferably used.

  Polyester ethers include aromatic dicarboxylic acids or alicyclic dicarboxylic acids having 8 to 12 carbon atoms (eg terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid), 2 to 10 carbon atoms. Aliphatic glycols or alicyclic glycols (eg, ethylene diol, propylene diol, 1,4-butane diol, neopentyl glycol, 1,6-hexane diol, 1,4-cyclohexane dimethanol and 1,5-pentane diol ), Polyether glycols having 2 to 4 carbon atoms between the ether units (for example, polytetramethylene ether glycol, in particular 1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexanedimethanol and polytetramethylene ether). Copolyester ether) to component a glycol. The blending amount of the polyester ether is preferably 5 to 30% by weight with respect to the main cellulose ester resin. By setting the blending amount within this range, a film exhibiting good plasticity can be obtained.

Examples of the polyester-urethane include polyester-urethane obtained by a reaction between polyester and diisocyanate. It has a repeating unit represented by the following general formula (1).

  In general formula (1), l represents 2, 3 or 4, m represents 2, 3 or 4, and n represents 1 to 100. R represents any of the structural units represented by structural unit formulas (2) to (7). In the structural unit formula (2), p represents 2 to 8.

  As the polyester constituting the polyester-urethane, the glycol component is ethylene glycol, 1,3-propanediol, or 1,4-butanediol, and the dibasic acid component is succinic acid, glutaric acid, or adipic acid. The polyester having a hydroxyl group at both ends and comprising a polymerization degree n of 1 to 100. A polyester having a molecular weight of 1,000 to 4,500 is particularly desirable.

  Examples of the diisocyanate component constituting the polyester-urethane include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, and the like, p-phenylene diisocyanate, and triethylene diisocyanate. Examples thereof include aromatic diisocyanates such as range isocyanate, p, p'-diphenylmethane diisocyanate, and 1,5-naphthylene diisocyanate, and m-xylylene diisocyanate. Among these, tolylene diisocyanate, m-xylylene diisocyanate, and tetramethylene diisocyanate are preferable because they are excellent in compatibility with cellulose ester resins.

  The molecular weight of the polyester-urethane is preferably 2,000 to 50,000, more preferably 5,000 to 15,000. The synthesis of the polyester-urethane can be easily obtained by a conventional synthesis method in which the above polyester and diisocyanate are mixed and heated with stirring. In addition, the raw material polyester can be obtained by a conventional method, a corresponding dibasic acid, or a hot melt condensation method using a polyesterification reaction or transesterification reaction between these alkyl esters and glycols, or an acid chloride of these acids. It can be easily synthesized by appropriately adjusting the terminal group to be a hydroxyl group by any method of interfacial condensation with glycols.

  As for the compounding quantity of polyester-urethane, 5 to 30 weight% is preferable with respect to main resin. When the blending amount is within this range, a film exhibiting good plasticity can be obtained.

  The polyester is a polyester composed of polyethylene glycol and an aliphatic dibasic acid, and the average molecular weight is preferably 700 to 10,000.

Polyethylene glycol has the general formula HO— (CH ₂ CH ₂ —O) _n —H
(Where n is an integer). n is preferably 4 or less.

In addition, the aliphatic dibasic acid has the general formula HOOC-R-COOH
(Wherein R is an aliphatic divalent hydrocarbon group) represented by succinic acid, malonic acid, succinic acid, adipic acid, and the like, preferably having 9 or less carbon atoms.

  Polyesters can be synthesized by a conventional method using a polyesterification reaction between the dibasic acid or an alkyl ester thereof and a glycol, or a hot melt condensation method using a transesterification reaction, or an acid chloride of these acids and a glycol. It can be easily synthesized by any of the interfacial condensation methods.

  As for the compounding quantity of polyester, 5 to 30 weight% is preferable with respect to main resin. By setting the blending amount within this range, a film exhibiting good plasticity can be obtained.

  As the antioxidant, hindered phenol compounds are suitable. Specific examples thereof include 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [ 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-butylanilino) -1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadec -3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxy Benzyl) benzene and tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and 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 order to obtain the effect, the amount of these compounds added is preferably 1 ppm to 1.0% by weight, particularly preferably 10 to 1000 ppm, based on the cellulose ester resin.

  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 also preferably used.

  As an ultraviolet absorber, from the viewpoint of preventing the deterioration of polarizers and liquid crystals, 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.

  Specific examples of useful UV absorbers in the present invention include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-). Butylphenyl) 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- A mixture of 5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate and the like can be mentioned, but 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 with respect to the cellulose ester resin. 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.

  In the present invention, inorganic fine particles (matting agent) are added in order to impart slipperiness of the film and to reduce dimensional change even under various conditions in the state of the film after film formation. As the inorganic fine particles used in the present invention, an inorganic compound having heat resistance during melting is used.

  Examples of inorganic compounds include silicon-containing compounds, silicon dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate and Calcium phosphate or the like is preferable, and an inorganic compound containing silicon or zirconium oxide is more preferable. Among these, silicon dioxide is particularly preferably used because haze can be kept small. 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, manufactured by Nippon Aerosil Co., Ltd.) are preferably used. it can.

  In the optical film according to the present invention, as described above, two or more resin layers containing a cellulose ester-based resin are laminated, and inorganic fine particles (mat agent) having a water content of 1% by weight or less are formed in at least one of the resin layers. ) Is included.

  Here, as a method for measuring the moisture content of the inorganic fine particles (mat agent), first, the mat agent is weighed with an electronic balance, and the weight at this time is defined as W1 (g). Next, this matting agent was placed in a hot air oven-type dryer maintained at 150 ° C., dried for 5 hours, then allowed to cool in a desiccator for 30 minutes, and weighed as W2 (g). The following formula is used.

Water content of matting agent (%) = {(W1−W2) / W1} × 100
In the optical film of the present invention, two or more resin layers containing a cellulose ester-based resin are laminated, and at least one of the resin layers contains inorganic fine particles (mat agent) having a water content of 1% by weight or less. Therefore, there is little dimensional change even under various conditions, there is no density unevenness, and it is suitable as a retardation film.

  Here, the density unevenness means uneven brightness when viewing the screen of the liquid crystal panel.

  Moreover, in the liquid crystal display device using the retardation film made of the optical film of the present invention, a stable display quality can always be obtained regardless of the conditions under the usage environment.

  The optical film according to the present invention is applicable not only to two resin layers containing a cellulose ester resin but also to a multilayer film having three or more layers.

  The method for producing an optical film according to the present invention is a method in which two or more resin layers containing a cellulose ester resin are coextruded from a casting die by a melt casting film forming method, and cooled and solidified to form an unstretched laminated web. A method for producing an optical film that grips both ends of a laminated web and stretches in the width direction and winds up the obtained stretched laminated film, wherein at least one of two or more resin layers containing a cellulose ester-based resin The resin layer contains inorganic fine particles (mat agent) having a water content of 1% by weight or less.

  FIG. 1 is a schematic flow sheet showing one embodiment of an apparatus for carrying out the method for producing an optical film of the present invention. In this embodiment, the case where two resin layers containing a cellulose ester resin are laminated is shown.

  Referring to the figure, first, a first layer material 11 of a cellulose ester resin film, for example, dried under hot air, vacuum or reduced pressure, is introduced from a hopper into a uniaxial or biaxial extruder 1, and an extrusion temperature is obtained. Melting is performed at about 200 to 300 ° C., and the matting agent 13 and the ultraviolet absorber are sequentially added and mixed in the course of melting. In addition, when introducing the material 11 for the first layer of the cellulose ester-based resin film from the supply hopper to the extruder 1, it is preferable to prevent oxidative decomposition and the like under vacuum, reduced pressure, or inert gas atmosphere. .

  On the other hand, without mixing the matting agent, the second layer material 12 which is the same as the first layer is introduced into the uniaxial or biaxial extruder 2 from the hopper, and the extrusion temperature is 200 to 300 ° C. Melt and mix to the extent. Similarly, when the material 12 for the second layer of the cellulose ester resin film is introduced from the supply hopper into the extruder 2, it is possible to prevent oxidative decomposition and the like under vacuum, reduced pressure, or inert gas atmosphere. preferable.

  Next, the flow rate ratio between the first layer and the second layer is adjusted to, for example, about 0.5 to 2: 4.5 to 6, preferably about 1: 5, and filtered with a leaf disk type filter or the like. Then, after removing the foreign matter, it is sent to the casting die 3.

  Lamination of the resin layer containing the cellulose ester resin by the casting die 3 is achieved by, for example, using a multi-manifold coextrusion die, simultaneously laminating two or more layers in the die, and extruding it on the cooling drum 4. The Alternatively, the two layers can be merged within the feed block and extruded with a single layer die.

  In the present invention, the first layer material 11 containing the matting agent of the cellulose ester resin film and the second layer material 12 not containing the matting agent are supplied to the multi-manifold coextrusion die 3, and the die 3 The melted film layer materials joined together are melt-extruded into a film at a melting temperature on a cooling drum 4 at a predetermined temperature, and cooled and solidified to obtain an unstretched resin web W.

  Here, the extrusion flow rate of the molten resin is preferably performed stably by introducing a gear pump or the like. Further, a stainless fiber sintered filter is preferably used as a filter used for removing foreign substances.

  In the present invention, additives such as a plasticizer and inorganic fine particles (mat agent) may be mixed with a resin in advance, or may be kneaded in the middle of the extruder 1. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer.

  The temperature of the cooling drum 4 is preferably in the range from the normal temperature of the cellulose ester resin to the glass transition temperature (Tg) or less. By setting it as this range, generation | occurrence | production of slight retardation nonuniformity by conveyance tension etc. can be suppressed. In order to bring the resin into close contact with the cooling drum 4, 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 attached in a nip, a method in which the resin is brought into contact with reduced pressure.

  Next, the cooled and solidified dope film (web) W peeled off from the cooling drum 4 by the peeling roll 5 is guided to a stretching machine 7 through a dancer roll (film tension adjusting roll) 6, where the web W is moved in the width direction. Stretch. By this stretching, the molecules in the web W are oriented. As a method of stretching the web W in the width direction, a known tenter or the like can be preferably used. In particular, it is preferable to set the stretching direction to the width direction because lamination with the polarizing film can be performed in a roll form. By stretching the web W in the width direction, the slow axis of the optical film made of the cellulose ester resin film becomes the width direction. On the other hand, the transmission axis of the polarizing film is also usually in the width direction. By incorporating a polarizing plate in which the transmission axis of the polarizing film and the slow axis of the optical film are parallel to each other into the liquid crystal display device, the display contrast of the liquid crystal display device can be increased and a good viewing angle can be obtained. Is obtained.

  As the stretching conditions in the stretching machine 7, the temperature and the 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 draw temperature is usually Tg to, where Tg is the glass transition temperature of the resin constituting the optical film. It is carried out in the temperature range of Tg + 50 ° C., preferably Tg to Tg + 40 ° C. If the draw ratio is too small, the desired retardation may not be obtained. Conversely, if it is too large, the film may be broken. If the stretching temperature is too low, the film may break, and if it is too high, the desired retardation may not be obtained.

  The stretching in the width direction of the film is preferably performed under a controlled uniform temperature distribution. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

  The film may be stretched or shrunk in the length direction or the width direction for the purpose of reducing the retardation of the cellulose ester resin film produced by the above method and reducing the dimensional change rate. In order to shrink in the length direction, for example, a method of contracting the film by temporarily clipping out the width stretching and relaxing in the length direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine. There is. 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. You may combine with extending | stretching of arbitrary directions (diagonal direction) as needed. The dimensional change rate of the optical film can be reduced by shrinking 0.5% to 10% in both the longitudinal direction and the width direction.

  The film thickness of the optical film varies depending on the purpose of use, but as a finished film, the film thickness range used in the present invention is 30 to 200 μm, and in the recent thin trend, the film thickness is 40 to 120 μm. A range is preferable, and a range of 40 to 100 μm is particularly preferable. The average film thickness of the film can be adjusted by controlling the extrusion flow rate, the gap at the casting port of the casting die 3, the rotational speed of the cooling drum 4 and the like so as to obtain a desired thickness.

  The film F after stretching is cut off by slitting the film end with a slitter 8 to a width to be a product before being wound by the winder 10.

  After slitting the edge of the film to a product width by slitter 8 and cutting it off, a knurling process consisting of an embossing ring and a back roll is used to prevent sticking and scratching in the wound optical film (winding) F. The apparatus 9 may perform knurling (embossing) on both ends. The knurling method can process a metal ring having an uneven pattern on its side surface by heating 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.

  Thus, the optical film made of the laminated cellulose ester resin produced by the melt casting film forming method of the present invention is different from the resin film formed by the solution casting film forming method, and is dimensioned under various conditions. There is little change, density unevenness does not occur, and an optical film useful as a retardation film can be produced stably.

  In addition, the manufacturing method of the optical film by this invention is applicable not only to the resin layer containing a cellulose-ester-type resin but two layers, and the manufacturing method of a multilayer film of 3 layers or more.

  When the optical film according to the present invention is used as a protective film for a polarizing plate of a liquid crystal display device (LCD), an elliptical polarizing plate can be obtained by bonding the optical film to at least one surface of the 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. The optical film obtained by the present invention may be prepared by bonding to the polarizing plate with the protective film, or may also be prepared by directly bonding to the polarizing film also serving as the protective film.

  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). It can be easily attached to a cell or the like.

  The polarizing plate thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal cell in which liquid crystal molecules are substantially vertically aligned when no voltage is applied is preferable.

  The optical film according to the present invention is used for the protective film for polarizing plate of the above-mentioned liquid crystal display (LCD), as well as various functional films such as retardation film, wide viewing angle film, antireflection film in plasma display, and organic film. It can also be used for various functional films used in EL displays and the like.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Examples 1 and 2
Cellulose acetate propionate 100 parts by weight (acetyl group substitution degree 2.0, propionyl group substitution degree 0.7)
Plasticizer 5 parts by weight 1) Trimethylolpropane tribenzoate Td (1.0) = 262 ° C.
2) Ethyl phthalyl ethyl glycolate Td (1.0) = 172 ° C.
3) Triphenyl phosphate Td (1.0) = 205 ° C.
Here, the temperature Td (1.0) is measured with a temperature increase rate of 10 ° C./min in the range of 25 to 300 ° C. with a differential thermal mass measuring device (TG / DTA200 manufactured by Seiko Denshi Kogyo Co., Ltd.), The temperature decreased by 1.0 mass% with respect to the mass before heating was defined as Td (1.0).

Stabilizer 0.5 part by weight IRGANOX 1010 (Ciba Specialty Chemicals)
UV absorber 2 parts by weight Tinuvin 109 (Ciba Specialty Chemicals)
Matting agent 0.1 part by weight Aerosil R972V (Nippon Aerosil Co., Ltd., specific surface area 110 m ² / g)
Drying of matting agent The matting agent was dried with a hot air oven dryer at 120 ° C., and as shown in Table 1, in Example 1, the water content of the matting agent was within the range of the present invention. Weight% In Example 2, the drying time was adjusted so that the water content of the matting agent was 0.6% by weight, which was within the range of the present invention.

  Here, as a method for measuring the moisture content of the matting agent, first, the matting agent is weighed with an electronic balance, and the weight at this time is defined as W1 (g). Next, this matting agent was placed in a hot air oven-type dryer maintained at 150 ° C., dried for 5 hours, then allowed to cool in a desiccator for 30 minutes, and weighed as W2 (g). The following formula was used.

Water content of matting agent (%) = {(W1−W2) / W1} × 100
Next, the cellulose acetate propionate film of this invention was manufactured using the apparatus which implements the manufacturing method of the optical film of this invention shown in FIG.

  First layer: First layer material 11 comprising 5 parts by weight of the plasticizers 1), 2) and 3) and 0.5 parts by weight of the stabilizer with respect to 100 parts by weight of cellulose acetate propionate. Were mixed in advance, and the mixture was melt-mixed at 250 ° C. using a twin-screw extruder 1. Further, the matting agent 13 and the ultraviolet absorber were added and mixed in the course of melting.

  Second layer: Without mixing the matting agent, the second layer material 12 made of the same material as that of the first layer was melt-mixed at 250 ° C. using the biaxial extruder 2.

  Next, the flow rate ratio between the first layer and the second layer is adjusted to be 1: 5, and then supplied to the casting die 3 made of a multi-manifold type coextrusion die, and these molten resins are merged in the die 3. Then, the film was melt-extruded into a film at a melting temperature of 250 ° C. on the cooling drum 4 at 80 ° C., and cooled and solidified to obtain an unstretched resin web W.

  Then, the cooled and solidified dope film (web) W peeled off from the cooling drum 4 by the peeling roll 5 is continuously introduced into the tenter 7 via the dancer roll (film tension adjusting roll) 6 and is 160 ° C. in the width direction. After stretching 1.5 times, it was cooled to 30 ° C. while relaxing 3% in the width direction, and then released from the clip. Before the film F after being stretched is wound by the winder 10, the clip gripping end is slit by the slitter 8 to a width to be a product and cut off.

  Embossing ring and back roll to prevent sticking scratches in cellulose acetate propionate film (rolled) F after slitting the end of the film to slit to the product width by slitter 8 The both ends of the film were subjected to a knurling process (embossing process) by a knurling apparatus 9 comprising the optical film made of cellulose acetate propionate having a film thickness of 80 μm.

  About the obtained cellulose acetate propionate film, the dimensional change was evaluated as follows. The obtained results are shown in Table 1.

Measurement of dimensional change rate The obtained cellulose acetate propionate film was held in an environment of a temperature of 90 ° C. and a relative humidity of 5% RH for 120 hours, and the dimensional change rate of the film before and after that was measured.

Comparative Examples 1 and 2
For comparison, the same procedure as in Examples 1 and 2 is performed. In Comparative Example 1, the water content of the matting agent is 2.0% by weight, which is outside the range of the present invention. The drying time was adjusted so that the water content was 1.2 wt%, which is outside the range of the present invention. A cellulose acetate propionate film having a thickness of 80 μm was obtained in the same manner as in Example 1 except that these matting agents were used.

About the obtained cellulose acetate propionate film, it carried out similarly to the case of Example 1 and 2, and evaluated the dimensional change. The obtained results are shown in Table 1.

  As is clear from the results of Table 1 above, in Examples 1 and 2 of the present invention, two resin layers containing cellulose acetate propionate are laminated, and the first resin layer has a moisture content of 1 weight. % Of inorganic fine particles (matting agent) is contained, so there is little dimensional change even under various conditions, and there is no density unevenness, and it is made of a cellulose acetate propionate film suitable for retardation films. A film was obtained.

  In the liquid crystal display device using such a retardation film made of the cellulose acetate propionate film of the present invention, a stable display quality can always be obtained regardless of the conditions under the usage environment.

  On the other hand, in Comparative Examples 1 and 2, two resin layers containing cellulose acetate propionate are laminated, and the first resin layer includes inorganic fine particles whose water content is outside the range of the present invention ( Therefore, the cellulose acetate propionate films of Comparative Examples 1 and 2 have large dimensional changes and uneven density, and are not suitable for retardation films.

<Preparation of polarizing plate>
Using the cellulose acetate propionate film prepared in Examples 1 and 2, a polarizing plate was prepared by the following method.

  A 120 μm-thick polyvinyl alcohol film was immersed in 100 g of water containing 1 g of iodine and 4 g of boric acid, and stretched 6 times at 50 ° C. to produce a polarizing film. Cellulose triacetate propionate films subjected to the following alkali saponification treatment were bonded to both surfaces of the polarizing film, respectively, using a completely saponified polyvinyl alcohol 5% aqueous solution as an adhesive to produce polarizing plates.

(Alkaline saponification treatment)
Process Treatment liquid Treatment temperature Treatment time Saponification process: 2 mol / L / NaoH solution 50 ° C. 90 seconds Water washing process: Water 30 ° C. 45 seconds Neutralization process: 100 wt% HCl solution 30 ° C. 45 seconds Water washing process: Water 30 ° C. 45 Second Under the above conditions, each cellulose triacetate propionate film was treated in the order of saponification, water washing, neutralization and water washing, and then dried at 80 ° C.

<< Evaluation of density unevenness by liquid crystal display panel >>
The cellulose acetate pro obtained in Examples 1 and 2 was prepared by carefully peeling off the polarizing plates on both sides of a commercially available liquid crystal panel (manufactured by NEC, color liquid crystal display, MultiSync LCD1525J: model name LA-1529HM) and adjusting the polarization direction to this. A pionate film was attached to prepare a liquid crystal display panel, and the density unevenness was evaluated as follows.

  Under the environmental conditions of a temperature of 25 ° C. and a relative humidity of 60% RH, the backlight was continuously turned on for 5 hours, and the entire black display state was visually observed in a dark room to evaluate density unevenness. The obtained results are shown in Table 1 above. The density unevenness means uneven brightness when the screen of the liquid crystal panel is viewed.

  Further, for the cellulose acetate propionate films obtained in Comparative Examples 1 and 2, a polarizing plate was prepared in the same manner as described above, and density unevenness was evaluated by a liquid crystal display panel. Is also shown in Table 1 above.

  As is clear from the results in Table 1 above, no density unevenness was observed at all in the liquid crystal display panel produced by the polarizing plates using the cellulose acetate propionate films of Examples 1 and 2 of the present invention.

  On the other hand, in the liquid crystal display panel produced by the polarizing plate using the cellulose acetate propionate film of Comparative Example 1, a portion having a low concentration was observed around the liquid crystal, and the cellulose acetate propionate film of Comparative Example 2 was used. In the liquid crystal display panel produced by using the polarizing plate, a portion with a thin black density was observed around the liquid crystal.

It is a general | schematic flow sheet which shows one Embodiment of the apparatus which enforces the manufacturing method of the optical film of this invention.

Explanation of symbols

1: biaxial extruder for first layer 2: biaxial extruder for second layer 3: melt casting co-extrusion die 4: cooling drum 5: peeling roll 5
6: Dancer roll 7: Tenter (stretching machine)
8: Slitter 9: Knurling device 10: Winder 11: Resin film first layer material 12: Resin film second layer material 13: Matting agent W: Unstretched resin web F: Optical film

Claims (4)

  Two or more resin layers containing a cellulose ester resin are laminated, and at least one of the resin layers contains inorganic fine particles having a water content of 1% by weight or less.   The cellulose ester resin is at least one compound selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. The optical film according to claim 1, wherein the optical film is provided.   Two or more resin layers containing a cellulose ester resin are coextruded from a casting die by a melt casting film forming method, cooled and solidified to form an unstretched laminated web, and both ends of the unstretched laminated web are gripped in the width direction. Is a method for producing an optical film that winds up the obtained stretched laminated film, wherein at least one resin layer of two or more resin layers containing a cellulose ester resin has a water content of 1% by weight or less. The manufacturing method of the optical film characterized by including the inorganic fine particle of this.   The cellulose ester resin is at least one compound selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. The method for producing an optical film according to claim 3, wherein the method is provided.

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