JP2009220285A - Optical film and polarization plate using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film manufactured by a solution casting film forming method, increased in tear strength in a feed direction (MD direction) by highly stretching a wide film in a lateral direction (TD direction), improved in the exfoliability of the film at the time of reworking a polarization plate equipped with the optical film, suppressing rupture in a specific direction, suppressing curling of the polarization plate, suppressing rupture at the time of reworking and capable of satisfying requirement of increase of film width and high quality of the film in recent years, and a polarization plate. <P>SOLUTION: The optical film has the ratio of the tear strength in the film feed direction (MD direction) and the tear strength in the film width lateral direction (TD direction), i.e., (MD tear strength/TD tear strength) of 1.1-2.0, preferably 1.5-2.0. The stretching ratio of a web in a stretching process is preferably 20-60%. Further, the sum of the shrinkage factor in the MD direction and the shrinkage factor in the TD direction in all the manufacturing processes of the film is preferably 15-50%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention can be used for various functional films such as a protective film for a polarizing plate used for a liquid crystal display (LCD), a retardation film, a viewing angle widening film, and an antireflection film used for a plasma display. The present invention relates to an optical film as a film.

  Optical films used in liquid crystal display devices (LCDs) are increasing in production year by year due to the increase in size and spread of liquid crystal display devices. High quality film is being studied.

  In general, a polarizing plate used for a liquid crystal display (LCD) is a key device of LCD, and an adhesive layer made of an acrylic adhesive or the like is provided in advance for the purpose of preventing variation in quality and improving the efficiency of LCD assembly. In this state, a method of adhering to the liquid crystal cell is employed.

  In that case, if foreign matter such as contaminants or bubbles is mixed when adhering to the liquid crystal cell, that part becomes a visual hindrance after the display is mounted. The liquid crystal cell is reused.

  However, in the conventional polarizing plate, when peeling from the liquid crystal cell, the purpose of reusing the liquid crystal cell cannot be achieved by giving a gap change to the cell or damaging the glass substrate. There was a problem of high frequency.

  Therefore, conventionally, for the purpose of easy peeling of the polarizing plate, a method of reducing the adhesive force of the adhesive layer to which the polarizing plate is bonded has been proposed. However, there is a problem in that there is a limit to prevent peeling or floating due to the influence of humidity or heat.

  Further, if the polarizing plate itself is a thin film product, there is a problem that it may be broken when it is peeled off from the liquid crystal cell, and a peeling residue may be generated, which may not be completely removed.

  Patent Document 1 below discloses a cellulose ester film, a polarizing plate using the cellulose ester film, and a liquid crystal display device. The thickness direction retardation and the in-plane retardation are small, and cutting and the like hardly occur during production. Cellulose ester film balanced in mechanical properties and dimensional stability in the direction perpendicular to it, optical compensation film that can improve viewing angle characteristics when the cellulose ester film is incorporated into a liquid crystal display device, and polarization Techniques for plates are disclosed.

In Patent Document 1, the tearing strength of the cellulose ester film in the casting direction and the direction perpendicular to the casting direction is both 0.01 N or more, and the transverse direction with respect to the tearing strength in the film transport direction (MD direction). It is described that the tear strength ratio in the (TD direction) is 0.7 or more and 1.4 or less.
JP 2007-106794 A

  However, in the prior art described in Patent Document 1 described above, the purpose is to balance physical properties in the MD direction / TD direction by giving a weak tension in a balanced manner in the MD direction and the TD direction during film formation. The ratio of the tear strength in the MD direction and the TD direction is about ± 30% centering on 1.0.

  By the way, the polarizing plate is configured by bonding a protective film or a retardation film on both sides of the polarizer, but the main constituent molecules of the polarizer are oriented in one direction. By laminating a film having a high tear strength in a direction orthogonal to the orientation direction, a balance is achieved and the tear strength as a polarizing plate is higher than that of the film.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and is an optical film manufactured by a solution casting film forming method. In the MD direction, the film is highly stretched in the TD direction to take a wide film. The tear strength is increased, and by sticking this film on both sides of the polarizer, the peelability of the film during rework can be improved, and tearing in a specific direction can be suppressed. An object of the present invention is to provide an optical film and a polarizing plate using the same, which can suppress breakage and can meet the recent demands for widening the film width and improving the quality of the film.

  In order to achieve the above object, the invention of claim 1 forms a casting film (web) by casting a thermoplastic resin solution (dope) on a metal support by a solution casting film forming method, After evaporating a part of the solvent, the web is peeled from the metal support, the peeled web is stretched in the width direction at a stretch ratio of 20% or more, dried after stretching, and the film is wound into a roll after drying. An optical film manufactured by the method, wherein the ratio of the tear strength in the film conveying direction (MD direction) and the tear strength in the same width direction (TD direction): (MD tear strength / TD tear strength) is 1 .1 to 2.0.

  Here, the ratio of MD tear strength / TD tear strength is preferably 1.5 to 2.0.

  A third aspect of the invention is the optical film according to the first or second aspect, wherein the stretch ratio is 20 to 60%.

  Invention of Claim 4 is an optical film as described in any one of Claims 1-3, Comprising: Shrinkage | contraction of the conveyance direction (MD direction) of a film after peeling from a metal support body and winding up The sum of the rate and the shrinkage rate in the same width direction (TD direction): (MD shrinkage rate + TD shrinkage rate) is manufactured at 15 to 50%.

Invention of Claim 5 is an optical film as described in any one of Claims 1-4, Comprising: The shrinkage rate of the film conveyance direction (MD direction) after peeling from a metal support body and winding up And the shrinkage rate in the same width direction (TD direction)
It is manufactured under the condition of TD shrinkage ratio> MD shrinkage ratio.

  The invention according to claim 6 is the optical film according to any one of claims 1 to 5, wherein the thermoplastic resin is a cellulose ester.

  The invention of a polarizing plate according to a seventh aspect is characterized in that the optical film according to any one of the first to sixth aspects is bonded to both surfaces of a polarizer.

  In the first aspect of the present invention, a thermoplastic resin solution (dope) is cast on a metal support by a solution casting film forming method to form a casting film (web), and a part of the solvent is evaporated. An optical film produced by peeling a web from a metal support, stretching the peeled web in the width direction at a stretch ratio of 20% or more, drying after stretching, and winding the film into a roll after drying. The ratio of the tear strength in the film transport direction (MD direction) and the tear strength in the same width direction (TD direction): (MD tear strength / TD tear strength) is 1.1 to 2.0 Thus, according to the invention of claim 1, it is an optical film produced by a solution casting film forming method, and it is highly stretched in the TD direction to take a wide film, thereby increasing the tear strength in the MD direction, The film is polarized on both sides of the polarizer. By sticking in the direction perpendicular to the orientation direction of the main constituent molecules of the film, it is possible to improve the peelability of the film at the time of rework, suppress the tearing in a specific direction, suppress the curling of the polarizing plate, suppress the tearing at the rework Thus, there is an effect that it is possible to meet the recent demands for increasing the width of the film and improving the quality of the film.

  In the above, in order to take a wide film, the stretch ratio at the time of highly stretching in the TD direction is preferably 20 to 60%.

  The ratio of MD tear strength / TD tear strength is preferably 1.5 to 2.0.

  Invention of Claim 4 is an optical film as described in any one of Claims 1-3, Comprising: Shrinkage | contraction of the conveyance direction (MD direction) of a film after peeling from a metal support body and winding up According to the invention of claim 4, the sum of the rate and the shrinkage rate in the width direction (TD direction): (MD shrinkage rate + TD shrinkage rate) is manufactured at 15 to 50%. The shrinkage ratio is large and the tensile strength as a film is enhanced.

Invention of Claim 5 is an optical film as described in any one of Claims 1-4, Comprising: The shrinkage rate of the film conveyance direction (MD direction) after peeling from a metal support body and winding up And the shrinkage rate in the same width direction (TD direction)
According to the invention of claim 5, since it is oriented in the TD direction, the tear strength in the MD direction is enhanced.

  Invention of Claim 6 is an optical film as described in any one of Claims 1-5, Comprising: A thermoplastic resin is a cellulose ester, According to invention of Claim 6, TD By increasing the stretching ratio in the direction, a wide film can be obtained, and it can be used for a large-screen liquid crystal display device without a joint.

  The invention of a polarizing plate according to claim 7 is one in which the optical film according to any one of claims 1 to 6 is bonded to both surfaces of a polarizer. The polarizing plate can be obtained, and the loss of the polarizing plate due to tearing during rework can be reduced.

  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 present invention, a thermoplastic resin solution (dope) is cast on a metal support by a solution casting film forming method to form a casting film (web), and after evaporating a part of the solvent, the web is An optical film produced by peeling a web from a metal support, stretching the peeled web in the width direction at a stretch ratio of 20% or more, drying after stretching, and winding the film into a roll after drying. Ratio of tear strength in the transport direction (MD direction) and tear strength in the same width direction (TD direction): (MD tear strength / TD tear strength) is 1.1 to 2.0. Yes.

  Here, if the ratio of MD tear strength / TD tear strength is less than 1.1, the tear strength as a polarizing plate becomes small, and therefore breakage during reworking or the like occurs, which is not preferable. In addition, when the ratio of MD tear strength / TD tear strength exceeds 2.0, the film itself is easily torn in the TD direction, so the film is broken and transported in the film forming process and the polarizing plate processing process. This is not preferable because it cannot be performed.

  The ratio of MD tear strength / TD tear strength is preferably 1.5 to 2.0.

  The tear strength in the film transport direction (MD direction) and the tear strength in the same width direction (TD direction) are determined according to JIS K 7128-1991, for example, a light load manufactured by Toyo Seiki Co., Ltd. The tear strength can be measured with a tearing device.

  Moreover, in the above, in order to take a wide film, it is preferable that the stretch ratio at the time of highly stretching in the TD direction is 20 to 60%. This is because a stretch ratio of 20 to 60% is generally required to obtain an optical film having a width of 1800 mm or more.

  The optical film according to the present invention is the sum of the shrinkage rate in the film transport direction (MD direction) and the shrinkage rate in the width direction (TD direction) from peeling to winding after the metal support: (MD shrinkage) (Rate + TD shrinkage) is preferably 15 to 50%.

  Here, if the sum of MD shrinkage rate + TD shrinkage rate is less than 15%, a wide film cannot be obtained, which is not preferable. On the other hand, if the sum of the MD shrinkage rate and the TD shrinkage rate exceeds 50%, the haze of the film rises and the light transmittance falls, so that the contrast is lowered when incorporated in a liquid crystal display device, which is not preferable.

The optical film according to the present invention has a shrinkage rate in the film conveyance direction (MD direction) and a shrinkage rate in the same width direction (TD direction) until it is peeled off from the metal support.
It is preferable to be produced under the condition of TD shrinkage> MD shrinkage. This is because the tear strength of the polarizing plate is increased by bonding in a direction orthogonal to the orientation direction of the main constituent molecules of the polarizer.

  In general, a polarizer is a polyvinyl alcohol film that is a polarizing film that has been stretched several times in the transport direction, so by laminating a film that has been stretched in the width direction (TD direction) that is the orthogonal direction, The tear strength as a polarizing plate increases.

  Here, the film shrinkage rate (MD direction) is defined by the following formula.

Film shrinkage (MD direction) (%) =
[1- (Conveying speed / winding speed of metal support)] × 100
Further, the film shrinkage rate (TD direction) is defined by the following formula.

Film shrinkage (TD direction) (%) =
[Product width / (casting width−trim total width) -1] × 100
According to the optical film of the present invention, the film is highly stretched in the TD direction to take a wide film, thereby increasing the tear strength in the MD direction, and the orientation direction of the main constituent molecules of the polarizer on the both sides of the polarizer. By bonding in a direction orthogonal to the film, the peelability of the film at the time of rework (reproduction) can be improved, and tearing in a specific direction can be suppressed.

  In general, the polarizer is stretched in the transport direction (MD direction), and as a polarizing plate protective film and a retardation film to be bonded to the polarizer, a film stretched in the width direction (TD direction). The film is bonded to each other by roll-to-roll, so that the rework strength of the film can be increased by bonding to both sides of the polarizer in a direction perpendicular to the orientation direction of the main constituent molecules of the polarizer.

  In addition, the rework property of a polarizing plate is performed as follows, for example. That is, a polarizing plate produced using the optical film of the present invention is cut into a square having a predetermined size, and is bonded to a glass substrate using, for example, an adhesive. Next, the bonded polarizing plate is peeled off from the glass with a predetermined strength from the corners. This operation is carried out for each type of polarizing plate as many times as necessary, and the number of polarizing plates that are not completely peeled off due to tears in the polarizing plate is counted and ranked according to a predetermined standard.

  In the optical film of the present invention, the roll length of the roll film is preferably 3900 m or more and 9100 m or less.

  Here, if the winding length of the roll film is less than 3900 m, it is not preferable because the time for switching the rolled-up roll becomes insufficient when the production speed is increased. Moreover, since the frequency of the film switching operation increases during the polarizing plate processing, the productivity is lowered. On the other hand, if the roll length of the roll film exceeds 9100 m, the load on the core increases due to the film's own weight, and even if the emboss is increased, the effective knurl cannot be maintained and a sticking failure occurs.

  Hereinafter, the present invention will be described in detail.

  The optical film of the present invention is produced by a solution casting method. In the method for producing an optical film, various resins can be used as the film material, and cellulose ester is particularly preferable.

  A 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 triacetate, cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among these, cellulose acetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. Other substituents may be included as long as the effects of the present invention are not impaired.

  As an example of cellulose triacetate, the substitution degree of acetyl groups is preferably 2.0 or more and 3.0 or less. By setting the degree of substitution within this range, good moldability can be obtained, and desired in-plane retardation (Ro) and thickness direction retardation (Rt) can be obtained. If the substitution degree of the acetyl group is lower than this range, the heat resistance as a retardation film, particularly the dimensional stability under wet heat may be inferior, and if the substitution degree is too large, the necessary retardation characteristics will not be exhibited. There is a case.

  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 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. The cellulose ester used in the present invention preferably has an Mw / Mn ratio of 1.4 to 3.0, more preferably 1.4 to 2.3.

  Since the average molecular weight and molecular weight distribution of the cellulose ester can be measured using high performance liquid chromatography, the number average molecular weight (Mn) and the weight average molecular weight (Mw) can be calculated using this, and the ratio can be calculated.

  The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G
(Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by weight
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 1,000,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

  The total acyl group substitution degree of the cellulose ester is 2.3 to 2.9, and 2.6 to 2.9 is preferably used. The total acyl group substitution degree can be measured according to ASTM-D817-96.

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

  In the method for producing an optical film according to the present invention, an organic solvent having good solubility with respect to the cellulose derivative is referred to as a good solvent, and has a main effect on dissolution, and an organic solvent used in a large amount among them is mainly used. It is called (organic) solvent or main (organic) solvent.

  Examples of good solvents include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, formic acid Esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, sulfolane, nitroethane, methylene chloride And 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferable.

  In addition to the organic solvent, the dope preferably contains 1 to 40% by weight of an alcohol having 1 to 4 carbon atoms. After casting the dope on the metal support, the solvent starts to evaporate and the alcohol ratio increases, so the web (name of the dope film after casting the cellulose derivative dope on the metal support) Is used as a gelling solvent that makes the web strong and makes it easy to peel off from the metal support, or when these ratios are small, cellulose derivatives of non-chlorine organic solvents There is also a role to promote the dissolution of.

  Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, and propylene glycol monomethyl ether. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, good drying properties, and no toxicity. These organic solvents alone are not soluble in cellulose derivatives and are called poor solvents.

  The most preferable solvent for dissolving a cellulose derivative, which is a preferable polymer compound satisfying such conditions, at a high concentration is a mixed solvent having a ratio of methylene chloride: ethyl alcohol of 95: 5 to 80:20. Alternatively, a mixed solvent of methyl acetate: ethyl alcohol 60:40 to 95: 5 is also preferably used.

  The film according to the present invention includes a plasticizer that imparts processability, flexibility, and moisture resistance to the film, fine particles that impart slipperiness to the film (matting agent), an ultraviolet absorber that imparts an ultraviolet absorbing function, and deterioration of the film. You may contain the antioxidant etc. which prevent.

  The plasticizer used in the present invention is not particularly limited. However, a cellulose derivative or a reactive metal compound capable of hydrolytic polycondensation can be used so as not to cause haze, bleed out or volatilize from the film. It preferably has a functional group capable of interacting with the condensate by hydrogen bonding or the like.

  Examples of such functional groups include hydroxyl groups, ether groups, carbonyl groups, ester groups, carboxylic acid residues, amino groups, imino groups, amide groups, imide groups, cyano groups, nitro groups, sulfonyl groups, sulfonic acid residues, Examples thereof include a phosphonyl group and a phosphonic acid residue, and a carbonyl group, an ester group and a phosphonyl group are preferred.

  Examples of such plasticizers include phosphate ester plasticizers, phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol ester plasticizers, glycolate plasticizers. Agents, citric acid ester plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, polyester plasticizers, etc. can be preferably used, but polyhydric alcohol ester plasticizers, glycolate plasticizers are particularly preferred. And non-phosphate ester plasticizers such as polycarboxylic acid ester plasticizers.

  The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

  The polyhydric alcohol used in the present invention is represented by the following general formula (1).

R _1- (OH) n (1)
(Wherein R ₁ represents an n-valent organic group, and n represents a positive integer of 2 or more)
Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

  Examples of preferred polyhydric alcohols include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1, 2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, gallium Examples include lactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  In the present invention, the monocarboxylic acid used in the polyhydric alcohol ester is not particularly limited, and known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid and the like can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose derivative is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Examples of preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, Tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, mellicic acid, laccellic acid, etc., undecylen Examples thereof include unsaturated fatty acids such as acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. Examples thereof include aromatic monocarboxylic acids and derivatives thereof, and benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose derivatives.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  The glycolate plasticizer is not particularly limited, but a glycolate plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. As preferred glycolate plasticizers, for example, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate and the like can be used.

  For phosphate ester plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate, and the like can be used, but in the present invention, it is preferable that a phosphate ester plasticizer is not substantially contained.

  Here, “substantially does not contain” means that the content of the phosphoric ester plasticizer is less than 1% by weight, preferably 0.1% by weight, and particularly preferably not added.

  These plasticizers can be used alone or in combination of two or more.

  The amount of the plasticizer used is preferably 1 to 20% by weight. 6 to 16% by weight is further preferable, and 8 to 13% by weight is particularly preferable. If the amount of the plasticizer used is less than 1% by weight relative to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so this is not preferred. If it exceeds 20% by weight, the plasticizer bleeds out from the film, and the film Since the physical properties of the material deteriorate, it is not preferable.

  In order to impart slipperiness to the cellulose derivative in the present invention, it is preferable to add fine particles such as a matting agent. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound.

  Examples of the fine particles of the inorganic compound include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

  Examples of the organic compound fine particles include fine particles such as acrylic resin, silicone resin, fluorine compound resin, and urethane resin.

  The primary particle size of the fine particles is not particularly limited, but the average particle size in the film is preferably about 0.05 to 5.0 μm. More preferably, it is 0.1-1.0 micrometer.

  When the cellulose ester film is observed with an electron microscope or an optical microscope, the average particle diameter of the fine particles indicates an average value of the lengths in the major axis direction of the particles at the observation position of the film. As long as the particles are observed in the film, they may be primary particles or secondary particles in which the primary particles are aggregated, but most of the particles that are usually observed are secondary particles.

As an example of the measurement method, 10 vertical cross-sectional photographs are taken at random for each film, and the number of particles in 100 μm ² whose major axis length is in the range of 0.05 to 5 μm for each cross-sectional photograph. Count. The average value of the major axis lengths of the particles counted at this time is obtained, and a value obtained by averaging the average values of 10 locations is defined as the average particle size.

  In the case of fine particles, the primary particle size, the particle size after being dispersed in a solvent, and the particle size added to the film often change, and it is important that the fine particles are finally combined with the cellulose ester in the film. It is to control the particle size formed by aggregation.

  Here, if the average particle size of the fine particles exceeds 5 μm, haze deterioration or the like may be observed, or it may cause a failure in a wound state as a foreign matter. Moreover, when the average particle diameter of fine particles is less than 0.05 μm, it becomes difficult to impart slipperiness to the film.

  The fine particles are used by adding 0.04 to 0.5% by weight to the cellulose ester. Preferably, 0.05 to 0.3% by weight, more preferably 0.05 to 0.25% by weight is added. When the amount of fine particles added is 0.04% by weight or less, the film surface roughness becomes too smooth and blocking occurs due to an increase in the friction coefficient. If the amount of fine particles added exceeds 0.5% by weight, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

  For the dispersion of the fine particles, it is preferable to treat the composition in which the fine particles and the solvent are mixed with a high-pressure dispersion apparatus. The high-pressure dispersion apparatus used in the present invention is an apparatus that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube.

It is preferable that the maximum pressure condition inside the apparatus is 980 N / cm ² or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by processing with a high-pressure dispersion apparatus. More preferably, the maximum pressure condition inside the apparatus is 1960 N / cm ² or more. Further, at that time, those having a maximum reaching speed of 100 m / sec or more and those having a heat transfer speed of 100 kcal / hr or more are preferable.

  Examples of the high-pressure dispersing apparatus as described above include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other examples include a Manton Gorin type high-pressure dispersing apparatus such as Izumi Food Machinery. Examples thereof include a homogenizer.

  In the present invention, the fine particles are dispersed in a solvent containing 25 to 100% by weight of a lower alcohol, and then mixed with a dope in which a cellulose ester (cellulose derivative) is dissolved in a solvent, and the mixed solution is placed on a metal support. A cellulose ester film is obtained which is cast and dried to form a film.

  Here, the content ratio of the lower alcohol is preferably 50 to 100% by weight, more preferably 75 to 100% by weight.

  Examples of lower alcohols preferably include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like.

  Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film formation of a cellulose ester.

  The fine particles are dispersed in the solvent at a concentration of 1 to 30% by weight. Dispersing at a concentration higher than this is not preferable because the viscosity increases rapidly. The concentration of the fine particles in the dispersion is preferably 5 to 25% by weight, more preferably 10 to 20% by weight.

  The ultraviolet absorbing function of the film is preferably imparted to various optical films such as a polarizing plate protective film, a retardation film, and an optical compensation film from the viewpoint of preventing deterioration of the liquid crystal. For such an ultraviolet absorbing function, a material that absorbs ultraviolet rays may be included in the cellulose derivative, and a layer having an ultraviolet absorbing function may be provided on a film made of the cellulose derivative.

  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. In addition, 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 the ultraviolet absorber, those having excellent absorption ability of ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of a polarizer or liquid crystal and those having little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties. preferable.

  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-5 A mixture of-(5-chloro-2H-benzotriazol-2-yl) phenyl] propionate can be mentioned, but is not limited thereto.

  Further, as commercially available products of ultraviolet absorbers, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Specific examples of the benzophenone-based compound that is an ultraviolet absorber that can be used in the present invention include 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5- Examples thereof include, but are not limited to, sulfobenzophenone and bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane).

  In this invention, the compounding quantity of these ultraviolet absorbers has the preferable range of 0.01 to 10 weight% with respect to a cellulose ester (cellulose derivative), and also 0.1 to 5 weight% is preferable. If the amount of the ultraviolet absorber used is too small, the ultraviolet absorbing effect may be insufficient. If the amount of the ultraviolet absorber is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

  Further, as the ultraviolet absorber that can be used in the optical film of the present invention, the polymer ultraviolet absorber (or ultraviolet absorbing polymer) described in JP-A-6-148430 and JP-A-2002-47357 is preferably used. be able to. In particular, the general formula (1) described in JP-A-6-148430, the general formula (2), or the general formulas (3), (6), and (7) described in JP-A-2002-47357. Molecular ultraviolet absorbers are preferably used.

  In general, the antioxidant is also referred to as a deterioration inhibitor, but is preferably contained in a cellulose ester film as an optical film. That is, when a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film as an optical film may be deteriorated. The antioxidant has a role of delaying or preventing the film from being decomposed by, for example, halogen in the residual solvent in the film or phosphoric acid of the phosphoric acid plasticizer, so that it is preferably contained in the film. .

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-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-hydroxy Benzyl) -isocyanurate and the like. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination.

  The amount of these compounds added is preferably 1 ppm to 1.0% by weight, more preferably 10 to 1000 ppm by weight with respect to the cellulose derivative.

  Hereinafter, the method for producing the optical film according to the present invention will be described in detail. The optical film can be produced by a solution casting method.

  FIG. 1 is a flow sheet showing a specific example of an apparatus for carrying out a method for producing an optical film of the present invention by a solution casting film forming method. Note that the implementation of the present invention is not limited to the process of FIG.

  In the solution casting film forming method for producing an optical film according to the present invention, a thermoplastic resin solution (dope) is cast on a metal support (1) to form a casting film (web), and a part of the solvent After evaporating the film, the step of peeling the web (10) from the metal support (1), the step of stretching the peeled web (10) in the width direction by the tenter (4), and winding the stretched film A winding process.

  First, in a melting pot (not shown), a thermoplastic resin, for example, a cellulose ester resin is dissolved in a mixed solvent of a good solvent and a poor solvent, and an additive such as the above plasticizer or ultraviolet absorber is added to the resin. A solution (dope) is prepared.

  Next, the dope adjusted in the melting pot is fed to the casting die (2) by a conduit through, for example, a pressurized metering gear pump, and is made of a metal made of a rotationally driven stainless steel endless belt as shown in FIG. The dope is cast from the casting die (2) to the casting position on the support (1).

  Although not shown in the drawings, for example, a dope fed to the casting die (2) through, for example, a pressurized metering gear pump is rotated by a stainless steel having a surface mirror-treated by hard chrome plating from the casting die (2). It may be cast on a cooling drum.

  In order to cast the dope by the casting die (2), there is a doctor blade method in which the film thickness of the cast dope film (web) is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll. However, a pressure die that can adjust the slit shape of the die portion and can easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

  In addition, as a casting die (2), the pressure die which can adjust the slit shape of a nozzle | cap | die part and is easy to make a film thickness uniform is preferable.

  Here, it is preferable that the solid content concentration of the cellulose ester solution (dope) is 20 to 30% by weight.

  Here, if the solid content concentration of the cellulose ester solution (dope) is less than 20% by weight, sufficient drying cannot be performed on the metal support (1), and a part of the dope film is removed from the metal support (at the time of peeling). 1) Since it remains on top and leads to drum contamination, it is not preferable. If the solid content concentration exceeds 30%, the dope viscosity increases, filter clogging becomes faster in the dope adjustment process, or the pressure increases during casting on the metal support (1), and cannot be extruded. It is not preferable.

  In the illustrated film forming apparatus provided with a rotationally driven endless belt as the metal support (1), the belt metal support (1) is disposed between a pair of drums and the endless belt metal support (1 ), A plurality of rolls (not shown) that respectively support the upper transition portion and the lower transition portion from the back side.

  One or both of the winding drums at both ends of the rotationally driven endless belt metal support (1) is provided with a drive device for applying tension to the belt metal support (1), whereby the belt metal. The support (1) is used in a tensioned state.

  The width of the metal support is 1800 to 2200 mm, the casting width of the cellulose ester solution is 1600 to 2150 mm, and the width of the film after winding is 1490 to 3000 mm. Thereby, the wide cellulose-ester film for liquid crystal display devices can be manufactured by a metal support body system.

  Here, when the width of the metal support (1), the casting width of the cellulose ester solution, and the width of the film after winding are less than the above lower limit values, respectively, it is possible to cope with the recent enlargement of liquid crystal display devices. If the width of the metal support (1), the casting width of the cellulose ester solution, and the width of the film after winding exceed the upper limit values, the residual solvent amount of the film after peeling In a state where there is a large amount of film, the film hangs down at the entrance of a tenter in the stretching process described later, unevenness in width is generated, and dispersion of retardation is increased, which is not preferable. In addition, the sagging film may hit the guide of the tenter, and the film may break and stop production.

  Moreover, in the method for producing the optical film of the present invention, the peripheral speed of the metal support (1) is preferably 80 to 200 m / min.

  That is, since the amount of solvent to be dried is small in a thin film, the production speed of the film can be increased by making the peripheral speed of the metal support (1) faster than the conventional drum peripheral speed. Productivity can be increased.

  When an endless belt is used as the metal support (1), the belt temperature during film formation is a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and the mixed solvent is lower than the boiling point of the lowest boiling solvent. The temperature is more preferably in the range of 5 ° C to the boiling point of the solvent-5 ° C. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  The dope cast on the surface of the metal support (1) as described above increases the gel film strength (film strength) due to cooling gelation, and further promotes drying until stripping. This also increases the strength (film strength) of the gel film.

  Further, in order to increase the film forming speed, two or more pressure casting dies (2) may be provided on the casting metal support (1), and the dope amount may be divided to form a multilayer film.

  In the system using an endless belt as the metal support (1), the film strength on which the web (10) can be peeled from the metal support (1) by the peeling roll (3) on the metal support (1). In order to dry and solidify until it becomes, it is preferable to dry to 150 weight% or less of the residual solvent amount in a web (10), and 80 to 120 weight% is more preferable. Moreover, as for web temperature when peeling a web (10) from metal support bodies (1), 0-30 degreeC is preferable. Further, immediately after the web (10) is peeled off from the metal support (1), the temperature rapidly decreases once due to the solvent evaporation from the metal support (1) adhesion surface side, and water vapor or solvent vapor in the atmosphere. For example, the web temperature at the time of peeling is more preferably 5 to 30 ° C. because volatile components are easily condensed.

  Here, the residual solvent amount can be expressed by the following equation.

Residual solvent amount (% by weight) = {(M−N) / N} × 100
In the formula, M represents the weight of the film at an arbitrary time point, and N represents the weight after drying a film having a weight of M at 110 ° C. for 3 hours.

  The dope film (web) formed by the dope cast on the endless belt metal support (1) is heated on the metal support (1), and the release roll ( The solvent is evaporated until the web is peelable by 3).

  In order to evaporate the solvent, there are a method of blowing air from the web side, and / or a method of transferring heat from the back surface of the metal support (1) by a liquid, a method of transferring heat from the front and back by radiant heat, and the like.

  In the system using an endless belt for the metal support (1), the peeling tension when the metal support (1) and the web (10) are peeled by the peeling roll (3) is usually 100 N / m to 200 N / In the optical film according to the present invention, which is made thinner than the conventional film, the amount of residual solvent of the web (10) is large at the time of peeling, and it is easy to extend in the transport direction. The film is easy to shrink, and when drying and shrinking overlap, the edge curls and folds, so that wrinkles easily occur. Therefore, the film is preferably peeled at a minimum tension of 170 N / m, more preferably the minimum tension. It is peeling at ~ 140 N / m.

  After drying and solidifying until the web (10) has a peelable film strength on the metal support (1), the web (10) is peeled off by the peeling roll (3).

  Next, the peeled web (10) is introduced into a tenter (4) in the stretching process. In the present invention, as the tenter (4) in the stretching step, a pin tenter and a clip tenter can be used. Among them, as the film for a liquid crystal display device, both side edges of the web (or film) (10) are used. It is preferably a clip tenter that is fixed with a clip and stretched, and is preferred for improving the flatness and dimensional stability of the film.

  The residual solvent amount of the web (film) (10) immediately before entering the tenter (4) in the stretching step is preferably 10 to 50% by weight.

  In the stretching process, warm air is blown from the warm air blowing means at the front portion of the bottom of the tenter (4), that is, the warm air blowing slit port, and exhaust air is blown from the discharge port at the rear portion of the ceiling of the tenter (4). By being discharged, the web (10) is stretched and dried.

  In the present invention, the stretch ratio of the web (10) in the tenter (4) is preferably 20 to 60%. This is because a stretch ratio of 20 to 60% is generally required to obtain an optical film having a width of 1800 mm or more. And a film becomes soft by extending | stretching by a high extending | stretching rate in this way.

  In addition, the hot air blowing means in the stretching step specifically refers to the hot air blowing slit port of the tenter (4) in the stretching step, but any shape that efficiently heats the film by blowing hot air. There is no particular limitation. The temperature of the warm air is preferably 165 to 190 ° C, and more preferably 170 to 185 ° C.

  Next, the stretched film (web) (10) is introduced into the roll conveyance drying device (5) and dried while being conveyed by the conveyance roll (7) composed of a non-driven free roll in the drying device (5). .

  In this drying device (5), the web (10) is meandered by the conveying rolls (7) arranged in a staggered manner as viewed from the side of 50 to 1000, and the web (10) is dried in the meantime. is there. Moreover, although the film conveyance tension | tensile_strength in drying apparatus (5) is influenced by the physical property of dope, the amount of residual solvents at the time of peeling and a film conveyance process, the temperature in drying apparatus (5), etc., it is 30-250 N / m. Is preferable, and 60 to 150 N / m is more preferable. 80 to 120 N / m is most preferable.

  The means for drying the web (or film) (10) is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the viewpoint of simplicity. For example, it is dried by the drying air blown from the warm air inlet at the front portion of the bottom of the drying device (5), and the rear portion of the ceiling of the drying device (5). It is dried by exhausting the exhaust air from the outlet. The temperature of the drying air is preferably 40 to 160 ° C, and more preferably 50 to 160 ° C in order to improve the flatness and dimensional stability.

  The process from casting to final post-drying may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas. In this case, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

  After drying by the roll conveyance drying device (5), both ends of the film were slit into a product width by a pair of upper and lower slitters (11) and (12), cut and cut, and a base film was formed according to the product width. Then, a roll-shaped optical film is manufactured by giving an embossed part by giving a knurling process to the width direction Shiro of this base film, and winding up.

  Moreover, in the method for producing the optical film of the present invention, it is preferable to apply cold air of 10 to 20 ° C. to the film discharge side of the embossing stamp roll during knurling. Here, during the knurling process, 10-20 ° C cold air is applied to the film discharge side of the embossing stamping roll because the resin part melted by heat is cooled and solidified by cooling the film and the ring part immediately after the embossing process. For this reason, the generation of thread-like foreign matters (beard-like foreign matters) can be suppressed, and a sufficiently high embossing height can be obtained.

  In the optical film according to the present invention, the ratio of the tear strength in the film conveying direction (MD direction) to the tear strength in the same width direction (TD direction): (MD tear strength / TD tear strength) is 1.1 to 2. .0.

  According to the optical film of the present invention, the film is highly stretched in the TD direction to take a wide film, thereby increasing the tear strength in the MD direction, and the orientation direction of the main constituent molecules of the polarizer on the both sides of the polarizer. By sticking in the direction orthogonal to the film, the peelability of the film at the time of rework can be improved, the tearing in a specific direction can be suppressed, the curling of the polarizing plate can be suppressed, the tearing in the rework can be suppressed, In recent years, it is possible to meet the demand for increasing the film width and improving the quality of the film.

  In addition, the optical film of the present invention is the sum of the shrinkage rate in the film conveyance direction (MD direction) and the shrinkage rate in the same width direction (TD direction) from peeling to winding after the metal support: ( MD shrinkage rate + TD shrinkage rate) is manufactured at 15-50%. According to the optical film of the present invention, there is an advantage that reworkability can be secured while obtaining a wide-width film that can be used without a joint in a large-screen liquid crystal display device.

The optical film of the present invention has a shrinkage rate in the film transport direction (MD direction) and a shrinkage rate in the same width direction (TD direction) until it is peeled off from the metal support.
It is manufactured under the condition of TD shrinkage> MD shrinkage. Thereby, there exists an advantage that the tearing strength as a polarizing plate after bonding with a polarizer becomes high.

  In the optical film according to the present invention, the roll length of the roll film is preferably 3900 m or more and 9100 m or less.

  Here, if the winding length of the roll film is less than 3900 m, it is not preferable because the time for switching the rolled-up roll becomes insufficient when the production speed is increased. Moreover, since the frequency of the film switching operation increases during the polarizing plate processing, the productivity is lowered.

  On the other hand, if the roll length of the roll film exceeds 9100 m, the load on the core increases due to the film's own weight, and even if the emboss is increased, the effective knurl cannot be maintained and a sticking failure occurs.

  In addition, a film with good dimensional stability can be obtained by setting the residual solvent amount of the film taken up by the take-up device (15) to 0.5% by weight or less, preferably 0.1% by weight or less.

(Polarizer)
Next, a polarizing plate using the optical film of the present invention will be described.

  The polarizing plate can be produced by a general method. It is preferable that the back side of the optical film according to the present invention is subjected to alkali saponification treatment, and the treated film is bonded to both surfaces of a polarizing film prepared by immersing and stretching in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. . In some cases, the optical film according to the present invention is bonded to one surface of the polarizing film, and a commercially available retardation film is bonded to the other surface of the polarizing film.

  The polarizing film, which is the main component of the polarizing plate, is an element that transmits only light having a polarization plane in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol film. There are those in which iodine is dyed on a system film and those in which dichroic dye is dyed, but it is not limited to this. As the polarizing film, a polyvinyl alcohol aqueous solution is formed and dyed by uniaxially stretching or dyed, or uniaxially stretched after dyeing, and then preferably subjected to a durability treatment with a boron compound. A polarizing film having a thickness of 5 to 30 μm, preferably 8 to 15 μm, is preferably used. It is preferable to form a polarizing plate by laminating the optical films of the present invention on both sides of the polarizing film.

(Image display device)
By incorporating the polarizing plate using the optical film of the present invention on the viewing surface side of the image display device, various image display devices with excellent visibility can be produced. The optical film of the present invention is preferably a reflective type, transmissive type, transflective type LCD, or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type, etc. Used. Moreover, it is excellent in flatness and is preferably used for various display devices such as a plasma display, a field emission display, an organic EL display, an inorganic EL display, and electronic paper. In particular, a large-screen image display device having a screen size of 30 or more has the effect of good visibility and prevents eyes from being tired even during long-time viewing.

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

Example 1
An optical film made of the cellulose triacetate film of the present invention was produced by the solution casting film forming method as follows.

(Dope composition 1)
100 parts by weight of cellulose triacetate (Mn = 148000, Mw = 310000, Mw / Mn = 2.1)
Triphenyl phosphate 8 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Methylene chloride 440 parts by weight Ethanol 40 parts by weight Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 0.5 part by weight Tinuvin 171 (Ciba Specialty Chemicals) 0.5 parts by weight Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd.) 0.2 parts by weight The material of the above dope composition 1 was put into a sealed container, heated, stirred and completely dissolved and filtered. . The filtration was performed through a sintered metal filter (capture particle size = 10 microns) after filtration by a filter press. Subsequently, the dope was uniformly cast to a width of 1950 mm on a stainless steel band support (1) having a width of 2050 mm at a temperature of 35 ° C. using the belt casting apparatus shown in FIG.

  On the stainless steel band support (1), the solvent was evaporated until the residual solvent amount reached 100% by weight, and the web (film) (10) was peeled from the stainless steel band support (1). Next, both ends of the web (10) in the width direction (TD direction) were held by the tenter (4), and the web (10) was stretched at a stretch ratio of 20% in the width direction. In addition, the residual solvent amount of the web (film) (10) immediately before entering the tenter (4) in the stretching process was 30% by weight.

  In the stretching step, warm air is blown at a temperature of 180 ° C. from the warm air blowing means at the front part of the bottom of the tenter (4), that is, the warm air blowing slit port, and the outlet of the rear part of the ceiling of the tenter (4). The web (10) was stretched and dried by the exhaust air being discharged from.

  Next, the stretched film (web) (10) is introduced into a roll transport dryer (5), and this film is mirror transported with a surface roughness (Rmax) of 0.8 μm in the roll transport dryer (5). It dried, conveying with the conveyance roll (7) comprised by 500 non-driving free rolls which consist of a roll (surface length 2700mm, diameter 110mm). The film conveyance tension in the drying device (5) was 80 N / m. In the drying device (5), drying was performed by a drying air having a temperature of 120 ° C. blown from a hot air inlet at a front portion of the bottom of the drying device.

  After drying with the drying device (5), both ends of the film were slit into a product width by a pair of upper and lower slitters (11) and (12) and cut and cut.

  Subsequently, the left and right ends of the slit film (10) were knurled by an embossing ring (13) and a back roll (14) to give an embossed portion (not shown) having a width of 10 mm to the film end. In the knurling process, cold air having a temperature of 20 ° C. was applied to the embossing ring, that is, the film discharge side of the embossing stamp roll (13).

  Thereafter, the cellulose triacetate film (F) having an end product width of 1800 mm and a film thickness of 80 μm having an embossed portion was wound up by a winding device (15). The wound length of the rolled cellulose triacetate film (F) was 3900 m.

  The cellulose triacetate film obtained in Example 1 has a ratio of tear strength in the film transport direction (MD direction) to tear strength in the same width direction (TD direction): (MD tear strength / TD tear strength). 1.1.

  Here, the tear strength in the film transport direction (MD direction) and the tear strength in the same width direction (TD direction) are determined by applying the tear load of the Elmendorf method in accordance with JIS K 7128-1991, a light load manufactured by Toyo Seiki Co., Ltd. Each was measured with a tearing device.

  Moreover, while calculating the shrinkage rate of the conveyance direction (MD direction) of a film after peeling from a metal support body and winding up, and the shrinkage rate of the same width direction (TD direction) by a following formula, The sum of the shrinkage rate in the transport direction (MD direction) and the shrinkage rate in the same width direction (TD direction): (MD shrinkage rate + TD shrinkage rate) was calculated.

  Here, the film shrinkage rate (MD direction) is defined as follows.

Film shrinkage (MD direction) (%) =
[1- (Conveying speed / winding speed of metal support)] × 100
The film shrinkage rate (TD direction) is defined as follows.

Film shrinkage (TD direction) (%) =
[Product width / (casting width−trim total width) -1] × 100
The obtained results are shown in Table 1 below. In Table 1, the type of dope composition, stretch ratio (%), casting width (mm), film product width (mm), tear strength ratio: MD / TD, shrinkage ratio in the film MD direction, film TD direction , The sum of the shrinkage in the MD direction and the shrinkage in the TD direction (MD shrinkage + TD shrinkage) are shown together.

Examples 2-5
A cellulose triacetate film is prepared in the same manner as in Example 1 above. However, the stretching rate is 30% in Example 2, 40% in Example 3, and in Example 4 as in Example 1 above. Cellulose triacetate films were produced under different conditions of 50% and in Example 5, respectively, by increasing the tension in the transport direction and by changing the shrinkage in the MD direction to + 5.0%.

  The cast width of the dope on the stainless steel band support (1) is the same at 1950 mm. However, since the stretch ratios are different, the final product widths having the embossed portions are different from each other. The results are shown in Table 1 below.

  And about the obtained cellulose triacetate films of Examples 2 to 5, the ratio between the film final product width and the tear strength in the film conveyance direction (MD direction) and the tear strength in the same width direction (TD direction): ( (MD tear strength / TD tear strength) was measured in the same manner as in Example 1 above. In addition, the shrinkage rate in the film transport direction (MD direction) and the shrinkage rate in the same width direction (TD direction) from peeling off from the metal support to winding up are the same as in Example 1 above. In addition, the sum of the shrinkage rate in the film conveyance direction (MD direction) and the shrinkage rate in the width direction (TD direction): (MD shrinkage rate + TD shrinkage rate) was calculated. The obtained results are shown in Table 1 below.

Comparative Examples 1 and 2
For comparison, a cellulose triacetate film is prepared in the same manner as in Example 1 above. The difference from the case of Example 1 is that in Comparative Examples 1 and 2, the stretch ratio was less than 20%. In the point.

  And about the obtained cellulose triacetate film, ratio of tear strength of a film final product width and a film conveyance direction (MD direction), and tear strength of the same width direction (TD direction): (MD tear strength / TD tear Strength) was measured in the same manner as in Example 1 above. In addition, the shrinkage rate in the film transport direction (MD direction) and the shrinkage rate in the same width direction (TD direction) from peeling off from the metal support to winding up are the same as in Example 1 above. In addition, the sum of the shrinkage rate in the film conveyance direction (MD direction) and the shrinkage rate in the width direction (TD direction): (MD shrinkage rate + TD shrinkage rate) was calculated. The obtained results are shown in Table 1 below.

Examples 6-9
A cellulose ester film is produced in the same manner as in Example 1, but the difference from Example 1 is that cellulose acetate propionate was produced using the following dope composition 2. .

(Dope composition 2)
Cellulose acetate propionate 100 parts by weight (acetyl group substitution degree + propionyl group substitution degree = 2.45,
Mn = 60000, Mw = 18000, Mw / Mn = 3.00)
Triphenyl phosphate 8 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Methylene chloride 360 parts by weight Ethanol 60 parts by weight Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 0.5 part by weight Tinuvin 171 (Ciba Specialty Chemicals) 0.5 parts by weight Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd.) 0.2 parts by weight And the stretching ratio is 20% in Example 6, 30% in Example 7, 40% in Example 8, and Example In No. 9, a cellulose acetate propionate film was produced under various conditions of 50%.

  And about the cellulose acetate propionate film of obtained Examples 6-9, tear strength of a film final product width and a film conveyance direction (MD direction), and tear strength of the same width direction (TD direction) Ratio: (MD tear strength / TD tear strength) was measured in the same manner as in Example 1 above. In addition, the shrinkage rate in the film transport direction (MD direction) and the shrinkage rate in the same width direction (TD direction) from peeling off from the metal support to winding up are the same as in Example 1 above. In addition, the sum of the shrinkage rate in the film conveyance direction (MD direction) and the shrinkage rate in the width direction (TD direction): (MD shrinkage rate + TD shrinkage rate) was calculated. The obtained results are shown in Table 1 below.

Comparative Examples 3-6
For comparison, a cellulose acetate propionate film is prepared using the dope composition 2 in the same manner as in Example 6 above. The difference from Example 6 is as shown in Table 1. In Comparative Examples 3 and 4, the stretch ratio was less than 20%, and in Comparative Examples 5 and 6, it was over 60%, which was outside the scope of the present invention.

  And about the obtained cellulose acetate propionate film of Comparative Examples 3-6, tear strength of a film final product width and a film conveyance direction (MD direction), and tear strength of the same width direction (TD direction) Ratio: (MD tear strength / TD tear strength) was measured in the same manner as in Example 1 above. In addition, the shrinkage rate in the film transport direction (MD direction) and the shrinkage rate in the same width direction (TD direction) from peeling off from the metal support to winding up are the same as in Example 1 above. In addition, the sum of the shrinkage rate in the film conveyance direction (MD direction) and the shrinkage rate in the width direction (TD direction): (MD shrinkage rate + TD shrinkage rate) was calculated. The obtained results are shown in Table 1 below.

  Next, using the cellulose ester films of Examples 1 to 9 and Comparative Examples 1 to 6, polarizing plates were produced as described below, and the reworkability of each polarizing plate was evaluated.

(Preparation of polarizing film)
A 120 μm thick polyvinyl alcohol film is immersed in an aqueous solution containing 1 part by weight of iodine, 2 parts by weight of potassium iodide, and 4 parts by weight of boric acid, and stretched 4 times in the transport direction at a temperature of 50 ° C. to produce a polarizer. did. Next, the cellulose triacetate film (polarizing plate protective film) having a film thickness of 60 μm prepared in Examples 1 to 9 and Comparative Examples 1 to 6 is a sodium hydroxide aqueous solution having a concentration of 2.5 mol / L at a temperature of 40 ° C. Each surface was alkali-treated for 60 seconds, further washed with water and dried, and the surface was alkali-treated.

  Next, the alkali-treated surfaces of the cellulose ester film sample of the present invention and the cellulose ester film sample of the comparative example are both rolled onto both sides of the polarizer, using a fully saponified polyvinyl alcohol 5% aqueous solution as an adhesive, and rolled from both sides of the polarizer. Bonding was performed with a toe roll to prepare a polarizing plate according to the present invention and a polarizing plate of a comparative example.

(Evaluation of reworkability)
The polarizing plate according to the present invention produced as described above and the polarizing plate of the comparative example are cut into squares each having a size of 20 cm × 20 cm, and bonded to a glass substrate using an acrylic adhesive. Next, the bonded polarizing plate is peeled off from the glass with a strength of 5 N from the corner. This operation was performed with 100 polarizing plates for one type of sample, and the number of polarizing plates that were not peeled completely due to tears in the polarizing plate was counted. The obtained results are shown in Table 1 below.

  Reworkability was evaluated by ranking according to the following criteria.

A: The number of polarizing plates that were not completely peeled was 0 to 5 ○: The number of polarizing plates that were not completely peeled was 6 to 10 Δ: The number of polarizing plates that were not completely peeled was 11 to 15 sheets ×: The number of polarizing plates that have not been completely peeled is 16 or more. Note that the reworkability of the polarizing plates is practically acceptable as long as it is equal to or higher than Δ, but is equal to or higher than the level of ○. Is preferable, and the level of ◎ is particularly preferable.

  As is clear from the results in Table 1 above, according to the cellulose ester films produced in Examples 1 to 9 of the present invention, the tear strength in the MD direction is obtained by highly stretching in the TD direction in order to take a wide film. Up. In addition, the film produced in Examples 1 to 9 of the present invention is bonded to both sides of the polarizer in a direction perpendicular to the orientation direction of the main constituent molecules of the polarizer, thereby improving the releasability of the film during rework. It was possible to suppress tearing in a specific direction, curl of the polarizing plate, and tearing during rework. Furthermore, a wide width polarizing plate with good reworkability could be obtained. As a result, it has been possible to meet the recent demands for increasing the film width, increasing the screen size of the liquid crystal display device, and improving the quality of the film.

  On the other hand, in the cellulose ester film produced in Comparative Examples 1-6, since rework property is bad, loss increases and cost becomes high, and it becomes difficult to obtain a size for a large screen. This becomes even more prominent with thin films.

It is a schematic longitudinal cross-sectional view of the apparatus which enforces the method to manufacture the optical film of this invention.

Explanation of symbols

1: Endless belt support 2: Casting die 3: Peeling roll 4: Tenter 5: Roll transporting and drying device 7: Transporting roll 10: Web 11: Upper slitter roll 12: Lower slitter roll 13: Embossing ring 14: Back roll 15: Winding device F: Cellulose ester film (optical film)

Claims (7)

  A thermoplastic resin solution (dope) is cast on a metal support by a solution casting film forming method to form a cast film (web), a part of the solvent is evaporated, and then the web is removed from the metal support. It is an optical film produced by peeling, stretching the peeled web in the width direction at a stretch ratio of 20% or more, drying after stretching, and winding the dried film into a roll, The ratio between the tear strength in the MD direction) and the tear strength in the same width direction (TD direction): (MD tear strength / TD tear strength) is 1.1 to 2.0. the film.   Ratio of tear strength in the film conveying direction (MD direction) and tear strength in the same width direction (TD direction): (MD tear strength / TD tear strength) is 1.5 to 2.0. The optical film according to claim 1.   The optical film according to claim 1 or 2, wherein the stretch ratio is 20 to 60%.   The sum of the shrinkage rate in the film transport direction (MD direction) and the shrinkage rate in the same width direction (TD direction) from peeling from the metal support to winding up: (MD shrinkage rate + TD shrinkage rate) is: The optical film according to any one of claims 1 to 3, wherein the optical film is manufactured at 15 to 50%. The shrinkage rate in the film transport direction (MD direction) and the shrinkage rate in the same width direction (TD direction) from peeling from the metal support to winding up,
The optical film according to any one of claims 1 to 4, wherein the optical film is produced under a condition of TD shrinkage> MD shrinkage.   The optical film according to any one of claims 1 to 5, wherein the thermoplastic resin is a cellulose ester.   The optical film as described in any one of Claims 1-6 is bonded together on both surfaces of a polarizer, The polarizing plate characterized by the above-mentioned.

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