JP2007065184A - Optical film, its manufacturing method, polarizing plate using optical film, and liquid crystal display device using polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film which has no unevenness over whole width of the film, has a retardation value of substantially zero and has excellent flatness, to provide a manufacturing method of the optical film and further to provide a polarizing plate using the optical film which can assure a stable retardation value, an image display which has high contrast ratio over a wide range and can realize display being easy to see and a liquid crystal display device which operates especially in an in-plane switching mode. <P>SOLUTION: In the manufacturing method of the optical film by a solution casting film-forming method, a first stretching process is started when residual solvent amount of a web is between 80 weight% and 120 weight% and a second stretching process is started when residual solvent amount of the web is between 10 weight% and 60 weight%. Thereby the optical film in which the retardation value of an in-plane direction (R<SB>0</SB>) is between 0 and 5 and the retardation value of a thickness direction (Rt) is between -10 and 10 is manufactured. <P>COPYRIGHT: (C)2007,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 a film, a manufacturing method thereof, a polarizing plate using an optical film, and a liquid crystal display device using the polarizing plate.

  In recent years, liquid crystal display devices (LCDs) have been developed to be thinner and lighter, larger screens, and higher definition. Along with this, the demand for thinner, wider and higher quality protective films for polarizing plates has become stronger, and the required level of optical film quality has become stricter as the image quality of liquid crystal display devices increases. .

  In general, cellulose ester resin films are widely used as protective films for polarizing plates. However, with the recent trend toward larger screens, a wider film width and a longer film length are required. .

  On the other hand, a liquid crystal display device widely used as a display element is composed of a liquid crystal cell composed of a pair of substrates sandwiching a liquid crystal layer, a pair of polarizing plates arranged in an orthogonal state on both sides of the liquid crystal cell, and the like. Various display modes such as IPS (In-Plane Switching), TN (Twisted Nematic), and VA (Vertically Aligned) have been proposed. In the IPS mode, since the liquid crystal molecules rotate mainly in a plane parallel to the substrate, the difference in the degree of birefringence between when an electric field is applied and when it is not applied is small, and the viewing angle is small. It is known to spread.

  The IPS mode uses liquid crystal molecules that are homogeneously aligned in the horizontal direction and two polarizing plates that are arranged so that the transmission axis is perpendicular to the front and the left and right directions with respect to the front of the screen. When the screen is viewed obliquely from the direction, sufficient contrast can be obtained. On the other hand, when the screen is viewed obliquely from a direction with an azimuth angle of 45 degrees, the transmitted light is birefringent because the angle formed by the transmission axes of the two polarizing plates appears to deviate from 90 degrees. As a result of light leakage, sufficient black cannot be obtained and the contrast is lowered. That is, in the polarizing plate using the cellulose ester-type resin film generally used as a protective film, there existed a problem that a viewing angle became narrow by the birefringence which a film has.

  Conventionally, in the method for producing a cellulose ester-based resin film, in order to express a desired retardation, the film formed is in the same direction as the film transport direction, that is, the machine direction (MD direction) or the direction orthogonal to the transport direction, that is, Stretching in the width direction (TD direction) is performed.

As a method of stretching the film after peeling from the support, those described in the following prior patent documents are known.
Japanese Patent Laid-Open No. 2003-170492 discloses a technique for improving the uniformity of an optical film by adjusting the amount of residual solvent at the start of the stretching process, the temperature, and the stretching ratio. JP-A-2005-134608 discloses a technique for improving the durability of an optical film by adjusting the draw ratio and the film transport tension. JP-A-2005-105140 discloses a technique for obtaining a polymer film having low optical anisotropy by using a specific additive.

  However, the techniques disclosed in Patent Document 1 and Patent Document 2 are both techniques for an optical film having a constant retardation value in the in-plane and thickness directions, and the in-plane and thickness direction retardation values are close to zero. The optical film is not described at all, and there is no description about a technique that has two stretching steps and adjusts the residual solvent amount in each stretching step. Patent Document 3 describes a technique for improving the brittleness of an optical film having a retardation value in the plane and in the thickness direction close to zero by using a specific additive, but has two stretching steps. In addition, there is no mention of a technique for adjusting the residual solvent amount in each stretching step and a technical effect resulting therefrom.

  The object of the present invention is to solve the above-mentioned problems of the prior art, and for an optical film used as a protective film for a liquid crystal display element, that is, a polarizing plate, there is no unevenness across the entire width of the film, and the retardation value is substantially zero Another object of the present invention is to provide an optical film having excellent flatness and a method for producing the same.

  An object of the present invention is an optical film capable of realizing an easy-to-see display having a high contrast ratio over a wide range when applied to an image display device, and can be peeled off even under high temperature and high humidity. And providing an optical film and a polarizing plate capable of ensuring a stable retardation value.

  Further, the object of the present invention is to provide an image display device capable of realizing an easy-to-see display having a high contrast ratio over a wide range, particularly using the polarizing plate of the present invention, particularly a liquid crystal display device operating in an IPS (In-Plan Switching) mode. Is to provide.

  In order to achieve the above object, the invention of claim 1 is characterized in that a dope (resin solution) is cast on a metal rotating drum or a metal rotating endless belt (support) by a solution casting film forming method, and then peeled off. Thereafter, the right and left ends of the continuous resin film (web) are gripped and stretched using a stretching apparatus that transports and stretches the resin film while applying tension in the width direction, and winds the stretched film. The first stretching step is started when the residual solvent amount of the web is 80 to 120% by weight, and the second stretching step is started when the residual solvent amount of the web is 10 to 60% by weight. An in-plane retardation (Ro) value of 0 to 5 and a thickness direction retardation (Rt) value of the film of −10 to 10 are produced.

  Moreover, invention of Claim 2 is a manufacturing method of the optical film of Claim 1, Comprising: Dope (resin solution) contains the cellulose ester-type resin and the additive which reduces thickness direction retardation (Rt). The additive for reducing the thickness direction retardation (Rt) is an additive having a negative intrinsic birefringence.

  Invention of Claim 3 is a manufacturing method of the optical film of Claim 1 or 2, Comprising: A 1st extending | stretching process is a process of extending | stretching a web 1.03 times to 1.3 times in the width direction. The second stretching step is characterized in that the web is stretched from 1.03 times to 1.1 times in the width direction.

  Invention of Claim 4 is a manufacturing method of the optical film as described in any one of Claims 1-3, Comprising: The temperature of a 1st extending | stretching process is 50 degreeC or more and 100 degrees C or less, 2nd The stretching process is characterized in that the temperature is 120 ° C. or higher and 160 ° C. or lower.

  Invention of Claim 5 is a manufacturing method of the optical film as described in any one of Claims 1-4, Comprising: The residual solvent amount at the time of the drying process start after a 2nd extending | stretching process is 2-8. It is characterized by weight percent.

  Invention of Claim 6 is a manufacturing method of the optical film as described in any one of Claims 1-5, Comprising: The conveyance tension in the drying process after a 2nd extending | stretching process is 30 N / m or more and 120 N / M or less.

  Invention of Claim 7 is a manufacturing method of the optical film as described in any one of Claims 1-6, Comprising: The film temperature in the drying process after a 2nd extending | stretching process is 100 degreeC or more and 160 degreeC. It is characterized by the following.

  Invention of Claim 8 is a manufacturing method of the optical film as described in any one of Claims 1-7, Comprising: Cellulose-ester-type resin is a cellulose acetate, It is characterized by the above-mentioned.

  Invention of Claim 9 is a manufacturing method of the optical film as described in any one of Claims 1-8, Comprising: A dope composition reduces cellulose ester-type resin and thickness direction retardation (Rt). The dope composition is cast on a support having a surface temperature of −50 ° C. or more and −10 ° C. or less to form a gel film having self-supporting properties. Thereafter, a continuous resin film (web) peeled from the support by a peeling roller is processed.

  Invention of Claim 10 is a manufacturing method of the optical film as described in any one of Claims 1-9, Comprising: A dope composition is a non-chlorine type organic solvent, a cellulose-ester type resin, and retardation. Reduction additive is mixed, the obtained mixture is cooled at −100 to −10 ° C., and the mixture after cooling is processed at 0 to 120 ° C. It is characterized by processing a continuous resin film (web) cast on a support and peeled off from the support by a peeling roller.

  The invention of an optical film according to an eleventh aspect is characterized by being manufactured by the method for manufacturing an optical film according to any one of the first to tenth aspects.

  The invention of a polarizing plate of claim 12 is a polarizing plate comprising a polarizing film and transparent protective layers disposed on both sides thereof, and at least one of the two transparent protective layers, the optical film according to claim 11. Is used.

  According to a thirteenth aspect of the present invention, there is provided a polarizing plate including a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and transparent protective layers disposed on both sides thereof. A liquid crystal display device having a plate, wherein one of the two polarizing plates has an in-plane retardation (Ro) value of 150 to 300 and a film thickness direction retardation (Rt). ) A value of −20 or more and 20 or less is provided, and another polarizing plate is provided with the optical film according to claim 11.

  According to the method for producing an optical film of the present invention, in producing an optical film, there are two stretching steps, and by adjusting the amount of residual solvent in each stretching step, a retardation value with no unevenness over the entire width of the film is substantially obtained. Can produce an optical film having a low birefringence and excellent flatness suitable for a protective film for a polarizing plate, and can be widely applied when applied to an image display device. It is possible to obtain an optical film that can realize an easy-to-view display with a high contrast ratio, and that can secure a stable retardation value without peeling even under high temperature and high humidity. There is an effect that can be.

  Further, according to the present invention, there is provided an image display device capable of realizing an easy-to-see display having a high contrast ratio over a wide range, particularly using the optical film of the present invention, particularly a liquid crystal display device operating in the IPS mode. There is an effect that can be.

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

  In the method for producing an optical film of the present invention, various resins can be used as a film material, and among them, a cellulose ester resin is preferable.

  The cellulose ester resin is a cellulose ester resin in which a cellulose-derived hydroxyl group 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 group is preferably 1.4 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 direction 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.

  Although there is no limitation in particular as a raw material of the cellulose ester-type resin used for this invention, Cotton linter, wood pulp, kenaf, etc. can be mentioned. Moreover, the cellulose ester-type resin 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 resin is preferably in the range of 60,000 to 300,000, since the mechanical strength of the obtained film is strong. Furthermore, 70000-200000 are preferable.

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

  In the method for producing an optical film according to the present invention, a dope composition containing a cellulose ester resin and an additive for reducing the thickness direction retardation (Rt) is used.

  In the present invention, reducing the thickness direction retardation (Rt) of the optical film is important in terms of widening the viewing angle of the IPS mode liquid crystal display device. In the present invention, such thickness direction retardation (Rt) is used. Examples of the additive for reducing the above include the following.

  In general, retardation of an optical film made of a cellulose ester resin film appears as the sum of retardation derived from a cellulose ester resin and retardation derived from an additive. Therefore, the additive for reducing the retardation of the cellulose ester resin is an agent that disturbs the orientation of the cellulose ester resin and is difficult to orient itself and / or has a small polarizability anisotropy. It is a compound that effectively reduces (Rt). Therefore, an aliphatic compound is preferable to an aromatic compound as an additive for disturbing the orientation of the cellulose ester resin.

  Here, as a specific retardation reducing agent, for example, a polyester represented by the following general formula (1) or (2) may be mentioned.

Formula (1) B _1- (GA-) mG-B ₁
Formula _{(2) B 2 - (G} -A-) nG-B 2
In the above formula, B ₁ represents a monocarboxylic acid component, B ₂ represents a monoalcohol component, G represents a divalent alcohol component, A represents a dibasic acid component, and these are synthesized. . B ₁ , B ₂ , G, and A are all characterized by not containing an aromatic ring. m and n represent the number of repetitions.

Monocarboxylic acid component represented by B _1, not particularly limited, and may be known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid.

  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 a 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 1-12. When acetic acid is contained, the compatibility with the cellulose ester resin is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred monocarboxylic acids include formic acid, 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 , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecinic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

The monoalcohol component represented by B ₂ is not particularly limited ,, and may be a known alcohol. For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a 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 1-12.

  Examples of the divalent alcohol component represented by G include the following, but the present invention is not limited thereto. For example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6- Hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and the like can be mentioned. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol, and triethylene glycol are preferable, and 1,3-propylene glycol, 1,4-butylene Call, 1,6-hexanediol, diethylene glycol is preferably used.

  The dibasic acid (dicarboxylic acid) component represented by A is preferably an aliphatic dibasic acid or an alicyclic dibasic acid. Examples of the aliphatic dibasic acid include malonic acid, succinic acid, glutaric acid, and adipic acid. , Pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like, in particular, aliphatic carboxylic acid having 4 to 12 carbon atoms, at least one selected from these To do. That is, two or more dibasic acids may be used in combination.

  The number of repetitions m and n in the above general formula (1) or (2) is preferably 1 or more and 170 or less.

  The weight average molecular weight of the polyester is preferably 20000 or less, and more preferably 10,000 or less. In particular, a polyester having a weight average molecular weight of 500 to 10,000 has good compatibility with a cellulose ester resin, and neither evaporation nor volatilization occurs in film formation.

  Polycondensation of polyester is carried out by a conventional method. For example, a direct reaction of the dibasic acid and glycol, a hot melt condensation method by the polyesterification reaction or transesterification reaction of the dibasic acid or alkyl esters thereof, for example, a methyl ester of dibasic acid and glycols, or Although it can be easily synthesized by any method of dehydrohalogenation reaction between acid chloride of these acids and glycol, it is preferable that polyester having a weight average molecular weight not so large is by direct reaction. A polyester having a high distribution on the low molecular weight side has a very good compatibility with the cellulose ester resin, and after forming the film, a moisture permeability is small, and a cellulose ester resin film having high transparency can be obtained.

  The method for adjusting the molecular weight is not particularly limited, and a conventional method can be used. For example, although depending on the polymerization conditions, the amount of these monovalent compounds can be controlled by a method of blocking the molecular ends with a monovalent acid or monovalent alcohol. In this case, a monovalent acid is preferable from the viewpoint of polymer stability. For example, acetic acid, propionic acid, butyric acid, etc. can be mentioned, but during the polycondensation reaction, it is not distilled out of the system, but is stopped and such monovalent acid is removed from the reaction system. The one that is easy to accumulate is selected. These may be used in combination. In the case of direct reaction, the weight average molecular weight can also be adjusted by measuring the timing of stopping the reaction by the amount of water distilled off during the reaction. In addition, it can be adjusted by biasing the number of moles of glycol or dibasic acid to be charged, or can be adjusted by controlling the reaction temperature.

  The polyester represented by the general formula (1) or (2) is preferably contained in an amount of 1 to 40% by weight based on the cellulose ester resin. It is particularly preferable to contain 5 to 15% by weight.

  In the present invention, examples of the additive for reducing the thickness direction retardation (Rt) include the following.

  The dope used in the production of the optical film of the present invention is mainly composed of a cellulose ester resin, a polymer as an additive for reducing retardation (Rt) (a polymer obtained by polymerizing an ethylenically unsaturated monomer, an acrylic polymer). ), And an organic solvent.

  In the present invention, in order to synthesize a polymer as an additive for reducing the thickness direction retardation (Rt), it is difficult to control the molecular weight in normal polymerization, and a method that can make the molecular weight as uniform as possible by a method that does not increase the molecular weight too much. It is desirable to use it. Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and JP-A No. 2000-128911 or JP-A No. 2000-344823. Examples include a compound having a single thiol group and a secondary hydroxyl group as described in the publication, or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. In particular, the method described in the publication is preferred.

  In the present invention, monomers as monomer units constituting a polymer as an additive for reducing useful thickness direction retardation (Rt) are listed below, but are not limited thereto.

  As the ethylenically unsaturated monomer unit constituting the polymer as an additive for reducing the thickness direction retardation (Rt) obtained by polymerizing an ethylenically unsaturated monomer, first, as a vinyl ester, for example, vinyl acetate, propionic acid, etc. Vinyl, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, Examples include vinyl crotonate, vinyl sorbate, vinyl benzoate, and vinyl cinnamate.

  Next, as acrylate ester, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate ( n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), cyclohexyl acrylate, acrylic acid (2-ethylhexyl), benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl) ), Acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2- Dorokishibuchiru) acrylate-p-hydroxymethylphenyl,-p-acrylic acid (2-hydroxyethyl) phenyl and the like; as methacrylic acid ester, the acrylic acid ester include those changed to methacrylic acid esters.

  Furthermore, examples of the unsaturated acid include acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid, and the like.

  The polymer composed of the above monomers may be a copolymer or a homopolymer, and is preferably a vinyl ester homopolymer, a vinyl ester copolymer, or a copolymer of vinyl ester and acrylic acid or methacrylic acid ester.

  In the present invention, an acrylic polymer (simply referred to as an acrylic polymer) refers to a homopolymer or copolymer of acrylic acid or alkyl methacrylate having no monomer unit having an aromatic ring or a cyclohexyl group.

  Examples of the acrylate monomer having no aromatic ring and cyclohexyl group include, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-) , Nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic acid (2-ethylhexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid 2-methoxy-ethyl), acrylic acid (2-ethoxyethyl), or the acrylic acid ester may include those obtained by changing the methacrylic acid ester.

  The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30% by weight or more, and the methacrylic acid methyl ester monomer unit has 40% by weight or more. It is preferable. In particular, a homopolymer of methyl acrylate or methyl methacrylate is preferred.

  Polymers obtained by polymerizing the above ethylenically unsaturated monomers and acrylic polymers are both excellent in compatibility with cellulose ester resins, excellent in productivity without evaporation and volatilization, and as protective films for polarizing plates. Good holdability, low moisture permeability, and excellent dimensional stability.

  In the present invention, an acrylic acid or methacrylic acid ester monomer having a hydroxyl group is not a homopolymer but a constituent unit of a copolymer. In this case, the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is preferably contained in the acrylic polymer in an amount of 2 to 20% by weight.

  In the method for producing an optical film of the present invention, the dope composition contains a cellulose ester resin and an acrylic polymer having a weight average molecular weight of 500 or more and 3000 or less as an additive for reducing the thickness direction retardation (Rt). It is preferable.

  In the method for producing an optical film of the present invention, the dope composition comprises a cellulose ester resin and an acrylic polymer having a weight average molecular weight of 5,000 to 30,000 as an additive for reducing the thickness direction retardation (Rt). It is preferable to contain.

  In the present invention, if the weight average molecular weight of the polymer as an additive for reducing the thickness direction retardation (Rt) is 500 or more and 3000 or less, or if the polymer has a weight average molecular weight of 5000 or more and 30000 or less, the cellulose ester resin Is compatible with the material, and neither evaporation nor volatilization occurs during film formation. Moreover, the transparency of the cellulose ester-based resin film after film formation is excellent, the moisture permeability is extremely low, and excellent performance as a protective film for a polarizing plate is exhibited.

  In the present invention, a polymer having a hydroxyl group in the side chain can also be preferably used as an additive for reducing the thickness direction retardation (Rt). The monomer unit having a hydroxyl group is the same as the monomer described above, but acrylic acid or methacrylic acid ester is preferable. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids. The thing replaced by methacrylic acid can be mentioned, Preferably, it is 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. The acrylic acid ester or methacrylic acid ester monomer unit having a hydroxyl group in the polymer is preferably contained in the polymer in an amount of 2 to 20% by weight, more preferably 2 to 10% by weight.

  A polymer containing 2 to 20% by weight of the above-mentioned monomer unit having a hydroxyl group is, of course, excellent in compatibility with cellulose ester resin, retention property, dimensional stability, and low moisture permeability. In particular, it has excellent adhesiveness with a polarizer as a protective film for a polarizing plate, and has an effect of improving the durability of the polarizing plate.

  In the present invention, it is preferable that at least one terminal of the main chain of the polymer has a hydroxyl group. The method of having a hydroxyl group at the end of the main chain is not particularly limited as long as it has a hydroxyl group at the end of the main chain, but radical polymerization having a hydroxyl group such as azobis (2-hydroxyethylbutyrate). A method of using an initiator, a method of using a chain transfer agent having a hydroxyl group such as 2-mercaptoethanol, a method of using a polymerization terminator having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ion polymerization, Using a polymerization catalyst in which a compound having one thiol group and a secondary hydroxyl group as disclosed in JP-A No. 2000-128911 or JP-A No. 2000-344823, or a combination of the compound and an organometallic compound is used. It can be obtained by a polymerization method or the like, and the method described in the publication is particularly preferable. The polymer produced by the method related to the description in this publication is commercially available as Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used.

  In the present invention, the polymer having a hydroxyl group at the terminal and / or the polymer having a hydroxyl group in a side chain has an effect of significantly improving the compatibility and transparency of the polymer with respect to the cellulose ester resin.

  In the present invention, useful additives for reducing the thickness direction retardation (Rt) include, in addition to the above, for example, an ester compound of diglycerin polyhydric alcohol and fatty acid described in JP-A No. 2000-63560, An ester or ether compound of a hexose sugar alcohol described in JP-A-2001-247717, a trialiphatic alcohol phosphate compound described in JP-A-2004-315613, and a general formula (1) described in JP-A-2005-41911 A phosphoric acid ester compound described in JP-A No. 2004-315605, a styrene oligomer described in JP-A No. 2005-105139, and a polymer of a styrene monomer described in JP-A No. 2005-105140. .

  Furthermore, examples of the additive for reducing the thickness direction retardation (Rt) useful in the present invention include compounds described in paragraphs [0031] to [0100] in the specification of JP-A No. 2005-154664.

  Moreover, as an additive used for this invention, the thing with high compatibility with a cellulose acylate and a plasticizing effect is preferable. For example, the low molecular weight compounds described in paragraphs [0011] to [034] in the specification of JP-A-2005-138375 can also be preferably used.

  In the present invention, an additive for reducing the thickness direction retardation (Rt) can also be found by the following method.

  A dope formulation in which a cellulose ester resin is dissolved in methylene chloride is formed on a glass plate and dried at 120 ° C./15 min to prepare a cellulose ester resin film having a thickness of 80 μm. The retardation in the thickness direction of the cellulose ester-based resin film is measured, and this is defined as Rt1.

  Next, 10% by weight of the above polymer additive is added to the cellulose ester resin and dissolved in methylene chloride to prepare a dope formulation. A cellulose ester resin film having a film thickness of 80 μm is prepared in the same manner as described above for this dope formulation. The retardation in the thickness direction of the cellulose ester-based resin film is measured, and this is defined as Rt2.

And the relationship of retardation in the thickness direction of the above two cellulose ester resin films is Rt2 <Rt1
If so, it can be said that the polymer additive added to the cellulose ester-based resin is an additive for reducing the thickness direction retardation (Rt).

  In the present invention, the thickness direction retardation (Rt) of the cellulose ester-based resin is −10 nm to +10 nm, preferably −5 nm to +5 nm. Here, in either case where the thickness direction retardation (Rt) of the cellulose ester resin is smaller than −10 nm or larger than +10 nm, the viewing angle is narrowed, and the effect of the present invention does not appear.

  In the present invention, the in-plane retardation (Ro) of the cellulose ester resin is 0 nm to +5 nm, preferably 0 nm to +2 nm. Particularly preferably, it is about 0 nm. Here, in any case where the in-plane retardation (Ro) is larger than +5 nm, the viewing angle becomes narrow and the effect of the present invention does not appear.

  In the method of the present invention, the solvent used for dissolving the cellulose ester may be used alone or in combination, but it is preferable to use a mixture of a good solvent and a poor solvent in terms of increasing production efficiency, and the more good solvent, This is preferable from the viewpoints of the solubility of cellulose ester and the reduction of film foreign matter due to minute insoluble matter. The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by weight for the good solvent and 30 to 2% by weight for the poor solvent.

  Here, the good solvent and the poor solvent used in the present invention define a good solvent that dissolves the cellulose ester used alone, and a poor solvent that swells or does not dissolve alone.

  The good solvent used in the present invention is not particularly limited. For example, in the case of cellulose triacetate, organic halogen compounds such as methylene chloride and dioxolanes, and in the case of cellulose acetate propionate, methylene chloride, acetone, methyl acetate, etc. Can be mentioned. Moreover, it is although it does not specifically limit as a poor solvent, For example, methanol, ethanol, i-propyl alcohol, n-butanol, cyclohexane, acetone, cyclohexanone etc. are used preferably.

  By the way, in recent years, the use of chlorinated hydrocarbon solvents such as methylene chloride is in the direction of being restricted from the viewpoint of protecting the global environment, and there is a desire to avoid the use of chlorinated hydrocarbon solvents such as methylene chloride. Is growing.

  In the method of the present invention, it is preferable to use a non-chlorine organic solvent as the solvent for the cellulose ester resin.

  Here, examples of the non-chlorine organic solvent include acetone, methyl acetate (MA), cyclohexanone, ethyl formate, 1,3-dioxolane, 2,2,2-trifluoroethanol, 2,2,3,3- Tetrafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3 Examples include 3-hexafluoro-2-propanol and 2,2,3,3,3-pentafluoro-1-propanol. These solvents may be used alone or in combination of two or more.

  Among these, methyl acetate and acetone are most preferable as the non-chlorine organic solvent. Methyl acetate and acetone can obtain a film having good solubility and excellent transparency.

  In the present invention, when a cellulose ester resin is dissolved in a non-chlorine organic solvent to prepare a cellulose ester resin solution, the blending weight ratio of the non-chlorine organic solvent to the cellulose ester resin is 2 or more and 5 or less. The blending weight ratio of the non-chlorine organic solvent to the cellulose ester resin is preferably 2.5 or more and 4.5 or less, and more preferably 3 or more and 4 or less.

  In the present invention, the cellulose ester resin solution is a lower one having 1 to 6 carbon atoms for the purpose of improving solubility, adjusting viscosity, adjusting drying speed, and promoting gelation when the solution is cast. Alcohol may be included. Examples of these lower alcohols include methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, isobutyl alcohol, 2-butanol, t-butyl alcohol, and cyclohexanol. Of these, methanol, ethanol, and 1-butanol are preferable. These lower alcohols are preferably contained in an amount of 2 to 20% by weight based on the total organic solvent. A cellulose ester solution containing a lower alcohol having 1 to 6 carbon atoms has a strong film strength even when it contains a large amount of residual solvent during casting, and is a belt or drum that is a support used for casting. Easy to peel off from above.

  In the present invention, it is preferable to add a so-called plasticizer in order to improve dimensional stability under wet heat. It has not been known so far that a plasticizer has an effect of improving dimensional stability under wet heat. As the plasticizer, conventionally known plasticizers for cellulose ester resins can be preferably used. In particular, those having excellent compatibility are preferred, and for example, phosphate esters and carboxylic acid esters are preferred. Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like. Examples of carboxylic acid esters include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate, diethyl phthalate, dioctyl phthalate, and diethyl hexyl phthalate. Citric acid esters include acetyltriethyl citrate and acetyl citrate. Mention may be made of tributyl. In addition, butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, triacetin, and the like are also included. Alkylphthalylalkyl glycolates are also preferably used for this purpose. The alkyl in the alkylphthalylalkyl glycolate is an alkyl group having 1 to 8 carbon atoms. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl glycolate, Ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, propyl phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl Phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl Collate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate and the like can be mentioned, such as methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, Octyl phthalyl octyl glycolate is preferable, and ethyl phthalyl ethyl glycolate is particularly preferably used. A plasticizer having a large molecular weight is preferable because it can suppress volatilization during extrusion. Examples of these include aliphatic polyesters composed of glycol and dibasic acids such as polyethylene adipate, polybutylene adipate, polyethylene succinate and polybutylene succinate, and fats composed of oxycarboxylic acids such as polylactic acid and polyglycolic acid. Aliphatic polyesters composed of lactones such as aromatic polyesters, polycaprolactone, polypropiolactone and polyvalerolactone, and vinyl polymers such as polyvinylpyrrolidone. These plasticizers can be used alone or in combination.

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

  Examples of ultraviolet absorbers that can be used in the present invention include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. A benzotriazole-based compound with little coloring is preferable. Further, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574, and polymer ultraviolet absorbers described in JP-A-6-148430 are 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 UV absorbers useful 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'- ert-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- (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 UV absorption effect may be insufficient, and if it is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

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

  As the antioxidant, a hindered phenol compound is preferably used, and 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl- 4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5 -Di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3,5 -Triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3 -Di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl -2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate, etc. Can be mentioned. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination.

  In 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.

  The average particle diameter of the fine particles refers to the average value of the lengths of the particles in the major axis direction when the cellulose ester resin film is observed with an electron microscope or an optical microscope. 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 the important thing is that the fine particles finally become cellulose ester resin in the film. It is to control the particle diameter formed by aggregation and aggregation.

  When the average particle diameter 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 resin. 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 device as described above include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other manton gorin type high-pressure dispersing devices such as those manufactured by Izumi Food Machinery. A homogenizer etc. are mentioned.

  The method for producing an optical film according to the present invention is a method in which a dope (resin solution) is cast on a metal rotating drum or a metal rotating endless belt (support) by a solution casting film forming method. The web is stretched by using a stretching apparatus that stretches the web by stretching the resin film while gripping the left and right ends of the web and applying tension in the width direction.

  In the method for producing an optical film of the present invention, the dope (resin solution) contains a cellulose ester resin and an additive for reducing the thickness direction retardation (Rt), and reduces the thickness direction retardation (Rt). The additive is preferably an additive having a negative intrinsic birefringence.

  Moreover, in the manufacturing method of the optical film of this invention, it is preferable that cellulose-ester-type resin is a cellulose acetate.

  When the method for producing an optical film of the present invention is carried out by a solution casting film forming method, although not shown, an endless metal belt for infinitely transferring a dope that is a raw material solution of a cellulose ester film by a casting die Alternatively, it is cast on a rotating metal drum casting support. The dope film, that is, the web formed on the support by casting is peeled off by a peeling roll when it has made a full turn on the support. The peeled web (film) is then introduced into a stretching device comprising a tenter.

  The casting step is a step in which, for example, the dope is fed to a pressure die through a pressurized metering gear pump, and the dope is cast from the pressure die onto the support at the casting position. The surface of the casting support is a mirror surface.

  Other casting methods include a doctor blade method in which the film thickness of the cast dope film is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll. A pressure die that can be prepared and facilitates uniform film thickness is preferred. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

  Moreover, in the manufacturing method of the cellulose-ester-type resin film by this invention, when forming a cellulose-ester-type resin film by the solution casting film-forming method, it is preferable to use a cellulose acylate resin as a resin material of a film.

  To adjust the film thickness, it is necessary to control the dope concentration, the pumping amount of the pump, the slit gap of the die base, the extrusion pressure of the die, the speed of the casting support, etc. so as to obtain the desired thickness. Good.

  Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

  In the method for producing an optical film of the present invention, the dope composition is a mixture of a non-chlorine organic solvent, a cellulose ester resin, and a retardation reducing additive, and the resulting mixture is at −100 to −10 ° C. A continuous resin film produced by subjecting the mixture to a cooling treatment and treating the mixture after the cooling treatment at 0 to 120 ° C., casting the dope composition on the support, and peeling the dope composition from the support by a peeling roller. It is preferable to process (web).

  Here, the cooling temperature of a mixture should just be the temperature more than the freezing point of a solvent, and the temperature range of -100--10 degreeC is preferable from the point of solubility and the temperature which is easy to handle. When this cooled mixture is heated to a temperature of 0 to 120 ° C., the cellulose ester resin is dissolved in the solvent, and a uniform solution is obtained. In order to accelerate dissolution, the cooling and heating operations may be repeated. Whether the dissolution is sufficient or not can be judged by visually observing the appearance of the solution. In the cooling and dissolving method, it is preferable to use a sealed container in order to avoid mixing of moisture due to condensation during cooling. Further, in the cooling operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be further shortened. In order to perform pressurization and pressure reduction, it is preferable to use a pressure-resistant container.

  In the method for producing an optical film of the present invention, the dope composition contains a cellulose ester-based resin, an additive for reducing the thickness direction retardation (Rt), and an organic solvent. After casting on a support having a surface temperature of −50 ° C. or more and −10 ° C. or less to form a self-supporting gel film, a continuous resin film (web) peeled from the support by a peeling roller is processed. It is preferable.

  In this case, for example, it is preferable to provide a flow path for a cooling medium (refrigerant) inside the rotating drum and its rotating shaft. By supplying a refrigerant as an antifreeze heat medium to the flow path, the rotating drum and The rotating shaft is cooled. In the present invention, the surface temperature of the rotating drum is preferably -10 ° C or lower, more preferably -30 ° C or lower, most preferably -50 ° C.

  Here, as the refrigerant, for example, a glycol refrigerant, a fluorine refrigerant, an alcohol refrigerant, or the like is used.

  In the solvent evaporation step, the web (dope film) is heated on the casting support to evaporate the solvent. In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. Drying efficiency is preferred. A method of combining them is also preferable. The web on the support after casting is preferably dried on the support in an atmosphere at a temperature of 20 to 100 ° C. In order to maintain the atmosphere at a temperature of 20 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or to heat by means such as infrared rays.

  In the peeling step, the web in which the solvent has evaporated on the support is peeled off from the support at the peeling position. The peeled web is sent to the next process. If the residual solvent amount of the web at the time of peeling (the following formula) is too large, it will be difficult to peel, or conversely, if it is peeled off after sufficiently drying on the support, part of the web will be peeled off .

  The temperature at the peeling position on the support is preferably 10 to 40 ° C, more preferably 11 to 30 ° C. The residual solvent amount of the web at the peeling position is preferably 60 to 125% by weight.

  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 is the weight of the web at an arbitrary time point, and N is the weight when the weight M is dried at 110 ° C. for 3 hours.

  In order to adjust the residual solvent amount at the time of peeling as described above, the surface temperature of the casting support after casting is controlled, and the casting of the organic solvent from the web can be performed efficiently. It is preferable to set the temperature at the peeling position on the support for the above-mentioned temperature range. In order to control the temperature of the support, it is preferable to use a heat transfer method with good heat transfer efficiency. For example, a back surface heat transfer method using a liquid is preferable.

  In the web (film) drying process, in general, a pin tenter method in which both ends of the peeled web are held by pins (needle) and dried while being transported by the pin tenter, and both ends of the peeled web. A clip tenter method is known in which a paper is held by a clip and dried while being transported.

  The tenter stretching device is provided with, for example, a pair of left and right rotational drive devices (ring-shaped chains) formed of endless chains wound around front and rear sprockets on both left and right sides of the housing, and a number of pins or clips are provided on these rotational drive devices. Are provided in a single row state.

  Here, a large number of pins or clips are connected to each other to finally form a ring-shaped chain, which travels on a guide rail (like a monorail of a vehicle). These chains are “stretched” so that they do not loosen under pressure, and the rails are structured to change according to the length of the chain.

  This chain tensioning equipment is called a tensioner, and the overall tension of the ring chain is changed by changing the tension of the chain on the left and right.

  Then, the left and right edges of the film are supported by the pins or clips of the tenter, and are introduced into the entrance of the tenter in this state. In the tenter, the left and right edges of the film are stretched by being supported by pins or clips on the left and right sides of the tenter, and the film is dried while being transported together.

  The optical film manufacturing method of the present invention is characterized in that, in the optical film manufacturing method, the first stretching step is started when the residual solvent amount of the web is 80 to 120% by weight, and the residual solvent amount of the web is 10 to 60. By starting the second stretching step by weight%, the in-plane direction retardation (Ro) value of the film is 0 or more and 5 or less, and the thickness direction retardation (Rt) value of the film is −10 or more and 10 or less. It is to produce a film.

  Here, in the method for producing an optical film of the present invention, it is preferable that the first stretching step of the web is performed by a pin tenter method and the second stretching step of the web is performed by a clip tenter method.

  In the present invention, the retardation value of the film is measured by three-dimensional refractive index measurement at a wavelength of 590 nm using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), and the obtained refractive indexes Nx and Ny. , Nz.

Ro = (Nx−Ny) × d
Rt = ((Nx + Ny) / 2−Nz) × d
(In the formula, Nx, Ny, and Nz represent the refractive indexes in the principal axes x, y, and z, respectively, of the refractive index ellipsoid, and Nx, Ny represent the refractive index in the film in-plane direction, and Nz represents the thickness direction of the film. In addition, Nx ≧ Ny, and d represents the thickness (nm) of the film.
In the present invention, the cellulose ester-based resin film has an angle θ (radian) formed between the slow axis direction and the film forming direction and a retardation value (Ro) in the in-plane direction, and in particular, a protective film for a polarizing plate. It is preferably used as a cellulose ester resin film.

P ≦ 1-sin ² (2θ) sin ² (πRo / λ)
Here, P is 0.9999 or less.

  θ is the angle (° radians) formed between the slow axis direction in the film plane and the film forming direction (straight scale direction of the film), and λ is the three-dimensional refractive index measurement for determining Nx, Ny, Nz, and θ. The wavelength of light is 590 nm, and π is the circumference.

In the method for producing an optical film of the present invention, the first stretching step is a step of stretching the web in the width direction by 1.03 times to 1.3 times, and the second stretching step is a width of the web. It is preferably a step of stretching 1.03 times to 1.1 times in the direction.

  In the method for producing an optical film of the present invention, the temperature in the first stretching step is preferably 50 ° C. or higher and 100 ° C. or lower, and the temperature in the second stretching step is preferably 120 ° C. or higher and 160 ° C. or lower.

  In the method for producing an optical film of the present invention, the residual solvent amount at the start of the drying step after the second stretching step is preferably 2 to 8% by weight.

  In the manufacturing method of the optical film of this invention, it is preferable that the conveyance tension in the drying process after a 2nd extending | stretching process is 30 N / m or more and 120 N / m or less.

  In the manufacturing method of the optical film of this invention, it is preferable that the film temperature in the drying process after a 2nd extending | stretching process is 100 degreeC or more and 160 degrees C or less.

  After stretching, the film is fed into the drying device, transported through all the transport rolls arranged in a staggered manner in the housing of the drying device, and dried by the drying air blown from the drying air blowing port during the transport. By making it, a cellulose-ester film is obtained and this film is wound up by a winding roll.

  In addition, the conveyance speed of a film is 2-200 m / min normally, Preferably it is 10-100 m / min.

  Since the retardation film according to the present invention is composed of the optical film produced by the method according to the present invention, the alignment angle is uniform in the width direction (TD direction) over almost the entire region of the film, and excellent retardation compensation. Has performance and viewing angle expansion function.

  Moreover, since the optical film according to the present invention is manufactured by the method according to the present invention and the resin film is made of a cellulose ester film, the orientation angle is also in the width direction (TD direction) over almost the entire area of the film. ) With uniform and excellent phase difference compensation performance and viewing angle expansion function.

  In the film drying step, generally, a method of drying while transporting the film by a roll suspension method or the pin tenter method as described above is adopted. The means for drying the film is not particularly limited, and is generally performed with hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to carry out with hot air in terms of simplicity. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably carried out from about 8% by weight or less of residual solvent. Throughout the whole, the drying temperature is approximately 40 to 250 ° C. It is particularly preferable to dry at 40 to 160 ° C.

  Maintaining the conveyance tension in the drying step as low as possible is preferable because the retardation value (Ro) can be maintained low, and is preferably 190 N / m or less. Further, it is preferably 170 N / m or less, more preferably 140 N / m or less, and particularly preferably 100 to 130 N / m. In particular, it is effective to maintain the conveyance tension or less until the residual solvent amount in the film is at least 5% by weight or less.

  In the process from immediately after casting through the solution casting film forming method to drying, the atmosphere in the drying apparatus may be air, but may be performed in an inert gas atmosphere such as nitrogen gas, carbon dioxide gas, or argon. Good.

  Of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be taken into account.

  The winding step is a step of winding as a cellulose ester resin film after the residual solvent amount in the web is 2% by weight or less, and the dimensional stability is reduced by making the residual solvent amount 0.4% by weight or less. A good film can be obtained.

  As a winding method, a generally used method may be used. There are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

  Next, the polarizing plate according to the present invention is a polarizing plate comprising a polarizing film and a transparent protective layer disposed on both sides thereof, and at least one of the two transparent protective layers includes the above-described optical film of the present invention. It is preferably used.

  By using the protective film for a polarizing plate comprising the optical film of the present invention, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as thinning.

  Here, the polarizing film is obtained by longitudinally stretching a conventionally used film, such as a polyvinyl alcohol film, that can be stretched and oriented with a dichroic dye such as iodine. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose triacetate film having no anisotropy as a protective film to both sides thereof.

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

  A liquid crystal display device according to the present invention includes two liquid crystal cells each having a rod-like liquid crystal molecule sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and transparent protective layers disposed on both sides thereof. A liquid crystal display device having a polarizing plate, wherein one of the two polarizing plates has an in-plane direction retardation (Ro) value of 150 or more and 300 or less and a film thickness direction retardation ( An optical film having an Rt) value of −20 or more and 20 or less is provided, and another polarizing plate is provided with the optical film according to claim 11.

  According to the liquid crystal display device of the present invention, an easy-to-see display having a high contrast ratio over a wide range can be realized, and in particular, a liquid crystal display device operating in the IPS mode is provided. Stable display performance can be maintained over a period.

  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
By the method of the present invention, an optical film made of cellulose triacetate resin by a solution casting film forming method was produced.

(Preparation of dope)
A cellulose acetate dope was prepared as follows.

Cellulose triacetate 100 parts by weight Methylene chloride 300 parts by weight Ethylphthalylethylglycoate 2 parts by weight Retardation lowering additive made of acrylic resin 10 parts by weight Ethanol 40 parts by weight Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 1 part by weight AEROSIL 972V (manufactured by Nippon Aerosil Co., Ltd.) 0.1 part by weight The retardation reducing additive made of an acrylic resin is manufactured as follows.

Methyl acrylate 10 parts by weight 2-Hydroxyethyl acrylate 1 part by weight Azobisisobutyronitrile (AIBN) 2 parts by weight Toluene 30 parts by weight The above materials are put in a sealed container sequentially, and the temperature in the container is changed from 20 ° C. After heating up to 80 degreeC, it stirred for 3 hours, keeping temperature at 80 degreeC, and the cellulose triacetate was melt | dissolved completely. Then, stirring was stopped and the liquid temperature was lowered to 43 ° C. The dope was filtered using a filter paper (Azumi filter paper No. 244, manufactured by Azumi Filter Paper Co., Ltd.) to obtain a dope.

  The dope prepared as described above is cast through a casting die kept at 30 ° C. onto a 30 ° C. support made of a stainless steel endless belt to form a web (dope film), and finally, After drying on the support until the amount of residual solvent in the web reached 110% by weight, the web was peeled from the support with a peeling roll.

  Next, the web was dried with a drying air at 120 ° C., and the residual solvent amount was 100% by weight, and was introduced into the first stretching step. In the first stretching process, both ends of the web were gripped by a web gripping device and stretched 1.2 times in the width direction (TD direction).

  Subsequently, the residual solvent amount was 50% by weight and was introduced into the second stretching step. In the second stretching step, stretching was performed 1.05 times in the width direction (TD direction).

  Furthermore, the web was dried at 110 ° C. while being conveyed at 80 N / m in the drying step, and wound with a winder to finally produce a cellulose triacetate film having a thickness of 40 μm.

  Table 1 below shows the stretching ratio (times) in the first stretching step and the residual solvent amount (% by weight) at the start of stretching, and the stretching ratio (times) in the second stretching step and the residual solvent amount at the start of stretching. (% By weight).

Examples 2-6
A cellulose triacetate film having a film thickness of 40 μm is produced in the same manner as in Example 1 above, but the stretching ratio (times) in the first stretching step, the residual solvent amount (% by weight) at the start of stretching, and the second stretching. The conditions of the stretching ratio (times) in the process and the residual solvent amount (% by weight) at the start of stretching were changed as shown in Table 1 below, and the method of the present invention was carried out.

Comparative Examples 1-7
Next, for comparison, a cellulose triacetate film having a film thickness of 40 μm is produced in the same manner as in Example 1 above. As shown in Table 1 below, the stretch ratio in the first stretching step (times) And the residual solvent amount (% by weight) at the start of stretching, and the stretching rate (times) in the second stretching step and the residual solvent amount (% by weight) at the start of stretching are outside the scope of the present invention. A cellulose triacetate film was produced.

  Thus, about the cellulose triacetate film produced in Examples 1-6 and Comparative Examples 1-7, while evaluating retardation, the flatness of a film was evaluated as follows, respectively, and the obtained result was obtained. The results are shown in Table 1 below.

(Evaluation of retardation)
The cellulose triacetate films prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were cut into 200 mm squares, and the temperature was 23 ° C. and the humidity was 55% using an automatic birefringence meter KOBRA-21-ADH (manufactured by Oji Scientific Instruments). Under the RH environment, the refractive indexes Nx, Ny, and Nz at a wavelength of 590 nm were obtained at a pitch of 5 mm, and the retardation in the film plane direction (Ro) and the retardation in the thickness direction (Rt) were calculated according to the following formulas. .

Ro = (Nx + Ny) × d
Rt = ((Nx + Ny) / 2−Nz) × d
Here, Nx represents the refractive index in the slow axis direction in the film plane, Ny represents the refractive index in the fast axis direction in the film plane, and d represents the thickness (nm) of the film.

(Evaluation of film flatness)
Regarding the flatness of the film, the cellulose triacetate films prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were visually observed, and the flatness was evaluated in the following four stages.

A: No unevenness was observed on the film. B: A slight unevenness was observed on the film. C: Unevenness was observed on the film. D: Large unevenness was observed on the film. 1 is shown collectively.

  As is clear from the results in Table 1 above, the cellulose triacetate films produced in Examples 1 to 6 of the present invention all have a retardation (Ro) value in the film in-plane direction and a retardation (Rt) value in the thickness direction. It was low. Moreover, the planarity of the cellulose triacetate film was good.

  As described above, according to the method for producing a cellulose triacetate film according to the embodiment of the present invention, in producing an optical film, there are two stretching steps, and by adjusting the residual solvent amount in each stretching step, the entire film width is adjusted. An optical film having a substantially zero retardation value could be produced, and an optical film having a small birefringence and excellent flatness suitable for a protective film for a polarizing plate could be obtained.

  On the other hand, in Comparative Examples 1-7, the desired retardation value of the cellulose triacetate film was not obtained, and the flatness of the film was inferior. In Comparative Example 1 and Comparative Example 2, the second stretching step was not performed. In Comparative Example 7, a cellulose triacetate film could not be produced.

Example 7
A cellulose triacetate film having a film thickness of 40 μm is produced in the same manner as in Example 1 above. As shown in Table 2 below, the temperature and tension of the drying step after the second stretching step are set as shown in Table 2 below. The cellulose triacetate film was manufactured by changing.

Comparative Examples 8-10
Next, for comparison, a cellulose triacetate film having a film thickness of 40 μm is produced in the same manner as in Example 1 above. As shown in Table 2 below, Example 1 is subjected to the second stretching step. The cellulose triacetate film was produced by changing the temperature and tension in the drying step so that the temperature and tension were outside the scope of the present invention.

Thus, the cellulose triacetate films produced in Examples 1 and 7 and Comparative Examples 8 to 10 were obtained in the same manner as in Example 1 above, while evaluating the retardation and evaluating the flatness of the film. The results are shown in Table 2 below.

  As is clear from the results in Table 1 above, the cellulose triacetate films prepared in Examples 1 and 7 of the present invention both have a retardation (Ro) value in the film in-plane direction and a retardation (Rt) value in the thickness direction. It was low. Moreover, the planarity of the cellulose triacetate film was good.

  On the other hand, in Comparative Examples 8 to 10, the desired retardation value of the cellulose triacetate film was not obtained, and the flatness of the film was inferior.

  In Comparative Example 8, the film could not be obtained on the web. In Comparative Example 9, a uniform cellulose triacetate film was not obtained, and the flatness of the film could not be evaluated.

Example 8
By the method of the present invention, an optical film made of cellulose acetate resin by a solution casting film forming method was produced.

(Dope adjustment)
A cellulose acetate dope was prepared as follows.

Cellulose acetate 100 parts by weight Methylene chloride 300 parts by weight Methanol 40 parts by weight Butanol 20 parts by weight Ethylphthalylethylglycoate 2 parts by weight Low molecular weight compound additive represented by the following formula (1) 10 parts by weight Tinuvin 326 (Ciba Specialty) Chemicals) 1 part by weight AEROSIL 972V (Nippon Aerosil Co., Ltd.) 0.1 parts by weight

  The above materials are sequentially put into a sealed container, the temperature in the container is stirred at 25 ° C. for 3 hours, then cooled at −75 ° C. for 3 minutes, then heated up and stirred at 50 ° C. for 2 hours, Cellulose acetate was completely dissolved. The dope was filtered using a filter paper (Azumi filter paper No. 244, manufactured by Azumi Filter Paper Co., Ltd.) to obtain a dope. This dope was cast on a drum support having a diameter of 3 m set at -5 ° C. The cast film was peeled off when the residual solvent amount in the web was 110% by weight.

  Subsequently, in the first stretching step, the web was stretched 1.2 times in the width direction (TD direction) while carrying the web with the residual solvent amount of 100% by weight and carrying both ends of the web by the pin tenter method.

  Subsequently, the web (film) was introduced into the second stretching step. In the second stretching step, the amount of residual solvent was 50% by weight, and both ends of the web were stretched 1.05 times while being carried and transported by the clip tenter method. The web thus obtained was dried while being conveyed with a drying air of 130 ° C. and a tension of 100 (N / m).

  Thus, about the obtained cellulose acetate film, while evaluating retardation similarly to the case of the said Example 1, the planarity of a film is evaluated and in-plane direction retardation (Ro) = 0, thickness direction retardation (Rt) ) =-3. Moreover, the evaluation rank of the planarity of the obtained cellulose acetate film was “A”.

  Next, the polarizing plate 1 was produced using the cellulose acetate film produced in Example 8 on the liquid crystal side. On the other hand, a polarizing plate 2 having an optical film of in-plane direction retardation (Ro) = 250 and thickness direction retardation (Rt) = 5 nm on the liquid crystal cell side was produced. Further, the polarizing plate 1 and the polarizing plate 2 were attached to both sides of the IPS mode liquid crystal to produce a liquid crystal panel.

  When this liquid crystal panel was observed by moving the viewpoint 360 degrees with respect to the center at an angle of 45 degrees from the vertical direction of the front of the panel, there was little change in the image with respect to the movement of the viewpoint.

  On the other hand, when the polarizing plate 1 was produced using the cellulose triacetate film obtained by the said comparative example 1, when the liquid crystal panel was produced similarly to said case using this polarizing plate 1, it was obtained. In the liquid crystal panel, the change of the image was large with respect to the movement of the viewpoint, and a part of the image was reversed.

Claims (13)

  The dope (resin solution) is cast on a metal rotating drum or a metal rotating endless belt (hereinafter referred to as a support) by a solution casting film forming method, and after peeling, the left and right ends of a continuous resin film (web) are It is a method for producing an optical film, which is stretched using a stretching apparatus that conveys and stretches a resin film while gripping and applying tension in the width direction, and winding up the stretched film. The in-plane direction retardation (Ro) value of the film is 0 or more and 5 by starting the first stretching step at 80 to 120% by weight and starting the second stretching step with the residual solvent amount of the web being 10 to 60% by weight. The manufacturing method of an optical film characterized by manufacturing the optical film which is below and the thickness direction retardation (Rt) value of a film is -10 or more and 10 or less.   The dope (resin solution) contains a cellulose ester resin and an additive for reducing the thickness direction retardation (Rt), and the additive for reducing the thickness direction retardation (Rt) has a negative intrinsic birefringence. The method for producing an optical film according to claim 1, wherein the optical film has an additive.   The first stretching step is a step of stretching the web in the width direction from 1.03 times to 1.3 times, and the second stretching step is to stretch the web in the width direction from 1.03 times to 1.1 times. It is a process, The manufacturing method of the optical film of Claim 1 or 2 characterized by the above-mentioned.   The temperature of a 1st extending process is 50 degreeC or more and 100 degrees C or less, The temperature of a 2nd extending process is 120 degreeC or more and 160 degrees C or less, It is any one of Claims 1-3 characterized by the above-mentioned. The manufacturing method of the optical film of description.   The method for producing an optical film according to any one of claims 1 to 4, wherein a residual solvent amount at the start of the drying step after the second stretching step is 2 to 8% by weight.   The method for producing an optical film according to any one of claims 1 to 5, wherein a conveyance tension in the drying step after the second stretching step is 30 N / m or more and 120 N / m or less.   The film temperature in the drying process after a 2nd extending process is 100 degreeC or more and 160 degrees C or less, The optical film manufacturing method as described in any one of Claims 1-6 characterized by the above-mentioned.   The method for producing an optical film according to claim 1, wherein the cellulose ester-based resin is cellulose acetate.   The dope composition contains a cellulose ester resin, an additive for reducing the thickness direction retardation (Rt), and an organic solvent. The dope composition has a surface temperature of −50 ° C. or more and −10 ° C. or less. 9. A continuous resin film (web) peeled from the support by a peeling roller is processed after casting on the support and forming a gel film having self-supporting properties. The optical film manufacturing method as described in any one of these.   The dope composition is a mixture of a non-chlorine organic solvent, a cellulose ester resin, and a retardation reducing additive, and the resulting mixture is cooled at −100 to −10 ° C., and the mixture after the cooling is 0 It is produced by treating at ˜120 ° C., and is characterized by casting the dope composition onto a support and treating a continuous resin film (web) peeled from the support with a peeling roller. The optical film manufacturing method as described in any one of Claims 1-9.   It manufactured with the manufacturing method of the optical film as described in any one of Claims 1-10, The optical film characterized by the above-mentioned.   A polarizing plate comprising a polarizing film and a transparent protective layer disposed on both sides thereof, wherein the optical film according to claim 11 is used for at least one of the two transparent protective layers. ,Polarizer.   A liquid crystal display device having two polarizing plates comprising a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and transparent protective layers disposed on both sides thereof. In one of the two polarizing plates, the in-plane retardation (Ro) value of the film is 150 to 300 and the thickness direction retardation (Rt) value of the film is −20 to 20 A liquid crystal display device comprising the following optical film, wherein the other polarizing plate comprises the optical film according to claim 11.