JP2007098690A - Method for producing optical film and liquid crystal display using the film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film which is excellent in dimensional stability after being produced and suitable for the polarizing plate protecting film of a VA type liquid crystal display. <P>SOLUTION: A production method includes a stretching process for stretching a film in the width direction crossing at right angles with the film-making transportation direction and a relaxation process for relaxing the stretched film in the width direction. The time θ(second) and temperature T(°C) of the relaxation process are set to meet the condition: 3.35×10<SP>-4</SP>≤(Rth/d)×(1/θ)×[1/(273+T)]≤1.47×10<SP>-3</SP>. [Rth is the retardation(nm) in the thickness direction of the film; and d is the thickness(μm) of the film]. By the retardation process, the residual stress of the film can be reduced. As a result, the dimensional stability of the produced film is improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device and a protective film for the polarizing plate.

  In this specification, the cast dope is dried on the endless belt to become a dope film that can be peeled off from the endless belt.

  In recent years, 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 TN (twisted nematic), STN (super twisted nematic), and VA (vertical alignment) have been proposed. In particular, the VA liquid crystal cell is a so-called vertical alignment mode liquid crystal cell in which liquid crystal molecules are aligned perpendicular to the alignment plate when the voltage is off and parallel to the alignment plate when the voltage is on. For this reason, black has a feature that it is displayed as black, has a high contrast, and has a relatively wide viewing angle compared to the TN type and STN type. However, as the liquid crystal screen becomes larger, there is an increasing demand for further widening the viewing angle.

  By the way, for the purpose of protecting the polarizer, a polarizing plate is formed by attaching a protective film to at least one surface of the polarizer. In order to further widen the viewing angle of the liquid crystal display device, it is necessary to increase the retardation in the thickness direction of the polarizing plate protective film. Therefore, Patent Document 1 proposes a method of increasing the retardation by increasing the content of hydroxyl groups.

Japanese Patent Laid-Open No. 2001-100027

  However, the protective film described in Patent Document 1 does not have sufficient thickness direction retardation. If the film is made thicker, the retardation can be further increased, but it goes against the market demand for making the film thinner. Patent Document 1 proposes increasing the thickness direction retardation by increasing the hydroxyl group content. However, when many hydroxyl groups remain in the film, the stress in the stretching direction and the direction orthogonal thereto in the stretching process during production works strongly due to the strong chemical interaction between the hydroxyl groups. For this reason, in the conventional manufacturing method of an optical film, the dimension of a film will change a lot after manufacture due to residual stress.

  This invention is made | formed in view of such a condition, and it aims at providing the manufacturing method of an optical film with a small dimensional change of the film after manufacture.

  In order to achieve the above object, the invention described in claim 1 is a method for producing an optical film containing cellulose ester as a main component, wherein the dope is cast on a support to form a film. And a peeling step for peeling the film from the support, a stretching step for stretching the peeled film in the width direction orthogonal to the transport direction, and a relaxation step for relaxing the stretched film in the width direction. The manufacturing method of the optical film characterized by satisfy | filling the following conditional expressions (A).

3.35 × 10 ⁻⁴ ≦ (Rth / d) × (1 / θ) × (1 / (273 + T)) ≦ 1.47 × 10 ⁻³
... (A)
However,
Rth: Thickness direction retardation (nm) (= ((nx + ny) / 2−nz) × d)
d: Film thickness (μm)
Refractive index of the film in a direction parallel to the film forming direction of the nx film ny: Refractive index of the film in a direction perpendicular to the film forming direction of the film nz: Refractive index in the thickness direction of the film θ: Time of the relaxation process ( Seconds)
T: Temperature of relaxation process (° C)
It is.

  The invention according to claim 2 is characterized in that, in the manufacturing method according to claim 1, the following conditional expression (B) is satisfied.

2.4 ≦ Rth / d ≦ 3.6. ... (B)
The invention according to claim 3 is characterized in that, in the production method according to claim 1 or 2, the total substitution degree of the acyl groups of the cellulose ester is 2.40 or more and 2.70 or less.

  The invention according to claim 4 is the production method according to any one of claims 1 to 3, wherein the substitution degree of the acyl group having 3 or more carbon atoms of the cellulose ester is more than 0 and 1.1 or less. It is characterized by being.

  The invention according to claim 5 is a liquid crystal display device comprising a polarizing plate and a liquid crystal cell, wherein the liquid crystal cell uses a vertical alignment type liquid crystal, and the protective film of the polarizing plate is the invention. It uses the optical film manufactured by the manufacturing method as described in any one of 1-4 thru | or 4, It is characterized by the above-mentioned.

  By setting the time and temperature of the relaxation step as in the first aspect of the invention, the residual stress of the film can be effectively reduced in the relaxation step. For this reason, the dimensional fluctuation after manufacture can be suppressed small. Moreover, according to invention of Claim 2, thickness direction retardation can be enlarged, without increasing the thickness of a film compared with the past. For this purpose, the degree of substitution may be set as described in claim 3 or 4. Further, according to the invention described in claim 5, it is possible to provide a VA liquid crystal display device having a wide viewing angle.

  Hereinafter, the present invention will be specifically described.

  The cellulose ester used in the protective film for polarizing plate of the present embodiment has a total substitution degree of acyl groups of 2.40 or more and 2.70 or less and a substitution degree of acyl groups of 3 or more carbon atoms of more than 0 and 1. It is 1 or less, and the degree of substitution is kept somewhat lower than that of conventional cellulose ester films. Thereby, the thickness direction retardation value can be increased, and a polarizing plate protective film excellent in viewing angle characteristics can be obtained.

  A cellulose ester having a total substitution degree of acyl groups of 2.40 or more and 2.70 or less is one in which the hydroxyl group of cellulose is substituted with a predetermined substitution degree by an acetyl group or a propionyl group. Specific examples include cellulose triacetate, cellulose acetate propionate, and cellulose propionate. Of these, cellulose triacetate and cellulose acetate propionate are preferable, and cellulose acetate propionate is most preferable. The number average molecular weight of the cellulose ester is preferably from 70,000 to 300,000, more preferably from 80,000 to 200,000, in order to obtain a preferable mechanical strength as a protective film for a polarizing plate. The cellulose ester can be synthesized by an ordinary method. For example, it can be synthesized by the method described in JP-A-10-45804. The measuring method of the substitution degree of an acyl group can be measured by ASTM-D817-96.

  As the cellulose ester of the present embodiment, either a cellulose ester synthesized from cotton linter or a cellulose ester synthesized from wood pulp can be used alone or in combination. It is preferable to use a large amount of cellulose ester synthesized from a cotton linter that has good releasability from a belt or a drum because of high productivity efficiency. When the ratio of cellulose ester synthesized from cotton linter is 60% by weight or more and the effect of releasability becomes remarkable, 60% by weight or more is preferable, more preferably 85% by weight or more, and further, it can be used alone. Most preferred.

  Examples of the cellulose ester that is the main component of the cellulose ester film of the present embodiment include cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, and cellulose acetate propionate.

  Examples of the cellulose ester solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and n-butyl alcohol, lower aliphatic chlorinated hydrocarbons such as cyclohexane, dioxane, and methylene chloride. Can be used.

  After dissolution, it is taken out from the container while cooling, or extracted from the container with a pump or the like and cooled with a heat exchanger or the like, and used for film formation.

  The polarizing plate protective film of this embodiment contains a plasticizer in addition to the cellulose ester and the solvent. One type of plasticizer contained in the film of the present embodiment is an aromatic terminal ester plasticizer represented by the following general formula (I).

B- (GA) n-GB ... (I)
(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (I), a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic group represented by A It is composed of an acid residue and can be obtained by a reaction similar to that of a normal polyester plasticizer.

  Examples of the benzene monocarboxylic acid component of the ester plasticizer used in this embodiment include benzoic acid, paratertiarybutylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, normal There are propylbenzoic acid, aminobenzoic acid, acetoxybenzoic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the ester plasticizer of the present embodiment include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, and 1,3-butane. Diol, 2-methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl- 1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentane Diol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-hexanediol , 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc., and these glycols are used as one kind or a mixture of two or more kinds Is done.

  In addition, examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the aromatic terminal ester of the present embodiment include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Can be used as one or a mixture of two or more.

  Moreover, as C6-C12 aryl glycol component of the aromatic terminal ester of this embodiment, there exist hydroquinone, resorcinol, bisphenol A, bisphenol F, bisphenol etc., for example, these glycols are 1 type, or 2 types. It can be used as a mixture of the above.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the aromatic terminal ester of the present embodiment include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. They are each used as one or a mixture of two or more. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, 1,5 naphthalene dicarboxylic acid, 1,4 naphthalene dicarboxylic acid, and the like.

  Examples of the compounds are shown in (1) to (13).

  The ester plasticizer used in the present embodiment has a number average molecular weight of preferably 300 to 2000, more preferably 500 to 1500. The acid value is preferably 0.5 mgKOH / g or less, the hydroxyl value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl value is 15 mgKOH / g or less.

  In addition, an acid value means the milligram number of potassium hydroxide required in order to neutralize the acid (carboxyl group which exists in a molecule terminal) contained in 1g of samples. The acid value and the hydroxyl value are measured according to JIS K0070.

  The cellulose ester film of this embodiment preferably contains an ultraviolet absorber. As the ultraviolet absorber, those which are excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal and absorb visible light having a wavelength of 400 nm or more as much as possible from the viewpoint of good liquid crystal display properties are preferable. Used. In particular, the transmittance at a wavelength of 370 nm needs to be 10% or less, preferably 5% or less, more preferably 2% or less. Examples of commonly used compounds include, but are not limited to, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. One or more of these ultraviolet absorbers are preferably used, and may contain two or more different ultraviolet absorbers. The ultraviolet absorber may be added to the dope after dissolving the ultraviolet absorber in an organic solvent such as alcohol, methylene chloride, dioxolane, or directly into the dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose ester to disperse and then added to the dope. The amount of the ultraviolet absorber used in the present invention is 0.1% by weight to 2.5% by weight, preferably 0.5% by weight to 2.0% by weight, more preferably 0.8% by weight based on the cellulose ester. % By weight to 2.0% by weight. When the amount of the ultraviolet absorber used is more than 2.5% by weight, the transparency tends to deteriorate, which is not preferable.

  In addition, the cellulose ester film of the present invention has, for example, silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, silicic acid in order to improve handleability. It is preferable to include a matting agent such as inorganic fine particles such as aluminum, magnesium silicate and calcium phosphate, and a crosslinked polymer. Of these, silicon dioxide is preferable because it can reduce the haze of the film. The fine particles preferably have an average secondary particle size of 0.01 to 1.0 μm and a content of 0.005 to 0.3% by weight based on the cellulose ester. It is preferable that fine particles such as silicon dioxide are surface-treated with an organic substance because the haze of the film can be reduced. Preferred organic materials for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like. The larger the average diameter of the fine particles, the greater the mat effect, and the smaller the average diameter, the better the transparency. Therefore, the preferable average primary particle diameter of the fine particles is 5 to 50 nm, more preferably 7 to 14 nm. These fine particles are usually present as aggregates in the film, and it is preferable to generate irregularities of 0.01 to 1.0 μm on the film surface. Examples of the silicon dioxide fine particles include Aerosil 200, 300, R972, R974, R202, R812, OX50, and TT600 manufactured by Aerosil Co., Ltd., preferably AEROSILR972, R974, R202, and R812.

  In the present invention, the vertical alignment (VA) type liquid crystal display device uses a liquid crystal cell in a vertical alignment mode in which liquid crystal molecules are perpendicular to the alignment plate when the voltage is turned off and liquid crystal molecules are aligned parallel to the alignment plate when the voltage is turned on. A liquid crystal display device. A conventionally well-known thing can be used for the polarizer with which the protective film for polarizing plates of this embodiment is provided in the surface. For example, a film made of a hydrophilic polymer such as polyvinyl alcohol, which has been stretched by treatment with a dichroic dye such as iodine can be used. And a polarizing plate is comprised as what laminated | stacked the said protective film for polarizing plates on the at least single side | surface side of the polarizer. A vertical alignment (VA) type liquid crystal display device can be obtained by providing the polarizing plate thus obtained on one side or both sides of the VA type liquid crystal cell.

  In the protective film for polarizing plate of the present invention, the thickness direction retardation Rth (nm) and the thickness d (μm) satisfy the following conditional expression (B).

2.4 ≦ Rth / d ≦ 3.6 (B)
Here, the thickness direction retardation is a value defined by the following equation.

Rth = ((nx + ny) / 2−nz) × d
However,
Refractive index of the film in a direction parallel to the film forming direction of the nx film ny: Refractive index of the film in a direction perpendicular to the film forming direction of the film nz: Refractive index in the thickness direction of the film.

  By setting Rth / d to 2.4 or more, it is possible to achieve a large thickness direction retardation without increasing the thickness of the film, and to obtain a VA liquid crystal display device having a wider viewing angle than before. it can. However, if Rth / d exceeds 3.6, desired characteristics cannot be obtained for characteristics other than thickness direction retardation.

  The thickness direction retardation value (Rth value) was measured using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments) at 23 ° C. and 55% RH at a wavelength of 590 nm. It is obtained by measuring the dimensional refractive index and obtaining the refractive indexes nx, ny and nz.

  In this embodiment, the dope obtained by dissolving the cellulose ester is cast on a support (casting process), then peeled from the support (peeling process), and the peeled film is stretched (stretching process). After relaxing (relaxing step), drying (post-drying step), winding on a roll (winding step), a cellulose ester film is obtained.

  This will be described with reference to the drawings. First, as shown in FIG. 1, a dope that is a raw material solution of a cellulose ester film is cast on a support 1 made of a rotating metal endless belt by a casting die 2. (Casting process). As the support 1 in the casting process, a support having a mirror-finished belt-like or drum-like stainless steel as shown in FIG. 1 is used. The web W formed on the support 1 by casting is peeled off by the peeling roll 3 when it has made a full turn on the support 1 (peeling step). The film F peeled from the support 1 is subjected to a stretching process and a relaxation process in the tenter 4. After passing through the tenter 4, the film F is fed into the drying device 5. The drying device 5 is generally transported through all the transport rolls 6 arranged in a staggered manner in the housing by the roll suspension method, and is dried by the dry air blown from the dry air blowing port 7 during the transport. The cellulose ester film F obtained by drying is wound on a winding roll 8.

  In producing the film, it is useful and preferable to obtain a high thickness direction retardation value by using the following method.

  (1) Retardation (Rth value) increases when the amount of residual solvent when the film F is peeled from the support 1 is decreased, and decreases when it is increased. The residual solvent amount at the time of peeling is preferably 5% to 100%, more preferably 5% to 80%, and still more preferably 10% to 45%.

  The amount of residual solvent in the film is represented by the following formula.

Residual solvent amount = residual volatile matter weight / film weight after heat treatment × 100%
The residual volatile matter weight is a value obtained by subtracting the film weight after the heat treatment from the film weight before the heat treatment when the film is heat treated at 115 ° C. for 1 hour.

  (2) Retardation (Rth value) decreases when the tension at which the film F is peeled from the support 1 (peeling tension) and the tension at which the film F is transported in the drying device 5 (transport tension) are increased. However, it increases when it is small. A preferable peeling tension is 5 to 40 kg / m, more preferably 10 to 30 kg / m, and still more preferably 10 to 25 kg / m. The transport tension is preferably 5 to 20 kg / m, more preferably 8 to 15 kg / m, and still more preferably 8 to 12 kg / m.

  (3) When drying while stretching the film with the tenter 4, the retardation (Rth value) increases as the stretching ratio (ratio of dimensions before and after stretching) increases, and decreases as it decreases. A preferable draw ratio is 2 to 50%, more preferably 5 to 40%, and still more preferably 10 to 30%.

  FIG. 2 shows an example of the mechanism of the tenter 4. As shown in FIG. 2, the tenter 4 has a large number of clips 11 connected in a chain state on the left and right side portions of the housing 10, and these clips 11 run as one wheel on the rail 12. The film F is gripped and conveyed. Although not shown in the drawings, each clip 11 is provided with a swingable presser arm, and on both the left and right sides of the tenter 4, both ends in the width direction of the film F on the cradle are curved surfaces of the presser arm of the tenter 4. It is sandwiched (clipped) between the tip of the shape and the cradle and is transported together while being stretched, and simultaneously dried. The width direction is a direction orthogonal to the transport direction of the film F in the plane of the film F.

  In the tenter 4, the cellulose ester film F is held in the width direction both ends thereof, and the film F width holding zone A, the film width direction stretching zone B, and the film width holding zone C in the stretched state. And the relaxation zone D are sequentially passed through and the film width direction stretching process is performed.

  Here, the film width holding zone A in the tenter 4 is a zone in which the distance between grip clips of the film width (both ends of the base) from the entrance of the tenter 4 to the stretching start point a is constant. The stretching zone B refers to a zone in which the distance between grip clips of the film width (both ends of the base) from the stretching start point a to the stretching end point b of the tenter 4 spreads in the traveling direction (conveying direction). The film width holding zone C in the stretched state is a zone in which the distance between grip clips of the stretched film width (both ends of the base) from the stretching end point b to the relaxation start point c of the tenter 4 is constant.

  Further, the relaxation zone D is a zone in which the distance between grip clips of the film width (both ends of the base) from the relaxation start point c to the relaxation end point d of the tenter 4 is narrowed in the traveling direction (conveying direction). In this case, the relaxation treatment refers to a grip pattern that narrows the film width in the advancing direction (conveying direction) as described above, and the film F does not stretch in the width direction, that is, stress in the film width direction. A process that does not give a film is called relaxation processing, and this relaxation processing is performed while the film edge is gripped.

  The rail 12 in the tenter 4 is usually a bendable rail, and when the rail 12 is bent, the distance between the clips on the left and right ends changes, and the width holding zone A, the stretching zone B, the width holding zone C, and the relaxation Zone D can be configured. The stretching zone B corresponds to the stretching process of the present invention, and the relaxation zone D corresponds to the relaxation process. Note that the combinations of these zones are not limited to those shown in the drawings, and may be combined in any order.

  In addition, the illustrated tenter 4 is a clip tenter method, but this may be a pin tenter method, and in any case, it is possible to maintain the width of the film F by the tenter method and to achieve dimensional stability. It is preferable for improving the property.

  In the present embodiment, the time θ (second) required for the film F to pass through the relaxation zone D and the temperature T (° C.) of the relaxation zone D are set so as to satisfy the following conditional expression (A). .

3.35 × 10 ⁻⁴ ≦ (Rth / d) × (1 / θ) × (1 / (273 + T)) ≦ 1.47 × 10 ⁻³
... (A)
By satisfying this conditional expression (A), the residual stress of the film F can be moderated moderately. Thereby, the dimensional fluctuation | variation by the residual stress after manufacture can be restrained small.

  If the upper limit of conditional expression (A) is exceeded, that is, the relaxation time is too short or the relaxation temperature is too low, the residual stress of the film cannot be relaxed. For this reason, it becomes impossible to suppress the dimensional variation after manufacture.

  On the other hand, in the case where the lower limit of conditional expression (A) is exceeded, when the relaxation time is increased, the distance of the relaxation process must be increased, which is not preferable. If the relaxation temperature is too high, the plasticizer will evaporate and decrease.

  Hereinafter, Examples 1 to 9 of the present invention will be described together with Comparative Examples 1 to 3, but the present invention is not limited to these Examples.

  Examples 1 to 9 and Comparative Examples 1 to 3 have different manufacturing conditions, but the dope solution is common. First, 100 parts by weight of cellulose acetate propionate having a degree of acetyl substitution of 2.55 (number average molecular weight 170000), 5 parts by weight of an aromatic terminal ester plasticizer (example of compound (13)), 2- (2′-hydroxy- 3 ', 5'-di-t-butylphenyl) benzotriazole and 4 parts by weight of ethylphthalylethyl glycolate were mixed in a mixed solvent of 450 parts by weight of dichloromethane and 50 parts by weight of ethyl alcohol to obtain a dope. It was.

  This dope was formed under the conditions of Examples 1 to 9 and Comparative Examples 1 to 3 to obtain a cellulose ester film. The results are shown in Table 1. Table 1 also shows conditions other than the film forming conditions. These will be described sequentially.

  As shown in Table 1, Examples 1 to 9 and Comparative Examples 1 to 3 have different relaxation times θ and relaxation temperatures T from each other. In the film obtained as a result, the thickness d and the thickness direction retardation Rth are different from each other. However, the manufacturing conditions other than the relaxation conditions are adjusted so that the values of Rth / d all satisfy the conditional expression (A) in Examples 1 to 9 and Comparative Examples 1 to 3. As a result, regarding the corresponding value ((Rth / d) × (1 / θ) × (1 / (273 + T))) of the conditional expression (B), Examples 1 to 9 satisfy the conditional expression (B). In Comparative Examples 1 to 3, the conditional expression (B) is not satisfied.

  The two columns (MD and TD) at the right end of Table 1 are the results of measuring the dimensional variation rate. This dimensional variation rate is obtained by dividing the amount of dimensional variation when a manufactured film is left in an environment of temperature 80 ° C. and humidity 90% for 100 hours by the size before leaving, and MD in the film transport direction. The dimensional variation rate, TD, indicates the dimensional variation rate in the width direction of the film. In Comparative Examples 1 to 3 that do not satisfy the conditional expression (B), all shrinkage was 0.6% or more, whereas in Examples 1 to 9 that satisfy the conditional expression (B), the dimensional variation rate was plus or minus. Good results of 0.25% or less could be obtained.

It is a schematic side view of the manufacturing apparatus which enforces the manufacturing method of the cellulose-ester film of this invention. It is a schematic plan view of the extending | stretching apparatus (tenter) in the manufacturing apparatus of FIG.

Explanation of symbols

F: Cellulose ester film 1: Stainless steel endless belt (support)
3: Peeling roll 4: Tenter 5: Drying device 6: Conveying roll 8: Winding roll

Claims (5)

A method for producing an optical film comprising cellulose ester as a main component,
A casting step of casting a dope on a support to form a film;
A peeling step of peeling the film from the support;
Including a stretching step of stretching the peeled film in the width direction orthogonal to the transport direction, and a relaxation step of relaxing the stretched film in the width direction,
An optical film manufacturing method characterized by satisfying the following conditional expression:
3.35 × 10 ⁻⁴ ≦ (Rth / d) × (1 / θ) × (1 / (273 + T)) ≦ 1.47 × 10 ⁻³
However,
Rth: Thickness direction retardation (nm) (= ((nx + ny) / 2−nz) × d)
d: Film thickness (μm)
Refractive index of the film in a direction parallel to the film forming direction of the nx film ny: Refractive index of the film in a direction perpendicular to the film forming direction of the film nz: Refractive index in the thickness direction of the film θ: Time of the relaxation process ( Seconds)
T: Temperature of relaxation process (° C)
It is. The manufacturing method according to claim 1, wherein the following conditional expression is satisfied:
2.4 ≦ Rth / d ≦ 3.6. The production method according to claim 1 or 2, wherein the total substitution degree of the acyl group of the cellulose ester is 2.40 or more and 2.70 or less. The production method according to any one of claims 1 to 3, wherein the substitution degree of the acyl group having 3 or more carbon atoms of the cellulose ester is more than 0 and 1.1 or less. In a liquid crystal display device comprising a polarizing plate and a liquid crystal cell,
The liquid crystal cell uses a vertical alignment type liquid crystal,
A liquid crystal display device, wherein the protective film for the polarizing plate is an optical film produced by the production method according to claim 1.

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