JP2013080117A - Optical film and manufacturing method thereof, polarizer and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film with low haze and having excellent blocking resistance and brittleness.SOLUTION: An optical film includes cellulose acetate having a total substitution degree of an acetyl group of 2.0-2.6. The cellulose acetate satisfies requirements A) and B). A) The cellulose acetate of 10 pts. by mass is dissolved in a mixed solvent of 171 pts. by mass including methylene chloride of 92 mass% and ethanol of 8 mass%, and thereafter, filtered by a filter paper with filtration accuracy of 7 μm to obtain a cellulose acetate solution having turbidity of 0.3-4.0. B) The cellulose acetate satisfies an equation: 29.5≤DS6/DSt×100≤34.0 (In the formula, DSt represents a total substitution degree of an acetyl group. DS6 represents a sixth substitution degree of an acetyl group.), and the total amount (A) of alkali metal ion and alkaline earth metal ion included in a film corresponding to 1 kg of the cellulose acetate is 35 mg-250 mg.

Description

  The present invention relates to an optical film, a manufacturing method thereof, a polarizing plate, and a liquid crystal display device.

  Resin films such as cellulose ester, polycarbonate, and polyolefin are used as optical films for liquid crystal display devices. Especially, since the resin film (cellulose ester film) containing a cellulose ester is easy to bond with the polyvinyl alcohol film which is a polarizer, it is widely used.

  In recent years, development of thin and light notebook computers and thin and large-screen TVs has been progressing. Along with this, optical films for liquid crystal display devices are also required to be thinner and larger and to have a function of increasing contrast. In order to increase the contrast of the liquid crystal display device, it is effective to reduce the haze of the optical film.

  As a film with reduced haze, a film containing purified cellulose ester (for example, Patent Document 1), a film containing cellulose ester having low turbidity (for example, Patent Document 2), and the like have been proposed.

  Cellulose esters are easily hydrolyzed. Therefore, an optical film containing a cellulose ester in which the content of calcium ions is adjusted to a predetermined range has been proposed as a cellulose ester film that is difficult to hydrolyze (for example, Patent Document 3).

  Furthermore, an optical film containing cellulose diacetate having a high ratio of the 6-position acetyl group substitution degree to the total acetyl group substitution degree has also been proposed (for example, Patent Document 4).

JP 2009-286931 A JP 2008-115298 A International Publication No. 2004/076490 JP 2009-155555 A

  However, the film described in Patent Document 3 tends to have high haze. On the other hand, the films described in Patent Documents 1 and 2 have low haze but low blocking resistance. In order to suppress blocking, conventionally, a film containing a matting agent such as silica-based fine particles has been studied. However, since the matting agent is composed of a material different from the film material, scattering is likely to occur due to a difference in refractive index between the film material and the matting agent, and haze is likely to increase.

  Thus, it was difficult to obtain a film having a low haze and a suppressed blocking. In particular, a film having a small film thickness has a problem that the blocking resistance is lower.

  In addition, a film having a small film thickness has a problem that brittleness is likely to be significantly lowered (easily brittle) than a film having a normal film thickness. In the optical film manufacturing process, the film is slipped in order to remove the sandwiched portion of the film during transverse stretching and the knurling portion of the stretched film, or to adjust the wide original film to a predetermined width. Sometimes. Therefore, a film having low brittleness is liable to cause the slitting surface to be rough or cracked, and the productivity is likely to decrease. In addition, a minute film scrap generated by slitting may adhere to the film surface and cause a failure.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical film having low haze, blocking sufficiently suppressed, and having good brittleness, a polarizing plate including the optical film, and a liquid crystal display device. And

[1] An optical film containing cellulose acetate having a total substitution degree of acetyl groups of 2.0 or more and 2.6 or less,
The cellulose acetate satisfies the following requirements A) and B):
A) After dissolving 10 parts by mass of cellulose acetate in 171 parts by mass of a mixed solvent of 92% by mass of methylene chloride and 8% by mass of ethanol, the turbidity of the cellulose acetate solution obtained by filtering with a filter paper having a filtration accuracy of 7 μm is 0 B) Cellulose acetate satisfies the following formula 29.5 ≦ DS6 / DSt × 100 ≦ 34.0
(In the formula, DSt represents the total degree of substitution of the acetyl group, and DS6 represents the degree of substitution of the acetyl group at the 6-position)
And the optical film whose total amount (A) of the alkali metal ion and alkaline-earth metal ion which are contained in the said film of cellulose acetate 1kg is 35 mg or more and 250 mg or less.
[2] The cellulose acetate, wherein the alkali metal ion and alkaline earth metal ion contained in the cellulose acetate include an alkali metal ion and an alkaline earth metal ion present as a counter ion with the acidic group contained in the cellulose acetate, Of the total amount (B) of alkali metal ions and alkaline earth metal ions present as counter ions with the acidic groups contained in the cellulose acetate to the total amount (A) of alkali metal ions and alkaline earth metal ions contained in the cellulose acetate The optical film according to [1], wherein (B / A) is 0.5 or more and 0.9 or less.
[3] The optical film according to [1] or [2], wherein the ratio (B / A) is 0.75 or more and 0.90 or less.
[4] The optical film according to any one of [1] to [3], wherein an internal haze measured by a method according to JIS K-7136 is 0.05% or less.
[5] The optical film according to any one of [1] to [4], wherein the optical film has a thickness of 15 to 60 μm.

[6] A polarizing plate comprising a polarizer and the optical film according to any one of [1] to [5], which is disposed on at least one surface of the polarizer.
[7] A liquid crystal display device including a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell, wherein at least one of the pair of polarizing plates is a polarizer and at least one of the polarizers. A liquid crystal display device comprising: the optical film according to any one of [1] to [5] disposed on a surface.

[8] A method for producing an optical film according to any one of [1] to [5], wherein all of the following requirements A), B) and C) are satisfied, and the total degree of substitution of acetyl groups is 2. Obtaining a resin composition comprising cellulose acetate that is not less than 0 and not more than 2.6;
A) After dissolving 10 parts by mass of cellulose acetate in 171 parts by mass of a mixed solvent of 92% by mass of methylene chloride and 8% by mass of ethanol, the turbidity of the cellulose acetate solution obtained by filtering with a filter paper having a filtration accuracy of 7 μm is 0 B) Cellulose acetate satisfies the following formula 29.5 ≦ DS6 / DSt × 100 ≦ 34.0
(In the formula, DSt represents the total degree of substitution of the acetyl group, and DS6 represents the degree of substitution of the acetyl group at the 6-position)
C) The total amount of alkali metal ions and alkaline earth metal ions contained in 1 kg of cellulose acetate is 30 mg or more and 250 mg or less, and molding the resin composition to form an optical film.
[9] The cellulose acetate, wherein the alkali metal ion and the alkaline earth metal ion contained in the cellulose acetate include an alkali metal ion and an alkaline earth metal ion which are present as a counter ion with the acidic group contained in the cellulose acetate, Of the total amount (B) of alkali metal ions and alkaline earth metal ions present as counter ions with the acidic groups contained in the cellulose acetate to the total amount (A) of alkali metal ions and alkaline earth metal ions contained in the cellulose acetate (B / A) is 0.5 or more and 0.9 or less, The manufacturing method of the optical film as described in [8].

  The optical film of the present invention has low haze, blocking is sufficiently suppressed, and has good brittleness. Therefore, the front contrast of the liquid crystal display device including the optical film of the present invention can be increased.

It is a schematic diagram which shows the measurement procedure of the haze of the sample containing an optical film. It is a schematic diagram which shows the measurement procedure of the haze of the sample containing an optical film. It is a schematic diagram which shows the measurement procedure of the haze of the sample containing an optical film. It is a schematic diagram which shows the measurement procedure of the haze of the sample containing an optical film. It is a schematic diagram which shows the basic composition of one Embodiment of the liquid crystal display device which concerns on this invention.

1. Optical film The optical film of the present invention contains a cellulose ester, and may further contain a plasticizer or the like as necessary.

Cellulose ester The cellulose ester contained in the optical film of the present invention is a compound obtained by esterifying cellulose with an aliphatic carboxylic acid or aromatic carboxylic acid having 2 to 22 carbon atoms, and preferably cellulose is converted to 7 carbon atoms. It is a compound esterified with the following aliphatic carboxylic acid.

  The aliphatic acyl group contained in the cellulose ester may be linear or branched, and may have a ring. Usually, when the aliphatic acyl group has too many carbon atoms, retardation is hardly exhibited. Therefore, the number of carbon atoms in the aliphatic acyl group is preferably 2-7, more preferably 2-6, and even more preferably 2-4. The aliphatic acyl group may be one type or two or more types.

  Examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, and the like, preferably cellulose acetate.

  The total substitution degree of the acyl group of the cellulose ester is preferably 1.5 to 2.6 in order to facilitate the development of retardation or increase the flexibility of the film. .6 is more preferable, and 2.3 to 2.5 is more preferable. The acyl group substitution degree of cellulose ester can be measured according to ASTM-D817-96.

  Of the acyl groups contained in the cellulose ester, the degree of substitution of the acyl group having 3 or more carbon atoms is preferably 2.6 or less, more preferably 0, in order to easily develop retardation. preferable. That is, cellulose acetate having an acetyl group substitution degree of preferably 1.5 to 2.6, more preferably 2.0 to 2.6, and still more preferably 2.3 to 2.5 is preferable. .

The cellulose acetate preferably satisfies the following formulas (a) and (b) at the same time.
Formula (a) 2.0 ≦ DSt ≦ 2.6
Formula (b) 29.5 ≦ DS6 / DSt × 100 ≦ 34.0
(In the formula, DSt represents the total substitution degree of the acetyl group, and DS6 represents the substitution degree of the 6-position acetyl group)

  Cellulose acetate with a low degree of substitution, such as cellulose acetate having a total degree of substitution of acetyl groups of 2.0 or more and 2.6 or less, is a substitution degree or substitution position of acetyl groups compared to cellulose acetate with a high degree of substitution such as cellulose triacetate. However, since the film contains a lot of different cellulose acetates, the flexibility of the film tends to be high. Furthermore, cellulose acetate having a high ratio of substitution degree of 6-position acetyl group (DS6 / DSt × 100) is considered to have high flexibility (low brittleness) because of weak hydrogen bonding between molecules. Cellulose acetate, which has weak intermolecular hydrogen bonding, is considered to have high blocking resistance because it is difficult for films to stick to each other.

Cellulose acetate preferably satisfies the following formulas (c) and (d) at the same time in order to further enhance the flexibility and blocking resistance of the resulting film.
Formula (c) 2.3 ≦ DSt ≦ 2.5
Formula (d) 30.0 ≦ DS6 / DSt × 100 ≦ 33.5

  The ratio of the substitution degree of the acetyl group at the 6-position of cellulose acetate (DS6 / DSt × 100) depends on the synthesis conditions for synthesizing cellulose acetate from the raw material cellulose (for example, the sulfuric acid used as a catalyst in the cellulose esterification step). The amount of glacial acetic acid added in the esterification step, the concentration of acetic acid in the aqueous acetic acid solution after the esterification step or in the aging step, etc.). For example, in order to increase the degree of substitution of the acetyl group at the 6-position, as described in JP-A-2009-155555, the amount of sulfuric acid as a catalyst in the esterification step of cellulose is reduced, or the ester of cellulose The amount of glacial acetic acid in the crystallization step may be increased, or the concentration of acetic acid after the esterification step or in the aging step may be increased (the amount of water is reduced).

  The degree of substitution of the acetyl groups at the 2nd, 3rd and 6th positions of cellulose acetate is T.W. Sei, K .; Ishitani, R .; Suzuki, K .; Ikematsu, Polim. J. et al. 17, 1065-1069 (1985).

In order to obtain a film having high mechanical strength, the number average molecular weight of the cellulose ester is preferably in the range of 3.0 × 10 ^{4 to} 2.0 × 10 ⁵ , and 4.0 × 10 ⁴ to 1. The range of 0 × 10 ⁵ is more preferable. The number average molecular weight of the cellulose ester can be measured by gel permeation chromatography (GPC).

The measurement conditions are as follows.
Solvent: Methylene chloride Column: Three Shodex K806, K805, K803G (manufactured by Showa Denko KK) are connected and used.
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 1.0 × 10 ^{6 to} 5.0 × 10 ² 13 calibration curves are used. The 13 samples are preferably selected at approximately equal intervals.

  Cellulose esters can be synthesized by known methods. Specifically, it can be synthesized by esterifying cellulose with an organic acid having 3 or more carbon atoms or acetic anhydride containing at least acetic acid or acetic anhydride (described in JP-A-10-45804). See how).

  As the raw material cellulose, for example, cotton linter, wood pulp (derived from coniferous tree, derived from broadleaf tree), kenaf and the like can be used. The cellulose used as a raw material may be only one type or a mixture of two or more types.

  In order to obtain a film having a low internal haze, the cellulose ester is obtained by dissolving a solution obtained by dissolving 10 parts by weight of a cellulose ester in 171 parts by weight of a mixed solvent of 92% by weight of methyl chloride and 8% by weight of ethanol. The turbidity of the cellulose acetate solution obtained by filtration with is preferably 0.3 or more and 4.0 or less, and more preferably 0.5 or more and 3.0 or less.

  A film containing a cellulose ester whose turbidity of the solution is too low has a low internal haze, but the film surface becomes too smooth, so that the blocking resistance tends to be low. That is, the cellulose ester whose solution turbidity is not lower than a certain level contains moderately fine gels. Since the surface of the film containing such a cellulose ester has minute gel irregularities, it is considered that the blocking resistance is enhanced.

  The fine gel is composed of aggregates of low or high substitution components (more than the average substitution degree) of cellulose acetate formed in methylene chloride / ethanol mixed solvents, respectively; These include hemicellulose derivatives contained in cellulose acetate.

  On the other hand, a film containing a cellulose ester in which the turbidity of the solution is too high may have an internal haze that is too high.

The turbidity of the cellulose ester solution can be measured by the following method.
1) 92 parts by weight of methylene chloride and 8 parts by weight of ethanol are mixed to prepare a methylene chloride / ethanol mixed solvent. 10 g of cellulose ester is added to 171 g of this methylene chloride / ethanol mixed solvent, and the mixture is stirred for 2 hours to dissolve the cellulose ester until there is no remaining dissolution.
2) The obtained cellulose ester solution was added to Azumi Filter Paper No. It is put into a filter having 244 (filtration accuracy 7 μm) and filtered under a pressure of 0.4 MPa, and the filtrate is recovered.
3) Put the above methylene chloride / ethanol mixed solvent in a glass cell (light path length 5 mm) manufactured by Nippon Denshoku Industries Co., Ltd. and set it on a haze meter NDH-2000 manufactured by Nippon Denshoku Industries Co., Ltd. Do.
4) After removing the above-mentioned glass cell, the filtrate obtained in 2) above was placed in a glass cell made by Nippon Denshoku Industries Co., Ltd. and set in a haze meter NDH-2000, and the turbidity of the solution (Turb) ).

  The turbidity of the cellulose acetate solution can be adjusted by 1) the type of cellulose acetate raw pulp, 2) the cellulose acetate synthesis conditions, 3) the purification of cellulose acetate, 4) the mixing of a plurality of types of cellulose acetate, and the like.

  Examples of the raw material pulp of 1) include cotton linter, wood pulp (derived from conifers and hardwoods), kenaf and the like. In order to reduce the turbidity of the cellulose acetate solution, cotton linter or wood pulp having a low hemicellulose content may be selected.

  Examples of the synthesis conditions of cellulose acetate in 2) include a method of adjusting the amount of catalyst, reaction temperature, reaction time, amount or concentration of a solvent (for example, glacial acetic acid), water content and the like. In order to reduce the turbidity of the solution, the amount of sulfuric acid used as a catalyst may be increased (for example, see JP2003-201301A).

  Examples of the method for purifying cellulose acetate in 3) include a method in which the obtained cellulose ester is suspended and washed with a predetermined solvent, and after dissolving the cellulose acetate in a good solvent, the poor solvent is added to reconstitute the cellulose acetate. A method of precipitation (for example, a method described in JP-A-2008-56819), a method of collecting a cellulose acetate solution from an obtained filtrate after filtering the cellulose acetate solution using an appropriate filter medium, and centrifuging the cellulose acetate solution And a method of recovering cellulose acetate from the resulting supernatant.

  Examples of the method 4) of mixing a plurality of types of cellulose esters include a method of mixing cellulose acetates having different turbidities.

  In the cellulose ester, the total amount (A) of alkali metal ions and alkaline earth metal ions contained in 1 kg of the cellulose ester is preferably 30 mg or more and 250 mg or less, and more preferably 40 mg or more and 200 mg or less.

  When the total amount (A) of alkali metal ions and alkaline earth metal ions contained in the cellulose ester is too large, the metal salt is aggregated and easily crystallized in the film containing the cellulose ester. Since the crystallized metal salt becomes a scattering factor, it tends to increase the internal haze of the film. On the other hand, if the total amount (A) of alkali metal ions and alkaline earth metal ions contained in the cellulose ester is too small, the above-mentioned fine gel that causes the turbidity of the cellulose acetate solution may cause the aforementioned alkali metal ions or alkalis. Since it is not dispersed by earth metal ions, it tends to aggregate. Since the fine gel aggregate becomes a scattering factor, it tends to increase the internal haze of the film.

  On the other hand, when the total amount (A) of alkali metal ions and alkaline earth metal ions contained in the cellulose ester is in the above range, the metal salt does not crystallize in the film and is easily dispersed uniformly. Furthermore, the metal salt can facilitate the dispersion of a fine gel. Therefore, the film in which the total amount (A) of alkali metal ions and alkaline earth metal ions contained in the cellulose ester is adjusted to the above range is considered to have low internal haze. Furthermore, since the micro unevenness formed by the micro gel is highly dispersed on the surface of the film, it is considered that the blocking resistance is also high.

  Examples of alkali metal ions contained in the cellulose ester include lithium ions, sodium ions, potassium ions, cesium ions, and the like, preferably sodium ions or potassium ions. Examples of alkaline earth metal ions include calcium ions, magnesium ions, barium ions, etc., preferably calcium ions or magnesium ions.

  The alkali metal ions and alkaline earth metal ions contained in cellulose acetate may be contained in any form, for example, may be contained as a free acid salt (acetate, sulfate, etc.); It may be contained as a counter ion of an acidic group (carboxyl group or sulfone group).

  The total amount (A) of alkali metal ions and alkaline earth metal ions contained in cellulose acetate can be measured by a known method. For example, after the ash obtained after completely burning cellulose acetate is dissolved in hydrochloric acid to obtain a pretreatment solution; the amount of alkali metal ions and alkaline earth metal ions contained in the obtained pretreatment solution, It can be measured by atomic absorption method. In addition, after the cellulose acetate that has been completely dried is decomposed with nitric acid and melted with alkali in a micro digest wet cracking apparatus to obtain a pretreatment solution; alkali metal ions and alkaline earth contained in the obtained pretreatment solution The amount of metal ions can also be measured by ICP-AES (Dielectric Coupled Plasma Atomic Emission Spectrometer).

  The total amount (A) of alkali metal ions and alkaline earth metal ions contained in cellulose acetate is 1) the amount of metal salt (neutralizing agent, stabilizer) added when synthesizing cellulose acetate from raw pulp, 2) It can be adjusted by washing cellulose acetate, 3) adding a metal salt to the cellulose acetate after synthesis, and the like.

  The addition of a metal salt (neutralizing agent, stabilizer) when synthesizing cellulose acetate from the raw material pulp of 1) varies depending on the method for producing cellulose acetate, as described in International Publication No. 2004/076490. It is done at the timing. A metal salt may be added after the completion of the acylation step, after the acylation step and before the ripening step, or in the ripening step; the metal is added to the coagulation liquid when the liquid cellulose acetate after the ripening step is coagulated and precipitated. A salt may be added; the cellulose acetate particles after drying may be added by spraying an aqueous solution of a metal salt. These metal salt addition steps may be combined. What is necessary is just to adjust the addition amount of a metal salt in the addition process of at least 1 metal salt among these.

  Examples of alkali metal or alkaline earth metal salts used as neutralizers or stabilizers include sodium acetate, magnesium acetate, potassium acetate, calcium acetate, sodium hydroxide, magnesium hydroxide, potassium hydroxide, water Calcium oxide is included.

  In the example of 2) cellulose acetate washing method, the synthesized cellulose acetate is washed with a solvent capable of dissolving a metal salt (water, methanol, ethanol, etc.) or a dilute acidic aqueous solution (hydrochloric acid or sulfuric acid, etc.). Methods are included. The acid concentration of the dilute acidic aqueous solution is preferably 0.1 mol / L or less, and more preferably 0.01 mol / L or less in order to suppress hydrolysis of cellulose acetate during washing. The washing method is not particularly limited, and may be a suspension washing method, for example.

  The addition of the metal salt to the cellulose acetate after the synthesis of 3) is performed by, for example, immersing the synthesized cellulose acetate in a metal salt solution, followed by filtration and drying.

  Examples of the metal salt contained in the metal salt solution include sodium acetate, magnesium acetate, potassium acetate, calcium acetate, sodium hydroxide, magnesium hydroxide, potassium hydroxide, calcium hydroxide and the like. The solvent contained in the metal salt solution may be any solvent that dissolves the metal salt, preferably water, methanol or ethanol, more preferably water. The concentration of the metal salt solution is preferably 0.1 mol / L or less, and more preferably 0.01 mol / L or less.

  As described above, alkali metal ions and alkaline earth metal ions contained in cellulose acetate include not only those contained as acetates and sulfates (free acid salts), but also acid groups (carboxyl groups or sulfones) of cellulose acetate. Some of them are included as counter ions of the group.

  “Total amount of alkali metal ions and alkaline earth metal ions contained in 1 kg of cellulose acetate (A)” of “alkali metal ions and alkaline earth metal ions present as counter ions of cellulose acetate contained in 1 kg of cellulose acetate” The ratio (B / A) of the “total amount (B)” is preferably 0.5 or more and 0.9 or less, and more preferably 0.75 or more and 0.9 or less.

  “Alkali metal ions and alkaline earth metal ions present as counter ions of cellulose acetate” can highly disperse fine gels that cause turbidity of the cellulose acetate solution described above. That is, the fine gel that causes the turbidity of the cellulose acetate solution is stabilized (dispersed) by the metal ions present as counterions of itself (cellulose diacetate); and the free acid surrounding the fine gel It is thought that it is further stabilized (dispersed) by the metal ion present as a salt. Therefore, by setting the ratio (B / A) within the above range, a fine gel can be highly dispersed, and the internal haze of the resulting film can be lowered. Furthermore, since the unevenness formed by the fine gel is uniformly dispersed on the surface of the obtained film, it is considered that the blocking resistance is also improved.

  The amount (B) of alkali metal ions and alkaline earth metal ions present as counter ions of cellulose acetate contained in cellulose acetate is, for example, contained in cellulose acetate obtained after thoroughly washing cellulose acetate with pure water. The amount of alkali metal ions and alkaline earth metal ions to be produced may be measured by the same method as described above.

  The ratio (B / A) adjusts the synthesis conditions (for example, the amount of catalyst) of cellulose acetate; the cellulose acetate has “an alkali metal ion and an alkaline earth metal ion present as a counter ion of cellulose acetate” or “free acid. It can be adjusted by adding "alkali metal ions and alkaline earth metal ions" which are present as salts.

  Among these, in order to accurately adjust the ratio (B / A) to the above range, “alkaline metal ions and alkaline earth metal ions present as counter ions of cellulose acetate” or “free” A method of adjusting by adding alkali metal ions and alkaline earth metal ions (metal salts) existing as acid salts is preferable. In that case, 1) after sufficiently washing cellulose acetate with a solvent such as pure water and measuring the amount of “alkali metal ions and alkaline earth metal ions present as counter ions of cellulose acetate”; 2) ratio (B It is preferable to add a metal salt so that / A) becomes a desired value.

  “Alkali metal ions and alkaline earth metal ions present as free acid salts” are water-soluble. Therefore, the “alkali metal ions and alkaline earth metal ions present as counter ions of the acidic group of cellulose acetate” means that after washing cellulose acetate thoroughly with pure water, the alkali metal ions and alkaline earth ions remaining in cellulose acetate It can be isolated as a metal ion.

  Judgment as to whether or not “alkaline metal ions and alkaline earth metal ions present as counter ions of the acidic groups of cellulose acetate” could be completely isolated: 1) After each washing operation, the cellulose acetate was washed several times. 2) The total amount of alkali metal ions and alkaline earth metal ions contained in the cellulose acetate was measured. 2) The total amount of measured alkali metal ions and alkaline earth metal ions did not change depending on the number of washings (approximately constant). It can be done by a method to confirm that. For example, under the above washing conditions, “alkaline metal ions and alkaline earth metal ions present as counter ions of the acidic group of cellulose acetate” can be almost completely isolated by a single washing operation.

  For example, in order to reduce the ratio (B / A), cellulose acetate is impregnated with a solution containing a metal salt, and then filtered and dried. The amount of “alkaline earth metal ions” may be increased; the amount of catalyst, which is a synthesis condition of cellulose acetate, may be decreased. On the other hand, in order to increase the ratio (B / A), for example, cellulose acetate is washed with a solvent capable of dissolving the free acid salt (pure water, methanol, ethanol, etc.), etc. The amount of “alkaline metal ions and alkaline earth metal ions” present may be reduced; or the amount of catalyst, which is a synthesis condition of cellulose acetate, may be increased.

  The cellulose acetate contained in the optical film of the present invention satisfies the ratio of the substitution degree of the 6-position acetyl group, the turbidity of the solution, and the total amount (A) of alkali metal ions and alkaline earth metal ions. It is more preferable that the ratio (B / A) of the total amount (B) of the alkali metal ions and alkaline earth metal ions present as the counter ions described above is further satisfied.

  One type of cellulose ester may be sufficient as the cellulose ester contained in the optical film of this invention, for example, the mixture of two or more types of cellulose esters from which substitution degree differs may be sufficient. The mixing ratio in the mixture of two types of cellulose esters can be 10:90 to 90:10 (mass ratio).

  The optical film of the present invention may further contain a sugar ester compound, a plasticizer, a retardation control agent, a wavelength dispersion control agent, an ultraviolet absorber, an antioxidant, fine particles and the like in addition to the cellulose acetate described above.

Sugar ester compound The sugar ester compound contained in the optical film of the present invention is a compound obtained by esterifying a hydroxyl group contained in sugar and a monocarboxylic acid.

  The sugar constituting the sugar ester compound is preferably a compound in which at least one of the furanose structure and the pyranose structure is bonded to 1 or more and 12 or less.

Examples of sugars constituting the sugar ester compound include monosaccharides such as glucose, galactose, mannose, fructose, xylose and arabinose; disaccharides such as lactose, sucrose, maltitol, lactitol, lactulose, cellobiose, maltose, gentiobiose;
Contains trisaccharides such as cellotriose, maltotriose, raffinose, kestose, gentiotriose, and xylotriose; polysaccharides with more than tetrasaccharides such as nystose, 1F-fructosylnystose, stachyose, gentiotetraose, galactosyl sucrose, etc. It is. Examples of sugars constituting the sugar ester compound include oligosaccharides such as maltooligosaccharide, isomaltooligosaccharide, fructooligosaccharide, galactooligosaccharide, and xylo-oligosaccharide. These oligosaccharides are produced by allowing an enzyme such as amylase to act on starch or sucrose.

  Of these, sugars having both a pyranose structure and a furanose structure are preferable, sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose and the like are more preferable, and sucrose is more preferable.

  The monocarboxylic acid constituting the sugar ester compound is not particularly limited, and may be a known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, or aromatic monocarboxylic acid. In order to easily develop the retardation of the film, an aromatic monocarboxylic acid is preferable. The monocarboxylic acid may be one kind or a mixture of two or more kinds. For example, an aliphatic monocarboxylic acid and an aromatic monocarboxylic acid may be combined.

  Examples of aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid Saturated fatty acids such as acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid Unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid, octenoic acid and the like are included.

  Examples of the alicyclic monocarboxylic acid include acetic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, and cyclooctanecarboxylic acid.

  The aromatic monocarboxylic acid is a monocarboxylic acid having one or more benzene rings, and the benzene ring may further have a substituent such as an alkyl group or an alkoxy group. Examples of aromatic monocarboxylic acids include benzoic acid, xylic acid, hemelitic acid, mesitylene acid, prenicylic acid, γ-isoduric acid, jurylic acid, mesitonic acid, α-isoduric acid, cumic acid, α-toluic acid, hydroatropa Acid, atropic acid, hydrocinnamic acid, salicylic acid, o-anisic acid, m-anisic acid, p-anisic acid, creosote acid, o-homosalicylic acid, m-homosalicylic acid, p-homosalicylic acid, o-pyrocatechuic acid, β-resorcylic acid, vanillic acid, isovanillic acid, veratromic acid, o-veratrumic acid, gallic acid, asaronic acid, mandelic acid, homoanisic acid, homovanillic acid, homoveratrumic acid, o-homoveratrumic acid, phthalonic acid, p-coumaric acid, etc. Among them, benzoic acid is particularly preferable.

  It is preferable that 70% or more of the hydroxyl groups contained in the constituent sugar having a pyranose structure or furanose structure are esterified with a monocarboxylic acid.

The sugar ester compound is a compound obtained by esterifying a sugar obtained by condensing at least one of the pyranose structure or furanose structure represented by the following general formula (A) with 1 or more and 12 or less with a monocarboxylic acid. Preferably there is.

In the formula (A), R _{11 to} R ₁₅ and R _{21 to} R ₂₅ represent an acyl group having 2 to 22 carbon atoms or a hydrogen atom. m and n each represent an integer of 0 to 12, and m + n represents an integer of 1 to 12.

  The acyl group having 2 to 22 carbon atoms is preferably a benzoyl group. The benzoyl group may further have a substituent, and examples of such a substituent include an alkyl group, an alkenyl group, an alkoxyl group, and a phenyl group.

Specific examples of the sugar ester compound are shown below, but are not limited thereto.

  The content of the sugar ester compound is preferably 1 to 30% by mass with respect to the cellulose ester in order to suppress the fluctuation of the retardation value due to the fluctuation of the humidity of the optical film and stabilize the display quality. It is particularly preferably 5 to 30% by mass.

Plasticizer Examples of plasticizers include polyester plasticizers, polyhydric alcohol ester plasticizers, polycarboxylic acid ester plasticizers (including phthalate ester plasticizers), glycolate plasticizers, ester plasticizers. Agents (including fatty acid ester plasticizers) and acrylic plasticizers are preferred. These may be used alone or in combination of two or more.

Polyester Plasticizer The polyester plasticizer is preferably a compound represented by the following general formula (1).
General formula (1)
B- (GA) n-GB

  In the formula (1), A represents a divalent group derived from an alkylene dicarboxylic acid having 4 to 12 carbon atoms or a divalent group derived from an aryl dicarboxylic acid having 8 to 14 carbon atoms. G is a divalent group derived from an alkylene glycol having 2 to 12 carbon atoms, a divalent group derived from an aryl glycol having 6 to 12 carbon atoms, or an oxyalkylene having 4 to 12 carbon atoms. Represents a divalent group derived from glycol. B represents a monovalent group derived from a hydrogen atom or a monocarboxylic acid. n represents an integer of 1 or more.

  Examples of the divalent group of A derived from an alkylene dicarboxylic acid having 4 to 12 carbon atoms include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid And divalent groups derived from the above. Examples of divalent groups derived from aryl dicarboxylic acids having 8 to 14 carbon atoms in A include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, etc. A divalent group derived from is included.

  Examples of the divalent group of G derived from an alkylene glycol having 2 to 12 carbon atoms include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, , 3-butanediol, 1,2-propanediol, 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-didiol) Methylol heptane), 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2- Methyl-1,8-octanediol, 1, - nonanediol, include divalent groups derived from 1,10-decanediol, and 1,12-octadecanediol like.

  Examples of the divalent group of G derived from an aryl glycol having 6 to 12 carbon atoms include 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), and 1,4-dihydroxy. Divalent groups derived from benzene (hydroquinone) and the like are included. Examples of the divalent group derived from oxyalkylene glycol having 4 to 12 carbon atoms in G are derived from diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol and the like. Divalent groups are included.

  G is preferably a divalent group derived from an alkylene glycol having 2 to 12 carbon atoms. This is to increase the compatibility of the polyester plasticizer with the cellulose ester.

  Examples of the monovalent group of B derived from monocarboxylic acid include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, and normal propyl benzoic acid. Monovalent groups derived from, for example, aromatic monocarboxylic acids such as aminobenzoic acid, and acetoxybenzoic acid; aliphatic monocarboxylic acids such as acetic acid, propionic acid, and butyric acid.

  The number average molecular weight of the polyester plasticizer is preferably 300 to 1500, and more preferably 400 to 1000. A polyester plasticizer having a number average molecular weight of less than 300 may be easily eluted from the optical film.

  The acid value of the polyester-based plasticizer is preferably 0.5 mgKOH / g or less from the viewpoint of enhancing the adhesion between the optical film containing the plasticizer and another functional layer such as a hard coat layer, and the like. / G or less is more preferable. The acid value of the polyester plasticizer is defined as the number of milligrams of potassium hydroxide required to neutralize the acid (carboxyl group present in the sample) contained in 1 g of the sample. The acid value of the polyester plasticizer can be measured according to JIS K0070.

  The hydroxyl value of the polyester plasticizer is preferably 25 mgKOH / g or less, and more preferably 15 mgKOH / g or less, from the viewpoint of enhancing the compatibility with the cellulose ester. The hydroxyl value of the polyester plasticizer is defined as the number of milligrams of potassium hydroxide required to neutralize unreacted acetic acid when 1 g of a sample is reacted with acetic anhydride and acetylated. The hydroxyl value of the polyester plasticizer can be measured according to JIS K 0070 (1992).

Specific examples of the polyester plasticizer represented by the formula (1) are shown below.

Polyhydric alcohol ester plasticizer The polyhydric alcohol ester plasticizer is an ester compound (alcohol ester) of a divalent or higher aliphatic polyhydric alcohol and a monocarboxylic acid, preferably a 2-20 valent aliphatic. It is a polyhydric alcohol ester. The polyhydric alcohol ester compound preferably has an aromatic ring or a cycloalkyl ring in the molecule.

  Preferred examples of the aliphatic polyhydric alcohol include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol , Galactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like. Of these, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, xylitol and the like are preferable.

  The monocarboxylic acid is not particularly limited, and may be an aliphatic monocarboxylic acid, an alicyclic monocarboxylic acid, an aromatic monocarboxylic acid, or the like. In order to increase the moisture permeability of the film and make it less likely to volatilize, an alicyclic monocarboxylic acid or an aromatic monocarboxylic acid is preferred. One type of monocarboxylic acid may be sufficient and a 2 or more types of mixture may be sufficient as it. Further, all of the OH groups contained in the aliphatic polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  The aliphatic monocarboxylic acid is preferably a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms. The carbon number of the aliphatic monocarboxylic acid is more preferably 1-20, and still more preferably 1-10. Examples of such aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanoic acid, undecylic acid, lauric acid , Saturated fatty acids such as tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid; Examples include unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid. Especially, in order to improve compatibility with a cellulose ester, the mixture of an acetic acid or an acetic acid and another monocarboxylic acid is preferable.

  Examples of the alicyclic monocarboxylic acid include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid and the like.

  Examples of aromatic monocarboxylic acids include those in which 1 to 3 alkoxy groups such as an alkyl group, a methoxy group or an ethoxy group are introduced into the benzene ring of benzoic acid such as benzoic acid or toluic acid; biphenylcarboxylic acid, naphthalene Aromatic monocarboxylic acids having two or more benzene rings such as carboxylic acid and tetralincarboxylic acid are included, and benzoic acid is preferable.

  The molecular weight of the polyhydric alcohol ester plasticizer is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. In order to make it difficult to volatilize, a higher molecular weight is preferable; in order to improve moisture permeability and compatibility with cellulose ester, a lower molecular weight is preferable.

Polyvalent carboxylic ester plasticizer The polyvalent carboxylic ester plasticizer is an ester compound of a divalent or higher, preferably 2-20 valent polycarboxylic acid and an alcohol compound. The polyvalent carboxylic acid is preferably a 2-20 valent aliphatic polyvalent carboxylic acid, or a 3-20 valent aromatic polyvalent carboxylic acid or a 3-20 valent alicyclic polyvalent carboxylic acid. .

  Preferred examples of the polyvalent carboxylic acid include trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid; succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid Aliphatic polycarboxylic acids such as maleic acid and tetrahydrophthalic acid; oxypolyvalent carboxylic acids such as tartaric acid, tartronic acid, malic acid and citric acid are included. Carboxylic acid.

  Examples of alcohol compounds include known alcohol compounds and phenol compounds. Examples of the alcohol compound include linear or branched aliphatic saturated alcohols or aliphatic unsaturated alcohols having 1 to 32 carbon atoms, more preferably 1 to 20 carbon atoms, and still more preferably 1 to 10 carbon atoms; Examples include alicyclic alcohol compounds such as pentanol and cyclohexanol; aromatic alcohol compounds such as benzyl alcohol and cinnamyl alcohol. The alcohol compound may be one kind or a mixture of two or more kinds.

  In the oxypolycarboxylic acid as the polyvalent carboxylic acid, an alcoholic or phenolic hydroxyl group may be esterified with a monocarboxylic acid. The monocarboxylic acid used for esterification can be an aliphatic monocarboxylic acid, an alicyclic monocarboxylic acid, or an aromatic monocarboxylic acid.

  The aliphatic monocarboxylic acid includes a linear or branched fatty acid having 1 to 32 carbon atoms, preferably 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms. Examples of such aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid. Saturated fatty acids such as acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid An unsaturated fatty acid such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and the like;

  Examples of the alicyclic monocarboxylic acid include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid and the like. Examples of aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid Aromatic monocarboxylic acids and the like are included. Of these, acetic acid, propionic acid, and benzoic acid are particularly preferable.

  The molecular weight of the polycarboxylic acid ester plasticizer is not particularly limited, but is preferably 300 to 1000, and more preferably 350 to 750. The molecular weight of the polyvalent carboxylic acid ester plasticizer is preferably larger from the viewpoint of suppressing bleed-out; it is preferably smaller from the viewpoint of moisture permeability and compatibility with the cellulose ester.

  The acid value of the polyvalent carboxylic acid ester plasticizer is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. It is preferable to set the acid value within the above range because retardation fluctuations in the retardation are also suppressed.

  The acid value of the polyvalent carboxylic ester plasticizer is defined as the number of milligrams of potassium hydroxide required to neutralize the acid (carboxyl group present in the sample) contained in 1 g of the sample. The acid value can be measured according to JIS K0070.

  Examples of polycarboxylic acid ester plasticizers include triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl triphenyl citrate. Benzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, tributyl trimellitic acid, tetrabutyl pyromellitic acid and the like are included.

  The polyvalent carboxylic acid ester plasticizer may be a phthalic acid ester plasticizer. Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, dicyclohexyl terephthalate and the like.

  Examples of glycolate plasticizers include alkylphthalyl alkyl glycolates. 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, 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 glycolate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl Glycolate, and the like are included.

  The ester plasticizer includes a fatty acid ester plasticizer, a citrate ester plasticizer, a phosphate ester plasticizer, and the like.

  Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate. Examples of the citrate plasticizer include acetyltrimethyl citrate, acetyltriethyl citrate, and acetyltributyl citrate. Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, and the like.

Acrylic plasticizer Acrylic plasticizer includes at least an ethylenically unsaturated monomer Xa that does not have both an aromatic ring and a hydroxyl group in the molecule, and an ethylenically unsaturated monomer Xb that does not have an aromatic ring in the molecule and has a hydroxyl group. And a polymer Y having an ethylenically unsaturated monomer Ya having no aromatic ring in the molecule as a polymerization component. The ethylenically unsaturated monomer is preferably a (meth) acrylic acid ester.

The polymer X preferably has a structure represented by the following general formula (X). The following formula _{(X) - [CH 2 -C} (-Rc) (- CO 2 Rd)] m- is a group derived from an ethylenically unsaturated monomer _{Xa; - [CH 2 -C (} -Re ) (— CO ₂ Rf—OH) —] n— is a group derived from the ethylenically unsaturated monomer Xb.
Formula (X)
_{- [CH 2 -C (-Rc)} (- CO 2 Rd)] m- [CH 2 -C (-Re) (- CO 2 Rf-OH) -] n- [Xc] p-

  Rc and Re in the formula (X) represent a hydrogen atom or a methyl group. Rd represents an alkylene group having 1 to 12 carbon atoms or a cycloalkylene group. Rf represents a methylene group, an ethylene group or a propylene group. Xc represents a monomer unit polymerizable to Xa and Xb. m, n and p represent molar composition ratios. However, m and n are not 0, and m + n + p = 100. The weight average molecular weight of the polymer X is preferably 3000 to 30000.

The polymer Y preferably has a structure represented by the following general formula (Y). The following formula _{(Y) - [CH 2 -C} (-Rg) (- CO 2 Rh-OH) -] k- is a group derived from an ethylenically unsaturated monomer Ya.
General formula (Y)
_{Ry- [CH 2 -C (-Rg)} (- CO 2 Rh-OH) -] k- [Yb] q-

  Rg in the formula (Y) represents a hydrogen atom or a methyl group. Rh represents a methylene group, an ethylene group or a propylene group. Ry represents a hydrogen atom, a hydroxyl group, or an alkyl group having 1 to 3 carbon atoms. Yb represents a monomer unit copolymerizable with Ya. k and q represent a molar composition ratio. However, k is not 0 and k + q = 100. The weight average molecular weight of the polymer Y is preferably 500 or more and 3000 or less.

  The total content of these plasticizers is preferably 0.5 to 30% by mass and more preferably 5 to 20% by mass with respect to the cellulose ester.

Retardation Control Agent The optical film of the present invention may further contain a retardation control agent in order to improve the liquid crystal display quality. The retardation control agent includes an aromatic compound having two or more aromatic rings as described in European Patent No. 91656A2, a rod-shaped compound described in JP-A-2006-2025, and the like. One type of retardation control agent may be sufficient, and a 2 or more types of mixture may be sufficient as it.

  The aromatic ring contained in the aromatic compound includes an aromatic hydrocarbon ring and an aromatic heterocycle, and is preferably an aromatic heterocycle. As a preferred example of the aromatic heterocycle, a 1,3,5-triazine ring is particularly preferred.

  It is preferable that it is 0.5-20 mass% with respect to the resin component contained in an optical film, and, as for content of a retardation control agent, it is more preferable that it is 1-10 mass%.

Wavelength Dispersion Control Agent The optical film of the present invention may further contain a wavelength dispersion control agent. The wavelength dispersion controlling agent has a function of adjusting the wavelength dispersion characteristic of the retardation of the film.

  The wavelength dispersion controlling agent is preferably a compound having an absorption maximum in a wavelength range of 250 nm to 400 nm, and more preferably a compound having an absorption maximum in a wavelength range of 270 nm to 380 nm in the light absorption spectrum. Preferable examples of the wavelength dispersion control agent include discotic compounds described in JP-A Nos. 2001-166144 and 2003-3446556; compounds described in JP-A 2010-163482, and the like.

  The content of the wavelength dispersion controlling agent is preferably 0.5 to 20% by mass and more preferably 1 to 10% by mass with respect to the entire resin component contained in the optical film.

Ultraviolet Absorber The optical film of the present invention may further contain an ultraviolet absorber in order to improve the durability of the optical film. The ultraviolet absorber is a compound that absorbs ultraviolet rays having a wavelength of 400 nm or less, preferably a compound having a transmittance at a wavelength of 370 nm of 10% or less, more preferably 5% or less, and even more preferably 2% or less.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders, etc. Is a benzotriazole ultraviolet absorber, a benzophenone ultraviolet absorber, or a triazine ultraviolet absorber, more preferably a benzotriazole ultraviolet absorber or a benzophenone ultraviolet absorber.

  Specific examples of the ultraviolet absorber include 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl)- In addition to 6- (linear and side chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., commercially available products Tinobine 109 and Tinuvin manufactured by BASF Japan 171, Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328, Tinuvin 928 and the like are included. These ultraviolet absorbers may be only one kind or a mixture of two or more kinds.

  In addition to these, polymer ultraviolet absorbers and discotic compounds are also preferably used as ultraviolet absorbers. Examples of polymer ultraviolet absorbers include polymer type ultraviolet absorbers described in JP-A-6-148430; examples of discotic compounds include compounds having a 1,3,5-triazine ring. It is.

  Although content of a ultraviolet absorber is based also on the kind of ultraviolet absorber, etc., it is preferable that it is 0.5-10 mass% with respect to the whole optical film, and it is more preferable that it is 0.6-4 mass%. preferable.

Antioxidant The optical film of the present invention may further contain an antioxidant, for example, in order to prevent deterioration of the optical film that is likely to occur under high humidity and high temperature. The antioxidant has a function of delaying or preventing the decomposition of the residual solvent amount in the optical film by halogen or phosphoric acid based plasticizer.

  The antioxidant is preferably a hindered phenol compound, and specific examples thereof include 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-oxide). -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl- -(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-tert-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 and the like are included. 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.

  These compounds include, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine, tris (2,4 It may be used in combination with a phosphorus processing stabilizer such as -di-t-butylphenyl) phosphite.

  The content of the antioxidant is preferably 1 ppm to 1.0% by mass ratio with respect to the cellulose ester, and more preferably 10 to 1000 ppm.

Fine particles The optical film of the present invention may further contain fine particles in order to improve slipperiness. The fine particles may be inorganic fine particles or organic fine particles.

  Examples of inorganic fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate And calcium phosphate. Examples of organic fine particles include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene resin, silicone resin, polycarbonate resin, benzoguanamine resin, melamine Resin, polyolefin powder, polyester resin, polyamide resin, polyimide resin, polyfluorinated ethylene resin, pulverized classification of organic polymer compounds such as starch, polymer compound synthesized by suspension polymerization method, spray High molecular compounds made spherical by a dry method or a dispersion method are included. In order to reduce the increase in the haze of the film, fine particles containing silicon are preferable, and silicon dioxide is particularly preferable.

  Examples of the silicon dioxide fine particles include Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (commercially available from Nippon Aerosil Co., Ltd.). Of these, Aerosil 200V and Aerosil R972V are preferred because of the great effect of reducing the coefficient of friction while keeping the haze of the optical film low.

  The primary average particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm. The fine particles are preferably contained in the optical film so that the dynamic friction coefficient of at least one surface of the optical film is 0.2 to 1.0. The content of the fine particles is preferably 0.01 to 1% by mass and more preferably 0.05 to 0.5% by mass with respect to the optical film.

  Although the thickness of an optical film is not specifically limited, It is preferable that it is 10-200 micrometers, It is more preferable that it is 10-100 micrometers, It is further more preferable that it is 15-60 micrometers. If the thickness of the optical film is too large, the variation in retardation tends to increase due to humidity. On the other hand, if the thickness of the film is too small, it is difficult to obtain a desired retardation.

  The total amount (A) of alkali metal ions and alkaline earth metal ions contained in an optical film equivalent to 1 kg of cellulose ester is preferably 30 mg or more and 250 mg or less, and more preferably 40 mg or more and 200 mg or less. The total amount (A) of alkali metal ions and alkaline earth metal ions contained in an optical film equivalent to 1 kg of cellulose ester is, for example, an acid film obtained by completely burning and ashed an optical film equivalent to 1 kg of cellulose acetate. The amount of alkali metal ions and alkaline earth metal ions contained in the pretreatment solution can be measured by atomic absorption spectrometry.

  The optical film of the present invention is preferably used as an optical compensation film. That is, since the liquid crystal display has an anisotropic liquid crystal material and a polarizing plate, the display screen may be displayed well when viewed from the front, but may not be displayed well when viewed from an oblique direction. (There is viewing angle dependency). The optical compensation film is effective in reducing such viewing angle dependency.

  The refractive index distribution of the liquid crystal cell is usually large in the thickness direction of the liquid crystal cell and small in the in-plane direction. Therefore, it is preferable that the optical compensation film cancels the anisotropy of the refractive index; that is, the refractive index distribution has a negative uniaxiality that is small in the thickness direction and large in the in-plane direction. The optical film of the present invention is preferably used as a film having such an optical compensation function.

The retardation Ro measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH of the optical film of the present invention is preferably 20 to 100 nm. The retardation Rth measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH is preferably 70 to 300 nm. The retardations _R0 and Rth of the optical film can usually be adjusted by stretching conditions.

The in-plane direction retardation R ₀ and the thickness direction retardation Rth are each expressed by the following equations.
Formula (I) R ₀ = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx: refractive index in the slow axis direction in the film plane, ny: refractive index in the direction perpendicular to the slow axis in the film plane, nz: refractive index of the film in the thickness direction, d: film thickness (Nm))

The retardations _R0 and Rth can be determined by the following method, for example.
1) The average refractive index of the film is measured with a refractometer.
2) The retardation _R0 in the in-plane direction when light having a wavelength of 590 nm from the normal direction of the film is incident is measured by KOBRA-21ADH manufactured by Oji Scientific Instruments.
3) The retardation value R (θ) when light having a wavelength of 590 nm is incident from the angle θ (incident angle (θ)) with respect to the film normal direction is measured by KOBRA-21ADH manufactured by Oji Scientific Instruments. . θ is larger than 0 °, preferably 30 ° to 50 °.
4) From the measured R ₀ and R (θ) and the above-described average refractive index and film thickness, nx, ny and nz are calculated by KOBRA-21ADH manufactured by Oji Scientific Instruments, and Rth is calculated. The measurement of retardation can be performed under conditions of 23 ° C. and 55% RH.

  The optical film of the present invention has a slow axis or a fast axis in the film plane. The angle θ1 (orientation angle) between the slow axis and the film forming direction is preferably from −1 ° to + 1 °, and more preferably from −0.5 ° to + 0.5 °. Since the light leakage can be suppressed when the orientation angle θ1 satisfies the above range, the luminance of the display image can be increased.

The retardation _R0 and Rth of the optical film and the orientation angle θ1 can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments).

  The internal haze of the optical film measured in accordance with JIS K-7136 is preferably 0.05% or less, and more preferably 0.03% or less.

The internal haze of the optical film can be measured by a method according to JIS K-7136; specifically, the following method.
A haze meter (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.) is prepared. The light source is a halogen bulb of 5V9W, and the light receiving part is a silicon photocell (with a relative visibility filter).

1) Measurement of blank haze One drop (0.05 ml) of glycerin is dropped on the washed slide glass. At this time, care is taken so that bubbles do not enter the droplet.
Next, a cover glass is placed on the dropped glycerin. Glycerin spreads without pressing the cover glass.
A blank measurement sample (cover glass / glycerin / slide glass) obtained in this manner is set on a haze meter, and haze 1 (blank haze) is measured.
2) Measurement of haze of sample including optical film FIGS. 1A to 1D are schematic diagrams illustrating a measurement procedure of haze of a sample including an optical film.
In the same manner as in 1) above, glycerin is dropped on the washed slide glass (see FIG. 1A).
On the other hand, the optical film to be measured is conditioned at 23 ° C. and 55% RH for 5 hours or more. Next, the conditioned optical film is placed on the dropped glycerin so as not to contain air bubbles (see FIG. 1B).
Further, 0.05 ml of glycerin is dropped on the optical film (see FIG. 1C), and then a cover glass is further placed (see FIG. 1D).
The sample for measurement (cover glass / glycerin / sample film / glycerin / slide glass) obtained in this way is set in the above-mentioned haze meter, and haze 2 is measured.
3) The haze 1 of the optical film is calculated by applying the haze 1 obtained in 1) and the haze 2 obtained in 2) to the following formula.
Internal haze (%) of optical film = Haze 2 (%) − Haze 1 (%)

  The internal haze is measured at 23 ° C. and 55% RH. The glass used for measuring the internal haze is MICRO SLIDE GLASS S9213 MATSANAMI. Glycerin is manufactured by Kanto Kagaku deer grade (purity> 99.0%) and has a refractive index of 1.47.

  In order to reduce the internal haze of the optical film, as described above, the turbidity of the cellulose acetate solution is lowered, or the total amount (A) of alkali metal ions and alkaline earth metal ions contained in the cellulose acetate is reduced. do it.

The moisture permeability of the optical film at 40 ° C. and 90% RH measured in accordance with JIS Z 0208 is preferably 10 to 1200 g / m ² · 24 h. In order to reduce the moisture permeability of the optical film, for example, the total acyl group substitution degree of the cellulose ester contained in the optical film is increased, the ratio of the acyl group substitution degree of 3 or more carbon atoms is increased, a plasticizer, etc. A large amount of the additive may be contained.

  The visible light transmittance of the optical film of the present invention is preferably 90% or more, and more preferably 93% or more. The breaking elongation of the optical film of the present invention is preferably 10 to 80%.

2. Method for Producing Optical Film The optical film of the present invention can be produced through a step of obtaining a resin composition containing the cellulose ester described above and a step of forming the resin composition into an optical film. Examples of the method for molding the resin composition include a solution casting method and a melt casting method, but the solution casting method is preferable from the viewpoint of obtaining a thin film with high flatness. .

  The step of producing the optical film of the present invention by the solution casting method is 1) a step of preparing a dope (resin composition) by dissolving at least the above cellulose ester and, if necessary, a plasticizer in a solvent, ) A step of casting the dope onto an endless metal support, 3) a step of drying the cast dope to form a web, 4) a step of peeling the web from the metal support, and 5) stretching the web to form a film. 6) a step of further drying the film, and 7) a step of winding up the obtained film.

1) Process for preparing dope The dope is prepared by dissolving the above cellulose ester and, if necessary, an additive in a solvent. The concentration of the cellulose ester contained in the dope is preferably high in order to reduce the drying load. However, if the concentration of the cellulose ester is too high, it is difficult to filter, and the filtration accuracy tends to decrease. For this reason, it is preferable that the density | concentration of the cellulose ester contained in dope is 10-35 mass%, and it is more preferable that it is 15-25 mass%.

  The solvent contained in the dope may be one kind or a combination of two or more kinds. From the viewpoint of increasing production efficiency, it is preferable to use a combination of a good solvent and a poor solvent for cellulose ester. A good solvent refers to a solvent that dissolves cellulose ester alone, and a poor solvent refers to a solvent that swells cellulose or does not dissolve alone. Therefore, the good solvent and the poor solvent differ depending on the average acyl group substitution degree (acetyl group substitution degree) of the cellulose ester.

  When a good solvent and a poor solvent are used in combination, it is preferable that the good solvent is more than the poor solvent in order to increase the solubility of the cellulose ester. The mixing ratio of the good solvent and the poor solvent is preferably 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent.

  Examples of the good solvent include organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate, and preferably methylene chloride or methyl acetate. Examples of the poor solvent include methanol, ethanol, n-butanol, cyclohexane, cyclohexanone and the like. The dope preferably contains 0.01 to 2% by mass of water.

  The method of dissolving the cellulose ester in the solvent may be a general method, for example, a method of dissolving under heating and pressure, a poor solvent added to the cellulose ester to swell, and then adding a good solvent to dissolve. It can be a method. Especially, since it can heat beyond the boiling point in a normal pressure, the method of making it melt | dissolve under a heating and pressurization is preferable. Specifically, when stirring and dissolving while heating to a temperature in the range where the solvent is boiling or higher under normal pressure and the solvent does not boil under pressure, the generation of bulk undissolved material called gel or mamako can be suppressed.

  The pressurization can be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature is preferably higher from the viewpoint of increasing the solubility of the cellulose ester, but if it is too high, the pressure needs to be increased, and the productivity is lowered. For this reason, it is preferable that heating temperature is 45-120 degreeC, 60-110 degreeC is more preferable, and it is further more preferable that it is 70-105 degreeC. The pressure is adjusted to a range in which the solvent does not boil at the set heating temperature.

  Additives such as UV inhibitors and fine particles may be added batchwise to the dope, or an additive solution prepared separately may be added inline. The additive solution is obtained by dissolving an additive in an alcohol such as methanol, ethanol or butanol, a solvent such as methylene chloride, methyl acetate, acetone or dioxolane, or a mixed solvent thereof.

  In particular, part or all of the fine particles are preferably added in-line in order to reduce the load on the filter medium. When the additive solution is added in-line, it is preferable to dissolve a small amount of cellulose ester in the additive solution in order to improve mixing with the dope. The amount of the cellulose ester added to the additive solution is preferably 1 to 10 parts by mass and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  The in-line addition can be performed using an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer), or the like.

  The obtained dope may contain insoluble matters such as impurities contained in the cellulose ester as a raw material, for example. Such an insoluble matter can become a bright spot foreign material in the obtained film. In order to remove such insoluble matter and the like, it is preferable to filter the obtained dope.

  The dope is filtered by a filter medium such as filter paper. The absolute filtration accuracy of the filter medium is preferably small in order to highly remove insoluble matters and the like contained in the dope, but if it is too small, clogging tends to occur. For this reason, the absolute filtration accuracy of the filter medium is preferably 0.008 mm or less, more preferably 0.001 to 0.008 mm, and still more preferably 0.003 to 0.006 mm.

  The type of the filter medium may be a normal filter medium, and may be a plastic filter medium such as polypropylene or Teflon (registered trademark), or a metal filter medium such as stainless steel. Among these, a metal filter medium is preferable from the viewpoint of less fiber dropping.

  In order to reduce the differential pressure before and after filtration, the dope is preferably filtered under heating and pressure as in the preparation of the dope. Similarly to the preparation of the dope, the heating temperature is preferably not less than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure, specifically 45 to 120 ° C. It is preferably 45 to 70 ° C, more preferably 45 to 55 ° C. The filtration pressure is preferably low, specifically 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

The dope filtration is preferably performed so that the number of bright spot foreign matters in the obtained film is not more than a certain value. Specifically, the number of bright spot foreign matters having a diameter of 0.01 mm or more is 200 / cm ² or less, preferably 100 / cm ² or less, more preferably 50 / m ² or less, and still more preferably 0. -10 pieces / cm ² or less. It is preferable that the number of bright spot foreign materials having a diameter of 0.01 mm or less is also small.

The number of bright spot foreign matter on the film can be measured by the following procedure.
i) Two polarizing plates are arranged in a crossed Nicol state, and the obtained film is arranged between them.
ii) Count the number of spots (foreign matter) where light is leaked when light is applied from one polarizing plate and observed from the other polarizing plate.

2) Step of casting dope The metal support on which the dope is cast preferably has a mirror-finished surface. Preferred examples of the metal support include a stainless steel belt and a drum whose surface is plated with a casting.

  The surface temperature of the metal support on which the dope is cast is preferably high in order to increase the drying speed of the web, but if it is too high, the web may foam or the smoothness of the web may be reduced. . Therefore, the surface temperature of the metal support is preferably set to −50 ° C. or higher and lower than the boiling point of the solvent, more preferably 0 to 40 ° C., and further preferably 5 to 30 ° C.

  The method for controlling the surface temperature of the metal support is not particularly limited, and may be a method of blowing warm air or cold air, a method of bringing hot water into contact with the back side of the metal support, or the like. From the viewpoint of efficiently transferring heat and shortening the time until the temperature of the metal support becomes constant, a method of bringing hot water into contact with the back side of the metal support is preferable.

3) About the process of drying the cast dope The cast dope is dried so that a residual solvent may become below fixed. The amount of residual solvent in the web when peeling the web from the metal support is preferably 10 to 150% by mass in order to improve the flatness of the resulting film, and 20 to 40% by mass (low residual solvent amount). Or it is more preferable that it is 60-130 mass% (high residual solvent amount), and it is further more preferable that it is 20-30 mass% (low residual solvent amount) or 70-120 mass% (high residual solvent amount).

The amount of residual solvent in the web is defined by the following formula. In the following formula, M represents the mass of a sample collected at an arbitrary point from the web being manufactured or the film after manufacture. N represents the mass of the sample after heating the sample at 115 ° C. for 1 hour.
Residual solvent amount (% by mass) = {(MN) / N} × 100

4) About the process of peeling a web Although peeling of a web is performed by a general method, it is preferable to peel with a peeling roll. Peeling with a peeling roll is preferably carried out when the web reaches the lower surface of the metal support and almost completes a round. The web peeling tension is preferably 300 N / m or less.

  The peeling of the web is not only the method of peeling after the web is dried in the step 3), but also after the step 2), the cast film is cooled without being dried and contains a large amount of residual solvent. After gelling as it is, it may be peeled off.

  The peeled web may be further dried. In general, the peeled web can be dried while the web is conveyed. Specifically, there are a roll drying method and a tenter method in which the peeled web is dried while being conveyed by a large number of rolls arranged vertically.

  The method for drying the web is not particularly limited, but in general, it may be a method of drying with hot air, infrared rays, heating rolls, microwaves, or the like, and from the viewpoint of simplicity, a method of drying with hot air is preferable. The drying temperature of the web is preferably increased stepwise from 40 ° C to 200 ° C.

5) About the process of extending | stretching a web The optical film which has desired retardation value Ro and Rth is obtained by extending | stretching a web. The retardation values Ro and Rth of the optical film can be controlled by adjusting the magnitude of the tension applied to the web at least in the direction (width direction) perpendicular to the web conveyance direction (the dope casting direction). it can.

  The web may be stretched at least in the width direction, and may be uniaxial stretching or biaxial stretching. The web may be stretched in the width direction or in an oblique direction with respect to the casting direction of the dope. Biaxial stretching includes stretching in both the web conveyance direction (longitudinal direction) and the width direction (lateral direction). Stretching may be sequential stretching or simultaneous stretching.

  When the web is stretched biaxially in directions orthogonal to each other, the web is finally 1.1 to 2.5 times in the width direction (lateral direction) and 0.8 in the transport direction (longitudinal direction). It is preferable to set it to -1.5 times; It is more preferable to set it to 1.2 to 2.0 times in the width direction (horizontal direction) and 0.9 to 1.0 times in the conveyance direction (vertical direction).

  The web stretching temperature is preferably 120 ° C to 200 ° C, and more preferably 140 ° C to 180 ° C. The residual solvent of the stretched web is preferably 20% by mass or less, and preferably 15% by mass or less.

  The method of stretching the web is not particularly limited, and a method in which a difference in peripheral speed is applied to a plurality of rolls and the roll is stretched in the longitudinal direction using the difference in the peripheral speed of the roll (roll stretching method). The clip and pin spacing is widened in the vertical direction and stretched in the vertical direction. Law). These stretching methods may be combined.

  In the tenter stretching method, the clip portion is preferably driven by a linear drive method. This is because the movement of the clip portion is smooth, so that it is easy to stretch and the risk of web breakage can be reduced.

  It is preferable to carry out the web width maintenance and the transverse stretching by a tenter method. The tenter method may be a pin tenter method or a clip tenter method.

  The width of the optical film obtained by stretching is preferably 4 m or less, more preferably 1 to 4 m, even more preferably 1.4 to 4 m, from the viewpoint of facilitating conveyance. It is particularly preferably 1.6 to 3 m. The optical film obtained by stretching is further dried as necessary and then wound.

  The optical film of the present invention is used as a functional film for various display devices such as liquid crystal displays, plasma displays, and organic EL displays. In particular, the optical film of the present invention includes a polarizing plate protective film, a retardation film, an antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an optical compensation film for expanding the viewing angle, etc. for liquid crystal display devices. It can be.

3. Polarizing plate The polarizing plate of the present invention includes a polarizer and the optical film of the present invention disposed on one surface thereof, and further includes a polarizing plate protective film disposed on the other surface of the polarizer as necessary. May be included.

  A polarizer is an element that allows only light having a polarization plane in a certain direction to pass therethrough. A typical example of the polarizer is a polyvinyl alcohol-based polarizing film, and there are one in which a polyvinyl alcohol-based film is dyed with iodine and one in which a dichroic dye is dyed.

  The polarizer may be a film obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing with iodine or a dichroic dye, or after dyeing a polyvinyl alcohol film with iodine or a dichroic dye, A uniaxially stretched film (preferably a film further subjected to durability treatment with a boron compound) may be used. The thickness of the polarizer is preferably 5 to 30 μm, and more preferably 10 to 20 μm.

  The polyvinyl alcohol film may be a film formed from a polyvinyl alcohol aqueous solution. The polyvinyl alcohol film is preferably an ethylene-modified polyvinyl alcohol film because it is excellent in polarizing performance and durability performance and has few color spots. Examples of the ethylene-modified polyvinyl alcohol film include an ethylene unit content of 1 to 4 mol%, a polymerization degree of 2000 to 4000, and a saponification degree of 99 described in JP2003-248123A, JP2003-342322A, and the like. 0.0 to 99.99 mol% film is included.

  Examples of dichroic dyes include azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes and anthraquinone dyes.

  The optical film of the present invention may be disposed directly on one surface of the polarizer, or may be disposed via another film or layer. The optical film of the present invention is preferably an optical compensation film that also functions as a polarizing plate protective film. This is because it is not necessary to further use an optical compensation film separately from the polarizing plate protective film, and not only the liquid crystal display device can be thinned but also the manufacturing process can be simplified.

  The polarizing plate protective film other than the optical film of the present invention is not particularly limited, and may be a normal cellulose ester film or the like. Examples of commercially available cellulose ester films include commercially available cellulose ester films (for example, Konica Minoltak KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8UY-X KC8UXW-RHA-C, KC8UXW-RHA-NC, KC4UXW-RHA-NC, manufactured by Konica Minolta Opto Co., Ltd.) are preferably used.

  The polarizing plate can usually be produced by laminating the polarizer and the optical film or polarizing plate protective film of the present invention. For example, the surface of the optical film of the present invention on the side in contact with the polarizer is preferably subjected to alkali saponification treatment and then bonded to the polarizer via an adhesive such as a completely saponified polyvinyl alcohol aqueous solution.

4). Liquid Crystal Display Device The liquid crystal display device of the present invention includes a liquid crystal cell and a pair of polarizing plates that sandwich the liquid crystal cell. And at least one is a polarizing plate which has the above-mentioned optical film among a pair of polarizing plates, Preferably both a pair of polarizing plates are polarizing plates which have the above-mentioned optical film.

  FIG. 2 is a schematic diagram showing a basic configuration of an embodiment of the liquid crystal display device according to the present invention. As shown in FIG. 2, the liquid crystal display device 10 includes a liquid crystal cell 20, a first polarizing plate 40 and a second polarizing plate 60 that sandwich the liquid crystal cell 20, and a backlight 80.

  The display method of the liquid crystal cell 20 is not particularly limited, and is a TN (Twisted Nematic) method, an STN (Super Twisted Nematic) method, an IPS (In-Plane Switching) method, an OCB (Optically Compensated Birefringence Ventilating Ventilation method). There are systems (including MVA; Multi-domain Vertical Alignment and PVA; including Patterned Vertical Alignment), and HAN (Hybrid Aligned Nematic). In order to increase the contrast, the VA (MVA, PVA) method is preferable.

  A VA liquid crystal cell usually includes a pair of opposing transparent substrates and a liquid crystal layer that is sandwiched between the pair of transparent substrates and includes positive liquid crystal.

  Of at least one of the pair of transparent substrates, a pixel electrode for applying a voltage to the positive liquid crystal and a counter electrode corresponding to the pixel electrode are disposed.

  The liquid crystal layer includes positive liquid crystal molecules that are nematic liquid crystal materials having positive dielectric anisotropy. This positive type liquid crystal molecule is not applied with voltage (when no electric field is generated between the pixel electrode and the counter electrode) due to the alignment regulating force of the alignment film provided on the liquid crystal layer side surface of the transparent substrate. The major axis of the liquid crystal molecules is aligned so as to be substantially perpendicular to the surface of the transparent substrate.

  In the liquid crystal cell thus configured, an image signal (voltage) is applied to the pixel electrode, thereby generating an electric field in the horizontal direction with respect to the substrate surface between the pixel electrode and the counter electrode. Thereby, the liquid crystal molecules initially aligned perpendicularly to the surface of the transparent substrate are aligned so that the major axis thereof is in the horizontal direction with respect to the substrate surface. In this way, the liquid crystal layer is driven, and the image display is performed by changing the transmittance and reflectance of each sub-pixel.

  The 1st polarizing plate 40 is arrange | positioned at the visual recognition side, and has the 1st polarizer 42 and polarizing plate protective film 44 (F1) and 46 (F2) which clamps it. The 2nd polarizing plate 60 is arrange | positioned at the backlight 80 side, and has the 2nd polarizer 62, the polarizing plate protective film 64 (F3) and polarizing plate protective film 66 (F4) which clamps it. . One of the polarizing plate protective films 46 (F2) and 64 (F3) may be omitted as necessary.

  Of the polarizing plate protective films 44 (F1), 46 (F2), 64 (F3) and 66 (F4), at least one of the polarizing plate protective films 46 (F2) and 64 (F3) disposed on the liquid crystal cell side is used. The optical film of the present invention is preferred. The polarizing plate protective film 44 (F1) disposed on the display side may further include an antiglare layer, a clear hard coat layer, an antireflection layer, an antistatic layer, an antifouling layer, or a backcoat layer.

  In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

1. Synthesis of cellulose diacetate (Synthesis Example 1)
To 100 parts by weight of hardwood kraft pulp, 50 parts by weight of glacial acetic acid was sprayed and stirred well, and allowed to stand at 24 ° C. for 1 hour (activation process by pretreatment). A mixed solution consisting of 350 parts by weight of glacial acetic acid, 300 parts by weight of acetic anhydride and 12 parts by weight of sulfuric acid was added thereto, and the mixture was stirred at 50 ° C. for 3 hours to carry out an esterification reaction of cellulose. To the resulting solution, 80 parts by weight of pure water and 10 parts by weight of magnesium acetate were added to stop the esterification reaction. The resulting solution was stirred at 80 ° C. for 2 hours to carry out an aging reaction. After completion of the reaction, 25 parts by weight of pure water and 1 part by weight of magnesium acetate were added to the resulting solution to stop the aging reaction. The resulting solution was poured into dilute acetic acid with stirring to precipitate the product. And after separating a deposit by filtration, the obtained solid content was fully wash | cleaned and dried with the pure water, and cellulose diacetate A1 was obtained.

  In the obtained cellulose diacetate A1, 1) the turbidity of the solution, 2) the total amount of alkali metal ions and alkaline earth metal ions (A) and the proportion of alkali metal ions and alkaline earth metal ions present as counter ions ( B / A), 3) The ratio of the substitution degree of acetyl group at the 6-position (DS6 / DSt × 100) was measured by the following methods, respectively.

1) Turbidity of cellulose acetate solution 92 parts by weight of methylene chloride and 8 parts by weight of ethanol were mixed to prepare a methylene chloride / ethanol mixed solvent. 10 g of cellulose diacetate A1 was added to 171 g of this methylene chloride / ethanol mixed solvent and stirred for 2 hours to dissolve the cellulose diacetate. It was confirmed visually that the obtained cellulose diacetate solution had no dissolved residue.

  The obtained cellulose diacetate solution was added to Azumi Filter Paper No. The solution was put into a filter having 244 (filtration accuracy: 7 μm) and filtered under a pressure of 0.4 MPa, and the filtrate was recovered. And the above-mentioned methylene chloride / ethanol mixed solvent was put into a glass cell (optical path length: 5 mm) manufactured by Nippon Denshoku Industries Co., Ltd., and set on a haze meter NDH-2000 manufactured by Nippon Denshoku Industries Co., Ltd. to perform standard matching. . Thereafter, the glass cell was removed. Furthermore, the cellulose diacetate solution filtrate collected above was put in a glass cell made by Nippon Denshoku Industries Co., Ltd. and set in a haze meter NDH-2000, and the turbidity (Turb) of the cellulose diacetate solution was set. It was measured. These operations were performed in an atmosphere of 23 ° C. and 55% RH.

2) Determination of alkali metal ions and alkaline earth metal ions 2-1) Total amount of alkali metal ions and alkaline earth metal ions (A)
Cellulose diacetate A1 was dried and then completely burned to obtain ash. The obtained ash was dissolved in hydrochloric acid to obtain a pretreatment solution. The amount of alkali metal ions and alkaline earth metal ions contained in the obtained pretreatment solution was measured by an atomic absorption method. The measured value was obtained as the content (unit: mg) of each alkali metal ion or alkaline earth metal ion in 1 kg of completely dried cellulose diacetate. The total content of alkali metal ions or alkaline earth metal ions was defined as the total amount (A) (unit: ppm) of alkali metal ions and alkaline earth metal ions contained in cellulose diacetate.

2-2) Total amount of alkali metal ions and alkaline earth metal ions present as counter ions (B)
100 g of pure water was added to 10 g of cellulose diacetate A1, and the mixture was stirred at 25 ° C. for 24 hours. After stirring, the cellulose diacetate obtained by filtering the resulting solution was washed with 100 g of pure water and then dried.

  The obtained cellulose diacetate A1 was completely burned in the same manner as described above to obtain ash. The obtained ash was dissolved in hydrochloric acid to obtain a pretreatment solution. The total amount (B) (unit: ppm) of alkali metal ions and alkaline earth metal ions present as counter ions with the acidic groups contained in cellulose diacetate A1 contained in the obtained pretreatment solution is the same as described above. Further, it was measured by an atomic absorption method.

3) Measurement of 6th-position acetyl group substitution ratio (DS6 / DSt × 100) Total acetyl group substitution degree (DSt) of cellulose diacetate A1, substitution degree of 2-position acetyl group (DS2), 3-position substitution The degree of substitution of the acetyl group (DS3) and the degree of substitution of the 6-position acetyl group (DS6) Sei, K .; Ishitani, R .; Suzuki, K .; Ikematsu, Polim. J. et al. 17, 1065-1069 (1985). Then, the sum of DS2 + DS3 + DS6 was defined as DSt, and the ratio of the substitution degree of the 6-position acetyl group (DS6 / DSt × 100) was calculated.

(Synthesis Example 2)
Cellulose diacetate A1 obtained in Synthesis Example 1 was immersed in a 50 ppm aqueous calcium acetate solution at 25 ° C. for 1 hour. After filtering this solution, the obtained solid content was dried to obtain cellulose diacetate A2.

(Synthesis Example 3)
Cellulose diacetate A1 obtained in Synthesis Example 1 was immersed in a 100 ppm calcium acetate aqueous solution at 25 ° C. for 1 hour. After filtering this solution, the obtained solid content was dried to obtain cellulose diacetate A3.

(Synthesis Example 4)
Cellulose diacetate A1 obtained in Synthesis Example 1 was immersed in a 200 ppm calcium acetate aqueous solution at 25 ° C. for 1 hour. After filtering this solution, the obtained solid content was dried to obtain cellulose diacetate A4.

(Synthesis Example 5)
Cellulose diacetate A1 obtained in Synthesis Example 1 was immersed in a 400 ppm calcium acetate aqueous solution at 25 ° C. for 1 hour. After filtering this solution, the solid content obtained was dried to obtain cellulose diacetate A5.

(Synthesis Example 6)
In the synthesis of cellulose diacetate A2, cellulose diacetate A6 was obtained in the same manner as in Synthesis Example 2 except that the hardwood kraft pulp as the raw material pulp was changed to cotton linter pulp.

(Synthesis Example 7)
1 part by weight of cellulose diacetate A6 obtained in Synthesis Example 6 was added to a mixed solvent of 1 part by weight of methanol and 12 parts by weight of methylene chloride to completely dissolve the cellulose diacetate A6. To the resulting solution, 80 parts by weight of methanol was added dropwise to reprecipitate cellulose diacetate, and then filtered off. The obtained cellulose diacetate was washed with methanol and dried to obtain cellulose diacetate A7.

(Synthesis Examples 8-9)
In the synthesis of cellulose diacetate A2, cellulose diacetate A8 was prepared in the same manner as in Synthesis Example 2 except that the amount of sulfuric acid used as a catalyst in the esterification step was changed so that the turbidity of the solution became the value shown in Table 1. -A9 was obtained.

(Synthesis Example 10)
In the synthesis of cellulose diacetate A2, the same procedure as in Synthesis Example 2 was conducted except that the amount of sulfuric acid used as a catalyst in the esterification step was changed so that the ratio (B / A) was a value as shown in Table 1. Cellulose diacetate A10 was obtained.

(Synthesis Example 11)
In the synthesis of cellulose diacetate A2, except that the amount of pure water added after the esterification step was changed so that the ratio of the 6-position acetyl group substitution degree (DS6 / DSt × 100) was the value shown in Table 1 Produced cellulose diacetate A11 in the same manner as in Synthesis Example 2.

(Synthesis Examples 12 to 13)
In the synthesis of cellulose diacetate A2, except that the amount of glacial acetic acid added in the esterification step was changed so that the ratio of the degree of acetyl group substitution at the 6-position (DS6 / DSt × 100) was the value shown in Table 1. Produced cellulose diacetate A12-13 in the same manner as in Synthesis Example 2.

Table 1 summarizes the physical properties of the obtained cellulose diacetates A1 to A13.

2. Production of optical film (Example 1)
Preparation of dope solution A dope solution having the following composition was prepared. First, methylene chloride and ethanol were charged into a pressure dissolution tank. Cellulose diacetate A2 was added to these solvents while stirring. The obtained solution was dissolved while stirring under heating, and the sugar ester compound 4 was further added and stirred until completely dissolved. The obtained solution was used as Azumi Filter Paper No. Filtration using 244 gave a dope solution.
[Composition of dope solution]
Methylene chloride 440 parts by mass Ethanol 38 parts by mass Cellulose diacetate A2 100 parts by mass Sugar ester compound 4 5 parts by mass

  Next, the dope liquid adjusted to 35 ° C. was uniformly cast on a stainless steel belt support of an endless belt casting apparatus so as to have a width of 1500 mm. The temperature of the stainless steel belt support was 30 ° C. After the solvent was evaporated on the stainless steel belt support until the residual solvent amount in the cast film was 75%, the paint film was applied from the stainless steel belt support at a peeling tension of 130 N / m. It peeled. The web obtained by peeling was stretched by 20% in the width direction using a tenter while applying heat at 140 ° C. The residual solvent amount of the web at the start of stretching was 15%. Next, drying was terminated while the drying zone was conveyed by a number of rolls. Drying was performed at a conveyance tension of 100 N / m and a temperature of 130 ° C. As a result, an optical film having a thickness of 40 μm was obtained.

(Examples 2 to 8)
As shown in Table 2, an optical film was obtained in the same manner as in Example 1 except that the type of cellulose diacetate was changed.

(Examples 9 to 13)
An optical film was obtained in the same manner as in Example 1 except that the dope flow rate was changed so that the film thickness shown in Table 2 was obtained.

(Examples 14 to 18)
An optical film was obtained in the same manner as in Example 2 except that the dope flow rate was changed so that the film thickness shown in Table 2 was obtained.

(Examples 19 to 23)
An optical film was obtained in the same manner as in Example 7 except that the dope flow rate was changed so that the film thickness shown in Table 2 was obtained.

(Comparative Examples 1-5)
As shown in Table 2, an optical film was obtained in the same manner as in Example 1 except that the type of cellulose diacetate was changed.

  The internal haze, blocking resistance and slitting characteristics of the obtained optical film were evaluated by the following methods.

Measurement of internal haze The internal haze of the optical film was measured by a method according to JIS K-7136; specifically, the following method was used. A haze meter (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.) was prepared. The light source was a halogen bulb of 5V9W, and the light receiving part was a silicon photocell (with a relative visibility filter).

1) Measurement of blank haze One drop (0.05 ml) of glycerin was dropped on the washed slide glass. At this time, care was taken to prevent bubbles from entering the droplets.
Next, a cover glass was placed on the dropped glycerin. The glycerin spreads without holding the cover glass.
A blank measurement sample (cover glass / glycerin / slide glass) obtained in this manner was set on a haze meter, and haze 1 (blank haze) was measured.
2) Measurement of haze of sample containing optical film Glycerin was dropped on the washed slide glass in the same manner as in 1) above.
On the other hand, the optical film to be measured was conditioned at 23 ° C. and 55% RH for 5 hours or more. Next, the conditioned optical film was placed on the dropped glycerin so as not to contain air bubbles.
Further, 0.05 ml of glycerin was dropped on the optical film, and then a cover glass was further placed.
A sample for measurement (cover glass / glycerin / sample film / glycerin / slide glass) obtained in this manner was set in the aforementioned haze meter, and haze 2 was measured.
3) The haze 1 of the optical film was calculated by applying the haze 1 obtained in 1) above and the haze 2 obtained in 2) above to the following formula.
Internal haze (%) of optical film = Haze 2 (%) − Haze 1 (%)

  The internal haze was measured under conditions of 23 ° C. and 55% RH. Moreover, the glass used for the measurement was MICRO SLIDE GLASS S9213 MATSANAMI. The glycerin used in the measurement was Kanto Chemical's deer special grade (purity> 99.0%) and a refractive index of 1.47.

Measurement of blocking resistance The obtained long optical film having a length of 2600 m was wound into a reel shape to obtain a wound body. The obtained wound body was double wrapped with a polyethylene sheet, and then stored for 30 days under conditions of 25 ° C. and 50% RH. Then, the wound body was taken out from the polyethylene sheet, and the presence or absence of blocking when the film was unwound from the wound body was visually observed. The blocking resistance was evaluated based on the following criteria.
A: In the wound state of the wound body, no unevenness (deformation of winding) due to sticking between the films is seen at all. B: There is a light peeling sound when unwinding the film, but no deformation is seen in the winding C : There is a slight resistance when unwinding the film, but there is no deformation in the winding. D: There is a slight resistance when unwinding the film, and there is a deformation in the winding. E: There is a strong resistance when unwinding the film. A, B, and C were judged to be practically acceptable levels.

Slitting suitability (brittleness)
An upper blade whose blade edge was worn at 60 ° and a lower blade of 90 ° were attached to a hydraulic table press so that the horizontal interval was 30 μm. Then, the obtained film is set between the tip of the upper blade and the tip of the lower blade, and a sample piece having a width of 90 cm and a length of 100 cm under the condition of the lowering speed of the upper blade of 6 m / min, 100 sheets were cut out continuously. The cut surface of each sample piece cut out was observed 50 times using an optical microscope. The number of films with defects such as burrs, cleavage, inability to cut, and generation of chips was counted and applied to the following formula to calculate the defect rate.
Defect rate (%) = (number of films with defects / number of all cut out films (100 sheets)) × 100

The evaluation of slitting suitability was performed based on the following criteria.
A: The defect rate is less than 1% B: The defect rate is 1% or more and less than 2% C: The defect rate is 2% or more and less than 5% D: The defect rate is 5% or more and less than 10% E: The defect rate is 10% or more A , B and C were judged to be at a level that is practically acceptable.

Table 2 shows the evaluation results of the optical films of Examples 1 to 23 and Comparative Examples 1 to 5.

  As shown in Table 2, the turbidity of the solution, the total amount of alkali metal ions and alkaline earth metal ions (A), and the ratio of the 6-position acetyl group substitution degree all include a cellulose ester that satisfies the scope of the present application. It can be seen that the optical films of Examples 1 to 23 have low internal haze and good blocking resistance and slitting suitability.

  On the other hand, the optical film of Comparative Example 1 containing cellulose ester in which the total amount (A) of alkali metal ions and alkaline earth metal ions is too low has low blocking resistance, and the total amount of alkali metal ions and alkaline earth metal ions (A). It can be seen that the optical film of Comparative Example 2 containing too much cellulose ester has a high internal haze. Moreover, the optical film of Comparative Example 3 in which the turbidity of the cellulose diacetate solution is too low has low blocking resistance, and the optical film of Comparative Example 4 in which the turbidity of the cellulose diacetate solution is too high has high internal haze. . Further, it can be seen that the optical film of Comparative Example 5 in which the ratio of the 6-position acetyl group substitution degree is too low has low blocking resistance and slitting suitability.

  Moreover, the ratio (B / A) of the amount (B) of alkali metal ions and alkaline earth metal ions present as counter ions includes cellulose esters in the range of 0.5 to 0.9. It can be seen that the optical film has lower internal haze and better blocking resistance than the optical films of Examples 4 to 5 and 10 that do not satisfy the above range.

  Further, it can be seen that the optical films of Examples 11 to 13, 16 to 18, and 21 to 23 exhibit good blocking resistance and slitting suitability despite the small film thickness. Moreover, the optical film of Examples 1-5 containing the cellulose ester which has the ratio (B / A) of the alkali metal ion and alkaline-earth metal ion which exist as a counter ion in the range of 0.75-0.9 is a film | membrane. It can be seen that although the thickness is small, the blocking resistance hardly decreases.

  The optical film of the present invention has low haze, blocking is sufficiently suppressed, and has good brittleness.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 20 Liquid crystal cell 40 1st polarizing plate 42 1st polarizer 44 Polarizing plate protective film (F1)
46 Polarizing plate protective film (F2)
60 Second polarizing plate 62 Second polarizer 64 Polarizing plate protective film (F3)
66 Polarizing plate protective film (F4)
80 Backlight

Claims (9)

An optical film containing cellulose acetate having a total substitution degree of acetyl groups of 2.0 or more and 2.6 or less,
The cellulose acetate satisfies the following requirements A) and B):
A) After dissolving 10 parts by mass of cellulose acetate in 171 parts by mass of a mixed solvent of 92% by mass of methylene chloride and 8% by mass of ethanol, the turbidity of the cellulose acetate solution obtained by filtering with a filter paper having a filtration accuracy of 7 μm is 0 B) Cellulose acetate satisfies the following formula 29.5 ≦ DS6 / DSt × 100 ≦ 34.0
(In the formula, DSt represents the total degree of substitution of the acetyl group, and DS6 represents the degree of substitution of the acetyl group at the 6-position)
And the optical film whose total amount (A) of the alkali metal ion and alkaline-earth metal ion which are contained in the said film of cellulose acetate 1kg is 35 mg or more and 250 mg or less. The alkali metal ions and alkaline earth metal ions contained in the cellulose acetate include alkali metal ions and alkaline earth metal ions present as counter ions with the acidic groups contained in the cellulose acetate,
The total amount of alkali metal ions and alkaline earth metal ions (B) present as counter ions with the acid groups contained in the cellulose acetate (A), and the total amount of alkali metal ions and alkaline earth metal ions (A) contained in the cellulose acetate (A) The optical film according to claim 1, wherein a ratio (B / A) to) is 0.5 or more and 0.9 or less.   The optical film according to claim 2, wherein the ratio (B / A) is 0.75 or more and 0.90 or less.   The optical film as described in any one of Claims 1-3 whose internal haze measured by the method based on JISK-7136 is 0.05% or less.   The optical film as described in any one of Claims 1-4 whose thickness of the said optical film is 15-60 micrometers. A polarizer,
The optical film according to any one of claims 1 to 5, disposed on at least one surface of the polarizer,
A polarizing plate including A liquid crystal display device comprising a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell,
At least one of the pair of polarizing plates includes a polarizer and the optical film according to any one of claims 1 to 5 disposed on at least one surface of the polarizer. . It is a manufacturing method of the optical film according to claim 1,
Obtaining a resin composition comprising cellulose acetate that satisfies all of the following requirements A), B) and C) and has a total substitution degree of acetyl groups of 2.0 or more and 2.6 or less;
A) After dissolving 10 parts by mass of cellulose acetate in 171 parts by mass of a mixed solvent of 92% by mass of methylene chloride and 8% by mass of ethanol, the turbidity of the cellulose acetate solution obtained by filtering with a filter paper having a filtration accuracy of 7 μm is 0 B) Cellulose acetate satisfies the following formula 29.5 ≦ DS6 / DSt × 100 ≦ 34.0
(In the formula, DSt represents the total degree of substitution of the acetyl group, and DS6 represents the degree of substitution of the acetyl group at the 6-position)
C) The step of molding the resin composition into an optical film, wherein the total amount of alkali metal ions and alkaline earth metal ions contained in 1 kg of cellulose acetate is 30 mg or more and 250 mg or less;
A method for producing an optical film, comprising: The alkali metal ions and alkaline earth metal ions contained in the cellulose acetate include alkali metal ions and alkaline earth metal ions present as counter ions with the acidic groups contained in the cellulose acetate,
The total amount of alkali metal ions and alkaline earth metal ions (B) present as counter ions with the acid groups contained in the cellulose acetate (A), and the total amount of alkali metal ions and alkaline earth metal ions (A) contained in the cellulose acetate (A) The method for producing an optical film according to claim 8, wherein a ratio (B / A) to (A) is 0.5 or more and 0.9 or less.

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