JP2011128250A - Optical film, method for manufacturing optical film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film whose front contrast when it is incorporated into a liquid crystal display device after a polarizing plate forming process is high, whose view angle characteristics are improved, whose dimensional change is comparable to that of other members, and whose manufacturing cost is low. <P>SOLUTION: The optical film contains cellulose acylate resin whose entire acyl substitution degree is 2.30-2.70 and satisfies a slow axis change of ¾ΔP1-ΔP0¾<0.5° when heat treatment is carried out for one hour under the condition of 80°C and the relative humidity of 90%. ΔP1 represents a difference between a maximum value and a minimum value of an angle formed of a film conveying direction and a slow axis in a film width direction when heat treatment is carried out for one hour under the condition of 80°C and the relative humidity of 90%, and ΔP0 represents a difference between a maximum value and a minimum value of an angle formed of a film conveying direction and the slow axis in a film width direction before the heat treatment. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  In recent years, liquid crystal display devices have been used for TVs, and with the increase in screen size, higher image quality and lower prices are increasingly required. At the same time, it is required to improve the viewing angle characteristics of the liquid crystal display device. In order to improve the viewing angle characteristics of a liquid crystal display device, a retardation film whose retardation is controlled is incorporated in a liquid crystal display device together with a polarizing plate. In order to ensure that the slow axis of the retardation film is mounted on the panel, the retardation film needs to be controlled to be 90 ° with respect to the polarizing plate absorption axis. In addition, the use environment of liquid crystal display devices has been diversified, and stable high image quality is required not only in general use environments but also in hot and humid environments. It is also required that the optical film itself changes in size to some extent in accordance with the amount of change in size according to the usage environment of the other members when bonded together.

  As such an optical film, Patent Document 1 discloses an in-plane direction retardation Re of 20 to 70 nm, a film thickness direction retardation Rth of 70 to 400 nm, and an axis formed by a slow axis angle and a stretching direction. An optical compensation film in which display unevenness (color spots) is suppressed by controlling the shift to 5 ° or less is disclosed.

  However, even if an optical film with a controlled slow axis distribution is produced, if the distribution of the slow axis of the optical film changes in the subsequent polarizing plate processing process, the front contrast when the liquid crystal display device is mounted is reduced. You ca n’t make it higher. In Patent Document 1, there is no mention of such a slow axis change in the polarizing plate processing process, and when a polarizing plate was produced by laminating an optical compensation film with a polarizing film (polarizer), It is described that the angle formed by the average direction of the slow axis and the transmission axis of the polarizing film is 0.5 °. Therefore, from the viewpoint of increasing the front contrast of the liquid crystal display device and improving the image quality, the optical compensation film described in Patent Document 1 is not sufficiently satisfactory.

  The optical compensation film of Patent Document 1 is a cellulose acetate film having an acetylation degree of 59.0 to 61.5%, that is, a total acyl substitution degree of 2.72 to 2.88, and the film thickness is increased. Thus, the expression level of retardation was adjusted. In response to the recent demand for cost reduction of liquid crystal display devices, it is required to reduce the manufacturing cost by reducing the amount of material used by reducing the film thickness of the optical film. For this reason, the optical compensation film described in Patent Document 1 is not sufficiently satisfactory from the viewpoint of the production cost of the optical film that greatly expresses retardation.

JP 2003-66230 A

  The present invention has been made in view of such circumstances, and has high front contrast when incorporated into a liquid crystal display device through a polarizing plate processing process, improved viewing angle characteristics, and the same size as other members. It is an object of the present invention to provide an optical film that changes and has a low manufacturing cost, and a manufacturing method thereof.

  When the present inventors examined the optical compensation film described in Patent Document 1 in detail, it was found that the slow axis distribution changes in the polarizing plate processing step. Therefore, when the cause of the change in the slow axis distribution was examined, it was not bound to any theory, but the optical compensation film was processed at high humidity and high temperature during the processing of the polarizing plate. It was expected that the stress remaining in the film after the stretching step was released and the molecular orientation in the film was changed.

  Therefore, in order to suppress the slow axis change described above, it is necessary to release the stress remaining in the film during film production. As a specific method for releasing the residual stress, Patent Document 1 discloses a method (thermal relaxation treatment) in which heat is applied as a post-treatment after the formed film is stretched and then contracted. It was found that the amount of dimensional change of the optical film becomes too small when it is performed, and there is a problem that when it is attached to another member and incorporated in a liquid crystal display device, the image quality is lowered. In addition, it was also found that the retardation caused by stretching is reduced by performing the thermal relaxation treatment, and there is a problem that the retardation development property is lowered. Furthermore, it has been found that when the thermal relaxation treatment is performed, the production load during the production of the optical film increases, and the problem of the production cost cannot be solved yet.

As a result of intensive investigations by the present inventors to solve the above-mentioned problems, surprisingly, when the solvent remains in the film containing a low-substituted cellulose acylate resin having a total acyl substitution degree of around 2.45, It was found that when an optical film was produced by stretching in a specific temperature range, the amount of change in the slow axis of the optical film after the polarizing plate processing step was greatly reduced without performing such a thermal relaxation treatment. did.
Furthermore, it has been found that such a film containing a cellulose acylate resin having a low degree of substitution can exhibit sufficient retardation even when the film thickness is thin. For this reason, since it is possible to reduce the film thickness without increasing the manufacturing cost due to the thermal relaxation treatment, it has been found that the manufacturing cost can be lowered simultaneously with the improvement of the retardation development.
Moreover, since the stretching temperature in the stretching process can be lowered and the thermal relaxation treatment can be omitted, the optical film having an appropriate dimensional change amount is obtained without the dimensional change amount depending on the use environment becoming too small. Turned out to be.

  Accordingly, the present inventors have further intensively studied and stretched a film containing a low-substituted cellulose acylate resin having a total acyl substitution degree in a specific range within a specific temperature range in a specific residual solvent amount range. As a result, an optical film with high front contrast when incorporated into a liquid crystal display device through a polarizing plate processing process, improved viewing angle characteristics, dimensional changes as much as other members, and low manufacturing costs. I found out that I could get it. That is, the said subject is solved by the following means.

[1] The slow axis change when the cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70 is heat-treated at 80 ° C. and a relative humidity of 90% for 1 hour is expressed by the following formula (1): An optical film characterized by satisfying
Formula (1) | ΔP1−ΔP0 | <0.5 °
(In formula (1), ΔP1 is the difference between the maximum value and the minimum value of the angle formed by the film transport direction and the slow axis in the film width direction when heat-treated for 1 hour at 80 ° C. and 90% relative humidity. ΔP0 represents the difference between the maximum value and the minimum value of the angle formed by the film transport direction and the slow axis in the film width direction before the heat treatment.
[2] Either the absolute value of the dimensional change rate in the film transport direction or the absolute value of the dimensional change rate in the direction perpendicular to the film transport direction when left at 60 ° C. and a relative humidity of 90% for 24 hours. One of them is 0.5% or more, The optical film as described in [1].
[3] Both the absolute value of the dimensional change rate in the film transport direction and the absolute value of the dimensional change rate in the direction perpendicular to the film transport direction when left for 24 hours at 60 ° C. and 90% relative humidity. The optical film as described in [1] or [2], which is 0.5% or more.
[4] The optical film according to any one of [1] to [3], wherein the following expressions (2) to (4) are satisfied.
Formula (2) 20 nm ≦ Re (590) ≦ 200 nm
(In formula (2), Re (590) represents the front retardation value at a wavelength of 590 nm.)
Formula (3) 70 nm ≦ Rth (590) ≦ 400 nm
(In Formula (3), Rth (590) represents the retardation value in the film thickness direction at a wavelength of 590 nm.)
Formula (4) Re (630)> Re (450)
(In formula (4), Re (630) represents the front retardation value at a wavelength of 630 nm, and Re (450) represents the front retardation value at a wavelength of 450 nm.)
[5] The optical film according to any one of [1] to [4], wherein the film thickness is 20 to 50 μm.
[6] A low substitution degree layer containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70;
[1] to [5], wherein at least one high substitution layer containing a cellulose acylate resin having a total acyl substitution degree exceeding 2.70 is provided on both sides of the low substitution degree layer. The optical film as described in any one (However, the composition of each high substitution degree layer is independent, and the same composition may be sufficient.).
[7] The optical film as described in [6], wherein all layers contain a cellulose acylate resin.
[8] The optical film according to any one of [1] to [7], wherein the cellulose acylate resin is cellulose acetate.
[9] A residual solvent at the start of stretching, comprising a step of stretching an unstretched film containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70 at a temperature of Tg-50 ° C to Tg. The amount is 5% by mass or more based on the total mass of the film, wherein Tg represents the glass transition temperature (unit: ° C.) of the optical film.
[10] A core layer dope containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70 and a skin layer dope containing a cellulose acylate resin having a total acyl substitution degree exceeding 2.70, The optical film according to [9], wherein the unstretched film is formed by sequential casting or simultaneous co-casting so that the skin layer dope is laminated on both surfaces of the core layer dope. Production method.
[11] The method for producing an optical film as described in [10], wherein co-casting is performed so that the skin layer dope is laminated on both surfaces of the core layer dope.
[12] The method for producing an optical film as described in any one of [9] to [11], wherein all the dopes contain a cellulose acylate resin.
[13] The method for producing an optical film as described in any one of [9] to [12], wherein the cellulose acylate resin is cellulose acetate.
[14] An optical film produced by the method for producing an optical film according to any one of [9] to [13].
[15] A polarizing plate comprising a polarizer and at least one optical film according to any one of [1] to [8] and [14].
[16] A liquid crystal display device comprising at least one optical film according to any one of [1] to [8] and [14] or a polarizing plate according to [15].

  According to the present invention, an optical film having high front contrast when incorporated into a liquid crystal display device through a polarizing plate processing process, improved viewing angle characteristics, dimensional changes to the same extent as other members, and low manufacturing costs. Can be provided. Moreover, according to this invention, this film can be manufactured simply and stably, and manufacturing cost is also low.

It is a schematic sectional drawing of an example of the liquid crystal display device of this invention. It is the schematic which shows an example when laminating | stacking the laminated cellulose acylate film of a three-layer structure by simultaneous co-casting using a co-casting die.

Below, the optical film of this invention, its manufacturing method, the additive used for it, etc. are demonstrated in detail.
The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. In the present specification, when Re and Rth are used without particular notice, these Re and Rth represent values at a measurement wavelength of 590 nm, respectively.

[Optical film]
The optical film of the present invention (hereinafter also referred to as the film of the present invention) contains a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70, and is 1 hour under conditions of 80 ° C. and 90% relative humidity. The slow axis change upon heat treatment satisfies the following formula (1).
Formula (1) | ΔP1−ΔP0 | <0.5 °
(In formula (1), ΔP1 is the difference between the maximum value and the minimum value of the angle formed by the film transport direction and the slow axis in the film width direction when heat-treated for 1 hour at 80 ° C. and 90% relative humidity. ΔPO represents the difference between the maximum value and the minimum value of the angle formed by the film conveyance direction and the slow axis in the film width direction before heat treatment.
Hereinafter, the present invention will be specifically described with reference to preferred embodiments of the film of the present invention.

(Cellulose acylate resin)
The cellulose acylate used in the present invention is not particularly limited except that it includes at least a cellulose acylate having an acyl group with a total acyl substitution degree of 2.30 to 2.70. Examples of the acylate raw material cellulose include cotton linter and wood pulp (hardwood pulp, conifer pulp). Cellulose acylate obtained from any raw material cellulose can be used, and in some cases, it may be mixed and used. Detailed descriptions of these raw material celluloses can be found in, for example, Marusawa and Uda, “Plastic Materials Course (17) Fibrous Resin”, published by Nikkan Kogyo Shimbun (published in 1970), and the Japan Institute of Invention and Technology Publication No. 2001. The cellulose described in No.-1745 (pages 7 to 8) can be used.

  Only one type of acyl group may be used in the film of the present invention, or two or more types of acyl groups may be used. When two or more types of acyl groups are used, one of them is preferably an acetyl group, and the acyl group having 2 to 4 carbon atoms is preferably a propionyl group or a butyryl group. With these films, a solution having a preferable solubility can be prepared, and in particular, in a non-chlorine organic solvent, a good solution can be prepared. Furthermore, it becomes possible to produce a solution having a low viscosity and good filterability.

  First, the cellulose acylate preferably used in the present invention will be described in detail. Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by acylating part or all of these hydroxyl groups with an acyl group. The degree of acyl substitution means the sum of the ratios of acylation of the hydroxyl groups of cellulose located at the 2-position, 3-position and 6-position (100% acylation at each position is substitution degree 1).

  The acyl group of cellulose acylate in the present invention may be an aliphatic group or an allyl group and is not particularly limited. These are, for example, cellulose alkylcarbonyl esters, alkenylcarbonyl esters, aromatic carbonyl esters, aromatic alkylcarbonyl esters, and the like, each of which may further have a substituted group. Preferred examples of these are acetyl group, propionyl group, butanoyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, isobutanoyl group. Group, tert-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like. Among these, an acetyl group, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a tert-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and an acetyl group is particularly preferable. A propionyl group and a butanoyl group (when the acyl group has 2 to 4 carbon atoms), more preferably an acetyl group (when the cellulose acylate is cellulose acetate).

  In the acylation of cellulose, when an acid anhydride or acid chloride is used as an acylating agent, an organic acid such as acetic acid or methylene chloride is used as an organic solvent as a reaction solvent.

As the catalyst, when the acylating agent is an acid anhydride, a protic catalyst such as sulfuric acid is preferably used, and when the acylating agent is an acid chloride (for example, CH ₃ CH ₂ COCl), Basic compounds are used.

  The most common industrial synthesis method of cellulose mixed fatty acid ester is to use cellulose corresponding to fatty acid corresponding to acetyl group and other acyl groups (acetic acid, propionic acid, valeric acid, etc.) or their anhydrides. This is a method of acylating with a mixed organic acid component.

  The film of the present invention contains a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70, but may contain other cellulose acylate resins in the range of the total acyl substitution degree. Details will be described in the description of the layer constitution of the film of the invention.

  The cellulose acylate used in the present invention can be synthesized, for example, by the method described in JP-A-10-45804.

  The optical film of the present invention may contain other resins in addition to the cellulose acylate resin, but preferably contains a cellulose acylate resin or a cyclic olefin resin, and more preferably contains a cellulose acylate resin.

(Dimension change rate)
The film of the present invention has the absolute value of the dimensional change rate in the film transport direction and the dimensional change rate in the direction orthogonal to the film transport direction when left at 24O 0 C and 90% relative humidity for 24 hours. It is preferable that either one of the values is 0.5% or more. The absolute value of the dimensional change rate is more preferably 0.5 to 1.5%, and particularly preferably 0.5 to 1.0%.
The film of the present invention has the absolute value of the dimensional change rate in the film transport direction and the dimensional change rate in the direction orthogonal to the film transport direction when left at 24O 0 C and 90% relative humidity for 24 hours. Both values are preferably 0.5% or more, more preferably 0.5 to 1.5%, and particularly preferably 0.5 to 1.0%.

(Slow axis change)
In the film of the present invention, the slow axis change (hereinafter also referred to as WET axis change) when heat-treated for 1 hour under the conditions of 80 ° C. and 90% relative humidity satisfies the following formula (1).
Formula (1) | ΔP1−ΔP0 | <0.5 °
(In formula (1), ΔP1 is the difference between the maximum value and the minimum value of the angle formed by the film transport direction and the slow axis in the film width direction when heat-treated for 1 hour at 80 ° C. and 90% relative humidity. ΔPO represents the difference between the maximum value and the minimum value of the angle formed by the film conveyance direction and the slow axis in the film width direction before heat treatment.
The heat treatment here does not mean a heat relaxation treatment in a conventionally known production method.
ΔP1 and ΔP0 preferably satisfy | ΔP1−ΔP0 | <0.4 °, and more preferably satisfy | ΔP1−ΔP0 | <0.3 °.

(Re, Rth)
The film of the present invention preferably satisfies the following formulas (2) to (4).
Formula (2) 20 nm ≦ Re (590) ≦ 200 nm
(In formula (2), Re (590) represents the front retardation value at a wavelength of 590 nm.)
Formula (3) 70 nm ≦ Rth (590) ≦ 400 nm
(In Formula (3), Rth (590) represents the retardation value in the film thickness direction at a wavelength of 590 nm.)
Formula (4) Re (630)> Re (450)
(In formula (4), Re (630) represents the front retardation value at a wavelength of 630 nm, and Re (450) represents the front retardation value at a wavelength of 450 nm.)
With such a wavelength dispersion characteristic, when the film of the present invention is incorporated in a liquid crystal display device, it is possible to solve the problem of color shift when observed obliquely when the liquid crystal display screen is displayed in black.

In the case of using the film of the present invention for a retardation film, Re and Rth are appropriately selected depending on the design of the liquid crystal cell and the optical film, but from the viewpoint of being used for optical compensation for a liquid crystal display device as a retardation film, The retardation Re in the in-plane direction at the measurement wavelength of 590 nm is more preferably 30 nm ≦ Re ≦ 150 nm, and particularly preferably 35 nm ≦ Re ≦ 90 nm.
In the film of the present invention, the retardation Rth in the film thickness direction is more preferably 100 nm ≦ Rth ≦ 300 nm, and particularly preferably 100 nm ≦ Rth ≦ 250 nm.

The film of the present invention is preferably a biaxial optical compensation film.
Here, the optical compensation film is biaxial means nx, ny and nz of the optical compensation film (nx represents the refractive index in the slow axis direction in the plane, and ny is the refraction in the direction perpendicular to nx in the plane. Nz represents the refractive index in the direction orthogonal to nx and ny), and in the present invention, it is more preferable that nx>ny> nz.
The fact that the film of the present invention exhibits biaxial optical characteristics is a preferable characteristic for reducing the problem of color shift when observed from an oblique direction in a liquid crystal display device, particularly a VA mode liquid crystal display device.

  In this specification, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at the wavelength λ, respectively. In the present specification, the wavelength λ is 590 nm unless otherwise specified. Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH (manufactured by Oji Scientific Instruments). Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH) as the tilt axis (rotary axis) (in the absence of the slow axis, any direction in the film plane) Is measured in 6 points from the inclined direction in 10 degree steps from the normal direction to 50 degrees on one side with respect to the normal direction of the film. KOBRA 21ADH calculates based on the retardation value, the assumed average refractive index, and the input film thickness value. The retardation value is measured from any two directions with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), and the value Rth can also be calculated from the following formula (A) and formula (B) based on the assumed average refractive index and the input film thickness value. Here, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). The KOBRA 21ADH calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

Here, Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction, nx, ny, and nz represent refractive indexes in respective principal axis directions of the refractive index ellipsoid, and d represents a film. Represents thickness.
Rth = ((nx + ny) / 2−nz) × d Formula (B)
At this time, an average refractive index n is required as a parameter, and a value measured by an Abbe refractometer (“Abbe refractometer 2-T” manufactured by Atago Co., Ltd.) was used.

(Layer structure of optical film)
The film of the present invention may be a single layer film or may have a laminated structure of two or more layers, but preferably has a laminated structure of two or more layers.
In addition, the acyl substitution degree of cellulose acylate in each layer may be uniform, or a plurality of cellulose acylates may be mixed in one layer, but the acyl substitution degree of cellulose acylate in each layer is all It is preferable that it is constant from the viewpoint of adjustment of optical characteristics.

The film of the present invention preferably has a laminate structure of three or more layers, and the film of the present invention comprises a low substitution layer containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70, Having at least one high substitution layer containing a cellulose acylate resin having a total acyl substitution degree exceeding 2.70 on both surfaces of the low substitution degree layer realizes desired optical characteristics as an optical compensation film. It is preferable from the viewpoint of improving the degree of freedom in the process (however, the composition of each high substitution degree layer is independent and may be the same composition).
The total acyl substitution degree of the cellulose acylate used in the high substitution degree layer is preferably more than 2.70 and not more than 2.95, more preferably 2.73 to 2.95, and 2.75. It is especially preferable that it is -2.95.

  In the film of the present invention, a layer in contact with the support (hereinafter also referred to as skin B layer) when produced by solution casting is the high substitution layer, and the other layers are the low substitution layer. It is preferable from the viewpoint of further improving the peelability from the support during solution casting. Only when the film of the present invention has a laminated structure of three or more layers, the surface layer on the side that is not in contact with the support during film formation is also referred to as a skin A layer.

The film of the present invention preferably has a three-layer structure of skin B layer / core layer / skin A layer. In the case where the film of the present invention has a three-layer structure, even a high substitution layer / low substitution layer / high substitution layer configuration is a low substitution layer / high substitution layer / low substitution layer. However, a high substitution layer / low substitution layer / high substitution layer configuration is preferred from the viewpoint of improving the peelability from the support during solution casting and from the viewpoint of dimensional stability.
When the film of the present invention has a three-layer structure, it is preferable from the viewpoint of production cost that the cellulose acylate contained in the surface layers on both sides uses a cellulose acylate having the same acyl substitution degree.

  As for the film of this invention, it is preferable from a viewpoint of the haze of a film compared with the aspect in which all the layers contain a cellulose acylate resin compared with the aspect in which the layer containing only cyclic olefin resin is formed.

When the film of the present invention is composed of two or more layers, it is preferable from the viewpoint of reducing the production process that no adhesive or pressure-sensitive adhesive is included between the respective layers. An optical film having such a layer structure is a laminated casting described later. It can be manufactured by the method.
In addition, as an adhesive agent and an adhesive used when manufacturing the film of the multilayer structure adhere | attached through the adhesive agent or the adhesive, there exists description in Unexamined-Japanese-Patent No. 11-295527, for example.

(Film thickness)
The film of the present invention preferably has a thickness of 20 to 50 μm from the viewpoint of reducing production costs, more preferably 30 to 50 μm, and particularly preferably 35 to 50 μm. When the film of the present invention is a laminated film, the range of the total film thickness of the film is preferably within the above-mentioned preferable range.
The average thickness of the low substitution degree layer is preferably 30 to 50 μm, more preferably 30 to 48 μm, and particularly preferably 30 to 45 μm.

  The film of the present invention is peeled off if the average film thickness of at least one of the high substitution layers is 0.2% or more and less than 25% of the low substitution layer average film thickness, if it is 0.2% or more. And the unevenness of streaks, non-uniform film thickness or non-uniform optical properties is suppressed, and if it is less than 25%, the optical development of the core layer can be used effectively, and the laminated film is sufficient. From the viewpoint of obtaining excellent optical characteristics. The average film thickness of at least one of the high substitution degree layers is more preferably from 0.5 to 15%, particularly preferably from 1.0 to 10%, of the low substitution degree layer average film thickness. Moreover, it is more preferable that the average film thicknesses of the skin A layer and the skin B layer are both 0.2% or more and less than 25% of the core layer average film thickness.

(Film width)
The film of the present invention preferably has a film width of 700 to 3000 mm, more preferably 1000 to 2800 mm, and particularly preferably 1500 to 2500 mm.

<Additives>
In the film of the present invention, as additives, non-phosphate ester compounds; retardation modifiers (retardation enhancers and retardation reducers); plasticizers such as phthalate esters and phosphate ester compounds An additive such as a carbohydrate derivative; an ultraviolet absorber; an antioxidant; an inorganic fine particle (mat agent) may be added. Hereinafter, additives that can be used in the film of the present invention will be described in detail.

(Non-phosphate compound)
The film preferably contains a compound of a non-phosphate ester compound in order to suppress a phenomenon in which the additive begins to cry from the film during wet heat durability.

The film preferably contains a non-phosphate ester compound in the low substitution degree layer. By including such a non-phosphate ester compound, the film has the effect of being less likely to be whitened.
In the present specification, the “non-phosphate ester compound” refers to a “compound having an ester bond and the acid contributing to the ester bond other than phosphoric acid”. That is, the “non-phosphate ester compound” means a compound that does not contain phosphoric acid and is an ester compound.
Further, the non-phosphate ester compound may be a low molecular compound or a polymer (polymer compound). Hereinafter, a non-phosphate ester compound which is a polymer (polymer compound) is also referred to as a non-phosphate ester polymer.

  As the non-phosphate ester compound, known high molecular weight additives and low molecular weight additives can be widely employed as additives for cellulose acylate films. The content of the additive is preferably 1 to 35% by mass, more preferably 4 to 30% by mass, and still more preferably 10 to 25% by mass with respect to the cellulose resin.

  The high molecular weight additive used as the non-phosphate ester compound has a repeating unit in the compound, and preferably has a number average molecular weight of 700 to 10,000. The high molecular weight additive has a function of increasing the volatilization rate of the solvent and a function of reducing the residual solvent amount in the solution casting method. Furthermore, it exhibits useful effects from the viewpoint of film modification such as improvement in mechanical properties, imparting flexibility, imparting water absorption resistance, and reducing moisture permeability.

Here, the number average molecular weight of the high molecular weight additive which is the non-phosphate ester compound is more preferably a number average molecular weight of 700 to 8000, still more preferably a number average molecular weight of 700 to 5000, and particularly preferably. The number average molecular weight is 1000 to 5000.
Hereinafter, the high molecular weight additive which is a non-phosphate ester compound used in the present invention will be described in detail with specific examples, but the high molecular weight which is a non-phosphate ester compound used in the present invention. Needless to say, the additives are not limited to these.

  Examples of the polymer additive that is a non-phosphate ester compound include polyester polymers (aliphatic polyester polymers, aromatic polyester polymers, etc.), copolymers of polyester components and other components, and the like. Aliphatic polyester polymers, aromatic polyester polymers, polyester polymers (aliphatic polyester polymers, aromatic polyester polymers, etc.) and acrylic polymers and polyester polymers (aliphatic polyester polymers, A copolymer of an aromatic polyester polymer or the like) and a styrene polymer is preferable, and a polyester compound containing an aromatic ring as at least one of the copolymer components is more preferable.

  Examples of the aliphatic polyester-based polymer include at least one diol selected from aliphatic dicarboxylic acids having 2 to 20 carbon atoms, aliphatic diols having 2 to 12 carbon atoms, and alkyl ether diols having 4 to 20 carbon atoms. The both ends of the reaction product may be left as the reaction product, or the monocarboxylic acid, monoalcohol or phenol may be further reacted to carry out so-called end-capping. Good. It is effective in terms of storage stability that the end capping is performed in particular so as not to contain free carboxylic acids. The dicarboxylic acid used in the polyester polymer of the present invention is preferably an aliphatic dicarboxylic acid residue having 4 to 20 carbon atoms or an aromatic dicarboxylic acid residue having 8 to 20 carbon atoms.

  Examples of the aliphatic dicarboxylic acid having 2 to 20 carbon atoms include oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dodecane. Examples include dicarboxylic acid and 1,4-cyclohexanedicarboxylic acid.

  Among these, preferable aliphatic dicarboxylic acids are malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, and 1,4-cyclohexanedicarboxylic acid. Particularly preferably, the aliphatic dicarboxylic acid component is succinic acid, glutaric acid, or adipic acid.

  The diol utilized for the high molecular weight additive is selected from, for example, an aliphatic diol having 2 to 20 carbon atoms and an alkyl ether diol having 4 to 20 carbon atoms.

  Examples of the aliphatic diol having 2 to 20 carbon atoms include alkyl diols and alicyclic diols, such as ethane diol, 1,2-propanediol, 1,3-propanediol, and 1,2-butane. Diol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol) ), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3 -Methyl-1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl 1,3-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, and the like. Used as a mixture of two or more.

  Preferred aliphatic diols include ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1 , 4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, particularly preferred Is ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6- Hexanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol.

  Preferred examples of the alkyl ether diol having 4 to 20 carbon atoms include polytetramethylene ether glycol, polyethylene ether glycol and polypropylene ether glycol, and combinations thereof. The average degree of polymerization is not particularly limited, but is preferably 2 to 20, more preferably 2 to 10, further 2 to 5, and particularly preferably 2 to 4. As examples of these, commercially useful polyether glycols typically include Carbowax, Pluronics and Niax resins.

In the present invention, a high molecular weight additive whose end is blocked with an alkyl group or an aromatic group is also preferred. This is because the terminal is protected with a hydrophobic functional group, which is effective against deterioration with time at high temperature and high humidity, and is due to the role of delaying hydrolysis of the ester group.
It is preferable to protect with a monoalcohol residue or a monocarboxylic acid residue so that both ends of the polyester additive of the present invention are not carboxylic acid or OH group.
In this case, the monoalcohol is preferably a substituted or unsubstituted monoalcohol having 1 to 30 carbon atoms, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol, hexanol, isohexanol, cyclohexyl alcohol. , Octanol, isooctanol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl alcohol, tert-nonyl alcohol, decanol, dodecanol, dodecahexanol, aliphatic alcohol such as dodecaoctanol, allyl alcohol, oleyl alcohol, benzyl alcohol, 3-phenyl Examples thereof include substituted alcohols such as propanol.

  End-capping alcohols that can be preferably used are methanol, ethanol, propanol, isopropanol, butanol, isobutanol, isopentanol, hexanol, isohexanol, cyclohexyl alcohol, isooctanol, 2-ethylhexyl alcohol, isononyl alcohol, oleyl alcohol Benzyl alcohol, in particular methanol, ethanol, propanol, isobutanol, cyclohexyl alcohol, 2-ethylhexyl alcohol, isononyl alcohol, benzyl alcohol.

  Moreover, when sealing with a monocarboxylic acid residue, the monocarboxylic acid used as a monocarboxylic acid residue is preferably a substituted or unsubstituted monocarboxylic acid having 1 to 30 carbon atoms. These may be aliphatic monocarboxylic acids or aromatic ring-containing carboxylic acids. Preferred aliphatic monocarboxylic acids are described, for example, acetic acid, propionic acid, butanoic acid, caprylic acid, caproic acid, decanoic acid, dodecanoic acid, stearic acid, oleic acid, and examples of the aromatic ring-containing monocarboxylic acid include Benzoic acid, p-tert-butylbenzoic acid, p-tert-amylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, normal propylbenzoic acid, aminobenzoic acid, acetoxybenzoic acid, etc. Yes, these can be used alone or in combination of two or more.

  The synthesis of the high molecular weight additive may be a hot melt condensation method using a polyesterification reaction or a transesterification reaction between the aliphatic dicarboxylic acid and a diol and / or a monocarboxylic acid or monoalcohol for end-capping by a conventional method. Alternatively, it can be easily synthesized by any of the interfacial condensation methods of acid chlorides of these acids and glycols. These polyester-based additives are described in detail in Koichi Murai, “Additives, Theory and Application” (Kokaibo Co., Ltd., first edition published on March 1, 1973). Also, JP-A Nos. 05-155809, 05-155810, JP-A-5-97073, JP-A-2006-259494, JP-A-07-330670, JP-A-2006-342227, JP-A-2007-003679. The materials described in each publication can also be used.

The aromatic polyester polymer is obtained by copolymerizing a monomer having an aromatic ring with the polyester polymer. The monomer having an aromatic ring is at least one monomer selected from aromatic dicarboxylic acids having 8 to 20 carbon atoms and aromatic diols having 6 to 20 carbon atoms.
Examples of the aromatic dicarboxylic acid having 8 to 20 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,8- There are naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid. Among these, preferable aromatic dicarboxylic acids are phthalic acid, terephthalic acid, and isophthalic acid.

  Examples of the aromatic diol having 6 to 20 carbon atoms include, but are not limited to, bisphenol A, 1,2-hydroxybenzene, 1,3-hydroxybenzene, 1,4-hydroxybenzene, and 1,4-benzenedimethanol. Bisphenol A, 1,4-hydroxybenzene and 1,4-benzenedimethanol are preferred.

  The aromatic polyester polymer is used in combination with at least one kind of aromatic dicarboxylic acid or aromatic diol with the above-mentioned polyester, but the combination is not particularly limited, and several kinds of respective components are combined. There is no problem. As described above, a high molecular weight additive having a terminal sealed with an alkyl group or an aromatic group is particularly preferable, and the above-described method can be used for sealing.

  As a retardation reducing agent other than the non-phosphate ester compound, for example, a phosphate ester compound or a compound other than a known ester compound as an additive for a cellulose acylate film can be widely used.

  The polymer retardation reducing agent is selected from phosphoric acid polyester polymers, styrene polymers, acrylic polymers, and copolymers thereof, and acrylic polymers and styrene polymers are preferred. Moreover, it is preferable that at least one polymer having negative intrinsic birefringence, such as a styrene polymer and an acrylic polymer, is included.

  Examples of the low molecular weight retardation reducing agent that is a compound other than a non-phosphate ester-based compound include the following. These may be solid or oily. That is, the melting point and boiling point are not particularly limited. For example, mixing of an ultraviolet absorbing material at 20 ° C. or lower and 20 ° C. or higher, and a mixture of deterioration preventing agents are also possible. Furthermore, infrared absorbing dyes are described, for example, in JP-A No. 2001-194522. Moreover, the addition time may be added at any time in the cellulose acylate solution (dope) preparation step, but it may be added by adding a preparation step to the final preparation step of the dope preparation step. Furthermore, the amount of each material added is not particularly limited as long as the function is manifested.

  Although it does not specifically limit as a low molecular weight retardation reducing agent which is compounds other than a non-phosphate ester type | system | group, The detail is described in Unexamined-Japanese-Patent No. 2007-272177 [0066]-[0085].

The compound described as the general formula (1) in [0066] to [0085] of JP-A-2007-272177 can be prepared by the following method.
The compound of the general formula (1) in the publication can be obtained by a condensation reaction between a sulfonyl chloride derivative and an amine derivative.

  JP, 2007-272177, A The compound of general formula (2) is a dehydration condensation reaction of carboxylic acids and amines using a condensing agent (for example, dicyclohexylcarbodiimide (DCC) etc.), or a carboxylic acid chloride derivative, It can be obtained by a substitution reaction with an amine derivative.

  The retardation reducing agent is more preferably an Rth reducing agent from the viewpoint of realizing a suitable Nz factor. Among the retardation reducing agents, examples of the Rth reducing agent include acrylic polymers and styrene polymers, and low molecular compounds represented by general formulas (3) to (7) in JP-A-2007-272177, and the like. Of these, acrylic polymers and styrene polymers are preferred, and acrylic polymers are more preferred.

The retardation reducing agent is preferably added at a rate of 0.01 to 30% by mass, more preferably 0.1 to 20% by mass, more preferably 0.1 to 10%, based on the cellulose resin. It is particularly preferable to add at a ratio of mass%.
By making the said addition amount 30 mass% or less, compatibility with a cellulose resin can be improved and whitening can be suppressed. When two or more types of retardation reducing agents are used, the total amount is preferably within the above range.

(Plasticizer)
As the plasticizer, many compounds known as cellulose acylate plasticizers can also be usefully used. As the plasticizer, phosphate ester compounds or carboxylic acid esters are used. Examples of the phosphate ester-based compound include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.

(Retardation expression agent)
The film of the present invention may contain a retardation developer. By adopting a retardation developer, high Re developability can be obtained at a low draw ratio. The type of the retardation developing agent is not particularly defined, and examples thereof include those composed of a rod-like or discotic compound and compounds exhibiting retardation development among the non-phosphate ester compounds. As the rod-like or discotic compound, a compound having at least two aromatic rings can be preferably used as a retardation developer.
Two or more retardation developing agents may be used in combination.
The retardation developer preferably has a maximum absorption in the wavelength region of 250 to 400 nm, and preferably has substantially no absorption in the visible region.

As the retardation developing material, for example, compounds described in JP-A-2004-50516 and JP-A-2007-86748 can be used, but the present invention is not limited thereto.
Examples of the discotic compound include a compound described in European Patent Application No. 0911656A2, a triazine compound described in Japanese Patent Application Laid-Open No. 2003-344655, and a method described in Japanese Patent Application Laid-Open No. 2008-150592 [0097] to [0108]. The triphenylene compound to be used can also be preferably used.

  The discotic compound can be synthesized by a known method such as a method described in JP-A No. 2003-344655 and a method described in JP-A No. 2005-134484.

  In addition to the aforementioned discotic compound, a rod-shaped compound having a linear molecular structure can also be preferably used. For example, the rod-shaped compounds described in JP 2008-150592 A [0110] to [0127] are preferably used. it can.

Two or more rod-shaped compounds having a maximum absorption wavelength (λmax) longer than 250 nm in the ultraviolet absorption spectrum of the solution may be used in combination.
The rod-like compound can be synthesized with reference to methods described in the literature. References include Mol. Cryst. Liq. Cryst., 53, 229 (1979), 89, 93 (1982), 145, 111 (1987), 170, 43 Page (1989), J. Am. Chem. Soc., 113, 1349 (1991), 118, 5346 (1996), 92, 1582 (1970), J. Org Chem., 40, 420 (1975), Tetrahedron, 48, 16, 3437 (1992).

(Carbohydrate derivative)
The film of the present invention may contain a carbohydrate derivative. By adding a carbohydrate derivative to a cellulose acylate film, the moisture content of the film can be significantly reduced without impairing the expression of optical properties and without increasing haze.
Furthermore, by using the cellulose acylate film as a polarizing plate protective film, the performance deterioration of the polarizer under high temperature and high humidity can be significantly improved.

The carbohydrate derivative used in the present invention preferably has a structure represented by the following general formula (1) including the substituent used.
General formula (1)
^{_{(OH) p -G- (L 1}} -R 1) q (L 2 -R 2) r
In General Formula (1), G represents a monosaccharide residue or a polysaccharide residue, and L ¹ and L ² each independently represent any one of —O—, —CO—, and —NR ³ —. , R ¹ , R ² and R ³ each independently represents a hydrogen atom or a monovalent substituent, and at least one of R ¹ and R ² preferably has an aromatic ring. p, q, and r each independently represents an integer of 0 or more, at least one of q and r is an integer of 1 or more, and p + q + r is a value when G is an unsubstituted saccharide having a cyclic acetal structure. Equal to the number of hydroxyl groups.

  The preferable range of G is the same as the preferable range of the constituent sugar described later.

L ¹ and L ² are preferably —O— or —CO—, and more preferably —O—. When L ¹ and L ² are —O—, a linking group derived from an ether bond or an ester bond is particularly preferable, and a linking group derived from an ester bond is more preferable.
Further, when there are a plurality of L ¹ and L ² , they may be the same or different from each other.

R ¹ , R ² and R ³ are preferably monovalent substituents. In particular, when L ¹ and L ² are —O— (ie, when R ¹ , R ² and R ³ are substituted on the hydroxyl group in the carbohydrate derivative), R ¹ , R ² and R ³ Is preferably selected from a substituted or unsubstituted acyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted alkyl group, a substituted or unsubstituted amino group, and a substituted or unsubstituted acyl group. It is more preferably a group, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group, and an unsubstituted acyl group, a substituted or unsubstituted alkyl group, or an unsubstituted aryl group. Particularly preferred.
Further, when there are a plurality of R ¹ , R ² and R ³ , they may be the same or different from each other.

Said p represents an integer greater than or equal to 0, and its preferable range is the same as the preferable range of the number of hydroxyl groups per monosaccharide unit mentioned later.
Q and r each independently represents an integer of 0 or more, and at least one of them represents an integer of 1 or more. It is preferable that one of q and r is 0.
Moreover, since p + q + r is equal to the number of hydroxyl groups assuming that G is an unsubstituted saccharide having a cyclic acetal structure, the upper limit values of p, q and r are uniquely determined according to the structure of G. Is done.

  Preferable examples of the substituent of the carbohydrate derivative include an alkyl group (preferably an alkyl group having 1 to 22 carbon atoms, more preferably an alkyl group having 1 to 12 carbon atoms, and particularly preferably an alkyl group having 1 to 8 carbon atoms, such as a methyl group and an ethyl group. Group, propyl group, hydroxyethyl group, hydroxypropyl group, 2-cyanoethyl group, benzyl group, etc.), aryl group (preferably 6 to 24 carbon atoms, more preferably 6 to 18 carbon atoms, particularly preferably 6 to 12 aryl groups). , For example, phenyl group, naphthyl group), acyl group (preferably having 1 to 22 carbon atoms, more preferably 2 to 12 carbon atoms, particularly preferably 2 to 8 carbon atoms, for example, acetyl group, propionyl group, butyryl). Group, pentanoyl group, hexanoyl group, octanoyl group, benzoyl group, toluyl group, phthalyl group), amide group (preferred) Is an amide having 1 to 22 carbon atoms, more preferably 2 to 12 carbon atoms, particularly preferably 2 to 8 carbon atoms, such as a formamide group or an acetamide group, and an imide group (preferably having 4 to 22 carbon atoms, more preferably Examples thereof include amide groups having 4 to 12 carbon atoms, particularly preferably 4 to 8 carbon atoms such as succinimide group and phthalimide group. Among these, an acyl group is more preferable, and an acetyl group is particularly preferable.

-Number of hydroxyl groups per monosaccharide unit-
The number of hydroxyl groups per monosaccharide unit in the carbohydrate derivative (hereinafter also referred to as hydroxyl group content) is preferably 1 or less. By controlling the hydroxyl group content within the above range, the transfer of carbohydrate derivatives to the polarizer layer and the destruction of the PVA-iodine complex during high temperature and high humidity can be suppressed, and the deterioration of the polarizer performance during high temperature and high humidity can be suppressed. This is preferable.

-Constituent sugar-
The carbohydrate derivative is preferably a monosaccharide or a carbohydrate derivative containing 2 to 5 monosaccharide units, and more preferably a monosaccharide or a carbohydrate derivative containing 2 monosaccharide units.

In the monosaccharide or polysaccharide preferably constituting the carbohydrate derivative, a substitutable group in the molecule (for example, a hydroxyl group, a carboxyl group, an amino group, a mercapto group, etc.) is substituted with at least two kinds of substituents, and It is preferable that at least one of the substituents is substituted with a substituent having at least one aromatic ring.
Examples of the monosaccharide or carbohydrate containing 2 to 10 monosaccharide units include, for example, erythrose, threose, ribose, arabinose, xylose, lyxose, allose, altrose, glucose, fructose, mannose, gulose, idose, galactose , Talose, trehalose, isotrehalose, neotrehalose, trehalosamine, caudibiose, nigerose, maltose, maltitol, isomaltose, sophorose, laminaribiose, cellobiose, gentiobiose, lactose, lactosamine, lactitol, lactulose, melibiose, primebelloose, rutiose , Sucrose, sucralose, turanose, vicyanose, cellotriose, cacotriose, gentianose, isomal Triose, isopanose, maltotriose, manninotriose, melezitose, panose, planteose, raffinose, solatriose, umbelliferose, lycotetraose, maltotetraose, stachyose, baltopentaose, velval course, maltohexaose, Examples include α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin, xylitol, sorbitol and the like.

  Preferably, ribose, arabinose, xylose, lyxose, glucose, fructose, mannose, galactose, trehalose, maltose, cellobiose, lactose, sucrose, sucralose, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin Xylitol, sorbitol, more preferably arabinose, xylose, glucose, fructose, mannose, galactose, maltose, cellobiose, sucrose, β-cyclodextrin, γ-cyclodextrin, particularly preferably xylose, glucose, fructose , Mannose, galactose, maltose, cellobiose, sucrose, xylitol, sorbitol.

  As a method for obtaining the carbohydrate derivative, it can be obtained as a commercial product from Tokyo Kasei Co., Ltd., Aldrich, etc., or known ester derivatization methods for commercially available carbohydrates (for example, JP-A-8-245678). Can be synthesized by carrying out the method described in the publication.

[Method for producing optical film]
The method for producing an optical film of the present invention (hereinafter also referred to as the production method of the present invention) is an unstretched film containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70. The residual solvent amount when starting the stretching is 5% by mass or more based on the total mass of the film (where Tg is the glass transition temperature of the optical film). Represents.)
Hereinafter, the production method of the present invention will be described in detail.

  The optical film is preferably manufactured by a solvent cast method. Examples of production of an optical film containing cellulose acylate using a solvent cast method are described in U.S. Pat. Nos. 2,336,310, 2,367,603, 2,492,078, and 2,492. , 977, 2,492,978, 2,607,704, 2,739,069 and 2,739,070, British Patent Nos. 640731 and 736892 Reference can be made to each specification, and Japanese Patent Publications Nos. 45-4554, 49-5614, JP-A-60-176834, 60-203430, and 62-115035. The optical film is stretched at a stretching temperature of Tg-50 ° C. to Tg under a condition that the residual solvent amount when starting stretching is 5% by mass or more based on the mass of the entire film. For other stretching methods and conditions, for example, JP-A-62-115035, JP-A-4-152125, 4-284221, 4-298310, 11-48271, etc. Can be helpful.

<Casting method>
As a solution casting method, a method in which the prepared dope is uniformly extruded from a pressure die onto a metal support, and a method using a doctor blade in which the dope once cast on the metal support is adjusted with a blade is used. Although there is a method using a reverse roll coater that adjusts with a reverse rotating roll, a method using a pressure die is preferred. The pressure die includes a coat hanger type and a T die type, and any of them can be preferably used. In addition to the methods mentioned here, it can be carried out by various known methods for casting a cellulose triacetate solution, and each condition is set in consideration of differences in the boiling point of the solvent used. Thus, the same effects as those described in the respective publications can be obtained.

  In the production method of the present invention, a dope containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70 is fluent, and a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70 is contained. An unstretched film is formed. In the production method of the present invention, the unstretched film is produced by a process including a step of forming a cellulose acylate solution for the core layer (core layer dope) and a skin layer dope on the support. preferable.

In the formation of the film of the present invention, it is preferable to use a lamination casting method such as a co-casting method, a sequential casting method, and a coating method, and in particular, the simultaneous co-casting method can be used to stabilize production and reduce production costs. Particularly preferable from the viewpoint.
When producing by the co-casting method and the sequential casting method, first, a cellulose acetate solution (dope) for each layer is prepared.
In the co-casting method (multi-layer simultaneous casting), a casting dope for each layer (or three layers or more) may be simultaneously applied from another slit or the like on a casting support (band or drum). This is a casting method in which a dope is extruded from a casting caster to be extruded, and each layer is cast simultaneously, peeled off from a support at an appropriate time, and dried to form a film. FIG. 2 is a cross-sectional view showing a state in which the co-casting giesser 3 is used to simultaneously extrude and cast the surface layer dope 1 and the core layer dope 2 on the casting support 4.

  In the sequential casting method, the casting dope for the first layer is first extruded from the casting giusa on the casting support, cast, and dried on the second without drying or drying. The dope for casting for the layer is extruded from the caster for casting, and if necessary, the dope is cast and laminated successively up to the third layer and peeled off from the support at an appropriate time and dried. This is a casting method for forming a film. In general, the core layer film is formed into a film by a solution casting method to prepare a coating solution to be applied to the surface layer, and then applied to the film one side at a time or both sides simultaneously using an appropriate applicator. This is a method of forming a film having a laminated structure by applying and drying a liquid.

  The production method of the present invention includes a dope for a core layer containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70, and a skin layer containing a cellulose acylate resin having a total acyl substitution degree exceeding 2.70 It is preferable to form the unstretched film by sequentially casting or co-casting the dope for use so that the dope for the skin layer is laminated on both sides of the dope for the core layer. In the production method of the present invention, it is more preferable to perform simultaneous co-casting so that the skin layer dope is laminated on both surfaces of the core layer dope.

  In the production method of the present invention, it is preferable that all the dopes contain a cellulose acylate resin from the viewpoint of haze of the film as compared with an embodiment using a dope containing only a cyclic olefin resin.

  As a support used for producing the film of the present invention, a metal support that travels endlessly, a drum whose surface is mirror-finished by chrome plating, or a stainless steel belt that is mirror-finished by surface polishing (referred to as a band). May be used). One or more pressure dies may be installed above the metal support. Preferably 1 or 2 groups. When two or more are installed, the amount of dope to be cast may be divided into various ratios for each die, or the dope may be fed to the dies from each of a plurality of precision quantitative gear pumps. The temperature of the cellulose acylate solution used for casting is preferably −10 to 55 ° C., more preferably 25 to 50 ° C. In that case, all solution temperatures in the process may be the same or different at different points in the process. If they are different, the temperature may be a desired temperature just before casting.

<Extension process>
The production method of the present invention includes a step of stretching the formed unstretched film at a temperature of Tg-50 ° C. to Tg, and the amount of residual solvent when starting the stretching is 5 with respect to the mass of the entire film. It is at least mass%. The above-mentioned characteristics of the film of the present invention can be imparted by a stretching treatment under such conditions, and further, a desired retardation can be imparted to the film of the present invention.

(Stretching temperature)
The stretching temperature is Tg-50 ° C to Tg, preferably Tg-40 ° C to Tg-5 ° C, and particularly preferably Tg-40 ° C to Tg-10 ° C.

(Residual solvent amount)
In the method for producing a film of the present invention, the residual solvent amount when starting stretching is 5% by mass or more, preferably 5 to 40% by mass, and preferably 10 to 35% by mass with respect to the mass of the entire film. Is more preferable, and it is especially preferable that it is 15-30 mass%.
The residual solvent amount was determined according to the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at an arbitrary point, and N is the mass when the web of which M is measured is dried at 120 ° C. for 2 hours.

  The draw ratio in the production method of the present invention is preferably 5% to 200%, more preferably 10% to 100%, and particularly preferably 20% to 50%.

  The stretching direction of the cellulose acylate film is preferably either the film conveyance direction or the direction (width direction) perpendicular to the conveyance direction, but the direction that is perpendicular to the film conveyance direction (width direction) is used for the subsequent film. This is particularly preferable from the viewpoint of workability in the conventional polarizing plate processing process.

  Methods for stretching in the width direction are described in, for example, JP-A-62-115035, JP-A-4-152125, JP-A-2842211, JP-A-298310, and JP-A-11-48271. Yes. In the case of stretching in the longitudinal direction, for example, the film is stretched by adjusting the speed of the film transport roller so that the film winding speed is higher than the film peeling speed. In the case of stretching in the width direction, the film can also be stretched by conveying while holding the width of the film with a tenter and gradually widening the width of the tenter. After the film is dried, it can be stretched using a stretching machine (preferably uniaxial stretching using a long stretching machine).

  Moreover, the stretching direction of the cellulose acylate film may be stretched in both the film transport direction and the direction orthogonal to the transport direction. However, when the optical film is used as a protective film for the polarizer, the polarizing plate is obliquely In order to suppress light leakage when viewed, it is necessary to arrange the transmission axis of the polarizer and the slow axis in the plane of the cellulose acylate film in parallel. Since the transmission axis of the roll film-shaped polarizer produced continuously is generally parallel to the width direction of the roll film, the roll film-shaped polarizer and the roll film-shaped optical film of the present invention are used. In order to continuously bond a certain protective film, the in-plane slow axis of the roll film-shaped protective film needs to be parallel to the width direction of the film. Therefore, it is preferable to stretch more in the width direction. In addition, the stretching treatment may be performed during the film forming process, or the raw film that has been formed and wound may be stretched, but in the production method of the present invention, the stretching is performed in a state containing a residual solvent. In order to carry out, it is preferable to extend | stretch in the middle of a film forming process.

  In the film manufacturing method of the present invention, it is preferable not to include a heat relaxation treatment step after the stretching step. That is, the film production method of the present invention preferably does not include a step of stretching the film while heating after the stretching step, and does not include a step of bringing the film to a temperature higher than the stretching temperature after the stretching step. preferable.

<Drying>
The production method of the present invention preferably includes a step of drying the obtained optical film as long as it is not contrary to the gist of the present invention.

  The dope drying on the metal support involved in the production of the cellulose acylate film is generally applied with hot air from the surface side of the metal support (drum or belt), that is, the surface of the web on the metal support. Method, method of applying hot air from the back of the drum or belt, contact the temperature-controlled liquid from the back of the belt or drum opposite the dope casting surface, and heat the drum or belt by heat transfer to control the surface temperature There is a back surface liquid heat transfer method, and the back surface liquid heat transfer method is preferable. The surface temperature of the metal support before casting may be any number as long as it is not higher than the boiling point of the solvent used in the dope, unless it is contrary to the spirit of the present invention. preferable. However, in order to promote drying and to lose fluidity on the metal support, the temperature should be set to 1 to 10 ° C. lower than the boiling point of the lowest boiling solvent. Is preferred. This is not the case when the cast dope is cooled and peeled off without drying.

  The film thickness may be adjusted by adjusting the solid content concentration contained in the dope, the slit gap of the die base, the extrusion pressure from the die, the metal support speed, and the like so as to obtain a desired thickness.

  The length of the cellulose acylate film obtained as described above is preferably wound at 100 to 10,000 m per roll, more preferably 500 to 7000 m, and still more preferably 1000 to 6000 m. When winding, it is preferable to give knurling to at least one end, the knurling width is preferably 3 mm to 50 mm, more preferably 5 mm to 30 mm, and the height is preferably 0.5 to 500 μm, more preferably 1 to 200 μm. is there. This may be a single push or a double push.

  The film of the present invention is particularly suitable for use in a large screen liquid crystal display device. When used as an optical compensation film for a large-screen liquid crystal display device, for example, the film width is preferably set to 1470 mm or more. In addition, the film of the present invention is not only an optical film in the form of a film piece cut to a size that can be incorporated into a liquid crystal display device as it is, but also is produced in a long shape by continuous production, and in a roll shape. A rolled up optical film is also included. The optical film of the latter mode is stored and transported in that state, and is cut into a desired size and used when actually assembled into a liquid crystal display device or bonded to a polarizer or the like. Similarly, it is cut into a desired size when it is actually assembled into a liquid crystal display device after being bonded together with a polarizer made of a polyvinyl alcohol film or the like that has been formed into a long shape. Used. As one mode of the optical compensation film wound up in a roll shape, a mode in which the roll length is rolled up to 2500 m or more can be mentioned.

[Polarizer]
The present invention also relates to a polarizing plate using a polarizer and at least one film of the present invention.
The polarizing plate of the present invention preferably has a polarizer and the film of the present invention on one side of the polarizer. Similar to the optical compensation film of the present invention, the polarizing plate of the present invention is not limited to the polarizing plate in the form of a film piece that has been cut into a size that can be incorporated into a liquid crystal display device as it is. A polarizing plate of an aspect (for example, an aspect having a roll length of 2500 m or more or 3900 m or more) that is produced in a scale shape and rolled up is also included. In order to use for a large-screen liquid crystal display device, the width of the polarizing plate is preferably 1470 mm or more as described above.
The specific configuration of the polarizing plate of the present invention is not particularly limited, and a known configuration can be employed. For example, the configuration described in FIG. 6 of JP-A-2008-262161 can be employed.

[Liquid Crystal Display]
The present invention also relates to a liquid crystal display device having the polarizing plate of the present invention.
The liquid crystal display device of the present invention is a liquid crystal display device having a liquid crystal cell and a pair of polarizing plates disposed on both sides of the liquid crystal cell, wherein at least one of the polarizing plates is the polarizing plate of the present invention. An IPS, OCB or VA mode liquid crystal display device is preferable.
The specific configuration of the liquid crystal display device of the present invention is not particularly limited, and a known configuration can be adopted. For example, an example having the configuration shown in FIG. 1 can be adopted. Further, the configuration described in FIG. 2 of JP-A-2008-262161 can also be preferably employed.

  The present invention will be described more specifically with reference to the following examples. The materials, reagents, amounts and ratios of substances, operations, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples.

[Examples 1 to 13, Comparative Examples 1 to 5]
(Preparation of cellulose acylate)
Cellulose acylate was synthesized by the method described in JP-A Nos. 10-45804 and 08-231761, and the degree of substitution was measured. Specifically, sulfuric acid (7.8 parts by mass with respect to 100 parts by mass of cellulose) was added as a catalyst, carboxylic acid serving as a raw material for the acyl substituent was added, and an acylation reaction was performed at 40 ° C. At this time, the kind and substitution degree of the acyl group were adjusted by adjusting the kind and amount of the carboxylic acid. In addition, aging was performed at 40 ° C. after acylation. Further, the low molecular weight component of the cellulose acylate was removed by washing with acetone.

(Preparation of cellulose acylate solution for core layer)
The following composition was put into a mixing tank and stirred to dissolve each component to prepare a cellulose acylate solution for core layer of Example 1.
Cellulose acetate (substitution degree 2.45) 100.0 parts by mass Compound A 15.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass

(Preparation of cellulose acylate solution for skin layer)
The following composition was put into a mixing tank and stirred to dissolve each component to prepare a cellulose acylate solution for skin layer of Example 1.
Cellulose acetate (substitution degree 2.79) 100.0 parts by mass Compound A 15.0 parts by mass Methylene chloride 395.0 parts by mass Methanol 59.0 parts by mass

  The composition of Compound A used as an additive is shown below together with the structures of other additives used in other Examples and Comparative Examples.

  In Table 1, TPA represents terephthalic acid, PA represents phthalic acid, AA represents adipic acid, SA represents succinic acid, EG represents ethylene glycol, and PG represents propylene glycol. In addition, all of compounds A to C are non-phosphate ester compounds, and are also retardation developers. Compound F represents a compound having the following structure listed as an example of the structure of the retardation enhancer, which is a compound described in JP-A-2008-262161.

Compound D

Compound E

Compound F

As shown in Table 2 below, other cellulose acylate solutions were prepared in the same manner as in Example 1 except that the acyl group type and substitution degree, additive amount, and additive type of cellulose acylate were changed.
CAP2.50 used in Example 13 represents cellulose acetate propionate.
In Example 13 and Comparative Examples 1 and 5, only the core layer dope was fluent in a single layer.

(Creation of optical film)
So that the cellulose acylate solution for the core layer becomes a core layer having a film thickness described in Table 2 below, the cellulose acylate solution for the skin layer becomes a skin layer having a film thickness described in Table 3 below. Each was cast. The obtained web (film) was peeled off from the band, sandwiched between clips, and then stretched horizontally using a tenter under the conditions shown in Table 2 below when the amount of residual solvent relative to the total mass of the film was 15-30%. Started. Thereafter, the clip was removed from the film and dried at the drying temperature shown in Table 2 below for 20 minutes.
Moreover, Tg (glass transition temperature) of the obtained film was calculated | required from the following method. After adjusting the humidity of a sample of 5 mm × 30 mm at 25 ° C. and 60% RH for 2 hours or more, using a dynamic viscoelasticity measuring device DVA-225 (made by IT Measurement Control Co., Ltd.), the distance between grips is 20 mm, the frequency The temperature of tan δ at which the storage elastic modulus (E ′) and loss elastic modulus (E ″) obtained by measuring at 1 Hz were interchanged was determined and this was defined as Tg. The results obtained are shown in Table 2 below.

<Evaluation of film properties>
The following measurements and evaluations were performed on the characteristics of the films of the examples and comparative examples.

(Film retardation)
By using the automatic birefringence meter KOBRA-WR (manufactured by Oji Scientific Instruments) according to the method described above, three-dimensional birefringence measurement is performed at a wavelength of 590 nm, and the in-plane retardation Re (590) and the tilt angle are changed. The retardation Rth (590) in the film thickness direction obtained by measuring Re was determined. The values of Re and Rth are shown in Table 2 below.

(Dimension change)
The dimensional change rate before and after 24 hours at 60 ° C. and 90% relative humidity, that is, a value of (L′−L0) / L0} × 100% was determined in the film transport direction and the direction orthogonal thereto. Here, L0 represents the film length (unit: mm) before lapse of 24 hours at 60 ° C. and 90% relative humidity, and L ′ is lapsed for 24 hours at 60 ° C. and 90% relative humidity, and further adjusted for 2 hours. It represents the film length (unit: mm) after wetting. The sample film used was 30 mm × 120 mm, and other conditions were as follows.
After conditioning for 2 hours or more in an atmosphere of 25 ° C. and relative humidity 60%, automatic pin gauges (manufactured by Shinbun Kagaku Co., Ltd.) are used to open 6 mmφ holes at 100 mm intervals so that they are parallel to the 120 mm side of the film. , The original size (L0) of the interval is measured to a minimum scale of 1/1000 mm. Then, after wet heat treatment under the above conditions, after adjusting the humidity for 2 hours in an atmosphere of 25 ° C. and a relative humidity of 60%, the dimension L ′ of the punch interval is measured.
The obtained results are shown in Table 2 below.

(WET axis change)
The amount of change in the slow axis before and after the lapse of 24 hours at 60 ° C. and 90% relative humidity represented by the following formula (1) was determined in the direction perpendicular to the film transport direction.
Formula (1) | ΔP1−ΔP0 | <0.5 °
(In formula (1), ΔP1 is the difference between the maximum value and the minimum value of the angle formed by the film transport direction and the slow axis in the film width direction when heat-treated for 1 hour at 80 ° C. and 90% relative humidity. ΔP0 represents the difference between the maximum value and the minimum value of the angle formed by the film conveyance direction and the slow axis in the film width direction before heat treatment.
The ΔP1 and the ΔP0 are 70 mm × 110 mm sample film in the direction perpendicular to the film transport direction, one point from the center of the film, and one point at each end at a distance of 600 mm from the center to the end, total width direction 3 points were cut out, and the difference between the maximum value and the minimum value of the shift amount of the slow axis of each sample film was calculated. The slow axis was measured using a birefringence meter (KOBRA DH, manufactured by Oji Scientific Instruments).
The obtained results are shown in Table 2 below. In Comparative Example 1, the initial slow axis deviation was very large, and the display performance when incorporated in a liquid crystal display device was poor. Therefore, the evaluation of the amount of change in the WET axis was not performed.

From Table 2 above, the film of the present invention obtained by the production method of the present invention has a sufficiently developed retardation expression amount despite its thin film thickness, and the absolute value of the dimensional change is somewhat high, It was found that the amount of change in the slow axis under the humid heat environment was small.
On the other hand, the film of Comparative Example 1 was produced by setting the stretching temperature to a temperature exceeding the range of the present invention, and it was found that the dimensional change amount of the obtained film was too small. The film of Comparative Example 2 was produced by setting the total acyl substitution degree of the cellulose acylate resin to a value exceeding the range of the present invention. In the film of Comparative Example 2, the amount of change in the slow axis of the film obtained was large. I understood that. The films of Comparative Examples 3 and 4 were produced by setting the stretching temperature to a temperature lower than the range of the present invention, and it was found that the obtained film had a large amount of change in the slow axis. In the film of Comparative Example 5, the total acyl substitution degree of the cellulose acylate resin was set to a value lower than the range of the present invention, and the obtained film did not form an optical film body.

(Preparation of polarizing plate sample)
The surface of the optical film of each Example and Comparative Example produced above was subjected to alkali saponification treatment. It was immersed in a 1.5 N aqueous sodium hydroxide solution at 55 ° C. for 2 minutes, washed in a water bath at room temperature, and neutralized with 0.1 N sulfuric acid at 30 ° C. Again, it was washed in a water bath at room temperature and further dried with hot air at 100 ° C. Subsequently, a roll-shaped polyvinyl alcohol film having a thickness of 80 μm was continuously stretched 5 times in an aqueous iodine solution and dried to obtain a polarizer having a thickness of 20 μm. Using the 3% aqueous solution of polyvinyl alcohol (Kuraray PVA-117H) as an adhesive, the optical films of the examples and comparative examples subjected to the above alkali saponification treatment and the same alkali saponification treatment Fujitac TD80UL (manufactured by Fujifilm) are prepared. A polarizing plate in which these saponified surfaces are bonded so that the polarizer is sandwiched between them, and the optical films, polarizers, and TD80UL of each example and comparative example are bonded in this order. I got each. Under the present circumstances, it affixed so that the MD direction of each optical film and the slow axis of TD80UL might become parallel to the absorption axis of a polarizer.

(Production of liquid crystal display device)
The front and back polarizing plates and retardation plates of a VA mode liquid crystal TV (LCD-40MZW100, manufactured by Mitsubishi Corporation) were peeled off and used as a liquid crystal cell. As shown in the configuration of FIG. 1 (upper side is the front side), an outer protective film (not shown), a polarizer 11, and optical films 14 of the examples and comparative examples described in the following table (rear side cellulose acylate film) , Liquid crystal cell 13 (the above VA liquid crystal cell), film 15 (front side cellulose acylate film), polarizer 12 and outer protective film (not shown) of each example and comparative example described in the following table in this order. The liquid crystal display device of each Example and comparative example (except Example 5 and Comparative Example 2) was produced by bonding using an adhesive. At this time, they were bonded so that the absorption axes of the upper and lower polarizing plates were orthogonal to each other. In Example 5 and Comparative Example 2, the cellulose acylate film 15 on the front side (viewing side) is “Fujitac TD80UF” manufactured by Fuji Film, and the optical film of the present invention or the optical film 14 of the comparative example is provided on the rear side. A liquid crystal display device was produced in the same manner except that it was used.

<Evaluation of liquid crystal display device>
The viewing angle dependence of the transmittance of the manufactured liquid crystal display device was measured. The tilt angle was measured from the front in an oblique direction up to 80 ° every 10 °, and the azimuth was measured up to 360 ° every 10 ° on the basis of the horizontal right direction (0 °).
As a result, it was also found that the luminance at the time of black display increased as the tilt angle increased from the front direction, and the leakage light transmittance increased, and the contrast deteriorated in the vicinity of the tilt angle of 70 °.

(Front contrast evaluation)
The front black display transmittance was evaluated. The evaluation criteria are as follows.
○: Good.
Δ: Slightly decreased.
X: Decrease.
Xx: Remarkably reduced.
The obtained results are shown in Table 3 below.

(Viewing angle change with WET)
In addition, as a display performance evaluation in a WET environment, a viewing angle contrast of a panel left to stand at 60 ° C. and 90% relative humidity for 100 hours was evaluated.
◯: Good with little change in viewing angle contrast.
Δ: Large change in viewing angle contrast.
X: The change in the viewing angle contrast is very large.
The obtained results are shown in Table 3 below.

  From Table 3, it was found that the liquid crystal display device of the present invention had high front contrast when incorporated into the liquid crystal display device through a polarizing plate processing process, and improved viewing angle characteristics. On the other hand, it was found that the liquid crystal display device of the comparative example could not achieve both the front contrast and the improvement in viewing angle characteristics.

DESCRIPTION OF SYMBOLS 1 Dope for skin layers 2 Dope for core layers 3 Co-casting Giesa 4 Casting support 11 Polarizer 12 Polarizer 13 Liquid crystal cell 14 Cellulose acylate film of each Example and Comparative Example (Example 5, Comparative) Example 2 uses an optically anisotropic film (Fujitac TD80UF)
15 Cellulose acylate films of Examples and Comparative Examples

Claims (16)

A cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70,
An optical film characterized in that a slow axis change when heat-treated for 1 hour under conditions of 80 ° C. and 90% relative humidity satisfies the following formula (1).
Formula (1) | ΔP1−ΔP0 | <0.5 °
(In formula (1), ΔP1 is the difference between the maximum value and the minimum value of the angle formed by the film transport direction and the slow axis in the film width direction when heat-treated for 1 hour at 80 ° C. and 90% relative humidity. ΔP0 represents the difference between the maximum value and the minimum value of the angle formed by the film conveyance direction and the slow axis in the film width direction before heat treatment.   Either the absolute value of the dimensional change rate in the film conveyance direction or the absolute value of the dimensional change rate in the direction orthogonal to the film conveyance direction when left at 60 ° C. and 90% relative humidity for 24 hours. It is 0.5% or more, The optical film of Claim 1 characterized by the above-mentioned.   The absolute value of the dimensional change rate in the film transport direction and the absolute value of the dimensional change rate in the direction orthogonal to the film transport direction when both are left to stand for 24 hours under the conditions of 60 ° C. and 90% relative humidity are both 0.5. The optical film according to claim 1, wherein the optical film is at least%. The following films (2) to (4) are satisfied, The optical film according to any one of claims 1 to 3.
Formula (2) 20 nm ≦ Re (590) ≦ 200 nm
(In formula (2), Re (590) represents the front retardation value at a wavelength of 590 nm.)
Formula (3) 70 nm ≦ Rth (590) ≦ 400 nm
(In Formula (3), Rth (590) represents the retardation value in the film thickness direction at a wavelength of 590 nm.)
Formula (4) Re (630)> Re (450)
(In formula (4), Re (630) represents the front retardation value at a wavelength of 630 nm, and Re (450) represents the front retardation value at a wavelength of 450 nm.)   A film thickness is 20-50 micrometers, The optical film as described in any one of Claims 1-4 characterized by the above-mentioned. A low substitution degree layer comprising a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70;
6. The high substitution degree layer comprising at least one high substitution degree layer containing a cellulose acylate resin having a total acyl substitution degree exceeding 2.70 on both surfaces of the low substitution degree layer. The optical film according to one item (however, the composition of each high substitution degree layer is independent and may be the same composition).   All the layers contain a cellulose acylate resin, The optical film of Claim 6 characterized by the above-mentioned.   The optical film according to claim 1, wherein the cellulose acylate resin is cellulose acetate. Stretching a non-stretched film containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70 at a temperature of Tg-50 ° C. to Tg,
The method for producing an optical film, wherein the amount of residual solvent when starting the stretching is 5% by mass or more based on the mass of the entire film (where Tg is the glass transition temperature of the optical film (unit: ° C.) )   A core layer dope containing a cellulose acylate resin having a total acyl substitution degree of 2.30 to 2.70, and a skin layer dope containing a cellulose acylate resin having a total acyl substitution degree exceeding 2.70. The method for producing an optical film according to claim 9, wherein the unstretched film is formed by sequential casting or simultaneous co-casting so that the dope for skin layer is laminated on both sides of the dope for coating.   The method for producing an optical film according to claim 10, wherein simultaneous casting is performed so that the skin layer dope is laminated on both surfaces of the core layer dope.   All the dopes contain a cellulose acylate resin, The manufacturing method of the optical film as described in any one of Claims 9-11 characterized by the above-mentioned.   The method for producing an optical film according to any one of claims 9 to 12, wherein the cellulose acylate resin is cellulose acetate.   An optical film manufactured by the method for manufacturing an optical film according to claim 9.   A polarizing plate comprising a polarizer and at least one optical film according to claim 1.   A liquid crystal display device comprising at least one optical film according to claim 1 or at least one polarizing plate according to claim 15.

Images