JP2014085604A - Optical film, circularly polarizing plate, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film which exhibits high phase-difference expressibility and superior inverse-wavelength dispersibility but shows little phase-difference unevenness and offers superior embrittlement resistance, and to provide a circularly polarizing plate having the same and an image display device with little color unevenness, having the optical film.SOLUTION: An optical film contains cellulose ester and a wavelength dispersion adjuster. The cellulose ester has an acyl group having a carbon number in a range of 3 to 6, and the wavelength dispersion adjuster is either a compound having a melting point in a range of 50 to 180°C as measured with a differential scanning calorimeter and a cooling crystallization temperature of not more than 130°C or a compound having no observable crystallization exothermic peak. An angle between an in-plane slow axis of the optical film and a conveying direction of the optical film is in a range of 40 to 50°.

Description

  The present invention relates to an optical film exhibiting high retardation development and excellent reverse wavelength dispersion, a circularly polarizing plate provided with the optical film, and an image display device.

  The λ / 4 retardation film can convert linearly polarized light into circularly polarized light and elliptically polarized light, and can convert circularly polarized light and elliptically polarized light into linearly polarized light. Such a λ / 4 retardation film is widely used in various optical applications in image display devices, optical pickup devices, and the like.

In recent years, a self-luminous display device such as an organic electroluminescence (EL) display device has attracted attention as a new image display device.
In the organic EL display device, a reflector such as an aluminum plate is provided on the back side of the display in order to increase the light extraction efficiency. However, external light incident on the display is reflected by the reflector and the contrast of the image is increased. There is a problem of lowering. As a countermeasure, a circularly polarizing plate obtained by bonding a λ / 4 retardation film and a polarizer is generally disposed on the surface of the display. Such a circularly polarizing plate is also used in a so-called 3D liquid crystal display device that displays a stereoscopic image.

The circularly polarizing plate needs to be disposed and bonded so that the slow axis in the plane of the λ / 4 retardation film is inclined at an angle of about 45 ° with respect to the absorption axis of the polarizer.
A general polarizer (polarizing film) is a long film obtained by longitudinal stretching at a high magnification, and its absorption axis coincides with the transport direction. On the other hand, the conventional λ / 4 retardation film is a long film stretched longitudinally or transversely, and in principle, the angle formed between the in-plane slow axis and the transport direction is 0 ° or 90 °. Are in a relationship. Therefore, in order to incline the absorption axis of the polarizing film and the slow axis of the λ / 4 retardation film at an angle of about 45 ° as described above, one piece of the polarizing film or λ / 4 retardation film is cut out. It must be done in a batch system where each is bonded together. In such a batch method, productivity is lowered, and the yield of products is also lowered due to adhesion of chips and the like. In particular, in recent years when displays are being increased in size, if the films are cut out and bonded one by one, not only the productivity is lowered but also the utilization efficiency of the film is lowered.

  By obliquely stretching, a λ / 4 retardation film having a slow axis inclined at about 45 ° with respect to the transport direction in advance can be produced. If such a λ / 4 retardation film is used, a long polarizing film and a long λ / 4 retardation film can be rolled to roll regardless of the conventional batch method. It becomes possible to manufacture a circularly polarizing plate by bonding. As a result, productivity can be dramatically improved and yield can be greatly improved. When manufacturing a circularly polarizing plate for use in a large display, the use efficiency of the film can be improved and the manufacturing cost can be greatly reduced.

By the way, a λ / 4 retardation film used with a laser light source of a specific wavelength, such as an optical pickup device, only needs to give a phase difference of ¼ wavelength only to light of a specific wavelength.
On the other hand, a λ / 4 retardation film used for an antireflection film or the like of a color image display device or an organic EL display device needs to give a quarter wavelength retardation to light in the entire visible light range. For this purpose, the λ / 4 retardation film is required to have reverse wavelength dispersibility in which the longer the wavelength of light, the greater the phase difference imparted to the light.
However, it is difficult to obtain a film that imparts a retardation of λ / 4 and exhibits excellent reverse wavelength dispersion, particularly a single layer having such characteristics.

Films using cellulose esters are known to exhibit reverse wavelength dispersion, but in order to obtain a phase difference of λ / 4 with cellulose esters alone, the stretching ratio is increased or the film thickness is increased. It must be thick. Further, the reverse wavelength dispersion is not sufficient, and it is difficult to achieve a phase difference of λ / 4 in a wide wavelength region.
Therefore, the phase difference developability and reverse wavelength dispersibility of the optical film are improved by using a wavelength dispersion adjusting agent in combination with the cellulose ester.
As the chromatic dispersion adjusting agent, for example, a low molecular compound has been proposed in which the magnitude of the dipole moment in the direction orthogonal to the molecular long axis direction is larger than the magnitude of the dipole moment in the direction parallel to the molecular long axis direction ( For example, see Patent Document 1).

The optical film containing the low molecular weight compound described in Patent Document 1 is produced by longitudinal stretching or lateral stretching. In order to obtain a long circularly polarizing plate, the present inventors produced a λ / 4 retardation film containing a low molecular weight compound described in Patent Document 1 by oblique stretching. As a result, the film is fragile and easily damaged. It has been found.
In addition, the λ / 4 retardation film had retardation unevenness. When a circularly polarizing plate using a λ / 4 retardation film was mounted on an organic EL display device and an image at the time of black display was viewed, a red or blue color was seen with respect to black. Furthermore, a phenomenon of so-called color unevenness in which the color differs depending on the position on the display was also observed.

JP 2007-249180 A

  The present invention has been made in view of the above problems and circumstances, and the solution to the problem is that, while exhibiting high retardation development and excellent reverse wavelength dispersion, there is little retardation unevenness and excellent brittleness resistance. It is to provide an optical film. Moreover, it is providing the circularly-polarizing plate which comprises the said optical film, and the said optical film, and providing an image display apparatus with few color irregularities.

As a result of the study by the present inventors, when an optical film is produced by oblique stretching, it is necessary to stretch at a higher magnification than longitudinal stretching and lateral stretching, so that the film is likely to become hard and brittle. A problem that is likely to occur was found.
The inventors of the present invention have studied a film base that increases the flexibility of the film, and found that an optical film having excellent brittleness resistance can be obtained by using a cellulose ester having an acyl group having at least 3 carbon atoms. I found it.

  Further, as a further problem, it has been found that the added wavelength dispersion adjusting agent tends to aggregate locally at the time of oblique stretching, and phase difference unevenness that has not been revealed by conventional longitudinal stretching or lateral stretching occurs. When the cause was investigated in detail, the chromatic dispersion adjusting agent melted and precipitated out of the film (bleed out) or crystallized and precipitated in the film due to changes in the environmental temperature. I found out that it was the cause of unevenness. Bleed-out to the outside of the film can be suppressed by increasing the melting point of the wavelength dispersion adjusting agent. On the other hand, if the melting point is increased, crystallization tends to occur. However, the present inventors thought that precipitation at the inside of the film due to crystallization can be suppressed by lowering the cooling crystallization temperature even if the melting point is high. As a result of various studies based on the technical idea, the present invention has been achieved.

That is, the subject concerning this invention is solved by the following means.
1. An optical film containing a cellulose ester and a wavelength dispersion adjusting agent,
The cellulose ester has an acyl group having 3 to 6 carbon atoms,
The wavelength dispersion adjusting agent is a compound having a melting point in the range of 50 to 180 ° C. measured by a differential scanning calorimeter, and a temperature drop crystallization temperature is 130 ° C. or lower, or an exothermic peak during crystallization is not observed. And
An optical film characterized in that an angle formed by an in-plane slow axis of the optical film and a transport direction of the optical film is within a range of 40 to 50 °.

〔上記一般式（Ａ）において、Ｑは、芳香族炭化水素環、非芳香族炭化水素環、芳香族複素環又は非芳香族複素環を表す。Ｗａ及びＷｂは、それぞれ独立に、Ｑの環を構成する原子に結合する水素原子又は置換基であり、ＷａとＷｂとは互いに同じでも異なっていてもよく、ＷａとＷｂは互いに結合して環を形成してもよい。Ｒ_３は、置換基を表す。ｍは、０〜２の整数を表し、ｍが２の場合、２つのＲ_３は互いに同じでも異なっていてもよい。ｎは、１〜１０の整数を表し、ｎが２以上である場合、２以上のＱ、Ｌ_２、Ｗａ、Ｗｂ、Ｒ_３及びｍのそれぞれは、互いに同一であっても異なっていてもよい。Ｌ_１及びＬ_２は、それぞれ独立に、アルキレン基、アルケニレン基、アルキニレン基、Ｏ、（Ｃ＝Ｏ）、（Ｃ＝Ｏ）−Ｏ、ＮＲ_Ｌ、Ｓ、（Ｏ＝Ｓ＝Ｏ）及び（Ｃ＝Ｏ）−ＮＲ_Ｌからなる群より選ばれる２価の連結基であるか、それらの組合せであるか又は単結合を表す。Ｒ_Ｌは、水素原子又は置換基を表す。Ｒ_１及びＲ_２は、それぞれ独立に、置換基を表す。〕 2. 2. The optical film according to item 1, wherein the wavelength dispersion adjusting agent is a compound represented by the following general formula (A).

[In the general formula (A), Q represents an aromatic hydrocarbon ring, a non-aromatic hydrocarbon ring, an aromatic heterocyclic ring or a non-aromatic heterocyclic ring. Wa and Wb are each independently a hydrogen atom or a substituent bonded to an atom constituting the ring of Q. Wa and Wb may be the same as or different from each other, and Wa and Wb are bonded to each other to form a ring. May be formed. R ₃ represents a substituent. m represents an integer of 0 to 2, and when m is 2, two R _{3 s} may be the same as or different from each other. n represents an integer of 1 to 10, and when n is 2 or more, each of 2 or more of Q, L ₂ , Wa, Wb, R ₃ and m may be the same as or different from each other. . L ₁ and L ₂ are each independently an alkylene group, an alkenylene group, an alkynylene group, O, (C═O), (C═O) —O, NR _L , S, (O═S═O) and ( C═O) —NR 2 represents a divalent linking group selected from the group consisting of _L , a combination thereof, or a single bond. R _L represents a hydrogen atom or a substituent. R ₁ and R ₂ each independently represents a substituent. ]

  3. 3. The optical film according to item 1 or 2, wherein the chromatic dispersion adjusting agent is a compound having a cooling crystallization temperature of 80 ° C. or lower or an exothermic peak at the time of crystallization not observed.

4). In the cellulose ester, when the substitution degree of the acetyl group is DSA and the substitution degree of the acyl group having 3 to 6 carbon atoms is DSB, the DSA and DSB are represented by the following formulas (b1) and ( Item 4. The optical film according to any one of Items 1 to 3, which satisfies b2).
(B1) 2.2 ≦ DSA + DSB ≦ 2.8
(B2) 0.5 ≦ DSB ≦ 2.0

5. The optical film has Ro (450), Ro (550) when the in-plane retardation values Ro at wavelengths of 450 nm, 550 nm, and 650 nm are Ro (450), Ro (550), and Ro (650), respectively. ) And Ro (650) satisfy the following formulas (a1) to (a3): The optical film according to any one of the first to fourth items.
(A1) 110 ≦ Ro (550) ≦ 170
(A2) 0.72 ≦ Ro (450) / Ro (550) ≦ 0.96
(A3) 0.83 ≦ Ro (550) / Ro (650) ≦ 0.97

  6). A circularly polarizing plate comprising the optical film according to any one of items 1 to 5.

  7). 6. An image display device comprising the optical film according to any one of items 1 to 5.

  By the above means of the present invention, it is possible to provide an optical film excellent in brittleness resistance with little retardation unevenness while exhibiting high retardation development and excellent reverse wavelength dispersion. In addition, a circularly polarizing plate including the optical film and an image display device including the optical film and having less color unevenness can be provided.

The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.
The optical film of the present invention can sufficiently impart a necessary phase difference to light in a wide wavelength region by the wavelength dispersion adjusting agent.
Since the chromatic dispersion adjusting agent according to the present invention has a melting point within a high range of 50 to 180 ° C., the chromatic dispersion adjusting agent is hardly melted even when the environmental temperature is increased. As a result, it is estimated that the retardation unevenness caused by the chromatic dispersion adjusting agent melting and bleeding out on the surface can be suppressed.
On the other hand, when the melting point is high, the chromatic dispersion adjusting agent is easily crystallized. However, the chromatic dispersion adjusting agent according to the present invention has a low temperature crystallization temperature of 130 ° C. or lower and is not easily crystallized, or at the time of crystallization. The exothermic peak itself is not observed, and the crystallization phenomenon does not occur. Therefore, it is estimated that the retardation unevenness due to the crystallization of the wavelength dispersion adjusting agent can be suppressed.

The color unevenness of the image display device is considered to be caused by the phase difference unevenness of the optical film, and the color unevenness of the image display device can be eliminated by using the optical film of the present invention with little phase difference unevenness.
In addition, the optical film of the present invention has a structurally large acyl group in the range of 3 to 6 carbon atoms in the cellulose ester as the base material, thereby increasing the flexibility of the film and improving the brittleness resistance. Estimated to improve.

The block diagram of the organic electroluminescence display which is an example of an image display apparatus. The figure explaining the reflection preventing function by the circular deflection plate of FIG. 1 is a configuration diagram of a liquid crystal display device which is an example of an image display device.

  The optical film of the present invention comprises a cellulose ester having an acyl group having 3 to 6 carbon atoms, and a wavelength dispersion adjusting agent having a melting point and a temperature-falling crystallization temperature within the above-mentioned ranges. To do. This feature is a technical feature common to the inventions according to claims 1 to 7.

As an embodiment of the present invention, it is preferable that the wavelength dispersion adjusting agent is a compound represented by the above general formula (A) from the viewpoint of manifesting the effects of the present invention.
In addition, it is preferable that the wavelength dispersion preparation has a cooling crystallization temperature of 80 ° C. or less, or an exothermic peak during crystallization is not observed.

In the cellulose ester, the substitution degree DSA of the acetyl group and the substitution degree DSB of the acyl group having 3 to 6 carbon atoms preferably satisfy the above formulas (b1) and (b2).
Thereby, an optical film having excellent brittleness resistance, high retardation development property, and little retardation unevenness can be obtained.

As an embodiment of the present invention, the optical film has in-plane retardation values Ro (450), Ro (550), and Ro (650) at wavelengths of 450 nm, 550 nm, and 650 nm, respectively, in the above formulas (a1) to (a3). ) Is preferably satisfied.
Thereby, the optical film can be preferably used as a λ / 4 retardation film that imparts a high retardation to light in a wide wavelength region.

  The optical film of the present invention can be suitably included in a circular deflection plate and an image display device. Thereby, the effect of suppressing color unevenness of the image display device can be obtained.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

<Optical film>
The optical film of the present invention contains the following cellulose ester and a wavelength dispersion adjusting agent.

(Cellulose ester)
The cellulose ester used in the present invention has an acyl group having 3 to 6 carbon atoms.
By having an acyl group having 3 to 6 carbon atoms, an optical film having excellent brittleness resistance can be obtained even when stretching at a high magnification such as oblique stretching. When the carbon number of the acyl group is large, the flexibility of the film is increased and the brittleness resistance is improved. On the other hand, the larger the carbon number of the acyl group is, the more easily birefringence is lowered. More preferably, it has a certain acyl group.

The cellulose ester used in the present invention is a compound obtained by esterifying cellulose with at least one of an aliphatic carboxylic acid or an aromatic carboxylic acid having about 2 to 22 carbon atoms.
Specific examples of the cellulose ester having an acyl group having 3 to 6 carbon atoms include cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate. And cellulose mixed fatty acid esters such as The butyryl group that can be contained in the cellulose ester may be linear or branched.
The optical film of the present invention may be used by mixing a plurality of cellulose esters having an acyl group having 3 to 6 carbon atoms.

  The total substitution degree of the acyl group of the cellulose ester can be in the range of about 2.0 to 3.0. The total substitution degree of the acyl group is preferably smaller from the viewpoint of enhancing the retardation development. On the other hand, the smaller the degree of substitution, the stronger the interaction between cellulose esters, so that the wavelength dispersion adjusting agent tends to aggregate and the retardation unevenness tends to increase. For this reason, it is preferable that the total substitution degree of an acyl group exists in the range of 2.1-2.9, and it is more preferable that it exists in the range of 2.2-2.8.

  As the substitution degree of the acyl group having 3 or more carbon atoms of the cellulose ester decreases, the brittleness resistance of the film decreases. Further, since the interaction between the cellulose esters becomes strong, the wavelength dispersion adjusting agent tends to aggregate and the retardation unevenness tends to increase. On the other hand, the greater the degree of substitution of the acyl group having 3 or more carbon atoms, the smaller the birefringence and the less the retardation. Considering these, the substitution degree of the acyl group having 3 or more carbon atoms is preferably in the range of 0.2 to 2.5, and more preferably in the range of 0.5 to 2.0.

In the cellulose ester used in the present invention, when the substitution degree of the acetyl group is DSA and the substitution degree of the acyl group having 3 to 6 carbon atoms is DSB, the DSA and DSB are represented by the following formula (b1). And satisfying the formula (b2).
(B1) 2.2 ≦ DSA + DSB ≦ 2.8
(B2) 0.5 ≦ DSB ≦ 2.0
By using a cellulose ester in which DSA and DSB satisfy the above formulas (b1) and (b2), an optical film having excellent brittleness resistance, high retardation development, and little retardation unevenness can be obtained.
The substitution degree of the acyl group of cellulose ester can be measured by the method prescribed in ASTM-D817-96.

The number average molecular weight (Mn) of the cellulose ester is preferably in the range of 6 × 10 ^{4 to} 3 × 10 ⁵ in order to increase the mechanical strength of the obtained film, and 7 × 10 ⁴ to 2 × 10 ^5. It is more preferable to be within the range.
The weight average molecular weight Mw and the number average molecular weight Mn of the cellulose ester are measured using gel permeation chromatography (GPC). The measurement conditions are as follows.
Solvent: methylene chloride;
Column: Three Shodex K806, K805, K803G (made by Showa Denko KK) are connected and used;
Column temperature: 25 ° C .;
Sample concentration: 0.1% by mass;
Detector: RI Model 504 (manufactured by GL Sciences);
Pump: L6000 (manufactured by Hitachi, Ltd.);
Flow rate: 1.0 ml / min
Calibration curve: A calibration curve with 13 samples of standard polystyrene (STK standard polystyrene, manufactured by Tosoh Corporation, Mw = 100000 to 500) is used. Thirteen samples are used at approximately equal intervals.

The content of residual sulfuric acid in the cellulose ester is preferably in the range of 0.1 to 45.0 mass ppm in terms of elemental sulfur, and more preferably in the range of 1 to 30 mass ppm. Sulfuric acid is considered to remain in the film in a salt state. If the content of residual sulfuric acid is within 45.0 ppm by mass, it will be difficult to break during the heat stretching of the film or during the cutting after the heat stretching.
The residual sulfuric acid content can be measured by a method prescribed in ASTM D817-96.

The content of free acid in the cellulose ester is preferably in the range of 1 to 500 ppm by mass, more preferably 1 to 100 ppm by mass, and further preferably in the range of 1 to 70 ppm by mass. preferable. When the content of the free acid is within the above range, as described above, the film is not easily broken during the heat stretching of the film or during the cutting after the heat stretching.
The content of free acid can be measured by the method prescribed in ASTM D817-96.

  Cellulose esters may contain trace amounts of metal components. It is thought that a trace amount metal component originates in the water used in the cellulose ester synthesis process. Like these metal components, the content of components that can become insoluble nuclei is preferably as small as possible. In particular, metal ions such as iron, calcium, and magnesium may form an insoluble matter by forming a salt with a resin decomposition product or the like that may contain an organic acidic group. In addition, the calcium (Ca) component easily forms a coordination compound (that is, a complex) with an acidic component such as a carboxylic acid or a sulfonic acid, and many ligands. May form insoluble starch, turbidity).

  Specifically, the content of the iron (Fe) component in the cellulose ester is preferably 1 mass ppm or less. Moreover, content in the calcium (Ca) component in a cellulose ester becomes like this. Preferably it is 60 mass ppm or less, More preferably, it exists in the range of 0-30 mass ppm. The content of the magnesium (Mg) component in the cellulose ester is preferably in the range of 0 to 70 ppm by mass, and particularly preferably in the range of 0 to 20 ppm by mass.

The content of metal components such as iron (Fe) component, calcium (Ca) component, magnesium (Mg) component, etc. can be either by treating the completely dried cellulose ester with a micro digest wet cracking device (sulfuric acid decomposition) or by alkali melting. After the pretreatment, the measurement can be performed using an ICP-AES (inductively coupled plasma emission spectrometer).
The content of residual alkaline earth metal, residual sulfuric acid and residual acid can be adjusted by thoroughly washing the cellulose ester obtained by synthesis.

The cellulose ester according to the present invention can be produced by a known method. Generally, cellulose is esterified by mixing raw material cellulose, aliphatic carboxylic acid or aromatic carboxylic acid with carboxylic anhydride, catalyst (sulfuric acid, etc.) and the like. The raw material cellulose is not particularly limited, and may be cotton linter, wood pulp, kenaf or the like. You may mix and use the cellulose ester from which a raw material differs. The esterification reaction proceeds until a cellulose triester is formed. In the triester, the three hydroxy groups of the glucose unit are substituted with an acyl acid of an aliphatic or aromatic carboxylic acid. When two types of aliphatic carboxylic acids or aromatic carboxylic acids are used at the same time, mixed cellulose esters such as cellulose acetate propionate and cellulose acetate butyrate can be produced. Next, a cellulose ester having a desired acyl group substitution degree is synthesized by hydrolyzing the cellulose triester. Thereafter, a cellulose ester is obtained through steps such as filtration, precipitation, washing with water, dehydration, and drying.
Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

In the optical film of the present invention, another resin may be used in combination with the cellulose ester having an acyl group having 3 to 6 carbon atoms.
The content of the other resin in the mixture of the cellulose ester having an acyl group having 3 or more carbon atoms and the other resin is preferably about 5 to 70% by mass with respect to the entire mixture.

  As other resins, cellulose derivatives other than the above-described cellulose esters (for example, cellulose ester resins, cellulose ether resins, etc.), polycarbonate resins, polystyrene resins, polysulfone resins, polyester resins, polyarylate resins, (Meth) acrylic resins, olefin resins (for example, norbornene resins, cyclic olefin resins, cyclic conjugated diene resins, vinyl alicyclic hydrocarbon resins) and the like. Of these, cellulose derivatives, (meth) acrylic resins, polycarbonate resins or cyclic olefin resins are preferred, cellulose derivatives are more preferred, and cellulose ester resins are most preferred.

(Cellulose derivative)
A cellulose derivative is a compound (compound having a cellulose skeleton) using cellulose as a raw material. Examples of cellulose derivatives include cellulose ethers (eg, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cyanoethyl cellulose, etc.), cellulose esters, cellulose ether esters (eg, acetyl methyl cellulose, acetyl ethyl cellulose, acetyl hydroxyethyl cellulose, benzoyl hydroxypropyl). Cellulose, etc.), cellulose carbonate (eg, cellulose ethyl carbonate, etc.), cellulose carbamate (eg, cellulose phenylcarbamate, etc.), and the like, preferably cellulose ester.

((Meth) acrylic resin)
The (meth) acrylic resin that can be used in the present invention can be a homopolymer of a (meth) acrylic acid ester or a copolymer of a (meth) acrylic acid ester and another copolymerizable monomer. The (meth) acrylic resin may be one type or a mixture of two or more types. The (meth) acrylic acid ester is preferably methyl methacrylate. The content ratio of the structural unit derived from methyl methacrylate in the copolymer is preferably 50% by mass or more, and more preferably 70% by mass or more.

  Examples of copolymer monomers that form a copolymer with methyl methacrylate include alkyl methacrylates having 2 to 18 carbon atoms in the alkyl moiety; alkyl acrylates having 1 to 18 carbon atoms in the alkyl moiety; and a lactone ring structure described below. Obtained alkyl (meth) acrylates having 1 to 18 carbon atoms in the alkyl moiety having a hydroxy group (hydroxyl group); α, β-unsaturated acids such as acrylic acid and methacrylic acid; maleic acid, fumaric acid, itaconic acid and the like Unsaturated group-containing divalent carboxylic acids; aromatic vinyl compounds such as styrene and α-methylstyrene; α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile; maleic anhydride, maleimide, N-substituted maleimide, glutaric acid Acrylamide derivatives such as anhydrides and acryloylmorpholine (ACMO); N-vinylpyrrolidone ( VP) and the like. These may be used alone or in combination of two or more.

  Of these, alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate; Alkyl (meth) acrylates having a hydroxy group such as methyl (hydroxymethyl) acrylate and ethyl 2- (hydroxymethyl) acrylate are preferred. In order to enhance the compatibility with the cellulose ester, acryloylmorpholine and the like are preferable.

The (meth) acrylic resin preferably contains a lactone ring structure from the viewpoint of enhancing the heat resistance of the obtained optical film or adjusting the photoelastic coefficient. The lactone ring structure contained in the (meth) acrylic resin is preferably represented by the following general formula (1).

In General formula (1), R < ¹ > -R < ³ > represents a hydrogen atom or a C1-C20 organic residue each independently. The organic residue may contain an oxygen atom. Examples of organic residues include linear or branched alkyl groups, linear or branched alkylene groups, aryl groups, —OAc groups (Ac is an acetyl group), —CN groups, and the like.
The lactone ring structure represented by the general formula (1) is a structure derived from an alkyl (meth) acrylate having a hydroxy group, as will be described later.

一般式（２）におけるＲ^４は、水素原子又はメチル基を表す。Ｘは、水素原子、炭素数１〜２０のアルキル基、アリール基、−ＯＡｃ基（Ａｃはアセチル基）、−ＣＮ基、アシル基又は−Ｃ−ＯＲ基（Ｒは水素原子又は炭素数１〜２０の有機残基）を表す。 The (meth) acrylic resin containing a lactone ring structure further contains a structural unit derived from an alkyl (meth) acrylate having 1 to 18 carbon atoms in the alkyl portion, and if necessary, a monomer containing a hydroxy group, unsaturated A structural unit derived from a carboxylic acid, a monomer represented by the following general formula (2), or the like may further be included.

R ⁴ in the general formula (2) represents a hydrogen atom or a methyl group. X is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, -OAc group (Ac is an acetyl group), -CN group, acyl group, or -C-OR group (R is a hydrogen atom or a carbon atom having 1 to 2 carbon atoms). 20 organic residues).

  The content ratio of the lactone ring structure represented by the general formula (1) in the (meth) acrylic resin containing a lactone ring structure is preferably in the range of 5 to 90% by mass, more preferably 10 to 80% by mass. %, And more preferably in the range of 15 to 70% by mass. When the content of the lactone ring structure is 5% by mass or more, a film having a necessary retardation is easily obtained, and the heat resistance, solvent resistance, and surface hardness of the film are sufficient. When the content of the lactone ring structure is 90% by mass or less, the moldability is high, and the flexibility of the obtained film tends to be high.

The content ratio of the structural unit derived from the alkyl (meth) acrylate in the (meth) acrylic resin containing a lactone ring structure is preferably in the range of 10 to 95% by mass, more preferably 20 to 90% by mass. It is in the range, and more preferably in the range of 30 to 85% by mass.
In the (meth) acrylic resin containing a lactone ring structure, the content ratio of the structural unit derived from the hydroxy group-containing monomer, the unsaturated carboxylic acid, or the monomer represented by the general formula (2) is preferably 0 independently. It is in the range of -30 mass%, More preferably, it is 0-20 mass%, More preferably, it exists in the range of 0-10 mass%.

  A (meth) acrylic resin containing a lactone ring structure is polymerized by a monomer component containing at least an alkyl (meth) acrylate having a hydroxy group and another alkyl (meth) acrylate to form a hydroxy group in the molecular chain. It can be produced through a step of obtaining a polymer having a group and an ester group, and a step of introducing a lactone ring structure by heat-treating the obtained polymer.

The weight average molecular weight Mw of the (meth) acrylic resin is preferably in the range of 8.0 × 10 ^{4 to} 5.0 × 10 ⁵ , more preferably 9.0 × 10 ^{4 to} 4.5 × 10 ⁵ . It is in the range, and more preferably in the range of 1.0 × 10 ^{5 to} 4.0 × 10 ⁵ . If the weight average molecular weight Mw of the (meth) acrylic resin is 8.0 × 10 ⁴ or more, the brittleness resistance of the film is easily improved, and if it is 5.0 × 10 ⁵ or less, the haze of the film tends to be low.

  The weight average molecular weight Mw of the (meth) acrylic resin can be measured by gel permeation chromatography in the same manner as the method for measuring the weight average molecular weight Mw of the cellulose ester.

(Wavelength dispersion adjusting agent)
The wavelength dispersion adjusting agent used in the present invention is a compound used for adjusting the optical wavelength dependency of the retardation of the optical film, that is, the wavelength dispersion. In particular, in the present invention, when the compound is contained in an optical film, it refers to a compound that exhibits the effect of improving reverse wavelength dispersion and satisfies the following formulas (c1) and (c2).
(C1) Ro (550)> Ro (550) _P
(C2) {Ro (450) -Ro (450) _P } / {Ro (550) -Ro (550) _P } <1.0
[In Formula (c1) and Formula (c2), Ro (450) and Ro (550) are retardation values in the in-plane direction of the optical film containing the wavelength dispersion adjusting agent, measured at wavelengths of 450 nm and 550 nm, respectively. Represents. Ro (450) _P and Ro (550) _P represent the retardation value in the in-plane direction of the optical film not containing the wavelength dispersion adjusting agent, measured at each wavelength of 450 nm and 550 nm. ]

In order to give a phase difference of a constant wavelength to light in a wide wavelength region in the entire visible light region, the birefringence increases as the wavelength of the light increases, and the reverse wavelength dispersion (negative wavelength dispersion) increases in phase difference. An optical film showing the above is also required.
The cellulose ester used as the base material of the optical film exhibits reverse wavelength dispersibility, but the reverse wavelength dispersibility is insufficient and the retardation development property is low only with the cellulose ester. In the present invention, the retardation development property and the reverse wavelength dispersion property of the optical film are further enhanced by adding the wavelength dispersion adjusting agent to the cellulose ester.
In the present invention, in contrast to the reverse wavelength dispersion in which the phase difference increases as the light wavelength increases, the wavelength dispersion in which the phase difference decreases as the light wavelength increases is referred to as forward wavelength dispersion (positive wavelength dispersion). Also called sex).

  The chromatic dispersion adjusting agent according to the present invention has a melting point measured by a differential scanning calorimeter in the range of 50 to 180 ° C., and the cooling crystallization temperature is 130 ° C. or lower, or an exothermic peak during crystallization is observed Is not a compound. An exothermic peak is not observed when there is almost no change in the baseline, when the change is a shift of the baseline, even if there is an exothermic peak, the size is in the range of about −2 to 0 mJ / mg, This means a case where no significant difference from noise is observed and it is not derived from crystallization of a compound.

If the melting point of the chromatic dispersion adjusting agent is 50 ° C. or higher, the chromatic dispersion adjusting agent is difficult to melt during oblique stretching, and the occurrence of retardation unevenness due to the chromatic dispersion adjusting agent melting and bleeding out to the surface is suppressed. be able to. Further, from the viewpoint of production suitability, a higher melting point of 50 ° C. or higher can reduce the load of the drying process and can suppress the production cost. When the melting point is 180 ° C. or lower, the chromatic dispersion adjusting agent is difficult to crystallize in the film during oblique stretching, and the occurrence of uneven retardation due to crystallization of the chromatic dispersion adjusting agent can be suppressed.
The melting point of the wavelength dispersion adjusting agent is more preferably in the range of 50 to 150 ° C, and further preferably in the range of 60 to 130 ° C.

If the temperature drop crystallization temperature of the chromatic dispersion adjusting agent is 130 ° C. or lower, the chromatic dispersion adjusting agent is difficult to crystallize even when the melting point is as high as 50 ° C. or higher. Can do.
In order to further enhance the effect of the present invention, it is preferable that the temperature-falling crystallization temperature is 100 ° C. or lower, or an exothermic peak during crystallization is not observed, and the temperature-falling crystallization temperature is 80 ° C. or lower or crystallization More preferably, no exothermic peak is observed.

The melting point and temperature-falling crystallization temperature of the wavelength dispersion adjusting agent in the present invention are measured under the following conditions using a differential scanning calorimeter.
10 mg of a sample of the wavelength dispersion adjusting agent is weighed in an aluminum pan, covered with an aluminum cover, and sealed. As a reference, an aluminum pan and cover (total mass about 35 mg) are used. Using a differential scanning calorimeter DSC 6220 (manufactured by SII Nano Technology Co., Ltd.), the temperature was raised from 30 ° C. to 250 ° C. in a nitrogen atmosphere (50 ml / min) at a heating rate of 10 ° C./min. After the minute holding, the temperature is decreased from 250 ° C. to 30 ° C. at a temperature decreasing rate of 20 ° C./min. The temperature at the minimum point of the endothermic peak observed in the temperature raising process is taken as the melting point of the sample. Although there may be a plurality of endothermic peaks depending on the sample, the melting point is determined from the endothermic peak located on the highest temperature side. Further, the temperature at the maximum point of the exothermic peak observed in the temperature lowering process is defined as the temperature lowering crystallization temperature of the sample. Depending on the sample, there may be a plurality of exothermic peaks, and the cooling crystallization temperature is determined from the exothermic peak located on the highest temperature side. Depending on the sample, an exothermic peak at the time of crystallization may not be observed.

The wavelength dispersion adjusting agent used in the present invention is not particularly limited in structure as long as the melting point and the falling crystallization temperature are within the above ranges, but from the viewpoint of imparting good reverse wavelength dispersion to the optical film, the following general formula It is preferable that it is a compound represented by (A).

Q in the general formula (A) represents an aromatic hydrocarbon ring, a non-aromatic hydrocarbon ring, an aromatic heterocyclic ring or a non-aromatic heterocyclic ring.
The aromatic hydrocarbon ring may be a single ring or a condensed ring, but is preferably a single ring. Preferred examples of the aromatic hydrocarbon ring include benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, perylene ring, tetracene ring, pyrene ring, benzopyrene ring, chrysene ring, triphenylene ring, acenaphthene ring, fluoranthene ring, fluorene ring, etc. More preferably, it is a benzene ring.

  The non-aromatic hydrocarbon ring may be a single ring or a condensed ring, but is preferably a single ring. Preferred examples of the non-aromatic hydrocarbon ring include cyclopropane ring, cyclobutane ring, cyclopentane ring, cyclohexane ring, cycloheptane ring, cyclooctane ring, cyclobutene ring, cyclopentene ring, cyclohexene ring, cycloheptene ring, cyclooctene ring, Examples thereof include an adamantane ring, a bicyclononane ring, a norbornane ring, a norbornene ring, a cyclonorbornene ring, a dicyclopentadiene ring, a hydrogenated naphthalene ring, and a hydrogenated biphenyl ring. Of these, a cyclopentane ring, a cyclohexane ring, a cycloheptane ring, a cyclonorbornene ring, and the like are more preferable.

  The aromatic heterocyclic ring may be a monocyclic ring or a condensed ring, but is preferably a monocyclic ring. Preferred examples of the aromatic heterocycle include furan ring, benzofuran ring, thiophene ring, benzothiophene ring, pyrrole ring, pyrazole ring, imidazole ring, oxadiazole ring, indole ring, carbazole ring, azacarbazole ring (azacarbazole ring) Is one in which at least one carbon atom constituting the carbazole ring is replaced with a nitrogen atom), triazole ring, pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring, thienopyrrole ring, thienothiophene ring, fluropyrrole ring, Furofuran ring, thienofuran ring, benzoisoxazole ring, benzothiazole ring, benzoxazole ring, benzisothiazole ring, benzimidazole ring, pyridine ring, pyrazine ring, pyridazine ring, pyrimidine ring, triazine ring, quinoline ring, isoquino Ring, sinoline ring, quinoxaline ring, phenanthridine ring, benzimidazole ring, perimidine ring, quinazoline ring, quinazolinone ring, azulene ring, silole ring, dibenzofuran ring, dibenzothiophene ring, dibenzocarbazole ring, benzodifuran ring, benzodithiophene Ring, phenanthroline ring, acridine ring, benzoquinoline ring, phenazine ring, phenanthridine ring, cyclazine ring, kindlin ring, tepenidine ring, quinindrine ring, triphenodithiazine ring, triphenodioxazine ring, phenanthrazine ring, anthrazine ring Perimidine ring, naphthofuran ring, naphthothiophene ring, naphthodifuran ring, naphthodithiophene ring, anthrafuran ring, anthradifuran ring, anthrathiophene ring and the like. Of these, a pyridine ring, a benzothiazole ring, a benzoxazole ring, and the like are more preferable.

  The non-aromatic heterocyclic ring may be a monocyclic ring or a condensed ring, and is preferably a monocyclic ring. Preferred examples of the non-aromatic heterocycle include tetrahydrofuran ring, tetrahydropyran ring, dioxolane ring, dioxane ring, pyrrolidine ring, pyridone ring, pyridazinone ring, imide ring, piperidine ring, dihydropyrrole ring, dihydropyridine ring, tetrahydropyridine ring, Piperazine ring, morpholine ring, dihydrooxazole ring, dihydrothiazole ring, piperidine ring, aziridine ring, azetidine ring, azepine ring, azepan ring, imidazolidine ring, diazepine ring, tetrahydrothiophene ring and the like are included. Of these, a pyridone ring, an imide ring, a pyrrolidine ring and the like are more preferable.

In the general formula (A), Wa and Wb each independently represent a hydrogen atom or a substituent bonded to an atom constituting the ring of Q. Wa and Wb may be the same or different from each other, and Wa and Wb may be bonded to each other to form a ring.
The following examples are given as substituents represented by Wa and Wb.
Halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), alkyl group (methyl group, ethyl group, n-propyl group, isopropyl group, tert-butyl group, n-octyl group, 2-ethylhexyl group, etc.) Cycloalkyl group (cyclohexyl group, cyclopentyl group, 4-n-dodecylcyclohexyl group, etc.), alkenyl group (vinyl group, allyl group, etc.), cycloalkenyl group (2-cyclopenten-1-yl, 2-cyclohexene-1- Yl group), alkynyl group (ethynyl group, propargyl group, etc.), aryl group (phenyl group, p-tolyl group, naphthyl group, etc.), heteroaryl group (2-pyrrole group, 2-furyl group, 2-thienyl group). , Pyrrole group, imidazolyl group, oxazolyl group, thiazolyl group, benzimidazolyl group, benzoxazolyl 2-benzothiazolyl group, pyrazolinone group, pyridyl group, pyridinone group, 2-pyrimidinyl group, etc.), cyano group, hydroxy group, nitro group, carboxy group, alkoxy group (methoxy group, ethoxy group, isopropoxy group, tert-butoxy group) Group, n-octyloxy group, 2-methoxyethoxy group, etc.), aryloxy group (phenoxy group, 2-methylphenoxy group, 4-tert-butylphenoxy group, 3-nitrophenoxy group, 2-tetradecanoylaminophenoxy) Group), acyl group (acetyl group, pivaloylbenzoyl group, etc.), acyloxy group (formyloxy group, acetyloxy group, pivaloyloxy group, stearoyloxy group, benzoyloxy group, p-methoxyphenylcarbonyloxy group, etc.), Amino group (amino group, methylamino Group, dimethylamino group, anilino group, N-methyl-anilino group, diphenylamino group, etc.), acylamino group (formylamino group, acetylamino group, pivaloylamino group, lauroylamino group, benzoylamino group, etc.), alkyl and arylsulfonyl Amino group (methylsulfonylamino group, butylsulfonylamino group, phenylsulfonylamino group, 2,3,5-trichlorophenylsulfonylamino group, p-methylphenylsulfonylamino group, etc.), mercapto group, alkylthio group (methylthio group, ethylthio group) Group, n-hexadecylthio group, etc.), arylthio group (phenylthio group, p-chlorophenylthio group, m-methoxyphenylthio group, etc.), sulfamoyl group (N-ethylsulfamoyl group, N- (3-dodecyloxypropyl)) Sulfamoyl group, N, N-dimethylsulfamoyl group, N-acetylsulfamoyl group, N-benzoylsulfamoyl group, N- (N′phenylcarbamoyl) sulfamoyl group, etc.), sulfo group, carbamoyl group (carbamoyl group) N-methylcarbamoyl group, N, N-dimethylcarbamoyl group, N, N-di-n-octylcarbamoyl group, N- (methylsulfonyl) carbamoyl group, etc.).

R _{3 in the} general formula (A) represents a substituent. Although there is no restriction | limiting in particular in a substituent, The following examples are given.
Hydrogen atom, halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), alkyl group (methyl group, ethyl group, n-propyl group, isopropyl group, tert-butyl group, n-octyl group, 2-ethylhexyl) Group), alkenyl group (vinyl group, allyl group, etc.), alkynyl group (ethynyl group, propargyl group, etc.), cyano group, hydroxy group, nitro group, carboxy group, alkoxy group (methoxy group, ethoxy group, isopropoxy group) , Tert-butoxy group, n-octyloxy group, 2-methoxyethoxy group, etc.), acyloxy group (formyloxy group, acetyloxy group, pivaloyloxy group, stearoyloxy group etc.), alkoxycarbonyl group (methoxycarbonyl group, ethoxycarbonyl) Group), aryloxy group (phenoxy group, 2-methyl group) Ruphenoxy group, 4-tert-butylphenoxy group, 3-nitrophenoxy group, 2-tetradecanoylaminophenoxy group, etc.), aryloxycarbonyl group (phenoxycarbonyl group etc.), amino group (amino group, methylamino group, Dimethylamino group, etc.), acylamino group (formylamino group, acetylamino group, pivaloylamino group, lauroylamino group, etc.), alkylsulfonylamino group (methylsulfonylamino group, butylsulfonylamino group, etc.), mercapto group, alkylthio group (methylthio) Group, ethylthio group, n-hexadecylthio group, etc.), sulfamoyl group (N-ethylsulfamoyl group, N- (3-dodecyloxypropyl) sulfamoyl group, N, N-dimethylsulfamoyl group, N-acetylsulfa Moyl group), Rupho group, acyl group (acetyl group, etc.), carbamoyl group (carbamoyl group, N-methylcarbamoyl group, N, N-dimethylcarbamoyl group, N, N-di-n-octylcarbamoyl group, N- (methylsulfonyl) carbamoyl Group), aryl group (phenyl group, p-tolyl group, naphthyl group, etc.), heteroaryl group (2-furyl group, 2-thienyl group, 2-pyrimidinyl group, 2-benzothiazolyl group, 2-pyridyl group, etc.) etc.

Among them, R ₃ is a hydrogen atom, a halogen atom, an alkyl group (preferably having 1 to 20 carbon atoms), an alkenyl group (preferably having 3 to 20 carbon atoms), an aryl group (preferably having 6 to 20 carbon atoms), hetero, Aryl group (preferably 4 to 20 carbon atoms), hydroxy group, carboxy group, alkoxy group (preferably 1 to 20 carbon atoms), aryloxy group (preferably 6 to 20 carbon atoms), acyl group, acyloxy group, cyano Group and amino group are preferable, and a hydrogen atom, a halogen atom, an alkyl group, a cyano group, and an alkoxy group are more preferable. These substituents may further have the same substituent.

M in the general formula (A) is the number of the substituents is _{R 3} represents an integer of 0 to 2. When m is 2, two R _{3 s} may be the same or different from each other.
N in the general formula (A) represents an integer of 1 to 10, and is preferably 1. When n is 2 or more, each of 2 or more of Q, L ₂ , Wa, Wb, R ₃ and m may be the same as or different from each other.

L ₁ and L _{2 in} the general formula (A) are each independently an alkylene group, an alkenylene group, an alkynylene group, O, (C═O), (C═O) —O, NR _L , S, (O═ S = O) and (C = O) or a divalent connecting group selected from the group consisting of -NR _L, or combinations thereof, or a single bond. Preferred L ₁ and L ₂ are O, (C═O) —O, O— (C═O), (C═O) —NH or NH— (C═O).
R _L represents a hydrogen atom or a substituent. Examples of the substituent represented by R _L include an alkyl group (methyl group, ethyl group, n-propyl group, isopropyl group, tert-butyl group, n-octyl group, 2-ethylhexyl group, etc.), a cycloalkyl group. (Cyclohexyl group, cyclopentyl group, 4-n-dodecylcyclohexyl group, etc.), aryl group (phenyl group, p-tolyl group, naphthyl group, etc.), heteroaryl group (2-furyl group, 2-thienyl group, 2-pyrimidinyl) Group, 2-benzothiazolyl group, 2-pyridyl group and the like), cyano group and the like.

R ₁ and R _{2 in} formula (A) each independently represent a substituent. R ₁ and R ₂ may be the same or different from each other. Examples of the substituent represented by R ₁ and R ₂ include the following examples.
Halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), alkyl group (methyl group, ethyl group, n-propyl group, isopropyl group, tert-butyl group, n-octyl group, 2-ethylhexyl group, etc.) Cycloalkyl group (cyclohexyl group, cyclopentyl group, 4-n-dodecylcyclohexyl group, etc.), alkenyl group (vinyl group, allyl group, etc.), cycloalkenyl group (2-cyclopenten-1-yl, 2-cyclohexene-1- Yl group), alkynyl group (ethynyl group, propargyl group, etc.), aryl group (phenyl group, p-tolyl group, naphthyl group, etc.), heteroaryl group (2-furyl group, 2-thienyl group, 2-pyrimidinyl group). , 2-benzothiazolyl group, 2-pyridyl group, etc.), cyano group, hydroxy group, nitro group, carboxy group, a Coxy group (methoxy group, ethoxy group, isopropoxy group, tert-butoxy group, n-octyloxy group, 2-methoxyethoxy group, etc.), aryloxy group (phenoxy group, 2-methylphenoxy group, 4-tert-butyl) Phenoxy group, 3-nitrophenoxy group, 2-tetradecanoylaminophenoxy group, etc.), acyloxy group (formyloxy group, acetyloxy group, pivaloyloxy group, stearoyloxy group, benzoyloxy group, p-methoxyphenylcarbonyloxy group, etc. ), Amino group (amino group, methylamino group, dimethylamino group, anilino group, N-methyl-anilino group, diphenylamino group, etc.), acylamino group (formylamino group, acetylamino group, pivaloylamino group, lauroylamino group, Benzoylamino group ), Alkyl and arylsulfonylamino groups (methylsulfonylamino group, butylsulfonylamino group, phenylsulfonylamino group, 2,3,5-trichlorophenylsulfonylamino group, p-methylphenylsulfonylamino group, etc.), mercapto group, alkylthio Group (methylthio group, ethylthio group, n-hexadecylthio group, etc.), arylthio group (phenylthio group, p-chlorophenylthio group, m-methoxyphenylthio group, etc.), sulfamoyl group (N-ethylsulfamoyl group, N- ( 3-dodecyloxypropyl) sulfamoyl group, N, N-dimethylsulfamoyl group, N-acetylsulfamoyl group, N-benzoylsulfamoyl group, N- (N′phenylcarbamoyl) sulfamoyl group, etc.), sulfo group , Acyl group (acetyl Group, pivaloylbenzoyl group, etc.), carbamoyl group (carbamoyl group, N-methylcarbamoyl group, N, N-dimethylcarbamoyl group, N, N-di-n-octylcarbamoyl group, N- (methylsulfonyl) carbamoyl group And so on.

Among them, R ₁ and R ₂ are an alkyl group (preferably an alkyl group having 1 to 20 carbon atoms), a cycloalkyl group (preferably a cycloalkyl group having 3 to 20 carbon atoms), an aryl group (preferably a carbon number of 6 ˜20 aryl group) or heteroaryl group (preferably an aryl group having 4 to 20 carbon atoms), more preferably an aryl group or a cycloalkyl group. The aryl group is preferably a substituted or unsubstituted phenyl group, more preferably a phenyl group having a substituent, and still more preferably a phenyl group having a substituent at the 4-position. The cycloalkyl group is preferably a substituted or unsubstituted cyclohexyl group, more preferably a cyclohexyl group having a substituent, and further preferably a cyclohexyl group having a substituent at the 4-position. The substituent represented by R ₁ and R ₂ may further have the same substituent.

一般式（Ｂ）のＷａ、Ｗｂ、Ｒ_３、ｍ、Ｌ_１、Ｌ_２、Ｒ_Ｌ、Ｒ_１及びＲ_２は、一般式（Ａ）におけるＷａ、Ｗｂ、Ｒ_３、ｍ、Ｌ_１、Ｌ_２、Ｒ_Ｌ、Ｒ_１及びＲ_２とそれぞれ同様に定義される。 The compound represented by the general formula (A) is preferably a compound represented by the general formula (B).

Wa, Wb, R ₃ , m, L ₁ , L ₂ , R _L , R ₁ and R ₂ in the general formula (B) are Wa, Wb, R ₃ , m, L ₁ , L in the general formula (A). ₂ , R _L , R ₁ and R ₂ are defined similarly.

一般式（Ｃ）のＷａ、Ｗｂ、Ｒ_３、ｍ、Ｌ_１、Ｌ_２、Ｒ_Ｌ、Ｒ_１及びＲ_２は、一般式（Ａ）におけるＷａ、Ｗｂ、Ｒ_３、ｍ、Ｌ_１、Ｌ_２、Ｒ_Ｌ、Ｒ_１及びＲ_２のそれぞれと、定義が同じである。 The compound represented by the general formula (B) is preferably a compound represented by the general formula (C).

Wa, Wb, R ₃ , m, L ₁ , L ₂ , R _L , R ₁ and R ₂ in the general formula (C) are Wa, Wb, R ₃ , m, L ₁ , L in the general formula (A). ₂ , R _L , R ₁ and R ₂ each have the same definition.

Ｒ_ｉ〜Ｒ_iiiは、それぞれ独立に、水素原子又は置換基を表す。 When Wa and Wb of the general formula (C) are bonded to each other to form a ring, the formed ring is preferably a nitrogen-containing heterocycle. Examples of the compound represented by the general formula (C) include the following.

R _{i to} R _iii each independently represents a hydrogen atom or a substituent.

  For example, in the exemplary compound C1, Q in the general formula (A) is a benzene ring, Wa is a group containing an oxygen atom bonded to the benzene ring, and Wb contains a nitrogen atom bonded to the benzene ring. It is a group.

On the other hand, in the exemplary compound A0 represented by the following formula, Q in the general formula (A) is a naphthalene ring.

Specific examples of the compound represented by the general formula (A), the general formula (B), or the general formula (C) are shown below. The wavelength dispersion adjusting agent that can be used in the present invention includes the following exemplified compounds A1 to A1. There is no limitation by A24.

  In the above exemplified compounds, when there are geometric isomers (trans isomer and cis isomer), any isomer is not limited, but the trans isomer having higher retardation development is more preferable than the cis isomer.

In addition, the wavelength dispersion adjusting agent that can be used in the present invention is represented by the general formula (A), the general formula (B), or the general formula (C) as long as the melting point and the cooling crystallization temperature satisfy the above ranges. The following exemplary compounds D1 to D4 can also be used.

The wavelength dispersion adjusting agent used in the present invention can be synthesized by a known method. For example, the exemplary compound A1 can be synthesized according to the following scheme.
[Synthesis Example of Exemplified Compound A1]

  To a reaction vessel equipped with an ester tube, 125 ml of toluene, 12.5 g (0.12 mol) of malonic acid, 31.7 g (0.26 mol) of diethylene glycol monomethyl ether and 11.42 g of p-toluenesulfonic acid monohydrate were added, The mixture was stirred for 5 hours while heating under reflux in a nitrogen atmosphere. Distillation of water was confirmed as the reaction progressed. Thereafter, the solvent was distilled off from the reaction solution under reduced pressure, and the residue was purified by silica gel chromatography (ethyl acetate / heptane) to obtain 27.7 g of compound (l). The yield was 75% based on malonic acid.

  To 200 ml of N, N-dimethylformamide, 6.9 g (0.05 mol) of 2,5-dihydroxybenzaldehyde, 31.6 g (0.11 mol) of the compound (m), 13.8 g of potassium carbonate, and 3.3 g of potassium iodide were added. In addition, the mixture was stirred at 100 ° C. for 5 hours in a nitrogen atmosphere. After cooling the reaction solution, water and ethyl acetate were added for extraction. The solvent was distilled off from the organic layer under reduced pressure, and the resulting crude crystals were purified by silica gel chromatography (ethyl acetate / heptane) to obtain 13.2 g of compound (n). The yield was 48% based on 2,5-dihydroxybenzaldehyde.

  To a reaction vessel equipped with an ester tube, 50 ml of toluene, 5.5 g (0.01 mol) of compound (n), 3.1 g (0.01 mol) of compound (l) and 1.5 g of piperidine are added and heated in a nitrogen atmosphere. The mixture was stirred for 5 hours while refluxing. Distillation of water was confirmed as the reaction progressed. After cooling the reaction solution, water and ethyl acetate were added for extraction. The solvent was distilled off from the organic layer under reduced pressure, and the resulting crude crystals were purified by silica gel chromatography (ethyl acetate / heptane) to obtain 6.1 g of exemplary compound A1. The yield was 72% based on the compound (n).

It is known that the melting point and the temperature-falling crystallization temperature of a compound affect the structure of the compound, and the melting point generally increases as the molecular symmetry, polarity and rigidity of the compound increase.
The compound represented by the general formula (A) can be controlled by -L ₁ -R ₁ and -L ₂ -R ₂ so that the symmetry of the chemical structure is increased. The polarity can be increased when Wa, Wb, L ₁ or L ₂ contains a polar group. Further, since Q, Wa and Wb, R ₁ or R _{2 includes a} ring structure (aromatic hydrocarbon ring, non-aromatic hydrocarbon ring, aromatic heterocycle or non-aromatic heterocycle), the rigidity is large. Can be controlled. In this way, the melting point of the wavelength dispersion adjusting agent can be set within a specific range depending on the molecular structure of the compound.

In general, the higher the melting point of the compound, the higher the temperature-falling crystallization temperature, but the temperature-falling crystallization temperature can be greatly reduced by introducing a branched structure or a flexible group.
The compound represented by the general formula (A) can adjust the temperature-falling crystallization temperature to a specific range by including a branched structure or a flexible group in Wa, Wb, L ₁ or L ₂ . Examples of the branched structure include i-propyl group, i-butyl group, t-butyl group, 2-ethylhexyl group and the like. Examples of the flexible group include a chain alkyl group (for example, n-butyl group, n-hexyl group, n-octyl group, etc.), a polyoxyalkylene group (for example, polyoxyethylene group, polyoxypropylene group, etc.), etc. Is mentioned.

  The content of the wavelength dispersion adjusting agent used in the present invention is appropriately set to such an extent that the required reverse wavelength dispersion and retardation can be imparted. Specifically, the content of the compound used in the present invention is preferably in the range of 1 to 15% by mass and more preferably in the range of 2 to 10% by mass with respect to the cellulose ester. When the content of the wavelength dispersion adjusting agent is 1% by mass or more, high retardation expression and sufficient reverse wavelength dispersion can be imparted to the optical film. If the content of the wavelength dispersion adjusting agent is 15% by mass or less, the optical film is less likely to cause bleed out.

  The optical film of the present invention may further contain various additives as described below as required.

(Sugar ester)
The optical film of the present invention can contain a sugar ester other than the cellulose ester described above from the viewpoint of improving the plasticity of the optical film.
The sugar ester that can be used in the present invention is a compound having 1 to 12 furanose structures or pyranose structures, in which all or part of the hydroxy groups in the compound are esterified.

Preferable examples of such sugar esters include sucrose esters represented by the following general formula (FA).

R _{1 to} R _{8 in} Formula (FA) each independently represent a hydrogen atom, a substituted or unsubstituted alkylcarbonyl group, or a substituted or unsubstituted arylcarbonyl group. R _{1 to} R ₈ may be the same as or different from each other.

  The substituted or unsubstituted alkylcarbonyl group is preferably a substituted or unsubstituted alkylcarbonyl group having 2 or more carbon atoms. Examples of the substituted or unsubstituted alkylcarbonyl group include a methylcarbonyl group (acetyl group). Examples of the substituent that the alkyl group has include an aryl group such as a phenyl group.

  The substituted or unsubstituted arylcarbonyl group is preferably a substituted or unsubstituted arylcarbonyl group having 7 or more carbon atoms. Examples of the arylcarbonyl group include a phenylcarbonyl group. Examples of the substituent that the aryl group has include an alkyl group such as a methyl group, an alkoxyl group such as a methoxy group, and the like.

  The average substitution degree of the acyl group of the sucrose ester is preferably in the range of 3.0 to 7.5. When the average substitution degree of the acyl group is within this range, sufficient compatibility with the cellulose ester is easily obtained.

Specific examples of the sucrose ester represented by the general formula (FA) include the following exemplified compounds FA-1 to FA-24. The table below, the _R 1 to R ₈ in the general formula of Exemplified Compound FA-1~FA-24 (FA) , shows the average degree of substitution of acyl groups.

Examples of other sugar esters include the compounds described in JP-A-62-42996 and JP-A-10-237084.
The content of the sugar ester is preferably in the range of 0.5 to 35.0% by mass and more preferably in the range of 5.0 to 30.0% by mass with respect to the cellulose ester.

(Plasticizer)
The optical film of the present invention may contain a plasticizer in order to improve the fluidity of the composition during film production and the flexibility of the film. Examples of plasticizers include polyester plasticizers, polyhydric alcohol ester plasticizers, polycarboxylic acid ester plasticizers (including phthalate ester plasticizers), glycolate plasticizers, ester plasticizers ( Citrate ester plasticizers, fatty acid ester plasticizers, phosphate ester plasticizers, trimellitic ester plasticizers, and the like). These may be used alone or in combination of two or more.

The polyester plasticizer is a compound obtained by reacting a 1-4 carboxylic acid and a 1-6 valent alcohol, preferably a compound obtained by reacting a divalent carboxylic acid with a glycol. It is.
Examples of the divalent carboxylic acid include succinic acid, glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like. In particular, a compound using succinic acid, adipic acid, phthalic acid or the like as the divalent carboxylic acid can impart good plasticity.

  Examples of glycols include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, neopentylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol and the like. included. Each of the divalent carboxylic acid and glycol may be one kind, or two or more kinds may be used in combination.

The polyester plasticizer may be any of ester, oligoester, and polyester. The molecular weight of the polyester plasticizer is preferably in the range of 100 to 10000, and more preferably in the range of 600 to 3000 since the effect of imparting plasticity is great.
The viscosity of the polyester plasticizer depends on the molecular structure and molecular weight, but in the case of an adipic acid plasticizer, the compatibility with the cellulose ester is high and the effect of imparting plasticity is high. It is preferably in the range of s (25 ° C.). The polyester plasticizer may be used alone or in combination of two or more.

The polyhydric alcohol ester plasticizer is an ester compound (alcohol ester) of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, preferably a 2-20 valent aliphatic polyhydric alcohol ester. The polyhydric alcohol ester compound preferably has an aromatic ring or a cycloalkyl ring in the molecule.
Examples of the aliphatic polyhydric alcohol include ethylene glycol, propylene glycol, trimethylolpropane, pentaerythritol and the like.
The monocarboxylic acid can be an aliphatic monocarboxylic acid, an alicyclic monocarboxylic acid, an aromatic monocarboxylic acid, or the like. One type of monocarboxylic acid may be sufficient and a 2 or more types of mixture may be sufficient as it. Further, all of the OH groups contained in the aliphatic polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

The aliphatic monocarboxylic acid is preferably a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms. The carbon number of the aliphatic monocarboxylic acid is more preferably 1-20, and still more preferably 1-10. Examples of such aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, and the like, and acetic acid may be preferable in order to enhance compatibility with the cellulose ester.
Examples of the alicyclic monocarboxylic acid include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid and the like.
Examples of aromatic monocarboxylic acids include: benzoic acid; one having 1 to 3 alkyl groups or alkoxy groups (for example, methoxy group or ethoxy group) introduced into the benzene ring of benzoic acid (for example, toluic acid); benzene ring Aromatic monocarboxylic acids having two or more (for example, biphenyl carboxylic acid, naphthalene carboxylic acid, tetralin carboxylic acid, etc.) are included, and benzoic acid is preferred.

  The molecular weight of the polyhydric alcohol ester plasticizer is not particularly limited, but is preferably in the range of 300 to 1500, and more preferably in the range of 350 to 750. In order to make it hard to volatilize, the one where molecular weight is larger is preferable. In order to improve moisture permeability and compatibility with the cellulose ester, a smaller molecular weight is preferable.

  Specific examples of the polyhydric alcohol ester plasticizer include trimethylolpropane triacetate, pentaerythritol tetraacetate, ester compound (A) represented by the general formula (I) described in JP-A-2008-88292, and the like. It is.

The polycarboxylic acid ester plasticizer is an ester compound of a divalent or higher, preferably 2-20 valent polycarboxylic acid and an alcohol compound. The polyvalent carboxylic acid is preferably a 2-20 valent aliphatic polyvalent carboxylic acid, a 3-20 valent aromatic polyvalent carboxylic acid, or a 3-20 valent alicyclic polyvalent carboxylic acid.
Examples of polyvalent carboxylic acids include trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid or derivatives thereof; succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid Contains aliphatic polycarboxylic acids such as fumaric acid, maleic acid and tetrahydrophthalic acid; oxypolycarboxylic acids such as tartaric acid, tartronic acid, malic acid and citric acid, etc., and suppresses volatilization from the film. For this, oxypolycarboxylic acids are preferred.

  Examples of the alcohol compound include an aliphatic saturated alcohol compound having a straight chain or a side chain, an aliphatic unsaturated alcohol compound having a straight chain or a side chain, an alicyclic alcohol compound, an aromatic alcohol compound, and the like. Carbon number of an aliphatic saturated alcohol compound or an aliphatic unsaturated alcohol compound becomes like this. Preferably it is 1-32, More preferably, it is 1-20, More preferably, it is 1-10. Examples of the alicyclic alcohol compound include cyclopentanol, cyclohexanol and the like. Examples of the aromatic alcohol compound include phenol, paracresol, dimethylphenol, benzyl alcohol, cinnamyl alcohol and the like. One kind of alcohol compound may be used, or a mixture of two or more kinds may be used.

  The molecular weight of the polycarboxylic acid ester plasticizer is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. A larger molecular weight of the polyvalent carboxylic acid ester plasticizer is preferable from the viewpoint of suppressing bleeding out. From the viewpoint of moisture permeability and compatibility with cellulose ester, a smaller one is preferable.

  The acid value of the polyvalent carboxylic acid ester plasticizer is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. The acid value refers to the number of milligrams of potassium hydroxide necessary for neutralizing the acid (carboxy group present in the sample) contained in 1 g of the sample. The acid value is measured according to JIS K0070.

Examples of the polycarboxylic acid ester plasticizer include an ester compound (B) represented by the general formula (II) described in JP-A-2008-88292.
The polyvalent carboxylic acid ester plasticizer may be a phthalic acid ester plasticizer. Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate, dicyclohexyl terephthalate and the like.

Examples of glycolate plasticizers include alkylphthalyl alkyl glycolates. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate and the like. .
The ester plasticizer includes a fatty acid ester plasticizer, a citrate ester plasticizer, a phosphate ester plasticizer, a trimellitic acid plasticizer, and the like.

  Examples of the fatty acid ester plasticizer include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate and the like. Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, acetyl tributyl citrate and the like. Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like. Examples of trimellitic acid plasticizers include octyl trimellitic acid, n-octyl trimellitic acid, isodecyl trimellitic acid, and isononyl trimellitic acid.

  It is preferable that content of a plasticizer exists in the range of 0.5-30.0 mass% with respect to a cellulose ester. If the content of the plasticizer is 30.0% by mass or less, the optical film hardly causes bleed out.

(UV absorber)
The optical film of the present invention may further contain an ultraviolet absorber. The ultraviolet absorber may be benzotriazole, 2-hydroxybenzophenone, salicylic acid phenyl ester, or the like. Specifically, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- Triazoles such as (3,5-di-t-butyl-2-hydroxyphenyl) benzotriazole; 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4 -Benzophenones such as methoxybenzophenone.

Among them, an ultraviolet absorber having a molecular weight of 400 or more is difficult to volatilize at a high boiling point, and is difficult to scatter even at high temperature molding. Therefore, even if the addition amount is relatively small, weather resistance is imparted to the obtained film. Can do.
Examples of ultraviolet absorbers having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- Benzotriazoles such as (1,1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol];
Hindered amines such as bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate;
2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy] ethyl] -4- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy]- A hybrid system having both hindered phenol and hindered amine structures in the molecule such as 2,2,6,6-tetramethylpiperidine;
Preferably, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole or 2,2-methylenebis [4- (1,1,3, 3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol]. These may be used alone or in combination of two or more.

(Fine particles)
The optical film of the present invention may contain fine particles composed of an inorganic compound or an organic compound.
Examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate , Calcium phosphate and the like.
Examples of organic compounds include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene resin, silicone resin, polycarbonate resin, benzoguanamine resin, melamine Resin, polyolefin-based powder, polyester-based resin, polyamide-based resin, polyimide-based resin, pulverized classification of organic polymer compound (polyfluorinated ethylene-based resin, starch, etc.), polymer compound synthesized by suspension polymerization method, spray drying High molecular compounds made spherical by the method or dispersion method are included.

The fine particles can be composed of a compound containing silicon, preferably silicon dioxide, from the viewpoint that the haze of the obtained film can be kept low.
Examples of the fine particles of silicon dioxide include Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above, Nippon Aerosil Co., Ltd.) and the like.
Among these, Aerosil 200V and Aerosil R972V are particularly preferable because they can increase the slipperiness of the film surface while keeping the haze of the optical film low.
Examples of the fine particles of zirconium oxide include Aerosil R976, R811 (manufactured by Nippon Aerosil Co., Ltd.) and the like.

  Examples of the polymer compound include a silicone resin, a fluororesin, a (meth) acrylic resin, and the like, preferably a silicone resin, and more preferably a silicone resin having a three-dimensional network structure. Examples of such silicone resins include Tospearl 103, 105, 108, 120, 145, 3120, 240 (above, manufactured by Toshiba Silicone Co., Ltd.) and the like.

The average particle diameter of the primary particles of the fine particles is preferably in the range of 5 to 400 nm, more preferably in the range of 10 to 300 nm. The fine particles may mainly form secondary aggregates having a particle size in the range of 0.05 to 0.30 μm. If the average particle size of the fine particles is in the range of 100 to 400 nm, they can exist as primary particles without agglomeration.
It is preferable to contain fine particles so that the dynamic friction coefficient of at least one surface of the optical film is in the range of 0.2 to 1.0.
The content of the fine particles is preferably in the range of 0.01 to 1.00% by mass, more preferably in the range of 0.05 to 0.50% by mass with respect to the cellulose ester.

(Dispersant)
The optical film of the present invention may further contain a dispersant from the viewpoint of enhancing the dispersibility of the fine particles. The dispersant is one or more selected from amine-based dispersants and carboxy group-containing polymer dispersants.

  The amine dispersant is preferably an alkylamine or an amine salt of polycarboxylic acid, and specific examples thereof include polyester acid, polyether ester acid, fatty acid, fatty acid amide, polycarboxylic acid, alkylene oxide, polyalkylene oxide. , A compound obtained by aminating polyoxyethylene fatty acid ester, polyoxyethylene glycerin fatty acid ester, and the like. Examples of amine salts include amidoamine salts, aliphatic amine salts, aromatic amine salts, alkanolamine salts, polyvalent amine salts and the like.

  Specific examples of the amine dispersant include polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, tripropylamine, diethylaminoethylamine, dimethylaminopropylamine, diethylaminopropylamine and the like. Examples of commercially available products include Solspers series (manufactured by Lubrizol), Ajisper series (manufactured by Ajinomoto Co., Inc.), BYK series (manufactured by Big Chemie), EFKA series (manufactured by EFKA), and the like.

  The carboxy group-containing polymer dispersant is preferably a polycarboxylic acid or a salt thereof, and may be, for example, polycarboxylic acid, ammonium polycarboxylate, sodium polycarboxylate, or the like. Specific examples of the carboxy group-containing polymer dispersant include polyacrylic acid, ammonium polyacrylate, sodium polyacrylate, ammonium polyacrylate copolymer, polymaleic acid, ammonium polymaleate, sodium polymaleate and the like.

The amine-based dispersant and the carboxy group-containing polymer dispersant may be used after being dissolved in a solvent component, or may be commercially available.
The content of the dispersant is preferably 0.2% by mass or more based on the fine particles, although it depends on the type of the dispersant. When the content of the dispersant is 0.2% by mass or more with respect to the fine particles, the dispersibility of the fine particles can be sufficiently improved.

  When the optical film of the present invention further contains a surfactant or the like, adsorption of the dispersant to the surface of the fine particles is less likely to occur than the surfactant, and the fine particles may be easily reaggregated. Since the dispersant is expensive, its content is preferably as small as possible. On the other hand, when the content of the dispersant is too small, poor wettability of fine particles and a decrease in dispersion stability are likely to occur. Therefore, the content of the dispersant when the optical film of the present invention further contains a surfactant or the like can be about 0.05 to 10.00 parts by mass with respect to 10.00 parts by mass of the fine particles.

(Phase difference control agent)
In order to improve the display quality of an image display device such as a liquid crystal display device, a retardation control agent is added to the optical film or an alignment film is formed to provide a liquid crystal layer. By combining the phase difference, the optical compensation ability can be imparted to the optical film.
Examples of the retardation control agent include aromatic compounds having two or more aromatic rings as described in the specification of European Patent 911,656A2, rod-shaped compounds described in JP-A-2006-2025, and the like. It is done. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound is preferably an aromatic heterocyclic ring including an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. The aromatic heterocycle is generally an unsaturated heterocycle. Of these, the 1,3,5-triazine ring described in JP-A-2006-2026 is preferable.
The addition amount of these retardation control agents is preferably in the range of 0.5 to 20.0% by mass with respect to 100% by mass of the resin used as the film substrate, and in the range of 1 to 10% by mass. More preferably, it is within.

(Other additives)
The optical film of the present invention may further contain an antioxidant, an antistatic agent, a flame retardant and the like for preventing thermal decomposition during molding and coloring due to heat.
Phosphorus flame retardants include red phosphorus, triaryl phosphate ester, diaryl phosphate ester, monoaryl phosphate ester, aryl phosphonate compound, aryl phosphine oxide compound, condensed aryl phosphate ester, halogenated alkyl phosphate ester, One or more kinds selected from halogen condensed phosphoric acid ester, halogen-containing condensed phosphonic acid ester, halogen-containing phosphorous acid ester and the like can be mentioned. Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloropropyl) phosphate. , Tris (tribromoneopentyl) phosphate, and the like.

<Physical properties of optical film>
The optical film of the present invention has in-plane retardation values Ro measured at wavelengths of 450 nm, 550 nm, and 650 nm under the conditions of a temperature of 23 ° C. and a relative humidity of 55%, respectively, Ro (450) and Ro (550). And Ro (650), it is preferable that the Ro (450), Ro (550), and Ro (650) satisfy the following formulas (a1) to (a3).
(A1) 110 ≦ Ro (550) ≦ 170
(A2) 0.72 ≦ Ro (450) / Ro (550) ≦ 0.96
(A3) 0.83 ≦ Ro (550) / Ro (650) ≦ 0.97

An optical film in which Ro (550) satisfies the formula (a1) can preferably function as a λ / 4 retardation film. Especially, it is more preferable to satisfy | fill 120 <= Ro (550) <= 160, and it is still more preferable to satisfy | fill 130 <= Ro (550) <= 150.
An optical film in which Ro (450), Ro (550) and Ro (650) satisfy the above formulas (a2) and (a3) is excellent in reverse wavelength dispersion and can function more preferably as a λ / 4 retardation film. . In addition, light leakage or the like when an image display device using an optical film is displayed in black can be reduced. Specifically, when the formula (a2) is satisfied, the blue reproducibility is high, and when the formula (a3) is satisfied, the red reproducibility is high. Especially, it is more preferable to satisfy | fill 0.79 <= Ro (450) / Ro (550) <= 0.89, and it is more preferable to satisfy | fill 0.84 <= Ro (550) / Ro (650) <= 0.93. .

  Ro (550) representing phase difference development, Ro (450) / Ro (550) and Ro (550) / Ro (650) representing wavelength dispersion should be adjusted according to the compound used in the present invention and stretching conditions. Can do. In order to satisfy all of the above formulas (a1) to (a3), the wavelength dispersion adjusting agent used in the present invention may be contained, and the stretching conditions may be further adjusted.

  The optical film of the present invention has a thickness direction retardation value Rt measured at a wavelength of 550 nm under the conditions of 23 ° C. and 55% RH, where Rt (550) is Rt (550), It is preferable to satisfy 50 ≦ Rt (550) ≦ 250.

The above Ro and Rt are defined by the following formulas (I) and (II), respectively.
Formula _{(I): Ro = (n} x -n y) × d
Formula (II): Rt = {(n _x + n _y ) / 2−n _z } × d
In [Formula (I) and (II), n _x represents a refractive index in the slow axis direction x in which the refractive index is maximized in the plane direction of the optical film. n _y represents a refractive index in the direction y orthogonal to the slow axis direction x in the in-plane direction of the optical film. _nz represents the refractive index in the thickness direction z of the optical film. d represents the film thickness (nm) of the optical film. )

The above Ro and Rt can be measured using an automatic birefringence meter, for example, AxoScan manufactured by Axometric, and KOBRA-21ADH manufactured by Oji Scientific Instruments. When using AxoScan, specifically, it can be measured by the following method.
1) Condition the optical film at 23 ° C. and 55% RH. The average refractive index of the optical film after humidity adjustment at each of wavelengths of 450 nm, 550 nm and 650 nm is measured using an Abbe refractometer and a spectral light source. Moreover, the film thickness d (nm) of an optical film is measured using a film thickness meter.
2) In-plane retardation values Ro (450) and Ro (550) when light having a wavelength of 450 nm, 550 nm, or 650 nm is incident on the optical film after humidity adjustment in parallel with the normal line of the film surface. And Ro (650) are measured with an AxoScan. The measurement is performed under conditions of 23 ° C. and 55% RH.
3) Check the in-plane slow axis of the optical film by AxoScan. When light having wavelengths of 450 nm, 550 nm, and 650 nm is incident from an angle of φ (incident angle (φ)) with respect to the normal of the surface of the optical film, with the confirmed slow axis as the tilt axis (rotation axis) The phase difference value R (φ) is measured. R (φ) can be measured at 6 points every 10 ° in the range of 0 to 50 °. The measurement is performed under conditions of 23 ° C. and 55% RH.
4) Ro (450), Ro (550) and Ro (650) measured in 2) above, and R (φ) measured in each wavelength of 450 nm, 550 nm or 650 nm in 3) above, and 1) above in from the measured average refractive index and the film thickness d, by _AxoScan, calculates the n x, _{n y} and _{n z.} Then, based on the above formula (II), thickness direction retardation values Rt (450), Rt (550), and Rt (650) at wavelengths of 450 nm, 550 nm, and 650 nm, respectively, are calculated.

The optical film of the present invention, N _z defined by the following formula (a4) preferably satisfies the following formula (a5).
(A4) N _z = Rt (550) / Ro (550) +0.5
(A5) 0 ≦ N _z ≦ 1
Satisfies N _z is the equation (a5), the retardation value Rt in the thickness direction, because relatively smaller than the retardation value Ro in the plane direction, an image display device comprising the optical film of the present invention obliquely The change in color when observed from the direction can be reduced.

The angle (referred to as the orientation angle) formed by the in-plane slow axis of the optical film of the present invention and the film transport direction is in the range of 40 to 50 °.
If the orientation angle is within this range, an optical film having a slow axis in an oblique direction with respect to the long direction (transport direction) and a polarizing film having a transmission axis parallel to the long direction (transport direction) The circularly polarizing plate can be easily manufactured by unwinding from the rolls and bonding them with a roll-to-roll so that the longitudinal directions of the rolls overlap each other. There is little cut loss of the film, which is advantageous in production. The orientation angle is particularly preferably 45 °. The orientation angle of the optical film can be measured with an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments).

  The film thickness of the optical film is preferably 250 μm or less, more preferably 100 μm or less, and even more preferably 70 μm or less in order to reduce the variation in retardation due to heat or humidity. On the other hand, the film thickness of the optical film is preferably 10 μm or more, and more preferably 20 μm or more, in order to express a certain level of film strength or retardation. When the film thickness of the optical film is within these ranges, it is preferable from the viewpoint of thinning and productivity of the image display device.

The haze (total haze) of the optical film is preferably less than 1%, more preferably 0.5% or less, and even more preferably 0.2% or less. If the haze is less than 1%, the transparency of the film does not decrease and the film functions sufficiently as an optical film.
The haze (total haze) of the optical film can be measured with a haze meter NDH-2000 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K-7136. The light source of the haze meter may be a 5V9W halogen sphere, and the light receiving portion may be a silicon photocell (with a relative visibility filter). The haze can be measured under conditions of 23 ° C. and 55% RH.

The visible light transmittance of the optical film of the present invention is preferably 90% or more, and more preferably 93% or more.
In the optical film of the present invention, the elongation at break in at least one direction measured in accordance with JIS-K7127-1999 is preferably 10% or more, more preferably 20% or more, and further preferably 30. % Or more.

As described above, the optical film of the present invention has a high in-plane retardation and exhibits excellent reverse wavelength dispersion. Therefore, the optical film of the present invention can impart a high retardation to light in a wide wavelength region.
The optical film of the present invention is used as an optical film for image display devices such as organic EL display devices and liquid crystal display devices. Specifically, it is used as a polarizing plate protective film, a retardation film, an optical compensation film or an antireflection film, and preferably used as a λ / 4 retardation film.
The λ / 4 retardation film has an in-plane retardation value Ro of about ¼ of a predetermined light wavelength (usually visible light region). The λ / 4 retardation film is preferably composed of a single layer of the optical film of the present invention. The λ / 4 retardation film is preferably used for an antireflection film of an organic EL display device.

<Method for producing optical film>
The optical film of the present invention can be produced by a solution casting method or a melt casting method. The solution casting method is preferable from the viewpoint of suppressing optical defects such as coloring of the optical film, foreign matter defects, and die lines, and the melt casting method is preferable from the viewpoint of suppressing the solvent from remaining in the optical film.

A) Solution casting method An optical film containing a cellulose ester is produced by the solution casting method. A1) A step of preparing a dope by dissolving at least a cellulose ester and, if necessary, other additives in a solvent. A2) a step of casting the dope on an endless metal support, A3) a step of evaporating the solvent from the cast dope to form a web, A4) a step of peeling the web from the metal support, and A5) After drying, it includes a step of drawing to obtain a film.

A1) Dope preparation step In a dissolution vessel, a dope is prepared by dissolving cellulose ester and other additives as required in a solvent.
A solvent can be used without a restriction | limiting, if a cellulose ester, another additive, etc. are melt | dissolved. For example, as a chlorinated organic solvent, methylene chloride, as a non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro- Examples include 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, and nitroethane. Preferably, methylene chloride, methyl acetate, ethyl acetate, acetone or the like can be used.

The dope preferably further contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the ratio of the alcohol in the dope is high, the web is gelled and peeling from the metal support becomes easy. On the other hand, when the ratio of alcohol in the dope is small, dissolution of cellulose acetate in a non-chlorine organic solvent system can be promoted.
Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol and the like. Of these, ethanol is preferred because of high dope stability, relatively low boiling point, and high drying properties.
Especially, it is preferable that dope contains the methylene chloride of a solvent, and a C1-C4 linear or branched aliphatic alcohol.

  The concentration of the cellulose ester in the dope is preferably high in order to reduce the drying load, but if the concentration of the cellulose ester is too high, it is difficult to filter. Therefore, the concentration of the cellulose ester in the dope is preferably in the range of 10 to 35% by mass, more preferably in the range of 15 to 25% by mass.

  The method for dissolving the cellulose ester in the solvent may be, for example, a method for dissolving under heating and pressure. A higher heating temperature is preferable from the viewpoint of increasing the solubility of the cellulose ester. If the temperature is too high, the pressure needs to be increased, and the productivity is lowered. Therefore, the heating temperature is preferably within the range of 45 to 120 ° C.

The additive may be added batchwise to the dope, or an additive solution may be separately prepared and added inline. In particular, it is preferable to add all or part of the fine particles in-line in order to reduce the load on the filter medium.
When the additive solution is added in-line, it is preferable to dissolve a small amount of cellulose ester to facilitate mixing with the dope. The content of the preferred thermoplastic resin can be in the range of 1 to 10 parts by mass, more preferably in the range of 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.
For in-line addition and mixing, for example, a static mixer (manufactured by Toray Engineering), an in-line mixer such as SWJ (Toray Static In-Pipe Mixer Hi-Mixer), or the like is preferably used.

The obtained dope may contain insoluble matters such as impurities contained in the cellulose ester as a raw material, for example. Such an insoluble matter can become a bright spot foreign material in the obtained film. In order to remove insoluble matter, it is preferable to further filter the obtained dope.
The dope filtration is preferably performed so that the number of bright spot foreign substances in the obtained film is a certain value or less. Specifically, the number of bright spot foreign matters having a diameter of 0.01 mm or more is 200 / cm ² or less, preferably 100 / cm ² or less, more preferably 50 / cm ² or less, and still more preferably 30 Filtration is performed so that the number of particles / cm ² or less, particularly preferably 10 / cm ² or less.

The bright spot foreign matter having a diameter of 0.01 mm or less is also preferably 200 pieces / cm ² or less, more preferably 100 pieces / cm ² or less, further preferably 50 pieces / cm ² or less, It is more preferably 30 pieces / cm ² or less, particularly preferably 10 pieces / cm ² or less, and most preferably none.

The number of bright spot foreign matter on the film can be measured by the following procedure.
1) Two polarizing plates are arranged in a crossed Nicol state, and the obtained film is arranged between them.
2) When light is applied from the side of one polarizing plate and observed from the side of the other polarizing plate, the number where the light appears to leak is counted as a foreign object.

A2) Casting step The dope is cast on the endless metal support from the slit of the pressure die.
As the metal support, a stainless steel belt or a drum whose surface is plated with a casting is preferably used. The surface of the metal support is preferably mirror-finished.
The width of the cast can be in the range of 1-4 m. The surface temperature of the metal support in the casting process is set to −50 ° C. or higher and below the temperature at which the solvent boils and does not foam. A higher temperature is preferable because the web can be dried at a higher speed, but it is within a temperature range in which foaming of the web and deterioration of flatness can be prevented.

  The surface temperature of the metal support is preferably in the range of 0 to 100 ° C, more preferably in the range of 5 to 30 ° C. Alternatively, the metal support may be cooled so that the web is gelled and can be peeled off from the drum in a state containing a large amount of residual solvent.

The method for adjusting the temperature of the metal support is not particularly limited, and there are a method of blowing hot air or cold air, and a method of bringing hot water into contact with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short.
When using warm air, considering the temperature drop of the web due to the latent heat of vaporization of the solvent, while using warm air above the boiling point of the solvent, there may be cases where wind at a temperature higher than the target temperature is used while preventing foaming. . In particular, it is preferable to efficiently dry by changing the temperature of the metal support and the temperature of the drying air during the period from casting to peeling.

A3) Solvent evaporation step The web (dope film obtained by casting the dope on the metal support) is heated on the metal support to evaporate the solvent. The drying method and drying conditions of the web can be the same as in the above-described A2) casting step.

A4) Peeling Step The web obtained by evaporating the solvent on the metal support is peeled off at the peeling position on the metal support.
The residual solvent amount of the web at the time of peeling at the peeling position on the metal support is preferably within the range of 10 to 150% by mass in order to improve the flatness of the obtained film. % Or in the range of 60 to 130 mass%, more preferably in the range of 20 to 30 mass% or 70 to 120 mass%.

The amount of residual solvent in the web is defined by the following formula.
Residual solvent amount (%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Note that the heat treatment for measuring the residual solvent amount means a heat treatment at 115 ° C. for 1 hour.

A5) Drying and stretching step The web obtained by peeling from the metal support is dried as necessary and then stretched. The web may be dried while being conveyed by a large number of rollers arranged above and below, or may be dried while being conveyed while fixing both ends of the web with clips.
The method of drying the web may be a method of drying with hot air, infrared rays, a heating roller, microwaves, or the like, and a method of drying with hot air is preferable because it is simple.

An optical film having a desired retardation is obtained by stretching the web. The retardation of the optical film can be controlled by adjusting the magnitude of tension on the web.
In the optical film of the present invention, the web is stretched in an oblique direction (obliquely stretched) in order to make the angle formed by the slow axis in the plane of the optical film and the transport direction of the film within a range of 40 to 50 °. . The oblique direction is a direction having an angle in the range of 40 to 50 ° with respect to the web conveyance direction, and is preferably stretched in a direction at an angle of 45 ° with respect to the web conveyance direction.
As described above, a polarizing film unwound from a roll body and having a transmission axis in the longitudinal direction, and an optical film unwound from the roll body and having a slow axis in a direction at an angle of 45 ° with respect to the longitudinal direction. Can be easily manufactured by simply laminating them in a roll-to-roll manner so that their longitudinal directions overlap each other. Moreover, the cut loss of the film can be reduced, which is advantageous in production.

The draw ratio is represented by the ratio W / W0 of the width of the film before and after stretching (W is before stretching, W0 is the width after stretching), and the film thickness of the obtained optical film and the required retardation However, it is preferably in the range of 1.3 to 3.0 times, more preferably in the range of 1.5 to 2.8 times.
The stretching temperature is preferably in the range of 120 to 230 ° C, more preferably in the range of 150 to 220 ° C, and even more preferably greater than 150 ° C and 210 ° C or less.

  It does not restrict | limit especially as a method of producing the film in which a slow axis inclines within the range of 40-50 degrees with respect to a conveyance direction. For example, there is a method in which the right and left in the width direction are gripped by the gripping means, and the web is stretched using a tenter that can independently control the gripping length of the web (distance from the start of gripping to the end of gripping).

Examples of the stretching apparatus having a mechanism for stretching in an oblique direction include the stretching apparatus described in Example 1 of Japanese Patent Application Laid-Open No. 2003-340916, the stretching apparatus illustrated in FIG. The stretching apparatus described in 2007-30466, the stretching apparatus used in Example 1 of JP 2007-94007 A, and the like are included.
Moreover, the method of using the linear diagonal stretch apparatus (simultaneous biaxial stretching apparatus) and not having to incline the direction which pays out a long film and the direction which winds up the long film after extending | stretching is also mentioned. Specifically, gripping both ends of the film with a plurality of gripping tools, and conveying the film, the difference in travel speed between the gripping tool gripping one end and the gripping tool gripping the other end. And a method of obliquely stretching the film. For example, the method described in JP2008-23775A can be mentioned.

The residual solvent of the web at the start of stretching is preferably 20% by mass or less, more preferably 15% by mass or less.
The stretched film is dried as necessary and then wound. As described above, the film may be dried while being transported by a large number of rollers arranged above and below (roller method), or the both ends of the web may be fixed with clips and dried while being transported. Also good (tenter method).

B) Melt Casting Method The method for producing the optical film of the present invention by the melt casting method is as follows: B1) Step of producing molten pellets (pelletizing step), B2) Step of extruding after melting and kneading the molten pellets (melting) Extruding step), B3) a step of cooling and solidifying the molten resin to obtain a web (cooling solidification step), and B4) a step of stretching the web (stretching step).

B1) Pelletization process It is preferable that the resin composition containing the cellulose ester which is the main component of the optical film is previously kneaded and pelletized. Pelletization can be performed by a known method. For example, a resin composition containing the aforementioned cellulose ester and, if necessary, an additive such as a plasticizer, is melt-kneaded with an extruder, and then from a die. Extrude into a strand. The molten resin extruded in a strand form can be cooled with water or air, and then cut to obtain pellets.
The pellet raw material is preferably dried before being supplied to the extruder in order to prevent decomposition.

  The mixture of the antioxidant and the cellulose ester may be mixed with each other, or the cellulose ester may be mixed with an antioxidant dissolved in a solvent, or the antioxidant may be mixed with the cellulose ester. You may spray and mix. The atmosphere around the feeder portion of the extruder and the outlet portion of the die is preferably an atmosphere of dehumidified air or nitrogen gas in order to prevent deterioration of the raw material of the pellet.

In an extruder, it is preferable to knead at a low shearing force or at a low temperature so as not to cause deterioration of the resin (decrease in molecular weight, coloring, gel formation, etc.). For example, when kneading with a twin screw extruder, it is preferable to use a deep groove type screw and to rotate the two screws in the same direction. In order to knead uniformly, it is preferable that two screw shapes mesh with each other.
Instead of pelletizing the resin composition containing cellulose ester, an optical film may be produced by melt-kneading a cellulose ester not melt-kneaded as a raw material with an extruder.

B2) Melt extrusion step The obtained molten pellets and other additives as required are supplied from the hopper to the extruder. The supply of pellets is preferably performed under vacuum, reduced pressure, or an inert gas atmosphere in order to prevent oxidative decomposition of the pellets. And it melt-kneads the melt pellet which is a film material, and another additive as needed with an extruder.

The melting temperature of the film material in the extruder is preferably in the range of Tg to (Tg + 100) ° C., more preferably when the glass transition temperature of the film is Tg (° C.), although it depends on the type of film material. Is within the range of (Tg + 10) to (Tg + 90) ° C.
Furthermore, when additives such as plasticizers and fine particles are added in the middle of the extruder, a mixing device such as a static mixer is further arranged on the downstream side of the extruder to uniformly mix these components. May be.

The molten resin extruded from the extruder is filtered through a leaf disc filter or the like as necessary, and further mixed with a static mixer or the like, and extruded from a die into a film.
The extrusion flow rate is preferably stabilized using a gear pump. Moreover, it is preferable that the leaf disk filter used for removal of a foreign material is a stainless fiber sintered filter. The stainless steel fiber sintered filter is an integrated, intricately intertwined stainless steel fiber body that is compressed and sintered by integrating the contact points. The density is changed according to the thickness of the fiber and the amount of compression, and the filtration accuracy is adjusted. it can.
The melting temperature of the resin at the exit portion of the die can be in the range of about 200-300 ° C.

B3) Cooling and solidifying step The resin extruded from the die is nipped between the cooling roller and the elastic touch roller to make the film-like molten resin a predetermined thickness. Then, the film-like molten resin is cooled and solidified stepwise by a plurality of cooling rollers.

The surface temperature of the cooling roller can be Tg (° C.) or less when the glass transition temperature of the film is Tg (° C.). The surface temperatures of the plurality of cooling rollers may be different.
The elastic touch roller is also called a pinching rotary body. A commercially available elastic touch roller can also be used. The film surface temperature on the elastic touch roller side can be in the range of Tg to (Tg + 110) ° C. of the film.

  The film-like molten resin solidified from the cooling roller is peeled off by a peeling roller or the like to obtain a web. When peeling the film-like molten resin, it is preferable to adjust the tension in order to prevent deformation of the obtained web.

B4) Stretching step As in the solution casting method, the obtained web is stretched in an oblique direction with a stretching machine to obtain a film. The web stretching method, stretching ratio, and stretching temperature may be the same as in the solution casting method.

<Circularly polarizing plate>
The circularly polarizing plate of the present invention includes a polarizer (linearly polarizing film) and the optical film of the present invention disposed on at least one surface thereof. The optical film of the present invention may be directly bonded to the polarizer, or may be disposed via another layer or film.

  The polarizer may be an iodine polarizing film, a dye polarizing film using a dichroic dye, or a polyene polarizing film. The iodine polarizing film and the dye polarizing film may generally be a film obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing with iodine or a dichroic dye. After the film is dyed with iodine or a dichroic dye, it may be a uniaxially stretched film (preferably a film further subjected to a durability treatment with a boron compound). The transmission axis of the polarizer is parallel to the stretching direction of the film.

The polyvinyl alcohol film may be a film formed from a polyvinyl alcohol aqueous solution. The polyvinyl alcohol film is preferably an ethylene-modified polyvinyl alcohol film because it is excellent in polarizing performance and durability performance, and has few color spots.
Examples of dichroic dyes include azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes and anthraquinone dyes.

The thickness of the polarizer is preferably in the range of 5 to 30 μm, and more preferably in the range of 10 to 20 μm.
The angle formed between the transmission axis of the polarizer and the in-plane slow axis of the optical film of the present invention is in the range of 40 to 50 °, and preferably 45 °.
A reflective polarizing plate may be further disposed between the polarizer and the optical film of the present invention. The reflective polarizing plate transmits linearly polarized light in a direction parallel to the transmission axis of the polarizer and reflects linearly polarized light in a direction different from the transmission axis. The organic EL display device having such a circularly polarizing plate can emit more light emitted from the light emitting layer to the outside.

  Examples of the reflective polarizing plate include a birefringent optical polarizer (described in JP-A-8-503313) in which polymer thin films having different refractive indexes in one direction are alternately laminated, and a polarization separation film having a cholesteric structure (special Described in Kaihei 11-44816). Moreover, you may arrange | position a protective film further on the surface of a polarizer.

  When the optical film of the present invention is disposed on one surface of the polarizer, a transparent protective film other than the optical film of the present invention may be disposed on the other surface of the polarizer. The transparent protective film is not particularly limited, and may be a normal cellulose ester film or the like. Examples of the cellulose ester film include commercially available cellulose ester films (for example, Konica Minoltak KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8UY-X8 -C, KC8UXW-RHA-NC, KC4UXW-RHA-NC (manufactured by Konica Minolta Advanced Layer Co., Ltd.) and the like are preferably used.

The thickness of the transparent protective film is not particularly limited, but can be in the range of about 10 to 200 μm, preferably in the range of 10 to 100 μm, and more preferably in the range of 10 to 70 μm.
When the transparent protective film or the λ / 4 retardation film is disposed on the outermost surface of the display, the transparent hard coat layer, the antiglare layer, the outermost surface of the transparent protective film or the λ / 4 retardation film, An antireflection layer or the like may be further provided.

The circularly polarizing plate can be manufactured through a step of laminating the polarizer and the optical film of the present invention. As the adhesive used for bonding, for example, a completely saponified polyvinyl alcohol aqueous solution or the like is preferably used.
The circularly polarizing plate can be preferably used for an image display device such as an organic EL display device or a liquid crystal display device described later.

<Image display device>
The image display device of the present invention includes the optical film of the present invention. Examples of the image display device of the present invention include an organic EL display device and a liquid crystal display device.

FIG. 1 is a schematic diagram illustrating an example of a configuration of an organic EL display device.
As shown in FIG. 1, the organic EL display device 10 includes a light reflecting electrode 12, a light emitting layer 14, a transparent electrode layer 16, a transparent substrate 18, and a circularly polarizing plate 20 in this order. The circularly polarizing plate 20 includes a λ / 4 retardation film 20A and a polarizer 20B. The λ / 4 retardation film 20A can be the optical film of the present invention, and the polarizer 20B is a linear polarizing film.

The light reflecting electrode 12 is preferably made of a metal material having a high light reflectance. Examples of the metal material include Mg, MgAg, MgIn, Al, LiAl, and the like. The flatter surface of the light reflecting electrode 12 is preferable because irregular reflection of light can be prevented.
The light reflecting electrode 12 can be formed by a sputtering method. The light reflecting electrode 12 may be patterned. Patterning can be performed by etching.

The light emitting layer 14 includes R (red), G (green), and B (blue) light emitting layers. Each light emitting layer contains a light emitting material. The light emitting material may be an inorganic compound or an organic compound, and is preferably an organic compound.
Each of the R, G, and B light-emitting layers further includes a charge transport material, and may further have a function as a charge transport layer. Each of the R, G, and B light emitting layers further includes a hole transport material, and may further have a function as a hole transport layer. When each of the R, G, and B light emitting layers does not include a charge transport material or a hole transport material, the organic EL display device 10 may further include a charge transport layer or a hole transport layer.

  The light emitting layer 14 can be formed by evaporating a light emitting material. Each of the R, G, and B light emitting layers is obtained by patterning. Patterning can be performed using a photomask or the like.

The transparent electrode layer 16 can generally be an ITO (indium tin oxide) electrode. The transparent electrode layer 16 can be formed by a sputtering method or the like. The transparent electrode layer 16 may be patterned. Patterning can be performed by etching.
The transparent substrate 18 only needs to be capable of transmitting light, and may be a glass substrate, a plastic film, or the like.

  The circularly polarizing plate 20 is disposed such that the λ / 4 retardation film 20A is located on the transparent substrate 18 side and the polarizer 20B is located on the viewing side.

  When the organic EL display device 10 is energized between the light reflecting electrode 12 and the transparent electrode layer 16, the light emitting layer 14 emits light and can display an image. In addition, since each of the R, G, and B light-emitting layers is configured to be energized, a full-color image can be displayed.

  The optical film of the present invention or the circularly polarizing plate including the optical film is not limited to the organic EL display device having the above-described configuration, but also includes international patent application WO96 / 34514, JP-A-9-127858, and 11-45058. The present invention can also be applied to the organic EL display device described in the publication. In that case, the optical film or the circularly polarizing plate of the present invention may be disposed instead of or together with the antireflection means of the organic EL display device provided in advance. The optical film or circularly polarizing plate of the present invention can also be applied to an inorganic EL display device described in, for example, “Electroluminescence Display” (Toshio Higuchi, Sangyo Tosho Co., Ltd., published in 1991).

FIG. 2 is a schematic diagram for explaining the antireflection function of the circularly polarizing plate 20.
When light including linearly polarized light a1 and b1 is incident from the outside in parallel to the normal line of the display screen of the organic EL display device 10, only linearly polarized light b1 parallel to the transmission axis direction of the polarizer 20B passes through the polarizer 20B. . The other linearly polarized light a1 that is not parallel to the transmission axis of the polarizer 20B is absorbed by the polarizer 20B. The linearly polarized light b2 that has passed through the polarizer 20B is converted to circularly polarized light c2 by passing through the λ / 4 retardation film 20A. When the circularly polarized light c2 is reflected by the light reflecting electrode 12 (see FIG. 1) of the organic EL display device 10, the circularly polarized light c2 becomes reverse circularly polarized light c3. The reversely polarized circularly polarized light c3 passes through the λ / 4 retardation film 20A and is converted into linearly polarized light b3 orthogonal to the transmission axis of the polarizer 20B. This linearly polarized light b3 is absorbed by the polarizer 20B and cannot pass through.

  Thus, since all the light (including linearly polarized light a1 and b1) incident on the organic EL display device 10 from the outside is absorbed by the polarizer 20B, it is reflected by the light reflecting electrode 12 of the organic EL display device 10. However, it does not exit to the outside. Therefore, it is possible to prevent a decrease in image display characteristics due to the reflection of the background.

  The λ / 4 retardation film 20A using the optical film of the present invention exhibits excellent reverse wavelength dispersion, and therefore can impart a λ / 4 retardation to light in a wide wavelength region. Therefore, most of the light incident from the outside can be prevented from leaking outside the organic EL display device 10. Therefore, the light leakage in the front direction when the organic EL display device 10 is displayed in black can be suppressed, and reflection can be prevented.

  Furthermore, since the λ / 4 retardation film 20A using the optical film of the present invention has high retardation development and excellent reverse wavelength dispersion, the thickness of the film can be reduced. Therefore, the difference between the color in the front direction and the color in the oblique direction can be reduced. As a result, visibility from an oblique direction can be improved.

  The light from the inside of the organic EL display device 10, that is, the light from the light emitting layer 14, includes two circularly polarized components of circularly polarized light c3 and c4. One circularly polarized light c3 is converted to linearly polarized light b3 by passing through the λ / 4 retardation film 20A as described above, and is absorbed without passing through the polarizer 20B. The other circularly polarized light c4 passes through the λ / 4 retardation film 20A and is converted into linearly polarized light b4 parallel to the transmission axis of the polarizer 20B. The linearly polarized light b4 passes through the polarizer 20B and becomes linearly polarized light b4, which is recognized as an image.

  A reflective polarizing plate (not shown) may be further disposed between the polarizer 20B and the λ / 4 retardation film 20A to reflect the linearly polarized light b3 orthogonal to the transmission axis of the polarizer 20B. The reflective polarizing plate can reflect the linearly polarized light b3 without being absorbed by the polarizer 20B, reflect it again by the light reflecting electrode 12, and convert it into linearly polarized light b4 parallel to the transmission axis of the polarizer 20B. . By further disposing a reflective polarizing plate, all of the light emitted by the light emitting layer 14 (circularly polarized light c3 and c4) can be emitted to the outside.

FIG. 3 is a schematic diagram illustrating an example of the configuration of the liquid crystal display device.
As shown in FIG. 3, the liquid crystal display device 30 includes a liquid crystal cell 40, two polarizing plates 50 and 60 that sandwich the liquid crystal cell 40, and a backlight 70.

  The display method of the liquid crystal cell 40 is not particularly limited, and is a TN (Twisted Nematic) method, STN (Super Twisted Nematic) method, IPS (In-Plane Switching) method, OCB (Optically Compensated Birefringence) method, VA (Vertical Alignment). There are methods (including MVA: Multi-domain Vertical Alignment, PVA: Patterned Vertical Alignment), and HAN (Hybrid Aligned Nematic). In order to increase the contrast, the VA (MVA, PVA) method is preferable.

A VA liquid crystal cell includes a pair of transparent substrates and a liquid crystal layer sandwiched between them.
Of the pair of transparent substrates, one transparent substrate is provided with a pixel electrode for applying a voltage to the liquid crystal molecules. The counter electrode may be disposed on one transparent substrate (transparent substrate on which the pixel electrode is disposed) or may be disposed on the other transparent substrate.

  The liquid crystal layer includes liquid crystal molecules having negative or positive dielectric anisotropy. When the liquid crystal molecules are not applied with voltage due to the alignment regulating force of the alignment film provided on the liquid crystal layer side surface of the transparent substrate and no electric field is generated between the pixel electrode and the counter electrode, the liquid crystal molecules The major axis is oriented so as to be substantially perpendicular to the surface of the transparent substrate.

  In the liquid crystal cell configured as described above, an electric field is generated between the pixel electrode and the counter electrode by applying a voltage corresponding to the image signal to the pixel electrode. Thereby, the liquid crystal molecules initially aligned perpendicularly to the surface of the transparent substrate are aligned so that the major axis thereof is in the horizontal direction relative to the substrate surface. In this way, the liquid crystal layer is driven, and the image display is performed by changing the transmittance and reflectance of each sub-pixel.

The polarizing plate 50 is disposed on the viewing side, and includes a polarizer 52 and protective films 54 and 56 that sandwich the polarizer 52.
The polarizing plate 60 is disposed on the backlight 70 side, and includes a polarizer 62 and protective films 64 and 66 that sandwich the polarizer 62. One of the protective films 56 and 64 may be omitted as necessary.
Any of the protective films 54, 56, 64 and 66 can be used as the optical film of the present invention.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" may be used in an Example, unless there is particular notice, it represents "mass part" or "mass%".

[Example 1]
<Preparation of optical film 1>
The following components were stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin to prepare a fine particle dispersion.
(Fine particle dispersion)
Fine particles (Aerosil R972V manufactured by Nippon Aerosil Co., Ltd.): 11 parts by mass Ethanol: 89 parts by mass

Among the components of the following fine particle addition liquid, methylene chloride was put into a dissolution tank, and the prepared fine particle dispersion was slowly added with sufficient stirring with the following addition amount. Subsequently, after being dispersed with an attritor so that the particle size of the secondary particles of the fine particles becomes a predetermined size, the fine particles are filtered through Finemet NF (manufactured by Nippon Seisen Co., Ltd.) to obtain a fine particle additive solution. .
(Particulate additive solution)
Methylene chloride: 99 parts by mass Fine particle dispersion: 5 parts by mass

Among the main dope components below, methylene chloride and ethanol were charged into a pressure dissolution tank. Subsequently, the following cellulose ester e1, sugar ester S, exemplary compound A1 and the prepared fine particle addition liquid were added while stirring, and were heated and stirred to be completely dissolved. The obtained solution was used as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. The main dope was prepared by filtration using 244.
(Main dope composition)
Methylene chloride: 520 parts by mass Ethanol: 45 parts by mass Cellulose ester: Cellulose ester e1 (acetyl group substitution degree 1.95, propionyl group substitution degree 0.71, total acyl group substitution degree 2.66, number average molecular weight (Mn) 78000) 100 parts by weight Sugar ester S: 5 parts by weight Wavelength dispersion adjusting agent: 4 parts by weight of Exemplified Compound A1 Fine particle additive solution: 1 part by weight

The structure of sugar ester S is shown below.

  The obtained dope was uniformly cast on a stainless belt support using an endless belt casting apparatus. On the stainless steel belt support, the solvent in the dope film cast (cast) was evaporated until the residual solvent amount became 75%, and the obtained web was peeled off from the stainless steel belt support. The peeled web was conveyed while being gripped by a clip of a tenter stretching apparatus. Next, the obtained film was dried while being conveyed by a number of rollers in a drying zone. The width direction end of the film held by the tenter clip was slit-removed with a laser cutter, and then wound up to obtain an original film.

  Unwinding the obtained raw film, stretched in an oblique direction inclined by 45 ° with respect to the film conveying direction at a glass transition temperature Tg + 20 ° C stretching temperature of the raw film, and a stretching ratio of 2.5 times, An optical film 1 was obtained. The film thickness of the optical film 1 was 40 μm. The angle formed between the slow axis in the plane of the optical film 1 and the film transport direction was 45 °.

<Preparation of optical films 2 to 23>
Optical films 2 to 21 and 23 were prepared in the same manner except that the types of the cellulose ester and the wavelength dispersion adjusting agent were changed as shown in Table 2 below.
Further, in the production of the optical film 1, the optical film 22 was produced in the same manner except that the wavelength dispersion adjusting agent was not added.
In addition, all the angles which the slow axis in the surface of the obtained optical films 2-23 make and the conveyance direction of a film were 45 degrees. Moreover, all the film thicknesses of the optical films 2-23 were 40 micrometers.

Table 1 below shows the cellulose esters e1 to e9 in Table 2.

A1 to A9 and D1 in Table 2 represent the exemplified compounds A1 to A9 and D1 described above as specific examples of the wavelength dispersion adjusting agent.
Comparative compounds h1 to h4 in Table 2 are shown below.

<Evaluation>
Each optical film 1-23 was evaluated as follows.

(Measurement of melting point and cooling crystallization temperature of wavelength dispersion adjusting agent)
The melting point and temperature-falling crystallization temperature of the wavelength dispersion adjusting agent used in each of the optical films 1 to 23 were measured using a differential scanning calorimeter DSC 6220 as follows.
10 mg of the sample of the wavelength dispersing agent was weighed in an aluminum pan, sealed with an aluminum cover. As a reference, an aluminum pan and cover (total mass of about 35 mg) were used. Using a differential scanning calorimeter DSC 6220 (manufactured by SII Nano Technology Co., Ltd.), the temperature was raised from 30 ° C. to 250 ° C. in a nitrogen atmosphere (50 ml / min) at a heating rate of 10 ° C./min. After the minute holding, the temperature was decreased from 250 ° C. to 30 ° C. at a temperature decreasing rate of 20 ° C./min. The temperature at the minimum point of the endothermic peak observed in the temperature raising process was taken as the melting point of the sample. For samples having a plurality of endothermic peaks, the melting point was determined from the endothermic peak on the highest temperature side. Further, the temperature at the maximum point of the exothermic peak observed in the temperature lowering process was defined as the temperature lowering crystallization temperature of the sample. For a sample having a plurality of exothermic peaks, the cooling crystallization temperature was determined from the exothermic peak on the highest temperature side. Even if there is no change in the baseline, the change in the baseline is a shift, or there is an exothermic peak, if it is an exothermic peak of about -2 to 0 mJ / mg, no exothermic peak at the time of crystallization is observed. Judged that.

(Optical characteristics of optical film)
Ro (550) representing the retardation development property of each optical film 1 to 23, Ro (450) / Ro (550) and Ro (550) / Ro (650) representing the wavelength dispersion were measured as follows. did.

1) The optical film was conditioned at 23 ° C. and 55% RH. About the optical film after humidity control, the average refractive index in each of wavelength 450nm, 550nm, and 650nm was measured using the Abbe refractometer and the spectral light source, respectively. Moreover, the film thickness d (nm) of the optical film was measured using a film thickness meter.
2) In-plane retardation values Ro (450) and Ro (550) when light having wavelengths of 450 nm, 550 nm, and 650 nm is incident on the optical film after humidity adjustment in parallel with the normal line of the film surface. And Ro (650) were measured with AxoScan. The measurement was performed under conditions of 23 ° C. and 55% RH.
3) Ro (450) / Ro (550) was calculated from Ro (450) and Ro (550) measured in 2). Further, Ro (550) / Ro (650) was calculated from Ro (550) and Ro (650).

(Uneven phase difference)
The phase difference value Ro (550) was measured as described above at 10 points at intervals of 50 mm in the width direction of each of the optical films 1 to 23. The difference between the maximum value and the minimum value of all measured values was regarded as phase difference unevenness and evaluated according to the following criteria.
A: Phase difference unevenness is less than 1 nm B: Phase difference unevenness is not less than 1 nm and less than 2 nm C: Phase difference unevenness is not less than 2 nm and less than 4 nm D: Phase difference unevenness is not less than 4 nm and less than 6 nm E: Phase difference unevenness is not less than 6 nm where C If it is above the level, there is no practical problem, it is preferably the B level, and more preferably the A level.

(Brittle resistance)
The brittleness resistance of each optical film 1 to 23 was evaluated as follows.
A 60 ° upper blade and a 90 ° lower blade worn on a hydraulic table press were attached so as to have an interval of 30 μm. The optical films 1 to 23 were placed between the two blades, and 100 samples having a width of 90 cm and a length of 100 cm were continuously cut at a descending speed of the upper blade of 6 m / min. The cut surface of the sample was observed at an enlargement ratio of 50 times using an optical microscope, and the number of films in which some defects due to film breakage such as the occurrence of burrs and chips were observed was counted, and the defect rate was calculated. From the obtained defect rate, the brittleness resistance was evaluated according to the following criteria.
A: The defect rate is less than 2% and exhibits very excellent brittleness resistance B: The defect rate is 2 or more and less than 5% and exhibits excellent brittleness resistance C: The defect rate is 5 or more and less than 10% The brittleness resistance is inferior. D: The defect rate is 10% or more, and the brittleness resistance is very inferior.

Table 2 below shows the evaluation results.

  As is clear from Table 2, it can be seen that the optical film of the present invention has high retardation and excellent reverse wavelength dispersion. Further, it is clear that the optical film of the present invention has little retardation unevenness and excellent brittleness resistance. On the other hand, the optical film according to the comparative example, in particular, the optical film 22 that does not contain the wavelength dispersion adjusting agent has very low retardation, and sufficient reverse wavelength dispersion is not obtained. Even if such an optical film is used in an organic EL display device, reflection of external light cannot be sufficiently suppressed.

[Example 2]
<Preparation of Circular Polarizing Plate 1>
(Production of polarizer)
A 120 μm-thick polyvinyl alcohol film was uniaxially stretched under conditions of a stretching temperature of 110 ° C. and a stretching ratio of 5 times. The obtained film was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds. Subsequently, it was immersed in an aqueous solution at 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water, washed with water and dried to obtain a polarizer having a thickness of 20 μm.

  One surface of the optical film 1 produced in Example 1 was subjected to alkali saponification treatment. Konica Minolta Tack Film KC6UA (manufactured by Konica Minolta Advanced Layer Co., Ltd.) was prepared, and one surface was similarly subjected to alkali saponification treatment. In any case, the saponified surface is a bonding surface with the polarizer. Then, the saponified surface of the optical film 1 was bonded to one surface of the polarizer via a 5% aqueous solution of polyvinyl alcohol as an adhesive. In addition, the saponified surface of the Konica Minolta-tack film KC6UA was bonded to the other surface of the polarizer through a 5% aqueous solution of polyvinyl alcohol to produce a circularly polarizing plate 1. The optical film 1 and the polarizer were bonded so that the angle formed by the transmission axis of the polarizer and the slow axis of the optical film 1 was 45 °.

<Production of circularly polarizing plates 2 to 23>
In the production of the circularly polarizing plate 1, the circularly polarizing plates 2 to 23 were produced in the same manner as the circularly polarizing plate 1 except that the optical film 1 was changed to the respective optical films 2 to 23.

<Production of Organic EL Display Device 1>
A light reflecting electrode made of chromium having a thickness of 80 nm was formed on a glass substrate by sputtering. An ITO thin film having a thickness of 40 nm was formed as an anode on the light reflecting electrode. Next, a hole transport layer made of poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT: PSS) having a thickness of 80 nm was formed on the anode by sputtering. Further, each of the RGB light emitting layers was formed by patterning on the hole transport layer using a shadow mask. The thickness of the light emitting layer was 100 nm for each color. The red light-emitting layer contains tris (8-hydroxyquinolinate) aluminum (Alq ₃ ) as a host and a light-emitting compound [4- (dicyanomethylene) -2-methyl-6 (p-dimethylaminostyryl) -4H-pyran] (DCM). Were co-evaporated (mass ratio 99: 1), and the green light-emitting layer was formed by co-evaporating Alq ₃ and the luminescent compound coumarin 6 (mass ratio 99: 1) as a host. The blue light emitting layer was formed by co-evaporating the following compound Balq and the light emitting compound Perylene as a host (mass ratio 90:10).

  On the obtained RGB light-emitting layer, a thin film having a thickness of 4 nm made of calcium having a low work function was formed as a first cathode capable of efficiently injecting electrons by vacuum deposition. On the first cathode, a thin film made of aluminum having a thickness of 2 nm was formed as a second cathode to obtain an organic light emitting layer. The aluminum used as the second cathode has a role of preventing the first cathode calcium from being chemically altered when a transparent electrode is formed thereon by sputtering.

Next, a transparent conductive film made of ITO and having a thickness of 80 nm (the first cathode, the second cathode, and the transparent conductive film are combined to form a transparent electrode layer) is formed on the second cathode by sputtering. . Further, a thin film having a thickness of 200 nm made of silicon nitride was formed on the transparent conductive film by a CVD method to obtain an insulating film (transparent substrate).
On the obtained insulating film (transparent substrate), the produced circularly polarizing plate 1 was bonded via an adhesive to produce an organic EL display device 1. The circularly polarizing plate 1 was bonded so that the optical film 1 was positioned on the insulating film side.

<Production of organic EL display devices 2 to 23>
In the production of the organic EL display device 1, organic EL display devices 2 to 23 were produced in the same manner as the organic EL display device 1 except that the circularly polarizing plate 1 was changed to each of the circularly polarizing plates 2 to 23.

<Evaluation>
Color unevenness when each organic EL display device 1 to 23 was displayed in black was evaluated by the following method.

(Evaluation criteria for uneven color)
A: No difference in color depending on the position B: A slight difference in color depending on the position is observed.
C: There is a difference in color depending on the position, but there is no problem in use. D: There is a difference in color depending on the position and it cannot be used as a product. E: The difference in color is large depending on the position. It cannot be used as a product

Table 3 below shows the evaluation results.

  As is apparent from Table 3, the organic EL display device of the present invention shows almost no color unevenness even when displaying black. It can be seen that the organic EL display device of the present invention is superior in image reproducibility as compared with the organic EL display device according to the comparative example. On the other hand, the organic EL display device according to the comparative example has color unevenness that cannot be used as a product. Among them, the organic EL display device 22 has little color unevenness, but as shown in Table 2, the optical film 22 has very low retardation and is inferior in reverse wavelength dispersion. Therefore, the organic EL display device 22 cannot sufficiently suppress external light reflection, and a decrease in contrast was recognized.

DESCRIPTION OF SYMBOLS 10 Organic electroluminescent display device 14 Light emitting layer 20 Circularly-polarizing plate 20A (lambda) / 4 phase difference film 20B Polarizer 30 Liquid crystal display device 40 Liquid crystal cell 50, 60 Polarizing plate 52, 62 Polarizer 54, 56, 64, 66 Protective film

Claims (7)

An optical film containing a cellulose ester and a wavelength dispersion adjusting agent,
The cellulose ester has an acyl group having 3 to 6 carbon atoms,
The wavelength dispersion adjusting agent is a compound having a melting point in the range of 50 to 180 ° C. measured by a differential scanning calorimeter, and a temperature drop crystallization temperature is 130 ° C. or lower, or an exothermic peak during crystallization is not observed. And
An optical film characterized in that an angle formed by an in-plane slow axis of the optical film and a transport direction of the optical film is within a range of 40 to 50 °. The optical film according to claim 1, wherein the wavelength dispersion adjusting agent is a compound represented by the following general formula (A).

[In the general formula (A), Q represents an aromatic hydrocarbon ring, a non-aromatic hydrocarbon ring, an aromatic heterocyclic ring or a non-aromatic heterocyclic ring. Wa and Wb are each independently a hydrogen atom or a substituent bonded to an atom constituting the ring of Q. Wa and Wb may be the same as or different from each other, and Wa and Wb are bonded to each other to form a ring. May be formed. R ₃ represents a substituent. m represents an integer of 0 to 2, and when m is 2, two R _{3 s} may be the same as or different from each other. n represents an integer of 1 to 10, and when n is 2 or more, each of 2 or more of Q, L ₂ , Wa, Wb, R ₃ and m may be the same as or different from each other. . L ₁ and L ₂ are each independently an alkylene group, an alkenylene group, an alkynylene group, O, (C═O), (C═O) —O, NR _L , S, (O═S═O) and ( C═O) —NR 2 represents a divalent linking group selected from the group consisting of _L , a combination thereof, or a single bond. R _L represents a hydrogen atom or a substituent. R ₁ and R ₂ each independently represents a substituent. ]   3. The optical film according to claim 1, wherein the wavelength dispersion adjusting agent is a compound having a cooling crystallization temperature of 80 ° C. or lower or an exothermic peak at the time of crystallization is not observed. In the cellulose ester, when the substitution degree of the acetyl group is DSA and the substitution degree of the acyl group having 3 to 6 carbon atoms is DSB, the DSA and DSB are represented by the following formulas (b1) and ( The optical film according to any one of claims 1 to 3, wherein b2) is satisfied.
(B1) 2.2 ≦ DSA + DSB ≦ 2.8
(B2) 0.5 ≦ DSB ≦ 2.0 The optical film has Ro (450), Ro (550) when the in-plane retardation values Ro at wavelengths of 450 nm, 550 nm, and 650 nm are Ro (450), Ro (550), and Ro (650), respectively. ) And Ro (650) satisfy the following formulas (a1) to (a3): The optical film according to any one of claims 1 to 4.
(A1) 110 ≦ Ro (550) ≦ 170
(A2) 0.72 ≦ Ro (450) / Ro (550) ≦ 0.96
(A3) 0.83 ≦ Ro (550) / Ro (650) ≦ 0.97   A circularly polarizing plate comprising the optical film according to any one of claims 1 to 5.   An image display device comprising the optical film according to claim 1.

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