WO2025164148A1 - Cellulose acylate film, method for manufacturing cellulose acylate film, polarization plate, and liquid crystal display device - Google Patents

Abstract

The cellulose acylate film according to the present invention contains a hydrogen-binding compound that satisfies the requirements in (A), and satisfies the optical values in (B).　(A): The hydrogen-binding compound has a fluorene skeleton and has an atomic group including an amide bond at the position 9 of the fluorene skeleton, or the hydrogen-binding compound has a carbazole skeleton and has an atomic group containing an amide bond at the position 9 of the carbazole skeleton.　(B): The retardation value Ro is within the range of 40-70 nm, the retardation value Rt is within the range of 100-220 nm, and the value Rt/Ro of the ratio of the retardation values is within the range of 2.0-5.5.

Description

Cellulose acylate film, method for producing cellulose acylate film, polarizing plate and liquid crystal display device

The present invention relates to a cellulose acylate film, a method for producing a cellulose acylate film, a polarizing plate, and a liquid crystal display device. In particular, the present invention relates to a cellulose acylate film that can obtain a high retardation ratio (Rt/Ro) required for VA mode optical compensation even when stretched at a high magnification in the TD direction.

As disclosed in Patent Document 1, a cellulose acylate film containing a hydrogen-bonding compound is known to have small changes in retardation depending on environmental humidity, and is also known to be able to suppress deterioration of a polarizer when the cellulose acylate film is attached to a polarizing plate and left to stand under high temperature and high humidity conditions.
In recent years, displays have become larger, and there is a demand for more efficient production of polarizing plates for large displays, with polarizing plates having a width of 2500 mm or more being required.
To produce a film with a width of 2500 mm or more, there are two methods: widening the width of the raw sheet and widening the stretch ratio in the transverse direction (TD). Of these methods, widening the stretch ratio in the TD can reduce the cost of the production equipment. However, Patent Document 1 discloses a stretch ratio in the TD direction of only up to 1.4 times.

On the other hand, Patent Documents 2 and 3 disclose cellulose acylate films stretched at a high magnification in the TD direction.
However, a cellulose acylate film produced at a stretching ratio of 1.5 times or more in the TD direction has a retardation ratio (Rt/Ro) of 0.9 to 1.35. Therefore, although it has been used for optical compensation of IPS mode liquid crystal displays, it has not been used for optical compensation of VA mode liquid crystal displays, which require a higher Rt/Ro. In other words, there has been a problem that a cellulose acylate film stretched at a high stretching ratio of 1.5 times or more in the TD direction cannot obtain a high Rt/Ro required for optical compensation of VA mode.

JP 2012-82235 A Japanese Patent Application Laid-Open No. 2013-235232 JP 2014-101477 A

The present invention has been made in consideration of the above problems and circumstances. The problem to be solved by the present invention is to provide a cellulose acylate film and a method for producing the same that can achieve a high retardation ratio (Rt/Ro) required for VA mode optical compensation even when stretched at a high magnification in the TD direction. Another problem to be solved by the present invention is to provide a polarizing plate and a liquid crystal display device that use the cellulose acylate film.

The present inventors have investigated the causes of the above problems in order to solve the above problems, and have found that a high retardation ratio required for optical compensation in VA mode can be obtained even when stretched at a high magnification by containing a hydrogen-bonding compound having a fluorene skeleton or a carbazole skeleton and an atomic group having an amide bond at the 9-position of the skeleton, and by satisfying specific optical values.
That is, the above-mentioned problems of the present invention are solved by the following means.

1. Contains a hydrogen-bonding compound that satisfies the following requirement (A):
A cellulose acylate film that satisfies the following optical values (B).
(A): A compound having a fluorene skeleton and an atomic group containing an amide bond at the 9th position of the fluorene skeleton, or a compound having a carbazole skeleton and an atomic group containing an amide bond at the 9th position of the carbazole skeleton.
(B): The retardation value Ro defined by the following formula is in the range of 40 to 70 nm, the retardation value Rt is in the range of 100 to 220 nm, and the retardation value ratio Rt/Ro is in the range of 2.0 to 5.5.
Formula (i) Ro = ( _nx - _ny ) x d
Formula (ii) Rt={(n _x + _ny )/2-n _z }×d
(In the above formulas (i) and (ii), _nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the film. _ny represents the refractive index in the direction y perpendicular to the direction x in the in-plane direction of the film. _nz represents the refractive index in the thickness direction z of the film. The refractive indices are measured at a wavelength of 550 nm in an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.)

2. The cellulose acylate film described in item 1, wherein the hydrogen-bonding compound has both a hydrogen bond donor moiety and a hydrogen bond acceptor moiety within one molecule.

3. The cellulose acylate film described in item 2, wherein the value obtained by dividing the weight-average molecular weight of the hydrogen-bonding compound by the total number of hydrogen-bond donors and hydrogen-bond acceptors is within the range of 30 to 80.

4. The cellulose acylate film described in item 1, wherein the total number of aromatic ring structures possessed by the hydrogen-bonding compound is within the range of 2 to 3.

5. The cellulose acylate film according to item 1, wherein the hydrogen-bonding compound has one or less carboxyl groups.

6. The cellulose acylate film described in item 1, wherein the hydrogen-bonding compound does not have a carboxy group.

7. The cellulose acylate film described in item 1, wherein the weight-average molecular weight of the hydrogen-bonding compound is 300 or more.

8. The cellulose acylate film described in paragraph 1, wherein the hydrogen-bonding compound has a 9-fluorenylmethyloxycarbonyl group.

9. The cellulose acylate film described in item 1, wherein the content of the hydrogen-bonding compound is within the range of 0.5 to 30% by mass relative to the cellulose acylate resin.

10. The cellulose acylate film described in paragraph 1, wherein the film width is 2,500 mm or more.

11. A method for producing the cellulose acylate film according to any one of items 1 to 10, comprising the steps of:
A method for producing a cellulose acylate film, wherein the film is stretched in the TD direction at a stretching ratio of 1.6 times or more.

12. A polarizing plate comprising the cellulose acylate film described in any one of items 1 to 10.

13. A liquid crystal display device equipped with the polarizing plate described in paragraph 12.

According to the above-mentioned means of the present invention, a cellulose acylate film and a method for producing the same can be provided which can obtain a high retardation ratio (Rt/Ro) required for optical compensation in VA mode even when stretched at a high magnification in the TD direction.
The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows.
The reason why the retardation ratio (Rt/Ro) of a film stretched at a high ratio in the TD direction becomes low is that the cellulose acylate resin and additives are oriented in the TD direction, which is the stretching direction, due to the high stretching ratio in the TD direction, resulting in an increase in Ro and a decrease in Rt/Ro.
Therefore, in the present invention, by stretching at a high magnification in the TD direction, atomic groups containing amide bonds of the cellulose acylate resin and the hydrogen-bonding compound are oriented in the TD direction, which is the stretching direction, and the fluorene skeleton (or carbazole skeleton) of the hydrogen-bonding compound is oriented in the MD direction, which is the direction perpendicular to the stretching direction. As a result, the fluorene skeleton (or carbazole skeleton) reduces the retardation value Ro. As a result, it is presumed that a cellulose acylate film with a high retardation value ratio (Rt/Ro) can be obtained.

Cross-sectional view of the basic layer structure of a polarizing plate Schematic diagram showing an example of the configuration of a display device

The cellulose acylate film of the present invention contains a hydrogen-bonding compound that satisfies the following requirement (A) and satisfies the following optical value (B).
(A): A compound having a fluorene skeleton and an atomic group containing an amide bond at the 9th position of the fluorene skeleton, or a compound having a carbazole skeleton and an atomic group containing an amide bond at the 9th position of the carbazole skeleton.
(B): The retardation value Ro defined by the following formula is in the range of 40 to 70 nm, the retardation value Rt is in the range of 100 to 220 nm, and the retardation value ratio Rt/Ro is in the range of 2.0 to 5.5.
Formula (i) Ro = ( _nx - _ny ) x d
Formula (ii) Rt={(n _x + _ny )/2-n _z }×d
(In the above formulas (i) and (ii), _nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the film. _ny represents the refractive index in the direction y perpendicular to the direction x in the in-plane direction of the film. _nz represents the refractive index in the thickness direction z of the film. The refractive indices are measured at a wavelength of 550 nm in an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.)
This feature is a technical feature common to or corresponding to each of the following embodiments.

In one embodiment of the present invention, the hydrogen-bonding compound preferably has both a hydrogen-bond donor moiety and a hydrogen-bond acceptor moiety within one molecule. This allows the compound to form strong hydrogen bonds with water, preventing water from coordinating with carbonyl groups in the cellulose acylate.

Furthermore, it is preferable that the value obtained by dividing the weight-average molecular weight of the hydrogen-bonding compound by the total number of hydrogen-bonding donors and hydrogen-bonding acceptors is within the range of 30 to 80. If the value obtained by dividing by the total number is too large, the hydrogen-bonding compound will have difficulty approaching the cellulose acylate. As a result, the effect of improving retardation changes due to environmental changes will be reduced. On the other hand, if the total number is too small, the interaction between the hydrogen-bonding compounds will be too strong, resulting in insufficient solubility in solvents and compatibility with cellulose acylate, which is undesirable.

It is preferable that the total number of aromatic ring structures possessed by the hydrogen-bonding compound is within the range of 2 to 3. By keeping the total number of aromatic ring structures within the range of 2 to 3, the molecular size of the hydrogen-bonding compound does not become too large. This makes it easier for the aromatic ring structures to approach the carbonyl groups in the cellulose acylate, thereby suppressing changes in optical properties due to environmental humidity.

The hydrogen-bonding compound preferably has one or less carboxyl groups in terms of the stability of the polarizer.
In addition, it is preferable that the hydrogen-bonding compound does not have a carboxy group in terms of the stability of the polarizer.

The weight average molecular weight of the hydrogen-bonding compound is preferably 300 or more, since this can prevent the hydrogen-bonding compound from scattering from the film when the film is heated.
Furthermore, it is preferable that the hydrogen-bonding compound has a 9-fluorenylmethyloxycarbonyl group in terms of the stability of the hydrogen-bonding compound.
The content of the hydrogen-bonding compound is preferably within a range of 0.5 to 30% by mass based on the cellulose acylate resin, from the viewpoint of the stability of the cellulose acylate film.

A cellulose acylate film with a width of 2,500 mm or more is preferable since it can be used as a polarizing plate for large displays.

The method for producing a cellulose acylate film of the present invention is characterized in that the film is stretched in the TD direction at a stretching ratio of 1.6 or more. By stretching the film in the TD direction at a stretching ratio of 1.6 or more, a film having a width of 2500 mm or more can be produced while suppressing the cost of production equipment.
The cellulose acylate film of the present invention is suitable for use in a polarizing plate, which is suitable for use in a liquid crystal display device.

The following describes the present invention, its components, and the modes and aspects for implementing the present invention. Note that in this application, the symbol "to" is used to mean that the numerical values before and after it are included as upper and lower limits.

[Summary of the Cellulose Acylate Film of the Present Invention]
The cellulose acylate film of the present invention is characterized by containing a hydrogen-bonding compound that satisfies the following requirement (A) and satisfies the following optical value (B).
(A): A compound having a fluorene skeleton and an atomic group containing an amide bond at the 9th position of the fluorene skeleton, or a compound having a carbazole skeleton and an atomic group containing an amide bond at the 9th position of the carbazole skeleton.
(B): The retardation value Ro defined by the following formula is in the range of 40 to 70 nm, the retardation value Rt is in the range of 100 to 220 nm, and the retardation value ratio Rt/Ro is in the range of 2.0 to 5.5.
Formula (i) Ro=(nx-ny)×d
Formula (ii) Rt={(nx+ny)/2-nz}×d
(In the above formulas (i) and (ii), nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the film; ny represents the refractive index in the direction y perpendicular to the direction x in the in-plane direction of the film; and nz represents the refractive index in the thickness direction z of the film. The refractive indices are measured at a wavelength of 550 nm in an environment of 23° C. and 55% RH. d [nm] represents the thickness of the film.)

<Requirement (A)>
The hydrogen-bonding compound has a fluorene skeleton and an atomic group containing an amide bond at the 9-position of the fluorene skeleton, or has a carbazole skeleton and an atomic group containing an amide bond at the 9-position of the carbazole skeleton.
Examples of the atomic group containing an amide bond at the 9-position of the fluorene skeleton include an amide bond, a urethane bond, a urea bond, etc. Among these, an amide bond, a urethane bond, etc. are preferred.
Examples of the atomic group containing an amide bond at the 9-position of the carbazole skeleton include an amide bond, a urethane bond, a urea bond, etc. Among these, an amide bond, a urethane bond, etc. are preferred.

<Requirements (B)>
The cellulose acylate film has a retardation value Ro of 40 to 70 nm, a retardation value Rt of 100 to 220 nm, and a retardation ratio Rt/Ro of 2.0 to 5.5, where Ro and Rt are values measured under an environment of 23° C. and 55% RH with respect to light having a wavelength of 550 nm.

The retardation values Ro and Rt are defined by the following formulas, respectively.
Formula (i) Ro = ( _nx - _ny ) x d
Formula (ii) Rt={(n _x + _ny )/2-n _z }×d
(In the above formulas (i) and (ii), _nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the film. _ny represents the refractive index in the direction y perpendicular to the direction x in the in-plane direction of the film. _nz represents the refractive index in the thickness direction z of the film. The refractive indices are measured at a wavelength of 550 nm in an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.)

The retardation value Ro is more preferably in the range of 45 to 65 nm, and the retardation value Rt is more preferably in the range of 110 to 210 nm.
The retardation ratio (Rt/Ro) is more preferably in the range of 2.0 to 4.5. When the ratio is in the above range, the viewing angle can be improved.

Means for ensuring that the retardation values Ro and Rt, and the ratio of the retardation values (Rt/Ro) fall within the above-mentioned specific ranges include using the hydrogen-bonding compound of the present invention in the cellulose acylate film, controlling the stretching conditions during film production, and adjusting the thickness of the cellulose acylate film.
The hydrogen-bonding compound used in the present invention is as described below. Regarding the stretching conditions during film production, for example, the film is preferably stretched at 1.6 times or more in the TD direction. The thickness of the cellulose acylate film is preferably within a range of 10 to 200 μm, more preferably within a range of 10 to 60 μm, and even more preferably within a range of 10 to 40 μm.

The retardation values Ro and Rt for light with a wavelength of 550 nm can be measured using an automatic birefringence meter at 23°C and 55% RH. Examples of automatic birefringence meters include the "Axo Scan" (manufactured by Optoscience).

[Configuration of Cellulose Acylate Film]
The cellulose acylate film contains a hydrogen-bonding compound that satisfies the requirement (A).
The cellulose acylate film contains a cellulose acylate resin in addition to the hydrogen-bonding compound.

<Hydrogen-bonding compounds>
The hydrogen-bonding compound preferably has both a hydrogen-bond donor moiety and a hydrogen-bond acceptor moiety in one molecule, which allows the compound to form a strong hydrogen bond with water and inhibits water from coordinating with the carbonyl group in the cellulose acylate.
Examples of functional groups that function as the hydrogen bond donor and hydrogen bond acceptor moieties are those described in Table 2 on page 15 of Introduction to Hydrogen Bonding by Jeffrey, George A., published by Oxford UP.
In the present invention, the total number of functional groups shown in this table in the hydrogen bond compound is used as the "total number of hydrogen bond donors (number of hydrogen bond donor moieties) and number of hydrogen bond acceptors (number of hydrogen acceptor moieties). In addition, in the case of a functional group that functions as both a hydrogen bond donor moiety and a hydrogen bond acceptor moiety, it is counted as only one of the functional groups.
Specifically, functional groups that act as hydrogen bond donor moieties, functional groups that act as hydrogen bond acceptor moieties, and functional groups that act as both hydrogen bond donor moieties and hydrogen bond acceptor moieties include the following.

(strong hydrogen bonds)
Functional groups that form strong hydrogen bonds and act as both hydrogen bond donor moieties and hydrogen bond acceptor moieties are shown below.

(moderate hydrogen bonding)
Functional groups that form moderate hydrogen bonds and act as both hydrogen bond donor moieties and hydrogen bond acceptor moieties, functional groups that act only as hydrogen bond donor moieties, and functional groups that act only as hydrogen bond acceptor moieties are shown below.

In particular, functional groups that act as hydrogen bond donor moieties containing "O-H" or "N" are preferred. Furthermore, functional groups that act as hydrogen bond acceptor moieties containing "C=O," "C-O-C," and "N" are preferred.

In terms of forming hydrogen bonds with water, the hydrogen-bonding compound preferably has 0 to 3 bonds connecting the hydrogen-bonding donor moiety and the hydrogen-bonding acceptor moiety, and more preferably 1 or 2 bonds.

The hydrogen-bonding compound preferably has a molecular weight that is within a range of 30 to 80, more preferably 50 to 80, when the molecular weight is divided by the total number of hydrogen-bond donors and hydrogen-bond acceptors.
If the value obtained by dividing the molecular weight by the total number of hydrogen bond donors and hydrogen bond acceptors is too large, the hydrogen bond compound becomes difficult to approach the cellulose acylate, and the effect of improving the retardation change due to environmental changes becomes small.On the other hand, if the value obtained by dividing the molecular weight by the total number of hydrogen bond donors and hydrogen bond acceptors is too small, the interaction between the hydrogen bond compounds becomes too strong, resulting in insufficient solubility in solvents and compatibility with cellulose acylate, which is not preferable.

Furthermore, when the total number of aromatic ring structures in the hydrogen-bonding compound is within the range of 2 to 3, the molecular size of the hydrogen-bonding compound does not become too large, which is preferable in that it becomes easily accessible to the carbonyl group in the cellulose acylate and has the effect of suppressing changes in optical properties due to environmental humidity.
The aromatic ring structure includes not only an aromatic hydrocarbon ring but also a heteroaromatic ring.
The number of aromatic ring structures is counted as one when aromatic rings are fused together, and as multiple when aromatic rings are connected to each other via a linking group. For example, an aromatic ring having 10 carbon atoms derived from naphthalene is counted as one aromatic ring structure. A fluorene ring and a carbazole ring are both counted as two aromatic ring structures.
If the number of aromatic ring structures is four or more, the molecular size of the hydrogen-bonding compound becomes too large, making it difficult for the compound to approach the carbonyl group in the cellulose acylate, and reducing the effect of suppressing changes in optical properties due to environmental humidity.
The hydrogen-bonding compound preferably contains at least one heteroaromatic ring, because the heteroatom in the heteroaromatic ring and another hydrogen-bonding acceptor moiety or hydrogen-bonding donor moiety in the hydrogen-bonding compound can easily form a cyclic hydrogen bond with water.

In terms of polarizer stability, it is preferable that the hydrogen-bonding compound have one or less carboxyl groups. Also, in terms of polarizer stability, it is preferable that the hydrogen-bonding compound have no carboxyl groups.

The weight average molecular weight of the hydrogen-bonding compound is preferably 300 or more in order to prevent the hydrogen-bonding compound from scattering from the film when the film is heated, and is preferably in the range of 300 to 2,000.
The hydrogen-bonding compound preferably has a 9-fluorenylmethyloxycarbonyl group (Fmoc group) in terms of stability of the hydrogen-bonding compound.

Below are listed preferred exemplary compounds as hydrogen-bonding compounds, but the present invention is not limited to these.

For the exemplary compounds 1 to 9, the weight-average molecular weight (Mw), the number of hydrogen bond donors, and the number of hydrogen bond acceptors per molecule of the hydrogen-bonding compound are shown in Table I below. Table I also shows the value (Mw/(A+D)) obtained by dividing the molecular weight (Mw) of the hydrogen-bonding compound by the total number of hydrogen bond donors and hydrogen bond acceptors.

The hydrogen-bonding compound is preferably contained in the cellulose acylate resin in an amount ranging from 0.5 to 30% by mass, and more preferably from 1.0 to 15% by mass.

<Cellulose acylate resin>
The cellulose acylate film contains a cellulose acylate resin. The cellulose acylate resin used in the present invention refers to a resin in which some or all of the hydrogen atoms of hydroxyl groups (—OH) at the 2-, 3-, and 6-positions in β-1,4-bonded glucose units constituting cellulose are substituted with acyl groups. Hereinafter, the cellulose acylate resin is also referred to as cellulose acylate.

The cellulose acylate to be used is not particularly limited, but is preferably an ester of a linear or branched carboxylic acid having about 2 to 22 carbon atoms.
The carboxylic acid constituting the ester may be an aliphatic carboxylic acid, may form a ring, or may be an aromatic carboxylic acid.

Examples include cellulose acylates in which the hydrogen atoms of the hydroxyl groups of cellulose are substituted with acyl groups having 2 to 22 carbon atoms, such as acetyl, propionyl, butyryl, isobutyryl, valeryl, pivaloyl, hexanoyl, octanoyl, lauroyl, and stearoyl.

The carboxylic acid (acyl group) constituting the ester may have a substituent.
The carboxylic acid constituting the ester is preferably a lower fatty acid having 6 or less carbon atoms, more preferably a lower fatty acid having 3 or less carbon atoms.
The cellulose acylate may contain a single type of acyl group or a combination of multiple acyl groups.

Specific examples of preferred cellulose acylates include cellulose acetates such as diacetyl cellulose (DAC) and triacetyl cellulose (TAC), as well as mixed fatty acid esters of cellulose to which a propionate group or a butyrate group is bonded in addition to an acetyl group, such as cellulose acetate propionate (CAP), cellulose acetate butyrate, and cellulose acetate propionate butyrate.
These cellulose acylates may be used singly or in combination of two or more kinds.

(Type and degree of substitution of acyl groups)
By adjusting the type and substitution degree of the acyl group of the cellulose acylate, it is possible to control the humidity fluctuation of the retardation within a desired range, and to improve the uniformity of the film thickness.

The smaller the substitution degree of the acyl group in the cellulose acylate, the more improved the retardation is, and therefore the thinner the film can be made.
On the other hand, if the degree of substitution of the acyl group is too small, the durability may be deteriorated, which is undesirable.

On the other hand, the greater the substitution degree of the acyl group in cellulose acylate, the less retardation is expressed, so it is necessary to increase the stretching ratio during film formation. However, it is difficult to achieve uniform stretching at a high stretching ratio, which results in greater (worsening) variation in film thickness.
Furthermore, the Rt humidity fluctuation, which is the retardation (phase difference) in the thickness direction, occurs when water molecules coordinate with the carbonyl groups of cellulose, so the higher the degree of acyl group substitution, i.e., the more carbonyl groups there are in the cellulose, the worse the Rt humidity fluctuation tends to be.

The cellulose acylate preferably has a total degree of substitution of acyl groups in the range of 2.1 to 2.5.
By setting the temperature in this range, environmental fluctuations (especially Rt fluctuations due to humidity) can be suppressed, and the uniformity of the film thickness can be improved.
More preferably, it is in the range of 2.2 to 2.45, from the viewpoint of improving the flowability and stretchability during film formation and further improving the uniformity of the film thickness.

More specifically, cellulose acylate satisfies both the following formulas (a) and (b). In the formulas (a) and (b), X represents the degree of substitution with acetyl groups, and Y represents the degree of substitution with propionyl groups or butyryl groups, or a mixture thereof.

Formula (a): 2.1≦X+Y≦2.5
Formula (b): 0≦Y≦1.5

The cellulose acylate is preferably cellulose acetate (Y=0) or cellulose acetate propionate (CAP) (Y: propionyl group, Y>0), and even more preferably cellulose acetate where Y=0 in order to reduce film thickness variation.

A particularly preferred cellulose acetate is cellulose diacetate (DAC) with X=2.1≦X≦2.5 (more preferably 2.15≦X≦2.45), as this allows for desired ranges of retardation expression, Rt humidity fluctuation, and film thickness variation.

Furthermore, when Y>0, the particularly preferred cellulose acetate propionate (CAP) has X values of 0.95≦X≦2.25, 0.1≦Y≦1.2, and 2.15≦X+Y≦2.45.

By using the above-mentioned cellulose acetate or cellulose acetate propionate, a film with excellent retardation, mechanical strength, and resistance to environmental changes can be obtained.

The degree of acyl substitution indicates the average number of acyl groups per glucose unit, and indicates how many hydrogen atoms of hydroxy groups at the 2nd, 3rd and 6th positions of one glucose unit are substituted with acyl groups.
Therefore, the maximum degree of substitution is 3.0, which means that all of the hydrogen atoms of the hydroxy groups at positions 2, 3, and 6 are substituted with acyl groups. These acyl groups may be substituted evenly at positions 2, 3, and 6 of the glucose units, or may be substituted with a distribution.
The degree of substitution is determined by the method specified in ASTM-D817-96.

Cellulose acetates with different degrees of substitution may be mixed to obtain the desired optical properties. In the above case, the mixing ratio of the different cellulose acetates is not particularly limited.

The number average molecular weight (Mn) of the cellulose acylate is preferably in the range of 2×10 ⁴ to 3×10 ⁵ , more preferably in the range of 2×10 ⁴ to 1.2×10 ^5. Furthermore, when the number average molecular weight is in the range of 4×10 ⁴ to 8×10 ⁴ , it is preferable from the viewpoint of increasing the mechanical strength of the obtained film.

The number average molecular weight Mn of cellulose acylate is calculated by measurement using gel permeation chromatography (GPC) under the measurement conditions described above.

The weight average molecular weight (Mw) of the cellulose acylate is preferably in the range of 2×10 ⁴ to 1×10 ⁶ , more preferably in the range of 2×10 ⁴ to 1.2×10 ^5. Furthermore, when the weight average molecular weight is in the range of 4×10 ⁴ to 8×10 ⁴ , it is preferable from the viewpoint of increasing the mechanical strength of the obtained film.

The raw material cellulose for cellulose acylate is not particularly limited, but examples thereof include cotton linter, wood pulp, and kenaf.
The cellulose acylates obtained from these materials can be mixed and used in any desired ratio.

Cellulose acylates such as cellulose acetate and cellulose acetate propionate can be produced by known methods.

Generally, the raw material cellulose is mixed with a specific organic acid (acetic acid, propionic acid, etc.), an acid anhydride (acetic anhydride, propionic anhydride, etc.), and a catalyst (sulfuric acid, etc.), and the cellulose is esterified, and the reaction is allowed to proceed until a cellulose triester is produced.

In triesters, the three hydroxy groups of the glucose units are replaced with acyl groups of organic acids.

Using two types of organic acids at the same time makes it possible to produce mixed ester cellulose acylates, such as cellulose acetate propionate and cellulose acetate butyrate.

Next, the triester of cellulose is hydrolyzed to synthesize cellulose acylate having a desired degree of acyl group substitution.
Thereafter, cellulose acylate is obtained through steps such as filtration, precipitation, washing with water, dehydration, and drying. Specifically, the synthesis can be carried out with reference to the method described in JP-A-10-45804.

<Other additives>
The cellulose acylate film of the present invention may contain the following additives.
(Plasticizer)
The cellulose acylate film preferably contains at least one plasticizer for the purpose of imparting processability to, for example, a polarizing plate protective film.
The plasticizers are preferably used alone or in combination of two or more.

Among the plasticizers, it is preferable to include at least one plasticizer selected from the group consisting of sugar esters, polyesters, and styrene-based compounds. By including such a plasticizer, it is possible to effectively control moisture permeability while achieving a high degree of compatibility with cellulose acylate, etc.

The molecular weight of the plasticizer is preferably 15,000 or less, and more preferably 10,000 or less, from the viewpoint of achieving both improved resistance to moist heat and compatibility with cellulose acylate, etc.

When the compound having a molecular weight of 10,000 or less is a polymer, it preferably has a weight average molecular weight (Mw) of 10,000 or less.
The weight average molecular weight (Mw) is preferably in the range of 100 to 10,000, and more preferably in the range of 400 to 8,000.

In particular, to obtain the effects of the present invention, it is preferable to contain the compound having a molecular weight of 1,500 or less in an amount within the range of 0.5 to 40 parts by mass, and more preferably within the range of 1.0 to 20 parts by mass, per 100 parts by mass of cellulose acylate resin.
By containing the component within the above range, it is possible to effectively control the moisture permeability and to ensure compatibility with the base resin, which is preferable.

<Sugar ester>
The cellulose acylate film of the present invention may contain a sugar ester compound for the purpose of preventing hydrolysis.
Specifically, the sugar ester compound may be a sugar ester having 1 to 12 of at least one kind of pyranose structure or furanose structure, in which all or part of the OH groups of the structure have been esterified.

<polyester>
The cellulose acylate film of the present invention may contain a polyester.
The polyester is not particularly limited, but examples thereof include a polymer (polyester polyol) having a terminal hydroxy group, which can be obtained by a condensation reaction between a dicarboxylic acid or an ester-forming derivative thereof and a glycol, and a polymer (terminal-capped polyester) in which the terminal hydroxy group of the polyester polyol is capped with a monocarboxylic acid.
The ester-forming derivatives referred to here include esters of dicarboxylic acids, dicarboxylic acid chlorides, and dicarboxylic acid anhydrides.

<Styrene-based compounds>
In the cellulose acylate film of the present invention, a styrene-based compound may be used in addition to or instead of the sugar ester and polyester for the purpose of improving the water resistance of the optical film.

The styrene-based compound may be a homopolymer of a styrene-based monomer, or a copolymer of a styrene-based monomer and another copolymerizable monomer.
The content of structural units derived from styrene-based monomers in the styrene-based compound is preferably in the range of 30 to 100 mol %, more preferably in the range of 50 to 100 mol %, so that the molecular structure has a certain level of bulkiness.

Examples of styrene-based monomers include styrene; alkyl-substituted styrenes such as α-methylstyrene, β-methylstyrene, and p-methylstyrene; halogen-substituted styrenes such as 4-chlorostyrene and 4-bromostyrene; hydroxystyrenes such as p-hydroxystyrene, α-methyl-p-hydroxystyrene, 2-methyl-4-hydroxystyrene, and 3,4-dihydroxystyrene; vinylbenzyl alcohols; alkoxy-substituted styrenes such as p-methoxystyrene, p-tert-butoxystyrene, and m-tert-butoxystyrene; 3-vinylbenzoic acid, 4-vinylbenzoic acid, and the like. amidostyrenes such as 2-butylamidostyrene, 4-methylamidostyrene, and p-sulfonamidostyrene; aminostyrenes such as 3-aminostyrene, 4-aminostyrene, 2-isopropenylaniline, and vinylbenzyldimethylamine; nitrostyrenes such as 3-nitrostyrene and 4-nitrostyrene; cyanostyrenes such as 3-cyanostyrene and 4-cyanostyrene; vinylphenylacetonitrile; arylstyrenes such as phenylstyrene, and indenes.
The styrene-based monomer may be one type or a combination of two or more types.

<Optional ingredients>
The cellulose acylate film of the present invention may contain other optional components such as antioxidants, colorants, ultraviolet absorbers, matting agents, acrylic particles, hydrogen-bonding solvents, and ionic surfactants.
These components can be added in an amount of 0.01 to 20 parts by mass per 100 parts by mass of the cellulose acylate resin.

(antioxidant)
In the cellulose acylate film of the present invention, commonly known antioxidants can be used.
In particular, lactone-based, sulfur-based, phenol-based, double bond-based, hindered amine-based, and phosphorus-based compounds can be preferably used.

These antioxidants and the like are added in an amount of 0.05 to 20% by mass, preferably 0.1 to 1% by mass, based on the cellulose acylate resin which is the main raw material of the cellulose acylate film.
A synergistic effect can be obtained by using several different types of compounds in combination with these antioxidants rather than using only one type.
For example, it is preferable to use lactone-based, phosphorus-based, phenol-based and double bond-based compounds in combination.

(Coloring agent)
The cellulose acylate film of the present invention preferably contains a colorant for adjusting the color tone within a range that does not impair the effects of the present invention.

The term "colorant" refers to a dye or pigment, and in this invention refers to a dye or pigment that has the effect of making the color tone of the LCD screen bluer, adjusting the yellow index, or reducing haze.

Various dyes and pigments can be used as colorants, but anthraquinone dyes, azo dyes, phthalocyanine pigments, etc. are effective.

(ultraviolet absorber)
The cellulose acylate film of the invention can be used on the viewing side or backlight side of a polarizing plate, and therefore may contain an ultraviolet absorber for the purpose of imparting an ultraviolet absorbing function.

The ultraviolet absorber is not particularly limited, but examples thereof include benzotriazole-based, 2-hydroxybenzophenone-based, and salicylic acid phenyl ester-based ultraviolet absorbers.
Examples include triazoles such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, and benzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 2,2′-dihydroxy-4-methoxybenzophenone.
The above ultraviolet absorbents may be used alone or in combination of two or more.

The amount of UV absorber used varies depending on the type of UV absorber, conditions of use, etc., but it is generally added in the range of 0.05 to 10% by mass, and preferably 0.1 to 5% by mass, relative to the cellulose acylate resin.

(fine particles)
The cellulose acylate film of the invention preferably contains fine particles that impart slip properties to the film.
In particular, the addition of fine particles is effective from the viewpoint of improving the lubricity of the surface of the cellulose acylate film, improving the lubricity during winding, and preventing the occurrence of scratches and blocking.

The fine particles may be either inorganic or organic as long as they do not impair the transparency of the resulting cellulose acylate film and have heat resistance during melting, but inorganic fine particles are more preferred.
These fine particles can be used alone or in combination of two or more kinds.

By combining particles with different particle sizes and shapes (e.g., needle-shaped and spherical), it is possible to achieve both high levels of transparency and lubricity.

Among the compounds that make up the above-mentioned fine particles, silicon dioxide is particularly preferred, as it has a refractive index close to that of cellulose acylate resin and therefore has excellent transparency (haze).

Specific examples of silicon dioxide that can be preferably used include commercially available products with trade names such as Aerosil (registered trademark) 200V, Aerosil (registered trademark) R972V, Aerosil (registered trademark) R972, R974, R812, 200, 300, R202, OX50, TT600, and NAX50 (all manufactured by Nippon Aerosil Co., Ltd.), Seahoster (registered trademark) KEP-10, Seahoster (registered trademark) KEP-30, and Seahoster (registered trademark) KEP-50 (all manufactured by Nippon Shokubai Co., Ltd.), Silohobic (registered trademark) 100 (manufactured by Fuji Silysia Corporation), Nipsil (registered trademark) E220A (manufactured by Nippon Silica Industry Co., Ltd.), and Admafine (registered trademark) SO (manufactured by Admatechs Co., Ltd.).

The particle shape can be any shape, including irregular, needle-like, flat, or spherical, but spherical particles are particularly preferred as they provide good transparency to the resulting film.

If the particle size is close to the wavelength of visible light, the light will be scattered and transparency will be reduced, so the particle size is preferably smaller than the wavelength of visible light, and more preferably 1/2 or less of the wavelength of visible light.

If the particle size is too small, the lubricity may not be improved, so it is particularly preferable that the particle size is within the range of 80 to 180 nm.
The particle size means the size of the aggregate when the particle is an aggregate of primary particles.
When the particle is not spherical, the particle diameter means the diameter of a circle equivalent to the projected area of the particle.

The microparticles are preferably added in an amount ranging from 0.05 to 10% by mass, and preferably from 0.1 to 5% by mass, relative to the base resin.

[Method of manufacturing cellulose acylate film]
The method for producing the cellulose acylate film may be a solution casting method or a melt casting method, among which the solution casting method is preferred.

The solution casting method for producing a film includes the steps of preparing a dope, casting the dope onto a metal support, drying the web, and peeling the film from the metal support. The solution casting method for producing a film also includes the steps of stretching or holding the width of the peeled film, further drying the film, and winding up the finished film.

(1) Dope Preparation Process In the dope preparation process, cellulose acylate and additives are dissolved in a solvent to prepare the dope. A higher concentration of cellulose acylate in the dope is preferable because it reduces the drying load after casting onto the metal support. Furthermore, by not increasing the cellulose acylate concentration too much, the pressure load during filtration can be suppressed, resulting in good filtration accuracy. From these viewpoints, the content of cellulose acylate is preferably within a range of 10 to 35% by mass, more preferably within a range of 15 to 25% by mass, based on the total mass of the dope.

The solvent used to prepare the dope may be one type alone or two or more types. However, from the viewpoint of production efficiency, it is preferable to mix a good solvent and a poor solvent for cellulose acylate, and from the viewpoint of cellulose acylate solubility, the more good solvent there is, the better. The mixing ratio of the good solvent to the poor solvent is preferably in the range of 70 to 98 mass% of the good solvent, and preferably in the range of 2 to 30 mass% of the poor solvent. Note that a solvent that dissolves cellulose acylate alone is defined as a "good solvent," and a solvent that swells or does not dissolve cellulose acylate alone is defined as a "poor solvent."

Good solvents are not particularly limited, and examples include organic halogen compounds (e.g., methylene chloride), dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Of these, methylene chloride or methyl acetate is preferred. Poor solvents are not particularly limited, and examples include methanol, ethanol, n-butanol, cyclohexane, and cyclohexanone.

The dope preferably contains water in the range of 0.01 to 2% by mass. The solvent used to dissolve the cellulose acylate may be removed from the film by drying and recovered, and then reused. The recovered solvent may contain trace amounts of additives (e.g., plasticizers, UV absorbers, polymers, monomer components, etc.). The recovered solvent can be reused even if it contains additives. The recovered solvent may be purified, if necessary, and reused.

When preparing the dope, known methods can be used to dissolve the cellulose acylate. For example, by combining a heating means and a pressurizing means, the dope can be heated to a temperature above the boiling point at normal pressure. Dissolving the cellulose acylate by stirring while heating the solvent at a temperature above the boiling point at normal pressure and within a range in which the solvent does not boil under pressure can prevent the formation of clumps of undissolved material (gel or lumps). Alternatively, the cellulose acylate may be mixed with a poor solvent to wet or swell it, and then a good solvent may be added to dissolve it.

Pressurization methods include injecting an inert gas such as nitrogen gas into the dissolution vessel, or increasing the vapor pressure of the solvent by heating. Heating is preferably performed externally, and a jacket type, for example, is preferred as it makes temperature control easier.

From the perspective of cellulose acylate solubility, a higher heating temperature is preferable. Furthermore, by not setting the heating temperature too high, pressure load can be suppressed, resulting in good productivity. From these perspectives, the heating temperature is preferably within the range of 45 to 120°C, more preferably within the range of 60 to 110°C, and even more preferably within the range of 70 to 105°C. The pressure is adjusted so that the solvent does not boil at the set temperature.

Another method for dissolving cellulose acylate is the cooling dissolution method. This method allows cellulose acylate to be dissolved in a solvent such as methyl acetate.

The cellulose acylate solution is filtered using a suitable filter material such as filter paper. From the perspective of removing insoluble matter, it is preferable that the filter material have a low absolute filtration accuracy. Furthermore, by not making the absolute filtration accuracy too low, clogging of the filter material can be suppressed. From these perspectives, the absolute filtration accuracy of the filter material is preferably 0.008 mm or less, more preferably in the range of 0.001 to 0.008 mm, and even more preferably in the range of 0.003 to 0.006 mm.

The material of the filter is not particularly limited, and any known filter material can be used. To prevent fiber shedding, the filter is preferably made of plastic (polypropylene, Teflon (registered trademark), etc.) or metal (stainless steel, etc.). Filtration can remove or reduce impurities, particularly bright spots, contained in the raw cellulose acylate.

Two polarizing plates are arranged in a crossed Nicol state, and a second optical film is placed between them. Light is applied from one polarizing plate side and observed from the other polarizing plate side. Spots where light leaks from the opposite side are called "foreign bright spots." The number of bright spots with a diameter of 0.01 mm or more is preferably 200/cm2 or less, and more preferably 100/ ^cm2 or less. The number of bright spots with a diameter of 0.01 mm or more is further preferably 50/ ^cm2 or less, and particularly preferably in the range of 0 to 10/ ^cm2 . The number of bright spots with a diameter of 0.01 mm or less is also preferably as low as possible.

The dope can be filtered using known methods. Among these, a method of filtering while heating the solvent at a temperature above the boiling point at normal pressure and within a range in which the solvent does not boil under pressure is preferred. This method results in a small increase in the difference in filtration pressure (differential pressure) before and after filtration. The heating temperature is preferably within the range of 45 to 120°C, more preferably within the range of 45 to 70°C, and even more preferably within the range of 45 to 55°C.

A smaller filtration pressure is preferable. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and even more preferably 1.0 MPa or less.

Various additives may be added in batches, or a separate additive solution may be prepared and added in-line. In particular, when adding fine particles to the dope, it is preferable to add some or all of the amount in-line in order to reduce the load of the fine particles on the filter material.

When adding the additive solution inline, it is preferable to add a small amount of acetyl cellulose to the additive solution and dissolve it in order to improve miscibility with the dope. The amount of acetyl cellulose added is preferably within the range of 1 to 10% by mass, and more preferably within the range of 3 to 5% by mass, based on the total mass of the solvent.

Inline addition and mixing can be carried out using, for example, a static mixer or an inline mixer. Examples of static mixers include those manufactured by Toray Engineering Co., Ltd. Examples of inline mixers include the Toray static in-pipe mixer "Hi-Mixer SWJ" (manufactured by Toray Engineering Co., Ltd.).

(2) Step of Casting the Dope onto a Metal Support In the step of casting the dope onto a metal support, the dope is cast onto an endless metal support that moves endlessly. The metal support used in the casting step preferably has a mirror-finished surface. The metal support is preferably a stainless steel belt or a cast drum with a plated surface. The casting width is preferably within the range of, for example, 1 to 4 m.

(3) Step of drying the web In the step of drying the web, the dope cast on the metal support is dried as a web.
The surface temperature of the metal support is preferably in the range of -50°C or higher and lower than the boiling point of the solvent. A higher surface temperature can increase the drying speed of the web. Furthermore, by not raising the surface temperature too high, foaming of the web can be prevented and good film flatness can be obtained. From these viewpoints, the surface temperature is preferably in the range of 0 to 40°C, and more preferably in the range of 5 to 30°C. Alternatively, the metal support may be cooled to gel the web, and the film may be peeled off from the drum in a state where it contains a large amount of residual solvent.

There are no particular limitations on the method for controlling the temperature of the metal support, and examples include blowing hot or cold air onto it. Another method is to bring hot water into contact with the back side of the metal support. Methods using hot water allow for efficient heat transfer, shortening the time it takes for the temperature of the metal support to stabilize. When using hot air, it is possible to use air with a temperature higher than the target temperature of the metal support.

(4) Step of Peeling the Film from the Metal Support From the viewpoint of obtaining good flatness of the film, the residual solvent amount when peeling the film (web) from the metal support is preferably in the range of 10 to 150 mass %. The residual solvent amount is more preferably in the range of 10 to 40 mass % or 60 to 130 mass %, and even more preferably in the range of 10 to 30 mass % or 70 to 120 mass %. Here, the residual solvent amount is defined by the following formula:

Residual solvent amount [mass %] = {(M - N) / N} × 100
where M is the mass of the web or film sample, and N is the mass of the web or film sample after heating at 115°C for 1 hour. The web or film sample can be taken at any time during or after production.

(5) Step of stretching or width-holding the peeled film In the step of stretching or width-holding the peeled film, the film with a large amount of residual solvent immediately after peeling is stretched or width-held. It is preferable to use a tenter method in which the film is stretched in the conveying direction (longitudinal direction, MD direction) and then both ends of the film are held with clips or the like. Alternatively, the film may be stretched simultaneously in the conveying direction and width direction (transverse direction, TD direction).

When stretching in the MD direction, the peel tension is preferably 210 N/m or more, and more preferably in the range of 220 to 300 N/m.

The stretching step allows the refractive index of the film to be controlled, and the retardation values Ro and Rt to be controlled.
The final stretching ratio in the MD direction is preferably in the range of 1.0 to 2.0 times, more preferably in the range of 1.01 to 1.5 times, and the final stretching ratio in the TD direction is preferably 1.6 times or more, more preferably in the range of 1.7 to 2.5 times.
In the present invention, the stretching ratio (times) in the MD direction is defined as the stretching direction size of the film after stretching in the MD direction/the stretching direction size of the film before stretching in the MD direction, and the stretching ratio (times) in the TD direction is defined as the stretching direction size of the film after stretching in the TD direction/the stretching direction size of the film before stretching in the TD direction.

The method for stretching the film is not particularly limited. For example, the stretching method may involve stretching the film in the longitudinal direction by using a plurality of rollers with different peripheral speeds.
Examples of stretching methods include a method in which both ends of the film are fixed with clips or pins, and the spacing between the clips or pins is increased in the conveying direction to stretch the film in the longitudinal direction. Similarly, a method in which the spacing between the clips or pins is increased in the width direction to stretch the film in the transverse direction. Similarly, a method in which the spacing between the clips or pins is increased simultaneously in both the conveying direction and the width direction to stretch the film in both the longitudinal and transverse directions.

These stretching methods may be used in combination. Furthermore, in the case of the tenter method, driving the clips with a linear drive system allows for smooth stretching and reduces the risk of film breakage.

These width holding and lateral stretching operations are preferably carried out using a tenter system, which may be a pin tenter or a clip tenter.

When the fast axis or slow axis of the film exists in the film plane and the angle it forms with the transport direction is θ1, θ1 is preferably within the range of −0.5 to +0.5°, more preferably within the range of −0.3 to +0.3°, and even more preferably within the range of −0.2 to +0.2°. This θ1 can be defined as the orientation angle.
θ1 can be measured using an automatic birefringence meter "KOBRA-21ADH" (Oji Scientific Instruments). When θ1 is within the above range, high brightness can be obtained in the displayed image. In addition, light leakage can be suppressed or prevented, and colors can be faithfully reproduced in a color liquid crystal display device.

(6) Step of Further Drying the Film In the step of further drying the film, the peeled film is further dried. Drying may be performed after or simultaneously with stretching.
The residual solvent content of the film after drying is preferably 1% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.01% by mass or less.

The drying method is not particularly limited, and examples include a roller drying method in which the film is dried by passing it alternately through multiple rollers arranged above and below. It is also possible to dry the film while stretching it using the tenter method described above.

There are no particular limitations on the means for drying the film, and examples include hot air, infrared rays, heated rollers, microwaves, etc. From the standpoint of simplicity, hot air is preferably used as the drying means.

It is preferable to increase the drying temperature stepwise within the range of 40 to 220°C. From the standpoint of dimensional stability, it is more preferable that the drying temperature be within the range of 50 to 140°C.

(7) Step of Winding the Finished Film The finished film is preferably wound into a roll and stored.

[Physical Properties of Cellulose Acylate Film]
Thickness The thickness of the film is preferably in the range of 10 to 200 μm, more preferably in the range of 10 to 60 μm, and even more preferably in the range of 10 to 40 μm.

Width The width of the film is preferably within the range of 1000 to 4000 mm, and is preferably 2500 mm or more in terms of application to polarizing plates for large displays.

[Polarizing plate]
The cellulose acylate film of the present invention is suitably used for a polarizing plate.
FIG. 1 is a cross-sectional view of the basic layer structure of a polarizing plate.
The polarizing plate 1 includes a first optical film 2, a polarizer 4, and a cellulose acylate film of the present invention as a second optical film 5, in this order. The polarizing plate 1 may further include any layer, if necessary. For example, another layer may be provided between the first optical film 2 and the polarizer 4. Furthermore, another layer may be provided between the polarizer 4 and the second optical film 5.

<First Optical Film>
The first optical film is an optical film that functions as a protective film, a retardation film, or the like in a polarizing plate.
The first optical film contains, for example, polyester, cellulose acylate, an ultraviolet absorber, or the like.

The polyester is preferably polyethylene terephthalate or polyethylene naphthalate. Polyethylene terephthalate and polyethylene naphthalate have large intrinsic birefringence, and therefore, even if the film is thin, a high retardation value can be obtained relatively easily. In particular, the effect of polyethylene naphthalate is remarkable.
As the film containing cellulose acylate, a commercially available cellulose acylate film may be used.

The ultraviolet absorber protects the liquid crystal display device (particularly the alignment film of the liquid crystal cell) from ultraviolet rays and improves the weather resistance of the liquid crystal display device.
Examples of the ultraviolet absorber include cyclic imino ester-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, salicylic acid ester-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, triazine-based ultraviolet absorbers, etc. Among these, the ultraviolet absorber is preferably a cyclic imino ester-based ultraviolet absorber or a benzotriazole-based ultraviolet absorber.
The content of the ultraviolet absorber is preferably within a range of 0.1 to 10% by mass relative to the total mass of the polyester.

The retardation value Ro of the first optical film for light with a wavelength of 550 nm under an environment of 23°C and 55% RH is preferably in the range of 3000 to 30,000 nm. By having Ro of 3000 nm or more, interference colors (rainbow unevenness due to observation angle) when the first optical film 10 is observed from an oblique direction can be reduced, resulting in good visibility. Furthermore, by having Ro of 30,000 nm or less, the thickness of the first optical film 10 can be reduced. Ro is preferably 5,000 nm or more, more preferably 8,000 nm or more, and even more preferably 10,000 nm or more.

The thickness of the first optical film is preferably 5 μm or more, more preferably 10 μm or more, more preferably 15 μm or more, and particularly preferably 20 μm or more. When the thickness of the first optical film is 5 μm or more, the first optical film can achieve good water resistance and mechanical strength. The thickness of the first optical film is preferably 300 μm or less, more preferably 200 μm or less, more preferably 100 μm or less, and particularly preferably 40 μm or less. When the thickness of the first optical film is 100 μm or less, the first optical film can achieve both thinness and visibility.

<Polarizer>
In the present invention, the term "polarizer" refers to an element that transmits only light polarized in a certain direction, or a layer that includes such an element.
An example of a polarizer is a polyvinyl alcohol polarizing film. The polyvinyl alcohol polarizing film includes a polyvinyl alcohol film dyed with iodine and a polyvinyl alcohol film dyed with a dichroic dye.

Polarizers can be manufactured by forming a film from an aqueous polyvinyl alcohol solution, stretching the resulting film uniaxially, and dyeing it. Alternatively, after dyeing, the film may be stretched uniaxially and then treated with a boron compound or the like for durability.

The thickness of the polarizer is preferably in the range of 2 to 30 μm, and more preferably in the range of 2 to 20 μm.

Examples of polyvinyl alcohol include ethylene-modified polyvinyl alcohols described in JP-A Nos. 2003-248123 and 2003-342322.
The ethylene-modified polyvinyl alcohol has an ethylene unit content of 1 to 4 mol%, a polymerization degree of 2000 to 4000, and a saponification degree of 99.0 to 99.99 mol%. Among these, an ethylene-modified polyvinyl alcohol having a hot water cutting temperature of 66 to 73°C is preferred.
This ethylene-modified polyvinyl alcohol polarizing film has excellent polarizing properties and durability, and exhibits little color unevenness, making it particularly suitable for use in large-sized liquid crystal displays.

[Method of manufacturing polarizing plate]
The polarizing plate of the present invention can be produced by a general method.
The surface of the first optical film facing the polarizer is appropriately surface-treated, and the polarizer is prepared by immersing the film in an iodine solution and stretching it. The polarizer is then bonded to at least one surface of the first optical film using an ultraviolet-curable adhesive or a water-based adhesive, as described below. A second optical film (cellulose acylate film of the present invention) is similarly bonded to the other surface of the polarizer.

The direction of lamination with the polarizer is preferably such that, for example, the absorption axis of the polarizer and the slow axis of each optical film are perpendicular to each other.

(1) UV-Curable Adhesive The polarizing plate of the present invention is preferably produced by bonding the optical film and the polarizer together via a UV-curable adhesive. By using a UV-curable adhesive, a polarizing plate that is thin but has high strength and excellent flatness can be obtained.

(Composition of UV-curable adhesive)
Examples of ultraviolet-curable adhesive compositions for polarizing plates include photoradical polymerization compositions that utilize photoradical polymerization and photocationic polymerization compositions that utilize photocationic polymerization. Examples of ultraviolet-curable adhesive compositions for polarizing plates also include hybrid compositions that utilize both photoradical polymerization and photocationic polymerization.

An example of a photo-radical polymerization composition is the composition described in JP 2008-009329 A. This composition contains a specific ratio of a radical polymerizable compound containing a polar group such as a hydroxy group or a carboxy group, and a radical polymerizable compound without a polar group.

The radically polymerizable compound contained in the photoradical polymerization composition is preferably a compound having a radically polymerizable ethylenically unsaturated bond. Examples of compounds having a radically polymerizable ethylenically unsaturated bond include compounds having a (meth)acryloyl group. Examples of compounds having a (meth)acryloyl group include N-substituted (meth)acrylamide compounds and (meth)acrylate compounds.

Note that the term "(meth)acryloyl group" refers to an acryloyl group or a methacryloyl group, and "(meth)acrylate" refers to an acrylate or a methacrylate. Furthermore, the term "(meth)acrylamide" refers to an acrylamide or a methacrylamide.

An example of a photocationic polymerization composition is the composition described in JP 2011-028234 A. This composition contains (α) a cationically polymerizable compound, (β) a photocationic polymerization initiator, (γ) a photosensitizer that exhibits maximum absorption at wavelengths longer than 380 nm, and (δ) a naphthalene-based photosensitization aid.
Examples of the cationically polymerizable compound include epoxy compounds and oxetane compounds.
The ultraviolet curing adhesive is not limited to these, and any known adhesive can be used.

(2) Method for manufacturing a polarizing plate After pre-treating the optical film and the polarizer, a UV-curable adhesive is applied. Next, the optical film and the polarizer are bonded together via the UV-curable adhesive. Then, the UV-curable adhesive is cured.

(2.1) Pretreatment Step In the pretreatment step, the bonding surface between the optical film and the polarizer is subjected to an adhesion-facilitating treatment. Examples of the adhesion-facilitating treatment include a corona treatment and a plasma treatment.

(2.2) Coating Step In the coating step, the ultraviolet-curable adhesive is applied to at least one of the adhesive surfaces between the optical film and the polarizer. When the ultraviolet-curable adhesive is applied directly to the surface of the optical film or the polarizer, the coating method is not limited. Examples of the coating method include a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater, and various wet coating methods can be used. Furthermore, after the ultraviolet-curable adhesive is applied between the optical film and the polarizer, pressure may be applied with a roller or the like to uniformly spread the ultraviolet-curable adhesive.

(2.3) Bonding Step In the bonding step, when an ultraviolet-curable adhesive is applied to the surface of the polarizer in the previous coating step, an optical film is superimposed on the ultraviolet-curable adhesive. When an ultraviolet-curable adhesive is applied to the surface of the optical film, a polarizer is superimposed on the ultraviolet-curable adhesive.

When a UV-curable adhesive is cast between the optical film and the polarizer, the optical film and polarizer are superimposed in this state. In this state, pressure is usually applied by sandwiching the optical film on both sides with pressure rollers or the like. Examples of materials for the pressure roller include metal and rubber. The pressure rollers placed on both sides may be made of the same material or different materials.

(2.4) Curing Step In the curing step, the applied ultraviolet-curable adhesive is irradiated with ultraviolet light. The ultraviolet-curable adhesive is then cured, and the optical film and the polarizer, which are superposed via the ultraviolet-curable adhesive, are bonded together. In the present invention, optically transparent optical films are superposed on both sides of the polarizer, each via an ultraviolet-curable adhesive. In this state, ultraviolet light is preferably irradiated to simultaneously cure the ultraviolet-curable adhesive on both sides.

The conditions for ultraviolet irradiation are not particularly limited as long as they allow the ultraviolet-curable adhesive to be cured. The dose of ultraviolet irradiation is preferably within a range of 50 to 1500 mJ/ ^cm2 , more preferably within a range of 100 to 500 mJ/ ^cm2 , in terms of cumulative light amount. In the present invention, it is preferable to irradiate ultraviolet light from the second optical film side, from the viewpoint of improving yield.

When polarizing plates are produced on a continuous line, the line speed is preferably within a range of 1 to 500 m/min, more preferably within a range of 5 to 300 m/min, and even more preferably within a range of 10 to 100 m/min.
By setting the line speed to 1 m/min or more, productivity can be ensured, and damage to the optical film can be suppressed, resulting in a polarizing plate with excellent durability.
By setting the line speed to 500 m/min or less, the ultraviolet-curable adhesive can be sufficiently cured. An adhesive layer having the desired hardness and excellent adhesiveness can be formed. Note that the line speed is preferably adjusted taking into account the curing time of the adhesive.

[Liquid crystal display device]
The cellulose acylate film of the present invention is suitable for use in a liquid crystal display device. That is, the liquid crystal display device preferably includes the polarizing plate, and the second optical film (the cellulose acylate film of the present invention) is preferably disposed on the liquid crystal cell side. By including the polarizing plate, color unevenness and contrast variation due to moisture content can be suppressed.

The polarizing plate can be used in liquid crystal display devices with various drive methods, such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, and OCB. Among these, it is preferable to use it in VA-type liquid crystal display devices.

Liquid crystal display devices typically use two polarizing plates: one on the viewing side and one on the backlight side. The polarizing plate may be used on both sides, or on just one side.

The liquid crystal cell according to the present invention comprises a liquid crystal layer and a pair of substrates sandwiching the liquid crystal layer. From the viewpoint of reducing the thickness and weight of the display device, it is preferable that the pair of substrates be glass substrates with a thickness in the range of 0.3 to 0.7 mm.

Figure 2 is a schematic cross-sectional view showing an example of the configuration of a display device (100) in which polarizing plates (101A and 101B) of the present invention are arranged on both sides of a liquid crystal cell (101C).

In Figure 2, both sides of the liquid crystal layer (107) are sandwiched between glass substrates (108A and 108B) as transparent base materials to form a liquid crystal cell (101C). Polarizing plates (101A and 101B) are placed on the surfaces of each of the glass substrates (108A and 108B) via adhesive layers (106), forming the display device (100).

In the polarizing plates (101A and 101B), the first optical film is attached at positions 102A and 102B, and the second optical film is attached at positions 105A and 105B.
The optical films are bonded to the polarizers (104A and 104B) by ultraviolet curing adhesives (103A to 103D), respectively.

The liquid crystal cell (101C) has an alignment film, transparent electrodes, and glass substrates (108A and 108B) on both sides of the liquid crystal material. Examples of materials for the glass substrate include soda-lime glass and silicate glass. Among these, silicate glass is preferred, and more specifically, silica glass or borosilicate glass is more preferred.

The glass constituting the glass substrate is preferably alkali-free glass that does not substantially contain alkali components. Specifically, the content of alkali components in the glass substrate is preferably 1000 ppm or less.
The content of alkali components in the glass substrate is more preferably 500 ppm or less, and even more preferably 300 ppm or less.
The alkali-free glass, which contains substantially no alkali components, can suppress soda blisters caused by the substitution of cations on the optical film surface, thereby preventing a decrease in density on the optical film surface and breakage of the glass substrate.

Glass substrates can be produced by known methods, such as the float method, downdraw method, and overflow downdraw method. Among these, the overflow downdraw method is preferred because the surface of the glass substrate does not come into contact with the forming member during molding, and the surface of the resulting glass substrate is less likely to be scratched.

The glass substrate may be a commercially available product.
Examples of commercially available glass substrates include "AN100" (thickness: 500 μm, manufactured by Asahi Glass Co., Ltd.), "EAGLE XG(r) Slim" (thickness: 300 μm, 400 μm, etc., manufactured by Corning Incorporated), and glass base material (thickness: within the range of 100 to 200 μm, manufactured by Nippon Electric Glass Co., Ltd.).

As shown in FIG. 2, the polarizing plates (101A, 101B) and the liquid crystal cell (101C) are bonded together via an adhesive layer (106).
Examples of the adhesive layer include a layer formed using a double-sided tape, an ultraviolet-curing adhesive, or the like.
An example of the double-sided tape is substrate-less tape "MO-3005C" (thickness: 25 μm, manufactured by Lintec Corporation). The lamination method is not particularly limited, and known methods can be used.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, operations were performed at room temperature (25°C). Furthermore, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass," respectively.

The cellulose acylate, additives, etc. used in the preparation of the optical film are as follows: <Cellulose acylate>
As the cellulose acylate, the following cellulose diacetates (DAC1, DAC2, DAC3), cellulose acetate propionate (CAP1, CAP2), and cellulose triacetate (CTA) were used.
DAC1: acetyl group substitution degree 2.40
DAC2: acetyl group substitution degree 2.42
CAP1: acetyl group substitution degree 1.50, propionyl group substitution degree 0.95
CAP2: acetyl group substitution degree 1.50, propionyl group substitution degree 0.85
CTA: acetyl group substitution degree 2.83
DAC3: acetyl group substitution degree 2.1

<Additive 1 and Additive 2>
As Additive 1 and Additive 2, the following were used.

Polycondensation ester J-31: a polycondensation ester obtained from a dicarboxylic acid in which terephthalic acid (aromatic dicarboxylic acid) and succinic acid (aliphatic dicarboxylic acid) are mixed in a molar ratio of 55:45, and a diol in which ethanediol and propanediol are mixed in a molar ratio of 45:55, and which has a propionyl ester group at the end (this is polycondensation ester J-31 described in Table 5 in paragraph [0145] of JP2012-82235A).
Sucrose benzoate Sugar 1: In the following general formula (10), five R's are substituted with the following substituents (benzoyl groups), and the remaining three R's are hydrogen atoms.

<Preparation of Dope>
<Fine particle dispersion>
The following components were mixed by stirring for 50 minutes in a dissolver, and then dispersed in a Manton-Gaulin to obtain a fine particle dispersion.
Fine particles "Aerosil (registered trademark) R812" (manufactured by Nippon Aerosil Co., Ltd.)
11.0 parts by mass Ethanol 89.0 parts by mass

<Fine particle additive liquid>
Diacetyl cellulose (DAC1) with a degree of substitution of 2.40 was added to a dissolution tank containing methylene chloride and heated to completely dissolve. This solution was then filtered using "Azumi Filter Paper No. 244" (manufactured by Azumi Filter Paper Co., Ltd.). While thoroughly stirring the filtered diacetyl cellulose solution, the above-mentioned microparticle dispersion was slowly added thereto. The mixture was then dispersed using an attritor so that the secondary particles had a predetermined particle size. The resulting dispersion was filtered using "Finemet NF" (manufactured by Nippon Seisen Co., Ltd.) to prepare a microparticle-added solution.
Methylene chloride 99.0 parts by mass Diacetyl cellulose (DAC1) 4.0 parts by mass Fine particle dispersion 11.0 parts by mass

Next, a main dope solution having the following composition was prepared.
First, methylene chloride and ethanol were added to a pressure dissolution tank. Diacetyl cellulose (DAC1) with a degree of substitution of 2.40 was added to the pressure dissolution tank while stirring. This was heated and stirred until completely dissolved. Two additional additives were added to the solution and dissolved. The solution was filtered using "Azumi Filter Paper No. 244" (manufactured by Azumi Filter Paper Co., Ltd.) to prepare a main dope solution.

<Composition of main dope solution>
Methylene chloride 300.0 parts by mass Ethanol 30.0 parts by mass Diacetyl cellulose (DAC1) 100.0 parts by mass Exemplary compound 3 as additive 2 5.0 parts by mass

2 parts by mass of the microparticle additive solution were added to 100.0 parts by mass of the main dope solution and thoroughly mixed using an in-line mixer (Toray static in-tube mixer) "Hi-Mixer, SWJ" (manufactured by Toray Engineering Co., Ltd.) to prepare the dope. The content of Exemplary Compound 3 in the dope was 5% by mass relative to the mass of diacetyl cellulose in the main dope.

<Preparation of Optical Film 1>
The dope prepared above was uniformly cast onto a 2-m wide stainless steel belt at 22°C using a belt casting apparatus. The solvent in the web was evaporated on the stainless steel belt until the residual solvent amount was less than 100%. Then, the film was peeled off from the stainless steel belt with a peeling tension of 160 N/m.

Then, the solvent was evaporated from the peeled film at 35°C and the film was slit. The film was then stretched in the width direction (TD direction) at 195°C using a tenter stretching machine at 1.8 times the original width. When stretching using the tenter began, the residual solvent content of the film was 3 to 15% by mass.

The film was then dried in drying zones at 120°C and 140°C while being transported by multiple rollers. The film was slit to a width of 2500 mm, and knurling was applied to both ends of the film to a width of 10 mm and a height of 2.5 μm. The film was then wound around a core, yielding Optical Film 1 with a thickness of 35 μm and a wound length of 3900 m.

<Preparation of Optical Films 2 to 22>
Optical films 2 to 22 were obtained in the same manner as in the preparation of optical film 1, except that the type of cellulose acylate, the types and contents of additives 1 and 2, the stretching ratio in the TD direction, and the film width were changed as shown in the table below. The thicknesses of the obtained optical films are shown in the table below.

The retardation values Ro and Rt of each obtained optical film were measured for light with a wavelength of 550 nm using an automatic birefringence meter at 23°C and 55% RH, and the measurement results are shown in the table below. The automatic birefringence meter used was an "Axo Scan" (manufactured by Optoscience).

<Preparation of Polarizer>
A 60 μm-thick long polyvinyl alcohol film was prepared. While continuously transporting the film via guide rollers, the film was immersed in a dye bath (30°C) containing iodine and potassium iodide for dyeing treatment, and the film was stretched 2.5 times. The film was then stretched a total of 5 times and crosslinked in an acid bath (60°C) containing boric acid and potassium iodide. The resulting 12 μm-thick iodine-PVA polarizer film was dried in a dryer at 50°C for 30 minutes. A polarizer with a moisture regain of 4.9% was obtained.

<Preparation of Polarizing Plate 1>
As the first optical film, a cellulose triacylate film (Konica Minolta TAC6UA, manufactured by Konica Minolta, Inc.) was used.
The above-obtained optical film 1 was laminated as a first optical film and a second optical film, and a polarizer was laminated to prepare a polarizing plate 1.

(Preparation of Water-Based Adhesive)
The following components were mixed to prepare a water-based adhesive.
Pure water 100.0 parts by mass Carboxy group-modified polyvinyl alcohol "Kuraray Poval (registered trademark) KL318" (manufactured by Kuraray Co., Ltd.)
3.0 parts by mass of water-soluble polyamide epoxy resin "Sumirese (registered trademark) Resin 650" (aqueous solution with a solids concentration of 30%, manufactured by Sumika Chemtex Co., Ltd.)
1.5 parts by mass

(Pretreatment of Second Optical Film)
Optical film 1, which was a second optical film, was immersed in a saponification treatment solution (aqueous sodium hydroxide solution at 60°C, concentration 10% by mass) for 30 seconds. Next, optical film 1 was immersed in a water bath for 5 seconds. This was repeated twice. Thereafter, optical film 1 was washed with a water shower for 5 seconds and then dried. The drying conditions were 70°C and 2 minutes.
Next, Optical Film 1 was immersed in water at 30° C. for 10 seconds for swelling treatment, and then dried at 40° C. for 53 seconds.

(Pretreatment of First Optical Film)
The first optical film was also subjected to the same pretreatment as the second optical film (optical film 1).

(Laminating optical film and polarizer)
The surfaces of the first optical film and the second optical film (optical film 1) to be bonded to the polarizer were subjected to a corona treatment. Then, the aqueous adhesive was applied to the surfaces to be bonded to the polarizer, and each optical film was bonded to both sides of the polarizer. Immediately thereafter, the bonded laminate was dried for 5 minutes in a hot air circulation dryer set at 80°C, thereby obtaining polarizing plate 1.

<Preparation of Polarizing Plates 2 to 22>
Polarizing plates 2 to 22 were produced in the same manner as in the production of polarizing plate 1, except that optical film 1 was replaced with the optical films shown in the table below as the second optical film.

<Fabrication of Liquid Crystal Display Device>
Using the polarizing plates 1 to 22 prepared above, liquid crystal displays 1 to 22 were prepared according to the following method.
A VA-mode liquid crystal cell was prepared, having two 0.5 mm-thick glass substrates and a liquid crystal layer disposed between them. The polarizing plates 1 to 22 prepared above were then bonded together via an adhesive layer, with the second optical film facing the liquid crystal cell, to obtain liquid crystal display devices 1 to 22. The polarizing plates were bonded together so that the absorption axis of the polarizer of the viewing-side polarizing plate (101A in FIG. 2 ) was perpendicular to the absorption axis of the polarizer of the backlight-side polarizing plate (101B in FIG. 2 ).

In the table below, "-" indicates that the corresponding component is not contained or the requirements are not met.
The contents of Additive 1 and Additive 2 in the following table represent the ratio of each additive to the mass of cellulose acylate, which is the main dope.
In addition, in the items in the table below, (A) to (F) are as follows:
(A): When Additive 2 (hydrogen-bonding compound) has a fluorene skeleton and an atomic group containing an amide bond at the 9th position of the fluorene skeleton, or when Additive 2 has a carbazole skeleton and an atomic group containing an amide bond at the 9th position of the carbazole skeleton, it is represented as "Y." When Additive 2 does not have the atomic group, it is represented as "N."
(B): The retardation values Ro, Rt, and Rt/Ro were recorded.
(C): Additive 2 (hydrogen bond compound) When both a hydrogen bond donor moiety and a hydrogen bond acceptor moiety are present in one molecule, this is indicated as "Y", and when neither is present, this is indicated as "N".
(D): The value obtained by dividing the weight average molecular weight of Additive 2 (hydrogen bond compound) by the total number of hydrogen bond donors and hydrogen bond acceptors is recorded.
(E): The total number of aromatic ring structures contained in Additive 2 (hydrogen-bonding compound) is recorded.
(F): The number of carboxy groups contained in Additive 2 (hydrogen-bonding compound) is recorded.

[evaluation]
<Polarizer Stability>
The polarizing plates prepared above were subjected to a forced deterioration test by being kept in an environment of 60°C and 90% RH for 50 hours. After the test, the polarizing plates were visually observed for color change in the visible light region and evaluated according to the following criteria. The results are shown in the table below. In the following criteria, "A" and "B" were considered to be acceptable for practical use.
(standard)
A: No change B: Slight coloring C: Coloring D: Significant coloring

<Scatterability>
The obtained optical film was subjected to a heat treatment at 200°C for 10 minutes, and then conditioned at 23°C and 55% RH for 24 hours, and the mass was measured. The mass change before and after the heat treatment was used to evaluate the scattering of the hydrogen-bonding compound from the film when the film was heated during stretching. In the following criteria, "A" and "B" were determined to be acceptable for practical use.
(standard)
A: Mass loss of 1% or less after heat treatment B: Mass loss of more than 1% or less and 2% or less after heat treatment C: Mass loss of more than 2% or less and 3% or less after heat treatment D: Mass loss of more than 3% after heat treatment

<Viewing angle of liquid crystal display device in VA mode>
Liquid crystal display devices 1 to 18 using optical films 1 to 18 have a retardation value ratio (Rt/Ro) of 2.0 or more, and therefore can be applied to optical compensation of VA mode liquid crystal display devices.
The liquid crystal display devices 21 and 22 using the optical films 21 and 22 have a retardation value ratio (Rt/Ro) of less than 2.0, and therefore cannot be applied to optical compensation of VA mode liquid crystal display devices.
Furthermore, since the optical films 19 and 20 have a retardation ratio (Rt/Ro) of 2.0 or more, they can be used for optical compensation in VA-mode liquid crystal displays. However, the stretching ratio in the TD direction is low, so a film with a width of 2500 mm cannot be obtained.

As shown in the above results, the optical film of the present invention can obtain a high retardation ratio (Rt/Ro of 2.0 or more) required for optical compensation in VA mode even when stretched at a high magnification (1.5 times or more) in the TD direction, and therefore can be applied to optical compensation in VA mode liquid crystal displays.
In contrast, when the optical films of the comparative examples are stretched at a high ratio in the TD direction, they do not achieve a high retardation ratio (Rt/Ro of 2.0 or more) required for optical compensation in the VA mode. Furthermore, it is clear that the stretching ratio in the TD direction becomes low when an attempt is made to achieve a high retardation ratio.

The present invention can be used in cellulose acylate films that can achieve the high retardation ratio (Rt/Ro) required for VA mode optical compensation even when stretched at a high magnification in the TD direction, as well as in cellulose acylate film manufacturing methods, polarizing plates, and liquid crystal display devices.

REFERENCE SIGNS LIST 1 Polarizing plate 2 First optical film 4 Polarizer 5 Second optical film 100 Display device 101A, 101B Polarizing plate 101C Liquid crystal cell 102A, 102B First optical film 103A, 103B, 103C, 103D Adhesive layer 104A, 104B Polarizer 105A, 105B Second optical film 106 Pressure-sensitive adhesive layer 107 Liquid crystal layer 108A, 108B Glass substrate

Claims (13)

The composition contains a hydrogen-bonding compound that satisfies the following requirement (A):
A cellulose acylate film that satisfies the following optical values (B).
(A): A compound having a fluorene skeleton and an atomic group containing an amide bond at the 9th position of the fluorene skeleton, or a compound having a carbazole skeleton and an atomic group containing an amide bond at the 9th position of the carbazole skeleton.
(B): The retardation value Ro defined by the following formula is in the range of 40 to 70 nm, the retardation value Rt is in the range of 100 to 220 nm, and the retardation value ratio Rt/Ro is in the range of 2.0 to 5.5.
Formula (i) Ro = ( _nx - _ny ) x d
Formula (ii) Rt={(n _x + _ny )/2-n _z }×d
(In the above formulas (i) and (ii), _nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the film. _ny represents the refractive index in the direction y perpendicular to the direction x in the in-plane direction of the film. _nz represents the refractive index in the thickness direction z of the film. The refractive indices are measured at a wavelength of 550 nm in an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.) The cellulose acylate film according to claim 1, wherein the hydrogen-bonding compound has both a hydrogen-bond donor moiety and a hydrogen-bond acceptor moiety within one molecule. The cellulose acylate film according to claim 2, wherein the value obtained by dividing the weight-average molecular weight of the hydrogen-bonding compound by the total number of hydrogen-bond donors and hydrogen-bond acceptors is within the range of 30 to 80. The cellulose acylate film according to claim 1, wherein the total number of aromatic ring structures possessed by the hydrogen-bonding compound is within the range of 2 to 3. The cellulose acylate film according to claim 1, wherein the hydrogen-bonding compound has one or less carboxyl groups. The cellulose acylate film according to claim 1, wherein the hydrogen-bonding compound does not have a carboxy group. The cellulose acylate film according to claim 1, wherein the weight-average molecular weight of the hydrogen-bonding compound is 300 or more. The cellulose acylate film according to claim 1, wherein the hydrogen-bonding compound has a 9-fluorenylmethyloxycarbonyl group. The cellulose acylate film according to claim 1, wherein the content of the hydrogen-bonding compound is within the range of 0.5 to 30% by mass relative to the cellulose acylate resin. The cellulose acylate film according to claim 1, wherein the film width is 2500 mm or more. A method for producing the cellulose acylate film according to any one of claims 1 to 10, comprising the steps of:
A method for producing a cellulose acylate film, wherein the film is stretched in the TD direction at a stretching ratio of 1.6 times or more. A polarizing plate comprising the cellulose acylate film described in any one of claims 1 to 10. A liquid crystal display device comprising the polarizing plate according to claim 12.