Cellulose acylate film, method for manufacturing cellulose acylate film, polarizer and liquid crystal display device

Abstract

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

Description

Technology Field

[0001] The present invention relates to a cellulose acylate film, a method for manufacturing a cellulose acylate film, a polarizer, and a liquid crystal display device. In particular, the present invention relates to a cellulose acylate film, etc., in which a ratio of high retardation values ​​(Rt / Ro) required for optical compensation in VA mode is obtained even when stretched at a high magnification in the TD direction. Background Technology

[0002] As disclosed in Patent Document 1, a cellulose acylate film containing a hydrogen bonding compound is known to have a small change in retardation depending on environmental humidity. In addition, a cellulose acylate film containing a hydrogen bonding compound is known to be able to suppress the deterioration of a polarizer when bonded to a polarizer and subjected to high temperature and high humidity over time.

[0003] In recent years, as displays have become larger, there is a demand to manufacture polarizers for large displays more efficiently, and polarizers with a width of 2500 mm or more are required.

[0004] To manufacture a film with a width of 2500 mm or more, there are methods of widening the width of the raw material and widening the stretching ratio in the TD direction (width direction). Among these methods, the method of widening the stretching ratio in the TD direction can reduce the cost of manufacturing equipment. However, in the above-mentioned Patent Document 1, the stretching ratio in the TD direction is disclosed only up to 1.4 times.

[0005] Meanwhile, patent documents 2 and 3 disclose a cellulose acylate film that has been stretched at a high magnification in the TD direction.

[0006] However, cellulose acylate films manufactured with a stretching ratio of 1.5 times or more in the TD direction have a ratio of retardation values ​​(Rt / Ro) of 0.9 to 1.35. For this reason, they are used for optical compensation in IPS mode liquid crystal displays, but they are not used for optical compensation in VA mode liquid crystal displays, where a higher Rt / Ro is required. In other words, there was a problem in that cellulose acylate films subjected to high-magnification stretching of 1.5 times or more in the TD direction could not obtain the high Rt / Ro required for optical compensation in VA mode. Prior art literature

[0007] Japanese Patent Publication No. 2012-82235 Japanese Patent Publication No. 2013-235232 Japanese Patent Publication No. 2014-101477 The problem to be solved

[0008] The present invention has been made in consideration of the above-mentioned problems and situations. The problem to be solved by the present invention is to provide a cellulose acylate film and a method for manufacturing the same, in which a ratio of high retardation values ​​(Rt / Ro) required for optical compensation in VA mode is obtained even when stretched at a high magnification in the TD direction. In addition, the problem to be solved by the present invention is to provide a polarizer and a liquid crystal display device using the cellulose acylate film. means of solving the problem

[0009] In order to solve the above problem, the inventors examined the causes of the problem, etc. As a result, it was discovered that by containing a hydrogen bonding compound having a fluorene backbone or a carbazole backbone and an atomic group having an amide bond at the 9th position of these backbones, and by satisfying a specific optical value, a ratio of high retardation values ​​required for optical compensation of the VA mode is obtained even when stretched at high magnification.

[0010] That is, the above problem regarding the present invention is solved by the following means.

[0011] 1. Containing a hydrogen-bonding compound that satisfies the requirements of (A) below, and

[0012] A cellulose acylate film satisfying the optical values ​​of (B) below.

[0013] (A): It has a fluorene backbone and has an atomic group containing an amide bond at the 9th position of the fluorene backbone, or has a carbazole backbone and has an atomic group containing an amide bond at the 9th position of the carbazole backbone.

[0014] (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 ratio of the retardation values ​​Rt / Ro is in the range of 2.0 to 5.5.

[0015] Equation (i) Ro=(n x -n y )×d

[0016] Equation (ii) Rt={(n x +n y ) / 2-n z}×d

[0017] (Among the above equations (i) and (ii), n x represents the refractive index in direction x where the refractive index is maximum in the in-plane direction of the film. y n represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the film. z represents the refractive index in the thickness direction z of the film. The above refractive index was measured at a wavelength of 550 nm under an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.)

[0018] 2. A cellulose acylate film according to claim 1, having both a hydrogen bonding donor part and a hydrogen bonding acceptor part within one molecule of the above-mentioned hydrogen bonding compound.

[0019] 3. A cellulose acylate film described in claim 2, wherein the weight average molecular weight of the hydrogen bonding compound is calculated by dividing the total number of hydrogen bonding donors and hydrogen bonding acceptors by the total number of hydrogen bonding acceptors, and the result is within the range of 30 to 80.

[0020] 4. A cellulose acylate film according to claim 1, wherein the total number of aromatic ring structures of the hydrogen bonding compound is within the range of 2 to 3.

[0021] 5. A cellulose acylate film according to claim 1, wherein the hydrogen bonding compound has one or fewer carboxyl groups.

[0022] 6. A cellulose acylate film according to claim 1, wherein the hydrogen bonding compound does not have a carboxyl group.

[0023] 7. A cellulose acylate film described in claim 1, wherein the weight average molecular weight of the hydrogen bonding compound is 300 or more.

[0024] 8. A cellulose acylate film according to claim 1, wherein the hydrogen bonding compound has a 9-fluorenylmethyloxycarbonyl group.

[0025] 9. A cellulose acylate film according to claim 1, wherein the content of the hydrogen bonding compound is within the range of 0.5 to 30 mass% with respect to the cellulose acylate resin.

[0026] 10. A cellulose acylate film as described in claim 1, having a film width of 2500 mm or more.

[0027] 11. A method for manufacturing a cellulose acylate film for manufacturing a cellulose acylate film as described in any one of claims 1 to 10, and

[0028] A method for manufacturing a cellulose acylate film by stretching the stretching ratio in the TD direction by 1.6 times or more.

[0029] 12. A polarizing plate having a cellulose acylate film as described in any one of claims 1 to 10.

[0030] 13. A liquid crystal display device having a polarizing plate as described in paragraph 12. Effects of the invention

[0031] By means of the above invention, a cellulose acylate film and a method for manufacturing the same can be provided, in which a ratio of high retardation values ​​(Rt / Ro) required for optical compensation of the VA mode is obtained even when stretched at a high magnification in the TD direction.

[0032] Although the mechanism of manifestation or mechanism of action of the present invention is not clearly defined, it is presumed as follows.

[0033] In a film stretched at a high magnification in the TD direction, the reason the ratio of retardation values ​​(Rt / Ro) decreases is that the cellulose acylate resin and additives are oriented in the TD direction, which is the stretching direction, as a result of stretching at a high magnification in the TD direction. As a result, Ro increases, and consequently, Rt / Ro decreases.

[0034] Therefore, in the present invention, by stretching at a high magnification in the TD direction, the atomic group containing the amide bond of the cellulose acylate resin and the hydrogen bonding compound is oriented in the TD direction, which is the stretching direction, and the fluorene backbone (or carbazole backbone) of the hydrogen bonding compound is oriented in the MD direction, which is a direction orthogonal to the stretching direction. As a result, the fluorene backbone (or carbazole backbone) takes on a form that reduces the retardation value Ro. Consequently, it is estimated that a cellulose acylate film with a high ratio of retardation values ​​(Rt / Ro) is obtained. Brief explanation of the drawing

[0035] Figure 1 is a cross-sectional view of the basic layer configuration of a polarizer. Figure 2 is a schematic diagram showing an example of the configuration of a display device. Specific details for implementing the invention

[0036] The cellulose acylate film of the present invention contains a hydrogen bonding compound that satisfies the requirements of (A) below and satisfies the optical value of (B) below.

[0037] (A): It has a fluorene backbone and has an atomic group containing an amide bond at the 9th position of the fluorene backbone, or has a carbazole backbone and has an atomic group containing an amide bond at the 9th position of the carbazole backbone.

[0038] (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 ratio of the retardation values ​​Rt / Ro is in the range of 2.0 to 5.5.

[0039] Equation (i) Ro=(n x -n y )×d

[0040] Equation (ii) Rt={(n x +n y ) / 2-n z}×d

[0041] (Among the above equations (i) and (ii), n x represents the refractive index in direction x where the refractive index is maximum in the in-plane direction of the film. y n represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the film. z represents the refractive index in the thickness direction z of the film. The above refractive index was measured at a wavelength of 550 nm under an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.)

[0042] This feature is a technical feature common to or corresponding to each of the following embodiments.

[0043] In an embodiment of the present invention, it is preferable to have both a hydrogen bond donor group and a hydrogen bond acceptor group within one molecule of the hydrogen bondable compound. By doing so, strong hydrogen bonds can be formed with water, thereby suppressing water from coordinating with carbonyl groups in cellulose acylate.

[0044] In addition, it is preferable that the weight-average molecular weight of the hydrogen-bonding compound, when divided by the sum of the number of hydrogen bond donors and hydrogen bond acceptors, is within the range of 30 to 80. If the value calculated by dividing by the sum is excessively large, it becomes difficult for the hydrogen-bonding compound to approach the cellulose acylate. Consequently, the improvement effect on retardation changes accompanying environmental changes is reduced. On the other hand, if the sum is excessively small, the interaction between the hydrogen-bonding compounds becomes excessively strong, which is undesirable because it results in insufficient solubility in solvents or compatibility with the cellulose acylate.

[0045] It is preferable that the total number of aromatic ring structures of the above 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 excessively large. Consequently, it becomes easier to approach the carbonyl groups in the cellulose acylate, and an inhibitory effect on changes in optical properties due to environmental humidity is obtained.

[0046] It is desirable for the above hydrogen bonding compound to have one or fewer carboxyl groups in terms of polarizer stability.

[0047] In addition, it is desirable for the hydrogen bonding compound not to have a carboxyl group in terms of polarizer stability.

[0048] It is desirable that the weight average molecular weight of the above hydrogen bonding compound be 300 or more, as this can prevent the hydrogen bonding compound from scattering from the film when the film is heated.

[0049] In addition, it is desirable for the hydrogen bonding compound to have a 9-fluorenylmethyloxycarbonyl group in terms of the stability of the hydrogen bonding compound.

[0050] It is preferable that the content of the above hydrogen bonding compound be within the range of 0.5 to 30 mass% with respect to the cellulose acylate resin in terms of the stability of the cellulose acylate film.

[0051] It is desirable that the width of the cellulose acylate film be 2500 mm or more, as this allows it to be applied to polarizing plates for large displays.

[0052] The method for manufacturing a cellulose acylate film of the present invention is characterized by stretching the film in the TD direction by a ratio of 1.6 times or more. By making the stretching ratio in the TD direction 1.6 times or more, it is possible to manufacture a film with a width of 2500 mm or more while suppressing the cost of manufacturing equipment.

[0053] The cellulose acylate film of the present invention is suitable for use in a polarizing plate. In addition, the polarizing plate is suitable for use in a liquid crystal display device.

[0054] Hereinafter, the present invention, its components, and forms and modes for carrying out the present invention will be described. Additionally, in this document, "to" is used to mean including the numerical values ​​described before and after it as lower and upper limits.

[0055] [Overview of the Cellulose Acylate Film of the Present Invention]

[0056] The cellulose acylate film of the present invention is characterized by containing a hydrogen bonding compound that satisfies the requirements of (A) below and satisfying the optical value of (B) below.

[0057] (A): It has a fluorene backbone and has an atomic group containing an amide bond at the 9th position of the fluorene backbone, or has a carbazole backbone and has an atomic group containing an amide bond at the 9th position of the carbazole backbone.

[0058] (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 ratio of the retardation values ​​Rt / Ro is in the range of 2.0 to 5.5.

[0059] Equation (i) Ro=(n x -n y )×d

[0060] Equation (ii) Rt={(n x +n y ) / 2-n z}×d

[0061] (Among the above equations (i) and (ii), n x represents the refractive index in direction x where the refractive index is maximum in the in-plane direction of the film. y n represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the film. z represents the refractive index in the thickness direction z of the film. The above refractive index was measured at a wavelength of 550 nm under an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.)

[0062] <Requirements of (A)>

[0063] The above hydrogen bonding compound has a fluorene backbone and has an atomic group containing an amide bond at the 9th position of the fluorene backbone, or has a carbazole backbone and has an atomic group containing an amide bond at the 9th position of the carbazole backbone.

[0064] Examples of atomic groups containing an amide bond at the 9th position of the fluorene backbone include amide bonds, urethane bonds, and urea bonds. Among these, amide bonds and urethane bonds are preferred.

[0065] Examples of atomic groups containing an amide bond at the 9th position of the carbazole backbone include amide bonds, urethane bonds, and urea bonds. Among these, amide bonds and urethane bonds are preferred.

[0066] <Requirements of (B)>

[0067] The above cellulose acylate film has a retardation value Ro in the range of 40 to 70 nm, a retardation value Rt in the range of 100 to 220 nm, and a ratio of retardation values ​​Rt / Ro in the range of 2.0 to 5.5. Additionally, the retardation values ​​Ro and Rt are values ​​for light of wavelength 550 nm under an environment of 23°C and 55% RH.

[0068] The above retardation values ​​Ro and Rt are each defined by the following formulas.

[0069] Equation (i) Ro=(n x -n y )×d

[0070] Equation (ii) Rt={(n x +n y ) / 2-n z}×d

[0071] (Among the above equations (i) and (ii), n x represents the refractive index in direction x where the refractive index is maximum in the in-plane direction of the film. y n represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the film. z represents the refractive index in the thickness direction z of the film. The above refractive index was measured at a wavelength of 550 nm under an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.)

[0072] 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.

[0073] It is more preferable that the ratio of the retardation value (Rt / Ro) be within the range of 2.0 to 4.5. By having the ratio value within the above range, the viewing angle can be improved.

[0074] Means for satisfying the above specific range of retardation values ​​Ro and Rt and the ratio of retardation values ​​(Rt / Ro) include using a hydrogen bonding compound according to the present invention in a cellulose acylate film, controlling stretching conditions during film manufacturing, and adjusting the thickness of the cellulose acylate film.

[0075] The hydrogen bonding compound used in the present invention is as described below. In addition, regarding the stretching conditions during film manufacturing, it is preferable to stretch the film by at least 1.6 times in the TD direction. Furthermore, the thickness of the cellulose acylate film is preferably within the range of 10 to 200 μm, more preferably within the range of 10 to 60 μm, and even more preferably within the range of 10 to 40 μm.

[0076] Under conditions of 23°C and 55% RH, the retardation values ​​Ro and Rt for light with a wavelength of 550 nm can be measured using an automatic birefringence meter. Examples of automatic birefringence meters include the "Axo Scan" (manufactured by Opt Science).

[0077] [Composition of Cellulose Asylate Film]

[0078] The above cellulose acylate film contains a hydrogen bonding compound that satisfies the requirements of (A).

[0079] In addition, the cellulose acylate film contains a cellulose acylate resin in addition to the hydrogen bonding compound mentioned above.

[0080] Hydrogen-bonding compounds

[0081] It is preferable that the above hydrogen bonding compound has both a hydrogen bonding donor group and a hydrogen bonding acceptor group within one molecule. By doing so, it can form a strong hydrogen bond with water, thereby inhibiting water from coordinating with the carbonyl group in the cellulose acylate.

[0082] Examples of functional groups acting as the above hydrogen bond donor and hydrogen bond acceptor are, for instance, as described in Table 2 on page 15 of Introduction to Hydrogen Bonding by Jeffrey, George A., Oxford UP.

[0083] In the present invention, the sum of the number of functional groups listed in this table in the above hydrogen-bonding compounds is used as the sum of the number of hydrogen bond donors (number of hydrogen-bonding donor parts) and the number of hydrogen bond acceptors (number of hydrogen acceptor parts). Furthermore, in the case of a functional group that acts as either a hydrogen-bonding donor part or a hydrogen-bonding acceptor part, it is counted as only one of the functional groups.

[0084] Specifically, the following can be cited as functional groups acting as hydrogen bond donors, functional groups acting as hydrogen bond acceptors, and functional groups acting as either hydrogen bond donors or hydrogen bond acceptors.

[0085] (strong hydrogen bond)

[0086] A functional group that forms a strong hydrogen bond and acts as either a hydrogen-bonding donor part or a hydrogen-bonding acceptor part is shown below.

[0087]

[0088] (moderate hydrogen bonding)

[0089] Functional groups that form moderate hydrogen bonds and act as either a hydrogen-bonding donor group or a hydrogen-bonding acceptor group, functional groups that act only as a hydrogen-bonding donor group, and functional groups that act only as a hydrogen-bonding acceptor group are shown below.

[0090]

[0091] In particular, it is preferable to include "OH" or "N" as a functional group acting as a hydrogen bond donor. Additionally, it is preferable to include "C=O", "COC", or "N" as a functional group acting as a hydrogen bond acceptor.

[0092] In the above hydrogen-bonding compound, the number of bonds connecting the hydrogen-bonding donor part and the hydrogen-bonding acceptor part is preferably 0 to 3 in terms of forming hydrogen bonds with water, and 1 or 2 is more preferable.

[0093] The above hydrogen bonding compound is preferably such that the molecular weight of the hydrogen bonding compound, when divided by the sum of the number of hydrogen bond donors and hydrogen bond acceptors, is within the range of 30 to 80, and more preferably within the range of 50 to 80.

[0094] If the value obtained by dividing the above molecular weight by the sum of the number of hydrogen bond donors and hydrogen bond acceptors is excessively large, it becomes difficult for hydrogen bonding compounds to approach cellulose acylate, and the improvement effect of retardation changes accompanying environmental changes becomes small. On the other hand, if the value obtained by dividing the molecular weight by the sum of the number of hydrogen bond donors and hydrogen bond acceptors is excessively small, the interaction between hydrogen bonding compounds becomes excessively strong, which is undesirable because it results in insufficient solubility in solvents and compatibility with cellulose acylate.

[0095] In addition, the total number of aromatic ring structures of the hydrogen-bonding compound is within the range of 2 to 3, so that the molecular size of the hydrogen-bonding compound does not become excessively large. This is desirable in that it makes it easier to approach the carbonyl groups in the cellulose acylate, thereby obtaining an effect of suppressing changes in optical properties due to environmental humidity.

[0096] The above aromatic ring structure includes complex aromatic rings in addition to aromatic hydrocarbon rings.

[0097] The number of aromatic ring structures is counted as one when the aromatic rings are condensed into a condensed ring, and as multiple when the aromatic rings are connected to each other through linkers. For example, a carbon-10 aromatic ring derived from naphthalene is counted as one aromatic ring structure. Fluorene rings and carbazole rings are both counted as having two aromatic ring structures.

[0098] When the number of aromatic ring structures is 4 or more, the molecular size of the hydrogen bonding compound becomes excessively large, making it difficult to approach the carbonyl group in the cellulose acylate, and thus reducing the inhibitory effect on changes in optical properties due to environmental humidity.

[0099] In addition, it is preferable that the hydrogen-bonding compound comprises at least one complex aromatic ring. It is desirable that the inclusion of the complex aromatic ring facilitates the formation of cyclic hydrogen bonds between the heteroatom in the complex aromatic ring and another hydrogen-bonding acceptor or hydrogen-bonding donor portion in the hydrogen-bonding compound with water.

[0100] It is preferable for the stability of the polarizer that the hydrogen bonding compound has one or fewer carboxyl groups. In addition, it is preferable for the stability of the polarizer that the hydrogen bonding compound does not have carboxyl groups.

[0101] It is preferable that the weight average molecular weight of the above hydrogen bonding compound be 300 or more, as this prevents the hydrogen bonding compound from scattering from the film when the film is heated, and it is preferable that it be within the range of 300 to 2000.

[0102] It is desirable for the above hydrogen bonding compound to have a 9-fluorenylmethyloxycarbonyl group (Fmoc group) in terms of the stability of the hydrogen bonding compound.

[0103] Preferred exemplary compounds as hydrogen bonding compounds are listed below, but the present invention is not limited to these.

[0104]

[0105]

[0106] For the above example compounds 1 to 9, the weight average molecular weight (Mw), the number of hydrogen bond donors, and the number of hydrogen bond acceptors in one molecule of the hydrogen bonding compound are shown in Table 1 below. In addition, the value (Mw / (A+D)) calculated by dividing the molecular weight (Mw) of the hydrogen bonding compound by the sum of the number of hydrogen bond donors and hydrogen bond acceptors is also shown in Table 1 below.

[0107]

[0108] The above hydrogen bonding compound is preferably contained in the cellulose acylate resin in a range of 0.5 to 30 mass%, and more preferably in a range of 1.0 to 15 mass%.

[0109] Cellulose acylate resin

[0110] 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 the hydroxyl groups (-OH) at the 2nd, 3rd, and 6th positions of the glucose units that are β-1,4-bonded to the cellulose are substituted with acyl groups. Hereinafter, the cellulose acylate resin is also referred to as cellulose acylate.

[0111] The cellulose acylate used is not particularly limited, but it is preferably an ester of a straight-chain or branched carboxylic acid having about 2 to 22 carbon atoms.

[0112] The carboxylic acid constituting the ester may be an aliphatic carboxylic acid, may form a ring, or may be an aromatic carboxylic acid.

[0113] For example, cellulose acylates can be used in which a hydrogen atom of the hydroxyl group portion of cellulose is substituted with an acyl group having 2 to 22 carbon atoms, such as an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, a valeryl group, a pivaloyyl group, a hexanoyl group, an octanoyl group, a lauroyl group, or a stearoyl group.

[0114] The carboxylic acid (acyl group) constituting the ester may have a substituent.

[0115] The carboxylic acid constituting the ester is preferably a lower fatty acid having 6 or fewer carbon atoms, and more preferably a lower fatty acid having 3 or fewer carbon atoms.

[0116] In addition, the acyl group in the cellulose acylate may be a single type or a combination of multiple acyl groups.

[0117] Specific examples of preferred cellulose acylates include, in addition to cellulose acetates such as diacetylcellulose (DAC) and triacetylcellulose (TAC), mixed fatty acid esters of cellulose in which a propionate group or a butyrate group is attached to an acetyl group, such as cellulose acetate propionate (CAP), cellulose acetate butyrate, and cellulose acetate propionate butyrate.

[0118] These cellulose acylates may be used as a single type or in combination of multiple types.

[0119] (Types and substitutions of acils)

[0120] By controlling the type and degree of substitution of acyl groups in cellulose acylate, humidity fluctuations in the phase difference can be controlled to a desired range, thereby improving the uniformity of the film thickness.

[0121] As the degree of substitution of the acyl groups in cellulose acylate decreases, the expression of phase difference improves, making thin film formation possible.

[0122] On the other hand, if the degree of substitution of the acyl group is excessively small, it is undesirable as there is a risk of deterioration in durability.

[0123] Meanwhile, as the degree of substitution of the acyl groups of cellulose acylate increases, the phase difference does not occur, so it is necessary to increase the stretching ratio during film formation, but it is difficult to stretch uniformly at a high stretching ratio, and for this reason, the variation in film thickness increases (worsens).

[0124] In addition, since the Rt humidity fluctuation, which is the retardation (phase difference) in the thickness direction, is caused by water molecules coordinating with the carbonyl groups of cellulose, the higher the degree of substitution of the acyl groups, that is, the more carbonyl groups there are in the cellulose, the worse the Rt humidity fluctuation tends to be.

[0125] It is preferable that the total degree of substitution of acyl groups in the cellulose acylate be within the range of 2.1 to 2.5.

[0126] By limiting it to this range, environmental fluctuations (especially Rt fluctuations due to humidity) can be suppressed, and film thickness uniformity can be improved.

[0127] More preferably, it is within the range of 2.2 to 2.45 in terms of improving flexibility and elongation during film formation and further improving the uniformity of the film thickness.

[0128] More specifically, the cellulose acylate satisfies both of the following formulas (a) and (b). In formulas (a) and (b), X is the degree of substitution of the acetyl group, and Y is the degree of substitution of the propionyl group or butyryl group, or a mixture thereof.

[0129] Equation (a): 2.1≤X+Y≤2.5

[0130] Equation (b): 0≤Y≤1.5

[0131] The cellulose acylate is a cellulose acetate (Y=0) and a cellulose acetate propionate (CAP) (Y; propionyl group, Y>0), which is more preferable and even more preferably a cellulose acetate with Y=0 in that it reduces film thickness variation.

[0132] The cellulose acetate that is particularly preferably used is cellulose diacetate (DAC) with a phase difference expression property, Rt humidity variation, and film thickness variation of 2.1≤X≤2.5 (more preferably 2.15≤X≤2.45).

[0133] In addition, when Y>0, the cellulose acetate propionate (CAP) particularly preferably used is 0.95≤X≤2.25, 0.1≤Y≤1.2, and 2.15≤X+Y≤2.45.

[0134] By using the aforementioned cellulose acetate or cellulose acetate propionate, a film with excellent retardation, mechanical strength, and environmental variation is obtained.

[0135] In addition, the degree of substitution of the acyl group indicates the average number of acyl groups per glucose unit and indicates whether some hydrogen atoms of the hydroxyl groups at the 2nd, 3rd, and 6th positions of the glucose unit are substituted with acyl groups.

[0136] Therefore, the maximum degree of substitution is 3.0, which means that the hydrogen atoms of the hydroxyl groups at the 2nd, 3rd, and 6th positions are all substituted with acyl groups. These acyl groups may substitute the 2nd, 3rd, and 6th positions of the glucose unit on average, or they may substitute them with a distribution.

[0137] The degree of substitution can be obtained by the method specified in ASTM-D817-96.

[0138] To obtain desired optical properties, cellulose acetates with different degrees of substitution may be mixed and used. In the above case, the mixing ratio of the different cellulose acetates is not particularly limited.

[0139] The number average molecular weight (Mn) of cellulose acylate is 2×10 4 Up to 3×10 5 Within the range of, furthermore 2×10 4 Up to 1.2×10 5 The range of is desirable. Furthermore, the number average molecular weight is 4×10 4 Up to 8×10 4 If it is within the range, it is desirable from the perspective of increasing the mechanical strength of the resulting film.

[0140] The number average molecular weight Mn of cellulose acylate is calculated by measurement using gel permeation chromatography (GPC) under the measurement conditions described above.

[0141] The weight-average molecular weight (Mw) of cellulose acylate is 2×10 4 Up to 1×10 6 Within the range of, furthermore 2×10 4 Up to 1.2×10 5The range of is desirable. Furthermore, the weight-average molecular weight is 4×10 4 Up to 8×10 4 If it is within the range, it is desirable from the perspective of increasing the mechanical strength of the resulting film.

[0142] The cellulose used as a raw material for cellulose acylate is not particularly limited, but examples include cotton lint, wood pulp, kenaf, etc.

[0143] In addition, the cellulose acylates obtained from them can be mixed and used in any proportion.

[0144] Cellulose acylates such as cellulose acetate and cellulose acetate propionate can be manufactured by known methods.

[0145] Generally, raw cellulose is mixed with a specified organic acid (acetic acid, propionic acid, etc.), an acid anhydride (acetic anhydride, propionic anhydride, etc.), and a catalyst (sulfuric acid, etc.) to esterify the cellulose, and the reaction is carried out until the cellulose triester is formed.

[0146] In triesters, the three hydroxyl groups of the glucose unit are substituted with acyl groups of an organic acid.

[0147] By using two types of organic acids at the same time, mixed ester-type cellulose acylates, such as cellulose acetate propionate or cellulose acetate butyrate, can be produced.

[0148] Next, a cellulose acylate having a desired degree of acyl substitution is synthesized by hydrolyzing a cellulose tryster.

[0149] Subsequently, cellulose acylate is completed through processes such as filtration, precipitation, washing, dehydration, and drying. Specifically, it can be synthesized by referring to the method described in Japanese Patent Publication No. Hei 10-45804.

[0150] Other Additives

[0151] The cellulose acylate film of the present invention may contain the following as other additives.

[0152] (Plasticizer)

[0153] The above cellulose acylate film preferably contains at least one plasticizer for the purpose of imparting processability to, for example, a polarizing plate protective film.

[0154] It is preferable to use plasticizers alone or in a mixture of two or more types.

[0155] 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, effective control of moisture permeability and high compatibility with cellulose acylates, etc., can be achieved.

[0156] It is desirable that the plasticizer has a molecular weight of 15,000 or less, and furthermore 10,000 or less, from the perspective of achieving both improved heat resistance and compatibility with cellulose acylates, etc.

[0157] When the compound with a molecular weight of 10,000 or less is a polymer, it is preferable that the weight average molecular weight (Mw) be 10,000 or less.

[0158] The preferred range of weight average molecular weight (Mw) is within the range of 100 to 10000, and more preferably within the range of 400 to 8000.

[0159] In particular, to obtain the effects of the present invention, it is preferable to contain a compound having a molecular weight of 1500 or less in a range of 0.5 to 40 parts by mass per 100 parts by mass of cellulose acylate resin, and more preferable to contain it in a range of 1.0 to 20 parts by mass.

[0160] It is desirable to include it within the above range so that effective control of moisture permeability and compatibility with the substrate resin can be achieved.

[0161] Sugar ester

[0162] The cellulose acylate film of the present invention may contain a sugar ester compound for the purpose of preventing hydrolysis.

[0163] Specifically, as a sugar ester compound, a sugar ester having at least one or more and 12 or fewer of at least one type of pyranose structure or furanose structure, and having all or part of the OH groups of the structure esterified, may be used.

[0164] Polyester

[0165] The cellulose acylate film of the present invention may also contain polyester.

[0166] Polyesters are not particularly limited, but, for example, polymers with hydroxyl groups at the ends (polyester polyols) obtained by the condensation reaction of dicarboxylic acids or their ester-forming derivatives with glycols, or polymers in which the hydroxyl groups at the ends of the polyester polyols are sealed with monocarboxylic acids (end-sealed polyesters) may be used.

[0167] The ester-forming derivatives referred to here are esters of dicarboxylic acids, dicarboxylic acid chlorides, and anhydrous dicarboxylic acids.

[0168] Styrene compounds

[0169] 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.

[0170] The styrene-based compound may be a homopolymer of a styrene-based monomer, or a copolymer of a styrene-based monomer and other copolymer monomers.

[0171] In order for the molecular structure to have a volume of at least a certain amount, the content ratio of constituent units derived from styrene monomers in a styrene-based compound may preferably be within the range of 30 to 100 mol%, and more preferably within the range of 50 to 100 mol%.

[0172] 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; vinylbenzoic acids such as 3-vinylbenzoic acid and 4-vinylbenzoic acid; 4-vinylbenzyl acetate; and 4-acetoxystyrene. Amide styrenes such as 2-butylamidestyrene, 4-methylamidestyrene, p-sulfonamidestyrene; amino styrenes such as 3-aminostyrene, 4-aminostyrene, 2-isopropenianiline, vinylbenzyldimethylamine; nitrostyrenes such as 3-nitrostyrene, 4-nitrostyrene; cyanostyrenes such as 3-cyanostyrene, 4-cyanostyrene; vinylphenylacetonitrile; aryl styrenes such as phenylstyrene; indenes, etc. are included.

[0173] Styrene-based monomers may be one type or a combination of two or more types.

[0174] <Arbitrary component>

[0175] The cellulose acylate film of the present invention may include other optional components such as antioxidants, colorants, UV absorbers, matting agents, acrylic particles, hydrogen-bonding solvents, and ionic surfactants.

[0176] These components may be added in the range of 0.01 to 20 parts by mass per 100 parts by mass of cellulose acylate resin.

[0177] (Antioxidant)

[0178] The cellulose acylate film of the present invention may use commonly known antioxidants.

[0179] In particular, lactone-based, sulfur-based, phenol-based, double-bond-based, hindered amine-based, and phosphorus-based compounds can be preferably used.

[0180] These antioxidants, etc. are added in a range of 0.05 to 20 mass%, preferably in a range of 0.1 to 1 mass%, with respect to the cellulose acylate resin, which is the main raw material of the cellulose acylate film.

[0181] These antioxidants, etc., can achieve a synergistic effect by using several types of compounds from different systems in combination rather than using only one type.

[0182] For example, the combined use of lactone-based, phosphorus-based, phenol-based, and double-bond-based compounds is desirable.

[0183] (coloring agent)

[0184] The cellulose acylate film of the present invention preferably includes a coloring agent for color adjustment within a range that does not impair the effects of the present invention.

[0185] The term "coloring agent" refers to a dye or pigment, and in the present invention, it refers to having the effect of making the color tone of a liquid crystal screen blue, adjusting the yellow index, or reducing haze.

[0186] Various dyes and pigments can be used as coloring agents, but anthraquinone dyes, azo dyes, and phthalocyanine pigments are effective.

[0187] (UV absorber)

[0188] Since the cellulose acylate film of the present invention may be used on the viewing side or backlight side of a polarizer, it may contain an ultraviolet absorber for the purpose of imparting an ultraviolet absorption function.

[0189] As for ultraviolet absorbers, they are not particularly limited, but examples include ultraviolet absorbers such as benzotriazole-based, 2-hydroxybenzophenone-based, or salicylic acid phenyl ester-based absorbers.

[0190] 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.

[0191] The above-mentioned ultraviolet absorber can be used as a single type or in combination of two or more types.

[0192] The amount of UV absorber used is not uniform depending on the type of UV absorber, usage conditions, etc., but generally, it is added in the range of 0.05 to 10 mass%, preferably in the range of 0.1 to 5 mass%, with respect to the cellulose acylate resin.

[0193] (microparticles)

[0194] In the cellulose acylate film of the present invention, it is preferable to add fine particles that impart slipperiness to the film.

[0195] In particular, adding fine particles is effective from the perspective of improving the slipperiness of the surface of the cellulose acylate film, improving the slipperiness during winding, and preventing the occurrence of scratches or blocking.

[0196] As for the fine particles, either inorganic fine particles or organic fine particles may be used as long as they do not impair the transparency of the obtained cellulose acylate film and have heat resistance when melted, but inorganic fine particles are more preferable.

[0197] These microparticles can be used alone or in combination of two or more types.

[0198] High transparency and slipperiness can be achieved simultaneously by using particles with different particle sizes or shapes (e.g., needle-shaped and spherical).

[0199] Among the compounds constituting the above-mentioned fine particles, silicon dioxide is particularly preferably used because it has excellent transparency (haze) due to having a refractive index close to that of cellulose acylate resin.

[0200] As specific examples of silicon dioxide, commercially available products having trade names such as Aerosil (registered trademark) 200V, Aerosil (registered trademark) R972V, Aerosil (registered trademark) R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (all manufactured by Nippon Aerosil Co., Ltd.), Seahorstar (registered trademark) KEP-10, Seahorstar (registered trademark) KEP-30, Seahorstar (registered trademark) KEP-50 (all manufactured by Nippon Shokubai Co., Ltd.), Silophovic (registered trademark) 100 (manufactured by Fuji Silicia Co., Ltd.), Nipsil (registered trademark) E220A (manufactured by Nippon Silica Kogyo Co., Ltd.), and Admafine (registered trademark) SO (manufactured by Admatex Co., Ltd.) are preferably used. It can be used.

[0201] Regarding the shape of the particles, they can be irregular, needle-shaped, flat, spherical, etc., without any particular restrictions; however, using spherical particles is particularly desirable as it can improve the transparency of the resulting film.

[0202] Since a particle size close to the wavelength of visible light causes light scattering and reduces transparency, it is desirable for the particle size to be smaller than the wavelength of visible light, and also desirable for it to be less than or equal to half the wavelength of visible light.

[0203] If the particle size is excessively small, the slipperiness may not be improved, so it is particularly desirable to have a size within the range of 80 to 180 nm.

[0204] In addition, particle size refers to the size of the aggregate when the particle is an aggregate of primary particles.

[0205] In addition, if the particle is not spherical, it refers to the diameter of the circle corresponding to its projected area.

[0206] It is preferable that fine particles be added to the base resin in a range of 0.05 to 10 mass%, preferably in a range of 0.1 to 5 mass%.

[0207] [Method for manufacturing cellulose acylate film]

[0208] The method for manufacturing the above cellulose acylate film may be a solution softening method or a melt softening method. Among these, a solution softening method is preferred.

[0209] A method for manufacturing a film by the solution stretching method comprises a process of preparing a dope, a process of stretching the dope onto a metal support, a process of drying the web, and a process of peeling the film from the metal support. Additionally, a method for manufacturing a film by the solution stretching method comprises a process of stretching or maintaining the width of the peeled film, a process of drying the film, and a process of winding the finished film.

[0210] (1) Process of preparing dope

[0211] In the process of preparing the dope, the dope is prepared by dissolving cellulose acylate and additives in a solvent. The concentration of cellulose acylate in the dope is desirable because it can reduce the drying load after flexibility on a metal support. In addition, by not making the concentration of cellulose acylate excessively high, the pressure load during filtration can be suppressed, thereby obtaining good filtration precision. From this perspective, the content of cellulose acylate is preferably within the range of 10 to 35 mass% with respect to the total mass of the dope, and more preferably within the range of 15 to 25 mass%.

[0212] The solvent used in the preparation of the dope may be a single type or two or more types. However, from the perspective of production efficiency, it is preferable to mix a good solvent and a poor solvent for cellulose acylate, and from the perspective of the solubility of cellulose acylate, it is preferable to have a larger amount of the good solvent. The mixing ratio of the good solvent and the poor solvent is preferably such that the good solvent is within the range of 70 to 98 mass% and the poor solvent is within the range of 2 to 30 mass%. In addition, a solvent that dissolves cellulose acylate alone is defined as a "good solvent," and a solvent that does not swell or dissolve alone is defined as a "poor solvent."

[0213] As solvents, there are no particular limitations, and examples include organic halogen compounds (methylene chloride, etc.), dioxolanes, acetone, methyl acetate, methyl acetoacetate, etc. Among these, methylene chloride or methyl acetate is preferred. As solvents, there are no particular limitations, and examples include methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc.

[0214] It is preferable that the dope contains water in the range of 0.01 to 2 mass%. The solvent used for dissolving the cellulose acylate may be the solvent removed from the film by drying, recovered and reused. The recovered solvent may contain trace amounts of additives (e.g., plasticizers, UV absorbers, polymers, monomer components, etc.). The recovered solvent may be reused even if it contains additives. If necessary, the recovered solvent may be purified and reused.

[0215] When preparing the dope, known methods may be used for dissolving the cellulose acylate. For example, by combining a heating means and a pressurizing means, the dope can be heated above the boiling point at atmospheric pressure. If the cellulose acylate is stirred and dissolved while heating the solvent at a temperature above the boiling point at atmospheric pressure and within a range where the solvent does not boil under pressure, the formation of bulky undissolved products (gels or lumps) can be prevented. Additionally, the cellulose acylate may be mixed with a solvent to wet or swell it, and then dissolved by adding both solvents.

[0216] 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. It is preferable to perform the heating from the outside; for example, a jacket type is preferred as it facilitates temperature control.

[0217] From the perspective of the solubility of cellulose acylate, a high heating temperature is preferable. In addition, by not raising the heating temperature excessively, the pressure load can be suppressed, thereby achieving good productivity. From this perspective, 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°C to 105°C. The pressure is adjusted so that the solvent does not boil at the set temperature.

[0218] Other methods for dissolving cellulose acylate include the cooling dissolution method. By the cooling dissolution method, cellulose acylate can be dissolved in a solvent such as methyl acetate.

[0219] A cellulose acylate solution is filtered using a suitable filter material, such as filter paper. From the perspective of removing insoluble matter, it is preferable for the filter material to have a small absolute filtration precision. In addition, by not making the absolute filtration precision excessively small, clogging of the filter material can be suppressed. From this perspective, the absolute filtration precision of the filter material is preferably 0.008 mm or less, more preferably within the range of 0.001 to 0.008 mm, and even more preferably within the range of 0.003 to 0.006 mm.

[0220] The material of the filter media is not particularly limited, and known filter media may be used. From the perspective of preventing fiber shedding, the filter media is preferably made of plastic (polypropylene, Teflon (registered trademark), etc.) or metal (stainless steel, etc.). Through filtration, impurities contained in the cellulose acylate of the raw material, particularly white spot foreign matter, can be removed or reduced.

[0221] Two polarizing plates are arranged in a cross-Nicol configuration, and a second optical film is placed between them. Then, light is irradiated from one polarizing plate side and observed from the other polarizing plate side. At this time, any spot where light leaking from the opposite side is visible is referred to as a "bright spot foreign matter." 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 even more preferably 50 / cm² or less, and particularly preferably within the range of 0 to 10 / cm². Additionally, the number of bright spots with a diameter of 0.01 mm or less is also preferably low.

[0222] For the filtration of the dope, known methods may be used. Among these, a method of filtering while heating the solvent at a temperature above the boiling point at atmospheric pressure and within a range where the solvent does not boil under pressure is preferred. In this method, the increase in the difference in filtration pressure (differential pressure) before and after filtration is small. 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.

[0223] It is preferable for the filtration pressure to be low. It is preferable for the filtration pressure to be 1.6 MPa or less, more preferable for it to be 1.2 MPa or less, and even more preferable for it to be 1.0 MPa or less.

[0224] Various additives may be added in batches, or an additive solution may be prepared separately and added inline. In particular, when adding fine particles to the dope, it is desirable to add some or all of them inline from the perspective of reducing the load of the fine particles on the filter material.

[0225] When adding the additive solution in-line, it is preferable to add and dissolve a small amount of acetylcellulose in the additive solution for the sake of miscibility with the dope. The amount of acetylcellulose added is preferably within the range of 1 to 10 mass% with respect to the total mass of the solvent, and more preferably within the range of 3 to 5 mass%.

[0226] Inline addition and mixing can be performed using, for example, static mixers, inline mixers, etc. Examples of static mixers include those manufactured by Toray Engineering. Examples of inline mixers include the Toray stationary in-pipe mixer "Hi-Mixer SWJ" (manufactured by Toray Engineering).

[0227] (2) Process of bending the dope onto a metal support

[0228] In the process of spreading the dope onto a metal support, the dope is spread onto an infinitely spreading, continuous metal support. The metal support in the spreading (casting) process preferably has a mirror-finished surface. The metal support is preferably a stainless steel belt or a drum with a plated surface made by casting. The width of the cast is preferably within the range of, for example, 1 to 4 m.

[0229] (3) Process of drying the web

[0230] In the process of drying the web, a flexible dope is dried as a web on a metal support.

[0231] It is preferable that the surface temperature of the metal support be within a range of -50°C or higher and below the boiling point of the solvent. A higher surface temperature can accelerate the drying speed of the web. In addition, by not making the surface temperature excessively high, foaming of the web is prevented, and good flatness of the film is obtained. From this perspective, it is preferable that the surface temperature be within a range of 0 to 40°C, and more preferable that it be within a range of 5 to 30°C. Furthermore, by cooling the metal support, the web can be gelled, and the film can be peeled from the drum while containing a large amount of residual solvent.

[0232] Methods for controlling the temperature of the metal support are not particularly limited and may include, for example, blowing hot or cold air. Additionally, a method of bringing hot water into contact with the other side of the metal support may be used. Since the method using hot water allows for efficient heat transfer, the time required for the temperature of the metal support to reach a constant level can be shortened. When using hot air, air at a temperature higher than the target temperature of the metal support may be used.

[0233] (4) Process of peeling the film from the metal support

[0234] From the perspective of obtaining good flatness of the film, the amount of residual solvent when peeling the film (web) from the metal support is preferably within the range of 10 to 150 mass%. The amount of residual solvent is more preferably within the range of 10 to 40 mass% or 60 to 130 mass%, and even more preferably within the range of 10 to 30 mass% or 70 to 120 mass%. Here, the amount of residual solvent is defined by the following formula.

[0235] Residual solvent amount [mass%] = {(MN) / N} × 100

[0236] In the formula, M is the mass of the web or film sample. N is the mass of the web or film sample after heating it at 115°C for 1 hour. Additionally, the web or film sample may be taken at any point during or after manufacturing.

[0237] (5) Process of stretching or maintaining the width of the peeled film

[0238] In the process of stretching or width-holding the peeled film, the film with a large amount of residual solvent immediately after peeling is stretched or width-holded. It is preferable to use a tenter method in which the film is stretched in the conveying direction (longitudinal direction, MD direction) and both ends of the film are gripped with clips, etc. Additionally, it may be stretched simultaneously in the conveying direction and the width direction (transverse direction, TD direction).

[0239] In the elongation in the MD direction, the peeling tension is preferably 210 N / m or more, and more preferably within the range of 220 to 300 N / m.

[0240] By the stretching process, the refractive index of the film can be controlled, and thus the retardation values ​​Ro and Rt can be controlled.

[0241] The final elongation ratio is preferably within the range of 1.0 to 2.0 times in the MD direction, and more preferably within the range of 1.01 to 1.5 times. The final elongation ratio is preferably 1.6 times or more in the TD direction, and preferably within the range of 1.7 to 2.5 times.

[0242] 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. 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.

[0243] The method of stretching the film is not particularly limited. For example, as a stretching method, a method of stretching the film in the longitudinal direction can be used by setting a difference in peripheral speed between multiple rollers and utilizing the difference in roller peripheral speed between them.

[0244] As for the stretching method, one can fix both ends of the film with clips or pins and extend the spacing between the clips or pins in the conveying direction to stretch the film in the vertical direction. Similarly, one can extend the film in the horizontal direction by extending the spacing between the clips or pins in the width direction. Likewise, one can extend the film in both the vertical and horizontal directions by extending the spacing between the clips or pins simultaneously in both the conveying and width directions.

[0245] These stretching methods may be used in combination. In addition, in the case of the tenter method, if the clip part is driven by a linear drive, smooth stretching can be achieved and the risk of film breakage can be reduced.

[0246] It is preferable to perform such width maintenance or transverse stretching by a tenter method, and it may be a pin tenter or a clip tenter.

[0247] If the leading axis or the terminating axis of the film exists within the film plane and the angle formed with the transport direction is denoted as θ1, then 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 an orientation angle.

[0248] θ1 can be measured using an automatic birefringent meter “KOBRA-21ADH” (Oji Keisoku Kiki). Since θ1 is within the above range, high brightness is obtained in the displayed image. In addition, light leakage can be suppressed or prevented, so colors can be faithfully reproduced in a color liquid crystal display device.

[0249] (6) Process of further drying the film

[0250] In the process of further drying the film, the peeled film is further dried. Drying may be performed after stretching or simultaneously.

[0251] The residual solvent amount of the film after drying is preferably 1 mass% or less, more preferably 0.1 mass% or less, and even more preferably 0.01 mass% or less.

[0252] The drying method is not particularly limited, and, for example, a roller drying method in which the film is alternately passed through a plurality of rollers arranged vertically to dry it may be used. In addition, the film may be stretched by the above tenter method while simultaneously drying the film.

[0253] The means for drying the film are not particularly limited and may include, for example, hot air, infrared rays, heating rollers, microwaves, etc. For the sake of convenience, it is preferable that the drying means be hot air.

[0254] It is preferable to gradually increase the drying temperature within the range of 40 to 220°C. From the perspective of dimensional stability, it is more preferable that the drying temperature be within the range of 50 to 140°C.

[0255] (7) Process of winding the finished film

[0256] It is preferable that the finished film be stored, for example, wound into a roll.

[0257] [Physical properties of cellulose acylate film]

[0258] ·thickness

[0259] The thickness of the film is preferably within the range of 10 to 200 μm, more preferably within the range of 10 to 60 μm, and even more preferably within the range of 10 to 40 μm.

[0260] ·width

[0261] The width of the film is preferably within the range of 1,000 to 4,000 mm, and is preferably 2,500 mm or more in that it can be applied to a polarizing plate for a large display.

[0262] [Polarizing plate]

[0263] The cellulose acylate film of the present invention is suitable for use in polarizing plates.

[0264] Figure 1 is a cross-sectional view of the basic layer configuration of a polarizer.

[0265] The polarizing plate (1) comprises the cellulose acylate film of the present invention as the first optical film (2), the polarizer (4), and the second optical film (5) in that order. The polarizing plate (1) may additionally have any additional layer as needed. For example, it may have other layers between the first optical film (2) and the polarizer (4). Additionally, it may have other layers between the polarizer (4) and the second optical film (5).

[0266] <First Optical Film>

[0267] The first optical film is an optical film that functions as a protective film, a phase difference film, etc., in a polarizer.

[0268] The first optical film contains, for example, polyester, cellulose acylate, or an ultraviolet absorber.

[0269] The polyester is preferably polyethylene terephthalate or polyethylene naphthalate. Polyethylene terephthalate and polyethylene naphthalate have high intrinsic birefringence, so it is relatively easy to obtain high phase difference values ​​even when the film is thin. In particular, the effect is remarkable for polyethylene naphthalate.

[0270] As a film containing cellulose acylate, a commercially available cellulose acylate film may be used.

[0271] UV absorbers protect the liquid crystal display (especially the alignment layer of the liquid crystal cell) from ultraviolet rays, thereby improving the weather resistance of the liquid crystal display.

[0272] Examples of ultraviolet absorbers include cyclic iminoester-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, salicylic acid ester-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and triazine-based ultraviolet absorbers. Among these, it is preferable that the ultraviolet absorber be a cyclic iminoester-based ultraviolet absorber or a benzotriazole-based ultraviolet absorber.

[0273] The content of the ultraviolet absorber is preferably in the range of 0.1 to 10 mass% with respect to the total mass of the polyester.

[0274] The retardation value Ro of the first optical film for light of a wavelength of 550 nm under an environment of 23°C and 55% RH is preferably within the range of 3,000 to 30,000 nm. Since Ro is 3,000 nm or higher, interference color (rainbow stains depending on the observation angle) when the first optical film (10) is observed in an oblique direction can be reduced, and good visibility is obtained. In addition, since Ro is 30,000 nm or lower, the thickness of the first optical film (10) can be made thin. Ro is preferably 5,000 nm or higher, more preferably 8,000 nm or higher, and more preferably 10,000 nm or higher.

[0275] 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. By having a thickness of 5 μm or more, the first optical film can obtain 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. By having a thickness of 100 μm or less, the first optical film can achieve both thinness and visibility.

[0276] Polarizer

[0277] In the present invention, "polarizer" refers to a device that transmits only light of a polarization plane in a certain direction, and also refers to a layer including said device.

[0278] Examples of polarizers include polyvinyl alcohol-based polarizing films. Polyvinyl alcohol-based polarizing films include polyvinyl alcohol-based films dyed with iodine and films dyed with dichromatic dyes.

[0279] As a method for manufacturing a polarizer, a polyvinyl alcohol aqueous solution film can be formed, and the resulting film can be uniaxially stretched and dyed. Additionally, after dyeing, the film may be uniaxially stretched and then subjected to a durability treatment with a boron compound or the like.

[0280] The thickness of the polarizer is preferably within the range of 2 to 30 μm, and more preferably within the range of 2 to 20 μm.

[0281] Examples of polyvinyl alcohol include ethylene-modified polyvinyl alcohol described in Japanese Patent Publication No. 2003-248123 and Japanese Patent Publication No. 2003-342322.

[0282] The ethylene-modified polyvinyl alcohol has an ethylene unit content in the range of 1 to 4 mol%, a degree of polymerization in the range of 2000 to 4000, and a degree of saponification in the range of 99.0 to 99.99 mol%. Among these, it is preferable that the ethylene-modified polyvinyl alcohol has a hot water cutting temperature in the range of 66 to 73°C.

[0283] This ethylene-modified polyvinyl alcohol polarizing film has excellent polarization performance and durability performance, and has low color staining, making it particularly suitable for use in large liquid crystal display devices.

[0284] [Method for manufacturing a polarizing plate]

[0285] The polarizing plate of the present invention can be manufactured by a general method.

[0286] The side of the first optical film facing the polarizer is appropriately surface-treated, and at least one side of the polarizer, which is produced by immersion stretching in an iodine solution, is bonded using a UV-curing adhesive or a water-based adhesive as described later. A second optical film (the cellulose acylate film of the present invention) is bonded to the other side of the polarizer in the same manner.

[0287] For the bonding orientation with the polarizer, it is preferable to bond in such a way that, for example, the absorption axis of the polarizer and the ground axis of each optical film are orthogonal.

[0288] (1) UV-curing adhesive

[0289] The polarizing plate of the present invention is preferably manufactured by bonding the optical film and the polarizer using a UV-curing adhesive. By using a UV-curing adhesive, a polarizing plate with high strength and excellent flatness is obtained even when thin.

[0290] (Composition of UV-curing adhesive)

[0291] Examples of UV-curing adhesive compositions for polarizing plates include photoradical polymerization compositions utilizing photoradical polymerization and photocationic polymerization compositions utilizing photocationic polymerization. Additionally, examples of UV-curing adhesive compositions for polarizing plates include hybrid compositions utilizing both photoradical polymerization and photocationic polymerization.

[0292] Examples of photoradical polymerization compositions include the composition described in Japanese Patent Publication No. 2008-009329. The said composition contains a radical polymerizable compound containing polar groups such as hydroxyl groups and carboxyl groups, and a radical polymerizable compound not containing polar groups, in specific proportions.

[0293] The radical polymerizable compound contained in the photo-radical polymerization type composition is preferably a compound having an ethylenically unsaturated bond capable of radical polymerization. Examples of compounds having an ethylenically unsaturated bond capable of radical polymerization include compounds having a (meth)acryloyl group. Examples of compounds having a (meth)acryloyl group include N-substituted (meth)acrylamide compounds, (meth)acrylate compounds, etc.

[0294] Furthermore, (meth)acryloyl group means acryloyl group or methacryloyl group, and (meth)acrylate means acrylate or methacrylate. Also, (meth)acrylamide means acrylamide or methacrylamide.

[0295] Examples of photocationic polymerization compositions include, for instance, the composition described in Japanese Patent Publication No. 2011-028234. The composition comprises (α) a cationic polymerizable compound, (β) a photocationic polymerization initiator, (γ) a photosensitizer that exhibits maximum absorption of light with a wavelength longer than 380 nm, and (δ) a naphthalene-based photosensitizer.

[0296] Examples of cationic polymerizable compounds include epoxy compounds and oxetane compounds.

[0297] UV-curing adhesives are not limited to these, and known ones may be used.

[0298] (2) Method for manufacturing a polarizing plate

[0299] After pre-treating the optical film and polarizer, a UV-curing adhesive is applied. Subsequently, the optical film and polarizer are bonded using the UV-curing adhesive. Then, the UV-curing adhesive is cured.

[0300] (2.1) Pretreatment Process

[0301] In the pretreatment process, an adhesion facilitation treatment is performed on the bonding surface between the optical film and the polarizer. Examples of adhesion facilitation treatments include corona treatment and plasma treatment.

[0302] (2.2) Coating Process

[0303] In the coating process, the UV-curing adhesive is applied to at least one of the bonding surfaces of the optical film and the polarizer. When the UV-curing adhesive is applied directly to the surface of the optical film or the polarizer, the application method is not limited. Examples of application methods include a doctor blade, a wire bar, a die coater, a comma coater, a gravure coater, and various wet coating methods can be used. Additionally, after applying the UV-curing adhesive between the optical film and the polarizer, the UV-curing adhesive may be uniformly spread by applying pressure with a roller or the like.

[0304] (2.3) Bonding Process

[0305] In the bonding process, when a UV-curing adhesive is applied to the surface of the polarizer in the preceding coating process, an optical film is superimposed on the UV-curing adhesive. When a UV-curing adhesive is applied to the surface of the optical film, the polarizer is superimposed on the UV-curing adhesive.

[0306] When a UV-curing adhesive is applied between an optical film and a polarizer, the optical film and the polarizer overlap each other in that state. Typically, in this state, pressure is applied from the optical film sides on both sides using a pressure roller or similar device. Examples of materials for the pressure roller include metal or rubber. The pressure rollers placed on both sides may be made of the same material or different materials.

[0307] (2.4) Curing Process

[0308] In the curing process, ultraviolet light is irradiated onto the applied UV-curable adhesive. The UV-curable adhesive is then cured to bond the superimposed optical film and the polarizer through the UV-curable adhesive. In the present invention, a light-transmitting optical film is superimposed on each side of the polarizer through the UV-curable adhesive. In this state, it is preferable to irradiate ultraviolet light to simultaneously cure the UV-curable adhesives on both sides.

[0309] The conditions for irradiating ultraviolet light are not particularly limited, as long as they are conditions capable of curing the ultraviolet-curing adhesive. The amount of ultraviolet light irradiated is preferably within the range of 50 to 1500 mJ / cm² as an integrated light amount, and more preferably within the range of 100 to 500 mJ / cm². In the present invention, irradiating ultraviolet light from the second optical film side is preferable from the viewpoint of improving yield.

[0310] When manufacturing a polarizing plate using a continuous line, the line speed is preferably within the range of 1 to 500 m / min, more preferably within the range of 5 to 300 m / min, and even more preferably within the range of 10 to 100 m / min.

[0311] Productivity can be secured by having a line speed of 1 m / min or more. In addition, damage to the optical film can be suppressed, so a polarizing plate with excellent durability is obtained.

[0312] By keeping the line speed at 500 m / min or less, the UV-curable adhesive can be sufficiently cured. An adhesive layer with the desired hardness and excellent adhesion can be formed. Additionally, it is desirable to adjust the line speed in consideration of the curing time of the adhesive.

[0313] [Liquid Crystal Display]

[0314] 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 is equipped with the polarizing plate, and it is preferable that the second optical film (cellulose acylate film of the present invention) is disposed on the liquid crystal cell side. By providing the polarizing plate, color stains and fluctuations in contrast caused by functions can be suppressed.

[0315] The above polarizer can be used in liquid crystal display devices of various driving types, such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, and OCB. Among these, it is preferable to use it in a VA-type liquid crystal display device.

[0316] In a liquid crystal display, two polarizing plates are typically used: one on the viewing side and one on the backlight side. The polarizing plates may be used as polarizing plates on both sides or as polarizing plates on one side.

[0317] A liquid crystal cell according to the present invention comprises a liquid crystal layer and a pair of substrates that support the liquid crystal layer. For the sake of thinning and reducing the weight of a display device, the pair of substrates is preferably a glass substrate with a thickness in the range of 0.3 to 0.7 mm.

[0318] FIG. 2 is a schematic cross-sectional view illustrating 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).

[0319] In FIG. 2, a liquid crystal cell (101C) is formed by fitting and supporting both sides of a liquid crystal layer (107) with glass substrates (108A and 108B) as transparent substrates. Polarizing plates (101A and 101B) are arranged on each surface of each glass substrate (108A and 108B) with an adhesive layer (106) interposed therebetween, thereby forming a display device (100).

[0320] In the polarizing plates (101A and 101B), the first optical film is bonded at positions 102A and 102B, and the second optical film is bonded at positions 105A and 105B.

[0321] The optical films are each bonded to polarizers (104A and 104B) by means of UV-curing adhesives (103A to 103D).

[0322] The liquid crystal cell (101C) is provided with an alignment layer, a transparent electrode, and a glass substrate (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 specifically, silica glass or borosilicate glass is more preferred.

[0323] It is preferable that the glass constituting the glass substrate be alkali-free glass that does not substantially contain alkali components. Specifically, it is preferable that the alkali content in the glass substrate be 1000 ppm or less.

[0324] The content of the alkali component in the glass substrate is more preferably 500 ppm or less, and even more preferably 300 ppm or less.

[0325] As it is an alkali-free glass that substantially does not contain alkali components, it is possible to suppress cloudiness caused by the exchange of cations on the surface of the optical film. By doing so, the decrease in density of the optical film surface can be suppressed, thereby preventing breakage of the glass substrate.

[0326] A glass substrate can be manufactured by known methods, such as the float method, downdraw method, and overflow downdraw method. Among these, the overflow downdraw method is preferred because, during molding, the surface of the glass substrate does not come into contact with the molding member, and it is difficult for scratches to form on the surface of the resulting glass substrate.

[0327] The glass substrate may be a commercially available product.

[0328] Examples of commercially available glass substrates include “AN100” (thickness 500 μm, manufactured by Asahi Glass Co.), “EAGLE XG(r) Slim” (thickness 300 μm, 400 μm, etc., manufactured by Corning Co.), and glass substrates (thickness in the range of 100 to 200 μm, manufactured by Nippon Denki Glass Co.).

[0329] As shown in FIG. 2, the polarizing plates (101A, 101B) and the liquid crystal cell (101C) are bonded together via an adhesive layer (106).

[0330] Examples of adhesive layers include a layer formed using double-sided tape, UV-curing adhesive, etc.

[0331] Examples of double-sided tapes include the non-material tape “MO-3005C” (thickness 25㎛, manufactured by Lintec Co., Ltd.). The bonding method is not particularly limited, and known methods may be used.

[0332] Examples

[0333] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. Furthermore, in the following examples, unless otherwise noted, the operation was performed at room temperature (25°C). Also, unless otherwise noted, "%" and "parts" mean "mass%" and "mass parts," respectively.

[0334] The cellulose acylate, additives, etc. used in the production of the optical film are as follows.

[0335] Cellulose acylate

[0336] As cellulose acylates, the following cellulose diacetate (DAC1, DAC2, DAC3), cellulose acetate propionate (CAP1, CAP2), and cellulose australacetate (CTA) were used.

[0337] DAC1: Acetyl substitution degree 2.40

[0338] DAC2: Acetyl substitution degree 2.42

[0339] CAP1: Acetyl substitution degree 1.50, propionyl substitution degree 0.95

[0340] CAP2: Acetyl substitution degree 1.50, propionyl substitution degree 0.85

[0341] CTA: Acetyl substitution degree 2.83

[0342] DAC3: Acetyl substitution degree 2.1

[0343] Additive 1 and Additive 2

[0344] As additive 1 and additive 2, the following were used.

[0345]

[0346]

[0347]

[0348] · Polycondensation ester J-31: A polycondensation ester obtained from a dicarboxylic acid in which the molar ratio of terephthalic acid (aromatic dicarboxylic acid) to succinic acid (aliphatic dicarboxylic acid) is 55:45, and a diol in which the molar ratio of ethanediol to propanediol is 45:55, and the terminal end is a propionyl ester group (this is the polycondensation ester J-31 described in Table 5 of paragraph

[0145] of Japanese Patent Publication No. 2012-82235).

[0349] Saccharose benzoate

[0350] · 1: In the following general formula (10), 5 Rs are substituted with the following substituent (benzoyl group), and the remaining 3 Rs are hydrogen atoms.

[0351]

[0352]

[0353] Dope's Josee

[0354] <Fine particle dispersion>

[0355] The following components were mixed by stirring with a dissolver for 50 minutes, then dispersed with 10,000 tons of gaulin to obtain a fine particle dispersion.

[0356] 11.0 parts by mass of fine particle "Aerosil (registered trademark) R812" (manufactured by Nippon Aerosil Co., Ltd.)

[0357] 89.0 parts by mass of ethanol

[0358] <Microp Additive Solution>

[0359] Diacetylcellulose (DAC1) with a degree of substitution of 2.40 was added to a dissolution tank containing methylene chloride and heated to completely dissolve it. Afterward, this solution was filtered using "Azumi Rosi No. 244" (manufactured by Azumi Rosi Co., Ltd.). While stirring the diacetylcellulose solution after filtration sufficiently, the above-mentioned fine particle dispersion was slowly added to it. Then, the mixture was dispersed using an atter so that the particle size of the secondary particles became a predetermined size. The obtained dispersion was filtered using "Finemet NF" (manufactured by Nihon Seisen Co., Ltd.) to prepare a fine particle addition solution.

[0360] 99.0 parts by mass of methylene chloride

[0361] 4.0 parts by mass of diacetylcellulose (DAC1)

[0362] 11.0 parts by mass of fine particle dispersion

[0363] Next, a main dope solution of the following composition was prepared.

[0364] First, methylene chloride and ethanol were added to a pressurized dissolution tank. Diacetylcellulose (DAC1) with a degree of substitution of 2.40 was added to the pressurized dissolution tank containing the solvent while stirring. This was heated and stirred to completely dissolve it. Two types of additives were also added to the solution and dissolved. The solution was filtered using "Azumi Rossi No. 244" (manufactured by Azumi Rossi Co., Ltd.) to prepare the main dope solution.

[0365] <Composition of the main dope solution>

[0366] 300.0 parts by mass of methylene chloride

[0367] 30.0 parts by mass of ethanol

[0368] 100.0 parts by mass of diacetylcellulose (DAC1)

[0369] 5.0 parts by mass of Example Compound 3 as Additive 2

[0370] 2 parts by mass of a fine particle additive solution were added to 100.0 parts by mass of the main dope solution and thoroughly mixed using an inline mixer (Toray stationary tube mixer) "Hi-Mixer, SWJ" (manufactured by Toray Engineering Co., Ltd.) to prepare the dope. In addition, the content of Example Compound 3 in the dope was 5% by mass relative to the mass of diacetylcellulose in the main dope.

[0371] <Production of Optical Film 1>

[0372] The above-described dope was uniformly stretched onto a stainless steel belt at a temperature of 22°C and a width of 2 m using a belt stretching device. On the stainless steel belt, the solvent in the web was evaporated 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.

[0373] Next, the solvent was evaporated at 35°C and the peeled film was slit. After that, the film was stretched in the width direction (TD direction) by 1.8 times its original width using a tenter stretcher at a temperature of 195°C. The amount of residual solvent in the film at the start of stretching by the tenter was 3 to 15 mass%.

[0374] Subsequently, the film was dried in a drying zone at 120°C and 140°C while being conveyed by multiple rollers. The film was slit to a width of 2500 mm, and knurling with a width of 10 mm and a height of 2.5 μm was performed on both ends of the film. Afterward, the film was wound onto a core to obtain an optical film 1 with a thickness of 35 μm and a winding length of 3900 m.

[0375] <Production of Optical Films 2 to 22>

[0376] Optical films 2 to 22 were obtained in the same manner, except that in the production of optical film 1, the type of cellulose acylate, the type and content of additive 1 and additive 2, the stretching ratio in the TD direction, and the width of the film were changed as described in the table below. The thickness of the obtained optical films is as shown in the table below.

[0377] For each obtained optical film, the retardation values ​​Ro and Rt for light with a wavelength of 550 nm were measured using an automatic birefringence meter under conditions of 23°C and 55% RH, and the measurement results are shown in the table below. An "Axo Scan" (manufactured by Opt Science) was used as the automatic birefringence meter.

[0378] Fabrication of a Polarizer

[0379] A long polyvinyl alcohol film with a thickness of 60 μm was prepared. While continuously conveying the film through a guide roller, the film was immersed in a dyeing bath (30°C) containing iodine and potassium iodide for dyeing treatment, and the film was subjected to a 2.5-fold stretching treatment. Subsequently, the film was subjected to a total of 5-fold stretching treatment and crosslinking treatment in an acidic bath (60°C) containing boric acid and potassium iodide. The obtained iodine-PVA-based polarizer film with a thickness of 12 μm was dried in a dryer at 50°C for 30 minutes. A polarizer with a moisture content of 4.9% was obtained.

[0380] <Fabrication of Polarizer 1>

[0381] As the first optical film, a cellulose-australia silate film (Konica Minolta TAC6UA, manufactured by Konica Minolta) was used.

[0382] A polarizer 1 was produced by bonding the optical film 1 obtained above and a polarizer as the first optical film and the second optical film.

[0383] (Preparation of water-based adhesives)

[0384] A water-based adhesive was prepared by mixing the following ingredients.

[0385] 100.0 parts by mass of pure

[0386] 3.0 parts by mass of carboxyl group modified polyvinyl alcohol "Curare Poval (registered trademark) KL318" (manufactured by Curare Co., Ltd.)

[0387] 1.5 parts by mass of water-soluble polyamide epoxy resin "Sumires (registered trademark) Resin 650" (aqueous solution with a solid content of 30%, manufactured by Sumika Chemtex Co., Ltd.)

[0388] (Pretreatment of the second optical film)

[0389] Optical film 1, which is the second optical film, was immersed in a saponification treatment solution (aqueous sodium hydroxide solution at 60°C, concentration 10 mass%) for 30 seconds. Subsequently, optical film 1 was immersed in a water bath for 5 seconds. This was done twice. Afterward, optical film 1 was washed with a water shower for 5 seconds and then dried. The drying conditions were set to 70°C for 2 minutes.

[0390] Next, optical film 1 was immersed in water at 30°C for 10 seconds to undergo swelling treatment. Afterward, optical film 1 was dried at 40°C for 53 seconds.

[0391] (Pretreatment of the first optical film)

[0392] Pretreatment was performed on the first optical film in the same way as on the second optical film (optical film 1).

[0393] (Synthesis of optical film and polarizer)

[0394] The bonding surfaces with the polarizer of each of the first optical film and the second optical film (optical film 1) were corona treated. Then, the above-mentioned water-based adhesive was applied to the bonding surfaces with 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 circulating dryer set to 80°C to obtain a polarizing plate 1.

[0395] <Production of Polarizers 2 to 22>

[0396] Polarizers 2 to 22 were produced in the same manner, except that in the production of polarizer 1, optical film 1 was changed to the optical film shown in the table below as the second optical film.

[0397] <Manufacturing of Liquid Crystal Displays>

[0398] Using the polarizing plates 1 to 22 produced above, liquid crystal display devices 1 to 22 were produced according to the following method.

[0399] A VA-type liquid crystal cell was prepared having two glass substrates with a thickness of 0.5 mm and a liquid crystal layer disposed between them. Then, the polarizers 1 to 22 prepared above were bonded with an adhesive layer interposed such that the second optical film was positioned toward the liquid crystal cell side, thereby obtaining liquid crystal display devices 1 to 22. The bonding was performed such that the absorption axis of the polarizer of the viewing-side polarizer (101A described in FIG. 2) and the absorption axis of the polarizer of the backlight-side polarizer (101B described in FIG. 2) were orthogonal.

[0400] In addition, “-” in the table below indicates that it does not contain the corresponding ingredient or does not meet the requirements.

[0401] The content of additive 1 or additive 2 in the table below represents the ratio of each additive to the mass of the main dope, cellulose acylate.

[0402] In addition, in the items of the table below, (A) to (F) are as follows.

[0403] (A): Additive 2 (hydrogen-bonding compound) is denoted as “Y” if it has a fluorene backbone and an atomic group containing an amide bond at the 9th position of the fluorene backbone, or has a carbazole backbone and an atomic group containing an amide bond at the 9th position of the carbazole backbone, and as “N” if it does not have the above atomic group.

[0404] (B): The retardation values ​​Ro, Rt, and Rt / Ro are listed.

[0405] (C): If one molecule of additive 2 (hydrogen-bonding compound) has both a hydrogen bonding donor part and a hydrogen bonding acceptor part, it is indicated as “Y”, and if it does not have both, it is indicated as “N”.

[0406] (D): The weight average molecular weight of additive 2 (hydrogen bonding compound) was calculated by dividing the total number of hydrogen bonding donors and hydrogen bonding acceptors.

[0407] (E): The total number of aromatic ring structures of additive 2 (hydrogen bonding compound) is listed.

[0408] (F): The number of carboxyl groups of additive 2 (hydrogen bonding compound) was described.

[0409]

[0410]

[0411] [evaluation]

[0412] <Stability of Polarizers>

[0413] A forced degradation test was conducted on the polarizing plate fabricated above by maintaining it for 50 hours in an environment of 60°C and 90% RH humidity. After the test, the polarizing plate was visually observed for any color change in the visible range and evaluated according to the following criteria. The results obtained are shown in the table below. According to the following criteria, "A" and "B" were deemed to have no practical issues.

[0414] (standard)

[0415] A: No change

[0416] B: Slightly discolored

[0417] C: Coloration present

[0418] D: Significant discoloration

[0419] Non-acidic

[0420] The obtained optical film was heat-treated at 200°C for 10 minutes, humidified at 23°C and 55% RH for 24 hours, and its mass was measured. Based on the change in mass before and after heat treatment, an evaluation was performed to assess the potential for the release of hydrogen-bonding compounds from the film when the film is heated during stretching. Under the following criteria, "A" and "B" were deemed to have no practical issues.

[0421] (standard)

[0422] A: Mass loss of 1% or less after heat treatment

[0423] B: Mass loss of more than 1% and less than or equal to 2% after heat treatment

[0424] C: Mass loss of more than 2% and less than or equal to 3% after heat treatment

[0425] D: Mass loss of more than 3% after heat treatment

[0426] <Viewing angle of VA mode on liquid crystal display>

[0427] It can be seen that liquid crystal display devices 1 to 18 using optical films 1 to 18 can be applied to optical compensation of a liquid crystal display device in VA mode, since the ratio of the optical film's retardation value (Rt / Ro) is 2.0 or higher.

[0428] It is confirmed that the liquid crystal display device 21, 22 using optical film 21, 22 cannot be applied to optical compensation of the liquid crystal display device in VA mode because the ratio of the optical film's retardation value (Rt / Ro) is less than 2.0.

[0429] In addition, optical films 19 and 20 can be applied to optical compensation of liquid crystal display devices in VA mode because the ratio of retardation values ​​(Rt / Ro) is 2.0 or higher, but a film with a width of 2500 mm cannot be obtained because the stretching ratio in the TD direction is low.

[0430]

[0431] As shown in the above results, it can be seen that the optical film of the present invention obtains a ratio of high retardation values ​​(Rt / Ro is 2.0 or higher) required for optical compensation in VA mode even when stretched at a high magnification (1.5 times or more) in the TD direction. Therefore, it can be applied to optical compensation of a liquid crystal display device in VA mode.

[0432] In contrast, when the optical film of the comparative example is stretched at a high magnification in the TD direction, a high ratio of retardation value (Rt / Ro of 2.0 or higher) required for optical compensation in the VA mode is not obtained. Furthermore, it can be seen that the stretching magnification in the TD direction is lowered in order to obtain a ratio of retardation value.

[0433] Industrial applicability

[0434] The present invention can be used for a cellulose acylate film, a method for manufacturing a cellulose acylate film, a polarizer, and a liquid crystal display device, wherein a ratio of high retardation values ​​(Rt / Ro) required for optical compensation of the VA mode is obtained even when stretched at a high magnification in the TD direction. Explanation of the symbols

[0435] 1: Polarizer 2: First optical film 4: Polarizer 5: Second optical film 100: Display device 101A, 101B: Polarizers 101C: Liquid crystal cell 102A, 102B: First optical film 103A, 103B, 103C, 103D: Adhesive layer 104A, 104B: Polarizer 105A, 105B: Second optical film 106: Adhesive layer 107: Liquid crystal layer 108A, 108B: Glass substrate

Claims

Claim 1 A cellulose acylate film containing a hydrogen-bonding compound satisfying the requirements of (A) below and satisfying the optical values ​​of (B) below. (A): having a fluorene backbone and having an atomic group containing an amide bond at the 9th position of said fluorene backbone, or having a carbazole backbone and having an atomic group containing an amide bond at the 9th position of said carbazole backbone. (B): a retardation value Ro defined by the following formula is in the range of 40 to 70 nm, a retardation value Rt is in the range of 100 to 220 nm, and a ratio of retardation values ​​Rt / Ro is in the range of 2.0 to 5.

5. Formula (i) Ro=(n x -n y )×d equation (ii) Rt={(n x +n y ) / 2-n z }×d(of the above equations (i) and (ii), n x represents the refractive index in direction x where the refractive index is maximum in the in-plane direction of the film. y n represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the film. z represents the refractive index in the thickness direction z of the film. The above refractive index was measured at a wavelength of 550 nm under an environment of 23°C and 55% RH. d [nm] represents the thickness of the film.) Claim 2 A cellulose acylate film according to claim 1, having both a hydrogen bonding donor part and a hydrogen bonding acceptor part within one molecule of the hydrogen bonding compound. Claim 3 A cellulose acylate film according to paragraph 2, wherein the weight average molecular weight of the hydrogen bonding compound, calculated by dividing it by the sum of the number of hydrogen bond donors and hydrogen bond acceptors, is within the range of 30 to 80. Claim 4 A cellulose acylate film according to claim 1, wherein the total number of aromatic ring structures of the hydrogen bonding compound is within the range of 2 to 3. Claim 5 A cellulose acylate film according to claim 1, wherein the hydrogen bonding compound has one or fewer carboxyl groups. Claim 6 A cellulose acylate film according to claim 1, wherein the hydrogen bonding compound does not have a carboxyl group. Claim 7 A cellulose acylate film according to claim 1, wherein the weight average molecular weight of the hydrogen bonding compound is 300 or more. Claim 8 A cellulose acylate film according to claim 1, wherein the hydrogen bonding compound has a 9-fluorenylmethyloxycarbonyl group. Claim 9 A cellulose acylate film according to claim 1, wherein the content of the hydrogen bonding compound is within the range of 0.5 to 30 mass% with respect to the cellulose acylate resin. Claim 10 A cellulose acylate film according to claim 1, wherein the width of the film is 2500 mm or more. Claim 11 A method for manufacturing a cellulose acylate film, wherein the cellulose acylate film described in any one of claims 1 to 10 is manufactured by stretching the cellulose acylate film in the TD direction by a stretching ratio of 1.6 times or more. Claim 12 A polarizing plate having a cellulose acylate film as described in any one of claims 1 to 10. Claim 13 A liquid crystal display device having a polarizing plate as described in paragraph 12.

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