WO2015076250A1

WO2015076250A1 - Optical film, polarizing plate and liquid crystal display device

Info

Publication number: WO2015076250A1
Application number: PCT/JP2014/080469
Authority: WO
Inventors: 隆建部
Original assignee: コニカミノルタ株式会社
Priority date: 2013-11-19
Filing date: 2014-11-18
Publication date: 2015-05-28
Also published as: JPWO2015076250A1

Abstract

The purpose of the present invention is to provide an optical film which is capable of suppressing panel bending, thereby decreasing display unevenness caused by panel bending. An optical film according to the present invention contains: a resin (A) that has a CHE/CTE of 0.6 or more, if CHE is the coefficient of moisture-absorption expansion thereof and CTE is the coefficient of thermal expansion thereof, and a tensile modulus of elasticity of 2GPa or more in an environment at 40°C at 20% RH; and a resin (B) that has a CHE/CTE of less than 0.6. The ratio of the coefficient of moisture-absorption expansion (CHE) of the optical film in an arbitrary in-plane direction (X) to the coefficient of thermal expansion (CTE) thereof in the direction (X), namely CHE/CTE is 0.6 or less, and the tensile modulus of elasticity in the direction (X) in an environment at 40°C at 20% RH is 2-6 GPa.

Description

Optical film, polarizing plate, and liquid crystal display device

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

Liquid crystal display devices are widely used as liquid crystal displays for televisions and personal computers. A liquid crystal display device usually includes a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell. The liquid crystal cell includes a transparent electrode, a liquid crystal layer, a color filter, and a pair of glass substrates that sandwich them; the polarizing plate includes a polarizer and a pair of polarizing plate protective films that sandwich the polarizer.

As a polarizing plate protective film, a cellulose triacetate film (TAC) is often used because it is transparent and has low birefringence and is easily adhered to a polarizer using water glue. As the transparent film, an extruded film of a composition comprising a vinyl acetate resin and cellulose acetate butyrate or cellulose acetate propionate is disclosed (for example, Patent Document 1).

In recent years, the glass substrate constituting the liquid crystal cell has been made thinner. Further, an LED backlight is used as a light source of the liquid crystal display device. Along with these, bending of the liquid crystal display panel (polarizing plate / liquid crystal cell / polarizing plate laminate) is likely to occur.

Japanese Patent No. 5182778

Panel bend is likely to occur after the backlight of a liquid crystal display device immediately after manufacturing or immediately after transportation is turned on for a certain period of time. This is considered to be because water escapes from the polarizer containing water during production or transportation, and the polarizer contracts due to the heat of the backlight.

If the glass substrate constituting the liquid crystal cell is thin, the glass substrate cannot withstand the force of the polarizer trying to contract, and panel bend is likely to occur. In addition, a liquid crystal display device using an LED backlight has a smaller distance between the backlight and the panel than a liquid crystal display device using a conventional backlight, so that the polarizer is more susceptible to the heat of the backlight. Panel bend is likely to occur.

Such a panel bend is likely to cause display unevenness of the liquid crystal display device. Further, when panel bend occurs, the panel comes into contact with the diffusion plate, which may further cause egg unevenness.

This invention is made | formed in view of the said situation, and it aims at providing the optical film which can suppress a panel bend and can reduce the display nonuniformity by it.

[1] Resin having a CHE / CTE of 0.6 or more and a tensile modulus of elasticity of 2 GPa or more in a 40 ° C., 20% RH environment when the hygroscopic expansion coefficient is CHE and the thermal expansion coefficient is CTE (A ) And a resin (B) having a CHE / CTE of less than 0.6, wherein the hygroscopic expansion coefficient CHE in any one direction X in the plane of the optical film and the thermal expansion in the direction X An optical film having a ratio CHE / CTE to a coefficient CTE of 0.6 or less and a tensile elastic modulus in the direction X of 2 to 6 GPa in a 40 ° C., 20% RH environment.
[2] The optical film according to [1], wherein the direction X is at least one of an in-plane slow axis direction of the optical film and a direction orthogonal to the in-plane slow axis direction.
[3] The optical film according to [1] or [2], wherein the direction X matches the longitudinal direction of the optical film.
[4] When the glass transition temperature of the resin (A) is Ta, the glass transition temperature of the resin (B) is Tb, and the glass transition temperature of the optical film is Tg, the following formulas (1) to (3) are satisfied. The optical film according to any one of [1] to [3], which is satisfied.
(Formula 1) Ta>Tg> Tb
(Formula 2) Ta ≧ Tb + 80
(Formula 3) 150 ≧ Tg ≧ 100
[5] The optical film according to any one of [1] to [4], wherein a weight average molecular weight of the resin (A) and a weight average molecular weight of the resin (B) are both 90,000 to 1,000,000. .
[6] The content mass ratio between the resin (A) and the resin (B) is (A) :( B) = 30: 70 to 90:10, any one of [1] to [5] Optical film.
[7] A step of casting a dope containing the resin (A) and the resin (B) and a solvent on a metal support plate and then drying to obtain a film-like material; and It is obtained through a step of stretching in both the transport direction and the direction orthogonal to the transport direction so that the sum of the stretch ratios in both the transport direction and the direction orthogonal to the transport direction is 110 to 400%. [1] to [6] The optical film according to any one of [6].
[8] The optical film according to any one of [1] to [7], wherein the resin (A) is a cellulose ester.
[9] The resin (B) contains at least one selected from the group consisting of polyvinyl acetate, polylactic acid, polyacetal, polyurethane, ethylene-vinyl acetate polymer, and rubber particles [1] to [8] The optical film in any one of.
[10] The optical film according to any one of [1] to [9], wherein the CHE / CTE of the optical film is 0.2 to 0.6.
[11] The optical film according to any one of [1] to [10], wherein the weight average molecular weight of the resin (A) and the weight average molecular weight of the resin (B) are both 150,000 to 500,000.
[12] The optical film according to any one of [1] to [11], which is a polarizing plate protective film.

[13] A polarizing plate comprising a polarizer and the optical film according to any one of [1] to [12].
[14] The polarizing plate according to [13], wherein an in-plane direction X of the optical film and an absorption axis of the polarizer are parallel to each other.
[15] A liquid crystal display device including a first polarizing plate, a liquid crystal cell, a second polarizing plate, and a backlight in this order, wherein the first polarizing plate includes a first polarizer, A polarizing plate protective film F1 disposed on the surface of the first polarizer opposite to the liquid crystal cell, and a polarizing plate protective film F2 disposed on the surface of the first polarizer on the liquid crystal cell side The second polarizing plate is a second polarizer, a polarizing plate protective film F3 disposed on the surface of the second polarizer on the liquid crystal cell side, and the second polarizer. A polarizing plate protective film F4 disposed on a surface opposite to the liquid crystal cell, and one or both of the polarizing plate protective film F1 and the polarizing plate protective film F4 are any one of [1] to [12] A liquid crystal display device, which is the optical film described in 1.
[16] The liquid crystal cell includes a liquid crystal layer and a pair of substrates sandwiching the liquid crystal layer, and the pair of substrates is a glass substrate having a thickness of 0.3 mm or more and less than 0.7 mm. The liquid crystal display device described.
[17] The liquid crystal display device according to [15] or [16], wherein at least the polarizing plate protective film F1 is the optical film according to any one of [1] to [12].
[18] The liquid crystal display device according to [17], wherein an in-plane direction X of the polarizing plate protective film F1 and an absorption axis of the first polarizer are parallel to each other.

According to the present invention, it is possible to provide an optical film that can suppress panel bend and thereby reduce display unevenness.

It is a schematic diagram which shows an example of the fundamental structure of a liquid crystal display device. It is a schematic diagram which shows the relationship between the absorption axis of the polarizer and the direction X of a protective film in a liquid crystal display device.

As described above, it is considered that the panel bend is caused by contraction of the polarizer due to the escape of water from the polarizer containing water at the time of manufacture or transportation, due to the heat of the backlight. On the other hand, the present inventors have found that the panel bend can be suppressed by expanding the optical film so as to counteract the contraction of the polarizer when receiving the heat of the backlight.

Specifically, an optical film that has received heat from a backlight tends to simultaneously expand due to heat and shrink due to the removal of water. It has been found that the optical film as a whole can be easily expanded by making the “expansion force due to heat” in the optical film relatively larger than the “shrinkage force due to the removal of water”.

That is, when the thermal expansion coefficient in any one direction X in the plane of the optical film is CTE (unit: ppm / ° C.) and the hygroscopic expansion coefficient in direction X is CHE (unit: ppm /% RH), these ratios CHE / CTE is preferably not more than a certain value, specifically 0.6 or less.

“Any one direction X in the plane of the optical film” is preferably a direction parallel to the absorption axis of the polarizer when the optical film and the polarizer are superimposed; (MD direction), that is, the longitudinal direction of the optical film in the wound body of the optical film is more preferable. Specifically, “any one direction X in the plane of the optical film” is preferably at least one of the in-plane slow axis direction of the optical film and the direction orthogonal thereto. The in-plane slow axis of the optical film is the slow axis in the direction in which the refractive index is maximum in the optical film plane, and can be specified by an automatic birefringence meter KOBRA-WR (Oji Scientific Instruments) as will be described later. .

Also, in order to increase the “thermal expansion force” of the optical film, it is preferable that the optical film has a certain tensile elastic modulus under heating. This is because the thermal expansion force of the optical film is proportional to the product of the tensile elastic modulus, thickness, and dimensional change of the optical film.

That is, it is preferable that the tensile elastic modulus at 40 ° C. in any one direction X in the plane of the optical film is 2 GPa or more. When the tensile elastic modulus at 40 ° C. is above a certain level, the expansion force of the optical film due to heat can be easily increased. On the other hand, the tensile elastic modulus at 40 ° C. in the direction X of the optical film is preferably 6 GPa or less in order to improve the winding shape of the optical film (the appearance of the wound body wound up in a roll shape). When an optical film having a tensile modulus of elasticity exceeding 6 GPa at 40 ° C. is wound, appearance defects such as “smooth” and “wrinkle” are likely to occur.

In order to set the CHE (Hygroscopic expansion coefficient) / CTE (Thermal expansion coefficient) in the direction X of the optical film to 0.6 or less and the tensile modulus at 40 ° C. in the direction X to 2 GPa or more, the tensile modulus at 40 ° C. It is preferable to combine a resin (A) having a high CHE / CTE and a resin (B) having a relatively low CHE / CTE. Specifically, a resin (A) having a tensile elastic modulus at 40 ° C. of 2 GPa or more and a CHE / CTE of 0.6 or more, and a resin (B) having a CHE / CTE of less than 0.6 It is preferable to further adjust the content ratio, the molecular weight of the resin (B), and one or more stretching conditions.

The CHE / CTE in the direction X of the optical film can be adjusted mainly by the types of the resin (A) and the resin (B), their content ratio, stretching in the direction X, and the stretching ratio in the direction X. The tensile elastic modulus at 40 ° C. in the direction X of the optical film is mainly the type and molecular weight of the resin (A) and the resin (B), the content ratio of the resin (A) and the resin (B), and stretching in the direction X. And it can be adjusted by the draw ratio in the direction X.

1. Optical Film The optical film of the present invention contains a resin (A) having a high tensile elastic modulus under heating and a relatively high CHE / CTE and a resin (B) having a relatively low CHE / CTE.

<About Resin (A)>
The resin (A) can function not only as the main polymer of the optical film, but also has a function of increasing the tensile elastic modulus under heating.

The tensile elastic modulus of the resin (A) in a 40 ° C., 20% RH environment is preferably 2 GPa or more, and more preferably 3 GPa or more in order to increase the expansion force under heating. On the other hand, the tensile elastic modulus of the resin (A) in a 40 ° C., 20% RH environment is preferably 6 GPa or less in order not to impair the rolled form of the optical film (appearance of the roll-shaped wound body). More preferably, it is 5 GPa or less.

The tensile elastic modulus of the resin (A) under a 40 ° C. and 20% RH environment can be measured by the following method. That is,
1) A 40 μm thick film made of the resin (A) is prepared. The film production method is preferably a solution casting film forming method from the viewpoint of easy handling of the high molecular weight resin (A). The obtained film is cut into a size of 100 mm (MD direction) × 10 mm (TD direction) to obtain a test piece.
2) In accordance with JIS K7127, the test piece is measured for tensile elastic modulus in the MD direction using a Tensilon RTC-1225A manufactured by Orientec Co., Ltd. with a distance between chucks of 50 mm. The MD direction represents the film forming direction of the film made of the resin (A) (the longitudinal direction of the film in the film winding body); the TD direction represents the width direction of the film. The measurement is performed at 40 ° C. and 20% RH.

The CHE / CTE of the resin (A) is preferably 0.6 or more, more preferably 0.8 or more, further preferably 1.0 or more, and 1.2 or more. Particularly preferred. The upper limit of the CHE / CTE of the resin (A) can be about 2.0, preferably about 1.5.

The CHE / CTE of the resin (A) can be obtained, for example, by the following procedure.
1) A film having a thickness of 40 μm made of resin (A) is prepared by the solution casting method, and cut into a predetermined size as a test piece, in the same manner as the film used for measurement of the tensile modulus. Then, the CTE of the test piece is measured by the TMA method in accordance with ASTM E-831 or JIS K7197 to obtain the CTE (unit: ppm / ° C.) of the resin (A).
2) The dimension in the MD direction after storing a test piece of 40 μm thickness made of resin (A) for 24 hours in an environment of 23 ° C. and 20% RH and 23 ° C. and 80% RH The dimension in the MD direction after storage for 24 hours under the environment is measured. The obtained measured value is applied to the following formula to obtain CHE (unit: ppm /% RH) of the resin (A) (see the following formula).
CHE (ppm /% RH) = {(MD direction dimension of specimen after storage at 23 ° C. and 80% RH−MD direction dimension of specimen after storage at 23 ° C. and 20% RH) / 23 ° C. and 20% RH Dimension of specimen after storage under MD} / (80% RH-20% RH)
3) The CHE / CTE of the resin (A) is calculated from the CTE and CHE of the resin (A) obtained in 1) and 2) above.

Examples of the resin (A) in which the tensile modulus at 40 ° C. and the CHE / CTE satisfy the above range include cellulose ester and (meth) acrylic resin, etc. is there.

Cellulose ester Cellulose ester is a compound obtained by esterifying cellulose and at least one of aliphatic carboxylic acid and aromatic carboxylic acid. That is, the cellulose ester contains at least one of an aliphatic acyl group and an aromatic acyl group, and preferably contains an aliphatic acyl group.

The number of carbon atoms in the aliphatic acyl group is preferably 2 to 7, and more preferably 2 to 4. Examples of the aliphatic acyl group include acetyl group, propionyl group, butanoyl group and the like.

Specific examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate and the like, and cellulose acetate and cellulose acetate propionate are preferable because they have appropriate hydrophobicity.

The total substitution degree of the acyl group of the cellulose ester is 2.0 or more, preferably 2.5 or more, more preferably 2.6 or more, and further preferably 2.8 or more. By increasing the total substitution degree of the acyl group, it is possible to make it difficult to express the retardation of the film. The upper limit of the total substitution degree of the acyl group can be, for example, 3.0, preferably 2.99.

The acyl group of the cellulose ester preferably contains an acetyl group. The acyl group of the cellulose ester may further contain an acyl group having 3 or more carbon atoms, and the degree of substitution may be 2.7 or less.

The degree of substitution of the acyl group of the cellulose ester can be measured by the method prescribed in ASTM-D817-96.

(Meth) acrylic resin The (meth) acrylic resin can be a homopolymer of (meth) acrylic acid ester; or a copolymer of (meth) acrylic acid ester and another monomer copolymerizable therewith.

The (meth) acrylic acid ester is preferably a (meth) acrylic acid alkyl ester, and more preferably methyl methacrylate.

Examples of other monomers copolymerizable with methyl methacrylate include: alkyl methacrylates having 2 to 18 carbon atoms in the alkyl moiety; alkyl alkyl esters having 1 to 18 carbon atoms in the alkyl moiety; acrylic acid Α, β-unsaturated acids such as methacrylic acid; unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid; aromatic vinyl compounds such as styrene, α-methylstyrene and nucleus-substituted styrene; acrylonitrile And α, β-unsaturated nitriles such as methacrylonitrile; maleic anhydride; maleimide, N-substituted maleimide; glutaric anhydride and the like. The alkyl group in the acrylic acid alkyl ester and methacrylic acid alkyl ester may be cyclic or chain-like. These other monomers may be used alone or in combination of two or more.

The content ratio of the structural unit derived from methyl methacrylate with respect to all the structural units constituting the copolymer is preferably 50% by mass or more, and more preferably 70% by mass or more.

The weight average molecular weight of the resin (A) is preferably 90,000 or more and more preferably 150,000 or more in order to easily increase the tensile elastic modulus of the film under heating. The upper limit of the weight average molecular weight of the resin (A) is preferably 1 million, preferably 500,000 so that compatibility with the resin (B) is easily obtained and the moldability to the film is not impaired. Is more preferable.

The weight average molecular weight of the resin (A) can be measured by gel permeation chromatography (GPC). The measurement conditions are as follows.
Solvent: Methylene chloride Column: Three Shodex K806, K805, K803G (manufactured by Showa Denko KK) are connected and used.
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 1.0 × 10 ⁶ to 5.0 × 10 ² 13 calibration curves are used. The 13 samples are preferably selected so that the molecular weights are approximately equidistant.

The glass transition temperature Ta of the resin (A) preferably satisfies the expressions (1) to (3) described later. For example, the glass transition temperature Ta of the resin (A) can be about 105 to 180 ° C.

The glass transition temperature Ta of the resin (A) is a method according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) as a midpoint glass transition temperature (Tmg). Can be measured. The heating rate can be 20 ° C./min.

<About Resin (B)>
The resin (B) has a function of making the optical film easily stretched (or easily expanded) under heating. Accordingly, the CHE / CTE of the resin (B) is preferably relatively low, preferably less than 0.6, more preferably 0.5 or less, and further preferably 0.4 or less. . The lower limit of the CHE / CTE of the resin (B) can be about 0 or about 0.05. The CHE / CTE of the resin (B) can be measured in the same manner as the CHE / CTE of the resin (A) described above.

The tensile elastic modulus of the resin (B) under a 40 ° C. and 20% RH environment may be such that the tensile elastic modulus of the obtained optical film falls within the above range. Specifically, the tensile elastic modulus of the resin (B) in a 40 ° C., 20% RH environment can be 6 GPa or less, preferably 4.5 GPa or less. The tensile elastic modulus of the resin (B) under a 40 ° C. and 20% RH environment can be measured in the same manner as the tensile elastic modulus of the resin (A) under a 40 ° C. and 20% RH environment.

The glass transition temperature Tb of the resin (B) is preferably lower than the glass transition temperature Ta of the resin (A) by a certain level or more in order to make the optical film easily stretched under heating. Specifically, it is preferable to satisfy the following formula (2).
Formula (2) Ta ≧ Tb + 80

Tb is preferably lower than Ta by 100 ° C. or more. Tb can be, for example, in the range of −50 ° C. to 70 ° C.

The glass transition temperature Tb of the resin (B) can be measured by the same method as the glass transition temperature Ta of the resin (A).

Examples of the resin (B) satisfying the above CHE / CTE range include vinyl acetate resin, polylactic acid, polyacetal, polyurethane, and rubber particles.

The vinyl acetate resin is a polymer containing a repeating unit derived from vinyl acetate, and examples thereof include polyvinyl acetate (a homopolymer of vinyl acetate), an ethylene-vinyl acetate copolymer, and the like.

Polyacetal is a polymer containing oxymethylene repeating units, and may further contain a small amount (for example, 5% or less) of oxyethylene repeating units.

Polyurethane is a resin obtained by reacting polyol and polyisocyanate. Examples of polyols include alkylene diols, polyester polyols, polyether polyols, and the like, preferably alkylene diols and polyester polyols. Examples of the polyisocyanate include alkylene diisocyanate and arylene diisocyanate, and alkylene diisocyanate is preferable. Preferable examples of the polyurethane include a polymer of alkylene diisocyanate and alkylene diol.

The rubber particles are preferably fine particles having a core-shell structure, and examples thereof include acrylic fine particles; and styrene-butadiene copolymer fine particles.

As an example of acrylic fine particles having a core-shell structure, a mixture of 80 to 98.9% by mass of methyl methacrylate, 1 to 20% by mass of alkyl acrylate and 0.01 to 0.3% by mass of a polyfunctional grafting agent is polymerized. A mixture of 75-98.5% by mass of alkyl acrylate, 0.01-5% by mass of polyfunctional crosslinking agent, and 0.5-5% by mass of polyfunctional grafting agent. And a soft layer obtained by polymerization; and an outermost hard layer obtained by polymerizing a mixture of 80 to 99% by mass of methyl methacrylate and 1 to 20% by mass of alkyl acrylate.

Examples of fine particles of a styrene-butadiene copolymer having a core-shell structure include: a core portion made of a soft polymer; and a shell portion covering the periphery of the core portion made of another polymer. Includes fine particles.

The soft polymer includes a structural unit derived from a conjugated diene monomer and, if necessary, a structural unit derived from another monomer. Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, myrcene, etc. Of these, butadiene and isoprene are preferred. Examples of other monomers include styrene components such as styrene and α-methylstyrene. The content ratio of the structural unit derived from the conjugated diene monomer in the soft polymer is usually 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more.

Examples of other polymers include copolymers of acrylonitrile and styrene, and polymers mainly composed of methacrylic acid esters such as methyl methacrylate.

The volume average particle diameter of the elastic organic fine particles is 0.350 μm or less, preferably 0.010 to 0.350 μm, more preferably 0.050 to 0.300 μm. If the particle size is above a certain value, the film can be easily stretched under heating; if the particle size is below a certain value, it is difficult to impair the transparency of the resulting film.

The weight average molecular weight of the resin (B) is preferably 90,000 or more and is preferably 150,000 or more in order to facilitate the compatibility with the resin (A) or to increase the tensile elastic modulus of the film. More preferably. The upper limit of the weight average molecular weight of the resin (B) is preferably 1,000,000 and more preferably 500,000 in order not to impair the compatibility with the resin (A) and the moldability to a film. In particular, when the weight average molecular weight of the resin (B) exceeds 1,000,000, the compatibility with the resin (A) is deteriorated, and it is difficult to obtain a desired physical property value. The weight average molecular weight of the resin (B) can be measured by the same method as described above.

The content ratio of the resin (A) to the resin (B) is preferably (A) :( B) = 10: 90 to 95: 5 (mass ratio), and (A) :( B) = 30: 70 More preferably, it is ˜90: 10 (mass ratio), and more preferably (A) :( B) = 50: 50 to 90:10 (mass ratio). By setting the content ratio of the resin (B) to a certain value or more, the optical film can be easily stretched (easily expanded) under heating. By setting the content ratio of the resin (B) to a certain value or less, it is easy to maintain a high tensile elastic modulus under heating of the optical film.

The optical film of the present invention may further contain various additives such as a plasticizer, a peeling aid, an ultraviolet absorber, and fine particles (matting agent) for imparting slipperiness, if necessary.

<About plasticizer>
Examples of the plasticizer include sugar ester compounds, polyester compounds, phthalate ester compounds, phosphate ester compounds and the like. These may be used alone or in combination of two or more.

(Sugar ester compound)
The sugar ester compound is a compound obtained by reacting a hydroxyl group contained in sugar with a monocarboxylic acid. That is, the sugar ester compound includes a structure derived from sugar and an acyl group derived from a reaction product of a hydroxyl group (contained in sugar) and a monocarboxylic acid.

The sugar-derived structure contained in the sugar ester compound is preferably a structure in which one to both of the furanose structure and the pyranose structure are bonded to 1 to 12; one to both of the furanose structure and the pyranose structure is 1 to 3, A structure in which two are bonded is preferable. Especially, what contains both a pyranose structure and a furanose structure is preferable.

Examples of sugar-derived structures include monosaccharides such as glucose, galactose, mannose, fructose, xylose and arabinose; disaccharides such as lactose, sucrose, maltitol, cellobiose and maltose; derived from trisaccharides such as cellotriose and raffinose Structure to be included.

The acyl group contained in the sugar ester compound may be an aliphatic acyl group or an aromatic acyl group.

The number of carbon atoms in the aliphatic acyl group can be 1 to 22, more preferably 2 to 12, and particularly preferably 2 to 8. Examples of the aliphatic acyl group include acetyl group, propionyl group, butyryl group, pentanoyl group, hexanoyl group, octanoyl group and the like. Examples of the aromatic acyl group include a benzoyl group, a toluyl group, and a phthalyl group.

Among them, the acyl group contained in the sugar ester compound preferably contains at least a benzoyl group in order to enhance compatibility with the cellulose ester that can be used as the resin (A). The plurality of acyl groups contained in the sugar ester compound may be the same as or different from each other.

In the sugar ester compound, an unreacted hydroxyl group that is not substituted with an acyl group may usually remain as a hydroxyl group.

The sugar ester compound may be a mixture of a plurality of sugar ester compounds having the same type of acyl group and different degrees of substitution. Such a mixture may contain an unsubstituted form. The average ester substitution rate in the mixture is preferably 62 to 94%. The average ester substitution rate in the mixture can be defined by the following formula.
Average ester substitution rate = 100% × (content of each sugar ester compound in the mixture) × (number of esterified OH in each molecule of sugar ester compound in the mixture) / (in one molecule of unsubstituted sugar) Total number of OH)

Specific examples of the sugar ester compound include the following.

The polyester compound contains a repeating unit derived from a condensate of dicarboxylic acid and diol.

The dicarboxylic acid can be an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aromatic dicarboxylic acid. The number of carbon atoms in the aliphatic dicarboxylic acid is preferably 4 to 20, and more preferably 4 to 12. Examples of the aliphatic dicarboxylic acid include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like.

The number of carbon atoms in the aromatic dicarboxylic acid is preferably 8 to 20, and more preferably 8 to 12. Examples of aromatic dicarboxylic acids include 1,2-benzenedicarboxylic acid (phthalic acid), 1,3-benzenedicarboxylic acid (isophthalic acid), 1,4-benzenedicarboxylic acid (terephthalic acid), 1,5-naphthalene Dicarboxylic acid, 1,4-xylidene dicarboxylic acid and the like are included, and 1,4-benzenedicarboxylic acid (terephthalic acid) is preferable.

The number of carbon atoms of the alicyclic dicarboxylic acid is preferably 6 to 20, and more preferably 6 to 12. Examples of the alicyclic dicarboxylic acid include 1,3-cyclobutane dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,4-cyclohexane diacetic acid and the like.

The dicarboxylic acid for obtaining the polyester compound may be one type or two or more types. The dicarboxylic acid for obtaining the polyester compound preferably contains an aromatic dicarboxylic acid in order to enhance the compatibility with the cellulose ester that can be used as the resin (A). The aromatic dicarboxylic acid and the aliphatic dicarboxylic acid are preferably included. More preferably, both acids are included.

The diol can be an aliphatic diol, an alkyl ether diol, an alicyclic diol or an aromatic diol.

The carbon number of the aliphatic diol is preferably 2 to 20, and more preferably 2 to 12. Examples of the aliphatic diol include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-propanediol, and the like. The number of carbon atoms of the alkyl ether diol is preferably 4 to 20, and more preferably 4 to 12. Examples of the alkyl ether diol include polytetramethylene ether glycol, polyethylene ether glycol and polypropylene ether glycol.

The number of carbon atoms of the alicyclic diol is preferably 4 to 20, and more preferably 4 to 12. Examples of the alicyclic diol include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and the like.

The number of carbon atoms in the aromatic diol is preferably 6 to 20, and more preferably 6 to 12. Examples of aromatic diols include 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), 1,4-dihydroxybenzene (hydroquinone), and the like. The diol for obtaining the polyester compound may be one kind or two or more kinds. The diol for obtaining the polyester compound preferably contains an aliphatic diol.

Among them, the polyester compound containing a repeating unit derived from a condensate of an aliphatic diol and a dicarboxylic acid containing an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid is preferable because the transparency of the film containing the polyester compound is good. ,preferable.

The molecular terminal of the polyester compound may be sealed with monocarboxylic acid or monoalcohol as necessary.

The monocarboxylic acid can be an aliphatic monocarboxylic acid, an alicyclic monocarboxylic acid or an aromatic monocarboxylic acid. The number of carbon atoms of the aliphatic monocarboxylic acid can be preferably 2-30, more preferably 2-4. Examples of the aliphatic carboxylic acid include acetic acid, propionic acid and the like. Examples of the alicyclic monocarboxylic acid include cyclohexyl monocarboxylic acid. Examples of aromatic monocarboxylic acids include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid, Phenylacetic acid, 3-phenylpropionic acid and the like are included.

The monoalcohol can be an aliphatic monoalcohol, an alicyclic monoalcohol or an aromatic monoalcohol. The number of carbon atoms of the aliphatic monoalcohol is 1 to 30, preferably 1 to 3. Examples of the aliphatic monoalcohol include methanol, ethanol, propanol, isopropanol and the like. Examples of the alicyclic monoalcohol include cyclohexyl alcohol and the like. Examples of the aromatic monoalcohol include benzyl alcohol, 3-phenylpropanol and the like.

Specific examples of the polyester compound include the following. In Table 1, TPA: terephthalic acid, PA: phthalic acid, SA: succinic acid, AA: adipic acid are shown.

Examples of the phthalic acid ester compound include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, dicyclohexyl terephthalate and the like.

Examples of the phosphate compound include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, and the like.

The content of the plasticizer is preferably 5 to 30% by mass and more preferably 5 to 20% by mass with respect to the total of the resin (A) and the resin (B). When the content of the plasticizer is a certain level or more, a sufficient plasticizing effect is easily obtained. On the other hand, when the content of the plasticizer is below a certain level, precipitation on the film surface after stretching can be highly suppressed.

<About peeling aid>
Since a part of the peeling aid or antistatic agent easily aggregates on the surface of the film-like material on the metal support side, the peelability of the film-like material from the metal support can be improved. The peeling aid or antistatic agent can be an organic or inorganic acidic compound, a surfactant, a chelating agent, and the like.

Examples of acidic compounds include organic acids, partial alcohol esters of polyvalent carboxylic acids (for example, oxalic acid and citric acid), and the like. Specific examples of the partial alcohol ester of polyvalent carboxylic acid include the compounds described in paragraph (0049) of JP-A-2006-45497.

Examples of surfactants include phosphate ester surfactants, carboxylic acid or carboxylate surfactants, sulfonic acid or sulfonate surfactants, sulfate ester surfactants, etc. It is. Examples of the phosphate ester-based surfactant include the compounds described in paragraph (0050) of JP-A-2006-45497.

The chelating agent is a compound capable of coordinating (chelating) multivalent ions such as metal ions such as iron ions and alkaline earth metal ions such as calcium ions. Examples of the chelating agents include Japanese Patent Publication No. 6-8956, Includes compounds described in JP-A-11-190892, JP-A-2000-18038, JP-A-2010-158640, JP-A-2006-328203, JP-A-2005-68246, and JP-A-2006-306969. It is.

Examples of commercially available peeling aids or antistatic agents include Hostastat HS-1, manufactured by Clariant Japan, Elecut S-412-2, Elecut S-418, manufactured by Takemoto Yushi Co., Ltd., and Kao Co., Ltd. Neoperex G65 and the like are included.

The content of the peeling aid or antistatic agent is preferably 0.005 to 1% by mass, more preferably 0.05 to 0.5% by mass with respect to the total amount of the resin (A) and the resin (B). %.

<About UV absorber>
The ultraviolet absorber may be a benzotriazole compound, a 2-hydroxybenzophenone compound, a salicylic acid phenyl ester compound, or the like. Specifically, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- Triazoles such as (3,5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2'-dihydroxy-4 -Benzophenones such as methoxybenzophenone.

The UV absorber may be a commercially available product. Examples thereof include Tinuvin 109, Tinuvin 171, Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328, and Tinuvin 928 manufactured by BASF Japan, or 2, 2'-methylenebis [6- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol] (molecular weight 659; examples of commercially available products are manufactured by ADEKA Corporation LA31) and the like.

The content of the ultraviolet light inhibitor is preferably from 1 ppm to 1000 ppm, more preferably from 10 to 1000 ppm, by mass with respect to the optical film.

<About matting agent>
The matting agent can impart slipperiness to the polarizing plate protective film. The matting agent may be fine particles made of an inorganic compound or an organic compound having heat resistance in the film forming process without impairing the transparency of the resulting film.

Examples of inorganic compounds constituting the matting agent include silicon dioxide (silica), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and hydrated calcium silicate. , Aluminum silicate, magnesium silicate and calcium phosphate. Of these, silicon dioxide and zirconium oxide are preferable, and silicon dioxide is more preferable in order to reduce an increase in haze of the obtained film.

Specific examples of silicon dioxide include Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (above, Nippon Aerosil Co., Ltd.), Sea Hoster KEP-10, Sea Hoster KEP -30, Seahoster KEP-50 (manufactured by Nippon Shokubai Co., Ltd.), Silo Hovic 100 (manufactured by Fuji Silysia), nip seal E220A (manufactured by Nippon Silica Kogyo), Admafine SO (manufactured by Admatechs) and the like.

The particle shape of the matting agent is indefinite, needle-like, flat or spherical, and may preferably be spherical in view of easy transparency of the resulting film.

When the size of the matting agent particles is close to the wavelength of visible light, the light is scattered and the transparency is lowered. Therefore, the size of the particles of the matting agent is preferably smaller than the wavelength of visible light. / 2 or less is preferable. However, if the size of the particles is too small, the effect of improving slipperiness may not be manifested. Therefore, the size of the particles is preferably in the range of 80 to 180 nm.

The particle size means the size of the aggregate when the particle is an aggregate of primary particles. When the particles are not spherical, the size of the particles means the diameter of a circle corresponding to the projected area.

The content of the matting agent can be about 0.05 to 1.0% by mass, preferably 0.1 to 0.8% by mass with respect to the total amount of the resin (A) and the resin (B). sell.

<Physical properties of optical film>
(Thickness)
When used as a polarizing plate protective film, the thickness of the optical film is preferably 10 to 60 μm and more preferably 20 to 40 μm in order to make the polarizing plate thinner.

(Tensile modulus)
As described above, the tensile elastic modulus of the optical film in the in-plane direction X under the environment of 40 ° C. and 20% RH is preferably 2 GPa or more in order to increase the expansion force due to heat, and is 3 GPa or more. Is more preferably 3.5 GPa or more. On the other hand, in order to easily maintain the shape of the wound body when winding the long optical film, the tensile modulus of elasticity in the direction X in the optical film plane at 40 ° C. and 20% RH is , 6 GPa or less is preferable, and 5.5 GPa or less is more preferable.

As described above, the direction X in the optical film plane is preferably the MD direction of the optical film; more preferably at least one of the in-plane slow axis direction and the direction orthogonal thereto.

The tensile elastic modulus at 40 ° C. and 20% RH in the direction X of the optical film can be measured by the same method as described above. For example, when the MD direction of the optical film is known,
1) An optical film is cut out to a size of 100 mm (MD direction) × 10 mm (TD direction) to obtain a test piece. The MD direction represents the long direction of the optical film in the wound body of the long optical film; the TD direction represents the width direction of the optical film.
2) In accordance with JIS K7127, this test piece was pulled in the MD direction of the test piece using a Tensilon RTC-1225A manufactured by Orientec Co., Ltd., and the tensile elastic modulus in the MD direction was measured. To do. The measurement is performed at 40 ° C. and 20% RH.

When the MD direction of the optical film is not known, the optical film is pulled in any one measurement direction within the surface of the test piece, and the tensile elastic modulus in the direction is measured. While changing the measurement direction by 10 ° from 0 ° to 180 °, the sample is pulled in each measurement direction in the same manner as described above, and the tensile elastic modulus in each measurement direction is measured. Of the obtained measurement values, the measurement direction in which the tensile modulus is 2 GPa or more is defined as direction X. At least one of the directions X may be the MD direction described above.

(CHE / CTE)
The ratio CHE / CTE between the hygroscopic expansion coefficient CHE (unit: ppm /% RH) in the direction X of the optical film and the thermal expansion coefficient CTE (unit: ppm / ° C.) in the direction X is, as described above, “ In order to make the “expansion force due to water” relatively larger than “the contraction force due to water removal”, it is preferably 0.6 or less, more preferably 0.57 or less, and 0.55 or less. More preferably. CHE / CTE can be 0 or more, preferably 0.2 or more.

The CHE / CTE in the direction X of the optical film can be obtained by the following procedure as described above. For example, when the MD direction of the optical film is known,
1) Cut an optical film into a predetermined size to obtain a test piece. The in-plane MD direction CTE (unit: ppm / ° C.) of the test piece is measured by the TMA method according to ASTM E-831 or JIS K7197.
2) The optical film test piece prepared in the same manner as described above was stored in the MD direction after being stored at 23 ° C. and 20% RH for a certain period of time (24 hours). ) Measure the dimensions in the MD direction after storage. The obtained measured value is applied to the following formula to obtain CHE (unit: ppm /% RH) in the MD direction of the optical film (see the following formula).
CHE (ppm /% RH) = {(MD direction dimension of specimen after storage at 23 ° C. and 80% RH−MD direction dimension of specimen after storage at 23 ° C. and 20% RH) / 23 ° C. and 20% RH Dimension of specimen in MD direction after storage} (ppm) / (80-20) (% RH)
3) The CHE / CTE in the MD direction of the optical film is calculated from the CTE and CHE of the optical film obtained in 1) and 2) above.

When the MD direction of the optical film is not known, CTE and CHE in any one direction within the surface of the test piece are measured, and CHE / CTE is calculated. While changing the measurement direction by 10 ° from 0 ° to 180 °, CTE and CHE in each measurement direction are measured in the same manner as described above to calculate CHE / CTE. Among the obtained measurement values, a measurement direction in which CHE / CTE is 0.6 or less is defined as direction X. At least one of the directions X may be the MD direction described above.

(Tg)
The glass transition temperature Tg of the optical film preferably satisfies the following formulas (1) to (3) at the same time. This is because an optical film having a Tg of 100 ° C. or higher has good heat resistance.
(Formula 1) Ta>Tg> Tb
(Formula 2) Ta ≧ Tb + 80
(Formula 3) 150 ≧ Tg ≧ 100

As described above, Tg of the optical film is a method according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer) as a midpoint glass transition temperature (Tmg). Can be measured. The heating rate can be 20 ° C./min.

(Retardation)
The retardation R ₀ in the in-plane direction measured under the conditions of a measurement wavelength of 590 nm and 23 ° C. and 55% RH of the optical film is preferably 0 nm or more and 20 nm or less, and more preferably 0 nm or more and 10 nm or less. . The thickness direction retardation Rth of the optical film measured under conditions of a measurement wavelength of 590 nm and 23 ° C. and 55% RH is preferably 0 nm or more and 80 nm or less, and more preferably 0 nm or more and 50 nm or less. The optical film having such a retardation value is preferably used as a polarizing plate protective film (F1 or F4) for a liquid crystal display device, as will be described later.

Retardation _R0 and Rth are defined by the following equations, respectively.
Formula (I): R ₀ = (nx−ny) × d (nm)
Formula (II): Rth = {(nx + ny) / 2−nz} × d (nm)
(In formulas (I) and (II),
nx represents the refractive index in the slow axis direction x where the refractive index is maximum in the in-plane direction of the film;
ny represents the refractive index in the direction y perpendicular to the slow axis direction x in the in-plane direction of the film;
nz represents the refractive index in the thickness direction z of the film;
d (nm) represents the thickness of the film)

The retardations _R0 and Rth can be determined by the following method, for example.
1) The optical film is conditioned at 23 ° C. and 55% RH. The average refractive index of the optical film after humidity adjustment is measured with an Abbe refractometer or the like.
The optical film after 2) humidity, measuring the _{R 0} when the light is incident in parallel to the measurement wavelength 590nm to normal of the film surface, KOBRA21DH, in Oji Scientific Corporation.
3) With KOBRA21ADH, the in-plane slow axis of the optical film is used as the tilt axis (rotation axis), and light with a measurement wavelength of 590 nm is incident from the angle of θ (incident angle (θ)) with respect to the normal of the optical film surface. The retardation value R (θ) when measured is measured. The in-plane slow axis of the optical film refers to a slow axis in the direction in which the refractive index is maximum in the optical film plane, and may preferably be the MD direction. The retardation value R (θ) can be measured at 6 points every 10 ° in the range of 0 ° to 50 °. The in-plane slow axis of the optical film can be confirmed by KOBRA21ADH.
4) nx, ny, and nz are calculated by KOBRA21ADH from the measured R ₀ and R (θ) and the above-described average refractive index and film thickness, and Rth at a measurement wavelength of 590 nm is calculated. The measurement of retardation can be performed under conditions of 23 ° C. and 55% RH.

The angle θ1 (orientation angle) formed by the in-plane slow axis of the optical film and the width direction of the optical film is preferably −1 ° to + 1 °, more preferably −0.5 ° to + 0.5 °. It is. The orientation angle θ1 of the optical film can be measured using an automatic birefringence meter KOBRA-WR (Oji Scientific Instruments).

(Haze)
The haze of the optical film is preferably 1.0% or less, and more preferably 0.5% or less. The haze of the optical film can be measured with a haze meter (turbidimeter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.) in accordance with JIS K-7136.

(Total light transmittance)
The total light transmittance of the optical film is preferably 90% or more, and more preferably 93% or more.

The optical film can be preferably used as a polarizing plate protective film. Examples of the polarizing plate protective film include not only a protective film having no retardation control function but also a retardation film having a retardation control function.

2. Method for Producing Optical Film The optical film of the present invention may be produced by a solution casting method or by a melt casting method. It is preferable that the optical film of the present invention is produced by a solution casting film forming method because melting at a high temperature is unnecessary and it is easy to form a film with a relatively high molecular weight resin (A) or (B). .

That is, the production process of the optical film of the present invention by the solution casting film forming method includes 1) a process of obtaining the dope by dissolving each of the above components in a solvent, and 2) casting the dope on an endless metal support. After that, the method includes a step of drying to obtain a film-like material, 3) a step of peeling the obtained film-like material from the metal support, and 4) a step of stretching the peeled film-like material.

1) Dissolution Step A dope is prepared by stirring and dissolving the above-mentioned components in an organic solvent while adding them.

The organic solvent used for the preparation of the dope can be used without limitation as long as it dissolves the above-described components including the above-described resins (A) and (B).

Examples of organic solvents include chlorinated organic solvents such as dichloromethane; methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2, 2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl- Non-chlorine organic solvents such as 2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, etc. included. Of these, dichloromethane, methyl acetate, ethyl acetate and acetone are preferred.

The organic solvent may further contain 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. By containing these aliphatic alcohols in the dope, the film-like material is gelled and easily peeled off from the metal support.

Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, s-butanol, t-butanol and the like. Of these, ethanol and butanol are preferred because they contribute to the stability of the dope, have a relatively low boiling point, and have a high drying property.

The organic solvent is preferably a mixture of dichloromethane and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms.

For dissolution of the resin (A) or (B), a method performed at normal pressure, a method performed at a temperature lower than the boiling point of the main solvent, a method performed at a temperature higher than the boiling point of the main solvent, JP-A-9-95544, Various methods such as a method performed by applying the cooling dissolution method described in JP-A-9-95557 or JP-A-9-95538, a method performed at high pressure described in JP-A-11-21379, etc. Although a dissolution method can be used, a method in which pressure is applied at a temperature equal to or higher than the boiling point of the main solvent is particularly preferable.

The total concentration of the resins (A) and (B) in the dope can be in the range of 15 to 45% by mass with respect to the total mass of the dope.

After adding and dissolving the additive in the dope, the obtained dope is filtered with a filter medium. Next, the filtered dope is defoamed, and then fed by a liquid feed pump. The filter medium used preferably has a collected particle diameter in the range of 0.5 to 5 μm and a drainage time in the range of 10 to 25 sec / 100 ml. By using the filter medium, aggregates remaining at the time of dope dispersion and aggregates generated at the time of dope preparation can be efficiently removed.

2) Casting step The obtained dope is fed to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump). Then, the dope is cast on the endless metal support from the slit of the pressure die. The metal support may be, for example, a metal belt such as a stainless steel belt; it may be a rotating metal drum or the like.

Examples of pressure dies include coat hanger dies and T dies. The surface of the metal support is preferably a mirror surface.

Next, the cast dope is heated on a metal support, and the solvent is evaporated to obtain a film.

The method of evaporating the solvent includes a method of blowing air on the surface of the dope, a method of transferring heat from the back surface of the metal support by a liquid, a method of transferring heat from the front and back of the dope by radiant heat, and the like. Especially, since the drying efficiency is high, the method of transferring heat with a liquid from the back surface of the metal support is preferable.

The drying of the dope on the metal support is preferably performed in an atmosphere of 40 to 100 ° C. In order to obtain an atmosphere of 40 to 100 ° C., it is preferable to heat the dope by applying warm air of this temperature to the surface of the dope film or applying infrared rays.

3) Stripping step The film-like material obtained by evaporating the solvent on the metal support is stripped at the stripping position. From the viewpoint of improving the surface quality and peelability of the obtained film-like material, it is preferable to peel the film-like material from the metal support within 30 to 120 seconds after casting.

The amount of the residual solvent of the film-like material upon peeling from the metal support is preferably about 50 to 120% by mass, although it depends on the strength of drying conditions and the length of the metal support. When the film is peeled off when the amount of the residual solvent is larger, if the film-like material is too soft, the flatness is liable to be lost due to nonuniform elongation at the time of peeling, and slippage and vertical stripes due to peeling tension are likely to occur. Therefore, the residual solvent amount at the time of peeling can be determined within a range that does not impair the flatness.

The amount of residual solvent in the film is defined by the following formula.
Residual solvent amount (%) = (mass before heat treatment of film-like material−mass after heat treatment of film-like material) / (mass after heat treatment of film-like material) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 140 ° C. for 1 hour.

The peeling tension when peeling the film-like material from the metal support is usually preferably 196 to 245 N / m. In the case where wrinkles easily occur during peeling, the peeling tension is preferably 190 N / m or less.

The temperature of the film-like material at the peeling position of the metal support is preferably −50 to 40 ° C., more preferably 10 to 40 ° C., and further preferably 15 to 30 ° C.

4) Drying and stretching step The peeled film-like material is dried while being transported in the tenter stretching apparatus, or is dried while being transported by a plurality of rollers arranged in the drying apparatus. The drying method is not particularly limited, but a method of blowing hot air on both surfaces of the film-like material is common.

Since rapid drying tends to impair the flatness of the resulting film, drying at a high temperature is preferably performed under conditions where the residual solvent is 8% by mass or less. Throughout the drying process, the drying temperature is preferably in the range of 40-250 ° C, more preferably in the range of 40-200 ° C.

It is preferable to further stretch the film-like material obtained after drying. By stretching, it is easy to increase the degree of orientation of the resin (A) or the resin (B) and to increase the tensile modulus of the resulting film.

The stretching is preferably performed at least in the direction X described above. The direction X may be either the casting direction (MD direction) or the width direction (TD direction). There may be one stretching direction or two or more stretching directions. Stretching in two directions (biaxial stretching) is preferably performed in the casting direction (MD direction) and the width direction (TD direction), respectively. The biaxial stretching may be simultaneous biaxial stretching or stepwise biaxial stretching (sequential biaxial stretching).

Stepwise biaxial stretching includes sequentially performing stretching in different stretching directions; and performing stretching in the same direction in multiple stages. Examples of stepwise biaxial stretching include the following.
a) Stretch in the casting direction → Stretch in the width direction → Stretch in the casting direction → Stretch in the casting direction b) Stretch in the width direction → Stretch in the width direction → Stretch in the casting direction → Stretch in the casting direction

The stretching ratio is the total of the casting direction (MD direction) and the width direction (TD direction), preferably in the range of 110% to 400%, more preferably in the range of 120 to 300%, and still more preferably It is in the range of 130 to 250%. By increasing the draw ratio, it is easy to increase the tensile modulus of the resulting film; it is easy to decrease CHE / CTE. The draw ratio (%) is defined as the length of the film-like product after stretching (in the drawing direction) / the length of the film-like material before drawing (in the drawing direction) × 100. For example, when the draw ratio in the casting direction is 110% and the draw ratio in the width direction is 120%, the sum of the draw ratios is defined as the sum thereof; 100+ (10 + 20) = 130%.

The stretching temperature is preferably Tg to (Tg + 50) ° C. of the optical film, and more preferably Tg to (Tg + 40) ° C. Specifically, when an optical film containing cellulose ester as a main component is obtained, the stretching temperature can be about 100 to 200 ° C.

When stretching with a tenter stretching apparatus, the residual solvent amount of the film-like material at the start of tenter stretching is preferably 20 to 100% by mass. Furthermore, it is preferable to dry until the amount of residual solvent in the film-like material is 10% by mass or less, preferably 5% by mass or less. The drying temperature is preferably in the range of 30 to 160 ° C, more preferably in the range of 50 to 150 ° C.

5) Winding process The optical film may be provided in a long shape or in a single sheet shape. The long optical film can usually be wound into a roll in the long direction to form a wound body. The film winding method may be a commonly used one, such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like. Or in combination.

The length of the long optical film can be in the range of 100 to 10,000 m. The width of the long optical film can be in the range of 1 to 4 m, preferably in the range of 1.4 to 3 m.

3. Polarizing plate The polarizing plate of this invention contains a polarizer and a polarizing plate protective film.

<About the polarizer>
A polarizer is an element that passes only light having a plane of polarization in a certain direction, and a typical polarizer known at present is a polyvinyl alcohol polarizing film. The polyvinyl alcohol polarizing film includes those obtained by dyeing iodine on a polyvinyl alcohol film and those obtained by dyeing a dichroic dye.

The polyvinyl alcohol polarizing film may be a film (preferably a film further subjected to durability treatment with a boron compound) dyed with iodine or a dichroic dye after uniaxially stretching the polyvinyl alcohol film; A film obtained by dying an alcohol film with iodine or a dichroic dye and then uniaxially stretching (preferably a film further subjected to a durability treatment with a boron compound) may be used.

The thickness of the polarizer is preferably 2 to 30 μm, and more preferably 5 to 25 μm in order to reduce the thickness of the polarizing plate.

<About polarizing plate protective film>
The polarizing plate protective film may be disposed directly or via another layer on at least one surface of the polarizer. The polarizing plate protective film can be used as the optical film of the present invention.

The lamination of the polarizing plate protective film and the polarizer is preferably performed so that the in-plane direction X of the polarizing plate protective film and the absorption axis direction of the polarizer are parallel to each other. The in-plane direction X of the polarizing plate protective film is “the direction in which the CHE / CTE of the polarizing plate protective film is 0.6 or less and the tensile elastic modulus at 40 ° C. is 2 to 6 GPa”; It is preferably the MD direction of the film, and more preferably at least one of the in-plane slow axis direction and the direction orthogonal thereto.

<About retardation film>
A retardation film may be further disposed on the other surface of the polarizer where the polarizing plate protective film is not disposed.

The retardation film is not particularly limited, and may be, for example, a cellulose ester film. Examples of cellulose esters contained in the cellulose ester film include cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose acetate propionate benzoate, cellulose propionate, and cellulose butyrate. , Cellulose acetate biphenylate, cellulose acetate propionate biphenylate, and the like.

The cellulose ester preferably has a total acyl group substitution degree of 1.5 or more and 2.5 or less, and more preferably satisfies the following formulas (a) and (b).
Formula (a) 2.0 ≦ X + Y ≦ 2.5
Formula (b) 0 ≦ Y ≦ 1.5 (wherein X represents the degree of substitution of the acetyl group, and Y represents the degree of substitution of the propionyl group or butyryl group, or a mixture thereof)

The weight average molecular weight (Mw) of the cellulose ester is preferably 75,000 or more, more preferably 100,000 to 1,000,000, from the viewpoints of film strength and appropriate viscosity during film formation. It is particularly preferable that it is ˜500,000.

The retardation film may be a commercially available product. For example, examples of the retardation film for vertical alignment (VA) include Konica Minoltak KC8UCR3, KC8UCR4, KC8UCR5, KC4FR, KC4KR, KC4DR, KC4SR (above, manufactured by Konica Minolta Co., Ltd.). In addition, as a film that can be used other than the retardation film for VA, KC4UE, KC8UE, KC8UX, KC5UX, KC8UY, KC4UY, KC4CZ, KC6UA, KC4UA (above, manufactured by Konica Minolta Co., Ltd.) and the like can be used. .

The cellulose ester film may be a single layer film or a laminated film. When the cellulose ester film is a laminated film, it is a laminate of a core layer mainly composed of a cellulose ester having a low degree of substitution and a skin layer mainly composed of a cellulose ester having a high degree of substitution disposed on both sides thereof. It is preferable. The cellulose ester having a low degree of substitution preferably satisfies the above formulas (a) and (b), and the cellulose ester having a high degree of substitution preferably has a total acyl group substitution degree of more than 2.5, and preferably 2.7. It is preferable that it is 2.98 or less, and it is preferable that all acyl groups contained in the cellulose ester are acetyl groups.

The retardation of the retardation film can be set according to the type of liquid crystal cell to be combined. For example, the retardation Ro (590) in the in-plane direction measured at a wavelength of 590 nm at 23 ° C. and 55% RH is preferably in the range of 30 to 150 nm, and the retardation Rt (590 in the thickness direction). ) Is preferably in the range of 70 to 300 nm. A retardation film having a retardation in the above range can be preferably used as a retardation film such as a VA liquid crystal cell. The retardation Ro in the in-plane direction and the retardation Rt in the thickness direction can be defined and measured in the same manner as described above.

The thickness of the retardation film is not particularly limited, but is preferably 10 to 250 μm, more preferably 10 to 100 μm, and particularly preferably 30 to 60 μm.

The polarizing plate of the present invention is preferably used for a liquid crystal display device. The polarizing plate of the present invention can be used by being disposed so that the polarizing plate protective film is on the side opposite to the liquid crystal cell (side not bonded to the liquid crystal cell).

The polarizing plate can be obtained through a step of bonding a polarizing plate protective film and a polarizer. The polarizing plate protective film and the polarizer may be bonded using a completely saponified polyvinyl alcohol adhesive, an acetoacetyl group-modified polyvinyl alcohol adhesive, an active energy ray-curable adhesive, or the like. it can. When an active energy ray-curable adhesive is used, the thickness of the cured layer of the active energy ray-curable adhesive is usually in the range of 0.01 to 10 μm, and preferably in the range of 0.5 to 5 μm.

4). Liquid Crystal Display Device The liquid crystal display device of the present invention includes a liquid crystal cell and a pair of polarizing plates that sandwich the liquid crystal cell. And at least one of a pair of polarizing plates can be used as the polarizing plate of the present invention.

FIG. 1 is a schematic diagram showing an example of a basic configuration of a liquid crystal display device. As shown in FIG. 1, the liquid crystal display device 10 of the present invention includes a liquid crystal cell 30, a first polarizing plate 50 and a second polarizing plate 70 that sandwich the liquid crystal cell 30, and a backlight 90.

The liquid crystal cell 30 has a pair of

transparent substrates

31 and 33 and a liquid crystal layer 35 sandwiched between them. The

transparent substrates

31 and 33 are preferably glass substrates. The thickness of the glass substrate is preferably not more than a certain value in order to reduce the thickness of the liquid crystal display device, preferably not less than 0.3 mm and less than 0.7 mm, and preferably 0.3 to 0.5 mm. More preferred.

The display mode of the liquid crystal cell 30 may be various display modes such as STN, TN, OCB, HAN, VA (MVA, PVA), and IPS. For obtaining high contrast, the VA (MVA, PVA) mode is used. It is preferable that

When the liquid crystal cell 30 is a VA liquid crystal cell, a pixel electrode for applying a voltage to the liquid crystal molecules is disposed on one of the pair of transparent substrates. The counter electrode may be disposed on the one transparent substrate (where the pixel electrode is disposed) or may be disposed on the other transparent substrate.

When the liquid crystal cell 30 is a VA liquid crystal cell, the liquid crystal layer includes liquid crystal molecules having negative or positive dielectric anisotropy. The liquid crystal molecules are liquid crystal molecules when no voltage is applied (when an electric field is not generated between the pixel electrode and the counter electrode) due to the alignment regulating force of the alignment film provided on the liquid crystal layer side surface of the transparent substrate. Are oriented so that their long axes are substantially perpendicular to the surface of the transparent substrate.

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

The first polarizing plate 50 is disposed on the viewing side surface of the liquid crystal cell 30, and is disposed on the first polarizer 51 and the surface of the first polarizer 51 opposite to the liquid crystal cell 30. A polarizing plate protective film 53 (F1) and a retardation film 55 (F2) disposed on the surface of the first polarizer 51 on the liquid crystal cell 30 side are included.

The second polarizing plate 70 is disposed on the surface of the liquid crystal cell 30 on the backlight 90 side, and is disposed on the surface of the second polarizer 71 and the surface of the second polarizer 71 on the liquid crystal cell 30 side. The phase difference film 73 (F3) and the polarizing plate protective film 75 (F4) arrange | positioned at the surface on the opposite side to the liquid crystal cell 30 of the 2nd polarizer 71 are included.

And at least one of the polarizing plate protective film 53 (F1) and the polarizing plate protective film 75 (F4); preferably, the polarizing plate protective film 53 (F1) can be used as the optical film of the present invention.

FIG. 2 is a schematic diagram showing the relationship between the absorption axis of the polarizer and the direction X of the protective film in the liquid crystal display device. As shown in FIG. 2, the absorption axis of the first polarizer 51 and the absorption axis of the second polarizer 71 can be arranged to be orthogonal to each other.

And at least one of the polarizing plate protective film 53 (F1) and the polarizing plate protective film 75 (F4); preferably, the polarizing plate protective film 53 (F1) can be used as the optical film of the present invention. For example, when both the polarizing plate protective film 53 (F1) and the polarizing plate protective film 75 (F4) are the optical films of the present invention, the direction X in the plane of the polarizing plate protective film 53 (F1) and the first polarizer 51 is preferably parallel to each other; the direction X in the plane of the polarizing plate protective film 75 (F4) and the absorption axis of the second polarizer 71 are preferably parallel to each other (see FIG. 2). ). The direction X of the optical film to be the polarizing plate protective film 53 (F1) coincides with the longitudinal direction of the optical film.

The absorption axis of the first polarizer 51 is often parallel to the long axis direction of the display (display screen) of the liquid crystal display device. Therefore, when the first polarizer 51 receives heat from the backlight, the first polarizer 51 easily contracts in the major axis direction of the display (display screen). On the other hand, the absorption axis of the second polarizer 71 is often parallel to the minor axis direction of the display (display screen). Therefore, the second polarizer 71 tends to contract in the short axis direction of the display (display screen).

The contraction force of the first polarizer 51 can be canceled by the expansion force of the polarizing plate protective film 53 (F1); the contraction force of the second polarizer 71 is the expansion force of the polarizing plate protective film 75 (F4). Can be countered by.

Particularly, the contraction force of the first polarizer 51 contracting in the major axis direction of the display (display screen) is larger than the contraction force of the second polarizer 71 contracting in the minor axis direction of the display (display screen). Therefore, it is preferable to apply the optical film of the present invention to the polarizing plate protective film 53 (F1).

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

1. Optical film materials 1) Resin (A)
Resin (A-1): CAP482-20 (acetyl acetate substitution degree 0.19, propionyl group substitution degree 2.56, total acyl group substitution degree 2.75 cellulose acetate propionate, weight average molecular weight Mw = 200,000)
Resin (A-2): TAC (cellulose triacetate having an acetyl group substitution degree of 2.87 and a total acyl group substitution degree of 2.87, weight average molecular weight Mw = 300,000)
Resin (A-3): PMMA (polymethyl methacrylate, weight average molecular weight Mw = 300,000)
Comparative resin (X-1): CAB381-20 (cellulose acetate butyrate having an acetyl group substitution degree of 1.08, a butyryl group substitution degree of 1.84, and a total acyl group substitution degree of 2.92, weight average molecular weight Mw = 200,000 )

The hygroscopic expansion coefficient CHE, thermal expansion coefficient CTE, tensile elastic modulus and Tg of these resins were measured by the following methods. The results are shown in Table 2.

(Resin CHE, CTE)
The CHE / CTE of the resin (A) was determined by the following procedure.
1) A film made of resin (A) having a thickness of 40 μm was produced by a solution casting film forming method. In the production of the film, intentional stretching was not performed. The obtained film was cut into a predetermined size and used as a test piece. And the CTE of MD direction of the said test piece was measured by TMA method based on JISK7197, and CTE (unit: ppm / degreeC) of resin (A) was obtained.
2) In the same manner, a test piece made of resin (A) and having a thickness of 40 μm was stored for 24 hours in an environment of 23 ° C. and 20% RH, in the MD direction, and in an environment of 23 ° C. and 80% RH. The dimension in the MD direction after storage for 24 hours was measured. The obtained measured value was applied to the following formula to obtain CHE (unit: ppm /% RH) of the resin (A) (see the following formula).
CHE (ppm /% RH) = {(MD direction dimension of specimen after storage at 23 ° C. and 80% RH−MD direction dimension of specimen after storage at 23 ° C. and 20% RH) / 23 ° C. and 20% RH Dimension of specimen after storage under MD} / (80% RH-20% RH)
3) CHE / CTE was calculated from CTE and CHE of the resin (A) obtained in 1) and 2) above.

(Tensile modulus of resin)
1) In the same manner as described above, a film made of resin (A) having a thickness of 40 μm was prepared by a solution casting film forming method. The obtained film was cut into a size of 100 mm (MD direction) × 10 mm (TD direction) to obtain a test piece.
2) Based on JIS K7127, the obtained test piece was pulled in the MD direction using a Tensilon RTC-1225A manufactured by Orientec Co., Ltd., and the tensile elastic modulus in the MD direction was measured. The measurement was performed at 40 ° C. and 20% RH.

(Glass transition temperature of resin Ta)
The glass transition temperature Ta of the resin (A) was determined as a midpoint glass transition temperature (Tmg) by a method according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer). It was measured. The heating rate was 20 ° C./min.

2) Resin (B)
Resin (B-1): Polyvinyl acetate (weight average molecular weight Mw: 100,000)
Resin (B-2): Polyvinyl acetate (weight average molecular weight Mw: 200,000)
Resin (B-3): Polyvinyl acetate (weight average molecular weight Mw: 80,000)
Resin (B-4): Polylactic acid (weight average molecular weight Mw: 100,000)
Resin (B-5): Polyacetal (weight average molecular weight Mw: 100,000)
Resin (B-6): Polyurethane (Composition: Copolymer of MDI (diphenylmethane diisocyanate) and ethylene glycol, weight average molecular weight Mw: 100,000)
Resin (B-7): EVA (composition: ethylene / vinyl acetate (50/50 molar ratio) copolymer, weight average molecular weight Mw: 100,000)
Resin (B-8): Rubber particles (composition: styrene-butadiene copolymer, weight average molecular weight Mw: 500,000, particle diameter: 10 to 200 nm)
Resin for comparison (Y-1): Nylon 66

The hygroscopic expansion coefficient CHE, thermal expansion coefficient CTE, tensile modulus and Tg of these resins were measured in the same manner as described above. The results are shown in Table 3.

2. Production of optical film (Example 1-1)
The following components were sufficiently dissolved with stirring and heating to prepare a dope.
(Composition of dope)
Resin (A-1) as resin (A): 60 parts by mass Resin (B-1) as resin (B): 40 parts by mass 2,2′-methylenebis [6- (2H-benzotriazole-2] as an ultraviolet absorber -Yl) -4- (1,1,3,3-tetramethylbutyl) phenol] (LA31 manufactured by ADEKA, molecular weight 659): 3.0 parts by mass R972V (silica particles manufactured by Nippon Aerosil Co., Ltd.) as a matting agent , Average particle size 16 nm): 0.30 parts by mass Elecut S412 (manufactured by Takemoto Yushi Co., Ltd.) as a peeling aid: 0.50 parts by mass Dichloromethane: 300 parts by mass Ethanol: 40 parts by mass

The prepared dope was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the residual solvent amount reached 100%, and the obtained film-like material was peeled off from the stainless steel band support with a peeling tension of 162 N / m.

Next, the solvent was evaporated from the peeled film at 35 ° C., and the film was slit to a width of 1 m. Then, it was dried at a drying temperature of 135 ° C. while stretching 10% in the transport direction (MD direction) by zone stretching and 20% stretching in the width direction (TD direction) by tenter stretching (the total stretching ratio was 130%). . The residual solvent amount at the start of stretching by the tenter was 8.0%.

After stretching with a tenter, relaxation treatment is performed at 130 ° C. for 5 minutes, and then drying is completed while conveying a drying zone at 120 ° C. and 140 ° C. with a number of rollers to obtain an optical film 101 having a thickness of 40 μm. It was.

(Examples 1-2 to 1-9 and Comparative Examples 1-1 to 1-3)
Optical films 102 to 112 were obtained in the same manner as in Example 1-1 except that the resins (B), (A) / (B) and the stretching conditions were changed as shown in Table 4.

(Example 1-10)
Optical film 113 was obtained in the same manner as in Example 1-1 except that resin (A) and resin (A) / resin (B) were changed as shown in Table 4.

(Examples 1-11 to 1-15, Comparative Example 1-4)
Optical films 114 to 119 were obtained in the same manner as in Example 1-10 except that the resin (B) was changed as shown in Table 4.

(Example 1-16)
Optical film 120 was obtained in the same manner as in Example 1-1 except that resin (A) and resin (A) / resin (B) were changed as shown in Table 4.

(Examples 1-17 to 1-21)
Optical films 121 to 125 were obtained in the same manner as in Example 1-16, except that the resin (B) was changed as shown in Table 4.

(Comparative Examples 1-5 to 1-6)
The types and amounts of resin (A) and resin (B) shown in Table 5 and the same type and amount of UV absorber and stripping aid as in Example 1-1 were combined with an internal mixer (Toyo Seiki Seisakusho Co., Ltd.) with an internal volume of 60 cc. For 5 minutes at 200 ° C. and 30 rpm. The obtained mixture was molded into a film with a small compression molding machine (manufactured by Tester Sangyo Co., Ltd.) to obtain optical films 126 to 127 having a film thickness of 40 μm.

The tensile modulus and CHE / CTE of the obtained optical film at 40 ° C. in the MD direction (direction X) were measured by the following methods. Further, the glass transition temperature Tg of the obtained optical film was measured in the same manner as described above.

(Tensile modulus of optical film)
1) The optical film was cut into a size of 100 mm (MD direction) × 10 mm (TD direction) to obtain a test piece.
2) In accordance with JIS K7127, the test piece was pulled in the MD direction (direction X) of the test piece using a Tensilon RTC-1225A manufactured by Orientec Co., Ltd. ) Was measured. The measurement was performed at 40 ° C. and 20% RH.

(CHE / CTE of optical film)
1) The optical film was cut out to a predetermined size to obtain a test piece. The CTE in the MD direction (direction X) of the test piece was measured by the TMA method according to ASTM E-831 or JIS K7197.
2) The test piece of the optical film prepared in the same manner as described above was stored for 24 hours in an environment of 23 ° C. and 20% RH, and the dimension in the MD direction (direction X) and in an environment of 23 ° C. and 80% RH. The dimension in the MD direction (direction X) after storage for 24 hours was measured. The obtained measured value was applied to the following formula to obtain CHE (ppm /% RH) in the MD direction (direction X) of the optical film (see the following formula).
CHE (ppm /% RH) = {(MD direction dimension of specimen after storage at 23 ° C. and 80% RH−MD direction dimension of specimen after storage at 23 ° C. and 20% RH) / 23 ° C. and 20% RH Dimension of specimen in MD direction after storage} (ppm) / (80-20) (% RH)
3) CHE / CTE in the MD direction (direction X) of the optical film was calculated from the CTE and CHE of the optical film obtained in 1) and 2) above.

These evaluation results are shown in Table 4. In each example / comparative example, the total amount of the resin (A) and the resin (B) was 100 parts by mass.

As shown in Table 4, it can be seen that the films of Comparative Examples 1-3 and 1-4 containing the resin (Y-1) having a CHE / CTE of more than 0.6 have too high CHE / CTE.

Further, even if the resin (B) having CHE / CTE of 0.6 or less is contained, the film of Comparative Example 1-2 in which the content of the resin (B) is too large has a low tensile elastic modulus; It can be seen that the film of Comparative Example 1-1 in which the content of) is too low has a high CHE / CTE, and none of them satisfies the scope of the present invention.

Further, the films of Comparative Examples 1-5 and 1-6 that were formed by the melt film forming method and were not stretched even when the resin (B) having a CHE / CTE of 0.6 or less were included, It can be seen that the tensile modulus is low.

From these, in order to obtain an optical film having a CHE / CTE of 0.6 or less and a tensile elastic modulus at 40 ° C. of 2 to 6 GPa, a resin (CHE / CTE of 0.6 or less) ( It can be seen that it is effective to include B) in an appropriate amount or to stretch at a certain ratio or more.

In addition, among the examples, the films of Examples 1-1 and 1-2 in which the molecular weight of the resin (B) is large are higher in CHE / CTE than the film of Example 1-3 in which the molecular weight of the resin (B) is small. It can be seen that the range is easily set to an appropriate range.

Furthermore, it can be seen that the stretched film of Example 1-1 can lower the CHE / CTE and increase the tensile elastic modulus than the film of Example 1-9 that has not been stretched.

3. Production of retardation film (retardation film C)
The following components were stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin to obtain a fine particle dispersion 1.
(Fine particle dispersion 1)
Fine particles (Aerosil R812 manufactured by Nippon Aerosil Co., Ltd.): 11 parts by mass Ethanol: 89 parts by mass

The above-prepared fine particle dispersion 1 was slowly added to the dissolution tank containing methylene chloride and sufficiently stirred. The resulting solution was dispersed with an attritor so that the secondary particles had a predetermined particle size, and then filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution 1 did.
(Fine particle addition liquid 1)
Methylene chloride: 99 parts by mass Fine particle dispersion 1: 5 parts by mass

A main dope solution having the following composition was prepared. First, after adding methylene chloride and ethanol to the pressure dissolution tank, the cellulose acetate, sugar ester compound, polycondensation ester, retardation increasing agent and fine particle additive liquid 1 having an acetyl group substitution degree of 2.40 are added with stirring. did. This was heated and dissolved completely with stirring. The obtained solution was used as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. The main dope solution was prepared by filtration using 244.

(Main dope composition)
Methylene chloride: 365 parts by mass Ethanol: 50 parts by mass Cellulose acetate (acetyl substitution degree 2.40): 84 parts by mass Sugar ester 1: Saccharose benzoate having an average substitution degree of 5.5: 10 parts by mass Polycondensation ester: (phthalic acid / Adipic acid / 1,2-propanediol = 25/75/100 molar condensate having both ends sealed with benzoate groups, molecular weight 440): 3 parts by mass Retardation adjuster (compound A): 3 parts by mass Particulate additive solution 1: 1 parts by mass

The obtained main dope solution was evaporated on a stainless belt support until the amount of residual solvent in the cast film was 75%. The obtained film was peeled from the stainless steel belt support with a peeling tension of 130 N / m. The film-like material obtained by peeling was stretched 30% in the width direction using a tenter while applying heat at 150 ° C. The residual solvent at the start of stretching was 15%.

Next, drying was terminated while the drying zone was conveyed by a number of rolls. The drying temperature was 130 ° C. and the transport tension was 100 N / m. As described above, a retardation film C having a dry film thickness of 35 μm was obtained.

4). Preparation of Protective Film F4 for Backlight “KC6UA” manufactured by Konica Minolta Co., Ltd. was prepared as the protective film F4 for the backlight, and used as an optical film 130.

5. Production of Polarizing Plate and Liquid Crystal Display Device (Example 2-1)
1) Production of Polarizer A polyvinyl alcohol film having a thickness of 75 μm was swollen with water at 35 ° C. The obtained film was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and further immersed in an aqueous solution at 45 ° C. consisting of 3 g of potassium iodide, 7.5 g of boric acid and 100 g of water. . The obtained film was uniaxially stretched under conditions of a stretching temperature of 55 ° C. and a stretching ratio of 3 times. This uniaxially stretched film was washed with water and dried to obtain a polarizer having a thickness of 25 μm.

2) Preparation of polarizing plate The optical film 101 prepared above was prepared as a polarizing plate protective film. Then, as shown below, the optical film 101 was alkali saponified and then washed with water, neutralized and washed with water.
Saponification step 2M-NaOH 50 ° C. 90 seconds Water washing step Water 30 ° C. 45 seconds Neutralization step 10% HCl 30 ° C. 45 seconds Water washing step Water 30 ° C. 45 seconds Thereafter, the obtained optical film 101 was dried at 80 ° C. . Similarly, the produced retardation film C was also subjected to alkali saponification treatment.

Then, the above-mentioned optical film 101 subjected to alkali saponification treatment was bonded to one surface of the produced polarizer using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive. Similarly, the retardation film C subjected to alkali saponification treatment was bonded to the other surface of the polarizer using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive. The bonding was performed so that the MD direction of the optical film 101 serving as the protective film F1 on the viewing side is parallel to the absorption axis of the polarizer (first polarizer). The laminated laminate was dried at 60 ° C. to obtain a polarizing plate 201 on the viewing side.

Similarly, the optical film 130 which is the protective film F4 on the backlight side, which has been subjected to alkali saponification treatment, on one surface of the produced polarizer, its MD direction and the absorption axis of the polarizer (second polarizer). Were laminated through a 5% aqueous solution of a completely saponified polyvinyl alcohol so that they were parallel to each other. A retardation film C subjected to alkali saponification treatment on the other surface of this polarizer is laminated and bonded together through a 5% aqueous solution of completely saponified polyvinyl alcohol, and a polarizing plate 228 (second polarization) on the backlight side is laminated. Plate).

3) Production of liquid crystal display panel As a liquid crystal cell, a VA liquid crystal cell having two glass substrates having a thickness of 0.5 mm and a liquid crystal layer disposed therebetween was prepared. Then, the polarizing plate 201 on the viewing side and the polarizing plate 228 on the backlight side were prepared on both sides of the prepared liquid crystal cell via a 25 μm-thick double-sided tape (baseless tape MO-3005C) manufactured by Lintec. Were bonded together to obtain a liquid crystal display panel. In the bonding, the absorption axis of the polarizer of the polarizing plate 201 on the viewing side is orthogonal to the absorption axis of the polarizer of the polarizing plate 228 on the backlight side, and the MD direction of the optical film 101 of the polarizing plate 201 on the viewing side is The long axis direction of the liquid crystal display panel was set (see FIG. 2). Moreover, it performed so that the phase difference film C of the polarizing plates 201 and 228 might contact | connect a liquid crystal cell.

4) Production of liquid crystal display device After removing the liquid crystal display panel (polarizing plate / liquid crystal cell / laminate of polarizing plate) from the 40-inch display BRAVIA KLV-40J3000 (VA method) manufactured by SONY, the liquid crystal display produced above A panel was arranged to obtain a liquid crystal display device 301. Further, in the liquid crystal display panel, the slow axis of the retardation film C and the slow axis of the polarizing plate attached in advance were made parallel.

(Examples 2-2 to 2-21, Comparative Examples 2-1 to 2-6)
Polarizing plates 202 to 227 were produced in the same manner as in Example 2-1, except that the type of the polarizing plate protective film F1 was changed as shown in Table 5, and liquid crystal display devices 302 to 327 were obtained.

The warpage amount, display unevenness and color shift of the liquid crystal display panel in the obtained liquid crystal display device were evaluated by the following methods.

(Panel warpage)
The produced liquid crystal display device was treated for 24 hours in an environment of 40 ° C. and 95% RH, and then treated for 2 hours in an environment of 40 ° C. and 20% RH. Thereafter, the amount of warpage of the liquid crystal display panel of the liquid crystal display device was measured using a laser displacement meter. The measured values were obtained by measuring the heights of the four corners of the display surface with the center of the display as the zero point, and calculating the average value. The case where the four corners of the display surface are on the viewing side is defined as +, and the case where the four corners on the display side are exposed is denoted as-.

(Display unevenness)
The display screen of the liquid crystal display device after the above treatment (after treatment for 24 hours in an environment of 40 ° C. and 95% RH and then for 2 hours in an environment of 40 ° C. and 20% RH) was observed from the front of the screen. The display unevenness was evaluated based on the following criteria.
◎: No unevenness ○: Slightly uneven △: Some weak unevenness ×: Strong regularity unevenness

(Color shift)
The display of the produced liquid crystal display device was displayed in black under an environment of 23 ° C. and 55% RH, and the color was observed from an angle of 45 ° with respect to the normal to the display surface. Next, the liquid crystal display device is processed under the above-described conditions (processed for 24 hours in an environment of 40 ° C. and 95% RH, then processed for 2 hours in an environment of 40 ° C. and 20% RH). The same observation was made. Then, the color shift observed from the oblique 45 ° angle of the liquid crystal display device before the treatment is compared with the color observed from the oblique 45 ° angle of the liquid crystal display device after the treatment, and the color shift is performed. Was evaluated based on the following criteria.
◎: No color change ○: Color change is slightly recognized △: Color change is known ×: Color change is remarkable

The evaluation results are shown in Table 5.

As shown in Table 5, the liquid crystal display panels of Examples 2-1 to 2-21 including the optical film in which the CHE / CTE and the tensile elastic modulus at 40 ° C. are both adjusted to a predetermined range are warped. It can be seen that it has been reduced. Thereby, it can be seen that the display unevenness of the liquid crystal display device of this example is reduced.

On the other hand, it can be seen that the liquid crystal display panels of Comparative Examples 2-1 to 2-6 including the optical film in which at least one of CHE / CTE and the tensile elastic modulus at 40 ° C. is not within the predetermined range are greatly warped. Thereby, it can be seen that display unevenness of the liquid crystal display device of the comparative example occurs.

This application claims priority based on Japanese Patent Application No. 2013-238943 filed on November 19, 2013. The contents described in the application specification and the drawings are all incorporated herein.

An object of the present invention is to provide an optical film that can suppress panel bend and reduce display unevenness.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 30 Liquid crystal cell 50 1st polarizing plate 51 1st polarizer 53 Protective film (F1)
55 Retardation film (F2)
70 Second Polarizer 71 Second Polarizer 73 Retardation Film (F3)
75 Protective film (F4)
90 backlight

Claims

When the hygroscopic expansion coefficient is CHE and the thermal expansion coefficient is CTE,
A resin (A) having a CHE / CTE of 0.6 or more and a tensile elastic modulus of 2 GPa or more in a 40 ° C., 20% RH environment;
An optical film comprising a resin (B) having a CHE / CTE of less than 0.6,
The ratio CHE / CTE between the hygroscopic expansion coefficient CHE in any one direction X in the plane of the optical film and the thermal expansion coefficient CTE in the direction X is 0.6 or less, and the 40 ° C. and 20% RH environment An optical film having a tensile elastic modulus in the direction X of 2 to 6 GPa.
2. The optical film according to claim 1, wherein the direction X is at least one of an in-plane slow axis direction of the optical film and a direction orthogonal to the in-plane slow axis direction.
The optical film according to claim 1, wherein the direction X and the longitudinal direction of the optical film coincide with each other.
When the glass transition temperature of the resin (A) is Ta, the glass transition temperature of the resin (B) is Tb, and the glass transition temperature of the optical film is Tg, the following formulas (1) to (3) are satisfied: Item 5. The optical film according to Item 1.
(Formula 1) Ta>Tg> Tb
(Formula 2) Ta ≧ Tb + 80
(Formula 3) 150 ≧ Tg ≧ 100
The optical film according to claim 1, wherein the weight average molecular weight of the resin (A) and the weight average molecular weight of the resin (B) are both from 90,000 to 1,000,000.
2. The optical film according to claim 1, wherein the mass ratio of the resin (A) and the resin (B) is (A) :( B) = 30: 70 to 90:10.
A step of casting a dope containing the resin (A) and the resin (B) and a solvent on a metal support plate and then drying to obtain a film-like material;
The film-like material is stretched in both the transport direction and the direction perpendicular to the transport direction so that the total stretch ratio in both the transport direction and the direction orthogonal to the transport direction is 110 to 400%. The optical film of Claim 1 obtained through a process.
The optical film according to claim 1, wherein the resin (A) is a cellulose ester.
The optical film according to claim 1, wherein the resin (B) contains at least one selected from the group consisting of polyvinyl acetate, polylactic acid, polyacetal, polyurethane, ethylene-vinyl acetate polymer, and rubber particles.
The optical film according to claim 1, wherein the CHE / CTE of the optical film is 0.2 to 0.6.
2. The optical film according to claim 1, wherein the weight average molecular weight of the resin (A) and the weight average molecular weight of the resin (B) are both 150,000 to 500,000.
The optical film according to claim 1, which is a polarizing plate protective film.
A polarizing plate comprising a polarizer and the optical film according to claim 1.
The polarizing plate according to claim 13, wherein the in-plane direction X of the optical film and the absorption axis of the polarizer are parallel to each other.
A liquid crystal display device including a first polarizing plate, a liquid crystal cell, a second polarizing plate, and a backlight in this order,
The first polarizing plate includes a first polarizer, a polarizing plate protective film F1 disposed on a surface of the first polarizer opposite to the liquid crystal cell, and the first polarizer. Including a polarizing plate protective film F2 disposed on the liquid crystal cell side surface,
The second polarizing plate is a second polarizer, a polarizing plate protective film F3 disposed on the surface of the second polarizer on the liquid crystal cell side, and the liquid crystal cell of the second polarizer. Includes a polarizing plate protective film F4 disposed on the opposite surface,
The liquid crystal display device in which one or both of the polarizing plate protective film F1 and the polarizing plate protective film F4 is the optical film according to claim 1.
The liquid crystal cell includes a liquid crystal layer and a pair of substrates sandwiching the liquid crystal layer,
The liquid crystal display device according to claim 15, wherein the pair of substrates is a glass substrate having a thickness of 0.3 mm or more and less than 0.7 mm.
The liquid crystal display device according to claim 15, wherein at least the polarizing plate protective film F <b> 1 is the optical film according to claim 1.
The liquid crystal display device according to claim 17, wherein the in-plane direction X of the polarizing plate protective film F1 and the absorption axis of the first polarizer are parallel to each other.