WO2010026832A1

WO2010026832A1 - Liquid crystal display device

Info

Publication number: WO2010026832A1
Application number: PCT/JP2009/062437
Authority: WO
Inventors: 隆裕高木
Original assignee: コニカミノルタオプト株式会社
Priority date: 2008-09-05
Filing date: 2009-07-08
Publication date: 2010-03-11
Also published as: JP5360063B2; JPWO2010026832A1

Abstract

Provided is a liquid crystal display device having a high-stability VA optical compensation system. The liquid crystal display device includes at least a first polarizer, a first phase difference film in which the absorption axis and the slow axis of the first polarizer are parallel or perpendicular to each other, a liquid crystal cell in which a liquid crystal layer is sandwiched by a pair of substrates, a second phase difference film, and a second polarizer. The liquid crystal molecules in the liquid crystal layer are aligned perpendicularly with respect to the surfaces of the paired substrates when black is displayed. The liquid crystal display device is characterized in that the first phase difference film has an in-plane retardation Ro of 10 to 30 nm and a thickness direction retardation Rth of 80 to 120 nm, the second phase difference film has an in-plane retardation Ro of 30 to 80 nm and a thickness direction retardation Rth of 130 to 300 nm, and the first phase difference film and the second phase difference film contain a cellulose ester.

Description

Liquid crystal display

The present invention relates to a liquid crystal display device.

Liquid crystal display devices are used in various display devices, and as TV applications, nematic liquid crystal molecules having negative dielectric anisotropy are used as LCD methods for improving viewing angle characteristics, and no voltage is applied. In this state, a vertical alignment nematic liquid crystal display device (hereinafter referred to as VA mode) in which the major axis of liquid crystal molecules is aligned in a direction substantially perpendicular to the substrate and driven by a thin film transistor is mainly used.

In this VA mode, a wider viewing angle characteristic can be obtained by using two negative uniaxial retardation films (also referred to as negative C plates) having an optical axis in a direction perpendicular to the film surface, above and below the liquid crystal cell. A wider viewing angle characteristic is realized by using a uniaxially oriented retardation film (also called a positive A plate) with positive refractive index anisotropy that has an in-plane retardation value. It is also known that it can be done (see Non-Patent Document 1).

However, the use of three retardation films not only causes an increase in production cost, but also causes problems such as a decrease in yield because a large number of films are bonded together.

Also, there was a problem that light leakage from the oblique direction of the polarizing plate during black display was not completely suppressed in the visible light region, and the viewing angle was not sufficiently expanded.

To solve this problem, a technique of combining a biaxial film with a negative C plate has been proposed (Patent Documents 1 and 2).
This technology eliminates the problem of compensation for light leakage at all wavelengths of visible light, that is, the azimuthal dependence of color misregistration for incident light in the oblique direction of the black display polarizing plate. I thought.

However, this technique is a technical idea that facilitates optical compensation as a whole by increasing only one of the in-plane retardation Ro and the thickness direction retardation Rth for both the negative C plate and the biaxial film. When actually trying to achieve this, it became clear that there was a problem of large variations in retardation within the same production lot of these films, and that the stability as an optical compensation system was lacking. .

JP 2006-119623 A JP 2007-1408016 A

An object of the present invention is to provide a liquid crystal display device having a highly stable optical compensation system for VA.

The object of the present invention was achieved by the following means.

1. At least a first polarizer, a first retardation film in which an absorption axis and a slow axis of the first polarizer are arranged orthogonally or in parallel, a liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates, a second retardation A liquid crystal display device having a film and a second polarizer, wherein the liquid crystal molecules of the liquid crystal layer are aligned perpendicularly to the surfaces of the pair of substrates during black display, and the in-plane of the first retardation film The retardation Ro is 10 to 30 nm, the thickness direction retardation Rth is 80 to 120 nm, the in-plane retardation Ro of the second retardation film is 30 to 80 nm, and the thickness direction retardation Rth is 130 nm to 300 nm. A liquid crystal display device, wherein the first retardation film and the second retardation film contain a cellulose ester.

2. The acyl substitution degree of cellulose ester CE (1) contained in the first retardation film and cellulose ester CE (2) contained in the second retardation film is 2.4 to 2.9. , CE (1) and CE (2) have an acyl substitution degree difference of 0.3 or more and 2.0 or less, and both the first retardation film and the second retardation film have at least a pyranose structure or a furanose structure. Cellulose ester containing at least one selected from an ester compound in which one or more and one or less of 12 OH groups are esterified, and a compound having a structure represented by the following general formula (c) 2. The liquid crystal display device as described in 1 above, which is a retardation film containing 0.01 to 20% by mass with respect to the solid content.

Formula (c) B- (GA) n-GB
(Wherein B is an arylcarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A Represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)

According to the present invention, a liquid crystal display device having a highly stable optical compensation system for VA can be provided.

It is the schematic of the liquid crystal display device of this invention.

The liquid crystal display device having the optical compensation system for VA of the present invention has, as a basic structure, two polarizers sandwiching a VA mode liquid crystal cell, and two retardations arranged between the two polarizers. The film is characterized by the values of Ro and Rt distributed to the two retardation films themselves and means for achieving the values.

That is, the in-plane retardation Ro of the first retardation film is 10 to 30 nm, the retardation Rth in the thickness direction is 80 to 120 nm, the in-plane retardation Ro of the second retardation film is 30 to 80 nm, The liquid crystal display device is characterized in that the retardation Rth in the thickness direction is 130 nm to 300 nm, and both the first retardation film and the second retardation film contain a cellulose ester.

In the conventional optical compensation system for VA, since the configuration is simple, the optical compensation system based on the use of the negative C plate has been designed. However, in the present invention, the optimal solution for design is actually I found that it was not the optimal solution.

The range of Ro and Rt of the first retardation film and the second retardation film of the present invention is not a range that can be derived from simple optical design.
<Liquid crystal display device in which liquid crystal molecules of the liquid crystal layer are aligned perpendicularly to the surfaces of the pair of substrates during black display>
In the present invention, the liquid crystal display device in which liquid crystal molecules of the liquid crystal layer are aligned perpendicularly to the surfaces of the pair of substrates during black display refers to a VA mode liquid crystal display device.

In this specification, “parallel” or “orthogonal” means that the angle is within the range of a strict angle ± 5 °.

The error from the exact angle is preferably less than 4 °, and more preferably less than 3 °.

Also, “slow axis” means the direction in which the refractive index is maximum. The “visible light region” means 380 nm to 780 nm. Further, the measurement wavelength of the refractive index and the phase difference is a value at λ = 590 nm in the visible light region unless otherwise specified.

In this specification, unless otherwise specified, the term “polarizing plate” is cut into a size to be incorporated into a long polarizing plate and a liquid crystal device (in this specification, “cutting” includes “punching” and “cutting out”. It is used in the meaning including both of the polarizing plates.

In this specification, “polarizer” and “polarizing plate” are distinguished from each other, and “polarizing plate” is a laminate having a protective film for protecting the polarizer on at least one surface of the “polarizer”. Shall mean.

An embodiment applied to a VA mode liquid crystal display device of the present invention will be described with reference to FIG.

The liquid crystal display device shown in FIG. 1 has an upper polarizer 1 (viewing side) and a lower polarizer 5 (backlight side) arranged with a liquid crystal cell 3 interposed therebetween. Between the first retardation film 2 of the present invention, the second retardation film 4 is positioned between the lower polarizer 5 and the liquid crystal cell.

The VA mode liquid crystal cell can use a nematic liquid crystal material having a negative dielectric anisotropy between the upper and lower substrates and having Δn = 0.0815 and Δε = −4.5.

The thickness d of the liquid crystal layer is not particularly limited, but can be set to about 3.5 μm when a liquid crystal having the above characteristics is used.

Since the brightness at the time of white display changes depending on the magnitude of the product Δn · d of the thickness d and the refractive index anisotropy Δn, Δn · d is 0.2 to 0.0 in order to obtain the maximum brightness. It is preferable to set it in the range of 5 μm.

In a VA mode liquid crystal display device, the addition of a chiral material generally used in a TN mode liquid crystal display device is rarely used to degrade dynamic response characteristics, but to reduce alignment defects. May be added.

Further, when the multi-domain structure is used, it is advantageous for adjusting the alignment of the liquid crystal molecules in the boundary region between the domains.

The multi-domain structure refers to a structure in which one pixel of a liquid crystal display device is divided into a plurality of regions. For example, in the VA mode, since the liquid crystal molecules are tilted when displaying white, the magnitude of birefringence of the liquid crystal molecules when viewed from an oblique direction is different between the tilt direction and the opposite direction, resulting in differences in luminance and color tone. However, a multi-domain structure is preferable because the viewing angle characteristics of luminance and color tone are improved.

Specifically, each pixel is composed of two or more (preferably 4 or 8) regions in which the initial alignment state of the liquid crystal molecules is different from each other, and averaging is performed. Can be reduced. Further, the same effect can be obtained even if each pixel is constituted by two or more different regions where the alignment direction of liquid crystal molecules continuously changes in a voltage application state.

To form multiple regions with different alignment directions of liquid crystal molecules within one pixel, for example, use methods such as providing slits on electrodes, providing protrusions, changing the electric field direction, or biasing the electric field density. can do.

In order to obtain a uniform viewing angle in all directions, the number of divisions may be increased. However, a substantially uniform viewing angle can be obtained by using four or more divisions. In particular, it is preferable that the polarizing plate absorption axis can be set at an arbitrary angle when dividing into eight.

液晶 At the domain boundary of each domain, liquid crystal molecules tend to be difficult to respond. In the normally black mode such as the VA mode, since black display is maintained, a decrease in luminance becomes a problem. Therefore, it is possible to reduce the boundary region between domains by adding a chiral agent to the liquid crystal material.

On the other hand, since the white display state is maintained in the normally white mode, the front contrast is lowered. Therefore, a light shielding layer such as a black matrix covering the region may be provided.

The polarizers 1 and 5 are arranged so that the absorption axes 2a and 5a are orthogonal to each other. Further, the in-plane slow axis 2a of the first retardation film 2 is preferably arranged so as to be parallel or orthogonal to the absorption axis 1a of the polarizer 1 positioned closer to the first retardation film 2 (FIG. 1 shows the case of being parallel). ing).

On the other hand, it is preferable to arrange the in-plane slow axis of the second retardation film 4 so as to be parallel or orthogonal to the absorption axis 5a of the polarizer 5 located closer (FIG. 1 shows a parallel case). )

In such an arrangement, the second retardation film 4 causes retardation with respect to the incident light from the normal direction, does not cause light leakage, and with respect to the incident light from the oblique direction. Can sufficiently exhibit the effects of the present invention.

The first retardation film and the second retardation film of the present invention function as protective films for the first polarizer and the second polarizer, respectively, and are preferably used as polarizing plate protective films sandwiching a so-called polarizer.
<First retardation film>
The first retardation film of the present invention has an in-plane retardation Ro of 10 to 30 nm, a thickness direction retardation Rth of 80 to 120 nm, and an in-plane retardation Ro of 20 to 30 nm. Is preferred.

The film thickness d is 40 to 100 μm, preferably 40 to 70 μm.

The first retardation film of the present invention comprises cellulose ester CE (1), a plasticizer and other additives.
<Second retardation film>
The second retardation film of the present invention has an in-plane retardation Ro of 30 to 80 nm and a thickness direction retardation Rth of 130 to 300 nm.

The film thickness d is 40 to 100 μm, preferably 40 to 70 μm.

The second retardation film of the present invention comprises cellulose ester CE (2), a plasticizer and other additives.
[Cellulose ester]
The cellulose esters CE (1) and CE (2) of the present invention can be used in common as long as the acyl substitution degree difference is 0.3 or more and 2.0 or less. The carboxylic acid ester may be an aromatic carboxylic acid ester, and is preferably a lower fatty acid ester having 6 or less carbon atoms.

The acyl group bonded to the hydroxyl group may be linear or branched or may form a ring. Furthermore, another substituent may be substituted. In the case of the same degree of substitution, birefringence decreases when the number of carbon atoms is large. Therefore, the number of carbon atoms is preferably selected from acyl groups having 2 to 6 carbon atoms. The cellulose acylate preferably has 2 to 4 carbon atoms, more preferably 2 to 3 carbon atoms.

Specifically, the cellulose ester includes cellulose acetate propionate, cellulose acetate butyrate, or a mixed fatty acid ester of cellulose to which a propionate group or a butyrate group is bonded in addition to an acetyl group such as cellulose acetate propionate butyrate. Can be used.

The butyryl group that forms butyrate may be linear or branched. As the cellulose ester preferably used in the present invention, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cellulose acetate phthalate are particularly preferably used.

Preferred cellulose esters for the present invention are those that simultaneously satisfy the following formulas (1) and (2).

Formula (1) 2.4 <= X + Y <= 2.9
Formula (2) 0 ≦ Y ≦ 1.5
In the formula, X is the degree of substitution of the acetyl group, and Y is the degree of substitution of the propionyl group or butyryl group, or a mixture thereof.

Also, in order to obtain optical characteristics that meet the purpose, resins having different degrees of substitution may be mixed and used. The mixing ratio is preferably 10:90 to 90:10 (mass ratio).

Of these, cellulose acetate propionate is particularly preferably used. In cellulose acetate propionate, 1.0 ≦ X ≦ 2.5, and preferably 0.1 ≦ Y ≦ 1.5, 2.4 ≦ X + Y ≦ 2.9.

The method for measuring the substitution degree of the acyl group can be measured according to ASTM-D817-96.

Cellulose esters CE (1) and CE (2) have an acyl group substitution degree difference of 0.3 to 2.0 and preferably have a larger CE (1), but can be appropriately selected.

The number average molecular weight of the cellulose ester used in the present invention is preferably in the range of 60,000 to 300,000, and the resulting film is preferably strong in mechanical strength. Furthermore, 70,000-200000 are preferably used.

The weight average molecular weight Mw and number average molecular weight Mn of the cellulose ester were measured using gel permeation chromatography (GPC).

The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 1000,000 to 500 13 calibration curves were used. Thirteen samples are used at approximately equal intervals.

The cellulose used as a raw material of the cellulose ester used in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

The cellulose ester such as cellulose acetate phthalate of the present invention can be produced by a known method. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.
[Plasticizer]
As a plasticizer that can be used in the first and second retardation films of the present invention, at least one of a pyranose structure or a furanose structure is 1 to 12, and all or a part of the OH groups of the structure are contained. 1 type selected from the esterified ester compound and the compound of the structure shown in general formula (c) is contained.

<Ester compound in which at least one of pyranose structure or furanose structure is 1 or more and 12 or less and all or part of OH groups of the structure are esterified>
The cellulose ester film of the present invention is characterized by comprising an ester compound having at least one pyranose structure or at least one furanose structure and having all or part of OH groups in the structure esterified.

The proportion of esterification is preferably 70% or more of the OH groups present in the pyranose structure or furanose structure.

In the present invention, ester compounds are collectively referred to as sugar ester compounds.

Examples of the ester compound of the present invention include the following, for example, but the present invention is not limited to these.

Glucose, galactose, mannose, fructose, xylose or arabinose, lactose, sucrose, nystose, 1F-fructosyl nystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose .

Other examples include gentiobiose, gentiotriose, gentiotetraose, xylotriose, and galactosyl sucrose.

Among these compounds, compounds having both a pyranose structure and a furanose structure are particularly preferable.

For example, sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose and the like are preferable, and sucrose is more preferable.

The monocarboxylic acid used for esterifying all or part of the OH groups in the pyranose structure or furanose structure of the present invention is not particularly limited, and known aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, An aromatic monocarboxylic acid or the like can be used. The carboxylic acid used may be one type or a mixture of two or more types.

Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid , Saturated fatty acids such as tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, Examples include unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and octenoic acid.

Examples of preferable alicyclic monocarboxylic acids include acetic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

Examples of preferred aromatic monocarboxylic acids include aromatic monocarboxylic acids having an alkyl group or alkoxy group introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, cinnamic acid, benzylic acid, biphenylcarboxylic acid, and naphthalene. Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as carboxylic acid and tetralin carboxylic acid, or derivatives thereof. More specifically, xylyl acid, hemelic acid, mesitylene acid, prenylic acid, γ-isoduric acid, jurylic acid, mesitic acid, α-isoduric acid, cumic acid, α-toluic acid, hydroatropic acid, atropic acid, hydrocinnamic acid, salicylic acid, o-anisic acid, m-anisic acid, p-anisic acid Creosote acid, o-homosalicylic acid, m-homosalicylic acid, p-homosalicylic acid, o-pyro Technic acid, β-resorcylic acid, vanillic acid, isovanillic acid, veratromic acid, o-veratrumic acid, gallic acid, asaronic acid, mandelic acid, homoanisic acid, homovanillic acid, homoveratrumic acid, o-homoveratrumic acid, phthalonic acid, p- Although coumaric acid can be mentioned, benzoic acid is particularly preferable.

Oligosaccharide ester compounds can be applied as compounds having 1 to 12 at least one of the pyranose structure or furanose structure according to the present invention.

Oligosaccharides are produced by allowing an enzyme such as amylase to act on starch, sucrose, etc. Examples of oligosaccharides that can be applied to the present invention include maltooligosaccharides, isomaltooligosaccharides, fructooligosaccharides, galactooligosaccharides, and xylooligos. Sugar.

Moreover, the said ester compound is a compound which condensed 1 or more and 12 or less of at least 1 sort (s) of the pyranose structure or furanose structure represented with the following general formula (A). R ₁₁ to R ₁₅ and R ₂₁ to R _{25 each} represents an acyl group having 2 to 22 carbon atoms or a hydrogen atom, m and n each represents an integer of 0 to 12, and m + n represents an integer of 1 to 12.

R ₁₁ to R ₁₅ and R ₂₁ to R ₂₅ are preferably a benzoyl group or a hydrogen atom. The benzoyl group may further have a substituent R ₂₆ (p is 0 to 5), and examples thereof include an alkyl group, an alkenyl group, an alkoxyl group, and a phenyl group, and further, these alkyl groups, alkenyl groups, and phenyl groups. May have a substituent. Oligosaccharides can also be produced by the same method as the ester compound of the present invention.

Specific examples of the ester compound according to the present invention will be given below, but the present invention is not limited thereto.

The cellulose ester film of the present invention preferably contains the ester compound of the present invention in an amount of 1 to 30% by mass of the cellulose ester film, in order to stabilize the display quality by suppressing the fluctuation of the retardation value. It is preferable to contain 5 to 30% by mass.
<Compound with structure shown in general formula (c)>
The compound having a structure represented by the general formula (c) of the present invention is a polyester plasticizer, and a polyester plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be used.

Formula (c) B- (GA) n-GB
(Wherein B is an arylcarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A Represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (c), a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic group represented by A It is composed of an acid residue and can be obtained by a reaction similar to that of a normal polyester plasticizer.

Examples of the aryl carboxylic acid component of the polyester plasticizer used in the present invention include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, and normal propyl benzoic acid. There are acid, aminobenzoic acid, acetoxybenzoic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively.

Examples of the alkylene glycol component having 2 to 12 carbon atoms of the polyester plasticizer that can be used in the present invention include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1, 3-butanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neo Pentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane) 3-methyl-1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pen Diols, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc. It is used as one kind or a mixture of two or more kinds.

Particularly, alkylene glycols having 2 to 12 carbon atoms are particularly preferable because of excellent compatibility with cellulose esters.

Examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the aromatic terminal ester include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. These glycols include 1 It can be used as a seed or a mixture of two or more.

Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are used as one kind or a mixture of two or more kinds. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

The number average molecular weight of the polyester plasticizer used in the present invention is preferably in the range of 300 to 1500, more preferably 400 to 1000. The acid value is 0.5 mgKOH / g or less, the hydroxyl value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl value is 15 mgKOH / g or less.

Hereinafter, specific compounds of the aromatic terminal ester plasticizer having a structure represented by the general formula (c) that can be used in the present invention are shown, but the present invention is not limited thereto.

<Other additives>
Examples of other additives that can be used in the present invention include other plasticizers, ultraviolet absorbers, antioxidants, and fine particles.

(Other plasticizers)
The retardation film of the present invention can contain other plasticizers as necessary to obtain the effects of the present invention.

The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a glycolate plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or a polyester plasticizer. Agent, acrylic plasticizer and the like.

Of these, when two or more plasticizers are used, at least one is preferably a polyhydric alcohol ester plasticizer.

The polyhydric alcohol ester plasticizer is a plasticizer composed of an ester of a divalent or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. A divalent to 20-valent aliphatic polyhydric alcohol ester is preferred.

The polyhydric alcohol preferably used in the present invention is represented by the following general formula (a).

Formula (a) R1- (OH) n
However, R1 represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic and / or phenolic hydroxyl group.

Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol.

In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

Preferred examples of the monocarboxylic acid include the following, but the present invention is not limited to this.

As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanoic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

Examples of preferable alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, and derivatives thereof.

Examples of preferred aromatic monocarboxylic acids include those in which 1 to 3 alkoxy groups such as alkyl group, methoxy group or ethoxy group are introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, biphenylcarboxylic acid, Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as naphthalenecarboxylic acid and tetralincarboxylic acid, or derivatives thereof. Benzoic acid is particularly preferable.

The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

The carboxylic acid used in the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

The following are specific compounds of polyhydric alcohol esters.

The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used.

Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl Glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycol Butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalate Ethyl glycolate, and the like.

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

Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate.

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

The polyvalent carboxylic acid ester compound is composed of an ester of a divalent or higher, preferably a divalent to 20valent polyvalent carboxylic acid and an alcohol. The aliphatic polyvalent carboxylic acid is preferably divalent to 20-valent, and in the case of an aromatic polyvalent carboxylic acid or alicyclic polyvalent carboxylic acid, it is preferably trivalent to 20-valent.

The polyvalent carboxylic acid is represented by the following general formula (b).

Formula (b) R2 (COOH) m (OH) n
(Wherein R2 is an (m + n) -valent organic group, m is a positive integer of 2 or more, n is an integer of 0 or more, a COOH group is a carboxyl group, and an OH group is an alcoholic or phenolic hydroxyl group)
Examples of preferable polyvalent carboxylic acids include the following.

Trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid or derivatives thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, tetrahydrophthal An aliphatic polyvalent carboxylic acid such as an acid, an oxypolyvalent carboxylic acid such as tartaric acid, tartronic acid, malic acid and citric acid can be preferably used. In particular, it is preferable to use an oxypolycarboxylic acid from the viewpoint of improving retention.

The alcohol used in the polyvalent carboxylic acid ester compound that can be used in the present invention is not particularly limited, and known alcohols and phenols can be used.

For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. More preferably, it has 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms.

Also, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can be preferably used.

When an oxypolycarboxylic acid is used as the polycarboxylic acid, the alcoholic or phenolic hydroxyl group of the oxypolycarboxylic acid may be esterified with a monocarboxylic acid. Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

As the aliphatic monocarboxylic acid, a straight-chain or side-chain fatty acid having 1 to 32 carbon atoms can be preferably used. More preferably, it has 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms.

Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, and tetralin carboxylic acid. And aromatic monocarboxylic acids possessed by them, or derivatives thereof. Particularly preferred are acetic acid, propionic acid, and benzoic acid.

The molecular weight of the polyvalent carboxylic acid ester compound is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. The larger one is preferable in terms of improving the retention, and the smaller one is preferable in terms of moisture permeability and compatibility with the cellulose ester.

The alcohol used for the polyvalent carboxylic acid ester that can be used in the present invention may be one kind or a mixture of two or more kinds.

The acid value of the polyvalent carboxylic acid ester compound that can be used in the present invention is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. Setting the acid value in the above range is preferable because the environmental fluctuation of retardation is also suppressed.

The acid value refers to the number of milligrams of potassium hydroxide necessary to neutralize the acid (carboxyl group present in the sample) contained in 1 g of the sample. The acid value is measured according to JIS K0070.

Examples of particularly preferred polyvalent carboxylic acid ester compounds are shown below, but the present invention is not limited thereto.

For example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, Examples include tributyl trimellitic acid and tetrabutyl pyromellitic acid.

(UV absorber)
The cellulose ester film according to the present invention can also contain an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet light having a wavelength of 400 nm or less, and the transmittance at a wavelength of 370 nm is particularly preferably 10% or less, more preferably 5% or less. Preferably it is 2% or less.

Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body.

For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6- (linear and side Chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, and the like, and tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, tinuvin 328, etc. These are commercially available products made by Ciba Japan Co., Ltd. and can be preferably used.

The UV absorbers preferably used in the present invention are benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers, particularly preferably benzotriazole UV absorbers and benzophenone UV absorbers. .

In addition, a discotic compound such as a compound having a 1,3,5 triazine ring is also preferably used as an ultraviolet absorber.

The polarizing plate protective film according to the present invention preferably contains two or more ultraviolet absorbers.

Also, as the ultraviolet absorber, a polymeric ultraviolet absorber can be preferably used, and in particular, a polymer type ultraviolet absorber described in JP-A-6-148430 is preferably used.

The method of adding the UV absorber can be added to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as methylene chloride, methyl acetate, acetone or dioxolane or a mixed solvent thereof. Or you may add directly in dope composition.

For inorganic powders that do not dissolve in organic solvents, use a dissolver or sand mill in the organic solvent and cellulose ester to disperse them before adding them to the dope.

The amount of the UV absorber used is not uniform depending on the type of UV absorber, the operating conditions, etc., but when the dry film thickness of the polarizing plate protective film is 30 to 200 μm, the amount used is 0.5 to the polarizing plate protective film. Is preferably 10 to 10% by mass, and more preferably 0.6 to 4% by mass.

(Antioxidant)
Antioxidants are also referred to as deterioration inhibitors. When a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film may be deteriorated.

The antioxidant has a role of delaying or preventing the cellulose ester film from being decomposed by, for example, a residual solvent amount of halogen in the cellulose ester film or phosphoric acid of a phosphoric acid plasticizer. It is preferable to make it contain in a film.

As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], oct Decyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

The amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose derivative.

(Fine particles)
The retardation film of the present invention preferably contains fine particles.

As fine particles used in the present invention, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and hydrated silicic acid. Mention may be made of calcium, aluminum silicate, magnesium silicate and calcium phosphate.

Also, organic compound fine particles can be preferably used. Examples of organic compounds include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene resin, silicone resin, polycarbonate resin, benzoguanamine resin, melamine resin Also, pulverized and classified products of organic polymer compounds such as polyolefin-based powders, polyester-based resins, polyamide-based resins, polyimide-based resins, polyfluorinated ethylene-based resins, and starches.

Alternatively, a polymer compound synthesized by a suspension polymerization method, a polymer compound made spherical by a spray dry method or a dispersion method, or an inorganic compound can be used.

Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

The average primary particle size of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm.

These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable.

The content of these fine particles in the retardation film is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass. In the case of a polarizing plate protective film having a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

Silicon dioxide fine particles are commercially available, for example, under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.). it can.

Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.).

Examples of the polymer include silicone resin, fluororesin and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120 and 240 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the turbidity of the polarizing plate protective film low. In the polarizing plate protective film used in the present invention, it is preferable that the dynamic friction coefficient of at least one surface is 0.2 to 1.0.

Various additives may be batch-added to a dope that is a cellulose ester-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the fine particles in-line in order to reduce the load on the filter medium.

When the additive solution is added in-line, it is preferable to dissolve a small amount of cellulose ester in order to improve mixing with the dope. A preferable amount of the cellulose ester is 1 to 10 parts by mass, and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

In the present invention, for in-line addition and mixing, for example, a static mixer (manufactured by Toray Engineering) or an in-line mixer such as SWJ (Toray static type in-tube mixer Hi-Mixer) is preferably used.
<Method for producing retardation film>
The retardation film of the present invention is a kind of cellulose ester film, and can be produced according to a usual method for producing a cellulose ester film.

The retardation film of the present invention can be preferably used regardless of whether it is a film produced by a solution casting method or a film produced by a melt casting method.

The production of the retardation film of the present invention comprises the steps of preparing a dope by dissolving a cellulose ester and an additive in a solvent, a step of casting the dope on an endless metal support that moves infinitely, and a cast dope. The step of drying as a web, the step of peeling from the metal support, the step of stretching or maintaining the width, the step of further drying, and the step of winding up the finished film are performed.

The process for preparing the dope will be described. The concentration of cellulose ester in the dope is preferably higher because the drying load after casting on the metal support can be reduced. However, if the concentration of cellulose ester is too high, the load during filtration increases and the filtration accuracy is poor. Become. The concentration that achieves both of these is preferably 10 to 35% by mass, and more preferably 15 to 25% by mass.

The solvent used in the dope may be used alone or in combination of two or more, but it is preferable to use a mixture of a good solvent and a poor solvent of cellulose ester in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of the solubility of the cellulose ester.

A preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what dissolve | melts the cellulose ester to be used independently is defined as a good solvent, and what poorly swells or does not melt | dissolve is defined as a poor solvent.

Therefore, depending on the average acetylation degree (acetyl group substitution degree) of the cellulose ester, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, the cellulose ester acetate ester (acetyl group substitution degree 2.4), cellulose Acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent.

The good solvent used in the present invention is not particularly limited, and examples thereof include organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Particularly preferred is methylene chloride or methyl acetate.

The poor solvent used in the present invention is not particularly limited, but for example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone and the like are preferably used. The dope preferably contains 0.01 to 2% by mass of water.

Also, the solvent used for dissolving the cellulose ester is used by collecting the solvent removed from the film by drying in the film-forming process and reusing it.

The recovery solvent may contain trace amounts of additives added to the cellulose ester, such as plasticizers, UV absorbers, polymers, monomer components, etc., but these are preferably reused even if they are included. Can be purified and reused if necessary.

As a method for dissolving the cellulose ester when preparing the dope described above, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure.

It is preferable to stir and dissolve while heating at a temperature that is higher than the boiling point of the solvent at normal pressure and does not boil under pressure, in order to prevent the formation of massive undissolved material called gel or mamako.

In addition, a method in which a cellulose ester is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

Pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

The heating temperature with the addition of the solvent is preferably higher from the viewpoint of the solubility of the cellulose ester, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates.

The preferred heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

Alternatively, a cooling dissolution method is also preferably used, whereby the cellulose ester can be dissolved in a solvent such as methyl acetate.

Next, the cellulose ester solution is filtered using an appropriate filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small.

For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable.

It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose ester by filtration.

Bright spot foreign matter means that when two polarizing plates are placed in a crossed Nicol state, an optical film or the like is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less.

More preferably, it is 100 pieces / cm ² or less, still more preferably 50 pieces / m ² or less, still more preferably 0 to 10 pieces / cm ² . Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The increase in the difference (referred to as differential pressure) is small and preferable.

The preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

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

Here, the dope casting will be described.

The metal support in the casting process is preferably a mirror-finished surface, and a stainless steel belt or a drum whose surface is plated with a casting is preferably used as the metal support.

The cast width can be 1 ~ 4m. The surface temperature of the metal support in the casting step is −50 ° C. to less than the boiling point of the solvent, and a higher temperature is preferable because the web drying speed can be increased. May deteriorate.

The preferred support temperature is 0 to 55 ° C, more preferably 25 to 50 ° C. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent.

The method for controlling the temperature of the metal support is not particularly limited, but there are a method of blowing hot air or cold air, and a method of contacting hot water with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short. When warm air is used, wind at a temperature higher than the target temperature may be used.

In order for the cellulose ester film to exhibit good flatness, the amount of residual solvent when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass. Particularly preferred is 20 to 30% by mass or 70 to 120% by mass.

In the present invention, the amount of residual solvent is defined by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
M is the mass of a sample collected during or after the production of the web or film, and N is the mass after heating M at 115 ° C. for 1 hour.

Further, in the drying step of the cellulose ester film, the web is peeled off from the metal support, and further dried, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less, Particularly preferred is 0 to 0.01% by mass or less.

In the film drying process, generally, a roll drying method (a method in which webs are alternately passed through a plurality of rolls arranged above and below) and a method in which the web is dried while being conveyed by a tenter method are employed.

In order to produce the cellulose ester film of the present invention, it is particularly preferable to perform stretching in the width direction (lateral direction) by a tenter method in which both ends of the web are held with clips or the like. Peeling is preferably performed at a peeling tension of 300 N / m or less.

The means for drying the web is not particularly limited, and can be generally performed with hot air, infrared rays, a heating roll, microwave, or the like, but is preferably performed with hot air in terms of simplicity.

It is preferable that the drying temperature in the web drying process is increased stepwise from 40 to 200 ° C.

The retardation film of the present invention has a width of 1 to 4 m. Particularly, those having a width of 1.4 to 4 m are preferably used, and particularly preferably 1.6 to 3 m.

In order to obtain the target retardation values Ro and Rt in the present invention, it is preferable that the cellulose ester film has the material composition of the present invention, and further the refractive index is controlled by controlling the transport tension and stretching.

For example, the retardation value can be changed by lowering or increasing the tension in the longitudinal direction.

In addition, the film can be biaxially or uniaxially stretched sequentially or simultaneously in the longitudinal direction (film forming direction) of the film and the direction orthogonal to the longitudinal direction of the film, that is, the width direction.

The draw ratios in the biaxial directions perpendicular to each other are preferably in the range of 0.8 to 1.5 times in the casting direction and 1.1 to 2.5 times in the width direction, respectively. It is preferable to carry out in the range of 0.8 to 1.0 times in the direction and 1.2 to 2.0 times in the width direction.

The stretching temperature is preferably 120 ° C. to 200 ° C., more preferably 150 ° C. to 200 ° C., more preferably more than 150 ° C. and 190 ° C. or less.

The residual solvent in the film is preferably 20 to 0%, more preferably 15 to 0%.

Specifically, it is preferable that the residual solvent is stretched by 11% at 155 ° C., or the residual solvent is stretched by 2% at 155 ° C. Alternatively, it is preferable that the residual solvent is stretched at 11% at 160 ° C, or the residual solvent is stretched at less than 1% at 160 ° C.

There is no particular limitation on the method of stretching the web. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction, the both ends of the web are fixed with clips and pins, and the interval between the clips and pins is increased in the traveling direction. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions and stretching in both the vertical and horizontal directions, and the like. Of course, these methods may be used in combination.

Also, in the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

It is preferable to carry out the width maintenance or lateral stretching in the film forming step by a tenter, and it may be a pin tenter or a clip tenter.

The slow axis or the fast axis of the cellulose ester film of the present invention exists in the film plane, and θ1 is preferably −1 ° or more and + 1 ° or less, assuming that the angle formed with the film forming direction is θ1. More preferably, it is 5 ° or more and + 0.5 ° or less.

This θ1 can be defined as an orientation angle, and the measurement of θ1 can be performed using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments). Each of θ1 satisfying the above relationship can contribute to obtaining high luminance in a display image, suppressing or preventing light leakage, and contributing to obtaining faithful color reproduction in a color liquid crystal display device.
<Physical properties of retardation film>
The water vapor permeability of the retardation film of the present invention is preferably 300 to 1800 g / m ² · 24 h at 40 ° C. and 90% RH, more preferably 400 to 1500 g / m ² · 24 h, and 40 to 1300 g / m ² · 24 h. Is particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

The retardation film of the present invention has a breaking elongation of preferably 10 to 80%, more preferably 20 to 50%.

The visible light transmittance of the retardation film of the present invention is preferably 90% or more, and more preferably 93% or more.

The haze of the retardation film of the present invention is preferably less than 1%, particularly preferably 0 to 0.1%.

Further, by further applying a liquid crystal layer to the retardation film of the present invention, retardation values over a wider range can be obtained.

<Polarizer>
The cellulose ester film which is the retardation film of the present invention can be used for a polarizing plate having a polarizing plate protective film and the liquid crystal display device of the present invention using the polarizing plate.

The polarizing plate of the present invention is characterized in that it is a polarizing plate bonded to at least one surface of a polarizer using the cellulose ester film of the present invention as a polarizing plate protective film. The liquid crystal display device of the present invention is characterized in that the polarizing plate according to the present invention is bonded to at least one liquid crystal cell surface via an adhesive layer.

The polarizing plate of the present invention can be produced by a general method. The cellulose ester film of the present invention is preferably bonded to at least one surface of a polarizer produced by subjecting the polarizer side to alkali saponification treatment and immersion drawing in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution.

Even if the cellulose ester film is used on the other surface, it is preferable to paste another polarizing plate protective film.

For example, commercially available cellulose ester films (for example, Konica Minoltack KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC8UX-RHA, KC8UX-RHA, KC8UX KC4UXW-RHA-NC, manufactured by Konica Minolta Opto Co., Ltd.) is also preferably used.

The polarizing plate protective film used on the surface side of the display device preferably has an antireflection layer, an antistatic layer, an antifouling layer, and a backcoat layer in addition to the antiglare layer or the clear hard coat layer.

A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

The polarizer is formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing the film by uniaxial stretching or dyeing or uniaxially stretching, and then performing a durability treatment with a boron compound. The film thickness of the polarizer is preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is also preferably used.

Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used.

The difference in hot water cutting temperature between two points 5 cm away in the TD direction of the film is more preferably 1 ° C. or less in order to reduce color spots, and two points separated 1 cm in the TD direction of the film. In order to reduce color spots, it is more preferable that the difference in the hot water cutting temperature is 0.5 ° C. or less.

A polarizer using this ethylene-modified polyvinyl alcohol film is excellent in polarization performance and durability performance and has few color spots, and is particularly preferably used for a large liquid crystal display device.

The polarizer obtained as described above is usually used as a polarizing plate with a protective film bonded to both sides or one side. Examples of the adhesive used for pasting include a PVA-based adhesive and a urethane-based adhesive. Among them, a PVA-based adhesive is preferably used.

<Liquid crystal display device>
The retardation film of the present invention can be used for liquid crystal display devices of various drive systems of VA (MVA, PVA).

In particular, even a large-screen liquid crystal display device with a 30-inch screen or more can obtain a liquid crystal display device with excellent visibility such as uneven coloring and front contrast with little environmental fluctuation, reduced light leakage.

Hereinafter, although an example is given and the present invention is explained, the present invention is not limited to these.

Example 1
<Preparation of First Retardation Film 1-101>
<Fine particle dispersion 1>
Fine particles (Aerosil R812V manufactured by Nippon Aerosil Co., Ltd.)
11 parts by mass Ethanol 89 parts by mass The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle addition liquid 1>
The fine particle dispersion 1 was slowly added to the dissolution tank containing methylene chloride with sufficient stirring. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution 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, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose esters A and B were added to a pressurized dissolution tank containing a solvent while stirring. This is completely dissolved with heating and stirring. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

<Composition of main dope solution>
Methylene chloride 440 parts by mass Ethanol 40 parts by mass Cellulose ester C of the present invention 100 parts by mass Polyester plasticizer 14 shown by the general formula (c) of the present invention 8.5 parts by mass Particulate additive solution 1 1 part by mass In a closed container The dope solution was prepared by charging and dissolving with stirring. Next, using an endless belt casting apparatus, the dope solution was uniformly cast on a stainless steel belt support at a temperature of 33 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled at 30-50 ° C.

On the stainless steel belt support, the solvent was evaporated until the amount of residual solvent in the cast (cast) film reached 75%, and then peeled off from the stainless steel belt support with a peeling tension of 130 N / m.

The peeled film was stretched 30% in the width direction using a tenter while applying heat of 140 ° C. to 160 ° 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.

Thus, a first retardation film 1-101 having a dry film thickness of 50 μm was obtained.

Hereinafter, the first retardation film 1 is substantially the same except that a plasticizer is further added to 1-109, 1-111, 1-112, and the solvent type, film thickness, and draw ratio are changed as shown in Table 2. -102 to 1-118 were produced.

Plasticizer A: Triphenyl phosphate Plasticizer B: Ethyl phthalyl ethyl glycolate Plasticizer C: Trimethylolpropane 2, 4, 6 trimethoxy benzoate Further, for comparison, 1-201 to 1-207 were prepared.
<Preparation of Second Retardation Film 2-101>
<Fine particle dispersion 1>
Fine particles (Aerosil R812V manufactured by Nippon Aerosil Co., Ltd.)
11 parts by mass Ethanol 89 parts by mass The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Composition of main dope solution>
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Cellulose ester C of the present invention 100 parts by mass Polyester plasticizer 14 represented by the general formula (c) of the present invention 2.5 parts by mass Sugar ester compound 3 of the present invention 10.0 parts by mass 1 part by mass or more of the fine particle additive solution 1 was put into a closed container and dissolved while stirring to prepare a dope solution. Next, using an endless belt casting apparatus, the dope solution was uniformly cast on a stainless steel belt support at a temperature of 33 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled at 30-50 ° C.

The peeled cellulose ester film was stretched 30% in the width direction using a tenter while applying heat of 140 ° C. to 160 ° C. The residual solvent at the start of stretching was 15%.

As described above, a second retardation film 2-101 having a dry film thickness of 48 μm was obtained.

Hereinafter, the second retardation film 2 was substantially the same except that a plasticizer was further added to 2-109, 2-111, and 1122, and the solvent type, film thickness, and draw ratio were changed as shown in Table 2. -102 to 2-118 were produced.

Plasticizer A: Triphenyl phosphate Plasticizer B: Ethylphthalyl ethyl glycolate Plasticizer C: Trimethylolpropane 2,4,6 trimethoxy benzoate Further, for comparison, 2-201 to 2-207 were prepared.

For each sample obtained, the retardation value at each wavelength was measured in the following manner. The results are shown in Table 3.

<< Measurement of Retardation Ro, Rt >>
A 35 mm × 35 mm sample was cut out from the obtained film, conditioned at 25 ° C. and 55% RH for 2 hours, and measured with an automatic birefringence meter (KOBRA21DH, Oji Scientific Co., Ltd.) from the vertical direction at 590 nm and the film surface. It calculated from the extrapolation value of the retardation value measured similarly, inclining.
<Preparation of polarizing plate>
A polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times).

This 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 then immersed in an aqueous solution of 68 ° C. consisting of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer.

Next, according to the following steps 1 to 5, the polarizer and the first retardation film 1-101 to 1-207 are used as a polarizing protective film, and on the back side, Konica Minoltak KC4UY (Konica Minolta Opto's cellulose ester film) ) Were bonded together to produce a polarizing plate. Similarly, for the second retardation films 2-101 to 2-207, polarizing plates were similarly prepared as polarizing plate protective films.

Step 1: Soaked in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain a saponified cellulose ester film bonded to the polarizer.

Step 2: The polarizer was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

Step 3: Excess adhesive adhered to the polarizer in Step 2 was gently wiped off and placed on the cellulose ester film treated in Step 1.

Step 4: The first retardation films 1-101 to 1-207 laminated in Step 3 were bonded to the polarizer and the back side cellulose ester film at a pressure of 20 to 30 N / cm ² and a conveying speed of about 2 m / min. The same applies to the second polarizer.

Step 5: A sample obtained by bonding the polarizer prepared in Step 4 in the dryer at 80 ° C., the first retardation films 1-101 to 1-207, and Konica Minoltack KC4UY is dried for 2 minutes, and the polarizing plate 101 To 121 and 201 to 207 were prepared. The same applies to the second polarizer. <Production of liquid crystal display device>
A polarizing plate on both sides of a commercially available 32-inch MVA liquid crystal television (Sharp Aquos 32AD5) was peeled off, and the above-prepared polarizing plates were attached to both sides to produce a liquid crystal display device. At that time, the direction of bonding of the polarizing plate is the same as the polarizing plate previously bonded at the time of purchase so that the first retardation film side and the second retardation film side are the liquid crystal cell side. A liquid crystal display device was manufactured by making the absorption axis in the direction.

This liquid crystal display device was evaluated for color variation and front contrast. The results are shown in Table 4.

<Evaluation of color variation>
About each produced said liquid crystal display device, the color fluctuation was measured using the measuring machine (EZ-Contrast160D, ELDIM company make). In the CIE 1976 and UCS coordinates, the maximum color variation width Δu′v ′ in the vertical direction (80 ° to 80 ° below the display normal) was compared.

<< Evaluation of viewing angle >>
The measurement was performed after the backlight of each liquid crystal display device was lit continuously for one week in an environment of 23 ° C. and 55% RH. For the measurement, EZ-Contrast 160D manufactured by ELDIM was used, and the viewing angle (contrast ratio of 50 or more) was measured in 8 stages from black display (L1) to white display (L8).

From the results of Table 4, it is clear that the liquid crystal display devices 101 to 120 of the present invention are liquid crystal display devices with stable color variation and a stable viewing angle.

DESCRIPTION OF SYMBOLS 1 1st polarizer 1a Absorption axis of 1st polarizer 2 1st phase difference film 2a Slow axis of 2nd phase difference film 3 VA system liquid crystal cell 4 2nd phase difference film 4a Slow axis of 2nd phase difference film 5 Second polarizer 5a Absorption axis of the second polarizer

Claims

At least a first polarizer, a first retardation film in which an absorption axis and a slow axis of the first polarizer are arranged orthogonally or in parallel, a liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates, a second retardation A liquid crystal display device having a film and a second polarizer, wherein the liquid crystal molecules of the liquid crystal layer are aligned perpendicularly to the surfaces of the pair of substrates during black display, and the in-plane of the first retardation film The retardation Ro is 10 to 30 nm, the thickness direction retardation Rth is 80 to 120 nm, the in-plane retardation Ro of the second retardation film is 30 to 80 nm, and the thickness direction retardation Rth is 130 nm to 300 nm. A liquid crystal display device, wherein the first retardation film and the second retardation film contain a cellulose ester.
The acyl substitution degree of cellulose ester CE (1) contained in the first retardation film and cellulose ester CE (2) contained in the second retardation film is 2.4 to 2.9. , CE (1) and CE (2) have an acyl substitution degree difference of 0.3 or more and 2.0 or less, and both the first retardation film and the second retardation film have at least a pyranose structure or a furanose structure. Cellulose ester containing at least one selected from an ester compound in which one or more and one or less of 12 OH groups are esterified, and a compound having a structure represented by the following general formula (c) 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a retardation film containing 0.01 to 20% by mass with respect to the solid content.
Formula (c) B- (GA) n-GB
(Wherein B is an arylcarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A Represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)