WO2011104855A1 - Retardation film and method for producing retardation film - Google Patents

Abstract

In order to provide a long retardation film that is physically stable under both the environmental conditions during production and during processing, disclosed is an elongated retardation film—which uses cellulose acetate and of which the retardation (Ro) in the in-plane direction represented by the belowmentioned formula is 30-150 nm and the ratio (Rth/Ro) of the retardation (Rth) in the direction of thickness to the aforementioned retardation (Ro) in the in-plane direction is greater than 0.8—characterized by the degree of acetyl group substitution of the aforementioned cellulose acetate being between 2.1 and 2.6 inclusive, and by the ratio (tear strength in the MD direction / tear strength in the TD direction) between the tear strength in the lengthwise direction (MD direction) of the aforementioned retardation film and the tear strength in the widthwise direction (TD direction) of same being 0.8-1.2 under both conditions of 23°C/55%RH and 60°C/10%RH. Ro=(nx-ny)×d, Rth={(nx+ny)/2-nz}×d

Description

Retardation film and method for producing retardation film

The present invention relates to a retardation film using a cellulose acetate film, a polarizing plate using the same, a liquid crystal display device, and a method for producing a cellulose acetate film, and particularly when used as a retardation film for a liquid crystal display device. A retardation film capable of improving viewing angle characteristics by exhibiting a good optical compensation function, exhibiting excellent contrast, and being excellent in physical isotropy, a polarizing plate and a liquid crystal display using the same Relates to the device.

Liquid crystal display devices are widely used in monitors for personal computers and portable devices, and for television applications because of their various advantages such as low voltage and low power consumption, and enabling miniaturization and thinning.

In particular, liquid crystal display devices for television that are expected to be viewed from various angles on a large screen have severe demands for viewing angle dependency, and recently, the performance requirements for liquid crystal display devices for monitors are also increasing.

Therefore, various modes in which the viewing angle dependency is reduced by devising the alignment state of the liquid crystal in the liquid crystal cell have been proposed. Various studies have been made on liquid crystal display devices such as (Vertically Aligned) mode.

Usually, a liquid crystal display device is composed of a liquid crystal cell, a retardation film (also called a retardation plate) for improving viewing angle characteristics, and a polarizing plate.

The phase difference film is used to eliminate image coloring or enlarge the viewing angle. A film provided with birefringence by stretching a resin film is attached to a polarizing plate, or isotropic. A technique for providing birefringence as a retardation film by providing a protective film for polarizing plate with a liquid crystal layer in which liquid crystal molecules are aligned in an arbitrary direction is known.

However, these techniques require the provision of a retardation film or retardation layer separately from the protective film for polarizing plate, and there is a problem that the manufacturing method of the polarizing plate becomes complicated and costs increase.

In contrast, a retardation film capable of producing a polarizing plate capable of improving viewing angle characteristics with a simple structure by imparting a function as a retardation film to a cellulose ester film widely used as a protective film for a polarizing plate. Has been proposed (for example, Patent Document 1 and Patent Document 2).

Patent Document 1 discloses a technique in which a retardation film obtained by stretching a mixed fatty acid ester film of cellulose in the width direction is applied to a VA mode liquid crystal cell to widen the viewing angle.

Further, in Patent Document 2, there is described a retardation film in which a desired retardation value is given by adding a retardation increasing agent to cellulose triacetate.

However, in order to impart a function as a retardation film as described above to the cellulose ester film, the film is stretched at a high magnification in order to obtain a desired in-plane and depth retardation, or a cited document. It was necessary to add an additive such as a retardation increasing agent as in 2.

However, since such a cellulose ester film needs to be highly stretched, the physical properties of the normal direction (hereinafter also referred to as MD direction) and the width direction (hereinafter also referred to as TD direction) of the retardation film are generally used. The characteristics sometimes differed greatly.

On the other hand, in a liquid crystal display device, it is necessary to use one polarizing plate on each side of the liquid crystal cell, and each polarizing plate is usually arranged so that the absorption axes of the polarizers are orthogonal to each other.

In addition, a retardation film is disposed on the liquid crystal cell side of each polarizing plate, but the two retardation films sandwiching the liquid crystal cell are so that the in-plane retardation directions are orthogonal to each other like the polarizer. Need to be placed in.

As described above, if the physical properties of the retardation film are different in the MD direction and the TD direction, it is necessary to adjust the processing conditions by each polarizing plate when cutting the polarizing plate into the shape of a liquid crystal cell. There is a problem in terms of processing stability because it is necessary to bond the polarizing plate to the liquid crystal cell under different conditions.

In response to this problem, a technique has been proposed for making the physical properties in the MD direction and TD direction more equal under the retardation film processing condition atmosphere (Patent Document 3).

However, due to the recent demand for thinner polarizing plates, not only when processing retardation films, but also when manufacturing long retardation films, problems such as breakage tend to occur. Improvements were sought in all environmental conditions.

Japanese Patent No. 4337345 European Patent 0911656A2 JP 2010-1383 A

An object of the present invention is to provide a long retardation film that is physically stable under any environmental conditions during manufacturing and processing.

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

1. The in-plane retardation Ro represented by the following formula is 30 to 150 nm, and the ratio Rth / Ro between the thickness direction retardation Rth and the in-plane retardation Ro is greater than 0.8 and less than 5. , A long retardation film using cellulose acetate, wherein the cellulose acetate has an acetyl group substitution degree of 2.1 or more and 2.6 or less, and under conditions of 23 ° C. 55% RH and 60 ° C. 10% RH. The ratio of the tear strength in the longitudinal direction (MD direction) and the tear strength in the same width direction (TD direction) of the above retardation film: (Tear strength in the MD direction / Tear strength in the TD direction) A retardation film having a thickness of 0.8 to 1.2.
Ro = (nx−ny) × d
Rth = {(nx + ny) / 2−nz} × d
Here, d represents the thickness (nm) of the retardation film, nx is the maximum refractive index in the plane of the film, ny is the refractive index in the direction perpendicular to the nx direction in the film plane, and nz is the thickness. Represents the refractive index of the film in the direction. The wavelength is 590 nm.

2. In the retardation film, the tear strength in the film transport direction (MD direction) and the tear strength in the same width direction (TD direction) are both 30 mN or more and 120 mN or less at 60 ° C. and 10% RH. 2. The retardation film as described in 1 above.

3. A cellulose acetate dope having an acetyl group substitution degree of 2.1 or more and 2.6 or less is prepared, the dope is cast on a metal support, the casting film is peeled off as a film from the support, and the peeled film A method for producing a retardation film in which both widthwise ends of a film are held by a tenter to hold the width of the film and the film is dried, and the film is further dried after being detached from the tenter. A method for producing a retardation film, wherein a drying temperature is in a range of 140 ° C. to 200 ° C. in a gripping section, and a tension applied in a film width direction is 30 N / m or more and less than 100 N / m.

That is, as a result of the study by the present inventors, a specific additive is contained in cellulose acetate having an acetyl group substitution degree of 2.1 or more and 2.6 or less, and production conditions within a predetermined range are used. Under any conditions during processing, the in-plane retardation Ro is 30 to 150 nm, and the ratio Rth / Ro between the thickness direction retardation Rth and the in-plane retardation Ro is greater than 0.8 and more than 5. It has been found that a small retardation film can be produced without greatly different physical properties in the long direction and the width direction.

Specifically, when tear strength is used as an index of physical properties, the ratio of tear strength in the longitudinal direction (also referred to as MD direction) to the width direction (also referred to as TD direction) (Tear strength in MD direction / TD direction) It was found that a retardation film having a tear strength of 0.8 to 1.2 can be obtained.

It is a schematic diagram which shows the state which dripped glycerin on the slide glass. It is a schematic diagram which shows the state which put the sample film on glycerol. It is a schematic diagram which shows the state which dripped glycerin on the sample film. It is a schematic diagram which shows the state which put the cover glass on glycerol. It is the schematic of the liquid crystal display device using the retardation film of this invention.

Hereinafter, the present invention will be described in detail.
<Phase difference film>
In the retardation film of the present invention, the in-plane retardation Ro represented by the following formula is 30 to 150 nm, and the ratio Rth / Ro between the thickness direction retardation Rth and the in-plane direction retardation Ro is as follows. A long retardation film using cellulose acetate larger than 0.8, wherein the cellulose acetate has an acetyl group substitution degree of 2.1 or more and 2.6 or less, 23 ° C. 55% RH and 60 ° C. 10 Ratio of tear strength in the longitudinal direction (MD direction) and tear strength in the same width direction (TD direction) of the retardation film under the condition of% RH: (Tear strength in MD direction / Tear strength in TD direction) ) Is 0.8 to 1.2.
<Tear strength>
A normal retardation film is subjected to a stretching process in the production process for adjusting the retardation, which causes a difference in physical properties between the MD direction and the TD direction. However, by using the cellulose acetate of the present invention, retardation is achieved. The physical properties in the MD direction and the TD direction can be made uniform during manufacturing and processing while expressing.

That is, the ratio between the tear strength in the longitudinal direction (MD direction) and the tear strength in the same width direction (TD direction) under the conditions of 23 ° C. and 55% RH and 60 ° C. and 10% RH: (MD direction tear strength) / TD direction tear strength) is 0.8 to 1.2 in all cases.

The tear strength at 23 ° C. and 55% RH is 40 mN or more and 150 mN or less, preferably 50 mN or more and 130 mN or less. In 60 degreeC10% RH, it is 30 mN or more and 120 mN or less, Preferably it is 40 mN or more and 120 mN or less.

The tear strength can be measured with a light weight tear device manufactured by Toyo Seiki Co., Ltd. according to the elemendorf method JIS K 7128 / 2-1991.
<Retardation Ro, Rth>
Since the retardation film of the present invention is suitable for VA, the in-plane retardation Ro is in the range of 30 to 150 nm, and is the ratio of the retardation Rth in the thickness direction to the retardation Ro in the in-plane direction. Rth / Ro is larger than 0.8 and smaller than 5. Furthermore, it is preferably larger than 1.5 and smaller than 4.

In the present invention, Ro is preferably in the range of 40 nm to 100 nm. Is more preferably 40 nm or more and 80 nm or less, and particularly preferably 45 nm or more and 60 nm or less.

Rth is preferably in the range of 90 nm to 300 nm, more preferably 90 nm to 200 nm, and particularly preferably 100 nm to 130 nm.

Retardation can be measured by KOBRA · 21ADH (manufactured by Oji Scientific Instruments).
<Cellulose acetate>
The cellulose acetate of the present invention has a acetyl group substitution degree of 2.1 to 2.6. The degree of acetyl group substitution is determined by the method prescribed in ASTM-D817-96.

The cellulose acetate α of the present invention preferably has a 6% viscosity of 70 to 250 mPa · s, more preferably 80 to 220 mPa · s.

6% viscosity can be measured by the following method.

(Measurement method of 6% viscosity)
In the present invention, the 6% viscosity is measured with an Ostwald viscometer using a 95% acetone solution having a concentration of 6% by mass of cellulose acetate at 25 ° C. ± 1 ° C.

Put 3.00 g of dry sample and 39.90 g of 95% acetone aqueous solution in Erlenmeyer flask, seal tightly and stir for about 1.5 hours (6 mass / volume% solution). Then, it is completely dissolved by shaking for about 1 hour on a rotary shaker. The obtained 6 mass / volume% solution is transferred to a predetermined Ostwald viscometer mark, and the temperature is adjusted at 25 ± 1 ° C. for about 15 minutes. Measure the flow time between the time marks.

Calculate 6% viscosity by the following formula.

6% viscosity (mPa · s) = flow time (s) × viscosity coefficient The viscometer coefficient is obtained by measuring the flow time by the same operation as described above using a viscometer calibration standard solution.

Viscometer coefficient = {standard solution absolute viscosity (mPa · s) × solution density (0.827 g / cm ³ )} / {standard solution density (g / cm ³ ) × standard solution flow time (s)}
The cellulose acetate of the present invention has a 6% viscosity lower than that of cellulose acetate α, and is preferably 40 to 80 mPa · s. Cellulose acetate can be further mixed.

The cellulose acetate of the present invention can be produced by a conventional method such as a sulfuric acid catalyst method, an acetic acid method, or a methylene chloride method, and the raw material is preferably wood pulp.

Cellulose acetate is usually pulp (cellulose) activated with acetic acid or the like (activation step), and then triacetate is prepared with acetic anhydride using a sulfuric acid catalyst (acetylation step). It can be produced by adjusting the degree of acetylation by aging (saponification / aging process).

In this method, the activation step can be performed by treating pulp (cellulose), for example, by spraying acetic acid or hydrous acetic acid, immersing in acetic acid or hydrous acetic acid, etc. The amount is about 10 to 100 parts by weight, preferably 20 to 80 parts by weight, and more preferably about 30 to 60 parts by weight with respect to 100 parts by weight of pulp (cellulose).

The amount of acetic anhydride used in the acetylation step (acetylation step) can be selected within the range of the acetylation degree. For example, 230 to 300 parts by weight, preferably 240 to 290, per 100 parts by weight of pulp (cellulose). Part by mass, more preferably about 250 to 280 parts by mass.

In the acetylation step, acetic acid is usually used as a solvent. The amount of acetic acid used is, for example, about 200 to 700 parts by weight, preferably 300 to 600 parts by weight, and more preferably about 350 to 500 parts by weight with respect to 100 parts by weight of pulp (cellulose).

As the acetylation or aging catalyst, sulfuric acid is usually used. The amount of sulfuric acid used is usually about 1 to 15 parts by mass, preferably about 5 to 15 parts by mass, and particularly about 5 to 10 parts by mass with respect to 100 parts by mass of cellulose. The saponification / ripening can be performed at a temperature of about 50 to 70 ° C., for example.

In order to improve the optical properties of cellulose acetate, the cellulose acetate produced may be treated with an oxidizing agent at an appropriate stage in the cellulose acetate production process, for example, after completion of acetylation, saponification or aging.

Examples of the oxidizing agent include hydrogen peroxide; peracids such as performic acid, peracetic acid, and perbenzoic acid; and organic peroxides such as diacetyl peroxide. The oxidizing agent can be used alone or in combination of two or more.

Preferred oxidizing agents include oxidizing agents that are easy to remove from cellulose acetate and have low persistence, such as hydrogen peroxide, performic acid, and peracetic acid, with hydrogen peroxide and peracetic acid being particularly preferred. The amount of the oxidizing agent used can be selected according to the desired level of optical properties. For example, 0.01 to 5 parts by mass, preferably 0.1 to 2.5 parts by mass with respect to 100 parts by mass of cellulose acetate. In particular, it is about 0.1 to 1 part by mass.

The treatment with the oxidizing agent can be performed at, for example, about 20 to 100 ° C., preferably about 30 to 70 ° C., depending on the type of the oxidizing agent.

The cellulose acetate of the present invention is cellulose acetate L-30, L-40, L-50, L-70 (manufactured by Daicel Chemical Industries), Ca398-6, Ca398-10, Ca398-30, Ca394-60S (yeast Commercial products such as Man Chemical Japan Co., Ltd. can be used.
<Additives>
The retardation film of the present invention can be obtained by incorporating cellulose ester into the following sugar ester compound and polyester D represented by the general formula (1).
<Sugar ester compound>
The proportion of esterification is preferably 60% or more, more preferably 75% or more of the OH group present in the pyranose structure or furanose structure.

Examples of sugars preferably used in the present invention include the following, 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.

Examples include sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose, and more preferably sucrose.

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, homoveratormic acid, o-homoveratrumic acid, phthalonic acid, p- Although coumaric acid can be mentioned, benzoic acid is particularly preferable.

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, isomaltoligosaccharides, fructooligosaccharides, galactooligosaccharides, xylooligos. Sugar.

The sugar ester compound of the present invention is a compound obtained by condensing 1 or more and 12 or less of at least one pyranose structure or furanose structure represented by 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 of the present invention are listed below, but the present invention is not limited thereto.

<Polyester D>
General formula (1) 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 (1), 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 arylcarboxylic acid component of the polyester D used in the present invention include benzoic acid, para-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, normal propylbenzoic acid, There are 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 polyester D that can be preferably used in the retardation film 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 (neopentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3propanediol (3,3 -Dimethylolheptane), 3-methyl-1,5-pentanediol 1,6-hexanediol, 2,2 4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol These glycols are used as one or a mixture of two or more.

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 polyester D used for the retardation film has a number average molecular weight of preferably 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 (1) that can be used in the present invention will be shown, but the present invention is not limited thereto.

<Other additives>
(Plasticizer)
The retardation film of the present invention includes a phosphate ester plasticizer, a phthalate ester plasticizer, a trimellitic acid ester plasticizer, a pyromellitic acid plasticizer, a glycolate plasticizer, and a citrate ester plasticizer. Polyester plasticizers and phosphate ester plasticizer plasticizers can also be preferably used.

Examples of other carboxylic acid esters include trimethylolpropane tribenzoate, butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. As the polyester plasticizer, a copolymer of a dibasic acid and a glycol such as an aliphatic dibasic acid, an alicyclic dibasic acid, or an aromatic dibasic acid can be used.

The aliphatic dibasic acid is not particularly limited, and adipic acid, sebacic acid, phthalic acid, terephthalic acid, 1,4-cyclohexyl dicarboxylic acid and the like can be used. As the glycol, ethylene glycol, diethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol and the like can be used.

These dibasic acids and glycols may be used alone or in combination of two or more.

The amount of these plasticizers to be used is preferably 1% by mass to 20% by mass, particularly preferably 3% by mass to 13% by mass with respect to the cellulose ester in terms of film performance, processability and the like.

(Metal salt)
Such a cellulose acetate usually has a heat resistance stabilizer such as an alkali metal (lithium, potassium, sodium, etc.) or a salt or compound thereof, an alkaline earth metal (calcium, magnesium, strontium, Barium etc.) or a salt thereof or a compound thereof.

The alkaline earth metal such as calcium contained in normal cellulose acetate is about 30 to 200 ppm per gram of cellulose acetate.

In addition, content of the metal salt in a cellulose acetate can be quantified with the following method.
<Measurement of metal salt (calcium) content>
(Pretreatment and measurement)
About 500 mg of the sample is cut, put into a decomposition tube of a sealed microwave sample decomposition apparatus, 8 ml of nitric acid (ultra high purity reagent) manufactured by Kanto Chemical Co., Ltd. is added, a wet decomposed sample is prepared, and the sample is transferred to a polypropylene container After finishing to 50 ml with ultrapure water, Ca can be quantified with an inductively coupled plasma optical emission spectrometer (ICP-AES).

(Usage equipment and conditions)
Decomposition Equipment Milestone General Co., Ltd. ETHOS-1
SII Nano Technology Co., Ltd. SPS3520UV
Measurement wavelength 3933.4769nm
Calibration curve reagent Kanto Chemical Co., Ltd. Calcium standard solution for chemical analysis (UV absorber)
An ultraviolet absorber is preferably used for the retardation film of the present invention. As the ultraviolet absorber, those excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and having little absorption of visible light having a wavelength of 400 nm or more are preferably used from the viewpoint of good liquid crystal display properties.

Specific examples of the ultraviolet absorber preferably used in the present invention include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. However, it is not limited to these.

As the ultraviolet absorber preferably used in the present invention, a benzotriazole-based ultraviolet absorber and a benzophenone-based ultraviolet absorber that are highly transparent and excellent in preventing the deterioration of the polarizing plate and the liquid crystal are preferable, and unnecessary coloring is less. A benzotriazole-based ultraviolet absorber is particularly preferably used.

Also, the ultraviolet absorber having a distribution coefficient of 9.2 or more described in JP-A No. 2001-187825 improves the surface quality of a long film and is excellent in coating properties. In particular, it is preferable to use an ultraviolet absorber having a distribution coefficient of 10.1 or more.

Further, the polymer ultraviolet absorber described in the general formula (1) or general formula (2) described in JP-A-6-148430 and the general formulas (3), (6), (7) of Japanese Patent Application No. 2000-156039 (Or UV-absorbing polymer) is also preferably used. As a polymer ultraviolet absorber, PUVA-30M (manufactured by Otsuka Chemical Co., Ltd.) and the like are commercially available.

(Fine particles)
In order to impart slipperiness to the retardation film of the present invention, it is preferable to add fine particles.

The primary average particle diameter of the fine particles is preferably 20 nm or less, more preferably 5 to 16 nm, and particularly preferably 5 to 12 nm.

These fine particles preferably form secondary particles having a particle diameter of 0.1 to 5 μm and are contained in the retardation film, and the preferable average particle diameter is 0.1 to 2 μm, more preferably 0.2 to 0.6 μm. As a result, irregularities having a height of about 0.1 to 1.0 μm are formed on the film surface, thereby providing appropriate slipperiness to the film surface.

The primary average particle diameter of the fine particles used in the present invention is measured by observing the particles with a transmission electron microscope (magnification of 500,000 to 2,000,000 times), observing 100 particles, measuring the particle diameter, and measuring the average. The value was taken as the primary average particle size.

The apparent specific gravity of the fine particles is preferably 70 g / liter or more, more preferably 90 to 200 g / liter, and particularly preferably 100 to 200 g / liter. A larger apparent specific gravity makes it possible to make a high-concentration dispersion, which improves haze and agglomerates, and is preferable when preparing a dope having a high solid content concentration as in the present invention. Are particularly preferably used.

Silicon dioxide fine particles having an average primary particle diameter of 20 nm or less and an apparent specific gravity of 70 g / liter or more are, for example, a mixture of vaporized silicon tetrachloride and hydrogen burned in air at 1000 to 1200 ° C. Can be obtained. For example, it is marketed with the brand name of Aerosil 200V and Aerosil R972V (above, Nippon Aerosil Co., Ltd. product), and can use them.

The apparent specific gravity described above is calculated by the following equation by taking a certain amount of silicon dioxide fine particles in a graduated cylinder, measuring the weight at this time.
Apparent specific gravity (g / liter) = silicon dioxide mass (g) / volume of silicon dioxide (liter)
<Method for producing retardation film>
Next, the manufacturing method of the retardation film of this invention is demonstrated in detail.

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 a step of preparing a dope by dissolving cellulose acetate and an additive in a solvent, a step of casting a dope on an endless metal support, 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.
<Dope adjustment process>
The process for preparing the dope will be described. The concentration of cellulose acetate 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 acetate 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. However, it is preferable to use a mixture of a good solvent and a poor solvent of cellulose acetate in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of solubility of cellulose acetate.

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 acetate to be used independently is defined as a good solvent, and what does not swell or dissolve independently is defined as a poor solvent.

Therefore, in general, depending on the average degree of acetylation (acetyl group substitution degree) of cellulose acetate, the good solvent and the poor solvent change. For example, when acetone is used as a solvent, cellulose acetate (acetyl group substitution degree 2.4) is used. Is a good solvent, and cellulose triacetate (acetyl group substitution degree 2.9) 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.

Further, as the solvent used for dissolving cellulose acetate, the solvent removed from the film by drying in the film forming process is recovered and reused.

The recovery solvent may contain trace amounts of additives added to cellulose acetate, 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.

A general method can be used as a method for dissolving cellulose acetate when preparing the dope described above. 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 that the solvent does not boil under pressure, in order to prevent the formation of massive undissolved material called gel or mamako.

Further, 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 even 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 cellulose acetate can be dissolved in a solvent such as methyl acetate.

Next, the cellulose acetate solution is filtered using a suitable 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 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 acetate by filtration.

The bright spot foreign matter is arranged in a crossed Nicols state with two polarizing plates, a retardation 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 sometimes leaks, 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, further preferably 50 pieces / m ² or less, and further 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.

A preferable temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and further preferably 45 to 55 ° C.

A smaller filtration pressure is preferred. 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.
<Casting process>
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 60 ° C, more preferably 25 to 55 ° 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 hot 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 residual solvent amount 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.
<Drying process>
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.

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 retardation film of the present invention, it is particularly preferable to stretch in the width direction (lateral direction) by a tenter method in which both ends of the web are gripped by 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 preferably has a width of 1 to 4 m. Particularly, those having a width of 1.3 to 4 m are preferably used, and particularly preferably 1.3 to 3 m.
<Extension process>
The retardation values Ro and Rth targeted by the present retardation film can be adjusted by the amount of sugar ester and polyester D to be added and the stretching ratio (control of tenter stretching and transport tension) during film production.

Biaxial stretching or uniaxial stretching can be performed sequentially or simultaneously with respect to 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 1.3 to 1.5 times in the width direction.

The stretching temperature is 140 ° C. to 200 ° C., and it is preferable that the stretching temperature is over 140 ° C. and 180 ° C. or less.

The residual solvent in the film is preferably 0 to 20% by mass, more preferably 5 to 15% by mass.

Further, the tension applied in the film width direction during stretching is desirably 30 N / m or more and less than 100 N / m, and preferably 40 N / m or more and less than 80 N / m.

There is no particular limitation on the method of stretching the web. For example, a method in which a circumferential speed difference is applied to a plurality of rolls, and the roll circumferential speed difference is used to stretch the rolls in the vertical direction. 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.

In the present invention, heat setting at a temperature of 140 ° C. to 180 ° C. after the stretching step is also effective for obtaining the tear strength in the present invention.

The heat setting at a stretching temperature of 140 ° C. to 180 ° C. or 140 ° C. to 180 ° C. after the stretching step is a temperature range that is specifically effective for cellulose acetate having an acetyl group substitution degree of 2.1 to 2.6. is there.

When the slow axis or the fast axis of the retardation film of the present invention exists in the film plane and the angle formed with the film forming direction is θ1, θ1 is preferably −1 ° or more and + 1 ° or less, −0 More preferably, it is 3 ° or more and + 0.3 ° or less.

This θ1 can be defined as an orientation angle, and θ1 can be measured in an atmosphere of 23 ° C. and 55% RH 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 transmission rate of the retardation film of the present invention is preferably 800 to 1600 g / m ² · 24 h at 40 ° C. and 90% RH, more preferably 1000 to 1600 g / m ² · 24 h, and 1200 to 1600 g / m ² · 24 h. Particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

The breaking elongation of the retardation film of the present invention is 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 0.2%.

When a retardation film with an additive such as a retardation increasing agent is used in a liquid crystal display device with a very high front contrast, such as a VA liquid crystal display device, the additive becomes a foreign substance and the film is caused by internal haze and internal scattering. In the retardation film of the present invention, the internal haze is preferably less than 0.1%, particularly preferably from 0 to 0.05%.

This haze can be achieved by using a cellulose ester as a raw material for pulp and containing the sugar ester and polyester D of the present invention.

The retardation film of the present invention has a refractive index difference between 5 × 10 ⁻⁴ to 5 × 10 ⁻³ between one surface thereof and the opposite surface (also referred to as film surface or back surface). preferable.

When this is a thin film polarizing plate, the stiffness of the polarizing plate becomes weak, and bubbles are likely to be generated or misaligned when bonded to a liquid crystal cell. Therefore, the above-mentioned failure at the time of pasting to a liquid crystal cell can be reduced by giving a curl intentionally to a retardation film and giving a stiffness to a polarizing plate.
<Functional layer>
The hard coat film can be provided with functional layers such as an antistatic layer, a backcoat layer, an antireflection layer, a slippery layer, an adhesive layer, an antiglare layer, and a barrier layer.

<Back coat layer>
The hard coat film may be provided with a back coat layer on the surface of the base film opposite to the side on which the hard coat layer is provided in order to prevent curling and sticking.

As particles added to the backcoat layer, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, tin oxide, and oxide. Mention may be made of indium, zinc oxide, ITO, hydrated calcium silicate, aluminum silicate, magnesium silicate and calcium phosphate. The particles contained in the back coat layer are preferably 0.1 to 50% by mass with respect to the binder. The increase in haze when the backcoat layer is provided is preferably 1.5% or less, more preferably 0.5% or less, and particularly preferably 0.1% or less. As the binder, a cellulose ester resin such as diacetylcellulose is preferable.

<Antireflection layer>
The hard coat film can be used as an antireflection film having an external light antireflection function by coating an antireflection layer on the hard coat layer. The antireflection layer is preferably laminated in consideration of the refractive index, the film thickness, the number of layers, the layer order, and the like so that the reflectance is reduced by optical interference. The antireflection layer is preferably composed of a low refractive index layer having a refractive index lower than that of the support, or a combination of a high refractive index layer having a refractive index higher than that of the support and a low refractive index layer. Particularly preferably, it is an antireflection layer composed of three or more refractive index layers. Three layers having different refractive indexes from the support side are divided into medium refractive index layers (high refractive index layers having a higher refractive index than the support). Are preferably laminated in the order of a layer having a lower refractive index) / a high refractive index layer / a low refractive index layer. Alternatively, an antireflection layer having a layer structure of four or more layers in which two or more high refractive index layers and two or more low refractive index layers are alternately laminated is also preferably used.

As the layer structure of the antireflection film, the following structure can be considered, but it is not limited to this.

Base film / hard coat layer / low refractive index layer Base film / hard coat layer / medium refractive index layer / low refractive index layer Base film / hard coat layer / medium refractive index layer / high refractive index layer / low refractive index Layer Base film / hard coat layer / high refractive index layer (conductive layer) / low refractive index layer Base film / hard coat layer / antiglare layer / low refractive index layer Low refraction essential for antireflection film The refractive index layer preferably contains silica-based fine particles, and the refractive index thereof is lower than the refractive index of the base film as a support, and is in the range of 1.30 to 1.45 at 23 ° C. and wavelength of 550 nm. Preferably there is.

The film thickness of the low refractive index layer is preferably 5 nm to 0.5 μm, more preferably 10 nm to 0.3 μm, and most preferably 30 nm to 0.2 μm. The composition for forming a low refractive index layer preferably contains at least one kind of particles having an outer shell layer and porous or hollow inside as silica-based fine particles. In particular, the particles having the outer shell layer and porous or hollow inside are preferably hollow silica-based fine particles.

Note that the composition for forming a low refractive index layer may contain an organosilicon compound represented by the following general formula (OSi-1), a hydrolyzate thereof, or a polycondensate thereof.

General formula (OSi-1): Si (OR) ₄
In the organosilicon compound represented by the above general formula, R represents an alkyl group having 1 to 4 carbon atoms. Specifically, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and the like are preferably used. In addition, a silane coupling agent, a curing agent, a surfactant and the like may be added as necessary.
<Polarizing plate>
A polarizing plate using the retardation film of the present invention will be described. The polarizing plate can be produced by a general method. The retardation film of the present invention is subjected to alkali saponification treatment, and the treated retardation film is bonded to at least one surface of a polarizer produced by immersing and stretching in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. Is preferred.

Alternatively, a hard coat film may be used on the other surface, or another polarizing plate protective film may be used.

Commercially available polarizing plate protective films that can be preferably used include KC4UA, KC6UA, KC8UX2MW, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC4UEW, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC4CCR-1, 2, KC8UE, KC4UE (manufactured by Konica Minolta Opto) and the like.

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 ones in which iodine is dyed on a system film and ones in which a dichroic dye is dyed, but it is not limited to this.

For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. A polarizer having a thickness of 5 to 30 μm, preferably 10 to 25 μm, is preferably used. On the surface of the polarizer, the retardation film of the present invention and one side of the hard coat film are bonded together to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like.
<Adhesive layer>
The pressure-sensitive adhesive layer used on one side of the protective film to be bonded to the substrate of the liquid crystal cell is preferably optically transparent and exhibits moderate viscoelasticity and adhesive properties.

Specific examples of the adhesive layer include adhesives or adhesives such as acrylic copolymers, epoxy resins, polyurethane, silicone polymers, polyethers, butyral resins, polyamide resins, polyvinyl alcohol resins, and synthetic rubbers. A film such as a drying method, a chemical curing method, a thermal curing method, a thermal melting method, a photocuring method, or the like can be formed and cured using a polymer such as the above. Among them, the acrylic copolymer can be preferably used because it is most easy to control the physical properties of the adhesive and is excellent in transparency, weather resistance, durability and the like.
<Liquid crystal display device>
By incorporating the polarizing plate of the present invention produced using the retardation film of the present invention into a display device, various image display devices with excellent visibility can be produced.

The retardation film of the present invention is incorporated in a polarizing plate, and is a reflection type, transmission type, transflective liquid crystal display device or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type. It is preferably used in liquid crystal display devices of various drive systems such as the OCB type and is particularly suitable for the VA type.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples, “%” and “part” represent “% by mass” and “part by mass”, respectively, unless otherwise specified.
Synthetic synthesis example 1 of cellulose acetate
After pretreatment activation by spraying 50 parts by mass of glacial acetic acid on 100 parts by mass of kraft pulp (α-cellulose content 98.2%), 470 parts by mass of glacial acetic acid, 265 parts by mass of acetic anhydride, and 8.3 parts of sulfuric acid. A part by mass of the mixture was added and esterification was carried out by a conventional method. Thereafter, 95 parts by mass of acetic acid and 33 parts by mass of water were added for hydrolysis and aging, and 5.7 parts by mass of calcium acetate was added to neutralize sulfuric acid in the system.

Thus, cellulose acetate D having an acetyl substitution degree of 2.4 and a viscosity average polymerization degree of 180 was obtained.
Synthesis example 2
Cellulose acetate was produced in the same manner as in Synthesis Example 1 except that the amount of calcium acetate and the amount of water added in the synthesis process were changed as shown in Table 1. The obtained cellulose acetates were designated as A to C and E to J. The amount of calcium acetate and the amount of water shown in Table 1 indicate parts by mass.

Example 1
<Cellulose Acetate Film 1: Production of PL1>
(Silicon dioxide dispersion)
Aerosil R812 (manufactured by Nippon Aerosil Co., Ltd.) 12 parts by mass (average diameter of primary particles 12 nm, apparent specific gravity 90 g / liter)
88 parts by mass of ethanol or more was stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin. 88 parts by mass of methylene chloride was added to the silicon dioxide dispersion while stirring, and the mixture was stirred and mixed for 30 minutes with a dissolver to prepare a silicon dioxide dispersion dilution.
(Production of in-line additive solution)
Tinuvin 109 (manufactured by Ciba Japan Co., Ltd.) 11 parts by mass Tinuvin 171 (manufactured by Ciba Japan Co., Ltd.) 5 parts by mass Methylene chloride 100 parts by mass Dissolved and filtered.

To this was added 36 parts by mass of the silicon dioxide dispersion diluted with stirring, and further stirred for 30 minutes. Then, 6 parts by mass of the following cellulose triacetate was added with stirring and further stirred for 60 minutes, and then Advantech Toyo Corp. The polypropylene wind cartridge filter TCW-PPS-1N was used to prepare an in-line additive solution.
(Preparation of dope solution)
Cellulose triacetate KTL (manufactured by Daicel Chemical Industries, Ltd .: acetyl group substitution degree 2.9) 100 parts by weight Trimethylolpropane tribenzoate 5.0 parts by weight Ethylphthalylethyl glycolate 5.5 parts by weight Methylene chloride 440 parts by weight Ethanol 40 parts by mass or more was put into a closed container, heated and stirred to dissolve completely, and Azumi Filter Paper No. No. 24 was used for filtration to prepare a dope solution.

The dope solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. in the film production line. In the inline additive solution line, the inline additive solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. Add 2 parts by weight of the filtered in-line additive to 100 parts by weight of the filtered dope solution, mix thoroughly with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and then use a belt casting apparatus. Used at a temperature of 35 ° C. and a width of 1.8 m and uniformly cast on a stainless steel band support.

Using a stainless steel band support, the solvent was evaporated until the residual solvent amount became 120%, and the stainless steel band support was peeled off. The peeled cellulose ester web was evaporated at 35 ° C., slit to 1.65 m width, and then stretched by 1.05 times in the TD direction (direction perpendicular to the film transport direction) with a tenter. Drying was performed at a drying temperature of ° C. At this time, the residual solvent amount when starting stretching with a tenter was 30%.

Then, drying is completed while transporting a drying zone of 110 ° C. and 120 ° C. with a number of rolls, slitting to a width of 1.5 m, and knurling of a width of 15 mm and an average height of 10 μm is performed on both ends of the film, and the average film thickness Produced a cellulose triacetate film 1 having a thickness of 60 μm.

When the retardation value was measured, Ro and Rth were 3 nm and 50 nm, respectively.

<Preparation of hard coat film 1>
On the produced cellulose triacetate film 1, the following hard coat layer coating composition 1 is filtered through a polypropylene filter having a pore size of 0.4 μm to prepare a hard coat layer coating solution, which is applied using a micro gravure coater, after drying at 80 ° C., using an ultraviolet lamp, the illuminance of the irradiated portion is 80 mW / cm ^2, thereby curing the coated layer with irradiation dose as 80 mJ / cm ^2, to form a hard coat layer 1 dry thickness 9 .mu.m, Winding and roll-shaped hard coat film 1 were produced.
<Preparation of hard coat film 2>
On a commercially available polarizing plate protective film (cellulose triacetate film) KC6UA (manufactured by Konica Minolta Co., Ltd.), the following hard coat layer coating composition 1 is filtered through a polypropylene filter having a pore size of 0.4 μm to apply a hard coat layer. liquid was prepared, was applied with a micro gravure coater, after drying at 80 ° C., using a UV lamp to cure the coated layer illuminance of the irradiated portion is 80 mW / cm ^2, the irradiation amount as 80 mJ / cm ² Then, a hard coat layer 1 having a dry film thickness of 9 μm was formed, wound up, and a roll-shaped hard coat film 2 was produced.

<Hardcoat layer coating composition 1>
The following materials were stirred and mixed to obtain hard coat layer coating composition 1.

Thermoplastic resin, polyester urethane resin (manufactured by Toyobo Co., Ltd., trade name “Byron UR1350”, solid content concentration 33% (toluene / methyl ethyl ketone solvent = 65/35)) 6.0 parts by mass (as polyester urethane resin 2 .0 parts by mass)
Pentaerythritol triacrylate 30 parts by mass Pentaerythritol tetraacrylate 30 parts by mass Irgacure 184 (manufactured by Ciba Japan, photopolymerization initiator)
3.0 parts by mass Irgacure 907 (manufactured by Ciba Japan, photopolymerization initiator)
1.0 part by mass Polyether-modified polydimethylsiloxane (BYK-UV3510, manufactured by Big Chemie Japan)
2.0 parts by mass Propylene glycol monomethyl ether 150 parts by mass Methyl ethyl ketone 150 parts by mass <Preparation of retardation film 101>
The retardation film 101 was produced as follows.

<Fine particle dispersion>
Fine particles (Aerosil R812 (Nippon Aerosil Co., Ltd.))
11 parts by mass (average primary particle diameter 16 nm, apparent specific gravity 90 g / liter)
89 parts by mass or more of ethanol was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle additive solution>
Cellulose ester A was added to a dissolution tank containing methylene chloride and heated to completely dissolve, and this was then added to Azumi filter paper No. 3 manufactured by Azumi Filter Paper Co., Ltd. Filtered using 244.

The fine particle dispersion was slowly added to the cellulose ester solution after filtration while sufficiently 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.

Methylene chloride 99 parts by mass Fine particle dispersion 11 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 ester F was charged into a pressure dissolution tank containing a solvent while stirring. This was heated and stirred to dissolve completely, and a plasticizer and an ultraviolet absorber were added and dissolved.

This is Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

In addition to 100 parts by mass of the main dope solution and 5 parts by mass of the fine particle additive solution, thoroughly mix with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), then use a belt casting device to It was cast uniformly on a 2 m stainless steel band support.

On the stainless steel band support, the solvent was evaporated until the residual solvent amount became 110%, and the stainless steel band support was peeled off. The film was stretched so that the longitudinal (MD) stretch ratio was 1.0 times by applying tension at the time of peeling, and then both ends of the web were gripped by a tenter, and the stretch ratio in the width (TD) direction was 1.4. It extended | stretched so that it might become double (40%). The tension in the width direction applied to the film at this time was 45 m / N.

After stretching, hold for several seconds while maintaining its width, release the width holding after relaxing the tension in the width direction, further carry for 30 minutes in the third drying zone set at 125 ° C., and perform drying, A retardation film 101 having a film thickness of 40 μm having a width of 1.5 m, a knurling having a width of 1 cm at the end and a height of 8 μm was produced.

<Composition of main dope solution>
Methylene chloride 390 parts by weight Ethanol 80 parts by weight Cellulose acetate C 35 parts by weight Cellulose acetate D 65 parts by weight Additive: Sugar ester compound 4 10 parts by weight Additive: Polyester D 21 2.5 parts by weight Composition of dope solution (cellulose acetate, Retardation films 102 to 119 were produced in the same manner as described above except that the additive was changed as shown in Table 2.

In Table 2, TPP represents triphenyl phosphate, and AB represents the following triazine compound.

The obtained retardation film was measured for the in-plane retardation value Ro, the retardation value Rth in the thickness direction, the tear strength ratio and the internal haze / internal scattering by the following measurements. The results are shown in Table 3.

<Measurement of retardation value>
Ro = (nx−ny) × d
Rth = ((nx + ny) / 2−nz) × d
(In the formula, nxny and nz represent the refractive indexes in the principal axes x, y and z directions of the refractive index ellipsoid, respectively, and nx and ny represent the refractive index in the film in-plane direction, and nz represents the thickness direction of the film. Refractive index, nx> ny, and d represents film thickness (nm).
Attach eyepiece with polarizing plate to Abbe refractometer (1T), and use spectral light source to change the refractive index in one direction on both sides of the retardation film, the direction perpendicular to it and the direction perpendicular to the film surface. The average refractive index was determined from the average value obtained by measurement. Moreover, the thickness d of the film was measured using a commercially available micrometer.

Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), film retardation measurement at a wavelength of 590 nm was performed in a film that was allowed to stand for 24 hours in an environment of 23 ° C. and 55% RH. went. The average refractive index and film thickness described above were input into the above formula, and values for in-plane retardation value (Ro) nm and thickness direction retardation value (Rth) nm were obtained.

<Measurement of tear strength>
The tear strength in the film transport direction (MD direction) and the tear strength in the same width direction (TD direction) are determined by applying a tear load of the Elmendorf method in accordance with JISK7128 / 2-1991. Then, the samples conditioned at 23 ° C. 55% RH and 60 ° C. 10% RH for 24 hours were measured under the same atmosphere.

<Internal haze measurement>
A solvent (glycerin) having a refractive index of film refractive index ± 0.05 is dropped on the film interface to make the haze on the film surface as negligible as possible, and the measurement is performed with a haze meter.

In addition, scattering means the haze of the whole film including the state (film surface haze) which does not dripping glycerol.

<Measurement of haze inside film (hereinafter abbreviated as internal haze)>
Haze meter (turbidity meter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.)
The light source uses a 5V9W halogen bulb, and the light receiving unit uses a silicon photocell (with a relative visibility filter).

In the present invention, in this apparatus, the value is 0.02 or less in the haze measurement of a film when a solvent having a refractive index of ± 0.05 is used as the film interface.

Measured according to JIS K-7136.

Measure internal haze as follows. A description will be given with reference to FIGS.

First, the blank haze 1 of a measuring instrument other than a film is measured.
1. Drip a drop (0.05 ml) of glycerin on a cleaned glass slide. At this time, care is taken so that bubbles do not enter the droplet. Be sure to use glass that has been cleaned with a detergent because it may look dirty even if it looks clean. See FIG. Place the cover glass on top of it. Glycerin spreads without pressing the cover glass.
3. Set on a haze meter and measure blank haze 1.

Next, the haze 2 including the sample is measured.
4). Glycerol is dropped on the slide glass. (0.05ml)
See FIG. A sample film to be measured is placed thereon. See FIG. Glycerol is dropped on the sample film. (0.05ml)
See FIG. Place the cover glass on top of it. See FIG. Set in a haze meter and measure haze 2.
9. (Haze 2) − (Haze 1) = (Internal haze of the present invention) is calculated.

The glass and glycerin used in the above measurement are as follows.

Glass: MICRO SLIDE GLASS S9213 MATUNAMI
Glycerin: Deer special grade manufactured by Kanto Chemical

From Table 3, it can be seen that in the present invention, the tear strengths in the MD direction and the TD direction are substantially equal.
<Preparation of polarizing plate>
(Alkaline saponification treatment)
A polarizing plate was produced using one each of the hard coat film 1 and the retardation films 101 to 117 as a protective film for the polarizing plate.

(A) Production of Polarizer What was impregnated with 10 parts by mass of glycerin and 170 parts by mass of water in 100 parts by mass of polyvinyl alcohol (hereinafter abbreviated as PVA) having a saponification degree of 99.95 mol% and a polymerization degree of 2400. After melt-kneading and defoaming, it was melt-extruded from a T-die onto a metal roll to form a film. Then, it dried and heat-processed and obtained the PVA film.

The obtained PVA film had an average thickness of 25 μm, a moisture content of 4.4%, and a film width of 3 m. Next, the obtained PVA film was continuously treated in the order of pre-swelling, dyeing, uniaxial stretching by a wet method, fixing treatment, drying, and heat treatment to produce a polarizer.

That is, the PVA film was preliminarily swollen in water at a temperature of 30 ° C. for 30 seconds, and immersed in an aqueous solution having an iodine concentration of 0.4 g / liter and a potassium iodide concentration of 40 g / liter at a temperature of 35 ° C. for 3 minutes. Subsequently, the film was uniaxially stretched 6 times in a 50% aqueous solution with a boric acid concentration of 4% under a tension of 700 N / m. The potassium iodide concentration was 40 g / liter, and the boric acid concentration was 40 g / liter. Then, it was immersed in an aqueous solution having a zinc chloride concentration of 10 g / liter and a temperature of 30 ° C. for 5 minutes for fixing treatment.

Thereafter, the PVA film was taken out, dried with hot air at a temperature of 40 ° C., and further heat-treated at a temperature of 100 ° C. for 5 minutes. The obtained polarizer had an average thickness of 13 μm, a polarization performance of 43.0% transmittance, a polarization degree of 99.5%, and a dichroic ratio of 40.1.

(B) Preparation of Polarizing Plate 201 A polarizer, a retardation film 101, and a hard coat film 1 were bonded together according to the following steps 1 to 5 to prepare a polarizing plate.
Step 1: The aforementioned polarizer was immersed in a storage tank of a polyvinyl alcohol adhesive solution having a solid content of 2% by mass for 1 to 2 seconds.
Process 2: The alkali saponification process was implemented on the hard coat film which stuck the peelable protective film (product made from PET) to retardation film and the hard coat layer on the following conditions. Next, the excess adhesive adhered to the polarizer immersed in the polyvinyl alcohol adhesive solution in Step 1 is gently removed, and the retardation film and the hard coat film 1 are sandwiched between the polarizers as shown in FIG. Arranged.

(Alkaline saponification treatment)
Saponification step 1.5M-KOH 50 ° C 45 seconds Water washing step Water 30 ° C 60 seconds Neutralization step 10 parts HCl 30 ° C 45 seconds Water washing step Water 30 ° C 60 seconds After saponification treatment, water washing, neutralization, water washing in this order And then dried at 100 ° C.
Step 3: The laminate was bonded with a rotating roller at a pressure of 20 to 30 N / cm ² at a speed of about 2 m / min. At this time, it was carried out with care to prevent bubbles from entering.
Step 4: The sample prepared in Step 3 was dried in a dryer at a temperature of 80 ° C. for 5 minutes to prepare a polarizing plate.
Step 5: A commercially available acrylic pressure-sensitive adhesive is applied to the polarizing plate prepared in Step 4 so that the thickness after drying is 25 μm, and dried in an oven at 110 ° C. for 5 minutes to form an adhesive layer. A peelable protective film was attached to the film. This polarized light was cut (punched) into a size of 576 × 324 mm to produce a polarizing plate.
<Preparation of polarizing plate>
In the production of the polarizing plates, as shown in Table 4, a hard coat film and a retardation film were arranged to produce polarizing plates 202 to 223.

In preparing the polarizing plates 203 and 223, the cellulose ester film 1 (PL1) was used as the retardation film.
<Production of liquid crystal display device>
The viewing side polarizing plate of the liquid crystal panel of the 40-inch display KDL-40V5 manufactured by Sony Corporation is peeled off, and the polarizing plate prepared above (see FIG. 5 for the configuration) is used as the polarizing plate instead so that the hard coat layer is on the viewing side. Then, the pressure-sensitive adhesive layer and the liquid crystal cell glass were bonded to prepare liquid crystal display devices 401 to 423.

<Evaluation>
The following evaluations were performed on the produced retardation films 101 to 119, polarizing plates 201 to 223, and image display devices 401 to 423.
<Polarizing plate>
(Liquid crystal display device)
<Evaluation of visibility>
About each produced said liquid crystal display device, after leaving for 100 hours on 60 degreeC and 90% RH conditions, it returned to 23 degreeC and 55% RH. Thereafter, the surface of the display device was visually observed and evaluated according to the following criteria.
A: No wavy unevenness is observed on the surface.
○: Slight wavy unevenness is observed on the surface.
Δ: Small wavy unevenness is slightly observed on the surface.
X: Fine wavy unevenness is observed on the surface.
<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 front contrast >>
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 measurement, EZ-Contrast 160D manufactured by ELDIM was used, the luminance from the normal direction of the display screen of white display and black display was measured with a liquid crystal display device, and the ratio was defined as the front contrast.

Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)
The results obtained are shown in Table 4.

It can be seen from Table 4 that good optical compensation can be achieved with a polarizing plate using the retardation film of the present invention.

P1 Cellulose triacetate film P2 Hard coat layer P3 Polarizer P4 Retardation film of the present invention P5 Adhesive layer P6 Hard coat film P7 Polarizing plate

Claims (3)

1. The in-plane retardation Ro represented by the following formula is 30 to 150 nm, and the ratio Rth / Ro between the thickness direction retardation Rth and the in-plane retardation Ro is greater than 0.8 and less than 5. , A long retardation film using cellulose acetate, wherein the cellulose acetate has an acetyl group substitution degree of 2.1 or more and 2.6 or less, and under conditions of 23 ° C. 55% RH and 60 ° C. 10% RH. The ratio of the tear strength in the longitudinal direction (MD direction) and the tear strength in the same width direction (TD direction) of the above retardation film: (Tear strength in the MD direction / Tear strength in the TD direction) A retardation film having a thickness of 0.8 to 1.2.
   Ro = (nx−ny) × d
   Rth = {(nx + ny) / 2−nz} × d
   Here, d represents the thickness (nm) of the retardation film, nx is the maximum refractive index in the plane of the film, ny is the refractive index in the direction perpendicular to the nx direction in the film plane, and nz is the thickness. Represents the refractive index of the film in the direction. The wavelength is 590 nm.
2. In the retardation film, the tear strength in the film transport direction (MD direction) and the tear strength in the same width direction (TD direction) are both 30 mN or more and 120 mN or less at 60 ° C. and 10% RH. The retardation film according to claim 1.
3. A cellulose acetate dope having an acetyl group substitution degree of 2.1 or more and 2.6 or less is prepared, the dope is cast on a metal support, the casting film is peeled off as a film from the support, and the peeled film A method for producing a retardation film in which both widthwise ends of a film are held by a tenter to hold the width of the film and the film is dried, and the film is further dried after being detached from the tenter. A method for producing a retardation film, wherein a drying temperature is in a range of 140 ° C. to 200 ° C. in a gripping section, and a tension applied in a film width direction is 30 N / m or more and less than 100 N / m.

Images