JP2002221620A - Film for polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film for a polarizing plate in which stripe irregularity is invisible and which gives preferably quality of the screen of a liquid crystal display device. SOLUTION: The film is a cellulose ester film produced by dissolving cellulose esters in an organic solvent to prepare a dope and casting the dope from a flow casting die to a cast supporting body. The stripe irregularity 3 having 3 to 15 mm pitches P1, P2, etc., in the lateral direction shows <0.04 deg. inclination angles θ1, θ2, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polarizing plate film capable of improving the quality of a liquid crystal display screen.

[0002]

2. Description of the Related Art In general, a liquid crystal display device is constituted by laminating a polarizing plate on a liquid crystal cell with an adhesive layer. The liquid crystal cell has a liquid crystal compound layer and a liquid crystal compound layer. , And an electrode layer for applying a voltage to the liquid crystal compound layer provided inside the glass plate.

[0003] The polarizing plate is, for example, a polarizer, an optical compensation film having a protective function laminated on one surface (the surface on the liquid crystal cell side) of the polarizer, and a polarizing plate protective film laminated on the other surface. And a membrane. This optical compensation film has a function of removing coloring of the liquid crystal screen, and generally, a support, an adhesion layer laminated on one surface of the support,
It is composed of an orientation providing layer and an optical compensation layer, and a back layer laminated on the other surface.

[0004] As a support of this optical compensation film,
Cellulose ester films are used because they have good transparency, high mechanical strength, and small dimensional fluctuations due to changes in humidity and heat (good dimensional stability). The cellulose ester film is produced by a solution casting method. In this solution casting method, a dope in which a cellulose ester is dissolved in an organic solvent is cast from a casting die onto a casting support, and the casting support is cast on the casting support. After drying the base consisting of the dope cast to some extent, peel it off, and
It is further dried to produce a film.

[0005]

By the way, streak-like unevenness may be seen on the screen of the liquid crystal display device, and it has been desired to improve the quality of the screen by making the streak-like unevenness invisible. However, no effective technique for making the stripe-like unevenness invisible has been proposed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing plate film which solves the above-mentioned problems and does not show streak-like unevenness and can improve the quality of the screen of a liquid crystal display device.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on the cause of streaky unevenness and found that streaky unevenness is present on a support used for an optical compensation film of a polarizing plate. Then, they found that the streaky unevenness appears as streaky unevenness. Further, the enthusiastic study on the streaky unevenness was conducted, and the inclination of the streaky unevenness was 0.04.
It was found that when the temperature is lower than the degree, the streak-like unevenness becomes difficult to see.

Further, it has been found that the streaky unevenness which deteriorates the surface shape is caused by the size of the thickness unevenness at the time of casting and the surface shrinkage force generated during the drying process. It has been found that the solid concentration of the dope in the outer layer should be smaller than the solid concentration of the dope in the inner layer.

The present invention has been made based on the above findings. The polarizing plate film according to the present invention is formed by casting a dope in which a cellulose ester is dissolved in an organic solvent from a casting die onto a casting support. Wherein the inclination of the streaky unevenness having a horizontal pitch of 3 to 15 mm is less than 0.04 degrees.

In the polarizing plate film of the present invention, when the pitch of the stripe-like unevenness in the horizontal direction is 3 to 15 mm, the inclination is specified to be less than 0.04 degrees. This was almost invisible when the pitch of the streak unevenness was less than 3 mm or more than 15 mm, and was visible at a pitch of 3 to 15 mm. Therefore, by setting the inclination to be less than 0.04 degrees in a range where the streaky unevenness can be seen, it was possible to make it almost invisible.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the polarizing plate film according to the present invention, the inclination of streaky unevenness having a horizontal pitch of 3 to 15 mm is less than 0.04 degrees, preferably less than 0.02 degrees. Here, the lateral direction is a direction perpendicular to the casting method.

Regarding the pitch and inclination of the streak unevenness,
This will be described with reference to FIGS. FIG. 1 is a partial plan view showing a film on a casting support, and FIG. 2 is a cross-sectional view of the film cut in a lateral direction.

In FIGS. 1 and 2, reference numeral 1 denotes a casting support, on which a dope is cast to form a film 2. On the surface of the film 2, streaky unevenness 3 is generated in the vertical direction (casting direction). When the pitches p1, p2... Of the streaky unevenness 3 are in the range of 3 to 15 mm, Slope θ1, θ2 of streak unevenness 3
Is less than 0.04 degrees.

In the polarizing plate film of the present invention, in order to make the angle of the line-like unevenness less than 0.04 degrees, for example,
Two or more layers by co-casting, wherein the solid content of the dope in the outer layer is 1% by weight or more lower than that of the inner layer, preferably 2% or more, more preferably 3%. The above can be carried out by making the concentration low. Here, the outer layer is a layer exposed on the surface, and the inner layer is a layer disposed inside (in the case of two layers, a layer in contact with the casting support, and in the case of three layers, Layer sandwiched in the middle)
That is.

The thickness of the outer layer in the wet state immediately after casting is preferably 2 μm or more, more preferably 3 μm or more. If the thickness of the outer layer in a wet state is less than 2 μm, sufficient flatness cannot be ensured.

When co-casting two or more layers, for example,
Performed using a single-layer die and a feed block having a junction where two or more layers are provided at the entrance of the single-layer die, or having two or more manifolds and having two or more layers This can be performed using a multi-manifold type die to be laminated.

In the feed block, it is preferable that trapezoidal grooves are formed in distribution pins provided at the junction of two or more layers so that the casting width of the outer layer can be changed. By providing such a groove, when the outer layer has a low-concentration layer, non-uniformity of the low-concentration layer due to a wrapping phenomenon occurring in the flow path can be suppressed, and the width of the outer layer can be arbitrarily changed. Can be.

Representative examples of the cellulose ester include lower fatty acid esters of cellulose (eg, cellulose acetate, cellulose acetate butyrate and cellulose acetate propionate). Lower fatty acids are
It means a fatty acid having 6 or less carbon atoms. Cellulose acetate includes triacetyl cellulose (TAC) and cellulose diacetate (DAC).

The degree of acetylation of cellulose acetate is 50 to 50%.
70% is preferable, and especially 55 to 65% is preferable. The weight average molecular weight is preferably from 70,000 to 120,000, particularly preferably from 80,000 to 100,000. The cellulose acetate may be partially esterified with not only acetic acid but also a fatty acid such as propionic acid or butyric acid as long as the degree of acetylation is satisfied. Alternatively, the cellulose triacetate may contain a cellulose ester such as cellulose propionate or cellulose butyrate as long as the total amount satisfies the degree of acetylation.

The solvent used in the present invention may be any solvent as long as it can dissolve cellulose acetate.
In addition, a solvent that cannot be dissolved alone can be used as long as it can be dissolved by mixing with another solvent. Examples of the solvent include aliphatic hydrocarbons such as pentane, hexane, heptane, octane, isooctane and cyclohexane; aromatic hydrocarbons such as pentane, toluene and xylene; methyl chloride, methylene chloride (methylene chloride), carbon tetrachloride And halogenated hydrocarbons such as trichloroethane; alcohols such as methanol, ethanol, isopropyl alcohol and n-butyl alcohol; and esters such as methyl formate, ethyl formate, methyl acetate and ethyl acetate.

In general, a mixed solvent of methylene chloride and methanol is used. However, as long as cellulose acetate is not precipitated (during the preparation of the dope or at the time of adding the fine particle dispersion later), another solvent such as isopropyl alcohol or n- Butyl alcohol may be used. The weight ratio of cellulose acetate to solvent in the dope is preferably in the range of 10:90 to 30:70.

In the dope of the present invention, various additives depending on the use in each preparation step can be added. The doping may be added at any point in the dope preparation step, but may be performed by adding a step of adding and preparing an additive to the last preparation step of the dope preparation step.

As a plasticizer preferably added, a phosphoric acid ester or a carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCC).
P), cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate. Representative carboxylic esters include phthalic esters and citric esters. Examples of phthalate esters include dimethyl phthalate (DM
P), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include O-acetyl triethyl citrate (OACT
E) and tributyl O-acetylcitrate (OACT
B), acetyltriethyl citrate, acetyltributyl citrate.

Examples of other carboxylic esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic esters. Examples of glycolic acid esters include triacetin, tributyrin, butylphthalylbutyl glycolate, ethylphthalylethyl glycolate, methylphthalylethyl glycolate, butylphthalylbutyl glycolate and the like. Among them, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, tributyl phosphate, dimethyl phthalate,
Preferred are diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diethylhexyl phthalate, triacetin, and ethyl phthalyl ethyl glycolate. Particularly, triphenyl phosphate, diethyl phthalate, and ethyl phthalyl ethyl glycolate are preferred. These plasticizers may be used alone or in combination of two or more.

The amount of the plasticizer to be added is preferably 5 to 30% by weight or less, particularly preferably 8 to 16% by weight or less, based on cellulose acetate. These compounds may be added together with cellulose acetate or a solvent when preparing a cellulose acetate solution, or may be added during or after solution preparation.

In the present invention, as a plasticizer for reducing the optical anisotropy, JP-A-11-12444 is used.
5, diglycerol esters described in JP-A-11-246704, diglycerol esters described in JP-A-2000-63560, and citric acid described in JP-A-11-92574. Esters, substituted phenyl phosphate esters described in JP-A-11-90946, and the like are preferably used.

The cellulose acetate film may be added with a deterioration inhibitor (eg, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, an amine) or an ultraviolet inhibitor. good. These degradation inhibitors and ultraviolet inhibitors are described in JP-A-60-235852, JP-A-3-199201, JP-A-5-1907073, and JP-A-5-1907073.
194789, 5-271471, 6-107
No. 854, No. 6-118233, No. 6-148430
Nos. 7-11056, 7-11055, 7-
No. 11056, No. 8-29619, No. 8-23950
9 and JP-A-2000-204173.

The addition amount of the deterioration inhibitor is preferably 0.01 to 1% by weight of the dope to be prepared, and 0.01 to 1% by weight.
More preferably, it is 0.2% by weight. If the amount is less than 0.01% by weight, the effect of the deterioration inhibitor is hardly recognized. If the addition amount exceeds 1% by weight, bleed out (bleed out) of the deterioration inhibitor on the film surface.
May be allowed. A particularly preferred example of the deterioration inhibitor is butylated hydroxytoluene (BHT).

It is particularly preferable that the dope in the present invention contains one or more ultraviolet absorbers. It is preferable that the UV absorber for liquid crystal is excellent in absorbing ability of UV light having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal, and has little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display property. For example, oxybenzophenone-based compounds, benzotriazole-based compounds, salicylate-based compounds, benzophenone-based compounds,
Examples include a cyanoacrylate-based compound and a nickel complex salt-based compound. Particularly preferred ultraviolet absorbers are benzotriazole-based compounds and benzophenone-based compounds. Above all, benzotriazole-based compounds are preferable because unnecessary coloring of the cellulose ester is small.

Preferred UV inhibitors are 2,6-di-tert-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], Triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3
5-di-tert-butyl-4-hydroxyphenyl)
Propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-
Butylanilino) -1,3,5-triazine, 2,2-
Thio-diethylenebis [3- (3,5-di-tert-
Butyl-4-hydroxyphenyl) propionate],
Octadecyl-3- (3,5-di-tert-butyl-
4-hydroxyphenyl) propionate, N, N'-
Hexamethylene bis (3,5-di-tert-butyl-
4-hydroxy-hydrocinnamide), 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert)
-Butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate and the like. In particular,
2,6-di-tert-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-te
rt-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-te
rt-butyl-5-methyl-4-hydroxyphenyl)
Propionate] is most preferred. Also, for example, N,
N'-bis [3- (3,5-di-tert-butyl-4
-Hydroxyphenyl) propionyl] hydrazine-based metal deactivators such as hydrazine and tris (2,4-di-
A phosphorus-based processing stabilizer such as tert-butylphenyl) phosphite may be used in combination. The amount of addition of these compounds is 1 ppm by weight based on cellulose acetate.
~ 5% is preferred.

In the present invention, a retardation increasing agent for controlling optical anisotropy is optionally added. In order to adjust the retardation of the cellulose acetate film, it is preferable to use an aromatic compound having at least two aromatic rings as a retardation increasing agent. The aromatic compound is used in an amount of 0.01 to 100 parts by mass of cellulose acetate.
Used in the range of 20 parts by mass. The aromatic compound is used in an amount of 0.05 to 15 parts by mass per 100 parts by mass of cellulose acetate.
It is preferable to use in the range of parts by mass, and 0.1 to 10
More preferably, it is used in the range of parts by mass. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.

The aromatic hydrocarbon ring is a six-membered ring (ie,
Benzene ring). Aromatic heterocycles are generally unsaturated heterocycles. The aromatic hetero ring is preferably a 5-, 6-, or 7-membered ring, more preferably a 5- or 6-membered ring.
Aromatic heterocycles generally have the most double bonds.
As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of the aromatic hetero ring include a furan ring, a thiophene ring, a pyrrole ring,
Oxazole ring, isoxazole ring, thiazole ring,
Isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,
Includes a 5-triazine ring.

Further, if necessary, various additives may be added to the dope of the present invention at any stage after preparing the solution or after preparing the solution. Additives include UV absorbers, silica, kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, inorganic fine particles such as alumina, and salts of alkaline earth metals such as calcium and magnesium. Agents, antistatic agents, flame retardants, lubricants, oils and the like.

Further, in the present invention, it is preferable to add a peeling accelerator in order to reduce the load at the time of peeling. These are effective surfactants and are not particularly limited to phosphoric acid type, sulfonic acid type, carboxylic acid type, nonionic type and cationic type. These are described, for example, in JP-A-61-24383.
No. 7, for example. The polarizing plate film of the present invention can be produced, for example, by the method described below.

A solvent, cellulose triacetate and a plasticizer are charged into a mixing tank for dope, and stirred (with heating and, if necessary, under pressure) to dissolve cellulose triacetate to prepare a dope. Put the solvent and the UV absorber into another mixing tank and stir to dissolve the UV absorber. (When adding fine particles to improve the slipperiness, add and mix them further, transfer them to the disperser, and remove the fine particles. Disperse well to prepare dispersion). This ultraviolet absorber-containing solution is appropriately sent to a dope mixing tank,
The mixed solution is mixed with the above-mentioned dope, and the obtained mixed solution is sent to a casting port through a dope filter, and the mixed solution (dope) is cast on a drum from the casting port.

After the mixed solution (dope) has been cast on the drum from the casting port, the layer is dried to the extent that it has a self-supporting property during one rotation of the drum. After being peeled and dried sufficiently, it is wound up on a drum. An endless band may be used instead of the drum.

The mixing of the dope and the solution containing the ultraviolet absorbent is not performed in a tank, but by a static mixer arranged in the middle of the pipe before the casting port, sent to the casting port, and sent from the casting port. The mixture (dope) may be cast on a drum.

The film for a polarizing plate of the present invention is a polarizing plate protective film provided on both surfaces or one surface of a polarizer of a polarizing plate, a support of an optical compensation film also serving as a protective film, and an optical layer laminated on the polarizing plate protective film. It can be used as a support for a compensation film. That is, the polarizing plate has a mode in which a polarizing plate protective film is laminated on both surfaces of a polarizer, and a mode in which a polarizing plate protective film is laminated on one of the polarizers and an optical compensation film also serving as a protective film is laminated on the other. A mode in which an optical compensation film serving also as a protective film is laminated on both surfaces of the polarizer, a mode in which a polarizing plate protective film is laminated on both surfaces of the polarizer, and an optical compensation film is further laminated on the polarizer protective film, and the like. .

The optical compensation film is generally provided with an adhesion layer as an undercoat layer, an orientation imparting layer and an optical compensation layer on one surface of a support, and a back layer as an undercoat layer on the other surface. Is provided.

The adhesion layer is formed on a cellulose ester support by polymer coating or surface treatment. The adhesion layer is described in JP-A-8-50206 and JP-A-11-248.
No. 940 can be used, and gelatin is particularly preferable.

The orientation-imparting layer forms a layer containing polyvinyl alcohol, and imparts orientation by rubbing.

It is preferable to use modified polyvinyl alcohol for the orientation-providing layer. Polyvinyl alcohol is
A polymer in which polyvinyl acetate is saponified to convert a part or all of the vinyl acetate units into vinyl alcohol units. The modified polyvinyl alcohol is preferably a polymer in which a hydrophobic group is bonded to polyvinyl alcohol. The hydrophobic group has an affinity for the liquid crystal compound of the optical compensation layer, and the introduction of the hydrophobic group improves the alignment function of the alignment providing layer. The hydrophobic group is bonded to the main chain terminal or side chain of polyvinyl alcohol.

The hydrophobic group is preferably an aliphatic group having 6 or more carbon atoms (preferably an alkyl group or an alkenyl group) or an aromatic group.

When a hydrophobic group is bonded to the terminal of the main chain of polyvinyl alcohol, it is preferable to introduce a linking group between the hydrophobic group and the terminal of the main chain. Examples of linking groups include -S
—, —C (CN) R ¹ —, —NR ² —, —CS— and combinations thereof. The above R ¹ and R
² is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (an alkyl group having 1 to 6 carbon atoms), respectively.

When a hydrophobic group on the side chain of polyvinyl alcohol is introduced, a part of the acetyl group (—CO—CH ₃ ) of the vinyl acetate unit of polyvinyl alcohol is replaced with an acyl group (−) having 7 or more carbon atoms. CO-R ³ ). R ³ is an aliphatic group or an aromatic group having 6 or more carbon atoms.

The degree of saponification of the (modified) polyvinyl alcohol used in the orientation-imparting layer is preferably at least 80%. (Modification) The polymerization degree of polyvinyl alcohol is 200
It is preferable that it is above.

The rubbing treatment is carried out by rubbing the surface of the orientation imparting layer several times in a certain direction with paper or cloth. It is preferable to use a cloth in which fibers having uniform length and thickness are uniformly planted.

The optical compensation layer is formed by aligning a liquid crystalline compound by the above-mentioned alignment imparting layer and fixing the liquid crystalline compound in the aligned state. The liquid crystal compound is
It is preferable to fix by a polymerization reaction.

It is preferable to use a discotic liquid crystalline compound for the optical compensation layer. Discotic liquid crystalline compounds are described in various documents (C. Destrade et al., Mol. Cr.
ysr. Liq. Cryst. vol. 71, page
111 (1981); edited by The Chemical Society of Japan, quarterly chemistry review,
No. 22, Chemistry of Liquid Crystals, Chapter 5, Chapter 10, Section 2 (1994); Kohne et al. , Ang
w. Chem. Soc. Chem. Comm. , Pag
e 1794 (1985); Zhang eta
l. , J. et al. Am. Chem. Soc. , Vol. 11
6, page 2655 (1994)). Regarding the crosslinking of the discotic liquid crystalline compound, see JP-A-8-
No. 27284.

In order to fix the discotic liquid crystalline compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline compound. However, when a polymerizable group is directly connected to the disc-shaped core, it is difficult to maintain the alignment state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystalline compound having a polymerizable group is preferably a compound represented by the following formula (I).

(I) D (-LP)_n  Wherein D is a discotic core; L is a divalent linking group
P is a polymerizable group; and n is an integer of 4-12
It is.

Examples of the disc-shaped core (D) are shown below. In each of the following examples, LP (or PL) means a combination of a divalent linking group (L) and a polymerizable group (P).

[0053]

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[0054]

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[0055]

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[0056]

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In the formula (I), the divalent linking group (L)
Is an alkylene group, an arylene group, -CO-, -NH
It is preferably a divalent linking group selected from the group consisting of-, -O-, -S- and a combination thereof. The divalent linking group (L) is an alkylene group, an arylene group,-
More preferably, the divalent linking group is a combination of at least two divalent groups selected from the group consisting of CO-, -NH-, -O- and -S-. The divalent linking group (L) is most preferably a divalent linking group obtained by combining at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO- and -O-. . The alkylene group preferably has 1 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbon atoms.

Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is a polymerizable group (C).
To join.

L1: -alkylene-CO-O-alkylene-O-CO- L2: -alkylene-CO-O-alkylene-O-L3: -alkylene-CO-O-alkylene-O-alkylene- L4: -alkylene -CO-O-alkylene-L5: -O-alkylene-O-CO-L6: -O-alkylene-O-L7: -O-alkylene-O-CO-NH-alkylene-L8: -O-alkylene-S -Alkylene- L9: -O-alkylene- L10: -CO-arylene-O-alkylene-OC
O-L11: -CO-arylene-O-alkylene-L12: -CO-arylene-O-alkylene-O-L13: -CO-NH-alkylene-L14: -NH-alkylene-O-CO-L15: -NH -Alkylene-O- L16: -S-alkylene-S-alkylene- L17: -S-alkylene- L18: -S-alkylene-O-

The polymerizable group (P) is determined according to the type of the polymerization reaction. Examples of the polymerizable group (P) are shown below.

[0061]

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[0062]

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[0063]

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[0064]

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[0065]

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The polymerizable group (P) is an unsaturated polymerizable group (P
1, P2, P3, P7, P8) or epoxy group (P
6), more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group (P
1, P7, P8).

In the formula (I), it is an integer of 4 to 12. Specific numbers are determined according to the type of the disc-shaped core (D). The combination of a plurality of L and P may be different, but is preferably the same.

The optical compensation layer can be formed by applying a coating solution containing a liquid crystal compound and, if necessary, a polymerizable initiator and optional components onto the orientation-imparting layer.

The discotic liquid crystal phase has a columnar phase in which a discotic core is stacked in a columnar shape by an intermolecular force.
se), the optical axes of the discotic cores are aligned, and the discotic core is classified into a discotic nematic phase in which the position of the center of gravity is irregularly aggregated, and a chiral dicotic nematic phase corresponding to the cholesteric phase of rod-like liquid crystal molecules. It is preferable that the optical compensation film has a disk-like nematic phase.

The aligned discotic liquid crystalline compound is fixed while maintaining the aligned state. The immobilization is preferably performed by a polymerization reaction. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator or a photopolymerization reaction using a photopolymerization initiator. Photopolymerization reactions are preferred.

Examples of photopolymerization initiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670) and acyloin ethers (US Pat.
No. 48828), α-hydrocarbon-substituted aromatic acyloin compounds (US Pat. No. 2,722,512), polynuclear quinone compounds (US Pat. No. 3,046,127),
No. 2,951,758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), an acridine and phenazine compound (JP-A-60-105).
667, US Pat. No. 4,239,850)
And oxadiazole compounds (US Pat.
0 specification).

The use amount of the photopolymerization initiator is preferably 0.01 to 20% by weight of the solid content of the coating solution,
More preferably, it is 5% by weight.

The light irradiation for the polymerization of the discotic liquid crystalline compound is preferably performed using ultraviolet rays, similarly to the light irradiation for forming the orientation-imparting layer. However, unlike the case of the orientation-imparting layer, it is not necessary to irradiate from a single direction, and it is sufficient to irradiate the entire surface of the layer containing the discotic liquid crystalline compound with light having an energy amount required for the polymerization reaction.

The irradiation energy is preferably from 20 to 5000 mJ, more preferably from 100 to 800 mJ. Light irradiation may be performed under heating conditions to accelerate the photopolymerization reaction.

The back layer is coated for the purpose of preventing the cellulose ester support from being damaged, improving the transportability, preventing static charge, imparting curl balance, and the like. The polymer used is
The same thing as the adhesion layer can be used. Further, various additives can be contained as required. For example, surfactants, antistatic agents, pigments, coating aids, matting agents and the like can be mentioned. Particularly preferably, a cellulose derivative is used.

The above-mentioned polarizing plate is laminated on a liquid crystal cell to constitute a liquid crystal display device. When the optical compensation film is separately laminated on the protective film of the polarizing plate, the optical compensation film is provided between the polarizing plate and the liquid crystal cell.

The liquid crystal cell comprises a liquid crystal compound, two glass substrates for enclosing the compound, and an electrode layer for applying a voltage to the liquid crystal compound. In order to orient the encapsulated liquid crystalline compound, an alignment layer (double-sided alignment layer) is provided on the two substrates.

The adhesive (adhesive) used for assembling the liquid crystal display device is described in JP-A-7-92323. As the adhesive, an acrylic polymer, a methacrylic polymer or a styrene-based polymer is generally used. As described above, in order to reuse the liquid crystal cell, the strength of the adhesive (the type and amount of the polymer) is preferably set to a relatively low value. However, since the strength of the adhesive layer of the optical compensation film was improved by the present invention, it was not necessary to reduce the strength of the adhesive so that a problem occurred in the strength of the liquid crystal display device.

One embodiment of a polarizing plate using the polarizing plate film according to the present invention will be described with reference to the drawings.

FIG. 3 is a partial sectional view showing a layer structure of an optical compensation film used for a polarizing plate, FIG. 4 is a partial sectional view showing a layer structure of a polarizing plate film used for a support of the optical compensation film, and FIG. It is a fragmentary sectional view showing layer composition of a board.

In FIG. 3, the optical compensation film 10 is
A support 11 using a polarizing plate film according to the present invention is provided. On one surface of the support 11, an adhesion layer 12, an orientation imparting layer 13, and an optical compensation layer 14 as an undercoat layer are provided in this order. A back layer 15 as an undercoat layer is laminated on the other surface.

The support 11 is, as shown in FIG.
1a and an outer layer 11b laminated on both sides of the inner layer 11a.
The solid content of the dope used for the outer layer 11b is lower than the solid content of the dope used for the inner layer 11a by 1% by weight or more.

Then, such an optical compensation film 10
As shown in FIG. 4, the polarizer 16 is laminated on one surface of the polarizer 16, and the polarizer protective film 17 is laminated on the other surface of the polarizer 16.

An embodiment of a casting die for forming the polarizing plate film of the present invention will be described with reference to the drawings.

FIG. 6 is a cross-sectional view of a casting die. The casting die 20 shown in FIG. 6 is a multi-manifold type co-casting die, which is provided with an inner layer manifold 21 into which an inner layer dope is fed. On both sides thereof, an outer layer manifold 22 into which the dope for the outer layer is fed is provided. An inner layer slit 23 communicates with the inner layer manifold 21, and an outer layer slit 24 communicates with the outer layer manifold 22, and the outer layer slit 24 joins the inner layer slit 23.

FIG. 7 is a sectional view of a casting die using a feed block, FIG. 8 is a perspective view of a vane and a distribution pin portion of the feed block, and FIG. 9 is a side view of a distribution pin of the feed block.

In FIG. 7, reference numeral 30 denotes a single-layer casting die.
One manifold 31 is formed and the slit 3
2 are formed. A feed block 40 is provided in close contact with the upper part of the casting die 30, and an inner layer flow path 41 is formed in the feed block 40, and an outer layer flow path 42 is formed on both sides thereof. The outer-layer flow path 42 joins the inner-layer flow path 41 at the junction a.

The junction a is provided with a vane 43 and a distribution pin 44. The vane 43 is provided rotatably about a shaft 45, and the flow rate can be adjusted by changing the opening degree of the vane 43 with the distribution pin 44. The distribution pin 44
It is provided so as to be rotatable about an axis, and a groove 46 is formed on the surface thereof. The groove 46 is formed in a trapezoidal shape in which the width is reduced from one side to the other side, and the portion of the groove 46 facing the vane 43 is used for the outer layer for the outer layer merging from the outer layer flow path 42 to the inner layer flow path 41. The width of the dope can be changed.

[0089]

EXAMPLES [Example 1] <Optical compensation film> An optical compensation film having a layer structure shown in Fig. 3 was produced.

<Support> A dope described below was co-cast, and an inner layer and an outer layer on both sides of the same as shown in FIG.
A triacetyl cellulose film having a layer structure was produced.

Inner layer dope: Triacetyl cellulose 23 parts Triphenyl phosphate 12 parts UV absorber (see the following chemical structural formula) 0.1 part

[0092]

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Outer layer dope: A solution prepared by adding a solvent having the same composition to the inner layer dope formulation so that triacetyl cellulose becomes 20 parts.

Dope for Example 2 The same as the above except that the above UV absorber had the following chemical structural formula. 0.6 parts of 2-hydroxy-4-benzyloxy-benzophenone

[0095]

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On the support described above, an adhesion layer, a back layer, an orientation-imparting layer and an optical compensation layer as shown below are sequentially applied, and after drying the optical compensation layer, it is irradiated with ultraviolet rays to cure the crosslinked hard layer. The film was formed into an optical compensation film.

<Adhesion Layer> Gelatin 200 mg / m²  Solvent 25cc / m²  (Acetone: methanol: methylene chloride = 5: 3: 2)

<Back Layer> Diacetylcellulose 200 mg / m²  0.01 μm silica 10 mg / m²  Solvent 25cc / m²  (Acetone: methanol: methylene chloride = 5: 3: 2)

<Orientation-Providing Layer> Polyvinyl Alcohol 500 mg / m²  Solvent (water) 20cc / m²

<Optical Compensation Layer> Discotic Liquid Crystal (D-4) 2 g / m²  UV curing initiator 0.01 g / m²  Solvent 5cc / m²  (Methyl ethyl ketone)

The optical compensation film as described above, the polarizer, and the protective film for the polarizing plate were bonded to each other to produce a polarizing plate having a diagonal length of 15 inches.

<Polarizing Plate Protective Film> Fuji Photo Film Co., Ltd.
Made by Fuji Tack

<Polarizer> A polyvinyl alcohol film was immersed in an iodine solution, stretched and dried to produce a polarizing element.

Example 2 Example 2 was the same as Example 1 except that the concentration of the solid component in the outer layer was changed.

[Example 3] In comparison with Example 1, a low solid type concentration layer having a lower casting speed and the same thickness was laminated only on the air surface side.

Example 4 The wetness of the outer layer was set to 2 μm as compared with Example 1.

[Example 5] In comparison with Example 1, the concentration of the solid component in the outer layer was lowered to 18 wt%.

Example 6 The casting speed was increased compared to Example 1.

[Example 7] The solid content of the outer layer was reduced to 18 wt% as compared with Example 6.

Comparative Example 1 As a support, 22 parts of triacetyl cellulose and 11.5 parts of triphenyl phosphate (plasticizer) were dissolved in a solvent consisting of 80 parts of methylene chloride, 15 parts of methanol and 5 parts of butanol. It is the same as Example 1 except that a dope was used and a single-layer triacetyl cellulose film was used.

Comparative Example 2 As a support, a dope obtained by dissolving 23 parts of triacetyl cellulose and 12 parts of triphenyl phosphate (plasticizer) in a solvent composed of 80 parts of methylene chloride, 15 parts of methanol and 5 parts of butanol was used. Use
This example is the same as Example 1 except that a single-layer triacetyl cellulose film was used.

In the above Examples and Comparative Examples, the inclination angle of the surface unevenness of the film in the state where the adhesion layer and the back layer were coated on the support was measured. Further, the surface state of the polarizing plate was evaluated.

Comparative Example 3 The outer layer wet thickness was set to 1 μm as compared with Example 3.

Comparative Example 4 The wet thickness of the outer layer was set to 1 μm in comparison with Example 4.

The results are shown in Table 1.

[0116]

[Table 1]

[Inclination of streak unevenness] Diagonal length is 15
The maximum inclination angle of the streaky unevenness having a pitch of 3 to 15 mm in the area of inch was determined. The measurement of the inclination angle used a laser displacement meter (KL130MA) manufactured by Anritsu. The measurement conditions are as follows. Displacement meter moving speed: 25 mm / s Number of displacement meter averaging: 64 Evaluation interval: 100 μm Minimum resolution: 0.039 μm

[Evaluation of Surface Condition of Polarizing Plate] Sensory evaluation was performed visually with transmitted light on a polarizing plate having a diagonal length of 15 inches. ：: Streaky unevenness cannot be confirmed visually. Δ: Streak-like unevenness can be visually confirmed (weak). X: Streak unevenness can be visually confirmed (strong).

[0119]

According to the present invention, the inclination of the streaky unevenness is set to 0.0.
By setting the angle to less than 4 degrees, the quality of the screen of the liquid crystal display device can be improved.

[Brief description of the drawings]

FIG. 1 is a partial plan view showing a film on a casting support.

FIG. 2 is a cross-sectional view of a state where the film is cut in a lateral direction.

FIG. 3 is a partial cross-sectional view illustrating a layer configuration of an optical compensation film using the polarizing plate film according to the present invention.

FIG. 4 is a partial cross-sectional view showing a layer structure of a polarizing plate film according to the present invention.

FIG. 5 is a partial cross-sectional view showing a layer configuration of a polarizing plate using the polarizing plate film according to the present invention.

FIG. 6 is a sectional view of a co-casting die for forming a polarizing plate film according to the present invention.

FIG. 7 is a cross-sectional view of a single-layer die and a feed block for forming a polarizing plate film according to the present invention.

FIG. 8 is a perspective view of a vane and a distribution pin of a feed block used for forming a polarizing plate film according to the present invention.

FIG. 9 is a side view of a distribution pin of a feed block used for forming a polarizing plate film according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cast support 2 ... Film 3 ... Streaky unevenness 10 ... Optical compensation film 11 ... Support 11a ... Inner layer 11b ... Exterior 12 ... Adhesion layer 13 ... Orientation imparting layer 14 ... Optical compensation layer 15 ... Back layer 16 ... Polarizer 17 ... Protective film for polarizing plate 20 ... Casting die 30 ... Single layer die 40 ... Feed block 43 ... Vane 44 ... Distribution pin

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA01 BA25 BA27 BB03 BB33 BB43 BB49 BB51 BB67 BC03 BC04 BC05 BC09 BC14 BC22 4F071 AA09 AH12 BA02 BB02 BC01

Claims (9)

[Claims] 1. A cellulose ester film formed by casting a dope in which a cellulose ester is dissolved in an organic solvent from a casting die onto a casting support, and having a pitch in the horizontal direction of 3 to 15 mm. The film for a polarizing plate, wherein the inclination of the unevenness is less than 0.04 degrees. 2. The cellulose ester film is composed of two or more layers formed by co-casting, wherein the solid content of the dope of the outer layer is 1% by weight or more lower than the solid content of the dope of the inner layer. The polarizing plate film according to claim 1. 3. The polarizing plate film according to claim 2, wherein the thickness of the outer layer is 2 μm or more in a wet state immediately after casting. 4. The co-casting of two or more layers is performed by using a single-layer die,
3. The polarizing plate film according to claim 2, wherein the film is formed by using a feed block provided at the entrance of the single-layer die and having a junction where two or more layers are stacked. 5. A feed block, wherein a trapezoidal groove is formed in a distribution pin provided at a junction where two or more layers are stacked, and a casting width of an outer layer can be changed. 5. The film for a polarizing plate according to 4. 6. The polarizing plate according to claim 2, wherein the co-casting of the two or more layers is performed by using a multi-manifold type casting die having two or more manifolds and stacking two or more layers. For film. 7. The polarizing plate film according to claim 1, wherein the cellulose ester is triacetyl cellulose. 8. The polarizing plate film according to claim 1, wherein at least one undercoat layer is laminated. 9. The polarizing plate film according to claim 8, wherein at least one optical compensation layer is laminated on the undercoat layer.