JP2001122980A - Cellulose ester film, protective film for polarizing plate and member for liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cellulose ester film never deteriorating the durability of a polarizing plate even if used as a protective thin film therefor, to obtain a protective film for polarizing plates by using the above film, and to obtain a member for liquid crystal displays by using the above film. SOLUTION: This cellulose ester film is such as to be 20-65 μm in thickness and 1.0-4.5 wt.% in water absorption when immersed in water at 23 deg.C for 24 h.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cellulose ester film, and more particularly to a cellulose ester film suitable as a protective film for a polarizing plate of a liquid crystal display and a member for a liquid crystal display.

[0002]

2. Description of the Related Art In recent years, as a liquid crystal display (LCD) is used in various places, it is required to be thinner and lighter, and a polarizing plate used in the LCD is also required to be thinner and lighter. Have been.

At present, a cellulose triacetate (TAC) film is mainly used as a protective film for a polarizing plate used in LCDs, but its thickness is relatively thick, 80 μm or more. Since four protective films are usually used as LCD members, it is urgently desired to make them thinner.

However, the above-mentioned protective film, TAC,
When the film is made thinner, there arises a problem that the durability of the polarizing plate itself is deteriorated, and it is not easy to make the film thinner.

[0005]

SUMMARY OF THE INVENTION A cellulose ester film, a protective film for a polarizing plate, which does not deteriorate the durability of the polarizing plate even if the protective film for a polarizing plate is made thinner as the liquid crystal display element becomes thinner. And a liquid crystal display member.

[0006]

The above object of the present invention is attained by the following constitutions.

[0007] 1. The film thickness is 20 μm to 65 μm, and the water absorption when immersed in 23 ° C. water for 24 hours is 1.
A cellulose ester film, which is 0% to 4.5%.

[0008] 2. The film thickness is 20 μm to 65 μm, and the moisture content under an atmosphere of 23 ° C. and 80% RH is 0.5%.
A cellulose ester film, which is about 4.5%.

3. The film thickness is 20 μm to 65 μm, and the moisture content under the conditions of 23 ° C. and 80% RH is 0.5%.
The cellulose ester film according to the item 1, wherein the content is from 4.5 to 4.5%.

[0010] 4. A cellulose ester film having a thickness of 20 μm to 65 μm and a transmittance of light having a wavelength of 370 nm of 10% or less.

5. The cellulose ester film as described in any one of the above items 1 to 3, wherein the film thickness is 20 µm to 65 µm, and the transmittance of light having a wavelength of 370 nm is 10% or less.

6. The plasticizer is contained in the cellulose ester film, and the content of the plasticizer is 3 mass% to 30 mass% with respect to the cellulose ester. Cellulose ester film.

7. The vapor pressure of the plasticizer at 200 ° C is 1
6. The plasticizer according to item 6, wherein the plasticizer is less than 333 Pa.
The cellulose ester film according to the above.

8. The cellulose ester film according to any one of Items 1 to 7, wherein the content of the plasticizer is 10% by mass to 25% by mass based on the cellulose ester.

9. 9. The cellulose ester film as described in any one of 1 to 8 above, further comprising an ultraviolet absorber containing two or more aromatic rings in a molecule.

10. The cellulose ester film contains a benzotriazole-based compound represented by the general formula [1] as an ultraviolet absorber, and the content of the ultraviolet absorber is 0.1% by mass based on the cellulose ester.
The cellulose ester film according to any one of the above items 1 to 9, wherein the content is from 2.5 to 2.5% by mass.

11. In the method for producing a cellulose ester film, in which the cellulose ester solution is cast on a support and then peeled off and dried, the film is peeled off from the support, and when the residual solvent amount is 10 to 100% by mass, 80 to 130 ° C.
Alternatively, when the residual solvent amount is 5 to 10% by mass, 110 to 15
A method for producing a cellulose ester film, wherein a total time for maintaining the resin in a temperature range under at least one holding condition selected from 0 ° C. is 15 seconds or more.

[12] After the cellulose ester solution is cast on a support, the cellulose ester film obtained by peeling is peeled off from the support in a drying step of the cellulose ester film. Or 110 to 150 ° C. when the residual solvent amount is 5 to 10% by mass.
11. The cellulose ester film as described in any one of 1 to 10 above, wherein a total time of keeping the resin in the temperature range under at least one holding condition selected from the group consisting of 15 seconds or more.

13. 13. A protective film for a polarizing plate, comprising using the cellulose ester film described in any one of the above items 1 to 10.

[14] 13. A member for a liquid crystal display, comprising using the cellulose ester film described in any one of the above items 1 to 10.

That is, the present inventors have proposed to reduce the water absorption of the cellulose ester film itself in order to reduce the durability of the polarized light itself as the cellulose ester film as the protective film is made thinner. Also,
We found that it could be overcome by lowering the amount of transmitted ultraviolet light.

Hereinafter, the present invention will be described in more detail. Examples of the cellulose ester film of the present invention include cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, and cellulose acetate propionate. In the case of cellulose triacetate, especially the polymerization degree is 250 to 400, and the amount of bound acetic acid is 54 to
A cellulose triacetate of 62.5% is preferable, and an amount of bound acetic acid of 58 to 62.5% has a strong base strength and is more preferable. As the cellulose triacetate, either cellulose triacetate synthesized from cotton linter or cellulose triacetate synthesized from wood pulp can be used alone or in combination.

It is preferable to use a large amount of cellulose triacetate synthesized from cotton linter, which has good releasability from a belt or a drum, because of high productivity efficiency. The ratio of cellulose triacetate synthesized from cotton linter is 60
When the amount is at least 70% by mass, the effect of the releasability becomes remarkable, so the amount is preferably at least 60% by mass, more preferably at least 85% by mass, and most preferably used alone.

In the cellulose ester film of the present invention, it is preferable to use an ultraviolet absorber. The ultraviolet absorber has an excellent ability to absorb ultraviolet light having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal and has a good liquid crystal display. From the viewpoint of properties, those having absorption of visible light having a wavelength of 400 nm or more as small as possible are preferably used.

In the present invention, the transmittance at a wavelength of 370 nm is 10% in a thin film having a thickness of 20 to 65 μm.
The following can provide a preferable polarizing plate without deteriorating the durability of the polarizing plate. Wavelength 3
The transmittance at 70 nm is more preferably 5% or less, and particularly preferably 2% or less.

As the ultraviolet absorber added to the cellulose ester film of the present invention, an ultraviolet absorber having two or more aromatic rings in the molecule is particularly preferably used.

Examples of commonly used compounds include, but are not limited to, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex salt compounds, and the like.

In the present invention, these ultraviolet absorbers may be used alone or in combination of two or more different types.

The UV absorber preferably used in the present invention is a benzotriazole UV absorber or a benzophenone UV absorber. An embodiment in which a benzotriazole-based ultraviolet absorber with less unnecessary coloring is added to the cellulose ester film is particularly preferable.

The method of adding the ultraviolet absorber may be such that the ultraviolet absorber is dissolved in an organic solvent such as alcohol, methylene chloride or dioxolane and then added to the dope, or may be added directly to the dope composition. Those that do not dissolve in an organic solvent, such as inorganic powder, are dispersed in an organic solvent and a cellulose ester using a dissolver or a sand mill, and then added to the dope.

The amount of the ultraviolet absorber preferably used in the present invention is from 0.1% by mass to 2.5% by mass based on the cellulose ester from the viewpoint of the ultraviolet absorbing effect and transparency.
%, More preferably 0.5% by mass.
Mass% to 2.0 mass%, more preferably 0.8 mass% to
2.0% by mass.

The cellulose ester film of the present invention preferably contains the benzotriazole-based UV absorber of the general formula [1].

In the general formula [1], R ₁ , R ₂ , R
₃ , R ₄ and R ₅ may be the same or different and include a hydrogen atom, a halogen atom (each atom of chlorine, bromine, iodine, fluorine, etc.),
Nitro group, hydroxyl group, alkyl group (for example, methyl, ethyl, n-propyl, iso-propyl, aminopropyl, n-butyl, sec-butyl, tert-butyl, chlorobutyl, n-amyl, iso-amyl, hexyl, Octyl, nonyl, stearylamidobutyl,
Groups such as decyl, dodecyl, pentadecyl, hexadecyl, cyclohexyl, benzyl, phenylethyl, and phenylpropyl), alkenyl groups (eg, groups such as vinyl, allyl, methallyl, dodecenyl, tridecenyl, tetradecenyl, octadecenyl), and aryl groups ( For example, phenyl, 4-methylphenyl, 4-ethoxyphenyl, 2-hexoxyphenyl, 3-hexoxyphenyl, etc.), alkoxy group (for example, methoxy, ethoxy, propoxy, butoxy, chlorobutoxy, decoxy, diaminophenoxy) , Ethoxy, pentadecoxy, each group such as octadecoxy), oxycarbonyl group (for example, each group such as carbomethoxy, carbobutoxy, carbohexoxy, carbopentadecoxy),
Aryloxy groups (eg, phenoxy, 4-methylphenoxy, 2-propylphenoxy, 3-amylphenoxy, etc.), alkylthio groups (eg, methylthio, ethylthio, t-butylthio, t-octylthio,
Each group such as benzylthio), an arylthio group (for example,
Phenylthio, methylphenylthio, ethylphenylthio, methoxyphenylthio, ethoxyphenylthio, naphthylthio, etc.), mono- or dialkylamino group (for example, N-ethylamino, Nt-octylamino, N, N-diethylamino) , N, N-di-t-butylamino, etc.), an acylamino group (eg, acetylamino, benzoylamino, methanesulfonylamino, etc.), a 5- or 6-membered complex containing an oxygen atom or a nitrogen atom. A ring residue (for example, a heterocyclic residue such as piperidino, morpholino, pyrrolidino, piperazino, etc.), wherein R _{4 and} R ₅ may form a 5- or 6-membered ring composed of carbon atoms.

In the general formula [1], the substituent represented by R _{1 to} R ₅ preferably has ₅ to 36 carbon atoms, and the alkyl group preferably has 1 to 18 carbon atoms.

Examples of the compound represented by the above general formula are shown below, but the present invention is not limited thereto.

(1-1) 2- (2'-hydroxy-5 '
-T-butylphenyl) -benzotriazole (1-2) 2- (2'-hydroxy-3 ', 5'-di-
t-butylphenyl) -benzotriazole (1-3) 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole (1-4) 2- (2 ' -Hydroxy-3 ', 5'-di-
t-butylphenyl) -5-chlorobenzotriazole (1-5) 2- (2'-hydroxy-5'-isooctylphenyl) -benzotriazole (1-6) 2- (2'-hydroxy-5'- n-octylphenyl) -benzotriazole (1-7) 2- (2'-hydroxy-3 ', 5'-di-
t-Amylphenyl) -benzotriazole (1-8) 2- (2'-hydroxy-5'-dodecylphenyl) -benzotriazole (1-9) 2- (2'-hydroxy-5'-hexadecylphenyl) -Benzotriazole (1-10) 2- (2'-hydroxy-3'-t-amyl-5'-benzophenyl) -benzotriazole In the present invention, the same application as that of the present invention including the above-mentioned compounds is included. Examples of the compounds described in (JP-A-60-128434), page 10 to page 12, of the compound (IV-
1) to (IV-39) can be used. The above-mentioned benzotriazole-based compound used in the present invention can be easily synthesized, for example, by the method described in JP-B-44-29620 or a method analogous thereto.

In the present invention, when making the protective film for a polarizing plate thinner, the water absorption or the water content of the cellulose ester film must be within a specific range to ensure the adhesion between the polarizer and the protective film and the durability of the polarizing plate. It is necessary to improve the performance.

In the present invention, the water absorption refers to the amount of water when immersed in water at 23 ° C. for 24 hours, and is measured by the following method.

(Measurement method of water absorption)
It was cut into a size of 10 cm, immersed in water at 23 ° C. for 24 hours, and immediately after being taken out, the surrounding water droplets were wiped off with a filter paper.
And measuring the mass and the W _1. Next, this film
After conditioning for 24 hours in an atmosphere of 23 ° C. and 55% RH,
To measure its mass, and the W _0. The water absorption when immersed in water at 23 ° C. for 24 hours is calculated from the following formulas based on the measured values.

Water absorption (%) = ((W ₁ −W ₀ ) / W ₀ ) × 100 The water absorption of the cellulose ester film in the case of a thin film is 4.5% or less, so that the durability of the polarizing plate is reduced. Can be improved, and when the content is 1.0% or more, the drying property when the polarizer and the protective film are bonded and dried can be improved. Preferably it is 1.0% to 3.0%, more preferably 1.0% to 2.5%.

In the present invention, the moisture content under an atmosphere of 23 ° C. and 80% RH is measured by the following method.

(Measurement method of moisture content)
It was cut into a size of 10 cm, humidified in an atmosphere of 23 ° C. and 80% RH for 48 hours, and its mass was measured to be W ₃ . Next, the weight of this film after drying at 120 ° C. for 45 minutes was measured, and the result was defined as W ₂ . The moisture content at 23 ° C. and 80% RH can be obtained by calculating the following formula from the measured values.

Moisture (%) = ((W ₃ −W ₂ ) / W ₂ ) × 100 When the cellulose ester film is made into a thin film, the moisture is adjusted to 0.5% to 4.5% to be polarized. The adhesiveness between the child and the protective film can be improved. Preferably 1.
5% to 3.5%, more preferably 1.5% to 3.0%.

In the present invention, in order to control the water absorption and the water content of the cellulose ester film,
There are a method of containing a certain amount of a plasticizer in the cellulose ester film, a method of changing the type and ratio of the substituent of the cellulose ester, and a method of adjusting drying conditions at the time of forming the cellulose ester film.

In the present invention, the amount of the plasticizer added is from 3% by mass to the cellulose ester in terms of the mechanical strength and the stability of the step, with the water absorption and the water content being within the specified ranges. The content is preferably 30% by mass, more preferably 10% by mass to 30% by mass, and particularly preferably 15% by mass to 25% by mass.

The plasticizer that can be used in the present invention is not particularly limited, but includes a phosphate ester plasticizer, a phthalate ester plasticizer, a trimellitate ester plasticizer, a pyromellitic acid plasticizer, and a glycolate. Plasticizer,
Citrate plasticizers, polyester plasticizers, and the like can be preferably used.

In the phosphate ester system, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate,
Phthalates such as diphenylbiphenyl phosphate, trioctyl phosphate and tributyl phosphate include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate,
Dibutyl phthalate, di-2-ethylhexyl phthalate, butyl benzyl phthalate, etc., as a trimellitic acid plasticizer, tributyl trimellitate, triphenyl trimellitate, triethyl trimellitate, etc. For glycolic acid esters such as butyl pyromellitate, tetraphenyl pyromellitate and tetraethyl pyromellitate, triacetin, tributyrin, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. As acid ester plasticizers, triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, acetyl tri-n- (2
-Ethylhexyl) citrate and the like can be preferably used. As the polyester plasticizer, a copolymer of glycol and a dibasic acid 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, but adipic acid,
Sebacic acid, phthalic acid, terephthalic acid, 1,4-cyclohexyldicarboxylic acid and the like can be used.

Examples of the glycol include ethylene glycol, diethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, and 1,2-butyl glycol.
Butylene glycol or the like can be used. These dibasic acids and glycols may be used alone or in combination of two or more. The molecular weight of the polyester is preferably in the range of 500 to 2,000 in terms of weight average molecular weight from the viewpoint of compatibility with the cellulose resin.

In the present invention, it is particularly preferable to use a plasticizer having a vapor pressure at 200 ° C. of less than 1333 Pa, more preferably a compound having a vapor pressure of 666 Pa or less, further preferably 1 to 133 Pa. The non-volatile plasticizer is not particularly limited, and examples thereof include arylene bis (diaryl phosphate) ester, tricresyl phosphate, and tri (2-ethylhexyl) trimellitate.

These plasticizers can be used alone or in combination of two or more. Further, as a method for controlling the water absorption or the water content of the cellulose ester film of the present invention, a method of changing the type and ratio of the substituents of the ester and a method of changing the overall degree of substitution are also mentioned. In other words, the ester group is replaced with an acetyl group having a high water absorbency and an acyl group having 3 to 4 carbon atoms having a low water absorbency. As the acyl group having 3 to 4 carbon atoms, a propionyl group and / or a butyl group are preferable. Further, it is preferable that the overall degree of substitution is close to 3 from the viewpoint of water absorption.

The acylating agents for these acyl groups include:
In the case of an acid anhydride or an acid chloride, an organic acid such as acetic acid or methylene chloride is used as an organic solvent as a reaction solvent.

As the catalyst, a protic catalyst such as sulfuric acid is preferably used. When the acylating agent is an acid chloride (for example, CH ₃ CH ₂ COCl), a basic compound is used.

The most common industrial process is to mix cellulose with fatty acids corresponding to acetyl and other acyl groups (eg acetic acid, propionic acid, butyric acid, valeric acid) or mixed organic acids containing their anhydrides. The cellulose ester is synthesized by acylation with the components.

The specific production method of the cellulose ester of the present invention can be synthesized, for example, by the method described in JP-A-10-45804.

Further, in order to obtain the desired substitution ratio, two or more acyl groups may be mixed in advance after a certain amount of substitution with each type of acyl group.

If the number average molecular weight of the cellulose ester of the present invention is too low, the strength is low, and if it is too high, the viscosity of the solution may be too high.
0000 is preferable, and 80,000 to 200,000 is more preferable.

As a method for controlling the water absorption and the water content by adjusting the drying conditions at the time of forming the cellulose ester film, for example, the following methods are available.

In the present invention, a dope solution obtained by dissolving a cellulose ester in a solvent is cast on a support (casting step) and then heated to remove a part of the solvent (drying step on the support). Then, the film is peeled from the support, and the peeled film is dried (film drying step) to obtain a cellulose ester film.

In the film drying step, after peeling from the support, when the residual solvent amount is 10 to 100% by mass,
By setting the time maintained at 110 ° C. to 150 ° C. at 15 ° C. or more when the temperature is 130 ° C. and / or the residual solvent amount is 5 to 10% by mass, the water absorption and the water content can be improved. The longer the time of keeping the above temperature range, the lower the water absorption and the water content. Although there is no particular upper limit, 3
It is preferably 0 minutes or less, more preferably 15 minutes or less, and particularly preferably 5 minutes or less.

When maintaining the above temperature range, it is preferable to maintain the width by a tenter or to stretch the film about 1 to 20% of the film width, since the flatness of the cellulose ester film is improved.

The residual solvent amount in the film in the present invention is represented by the following formula. Residual solvent amount = ((mass before heat treatment−mass after heat treatment) / mass after heat treatment) × 100 (%) The heat treatment when measuring the amount of residual solvent means that the film is heated at 115 ° C. This indicates that heat treatment is performed for one hour.

The method for producing the cellulose ester film of the present invention is not particularly limited, and may be a method generally used in the art, for example, US Pat. No. 2,492,978,
2,739,070, 2,739,069, 2,492,977, 2,336,310, 2,367,603, 2,607,704, UK Patent Nos. 64,071 and 735,892, Shoko 45
Nos. -9074, 49-4554, 49-5614
Nos. 60-27662, 61-39890 and 62-4208 can be referred to.

The solvent used in the dope solution of the present invention may be used alone or in combination. However, it is preferable to use a mixture of a good solvent and a poor solvent for the cellulose ester from the viewpoint of production efficiency. Is preferred from the viewpoint of solubility of the cellulose ester. A preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass of the good solvent and 30% by mass of the poor solvent.
~ 2% by mass.

The good solvent and poor solvent used in the present invention include:
Those that dissolve the cellulose ester used alone are defined as good solvents, and those that swell or do not dissolve alone are defined as poor solvents. Therefore, depending on the average degree of acetylation of the cellulose ester, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, a good solvent is obtained when the acetic acid content of the cellulose ester is 55%, and the amount of the acetic acid is 6%.
At 0%, it becomes a poor solvent.

The good solvent used in the present invention is not particularly limited. For example, in the case of cellulose triacetate, organic halogen compounds such as methylene chloride, dioxolanes, and in the case of cellulose acetate propionate, methylene chloride, acetone, methyl acetate And the like.

The poor solvent used in the present invention is not particularly limited. For example, methanol, ethanol, i-propyl alcohol, n-butanol, cyclohexane, acetone, cyclohexanone and the like are preferably used.

As a method for dissolving the cellulose ester at the time of preparing the above-mentioned dope solution, a general method can be used, but the pressure is not lower than the boiling point of the solvent at normal pressure and the solvent is boiling. A method in which heating is performed at a temperature within a range not to be carried out and dissolving while stirring is more preferable in order to prevent generation of massive undissolved substances called gel or mamako. Further, a method in which a cellulose ester is mixed with a poor solvent to wet or swell, and then mixed with a good solvent and dissolved is also preferably used.

The type of the pressurized container is not particularly limited, as long as it can withstand a predetermined pressure and can be heated and stirred under pressure. For the pressurized container, other instruments such as a pressure gauge and a thermometer are appropriately arranged. Pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or by 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 after the addition of the solvent is preferably not lower than the boiling point of the solvent used at normal pressure and not exceeding the boiling point from the viewpoint of the solubility of the cellulose ester, but the heating temperature is too high. The required pressure increases and productivity decreases. The preferred heating temperature range is 45-45.
120 ° C., more preferably 60 to 110 ° C., and 70
More preferably, the temperature is in the range of from 105C to 105C. The pressure is adjusted at the set temperature so that the solvent does not boil.

In addition to the cellulose ester and the solvent, necessary additives such as a plasticizer and an ultraviolet absorber may be mixed with the solvent in advance, dissolved or dispersed, and then added to the solvent before dissolving the cellulose ester. It may be added to the dope after dissolution.

After the dissolution, it is taken out of the container while cooling, or it is taken out of the container by a pump or the like, cooled with a heat exchanger or the like, and supplied for film formation. However, it is more preferable to cool to a temperature lower than the boiling point by 5 to 10 ° C. and perform casting at that temperature because the viscosity of the dope can be reduced.

In the casting step, a belt-shaped or drum-shaped stainless steel mirror-finished support is used. The temperature of the support in the casting step can be cast at a temperature in a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, but it is better to cast on a support at 5 ° C. to 30 ° C.
The dope is preferably gelled to increase the peeling limit time, and is more preferably cast on a support at 5 ° C to 15 ° C. The peeling limit time refers to the time during which the cast dope remains on the support at the limit of the casting speed at which a transparent film having good flatness can be continuously obtained. It is preferable that the peeling limit time is short because the productivity is excellent.

In the on-substrate drying step, the time required for casting the dope, gelling it once, and separating it from the casting is 10 minutes.
Assuming 0%, dope temperature within 4% within 30% of casting.
By setting the temperature to 0 ° C. to 70 ° C., the evaporation of the solvent is promoted, the film can be peeled off from the support more quickly, and the peeling strength is further increased.
It is more preferable that the temperature be 5 ° C to 70 ° C. This temperature is 2
It is preferably maintained at 0% or more, more preferably at least 40%. Drying on the support is carried out with a residual solvent content of 60% to 15%.
Peeling from the support at 0% is preferable because the peel strength from the support is reduced, and 80 to 120% is more preferable. The temperature of the dope at the time of peeling is preferably from 0 ° C. to 30 ° C. because the base strength at the time of peeling can be increased and the base can be prevented from breaking at the time of peeling.
0 ° C. is more preferred.

In the film drying step, the film peeled from the support is further dried so that the amount of residual solvent upon winding is 3% by mass or less, preferably 1% by mass or less, more preferably 0.5% by mass or less. This is preferable in obtaining a film having good dimensional stability. In the film drying step, a method of drying while transporting a film by a roll suspension method, a pin tenter method, or a clip tenter method is generally employed. For a liquid crystal display member, it is preferable to dry while maintaining the width by a tenter method in order to improve dimensional stability. In particular, to maintain the width at a large residual solvent amount immediately after peeling from the support,
More effective in improving dimensional stability.

In particular, in the drying step after peeling from the support, the film tends to shrink in the width direction due to evaporation of the solvent. The higher the temperature, the greater the shrinkage. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the resulting film. From this point, for example, a method of drying all the steps or a part of the steps as described in JP-A-62-46625 while drying both ends of the web with a clip in the width direction / tenter method Is preferred.

When the temperature is maintained at 80 to 130 ° C. when the amount of the residual solvent is 10 to 100% by mass and / or at 110 to 150 ° C. when the amount of the residual solvent is 5 to 10% by mass, the width is maintained by a tenter or the film is held. Stretching of about 1 to 20% with respect to the width is particularly preferable because the effect of improving the flatness of the cellulose ester film is large.

The means for drying the film is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. Drying with hot air is preferred in terms of simplicity. The drying temperature is preferably divided into three to five stages in the range of 40 ° C. to 150 ° C., and is gradually increased.
It is more preferable to perform the heating at a temperature in the range of 50 ° C. in order to improve flatness and dimensional stability.

The steps from casting to post-drying may be performed in an air atmosphere or in an inert gas atmosphere such as nitrogen gas. It is a matter of course that the drying atmosphere is performed in consideration of the explosive limit concentration of the solvent.

The winding machine relating to the production of the cellulose ester film of the present invention may be a commonly used winding machine, such as a constant tension method, a constant torque method, a taper tension method, and a program tension control method for constant internal stress. It can be wound by a winding method.

The thickness of the cellulose ester film of the present invention is from 20 to 65 μm, preferably from 30 to 6 μm, in order to reduce the thickness and weight of the polarizing plate used for LCD.
0 μm, more preferably 35 to 50 μm. If it is thinner than this, the waist strength of the film will decrease,
Troubles such as wrinkles are likely to occur in the polarizing plate manufacturing process, and when the thickness is more than that, there is little contribution to making the LCD thinner.

Further, if necessary, fine particles such as silicon oxide may be added as a matting agent to the cellulose ester film of the present invention. Fine particles such as silicon oxide are preferably surface-treated with an organic substance because the haze of the film can be reduced. Preferred organic substances for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes and the like. The larger the average diameter of the fine particles, the greater the matting effect, and the smaller the average diameter, the more excellent the transparency. Therefore, the average primary particle diameter of the preferable fine particles is 5 to 50 nm, more preferably 7 to 1 nm.
4 nm.

As fine particles of silicon oxide, AEROSIL 200, 200 V, 30 manufactured by Aerosil Co., Ltd.
0, R972, R972V, R974, R202, R8
12, OX50, TT600, etc., preferably AEROSIL 200, 200V, R972, R9
72V, R974, R202, R812 and the like.

In the present invention, it is preferable that the amount of foreign matter in the cellulose ester film is small. In particular, it is preferable that the number of foreign substances recognized in the polarization crossed Nicols state is small.

The foreign substance recognized in the polarization crossed Nicols state refers to a substance measured by placing two polarizing plates in a perpendicular (crossed Nicols) state and placing a cellulose ester film between them. In a polarization crossed Nicol state, such foreign matter is observed only in the place of the foreign matter in the dark field, so that its size and number can be easily identified.

As the number of foreign matters, the size perceived in the polarization crossed Nicols state per area of 250 mm 2 is 5 to 5.
It is preferable that the number of foreign substances having a size of 50 μm is 200 or less and the number of foreign substances having a size of 50 μm or more is substantially zero. More preferably, 5-
The number of foreign substances having a size of 50 μm is 100 or less, more preferably 50 or less.

The above-mentioned cellulose ester film having a small amount of foreign matter can be obtained by, for example, filtering a dope composition obtained by dissolving a cellulose ester in a solvent using a filter paper as described below.

The filter material in the present invention preferably has a small absolute filtration accuracy in order to remove insolubles and the like. However, if the absolute filter accuracy is too small, clogging of the filter material tends to occur. For this reason, a filter medium having an absolute filtration accuracy of 0.008 mm or less is preferable,
A filter medium in the range of 0.008 mm is more preferable and 0.00
Filter media in the range of 3-0.006 mm are more preferred.

There is no particular limitation 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 may cause fibers to fall off. Preferred. Also,
It is more preferable to use two or more of the filter papers.

The filtration of the dope solution can be carried out by a usual method, but a method of filtering under heating while heating at a temperature not lower than the boiling point of the solvent at normal pressure and not boiling the solvent is known as a filtering material. Differential pressure before and after (hereinafter sometimes referred to as filtration pressure)
Is small and preferable. The preferred temperature range is 45 to
120 ° C., more preferably 45 to 70 ° C.
More preferably, it is in the range of 55 ° C.

The smaller the filtration pressure, the better. Filtration pressure is 1.6
× 10 ⁶ Pa or less, preferably 1.2 × 10 ⁶ Pa
6 Pa or less, more preferably 1.0 × 10 ⁶
More preferably, it is Pa or less. The filtration pressure can be controlled by appropriately selecting the filtration flow rate and the filtration area.

The method for producing the polarizing plate of the present invention is not particularly limited, and it can be produced by a general method. For example, 2
There is a method in which two cellulose triester films are subjected to an alkali saponification treatment and then immersed and stretched in an iodine solution to be laminated to both surfaces of a polarizing film using a completely saponified polyvinyl alcohol aqueous solution. Instead of the alkali treatment, a method for increasing the adhesiveness described in JP-A-6-94915 and JP-A-6-118232 may be used.

The liquid crystal display member is a member used for a liquid crystal display device, and includes, for example, a polarizing plate, a protective film for a polarizing plate, a retardation plate, a reflector, a viewing angle improving film, an antiglare film, and an anti-reflection film Films, antistatic films and the like.

Among them, the present invention is more preferably applied to a polarizing plate, a protective film for a polarizing plate, a retardation plate, and a viewing angle improving film which have strict requirements for dimensional stability.

The method for producing the polarizing plate of the present invention is not particularly limited, and it can be produced by a general method. For example, there is a method in which a cellulose triester film is subjected to an alkali treatment and immersed and stretched in an iodine solution, and bonded to both surfaces of a polarizing film using a completely saponified polyvinyl alcohol aqueous solution. JP-A-6-94 instead of alkali treatment
No. 915 and No. 6-118232 may be used.

[0095]

EXAMPLES The present invention will now be described specifically with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1 <Preparation of Sample 1> (Dope Composition A) Cellulose Triacetate Synthesized from Cotton Linter (Acetification 61.0%) 85 kg Cellulose Triacetate Synthesized from Wood Pulp (Acetification 61. 0%) 15 kg 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) benzotriazole (ultraviolet absorber I) 1 kg ethylphthalylethyl glycolate (plasticizer A) 4 kg methylene chloride 475 kg ethanol 50 kg Plasticizer A: A vapor pressure of 1.333 Pa or more was charged into a sealed container, heated to 70 ° C., and stirred to completely dissolve cellulose triacetate (TAC) to obtain a dope. The time required for dissolution was 4 hours.
After filtering the dope, using a belt casting apparatus, the dope is uniformly cast on a stainless steel band support at a dope temperature of 35 ° C. and dried to a peelable range. Was peeled off.

At this time, the residual solvent amount of the dope was 25%. The time required from dope casting to peeling was 3 minutes. After peeling from the stainless steel band support, drying was completed in a drying zone at 50 ° C., 90 ° C., and 120 ° C. while being conveyed by a number of rolls, to obtain a sample film 1 of a cellulose triacetate film having a thickness of 40 μm.

(Preparation of Polarizing Plate) Sample film 1 was heated at 40 ° C.
Was treated with a 2.5 mol / L aqueous sodium hydroxide solution for 60 seconds and washed with water for 3 minutes to form a saponified layer, thereby obtaining an alkali-treated film.

Next, a polyvinyl alcohol film having a thickness of 120 μm was coated with an aqueous solution containing 1 kg of iodine and 4 kg of boric acid.
It was immersed in 00 kg and stretched 4 times at 50 ° C. to form a polarizing film. The alkali-treated film was bonded to both surfaces of the polarizing film using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive to prepare a polarizing plate sample. <Preparation of Samples 2 to 11> A film was prepared in the same manner as in Preparation of Sample 1, except that the amounts of the plasticizer A and the ultraviolet absorber I, and the thickness of the cellulose triacetate film were changed as shown in Table 1. A sample and a polarizing plate were prepared.

Evaluation Method The following performance evaluation was performed on the sample films 1 to 11 and the polarizing plate samples 1 to 11 produced as described above.

(1) Water Absorption The produced sample film was cut into a size of 10 cm × 10 cm, immersed in water at 23 ° C. for 24 hours, and immediately after being taken out, surrounding water droplets were wiped off with filter paper, and the mass was measured. then, it was the W _1. Next, the film was heated at 23 ° C.
After dampening 24 hours adjusted under the conditions of RH, measuring its mass, and the W _0. The water absorption when immersed in water at 23 ° C. for 24 hours was calculated from the measured values according to the following formula.

Water absorption rate (%) = ((W ₁ −W ₀ ) / W ₀ ) × 100 (2) Moisture rate The prepared sample film was cut into a size of 10 cm × 10 cm, and 23 ° C., 80% RH. under atmosphere measuring its mass after moisture conditioning was 48 hours tone was W _3. Next, the weight of this film after drying at 120 ° C. for 45 minutes was measured, and the result was defined as W ₂ . The moisture content was calculated under the conditions of 23 ° C. and 80% RH by calculating from the measured values according to the following formula.

Moisture percentage (%) = ((W ₃ −W ₂ ) / W ₂ ) × 100 (3) Spectral Characteristics The prepared sample film was measured using a spectrophotometer (U-3400,
The transmittance of light at 370 nm was measured using Hitachi, Ltd.).

(4) Measurement of Change in Polarization Degree For the produced polarizing plate sample, first, the parallel transmittance and the orthogonal transmittance were measured, and the degree of polarization was calculated according to the following equation. After that, each polarizing plate was left for 500 hours under xenon long life weather meter at an illuminance of 70,000 lux at 60 ° C. and 80% RH (forcible deterioration), and then the parallel transmittance and the direct transmittance were measured again, and the polarization was calculated according to the following formula. The degree was calculated. The amount of change in the degree of polarization was determined by the following equation. Sample film 2 (Comparative Example 2)
The degree of change in the degree of polarization of the polarizing plate manufactured by using the sample of the present invention with respect to the degree of change in the degree of polarization of the polarizing plate manufactured by using the method was obtained. Degree of polarization P (%) = ((H ₀ −H ₉₀ ) / (H ₀ + _H90 ))
^1/2 × 100 polarization degree change ΔP (%) = P ₀ −P ₅₀₀ H0 = parallel transmittance H90 = direct transmittance P0 = degree of polarization before forced degradation P500 = degree of polarization after 500 hours of forced degradation polarization degree change The amount ΔP (%) was classified and evaluated as follows.

：: Difference between before and after forced deterioration is ± 1% or less, Δ: Difference between before and after forced deterioration is ± 1% to less than 2%, ×: Difference between before and after forced deterioration is ± 2% to less than 5% , Xx: Difference from before and after forced deterioration is ± 5% or more.

If the level is equal to or higher than the level, there is no practical problem. (5) Peeling off of the adhesive interface of the polarizing plate The prepared polarizing plate sample was subjected to the following conditions at 60 ° C. and 80% RH.
After the thermotreatment for 00 hours, the peeling state of the end face of the polarizing plate was evaluated.

：: No peeling of the end face was observed. Δ: No peeling of the end face was observed. The color appeared to be slightly white at the end. ×: Peeling of the end face was observed. There is no problem level.

[0108]

[Table 1]

As can be seen from Table 1, according to the method of the present invention, even when the cellulose ester film, which is a protective film for a polarizing plate, is made thinner for the purpose of making the LCD thinner and lighter, the polarizing plate itself becomes thinner. It can be seen that the durability does not deteriorate.

Example 2 <Preparation of Samples 12 to 21> In Example 1, a plasticizer B and an ultraviolet absorber II were used in place of the plasticizer A and the ultraviolet absorber I in the same manner as in Table 1. As shown in 2, a film sample and a polarizing plate sample were prepared.

Plasticizer B: Tri (2-ethylhexyl) trimellitate: Vapor pressure at 200 ° C. 66.7 Pa Ultraviolet absorber II: 2- (2H-benzotriazole-2)
-Yl) -4,6-di-tert-bentylphenol The results of evaluation in the same manner as in Example 1 are shown in Table 2.

[0112]

[Table 2]

As can be seen from Table 2, according to the method of the present invention, even when the cellulose ester film, which is a protective film for a polarizing plate, is made thinner for the purpose of making the LCD thinner and lighter, the polarizing plate itself becomes thinner. It can be seen that the durability does not deteriorate.

Example 3 <Production of Samples 22 to 28> Samples 22 to 27 were produced in the same manner as Sample 3 except that the drying conditions after peeling the film from the support were changed as shown in Table 3. .

A sample 28 was prepared in the same manner as in Example 15 except that the drying conditions were polarized as shown in Table 3. The drying time was adjusted by changing the transport distance by adjusting the number of rolls in the drying zone, or by changing the transport speed.

Further, a polarizing plate was manufactured in the same manner as in Example 1, and the same evaluation as in Example 1 was performed. Table 3 shows the results.

[0117]

[Table 3]

As can be seen from Table 3, according to the method of the present invention, even if the cellulose ester film, which is a protective film for a polarizing plate, is made thinner for the purpose of making the LCD thinner and lighter, the polarizing plate itself becomes thinner. It can be seen that the durability does not deteriorate.

[0119]

As demonstrated in the examples, the cellulose ester film, the protective film for a polarizing plate and the member for a liquid crystal display according to the present invention can deteriorate the durability of the polarizing plate even if the protective film for the polarizing plate is made thin. And has excellent effects.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 1/08 C08L 1/08 G02B 5/30 G02B 5/30 G02F 1/1335 510 G02F 1/1335 510 / / B29K 1:00 B29K 1:00 B29L 7:00 B29L 7:00 (72) Inventor Noriaki Tachibana 1 Konica Stock Company, Sakuracho, Hino City, Tokyo

Claims (14)

[Claims] 1. A film having a thickness of 20 μm to 65 μm and having a water absorption of 1.% when immersed in water at 23 ° C. for 24 hours.
A cellulose ester film, which is 0% to 4.5%. 2. A film having a thickness of 20 μm to 65 μm and a moisture content of 0.5% in an atmosphere of 23 ° C. and 80% RH.
A cellulose ester film, which is about 4.5%. 3. A film having a thickness of 20 μm to 65 μm and a water content of 0.5% at 23 ° C. and 80% RH.
The cellulose ester film according to claim 1, wherein the content is from 4.5 to 4.5%. 4. A cellulose ester film having a thickness of 20 μm to 65 μm and a transmittance of light having a wavelength of 370 nm of 10% or less. 5. The cellulose ester film according to claim 1, wherein the film thickness is 20 μm to 65 μm, and the transmittance of light having a wavelength of 370 nm is 10% or less. . 6. The cellulose ester film according to claim 1, wherein the cellulose ester film contains a plasticizer, and the content of the plasticizer is 3% by mass to 30% by mass based on the cellulose ester. The cellulose ester film according to claim 1. 7. A plasticizer having a vapor pressure at 200 ° C. of 13
7. A plasticizer of less than 33 Pa.
The cellulose ester film according to the above. 8. The cellulose ester film according to claim 1, wherein the content of the plasticizer is from 10% by mass to 25% by mass with respect to the cellulose ester. 9. The cellulose ester film according to claim 1, further comprising an ultraviolet absorber containing two or more aromatic rings in the molecule. 10. The cellulose ester film contains a benzotriazole-based compound represented by the following general formula [1] as an ultraviolet absorber, and the content of the ultraviolet absorber is 0.1 to 100% of the cellulose ester. 1 mass%
The cellulose ester film according to any one of claims 1 to 9, wherein the content is from 2.5 to 2.5% by mass. Embedded image [Wherein, R ₁ , R ₂ , R ₃ , R ₄ and R ₅ may be the same or different and include a hydrogen atom, a halogen atom, a nitro group, a hydroxyl group, an alkyl group, an alkenyl group, an aryl group,
Alkoxy group, an acyloxy group, an aryloxy group, an alkylthio group, an arylthio group, a mono- or dialkylamino group, an acylamino group or a 5 to 6 membered heterocyclic group, R ₄ is a carbocyclic ring of 5-6 membered with R ₅ It may be formed. ] 11. A method for producing a cellulose ester film in which a cellulose ester solution is cast on a support and then peeled off and dried. 110 to 150 ° C. or 110 to 150 when the residual solvent amount is 5 to 10% by mass.
A method for producing a cellulose ester film, characterized in that the temperature maintained in the temperature range is at least 15 seconds or more under at least one holding condition selected from ° C. 12. A method for drying a cellulose ester film obtained by casting a cellulose ester solution on a support and peeling the cellulose ester solution from the support, when the residual solvent amount is 10 to 100% by mass. A total of 15 seconds or more of a time maintained in a temperature range under at least one holding condition selected from 110 to 150 ° C. when the residual solvent amount is 5 to 10% by mass at 80 to 130 ° C. The cellulose ester film according to claim 1. 13. A protective film for a polarizing plate, comprising the cellulose ester film according to any one of claims 1 to 10. 14. A liquid crystal display member using the cellulose ester film according to any one of claims 1 to 10.