JP2002022956A - Protective film for polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective film for polarizing plate, which has less moisture permeability without depositing a plasticizer and a UV absorbing agent during film formation and stable and excellent dimensional stability even under a severe condition such as a high temperature and high humidity. SOLUTION: The protective film for polarizing plate is a cellulose ester film which contains a polymer and is characterized in that the polymer is selected from polyester and polyester-ether and has a weight average molecular weight of 400-5,000 and glass transition temperature of the cellulose ester film which contains the polymer is not lower than that of the cellulose ester film which contains no additive at all by 20 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective film for a polarizing plate having excellent dimensional stability of a liquid crystal image display device, and more particularly to a protective film for a polarizing plate containing a polymer.

[0002]

2. Description of the Related Art Conventionally, cellulose triacetate films have been used as base films for silver halide photographic light-sensitive materials. This cellulose triacetate film has been diverted to a protective film for a polarizing plate, but there are demands for applications that are not found in silver halide photographic materials.
Similarly to the silver halide photographic light-sensitive material, in the protective film for a polarizing plate, the cellulose triacetate film contains a plasticizer for the purpose of imparting flexibility and hydrophobicity.

[0003] In recent years, developments relating to thinner and lighter information devices equipped with liquid crystal, such as notebook personal computers, car navigation systems, mobile phones, game machines, and the like, have been progressing. Accordingly, there is an increasing demand for a protective film for a polarizing plate used in a liquid crystal display device to be made thinner.
Therefore, the protective film for a polarizing plate tends to be extremely thinner than the silver halide photographic material base film. When the film is made thinner, the moisture permeability decreases, and the function of the liquid crystal image display device deteriorates in an environment of humidity, particularly high temperature and high humidity.

[0004] After casting, the plasticizer migrates in the thickness direction of the web during drying and becomes uneven in the web, and the plasticizer precipitates on the web surface, evaporates or volatilizes, and the wall of the apparatus is removed. It accumulates and accumulates on the web and rolls and contaminates the web and rolls. If the cellulose triacetate film is simply made thinner, the moisture permeability deteriorates and the moisture cannot be cut off sufficiently. Deterioration could occur. As a countermeasure against this, it is conceivable to increase the amount of plasticizer by the amount of the thinner film.However, simply increasing the amount of the plasticizer increases the precipitation of the plasticizer on the surface of the cellulose triacetate film and the like. It has been found that it causes a new problem that has been exhibited in a base film for photographic light-sensitive materials. Under the environment of high temperature and high humidity, the property that the mass of the film is reduced due to the deposition and volatilization of additives such as a plasticizer outside the film is called a retaining property. The function of the display device has been reduced.

[0005] Further, by increasing the amount of the plasticizer, the glass transition point (hereinafter, Tg) of the cellulose triacetate film is increased.
), And the dimensional stability (shrinkage rate, coefficient of hygroscopic expansion, coefficient of thermal expansion) of the cellulose triacetate film deteriorates (increases) due to softening of the film.

As a countermeasure against these problems, a technique has been proposed in which a polymer such as polyester, polyester ether or polyurethane ether is contained as a high molecular weight plasticizer in combination with a low molecular weight plasticizer. For example, Japanese Patent Publication Nos. 47-760 and 43-16305,
No. 197 073, U.S. Pat. No. 3,054,673
And No. 3,277,031. Further, a technique has been proposed in which an acrylic polymer is contained in a cellulose triacetate film or an acrylic monomer is polymerized and contained in the presence of cellulose triacetate. However, after the formation of the cellulose triacetate dope, the drying web, or the film during the formation of the cellulose triacetate polymer, the cellulose triacetate and the polymer phase-separate, lowering the transparency, lowering the permeability of moisture, or causing the film to be uniform. It was found that there were problems such as not shrinking and reduction in expansion ratio. Also, an ultraviolet absorber may be added to the protective film for the polarizing plate, but like the plasticizer, it is deposited on the film surface during film formation, or becomes a cause of contamination by evaporation or volatilization, or cellulose. The ultraviolet absorber added during the saponification treatment of the ester film may become particles or crystallize and precipitate. As a countermeasure, JP-A-6
In JP-A-148430, a polymer ultraviolet absorber is added to a dope to form a film.

[0007]

When a conventionally used thick cellulose ester film is simply thinned, the Tg of the film is reduced due to the presence of a low-molecular plasticizer in the cellulose ester film, and the film is easily shrunk. , A low molecular plasticizer contained in a cellulose ester film may partly come out of the film during film production or in a high-temperature and high-humidity atmosphere, thereby contaminating the film or device, or shrinking the film. As a result of studying in detail that various problems such as those described above occur due to the above-mentioned problems, the above-mentioned problem has been solved.

A first object of the present invention is to provide a cellulose ester film as a protective film for a polarizing plate, in which an additive such as a low molecular weight plasticizer is precipitated, volatilized or evaporated during film formation and does not stain a film or an apparatus. It is in. A second object is to provide a cellulose ester film as a protective film for a polarizing plate whose glass transition point does not decrease even when an additive is contained. A third object is to provide a cellulose ester film as a protective film for a polarizing plate having excellent dimensional stability which has resistance to moisture permeability and does not expand or contract under the conditions of high temperature and high humidity or high humidity. It is in.

[0009]

The present invention has the following constitution.

(1) In a normal temperature and normal humidity atmosphere of 23 ± 3 ° C. and 55 ± 3% RH, a dimension in a casting direction or a width direction of a film is defined as L ₀ (mm), and 80 ± 3 ° C. and 90 ± 3%
After leaving for 50 hours in a high-temperature, high-humidity atmosphere of RH, when the dimensions when returned to the normal temperature and normal humidity atmosphere are defined as L ₁ (mm),
The expansion and contraction ratio (S50h) in the following formula is within ± 0.3% in both the casting direction and the width direction, and the moisture permeability is 250 g / m ^2.
A protective film for a polarizing plate having a length of 24 hours or less.

S50h (%) = {(L ₁ −L ₀ ) / L ₀ } × 100 (2) The expansion and contraction ratio (S50h) is within ± 0.1% in each case. The protective film for a polarizing plate according to the above.

(3) In a normal temperature and normal humidity atmosphere of 23 ± 3 ° C. and 55 ± 3% RH, the dimension in the casting direction or width direction of the film is defined as L ₀ (mm), and 80 ± 3 ° C. and 90 ± 3%
After leaving for 24 hours and 100 hours in a high-temperature and high-humidity atmosphere of RH, the dimensions for 24 hours left when the atmosphere was returned to the normal-temperature and normal-humidity environment again were defined as L ₂ (mm), and the dimensions for 100 hours were also determined. When L ₃ (mm), the difference between the stretch ratio (S100h) of the film left for 100 hours and the stretch ratio (S24h) of the film left for 24 hours in the following formula is ± 0.1 in both the casting direction and the width direction. % And moisture permeability is 250g
/ M ² · 24 h or less.

S24h (%) = {(L ₂ −L ₀ ) / L ₀ } × 100 S100h (%) = {(L ₃ −L ₀ ) / L ₀ } × 100 (4) The moisture permeability is 200 g / m. ^The protective film for a polarizing plate according to any one of (1) to (3), which is not more than 2.24 h.

(5) In a protective film for a polarizing plate containing a polymer in a cellulose ester film, the polymer is selected from polyester and polyester ether, and the polymer has a weight average molecular weight of 400 to 5,000, A protective film for a polarizing plate, wherein the glass transition point of a cellulose ester film containing the polymer is not lower than that of a cellulose ester film containing no additives by 20 ° C.

(6) The protective film for a polarizing plate according to (5), wherein the polymer selected from polyester and polyester ether has a weight average molecular weight of 400 to 2,000.

(7) The protective film for a polarizing plate as described in (5) or (6), containing 5 to 30% by mass of a polymer selected from polyester and polyester ether.

(8) In a protective film for a polarizing plate containing a polymer in a cellulose ester film, the polymer is a homopolymer or a copolymer containing a vinyl ester, and the polymer has a weight average molecular weight of 5,000 to 150,000. A protective film for a polarizing plate, wherein the glass transition point of a cellulose ester film containing the polymer is not lower than that of a cellulose ester film containing no additives by 20 ° C.

(9) The protective film for a polarizing plate according to (8), wherein the homopolymer or copolymer containing a vinyl ester has a weight average molecular weight of 10,000 to 80,000.

(10) The protective film for a polarizing plate as described in (8) or (9), which contains a homopolymer or a copolymer containing a vinyl ester in an amount of 5 to 45% by mass.

(11) The cellulose ester film contains a polymer ultraviolet absorber (5).
The protective film for a polarizing plate according to any one of (1) to (10).

(12) When the amount of the polymer ultraviolet absorber is 0.5 to
The protective film for a polarizing plate according to (11), which contains 6.0% by mass.

(13) The protective film for a polarizing plate according to any one of (5) to (12), wherein the cellulose ester is cellulose triacetate or cellulose acetate propionate.

(14) The protective film for a polarizing plate according to any one of (5) to (13), wherein the thickness of the cellulose ester film after drying is 10 to 65 μm.

(15) In a normal temperature and normal humidity atmosphere of 23 ± 3 ° C. and 55 ± 3% RH, the dimension in the casting direction or width direction of the film is defined as L ₀ (mm), and 80 ± 3 ° C. and 90 ± 3.
% RH after leaving for 50 hours in a high-temperature and high-humidity atmosphere, and when the dimensions when returned to the normal-temperature and normal-humidity atmosphere are L ₁ (mm), the expansion and contraction ratio (S50h) of the following equation is different from the casting direction. It is within ± 0.3% in both width directions and the moisture permeability is 250 g / m.
And characterized in that ² · 24h or less (5) to (1
4. The protective film for a polarizing plate according to any one of 4).

S50h (%) = {(L ₁ −L ₀ ) / L ₀ } × 100 (16) The expansion ratio (S50h) is within ± 0.1% in each case (15). The protective film for a polarizing plate according to the above.

(17) In the atmosphere of 23 ± 3 ° C. and 55 ± 3% RH at room temperature and normal humidity, the dimension in the casting direction or width direction of the film is defined as L ₀ (mm), and 80 ± 3 ° C., 90 ± 3.
After% at high temperature and high humidity atmosphere of RH for 24 hours and 100 hours standing, again the dimensionally method left for 24 hours and L ₂ (mm) when returned to the atmosphere of the normally temperature and normal humidity, and the dimensionally method of 100 hours Is defined as L ₃ (mm), the difference between the stretch ratio (S100h) of the film left for 100 hours and the stretch ratio (S24h) of the film left for 24 hours in the following formula is ± 0.2 in both the casting direction and the width direction. Within 1% and moisture permeability of 250
g / m ² · 24 h or less.
17. The protective film for a polarizing plate according to any one of claims 16 to 16.

S24h (%) = {(L ₂ −L ₀ ) / L ₀ } × 100 S100h (%) = {(L ₃ −L ₀ ) / L ₀ } × 100 (18) The moisture permeability is 200 g / m. ^The protective film for a polarizing plate according to any one of (15) to (17), which is not more than 2.24 h.

(19) The coefficient of hygroscopic expansion in the casting direction is 6 ×
The protective film for a polarizing plate according to any one of (5) to (18), which is 10 ^-5 (1 /% RH) or less.

Hereinafter, the present invention will be described in detail. First, the cellulose ester used in the present invention will be described.

The cellulose ester used in the cellulose ester film according to the present invention uses cellulose selected from linter pulp, wood pulp and kenaf pulp, and reacts them with acetic anhydride, propionic anhydride or butyric anhydride in a conventional manner. The degree of substitution of all acyl groups with respect to hydroxyl groups of cellulose is 2.5 to 3.
Cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate of 0 are preferably used. The cellulose ester according to the present invention preferably has an acetyl group substitution degree of at least 1.5 or more. In the present invention, cellulose triacetate (hereinafter sometimes abbreviated as TAC) and cellulose acetate propionate (hereinafter sometimes abbreviated as CAP) are preferred. As a method for measuring the degree of substitution of the acyl group of the cellulose ester, ASTM D-8
It can be carried out according to 17-91. The molecular weight of these cellulose esters is 7 as a number average molecular weight.
The range of from 000 to 300,000 is preferable because the mechanical strength when formed into a film is strong. 80,00
0 to 200,000 is preferred. Usually, the cellulose ester is formed into a flake shape after a treatment such as washing with water after the reaction, and is used in that shape.
When the thickness is in the range of from 0.05 to 2.0 mm, the solubility can be accelerated, which is preferable.

In the present invention, the degree of acetyl group substitution is 2.
The glass transition point (hereinafter sometimes abbreviated as Tg) of cellulose triacetate without additives as a film measured at 88 is 199 to 200 ° C. using a value measured by the following vibron method. Similarly, a cellulose acetate propionate having an acetyl group substitution degree of 2.00 and a propionyl group of 0.9 and having no additives was used.
g is 199-200 ° C.

Tg in the present invention is Rheometr
ICS 'SOLIDS ANALYZER-RSA
Using II, set the frequency (Frequency) to 100ra
The temperature at which the peak value of tan δ was attained was taken as the glass transition point (Tg), which was measured with d / sec and the strain being 8.0E-4.

A solution obtained by dissolving cellulose ester in an organic solvent is called a dope. The concentration of the cellulose ester in the dope is about 10 to 35% by mass. More preferably, it is 15 to 25% by mass.

Organic solvents as good solvents for cellulose esters include methyl acetate, ethyl acetate, amyl acetate, ethyl formate, acetone, cyclohexanone, methyl acetoacetate, tetrahydrofuran, 1,3-dioxolan, and 4-methyl-1,3. -Dioxolan, 1,4-dioxane, 2,2,2-trifluoroethanol, 2,
2,3,3-hexafluoro-1-propanol, 1,
3-difluoro-2-propanol, 1,1,1,3,
3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1
-Propanol, nitroethane, 2-pyrrolidone, N-
Examples thereof include methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, methylene chloride, and bromopropane. Of these, methyl acetate, acetone, and methylene chloride are preferably used. However, due to recent environmental problems, non-chlorine organic solvents tend to be more preferable. It is preferable to use a lower alcohol such as methanol, ethanol, or butanol in combination with these organic solvents, because the solubility of the cellulose ester in the organic solvent can be improved and the viscosity of the dope can be reduced. Particularly, ethanol having a low boiling point and low toxicity is preferable. The organic solvent used in the dope according to the present invention is preferably used by mixing a good solvent and a poor solvent of the cellulose ester from the viewpoint of production efficiency, and a preferable range of the mixing ratio of the good solvent and the poor solvent is good. Solvent 70-98
% By mass, and the content of the poor solvent is 30 to 2% by mass. The good solvent and the poor solvent used in the present invention are defined as those which dissolve the cellulose ester used alone as a good solvent and those which do not dissolve alone as a poor solvent. The poor solvent used in the dope according to the present invention is not particularly limited. For example, methanol, ethanol, n-butanol, cyclohexane, acetone, cyclohexanone, and the like can be preferably used.

The characteristics of the protective film for a polarizing plate of the present invention are as follows.
Since the cellulose ester film contains a polymer mainly composed of polyester, polyester ether, or vinyl ester, it is possible to eliminate those that precipitate, evaporate or evaporate from the film. In addition, the additive does not come out of the film, and the transparency does not decrease.

The protective film for a polarizing plate of the present invention is characterized in that it has extremely low elasticity even when exposed to a high-temperature and high-humidity atmosphere.

The expansion ratio in the present invention is 23 ± 3 ° C., 5
A film left in a state of normal temperature and normal humidity of 5 ± 3% RH,
The film is irreversible when exposed to a high-temperature and high-humidity state of 80 ± 3 ° C. and 90 ± 3% RH for a predetermined time and then returned to a normal temperature and normal humidity state of 23 ± 3 ° C. and 55 ± 3% RH. Refers to dimensional change (elongation or contraction). A conventional cellulose ester film containing a low-molecular plasticizer has a large expansion and contraction rate (particularly, a contraction rate) at high temperature and high humidity due to weight loss mainly caused by deposition volatilization and evaporation. On the other hand, in the present invention, since a polymer useful in the present invention is contained, there is no such thing as precipitation, and the expansion ratio is very small. 8
0 ± 3 ℃, 90 ± 3% RH in high temperature and high humidity atmosphere
The extensibility after exposure for 0 hours is within ± 0.3%, preferably within ± 0.1%. In addition, the difference (S100h-) between the expansion and contraction rate (S100h) when exposed to the same high temperature and high humidity state for 100 hours and the expansion and contraction rate (S24h) when exposed for 24 hours.
S24h) is within ± 0.1%, and is characterized in that it does not change much from the change occurring within 24 hours even if the time progress is large in a high temperature and high humidity state.

The expansion and contraction ratio in the high temperature and high humidity state in the present invention will be described in detail. 23 ± 3 ℃, 55 ± 3% R
The dimension in the casting direction or width direction of the film in an atmosphere of normal temperature and normal humidity of H is defined as L ₀ (mm), and 80 ± 3 ° C., 90
After leaving for 50 hours in a high-temperature and high-humidity atmosphere of ± 3% RH, when the dimensions when returned to the normal-temperature and normal-humidity atmosphere are L ₁ (mm), the expansion ratio (S50h) is expressed by the following formula. Can be done. Of course, the casting direction and the width direction of the film are measured separately.

S50h (%) = {(L ₁ −L ₀ ) / L ₀ } × 100 In addition, the difference in the expansion and contraction rate over time in the high temperature and high humidity state of the present invention is also an important check point. That is, in a normal temperature and normal humidity atmosphere of 23 ± 3 ° C. and 55 ± 3% RH, the dimension of the film in the casting direction or the width direction is L.
₀ (mm), and after 24 hours and 100 hours of treatment in a high-temperature and high-humidity atmosphere of 80 ± 3 ° C. and 90 ± 3% RH, the dimensions of the 24-hour treatment when returning to the normal temperature and normal humidity atmosphere are L _Two
(Mm), and the dimension left for 100 hours is L ₃ (m
m), the stretch ratio (S100h) of the film left for 100 hours and the stretch ratio (S2
4h) (S100h-S24h) shows the temporal change of the expansion and contraction rate at high temperature and high humidity.

S24h (%) = {(L ₂ −L ₀ ) / L ₀ } × 100 S100h (%) = {(L ₃ −L ₀ ) / L ₀ } × 100 Only the cellulose ester contains the additive. Untreated films have poor moisture permeability and are conventionally improved by the addition of low molecular weight plasticizers. However, if the addition amount is not large, it does not lead to improvement in moisture permeability, and such an increase in the addition amount rather increases stains such as precipitation.

On the other hand, although the above-mentioned expansion and contraction rate of the cellulose ester film not added is very excellent, the expansion and contraction rate of the one to which a low molecular weight plasticizer is added tends to deteriorate as the amount increases.

The protective film for polarizing plate of the present invention has the above-mentioned expansion and contraction ratio S50h of ± 0.3% or less and a moisture permeability of 250 g / h.
and those that are m ² · 24h, also, S100h and S
The difference in expansion and contraction rate of 24h is ± 0.1 or less and the moisture permeability is 25
0 g / m ² · 24 h.

As a method for satisfying the above-mentioned stretching ratio and moisture permeability, or a difference between stretching ratio and moisture permeability, it can be achieved by using a cellulose ester film useful in the present invention described below as a polarizing plate protective film. I can do it.
The protective film for a polarizing plate of the present invention can be obtained by adding a polymer useful in the present invention to moisture permeability, dimensional stability (stretch ratio, difference in stretch ratio, coefficient of hygroscopic expansion), retention property, film stain, etc. Can be improved. If the amount of conventional low molecular weight plasticizers is increased, the film and equipment will be soiled by precipitation, evaporation and volatilization from the web, and not only will the film quality and productivity deteriorate, but also the Tg will decrease and the dimensional stability will deteriorate. Let me do it. On the other hand, the polarizing plate protective film containing the polymer useful in the present invention can be increased to the upper limit of the content of the present invention, and a film having sufficiently small moisture permeability can be obtained.

In the present invention, the moisture permeability is 200 g.
/ M ² · 24 h or less, more preferably 20 to 150 g /
m ² · 24h is more preferred.

The polymer useful in the present invention is selected so that no phase separation occurs in a cellulose ester dope or a cellulose ester film. As a result of the study by the present inventors, it has been found that there is a relationship between the weight average molecular weight (hereinafter sometimes abbreviated as Mw) and the compatibility with the cellulose ester. The polymer useful in the present invention is added to the cellulose ester dope, in the process of casting to form a film, or over time of the finished cellulose ester film, even in a state exposed to bad conditions such as high temperature and high humidity, It does not undergo phase separation, turbidity or bleed-out, has a very small dimensional change after film formation and has excellent retention properties, and has a weight average molecular weight of 40.
Polyesters and polyester ethers having a weight average molecular weight of 5000 to 150,000, preferably 7000 to 10
It is a polymer having mainly a vinyl ester having 0000, more preferably 10,000 to 80,000.
If the weight average molecular weight is larger than the above range, the compatibility is deteriorated, the effect of reducing the moisture permeability is small, and the retention tends to be easily deteriorated. Therefore, the above range of the weight average molecular weight is preferable. Therefore, the polymer according to the present invention also includes what is called an oligomer.

The above polymer useful in the present invention has a ratio Mw between the weight average molecular weight (Mw) and the number average molecular weight (Mn).
/ Mn is preferably in the range of 1 to 5, more preferably 2 to 5, and still more preferably 3 to 5. M
The fact that w / Mn is large means that the polymer contains a larger amount of the polymer on the low molecular side, and in the present invention, those having a high distribution on the low molecular side are preferable. It is characterized by containing more low-molecular side polymer (oligomer-like) and has good compatibility and is preferable because it does not cause phase separation bleed-out, cloudiness, and the like.

Further, the above polymers useful in the present invention include a polymer having a Z-average molecular weight (Mz) and a weight-average molecular weight (Mz).
The ratio Mz / Mw to w) is preferably in the range of 1 to 3, and more preferably 1 to 2.5. The reason is the same as above.

Note that Mn, Mw and Mz are GPC (Ge
l Permeation Chromatograph
hy) can be measured by an ordinary method. For example, a column (SHODEX-K806, manufactured by Showa Denko KK)
-K803) at 25 ° C., using methylene chloride as an eluent, a flow rate of 1.0 ml / min, detection R1, injection volume of 100 μl, and sample concentration of 0.1 μl.
(Mass / volume%) and using polystyrene as a standard sample.

The polyester or polyester ether useful in the present invention is contained in the cellulose ester film in an amount of 5 to 30% by mass relative to the cellulose ester, more preferably 7 to 20% by mass. In addition, a polymer mainly comprising a vinyl ester useful in the present invention is contained in a cellulose ester film in an amount of 5 to 5% with respect to the cellulose ester.
It contains 45% by mass, more preferably 7 to 35% by mass. Actually, the content of the polymer in the film depends on the type and weight average molecular weight of the polymer, and in the dope, in the web, and within the range that does not cause phase separation after the film is formed, the performance such as dimensional stability, retention, transmittance, etc. It is decided according to.

The above Mw, Mw / Mn, M useful in the present invention
The polymer in the range of z / Mw can be used without limitation as long as it does not cause phase separation after the formation of the film in the dope, the web, and the cellulose ester.

The polyester useful in the present invention will be described. As the dibasic acid which is one of the components of the polyester, aliphatic dibasic acids, alicyclic dibasic acids, and aromatic dibasic acids are preferable.For example, as the aliphatic dibasic acids, malonic acid, succinic acid , Glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, etc., and aromatic dibasic acids such as phthalic acid, terephthalic acid, isophthalic acid, and 1,4-xylyl. Examples of alicyclic dibasic acids such as dendicarboxylic acid include 1,3-cyclobutanedicarboxylic acid,
Examples thereof include 3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 1,4-cyclohexanediacetic acid. In particular, as the aliphatic dicarboxylic acid, those having 4 to 12 carbon atoms, alicyclic dibasic acids and aromatic dicarboxylic acids are preferable, and at least one selected from these is used. That is, two or more dibasic acids may be used in combination. Examples of the glycol that is the other component include ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, and 1,4-butyl glycol.
Butylene glycol, 1,5-pentanediol, 1,
6-hexanediol, 1,4-cyclohexanediol, 1,5-pentylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tetraethylene glycol, and the like. ,
1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6
-Hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol are preferred, and furthermore, 1,3-propylene glycol,
1,4-butylene glycol 1,6-hexanediol and diethylene glycol are preferably used. Preferably, the polyester is hardly crystallized. Polycondensation of the polyester is carried out by a conventional method. For example, a hot-melt condensation method by a direct reaction of the above-mentioned dibasic acid and glycol, a polyesterification reaction or a transesterification reaction of the above-mentioned dibasic acid or alkyl esters thereof, for example, a methyl ester of dibasic acid and glycols, Alternatively, it can be easily synthesized by any method of a dehydrohalogenation reaction of an acid chloride of these acids with a glycol. However, a polyester whose weight average molecular weight is not so large is preferably subjected to a direct reaction. Polyester having a high distribution on the low molecular weight side has very good compatibility with the cellulose ester, and after forming the film, a cellulose ester film having low moisture permeability and high transparency can be obtained. Conventional methods can be used for adjusting the molecular weight without any particular limitation. For example, depending on the polymerization conditions, it can be controlled by a method of blocking the molecular terminals with a monovalent acid or a monovalent alcohol, and by controlling the amount of these monovalent compounds to be added.
In this case, monovalent acids are preferred from the viewpoint of polymer stability.
For example, acetic acid, propionic acid, butyric acid, pivalic acid, benzoic acid, etc. can be used. However, during the polycondensation reaction, such a monovalent acid is not removed from the reaction system but stopped and stopped outside the reaction system. Although those which are easily distilled off when removing from the system are selected, these may be mixed and used. In the case of a direct reaction, the weight average molecular weight can also be adjusted by measuring the timing of stopping the reaction based on the amount of water distilled off during the reaction. In addition, it can be adjusted by biasing the number of moles of glycol or dibasic acid to be charged or by controlling the reaction temperature.

The polyester ethers useful in the present invention are:
The polyester or the dibasic acid or an alkyl ester thereof and a compound having OH groups at both ends of an ether unit are converted into a polyester having a terminal OH group by a hot melt condensation method by a polyesterification reaction or a transesterification reaction. A polyester ether can be obtained by a reaction method of etherification. The ether unit is not particularly limited. For example, HO (RO) _n ROH (where R is an alkylene group, an arylene group, an aralkylene group,
These may be mixed with each other by a bifunctional alicyclic group or the like, and n is 1 to 100) such as diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, polyphenylene glycol, and polycycloalkyl. Hexylene glycol and the like can be mentioned,
These may be used in combination. The method for adjusting the molecular weight of the polymer can be used without any particular limitation, and can be carried out in the same manner as in the case of polyester.

Polyester ethers suitable for the present invention can be obtained from commercial products. For example, Hytrel copolyesters manufactured by Dupont, G
AFflex Galflex polymer,
"Adeka Sizer RS Series manufactured by Asahi Denka Kogyo Co., Ltd."
Can be mentioned.

The amount of these polyester ethers mixed with the cellulose ester is the same as that of the above-mentioned polyester, and the transparency of the cellulose ester film after film formation is not deteriorated, and excellent mechanical properties, particularly, tear strength are obtained. Show.

The type of the polymer mainly containing a vinyl ester useful in the present invention is not particularly limited as long as it does not cause phase separation. Examples of monomers forming a polymer mainly composed of vinyl esters include vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, isovaleric acid, methyl ethyl vinyl acetate, and vinyl pivalate. And vinyl caproate, vinyl isocaproate, vinyl enanthate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, and the like. The term “mainly vinyl ester” means a polymer containing vinyl ester in an amount of 40% by mass or more. Examples of the copolymerization component with a vinyl ester include vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, and butyl vinyl ether; and vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone, and butyl vinyl ketone, and acrylic acid. Or as methacrylic acid esters, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, cyclohexyl acrylate, heptyl acrylate, octyl acrylate, benzyl acrylate,
Examples include phenethyl acrylate and the like, and those obtained by using these acrylates as methacrylate. Further, in addition to the above-mentioned monomers, examples thereof include maleic esters, fumaric esters, vinyl chloride, butadiene, and other monomers as copolymerizable components. In the present invention,
In particular, a polymer derived from a vinyl ester monomer is excellent in compatibility with a cellulose ester, and a weight average molecular weight sufficient for improving compatibility can be added in the same range as in the polyester. Mw / Mn, Mz / Mw
It is also preferable that the same applies to the above. In addition, as a method for adjusting the molecular weight of such a polymer mainly containing a vinyl ester, a conventional method can be used without particular limitation. For example, a method of increasing the amount of a polymerization initiator added, a method of increasing the amount of a solvent for solution polymerization, a method of increasing a polymerization temperature, a method of increasing a monomer concentration, a method of adding a chain transfer agent or a polymerization inhibitor, and the like. There is. Examples of the chain transfer agent include, for example, halogenated hydrocarbons such as carbon tetrachloride, ethane tetrachloride, chloroform, ethane trichloride, and carbon tetrabromide, aromatic hydrocarbons such as benzene, toluene, and ethylbenzene, and n-butyl. Sulfur-containing hydrocarbons such as mercaptan, t-butyl mercaptan, n-dodecyl mercaptan, ethyl thioglycolate, disulfide, dodecyl mercaptan, and diazothioether; alcohols such as n-butanol, i-butanol, s-butanol and t-butanol , Acetone, methyl ethyl ketone,
Examples thereof include ketones such as methyl isopropyl ketone and methyl isobutyl ketone. Also, a polymerization inhibitor can be used, and examples thereof include benzoquinone, nitrobenzene, diphenylpicrylhydrazyl and the like.

The state of the polyester useful in the present invention at normal temperature and normal humidity is various such as a viscous liquid state, a gum state, and a soft resin state. Further, polymers mainly composed of vinyl esters range from viscous liquid to solid.

The Tg of the cellulose ester film containing these polymers is not so different from that of the cellulose ester film without additives, and is in a range not lower than 20 ° C. from the latter Tg. Here, the Tg of the cellulose ester film without any additive was defined as Tg (a).
(° C.), and Tg (difference) as Tg (b) (° C.) of Tg of a cellulose ester film to which something is added.
(° C.), and Tg (difference) in the following equation is Tg (difference) = Tg (a) −Tg (b). That is, as described above, for Tg (b) to which the polymer according to the present invention is added, 20 ° C ≧ Tg (a) −Tg (b). In the present invention, it is a feature of the present invention that by containing a polymer, the thermal properties are almost the same as those without additives, for example, dimensional stability is improved and retention is excellent. The Tg of a commonly used cellulose ester film containing a low molecular weight plasticizer is, for example, a cellulose triacetate film having a degree of acetyl substitution of 2.88, 8.5 mass% of triphenyl phosphate (TPP) as a plasticizer and The Tg of the cellulose triacetate film to which 2% by mass of ethyl phthalylethyl glycolate (EPEG) was added was 164 ° C., which was 36 ° C. lower than that without addition, and although the moisture permeability was small,
The dimensional stability under high-temperature and high-humidity conditions deteriorates (shrinkage increases), and the retention property also deteriorates. If the polymer useful in the present invention is added in the same amount as the low-molecular plasticizer, the effect of reducing the moisture permeability is smaller than the addition of the low-molecular plasticizer, but the polymer useful in the present invention may be added in an increased amount. The moisture permeability can be reduced without affecting other properties. However, when it is not possible to add a large amount of the polymer, a low-molecular plasticizer may be mixed to such an extent that no trouble occurs in the process or the retention property is not deteriorated. 0.1 to 4.0% by mass is preferable, and more preferably 0.5 to 3.0% by mass.
The low-molecular plasticizer that can be added to the present invention is not particularly limited, but a phosphate ester plasticizer, a phthalate ester plasticizer, a glycolate plasticizer, or the like can be preferably used. Phosphate ester plasticizers such as the above-mentioned triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc., and phthalate ester plasticizers such as diethyl phthalate Dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl benzyl phthalate, dibenzyl phthalate, butyl phthalyl butyl glycolate as a glycolate plasticizer, ethyl phthalyl ethyl glycoate Rate, methylphthalylethyl glycolate and the like can be preferably used. These plasticizers can be used alone or in combination of two or more.

The polymer useful in the present invention is contained in a cellulose ester film so that the above Tg difference is 20%.
By being within ° C, the present invention has excellent compatibility with the cellulose ester, no contamination of the film, excellent transparency and dimensional stability, excellent retention, and excellent cellulose ester film having a small moisture permeability, that is, A protective film for a polarizing plate is obtained.

As measures of dimensional stability, there are irreversible ones and reversible ones. The former is the expansion ratio, and the latter is the coefficient of hygroscopic expansion and the coefficient of thermal expansion. The former expansion and contraction ratio has been described above.

As an important measure of reversible dimensional stability,
There is a hygroscopic expansion coefficient. The coefficient of hygroscopic expansion β is a change in dimensions per 1% of relative humidity, and indicates whether the film has a large or small change due to a change in humidity. As the film expands and contracts, a force is generated. In a laminate having a three-layer structure such as a cellulose ester film / a polarizing film / a cellulose ester film, as in a polarizing plate, the polarizing film in the middle layer is a uniaxially stretched polyvinyl alcohol film which has high water absorption and is stretched by moisture. The power is relaxed and the force to shrink works. As the film thickness of the polarizing plate protective film attached to the polarizing film becomes thinner, it cannot withstand the force of shrinking of the polarizing film and tends to be deformed. In the present invention, the coefficient of hygroscopic expansion is 6 × 10 ⁻⁵ (1
/% RH) or less, preferably 3 × 10 ⁻⁵ (1
/% RH) or less, more preferably 1 × 10 ^−5.
(1 /% RH) or less. Since the protective film for a polarizing plate of the present invention has a small hygroscopic expansion coefficient even at a humidity that shrinks the polarizing film, the dimensional change is small and the Tg is smaller than that of the polarizing plate protective film containing a low molecular weight plasticizer. The present inventor believes that the film has a high elastic modulus and is hardly deformed against the force of the polarizing film to shrink. Since the protective film for a polarizing plate of the present invention contains a polymer useful in the present invention, it can reduce moisture permeability and suppress the invasion of moisture into the polarizing film, so that the polarizing plate is further deformed very much. Become smaller.

Here, the coefficient of hygroscopic expansion β (1 /% RH) is expressed by the following equation. In the following, L ₄ is the length (mm) of the film sample when the relative humidity (RH ₄ ) is changed to 23 ° C., and L ₀ is the original size of the film sample in the standard state (23 ° C., 55% RH). mm), RH ₀ is the standard relative humidity (% RH), and RH ₄ is the relative humidity (% RH) changed as described above.

Β = {(L ₄ −L ₀ ) / L ₀ } / (RH ₄ −RH ₀ ) In the present invention, the retention is related to the elasticity at high temperature and high humidity, and is precipitated and volatilized from the inside of the film to the outside. Alternatively, it is related to the amount of the evaporated component. The retention is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less.

Another measure of dimensional stability is the coefficient of thermal expansion. This means that the sample is TMA / SS6100 (S
eiko Instrument Inc. ), And the measured load is 50, 100,
The thermal expansion rate is measured by changing the temperature at a rate of 2 (° C./min) and a temperature in the range of 60 to 100 ° C. with three loads of 150 g at each load and obtaining the approximate straight line by the least square method. Then, the value at a load of 0 g is calculated, and the coefficient of thermal expansion is measured.
Since the liquid crystal image display device is also installed at the dashboard of the automobile, it may be considerably heated in a summer sunshine place and may be thermally expanded and deformed. The smaller the coefficient of thermal expansion, the better, and preferably 5 × 10 ⁻⁵ (1 / ° C.) or less.

The polarizing plate protective film and other films used in the liquid crystal image display device contain an ultraviolet absorber, and the ultraviolet absorber plays a role in preventing deterioration of the liquid crystal and the polarizing film when used outdoors. . Also in the present invention, an ultraviolet absorber is preferably used. UV absorber wavelength 370nm
Excellent performance of absorbing the following ultraviolet rays and wavelength of 400n
Those that absorb as little as possible visible light of m or more are preferably used. In particular, the transmittance at a wavelength of 370 nm is 10%.
It is necessary to be not more than 5%, preferably not more than 5%, more preferably not more than 2%. In the present invention, examples of the ultraviolet absorber that can be used include oxybenzophenone-based compounds, benzotriazole-based compounds, salicylate-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, nickel complex-based compounds, and the like. Benzotriazole-based compounds with little coloring are preferred. Benzotriazole-based UV absorbers and benzophenone-based UV absorbers having light stability are preferred, and benzotriazole-based UV absorbers with less unnecessary coloring are particularly preferred. For example, TINUVIN109 manufactured by Ciba Specialty Chemicals Co., Ltd.
(UV-1), TINUVIN171, TINU
VIN326, TINUVIN327, TINUVIN
328 or the like can be preferably used. However, depending on the amount of the low molecular ultraviolet absorber used, the low molecular ultraviolet absorber may precipitate or evaporate on the web during film formation similarly to the plasticizer. %.

In the present invention, a high molecular weight UV absorber which is less likely to precipitate than the above low molecular weight UV absorber is used.
It is more preferable that the polymer is contained in the cellulose ester film together with the polymer according to the present invention. Can be cut. As the polymeric ultraviolet absorber useful in the present invention, the polymeric ultraviolet absorber described in JP-A-6-148430 and a polymer containing an ultraviolet absorbent monomer can be used without limitation. Commercially available UV absorber monomers include 1- (2-benzotriazole) -2-hydroxy-5- (2-vinyloxycarbonylethyl) benzene of UVM-1, a reactive UV absorber RUVA manufactured by Otsuka Chemical Co., Ltd. -93 1- (2-benzotriazole) -2-hydroxy-5- (2-methacryloyloxyethyl) benzene or analogs thereof. A polymer or copolymer obtained by homo- or copolymerization of these is also preferably used, but is not limited thereto.
For example, as a commercially available polymer ultraviolet absorber, PUVA-30M manufactured by Otsuka Chemical Co., Ltd. is also preferably used. In the present invention, the amount of the polymeric ultraviolet absorber used is not uniform depending on the type of the compound and the conditions of use, but is preferably 0.5 to 6.0% by mass based on the cellulose ester film. Two or more ultraviolet absorbers may be used. As a method of adding the ultraviolet absorber to the dope, the ultraviolet absorber may be added after dissolving the ultraviolet absorber in an organic solvent such as alcohol, methylene chloride, dioxolan, or methyl acetate, or may be directly added to the dope composition.

Examples of polymerization of polymers mainly containing polyesters, polyester ethers and vinyl esters particularly useful in the present invention are shown below.

(Polymerization Example of Polyester, Polymerization of PE-1) A 1-liter three-necked flask was equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a water removal tube. The water removal pipe is a fractionation pipe,
A head thermometer, a cooling pipe, and a water receiver with a scale (ml) are provided below the cooling pipe, and the receiver has an exhaust pipe at the top. 180 g of propylene glycol and 292 g of adipic acid are put in a flask, and the internal temperature is heated to 80 to 90 ° C. while slowly flowing nitrogen gas, and stirring is started. Raise the temperature to 150-160 ° C over 1 hour. At this time, the head temperature does not exceed 100 ° C. (only water is distilled out of the system and glycol is not distilled out), water is discharged, and the temperature is further increased to 190 to 200 ° C.
When 58 g of water was distilled, the internal temperature was adjusted to 110 to 1
The temperature was lowered to 20 ° C and further to 80 ° C. The precipitate was collected by acetone, the precipitate was collected by filtration, and the molecular weight of PE-1 was measured by GPC. As a result, the weight average molecular weight was 600.

(Polymerization Example of Polyester, Polymerization of PE-2 to 6) PE-2 to 6 were obtained in the same manner as for PE-1 by changing the amount of distilled water. The weight average molecular weight was as follows. The values in parentheses below are weight average molecular weights. PE-2 (980), PE-3 (180
0), PE-4 (4800), PE-5 (350), P
E-6 (5500).

(Polymerization Example of Polyester Ether, PEE
Except for the 1.5 liter flask, the same apparatus as used for the polymerization of PE-1 was used, and 460 g of polyethylene glycol (PEG) (weight average molecular weight 250),
46 g of adipic acid was added, and polymerization was carried out in the same manner as in PE-1 while slowly flowing nitrogen gas. When 32 g of water was distilled off, the temperature was lowered, and filtration was carried out in the same manner to obtain PEE-1. As a result of measuring the molecular weight of PEE-1 by GPC, the weight average molecular weight was 650.

(Polymerization Example of Polyester Ether, PEE
-2-4 polymerization) By changing the amount of distillate water,
PEE-2 to 6 were obtained in the same manner as in PEE-1. However, the weight average molecular weight of PEG was changed as follows. The numbers in parentheses below are PEG in the first half and PEE in the second half.
Is the weight average molecular weight. PEE-2 (400, 100
0), PEE-3 (875, 1900), PEE-4
(2500, 5200).

(Polymerization Example of Polyvinyl Acetate, Polymerization of PV-1) A three-necked flask equipped with a stirrer, a cooling tube, a nitrogen inlet tube, and a monomer inlet tube was prepared. The flask was placed in a flask, and 100 ml of dehydrated tetrahydrofuran was added thereto while introducing and mixing and dissolving the mixture. Then, nitrogen was further introduced for 5 minutes to replace the inside of the vessel with nitrogen. To this solution, dehydrated tetrahydrofuran containing 2 mg of 2,2'-azobisisobutyronitrile was introduced into a flask, and refluxed at 50 ° C. for 3 hours to carry out polymerization. A small amount of a solution of nitrobenzene in tetrahydrofuran is used as a polymerization inhibitor to terminate the polymerization. After the polymerization reaction, unreacted vinyl acetate monomer is distilled off together with tetrahydrofuran while blowing steam into the tetrahydrofuran solution. When the temperature of the distillate reached the boiling point of tetrahydrofuran of 65 ° C., the expelling was completed, the content of polyvinyl acetate was taken out, purified, and the weight average molecular weight was measured by GPC.
00.

(Example of polymerization of polyvinyl acetate, polymerization of P-2 to 5) Polymerization and purification were carried out in the same manner as for PV-1, except that the timing of adding the polymerization inhibitor nitrobenzene was changed.
PV-2 to PV-4 having different weight average molecular weights were obtained. The values in parentheses are weight average molecular weights. PV-2 (60000), P
V-3 (15000), PV-4 (7000), PV-
5 (3000).

Further, examples of polymerization of a high-molecular ultraviolet absorber useful in the present invention are shown below. (Polymerization example of high-molecular ultraviolet absorber, polymerization of UVP-1)
57.6 g of VM-1 and 43.1 of vinyl acetate monomer
g, mixed into 200 ml of the same three-necked flask as the PV-1.
After dissolving in 0 ml, nitrogen was flowed through the solution for 5 minutes to replace the air in the flask with nitrogen. To this solution was added a solution of 2 mg of 2,2'-azobisisobutyronitrile in dehydrated tetrahydrofuran, and the mixture was heated under reflux at 50 ° C. for 3 hours to carry out polymerization. After completion of the polymerization, the reaction solvent was distilled off under reduced pressure, and then precipitated with acetone. The precipitate was collected by filtration to obtain 90 g of UVP-1. As a result of measuring the molecular weight of UVP-1 by GPC,
The number average molecular weight was 19,500. The structure of UVP-1 was confirmed by ¹ H-NMR to have a unit ratio of UVM-1 to vinyl acetate monomer of 25:75 (molar ratio).

(Example of polymerization of high-molecular ultraviolet absorber, UVP-
Polymerization of 2) 57.6 g of PUVA-93 and 43.1 g of methyl acrylate monomer were mixed and placed in a similar 300 ml three-necked flask, dissolved in 200 ml of dehydrated tetrahydrofuran under introduction of nitrogen, and nitrogen was flowed into the solution for 5 minutes. The air in the flask was replaced with nitrogen. 2,
A solution of 37 mg of 2'-azobisisobutyronitrile in dehydrated tetrahydrofuran was added, and the mixture was heated under reflux at 50 ° C. for 3 hours to carry out polymerization. After completion of the polymerization, the reaction solvent was distilled off under reduced pressure, and then precipitated with acetone. The precipitate is collected by filtration, and UVP-
90 g were obtained. As a result of measuring the molecular weight of UVP-2 by gel permeation chromatography (GPC), the number average molecular weight was 16,800. UVP-
The structure of ^No. 2 was confirmed by ¹ H-NMR to have a unit ratio of RUVM-93 to a methyl acrylate monomer of 24:76 (molar ratio).

Further, the cellulose ester film of the present invention may contain an antioxidant. For example, it may contain a peroxide decomposing agent, a radical chain inhibitor, a metal deactivator or an acid scavenger as described in JP-A-5-1970073. The addition amount of these compounds is 1 pp in mass ratio to the cellulose ester.
m-1.0% is preferable, and 10-1000 ppm is more preferable.

In the present invention, the cellulose ester film preferably contains a fine particle matting agent. Examples of the fine particle matting agent include silicon dioxide,
Titanium dioxide, aluminum oxide, zirconium oxide,
It is preferable to include inorganic fine particles such as calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate and calcium phosphate, and crosslinked polymer fine particles. Among them, silicon dioxide is preferable because the haze of the film can be reduced. The average secondary particle size of the fine particles is 0.01-1.
In the range of 0 μm, the content is preferably 0.005 to 0.3% by mass relative to the cellulose ester. Fine particles such as silicon dioxide are often surface-treated with an organic substance, but such particles are preferable because the haze of the film can be reduced. Preferred organic substances for the surface treatment include halosilanes, alkoxysilanes (especially alkoxysilanes having a methyl group), silazane, siloxane and the like. The larger the average particle size of the fine particles, the greater the matting effect, and the smaller the average particle size, the better the transparency. Therefore, the average primary particle size of the preferred fine particles is 5 to 50 nm, and more preferably 7 to 16 nm. It is.
These fine particles are in the cellulose ester film,
In general, it is preferable to form irregularities of 0.01 to 1.0 μm on the surface of the cellulose ester film which are present as aggregates. AEROSIL 200, 200V, 30 manufactured by Aerosil Co., Ltd.
0, R972, R972V, R974, R202, R8
12, OX50, TT600, etc., preferably AEROSIL 200V, R972, R97
2V, R974, R202, and R812. Two or more of these matting agents may be used in combination. When two or more kinds are used in combination, they can be used by mixing at an arbitrary ratio. In this case, a matting agent having a different average particle size or material, such as AE
ROSIL 200V and R972V in a mass ratio of 0.1:
It can be used in the range of 99.9 to 99.9 to 0.1.

Next, a method for preparing a cellulose ester dope in the present invention will be described. The flake-shaped cellulose ester is dissolved in an organic solvent, mainly a good solvent for the cellulose ester, with stirring in a dissolving vessel to form a dope. The dissolution is carried out at normal pressure, below the boiling point of the main solvent, under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557 or JP-A-9-95538. There are various dissolving methods such as a method of cooling and dissolving as described in JP-A-11-21379, and a method of conducting at a high pressure as described in JP-A-11-21379. After dissolution, the dope is filtered with a filter medium, defoamed, and sent to the next step by a pump. The concentration of the cellulose ester in the dope is about 10 to 35% by mass. More preferably, it is 15 to 25% by mass. In order to incorporate a polymer useful in the present invention into the cellulose ester dope, the polymer may be dissolved in an organic solvent in advance and then added or directly added to the cellulose ester dope. In this case, the polymer is added so that the polymer does not become clouded or phase-separated in the dope. The amount of addition is as described above.

Organic solvents as good solvents for cellulose esters include methyl acetate, ethyl acetate, amyl acetate, ethyl formate, acetone, cyclohexanone, methyl acetoacetate, tetrahydrofuran, 1,3-dioxolan, and 4-methyl-1,3. -Dioxolan, 1,4-dioxane, 2,2,2-trifluoroethanol, 2,
2,3,3-hexafluoro-1-propanol, 1,
3-difluoro-2-propanol, 1,1,1,3,
3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1
-Propanol, nitroethane, 2-pyrrolidone, N-
Examples thereof include methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, methylene chloride, and bromopropane. Of these, methyl acetate, acetone, and methylene chloride are preferably used. However, due to recent environmental problems, non-chlorine organic solvents tend to be more preferable. It is preferable to use a lower alcohol such as methanol, ethanol, or butanol in combination with these organic solvents, because the solubility of the cellulose ester in the organic solvent can be improved and the viscosity of the dope can be reduced. Particularly, ethanol having a low boiling point and low toxicity is preferable. The organic solvent used in the dope according to the present invention is preferably used by mixing a good solvent and a poor solvent of the cellulose ester from the viewpoint of production efficiency, and a preferable range of the mixing ratio of the good solvent and the poor solvent is good. Solvent 70-98
% By mass, and the content of the poor solvent is 2 to 30% by mass. The good solvent and the poor solvent used in the present invention are defined as those which dissolve the cellulose ester used alone as a good solvent and those which do not dissolve alone as a poor solvent. The poor solvent used in the dope according to the present invention is not particularly limited. For example, methanol, ethanol, n-butanol, cyclohexane, acetone, cyclohexanone, and the like can be preferably used. For the polymer useful in the present invention, the organic solvent is preferably selected using a good solvent for the cellulose ester. As described above, when a low-molecular plasticizer is used, it can be performed by a normal addition method, even if it is directly added to the dope, or it is dissolved in an organic solvent and then poured into the dope. Good.

In the present invention, when the various additives as described above are added to the cellulose ester dope, the cellulose ester dope and various additives are added in-line in a solution in which a small amount of the cellulose ester is dissolved, and the mixture is mixed. It is also possible to perform it, which is preferable. For example, Static Mixer SWJ (Toray Stationary In-Pipe Mixer Hi-Mixer)
It is preferable to use an in-line mixer such as (manufactured by Toray Engineering). When using an inline mixer, it is preferable to apply the cellulose ester to a dope in which the cellulose ester is concentrated and dissolved under high pressure, and the type of pressurized container is not particularly limited. I just want to be able.

In the present invention, it is necessary to remove foreign matter, particularly foreign matter that may be recognized as an image in a liquid crystal image display device, by filtering the cellulose ester dope. It can be said that the quality of the protective film for a polarizing plate is determined by this filtration. It is preferable that the filtration material used for filtration has a small absolute filtration accuracy, but if the absolute filtration accuracy is too small, clogging of the filtration material is likely to occur, and the replacement of the filtration material must be performed frequently, which reduces productivity. There is a problem. Therefore, the cellulose ester dope filter medium of the present invention preferably has an absolute filtration accuracy of 0.008 mm or less, more preferably 0.001 to 0.008 mm, and more preferably 0.003 to 0.006 mm. More preferred. There is no particular limitation on the material of the filter medium, and a normal filter medium can be used. However, a filter medium made of a plastic fiber such as polypropylene or Teflon or a metal filter medium such as a stainless steel fiber is preferable because the fibers do not fall off. Filtration of the cellulose ester dope of the present invention can be performed by a usual method, but a method of filtering while heating under pressure at a temperature not lower than the boiling point of the solvent at normal pressure and a range in which the solvent does not boil, before and after filtration The rise in the differential pressure (hereinafter, sometimes referred to as the filtration pressure) is small, which is preferable. The preferred temperature range is 45-1.
20 ° C., more preferably 45 to 70 ° C.
More preferably, it is in the range of 5 ° C. The smaller the filtration pressure, the better. The filtration pressure is preferably 1.6 × 10 ⁶ Pa or less, more preferably 1.2 × 10 ⁶ Pa or less, and even more preferably 1.0 × 10 ⁶ Pa or less. When the raw material cellulose contains a cellulose ester having an unsubstituted or low-substituted acyl group, foreign matter failure (hereinafter sometimes referred to as a luminescent spot) may occur. When the cellulose ester film is placed between two polarizing plates in a crossed state (crossed Nicols), light is irradiated from one side and observed with an optical microscope (50 ×) from the other side. if there is,
This is a phenomenon in which the light is blocked and nothing appears black, but if there is a foreign substance, the light leaks from it and appears to shine like a spot. The greater the diameter of the luminescent spot, the greater the harm when the liquid crystal image display device is used, preferably 50 μm or less, more preferably 10 μm or less, and further preferably 8 μm or less. The diameter of a bright point means a diameter measured by approximating the bright point to a perfect circle. The bright spot is 4 with the above diameter
If the number is not more than 00 pieces / cm ² , there is no problem in practical use.
Pcs / cm ² or less, more preferably 200 pcs / cm ² or less. In order to reduce the number and size of such bright spots, it is necessary to sufficiently filter fine foreign matter. In addition, as described in JP-A-2000-137115, a method in which a pulverized product of a once-formed cellulose ester film is re-added to a dope at a certain ratio and used as a raw material for a cellulose ester and its additive has a bright spot. Since it can be reduced, it can be preferably used.

Next, the step of casting the cellulose ester dope on a metal support, the step of drying on the metal support, and the step of peeling the web from the metal support will be described. The metal support is an endless metal belt or a rotating metal drum that moves infinitely, and its surface is a mirror surface. The casting step is a step in which the above-mentioned dope is fed to a press die through a pressurized metering gear pump, and the dope is cast from the press die onto the metal support at the casting position. Other methods of casting include the doctor blade method of adjusting the film thickness of the cast dope film with a blade, and the method of using a reverse roll coater to adjust the film with a counter-rotating roll. A pressure die that can be formed and is easy to make the film thickness uniform is preferable. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the doping amount may be divided to form a plurality of layers. In order to adjust the film thickness, it is preferable to control the dope concentration, the amount of liquid sent from the pump, the slit gap of the die cap, the extrusion pressure of the die, the speed of the metal support, and the like so as to obtain a desired thickness.

The drying step on the metal support is a step of heating the web (the web is called a dope film after casting on the metal support) on the support to evaporate the solvent. To evaporate the solvent, there are a method in which heated air is blown from the web side and the back side of the support, a method in which heat is transferred from the back side of the support by a heating liquid, and a method in which heat is transferred from the front and back sides by radiant heat. A method of combining them is also preferable. In addition, if the thickness of the web is thin, drying is quick. The temperature of the metal support may be the same as a whole or different depending on the position.

In the method of drying on a metal support suitable for the present invention, for example, the casting is preferably performed at a metal support temperature of 0 to 40 ° C., preferably 5 to 30 ° C. The drying air applied to the web is preferably about 30 to 45 ° C., but is not limited thereto.

The peeling step is a step in which the organic solvent is evaporated on the metal support and the web is peeled before the metal support makes one round, and then the web is sent to a drying step. The position at which the web is peeled off from the metal support is referred to as a peeling point, and the roll that assists peeling is referred to as a peeling roll. Although it depends on the thickness of the web, if the residual solvent amount of the web at the peeling point (the following formula) is too large, it is difficult to peel off. Conversely, if the web is sufficiently dried on the support and then peeled off, the web May be peeled off. Usually, the web is peeled when the amount of the residual solvent is 20 to 150% by mass. In the present invention, the preferable amount of the peeling residual solvent is 20 to 40% by mass.
Or 60 to 120% by mass, particularly preferably 20 to 3% by mass.
0% by mass or 70 to 115% by mass. As a method for increasing the film forming speed (the film forming speed can be increased because the film is peeled off while the amount of the residual solvent is as large as possible), there is a gel casting method in which the film can be peeled even when the amount of the residual solvent is large. Examples of the method include a method in which a poor solvent for the cellulose ester is added to the dope, gelling is performed after casting the dope, and a method in which gelling is performed by lowering the temperature of the support. There is also a method of adding a metal salt to the dope.
By gelling on the support to strengthen the film, separation can be accelerated and the film forming speed can be increased. If the web is peeled off at a point where the residual solvent amount is larger, if the web is too soft, the flatness at the time of peeling will be impaired, or shear and vertical streaks will easily occur due to peel tension, and the residual solvent amount will be determined based on the balance between economic speed and quality. Can be

The amount of the residual solvent used in the present invention can be represented by the following formula. Residual solvent amount (% by mass) = {(M−N) / N} × 100 where M is the mass of the web at any time, and N is M
The mass when dried at 0 ° C. for 3 hours.

In the drying step of the cellulose ester film, the film peeled from the support is further dried to reduce the residual solvent content to 2.0% by mass or less, more preferably 1.0% by mass or less. More preferably,
It is 0.5% by mass or less.

In the web drying step, there is a roll drying apparatus in which the rolls are arranged in a staggered manner, and a method in which the web is dried while being conveyed by a tenter drying apparatus which holds the width of the web with clips and stretches the web slightly in the width direction. Taken. In the present invention, it is particularly preferable that the dimensional stability can be improved by maintaining or stretching the width in an optional step after peeling from the support of the tenter drying apparatus or in an area where the amount of the residual solvent is large. The means for drying the web is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, a microwave, or the like. It is preferable to use hot air in terms of simplicity. The drying temperature is preferably increased stepwise in the range of 40 to 150 ° C, and more preferably in the range of 50 to 140 ° C in order to improve dimensional stability.

It is preferable that the thickness of the cellulose ester film is thinner because the resulting polarizing plate becomes thinner and the thinning of the liquid crystal display is facilitated. The film thickness of the cellulose ester film that balances these is 10 to 65 μm.
Is preferably 20 to 60 μm, more preferably 35 to 5 μm.
0 μm is particularly preferred.

The cellulose ester film of the present invention comprises
It is preferably used for a liquid crystal display member because of its high moisture permeability and dimensional stability. 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, a non-reflective film, and charging. Prevention films and the like. Among the above descriptions, it is preferable to use it for a polarizing plate and a protective film for a polarizing plate.

As the polarizing plate, a protective film for a polarizing plate formed of a cellulose ester film was formed at 40 ° C. by 2.5 mol / mol.
The surface was saponified with 1 l of an aqueous sodium hydroxide solution for 60 seconds, washed with water for 3 minutes, and dried. Separately, polyvinyl alcohol having a thickness of 120 μm was mixed with 1 part by mass of iodine and 4 parts of boric acid.
Immersed in 100 parts by mass of an aqueous solution containing
A polarizing film stretched in the vertical direction is prepared, and a cellulose ester film subjected to the surface saponification treatment is attached to both sides of the polarizing film using a 5% by mass aqueous solution of completely saponified polyvinyl alcohol as an adhesive to prepare a polarizing plate.

The smaller the retardation R ₀ (nm) in the in-plane direction of the cellulose ester film, which is the protective film for a polarizing plate of the present invention, the better, preferably 100 nm or less, more preferably 10 nm or less. More preferably, it is 5 nm or less. Further, the polarizing protection (corresponding to the longitudinal direction) film forming direction of the cellulose ester film of the film for plate and the angle theta ₁ is 0 ° and the slow axis of the present invention, preferably as close to + 90 ° or -90 °. Here, θ ₁ is a narrow angle formed between the film forming direction and the slow axis, and is in a range of + 90 ° to −90 °. By doing so, the degree of polarization of the polarizing plate using the protective film for a polarizing plate of the present invention is improved. Here, the slow axis is the direction in which the refractive index in the film plane is highest. More preferably, θ ₁ and the in-plane retardation R ₀ have the following relationship.

P ≦ 1−sin ² (2θ ₁ ) × sin ² (πR ₀ / λ) Here, when P is 0.999, it is preferable that θ ₁ and R ₀ satisfy the above expression, more preferably P is 0.9995
It is preferable to satisfy the above equation in theta ₁ and R ₀ is when it is preferable to satisfy the theta ₁ and R ₀ is the above formula, more preferably P is 0.9998 when it is, more preferably P is 0.9
When P is 999, more preferably 0.99995, even more preferably 0.99998, particularly 0.99999, it is preferable that θ ₁ and R ₀ satisfy the above formula. λ represents the wavelength of light at the time of three-dimensional refractive index measurement for obtaining θ ₁ and R ₀ ,
It is in the range of 80-650 nm. Preferably λ is 590
It is preferable that the above formula be satisfied when nm is satisfied, and more preferable that the above formula be satisfied when λ is 400 nm.

The protective film for a polarizing plate of the present invention preferably has a light transmittance (of visible light) of 90% or more, more preferably 95% or more, and even 9%, even after the saponification treatment.
It is preferably at least 4%, and the haze is preferably less than 1%, more preferably less than 0.5%,
More preferably, it is less than 0.1%. Most preferably, it is 0%.

[0094]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to Examples, but the present invention is not limited thereto.

Example 1 (Samples 1 to 12) (Preparation of dope solution) TAC (raw material: linter, degree of acetyl group substitution 2.88) 160 parts by mass Polyester (type and amount relative to film as shown in Table 1) AEROSIL 200V 0.1 parts by mass PUV-1, PUV-2 or UV-1 (type and amount are added to the film as shown in Table 1) Methylene chloride 770 parts by mass Ethanol 65 parts by mass The composition was put into a closed container and dissolved with stirring to prepare a cellulose ester dope.
Using a filter paper of 05 mm, filtration flow rate 300 l / m ² · hour,
The filtration pressure was 1.0 × 10 ⁶ Pa. (Casting and drying) The dope was cast on a stainless steel belt through a die, and the temperature of the stainless steel belt was adjusted to 25%.
° C, and a 45 ° C wind is obliquely applied from the web side at a wind speed of 10 m / sec. At the part where the stainless steel belt is on the lower side, the first half is vertically blown by a 40 ° C wind at 10 m / sec. The web was dried, and the solvent was evaporated until the amount of the residual solvent in the web became 25% by mass. Thereafter, the web is dried at 60 ° C. with a roll drier arranged in a staggered manner, and then introduced into a tenter dryer as described in JP-A-62-115035, and the web is held at 90 ° while maintaining the width. ~ 1
Dried at 10 ° C. Finally, roll drying device again 110
Dry at １３０130 ° C., finally cool to 20 ° C., take up, thickness as shown in Table 1
A μm cellulose triacetate film was obtained.

Example 2 (Samples 13 to 16) (Preparation of Dope) CAP (raw material: linter, degree of acetyl group substitution 2.00, degree of propionyl group substitution 0.80) 160 parts by mass polyester ether (described in Table 1) AEROSIL 200V 0.1 parts by mass PUV-1 (Types and amounts are added to the film as shown in Table 1) Methyl acetate 770 parts by mass Ethanol 65 parts by mass A dope was prepared in the same manner as in Example 1. (Casting and drying) Using the dope obtained above, Example 1
Casting was performed in the same manner as in Example 1, and drying was performed in the same manner as in Example 1 to obtain cellulose acetate propionate films of Samples 13 to 16 having a film thickness of 40 μm.

Example 3 (Samples 17 to 21) (Preparation of dope) TAC (raw material: linter, degree of acetyl group substitution 2.88) 160 parts by mass Vinyl acetate polymer (type and amount as shown in Table 1 were used for film) AEROSIL R972V 0.1 parts by mass PUV-1 or 2 (type and amount are added to the film as shown in Table 1) Methylene chloride 770 parts by mass Ethanol 65 parts by mass A dope was prepared in the same manner as described above. (Casting and drying) Using the dope obtained above, Example 1
Casting was performed in the same manner as described above, and drying was performed in the same manner as in Example 1 to obtain cellulose triacetate films of Samples 17 to 21 having a film thickness of 40 μm.

Example 4 (Samples 22 to 27) TAC (raw material: linter, degree of acetyl group substitution 2.88) 160 parts by mass PE-1 (add the amount shown in Table 1 to the film) AEROSIL 200V UV -1 and PUV-1 (The amount described in Table 1 is added to the film) Low molecular weight plasticizer (The amount described in Table 1 is added to the film) Methylene chloride 770 parts by mass Ethanol 65 parts by mass A dope was prepared in the same manner as in Example 1. (Casting and drying) Using the dope obtained above, Example 1
Casting was carried out in the same manner as in Example 1, and drying was carried out in the same manner as in Example 1 to obtain cellulose triacetate films of Samples 22 to 27 having a film thickness of 20 μm and 40 μm.

[0099]

[Table 1]

The samples 1 to 27 of Examples 1 to 4 were measured and evaluated for Tg difference, dirt on the film, elasticity, moisture permeability, coefficient of hygroscopic expansion, retention, and ultraviolet transmittance as described below. The results are shown in Table 2. [Evaluation / Measurement Method] <Stained film after film formation> Cut the cellulose ester film after film formation to 1 m in length, keeping the width, and arrange three fluorescent lamps for the sample. The number of stains in the entire area is counted by reflecting or transmitting the light through a fluorescent lamp, and the number of stains is classified and evaluated as follows.
At this time, the size of the stain is also measured with a loupe.

A: No dirt B: 1 to 3 dirts of 10 μm or less C: Within 3 dirts of 10 μm or less, 1 to 3 dirts of 11 to 20 μm D: 7 to 7 including large and small There are 20 E: There are 21 or more including large and small.

<Dimensional stability: measurement of expansion ratio (S50h)> 30 m each in the casting direction and the width direction of the film.
Three test pieces of m width × 120 mm length are collected. Holes of 6 mmφ are punched at both ends of the test piece at 100 mm intervals. This is conditioned in a room at 23 ± 3 ° C. and 55 ± 5% RH for 5 hours or more. Automatic pin gauge (Shinto Kagaku Co., Ltd.)
Ltd.) is used to measure the full size hole distance (L ₀₎ to the minimum scale 1/1000 mm. Next, the test piece was heated to 80 ° C.
After heat treatment for 50 hours hung in a thermo-humidistat of RH 90%, 23 ± 3 ℃ , 55 ± 5% RH in the room at 5 hours or more moisture adjustment, the dimensions of the hole distance after heat treatment the (L ₂₎ Measure with an automatic pin gauge. Then, the expansion and contraction ratios in the casting direction and the width direction are calculated on the basis of the above formulas on the average of three samples.

The expansion ratio S50h (%) = ｛(L ₂ −L ₀ ) /
L ₀ ｝ × 100 <Dimensional stability: measurement of difference in expansion and contraction ratio (S100h-S24h)> Similar to the measurement of the expansion and contraction ratio S50h, the sample in the casting direction and the width direction of the film was measured at 23 ° C. and 55% RH. Then, the test piece was suspended in a thermo-hygrostat at 80 ° C. and 90% RH and allowed to stand for 24 hours.
After adjusting the humidity for 5 hours or more in a room of 5% RH, measure the distance between the punches after heat treatment with an automatic pin gauge to obtain the expansion / contraction ratio S24h, and suspend the test piece in the room again in a constant temperature and humidity chamber at 80 ° C. and 90% RH. After leaving for 76 hours (total 100 hours), 2
After humidity control for more than 5 hours in a room of 3 ± 3 ° C and 55 ± 5% RH,
The dimension of the punch interval after the heat treatment is measured with an automatic pin gauge, and the expansion ratio S100h is obtained. The difference between the expansion and contraction ratio S100h and the expansion and contraction ratio S24h (the above formula) is determined by averaging three sheets.

<Measurement of Moisture Permeability> The moisture permeability of each sample was measured according to the method described in JIS Z 0208.

<Dimensional Stability: Measurement of Coefficient of Hygroscopic Expansion> Three samples are taken in the casting direction of the film as test specimens having a width of 30 mm and a length of 220 mm. Holes of 6 mmφ are punched at 200 mm intervals on both ends of three test pieces of each level. These were placed in a room at 23 ± 3 ° C. and 55 ± 5% RH for 5 minutes.
Condition for more than an hour. Automatic pin gauge (Shinto Kagaku Co., Ltd.)
Ltd.) is used to measure the full size hole distance (L ₀₎ to the minimum scale 1/1000 mm. Next, the test specimen is left in a room at 23 ± 3 ° C. and 80 ° C. and 80 ± 5% RH for 5 hours or more, and the dimension (L ₁ ) of the punch interval after the heat treatment in the room is measured with an automatic pin gauge. Then, the coefficient of hygroscopic expansion (average of three sheets) is calculated by the above equation.

<Evaluation of Retention Property> Sample was 10 cm × 10 c
m, cut in an atmosphere of 23 ° C. and 55% RH for 24 hours, and measured for mass at 80 ° C. and 90% RH.
Was left for 2 weeks. The surface of the sample after the treatment was gently wiped, the mass after one day of standing at 23 ° C. and 55% RH was measured, and the retention was calculated by the following method.

Retention (mass%) = {(mass before standing−mass after standing) / mass before standing} × 100 <Measurement of ultraviolet transmittance> Spectrophotome
ter U-3200 (manufactured by Hitachi, Ltd.) was used to measure the spectrum of the film sample, and measured at 380 nm.
Was determined.

[0108]

[Table 2]

(Results) The cellulose ester film to which the polymer according to the present invention was added did not stain the film.
The expansion ratio S50h and the difference between the expansion ratio S100h and S24h, the moisture permeability, the coefficient of hygroscopic expansion, and the retention were also very small, indicating that they were excellent as protective films for polarizing plates. On the other hand, in Sample No. to which a polymer other than the present invention having a low molecular weight was added. 5, no. 16 and No. In the case of Sample No. 21, the moisture permeability was large. 5 also had a large expansion rate. Cellulose ester films containing low molecular weight plasticizers (particularly a combination of TPP and EPEG) were heavily soiled and poor in retention. Also low-molecular plasticizer EPEG
When a small amount of is used, the dirt is not so large and the expansion and contraction rate is small, but the moisture permeability and the coefficient of hygroscopic expansion are large. On the other hand, Sample No. 1 containing a small amount of EPEG and the polymer according to the present invention was added. In No. 22, all the evaluation items were clear, and it was found that addition of a small amount of a low-molecular plasticizer was possible.

[0110]

As described above, a cellulose ester film having various resistances can be provided as a protective film for a polarizing plate.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C08L 1/10 C08L 1/10 G02F 1/1335 510 G02F 1/1335 510 // (C08L 1/10 (C08L 1/10 67:00) 67:00) (C08L 1/10 (C08L 1/10 31:02) 31:02) B29K 1:00 B29K 1:00 B29L 7:00 B29L 7:00 F term (reference) 2H049 BB13 BB14 BB23 BB33 BB37 BB62 BC09 BC14 BC22 2H091 FA08X FA08Z LA02 LA06 4F071 AA09 AA28 AA43 AA44 AC07 AC12 AE05 AF10 AH12 BB02 BC01 4F205 AA01K AA24 AA32 AB14 AE10 AG01 AH42 GA02 CF02 GF02 CF02 GF02 GQ00

Claims (19)

[Claims] 1. A film in a casting direction or a width direction in a normal temperature and normal humidity atmosphere of 23 ± 3 ° C. and 55 ± 3% RH is defined as L ₀ (mm), and 80 ± 3 ° C. and 90 ± 3% RH. After leaving for 50 hours in a high-temperature, high-humidity atmosphere, and when the dimensions when returned to the normal-temperature, normal-humidity atmosphere are L ₁ (mm), the expansion and contraction ratio (S50h) of the following formula is determined in the casting direction and the width direction. Both are ± 0.
It is within 3%, and moisture permeability of 250g / m ² · 24h
A protective film for a polarizing plate, comprising: S50h (%) = {(L ₁ −L ₀ ) / L ₀ } × 100 2. The expansion and contraction ratio (S50h) is ± 0.1% in each case.
The protective film for a polarizing plate according to claim 1, wherein: 3. A film in a casting direction or width direction in an atmosphere of normal temperature and normal humidity of 23 ± 3 ° C. and 55 ± 3% RH is defined as L ₀ (mm), and 80 ± 3 ° C. and 90 ± 3% RH. After leaving for 24 hours and 100 hours in a high-temperature, high-humidity atmosphere, and then returning to the normal-temperature, normal-humidity atmosphere for 24 hours, the dimension is defined as L ₂ (mm). ₃ (mm), the difference between the stretch ratio (S100h) of the film left for 100 hours and the stretch ratio (S24h) of the film left for 24 hours in the following formula is ± 0.1% in both the casting direction and the width direction. Within 250g / m ²
-A protective film for a polarizing plate, which has a length of 24 hours or less. S24h (%) = {(L 2 -L 0) / L 0} × 100 S100h (%) = {(L 3 -L 0) / L 0} × 100 4. The protective film for a polarizing plate according to claim 1, wherein the moisture permeability is 200 g / m ² · 24 h or less. 5. A protective film for a polarizing plate comprising a polymer in a cellulose ester film, wherein the polymer is selected from polyester and polyester ether, wherein the polymer has a weight average molecular weight of 400 to 5000, and The glass transition point of the cellulose ester film containing the polymer is 2 points lower than that of the cellulose ester film not containing any additives.
A protective film for a polarizing plate, which does not fall below 0 ° C. 6. The protective film for a polarizing plate according to claim 5, wherein the polymer selected from polyester and polyester ether has a weight average molecular weight of 400 to 2,000. 7. The protective film for a polarizing plate according to claim 5, comprising 5 to 30% by mass of a polymer selected from polyester and polyester ether. 8. A protective film for a polarizing plate containing a polymer in a cellulose ester film, wherein the polymer is a homopolymer or a copolymer containing a vinyl ester, and the polymer has a weight average molecular weight of 5,000 to 150,000. And the glass transition point of the cellulose ester film containing the polymer is 2 times lower than that of the cellulose ester film containing no additives.
A protective film for a polarizing plate, which does not fall below 0 ° C. 9. The protective film for a polarizing plate according to claim 8, wherein the homopolymer or copolymer containing a vinyl ester has a weight average molecular weight of 10,000 to 80,000. 10. The protective film for a polarizing plate according to claim 8, wherein a homopolymer or a copolymer containing a vinyl ester is contained in an amount of 5 to 45% by mass. 11. The protective film for a polarizing plate according to claim 5, wherein the cellulose ester film contains a polymer ultraviolet absorber. 12. A high-molecular ultraviolet absorber in an amount of 0.5 to 6.0.
The protective film for a polarizing plate according to claim 11, wherein the protective film is contained by mass%. 13. The protective film for a polarizing plate according to claim 5, wherein the cellulose ester is cellulose triacetate or cellulose acetate propionate. 14. The protective film for a polarizing plate according to claim 5, wherein the dried cellulose ester film has a thickness of 10 to 65 μm. 15. A film in a casting direction or a width direction in an atmosphere of normal temperature and normal humidity of 23 ± 3 ° C. and 55 ± 3% RH is defined as L ₀ (mm), and 80 ± 3 ° C. and 90 ± 3% RH.
After leaving for 50 hours in a high-temperature, high-humidity atmosphere, and when the dimensions when returned to the normal-temperature, normal-humidity atmosphere are L ₁ (mm), the expansion and contraction ratio (S50h) of the following formula is determined in the casting direction and the width direction. Both ±
Is within 0.3%, and moisture permeability of 250g / m ² · ²
The protective film for a polarizing plate according to any one of claims 5 to 14, wherein the length is 4 hours or less. S50h (%) = {(L ₁ −L ₀ ) / L ₀ } × 100 16. The expansion ratio (S50h) is ± 0.1
%. The protective film for a polarizing plate according to claim 15, wherein 17. Room temperature and normal temperature of 23 ± 3 ° C. and 55 ± 3% RH
In the direction of film casting or width in a humid atmosphere
Dimension L₀(Mm), 80 ± 3 ° C, 90 ± 3% RH
After leaving for 24 hours and 100 hours in a high temperature and high humidity atmosphere,
After returning to the normal temperature and normal humidity atmosphere for 24 hours,
Dimension L_Two(Mm), and the dimensions left for 100 hours
To L_Three(Mm) and left for 100 hours with the following formula
The stretch ratio of the film (S100h) and the film left for 24 hours
What is the difference in film stretching ratio (S24h)?
All are within ± 0.1% and have a moisture permeability of 250 g / m
^Two· It is 24 hours or less.
7. The protective film for a polarizing plate according to any one of 6. S24h (%) = ｛(L_Two-L₀) / L₀｝ × 100 S100h (%) = ｛(L_Three-L₀) / L₀｝ × 100 18. The method according to claim 15, wherein the water vapor transmission rate is 200 g / m ² · 24 h or less.
Item 6. The protective film for a polarizing plate according to item 1. 19. The coefficient of hygroscopic expansion in the casting direction is 6 × 10 ^−5.
(1 /% RH) or less, The protective film for polarizing plates as described in any one of Claims 5-18 characterized by the above-mentioned.