WO2014148476A1 - Polarizing plate, method for manufacturing polarizing plate, and liquid crystal display device - Google Patents

Abstract

The purpose of the present invention is to provide a polarizing plate that can mitigate uneven display resulting from changes in temperature and humidity, a method for manufacturing the polarizing plate, and a liquid crystal display device provided with the polarizing plate. This polarizing plate has a protective film containing a cellulose ester disposed on at least one surface of a polarizing element, the polarizing plate being characterized in that a maximum value for tanδ is 0.6 or greater when tanδ is obtained by measuring the dynamic viscoelasticity of the protective film at a frequency of 1Hz while the temperature is changed within a range of 25-190˚C, and in that E1/E2 is 1.5 to 3.0 where values of elastic moduli (MPa) for an MD direction and a TD direction during production of the protective film are expressed respectively as E1 and E2, which are obtained through measurement at a temperature of 23˚C and a relative humidity of 55%, E1/E2 being a ratio of elastic moduli for the MD direction and the TD direction.

Description

Polarizing plate, manufacturing method of polarizing plate, and liquid crystal display device

The present invention relates to a polarizing plate provided with a protective film on at least one surface of a polarizer, a method for producing the polarizing plate, and a liquid crystal display device including the polarizing plate.

In liquid crystal display devices, polarizing plates in which a protective film and a retardation film are respectively disposed on both sides of a polarizer using polyvinyl alcohol and iodine are widely used. As the protective film, a cellulose ester film is preferably used because of its excellent transparency and small haze.

In a liquid crystal display device, a transparent substrate used for a liquid crystal cell is thinned according to the needs of a thin liquid crystal screen. As the thickness of the transparent substrate is reduced, display unevenness occurs when the liquid crystal display device returns to room temperature after being placed under high temperature and high humidity.
It is known that the display unevenness occurs because the polarizer of the polarizing plate absorbs moisture under high temperature and high humidity and contracts when returning to room temperature. Although the force at the time of contraction propagates to the liquid crystal cell, the entire liquid crystal cell is bent without being able to withstand the thin transparent substrate. At this time, since the retardation film adjacent to the liquid crystal cell is also bent, stress is applied to the retardation film, the retardation is changed, and display unevenness occurs.

For the problem of display unevenness, it is known that reducing the photoelastic coefficient of the retardation film is effective in improving display unevenness.
Moreover, the method of reducing the force of shrinkage | contraction and suppressing the bending of a liquid crystal cell is proposed by using a cellulose-ester film with a high elasticity modulus as a protective film (for example, refer patent document 1).
There has also been proposed a method in which a cellulose ester film is allowed to contain a styrene / maleic anhydride copolymer to suppress a change in phase difference due to humidity fluctuations (see, for example, Patent Document 2).

However, as the transparent substrate is further thinned, the bending of the liquid crystal cell is also increasing. The conventional method does not sufficiently improve display unevenness, and further improvement has been demanded.

JP 2007-119717 A JP 2007-304376 A

The present invention has been made in view of the above problems and situations, and a solution to the problem is to provide a polarizing plate capable of suppressing display unevenness due to temperature and humidity changes, a method for manufacturing the polarizing plate, and a liquid crystal display device including the polarizing plate. That is.

The present inventors examined a protective film that can reduce the force acting in the absorption axis direction because the polarizer contracts in the absorption axis direction of light. In general, both the polarizer and the protective film are formed and bonded as a long film, and the absorption axis direction of the polarizer and the MD direction of the protective film (Machine Direction, the fluent direction or transport direction of the film in the manufacturing process) coincide. ing. From this, the present inventors considered that the force by which the polarizer contracts can be reduced by increasing the elastic modulus in the MD direction of the protective film, and have reached the present invention.
That is, the subject concerning this invention is solved by the following means.

1. A polarizing plate in which a protective film containing a cellulose ester is disposed on at least one surface of a polarizer,
The maximum value of tan δ obtained when the dynamic viscoelasticity of the protective film is measured at a frequency of 1 Hz while changing the temperature within a temperature range of 25 to 190 ° C. is 0.6 or more,
Value obtained by measuring the elastic modulus (MPa) in the MD direction and the TD direction (Transverse Direction, direction perpendicular to the MD direction) during the production of the protective film in an environment of a temperature of 23 ° C. and a relative humidity of 55%. The polarizing plate is characterized in that the ratio E1 / E2 of the elastic modulus ratio in the MD direction and the TD direction is in the range of 1.5 to 3.0, where E1 and E2 respectively.

2. The protective film is a film stretched in the MD direction;
2. The polarizing plate according to item 1, wherein a stretching ratio in the MD direction is 1.6 times or more.

3. The protective film is a film stretched in the MD direction and the TD direction,
The MD direction stretch ratio is larger than the TD direction stretch ratio, the MD direction stretch ratio is 1.6 times or more, and the TD direction stretch ratio is 1.3 times or more. 2. A polarizing plate according to item 1.

4. The polarizing plate according to any one of Items 1 to 3, wherein the protective film contains a styrene polymer.

5. 5. The polarizing plate according to item 4, wherein the styrenic polymer is a copolymer of a monomer having a hydroxy group and a monomer containing styrene.

6. The polarizing film according to any one of items 1 to 5, wherein the protective film and the polarizer are long films, and are bonded so that the major axis directions thereof coincide with each other. Board.

7. The polarizing plate according to any one of claims 1 to 6, wherein an MD direction of the protective film coincides with an absorption axis direction of the polarizer.

8). A method for producing a polarizing plate in which a protective film is disposed on at least one surface of a polarizer,
Including a production process for producing a protective film containing cellulose ester,
In the production process, the maximum value of tan δ obtained when the dynamic viscoelasticity of the protective film after production is measured at a frequency of 1 Hz while changing the temperature within a temperature range of 25 to 190 ° C. is 0.6 or more. When the values obtained by measuring the elastic modulus (MPa) in the MD direction and the TD direction at the time of film production of the protective film in an environment of a temperature of 23 ° C. and a relative humidity of 55% are expressed as E1 and E2, respectively. A method for producing a polarizing plate, comprising producing the protective film so that the ratio E1 / E2 of the elastic modulus ratio in the MD direction and the TD direction is in the range of 1.5 to 3.0.

9. The manufacturing process includes a process of stretching the protective film in the MD direction during film manufacturing,
The method for producing a polarizing plate according to item 8, wherein the MD magnification is 1.6 times or more.

10. The manufacturing process includes a step of stretching the protective film in the MD direction and the TD direction during film manufacturing,
The stretching ratio in the TD direction is smaller than the stretching ratio in the MD direction, the stretching ratio in the MD direction is 1.6 times or more, and the stretching ratio in the TD direction is 1.3 times or more. The manufacturing method of the polarizing plate of claim | item 8.

11. In the manufacturing process, the protective film is manufactured by a solution casting method using a dope containing the cellulose ester and a styrenic polymer. Any one of Items 8 to 10 The manufacturing method of the polarizing plate of claim | item.

12. 12. The method for producing a polarizing plate according to item 11, wherein the styrenic polymer is a copolymer of a monomer having a hydroxy group and a monomer containing styrene.

13. The polarizer is a long film,
In the manufacturing process, the protective film is manufactured as a long film,
In any one of the eighth to twelfth aspects, the method includes a bonding step of bonding the protective film and the polarizer, which are long films, so that the major axis directions thereof are matched. The manufacturing method of the polarizing plate of description.

14. A liquid crystal display device comprising the polarizing plate according to any one of items 1 to 7 on at least one surface of a liquid crystal cell.

15. The liquid crystal screen composed of the liquid crystal cell is rectangular,
Of the two polarizing plates respectively provided on both surfaces of the liquid crystal cell, any one of the first to seventh items is used as a polarizing plate in which at least the major axis direction of the liquid crystal screen and the absorption axis direction of the polarizer coincide. Item 15. A liquid crystal display device according to item 14, comprising the polarizing plate according to item 1.

16. 16. The liquid crystal display device according to item 15, wherein the polarizing plate in which the major axis direction of the liquid crystal screen coincides with the absorption axis direction of the polarizer is a polarizing plate provided on a front side surface of the liquid crystal cell. .

By the above means of the present invention, it is possible to provide a polarizing plate capable of suppressing display unevenness even when there is a change in temperature and humidity, a method for manufacturing the polarizing plate, and a liquid crystal display device including the polarizing plate.
The present inventors considered that display unevenness due to the contraction of the polarizer can be improved by the following function.
When the temperature changes from high temperature and high humidity to room temperature, the polarizer contracts in the absorption axis direction, but the protective film in the polarizing plate of the present invention has an elastic modulus E1 in the MD direction from an elastic modulus E2 in the TD direction. The stress for the force applied in the MD direction is large. In general, a polarizer and a protective film are bonded as a long film by roll-to-roll, and the MD direction of the protective film and the absorption axis direction of the polarizer coincide with each other. The shrinking force can be greatly reduced by the protective film. As a result, the force propagating from the polarizer to the liquid crystal cell can be reduced enough to withstand even a thin transparent substrate, and the bending of the liquid crystal cell and the retardation film adjacent to the liquid crystal cell can be suppressed. It is speculated that it is possible. If the bending of the retardation film can be suppressed, it is presumed that the change in the retardation, and thus the display unevenness, can be suppressed.

FIG. 6 is a cross-sectional view illustrating an example of a structure of a liquid crystal display device according to an embodiment of the present invention. The figure which represented two polarizing plates each arrange | positioned on both surfaces of the liquid crystal cell of FIG. 1, and a liquid crystal cell hierarchically. Sectional drawing showing the bending of the liquid crystal cell of FIG.

The polarizing plate of the present invention includes a protective film on at least one surface of the polarizer, and the dynamic viscoelasticity of the protective film is measured at a frequency of 1 Hz while changing the temperature within a temperature range of 25 to 190 ° C. The maximum value of tan δ obtained is 0.6 or more, and the elastic modulus (MPa) in the MD direction and TD direction at the time of film production of the protective film is measured in an environment at a temperature of 23 ° C. and a relative humidity of 55%. When the values obtained in this way are expressed as E1 and E2, respectively, the ratio E1 / E2 of the elastic modulus ratio in the MD direction and the TD direction is in the range of 1.5 to 3.0. This feature is a technical feature common to the inventions according to claims 1 to 16.

As an embodiment of the present invention, from the viewpoint of obtaining the value E1 / E2 of the elastic modulus ratio within the above range, the protective film is a film stretched at least in the MD direction, and the stretch ratio in the MD direction is 1.6. It is preferable that it is twice or more. A normal protective film for polarizing plate is often stretched in the TD direction, but in the present invention, it is particularly preferable that the protective film is largely stretched in the MD direction. Further, it is preferable that the film is also stretched in the TD direction.
In order to perform stretching at such a large stretching ratio, it is necessary to adjust the tan δ of the film to 0.6 or more. The protective film preferably contains a styrenic polymer from the viewpoint of obtaining a maximum value of tan δ of 0.6 or more.

As a manufacturing method of the polarizing plate of the present invention, including the manufacturing process for manufacturing the protective film, the manufacturing process is an aspect including a process of stretching the protective film in the MD direction during film manufacturing, It is preferable from the viewpoint of obtaining the ratio E1 / E2 of the elastic modulus ratio within the range.

The polarizing plate of the present invention can be suitably provided on at least one surface of a liquid crystal cell of a liquid crystal display device. Thereby, even if there is a change in temperature and humidity, display unevenness can be suppressed. In the present invention, the protective film having the elastic modulus ratio value E1 / E2 in the range of 1.5 to 3.0 according to the present invention may be installed on the surface of the polarizer farther from the liquid crystal cell. preferable. This is because the surface is easily affected by the external temperature, humidity, and heat of the light source, and the effects of the present invention are more easily exhibited.

Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In the present application, “˜” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

<Polarizing plate>
In the polarizing plate of the present invention, a protective film is disposed on at least one surface of the polarizer.

<Protective film>
The protective film according to the present invention contains a cellulose ester, and the maximum value of tan δ obtained when the dynamic viscoelasticity of the protective film is measured at a frequency of 1 Hz while changing the temperature within a temperature range of 25 to 190 ° C. Is 0.6 or more.

Tan δ is called loss tangent and is defined as tan δ = E ′ / E ″, where E ′ and E ″ represent the storage elastic modulus and loss elastic modulus obtained by measuring the dynamic viscoelasticity of the protective film, respectively. The
δ is a phase difference between the strain generated when a force that vibrates sinusoidally is applied to the sample and the applied force. The real part of the complex elastic modulus, which is the ratio of applied force and strain, is the storage elastic modulus E ′, and the imaginary part is the loss elastic modulus E ″. The storage elastic modulus E ′ and loss elastic modulus E ″ of the protective film are It can be measured by a dynamic viscoelasticity measuring device RSAIII (manufactured by TI Instruments).

Specifically, tan δ is obtained as follows.
The sample is conditioned for 24 hours in an atmosphere at a temperature of 23 ° C. and a relative humidity of 55%. The dynamic viscoelasticity of the sample after humidity control was measured under the following measurement conditions while changing the temperature in a temperature range of 25 to 190 ° C. under 55% RH, and the maximum value of tan δ obtained by the measurement was Ask.
Measuring device: RSAIII (manufactured by TA Instruments)
Sample: width 5 mm, length 50 mm (gap set to 20 mm)
Measurement mode: Tensile mode Measurement temperature: Increased at a rate of 5 ° C / min within a range of 25 to 190 ° C Humidity: 55% relative humidity
Frequency of force applied during measurement: 1 Hz
In addition, when a protective film is extended | stretched and manufactured, the said tan-delta is measured before extending | stretching.

If the maximum value of tan δ of the protective film according to the present invention is 0.6 or more, the protective film can be stretched at a high magnification, and the elastic modulus of the protective film can be easily adjusted to a desired value by stretching.
The maximum value of tan δ of the protective film can be adjusted by selecting the type or amount of plasticizer.

The protective film which concerns on this invention represents the value obtained by measuring the elasticity modulus (MPa) of MD direction at the time of film manufacture and TD direction in the environment of temperature 23 degreeC and relative humidity 55% as E1 and E2, respectively. The ratio value E1 / E2 of the elastic modulus in the MD direction and the TD direction is in the range of 1.5 to 3.0.
The MD direction means the film casting direction when the protective film is produced by the solution casting method, and the film conveying direction when the protective film is produced by the melt casting method. In either case, the MD direction coincides with the major axis direction of the protective film.
The TD direction refers to a direction perpendicular to the MD direction.

Each elastic modulus E1 and E2 can be measured as follows.
The sample is conditioned for 24 hours in an environment of 23 ° C. and 55% RH. According to the method described in JIS K7127, the tensile modulus tester Tensilon RTA-100 (manufactured by Orientec Co., Ltd.) under the same environment as the humidity control, the modulus of elasticity of each sample in the MD direction and TD direction ( MPa). The shape of the sample is type 1 test piece type, and the tensile speed is 10 mm / min.

The protective film according to the present invention has an MD elastic modulus E1 in the range of 3.0 to 7.5 MPa, and an elastic modulus E2 in the TD direction from the viewpoint of obtaining a constant stress with respect to the applied force. It is preferably in the range of 2.0 to 5.0 MPa. More preferably, the elastic modulus E1 in the MD direction is in the range of 5.0 to 7.5 MPa, and the elastic modulus E2 in the TD direction is in the range of 2.2 to 4.0 MPa.
The elastic modulus ratio value E1 / E2 can be adjusted within the above range by selecting the stretching conditions.

(Cellulose ester)
The cellulose ester used in the present invention is a compound obtained by esterifying cellulose.

The cellulose ester is preferably a cellulose acetate having a degree of acetyl group substitution in the range of 2.80 to 2.95 because a film having good hardness and low water absorption is easily obtained. The degree of acetyl group substitution is measured according to ASTM-D817-96.

The number average molecular weight Mn of the cellulose ester is preferably in the range of 125000 to 155000, more preferably in the range of 129000 to 152000, from the viewpoint of increasing the mechanical strength of the resulting film.
From the same viewpoint, the weight average molecular weight Mw of the cellulose ester is preferably in the range of 265,000 to 310000.
The ratio Mw / Mn of the ratio of the number average molecular weight Mn to the weight average molecular weight Mw of the cellulose ester is preferably in the range of 1.9 to 2.1.

The number average molecular weight Mn and the weight average molecular weight Mw of the cellulose ester are measured using gel permeation chromatography (GPC). The measurement conditions are as follows.
Solvent: Methylene chloride Column: Shodex K806, K805, K803G (manufactured by Showa Denko KK) are connected and used Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: A calibration curve with 13 samples of standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation, Mw = 500 to 1000000) is used. Thirteen samples are used at approximately equal intervals.

The cellulose ester according to the present invention can be produced by a known method such as a sulfuric acid catalyst method, an acetic acid method, or a methylene chloride method.
In general, cellulose is esterified by mixing raw material cellulose with carboxylic acid, carboxylic anhydride, catalyst (such as sulfuric acid) and the like. The raw material cellulose is not particularly limited, and may be cotton linter, wood pulp, kenaf or the like. You may mix and use the cellulose ester from which a raw material differs. The esterification reaction proceeds until a cellulose triester is formed. In the triester, the three hydroxy groups of the glucose unit are substituted with an aliphatic carboxylic acid or an acyl acid of an aromatic carboxylic acid. When two types of aliphatic carboxylic acids or aromatic carboxylic acids are used at the same time, mixed cellulose esters such as cellulose acetate propionate and cellulose acetate butyrate can be produced. By hydrolyzing the cellulose triester, a cellulose ester having a desired acyl group substitution degree, for example, a cellulose acetate having an acetyl substitution degree within the above preferred range can be synthesized. Thereafter, a cellulose ester is obtained through steps such as filtration, precipitation, washing with water, dehydration, and drying.
Specifically, it can be synthesized with reference to the methods described in JP-A Nos. 10-45804 and 2005-281645.

(Plasticizer)
The protective film according to the present invention can contain a plasticizer.
The plasticizer used in the present invention is preferably a styrenic polymer because it is easy to obtain a protective film having a maximum value of tan δ of 0.6 or more, and among them, a monomer having a hydroxy group and a monomer containing styrene, It is preferable that it is a copolymer.

As the monomer of the styrene polymer, a styrene monomer having a structure represented by the following general formula (1) can be used.

In the general formula (1), R ¹⁰¹ to R ¹⁰³ each independently represents a hydrogen atom, an alkyl group having 1 to 30 carbon atoms, or an aryl group. R ¹⁰⁴ is a hydrogen atom, an alkyl group having 1 to 30 carbon atoms, a cycloalkyl group, an aryl group, an alkoxy group having 1 to 30 carbon atoms, an aryloxy group, an alkyloxycarbonyl group having 2 to 30 carbon atoms, an aryloxycarbonyl Group, an alkylcarbonyloxy group having 2 to 30 carbon atoms, an arylcarbonyloxy group, a hydroxy group, a carboxy group, a cyano group, an amino group, an amido group or a nitro group. Each of these groups that can be R ¹⁰⁴ may further have a substituent (eg, a hydroxy group, a halogen atom, an alkyl group, and the like). The five R ¹⁰⁴ may be the same or different from each other, and may be bonded to each other to form a ring.

Specific examples of the styrene monomer having the structure represented by the general formula (1) include styrene; alkyl-substituted styrenes such as α-methylstyrene, β-methylstyrene, and p-methylstyrene; 4-chlorostyrene, Halogen-substituted styrenes such as 4-bromostyrene; hydroxystyrenes such as p-hydroxystyrene, α-methyl-p-hydroxystyrene, 2-methyl-4-hydroxystyrene, and 3,4-dihydroxystyrene; vinylbenzyl alcohols Alkoxy-substituted styrenes such as p-methoxystyrene, p-tert-butoxystyrene and m-tert-butoxystyrene; vinylbenzoic acids such as 3-vinylbenzoic acid and 4-vinylbenzoic acid; 4-vinylbenzyl acetate; 4 -Acetoxystyrene; 2-butylamidostyrene, 4-methylamido Amidostyrenes such as styrene and p-sulfonamidostyrene; aminostyrenes such as 3-aminostyrene, 4-aminostyrene, 2-isopropenylaniline, vinylbenzyldimethylamine; 3-nitrostyrene, 4-nitrostyrene, etc. Nitrostyrenes; cyanostyrenes such as 3-cyanostyrene and 4-cyanostyrene; vinylphenylacetonitrile; arylstyrenes such as phenylstyrene; indenes and the like.
The styrenic polymer may be a single homopolymer among the above styrenic monomers, or may be a copolymer in which two or more types are combined.

When the protective film which concerns on this invention contains the said styrenic polymer, when the cellulose ester which is a film base material is orientated by extending | stretching, a styrenic polymer interposes between the polymer chains of the said cellulose ester. Become. The styrene group of the styrenic polymer has a three-dimensionally bulky structure and widens the distance between the polymer chains, so that the interaction between the polymer chains is reduced and the maximum value of tan δ of the protective film is 0.6. It is easy to become the above value.

Among the styrenic polymers, a copolymer of a monomer having a hydroxy group and a monomer containing styrene has high compatibility with the cellulose ester, and the styrenic polymer is uniform between the polymer chains of the cellulose ester. It is preferable because it is easy to be introduced into.
The copolymer of a monomer having a hydroxy group and a monomer containing styrene is a homopolymer of a styrene monomer having a hydroxy group among the styrene monomers having the structure represented by the general formula (1). Alternatively, it may be a copolymer of two or more styrene monomers including at least a styrene monomer having a hydroxy group.
The copolymer of the monomer having a hydroxy group and the monomer containing styrene is a copolymer of a styrene monomer having a structure represented by the general formula (1) and a monomer having a hydroxy group. You can also.
Examples of the monomer having a hydroxy group that can be combined with the styrenic monomer include vinyl alcohol and the like and a compound having a structure represented by the following formula (2).

In the general formula (2), R ¹⁰⁵ to R ¹⁰⁷ each independently represent a hydrogen atom, a carboxy group, or an alkyl group having 1 to 30 carbon atoms or an aryl group which may have a substituent. R ¹⁰⁵ to R ¹⁰⁷ may combine with each other to form a ring. R ¹⁰⁸ represents a hydrogen atom or an alkyl group or aryl group having 1 to 30 carbon atoms, and the alkyl group or aryl group has a hydroxy group or a substituent containing a hydroxy group.

Specific examples of the compound represented by the general formula (2) include (meth) acrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, maleic acid, citraconic acid, cis-1-cyclohexene-1,2-dicarboxylic acid, 3-methyl-cis-1-cyclohexene-1,2-dicarboxylic acid and 4-methyl-cis-1-cyclohexene-1,2-dicarboxylic acid are included.

The content ratio of the structural unit derived from the styrene monomer in the copolymer of the styrene monomer having the structure represented by the general formula (1) and the monomer having the structure represented by the general formula (2). Is preferably in the range of 30 to 80 mol%, more preferably in the range of 50 to 80 mol%, from the viewpoint of compatibility with the cellulose ester.

The content of the styrene polymer in the protective film is not particularly limited, but is preferably in the range of 5 to 30% by mass, and more preferably in the range of 5 to 20% by mass. Within this range, the film can be stretched at a high magnification, and bleeding out can be suppressed.
The weight average molecular weight Mw of the styrene polymer is preferably in the range of 1500 to 12000.

The protective film according to the present invention can contain polyester as a plasticizer.
The polyester that can be used in the present invention contains a repeating unit derived from a condensate of a dicarboxylic acid and a diol.
The repeating unit preferably contains a non-aromatic ring structure or an aromatic ring structure. That is, at least one of the dicarboxylic acid and diol constituting the polyester preferably includes a non-aromatic ring structure or an aromatic ring structure, but more preferably the dicarboxylic acid includes a non-aromatic ring structure or an aromatic ring structure.

The dicarboxylic acid can be an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aromatic dicarboxylic acid.
The carbon number of the aliphatic dicarboxylic acid is preferably 4 to 20, and more preferably 4 to 12.
Examples of the aliphatic dicarboxylic acid include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like.

The carbon number of the aromatic dicarboxylic acid is preferably 8 to 20, and more preferably 8 to 12.
Examples of aromatic dicarboxylic acids include 1,2-benzenedicarboxylic acid (phthalic acid), 1,3-benzenedicarboxylic acid (isophthalic acid), 1,4-benzenedicarboxylic acid (terephthalic acid), 1,5-naphthalene Dicarboxylic acids, 1,4-xylidene dicarboxylic acids and the like are included.

The dicarboxylic acid constituting the polyester may be one type or two or more types.
The dicarboxylic acid constituting the polyester preferably contains an aromatic dicarboxylic acid, and more preferably contains both an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid. The aromatic dicarboxylic acid is particularly preferably 1,4-benzenedicarboxylic acid (terephthalic acid).

The diol can be an aliphatic diol, an alkyl ether diol, an alicyclic diol, or an aromatic diol.
The carbon number of the aliphatic diol is preferably 2 to 20, and more preferably 2 to 12.
Examples of aliphatic diols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-propanediol, 2-methyl- 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl-1,3-propane Diol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentanediol, 1, 6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1 , 10-decanediol, 1,12-oct Decanediol, and the like are included. The carbon number of the alkyl ether diol is preferably 4 to 20, and more preferably 4 to 12. Examples of the alkyl ether diol include polytetramethylene ether glycol, polyethylene ether glycol, polypropylene ether glycol and the like.

The diol constituting the polyester may be one type or two or more types. The diol constituting the polyester preferably contains an aliphatic diol.

Among these, a polyester containing a repeating unit derived from a condensate of a dicarboxylic acid containing an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid and an aliphatic diol has good stretchability and transparency of a film containing the polyester. From this point, it is preferable.

The molecular terminal of the polyester may be sealed with monocarboxylic acid or monoalcohol as necessary.

The monocarboxylic acid can be an aliphatic monocarboxylic acid, an alicyclic monocarboxylic acid or an aromatic monocarboxylic acid.
The carbon number of the aliphatic monocarboxylic acid can be preferably 2-30, more preferably 2-4.
Examples of the aliphatic carboxylic acid include acetic acid, propionic acid, butanoic acid, caprylic acid, caproic acid, decanoic acid, dodecanoic acid, stearic acid, oleic acid and the like. Examples of the alicyclic monocarboxylic acid include cyclohexyl monocarboxylic acid and the like. Examples of aromatic monocarboxylic acids include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid, Phenylacetic acid, 3-phenylpropionic acid and the like are included.

The monoalcohol can be an aliphatic monoalcohol, an alicyclic monoalcohol, or an aromatic monoalcohol.
The aliphatic monoalcohol has 1 to 30 carbon atoms, preferably 1 to 3 carbon atoms.
Examples of aliphatic monoalcohols are methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol, hexanol, isohexanol, octanol, isooctanol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl alcohol , Tert-nonyl alcohol, decanol, dodecanol, dodecahexanol, dodecaoctanol, allyl alcohol, oleyl alcohol and the like. Examples of the alicyclic monoalcohol include cyclohexyl alcohol and the like. Examples of the aromatic monoalcohol include benzyl alcohol, 3-phenylpropanol and the like.

The polyester preferably has a weight average molecular weight Mw in the range of 300 to 3000, more preferably 400 to 2000.
The polyester content in the protective film is preferably in the range of 5 to 30% by mass, more preferably in the range of 5 to 20% by mass. Within this range, the film can be stretched at a high magnification, and bleeding out can be suppressed.

In the protective film according to the present invention, sugar esters other than the above-described cellulose esters can also be used as plasticizers.
The sugar ester that can be used in the present invention is a compound having 1 to 12 furanose structures or pyranose structures, in which all or part of the hydroxy groups in the compound are esterified.
Preferable examples of such sugar esters include sucrose esters represented by the following general formula (FA).

R ₁ to R _{8 in} the general formula (FA) each independently represent a hydrogen atom, a substituted or unsubstituted alkylcarbonyl group, or a substituted or unsubstituted arylcarbonyl group. R ₁ to R ₈ may be the same as or different from each other.
The substituted or unsubstituted alkylcarbonyl group is preferably a substituted or unsubstituted alkylcarbonyl group having 2 or more carbon atoms. Examples of the substituted or unsubstituted alkylcarbonyl group include a methylcarbonyl group (acetyl group). Examples of the substituent that the alkyl group has include an aryl group such as a phenyl group.
The substituted or unsubstituted arylcarbonyl group is preferably a substituted or unsubstituted arylcarbonyl group having 7 or more carbon atoms. Examples of the arylcarbonyl group include a phenylcarbonyl group. Examples of the substituent that the aryl group has include an alkyl group such as a methyl group and an alkoxy group such as a methoxy group.

The average substitution degree of the acyl group of the sucrose ester is preferably in the range of 3.0 to 7.5. When the average substitution degree of the acyl group is within this range, sufficient compatibility with the cellulose ester as the film substrate is easily obtained.

Examples of the sugar ester include the compounds described in JP-A-62-42996 and JP-A-10-237084.
The content of the sugar ester in the protective film is preferably in the range of 5 to 30% by mass, more preferably in the range of 5 to 20% by mass. Within this range, the film can be stretched at a high magnification, and bleeding out can be suppressed.

(UV absorber)
The protective film according to the present invention may contain an ultraviolet absorber.
Examples of the ultraviolet absorber include benzotriazole compounds, 2-hydroxybenzophenone compounds, salicylic acid phenyl ester compounds, and the like.

Among these, UV absorbers having a molecular weight of 400 or more are difficult to sublimate or volatilize at a high boiling point, and are difficult to disperse even when the film is dried at high temperature. Therefore, the weather resistance is effectively improved by adding a relatively small amount. From the viewpoint of being able to do so.
Examples of the ultraviolet absorber having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- (1 , 1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol], bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis Hindered amines such as (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] ethyl ] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine etc. in the molecule, the structure of hindered phenol and hindered amine These can be used alone or in combination of two or more.
Among them, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- (1,1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] is particularly preferred.

The UV absorber may be a commercially available product, for example, Tinuvin 109, Tinuvin 171, Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328, Tinuvin 928, etc. manufactured by BASF Japan, LA31 manufactured by ADEKA Such 2,2'-methylenebis [6- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol] (molecular weight 659) can be preferably used.

The content of the ultraviolet light inhibitor in the protective film is preferably in the range of 1 to 1000 ppm, more preferably in the range of 10 to 1000 ppm by mass ratio.

(Matting agent)
The protective film according to the present invention may further contain a matting agent in order to impart slipperiness to the film.
The matting agent may be an inorganic compound or an organic compound as long as it does not impair the transparency of the resulting film and has heat resistance during film production. A matting agent may be used independently and may use 2 or more types together.

Of these, silicon dioxide having a refractive index close to that of cellulose ester and excellent in transparency (haze) of the film is preferably used.
Specific examples of silicon dioxide include commercially available products such as Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (above, Nippon Aerosil Co., Ltd.), Seahoster KEP-10, Seahoster KEP-30, Seahoster KEP-50 (manufactured by Nippon Shokubai Co., Ltd.), Silo Hovic 100 (manufactured by Fuji Silysia), Nip Seal E220A (manufactured by Nippon Silica Industry), Admafine SO (manufactured by Admatechs) It can be preferably used.

The shape of the particles is not particularly limited, such as an indefinite shape, a needle shape, a flat shape, and a spherical shape. Use of spherical particles is preferable because the resulting film can have good transparency.
When the particle size is close to the wavelength of visible light, light is scattered and the transparency is deteriorated. Therefore, the particle size is preferably smaller than the wavelength of visible light, and more preferably ½ or less of the wavelength of visible light. . In order to sufficiently improve the slipperiness, the particle size is preferably in the range of 80 to 180 nm. The size of the particle means the size of the aggregate when the particle is an aggregate of primary particles. Moreover, when a particle is not spherical, it means the diameter of a circle corresponding to the projected area.

The content of the matting agent can be in the range of about 0.05 to 1.00% by mass with respect to the cellulose ester, and preferably in the range of 0.10 to 0.80% by mass.

(Peeling aid)
The protective film according to the present invention can also contain a peeling aid.
The peeling aid is present on the surface and absorbs moisture in the air, has a function of increasing the electrical conductivity and greatly reducing the surface resistance, and further partially agglomerates on the metal belt surface, Improve peelability.
Examples of the peeling aid include alkyl sulfonates and alkyl benzene sulfonates. Examples of the salt include sodium salt, potassium salt, amine salt, ammonium salt, phosphonium salt and the like.

Specific examples include sodium decyl sulfonate, sodium decyl benzene sulfonate, potassium decyl benzene sulfonate, sodium dodecyl sulfonate, potassium dodecyl sulfonate, sodium dodecyl benzene sulfonate, potassium dodecyl benzene sulfonate, tetrabutyl dodecyl benzene sulfonate. Ammonium, tetrabutylphosphonium dodecylbenzenesulfonate, sodium tetradecylsulfonate, sodium tetradecylbenzenesulfonate, potassium tetradecylbenzenesulfonate, sodium hexadecylsulfonate, sodium hexadecylbenzenesulfonate, potassium hexadecylbenzenesulfonate, etc. Is mentioned. Examples of these commercially available products include Hostastat HS-1 manufactured by Clariant Japan, Elecut S-412 and Elecut S-418 manufactured by Takemoto Yushi Co., Ltd., Neoperex G65 manufactured by Kao Corporation, and the like.

<Method for producing protective film>
The protective film according to the present invention can be produced by a solution casting method or a melt casting method from the viewpoints of suppressing coloring, suppressing foreign matter defects, and suppressing optical defects such as die lines. Of these, the solution casting method is preferred because the flatness of the film obtained, failure resistance such as streaks, and the accuracy of the film thickness are improved.

The production of a protective film by the solution casting method includes 1) a step of preparing a dope by dissolving or dispersing a cellulose ester and other additives such as a plasticizer in a solvent, if necessary, and 2) endless the dope. A step of casting on a metal support, 3) a step of removing a film obtained by drying the cast dope from the metal support to obtain a film, and 4) stretching the obtained film. It is preferable to carry out through the step of 5) the step of winding up the stretched film.

1) Dope preparation process The organic solvent useful for the preparation of the dope can be used without limitation as long as it dissolves or disperses cellulose ester, additives and the like simultaneously.
For example, a methylene chloride (dichloromethane) is mentioned as a chlorinated organic solvent. Non-chlorine organic solvents include methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 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, Examples include 1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, and nitroethane. Of these, methylene chloride, methyl acetate, ethyl acetate, and acetone are preferable.

In addition to the organic solvent, the dope preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. By containing alcohol in the dope, the film-like material is gelled, and peeling from the metal support becomes easy.
Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Of these, ethanol is preferable because the stability of the dope is obtained, the boiling point is relatively low, and the drying property is good.
In particular, it is preferable to dissolve or disperse at least 15 to 45 mass% of the total amount of cellulose ester and additives in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms.

Dissolution or dispersion of cellulose ester or the like is carried out at normal pressure, carried out below the boiling point of the main solvent, carried out under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557. There are various methods such as a method using a cooling dissolution method as described in JP-A-9-95538 and a method using high pressure as described in JP-A-11-21379. A method in which pressure is applied at a boiling point or higher is preferred.

The prepared dope may contain aggregates. In order to remove aggregates, it is preferable to filter the dope.
For the filtration, it is preferable to use a filter medium having a collected particle diameter of 0.5 to 5.0 μm and a drainage time of 10 to 25 sec / 100 ml. By using such a filter medium, only aggregates can be removed.

2) Casting step The prepared dope is fed to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump). Then, the dope is cast from the slit of the pressure die to a casting position on an endless metal support (for example, a stainless belt, a rotating metal drum, etc.) that is transferred infinitely.
The pressure die is preferably a pressure die that can adjust the slit shape of the die portion and can easily control the film thickness uniformly. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope flow rate may be divided to be stacked. Or you may obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

3) Solvent evaporation and stripping step The dope cast on the metal support is heated on the metal support to evaporate the solvent in the dope to obtain a film.
To evaporate the solvent, there are a method of blowing air from the liquid surface side of the dope, a method of transferring heat from the back surface of the support by a liquid, a method of transferring heat from the front and back by radiant heat, etc. The drying efficiency is preferable. Moreover, the method of combining these is also preferably used. The dope on the metal support is preferably dried on the support in an atmosphere within a range of 40 to 100 ° C. In order to maintain the atmosphere in the range of 40 to 100 ° C., it is preferable to apply hot air at this temperature to the liquid surface of the dope on the metal support or to heat by means such as infrared rays.

Next, the film-like material obtained by evaporating the solvent on the metal support is peeled off at the peeling position to obtain a film. From the viewpoint of the surface quality, moisture permeability and peelability of the resulting film, it is preferable to peel the film-like material from the metal support within 30 to 120 seconds after casting. The temperature at the peeling position on the metal support is preferably in the range of 10 to 40 ° C, more preferably in the range of 11 to 30 ° C.

The amount of residual solvent in the film-like material on the metal support at the time of peeling is preferably in the range of 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. However, when peeling off at a time when the amount of residual solvent is larger, if the film-like material is too soft, the flatness is impaired at the time of peeling, and the resulting film is likely to be distorted or vertical streaks due to peeling tension. Therefore, the amount of residual solvent at the time of peeling is determined from the balance between production speed and quality.

The amount of residual solvent in the film-like material is defined by the following formula.
Residual solvent amount (mass%) = (mass before heat treatment of film-like material−mass after heat treatment of film-like material) / (mass after heat treatment of film-like material) × 100
Note that the heat treatment for measuring the residual solvent amount represents a treatment for heating at 140 ° C. for 1 hour.

The peeling tension when peeling the metal support from the film is usually in the range of 196 to 245 N / m. However, if wrinkles easily occur during peeling, the peeling tension should be 190 N / m or less. Is preferred.

4) Drying step and stretching step The peeled film is dried while being conveyed through the drying device by a plurality of rollers provided in the drying device. Next, in the tenter stretching apparatus, the film is transported while sandwiching both ends of the film with clips to stretch the film (tenter stretching method). You may use the method (roller extending | stretching method) which gives a circumferential speed difference to the several roller which conveys a film, and draws using the circumferential speed difference.

Drying is generally performed by applying hot air to both sides of the film, but may be heated by applying microwaves instead of hot air. Too rapid drying tends to impair the flatness of the resulting film. Drying at a high temperature is preferably performed after the amount of residual solvent is reduced to about 8% by mass or less. Throughout, the drying is generally carried out within the range of 40-250 ° C. In particular, it is preferable to dry within the range of 40 to 200 ° C.

It can also be dried with a tenter stretching apparatus. In this case, the drying temperature is preferably in the range of 30 to 160 ° C, more preferably in the range of 50 to 150 ° C. In the tenter stretching apparatus, it is preferable that the temperature distribution of the atmosphere is small in the TD direction from the viewpoint of improving the uniformity of the film. Therefore, the temperature distribution in the TD direction in the tenter stretching apparatus is preferably within ± 5 ° C., more preferably within ± 2 ° C., and most preferably within ± 1 ° C.

Stretching at least in the MD direction of the protective film in the MD direction and the TD direction results in a ratio value E1 / E2 of the elastic modulus E1 in the MD direction and the elastic modulus E2 in the TD direction of 1.5 to 3 It is preferable because it is easy to adjust within the range of 0.0.
The draw ratio in the MD direction is preferably 1.6 times or more, and more preferably in the range of 1.6 to 3.0 times.

In addition to the MD direction, biaxial stretching that performs stretching in the TD direction is also preferable from the viewpoint of obtaining the strength of the film.
In the case of biaxial stretching, it is preferable that the stretching ratio in the MD direction is larger than the stretching ratio in the TD direction, the stretching ratio in the MD direction is 1.6 times or more, and the stretching ratio in the TD direction is 1.3 times or more. . In particular, the draw ratio in the MD direction is preferably in the range of 1.6 to 3.0 times. Further, the draw ratio in the TD direction is preferably in the range of 1.3 to 4.0 times, and more preferably in the range of 1.5 to 3.0 times.
In addition, the draw ratio of the said MD direction and TD direction is calculated | required by a following formula from the length of the film before and behind extending | stretching of each direction.
Stretch ratio = length of film after stretching / length of film before stretching

Biaxial stretching may be performed simultaneously or stepwise.
Simultaneous biaxial stretching includes stretching in one direction and reducing the tension in the other direction to cause contraction.
In biaxial stretching performed stepwise, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible.
For example, the following stretching steps are possible.
-Stretch in MD direction-> Stretch in TD direction-Stretch in TD direction-> Stretch in MD direction-Stretch in MD direction-> Stretch in TD direction-> Stretch in TD direction-Stretch in TD direction-> Stretch in TD direction-> Stretch in MD direction

The stretching can be performed within a temperature range of 25 to 190 ° C.
The residual solvent amount of the film at the start of stretching is preferably in the range of 20 to 100% by mass. The film obtained after completion of stretching is preferably dried until the residual solvent amount is 5% by mass or less, preferably 1% by mass or less.

5) Winding process The film after stretching and drying is wound into a roll with a winder. As a winding method, a generally used method may be used, and there are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

The protective film according to the present invention can be a long film. For example, a long film having a winding length in the range of about 100 to 10,000 m and a length in the TD direction of 1.0 to 4.0 m, preferably in the range of 1.4 to 3.0 m can be obtained. A long film can be preserve | saved as a roll body wound up by MD direction which is a major axis direction normally.
Before winding up, after slitting off the TD direction end of the protective film in accordance with the width of the product, to prevent sticking of the wound inner surface and scratches, for example, a knurling like embossing Processing may be applied to both ends in the TD direction. For example, the knurling process can be performed by heating or pressurizing the film with a metal ring having an uneven pattern on the side surface.

<Physical properties of protective film>
(Film thickness)
The thickness of the protective film according to the present invention is preferably in the range of 15 to 35 μm, more preferably in the range of 15 to 30 μm. If the film thickness is within the above range, the film has sufficient strength, can suppress the bending of the liquid crystal cell to improve display unevenness, and when the roll body is stored so that the core is horizontal, the TD of the film It is also possible to suppress deformation (change in winding shape) such that the central portion in the direction is recessed by its own weight.

(Haze)
The haze value of the protective film according to the present invention is preferably 1.0% or less, and more preferably 0.5% or less.
When using the protective film of this invention as a scattering film, haze value may exceed said range.
The haze can be measured with a haze meter (turbidimeter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.) in accordance with JIS K-7136.

The protective film according to the present invention may further have functional layers such as a hard coat layer, an antistatic layer, a back coat layer, an antireflection layer, a slippery layer, an adhesive layer, an antiglare layer, and a barrier layer. .

<Polarizer>
The polarizer may be an iodine polarizing film, a dye polarizing film using a dichroic dye, or a polyene polarizing film. In general, the iodine polarizing film and the dye polarizing film may be a film obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing with iodine or a dichroic dye. After the film is dyed with iodine or a dichroic dye, it may be a uniaxially stretched film (preferably a film further subjected to a durability treatment with a boron compound).

The polyvinyl alcohol film may be a film formed from a polyvinyl alcohol aqueous solution. The polyvinyl alcohol film is preferably an ethylene-modified polyvinyl alcohol film because it is excellent in polarizing performance and durability performance and has few color spots.
Examples of dichroic dyes include azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes, anthraquinone dyes, and the like.

The thickness of the polarizer is preferably in the range of 5 to 30 μm, and more preferably in the range of 10 to 20 μm.

<Phase difference film>
When the protective film according to the present invention is disposed on one surface of the polarizer, a retardation film is disposed on the other surface of the polarizer.
The angle at which the slow axis in the plane of the retardation film intersects with the absorption axis of the polarizer may be an appropriate angle depending on the purpose. For example, in the case of a λ / 4 retardation film, it is preferably within a range of 40 to 50 °, and more preferably 45 °.

The retardation value of the retardation film can be set according to the type of liquid crystal cell to be combined. For example, when the retardation values Ro in the in-plane direction and the thickness direction measured at a wavelength of 590 nm under a temperature of 23 ° C. and 55% RH are Ro (590) and Rt (590), respectively, Ro (590) is preferably in the range of 30 to 150 nm, and Rt (590) is preferably in the range of 70 to 300 nm. A retardation film having retardation values Ro (590) and Rt (590) in the above range can be preferably used for, for example, a VA liquid crystal cell.

In addition, the retardation value of the protective film according to the present invention may be adjusted to function as the retardation film.

<Production method of polarizing plate>
The method for producing a polarizing plate of the present invention includes a production process for producing the above-described protective film, and in the production process, the maximum value of tan δ of the produced protective film is 0.6 or more, and the protective film The protective film is manufactured so that the value E1 / E2 of the ratio of the elastic modulus in the MD direction and the TD direction is in the range of 1.5 to 3.0.
Furthermore, the polarizing plate of this invention can be obtained through the process of bonding the protective film after manufacture to a polarizer. As an adhesive used for bonding, for example, a completely saponified polyvinyl alcohol aqueous solution is preferable.

When making a polarizing plate by making a polarizer and a protective film into a long film and laminating them with roll-to-roll so that the respective major axis directions coincide, the absorption axis of the polarizer is the stretching direction of the polarizer. Since it is parallel, the absorption axis direction of a polarizer and MD direction of a protective film correspond.
In addition, that the major axis direction coincides or that the absorption axis direction coincides with the MD direction means that the angle formed by each direction is within a range of about ± 5 °.

<Liquid crystal display device>
The liquid crystal display device of the present invention comprises the polarizing plate described above on at least one surface of the liquid crystal cell. Thereby, a liquid crystal display device with less display unevenness due to temperature and humidity changes can be provided.

FIG. 1 is a cross-sectional view showing an example of the configuration of the liquid crystal display device of the present invention.
As shown in FIG. 1, the liquid crystal display device 100 includes a liquid crystal cell 40, two polarizing plates 50 and 60 disposed on both surfaces of the liquid crystal cell 40, and a backlight 70.

The display method of the liquid crystal cell 40 is not particularly limited, and is a TN (Twisted Nematic) method, an STN (Super Twisted Nematic) method, an IPS (In-Plane Switching) method, an OCB (Optically Compensated Birefringence) method, and VA (Vertical Alignment). There are methods (including MVA: Multi-domain Vertical Alignment and PVA: Patterned Vertical Alignment), HAN (Hybrid Aligned Nematic) method and the like. In order to increase the contrast, the VA (MVA, PVA) method is preferable.

A VA liquid crystal cell includes a pair of transparent substrates and a liquid crystal layer sandwiched between the pair of transparent substrates.
The transparent substrate is, for example, a glass substrate. The film thickness of the transparent substrate is preferably in the range of 0.2 to 0.5 mm from the viewpoint of thinning the liquid crystal screen.
Of the pair of transparent substrates, one transparent substrate is provided with a pixel electrode for applying a voltage to the liquid crystal molecules. The counter electrode may be disposed on one transparent substrate (transparent substrate on which the pixel electrode is disposed) or may be disposed on the other transparent substrate.

The liquid crystal layer includes liquid crystal molecules having negative or positive dielectric anisotropy. Liquid crystal molecules are liquid crystal molecules when no voltage is applied (when no electric field is generated between the pixel electrode and the counter electrode) due to the alignment regulating force of the alignment film provided on the liquid crystal layer side surface of the transparent substrate. Are oriented so that their long axes are substantially perpendicular to the surface of the transparent substrate.

In the liquid crystal cell 40, when a voltage corresponding to an image signal is applied to the pixel electrode, an electric field is generated between the pixel electrode and the counter electrode. Thereby, the liquid crystal molecules initially aligned perpendicularly to the surface of the transparent substrate can be aligned so that the major axis thereof is in the horizontal direction with respect to the surface of the transparent substrate. In this way, the liquid crystal layer is driven, and the image display is performed by changing the transmittance and reflectance of each sub-pixel.

The polarizing plate 50 is disposed on the surface of the liquid crystal cell 40 on the front side (viewing side), and includes a protective film 51, a polarizer 52, and a retardation film 53 in order from the front side. The front side is a side on which the liquid crystal screen is visually recognized by the user 80.
The polarizing plate 60 is disposed on the surface of the liquid crystal cell 40 on the rear side, and includes a protective film 63, a polarizer 62, and a retardation film 61 in order from the rear side. The rear side is the side where the backlight 70 is provided.
The polarizing plates 50 and 60 are arranged such that the angle formed by the respective absorption axes is 90 °.

FIG. 2 is a diagram hierarchically showing the liquid crystal cell 40 and the two polarizing plates 50 and 60 of FIG.
As shown in FIG. 2, when there is a change in the temperature and humidity of the environment where the liquid crystal display device 100 is placed, the polarizers 52 and 62 that have absorbed moisture contract in the respective absorption axis directions 52d and 62d. In FIG. 2, this contracting force is represented by a white arrow. The shrinking force propagates to the liquid crystal cell 40. If the transparent substrate of the liquid crystal cell 40 cannot withstand this force, the liquid crystal cell 40 is bent, and the retardation films 53 and 61 adjacent to the liquid crystal cell 40 are also bent. End up. Due to the bending of the phase difference films 53 and 61, the phase difference changes, causing display unevenness.

However, when the polarizing plate of the present invention is used for at least one of the polarizing plates 50 or 60, the polarizing plate of the present invention has a high elastic modulus in the MD direction of the protective film, and thus is resistant to the force applied in the MD direction. Stress is large.
In general, the polarizer and the protective film are bonded as a long film by roll-to-roll, and as shown in FIG. 2, the MD direction 51d of the protective film 51 and the absorption axis direction 52d of the polarizer 52 coincide with each other. The MD direction 63d of 63 coincides with the absorption axis direction 62d of the polarizer 62. Therefore, it is possible to greatly reduce the force by which the polarizers 52 and 62 contract by the protective films 51 and 63 bonded to each other.
As a result, the force propagating to the liquid crystal cell 40 can be reduced to such an extent that even a thin transparent substrate can withstand, and the liquid crystal cell 40 and the retardation films 53 and 61 adjacent to the liquid crystal cell 40 can be reduced. Bending can be suppressed. If the bending of the retardation film can be suppressed, it is possible to suppress a change in the retardation, and thus display unevenness.

When the liquid crystal screen composed of the liquid crystal cell is rectangular, a polarizing plate in which at least the absorption axis direction of the polarizer coincides with the long axis direction of the liquid crystal screen among the two polarizing plates used on both sides of the liquid crystal cell. It is preferable to use the polarizing plate of the present invention.
The moment of force with which the polarizer contracts increases as the length of the polarizer in the absorption axis direction increases. Therefore, when the liquid crystal screen is rectangular, the moment of force with which the polarizer of each polarizing plate contracts is not the same, and the moment is larger in the polarizing plate in which the major axis direction of the liquid crystal screen matches the absorption axis direction. . Due to the difference in moment, the liquid crystal cell is warped.

Generally, as shown in FIG. 2, the polarizing plate 50 provided on the front side of the liquid crystal cell 40 is arranged so that the major axis direction of the liquid crystal screen and the absorption axis direction 52d coincide. Since the polarizing plate 50 has a larger moment of contraction force than the polarizing plate 60, the liquid crystal cell 40 warps so as to protrude to the rear side as shown in the cross-sectional view of FIG.

At this time, the protective film 51 located at the outermost outermost side of the front side is most bent. However, by using the polarizing plate of the present invention as the front-side polarizing plate 50, the elastic modulus E1 of the protective film 51 in the MD direction 51d is increased, and the contracting force of the polarizer 52 can be greatly reduced. As a result, the bending of the liquid crystal cell 40 that protrudes to the rear side can be effectively suppressed.

Not only the polarizing plate 50 on the front side but also the polarizing plate 60 on the rear side can be used as the polarizing plate of the present invention.
Thereby, the force by which the rear-side polarizer 62 contracts in the absorption axis direction 62 d can also be greatly reduced by the protective film 63 provided on the polarizing plate 60.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless there is particular notice, it represents "mass part" or "mass%".

<Preparation of protective film 11>
The following components were sufficiently dissolved with stirring and heating to prepare a dope.
(Composition of dope)
Cellulose ester (acetyl group substitution degree 2.87, weight average molecular weight Mw 300000):
100.0 parts by mass Polyester (end-capped product of condensate containing succinic acid, terephthalic acid and ethylene glycol as monomers, succinic acid / terephthalic acid / ethylene glycol molar ratio 50/50/100, weight average molecular weight Mw2000) : 10.0 parts by weight UV absorber; Tinuvin 928 (2- (2H-benzotriazol-2-yl) -6- (1-methyl-1-phenylethyl) -4- (1,1,3,3- Tetramethylbutyl) phenol, manufactured by BASF Japan Ltd.): 3.0 parts by weight Matting agent: R972V (manufactured by Nippon Aerosil Co., Ltd., silica particles, average particle size 16 nm):
0.3 parts by mass peeling aid; ELECUT S412 (manufactured by Takemoto Yushi Co., Ltd.): 0.5 parts by mass Methylene chloride: 300.0 parts by mass Ethanol: 40.0 parts by mass

The obtained dope was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. Further, the solvent in the dope was evaporated on the stainless steel band support until the residual solvent amount reached 100% by mass. The obtained film was peeled from the stainless steel band support with a peel tension of 162 N / m to obtain a film.

After the obtained film was further dried at a temperature of 35 ° C., the end in the TD direction was slit so that the length in the TD direction was 1.5 m. The film after the slit was stretched 2.0 times in the MD direction with a roller at a stretching temperature of 190 ° C. and stretched 1.5 times in the TD direction at a stretching temperature of 190 ° C. with a tenter stretching device. The residual solvent amount at the start of stretching by the tenter stretching apparatus was 8% by mass.
After stretching by a tenter stretching apparatus, relaxation treatment was performed at 130 ° C. for 5 minutes, and the obtained film was transported to each drying zone at 120 ° C. and 140 ° C. by a number of rollers, and dried while being transported. Next, the end in the TD direction was slit so that the length in the TD direction was 1.35 m. Then, the knurl process of width 10mm and height 5micrometer was given to the TD direction both ends of the film, and it wound up on the core, and obtained the roll body of the protective film 11. The film thickness of the protective film 11 was 25 μm, and the winding length was 4000 m.

<Preparation of protective film 12>
In preparation of the protective film 11, the protective film 12 was produced similarly to the protective film 11 except having changed the addition amount of polyester in dope as shown in Table 1 below.
Similar to the protective film 11, the protective film 12 had a thickness of 25 μm and a winding length of 4000 m.

<Preparation of protective films 13-15>
In the production of the protective film 11, the protective films 13 to 15 were produced in the same manner as the protective film 11 except that the polyester in the dope was changed to the following styrene polymers 1 to 3, respectively.
Styrene polymer 1: SMA 2625 (copolymer of styrene and maleic acid, molar ratio of styrene and maleic acid (styrene / maleic acid) 67/33, weight average molecular weight Mw 9000), manufactured by Sartomer): 10.0 parts by mass Styrene polymer 2: SMA 17325 (copolymer of styrene and maleic acid, molar ratio of styrene and maleic acid (styrene / maleic acid) 50/50, weight average molecular weight Mw 7000), manufactured by Sartomer): 10.0 parts by mass Styrene polymer 3: Marcalinker CST50 (copolymer of styrene and hydroxystyrene, molar ratio of styrene to hydroxystyrene (styrene / hydroxystyrene) 50/50, weight average molecular weight Mw2000, manufactured by Maruzen Petrochemical Co., Ltd.): 0 parts by mass Same as protective film 11 The thickness of the protective film 13-15 25 [mu] m, the winding length (length in the MD direction) was 4000 m.

<Preparation of protective films 16 and 17>
In the production of the protective film 13, protective films 16 and 17 were produced in the same manner as the protective film 13, except that the stretching ratio in the MD direction and the TD direction during stretching was changed as shown in Table 1 below. In addition, the protective film 17 did not extend | stretch in TD direction but performed only extending | stretching of MD direction.
Similar to the protective film 11, the protective films 16 and 17 had a film thickness of 25 μm and a winding length of 4000 m.

<Preparation of protective films 18 and 19>
In the production of the protective film 13, a protective film 18 was produced in the same manner as the protective film 13, except that the addition amount of the styrene polymer 1 was changed as shown in Table 1 below.
In the production of the protective film 14, a protective film 19 was produced in the same manner as the protective film 14 except that the addition amount of the styrene polymer 2 was changed as shown in Table 1 below.
Similarly to the protective film 11, the film thickness of each protective film 18 and 19 was 25 micrometers, and the winding length was 4000 m.

<Preparation of protective films 20 and 21>
In the production of the protective film 11, the protective films 20 and 21 were produced in the same manner as the protective film 11 except that the stretching ratios in the MD direction and the TD direction were changed as shown in Table 1 below.
Similar to the protective film 11, the protective films 20 and 21 had a film thickness of 25 μm and a winding length of 4000 m.

<Preparation of protective film 22>
In the production of the protective film 11, a protective film 22 was produced in the same manner as the protective film 11 except that the polyester was changed to the following sugar ester.
Sugar ester (in the general formula (FA), R ₁ to R ₈ are each a benzoyl group or a hydrogen atom, and the average degree of substitution of the benzoyl group is 5.5): 10 parts by mass Similar to the protective film 11 Further, the protective film 22 had a film thickness of 25 μm and a winding length of 4000 m.

<Preparation of protective film 31>
When a film was prepared in the same manner as the protective film 11 except that no polyester was added to the dope, the film was broken when attempting to stretch at the same draw ratio as that of the protective film 11. Therefore, the protective film 31 was produced by extending the draw ratio in the MD direction and the TD direction to 1.6 and 1.3, respectively.
Similar to the protective film 11, the protective film 31 had a film thickness of 25 μm and a winding length of 4000 m.

<Preparation of protective films 32 and 33>
In the production of the protective film 11, the polyester in the dope is added in the addition amount shown in Table 1 below instead of ethylphthalylethyl glycolate, and the draw ratios in the MD direction and the TD direction at the time of drawing are shown in Table 1 below. The protective films 32 and 33 were respectively produced in the same manner as the protective film 11 except that the above changes were made. In preparation of the protective films 32 and 33, when the film was broken at the same draw ratio as that of the protective film 11, the film was broken, so the draw ratio was lowered as shown in Table 1 below.
Similarly to the protective film 11, the film thickness of each protective film 32 and 33 was 25 micrometers, and the winding length was 4000 m.

<Preparation of protective films 34 and 35>
In the production of the protective film 11, the protective film 34 and the protective film 11 were changed in the same manner as the protective film 11 except that the addition amount of the polyester in the dope and the stretching ratio in the MD direction and TD direction during stretching were changed as shown in Table 1 below. 35 were produced.
Similar to the protective film 11, the protective films 34 and 35 had a film thickness of 25 μm and a winding length of 4000 m.

<Preparation of protective film 36>
A protective film 36 was prepared in the same manner as the protective film 31 except that the protective film 31 was not stretched.
Similar to the protective film 31, the protective film 36 had a thickness of 25 μm and a winding length of 4000 m.

<Production of protective films 37 and 38>
In the production of the protective film 13, protective films 37 and 38 were produced in the same manner as the protective film 13 except that the addition amount of the styrene polymer 1 and the stretching ratio were changed as shown in Table 1 below.
Similar to the protective film 13, the protective films 37 and 38 had a film thickness of 25 μm and a winding length of 4000 m.

<Preparation of polarizing plates 11 to 22 and 31 to 38>
A polarizer was produced by the following procedure.
A 120 μm thick polyvinyl alcohol film was uniaxially stretched in the MD direction (temperature 110 ° C., stretch ratio 5 times). After extending | stretching, it was immersed for 60 second in the aqueous solution which consists of 0.075 mass part of iodine, 5 mass parts of potassium iodide, and 100 mass parts of water. Subsequently, after immersing in 68 degreeC aqueous solution which consists of 6 mass parts of potassium iodide, 7.5 mass parts boric acid, and 100 mass parts of water, it washed with water and dried and obtained the polarizer of a long film.
The obtained polarizer had a film thickness of 10 μm.

Next, according to the following steps 1 to 5, polarizing plates 11 to 22 and 31 to 38 having protective films 11 to 22 and 31 to 38, respectively, were produced.
Step 1: One surface of the protective film was immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, washed with water, dried and saponified. The saponified surface is the bonding surface with the polarizer.
Step 2: The prepared polarizer was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.
Step 3: Excess adhesive adhered to the polarizer in Step 2 was lightly wiped away, and then the polarizer was stacked on the surface of the protective film saponified in Step 1 and bonded together.
Step 4: On the other surface of the polarizer layered on the protective film in Step 3, Konica Minoltack KC4DR (cellulose ester film manufactured by Konica Minolta Advanced Layer) is stacked as a retardation film, and the pressure is 20 to 30 N / cm 2. Bonding was performed at a conveyance speed of about 2 m / min.
Step 5: The protective film, polarizer, and Konica Minoltack KC4DR bonded together in Step 4 were dried for 2 minutes in a dryer at 80 ° C. to prepare a polarizing plate.

<Production of liquid crystal display devices 11 to 22 and 31 to 38>
In BRAVIA KDL-52W5 (manufactured by Sony Corporation) which is a VA mode type liquid crystal display device, one of the two polarizing plates previously bonded to both surfaces of the liquid crystal cell is bonded to the front surface of the liquid crystal cell. The liquid crystal display device 11 was produced by peeling off the one and attaching the polarizing plate 11 instead. The polarizing plate 11 was bonded so that the retardation film was positioned on the liquid crystal cell side.

The liquid crystal screen of BRAVIA KDL-52W5 was a rectangle longer in the left-right direction than in the up-down direction.
In addition, the polarizing plate disposed on the front side of the BRAVIA KDL-52W5 liquid crystal cell has a polarizing axis disposed on the rear side of the liquid crystal cell with the absorption axis direction coinciding with the long axis direction (left-right direction) of the liquid crystal screen. The absorption axis direction of the plate coincided with the minor axis direction (vertical direction) of the liquid crystal screen. Therefore, the polarizing plate 11 was similarly formed in a rectangular shape and arranged so that the absorption axis direction coincided with the major axis direction of the liquid crystal screen.
In the same manner as in the liquid crystal display device 11, the polarizing plates 12 to 22 and 31 to 38 were used to prepare the liquid crystal display devices 12 to 22 and 31 to 38, respectively.

<Production of Liquid Crystal Display Device 23>
In the production of the liquid crystal display device 13, except that the two polarizing plates attached to both surfaces of the BRAVIA KDL-52W5 liquid crystal cell were peeled off and the two polarizing plates 13 were attached to both surfaces of the liquid crystal cell, respectively. In the same manner as in Example 13, a liquid crystal display device 23 was produced. The two polarizing plates 13 were bonded together so that the retardation film was positioned on the liquid crystal cell side. Further, in the same manner as the original polarizing plate, the absorption axis direction of the polarizing plate 13 disposed on the front side surface of the liquid crystal cell coincides with the major axis direction of the liquid crystal screen, and the polarizing plate 13 disposed on the rear side surface. Each polarizing plate 13 was arranged so that the absorption axis direction of the liquid crystal coincides with the minor axis direction of the liquid crystal screen.

<Evaluation>
(1) Tan δ of protective film
The dynamic viscoelasticity of each of the protective films 11 to 22 and 31 to 38 was measured, and the maximum value of tan δ in the temperature range of 25 to 190 ° C. was obtained. In addition, about the protective film produced by extending | stretching, the dynamic viscoelasticity of the protective film before extending | stretching was measured, and the maximum value of tan-delta was calculated | required.
First, samples were cut out from each of the protective films 11 to 22 and 31 to 38, and conditioned in an environment of 23 ° C. and 55% RH for 24 hours. The dynamic viscoelasticity of the sample after conditioning was measured under the following measurement conditions while raising the temperature from 25 ° C. to 190 ° C. under 55% RH. The maximum value of tan δ in the temperature range of 25 to 190 ° C. obtained by measurement was determined. The second decimal place of the maximum value obtained was rounded off.
Measuring device: RSAIII (manufactured by TA Instruments)
Sample: width 5 mm, length 50 mm (gap set to 20 mm)
Measurement mode: Tensile mode Measurement temperature: Temperature rising within a temperature range of 25 to 190 ° C at a rate of 5 ° C / min Humidity: 55% relative humidity
Temperature increase rate: 5 ° C / min
Frequency of force applied during measurement: 1 Hz

(2) E1 / E2 of the ratio of the elastic modulus in the MD direction and the TD direction of the protective film
The samples of the protective films 11 to 22 and 31 to 38 were conditioned for 24 hours in an environment of 23 ° C. and 55% RH. The elastic modulus E1 and E2 (MPa) in the MD direction and TD direction of the sample after humidity control were measured by a tensile tester Tensilon RTA-100 (manufactured by Orientec Co., Ltd.) according to the method described in JIS K7127. The measurement was performed in the same environment as during humidity control. The shape of the sample was No. 1 type test piece type, and the tensile speed was 10 mm / min.
From the obtained elastic moduli E1 and E2, the ratio value E1 / E2 of the elastic modulus was obtained.

(3) Display unevenness of liquid crystal display device Each of the liquid crystal display devices 11 to 23 and 31 to 38 was wet-heat treated in an environment of 50 ° C. and 90% RH for 24 hours. After that, 2 hours after the backlights of the liquid crystal display devices 11 to 23 and 31 to 38 are turned on in an environment of 23 ° C. and 55% RH, the luminance unevenness when displaying black and the luminance when displaying an image are displayed. The unevenness was confirmed visually. This luminance unevenness was evaluated as display unevenness according to the following criteria.
○: There is almost no luminance unevenness during black display and image display. △: There is much luminance unevenness during black display, but there is little concern about luminance unevenness during image display ×: Many luminance unevenness during black display If the evaluation is ◯ or Δ, it is a level that can be used without any problem in practice.

Table 1 below shows the evaluation results.

As shown in Table 1, it can be seen that the liquid crystal display devices 11 to 23 using the polarizing plates 11 to 22 according to the examples sufficiently suppress display unevenness due to temperature and humidity changes.

The present invention can be applied to reduce display unevenness of a liquid crystal display device having a thin liquid crystal screen.

DESCRIPTION OF SYMBOLS 100 Liquid crystal display device 40 Liquid crystal cell 50 Polarizing plate 51 Protective film 52 Polarizer 53 Phase difference film 60 Polarizing plate 61 Phase difference film 62 Polarizer 63 Protective film

Claims (16)

1. A polarizing plate in which a protective film containing a cellulose ester is disposed on at least one surface of a polarizer,
   The maximum value of tan δ obtained when the dynamic viscoelasticity of the protective film is measured at a frequency of 1 Hz while changing the temperature within a temperature range of 25 to 190 ° C. is 0.6 or more,
   When the values obtained by measuring the elastic modulus (MPa) in the MD direction and TD direction at the time of manufacturing the protective film in an environment of a temperature of 23 ° C. and a relative humidity of 55% are expressed as E1 and E2, respectively, the MD direction And a ratio E1 / E2 of elastic modulus ratios in the TD direction is in the range of 1.5 to 3.0.
2. The protective film is a film stretched in the MD direction;
   The polarizing plate according to claim 1, wherein a stretching ratio in the MD direction is 1.6 times or more.
3. The protective film is a film stretched in the MD direction and the TD direction,
   The MD direction stretch ratio is larger than the TD direction stretch ratio, the MD direction stretch ratio is 1.6 times or more, and the TD direction stretch ratio is 1.3 times or more. The polarizing plate according to claim 1.
4. The polarizing plate according to any one of claims 1 to 3, wherein the protective film contains a styrene polymer.
5. The polarizing plate according to claim 4, wherein the styrenic polymer is a copolymer of a monomer having a hydroxy group and a monomer containing styrene.
6. The polarized light according to any one of claims 1 to 5, wherein the protective film and the polarizer are long films, and are bonded so that the major axis directions thereof coincide with each other. Board.
7. The polarizing plate according to any one of claims 1 to 6, wherein an MD direction of the protective film coincides with an absorption axis direction of the polarizer.
8. A method for producing a polarizing plate in which a protective film is disposed on at least one surface of a polarizer,
   Including a production process for producing a protective film containing cellulose ester,
   In the production process, the maximum value of tan δ obtained when the dynamic viscoelasticity of the protective film after production is measured at a frequency of 1 Hz while changing the temperature within a temperature range of 25 to 190 ° C. is 0.6 or more. When the values obtained by measuring the elastic modulus (MPa) in the MD direction and the TD direction at the time of film production of the protective film in an environment of a temperature of 23 ° C. and a relative humidity of 55% are expressed as E1 and E2, respectively. A method for producing a polarizing plate, comprising producing the protective film so that the ratio E1 / E2 of the elastic modulus ratio in the MD direction and the TD direction is in the range of 1.5 to 3.0.
9. The manufacturing process includes a process of stretching the protective film in the MD direction during film manufacturing,
   The method for producing a polarizing plate according to claim 8, wherein a draw ratio in the MD direction is 1.6 times or more.
10. The manufacturing process includes a step of stretching the protective film in the MD direction and the TD direction during film manufacturing,
    The stretching ratio in the TD direction is smaller than the stretching ratio in the MD direction, the stretching ratio in the MD direction is 1.6 times or more, and the stretching ratio in the TD direction is 1.3 times or more. The manufacturing method of the polarizing plate of Claim 8.
11. The said manufacturing process WHEREIN: The said protective film is manufactured by the solution casting method using the dope containing the said cellulose ester and a styrene-type polymer, The any one of Claim 8-10 characterized by the above-mentioned. The manufacturing method of the polarizing plate as described in a term.
12. The method for producing a polarizing plate according to claim 11, wherein the styrenic polymer is a copolymer of a monomer having a hydroxy group and a monomer containing styrene.
13. The polarizer is a long film,
    In the manufacturing process, the protective film is manufactured as a long film,
    The bonding process which bonds together the said protective film which is a long film, and the said polarizer so that each long-axis direction may correspond is included, The Claim 1 characterized by the above-mentioned. The manufacturing method of the polarizing plate of description.
14. A liquid crystal display device comprising the polarizing plate according to any one of claims 1 to 7 on at least one surface of a liquid crystal cell.
15. The liquid crystal screen composed of the liquid crystal cell is rectangular,
    Of the two polarizing plates provided on both surfaces of the liquid crystal cell, as a polarizing plate in which at least the major axis direction of the liquid crystal screen coincides with the absorption axis direction of the polarizer, any one of claims 1 to 7 The liquid crystal display device according to claim 14, comprising the polarizing plate according to claim 1.
16. 16. The liquid crystal display device according to claim 15, wherein the polarizing plate in which the major axis direction of the liquid crystal screen and the absorption axis direction of the polarizer coincide with each other is a polarizing plate provided on a front side surface of the liquid crystal cell. .

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