JP5386740B2 - Protective film for polarizing plate, polarizing plate, and liquid crystal display device - Google Patents

Description

  The present invention relates to a protective film for a polarizing plate and the like.

  The polarizing plate is an optical film used for a liquid crystal display device or the like. The polarizing plate usually has a polarizing film and a protective film laminated on the polarizing film in order to protect the polarizing film. The polarizing film is a film having a function of transmitting a specific linearly polarized light from natural light or polarized light.

Conventionally, a step of obtaining a laminate composed of a base film and a polyvinyl alcohol-based resin layer by applying a polyvinyl alcohol-based resin to the base film, a step of laterally stretching the laminate, and the polyvinyl alcohol There is known a method for producing a polarizing plate having a step of adsorbing a dichroic substance on a resin layer (Patent Document 1). Patent Document 1 discloses that a polyester resin film, a polyolefin resin film, or the like is used as a base film.
The base film in this production method serves as a support for forming a polyvinyl alcohol-based resin layer (polarizing film) during the production of the polarizing plate. Moreover, the said base film can be used as a protective film of a polarizing plate after manufacture of a polarizing plate.

JP 2003-43257 A

However, a base film made of a polyester resin film, a polyolefin resin film, or the like tends to have a low mechanical strength after stretching. Further, when the substrate film is exposed to a high temperature and / or high humidity, its dimensions are likely to change (hereinafter, “high temperature and / or high humidity” is referred to as “high temperature and high humidity”). Write down).
Since the polarizing film laminated | stacked on this also distorts with the dimensional change of a base film, as a result of the absorption axis of the said polarizing film shifting | deviating, a polarizing plate produces light leakage. When such a polarizing plate is incorporated in a liquid crystal display device, the light leakage of the polarizing plate increases depending on the usage time, and the display characteristics of the liquid crystal display device may deteriorate.
On the other hand, a cellulose-based resin film or a polyarylate-based resin film can be used as the base film, but these films have a problem that it is difficult to stretch at a high magnification.
Moreover, since a base film can be used as a protective film, it must be excellent in transparency even after stretching.

The first object of the present invention is a polarizing plate protective film that can be stretched at a high magnification, is excellent in transparency and mechanical strength even after stretching, and hardly changes in dimensions even when exposed to high temperature and high humidity. Is to provide.
The second object of the present invention is to provide a polarizing plate which is excellent in transparency and mechanical strength and whose polarization characteristics are hardly deteriorated even when exposed to high temperature and high humidity.

The protective film for polarizing plate of the present invention comprises a polyarylate having a repeating unit represented by the general formula (I) and a repeating unit represented by the general formula (II), and a repeating unit represented by the general formula (III). and look-containing polyester having a repeating unit represented by the general formula (IV), the molar ratio of the repeating units represented by repeating units of the general formula (II) represented by the general formula (I), 4: 10-6: 10 .

  In the general formulas (I) to (III), A, B, D and E are each independently halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted carbon number 1 to 1 4 represents an alkoxy group, a hydroxyl group, a sulfonic acid group, a nitro group or a cyano group, and when there are a plurality of A, B, D and E, respectively, a, b, d and e are the same as A , B, D and E represent an integer of 0 to 4 as the number of substitutions.

  In general formula (II), R1 and R2 each independently represent a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms. In general formula (IV), Ak represents a C1-C8 alkylene group.

In a preferred protective film for polarizing plate of the present invention, the polyarylate and polyester are compatible.
In a preferred protective film for polarizing plate of the present invention, the mass ratio of the polyarylate to the polyester is 60:40 to 10:90.
In a preferred protective film for polarizing plate of the present invention, Ak in the formula (IV) is a linear alkylene group having 1 to 8 carbon atoms.

According to another aspect of the present invention, a polarizing plate is provided.
The polarizing plate of this invention has one of the said protective films for polarizing plates, and a polarizing film.
A preferable polarizing plate of the present invention is a hydrophilic polymer layer containing a dichroic substance, wherein the polarizing film is provided on one surface of the polarizing plate protective film.
The preferable polarizing plate of this invention is extended | stretched in the state by which the said protective film for polarizing plates and the hydrophilic polymer layer were laminated | stacked.

According to still another aspect of the present invention, a liquid crystal display device is provided.
The liquid crystal display device of the present invention has any one of the above polarizing plates.

The protective film for polarizing plates of the present invention can be stretched at a high magnification and is excellent in transparency and mechanical strength even after stretching. Furthermore, the dimension of the protective film for polarizing plate of the present invention hardly changes even when exposed to high temperature and high humidity.
The polarizing plate having the protective film for polarizing plate and the polarizing film of the present invention is excellent in transparency and mechanical strength, and has polarizing properties such as single transmittance and polarization degree even when exposed to high temperature and high humidity. It is hard to decline. By incorporating the polarizing plate of the present invention into, for example, a liquid crystal display device, it is possible to provide a liquid crystal display device in which unevenness due to light leakage is reduced and display performance does not change over a long period of time.

Sectional drawing of the polarizing plate of this invention which concerns on one preferable embodiment. Sectional drawing of the polarizing plate of this invention which concerns on other preferable embodiment.

[Protective film for polarizing plate]
The protective film for polarizing plate of the present invention is represented by the polyarylate having the repeating unit represented by the following general formula (I) and the repeating unit represented by the general formula (II), and the following general formula (III). And a polyester having a repeating unit and a repeating unit represented by formula (IV).
The protective film for polarizing plates of this invention is obtained by mixing the said polyarylate and polyester and forming this mixture into a film.

In general formula (I), A represents halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a sulfonic acid group, a nitro group, or cyano. Represents a group, and when A is plural, they are the same or different, and a represents an integer of 0 to 4 which is the number of substitution of A. In the general formula (II), B represents halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a sulfonic acid group, a nitro group, or cyano. Represents a group, and when B is plural, they are the same or different, and b represents an integer of 0 to 4 which is the number of substitution of B. D represents a halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a sulfonic acid group, a nitro group, or a cyano group. In a plurality of cases, they are the same or different, and d represents an integer of 0 to 4 which is the number of substitutions of D. R1 and R2 each independently represent a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms.
In the present specification, “substituted or unsubstituted” means “having a substituent or not having a substituent”.

When A, B and / or D is a substituted alkyl group having 1 to 4 carbon atoms or a substituted alkoxy group having 1 to 4 carbon atoms, examples of the substituent include halogen, hydroxyl group, carboxyl group, An amino group, a sulfonic acid group, a nitro group, a cyano group, etc. are mentioned, Preferably it is a halogen.
A, B and D are each independently preferably halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, or a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, and more preferably Is a halogen, an unsubstituted alkyl group having 1 to 4 carbon atoms, or an unsubstituted alkoxy group having 1 to 4 carbon atoms, more preferably a halogen, an unsubstituted alkyl group having 1 to 2 carbon atoms, or an unsubstituted group Or an alkoxy group having 1 to 2 carbon atoms. The polyarylate having each repeating unit represented by the formula (I) and the formula (II) may have a group represented by A, B and / or D on the benzene ring or may have this group. Even if not, it is excellent in rigidity and transparency, and can be compatible with the polyester.

The a, b and d are each independently preferably an integer of 0 to 2, more preferably an integer of 0 to 1, and still more preferably 0.
The repeating units of the formulas (I) and (II) in which a, b and d are 0 are represented by the following general formulas (Ia) and (II-a). In formula (II-a), R1 and R2 are the same as in formula (II).

In the formula (I), the phthalic acid unit may be any of an ortho structure, a meta structure (isophthalic acid), and a para structure (terephthalic acid), preferably a meta structure or a para structure, more preferably a meta structure. is there.
The repeating unit of the formula (I) in which the phthalic acid unit is a meta structure is represented by the following general formula (Ib). In the formula (Ib), Aa is the same as in the formula (I).

When R1 and / or R2 in the above formula (II) is a substituted alkyl group having 1 to 4 carbon atoms, examples of the substituent include halogen, hydroxyl group, carboxyl group, amino group, sulfonic acid group, nitro group, And cyano group and the like, preferably halogen.
R1 and R2 are each independently preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 2 carbon atoms, More preferably, it is an unsubstituted alkyl group having 1 to 2 carbon atoms. R1 and R2 are particularly preferably each a methyl group.

  In the molecular structure of the polyarylate, the number of repeating units represented by the general formula (I) is not particularly limited, but is preferably 15 to 170. Similarly, the number of repeating units represented by the general formula (II) is not particularly limited, but is preferably 20 to 200. When the number of repeating units of the formula (I) and the formula (II) is less than the above range, the heat resistance and mechanical strength of the protective film are deteriorated, and the film forming stability is further improved when the protective film is produced. May decrease. On the other hand, when each of the numbers exceeds the above range, the molecule becomes rigid and the protective film may not be stretched at a high magnification.

In the molecular structure of the polyarylate, the ratio (molar ratio) of the repeating unit represented by the formula (I) and the repeating unit represented by the formula (II) is not particularly limited, but preferably the formula ( I ) : The molar ratio of formula ( II ) is 4:10 to 6:10, more preferably 4.5: 10 to 5.5: 10. When the molar ratio between the formula ( I ) and the formula ( II ) is in the above range, the mechanical strength of the protective film can be improved.

  The polyarylate may have other repeating units in addition to the repeating units represented by the formulas (I) and (II). When the polyarylate has other repeating units in its molecular structure, the molar ratio of the sum of the repeating units of formula (I) and formula (II) to the other repeating units is 90:10 to 99: 1. Preferably there is.

  The protective film for polarizing plates of this invention contains the said polyarylate and polyester which has a repeating unit represented by the following general formula (III), and a repeating unit represented by general formula (IV).

  In the general formula (III), E represents halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a sulfonic acid group, a nitro group, or a cyano group. Represents a group, and when E is plural, they are the same or different, and e represents an integer of 0 to 4 which is the number of substitutions of E. In general formula (IV), Ak represents a C1-C8 alkylene group.

In the case where E is a substituted alkyl group having 1 to 4 carbon atoms or a substituted alkoxy group having 1 to 4 carbon atoms, the substituent includes halogen, hydroxyl group, carboxyl group, amino group, sulfonic acid group , A nitro group, a cyano group, and the like, preferably halogen.
E is preferably a halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, or a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, more preferably a halogen or an unsubstituted carbon number of 1 An alkyl group having 1 to 4 carbon atoms, or an unsubstituted alkoxy group having 1 to 4 carbon atoms, more preferably a halogen, an unsubstituted alkyl group having 1 to 2 carbon atoms, or an unsubstituted alkoxy group having 1 to 2 carbon atoms. It is. The polyester having each repeating unit represented by the formula (III) and the formula (IV) is flexible even if it has a group represented by E on its benzene ring or does not have this group. In addition, it is excellent in transparency and can be compatible with the polyarylate.

The e is preferably an integer of 0 to 2, more preferably an integer of 0 to 1, and still more preferably 0.
The repeating unit of the formula (III) in which e is 0 is represented by the following general formula (III-a).

Ak in the above formula (IV) may be a linear alkylene group having 1 to 8 carbon atoms or a branched alkylene group having 1 to 8 carbon atoms. Examples of the linear alkylene group having 1 to 8 carbon atoms include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, and a hexylene group. Examples of the branched alkylene group having 1 to 8 carbon atoms include a methylethylene group, a dimethylmethylene group, a 2,3-dimethylbutylene group, and a 3-methylpentylene group. The Ak is preferably a linear alkylene group having 1 to 8 carbon atoms (— (CH ₂ ) _1-8 —), more preferably a linear alkylene group having 2 to 4 carbon atoms (— ( CH ₂₎ 2~4 -), and particularly preferably an ethylene group.

  In the molecular structure of the polyester, the number of repeating units represented by the general formula (III) is not particularly limited, but is preferably 50 to 600. Similarly, the number of repeating units represented by the general formula (IV) is not particularly limited, but is preferably 30 to 400. When the number of repeating units of the formula (II) and the formula (IV) is less than the above range, the heat resistance and mechanical strength of the protective film are deteriorated, and the film forming stability is further improved when the protective film is produced. May decrease. On the other hand, when each of the numbers exceeds the above range, the molecule becomes rigid and the protective film may not be stretched at a high magnification.

  In the molecular structure of the polyester, the ratio (molar ratio) of the repeating unit represented by the formula (III) and the repeating unit represented by the formula (IV) is not particularly limited, but preferably the formula (III): The molar ratio of formula (IV) is 12:10 to 18:10, more preferably 14:10 to 16:10.

  The polyester may have other repeating units in addition to the repeating units represented by formula (III) and formula (IV). When the polyarylate has other repeating units in its molecular structure, the molar ratio of the sum of the repeating units of formula (III) and formula (IV) to the other repeating units is 90:10 to 99: 1. It is preferable that

The polyarylate can be obtained, for example, by polycondensing a bisphenol derivative and a phthalic acid derivative by an interfacial polymerization method, a solution polymerization method, or a melt polymerization method.
The polyester can be obtained, for example, by polycondensation of a terephthalic acid derivative and an aliphatic diol.

The protective film for polarizing plates of the present invention can be obtained by mixing the polyarylate and the polyester at a predetermined ratio and forming a film.
Content of the said polyarylate and polyester in the protective film for polarizing plates of this invention is not specifically limited, It can set suitably. However, when the polyarylate is contained in a large amount, the stretchability of the film is lowered. On the other hand, when the polyester is contained in a large amount, the dimensional stability under high temperature and high humidity is lowered. Considering such points, the content ratio (mass ratio) of the polyarylate and polyester in the protective film for polarizing plate of the present invention is preferably 60:40 to 10:90, more preferably 60:40. It is -20: 80, More preferably, it is 60: 40-40: 60. Moreover, it is preferable that a protective film contains more polyester than polyarylate (in mass conversion). A protective film containing more polyester than polyarylate has a good balance between thermal stability and mechanical strength, and also has excellent processability.

In addition, in the range which does not impair the effect of this invention, the protective film for polarizing plates of this invention may contain other components other than the said polyarylate and polyester.
Examples of other components include polymers other than the polyarylate and polyester, various additives, and the like.
When the protective film for polarizing plates of this invention contains the said other component, content of another component is although it does not specifically limit, It is preferable that it is 1 mass%-10 mass% in the said film.

The protective film for polarizing plates can be obtained by forming a mixture containing the polyarylate and polyester using a known film forming method such as a melt extrusion method or a solution casting method.
The polyarylate and the polyester are compatible by mixing both without using a compatibilizing agent. For example, when the polyarylate and polyester are kneaded by the reactive extrusion method, both are compatible. When the polyarylate and the polyester are compatible, a protective film for a polarizing plate that is excellent in transparency and hardly changes in dimensions can be obtained. The term “compatible” refers to a state in which polyarylate and polyester are mixed without substantially causing phase separation.

[Characteristics of protective film for polarizing plate]
The protective film for polarizing plate of the present invention has a transmittance of 85% or more, preferably 88% or more, more preferably 90% or more, and a haze value of 1% or less, preferably 0.5% or less. Preferably it is 0.3% or less.
However, the said transmittance | permeability is the total light transmittance in visible light, and can be measured based on JISK7375 (how to obtain | require total light transmittance and total light reflectance). Moreover, a haze value can be measured based on JISK7136 (how to obtain the haze of a transparent material).

The protective film for polarizing plates of the present invention can be stretched 3 times or more, preferably 5 times or more in at least one axial direction (MD direction and / or TD direction). The reason that the protective film can be stretched at a high magnification of 5 times or more is presumed to be due to the inclusion of the polyester.
The protective film for polarizing plates of the present invention is excellent in transparency and mechanical strength even after stretching. The reason why the protective film is excellent in transparency before stretching and after stretching is presumed to be due to the compatibility of the polyarylate and the polyester. The protective film has excellent mechanical strength before and after stretching because it contains the rigid polyarylate and the flexible polyester, and is compatible with each other. It is estimated that.
Moreover, even if the protective film for polarizing plates of the present invention is stretched and then exposed to high temperature and high humidity, the dimensional change is small. For example, the dimensional change rate of the protective film for polarizing plate is preferably 1% or less under the condition that the protective film for polarizing plate after stretching is allowed to stand at 80 ° C. or 60 ° C. and 90% humidity for 500 hours. Preferably it is 0.5% or less, More preferably, it is 0.1% or less. It is presumed that the size of the protective film hardly changes due to the inclusion of the polyarylate. In addition, the said dimensional change rate can be calculated | required by the method as described in the following Example.
The thickness of the protective film for polarizing plates of this invention can be set suitably. The said protective film for polarizing plates is extended | stretched when forming a polarizing plate. In consideration of stretching, the thickness of the protective film for polarizing plate is preferably 50 μm to 200 μm, and more preferably 100 μm to 200 μm.
The protective film for polarizing plates of the present invention is usually formed in a long shape. In the present specification, the long shape means a shape whose length is 10 times or more, preferably 50 times or more with respect to the width. For example, the protective film for a polarizing plate is formed with a length of 300 m or more.

[Polarizer]
The polarizing plate of this invention has the protective film for polarizing plates of this invention, and a polarizing film.
In one preferable embodiment, as shown in FIG. 1, the polarizing plate 1 is formed by laminating a polarizing plate protective film 2 and a polarizing film 3. In another preferred embodiment, as shown in FIG. 2, the polarizing plate 1 includes a polarizing plate protective film 2, a polarizing film 3, and an optical film 4 laminated in this order. Examples of the optical film 4 include a retardation film and a protective film (this protective film may be the protective film for polarizing plate of the present invention, or may be a conventionally known protective film). Is mentioned.

When the optical film is a retardation film, the retardation film is preferably laminated so that the slow axis of the retardation film and the absorption axis of the polarizing film are substantially perpendicular to each other.
The polarizing plate of the present invention is formed in a long shape. When a polarizing plate is elongate, it is preferable to have the absorption axis of the said polarizing film in the width direction (TD direction).

The polarizing plate of the present invention can be obtained, for example, by providing a hydrophilic polymer layer (corresponding to a polarizing film) containing a dichroic substance on one surface of a protective film for a polarizing plate.
Specifically, the polarizing plate of the present invention can be obtained through the following steps 1 to 3 and other steps as necessary.
Process 1: The process of applying the resin composition containing a hydrophilic polymer to one surface of the protective film for polarizing plates of this invention, and drying a coating film.
Process 2: The process of extending | stretching the laminated body on which the said protective film and the dry coating film were laminated | stacked.
Process 3: The process of dyeing | stacking the laminated body on which the said protective film and the dry coating film were laminated | stacked using a dichroic substance, and obtaining a polarizing plate.
In addition, although it is preferable to perform the process 3 after performing the said process 2, you may perform the process 2 after performing the process 3, or you may perform the process 2 and the process 3 simultaneously.

(Process 1)
Step 1 is a step of forming a coating film containing a hydrophilic polymer on one surface of the protective film for a polarizing plate and curing the coating film.
The hydrophilic polymer is not particularly limited, and generally a polymer having a hydrophilic group such as an OH group or a COOH group can be used, and a vinyl alcohol resin can be preferably used. Examples of the vinyl alcohol resin include polyvinyl alcohol, partially formalized PVA, ethylene-vinyl alcohol copolymer, and partially saponified products thereof. PVA is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification is preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined according to JIS K6726-1994. By using a vinyl alcohol resin having a saponification degree within the above range, a polarizing film having excellent durability can be obtained.
The average degree of polymerization of the vinyl alcohol resin is appropriately set. The average degree of polymerization is preferably 1200 to 4500, more preferably 2500 to 4300. The average degree of polymerization can be determined according to JIS K6726-1994.

The resin composition containing the hydrophilic polymer is typically a solution in which a vinyl alcohol resin is dissolved in a solvent. Examples of the solvent include water, warm water, and a hydrophilic solvent. The concentration of the vinyl alcohol resin in the solution is preferably 3% by mass to 20% by mass. If a solution having the concentration range is used, a substantially uniform coating film can be formed.
The resin composition containing the hydrophilic polymer may contain various additives. As an additive, Preferably a plasticizer, surfactant, etc. are mentioned. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol. Examples of the surfactant include nonionic surfactants. The plasticizer and surfactant have a function of improving the stretchability and dyeability of the coating film.

A coating film is formed by coating the resin composition containing the hydrophilic polymer on one surface of a protective film for a polarizing plate. Before applying the resin composition, one surface of the protective film may be surface-treated. Examples of the surface treatment include corona treatment, flame treatment, plasma treatment, and primer treatment. By performing such surface treatment, the coating film can be firmly adhered to one surface of the protective film for polarizing plate.
The method for applying the resin composition is not particularly limited. Examples of the coating method include a roll coating method, a gravure coating method, a spin coating method, a wire bar coating method, a dip coating method, and a spray auto method.
By drying the coating film, a laminate in which the polarizing plate protective film and the dried coating film are laminated is obtained. Drying may be natural drying, heat drying, or a combination thereof. The thickness of the dried coating film is preferably 1 μm to 50 μm.
According to the present invention, only by applying the resin composition, the polarizing plate protective film and the dried coating film (hydrophilic polymer layer) can be directly adhered and laminated without interposing an adhesive layer. For this reason, a polarizing plate with a small dimensional change rate can be obtained.

(Process 2)
The laminated body of the protective film for polarizing plates obtained by the process 1 and a dry coating film is extended | stretched. A polarizing plate having a small dimensional change rate can be obtained by stretching in a state where the protective film and the dried coating film are laminated (stretching the laminate).
The stretching method is not particularly limited. Examples of the stretching method include a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse simultaneous biaxial stretching method, and a longitudinal and transverse sequential biaxial stretching method. In one embodiment, it is preferable to perform uniaxial stretching in the width direction (TD direction) of the long laminate. Thus, by extending | stretching in the width direction, the absorption axis of a polarizing film can be expressed in the width direction of the protective film for polarizing plates.
Examples of the stretching means include a roll stretching machine, a tenter stretching machine, and a biaxial stretching machine. The draw ratio is preferably 3 to 7 times, more preferably 4 to 7 times. When the draw ratio is lower than the above range, a polarizing film having insufficient polarization characteristics may be obtained. When the stretching field ratio is higher than the above range, there is a possibility that cracks may occur in the dried coating film (hydrophilic polymer layer). As mentioned above, since the protective film for polarizing plates of the present invention can be stretched 5 times or more without breaking, it is possible to stretch the laminate to about 7 times.
The stretching temperature is set to a temperature at which the laminate is not thermally deteriorated. For example, the stretching temperature is preferably from the glass transition temperature of the protective film for a polarizing plate (a mixture of polyarylate and polyester) to the glass transition temperature + 50 ° C.
Although the glass transition temperature of the protective film for polarizing plates of this invention changes with content ratios of a polyarylate and polyester, etc., it is the range of 100 to 170 degreeC, Preferably it is 120 to 160 degreeC. However, the said glass transition temperature can be calculated | required by DSC method based on JISK7121.
In addition, you may provide suitably each process, such as preheating, heat processing, and cooling, before and after the extending | stretching process.

(Process 3)
The stretched laminate obtained in step 2 is dyed with a dichroic substance. Examples of the dichroic substance include iodine and a dichroic dye.
For example, the laminate is immersed in a dyeing solution in which a dichroic substance is dissolved in water. When the dichroic dye is iodine, an aqueous solution containing iodine and potassium iodide is used as the staining solution. Content of the iodine in this aqueous solution is 0.01-2 mass with respect to 100 mass parts of water, for example. Moreover, content of the potassium iodide in the said aqueous solution is 0.5-10 mass parts with respect to 100 mass parts of water, for example. The temperature of the aqueous solution is preferably 20 to 40 ° C., and the immersion time is preferably 5 seconds to 240 seconds. Depending on the temperature range and immersion time, the dichroic substance can be satisfactorily impregnated or adsorbed in the dried coating film. A dry coating dyed with a dichroic material produces polarizing properties. That is, the dried coating film after dyeing is a polarizing film.

(Other processes)
Before dyeing the dried coating film, a step of swelling the dried coating film may be performed. For example, the dried coating film can be swollen by immersing the laminate in water at about 20 to 50 ° C. The swelling step is performed in order to remove dirt on the surface of the dried coating film and swell the dried coating film with water to prevent uneven introduction of the dichroic substance.
Moreover, after dyeing the dried coating film, a crosslinking step, a washing step, and a drying step may be performed in order. The crosslinking step is a step of impregnating a dried coating film after dyeing with a crosslinking agent such as boric acid. The cleaning step is a step of washing away unnecessary residues adhering to the laminate. A drying process is a process of drying the laminated body after washing | cleaning.
Since the swelling process, the crosslinking process, the washing process and the drying process can be performed under conventionally known conditions, detailed description thereof is omitted.

As described above, a polarizing plate in which a polarizing plate protective film and a polarizing film (a hydrophilic polymer layer containing a dichroic substance) are laminated can be obtained.
The thicknesses of the protective film for polarizing plate and the polarizing film become thinner than the original by stretching. The thickness of the protective film after stretching is preferably 20 μm to 80 μm, more preferably 20 μm to 60 μm. Although the thickness of the polarizing film in the said polarizing plate is not specifically limited, Preferably it is 1 micrometer-10 micrometers, More preferably, they are 1 micrometer-6 micrometers.
The obtained polarizing plate has a form as shown in FIG. In practical use, it is preferable to attach another optical film such as a retardation film to the surface of the polarizing film of the polarizing plate. When a long polarizing plate protective film is used in the above production method, a long polarizing plate is obtained. When the other optical film is bonded to a long polarizing plate, a bonding process using a so-called roll-to-roll process can be performed.

The polarizing plate (polarizing film) of the present invention exhibits absorption dichroism at at least a part of wavelengths in the visible light region.
The single transmittance (23 ° C., wavelength 550 nm) of the polarizing plate is 35% to 46%, preferably 39% to 46%.
The polarization degree of the polarizing plate is 95% or more, preferably 98% or more.

The polarizing plate of this invention has the said protective film for polarizing plates, and the polarizing film which consists of a hydrophilic polymer layer containing the said dichroic substance. Since the thickness of the polarizing film is much thinner than that of the protective film, the mechanical strength and dimensional change rate of the polarizing plate depend on the protective film for polarizing plate. As described above, the protective film for polarizing plate of the present invention is not only excellent in transparency and mechanical strength but also has a small dimensional change rate after being stretched. Therefore, the polarizing plate of the present invention is also excellent in transparency and mechanical strength, and has a small dimensional change rate even when exposed to high temperature and high humidity.
The conventional protective film changes its dimensions greatly when exposed to high temperature and high humidity. Therefore, the polarizing film laminated on the protective film is distorted. As a result, the absorption axis of the polarizing film is shifted and light leakage occurs. . Since the protective film for polarizing plates of this invention has a small dimensional change rate, it can prevent the distortion of the polarizing film laminated | stacked on this. Therefore, the polarizing plate of the present invention hardly deteriorates in polarization characteristics even when exposed to high temperature and high humidity, and can prevent light leakage over a long period of time.

[Use of polarizing plate]
The polarizing plate of the present invention can be used in the mode shown in FIG. 1 or in a mode in which another optical film 4 is laminated on the surface of the polarizing film 3 as shown in FIG.
As shown in FIG. 2, the preferred polarizing plate 1 of the present invention includes a polarizing plate protective film 2, a polarizing film 3, and an optical film 4. More preferably, the optical film 4 is a retardation film.
When the polarizing plate of the present invention is long, it is practically used by punching it into an appropriate shape.
The polarizing plate of the present invention is preferably incorporated in a liquid crystal display device. Preferable uses of the liquid crystal display device having the polarizing plate are a television, a mobile phone, a camera, and the like.

  The present invention will be described in detail with reference to examples and comparative examples. In addition, this invention is not limited only to the following Example.

[Example 1]
20 parts by mass of a polyarylate having a repeating unit represented by the following formula (V) and 80 parts by mass of a polyester having a repeating unit represented by the following formula (VI) are blended, and a twin screw extruder with a vent is used. The mixture was kneaded at 280 ° C. to form pellets. However, p = 75 and q = 150 in the formula (V). In the formula (VI), r = 279 and s = 186.
The polyarylate having a repeating unit represented by the formula (V) can be obtained by interfacial polymerization reaction of bisphenol A and isophthalic acid at a molar ratio of 1: 2.
The polyester having a repeating unit represented by the formula (VI) can be obtained by dehydrating and condensing terephthalic acid and ethylene glycol at a molar ratio of 3: 2.
A film having a thickness of 150 μm was produced by forming the pellets by a known T-die method (extrusion temperature: 280 ° C.).

  When the film of Example 1 was observed using a scanning electron microscope (manufactured by Hitachi, Ltd., product name “H-7650”), it was confirmed that the polyarylate and the polyester were compatible. Similarly, using an atomic force microscope (product name “Na No Scope V + D3100” manufactured by Becco Instruments, Inc.) was confirmed to be compatible with both polymers.

[Example 2]
Except having changed the polyarylate which has a repeating unit represented by Formula (V) into 45 mass parts, and having changed the polyester which has a repeating unit represented by Formula (VI) into 55 mass parts, it carries out similarly to Example 1. A film was prepared.
When Example 2 was confirmed in the same manner as in Example 1, both polymers were compatible.

[Example 3]
Except having changed the polyarylate which has a repeating unit represented by Formula (V) into 55 mass parts, and having changed the polyester which has a repeating unit represented by Formula (VI) into 45 mass parts, it is the same as that of Example 1. A film was prepared.
Example 3 was also confirmed in the same manner as in Example 1. As a result, both polymers were compatible.

[Comparative Example 1]
A film having a thickness of 150 μm was produced by forming only a polyarylate having a repeating unit represented by the formula (V) by a known T-die method (extrusion temperature 260 ° C.).

[Comparative Example 2]
A film having a thickness of 150 μm was produced by forming only a polyester having a repeating unit represented by the formula (VI) by a known T-die method (extrusion temperature 260 ° C.).

[Comparative Example 3]
A triacetyl cellulose film (manufactured by Fuji Film Co., Ltd., product name “TD80UL film”, thickness 80 μm) was used.

[Comparative Example 4]
A film having a thickness of 150 μm was prepared by forming a film of polyethylene terephthalate (manufactured by Eastman Chemical Co., Ltd., product name “Eastman PET9921”) by a known T-die method (extrusion temperature: 270 ° C.).

[Comparative Example 5]
An acrylic resin (Mitsubishi Rayon Co., Ltd., product name “Acrypet V”) was formed by a known T-die method (extrusion temperature: 250 ° C.) to prepare a film having a thickness of 150 μm.

[Comparative Example 6]
A cyclic olefin resin film (manufactured by JSR Corporation, product name “Arton Film”, thickness 150 μm) was used.

[Comparative Example 7]
A film having a thickness of 150 μm was produced by forming nylon 6 (product name “A1030BRT” manufactured by Unitika Ltd.) by a known T-die method (extrusion temperature: 270 ° C.).

[Comparative Example 8]
A film having a thickness of 150 μm was produced by forming nylon 12 (product name “UBESTA3030XA” manufactured by Ube Industries, Ltd.) by a known T-die method (extrusion temperature: 270 ° C.).

[Extensible]
The film of each Example and Comparative Example was cut into 12 cm × 12 cm in length and width, and stretched 5 times in the TD direction using a batch type stretching machine (manufactured by Bruckner). The stretching temperatures of the films of Examples 1 to 3 and Comparative Examples 3 and 5 were 150 ° C., the stretching temperatures of Comparative Examples 1 and 6 were 160 ° C., the stretching temperatures of Comparative Examples 2 and 4 were 100 ° C., respectively. In each of Examples 7 and 8, the stretching temperature was 120 ° C.

The results are shown in Table 1. In addition, in the stretchability of Table 1, “good” means that the film was not broken even when stretched 5 times and could be stretched satisfactorily. In the stretchability of Table 1, the indication “to times” is a case where the film is broken during stretching, and represents the stretch ratio at the time of the break.
For films with good stretchability, the following mechanical strength is measured. For films with poor stretchability (films that could not be stretched 5 times), the following tests and measurements including the following mechanical strength are performed. Did not do.

[Mechanical strength]
The stretched film (thickness: about 30 μm) was subjected to bending tests in the MD direction and the TD direction, respectively, using an MIT type folding resistance tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS P8115. In the bending test in the MD direction (mechanical strength in the MD direction of Table 1), the film was reciprocally bent 500 times so that a fold line was generated in a direction parallel to the TD direction at the center of the stretched film. In the bending test in the TD direction (Mechanical strength in the TD direction of Method 1), the film was bent back and forth 500 times so that a fold line was generated in a direction parallel to the MD direction at the center of the stretched film.
The results are shown in Table 1. In addition, in the mechanical strength of Table 1, “good” means that the film did not break even when the film was bent 500 times in a reciprocating manner. In the mechanical strength of Table 1, the indication “to times” represents a case where the film broke during the test, and represents the number of times of bending at the time of the break.
And about the film with favorable mechanical strength of MD direction and TD direction, the following transmittance | permeability and a haze value are measured, and the film with poor mechanical strength (at least any one of MD direction and TD direction is less than 500 roundtrips. For the film broken at), the following tests and measurements including the following transmittance were not performed.

[Transmissivity]
The total light transmittance of the stretched film was measured using a transmittance measuring device (manufactured by Hitachi High-Technology Corporation, product name “Hitachi Spectrophotometer U-4100”) based on JIS K7375. The results are shown in Table 1.

[Haze value]
The haze value of the stretched film was measured using a haze measuring apparatus (product name “Haze Meter HM-150” manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K7136. The results are shown in Table 1.

[Dimensional change]
The stretched film is cut into 10 cm × 10 cm in length and width to form four test pieces, each exposed to the following four conditions, and then the dimensions in the MD direction and TD direction of the test piece from the following formulas 1 and 2. The rate of change was determined.
Condition 1: The test piece is left in an oven at 80 ° C. for 500 hours.
Condition 2: The test piece is left in an oven at 100 ° C. for 500 hours.
Condition 3: The test piece is left in a constant temperature and humidity apparatus at 60 ° C. and a humidity of 90% for 500 hours.
Condition 4: The test piece is left in a constant temperature and humidity apparatus at 85 ° C. and a humidity of 85% for 500 hours.
Formula 1: Dimensional change rate in the MD direction of the test piece (%) = {(length of the test piece in the MD direction before being left--length of the test piece in the MD direction after being left for 500 hours) / test piece before being left to stand Length in MD direction} × 100.
Formula 2: Dimensional change rate (%) in the TD direction of the test piece = {(Length in the TD direction of the test piece before being left--Length of the test piece in the TD direction after being left for 500 hours) / Test piece before being left to stand Length in the TD direction} × 100.
The results are shown in Table 1. In addition, about the dimensional change rate of Table 1, the worst value (largest dimensional change rate) was described typically among the dimensional change rates in MD direction and TD direction in said each condition.

[Evaluation]
The films of Examples 1 to 3 could be stretched 5 times or more, and were excellent in mechanical strength and transparency even after stretching. Furthermore, the dimensions of the films of Examples 1 to 3 hardly changed under high temperature and high humidity.
On the other hand, the dimensions of the films of Comparative Examples 2 and 4 greatly changed under high temperature and high humidity.

  The protective film for polarizing plates of this invention can be utilized as a structural member of a polarizing plate. In particular, when a polarizing film is formed by providing a polarizing film on one surface of the protective film and then forming a polarizing plate, the polarizing plate protective film of the present invention is useful.

  DESCRIPTION OF SYMBOLS 1 ... Polarizing plate, 2 ... Protective film for polarizing plates, 3 ... Polarizing film, 4 ... Optical film

Claims (8)

Polyarylate having a repeating unit represented by general formula (I) and a repeating unit represented by general formula (II), a repeating unit represented by general formula (III) and represented by general formula (IV) look-containing polyester having a repeating unit, the molar ratio of the repeating unit represented by the general formula repeating unit and the formula represented by (I) (II) is 4: 10-6: polarization 10 Board protective film.

A, B and D are each independently a halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a sulfonic acid group, or a nitro group. Or a cyano group, and when A, B and D are plural, they are the same or different, and a, b and d each represent an integer of 0 to 4 which is the number of substitutions of A, B and D, R1 and R2 each independently represent a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms.

E represents a halogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a sulfonic acid group, a nitro group, or a cyano group. , Each represents the same or different, e represents an integer of 0 to 4 which is the number of substitutions of E, and Ak represents an alkylene group having 1 to 8 carbon atoms.   The protective film for polarizing plates according to claim 1, wherein the polyarylate and the polyester are compatible.   The protective film for a polarizing plate according to claim 1 or 2, wherein the mass ratio of the polyarylate to the polyester is 60:40 to 10:90.   Ak of said Formula (IV) is a C1-C8 linear alkylene group, The protective film for polarizing plates in any one of Claims 1-3.   The polarizing plate which has the protective film for polarizing plates in any one of Claims 1-4, and a polarizing film.   The polarizing plate according to claim 5, wherein the polarizing film is a hydrophilic polymer layer containing a dichroic material provided on one surface of the protective film for polarizing plate.   The polarizing plate according to claim 6, wherein the polarizing plate is stretched in a state where the protective film for the polarizing plate and the hydrophilic polymer layer are laminated.   A liquid crystal display device comprising the polarizing plate according to claim 5.

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