KR20140080421A - Polarizing plate and liquid crystal display apparatus comprising the same - Google Patents

Abstract

The present invention relates to a polarizing plate and a liquid crystal display apparatus comprising the same, which comprise a polarizer; a first optical film formed on the top of the polarizer; and a second optical film formed on the bottom of the polarizer, wherein more than one of the first optical film and the second optical film contains a polyester film, wherein the polyester film has -0.1 to +0.1% of a difference of a length shrinkage ratio between the length shrinkage ratio of a first diagonal direction of equation 1 and the length shrinkage ratio of a second diagonal direction of equation 2 based on one of a machine direction (MD) or a transverse direction (TD) of the film.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate and a liquid crystal display including the polarizing plate.

The present invention relates to a polarizing plate and a liquid crystal display including the same.

The polarizing plate includes a polarizer and a protective film for a polarizing plate formed on one surface of the polarizer. Triacetylcellulose (TAC) films have been used as protective films for polarizing plates. Since the TAC film has a high glass transition temperature (Tg) and is manufactured by casting, the shrinkage ratio of the machine direction (MD) or transverse direction (TD) is stable. In addition, the TAC film has no stretching process and no heat shrinkage phenomenon.

A polyester film such as a polyethylene terephthalate (PET) film is used as a protective film for a polarizing plate due to diversification of a protective film for a polarizing plate. The PET film is a stretched film having a relatively large MD or TD elongation, and thus can exhibit shrinkage and expansion behavior due to heat. In addition, the PET film has a lower glass transition temperature than that of the TAC film, so that heat shrinkage may occur. Thus, the polarization degree of the PET film can be lowered by turning the optical axis of the polarizer during the manufacturing process of the polarizer. There is a method of controlling the MD or TD shrinkage ratio of the PET film. However, this method can control the basic physical properties or warpage of the PET film, but since it displays only longitudinal / transverse shrinkage, There was a difficulty in explaining the inaxial deformation. In this regard, Japanese Patent Laid-Open No. 1997-127332 discloses a protective film for a polarizing plate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing plate comprising a polyester film as a protective film and capable of preventing axial twisting during production or use of the polarizing plate.

Another object of the present invention is to provide a polarizing plate comprising a polyester film as a protective film and having a high degree of polarization.

The polarizing plate of the present invention comprises a polarizer, a first optical film formed on the upper portion of the polarizer, and a second optical film formed on the lower portion of the polarizer, wherein at least one of the first optical film and the second optical film includes a polyester film , The polyester film has a length contraction ratio in the first oblique direction of the following formula 1 and a length contraction ratio in the second oblique direction of the following formula 2 based on any one of MD (Machine Direction) or TD (Transverse Direction) The difference in length shrinkage ratio can be from -0.1 to + 0.1%

<Formula 1>

Length contraction ratio (%) in the first diagonal direction = (A-B) / A x 100

(In the above formula 1, A and B are as defined in the detailed description below)

<Formula 2>

Length contraction ratio (%) in the second diagonal direction = (C-D) / C x 100

(In the above formula 2, C and D are as defined in the detailed description below)

However, the angle between the first oblique direction and the second oblique direction is not 0 °.

The liquid crystal display device of the present invention may include the polarizing plate.

The present invention provides a polarizing plate comprising a polyester film as a protective film and capable of preventing axial twisting during production or use of the polarizing plate. The present invention provides a polarizing plate comprising a polyester film as a protective film and having a high degree of polarization.

1 is a sectional view of a polarizing plate of one embodiment of the present invention.
2 is a sectional view of a polarizing plate of another embodiment of the present invention.
3 is a cross-sectional view of a module for a liquid crystal display device according to an embodiment of the present invention.
4 is a conceptual diagram of the length contraction ratio of the film.
Fig. 5 shows the length shrinkage measurement region in the film.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification. In the present specification, 'upper' and 'lower' are defined with reference to drawings, and 'upper' may be changed to 'lower' and 'lower' may be changed to 'upper' depending on viewing time.

4, the x-axis direction is the TD (transverse direction) of the film 50, the y-axis direction is the MD (machine direction), and the y- , and the x-axis direction and the y-axis direction are orthogonal to each other. A film sample 50A (for example, a square shape such as a square) of the film 50 is taken and a first oblique direction of the film sample 50A is formed with angle α based on TD and the length is A, 50A) is left at 85 占 폚 for 30 minutes, the length B of the portion in the first diagonal direction is measured, and the length contraction ratio is calculated according to the following Formula 1:

<Formula 1>

Length contraction ratio (%) in the first diagonal direction = (A-B) / A x 100

(Where A is the initial length of the portion in the first diagonal direction with respect to the reference direction in the film sample and B is the length in the first diagonal direction after leaving the sample at 85 +/- 5 DEG C for 30 minutes In length).

The second oblique direction of the film sample 50A is an angle β with respect to TD, and the length thereof is C. The second oblique direction of the film sample 50A is defined as a portion in the second diagonal direction after leaving the film sample 50A at 85 ± 5 ° C. for 30 minutes And the length contraction ratio is calculated according to the following equation (2): &lt; RTI ID = 0.0 &gt;

<Formula 2>

Length contraction ratio (%) in the second diagonal direction = (C-D) / C x 100

(Where C is the initial length of the portion in the second oblique direction with respect to the reference direction in the film sample and D is the length in the second oblique direction after leaving the sample at 85 占 5 占 폚 for 30 minutes In length).

However, the angle between the first oblique direction and the second oblique direction is not 0 °. Although the difference in the ideal length shrinkage ratio is described based on TD, the same can be applied to the MD.

Hereinafter, a polarizing plate of one embodiment of the present invention will be described with reference to FIG. 1 is a sectional view of a polarizing plate of one embodiment of the present invention.

1, a polarizing plate 100 according to an embodiment of the present invention includes a polarizer 10, a first optical film 20 formed on a top of the polarizer 10, and a second optical film 20 formed on a lower portion of the polarizer 10. [ (30), and the first optical film (20) may be a polyester film whose difference in length shrinkage ratio is -0.1 to + 0.1%. If the difference in the length shrinkage percentage of the polyester film is less than -0.1% or exceeds + 0.1%, shrinkage of the polyester film occurs due to the heat generated during the manufacturing process or driving of the polarizer, and the optical axis of the polarizer is distorted, The degree of polarization can be lowered.

Referring to FIG. 4, the angle? Can be 30 to 60 degrees, for example 45 degrees, based on TD, and the angle? Can be 120 to 150 degrees, for example 135 degrees, The difference between angles? And? Can be between 60 and 120 degrees.

In the polyester film, the length shrinkage ratio in the first oblique direction and the second oblique direction can be -0.15% to + 0.15%, respectively. In this range, the shrinkage of the polarizer due to the shrinkage ratio affects the degree of polarization .

The length shrinkage can be measured using a film specimen taken at any position in the film. However, when the film is a stretched film, the center portion of the film is stretched through the stress concentration phenomenon, and the degree of stretching becomes weaker toward the end portion, with the heat generated during the manufacturing process or driving of the polarizer plate When the polarizer shrinks, it also affects the heat shrinkage direction. Therefore, it is preferable that the length shrinkage ratio is measured at the end portion with respect to the width direction of the film. The end portion may refer to a portion of from 0 to 2.5% from one end of the film with respect to the entire width of the film based on the film TD.

5, the x-axis direction is the TD (transverse direction) of the film 50, the y-axis direction is the MD (machine direction), and the x- The directions are orthogonal to each other. On the basis of TD, the film is composed of d1, d2, and d3, and d1 and d3 are sections within 0 to 2.5% from the end of the film, respectively. The length shrinkage can be measured from a sample taken from dl or d3. More specifically, the length shrinkage percentage can be measured with a specimen taken from an interval of more than 0 to 2.5%, more preferably 0.001 to 2.5% from one end of the film with respect to the entire width of the film on the basis of the film TD.

The polyester film has an ultra-high retardation in a stretched film at a high magnification, and when a polarizing plate is attached to a liquid crystal display device, the occurrence of rainbow stains is inhibited, and image quality deterioration can be prevented. In a specific example, the polyester film may have a thickness of 25 to 500 탆, specifically 25 to 115 탆, and a front retardation Ro at a wavelength of 550 nm of 5,000 nm to 15,000 nm, specifically 10,100 nm to 12,000 nm. In the above range, when used as a protective film of a polarizer, it is possible to prevent occurrence of rainbow stains, to inhibit the light leakage phenomenon in which light leaks from the side, and to prevent a difference in retardation value from being increased by preventing a change in retardation value according to an incident angle .

In the polyester film, one of the refractive indices ny in the y-axis direction at a wavelength of 550 nm may be 1.65 or more. When both of nx and ny are less than 1.65 or both of nx and ny are more than 1.65, rainbow stains may occur due to birefringence due to a change in the retardation value depending on the incident angle and wavelength when used as a protective film. In one embodiment, nx can be 1.65 or more, specifically 1.67 to 1.75, and ny can be 1.45 to 1.55. In other embodiments, ny can be 1.65 or more, specifically 1.67 to 1.72, more specifically 1.69 to 1.72, and nx can be 1.45 to 1.55. At this time, by setting the absolute value (| nx-ny |) of the difference between nx and ny to be 0.1 to 0.2, specifically 0.12 to 0.18, the viewing angle can be further improved, and rainbow stains can be prevented from occurring.

The polyester film may have a degree of biaxiality (NZ) of the following formula 3 at a wavelength of 550 nm of 1.8 or less, specifically 1.0 to 1.8, and may have a stain control effect by birefringence in the above range:

<Formula 3>

NZ = (nx - nz) / (nx - ny)

(Where nx, ny, and nz are refractive indices in the x-axis, y-axis, and z-axis directions of the polyester film at a wavelength of 550 nm, respectively).

The polyester film may have a retardation difference (Rth) in the thickness direction of the following formula (4) at a wavelength of 550 nm of 15,000 nm or less, for example, 10,000 nm to 12,000 nm, and may have a stain control effect by birefringence in the above range :

<Formula 4>

Rth = ((nx + ny) / 2 - nz) xd

(Where nx, ny and nz are the refractive indexes in the x, y and z axis directions of the polyester film at a wavelength of 550 nm, respectively, and d is the thickness (unit: nm) of the film).

The stretching ratio in the TD direction is 2 to 10 times, the stretching ratio in the MD direction is 1 to 1.1, the stretching ratio in the MD direction is 1 to 1.1, and the stretching ratio in the machine direction ), And the stretching ratio 1 means the non-stretched state in which the stretching is not performed. Within the above-mentioned range, an ultra violet ray film is formed to prevent the occurrence of rainbow stains and to improve the image quality. In an embodiment, the polyester film is stretched only in the TD direction so that the absolute value of the molecular orientation angle? R of the polyester molecules in the TD direction is 5 ° or less, for example, 0 to 5 °. Within the above range, it is possible to prevent the occurrence of rainbow stains as an ultra violet ray film and to improve the image quality. The polyester film 120 is stretched at a high magnification in the TD direction and can exhibit an asymmetric molecular orientation angle with respect to the TD direction. The molecular orientation angle can be measured by a conventional method, for example, by the method of KOBRA-21ADH2 (Oji) and AXOSCAN (AXOMETRIS).

The polyester film is not particularly limited as long as it is a transparent film of a polyester resin. In a specific example, the polyester film is a film made of one or more resins selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and polybutylene naphthalate .

The polyester film may have a thickness of 25 占 퐉 to 500 占 퐉 and may be used as a protective film for a polarizing plate in the above range.

The polyester film can be produced by a polyester film production method comprising a step of stretching a melt-extruded polyester resin by 2 to 10 times in the TD direction only. There may be an effect that iridescence does not occur in the range of the stretching ratio, and in particular, the stretching ratio may be 3 to 8 times.

The stretching can be carried out by at least one of dry stretching and wet stretching. The stretching temperature is (Tg - 20) ° to (Tg + 50) °, specifically 70 ° C to 150 ° C Specifically, 80 占 폚 to 130 占 폚 is preferable, and more specifically, 90 占 폚 to 120 占 폚. Within this range, there can be uniformly the same stretching effect.

After the stretching step, the polyester film manufacturing method may further include a tension-relaxation step of lowering the degree of stretching at the same time as heating at a predetermined temperature. By stretching the polyester film in the TD direction by tension-relaxation, crystallization and stabilization of the film can be realized through heat treatment, and a polyester film having the difference in the length shrinkage ratio of the present invention can be produced. Specifically, in tension-relaxation, the heating may be performed in an oven at a temperature not lower than the glass transition temperature (Tg) of the polyester resin, for example, 100 to 300 ° C for 1 second to 2 hours, 3 times or less, specifically 0.1 to 2 times, more specifically 0.1 to 1 times.

The polarizer 10 aligns the direction of light passing through the optical film and divides the incident light into two polarizing components orthogonal to each other, allowing only one component to pass therethrough and the other component to absorb or disperse. The polarizer can be used without limitation as long as it is a polarizer commonly used in the production of a polarizing plate. Polarizers are prepared by dyeing a polyvinyl alcohol film with iodine or a dichroic dye and stretching it in a certain direction. Specifically, it is produced through a swelling process, a dyeing step, a stretching step and a crosslinking step. Methods of performing each step are commonly known to those skilled in the art.

Although the thickness of the polarizer 10 is not particularly limited, it can be specifically 20 占 퐉 to 100 占 퐉 and can be used for the polarizer in the above range.

The second optical film 30 may be a conventional transparent optical film. For example, the second optical film may be a film other than a polyester, such as a cellulose-based, polycarbonate-based, or polycarbonate-based film including triacetyl cellulose, Acrylic, and olefin based resins including cycloolefins.

The second optical film 30 has a length contraction ratio in the first oblique direction of -0.1 to + 0.1%, a length contraction ratio in the second oblique direction of -0.1 to + 0.1%, a length contraction ratio in the first oblique direction and a second oblique direction May be in the range of -0.05 to +0.05%, and there is no occurrence of warpage of the polarizer in the above range, and there may be an effect of eliminating optical axis distortion in the driving of the polarizer.

The thickness of the second optical film 30 may be 25 탆 to 500 탆, and within this range, the second optical film 30 may be used as a protective film for a polarizing plate.

Although not shown in FIG. 1, the first optical film and the second optical film may be surface-treated to provide an additional function. The surface treatment is for imparting functionality to the optical film. For example, , Diffusing / low reflection treatment, hard coating treatment, and the like. Although not shown in FIG. 1, the polarizing plate of one embodiment of the present invention may further include a retardation compensation film, a retardation film, an adhesive layer, and a pressure-sensitive adhesive layer depending on the use.

The polarizing plate can be manufactured by laminating a first optical film on one surface of a polarizer and laminating a second optical film on the other surface of the polarizer. The lamination method is not limited, and one or more of ordinary adhesives such as an aqueous adhesive and a pressure-sensitive adhesive can be used.

Hereinafter, with reference to FIG. 2, a polarizing plate of another embodiment of the present invention will be described. 2 is a sectional view of a polarizing plate of another embodiment of the present invention.

2, the polarizing plate 200 of another embodiment of the present invention includes a polarizer 10, a first optical film 20 formed on the upper portion of the polarizer 10, and a second optical film 20 formed on the lower portion of the polarizer 10. [ (20), and the first optical film (20) may be a polyester film having a difference in length shrinkage ratio of -0.1 to + 0.1%. The first optical film formed on the lower surface of the polarizer is substantially the same as the polarizing plate of the embodiment of the present invention, except that the difference in length shrinkage ratio is -0.1 to + 0.1%.

The optical display device of the present invention may include the polarizer of the embodiments of the present invention. The optical display device may include, but is not limited to, an organic light emitting diode display device or a liquid crystal display device.

An optical display device according to an embodiment of the present invention will be described with reference to Fig. 3, a liquid crystal display 300 according to an embodiment of the present invention includes a liquid crystal panel 270, a first polarizer 210 formed on the liquid crystal panel 270, a second polarizer 210 formed on a lower portion of the liquid crystal panel 270, And a polarizer 240. At least one of the first polarizer 210 and the second polarizer 240 may be a polarizer of the embodiments of the present invention.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

Specific specifications of the components used in the following examples and comparative examples are as follows.

(A) Polarizer Material: polyvinyl alcohol film (VF-PS6000, Kuraray Co., Ltd., thickness 60 占 퐉)

(PET) film or triacetylcellulose (TAC) film as shown in Table 1 below in the first oblique direction (45 deg.) And the second oblique direction (135 deg. Were used.

The optical film 1 was produced by melt-extruding a polyethylene terephthalate resin, stretching it to 6.1 times in the TD direction without stretching in the MD direction, and subjecting it to tension-relaxation treatment under the conditions shown in Table 1 below. Optical films 2 to 5 were prepared in the same manner except that the tension-relaxation conditions were changed as shown in Table 1 below. The optical film 6 was a triacetyl cellulose film of Konica KC4DR-1 (thickness: 40 m) having a length contraction ratio in the first oblique direction and a length contraction ratio in the second oblique direction of 0.1%, respectively.

The length contraction ratio was taken from the end portion of the film having a thickness of 100 占 퐉 (the portion corresponding to 2.5% from the end on the basis of TD), and the square of the length of each side of 100 mm x 100 mm (width x length) , And the difference in length contraction ratio was calculated therefrom. Referring to FIG. 4, the length shrinkage ratio was calculated at angle 45 ° and angle? 135 ° based on TD. The Ro of the film was measured using an Axoscan (Axometrix) device.

Film material Tension-Relaxation Length contraction ratio (%) in the first diagonal direction The length contraction ratio in the second diagonal direction
(%) Difference in length contraction ratio (%) nx ny d
(탆) Ro
(nm) Whether or not to process Temperature
(° C) Optical film 1 PET O 250 0.05 0.05 0 1.69 1.56 80 10,100 Optical film 2 PET O 150 0.05 0.10 0.05 1.69 1.56 80 10,100 Optical film 3 PET O 100 0.05 0.15 0.10 1.69 1.56 80 10,100 Optical film 4 PET O 200 0.15 0.15 0 1.69 1.56 80 10,100 Optical film 5 PET X - 0.05 0.20 0.15 1.69 1.56 80 10,100

Example  1 to 4 and Comparative Example  One

Polarizers were prepared by subjecting the material of the polarizer to a process such as dyeing and drawing. Specifically, the polyvinyl alcohol film was stretched twice at 150 ° C, adsorbed iodine, and then stretched 2.5 times in an aqueous boric acid solution at 40 ° C to prepare a polarizer. A polarizing plate was prepared by laminating a protective film having the combination shown in Table 2 below on both sides of a polarizer using an acrylic adhesive on the upper and lower sides.

On the polarizing plate thus prepared, r-axis scattering indicating axial strain was measured. The r-axis scattering was calculated by measuring the number of pol axes twisted relative to the fast axis of the polarizer using an Axoscan (Traverse System).

The degree of polarization was measured with respect to the polarizing plate using V-7100 (JASCO, Japan).

Protective film r-axis dispersion
(°) Polarization degree (%) Top bottom Example 1 Optical film 1 Optical film 6 0.20 ± 0.10 99.997 Example 2 Optical film 2 Optical film 6 0.54 + - 0.12 99.995 Example 3 Optical film 3 Optical film 6 0.62 + - 0.10 99.988 Example 4 Optical film 4 Optical film 6 0.30 0.10 99.996 Comparative Example 1 Optical film 5 Optical film 6 0.76 + 0.11 99.979

As shown in Table 2, the polarizing plate of the present invention controls the difference in the length contraction ratio of the polyethylene terephthalate film as the protective film to -0.1% to 0.1%, so that even if the polarizing plate is adhered to the polarizer, The distortion was low. Therefore, the polarizing plate can be prevented from being twisted during manufacture or use of the polarizing plate, and a polarizing plate having a high degree of polarization can be provided.

On the other hand, in the polarizing plate of Comparative Example 1 in which the difference in the length contraction ratio deviates from -0.1% to 0.1%, the r axis scatter exceeded 0.5 deg and the polarization degree was low, and the effect of the present invention could not be realized.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

A polarizer, a first optical film formed on an upper portion of the polarizer, and a second optical film formed on a lower portion of the polarizer,
Wherein at least one of the first optical film and the second optical film comprises a polyester film,
The polyester film has, on the basis of one of MD (Machine Direction) or TD (Transverse Direction) of the film, a length shrinkage ratio in the first oblique direction and a second shrinkage ratio in the second oblique direction of the following formula Polarizer having a difference of -0.1 to + 0.1%
<Formula 1>
Length contraction ratio (%) in the first diagonal direction = (AB) / A x 100
(Where A is the initial length of the portion in the first diagonal direction with respect to the reference direction in the film sample and B is the length in the first diagonal direction after leaving the sample at 85 +/- 5 DEG C for 30 minutes In length)
<Formula 2>
Length contraction ratio in the second diagonal direction (%) = (CD) / C x 100
(Where C is the initial length of the portion in the second oblique direction with respect to the reference direction in the film sample and D is the length in the second oblique direction after leaving the sample at 85 占 5 占 폚 for 30 minutes In length)
However, the angle between the first oblique direction and the second oblique direction is not 0 °. The polarizer according to claim 1, wherein the first oblique direction is 30 to 60 degrees with respect to the reference, and the second oblique direction is 120 to 150 degrees with respect to the reference. The polarizing plate according to claim 1, wherein an angle between the first oblique direction and the second oblique direction is 60 to 120 degrees. The polarizing plate according to claim 1, wherein the polyester film has a length contraction ratio in the first diagonal direction and a length contraction ratio in the second diagonal direction of -0.15% to + 0.15%. The polarizing plate according to claim 1, wherein the polyester film is a film made of one or more resins selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and polybutylene naphthalate. The optical film according to claim 1, wherein the first optical film is the polyester film,
Wherein the second optical film has a difference between a length contraction ratio in the first oblique direction and a length contraction ratio in the second oblique direction of -0.05 to + 0.05%. A liquid crystal display device comprising the polarizing plate according to any one of claims 1 to 6.

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