KR20140091363A - Liquid crystal display device - Google Patents

Abstract

[0001] The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display comprising an upper polarizer and a lower polarizer each including a polarizer having a protective film bonded to at least one side thereof, Wherein the lower polarizer has at least one optically functional layer and the absorption axes of the upper and lower polarizers are perpendicular to each other and the contracting force of the lower polarizer is less than 3.5 N / The retraction force of the polarizer) is 1 or less, thereby suppressing the warpage of the liquid crystal display device, in particular, the warpage of the CAP type, and suppressing the occurrence of light leakage phenomenon and Newton ring phenomenon.

Description

[0001] Liquid crystal display device [0002]

The present invention relates to a liquid crystal display device.

2. Description of the Related Art A liquid crystal display device (LCD) is one of image display devices, and has advantages of realizing light weight shortening and low power consumption compared to a cathode ray tube (CRT), which is a typical image display device Since a liquid crystal display device is not a self light emitting device, unlike a CRT, a light source is required in addition to a liquid crystal panel. A fluorescent lamp is mainly used as a light source of such a liquid crystal display device, The lower polarizer plate and the upper polarizer plate are attached to the lower polarizer plate and the upper polarizer plate, respectively.

Usually, the polarizing plate has a structure in which a pressure-sensitive adhesive layer for bonding with a liquid crystal cell and a surface protective film are provided on one side of a laminate composed of a first polarizer protective film, a polarizer and a second polarizer protective film. At this time, a polarizing plate having the same configuration as the upper polarizer and the lower polarizer can be bonded to both sides of the liquid crystal cell.

In recent years, as the liquid crystal display device has become larger and thinner and its use has expanded, there has been an increasing demand for function improvement of the polarizing plate. Accordingly, polarizing plates having different characteristics as the upper polarizing plate and the lower polarizing plate have been applied . For example, as the upper polarizer, a polarizing plate having a wide view angle compensation film, a functional coating layer (hard coat layer, antistatic layer, antireflection layer, etc.) or a laminate thereof is applied on the viewer's side of the polarizer, As the polarizing plate, a polarizing plate provided with a brightness enhancement film, a diffusion protective film, a laminate thereof, or the like is applied on the backlight unit side surface of the polarizer, in addition to the polarizer protective film. The functional film, coating layer or laminate for imparting such different properties are different from each other in physical properties such as material, thickness, stretching direction, and moisture permeability.

Conventional polarizing plates include a polyvinyl alcohol (PVA) film stretched in a certain direction and dyed with a dichroic dye as a polarizer, and the stretched PVA film is contracted in the stretching axis direction according to a change in temperature or humidity . In particular, when a polarizing plate having a different functional film, a coating layer or a laminate on a polarizer is applied to the upper polarizer and the lower polarizer, the shrinkage ratio increases due to the difference in the moisture permeability, The phenomenon is severe. As a result, a phenomenon of light leakage may occur, which may cause defects of the liquid crystal panel.

Korean Patent Laid-Open Publication No. 2012-99172 discloses a polarizing plate, a manufacturing method thereof, and an image display apparatus using the same, but fails to provide an alternative to the above problem.

Korea Patent Publication No. 2012-99172

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device with improved warpage and suppressed light leakage.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device in which a Newton ring phenomenon is suppressed.

1. A liquid crystal display device, comprising: an upper polarizer and a lower polarizer plate each including a polarizer having a protective film bonded to at least one surface thereof; and a liquid crystal cell disposed between the upper polarizer plate and the lower polarizer plate, Wherein the absorption axes of the upper polarizer and the lower polarizer are perpendicular to each other, the shrinking force of the lower polarizer is 3.5 N / 2 mm or less, and the shrinkage force of the lower polarizer / shrinkage force of the upper polarizer is 1 or less.

2. The liquid crystal display of claim 1, wherein the upper polarizer and the lower polarizer have a thickness of 15 to 35 占 퐉.

3. The liquid crystal display of claim 1, wherein the upper polarizer and the lower polarizer have the same thickness.

4. The liquid crystal display of claim 1, wherein the upper polarizer is bonded to the upper surface of the liquid crystal cell, and the lower polarizer is bonded to the lower surface of the liquid crystal cell.

5. The liquid crystal display of claim 4, wherein the lower polarizer plate has an optically functional layer on a side opposite to the side in contact with the liquid crystal cell.

6. The liquid crystal display according to 1 above, wherein the optically functional layer is selected from the group consisting of a reflection type polarization separation layer, a retardation layer, an antireflection layer, a reflection layer and a brightness enhancement layer.

INDUSTRIAL APPLICABILITY The present invention suppresses the warpage of a liquid crystal display device, in particular, the warping of the CAP type, thereby suppressing the occurrence of light leakage phenomenon and Newton ring phenomenon.

1 is a cross-sectional view showing an embodiment of a liquid crystal display device of the present invention.
Fig. 2 is a warp image of Example 1. Fig.
3 is a light source image of Example 1. Fig.
4 is a warp image of Comparative Example 3. Fig.
5 is a light source image of Comparative Example 3. Fig.

A liquid crystal cell is disposed between the upper polarizer plate and the lower polarizer plate, and the lower polarizer plate has an optical functional layer on at least one side thereof, and the liquid crystal cell is disposed between the upper polarizer plate and the lower polarizer plate. The upper polarizer plate and the lower polarizer plate each include a polarizer having a protective film, Wherein the absorption axes of the upper polarizer and the lower polarizer are perpendicular to each other, the shrinking force of the lower polarizer is 3.5 N / 2 mm or less, and the shrinkage force of the lower polarizer / shrinkage force of the upper polarizer is 1 or less, To a liquid crystal display device capable of suppressing warpage of a liquid crystal display device, in particular, CAP-type warpage, and suppressing occurrence of a light leakage phenomenon and a Newton ring phenomenon.

The liquid crystal display of the present invention includes an upper polarizer and a lower polarizer, each of which includes a polarizer having a protective film bonded to at least one surface thereof, and a liquid crystal cell is disposed between the upper polarizer and the lower polarizer, And the upper polarizer and the lower polarizer are arranged such that their absorption axes are perpendicular to each other.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

Fig. 1 schematically shows a cross-sectional view of one embodiment of the liquid crystal display of the present invention.

In the present invention, the upper polarizer 107 is a polarizer positioned to allow the light emitted from the light source to pass through the polarizer after passing through the liquid crystal cell 103, and the lower polarizer 108 reflects light emitted from the light source to the liquid crystal cell 103 before passing through the polarizing plate.

The upper polarizer 107 and the lower polarizer 108 have protective films 101a, b and 104a, b bonded to at least one side of the polarizers 102 and 105, respectively.

The upper polarizer 102 and the lower polarizer 105 are formed by adsorbing and orienting a dichroic dye on a polyvinyl alcohol film.

The polyvinyl alcohol resin constituting the polarizers 102 and 105 can be obtained by saponifying a polyvinyl acetate resin.

Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith.

Other monomers copolymerizable with vinyl acetate include acrylamide monomers having an unsaturated carboxylic acid type, an unsaturated sulfonic acid type, an olefin type, a vinyl ether type, and an ammonium group. In addition, the polyvinyl alcohol resin may be modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The saponification degree of the polyvinyl alcohol resin is usually 85 to 100 mol%, preferably 98 mol% or more, and the polymerization degree is usually 1,000 to 10,000, preferably 1,500 to 5,000.

Such a polyvinyl alcohol-based resin film is used as the original film of the polarizer. The film forming method of the polyvinyl alcohol resin is not particularly limited, and a known method can be used. The thickness of the polyvinyl alcohol original film is not particularly limited, and may be, for example, 10 to 150 mu m.

Polarizers 102 and 105 are usually produced by swelling, dyeing, crosslinking, stretching, washing, and drying the polyvinyl alcohol original film as described above. The order of each process, the number of repetitions, the process conditions, and the like are not particularly limited as long as they do not deviate from the object of the present invention, and some steps may be omitted if necessary.

(The contracting force of the lower polarizer) / (the contracting force of the upper polarizer) may be 1 or less, preferably 0.95 or less. It is possible to prevent warping of the liquid crystal display device 100 and particularly to prevent the shrinking force of the lower polarizer 105 from being applied to the upper polarizer 102 when the relationship between the contracting force of the lower polarizer 105 and the contracting force of the upper polarizer 102 satisfies the above- It is possible to suppress the warping of the CAP type, thereby suppressing the occurrence of light leakage and Newton ring phenomenon.

The contracting force of the lower polarizer 105 may be 3.5 N / 2 mm or less, and preferably 3.4 N / 2 mm or less. When the shrinking force of the lower polarizer 105 is within the above range, the CAP-type bending prevention effect can be maximized.

The method of controlling the contracting force of the polarizers 102 and 105 is not particularly limited and may be a conventional method used in the art to control the contracting force. For example, the stretching ratio in the stretching step in the polarizer manufacturing step, Temperature, concentration of boric acid in the aqueous solution for crosslinking, and the like.

The thickness of the polarizers 102 and 105 is not particularly limited, and may be, for example, 15 to 35 占 퐉. It is preferable that the thicknesses of the upper polarizer 102 and the lower polarizer 105 are the same in terms of efficiency and productivity in the manufacturing process.

The thickness of the polarizers 102 and 105 can be controlled by changing the stretching ratio and the total cumulative stretching ratio at each step in the manufacturing process or by using a thin film polyvinyl alcohol original film having a small thickness. Usually, the total cumulative stretching ratio may be 4 to 8 times, preferably 4.5 to 7 times, more preferably 5 to 6.5 times.

The protective films (101a, b; 104a, b) are not particularly limited as long as they are films excellent in transparency, mechanical strength, thermal stability, moisture barrier properties and isotropy. Specifically, polyester films such as polyethylene terephthalate, polyethylene isophthalate and polybutylene terephthalate; Cellulose-based films such as diacetylcellulose and triacetylcellulose; Polycarbonate-based films; Acrylic films such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene-based films such as polystyrene and acrylonitrile-styrene copolymer; Polyolefin films; Vinyl chloride film; Polyamide-based films such as nylon and aromatic polyamide; Imidazole film; Sulfone based films; Polyether ketone-based films; A sulfided polyphenylene-based film; Vinyl alcohol film; Vinylidene chloride films; Vinyl butyral film; Allylate-based films; Polyoxymethylene-based films; Urethane-based films; Epoxy-based films; Silicone-based films, and the like. Among them, a cellulose-based film having a surface saponified (saponified) by alkali or the like is preferable in consideration of polarization characteristics or durability. Further, the protective films 101a, b (104a, b) may be a film having an optical compensation function such as a retardation function.

The bonding may be made of an adhesive commonly used in the art for polarizing plate manufacture, and may be subjected to a drying step after bonding.

The drying temperature and time are not particularly limited, and can be performed, for example, at 40 to 100 DEG C for 20 to 1,200 seconds.

The upper polarizer 102 included in the upper polarizer 107 and the lower polarizer 105 included in the lower polarizer 108 are disposed such that their absorption axes are perpendicular to each other. For example, the direction of the long side of the upper polarizer 102 may be parallel to the stretching direction, and the direction of the long side of the lower polarizer 105 may be perpendicular to the stretching direction, or vice versa.

The liquid crystal cell 103 is placed between the upper polarizer 107 and the lower polarizer 108. [ The upper polarizing plate 107 is bonded to the upper surface of the liquid crystal cell 103 and the lower polarizing plate 108 is bonded to the lower surface of the liquid crystal cell 103, respectively. The lower polarizing plate 108 is provided with an optically functional layer 106 on the opposite side to the side in contact with the liquid crystal cell 103.

The liquid crystal cell 103 is not particularly limited and may be a liquid crystal cell commonly used in the art.

The optically functional layer 106 may be applied by a coating method or may be a separate functional film.

The optically functional layer 106 is not particularly limited, and examples thereof include a reflection type polarization separation layer, a retardation layer, an antireflection layer, a reflection layer, and a brightness enhancement layer.

As the brightness enhancement layer, for example, a multilayer laminate of a dielectric multilayer film or a multilayer laminate of a thin film having a different refractive index anisotropy may be used (Sumitomo 3M Co., Ltd.) exhibiting properties of transmitting linearly polarized light of a predetermined polarization axis to reflect other light, Manufactured by Nippon Denshoku Industries Co., Ltd., D-BEF, etc.), an orientation film of cholesteric liquid crystal polymer, or a substrate on which the alignment liquid crystal layer is supported on a film base (PCF350 manufactured by Nitto Denko or Transmax manufactured by Merck) Or the like, which reflects circularly polarized light of other wavelengths and transmits other light.

Including the optically functional layer improves the optical performance of the liquid crystal display, but may cause warping of the liquid crystal display. However, since the warpage is improved in the liquid crystal display device of the present invention, the occurrence of warpage can be minimized even when the optical functional layer is included.

The bonding is performed by an adhesive layer.

The pressure-sensitive adhesive layer may be formed from a pressure-sensitive adhesive composition comprising a pressure-sensitive adhesive resin, a crosslinking agent and, if necessary, a silane coupling agent. As the pressure-sensitive adhesive resin, an acrylic-based or urethane-based resin may be used as a main component. Among them, an acrylic resin is preferable because of its good transparency.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to be illustrative of the invention and are not intended to limit the scope of the claims. It will be apparent to those skilled in the art that such variations and modifications are within the scope of the appended claims.

Example  One.

(1) Preparation of Upper Polarizer

A polyvinyl alcohol film having a thickness of 75 탆 was immersed in a 0.3% iodine aqueous solution at 30 캜 and stretched 3-fold, immersed in a crosslinking aqueous solution containing 4% boric acid at 60 캜 and 10% potassium iodide, . Thereafter, the substrate was immersed in a 1.5% aqueous solution of potassium iodide at 30 DEG C for 10 seconds, washed and dried at 50 DEG C for 4 minutes to prepare a polarizer.

A saponified cellulose triacetyl cellulose film having a thickness of 40 탆 was bonded to both sides of the prepared polarizer using a polyvinyl alcohol adhesive and dried at 60 캜 for 4 minutes to prepare a polarizing plate.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer except that the content of boric acid in the aqueous crosslinking solution was 2%.

Example  2.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 1, except that the content of boric acid in the aqueous crosslinking solution was 6%.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 1.

Example  3.

(1) Preparation of Upper Polarizer

The polarizing plate was prepared in the same manner as in the production of the upper polarizer of Example 1, except that the aqueous solution for crosslinking was stretched so that the boric acid content was 6% and the total stretching ratio was 6 times.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 1.

Example  4.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 1.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 1.

Comparative Example  One.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the lower polarizing plate of Example 1.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 1.

Comparative Example  2.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 1.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 2.

Comparative Example  3.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 2.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 2.

Comparative Example  4.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 3.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 2.

Comparative Example  5.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 1.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 3.

Comparative Example  6.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 2.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 3.

Comparative Example  7.

(1) Preparation of Upper Polarizer

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 3.

(2) Preparation of lower polarizer plate

A polarizing plate was prepared in the same manner as in the preparation of the upper polarizer of Example 3.

Experimental Example  .

(1) Measurement of contraction force

The polarizers prepared in Examples and Comparative Examples were heated at 80 DEG C for 240 minutes, cut into a size of 10 mm * 2 mm (long side stretching direction), and measured for shrinkage force with SII SS6100 equipment.

The measurement results are shown in Table 1 below.

(2) Measurement of bending

The polarizing plates produced in the above Examples and Production Examples were bonded to both sides of 0.5 T Glass. Thereafter, the sample was allowed to stand in an oven at 60 DEG C for 24 hours, and then allowed to stand at room temperature for 2 hours. Thereafter, warpage was measured with a two-dimensional measuring machine of INTEK IMS Co. and the maximum value thereof is shown in Table 1 below.

The warp images of Example 1 and Comparative Example 3 are shown in Fig. 2 and Fig. 4, respectively.

 (3) Light beam  observe

The polarizing plates produced in the above Examples and Production Examples were bonded to both sides of 0.5 T Glass. Thereafter, it was left in an oven at 60 ° C for 24 hours, and then left at room temperature for 1 hour. Then, it was mounted on a backlight to observe whether light leakage occurred.

Observation results are shown in Table 1 below, and the light leakage images of Example 1 and Comparative Example 3 are shown in FIG. 3 and FIG. 5, respectively.

○: Light leakage occurs at the edge.

Δ: Light leakage occurs at the edge part finely.

Ⅹ: Light leakage phenomenon does not occur.

division The shrinkage force of the upper polarizer
(N / 2 mm) Shrinkage of the lower polarizer
(N / 2 mm) Shrinkage force of the lower polarizer / shrinkage force of the upper polarizer Maximum value of CAP type bending height (mm) Presence or absence of light leakage Example 1 3.4 3.0 0.88 0.15 X Example 2 3.7 3.4 0.92 0.17 X Example 3 4.1 3.4 0.83 0.13 X Example 4 3.4 3.4 1.00 0.22 X Comparative Example 1 3.0 3.4 1.13 0.37 △ Comparative Example 2 3.4 3.7 1.09 0.46 ○ Comparative Example 3 3.7 3.7 1.00 0.4 ○ Comparative Example 4 4.1 3.7 0.90 0.38 △ Comparative Example 5 3.4 4.1 1.21 0.63 ○ Comparative Example 6 3.7 4.1 1.11 0.58 ○ Comparative Example 7 4.1 4.1 1.00 0.53 ○

Referring to Table 1 and FIGS. 2 to 5, in Examples 1 to 4 in which the relationship between the contracting force of the lower polarizer and the contracting force of the upper polarizer is included in the scope of the present invention, the maximum value of the CAP type bending height is 0.13 to 0.22 It can be seen that the light leakage does not occur.

However, in Comparative Examples 1 to 7, the maximum value of the CAP type bending height was significantly bent to 0.37 to 0.63, and light leakage occurred at the edge portion.

100: liquid crystal display device 101a, b: protective film
102: upper polarizer 103: liquid crystal cell
104a, b: protective film 105: lower polarizer
106: Optical functional layer 107: Upper polarizer
108: Lower polarizer plate

Claims (6)

And an upper polarizer and a lower polarizer each including a polarizer having a protective film bonded on at least one surface thereof,
A liquid crystal cell is disposed between the upper polarizer and the lower polarizer,
Wherein the lower polarizer plate has an optically functional layer on at least one side thereof,
Wherein the upper polarizer and the lower polarizer have absorption axes perpendicular to each other,
The contracting force of the lower polarizer is 3.5 N / 2 mm or less,
(Shrinking force of the lower polarizer / shrinking force of the upper polarizer) is 1 or less.
The liquid crystal display of claim 1, wherein the upper polarizer and the lower polarizer have a thickness of 15 to 35 μm.
The liquid crystal display of claim 1, wherein the upper polarizer and the lower polarizer have the same thickness.
The liquid crystal display of claim 1, wherein the upper polarizer is bonded to the upper surface of the liquid crystal cell, and the lower polarizer is bonded to the lower surface of the liquid crystal cell.
5. The liquid crystal display of claim 4, wherein the lower polarizer plate comprises an optically functional layer on a side opposite to a side in contact with the liquid crystal cell.
The liquid crystal display device according to claim 1, wherein the optically functional layer is selected from the group consisting of a reflection type polarization separation layer, a retardation layer, an antireflection layer, a reflection layer, and a brightness enhancement layer.

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