WO2014109489A1 - Liquid crystal display - Google Patents

Abstract

The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display comprising: an upper and a lower polarizing plate each having a polarizer with a protective film laid on at least one side, a liquid crystal cell interposed between the upper and the lower polarizing plate, and an optical function layer laid on at least one side of the lower polarizing plate, wherein the absorption axes of the upper and the lower polarizer are perpendicular to each other, the contractile force of the lower polarizer is equal to or less than 3.5N/2mm, the ratio of the contractile force of the lower polarizer/the contractile force of the upper polarizer is equal to or less than 1, so that bending of the liquid crystal display, especially CAP-type bending is prevented, thus inhibiting phenomena of light leaks and Newton rings.

Description

LCD Display

The present invention relates to a liquid crystal display device.

Liquid crystal display device (LCD) is one of the image display devices, and has the advantage of realizing light and small size and low power consumption compared to the cathode ray tube (CRT) which is a typical image display device. Since CRTs are not devices that emit light by themselves, unlike CRTs, they require light sources other than liquid crystal panels, and fluorescent lamps are mainly used as light sources for liquid crystal display devices. The lower polarizer and the upper polarizer are attached, respectively, The lower polarizer and the upper polarizer block or pass light from the lamp.

Typically, the polarizing plate has a structure including a pressure-sensitive adhesive layer for bonding to a liquid crystal cell on one side of a laminate including a first polarizer protective film, a polarizer and a second polarizer protective film, and a surface protective film on the other side. In this case, a polarizing plate having the same configuration as the upper polarizing plate and the lower polarizing plate may be bonded to both surfaces of the liquid crystal cell.

On the other hand, in recent years, as the liquid crystal display device has been enlarged and thinned and its use has been expanded, the demand for improving the function of the polarizing plate is increasing. Accordingly, polarizing plates having different characteristics as upper and lower polarizing plates have been applied. . For example, a polarizer having a wide viewing angle compensation film, a functional coating layer (hard coating layer, an antistatic layer, an antireflection layer, etc.) or a laminate thereof is further applied to the upper polarizer in addition to the polarizer protective film on the viewing side of the polarizer. As a polarizing plate, in addition to a polarizer protective film, the polarizing plate provided with the brightness improving film, a diffusion protective film, these laminated bodies, etc. are applied to the backlight unit side surface of a polarizer. Functional films, coating layers or laminates for imparting these different properties have different physical properties such as material, thickness, stretching direction, and moisture permeability, respectively.

Conventional polarizers include a polyvinyl alcohol (PVA) film drawn in a direction and dyed with a dichroic dye as a polarizer, and the stretched PVA film shrinks in the stretching direction according to temperature or humidity change. . In particular, when polarizing plates having different functional films, coating layers or laminates on the polarizers are applied to the upper polarizing plate and the lower polarizing plate, respectively, the shrinkage is increased due to the difference in their moisture permeability, which causes the liquid crystal panel to curl. The phenomenon occurs badly. As a result, light leakage may occur and cause a defect of the liquid crystal panel.

Korean Patent Laid-Open No. 2012-99172 discloses a polarizing plate, a method of manufacturing the same, and an image display apparatus using the same, but does not provide an alternative to the problem.

<Preceding technical literature>

<Patent Documents>

Korean Laid-Open Patent No. 2012-99172

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device in which light leakage is suppressed by improving warpage.

An object of the present invention is to provide a liquid crystal display device in which the Newton ring phenomenon is suppressed.

1. An upper polarizing plate and a lower polarizing plate each comprising a polarizer having a protective film bonded to at least one surface, wherein a liquid crystal cell is disposed between the upper polarizing plate and the lower polarizing plate, the lower polarizing plate has at least one optical functional layer 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, and the contracting force of the lower polarizer / shrinkage of the upper polarizer is 1 or less.

2. In the above 1, wherein the upper polarizer and the lower polarizer has a thickness of 15 to 35㎛ liquid crystal display device.

3. In the above 1, wherein the thickness of the upper polarizer and the lower polarizer is the same.

4. In the above 1, wherein the upper polarizer is bonded to the upper surface of the liquid crystal cell, the lower polarizer is bonded to the lower surface of the liquid crystal cell, respectively.

5. In the above 4, wherein the lower polarizing plate is provided with an optical functional layer on the opposite side of the surface in contact with the liquid crystal cell.

6. In the above 1, wherein the optical functional layer is a liquid crystal display device selected from the group consisting of a reflective polarization separation layer, a phase difference layer, an antireflection layer, a reflection layer and a brightness enhancement layer.

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

1 is a cross-sectional view showing an embodiment of a liquid crystal display of the present invention.

2 is a warpage image of Example 1. FIG.

3 is a light leakage image of Example 1. FIG.

4 is a bending image of Comparative Example 3.

5 is a light leakage image of Comparative Example 3.

The present invention includes an upper polarizing plate and a lower polarizing plate each including a polarizer having a protective film bonded to at least one surface, wherein a liquid crystal cell is disposed between the upper polarizing plate and the lower polarizing plate, and the lower polarizing plate has optical functionality on at least one surface. A layer, wherein the upper and lower polarizers have perpendicular absorption axes to each other, the contracting force of the lower polarizer is 3.5 N / 2 mm or less, and the contracting force of the lower polarizer / shrinkage of the upper polarizer is 1 or less, The present invention relates to a liquid crystal display device capable of suppressing warpage of a liquid crystal display device, in particular, warping of a CAP type, thereby suppressing light leakage phenomenon and Newton ring phenomenon.

The liquid crystal display of the present invention includes an upper polarizing plate and a lower polarizing plate each including a polarizer having a protective film bonded to at least one surface, and a liquid crystal cell is disposed between the upper polarizing plate and the lower polarizing plate, and the lower polarizing plate is at least An optical functional layer is provided on one surface, and the upper polarizer and the lower polarizer are disposed such that absorption axes are perpendicular to each other.

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

1 is a schematic cross-sectional view of an embodiment of a liquid crystal display of the present invention.

In the present invention, the upper polarizing plate 107 is a polarizing plate positioned so that the light emitted from the light source passes through the liquid crystal cell 103 and passes through the polarizing plate, and the lower polarizing plate 108 is the light emitted from the light source. A polarizing plate positioned to pass through the polarizing plate before passing through 103.

The upper polarizer 107 and the lower polarizer 108 are provided with protective films 101a, b; 104a, b bonded to at least one surface of the polarizers 102, 105, respectively.

The upper polarizer 102 and the lower polarizer 105 have a dichroic dye adsorbed on a polyvinyl alcohol-based film.

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

As polyvinyl acetate type resin, the copolymer etc. of vinyl acetate and the other monomer copolymerizable with this besides the polyvinyl acetate which is a homopolymer of vinyl acetate are mentioned.

As another monomer copolymerizable with vinyl acetate, an unsaturated carboxylic acid type, an unsaturated sulfonic acid type, an olefin type, a vinyl ether type, an acrylamide type monomer which has an ammonium group, etc. are mentioned. The polyvinyl alcohol resin may be modified, for example, polyvinyl formal, polyvinyl acetal, or the like modified with aldehydes may also be used. The saponification degree of the polyvinyl alcohol-based 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.

What formed such a polyvinyl alcohol-type resin into a film is used as a raw film of a polarizer. The film formation method of polyvinyl alcohol-type resin is not specifically limited, A well-known method can be used. The film thickness of the polyvinyl alcohol based film is not particularly limited, and may be, for example, 10 to 150 μm.

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

The value of (shrinkage force of the lower polarizer) / (shrinkage force of the upper polarizer) is 1 or less, preferably 0.95 or less. When the relation between the contracting force of the lower polarizer 105 and the contractive force of the upper polarizer 102 satisfies the above range, the bending of the liquid crystal display device 100 is prevented, and in particular, the contracting force of the lower polarizer 105 is the upper polarizer 102. Since it is less than the contraction force of, the warpage of the CAP type can be suppressed, and thus the occurrence of light leakage and the Newton ring phenomenon can be suppressed.

In addition, the contracting force of the lower polarizer 105 may be 3.5N / 2mm or less, preferably 3.4N / 2mm or less. When the contracting force of the lower polarizer 105 is within the above range, the effect of preventing the CAP type warpage may be maximized.

The method of controlling the contraction force of the polarizers 102 and 105 is not particularly limited and may be a conventional method used for controlling the contraction force in the art, for example, the draw ratio in the stretching step in the polarizer manufacturing process, performing the crosslinking step. It can be adjusted by the temperature, boric acid concentration of the aqueous solution for crosslinking.

The thickness of the polarizers 102 and 105 is not particularly limited, and may be, for example, 15 to 35 μm. The same thickness of the upper polarizer 102 and the lower polarizer 105 is preferable in view of efficiency and productivity improvement in the manufacturing process.

The thickness of the polarizers 102 and 105 may be adjusted by a method of changing the draw ratio and the total cumulative draw ratio in each step during manufacturing, or by using a thin film of polyvinyl alcohol-based raw film having a thin thickness. Usually the total cumulative draw ratio can 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 excellent in transparency, mechanical strength, thermal stability, moisture shielding, and isotropy. Specifically, polyester film, such as polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate; Cellulose films such as diacetyl cellulose and triacetyl cellulose; Polycarbonate film; Acrylic films such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene films such as polystyrene and acrylonitrile-styrene copolymers; Polyolefin-based film; Vinyl chloride film; Polyamide films such as nylon and aromatic polyamides; Imide film; Sulfone film; Polyether ketone film; Sulfided polyphenylene-based films; Vinyl alcohol film; Vinylidene chloride-based film; Vinyl butyral film; Allylate film; Polyoxymethylene film; Urethane film; Epoxy film; Silicone film etc. are mentioned. Among these, especially the cellulose type film which has the surface saponified by saponification by alkali etc. is preferable in consideration of polarization characteristic or durability. In addition, the protective films 101a and b; 104a and b may be films having an optical compensation function such as a retardation function.

Bonding may be made of an adhesive commonly used in the manufacture of polarizers in the art, and may be subjected to a drying step after bonding.

The drying temperature and time are not particularly limited, and for example, may be performed at 40 to 100 ° C. for 20 to 1200 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 absorption axes are perpendicular to each other. For example, the upper polarizer 102 may have a long side direction parallel to the stretching direction, and the lower polarizer 105 may have a long side direction perpendicular to the stretching direction, or vice versa.

The liquid crystal cell 103 is disposed between the upper polarizer 107 and the lower polarizer 108. The upper polarizer 107 is bonded to the upper surface of the liquid crystal cell 103, and the lower polarizer 108 is bonded to the lower surface of the liquid crystal cell 103, respectively. The lower polarizer 108 includes an optical functional layer 106 on a surface opposite to the surface 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 optical functional layer 106 may be applied by a coating method or may be a separate functional film.

The optical functional layer 106 is not particularly limited, and examples thereof include a reflective 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 thin film of a dielectric material or a multilayer laminate of a thin film film having a different refractive index anisotropy, which exhibits a characteristic of transmitting other linearly polarized light of a predetermined polarization axis and reflecting other light (Sumitomo 3M Co., Ltd.) Manufactured D-BEF, etc.), the one which turns left or turns right, such as supporting the oriented film of the cholesteric liquid crystal polymer or the oriented liquid crystal layer on the film substrate (such as PCF350 manufactured by Nitto Denko Co. or Transmax manufactured by Merck) And reflecting circularly polarized light and transmitting other light.

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

Bonding is performed by an adhesion layer.

The pressure-sensitive adhesive layer may be formed from a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive resin, a crosslinking agent, and a silane coupling agent as necessary. Moreover, as adhesive resin, what has acrylic or urethane resin as a main component can be used, Among these, acrylic resin is preferable at the point that transparency is favorable.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but these examples are merely illustrative of the present invention and are not intended to limit the scope of the appended claims, which are within the scope and spirit of the present invention. It is apparent to those skilled in the art that various changes and modifications can be made to the present invention, and such modifications and changes belong to the appended claims.

Example 1.

(1) Production of upper polarizing plate

The polyvinyl alcohol film having a thickness of 75 μm was stretched three times while immersing in an aqueous solution of iodine at 30 ° C. and 0.3%, and stretched 5.5 times in total by immersing in an aqueous solution for crosslinking containing 4% boric acid and 10% potassium iodide at 60 ° C. . Thereafter, the solution was immersed in 1.5% aqueous potassium iodide solution at 30 ° C. for 10 seconds, washed, and dried at 50 ° C. for 4 minutes to prepare a polarizer.

A 40-μm saponified triacetylcellulose film was bonded to both surfaces of the prepared polarizer with a polyvinyl alcohol adhesive and dried at 60 ° C. for 4 minutes to prepare a polarizing plate.

(2) Preparation of lower polarizer

Except that the boric acid content of the aqueous solution for crosslinking was 2%, a polarizing plate was manufactured in the same manner as in the preparation of the upper polarizing plate.

Example 2.

(1) Production of upper polarizing plate

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

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 1.

Example 3.

(1) Production of upper polarizing plate

A polarizing plate was manufactured in the same manner as in the preparation of the upper polarizing plate of Example 1, except that the boric acid content of the aqueous solution for crosslinking was 6% and the total draw ratio was 6 times.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 1.

Example 4.

(1) Production of upper polarizing plate

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 1.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 1.

Comparative Example 1.

(1) Production of upper polarizing plate

The polarizing plate was manufactured by the same method as the manufacturing of the lower polarizing plate of Example 1.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 1.

Comparative Example 2.

(1) Production of upper polarizing plate

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 1.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 2.

Comparative Example 3.

(1) Production of upper polarizing plate

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 2.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 2.

Comparative Example 4.

(1) Production of upper polarizing plate

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 3.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 2.

Comparative Example 5.

(1) Production of upper polarizing plate

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 1.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 3.

Comparative Example 6.

(1) Production of upper polarizing plate

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 2.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 3.

Comparative Example 7.

(1) Production of upper polarizing plate

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 3.

(2) Preparation of lower polarizer

The polarizing plate was manufactured by the same method as the manufacturing of the upper polarizing plate of Example 3.

Experimental Example.

(1) Shrinkage force measurement

After heating the polarizers prepared in Examples and Comparative Examples 240 minutes at 80 ℃, cut to 10mm * 2mm (long side stretch direction) size was measured by the SII SS6100 equipment shrinkage force.

The measurement results are shown in Table 1 below.

(2) warpage measurement

The polarizers prepared in Examples and Preparation Examples were bonded to both surfaces of 0.5T Glass. After leaving for 24 hours in an oven at 60 ℃ and again for 2 hours at room temperature after measuring the warp in a two-dimensional measuring instrument of INTEK IMS, the maximum value is shown in Table 1 below.

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

 (3) light leakage observation

The polarizers prepared in Examples and Preparation Examples were bonded to both surfaces of 0.5T Glass. After leaving for 24 hours in an oven at 60 ℃ and again for 1 hour at room temperature, it was mounted on the backlight to observe whether the light leakage occurs.

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

○: Light leakage occurs at the edges.

(Triangle | delta): The light leakage phenomenon generate | occur | produces in an edge part minutely.

Note: Light leakage does not occur.

Table 1

Referring to Table 1 and FIGS. 2 to 5, Examples 1 to 4 in which the relationship between the contracting force of the lower polarizer and the contracting force of the upper polarizer are included in the scope of the present invention have a maximum value of the CAP type bending height of 0.13 to 0.22. You can see that no light leakage occurs.

However, in Comparative Examples 1 to 7, the maximum value of the CAP-type bending height is bent to 0.37 to 0.63, and it can be seen that light leakage occurs at the edge portion.

<Description of the code>

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 polarizing plate

108: lower polarizer

Claims (6)

An upper polarizing plate and a lower polarizing plate each including a polarizer having a protective film bonded to at least one surface thereof, The liquid crystal cell is disposed between the upper polarizer and the lower polarizer, The lower polarizer includes an optical functional layer on at least one surface thereof, The upper and lower polarizers have absorption axes perpendicular to each other, The contracting force of the lower polarizer is less than 3.5N / 2mm, (Shrinkage force of the lower polarizer / contraction force of the upper polarizer) is 1 or less. The liquid crystal display device of claim 1, wherein the upper polarizer and the lower polarizer have a thickness of 15 to 35 μm. The liquid crystal display device 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 an upper surface of the liquid crystal cell, and the lower polarizer is bonded to a lower surface of the liquid crystal cell. The liquid crystal display of claim 4, wherein the lower polarizer includes an optical functional layer on a surface opposite to a surface of the lower polarizer. The liquid crystal display device of claim 1, wherein the optical functional layer is selected from a group consisting of a reflective polarization separation layer, a retardation layer, an antireflection layer, a reflection layer, and a brightness enhancement layer.

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