JPH1048420A - Wide visual field angle polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to expand the region of good visibility which is excellent in contrast and brightness and to make the visual field angle wider without color change and gradation inversion by arranging a double refractive layer on one surface of a polarization layer so that the transmission axis and delay phase axis thereof have a parallel relation or orthogonal relation to each other. SOLUTION: The double refractive phase 2 is arranged via an adhesive phase 2 on one side of the polarization layer 1 in such a manner that the transmission axis and delay phase axis thereof have the parallel relation or orthogonal relation. Arrows indicate the directions of the transmission axis and the delay phase axis. The polarization layer 1 with which the light of a prescribed polarization state is obtainable is used. Above all, polyvinyl alcohol-based films, etc., with which the transmitted light of a linear polarization state is obtainable are more preferably enumerated. The double refractive phase 2 is preferably the double refractive phase formed by imparting double refractiveness to a light transparent film exhibiting a phase difference by double refraction by subjecting the film to a stretching treatment and the oriented film of a liquid crystal polymer or the double refractive phase formed by orienting an anisotropic material, such as liquid crystal polymer, on the oriented film on a base material, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate having a wide viewing angle which can form a liquid crystal display device having a wide viewing angle with good visibility.

[0002]

2. Description of the Related Art OA equipment such as a word processor and a personal computer, a television, a car, etc. are focused on many features such as low voltage, low power consumption, direct connection to an IC circuit, various display functions, and excellent lightness. Liquid crystal display devices are widely used as various display means such as navigation monitors and monitors for aircraft cockpits.
It has long been pointed out that the narrow viewing angle of good visibility is compared to.

[0003] The narrow viewing angle is such that the optical anisotropy peculiar to the liquid crystal affects the viewing angle characteristic of the visibility, and the linearly polarized light incident on the liquid crystal cell via the polarizing layer becomes elliptically polarized. It is thought that the cause is that the azimuth changes. That is, when the display light in the polarization state transmitted through the liquid crystal cell is directly incident on the polarizing layer on the viewing side, the transmittance decreases with an increase in the viewing angle as the viewing angle, and the display brightness becomes insufficient or the gradation becomes poor. Is considered to cause a reduction in visibility such as inversion of the color or a color change such as coloring.

Conventionally, a method using a phase difference plate has been known as a method for enlarging a good viewing area of a liquid crystal display device, that is, a method for enlarging a viewing angle, and various types of phase difference plates have been proposed. (JP-A-4-229828,
JP-A-4-258923, JP-A-6-75116
JP, JP-A-6-174920, JP-A-6-222
213 publication). However, in each case, the improvement effect was poor and the satisfactory viewing angle was not satisfactory.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to enlarge a good viewing area in a liquid crystal display device by improving a polarizing layer disposed on a liquid crystal cell.

[0006]

The present invention is characterized in that a birefringent layer is arranged on one side of a polarizing layer such that the transmission axis and the slow axis thereof are in a parallel or orthogonal relationship. A polarizing plate is provided.

[0007]

According to the above structure in which the polarizing layer and the birefringent layer are superposed so that the transmission axis and the slow axis have a parallel relationship or an orthogonal relationship, the phase difference of the birefringent layer in the front direction perpendicular to the polarizing layer surface is reduced. It is possible to prevent a decrease in brightness and contrast without being affected, and to compensate for changes in the state of linearly polarized light due to the birefringence of the liquid crystal cell via the birefringent layer, eliminating color changes such as coloring and gradation inversion. It is possible to enlarge a region of good visibility excellent in contrast and brightness, and to obtain a liquid crystal display device having a wide viewing angle.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The wide viewing angle polarizing plate of the present invention has a birefringent layer disposed on one side of a polarizing layer such that the transmission axis and the slow axis thereof are in a parallel or orthogonal relationship. Examples thereof are shown in FIGS. Reference numeral 1 denotes a polarizing layer, 3 denotes a birefringent layer, and arrows indicate directions of a transmission axis and a slow axis. 2
Is an adhesive layer.

As the polarizing layer, an appropriate layer capable of obtaining light of a predetermined polarization state can be used. Above all, those capable of obtaining transmitted light in a linearly polarized state are preferable. Examples thereof include stretching a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and an ethylene-vinyl acetate copolymer-based partially saponified film by adsorbing iodine and / or a dichroic dye. And a polarizing film made of a polyene-oriented film, such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride.

The polarizing layer, especially the polarizing film, may have a transparent protective layer on one or both sides. The polarizing layer may be a reflection type having a reflection layer. The reflective polarizing layer is used to form a liquid crystal display device or the like that reflects and reflects incident light from the viewing side (display side). There are advantages such as easy reduction in thickness of the display device.

The above-mentioned transparent protective layer may be appropriately formed as a plastic coating layer or a laminate of protective films, and the formation thereof is excellent in transparency, mechanical strength, heat stability, moisture shielding property and the like. Plastic and the like are preferably used. Examples thereof include polyester resins and acetate resins, polyethersulfone resins and polycarbonate resins, polyamide resins and polyimide resins, polyolefin resins and acrylic resins, or acrylic, urethane and acrylic urethane resins. And thermosetting resins such as epoxy resins and silicone resins, and ultraviolet curing resins. The surface of the transparent protective layer may be formed into a fine uneven structure by containing fine particles.

The reflective polarizing layer can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is provided on one surface of the polarizing layer via a transparent resin layer or the like as necessary. Specific examples thereof include a transparent resin layer such as a protective film that has been subjected to a mat treatment as required, and a foil or vapor-deposited film made of a reflective metal such as aluminum provided on one surface, or a surface containing fine particles of the transparent resin layer. An example in which a metal reflective layer is provided on a fine uneven structure by an appropriate method such as a vapor deposition method or a plating method is exemplified.

As the birefringent layer, an appropriate layer showing a phase difference due to birefringence can be used. Above all, a birefringence imparted by stretching a suitable light-transmitting film,
An alignment film of a liquid crystal polymer, an alignment film of a base material, or the like on which an anisotropic material such as a liquid crystal polymer is aligned can be preferably used. In particular, a film having a light transmissivity of 70% or more, preferably 80% or more, more preferably 85% or more and having excellent birefringence and imparted with birefringence is preferable.

Examples of the light-transmitting film include polycarbonate, polyarylate, polysulfone and polyethylene terephthalate, polyethersulfone and polyvinyl alcohol, polyolefins such as polyethylene and polypropylene, cellulosic polymers, polystyrene, polymethyl methacrylate, polyvinyl chloride and the like. A film made of polyvinylidene chloride, polyamide or the like is particularly preferred.

The orientation treatment for imparting birefringence to the translucent film can be performed by an appropriate method such as a uniaxial stretching treatment or a biaxial stretching treatment at a free end or a fixed end. In the present invention, a film oriented in the thickness direction or a film whose main refractive index in the thickness direction is inclined with respect to the normal direction of the film can be used for forming the birefringent layer. Further, the birefringent layer may be formed as an overlapping layer of two or more retardation layers.

In the present invention, the birefringent layer is arranged such that the transmission axis of the polarizing layer and the slow axis of the birefringent layer are in a parallel relationship or an orthogonal relationship. The direction of the slow axis changes, causing a shift in the parallel relationship or the orthogonal relationship, and the optical anisotropy of the birefringent layer develops in accordance with the shift amount. _{x -n z) / (n x} -n y) based on defined as n _z by controlling the amount of change of the slow axis, it is preferably used to regulate the expression of the birefringent layer.

In the above equation, _nx and _ny are in-plane main refractive indices ( _nx > _ny ), _nz is a refractive index in the thickness direction, and the in-plane retardation is a birefringent refractive index. the difference _{(△ n: n x -n y} ) and can be calculated as the product of the layer thickness (d) (△ nd). In addition, each said refractive index is based on a sodium D line.

That is, the above means that optimizing the in-plane retardation and N _z of the birefringent layer is advantageous for widening the viewing angle for good visibility. In the present invention, the in-plane retardation of the birefringent layer is 50 to 200 nm, preferably 70 to 170 nm, especially 100 to 200 nm.
Preferably it is 140 nm. The in-plane phase difference is 50
If it is less than nm, the effect of compensating for a change in the viewing angle may be poor. If it exceeds 200 nm, a color change such as coloring may occur due to the wavelength dispersion of Δn.

[0019] N _z is, -1～3, especially 0 to 1.5,
In particular, the range of 0.8 to 1.2 is preferable, and if the value is less than -1 or more than 3, the change of the slow axis due to the viewing angle becomes large, and the range of the compensable viewing angle becomes narrow, and it is difficult to widen the viewing angle. Become.

Since the thickness of the birefringent layer is related to the in-plane retardation as described above, it can be appropriately determined according to the intended retardation characteristics. Generally, 5-500μ
m, especially 10 to 350 μm, especially 20 to 200 μm.

The wide viewing angle polarizing plate of the present invention can be preferably used for compensating viewing angle characteristics due to birefringence of a liquid crystal cell. The polarizing plate is formed by sequentially laminating a birefringent layer and a polarizing layer separately in the process of manufacturing a liquid crystal display device. Or a suitable method such as a method of using it as a laminate in advance. The latter pre-lamination method has an advantage that the stability of the quality, the laminating workability and the like are excellent and the production efficiency of the liquid crystal display device can be improved.

When the birefringent layer is arranged on one side of the polarizing layer, the transmission axis of the polarizing layer and the slow axis of the birefringent layer are parallel or orthogonal. The relationship or the orthogonal relationship is not limited to a strictly parallel or orthogonal state, and a work placement error or the like is allowed. When there is a variation in the direction of the transmission axis or the slow axis, for example, they are arranged in a parallel relationship or an orthogonal relationship based on the average direction as a whole.

In the above, when laminating the polarizing layer and the birefringent layer, they can be fixed via an adhesive or the like as necessary. Adhesion and fixing are preferred from the viewpoint of preventing axial displacement. For the bonding, for example, an appropriate adhesive such as a transparent pressure-sensitive adhesive such as an acrylic-based, silicone-based, polyester-based or polyurethane-based, polyether-based, or rubber-based adhesive can be used. Absent. It is preferable that a high-temperature process is not required at the time of curing and drying, and that a long-time curing treatment and drying time are not required, rather than preventing a change in optical characteristics.
Further, a material that does not cause peeling or the like under heating or humidifying conditions is preferable.

From this point, the weight average molecular weight containing a monomer such as butyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate or (meth) acrylic acid as a component is 100,000 or more, and glass An acrylic pressure-sensitive adhesive made of an acrylic polymer having a transition temperature of 0 ° C. or less can be particularly preferably used. Acrylic pressure-sensitive adhesives are more preferable than those having excellent transparency, weather resistance and heat resistance. When layers having different refractive indices are laminated, an adhesive or the like having an intermediate refractive index is preferably used from the viewpoint of suppressing reflection loss.

If necessary, the adhesive may be, for example, a natural or synthetic resin, a filler or pigment comprising glass fibers, glass beads, metal powder or other inorganic powder, a coloring agent or an antioxidant. Can be added.
Further, an adhesive layer exhibiting light diffusing properties can be formed by incorporating fine particles.

The above-mentioned layers such as the polarizing layer, the birefringent layer, the transparent protective layer and the adhesive layer are made of, for example, salicylate compounds, benzophenol compounds, benzotriazole compounds, cyanoacrylate compounds, nickel complex salt compounds. UV-absorbing ability can be imparted by a method of treating with an ultraviolet absorber such as described above.

The formation of the liquid crystal display device using the wide viewing angle polarizing plate of the present invention can be performed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing layer, a birefringent layer for optical compensation, and an illumination system as needed, and incorporating a driving circuit. However, in the present invention, there is no particular limitation except that the wide-viewing-angle polarizing plate is provided on at least one side of the liquid crystal cell, and it can be in accordance with the conventional art.

Therefore, it is possible to form a suitable liquid crystal display device such as a liquid crystal display device having a wide viewing angle polarizing plate disposed on one or both sides of a liquid crystal cell, or a device using a backlight or a reflector for an illumination system. . In that case, it is more preferable to arrange the birefringent layer between the liquid crystal cell and the polarizing layer, particularly between the viewing side and the polarizing layer, from the viewpoint of the compensation effect. When the wide viewing angle polarizing plate is put to practical use, it can be used in an appropriate form such as a laminate with another optical element or the like for forming a liquid crystal display device.

FIGS. 3 and 4 show examples of the structure of a liquid crystal display device using a polarizing plate having a wide viewing angle. 4 is a liquid crystal cell, 5 is a backlight system, and 6 is a reflective layer. Reference numeral 7 denotes a light diffusion plate. FIG. 3 shows a backlight type illumination system in which a wide viewing angle polarizing plate is arranged on both sides, and FIG. 4 shows a reflection type illumination system in which a wide viewing angle polarizing plate is arranged only on one side.

In the above description, the forming parts of the liquid crystal display device are as follows:
They may be laminated and integrated, or may be in a separated state. In forming a liquid crystal display device, for example, appropriate optical elements such as a diffusion plate, an antiglare layer, an antireflection film, a protective layer and a protective plate can be appropriately arranged. The wide viewing angle polarizing plate of the present invention can be preferably used for various display devices such as a TFT type and an MIM type using a liquid crystal cell exhibiting birefringence such as a TN type or an STN type.

[0031]

【Example】

Example 1 A polyvinyl alcohol film having a thickness of 80 μm was stretched 5 times in an aqueous iodine solution and then dried to obtain a polarizing film. On the other hand, a polycarbonate film having a thickness of 60 μm was subjected to 1.a.
Stretching 23 times, Δnd: 120 nm, N _z : 2.0
Was obtained, and this was adhered to the above-mentioned polarizing film via an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm to obtain a wide-viewing-angle polarizing plate. The bonding was performed so that the transmission axis of the polarizing film and the slow axis of the birefringent film had a parallel relationship.

Example 2 A polycarbonate film having a thickness of 60 μm was passed through rolls having different peripheral speeds in an atmosphere at 160 ° C. to obtain a film having a thickness of 1.08 mm.
Δnd: 115 nm, N _z : 1.0
A wide viewing angle polarizing plate was obtained in the same manner as in Example 1 except that the birefringent film was used.

Example 3 On both sides of a polycarbonate film having a thickness of 60 μm, heat-shrinkable films (shrinkage ratio at 150 ° C .: MD: 6%, T
D: 8%) and passed through rolls having different peripheral speeds in an atmosphere of 152 ° C. and stretched 0.95 times to obtain Δnd: 135 nm, N _z : 0.3 birefringence A wide viewing angle polarizing plate was obtained according to Example 1, except that a film was used.

Example 4 The above-mentioned heat-shrinkable film was adhered to both sides of a polycarbonate film having a thickness of 60 μm and stretched 1.08 times by passing between rolls having different peripheral speeds in an atmosphere of 152 ° C. A wide viewing angle polarizing plate was obtained in the same manner as in Example 1 except that a birefringent film having a Δnd of 120 nm and a N _{z of} 0.9 was used.

Comparative Example 1 Only the polarizing film obtained according to Example 1 was used.

Comparative Example 2 A polycarbonate film having a thickness of 60 μm was passed through rolls having different peripheral speeds in an atmosphere of 160 ° C. to obtain a film having a thickness of 1.25.
The film was stretched 1.4 times with a tenter stretching machine at 170 ° C. in an atmosphere of 170 ° C. Δnd: 90 nm, N
_z : Example 1 except that a birefringent film of 6.0 was used.
A polarizing plate was obtained according to the following.

COMPARATIVE EXAMPLE 3 A polycarbonate film having a thickness of 60 μm was passed through rolls having different peripheral speeds in an atmosphere of 160 ° C. to give 1.15.
Δnd: 300 nm, N _z : 1.0
A polarizing plate was obtained in the same manner as in Example 1 except that the birefringent film was used.

Evaluation Test The polarizing plates (wide viewing angles) obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were arranged on both sides (front / rear) of a TFT type liquid crystal cell in the combinations shown in the table, and And the viewing angle 60 on the left and right
The viewing angle characteristics in degrees were examined, and the best condition was set to 5, and evaluated on a 5-point scale. The BWG attached to each numerical value is a main cause of the decrease in visibility. B: the degree of blackout which causes a decrease in contrast due to blackening of the display, W: the degree of white spotting in which the contrast decreases due to whitening of the display, and G : Means the degree of inversion of gradation. Therefore, 3B, 3W, and 3G are the respective intermediate states.
Note that 5G means that no grayscale inversion has occurred.

The results are shown in the following table. *: Colored yellow

As can be seen from the table, gradation inversion occurs due to a change in left and right viewing angles only in the polarizing film of Comparative Example 1, whereas gradation inversion is prevented in Examples 1 to 3 using a wide viewing angle polarizing plate. It can also be seen that the vertical viewing angle is slightly improved. Further, the in-plane phase difference: 50 compared with Comparative Examples 2 and 3.
It can be seen that satisfying Ｎ200 nm and N _z -1１〜３3 is advantageous for expanding the viewing angle.

The polarizers obtained in Example 4 and Comparative Example 1 (wide viewing angle) were combined with each other in Example 4 or Comparative Example 1 to form a TFT.
The liquid crystal cell was disposed on both sides (front / rear) of the liquid crystal cell, and the viewing angle characteristics on the left and right were examined.
This is shown in FIG. 6 (Comparative Example 1).

In FIGS. 5 and 6, reference numerals a to h denote respective luminances in eight gradation display from white display of a to black display of h. It can be seen that it is prevented.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional perspective view of an example of a wide viewing angle polarizing plate.

FIG. 2 is a partial cross-sectional perspective view of another example of a wide viewing angle polarizing plate.

FIG. 3 is a cross-sectional view of an example of a liquid crystal display device.

FIG. 4 is a cross-sectional view of another example of a liquid crystal display device.

FIG. 5 is a graph showing viewing angle characteristics of a liquid crystal display device using the wide viewing angle polarizing plate of Example 4.

FIG. 6 is a graph showing viewing angle characteristics of a liquid crystal display device using the polarizing plate of Comparative Example 1.

[Explanation of symbols]

 1: polarizing layer 2: adhesive layer 3: birefringent layer 4: liquid crystal cell

Claims (5)

[Claims] 1. A wide viewing angle polarizing plate, wherein a birefringent layer is disposed on one side of a polarizing layer such that its transmission axis and slow axis have a parallel or orthogonal relationship. 2. The method of claim 1, the in-plane retardation of the birefringent layer is 50 to 200 nm, and a main refractive index in the in-plane n _x
And n _y and the refractive index in the thickness direction as _nz , the expression: (n
_{x -n z) / (n x} -n y) wide viewing angle polarizing plate in which N _z is in the range of -1～3 defined by. 3. The method of claim 2, in-plane retardation of the birefringent layer in 100 to 140 nm, wide viewing angle polarizing plate in which N _z is in the range of 0.8 to 1.2. 4. The wide viewing angle polarizing plate according to claim 1, wherein one or both of the polarizing layer and the birefringent layer are made of a polymer film. 5. A liquid crystal display device comprising the wide-viewing-angle polarizing plate according to claim 1 on at least one side of a liquid crystal cell.