JPH10142423A - Polarizing plate with wide visual field - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polarizing layer which can enlarge a well-visible region in a liquid crystal display device. SOLUTION: A polarizing plate with wide visual field has a double refractive layer A31 having <=300μm phase difference in a thickness direction defined by a formula: (ns -nz )d and <=20nm intra-plane phase difference defined by a formula: (ns -nf )d and a double refractive layer B32 having 50 to 200nm intra-plane phase difference and 0.8 to 3.5Nz defined by a formula: (ns -nz )/(ns -nf ) at one side of the polarizing layer 1 (in the formulas, ns is a refractive index in a lagging axis direction, nz is a refractive index in a leading axis direction, nz is a refractive index in a thickness direction and (d) is a layer thickness). Further, a lagging axis of the double refractive layer B32 and a transmission axis of the polarizing layer 1 are in relation of being parallel or orthogonal to each other. Therefore, degrading of brightness and contrast can be prevented in a front surface direction perpendicular to the polarizing layer surface, state change of linear polarized light by double refractivity of a liquid crystal cell is compensated, a well-visible region which has no color change such as coloring and no gradation inversion and is excellent in contrast and brightness can be enlarged and the liquid crystal display device having the wide visible angle range can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-field polarizing plate capable of forming a liquid crystal display device having a wide viewing angle range for 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 range of good visibility is compared to.

[0003] The narrow viewing angle range is because the optical anisotropy peculiar to the liquid crystal affects the viewing angle characteristic of visibility, and 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, that is, the viewing angle with respect to the front (vertical) direction, and the display decreases. It is considered that the visibility is lowered, such as lack of brightness, inversion of gradation, and color change such as coloring.

Hitherto, as a method of enlarging a good viewing area of a liquid crystal display device, that is, a method of enlarging a viewing angle range, a method using a phase difference plate has been known, and various types of phase difference plates have been proposed. (JP-A-4-229828, JP-A-4-258923, JP-A-6-751
16, JP-A-6-174920, JP-A-6-2
22213 publication). However, in any case, the improvement effect was poor and not satisfactory in terms of the expandability of the viewing angle range for good visibility.

[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]

According to the present invention, the refractive index in the slow axis direction is n _s , the refractive index in the fast axis direction is n _f , the refractive index in the thickness direction is _nz , and the layer thickness is one side of the polarizing layer. as the d, formula: (n _s -n _z)
When the thickness direction retardation defined by d is 300 nm or less, the equation:
And (n _s -n _f) the birefringent layer plane retardation is defined following 20nm in d A, the in-plane retardation is in 50 to 200 nm,
_{Formula: (n s -n z) /} (n s -n f) N z defined by having a birefringent layer B of 0.8 to 3.5, and late phases of the birefringent layer B The present invention provides a wide-field polarizing plate, wherein an axis and a transmission axis of the polarizing layer are in a parallel relationship or an orthogonal relationship.

[0007]

The superimposed birefringent layer comprising the birefringent layer A and the birefringent layer B is arranged on one side of the polarizing layer, and the transmission axis of the polarizing layer and the slow axis of the birefringent layer B are parallel or orthogonal. With the above configuration, in the front direction perpendicular to the polarizing layer surface, a decrease in luminance and contrast can be prevented without being affected by the phase difference between the birefringent layers, and the birefringence of the liquid crystal cell can be prevented via the birefringent layers A and B. By compensating for the change in the state of linearly polarized light due to refraction, it is possible to expand the area of good visibility that is excellent in contrast and brightness without color change such as coloring and gradation inversion, and obtains a liquid crystal display device with a wide viewing angle range. be able to.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The wide-field polarizing plate of the present invention has a refractive index in the slow axis direction of n _s , a refractive index in the fast axis direction of n _f , and a refractive index in the thickness direction on one side of the polarizing layer. _nz and layer thickness d
Formula: (n _s -n _z) thickness retardation defined by d is 30
0nm the following formula: (n _s -n _f) and the birefringent layer A plane retardation following 20nm defined by d, the in-plane retardation is 50
In to 200 nm, _{wherein: (n s -n z) /} (n s -n f) N z defined by having a birefringent layer B of 0.8 to 3.5, and the birefringent layer The slow axis of B and the transmission axis of the polarizing layer have a parallel relationship or an orthogonal relationship. An example is shown in FIG.
As shown in FIG. 1 is a polarizing layer, 3 is a superimposed birefringent layer composed of a birefringent layer A31 and a birefringent layer B32, and arrows indicate directions of a transmission axis and a slow axis. Reference numeral 2 denotes 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. In that case, a birefringent layer A or B in the present invention may be used by using a transparent protective layer having predetermined birefringence characteristics. The polarizing layer may be a reflection type having a reflection layer. The reflective polarizing layer is on the viewing side (display side).
This is for forming a liquid crystal display device or the like of a type that reflects and reflects incident light from the liquid crystal display device, and has an advantage that the incorporation of a light source such as a backlight can be omitted and the thickness of the liquid crystal display device can be easily reduced. .

The transparent protective layer can be suitably formed as a plastic coating layer or a laminate of a protective film, and is preferably formed of a plastic having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like. Can be used. Examples thereof include polyester-based resins and acetate-based resins, polyethersulfone-based resins and polycarbonate-based resins, polyamide-based resins and polyimide-based resins, polyolefin-based resins and acrylic-based resins, or acrylic-based, urethane-based, and acrylic-urethane-based resins. Examples of such resins include 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 layers A and B, an appropriate one showing a predetermined phase difference or the like due to birefringence can be used. Above all, various types of light-transmitting films with birefringence imparted by stretching treatment, or alignment films of liquid crystal polymer, or anisotropic materials such as liquid crystal polymer are aligned on the alignment film of the substrate. And the like 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, polyether sulfone and polyvinyl alcohol, polyolefins such as polyethylene and polypropylene, cellulosic polymers such as triacetyl cellulose, polystyrene and polymethyl methacrylate. And a film made of polyvinyl chloride, polyvinylidene chloride, polyamide or the like.

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. The retardation characteristics due to birefringence can be adjusted by controlling the orientation treatment conditions such as the stretching method and stretching conditions, and changing the forming material, and the birefringent layer that can be used in the present invention can be formed. The birefringent layers A and B used in the present invention may be formed by laminating a plurality of retardation plates so as to exhibit predetermined retardation characteristics.

In the present invention, the birefringent layer disposed on one side of the polarizing layer is formed of a superimposed birefringent layer of a birefringent layer A and a birefringent layer B, and the birefringent layer A has a phase difference in the thickness direction. 300
It is assumed that the in-plane phase difference is 20 nm or less at nm or less. The birefringent layer B has an in-plane retardation is assumed N _z is 0.8 to 3.5 at 50 to 200 nm, and the birefringent layer B is its slow axis parallel relationship with the transmission axis of the polarizing layer Alternatively, they are arranged in an orthogonal relationship. Note the thickness retardation of said, a refractive index in a slow axis direction n _s, a refractive index n _f of the fast axis direction, a refractive index in the thickness direction n _z, the layer thickness as d, the formula: (n _s -n _z)
d. The in-plane retardation (△ nd) is given by the following equation:
Is defined by _{(n s -n f) d,} N z is the formula: (n _s -n _z)
Is defined by / (n _s -n _f). Each refractive index is based on the sodium D line.

In the above, the arrangement of the parallel axis or the orthogonal axis of the slow axis of the birefringent layer B with respect to the transmission axis of the polarizing layer prevents the influence of the phase difference of each birefringent layer in the front direction as described above. The purpose is to avoid a decrease in brightness and contrast. In addition, in the superimposition of the birefringent layers, when the viewing angle is deviated from the front direction in the above-described arrangement state of the parallel or orthogonal relation, the slow axis direction of the birefringent layer B changes and the birefringent layer B shifts to the parallel or orthogonal relation. occurs, that in accordance with the deviation amount from expressing optical anisotropy of the birefringent layer, the change of the slow axis which is on the basis of the in-plane retardation and N _z of the birefringent layer a and birefringence layer B The purpose is to control the amount to control the amount of optical anisotropy in the birefringent layer.

That is, the above-described method controls the phase difference in the thickness direction through the birefringent layer A having as small an in-plane phase difference as possible while optimizing the in-plane phase difference and N _z of the birefringent layer B. Is advantageous for expanding the viewing angle range for good visibility. The birefringent layer A, which is preferable from the viewpoint of widening the viewing angle range for good visibility, has an in-plane retardation of 18 nm or less, particularly 15 nm or less, particularly 0 to 10 nm.
The phase difference in the thickness direction is 250 nm or less, particularly 220 nm or less, particularly 30 to 200 nm. In-plane retardation is 2
Birefringent layer A exceeding 0 nm or a thickness direction retardation of 300
In the birefringent layer A exceeding nm, the controllability of the change of the slow axis described above is poor and the power for expanding the viewing angle range for good visibility is poor.

The birefringent layer B, which is preferable from the viewpoint of widening the viewing angle range for good visibility, has an in-plane retardation of 60 to 190 nm, especially 8
0~170nm, especially in 100~140nm, N _z is 3.3
Hereinafter, it is particularly 3.0 or less, especially 2.8 or less.
If the in-plane retardation is less than 50 nm, the effect of compensating for a change in viewing angle may be poor, and if it exceeds 200 nm, color change such as coloring may occur due to wavelength dispersion of the birefringence difference. In the value N _z exceeds 0.8 below and 3.5, the viewing angle range that can be compensated for changes in the slow axis depending on the viewing angle increases becomes narrow, wide viewing angle difficult.

The order of arrangement of the birefringent layers A and B with respect to the polarizing layer is arbitrary, but the birefringent layer A31 is used as the polarizing layer side as shown in FIG. It is preferable that the layer 1 also serves as the transparent protective layer. In this case, a triacetyl cellulose film is particularly preferably used for forming the birefringent layer A from the viewpoint of retardation characteristics and the like. The thickness of the birefringent layers A and B can be appropriately determined depending on the intended retardation characteristics and the like because it is related to the in-plane retardation as described above.
It is 0 to 350 μm, especially 20 to 200 μm.

The wide-field polarizing plate of the present invention can be preferably used for compensating viewing angle characteristics due to birefringence of a liquid crystal cell. The formation of the polarizing plate is performed by sequentially separating the birefringent layers A and B and the polarizing layer during the manufacturing process of the liquid crystal display device. Or a method of using a two- or three-layer laminate composed of an appropriate combination of a birefringent layer A, a birefringent layer B, and a polarizing layer 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 B is laminated on one side of the polarizing layer, the transmission axis of the polarizing layer and the slow axis of the birefringent layer B are parallel or orthogonal. The parallel 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 layers A and B, they can be fixed via an adhesive or the like, if 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 and the birefringent layers A and B, the transparent protective layer and the adhesive layer are made of, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, cyanoacrylate compounds, nickel Ultraviolet absorbing ability can be provided by a method of treating with an ultraviolet absorbent such as a complex salt compound.

The formation of a liquid crystal display device using the wide-field polarizing plate of the present invention can be performed according to a 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-view 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, an appropriate liquid crystal display device such as a liquid crystal display device in which a wide-field polarizing plate is arranged on one side or both sides of a liquid crystal cell or a device using a backlight or a reflector for an illumination system can be formed. In this case, it is more preferable to arrange the birefringent layers A and B 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-field 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 wide-field polarizing plate. 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-field polarizing plate is arranged on both sides, and FIG. 4 shows a reflection-type illumination system in which a wide-field polarizing plate is arranged on only one side.

In the above description, the forming parts of the liquid crystal display device are as follows:
It may be in a laminated integrated state or an appropriate 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-field polarizing plate of the present invention can be preferably used for various display devices such as TFT type and MIM type using a liquid crystal cell exhibiting birefringence such as TN type or 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. One side of a polarizing film obtained was subjected to triacetyl cellulose via a 15 μm-thick polyvinyl alcohol-based adhesive layer. Δnd: 6 nm (N _z : 10) consisting of a biaxially stretched product of the film,
A birefringent film A having a thickness direction retardation of 60 nm is adhered, and a 20 μm thick acrylic pressure-sensitive adhesive layer is formed thereon,
A polycarbonate film having a thickness of 60 μm was passed through rolls having different peripheral speeds in an atmosphere of 160 ° C. to form 1.08 μm.
Δnd: 115 nm, N _z : 1.0
Was bonded to obtain a wide-field polarizing plate. The bonding was performed such that the transmission axis of the polarizing film and the slow axis of the birefringent film B had a parallel relationship.

Example 2 As a birefringent film B, a polycarbonate film having a thickness of 60 μm and a biaxial stretching treatment at 160 ° C. in an atmosphere of Δnd: 80 nm and N _z : 2.0 was used. In accordance with Example 1, a wide-field polarizing plate was obtained.

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

Comparative Example 2 A polarizing plate was obtained in the same manner as in Example 1, except that the acrylic adhesive layer and the birefringent film B were not provided outside the birefringent film A.

Comparative Example 3 A polarizing plate was obtained in the same manner as in Example 1 except that the polarizing film and the birefringent film B were directly bonded via an acrylic adhesive layer without using the birefringent film A.

Comparative Example 4 As a birefringent film B, a polycarbonate film having a thickness of 60 μm was stretched 1.15 times by passing between rolls having different peripheral speeds in an atmosphere of 160 ° C. to obtain Δn.
A polarizing plate was obtained according to Example 1, except that d: 350 nm and N _z : 1.0 were used.

Comparative Example 5 As a birefringent film B, a polycarbonate film having a thickness of 60 μm was stretched 1.03 times by passing between rolls having different peripheral speeds in an atmosphere of 160 ° C. to obtain Δn.
A polarizing plate was obtained according to Example 1, except that d: 40 nm and N _z : 1.0 were used.

Comparative Example 6 A birefringent film A was obtained by biaxially stretching a polycarbonate film having a thickness of 60 μm in an atmosphere of 160 ° C. and having a Δnd of 20 nm and a retardation in the thickness direction of 350 nm. A polarizing plate was obtained according to Example 1.

Evaluation Test The polarizing plates obtained in Examples and Comparative Examples (wide field of view) were arranged on both sides (front / rear) of a TFT-type liquid crystal cell. ), The viewing angle ranges in the left-right direction and the up-down direction showing good visibility without lowering the contrast and inverting the gradation were examined.

The results are shown in the following table.

From the table, it can be seen that the left and right viewing angle ranges are remarkably improved and the up and down viewing angle range is slightly improved, as compared with the example and the comparative example 1 in which only the polarizing film is used. Also, from comparison with Comparative Examples 2 to 6, it can be seen that superimposing layers satisfying a predetermined birefringence characteristic is advantageous for expanding the viewing angle range. The visual defect in the example and the comparative example 1 is due to the inversion of the gradation.

[Brief description of the drawings]

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

FIG. 2 is a partial cross-sectional perspective view of another example of a wide-field 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.

[Explanation of symbols]

 1: polarizing layer 2: adhesive layer 3: superimposed birefringent layer 31: birefringent layer A 32: birefringent layer B 4: liquid crystal cell

Continued on the front page (72) Inventor Shinichi Sasaki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (5)

[Claims] 1. A refractive index in a slow axis direction is n _s , a refractive index in a fast axis direction is n _f , and a refractive index in a thickness direction is n on one side of a polarizing layer.
_z, the layer thickness as d, the formula: (n _s -n _z) thickness retardation defined by d is at 300nm following formula: (n _s -n _f) d
A birefringent layer A having an in-plane retardation of 20 nm or less,
The in-plane retardation is at 50 to 200 nm, wherein: (n _s -n _{z)
/ (N s -n f) N} z defined by having a birefringent layer B of 0.8 to 3.5, and the transmission axis of the slow axis and the polarizing layer of the birefringent layer B Are in a parallel relationship or an orthogonal relationship. 2. The wide-field polarizing plate according to claim 1, wherein the birefringent layer A also functions as a transparent protective layer of the polarizing layer. 3. The birefringent layer A according to claim 1,
A wide-field polarizing plate in which part or all of the birefringent layer B and the polarizing layer are made of a polymer film. 4. The wide-view polarizing plate according to claim 1, wherein the birefringent layer A is made of triacetyl cellulose. 5. A liquid crystal display device comprising the wide-field polarizing plate according to claim 1 on at least one side of a liquid crystal cell.