JP2000206328A - Phase difference plate, its continuous manufacture, optical member and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain efficiently a thin and highly heat-resistant phase difference plate capable of compensating highly double refraction caused by a liquid crystal cell, and to obtain a liquid crystal display device having excellent visibility of a contrast, a black-and-white display or the like in a wide visual angle range. SOLUTION: This continuous manufacturing method of a phase difference plate comprises treatment of a lengthy translucent film obtained by bonding a thermal shrinkage type film on one face or on both faces by a roll drawing machine having a roll speed ratio of one or less under the function of contractile force of the thermal shrinkage type film by a heating treatment, and shrinkage of the translucent film. The phase difference plate 1 satisfies the relations, nx<nz and (nx-ny)d<500 nm, where main refractive indices in the face are nx and ny, the main refractive index in the thickness direction is nz, on the condition of nx>ny, and the thickness is (d). The optical member comprises a laminate having at least the phase difference plate 1 and a polarizing plate 3. This liquid crystal display device has the phase difference plate 1, or that and the polarizing plate 3, on one side or on both sides of a liquid crystal cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate suitable for improving the viewing angle characteristics of a liquid crystal display device by optical compensation of a liquid crystal cell, a continuous production method thereof, and an optical member using the retardation plate.

[0002]

2. Description of the Related Art A retardation plate is disposed in a liquid crystal cell to compensate for optical characteristics based on birefringence in order to prevent a display color or contrast from being changed by a viewing angle of a display device due to birefringence of liquid crystal. A technique for improving the viewing angle characteristics has been proposed. Conventionally, as such a retardation plate for compensation,
A biaxially stretched film made of a laminate of uniaxially stretched films and a polymer having negative birefringence such as polystyrene has been known.

However, the above-mentioned lamination type has a problem that the lamination process is required and the crossing angle of the stretching axis needs to be controlled at a high degree, so that the production efficiency is poor and the lamination becomes bulky. Further, a biaxially stretched film made of a polymer having negative birefringence properties has a problem that it is difficult to use it for forming a liquid crystal display device due to poor heat resistance and a problem of phase difference fluctuation.

[0004]

SUMMARY OF THE INVENTION The present invention efficiently obtains a thin and heat-resistant retardation plate capable of highly compensating for birefringence caused by a liquid crystal cell, and has excellent contrast and wide visibility in a wide viewing angle range. It is an object to obtain a liquid crystal display device.

[0005]

According to the present invention, a long light-transmitting film having a heat-shrinkable film adhered to one or both surfaces thereof can be rolled with a roll speed ratio of 1 under the action of the heat-shrinkable film shrinkage force caused by heat treatment. A continuous production method of a retardation plate, characterized in that the translucent film is shrunk by processing with the following roll stretching machine, and the in-plane main refractive index is nx, ny, the main refractive index in the thickness direction. Is nz, nx> ny and the thickness is d, nx <
An object of the present invention is to provide a retardation plate characterized by satisfying nz and (nx-ny) d <500 nm.

Further, the present invention provides an optical member comprising a laminate having at least the above-mentioned retardation plate and a polarizing plate, and the above-mentioned retardation plate on one or both sides of a liquid crystal cell, or the retardation plate thereof And a polarizing plate.

[0007]

According to the present invention, a thin and heat-resistant phase difference plate capable of highly compensating for a change in display characteristics due to a viewing angle based on birefringence of a liquid crystal cell can be obtained with high manufacturing efficiency, and a contrast can be obtained in a wide viewing angle range. And a liquid crystal display device having excellent visibility such as monochrome display.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The production method according to the present invention comprises the steps of rolling a long light-transmitting film having a heat-shrinkable film adhered to one or both sides thereof under the action of the heat-shrinkable film by the heat treatment. By processing with a roll stretching machine having a speed ratio of 1 or less, the translucent film is shrunk to continuously obtain a retardation plate.

As the light-transmitting film to be processed, an appropriate light-transmitting film can be used, and there is no particular limitation. A film which is excellent in light transmittance and has a light transmittance of 75% or more, particularly 85% or more, and little alignment unevenness can be preferably used. There is no particular limitation on the polymer forming the light-transmitting film, and an appropriate polymer can be used. The polymer is
The film can be classified as positive or negative according to the birefringence characteristics depending on the relationship between the stretching direction and the refractive index when the film is stretched, and any of them can be used in the present invention.

[0010] Above all, a translucent film made of a polymer having a positive birefringence characteristic, which increases the refractive index in the stretching direction, can be preferably used from the viewpoint of processing efficiency, heat resistance and the like. Incidentally, examples of the polymer include polycarbonate, polyvinyl alcohol, cellulose-based polymer, polyester such as polyethylene terephthalate and polyethylene naphthalate, polyarylate, polyimide, norbornene-based polymer, polysulfone, ponoether sulfone,
Examples include polyolefins such as polyethylene and polypropylene. In particular, an amorphous polymer having excellent heat resistance can be preferably used.

The light-transmitting film may be formed by an appropriate method such as a casting method such as a casting method or an extrusion method. A solution casting method such as a casting method is more preferred from the viewpoint of obtaining a light-transmitting film with less thickness unevenness and orientation distortion unevenness. The thickness of the translucent film can be appropriately determined depending on the intended retardation and the like, but is generally 10 to 5
00 μm, especially 20 to 300 μm. As the translucent film, an elongated body such as a wound body is used for the purpose of continuous production, but its length and width are arbitrary.

A heat-shrinkable film adhered to one or both surfaces of a light-transmitting film shrinks the light-transmitting film by transmitting a contraction force due to its heating, thereby controlling its retardation characteristics, particularly the refractive index in the thickness direction. And so on. As the heat-shrinkable film, any suitable heat-shrinkable film exhibiting shrinkage by a heat treatment comprising a stretched product of a polymer film can be used, and is not particularly limited. The heat-shrinkable film made of the polymer having the above-described positive birefringence property can be preferably used from the viewpoint of the controllability of the retardation in the translucent film.

[0013] A heat-shrinkable film exhibiting heat-shrinkability in the vicinity of the glass transition temperature of the light-transmitting film can be preferably used from the viewpoint of imparting shrinkage force. The shrinkage force of the heat-shrinkable film can be controlled by, for example, the type of polymer, stretching conditions such as stretching ratio, and film thickness. A heat-shrinkable film having a heat-shrinking force as uniform as possible over the entire surface of the film can be preferably used because it imparts a uniform orientation to the translucent film.

For bonding the heat-shrinkable film and the light-transmitting film, it is preferable to use an adhesive from the viewpoint of propagation of shrinkage force due to good adhesion. As the adhesive, the shrinking force of the heat-shrinkable film is transmitted to the light-transmitting film at the time of the heat-shrinking treatment, and after the treatment, the optical properties of the heat-shrinkable film are not deteriorated as much as the processed material of the light-transmitting film. What can separate the heat-shrinkable film after the process is preferably used.

From the above point, an adhesive layer or the like is preferably used. As the adhesive layer, for example, an acrylic or silicone type, a polyester type or a polyurethane type, a suitable material such as a polyether type or a rubber type can be used.
There is no particular limitation on the type. The heat-shrinkable film may have one or more layers of the same type or different types bonded to one or both sides of the translucent film.

The heat-shrinkable film adhered to the translucent film develops its shrinking force by heat treatment, but the heat treatment can be performed by an appropriate method and is not particularly limited. In general, a heating method via a roll in a roll stretching machine, an atmosphere heating method, or a method using them in combination is adopted.

The dimensional change based on the length direction (MD) / width direction (TD) of the heat-shrinkable film rather than the point that the processing by the roll stretching machine is stably achieved under the action of the shrinkage force of the heat-shrinkable film. It is preferable to perform the heat treatment under a temperature condition at which the rate ratio is 1.5 or less. The dimensional change ratio is 1.
If the heat treatment exceeds 5, the light-transmitting film running between the rolls is likely to meander due to insufficient tension, and the light-transmitting film is not deformed according to the speed ratio of the rolls and nx <
It is difficult to satisfy the condition of nz.

Rather than achieving the dimensional change ratio described above,
The heat treatment is preferably performed in a temperature range of Tg ± 20 ° C. based on the glass transition temperature (Tg) of the polymer forming the heat-shrinkable film. Note that the dimensional change ratio is defined as the initial dimension before shrinkage of MD and TD being 1, and M
It is defined by D dimension / TD dimension.

In the above, the roll stretching machine used for the shrinkage treatment of the translucent film is not particularly limited, and an appropriate type may be used. The processing conditions are set to a roll speed ratio of 1 or less from the viewpoint of achieving shrinkage of the light-transmitting film. The retardation characteristics such as the refractive index of the obtained retardation plate can be controlled by the type and thickness of the light-transmitting film, the thickness change rate, the shrinkage rate, the processing temperature, and the like.

The retardation plate according to the present invention is preferably used as a single layer or a laminate of the same type or different types for compensating a phase difference due to birefringence for the purpose of expanding a viewing angle of a liquid crystal cell and improving contrast. Can be used. In particular, in order to compensate for birefringence of a liquid crystal cell, the in-plane principal refractive index is nx, ny, the principal refractive index in the thickness direction is nz, and nx> n in view of the compensation characteristics and the like.
When the thickness is d in y, nx <nz and Re <500 nm
Can be preferably used. Re is
It is defined by (nx-ny) d.

In practical use of a retardation plate, for example, a retardation plate provided with an adhesive layer on one or both sides, a polarizing plate or an isotropic transparent resin layer or a glass layer via the adhesive layer Or 3 layers, such as a layer in which a protective layer made of
It can also be applied as an optical member of an appropriate form composed of a laminate of layers or more.

FIG. 1 shows a phase difference plate 1 and a polarizing plate 3 combined with an adhesive layer 2.
The optical member formed by bonding and laminating through is illustrated. As the polarizing plate, an appropriate one may be used, and examples thereof include iodine on 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. And / or a stretched film obtained by adsorbing a dichroic dye, and a polarizing film made of a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product.

The polarizing plate, especially the polarizing film, may have a transparent protective layer on one or both sides. Further, the polarizing plate may be a reflection type having a reflection layer. The reflective polarizing plate 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 transparent protective layer can be suitably formed as a coating layer of a polymer or a laminate of a protective film, for example, a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like. Is 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 plate 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 side of the polarizing plate via a transparent resin layer or the like, if 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 reflection layer is provided on a fine uneven structure by an appropriate method such as a vapor deposition method or a plating method, or the like is given.

In laminating the retardation plate and the polarizing plate, the arrangement angles of the optical axes such as the transmission axis and the fast axis are not particularly limited, and can be appropriately determined. Incidentally, when it is applied to STN type liquid crystal cells, it is often arranged at an oblique crossing angle such as 45 degrees, and when it is applied to TN type liquid crystal cells, it is arranged at a substantially parallel or substantially orthogonal crossing angle. There are many.

In the above, the lamination of the retardation plate and the polarizing plate etc. can be performed by a method of sequentially laminating the liquid crystal display device in the manufacturing process. There is an advantage that the manufacturing efficiency of the liquid crystal display device can be improved due to excellent stability and workability of lamination. For the lamination, an appropriate transparent adhesive or pressure-sensitive adhesive can be used, and there is no particular limitation on the kind of the adhesive or the like. 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.

From the viewpoint of preventing a change in optical characteristics, it is preferable that a high-temperature process such as curing or drying is not required at the time of lamination, and that a long-time curing treatment or drying time is not required. From that point, a lamination method using an adhesive layer is preferable. As the pressure-sensitive adhesive layer, an appropriate one such as the one exemplified for the adhesion of the heat-shrinkable film can be used. Above all,
Acrylic materials are preferably used in terms of heat resistance and optical characteristics.

In the adhesive layer, if necessary, fillers, pigments, coloring agents and antioxidants made of, for example, natural and synthetic resins, glass fibers and glass beads, metal powders and other inorganic powders, etc. An appropriate additive such as the above can also be blended. In addition, an adhesive layer exhibiting light diffusing properties can be formed by incorporating fine particles.

The formation of the liquid crystal display device using the retardation plate according to 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 and a retardation plate for optical compensation, and a polarizing plate and an illumination system as needed, and incorporating a drive circuit, In the present invention, as described above, there is no particular limitation except that the retardation plate according to the present invention is used for optical compensation and provided on one or both sides of the liquid crystal cell, and can be in accordance with the conventional one.

Therefore, it is possible to form a suitable liquid crystal display device such as a liquid crystal display device in which a polarizing plate is disposed on one or both sides of a liquid crystal cell, or a lighting system using a backlight or a reflector. In the case of a liquid crystal display device using a polarizing plate, a retardation plate for optical compensation is a liquid crystal cell and a polarizing plate,
In particular, it is more preferable to dispose it between the polarizing plate on the viewing side and the compensation effect. In the arrangement, the optical member described above may be used.

FIGS. 2 and 3 show examples of the structure of a liquid crystal display device using a polarizing plate. 4 is a liquid crystal cell, 5 is a backlight system, and 7 is a reflective layer. Reference numeral 6 denotes a light diffusion plate.
In FIG. 2, a retardation plate 1 for optical compensation is arranged on both sides, and the illumination system is of a backlight type. 3 is a reflection type illumination system in which the retardation plate 1 for optical compensation is arranged only on one side.

In the above, 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 the liquid crystal display device, for example, appropriate optical elements such as a diffusion plate, an anti-glare layer, an antireflection film, a protective layer and a protective plate can be appropriately arranged, and these are arranged as an optical member pre-laminated with a retardation plate. You can also.

Although it has been described above that two or more retardation plates can be used by laminating them, this is for the purpose of improving the compensation effect and the like. It can also be a laminate. As the retardation plate, an appropriate one such as a uniaxially or biaxially stretched product of the above-mentioned translucent film, a discotic or nematic liquid crystal alignment plate, or the like can be used.

The above-mentioned layers such as the retardation plate and the polarizing plate, the transparent protective layer and the adhesive layer are made of, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, cyanoacrylate compounds, nickel complex compounds, etc. UV-absorbing ability can be imparted by a method of treating with an ultraviolet absorbent.

The retardation plate or the optical member according to the present invention is a liquid crystal exhibiting birefringence such as TN type or STN type for the purpose of compensating a phase difference due to birefringence of a liquid crystal cell, such as expansion of a viewing angle and improvement of contrast. It can be preferably used for various display devices such as TFT type and MIM type using cells.

As the retardation plate for optical compensation, a retardation plate for compensating a phase difference due to birefringence of a liquid crystal cell over a wide viewing angle range is preferably used. Thereby, prevention of coloring or the like is achieved over a wide viewing angle range. The liquid crystal cell to be applied is arbitrary, but can be preferably applied to a TN type or π type liquid crystal cell for forming a TFT type liquid crystal display device or the like.

[0038]

EXAMPLE 1 Polycarbonate having a molecular weight of about 80,000 and comprising polycondensate of phosgene and bisphenol A was treated with methylene dichloride.
The weight% solution was continuously cast on a steel drum, which was sequentially peeled off and dried to obtain a polycarbonate film having a thickness of 60 μm and a phase difference of almost 0.

Next, a polyester film having a dimensional change ratio (MD / TD) at 162 ° C. of 1.15 (MD / TD) was adhered to both sides of the film via an acrylic pressure-sensitive adhesive layer. After the polycarbonate was shrunk by treating at a normal temperature atmosphere with a roll temperature of 162 ° C. under the conditions of 0.97, the polyester film was peeled off, and a retardation plate was continuously obtained.

Example 2 A polyester film having a dimensional change ratio of 1.23 at 150 ° C. was adhered, and a roll speed ratio of 0.96 and a roll temperature of 1 were applied.
Example 1 except that the treatment was performed at 50 ° C. and an ambient temperature of 155 ° C.
A retardation plate was continuously obtained according to the method described in Example 1.

Example 3 A polystyrene film having a dimensional change ratio of 0.68 at 157 ° C. was adhered and treated at a roll speed ratio of 0.80, a normal roll temperature of 157 ° C., and an ambient temperature of 157 ° C. A retardation plate was continuously obtained according to the method.

Example 4 A polypropylene film having a dimensional change ratio of 1.25 at 158 ° C. was adhered and treated at a roll speed ratio of 0.99, a roll temperature of normal temperature, and an atmosphere temperature of 158 ° C. A retardation plate was continuously obtained according to the method.

COMPARATIVE EXAMPLE 1 A polyester film having a dimensional change ratio of 1.06 at 157 ° C. was adhered and treated at a roll speed ratio of 1.15, a normal roll temperature of 158 ° C. and an ambient temperature of 158 ° C. A retardation plate was continuously obtained according to the method.

COMPARATIVE EXAMPLE 2 A polystyrene film having a dimensional change ratio of 1.59 at 165 ° C. was adhered and treated in the same manner as in Example 1 at a roll speed ratio of 0.98, a normal roll temperature, and an ambient temperature of 165 ° C. ,
The film was meandered without generating the tension required for running, and the resulting retardation plate was broken and wrinkled, and was not practical.

Evaluation Test With respect to the retardation films obtained in Examples 1 to 4 and Comparative Example 1, the in-plane and thickness directions of the main refractive indexes nx, ny and nz were examined (KOBRA-21ADH, manufactured by Oji Scientific Instruments; parallel). Re [(nx−ny) d] was calculated from the value.

The above results are shown in the following table. nx ny nz d (μm) Re (nm) Example 1 1.5848 1.5842 1.5860 85 55 Example 2 1.5846 1.5844 1.5860 70 14 Example 3 1.5850 1.5830 1.5870 84 170 Example 4 1.5845 1.5815 1.5890 90 271 Comparative example 1 1.5873 1.5814 1.5863 79 471

Polarizing plates were arranged on both sides of the TN type liquid crystal cell via the retardation films obtained in Examples 1 to 4, and the contrast in the front direction and the display characteristics due to the change in viewing angle were examined. There was no change in the display characteristics over a wide viewing angle range, and the liquid crystal display device was of high display quality and excellent in visibility.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of an optical member.

FIG. 2 is a cross-sectional view of an example of a liquid crystal display device.

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

[Explanation of symbols]

 1: retardation plate 2: adhesive layer 3: polarizing plate 4: liquid crystal cell

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 9:00 11:00 (72) Inventor Satoshi Kawahara 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Inside TEPCO (72) Inventor Tadayuki Kameyama 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Prefecture Inside TEPCO (72) Inventor Hiroaki Kuki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Inside TEPCO (72) Inventor Hiroyuki Yoshimi 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA06 BA42 BB03 BB42 BB43 BB44 BB46 BB47 BB49 BB51 BC03 BC09 BC22 2H091 FA08X FA08Z FA11X FA11Z FA14Z FA31X FA31Z FA37X FA37Z FB02 HA07 HA10 LA16 LA17 4F100 AK25G AK41A AK41C AK45B AR00A AR00C AS00D AT00B BA02 BA03 BA04 BA06 BA07 CB05 EJ372 EJ422 GB41 JA11A JA03B JA03D JN18A JN18B JN18C YY00 4F210 AA24 AA28 AG03 AH73 RA01 RC02 RG02 RG04

Claims (7)

[Claims] 1. A long light-transmitting film having a heat-shrinkable film bonded to one or both sides thereof is roll-stretched with a roll speed ratio of 1 or less under the action of shrinkage of the heat-shrinkable film by heat treatment. A continuous process for producing a retardation plate, wherein the translucent film is shrunk by treating with a machine. 2. The method according to claim 1, wherein the heat treatment is performed by at least one of a roll heating method and an atmosphere heating method. 3. The method according to claim 1, wherein the heat-shrinkable film and the light-transmitting film are made of a polymer having a positive birefringence characteristic. 4. The continuous production of a retardation plate according to claim 1, wherein a heat treatment is performed under a temperature condition in which a dimensional change ratio based on the length direction / width direction of the heat-shrinkable film is 1.5 or less. Law. 5. When the in-plane main refractive index is nx, ny, the main refractive index in the thickness direction is nz, and nx> ny, and the thickness is d,
A retardation plate satisfying nx <nz and (nx-ny) d <500 nm. 6. An optical member comprising a laminate obtained by the continuous production method according to claim 1 or 4 or having at least a retardation plate and a polarizing plate according to claim 5. 7. The method according to claim 1, wherein one or both sides of the liquid crystal cell are provided.
A liquid crystal display device comprising the retardation plate according to the continuous production method according to claim 4 or according to claim 5, or a polarizing plate and the retardation plate.