JP2000162436A - Manufacturing method for phase difference film, optical member, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement an efficient manufacturing method for a phase difference film excellent in controlling a refractive index in a surface and in a direction of thickness to a target phase difference by a high degree of control thereof and excellent in homogeneity of the phase difference and oriented axes in the surface by reducing their irregularities. SOLUTION: This manufacturing method for a phase difference film 1 shrinks a light transmissive film in at least one direction under application of a stretching/ shrinking force by a biaxial stretching machine and of a heat shrinking force by a heat shrinkable film, by holding the light transmissive film with the heat shrinkable film mounted on one side or both sides thereof in the simultaneous biaxial stretching machine stretchable/shrinkable both longitudinally and transversely. And, an optical member comprises the phase difference film 1 with an adhesive layer 2 or with a polarizing plate 3 mounted thereon by the adhesive layer 2, while a liquid crystal display device has the optical member on at least one side of its liquid crystal panel. Accordingly, a refractive index in a surface and in a direction of thickness can be controlled at a high degree in a wide range, so that the phase difference film excellent in homogeneity of optical characteristics is efficiently provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a retardation film having excellent controllability of retardation and suitable for improving the viewing angle and contrast of a liquid crystal display device, and an optical member using the retardation film.

[0002]

2. Description of the Related Art As the viewing angle of a liquid crystal display device is required to be increased and the contrast is improved, there is a demand for a retardation plate capable of compensating for a phase difference due to birefringence of a liquid crystal panel. Conventionally, as a method of controlling the retardation of the retardation plate, a stretching method such as uniaxial or biaxial, a heat-shrinkable film is adhered to a translucent film, and a stretching treatment is performed under the action of the heat-shrinking force. A method for obtaining a retardation film in which the retardation in the direction is controlled has been known (Japanese Patent Laid-Open No. 5-15791).
No. 1).

However, the uniaxial or biaxial stretching method cannot control the refractive index in the thickness direction required for the compensator, and the heat shrinkable film bonding method does not allow the shrinkage force and the deformability of the translucent film to be adjusted. It is difficult to control the stretching state due to mutual changes in the stretching temperature, and there is also a region where the refractive index cannot be controlled.In addition, the retardation and the orientation axis are apt to vary, and in general, the desired in-plane and thickness directions. There was a problem that it was difficult to control the refractive index.

[0004]

The present invention is capable of controlling the refractive index in the plane and in the thickness direction at a high level, has excellent controllability to a target retardation, and has little variation in the retardation and orientation axis in the plane. Another object of the present invention is to develop a method for efficiently producing a retardation film having excellent uniformity.

[0005]

According to the present invention, a translucent film having a heat-shrinkable film adhered on one or both sides is held by a simultaneous biaxial stretching machine capable of stretching and contracting in both the vertical and horizontal directions, and the stretching force and the heat generated by the stretching machine are used. A method for producing a retardation film, comprising shrinking the translucent film in at least one direction under the action of the heat shrinkage force of the shrinkable film, and a polarizing plate via the adhesive layer or the adhesive layer on the retardation film. It is an object of the present invention to provide a liquid crystal display device comprising: an optical member; and the optical member on at least one side of a liquid crystal panel.

[0006]

According to the present invention, the in-plane and thickness-direction refractive indexes can be controlled to a high degree and in a wide range by the simultaneous action of the stretching force by the simultaneous biaxial stretching machine and the shrinking force of the heat-shrinkable film. As a result, a retardation film having excellent controllability to a target retardation, small variations in in-plane retardation and alignment axes, and excellent uniformity of optical characteristics can be efficiently obtained.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The production method according to the present invention is characterized in that a translucent film having a heat-shrinkable film adhered to one or both sides is held by a simultaneous biaxial stretching machine capable of stretching in both longitudinal and transverse directions, The light-transmitting film is contracted in at least one direction under the action of the force and the heat-shrinking force of the heat-shrinkable film to obtain a retardation film.

[0008] As the simultaneous biaxial stretching machine capable of expanding and contracting in both the vertical and horizontal directions, for example, an appropriate one capable of simultaneously changing the length of the translucent film in both the width direction and the length direction can be used. Any of the conventional simultaneous biaxial stretching machines can be used. By the way, as an example, the combination of appropriate methods such as rail width control method, pantograph method, and running speed control method using a linear motor controls the lateral length of the film, and the distance between the clips holding the film edges. And the length of the film in the longitudinal direction is controlled.

As the light-transmitting film, 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. Above all, polycarbonate, polyarylet, polyester such as polysulfone or PET or polyethylene naphthalate, polyether sulfone or polyvinyl alcohol,
A translucent film made of a polyolefin such as polyethylene or polypropylene, a cellulosic polymer, a polystyrene, a polymethyl methacrylate, a polyvinyl chloride, a polyvinylidene chloride, a polyamide, a norbornene-based polymer, or the like can be preferably used.

The thickness of the light-transmitting film can be appropriately determined according to the desired retardation characteristics of the retardation film. The phase difference can be determined as the product (Δn × d) of the refractive index difference of the birefringence (Δn) and the film thickness (d). The general thickness of the translucent film is 5 to 500 μm.
m, especially 10 to 350 μm, especially 20 to 200 μm.

The heat-shrinkable film adhered to one or both sides of the light-transmitting film is intended to control the retardation characteristic of the light-transmitting film, particularly the refractive index in the thickness direction, by transmitting the heat-shrinking force. And As a heat shrinkable film,
An appropriate material exhibiting shrinkage by heat treatment can be used, and there is no particular limitation. Above all, those exhibiting heat shrinkage near the glass transition temperature of the translucent film are preferably used from the viewpoint of imparting heat shrinkage.

The heat-shrinkable film can be obtained, for example, as a stretched plastic film. The difference in the heat shrink force of the heat shrinkable film can be provided by changing the stretching conditions such as the type of plastic and the stretching ratio. A heat-shrinkable film having a heat-shrinking force as uniform as possible over the entire surface of the film is more preferable 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 heat-shrinkage force due to good adhesion. As an adhesive, during heat shrink treatment of a heat shrinkable film, the shrinkage force is transmitted well to the light transmissive film, and after the treatment, the optical properties of the heat shrinkable film are altered as much as possible from the processed material of the light shrinkable film. Those which can separate the heat-shrinkable film after the treatment without being used are 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.

When a heat-shrinkable film is adhered to both sides of the light-transmitting film, the heat-shrinkable films on the front and back may be the same or different in heat-shrinkage characteristics such as heat-shrinkage. It may be.

In the treatment of the light-transmitting film to which the heat-shrinkable film is adhered, the light-transmitting film is stretched in one direction in the vertical and horizontal directions by applying a stretching force by a simultaneous biaxial stretching machine and a heat shrinking force by the heat-shrinkable film. Alternatively, it is performed by contracting in both directions. That is, the heat-shrinkable film is shrunk by the heat-shrinkable film while the heat-shrinkable film is heated to a temperature at which the light-transmissible film can be subjected to the orientation treatment, for example, a temperature from its glass transition temperature to a temperature lower than the melting temperature. Is controlled by the stretching force of a simultaneous biaxial stretching machine, in particular, the stretching force, so that the light-transmitting film is shrunk in one or both directions in the longitudinal and transverse directions.

The shrinkage of the translucent film according to the above, especially
By controlling the contraction direction and the degree of contraction in one direction or both directions in the vertical and horizontal directions, the refractive index in the plane and in the thickness direction can be changed. It is possible to obtain a retardation film exhibiting desired retardation characteristics by controlling the retardation to a high degree.

The retardation film obtained by the above-mentioned shrinkage treatment can be used for practical use as it is, or can be put to practical use as a product obtained by adjusting the retardation characteristics by further applying a stretching treatment or the like. . The preferred retardation film according to the present invention has as small a variation in retardation as possible due to birefringence and an orientation axis, and in particular, a variation in retardation in transmitted light perpendicular to the film surface (in the front direction) of 10 nm or less, In particular, it is formed at 5 nm or less and the variation of the orientation axis is 5 degrees or less, particularly 3 degrees or less.

The retardation film according to the present invention is preferably used as a single layer or a laminate of the same or different types, for example, for compensating retardation by birefringence for the purpose of expanding the viewing angle of a liquid crystal panel and improving contrast. Can be used. In practical use, for example, an adhesive layer is provided on one or both sides of a retardation film, or a polarizing plate, or a protective layer made of an isotropic transparent resin layer or a glass layer is bonded through the adhesive layer. It can also be applied as an optical member of an appropriate form such as a laminated one.

The above-described lamination with a polarizing plate or the like can be performed by a method of sequentially laminating the liquid crystal display device in the manufacturing process, but by preliminarily laminating as described above, the stability of quality and the laminating workability can be improved. There is an advantage that the manufacturing efficiency of the liquid crystal display device can be improved, and the like. The pressure-sensitive adhesive layer may be made of any suitable material such as the one exemplified for the adhesion of the heat-shrinkable film. Among them, an acrylic material is preferably used in view of heat resistance and optical characteristics.

If necessary, the adhesive layer may contain, for example, fillers, pigments, coloring agents, antioxidants and the like made of natural and synthetic resins, glass fibers and glass beads, metal powders and other inorganic powders. Can be added.
In addition, an adhesive layer exhibiting light diffusing properties can be formed by incorporating fine particles.

FIG. 1 illustrates an optical member obtained by bonding and laminating a retardation film 1 and a polarizing plate 3 via an adhesive layer 2. 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 above-mentioned transparent protective layer may be appropriately formed as a plastic coating layer or a laminate of a protective film, 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 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.

When laminating the retardation film and the polarizing plate, the arrangement angles of the optical axes such as the transmission axis and the fast axis thereof are not particularly limited, and can be appropriately determined. By the way, when applying to STN type liquid crystal panel, 45
It is often arranged at an oblique crossing angle such as a degree, and when applied to a TN type liquid crystal panel, it is often arranged at a substantially parallel or substantially orthogonal crossing angle.

Although it has been described above that two or more retardation films can be used by laminating them, this is for the purpose of improving the compensation effect and the like, and in this case, in the present invention, a position other than that according to the present invention is used. It can also be a laminate with a retardation plate. As the retardation plate, an appropriate one such as a uniaxially or biaxially stretched plastic film exemplified by 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 film, the polarizing plate, the retardation plate, the transparent protective layer and the adhesive layer may be made of, for example, a salicylic acid ester compound, a benzophenol compound,
Ultraviolet light absorbing ability can be provided by a method of treating with a UV absorber such as a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound.

The liquid crystal display device according to the present invention has an optical member using a retardation film on at least one side of a liquid crystal panel, and its formation can be in accordance with a conventional one. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal panel and a retardation film for optical compensation, and a polarizing plate and an illumination system as necessary, and incorporating a drive circuit, In the present invention, there is no particular limitation except that the retardation film according to the present invention is used for optical compensation and provided on at least one side of a liquid crystal panel, 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 having a polarizing plate disposed on one or both sides of a liquid crystal panel, or a lighting system using a backlight or a reflector. In the case of a liquid crystal display device using a polarizing plate, it is more preferable that the retardation film for optical compensation is disposed between the liquid crystal panel and the polarizing plate, particularly the polarizing plate on the viewing side, from the viewpoint of the compensation effect. In the arrangement,
The above-mentioned optical member can also 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 panel, 5 is a backlight system, and 7 is a reflective layer. Reference numeral 6 denotes a light diffusion plate. In FIG. 2, a retardation film for optical compensation is arranged on both sides, and the illumination system is of a backlight type.
In FIG. 3, a retardation film for optical compensation is arranged only on one side, and the illumination system is of a reflection type.

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 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 retardation film and the optical member according to the present invention are of the TN type or ST type for the purpose of compensating the phase difference due to the birefringence of the liquid crystal panel, such as enlarging the viewing angle and improving the contrast.
TFT type using a liquid crystal panel exhibiting birefringence such as N type or M type
It can be preferably used for various display devices such as an IM type.

[0034]

Embodiment 1 The refractive index in the slow axis direction is nx, the refractive index in the fast axis direction is ny,
Assuming that the refractive index in the thickness direction is nz and the film thickness is d, (nx
(Ny) d is 50 nm and (nx−nz) d is −100 nm.
A heat-shrinkable film made of a biaxially stretched polyester film is adhered to both sides of a transparent polycarbonate film of m through a weak adhesive type acrylic pressure-sensitive adhesive layer. Under the temperature atmosphere, the film is subjected to shrinkage treatment in two directions, and the film length direction is 0.9
The target retardation film was obtained by controlling the state of shrinking by 7 times and the width direction by 0.94 times.

Comparative Example (nx-ny) d is 50 nm, and (nx-nz) d is -100.
In order to obtain a material having a phase difference characteristic of
A heat-shrinkable film made of a biaxially stretched polyester film bonded to both sides of a 0 μm transparent polycarbonate film via a weak adhesive type acrylic pressure-sensitive adhesive layer at 155 ° C. is passed between rolls having different speeds. After contraction by 0.95 times, it was stretched 0.98 times by a tenter stretching machine to obtain a target retardation film.

Evaluation Test The following characteristics were examined for the retardation films obtained in Examples and Comparative Examples. Phase difference variation (nx-ny) d at arbitrary 20 points within a 300 mm square was measured, and the difference between the maximum value and the minimum value was determined.

Orientation Axis Variation The angles of the arbitrary 20 orientation axes within a 300 mm square were measured, and the difference between the maximum value and the minimum value was determined.

Phase difference unevenness A phase difference film of 300 mm square is arranged between polarizing plates arranged in crossed Nicols so that the crossing angle of the optical axis is 0 degree or 45 degrees, and the state of transmitted light is visually observed. The uniformity was checked.

Workability The working state in the manufacturing process was examined.

The results are shown in the following table. *: Generated during roll stretching

From the table, it can be seen that in the examples, the in-plane retardation and the dispersion of the light distribution axis are small, there is no phase difference unevenness, the workability is excellent, and a product of good quality can be stably obtained. The display performance was excellent even when mounted on a liquid crystal panel.

[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 film 2: adhesive layer 3: polarizing plate 4: liquid crystal panel

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shinichi Sasaki 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA02 BA06 BB03 BB42 BB43 BB44 BB46 BB49 BB51 BB63 BC02 BC03 BC22 2H091 FA08X FA08Z FA11X FA11Z FA14Z FA31X FA37X FB08 FC07 FC22 FC29 GA16 GA17 LA17 LA19

Claims (4)

[Claims] 1. A translucent film having a heat-shrinkable film adhered to one or both sides is held by a simultaneous biaxial stretching machine capable of expanding and contracting in both the vertical and horizontal directions. A method for producing a retardation film, comprising: contracting a light-transmitting film in at least one direction under the action of a contraction force. 2. An optical member comprising a retardation film produced by the method according to claim 1 and having an adhesive layer on one or both surfaces. 3. The optical member according to claim 2, comprising a polarizing plate via an adhesive layer. 4. A liquid crystal display device comprising the optical member according to claim 3 on at least one side of a liquid crystal panel.