JP2002365428A - Method for manufacturing optical film and laminated polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical film preventing visibility in a liquid crystal display device from lowering due to viewing angle variation in a wide range of directions and easily and stably forming large area goods with excellent quality, a laminated polarizing plate with wide viewing angle and the liquid crystal display device with excellent contrast and visibility such as a black and white display in a wide viewing angle range. SOLUTION: In the method for manufacturing the optical film composed of a translucent birefringent film having retardation values of inclined transmitted light rays, symmetrical to each other taking the normal surface as a standard, different from each other, a translucent resin is extruded in a film shape with fusion extrusion and subsequently the extruded film is passed through rotating two rolls with surface hardness different from each other and hardened by cooling so as to manufacture the optical film. Flat belts are preferably mounted on the rolls.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical film suitable for improving the display contrast of a liquid crystal cell and the viewing angle characteristics of a display color, and more particularly to a method for producing a tilt type retardation film, and a laminated polarizing plate using the same. The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Thin film transistor (TFT) or MIM (Metal In) using a twisted nematic (TN) type or super twisted nematic (STN) type liquid crystal cell.
Liquid crystal display devices such as sulator metal) have been widely used as display means for various devices such as word processors and personal computers, such as office automation equipment, with a focus on response speed and display contrast. (Viewing angle) In particular, there is a great reduction in contrast due to oblique viewing angles and a large decrease in visibility due to coloring of the screen, and there is a strong demand for improvement in viewing angle characteristics. Conventionally, as a method of improving the viewing angle characteristics, a method of arranging a retardation plate has been known (JP-A-4-229828, JP-A-4-24-2).
No. 58923).

[0003]

However, when the retardation plate is used, there is a problem that it is difficult to improve the viewing angle characteristics in all directions and the effect of improving the viewing angle characteristics in a specific direction is poor.

On the other hand, there has been proposed a method in which a main retardation direction of a refractive index ellipsoid is inclined with respect to a normal line direction to arrange a retardation plate so as to be able to cope with tilt of liquid crystal molecules (Japanese Patent Laid-Open No. Hei 10 (1994) -207). No. 6-75116). However, there is a problem that it is difficult to form the retardation plate. Further, there has been proposed a method of disposing a retardation plate, which is obtained by diagonally cutting an extruded rod along a central axis and having three different refractive indices in a main axis direction (JP-A-6-174920).
However, there is a problem that it is difficult to obtain a device having a necessary area for a liquid crystal display device or the like.

Further, there has been proposed a method of disposing a retardation plate whose optical axis is inclined with respect to the normal direction, which is formed by stretching with a shear force through rolls having different peripheral speeds (Japanese Patent Laid-Open No. Hei 6-1994). 222213). However, since the shearing force and stretching orientation temperature that can be imparted are poor, the inclination angle of the optical axis is small, and the effect of improving the viewing angle characteristics due to large variation in the angle is poor, and contact scratches with the roll on the surface are likely to occur. However, there is a problem that display quality is deteriorated.

In order to solve the above-mentioned conventional problems, the present invention can prevent a decrease in visibility of a liquid crystal display device due to a change in viewing angle in a wide range of orientations, and can easily and stably form a large-area object having excellent quality. An object of the present invention is to provide a method for producing a film, a polarizing plate using the same, and a liquid crystal display device having excellent visibility such as contrast and monochrome display in a wide viewing angle range.

[0007]

In order to achieve the above object, a method of manufacturing an optical film according to the present invention comprises a light-transmitting birefringent film, and is provided for obliquely transmitted light symmetrical to the left and right with respect to a normal plane. A method for producing an optical film having different retardation values, wherein a light-transmitting resin is extruded into a film shape by a melt extrusion method, and then the film is passed between two rolls having different surface hardnesses and cooled and cured. It is characterized by making it. In the method for producing an optical film of the present invention, it is preferable that a flat belt is mounted on the roll.

Further, in the method for producing an optical film of the present invention, the optical film produced by the above method is further subjected to at least one treatment selected from longitudinal uniaxial stretching treatment, horizontal uniaxial stretching treatment and thickness direction orientation treatment. It is characterized by the following.

Next, the laminated polarizing plate of the present invention is characterized in that at least one optical film selected from the optical films produced by the above method and a polarizing plate are laminated via a pressure-sensitive adhesive. And Thereby, a wide viewing angle polarizing plate is obtained.

Further, the liquid crystal display device of the present invention is characterized in that at least one optical film selected from the optical films manufactured by the above method is arranged on at least one side of a liquid crystal display cell.

Further, the liquid crystal display device of the present invention is characterized in that the laminated polarizing plate is arranged on at least one side of a liquid crystal display cell.

Further, the liquid crystal display device of the present invention comprises at least one optical film (A) selected from the optical films manufactured by the above method and / or the above-mentioned laminated polarizing plate.
(B), when the in-plane refractive index is nx, ny (nx> ny), and the thickness direction refractive index is nz, a retardation plate satisfying any of the following formulas (1) to (8) is obtained. And at least one selected phase difference plate (C). nx> ny = nz (1) nx = nz> ny (2) nx = ny> nz (3) nx = ny <nz (4) nx>ny> nz (5) nx>nz> ny (6) nz>nx> ny (7)

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the production method according to the present invention, a light-transmitting resin is extruded into a film by a melt extrusion method, and then the extruded film is rotated with a different surface hardness.
An optical film (light-transmitting birefringent film) is obtained by passing through the rolls of a book and hardening by cooling to obtain an optical film having excellent display contrast of a liquid crystal cell and excellent viewing angle characteristics of display colors. be able to. The manufactured optical film is a tilted retardation film having characteristics that retardation values of obliquely transmitted light of right and left symmetrics with respect to the normal plane are different from each other.

FIG. 1 is a view showing an example of the optical film of the present invention. As shown in FIG. 1, the optical film 1 of the present invention
Is a normal surface 1 on one or both of the slow axis and the fast axis.
At an inclination angle (θ) of 40 degrees with reference to 1, the difference in the phase difference due to birefringence in the obliquely transmitted light 12 and 13 on the left and right of the normal plane is substantially different.

As a method of manufacturing an optical film, a light-transmitting resin is extruded by, for example, a melt extrusion method such as a T-die method or an inflation method, and then the extruded film is placed directly under the resin having a different surface hardness. What is necessary is just to pass through between the rolls of a book, and to cool and harden. The cooling method is not particularly limited. For example, the cooling can be performed by pressurizing and cooling such that the roll is coated with a 200 mm diameter silicone rubber coated roll and a 200 mm diameter metal roll cap.

According to the manufacturing method of the present invention, the phase difference value based on the inclination angle with respect to the normal plane, that is, the phase difference value due to birefringence in the right and left obliquely transmitted light of the normal plane is different from each other (asymmetrically. The following are conceivable reasons why an inclined type retardation film can be produced. As described also in the conventional example, a method of performing a stretching process by a shearing force through rolls having different peripheral speeds to obtain a retardation plate whose optical axis is inclined with respect to the normal direction (Japanese Patent Laid-Open No. Hei 6-222213). In such a case, it is difficult to control the peripheral speed, and it is difficult to maintain accuracy. However, in the present invention, in order to compensate for such a defect, since the extruded film is sandwiched between rolls having different surface hardness, asymmetric deformation of the surface due to a difference in the elastic modulus of the roll occurs, and when the roll is rotated at a constant speed. However, it is considered that a shear force is generated in the film at the roll contact portion.

In order to further increase the adhesive force and increase the shearing force, a method may be used in which a flat belt is sandwiched between rolls and an extruded film is sandwiched between the belts. The flat belt is not particularly limited as long as it is designed so that the deformation generated due to the difference in roll hardness is transmitted to the extruded film via the flat belt. The thickness and material of the belt are not particularly limited, and are preferably made of metal from the viewpoint of surface properties and thermal conductivity.

The rolls are not particularly limited as long as the two rolls have different surface hardnesses. For example, there is a combination of rolls having different surface materials, such as a combination of a roll coated with silicone rubber and a metal roll as described above. Further, when a flat belt is mounted, the belts having different hardness may be mounted on rolls of the same material, and the shear forces generated when the rolls are rotated at a constant speed may be designed to be different from each other. The surface temperature of the roll, the diameter of the roll, the number of rotations of the roll, and the like are not particularly limited, and are appropriately set within a range where the object of the present invention can be achieved.

As described above, by applying the shearing force between the rolls having different surface hardnesses, the speed can be easily controlled.
In addition, by using a low-viscosity film immediately after melt extrusion or applying a flat belt, the magnitude of the shearing force can be easily controlled.

The light-transmitting resin material used for forming the optical film of the present invention is not particularly limited, and an appropriate light-transmitting film material can be used, and a uniform film can be obtained during melt extrusion film formation. For ease of use, a resin material having a low melt viscosity is preferable. The light transmittance of the film is 70% or more, preferably 80% or more, particularly preferably 85% or more, and a light-transmitting film having excellent light transmittance is preferable. Among them, polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyether sulfone, polyvinyl alcohol, polyolefins such as polyethylene or polypropylene, cellulosic polymers, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyamide, polynorbornene, etc. A translucent film is preferably used.

In order to form an inclined retardation film as in the present invention, a resin material extruded with an appropriate viscosity by a melt extrusion method or the like is preferable. Further, it is preferable that the film material is a film material that can be oriented by a stretching process or the like so that a uniaxially stretched film or a biaxially stretched film with a free end or a fixed end, and a film orientated in a thickness direction can be easily formed. .

In the present invention, the optical film to which the above-mentioned shear stress has been applied is subjected to a stretching treatment by an appropriate method such as a uniaxial stretching treatment or a biaxial stretching treatment, so that the optical film (inclined retardation film) is formed. You can also.

The thickness of the translucent film can be appropriately determined according to the retardation characteristics of the target optical 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 light-transmitting film or the optical film is 5 to 500 μm, preferably 10 to 3 μm.
It is 50 μm, particularly preferably 20 to 200 μm.

In the optical film of the present invention, based on the inclination angle of 40 degrees with respect to the normal plane on one or both of the slow axis and the fast axis, the transmitted light in the obliquely transmitted light on the left and right sides of the normal plane is used. The difference in phase difference due to birefringence is preferably 10 nm or more from the viewpoint of, for example, the range of the azimuth in which the viewing angle characteristics are improved. When the difference in the phase difference is less than 10 nm, the effect of improving the viewing angle characteristics, particularly, the effect of expanding the improved azimuth is poor. Further, from the viewpoint of preventing the occurrence of display unevenness and the reduction of contrast, the difference between the maximum value and the minimum value of the phase difference of the transmitted light perpendicular to the film surface (in the front direction) is 10 nm or less, preferably 7 nm or less.
nm or less, and particularly preferably 5 nm or less.

The optical film of the present invention is preferably used as a single layer or a laminate of the same type or different types for compensating viewing angle characteristics due to birefringence of a liquid crystal cell. In practical use, a laminate with a polarizing plate or a laminate with a retardation plate, a laminate with a protective layer made of an isotropic transparent resin layer or a glass layer, or the like can be used in an appropriate form. . A laminate with a polarizing plate or the like can be formed by sequentially laminating an optical film or a polarizing plate or the like sequentially in the process of manufacturing a liquid crystal display device. There are advantages, such as excellent lamination workability and the like, which can improve the manufacturing efficiency of the liquid crystal display device. Note that an appropriate bonding means such as an adhesive layer can be used for lamination.

FIG. 2 illustrates a laminated polarizing plate (B) in which an optical film (inclined retardation film) 1 and a polarizing plate 3 are bonded and laminated via a pressure-sensitive adhesive 2. Here, as the polarizing plate, for example, iodine and / or a dichroic dye may be used 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 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 plate may have a transparent protective layer on one side or both sides of the polarizing film. For laminating the optical film and the polarizing plate, an appropriate adhesive means such as an adhesive or an adhesive can be used. For example, a pressure-sensitive adhesive (adhesive)
It may be.

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 may be appropriately formed as a plastic coating layer or a laminate of a protective film, and the transparent protective layer may be formed with transparency, mechanical strength, heat stability, and moisture shielding property. Plastics and the like having excellent properties are preferably used. Examples thereof include polyester resin, acetate resin, polyethersulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, acrylic resin, or acrylic, urethane, acrylic urethane 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.

Further, as the retardation film (C) which may be laminated with the above-mentioned optical film or polarizing plate, for example,
Examples include a birefringent film obtained by stretching a film made of an appropriate plastic such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylate, and polyamide. Further, a birefringent film in which a liquid crystal compound is thinly coated may be used.

The characteristics of the retardation plate are not particularly limited, and examples thereof include a uniaxially stretched film and a film oriented in the thickness direction. The in-plane refractive index of the film is nx, n
When y (nx> ny) and the refractive index in the thickness direction are nz,
A retardation plate satisfying any of the above formulas (1) to (7),
They can be used alone or in combination. When the refractive index in the slow axis direction is nx, that in the fast axis direction is ny, and that in the thickness direction is nz, for example, nx>ny> nz
Biaxially stretched film exhibiting characteristics such as nx = ny> nz
And an appropriate phase difference characteristic such as a uniaxially stretched optical ellipsoid exhibiting characteristics such as nx = ny <nz.

In the above, the adhesive (adhesive) used for laminating the optical film and the polarizing plate is not particularly limited, and examples thereof include acrylic, silicone, polyester, polyurethane, polyether, and rubber. An appropriate adhesive such as a transparent pressure-sensitive adhesive such as a system can be used. From the viewpoint of preventing a change in optical properties of an optical film or the like, a film that does not require a high-temperature process for curing and drying is preferable, and a material that does not require a long curing treatment or drying time is desirable. Those that do not cause separation or the like under heating or humidification conditions are preferably used.

From this point, the weight average molecular weight obtained by polymerizing monomers such as butyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate and (meth) acrylic acid is 100,000 or more. , Glass transition temperature 0
An acrylic pressure-sensitive adhesive made of an acrylic polymer having a temperature of not more than ° C is particularly preferably used. In addition, acrylic pressure-sensitive adhesives are preferable in terms of excellent transparency, weather resistance, heat resistance, and the like. When layers having different refractive indices are laminated, an adhesive having a middle refractive index is preferably used from the viewpoint of suppressing reflection loss.

If necessary, the adhesive may be, for example, a filler made of natural or synthetic resin, glass fiber or glass beads, metal powder or other inorganic powder, a pigment, a colorant or an antioxidant. An appropriate additive such as an agent can also be blended. Further, an adhesive layer exhibiting light diffusing properties can be formed by incorporating fine particles.

The above-mentioned optical film, polarizing plate and the like may be provided with an adhesive layer for bonding to other members such as a liquid crystal cell. The pressure-sensitive adhesive layer can be formed with an appropriate pressure-sensitive adhesive, such as an acrylic resin, according to the related art. When the adhesive layer provided on the polarizing plate or the optical film is exposed on the surface, it is preferable to temporarily cover the adhesive layer with a separator until the adhesive layer is put to practical use for the purpose of preventing contamination and the like. The separator is formed by a method of providing a release coat with a suitable release agent such as a silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide on a suitable thin leaf according to the transparent protective film or the like as necessary. be able to.

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

The liquid crystal display device using the optical film of the present invention can be formed according to a conventional method. That is, the liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell and an optical film for optical compensation, and a polarizing plate and an illumination system as needed, and incorporating a drive circuit. In the liquid crystal display device of the present invention, there is no particular limitation, except that the optical film of the present invention is used for optical compensation and is provided on at least one side of the liquid crystal cell, and is the same as the conventional one.

Accordingly, an appropriate liquid crystal display device such as a liquid crystal display device having a polarizing plate disposed 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 the case of a liquid crystal display device using a polarizing plate, the optical film for optical compensation is preferably disposed between the liquid crystal cell 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 laminated polarizing plate may be used.

[0038]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 A 150 μm-thick transparent polycarbonate film extruded from a T-die by a melt extrusion method was cooled between a metal endless belt held by a metal roll having a diameter of 300 mm and a silicon roll. Then, an optical film was obtained. FIG. 3 shows the outline.

Comparative Example 1 A transparent polycarbonate film having a thickness of 100 μm was passed through rolls having different peripheral speeds in an atmosphere at 160 ° C., and stretched 1.15 times to obtain an optical film.

Comparative Example 2 A transparent polycarbonate film having a thickness of 100 μm was supplied between rolls having a drive system and subjected to a shearing treatment. One of the rolls has a surface temperature of 15
The conditions were 0 ° C. and a peripheral speed of 2.8 m / min, and the other condition was a surface temperature of 150 ° C. and a peripheral speed of 1.9 m / min.

With respect to the optical films obtained in Examples and Comparative Examples, the following characteristics were examined. Table 1 shows the results.

(Phase difference) ADR-100X manufactured by Oak
Using Y, the phase difference when tilted ± 40 degrees in the front direction and the slow axis direction was examined.

(Variation in phase difference) The phase difference in the front direction within a 100 mm square was measured at 100 points at intervals of 10 mm, and the difference between the maximum value and the minimum value was determined.

(Scratch) The appearance of the optical film was visually observed to determine the presence or absence of a scratch.

[0046]

TABLE 1-position phase difference (nm) wound positive surface +40 ° -40 ° variation Example 1 464 439 305 6 None Comparative Example 1 380 339 339 5 None Comparative Example 2 372 342 322 18 Yes

As can be seen from Table 1, in Example 1, the difference in phase difference between the left and right obliquely transmitted light with respect to the normal plane is large, the asymmetry is excellent, and the in-plane phase difference variation is small.
The quality was also good. On the other hand, in Comparative Example 1, there is no difference in the phase difference between the left and right oblique transmitted light, and the characteristics of a normal uniaxially stretched product are shown. In Comparative Example 2, the difference in the phase difference between the left and right oblique transmitted light is small. In addition, it can be seen that there is a large variation in the in-plane phase difference, and there is damage due to contact with the roll.

[0048]

As described above, although the mechanism of action of the asymmetric inclined retardation film of the present invention is unknown, the change in visibility due to the viewing angle based on the birefringence of the liquid crystal cell can be obtained over a wide range of orientations. And a liquid crystal display device having excellent visibility such as contrast and monochrome display can be obtained. Also, a large-area optical film having excellent quality can be easily and stably formed. Therefore, its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical film (inclined retardation film) of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration example of a laminated polarizing plate.

FIG. 3 is a schematic view illustrating a manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical film (tilt type retardation film) 2 Adhesion (adhesion) layer 3 Polarizer 11 Normal line 12 Oblique transmitted light 13 Oblique transmitted light

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // B29K 101: 12 B29K 101: 12 B29L 7:00 B29L 7:00 9:00 9:00 11:00 11:00 F term (reference) 2H049 BA02 BA06 BA42 BB03 BB44 BB51 BC03 BC09 BC22 2H091 FA08X FA08Z FA11X FA11Z FA14Z FA41Z FD06 FD14 GA13 HA07 HA10 LA17 LA19 4F207 AG01 AG03 AH73 KA01 KA17 KK64 KK84 KK84 KK84 KK84 K84

Claims (7)

[Claims] 1. A method for producing an optical film comprising a light-transmitting birefringent film and having different phase difference values in obliquely transmitted light symmetrical to the right and left with respect to a normal plane, wherein the light-transmitting resin is melted. A method for producing an optical film, comprising: extruding a film into a film by an extrusion method, and then passing the film between two rolls having different surface hardnesses for cooling and curing. 2. The method according to claim 1, wherein a flat belt is mounted on the roll. 3. The optical film produced by the method of claim 1 or 2, further comprising at least one treatment selected from a longitudinal uniaxial stretching treatment, a horizontal uniaxial stretching treatment, and a thickness direction orientation treatment. Manufacturing method of optical film. 4. At least one selected from optical films produced by the method according to claim 1.
A laminated polarizing plate, wherein two optical films and a polarizing plate are laminated via a pressure-sensitive adhesive. 5. At least one selected from optical films produced by the method according to claim 1.
A liquid crystal display device comprising a plurality of optical films disposed on at least one side of a liquid crystal display cell. 6. A liquid crystal display device, wherein the laminated polarizing plate according to claim 4 is arranged on at least one side of a liquid crystal display cell. 7. At least one selected from optical films produced by the method according to claim 1.
A plurality of optical films (A) and / or the laminated polarizing plate (B) according to claim 4, and an in-plane refractive index of nx, ny (nx> n).
y), when the refractive index in the thickness direction is nz, the following equation
A liquid crystal display device comprising at least one retardation plate (C) selected from retardation plates satisfying any of (1) to (7). nx> ny = nz (1) nx = nz> ny (2) nx = ny> nz (3) nx = ny <nz (4) nx>ny> nz (5) nx>nz> ny (6) nz>nx> ny (7)