JP2818983B2 - Method for producing birefringent film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to the production how suitable birefringent-fill beam to compensate for birefringence.

[0002]

2. Description of the Related Art High contrast liquid crystal display devices utilizing birefringence such as STN type are used for various screen displays such as personal computers and word processors.
In such a liquid crystal display device, there is a problem that incident light that has been converted into linearly polarized light through a polarizing plate becomes elliptically polarized light due to birefringence by a liquid crystal cell, and the display is colored yellow or blue when viewed through the polarizing plate. . Therefore, in order to return the elliptically polarized light after passing through the liquid crystal cell to linearly polarized light to prevent coloring,
As a means to compensate for the phase difference due to birefringence of the liquid crystal cell,
An FTN system in which a retardation film made of a stretched film is interposed between a liquid crystal cell and a polarizing plate has been proposed.

However, when a normal stretched film is used as the retardation plate in the FTN method, a viewing angle that can be viewed as a black and white display is narrow, for example, a colored display appears again by slightly changing the viewpoint, and a viewing angle is narrow. It has been found that the viewing angle that can be viewed with a good contrast is narrow and the visibility is inferior, and a retardation plate with a controlled refractive index in the thickness direction that can improve the viewing angle has been proposed (Japanese Patent Application Laid-Open (JP-A) No) 2-
No. 47629, JP-A-2-160204).

However, the above-mentioned Japanese Patent Application Laid-Open No. 2-4762
The retardation plate according to Japanese Patent Publication No. 9 is obtained by uniaxially stretching a film made of a resin having a negative birefringence property in which the refractive index decreases in the stretching direction. When the refractive index is selected in order to suppress the reflection loss and the like, there is a problem that the width is greatly restricted and a problem that the difference in the refractive index in each direction that can be provided by the stretching process is small.

On the other hand, the retardation plate according to Japanese Patent Application Laid-Open No. 2-160204 is obtained by stretching a plate obtained by slicing an extruded rod and having a molecular orientation in the thickness direction.
There is a problem that the manufacturing efficiency is inferior. Further, there is a problem that it is difficult to obtain a large-sized body applicable to a large liquid crystal screen of a high-definition television or the like.

[0006]

[SUMMARY OF THE INVENTION The present invention can be easily manufactured even large-sized body by using various resins, the large refractive index difference in each direction, yet have a different refractive index, has a wide viewing angle range Retardation plate or elliptically polarizing plate that can be compensated for by the above, and birefringence that can obtain a liquid crystal display device with excellent visibility
The task is to develop a method for producing films .

[0007]

According to the present invention, when a resin film is stretched, a shrinkable film is adhered to one or both surfaces of the resin film to form a laminate, and the laminate is heated and stretched. is to provide a manufacturing how the birefringent film, which comprises to impart the direction of the contraction force perpendicular to the stretching direction of the resin film.

[0008] The present invention also relates to a film arrangement in a plane direction of a film.
Oriented molecules and molecules oriented in the thickness direction
A method for producing a birefringent film.

Further, the present invention relates to
The refractive index in the thickness direction of the plate, respectively _{n x, n y, n}
when the _{z, 0} as _{n x> n y <(n} x -n z)
/ _(N x _-n y) <Fuku屈for obtaining a phase difference plate 1
An object of the present invention is to provide a method for producing a foldable film .

[0010]

When a resin film is stretched, a shrinkable film is adhered to one or both sides of the resin film to form a laminate, and the laminate is heated and stretched to apply a shrinkage force in a direction perpendicular to the stretching direction to the resin film. by birefringent film molecular groups oriented respectively in the stretch direction and thickness direction are mixed can be obtained, n _x> n _y in the molecular orientation of the thickness direction
In _{0 <(n x -n z)} / (n x -n y) < retardation plate satisfying the relation 1 is obtained. Such a retardation plate has a small change in retardation due to a viewing angle, and can be applied to a birefringent liquid crystal cell to improve the contrast and the visibility of a monochrome display area.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the production method of the present invention, when a resin film is stretched, a shrinkable film is adhered to one or both surfaces of the resin film to form a laminate, and the laminate is heated and stretched. A birefringent film is obtained by applying a contraction force in a direction perpendicular to the stretching direction of the resin film.
Things. By such a method, in the plane direction of the film
Oriented molecules and thickness-oriented molecules coexist
Birefringent film can be obtained.

The resin film used for the stretching treatment may be formed by an appropriate method such as a casting method or an extrusion method. Further, it may be made of a resin exhibiting any of positive and negative birefringence characteristics, and it is preferable to form a film having excellent transparency. The thickness of the resin film is arbitrary, but is generally 10 to 500 μm, preferably 20 to 500 μm.
200 μm. In addition, the resin having a positive birefringence property is, as opposed to the resin having a negative birefringence property, a resin having an increased refractive index in a stretching direction (a resin having a slow axis in a molecular orientation direction). Say.

Examples of the resin having the positive birefringence characteristic include polycarbonate, polyvinyl alcohol, and the like.
General-purpose resins such as cellulose acetate, polyester, polyarylate, polyimide, and polyolefin are exemplified.
Above all, amorphous and transparent thermoplastic resins and aromatic polycarbonates are preferably used.

Examples of the resin having a negative birefringence characteristic include polystyrene and styrene copolymers, polymethyl methacrylate and methyl methacrylate copolymers. Above all, polystyrene, styrene-acrylonitrile copolymer, styrene-methacrylic acid copolymer,
Styrene methyl methacrylate copolymer, styrene
Styrene-based copolymers such as butadiene copolymer and styrene / maleic anhydride copolymer are preferably used.

The shrinking force in the direction perpendicular to the stretching direction at the time of stretching the resin film may be applied, for example, by shrinking the shrinkable film which shrinks in a direction orthogonal or intersecting with the stretching direction during heat stretching, on one side of the resin film to be stretched, or It can be carried out by a method in which the laminate is adhered to both surfaces and the laminate is heated and stretched. This makes it possible to generate a stretching stress in the thickness direction of the resin film based on the shrinking force of the shrinkable film in the orthogonal or cross direction.

By applying a stretching force in the thickness direction to stretch the resin film to mix molecules oriented in the thickness direction, the resin having either a positive or negative birefringence property can be obtained by the following method. as _{n x -n z) / (n} x -n y) = n z ( hereinafter the same), it is possible to obtain the birefringent film satisfying the 0 <n _z <1.

[0017] When it is simply stretching a resin film in the can a refractive index in the stretching direction as n _x, a resin exhibiting positive birefringence (n _x> n _y), the case of monoaxial stretching: N _z = 1, the case of biaxial stretching: n _z> 1, and the in resins exhibiting negative birefringence (n _x <n _y), the case of monoaxial stretching: n _z = 0, in the case of biaxial stretching: n _z <0, 0 <N
Those satisfying _z <1 cannot be obtained.

Examples of the shrinkable film used for applying the shrink force in the direction perpendicular to the stretching direction during the above stretching include a biaxially stretched film and a uniaxially stretched film. In particular, it is made of a resin such as polyester, polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, and has a shrinkage rate of 5 in the direction orthogonal to the stretching direction of the resin film to be processed.
% Or more, especially 10% or more, is preferably used.

The adhesion between the resin film and the shrinkable film is as follows:
The heat shrinking direction of the shrinkable film is performed so as to include at least a component in a direction orthogonal to the stretching direction of the resin film. That is, the heat shrinkage of the shrinkable film is performed so that all or a part of the heat shrinkage acts in a direction orthogonal to the stretching direction of the resin film. Therefore, the heat shrinkage direction of the shrinkable film may be oblique to the stretching direction of the resin film, and need not be completely orthogonal.

The adhesive treatment between the resin film and the shrinkable film may be appropriately performed using a peeling adhesive means such as the adhesive force of the film itself or an adhesive. In the target birefringent film, control of the mixture ratio of the molecular group oriented in the plane direction of the film and the molecular group oriented in the thickness direction of the film,
In addition, the control of the refractive index can be performed by adjusting the contraction force in the direction perpendicular to the stretching direction during the heat stretching of the shrinkable film. The retardation plate is usually put to practical use after removing the shrinkable film.

The birefringent film according to the present invention has a phase
It can be preferably used for forming a difference plate. Retardation of that is, using at least one of said birefringent film, n _x> n
0 as _{y <N} z _<1, i.e. _{n x> n z>} is obtained by forming such that _{n y.} Therefore, the phase difference plate (3)
May be composed of a single layer of the birefringent film 1 as illustrated in FIG. 1, or may be composed of a laminate of the birefringent films 1 as illustrated in FIG. In the latter case,
N _z may be a combination of the same birefringent films, or N _z may be a combination of different birefringent films. In addition, 2 in a figure is a transparent adhesive layer.

Further, the above-mentioned birefringent film 1 satisfying 0 <N _z <1 and a conventional uniaxially or biaxially stretched film (N _z ≧ 1, where the refractive index in the thickness direction is not controlled). N _z
≦ 0).

In the above, by laminating a birefringent film or a stretched film, the phase difference between the films can be superimposed or adjusted based on the crossing angle of the optical axis. In this case, the number of layers of the birefringent film or the like is arbitrary, but the smaller the number, the more advantageous it is in terms of suppression of light reflection loss and reduction in transmittance. Generally, the number of layers is two to three.

When laminating a birefringent film or the like, the optical rotation may be controlled by shifting each film so that the optical axis has an intersection angle of about 30 degrees or less. The birefringent film used for forming the retardation plate may be protected or reinforced with an isotropic transparent resin layer or glass layer.

For laminating the birefringent film or the like, for example, a transparent adhesive such as acrylic or an adhesive can be used. There is no particular limitation on the type of the adhesive or the like. From the viewpoint of preventing a change in optical properties of the birefringent film or the like, a film that does not require a high-temperature process for curing and drying is preferable, and a film that does not require a long curing treatment or drying time is desirable. When layers having different refractive indices are laminated, an adhesive having an intermediate refractive index is preferably used from the viewpoint of suppressing reflection loss.

[0026] When the phase difference plate can be preferably used in compensation to achieve a black and white display by preventing coloration of the liquid crystal cell, which is its thickness as _{d, 100nm <(n x -n} y) d <10
00 nm, that is, a phase difference of 100 to 1000
nm.

[0027] The present invention retardation plate described above by the Ru <br/> Let preferably used therewith <br/> and formation of elliptically polarizing plate obtained by laminating a polarizing plate. Figure 3 shows an example of Niso (5). 4 is a polarizing plate, 2 is an adhesive layer, and 3 is a retardation plate. In the illustrated example, an adhesive layer 2 made of a pressure-sensitive adhesive is attached to the outside of the retardation plate 3 to adhere to a liquid crystal cell or the like.

As the above-mentioned polarizing plate, an appropriate one can be used, and there is no particular limitation. In general, a film made of a hydrophilic polymer such as polyvinyl alcohol is stretched by treating with a dichroic dye such as iodine, or a film obtained by treating a plastic film such as polyvinyl chloride and orienting a polyene. Or a film obtained by sealing the same.

The bonding between the retardation plate 3 and the polarizing plate 4 may be performed as appropriate, but it is preferable that the fast axis of the retardation plate and the absorption axis of the polarizing plate are parallel to each other from the viewpoint of the compensation effect. Is preferred. For the bonding, for example, an appropriate adhesive such as an adhesive or a pressure-sensitive adhesive exemplified in the above-described lamination of the birefringent film or the like may be used.

The above retardation plate according to the present invention is a liquid crystal
It can be preferably used for forming a display device. Its liquid crystal display device is obtained by placing a polarizing plate through the phase difference plate side, or on both sides of the liquid crystal cell. The elliptically polarizing plate is preferably used for the formation. 4 and 5 illustrate the liquid crystal display device. 5 is an elliptically polarizing plate, 6
Is a liquid crystal cell. 4 has a retardation plate on both sides, and FIG. 5 has a retardation plate on only one side.

As the retardation plate, one that compensates for the retardation of the liquid crystal cell over a wide viewing angle range is preferably used. This achieves prevention of coloring over a wide viewing angle range. The liquid crystal cell used is arbitrary. For example, there are an active matrix driving type represented by a thin film transistor type, a simple matrix driving type represented by a twisted nematic type and a super twisted nematic type, and the like.

Example 1 A biaxially stretched polyester film was adhered to one surface of a polycarbonate film having a thickness of 50 μm via an acrylic weak pressure-sensitive adhesive (a type having a small increase in adhesive force by heating). After stretching in one direction by 15% at 160 ° C., the biaxially stretched polyester film was peeled off to obtain a birefringent film.

Example 2 A birefringent film was obtained in the same manner as in Example 1 except that a biaxially stretched polyester film was adhered to both surfaces of a polycarbonate film and stretched.

Example 3 A biaxially stretched polypropylene film was adhered to both sides of a polystyrene film having a thickness of 70 μm via an acrylic weak adhesive, and the laminate was uniaxially stretched at 100 ° C. by 50%. Thereafter, the biaxially stretched polypropylene film was peeled off to obtain a birefringent film.

Example 4 A biaxially stretched polystyrene film was adhered to both sides of a polyvinyl alcohol film having a thickness of 80 μm via an acrylic weak pressure-sensitive adhesive, and the laminate was heated at 115 ° C. for 8 hours.
After stretching in 0% unidirectionally, the biaxially stretched polystyrene film was peeled off to obtain a birefringent film.

Example 5 A biaxially stretched polystyrene film was adhered to both sides of a cellulose acetate film having a thickness of 50 μm via an acrylic weak tackiness adhesive, and the laminate was stretched 100% unidirectionally at 120 ° C. After that, the biaxially stretched polystyrene film was peeled off to obtain a birefringent film.

Example 6 A biaxially stretched polypropylene film was bonded to both sides of a 35 μm-thick polyester film via an acrylic weak adhesive, and the laminate was stretched in one direction at 150 ° C. by 20%. Thereafter, the biaxially stretched polypropylene film was peeled off to obtain a birefringent film.

Example 7 A biaxially stretched polyamide film was adhered to both sides of a polyarylate film having a thickness of 50 μm via an acrylic weak adhesive, and the laminate was stretched in one direction at 160 ° C. by 10%. After that, the biaxially stretched polyamide film was peeled off to obtain a birefringent film.

Example 8 A biaxially stretched polyester film was adhered to both sides of a polyimide film having a thickness of 50 μm via an acrylic weak adhesive, and the laminate was uniaxially stretched at 160 ° C. by 10%. Thereafter, the biaxially stretched polyester film was peeled off to obtain a birefringent film.

Comparative Example 1 A polycarbonate film having a thickness of 50 μm was unidirectionally stretched at 160 ° C. for 15% to obtain a birefringent film.

Comparative Example 2 A birefringent film was obtained in the same manner as in Example 1 except that an unstretched polyester film was used instead of the biaxially stretched polyester film.

Comparative Example 3 A polystyrene film having a thickness of 80 μm was treated at 40 ° C. for 40 hours.
% In one direction to obtain a birefringent film.

The above Examples 1-8, a birefringent film obtained in Comparative Examples 1 to 3, the phase difference in the plane [(n _x -n _y) d]
There is obtained by forming so that the 400 nm (wavelength 633 nm), showed that _{n x, n y, n z} , a N _z in Table 1. Note that in Example 3 and Comparative Example 3, _ny is the stretching direction,
In other cases, _nx is the stretching direction.

[0044]

[Table 1]

Evaluation Test Change in phase difference When the birefringent films obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were used as they were as retardation plates, and were tilted at 45 degrees on the slow axis or fast axis. Was measured. The value in the case of horizontal (inclination angle 0 degree) is 400 as described above.
nm.

The results are shown in Table 2.

[Table 2]

As can be seen from Table 2, in the case of Example 1 in which _Nz is 0.5, the phase difference is almost constant (about 400 nm) in any direction within the range of the inclination angle of 45 degrees or less.

Viewing Angle An elliptically polarizing plate composed of a laminate of the retardation plate obtained in Examples 1 to 6 or Comparative Examples 1 to 3 and a polyvinyl alcohol-based polarizing plate was adhered to both sides of an STN type liquid crystal cell. A display device is formed. No coloring is observed in the left-right (horizontal) direction and the up-down (vertical) direction, and the contrast ratio is 10: 1.
The above range was examined.

The results are shown in Table 3.

[Table 3]

[0050]

According to the present invention, the refractive index difference is large,
Birefringent films having various refractive indices are obtained. Also, large-sized bodies can be easily manufactured using various resins. Further, it is possible to obtain a retardation plate in which a change in a phase difference due to a change in a viewing angle is small. In addition, it can be used to prevent coloring over a wide viewing angle range, achieve black-and-white display with excellent contrast, and obtain a liquid crystal display device with excellent visibility.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a retardation plate.

FIG. 2 is a sectional view illustrating another retardation plate.

FIG. 3 is a cross-sectional view illustrating an elliptically polarizing plate.

FIG. 4 is a cross-sectional view illustrating a liquid crystal display device.

FIG. 5 is a cross-sectional view illustrating another liquid crystal display device.

[Explanation of symbols]

 1: birefringent film 2: adhesive layer 3: retardation plate 4: polarizing plate 5: elliptically polarizing plate 6: liquid crystal cell

Continuation of front page (72) Inventor Tatsuya Osuka 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (56) References JP-A-2-160204 (JP, A) JP-A-2- 191904 (JP, A) JP-A-3-24502 (JP, A) JP-A-3-23405 (JP, A) JP-A-3-23406 (JP, A) JP-A-4-139402 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 5/30

Claims (5)

(57) [Claims] When a resin film is stretched, a shrinkable film is adhered to one or both surfaces of the resin film to form a laminate, and the laminate is heated and stretched to stretch the resin film. A method for producing a birefringent film, characterized by applying a contraction force in a direction perpendicular to the film. 2. The method according to claim 1, wherein the shrinkage ratio of the shrinkable film in a direction perpendicular to the stretching direction is at least 5% larger than that of the resin film. 3. A process according to claim 1 to form a group of molecules oriented in the planar direction of the off Irumu, the birefringent film oriented molecules groups ing mixed in the thickness direction. Wherein the refractive index in the thickness direction of the orthogonal axis direction and the plate of the plate plane respectively n _x, n _y, in case of a n _z,
as _{n x> n y 0 <(} n x -n z) / (n x -n y)
<Form birefringent film for obtaining a 1 der Ru phase difference plate
The production method according to claim 1, wherein 5. When the thickness is d, 100 nm <
_(N x _-n y) d <請forming a birefringent film for obtaining a phase difference plate of claim 4 wherein 1000nm
The method according to claim 1 .