JP2811392B2 - Birefringent film and liquid crystal display device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a birefringent film used for correcting coloration of a liquid crystal display device and improving a viewing angle characteristic. More specifically, the present invention relates to a method of using the birefringent film as a retardation plate. The present invention relates to a liquid crystal display device having improved coloring or viewing angle characteristics.

[0002]

2. Description of the Related Art A liquid crystal display device has many features such as being able to be directly connected to an IC circuit with low voltage and low power consumption, having various display functions, and being light in weight. And are widely used as display devices for word processors, personal computers, and the like. Among them, a twisted nematic liquid crystal display device having a twist angle of liquid crystal molecules of 160 ° or more (hereinafter referred to as STN-LCD) has a larger capacity display than a conventional twisted nematic liquid crystal display device having a twist angle of 90 ° (TN-LCD). And is excellent in high-speed response, so that it is currently the mainstream of liquid crystal display devices.

However, the STN-LCD has a problem that a display image is colored blue or yellow (blue mode or yellow mode). Therefore, contrast and visibility are low in monochrome display, and colorization is extremely difficult. there were. So, to compensate for this coloring,
A black and white or color display of a two-layer liquid crystal system using a reverse twisted STN liquid crystal cell has been proposed. However, since a plurality of liquid crystal cells are used, the weight and volume of the display device are increased, or the cost is increased. Another problem is that the viewing angle characteristic deteriorates, such as a sharp decrease in contrast due to a slight change in the viewing angle or a change in the background color.

To solve this problem, Japanese Patent Application Laid-Open No.
No. 167303, No. 63-167304, No. 63-1
No. 89804, No. 63-261302, No. 63-14
No. 9624, JP-A-1-201607 and 1-201
No. 608, No. 1-105217, JP-A-2-2853
No. 03, No. 2-59702, No. 2-24406, No. 2-146002, No. 2-257103, JP-A-3
Nos. -23404, 3-126012 and 3-181
As described in specifications such as Japanese Patent Application Laid-Open Nos. 905 and 3-194503, a method using a retardation plate instead of a reverse twisted STN liquid crystal has been proposed.

According to these methods, the coloration of the STN-LCD is greatly improved, the weight and volume of the display device itself are significantly reduced, and the cost is reduced.
There was almost no improvement in viewing angle characteristics.

In order to improve the viewing angle characteristics,
Japanese Patent Application Laid-Open No. 2-285303 discloses a method in which a birefringent film having a refractive index in a thickness direction larger than a refractive index in a direction perpendicular to the birefringent optical axis is prepared by electric field orientation and is used as a retardation plate. was suggested. According to this method, the change in contrast due to the viewing angle is reduced, and the viewing angle characteristics are improved. However, the effect is still small, and it is necessary to apply a high voltage to the molten polycarbonate for a long time, and the manufacturing process is complicated. Therefore, it was difficult to increase the productivity and reduce the cost. Further, Japanese Patent Application Laid-Open No. 2-160204 proposes a method in which a rod-shaped polycarbonate obtained by extrusion is cut into a plate shape and polished polycarbonate is used as a retardation plate. It was extremely difficult to produce boards at low cost. Also, EP-0482620
A2, a method in which a heat-shrinkable film is attached to the surface of a polycarbonate film and stretched, and then the polycarbonate film obtained by peeling the heat-shrinkable film is used as a retardation plate. A heat-shrinkable film and an adhesive are required in addition to the film, and it is difficult to produce at low cost. And Japanese Patent Application No. 4-282907 and Japanese Patent Application No. 4-2858.
No. 93 describes a method for manufacturing a retardation plate in which the refractive index in the thickness direction is controlled by compressing a film using a roller or the like.

Further, JP-A-2-256033, JP-A-3-141303, JP-A-3-14122, and 3-24
Japanese Patent Publication No. 502 proposes a method in which films each having a positive and negative intrinsic birefringence are used one by one or laminated films are used as a retardation plate. According to this method, the birefringence of the two films can be adjusted in accordance with the characteristics of the liquid crystal cell, so that the viewing angle characteristics can be more precisely improved. However, two or more birefringent films prepared separately are used. Things need to be done and the cost is high. In addition, Japanese Patent Application No. 4-5
No. 1101 discloses a method for improving the viewing angle problem by using only a film having a negative intrinsic birefringence value as a retardation plate.

Although these methods of controlling the refractive index in the thickness direction can greatly improve the viewing angle characteristics, the contrast when viewed from the front cannot be said to be sufficiently high, and there is room for improvement. .

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ST.
It is an object of the present invention to provide a birefringent film capable of significantly improving the coloring, viewing angle characteristics and contrast of an N-LCD. Further, by using the birefringent film, the coloring in a display image is small, and the contrast and visibility are excellent. An object of the present invention is to provide a liquid crystal display device having good viewing angle characteristics.

[0010]

According to the present invention, the value of the refractive index in the thickness direction is between two in-plane refractive indexes, and is defined by the value A of the following equation (1). The chromatic dispersion value is 1.10
A birefringent film characterized by being in the range of 2.00: A = Re (450) / Re (590) --- (1) [However, two in-plane refractive indices are at least one stretching. It means the refractive index in the direction parallel to the axis and the refractive index in the direction perpendicular to it. Re (450) means a retardation value with respect to light having a wavelength of 450 nm, and Re (590)
Means a retardation value for light having a wavelength of 590 nm]. The present invention is also characterized in that at least one of a pair of polarizing plates disposed on both sides of the liquid crystal cell and the liquid crystal cell is provided with a retardation plate including the birefringent film. There is also a liquid crystal display device.

Although it is not clear why the front contrast of the conventional STN-LCD is low, the amount of transmitted light in the blue wavelength region does not reach a sufficiently low level in the black display portion, and a considerable amount of light is transmitted. it is conceivable that. This means that the wavelength dispersion value A of the birefringence Δn of the retardation plate does not match the A value of the liquid crystal, that is, in many cases, the A value of the retardation plate is smaller than the A value of the liquid crystal. It was considered that this was caused by the fact that the front contrast was increased by increasing the A value of the phase difference plate. In the present invention,
In order to improve the contrast when the liquid crystal display device is viewed from the front, the wavelength dispersion value A of the birefringence index Δn of the birefringent film is preferably set to 1.10 or more and 2.00 or less, more preferably 1 to 2.00. .12 or more and 1.50 or less.

The birefringent film of the present invention comprises a polymer having a positive or negative intrinsic birefringence value. Birefringence of a film made of a polymer having a positive intrinsic birefringence.
In order for the wavelength dispersion value A of n to be 1.10 or more, it is preferable that the polymer contains sulfur, halogen (chlorine, bromine, iodine) atoms and the like. Specific examples of this type of polymer include polysulfone , Polyether sulfone, polyphenylene sulfide, polythiophene and the like.
The polymer is not limited to a homopolymer but may be a copolymer, a derivative thereof, a blend, or the like.

Further, the wavelength dispersion value A of the birefringence index Δn of a film made of a polymer having a negative intrinsic birefringence is set to 1.
In order to make it 10 or more, it is preferable that the polymer contains a sulfur, a halogen (chlorine, bromine, iodine) atom or the like as in the polymer having the positive intrinsic birefringence described above. Examples include poly-p-chlorostyrene, poly-2,5-dichlorostyrene, poly-p-
Iodostyrene, sodium poly-p-vinylbenzenesulfonate, potassium poly-p-vinylbenzenesulfonate, sodium poly-styrene-co-p-vinylbenzenesulfonate, poly-styrene-co-β- (p-vinylbenzene Sulfonyl) propionamide, poly-styrene-co-p-styrenesulfonyl (β-chloroethyl) amide, poly-p-bromophenylacrylate-
Examples include co-methyl methacrylate, potassium poly-p-vinylbenzenesulfinate, sodium poly-p-vinylbenzenesulfinate and the like.

Further, specific examples of the polymer having a negative intrinsic birefringence value of the present invention include a polymer having at least an unsaturated double bond in a main chain or a side chain (referred to as (A)).
On the other hand, a graft polymer (referred to as polymer (C) of the present invention) obtained by addition-polymerizing a monomer containing at least one styrene-based monomer (referred to as (B)) is preferable, and is preferable from the viewpoint of brittleness. In order to make the wavelength dispersion value A of the birefringence Δn of the film made of these polymers to be 1.10 or more, the above-mentioned (A) or (B) needs to contain sulfur, halogen (chlorine, bromine, iodine) atoms. And the like.

First, the polymer (A) constituting the so-called trunk of the graft polymer (C) of the present invention will be described. The polymer (A) is specifically a polymer having at least an unsaturated double bond repeating unit in a main chain or a side chain. The repeating unit is preferably derived by polymerization of a monomer having a conjugated diene structure. The conjugated diene structure is described in Japanese Patent Application No. 4-141408.

The glass transition temperature (T) of the polymer (A) itself
g) is important for improving the film physical properties of the retardation film, and has a Tg of 50 ° C. or less, preferably 30 ° C. or less, and particularly preferably 0 ° C. or less. The proportion of the conjugated diene monomer component in the polymer (A) is not particularly limited as long as it is within the above-mentioned glass transition temperature, but is preferably in the range of 10 to 100% by weight.

Next, the monomer (B) used for obtaining the graft polymer (C) by addition polymerization with respect to the polymer (A) will be described. In the polymer (C) of the present invention, if the polymer (A) is referred to as a trunk,
The polymer of the monomer (B) can be referred to as a branch having a repeating unit extending in a comb shape starting from (A).

Specific examples of (B) of the present invention in which the wavelength dispersion value A of the birefringence index Δn of the film made of a polymer having a negative intrinsic birefringence value is 1.10 or more include p
-Chlorostyrene, 2,5-dichlorostyrene, p-iodostyrene, sodium p-vinylbenzenesulfonate, potassium p-vinylbenzenesulfonate, β- (p
-Vinylbenzenesulfonyl) propionamide, p
-Styrenesulfonyl (β-chloroethyl) amide, β
-Butyl (p-vinylbenzenesulfonyl) propionate, α-chloroacrylonitrile, β-chloroethyl methacrylate, p-bromophenyl acrylate, β-
Phenylsulfonylaminoethyl acrylate, 1 of benzenesulfinic acid and methylenebisacrylamide
Monoadduct, sodium vinyl sulfonate and the like. The proportion of the monomer containing sulfur and halogen (chlorine, bromine, iodine) atoms in (B) is appropriately adjusted according to the value of A.

Preferred examples of the graft polymer (C) of the present invention are as follows: (A) a polymer having at least an unsaturated double bond in the main chain or side chain (backbone); and (B) at least a styrene monomer. This is exemplified in the form of a polymer portion (backbone) to which one or more monomers are added, but the present invention is not limited to this. That is, (B) is graft-polymerized with (A). (A), (B) The ratio of the number in parentheses represents the copolymerization ratio (weight) of the monomer in each component,
(A) :( B) represents the weight percentage ratio of the polymer of the corresponding trunk component / branch component. P-1 (A) styrene / butadiene copolymer (50 /
50) (B) Styrene / p-styrenesulfonyl (β-chloroethyl) amide / acrylonitrile (60/20/2)
0) (A): (B) = 10: 90 P-2 (A) Styrene / butadiene copolymer (20 /
80) (B) Styrene / butyl- (p-vinylbenzenesulfonyl) propionate / acrylonitrile (50/3
0/20) (A): (B) = 15: 85 P-3 (A) Styrene / butadiene copolymer (50 /
50) (B) Styrene / β-phenylsulfonylaminoethyl acrylate (80/20) (A) :( B) = 15: 85

The exemplary graft polymer of the present invention is mainly prepared by preparing the polymer represented by (A) by an emulsion polymerization method or by purchasing a commercial product, Polymerization is performed at 65 ° C. using a redox initiator of potassium persulfate and sodium sulfite while the monomers represented by B) are charged or dropped at a time, and then an aqueous dispersion of the obtained graft polymer is obtained. Was synthesized by a process of aggregation under strong acid conditions or addition of a salt (eg, salt), or freeze-thaw of the solution, followed by filtration and drying.

The proportion of the backbone polymer (A) in the graft copolymer (C) used in the present invention can be uniquely determined because its structure can contribute to the physical properties of the membrane. Although difficult, it is preferably 1 to 30% by weight, particularly preferably 3 to 30% by weight, considering that the amount necessary for improving the physical properties of the film, or too much, the film becomes too flexible and the orientation of the polymer molecules may be relaxed by heat. To 20% by weight.

The molecular weight of the polymer is not particularly limited unless it is particularly small. However, considering the viscosity of the polymer solution when forming a film from a solution, the weight average molecular weight is 10%.
It is preferably in the range of 10,000 to 1,000,000, particularly preferably 15
It ranges from 10,000 to 500,000. The proportion of the styrene monomer component in all the constituent components in the graft polymer (C) is preferably at least 50% by weight, particularly preferably at least 60%, from the viewpoint of exhibiting birefringence characteristics.

The graft polymer (C) of the present invention can be synthesized by a conventional radical polymerization method (for example, an emulsion polymerization method or a solution polymerization method). The graft polymer (C) of the present invention may be used by mixing two kinds having different compositions and constitutions. Further, a polymer other than the graft polymer (C) may be mixed. Further, depending on the polymerization method, the polymer obtained in the present invention may be a graft polymer and another polymer, for example, a polymer (A) which has not undergone a graft reaction, or a styrene random which has not undergone a graft reaction. Copolymers may be present.

The film used for the birefringent film of the present invention, which is composed of a polymer having a positive or negative intrinsic birefringence value, can be mixed with the film by a melt extraction method, a solution casting method, a calendering method or the like using the polymer. After that, the refractive index in the thickness direction can be controlled by processing according to the method described in the above-mentioned publication. The temperature in this process is
The range of Tg-20 ° C to Tg + 50 ° C of the polymer is preferred. That is, when the processing temperature is much lower than Tg, the optical characteristics are significantly deteriorated due to unevenness of the film or cloudiness. Conversely, if the stretching temperature is much higher than Tg, thermal relaxation occurs even if the molecular chains are oriented, so that anisotropy in refractive index cannot be obtained.

Also in the film of the present invention comprising a polymer having a positive or negative intrinsic birefringence value, it is preferable that the light transmittance is 70% or more and achromatic, and the light transmittance is 85% or more and achromatic. It is even more preferred.
Even if the absolute value of the intrinsic birefringence value is small, it can be sufficiently used by increasing the thickness or increasing the molecular orientation, but in order to avoid such restrictions, the intrinsic birefringence value is preferably an absolute value. The value is 0.02 or more, more preferably 0.04 or more. In addition, the glass transition point of the birefringent film of the present invention is preferably 60 ° C. or higher, more preferably 90 ° C. or higher, in order to prevent the once-oriented molecules from relaxing the alignment due to the LCD manufacturing process and heating. Preferably it is 100 ° C. or higher. The molecular weight is not particularly limited as long as it is not particularly small, but is preferably in the range of 10,000 to 1,000,000, particularly preferably in the range of 30,000 to 700,000. As a method for synthesizing this polymer, a commonly used method can be applied. Also,
The thickness of the uniaxially stretched film having a birefringence value is not particularly limited, but is preferably in the range of 10 μm to 1 mm.

The refractive index characteristics of the birefringent film of the present invention are as follows:
It is preferable that the main refractive index in the thickness direction is smaller than at least one of the main refractive indexes parallel to the surface and larger than the other.

As the retardation plate of the present invention, the birefringent film of the present invention may be used alone.
Alternatively, a laminate may be formed with a uniaxially stretched film such as another type of birefringent film, another deflecting film or a protective film, or a biaxially stretched film. By lamination with the same or another birefringent film, the visual characteristics of the total birefringence and the wavelength dispersion as a retardation plate can be freely controlled, and the retardation of the birefringent liquid crystal cell can be controlled. Advanced compensation is possible. FIG. 1 shows an example in which a birefringent film is laminated with another birefringent film. 1 is a birefringent film, 2 is an adhesive layer, and 3 is another birefringent film. Depending on the combination of the birefringent films to be laminated, the number of laminated layers, the crossing angle of the optical axis, and the like, the wavelength characteristics of birefringence in the retardation plate can be changed. Therefore, the number of layers and the like may be appropriately determined according to the wavelength characteristics of the required birefringence or the phase difference to be compensated. However, from the viewpoint of suppressing a decrease in transmittance and visibility due to absorption loss and reflection loss at a laminate interface, the smaller the number of laminates, the more advantageous.

In the liquid crystal display device of the present invention, the refractive index in the thickness direction is smaller than one refractive index in the direction parallel to the surface, larger than the other refractive index, and is defined by the formula (1). A
Is at least 1.10, and a phase plate including at least a birefringent film is disposed between the polarizing film on one side or both sides of the birefringent liquid crystal cell. FIG. 2 exemplifies the configuration (a type in which a birefringent film is provided on both sides). 4 is a polarizing film, 5 is a retardation, and 6 is a birefringent liquid crystal cell. The upper part of the liquid crystal panel shown in FIG. 2 is the viewing side. Hereinafter, the present invention will be described in detail with reference to examples.

[0029]

【Example】

Preparation of Polysulfone Film (PS-F1) 51.0 g of polysulfone (trade name: Cordell P-3500, manufactured by Amoco Java) was methylene chloride 249.0.
g, and then cast on a stainless steel band, dried until the residual volatile content becomes 3%, peeled off, and dried to obtain a film having a residual volatile content of 1% or less and a film thickness of 75%.
A μm polysulfone film (PS-F1) was prepared.

Preparation of Polysulfone Film (PS-F2) A polysulfone film (trade name: FS-1200, manufactured by Sumitomo Bakelite Co., Ltd.) was purchased and used as a polysulfone film (PS-F2). Preparation of polystyrene-based film (PSt-F1) Graft polymerization of 90 parts by weight of a monomer mixture consisting of styrene: p-styrenesulfonyl (β-chloroethyl) amide: acrylonitrile = 60: 20: 20 (wt%) with 10 parts by weight of SBR Weight average molecular weight of about 3
After dissolving 38.0 g of 50,000 polystyrene copolymer in 262.0 g of methylene chloride, it is cast on a stainless steel band, dried until the residual volatile matter becomes 3%, peeled off, and further dried. As a result, a 100 μm-thick polystyrene film (PSt-
F1) was prepared.

Polystyrene film (PSt-F2)
Preparation of 38.0 g of a polystyrene copolymer having a weight-average molecular weight of about 300,000 obtained by graft-polymerizing 90 parts by weight of a monomer mixture composed of styrene: acrylonitrile = 80: 20 (wt%) with 10 parts by weight of SBR.
After dissolving in 2.0 g, it was cast on a stainless steel band, dried until the residual volatile content became 3%, peeled off, and further dried to obtain a film with a residual volatile content of 1% or less. Is 100 μm polystyrene film (PSt-
F2) was prepared.

[0032] Polycarbonate film (PC-F1)
Preparation of 42 g of polycarbonate having an average weight molecular weight of 50,000 (trade name: Lexan GE Plastics) in methylene chloride 258
g, then cast on a stainless steel band, dried until the residual volatile content becomes 3%, peeled off, and further dried to obtain a film with a residual volatile content of 1% or less and a film thickness of 10%.
A 0 μm polycarbonate film (PC-F1) was prepared.

Example 1 Preparation of Birefringent Film (FN-1) A biaxially stretched polyester film was adhered to one side of a polysulfone film (PS-F1) using an acrylic adhesive (a type that increases adhesive strength by heating). Attached, PS-F1
And a biaxially stretched polyester laminate was prepared. This laminate was stretched 14% under a temperature condition of 193 ° C., and then biaxially stretched polyester was peeled off to prepare a birefringent film (FN-1).

Example 2 Preparation of Birefringent Film (FN-2) Instead of the polysulfone film (PS-F1) of Example 1, a polysulfone film (PS-F2) was used, and the draw ratio was set to 12%. Except for this, the birefringent film (FN-2) was prepared in the same manner as in Example 1.

Example 3 Preparation of Birefringent Film (FN-3) A biaxially stretched polypropylene film was attached to both sides of a polystyrene film (PSt-F1) using an acrylic adhesive (a type that increases the adhesive force by heating). Attached, PSt
-A laminate of F1 and biaxially oriented polypropylene was prepared.
This laminate was stretched 200% under a temperature condition of 116 ° C., and then biaxially stretched polypropylene was peeled off to prepare a birefringent film (FN-3).

Example 4 Preparation of Birefringent Film (FN-4) A polysulfone film (PS-F1) was prepared as shown in FIG.
Hot / cold air is applied to the front and back of the film, and the film is contacted with a 193 ° C. heat roller (12.5 mm diameter) while maintaining a temperature difference. Was bent along the heat roller. Next, the film was turned in the opposite direction, and the same bending operation was performed. When this series of steps was defined as one cycle and the operation was performed for 10 cycles, the refractive index in the thickness direction increased by 0.005 as the birefringence Δn with respect to the in-plane refractive index in the transport direction. Next, the film was introduced into a tenter section and 193.degree.
% Biaxially-oriented birefringent film (FN-
4) was obtained.

Example 5 Preparation of Birefringent Film (FN-5) A polysulfone film (PS-F1) was prepared as shown in FIG.
Under a temperature condition of 193 ° C., the two rollers having a difference in speed are carried in from the high speed side and conveyed to the low speed side.
The birefringent film (FN-4) was obtained by stretching 10% in the width direction in the width direction at 100C.

Comparative Example 1 Preparation of Birefringent Film (FO-1) Polysulfone film (PS-F1) was uniaxially stretched by 14% at 193 ° C. to obtain birefringent film (FO-1). Was.

Comparative Example 2 Preparation of Birefringent Film (FO-2) A birefringent film (FO-2) was obtained by subjecting a polysulfone film (PS-F2) to 12% uniaxial stretching at a temperature of 193 ° C. Was.

Comparative Example 3 Preparation of Birefringent Film (FO-3) Polystyrene film (PSt-F1) was uniaxially stretched at 116 ° C. by 220% to obtain a birefringent film (FO-3).
-1) was obtained.

Comparative Example 4 Preparation of Birefringent Film (DN-1) A polystyrene-based film (PSt-F2) was exposed to hot / cold air on the front and back of the film as shown in FIG. The film was bent along the heat roller in a state where it was brought into contact with a heat roller of 1 ° C. (diameter of 12.5 mm) and air of 0 ° C. was blown on one surface. Next, the film was turned in the opposite direction, and the same bending operation was performed. When this series of steps was defined as one cycle and the operation was performed for 10 cycles, the in-plane refractive index in the transport direction increased 0.005 as the birefringence Δn with respect to the refractive index in the thickness direction. Next, this film was introduced into a tenter portion, and was heated at 116 ° C. in the width direction.
A birefringent film (DN
-1) was obtained.

Comparative Example 5 Preparation of Birefringent Film (CN-1) On one side of the polycarbonate film (PC-F1),
Axial stretched polyester film is attached using an acrylic adhesive (a type that increases the adhesive strength by heating), and the PC-
A laminate of F1 and biaxially stretched polyester was prepared. This laminate was stretched 14% under a temperature condition of 158 ° C.
The birefringent film (CN-1) was prepared by peeling off the axially stretched polyester.

Comparative Example 6 Preparation of Birefringent Film (DO-1) A birefringent film (DO-1) was stretched at 116 ° C. by 230% uniaxially at 116 ° C.
-1) was obtained.

Comparative Example 7 Preparation of Birefringent Film (CO-1) The polycarbonate film (PC-F1) was monoaxially stretched by 15% at 158 ° C. to obtain a birefringent film (CO-1).
1) was obtained.

Evaluation of Birefringence The refractive index (nx) in the optical axis direction for light having a wavelength of 633 μm in the birefringent film, the refractive index (ny) in the direction perpendicular to the optical axis in the plane, and the refractive index in the thickness direction. Refractive index (nz) and A value (wavelength dispersion value) defined by equation (1)
Are shown in Table 1.

[0046]

[Table 1]

In the relationship among nx, ny, and nz, (FN
-1), (FN-2), (FN-4), (FN-5),
And (CN-1) are nx>nz> ny, and (FN-
3) and (DN-1) satisfy ny>nz> nx. On the other hand, (FO-1), (FO-2) and (CO-
1) nx> nz ≧ nz, and (DO-1) and (F
In O-3), nz ≧ ny> nz. By the way, the chromatic dispersion value A is (FN-1), (FN-2), (FN-
3), (FN-4), (FN-5), (FO-1),
(FO-2) and (FO-3) were 1.10.

Evaluation of Dependence of Viewing Angle on Liquid Crystal Panel Commercially available liquid crystal display (Sharp word processor “Shoin” WD)
551A) is decomposed, and instead of the optical compensation film on the viewing side of the STN liquid crystal cell, a polarizing plate and the above-mentioned birefringent film are adhered to each other as a retardation plate to maximize the contrast when viewed from the front. The optical axis was configured as described above, and a liquid crystal panel of a monochrome display was manufactured. Table 2 shows the obtained frontal contrast in the driving state and the non-driving state of the liquid crystal panel and the viewing angle at which the contrast ratio was 5: 1 or more.

[0049]

[Table 2]

As can be seen from Table 2, when the refractive index of the film is in the relationship of nx>nz> ny or ny>nz> nx, the viewing angle characteristics are improved, and the wavelength dispersion value A of the film is 1 .10 or more have high front contrast. That is, the value of the refractive index in the thickness direction is
A liquid crystal panel compensated by using a retardation plate including the birefringent film of the present invention having an A value of 1.10 or more between two in-plane refractive indices has a contrast when viewed from the front. It can be seen that the contrast is high and the change in contrast due to the viewing angle is small.

[Brief description of the drawings]

FIG. 1 shows a specific example of a phase plate of the present invention.

FIG. 2 shows a specific example of the liquid crystal display device of the present invention.

FIG. 3 shows an example of a manufacturing process of the birefringent film of the present invention.

FIG. 4 shows an example of a production process of the birefringent film of the present invention.

[Explanation of symbols]

 1: Birefringent film 2: Adhesive layer 3: Birefringent film 4: Polarizing film 5: Birefringent film 6: Birefringent liquid crystal cell 7: Film 8: Heat roller

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-365002 (JP, A) JP-A-2-42406 (JP, A) JP-A-2-256003 (JP, A) JP-A-2- 285303 (JP, A) JP-A-3-24502 (JP, A) Patent 2723400 (JP, B2) Patent 2636995 (JP, B2) European Patent Application Publication 482620 (EP, A) (58) Fields investigated (Int. Cl. ^6, DB name) G02B 5/30 G02F 1/1335 510

Claims (2)

(57) [Claims] Wave value of 1. A thickness direction of the refractive index, is between two of the in-plane refractive index, and which is defined by the following formula A value
A birefringent film having a long dispersion value in the range of 1.10 to 2.00 : A = Re (450) / Re (590) [where, Re (450) is retardation to light having a wavelength of 450 nm] And Re (590) is wavelength 5
It is a retardation value for light of 90 nm. ] 2. A liquid crystal cell comprising: a pair of polarizing plates disposed on both sides of a liquid crystal cell;
A liquid crystal display device comprising a retardation plate including the birefringent film according to claim 1.