JP2892224B2 - Retardation film, method of manufacturing the same, and liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using a twisted nematic liquid crystal, a cholesteric liquid crystal, a smectic liquid crystal, or the like. The present invention relates to a retardation film and a method for producing the same.

[0002]

2. Description of the Related Art A liquid crystal display device can be directly connected to an IC circuit with low voltage and low power consumption, has various display functions, can have high productivity and can be reduced in weight. It has features and its applications have expanded. Currently, a super-twisted nematic liquid crystal display device (hereinafter, STN-LCD) having a twist angle of liquid crystal molecules of 160 ° or more has been put into practical use as a dot matrix type liquid crystal display device used for OA related devices such as a word processor and a personal computer. ing. This is because the STN-LCD can maintain a high contrast even at the time of high multiplex driving, as compared with a conventional twisted nematic liquid crystal display device (TN-LCD) having a twist angle of 90 °.

However, in STN-LCD,
It is difficult to make the background color of the display screen white, and the background usually has a green to yellow-red tint, and the display quality is insufficient. In order to solve the problem of coloring the background, a method has been proposed in which one or more birefringent films are arranged between a pair of polarizing plates.

For example, JP-A-63-189804 discloses that a retardation value (a product of a birefringence value and a film thickness) is 2
A method using a birefringent polycarbonate film uniaxially stretched so as to have a thickness of 00 to 350 nm or 475 to 625 nm is disclosed. Also, JP-A-63-16
No. 7303 discloses a cellulose-based birefringent film, and JP-A-2-42406 discloses a thermoplastic birefringent polymer film.

Further, JP-A-63-167304 discloses that
There is disclosed a film laminate in which two or more uniaxially stretched birefringent films or sheets are stacked so that their optical principal axes are orthogonal to each other. All of these inventions are aimed at removing the color of STN-LCDs, and in this regard have been considerably improved. That is, a polymer birefringent film,
By using it as a retardation film, the coloring of the background when viewed from the front is improved, but when viewed from a certain angle from the front, the contrast is reduced, or the viewing angle is such that the background is colored. The problem of the characteristics remained.

[0006] Regarding the improvement of the viewing angle characteristic that the contrast is reduced by the viewing angle, Japanese Patent Application No. 63-278 / 1987.
No. 592 discloses a method of correcting an increase in retardation due to a viewing angle (due to an increase in optical path length) using a retardation film in which a refractive index in a three-dimensional direction is controlled, and JP-A-3-306422 discloses a method. A method using a retardation film in which uniaxially stretched films of polymers having positive and negative intrinsic birefringence are laminated is disclosed. Further, JP-A-3-72
No. 315 discloses a method in which two or more uniaxially stretched films are used as a retardation film, and the optical axes thereof are laminated at an appropriate intersection angle with the rubbing axis of the liquid crystal.

In the method using a retardation film in which only the birefringence is controlled as described above, the problem of the viewing angle characteristic that the contrast is reduced by the viewing angle is improved, but it is still insufficient, and the background is colored by the viewing angle. The problem of doing so remained. In addition, a method of using a film having an optical rotatory power to improve the coloring of the background when viewed from the front has been devised.
No. 5, JP-A-3-35201 discloses a method using a film in which obliquely deposited layers are shifted by a predetermined angle, and JP-A-2-245725 discloses a method using a film in which a water-surface spread polymer film is laminated. It has been disclosed. JP-A-63-149624 and JP-A-63-271433.
JP-A-1-206318, JP-A-2-22222
0, JP-A-62-136602, JP-A-3-294
No. 821 and the like disclose a method using a liquid crystalline polymer film.

In the above-mentioned invention, the problem of coloring when viewed from the front is considerably improved by using a film having optical rotation. However, this type of film requires a complicated manufacturing method, is expensive, and has an optical rotation. And its wavelength dependence (optical rotation dispersion)
Because of the difficulty in controlling the color, it was not possible to completely compensate for the coloring of the background. Further, the problem of the viewing angle characteristic still remains.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
Another object of the present invention is to provide a retardation film capable of improving the coloring and the viewing angle characteristics of the background of a liquid crystal display, that is, the reduction in contrast and the change in color tone due to the viewing angle, and a method for manufacturing the same at low cost. A second object of the present invention is to provide a liquid crystal display device having excellent display quality by using the retardation film having the above excellent characteristics.

[0010]

The above object of the present invention has been attained by the following means. (1) A retardation film comprising a mixture of a non-liquid crystal-forming polymer having no optical rotation and a non-liquid crystal-forming low molecular substance having optical rotation. (2) The retardation film according to the above (1), wherein the polymer has a positive intrinsic birefringence and has light transmittance. (3) The retardation film according to the above (1), wherein the polymer has a negative intrinsic birefringence and a light transmittance. (4) The retardation film according to (1), wherein a dope containing a mixture of a non-liquid crystal forming polymer having no optical rotation and a non-liquid crystal forming low molecular substance having optical rotation is cast. Manufacturing method. (5) A liquid crystal display device wherein the retardation film of (1), (2) or (3) is arranged on at least one side of a liquid crystal cell.

It is not clear why the above means significantly improves the coloring of the background and the viewing angle characteristics when viewed from the front, but the following is considered. By passing through the STN liquid crystal cell, the linearly polarized light becomes a complex elliptically polarized light having an ellipticity and an elliptic axis that vary depending on the wavelength. Also, this complicated elliptically polarized light has an ellipticity and an elliptic axis that vary depending on the viewing angle.

For complete removal of coloring and improvement of viewing angle characteristics, the complex elliptically polarized light is converted to R (630 nm), G (55
0 nm) and B (440 nm) in the visible wavelength region. In the present invention, the non-liquid crystal-forming polymer film having no optical rotation can independently control only the birefringence by an operation such as stretching, while the optical rotation, that is, the optical rotation can be improved by including an appropriate optical rotation substance. Optical rotation dispersion can be controlled independently.

That is, in the retardation film of the present invention, the birefringence and the optical rotation can be controlled independently, and the ellipticity of elliptically polarized light and the direction of the elliptical axis can be changed independently.
For this reason, it is considered that such optimization becomes easy, and it is considered that complicated elliptically polarized light transmitted through the liquid crystal cell can be returned to linearly polarized light with uniform axes. That is, the retardation film of the present invention is characterized in that it has both birefringence and optical rotation.By this retardation film, coloring of the background when viewed from the front, and with a certain angle from the front This can reduce the contrast when viewed and improve the coloring of the background.

Hereinafter, the present invention will be described in detail. The polymer used for the retardation film of the present invention has no optical rotation,
It is necessary to be capable of exhibiting birefringence, that is, to have positive or negative intrinsic birefringence. The polymer having a positive intrinsic birefringence is not particularly limited.
% Is preferably an achromatic color, more preferably 90% or more and achromatic. On the other hand, if the polymer has the ability to form a liquid crystal such as nematic, it becomes cholesteric liquid crystal due to the addition of the optical rotatory substance, and exhibits optical rotatory power. Specifically, polycarbonate, polyarylate, polyethylene terephthalate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallylsulfone, polyamide imide, polyimide, polyolefin, polyvinyl chloride, cellulose, polyester-based polymer, and the like are preferable. Polymers such as polymers, polyarylate polymers, and polyester polymers, which have a large intrinsic birefringence and are easy to form a planar homogeneous film by solution casting, are preferred. The polymer is not limited to a homopolymer but may be a copolymer, a derivative thereof, a blend, or the like.

In the polymer having a negative intrinsic birefringence value used in the retardation film of the present invention, the film preferably has an achromatic color with a light transmittance of 70% or more, and more preferably has an achromatic color. Achromatic at 90% or more.
Specifically, styrene-based polymers, acrylate-based polymers, methacrylate-based polymers, acrylonitrile-based polymers and methacrylonitrile-based polymers, vinylnaphthalene-based polymers, vinylpyridine-based polymers, and vinylcarbazole-based polymers Polymers and phenylacrylamide-based polymers are preferable, and polystyrene-based polymers have three viewpoints, that is, they have a large absolute value of an intrinsic birefringence value, have excellent transparency, are not colored, and can be formed into a solution film. Most preferred.

Here, the styrene polymer is a homopolymer of styrene and a styrene derivative, a copolymer of styrene and a styrene derivative, a blend, and the like. Styrene derivatives include, for example, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, o
-Nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-dichlorostyrene, and the like, but are not limited thereto. Copolymers and blends of styrene and a styrene derivative (hereinafter abbreviated as ST) are not particularly limited as long as they have an appropriate film-forming property with ST. Is an object of the present invention if is not impaired. For example, as a copolymer, S
T / acrylonitrile, ST / methacrylonitrile,
ST / methyl methacrylate, ST / ethyl methacrylate, ST / α-chloroacrylonitrile, ST-methyl acrylate, ST / ethyl acrylate, ST / butyl acrylate, ST / acrylic acid, ST / methacrylic acid, ST / butadiene, ST / isoprene, ST / maleic anhydride, ST / N-phenylmaleimide, ST / itaconic acid, ST / vinylcarbazole, ST / n-phenylacrylamide, ST / vinylpyridine, ST / vinylnaphthalene, α- Methylstyrene / acrylonitrile, α-methylstyrene / methacrylonitrile, ST /
Examples include vinyl acetate copolymers and styrene / styrene derivative copolymers. Of course, in addition to the above-mentioned binary copolymers, ternary or more copolymers such as ST / α-methylstyrene / acrylonitrile, ST / N-phenylmaleimide / acrylonitrile, and ST / α-methylstyrene / methyl methacrylate can also be used.

Further, a graft copolymer obtained by addition-polymerizing the styrene-based polymer to a rubber such as SBR, SBS, or BR can also be used. The blends include not only the above-mentioned styrene homopolymer, styrene derivative homopolymer, and a blend between styrene and styrene derivative copolymer, but also a polymer composed of styrene and styrene derivative (hereinafter abbreviated as PST) and a polymer not containing PST. Can also be used. These blends include, by way of example, PST / butyl cellulose, PST / chroman resin.

Next, an optically rotating substance for imparting optical rotation to the retardation film of the present invention (that is, a non-liquid crystal forming low molecular substance having optical rotation) will be described. As the optically active substance, a generally known non-liquid crystal forming compound having an asymmetric carbon and exhibiting optical activity can be used.
Those having a large optical rotation dispersion depending on specific rotation and wavelength are preferable. In particular, the absolute value of the specific rotation is preferably 70 ° or more. Also, in order not to reduce the transparency of the film,
Preferably, there is substantially no absorption of visible light. Also, as described below, when producing the retardation film of the present invention,
When the optical rotation substance described above is added to the polymer solution,
A homogeneous optical rotation is preferably obtained at low cost, but at this time, the optical rotation substance is preferably soluble in the solvent of the polymer and has good affinity with the polymer. Examples of optically active substances are shown below, but two or more optically active substances may be combined to achieve the required optical rotation and optical rotation dispersion.

[0019] P1 D - (-) - fructose P2 (2S, 3S) - ( -) - tartaric acid di Lee an isopropyl P3 (R) - (+) - malic acid dimethyl P4 D-arabinose P5 L-arabinose P6 D-arabitol P7 L-arabitol P8 D-cystine P9 L-cystine P10 3,9-dibromo-(+)-camphor P11 (-)-actinomycin P12 (S)-(+)-2,3-dihydro-1H-pyrrolo [2,1-C] [1,4] benzodiazepine-5
11 (10H, 11aH) dione P13 (-)-(R) -N, N-dimethyl-1-
[(S) -1 ′, 2-bis (diphenylphosphino)
Ferrocenyl] -ethylamine P14 (+)-(S) -N, N-dimethyl-1-
[(S) -1 ′, 2-bis (diphenylphosphino)
Ferrocenyl] -ethylamine P15 (-)-(R) -1-[(S) -2- (diphenylphosphino) ferrocenyl] ethyl methyl ether P16 (+)-(S) -1-[(S) -2- (Diphenylphosphino) ferrocenyl] ethyl methyl ether P17 (S)-(+)-mandelic acid P18 (R)- (-) -mandelic acid P19 (R)-(-)-α-methoxyphenylacetic acid P20 (S) -(+)-Α-methoxyphenylacetic acid P21 (R)-(−)-2-methoxy-2-phenylethanol P22 (S)-(+)-2-methoxy-2-phenylethanol

Next, a method for producing the retardation film of the present invention will be described. When the polymer having no optical rotation and the optical rotation substance have a common solvent or are compatible with each other, dope containing them is used to perform either casting in a heated and molten state or solution casting. The retardation film of the present invention can also be produced by the method. From the viewpoint of the stability of the optical rotatory substance and the smoothness of the film surface, solution casting is more preferred. In the case of solution casting, the solvent is preferably a common solvent of the polymer and the optical rotatory substance, and the optical rotatory substance may be added in a dope state, or may be added to the pipe immediately before casting.

[0021] used in the present invention, the non-liquid crystalline polymer having no handed light resistance, insoluble in most water, is dissolved in an organic solvent. Therefore a common solvent for the polymer and the optical rotation material, methylene chloride, dioxane, ethyl acetate, tetrahydrofuran, acetone, methyl ethyl ketone, toluene, cyclohexanone, benzyl alcohol, Mechiruse
B Sorupu, acid acid butyl, organic solvent etc. is preferred. After the dope cast on a stainless steel band or stainless drum, and dried while peeling roll transport, after the orientation operation such as stretching, by wound into a roll, the phase difference film of the present invention can get. The film thickness is 1
0～200Myu m is preferably the amount of optical rotation material 0.1
10 % is preferred.

When the optical rotation substance does not dissolve in the non-liquid crystal forming polymer solution, a dope for forming a retardation film may be prepared as a solid dispersion.

Next, the liquid crystal display device of the present invention and a display device equipped with the same will be described. The liquid crystal display device is a liquid crystal device handbook (JSPS No. 1
42 Committee) and at least a rear white light source (backlight) (BL), a polarizer (P1), a retardation film (D1), and a liquid crystal cell (L) as shown in FIG.
C), a retardation film (D2), and an analyzer (P2). At this time, as for the retardation film, only one film is mounted on D1 or D2, two films are separately mounted on D1 and D2, or two films are laminated and mounted on D1 or D2, or three or more films are mounted. And mounting the retardation film in combination with D1 and D2. In the present invention, one retardation film is D1 or D2, and two retardation films are D1 or D2.
The method of attaching to D1 and D2 is preferable, and this mode will be described.

In the present invention, the number of retardation films may be one, but preferably two. As shown in FIG. 1, at least one of D1 and D2 uses a retardation film containing the non-liquid crystal forming polymer having no optical rotation and the optical rotation substance as shown in FIG. When a plurality of retardation films of the present invention are used, the position may be anywhere, and the optically active substance used for each may be the same or different. When used in combination with a retardation film composed of a polymer having a positive intrinsic birefringence and a retardation film composed of a polymer having a negative intrinsic birefringence, at least one of the retardation films of the present invention,
In both cases, the retardation film of the present invention may be used. When both are laminated on one side of the liquid crystal cell, if the stretching axes of the respective films are overlapped, the retardation is canceled out, and the relative angle is preferably not more than 70 ° to 110 °. It is preferable to dispose both via a liquid crystal cell, rather than laminating. In this case, the relative angle is preferably 30 ° to 150 °.

When the above-mentioned retardation film is incorporated between two polarizing plates, the films are laminated using an adhesive so that the respective stretching axes are optimized. Although a protective film made of triacetyl cellulose is used before and after the polarizing plate, the protective film on the liquid crystal cell side can be replaced with the retardation film of the present invention.

[0026]

The present invention will be described in more detail with reference to the following examples. Example 1 20% by weight of polycarbonate having a weight average molecular weight of 100,000
The compound of P1 was mixed with the methylene chloride solution at a concentration of 1% by weight based on the polymer to prepare a polycarbonate solution for casting. Thereafter, the polymer solution was cast on a stainless steel band, dried until the residual solvent of the peeled film became 3%, and then uniaxially stretched at 158 ° C. to obtain a polycarbonate birefringent film (E). -1) was obtained.

The above-mentioned compounds P1 and P2 are mixed with a 20% by weight methylene chloride solution of polycarbonate having a weight-average molecular weight of 100,000 at a concentration of 1% by weight to the polymer to prepare a polymer solution for casting. did.
Thereafter, the polymer solution was cast on a stainless steel band, dried until the residual solvent of the peeled film became 3%, and then uniaxially stretched at a temperature of 158 ° C. to obtain a polycarbonate birefringent film (E). -2) was obtained.

Example 2 A styrene polymer having a weight average molecular weight of 400,000 ((A) styrene / butadiene copolymer (monomer copolymerization ratio: 20/8)
0) to (B) styrene / acrylonitrile / α-methylstyrene (copolymerization ratio 60/20/20) to (A):
(B) = grafted at a ratio of 10:90) 2
The compound of P1 was mixed with a 0% by weight methylene chloride solution at a concentration of 1% by weight with respect to the polymer. Thereafter, the mixture was cast on a stainless steel band, dried until the residual solvent became 3%, and then uniaxially stretched at a temperature of 105 ° C. to obtain a birefringent film (E-3).

The compounds P1 and P2 were mixed in a 20% by weight methylene chloride solution of the styrene-based polymer having a weight average molecular weight of 400,000, respectively, at a concentration of 1% by weight based on the polymer. Then, it was cast on a stainless steel band and dried until the residual solvent became 3%.
The film is uniaxially stretched under a temperature condition of 5 ° C. to obtain a birefringent film (E
-4) was obtained.

Comparative Example 1 20% by weight of polycarbonate having a weight average molecular weight of 100,000
A methylene chloride solution was cast on a stainless steel band, dried until the residual solvent of the peeled film became 3%, and then uniaxially stretched at a temperature of 158 ° C. to obtain a polycarbonate birefringent film (CO- 1)
I got

Comparative Example 2 A 20% by weight methylene chloride solution of the styrenic polymer described in Example 2 having a weight average molecular weight of 400,000 was cast on a stainless steel band, and dried until the residual solvent in the peeled film became 3%. After being stretched under a temperature condition of 105 ° C.,
A birefringent film (CO-2) was obtained.

Evaluation of Dependence of Viewing Angle on Liquid Crystal Panel Evaluation was performed using a black and white display liquid crystal panel using the STN liquid crystal cell shown in FIG. The birefringent film, E-1, E-2, E-3, E-4, CO-1, CO
-2 as a retardation film of the liquid crystal panel of FIG.
Liquid crystal panels 1 to 9 having the configurations shown in Table 1 were produced. A contrast ratio (luminance ratio between a driving state and a non-driving state) when viewed from the front of the obtained liquid crystal panel, a coloring state at that time, and a viewing angle at which the contrast ratio becomes 5: 1 or more;
The coloring state at the maximum viewing angle was evaluated and is shown in Table 1.

[0033]

[Table 1]

The liquid crystal display devices (1, 2, 4, 5, 7, 8) using the retardation films (E-1 to 4) of the present invention are:
Even if the viewing angle changes, the contrast is hardly lowered, and there is almost no coloring, and the retardation film of the comparative example (CO-1, 2)
It can be seen that the display quality is far superior to that of the liquid crystal display devices (3, 6, 9) using the same. Also, CO
It was confirmed that the same performance as that of E-1 was obtained even when a methanol solution of a rotatory substance such as the compound P1 or P2 was applied to -1, CO-2.

[Brief description of the drawings]

FIG. 1 shows an arrangement of a liquid crystal panel.

[Explanation of symbols]

 BL: backlight P1: polarizing plate D1: retardation film LC: liquid crystal cell D2: retardation film P2: polarizing plate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-97322 (JP, A) JP-A-1-161217 (JP, A) JP-A-2-136802 (JP, A) JP-A-3- 35201 (JP, A) JP-A-3-87720 (JP, A) JP-A-4-22917 (JP, A) Japanese Utility Model Application No. Sho 60-30425 (JP, U) 3 "Press 19th edition (Showa 51-9-10) Kyoritsu Publishing Co., Ltd. p. 493 (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 5/30 G02F 1/1335 510

Claims (5)

(57) [Claims] A retardation film comprising a mixture of a non-liquid crystal-forming polymer having no optical rotation and a non-liquid crystal-forming low molecular substance having optical rotation. 2. The retardation film according to claim 1, wherein the polymer has a positive intrinsic birefringence and has light transmittance. 3. The retardation film according to claim 1, wherein the polymer has a negative intrinsic birefringence and has light transmittance. 4. Mixing of a non-liquid crystal forming polymer having no optical rotation and a non-liquid crystal forming low molecular substance having optical rotation
The method for producing a retardation film according to claim 1, wherein a dope containing a substance is cast. 5. A liquid crystal display device comprising the retardation film according to claim 1, 2 or 3 disposed on at least one side of a liquid crystal cell.