JP2972892B2 - Liquid crystal display device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device.

[Prior Art and Problems to be Solved] Liquid crystal display elements of a type that modulates light by changing the birefringence of a liquid crystal layer by applying a voltage are already known. However, in this type of liquid crystal display element, the distance in the liquid crystal layer through which light actually passes varies depending on the viewing angle, and the apparent birefringence varies depending on the relative angle between the orientation direction of the liquid crystal molecules and the viewing angle direction. For this reason, the viewing angle dependence of the display characteristics is extremely large, and the visible angle range of the display is very small.

In order to reduce the viewing angle dependence of such display characteristics, it has been proposed to provide a birefringent layer between a liquid crystal layer and a polarizer. For example, JP-A-62-210423 discloses that
A voltage is applied to the vertically aligned liquid crystal layer to change the magnitude of the birefringence of the liquid crystal layer. It is disclosed that a polymer film is provided as a birefringent layer and the viewing angle is compensated by the birefringent layer. In general, the characteristics required for such a birefringent layer for viewing angle compensation are determined by the mode of the liquid crystal display element (STN, ECB, DAP, HAP).
AN, TB, etc.), cell parameters (optical axis direction of polarizer,
It depends on the birefringence of the liquid crystal layer Δn · d, etc.), the type of substrate, etc., and various types are possible.
Effective for viewing angle compensation of liquid crystal display devices such as AN, tilt alignment type,
Refractive index n _X, n _y is viewing angle compensation birefringent layer such as larger than the refractive index n _Z in the direction perpendicular to the plane of the plane, it could not be obtained as a well-characterized for the following reasons.

In a uniaxially stretched polymer, the direction in which viewing angle can be compensated is limited to a narrow range because n _X and _ny are different.

With polymers as described in JP-A-62-210423, it is necessary to perform very special molding, it is difficult to produce a uniform film, and it is very difficult to control the size of birefringence. Have difficulty.

 A cell in which a general liquid crystal composed of rod-like molecules is aligned
Is the refractive index n in the molecular long axis direction and the short axis direction , n_⊥Generally
n > N_⊥, So that a homogeneous orientation
Can produce cells with the same characteristics as above
However, as described above, the range in which the viewing angle can be compensated is limited.

The present invention was made Te Kan'i of the drawbacks inherent in the related art, n _X = n _y made by a simple method>
using homogeneous birefringent layer having an n _Z becomes properties, and to provide a high-quality liquid crystal display device viewing angle dependency was significantly reduced in the display characteristics.

[Means and actions for solving the problem]

To achieve the above object, according to the present invention, a liquid crystal layer sandwiched between a pair of substrates having electrodes, a birefringent layer,
In a liquid crystal display element comprising a pair of polarizers arranged so as to sandwich these two layers from the outside and performing an optical modulation by inputting an electric signal to the electrodes, a liquid crystal in which the birefringent layer shows a cholesteric liquid crystal phase It consists of a compound or a polymer film obtained by fixing the orientation by quenching a cholesteric phase of a polymer, and the product of the pitch and the refractive index of the cholesteric liquid crystal phase or the helix structure of the polymer film is 400 nm. A liquid crystal display element characterized by the following is provided.

In the present invention, a birefringent layer having the following characteristics ((i) and (ii)) is conventionally formed by aligning liquid crystal molecules of a cholesteric liquid crystal or a chiral nematic liquid crystal exhibiting a cholesteric liquid crystal phase substantially parallel to a substrate. The arrangement between the liquid crystal cell (hereinafter referred to as “driving cell”) and the polarizer significantly reduces the viewing angle dependence of the display characteristics of the liquid crystal display element.

(I) Being substantially isotropic with respect to visible light in a plane.

(Ii) The refractive index in the thickness direction is smaller than the average refractive index in the plane.

In order for a liquid crystal compound exhibiting a cholesteric liquid crystal phase oriented substantially parallel to the substrate (cholesteric liquid crystal and chiral nematic liquid crystal, the same applies hereinafter) to satisfy the characteristic (i), the size of the cholesteric pitch must be It is necessary to be smaller than the wavelength of visible light (400 to 800 nm), but just like this, the product of the refractive index and the pitch of the liquid crystal must be 400 nm to prevent coloring due to selective reflection by the helical structure. It is necessary to be smaller. The above (i
The characteristic (i) is always satisfied when general liquid crystal molecules are aligned substantially parallel to the substrate. In addition, if a polymer that is not a cholesteric phase at room temperature but has a cholesteric phase whose product of pitch and refractive index is smaller than 400 nm at a higher temperature than room temperature is used, the helical structure can be preserved by quenching from that temperature. It can be used similarly to the above-mentioned liquid crystal compound showing a cholesteric liquid crystal phase.

Next, the liquid crystal display device of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing a specific configuration example of a liquid crystal display device according to the present invention, in which 1, 9 is a polarizer, 2, 5, and 8 are substrates,
Reference numerals 3 and 6 denote alignment films, 4 and 7 denote sealing materials, 10 denotes a first liquid crystal layer, 11 denotes a second liquid crystal layer, and 12 denotes electrodes.

A portion sandwiched between the lower substrate 8 and the intermediate substrate 5 constitutes a driving liquid crystal cell, and a second liquid crystal layer aligned by the alignment film 6.
A voltage using the electrode 12 is applied to 11 to change the alignment state of the liquid crystal to perform light modulation. The portion sandwiched between the upper substrate 2 and the intermediate substrate 5 constitutes a viewing angle compensating liquid crystal cell. They are oriented parallel. According to the present invention, a polymer obtained by quenching a polymer cholesteric phase can be used in place of the viewing angle compensation cell having a liquid crystal layer made of a liquid crystal compound exhibiting a cholesteric liquid crystal phase. The portions need not be in cellular form. To obtain a cholesteric phase composed of a polymer oriented substantially parallel to the substrate, a general horizontal alignment agent may be used,
It is also possible by applying shear stress.

Representative examples of the liquid crystal compound exhibiting a cholesteric liquid crystal phase having a short pitch as used in the present invention include the following.

<Group I> Some of the substances included in Group I do not take a liquid crystal phase at room temperature, but it is possible to form a cholesteric phase at room temperature by mixing two or more substances in Group I or mixing with a nematic liquid crystal. is there.

In addition, the following polypeptides and polyesters are typical examples of polymers that take a cholesteric phase having a short pitch in a temperature range higher than room temperature and preserve a helical structure by rapid cooling.

<Group II> (a) Copolymer of benzyl-L-glutamate and dodecyl-L-glutamate (B) 4,4'-dihydroxybiphenyl and (+)-3-
Copolymers obtained by the reaction of methyladipic acid and alipatic dicarboxylic acid The compound used in the birefringent layer of the present invention is, of course, not limited to those exemplified above. Also, the first
In the configuration example shown in the figure, the intermediate substrate 5 is shared by the driving cell and the viewing angle compensation cell. However, it is also possible to form two liquid crystal cells completely separately using another substrate and then bond them. is there. Furthermore, when the above-mentioned polymer is used in place of the viewing angle compensation cell having a liquid crystal layer made of a liquid crystal compound exhibiting a cholesteric liquid crystal phase, the sealing material 4 and the like are not necessary, and the polymer oriented on one substrate may be used. Can be used.

〔Example〕

 Next, examples of the present invention will be described.

Example 1 A vertical alignment agent FC-805 manufactured by 3M was used as an alignment agent, and this was applied to a glass substrate provided with a transparent electrode by spinner coating, baked, and then rubbed with a sponge. After spraying plastic beads having an average diameter of 11.0 μm on this substrate, the two substrates were bonded together so that the rubbing directions were antiparallel to form a drive cell. The driving cell is a nematic liquid crystal with a negative induced anisotropy, ZLI-4318 (Merck)
Was enclosed. On the other hand, using a horizontal aligning agent HL-1110 manufactured by Hitachi Chemical Co., Ltd. as an aligning agent, a spinner was applied to a glass substrate without an electrode, baked, and then rubbed with a sponge. Plastic beads having an average diameter of 40 μm were sprayed on the substrate, and two substrates were bonded to form a viewing angle compensation cell. A liquid crystal represented by the following structural formula was sealed therein.

Since the temperature range in which the liquid crystal composition takes a liquid crystal phase is 4 to 76 ° C., it can be handled in the same manner as a general liquid crystal by itself. This visual compensation cell was transparent, and it was found from observation with a polarizing microscope that the helical axis was oriented almost perpendicular to the substrate. When a driving cell is sandwiched between two crossed Nicols so that the rubbing direction is 45 ° with respect to the transmission axis of the polarizing plate, a driving signal is input to the electrodes. Color appeared. This color changed remarkably with the viewing angle, and it was found that the viewing characteristics greatly depended on the viewing angle. Next, when a viewing angle compensating cell was sandwiched between the driving cell and the polarizing plate, it was confirmed that the viewing angle dependency of color change was reduced and the viewing angle was widened.

Example 2 A drive cell similar to that of Example 1 was prepared using a vertical alignment agent ZLI-3334 manufactured by Merck as an alignment agent.

On the other hand, for compensating the viewing angle, a polymer film prepared as follows was used instead of the cholesteric phase liquid crystal cell. In the group II (b) described above, n = 8, x: y = 0.
A small amount of the 4: 0.6 polymer was placed on a glass substrate and rolled with another glass substrate while heating at about 300 ° C. Thereafter, the temperature was lowered to about 250 ° C. to obtain a cholesteric phase, and the two glass substrates were shifted until the entire sample became transparent. The sample was then quenched. The thickness of the portion where the polymer sample was not narrowed between the two glass substrates was measured at several points and found to be about 45 μm.

When the polymer film thus prepared was sandwiched between the driving cell and the polarizing plate, it was confirmed that the viewing angle dependency of the display characteristics was reduced and the viewing angle was widened.

Example 3 A horizontal alignment agent HL1110 manufactured by Hitachi Chemical Co., Ltd.
After coating and drying to a thickness of 1000 mm, rubbing was performed in one direction with a sponge. The substrate subjected to the same treatment and the substrate were bonded together via a spacer having a diameter of 12 μm so that the alignment treatment surfaces faced each other. Then, a cholesteric liquid crystal composition in which BDH cholesteric liquid crystal CB15 is added to the cholesteric liquid crystal TM736 is added to the space between the two substrates, and then heated to 80 ° C. to make the liquid crystal isotropic. Then, it was cooled to room temperature to obtain a viewing angle compensation cell. TM736 used in this example has a product of pitch and refractive index of 4
It is 20 nm, and blue coloring can be seen as it is, but CB
By adding 15% by weight of 15, the product of pitch and refractive index becomes
It becomes 360 nm and coloring is hardly seen. The orientation of the liquid crystal was a substantially uniform domain. Observation of the present liquid crystal cell sandwiched between orthogonal polarizing plates revealed that a substantially complete dark field was obtained. Conoscopic observation with a polarizing microscope reveals a clear isogyre at the center of the field of view, revealing that the liquid crystal cell can be optically regarded as a uniaxial crystal with the optical axis oriented in the cell normal direction. It became. Further, when a sensitive color plate was inserted in the conoscopic observation, an increase or decrease in the retardation specific to the negative uniaxial crystal was observed. Retardation (n _X -n _Z ) · d of this liquid crystal cell
(D is the thickness of the liquid crystal layer) was 0.8 μm.

In addition, a vertical alignment agent 0DS-
After a 0.1% solution of E was applied and heat-treated at 120 ° C., a rubbing treatment was performed in one direction with a sponge. The opposite substrate and the substrate that have been subjected to the same treatment are bonded together via a 6.4 μm-diameter spacer so that the rubbing direction is antiparallel, and the space between the two substrates has a negative dielectric anisotropy. A nematic liquid crystal ZLI4318 (Δn = 0.243) manufactured was sealed to form a drive cell.

The driving cell and the viewing angle compensating cell produced above were superimposed, and a neutral gray polarizing plate was disposed above and below to obtain a liquid crystal display device of the present invention. The upper and lower polarizers were arranged so that their transmission axes were perpendicular to each other and at an angle of 45 ° with the rubbing direction of the driving cell. This liquid crystal display element was black when no voltage was applied and had complete light blocking performance, and became white (transparent) when a voltage of about 3 V or more was applied. The curves A in FIGS. 2 and 3 show the viewing angle when the liquid crystal display element is operated by time-division driving with a duty of 1/100.
It shows contrast characteristics. As is clear from these figures, it was confirmed that the present liquid crystal display device had an extremely wide viewing angle. 2 shows the contrast with respect to the front-back viewing angle, and FIG. 3 shows the contrast with respect to the right-left viewing angle. In these figures, the horizontal axis is the angle from the cell normal.

Comparative Example In Example 3, a liquid crystal display element was configured without using a viewing angle compensation cell. When viewed from the front, the liquid crystal display element was black and had a high light-shielding property when no voltage was applied, but when viewed obliquely, extremely remarkable light leakage occurred.
As a result, the viewing angle-contrast characteristic has an extremely narrow viewing angle as shown by the curves B in FIGS. 2 and 3.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to remarkably improve the visual dependence of a display characteristic by the birefringent layer with favorable characteristics manufactured by the simple method.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one configuration example of a liquid crystal display device according to the present invention, and FIGS. 2 and 3 are viewing angles (front-back and right-left) of each liquid crystal display device of Example 3 and Comparative Example. FIG. 4 is a diagram illustrating contrast characteristics. 1,9 ... polarizer 2,5,8 ... substrate 3,6 ... alignment film 4,7 ... sealant 10 ... first liquid crystal layer 11 ... second liquid crystal layer 12 ... electrode

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1335 G02F 1/1347

Claims (1)

(57) [Claims] 1. A liquid crystal layer sandwiched between a pair of substrates having electrodes, a birefringent layer, and a pair of polarizers arranged so as to sandwich these two layers from the outside. In a liquid crystal display element which performs optical modulation by inputting an electric signal, the birefringent layer is made of a liquid crystal compound showing a cholesteric liquid crystal phase, or a polymer obtained by fixing the orientation by quenching the polymer cholesteric phase. Consisting of a membrane,
A liquid crystal display device wherein the product of the pitch of the cholesteric liquid crystal phase or the helical structure of the polymer film and the refractive index is 400 nm or less.