JPH11131062A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject element developing excellent temperature characteristics comprising the resistance to the lowering of contrast ratio and the generation of the thickening of dark part, etc., even by varying the temperature and useful for a displaying device of a notebook computer, etc., by using a plurality of specific liquid crystal materials in combination. SOLUTION: This liquid crystal display element contains a liquid crystal composition (A) sandwiched between electrodes and displays by controlling the orientation state of the liquid crystal by the application of potential. Plural liquid crystal materials are used as the composition (A) in such a manner as to keep the value (Z) defined by the formula Δn.Δ ε/K (Δn is refractive index anisotropy; Δε is dielectric anisotropy; K is elasticity constant of orientation mode to elastic deformation) to a definite level even by the variation of temperature. For example, the plural liquid crystal materials contain a fluorine- containing liquid crystal having tricyclic molecular skeleton and positive temperature coefficient of Z (concretely the compound of the formula I) and a liquid crystal having tetracyclic molecular skeleton and having negative temperature coefficient of Z (concretely the compound of the formula II).

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 having improved temperature characteristics.

[0002]

2. Description of the Related Art Liquid crystal display devices have been actively used as display devices for OA equipment such as notebook computers and Japanese word processors because of their advantages of thinness, light weight and low power consumption. Most liquid crystal display elements use nematic liquid crystal, and the display method includes an optical rotation mode and an electric field control birefringence (ECB) mode.

For example, there is a twisted nematic (TN) type liquid crystal having a molecular arrangement twisted by 90 ° as an optical rotation mode element. In principle, a black-and-white display and a high contrast ratio are obtained. There is a problem that time is slow.

As an ECB mode element, a mode for compensating the problems of the TN type liquid crystal has been proposed, and an in-plane switching (IPS) mode having improved viewing angle characteristics, an OCB having improved response time, and a 180 ° (π) twist. , Vertical alignment mode, hybrid alignment mode, and the like.

[0005]

However, these ECB mode liquid crystal display elements depend on the temperature coefficient of various physical properties of the liquid crystal composition injected into the liquid crystal cell, and the normally white liquid crystal display element changes due to a change in temperature. In the mold, since the voltage indicating black (minimum transmittance) shifts greatly, an extreme reduction in contrast ratio and inversion occur. Further, in the normally black type, since the voltage indicating white (the transmittance is almost maximum) shifts greatly, problems such as an extreme decrease in the transmittance and coloring occur.

An object of the present invention is to provide a liquid crystal display device having an improved temperature characteristic which does not cause a decrease in contrast ratio or blackening even if the temperature changes and does not change the display quality. The purpose is to provide.

[0007]

According to the present invention, there is provided a liquid crystal display device in which a liquid crystal composition is sandwiched between electrodes, and an alignment state of the liquid crystal composition is controlled by a voltage applied to the electrodes to perform display. When the refractive index anisotropy of the composition is Δn, the dielectric anisotropy is Δε, and the elastic constant for the elastic deformation of the orientation mode is K, the temperature at which Δn · Δε / K becomes almost constant even when the temperature changes. A liquid crystal display element characterized by using a plurality of liquid crystal materials having a combination of Δn, Δε, and K having coefficients.

Further, in a liquid crystal display device having a liquid crystal composition sandwiched between electrodes, the liquid crystal composition contains at least a first liquid crystal and a second liquid crystal, the liquid crystal has a refractive index anisotropy of Δn, When the modulus of anisotropy is Δε and the elastic constant for elastic deformation is K, the temperature coefficient of Δn · Δε / K is the first coefficient.
And a liquid crystal display device in which the polarity of the liquid crystal is opposite to that of the second liquid crystal.

Further, the present invention provides a liquid crystal display device in which the molecular skeleton of the first liquid crystal is a three-ring liquid crystal and the molecular skeleton of the second liquid crystal is a four-ring liquid crystal.

Further, a liquid crystal display element in which the first liquid crystal has a positive temperature constant in which the molecular skeleton of the first liquid crystal is tricyclic and contains fluorine and the second liquid crystal has a negative temperature constant is obtained.

Further, an active matrix type liquid crystal display device in which switching elements and pixel electrodes are arranged on an array substrate and a common electrode is arranged on a counter substrate, and among optical rotation mode, electric field control birefringence (ECB) mode, and ECB mode. Thus, a liquid crystal display element applicable to each mode such as OCB / 180 ° (π) mode, vertical alignment mode, and hybrid alignment mode can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION When the refractive index anisotropy of a liquid crystal is Δn, the dielectric anisotropy is Δε, and the elastic constant for the elastic deformation of the alignment mode is K, the temperature of Δn · Δε / K is obtained. Focusing on the coefficient, as shown in Table 1,
It has been found that there are two positive and negative temperature coefficients of n · Δε / K, and that the display voltage also has positive and negative temperature coefficients. Table 1 shows the normally white type 180 °
It shows the temperature coefficient of the voltage at which the transmittance of each of the liquid crystals A to E in the twist mode becomes minimum (black display).

[0013]

[Table 1] The liquid crystals A to E containing the respective liquid crystal structural formulas are shown below.

[0014]

Embedded image For example, in the normally white type of OCB / 180 ° twist mode, when a liquid crystal containing a fluorine-based material having a three-ring molecular skeleton is used as the liquid crystal, Δn · Δε / K becomes positive as shown by the symbol a in FIG. A voltage indicating a temperature coefficient and indicating a minimum transmittance (black display) indicates a negative temperature coefficient, and shifts to a lower voltage side as the temperature increases. In an actual display, as the temperature increased, the contrast ratio decreased and blackout occurred.

In the case where a liquid crystal containing a material having a four-ring molecular skeleton is used as the liquid crystal, contrary to the above-mentioned liquid crystal, Δn · Δε /
K indicates a negative temperature coefficient (symbol “b” in FIG. 1), and a voltage indicating a minimum transmittance (black display) indicates a positive temperature coefficient. Declined.

Therefore, by mixing a liquid crystal having a material whose molecular skeleton has three rings and four rings at a certain ratio, Δn · Δε
Δn, Δε, K where / K is approximately constant even when the temperature changes
A liquid crystal material having a temperature coefficient (reference c in FIG. 1) of
By using this, it has been found that even if the temperature changes, a liquid crystal display element in which the contrast ratio does not decrease, the black level does not occur, and the display quality does not change can be obtained.

Table 2 shows the liquid crystal compositions X1 to X3 having a mixing ratio according to the examples of the present invention.

[0018]

[Table 2]

[0019]

【Example】

(Embodiment 1) In this embodiment, as shown in FIG.
A glass substrate 11 having a transparent common electrode formed thereon, and a glass array substrate 12 having scanning lines and signal lines, switching elements, and pixel electrodes connected to the switching elements in a matrix are prepared. ITO electrodes having a pixel size of 110 × 330 μm are connected to the switching elements in a matrix parallel to the substrate edge.

A polyimide (AL1051, made by Japan Synthetic Rubber) was formed as a liquid crystal alignment film 14 on the substrate 12 to a thickness of 850 A (angstrom) by a printing method. The alignment film 13 was similarly formed on the counter substrate 11. Next, rubbing was applied to both substrates so as to be twisted at 180 °. The rubbing direction is indicated by arrows 11a and 12a in the same direction in the figure. Next, a 10 μm spacer is sprayed on the opposing substrate 11,
An adhesive is printed along the periphery of the alignment film 14 printed on the array substrate 12 except for an injection port (not shown), and an electrode transfer material for applying a voltage from the switching element array substrate to the counter electrode (see FIG. (Not shown) was formed on the electrode transfer electrode around the adhesive. Then, the array substrate and the counter substrate were arranged so that the alignment films faced each other, and the adhesive was cured by heating and bonded. Thereafter, the liquid crystal composition 1 was prepared by a vacuum injection method.
7 was injected, and then the injection port was sealed with an ultraviolet curable resin to form a cell.

The liquid crystal compositions used at that time were X1 to X1 in Table 2.
Each of X3 was obtained by adding a chiral agent. The liquid crystal molecules 17a are twisted 180 ° between the substrates without applying a voltage.

A compensating plate for compensating the optical characteristics of the cell and a polarizing plate were attached to the front side of the cell, and a polarizing plate was attached to the back side to assemble a liquid crystal module. This is disclosed in Japanese Patent Application No. 7-2533.
It was operated in the display mode proposed in No. 02. The absorption axes 16a and 16b of both polarizing plates 16 are arranged at 90 ° intersections, and 45 ° respectively with the rubbing directions 11a and 12a.
Crossed.

In the liquid crystal display device manufactured in this manner, in the case of using the liquid crystals X1 and X3, the voltage for displaying black (minimum transmittance) slightly depends on the temperature change.
There was only a shift of 0 mV, and the decrease in contrast ratio was small compared to each single liquid crystal in Table 1.

On the other hand, when the liquid crystal uses X2, Δn ·
The temperature coefficient of Δε / K was 0.4 mV / ° C., there was almost no shift in the voltage for displaying black, and the display quality was the best, with no decrease in contrast ratio or black loss.

Although the 180 ° twist mode is used in this embodiment, it goes without saying that another mode may be used.

Embodiment 2 In this embodiment, as shown in FIG. 2B, a counter substrate 21 having no electrodes, scanning lines and signal lines, switching elements, and switching elements are connected in a matrix. Array substrate 2 having pixel electrodes
2 is prepared (an alignment film is not shown). Using these two substrates, two substrates were rubbed in parallel with each other so as to be uniaxially aligned in the same process as in Example 1, thereby producing a liquid crystal cell. Polarizing plates 26 were attached to both sides of the cell, and assembled into a liquid crystal module. The liquid crystal molecules 27a of the liquid crystal 27 are parallel to the substrate surface and are not twisted.

The liquid crystal display device thus manufactured is an IPS mode liquid crystal display device in which the liquid crystal is driven in a direction parallel to the substrate surface by the parallel electrodes 28 provided on the array substrate. Was used. With respect to the driving voltage applied to the electrodes, the display characteristics did not substantially depend on the temperature change, and very good display quality without coloring or reduction in transmittance could be obtained.

(1) In the first embodiment, 180
Although the description has been made in the ゜ (π) twist mode, other modes may be used.

(2) Examples of the switching element of the above-mentioned embodiment include a thin film transistor and a thin film diode.

(3) The switching element in the above-described embodiment may be amorphous silicon or polysilicon, and when polysilicon is used, a drive circuit may be built on an array substrate.

(4) In the above embodiment, the transmission type liquid crystal display element is used, but a reflection type liquid crystal display element may be used.

(5) In the above-described embodiment, the spacers are sprayed, but a spacer in which a columnar spacer is formed on one of the substrates may be used.

(6) The combination of the liquid crystals A to E in the above embodiment is not limited to two types such as a liquid crystal A having three rings and a D having four rings. Even if three or more liquid crystals including both liquid crystals are combined, the desired effect can be obtained. Needless to say, liquid crystals having similar properties can be appropriately selected.

[0034]

According to the present invention, it is possible to provide a liquid crystal display device in which the contrast ratio does not decrease or the image is not blackened due to a temperature change, and the display quality does not change.

[Brief description of the drawings]

FIG. 1 is a curve diagram showing an example of a temperature coefficient of Δn · Δε / K of a liquid crystal material.

2A is a schematic diagram illustrating a configuration of a 180 ° twist mode, and FIG. 2B is a schematic diagram illustrating a configuration of an in-plane switching (IPS) mode.

[Explanation of symbols]

 11, 21: counter substrate 12, 22: array substrate 13, 14: alignment film 15: compensator 16, 26: polarizing plate 17, 27: liquid crystal 28: electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Hato 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Masumi Manabe 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa (72) Inventor Atsuyuki Manabe, 8-8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture In-house Toshiba Yokohama Office

Claims (4)

[Claims] 1. A liquid crystal display device in which a liquid crystal composition is sandwiched between electrodes and an alignment state of the liquid crystal composition is controlled by a voltage applied to the electrodes to display an image. Is Δn, the dielectric anisotropy is Δε, and the elastic constant for elastic deformation of the orientation mode is K, Δn · Δ
A liquid crystal display element using a plurality of liquid crystal materials of a combination of Δn, Δε, and K having a temperature coefficient at which ε / K becomes substantially constant even when the temperature changes. 2. A liquid crystal display device having a liquid crystal composition sandwiched between electrodes, wherein said liquid crystal composition contains at least a first liquid crystal and a second liquid crystal, and has a refractive index anisotropy of Δn of the liquid crystal.
A liquid crystal display device in which the temperature coefficient of Δn · Δε / K is opposite between the first liquid crystal and the second liquid crystal when the dielectric constant anisotropy is Δε and the elastic constant for elastic deformation is K. 3. The molecular skeleton of the first liquid crystal is a three-ring liquid crystal, and the molecular skeleton of the second liquid crystal is a four-ring liquid crystal.
The liquid crystal display element as described in the above. 4. The liquid crystal display device according to claim 3, wherein the molecular skeleton of the first liquid crystal is a liquid crystal containing three rings and containing fluorine and has a positive temperature coefficient, and the second liquid crystal has a negative temperature coefficient.