JPH0146851B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device in which a nematic liquid crystal is sealed between a pair of electrode plates in a twisted structure, and more specifically to temperature dependence of threshold voltage of a liquid crystal display device. The present invention relates to a multiplexing drive liquid crystal display device that has been improved.

Generally, when driving a liquid crystal display element,
Multiplexing drive is desirable in order to simplify and downsize the circuit, lead, and connector parts.

Even in a liquid crystal display device, which is the subject of the present invention, in which a nematic liquid crystal is sealed between a pair of electrode plates so as to have a twisted structure, it is very important to be able to perform multiplexing driving for effective use of the display device. .

However, in the case of multiplexing driving, there is a problem in that the driving voltage is limited due to the relationship with the liquid crystal. For example, the selection waveform of the multiplexing drive waveform is shown in FIG.
FIG. 2 shows the relationship between the voltage of the liquid crystal cell and the light transmittance corresponding to this waveform. In Figure 2, Vth-1 and Vth-2 indicate the threshold values at which a change in light transmittance can be visually observed when selection waveform A and half-selection waveform B are applied to the liquid crystal cell, respectively. , the voltage Vd that can turn on and off the display is limited to the range of Vth-1≦Vd<Vth-2.

Almost the same effective voltage as Vth-1 and Vth-2, Vth
In order to have (r, m, s), as shown in Figure 1,
In the case of a 1/3 equalized waveform and a duty ratio of 1/N, The relationship is as follows.

Therefore, the smaller the duty ratio, the
The difference between Vth-1 and Vth-2 decreases. In practical terms,
It is desirable to be able to multiplex drive with a smaller duty ratio over a wide temperature range including room temperature, but there is a limit because liquid crystals exhibit temperature dependence of threshold voltage. When driving within a specified temperature range, set the threshold voltage on the high temperature side to Vth−
1(H), Vth-2(H), Vth-1(L), Vth- on the low temperature side
2(L), there is a relationship of Vth-1(H)≦Vth-1(L) Vth-2(H)≦Vth-2(L), and it is possible to display on/off in this temperature range. The voltage Vd' is Vth-1(L)≦Vd'<Vth-2(H).

In addition, in order to obtain a practically sufficient display contrast, the light transmittance in the selected waveform shown in Figure 2 must be
In relation to the threshold voltage Vth-3(L) on the low temperature side of 30%, it is desirable that Vd' be limited to Vth-3(L)≦Vd'<Vth-2(H). Liquid crystal display devices driven by multiplexing are generally required to be usable at temperatures between 0°C and 40°C, so Vth-3(L) and
Vth-2(H) are Vth-3(0℃) and Vth-
2 (40℃).

On the other hand, the drive voltage also fluctuates due to changes in battery voltage over time, variations in the circuit, and the like.

Therefore, the voltage margin (M) is defined as the following formula as a measure to allow fluctuations in drive voltage, M = Vth-2 (40℃) - Vth-3 (0℃) / Vc × 100 (%) However, Vc is a drive voltage, Vc=1/2 {Vth-2(40°C)+Vth-3(0°C)} It can represent the suitability of the liquid crystal display device for multiplexing drive at 0°C to 40°C. Therefore, in a liquid crystal display device for multiplexing drive, the voltage margin is large;
In other words, it is required that the temperature dependence of the threshold voltage be small, and various studies have been made in the past from the viewpoint of liquid crystal materials.

In contrast, the present invention aims to improve the temperature dependence of the threshold voltage by surface treatment of the electrode plate of a liquid crystal display device. Furthermore,
Hydrolyzable silicon compounds as surface treatment agents This is characterized by using a mixed solution of X: alkoxy group and a hydrolyzable titanium compound TiX′ ₄ X′: OC _o H _2o+1 (including side chains), in which the silicon compound The titanium compound, which will be described later, contributes to improving the temperature dependence of the voltage value, and when mixed, improves the uniformity of wetting to the electrode plate of a liquid crystal display device.

Examples of the present invention will be described below.

Example 1 A pair of glass substrates with transparent electrodes formed in a strip shape on the surface 0.2% by weight of Ti[ _OCH2CH ( _C2H5 ) _C4H9 ] ₄ and _0.1 % by weight of isopropyl alcohol mixed solution, pulled up _, dried, and heated at 140°C for 50 minutes. Next, after rubbing the surface on which the transparent electrode was formed with gauze in a certain direction, the rubbed surfaces of the substrates were placed opposite each other so that the rubbing directions were perpendicular to each other, and a 10μ
Keep the gap between them and seal the periphery with epoxy resin. Note that the peripheral sealing is performed except for the liquid crystal filling hole. Then, when pifhenyl liquid crystal was filled and the filled part was sealed, the liquid crystal showed a uniform twisted nematic structure. Polarizing plates were pasted on both sides of the liquid crystal cell so that the polarization axes were perpendicular to each other, and the relationship between voltage and light transmittance was measured at 0°C and 40°C, and the voltage margin (M) was determined with N = 3. , 11.7
It was %. Furthermore, when this cell was subjected to a humidity resistance test under conditions of 60°C and 90% relative humidity, no deterioration such as peeling of the seal occurred even after being left for 400 hours.
Moreover, no deterioration in orientation was observed even after 400 hours at a high temperature of 125°C.

Example 2 (Comparative example) A substrate was prepared in the same manner as in Example 1. 0.2% by weight of Ti[OCH ₂ CH (C ₂ H ₅ ) C ₄ H ₉ ] ₄ was immersed in a mixed solution of 0.1% by weight of isopropyl alcohol, and the same operation as in Example 1 was carried out.
The same biphenyl liquid crystal was filled, the relationship between voltage and light transmittance was measured, and the voltage margin (M) was found to be 10.1%.

Example 3 (Comparative example) Same as Example 2 As a result of comparison with Example 1 using , the voltage margin (M) was 10.2%.

As described above, it has been revealed that by carrying out the surface treatment according to the present invention, it is possible to improve the voltage margin and obtain a display with better contrast in a multiplex-driven liquid crystal display.

[Brief explanation of drawings]

FIG. 1 shows an example of waveforms for time-division driving, in which a shows a selection waveform and b shows a half-selection waveform. FIG. 2 is a diagram for explaining the relationship between voltage and light transmittance.

Claims (1)

[Scope of Claims] 1. In a multiplexing drive liquid crystal display device in which a nematic liquid crystal is enclosed in a twisted structure between a pair of electrode plates, the general formula [Formula] (X: The surface is treated with a mixed solution of a hydrolyzable silicon compound represented by an alkoxy group) and a hydrolyzable titanium compound represented by the general formula TiX′ ₄ (X′: OC _o H _2o+1 (including side chains)). A multiplexing drive liquid crystal display device characterized by: