JPS60220315A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To make the continuous thermal write operation possible by providing a highly heat-conductive layer, which has a heat conductivity higher than that of a substrate and a heat insulating layer, in a part of the surface of the substrate at least. CONSTITUTION:A highly heat-conductive layer 8, a heat insulating layer 2, and heating electrodes 3 are laminated on a glass substrate 1a, and transparent electrodes 5 are arranged on an upper glass substrate 1b facing the glass substrate 1a, and a smectic liquid crystal layer 4 is interposed between heating electrodes 3 and transparent electrodes 5. For example, a copper vapor-deposited film having 2mum thickness is used as the highly heat-conductive layer. In case of thermal write, a current is flowed to heating electrodes 3, and the liquid crystal layer 4 is heated by heat conduction from resistance heating of heating electrodes 3, thereby performing thermal write. In case of cancel of write, electrodes are heated, and a removing voltage is applied between transparent electrodes 5 and heating electrodes 3 when they are cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a liquid crystal display device, and particularly to a thermal writing type liquid crystal display device using smectic liquid crystal.

[Background of the invention]

Liquid crystal display devices are widely used in information equipment, particularly as display devices for information terminals. In a thermal writing type liquid crystal display device that uses smectic liquid crystal as a main component, current is passed through a liquid crystal heating electrode provided on a glass substrate, and the liquid crystal is heated by Joule heat generated in the heating electrode. For this reason, a conventional liquid crystal display device that can effectively apply the heat generated by the heating electrode to the liquid crystal layer is a combination of a Caloric heating electrode and a glass substrate, as shown in Japanese Patent Application Laid-open No. 57-192925. A method has been proposed in which a thermal layer (insulating layer) is provided between the two.

FIG. 1 is a sectional view showing the basic element structure of a conventional liquid crystal display device. A striped liquid crystal heating electrode 3 and a transparent electrode 5 are formed on the inner surfaces of the upper and lower glass substrates 1a and 1b, and a liquid crystal layer 4 is sandwiched between them. The heating electrode 3 and the transparent electrode 5 intersect with each other, and a matrix is formed between them. Further, a heat insulating layer 2 is provided between the heating electrode 3 and the lower glass substrate 1b so that the heat of the heating electrode 3 is easily conducted only in the direction of the liquid crystal layer 4. Due to the effect of this heat insulating layer 2, the heat generated by the heating electrode 3 effectively acts on heating the liquid crystal layer 4.

FIG. 2 is a diagram showing temperature changes in a liquid crystal layer when a pulse current is applied to a heating electrode in a conventional liquid crystal display device. In the figure, A shows the temperature change on the surface of the heating electrode shown in FIG. 1, and B shows the temperature change in the upper part of the liquid crystal layer. The duration to of the pulse current applied to the heating electrodes 3 is at most several ms to several io m9 for each heating electrode 3. For such an instantaneous energization time to, the liquid crystal layer 4 is effectively heated due to the heat insulating effect of the heat insulating layer 2. However, when we look at the cooling process after the electrical heating ends, we find that the cooling rate at point A on the electrode surface and point B at the top of the liquid crystal layer shown in Figure 1 is high immediately after heating ends, but over time. As time passes, the cooling rate decreases and the temperature decreases more slowly. Therefore,
If writing is performed once and then the writing operation is repeated repeatedly, the following inconvenience will occur.

FIG. 3 is a diagram showing the heating cycle of the liquid crystal layer when the thermal writing operation is repeated. T' in the figure
1, Tz...T is the liquid crystal temperature at the end of each thermal write operation, and gradually increases as the write operation is repeated.

Due to repeated thermal writing operations, if T is lower than the phase transition temperature T8N between the nematic phase and smectic phase of the liquid crystal, a disadvantage arises in that the thermal storage operation becomes impossible. Furthermore, in conventional liquid crystal display devices, Tm is T[
Even if TII does not exceed IN, there is a problem in that when TII approaches TIN, the display quality after writing varies.

[Purpose of the invention]

An object of the present invention is to provide a liquid crystal display device that can perform continuous thermal writing operations.

[Summary of the invention]

The present invention provides a means for rapidly cooling the liquid crystal layer and the heating electrode after the heating electrode finishes heating the liquid crystal layer. We decided to provide layers.

During thermal writing in such liquid crystal display devices, that is, instantaneous heating, the heat generated in the electrodes can be effectively applied to the liquid crystal layer by the heat insulating layer. The high heat conductive layer provided between the heat insulating layer absorbs the heat passing through the heat insulating layer, and allows the heat to be quickly transferred to the glass substrate having a large heat capacity. By controlling the cooling rate of the liquid crystal layer and the heating electrode in this way, continuous thermal writing can be performed.

Example of invention C] Embodiments of the present invention will be described below based on the drawings.

FIG. 4 and FIG. 5 are an exploded perspective view and a sectional structural view showing the element structure of the liquid crystal display device of the present invention. A high thermal conductivity layer 8, a heat insulating layer 2 and a heating electrode 3 are laminated in this order on the upper surface of one glass substrate 1, while a transparent electrode 5 is arranged on the upper glass substrate 1a facing the glass substrate 1b.
A smectic liquid crystal layer is sandwiched between the heating electrode 3 and the transparent electrode 5. This example shows a case where a highly thermally conductive layer is formed on the entire surface of the lower glass substrate 1a. The glass substrate that is an element of the liquid crystal display device configured in this manner has a thickness of 1.1 m t and a thermal conductivity of 0.0027 Ca1acrIT-' a FB
I-'a7::-' (25C), the high thermal conductivity layer is copper (thermal conductivity 0.943Catscrn-'an-"*"f
::-' ) vapor deposited film 2. lJm is used. Also,
The thermal conductivity of the heat insulating layer is 0.0003 Cat・crn-'
・It is a xylene polymer of group-1/C-1, and the film thickness is 5μ.
It is m. The heating electrode is aluminum (thermal conductivity 0.5
Cat*crn-'*8+30-'@C-'
) A film thickness of 1.0 μm is used. Further, as a transparent electrode, a 0.2 μm vapor-deposited film of In2O35-02 is used. Thermal writing in the liquid crystal display device configured in this way is carried out by passing a current through the heating electrode 3.
This is done by heating the liquid crystal layer 4 by heat conduction from resistance heat generation. Further, when writing is to be canceled, the electrode is heated and a removal voltage is applied between the transparent electrode 5 and the heating electrode 3 when the electrode is cooled.

FIG. 6 shows the relationship between the elapsed time and the liquid crystal temperature when a heating current was applied to the heating electrode for 10 hours.

The characteristics in the figure show the change in liquid crystal temperature over time at point B above the liquid crystal layer shown in Figure 1.
The temperature of the liquid crystal layer increases until the heating time of the heating electrode reaches 1o, and the temperature decreases after the electrical heating ends. In this figure, the solid line after to indicates the case where a high thermal conductivity layer is provided,
The broken line shows the case where no high thermal conductive layer is provided. As is clear from the figure, the time it takes for the liquid crystal layer to become below the phase transition temperature T II N between the nemastic phase and the smectic phase during the cooling process of the liquid crystal layer depends on the presence or absence of the high thermal conductivity layer, respectively (ts to ) + (t+' To), the cooling rate is higher when a high thermal conductivity layer is provided.

Increasing the cooling rate of the liquid crystal layer in this way has the following effects.

In other words, the pulsed current flowing through the heating electrode is several mis
This instantaneous heating is as short as ~10-odd msa+ (current application time to), and the liquid crystal layer side is effectively heated by the heat insulating effect of the heat insulating layer 2 during the heating time. On the other hand, on the high heat conductive layer side, due to the effect of the heat insulating layer 2, there is a time delay in the heat heated by the heating electrode 3 being conducted through the heat insulating layer 2 to the high heat conductive layer. Therefore, during the instantaneous energization time 1o, the temperature rise in the highly thermally conductive layer 8 is slight, and in this state heating ends and a cooling process begins, where heat is transferred to the glass substrate 1 through the heat insulating layer. In this cooling stage, the high thermal conductivity layer 8 is placed between the heat insulating layer 2 and the glass substrate 1a, so that the high thermal conductivity layer absorbs p heat by the endothermic action, and this heat is transferred to the glass substrate with a large heat capacity. This has the effect of quickly transferring heat toward 1a. Therefore, as shown in FIG. 6, the cooling rate after completion of heating increases.

Although copper is used as the high thermal conductivity layer in this example, from the viewpoint of quickly transferring heat from the insulation layer to the glass substrate during the cooling process, any material with higher thermal conductivity than the insulation layer and the substrate may be used. Either may be used. For example, aluminum (thermal conductivity 0.5C) is used as a metal material.
at・Crn-'@813G-'aC-'), Ag(
Thermal conductivity 0.934CatsCrn-'5ea-'
C″′1) is inorganic, and as an inorganic material, alumina (
Thermal conductivity 0.05cBLmcm-'1eO-' *C
-' ), 5aC with high thermal conductivity (thermal conductivity 0.6
cat・cm−′・reduction−1・C−1) is also effective.

FIGS. 7 and 8 are cross-sectional views showing other embodiments of the present invention. FIG. 7 shows a case where a high thermal conductivity layer 8 and a heat insulating layer 2 are provided on a glass substrate la with the same width as the heating electrode 3. FIG. 8 shows a case where the high thermal conductivity layer 8tl is provided over the entire surface of the glass substrate 1a, and the heat insulating layer 2 and the heating electrode 3 are provided with approximately the same width.

9 and 10 are cross-sectional views showing other embodiments of the present invention, in which the high heat conductive layer 8 is placed on a glass substrate 1.
In the embodiment shown in FIG. 10, the high thermal conductivity layer 8 is provided only on the outer surface of the glass substrate 1. The objects of the present invention can also be achieved in these embodiments.

〔Effect of the invention〕

According to the present invention, after the liquid crystal layer is heated by the heating electrode, the liquid crystal layer and the heating electrode can be rapidly cooled, and the heat-pushing operation can be performed continuously.

In addition, when the cooling rate is increased further, the difference in light transmittance between the scattered state of the liquid crystal of the pixel where writing is performed and the non-scattered state of the liquid crystal of the pixel where no writing is performed is large, and the display quality is affected. It also has the effect of allowing improvements to be made.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the basic element structure of a conventional liquid crystal display device, Fig. 2 is an explanatory diagram showing temperature changes in the elements of a conventional liquid crystal display device, and Fig. 3 is a cross-sectional view showing the basic element structure of a conventional liquid crystal display device. 4 and 5 are exploded perspective views and sectional views showing the element structure of the liquid crystal display device of the present invention, and FIG. 6 is an explanatory diagram of the temperature change of the element when writing operations are repeated. Comparison and explanatory diagram of the temperature change of the element with the product, No. 7
Figures 1 to 10 are cross-sectional views showing other embodiments of the present invention. DESCRIPTION OF SYMBOLS 1...Glass substrate, 2...Insulating layer, 3...Heating electrode, 4...Liquid crystal layer, 5...Transparent electrode, Hill = Brush porridge...High thermal conductivity layer. Agent Patent Attorney Tatsuyuki Unuma l 目） ト ２ Ｇｕｒｏｎａ ４． Eye l^ 5th eye 6th solid accumulation t (side 3 grass 7 eye b ! Kuhaya 8 eye 10- δ Kayaq Mouth

Claims (1)

[Claims] 1. In a thermal writing type liquid crystal display device using a smectic liquid crystal as a main component having a heat insulating layer and a liquid crystal heating electrode disposed on one glass substrate, at least a portion of the surface of the substrate is and a liquid crystal display device characterized by forming a highly thermally conductive layer having higher thermal conductivity than a heat insulating layer. 2. A liquid crystal display device according to claim 1, wherein the highly thermally conductive layer having high thermal conductivity is provided between a substrate and a heat insulating layer; 3. Claims 1 and 2. 3. The liquid crystal display device according to item 2, wherein the highly thermally conductive layer having high thermal conductivity is provided on the entire surface of the substrate. 4. The liquid crystal display device according to claim 2, wherein the highly thermally conductive layer having high thermal conductivity is provided only on a portion of the substrate facing the liquid crystal heating electrode.