JPS5936227A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent flickering phenomenon which is liable to arise under low frequency driving and obtain an excellent display quality, by adding alumina, carbon, etc. into a liquid crystal layer and adsorbing ionic impurities. CONSTITUTION:A liquid crystal layer 11 is sandwiched between a pair of substrates 12 and 12 provided with an electrode 14 and an oriented film 15 (a symbol 16 is a sealant and 17 is a spacer). Aluminum oxide particles, carbon particle, etc. of about 0.05mu grain size is sprinkled on the substrate 12 in the above- mentioned device, whereafter a cell is assembled so that the above-mentioned particle is incorporated into the liquid crystal layer.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a liquid crystal display device that displays images by controlling the alignment of liquid crystals.

<Prior art and problems> It is desirable to drive a liquid crystal display element at a lower frequency in order to reduce current consumption. However, when low frequency driving is performed, flickering of the displayed pattern becomes a problem, and it is currently believed that the limit is about 30H2.

That is, the flicker phenomenon is considered to be most closely related to the viscosity of the liquid crystal material. If the viscosity of the liquid crystal is K,
The mobility of liquid crystal molecules and ionic impurities contained in the liquid crystal is small, and the mobility also becomes small when the driving frequency is high.

However, when the viscosity is low and the frequency is low, the mobility of ionic impurities is high, which adversely affects the properties and reliability of the liquid crystal.

In particular, when an organic insulating film such as polyimide is used as an alignment film of a liquid crystal display element, the adverse effects of ionic impurities are significant. In conditions with high ionic impurities (especially
(in the case of low frequency drive), ionic impurities concentrate on the electrodes, causing an extremely high threshold voltage. In other words, an electric double layer is formed due to ionic impurities concentrating on the electrodes, and the voltage applied to the liquid crystal decreases, which is observed as a decrease in contrast. This decrease in contrast is the biggest cause of flicker.

1 to 3 model and explain the behavior of ionic impurities contained in a liquid crystal during low frequency driving.

FIG. 1 shows an ideal pulse shape applied to the liquid crystal when the liquid crystal does not contain ionic impurities.

FIG. 2 shows the pulse shape applied to the liquid crystal when ionic impurities are present. Figure 3 (a), (b),
(c) shows the behavior of ionic impurities at each time point A, B, and C shown in FIG. As shown in the figure, ionic impurities 1 that are randomly present in the liquid crystal are concentrated on the opposite electrode side 2 by applying a low frequency voltage, and the voltage drop ΔV (second
Figure) occurs. When the polarity of the electrode changes, a high voltage is temporarily applied to the liquid crystal, and the contrast increases. This repetition is observed as a flickering phenomenon.

Purpose of the present invention: It is an object of the present invention to provide a liquid crystal display device in which aluminum oxide (alumina), carbon, etc. are added to the liquid crystal layer to adsorb ionic impurities, thereby preventing the flickering phenomenon seen in low frequency driving. be.

<Example> An example of the present invention will be described below with reference to FIGS. 4 and 5.

FIG. 4 is a sectional view of a liquid crystal display device constructed according to the present invention.

In a liquid crystal display device, a set of substrates 1 sandwiching a liquid crystal layer 11
Sprinkling aluminum oxide 13 on at least one of 2,
They were bonded together to form a device.

The spraying was performed by dispersing aluminum oxide in the air and allowing it to settle on the surface of the glass substrate, which had been subjected to electrode formation and alignment treatment in advance. The aluminum oxide 13 used has a particle size of 0.05 μm. The same applies when carbon is used as the adsorbent.

In the figure, 14 and 15 are electrodes and alignment films formed on each substrate 12, 16 is a sealing material, and 17 is a spacer.

FIG. 5 shows the frequency f (H2) of the applied voltage and the threshold value Vt.
FIG. 3 is a characteristic diagram showing the relationship with hff (at a temperature of 60° C.), comparing the conventional example and the present example. The solid line is the conventional characteristic, and the broken line is the characteristic according to this example. According to the figure, as compared to the conventional cell, the lower the frequency, the higher the vth, indicating that the contrast is lower.

At lower frequencies, flicker occurs, making measurement difficult. In the aluminum oxide dispersion cell, vth hardly depends on the frequency and there is little flicker, so it is possible to drive at a lower frequency.

In order to increase the contact area with the liquid crystal material, and because the appearance of the element becomes a problem, it is preferable that the adsorbent be as fine as possible and uniformly distributed over the entire surface.

Furthermore, it is preferable that the adsorbent be pretreated such as vacuum heating to increase its activity. In addition to spraying on the surface of the alignment film, it has been confirmed that adding an adsorbent (5 wt % or more) to the alignment film material is also effective.

As a method to further enhance these effects, it is recommended to perform liquid crystal purification immediately before injection. Methods for purifying liquid crystals include: 1. Purification using a column packed with ion exchange resin Method 3: Purification using a column packed with Moetsu zeolite adsorbent 3. Purification using a column packed with alumina adsorbent Improved effectiveness can be obtained.

In addition to impurities in the liquid crystal layer, this adsorbent also adsorbs moisture that enters from the outside world, ionic impurities and unreacted residues eluted from the sealing material or encapsulant, and reduces the adverse effects of these ( It is very useful because it has the advantage of suppressing reactions with liquid crystal molecules and sagging of alignment. For example, the device fabricated as in this example has a current consumption of 2/2 compared to a device that does not spray ordinary aluminum oxide. 1 with ionic current. /1
The number of failure modes caused by impurities has been reduced and the life span has been doubled. Furthermore, the display quality was good and the driving characteristics were also improved.

Effect> As explained above, according to the present invention, ionic impurities can be removed with extremely high precision;

[Brief explanation of drawings]

Figure 1 shows the ideal pulse shape applied to the liquid crystal when ionic impurities are not included in the liquid crystal, and Figure 2 shows the pulse shape applied to the liquid crystal when ionic impurities are present. Figure 3(a). (b) and (C) are diagrams showing the behavior of ionic impurities at each time point A, B, and C in Figure 2, Figure 4 is a sectional view showing an embodiment of the present invention, and Figure 5 is a conventional example. FIG. 2 is a characteristic diagram showing the relationship between frequency and threshold voltage in comparison with one embodiment of the present invention. DESCRIPTION OF SYMBOLS 11... Liquid crystal layer, 12... Substrate, 13... Aluminum oxide, 14 - Electrode, 15... Alignment film.

Claims (1)

[Claims] (2) In a liquid crystal display device, a liquid crystal layer is interposed between opposing substrates, at least one of which is transparent, and the alignment of the liquid crystal is controlled by applying a potential between phased electrodes formed on the substrates. A liquid crystal display device characterized in that an adsorbent for ionic impurities such as aluminum oxide or carbon is added to the layer.