JPS6033865B2 - Liquid crystal composition for matrix display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nematic liquid crystal composition, and more particularly to a stable nematic liquid crystal composition that can be applied to a matrix display device utilizing the dynamic scattering effect (DSM).

It is known that the dynamic scattering effect of nematic liquid crystals (referred to as DSM) can be applied to electro-optical devices such as display devices.

In addition, to perform matrix display using this DSM, it is necessary to perform time-division driving, which eliminates crosstalk that occurs because the DSM does not have selectivity in the direction of the voltage applied to the liquid crystal. It is also known that the voltage averaging method is optimal for preventing this and effectively performing time-division driving. Other time-division driving methods that have been proposed so far, such as the dual-frequency driving method and methods that use a combination of non-linear elements or semiconductor elements, require complicated peripheral circuits to drive the liquid crystal display, are unreliable, and are inexpensive. This is because it is considered difficult to provide a suitable device. It is also known that in order to carry out the voltage averaging method, the electro-optical properties of the liquid crystal material must satisfy certain conditions. In particular, it is an important requirement to enable matrix display that the voltage (Vth) at which DSM occurs is constant over a wide frequency range. Generally, Vth shows a change as shown in FIG. 1 with respect to the frequency of the applied voltage. The value of the upper limit frequency fco at which the V ratio is constant is an important factor that influences the scale and performance of a matrix display device using the voltage averaging method. Let o be the cutoff frequency for convenience,
It can be said that the performance of matrix display devices is improved by using a liquid crystal composition with a high cutoff frequency. The reason is explained below. First, important experimental facts regarding the relationship between applied voltage and light scattering brightness in DSM will be described.

It is defined as ``the frequency range in which Vth has a constant value (fco
(below), the light scattering brightness depends on the effective voltage (vrme) of the applied voltage, not on the waveform of the applied voltage. These are important for voltage averaging matrix display where voltage waveforms vary depending on the display pattern.
This is because if the light scattering brightness differs depending on the voltage waveform, this will inevitably appear as display unevenness. This dependence of the light scattering luminance on the effective voltage makes it possible to perform time-division driving using the voltage averaging method. In other words, an effective voltage higher than Vth is applied to the points selected to be displayed among the display points formed by the intersections of striped electrodes arranged in a matrix, and an effective voltage lower than the V mark is applied to the unselected points. It is only necessary to decide the drive waveform accordingly. FIG. 2 shows a general form of such a drive waveform (with the Y electrode serving as a scanning electrode). In this figure, a certain voltage is applied to each of the striped electrodes labeled as an x electrode and a Y electrode, and the voltage applied to the liquid crystal layer is controlled by the combined voltage difference (or sum). a in Figure 2 is X/Y
Voltage waveform in a state where both are selected, that is, in a selected state, b
, c is a voltage waveform in a state in which only one of the X and Y electrodes is selected, that is, in a half-selected state, and d is a voltage waveform in a non-selected state in which neither the X nor Y electrode is selected. In time-division driving, each display point will take one of these states. When the number of scanning electrodes is N, the point selected to be displayed is in the state a for 1/N of one scanning period (referred to as one frame), and the remaining N-1/N is in the state b, c.
Or it will be in state d. On the other hand, for points that are not selected, 1/
Only N is in state c, and the rest are in either state b or d. FIG. 3 shows this situation using time as the horizontal axis. A is the voltage waveform of the selected display point, and b is the voltage waveform of the non-selected display point.
Although changes in the waveform due to the display pattern are ignored, as already explained, this does not pose any problem when considering the driving conditions. This figure is a waveform diagram when the applied voltage has the highest frequency, and can be used later to discuss the relationship with fco. When the effective voltage is calculated for each, that of the selected point (HiS) and that of the non-selected point (Himisaki) are as follows.

In order to perform a display without crosstalk, it is necessary to satisfy both S>V and Vth at the same time. Therefore.

This condition can be satisfied by appropriately selecting the values of Vo and a. Further, the larger the voltage difference between vs and uS, the more stable the display can be, and a measure of this is given by the ratio Q of his/uS. This does not depend on the value of Vo, but is determined by the values of N and a.

Finding the difficult problem of a' ma foundation = o where Q is maximum a = no N + 1 becomes.

As a result, the drive voltage waveform that maximizes Q, that is, the optimum drive condition, is determined. Next, we will discuss the relationship between applied voltage and frequency.

Liquid crystals are usually driven with alternating current voltage because their characteristics change in a short time when they are driven with direct current. An example of this is the case shown in FIG. This is a case where a complete AC waveform is generated within one frame. As can be seen from this waveform, the frequency of the driving voltage is the same for both the selected point and the non-selected point, and if one frame period is T, the driving frequency fD becomes .fo = possible.

If 1/T is the frame frequency fF, then fD=N×fF.

fF may be set as low as possible so long as flicker is not perceivable to the eye. Generally, since the fall time of the light scattering response of liquid crystal is relatively long, flicker does not occur even when fF is about 30 Hz.
So, if fF=30Hz, then N=100 and fD is 3
With kr12 and N=200, fo will be 6kHz2. Therefore, in each case, it is necessary that the effective voltage dependence holds true even at 3 kHz or 6 kHz. That is, in FIG. 1, materials with a cutoff frequency fco of 3 kHz and a vessel length of 2 are required. Efforts to lower the maximum driving frequency need to be made in order to ease the requirements for the frequency characteristics of the liquid crystal material and increase the number of scanning lines to increase the functionality of the display device. FIG. 4 shows a drive voltage waveform that allows the drive frequency to be lowered. In this waveform, the polarity of the first frame and the second frame are reversed, so that a complete alternating current occurs in two frames. In contrast to FIG. 3, where T/N constitutes one cycle, in this figure, 2r/N constitutes one cycle. Therefore, the drive frequency fD becomes N/2T, and when replaced by the Fray frequency fF, it becomes 2xf skin X) f.

= + fF (NMX = fF, and compared to Fig. 3, when fF is the same, fo is halved, making it possible to perform a matrix display with a large number of scanning lines even with a material having a low fco.

In any case, a liquid crystal material with N=100 and an fco of 1.5 kHz is required, and a liquid crystal material with a large fco is an essential element for increasing the size and functionality of a matrix display device. On the other hand, it is generally known to those skilled in the art that the cutoff frequency of a liquid crystal material is proportional to the electrical conductivity of that material.

Therefore, it is qualitatively understood that in order to obtain a liquid crystal composition with a high cutoff frequency, a composition with high conductivity is sufficient. A method used to increase the conductivity of liquid crystals is to mix a substance that dissolves as ion pairs in a liquid, usually called an electrolyte, into a composition composed of liquid crystal compounds. . but,
Because the solubility of the ionic substance in the liquid crystal substance is very low, the conductivity cannot be sufficiently increased, and therefore a liquid crystal composition with a high cutoff frequency cannot be obtained.
There was a drawback that it was impossible to increase the size and functionality of the matrix display device. An object of the present invention is to provide a liquid crystal composition with a high cutoff frequency, which eliminates the drawbacks of the prior art and enables the enlargement and functionality of a liquid crystal matrix display device using a voltage averaging method.

The present invention is based on the experimental fact that the solubility of electrolytes in liquid crystal materials is significantly increased in the presence of weak dibasic acids, which are highly conductive and therefore cut-resistant. This was a successful development of a liquid crystal composition with a high off-frequency. That is, the present invention provides at least one nematic liquid crystal compound with negative anisotropy and an onium salt having nitrogen as the core based on the liquid crystal compound.
5-0.5% by weight, about 0.5-2% organic monobasic acid or/and organic monoacid-base compound. % by weight and about 0.01 to 0.1% by weight of an organic dibasic acid.

It has been thought that the solubility of electrolytes in liquid crystal substances improves in the presence of weak acids or bases, but no definitive effect on increasing conductivity has been confirmed.

This is because in order for these weak acids and weak bases to exhibit sufficient effects, they must be present in a considerable amount (approximately 5%) in the liquid crystal composition, and on the other hand, the temperature range in which the composition exhibits a liquid crystal phase is limited. This is because it becomes extremely narrow, resulting in a serious practical drawback. However, as described above, according to the present invention, it has been found that a weak dibasic acid has a remarkable effect on increasing the electrical conductivity of a liquid crystal composition having an electrolyte. The behavior of weak acids and weak bases in liquid crystals is not necessarily clear, so it is not possible to clarify the theoretical basis for the above-mentioned effects of dibasic acids. In the case of basic acids, the effect of increasing conductivity is greater than one ping. In other words, it has been found that in order to equalize the conductivity of a liquid crystal composition in which an electrolyte is present, it is sufficient to have a dibasic acid nose that is 1/10 or less of that of a normal weak acid or weak base. Based on this fact, the side effect of narrowing the liquid crystal phase temperature range, which is a drawback of the conventional method, can be avoided.
A liquid crystal composition with increased conductivity and a high cutoff frequency can be obtained. In this way, it has become possible to obtain a liquid crystal composition with a high cutoff frequency, but in addition, the composition has a stable threshold voltage (V ratio) value or a stable cutoff frequency and Vth in the operating state where voltage is applied. Considering these conditions, it is important to minimize the amount of dibasic acid and increase the cutoff frequency by using monobasic acid (and) in combination with monobasic acid. method was found to be the most effective method. That is, the liquid crystal composition of the present invention is a composition comprising one or a mixture of two or more compounds exhibiting a nematic liquid crystal phase as described above, and which has negative dielectric anisotropy as a whole. It is made by adding a small amount of an electrolyte substance, a monoacid base, a monobasic acid, and a dibasic acid. Many compounds are known that exhibit a nematic liquid crystal phase, but in order to obtain a compound that exhibits a nematic liquid crystal phase in the temperature range where display devices are practically used (e.g. 0°C to 50 oo), it is necessary to combine two or more types of liquid crystals. It is common practice to mix compounds that exhibit phases to form a composition that takes advantage of the eutectic effect. For example, paramethoxybenzylidene-parabutylaniline (M old BA, liquid crystal temperature range (MR): 10-4800) and paramethoxybenzylidene-parabutylaniline (EBBA: MR; 36-78
An equimolar mixture of 00) has an MR of -15 to 5500, and an equimolar mixture of M old BA and baraethoxy besodylidene-barahexylaniline (EBHA:MR; 41 to 79.5o0) has a MR of -25 to 5500. 60 degrees, and both compositions have negative dielectric anisotropy.

Also, 4-methoxy-4-butylazoxybenzene, 4
The four-component mixed liquid crystal of -butyl-4'-methoxyazoxybenzene, 4-methoxy-4'-ethylazoxybenzene and 4-ethyl-4-methoxyazoxybenzene is M
R is -5 to 75 qo and dielectric anisotropy is negative. In this way, compositions exhibiting a nematic liquid crystal phase in a practical temperature range can be easily obtained, and any of them can be used in the present invention. Further, it is obvious that the above-mentioned liquid crystal compounds can be used alone without any explanation. As the electrolyte compound in the present invention, an onium salt having a nitrogen atom as a nucleus is used. The reason for this is that the onium salt has a relatively high solubility in liquid crystals compared to other onium salts. The onium salt having a nitrogen core in the present invention has a general formula (R,, R2, R3, R4: alkyl group or aryl group, X: 1, Br, CI, etc., n: 1, 3, 5)
Quaternary ammonium salts such as alkylammonium salts and alkylaryl ammonium salts represented by the general formula (R5: alkyl group, x: 1, Br, CI, etc., n = 1,
Alkylpyridinium salts represented by the general formula and (R6: alkyl group, X: 1, Br, CI, etc., n=1,
3,5), and the general formula (R7: alkyl group, X: 1, Br, CI, etc., n=1,
3 and 5) are included.

In particular, with viridinium salts, good compositions can be obtained with little deterioration in properties due to voltage application. Although these electrolyte compounds are originally thought to be relatively easy to dissolve in liquid crystal materials, the limit is still 0.01 to 0.03% by weight at most, and the cutoff frequency fc required in the present invention is
It is difficult to obtain a liquid crystal composition in which o is lkH2 or more. According to the present invention, it is possible to produce a liquid crystal composition in which the electrolyte compound is contained in an amount of 0.05 to 0.5% by weight based on the liquid crystal compound, thereby making it possible to produce a liquid crystal composition in which the value of o is greater than or equal to 1 kHz. A composition is obtained. Monobasic acids and monoacid-base compounds in the present invention include aliphatic and aromatic carboxylic acids and amines, as well as acidic substances having a phenolic hydroxyl group and basic heterocyclic compounds such as pyridine. Examples include butyric acid, isobutyric acid, crotonic acid,
Cabroic acid, Cabric acid, Dimethylbenzoic acid, Isof.
Lopylbenzoic acid, nitrobenzoic acid, dinitrobenzoic acid,
Chlorbenzoic acid, o-toluic acid, m-toluic acid, p
-Tolulic acid, cinnamic acid, o-chlorocinnamic acid, m-chlorocinnamic acid, p-k. Carboxylic acids such as lucinnamic acid, o-oxycinnamic acid, m-oxycinnamic acid, nitrocinnamic acid, Q-naphthoic acid, B-naphthoic acid, 3-oxy-2-naphthoic acid, o-cresol, m-cresol, p-
- Phenols such as creso, monol, nitrophenol, dinitrophenol, bromophenol, chlorphenol, dichlorophenol, aminophenol, triethylamine, octylamine, octadecylamine,
triethanolamine, nitroaniline, nitro-N,
Basic compounds include N-dimethylaniline, chloraniline, o-toluidine, m-toluidine, p-toluidine, 2-aminopyridine, 3-aminopyridine, and 4-aminopyridine. These are based on liquid crystal compounds.
5-2. These substances are added in a range of 1.0% by weight or less, but as mentioned above, adding a large amount of these substances has the side effect of narrowing M old, so it is preferably 1.0% by weight or less.

It has already been mentioned that these weak acids and weak bases have the effect of improving the solubility of the electrolyte compound in the liquid crystal material, but as a secondary effect, they also have the effect of lowering Vth, as well as the characteristics when voltage is applied. By using them in combination, it is possible to obtain a liquid crystal composition with even better performance. Next, examples of organic dibasic acids which are characteristic components of the liquid crystal composition of the present invention include aliphatic or aromatic dibasic acids such as succinic acid, malonic acid, methylmalonic acid, dimethylmalonic acid, jetylmalonic acid, fumaric acid, and maleic acid. Acids include malic acid, tartaric acid, dioxyditartaric acid and phthalic acid, terephthalic acid and the like.

Even if these are present in the liquid crystal material in an amount of about 0.01% by weight,
The solubility of the organic electrolyte compound already mentioned in the liquid crystal substance is improved. Therefore, by simply using an organic electrolyte compound and an organic dibasic acid compound, a liquid crystal composition with high conductivity and a high cutoff frequency, which is the main objective of the present invention, can be obtained. However, in this case, the characteristics vary greatly with respect to voltage application, and it is difficult to obtain practically satisfactory results. Therefore, in the present invention, in order to minimize the variation in characteristics due to voltage application, we succeeded in obtaining the object of the present invention by reducing the amount of organic dibasic acid used and also using the weak acids or weak bases mentioned above. This is what I did. Therefore, the organic dibasic acid is 0.01 to 0.1% by weight.
It is appropriate to use within the range of . As mentioned above, the liquid crystal composition of the present invention is composed of at least one nematic liquid crystal compound, an onium salt having a nitrogen core, an organic monobasic acid and/or an organic monoacid base, and an organic dibasic acid. It may also contain some water.

To explain the preparation of the liquid crystal composition of the present invention in the case where two types of liquid crystal compounds are used, first, the two types of liquid crystal compounds are weighed so that the total amount is about 10 days (laboratory amount). Weigh it into a bottle, heat it at about 80 qo, and stir to make a homogeneous mixture.

A portion of this mixture (approximately 5 ta) is accurately weighed into a separate weighing bottle, and the other ingredients are added to this by accurately weighing. This is heated again at about 8,000 ℃ for 4 to 88 degrees to obtain a liquid crystal composition. Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

Example 1 MBBA5.34 and EBBA5.6 as liquid crystal compounds
The mixture was placed in a weighed bottle, heated at about 8,000 ℃ for 10 minutes, and mixed.

Accurately take 5 parts of this mixture into another weighing bottle, and weigh 3 parts of hexadecylpyridinium bromide, 6 parts of p-aminophenol, and 0.6 parts of maleic acid into this using a precision balance. Added. This was left in a constant temperature bath of about 8000 for 8 hours to form a homogeneous mixture. Determine the above Vth and fco (HZ) for this composition,
From this, the scannability coefficient (maximum value) of a liquid crystal display device manufactured using this composition was determined.

These values are shown in Table 1.

In Examples 2 to 3 and Comparative Examples 1 to 4 in Table 1, liquid crystal compositions were manufactured according to the method described in Example 1.

From the above, it can be seen that the composition of the present invention is a composition that increases the number of scanning lines in a matrix display and enables large-sized displays. Next, the voltage EO of these compositions
Table 2 shows that the characteristics are stable even against swords and irons, in comparison with comparative examples.

In this method, two glass substrates each having a transparent conductive film of indium oxide formed by vapor deposition on the inner surface of the glass are arranged so that the conductive films face each other, and the gap between them is set to about 15 m by polyethylene terephthalate film. A liquid crystal composition was introduced between the glass substrates, and a voltage of 50Hz and 12V was applied to the liquid crystal through a transparent conductive film using an element in which the periphery of the substrates was adhesively fixed with an epoxy adhesive. The results of applying an alternating current rectangular wave of -p and measuring Vth and fco at regular intervals are shown in Table 2.

Shinoji sardine blended with 0.1 weight of K hexadecylpyridinium bromite and 0.2 weight of maleic acid*
This shows that although the composition of the present invention has a large fco, there is little decrease in foo due to energization, and it maintains characteristics that allow it to be used for a long time as a large display. It is well known among those skilled in the art that the effects of additives used in these liquid crystal compositions do not depend on the composition of the liquid crystal compound that is the main component of these compositions, but some examples are shown below. An example is shown below.

Examples 4 to 7 Examples 8 to 10 Examples 8 to 10 are shown to clarify the effects of the present invention on a liquid crystal composition comprising a combination of compound groups different from the liquid crystal compounds of Examples 1 to 7.

These Examples are examples in which a parent liquid crystal in which an ester type liquid crystal substance or an azo type liquid crystal substance is blended with a Schiff base type liquid crystal is used, and liquid crystal compositions were produced by the same method as in Example 1. From the above, it is clear that the composition of the present invention is effective for use in liquid crystal display devices that perform matrix display by time-division driving, particularly for display devices that scan 100 lines or more.

This is effective for display devices in which the light scattering of a panel filled with liquid crystal is viewed directly through transmitted light or reflected light, as well as in display devices in which the image is projected onto a screen using a projector. Needless to say.

[Brief explanation of drawings]

Figure 1 shows the dynamic scattering threshold of the liquid crystal composition, the value voltage (V
th) is a schematic diagram showing the frequency dependence of . Figure 2 shows the voltage averaging method when matrix driving is selected.
FIG. 7 is a diagram showing voltage waveforms during half selection and non-selection. FIG. 3 and FIG. 4 are diagrams showing voltage waveforms applied to selected points and non-selected points, respectively. 3 illustrations of spears, 1 illustration of tusks, 2 illustrations of spears, 4 illustrations

Claims (1)

[Claims] 1 At least one nematic liquid crystal compound with negative dielectric anisotropy, and based on the liquid crystal compound, about 0.05 to 0.5% by weight of an onium salt having a nitrogen core, an organic-basic acid or/and an organic Monoacid base compound approximately 0.5-2.0% by weight
and about 0.01 to 0.1% by weight of an organic dibasic acid.