JPH0730322B2 - Liquid crystal composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal composition for a display device, and more particularly to a liquid crystal composition having good dynamic driving characteristics in a field effect mode.

[Conventional technology]

Conventionally, a nematic liquid crystal composition for display devices has a general formula as disclosed in, for example, JP-A-54-83694. (R and R'each represent a linear alkyl group having an arbitrary carbon number)
Based on N _n liquid crystal such as the compound represented by (hereinafter abbreviated as ECH in the text) (R "is an arbitrary represents a straight chain alkyl group having a carbon number) (abbreviated as P-E At a later herein) compounds represented by the N _p liquid crystal added, such as, an optical threshold voltage allowed to decrease. However, the electro-optical characteristics such as the steepness of the later-described amount of n _p liquid crystal is increased is the addition of n _p liquid than necessary because the reduction is not advisable. Furthermore the n _n liquid crystal and n _p LCD In addition to the general formula By adding a compound represented by (R represents a linear alkyl group having an arbitrary carbon number), the clearing point is increased and the liquid crystal temperature range is widened.

[Problems to be solved by the invention]

Today, the condition of the characteristics required for nematic liquid crystal compositions is that the slope of the voltage-transmittance curve between the optical threshold voltage of the voltage-transmittance curve and the optical saturation voltage is steep (hereinafter, The steepness means the magnitude of the gradient.) The response speed of the transmittance is fast with respect to the change of the voltage. It can be driven in a wide temperature range around room temperature.
That is, it has a wide nematic liquid crystal range, is chemically stable, has excellent moisture resistance and light resistance, and the drive voltage (or optical threshold voltage) can be freely selected.

When dynamic driving is performed on a simple matrix display, the effective voltage applied to the liquid crystal of the selected electrode section or the non-selected electrode section by the drive circuit is set to V _on and V _off , respectively, and the number of scanning electrodes is n. If so, the ratio V _on / V _off is The ratio V _on / V _off decreases as n increases.

On the other hand, a twist nematic mode liquid crystal cell, which is one of the liquid crystal display devices, is placed between the crossed polarizers, and the transmittance of the cell 4 is converted into a photomultiplier tube by using the electro-optical characteristic measuring device shown in FIG. While observing, the effective voltage applied to the cell 4 is changed by the drive circuit 6, and an effective voltage-relative transmittance curve as shown in FIG. 2 is obtained. The optical threshold voltage V
_th (in this specification, the effective voltage value required to change the transmittance by 10% is V _th ), and the effective voltage at which the transmittance begins to saturate by further increasing the voltage is optically saturated. Voltage V
_Sat (in this specification, the effective voltage value required to change the transmittance by 90% is V _sat ), the effective voltage V _off applied to the non-selected electrode portion is the optical threshold. If it is smaller than the value voltage V _th , that is, V _off V _th (2), the transmittance does not change as compared with the case where the voltage is not applied, and no selection is made. If the effective voltage V _on is greater than the saturation voltage V _sat , that is, V _on V _sat (3), the transmittance is sufficiently changed and the transmission is selected. When the relational expression is established, the difference between the transmittances of the non-selected electrode and the selected electrode becomes sufficient when V _on / V _off ≧ V _sat / V _th (4). Furthermore, from equations (1) and (4) Becomes As the number of scanning lines n increases, the right side becomes smaller and approaches 1. Therefore, in order to obtain a sufficient contrast between the selective electrode and the non-selective electrode, it is advantageous that V _sat / V _th is also close to 1. That is, the steeper the gradient of the curve from the optical threshold voltage to the optical saturation voltage of the effective voltage-relative transmittance curve in FIG. 2 is, the contrast is made constant (or improved) and the number of scanning lines is increased. You can The above is the reason why the conditions are required. However, since the removal of the temperature dependence in the electro-optical characteristics has been emphasized in the past, no concrete measure for improving the condition itself has been shown, which is a problem. On the other hand, temperature dependence can be easily removed by incorporating the current temperature compensation circuit, which has become cheaper, into the drive circuit.

Another problem is the response speed.

The response speed does not matter so much when displaying a still image. However, when it is necessary to switch images frequently such as a computer terminal or a word processor, a high speed response is required. Needless to say, a faster response is required when displaying a moving image such as a television image.

The present invention is to solve the above problems, and an object of the invention is to improve the steepness of a nematic liquid crystal composition for a display device to improve the dynamic drive characteristics, and to widen the nematic liquid crystal temperature range to increase the operating temperature. Another object is to provide a nematic liquid crystal composition which has a broader range and is chemically stable.

[Means for solving problems]

The liquid crystal composition of the present invention comprises at least one compound represented by the following formula A, at least one compound represented by the following formula B, and compound represented by the following formula C. It is characterized by comprising at least one kind and at least one kind of compounds represented by the following general formula D.

However, R ₁ and R ₂ are linear alkyl groups having 1 to 10 carbon atoms, R ₃ and R ₄ are linear alkyl groups having 1 to 12 carbon atoms, and R ₅ and R ₆ are direct alkyl groups having 1 to 10 carbon atoms. The chain alkyl group R ₇ represents a straight chain alkyl group having 1 to 10 carbon atoms.

The compound represented by the general formula A (hereinafter abbreviated as compound A in the text) is used for improving the steepness and widening the liquid crystal temperature range. If it is less than 8% by weight, the effect is small and the content thereof is small. The more you have, the better. However, if it exceeds 90%, the deviation from the eutectic composition becomes too large, the effect of lowering the freezing point cannot be obtained, and precipitation occurs at low temperature.
% To 90% by weight is desirable.

The compound represented by the general formula B (hereinafter abbreviated as compound B in the text) improves the steepness by being added to a conventional nematic liquid crystal composition consisting of only N _n liquid crystal and N _p liquid crystal, and has a nematic property. It is used to widen the liquid crystal temperature range, and if it is less than 2% by weight, there is no effect and the larger the content, the better. However, if it exceeds 80% by weight, the deviation from the eutectic composition becomes too large, the effect of lowering the freezing point cannot be obtained, and precipitation occurs at low temperature, so 2% by weight to 80% by weight is desirable.

The compound represented by the general formula C (hereinafter abbreviated as compound C in the text) is also effective for improving the steepness by adding it to the conventional nematic liquid crystal composition consisting of only N _n liquid crystal and N _p liquid crystal. It is a N _n liquid crystal that is less than 3% by weight, and the smaller the effect, the better the content. But 4
If it exceeds 2.5% by weight, the deviation from the eutectic composition becomes too large, the effect of lowering the freezing point cannot be obtained, and precipitation occurs at a low temperature, so 3% by weight to 42.5% by weight is desirable.

Formula (abbreviated as Compound D At a during subsequent text) compounds represented by D may also increase lower optical threshold voltage by some N _p is the liquid crystal content thereof. If the optical threshold voltage is low, the maximum rated output voltage of the liquid crystal drive circuit can be proportionately low, which is advantageous because an inexpensive IC can be used. However, if the content of the P-E liquid crystal is too large, the performance of electro-optical characteristics such as steepness may be deteriorated, and undesired effects such as lowering the clearing point and narrowing the liquid crystal temperature range may occur. The content should not be excessive. That is, 5 wt% to 30 wt% is desirable, and more desirably 8 wt% to 22.5 wt%.

〔Example〕

 Hereinafter, the present invention will be described in detail based on examples.

The characteristics of the liquid crystal composition were measured as follows. FIG. 1 shows a measuring system for electro-optical characteristics.
The measuring cell 4 is provided with a transparent electrode such as tin oxide on one surface of a glass substrate by an operation such as vapor deposition, and the surface is covered with an organic thin film for orientation treatment, and is made of a nylon film that also serves as a spacer. Two glass substrates are opposed to each other and fixed so that a liquid crystal layer has a desired thickness when a liquid crystal is enclosed by sandwiching a frame between them. One polarizing plate is provided on each side of the cell. The direction of the polarization axis is adjusted so that the light is transmitted when no voltage is applied, and the light is blocked when a voltage is applied. In the text, the distance between the glass substrates (that is, the thickness of the liquid crystal layer) is abbreviated as cell thickness. The light beam 2 emitted from the white light source 1 passes through the lens system 3 and is incident on the cell 4 from the vertical direction, and the transmitted light intensity is measured by the detector provided at the rear. Cell 4 at this time
An AC rectangular voltage having a frequency of 1 kilohertz having an arbitrary effective voltage is applied by a drive circuit 6. First
FIG. 2 is an effective voltage-relative transmittance curve obtained by measuring a liquid crystal cell using the measurement system shown in FIG. In Fig. 2, the transmittance is expressed as 100% and 0% when the light is brightest and darkest in the normal applied voltage range, and the applied voltage is gradually increased starting from the voltage of 100%. To the optical threshold voltage V _th when the transmittance changes by 10% and the applied voltage is further increased to change the effective voltage when the transmittance changes from 100% to 90%. Is the optical saturation voltage V
_Set each as _sat . At this time, from the optical threshold (V _sat ) of the effective voltage-relative transmittance curve to the optical saturation voltage (V
The slope (steepness) of the curve over _th ) can be defined as β in the following equation.

β is a coefficient indicating how many times the optical saturation voltage (V _sat ) is equal to the optical threshold voltage (V _th ), and has a value larger than 1 (from V _sat > V _th ). When β = 1, the effective voltage becomes the optical threshold voltage and the transmittance becomes 90% at the same time, that is, the transmittance curve has the maximum slope. For example, when β = 2, the threshold value becomes It shows that the transmittance becomes 90% (optical saturation voltage) at a voltage twice the voltage.
Therefore, the slope of the curve from the optical threshold voltage (V _sat ) to the optical saturation voltage (V _th ), that is, the steepness is defined depending on how close the value of β is to 1. You can

The effective voltage (denoted as V _on ) when lit (selected in the matrix cell) is equal to V _sat , and the effective voltage (denoted as V _off ) when not lit (not selected) is V _{sat. When} an electric signal equal to _th is applied, the transmittance becomes 90% and 10%, respectively, and the lighting and non-lighting of the pixel are recognized. Furthermore, if V _on is slightly larger than V _sat and V _off is slightly smaller than V _th , the respective transmittances are 90% or more and 10% or less. At this time, V _on / V _sat > V _sat / V _th = β. On the contrary, when V _on is smaller than V _sat and V _off is larger than V _th , the respective transmittances are 90% or less and 10% or more, which deteriorates the visibility. That is, visibility is deteriorated when a signal voltage of V _on / V _off <V _sat / V _th = β is applied.
In this way, if the β value is smaller than the effective voltage ratio V _on / V _{off of the} electric signal, a pixel display with good visibility is obtained, and the V _on / V _off ratio is smaller as the β value is smaller to obtain the same image display. I'm done.
In a simple matrix display, the larger the number of scanning lines, the more V _on
Since / V _off is small, β value must be small (close to 1). The above β value is an index of the multiplex characteristic because it shows the minimum value that allows V _on / V _off .

The response speed to changes in applied voltage is as follows. When the applied effective voltage is instantaneously switched from V _th to V _sat , the time required for the transmittance to change by 90% of the difference between the transmittances for each effective voltage in the steady state (that is, the transmittance is 90%). The time required to change from 18% to 18%) is expressed as T _{on in} millisecond units, and similarly, when the effective voltage is instantaneously switched from V _sat to V _th , the transmittances of the respective effective voltages in the steady state are different from each other. The time required for the transmittance to change by 90% of the difference (time required for the transmittance to change from 10% to 82%) is represented by T _{off in} milliseconds. T _on and T _off
Is used as an index of the response speed.

Generally, the time required for the transmittance to change from 0 to 90% after the applied voltage is instantaneously switched from 0 to an arbitrary voltage ν (V) is t _on , and the applied voltage is instantly changed from ν to 0. switchable time transmittance required for changes by 10% to 100% of the state from, t _off to the be represented by the following formula is known (reference:. M.Schadt JSPS Committee Organic Materials for Information Science, 142nd Committee, Subcommittee A (Liquid Crystal Group), 11th Workshop, 1978).

(Where η is the bulk viscosity, ε ₀ is the vacuum permittivity, Δε is the anisotropy of the relative permittivity, E is the electric field, K is the elastic constant term of K ₁₁ + K ₃₃ −2K ₂₂ ) / 4, and d is the cell Representing thickness, η, Δε and K are unique to the liquid crystal composition). Therefore, t _on and t
Both _off increase in proportion to d ² .

The response speed T defined in this example also has a close relationship with the cell thickness, and it is qualitatively found that T is short when the cell thickness is thin and long when the cell thickness is large. Those relationships are not difficult for those skilled in the art to understand. Therefore, when a liquid crystal display is manufactured using the same liquid crystal composition, the thinner the cell thickness, the faster the response speed can be.

On the other hand, it has been found that the steepness β becomes the smallest (best) when the product Δn · d of the cell thickness d (μ) and the refractive index anisotropy Δn is around 0.8 to 1.0 ( References: Yoshio Yamazaki, Yutaka Takeyama, Mitsuo Nagata, Yukio Miyaji, Proceedings of the
3rd International Display Research Conference JAPA
N "DISPLAY'83". 320 pages: 1983,). Therefore, when the contrast is important, the cell thickness d is Δn · d is 0.8 to
It is the best practice to make a liquid crystal display so that the thickness is around 1.0, and it is considered most appropriate to compare the steepness of liquid crystal compositions with this cell thickness. Since the response time is also related to the cell thickness as described above, it is necessary to measure with an appropriate thickness in order to compare the response times of liquid crystal compositions.

In view of the above, in the present example, the steepness, the response speed, and the optical threshold voltage were all measured using a cell having a cell thickness that minimizes the steepness β.

All measurement temperatures were 20 degrees Celsius.

In addition, a nematic liquid crystal composition of the present invention to which a small amount of a cholesteric substance was added was sealed in a cell in order to enhance the uniformity of alignment.

The stability of the nematic liquid crystal phase was expressed by the high temperature liquid crystallinity and the low temperature liquid crystallinity in the state of being enclosed in the cell. That is, the average annual temperature is 15 degrees Celsius in Tokyo and 22 degrees Celsius in Naha (from “Statistics of Japan, Statistics of Japan”, 1980, pp. 6 and 7).
It is assumed that the cell is placed in a constant temperature bath assuming that the temperature is ℃, and that the nematic phase is stable at a temperature higher than that by 30 ℃ (that is, the temperature of the constant temperature of 50 ℃) is called high temperature liquid crystallinity. It is indicated by a circle for stable and I for an isotropic liquid. Low-temperature liquid crystallinity means that when the temperature of the thermostatic chamber with the cell is started at 20 ℃, and lowered by 5 ℃ per day,
When the temperature is lower than 20 ° C which is assumed as room temperature by 30 ° C (ie,
The temperature of the constant temperature bath is -10 ° C), and whether or not the nematic liquid crystal phase is stable is called low-temperature liquid crystallinity. If so, it is indicated by a cross.

[Example-1] Table 1 shows the composition and characteristics of Example-1 according to the present invention. However, in this example, the compound B is represented by the general formula A compound represented by the formula (wherein R ₃ and R ₄ represent a straight-chain alkyl group having 1 to 12 carbon atoms) (hereinafter abbreviated as PIR) in an amount of 30.0 wt% and compound C (Wherein R ₅ and R ₆ represent a straight-chain alkyl group having 1 to 10 carbon atoms) (hereinafter abbreviated as PAR in the text) is contained by 10.0% by weight. I am trying.

Table 2 shows the composition and characteristics of a liquid crystal composition containing ECH and PE as a conventional example.

While the β value representing steepness in the conventional example-1 is 1.265, the β value in the example-1 is 1.218, which is very good.

The response speed is 444 milliseconds in the conventional example-1 and 254 milliseconds in the example-1, which is considerably high.

The optical threshold voltage V _th is 2.59 V in the conventional example-1 as well, whereas the V _th in the example-1 is improved to 2.19 V.

Example-1 has a high temperature liquid crystallinity at 50 degrees Celsius and a low temperature liquid crystallinity at minus 10 degrees Celsius, and is sufficiently stable, and has a sufficiently wide nematic liquid crystal temperature range to be used for an ordinary display. . More specifically, it has a nematic liquid crystal temperature range of up to 61 degrees Celsius on the high temperature side, and can be used as a display body under considerably severe conditions.

As described above, the β value of Conventional Example-1 is 1.265, whereas Example-1 of the present invention is as good as 1.218. Further, the optical threshold voltage is low, the response speed is fast, and the nematic liquid crystal temperature range is sufficient.

[Examples-2, 3] Table 3 shows the compositions and characteristics of Examples-2, 3 according to the present invention. However, this example is characterized by containing 30% PIR and 10% PAR.

Table 2 shows the composition and characteristics of the conventional example.

The β value representing steepness in Conventional Example-1 is 1.265, whereas the β value in Example-2 is 1.226, and the β value in Example-3 is 1.
It has been greatly improved to 213.

The response speed is 444 ms in the conventional example-1 and 255 ms in the embodiment-2 and 231 ms in the embodiment-3, which are considerably high.

Also optical threshold voltage V _th, while the Conventional - 1 is 2.59V, V _th embodiment -2 1.88V, V _th examples -3 is summer low as 2.10V .

Examples-2 and 3 have a high temperature liquid crystallinity at 50 degrees Celsius and a low temperature liquid crystallinity at -10 degrees Celsius and are sufficiently stable, and have a nematic liquid crystal temperature range wide enough to be used for a normal display body. ing. More specifically, the example on the high temperature side
Example 2 has a nematic liquid crystal temperature range of up to 62 degrees Celsius and Example 3 has up to 63 degrees Celsius, and can be used as a display under considerably severe conditions.

As described above, the β value of Conventional Example-1 is 1.265, whereas Example-2 according to the present invention is 1.226, and Example-3 is 1.213, which are very good. Also, the optical threshold voltage is low,
The response speed is fast, and the nematic liquid crystal temperature range is sufficient.

[Examples 4,5] Table 4 shows compositions and characteristics of Examples-4 and 5 according to the present invention. However, this example is characterized by containing 30% PIR and 10% PAR.

Table 2 shows the composition and characteristics of the conventional example.

While the β value representing steepness in the conventional example-1 is 1.265, the β value in the example-4 is 1.223, and the β value in the example-5 is 1.
Very good with 213. That is, in a liquid crystal panel using a simple matrix electrode, in order to set the transmittance to 10% or less (dark state) for the selective electrode and 90% or more (bright state) for the non-selective electrode, the conventional example-1 In contrast, the number of scan electrodes can be driven only 17 or less, whereas in Example-4, 25 or more can be driven, and in Example-5, 28 or more can be driven.

The response speed is 444 msec in the conventional example-1, 250 msec in the example-4 and 282 msec in the example-5.

Optical threshold voltage V _th is that the Conventional - 1 is 2.59V, V _th examples -4 2.51V, V _th embodiment -5 is approximately the same as 2.56V .

Examples-4 and 5 have a high temperature liquid crystallinity at 50 degrees Celsius and a low temperature liquid crystallinity at -10 degrees Celsius and are sufficiently stable, and have a nematic liquid crystal temperature range wide enough to be used for a normal display body. ing. More specifically, Example-4 has a nematic liquid crystal temperature range from minus 30 degrees Celsius to 64 degrees Celsius and Example-5 has minus nematic liquid crystal temperature range from minus 15 degrees Celsius to 65 degrees Celsius. Can also be used.

As described above, the β value of Conventional Example-1 is 1.265, whereas Example-4 according to the present invention is 1.223, and Example-5 is 1.213, which are very good. The optical threshold voltage is appropriate, the response speed is fast, and the nematic liquid crystal temperature range is sufficient.

[Effects of the Invention] As described above, the liquid crystal composition of the present invention includes at least one compound represented by the general formula A,
At least one compound represented by the general formula B above,
At least one compound represented by the general formula C above,
By having at least one compound represented by the general formula D, the nematic liquid crystal temperature range is from -10 to 50 degrees Celsius and the widest nematic liquid crystal range is from -30 to 64 degrees Celsius. It was possible to obtain a nematic liquid crystal composition which can be driven in a temperature range, has excellent steepness, has a low optical threshold voltage, has a fast response speed, and has excellent dynamic drive characteristics.

Use of the nematic liquid crystal composition according to the present invention is very effective for obtaining excellent display contrast in display devices such as twisted nematic mode and kest / host effect mode (as host liquid crystal).

[Brief description of drawings]

FIG. 1 is a hardware diagram showing a measuring device used in the examples, and FIG. 2 is a curve diagram showing a change in relative transmittance-effective voltage generally obtained by using the measuring device. 1 ... Light source 2 ... Ray 3 ... Lens and filter system 4 ... Cell 5 ... Light receiving part (photomultiplier tube)

Claims (1)

[Claims] 1. At least one compound represented by the following general formula A, at least one compound represented by the following general formula B, and at least one compound represented by the following general formula C. And a liquid crystal composition comprising at least one compound represented by the general formula D below. However, R ₁ and R ₂ are linear alkyl groups having 1 to 10 carbon atoms, R ₃ and R ₄ are linear alkyl groups having 1 to 12 carbon atoms, and R ₅ and R ₆ are direct alkyl groups having 1 to 10 carbon atoms. The chain alkyl group R ₇ represents a linear alkyl group having 1 to 10 carbon atoms.