JPS6245685A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To provide a nematic liq. crystal compsn. which has excellent dynamic drive characteristics, steepness, chemical stability, moisture resistance and light resistance, a rapid response with respect to transmittance and a wide operating temp. range and which comprises particular three compds. CONSTITUTION:7-72wt% compd. of formula I (wherein R1-R2 are each a 1-12C straight-chain alkyl) is mixed with 5-38wt% compd. of formula II (wherein R3 is a 1-8C straight-chain alkyl) and 5-30wt% compd. of formula III (R4 is a 1-10C straight-chain alkyl).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal composition for display devices, and particularly to a liquid crystal composition that has good dynamic drive characteristics in field effect mode.

[Summary of the invention]

The present invention provides a liquid crystal composition in which at least general formula R1
Compound represented by -@→◇-0-R2, general formula R3-
◎-Yumito◎-CN Compound represented by general formula R4
No need to use the compound represented by Oo-@-ON, lowering of optical threshold voltage, improvement of steepness,
This is designed to speed up the response speed.

[Conventional technology]

Conventionally, liquid crystal compositions for display devices have been disclosed, for example, in Japanese Patent Application Laid-Open No. 54-8
As shown in Publication No. 5694, etc., the general formula R-
Compounds represented by @-Co opepo-R' (R and R' each represent a straight alkyl group with an arbitrary carbon number) (hereinafter abbreviated as !IC!H in the text), etc. Based on Nn liquid crystal, these have the general formula "'-@-c o
Compounds represented by o-◎-ON (R" represents an arbitrary number of carbon atoms) representing a straight-chain alkyl group (hereinafter referred to as p in the text)
-z) is added to lower the optical threshold voltage. However, if the amount of Np liquid crystal added increases, electro-optical properties such as steepness, which will be described later, will deteriorate, so it is not a good idea to add more Np liquid crystal than necessary.

[Problems and objectives to be solved by the present invention] The characteristics required for nematic liquid crystal compositions today are: ■ The rise of the voltage-transmittance curve near the optical threshold voltage is steep. (Hereinafter abbreviated as "steepness" in the text) ■ Fast response speed of transmittance to changes in voltage ■ Capable of driving in a wide temperature range centered around room temperature,
That is, it must have a wide nematic liquid crystal range; It must be chemically stable and have excellent moisture resistance and light resistance; and it must be able to freely select the driving voltage (or optical threshold voltage).

When a simple matrix display is dynamically driven, if the effective voltages applied by the drive circuit to the liquid crystal of the selected electrode part or non-selected electrode part are Von and Voff, respectively, and the number of scanning electrodes is n, then Ratio Von/Vof
f is Von/Voff= (-/n+1)/(v'n-1)
There is a relationship (1), and as n increases, the ratio VOn/Vof also decreases.

On the other hand, a twisted nematic mode liquid crystal cell, which is one type of liquid crystal display device, is placed between orthogonal polarizers, and the transmittance of the cell 4 is measured using the electro-optic characteristic measuring device shown in FIG. By changing the effective voltage applied to the cell 4 by the drive circuit 6 while observing the cell 4, an effective voltage-relative transmittance curve as shown in FIG. 2 is obtained. The optical threshold voltage v is the effective voltage at which the transmittance begins to change as the voltage is increased.
th (in the case of Honmon Hoshosei, the effective voltage value required to change the transmittance by 10% is vth), and as the voltage is further increased, the transmittance increases the optical saturation voltage by vaat (in this specification). In this paper, the effective voltage value required to change the transmittance by 90% is Vsat), then the effective voltage Voff applied to the non-selected electrode portion is equal to the optical threshold voltage Vth.
If it is smaller, that is, v ot t <, v th ・−” (
In case 2), the transmittance does not change compared to when no voltage is applied and is not selected at all, and if the effective voltage VOn applied to the selection electrode section is larger than the saturation voltage Vsat, that is, VOn≧ If Vsat...(3), the transmittance has changed sufficiently and has been selected.Therefore, if you divide equation (8) by equation (2), v o n Vsat≧ □
(4) Voff Vth When this relational expression holds true, the difference in transmittance between the non-selected electrode and the selected electrode becomes sufficient. Furthermore, from equations (1) and (4), we get (5). As the number n of scanning lines increases, the right side becomes smaller and approaches 1. Is there enough contrast between the selective and non-selective electrodes for this? To obtain V sat /
It is also advantageous for V th to be close to 1. That is, the steeper the slope from the optical threshold voltage to the optical saturation voltage of the voltage-transmittance curve shown in FIG. 2, the more the number of scanning lines can be increased while maintaining (or improving) the contrast. The above is the reason why condition (2) is necessary. However, since conventionally, emphasis has been placed on eliminating temperature dependence in electro-optical characteristics, no concrete measures have been proposed to improve condition (2) itself, which is a problem. On the other hand, temperature dependence can now be easily eliminated by incorporating a temperature compensation circuit into the drive circuit, as the cost of manufacturing has become cheaper.

Another problem is response speed.

When displaying still images, response speed is not so much of an issue. However, in cases where images need to be changed frequently, such as in combiator terminals and word processors, high-speed responsiveness is required. Needless to say, even faster response is required when displaying moving images such as television images.

One purpose of the present invention is to solve the above problems, and its purpose is to improve the steepness of nematic liquid crystal compositions for display devices, improve dynamic drive characteristics, and widen the nematic liquid crystal temperature range for operation. The object of the present invention is to provide a nematic liquid crystal composition that has a wider temperature range and is chemically stable.

[Means for problem decomposition method]

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

A...R1-@One 10-R2B...
R3÷←ON C・-=・R4-@-00o-@-c N However, R1 and R2 are straight chain alkyl groups having 1 to 12 carbon atoms R3 are straight chain alkyl groups having 1 to 8 carbon atoms R4 is Carbon number 1
~10 straight-chain alkyl groups.

The compound represented by the general formula A (hereinafter abbreviated as compound A in the text) is an effective Nn compound for increasing the response speed.
It is a liquid crystal, and if it is less than 7% by weight, the effect is small, so the higher the content, the better. However, since the clearing point is relatively low, if the content of Compound A exceeds 72 wt %, the clearing point of the nematic liquid crystal composition will also become low, which is undesirable because it will narrow the nematic liquid crystal range of the nematic liquid crystal composition. Therefore, the content of compound A is desirably 7% by weight to 72% by weight.

The compound represented by general formula B (hereinafter abbreviated as compound B in the text) is an Np liquid crystal, and the optical threshold voltage can be lowered or increased depending on its content. It is also advantageous in increasing the clearing point. However, if the content is too high, the performance of electro-optical properties such as steepness will deteriorate, and the deviation from the eutectic composition will become too large, making it impossible to obtain the effect of lowering the freezing point and causing precipitation at low temperatures. becomes.

Therefore, the content of compound B is preferably from 5% by weight to 38% by weight.

The compound represented by the general symbol 2 (hereinafter abbreviated as compound C in the text) is also an Np liquid crystal, and the optical threshold voltage can be lowered or increased depending on its content. If the optical threshold voltage is low, the maximum rated output voltage of the liquid crystal driving circuit can be proportionally low, which is advantageous because inexpensive IO can be used. However, if the content of P-E liquid crystal is too large, it may cause undesirable effects such as deterioration of electro-optical properties such as steepness, lowering the clearing point and narrowing the liquid crystal temperature range. It is better not to exceed the content. That is, it is preferably from 5% by weight to 30% by weight, more preferably from 8% by weight to 22.5% by weight.

〔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 measurement system for electro-optical characteristics.

The measurement cell 4 has a transparent electrode made of tin oxide or the like formed by vapor deposition on one side of a glass substrate, which is then covered with an organic thin film and subjected to alignment treatment, and then a nylon film that also serves as a spacer is formed. The two glass substrates are fixed facing each other so that the liquid crystal layer has the desired thickness when the liquid crystal is sealed with a frame in between, and one polarizing plate is placed on each side of the cell. The direction of the polarization axis is adjusted and pasted so that light is transmitted when no voltage is applied and light is blocked when voltage is applied. In the text, the distance between the glass substrates (ie, the thickness of the liquid crystal layer) is abbreviated as cell thickness. The light beam emitted from the white light source 1 passes through the lens system 5.
The light enters the cell 4 from the vertical direction, and the intensity of the transmitted light is measured by a detector provided at the rear. At this time, the cell 4 is supplied with a frequency 1 having an arbitrary effective value voltage by the drive circuit 5.
A kilohertz alternating rectangular voltage is applied. FIG. 2 shows an effective voltage-relative transmittance curve obtained by measuring a liquid crystal cell using the measurement system shown in FIG. In Figure 2, the transmittance is expressed as the brightest and darkest transmittance in the normal applied voltage range as 100% and 0%, respectively. The effective value voltage when the transmittance changes by 10% by increasing the applied voltage is the optical threshold voltage vth, or by further increasing the applied voltage, the transmittance changes by 1.
The effective value voltage when the voltage changes by 90% from the time of 00% is defined as the optical saturation voltage Vsat. At this time, the rise (that is, the steepness) of the voltage-transmittance curve near the optical threshold voltage is determined as the β value in the following equation.

Vsat β=7. h The effective value voltage (represented as Von) when the light is on (when selected in the IJ cell) is equal to Vsat, and the effective value voltage (represented as Voff) when the light is not on (when not selected) )
When an electric signal equal to vth is applied, the transmittance becomes 90% and 10%, respectively, and it is recognized whether the pixel is lit or not. Furthermore, if VoH is slightly larger than Vsat and Voff is slightly smaller than vth, the respective transmittances will be 90% or more and 10% or less. At this time vo
n/ V o f f ) V sat / V
th = β. On the contrary, if VOn is smaller than vsat and Voff is larger than vth, the respective transmittances will be 90% or less and 10% or more, resulting in poor visibility. That is, V on / V o f f (V
When a signal voltage of e a t /V th =β is applied, visibility deteriorates. In this way, if the β value is smaller than the effective voltage ratio V on / V Of of the electric signal, a pixel display with good visibility can be obtained, and the smaller the β value is, the more V On / V Of
The f ratio can also be made small. In a +J display, as the number of scanning lines increases, V On /V Off decreases, so the β value must also be small (approaching 1). Since the β value indicates the minimum value of Von/Voff allowed, it serves as an index of multiplex characteristics.

The response speed to changes in applied voltage is as follows. When the applied effective value voltage is instantaneously switched from vth to Vsat, the time required for the transmittance to change by 90% of the difference between the transmittances for each effective voltage in a steady state (
In other words, the time required for the transmittance to change from 90% to 18% is expressed in Ton in milliseconds, and similarly, when the effective value voltage is instantaneously switched from Vsat to vth, for each effective voltage in the steady state, The time required for the transmittance to change by 90% of the difference between the transmittances (i.e., the time required for the transmittance to change by 90%)
The time required to change from 18% to 18% is expressed in Ton in units of i IJ seconds, and similarly, when the effective value voltage is instantaneously switched from Vsat to vth, the transmittance for each effective voltage in the steady state is the same. The time required for the transmittance to change by 90% of the difference between (the time required for the transmittance to change from 10% to 82%) is expressed in milliseconds as Toff.

T (in milliseconds), which is the sum of τOn and Toff, is used as an index of response speed.

Generally, the time required for the transmittance to change from 0 to 90% after instantaneously switching the applied voltage from 0 to an arbitrary voltage v (V) is ton, and the time required for the transmittance to change from 0 to 90% is ton, and the time required for the transmittance to change from 0 to 90% is ton. After switching to , the transmittance changed from 100% to 10
It is known that if the time required for a % change is toff, it can be expressed by the following formula (Reference: M, 5c
hadt, Japan Society for the Promotion of Science, 142nd Committee on Organic Materials for Information Science, Subcommittee A (Liquid Crystal Group), 11th Study Group Materials, 1978).

t on = yl / (t oΔgK” −K(
−)” )=6”, η/(guΔg u” −7c”
)toff=-7,/K(-)"=d2・η/K?I:2 (where η is the bulk viscosity, eυ is the vacuum permittivity, Δe is the anisotropy of the relative permittivity, E is the electric field, K hani 11 +x,,
2 to 22)/4, where d represents the cell thickness, η, Δε and K are specific to the liquid crystal composition). Therefore, both ton and toff become longer in proportion to d2.

The response speed determined in this example also has a close relationship with the cell thickness, and although it is qualitative, it was found that the response speed tends to be shorter when the cell thickness is thinner, and longer when the cell thickness is thicker. Those skilled in the art will understand these relationships. Therefore, when a liquid crystal display is made using the same liquid crystal composition, the response speed can be increased as the cell thickness becomes thinner.

On the other hand, it has been found that the steepness β is the product of the cell thickness d (μ) and the refractive index anisotropy Δn, which is Δn−d, which is also small (best) in the vicinity of L8 to 1.0. (References: Yoshio Yamazaki, Yutaka Takeshita, Mitsuo Nagata, Yukio Miyaji, Proceed
ings of the 5th internship
nalDisplay Re5earch 0onfe
renee -JAPAN D-5PLAY'83"
1320 pages; 1985, ■5xD). Therefore, if contrast is important, the cell thickness d should be set so that Δn-d is 0.8 to 1.
It is most advisable to manufacture a liquid crystal display so that the cell thickness is around Q, and it is considered to be most appropriate to compare the steepness of liquid crystal compositions using this cell thickness. As mentioned above, the response time is also related to the cell thickness, so in order to compare the response times of liquid crystal compositions, it is necessary to measure at an appropriate thickness.

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

The measurement temperature was 20 degrees Celsius in all cases.

Further, in order to improve the uniformity of alignment, the nematic liquid crystal composition of the present invention with a trace amount of cholesteric substance added thereto was sealed in a cell.

The stability of the nematic liquid crystal phase was expressed by high-temperature liquid crystallinity and low-temperature liquid crystallinity when sealed in a cell.

In other words, the average annual temperature is 15℃ in Tokyo and 22℃ in Bugumi.
(Prime Minister's Office Statistics Bureau, Japan Statistics, 1980 edition, pages 6 and 7), we installed a cell in a constant temperature bath assuming that the room temperature was 20"C, and then set it at a temperature of 1/λ that was 50C higher than that. Whether the nematic phase is stable or not is referred to as high temperature liquid crystallinity.If the nematic phase is stable, it is marked as an isotropic liquid (1 set).
ropicliquid) is expressed in engineering. Low-temperature liquid crystallinity was determined by lowering the temperature of the thermostatic chamber in which the cell was installed starting from 20°C by 5°C per day, assuming that it was room temperature2.
When the temperature is 30°C lower than 0°C (i.e. thermostat temperature -1o'
c) Whether or not the nematic liquid crystal phase is stable is referred to as low-temperature liquid crystallinity. It is expressed as

[Example-1] Table 1 shows the composition and properties of Example-1 according to the present invention. However, in this example, Compound B was a compound represented by the general formula B3-◎-kuto◎→ON (in the formula, R3 is a straight-chain alkyl group having 1 to 8 carbon atoms) (hereinafter referred to as PM in the text).
It is characterized by containing 14.3% by weight of P-1 (abbreviated as B) and 9.8% by weight of P-1.

Furthermore, as a conventional example, the composition and characteristics of a liquid crystal composition containing EOH and P-E are shown in Table 2. In contrast to conventional example 1, which represents steepness, the β value is 1.265. The β value of Example-1 was 1.256, which was considerably improved.

The optical threshold voltage vth is 2.59V in conventional example-1.
On the other hand, Vth in Example-1 is 1.85 V
is significantly lower.

Furthermore, the response speed of Conventional Example-1 is 444 milliJ seconds, whereas Example-1 is considerably faster at 225 milliseconds.

Example-1 has high-temperature liquid crystallinity at 50 degrees Celsius and low-temperature liquid crystallinity at minus 10 degrees Celsius, and is sufficiently stable.
It has a sufficiently wide nematic liquid crystal temperature range for use in ordinary displays.

As described above, in Example-1 according to the present invention, as compared with Conventional Example-1, the optical threshold voltage vth is significantly lowered, and the β value is also significantly improved. Furthermore, the response speed is fast and the nematic liquid crystal temperature range is sufficient.

[Example-2] Table 5 shows the composition and properties of Example-2 according to the present invention. However, in this example, PMB was 162% by weight and P-K was 12% by weight.
．． It is characterized by containing 2% by weight.

Further, the composition and characteristics of Conventional Example-1 are shown in Table 2.

While the β value representing steepness in Conventional Example-1 is 1.265, the β value in Example-2 is 1.220, which is very good. In other words, in a liquid crystal panel using IJ square electrodes, in order to make the transmittance less than 10% (dark state) for selective electrodes and more than 90% (bright state) for non-selective electrodes, conventional methods are used. In Example-1, only 17 or less scanning electrodes can be driven, whereas in Example-2, 26 or more scanning electrodes can be driven.

The optical threshold voltage vth of conventional example-1 is 2.597.
On the other hand, vth in Example-2 is 1.84 V
has decreased significantly.

Further, the response speed of the conventional example-1 is 444"IJ seconds, whereas the response speed of the example-2 is considerably faster at 244 milliseconds.

Example-2 has high temperature liquid crystal properties at 50 degrees Celsius and low temperature liquid crystal properties at minus 10 degrees Celsius, and is sufficiently stable, and has a sufficiently wide ricematic liquid crystal temperature range for use in ordinary displays. There is. Furthermore, in detail, on the high temperature side, the temperature is 6 degrees Celsius.
It has liquid crystal properties even at 0 degrees Celsius and even at -25 degrees Celsius on the low temperature side, and can be used for displays under severe conditions.

As described above, in Example-2 according to the present invention, compared to Conventional Example-1, the optical threshold voltage vth is significantly lowered and the β value is greatly improved. Furthermore, the response speed is fast and the nematic liquid crystal temperature range is sufficiently wide.

Table 1 Table 2 Table 5 [Effects of the Invention] As described above, according to the present invention, at least the compound represented by the general formula 10-[Y]-〇-R2, the general formula R3-◎ -bow←◎-CN The compound represented by the general formula Ri-◎-c o o-@-c N is used to compose the nematic liquid crystal composition, making it the one with the widest nematic liquid crystal temperature range. It is possible to obtain a nematic liquid crystal composition that can be driven in a temperature range of -25 degrees Celsius to 60 degrees Celsius, has excellent steepness, has fast response speed, has a low optical threshold voltage, and has excellent dynamic drive characteristics. can.

The use of the nematic liquid crystal composition according to the present invention is highly effective in obtaining excellent display contrast in display elements such as twisted nematic mode and guest-host effect mode (as guest liquid crystal).

[Brief explanation of drawings]

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

Claims (1)

[Claims] (1) It is characterized by comprising at least one compound whose general formula is represented by the following A, at least one compound whose general formula is represented by the following B, and at least one compound whose general formula is represented by the following C. liquid crystal composition. Ａ・・・・・・▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ B・・・・・・▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ C・・・・・・▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (However, R1 and R2 are straight chain alkyl groups having 1 to 12 carbon atoms. R3 is a straight chain alkyl group having 1 to 8 carbon atoms. R4 is a straight chain alkyl group having 1 to 10 carbon atoms.)