JPS62218479A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To provide a nematic liq. crystal compsn. which is wide in the nematic liq. crystal temp. range, excellent in the steepness, high in the speed of response, low in the optical threshold voltage, and excellent in the dynamic drive characteristics and which comprises three particular kinds of compds. CONSTITUTION:8-90wt% at least one compd. (A) of formula I (wherein R1-R2 are each a 1-10C straight-chain alkyl) is mixed with 4-38wt% at least one compd. (B) of formula II (wherein R3-R4 are each a 1-10C straight-chain alkyl), and 5-38wt% at least one compd. (C) of formula III (wherein R5 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.

[Conventional technology]

Conventionally, nematic liquid crystal compositions for display devices have the general formula R+Coo-Q-o-R' (R and R' each have an arbitrary number of carbon atoms), as disclosed in, for example, Japanese Patent Application Laid-Open No. 54-85694. (hereinafter abbreviated as ECH in the text), etc.
Based on liquid crystals, these have the general formula R'-4-COO
Adding NP liquid crystal such as a compound represented by +CN (r represents a linear alkyl group with an arbitrary number of carbon atoms) (hereinafter abbreviated as P-E in the text) to lower the optical threshold voltage. urge

However, it is not a good idea to add more NP liquid crystal than necessary because as the amount of NP liquid crystal added increases, the electro-optical properties such as steepness, which will be described later, will deteriorate. Furthermore, the above Nn liquid crystal and NP
In addition to the liquid crystal, by adding a compound represented by the general formula ``-CN (R'' represents a linear alkyl group with any number of carbon atoms), the clearing point can be raised and the liquid crystal temperature range can be widened. are doing.

[Problems and Objectives to be Solved by the Invention] The characteristics required of nematic liquid crystal compositions today are: ■ A steep rise in the voltage-transmittance curve near the optical threshold voltage (hereinafter referred to in the main text) (abbreviated as “steepness”) ■ Fast response speed of transmittance to changes in voltage ■ Capable of driving in a wide temperature range centered around room temperature
That is, it has a wide nematic liquid crystal range, (1) it is chemically stable and has excellent moisture resistance and light resistance, and (2) the drive voltage (or optical threshold voltage) can be freely selected.

When a simple matrix display is dynamically driven, the effective voltage applied to the liquid crystal of the selected electrode part or non-selected electrode part by the driving circuit is set to van'off, and the number of scanning electrodes is set to n. V.n/voff is Vo n/Vot t=fnτfi-Ding "Ding...
(There is a following relationship, and as n increases, the ratio van/Voff 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 this specification, λ is the effective ridge pressure value required to change the transmittance by 10 cm, and vth is the value of λ).Vsat (in this specification, the voltage is further increased and the transmittance reaches the optical saturation voltage) In this book, the effective voltage required to change the transmittance by 90% is Vsat], and if the effective voltage Voff applied to the non-selected electrode part is smaller than the optical threshold value vth, that is, Vo f f<Vt h --(2)
If so, the transmittance is softer than when no voltage is applied, and the transmittance does not change and is not selected at all, and if the effective voltage Van applied to the selection electrode section is larger than the saturation voltage Vsat, that is, V o n ' :2V sat
--If it is (3), the transmittance has changed sufficiently and it has been selected.Therefore, dividing equation (3) by equation (2) gives □〉-□ ......(4) Voff Vth, When this relational expression holds true, the difference in transmittance between the non-selective electrode and the selective electrode becomes sufficient. Furthermore, it follows from equation (R) and equation (4). As the number of scanning lines increases, the right side becomes smaller and approaches 1. Therefore, in order to obtain sufficient contrast between the selected electrode and the non-selected electrode, V s at /
It is advantageous for V th to be close to 1 as well. That is, the second
The steeper the slope of the effective voltage-relative transmittance curve from the optical threshold voltage to the optical saturation voltage in the figure, the more the number of scanning lines can be increased while keeping (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 removed by incorporating a compensation circuit into the drive circuit now that ICs have 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 computer 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.

The present invention has been made 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 to increase the operating temperature. The purpose is to expand the scope of the invention and provide a chemically stable nematic liquid crystal composition.

[Means to solve the problem]

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 becoming.

A・----Rt-e-coo-o-o-R.

B・・・・・・R38ItoR4 C...R1+COO-toCN however, Sl and R1 are straight chain alkyl groups having 1 to 10 carbon atoms R1 and R4 are straight chain alkyl groups having 1 to 10 carbon atoms R1 represents a straight chain alkyl group having 1 to 10 carbon atoms.

The compound represented by General Shikijin (hereinafter abbreviated as Compound A in the text) was used to improve the steepness and expand the liquid crystal temperature range, and if it is less than 8% by weight, the effect is small. The higher the content, the better. However, 90% by weight
If it exceeds 8% by weight, the deviation from the eutectic composition becomes too large and the effect of lowering the freezing point cannot be obtained and precipitation occurs at low temperatures.

The compound represented by the general formula B (hereinafter abbreviated as compound B in the text) is effective for improving steepness when added to a conventional nematic liquid crystal composition consisting of a simple Nn liquid crystal and an NP liquid crystal. It is a Nn liquid crystal, and if it is less than 4% by weight, the effect is small, so the higher the content, the better. However, if it exceeds 38 wt%, the deviation from the eutectic composition will become too large (# solid point 1 red lower effect will not be obtained and precipitation will occur at low temperatures, desirable.

The compound represented by the general formula C (hereinafter referred to as compound C in the text) is an NP liquid crystal, and the optical threshold value 4 pressure 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.

〔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 for orientation treatment, and a nylon film that also serves as a spacer.

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 made of Luminous sandwiched between them, and one glass substrate is placed on each side of the cell. The direction of the polarizing axis is adjusted and pasted so that when no voltage is applied, light passes through the polarizing plate, and when voltage is applied, light is blocked.

In the text, the distance between the glass substrates (ie, the thickness of the liquid crystal layer) is abbreviated as cell thickness. A light beam emitted from a white light source 1 passes through a lens system 3 and enters a cell 4 from a vertical direction, and the intensity of the transmitted light is measured by a detector 4 provided at the rear. At this time, an alternating rectangular voltage having a frequency of 1 km/Bern and having an arbitrary effective value voltage is applied to the cell 4 by the driving circuit 5. Figure 42 shows an effective voltage-relative transmittance curve obtained by measuring a liquid crystal cell using the measurement system shown in Figure 1.

In Figure 2, the transmittance is the normal mark 71O'4 The transmittance when it is the brightest and the transmittance when it is the darkest in the pressure range is 1, respectively.
The applied voltage is expressed as 00 and 0, and the applied voltage is gradually increased starting from the voltage at a transmittance of 100, and the effective value voltage when the transmittance changes by 10 is the optical threshold voltage vth or as the applied voltage is further increased. When the transmittance is 100-90
The effective value voltage when the temperature changes is defined as the optical saturation voltage Vsat. At this time, the rise (that is, the steepness) of the effective voltage-relative transmittance curve near the optical threshold voltage is determined as the β value in the following equation.

β=□ vth The effective voltage (expressed as Van) when lit (selected in the matrix cell) is equal to vaat, and the effective voltage (expressed as Voff) when not lit (selected) is vt
When an electrical signal equal to h is applied, the transmittances become 90 and 10, respectively, and it is possible to recognize whether the pixel is lit or not. Furthermore, if Van is slightly larger than Vaat and Voff is slightly smaller than vth, the respective transmittances will be 90q6 or more and 10q or less. At this time Vo n/V
o f f)Vta a t/vth = β.

On the other hand, if Van is smaller than Vsat and Voff is larger than vth, the respective transmittances will be 90% or less and 10
% or more, visibility becomes poor. That is, Van
/Voff(Vaat/Vth:=β) If a signal voltage of β is applied, visibility will be poor.As shown above, if the β value is smaller than the effective voltage ratio of the electric signal Van/Voff, the pixel display will have good visibility. is obtained, and to obtain the same image display, the smaller the β value, the smaller the Von/Voff ratio.In a simple matrix display, the larger the number of scanning lines, the smaller the Von/Voff, so the β value is also smaller (1
) is necessary. The above β value is Van/Vof
Since f indicates the minimum allowable value, it is 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 value voltage in a steady state (
In other words, the time required for the transmittance to change from 9.0 inches to 18 inches is expressed as Ton in milliseconds, and similarly, Vsat
90 of the difference in transmittance for each effective 'd pressure in a steady state when the effective voltage is instantaneously switched from to vth.
The time required for the transmittance to change by
The time it takes to change from 1 to 82% is expressed as Toff in milliseconds. 'r which is the sum of Ton and Toff
(in microseconds) 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 ν(v) is t on n, and the applied voltage is changed from ν to 0.
It is said that the time required for the transmittance to change from 100% to 10 degrees after instantaneous switching to is expressed by the following formula (References: M,
5ehadt, Japan Society for the Promotion of Science Organic Materials for Information Science No. 14
2 Committee A Subcommittee (LCD Group) 11th Study Group Materials
(1978).

ton: η/(6o)#E"-K(-!-)")==
d! ++ η/ (16/ a E”-Kxritof
f=η/K(-!-)' = d"*η/[1" (where η is the bulk viscosity, -0 is the vacuum induction it4°]C
is the anisotropy of the relative permittivity, E is the electric field, and is K11+ KH
The elastic constant term is 32Kxl)/4, d represents the cell thickness, η, Conno and K are specific to the liquid crystal composition)0, so ton and toff are both .

It becomes longer in proportion to d2.

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

On the other hand, the steepness β is determined by the cell thickness d (/=) and the refractive index anisotropy Δ
It has been found that Δnod, which is the product of n, is the smallest (best) when it is around 0.8 to 1.0 (References: Yoshio Yamazaki, Yutaka Takeshita, Mitsuo Nagata, Yukio Miyaji,
Proceedings of the 3rd I
international Display Re5e
arch conf@rence'JAPAN DIS
PLAY '83', 520 pages: 1983, ■5
ID), therefore, when emphasis is placed on contrast, the cell thickness d
It is most advisable to manufacture a liquid crystal display so that Δnod is around α8 to 1.0, and it is considered 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 to which a trace amount of cholesterinic substance was added 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 15C in Tokyo and 220C in Naha.
(Japanese Statistics, edited by the Statistics Bureau of the Prime Minister's Office, 1980 edition 6, 7), assuming the room temperature is 20C, the cell is placed in a constant temperature oven, and the nematic phase is stable at a temperature 30C higher than that. If the nematic phase is stable, it is referred to as high-temperature liquid crystallinity.
c 1iquid) is represented by I. Low-temperature liquid crystallinity is determined when the temperature of the constant temperature chamber in which the cell is installed starts at 20℃ and is lowered by 5C per day, and when it becomes 500 degrees lower than the assumed room temperature of 20℃ (i.e., constant temperature chamber temperature - 1ΩC). ,
Whether the nematic liquid crystal phase is stable or not is referred to as low-temperature liquid crystallinity. It is expressed as

[Examples 1 and 2] Table 1 shows the compositions and properties of Examples 1 and 2 according to the present invention. However, this example is characterized in that the compound B contains a compound represented by the general formula: .

Further, as a conventional example, the composition and characteristics of a liquid crystal composition containing ECH and PE are shown in Table 2.

While the β value representing steepness in Conventional Example-1 is 1.265, the β value in Example-1 is 1.238. Example-2
The β value of is improved to 1.252. That is, in a liquid crystal panel using simple matrix electrodes, in order to make the transmittance less than 10% (dark state) for the selective electrode and more than 90% (portal #I) for the non-selective electrode, K is the conventional example - In Example 1, only 17 or less scanning electrodes can be driven, whereas in Example-1, 23 or more scanning electrodes can be driven, and in Example-2, 24 or more scanning electrodes can be driven.

The optical threshold voltage vth is 2.59V in Conventional Example-1, whereas vtb in Example-1 is 2.38v1, and vth in Example-2 is 2.16V, with considerable distortion. In good condition.

The response speed of Conventional Example-1 is 444 milliseconds, whereas that of Example-1 is 312 milliseconds, and that of Example-2 is 345 milliseconds.

Examples 1 and 2 have high-temperature liquid crystal properties at 50 degrees Celsius and low-temperature liquid crystal properties at -10 degrees Celsius, and are sufficiently stable and have a sufficiently wide nematic liquid crystal temperature range to be used in ordinary displays. ing. More specifically, Example 2 has liquid crystal properties even at a high temperature of 63 degrees Celsius, and can be used for displays under severe conditions.

As mentioned above, although the β value of conventional example -1 is 1.265, it is -17
On the other hand, Example-1 according to the present invention has a good value of 1.258, and Example-2 has a good value of 1.232. Furthermore, the optical threshold voltage is low, the response speed is fast, and the nematic liquid crystal temperature range is refreshingly sufficient.

Table 2 [Effects of the Invention] As described above, according to the present invention, at least a compound represented by the general formula RI +COo-Q-o-a, a compound represented by the general formula R3→h+R4, a compound represented by the general formula - R11
By constructing a nematic liquid crystal composition using a compound represented by -o-000-CF-CN, the nematic liquid crystal composition has the widest temperature range from -10 degrees Celsius to 50 degrees Celsius, and even 63 degrees Celsius on the high temperature side. It was possible to obtain a nematic liquid crystal composition that can be driven, has excellent steepness, has a fast response speed, has a low optical threshold voltage, and has excellent dynamic drive characteristics.

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 a host 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 ray 3...Lens and filter system 4...
Cell 5... Light receiving section (charge multiplier tube). that's all

Claims (1)

[Scope of Claims] Consists of 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. Characteristic 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, R_1 and R_2 have 1 to 10 carbon atoms. Straight chain alkyl groups R_3 and R_4 represent a straight chain alkyl group having 1 to 10 carbon atoms R_5 represents a straight chain alkyl group having 1 to 10 carbon atoms.