JPS62100583A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To provide a nematic liquid crystal composition composed of specific four kinds of compounds, drivable over a wide temperature range and having steep rise, quick response, moderate optical threshold voltage and good dynamic driving characteristics. CONSTITUTION:The objective liquid crystal composition is composed of (A) the compound of formula I (R1 and R2 are 1-12C straight-chain alkyl), (B) the compound of formula II (R3 is 1-12C straight-chain alkyl; R4 is 1-10C straight-chain alkoxy or alkyl), (C) the compound of formula III (R5 is 1-10C straight-chain alkyl) and (D) the compound of formula IV (R6 and R7 are 1-10C straight-chain alkyl). The amounts of the components A-D are preferably 7-62(wt)%, 2-80%, 5-30% and 3-30%, respectively.

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 having at least the general formula R1
→Compound represented by H-OR2, general formula R31H-R4, general formula R5-o-C0O-o
By using a compound represented by -CN1 and the general formula Ra-@-HtR,t, the steepness is excellent.

[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. 3694, etc., the general formula R+
Based on Nn liquid crystals such as the compound represented by COO-■-〇-R' (R and R' each represent a linear alkyl group with an arbitrary number of carbon atoms) (hereinafter abbreviated as ECH in the text). Then, the general formula R′→Σ−COO+CN(R“
represents a straight-chain alkyl group with any number of carbon atoms (hereinafter abbreviated as P-E in the text).
P liquid crystal 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 of nematic liquid crystal compositions today are: (1) The rise of the voltage-transmittance curve near the optical threshold voltage is steep (hereinafter referred to as (abbreviated as "steepness" in the text) ■ Fast response speed in transmittance to changes in voltage ■ Capable of driving in a wide temperature range centered around room temperature
In other words, it must have a wide nematic liquid crystal range, ■ It must be chemically stable and have excellent moisture resistance and light control properties, and ■ The driving voltage (currently the optical threshold voltage) can be freely selected.

When a simple matrix display is dynamically driven, the effective voltages applied to the liquid crystal of the selected electrode part or the non-selected electrode part by the driving circuit are Vo n and Vo f , respectively.
f and the number of scanning electrodes is n, the ratio Von
/Voff is Vo n/Vof f = A foot 1-i) wa (-,
There is the following relationship: r=-1) -11), and as n increases, the ratio V on/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, 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 to Vsat (in this specification, the effective voltage value required to change the transmittance by 10% is vth). (in this case, 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 v
If it is smaller than th, that is, V o f f <V th
--If (2), the transmittance does not change compared to when no voltage is applied and is not selected at all, and the effective voltage Von applied at the selection electrode section is the saturation voltage Vsa.
If it is larger than t, that is, Van≧v s a t ・=
- If it is (3), the transmittance has changed sufficiently and it has been selected.Therefore, dividing equation (6) by equation (2) gives Von, Vsat, and when this relational expression holds, it is selected as a non-selected electrode. The difference in transmittance of the electrodes is sufficient. Furthermore, it consists of equations (1) and (4). As the number n of scanning lines increases, the right side becomes smaller and approaches 1. In order to obtain sufficient contrast between the selected electrode and the non-selected electrode, Vsat/Vth must also be 1.
It is advantageous to be closer to . 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 removed by incorporating a temperature compensation circuit into the drive circuit as C has become less expensive.Another problem is the response speed.

When displaying still images, response speed is not so important, but when images need to be changed frequently, such as in computer terminals and word processors, high-speed response 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 a nematic liquid crystal composition for display positions, 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 solving problems]

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

A...Rl +Q-0-R2 R--R3-9-Q-R4 C--Rs@-COO-<G-CN ■] ...... R5-40-〇-( )~@-RF However, Ro and R2 are straight chain argyl groups having 1 to 12 carbon atoms.

R3 is a straight chain argyl group having 1 to 12 carbon atoms.

R and 4 are linear alkoxyalkyl groups having 1 to 10 carbon atoms.

R5 is a straight chain alkyl group having 1 to 10 carbon atoms.

R6 and R7 represent a straight chain argyl group having 1 to 10 carbon atoms.

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, because the clearing point is relatively low, the content is 6.
If it exceeds 2% by weight, it is not preferable because it narrows the nematic liquid crystal range.

Therefore, the content of compound A is preferably 7 to 62% by weight.

The compound represented by general formula B (hereinafter abbreviated as compound B in the text) is used to enhance steepness and speed up response speed, and its content ranges from 2% to 80% by weight. is desirable.

The compound represented by the general formula (hereinafter abbreviated as compound C in the text) is an Np liquid crystal, and depending on its content, the optical threshold voltage can be made low or high. If the optical threshold voltage is low, the maximum rated output voltage of the liquid crystal driving circuit can be correspondingly low, which is advantageous because inexpensive ICs can be used. However, if the content of P-E liquid crystal is too large, the electro-optical properties will deteriorate and the liquid crystal temperature range will be narrowed, so that the content is preferably 5% by weight to 30% by weight.

The compound represented by the general formula (hereinafter abbreviated as "compound" in the text) is effective in increasing the clearing point of a nematic liquid crystal composition. If it is less than 5% by weight, the effect is small;
The higher the content, the better. However, if it exceeds 30% by weight, it exhibits a smectic phase at low temperatures, which is not preferable. Therefore, 3% to 30% by weight is desirable.

〔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 is made of a nylon film that also serves as a spacer by breaking a transparent electrode made of tin oxide or other material on one side of a glass substrate by vapor deposition, then covering that surface with an organic thin film, and subjecting it to alignment treatment. 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 between them, and one polarized light plate is placed on each side of the cell. The direction of the polarization axis is adjusted and pasted so that light passes through the plate when no voltage is applied, and light is blocked when voltage is applied.

In this paper, the distance between the glass substrates (i.e., the thickness of the liquid crystal layer) is abbreviated as the 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 perpendicular direction, and the intensity of the transmitted light is measured by a detector provided at the rear. At this time, an alternating rectangular voltage having a frequency of 1 kilohertz and having an arbitrary effective value voltage is applied to the cell 4 by the driving circuit 5. 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 100% and 0%, respectively, when it becomes brightest and when it becomes darkest in the normal applied voltage range.
The applied voltage is gradually increased starting from the voltage at which the transmittance is 100%, and the effective value voltage when the transmittance changes by 10% is the optical threshold voltage vth.Also, when the applied voltage is further increased, the transmittance is 100%. The effective value voltage when the voltage changes by 90% from the time of % is defined as the optical saturation voltage Vsat.

At this time, the rise p (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 vth The effective value voltage (expressed as Von) when turned on (when selected in the matrix cell) is equal to Vsat.

When an electrical signal with an effective value voltage (denoted as Voff) equal to vth when not lit (non-selected) is applied, the transmittance becomes 90% and 10Φ, respectively. The light will be recognized. Furthermore, Van is Vsa
Slightly thicker than t (, if Voff is slightly smaller than vth, each transmittance will be 90% or more and 10% or less. In this case, Vo n /Voff f )Vs s t /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, Von/Voff <Vsat/vth=
When a signal voltage of β is applied, visibility deteriorates. In this way, the β value is the effective voltage ratio of the electrical signal Vo n
/ Vo f f The smaller the β value, the better the visibility of the image display can be obtained, and the smaller the β value, the smaller the Von/Voff ratio will be required to obtain the same image display.

In a simple Mado'Jx display, the larger the number of scanning lines, the more
Since on/Voff becomes small, the β value also needs to be small (close to 1). Since the β value indicates the minimum value of Von/Voff that is allowed, it serves as an index of multiplex characteristics.

The response speed to changes in applied voltage is as follows. When the applied effective 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 (that is, the transmittance The time required to change from 90% to 18% is expressed in Ton in J seconds, and similarly, V s
When the effective value voltage is instantaneously switched from a t to vth, the time required for the transmittance to change by 90% of the difference between the transmittances for each effective voltage in a steady state (the time required for the transmittance to change by 90%) (time required to change from 82% to 82%)
It is expressed as Toff in seconds. The sum of Ton and Toff (T (in microIJ seconds)) 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 υ (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 (References: M, 5
chadt, Japan Society for the Promotion of Science, 142nd Committee on Organic Materials for Information Science, Subcommittee A (Liquid Crystal Group) 11th Research Meeting Materials, 1978).

ton = η/(ε0ΔεE2−K(−)2)=d2・
η/(ε0Δeυ2− to π2)toff−+7/K()
” = d2・η/π2 (where η is the bulk viscosity, ε0 is the vacuum dielectric constant, r!L rate, J
ε is the anisotropy of relative permittivity, EH electric field, K is 21+2
22K22)/4, d each 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 T defined in this example also has a close relationship with the cell thickness, and although qualitatively, it was 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 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 smallest (best) when Δnod, which is the product of the cell thickness d (μ) and the refractive index anisotropy Δn, is around 0.8 to 1.0. (References: Yoshio Yamazaki, Yutaka Takeshita, Mitsuo Nagata, Yukio Miyaji, Proeaad
ings of the 3rd International
ional Display Re5earch”JA
PAN DISPLAY '85'', page 320; 1
983, ■5 ID). Therefore, if contrast is important, it is best to make a liquid crystal display with a cell thickness d such that Δnod is around 0.8 to 1.0, and the steepness of liquid crystal compositions is also compared using this cell thickness. is considered to be the most appropriate. 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 Office Statistics Bureau, Japan Statistics, 1982 edition, p. 6.7), assuming the room temperature is 20℃, the cell is placed in a constant temperature bath, and at a temperature 30℃ higher than that, the nematic phase is formed. Whether or not it is stable is referred to as high-temperature liquid crystallinity.If the nematic phase is stable, it is marked as an isotropic liquid (1sotropic liquid).
eliquid) is expressed in engineering. For low-temperature liquid crystallinity, the temperature of the constant temperature bath in which the cell is installed starts from 20℃ and is increased to 5℃ per day.
When lowering the temperature step by step, the temperature decreased by 3 degrees from the assumed room temperature of 20℃.
Whether or not the nematic liquid crystal phase is stable when the temperature drops by 0℃ (i.e., constant temperature If-10℃) is referred to as low-temperature liquid crystallinity. If precipitation occurs, it is indicated by an X mark.

[Examples 1, 2, and 3] The compositions and properties of Examples 1, 2, and 3 according to the present invention are shown in Tables 1, 2, and 3, respectively. However, in this example, Compound B was selected from the general formula R31HR4 (wherein R3 is a linear alkyl group having 1 to 12 carbon atoms, R4 is a straight chain alkyl group having 1 to 12 carbon atoms,
It is characterized by containing a compound represented by 10 linear alkoxy or alkyl groups.

Further, Table 4 shows the composition and characteristics of a liquid crystal composition containing ECH and PE as a conventional example.

Conventional Example-1 had a β value representing steepness of 1.265, whereas Example-1 had a β value of 1.23, Example-2 had a β value of 1.22, and Example-3. The β value of is 1.24,
Very good. In other words, in order to achieve a transmittance of 10% or less (dark state) for selective electrodes and 90% or more (bright state) for non-selective electrodes in a liquid crystal panel using simple matrix electrodes, in Conventional Example-1, scanning is required. Whereas only 17 or less electrodes can be driven, 25 or more electrodes can be driven in Example-1, 26 or more in Example-2, and 23 or more in Example-6.

The optical threshold voltage was also improved to 2.59V in Example-3, whereas it was 2□59V in the conventional example.

The response speed of Conventional Example-1 is 444 milliseconds, while that of Example-1 is 105. S miIJ seconds, Example-2 was 106.2 milliseconds, and Example-5 was 100.1 milliseconds, both of which were considerably improved.

Examples-1, 2, and 5 all have high-temperature liquid crystallinity at 50 degrees Celsius, and regarding low-temperature liquid crystallinity, Example-1 has a temperature of -20 degrees Celsius, and Example-2 has a temperature of -15gt%. -6, it is sufficiently stable up to minus 40 degrees Celsius, and has a sufficiently wide nematic liquid crystal temperature range for use in ordinary displays. In particular, Example 3 has an extremely wide nematic range from -40 degrees Celsius to 50 degrees Celsius, and therefore can be used as a display material even under fairly severe conditions.

As mentioned above, while the β value of Conventional Example-1 is 1°265, the β value of Example-1 according to the present invention is 1°23, and the β value of Example-1 is 1°265.
The β value of 2 is 1.22, and 1.24 in Example-3,
Both are extremely good, with low optical threshold voltage and fast response speed. Furthermore, the nematic liquid crystal temperature range is also sufficient.

Table 1 Table 3 Table 4 [Effects of the Invention] As described above, according to the present invention, at least a compound represented by the general formula R1→TO-OR2, a compound represented by the general formula R3+
■Compound represented by -R4, general formula Rs -+COO
→>Compounds represented by CN and general formula R64H
By constructing a nematic liquid crystal composition using the compound represented by -@-R7, the widest nematic liquid crystal range can be driven from -40 degrees Celsius to 50 degrees Celsius, and has excellent steepness and fast response speed. A nematic liquid crystal composition with an appropriate optical threshold voltage and excellent dielectric drive characteristics could be obtained.

Use of the nematic liquid crystal composition according to the present invention is highly effective in obtaining excellent display contrast in various display elements.

[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 beam 6...Lens and filter system 4...-Cell 5...Light receiving part (photomultiplier tube) That's it for fish U! Bar ■ Bao Figure 1 Kabuto Mutsutomu FL (v) Laughing effect gLFL-Japanese 1L5. Diagram 2

Claims (1)

[Scope of Claims] 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, at least one compound whose general formula is represented by the following C, and whose general formula is A liquid crystal composition comprising at least one compound represented by D below. 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.▼ D・・・・・・・・・▲There are mathematical formulas, chemical formulas, tables, etc.▼ However, R_1 and R_2 are linear alkyl groups with 1 to 12 carbon atoms, and R_3 is a straight-chain alkyl group with 1 to 12 carbon atoms. A straight chain alkyl group having 1 to 12 carbon atoms, R_4 is a straight chain alkoxy or alkyl group having 1 to 10 carbon atoms, R_5 is a straight chain alkyl group having 1 to 10 carbon atoms, R_6 and R_7 are straight chain alkyl groups having 1 to 10 carbon atoms. represents a straight chain alkyl group.