JPS62215686A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:A liquid crystal composition for display, which has improved dynamic drive characteristics especially in electric field effect mode and a wide nematic liquid crystal temperature range and is chemically stable, consisting of specific four compounds. CONSTITUTION:The aimed liquid crystal composition consisting of (A) preferably 7-72wt% compound shown by formula I (R1 and R2 are 1-12C straight-chain alkyl), (B) preferably 5-46.5wt% compound shown by formula II (R3 and R4 are 1-10C straight-chain alkyl), (C) preferably 5-38wt% compound shown by formula III (R5 is 1-10C straight-chain alkyl) and (D) preferably 3-30wt% (especially 5-25wt%) compound shown by formula IV (R6 and R7 are 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 the "1-field effect mode."

[Conventional technology]

Conventionally, a nematic liquid crystal composition for a display V device has a general formula R4TOC0O-o-0-R' (R), as disclosed in, for example, Japanese Patent Application Laid-Open No. 54-85694.

Each R' represents a linear alkyl group having an arbitrary number of carbon atoms.
-o-C00 BeniM3N (R' represents a straight-chain alkyl group with an arbitrary number of carbon atoms) is added with Np liquid crystal such as a compound (hereinafter abbreviated as p-z in the text). Lowers the threshold voltage. However, if the amount of Np liquid crystal added increases, the optical properties such as suddenness and susceptibility, which will be described later, will deteriorate, so it is not a good idea to add more Np liquid crystal than necessary. Formula R'#
The clearing point is raised and the liquid crystal temperature range is widened by adding a compound represented by J (R- represents a linear alkyl group having any number of carbon atoms).

(Problems to be Solved by the Invention) The characteristics required of nematic liquid crystal compositions today are: ■ The rise of the voltage-transmittance curve near the optical threshold voltage is @1.+. (Hereinafter, this will be abbreviated as "steepness" in the text.) (2) The response speed of transmittance to changes in pressure is fast (V) The ability to drive in a wide temperature range centered around room temperature, that is, the ability to operate in a wide nematic liquid crystal range. Possibilities ■ Be chemically stable and have moisture and light resistance ■ [There are things like being able to freely select the voltage threshold (or optical threshold voltage).

When a simple matrix display is dynamically driven, the effective voltage applied to the liquid crystal of the selected electrode part or the non-selected electrode part by the vibration circuit is V On and V Of , respectively.
f and the number of scanning electrodes t−n, the ratio V Or
x/V Off is yon/voff=1-Eng-F'T-1) -----
- Song (1) There is a relationship such that as n increases, the ratio ■
On/Voff also decreases.

10,000, a twisted nematic mode liquid crystal cell, which is one type of liquid crystal display, was placed between orthogonal polarizers, and the transmittance t-
By changing the effective voltage applied to the cell 4 by the eyelid driving circuit 6 while observing FM using a multiplier, an effective voltage-relative transmittance curve as shown in FIG. 2 is obtained. The effective voltage at which the transmittance begins to change as the voltage is increased is the optical threshold voltage vth (in this specification, the effective voltage value required to change the transmittance by f10% is defined as vth).

As the voltage is further increased, the transmittance reaches the optical saturation voltage V8A.
℃ (in this specification, the effective voltage value required to change the transmittance by 90%?Vaat), the effective voltage V off applied to the non-selected electrode portion is the optical threshold value. If the voltage is smaller than vth.

That is, Vuff<Vth...
・・・・・・・・・(If it is 21, the transmittance will not change compared to when no voltage is applied and it will not be selected at all.
In the selection electrode section, the effective voltage won applied is equal to the saturation voltage V
If it is larger than 8at, that is, Won≧V sat...
・・・・・・・・・(If it is 31, the transmission drive has changed sufficiently and has been selected. Therefore, if you divide the equation 31 by the equation (2), μ h h do σ)+ffl aJi+?
gσ h za r〆）Sho Sezuhi J 7 ma kashi oath L-[shares]
The difference in transmittance between the selective electrodes is sufficient. Furthermore, equation (1) and (4
) From the formula, V 5atF guest a completed □≦ ・Mountain...(5)
It becomes vth. As the number n of scanning lines increases, the right side becomes smaller and approaches t)1. Therefore, in order to obtain sufficient contrast between the selective electrode and non-selective polarization, Vh/Vt
It is also advantageous for h to be close to 1. That is, the effective voltage in Fig. 2 -
The steeper the slope vq of the relative transmittance curve from the optical threshold direct voltage to the optical saturation voltage, 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, the fA degree dependence can now be easily eliminated by incorporating an #A degree compensation circuit into the driver circuit as ICs have become cheaper.

A problem with the pond is the response speed IW.

Stillness 1. [1Ilf When displaying all images, the response speed is not that slow. However, in applications such as computer terminals and word processors, where images need to be changed frequently, 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-mentioned problems, and its purpose is to improve the steepness of nematic liquid crystal compositions for display devices, to improve the dynamic driving characteristics, and to widen the temperature range of nematic liquid crystals. The object of the present invention is to provide a nematic liquid crystal composition that has a wider operating temperature range and is chemically stable.

[Means for Solving Problem 1] 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, and at least one compound whose general formula is represented by the following C. It is characterized by comprising at least one kind of compound represented by the following and at least one kind of compound represented by the following general formula.

A...R1 needle O-R.

B...R1-0-yl-■-R2 C...R@-, ChiCOObe■-CN D...R6云0-(←◎→トRt However, R8 and R8 have 1 carbon number ~12 straight chain alkyl groups R3 and R4 are straight chain alkyl groups having 1 to 10 carbon atoms R1 are IK chain alkyl groups having 11 to 101 carbon atoms R8 and R1 are +! chain alkyl groups having 1 to 10 carbon atoms represents a group.

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.
Since it is a liquid crystal, the effect is small if the content is less than 7 times.
The higher the value of k, the better.However, since the clearing point is relatively low, if the content of compound A exceeds 72]t%, the clearing point of the nematic liquid crystal composition will also become low, which will narrow the nematic liquid crystal range of the nematic liquid crystal composition. Therefore, it is undesirable. Therefore, the content of compound A is desirably in the range of 7 to 72 layers.

The compound represented by the general formula B (hereinafter abbreviated as compound B in the text) is a Nn compound that is effective for completely 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 liquid crystal, and if it is less than 5% by weight, the effect is small, so the higher the content, the better. But 4
If it exceeds 6.5 weight, the deviation from the eutectic composition will become too large (the result of lowering the freezing point will not be obtained and precipitation will occur at low temperatures, so 5 weight, !1% to 4 & 5 weight weight is desirable).

The compound represented by the general formula C (hereinafter abbreviated as compound C in the text) is an Np liquid crystal, and the optical threshold voltage can be lowered or increased depending on its content. Also,
This is advantageous in increasing the clearing point. However, if the content is too high, the electro-optical properties such as steepness will decrease +4@, 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. become like that.

Therefore, the content of chemical component *B is preferably from 5 weight to 58 Qi.

Compounds represented by the general formula (hereinafter referred to in the text)
(abbreviated as q'sD) is effective in increasing the clearing point of a nematic liquid crystal composition. However, if the weight range is less than 5, the effect is small and the higher the content, the better. However, if it exceeds 50 weights, a smectic phase will appear at low temperatures, which is undesirable. Therefore, the content of the compound is preferably 5 to 50% by weight, more preferably 5 to 25% by weight.

[Implementation row]

EMBODIMENT OF THE INVENTION Below, one invention will be described in detail based on the series of implementations.

The characteristics of the liquid crystal composition were measured as follows.

FIG. 1 shows a measurement system for one-dimensional optical characteristics. The measurement cell 4 is made of a glass substrate with transparent T+FI made of tin oxide or the like by vapor deposition or other operations, and then covered with an organic thin film and subjected to an alignment treatment. The liquid crystal is completely enclosed in a film frame in the dark, and the two glass substrates are fixed facing each other so that the liquid crystal has the desired thickness. Each polarizing plate is pasted with its polarization axis oriented in such a way that the morning light to which no voltage is applied passes through, and the morning light to which a voltage is applied is blocked.

In the text, the distance between the glass substrates (ie, the thickness of the liquid crystal layer) is abbreviated as cell thickness. Nine light rays emitted from the white light source 1 pass through a lens system 5 and enter 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, an alternating rectangular voltage having a frequency of 1 kilohertz and having an arbitrary effective direct voltage is applied to the cell 4 by the rapid-acting circuit 5. FIG. 2 shows an effective cardiac pressure-relative transmittance curve obtained by measuring a liquid crystal cell using the measurement system shown in FIG. Second
In the figure, the transmittance is expressed as the brightest and darkest transmittance in the normal applied voltage range as 100 and 0, respectively, and the applied voltage is gradually increased starting from the voltage at which the transmittance is 100. The optical threshold voltage is the effective value voltage when the transmittance changes by 10%, or the optical threshold voltage is the effective value voltage when the applied voltage is further increased and the transmittance changes by 90% from 100mm. At this time, the rise of the effective voltage-relative transmittance curve near the optical threshold voltage (°, that is, the steepness) is defined as β1 in the following equation.

sat β=□ vth The effective value voltage (denoted as Von) when turned on (when selected in the matrix cell) is equal to V sat.

Effective voltage when not lit (not selected) (expressed in vOf)
When electricity g1 equal to Vth K is applied, the transmittance becomes 90% and 10 width, respectively, and one pixel is recognized as being lit or not being lit. Furthermore, if Ton is a little thicker than V sat (and Voff is vth, which is a little smaller than 6), the respective transmittances will be 90 or more and 10 or less.In this case, Won/Voff > Vliat/Vth = β. On the contrary, van is smaller than Vsat.

If VOf'f is larger than vth, each transmittance is 90
The visibility of children below 10 years of age and above 10 years is poor.

That is, Won/Voff<V13at, /'Vth=
When a signal voltage β is applied, visibility becomes poor. In this way, the β value is the effective voltage ratio von
/'Tl0f! The smaller the β value, the better the visibility of the pixel display, and the smaller the β value is, the more the Ton
/V, off ratio can also be small. In a simple matrix display, as the total number of scanning lines increases, '10n/Voff decreases, and the β value also needs to be small (approaching 1).

Since the β value indicates the minimum allowable value of VOn/Voff, it serves as an index of multiplex characteristics.

The response speed to changes in applied voltage is as follows: When the effective value voltage of Ω is instantaneously switched from Vth to Veat, the difference in transmittance for each effective value voltage in a steady state is 90#I. The time required for the transmittance to change by 1 (i.e., the time required for the transmittance to change from 90% to 18%) is expressed as Ton in milliseconds, and similarly vs.
When the effective value voltage is instantaneously switched from at to vth, the difference in transmittance for each effective voltage in a steady state is 9.
The time required for the transmittance to change by 0 (when the transmittance is 1)
The time required to change from 0 to 82 excellent) is expressed as T Off in units of t milliseconds. T (in milliseconds), which is the sum of Ton and Toff, is used as an index of response speed.

In general, the applied voltage 'fr: any voltage ν (V) from 0
The time fton required for the transmittance to change from 00 to 90 after instantaneously switching from ν to 0 is the time required for the transmittance to change from 100% to 1011 after instantaneously switching the applied voltage from ν to 0. It is known that the time required for Research group materials 1978).

ton = v/(ε0ΔεK”−K(7)”)=4
1・η/(ε.ΔεIt − πst Off ”Ma/
K(τ)2 = d”・ma/π2 (where η is the bulk viscosity, ε0 is the vacuum dielectric constant, lε is the anisotropy of the relative -11 index, is the electric field, and K is K. -2
Ktt)/' is the elastic constant term, each represents the cell thickness (%), Δε and K are specific to the liquid crystal composition), so ton, t, and off are both (L"&C become proportionally longer). .

The response speed T defined in this example is also closely related to the cell thickness, and qualitatively speaking, if the cell thickness is thin, T will be short (
, found that the longer the cell thickness is, the longer the cell thickness becomes. 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 is made thinner.

On the other hand, the steepness β is obtained when Δn-d, which is the product of the cell Ilj d (μ) and the refractive index anisotropy Δn, is around CL8 to 1.0.
It has been found that the smallest (best) result (References: Yoshio Yamazaki, Yutaka Takeshita, Mitsuo Nagata, Yukio Miyaji, P.
roceedinqs of the 5th grade
rnattonaIDisplay Re5earch
Oonforce 'JAPAN DI8PIaA
Y'86", p. 520: 1985, from ■S). Therefore, when emphasis is placed on contrast, @r, cell thickness ctyΔn
It is believed that it is most advantageous to make a liquid crystal display so that -a is around [18 to 1.0, and it is most appropriate to compare the steepness of liquid crystal compositions using this cell thickness. It will be done. As mentioned above, the response time is also related to the cell thickness, so it is necessary to measure at an appropriate thickness in order to compare the response Ivl of liquid crystal compositions.

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

The measurement temperature was 20 degrees Celsius in all cases.

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

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 Naha.
(a) compiled by the Rifu Statistics Bureau, "Japanese Statistics", 1980 edition, p. 6.7), the cell was installed in a thermostat in room rJA1, assuming the temperature to be 20°C, and the temperature was 60°C higher than that (in Ml). Whether the nematic phase is stable or not is referred to as total high-temperature liquid crystallinity.If the nematic phase is stable, it is marked as an isotropic liquid
ropic 1iqu1a) is represented by I. Low-temperature liquid crystallinity is achieved by using a constant temperature bath in which the cell is installed! [Starting from kzo℃1
When the temperature is lowered by 5℃ per day, when the room temperature is 50℃ lower than the assumed room temperature of 20℃ (i.e., the thermostatic chamber temperature -1
0°C) Whether or not the nematic liquid crystal phase is stable is referred to as low-temperature liquid crystallinity. If the nematic liquid crystal phase is stable, mark it with ○, if it is smectic liquid crystal phase, mark Sm'ft, and if it is in a solid state or has precipitation, × It is represented by a mark.

[Execution row-1] The composition and properties of implementation row-1 according to the present invention are shown in Table 1. However, this example row is a chemical compound B with the general formula R3-OA human R4 (wherein R4 and R1 are carbon It is characterized by containing all the compounds represented by (1 to 10 linear alkyl groups).

Further, Table 2 shows the composition and properties of a liquid crystal composition containing ECH and P-11i as a conventional liquid crystal composition.

Steepness with conventional Vly-1? The β value expressed is 1.265, whereas the β value of Example 9'1J-1 is 1.221, which is good. That is, in a liquid crystal panel using a single simple matrix pole, the transmittance can be reduced to 10% or less (dark state) using selective electrodes.
In order to achieve 90% or more (bright state) at the non-selection 1 pole, in the conventional fj+j-t, the number of scanning t+= can be driven only 17 or less, whereas in Example-1, the number of scanning t+= can be driven at 26 or more. jlA can be ordered.

Optical threshold voltage Vth? i, conventional example-1 is 2.59
In contrast, vth in Example-1 is λ51V, which is somewhat lower.

Furthermore, the response speed of the conventional train-1 is 444 < 17 seconds, whereas the response speed of the implementation train-1 is significantly faster, 168 < 17 seconds.

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.
Nematic liquid crystal is wide enough to be used as a normal display.
It has a degree range. Furthermore.

Specifically, it has liquid crystal properties even at a high temperature of 65 degrees Celsius and a low temperature of -20 degrees Celsius, and can be used for displays even under severe conditions.

As described above, the implementation row-1 according to the present invention has a somewhat lower optical threshold voltage vth than the conventional Shio l1-1, and β
The value has been greatly improved. Furthermore, the response speed is quite fast and the nematic liquid crystal TJA degree range is sufficiently wide.

Table 1 Table 2 [Effects of the Invention] As described above, according to the present invention, at least a compound represented by the general formula R3-@-+o-R, a compound of the general formula R$
Compound represented by -0-'I'→-R2, general formula island-
o-t: o o By constructing a nematic liquid crystal composition using a compound represented by CN and a compound represented by the general formula R6-R7, the nematic liquid crystal temperature range is -20 degrees Celsius. to 65 degrees Celsius, excellent steepness, and fast response speed.

Furthermore, a nematic liquid crystal composition having a low optical threshold voltage and excellent dynamic drive characteristics can be obtained.

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 the drawing] Blasphemy 1) 12I! 1st place, 1f, 1st place, 1192 imazuri
Fig. 2 is a curve diagram showing changes in relative transmittance-effective voltage generally obtained using the measuring device #. 1...Light source 2...Light beam 5...Lens and filter system 4...-Cell 5...Light receiving section (photocell doubler)

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...▲Mathematical formulas, chemical formulas , tables, etc. ▼ However, R_1 and R_2 are straight chain alkyl groups having 1 to 12 carbon atoms R_3 and R_4 are straight chain alkyl groups having 1 to 10 carbon atoms R_5 is a straight chain alkyl group having 1 to 10 carbon atoms Groups R_6 and R_7 represent straight-chain alkyl groups having 1 to 10 carbon atoms.