JPS62184089A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To lower an optical threshold voltage, improve steepness and, at the same time, increase the speed of response of transmission to the change in voltage, by forming a liquid crystal compsn. through a combination of any of four particular components. CONSTITUTION:A liq. crystal compsn. comprising at least one member selected from among compds. (A) of formula I, at least one member selected from among compds. (B) of formula II, at least one member selected from among compds. (C) of formula III, and at least one member selected from among compds. (C) of formula IV. In the above formulae, R1 and R2 are each a 1-12C straight- chain alkyl group; R3 is a 1-8C straight-chain alkyl group; R4 and R5 are each a 1-12C straight-chain alkyl group; and R6 is a 1-10C straight-chain alkyl group. It is pref. that the components A, B, C, and D be blended in proportions of 7-72wt%, 5-38wt%, 2-80wt%, and 5-30wt%, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal composition for display devices, 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
-0-o-0-R2, general formula R3-
Compound represented by 0-4pe←CN, general formula a 4
-Q-@-0-Rs Compound represented by general formula R
By using a 6-o-000-o-C'N compound, the optical threshold voltage is lowered, the steepness is improved, and the response speed is decreased. ] Conventionally, nematic liquid crystal compositions for display devices have been prepared using the general formula R+COO-@-0-R' (where RB1 is a straight line with an arbitrary number of carbon atoms), as disclosed in, for example, Japanese Unexamined Patent Publication No. 64-85694. Based on Nn liquid crystals such as compounds represented by a chain alkyl group (hereinafter abbreviated as meH in the text), the general formula R''-o-000-
By adding Np liquid crystal such as a compound represented by o-CN (R' represents a linear alkyl group having an arbitrary number of carbon atoms) (hereinafter abbreviated as P-11i in the text), the optical threshold voltage decreases. however,)! It is not a good idea to add more Np liquid crystal than necessary because as the number of P liquid crystals added increases, the electro-optical properties such as steepness, which will be described later, deteriorate. Furthermore, in addition to the above Nn liquid crystal and Np liquid crystal, the general formula R'''Ichiban Yabei
By adding a compound represented by cy (R/FF represents a linear alkyl group having an arbitrary number of carbon atoms), the clearing point is raised and the liquid crystal temperature range is widened.

[Problem that the invention seeks to solve]

Today, the characteristics required for nematic liquid crystal compositions are: 1. 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, the effective voltage applied by the drive circuit to the liquid crystal of the selected tli right part or the non-selected electrode part is set to VOn and VOff, respectively, and the number of scanning electrodes is set as arithmetic. Bahi'V On /
V Off is Von/Voff = 77 (JT-1 block...(1)
There is a relationship such that as n increases, the ratio VomVof
f also becomes smaller.

On the other hand, a twisted nematic mode liquid crystal cell, which is one type of liquid crystal display device, was placed between orthogonal polarizers, and the transmittance of the cell 4 was measured by photoelectric multiplication using the electro-optical characteristic measuring device shown in FIG. By changing the effective voltage applied to the cell 4 by the drive circuit 6 while observing with a tube, an effective relaxation pressure-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 10% is defined as vth). ), and as the voltage is further increased, the transmittance becomes the optical saturation voltage (vaatC, in this specification, the effective voltage value required to change the transmittance by 90% is Vgat), then the non-selective electrode In the section, the applied effective voltage v /-14Pr -hi 4
- a fir I -dk ikinuti 11j, FF V
If it is smaller than t h, that is, Voff≦v th ・−・−(2), the transmittance does not change compared to when no voltage is applied and is not selected at all, and no voltage is applied at the selection electrode section. If the effective voltage VOn is larger than the saturation voltage Vsat, that is, VOn≧V sat (8), the transmittance changes sufficiently and the selection has been made.
), □≧□ (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 consists of equations (1) and (4). As the number n 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, Vaat/Vth
The closer to 1, the more advantageous. In other words, the steeper the slope of the effective voltage-relative transmittance curve of the second fiA from the optical threshold voltage to the optical saturation voltage, the more the number of scanning lines can be increased while keeping the contrast constant (or improving it). can. The above is the reason why condition (2) is necessary. However, conventionally, emphasis has been placed on eliminating temperature dependence in electro-optic characteristics, and thus no concrete measures have been proposed to improve condition (2) itself, which is a problem. On the other hand, the temperature dependence is IC
Now that it has become cheaper, it has become possible to easily remove it by incorporating it into a temperature compensation circuit.

Another problem is response speed.

When displaying still images, the response speed is not so consistent. However, in cases where images need to be changed frequently, such as in combination terminals and word processors, high-speed responsiveness is required. Needless to say, even more responsiveness 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. It is possible to expand the scope and provide more chemically stable nematic liquid crystal compositions.

[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 formula A, at least one compound whose general formula is represented by the following formula B, at least one compound whose general formula is represented by the following formula C, and the general formula is characterized by comprising at least one of the compounds shown below.

A ・----Rx-8-@-0-R2B・・・・・・
-Rm→T÷-@-ON C・-----R4-9-@-0-R1iD......R
R6-o-C00-o-C However, R8 and R8 are straight chain alkyl groups R having 1 to 12 carbon atoms, and R4 and R are straight chain alkyl groups having 1 to 8 carbon atoms. The straight chain alkyl group R6 represents a straight chain alkyl group having 1 to 10 carbon atoms.

The compound represented by the general formula A (hereinafter abbreviated as compound A in the text) is an effective Nn compound for increasing the response speed.
Since 7i is a liquid crystal, if it is less than 11%, the effect is small, so the higher the content, the better. However, because the clearing point is relatively low, compound A
If the content exceeds 72%, the clearing point of the nematic liquid crystal composition will be lowered, and the nematic liquid crystal range of the nematic liquid crystal composition will be narrowed, which is not preferable. Therefore, the content of compound A is preferably 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 of M is too large, the performance of electro-optical properties such as steepness will deteriorate, and eutectic! J(r!? -A, 11l-17Npsi-A(+-k/fpc) effect is not obtained and it precipitates at low temperature.

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

The compound represented by the general formula C (hereinafter abbreviated as compound C in the text) is added to a conventional nematic liquid crystal composition consisting of a simple Nn liquid crystal and an Np liquid crystal to improve the steepness and the nematic liquid crystal temperature. It is used to widen the range, and if it is less than 2 wt%, it will not be effective, so the higher the content, the better. However, if it exceeds sowt%, 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.
0 tile outside is preferable.

The compound represented by the general formula (hereinafter abbreviated as "compound" in the text) is an Np liquid crystal, and depending on its content, the optical threshold voltage can be lowered or increased. If the optical threshold voltage is low, the maximum rated output voltage of the liquid crystal driving circuit will be proportionally low, which is advantageous because inexpensive engineering C can be used, but the liquid crystal content in P- will be too large. It is better not to add too much of this material, as this may cause undesirable effects such as deterioration of electro-optical properties such as steepness, lowering of the clearing point, and narrowing of the liquid crystal temperature range. That is, 5-fold R% to 30-fold R% is desirable, more preferably 8-fold R%! 1% to 22.5%.

〔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 the measurement system for the 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, and further includes a transparent electrode made of tin oxide.
Two sheets of the glass were covered with a film and subjected to alignment treatment, and a nylon film frame that also served as a spacer was sandwiched between them so that the liquid crystal layer would have the desired thickness when the liquid crystal was sealed. The substrates are fixed facing each other, and there is one polarizing plate on each side of the cell, and the polarization axis is set so that light passes through when no voltage is applied and is blocked when voltage is applied. Adjust the orientation and paste. 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 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 an arbitrary effective value voltage and a frequency ii1.1 K4.hertz is applied to the cell 4 by the driving circuit i&255. Diagram i2 is 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 is the brightest and the lowest 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.If the applied voltage is further increased, the transmittance is The effective value voltage when the voltage changes from 100% to 90% 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 by β in the following equation.
Defined as a value.

VSat! ” vth The effective value voltage (expressed as VOn) when the light is on (when selected in the matrix cell) is equal to 'Vaat&:, and the effective voltage when the light is not on (when not selected) (V o f f and 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.Moreover, VOn
If 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, V On / V Of f ) V E
l a t/Vth==β. On the contrary, VOn
If 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 of
When a signal voltage of f(V sat/Vth==β is applied, visibility deteriorates. In this way, if the β value is smaller than the effective voltage ratio of the electric signal V On / V Off f, visibility becomes poor. The smaller the rβ value of the IN 5k W display-h1μ name-surface 11 tears II landscape mixture, the more VOn/VOf
The f ratio can also be made small. In a simple 9x 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 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 value voltage is instantaneously switched from vth to vaat, the time required for the transmittance to change by 90% of the difference between the transmittances for each effective value voltage of 5 in a steady state (i.e., the transmittance The time required for the value to change from 90% to 18% is expressed as Ton in milliseconds, and similarly, Va
When the effective value voltage is instantaneously switched from at 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 from 10% to The time required for the change to 82%) is expressed as Toff in milliseconds. T (in milliseconds), which is the sum of Ton and Toff, is used as an index of response speed.

In general, 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 (1) is ton, and when the applied voltage is instantaneously changed from ν to 0, the time required for the transmittance to change from 0 to 90% is ton. After changing the transmittance from 100% to 1
It is known that if the time required for the hair to change by 0% is toff, it can be expressed by the following formula (References: M,
5chadt, Japan Society for the Promotion of Science Organic Materials for Information Science No. 1
42 Committee A Division Gold (Liquid Crystal Group) No. 11 @Study Group Materials 1978).

ton=η/(goΔtW”−K(7)!)=d!
mη/(ε0Δ#E! Kπ3)toff=η/K(
7)" = d2・η/Xπ2 (where η is the bulk viscosity, co is the vacuum permittivity, Δe is the anisotropy of the relative permittivity, E is the electric field, and K is the 1+Kss
2 K2t )/4, d each represents the cell thickness, η, Δe and X are specific to the liquid crystal composition). Therefore, both ton and toff are d! becomes longer in proportion to

The response speed T determined in this example also has a close relationship with the cell thickness, and although qualitatively, it was found that the thinner the cell, the shorter the T, and the thicker the cell, the longer the T. 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, it has been found that the steepness β is the smallest (best) when Δnad, which is the product of the cell thickness d (μ) and the refractive index anisotropy Δn, is around α8 to 1.Q ( References: Yoshio Yamazaki, Yutaka Takeshita, Mitsuo Nagata, Yukio Miyaji, pro
ceedinga of the 3rl engineer
national display research
Conforce', rAPjVDI8PLA
Y'83', 320 pages: 1983, ■5ID)
.

Therefore, when emphasis is placed on contrast, the cell thickness d should be set to Δno
It is most advisable to manufacture a liquid crystal display so that d 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, a nematic liquid crystal composition of the present invention to which a cholesterinic substance was added in an amount of ff 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 Naha.
(Japanese Statistics, compiled by the Statistics Bureau of the Prime Minister's Office, 1980 edition, p. 6.7), assuming that the room temperature is 20°C, the ce/p is placed in a thermostatic chamber, and the nematic cell is heated to a temperature 30°C higher than that. Whether the phase is stable or not is referred to as high-temperature liquid crystallinity.If the nematic phase is stable, it is marked O, and it is an isotropic liquid (1sotrop
ic 1iq1d) When the temperature of the oak was started from 20℃ and was lowered by 5℃ per day, when it became 30℃ lower than the assumed room temperature of 20℃ (i.e., a constant temperature bath! A degree - 10"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 an ○, if it is a smectic liquid crystal phase, mark it with sm, and if it is in a solid state or if precipitation occurs, mark it with an x. It is expressed as follows.

[Example-1] Table 1 shows the composition and properties of Example-1 according to the present invention. However, in this example, as compound B, general 2R3-o-@
-@-ca C formula 1'l'l R3 represents a straight alkyl group having 1 to 8 carbon atoms) and compound C and shite general 2 R4-Q-o-0-as C formula t4
zR4 and R5 represent straight chain alkyl groups having 1 to 12 carbon atoms) 6 In addition, as a conventional example, a liquid crystal composition containing EOH and P-E The composition and properties of the product are shown in Table 2. Conventional Example-1 has a β value representing steepness of 1.265, while Example-1 has a very good β value of 1.208. In other words, in a liquid crystal panel using a simple matrix voltage, the transmittance is set to 10% or less (dark state) for selective electrodes and 9% for non-selective electrodes.
In order to achieve 0% or more (bright state), conventional example-1 can drive only 17 or less scanning electrodes, whereas embodiment-1 can drive 29 or more scanning electrodes.

The optical threshold voltage vth is also 2.59V in Conventional Example-1, whereas vth in Example-1 is significantly lower to 1.98V.

Furthermore, the response speed of Conventional Example-1 is aaazv seconds, whereas Example-1 is considerably faster at 210 milliseconds.

Example-1 has high-temperature liquid crystallinity at 50 degrees Celsius and low-temperature liquid crystallinity at -10 degrees Celsius, and is sufficiently stable, and has a sufficiently wide nematic liquid crystal temperature range for use in ordinary displays. There is. Furthermore, in detail, on the high temperature side, the temperature is 5 degrees Celsius.
It has liquid crystal properties even at 8 degrees, and can be used for displays even under severe conditions.

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 greatly improved. Furthermore, the response speed is fast and the nematic liquid crystal temperature 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 R1-@-@-0-R2, a compound represented by the general formula R3-←4-@-ON By constructing a nematic liquid crystal composition using a compound represented by the general formula Ra -Q(o) O-R5, and a compound represented by the general formula R6+OOO+ON, the nematic liquid crystal temperature range can be reduced by -10 degrees Celsius. to 58 degrees Celsius,
It is possible to obtain a nematic liquid crystal composition that has excellent steepness, fast response speed, low optical threshold voltage, and 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 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 diagram showing the change in relative transmittance versus effective voltage generally obtained using the measuring device. J. 1...Light source 2...Light ray 3...Lens and filter system 4...Set
5... Light receiving section (photomultiplier tube) Above

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・・・・・・▲ Numerical formulas, chemical formulas, tables, etc. and R_5 represents a straight chain alkyl group having 1 to 12 carbon atoms, and R_6 represents a straight chain alkyl group having 1 to 10 carbon atoms.)