JPS6234799B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a liquid crystal composition and a liquid crystal display device using the same, and particularly to a liquid crystal composition and a liquid crystal display device that enable large-capacity display and keyboard support. Conventional Technology and Problems Liquid crystal displays are of a flat, moon-shaped type and have low power consumption, so there are growing expectations for them as displays for office automation and other applications. However, in the TN (twisted nematic) type, which is currently the mainstream liquid crystal display, the rise characteristics of the liquid crystal are not steep, so when trying to display a large-capacity dot matrix, half of the screen is displayed until the point where it does not display (non-display point). state, that is, crosstalk occurs, and large-capacity display is not possible. Furthermore, when trying to display a large capacity with a TN type, the viewing angle is severely restricted, resulting in an extreme drop in contrast. TN like this
Efforts have been made to make up for the shortcomings of the TN type, such as by creating a large matrix, but the TN type cannot overcome the fatal drawback of a large, solid-hand display: the viewing angle narrows as the number of scanning lines increases. In order to overcome the phenomenon of crosstalk in line-sequential scanning, which is inevitable for liquid crystals, storage type liquid crystal displays were devised that do not require refreshing once scanned. In the storage type liquid crystal display, due to the memory effect of the liquid crystal, the written information is stored unchanged even after the voltage is removed by applying a voltage only once. Therefore, since there is no crosstalk that occurs with TN type or DSM (dynamic scattering type), the number of scanning lines can be reduced.
Approximately 500 pieces are possible. However, this storage type liquid crystal display has the disadvantage that contrast cannot be obtained because it performs display using the grunge state and focal conic state, both of which are cholesteric phases. Furthermore, before writing, it is necessary to initialize it as a writing preparation stage.
This takes 500 to 300 milliseconds, so it takes a long time to type in or scroll, making it impossible to use a keyboard. In order to improve these drawbacks of storage type liquid crystal displays, we have developed a positive display refresh storage type liquid crystal display method that utilizes the cholesteric phase (focalconic state) and the nematic phase (homeotropic state) to perform display using polarizing plates. , which the present inventors developed and already disclosed (Japanese Patent Application No. 10147/1982).
In addition to the large-capacity display potential of storage type liquid crystal displays, this method has high contrast and a rewriting speed that enables keyboard compatibility. However, in this positive display refresh accumulation type liquid crystal display method, flickering occurs during refreshing, and there is a problem in actually using it in a keyboard-compatible manner. Therefore, as a result of research aimed at preventing flickering in addition to large-capacity display, high contrast, and high-speed rewriting, the present inventors and others developed an accumulation-type liquid crystal display method using a new driving method. This new liquid crystal display method utilizes the hysteresis of the liquid crystal composition with respect to applied voltage to achieve two optically different stable states at the same holding voltage, namely a focalconic state and a homeotropic state. to maintain display. This method is an extremely useful liquid crystal display method that allows for large-capacity display, high contrast, keyboard support, and no flicker. It is not possible to obtain a stable homeotropic state, and at a holding voltage the homeotropic state is
I could only maintain it for about 20-30 seconds. Purpose of the Invention In view of the problems of the prior art as described above, the purpose of the present invention is to provide a liquid crystal composition that can be used in the new driving liquid crystal display method described above, and to achieve a liquid crystal display that has a large capacity display and is compatible with a keyboard. It is to be. Structure of the Invention In order to achieve the above object, the present invention provides (i) general formula: (wherein R ¹ is a linear alkyl group having 2 to 9 carbon atoms); and 10 to 90 weight percent of a cyanobiphenyl component having the formula (ii): (wherein R ₂ is a butyl group or a pentyl group, and R ³ is a methoxy group, an ethoxy group or a pentoxy group), and a thioester cyclohexane component having the formula (iii) The present invention provides a liquid crystal composition comprising 7 to 30 weight percent of 4-cyano-4'-2-methylbutylbiphenyl, and a storage type liquid crystal display device using the same. Specific Description of the Structure of the Invention First, the driving principle of the storage type liquid crystal display in the present invention will be explained. FIG. 1 shows the relationship between the applied voltage and the change in light transmittance of a cholesteric-nematic mixed liquid crystal. First, a voltage corresponding to, for example, twice the voltage V _H (2V _d ) of the holding voltage V _d is applied between all electrodes of the XY matrix to bring the liquid crystal into the H (homeotropic) state, which is a nematic phase. In the H state, as shown in Figure 2A, all liquid crystal molecules 1 are oriented in the same direction as the electric field, that is, perpendicular to the substrate 2, and the incident light that has passed through the polarizing plate 3 is directed to the next one without changing the polarization angle. The light reaches the polarizing plate 4, but because the polarization angles of the polarizing plates 3 and 4 differ by 90 degrees, the light does not pass through, resulting in a dark state. When the voltage is reduced to zero from this state, the liquid crystal enters the F _p (focalconic) state, which is a cholesteric phase. Once the liquid crystal is in the F _p state, the holding voltage V _d
Even if Fp is applied, optically the F (focalconic) state is the same as F _p . In the F _p and F states, the liquid crystal 1' has a helical structure. The incident light is optically rotated or scattered by this spiral, and a light component that passes through the polarizing plate 4 shown in FIG. 2B is generated, resulting in a bright state.
On the other hand, in the H state, which is the initial state, the applied voltage is 2V _d
Even if the voltage is lowered from (=V _H ) to V _d , the H state can be maintained due to hysteresis. Here, in order to distinguish from the H state where V _H is applied, the H state where V _d is applied is referred to as the H' state. In this way, the storage type liquid crystal can take two optically different states F and H' depending on the history from the H state by applying the same applied voltage _Vd . A storage type liquid crystal display based on a new driving method uses this to fix and drive an image written by V _d . Although this method was thought to be possible in principle in the past, it was not possible in practice.
This is because, in conventional liquid crystal materials, the H state, that is, the H' state, caused by the application of V _d is a metastable state, and even if V _d is applied, the state shifts to the F state after 20 to 30 seconds and becomes a bright state. This is because you get used to it. Therefore, the present inventors improved the liquid crystal material and expanded the voltage hysteresis width ΔV in order to stabilize the H' state (homeotropic state at a holding voltage V _d based on hysteresis with respect to the applied voltage of the storage type liquid crystal). I tried that. As shown in Fig. 1, the voltage hysteresis width ΔV is the amount by which the light transmittance changes when the applied voltage is gradually increased and the liquid crystal transitions from the focal conic state (cholesteric phase) to the homeotropic state (nematic phase).
Light transmittance in homeotropic state (H state)
When the applied voltage is gradually _lowered , the light transmittance increases when the liquid crystal transitions from the homeotropic state to the focal conic state.
It was calculated as the difference in voltage from the voltage V ₂ which is 90%.
By expanding this voltage hysteresis width ΔV to widen the voltage range in which the holding voltage V _d can be set, the holding voltage V _d can be set to a higher voltage than V ₂ . By setting V _d higher than V ₂ , the H′ state is stabilized,
It is possible to prevent the H' state from transitioning to the F state. From this point of view, as a result of attempting to improve liquid crystal materials, the present inventors discovered that the new liquid crystal composition according to the present invention has a wide voltage hysteresis width, making it possible to create a storage type liquid crystal display with a new driving method. Ta. In the liquid crystal composition according to the present invention, the nematic component cyanobiphenyl component is generally 10 to 90% by weight, preferably 30 to 80% by weight, more preferably 40 to 70% by weight, and the nematic component thioester cyclohexane is contained as an essential component in the liquid crystal composition according to the present invention. System components generally 5 to 70% by weight, preferably 5 to 50% by weight,
More preferably 5 to 30% by weight, and generally 7 to 30% by weight, preferably 7 to 20% by weight, more preferably 9 to 20% by weight of 4-cyano-4'-2-methylbutylbiphenyl, which is a chiral nematic component. 16% by weight
include. Since liquid crystal is a liquid, its viscosity and
Dielectric constant etc. change. Normally, when used in an office, it is considered that it is sufficient to be able to drive stably in the range of about 5 to 40 degrees Celsius, but in order to do so, the liquid crystal material must not only have a large ΔV, but also the liquid crystal must have a liquid crystal phase in the above temperature range. and have sufficient response speed. The cyanobiphenyl liquid crystal of the present invention generally has a low mesorange (temperature range showing a liquid crystal phase) and a relatively low transition point from liquid crystal to isotropic liquid (NI point). Therefore, in order to expand the meso range and raise the NI point, we use liquid crystals with a high NI point, for example. etc. need to be mixed. Thus, the cyanobiphenyl component, thioester cyclohexane component, and chiral nematics are each generally
10-90wt%, 5-70wt%, 7-30wt%,
Moreover, 40-70wt% and 9-16wt% are most preferable.
Outside these ranges, for example, if the amount of cyanobiphenyl is too large, the temperature dependence of writing speed, drive voltage, etc. becomes too large. On the other hand, if it is too small, problems such as poor contrast and narrow meso range will occur. Furthermore, if the thioester cyclohexane component is too large, the viscosity of the liquid crystal increases, resulting in disadvantages such as an increase in driving voltage and a decrease in response speed. On the other hand, if it is less, ΔV
The effect of increasing , etc. becomes smaller. Furthermore, in the case of chiral nematics, the helical structure of the storage liquid crystal is greatly affected by the amount of the mixture; if it is too large, the mesorange will be narrow, and if it is too small, ΔV will not be large. In addition, as active ingredients, (1) thioester component Generally 5 to 70% by weight, preferably 5 to 50% by weight, more preferably 10 to 30% by weight, (2) Ester cyclohexane component Generally 5 to 70% by weight, preferably 5 to 50% by weight, more preferably 5 to 30% by weight, (3) Cyanopyrimidine component (wherein R ₄ is a pentyl group or a heptyl group), generally 5 to 60% by weight, preferably 5% by weight, preferably 5% by weight, preferably 5% by weight.
It is preferable to include up to 50% by weight, more preferably 5 to 30% by weight. In addition, as optional components, for example, (4) cyclohexane-based component (In the formula, R ₅ is an ethyl group, propyl group, pentyl group, or heptyl group, and R ₆ is a cyano group.) (5) Azoxy component (In the formula, R ₇ is a methoxy group or an ethyl group,
R ₈ is a butyl group or an ethyl group. ) (6) Cyanoterphenyl components (In the formula, R ₉ is a pentyl group.) or (7) dioxane-based component (In the formula, R ₁₀ is a propyl group, a butyl group, a pentyl group, a hexyl group, or a heptyl group.)
respectively, generally 2 to 40% by weight, preferably 2 to 30% by weight, more preferably 2 to 10% by weight, and (8) cholesteric liquid crystal generally 7 to 30% by weight,
Preferably 7 to 20% by weight, more preferably 9 to 20% by weight
May contain 16% by weight. By appropriately blending these active ingredients or optional ingredients, the operating temperature,
Contrast, drive voltage, writing speed, etc. can be appropriately selected. The operating temperature is 5 to 40°C, the contrast ratio (transmission) is 1:12 or more, and the lower the driving voltage, the better.
These active ingredients are also used to achieve a writing speed of 10ms/line or less. In general, esters (including thioesters) extend the operating temperature and provide faster writing. The pyrimidine type lowers the drive voltage and speeds up writing. Cyclohexane-based products can be used at a wider range of temperatures (especially on the low-temperature side). Azoxy series increase contrast ratio. Terphenyl-based products can be used at a wider range of temperatures (especially on the high-temperature side). Dioxane type lowers the driving voltage. Cholesteric is ΔV
The size of the temperature affects the operating temperature. Examples of the Invention Example 1 A liquid crystal composition A having the following composition was prepared by mixing each component.

【table】

[Table] Transparent electrode (ITO) with 500 scanning lines on a glass substrate
After patterning, clean and treat the surface with oxygen plasma, then apply epoxy adhesive to
A liquid crystal panel with a simple X,Y matrix display was prepared by assembling the sample into a micrometer, and the above liquid crystal composition was sealed therein. In this liquid crystal display device, the transparency of the liquid crystal cell was measured when the applied voltage was gradually increased from a cloudy state, and when the applied voltage was gradually lowered after applying a high voltage to a transparent state. The voltage hysteresis was investigated. Transparency measurement
Using He-Ne laser light as a light source, irradiating the liquid crystal,
Transmitted light is detected by a silicon photocell, and optical changes are converted into electrical changes based on its strength. The results are shown in FIG. Example 2 A liquid crystal composition B having the following composition was prepared.

[Table] Hysteresis was investigated. The results are shown in FIG. Example 3 A conventional cyclohexane-azoxy storage type liquid crystal composition C having the following composition was prepared.

【represent. Example 4 Another conventional cyclohexane-azoxy storage type liquid crystal composition D having the following composition was prepared.

[Table] In the same manner as in Example 1, the voltage hysteresis of the light transmittance of liquid crystal composition D was investigated. The results are shown in FIG. From FIGS. 3 to 6, the voltage hysteresis width ΔV defined previously was determined. The results are as follows. Liquid crystal composition voltage hysteresis width A 3.3V B 3.2V C 0V D 0V Example 5 A simple X, Y matrix display liquid crystal panel with 80 x 120 scanning lines and an effective display area of 60 x 90 mm ² was created in the same manner as in Example 1. The same liquid crystal composition A as in Example 1
was enclosed. This liquid crystal display device was used and driven according to the new driving method described above. Holding voltage V _d
is ±22.5V. Reflection contrast ratio is 1:5
That's all. The contrast did not decrease even after 5 hours. Effects of the Invention As is clear from the above description, the present invention provides a storage type liquid crystal composition with a large voltage hysteresis width, and provides a liquid crystal display device with high display quality, large display capacity, and keyboard compatibility. Ru.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing applied voltage vs. light transmittance change of a cholesteric-nematic mixed liquid crystal, FIG. 2 is a diagram showing liquid crystal molecular alignment, and FIGS. 3 and 4 are diagrams showing liquid crystal compositions of examples of the present invention. FIGS. 5 and 6 are diagrams showing voltage hysteresis of conventional liquid crystal compositions. 1,1'...Liquid crystal molecules, 2...Substrate, 3,4...
...polarizing plate, H, H'... homeotropic state,
F, F _p ...focalconic state, V _d ...holding voltage, ΔV ... voltage hysteresis width.

Claims (1)

[Claims] 1 (i) General formula: (wherein R ¹ is a straight chain alkyl group having 2 to 9 carbon atoms); (ii) 10 to 90 weight percent of a cyanobiphenyl component having the formula: (In the formula, R ² is a butyl group or a pentyl group, and R ³ is a methoxy group, an ethoxy group or a pentoxy group.)
~70 weight percent and (iii) Eq. 7 to 30 weight percent of 4-cyano-4'-2-methylbutylbiphenyl having the following properties. 2. A liquid crystal display device using a storage type liquid crystal composition of cholesteric-nematic phase transition type, which performs display by maintaining two optically different stable states at the same holding voltage based on hysteresis with respect to applied voltage, The liquid crystal composition has (i) general formula: (wherein R ¹ is a linear alkyl group having 2 to 9 carbon atoms); and 10 to 90 weight percent of a cyanobiphenyl component having the formula (ii): (wherein R ² is a butyl group or a pentyl group, and R ³ is a methoxy group, an ethoxy group or a pentoxy group), and a thioester cyclohexane component having the formula (iii) and 7 to 30 weight percent of 4-cyano-4'-2-methylbutylbiphenyl.