JPH0136516B2 - - Google Patents

Description

[Detailed description of the invention]

(R, R' are straight chain alkyl groups having 1 to 8 carbon atoms)
It relates to a nematic liquid crystal composition with positive dielectric anisotropy containing the compound () represented by (), and has the characteristic of having excellent multiplexing properties when used in a twisted nematic cell (hereinafter referred to as TN cell). In recent years, the field of application of liquid crystal display devices has been expanding significantly. In particular, dot matrix display cells are beginning to be used in electronic desktop calculators, office equipment, computer terminal display devices, and the like. As a result, the liquid crystal display cell is easier to see,
Additionally, there is a demand for devices with a larger number of display pixels. A dot matrix display is one that displays information such as figures or characters as a collection of dots.
Multiplex driving becomes necessary as the number of display pixels increases. Initially, single-line display cells driven at 1/7 or 1/8 duty were common, but recently there has been a demand for 1/32 duty or 1/64 duty, and the multiplex drive characteristics of TN cells have changed. Improving this has become an important issue. The multiplex drive characteristics of a TN cell are often expressed in terms of drive voltage, voltage margin, response speed, etc., but the voltage margin is the most important characteristic that directly affects display contrast. Voltage margin (M) is a value that expresses how much variation in drive voltage can be tolerated, and it is defined as the lowest voltage (Von) for sufficient lighting with the selected waveform and the highest voltage (Voff) at which crosstalk begins to occur with the half-selected waveform. ) is defined as the ratio of the difference with respect to the drive voltage as shown in the following equation. M≡(Voff−Von)/VD×100(%) (1) VD≡(Von+Voff)/2 (2) The larger the voltage margin, the more the number of scanning lines can be increased, and the better the display contrast. Become. In equations (1) and (2), Von and Voff are applied waveforms,
Since the meaning changes depending on the viewing angle, temperature, or the definition of the lighting state and crosstalk state, the following definitions will be used in the following explanation according to the usual method. First, as is known from the past, TN cells operate according to the effective value of the applied voltage, so even if the duty ratio of the waveform used or the bias changes, it is necessary to It is sufficient to compare different types of waveforms. Therefore, we will compare the voltage margin when using a 1/8 duty 1/4 bias waveform. The viewing angle (θ) is assumed to be in the range of 10° to 40° from the normal direction of the TN cell toward the low visual angle clear vision direction. Further, the temperature is set to 25°C, and Von is defined as the voltage at which the luminance change due to voltage application reaches 50% of its saturation value at θ = 10°, and Voff is defined as crosstalk occurs at 25% at θ = 40°. The voltage margin of a TN cell is affected by the liquid crystal composition used. As a result of investigating various liquid crystal materials, it was discovered that a liquid crystal composition containing the compound () is effective in improving the voltage margin. Table 1 shows the melting points and clearing points of representative examples of compound ().

【table】

[Table] Compounds No. 1 and 2 have poor liquid crystallinity when used alone, but can be used by mixing them with other materials. As a similar compound etc. are known, but all have low clearing points and are problematic in practice. The alkyl chain length of the compound () can be used as long as it is CH ₃ or more, but considering the clearing point, R,
It is desirable that both R' be n-C ₃ H ₇ or more. In addition, if the alkyl chain length is too large, a smectic phase tends to occur, which is a practical problem.
It is desirable that C ₅ H is ₁₁ or less, and R ₁ is preferably n-C ₄ H ₉ or less. On the other hand, compatibility with other liquid crystal materials can be determined using the general formula that has been used frequently in the past. It is inferior to the cyclohexyl carboxylate material represented by As a result, when used in large amounts, the melting point increases and phase separation occurs at low temperatures. Therefore, it is desirable that the content of compound () in the liquid crystal composition be 50% by weight or less. The dielectric anisotropy of compound () is -2 at 25℃
In order to use it in a TN cell, it must be used in conjunction with a liquid crystal that has positive dielectric anisotropy. Examples of compounds with positive dielectric anisotropy (referred to as _Np materials) that are suitable for these purposes are listed below. (R means a straight-chain alkyl group having 1 to 8 carbon atoms, and X means a halogen group such as F, Cl, Br, etc.) A preferable physical property for the _Np material is large dielectric anisotropy. Therefore, it is common to use compounds that have a CN group at the end, and particularly preferred compounds that have a CN group include etc. In addition, although the dielectric anisotropy is not as large as that of the above-mentioned compounds, _Np materials are excellent in terms of compatibility. etc. Further, it can also be used in combination with a material whose dielectric anisotropy is negative or close to zero. The purpose is to match the physical properties of the liquid crystal composition, such as dielectric anisotropy, nematic temperature range, and refractive index anisotropy, to the required specifications. (R, R' are straight chain alkyl groups having 1 to 8 carbon atoms)
etc. are used. Table 2 shows examples of the present invention that have been frequently used in the past.

[Formula] (abbreviated as ECH) is described together with a comparative example. In Table 2, as compound () (Compound No. 4) (Compound No. 5) was used as an equal weight mixture (abbreviated as mixture-1), and as ECH. Using an equal weight mixture of (abbreviated as mixture-2),
As an _Np material

[Formula] (ECN and abbreviation)

【table】

[Table] Considering power consumption, circuit cost, etc., it is desirable for TN cells to be driven at as low a voltage as possible. For example, 1/8 duty is often driven at 4 to 5V. Table 3 provides examples of compositions suitable for that purpose. In Table 3, the following abbreviations are used.

【table】

【table】

Claims (1)

[Claims] 1. General formula A nematic liquid crystal composition with positive dielectric anisotropy containing a compound represented by (In the formula, R and R' are linear alkyl groups having 1 to 8 carbon atoms.) 2 A patent claim characterized in that R has 3 to 5 carbon atoms, and R' has 3 to 4 carbon atoms. Range 1
The nematic liquid crystal composition described in . 3. The nematic liquid crystal composition according to claim 2, wherein the concentration of the compound () is 1 to 50% by weight.