JPH0160076B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a nematic liquid crystal composition, particularly
The present invention relates to a nematic liquid crystal composition having positive dielectric anisotropy suitable for TN (twisted nematic) type display devices and negative display type guest-host type display devices. TN display devices consume very little power, and because they are light-receiving displays, they are easy to read and do not cause fatigue, which are excellent features that other display devices do not have, so they are widely used in products such as wristwatches and calculators. .
All of these use small power sources such as mercury batteries, so in order to ensure long-term use,
In order to reduce the power consumption of the display device as much as possible, it is desirable to lower the driving voltage. Furthermore, from a design point of view, there is a demand for such a display device that has a driving voltage of 1.5 V or less, that is, can be dynamically driven with a single battery. On the other hand, when a chiral substance is added to a nematic liquid crystal with positive dielectric anisotropy to make a chiral nematic liquid crystal, and a dye is added to it, the chiral nematic liquid crystal (cholesteric liquid crystal) changes from a chiral nematic liquid crystal (cholesteric liquid crystal) to a nematic liquid crystal by applying a voltage. It can be used in guest-host type liquid crystal display devices that can display colors through phase transition, and this type of display device has recently been attracting attention because it can display vivid colors without using a polarizing plate. . However, the addition of chiral substances increases the driving voltage, which is a major obstacle in practical use. As a conventional liquid crystal compound with a low threshold voltage, P
-cyanophenyl-P'-alkylbenzoate,
Liquid crystal materials with large dielectric anisotropy such as P-cyanophenylthiol-P'-alkylbenzoate and 5-cyano-2-(4-alkylphenyl)-pyrimidine are known. , and 2-cyano-4-(4'-n-alkylphenyl)furan, 2-cyano-5-(4-n
It was known that it is possible to lower the threshold voltage by adding cyano compounds such as -alkylphenyl)thiophenes to nematic liquid crystal materials. However, if a nematic material having a desired threshold voltage is constructed using only these substances, there are problems such as precipitation of crystals at low temperatures, a marked increase in viscosity, and a marked delay in response. Ta. In view of this situation, the present inventors have arrived at the present invention as a result of various studies in search of a method for lowering the threshold voltage in a display device using a nematic liquid crystal material having positive dielectric anisotropy. That is, the present invention is based on the general formula (In the above formula, n is 0 to 24, and m is 0 or 1) 5-substituted-1,3-dioxa-2-
This is a nematic liquid crystal composition containing 1 to 30% by weight of at least one type of ion. In the present invention, 1,3-dioxa-2- represented by the general formula ()
at least one 5-substituted form of on is used,
The amount thereof is suitably in the range of 1 to 30% by weight of the liquid crystal composition. If the content is less than 1% by weight, the effect of lowering the operating voltage is small, and if the content is more than 30% by weight, the compound does not exhibit a liquid crystal phase, which lowers the upper limit of the operating temperature range of the display cell. In the present invention, the nematic liquid crystal compound or composition used with the compound of formula () is not particularly limited, but the most commonly used representative ones are listed below.

Cyanobiphenyl liquid crystal represented by [Formula] (R is an alkyl group or an alkoxy group, the same applies hereinafter),

PCH represented by [formula] system liquid crystal,

Cyanophenyl ester liquid crystal represented by the formula

Metadioxane liquid crystal represented by [Formula] and

Liquid crystal materials with positive dielectric anisotropy, such as pyrimidine liquid crystals represented by the formula, liquid crystal compositions containing them, and are often mixed with these liquid crystals with positive dielectric anisotropy.

ECH type liquid crystal represented by [Formula],

represented by [formula] Ester liquid crystal,

[Production of 5-pentyl-1,3-diox-2-one (n=5, m=0 in formula ())]

100 g of 2-pentyl-1,3-diol, 105 g of diethyl carbonate, and 0.5 g of sodium metal were placed in a distillation flask and heated, and the resulting ethanol was distilled off while heating until the liquid temperature reached 140°C. After adding toluene to the residue, it was washed with a small amount of water to make it neutral, and after distilling off the toluene, it was heated at 140°C under a reduced pressure of 3 mmHg.
Remove the fraction up to. The residue is viscous and oligomeric or polymeric. By adding sodium ethoxide to make it alkaline and depolymerizing it, distillation under reduced pressure yields the target product, 5-pertyl-
1,3-diox-2-one at 118-126℃/2mm
Obtained as a Hg fraction. This was further redistilled to obtain 65 g of a fraction with a temperature of 120-122°C/2 mmHg. The NMR spectrum and infrared absorption spectrum of this product were not consistent with the structural formula of 5-pertyl-1,3-diox-2-one. The elemental analysis values are as follows, which agree well with the theoretical values. Analysis value Theoretical value (as C ₉ H ₁₆ O ₃ ) C 62.6% 62.76% H 9.5% 9.36% Example 2 [5-(p-propylphenyl)-1,3-diox-2-one (in the formula ()) Production of 2-(p-propylphenyl)-1,3-diol (mp84.4-85.7℃) 50g, diethyl carbonate 61g
and 1 g of sodium ethoxide were placed in a distillation flask and heated, and the resulting ethanol was distilled off while heating until the liquid temperature reached 140°C, and further heated at 140°C for 3 hours. Excess diethyl carbonate was removed by vacuum distillation, and further distillation was performed under reduced pressure of 0.5 mmHg while depolymerizing to obtain a fraction with a bp of 160 to 178°C. Hexane was added and stirred to collect the precipitated crystals, which were then recrystallized from 50 ml of a mixed solvent of heptane:ethanol = 4:1 to yield 25 g of the target product, i.e. 5-
(p-propylphenyl)-1,3-dioxa-2
- Got on. mp is 96.5-97.5℃, its
The NMR spectrum and infrared absorption spectrum were inconsistent with the structural formula of the target product. Moreover, the elemental analysis values are in good agreement with the theoretical values as shown below. Analytical value Theoretical value (as C ₃ H ₁₆ O ₃ ) C 70.4% 70.88% H 7.4% 7.32% Examples 3-6, Comparative Examples 1-3 The N-I point of liquid crystal composition A is 63°C, and for comparison, a liquid crystal composition in which 5% by weight of each of the compound of formula () and a compound conventionally used as a voltage reducing agent was added. We created a device and measured the voltage dependence of the amount of transmitted light in a TN display device obtained using the device. The results are shown in Table 1. In Table 1, V ₁₀ , V ₅₀ , and V ₉₀ indicate the voltages at which the amount of transmitted light reaches 10%, 50%, and 90% of its saturation value, respectively, V ₁₀ is the threshold voltage, and V ₉₀ is the saturation voltage. Also, V ₅₀ /V ₁₀ indicates the degree of steepness in the amount of transmitted light-voltage curve, and the smaller this value is, the higher the degree of steepness is.
This indicates that it is suitable for dynamic driving.

【table】

[Table] As can be seen from Table 1, V ₁₀ was lowered by 0.1 to 0.5 V by adding only 5% by weight of the compound of formula (). As the chain length of the 5-substituent becomes longer, the degree of decrease in threshold voltage, etc. becomes smaller, but it is still comparable to the compounds of comparative examples. In addition, the value of V ₅₀ /V ₁₀ also decreases, and the degree of stimulation increases. Examples 7 to 12 Six types of liquid crystal compositions (mother liquid crystals) other than liquid crystal composition A were added with 5% by weight of 5-propyl-1,3-diox-2-one as a compound of formula (). Example 3 for what not to do
The transmitted light amount-voltage characteristics were measured in the same manner as in 6.
The measurement results are shown in Table 2. What is liquid crystal composition B in Table 2? What is liquid crystal composition C? Liquid crystal composition D is a composition consisting of Liquid crystal composition E is a composition consisting of Liquid crystal composition F is a composition consisting of Liquid crystal composition G is a composition consisting of It is a composition consisting of. Among the above, B to E are △ε
is positive, but in F and G, Δε is close to 0 or has a negative value. Both compounds are representative of liquid crystals currently in practical use.

[Table] From Table 2, it can be seen that V ₁₀ (threshold voltage) can be lowered by adding the compound of formula () to most of the liquid crystals currently in practical use. Even if it is added to a material with negative Δε such as Δε=−1.3), Δε becomes positive and it can be used in a TN device. Example 13 The liquid crystal composition H has an N-I point of 78° C., a threshold voltage V ₁₀ of 1.1V, and a saturation voltage V ₉₀ of 1.5V.
When 4 parts of 1,3-diox-2-one and 2 parts of 5-propyl-1,3-diox-2-one of the formula () are added to this liquid crystal composition H, the N-I point becomes 50
℃, V ₁₀ was 0.78V, and V ₉₀ was 1.13V, both lower. When a TN type display element was made using this composition and dynamically driven at 1/2 duty and 1/2 bias, the operating voltage was 1.5 V and the operating margin at 5 to 35 DEG C. was 2%. Being able to drive dynamically at 1.5V in this way is something that could not be achieved with conventional liquid crystal compositions, and is of great significance. Example 14 Liquid crystal composition J consisting of the following has an N-I point of 69°C, a threshold voltage of 2.0V, and a saturation voltage of 2.9V. In 96 parts of this liquid crystal composition J, 5-propyl-1 of formula (),
When 4 parts of 3-diox-2-one is added, N-I
The temperature at the point was 52.5°C, and the V ₁₀ and V ₉₀ of the TN display element made using this were 1.6 V and 2.1 V, both low. Further, V ₉₀ /V ₁₀ of Composition J was 1.45, while that of the composition containing 5-propyl-1,3-diox-2-one was 1.33, showing a considerable improvement in the steepness. By using such a liquid crystal composition with a high degree of suddenness, a liquid crystal display element with a high duty ratio can be produced. Example 15 The liquid crystal composition K has an N-I point of 75°C, and a V ₁₀ of
2.0V, _V90 is 2.85V and _V90 / _V10 is 1.45. In 97 parts of this liquid crystal composition, 5-methyl-
When 3 parts of 1,3-diox-2-one is added, N
−I point is 62℃, V ₁₀ is 1.6V, V ₉₀ is 2.1V, V ₉₀ /
V ₁₀ was 1.33. In this way, by adding only 3%, V ₁₀ and V ₉₀ were significantly lowered, and the steepness was improved. (For the conventional one, V ₁₀ ,
When V ₉₀ was lowered, V ₉₀ /V ₁₀ tended to increase. )

Claims (1)

[Claims] 1. General formula (In the above formula, n is 0 to 24, m is 0 or 1) 5-substituted-1,3-dioxa-2-
A nematic liquid crystal composition containing 1 to 30% by weight of at least one type of ion.