Liquid crystal composition

#This invention relates to liquid crystal compositions which are suitable to display elements using nematic liquid crystals having twisted arrangement, among liquid crystal compositions. More particularly, this invention relates to liquid crystal compositions consisting of materials selected from biphenyls and terphenyls having cyano groups in the 4-position; having high stability to water, air, light, heat, etc.; and being capable of holding the nematic structure over a broad temperature range. We had confirmed as the result of investigation that biphenyls having cyano groups in the 4-position are, in general, nematic crystals having stability to water, air, light, heat, etc. However, the liquid crystal compositions formed by optionally mixing these compounds have the drawback that the nematic range is narrow, as evident from referential examples hereinafter described. It goes without saying that the useful temperature range of liquid crystal display elements is preferably broader, but liquid crystal compositions which have a broad nematic temperature range and are stable to water, air, light, heat, etc., as shown later in the specific examples of the present invention, among the nematic liquid crystals having twisted arrangement (so-called twisted nematic display and hereinafter abbreviated as TND), have never been known, and a process for preparing such compositions has been, of course, entirely unknown. For such liquid crystal compositions, it is desirous to hold the nematic structure over the range from -10.degree. C to 60.degree. C, including room temperature, the requisite property for display elements. However, the TND liquid crystals having such a broad nematic temperature range have, in reality, never been known, and the advent of such liquid crystal compositions has been earnestly desired in the art.

#As a result of strenuous research with regard to TND liquid crystals capable of satisfying the above-mentioned desire, we have completed the present invention by finding special and complicated kinds and amounts (mol %) of biphenyls and terphenyls in combination, each having a cyano group in the 4-position as hereinafter described.

#Accordingly it is a first object of the present invention to provide liquid crystal compositions having a broad nematic temperature range including room temperature in the center thereof. It is a second object of the present invention to provide liquid crystal compositions which are stable to water, air, light, heat, etc. It is a third object of the present invention to provide TND compositions having a broadened, practically useful range. It is a fourth object of the present invention to provide a novel application field for biphenyls and terphenyls having a cyano group in the 4-position. Other objects and advantages will be evident from the detailed explanation of the invention hereinafter offered.

#The following referential examples and examples are offered to illustrate the present invention, but they are not intended to limit the scope of the invention.

#The liquid crystal compositions having the compounds shown in Table 1 were tested whereby the lowest limit of nematic temperature range was 0.degree. C (Referential example 2) and the highest limit thereof was 69.degree. C (Referential example 1). In these examples, as a compound corresponding to the compounds of group (1) of the present invention, only one kind of 4-cyano-4"-n-pentylterphenyl was used. As the second compound or compounds to be combined with said compound, 4-cyano-4'-n-pentylbiphenyl or this compound and 4-cyano-4'-n-heptylbiphenyl, both corresponding to the compounds of group (2), were used. With regard to the upper limit of nematic temperature range of the resultant liquid crystal compositions, almost satisfactory numerical values were obtained, but with regard to the lower limit, it was higher than 0.degree. C, i.e. extremely unsatisfactory numerical values were obtained.

#Table 1 ______________________________________ liquid crystal compositions of Referential examples 1 - 2 Referential examples Name of compounds 1 2 ______________________________________ 4-cyano-4'-n-pentylbiphenyl 86.7 52.6 4-cyano-4'-n-heptylbiphenyl 0 35.4 4-cyano-4"-n-pentylterphenyl 13.3 12.0 Total 100.0 100.0 Nematic temperature range lower limit .degree. C 13 - 14 0 upper limit .degree. C 66 - 69 65.5 range .degree. C 53 - 55 65.5 ______________________________________