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| Illumination apparatus |
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Liquid-crystalline dielectric
| Details |
Inventors: Eidenschink, Rudolf; Pohl, Ludwig; Weber, Georg; Del Pino, Fernando;
Assignee: Merck Patent Gesellschaft mit beschrankter Haftung (Darmstadt, DE)
Primary Examiner: Gron; Teddy S.
Assistant Examiner:
Attorney, Agent or Firm: Millen & White
A liquid-crystalline dielectric having a positive dielectric anisotropy comprises a biphenyl derivative of the formula ##STR1## wherein R.sub.1 is alkyl of 1-4 C atoms or alkoxy of 1-3 C atoms, and a phenylcyclohexane derivative of the formula ##STR2## wherein R.sub.2 is alkyl of 1-4 C atoms, in a weight ratio of 3:1 to 1:3. |
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DETAILED DESCRIPTION OF THE INVENTION The reason for this highly advantageous effect is not yet clear.
Possibly, the dispersion forces between the alkyl and alkoxy groups which are linked to aromatic or saturated rings, have the effect of lowering the resistances to the deformation forces acting in different directions so that lower elastic constants result, as compared with the cyanobiphenyls on the one hand and the cyanophenylcyclohexanes on the other hand.
The details of the dielectric of this invention as described above are critical to the attainment of the superior properties of DKA, low threshold voltage, etc.
As an example of this criticality, it is to be noted that U.
S.
Pat.
No.
4,130,502 (Japanese Laid-Open Application No.
53-23,957) describes a liquid-crystalline dielectric (Example 8) which consists of 30 parts by weight of a cyanobiphenyl derivative and 70 parts by weight of a mixture of 3 phenylcyclohexane derivatives; however, this dielectric, only one of the 4 components of which is covered by formula (II), surprisingly does not show the advantageous properties of the dielectric according to this invention.
In particular, that prior art dielectric exhibits a substantially higher threshold voltage of about 3 V, thereby requiring at least a 4.
5 V power source for the operation of liquid-crystal displays containing that prior art dielectric.
The components of the dielectric according to this invention, i.
e.
, the biphenyl derivatives of formula (I) and the phenylcyclohexane derivatives of formula (II), are known from German Offenlegungsschriften Nos.
2,356,085 and 2,636,684, and the mentioned equivalent references.
The disclosures thereof are incorporated by reference herein.
However, as single compounds, they have such unfavorable melting points and clear points--predominantly, they show only a monotropic nematic phase--that they have hitherto not been taken into consideration as base components of liquid-crystalline dielectrics.
In particular, this is because dielectrics having the particularly low threshold voltage of the products according to this invention were not obtained even by a combination with other known liquid-crystalline compounds having more favorable melting points and clear points
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LCD 
