Shown is a liquid crystal composition satisfying at least one of characteristics such as a high maximum temperature, a low minimum temperature, a large elastic constant, a suitable optical anisotropy and a large negative dielectric anisotropy, or has a suitable balance regarding at least two of the characteristics, and an AM device including the composition. The liquid crystal composition may contain a specific compound having a high maximum temperature, a low minimum temperature, a large elastic constant and a large negative dielectric anisotropy as a first component, a specific compound having a high maximum temperature or a small viscosity as a second component, a specific compound having negative dielectric anisotropy as a third component, or a specific compound having a polymerizable group as an additive component.

The present invention relates to a PSA-mode liquid crystal display device including a polymer produced by polymerizing a polymerizable compound by energy ray irradiation in a state in which a mixture of the polymerizable compound and a liquid crystal composition is held between the first substrate and the second substrate, the polymer having a number-average molecular weight of 50,000 or more in terms of polystyrene. In a PSA-mode display device in which alignment of liquid crystal molecules substantially vertically aligned between the substrates is controlled by applying a voltage, a pre-tilt angle can be properly given without being inhibited. Therefore, the present invention provides a PSA-mode display device with good alignment stability, uniform alignment within the substrates, and no or suppressed display defects and a method for producing the same.

The invention relates to a liquid crystal composition, a liquid crystal display element and a liquid crystal display comprising the liquid crystal composition, belonging to the field of liquid crystal display. The liquid crystal composition of the present disclosure comprises a compound represented by formula I and one or more compounds represented by formula II. The liquid crystal composition can increase the dielectric anisotropy and improve the voltage retention rate.

##STR00001##

To provide a liquid crystal display device having excellent liquid crystal vertical alignment properties, good transparency when a voltage is applied and good scattering properties when no voltage is applied, and good adhesion with the liquid crystal layer. The liquid crystal display device has a liquid crystal layer formed by irradiating and curing with ultraviolet rays a liquid crystal composition containing a liquid crystal and a polymerizable compound disposed between a pair of substrates provided with electrodes, and at least one of the substrates is provided with a liquid crystal alignment film to vertically align a liquid crystal. The liquid crystal composition contains a compound represented by the formula [1], and the liquid crystal alignment film is obtained from a liquid crystal alignment treating agent containing a polymer having a side chain structure represented by the following formula [2-1] or formula [2-2], and a side chain structure represented by the following formula [3]:

X.sup.1—X.sup.2—X.sup.3—X.sup.4—X.sup.5—X.sup.6x.sup.7.sub.pX.sup.8   [1]

(X.sup.1: the formula [1-a] to formula [1-g], etc., X.sup.2, X.sup.3, X.sup.4 and X.sup.6: a single bond, etc., X.sup.5 and X.sup.7: a benzene ring, etc., X.sup.8: a C.sub.1-18 alkyl group, etc.),

##STR00001##

(X.sup.A: H, etc., X.sup.B: a benzene ring, etc., X.sup.C: a C.sub.1-18 alkyl group, etc.),

—Y.sup.1—Y.sup.2—Y.sup.3—Y.sup.4Y.sup.5.sub.nY.sup.t   [2-1]

(Y.sup.1, Y.sup.2 and Y.sup.3: a single bond, etc., Y.sup.4 and Y.sup.5: a benzene ring, etc., Y.sup.6: a C.sub.1-18 alkyl group, etc.,

—Y.sup.7—Y.sup.8   [2-2]

(Y.sup.7: a single bond, Y.sup.8: a C.sub.8-22 alkyl group, etc.).

The present invention provides a liquid crystal composition having negative dielectric anisotropy, large refractive index anisotropy, and low viscosity and containing as a first component, one or two or more compounds represented by general formula (I) and, as a second component, one or two or more compounds represented by general formula (II), wherein dielectric anisotropy (Δ∈) at 25° C. is −2.0 or less. Also, provided is a liquid crystal display device having high contrast, fast response, and excellent display quality without causing image sticking and display defects.

A liquid crystal composition, and a liquid crystal display element or liquid crystal display comprising the liquid crystal composition, and belongs to the field of liquid crystal display. The liquid crystal composition comprises a compound represented by formula I, a compound represented by formula II, one or more compounds represented by formula III, and at least one polymerizable compound. The liquid crystal composition has a higher clearing point (CP), a large K value, a suitable optical anisotropy (Δn), and a fast response speed. ##STR00001##

A liquid crystal composition, and a liquid crystal display element or liquid crystal display comprising the liquid crystal composition, and belongs to the field of liquid crystal display, the liquid crystal composition of the present disclosure comprising a compound represented by formula I, one or more compounds represented by formula II, one or more compounds represented by formula III, and at least one polymerizable compound. The liquid crystal composition simultaneously has a low rotary viscosity (γ1), a larger dielectric anisotropy (Δε), and a fast response speed. ##STR00001##

The invention provides a liquid crystal compound satisfying at least one of physical properties such as a high stability to heat or light, a high clearing point (or a high maximum temperature), a low minimum temperature of a liquid crystal phase, a small viscosity, a suitable optical anisotropy, a small dielectric anisotropy, a suitable elastic constant and a good compatibility with other liquid crystal compounds, a liquid crystal composition including this compound, and a liquid crystal display device containing this composition. The invention provdes a compound represented by formula (1):

##STR00001##

where R.sup.1 and R.sup.2 is alkyl having 1 to 20 carbons or the like; one of L.sup.1 and L.sup.2 is both hydrogens, and the other is both fluorines; Z.sup.1 and Z.sup.2 are independently a single bond, —COO—, —OCO—, —OCH.sub.2—, —CH.sub.2O—, —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2CH.sub.2—, —CH═CH—, —C≡C— or the like.

In a process for the purification of a liquid-crystal mixture (7), the liquid-crystal mixture (7) is passed through a first electrodialysis cell (2) and a concentrate solution (14) is passed through a second electrodialysis cell (8) which is adjacent to the first electrodialysis cell (2) and is separated by an ion-exchanger membrane (9), and an electric field transverse to a direction of passage of the liquid-crystal mixture (7) through the first electrodialysis cell (2) is generated with the aid of an anode/cathode arrangement (15, 16) arranged outside the electrodialysis cells (2, 8) so that ionized constituents of the liquid-crystal mixture (7) are discharged at the ion-exchanger membrane (9) and removed from the liquid-crystal mixture (7).

The invention relates to a liquid-crystalline medium, preferably having a nematic phase and negative dielectric anisotropy, which comprises a) one or more compounds of formula I

##STR00001## and b) one or more compounds selected from the group of compounds of the formulae II and III

##STR00002##

in which the parameters have the respective meanings indicated in claim 1, to the use thereof in an electro-optical display, particularly in an active-matrix display based on the VA, ECB, PALC, IPS or FFS effect, to displays of this type which contain a liquid-crystalline medium of this type, and to the use of the compounds of formula I for reduction of the dispersion of the birefringence of a liquid-crystalline medium which comprises one or more compounds of the formulae II and/or III.