Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Reexamination Certificate
1998-09-16
2001-08-28
Wu, Shean C. (Department: 1756)
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
C252S299660, C349S002000
Reexamination Certificate
active
06280653
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal composition and a liquid crystal shutter arrangement containing such a composition, for example a liquid crystal display device including a multiplicity of liquid crystal shutters.
Liquid crystal devices including ferroelectric liquid crystal compositions are the subject of active research interest. It is particularly required for there to be a good contrast ratio between the switched states of the liquid crystal device. In this regard, the bistable nature of these devices, and the switching properties and memory angle (&thgr;
m
) thereof are important. The memory angle (&thgr;
m
) is half the angular difference between the optic axes of the two latched orientation states of the liquid crystal molecules and is optimally 22.5°, which is difficult to achieve in practice. A target value of greater than 15° is advantageous. The required alignment of the molecules within the liquid crystal layer results from appropriate treatment of substrates on opposite sides of such layer. The liquid crystal layer is formed by introducing the liquid crystal composition at an elevated temperature so as to cause it to be in the isotropic, free flowing, phase into a narrow gap (the cell gap) between the substrates. At this stage, the liquid crystal composition is at a temperature somewhat higher than its operating temperature.
The liquid crystal composition is then cooled in a controlled manner until an optically active tilted smectic phase is achieved, typically the smectic C phase, SmC*, (the * denotes chirality or optical activity). In order for the liquid crystal composition to have the required advantageous properties, it is desired for it to pass from the isotropic phase (I) through chiral nematic (N*) and smectic A (SmA) phases before reaching the operative smectic C* phase. This is referred to as an I-N*-SmA-SmC* phase sequence. These phases must be of acceptable width (greater than about 2° C. wide).
Liquid crystal compositions commonly comprise a host material such as those based on mixtures of two or more fluorinated phenylpyrimidinyl compounds exhibiting or capable of exhibiting a smectic C phase and, optionally, other materials (phase sequence enhancers) which may be included to modify the properties of the host material, for example to impart chirality if the host material is not inherently chiral, or to induce or enhance formation of certain phases so as to result in the required phase sequence.
U.S. Pat. No. 5,232,624 and EP-A-0332025 disclose a wide variety of chiral 1,2-difluorobenzene derivatives for imparting chirality in achiral smectic liquid crystal host mixtures. In one particular example, there is described the addition of 10% of a chiral dopant, ethyl 2-[4-(4′-nonyloxy-2′,3′-difluorobiphenyl4-yl)phenoxy] propionate, to a host mixture which consists mostly of unfluorinated phenylpyrimidine compounds and phenyl-substituted thiadiazoles but which contains minor proportions of two difluorinated phenylpyrimidines and a difluorinated biphenylpyrimidine.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid crystal composition which can have advantageous switching properties, a high memory angle and a good contrast ratio in a suitable device.
According to the present invention, there is provided a liquid crystal composition comprising (1) an achiral host mixture comprising (a) at least 20% by weight, based on the total weight of the host mixture, of at least two fluorinated phenylpyrimidine compounds capable of exhibiting an SmC phase, and (b) at least 10% by weight, based on the total weight of the host mixture, of at least one fluorinated terphenyl compound which enhances the phase sequence of said mixture, wherein the total amount of (a) and (b) is at least 50% by weight based on the total weight of the host mixture; and (2) at least one chiral dopant in an amount of not more than 10% by weight of the total weight of the composition.
Preferably, (a) is present in an amount of at least 30% by weight based on the total weight of the host mixture.
The total amount of (a) and (b) is preferably 50 to 98% by weight, and more preferably 60 to 95% by weight, based on the total weight of the host mixture.
The fluorinated phenylpyrimidine compounds are preferably difluorinated phenylpyrimidine compounds, particularly those which are difluorinated on the phenyl rings. Such compounds preferably fall within the following general formula [I]:
wherein X
1
and X
2
are usually independently selected from the group consisting of (C
1
-C
12
)alkyl and (C
1
-C
12
)alkoxy, more preferably (C
5
-C
10
)alkyl and (C
5
-C
10
)alkoxy, and most preferably (C
7
-C
9
)alkyl and (C
7
-C
9
)alkoxy. The alkyl groups are preferably linear. However, it is also within the scope of the present invention for either or both of X
1
and X
2
to be selected from (C
2
-C
12
)alkenyl, (C
2
-C
12
)alkenyloxy, (C
1
-C
12
)alkoxycarbonyl, (C
2
-C
12
)alkenyloxycarbonyl, (C
1
-C
12
)alkanoyl, (C
2
-C
12
)alkenoyl and (C
2
-C
12
)ether groups, whereof the carbon chain lengths are preferably (C
5
-C
10
), and most preferably (C
7
-C
9
). It is also within the scope of the invention for either or both of X
1
and X
2
to be at least partially fluorinated.
Such fluorinated phenylpyrimidinyl compounds will sometimes be referred to for convenience under the designation “FPYP”. Thus “diFPYP” designates compounds of the formula [I] above. Also for convenience, the lengths of the alkyl chains in X
1
and X
2
will be given by reference to the number of carbon atoms. Thus, for example, 8.O9diFPYP designates a compound of the formula [I] where X
1
is the alkyl group C
8
H
17
and X
2
is the alkoxy group OC
9
H
19
, and 9O.8diFPYP designates a compound of the formula [I] where X
1
is the alkoxy group C
9
H
19
O and X
2
is the alkyl group C
8
H
17
. In this designation, the substituent group X which is on the fluorinated ring is positioned adjacent “diF”.
The mixture of fluorinated phenylpyrimidinyl compounds may comprise at least two diFPYP compounds wherein (i) X
1
and X
2
in at least one diFPYP compound are both (C
1
-C
12
)alkoxy, for example (C
7
C
10
)alkoxy, and (ii) one of X
1
and X
2
in at least one other diFPYP compound is (C
1
-C
12
)alkyl, preferably (C
7
-C
9
)alkyl and the other of X
1
and X
2
is (C
1
-C
12
)alkoxy, preferably (C
7
-C
9
)alkoxy. It is preferred for these compounds (i) and (ii) to be present in a mutual weight ratio of about 1:4 to 4:1.
The fluorinated terphenyl compound is preferably a difluorinated compound, more preferably one in which the fluorine groups are adjacent substituents on one of the phenyl rings. The fluorinated terphenyl compound preferably has the general formula [II], [III], [IV] or [V]:
wherein X
1
and X
2
are as defined above.
Such fluorinated terphenyl compounds will sometimes be referred to for convenience under the designation “FTP”. Thus “diFTP” designates difluorinated FTP compounds of the formula [II] and/or [III] above, and “triFTP” designates trifluorinated FTP compounds of the formula [IV] and/or [V] above. The same designations as used above for X
1
and X
2
for FPYP compounds will also be used for the FTP compounds.
The liquid crystal composition may contain one such compound, for example a diFTP wherein both X
1
and X
2
are (C
1
-C
12
)alkyl, or it may contain at least two such compounds of the general formula [II] and/or [IlI]. As an example of this latter type, in at least one of such compounds, X
1
is (C
1
-C
12
)alkoxy and X
2
is (C
1
-C
12
)alkyl and, in at least one other of such compounds, X
1
and X
2
are both (C
1
-C
12
)alkyl. Preferably, the alkoxyalkyl compound is present in a lesser amount than the dialkyl compound, the ratio being preferably not more than about 0.5:1.
The liquid crystal composition may further include a fluorinated biphenyl compound which preferabl
Jones John Clifford
Slaney Andrew John
Renner, Otto, Boisselle and Sklar LLP
Sharp Kabushiki Kaisha
Wu Shean C.
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