Chip card with bistable display

Details Chip card with bistable display Chip card with bistable display

2000-01-21

2002-04-02

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299010, C235S380000

Reexamination Certificate

active

06365238

ABSTRACT:

RELATED APPLICATIONS
This application is filed pursuant to 35 U.S.C. §371 of international application No. PCT/EP98/02768, filed May 12, 1998, which in turn claims priority to German application 197 19 822.8, filed May 13, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The term “chip card” is generally taken to mean a plastic card, for example in conventional credit card format, provided with an integrated circuit containing electronically stored information.
Chip cards usually consist of PCV or ABS and, in addition to the integrated circuit, additionally contain an “antenna” in the form of a flat coil or electroconductive contacts.
Chip cards are already in widespread use, for example as telephone cards, credit cards, “medicards”, cash cards, etc.
In the future, it is expected that this technology will penetrate further into new areas, such as electronic money, replacement of cash, travel tickets and pay TV.
A smart card is a chip card whose integrated circuit controls who uses the stored information and for what purpose.
A desirable feature for chip cards is an electronic display on the card, for example showing the amount stored. Such a display facilitates, for example, display of the amount remaining on a telephone card.
Such a display should be visible even without application of an electric voltage, since neither the thickness nor the production costs of a card allow the installation of a battery. The display must thus be capable of optical storage.
2. Description of the Related Art
For reasons of optical bistability, ferroelectric liquid-crystal displays (FLCDs) and also bistable nematic displays have been proposed (see R. Bürkle, R. Klette, E. Lüder, R. Bunz, T. Kallfass, 1997 International Symposium, Seminar & Exhibition, Society of Information Display, Boston, Mass., Abstract 9.4, page 34).
The use of FLCDs would have the advantage of a low operating voltage, which can easily be in the range below 5 volts. This technology has the disadvantages of high sensitivity to shock, pressure and deformation, and the difficulty in aligning the smectic layers, which tend to form contrast-reducing deformations and defects in the crystal structure.
Besides likewise having high mechanical sensitivity, bistable nematic displays have the additional disadvantage of relatively high switching voltages, which are above 20 V.
The object of finding a mechanically and thermally stable, optically bistable chip card display which can be operated at voltages below 15 volts, preferably below five volts and has high contrast and high brightness or reflectivity is, surprisingly, achieved by using mixtures of low-molecular weight and polymeric or oligomeric FLCs.
SUMMARY OF THE INVENTION
The invention therefore relates to a chip card having a ferroelectric liquid-crystal display, wherein the liquid-crystal layer consists of a mixture of a low-molecular weight liquid crystal and a polymeric or oligomeric liquid crystal.
DETAILED DESCRIPTION
The display according to the invention can be switched at voltages >15 V, generally >5V, can be written in a broad temperature range and is robust to everyday loads, such as pressure, flexing or thermal deformation.
The display according to the invention has a high switching angle, a low switching voltage and low temperature dependence. Defect lines can be suppressed.
The low-molecular-weight, tilted smectic, optically active (ferroelectric) liquid-crystal (FLC) preferably consists of a mixture of low-molecular-weight compounds. The operating phase is preferably the S
C
* phase. The mixtures preferably comprise a non-optically active base mixture, preferably in a proportion of >50%, and one or more optically active compounds (dopants). The low-molecular-weight FLCD generally has a spontaneous polarization of from 2 to 40 nCcm
−2
.
Suitable compounds for the low-molecular-weight FLC are known to the person skilled in the art.
Generally suitable compounds can be described, for example, by the general formula (I),
R
1
(—A
1
—M
1
)
a
(—A
2
—M
2
)
b
—(—A
3
—M
3
)
c
(—A
4
)—R
2
  (I)
where the symbols and indices are defined as follows:
R
1
and R
2
are identical or different and are
a) hydrogen,
b) a straight-chain or branched alkyl radical (with or without an asymmetrical carbon atom) having 1 to 20 carbon atoms, where
b1) one or more non-adjacent and non-terminal —CH
2
— groups may be replaced by —O—, —S—, —CO—O—, —O—CO—, —O—CO—O— or —Si(CH
3
)
2
—, and/or
b2) one or more —CH
2
— groups may be replaced by —CH═CH—, —C/C—, cyclopropane-1,2-diyl, 1,4-phenylene, 1,4-cyclohexylene or 1,3-cyclopentylene, and/or
b3) one or more H atoms may be replaced by F and/or Cl, and/or
b4) the terminal CH
3
group may be replaced by one of the following chiral groups (optically active or racemic):
with the proviso that at most one of the radicals R
1
and R
2
is hydrogen;
R
3
, R
4
, R
5
, R
6
and R
7
are identical or different and are
a) hydrogen
b) a straight-chain or branched alkyl radical (with or without an asymmetrical carbon atom) having 1 to 16 carbon atoms, where
b1) one or more non-adjacent and non—terminal —CH
2
— groups may be replaced by —O—, and/or
b2) one or two CH
2
groups may be replaced by —CH═CH—,
c) R
4
and R
5
together may alternatively be —(CH
2
)
4
— or —(CH
2
)
5
— if they are bonded to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system;
M
1
, M
2
and M
3
are identical or different and are —CO—O—, —O—CO—, —CO—S—, —S—CO—, —CS—O—, —O—CS—, —CH
2
—O—, —O—CH
2
—, —CH
2
—S—, —S—CH
2
—, —CH═CH—, —C≡C—, —CH
2
—CH
2
—CO—O—, —O—CO—CH
2
—CH
2
— or a single bond;
A
1
, A
2
, A
3
and A
4
are identical or different and are 1,4-phenylene, in which one or more H atoms may be replaced by F, Cl and/or CN, pyrazine-2,5-diyl, in which one or two H atoms may be replaced by F, Cl and/or CN, pyridazine-3,6-diyl, in which one or two H atoms may be replaced by F, Cl and/or CN, pyridine-2,5-diyl, in which one or more H atoms may be replaced by F, Cl and/or CN, pyrimidine-2,5-diyl, in which one or two H atoms may be replaced by F, Cl and/or CN, 1,4-cyclohexylene, in which one or two H atoms may be replaced by CN and/or CH
3
and/or F, 1,3,4-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, 1,3-dithiane-2,5-diyl, 1,3-thiazole-2,4-diyl, in which one H atom may be replaced by F, Cl and/or CN, 1,3-thiazole-2,5-diyl, in which one H atom may be replaced by F, Cl and/or CN, thiophene-2,4-diyl, in which one H atom may be replaced by F, Cl and/or CN, thiophene-2,5-diyl, in which one or two H atoms may be replaced by F, Cl and/or CN, naphthalene-2,6-diyl, in which one or more H atoms may be replaced by F, Cl and/or CN, phenanthrene-2,7-diyl or 5,10-dihydrophenanthrene-2,7-diyl, in each of which one, two or more H atoms may be replaced by F and one or two CH groups may be replaced by N, or 1,3-dioxaborinane-2,5-diyl;
a, b and c are 0 or 1; and the sum of a, b and c is 1, 2 or 3.
The low-molecular-weight liquid crystal generally comprises from 2 to 35, preferably from 2 to 25, particularly preferably from 2 to 20 components.
The components of the low-molecular weight liquid crystal are preferably selected from known compounds having smectic and/or nematic and/or cholesteric phases, for example of the formula (I). These include, for example:
derivatives of phenylpyrimidine, as described, for example, in WO 86/06401 and U.S. Pat. No. 4,874,542,
meta-substituted six-membered-ring aromatic compounds, as described, for example, in EP-A 0 578 054,
silicon compounds, as described, for example, in EP-A 0 355 008,
mesogenic compounds having only one side chain, as described, for example, in EP-A 0 541 081,
hydroquinonone derivatives, as described, for example, in EP-A 0 603 786,
phenylbenzoates, as described, for example, in P. Keller, Ferroelectrics 1984, 58, 3, and J. W. Goodby et al., Liquid Crystals and Ordered Fluids, Vol. 4, New York, 1984, and
thiadiazoles, as described, for example, in EP-A 0 309 514.
Examples of suitable chiral, non-racemic dopants are the following:
optically active phenyl

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