Note: Descriptions are shown in the official language in which they were submitted.
~ w 096/03476 2 l 9 58 66 r~
LIQUID-CRYSTALLINE GLASSES
The present invention is directed to liquid-crystalline glasses for
optical applications and retardation layers.
Liquid-crystalline glasses are well-known. In the present patent
application. the term glasses refers to compositions which when
cooling (at a faster rate than 0.01~/s) from the melting point or from
3/2 Tg (if no melting point is observed) do not crystallise but are
transformed into the glassy state and remain frozen in that state. 3y
liquid-crystalline glasses are meant, glasses where the liquid-
crystalline phase is frozen in. The liquid-crystalline glasses
described here all have a nematic structure. J. Mater. Chem. 1, 3
(1991), 347-356 provides an overview of the presently known liquid-
crystalline glasses. The article shows that it is hard to prepare
liquid-crystalline glasses which are stable and also have a high
transition temperature (Tg above room temperature). The term stable
glasses refers to glasses which are not subject to cold
crystallisation upon being heated. In Liq. Cryst. 6 (1989), 47-62
dimeric liquid-crystalline molecules are described which are
interconnected via a sulphinyl or sulphonyl bridge. These compounds
having a Tg in the range of 12~ to 50~C display cold crystallisation
between Tg and Tc. DD-A1-242 627 discloses the same compounds as
described above, including mixtures thereof. In the mixtures the cold
crystallisation is suppressed. Mol. Cryst. Liq. Cryst. 191 (1990),
269-276 describes naphthalene-containing liquid-crystalline glasses.
These glasses are not stable. Crystallisation is suppressed in the
mixtures. Liquid Crystals Vol. 11, No 5 (1992), 785-789 describes a
number of liquid-crystalline glasses based on aminopyrene which have a
Tg (glass transition temperature) ranging from 35~ to 66~C. Several of
these glasses do not exhibit any crystallisation between Tg and Tc.
However, it is clear from Chem. Mater. 4 (1992), 1246-1253 that these
liquid-crystalline glasses have negative dielectric anisotropy and
hence cannot be properly oriented in an electric field, which is a
_
w0~6/03476 2 ~ 9 5 ~ 6 ~ r~llr . ~~ ~
drawback in the case of some optical applications. The same
publication discloses other liquid-crystalline glasses based on
aminopyrene of fairly high transition temperatures ~Tg ranging from
29~ to 54~C). It was found that two of these glasses do not exhibit
cold crystallisation. However, as the authors of this article report,
these LC glasses were found to be hydrolytically unstable on account
of the presence of Schiff's bases, and thus not suitable for use in
commercial applications. This also holds for the glasses from Liq.
Cryst. Vol. 11, No.5 (1992), 785-789.
The invention provides (hydrolytically and thermally) stable liquid-
crystalline glasses which have a high Tg and are readily orientable.
To this end the liquid-crystalline glasses according to the invention
comprise compounds according to formula 1:
R~ R3
N - R~ - N (formula 1)
R~ ~R3
wherein Rl: represents an aromatic Qroup having 5 to 24 carbon
atoms, an aromatic group-containing aliphatic group
having 6 to 24 carbon atoms, a heterocyclic group
having 4 to 24 carbon atoms, or a cyclic aliphatic
group having 6 to 24 carbon atoms;
R2: represents -H, a non-mesogenic group or a mesogenic
group with a spacer;
R~: may represent the same groups as R~, but may be
chosen independ~"Lly from R~, R- and R. ;
R.: may represent the same groups as R~, but may be
chosen indep~ndc"~ly from R2, R~, and R~;
R~: may represent the same groups as R~, but may be
chosen independently from R~, R~ and R-, with not
~ W096/03476 2 1 9~866 r~~ 3.-- El
more than 25% of all R2, R~, R4, and Rs groups
representing -H or a non-mesogenic group.
The liquid-crystalline glasses according to formula 1 were found to
have a high transition temperature (the LC glasses in the examples all
have a Tg above 50~C). Furthermore, the viscosity of the glasses is
sufficiently low between Tg and Tc to give trouble-free rapid
orientation. In addition, the glasses are so stable that even after
multiple heating cycles cold crystallisation does not occur. Moreover,
these liquid-crystalline glasses do not contain any Schiff's bases and
so are hydrolytically stable.
Consequently, the liquid-crystalline glasses according to the
invention are pre-eminently suited for use in a wide range of optical
applications, e.g., 1n optical data storage and retardation layers for
LCDs.
The glasses according to the invention are obtained by reacting a
diamine of the Rl group with mesogenic group-containing epoxides.
Examples of suitable R~ groups are given in the formulae below.
Diamines of these Rl groups are used to prepare glasses containing
these groups.
C = C C = C
- C C - C C -
C - C ~ ~
C - C
.
.
WO 96/03476 2 ? 9 ~ 8 6 ~ T~ 3.. 1 ~1
C = C C = C
C C - CH - C C - CH
~ ~ 3 ~ ~ 3
C - C C - C
C = C C = C
C C - CH3 - C C - CH3
C - C C - C
CH3 CH3
C=C C=C
CH3 - C C - - C C -
C - C C - C
CH3
/ CH3 CH3
C = C
f = C~
CH3 - C C - - C C -
C-C
C/3 f - C
CH3 CH3
C -
f = C/ f = C~ ~
C C - - C C - CH2
d
c - c c - c
o ~n o ~n o ~n ,
~I
I
~,~I ~ ~ ~ ,,0
C~
w 096/03476 2 1 9 5 8 6 6 r~
Cl3 H3 C = C
~CH2 - C~ C - CHz ~C - C
- CH2 C - C
CH3 CH3 CH3 CH
Cl CH2 - Cl Cl
C - C C = C
Cl - C C - Cl CH2 - C/ \C - CH2/
C - C C - C
Cl \CH2 - Cl Cl
C = C C = C
- C C -- C C -
C - C C - C
CH CH3
~C = C C = C/
- C C -- C C -
C - C C - C
CH~ CH3
C=C C=C
- C C -- C C -
C - C C - C
CH3 ~H3
~ w 096/03476 2 1 ~ 5 8 6 6 r~"~
OCH3
C=C C=C
- C C -- C C -
C - C C - C
CH30 OCH3
C = C C = C
- C C -- C C -
C - C C - C
Cl Cl
C=C C=C
-- C C -- C C -
C - C C - C
Cl Cl
C = C C = C
- C C -- C C -
C - C C - C
Cl Cl
Cl Cl
C = C C = C
- C C -- C C -
C - C C - C
CH30 OCH3
C = C C = C
- C C - CHz - C C -
C - C C - C
o ~n o ~n o
T
11 1 1I N N (~ C~
O~
~ W096/03476 2 1 ~ 5 ~ 5 6 r~~ Ll
C=C C=C
C - O - (CH2)3 - O - C C -
C - C - C
C = C C = C
C C ~ O ~ (CH2)n ~ O ~ C C
C - C C - C [n = 2, 3, 4]
C=C C=C C=C
-C C-O-C C-O-C C-
C - C C - C C - C
C
C = C C C C = C
- CC - O - C C - O - C C -
C - C ~ C / '~C - c~f
C/ ~C C C/
C - C ~ C / ~C - C~
- C-O-C C--C C-O-C
o ~n o ~n o ~n
~=o ~=o ~=o o o o
ll l ll l ll ~ ll l ll l ll
O = VI c3 0 Cl = V~= o r~--~--~ O _ _
ll l ll l ll c~
o o o
ll l ll l ll
~1 958~
WO 96/03476 F~ r.
C=C ~ C=C
- C C - - C C -
C - C J C - C
S C = C 1 C = C
C C - - C C
C - C 1l C - C
CH3 CH3
C=C C=C
- C C - O - C C -
C - C S/C - C
o~ ~o
C=C C=C
- C C - S - C C -
C - C C - C
- C C - C - C C -
C - C CF3 ~C - CR
C = C CF3 C = C
H3C - C C - C - C C - CH3
C - C CF3 C - C
21 95866
W0 96/03476
12
C = C C = C
/
C C-S-C C-
C -'C C - C
C = C CH C = C
1 3 /
- C C - C - C C -
C - C CH3 C - C
C~/C~, /C~/c~
C C C C C C
c c e c c c
C C C C
C ,~ / C ~
C C-----C C
l~
~ ~ c / ~ c / ~ c f~
C=C C=C C=C
- C C -- C C -- C C -
C - C C - C C - C
C = C N-N C = C
~ \ / \
-C C-C C-C C-
C - C O C - C
Preferred are the diamines of the R~ groups according to the formulae
bel ow .
~1 95866
W0 96/03476 P~_ll~l. _.
~C = C~ ~C = C~ ~C = C~
- C C -(X)n- C C - -(CH2)m- C C
C - C C - C , C - C
(CH2)m~
~C = C~ ~C = C~
C C -~X)n- C C
C C C - C
C = C C - C
-~CH2)m- C C - (CH2)m- , -(CH2)m- C C - (CH2)m-
C - C C - C
~C - C~ ~C - C~ ~C - C~
- C C -(X)n~ C C - -(CH2)m- C f
C - C C - C , C - C
(CH2)m~
wherein X stands for -0-, -S02-, -CH2-, -S-, -C(0)-, or
-C(CH3)2-,
n stands for 1 or 0, and
m stands for 0, 1, or 2.
Suitable mesogenic groups with spacers are depicted in the formulae
below. Glasses having such mesogenic groups are obtained by reacting
the epoxides corresponding to the groups below with a diamine.
wo 96/03476 2 1 q 5 8 6 6 P~
14
-CH2-CH-(CHR~o)t-(-O(CHR~ ~)UCH2)V-O-c i ~(Y)n- C \C R~
OH C - C C -, C
(R7)n (R')n
/C=C\ /C=C~
fH2-cH-(cHRlo)t-(-o(cHRl ')UCH2)V-o-c C -(Y)n- C , C - R~
OH C - C C -: C
(R7)n (R')n
/C-C\ /C=C
-cH2-cH-(cHRlo)t-(-o(cHR~l)ucH2)v-o-c\ i ~C ~(Y)n~ C~ i ~f'C - R~
15OH C - C C 1 C
(R')n (R')n
/C - C\ /C = C
CH2-cH-(cHRl~)t-(-o(cHRll)ucH2)v-o-c\ I f -(Y)n- C~ 7C - R~
OH C ~ C C l C
(R7~) n (R~ ) n
~ wo 96/034~6 2 l q 5 8~ l ,3,.
~C=C~ ~C-C~
-CH2-CH-(CHR~o)t-(-O(CHR~)UCH2)v-o-c I C -(Y)n- C ! C - R~
OH C l C C -i C
(R7)n (R')n
~C=C~ ~C-C~
CH2-CH-(CHR.~)t-(-O(CHR~~)UCH2)v-O-C~ i DC -(Y)n~ C~ , ~C - R'
OH C ~ C C -,C
(R7)n (R')n
~C - C~ ~C = C~
-CH2-CH-(CHR~o)t-(-O(CHRI ')UcH2)v-o-c\ 1 ~C -(Y)n~ C~ ~ DC - R~
15 OH C-~C C-!C
(R')n (R~)n
20 CH2-CH-(CHR1~)t-(-O(cHRl l)UCH2)V-O-C~ I ~ ~(Y)n~ C~ ~C - R~
(R7)n (R')n
21 q5866
WO 96/03476 r~ . El
~C = C~ ~C -
-CH2-CH-(CHR~7)t-(-O(CHRl~)uCH2)y-0-C ~ C ~(Y)n~ C C - R~
OH C ~ C C - C
(R')n (R')n
C = C C - C
fH2-CH-(CHRlo)t- (-0(CHRl~)uCH2)v-0-C ~ C ~(Y)n~ C C - R~
OH C -~C C - C
(R')n (F')n
wherein Y stands for -C(O)-0-, -C=C-, -O-C(0)-, -C~-C-. or
-N=N-;
R~ stands for -0-R~, -OCO-R~, -COOR~, -CN, -N02, or
-R~;
R7 stands for an alkyl group having l to 5 carbon
atoms;
R. stands for an alkyl group having 1 to 5 carbon
atoms;
R~ stands for an alkyl group having l to 15 carbon
atoms;
t is 1-6;
u ~s 1-7;
v is 0-3;
Rl~ stands for -H or -CH3;
R l stands for-H or alkyl, and n has the same meaning as
in the formulae above.
It should be noted that groups which act as a mesogenic group in
combination with a specific diamine, may act as a non-mesogenic group
in combination with another diamine. This unpredictability of liquid-
~ WO 96/03476
21 9 58 66 r~
crystalline materials is known to the artisan. The artisan can easilychoose the suitable side-groups for a specific diamine.
It is of advantage to intermix several of the compounds according to
formula 1 or to have different mesogenic groups present within one
compound according to formula 1. In this way the stability of the
liquid-crystalline glass can be enhanced, and it is even possible to
set the Tg and the Tc as desired. It was further noted that the use of
certain mixtures will give a reduction of the scattering of single-
domain films after heating during the orientation process.
Examples of R~ groups include:
-(CH2)x~CH3~
-cH2-cH(cH3)-(cH2)x-cH3~
-CH(CH3)-(CH2)X-CH3, wherein x = 1-14.
Some of these R~ groups contain an asymmetrical carbon atom. The use
of chiral (exclusively laevorotatory or dextrorotatory) R~ groups is
advantageous in a number of applications, e.g., in LCD retardation
layers.
Suitable non-mesogenic groups are groups obtained from the ring-
opening reaction of epoxides of methoxy biphenyls, cyanobiphenyls, and
biphenyls. Tt shouldnbe-noted that methoxy bephenyl epoxides can both
act as mesogenics and as nu.. sogenics depending on the diamine used.
Particular preference is given to liquid-crystalline glass containing
a polable mesogenic group. Polable groups contain one or more
permanent dipole moments directed more or less along the long axis of
the mesogenic group, such that there is positive dielectric
anisotropy. This makes it possible to orient films of the
liquid-crystalline glass using a static electric field. As Ri polable
2~ 9~866
W0 96/03476 r~
mesogenic groups contain, e.g., a -CN or -N02 group. For more detailed
1nformation on polability reference may be had to Vertogen and en de
Jeu, Thermotropic liquid crystals, fundamentals (Springer, 1987), pp.
195-Z01.
As was mentioned above, the liquid-crystalline glasses according to
the invention are especially suited to be used in optical
applications. For instance, the liquid-crystalline glasses according
to the invention are pre-eminently suited to be used in LCD
retardation layers. The functioning of retardation layers is described
1n EP-A1-0 565 18Z and EP-A3-0 380 338, which describe
liquid-crystalline polymers for use in retardation layers. For further
elucidation reference may be had to these patent publications. The
liquid-crystalline glasses according to the invention have a low
viscos1ty between Tg and Tc. This low viscoslty permits rapid
h~ g~neous arrangement of the liquid-crystalline glasses into a
nematic structure having an angle of rotation as desired. In the case
of an angle of rotation of 90~ (or -90), the film is called "twisted
nematlc"; if the angle of rotation ls greater, the film is called
"supertwisted nematic." In addition, the liquid-crystalline glasses
according to the invention are suitable for use in retardation layers
without twist. In that case the arrangement of the liquid-crystalline
layer wlll be homeotropical or un1form planar. At angles of rotation
exceeding 360~ the structure goes through more than one full rotation
w1thin a single layer. The length covered by the structure in a full
rotation is called the pitch. The liquid-crystalline glasses according
to the invention can be used to make retardation layers which have a
thickness of more than five times the pitch. It was even found
possible to make retardation layers which have a thickness of 20 times
the pitch. The orientation of this type of layers is usually called
cholesteric.
Because the liquid-crystalline glasses according to the invention have
a Tg of well above room temperature, the liquid-crystalline glass does
~ W096103476 71 95866 ~ q8l
19
not have to be incorporated into a rigid cell, as is the case with
low-molecular weight liquid-crystalline material. Since the different
compounds according to formula 1 are easily miscible, and also
different mesogenic groups can be present within one compound
according to formula 1, the birefringence and the dispersion of the
retardation layers can be exactly matched with the appropriate active
liquid-crystalline cell. By varying the mesogenic group the dispersion
can be varied. In this way the use of mesogenic groups containing a
cyclohexyl group or a bicyclooctane group instead of a phenyl group
will make it possible to alter the dispersion. The birefringence can
be lowered by reducing the mesogenic group density. The invention is
also directed to retardation layers containing liquid-crystalline
glasses according to the invention.
The retardation layers may be prepared as follows: a thin layer of
liquid-crystalline glass is applied between two orienting substrates.
Generally, a thin layer of liquid-crystalline glass will be provided
on either or both of the orienting substrates by means of spin
coating, screen printing, meter bar coating, melt coating, or some
other conventional coating technique. The two substrates are then
placed one on top of the other. To set the thickness of the
retardation layer, spacers of a specific diameter may be provided
between the two substrates. As a rule, spheres of glass, polymer or
silica are used to this end. Next, the whole is heated to a
temperature between Tg and Tc (usually to about 10~C below Tc), which
causes the glass to start arranging itself. On cooling to room
temperature the well-ordered structure is frozen in, and a stable film
is obtained which retains its shape. The substrates may be of either
glass or plastic. If they are of glass, it is preferred to use thin
glass substrates of a thickness of 20 to 500 micrometers. This allows
retardation layers to be made which are lightweight, thin, and
somewhat flexible.
2~ 95866
w 096/03476 P~ J
Various techniques are known for making an orienting substrate. For
instance, the substrate itself may be rubbed in a single direction.
The substrate in that case may be made of, e.g., polyimide, polyvinyl
alcohol, glass, etc. Alternatively, the substrate may be provided with
a thin orienting layer. This may be a thin polymer layer which can be
rubbed, e.g., polyimide, polyvinyl alcohol, etc. Alternatively, this
thin orienting layer may be a SiOx layer evaporated at an angle of
less than 90~, usually of 60~ or 86~. Generally, a substrate of poor
flexibility is used for SiOx evaporation, such as glass or quartz.
These orienting techniques are known to the skilled person and require
no further elucidation here. Of course, it is also possible to employ
other orienting techniques.
A twisted structure is obtained by giving one of the two substrates a
different orientation direction from that of the other substrate. To
control the direction of rotation of the director ~to the left or to
the right) and/or to obtain an angle of rotation greater than 90~, the
liquid-crystalline material is frequently mixed with a chiral
material: the so-called chiral dopant. In principle, any optically
active compound may be used to this end. As examples may be mentioned
cholesterol derivatives and 4-(4-hexyloxy-benzoyloxy) benzene acid
2-octyl-ester. Ordinarily speaking, for application as retardation
layers up to 5 wt.% of chiral dopant is employed in relation to the
total amount of liquid-crystalline material. Alternatively, some of
the compounds according to formula 1 may be provided with chiral
centres. Preferably, this is done by providing the mesogenic group
with a chiral chain (group R~) or spacer, since in this way the
transition temperatures will hardly if at all be adversely affected.
Examples of mesogenic groups with chiral chains have already been
described above. Since the carbon originally at the a-position of the
epoxide group is asymmetrical also, its chiral version may be used as
well. In that case, use is made of an epoxy-containing mesogenic group
with a chiral centre in the epoxide group. Of course, the chiral
centre may also be located in the diamine.
7~ 9~6~
~ WO 96/03476
r~
21
It is not necessary to use two substrates to make a retardation layer.
If the liquid-crystalline a~ssumes a sufficiently twisted structure of
its own accord, a single orienting substrate will suffice. A
sufficiently twisted structure can be obtatned if the
liquid-crystalline material contains a sufficient quantity of chiral
dopant, and the layer thickness is accurately controlled.
As mentioned above, is it also possible to make layers with a very
small pitch with the liquid-crystalline glass according to the
invention. These so-called cholestric layers can also be used as
cholesteric reflectors or cholesteric polarisers. In these cases, more
chiral dopant is employed than for the application in retardation
layers.
Further, the liquid-crystalline glasses according to the invention may
be used for digital data storage such as in Compact Discs (CDs, both
recordable and rewritable) or digital films. Digital films may be of
different shapes, e.g., tape, cards, and disks which cannot be
written or read as specified by the CD standard. The orientation in
these CDs or films may be either homeotropic or uniform planar. For
digital media various read out principles may be employed. For
instance, in the case of homeotropic orientation (i.e., perpendicular
to the substrate), dichroic dye may be blended in, making it possible
to read out data via the difference in absorption. Further, in the
case of homeotropic as well as uniform planar orientation contrast
results from an isotropic pit or trace giving a different optical path
length from a homeotropic or uniform planar background. Because of
this difference in path lengths, there is interference by the portion
of the incident light beam which falls adjacent to the pit with the
portion which falls within the pit. Generally, the different phenomena
are active within the CD simultaneously, and it is impossible to state
precisely where exactly the contrast originates.
21 95866
w 096/03476 ~,I/r,, ~
Here also it was found that because of the low viscosity of the
liquid-crystalline glass according to the invention it is possible to
attain rapid and, above all, homogeneous orientation.
When the film or CD contains dichroic dye, its orientation will be
along the same lines as that of the mesogenic groups of the liquid-
crystalline glass. The term dichroic dye refers to a dye which in an
oriented medium (e.g., a nematic liquid-crystalline phase) will have a
dichroic ratic (absorption ~/absorption 1~ > 1 in the desired
wavelength range, absorption 1I standing for the absorption of light
which is polarised parallel with the orientation direction of the
medium, and absorption 1 standing for the absorption of light which is
polarised perpendicularly. Dichroic dyes, in other words, will absorb
one polarisation direction of linearly polarised light to a much
greater extent than the other one.
In a virgin homeotroppically oriented film or CD the mesogenic groups,
and hence the dichroic dye molecules, are oriented perpendicular to
the film's surface, and there is only low absorption of the incident
light by the dichroic dye molecules. (It should be noted that the
polarisation direction of the light is perpendicular to its
propagation direction as the incident light travels in many cases
perpendicularly towards the film's surface). In the case of local
heating or irradiation (e.g., with a laser) of the film or CD to above
Tc, the homeotropic orientation is converted into an isotropic one.
Rapid cooling causes this local isotropic orientation to be frozen in.
In the case of such an isotropically written trace or pit, the
dichroic dye molecules will likewise be isotropically oriented,
resulting in a substantially higher absorption of the incident light.
In the isotropic state 2/3 of the dichroic dye molecules -on average-
is positioned with the long axis parallel with the CD surface (i.e, onaverage 1/3 along the x-axis of the plane of the film, and 1/3 along
the y-axis ). The polarisation direction of the incident light (either
x- or y-polarised) is now parallel with the long axis of the dichroic
dye molecules, and thus a high absorption is realised.
~ w 096/03476 ~ l 9 5 8 6 6 r ~
~ 23
The dichroic dye may be mixed or incorporated into the liquid-
crystalline glass. In the case of incorporation, an epoxy-
functionalised dichroic dye may be co-reacted with the other mesogenic
group-containing epoxides. In principle, any dichroic dye may be
employed, providing it is sufficiently stable to be mixed or
incorporated into the liquid-crystalline glass. For instance azo dyes,
anthraquinone dyes, croconium and squarilium based dyes are suitable.
The invention is also directed to novel croconium compounds with
mesogenic groups.
If other read out princpfes are used than the difference in absorption
of dichrioc dyes in a homeotropic medium, dichrioc dyes are not
necessary and the liquid-crystalline glass may be oriented
differently, e.g. uniform planar.
Writing out data with the aid of a solid state laser requires that the
liquid-crystalline glass film be, or be rendered, near-infrared light
absorbing. Generally, this is done by blending in or incorporating a
near-infrared absorbing dye. Preferably, the same (diode) laser can be
employed for writing as well as reading. CDs as specified by the CD
standard are read out by a solid state laser. In the case of a CD
wherein the read out principle is based in the difference in
absorption of dichroic dye in a homeotropic medium, use is made of a
dichroic dye which absorbs the laser light during writing and creates
a difference in absorption during reading. In such cases it is
advisable that the dichroic dye be greatly dichroic but not fully
oriented, so that a sufficient quantity of light will be absorbed
during the writing. The objective is a light absorption percentage in
the range of 2 to 40% of the incident light in the homeotropic
(virgin) state. Dichroic near-infrared dyes which can be blended in
are, among others, anthraquinone dyes: IR-750~, ex Nippon Kayaku Co.
Ltd, squarilium dyes: NK-2772~, ex Nippon Kankoh - Shikiso Kenkyusho
Co. Ltd.,3-(7-isopropyl-1-methyl)azulene-4-yl-2-ethyl-propionic acid-
21 95866
W096/03476 r~ . Ci--
24
n-butylester, and the dyes mentioned in EP-A2-0 310 080 , croconium
dyes: ST 1720, ex Syntec.
For high-density CDs lasers having a wavelength in the range of 620 to
6BO nm are employed for reading. The liquid-crystalline glasses
according to the invention can be employed also to make high-density
CDs based on the difference in absorption principle when dichroic dyes
having an absorption maximum in this range are used. Examples of
dichroic dyes having an absorption maximum in this range include: a~o
dyes: SI-361 0, ex Mitsui Toatsu Chemicals SmbH, anthraquinone dyes:
LCD 116 ~ and LCD 118 1, ex Nippon Kayaku Co. Ltd.,M-137 0, M-483 0,
SI-497 ~, ex Mitsui Toatsu Chemicals GmbH., squarilium dyes: ST 6l2 0
and ST 5/3 ~, ex Syntec. When other read out principles are used, the
620-680 nm absorbing dyes need not be dichroic.
In principle, the reading out and writing of data in the liquid-
crystalline glassldye system can take place at different wavelengths.
In the case of reading out with the difference in absorption
principle, use will be made of a dichroic dye, as mentioned-above, in
combination with a writing light absorbing dye. It is advisable that
said writing light absorbing dye is hardly susceptible to orientation,
or is not very dichroic, since otherwise absorption during the writing
would be unsatisfactory. For that reason preference is given to dyes
which are not elongated in shape (e.g., molecules in platelet form or
spherical molecules). These writing light absorbing dyes may be
incorporated into the liquid-crystalline glass by co-reacting the dye
diamines with the other diamines.
Ordinarily speaking, a film or CD is made by applying a solution of
the glass onto a substrate and evaporating the solvent. Suitable
substrates include PET, PET-ITO, metal, glass, cellulose acetate,
polycarbonate, polycarbonate-Al, silicon, amorphous polyolefins, etc.
Generally, these substrates are provided with a thin layer of metal
~ w 096/03476 ~ 6 r~
~ such as aluminium or gold or a layer of material with a high
dielectric constant such as silicium nitride, silicium oxide or ZNSe.
~ Usually, films having a thickness of 0.2 to 10 micrometers are
employed.
s
Homeotropic orientation of the liquid-crystalline material can be
attained in several ways:
1. By treating the surface of the substrate with homeotropic
orientation inducing surfactants. These may be, int. al., silanes,
higher alcohols, and the like, e.g., n-dodecanol and Liquicoat
PA, ex Merck.
2. By poling the liquid-crystalline layer in a magnetic or electric
field. The electric field may be generated by corona poling (using
a sharp needle or a thin wire as electrode). There will have to be
a counter-electrode on the other side of the liquid-crystalline
layer (e.g., an IT0-layer, a metal layer, or a conductive polymer
layer), so that the poling field will be positioned over the
liquid-crystalline layer. Alternatively, the liquid-crystalline
layer may be provided with a conductive layer on either side, and
an electric field applied thereto.
80th when homeotropic films are produced by means of a surface
treatment and in the case of poling, the viscosity and the layer
thickness of the glass film are of importance.
Uniform planar orientation can likewise be obtained by surface
treatment. Since the liquid-crystalline glasses according to the
invention have a low viscosity between Tg and Tc, they can be made
into fine uniform planar films or CDs.
Since poling is one of the easiest ways of obtaining homogeneous
homeotropic orientation, the use of polable liquid-crystalline glasses
is preferred for digital data storage. Such glasses have been
described hereinbefore.
21 95866
WO 96/03476
r~ J,~
The liquid-crystalline glasses according to the invention can easily
be made into homogeneously scattering films which permit local
isotropic writing after the addition of suitable dyes, with a laser or
some other source of heat. Thus, the liquid-crystalline glasses
according to the invention are rendered serviceable also for low
density digital storage and analog data storage. The term analog data
storage refers both to human readable rewritable displays such as
smart cards and thermal paper and to machine readable media (such as
media which can be read with a bar code reader). The films can be
prepared by spin coating, meter bar coating, melt coating, screen
printing, and any other conventional technique for coating on a
substrate. Suitable substrates are of PET, glass, polycarbonate, P~C,
ABS, polystyrene, metal, and paper. The films may have different
formats, such as disks, cards, and tape.
A homogeneously scattering film is obtained by heating the film to
above Tc and then leaving it to cool to room temperature. The creation
of small domains gives a scattering texture. It was found that films
of liquid-crystalline glasses according to the invention can be
initialised within 2 seconds in this way. This, in its turn, means
that written films can be erased within 2 seconds in this way and
prepared for rewriting.
To increase the contrast between the written and the virgin sections,
a contrast layer can be applied beneath the liquid-crystalline glass
layer. This may be a refelecting layer, which may be of any material
reflecting light. Examples include metal substrates or foils of
copper, aluminium, gold, silver, nickel, steel, metallised plastic
substrates or foils such as aluminised PET, metallised paper, metal
coated metal or plastic substrates such as used in the car industry.
Alternatively, the contrast layer may be made up of a layer having a
low index of refraction, e.g., a thin layer of air. The liquid-
crystalline glass layer may be provided with a protective coating.
~ W096103476 2~95866 r~
If epoxy-functionalised and/or diamine-functionalised dye are co-
reacted with the mesogenic group-containing epoxides and/or diamines,
or if dyes are blended in, glass is formed which can be used as a
polariser. the dyes, of course, should be dichroic and co-oriented
with the liquid-crystalline glass. To this end the liquid-crystalline
glass according to the invention is applied onto an optically
transparant substrate, after which the liquid-crystalline glass layer
is oriented uniformly planarly. The invention is also directed to
polarisers comprising a liquid-crystalline glass containing dye
according to the invention.
To enhance the glasses' UV-stability it is possible to add
UV-stabilisers. Alternatively, epoxy-functionalised UV-stabilisers may
be incorporated into the glasses. An example of such an epoxy-
functionalised UV-stabiliser is listed in Macromol. 26 (1993),
3227-3229.
The invention will be further illustrated with reference to a number
of purely illustrative, non-limitative examples.
EXAMPLES
Example 1
Synthesis of LC glasses (general method):
A mixture of 1 eq. of diamine and 4 eq. of epoxy was heated for 5-20
hours, depending on the diamine used, under a nitrogen atmosphere at a
temperature of 130~C. When two or more different diamines or epoxides
are used, 40 % of weight of chlorobenzene was added for obtaining a
h geneous melt. After 1 hour at 130 ~C the chlorobenzene was
distilled off. The melt was cooled down and dissolved in THF, and the
solution of approximately 20% (m/M) was precipitated in a 10-fold
excess of ethanol. The yields were in the range of 75 to 90%.
21 95866
WO 96/03476
28
Synthesis of epoxide monomers:
Example 2
. _. .,, ~ _ .. _ ... ._ _ . _ . _ . _ .. _ . _ .. . . _ ,
epoxide van cyanobiphenyl (epoxide 1)
A mixture of 39.0 9 (0.20 mole) of hydroxycyanobiphenyl, 100 ml (1.25
moles) of epichlorohydrin, and 0.44 9 (2.4 mmoles) of benzyl trimethyl
ammonium chloride was heated to 70CC. Next, a solution of 17 g (0.42
mole) of sodium hydroxide in 100 ml water was dispensed in 3 hours.
Following this addition there was one extra hour of stirring at 70~C.
The reaction mixture was cooled to 20CC, and 200 ml of dichloromethane
were added. The organic layer was separated from the aqueous one and
washed with, successively, NaCl solution (twice) and water (twice).
After drying on magnesium sulphate and concentration by evaporation
the crude product was converted to the crystallised form from 450 ml
of methanol. The yield was 38.30 9 (76%).
The epoxide of cyanobiphenyl was used to prepare glasses by the
general method for the synthesis of LC glasses specified above, using:
m-xylylene diamine (m-XDA), ex Fluka~
m-phenylene diamine (m-PDA), ex Jansen Chimica~
4,4'-oxydianiline (ODA), ex Fluka~
methylene diamine (MDA), ex Fluka
p-phenylene diamine (p-PDA), ex Jansen Chimica~
1,3-bismethylaminocyclohexane (CHDA), ex Aldrich~
3,3'-sulphonyl dianiline (3-SDA), ex Aldrich~
4,4'-sulphonyl dianiline (4-SDA), ex Fluka~
The properties of the resulting glasses are compiled in TA3LE 1. It
was found that the obtained liquid-crystalline glasses remained stable
even after multiple heating cycles.
~~ W096/03476 2~9~66
PCT/EP95/Ot981
Z9
Example 3
epoxide of nitrobiphenyl (epoxide 2)
In a manner analogous to that for the synthesis of the epoxide of
cyanobiphenyl, the epoxide of nitrobiphenyl (epoxide 2) was prepared.
Using various diamines glasses were prepared by the general method for
the synthesis of LC glasses specified above.
The properties of the resulting g1asses are compiled in TABLE I. It
was found that the obtained liquid-crystalline glasses remained stable
even after multiple heating cycles.
Example 4
epoxide of nitrostilbene (epoxide 3)
In a manner analogous to that for the synthesis of the epoxide of
cyanobiphenyl, the epoxide of nitrostilbene (epoxide 3) was prepared.
Using various diamines glasses were prepared by the general method forthe synthesis of LC glasses specified above.
The properties of the resulting glasses are compiled in TABLE I. It
was found that the obtained liquid-crystalline glasses remained stable
even after multiple heating cycles.
Example 5
epoxide of methoxyphenyl benzoate (epoxide 4
In a manner analogous to that for the synthesis of the epoxide of
cyanobiphenyl, the epoxide of methoxyphenyl benzoate (epoxide 4) was
prepared, except that only half the amount of caustic solution was
21 9~8&6
WO 96/03476 PCT/EP95/02981
used for epoxide 4. Using various diamines glasses were prepared by
the general method for the synthesis of LC glasses specified above.
Further, the epoxide o~ cyanostilbene (epoxide 5), and the epoxide of
nitrotolane (ph=ph-N02, epoxide 6) were prepared in a manner analogous
to that for the synthesis of the epoxide of cyanobiphenyl.
The properties of the obtained glasses are comp11ed in TABLE I. It was
found that the obtained liquid-crystalline glasses remained stable
even after multiple heating cycles.
~ w 096/03476 2 ~ q5866 P~
TABLE I
epoxide diamine Mw Tg Tc Tm
1 m-XDA 1140 64/70 127
1 m-PDA 1112 97/102 193 230
1 ODA 1204 94/99 142 213
1 MDA 1202 108/il3 161 229
1 p-PDA 1112 270
1 CHDA 1146 74/79 90 157
1 3-SDA 1252 106/111 137 210
1 4-SDA 1252 119/131 160 233
2 m-PDA 1192 91/98 138 200
2 ODA 1284 212 260
3 m-XDA 1324 71/77 159 --
4 m-PDA 1309 66/73 154 --
4 m-XDA
4 ODA 1400 66/72 100 --
4 MDA 1398 66/72 127 --
m-XDA 1236 65/69 154 --
3-SDA 1343 102/106 171 212
6 m-XDA 1316 63/66 114/130 --
6 3-SDA 1428 100/104 163 194
Example 6
1-(2,3-epoxypropyloxy)-4-(p-methoxyphenyl)bicyclo[2,2,2]octane
(epoxide 7)
3-Acetyl-1,5-dicyano-3-(p-methoxyphenyl)pentane
wos6/03476 ~ r~ ssl -
32
Cyanoethylene (53 g, 1.0 mole) was added dropwise to a stirred
solution of 82 g (0.5 mole) p-methoxyphenyl acetone and S.5 ml of a
40% w/v solution of benzyl trimethyl ammonium hydroxide (Triton B) in
methanol in 100 9 of t-butanol, while the temperature of the solution
was maintained between 10 and 15 ~C. After stirring the reaction for 4
hours, the almost solid mixture of product was filtered off, washed
with methanol, and dried. Yield: 99.2 9 (73%).
3-Acetyl-3-(p-methoxyphenyl)pentane-1~5-dicarboxylic acid
A mixture of 17.8 9 (0.44 mole) of NaOH, 175 g of water and 40 g (0.15
mol) of 3-acetyl-1,5-dicyano-3-(p-methoxyphenyl)pentane was refluxed
overnight. Concentrated hydrochloric acid was added to the cooled
solution and the product separated as an oil. The oil was taken up in
100 ml of dichloromethane. Upon standing and cooling to O ~C the pure
acid precipitated as a white solid. Yield: 39.5 9 (87%).
4-Acetyl-4-~p-methoxyphenyl)cyclohexanone
A solution of 38.0 9 (0.14 mole) of
3-acetyl-3-(p-methoxyphenyl)pentane- 1,5-dicarboxylic acid and 0.31 9
of potassium acetate in 140 ml of acetic anhydride was refluxed for 2
hours. The excess acetic acid was removed at reduced pressure, after
which the temperature was raised to 250 ~G in order to pyrolyze the
residue and to distill the formed cyclohexanone (pressure 0.05 mbar).
23.0 g (79~) of distillate were collected which rapidly solidified.
The product was used without further purification.
l-Hydroxy-4-(p-methoxyphenyl)bicyclo~2,2,2]oCtan-3-one
A solution of 23.0 g l0-11 mole) of 4-acetyl-4-(p-methoxyphenyl)cyclo-
hexanone and 19.2 g (0.29 mole) of KOH in 200 ml of water was heated
-- WO 96103476
2 ~ 9 5 ~ ~ 6 r~
33
at 70 OC for 6 hours. After cooling the precipated product was
filtered off, washed with water, and dried in vacuo. Yield: 18.9 g
t82%), m.p. 159-160 ~C.
1-Hydroxy-4-(p-methoxyphenyl)bicyclo[2,2,2]octane
A solution of 10.0 9 (0.048 mole) of
l-hydroxy-4-(p-methoxyphenyl)bicyclo[2,2,2]octan-3-one and 7.36 9
(0.15 mole) of hydrazine monohydrate in 40 ml of triethylene glycol
was subsequently heated at 100 ~C (3 hrs) and 165 ~C (15 min.). The
solution was cooled to 60 ~C and an equally warm solution of 9.28 9
(0.14 mole) of KOH in 40 ml of triethylene glycol was added. The
vessel was equipped with a Dean-Stark trap, and the mixture was heated
at 105 ~C for one hour and then at 185 ~Cfor half an hour. The
cooled solution was added to 150 ml of water and washed with
dichloromethane ~3 x 100 ml). The combined organlc layers were washed
with 50 ml 2 N HCl and 50 ml of water, dried and evaporated to
dryness. Yield: 7.83 g (84%). The product was purified by
recrystallization from toluene.
1-Allyloxy-4-(p-methoxyphenyl)bicyclo[2,2,2]octane
To a solution of 2.0 g (10 mmoles) of
l-hydroxy-4-(p-methoxyphenyl)bicyclo[2,2,2]octane in 15 ml of sleve
dried DMF under N2 was added 0.52 9 (13 mmoles) of a 60 % NaH
dispersion in oil. After stirring at room temperature for 4 hours the
evolution of hydrogen had stopped. There was added 70 mg (0.19 mmol)
of tetrabutyl ammonium iodide and (dropwise) 1.56 9 (13 mmoles) of a
solution of allyl bromide in 5 ml DMF. The resultant reaction mixture
was stirred for an additional 2 hours, poured into 150 ml of water,
and washed with diethyl ether (3 x 50 ml). The combined organic layers
were washed with 50 ml of water and 50 ml of brine, dried and
evaporated to dryness. The crude product was purified by column
21 95~66
WO 96/03476
34
chromatography (SiO2, eluent diethyl ether), and there was obtained
1.0 g (43%) of 1-allyloxy-4-(p-methoxyphenyl)bicyclo[2.2.2]-octane,
m.p. 62-63 ~C.
1-(2,3-epoxypropyloxy)-4-(p-methoxyphenyl)bicyclo[2,2,2]octane
A solution of 1.0 g (4.2 mmoles) of
1-allyloxy-4-(p-methoxyphenyl)bicyclo[2,2,2]octane and 1.9 g of 50%
(5.4 mmoles) of m-chloroperbenzoic acld in 10 ml of sieve dried
dich10romethane was stirred at room temperature overnight. The
reaction mixture was diluted with 10 ml of dichloromethane, washed
with a 10% aqueous solution of sodium carbonate (2 x 20 ml), water (20
ml), and brine (20 ml), dried and evaporated to dryness. The crude
product was recrystallized from methanol, yield O.lS g (14 %).
Example 7
. ., . . _ . . , _ _ _ _ _ . . _ .
1-bromo-4-(p-2,3-epoxypropyloxyphenyl)bicyclo[2,2,2] octane
(epoxide 8)
1-Bromo-4-(p-hydroxyphenyl)bicyclo[2,2,2]octane
To a solution of 2.7 g (0.14 mmoles) of
l-hydroxy-4-(p-methoxyphenyl)bicyclo[2.2.2]oct~ane in S0 ml of sieve
dried dichloromethane was added dropwise a solution of 8.8 g (0.35
mmoles) of boron tribromide in S0 ml of sieve dried dichloromethane
at 0 ~C. The solution was stirred overnight and allowed to re-attain
room temperature. The solution was poured in 400 ml of water, and the
aqueous phase was extracted with dichloromethane (2 x 100 ml). The
combined organic layers were washed with a 10% aqueous solution of
sodium carbonate (100 ml) and water (100 ml), dried and evaporated to
dryness. Yield 3.2 9 (93%). The product was used without further
purification.
21 9~866
~ WO 96/03476 PCT/EP95/02981
1-Bromo-4-(p-2,3-epoxypropyloxyphenyl)bicyclo[2,2,2]octane
A solution of 3.0 9 (0.12 mmoles) of l-bromo-4-(p-hydroxyphenyl)bicy-
clo[Z,2,2]octane and 0.023 9 (0.012 mmoles) of benzyl trimethyl
ammoniumchloride in 9.0 g (0.99 mmoles) of epichlorohydrin was stirred
at 70 ~C. A solution of l.O 9 (0.26 mmoles) of NaOH in 7.5 ml of water
was gradually added during 2.5 hours and the mixture was stirred
overnight. lO ml of water and 25 ml of dichloromethane were added, the
organic layer was separated off, and the aqueous layer was extracted
with dichloromethane (2 x 25 ml). The combined organic layers were
washed with water (25 ml) and brire (25 ml), dried, and evaporated to
dryness. The crude product was crystallized from methanol; yield 3.2
g (86~), m.p. 112-115 ~C
The epoxides 7 and 8 were used in the liquid-crystalline glasses
according to the invention to alter the dispersion of retardation
layers made of these liquid-crystalline glasses.
Example 8
Liquid-crystalline cyanobiphenyl glasses containing different diamines
were intermixed. The results in TABLE II show that by varying the
diamines the Tg and the Tc can be set as desired. Further, the use of
mixtures in optimal mixing ratios was found to promote the stability
of the liquid-crystalline glasses.
~1 9rJ8~
w 096/03476
r~ J,~ ssl _
TABLE Il
wt.% XDA wt.% m-PDA wt.% ODA Tg Tc Tm
. ..
o 100 0 97/102 139 --
Z5 75 0 79/92 175 --
SO O 75/82 159 --
0 64/74 141 --
100 0 0 62/68 124 --
561 19 25 74/80 131 1973
381 12 50 79/84 131 20~3
191 6 75 85/90 133 214
~' O 100 94/99 142 213
after the materla1 had been melted in a first heating cycle, no
cold crystallisation could be observed even with heating at lK/min
~ cold crystallisation could be observed with heating at l~/min
~ Tm in first heating cycle
Example 9
.. , . .................. . ~ _ . . ...
Blends were made of liquid-crystalline glasses of epoxlde 1 and 3-SDA
(glass 1) and liquid-crystalline glasses of epoxide 6 and m-XDA(glass 2). The results are given ln TABLE III. From the results it can
be seen that the Tg and Tc can be set by using blends of liquid-
crystalline glasses.
21 q5866
- ~ w o 96/03476 ~ r~
TABLE III
wt.% glass 1 wt.% glass 2 Tg Tc Tm
S
100 0 lO9/113 139 --
92/99 143 --
78/84 148 --
~ 75 67/73 153
Example 10
Liquid-crystalline glasses were obtained by reacting ODA with epoxide
1 and another epoxy. The results in TA3LE IV show that the
lncorporation of different epoxides in one liquid-crystalline glass
molecule does not destroy the liquid-crystalline behaviour and the Tg
and TC can be set by varying the amount of epoxides of a specific
type.
2 ~ 9 ~
WO 96/03476 J
38
TABLE IV
wt.% epoxide 1 wt.% R-epoxide Tg Tc Tm
100 O- 94/99 142 213
25, ph-ph-OCH3 87/91 134
25.ph-COO-ph-OCH3 87/90 125 225
35,ph-COO-ph-OCH3 79/83 119 --
50,ph-COO-ph-OCH3 81/86 119 --
ph is a phenyl group
Example 11
Liquid-crystalline glasses were obtained by reacting 3-SDA with
epoxide 1 and another epoxy. The results in TA3LE ~ again show that
the incorporation of different epoxides in one liquid-crystalline
glass molecule does not destroy the liquid-crystalline behaviour and
the Tg and Tc can be set by varying the amount of a specific epoxide.
~ wos6/03476 21 q5866 P~ll~l. I
39
TABLE V
wt.% epoxide 1 wt.% R-epoxide Tg Tc Tm
35,ph-ph-OCH3 1OO/104 143 --
25, ph-ph-OCH3 101/105 140 --
25,ph-ph-0C6H13 9O/98 131 --
25, ph-ph-N02 109/113 133
ph is a phenyl group
Example 12
Liquid-crystalline glasses were obtained by reacting SDA with epoxide
1 and a non-mesogenic group-containing epoxy. The
non-mesogenicBepoxides were obtained in a manner analogous to the
preparation of epoxide 1. The results in TABLE VI show that by
incorporating non-mesogenic groups in the liquid-crystalline glass the
liquid crystalline behaviour is not destroyed. It was further noticed
that a reduction of the scattereing of single domain films of these
liquid-crystalline glasses was obtained after heating during the
orientation process.
21 ~5866
WO 96/03476 P~
TABLE VI
wt.% epoxide 1 wt.% R-epoxide Tg Tc Tm
10,ph-0-CH3 104/109 125 --
10, ph-CN 107/112 125 --
5, 0-ph-ph 107/112 126 --
10,para-ph-ph 106/111 129 --
ph is a phenyl group
Exam~le 13
1 5 - ~
5ynthesis of croconium dyes in a manner analogous to that for LC
glasses
A mixture of 0.54 9 ~S mmoles) of m-aminophenol and 10 mmoles of
epoxide was me1ted under nitrogen at a temperature of 130~C. After 4
hours at 130~C the melt was dissolved in DMF, and the solution of
about 20% (m/M) was precipitated in a 10-fold excess of ethanol.
0.50 mmole of the product from the above step (phenol derivative) was
disso1ved under a nitrogen atmosphere in a mixture of 1 ml of DMS0 and
50 ml of n-butanol. Next, at reflux temperature 53 mg (0.25 mmole) of
croconic acid were added in one go. After 1 hour of refluxing the
mixture was cooled down and the precipitated product was filtered and
washed with ethanol. The product was purified with the aid of column
chromatography. In TABLE V11 the properties of croconium dyes with
various R~. groups according to the formula of claim 25 are comprised.
~ w 096103476 ~ l 95866 r~lr~
TABLE VII
Rli group Tg Tc Tm Amax 6
ph-O-CH3 73/81 -- 829 160 000
ph-COO-ph-O-CH3 170 --
ph-ph-CN 128/140 200 834 110 000
ph-ph-N02 190 -- 833 98 000
ph-ph-O-CH3 238 833 182 840
Example 10
- ~ = .
Application in retardation layer:
Used were two glass substrates of a thickness of 100 micrometers.
These substrates were coated with a thin layer of Merck Liquicoat ~
PA, which was precured at 60~C for 15 minutes, cured at 300~C for one
hour, and then rubbed in the desired direction with a felt cloth in
accordance with the Merck~ instructions. To ensure proper adhesion of
the PI layer the glass substrates were cleaned in advance, using the
following procedure:
- ultra-sonic cleaning with a detergent (Q9, Purum GmbH)
- KOH (1 M), 50 ~C/l hr
- HN03/H2504/H20 (1:1:2), 60 C/l hr
- refluxing in isopropyl alcohol vapour for 30 minutes.
There was flushing with demineralised water between all of the
cleaning steps. This is a variation of the method described by W.H. de
Jeu in Physical Properties of Liquid Crystals, 1st ed., Gordon and
Breach Science Publishers, p. 23.
W096/03476 2 1 9 58 66 I'~.1/P.I~ $~ --
Liquid-crystalline glass of m-XDA and epoxide 1 was dissolved in
cyclopentanone together with 5 wt.% of chiral dopant (Merck CB 15~).
To the filtered solution 0.5 wt.% (calculated on LC glass) of cross-
linked polymer spheres (Dynospheres DL-1060~, ex JSR) was added as
spacers. The solution of liquid-crystalline glass with spacers was
spin coated onto the two pretreated glass substrates. The layer
thickness obtained was 4 micrometers. The two glass films were dried
in a vacuum oven for 16 hours at 20~C. They were then placed one on
top of the other under a 60~ difference in orientation direction and
moulded at a temperature of 160~C. Next, the sample was cooled to
115~C, and after 5 minutes to room temperature. The quality of the
resulting retardation film was determined with the aid of various
optical techniques such as described in E.P. Raynes, "Molecular
Crystals," Liquid Crystals Letters 4(3-4) I1937),_69-75
Application for analog data storage:
Liquid-crystalline glass of m-XDA and epoxide 1 was dissolved in
cyclopentanone and filtered. Using a meter bar, the solution was
applied onto a 100 micrometers thick Alu-PET substrate (based on
Melinex 401~, ex ICI). The solvent was removed by drying at room
temperature for 5 minutes and heating to 60~C for 15 minutes. Obtained
was a film with a thickness of about 6 micrometers. The liquid-
crystalline layer was provided with a protective coating based on
Actilane 200~, ex Akcros Chemicals.
The film was rendered homogeneously light scattering by heating to
134~C, followed immediately by cooling to about 20~C in ~2 seconds.
Writing with a thermal printing head gave a very good contrast. The
film was erased by the same method.
