Note: Descriptions are shown in the official language in which they were submitted.
~315088
The present invention relates to light valves
and more particularly to improvements in the liquid
suspension of particles contained or adapted to be
contained within the light valve cell. Still more
particularly, the present invention relates to liquids
which may be included in such a liquid suspension of
particles.
Light valves have been known for more than fifty
years for modulation of light. In Edwin Land's U.S.
Patent No. 1,955,923 the light valve was defined as a
cell formed of two transparent sheets of insulating
material spaced apart a small distance and containing a
suspension of small particles in a liquid suspending
medium. As a practical matter, the suspension also in-
cludes a polymeric stabilizer dissolved in the liquid
suspending medium to prevent agglomeration of the
particles. Nitrocellulose was proposed as a polymeric
stabllizer in the beginning of the development of light
valves. More recently, U.S. Patents Nos. 4,164,365 and
4,273,422 disclosed polymeric stabilizers in the form of
copolymers or a mixture of polymers.
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In the absence of an applied electrical field,
the particles in the liquid suspension ex~bit random
Brownian movement, and hence a beam of light passing into
the cell is reflected, transmitted or absorbed, depending
upon the nature and concentration of the particles and the
energy content of the light. ~hen an electrical field is
applied through the suspension in the light valve, the
particles become aligned and for many suspensions a sub-
stantial part of the light can pass through the cell.
lOLight valves have been extensively described in
the literature. See U.S. Patent Nos. 1,955,923, 1,963,496,
3,512,876 and 3,773,684. In the early days of television,
Donal, ~ngmuir and &oldmark thoroughly investigated the
use of light valves in black and white as well as color
15television. See U.S. Patent Nos. 2,290,582, 2,481,621,
2,528,5L0 and 2,645,976. A more modern use of the light
valve is as an alpha-numeric display. Also, active matrix
addressed high information content light valve displays
including flat color television set replacements for the
cathode ray tube have been proposed by the assignee of
the present invention. Such displays could function in
a manner partly analogous to commercially available flat
color TV sets which use liquid crystals to produce images.
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Light valves have also been proposed for use in windows,
eye-glasses and the like to control the amount of sun-
light passing therethrough.
A wide variety of organic and inorganic particles
have been proposed for use in light valves including mica,
graphite, numerous ~etals, and halogen-containing light-
polarizing crystals including, for example, certain metal
halides and perhalides of alkaloid acid salts. Likewise,
a wide variety of liquids have been suggested as all or
part of the light valve li~uid suspending medium to sus-
pend the small particlesand dissolve the polymeric
stabilizer, such as certain esters, nitrobenzene, oils
and other liquids. See U.S. Patent Nos. 1,961,664,
2,290,582 and others.
Isopentyl acetate and isopentyl isobutyrate have
been proposed for use as a suspending liquid in a light
valve in U.S. Patent 4,442,019 to Marks. The suspending
liquids of the present invention have markedly improved
stability over the esters proposed by Marks.
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Dibutyl phthalate has been proposed for use as a
suspending liquid in a light valve in U.S. Patents 1,951,664
and 1,~55,923 to Land and 3,625,869 to ~Iarks. U. S. Patents
4,025,163 and 4,113,362 to Saxe et al. propose the use
of aromatic esters derived by reaction between an aromatic
alcohol and an aliphatic acid.
U. S. Patent No. 4,407,565 proposed to bring a
light valve suspension into substantial gravitational
equilibrium by using as the liquid suspending medium
13 therefor an electrically resisti~e, inert, low molecular
weight, liquid fluorocarbon polymer having a specific
- gravity at ro~m temperature of at least about 1.5 and
having at least about 50% of its atoms constituted by
halogen atoms, at least 60% of said halogen atoms being
fluorine and the balance chlorine and/or bromine, and
an electrically resistive organic liquid miscible there-
with. A wide variety o organic liquids can be used as
the aforesaid miscible organic liquid. These include
esters of aliphatic and aromatic acids and alcohols, e.g.,
alkyl acetates, such as isopentyl acetate and alkylphenyl
acetates, such as p-nonylphenyl acetate, dioctylphthalate,
diisodecyl adipate, dioctyl sebacate, as well as aromatic
hydrocarbons, e.g., benzene and toluene, and silicones.
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The choice of the miscible organic liquid is im-
portant. Its boiling point should preferably be well
above 100C so as to keep its vapor pressure relatively
low in the normal operating temperature range for a light
valve, which might be -40~C to +85C.
The liquid should also have a very high electrical
resistivity, preferably at least 1011 ohm-cm and more
preferably 1012 ohm-cm or higher. The higher its electri-
cal resistivity, the lower the voltage required to orient
the suspended particles and the lower the power losses
in the suspension.
For many purposes, for example suspensions for
use in displays, rapid response time is important. Be-
cause response time is related to the suspension vis-
cosity, the lower the viscosity of the liquid, the
better when fast speed of response is desired.
Finally, the liquid should be compatible with
other materials in the suspension and not degrade or be
degraded by them or any of the cell co~ponents.
The present invention provides liquids for use in
the suspending medium of a light valve that meet these
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criteria. In particular, the present invention provides
a light valve in which the liquid suspending medium
comprises a liquid ester or ether of formula (I):
Rl _ X - R2 (I)
wherein Rl is branched chain alkyl of at least 8 carbon
atoms, such as from 8 to about 20 carbon atoms, or the
group (III)
R3
- Y - C - Z- CH3 (III)
R4
wherein Y and Z are independently a direct bond or
straight or branched chain alkylene, such as from 1 to 8
carbon atoms, and R3 and R4 are lower alkyl, such as from
1 to 6, preferably 1 to 3,carbon atoms, R2 is branched
chain alkyl or cycloalkyl, such as from 3 to about 20 carbon
atoms; and
X is -O-, -O-C- or -C-O-. Preferably, Rl and R
contain from 3 to about 12 carbon atoms. Suitably, Y is
straight or branched chain alkylene of from 1 to about 6
carbon atoms and Z lS a direct bond.
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Embra~ced within formula (I) are the presently
preferred esters and ethers:
R5 - X - R~ (II)
wherein RS is tertiary butyl, neopentyl, 2-ethylhexyl or
3,5,5-trimethylhexyl:, and R4 is isopropyl, tertiary butyl,
2-ethylhexyl, 3,5,5-trimethylhexyl or neopentyl.
The liquids used in the present invention are
branched low polarity monoesters and monoethers in which the
ester or ether linkage, as the case may be,is at least
partially sterically hindered on both sides of the linkage
with suitable groups, preferabl~ branched alkyl Of
'O 3 to 12.carb.on ato~s, The aforesaid criteria of low
polarity and hindrance of the linkagè ser~e to reduce or
eliminate any tendency of the liquid: (a) to desorb polymer
from particles suspended in a light val~e suspension or (b)
: in suspensions which employ a first polymer bonded to the
suspended particles and a second polymer bonded to or
associated with the first polymer, to weaken or destroy
the bond or association between said first and second
polymers. Any such desorption and/or weakening or de-
,~ struction of interpolymer bonds or associations will usually
'~ ~û reduce the physical stability of the suspension and can
often cause agglomeration and/or precipitation of the
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suspended particles.
The steric hindrance o the ester or ether also
prevents oxidation reactions between the oxygen of the
ester or ether and the particles, a problem that prior
art esters and ethers frequently caused when polyiodide
particles were suspended in the suspension.
Thus, the presence of the liquids used in the
present invention in a light valve suspension does not
chemically or physically degrade the quality of the sus-
pension, as prior art liquids often did~
The liquids used in the present invention can have
a wide range of boiling points and~freezing points.
However, the boiling point is generally above 150C
and preferably above 175C. The freezing point is
usually below 22C and preferably below -40C.
The viscosity of the liquids of the present invention
can likewise vary substantially but where fast responding
suspensions are desired, should preferably be 25 cps
or less at room temperature.
When a liquid o the present invention is used
in a light valve suspension which employs only one type
of polymerJ it should preferably be a solvent for said
- polymer. When used in a light valve suspension which
employs two polymers as described above, it should prefer-
ably be a solvent for the second polymer.
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Examples of liquid esters of the present in-
vention include 3,5,5-trimethylhexyl isobutyrate,
3,5,5-trimethylhexyl neopentanoate and neopentyl neo-
pentanoate. Electrical resistivities of these three
liquids are respectively about 3.8 x 1011 ohm-cm
(undistilled), 1.2 x 1012 ohm-cm (distilled), and 2.8
x 1011 ohm-cm ~distilled).
Examples of liquid ethers of the preser.t invention
include.di-2-ethylhexyl ether, di-3,5,5-trimethylhexyl
ether and dineopentyl ether. Non-syl,ul,etrical branched
ethers are also useable.
~here low viscosity is especially important, the
ethers have an advantage over the corresponding esters.
For example, it is known from the prior art that the
YiSCosity of benzyl benæoate at 25C is 8.292 cps whereas
the viscosity of dibenzyl ether at 20C is 5.333 cps.
Also, the viscosity of ethyl acetate at 15C is 0.473
cps whereas the viscosity of diethyl ether at 15C is
0.247 cps. Assu~ing that this well-known relationship
remains valid for the branched esters and ethers of the
present invention, one may predict a lower viscosity for
a branched ether than for the corresponding ester. A
reason why this may be true is that in general an ester
linkage is relatively inflexible compared to an ether
linkage.
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The use of the liquids of the present invention in
suspensions for light valves is described in the following
Examples:
EX~MPLE 1
Formulation For Makin~ ~ Paste Of Crystals Of
Dihydrocinchonidine Sulfate Periodide (DCSI)-A typical
formulation which can be used to prepare colloidal particles
of dihydrocinchonidine sulfate periodide is as follows:
Solution A
A solution consisting of:
0.65 gm. cesium iodide (CsI~
2.48 gm. dihydrocinchonidine sulfate (DCS)
10.00 gm. 2-ethoxyethanol
5.00 gm. H O
3.00 gm. methanol
is combined with
1522.00 gm. of a 33 1/3 solution of nitrocellulose
in 2-ethyoxyethanol. The nitrocellu-
lose should be a mixture of low vis-
cosity (18.6 cps) and high viscosity
(15 seconds~ types, 50% each.
Solution B
3.00 gm. chloroform
10.00 gm. n-propanol
201.38 gm. I2
22.00 gm. Tricresylphosphate
Shake well for 15 minutes.
Pour solution A into a plastic blender cup and add
Solution B while blender is at high speed. In 3-5 minutes
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product will form having a deep blue color in a gel-like
wet paste.
The resulting wet paste should be spread on a glass plate
at an 8 mil thickness and allowed to dry at room tempera-
ture for at least one hour.
The unsulfated starting material for the afore-
said reaction, dihydrocinchonidine alkaloid (sometimes
called hydrocinchonidine~ is commercially available. The
alkaloid material is then sulfated by dissolving it in a
mixture of 1.5 parts of methanol and 0.32 parts of 975/, H2S04
and then evaporating to dryness. The resulting dihydro-
cinchonidine sulfate is in the form of a light tan colored
powder.
Procedure for Processing a DCSI Paste
1. In a suitable jar, place the dried paste
which has been prepared in accordance with the method
described in Example 1. Add isopentyl acetate (IPA) and
hexanes so that the final percentage totals will be:
Paste 11%
IPA 59%
Hexanes 30%
Shake the above mixture for about 15 minutes
and then place the jar into an ultrasonic generator for
10 hours.
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2. After ultrasonicing, centrifuge the jar con-
tents for eight hours at 2,500 RPM and discard the super-
natant.
3. Spread the sediments from the centrifuge
tubes onto a glass plate and record the weight. Hereafter
these sediments will be called SMP (Solvent ~Ioist Paste).
4. Add to the SMP one-eighth (1/8) the amount of
S~ by weight of dioctyl adipate (DOA), and dry off at
room temperature the remaining IPA in the SMP.
5. Grind the pasta materials for 20 to 30 seconds.
Collect the ground paste material and add enough IPA to
form a suspension. This suspension is then rapidly stirred
for one hour. After stirring,ultrasonically agitate for
another ten hours.
6. Centrifuge the ultrasoniced material for one-
half (1/2) hour and save the supernatant.
7. Centrifuge the supernatant material for ten
hours and pour its supernatant off, leaving only the
sediment. The sediment (or SMP) is then resuspended one
part SMP and four parts isopentyl acetate. --
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8. A~ter thoroughly mixing, ultrasonic sus-
pension for ten hours.
g Add to the above suspension enough dioctyl
adipate so that for each 2.6 gms. o~ solid paste material,
- 5 there will be 7.4 gms. o~ DOA. The isopentyl acetate
should now be vacuumed off leaving only a 2~% paste/DOA ~
concentrate. This concentrate is now ready to be dispersed
in the final suspending medium.
Dispersion Into The Final Suspending Medium
1~ 10. A copolymer consisting of 97% neopentyl acrylate/
3% methylol acrylamide (NPA-MOAM~, by weight, and having a
molecular weight of approximately 25,000 is dissolved in
dioctyl adipate, neopentyl neopentanoate or type 0.8 Halo-
carbon Oil in the following weight percentages to form three
solutions:
Dioctyl adipate/NPA-MOAM - 50/50%
Neopentyl neopentanoate/NPA-MOAM - 75/25%
Type 0.8 Halocarbon Oil/NPA-MOAM - 85/15%
To reduce their viscosity, the above solutions
are ultrasoniced for at least 50 hours.
ll. The dilution factor for a concentrate depends --
upon the cell spacing and whether the material is to be used
in a transmissive, transflective or reflective mode. I
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have found that much less copolymer is needed to stabilize
a suspension which has a relatively high percentage of
paste, and that preferably such paste percentage should
be at least 2.6%. To talie advantage of this information
and to also avoid too dark an off-state for the suspension,
as well as to minimize the voltage needed to activate the
suspension in a light valve, the cell spacing should
preferably be 2-mils or less.
12. Using the DOA/NPA-MOAM 50/50% solution, add
enough to the concentrate so that the final dilution re-
sult will show 2.6% paste and 10% for DOA. Be sure to
mix well. To this is added the 75/25~/o Neopentyl neo-
pentanoate /NPA-M~AM so that the final dilution result will
show 10% for neopentyl neopentanoate. Mix well. The 15lg5v~/~
Halocarbon Oil/NPA-MOAM solution should now be added and
mixed in well, The amount of this solution is determined
by the total percentagc of copolymer needed in the final
suspension, Halocar~on Oil alone is now added to bring
the total percentage up to 100%. The final suspension is
now ultrasoniced for at least one hour.
Final Suspension Percentages For A Cell
Having A Distance Of 2-mils Between Its
Electrodes
Paste - 2.6%
NPA-~IOAM Polymer - 15.0
' ~ DOA - 10.0
Neopentyl neopentanoate - 10.0
0.8 Halocarbon Oil - 62.4
100. 0%
Type 0.8 Halocarbon Oil is described in Saxe, U,S. Patent
4,407,565.
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EXAMPLES 2 7
Example 1 is repeated in each case except that
the neopentyl neopentanoate is replaced: ~a)
in Example 2 with 3,5,5-trimethylhexyl isobutyrate (b)
in Example 3 with 3,5,5-trimethylhexyl neopentanoate (c)
in Example 4 with dineopentyl ether (d) in Example 5 with
di-3,5,5-trimethylhexyl ether; (e) in Example 6 with
di-2-ethylhexyl ether, and (f) in Example 7 with isobutyl
neopentanoate.
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EXAMPLE 8
Liquid suspending media used in t~ present in-
vention were co~pared to isopentyl acetate and isopentyl
isobutyrate as follows.
The procedure of Example 1 was followed to prepare
five suspensions of DCSI in the candidate liquid, with the
following modification.s. In step 9, the amount of dioctyl
adipate was 7.0 grams. In step 10, the NPA-MOAM copolymer
was added to the candidate liquid suspending medium and in
step 12 the concentrate from step 9 is mixed with the
NPA-MOAM copolymer/candidate liquid. No halocarbon oil was
used in order to provide a direct comparison between the
five suspending liquids tested. The final suspensions
contained:
PERCENT
DCSI paste 2.6
NPA-MOAM Polymer 12.0
DOA 7.0
Candidate liquid 78.4
The candidate liquids were neopentyl neopentanoate
(Example 1), 3,5,5-trimethylhexyl isobutyrate (Example 2) and
isobutyl neopentanoate (Example 7) according to the present
invention, and isopentyl acetate and isopentyl isobutyrate
according to Marks U.S. Patent 4,442,019.
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Each of the final suspensions was subjected to
accelerated aging by storage at 85C for 66 hours. The
properties of the suspensions were measured after storage.
The results of the tests are reported below:
Properties Of Suspensions Before and After Storage
At 85C for 66 Hours
Color of Suspension OPtical Dknsity (Off) Optical Density
Ratio ~OFF/GN)
Li~ Suspend ~
Medium ~ Before After Before After Before After
EE~le 1 Blue Blue 3.0 3.0 1.3 1.3
Example 2 Blue Blue 3.3 3.1 1.3 1.2
Fx~mrle 7 Blue Blue 2.4 2.4 1.~ 1.2
Isopentyl acet te Blue k~ber 2.0 ~0.6 1.3 1.0
Isopentyl iso-
butyrate Blue Yellow 2.0 ~0.6 1.3 1.0
After storage, the prior art suspensions changed color,
which indicates that degradation products had formed. However,
the suspensions according to the invention didnot degrade and
showed no change in color.
The optical density of each suspension was measured
at a field strength of approximately 11 volts/mil RMS (ON) and
at no applied voltage (OFF), and the ratio of optical densities
at the OFF and ON states was calculated. ~
All five suspensions functioned satisfactorily be-
~ore storage at 85C for 66 hours, but after storage the two
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prior art suspensions had degraded, as see.~ by comparing their
optical density and optical density ratio before and after
storage. Indeed, an optical density ratio of 1.0, after
storage, for the prior art suspensions means that there is no
significant change in the optical density of the suspension
between the ON and OFF states, and hence the prior art sus-
pensions, after storage, had degraded to the point where they
were inoperative as light valve suspensions.
In contrast, the suspensions prepared according to
the present invention showed no significant change in their
excellent optical densities or optical density ratios after
storage. These data demonstrate the superior stability of the
liquid suspending media used in the present invention.
While specific embodiments of my invention have
been illustrated, it will be appreciated that the in-
vention is not limited thereto, since many modifications
may ~e made by one skilled in the art which fall within
the true spirit and scope of the invention.
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