CA1106954A - Light valve suspension materials - Google Patents
Light valve suspension materialsInfo
- Publication number
- CA1106954A CA1106954A CA311,023A CA311023A CA1106954A CA 1106954 A CA1106954 A CA 1106954A CA 311023 A CA311023 A CA 311023A CA 1106954 A CA1106954 A CA 1106954A
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- light valve
- particles
- acetate
- valve according
- phenyl acetate
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Abstract
Abstract of the Disclosure A light valve including suspending materials which have an ability to prevent or substantially retard agglomeration of the particles in suspen-sion during the application of a voltage to the suspension. The materials include aromatic esters which are derivable from aromatic alcohols such as phenyl acetate, cresyl acetate, para-butylphenyl acetate, paranonylphenyl acetate, and structurally similar compounds. The suspension also includes, as an additional suspending material, a polymer such as a branched polymeric coating material to coat the particles in suspension and act in combination with the aromatic ester suspending materials to prevent or substantially reduce agglomeration of the particles when a voltage is app?ied to the suspension Other suspending materials such as non-aqueous liquids or solids may also form part of the suspending medium of this invention.
Description
~ 6954 ll . I
. ¦ ckqround of the Invcntion his invention relates to suspending matcrials and more particularly to suspending materials which are used in fluid suspensions to prevent or substanti.all.y reduce the agglo- i meration of the particles in suspension. This aggl.omeration phenomenon is particularly marked when fluid suspensions are ¦ used in a light valve under the influence of an electric field.
., 1, In colloidal suspensions and especially liquid colloida~
. ¦ suspensions the ~articles in suspension have a tendency to group !
together to form large clusters of particles. This phenomenon, agglomeration, destroys the uniform distribution of the particles !
in suspension and in many cases renders the suspension o~ lit~le ;
value. The problem is particularly pronounced in suspen~ions that are used in light valves. A light valve is described in more detail in U. S. Patent 3,708,219, assigned to the assignce of the present invention. It usually consists of two transparentl flat substantially parallel walls which are separated by a rel.~- ¦
tively small distance, generally on the order of O.S mil to 50 mils, and is sealed around its periphcr~ to form an enc1osed c~
Thin, conductive, transparent coatings are ap"licd on tne ir.teriot~
surfaces of the walls and thc cell is fillecl with a fluid sus~en-¦
sion which may ~light polarizing particlcs. l`he sus?ended particles are norm~lly randomly disperscd in .he suspen.sion an~ i I in this ranclom condition, duc to ~rownian motion the ~luid sus-pension appears dar~i, bccause the particles al)sorb ligllt and tend to extinc3ui.sh visible ligllt rays attemptincJ to pdSS ~hrou~h the suspcnsion. }~owever, when a voltage.is applicd to th~ con-~ ductive coatings of thc lightivalve (i.e., across the suspen~iorl) j the particles, wllic21 are preferably ro~ e, acicular, or o~h~r-wise anisometri~, align ~erpelldi.cul~r ~o thc walls of thc ccl1.
l.l - 2 -~1~36~4 In this condition, light passes through the suspension and the suspension appears transparent. It is principally this applica-tion of the voltage to the suspension that causes agglomeration of the particles.
There has been substantial research in an effort to develop a light valve suspension where the particles in suspen-sion would stay uniformly distributed and not agglomerate or group together when an electric field is applied. Conventional suspensions will hold particles in suspension for various per-iods of time with no applied electric field. Examples of such suspensions are given in U.S. Patents 1,951,664 Land; 1,955,923 Land; 1,963,493 Land; 3,512,876 Marks; and 3,773,684 Marks.
However, when an electric field is applied, the suspending mater-ials in the art prior to this invention, are unable to maintain the partlcles in suspension in a dispersed condition; and the particles group together to form agglomerates. Various methods have been developed over the years to attempt to overcome this problem. One such method is described in U.S. Patent 2,481,621 Rosenthal; wherein supersonic waves are transmitted into a liquid suspension to agitate and disorient the suspended particles in order to break up and prevent agglomeration.
Another method is described in U.S. Patent 3,655,267 whereby a high frequency alternating current voltage is used to prevent agglomeration. Other patents propose to use a pulsating voltage as a means of reducing agglomeration. Still others use a smooth generally laminar flow to cause the constant movement of the particles and thereby prevent the particles from agglo- !
merating.
~Q6954 These prior art patents have required the use of elec-trical or sonic methods or fluid movement to either prevent or break up agglomerates. They each require the use of special equipment in conjunction with the light valve to accomplish the anti-agglomerat;on function.
Thus, a method of maintaining the dispersed condition of the particles by using a suspending material which maintains such dispersion upon the application of a voltage across the suspension would be extremely useful and of great value in the operation of light valves.
Summary of the Invention Suspending materials and a fluid suspension using said suspending materials which have a marked tendency to reduce or eliminate agglomeration of the colloidal particles in suspension upon the application of a voltage to the suspension. The sus-pending materials include an aromatic ester with the structure of the kind that results from reacting an aromatic alcohol sub-stituted or unsubstituted with an acid substituted or unsubsti-tuted. Said structure can also be obtained by other well-known chemical methods. The suspending material includes phenyl acetate, ortho or para-cresyl acetate or similar substances such as p-butylphenyl acetate or p-nonlphenyl acetate, taken alone or mixed with suitable non-aqueous solids and/or liquds. The sus-pension using the aforesaid suspending material also includes nitro-cellulose or more preferably a branched copolymer which can be used to coat the particles to inhibit their grouping together. Such branched polymeric coating materials comprise those discussed in U.S.
Application S.N. 596,198, invented by one of the inventors of ..
~lQ6~54 the present application and assigned to the assignee of the present application, which is included in this application by reference.
An object of this invention is suspending materials which prevent or substantially retard agglomeration of fluid suspensions which contain particles which are responsive to an electric field.
Another object of this invention is a light valve in-cluding a combination of suspending materials which prevent or substantially retard agglomeration of fluid suspensions which contain particles which are responsive to an electric field when an electric field is applied.
Another object of this invention is a first suspend-ing material which is used in cooperation with a second suspend-ing material, namely a polymeric coating material, to prevent or substantially retard agglomeration of the particles in sus-pension.
Another object of this invention is the use of aromatic esters, including aromatic esters having aliphatic components pendant from the aromatic ring, as suspending materials.
Preferred Embodiment of the Invention This invention relates to suspending materials which are used in conjunction with colloidal particles to form a fluid suspension. The fluid suspension is one which is particularly useful in light valve suspensions where an electric field is applied to the suspension. Essentially, the purpose of the suspending material is to maintain the uniform distribution of ;~
11~6~54 the colloldal particles in the suspension and prevent their grouping together. In fluid suspensions used in light valves, the uniform distribution is especially important because if the particles group together or agglomerate, the light valve, when activated, will not appear transparent but will include blotches of these agglomerates.
The anti-agglomerating suspending materials of this invention include electrically resistive material such as phenyl acetate, cresyl acetate, including ortho-cresyl acetate and para-cresyl acetate, and aromatic esters having aliphatic chain components, straight chain or branched, pendant from the aromatic ring, such as para-butylphenyl acetate and para-nonylphenyl acetate. They are highly resistive so that they will not adversely affect the ability of the particles to align when a voltage is applied across the suspension, (usually on the order of 8 x 107 ohm-cm and above).
The structures of some of these materials are diagrammed in FIGS. 1, 2 and 3. FIG. 1 is the structure of phenyl acetate which is the reaction product of phenol and acetic acid. FIG. 2 is the structure of ortho-cresyl acetate which is the reaction product of ortho-cresol and acetic acid. FIG. 3 is the structure of para-cresyl acetate which is the reaction product of para-cresol and acetic acid. FIG. 4 is a diagram of the structure of d-ibutyl phthalate which is distinctly different from the structures in FIGS. 1, 2 and 3.
In FIGS. 1 to 3, an oxygen atom, which is part of the ester, is attached directly and adjacent to the ring. This is a result of an aromatic alcohol that was reacted with an acid to form the aromatic ester. The effect of such materials in preventing agglomeration is unexpectedly different from the aromatic ester of FIG. 4, which is the reaction product of an aromatic acid and an alcohol. An example of an aromatic ~0~;954 ester of the last mentioned kind is dibutyl phthalate; see U.S. Patent 1,951,h64 Land, issued March 20, 1934; U.S. Patent 1,955,923 Land, issued April 24, 1934; and U.S. Patent 3,625,869 Marks, issued December 7, 1971. However, dibutyl phthalate is ineffective in retarding or preventing agglomeration compared to the materials of the present invention. A reason for this difference in behavior between aromatic esters derivable from aromatic alcohols on one hand, and aromatic esters derivable from aromatic acids on the other hand, is that esters derived from aromatic acids have a carbon atom, instead of an oxygen atom, which is part of the ester, attached directly to and adjacent to the ring. It is unexpected that this difference in chemical structure should make so marked a difference in the effect upon agglomeration.
The materials of this invention can be used alone or can be combined with non-aqueous liquids such as aliphatic esters including branched esters, e.g., isopentyl acetacte, and certain non-polar aromatic or aliphatic liquids such as toluene or trifluorotrichloroethane~ respectively. The materials of this invention, if liquids, should be liquids which are preferably not detrimental to the light valve and to other suspending materials and the suspended particles, and also be liquids which preferably are relatively stable to heat and ultraviolet radiation. It has been found useful but not essential! that about 55% of the final suspending material (by weight) be composed of liquids not of this invention;
45% by weight will be composed of the suspending materials of this invention.
i954 The above suspending materials may be combined in the final suspension with the suspended particles that are coated with a polymeric compound such as nitrocellulose or, more pre-ferably, the materials which are described in detail in Canadian Application No. 311,024filed September 11, 1978. me latter are copolymers.
Each such copolymer includes at least two different monomers, at least one of which includes an unhindered functional group taken from the group consisting of an OH group and an acidic group, at least one of said monomers being soluble in the suspending medium, and at least one of said monomers being branched, and wherein the distance from the backbone to the available functional group most distant from the backbone in one monomer is less than the distance from the backbone to a non-functional group in another monomer.
In one aspect the polymer is one which has branch units which contain at least one functional radical selected from CO- and COO-.
These materials include, among others, the following compounds: copolymers of 3,5,5 trimethyl hexyl acrylate/2-hydroxypropyl acrylate/bis-2-ethylhexyl fumarate/fumaric acid;
and bis-2-ethylhexyl fumarate/3,5,5 trimethyl hexyl acrylate/
vinylidene chloride/mesaconic acid. Because of their properties, including their size, their OH or acid functional groups, their solubility, and their branched nature, thece materials as des-cribed in the said application, tend to prevent the particles from agglomerating together. They are thought to bond to the surface of the particles. When these coating materials are used as additional suspending materials in conjunction with the ~1~J69~i4 aromatic ester suspending materials, the combination acts to significantly retard agglomeraticnand under some conditions can retard agglomeration to the point where it does apparently not occur at all.
It is not preferred to use DC fields with this in-vention.
It is understood that gels and similar substances are intended to be included in this invention. Liquids of relatively high electrical resistivity are preferred in order to permit an applied electric field to orient the particles readily with relatively low voltages.
In order for a suspension to remain viable over a long period of time, the liquid, the suspended particles, and the suspending materials including the polymeric coating materials must not deleteriously react with or degrade one another.
The suspended particles may be of many types, but are preferably colloidal in size, and light polarizing in character. The term "light polarizing particles" includes light polarizing perhalide particles, but is meant to include other kinds of light polarizing particles as well.
The following are examples of the use of the suspending materials of this invention, alone or in combinations with additional non-aqueous materials. Examples are also provided to illustrate use of the aromatic ester suspending materials aforementioned with the polymeric coating materials.
These exam~les are only intended to be illustrative and not limiting in any manner.
_ 9 _ 1~6~54 EXAMPLE I
A test cell was constructed with three separate com-partments alongside each other with common walls and common electrodes to which an activating alternating voltage was applied at 10 kilohertz and 300 volts peak-to-peak. The internal thick-ness of the cell, i.e., the thickness of the suspension, was 9 mils (.009 inch). The first compartment was filled with a liquid suspension of particles of quinine bisulfate periodide said particles having been made with a combination of calcium iodide and hydrogen iodide, (i.e., hydriodic acid) together with iodine, suspended in the liquid, isopentyl acetate. The suspension also included about 1% nitrocellulose. The second compartment was filled with a suspension o the same particles and about 1% nitro-cellulose in diisodecyl adipate. The third compartment was filled with the same particles suspended in phenyl acetate having a resistivity of 8 x 107 ohm-cm. This suspension also included about 1% nitrocellulose. All three compartments were activated simultaneously with the same voltage continuously applied for 2 hours. At the end of that time a great deal of agglomeration was observed in compartment 1, whereas only faint agglomeration was observed in compartment 2, and there was no observable agglo-meration in compartment 3.
EXAMPLE II
Two of the compartments of the test cell of Example 1 were filled as follows: The first compartment was filled with a suspension of cinchonidine sulfate periodide, made with hydro-gen iodide and iodine, in a liquid comprising 99% isopentyl acetate and approximately 1% nitrocellulose. The second compartment 1~6~S4 as filled with a suspension of the same particles in a liquid comprised of 49.5% isopentyl acetate, 49.5% ortho-cresyl acetate (having a resistivity of 6.5 x 108 ohm-cm) and 1% nitrocellulose.
An activating alternating voltage of 100 volts R.M.S. at 60 hertz was applied to the electrodes of both compartments simultaneously for 2 hours 35 minutes. The thickness of the suspension in the cell was 9 mils (.009 inch). At the end of the said test period, the~e was noticeable agglomeration of the particles in compart-ment 1, whereas there was no significant agglomeration in compart-ment 2.
EXAMPLE III
A test was made with the same cell operating under the same conditions as in Example II, using the same suspended par-ticles except that the suspending liquids in the three compart-ments were as follows: In compartment 1, the suspending liquid was 99% isopentyl acetate with 1% nitrocellulose therein. In compartment 2, the suspending liquid was 49.5/O isopentyl acetate, 49.5% ortho-cresyl acetate with 1% nitrocellulose therein. In compartment 3, the suspending liquid was 49.5% isopentyl acetate, 49.5% para-cresyl acetate with 1% nitrocellulose therein. The cell and all three compartments were activated simultaneously and continuously for 17.5 hours, at the end of which time the following observations were made. There was heavy agglomeration in compartment 1. In compartment 2, there was very slight agglo-meration at the top of the suspension i.e., at the air-suspension interface, but this agglomeration is attributed to initial inter-action with the air at the surface because this agglomeration started almost immediately after the cell was activated and then did not increase any further throught the 17.5 hours. Only )Ç;9~;4 slight agglomeration was observable in compartment 3 at the end of the 17.5 hours.
EXAMPLE IV
A suspension of dihydrocinchonidine sufate periodide was suspended in a liquid consisting of 51V/o isopentyl acetate and 41% phenyl acetate, with 8% nitroceIlulose therein. This suspension was placed in a display cell in which a symbol D was delineated by shaping the conductive coating on one wall of the cell in the shape of the character, as described in Canadian Patent No. 972,857 issued August 12, 1975. The suspension in the display cell was 4.5 mils thick. The cell was activated with an alternating voltage of 170 volts peak-to-peak at 60 hertz applied continuously for 7 (seven) weeks. At the end of this test no agglomeration was visible to the naked eye, not even around the edges of the display symbol. The fact that there was no agglomeration visible at the edge of the symbol is significant because the gradient of electric potential at the ed-ges of the symbol is greater than the gradient would be if the electrodes on both walls of the cell were continuously covered with conductive coatings in the areas where the display symbol was located. Without the benefits of this invention, high potential gradients produce more agglomeration than low potential gradients.
EXAMPLE V
A liquid suspension of particles of quinine bisulfate periodide, made from calcium iodide, hydrogen iodide and iodine, was placed in a 2 mil cell, and suspended in a liquid of the following composition:
.~ - 12 -Trichlorotrifluoroethane66.0%
Isopentyl acetate 705%
Chloroform 7,5%
Polymer 11.0%
Para-cresyl acetate 7.5%
Particles 0.5%
1 00 . 0%
The polymer was a tetrapolymer consisting of the following monomers in the indicated weight percent:
3,5,5 trimethyl hexyl acrylate 37.5%
bis-2-ethylhexyl fumarate3705%
. ¦ ckqround of the Invcntion his invention relates to suspending matcrials and more particularly to suspending materials which are used in fluid suspensions to prevent or substanti.all.y reduce the agglo- i meration of the particles in suspension. This aggl.omeration phenomenon is particularly marked when fluid suspensions are ¦ used in a light valve under the influence of an electric field.
., 1, In colloidal suspensions and especially liquid colloida~
. ¦ suspensions the ~articles in suspension have a tendency to group !
together to form large clusters of particles. This phenomenon, agglomeration, destroys the uniform distribution of the particles !
in suspension and in many cases renders the suspension o~ lit~le ;
value. The problem is particularly pronounced in suspen~ions that are used in light valves. A light valve is described in more detail in U. S. Patent 3,708,219, assigned to the assignce of the present invention. It usually consists of two transparentl flat substantially parallel walls which are separated by a rel.~- ¦
tively small distance, generally on the order of O.S mil to 50 mils, and is sealed around its periphcr~ to form an enc1osed c~
Thin, conductive, transparent coatings are ap"licd on tne ir.teriot~
surfaces of the walls and thc cell is fillecl with a fluid sus~en-¦
sion which may ~light polarizing particlcs. l`he sus?ended particles are norm~lly randomly disperscd in .he suspen.sion an~ i I in this ranclom condition, duc to ~rownian motion the ~luid sus-pension appears dar~i, bccause the particles al)sorb ligllt and tend to extinc3ui.sh visible ligllt rays attemptincJ to pdSS ~hrou~h the suspcnsion. }~owever, when a voltage.is applicd to th~ con-~ ductive coatings of thc lightivalve (i.e., across the suspen~iorl) j the particles, wllic21 are preferably ro~ e, acicular, or o~h~r-wise anisometri~, align ~erpelldi.cul~r ~o thc walls of thc ccl1.
l.l - 2 -~1~36~4 In this condition, light passes through the suspension and the suspension appears transparent. It is principally this applica-tion of the voltage to the suspension that causes agglomeration of the particles.
There has been substantial research in an effort to develop a light valve suspension where the particles in suspen-sion would stay uniformly distributed and not agglomerate or group together when an electric field is applied. Conventional suspensions will hold particles in suspension for various per-iods of time with no applied electric field. Examples of such suspensions are given in U.S. Patents 1,951,664 Land; 1,955,923 Land; 1,963,493 Land; 3,512,876 Marks; and 3,773,684 Marks.
However, when an electric field is applied, the suspending mater-ials in the art prior to this invention, are unable to maintain the partlcles in suspension in a dispersed condition; and the particles group together to form agglomerates. Various methods have been developed over the years to attempt to overcome this problem. One such method is described in U.S. Patent 2,481,621 Rosenthal; wherein supersonic waves are transmitted into a liquid suspension to agitate and disorient the suspended particles in order to break up and prevent agglomeration.
Another method is described in U.S. Patent 3,655,267 whereby a high frequency alternating current voltage is used to prevent agglomeration. Other patents propose to use a pulsating voltage as a means of reducing agglomeration. Still others use a smooth generally laminar flow to cause the constant movement of the particles and thereby prevent the particles from agglo- !
merating.
~Q6954 These prior art patents have required the use of elec-trical or sonic methods or fluid movement to either prevent or break up agglomerates. They each require the use of special equipment in conjunction with the light valve to accomplish the anti-agglomerat;on function.
Thus, a method of maintaining the dispersed condition of the particles by using a suspending material which maintains such dispersion upon the application of a voltage across the suspension would be extremely useful and of great value in the operation of light valves.
Summary of the Invention Suspending materials and a fluid suspension using said suspending materials which have a marked tendency to reduce or eliminate agglomeration of the colloidal particles in suspension upon the application of a voltage to the suspension. The sus-pending materials include an aromatic ester with the structure of the kind that results from reacting an aromatic alcohol sub-stituted or unsubstituted with an acid substituted or unsubsti-tuted. Said structure can also be obtained by other well-known chemical methods. The suspending material includes phenyl acetate, ortho or para-cresyl acetate or similar substances such as p-butylphenyl acetate or p-nonlphenyl acetate, taken alone or mixed with suitable non-aqueous solids and/or liquds. The sus-pension using the aforesaid suspending material also includes nitro-cellulose or more preferably a branched copolymer which can be used to coat the particles to inhibit their grouping together. Such branched polymeric coating materials comprise those discussed in U.S.
Application S.N. 596,198, invented by one of the inventors of ..
~lQ6~54 the present application and assigned to the assignee of the present application, which is included in this application by reference.
An object of this invention is suspending materials which prevent or substantially retard agglomeration of fluid suspensions which contain particles which are responsive to an electric field.
Another object of this invention is a light valve in-cluding a combination of suspending materials which prevent or substantially retard agglomeration of fluid suspensions which contain particles which are responsive to an electric field when an electric field is applied.
Another object of this invention is a first suspend-ing material which is used in cooperation with a second suspend-ing material, namely a polymeric coating material, to prevent or substantially retard agglomeration of the particles in sus-pension.
Another object of this invention is the use of aromatic esters, including aromatic esters having aliphatic components pendant from the aromatic ring, as suspending materials.
Preferred Embodiment of the Invention This invention relates to suspending materials which are used in conjunction with colloidal particles to form a fluid suspension. The fluid suspension is one which is particularly useful in light valve suspensions where an electric field is applied to the suspension. Essentially, the purpose of the suspending material is to maintain the uniform distribution of ;~
11~6~54 the colloldal particles in the suspension and prevent their grouping together. In fluid suspensions used in light valves, the uniform distribution is especially important because if the particles group together or agglomerate, the light valve, when activated, will not appear transparent but will include blotches of these agglomerates.
The anti-agglomerating suspending materials of this invention include electrically resistive material such as phenyl acetate, cresyl acetate, including ortho-cresyl acetate and para-cresyl acetate, and aromatic esters having aliphatic chain components, straight chain or branched, pendant from the aromatic ring, such as para-butylphenyl acetate and para-nonylphenyl acetate. They are highly resistive so that they will not adversely affect the ability of the particles to align when a voltage is applied across the suspension, (usually on the order of 8 x 107 ohm-cm and above).
The structures of some of these materials are diagrammed in FIGS. 1, 2 and 3. FIG. 1 is the structure of phenyl acetate which is the reaction product of phenol and acetic acid. FIG. 2 is the structure of ortho-cresyl acetate which is the reaction product of ortho-cresol and acetic acid. FIG. 3 is the structure of para-cresyl acetate which is the reaction product of para-cresol and acetic acid. FIG. 4 is a diagram of the structure of d-ibutyl phthalate which is distinctly different from the structures in FIGS. 1, 2 and 3.
In FIGS. 1 to 3, an oxygen atom, which is part of the ester, is attached directly and adjacent to the ring. This is a result of an aromatic alcohol that was reacted with an acid to form the aromatic ester. The effect of such materials in preventing agglomeration is unexpectedly different from the aromatic ester of FIG. 4, which is the reaction product of an aromatic acid and an alcohol. An example of an aromatic ~0~;954 ester of the last mentioned kind is dibutyl phthalate; see U.S. Patent 1,951,h64 Land, issued March 20, 1934; U.S. Patent 1,955,923 Land, issued April 24, 1934; and U.S. Patent 3,625,869 Marks, issued December 7, 1971. However, dibutyl phthalate is ineffective in retarding or preventing agglomeration compared to the materials of the present invention. A reason for this difference in behavior between aromatic esters derivable from aromatic alcohols on one hand, and aromatic esters derivable from aromatic acids on the other hand, is that esters derived from aromatic acids have a carbon atom, instead of an oxygen atom, which is part of the ester, attached directly to and adjacent to the ring. It is unexpected that this difference in chemical structure should make so marked a difference in the effect upon agglomeration.
The materials of this invention can be used alone or can be combined with non-aqueous liquids such as aliphatic esters including branched esters, e.g., isopentyl acetacte, and certain non-polar aromatic or aliphatic liquids such as toluene or trifluorotrichloroethane~ respectively. The materials of this invention, if liquids, should be liquids which are preferably not detrimental to the light valve and to other suspending materials and the suspended particles, and also be liquids which preferably are relatively stable to heat and ultraviolet radiation. It has been found useful but not essential! that about 55% of the final suspending material (by weight) be composed of liquids not of this invention;
45% by weight will be composed of the suspending materials of this invention.
i954 The above suspending materials may be combined in the final suspension with the suspended particles that are coated with a polymeric compound such as nitrocellulose or, more pre-ferably, the materials which are described in detail in Canadian Application No. 311,024filed September 11, 1978. me latter are copolymers.
Each such copolymer includes at least two different monomers, at least one of which includes an unhindered functional group taken from the group consisting of an OH group and an acidic group, at least one of said monomers being soluble in the suspending medium, and at least one of said monomers being branched, and wherein the distance from the backbone to the available functional group most distant from the backbone in one monomer is less than the distance from the backbone to a non-functional group in another monomer.
In one aspect the polymer is one which has branch units which contain at least one functional radical selected from CO- and COO-.
These materials include, among others, the following compounds: copolymers of 3,5,5 trimethyl hexyl acrylate/2-hydroxypropyl acrylate/bis-2-ethylhexyl fumarate/fumaric acid;
and bis-2-ethylhexyl fumarate/3,5,5 trimethyl hexyl acrylate/
vinylidene chloride/mesaconic acid. Because of their properties, including their size, their OH or acid functional groups, their solubility, and their branched nature, thece materials as des-cribed in the said application, tend to prevent the particles from agglomerating together. They are thought to bond to the surface of the particles. When these coating materials are used as additional suspending materials in conjunction with the ~1~J69~i4 aromatic ester suspending materials, the combination acts to significantly retard agglomeraticnand under some conditions can retard agglomeration to the point where it does apparently not occur at all.
It is not preferred to use DC fields with this in-vention.
It is understood that gels and similar substances are intended to be included in this invention. Liquids of relatively high electrical resistivity are preferred in order to permit an applied electric field to orient the particles readily with relatively low voltages.
In order for a suspension to remain viable over a long period of time, the liquid, the suspended particles, and the suspending materials including the polymeric coating materials must not deleteriously react with or degrade one another.
The suspended particles may be of many types, but are preferably colloidal in size, and light polarizing in character. The term "light polarizing particles" includes light polarizing perhalide particles, but is meant to include other kinds of light polarizing particles as well.
The following are examples of the use of the suspending materials of this invention, alone or in combinations with additional non-aqueous materials. Examples are also provided to illustrate use of the aromatic ester suspending materials aforementioned with the polymeric coating materials.
These exam~les are only intended to be illustrative and not limiting in any manner.
_ 9 _ 1~6~54 EXAMPLE I
A test cell was constructed with three separate com-partments alongside each other with common walls and common electrodes to which an activating alternating voltage was applied at 10 kilohertz and 300 volts peak-to-peak. The internal thick-ness of the cell, i.e., the thickness of the suspension, was 9 mils (.009 inch). The first compartment was filled with a liquid suspension of particles of quinine bisulfate periodide said particles having been made with a combination of calcium iodide and hydrogen iodide, (i.e., hydriodic acid) together with iodine, suspended in the liquid, isopentyl acetate. The suspension also included about 1% nitrocellulose. The second compartment was filled with a suspension o the same particles and about 1% nitro-cellulose in diisodecyl adipate. The third compartment was filled with the same particles suspended in phenyl acetate having a resistivity of 8 x 107 ohm-cm. This suspension also included about 1% nitrocellulose. All three compartments were activated simultaneously with the same voltage continuously applied for 2 hours. At the end of that time a great deal of agglomeration was observed in compartment 1, whereas only faint agglomeration was observed in compartment 2, and there was no observable agglo-meration in compartment 3.
EXAMPLE II
Two of the compartments of the test cell of Example 1 were filled as follows: The first compartment was filled with a suspension of cinchonidine sulfate periodide, made with hydro-gen iodide and iodine, in a liquid comprising 99% isopentyl acetate and approximately 1% nitrocellulose. The second compartment 1~6~S4 as filled with a suspension of the same particles in a liquid comprised of 49.5% isopentyl acetate, 49.5% ortho-cresyl acetate (having a resistivity of 6.5 x 108 ohm-cm) and 1% nitrocellulose.
An activating alternating voltage of 100 volts R.M.S. at 60 hertz was applied to the electrodes of both compartments simultaneously for 2 hours 35 minutes. The thickness of the suspension in the cell was 9 mils (.009 inch). At the end of the said test period, the~e was noticeable agglomeration of the particles in compart-ment 1, whereas there was no significant agglomeration in compart-ment 2.
EXAMPLE III
A test was made with the same cell operating under the same conditions as in Example II, using the same suspended par-ticles except that the suspending liquids in the three compart-ments were as follows: In compartment 1, the suspending liquid was 99% isopentyl acetate with 1% nitrocellulose therein. In compartment 2, the suspending liquid was 49.5/O isopentyl acetate, 49.5% ortho-cresyl acetate with 1% nitrocellulose therein. In compartment 3, the suspending liquid was 49.5% isopentyl acetate, 49.5% para-cresyl acetate with 1% nitrocellulose therein. The cell and all three compartments were activated simultaneously and continuously for 17.5 hours, at the end of which time the following observations were made. There was heavy agglomeration in compartment 1. In compartment 2, there was very slight agglo-meration at the top of the suspension i.e., at the air-suspension interface, but this agglomeration is attributed to initial inter-action with the air at the surface because this agglomeration started almost immediately after the cell was activated and then did not increase any further throught the 17.5 hours. Only )Ç;9~;4 slight agglomeration was observable in compartment 3 at the end of the 17.5 hours.
EXAMPLE IV
A suspension of dihydrocinchonidine sufate periodide was suspended in a liquid consisting of 51V/o isopentyl acetate and 41% phenyl acetate, with 8% nitroceIlulose therein. This suspension was placed in a display cell in which a symbol D was delineated by shaping the conductive coating on one wall of the cell in the shape of the character, as described in Canadian Patent No. 972,857 issued August 12, 1975. The suspension in the display cell was 4.5 mils thick. The cell was activated with an alternating voltage of 170 volts peak-to-peak at 60 hertz applied continuously for 7 (seven) weeks. At the end of this test no agglomeration was visible to the naked eye, not even around the edges of the display symbol. The fact that there was no agglomeration visible at the edge of the symbol is significant because the gradient of electric potential at the ed-ges of the symbol is greater than the gradient would be if the electrodes on both walls of the cell were continuously covered with conductive coatings in the areas where the display symbol was located. Without the benefits of this invention, high potential gradients produce more agglomeration than low potential gradients.
EXAMPLE V
A liquid suspension of particles of quinine bisulfate periodide, made from calcium iodide, hydrogen iodide and iodine, was placed in a 2 mil cell, and suspended in a liquid of the following composition:
.~ - 12 -Trichlorotrifluoroethane66.0%
Isopentyl acetate 705%
Chloroform 7,5%
Polymer 11.0%
Para-cresyl acetate 7.5%
Particles 0.5%
1 00 . 0%
The polymer was a tetrapolymer consisting of the following monomers in the indicated weight percent:
3,5,5 trimethyl hexyl acrylate 37.5%
bis-2-ethylhexyl fumarate3705%
2-hydroxypropyl acrylate2200%
fumaric acid 3.0%
100. 0%
A 60 hertz alternating potential of 405 volts peak-to-peak (a gradient of 2.25 volts peak-to-peak per mil) was applied continuously for 24 hours. At the end of this time, no agglomeration was visible to the naked eyeO
Similar results were obtained with compositions in which the polymer was a copolymer selected from the group consisting of 2-ethylhexyl acrylate/acrylic acid; 2-ethylhexyl acrylate/hydroxyethyl methacrylate;
ethyl acrylate/hydroxyethyl methacrylate; 2-ethylhexyl acrylate/2-hydroxy-propylacrylate/acrylic acid; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/
fumaric acid; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl meth-acrylate; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/di-2-ethylhexyl maleate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/
di-2-ethylhexyl fumarate/fumaric acid; 2,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 5,5-diethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; bis-2-ethylhexyl fumarate/
2-hydroxypropyl acrylate/acrylonitrile; and bis-2-ethylhexyl fumarate/
11~69S4
fumaric acid 3.0%
100. 0%
A 60 hertz alternating potential of 405 volts peak-to-peak (a gradient of 2.25 volts peak-to-peak per mil) was applied continuously for 24 hours. At the end of this time, no agglomeration was visible to the naked eyeO
Similar results were obtained with compositions in which the polymer was a copolymer selected from the group consisting of 2-ethylhexyl acrylate/acrylic acid; 2-ethylhexyl acrylate/hydroxyethyl methacrylate;
ethyl acrylate/hydroxyethyl methacrylate; 2-ethylhexyl acrylate/2-hydroxy-propylacrylate/acrylic acid; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/
fumaric acid; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl meth-acrylate; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/di-2-ethylhexyl maleate/fumaric acid; 3,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/
di-2-ethylhexyl fumarate/fumaric acid; 2,5,5-trimethyl hexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 5,5-diethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; bis-2-ethylhexyl fumarate/
2-hydroxypropyl acrylate/acrylonitrile; and bis-2-ethylhexyl fumarate/
11~69S4
3,5l5-trimethyl hexyl acrylate/vinylidene chloride/mesaconic acid.
Ortho-cresyl acetate or phenyl acetate can be substituted for para-cresyl acetate, except that somewhat higher voltage gradients will be required.
The Examples given above demonstrate that agglomeration is greatly reduced by the use of aromatic esters of the kind that may be produced from aromatic alcohols. These aromatic esters include phenyl acetate, ortho-cresyl acetate and para-cresyl acetate. In addition, many aromatic esters having aliphatic groups pendant from the ring may be used including methyl phenyl acetate, ethyl phenyl acetate, propyl phenyl acetate, butyl phenyl acetate, amyl phenyl acetate, hexyl phenyl acetate, heptyl phenyl acetate, octyl phenyl acetate, nonyl phenyl acetate, and decyl phenyl acetate, in particular when the aliphatic group is located in the para positionO
In one broad aspect the esters of the present invention are aromatic esters wherein the aromatic radical may be aryl, (eOgO benzyl phenyl) alkylaryl (methylbenzyl, methyl phenyl), naphthyl and the like.
These liquids are particularly effective in retarding agglomera-tion and maintaining the dispersion of a variety of different suspended particles even in the presence of an electric field when used in combination 2Q with a polymeric coating material as previously described.
The aforesaid Examples illustrate that by using the present invention, and assuming that an adequate amount of either natural or artificial ambient light is available, a light valve or suspension of the present inven-tion is capable, when an electric field is appropriately applied thereto, of transmitting at least two times as much light as when the field is not applied, and is capable of maintaining its suspension in a well dispersed condition, if required, for a period of at least two hoursO
The present invention and the invention embodied in our United States Patent No. 4,025,163, issed on May 24, 1977 represent the first in-3Q stances known to the inventors wherein a fluid suspension, such as a suspen-9~i4 sion usable in a light valve, has been stabilized from agglomeration, even when subjected to an electric field for a prolonged period of time, by solely chemical means.
The present invention can be used with light valves that are used as windows, windshields, displays, mirros and other similar devices.
While specific embodiments of the invention have been described it will be appreciated that the invention is not limited thereto and many modifications thereof may be made by one skilled in the art which falls with-in the spirit and scope of the invention.
Ortho-cresyl acetate or phenyl acetate can be substituted for para-cresyl acetate, except that somewhat higher voltage gradients will be required.
The Examples given above demonstrate that agglomeration is greatly reduced by the use of aromatic esters of the kind that may be produced from aromatic alcohols. These aromatic esters include phenyl acetate, ortho-cresyl acetate and para-cresyl acetate. In addition, many aromatic esters having aliphatic groups pendant from the ring may be used including methyl phenyl acetate, ethyl phenyl acetate, propyl phenyl acetate, butyl phenyl acetate, amyl phenyl acetate, hexyl phenyl acetate, heptyl phenyl acetate, octyl phenyl acetate, nonyl phenyl acetate, and decyl phenyl acetate, in particular when the aliphatic group is located in the para positionO
In one broad aspect the esters of the present invention are aromatic esters wherein the aromatic radical may be aryl, (eOgO benzyl phenyl) alkylaryl (methylbenzyl, methyl phenyl), naphthyl and the like.
These liquids are particularly effective in retarding agglomera-tion and maintaining the dispersion of a variety of different suspended particles even in the presence of an electric field when used in combination 2Q with a polymeric coating material as previously described.
The aforesaid Examples illustrate that by using the present invention, and assuming that an adequate amount of either natural or artificial ambient light is available, a light valve or suspension of the present inven-tion is capable, when an electric field is appropriately applied thereto, of transmitting at least two times as much light as when the field is not applied, and is capable of maintaining its suspension in a well dispersed condition, if required, for a period of at least two hoursO
The present invention and the invention embodied in our United States Patent No. 4,025,163, issed on May 24, 1977 represent the first in-3Q stances known to the inventors wherein a fluid suspension, such as a suspen-9~i4 sion usable in a light valve, has been stabilized from agglomeration, even when subjected to an electric field for a prolonged period of time, by solely chemical means.
The present invention can be used with light valves that are used as windows, windshields, displays, mirros and other similar devices.
While specific embodiments of the invention have been described it will be appreciated that the invention is not limited thereto and many modifications thereof may be made by one skilled in the art which falls with-in the spirit and scope of the invention.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A light valve, which comprises a cell con-taining a suspension in a liquid suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, said liquid suspending medium comprising an ester of a phenol and a carboxylic acid, and said liquid suspending medium having nitrocellulose dis-solved therein for preventing agglomeration of the particles.
2. The light valve according to claim 1, wherein said phenol ester is an acetate of a phenol.
3. The light valve according to claim 2, wherein said phenol ester is phenyl acetate, para-cresyl acetate or ortho-cresyl acetate.
4. The light valve according to claim 2, wherein the phenol moiety is substituted.
5. The light valve according to claim 4, wherein the substituted phenol ester is methyl phenyl acetate, ethyl phenyl acetate, propyl phenyl acetate, butyl phenyl acetate, amyl phenyl acetate, hexyl phenyl acetate, heptyl phenyl acetate, octyl phenyl acetate, nonyl phenyl acetate, or decyl phenyl acetate.
6. The light valve according to claim 1, wherein said liquid suspending medium comprises at least 45 % by weight of said phenol ester.
7. The light valve according to claim 1, wherein said liquid suspending material also comprises an aliphatic ester, an aromatic compound, or a halogenated organic liquid.
8. The light valve according to claim 7, wherein said halogenated liquid is a fluorocarbon.
9. The light valve according to claim 1, wherein at least a majority of the suspended particles is colloidal.
10. The light valve according to claim 9, wherein the suspended particles are light polarizing particles.
11. The light valve according to claim 10, wherein the suspended particles are perhalide particles.
12. The light valve according to claim 1, which is capable, when an electric field is applied, of transmitting at least two times as much light as when the field is not applied, and which is capable of maintaining such dispersion, if required, for a period of at least two hours.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA311,023A CA1106954A (en) | 1978-09-11 | 1978-09-11 | Light valve suspension materials |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA311,023A CA1106954A (en) | 1978-09-11 | 1978-09-11 | Light valve suspension materials |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1106954A true CA1106954A (en) | 1981-08-11 |
Family
ID=4112330
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA311,023A Expired CA1106954A (en) | 1978-09-11 | 1978-09-11 | Light valve suspension materials |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1106954A (en) |
-
1978
- 1978-09-11 CA CA311,023A patent/CA1106954A/en not_active Expired
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