[go: up one dir, main page]
More Web Proxy on the site http://driver.im/

GB1586122A - Light valves - Google Patents

Light valves Download PDF

Info

Publication number
GB1586122A
GB1586122A GB2121377A GB2121377A GB1586122A GB 1586122 A GB1586122 A GB 1586122A GB 2121377 A GB2121377 A GB 2121377A GB 2121377 A GB2121377 A GB 2121377A GB 1586122 A GB1586122 A GB 1586122A
Authority
GB
United Kingdom
Prior art keywords
light valve
particles
acrylate
suspension
acid
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB2121377A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Research Frontiers Inc
Original Assignee
Research Frontiers Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Research Frontiers Inc filed Critical Research Frontiers Inc
Priority to GB2121377A priority Critical patent/GB1586122A/en
Publication of GB1586122A publication Critical patent/GB1586122A/en
Expired legal-status Critical Current

Links

Classifications

    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/17Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on variable-absorption elements not provided for in groups G02F1/015 - G02F1/169
    • G02F1/172Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on variable-absorption elements not provided for in groups G02F1/015 - G02F1/169 based on a suspension of orientable dipolar particles, e.g. suspended particles displays

Landscapes

  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)

Description

(54) LIGHT VALVES (71) We, RESEARCH FRONTIERS INCORPORATED, of 31 Cain Drive, Plainview, New York, United States of America, a corporation organised under the Laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to light valves. In more general terms, the present invention relates to the use of certain polymeric materials which stabilize particles, including particles of colloidal size, to prevent them from grouping together, i.e. agglomerating, when the particles are in suspension. In colloidal systems, especially liquid colloidal suspensions, the particles in suspension tend to group or stick together to form large groups of particles.This phenomenon is often referred to as "agglomeration". The formation of large groups of particles destroys the substantially homogeneous distributions of the particles in suspension and essentially renders the suspension useless. This problem is particularly acute in suspensions which are used in light valves. In the operation of a light valve, a voltage is applied across the suspension. This voltage, because of the relative charges on or associated with the particles, may cause the particles to group together and form large groups of agglomerates. These masses prevent the proper functioning of the light valve and thereby destroy its utility.
There has been a need, therefore, to develop a material which would effectively act to prevent the suspended colloidal particles in a light valve from agglomerating.
Although the prior art is replete with references pertaining to dispersants including polymeric materials for maintaining particles in suspension, these materials are either unsuitable for use in a light valve suspension or greatly inferior for such purpose to the polymers used in accordance with the present invention.
Descriptions of light valves that use a liquid suspension may be found in U.S. Patent Nos.
1,955,923 and 3,708,219. Basically, they are devices which control the transmission of light.
In order to be suitable for use in a light valve suspension, a polymer should be soluble in the liquid suspending medium of the suspension. The polymer should, furthermore, be capable of associating with the surfaces of the suspended particles in order effectively to furnish steric protection from agglomeration, particularly when particles are aligned under the influence of an electric field, a condition which drastically increases the tendency to agglomerate. Also, the polymer should associate with the particles so that, if the polymer is present when the particles are initially formed, it will prevent the particles from growing too large and help to minimize formation of aggregates of particles during formation.The polymer should not attack the suspended particles so as to cause them to degrade and should not itself degrade at the temperature of use or at temperatures at which the suspension may be stored, lest its degradation products attach the suspended particles. Inter alia. degradation causes a loss of the polymer's ability to impart seric protection. The polymer should preferably have a wide range of solubility so that, if desired, it may be dissolved in the polar liquids in which many of the particles used in light valves are initially formed and also be soluble in relatively non-polar and low conductivity liquids used in operating light valves.The polymer should not coat the walls or the electrodes on the walls of the light valve, because a polymer that sticks to them creates a hazy appearance that destroys the clear view through the light valve and reduces the maximum light transmission or change of transmission attainable from the light valve.
Furthermore, the polymer should improve the voltage characteristics of the suspension in that it should enable one to obtain a greater change in light transmission for a given voltage gradient applied across the suspension, than is possible if one employed nitrocellulose, a known polymer for use in light valve suspensions. In this connection, it is especially important and preferred to be able to do so at low frequencies, e.g. 1000 Hertz or less, because electrical power usage is very much lower at low frequency than at higher activating frequencies.
Nitrocellulose, as mentioned above, has been in use for a considerable length of time and does work to a certain extent in light valve suspensions. Although it does somewhat prevent agglomeration, nitrocellulose has the significant disadvantage of being highly subject to degradation at only moderately high temperatures. For example, nitrocellulose will degrade at or below 150OF. At such temperatures nitrocellulose may break down and form degradation products including nitrous and nitric acids and these may attack the particles in suspension. If the particles degrade when attacked by such degradation products, the suspension will be destroyed. Nitrocellulose also has a further major disadvantage in that there are a limited number of suspending media in which it may be dissolved when it is used in light valves.These media are essentially limited to organic esters. For many functions, esters are not the most desirable liquids in which to suspend the particles. Therefore, nitrocellulose has very serious chemical and physical drawbacks which are overcome by the use of the polymeric materials in accordance with the present invention. These polymers have much greater thermal stability than nitrocellulose and will not generally break down unless temperatures are reached that are far above the point at which nitrocellulose will form nitrous and nitric acids. In addition, they are soluble in many relatively non-conductive liquid suspending media addition to esters.
The present invention relates to a light valve which comprises a cell containing a liquid suspension comprising: an electrically resistive liquid suspending medium; suspended therein, a plurality of anisometric polarizing, halogen - containing particles; and, substantially dissolved therein, a copolymer comprising at least one monomer having a sterically unhindered functional group, which is a hydroxyl group or an acidic group, and at least one monomer having a branched group, the distance from the backbone of the copolymer to the most distance sterically unhindered functional group being less than the distance to the terminal carbon atom of the branched group.
The present invention also relates to the production of such a light valve. The polymeric material stabilizes suspensions including colloidal particles and especially halogencontaining, light-polarizing particles and especially halogen-containing, e.g. herapathite, purpureocobaltchloridesulphateperiodide and cupric bromide.
The polymeric materials used are long chain molecular copolymers having available functional groups, in particular hydroxyl or acidic groups, in the structure thereof and are soluble in liquids in which the colloidal particles are suspendable. At least one of the monomers used to form the copolymer has a branched structure, which may include more than one branch. Some of the materials are copolymer of 3,5,5-trimethylhexyl acrylate/2hydroxypropyl acrylate/fumaric acid; 5,5-diethyl hexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; and bis-2-ethylhexyl fumarate/ 3,5 ,5-trimethyl hexyl acrylate/ vinylidene chloride/mesaconic acid. The polymers used act to prevent or retard agglomeration of the particles in suspension, especially when the suspension is in use in a light valve and a voltage is placed across the suspension.The polymers also make it possible for suspensions to be used at elevated temperatures without significant degradation and reduce the voltage gradient and electrical power needed to achieve a given change in light transmission for the light valve.
As indicated above, a principal purpose of the present invention is to maintain a substantially homogeneous distribution of colloidal particles in a suspending medium. In liquid suspensions, it is most important that the suspended particles be substantially uniformly distributed throughout the suspension. This uniform distribution is especially important when the liquid suspensions are used in light valves. The materials used in accordance with the present invention comprise copolymers, in particular copolymers which comprise at least one monomer having an available hydroxyl group or acidic group which is sterically unhindered and in a position to associate or bond with an element or part of the particles being stabilized. The remainder of the copolymer preferably comprises a monomer which is soluble in the liquid medium in which the particles are suspended.The polymeric stabilizing material thus has to be a material which both strongly bonds the copolymer to the particles and also must be soluble in the suspending medium. If neither part of the copolymer were soluble in the suspending medium, the polymer chains associated with particles would not be in a state or condition to extend a substantial distance outward from the particles to prevent agglomeration effectively.
Briefly, a light valve consists of two sheets of usu: !y transparent material. such as glass or plastic, which are spaced a very small distance apart. such as from 1 to 50 mils, and are connected around the periphery thereof by a sealing material. such as an adhesive. The sheets have transparent electrically-conductive coatings of a material. such as tin oxide or indium oxide. on the inner facing surfaces thereof and the coatings are connected via leads, such as conductive silver paint, and wiring to a source of power, preferably a source of AC voltage.
The space between the transparent sheets is filled with a suspension, such as a suspension of herapathite particles in a suspending medium, such as amyl acetate or isopentyl acetate.
The, say, herapathite particles used in a light valve are small, preferably colloidal sized, and are anisometrically-shaped, preferably lath-like, rod-shaped or needle-shaped particles, having an aspect ratio preferably ranging from 5 : 1 to 20 : 1. These anisometric particles, which are preferably light-polarizing, polyhalide particles, are normally unaligned, that is randomly oriented, i.e. totally disoriented, in the suspension. Provided that there is sufficiently high concentration of unaligned crystals in suspension, light cannot easily pass through the suspension because it is absorbed or blocked by the plurality of particles. The suspension will appear very dark. However, when an electric field is applied across the suspension, the particles align parallel to the field (perpendicular to the transparent light valve walls).This is accomplished by placing a voltage across the leads that are connected to the thin transparent conductive coatings which are applied on the thin transparent conductive coatings which are applied on the inside faces of the walls of the cell. The voltage is thus placed across the transparent walls or sheets so the field passes through the suspension. When a voltage exists through the suspension, the particles become aligned as aforesaid so that the long axes thereof are perpendicular to the transparent coatings, i.e. parallel to the electric field between the coatings. In this position the particles will block very little of the light passing through the suspension since the particles will generally have the long axes thereof parallel to the direction of the light passing through.Thus, when an electric field is placed across the cell or, in other words, when the cell is placed in the "on" condition, light may readily pass therethrough. The suspending medium in which the particles are suspended is preferably transparent so that, once the particles are aligned, there is little to block the transmission radiation, in particular visible light through the suspension. However, once the voltage is removed, Brownian movement quickly disaligns the particles so that the longer axes thereof will be at angles to the direction of the light in many cases and therefore, light will not be able to pass readily through the suspension.
As mentioned above, a major problem with these particles is that they tend to be attracted to each other. This is especially true when a voltage is placed across the suspension. Under the influence of an electric field the particles are thought to act like induced dipoles and the attraction between the positive and negative ends of proximate particles is sufficient so that once the voltage is placed across the suspension, they will start grouping together rapidly to form large groups of particles. This will defeat the purpose of the light valve since in the "on" condition it should preferably remain uniformly transparent. However, there will be relatively large black areas where the particles have grouped together and where the suspension is no longer transparent.What is needed therefor, is a material which will prevent the particles from grouping together or will essentially keep them in the normal properly dispersed suspended relationship thereof. The materials used in accordance with the present invention achieve this result. These materials readily associate with and stabilize the halogen-containing, light polarizing particles. The particles being stabilized are preferably ones that contain iodine, such as herapathite, or ones that contain other halogens, such as cupric bromide. The polymeric stabilizing materials not only associate with the polarizing particles, but also contain components which permit them to dissolve readily in the liquids in which the polarizing particles are suspended.Some of the polymeric materials that may be used include copolymers of 2-ethylhexyl acrylate/acrylic acid; 2-ethylhexyl acrylate/hydroxyethyl methacrylate; 2-ethylhexyl acrylate/ 2-hydroxypropyl acrylate/ acrylic acid; 2-ethylhexylacrylate/2- hydroxypropyl acrylate/fumaric acid; 2-ethylhexyl acrylate /2- hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 3.5,5-trimethyl hexyl acrylate/ 2-hydroxypropyl methacrylate; 3,5.5-trimethyl hexyl acrylate/ 2-hydroxypropyl methacrylate; 3,5 .5-trimethyl hexyl acrylate/ 2-hydroxypropyl acrylate/ fumaric acid; bis-2ethylhexyl fumarate / 2-hydroxypropyl acrylate/ acrylonitrile; 5,5-diethyl hexyl acrylate /2- hydroxypropyl acrylate/fumaric acid; and bis-2-ethylhexyl fumarate/3,5,5-trimethyl hexyl acrylate/vinylidene chloride/mesaconic acid.These materials have a functional group of a polar character. in particular a hydroxyl and/or an acidic group, in a position to associate readily with and form a bond with the particle. probably with the halogen. such as iodine, in the particles being stabilized, but possibly also or alternatively with another part of the particle. The association or bond formed by this group is thought to be a hydrogen bond, but may possibly be another type of bond or be in addition to another type of bond, such as a coordinate covalent bond. However. it appears that the hydroxyl or acidic group and not the hydrogen alone is needed for th bonding. It is -lso thought that the hydrogen bonding and/or coordinate covalency through the oxygen leads to effectiveness of the bond. These bonds between polymer and particles are extremely strong bonds.It is noted that in the case of certain substances, for example. acrylic acid. there is a COOH group available. It is thought that the OH is probably the primary reason for its effective action. However. the CO may also be active. It will be appreciated that in all cases some available, i.e. free, hydroxyl or acidic groups are present in the copolymers. By the term "free" is meant that the hydroxyl or acidic group is in a position that makes it available for bonding, that is it is sterically unhindered by the remaining structure of the molecule of which it is a part, so that it may readily act to form the hydrogen bond and/or coordinate covalent bond, in particular with halogen.If the hydroxyl or acidic group were not in this position, for example if in a copolymer it was constructed to by rigid groups in close proximity thereto, it would not be in as good a position to combine readily and therefore the material involved would not be one that would be an effective bonding or stabilizing agent. It will be appreciated that in the above copolymer materials, the acid or acidic monomers or monomers which include functional groups, e.g.
acrylic acid, fumaric acid, mesaconic acid, maleic acid or acrylonitrile, or one of the hydroxyalkyl ester monomers, e.g. hydroxyethylacrylate, hydroxyethyl methacrylate or 2-hydroxypropyl acrylate, are the substances which include available acidic or hydroxyl groups and act to combine with, in particular the halogen to form the association or bond.
These monomers, depending upon choice of monomer may or may not be branched and may or may not be soluble in the suspending medium depending upon choice of monomer and medium. Another part of these copolymers, for example 2-ethylhexyl acrylate, bis-2ethylhexyl fumarate, 5,5-diethylhexyl acrylate or 3,5,5-trimethyl hexyl acrylate, acts to dissolve the copolymers in the suspending liquid medium.
It is preferably a branched monomer and more preferably has two or more branches.
Branching greatly enhances the ability of the copolymer to retard agglomeration of a light valve suspension under the influence of an electric field and is necessary to be effective against agglomeration. Although even one branch, such as the ethyl group of the monomer 2-ethylhexyl acrylate, is helpful in this regard and considerably more effective than an unbranched monomer, such as octyl acrylate, it is much more useful to have a plurality of branches. Although the precise reason why branching impedes agglomeration is not known, one possible theoretical reason may be that, provided the branches do not block bonding groups from bonding to the particles to be stabilized, the space occupied by the branch may convey steric protection by preventing two particles from approaching one another too closely.If this theory is correct, it would be reasonable to expect that a plurality of branches will be more effective than one branch of about the same size, as is found experimentally. For reasons that are as yet unknown, the presence of a branched monomer in the copolymer also reduces the voltage gradient needed to achieve a given change in light transmission for a light valve.
Preferably at least one monomer, such as the aforesaid branched monomer, which serves, it is thought, a steric blocking function, should possess no functional bonding groups. Preferably also such monomer or monomers should constitute a majority of the copolymer by weight percent and should be the largest monomer or monomers therein in terms of the comparative molecular weights of the monomers. The branches may themselves be branched, i.e. have sub-branches attached thereto.
Although the branched monomers and many of the other monomers exemplified above are esters, they may be of numerous other types. For example, the copolymers may include monomers, such as ethers or cyclic monomers, and may include monomers having particularly useful substituent groups, such as halogenated monomers, in particular fluorinated monomers, which aid the copolymer in the attainment of solubility in fluorinated liquids which may be useful suspending media.
If desired, two or more copolymers of similar or differing characteristics may be used in a suspension simultaneously.
The suspending medium, which for light valves is preferably electrically non-conductive, may be such diverse fluids as aliphatic or aromatic hydrocarbons, silicones, esters and non-polar ethers, particularly halogenated chemically stable solvents, such as fluorinated alkanes, fluorinated esters or fluorinated ethers and mixtures thereof.
When using a fluorinated liquid in a suspending medium, it may be necessary to include with it a more polar, but relatively non-conductive liquid, such as an ester, e.g. isopentyl acetate, as part of the suspending medium of a suspension in order to achieve alignment of the particles at moderate voltages. Moreover, the weight percent or mole percent of each type of monomer or the weight percent of hydroxyl or acidic groups used in a copolymer may be tailored and adjusted to make possible solubility in a particular liquid or liquids. Thus, the copolymers combine the effective bonding action with the ability to dissolve in many types of liquid suspending media. The part of these polymeric materials that dissolves in the suspending medium should be sufficiently soluble that the copolymer as a whole may substantially dissolve in the suspending medium. It will be appreciated that, in the operation of light valves, the more non-conductive the suspending medium is, the better the light valve will function and perform. That is, the less conductive the liquid medium, the less electric power and voltage are usually required to cause the alignment of the particles, and hence the more readily operable the light valve will be. Thus, it is one of the advantages of the presently used copolymers that, Rt, they will readily dissolve in very non-conductive suspending media.
Some of these relatively non-conductive suspending media have been mentioned above, but it will be noted that they are numerous and generally it could be said that suspending media having an electrical resistivity of 5 x 107 ohm-cm or more, preferably 5 x 109 ohm-cm or more, will be operable. A suspension, which includes the suspended particles and copolymer, will be somewhat less resistive than the suspending medium alone.
The polymeric materials used in accordance with the present invention have particularly good thermal characteristics, that is, the copolymers may generally withstand a temperature ranging from as low as the freezing point of the suspending medium to temperatures in excess of 100"C without breaking down. This permits the light valves to operate over a wide range of temperatures and particularly with non-conductive suspending media.
Nitrocellulose, which was used in prior art light valve suspensions, has very poor thermal properties as mentioned above. At temperatures at or below 150OF, nitrocellulose soon begins to break down and form degradation products including nitrous acid and nitric acid.
Formation of such degradation products reduces the amount of nitrocellulose available to retard agglomeration and degradation products also attack and may substantially ruin a suspension. The materials described herein, however, overcome these disadvantages.
Furthermore, as mentioned above, a nitrocellulose has the disadvantage that it may only be dissolved in certain liquid suspending media. Obviously, the medium must be one in which nitrocellulose will dissolve. These are essentially organic esters, such as isopentyl acetate and amyl or ethyl acetate. The non-viscous types of esters, which have a viscosity at 25"C of 5 centipoises or less, are not particularly non-conductive. They generally have a resistivity of 2 x 10 ohm-cm or less. Such non-viscous media are desirable when rapid alignment and disalignment of particles is sought.However, using the presently disclosed copolymers, resistivities one or more orders of magnitude greater may be readily achieved because suspending media may be used with these copolymers that have higher resistivities, i.e. lower conductivity at the same viscosity, and thus lower conductivity suspensions may be achieved at the same viscosity.
These copolymeric materials may be used initially during the formation of the particles so that the particles do not agglomerate and group together during formation and may be left bonded to the particles so that the material continues to prevent agglomeration during all stages of the particles' life and the use or operation thereof. However, they may also be used subsequent to particle formation when they are about to be used in a suspension. A polymer may also be added to a suspension which already includes some of the same polymer or of a different polymer.
Some examples of polyhalide materials that will form the suspended particles and are capable of polarizing light and use able in light valves include the above-mentioned herapathite, purpureocobaltchloridesulphateperiodide and cupric bromide.
The following are Examples of the production of suspensions for light valves. In Examples 1 to 9 and 12, the copolymer is used during the formation of particles used in the suspension and is retained in association with the particles when the suspension is made and actually put in operation. In Examples 10 and 11, the copolymer is added to the particles after the particles are formed and the polymer-bonded particles then placed in suspension and then operated in a light valve.
The copolymers used are preferably ones having an extended chain length of from 600 to 4,200 angstroms or more. Although they may be of random structural composition, alternating, block or graft copolymers may also be used advantageously.
EXAMPLE 1 42.5 grams of a 3331% solution of the copolymer 2-ethylhexyl acrylate/acrylic acid (75 %/ 25 %, by weight) in 2-ethoxyethanol is combined with 3.75 grams of quinine bisulphate and 0.50 grams of fluoroalcohol. Then, 8.5 grams of methanol and an additional 10 grams of 2-ethoxyethanol are added. An alcoholic solution of a plasticizer (optional), iodine and hydriodic acid (HI) is reacted with the above ingredients by mixing to form a wet paste of herapathite. The paste is then dried to remove the volatile solvents.
At this point a liquid suspending medium is added to the paste which is dispersed therein by continuous mixing and grinding.
In this test, the content of acid-including monomer in the copolymer as noted above was only 25%, by weight, in order to enhance the chance for the copolymer to dissolve in the suspending medium of a light valve in order to effect dispersion of the dried paste. Favourable results occured. The optical density of the resulting suspension in isopentyl acetate in a light valve was observed to change from 3.0 to approximately 0.85 when activated, indicating a substantial opening.
EXAMPLE 2 Example 1 was repeated, except that the ingredients were as follows: 42.5 grams of a 30%, by weight, solution of 2-ethylhexyl acrylate/acrylic acid in 2-ethoxyethanol as in Example 1, 2.68 grams of quinine bisulphate, 7.30 grams of methanol and an additional 10 grams of 2-ethoxyethanol.
EXAMPLE 3 Example 2 was repeated, except that the additional 10 grams of 2-ethoxyethanol were omitted and 0.50 grams of chloroform added to the contents prior to reaction.
EXAMPLE 4 A copolymer of 2-ethylhexyl acrylate/acrylic acid (50%/50%, by weight) was prepared.
42.5 grams of the solution of the copolymer was prepared as a 25%, by weight, solution in 2-ethoxyethanol to which was added 3.75 grams of quinine bisulphate and 8.50 grams of methanol. As in Example 1, an alcoholic solution of a plasticizer, iodine and hydriodic acid was reacted with the above ingredients to form a wet paste. The dried paste, using heat to aid dispersion, was then suspended in decyl alcohol. The substance was placed in a light valve and satisfactory operation was achieved.
EXAMPLE 5 Example 1 was repeated, except that an 85 %/ 15 %, by weight, copolymer of 2-ethylhexyl acrylate/acrylic acid was substituted for the 75%/25% copolymer. The dried paste, unlike the paste in Example 1, was dispersible in the aromatic hydrocarbons, toluene, and, as in Example 1, displayed substantial opening in a light valve. Toluene has the advantages of having a high electrical resistivity and a low viscosity and therefore a fast response in a light valve.
EXAMPLE 6 Example 1 is repeated, but n-propanol is substituted for 2-ethoxyethanol to enhance copolymer solubility, and a 93.5%/6.5%, by weight, copolymer of 2-ethylhexyl acrylate/acrylic acid substituted for the copolymer of Example 1. The resulting dried paste of herapathite was dispersible in an aliphatic hydrocarbon, hexane. Aliphatic hydrocarbons have low viscosities than esters. Aliphatic hydrocarbons are therefore desirable suspending media for certain light valves.
EXAMPLE 7 Approximately 0.2 grams of purpureocobaltchloridesulphateperiodide, an inorganic polyiodide, was mortared in 1 gram of a 75%/25%, by weight, copolymer of 2-ethylhexyl acrylate/acrylic acid as a 33 3 % solution in 2-ethoxyethanol. After drying to evaporate the 2-ethoxyethanol, the particles were suspended in isopentyl acetate and the resulting suspension in a light valve had a grey appearance. Using a voltage gradient of between 30 and 90 volts per mil, in a pulsed mode of operation, the suspension was observed to pulse open arid closed continuously in response to the applied voltage without noticeable significant agglomeration. Under a continuous voltage gradient of approximately 30 volts per mil and greater a continuous opening of the suspension was observed for several seconds without significant agglomeration.
EXAMPLE 8 Approximately 0.04 grams of cupric bromide, a polyhalide material in which the halogen is bromine, was mortared in 1 gram of a 75%/25%, by weight, copolymer of 2-ethylhexyl acrylate/acrylic acid as a 33 3 % solution in 2-ethoxyethanol. After drying to evaporate the 2-ethoxyethanol, the resulting suspension was suspended in isopentyl acetate in a light valve and had a greenish-yellow appearance. Repeated pulsing was observed at a voltage gradient of 30 volts per mil or greater without significant agglomeration. Particles appeared to be in the size range of from 1 to 15 microns when observed through a microscope. Lower voltage gradients also produced good opening.
EXAMPLE 9 In order to demonstrate that other polar materials may also be used instead of acid in a copolymer formulation and still work, a 75%/25%, by weight, copolymer of 2-ethylhexyl acrylate / hydroxyethyl methacrylate was tested. The hydroxyethyl methacrylate monomer contains a hydroxyl functional group in each molecule. The hydroxyethyl methacrylate is also termed "ethylene glycol monomethacrylate". Using the method of Example 1, a successful well-protected suspension resulted. However, the 75 %/25 % composition of the copolymer prevented it from being completely soluble in isopentyl acetate alone and hence it was necessary to use a 2:1 mixture of isopentyl acetate and chloroform as the suspending medium for test purposes. It was observed in the test cell that the electrical resistivity of the resulting suspension (approximately 1.5 x 108 ohm-cm) was an order of magnitude greater than in cases where acid groups were present in the copolymer used to protect the suspended crystals.
Many of the aforesaid tests were conducted more than once using copolymers of various viscosities, i.e. molecular weights. In general, it is preferred to use the lowest molecular weight polymer possible consistent with, inter alia, anti-agglomeration objectives, because higher molecular weight polymers increase viscosity of the suspension and reduce the rise and decay (response) times of light valve suspensions.
Alternatively, the molecular weight of the copolymer may be chosen, if known, so that the length of the extended copolymer chain would be at least 600 angstroms, preferably from 2,000 to 4,200 angstroms or greater.
In order to avoid contamination of the final suspension, particularly in the case of a light valve suspension, the copolymer used should be as pure as possible. This is helpful in that it will prevent unnecessary conductivity in the final suspensions.
In the copolymer systems previously described, it has been established that the portion of the copolymer that was not of high polarity primarily affected the solubility of the copolymer.
In several of the aforesaid Examples, copolymers of 2-ethylhexyl acrylate/ acrylic acid resulted in good protection for crystals of herapathite and other materials that were formed or comminuted therewith. As a result of these tests, the conclusion was reached that probably the polar hydroxyl or acid functionality is responsible for the protection and that the non-polar groups in the copolymer serve the function of permitting the copolymer to be soluble in non-polar solvents or solvents of intermediate polarity depending upon chemical nature and quantities of the simple molecules contained in the copolymers.However, in order to be sure that the 2-ethylhexyl acrylate alone was not, by some chance, responsible for furnishing some or all of the protection, a homopolymer (not a copolymer) of 2-ethylhexyl acrylate was made, substituted for the copolymer in Example 1 and a paste of herapathite made in accordance with Example 1. As expected, poly(2-ethylhexyl acrylate) did not prevent agglomeration of particles either during the reaction, during drying, or in a light valve suspension of the dried herapathite paste. Accordingly, the conclusion that the hydroxyl or acid functionality was responsible for the favourable results previously observed was confirmed.
In the case of a colloidal fluid suspension, whether being stored for future use or actually in an unactivated light valve (power off), a copolymer used therein may be said adequately physically to protect the suspended crystals if no significant noticeable agglomeration takes place over a long period of time, at least days and preferably years.As a quick test of the efficacy of a polymer, a colloidal fluid suspension with the polymer is placed in a light valve having a low viscosity suspending medium (e.g. 5 centipoises or less) and the light valve activated by a 10 Kilohertz AC continuously applied electrical field (power on) having a continuous sinusoidal waveform and a voltage gradient strong enough to orient acicular crystals suspended therein, a copolymer used therein may be said adequately physically to protect the suspended crystals if the crystals do not noticeably agglomerate significantly for at least two seconds, preferably for at least 20 seconds.If the field is applied in a pulsed mode using short pulses, e.g. 20 milliseconds, with relatively longer periods without an applied field between pulses, but with sufficient voltage gradient to orient suspended crystals, suspensions in which the particles are adequately physically protected should change optical density repeatedly, i.e. open and close, in response to such pulses for at least 5 cycles, preferably for thousands of cycles or more, without noticeably agglomerating significantly.
Significant particle agglomeration may be visually noticed as dot-like or clump-like areas in the suspension, as well as by a substantial change in closed and/or open optical density for the suspension.
Suspensions containing a copolymer that does not adequately physically protect the particles will agglomerate substantially and, in many cases, cease to function almost entirely in less than the lower time intervals cited above under the above-mentioned test conditions.
For an inadequately protected suspension, upon application of a voltage gradient that would cause the particles to orient without agglomerating if the copolymer was effective, the poorly protected suspension is generally observed to open, but not to close. In this case, the "opening", i.e. reduction of optical density and increase of light transmission, is in large part caused by immediate agglomeration of the crystals; the agglomerated crystals are thought to be loosely stuck together and therefore cannot disorient, i.e. close through Brownian motion, as quickly as discrete oriented particles. Some poorly protected suspensions are so badly agglomerated before being placed in a light valve that the suspensions cannot be made to open at all.
It is thought that a copolymer that is effective in preventing or reducing agglomeration of particles in a suspension does so because part of the copolymer coils outward in solution in the suspending medium, possibly around the particles, thereby preventing or making difficult the close approach of another particle to the first particle.
In order that a material adequately physically protect suspended particles from agglomerating, two things are though necessary, namely. that the material at least partially bond to or associate with the particles and, secondly, that the material by forming a thick enough barrier around the particles and/or extending part of itself into solution prevents the close approach and agglomeration of two particles. Various materials that bond to or associate with the particles and have a long average length in solution relative to the average diameter of the particles might meet these requirements, but polymers have been found most effective, and the presently disclosed branched copolymers particularly efficacious and useful.
In order for a polymer to be useful in a light valve suspension, it is imperative that the polymer not coat the walls of the light valve and not coat the transparent electrically conductive coatings, i.e. the electrodes, that may cover all or part of the surfaces of the walls.
If the polymer does coat the walls or electrodes they will become hazy in appearance and will limit the maximum light transmission. It has been discovered that, in order to prevent the polymer from forming such an unwanted coating, the monomers in the copolymer must be selected so that, in a copolymer thereof, assuming all chains and branches fully extended and perpendicular to the source thereof, functional bonding groups, e.g. the hydroxyl and acidic groups, will be closer, preferably much closer, to the polymer backbone than non-bonding groups on at least one monomer that includes no functional bonding groups therein.Thus, if 3,5,5-trimethyl hexyl acrylate is copolymerized in a random terpolymer with fumaric acid and 2-hydroxypropyl acrylate, it is apparent from the known structures of these monomers that the terminal groups of the first-named monomer, which has no bonding groups therein, will extend further from the backbone than either the carboxyl groups in the fumaric acid monomer or the hydroxyl group in the 2-hydroxypropyl acrylate monomer. The same principle should be applied to the other polymers other than random copolymers, e.g. for any part of a graft copolymer that has bonding groups therein even if such part is itself a polymer.
Failure to follow the above-prescribed rule may lead to the undesirable result that the walls and electrodes become coated. It is theorized that this occurs because it becomes possible for the bonding groups to bond thereto. By following the above rule, the polymers may bond to the suspended particles, but not bond to the cell walls and electrodes.
In addition to retarding agglomeration and permitting use of suspensions at relatively high temperatures, the presently disclosed polymers are especially valuable in that they make it possible to use low activating voltages and small electric field gradients to operate light valve suspensions.
In the prior art relating to light valves, it has been suggested to use voltages at frequencies of 1 Kilohertz and higher. Use of lower frequencies would have resulted in the extremely rapid onset of agglomeration. This led to difficulty because low frequency power sources and outlets, such as 50 and 60 Hertz, are commonly available throughout the industrialized world and use of low frequencies would eliminate the need for expensive high frequency power supplies and would drastically reduce the amount of power required, as will as the attendant cost of power.
The present invention enables low frequencies to be used without agglomeration or with only slight agglomeration.
A factor that determines whether a suspension agglomerates and affects the rate of agglomeration if agglomeration does take place, is the voltage gradient applied across the suspension. "Voltage gradient" is defined as the voltage across the suspension, divided by the thickness of the suspensions, i.e. in an ohmic cell, the voltage applied between the two electrodes in the cell, divided by the distance between the electrodes. An "ohmic cell" is one in which the electrodes are in direct contact with the suspension. For example, when a voltage of 600 volts is applied across an ohmic cell in which the thickness of the suspension is 20 mils, i.e. 0.020 inch, the voltage gradient is 30 volts per mil. When an alternating voltage is used, it should be specified whether the stated voltage is peak-to-peak, or whether the stated voltage is a root-mean-square, i.e.RMS, value for a sine wave alternating voltage. A capacitative layer is placed between the electrodes and the suspension.
Large voltage gradients are known to cause agglomeration and to accelerate agglomeration; while small voltage gradients eliminate or retard agglomeration. However, prior to the present invention, small voltage gradients were not useful because they did not open the light valves sufficiently for practical application. The present invention enables small voltage gradients to be useful because they open the light valves to appreciable values of light transmission without agglomeration or with only small amounts of agglomeration.
Further advantages of small voltage gradients include: reduced electric power required to operate the light valve, with consequent savings of energy and cost; low voltage wiring, thereby requiring less electrical insulation around the electrical leads and terminals associated with the light valve; smaller power supplies. and power supplies of less weight; use of compact, mass-produced solid state electrical and clcctronic components; and reduction of the electric current that passes through the suspensioll with consequent reduction of the heat generated in the suspension. This last-mentioned advantage accrues from the observation that heat generated in the cell tends to degrade and decompose the suspension and may deteriorate the seals of the cell that contains the suspension within the light valve.
Another advantage of the present invention is that it enables liquid suspension light valves to be used to construct sunglasses and variable optical density spectacles, e.g. welding goggles. Prior to the present invention, such applications of liquid suspension light valves were not practical because they required high voltages, e.g. hundreds of volts, and such voltages carried close to the eyes and head of the wearer constituted a personnel safety hazard. The present invention enables such sunglasses, spectacles and goggles to be worn safely because the voltages are low, e.g. 4 volts.
Prior to the present invention, a polymer was used to protect the suspended particles in the light valve, but such prior art polymer had only relatively little effect in preventing agglomeration and relatively high voltage gradients were required to open the light valve when the prior art polymer was used. Nitrocellulose is representative of the prior art.
The following further Examples especially indicate the advantages of the presently disclosed polymers for the use of low voltages in light valves.
EXAMPLE 1OA Step 1: Dissolve the polymer in an alcohol, such as n-propanol or methanol, or an ether alcohol, such as 2-ethoxyethanol. Pour this solution into a high speed mixer, add 16.6 grams of tricresyl phosphate (TCP) and mix thoroughly. (Optionally, the TCP need not be added.) Step 2: Add 7.3 grams of methyl alcohol to 3.7 grams of quinine bisulphate (QBS) and stir until the QBS is dissolved. Add this solution to the mixture made in Step 1 and mix thoroughly in the high speed mixer.
Step 3: Make a solution of 20 percent iodine crystals in n-propanol which should age about 20 days. Take 8 grams of this solution and add 4 grams of n-propanol in which 0.27 grams of calcium iodide has been dissolved. Shake until well mixed.
Step 4: The mixture of Step 3 is poured into the mixture of Step 2 while the latter mixture is in the mixer operating at high speed. The mixer remains at high speed for approximately 35 seconds and is then stopped.
Step 5: The resulting mixture is spread on a glass plate to dry for approximately 90 minutes in an atmosphere of 50 percent relative humidity at 780F.
Step 6: The paste that results from Step 5 is scraped from the glass plate with a sharp blade. This paste is then ground in an electric mortar grinder for approximately 30 minutes.
90 grams of isopentyl acetate (IPA) is then added to the mortar bowl. This mixture is then added to a jar containing 33 milliliters of chloroform (CHCl3) and placed on a shaker for about one hour.
Step 7: The mixture resulting from Step 6 is diluted with IPA until it has an optical density of about 3 when placed in a light valve cell with a spacing of 33 mils, i.e. 0.033 inch.
Step 8: The suspension resulting from Step 7 is centrifuged for from 4 to 7 hours at a speed of 2500 revolutions per minute at a radius of about 3.5 inches.
Step 9, The supernatant from Step 8 is discarded; IPA is added to the sediment; and the diluted sediment is treated in an ultrasonic generator at a frequency of 47 KHz for from 1 to 2 hours.
Step 10: Centrifuge again for from 2 to 3 hours.
Step 11: Repeat Step 9.
Step 12: Centrifuge again for from 20 to 30 minutes and discard the supernatant.
Step 13: Dilute the sediment with IPA to give a suspension of the desired optical density.
The following are specific examples of the presently disclosed polymers and the processes for the production of suspensions using such polymers.
EXAMPLE 10 Tetrapolymer: 3,5,5 trimethyl- 1 -hexyl acrylate/2-hydroxy propyl acrylate/diethylhexyl maleate/fumaric acid, in the monomer percentages, by weight, 37.5/22/37.5/5.3.
A suspension was made in accordance with the method in the thirteen steps described above, with the following quantities used or exceptions. In Step 1, a solution of 2 grams of the tetrapolymer in 20 grams of alcohol was used. In Step 6, the mortar grinder is not used. After Step 7 and before Step 8. the diluted mixture is placed in an ultrasonic generator operating at about 47 KHz for about 17 hours.
Instead of Step 13. proceed as follows. Dilute the sediment with IPA and the tetrapolymer to give a suspension that contains 8 percent of the tetrapolymer. Thereafter, dilute further with an 8 percent tetrapolymer solution in IPA. to give a suspension of the desired optical density.
EXAMPLE 11 Tetrapolymer: 3.5,5 trimethyl- 1 -hexyl acrylate/2-hydroxy propyl acrylate/vinylidine chloride/fumaric acid. in the monomer percentages, by weight. 75/10/15/3.
A suspension was made in accordance with the method of Example 10, with the following exceptions. In Step l . the polymer of Example 11 was used instead of the polymer of Example 10.
EXAMPLE 12 Tetrapolymer: 3,5,5 trimethyl- 1-hexyl acrylate/ 2-hydroxypropyl acrylate/di-2ethylhexyl fumarate/fumaric acid, in the monomer percentages, by weight, 37.5/22/37.5/3.
A suspension was made as in Example 11, except that the polymer of Example 11 is replaced by the polymer of Example 12.
EXAMPLE 13 A suspension was prepared exactly as in the 13-step procedure above, using the homopolymer of the prior art, nitrocellulose (NC) instead of the presently used copolymers.
In Step 1, 6.6 grams of HA 17 NC and 7.5 grams of 21.6 centipoise NC (E.I. du Pont de Nemours & Co.) were dissolved in 2-ethoxyethanol.
Suspensions made with the tetrapolymers in three of the preceding four Examples, given above, do not agglomerate, or agglomerate very little compared to suspensions made with known polymers, when used in light valves. Furthermore, light valves made with the suspensions in the above three polymer Examples open much more, i.e. transmit much more radiation, than prior art suspensions for the same voltage gradient.
Suspensions made with the polymers in the above three Examples were tested and compared with a suspension made with nitrocellulose (NC). The tests were as follows. An ohmic light valve cell, that provided a 33 mil thickness for a suspension, was filled successively with a suspension made with NC and with suspensions in accordance with the three Examples. Each time the cell was filled, it was activated successively by alternating voltages at frequencies of 40, 60, 100 and 1000 Hz. In addition, 500 Hz was used for the polymer of Example 12. At each of the aforesaid frequencies, voltages of 01100, 200,300,400, 500 and 600 volts peak-to-peak were applied successively.At each and every combination of the aforesaid frequencies and voltages, the optical transmission of the cell was measured in the visible portion of the spectrum using an RCA photomultiplier No. 931-A manufactured by Radio Corporation of America. The results are given in the following Tables. The headings "NC" in the Tables means the transmissions of suspension made with NC. The headings "new polymer" means the transmissions of the suspensions made with the presently disclosed polymers in accordance with each respective Example. The ratio of transmission in each case is the quotient of the transmission of the suspension made with a "new polymer" divided by the transmission of the suspension made with NC.
USING COPOLYMER OF EXAMPLE 10 FREQUENCY: 40 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 0.955 0.977 100 3.03 1.02 1.32 1.29 200 6.06 1.26 3.47 2.75 300 9.09 1.74 6.61 3.79 400 12.12 2.51 10.23 4.07 500 15.15 3.98 12.59 3.16 600 18.18 6.17 14.13 2.29 USING COPOLYMER OF EXAMPLE 10 FREQUENCY: 60 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 0.955 0.977 100 3.03 1.02 1.32 1.29 200 6.06 1.35 3.31 2.45 300 9.09 2.00 6.61 3.30 400 12.12 2.95 10.47 3.54 500 15.15 4.47 12.88 2.75 600 18.18 6.46 14.79 2.28 USING COPOLYMER OF EXAMPLE 10 FREQUENCY: 100 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New 'missions Peak Mil Polymer 0 0 0.977 0.955 0.977 100 3.03 1.05 1.32 1.25 200 6.06 1.41 3.39 2.40 300 9.09 2.00 6.61 3.30 400 12.12 3.16 10.00 3.16 500 15.15 4.90 12.88 2.62 600 18.18 7.08 15.14 2.13 USING COPOLYMER OF EXAMPLE 10 FREQUENCY: 1,000 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0 955 0.955 0.977 100 3.03 1.26 1.45 1.15 200 6.06 2.51 3.63 1.44 300 9.09 5.01 7.59 1.51 400 12.12 8.51 11.22 1.31 500 15.15 12.59 13.49 1.07 600 18.18 15.85 15.95 1.01 USING COPOLYMER OF EXAMPLE 11 FREQUENCY: 40 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.18 1.20 100 3.03 1.02 2.34 2.30 200 6.06 1.26 6.31 5.00 300 9.09 1.74 9.77 5.81 400 12.12 2.51 12.59 5.01 500 15.15 3.98 14.79 3.96 600 18.18 6.17 15.85 2.56 USING COPOLYMER OF EXAMPLE 11 FREQUENCY: 60 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.18 1.20 100 3.03 1.02 2.24 2.19 200 6.06 1.35 6.31 4.67 300 9.09 2.00 10.00 5.00 400 12.12 2.95 13.18 4.46 500 15.15 4.47 15.85 3.54 600 18.18 6.46 17.78 2.75 USING COPOLYMER OF EXAMPLE 11 FREQUENCY: 100 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.18 1.20 100 3.03 1.05 2.34 2.22 200 6.06 1.41 6.31 4.47 300 9.09 2.00 9.55 477 400 12.12 3.16 12.88 4.07 500 15.15 4.90 15.85 3.23 600 18.18 7.08 18.62 2.62 USING COPOLYMER OF EXAMPLE 11 FREQUENCY: 1,000Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.18 1.20 100 3.03 1.26 2.51 1.99 200 6.06 2.50 6.31 2.51 300 9.09 5.01 10.47 2.08 400 12.12 8.51 14.13 1.66 500 15.15 12.59 16.60 1.31 600 18.18 15.85 19.05 1.20 USING COPOLYMER OF EXAMPLE 12 FREQUENCY: 40 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.02 1.04 100 3.03 1.02 1.86 1.82 200 6.06 1.26 5.01 3.97 300 9.09 1.74 9.77 5.61 400 12.12 2.51 13.18 5.25 500 15.15 3.98 15.85 3.98 600 18.18 6.17 18.20 2.94 USING COPOLYMER OF EXAMPLE 12 FREQUENCY: 60 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.02 1.04 100 3.03 1.02 1.86 1.82 200 6.06 1.35 4.68 3.46 300 9.09 2.00 11.22 5.61 400 12.12 2.95 15.49 5.25 500 15.15 4.47 18.62 4.16 600 18.18 6.46 19.50 3.01 USING COPOLYMER OF EXAMPLE 12 FREQUENCY: 100 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.02 1.04 100 3.03 1.05 1.95 1.85 200 6.06 1.41 4.79 3.39 300 9.09 2.00 11.22 5.61 400 12.12 3.16 15.49 4.88 500 15.15 4.90 18.62 3.80 600 18.18 7.08 19.95 2.81 USING COPOLYMER OF EXAMPLE 12 FREQUENCY: 500 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.02 1.04 100 3.03 1.18 2.04 1.72 200 6.06 1.95 5.50 2.82 300 9.09 3.55 10.96 3.08 400 12.12 6.03 15.14 2.51 500 15.15 8.91 17.78 1.99 600 18.18 12.02 19.05 1.58 USING COPOLYMER OF EXAMPLE 12 FREQUENCY: 1,000 Hz Applied Voltage Transmission Ratio of Voltage Gradient In Percent Trans Peak-to- Volts per NC New missions Peak Mil Polymer 0 0 0.977 1.02 1.04 100 3.03 1.26 1.95 1.54 200 6.06 2.51 5.75 2.29 300 9.09 5.01 11.22 2.23 400 12.12 8.51 15.85 1.86 500 15.15 12.59 19.05 1.51 600 18.18 15.85 20.42 1 Examination of this data reveals the following.
The use of the presently disclosed polymers results in more than a five-fold increase in the opening of the light valve compared to the use of prior art polymers. Inter alia, this is shown for the copolymer of Example 11 at 300 volts a:ltI and ! fix :r S shown also for the copolymer of Example 12 at 300 volts at 40, 60 and 100 Hz.
At all frequencies of the activating voltage and at all voltages. the presently disclosed polymers give greater valve openings, i.e. more transmission, than does the polymer of the prior art, i.e. NC. This is shown, without exception, in all rows of figures, in all Examples, at all frequencies, in all of the above Tables. In all cases, the use of the presently disclosed polymers enables the light valve to be opened more with a lower activating voltage.
The present invention may be applied to light valves that are used, for example, as displays, windows, including double glazed units, windshields and mirrors.
The previously-described liquid suspensions may also be set (hardened) by not adding plasticizer in the preparation thereof. The uses of such set suspensions include using these thin, hardened films of material as sheet polarizers.
The presently disclosed polymers are useful with a variety of particles including dye particles, dichroic, pleochroic or light-polarizing dye materials.
It is to be understood that the present invention may be applied to a light valve that operates in part or all of the infra-red andior ultra-violet portions of the electromagnetic spectrum, as well as the visible part of the electromagnetic spectrum, depending on the type of light valve and suspension employed.
It is understood that the term "liquid", where applicable, may include a gel or a thixotropic liquid, or a plastic liquid provided that the suspended particles may be oriented therein upon application of an electric field.
In the present context and in that of the related cases mentioned below, the terms "perhalide" and "polyhalide" may be used interchangeably.
U.K. Patent No. (Application No. 21214/77) (Serial No. 1586123) relates, inter alia, to a light valve which comprises a cell containing a liquid suspending medium, suspended therein, particles of one or more halogenated alkaloid acid salts (as herein defined) or metal halides and, dissolved therein, a polymeric stabilizer to prevent agglomeration of the particles, the liquid suspending medium comprising a liquid halogenated hydrocarbon having a ratio of halogen atoms to all other atoms therein of greater than 1:1, the halogen atoms of the particles being iodine and/or bromine and the halogen atoms of the halogenated hydrocar box being of lower atomic weight that the halogen atoms of the particles and at least 60% of the halogen atoms of the halogenated hydrocarbon being fluorine and/or chlorine.
U.K. Patent No. 1586125 (Application No. 21216/77) relates, inter alia, to a process for the preparation of a light-polarizing material which comprises: hydrogenating an unsaturated bond of a branch chain of an unsaturated alkaloid; forming an acid salt of the resulting saturated compound; forming an acid salt of the resulting saturated compound; and forming a polyhalide of the resulting alkaloid acid salt (as therein defined).
U.K. Patent No. 1586126 (Application No. 21217/77) relates, inter alia, to a light valve which comprises a cell containing a suspension in a liquid (as therein defined) suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, the liquid suspending medium comprising an ester of a phenol and a carboxylic acid, and the liquid suspending medium comprising, disclosed therein, a polymeric material for preventing agglomeration of the particles.
U.K. Patent No. 1586127 (Application No. 21218/77) relates, inter alia, to a light polarizing perhalide of and alkaloid acid salt having incorporated in its molecular structure at least one halide of calcium, rubidium or cesium the perhalide being the reaction product of an alkaloid acid salt (as therein defined), elemental iodine and the halide.
U.K. Patent No. 1586124 (Application No. 21215/77) relates, inter alia, to a light valve which comprises a cell contacting a suspension in a liquid suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, the liquid suspending medium comprising an ester of a phenol and a carboxylic acid.
WHAT WE CLAIM IS: 1. A light valve which comprises a cell containing a liquid suspension comprising: an electrically resistive liquid suspending medium; suspended therein, a plurality of anisometric, polarizing, halogen-containing particles; and, substantially dissolved therein, a copolymer comprising at least one monomer having a sterically unhindered functional group, which is a hydroxyl group or an acidic group, and at least one monomer having a branched group, the distance from the backbone of the copolymer to the most distant sterically unhindered functional group being less than the distance to the terminal carbon atom of the branched group.
2. A light valve as claimed in claim 1 wherein the branched group has a plurality of branches.
3.A light valve as claimed in claim 1 or claim 2 wherein the monomer having a branched group does not have a hydroxyl group or an acidic group.
4. A light valve as claimed in any of claims 1 to 3 wherein the copolymer comprises more than 50%, by weight, of the monomer having a branched group.
5. A light valve as claimed in any of claims 1 to 4 wherein the monomer having a branched group has a higher molecular weight than the other monomer(s).
6. A light valve as claimed in any of claims 1 to 5 wherein the particles are herapathite,
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (26)

**WARNING** start of CLMS field may overlap end of DESC **. prior art, i.e. NC. This is shown, without exception, in all rows of figures, in all Examples, at all frequencies, in all of the above Tables. In all cases, the use of the presently disclosed polymers enables the light valve to be opened more with a lower activating voltage. The present invention may be applied to light valves that are used, for example, as displays, windows, including double glazed units, windshields and mirrors. The previously-described liquid suspensions may also be set (hardened) by not adding plasticizer in the preparation thereof. The uses of such set suspensions include using these thin, hardened films of material as sheet polarizers. The presently disclosed polymers are useful with a variety of particles including dye particles, dichroic, pleochroic or light-polarizing dye materials. It is to be understood that the present invention may be applied to a light valve that operates in part or all of the infra-red andior ultra-violet portions of the electromagnetic spectrum, as well as the visible part of the electromagnetic spectrum, depending on the type of light valve and suspension employed. It is understood that the term "liquid", where applicable, may include a gel or a thixotropic liquid, or a plastic liquid provided that the suspended particles may be oriented therein upon application of an electric field. In the present context and in that of the related cases mentioned below, the terms "perhalide" and "polyhalide" may be used interchangeably. U.K. Patent No. (Application No. 21214/77) (Serial No. 1586123) relates, inter alia, to a light valve which comprises a cell containing a liquid suspending medium, suspended therein, particles of one or more halogenated alkaloid acid salts (as herein defined) or metal halides and, dissolved therein, a polymeric stabilizer to prevent agglomeration of the particles, the liquid suspending medium comprising a liquid halogenated hydrocarbon having a ratio of halogen atoms to all other atoms therein of greater than 1:1, the halogen atoms of the particles being iodine and/or bromine and the halogen atoms of the halogenated hydrocar box being of lower atomic weight that the halogen atoms of the particles and at least 60% of the halogen atoms of the halogenated hydrocarbon being fluorine and/or chlorine. U.K. Patent No. 1586125 (Application No. 21216/77) relates, inter alia, to a process for the preparation of a light-polarizing material which comprises: hydrogenating an unsaturated bond of a branch chain of an unsaturated alkaloid; forming an acid salt of the resulting saturated compound; forming an acid salt of the resulting saturated compound; and forming a polyhalide of the resulting alkaloid acid salt (as therein defined). U.K. Patent No. 1586126 (Application No. 21217/77) relates, inter alia, to a light valve which comprises a cell containing a suspension in a liquid (as therein defined) suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, the liquid suspending medium comprising an ester of a phenol and a carboxylic acid, and the liquid suspending medium comprising, disclosed therein, a polymeric material for preventing agglomeration of the particles. U.K. Patent No. 1586127 (Application No. 21218/77) relates, inter alia, to a light polarizing perhalide of and alkaloid acid salt having incorporated in its molecular structure at least one halide of calcium, rubidium or cesium the perhalide being the reaction product of an alkaloid acid salt (as therein defined), elemental iodine and the halide. U.K. Patent No. 1586124 (Application No. 21215/77) relates, inter alia, to a light valve which comprises a cell contacting a suspension in a liquid suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, the liquid suspending medium comprising an ester of a phenol and a carboxylic acid. WHAT WE CLAIM IS:
1. A light valve which comprises a cell containing a liquid suspension comprising: an electrically resistive liquid suspending medium; suspended therein, a plurality of anisometric, polarizing, halogen-containing particles; and, substantially dissolved therein, a copolymer comprising at least one monomer having a sterically unhindered functional group, which is a hydroxyl group or an acidic group, and at least one monomer having a branched group, the distance from the backbone of the copolymer to the most distant sterically unhindered functional group being less than the distance to the terminal carbon atom of the branched group.
2. A light valve as claimed in claim 1 wherein the branched group has a plurality of branches.
3.A light valve as claimed in claim 1 or claim 2 wherein the monomer having a branched group does not have a hydroxyl group or an acidic group.
4. A light valve as claimed in any of claims 1 to 3 wherein the copolymer comprises more than 50%, by weight, of the monomer having a branched group.
5. A light valve as claimed in any of claims 1 to 4 wherein the monomer having a branched group has a higher molecular weight than the other monomer(s).
6. A light valve as claimed in any of claims 1 to 5 wherein the particles are herapathite,
cupric bromide or purpureochobaltchloridesulphateperiodide particles.
7. A light valve as claimed in any of claims 1 to 5 wherein the particles are polyhalide particles.
8. A light valve as claimed in claim 7 wherein the particles are polybromide particles of colloidal size.
9. A light valve as claimed in any of claims 1 to 8 wherein the monomer having a functional group is a hydroxyalkyl ester.
10. A light valve as claimed in claim 9 wherein the ester is an acrylate.
11. A light valve as claimed in any of claims 1 to 8 wherein the monomer having a functional group is a polybasic acid.
12. A light valve as claimed in claim 11 wherein the acid is fumaric acid, maleic acid or mesaconic acid.
13. A light valve as claimed in any of claims 1 to 12 wherein the monomer having a branched group is an ether.
14. A light valve as claimed in any of claims 1 to 13 wherein the copolymer comprises a completely esterified polybasic acid.
15. A light valve as claimed in any of claims 1 to 14 wherein the monomer having a branched group is halogenated.
16. A light valve as claimed in claim 15 wherein the monomer having a branched group is fluorinated.
17. A light valve as claimed in any of claims 1 to 16 wherein the suspending medium is non-aqueous.
18. A light valve as claimed in any of claims 1 to 17 wherein the suspending medium is a non-polar ether.
19. A light valve as claimed in any of claims 1 to 18 wherein the suspending medium is halogenated.
20. A light valve as claimed in claim 19 wherein the suspending medium is a fluorinated alkane, ester or ether.
21. A light valve as claimed in any of claims 1 to 20 wherein the copolymer is 2-ethylhexyl acrylate/acrylic acid; 2-ethylhexyl acrylate/hydroxyethyl methacrylate; ethyl acrylate/hydroxyethyl methacrylate; 2-ethylhexyl acrylate/ 2-hydroxypropyl acrylate/acrylic acid; 2-ethylhexyl acrylate/ 2-hydroxypropyl acrylate/fumaric acid; 2-ethylhexyl acrylate/2hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 3,5,5, -trimethylhexyl acrylate/ 2-hydroxypropyl methacrylate; 3,5,5-trimethylhexy acrylate/ 2-hydroxypropyl acrylate/ fumaric acid; 3,5,5 trimethylbexyl acrylate/ 2-hydroxypropyl acrylate/di-2ethylhexyl maleate/fumaric acid; 3.5,5 -trimethylhexyl acrylate/2-hydroxy propyl acrylate/di-2- ethylhexyl fumarate/fumaric acid; 3,5 ,5-trimethylhexyl acrylate/ 2- hydroxypropyl acrylate / vinylidene chloride/ fumaric acid; 5,5 -diethylhexyl acrylate/ 2- hydroxypropyl acrylate/fumaric acid; bis-2-ethylhexyl fumarate/ 2-hydroxypropyl acrylate/acrylonitrile; or bis -2- ethylhexyl fumarate /3.5,5,-trimethylhexyl acrylate/vinylidene chloride/mesaconic acid.
22. A light as claimed in claim 1 substantially as herein described.
23. A light valve as claimed in claim 1 substantially as herein described with reference to the Examples.
24. A process for the production of a light valve as claimed in claim 1 substantially as herein described.
25. A process for the production of a light valve as claimed in claim 1 substantially as herein described with reference to the Examples.
26. A light valve as claimed in claim 1 when produced by a process as claimed in claim 24 or claim 25.
GB2121377A 1977-05-19 1977-05-19 Light valves Expired GB1586122A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB2121377A GB1586122A (en) 1977-05-19 1977-05-19 Light valves

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB2121377A GB1586122A (en) 1977-05-19 1977-05-19 Light valves

Publications (1)

Publication Number Publication Date
GB1586122A true GB1586122A (en) 1981-03-18

Family

ID=10159093

Family Applications (1)

Application Number Title Priority Date Filing Date
GB2121377A Expired GB1586122A (en) 1977-05-19 1977-05-19 Light valves

Country Status (1)

Country Link
GB (1) GB1586122A (en)

Similar Documents

Publication Publication Date Title
US4164365A (en) Light valve for controlling the transmission of radiation comprising a cell and a stabilized liquid suspension
US4273422A (en) Light valve containing liquid suspension including polymer stabilizing system
US4407565A (en) Light valve suspension containing fluorocarbon liquid
US4247175A (en) Light valve containing improved light valve suspension
CA1147546A (en) Electrophoretic display composition
JP3709210B2 (en) Light valve suspensions and films containing UV absorbers and light valves containing them
US5650872A (en) Light valve containing ultrafine particles
JP3779392B2 (en) Improved UV-stable light modulation film for light valves
US4025163A (en) Light valve, light valve suspension materials and suspension therefor
JP4484975B2 (en) Method for producing ultraviolet curable light modulation film for light valve
US5202063A (en) Method for making encapsulated liquid crystal material
EP0624814B1 (en) Light valve suspensions containing a trimellitate or trimesate and light valves containing the same
JPH06129168A (en) Film for dimming window in which optically polarized suspension is dispersed in high molecular resin and manufacture thereof
DE69232882T2 (en) LIGHT VALVE WITH A FILM CONTAINING AN ENCAPPED LIQUID SUSPENSION AND PRODUCTION METHOD FOR THIS FILM
US5279773A (en) Light valve incorporating a suspension stabilized with a block polymer
JPH10512311A (en) Method for producing liquid crystal composite containing dye
GB1586122A (en) Light valves
JPS6240389B2 (en)
CA1106955A (en) Materials, methods and suspensions for light valves
JPS641774B2 (en)
DE2839103A1 (en) Suspension for light valve, e.g. window, display mirror or lens - contains copolymer with free functional gps. to prevent agglomeration
JPH04217232A (en) Suspension for optical element
KR0145717B1 (en) Light valve in corporating a suspension stabilized with a block polymer
AU680231B2 (en) Light valve suspensions and films containing UV absorbers and light valves containing the same
GB1586123A (en) Light valves

Legal Events

Date Code Title Description
PS Patent sealed
PCNP Patent ceased through non-payment of renewal fee