JPS6240389B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a light valve consisting of a cell and a suspension in the cell. More specifically, the present invention relates to a polymer material that stabilizes particles in the suspension (including particles of colloidal particle size) and prevents them from agglomerating, that is, agglomerating. In colloidal systems, and especially in colloidal suspensions, the particles in suspension tend to agglomerate, ie, stick together into clusters of large particles. This phenomenon is often referred to as agglomeration, and the formation of large particle groups destroys the uniform distribution of particles in the suspension, rendering the suspension essentially useless. The above problem is particularly acute in suspensions used in light valves. When operating the light valve, a voltage is applied to the suspension. Because of the relative charges on or associated with the particles,
The voltage causes the particles to come together to form large aggregates. Such agglomerates interfere with the normal functioning of the light valve, thereby impairing its effectiveness. Accordingly, there was a recognized need to develop materials that are effective in preventing agglomeration of suspended colloid particles in light valves. Although there are a number of prior art patents for dispersants, including polymeric materials, to hold particles in suspension, these materials are either unsuitable for use in light valve suspensions or are not compatible with the present invention. Very inferior to polymers. Light valves using suspensions are described in US Pat. No. 1,955,923 (Land) and US Pat. No. 3,708,219 (Forlini et al.). These are basically devices that adjust the transmission of light. To be suitable for use in a light valve suspension, the polymer must be soluble in the liquid suspending medium of the suspension. Moreover, it provides effective steric protection from agglomeration, especially when suspended particles (hereinafter referred to as particles) are oriented under the influence of an electric field (a condition in which the tendency for agglomeration increases rapidly). First, the polymer must be able to associate with the surface of the suspended particles. Additionally, the polymer associates with the particles such that the presence of the polymer when the particles are initially formed can prevent particle growth and minimize agglomeration of the particles during formation. The polymer must not attack the suspended particles in order to prevent degradation of the particles at the use temperature or storage temperature of the suspension and degradation of the polymer itself to occur and attack the suspended particles with degraded products.
When degradation occurs, the ability of the polymer to provide steric protection and other benefits is compromised. Preferably, the solubility range of the polymer is wide, so that if necessary, the polymer is soluble in the polar liquid that initially generates many of the particles used in the light valve, and during operation of the light valve. It is also soluble in relatively nonpolar and low conductivity liquids used in applications. The light valve wall and the light valve wall electrodes must not be coated with polymer. The reason is that polymers that stick to the walls or electrodes destroy the clear field of view in the light valve and give a hazy appearance that reduces the maximum light transmittance or change in transmission obtained from the light valve. Furthermore, the change in light transmittance for a given voltage gradient across the suspension must be greater when using the polymer of the present invention than when using nitrocellulose, the polymer conventionally used in light valve suspensions. Therefore, the polymer must improve the voltage characteristics of the suspension. In this context, there is much less usage at low activation frequencies than at high activation frequencies, so low frequencies e.g.
It is especially important and preferable to do it below 1000 Hz. As mentioned above, nitrocellulose has been used for quite some time and has had some effect in light valve suspensions. Although nitrocellulose provides some protection against agglomeration, it has the significant drawback of strongly degrading even at slightly elevated temperatures. For example, nitrocellulose deteriorates below 150%.
At this temperature, nitrocellulose decomposes to produce nitrite and
It produces nitric acid and other degradation products that attack particles in suspension. Attack by such acids or other degradation products degrades the particles and destroys the suspension. Furthermore, the use of nitrocellulose in light valves has the significant disadvantage that the number of suspending media (ie, the continuous phase in the suspension) in which the nitrocellulose is dissolved is limited. Organic esters are the only medium for nitrocellulose. Due to a number of factors, esters are not preferred liquids to suspend particles in. Therefore, nitrocellulose has very serious chemical and physical drawbacks. The polymers of the present invention overcome these drawbacks. The polymers of this invention have greater thermal stability than nitrocellulose and generally do not decompose except at temperatures much higher than those at which nitrocellulose forms nitric acid and nitrite. Furthermore, the polymers of the present invention are soluble in many relatively nonconductive liquid suspension media in addition to esters. It is an object of the present invention to provide new and improved polymers for stabilizing liquid suspensions. Another object of the invention is to provide a polymer for use in liquid suspensions for light valves. Another object of the invention is to provide polymers for preventing or retarding the agglomeration of particles in suspension. Another object of the present invention is to provide a polymer that reduces the voltage and power required to consistently change the light transmission of a light valve. Another object of the invention is to provide effective functional groups such as OH
The object of the present invention is to provide a long chain copolymer having groups or acid groups in its structure. Another object of the invention is that at least one of the
The seed monomer provides a polymer with a branched structure. Another object of the invention is to provide polymers that impart thermal stability to liquid suspensions. Another object of the present invention is to provide polymers that exhibit a wide range of solubility in both polar and non-polar liquids. Yet another object of the invention is to provide a polymer that does not coat the light valve walls and electrodes. Yet another object of the invention is to provide a light valve suspension comprising the above polymer. Yet another object of the invention is to provide a light valve suspension stabilized by the addition of the above-mentioned polymers. In carrying out the objects of the invention, it is preferred to use a polymer which stabilizes suspensions containing colloidal particles and especially halogen-containing polarizing particles such as herapatite, purpureocobalt chloride sulfate periodide and cupric bromide. Provide coalescing materials. The present invention provides a light valve for adjusting the transmission of light consisting of a cell and a suspension in the cell, comprising:
The suspension comprises (i) a liquid suspending medium, (ii) a plurality of polarizing particles suspended in the liquid suspending medium, and (iii) a copolymer of at least two different monomers, at least one of the monomers. two are ethylenically unsaturated monobasic or dibasic acid monomers or ethylenically unsaturated monobasic or dibasic ester monomers, and at least one of the ethylenically unsaturated monomers is selected from the group consisting of OH groups and acidic groups. and at least one of the ethylenically unsaturated monomers has a branched group. The materials of the invention have effective functional groups in their structure, e.g.
It is a long-chain molecular copolymer with OH or acid groups and dissolves in liquids in which colloidal particles can be suspended. At least one of the monomers used to form the copolymer has a branched structure and may have one or more branches. Some of the materials of the invention include 3,5,5-trimethylhexyl acrylate/2-hydroxypropyl acrylate/fumaric acid; 5,5-diethylhexyl acrylate/2-hydroxypropyl acrylate/
fumaric acid; and copolymers of bis-2-ethylhexyl fumarate/3,5,5-trimethylhexyl acrylate/vinylidene chloride/mesaconic acid. The polymer has the effect of preventing or retarding the agglomeration of particles in the suspension, particularly when the suspension is used in a light bulb and a voltage is applied to the suspension. Furthermore, the polymers of the present invention can be used in suspension under high temperature conditions without significant degradation, and reduce the voltage gradient and power required to effect a given change in light transmission of a light valve. The present invention relates to polymeric materials for stabilizing colloidal particles, and more particularly to polymeric materials for associating colloidal particles to maintain particle stability and prevent particles from agglomerating into large groups. A primary objective of the present invention and the polymeric materials of the present invention is to maintain a substantially uniform distribution of colloidal particles in the suspending medium. In liquid suspensions, it is most important that the suspended particles be substantially uniformly distributed throughout the suspension. Uniform distribution is important, especially when suspensions are used in light valves. The material of the present invention consists of a copolymer, in particular a copolymer containing at least one monomer having an effective OH group or acid group without steric hindrance at the position where it associates or bonds with the elementary element or part of the particle to be stabilized. Become. The remainder of the copolymer is preferably a monomer that dissolves in the liquid medium in which the particles are suspended. Therefore, the polymeric stabilizing material must be a material that strongly binds the copolymer and particles while at the same time being soluble in the suspending medium. Unless a portion of the copolymer is dissolved in the suspending medium, the polymer chains associated with the particles are not in a position to extend a substantial distance outwardly from the particles to effectively prevent agglomeration. The materials of the invention are particularly suitable as suspensions for use in light valves. Briefly, two sheets of normally transparent material, such as glass or plastic, are spaced very closely apart, such as 1 to 50 mils apart, and surrounded by adhesive or other suitable sealant. The continuous light bulb is a light bulb. The inner surface of the sheet is coated with a coating of transparent, conductive material, such as tin oxide, indium oxide, and this coating is connected to a power source, preferably an AC voltage source, by leads, such as conductive silver paint and wires. The space between the transparent sheets is filled with suspended matter. Examples of such suspensions are suspensions of herapatite particles in a suspending medium such as amyl acetate or isopropyl acetate. The herapatite (or other) particles used in the light valve are small, preferably colloidal in size, and are preferably anisotropic in shape, such as cylindrical, rod-like or needle-like. The aspect ratio of the particles is preferably between 5:1 and 20:1. The anisotropic particles, preferably polarizing polyhalide particles, are usually not oriented in suspension but have a random orientation (completely disordered). If the concentration of unoriented crystals in a suspension is high enough, light cannot easily pass through the suspension because the large number of particles absorbs or blocks the light. This suspension appears very dark.
However, applying an electric field aligns the particles parallel to the field (perpendicular to the transparent light valve wall). An electric field is applied by applying a voltage across leads connected to a thin transparent conductive coating applied on the inner surface of the cell wall. The electric field is therefore passed through the suspension as the voltage is applied across the transparent wall or sheet. When there is a voltage in the suspension, the herapatite or other suitable particles are oriented as described above so that the long axis of the particles is perpendicular to the transparent coating.
That is, it becomes parallel to the electric field between the coatings. At this position, the long axis of the particle is parallel to the direction in which the light passes, so the particle hardly interferes with the light passing through it. Therefore, when an electric field is applied across the cell, in other words when the cell is in the "on" state, light can easily pass through the suspension. The suspending medium in which the particles are suspended is preferably transparent so that once the particles are oriented there is little obstruction to the transmission of visible light or optical radiation through the suspension.
However, once the voltage is removed, the particles rapidly become disordered due to Brownian motion, often creating an angle in the direction of the particle's long axis with respect to the direction of the light, so that the light does not disturb the suspension. You won't be able to pass through it easily. The main problem with the colloidal particles mentioned above is that the particles tend to attract each other. This is particularly a problem when a voltage is applied to the suspension. Under the influence of an electric field, the particles act like induced dipoles, and the attraction between the anode and cathode ends of the nearest particles is sufficient so that when a voltage is applied across the suspension, the particles gather rapidly. and form a large particle group.
Since it is preferable for the suspension to be uniformly transparent even when in the "on" state, the formation of particle clusters defeats the purpose of the light valve. however,
Relatively large dark areas form when the particles cluster together and when the suspension is not transparent. Therefore, there is a need for a material that prevents the particles from clumping together or essentially maintains the particles in a normally dispersed suspension. The novel materials of the present invention have achieved this. The materials of the present invention rapidly associate with and stabilize herapatite or other halogen-containing polarizing particles. The stabilized particles are preferably iodine-containing, such as herapatite, or those containing other halogens in the structure, such as cupric bromide. The polymerizable stabilizing material must not only associate with the polarizing particles, but must also contain components in its structure that allow the material to readily dissolve in the liquid in which the polarizing particles are suspended. Examples of polymeric materials that can be used in the present invention are 2-
Ethylhexyl acrylate/acrylic acid; 2-
Ethylhexyl acrylate/hydroxyethyl methacrylate; 2-ethylhexyl acrylate/2-hydroxypropyl acrylate/acrylic acid; 2-ethylhexyl acrylate/2-
Hydroxypropyl acrylate/fumaric acid; 2
-Ethylhexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid; 3,5,5-trimethylhexyl acrylate/2-hydroxypropyl methacrylate;
3,5,5-trimethylhexyl acrylate/
2-hydroxypropyl acrylate/fumaric acid; bis-2-ethylhexyl fumarate/2-
Hydroxypropyl acrylate/acrylonitrile; 5,5-diethylhexyl acrylate/
2-hydroxypropyl acrylate/fumaric acid; and bis-2-ethylhexyl fumarate/3,5,5-trimethylhexyl acrylate/vinyldene chloride/mesaconic acid copolymers. All of these materials have polar functional groups, such as OH and/or acid groups, in positions that readily associate and bond with the particles. Association and bonding with the particles probably occurs at the location of the halogen, such as iodine, or stabilizing helapatite particles in the structure, but also in other parts of the particle. OH
or the association or bond formed by the acid group is considered a halogen bond, but may be another type of bond, or may be a halogen bond and another type of bond, such as a coordinative covalent bond. . However, not only halogen alone, but also OH or acid groups are required for bonding. Hydrogen bonds and/or covalent bonds with oxygen are also useful bonds.
These bonds between polymer and particles are extremely strong. In the case of certain substances, for example acrylic acid, there are available COOH groups. OH is probably the main reason for the effect. However, CO
is also active. In all cases, some available or free OH or acid group is present in the copolymer. The term "free" refers to the state in which OH or acid groups are available for binding, i.e., not sterically blocked by the rest of the structure of the molecule to which they belong. It means,
As a result, the free radicals react rapidly to form hydrogen bonds and/or coordinate covalent bonds with halogens or, in the case of particles that do not contain halogens in their molecular structure, with the attracted atoms or groups. /or form a coordinate covalent bond. If the OH or acid group is not in this position, it is not a good position for rapid mixing, for example if the functional group is surrounded by unreactive groups in the copolymer.
Therefore, the material is not an effective binder or stabilizer. In the abovementioned copolymer materials acids or acidic monomers or monomers with functional groups, such as acrylic acid, fumaric acid, mesaconic acid, maleic acid or acrylonitrile, or one of the hydroxyalkyl ester monomers, such as hydroxyethyl acrylate, hydroxyethyl methacrylate or 2-Hydroxypropyl acrylate is a substance with an effective OH or acid group, which connects the halogen element with another part of the particle to form an association or bond. These monomers may be branched or unbranched, depending on the selection, and the monomers may or may not be dissolved in the suspending medium, depending on the selection of the monomer and suspending medium. Other parts of the copolymer, such as 2-ethylhexyl acrylate, bis-2-ethylhexyl fumarate,
5,5-diethylhexyl acrylate or 3,5,5-trimethylhexyl acrylate acts to dissolve the copolymer in the suspending medium. Branched monomers are preferred, especially monomers with two or more branches. Branching greatly increases the ability of the copolymer to retard flocculation of light valve suspensions under the influence of an electric field, and therefore branching is necessary for anti-flocculation effectiveness. In the case of a single branch, the ethyl group of the monomer 2-ethylhexyl acrylate, for example, is also useful in this respect, and is considerably more effective than unbranched monomers, such as octyl acrylate, but the more branched has a large effect. Although the exact reason why branching prevents aggregation is unknown, a theoretically possible reason is that if branching does not prevent the binding group from binding and stabilizing the particle, The space occupied by this is 2
provides steric protection by preventing individual particles from coming into close proximity to each other. If this theory is correct, as has been experimentally proven, it can be inferred that for the same size, having more branches will have a greater effect than having a single branch. For reasons I don't know yet,
The presence of branched monomers in the copolymer reduces the voltage gradient required to effect a given change in light transmission of the light valve, as described below. Preferably, at least one of the monomers, such as the branched monomers mentioned above which are believed to have a steric hindrance effect, should be free of functional linking groups. Furthermore, preferably the majority (wt %) of the copolymer consists of the monomer or monomers, and the monomer or monomers in the copolymer should be large compared to the molecular weight of the monomers. The branching group itself may be further branched, i.e., the branch may have a sub-branch.
It's okay if there is. Although the branching monomers and many other monomers shown in the examples above are esters, they may be various other types of monomers. For example, monomers such as ethers or cyclic monomers may be included in the copolymer, and monomers with particularly useful substituents may be included, such as halogenated monomers, especially fluorinated monomers. This monomer facilitates dissolution of the copolymer into the fluorinated liquid, which is a useful suspending medium. If desired, two or more copolymers with similar or different properties may be used simultaneously in suspension. Suspending media for light valves are preferably non-conductive, such as aliphatic or aromatic hydrocarbons, silicones, esters and non-polar ethers, and particularly chemically stable halogenated solvents, such as fluorine. A variety of fluids can be used, such as fluorinated alkanes, fluorinated esters and fluorinated ethers, and mixtures thereof. If a fluorinated liquid is used in the suspending medium, a highly polar but relatively nonconductive liquid, such as an ester (eg, isopentyl acetate), may be used with the fluorinated liquid to suspend the suspension. It must be used as part of the turbidity medium to orient the particles at low voltages. Additionally, the weight percent or mole percent of each type of monomer or weight percent of OH or acid groups used in the copolymer can be adjusted to achieve solubility in a particular liquid or liquids.
The copolymers thus combine the properties of effective binding and being soluble in many types of liquid suspension media. dissolved in a suspending medium;
A portion of these polymeric materials must be sufficiently dissolved to substantially dissolve the entire copolymer in the suspending medium. When operating a light valve, the more nonconducting the suspending medium, the better the action and behavior of the light valve. That is, the more nonconductive the liquid medium is, the less power and voltage is required to orient the particles, and thus the easier the light valve is to operate. Therefore, it is one of the advantages of the present invention that the copolymers of the present invention are readily soluble in a constant and very large suspension medium. Some of these relatively non-conductive suspending media, which are of many types as mentioned above, have an electrical resistance of greater than about 5 x 10 ⁷ ohm-cm, preferably greater than 5 x 10 ⁹ ohm-cm. Suspending media are suitable for use with the materials of the present invention. The electrical resistance of a suspension containing particles and copolymer is somewhat less than the resistance of the suspending medium alone. The thermal stability of the polymeric materials of the invention is particularly good and can generally withstand temperatures ranging from about the freezing point of the suspending medium to 100°C without decomposition. This property allows the operation of the light valve over a wide temperature range, and especially when a non-conductive suspending medium is used. The thermal properties of the nitrocellulose used in conventional light valve suspensions are very poor, as mentioned above. At temperatures below about 150°C, nitrocellulose rapidly decomposes to produce nitrite, nitric acid, and other degradation products. The formation of such degradation products reduces the amount of nitrocellulose available to retard flocculation, and the degradation products themselves attack the suspension causing losses. However, the new material according to the invention does not have such drawbacks. Additionally, nitrocellulose has the disadvantage that it is only soluble in certain liquid suspension media.
Therefore, a medium must be used which clearly dissolves the nitrocellulose. Such media are essentially organic esters, such as isopentyl acetate and amyl or ethyl acetate. Non-viscous esters with a viscosity of less than 5 centipoise at 25°C are particularly non-conducting. These esters typically exhibit resistances of less than 2×10 ⁸ ohm-cm. Non-viscous media are preferred for rapid particle orientation and disorientation. However, in the case of the copolymers of the present invention, the resistivity is more than one order of magnitude greater, allowing rapid orientation and disordering. This is because the copolymers of the invention can be used with suspension media which produce suspensions with high resistance, ie low conductivity at the same viscosity, and therefore low conductivity at the same viscosity. The copolymer material described above can be used during initial particle generation to prevent agglomeration and clumping during particle generation, and to bond the particles and copolymer material to form a copolymer material during the lifetime of the particle and during particle manipulation. It can also prevent agglomeration at all stages. However, when the copolymer materials of the invention are used in suspension, they may also be used after particle formation. Additionally, the polymer may be added to a suspension that already contains the same or different polymers. Examples of polyhalides that produce suspended particles and are polarizing and useful in light valves are the aforementioned herapatite, purpureocobalt chloride sulfate periodide, and cupric bromide. The following examples illustrate the use of herapatite and various copolymers to produce optic suspensions and other particles. Examples 1-9 and Example 12 used a copolymer during the formation of the particles used in the suspension, and the copolymer and particles remained associated after the suspension was formed and during the actual operation. In Examples 10 and 11, the copolymer was added to the particles after particle formation, and then the polymer-bound particles were placed in suspension before the light valve was operated. The copolymers used have chain lengths of approximately 600 to 4200
Angstrom or larger copolymers are preferred.
As these copolymers, copolymers with a random structure are preferred, but alternating polymerization copolymers, block copolymers and graft copolymers can also be used advantageously. Examples of the present invention are shown below. Example 1 3.75 g of quinine bisulfate and fluoroalcohol to 42.5 g of a 33 1/3% 2-ethoxyethanol solution of 2-ethylhexyl acrylate/acrylic acid (75 wt%/25 wt.%) copolymer
0.50g was mixed. Then 8.5 g of methanol and a further 10 g of 2-ethoxyethanol were added. These components were mixed and reacted with an alcoholic solution of a plasticizer (optional), iodine and hydroiodic acid to form a wet paste of herapatite. The paste was then dried to remove volatile solvents. At this point, a liquid suspension medium was added to the paste followed by continuous mixing and milling to disperse the paste in the medium. In this test, the monomer-containing acid content in the copolymer was only 25% by weight, as mentioned above, increasing the chance of dissolution of the copolymer into the suspension medium of the light valve to disperse the dry paste. It has an effect. The results were good. We measured the optical density of the isopentyl acetate suspension in the generated light valve and found that upon activation,
It changed from 3.0 to about 0.85. This represents a substantial opening. Example 2 The copolymer solution of Example 1 was made into 42.5 g of a 30% by weight solution of 2-ethylhexyl acrylate/acrylic acid copolymer in 2-ethoxyethanol, 2.68 g of quinine bisulfate, 7.30 g of methanol, and an additional 10 g of 2-ethoxyethanol. The method of Example 1 was repeated except that . Example 3 10g of 2-ethoxyethanol used in Example 2
The method of Example 2 was repeated except that 0.50 g of chloroform was added to the ingredients before the reaction. Example 4 A copolymer of 2-ethylhexyl acrylate/acrylic acid (50% by weight/50% by weight) was prepared. 42.5 g of copolymer solution as a 25% weight solution in 2-ethoxyethanol was prepared and 3.75 g of quinine bisulfate and 8.50 g of methanol were added. As in Example 1, these ingredients were reacted with an alcoholic solution of plasticizer, iodine, and hydroiodic acid to form a wet paste. The dry paste, whose dispersion was promoted by heating, was suspended in decyl alcohol and operated in a light bulb with satisfactory results. Example 5 The procedure of Example 1 was repeated, except that instead of the 75%/25% wt copolymer of 2-ethylhexyl acrylate/acrylic acid, an 85%/15% copolymer was used. Unlike in Example 1, the dried paste was dispersible in the aromatic hydrocarbon, toluene, and showed substantial opening in the light valve as in Example 1. Example 6 n-propanol was used instead of 2-ethoxyethanol to increase the solubility of the copolymer and the copolymer of Example 1 was replaced with a 93.5%/6.5% copolymer of 2-ethylhexyl acrylate/acrylic acid. The method of Example 1 was repeated with the exceptions. The resulting dry paste of herapatite was dispersible in an aliphatic hydrocarbon, hexane. Aliphatic hydrocarbons have low viscosities, and at low viscosities they are generally less conductive than esters. Therefore, aliphatic hydrocarbons are preferred as suspending media for certain light valves. Example 7 Approximately 0.2 g of purpureocobalt chloride sulfate periodide (inorganic polyiodide)
-Ethylhexyl acrylate/acrylic acid 75
Milled in 1 g of 33 1/3% 2-ethoxyethanol solution of wt%/25wt% copolymer. After drying and evaporating the 2-ethoxyethanol, the particles were suspended in isopentyl alcohol.
The appearance of the suspension in the resulting light bulb was gray. 30 or more voltage gradient in pulse mode of operation
At 90 volts/mil, the suspension was observed and pulsed sequentially opened and closed in response to the applied voltage without significant agglomeration. A continuous voltage gradient of approximately 30 volts/mil and continuous opening of the suspension were observed for several seconds without significant agglomeration occurring. Example 8 33 1/3% of 2-ethylhexyl acrylate/75% by weight/25% by weight copolymer of acrylic acid
- about cupric bromide in 1 g of ethoxyethanol solution
0.04g of polyhalide (halogen is bromine) was ground. After drying and evaporating the 2-ethoxyethanol, the resulting suspension was suspended in isopentyl acetate in a light bulb, resulting in a green-yellow color. When this pulsing was repeatedly observed with a voltage gradient of 30 volts/mil or higher, no significant aggregation was observed. Microscopic observation revealed particles with a particle size of 1-15 microns. Even when the voltage gradient was reduced, the opening was good. Example 9 A 75% by weight/25% by weight copolymer of 2-ethylhexyl acrylate/hydroxyethyl methacrylate was tested to demonstrate that another polar material can be used in place of the acid in the composition of the copolymer. Each molecule in the hydroxyethyl methacrylate monomer has an OH functionality. Hydroxyethyl methacrylate is also called ethylene glycol monomethacrylate. Using the method of Example 1, a well-protected suspension was obtained. However, when the copolymer composition was 75%/25%, it was not completely dissolved in isopentyl acetate alone. Therefore, a 2:1 mixture of isopentyl acetate and chloroform had to be used as the suspension medium for the test. The resistivity of the resulting suspension in the test cell (approximately
1.5×10 ⁸ ohm cm) was greater than when acid groups were present in the copolymer used to protect the suspended crystals. Many of the tests described above were repeated many times using copolymers of various viscosities and thus molecular weights. In general, it has been appropriate to use polymers with as low a molecular weight as possible for prevention of agglomeration and other purposes.
The reason is that higher molecular weight of the polymer increases the viscosity of the suspension and reduces the rise and decay (response) times of the light valve suspension. Alternatively, the molecular weight of the copolymer, if known, is selected to result in long copolymer chains of at least 600 angstroms, preferably 2000 to 4200 angstroms or more. In order to prevent contamination of the final suspension, especially in the case of light valve suspensions, the copolymers used must be as pure as possible. A pure copolymer will prevent unwanted conduction in the final suspension. It has been found that in the above-mentioned copolymer system, the non-polar copolymer portion does not fundamentally adversely affect the solubility of the copolymer. In some of the above examples, crystals of helapatite and other materials produced or crushed are
- Ethylhexyl acrylate/acrylic acid copolymers provided good protection. As a result of these tests, the polar OH or acid functionality likely responds for protection and, depending on the chemical nature and amount of the single molecule included in the copolymer, in a non-polar solvent or a solvent of intermediate polarity. The non-polar groups in the copolymer act to dissolve the copolymer.
However, in order to ensure that 2-ethylhexyl acrylate alone did not exhibit any spurious response that conferred some or all of the protection, Example 1
A paste of herapatite was prepared according to the method of Example 1 by preparing a homopolymer rather than a copolymer of 2-ethylhexyl acrylate. As expected, poly(2-ethylhexyl acrylate) did not prevent particle agglomeration during reaction, drying, or in the light bulb suspension of dried herapatite paste. Therefore, the conclusion that the OH or acid functionality reliably shows the favorable results observed earlier is confirmed. In the case of colloidal fluid suspensions, significant agglomeration does not occur over long periods of time (at least several days, preferably years) even when stored for future use or in light bulbs that are not actually activated. If not, it can be said that the copolymer used provided adequate physical protection for the suspended crystals. As a quick test of polymer efficiency, a polymer-loaded colloidal fluid suspension is placed into a light valve containing a low viscosity suspending medium (approximately 5 centipoise or less) that has a continuous sinusoidal waveform, and When the light valve is activated by a continuously applied electric field (power on) of 10 kHz AC with a voltage gradient sufficient to orient the turbid needles, for at least 2 seconds, preferably at least 20 seconds. If the crystals do not aggregate significantly, it can be said that the copolymer used adequately physically protected the suspended crystals. shot pulse (e.g.
Applying a field in pulsed mode for a relatively long period of time (20 ms) without applying a field between pulses, and at this time providing a voltage gradient sufficient to orient the suspended crystals, the particles are physically properly aligned. The protected suspension must change optical density repeatedly (ie, open and close) in response to a pulse for at least five cycles, preferably several thousand cycles, without significant agglomeration. Significant particle aggregation is visible to the naked eye as punctiform or clustered areas in the suspension, and can also be observed by substantial changes in the optical density of closed and/or open suspensions. Suspensions containing copolymers that do not physically adequately protect the particles will substantially agglomerate and are often almost completely ineffective below the low time intervals shown under the above test conditions. When a copolymer is effective, suspensions that are poorly protected generally remain closed when a voltage gradient is applied that orients the particles without causing agglomeration. It was observed that it was open without any problem. In this case, most of the opening, ie the decrease in optical density and increase in light transmission, is due to the rapid agglomeration of the crystals. Agglomerated crystals are considered to be loosely attached and therefore cannot be oriented, ie, they do not approach by Brownian motion as rapidly as individual oriented particles. Some poorly protected suspensions are so poorly agglomerated before entering the light bulb that it is not possible to release the suspension at all. A copolymer that is effective to prevent or reduce agglomeration of particles in a suspension may partially spiral outwardly around the particles in solution in the suspending medium, thus forming a bond to the first particle. It is believed to prevent or make it difficult for other particles to come into close proximity. Two elements are necessary for a material to be properly physically protected from particle agglomeration. That is, the material is at least partially bound or associated with the particles, and secondly, by forming a sufficiently thick barrier around the extended portion of the material itself to the particles and/or solution. prevents the close proximity and agglomeration of individual particles. Although any material associated with or associated with the particles and having a long average chain length compared to the average diameter of the particles will satisfy the above requirements, polymers are most effective, and the branched copolymers of the present invention are particularly useful. It turned out to be. For the polymer to be useful as a stabilizer in a light valve suspension or for other purposes, the polymer does not coat the light valve wall and a transparent conductive coating covers some or all of the wall surface. It is important that the electrodes (ie the electrodes) not be coated. When polymers coat the walls or electrodes, their appearance becomes unattractive and maximum light transmission is limited. To prevent the formation of such undesirable films, the monomers in the copolymer are selected such that all chains and branches in the copolymer are fully extended and perpendicular to their source; The functional binding groups (eg OH and acid groups) are preferably close to the polymer backbone, preferably closer than the non-binding groups on at least one monomer that is free of functional binding groups. Therefore, when copolymerizing 3,5,5-trimethylhexyl acrylate with fumaric acid and 2-hydroxypropyl acrylate to form a random terpolymer, the terminal group of the first monomer without a bonding group is the fumaric acid monomer. It is clear from the known structure of each monomer that the OH group of either the carboxylic acid or 2-hydroxypropyl acrylate monomer extends from the main chain. The above principles can also be applied to any part of the polymers of the invention other than random copolymers, such as graft copolymers. This portion of the graft copolymer is itself a polymer, but it has a linking group. Failure to follow the above rules will result in the undesirable result of wall and electrode coating. This is thought to be a result of the binding group being able to bind. According to the above rules, the polymer can bind to the particles but not to the cell walls and electrodes. In addition to retarding agglomeration and allowing the use of suspensions at relatively high temperatures, the polymers of the present invention enable operation of light valve suspensions using low activation voltages and small electric field gradients. Particularly valuable. Prior art related to light valves proposed the use of voltages with frequencies of 1 kilohertz or higher. Using low frequencies results in extremely early onset of aggregation. Low frequency power sources and outlets, such as 50 Hz and 60 Hz, are commonly used in industry and
The use of high frequencies is problematic because the use of low frequencies eliminates the need for expensive high-frequency power equipment, and furthermore, the required amount of power and associated costs are significantly lower. According to the present invention, low frequencies can be used without causing aggregation or with only slight aggregation. A factor that influences whether the suspension will flocculate, and if so, the rate of aggregation, is the voltage gradient applied to the suspension. In this specification, voltage gradient is defined as the voltage across the suspension divided by the thickness of the suspension, i.e. in a resistive cell, the voltage across the two electrodes of the cell is the voltage across the suspension. It is the number divided by the distance. A resistive cell is one in which the electrode is in direct contact with the suspension. For example, if a voltage of 600 volts is applied to a resistance cell with a suspension thickness of 20 mils, or 0.020 inches, the voltage slope is 30 volts/mil. When using an alternating current voltage, it must be specified whether the voltage in question is a peak-to-peak voltage or the root mean square of a sinusoidal alternating voltage. A capacitive cell is a cell in which the electrode is not in contact with the suspension, ie there is an insulating or capacitive layer between the electrode and the suspension. Large voltage gradients are known to cause and accelerate agglomeration, while small voltage gradients can prevent or retard agglomeration. However, prior to the present invention, small voltage gradients were not useful because they would not open the light valve enough to be practical. The method of the present invention is useful because it does not cause aggregation even when the voltage gradient is small, or only a small amount of aggregation causes the opening of the light valve to allow some light transmission. Another advantage of a small voltage gradient is: less power is required to operate the light valve; thus energy and cost savings; low voltage wiring requires less electrical insulation around the leads and terminals leading to the light valve. the power supply is small and its weight is low; the use of compact mass-produced solid-state electrical and electronic components; the reduction of the current passing through the suspension and thus the heat generated in the suspension; is to decrease. This last advantage is compounded by the observation that the heat generated in the cell tends to degrade and decompose the suspended material, and reduces the quality of the seal of the cell containing the suspended material in the light valve. This is an advantage that can be achieved. Another advantage of the present invention is that the suspension light valve can be used in sunglasses and various optical density glasses, such as welding goggles. Prior to the present invention, suspension light bulbs required high power (e.g., several hundred volts), and placing high voltages near the eyes and head of eyeglass users posed a safety problem. It has not been possible to apply light valves to the above-mentioned areas. According to the present invention, since the voltage is low, for example 4 volts, it can be safely used in sunglasses, glasses and goggles. Prior to this invention, polymers had been used to protect suspended particles in light valves, but known polymers had little anti-agglomeration effect and required relatively high voltages to open the light valve. . A typical example of a conventional polymer is nitrocellulose. Further examples below illustrate the advantages of the polymers of the present invention, particularly with respect to low voltage use in light valves. Example 10A Step 1: Dissolve the polymer in an alcohol such as n-propanol or methanol, or an ether alcohol such as 2-ethoxyethanol. Place this solution in a high-speed mixer and add 16.6 g of tricresyl phosphate (TCP).
was added and mixed thoroughly. (Addition of TCP is optional.) Step 2: 7.3 g of methyl alcohol was added to 3.7 g of quinine biphosphate (QBS) and stirred until QBS was dissolved. This solution was added to the Step 1 mixture and mixed thoroughly in a high speed mixer. Step 3: A 20% n-propanol solution of iodine crystals was prepared and aged for about 20 days. This solution
8g was added to 4g of n-propanol in which 0.27g of calcium iodide was dissolved and shaken until well mixed. Step 4: Pour the Step 3 mixture into the Step 2 mixture in the mixer running at high speed. The mixer was run at high speed for an additional approximately 35 seconds and then stopped. Step 5: The prepared mixture was spread on a glass plate and dried for about 90 minutes in an atmosphere with a temperature of 78°C and a relative humidity of 50%. Step 6: The paste prepared in step 5 was scraped off the glass plate with a sharp knife, and then the paste was ground in an electric grinder for about 30 minutes. Next, 90 g of isopentyl acetate (IPA) was added into the mortar bowl. This mixture was placed in a container containing 33 ml of chloroform (CHCl ₃ ) and placed on a shaker for about 1 hour. Step 7: Add the mixture prepared in step 6 to
33 mil (i.e. 0.033 inch) diluted with IPA
The optical density was set to about 3 when placed in a light valve cell with an interval of . Step 8: 4 to 7 hours at 2500 rpm and rotation radius of approximately 3.5 inches, Step 7
The suspension formed was centrifuged. Step 9: Discard the substances floating on the surface in Step 8, add IPA to the precipitate, and then soak the diluted precipitate in an ultrasonic generator with a frequency of 47KHz.
The mixture was treated for up to 2 hours. Step 10: Centrifuge again for 2 to 3 hours. Step 11: Step 9 was repeated. Step 12: Centrifuge again for 20 to 30 minutes and then discard the surface floaters. Step 13: Dilute the precipitate with IPA to obtain a suspension of desired optical density. The following examples illustrate specific polymers of the invention and methods of making suspensions using these polymers. Example 10 Tetrapolymer: Monomer wt% 37.5/
22/37.5/5.3 3,5,5-trimethyl-
1-hexyl acrylate/2-hydroxypropyl acrylate/di-ethylhexyl maleate/fumaric acid. Suspensions were prepared using the method of steps 1-13 above with the following amounts and exceptions. In step 1, a solution of 2 g of tetrapolymer in alcohol (20 g) was used. No mortar grinder was used in step 6. Approximately after Step 7 and before Step 8
The diluted mixture was placed in an ultrasonic generator operating at 47KHz for approximately 17 hours. The following method was used instead of step 13. The precipitate was diluted with IPA and tetrapolymer to obtain a suspension containing 8% tetrapolymer. This was followed by further dilution with an 8% IPA solution of the tetrapolymer to obtain a suspension of the desired optical density. Example 11 Tetrapolymer: Monomer weight % 75/
3,5,5-trimethyl- which is 10/15/3
1-hexyl acrylate/2-hydroxypropyl acrylate/vinylidene chloride/fumaric acid. A suspension was prepared by the method of Example 10 except for the following points. That is, in Step 1, the polymer of Example 11 was used in place of the polymer of Example 10. Example 12 Tetrapolymer: Monomer weight % 37.5/
3,5,5-trimethyl-1-hexyl acrylate/2-hydroxypropyl acrylate/di-2-ethylhexyl fumarate/fumaric acid which is 22/37.5/3. A suspension was prepared by the method of Example 11, except that the polymer of Example 12 was used instead of the polymer of Example 11. Example 13 A suspension was prepared according to steps 1 to 13 above, substituting the conventional homopolymer nitrocellulose (NC) for the copolymer of the invention. In step 1, HA17NC 6.6g and 21.6 centipoise NC (EI Dupont de Nimois) were used.
EIDu Pont de Nemours & Co.) 7.5g
was dissolved in 2-ethoxyethanol. Suspensions made using the three tetrapolymers of the four examples above do not agglomerate or only minimally agglomerate when used in light valves compared to suspensions made using conventional polymers. There was only slight aggregation. Additionally, suspension light valves made with the three new polymers were more open, ie, had greater light transmission, than conventional suspensions at equal voltage gradients. Suspensions made from the novel polymers of the three examples above were compared to suspensions made from nitrocellulose (NC). I tested it in the following way. Suspension made from NC sequentially into a resistive light bulb cell with a suspension thickness of 33 mils and Example 10
to 12 filled suspensions. Each time the cell was filled, it was activated sequentially by alternating current at frequencies of 40, 60, 100 and 1000 Hz. Furthermore, 500 Hz was also used for the polymer of Example 12. Peak-to-peak voltages of 0, 100, 200, 300, 400, 500, and 600 volts were applied sequentially at each of the above frequencies. At each frequency and voltage, and any combination thereof, Radio Corporation of America
Transmission of light in the visible spectrum was measured using an RCA photomultiplier tube manufactured by America. The results are shown in the table below. The heading 〓NC〓 indicates the transmittance of the suspension prepared by NC. The heading "New Polymer" indicates the permeability of suspensions made with the polymers of the invention according to each example. The permeability ratio in each case is the permeability of the suspension made from the new polymer.
It is the quotient divided by the transmittance of the suspension made from NC.

【table】

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[Table] After examining the above data, the following was clarified. Light valve opening was increased by a factor of five using the polymer of the present invention compared to using conventional polymers. This is shown at 300 volts and 400 Hz for the copolymer of Example 11. Further examples
12 copolymer 300 volts 40, 60 and 100Hz
The same applies to the case of . At all frequencies of activation voltage and at all voltages, the polymers of the present invention had higher open values, ie, higher transmittance, than conventional polymers, ie, nitrocellulose. This is shown in all examples without exception at all frequencies in the table above. In all cases, the polymers of the invention were able to open the light valve at low activation voltages. The invention can be used in light valves for displays, windows containing dual glazed units, windshields, mirrors and many similar devices. The aforementioned liquid suspensions harden without the addition of plasticizers during manufacture. A thin cured film of such a cured suspension can be used as a sheet polarizer. The polymers of the present invention can be usefully used with a variety of particles, including dye particles, dichroic, pleochroic or polarizing dye materials. The present invention can be used in light valves that operate in some or all of the infrared and/or ultraviolet parts of the electromagnetic spectrum and in the visible part of the electromagnetic spectrum, depending on the type of light valve and suspension. Use of the term "liquid" includes gels or thixotropic liquids, or plastic liquids if the suspended particles are oriented by the application of an electric field. Although the polymers of the present invention have been described herein for use in light valve suspensions, any other type of suspension if the properties are favorable, e.g. special paper coatings as binders; and in paint and ink compositions. Although specific examples of the present invention have been described above, it is clear to those skilled in the art that the present invention is not limited to these and that many changes can be made within the spirit of the present invention. . The embodiments of the present invention are as follows. (1) A material contained in a light valve suspension comprising a suspending medium and particles suspended in the medium to stabilize the suspension, the material comprising at least two different monomers. material, at least one of which has unhindered functional groups, at least one of which is soluble in the suspending medium, and at least one of which is branched. (2) The material according to item 1 above, wherein the unhindered functional group is a group selected from the group consisting of OH groups and oxygen. (3) The material according to item 2 above, wherein the branched monomer has at least two branches. (4) The material according to item 3 above, wherein the particles are polyhalide particles. (5) The material according to item 4 above, wherein the polyhalide particles are particles selected from the group consisting of polyiodide particles and polybromide particles of colloidal size that orient when a field is applied to the suspension. (6) The material according to item 5 above, wherein the copolymer contains a hydroxyalkyl ester monomer. (7) The material according to item 6 above, wherein the hydroxyalkyl ester is a hydroxyalkyl acrylate. (8) The material according to item 5 above, wherein the copolymer contains a polybasic acid monomer. (9) The material according to item 8 above, wherein the polybasic acid is an acid selected from the group consisting of fumaric acid, maleic acid and mesaconic acid. (10) The material according to item 5 above, wherein the copolymer contains an ether monomer. (11) The material of item 5 above, wherein the copolymer is a copolymer comprising a monomer selected from the group consisting of partially esterified polybasic acids and fully esterified polybasic acids. (12) The material according to item 5 above, wherein the copolymer contains at least one monomer without functional groups. (13) The material according to item 5 above, wherein the copolymer contains a halogenated monomer. (14) The material of item 5 above, wherein the copolymer is a copolymer selected from the group consisting of random, alternating block, and graft copolymers. (15) In paragraph 14 above, where the distance between the main chain and the effective functional group furthest from the main chain in one monomer in the copolymer is shorter than the distance between the main chain and the non-functional group in another monomer. Materials listed. (16) The material according to paragraph 15 above, wherein the suspending medium is non-aqueous. (17) The material according to item 16 above, wherein the suspending medium is a non-polar ether. (18) The material according to item 16 above, wherein the suspending medium is a halogenated liquid. (19) The material according to item 18 above, wherein the halogenated liquid is a liquid selected from the group consisting of fluorinated alkanes, fluorinated esters, and fluorinated ethers. (20) No. 1 above, wherein the material imparts stability to the suspension at temperatures above 100°C without significant deterioration.
Materials listed in Section. (21) Stabilize the suspension and thereby increase the light transmission through the suspension with a peak-to-peak voltage of at most 15 volts per mil of suspension thickness at AC frequencies below 1000 Hz. 2. The material of item 1 above, wherein the material is substantially altered. (22) When the visible light transmittance of the suspension is at most 1% and a peak-to-peak voltage of at most 12 volts per mil of suspension thickness is applied at an AC frequency of 1000 Hz or less. 2. A material according to item 1 above, which exhibits a light transmission of at least 10 times the amount of light transmitted. (23) The material according to item 1 above, wherein the particles are particles selected from the group consisting of herapatite, cupric bromide, and purpureocobalt chloride sulfate periodide. (24) 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/2-hydroxypropyl acrylate/vinylidene chloride/
Fumaric acid; 3,5,5-trimethylhexyl acrylate/2-hydroxypropyl methacrylate; 3,5,5-trimethylhexyl acrylate/2-hydroxypropyl acrylate/Fumaric acid; 3,5,5-trimethylhexyl acrylate/2- Hydroxypropyl acrylate/di-2-ethylhexyl maleate/fumaric acid; 3,5,5-trimethylhexyl acrylate/2-hydroxypropyl acrylate/di-2-ethylhexyl fumarate/fumaric acid; 2,5,5-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;
and bis-2-ethylhexyl fumarate/
2. The material according to item 1 above, which is a copolymer selected from the group consisting of 3,5,5-trimethylhexyl acrylate/vinylidene chloride/mesaconic acid.

Claims (1)

[Scope of Claims] 1. A light valve for adjusting the transmission of light consisting of a cell and a suspension in the cell, wherein the suspension comprises (i) a liquid suspending medium; (ii) the liquid suspension; (iii) a copolymer of at least two different monomers, at least two of said monomers being an ethylenically unsaturated monobasic or dibasic acid monomer or an ethylenically unsaturated monobasic acid monomer; a base or dibasic acid ester monomer, at least one of the ethylenically unsaturated monomers having a functional group selected from the group consisting of an OH group and an acidic group, and at least one of the ethylenically unsaturated monomers has a branched group; A light valve comprising: