JPS641774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to light valves, and more particularly to light valves used in suspensions to prevent or substantially reduce agglomeration of suspended particles thereof in suspensions. Regarding the medium. This agglomeration phenomenon is particularly noticeable when the suspension is used in a light valve under the influence of an electric field.

In a suspension of colloidal particles, the suspended particles in the suspension tend to group together to form large clumps of particles. This phenomenon, agglomeration, destroys the uniform distribution of suspended particles in a suspension and often renders the suspension of little value. The problem is particularly noticeable in suspensions used in light valves. Light valves are described in detail in commonly assigned US Pat. No. 3,708,219. Light bulbs are typically 0.5 mil to 50 mil (0.013 to 1.25 mm)
It consists of two transparent, flat, substantially parallel walls separated by a relatively short distance in units of , and having a peripheral seal forming a sealed cell. A thin, conductive, transparent coating is applied to the inner surface of the wall and the cell is filled with a suspension that may contain polarizing particles. The suspended particles are usually randomly dispersed in the suspension;
Under these random conditions, suspended particles tend to absorb light due to Brownian motion and annihilate visible light that attempts to pass through the suspension, making the suspension appear dark. However, when a voltage is applied to the conductive coating of the light valve (ie, across the suspension), the suspended particles, which are preferably rod-shaped or needle-shaped, align perpendicularly to the cell walls. In this state, light passes through the suspension and the suspension appears transparent. Applying a voltage to the suspension is primarily responsible for the aggregation of suspended particles.

Research has been conducted to develop suspensions for light valves in which the suspended particles in the suspension are uniformly distributed and do not aggregate or aggregate when an electric field is applied. Conventional suspensions maintain suspended particles in suspension for a significant period of time without an applied electric field. Examples of such suspensions are U.S. Pat.
1955923 and 1963493, 3512876 and 3773684
listed in the number. However, when an electric field is applied, the suspension media prior to this invention are unable to maintain the suspended particles in the suspension in a dispersed state, and the suspended particles come together to form aggregates. Various methods have been tried over the years to try to solve this problem. One such method is described in U.S. Patent No.
Described in No. 2481621. That is, ultrasonic waves are sent into a liquid suspension to agitate the suspended particles and make them irregularly arranged to break and prevent agglomeration.

Another method is described in US Pat. No. 3,655,267, which uses radio frequency varying voltages to prevent agglomeration. Other patents suggest the use of pulsating voltage as a means to reduce agglomeration. Still other patents utilize gentle laminar flow to create constant motion of particles, thereby preventing particle aggregation.

These prior art techniques utilize electrical or sonic methods or fluid motion to break up or prevent agglomeration. These conventional methods require the use of special equipment in conjunction with a light valve to obtain anti-agglomeration properties.

Therefore, a method of maintaining the dispersion of suspended particles using a suspending medium that maintains dispersion even when a voltage is applied across the suspension would be useful and of great value in the operation of light valves. .

Suspension media and suspensions using the suspension media have been developed in accordance with the present invention which reduce or eliminate agglomeration of colloidal suspended particles in the suspension when a voltage is applied to the suspension.

That is, the present invention provides a light valve comprising a cell containing a suspension of colloidal particles suspended in a medium and an electric field imparting member for applying an electric field through the suspension medium, wherein the particles are The present invention relates to a light valve which is sensitive to an electric field in order to alter the transmission of light through the suspension, characterized in that the liquid suspension medium comprises an ester of at least one phenol and a carboxylic acid. Nitrocellulose, a copolymer of at least two monomers, or a mixture thereof may be added to the above-mentioned ester of phenols and carboxylic acids.

In general, normal light vibrates in all directions and travels in all directions. When normal light passes through glass, it scatters in all directions.
However, when light passes through a suspension of polarizing particles, it travels in only one direction. That is, when light is passed through a suspension of polarized colloid particles, the light travels in only one direction. Such polarizing particles are conventionally known. For example, the polarizing particles are perhalides of alkaloid acids, metal halides, and metal perhalides.

The suspension medium of the present invention contains esters of phenols and carboxylic acids. The phenols may be substituted. A preferred ester is an acetate of one of the phenols. Preferred phenols constituting the ester are phenol and cresol. Specific examples of preferred esters are phenyl acetate, ortho- or para-cresyl acetate, para-butyl phenyl acetate, and para-nonyl phenyl acetate.

The structures of these materials are shown in Formulas 1, 2 and 3. Formula [1] is the structure of phenyl acetate, which is a reaction product of phenol and acetic acid. Formula [2] is the structure of ortho-cresyl acetate, which is a reaction product of ortho-cresol and acetic acid. Formula [3] is the structure of para-cresyl acetate, which is a reaction product of para-cresol and acetic acid. These formulas are shown below.

Formula [1] Formula [2] Formula [3] In these examples, the oxygen atom that is part of the ester is directly bonded to and adjacent to the ring. This is a result of aromatic alcohols reacting with acids to form aromatic esters.
The effectiveness of such substances in preventing agglomeration is quite different from that of aromatic esters, which are the reaction products of aromatic acids and alcohols. An example of the aromatic ester mentioned above is dibutyl phthalate; U.S. Pat.
See No. 3625869. However, dibutyl phthalate is less effective than the materials of the present invention in preventing or reducing agglomeration. This difference in behavior between aromatic esters derived from aromatic alcohols and aromatic esters derived from aromatic acids is due to the fact that esters derived from aromatic acids are part of the ester and bond directly to the ring. This is because the ring has a carbon atom instead of an oxygen atom adjacent to the ring. Formula [4] shows a structure of dibutyl phthalate that is clearly different from the structures of [1], [2], and [3]. It was unexpected that this difference in chemical structure was the cause of the difference in the effect on assembly.

The suspending medium of this invention can be used alone or in liquids such as aliphatic esters, including branched esters, e.g. isopentyl acetate, and certain non-polar aromatic compounds such as toluene or trifluorotrichloroethane, or non-polar aliphatic can be used with compounds. If the material of this invention is a liquid, it should be non-toxic to the light valve and other suspended solids and particles, and should be relatively stable to heat and ultraviolet light. Approximately 55% by weight of final suspension medium
It has been found that it is useful if the liquid is not of this invention and has more than 45% suspended material of this invention, but this is not necessary.

All colloidal particles that are sensitive to electric fields can be used as suspended colloidal particles in the present invention. Generally, colloidal particles cause Brownian motion in a medium. This Brownian motion depends on the size of the particle, but not on the properties of the particle itself.
In other words, Brownian motion is unrelated to the type of material that makes up the particle. Generally all colloidal particles can be used in light valves. All colloidal particles tend to aggregate when an electric field is applied. However, although the theoretical reason is not clear, when an ester of a phenol and a carboxylic acid is mixed into a suspension of colloidal particles, aggregation when an electric field is applied can be prevented. Brownian motion of colloidal particles, the application of an electric field to a suspension containing colloidal particles that are sensitive to electric fields to alter the transmission of light, and the effects of such colloidal particles when an electric field is applied with the addition of said ester. Prevention of aggregation is a phenomenon that occurs regardless of the type of substance that constitutes the colloidal particles. Therefore, any type of suspended colloid particles can be used in the present invention.

Suspensions made of suspension media containing such esters serve to prevent or substantially reduce agglomeration of suspensions containing suspended particles that are sensitive to electric fields.

The suspension of the present invention is prepared by applying a voltage (usually 8×
10 ⁷ Ω/cm or more), it has high and low resistance so as not to impair the ability of suspended particles to align in a straight line.

The suspension medium of the invention may also contain nitrocellulose and/or copolymer substances in addition to the above-mentioned esters. Preferably it comprises nitrocellulose or a branched copolymer. The copolymer is a copolymer of at least two monomers, at least one of the monomers containing an OH group or an acidic group, and at least one of the monomers is branched and the most distant from the backbone of the copolymer. The distance to the OH groups or acidic groups present is less than the distance from the backbone of the copolymer to the end groups of the branched groups. The branched groups in the copolymer are sufficiently soluble such that substantially the entire copolymer is dissolved in the liquid suspension medium.

In one feature, the copolymer comprises CO
It has a branch unit containing at least a functional group selected from - and COO-.

These copolymers are composed of the following compounds;
3,5,5-trimethylhexyl acrylate/
2-hydroxypropyl acrylate/bis-2
- copolymers of ethylhexyl fumarate/fumaric acid; and copolymers of bis-2-ethylexyl fumarate/3,5,5-trimethylhexyl acrylate/vinylidene chloride/mesaconic acid. Due to their size, their OH or acid functionality, their solubility, and their branched nature, these substances promote their anti-agglomeration action of suspended particles.

It is not preferred to use a direct current electric field in this invention.

It should be understood that gels and similar materials are to be encompassed by this invention. Relatively high electrical resistivity liquids are preferred because their applied electric fields can easily orient their particles at relatively low voltages.

In order for the suspension to remain visible over a long period of time,
The suspended particles and the suspending medium must not react in a harmful manner or deteriorate.

The suspended particles are of many types, but are preferably colloidal in size and polarized in character. The polarizing particles enclose the polarizing perhalogenated particles, but may of course include other types of polarizing particles.

Below are examples of the use of the suspending materials of this invention, alone or in combination with additional non-aqueous materials. Examples are also provided to demonstrate the use of the aforementioned aromatic ester suspension materials together with the polymeric coating materials. These examples are illustrative and not intended to be limiting.

Example 1 A three-compartment test cell was constructed with regular walls and regular electrodes to which an alternating current voltage was applied at 10 kilohertz and 300 volts peak voltage. The interior thickness of the cell, or suspension thickness, was 9 mils (0.0225 cm). 1st
The chamber was filled with particles of quinine bisulfate periodide, which is made by combining calcium iodide, hydrogen iodide (i.e., hydriodic acid), and iodine. The second chamber was filled with a suspension of the same particles and approximately 1% nitrocellulose in diisodecyl adipate. The third chamber was filled with the same particles suspended in phenyl acetate with a resistance of 8 x 10 ⁷ ohm-cm. This suspension also contained approximately 1% nitrocellulose. All three chambers were activated simultaneously with the same voltage applied continuously for 2 hours. At the end of this time, the first
In the chamber a lot of aggregation was observed, while in the second chamber there was little aggregation and in the third chamber no aggregation was observed.

Example 2 The two chambers of the test cell of Example 1 were filled as follows. The first chamber was filled with a suspension of cinchonidine sulfate periodide made of hydrogen iodide and iodine in a liquid consisting of 99% isopentyl acetate and about 1% nitrocellulose. Its second chamber contains 49.5% isopentyl acetate, 49.5% orthocresyl acetate (with a resistance of 6.5 x 10 ⁸ ohm-cm) and 1% nitrocellulose.
filled with a suspension of the same particles in a liquid consisting of An activating alternating current voltage of 100 volts RMS at 60 hertz was applied to the electrodes of the two chambers simultaneously for 2 hours and 35 minutes. The thickness of the suspension in the cell was 9 mils (0.009 inches, 0.23 mm). At the end of the test period, significant agglomeration of particles was observed in the first chamber, while no agglomeration was observed in the second chamber.

Example 3 Tests were conducted with the same conditions and cell operation as in Example, using the same suspended particles, except that the suspension in three chambers was filled as follows. In the first chamber the suspension contains 1% nitrocellulose.
It was 99% isopentyl acetate.
In the second chamber, the suspension is 49.5% isopentyl acetate, orthocresyl acetate.
49.5% and 1% nitrocellulose. In the third chamber, the suspension is 49.5% isopentyl acetate and 49.5% paracresyl acetate.
% and 1% nitrocellulose. The cell and all three chambers were activated simultaneously and sequentially for 17.5 hours and the following observations were made at the end of that time. There was heavy aggregation in the first chamber. In the second chamber, there was very little agglomeration at the top of the suspension, ie at the air-suspension interface. However, since this agglomeration formed as soon as the cell began to be activated, this agglomeration was the result of the initial interaction with air at the liquid surface, and over the next 17.5 hours the aggregation It will not increase more than that. Only slight aggregation was observed in the third chamber at the end of 17.5 hours.

Example 4 Dihydrocinchonidine sulfate periodide was suspended in a liquid from 51% isopentyl acetate, 41% phenyl acetate and 8% nitrocellulose. This suspension is placed in a display cell in which the symbol D is placed in one of the cells in the form of a letter as described in Canadian Patent No. 972,857.
It was painted by forming a conductive coating on the wall. The suspension in the display cell is
It was 4.5 mil (0.11 mm) thick. The cells were activated with 170 volts peak-to-peak alternating current at 60 hertz for seven consecutive weeks. At the end of this period, even around the edges of the display symbols were not visible to the naked eye. If the electrodes on both walls of the cell are coated continuously with a conductive coating in the area where the display symbol is located, then the potential gradient at the edge of the symbol is greater than the gradient at other areas, so that the display symbol The fact that no aggregation at the edges is observed is significant. Without the benefit of this invention, high potential gradients result in more agglomeration than low potential gradients.

Example 5 A suspension of particles of quinine bisulfate periodide made from calcium iodide, hydrogen iodide and iodine was placed in a 2 mil (0.051 mm) cell and suspended in a liquid having the following composition: It was done.

Trichlorotrifluoroethane 66.0% Isopentyl Acetate 7.5% Chloroform 7.5% Polymer 11.0% Paracresyl Acetate 7.5% Particles 0.5% 100.0% The polymer is a terpolymer consisting of the following weight percentages of monomers:

3,3,5-trimethyl hexyl acrylate 37.5% Bis-2-ethylhexyl fumarate 37.5% 2-hydroxypropyl acrylate 22.0% Fumaric acid 3.0% 100.0% 2.25 volts peak per mil (0.025 mm)
A 60 Hz alternating current potential of 4.5 volts peak to peak with a gradient of 4.5 volts peak to peak was applied continuously for 24 hours. At the end of this period, no aggregation was visually observed.

Ortho-cresyl acetate or phenyl acetate can be substituted for para-cresyl acetate, except that a somewhat higher voltage gradient is required.

The example provides proof that aggregation is greatly reduced by the use of aromatic alcohols. These aromatic esters include phenyl acetate, ortho-cresyl acetate and para-cresyl acetate. In addition, many aromatic esters having an aliphatic group hanging from the ring can be used, examples of which are methylphenyl acetate, ethylphenyl acetate, propylphenyl acetate, butylphenyl acetate, amylphenyl acetate, Hexyl phenyl acetate, heptyl phenyl acetate, octylphenyl acetate, nonylphenyl acetate and decyl phenyl acetate, especially in which the aliphatic group is present in the para position.

In a broad sense, the esters of the present invention are aromatic esters whose aromatic groups are aryl, (eg benzyl, phenyl), alkylaryl, (methylbenzyl, methylphenyl), naphthyl, and the like.

These liquids, especially when used in combination with polymeric coating materials such as those described above, retard aggregation and maintain dispersion of a variety of different suspended particles even in the presence of an electric field.

The foregoing example shows that, by using the present invention and assuming that a sufficient amount of natural or artificial light is available, the light valve or suspension of the present invention will cause an electric field to increase when an electric field is applied to it. Case 2 when not applicable
It allows for double the transmission of light and, if necessary, keeps the suspension in a sufficiently dispersed state for at least 2 hours.

The present invention presents an example known to the inventors in which suspensions usable in light valves were stabilized from agglomeration by only chemical means when subjected to a long-term electric field.

The invention can be used as a light valve for use as windows, windshields, displays, mirrors and other similar devices.

The above example is illustrative and not limiting, and many modifications are possible.

Claims (1)

[Scope of Claims] 1. A light valve comprising a cell containing a suspension of colloidal particles in a medium and an electric field imparting member for applying an electric field through the suspending medium, wherein the particles is sensitive to an electric field to alter the transmission of light through its suspension, and the liquid suspension medium comprises an ester of at least one phenol and a carboxylic acid. 2. A light valve comprising a cell containing a suspension of colloidal particles in a medium and an electric field imparting member for applying an electric field through the suspension medium, wherein the particles are suspended in the suspension. sensitive to electric fields to alter the transmission of light therethrough, said liquid suspending medium comprising (a) an ester of at least one phenol and a carboxylic acid; and (b) nitrocellulose, at least two monomers. A light valve characterized in that it comprises a copolymer material or a mixture thereof.