MXPA01000020A - Light-polarizing particles of improved particle size distribution - Google Patents

Abstract

A method of making particles of light-polarizing material comprising reacting a precursor suitable for forming polyhalide particles with elemental iodine and a hydrohalide acid or an ammonium, alkali metal or alkaline earth metal halide wherein the average size and/or median size of the precursor is less than 1 micron.

Description

"POLARIZATION PARTICLES OF ENHANCED PARTICLE SIZE DISTRIBUTION LIGHT" FIELD OF THE INVENTION The present invention relates to a method of manufacturing light polarization particles of improved particle size distribution for use in liquid suspensions and light valves, films and suspensions.

BACKGROUND Light beam valves have been known for more than sixty years for light modulation. As used herein, a light beam valve can be described as a cell formed of two walls that are spaced apart by a small distance, at least being a transparent wall, the walls having electrodes therein usually in the form of coatings. transparent conductors. The cell contains a light modulating element, which can either be a liquid suspension of particles or a plastic film in which the droplets of the liquid suspension of the particles are distributed and encapsulated.

The liquid suspension (sometimes referred to herein as a liquid suspension of light beam valve) comprises small particles suspended in a liquid suspension medium. In the absence of an applied electric field, the particles in the liquid suspension exhibit casual Brownian motion, and therefore a beam of light that passes into the cell is reflected, transmitted or absorbed, depending on the structure of the cell, nature and concentration of the particles and the energy content of the light. The light beam valve of this is therefore relatively dark in the DISCONNECTED state. However, when an electric field is applied through the light beam valve suspension in the light beam valve, the particles are aligned and for many suspensions most of the light can pass through the cell. The light beam valve is therefore relatively transparent in the CONNECTED state. Light beam valves have been proposed for many objects including, eg, alpha-numeric presentations, television displays, windows, sunroofs, anti-sun visors, mirrors, glasses and the like to control the amount of light passing through the same. Light beam valves of the type described herein are also known as "suspended particle devices" or SPDs ".

For many applications, it is preferable that the activatable material be a plastic film instead of a liquid suspension. For example, in a light beam valve used as the variable light transmission window, a plastic film in which the droplets of the liquid suspension are distributed in preference to a liquid suspension alone because the hydrostatic pressure effects, eg, the warpage associated with a high column of liquid suspension can be avoided through the use of a film, and the risk of possible escape can also be avoided. Another advantage of using a plastic film is that in a plastic film the particles are usually only present within very small droplets, and therefore do not agglomerate significantly when the film is activated repeatedly with a voltage. A "light beam valve film" as used herein is therefore a film having droplets of a liquid suspension of particles distributed in the film. A type of light beam valve film manufactured by phase separation of a homogeneous solution is disclosed in US Patent Number 5,409,734. Light beam valve films made by crosslinking emulsions are disclosed in U.S. Patent Nos. 5,463,491 and 5,463,492 assigned to the concessionaire of the present invention. All those patents and other patents and other sources cited herein are incorporated herein by reference thereto. For use in suspensions such as light polarization sheets, sometimes called "sheet polarizers", which can be cut and formed into polarized sunscreens or used as filters, the light polarization particles can be dispersed or distributed through a sheet of an appropriate film-forming material, such as acetate of cellulose or polyvinyl alcohol or a similar one. Methods for making suspensions for use in sheet polarizers are well known in the prior art. In these suspensions, however, the particles are immobile. See, eg, US Patents Nos. 2,178,996 and 2, 041, 138. SUSPENSION OF LIQUID LIGHT BEAM VALVE 1. Suspension Means Liquids and Stabilizers The liquid light beam valve suspension can be any beam valve suspension. of liquid light known in the art and can be formulated according to known techniques. The term "liquid light beam valve suspension" as used herein means a "liquid suspension medium" in which a plurality of small particles are dispersed. The "liquid suspension medium" comprises one or more non-aqueous electrically resistive liquids wherein preferably at least one type of polymeric stabilizer which acts to reduce the tendency of the particles to agglomerate and to keep them dispersed and in suspension is dissolved. The liquid light beam valve suspension of the present invention may include any liquid suspension means proposed above for use in light beam valves for suspending the particles. Liquid suspension media known in the art are useful herein, such as but not limited to the liquid suspension medium disclosed in U.S. Patent Nos. 4,247,175 and 4,407,565. Generally, one or both liquid suspension media or the polymeric stabilizer dissolved therein is selected in order to keep the suspended particles in gravitational equilibrium. The polymeric stabilizer when employed may be a single type of solid polymer that binds to the surface of the particles but also dissolves in the non-aqueous liquid or liquids of the liquid suspension medium. Alternatively, there may be two or more solid polymeric stabilizers that serve as the polymeric stabilizer system. For example, the particles may be coated with a first type of solid polymeric stabilizer such as nitrocellulose, which in fact, provides a surface coating for the particles and one or more additional types of solid polymeric stabilizer that are linked to or associated with the first type. of solid polymeric stabilizer and which also dissolve in the liquid suspension medium to provide dispersion and steric protection for the particles. Also, liquid polymeric stabilizers may advantageously be used, especially in the SPD light beam valve films, as described in U.S. Patent No. 5,463,492. 2. Particles As is known, inorganic and organic particles can be used in a light beam valve suspension. However, the present invention relates to an improved method for preparing particles which are polyhalides (which are sometimes referred to in the prior art as perhalides) of organic compounds, such as alkaloid acid salts and the like. The polyhalide batches of the present invention may be light polarizing, such as halogen-containing light polarization materials, e.g., the polyhalides of alkaloid acid salts.

(The term "alkaloid" is used herein to mean an organic nitrogen base, as defined in Hackh's Chemical Dictionary, Fourth Edition, McGra-Hill Book Company, New York, 1969). As is known, if a polyhalide of an alkaloid acid salt is prepared, the alkaloid residue may be a quinine alkaloid, as defined in Hackh's Chemical Dictionary, cited above. U.S. Patent Nos. 2,178,996 and 2,289,712 refer in detail to the use of polyhalides of quinine alkaloid acid salts. The particles may be light absorbing or light reflecting. Also, the particles may be particles of a hydrogenated polyhalide of a salt of the quinine alkaloid acid, such as dihydrocinconidy sulfate polyiodide, as described in U.S. Patent No. 4,131,334. More recently, improved polyhalide particles having advantageous features for use in light beam valves have been proposed in U.S. Patent Nos. 4,877,313, 5,002,701, 5,093,041 and 5,516,463. These "polyhalide particles" are formed by reacting the organic compounds, usually containing nitrogen, with elemental iodine and a hydrohalide acid or an alkali metal ammonium halide or alkaline earth metal halide. These organic compounds are referred to herein as "Precursor". The polyhalide particles of the prior art are also disclosed in detail in "The Optical Properties and Structure of Polyiodides" by D.A. Godina and G.P. Faerman published in The Journal of General Chemistry, U.S.S.R. Volume 20, pages 1005-1016 (1950). Herapatite, for example, is a quinine bisulfate polyiodide, and its formula is provided under the heading "quinine iodosulfate", as 4c20H24N2o2-3H2so4-2HI-I4-6H2 ° of the Merck Index, 10th Ed.

(Merck &Co., Inc. Rah ary, N.J.). In polyiodide compounds, the iodide anion is believed to form chains and the compounds are strong light polarizers. See U.S. Patent Number 4,877,313 and Teitelbaum and others JACS 100 (1978), pages 3215-3217. The term "polyhalide" is used herein to mean a compound such as polyiodide, but wherein at least some amount of the iodide anion can be replaced by another halide anion. As is known, polyhalide particles which are useful in light beam valves, preferably of colloidal size, ie, the particles will have a larger dimension averaging approximately 1 micron or less. It is preferred that the polyhalide particles have i-, its largest dimension is less than half the wavelength of blue light, that is, 2,000 Angstroms or less to keep the light scattering extremely low.

DESCRIPTION OF THE INVENTION The present invention provides a method for preparing polyhalide particles that are especially well suited for use as the particles of a liquid light beam valve suspension, which comprises reacting a "Precursor" of a specified particle size with elemental iodine and a hydrohalide acid or an ammonium halide, alkali metal or alkaline earth metal. The Precursor can be any of the compounds previously used to form organic polyhalide particles by reaction with elemental iodine and a hydrohalide acid or an ammonium halide, alkali metal or alkaline earth metal. For example, the Precursor may be a salt of quinine alkaloid acid (US Patent Nos. 2,178,996 and 2,289,712), a hydrogenated alkaloid acid salt (US Patent Number 4,131,334) or an organic compound containing one or more groups that are subjected to chelation to hydrogen, ammonium or metal ions (U.S. Patent Nos. 4,877,313, 5,002,701, 5,093,041 and 5,516,463), all of these North American patents having been incorporated herein by reference thereto. The Precursor can be of any color but usually consists of small white or almost white colored crystals (sometimes referred to as "particles"). We have surprisingly found that if the average size and / or average size of the Precursor is less than 1 micron, preferably less than 0.75 micron, the quality of the polyhalide particles made therefrom is considerably improved. The crushing (reduction of size) of the particles of the Precursor to provide the desired particle size can be achieved by any means that reduces its size, as long as the process does not cause the crushed particles to gather or agglomerate, which would counteract the advantages of crushing and could actually cause the effective particle size to increase. For example, the particles of the Precursor can be pulverized or ground with a mortar and pestle or with a ball mill or any other convenient means, either dry or wet with a liquid or other solid inert substance present to help the pulverization. Alternatively, the Precursor particles can be caused to collide with each other, subjecting to rapidly moving gas streams, for example, • ______ > making itself hit by a supersonic current or air currents. As used herein, the particles of the Precursor or crystals are said to have been crushed or reduced in size, which is meant to imply that their average size and / or their average size has been reduced. He "size" of a particle as used herein means and refers to the largest dimension of the particle. The present invention is illustrated in terms of its preferred embodiments in the following Examples. One modern type of the prior art typical of the polyhalide (crystal) particle is the calcium iodide polyiodide of pyrazine-2,5-dicarboxylic acid dihydrate. A method for preparing these crystals and a liquid suspension thereof for use as a light beam valve is disclosed in Example 1.

EXAMPLE 1 (PREVIOUS TECHNIQUE) Formulation for Manufacturing Poliyoduro Crystals and a Liquid Light Beam Valve Suspension of Themselves In an appropriately sized bottle, the following reagents are added in the order shown: 160 grams of a 6.98 percent nitrocellulose solution of type 1/4 ss sec (dry), dissolved in hexyl acetate 3 grams of pyrazine-2,5-dicarboxylic acid dihydrate (the "Precursor") 4.5 grams of iodine 2.64 grams of anhydrous calcium iodide 1.8 grams of methanol anhydrous 0.33 gram of water Cover and jar and shake for about half an hour. The bottle is placed in an ultrasonic sonicator until the solution becomes completely blue, about 10 hours. The solution is inspected under a microscope to determine that the Precursor, Cal2 and? 2 have been reacted completely, i.e., there is no considerable amount of the Precursor unreacted. A maximum yield is obtained when the initial decomposition time is between 8 and 15 milliseconds. If the decomposition time is less than 8 milliseconds, the formulation is re-treated with approximately 0.05 gram. H2O is added after methanol. The decomposition time is determined by the following procedure. A suspension of the particles formed in a light beam valve suspension means is filled in a light beam valve cell comprising glass sheets carrying appropriate electrodes spaced at a distance of .1270 mm. The light beam valve suspension is illuminated with continuous illumination such as a tungsten lamp. The suspension of the particles in the light beam valve is energized by applying the electrodes approximately 55 volts at 10 kHz to a baseline measurement. Approximately 2 to 3 milliseconds are required to reach the open state of the light beam valve, and approximately 20 milliseconds later the electric field is discontinued. The decomposition to the completely closed (disconnected) state of the light beam valve is subsequently measured. (See column 2, lines 37-48 of U.S. Patent Number 5,516,463). The solution is centrifuged at 11,500 revolutions per minute for 1 hour and the supernatant is discarded. The tubes are drained by turning up and down on a paper towel for 15 minutes. The sediment of the tubes is placed in a glass jar and the weight of the sediment is recorded. 15 grams of hexyl acetate are added for each gram of sediment. The sediment is dispersed by shaking for a half hour followed by 10 hours of ultrasonic sonication.

• »S,.%« * The dispersion is centrifuged at 2500 revolutions per minute for 5 to 15 minutes and the supernatant is decanted and collected. The decomposition time must be from 8 to 12 milliseconds; if it is higher, the supernatant liquid is centrifuged again. The supernatant fluid is centrifuged at 9,500 revolutions per minute for half an hour and the supernatant is discarded. The tubes are drained by turning up and down on a paper towel for 15 minutes. The sediment is collected in a glass jar and 10 grams of anhydrous isopentyl acetate are added for each gram of sediment. The sediment is dispersed by shaking for half an hour followed by 10 hours of sonification. This is referred to below as the "initial concentrate". Tri-n-pentyl trimellitate (TNPTM) is added, which is a plasticizing liquid as described in column 4, lines 48-66 of US Patent Number 5,463,491, to the initial concentrate in an amount of 9 grams and the combination is placed in a Rotovap apparatus for 2 hours at 60 ° C to evaporate the isopentyl acetate. The amount of TNPTM to be added can be determined empirically depending on how concentrated with particles the resulting final concentrate is desired (i.e., the initial concentrate dried). The final concentrate -. «# * Can then be diluted with any other solvent or solvents desired where the concentrated polymer is soluble. Other plasticizing liquids can be used. To prepare a concentrate for use in the SPD light beam valve film, in accordance with the teachings of one embodiment of US Patent Number 5,463,492, instead of adding TNP ™ to the aforementioned initial concentrate before evaporating the isopentyl acetate, a liquid polymer such as a copolymer of n-butyl acrylate / heptafluorobutyl acrylate / hydroxyethyl acrylate can be added. Various modifications of the aforementioned process can be made to prepare the polyiodide crystals such as changing the amounts of some of the reagents, altering the centrifugation times or the process, or varying the ultrasonic sonication. Example 2 discloses a prior art method for making the Precursor material used in Example 1, namely, the pyrazine-2,5-dicarboxylic acid dihydrate.

EXAMPLE 2 (PREVIOUS TECHNIQUE) Procedure to Fabricate Pirazin-2, 5-Dicarboxylic Acid Dihydrate 2, 5-dimethylpyrazine (25 grams), pyridine (500 milliliters), selenium dioxide (125 grams) and water (50 milliliters) were placed in a 1 liter round bottom flask equipped with a mechanical stirrer and a reflux condenser. The mixture was refluxed for 11 to 12 hours; The boiling solution assumes an orange-red color after approximately 20 minutes while the selenium system gradually precipitates. The suspension is allowed to cool to room temperature, and the precipitated material, a mixture of pyrazine-2,5-dicarboxylic acid and selenium, is filtered. The flask and the agitator are rinsed with a filtered reaction solvent. The reaction solvent is returned to the flask and reused. The precipitated material is washed with 2N H4 OH until all of the 2,5-dicarboxylic pyrazine acid dissolves. The 2N NH4OH with the pyrazine 2,5-dicarboxylic acid is passed through a Darco activated carbon chromatography column in suspension (12-20 mesh, 250 grams) at a rate of 30 milliliters per minute. ^ _______________________________________________________ Concentrated hydrochloric acid (100 milliliters) of 400 milliliter portions of the colorless eluent was added to give a white precipitated material of pyrazine-2,5-dicarboxylic acid, which was filtered, washed with 20 milliliters of 2N hydrochloric acid and with 20 milliliters of ice water, followed by 20 milliliters of acetone. After the precipitated material is air dried to remove the odor of acetone, the Precursor, which is the pyrazine-2,5-dicarboxylic acid dihydrate, is ready for use. In order to be able to demonstrate that the present invention has improved the quality of the polyhalide particles referred to herein, and in order to quantify that improvement, several terms need to be defined. The optical density of the test cell of the light beam valve window in the non-activated condition is in its optical density of disconnected state or "O ^ disconnected" • When a voltage is applied to the transparent conductive coatings of the cell (electrodes) the particles in the liquid suspension or film contained in the cell are oriented, causing the transmission of light to increase and causing the optical density to decrease. The optical density decreased when the cell is activated or connected is referred to herein as "ODconnected" • For the tests described herein a voltage of 55 volts RMS is applied at a frequency of 10 Kilohertz using a test cell that has an internal space of .1270 mm between their electrodes. Therefore, the field strength applied in a test cell would be 11 volts RMS per 25.40 microns. 0D disconnected divided by ODconnection is referred to herein as the optical density ratio or ODR. In Example 1 above, a method for measuring the decomposition time of a liquid suspension, t, in a test cell is disclosed. Generally, it is desirable that a liquid suspension of light beam valve have a large ODR and a t <; little. Therefore, to measure the total quality of a suspension we define its efficiency, E, to its ODR divided between its t < Measured in seconds. In this way for a liquid suspension having an optical density ratio of 2.0 and a decomposition time of 18 milliseconds (.018 sec.), Its efficiency would be calculated as follows: E = A_0 = 111 .018 The higher can be done E, better EXAMPLE 3A In an Erlenmeyer flask the following materials in the amounts shown were dissolved in 132. 5 grams of a solution of hexyl acetate (including 0.11 gram of water) comprising 6.98 percent nitrocellulose of type 1/4 ss: 4.5 grams of iodine 2.64 grams of anhydrous calcium iodide 1.8 grams of methanol 0.53 grams of water. Then, 3 grams of pyrazine-2,5-dicarboxylic acid dihydrate (Precursor) made by the prior art method described in Example 2 was added to the aforementioned solution, and the flask was placed for 3 hours at 45 °. C in a Waterbath Stirrer Model WB-20 manufactured by Elmeco Engmeering, of Rockville, Maryland. Then the suspension was stirred ultrasonically for two hours. The particle size of the precursor is disclosed in Table 1, which is presented below.

EXAMPLE 3B Example 3A was repeated with the exception that the Precursor had previously been ground by a supplier (Aveka, Inc., Woodbury, Minnesota) in a machine referred to herein as a "pan mill" which uses supersonic air currents to cause the particles of the Precursor to collide violently with each other. The particle size of the Precursor is disclosed in Table 1, which is presented below. The suspensions of Examples 3A and 3B were removed from the Erlenmeyer flasks and centrifuged after the procedure of Example 1, to obtain the initial concentrated material. Table 1 summarizes the data for each of the suspensions described in Examples 3A and 3B with respect to ODR, the decomposition time, the efficiency, and the average and median sizes of the precursor particles used. ? Ü¡ ^ __ ^ _ ^^ TABLE 1 Data Comparison for Two Suspensions of Poliyoduro, the First Elaborated with a Precursor Elaborated by the c Method of the Previous Technique and the Second Elaborated with a Crushed Precursor Size of Particles of Relation Time Effi- Precursor Used of Density of Dispersion- 0 Size Size Optical * component- Average Average Example 3A 6.33 microns 1.12 microns 3.13 23 ms 136 Example 3B 0.74 micron 0.68 micron 3.00 10.5 ms 285 5 * For the initial concentrate material (as described in Example 1), but with only 2 hours of sonification after the initial reaction, and additional agitation and two hours of sonification after each first and third C centrifugation steps. In addition, of the pyrazine-2,5-dicarboxylic acid hydrate, any solid precursor used in the prior art or subsequently invented, which can be used to make the polyhalide particles, can advantageously be comminuted as disclosed in the present invention. .

Although we do not wish to be limited to any specific theory why shredding leads to improved polyhalide particle efficiency, we believe that shredding can improve efficiency by allowing smaller particles to form and start growing at about the same time and so both can yield a suspension that is less polydispersed in the particle size distribution than the suspensions of the prior art.

Claims (12)

CLAIMS:

1. A method for making particles of a light polarization material comprising reacting an appropriate precursor to form polyhalide particles with elemental iodine and a polyhalide acid or an ammonium, alkali metal or alkaline earth metal halide wherein the average size and / or the median size of the precursor is less than 1 micron.

2. The method of claim 1, wherein the average and / or median size of the precursor is less than 0.75 micron.

The method of claim 1, further comprising providing a desired particle size for the precursor prior to the reaction by means that reduce the particle size of the precursor without causing the small sized particles to gather or agglomerate.

4. The method of claim 1, wherein the precursors are the polyhalides of the organic compounds.

The method of claim 4, wherein the polyhalides of the organic compounds are alkaloid acid salts and the like.

6. The method of claim 1, wherein the precursors are organic compounds containing nitrogen.

The method of claim 1, wherein the precursors are quinine alkaloid salts.

The method of claim 1, wherein the precursors are organic compounds that contain one or more groups that chelate the hydrogen, ammonium or metal ions.

9. The particle prepared by the method of any of claims 1 to 8.

10. In a light beam valve, comprising a cell containing a suspension of light polarization particles in a liquid suspension medium, the improvement wherein the particles are the particles according to claim 1.

11. A light polarization body comprising a plurality of particles according to claim 9, dispersed in a carrier, the polarization axis of the particles being oriented and it is held immovably by the carrier in considerable parallelism.

12. A liquid suspension comprising an electrically resistive liquid suspension medium, a plurality of small particles configured to jS-Cafc? A.- - _ j-t? r. > a > Anisometrically according to claim 9 dispersed therein, and at least one stabilization polymer material dissolved therein to disperse the particles in the suspension.