CN1308716A - 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 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

Light Polarizing Particles with Improved Particle Size Distribution

field of invention

The present invention relates to the manufacture of light polarizing particles with improved particle size distribution for use in liquid suspensions and light valves, films and solidified suspensions.

background

Light valves have been known for over sixty years to modulate light. As used herein, a light valve can be described as a chamber formed by two walls separated by a small distance, at least one of which is transparent , with electrodes on both walls, usually in the form of a transparent conductive coating. The chamber contains a light modulating element which may be a liquid suspension of particles, or a plastic film in which droplets of the liquid suspension of particles are distributed and encapsulated.

Liquid suspensions (sometimes referred to herein as liquid light valve suspensions) contain small particles suspended in a liquid suspending medium. In the absence of an applied electric field, particles in a liquid suspension exhibit random Brownian motion, so that a light beam passing through the chamber is reflected, transmitted, or absorbed depending on the structure of the chamber, the type and concentration of the particles, and the energy contained in the light. At this time, the light valve is in a relatively dark closed (OFF) state. However, when an electric field is applied through the light valve suspension in the light valve, the particles align and, for many suspensions, most of the light can pass through the chamber. At this time, the light valve is in a relatively transparent open (ON) state.

Light valves are proposed for many purposes including, for example, alphanumeric displays, television displays, windows, sunshades, visors, mirrors, eyeglasses, etc., to control the amount of light passing through them. The light valves described herein are also known as "suspended particle devices" or "SPDs."

For many applications, the activatable material is preferably a plastic film rather than a liquid suspension. For example, in a light valve used as a variable transmission window, a plastic film with droplets of a liquid suspension distributed therein is superior to a liquid suspension alone, because static pressure effects can be avoided by using the film, e.g. The associated bulging of the liquid suspension column also avoids possible leakage hazards. Another advantage of using plastic films is that, in plastic films, the particles are generally only present in very small droplets, so that no significant aggregation occurs when the film is repeatedly activated with an electrical voltage.

Thus, a "light valve film" as used herein is a film in which droplets of a liquid suspension of particles are distributed.

One type of light valve film fabricated from a homogeneous solution by phase separation is disclosed in US Patent No. 5,409,734. Light valve films made from crosslinked emulsions are disclosed in US Patent Nos. 5,463,491 and 5,463,492, assigned to the assignee of the present invention. All of these and other patents and other sources cited herein are incorporated herein by reference.

For applications in solidified suspensions such as light polarizers (sometimes called sheet polarizers, which can be cut into polarized sun lenses or used as optical filters), the light polarizing particles can be dispersed, or distributed in suitable formations. Sheets of film materials (such as cellulose acetate or polyvinyl alcohol, etc.). Methods for producing solidified suspensions for sheet polarizers are known in the prior art. However, in these solidified suspensions the particles are immobile. See US Patents 2,178,996 and 2,041,138.

liquid light valve suspension

1. Liquid suspension medium and stabilizer

The liquid light valve suspension may be any liquid light valve suspension known in the art and may be formulated according to known techniques. As used herein, the term "liquid light valve suspension" refers to a "liquid suspending medium" in which many small particles are dispersed. The "liquid suspending medium" contains one or several non-aqueous and electrically resistant liquids, in which at least one polymeric stabilizer is preferably dissolved, the function of which is to reduce the tendency of the particles to aggregate and keep them dispersed and in suspension status.

The liquid light valve suspension of the present invention may comprise any of the previously proposed liquid suspending media for suspending particles in light valves. Liquid suspending media used in the prior art, such as, but not limited to, those disclosed in US Pat. Nos. 4,247,175 and 4,407,565 may be used herein. In general, one or two liquid suspending media or polymeric stabilizers dissolved therein are selected so as to maintain the suspended particles under gravitational equilibrium.

When a polymeric stabilizer is used, it may be a single species of solid polymer capable of binding to the surface of the particles but also soluble in one or more non-aqueous liquids in the liquid suspending medium. In addition, there may be two or more solid polymeric stabilizers which serve as a polymeric stabilizing system. For example, the granules may be coated with a first solid polymeric stabilizer, such as nitrocellulose (which in effect provides a flat surface coating to the granules) and one or several other types of solid polymeric stabilizers (which combined with or linked to a first solid polymeric stabilizer and dissolved in a liquid suspending medium) to provide dispersion and steric protection to the particles. As described in US Pat. No. 5,463,492, liquid polymerization stabilizers can be used to promote light valve films, especially in SPDs.

2. Particles

It is well known that inorganic and organic particles can be used in light valve suspensions. However, the present invention relates to an improved method of preparing particles which are polyhalides (sometimes referred to in the prior art as perhalides) of organic compounds, such as acid salts of alkaloids and the like. The polyhalide particles of the present invention may be light polarizing, such as halogen containing light polarizing materials, eg polyhalides of acid salts of alkaloids. (The term "alkaloid" as used herein refers to an organic nitrogenous base, as defined in Hackh's Chemical Dictionary, Fourth Edition, McGraw-Hill Book Company, New York, 1969 ). It is well known that if polyhalides of acid salts of alkaloids are prepared, the alkaloid moiety may be a quinine alkaloid as defined in Hackh's Chemical Dictionary, supra. US Patents 2,178,996 and 2,289,712 detail the use of polyhalides of acid salts of quinine alkaloids. These particles can be light absorbing or light reflecting. The particles may also be hydrogenated polyhalides of acid salts of quinine alkaloids, such as the polyiodides of dihydrocinconidyl sulfate described in U.S. Patent No. 4,131,334.

More recently, improved polyhalide grains with superior characteristics for light valves have been proposed in US Patent Nos. 4,877,313, 5,002,701, 5,093,041 and 5,516,463. These "polyhalide particles" are obtained by reacting organic compounds, generally nitrogen-containing organic compounds, with elemental iodine and hydrohalic acids or ammonium, alkali metal halides or alkaline earth metal halides. Such organic compounds are referred to herein as "precursors".

In the former Soviet Union's "Journal of General Chemistry" (The Journal of General Chemistry), Volume 20, pages 1005-1016 (1950), the article "Optical properties and structures of polyiodides" by DA Godina and GPFaerman also discussed in detail the current There are polyhalide grains in technology. Such as quinine iodosulfate is polyiodide of quinine bisulfate, "The Merck Index" (The Merck Index) 10th edition (Merck & Co., Inc., Rahway, NJ) in "quinine iodosulfate" Its molecular formula is given under the formula 4C ₂₀ H ₂₄ N ₂ O ₂ .3H ₂ SO ₄ .2HI.I ₄ .6H ₂ O. In polyiodide compounds, which are assumed to form chains with iodide anions, the compounds are strong light polarizers. See US Patent 4,877,313 and Teitelbaum et al., Journal of the American Chemical Society (JACS) 100 (1978), pp. 3215-3217. As used herein, the term "polyhalide" refers to compounds such as polyiodides, but in which at least some of the iodide ions are replaced by other halide anions.

It is well known that polyhalide particles useful in light valves are preferably of colloidal size, that is to say the largest dimension of the particles averages about 1 micron or less. Preferably most polyhalide particles have a maximum dimension less than half the wavelength of blue light, ie 2000 Å or less, to keep light scatter very low.

Description of the invention

The present invention provides a process for the preparation of polyhalide particles particularly suitable as particles in liquid light valve suspensions, which comprises reacting "precursors" of defined particle size with elemental iodine and hydrohalic acids or ammonium, alkali metal Or the halide reaction of alkaline earth metals. The precursor may be any compound previously used to form organic polyhalide particles by reaction with elemental iodine and hydrohalic acid or ammonium, alkali metal or alkaline earth metal halides. For example, the precursor may be a quinine alkaloid acid salt (U.S. Patents 2,178,996 and 2,289,712), a hydrogenated alkaloid acid salt (U.S. Patent 4,131,334), or a compound containing one or more compounds capable of chelating hydrogen, ammonium, or metal ions. group of organic compounds (US Patents 4,877,313, 5,002,701, 5,093,041 and 5,516,463), all of which are incorporated herein by reference. The precursor may be of any color, but generally consists of off-white or nearly pure white crystals (sometimes referred to herein as "grains").

We have surprisingly found that the quality of the polyhalide particles produced therefrom is significantly improved if the precursors have an average and/or median size of less than 1 μm, preferably less than 0.75 μm. Comminution (size reduction) of the precursor particles to provide the desired particle size can be achieved by any device capable of reducing their size, as long as the process does not cause agglomeration or agglomeration of the comminuted particles, since aggregation or agglomeration Agglomeration would negate the benefits of comminution and would actually cause an increase in the effective size of the particles. For example, the precursor particles may be comminuted or ground with a mortar and pestle, or with a ball mill or any suitable device, either in the dry state or wetted with a liquid, or with other solid inert substances to aid pulverization. In addition, the precursor particles may collide with each other due to the effect of rapid air movement, such as blowing with ultrasonic flow or air flow.

As used herein, to say that precursor particles or crystals have been fragmented, or otherwise reduced in size, means that their average and/or median size has been reduced. Particle "size" as used herein means and refers to the largest dimension of the particle.

The invention is illustrated in preferred embodiments in the following examples.

A typical new prior art polyhalide particle (crystal) is pyrazine-2,5-dicarboxylic acid dihydrate calcium iodide polyiodide. The procedure for making such crystals and their liquid suspensions for use in light valves is disclosed in Example 1.

Embodiment 1 (prior art)

Recipe for making polyiodide crystals and their liquid light valve suspensions

In an appropriately sized jar add the following reagents in the order shown:

160g 1/4sec ss type nitrocellulose (dry) dissolved in hexyl acetate

6.98% solution in

3g pyrazine-2,5-dicarboxylic acid dihydrate (precursor)

4.5g iodine

2.64g Anhydrous calcium iodide

1.8g anhydrous methanol

0.33g of water Cover the jar and shake for about half an hour. Place the jar in the sonicator until the solution turns completely blue, which takes about 10 hours. Observe the solution under a microscope to ensure that the precursors, _CaI2 and iodine have reacted sufficiently, ie no appreciable amounts of unreacted precursor are present. The maximum yield was obtained when the initial decay time was 8-15 milliseconds. If the decay time is less than 8 milliseconds, reconstitute by adding about 0.05 g of water after adding methanol.

Determine the decay time as follows. The resulting suspension of particles in the light valve suspension medium was filled into a light valve chamber consisting of two glass plates with appropriate electrodes spaced 5 mils apart. The light valve suspension is illuminated with continuous light such as generated in a tungsten lamp. The particle suspension in the light valve was excited by applying a 10 Hz voltage across the electrodes measuring 55 V relative to the baseline. It takes about 2-3 milliseconds for the light valve to reach the open state, and the electric field is turned off after about 20 milliseconds. The decay time for the light valve to change to the fully closed state (OFF) is then measured. (See column 2, lines 37-48 of US Patent 5,516,463).

The solution was centrifuged at 11,500 rpm for 1 hr and the supernatant was discarded. Place drain side down on a paper towel for 15 minutes. Transfer the sediment from the tube into a weighed glass jar and record the weight of the sediment. Add 15 g of hexyl acetate per gram of precipitate, shake for half an hour, and then use ultrasonic treatment for 10 hr to disperse the precipitate.

Centrifuge the dispersion at 2,500 rpm for 5-15 min, decant and collect the supernatant. The decay time should be 8-12 milliseconds, if it is too high, centrifuge the supernatant again.

Centrifuge the supernatant at 9,500 rpm for half an hour, discard the supernatant, and place the drain head down on a paper towel for 15 minutes. Collect the precipitate in a weighed glass jar, and add 10 g of anhydrous isoamyl acetate per gram of the precipitate. Shake for half an hour, and then use ultrasonic treatment for 10 hr to disperse the precipitate. Hereinafter referred to as "initial concentrate".

In column 4 of U.S. Patent 5,463,491, lines 48 to 66 describe a liquid plasticizer, tri-n-pentyl trimellitate (TNPTM), which is added to the initial concentrate in an amount of 9 g, and put together The isoamyl acetate was evaporated in a rotary evaporator at 60°C for 2 hr. The amount of TNPTM to be added can be determined empirically based on what particle concentration is desired in the resulting final concentrate (ie, the dried initial concentrate). The final concentrate can then be diluted with any other desired solvent or solvent mixture in which the concentrated polymer can dissolve. Other liquid plasticizers may be used.

To prepare concentrates for use in SPD light valve films, following the guidance of one embodiment of U.S. Patent No. 5,463,492, instead of adding TNPTM to the above-mentioned initial concentrate prior to evaporation of the isoamyl acetate, a liquid polymer may be added, Such as n-butyl acrylate/heptafluorobutyl acrylate/hydroxyethyl acrylate copolymer.

Various changes can be made to the above-described operating procedures for producing polyiodide crystals, such as changing the amounts of some reactants, changing centrifugation time or operating procedures, or changing sonication.

Example 2 presents a prior art method of making the precursor material used in Example 1, pyrazine-2,5-dicarboxylic acid dihydrate.

Embodiment 2 (prior art)

Process for producing pyrazine-2,5-dicarboxylic acid dihydrate

In a 1 L round bottom flask equipped with mechanical stirring and reflux condenser was charged 2,5-dimethylpyrazine (25 g), pyridine (500 mL), selenium dioxide (125 g) and water (50 mL). The mixture was refluxed for 11-12 hours. After about 20 minutes, the boiling solution was orange-red, and selenium gradually precipitated out.

The suspension was allowed to cool to room temperature and the precipitate, a mixture of pyrazine-2,5-dicarboxylic acid and selenium, was filtered off. Rinse the flask and stirrer with the filtered reaction solvent. The reaction solvent was returned to the flask for reuse. The precipitate was washed with 2N ammonium hydroxide until all pyrazine-2,5-dicarboxylic acid was dissolved. 2N ammonium hydroxide and pyrazine-2,5-dicarboxylic acid were passed through a column of slurryed Darco activated carbon (12-20 mesh, 250 g) at a flow rate of 30 mL/min.

Concentrated hydrochloric acid (100 mL) was added to a 400 mL portion of the colorless eluent to give a white precipitate of pyrazine-2,5-dicarboxylic acid, which was filtered off, washed with 20 mL of 2N hydrochloric acid and 20 mL of ice-cold water, Then wash with 20 mL of acetone. After the precipitate was air-dried until there was no smell of acetone, the precursor, pyrazine-2,5-dicarboxylic acid dihydrate, was obtained for future use.

In order to demonstrate that the present invention improves the quality of polyhalide grains referred to herein, and to quantify this improvement, several terms need to be defined. The optical density of the light valve window test chamber under unactivated conditions is the optical density " _ODoff "of its closed state (OFF). When a voltage is applied to the conductive coating (electrode) of the test chamber, the particles in the liquid suspension or film contained in the chamber are oriented, causing an increase in transmitted light and a decrease in optical density. When the chamber is activated or otherwise turned on, this reduced optical density is referred to herein as "OD _on ". For the tests herein, an effective value (RMS) 55 V voltage was applied at a frequency of 10 KHz, using a test chamber with an electrode separation of 5 mils. Therefore, the electric field strength applied to the test chamber is 11Vrms/mil. Dividing OD _off by OD _on is called the optical density ratio, or ODR, in this paper. In Example 1 above, a method for measuring the decay time _td of a liquid suspension in a test chamber is disclosed. In general, a light valve liquid suspension is desired to have a larger ODR and a smaller _td . Therefore, to measure the bulk properties of a suspension, we define its efficiency E as its ODR divided by its _td in seconds. For example, for a liquid suspension with an optical density ratio of 2.0 and a decay time of 10 milliseconds (0.018 seconds), the calculated efficiency is E=2.0/0.018=111.

The higher the E that can be obtained, the better.

Example 3A

In an Erlenmeyer flask, the indicated amounts of the following were dissolved in 132.5 g of a solution of 6.98% dissolved 1/4ss type nitrocellulose in hexyl acetate (containing 0.11 g of water):

4.5g iodine

  2.64g  Anhydrous calcium iodide

1.8g Methanol

0.53g water

Then add 3g of pyrazine-2,5-dicarboxylic acid dihydrate (precursor) prepared by the prior art method described in the above-mentioned embodiment 2 in the above-mentioned solution, the flask is placed in a 45 ° C by 3 hr in a water bath shaker, Model WB-20, manufactured by Elmeco Engineering, Inc. (Rockville, Maryland). The suspension was then ultrasonically stirred for 2 hr. The particle sizes of the precursors are reported in Table 1 below.

Example 3B

Example 3A was repeated, except that the precursor was pre-crushed by the supplier (Aveka Corporation, Woodbury, Minnesota) in a machine referred to herein as a "pancake mill," which used ultrasonic air flow to induce The particles collide violently with each other. The particle sizes of the precursors are reported in Table 1 below.

The suspensions of Examples 3A and 3B were taken out from the Erlenmeyer flasks and centrifuged according to the operating procedure of Example 1 to obtain an initial concentrate.

Table 1 summarizes the data for the various suspensions described in Examples 3A and 3B, respectively ODR, decay time, efficiency and mean and median size of the precursor particles used.

Table 1

Comparison of data from two polyiodide suspensions

        The first is the preparation of precursors manufactured with existing technologies

The second is prepared from crushed precursors The size of the precursor particles used Optical Density Ratio* decay time* efficiency* average size median size Example 3A 6.33μm 1.12μm 3.13 23ms 136 Example 3B 0.74μm 0.68μm 3.00 10.5ms 285

*For the initial concentrate (as described in Example 1), but with only 2 hr of sonication after the initial reaction, additional shaking and 2 hr of sonication were added after the first and third centrifugation steps.

In addition to pyrazine-2,5-dicarboxylic acid dihydrate, any solid precursor used in the prior art or in future inventions, as long as it can be used to make polyhalide particles, can be used as disclosed in the present invention It is advantageously crushed.

While we do not wish to be bound by any particular theory as to why pulverization results in enhanced efficiency of polyhalide particles, we believe pulverization enhances efficiency because smaller particles are formed and at about the same time they begin growth and thus can produce suspensions with particle size distributions that are less polydisperse than prior art suspensions.

Claims (12)

1. A method of manufacturing light polarizing material particles, the method comprising reacting a precursor suitable for forming polyhalide particles with elemental iodine and hydrohalic acid or ammonium, alkali metal or alkaline earth metal halide, wherein the precursor The average and/or median size is less than 1 μm. 2. The method of claim 1, wherein the precursors have an average size and/or a median size of less than 0-75 [mu]m. 3. The method of claim 1, further comprising providing the precursor with a desired particle size prior to reacting by reducing the particle size of the precursor without causing agglomeration or agglomeration of the reduced size particles. 4. The method of claim 1, wherein the precursor is a polyhalide of an organic compound. 5. The method of claim 4, wherein the polyhalide of the organic compound is an acid salt of an alkaloid or the like. 6. The method of claim 1, wherein the precursor is a nitrogen-containing organic compound. 7. The method of claim 1, wherein the precursor is a salt of a quinine alkaloid. 8. The method of claim 1, wherein the precursor is an organic compound containing one or several groups capable of chelating hydrogen, ammonium or metal ions. 9. Granules prepared according to the method of any one of claims 1-8. 10. Improvement in a light valve comprising a chamber containing a suspension of light polarizing particles in a liquid suspending medium, wherein the particles are particles according to claim 1. 11. A light polarizer comprising a plurality of particles according to claim 9 dispersed in a carrier, the polarization axes of which are oriented and held stationary by the carrier in a substantially parallel state. 12. A liquid suspension comprising an electroresistant liquid suspension medium, a plurality of small particles having anisometric shape as claimed in claim 9 dispersed therein, and dissolved therein for dispersing the particles in the suspension, at least one stabilizing polymeric substance.