KR100391748B1 - Method of making light-polarizing particles of improved particle size distribution, light-polarizing particles made thereby and liquid suspensions, light-polarizing bodies and light valves including such particles - Google Patents

Abstract

The present invention is suitable for forming polyhalide particles and comprises reacting a precursor having an average size and / or median size of less than 1 micron with an element of iodine and hydrofluoric acid or ammonium, alkali metal or alkaline earth metal halide. Provided are methods for making the particles.

Description

METHOD OF MAKING LIGHT-POLARIZING PARTICLES OF IMPROVED PARTICLE SIZE DISTRIBUTION, LIGHT- A method for producing polarized particles with improved particle size distribution, polarized particles produced thereby, and liquid suspensions, polarizers and light valves comprising such particles POLARIZING PARTICLES MADE THEREBY AND LIQUID SUSPENSIONS, LIGHT-POLARIZING BODIES AND LIGHT VALVES INCLUDING SUCH PARTICLES}

Light control valves have been known for more than 60 years. As used herein, a light valve may be said to be a cell formed of two walls spaced apart at short distances, at least one of which is transparent, and generally these walls are provided with electrodes in the form of a transparent conductive coating. The cell includes a light control member, which may be a liquid suspension of particles or a plastic film in which droplets of a liquid suspension of particles are distributed and encapsulated.

Liquid suspensions (sometimes referred to herein as "liquid light valve suspensions") comprise small particles suspended in a liquid suspension. In the absence of an applied electric field, the particles in the liquid suspension exhibit irregular Brownian motion, and thus the light rays passing through the cell are reflected, transmitted or absorbed depending on the cell structure, the properties and concentration of the particles and the energy content of the light. Therefore, the light valve is relatively cloudy in the OFF state. However, when an electric field is applied through the light valve suspension in the light valve, the particles are aligned and for most of the suspension most of the light can pass through the cell. Thus, the light valve is relatively transparent in the ON state.

Light valves control the amount of light passing through them for many uses, such as displays that can handle both letters and numbers, television displays, windows, sun roofs, sun visors, mirrors, glasses, etc. It is proposed to use. Light valves of the type disclosed herein are 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 light transmission window, the use of a film can avoid hydrostatic pressure effects, such as bulging associated with high column liquid suspensions, and also a possible risk of leakage. As such, a plastic film in which droplets of the liquid suspension are distributed is preferable to the liquid suspension alone. Another advantage of using plastic films is that particles in plastic films are generally only present in very small droplets and therefore do not significantly aggregate when the film is repeatedly activated with voltage.

Thus, as used herein, a "light valve film" is a film that holds droplets of a liquid suspension of particles distributed in the film.

The kind of light valve film produced by phase separation from a homogeneous solution is disclosed in US Pat. No. 5,409,734. Light valve films obtained by crosslinking emulsions are disclosed in US Pat. Nos. 5,463,491 and 5,463,492, assigned to the assignee of the present invention. These and other patents and other sources cited herein are all incorporated herein by reference.

Plates of suitable film-forming materials, such as cellulose acetate or polyvinyl alcohol, can be cut and molded into polarized sunglass lenses or used as filters and for use in hardened suspensions such as polarizers, sometimes referred to as "plate polarizers." Through the polarizing particles can be dispersed or distributed. Methods of preparing cured suspensions for use in plate polarizers are known in the art. However, in these curing suspensions, the particles are immobilizable. See, eg, US Pat. Nos. 2,178,996 and 2,041,138.

Liquid light valve suspension

1. Liquid Suspensions and Stabilizers

The liquid light valve suspension can be any liquid light valve suspension known in the art and can be prepared by conventional techniques. As used herein, "liquid light valve suspension" means "liquid suspension medium" in which a number of small particles are dispersed. "Liquid suspension medium" includes one or more non-aqueous, electrically resistant liquids, one or more of which act to reduce the agglomeration propensity of the particles and to keep these particles dispersed or in suspension. It is preferable that the polymer stabilizer is dissolved.

The liquid light valve suspension of the present invention may comprise any liquid suspension medium previously proposed for use in light valves for particle suspension. Liquid suspensions known in the art are useful in the present invention. Liquid suspensions include, but are not limited to, those disclosed in US Pat. Nos. 4,247,175 and 4,407,565. In general, the liquid suspension or polymer stabilizer dissolved in the suspension is selected to maintain suspended particles in gravity equilibrium.

When a polymer stabilizer is used, the polymer stabilizer may be a single kind of solid polymer that binds to the surface of the particles but dissolves in the non-aqueous liquid (s) of the liquid suspension. As an alternative, the polymer stabilizer may be two or more solid polymer stabilizers that act as polymer stabilizers. For example, the particles can be coated with a first type of solid polymer stabilizer, such as nitrocellulose, which actually binds to or associates with the first type of solid polymer stabilizer, and dissolves in a liquid suspension. To provide one or more additional types of solid polymer stabilizers and planar coatings for the particles that provide steric protection for dispersions and particles. In addition, the use of liquid polymer stabilizers can advantageously be used particularly for SPD light valve films as disclosed in US Pat. No. 5,463,492.

2. Particles

As is known, inorganic and organic particles can be used in the light valve suspension. However, the present invention relates to an improved process for producing polyhalide (sometimes referred to in the prior art as perhalide) particles of organic compounds, such as alkaloidates. The polyhalide particles of the present invention may be polarizing materials such as halogen-containing polarizing materials such as polyhalides of alkaloid salts (the term "alkaloid" refers to organic nitrogen generating bases, Hackh's Chemical Dictionary, 4th edition) , McGraw-Hill Book Company, New York, 1969). As is known, when polyhalides of alkaloid salts are prepared, the alkaloid moiety can be a quinine alkaloid, as disclosed in Hackh's Chemical Dictionary (supra). U.S. Patents 2,178,996 and 2,289,712 are mentioned in detail with regard to the use of polyhalides of quinine alkaloidates. These particles can be absorbent or reflective. The particles can also be particles of hydrogenated polyhalides of quinine alkaloidates, such as dihydrocinconidine sulfate polyiodide, disclosed in US Pat. No. 4,131,334.

More recently, improved polyhalide particles having advantageous features for use in light valves have been proposed in US Pat. Nos. 4,877,313, 5,002,701, 5,093,041 and 5,516,463. These "polyhalide particles" are generally formed by reacting an organic compound containing nitrogen with an iodine element and hydrofluoric acid or ammonium alkali metal halide or alkaline earth metal halide. Such organic compounds are also referred to herein as "precursor".

Conventional polyhalide particles are discussed in detail in a paper by DA Godina and GPFaerman et al., Entitled "The Optical Properties and Structure of Polyiodides," published in The Journal of General Chemistry, USSR Vol 20. p 1005-1016 (1950). It is. For example, hepatite is a quinine bisulfate polyiodide, whose chemical formula is 4C ₂₀ H ₂₄ N ₂ O ₂ · Merck Index (10th Edition, Merck and Company, Rasway, NJ). 3H ₂ SO ₄ .2HI.I ₄ .6H ₂ O is provided under the heading "quinine iodide sulfate." In polyiodide compounds, iodide anions are thought to form chains, which are strong polarizers. See US Pat. No. 4,877,313 and Teitelbaum et al., JACS 100 (1978), p3215-3217. The term "polyhalide" is used herein to mean a compound such as polyiodide, and at least some of the iodide anion may be replaced with another halide anion.

As is known, polyhalide particles useful for light valves are preferably colloidal in size. That is, the maximum dimension of the particles will average up to about 1 micron. Most polyhalide particles preferably have a maximum dimension of less than 1/2 of the blue light wavelength, i.e. 2000 Hz or less, in order to keep light scattering extremely low.

The present invention relates to a method for producing polarized particles with improved particle size distribution for use in liquid suspensions, and to light valves, films and curing suspensions.

Detailed description of the invention

The present invention provides a process for preparing polyhalide particles that is particularly suitable for use as particles of liquid light valve suspensions, wherein the process comprises "precursors" of specific particle sizes, as well as elements of iodine and hydrofluoric acid or ammonium, alkali metals or alkalis Reacting the earth metal halide. The precursor may be any compound that has previously been used to form organic polyhalide particles by reaction with an iodine element and hydrofluoric acid or ammonium, alkali metal or alkaline earth metal halides. For example, the precursor contains quinine alkaloids (US Pat. Nos. 2,178,996 and 2,289,712), hydrogenated alkaloids (US Pat. No. 4,131,334), hydrogen, ammonium or one or more groups that chelate with metal ions. Organic compounds (US Pat. Nos. 4,877,313, 5,002,701, 5,093,041, and 5,516,463), all of which are incorporated herein by reference. The precursor may retain any color, but generally consists of small crystals of white or off-white (sometimes referred to herein as "particles").

The inventors have surprisingly found that if the average and / or median size of the precursor is less than 1 micron, preferably less than 0.75 micron, the quality of the polyhalide particles produced therefrom is significantly improved. Crushing (reducing the size) of the precursor particles to provide the desired particle size can be accomplished by any means of reducing the size. However, this process should not cause the pulverized particles to form clusters or clumps, which counteracts the benefits of crushing and substantially increases the effective size of the particles. For example, the precursor particles may use a mortar and pestle, wet or dry with a liquid, using a ball mill or any other convenient means, or another solid inert material provided to assist in grinding. Can be ground or powdered. Alternatively, the precursor particles can move the gas stream rapidly, for example by blowing supersonic air flow (s), and cause them to collide with each other.

As used herein, if the precursor particles or crystals were crushed or their size reduced, this means that their average size and / or median size were reduced. As used herein, "size" of a particle means and refers to the largest dimension of the particle.

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

A typical state-of-the-art conventional type of polyhalide particles (crystals) is pyrazine-2,5-dicarboxylic acid dihydrate calcium iodide polyiodide. Such crystals and procedures for preparing their liquid suspensions for use in light valves are disclosed in Example 1.

Example 1 (Prior Art)

Formulation to Prepare Polyiodide Crystals and Liquid Light Valve Suspensions thereof

To the appropriately sized bottle, add the following reactants in the order presented.

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

6.98% solution

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

4.5 g iodine

2.64 g anhydrous calcium iodide

1.8 g anhydrous methanol

0.33 g water

Stop the bottle and shake for about 1/2 hour. The bottle is left in the sonicator for about 10 hours until the solution turns completely blue. The solution is examined under a microscope to determine whether the precursors, CaI ₂ and I ₂ are fully reacted, ie there is no substantial amount of unreacted precursor. The maximum yield is obtained when the initial decay time is about 8-15 milliseconds. If the disintegration time is less than 8 milliseconds, the addition of methanol and the addition of water to about 0.05 g are repeated.

The disintegration time is measured by the following procedure. The suspension of particles formed in the light valve suspension is filled into a light valve cell comprising a glass plate having suitable electrodes spaced 5 mils apart. Continuous illumination, such as illumination from a tungsten lamp, is shined onto the light valve suspension. The suspension of particles in the light valve is energized by applying about 55 volts at 10 kHz to the electrode relative to the reference measurement. It takes about 2-3 milliseconds to reach the open state of the light valve, after which the electric field is discontinuous after about 20 milliseconds. The collapse to the fully closed (off) state of the light valve is then measured. (See column 2, lines 37-48 of US Pat. No. 5,516,463).

Centrifuge the solution at 11,500 RPM for 1 hour and drain the supernatant. Drain for 15 minutes with the top of the tube down on a paper towel. The precipitate from the tube is placed in a tared glass jar and the precipitate weight is recorded. 15 g of hexyl acetate are added per 1 g of precipitate. Shake for 1/2 hour and then sonicate for 10 hours to disperse the precipitate.

Centrifuge the dispersion at 2500 RPM for 5-15 minutes, and collect the supernatant by decanting. The decay time should be 8-12 milliseconds, if higher, the supernatant is centrifuged again.

Centrifuge the supernatant at 9,500 RPM for 1/2 hour and then discard the supernatant. Drain for 15 minutes with the top of the tube down on a paper towel. The precipitate is collected in a tared glass jar and 10 g of anhydrous isopentyl acetate is added per gram of precipitate. Shake for 1/2 hour and then sonicate for 10 hours to disperse the precipitate. This is referred to hereinafter as "initial concentrate."

Plasticizer liquid tri-n-pentyl-trimelitate (TNPTM), as disclosed in US Pat. No. 5,463,491, lines 48-66, was added to 9 g of the initial concentrate and the combination was added at 60 ° C. Place in a Rotovap apparatus for hours to evaporate isopentyl acetate. The amount of TNPTM to be added can be determined experimentally according to the method of concentration into particles to be the desired resulting final concentrate (ie, dried initial concentrate). The final concentrate may be diluted with other desired solvent (s) in which the concentrate polymer is soluble. Other plasticizer liquids can be used.

To prepare a concentrate for use in an SPD light valve film, according to the teachings of one embodiment disclosed in US Pat. No. 5,463,492, instead of adding TNPTM to the initial concentrate before evaporating isopentyl acetate liquid polymers such as copolymers of n-butyl acrylate / heptafluorobutyl acrylate / hydroxyethyl acrylate can be added.

Various modifications can be made to the aforementioned procedures for preparing polyiodide crystals, such as varying the amount of some reactants, changing centrifugation times or procedures, or varying sonication.

Example 2 describes a conventional method of preparing the precursor material used in Example 1, namely pyrazine-2,5-dicarboxylic acid dihydrate.

Example 2 (Prior Art)

Procedure for preparing pyrazine-2,5-dicarboxylic acid dihydrate

2,5-dimethylpyrazine (25 g), pyridine (500 mL), selenium dioxide (125 g) and water (50 mL) were charged to a 1 liter round bottom flask equipped with a mechanical stirrer and reflux condenser. The mixture was refluxed for 11-12 hours. As selenium gradually precipitates, the boiling solution is thought to turn red orange after about 20 minutes.

The suspension is cooled to room temperature and the precipitate, which is a mixture of pyrazine 2,5-dicarboxylic acid and selenium, is filtered off. The flask and stirrer are washed with filtered reaction solvent. The reaction solvent is returned to the flask for reuse. The precipitate is washed with 2N NH ₄ OH until all pyrazine 2,5-dicarboxylic acid is dissolved. 2N NH ₄ OH in which pyrazine 2,5-dicarboxylic acid is dissolved is developed at a rate of 30 ml / min through a chromatography column of slurry-type Darco activated carbon (12-20 mesh, 250 g). .

Concentrated hydrochloric acid (100 ml) was added to 400 ml portion of the colorless eluent to give a white precipitate of pyrazine 2,5-dicarboxylic acid. It was filtered and washed sequentially with 20 ml of 2N hydrochloric acid, 20 ml of ice water and 20 ml of acetone. After the precipitate is air dried until the odor of acetone disappears, the precursor pyrazine 2,5-dicarboxylic acid dihydrate can be used.

In order to demonstrate that the quality of the polyhalide particles referred to herein can be improved, and to determine the degree of improvement, some terminology needs to be defined. The optical density of the light valve window test cell in the deactivated condition is the off state optical density or "OD _off ". When a voltage is applied to the conductive transparent coating (electrode) of the test cell, particles in the liquid suspension or film are included at the cell origin, increasing the transmission of light and reducing the optical density. This reduced optical density is referred to as "OD _on " when the cell is activated or turned _on . For the tests disclosed herein, a test cell with an internal gap of 5 mils between electrodes is applied at a voltage of 55 volts RMS at a frequency of 10 KHz. Thus, the field strength applied to the test cell is 11 volts RMS per mil. OD _off divided by OD _on is referred to herein as optical density ratio or ODR. In Example 1 above, the procedure for determining the disintegration time t _d of the liquid suspension in the test cell is disclosed. In general, ODR is large and t _d is preferably a small light valve liquid suspension. Therefore, in order to measure the overall quality of the suspension, the ODR divided by t _d measured in seconds is defined as the efficiency E. Thus, for a liquid suspension with an optical density of 2.0 and a decay time of 18 milliseconds (0.018 seconds), the efficiency is calculated as follows.

E = 2.0 / 0.018 = 111

The larger E, the better.

Example 3A

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

4.5 g of iodine

2.64 g of anhydrous calcium iodide

1.8 g of methanol

0.53 g of water

Then, 3 g of pyrazine 2,5-dicarboxylic acid dihydrate (precursor) made by the conventional method disclosed in Example 2 was added to the above-described solution, and water prepared by Elmerco Engineering, Rockville, Maryland, USA The flask was placed at 45 ° C. for 3 hours in Bath Shaker Model-WB-20. The suspension was then sonicated for 2 hours and stirred. Particle sizes of the precursors are shown in Table 1 below.

Example 3B

The precursor (Aveca Inc., Woodbury, Minn.) Was pre-crushed in the machine referred to herein as a "pancake mill" using ultrasonic gas streams to cause the precursor particles to impinge heavily on each other. Example 3A was repeated except that The size of the precursor particles is shown in Table 1 below.

The suspensions of Examples 3A and 3B were separated from the Erenmeyer flasks and centrifuged according to the procedure of Example 1 to obtain an initial concentrate.

Table 1 summarizes the data of ORD, disintegration time, efficiency, and mean and median size of precursor particles used for each suspension disclosed in Examples 3A and 3B.

Comparison of two poly iodide suspensions, namely a first poly iodide suspension made using a precursor made by a conventional method and a second poly iodide suspension made from a ground precursor Size of precursor particles used Optical density ratio ^* Decay time ^* Efficiency ^* Average size Middle size Example 3A 6.33 micron 1.12 micron 3.13 23 ms 136 Example 3B 0.74 micron 0.68 micron 3.00 10.5 ms 285 * For the initial concentrate (as described in Example 1), but only 2 hours of sonication after the initial reaction, with further shaking and 2 hours of sonication after each step of the first and third centrifugation Performed

In addition to the pyrazine 2,5-dicarboxylic acid dihydrate, any solid precursor used in the prior art and hereinbelow may be used to prepare polyhalide particles and may be advantageously milled as disclosed herein.

While not wishing to be bound by any particular theory as to why the pulverization improves the efficiency of the polyhalide particles, the present inventors improve the efficiency by forming and growing smaller particles at about the same time, and thus particle size distribution over conventional suspensions. It is believed that a less polydisperse suspension can be produced in terms of aspects.

Claims (12)

Reacting a precursor suitable for forming polyhalide particles and having a mean size and / or median size of less than 1 micron with an element of iodine and hydrofluoric acid or ammonium, an alkali metal or an alkaline earth metal halide. Way. The method of claim 1, wherein the average and / or median size of the precursor is less than 0.75 microns. The method of claim 1, further comprising providing a desired particle size for the precursor prior to reaction by means of reducing the precursor particle size while preventing reduced sized precursor particles from forming clusters or clumping. A method for producing particles of the polarizing material characterized by the above. 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 alkaloid acid salt. The method for producing particles of polarizing material according to claim 1, wherein the precursor is an organic compound containing nitrogen. The method for producing particles of the polarizing material according to claim 1, wherein the precursor is a quinine alkaloid salt. The method of claim 1, wherein the precursor is an organic compound containing at least one group that chelates hydrogen, ammonium or metal ions. Particles produced by the method according to any one of claims 1 to 8. A light valve comprising a cell containing a suspension of polarized particles in a liquid suspension, wherein the particles are the particles according to claim 1. A polarizer comprising a plurality of particles according to claim 9 dispersed in a carrier, wherein the polarization axis of the particles is oriented and fixedly held by the carrier substantially parallel. An electrically resistant liquid suspending medium, the particles according to claim 9 dispersed therein, comprising a plurality of small particles having an isotropic shape, and at least one stabilizing polymer material dissolved therein for dispersing the particles in a suspension. Liquid suspension.