Light-Polarizing Materials and Suspensions Thereof

This invention relates to light-polarizing materials, to set suspensions and fluid suspensions thereof, and to light valves containing such fluid suspensions.

Light-polarizing materials, such as colloidal suspensions of herapathite and herapatathite-like light-polarizing crystals, are described in U.S. Pat. Nos. 1,951,664 (Land) and 2,178,996 (Land), respectively. U.S. Pat. No. 2,237,567 (Land) discloses the production of light-polarizing material in sheet form by various methods including application of a solution of iodine and an iodide to a sheet of polyvinyl alcohol which had been previously stretched to orient the molecules therein. Numerous other patents relating to light-polarizing materials, set suspensions thereof and laminated products derived therefrom and uses thereof are in the art including, for example, U.S. Pat. Nos. 2,041,138 (Land), 2,078,254 (Land), 2,168,220 (Land), 2,168,221 (Land), 2,185,018 (Sauer), 2,230,262 (Pollack), 2,246,087 (Bailey et al.), 2,256,108 (Blake), 2,263,249 (Rogers), 2,306,108 (Land et al.), 2,328,219 (Land), and 2,375,963 (Thomas). U.K. Pat. No. 433,455 discloses the use of particles of purpureocobaltchloridesulphateperiodide in the formation of light-polarizing bodies. These and the other patents referred to in this specification are incorporated herein by reference thereto.

At present, important uses for laminated set suspensions of light polarizing materials, often referred to as "sheet polarizers", include lenses for polarized sunglasses, components of the twisted nematic type of liquid crystal displays and filters of various types including contrast enhancement filters for use in conjunction with light emissive displays. However, the sheet polarizers thus employed are well known to be frequently subject to degradation due to high levels of heat, ultraviolet radiation and/or especially moisture.

Fluid suspensions of light-polarizing and other materials have been used in light valves, comprising a cell containing a fluid suspension of minute particles which can be oriented by an electric or magnetic field to change the transmission of light through the suspension. See for example, U.S. Pat. Nos. 3,708,219 (Forlini et al.), 3,743,382 (Rosenberg), 4,078,856 (Thompson et al.), 4,113,362 (Saxe et al.), 4,164,365 (Saxe), 4,407,565 (Saxe), and 4,422,963 (Thompson et al.).

U.S. Pat. No. 4,131,334 (Witte et al.) describes a process for forming light-polarizing particles by hydrogenation of a nitrogen-containing organic compound, which is then reacted with an appropriate acid to form a salt. The salt may then be reacted, usually with iodine and an inorganic iodide, to produce stable polyiodide particles.

An object of the present invention is to provide light-polarizing materials that have high stability with respect to ultraviolet radiation, elevated temperatures and/or high levels of moisture.

Polyhalides, including polyiodides, have been known for quite some time. A polyiodide is a complex of iodine atoms and an inorganic or organic matrix. Godina et al discuss polyiodides and other polyhalides in detail in J. Gen. Chem. USSR, 20, (1950), pp. 1005-1016. Among the known polyiodides is the light-polarizing crystalline material, herapathite, which is formed by reaction of quinine bisulfate, iodine and HI. Salts of other members of the quinine alkaloid family also form light-polarizing polyiodides by reaction with iodine and HI, such as cinchonidine bisulfate. In these materials, the elemental iodine combines with the alkaloid acid salt in the form of the polyiodide anion, which has been variously described as I.sub.3.sup.- by Godina et al. and as I.sub.5.sup.- by Teitelbaum et al.., JACS, 100 (1978), pp. 3215-3217. Godina et al.. show that the polyiodide anion is formed by reaction between iodine and HI, e.g.

(1) I.sub.2 +HI=H.sup.+ I.sub.3.sup.- Likewise, the I.sub.5.sup.- polyiodide anion would be formed by the reaction

(2) 2I.sub.2 +HI=H.sup.+ +I.sub.5.sup.-

Godina et al.. explain that light polarizing polyiodides comprise the polyiodide anion and the acid salt of quinine and the like as the cation. However, polyiodides can also be formed without any apparent cation being present, such as the starch-iodine complex and the stretched or oriented polyvinyl alcohol-iodine complex. Teitelbaum et al report that the starch-iodine complex contains adsorbed iodine in the form of chains of iodine within the amylase component of starch, the chains being made up of I.sub.5.sup.- polyiodide anions as the dominant species. Godina et al. theorize that herapathite, starch-iodine and oriented PVA-iodine complex are "adsorbing polyiodides" in which molecular iodine is adsorbed in layers on the polyiodide chains.

The light polarizing material of the present invention is a complex obtained by reacting (i) elemental iodine, (ii) a hydrohalide acid and/or an ammonium or alkali metal or alkaline earth metal halide and (iii) a compound of formula I-VI below. This complex contains adsorbed molecular iodine. We believe that the complex also contains the polyiodide anion, I.sub.x.sup.-, where x is 3 or 5, since Godina et al.. and Teitelbaum et al.. both report that the polyiodide anion is formed by reaction between (i) elemental iodine and (ii) an iodide. Moreover, Godina et al. report that crystals containing adsorbed molecular iodine and the polyiodide anion are light-polarizing. In the Examples that follow, we have been able to prepare light polarizing materials by reacting a compound I-VI with iodine and an iodide, bromide or chloride. In such cases, the respectively anions would be

-I-I-I-I-I-

-I-I-Br -I-I

-I-I-Cl -I-I

using the structure elucidated by Marks et al. as a model.

Godina et al. report that light-polarizing complexes containing adsorbed molecular iodine cannot be defined stoichiometrically by structural formula. Hence, the light-polarizing material of the present invention is defined in product-by-process format.

Compounds I-VI that are useful in forming the light polarizing materials of the invention are: ##STR1## wherein R.sup.1 is carboxy, hydroxy, 2-pyridyl or lower alkyl substituted by carboxy or hydroxy; A is alkylene forming with the depicted carbon atom a carbocyclic ring; R.sup.2 is carboxy, hydroxy or lower alkyl substituted by carboxy or hydroxy; and R.sup.3 and R.sup.4 are independently hydrogen or lower alkyl.

Preferably, A is alklyene of 3 to 8 carbon atoms, and most preferably alkylene of 3 to 5 carbon atoms.

It is also preferred that lower alkyl is of 1 to 4 carbon atoms.

Compounds I-VI are known per se or may be isomers, homologues or analogs of known compounds and may be prepared analogously to such known compounds.

Compounds I and IV that contain a 2-pyridyl group may be formed analogously to the formation of 2,2'-dipyridyl.

Useful compounds of formulas I-VI include:

1--Picolinic acid

2--2-hydroxypyridine

3--Glycine anhydride (2,5-piperazinedione)

4--Barbituric acid

5--Quinaldic acid

6--8-Hydroxyquinoline

7--Cycloleucine

8--2,2'-Dipyridyl

The light polarizing materials of this invention are formed by reacting compounds of formulas I-VI with elemental iodine and a hydrohalide acid and/or an ammonium, alkali metal or alkaline earth metal halide, in a suitable solvent, such as alcohol or etheralcohol. See U.S. Pat. Nos. 1,951,661, 2,176,516 and 2,289,712. The halide is usually an iodide, but can also be a bromide or chloride. Preferably, the reaction to form the polyhalide takes place in the presence of a protective colloid, such as nitrocellulose or a copolymer as disclosed in U.S. Pat. No. 4,164,365, issued Aug. 14, 1979. It is presently preferred to provide compounds I-VI in a first solution and a mixture of iodine and ammonium or alkali metal or alkaline earth metal halide in a second solution, but, if desired, the halide can be in either or both of the solutions. The solutions are then mixed together, and the polyhalides are readily formed even at room temperature. Light-polarizing polyhalide crystals are then recovered by any suitable technique, such as by filtering and the like.

For use in a light valve, the polyhalide particles are suspended in a liquid suspending medium. As is known, the liquid suspending medium may be virtually any electrically resistive liquid so long as it suspends the particles and dissolves the polymeric stabilizer. Preferably, the liquid suspending medium has a relatively high electrical resistivity and low vapor pressure, and does not degrade or attack the particles or other components of the suspension. See e.g. U.S. Pat. Nos. 4,270,841 and 4,407,565 to Saxe.

For use in set suspensions, the polyhalide particles are dispersed or distributed throughout a sheet formed of suitable film-forming material, such as cellulose acetate or polyvinylalcohol or the like. See e.g. U.S. Pat. Nos. 2,178,996 and 2,041,138.

Approximately 1.5 g. of compound 1 was dissolved in 13 g. of a mixed solvent comprising approximately 10 g. of 2-ethoxyethanol and 3 g. of methanol and that solution was then mixed with 10 g. of a solution of n-propanol in which 1.3 g. of iodine and 0.48 g. of a 57% HI solution in water were dissolved. Blue-colored light-polarizing crystals formed readily. The same procedure was followed and similar results observed using compounds 2 and 4-8 in place of compound 1.

Approximately 1.5 g. of compound 1 was dissolved in 13 g. of a solution comprising 10 g. of 2-ethoxyethanol and 3 g. of methanol, and that solution was then mixed with a solution of 10 g. of n-propanol in which 0.22 g. of calcium iodide and 1.3 g. of iodine were dissolved. Blue-colored light-polarizing crystals formed readily. The same procedure was followed and similar results observed for quinaldic acid, barbituric acid, cycloleucine and 2,2'-dipyridyl.

Examples 8-12 were repeated but with an effective amount of CaBr.sub.2 substituted for CaI.sub.2. Light-polarizing crystals having a somewhat different bluish color formed readily.

Examples 13-17 were repeated but with an effective amount of CaCl.sub.2 substituted for CaBr.sub.2. Light-polarizing crystals again having a somewhat different bluish color formed readily.

Approximately 1.5 g. of compound 1 was dissolved in 13 g. of a solution comprising 10 g. of 2-ethoxyethanol and 3 g. of methanol and that solution was then mixed with a solution formed by dissolving 0.58 g. of potassium iodide (KI) in about 0.58 g. of water to which a solution of 1.3 g. of iodine in 10 g. of n-propanol was added. Blue-colored light-polarizing crystals formed readily. The same procedure was followed and similar results observed for quinaldic acid, barbituric acid, cycloleucine and 2,2'-dipyridyl. These examples illustrate that the particles of the present invention will tolerate water and moisture since they were in fact made and remained undissolved in the presence of water.

Examples 23-27 were repeated but using 0.62 g. of CsI in place of 0.58 g. of KI, with similar results.

Although individual halides are employed in the above examples, mixtures of halides and in particular mixtures of iodides or mixtures of iodides and other halides, may be advantageously used in such reactions as those described above. For example, equimolar amounts of CsI and CaI.sub.2 in solution can be reacted with quinaldic acid and I.sub.2 in solution to form fine polarizing crystals.

Approximately 1 g. of glycine anhydride was dissolved in 40 g. of 2,2,3,3-tetrafluoro-1-propanol. One gram of that solution was then mixed with 1 g. of a solution consisting of 10 g. of n-propanol in which were dissolved 1 g. of calcium iodide and 2 g. of iodine. Small, blue-purple, light-polarizing, needle-shaped crystals readily formed. These crystals were stable and did not degrade when dispersed in isopentyl acetate.

Approximately 1.5 g. of 3-hydroxypyridine, was dissolved in a mixed solvent comprising approximately 10 g. of 2-ethoxyethanol and 3 g. of methanol. The resulting solution was mixed with a solution of n-propanol in which iodine and hydriodic acid were dissolved according to the same amounts and procedure as in Examples 1-7. No light-polarizing crystals were produced.

The failure to form light-polarizing crystals in comparative Example 34 wherein 3-hydroxypyridine was used, is in stark contrast to the success described above when 2-hydroxypyridine was used in its stead under otherwise similar reaction conditions. The position and greater distance of the hydroxy group from the ring nitrogen atom are the only significant differences that can account for the failure described in Example 34.

Some of the compound I-VI of the present invention are known to form metal salts and/or to be metal-chelating compounds. Accordingly, one possible explanation for the formation of the light-polarizing materials of this invention is that when the compounds I-VI are reacted with iodine and a halide, the halide and iodine enter into the reaction in an ionic form. For example, if the halide is calcium iodide, CaI.sub.2, iodine may enter the reaction as Ca.sup.+2 (I.sub.x).sub.2.sup.-, with the positively charged calcium ion being chelated by compounds I-VI and the (I.sub.x).sup.- anion being bonded to the positive calcium ion, thereby forming a polyiodide crystal. While this explanation seems reasonable, we do not wish to be bound by this theory.

Liquid suspensions of the polyhalide particles of this invention can be easily prepared by utilizing a procedure somewhat similar to that for preparing liquid suspensions of dihydrocinchonidine sulfate polyiodide described in Example 2 of U.S. Pat. No. 4,131,334 and in Example 1 of U.S. Pat. No. 4,407,565, but with compounds I-VI of the present invention substituted for dihydrocinchonidine sulfate and the quantities of the reactants adjusted as, for example, given in the aforesaid examples.

Solution A was prepared by dissolving 1.5 g. of quinaldic acid in 13 g. of a mixed solvent comprising 10 g. of 2-ethoxyethanol and 3 g. of methanol.

Solution B was a 40% solution of nitrocellulose in 2-ethoxyethanol. The nitrocellulose is the low viscosity (18-25 cps) type.

Solution A and 20 g. of Solution B were mixed to form Solution C.

Solution D was prepared by dissolving 0.22 g. of anhydrous CaI.sub.2 in 10 g. of n-propanol and then adding (1.06 g.) of I.sub.2, and 22.0 g. of tricresyl phosphate (TCP) and shaking for 15 minutes.

Solution C was combined with Solution D with vigorous mixing in a Waring Blender, while stirring with a polyethylene spatula along the inside walls of the cup, counter to the direction of blender flow. In a few seconds, a viscous wet paste was formed having a blue color. The wet paste was spread as an 8-mil film on a glass plate and dried about two hours in air until no odor from volatile solvents was detectable.

The dried paste was scraped off the glass plate and dispersed into 100 g. of isopentyl acetate (IPA) and well shaken so as to disperse the paste to form a liquid suspension. To this suspension 39 g. of hexane is added and shaken. The suspension is then ultrasonically agitated for 10 hours and centrifuged at 2,500 RPM for two hours. The sediment in the centrifuge tubes is discarded and the supernatant centrifuged at 2,500 RPM for an additional 40 hours. The sediment is then resuspended in IPA and an effective amount of a suitable polymer solution added thereto, e.g. 10-15 g. of a 15% solution of a 96.75%/3.25% copolymer of neopentyl acrylate/methylol acrylamide dissolved in neopentyl neopentanoate may be added. This new suspension is placed in a vacuum apparatus for approximately five hours to evaporate off nearly all of the IPA. Part of any other solvent present that does not have too high a boiling point may also evaporate. The suspension is then diluted to the extent desired with Halocarbon Oil type 0.8/100 (manufactured by Halocarbon Products, Hackensack, New Jersey) and any other desired solvents, such as neopentyl neopentanoate, to provide the wanted off-state optical density and response time. Additional polymer may be added.

Quinaldic acid polyiodide suspensions of this type have been tested at elevated temperatures with excellent results. Samples of these suspensions have been placed in glass test tubes at 85.degree. C. for 66 hours with no substantial change in their performance.

Such suspensions have also been subjected to intense ultraviolet radiation--also with excellent results. After about one month at about one foot distance from an ultraviolet lamp, a test cell containing a suspension of quinaldic acid polyiodide showed no substantial change in properties.

Liquid suspensions of the type described above can be used in light valves which utilize an AC electric field to orient the particles in said suspensions to change and/or control the transmission of light through the suspension. Such light valves can be used, for example, as variable transmission windows, filters, mirrors, and eyeglasses, and as electronic alphanumeric and graphic image displays.

By modifying the composition of the suspension, however, it is possible to produce what is known in the prior art as a net suspension, rather than a fluid suspension or liquid suspension usable in a light valve as described above. A set suspension of the particles of the present invention would comprise, for example, a light-polarizing sheet or film in which said particles would be incorporated along with other materials.

There are many processes known in the art for producing light-polarizing sheets and films. For example, U.S. Pat. No. 2,178,996 discloses a process for forming certain light-polarizing particles, mixing said particles into a dispersion medium which may include cellulose acetate, and subjecting the dispersion of particles to flow or extrusion or stretch, or rolling, so that the needle axis of the dispersed polarizing crystals may be oriented to substantial parallelism and a thin, sheet-like polarizing body produced. U.S. Pat. No. 2,041,138 discloses that polarizing bodies may preferably be made in the form of a relatively thin sheet or film comprising the suspending medium and the minute particles dispersed therein. If desired, the polarizing body may itself be permanently or detachably fixed to a suitable support, preferably transparent, as for example, to a plate of glass or to a sheet of celluloid. Such a support may be desirable with conditions where it is found that the polarizing body itself may require some form of protection. It also discloses the use of asymmetric particles, the flowing of the medium that includes said particles past an edge, and retaining said particles in an oriented position by setting or hardening said medium.

U.S. Pat. No. 2,168,220 discloses information relating to polarizing material sold under the trade name "Polaroid". Use of plasticizers, adhesives and various types of laminations and methods for forming said laminations are disclosed.

Numerous types of polarizing films and uses for polarizers are disclosed in U.S. Pat. No. 2,246,087 including, for example, use in windshields, windows, eyeglasses, goggles, sunglasses, camera lenses, microscopes, mirrors and in connection with three dimensional movies.

A process for transferring light-polarizing films from one support to another and various materials used in connection therewith are disclosed in U.S. Pat. No. 2,256,108.

The information available from any of the aforesaid patents and from numerous other patents and other sources known in the art can be used to make light-polarizing set suspensions, films and sheets which include particles oriented in substantial parallelism, and light-polarizing bodies and products made therefrom.

However, many light polarizers in commercial use today do not incorporate films or sheets having solid discrete particles oriented in parallel therein, but rather use a sheet of polyvinyl alcohol polyiodide which has its optic axis in the plane of the sheet and which transmits with substantially no absorption only light vibrating substantially perpendicularly to its optic axis, as described in U.S. Pat. Nos. 2,237,567 and 2,375,963 and other sources known in the art. The commercially available polarizers are known to be susceptible to degradation when subjected for prolonged periods to harsh environmental conditions such as high temperatures, high humidity, ultraviolet radiation and especially combinations of such conditions.

Despite the problems of commercially available sheet polarizers with respect to environmental degradation, it may be preferable or desirable from a manufacturing viewpoint to react a stretched sheet of polymer with dyes or stains or with iodine and an iodide to form a light-polarizing complex, rather than to use a plurality of individual polarizing crystals as previously described. To this end, useful embodiments of the present invention also include compounds comprising compounds I-VI of this invention, each molecule of which has attached thereto a polymerizable unsaturated group. These compounds are monomers, e.g., 4-vinyl picolinic acid and 4-vinyl-2-hydroxypyridine, which can be polymerized by known techniques and formed into sheets analogous to polyvinyl alcohol, which can then be reacted with suitable dyes or stains or with iodine and a halide to form polyiodides or other types of light-polarizers as in the prior art.

However, the polarizers made from set suspensions of the particles and other materials of the present invention are very stable to high levels of heat and ultraviolet radiation and will tolerate water excellently, as previously described. Accordingly, the present invention makes possible a substantial improvement in the quality of light-polarizing bodies and products incorporating such materials.

Although specific embodiments of the invention have been described, it will be appreciated that many modifications thereon may be made by one skilled in the art, which fall within the spirit and scope of this invention.