AQUEOUS MINERAL DISPERSIONS

Abstract: A process for making vermiculite lamellae that includes delamination of vermiculite ore to produce a dispersion con­ taining vermiculite particles in which an aqueous slurry of unexpanded vermiculite ore, that is untreated by heat or de­ laminating chemicals, is subjected to a shearing action until a dispersion of vermiculite lamellae having dimensions less than 200 microns is produced.

Description: This invention relates to a process for producing aqueous dispersions of delaminated vermiculite and solid articles from such dispersions. It is known that solid articles or products such as paper, films, coatings and non-sheet solids can be formed from aqueous dispersions of delaminated vermiculite ore, known as platelets or lamellae, by casting the dispersions against surfaces of various shapes and sizes and removing water from the vermiculite particles. Such dispersions can also be used to form rigid foams by gasifying the dispersion prior to removal of water from it. The term "vermiculite" refers to all layer minerals known as vermiculite in mineralogical or commercial contexts, and includes minerals consisting wholly or largely of vermiculite, including minerals of a mixed-layer type (phyllosilicates) that contain vermiculite layers as a constituent (such as hydrobiotites and chlorite-vermiculites) and that can be delaminated in the same way as vermiculite. Vermiculite platelets or lamellae are flat particles of vermiculite having a particle size typically less than 200 microns, preferably less than 50 microns. Such particles have an aspect ratio (i.e., length or breadth divided by thickness) of at least 10, preferably at least 100 and more preferably at least 1,000, for example 10,000. It is also known that vermiculite ore can be delaminated to produce aqueous dispersions of vermiculite lamellae by first expanding or exfoliating the mineral by application of heat, or by chemical means, followed by soaking or washing with water to swell the vermiculite particulate structure. The resulting expanded or swollen granules of vermiculite are then mechanically sheared to form an aqueous dispersion of vermiculite lamellae. Such processes typically involve heating the vermiculite mineral to temperatures of 1400°F or more or by treatment with hydrogen peroxide or with aqueous solutions of inorganic and/or organic salts prior to swelling and shearing the vermiculite particles. Both thermal and chemical delamination of vermiculite such as discussed above have serious disadvantages in that they are expensive and time consuming. For example, thermal exfoliation of vermiculite followed by mechanical shearing involves the high cost of maintaining high processing temperatures, as already mentioned, and chemical delamination also involves costly processing steps, involving treatment of vermiculite ore with various chemical salt solutions, washing out excess salts, and swelling the vermiculite ore prior to shearing to obtain lamellae of the desired size. It would be desirable to make available processes for producing dispersions of vermiculite lamellae that would eliminate most of the costly and time consuming steps associated with thermal and chemical delamination, and for producing paper, films, coatings, rigid foams and non-sheet solid articles from such dispersions. According to the invention, a process for making vermiculite lamellae having dimensions less than 200 microns and an aspect ratio of at least 10, that includes delamination of vermiculite ore to produce a dispersion containing vermiculite particles, is characterized in that an aqueous slurry of unexpanded vermiculite ore, that is untreated by heat or delaminating chemicals, is subjected to a shearing action until the said dispersion of vermiculite lamellae having dimensions less than 200 microns is produced. Preferably, the viscosity of such slurries is decreased by adding a dispersant or combination of dispersants to the aqueous slurry of vermiculite ore before or during the shearing operation (which permits slurries containing a higher content of solids to be produced) or after the shearing operation. Also preferably, aqueous slurries of vermiculite ore particles that are delaminated by shearing in accordance with the invention and/or the resultant dispersions of vermiculite lamellae to which are added the aforementioned dispersants comprise from about 10% to about 80% by weight total solids, the preferred range being from about 20% to about 70% by weight total solids, and most preferably from about 30% to about 55% by weight total solids. The weight percent solids content of said slurries is limited by such factors as the slurry viscosity, the means of shearing action employed, and the viscosity and corresponding final flowability of the resulting dispersion of vermiculite lamellae. The shearing force used to delaminate the vermiculite ore particles may be applied by means of such conventional shearing devices as rotary paddles, colloid mills, or Cowles blades. A Waring blender or a macerator of the type similar to those used for domestic purposes, or a small media or ball-type mill may also be used, as may suitable vibratory equipment that, for instance, applies ultrasonic agitation to the aqueous ore slurry. Preferably vermiculite lamellae or platelets produced by the process according to the invention have a particle size less than 50 microns and an aspect ratio of at least 100, and more preferably at least 1,000, for example 10,000. Thus, shearing should be applied for the minimum time necessary to achieve a dispersion containing particles of the desired dimensions. Delamination of the vermiculite ore particles, in accordance with the invention, may be carried out at any reasonable processing temperature, for example, 25°C. Processing temperatures may range, however, from 0°C to refluxing temperatures. Examples of inorganic compounds useful as dispersants include the alkali metal salts of polyphosphates, for example, tetrasodium pyrophosphate or sodium hexametaphosphate, soluble silicate and silicic acid derivatives such as sodium silicate, and alkali metal hydroxides such as sodium hydroxide. Examples of organic compounds useful as dispersants in accordance with this invention include derivatives of alkyl, aryl or alkylarylamines such as propylamine, derivatives of polyamines such as polyethylenimines, polyvinylpyrrolidones, poly(N-vinyl-2-oxazolidinones), polyvinyltrimethylammonium chlorides, polyallylamine chlorides, polyvinylbenzyltrimethylammonium chlorides, poly(N-vinyl-2,3-dimethylimidazolinium chlorides), poly(diallylammonium chlorides) such as poly(N-methyl-diallylamine hydrochloride-epichlorohydrin) available as Kymene® 2064 from Hercules Incorporated, and poly(N,N-dimethyl-3,5-methylene piperidinium chlorides). Also useful are polyamide derivatives such as polyacrylamide and copolymers of polyamide with acrylic acid or methacrylic acid, amine containing polyamides, polyalcohols such as polyvinylalcohols, free acids or alkali metal salts of polyorgano acids such as polyacrylic acid or polymethacrylic acids, sulfonated alkyl, aryl or alkylaryl organic acids such as polyvinylsulfonic acid and sulfonated oils such as the "Twitchell" line of products sold by Emery Chemicals. Further useful compounds as dispersants in accordance with this invention include water soluble or miscible free acids or salts of phosphoric acid and organo phosphoric acid derivatives, such as mono, di, or triesters of phosphoric acid containing polyether groups capped with alkylaryl or alkyl groups that are commercially available as the GAFAC line of products sold by the GAF Corporation. These dispersants can be characterized broadly as examples of high charge-density anionic or cationic compounds or as highly functionalized non-ionic compounds, which generally are suitable dispersants for this invention. The preferred dispersants include polyamine-epichlorohydrin derivatives such as poly(N-methyl-diallylamine hydrochloride-epichlorohydrin) available as Kymene® 2064 from Hercules Incorporated, alkali metal hydroxides, sodium silicate, sodium hexametaphosphate, tetrasodium pyrophosphate, polyvinylpyrrolidones, sulfonated mineral oils such as Twitchell 8262 and 8266 available from Emery Chemicals, water soluble free acids or salts of phosphoric acid such as GAFAC PE 510 and RE 610 available from GAF Corporation, polyethylenimines, polyallylamine hydrochlorides, and primary and secondary amines wherein the alkyl groups have from about 2 to about 6 carbon atoms. In accordance with this invention, such dispersants are typically added as a dilute aqueous dispersion or suspension to aqueous vermiculite ore slurries or to dispersions of vermiculite lamellae. Preferably, said dispersants can comprise from about 0.1% about 10% by weight of the total solids content of the vermiculite ore slurry or resultant dispersion, with about 0.5% to about 5.0% by weight being the more preferred range. The amount of dispersant necessary to control the viscosity of the vermiculite ore-water slurry or the resultant dispersion of vermiculite lamellae after shearing the slurry depends on such process variables as temperature, slurry or dispersion pH, the degree of conversion of slurried vermiculite ore to vermiculite lamellae, the shearing device employed, and of course, the solids-level of the vermiculite ore-water slurry and/or resultant dispersion. It is an aspect of this invention that the method of addition of the dispersant to the aqueous ore slurry or to the resultant dispersion of vermiculite lamellae is not critical. For example, the dispersant and the water for the slurry can be mixed before the subsequent addition of the ore thereto with stirring. More preferable is the addition of the dispersant to an aqueous ore slurry that has already been prepared. The invention also includes the use of dispersions made in accordance with the invention to make solid articles comprising vermiculite of the type already known, for example, such articles as films, coatings, and non-sheet solids composed of in part or substantially wholly vermiculite lamellae, using any method known in the art. Such solid articles may, for instances, be formed by disposing the dispersion of vermiculite lamellae on a surface and removing water from the vermiculite particles. Other materials may be added to dispersions of vermiculite lamellae made according to the invention, depending on the particular properties and end uses contemplated of articles manufactured therefrom. Such materials include, for example, inorganic fillers such as silica, silica glass, clay, aluminum hydroxide, talc and the like. Further, materials such as continuous (filamentary), discontinuous (chopped or staple), or agglomerates of carbon (graphite), glass, boron, silica or ceramic type fibers can also be incorporated into dispersions of vermiculite lamellae in accordance with this invention to manufacture solid articles therefrom comprising fibrous vermiculite composite structures. As already mentioned, methods for the manufacture of such vermiculite-containing articles are well known. Such films and coatings may be used, for example, as refractory-facing materials, fireproof packaging materials, thermal insulation materials, materials for gasket fabrication, and electrical insulating materials. The following examples illustrate preferred embodiments for the production of dispersions of vermiculite lamellae in accordance with one aspect of this invention, and the use of said dispersions to make solid articles in accordance with another aspect of this invention. Examples I to II These examples illustrate one aspect of this invention wherein a dispersant is added to an aqueous slurry of vermiculite ore therein allowing for the processing of higher solids content aqueous-ore slurries into dispersions of vermiculite lamellae. In Example I a slurry consisting of 175 grams of vermiculite grade 4 ore (ASTM material designation C-516) and 175 grams distilled water is sheared in a Waring blender for one hour. Distilled water is added as needed during shearing to maintain slurry flow resulting after one hour in a flowable dispersion of vermiculite lamellae containing about 33% by weight solids. The percent of vermiculite ore particles reduced to less than 38 microns in dimension (#400 mesh screen) is then determined. In Example II, Example I is repeated except that Kymene® 2064 is an amount equal to 4% by weight of vermiculite ore is added to the aqueous-ore slurry just prior to shearing resulting after one hour in a flowable weight solids. The percent of vermiculite ore particles reduced to less than 38 microns as set forth in Example I is then determined. The results of Examples I and II are summarized below in Table 1. Example No. Wt. % Conversion to less than 38 microns Wt. % solids I 71 33 II 72 52 Examples III to XI These examples further illustrate an aspect of the invention wherein preferred dispersants are added to an aqueous slurry of vermiculite ore therein allowing for the processing of higher solids content aqueous-ore slurries into dispersions of vermiculite lamellae. In Examples III to XI, Example I is repeated except that various preferred dispersants are added incrementally during ore shearing to maintain dispersion flow in the amounts indicated as summarized in Table 2 below. Weight percent conversions of vermiculite ore particles to dimensions of less than 38 microns and corresponding final flowable dispersion solids weight percent at the end of one hour of shearing for each dispersant represented is also summarized in the table. Example No. Dispersant Total Weight % Dispersant Wt. % Conversion to less than 38 microns Wt. % Solids I None -- 71 33 II Kymene® 2064 4.0 72 52 III sodium hydroxide 0.5 72 48 IV sodium silicate 0.5 75 48 V tetrasodiumpyrophosphate 0.7 71 46 VI Kymene® 2064 2.5 70 50 VII GAFAC PE 510 2.0 78 48 VIII polyvinylpyrrolidene 2.0 66 43 IX Twitchell 8262 2.2 67 48 X Twitchell 8266 2.2 64 48 XI poly-(ethylenimine) 2.3 58 46 Examples XII to XXV These examples illustrate another aspect of the invention wherein preferred dispersants are added to dispersions of delaminated vermiculite lamellae to determine dispersant effectiveness as measured by viscosity reduction. In these examples, various indicated dispersants are added in 0.15 wt. % increments to a 44.5 wt. % dispersion of delaminated grade 4 vermiculite ore using a Cowles blade rotated at 750 rpm to assure uniform mixing. Levels of dispersant needed to reduce the viscosity of the dispersion from 750 cps to less than 40 cps are summarized in Table 3. Addition of Dispersants to Delaminated Vermiculite Ore Example No. Dispersant Wt. % Addition XII propylamine 0.6 XIII sodium silicate 0.9 XIV tetrasodium pyrophosphate 0.9 XV sodium hydroxide 1.1 XVI polyallylamine hydrochloride 1.1 XVII polyethylenemine hydrochloride 1.1 XVIII polyethylenimine 1.5 XIX Kymene® 2064 1.5 XX GAFAC PE 510 1.7 XXI GAFAC RE 610 1.8 XXII Twitchell 8262 2.1 XXIII Kymene® 450 2.1 XXIV polyvinylpyrrolidone 2.1 XXV Twitchell 8266 2.1

Claims: A process for making vermiculite lamellae having dimensions less than 200 micrometer and an aspect ratio of at least 10, that includes delamination of vermiculite ore to produce a dispersion containing vermiculite particles, is characterized in that an aqueous slurry of unexpanded vermiculite ore, that is untreated by heat or delaminating chemicals, is subjected to a shearing action until the said dispersion of vermiculite lamellae having dimensions less than 200 micrometer is produced. A process for making vermiculite lamellae as claimed in claim 1, further characterized in that the viscosity of the slurry is decreased by adding a dispersant or combination of dispersants before, during or after the shearing operation. A process for making vermiculite lamellae as claimed in claim 1 or 2, further characterized in that the concentration of dispersant is from about 0.1% to about 10% by weight of the total solids content of the vermiculite ore slurry or dispersion of vermiculite lamellae. A process for making vermiculite lamellae as claimed in claim 1, 2, or 3, further characterized in that the concentration of dispersant is from about 0.5% to about 5.0% by weight. A process for making vermiculite lamellae as claimed in any of the preceding claims, further characterized in that the aqueous slurry of vermiculite ore contains from about 10% to about 80% by weight of solids. A process for making vermiculite lamellae as claimed in claim 5, further characterized in that the aqueous slurry of vermiculite ore contains about 20% to about 55% by weight of solids. A process for making vermiculite lamellae as claimed in any of the preceding claims, further characterized in that the dispersant is selected from the group consisting of alkali metal salts of polyphosphates, soluble silicate and silicic acid derivatives, alkali metal hydroxides, derivatives of alkyl, aryl or alkylarylamines, derivatives of polyamines and polyamides, amine containing polyamides, polyalcohols, free acids or alkali metal salts of polyorganoacids, sulfonate alkyl, aryl or alkylaryl organo acids, sulfonated oil and miscible free acids or salts of phosphoric acid or organo phosphoric acid derivatives. A process for making vermiculite lamellae as claimed in claim 7, further characterized in that the dispersant is poly(N-methyl-diallylamine hydrochloride-epichlorohydrin). A process for making vermiculite lamellae as claimed in claim 7, further characterized in that the dispersant is sodium hexametaphosphate. A process for making vermiculite lamellae as claimed in claim 7, further characterized in that the dispersant is tetrasodium phosphate. A process for making vermiculite lamellae as claimed in claim 7, further characterized in that the dispersant is sodium hydroxide. A process for making vermiculite lamellae as claimed in claim 7, further characterized in that the dispersant is sodium silicate.

Inventors: LU, CHENG-FA, NELSON, LAWRENCE LEE
Applicants: HERCULES INCORPORATED
Application year: 1988
Main classification: C04B14
IPC codes: C01B39, C04B14, C01B33, B01J13