MXPA99000778A - Polyisocyanate-based polymer comprising metal salts and preparation of metal powders therefrom - Google Patents

Abstract

A polyisocyanate-baser polymer having dispersed therein a metal salt, obtained by reacting an organic polyisocyanate with an aqueous composition of a metal salt. The polymer comprises the metal salt in an amount of from at least 10 weight percent based on total weight of the dry salt with the weight of the polyisocyanate-based polymer including salt therein. The polymer on calcication provides a metal-containing powder having an average particle size of 1 micrometer or less. Such metal-containing powders are of value in the preparation of industrial catalysts, ceramics, electronic components, or as fillers in plastics, paints or cosmetics.

Description

POLYMER BASED ON POLY-ISOCYANATE COM PRESSING METAL SALTS AND PREPARATION OF METAL POWDERS THEREOF This invention relates to a polymer based on polyisocyanate containing a metal salt, a process for the preparation of the polymer, and a process for calcining the obtained polymer to provide a powdery substance containing the metal, said powder having a size of average particle of less than 1 micrometer.

BACKGROUND OF THE INVENTION Submicron-sized metal or metal oxide particles are a valuable industrial commodity which finds use in many applications, including, for example, in the manufacture of industrial catalyst as it may be employed in the chemical industry, in the manufacture of ceramics, of electronic components, and as fillings for, for example, plastics, paints or cosmetics. A wide variety of techniques is available for the manufacture of metal or metal oxide powders having a very fine particle size. Such techniques include condensation phase synthesis and solution processes and high temperature gas phase. For a comprehensive review of the available general techniques reference is made to the recent publication entitled "Chemical Engineering Aspects of Advanced Ceramic Materials" by V. Hlavacek and J.A. Puszynski published in Journal of Industrial Engineering and Chemical Research, pages 349-377, Volume 35, 1996.

Despite the numerous procedures available, it is a common problem to a greater or lesser degree with almost all methods, the difficulty of obtaining consistently fine uniform particles of good purity and strength. Procedures that can provide greater consistency in this aspect invariably have high costs associated with their operation due to the complexity of the equipment required, the use of expensive raw materials, or high energy consumption. Therefore, it would be convenient to develop an effective cost method that leads to the production of metal powders or metal oxide having a consistently fine particle size. It would be of particular advantage if such a procedure could be operated using readily available raw materials and could be operated in the substantial absence of highly specialized equipment and expensive chemical processing aids or solvents. It would also be an advantage if such a process were able to provide the production of metal powders in a more attractive performance. A common goal is the production of a metal powder that has a fine particle size and does not exhibit the problem of agglomeration leading to a wide particle size distribution. To optimize this, it is necessary to develop a process which provides a homogeneous and uniform distribution, precipitation, of the metal-containing substance in the first case without providing subsequent opportunity for secondary formation of nuclei leading to agglomeration. With this in mind, laboratory studies have been undertaken to evaluate the use of reactive polymer chemistry to provide the desired homogeneous distribution starting from an aqueous metal salt solution. The reactive polymer of choice is polyurethane; Basic polyurethane reactive components comprising polyisocyanate are commercially available at low cost and exhibit compatibility with water. The patent publications, which describe the manufacture of polyurethane polymer containing metal particles or metal salts and the subsequent calcination or pyrolysis of the resulting polymer, include the US patents; 3,510,323; 4,569,821; and 5,338,334; and the published French patent application 2,609,915. These documents do not meet the particular needs indicated above.

BRIEF DESCRIPTION OF THE INVENTION In a first aspect, this invention relates to a polyisocyanate-based polymer having a metal salt dispersed therein., said polymer being obtained by reacting an organic polyisocyanate with an aqueous composition of a metal salt, characterized in that the polymer comprises the metal salt in an amount of at least 10 weight percent, based on the total dry weight of the polymer. the salt and the polymer based on polyisocyanate. In a second aspect, this invention relates to a process for preparing a polyisocyanate-based polymer having a metal salt dispersed therein by reacting an organic polyisocyanate with an aqueous composition of a metal salt characterized by: i) the amount of metal salt employed is sufficient to provide the resulting polymer with a metal salt content of at least 10 percent by weight, based on total dry weight of the salt and the polyisocyanate-based polymer; and in that ii) the polyisocyanate is present in an amount from at least parts by weight per 100 parts by weight of the aqueous composition with the proviso that when the aqueous composition comprises a substance that reacts with additional isocyanate in an amount of more than about 60 weight percent, the amount of polyisocyanate employed is not exceeds more than about 70 parts by weight. In a third aspect, this invention relates to a process for producing a metal-containing powder having an average particle size of less than 1 micrometer, said process comprises calcining a polyisocyanate-based polymer having a metal salt dispersed therein. , at a temperature from about 300 ° C to about 1500 ° C, characterized in that the polymer has a metal salt content of at least 10 weight percent, based on the total dry weight of the salt and the polymer-based polymer. isocyanate. In a fourth aspect, this invention relates to a metal-containing powder, which can be obtained by calcination of a polymer based on polyisocyanate, having dispersed in it a metal salt, characterized in that the powder has an average particle size of less than about 1 micrometer and an average BET surface area of more than 200 m2 / gram.

Still in a fifth aspect, this invention relates to a composition containing a metal-containing powder that can be obtained such as a calcination process characterized in that the composition comprises a bulk phase having dispersed therein from about 0.1 to about 50 percent. by weight of the powder based on the total weight of the bulk phase and powder. The present invention provides a relatively simple and cost-effective route for the manufacture of powders containing metals of submicron particle size. Such particles find value in the manufacture of ceramic articles, electronics, industrial catalysts and as fillers in plastics, paints or cosmetics, including creams and oils. When used as a filler, the smaller particles of the filler provide a minimum reflection of visible light, allowing exploitation of the properties of the filler with minimal alteration to the properties of visible light transmission or transparency of the substance to be filled. The transmission of electromagnetic radiation of other wavelengths can be blocked by the presence of the filling.

DETAILED DESCRIPTION OF THE INVENTION A polymer based on polyisocyanate is described hereinafter, having a metal salt dispersed therein; a process for the preparation of such a polymer; a process for calcining the obtained polymer to provide a powder containing metal; and a powder containing metal having a particle size of submicrons.

The metal in the "metal-containing" powder may be present as the elemental metal, or as an oxide, carbide or alloy thereof. Whether the powder, which is obtained, is a metal, an alloy, an oxide or a metal carbide, will depend on the salt (s) present in the polymer based on polyisocyanate and the conditions of pyrolysis or calcination. It will also be appreciated that the same factors can influence the characteristics of the particles, including their size and surface area. The metal containing powder obtained according to this invention is characterized in that it has an average particle size of less than 1 micrometer (1000 nanometer), preferably less than about 0.1 micrometer (100 nanometer), and more preferably less than 0.02 micrometer (20 nanometer). nanometers). By the term "average particle size" is meant that less than about 25, preferably less than about 10, and more preferably less than about 5 percent of the metal particles, will have a size in excess of the mentioned particle size. By the term "particle size" is meant the size of the particle in its longest dimension. The powder is further characterized in that it has an average BET surface area of at least 5, preferably at least 25, more preferably at least 100, and still more preferably at least 200 m2 / gram. In a preferred embodiment, the metal-containing powder has an average particle size of at least about 0.1 micrometer and an average BET surface area of at least 25 m2 / gram.

The powder obtainable according to this invention can comprise any desired metal. Conveniently, the metal, in a zero or appropriate oxidation state, is one or more of the elements lanthanum, barium, strontium, chromium, zirconium, yttrium, aluminum, lithium, iron, antimony, bismuth, lead, calcium, magnesium , copper, boron, cadmium, cesium, dysprosium, erbium, europium, gold, hafnium, holmium, lutetium, mercury, molybdenum, niobium, osmium, palladium, platinum, praseodymium, rhenium, rhodium, rubidium, ruthenium, samarium, scandium, sodium , tantalum, ytterbium, thorium, thulium, tin, zinc, nickel, titanium, tungsten, uranium, vanadium, or ytterbium. The powder is obtained by the pyrolysis and / or calcination of a particular polyisocyanate-based polymer, having dispersed therein a metal salt obtained by reacting an organic polyisocyanate with an aqueous composition of a metal salt soluble in water. Water. The metal salt content of the polymer should be as high as practically possible to provide attractive yields of any subsequent metal powder. For this reason, the polymer has a metal salt content of at least 10, preferably from 12 to 50, and more preferably from 15 to 30 percent by weight based on the total dry weight of the salt and the poly-based polymer. -isocyanate. By the term "dry weight" is meant the weight of the metal salt excluding any water of crystallization that may be present. In order to obtain an attractive performance of metal-containing powder, the polyisocyanate-based polymer conveniently has an overall density of more than 400 kg / m3, preferably from about 420 to about 1200 kg / m3, still more preferably from about 500 to approximately 1000 kg / m3. While it is possible to prepare polymer of a lower density, such a polymer of lower density occupies a larger volume and does not provide a subsequent cost-effective production of the metal-containing powder. The organic polyisocyanate used to prepare the polymer can be any aliphatic or aromatic organic polyisocyanate commonly used when polymers and polyurethane foams are prepared. Representative of these types are the diisocyanates, such as m- or p-phenylene di-isocyanate, toluene-2,4-di-isocyanate, toluene-2,6-diisocyanate, hexamethylene-1,6-diisocyanate. isocyanate, tetramethylene-1,4-di-isocyanate, cyclohexane-1,4-di-isocyanate, hexahydrotoluene di-isocyanate (and isomers), naphthalene-1,5-diisocyanate, 1-methylphenyl-2,4-phenyl di-isocyanate, diphenylmethane-4,4'-di-isocyanate, diphenylmethane-2,4'-di-isocyanate, 4,4'-biphenylene di-isocyanate, 3,3'-dimethoxy-4,4'-biphenylene di -isocyanate and 3,3'-dimethyldiphenylpropane-4,4'-di-isocyanate; tri-isocyanates, such as toluene-2,4,6-tri-isocyanate and polyisocyanates, such as 4,4'-dimethyldiphenylmethane-2,2 ', 5'5'-tetraisocyanate and the various polymethylene polyphenyl polyisocyanates. A crude polyisocyanate, such as the crude toluene di-isocyanate obtained by the phosgenation of a mixture of toluene diamines, or the crude diphenylmethane diisocyanate obtained by the phosgenation of crude diphenylmethanediamine can also be used. Preferred raw or undistilled polyisocyanates are described in U.S. Patent 3,215,652. Especially preferred are polymethylene polyphenyl polyisocyanates, having an average functionality from 2.05 to 3.5, preferably from 2.4 to 3.1 isocyanate moieties per molecule, due to their ability to crosslink the polyurethane. The aqueous composition comprises one or more metal cations in association with one or more anions, or a mixture of metal cations and anions with a metal oxide. To provide compatibility with the process of forming the polyisocyanate-based polymer and for the subsequent calcination process, it is convenient to have as the anion a halide, carbonate, bicarbonate, hydroxide, mercaptide. alkoxide, carboxylate, oxalate, sulfate, bisulfite or nitrate. Preferred anions include chloride, carbonate, hydroxide, alkoxide, carboxylate or nitrate. For reasons of good solubility in water, metal salts having a nitrate as the anion component are preferred. The metal cation may in principle be any metal from which a metal powder is desired, however, those which currently have a known industrial value and suitable for use in the present invention include lanthanum, barium, strontium, chromium, zirconium, yttrium , aluminum, lithium, iron, antimony, bismuth, lead, calcium, magnesium, copper, boron, cadmium, cesium, dysprosium, erbium, europium, gold, hafnium, holmium, lutetium, mercury, molybdenum, niobium, osmium, palladium, platinum , praseodymium, rhenium, rhodium, rubidium, ruthenium, samarium, scandium, sodium, tantalum, ytterbium, thorium, thulium, tin, zinc, nickel, titanium, tungsten, uranium, vanadium or ytterbium, or a mixture of two or more of the same. The concentration of metal salt present in the aqueous composition is advantageously as high as practically possible, considering its solubility limit and the restrictions of the polymer formation process. Where possible, it is preferred to use aqueous compositions which are essentially saturated solutions at room temperature. Optionally, but conveniently, the aqueous composition further contains an additional isocyanate-reactive substance. When the aqueous composition comprises both metal salt and additional isocyanate-reactive substance, the amount of additional isocyanate-reactive substance advantageously does not exceed about 90, preferably does not exceed about 60, more preferably does not exceed about 40 percent by weight based on total parts in weight of the aqueous composition. The additional isocyanate-reactive substance can be any substance reactive with isocyanate, excluding water. Such substances are collectively referred to herein as "poliales". The term "polyal" is used to describe any isocyanate-reactive substance containing two or more isocyanate-reactive portions per molecule. Such reactive portions include hydroxyl groups, primary or secondary amine, carboxylic acid or thiol. Polyols, for example, compounds having at least two hydroxyl groups per molecule, are especially preferred because of their desirable reactivity with polyisocyanates. Polials normally suitable for preparing rigid polyurethane include those having an equivalent weight from about 50 to about 700, preferably from about 70 to about 300 and more preferably from about 70 to about 150. Such polials also conveniently have at least one functionality 2, preferably about 3, and up to about 16, preferably up to about 8, active hydrogen atoms per molecule. Representatives of polyals include polyether polyols, polyester polyols, polyhydroxy-terminated acetal resins, polyamines and hydroxyl-terminated amines. Examples of these and other suitable isocyanate-reactive materials are more fully described in U.S. Patent 4,394,491, particularly in columns 3 to 5. To prepare rigid foams, on the basis of performance, availability and cost, a polyol is preferred to adding an alkylene oxide to an initiator having from about 2 to about 8, preferably about 3 to about 8, active hydrogen atoms. Examples of such polyols include those commercially available under the trademark designation VORANOL, including VORANOL 202, VORANOL 360, VORANOL 370, VORANOL 446, VORANOL 490, VORANOL 575, VORANOL 640 and VORANOL 800, all sold by The Dow Chemical Company, and PLURACOL 824, sold by BASF Wyandotte. Other highly preferred polyols include alkylene oxide derivatives of Mannich condensates, as described, for example, in U.S. Patents 3,297,597; 4, 137, 265 and 4383, 102; and polyethers initiated with aminoalkylpiperazine as described in US Patent 4,704,410 and 4,704.41 1. Other polyols distinguished from the foregoing by having a hydroxyl equivalent weight of more than 700, and normally contemplated for use when preparing a flexible polyurethane foam, can also be used in the present invention although rigid polyols are preferred for reasons of optimization in the final performance of the metallic powder. To provide a homogeneous dispersion of the metal salt within the polymer, polyols suitable for the preparation of rigid polyurethane, and especially polyether polyols initiated with amine, are conveniently employed. Such polyols provide a higher system reactivity leading to a desirable dispersion of the metal salt in the polymer and further restricting the opportunity for salt crystal formation within the polymer. It is currently believed that a high system reactivity is required so that the water of the aqueous composition is removed in a timely manner by its reaction with the isocyanate, leading to a fine dispersion of the salt in the polymer. In contrast, it is believed that minor reactivity leads to a slower removal of water, providing an opportunity for the growth of metal salt crystals during polymer formation. Such crystal formation locally provides a high concentration of metal salt within the polymer, which subsequently in the calcination can lead to the formation of a particle having a larger particle size. When the polymer of the invention is prepared, the polyisocyanate and the aqueous composition are present in relative proportions to provide a polymer with a metal salt content as described above. The amount of polyisocyanate employed is preferably from at least 10, preferably from 10 to 100, and more preferably from about 10 to about 70 parts by weight per 100 parts by weight of aqueous composition, with the proviso that when the The aqueous composition comprises an additional isocyanate-reactive substance in an amount of more than 60 weight percent, the amount of polyisocyanate employed does not exceed more than about 70, and preferably does not exceed more than about 60 parts by weight. Larger amounts are not practical if it is intended to provide an attractive performance of metallic powder of a given weight of polymer. The purity of a metal-containing powder can be important if it has value in certain applications including those in the electronics industry. Contaminants such as silicon, phosphorus and in some cases tin should be minimized. Accordingly, when preparing the polymer of the present invention, as an intermediate for the formation of the metal-containing powder, it is convenient for the resulting polymer product and its associated preparation process, that there is a substantial absence of silicone-based surfactants. , phosphorus-containing substances, or catalysts that promote metal-based polyurethane. When it is desired to increase the rate of polymer formation, a catalyst can be employed. Suitable catalysts include nitrogen-based substances, such as those well known to a person familiar in the art of making polyurethane polymer, and therefore need not be described here further. In the present invention, it is not necessary that the resulting polymer have a good cellular structure, a brittle and collapsed polymer with little or no cellular structure has equal value for the subsequent calcination process. Accordingly, a defoaming agent can be conveniently present when preparing the polyisocyanate-based polymer. Examples of common defoaming agents include hydrocarbon oils and non-silicone based grease. Any equipment commonly used in the continuous or discontinuous manufacture of polyurethane elastomers or foams can be employed to produce the polymer of this invention. Such equipment provides efficient mixing, under high cut conditions, of controlled amounts of polyisocyanate with the aqueous composition. To assist in the polymer production of the present invention, it is convenient to operate such equipment with a raw matepal temperature as high as possible, as well as mixing times as long as possible. The high component temperatures promote a faster reaction, leading to a desirable conversion of water or alternatively, its loss through evaporation. The high process temperatures also optimize the solubility of the metal salt in the aqueous composition and minimize any tendency for its crystallization as water is consumed by reaction with the polyisocyanate. The long mixing times provide the greatest opportunity for the optimum conversion of reagents to polymer. The metal salt-containing polymer dispersed therein, when calcined under controlled conditions, providing removal of the polyisocyanate-based polymer, results in the formation of an agglomerate-free, metal-containing powder of substantially uniform size. Normally, the calcination conditions require exposing the polymer at a temperature of from about 300 ° C to about 1500 ° C, and preferably from about 400 ° C to about 1000 ° C for a period of a few minutes to many hours. Prior to thermal treatment of the polymer, if it contains significant amounts of residual aqueous composition or polyisocyanate, it may be convenient to wash and dry the polymer. Optionally, a pyrolysis step can also be employed to assist in the removal of polyisocyanate-based polymer, prior to calcination. The described metal-containing powders having a particle size of submicrons are of value in the manufacture of ceramic articles, industrial catalysts, electronic components, and as fillers for plastics, paints or cosmetics. When used as a filler, the metal-containing powder will be present, based on the total weight of bulk matrix and powder, usually in an amount from about 0.1 to about 50, and more usually in an amount from about 1 to about 25 percent in volume. weight. The bulk matrix may be, for example, a plastic including a thermoset or thermoplastic polymer, a paint, or a cosmetic composition, cream or oil.

Specific embodiments of the invention The invention is illustrated by means of the following examples, which should not be considered as limiting the scope of the invention. Unless otherwise indicated, all quantities given are parts by weight (pbw).

Example 1 A polymer based on polyisocyanate containing a metal salt is prepared by reacting the following components: Aqueous composition 26.6 pbw VORANOL 1055 1 1.5 Ethanolamine 61 .9 36% by weight aqueous solution of aluminum nitrate (dry weight), with Polyisocyanate 26.8 pbw VORANATE M220. VORANOL 1055 is a glycerin-propylene oxide adduct with a molecular weight of about 1000 and available from The Dow Chemical Company. VORANATE M220 is a crude polymethyl polyphenyl polyisocyanate having an average NCO content of about 31.5% by weight, available from The Dow Chemical Company.

The resulting polymer has an essentially non-cellular structure and an overall density in excess of 1000 kg / m3. The metal salt content of the polymer is 23.2 percent by weight. The polymer is subjected to a milling process to provide coarse granules, which upon subsequent calcination for a period of about 3 hours at 700 ° C in an air environment yield a white or colorless powder. The yield of the powder containing aluminum is estimated to be approximately 6.7%. It is noted that the average BET surface area of the powder is 250 m2 / gram and indicative of an average particle size significantly less than one micrometer.

Claims (17)

REIVIN DICATIONS:

1. A polymer based on polyisocyanate having a metal salt dispersed therein, said polymer being obtained by reacting an organic polyisocyanate with an aqueous composition of a metal salt, characterized in that the resulting polymer comprises the metal salt in an amount from 10 to 50 percent by weight based on the total dry weight of the salt and the polyisocyanate-based polymer; wherein the polymer has an overall density of at least 400 kg / m3.

2. The polymer of claim 1, wherein the metal salt is present in an amount of at least 12 percent by weight.

The polymer of claim 1 or claim 2, wherein the metal salt comprises at least one metal cation; which includes lanthanum, barium, strontium, chromium, zirconium, trio, aluminum, lithium, iron, antimony, bismuth, lead, calcium, magnesium, copper, boron, cadmium, cesium, dysprosium, erbium, europium, gold, hafnium, holmium, lutetium, mercury, molybdenum, niobium, osmium, palladium, platinum, praseodymium, rhenium, rhodium, rubidium, ruthenium, samarium, scandium, sodium, tantalum, ytterbium, thorium, thulium, tin, zinc, nickel, titanium, tungsten, uranium, vanadium or ytterbium.

4. The polymer of claim 3, wherein the metal salt contains as an anion, a chloride, carbonate, hydroxide, alkoxide, carboxylate or nitrate.

5. The polymer of any of the preceding claims further characterized by the substantial absence of a silicone-based surfactant.

6. The polymer of any of the preceding claims further characterized by the substantial absence of a catalyst that promotes metal-based polyurethane.

The polymer of any of the preceding claims further characterized by the substantial absence of a phosphorus-containing substance.

8. A process for preparing a polyisocyanate-based polymer by having a metal salt dispersed therein, by reacting an organic polyisocyanate with an aqueous composition of a metal salt characterized by: i) the amount of salt of metal present in the process is sufficient to provide the resulting polymer with a metal salt content of 10 to 50 percent by weight, based on the total dry weight of the salt and the polyisocyanate-based polymer; ii) the resulting polymer has an overall density of at least 400 kg / m 3, and iii) the polyisocyanate is employed in an amount from at least 10 parts by weight per 100 parts by weight of the aqueous composition, with the proviso that when the aqueous composition comprises an additional isocyanate reactive substance in an amount of more than 60 weight percent, the amount of polyisocyanate employed does not exceed 70 parts by weight.

9. The process of claim 8, wherein the aqueous composition further contains an additional isocyanate-reactive component.

10. The process of claim 10, wherein the metal salt comprises at least one metal cation, including lanthanum, barium, strontium, chromium, zirconium, yttrium, aluminum, lithium, iron, antimony, bismuth, lead, calcium, magnesium, copper, boron, cadmium, cesium, dysprosium, erbium, europium, gold, hafnium, holmium, lutetium, mercury, molybdenum, niobium, osmium, palladium, platinum, praseodymium, rhenium, rhodium, rubidium, ruthenium, samarium, scandium, sodium, tantalum, ytterbium, thorium, thulium, tin, zinc, nickel, titanium, tungsten, uranium, vanadium or ytterbium. eleven .

The process of claim 10, wherein the metal salt contains as an anion a chloride, carbonate, hydroxide, alkoxide, carboxylate or nitrate.

The process of any of claims 8 to 11, characterized by the substantial absence of a silicone-based surfactant.

The process of any of claims 8 to 12, further characterized by the substantial absence of a catalyst that promotes metal-based polyurethane.

14. The process of any of claims 8 to 13, characterized by the substantial absence of a phosphorus-containing substance.

15. A process for producing a metal containing powder having an average particle size of less than 1 micrometer by calcining at a temperature of about 300 ° C to about 1500 ° C a polymer based on polyisocyanate, which has dispersed in the a metal salt itself, characterized in that the polymer has a metal salt content of 10 to 50 percent by weight based on the total dry weight of the salt with the weight of polyisocyanate-based polymer including salt therein, and wherein the polymer has an overall density of at least 400 kg / m3.

16. A powder containing metal obtainable by calcination of a polyisocyanate-based polymer having dispersed therein a metal salt, characterized in that the powder has an average particle size of less than about 1 micrometer and an area of average BET surface of at least 25 m / gram.

17. A composition containing a metal-containing powder obtained according to the process of claim 15, characterized in that the composition comprises a bulk phase having dispersed therein from about 0.1 to about 50 weight percent of the powder based on the total weight of bulk phase and powder.