MXPA98005186A - Procedure to prepare cru bodies - Google Patents

Abstract

The present invention provides a method for preparing semi-wet pressed pressed bodies having improved wet strength. This wet strength of the pressed raw bodies in semi-wet form is increased by the addition of at least one polymeric binder, having a molecular weight greater than 50,000 comprising, as polymerized units, at least 10 percent of one or more monoethylenically unsaturated masses, their salts or anhydrides, and further comprises at least one hydrophobic material per polymer chain on average. The present invention also supplies pressed bodies in semi-wet form, having improved wet strength, obtained by the above method. In one embodiment, the polymeric binder increases the wet strength of the raw ceramic bodies. In another embodiment, the polymeric binder increases the wet strength of metallurgical raw bodies. In yet another embodiment, the polymeric binder increases the wet strength of raw bodies of the cerm

Description

PROCEDURE FOR PREPARING RAW BODIES The present invention relates to a process for preparing raw bodies from particulate materials. More specifically, the present invention relates to a semi-wet pressing method for preparing raw bodies using selected binders. Raw bodies prepared using these selected binders have improved wet strength. As used herein, the term "particulate materials" refers to ceramic materials, metallurgical materials, and combinations thereof. In the manufacture of ceramic and metallurgical products, the particulate materials, in the form of a powder or paste, are subjected to high pressures to produce what is known as a "raw body", which is then sintered to form a product final. Methods for compacting, or subjecting the particulate materials to high pressures, to produce raw bodies, include pressing, extrusion, roll compaction and injection molding. The pressing methods include dry pressing, isostatic pressing and semi-wet pressing. With the use of these methods, raw bodies can be prepared in various configurations and sizes.

Ceramic materials are often used to prepare lightweight, strong, thermally and chemically resistant products, useful as chromatographic media, grinding aids, abrasives, catalysts, adsorbents, electronic components, construction components, refractory components and components of machines. Metallurgical materials are often used to prepare components of machines, electrical components and tools. Similar products can be prepared from ceramic materials combined with metallurgical materials, to form what is known as a "cerment". The properties of the raw body generally affects the properties of the final product. For example, if the density of the crude body (the "crude density") is too low, the mechanical properties of the final product, such as hardness, will decrease. If the resistance of the raw body (the "raw resistance") is too low, the process and handling of the raw body becomes difficult or impossible. Also, when the raw bodies are formed of non-dry precursor materials (for example, by semi-wet pressing), this raw body passes through several drying steps before sintering takes place. The strength of the raw body during the initial stages (the "wet strength") also affects the final product process.If the wet strength of the raw body is too low, it becomes difficult for the raw body to maintain its configuration and will be handled Thus, it is convenient to supply raw bodies with improved wet strength, Methods for increasing the raw strength of the raw ceramic bodies, which use binders as an auxiliary to the process, are known in the art. Polyvinyl alcohol ("PVA") and poly (ethylene glycol) ("PEG") are known to increase the raw strength of the raw ceramic bodies.These binders are sometimes effective in increasing the raw strength of the raw bodies. However, PEG and PVA suffer from several drawbacks: PEG does not result in a particularly good crude strength and has poor strength. The PVA results in an acceptable crude strength, but causes a decrease in the raw density and has poor wet strength. Another commonly used binder is lignosulfonate. Lignosulfonates, also known as lignin sulphonates and sulfite lignins, generally provide sufficient crude strength to make it possible to handle raw bodies. However, lignosulfonate suffers from other drawbacks. For example, when preparing ceramic products with the use of lignosulfonate, high levels of sulphurous by-products are released when the ceramic is baked. It is convenient to replace lignosulfonates with a binder that maintains or improves performance while reducing or eliminating harmful sulfur byproducts. Also, lignosulfonates do not always impart sufficient wet strength to withstand normal handling during the process. The E. U.A., No. 5,401,695 to Wu, discloses the use of polymeric binders, which overcome the aforementioned disadvantages, to improve the green strength of the ceramic products formed by the dry pressing process. Wu teaches the use of low molecular weight polymers comprising, as polymerized units, at least 20 weight percent of one or more monoethylenically unsaturated acids, or their salts, Although the invention disclosed by W results in improved resistance in Crude . Wu leaves the problem of improving the wet strength of raw bodies without solving. The present invention is directed to overcoming the problems associated with previously known methods. It is directed to provide a procedure to prepare crude ceramic bodies using polymeric additives, which (1) provide good release of the mold during the pressing step; (2) impart improved wet strength of the raw body; (3) they provide a high raw density to this raw body; (4) burn cleanly in the air and (5) leave low burning residues in nitrogen. In a first aspect of the present invention there is provided a method for preparing pressed semi-wet raw bodies, this method comprises: (a) mixing (i) the particulate material, selected from ceramics, metallurgical materials, and combinations thereof, and (ii) at least one polymeric binder, having a molecular weight of at least 50,000, comprising, as polymerized units, at least 10 weight percent of one or more monoethylenically unsaturated acids, their salts or anhydrides, this polymeric binder further comprises more than one hydrophobe, having an alkyl chain, saturated or unsaturated, of at least Cg per polymer chain on average, to form a semi-wet powder; and (b) pressing the semi-wet powder to form a crude body.

In a second aspect of the present invention a wet pressed raw body is provided, which has an improved wet strength, obtained by the method described above. particualdos materials suitable for the present invention include: (1) ceramic oxide, nitride and carbide (eg alumina, aluminum nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconia, zirconium nitride, carbide zirconium, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titanium boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, tin oxide, ruthenium oxide, oxide of yttrium, magnesium oxide, calcium oxide and ceramic superconductors) and their combinations; (2) metals, and their mixtures or alloys (for example, iron, nickel, copper, tungsten, titanium, stainless steel, bronze and metal superconductors); and (3) combinations of ceramic and metallurgical materials. The morphology of the particulate material is not critical but is preferably approximately spherical in shape. Polymeric binders, suitable for the present invention, are polymers comprising, as polymerized units, at least 10 percent by weight of one or more monoethylenically unsaturated acids, their salts or anhydrides. The monoethylenically unsaturated acids can be mono-acid or di-acid or poly-acids, and the acids can be carboxylic acids, sulfonic acids, phosphonic acids, their salts or combinations. Suitable monoethylenically unsaturated acids are, for example, acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid and their alkali metal and ammonium salts. Suitable dicarboxylic acids, monoethylenically unsaturated anhydrides and cis-dicarboxylic acids are, for example, maleic acid, maleic anhydride, 1, 2, 3, 6-tetrahydrophthalic anhydride, 3,6-epoxy-1, 2, 3, 6-tetrahidrof alico anhydride 5-norbornene-2, 3-dicarboxylic anhydride, bicyclo [2.2.3] -5-octen-2, 3-dicarboxylic anhydride 3-methyl-l, 2, 6-tetrahydrophthalic anhydride 2-methyl-l, 3, 6-tetrahydrophthalic, itaconic acid, mesaconic acid, fumaric acid, citraconic acid, 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, allylphosphonic acid, aliloxibencensulfónico acid, 2-hydroxy-3 - ( 2-propenyloxy) propanesulfonic acid. , isopropenylphosphonic acid, vinylphosphonic acid, styrenesulfonic acid, vinylsulfonic acid, and their alkali metal and ammonium salts. More preferably, the one or more monoethylenically unsaturated acids are acrylic acid, methacrylic acid or their alkali metal salts. The one or more monoethylenically unsaturated acids represent at least about 10 weight percent of the total monomer weight, preferably at least 40 weight percent of the total monomer weight. The polymers of the present invention further comprise at least one hydrophobe per chain on average. The term "hydrophobic", as used herein, refers to alkyl chains, saturated or unsaturated, of at least Cg. For the purposes of describing this invention, hydrophobes include: (1) monomers containing alkyl chains, saturated and unsaturated, of at least Cg; and (2) monomer blocks containing alkyl chains, saturated or unsaturated, of at least C. Preferred hydrophobes are at least C 2 - The average number of hydrophobes per chain can be calculated by multiplying the molecular weight of the polymer by the percentage of the hydrophobe in the polymer, then dividing this result by the molecular weight of the hydrophobe. For example, a polymer with a molecular weight of 750,000, containing 10% of the hydrophobic monomer of molecular weight 1234, will have an average of 61 hydrophobes per chain. Suitable hydrophobes are, for example: (1) Z-R where R is an alkyl group, saturated or unsaturated, selected in the range of Cg-C3Q and Z is a polymerizable group, such as (meth) acrylate, styryl or vinyl; (2) R- (EO) x-Z where R is an alkyl, saturated or unsaturated group, selected in the range of C -C3Q, Z is a polymerizable group, such as (meth) acrylate, styryl or vinyl, and EO is CH2CH2-0; (3) R- (PO) x) -Z where R R is an alkyl, saturated or unsaturated group, selected in the range of Cg-C3Q Z is a polymerizable group, such as (meth) acrylate, styryl or vinyl, and PO is CHCH3CH2-0; Y (4) Blocks of hydrophobic monomers, such as polyethylene, polypropylene, polypropylene oxide or similar materials, which obtain a hydrophobic segment in the polymer chain.

In addition, the polymers of the present invention may contain, as polymerized units, one or more monomers free of acid, monoethylenically unsaturated. Acid-free monoethylenically unsaturated monomers include the C ± -C alkyl esters of acrylic or methacrylic acids, such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and isobutyl methacrylate; hydroxyalkyl esters of acrylic or methacrylic acids, such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. Other monoethylenically unsaturated acid-free monomers are alkyl-substituted acrylamides and acrylamides, including acrylamide, methacrylamide, tertiary-N-butyl acrylamide, N-methyl acrylamide and N, N-dimethylacrylamide. Other examples of monoethylenically unsaturated acid-free monomers include acrylonitrile, methacrylonitrile, allyl alcohol, phosphoethyl methacrylate, 2-vinylpyridine, 4-methacrylonitrile, allyl alcohol, phosphoethyl methacrylate, 2-vinylpyridine, 4-vinylpyridene, N-vinylpyrrolidone. , N-vinylformamide, N-vinylimidazole, vinyl acetate and styrene. If used, the one or more monoethylenically unsaturated, acid-free monomers represent less than 80 weight percent of the total monomer weight, preferably less than 70 weight percent of the total monomer weight. If desired, it is possible to incorporate polyethylenically unsaturated compounds in the polymerization. The polyethylenically unsaturated compounds function as crosslinking agents and will result in the formation of higher molecular weight polymers. The polymers useful in the present invention preferably have a weight average molecular weight ("Mw") of at least about 50,000, more preferably greater than about 100,000 and especially preferred greater than 150,000. At molecular weights below about 50,000, the polymers do not perform well as wet-strength binders. The molecular weights mentioned herein are measured by gel permeation chromatography. Polymers having molecular weights greater than about 50,000 are generally considered polymers of high molecular weights. Various techniques for preparing high molecular weight polymers are known to those skilled in the art. The polymer can be formed, for example, by emulsion polymerization, solution polymerization, bulk polymerization and suspension polymerization. Aspects of polymerization, such as the selection and levels of the initiators, the process conditions (temperature, pressure, loading regimes, agitation), pH and the like, are known to those of ordinary skill in the art.

To obtain a polymer containing, as polymerized units, from 2 to 50 percent of one or more monoethylenically unsaturated acids, emulsion polymerization is the preferred method. Optional additives may be present in the emulsion, such as, for example, lubricants or sintering aids. The polymers useful in the present invention are generally prepared at a solids level of the polymers of about 20 to 70 percent, more preferably 25 to 65 percent by weight, based on the total weight of the emulsion. The polymers can be used in solid form, but are more preferably used in an aqueous solution or emulsion. The one or more particulate materials and the one or more polymeric binders of the present invention are mixed by any conventional means, such as by a ball mill or by mechanical mixing, to form a mixture. A typical formulation is from about 0.1 to 10 percent of the binder, from about 1 to 15 percent water (or another solvent) and about 90 percent of the particulate material. More preferably, a typical semi-wet formulation contains from about 0.15 to 5 percent of the binder, from about 2 to 10 percent of water (or other solvent) and about ninety percent of the particulate material. Especially preferred, a typical semi-wet formulation contains about 0.5 to 3 percent binder, about 3 to 7 percent water (or other solvent) and about 90 percent particulate material. In addition, the mixture may contain two or more conventional process auxiliaries or other conventional additives. These process aids and conventional additives include, for example, other binders, plasticizers, dispersants, lubricants, sintering aids and foam-suppressing agents. For example, water, poly (ethylene glycol) and alkyl alcohols are known plasticizers. If used, each of the one or more conventional process aids or other conventional additives may be present at a level of up to 15, preferably about 0.1 to 10 weight percent, based on the weight of one or more ceramic particles. To form a crude ceramic body, the ceramic precursor mixture is formulated and compacted. Methods for compaction, or subjecting the ceramic materials to high pressures, to produce the raw ceramic bodies, include pressing, extrusion, roll compaction and injection molding. Pressing methods include dry pressing, isostatic pressing and semi-wet pressing. Preferably, the crude ceramic body is formed from the ceramic mixture by pressing at room temperature at a pressure of at least 0.3 metric tons per square centimeter. Before the raw bodies are ground, drilled, ground, cut or subjected to other conventional machining processes, it is convenient to condition these raw bodies. The conditioning of raw bodies can result in the removal of trace amounts of water, plasticizers or other additives. The raw bodies can be conditioned by allowing them to stand at room temperature, but are preferably conditioned by subjecting them to an elevated temperature of about 30 to 300 ° C, more preferably of about 40 to 200 ° C. Depending on the temperature, the raw bodies are generally conditioned in about 5 minutes to about 5 days or more. To form a final ceramic product, the raw body is baked, or sintered. The preferred temperature and time needed to sinter a crude body to form a final ceramic product is partially dependent on the type of ceramic used to obtain the raw ceramic body. In general, it is preferred to sinter the crude ceramic body to obtain the final ceramic product by heating this crude ceramic body to a temperature of at least about 800 ° C, more preferably of about 1,000 to 2,000 ° C, preferably around 4 minutes to about 5 hours, more preferably for about 10 minutes to about 60 minutes. In order to use the polymeric binder of the present invention, it is generally preferred that the pH of the semi-wet powder be at least 8.5. If the pH is below 8.5, the polymeric binder may not dissolve or swell and the green strength and plasticity may not be acceptable for some applications. If the pH of the semi-moist powder, when it is formed, it is below 8.5, the pH can be increased by the addition of organic or inorganic bases. For example, useful organic bases include 2-amino-2-methyl-1-propanol and other amines. Useful inorganic bases in obtaining the desired pH level for the present invention include ammonium hydroxide, sodium hydroxide, calcium hydroxide, barium hydroxide and other alkali metal hydroxides.

Preparation of the Semi-humid Powder The semi-wet powders used to form the raw bodies analyzed in Table 1 were prepared in the following manner. 100 grams of silicon carbide, which has a particle size < . 10 millimeters, they were weighed in a bucket. An amount of the binder material, sufficient to result in the desired weight percentage of the binder, was added to the silicon carbide and mixed with a spatula for one minute. A quantity of water, sufficient to result in the desired weight percentage of water, was then added to the silicon carbide / binder mixture and mixed with a spatula for three minutes. When the semi-wet powders were obtained using the binders of the present invention, the pH of the semi-wet powder was adjusted to optimize the performance of the binder. The pH adjustments, thus made, usually involve the addition of sufficient ammonium hydroxide or 2-amino-2-methyl-1-propanol, so that the pH of the resulting powder is greater than 8.5. The above mixture was then placed in a sealed plastic bag to balance (usually at night).

Evaluation of the Resistance in Crude and Density in Crude Three samples of 30 grams of each semi-wet powder were taken. Each sample of 30 grams was placed in a cylindrical die that has a diameter of 2.86 centimeters. The die was then placed on a Carver press and compressed for one second at 0.4 metric tons / square centimeter. The pressure was then released from the die and re-applied for three seconds at 1.0 metric ton / square centimeter, to form a crude body. The wet strength of the raw ceramic bodies was evaluated by measuring the wet tensile strength, using a diametral compression test. The resistance to wet tension is calculated by the following formula: 2-p sF = p (D) (L) where CTp is the tensile force, p is the applied load to failure, D is the diameter of the sample and L is the thickness of the sample. Diametral compression tests were performed to determine the load applied to the fault, using a Soiltest® G-900 Versaloader charger, equipped with an electronic force gauge of 222.70 kg (available from Ametek), operated at a charge rate of 0.013 centimeters per minute, until the sample fractures. The wet resistances reported in the following tables are the average of at least three measurements, supplied in kPa. The densities of the raw ceramic bodies given in the following tables are densities based on an average of four measurements. The crude densities were calculated as follows Measured = mass / volume where pmediate is wet density and is given in the following table in units of grams per cubic centimeter ("g / cm3"). The following polymers that appear in the following table were evaluated as binders for semi-wet silicon carbide powders obtained according to the above procedure. The polymers had the following compositions and properties: Polymer A: poly (acrylic acid), having a weight-average molecular weight of 3,500; Polymer B: poly (acrylic acid), which has a weight average molecular weight of 10,000; Polymer C: poly (acrylic acid), having a weight average molecular weight of 50,000; Polymer D: poly (acrylic acid), having a weight average molecular weight of 200,000; Polymer E: copolymer of 34.5 weight percent ethylhexyl acrylate, 55 weight percent methyl methacrylate, 2.5 weight percent styrene and 8 weight percent methacrylic acid, which has a weight average molecular weight of 78,000; Polymer F: copolymer of 60 weight percent ethyl acrylate, 40 weight percent methacrylic acid and 0.22 weight percent diallyl phthalate, having a weight average molecular weight greater than 1,000,000; Polymer G: copolymer of 35 weight percent ethyl acrylate and 65 weight percent methacrylic acid, having a weight average molecular weight greater than 1,000,000; Polymer H: 50 weight percent copolymer of ethyl acrylate, 17 weight percent methyl methacrylate, and 33 weight percent methacrylic acid, having a weight average molecular weight greater than 1,000,000; Polymer I: 50 weight percent copolymer of ethyl acrylate, 45 weight percent methacrylic acid, 3.75 weight percent of a hydrophobic material, having the structure: CH2 = C (CH3) (C02) - ( CH2CH20) 2o-R 'where R is a linear hydrophobic C ^ Q - C ^ Q, and 1.25 per * weight percent of a hydrophobic material of the structure: CH2 = C (CH3) (C02) - (CH2CH20) 23- R, where R is a linear hydrophobe C_2-C] _4, having a weight-average molecular weight of 600,000; Polymer J: copolymer of 50 weight percent of ethyl acrylate, 40 weight percent of methacrylic acid and 10 weight percent of a hydrophobic of the structure .- CH2 = C (CH3) (C02) - (CH2CH20) 20-R, wherein R is a linear hydrophobe Ct.gC? _g, having a weight-average molecular weight of 750,000; Polymer K: 45 weight percent copolymer of ethyl acrylate, 40 weight percent methacrylic acid and 15 weight percent of a hydrophobic of the structure: CH2 = C (CH3) (C02) - (CH2CH20) 23 -R, where R is a linear hydrophobic C 2 ~ C? _4, and 0.8 weight percent of n-dodecyl mercaptan, which has a molecular weight of 61,300; Polymer L: 58 percent by weight copolymer of ethyl acrylate, 40 percent by weight methacrylic acid, 2 percent by weight of a hydrophobic of the structure: CH2 = C (CH3) (C02) - (C? 2CH20 ) 23-R, where R is a linear hydrophobe C] _2-C] _4, and 0.4 weight percent of n-dodecyl mercaptan, which has a molecular weight of 168,500; Polymer M: 58 weight percent copolymer of ethyl acrylate, 40 weight percent methacrylic acid and 2 weight percent of a hydrophobic of the structure: CH2 = C (CH3) (C02) - (CH2CH20) -R, where R is a linear hydrophobe Cig-Cig having a molecular weight greater than 1,000,000; Polymer N: 50 weight percent copolymer of ethyl acrylate, 40 weight percent methacrylic acid, 10 weight percent of a hydrophobic of the structure: CH2 = C (CH3) (C02) - (CH2CH20) 2o -R 'where R is a linear hydrophobe Ct_g-Ct_g, and 0.2 weight percent of n-dodecyl mercaptan, which has a molecular weight of 249,000.

SAMPLE POLYMER POLYMER WATER RESISTANCE DENSITY (%) (%) IN HUMID (g / ml) (kPa) 1 A 3.4 17.4 + 1.6 2.32 ± 0.01 2 A 5.4 21.0 + 0.7 2.37 ± 0.00 3 A 7.4 17.3 ± 1.7 2.35 ± 0.02 4 B 3 9.6 + 0.9 2.42 ± 0.02 B 5 9.3 + 0.3 2.38 ± 0.01 6 B 7 4.1 +0.08 2.44 ± 0.02 7 C 3.1 9.0 + 0.9 2.42 ± 0.01 8 C 5 8.2 ± 0.3 2.43 ± 0.00 9 C 7 8.5 ± 0.6 2.42 ± 0.02 D 3 9.5 ± 1.3 2.39 ± 0.02 11 D 5 8.7 ± 0.8 2.46 ± 0.01 12 D 7 11.1 ± 1.6 2.41 ± 0.02 13 E 3.4 5.4 ± 0.9 2.41 ± 0.02 14 E 5.4 6.0 ± 0.6 2.41 ± 0.01 E 7.4 6.0 ± 0.1 2.38 ± 0.01 16 F 5 19.7 ± 1.0 2.45 ± 0.01 17 G 5 19.3 ± 0.3 2.41 ± 0.00 18 H 5 7.3 ± 0.6 2.43 ± 0.01 19 5 15.2 + 1.1 2.43 ± 0.00 0.14 3 9.6 + 0.6 2.42 + 0.02 21 0.23 5 14.8 ± 1.1 2.45 ± 0.01 22 0.32 7 29.3 ± 1.0 2.42 ± 0.02 23 0.36 3 14.6 ± 0.8 2.39 ± 0.01 24 0.60 5 27.3 ± 1.7 2.43 ± 0.00 0.85 7 45.9 ± 3.2 2.41 ± 0.01 26 3 21.7+ 1.9 2.41 ± 0.01 27 5 35.8 ± 2.2 2.42 ± 0.01 28 7 51.6+ 1.5 2.39 + 0.01 29 K 5 7.9 ± 0.3 2.45 ± 0.01 L 5 4.8 ± 0.003 2.43 ± 0.01 31 M 5 16.7 ± 1.0 2.40 ± 0.02 32 N 5 25.3 + 2.3 2.41 +0.01 Samples 1-3 illustrate the performance of raw bodies prepared using a binder, as revealed by Wu in U.S. Patent No. 5,401,695, in column 6, lines 37 to 66, in the preferred range of molecular weight, as it is described in column 4, lines 1-7. While the density of the resulting bodies is good, the wet strength is unacceptably low. Samples 4-6 illustrate the performance of raw bodies prepared with the use of the binder as revealed by Wu, with the molecular weight greater than that in Samples 1-3, but still within the preferred range of Wu. The density of the resulting bodies is good, but the wet strength is lower than in Samples 1-3. Samples 7-9 illustrate the performance of a binder with a composition as revealed by Wu, but with a molecular weight greater than the preferred range by Wu While the density is good, wet strength is lower than in Samples 1-3. Samples 10-12 illustrate the performance of a binder as revealed by Wu, but with a higher molecular weight than in Samples 7-9. The density of these samples is good, but the wet strength is again lower than in Samples 1-3.

Samples 4-12 illustrate that increasing the molecular weight of the binders, as revealed by Wu, is not sufficient to meet the goal of increasing the wet strength of the pressed bodies of semi-wet mixes. Samples 16-18 illustrates the performance of the binders with the composition as revealed by Wu, but with an extremely high molecular weight. The molecular weights of these three polymers are too high for accurate measurement, but it is believed that their relative molecular weights increase in the order of I < H < G. The wet strength of these samples increases in the same order, suggesting that at a sufficiently high molecular weight, further increase in molecular weight can improve wet strength. Nevertheless, these binders do not meet the goal of increasing the wet strength of the pressed bodies from semi-wet mixtures. Samples 13-15 illustrate the performance of binders with the molecular weight in the range of the present invention and including at least one hydrophobic material per chain, but having less than 10% of a monoethylenically unsaturated acid. The density of the resulting pressed bodies is good, but the wet strength is poor.

Samples 19-28 illustrate the performance of binders as disclosed by the present invention. The density values of these samples remain in the desired range, while the wet strength is increased, in most cases, drastically. Samples 29-32 explores the relationship between molecular weight and the content of the hydrophobic material in the strength and density in raw bodies. While the samples presented do not represent optimal formulations for the respective binder compositions, it is believed that the relative performance of the binders will be similar in this optimal form.

Claims (10)

1. CLAIMS 1. A method for preparing pressed semi-wet raw bodies, which have improved wet strength, this method comprises: (a) mixing (i) the particulate material, selected from ceramics, metallurgical materials, and their combinations , and (ii) at least one polymeric binder, having a molecular weight of at least 50,000, comprising, as polymerized units, at least 10 weight percent of one or more monoethylenically unsaturated acids, their salts or anhydrides, this polymeric binder further comprises more than one hydrophobe, having an alkyl chain, saturated or unsaturated, of at least Cg per polymer chain on average, to form a semi-wet powder; and (b) pressing the semi-moist powder to form a crude body.
2. 2. The method of claim 1, further comprising mixing one or more organic or inorganic bases with the particulate material and the polymeric binder, to form a semi-wet powder.
3. 3. The method of claim 1, wherein the particulate material is selected from alumina, aluminum nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconium, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titanium boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, tin oxide, ruthenium oxide, yttrium oxide, magnesium oxide, calcium oxide and superconducting ceramic, iron, nickel, copper, tungsten, titanium, stainless steel, bronze and metal superconductors, or combinations thereof.
4. 4. The method of claim 1, wherein the one or more monoethylenically unsaturated acids, their salts or anhydrides, are selected from the monoethylenically unsaturated carboxylic acids, sulfonic acids, phosphonic acids, their salts or anhydrides.
5. 5. The method of claim 1, wherein the polymeric binder has a molecular weight of at least 100,000.
6. 6. The method of claim 1, wherein the polymeric binder has a molecular weight of at least 500,000.
7. 7. The method of claim 1, wherein the hydrophobic material is selected from alkyl chains, saturated or unsaturated, of at least C? _2.
8. 8. A crude body, pressed in semi-wet form, prepared by the method of claim 1.
9. 9. A crude body, pressed in semi-wet form, prepared by the method of claim 6.
10. 10. A crude body, pressed in semi-wet form, prepared by the method of claim 7.