MXPA96001454A - Method for forming extruded pieces from an inorgan material - Google Patents

Abstract

It is supplied in a method to produce extruded parts from inorganic materials. This method uses selected polymeric binders, which overcome the inadequacies observed with conventional polymeric binders for the extrusion of ceramic and metal pieces. For example, the use of the polymeric binders of the present invention in the extrusion processes provides the processability of a material during extrusion and the strength of the ceramic pieces, before and after sintering. The extruded pieces formed with the use of the binder of the present invention can be dried at room temperature or at elevated temperatures, and can be heated in an inert atmosphere. The binder of the present invention can be used with ceramics of oxide, nitride, boride and carbide, and with metals and combinations of minerals, such as clay and zeolites.

Description

METHOD FOR FORMING EXTRUDED PIECES FROM AN INORGANIC MATERIAL The present invention relates to a method for forming extruded parts from an inorganic material. More particularly, the present invention relates to a method for forming extruded parts from an inorganic material, with the use, as a binder for the inorganic material, of one or more polymers that consist, as polymerized units, of at least one 1 percent of one or more monoethylenically unsaturated acids. As used herein, the term "inorganic" refers to ceramics and metals, including alkali metals and alkaline earth metals. The agglutinants are useful in extrusion processes of ceramics and metals, to add plasticity, which helps the processability and improves the meinejo. Extrusion is commonly used to form complex parts from ceramic or metal materials. Extrusion is particularly valuable when precision or reproducibility is essential for a piece of ceramic or metal. In a typical process, a ceramic or metal powder is mixed with water, a lubricant and, optionally, other additives, by mechanical mixing. This mixture forms a paste. The paste can then be fed in a vertical or horizontal extruder. Extrusion is generally done at or above room temperature, typically from about 15 to 40SC. The extrudate is then cut to form pieces, these pieces are typically dried at room temperature or at an elevated temperature. Finally, the ceramic pieces are usually sintered and this requires an even higher temperature. The sintering is the heating of a ceramic piece to carry out the bonding of the ceramic pieces together to form a dense piece of ceramics. For example, alumina is sintered at 14002C or more. The ceramic piece, before sintering, is called a "raw" or "green" piece and the strength of a piece of ceramic is known as the "green resistance" or "green resistance". The removal of binders or other materials during the heating of ceramic pieces is known as "burning". The rheological properties of the paste are crucial for the extrusion of ceramic or metal pieces. The paste must be able to feed easily into the extruder and must flow easily under pressure. Additives, such as water and other liquids, can be used to help feed the country. The strength of the extruded parts, before sintering, known as the green strength, is essential for dimensional stability and for the stability of the parts during handling. Another requirement is the resistance of extruded parts at elevated temperatures. Because the parts are dried and sintered at elevated temperatures, these parts must be able to withstand these temperatures without cracking or shrinking. For the extrusion of ceramics, cellulose polymers are commonly used, such as methyl cellulose and hydroxyethyl cellulose. The cellulosic polymer binders provide the appropriate rheological properties and are capable of being satisfactorily removed during sintering. While it is known that cellulosic polymers gel at temperatures above the ambient temperature, which provides an added resistance to the pieces during drying, this resistance is not sufficient to avoid the collapse or buckling of the pieces. The temperature may increase, for example, during mixing. Also, during the drying of the ceramic pieces containing the cellulosic polymer binders, cracks frequently occur. Another drawback of cellulosic binders is that they can inconveniently produce a high amount of scorch, when heated in an inert atmosphere. This can present a problem when, for example, ceramic pieces will be heated under a nitrogen atmosphere. This is a problem particularly with non-oxide ceramic parts and metals. For these reasons, attempts have been made to develop binders that provide improved strength without sacrificing burned and rheological properties. As described in Japanese Patent No. HEI-27018, in an attempt to develop a binder, which provides improved properties over cellulosic binders, an alkyl methacrylate copolymer is used as a binder, for molding the ceramic parts. esters of alkyl acrylate, alkoxyalkyl methacrylate or esters of alkoxy acrylate, vinyl acetate and monomers containing one or more carboxyl groups. However, the presence of at least 10 percent vinyl acetate is required. It may be desirable to avoid the use of vinyl acetate in a polymeric binder. The present invention seeks to overcome the insufficiencies in the cellulosic polymeric binders for the formation of pieces by extrusion of the inorganic powder materials. It has been found, surprisingly, that the presence of vinyl acetate is not required in the polymeric binder of the present invention and, contrary to the description of the Japanese patent, mentioned above, the removal of vinyl acetate from the composition of the binder. Tinante provides improved resistance to breakage of a ceramic piece. The use of the polymeric binder of the present invention provides an increase in the modulus of rupture by 50 percent, typically exceeding 100 percent, over a comparable part, obtained using a polymeric binder containing vinyl acetate. Depending on the inorganic material and the composition of the binder, an increase in the modulus of rupture can be as much as 200 percent. The breaking module of ceramic pieces, obtained with the binder of the present invention, is compared with that of ceramic pieces with a comparative binder, by means of a flexure test, in accordance with ASTM C-1161. The test was modified in that the piece used for it was a cylindrical piece of 0.79 cm. in diameter and 11.4 cm. long. The test of ceramic pieces obtained using the method of the present invention produced the unexpected result of a breaking strength greater than three times that of a piece of ceramic obtained using a binder of the present invention, for a piece of ceramics obtained using a binder containing vinyl acetate. With the use of the selected polymeric binders of the present invention, the extruded pieces can be dried at room temperature or at elevated temperatures. The binders of the present invention can be easily mixed with ceramic or metal powders to form a homogeneous paste. These binders provide the rheological and mechanical properties necessary for the extrusion of a variety of configurations and materials, such as, for example, ribbons, tubes or ceramic rods.; stainless steel tapes; metal wires; ribbons and complex structures, including honeycomb monoliths, for use as catalytic substrates. The ceramic and metal products obtained using such a binder have a reduced fissure and stiffness formation, compared to ceramic and metal products, obtained using conventional extrusion binders and better mixing and green strength. The present invention relates to a method for forming extruded parts from an inorganic material, which comprises using, as a binder for the inorganic material, one or more polymers free of vinyl acetate, comprising, as polymerized units, minus 1 percent of one or more monoethylenically unsaturated acids; and from 1 to 99 percent of one or more acid-free monomers, selected from the group consisting of the alkyl acrylates, alkyl methacrylates, aryl acrylates and aryl methacrylates. The present invention provides extruded parts containing an acrylic polymer at a level of 1 to 30 percent by weight, based on the weight of the inorganic powder, in which the acrylic polymer is formed from, as polymerized units, at least 1. percent by weight of one or more monoethylenically unsaturated acids. The acrylic polymer of the present invention is formed of at least 1 weight percent of one or more monoethylenically unsaturated acids. This one or more monoethylenically unsaturated acids in the acrylic polymer can be present from 1 to 99 weight percent, but preferably from 5 to 50 percent and more preferably from 10 to 30 percent. Polymers suitable for the present invention are polymers comprising, as polymerized units, at least 1 percent by weight of one or more monoethylenically unsaturated acids. These monoethylenically unsaturated acids may be monoacids, diacids or polyacids, and they include, but are not limited to, carboxylic acids, sulfonic acids, phosphonic acids, or mixtures thereof. Suitable monoethylenically unsaturated acids are, for example, acrylic acid, methacrylic acid, crotonic acid and vinylacetic acid. Suitable monoethylenically unsaturated dicarboxylic acids are, for example, maleic acid, itaconic acid, mesaconic acid, fumaric acid, citrachonic acid, 2-acrylamido-2-methylpropanesulfonic acid, allyl sulfonic acid, allylphosphonic acid, allyloxybenzenesulfonic acid, -hydroxy-3- (2-propenyloxy) -propanesulfonic acid, iso-propenylphosphonic acid, vinylphosphonic acid, styrene-sulfonic acid and vinylsulfonic acid. More preferably, this one or more monoethylenically unsaturated acids are acrylic acid or methacrylic acid. The one or more monoethylenically unsaturated acids represent at least 1 weight percent of the total monomer weight, preferably 5 to 50 percent and more preferably 10 to 30 percent. In addition, the polymers of the present invention may contain, as polymerized units, one or more monomers extant of monoethylenically unsaturated acids. Monomers free of monoethylenically unsaturated unsaturated acids include the C ^ to Cg 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 acrylamides and alkyl-substituted acrylamides, including acrylamide, methacrylamide, tertiary N-butyl acrylamide, N-methyl acrylamide and N, N-dimethylamino acrylamide. Other examples of monomers free of monoethylenically unsaturated acids include acrylonitrile, methacrylonitrile, allyl alcohol, phosphoethyl methacrylate, 2-vinylpyridene, 4-vinylpyridene, N-vinylpyrrolidone, N-vinylformamide, N-vinylimidazole, vinyl acetate and styrene. If used, this one or more monomers free of monoethylenically unsaturated acids, represent less than 80 weight percent of the total monomer weight and more preferably less than 60 weight percent of the total monomer weight. The acrylic polymer of the present invention is a random copolymer and can be a dipolymer, terpolymer, tetrapolymer or can be obtained from the polymerization of any reasonable number of acrylic monomers. The polymer may optionally contain monomers of di-carboxylic acids. The polymer can be formed by any polymerization means, such as, for example, emulsion polymerization, solution polymerization, bulk polymerization, batch polymerization and suspension polymerization. Aspects of polymerization, such as the selection and levels of the initiators, the process conditions (temperature, pressure, feeding regimes, agitation), pH and the like, are known to those of ordinary skill in the art. To obtain a polymer containing, as polymerized binders, 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. If the polymer is formed by the emulsion polymerization, the emulsion of the resulting polymer is added to a ceramic or metal powder to form a paste. In an aqueous emulsion, the amount of the water may comprise about 30 weight percent of the emulsion and other optional additives in a total weight of 1 to 5 percent. The amount of the polymer in the emulsion added to the pulp may vary from 1 to 30 weight percent, based on the total weight of the ceramic or metal powder in the pulp. The amount of the ceramic or metal powder in the pulp can vary from 30 to 90 weight percent, based on the total weight of all the components in the pulp. If the polymer is formed by some other polymerization method, such as, for example, suspension polymerization or solution polymerization, the polymer can be isolated from any liquid present by conventional methods, such as freeze-drying or drying. by spraying, or it can be used in the presence of the liquid. If a dry polymer is used, it is added to the ceramic or metal powder with the liquid at 1 to 50 weight percent, based on the weight of the ceramic or metal. Optional additives can make up a total of 1 to 5 percent of the total weight of all the components in the paste. The formation of a paste suitable for extrusion is determined partly by the glass transition temperature (Tg) of the binder. This glass transition temperature is the temperature at which or above which a polymer will soften and become elastic or liquid. Regardless of the polymerization method used, the resulting polymer should have a Tg in the range of -70 to 1702C, preferably -30 to 70sc and more preferably -20 to 502C. A polymer with a Tg above 502C can be easily plasticized by the addition of water or other plasticizers, such as dimethyl phthalate or dibutyl phthalate, until the desired consistency is obtained. The binder of the present invention can be used with ceramics, including oxide, nitride, boride and carbide ceramics, and superconductors, and with metals, including alkaline earth metals and transition metals, and their oxides. The binder can also be used with other minerals and their combinations, such as, for example, clay and zeolites. Examples of ceramic materials useful with the binder of the present invention include alumina, aluminum nitride, silica, silicon carbide, silicon nitride, sialon, zirconium, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titanium boride, nitride boron, boron carbide, tungsten carbide, tungsten boron, tin oxide, ruthenium oxide, yttrium oxide, magnesium oxide, calcium oxide, and mixtures thereof. The ceramic material may be in the form of, for example, a powder or needles. Examples of metals useful with the binder of the present invention include iron, nickel, copper, tungsten, titanium and other transition metals. Examples of mixtures of two or more metals and metal oxides include stainless steel, bronze and metal superconductors. The binder can also be used with elemental materials, which can be extruded into pieces, such as, for example, elemental carbon and silicon. If desired, it is possible to incorporate polyethylenically unsaturated compounds within the polymer. The polyethylenically unsaturated compounds function as crosslinking agents and will result in the formation of higher molecular weight polymers. For some applications, it may be preferred to use a mixture of at least two of the polymeric binders of the present invention. For example, a polymeric binder may primarily improve its strength and another may primarily improve the rheological properties. A mixture of two polymeric binders can then be used in order to optimize both parameters. It is preferred that the polymers used in the method of the present invention have a weight average molecular weight greater than about 1,000. More preferably, the polymer will have a molecular weight of about 1,500 to 2 million and especially preferred of about 20,000 to 1 million. For the use of the polymeric binder of the present invention it is preferable that the pH of the ceramic or metal paste is at least 8.5. If the pH is below 8.5, the raw strength and plasticity may not be acceptable in some applications. If the pH of the ceramic paste when formed 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. Inorganic bases useful in obtaining the desired pH level for the present invention include ammonium hydroxide, sodium hydroxide, calcium hydroxide and barium hydroxide, and other alkali metal hydroxides. The following examples are provided as an illustration of the use of the present invention.

EXAMPLE 1 - Formation of an Extruded Part of Alumina with a Binder Containing Acid To 100.0 grams (g) of alumina powder, 3.5 grams of AMP-95® (95% solution of 2-amino-2-methyl- 1-propanol, from Angus Chemical Company), while mixing. After five minutes, a mixture of 19.6 grams of the acrylic emulsion binder A (86% ethyl acrylate, 10% methyl methacrylate and 4% acrylic acid) and 4.0 grams of the binder of acrylic emulsion (50 g) was added. % ethyl acrylate, 40% methacrylic acid and 10% polyethoxylated octadecanol methacrylate) and mixing was continued for another five minutes to form a homogeneous distribution of the acrylic binder, the liquid and the powder. Then, 7.0 g of water was added and the mixing was continued to form a uniform paste of the particulate material. The resulting particulate paste was laminated three times, using a three-roll press, prior to extrusion. This laminated, flake-like paste was worked in a food processor before being fed into a ram-type extruder. The paste was extruded at room temperature through a slit-type die, using a ram-type extruder (cylinder 5.08 cm in diameter, with stroke of 30.5 cm., Loo is 232-20L). The extrudates were laid flat on a board and allowed to dry at room temperature. After drying overnight at room temperature, drying was completed in an oven at 80 ° C for 2 hours. The present example illustrates the use in an extrusion process of two binders, as provided by the present invention.

Example 2 - Formation of an Extruded Part with a Binder Containing Acid and a Polyurethane Thickener A previously mixed slurry of 6.6 g of binder A and 6.6 g of binder B, as described in Example 1, was added to 100. grams of alumina powder. The addition was made with continuous manual mixing for 5 minutes in a 250 ml laboratory bucket, made of plastic, using a 20.32 cm stainless steel spatula. A solution of 4.4 g of a poly-urethane thickener (20% solids) in 11 grams of water was added. The mixture was continued for another 5 minutes more. The resulting paste-like material was extruded in a piston ram-type extruder with a round punch diameter of 0.9525 cm. The present example illustrates the use in an extrusion process of two polymeric binders, as supplied by the present invention, with a polyurethane thickener.

Example 3 - Formation of an Extruded Part with a Binder Containing Acid and a Polyurethane Thickener To 150 g of carbonyl iron powder was added 1.5 g of oleic acid. The addition was a continuous manual mix in a 250 ml laboratory bucket, made of plastic, using a 20.32 cm stainless steel spatula. After 5 minutes of mixing, a previously mixed paste of 11.0 grams of binder A and 5.5 grams of a polyurethane thickener (20% solids) was added. The mixture was then milled with the use of a micro-mill, during one minute. 2.2 g of ammonium carbonate was added to the mixture, followed by an additional 30 seconds of mixing. The resulting material was extruded in a ram-type extruder with a slit-type die, with an opening (thickness) of 0.8 mm. The present example illustrates the use of a polymeric binder, as supplied by the present invention, together with a polyurethane thickener.

Example 4 - Formation of an Extruded Part with a Binder Containing Acid, for the Resistance Test To 100.0 g of Alcoa A-14 alumina powder (from Alcoa Chemical Co.) 0.5 grams of PEG-500 2.5 were added and mixed, then 2.5 grams of AMP-95® were added with mixture. After five minutes, a mixture of 4.9 g of acrylic emulsion binder A and 4.4 g of acrylic emulsion binder B was added., and the mixing was continued for another five minutes to form a homogeneous distribution of the binder, the lucuid and the powder. 16.3 g of water were added and the mixture was continued to form a uniform paste of particulate material. The pH of the paste was 10.8. The resulting paste of the particulate material was laminated in a three-roll press three times, before extrusion. The laminated, flake-like dough was processed in a food processor apparatus, then fed into a ram extruder. This paste was extruded at room temperature through a round die, using a ram extruder (5.08 cm cylinder with a stroke of 30.5 cm., Loomis 232-20 L). The test method was modified ASTM C1161-90, as described above, with a 0.79 cm test piece. in diameter by 11.4 cm. The modulus of rupture ("MOR") of the extrudate was 12.2 ± 0.8 MPa.

Comparative Example A (for comparison with Example 4) To 100.0 grams of alumina powder, Alcoa A-14 (Alcoa Chemical Co.) was added 0.5 grams of PEG-400 2.5, followed by mixing. Then 2.5 g of AMP-95® (95% solution of 2-amino-2-methyl-1-propanol from Angus Chemical Company) were added with continuous mixing. After five minutes, 7.3 g of an emulsion binder was added, which was a 55% polymer (47% vinyl acetate, 27% butyl acrylate, 22% 2-ethylhexyl acrylate and 5% acrylic acid). The mixing was continued for another five minutes to form a homogeneous distribution of the binder, liquid and powder. 15.7 g of water were added and the mixing was continued to form a uniform paste of particulate. The pH of the cake was 10.9. The resulting particulate paste was laminated in a three-roll press three times, before extrusion. The laminated, flake-like pasta was broken into small pieces in a food processor, then fed into a ram extruder. This paste was extruded at room temperature through a round die, using a ram extruder (5.08 cm diameter cylinder with 30.5 cm stroke, Loomis 232-20L). The extrudates were placed flat on a board and allowed to dry at room temperature. After drying overnight at room temperature, the extrudates were dried at 80 ° C for two hours. A universal test apparatus (Instron 1122) was used to measure the rupture modulus ("MOR") of the extruded bars. The average MOR of the extrudate was 3.4 ± 0.1 MPa. The rupture modulus ("MOR") is well known in the art as a base for comparing the mechanical properties of ceramic materials and as an indicator of quality and consistency. In general, the better the agglutinant, the greater the modulus of rupture will be at a comparable level of use of the binder. The results of the MOR measurements in Example 4 and Comparative Example A indicate a MOR for a piece obtained using the binder of the present invention, which is greater by more than 300 percent compared to a ceramic piece made with a binder containing vinyl acetate.

Claims (16)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as property: CLAIMS 1. A method for forming extruded pieces from an inorganic material, which comprises using, as a binder for the inorganic material, one or more polymers free of vinyl acetate, which consist of, as polymerized units: at least 1 percent of one or more monoethylenically unsaturated acids; and from 99 to 1 percent of one or more of acid-free monomers, selected from the group consisting of the alkyl acrylates, alkyl methacrylates, aryl acrylates and aryl methacrylates. The method according to claim 1, further comprising the step of extruding a mixture of: a) the inorganic material; b) the binder; c) from 0 to 30 weight percent water; and d) from 0 to 20 weight percent of one or more processing aids. 3. The method according to claim 1, wherein this method comprises using, as a binder, a mixture of at least two polymers, which consist, as polymerized units, of at least 1 percent of one or more acids monoethylenically unsaturated; and from 99 to 1 percent of one or more acid-free monomers, selected from the group consisting of the alkyl acrylates, alkyl methacrylates, aryl acrylates and aryl methacrylates. 4. The method according to claim 1, further comprising the addition of one or more compounds selected from the group of organic and inorganic bases. The method according to claim 1, further comprising the one or more monoethylenically unsaturated acids are selected from the group consisting of the monoethylenically unsaturated carboxylic acids, sulfonic acids, phosphonic acids and combinations thereof. The method according to claim 1, wherein the one or more monoethylenically unsaturated acids are selected from the group consisting of: acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid, maleic acid, itaconic acid, mesaconic acid, acid fumaric, citraconic acid, 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, allylphosphonic acid, allyloxy-benzenesulfonic acid, 2-hydroxy-3- (2-propenyloxy) -propane-sulphonic acid, isopropenylphosphonic acid, vinylphosphonic acid, styrenesulfonic acid and vinylsulfonic acid. 7. The method according to claim 1, wherein the one or more acid-free monomers are selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and methacrylate. isobutyl; hydroxyalkyl esters of acrylic or methacrylic acids, such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. The method according to claim 1, wherein the one or more polymeric binders comprise, as polymerized units, one or more monomers selected from the group consisting of acrylonitrile, methacrylonitrile, allyl alcohol, phosphoethyl methacrylate, 2-vinylpyridiene, vinyl-pyrene, N-vinylpyrrolidone, N-vinylformamide, N-vinylimide-zol, vinyl acetate, styrene, acrylamide, methacrylamide, N- (tertiary butyl) -acrylamide, N-methylacrylamide and N, N-di-methylacrylamide. The method according to claim 1, wherein the inorganic material comprises one or more ceramic materials, selected from the group consisting of alumina, aluminum nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconia, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titanium boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, rust tin, ruthenium oxide, yttrium oxide, magnesium oxide and calcium oxide. 10. The method, according to claim 1, wherein the inorganic material comprises one or more materials selected from: carbon, iron, nickel, copper, tungsten, titanium, metal oxides, ceramic superconductors and metal superconductors. The method according to claim 1, wherein the one or more monoethylenically unsaturated acids are present at a level of 1 to 50 weight percent, based on the weight of the polymer. 12. A ceramic article, obtained according to the method according to claim 1. 13. A metal article, obtained according to the method of claim 1. 14. A method for forming extruded parts from an inorganic material. , which comprises using, as a binder for the inorganic material, one or more polymers free of vinyl acetate, which consist, as polymerized units, of: at least 1 percent and one or more monoethylenically unsaturated acids; and from 99 to 1 percent of one or more acid-free monomers, selected from the group consisting of: alkyl acrylates, alkyl methacrylates, aryl acrylates and aryl methacrylates, wherein the modulus of rupture of the extruded parts it is improved by more than 50 percent, compared to the extruded pieces formed using a binder containing vinyl acetate. 15. The method according to claim 14, wherein the rupture modulus is improved by more than 100 percent. 16. The method according to claim 14, wherein the rupture modulus is improved by more than 200 percent.