United States Patent (19) 11 Patent Number: 4,814,370 Kramer et al. (45) Date of Patent: Mar. 21, 1989 (54) CO2 COPOLYMER CERAMIC-BINDER (56) References Cited COMPOSITION U.S. PATENT DOCUMENTS Inventors: Daniel P. Kramer, Macungie; Joseph 3,706,713 12/1972 Hull et al. ........................... 528/405 75) G. Santangelo; James J. Weber, both 4,409,322 10/1983 Ezaki et al. .............. ... 430/523 of Allentown, all of Pa. 4,633,929 1/1987 Santangelo et al. ................ 521/189 FOREIGN PATENT DOCUMENTS (73) Assignee: Air Products and Chemicals, Inc., 21753 1/1987 Japan. Allentown, Pa. Primary Examiner-Lewis T. Jacobs Assistant Examiner-David W. Woodward 21 Appl. No.: 144,833 Attorney, Agent, or Firm-Willard Jones, II; James C. 22 Filed: Jan. 15, 1988 Simmons; William F. Marsh 57 ABSTRACT The present invention relates to a binder and a method Related U.S. Application Data for making and shaping a green body of ceramic pow 62 Division of Ser. No. 7,233, Jan. 27, 1987. der and subsequently producing a formed ceramic body. The method of the present invention comprises 51) int. Cl." .......................... C08K 3/34; C08K 3/22; admixing a ceramic powder with a binder comprising a C08K 3/14 polyalkylene carbonate to form a ceramic-binder mix (52) U.S. Cl. .................................... 524/391; 524/413; ture. The binder of the present invention comprises a 524/430; 524/435; 524/443; 524/445; 524/446; polyalkylene carbonate, preferably polyethylene car 524/456; 524/612 bonate or polypropylene carbonate. 58) Field of Search ............... 524/612, 391, 413, 430, 524/435, 443, 445, 446, 456 12 Claims, No Drawings 4,814,370 2 sintering the baked body. The binder is comprised of CO COPOLYMER CERAMIC-BINDER stearic acid and a thermoplastic of ethylene and 25 wt.% COMPOSITION vinyl acetate. U.S. Pat. No. 4,496,506 discloses a method for shap This is a divisional of co-pending application Ser. No. 5 ing a green body of a ceramic powder by use of a spe 07/007,233 filed on Jan. 27, 1987. cific organic binder, which is a modified polyvinyl alco hol comprising monomeric units expressed by the for TECHNICAL FIELD mula: The present invention relates to a process for the forming of ceramic bodies and to a ceramic-binder com O position for use in forming ceramic bodies. More specif -CH-i- ically, the present invention relates to the use of a CO2 (Z)-R copolymer, i.e. a polyalkylene carbonate, in the ceram ic-binder composition. in which R is a monovalent hydrocarbon group having BACKGROUND OF THE INVENTION 15 at least 4 carbon atoms, Z is a divalent linking unit of -O- or -O-CO- and c is zero or one, in a limited The ceramic industry depends on the use of binders mole fraction. Due to the strong binding power and to facilitate the fabrication of ceramic bodies. In classi lubricity of the binder polymer, the wet blend of ce cal ceramic triaxial bodies, the clay acts as the binder to ramic powder with an aqueous solution of the binder help form the body. However, advanced ceramic bod 20 has good workability in shaping and wet shaped body ies, (ZrO2, SiC, Si3N4, etc.) do not contain clay, and has good shape retainability. The shaped body after therefore binder materials must be used to impart work drying also has excellent mechanical strength to facili ability and green strength to ceramic compacts during tate handling. processing prior to sintering. Those binders used to U.S. Pat. No. 4,474,731 discloses a process for sinter impart workability must have several key properties 25 ing and densification of ceramic materials containing including: uniform mixing with the ceramic composi hydrocarbon materials to produce ceramic bodies sub tion, providing sufficient green strength to allow pro stantially free from carbonaceous residues of such hy cessing, not decomposing during processing of the drocarbon materials by compacting ceramic particles green body and complete burn-out during sintering thus and a binder containing a pyrolysis catalyst selected leaving minimal residual ash in the sintered body. Of 30 from the group consisting of nickel and palladium ions, these characteristics the most important is complete heating in a low oxygen atmosphere to a temperature in burn-out with minimal residual ash. Several processes the range of 350 to 780 C. to remove the carbonaceous for forming ceramic bodies and several binder materials residue and further heating the material to produce a have been either proposed or are in use to provide the sintered, dense ceramic material. workability necessary during forming of ceramic bod 35 U.S. Pat. No. 4,353,958 discloses a process for prepa ies, among these are the following. ration of green ceramic tapes which comprise a finely U.S. Pat. No. 4,608,361 discloses a process for pro divided ceramic powder and a water-compatible poly ducing a sheet for a catalyst carrier for vapor-phase urethane resin binder. The green tapes are prepared by reaction which comprises mixing highly heat resistant casting a water-based slip containing the ceramic pow ceramic fibers, organic fibers, and an organic binder to der and the water-compatible polyurethane resin binder form a slurry, forming the slurry into a paper sheet, in the form of a tape and then drying the formed tape. impregnating the paper sheet with a silicon compound The drying is conducted in two stages, in the first a converting the silicon compound to silica gel and heat relatively humid atmosphere is maintained, in the sec ing the impregnated sheet to burn up the organic fibers ond the humidity is reduced. and the organic binder. 45 U.S. Pat. No. 4,346,049 discloses a process for the U.S. Pat. No. 4,551,496 discloses a thermoplastically preparation of pressureless sintered silicon ceramic bod moldable ceramic composition comprised of from about ies having an equiaxed microstructure and an alpha 40 to about 60 percent by volume of a sinterable silicon crystalline habit. These ceramic bodies are produced by carbide powder and a binder comprised of an organic firing shaped bodies containing finely divided silicon acid and a copolymer of ethylene and from greater than 50 carbide, a boron source such as boron carbide, a carbon about 12 to about 33 weight percent vinyl acetate, said source such as phenolic resin and a temporary binder organic acid having a melting point ranging from about such as polyvinyl alcohol at sintering temperatures 44' C. to about 88 C. and ranging from greater than from about 1900 to about 2250 C. under conditions about 18 to about 45 weight percent of the binder. The such that a coating of carbon source is maintained on ceramic composition is thermoplastically molded into a 55 the finely divided silicon carbide. body which is baked to remove the binder and then U.S. Pat. No. 4,158,688 discloses a sacrificial binder sintered. for use in making molded ceramic bodies. The sacrifi U.S. Pat. No. 4,530,808 discloses a sintered SiC body cial binders used in this invention comprise block poly produced by forming a thermoplastically moldable ce mers having the structural formula: ramic composition comprised of sinterable silicon car bide powder and binder, thermoplastically molding the ceramic composition into a body, embedding the body in nominally spherical particles having a density greater wherein X is the linking group, A or B, m is 0 or a than 80% of the particle's theoretical density and being positive integer, m' is a positive integer greater than 2, A selected from the group consisting of polycrystalline 65 is a linear or branched polymer that is glassy or crystal silicon carbide, free carbon-coated polycrystalline sili line at room temperatures and has a softening point in con carbide and mixtures thereof, baking the embedded the range from about 80 to about 250 C. and B is body to remove the binder therefrom, recovering and polymer different from A that behaves as an elastomer 4,814,370 3 4. at processing temperatures, a plasticizer which may be erite, forsterite, titanates, ferrites, steatite and the like or oil, wax, or oil and wax, and optionally other compo the non-oxide-based materials like silicon carbide, sili nents such as supplementary resins, elastomers and anti con nitride and the like known in the ceramic arts. The oxidants. Examples of suitable Amaterials include poly process is particularly suited for ceramic powders styrene, poly(acrylonitrile) poly(p-bronostyrene) 5 which should not be exposed to an oxidizing atmo poly(methyl methacrylate), poly(alphamethylsytrene) sphere, e.g. Si3N4 and SiC, at elevated temperatures poly(2-methyl-5-vinylpyridine), poly(4-vinylpyridine), because the binder composition of the present invention poly(vinyl acetate), polyesters, polyamides, polyure can be burned-out in a non-oxidizing atmosphere. thanes, poly(vinyl chloride), polypropylene, polysul In the process, the binder content added to the ce fones, poly(phenylene sulfide) poly(4-methylpentene-1) O ramic powder may be as low as 0.1 weight percent and and poly(vinyl alcohol). Examples of suitable B materi as high as 60 weight percent based on the polymer in the als include polybutadiene, polyisoprene, polydimethyl binder. Typical binder contents range between 0.5 butadiene, poly(ethylene oxide), poly(isopropyl acry weight percent and 15 weight percent. The amount of late), poly(octamethylcyclotetrasiloxane), poly(tetrahy binder in the mixture will somewhat depend on the drofuran), polyisobutylene, ethylene propylene rubber, 15 method used for shaping the green body. ethylene propylene diene terpolymers, chlorosulfo The binder composition used in the method of the nated polyethylene, epichlorohyrin rubber, butyl rub present invention is any polyalkylene carbonate.