NO875413L

NO875413L - PROCEDURE FOR LIQUIDIZATION OF STRONGLY FILLED PARTICLE SUSPENSIONS.

Info

Publication number: NO875413L
Application number: NO875413A
Authority: NO
Inventors: Bruce D Novich; Mark A Occhionero
Original assignee: Ceramics Process Systems
Priority date: 1986-04-25
Filing date: 1987-12-23
Publication date: 1987-12-23
Also published as: NO875413D0

Description

FLYTENDEGJØRING AV STERKT FYLTE PARTIKKELSUSPENSJONER FLUIDIFICATION OF STRONGLY FILLED PARTICLE SUSPENSIONS

Ansøkningen er en delvis videreføring av US patentansøkning med løpenummer 856.806 inngitt 25. april 1986. The application is a partial continuation of US patent application serial number 856,806 filed on 25 April 1986.

BESKRIVELSE DESCRIPTION

Område for oppfinnelsen Field of the invention

Oppfinnelsen vedrører keramikkteknologi og beslektede områder og vedrører spesielt fremstilling av småpartiklede suspensjoner med mer enn 55 volum% faststoff, og hellbare suspensjoner med smalspektret partikkelstørrelsesfordeling og som har mer enn 55 volum% faststoff. The invention relates to ceramics technology and related areas and relates in particular to the production of small-particle suspensions with more than 55% solids by volume, and pourable suspensions with a narrow-spectrum particle size distribution and which have more than 55% solids by volume.

Tidligere teknikk Prior art

Fremskritt i keramikkbehandling har muliggjort at forskjel-lige komponenter i elektrisk og mekanisk utstyr kan erstattes med sintrede keramikkdeler. Keramikk har funnet utbredt anvendelse innenfor elektronikken som et substrat for inte-grerte kretspakninger. Keramiske substrater tildannes typisk ved sintring av klatter fremstilt fra suspensjoner av kera-msiek partikler. Keramiske stoffer har imidlertid fremvist problemer med sprekking, stor og uregelmessig krympning ved tørking og brenning, og ujevn formbarhet som fører til uens-artet mikrostruktur. Advances in ceramic processing have made it possible for various components in electrical and mechanical equipment to be replaced with sintered ceramic parts. Ceramics have found widespread use within electronics as a substrate for integrated circuit packages. Ceramic substrates are typically formed by sintering blobs prepared from suspensions of ceramic particles. However, ceramic materials have shown problems with cracking, large and irregular shrinkage during drying and firing, and uneven formability leading to non-uniform microstructure.

Bowen, et al (1980), "Basic Needs in High Temperature Ceramics" Journal of Material Schience and Engineering, vol. 44, p. 156ff; Rhoades (1981), "Agglomeration of Particle Size Affects Sintering of Y20^-Stabilized Zr02" Journal of Bowen, et al (1980), "Basic Needs in High Temperature Ceramics" Journal of Materials Science and Engineering, vol. 44, p. 156ff; Rhoades (1981), "Agglomeration of Particle Size Affects Sintering of Y20^-Stabilized Zr02" Journal of

the American Ceramics Society, vol. 64, pp. 19-22; og Lange, et al. (1983), "Processing Related Fracture Origins: I, II, III" Journal of the American Ceramics Society, vol. 65, pp. 396-408; og Aksai, et al..(1983) "Uniformity of Alumina-Zirconia Composites by Colloidal Filtration" Journal of the the American Ceramics Society, vol. 64, pp. 19-22; and Lange, et al. (1983), "Processing Related Fracture Origins: I, II, III" Journal of the American Ceramics Society, vol. 65, pp. 396-408; and Aksai, et al..(1983) "Uniformity of Alumina-Zirconia Composites by Colloidal Filtration" Journal of the

American Ceramics Society, vol. 66, nr. 10, pp. C190 og C193, har påvist at behandlingsforbundne mangler sterkt kan påvirke yteevnen til en keramisk artikkel med høy yteevne. Disse mangler kan videre og vil typisk være egenskapsbegrensende. Disse forskere viste også at ved våtbehandling av kolloidale keramiske partikler kan behandlingsfeil praktisk unngås. Dette gjennomføres ved å kontrollere pakkingen av partiklene på en partikkelmålestokk og ikke på en delstørrelsesskala. American Ceramics Society, vol. 66, No. 10, pp. C190 and C193, have demonstrated that processing-related defects can greatly affect the performance of a high-performance ceramic article. These deficiencies can and will typically be property-limiting. These researchers also showed that with wet processing of colloidal ceramic particles processing errors can practically be avoided. This is done by checking the packing of the particles on a particle scale and not on a part size scale.

Kommersiell kolloidal behandling har støtt på adskillige vanskeligheter ved tildannelse av keramikkdeler på grunn av en eller flere av de følgende faktorer: 1. På grunn av den manglende evne til å overvinne grense-flate- og fukte-kreftene av disse fine partikler som tjener til å holde partikler som separate suspensjons-enheter har behandlingen typisk vært begrenset til fortynnet suspensjon. 2. Typisk fortynnede suspensjoner resulterer i en lav utgangsdensitet for partikkelpakkingen, som generelt resulterer i vesentlige faktorer med hensyn til tørking, bindingsløsning, brenningskrympninger og deformasjoner, lav initial styrke, og innhomogene mikrostrukturfaktorer som frembringer ikke-reproduserbar behandling og egenskaper . 3. Fortynnede suspensjoner vil gjerne ha meget sakte hastighetsbegrensende prosesstrinn. Avvanning eller bindingsløsning mellom bærerens fine partikler skjer generelt meget sakte på grunn av permeabiliteten, avset-ningen, sedimentasjon og diffusjonsbegrensninger for partikler og kompakte deler av disse fine partikler og fine porestørrelser. Commercial colloidal processing has encountered several difficulties in forming ceramic parts due to one or more of the following factors: 1. Due to the inability to overcome the interfacial and wetting forces of these fine particles which serve to keeping particles as separate suspension units, treatment has typically been limited to dilute suspension. 2. Typically dilute suspensions result in a low initial density of the particle packing, which generally results in significant factors in terms of drying, debonding, firing shrinkage and deformation, low initial strength, and inhomogeneous microstructural factors that produce non-reproducible processing and properties. 3. Dilute suspensions will preferably have very slow rate-limiting process steps. Dewatering or bond dissolution between the carrier's fine particles generally occurs very slowly due to permeability, deposition, sedimentation and diffusion limitations for particles and compact parts of these fine particles and fine pore sizes.

Et kritisk trinn for å overvinne disse behandlingsvanskelig-heter ville være evnen til å danne konsentrerte (mer enn 55 volum%) hellbare suspensjoner av partikler med snever partik-kelstørrelse i området mikrometer og submikrometer. A critical step in overcoming these processing difficulties would be the ability to form concentrated (greater than 55% by volume) pourable suspensions of particles with narrow particle sizes in the micrometer and submicrometer range.

I den tidligere teknikk har typisk formeprosessen vært ansett som hovedsakelig komplett når partikkelpakkingsdensiteten har nådd en verdi på 55 volum%. Lav partikkeldensitet resulterer imidlertid i lav initial styrke, og problemet økes ved behovet for å fjerne bindemidlet anvendt ved støteprosessen. In the prior art, the molding process has typically been considered substantially complete when the particle packing density has reached a value of 55% by volume. However, low particle density results in low initial strength, and the problem is compounded by the need to remove the binder used in the impact process.

En høyere volum% av faststoffer ville resultere i mindre krympning ved tørking og sintring, større initial styrke, og en reduksjon i sannsynligheten for en stor feil eller tomrom i partikkelpakkingen. I tillegg ville hurtigere behandling resultere fra den reduserte volumandel av væske. En bedre keramikkstykke, dvs. et som fremviser god initial styrke og en mer kontrollerbar tørkekrympning kunne oppnås hvis man var i stand til å støpe eller forme en klatt inneholdende et høyt volum%-innhold av faststoffer av enten kolloidale partikler (typisk submikrometerstørrelse til omtrent 2 mikrometer størrelse) og/eller partikler med snever partikkelstørrelses-fordeling (som eventuelt kan være kolloidale). Tidligere forsøk på fremstilling av disse fine partikkelsuspensjoner til høye faststoffinnhold (> 55 volum-) har ikke ført frem, ettersom den konvensjonelle suspensjon vil ha tendens til å være så viskøs ved denne faststoff-fylling av den ikke er egnet ved våtformingsmetoder inklusive klattstøping, bånd-støping, ekstrudering og injeksjonsstøping. A higher volume % of solids would result in less shrinkage on drying and sintering, greater initial strength, and a reduction in the likelihood of a large defect or void in the particle packing. In addition, faster processing would result from the reduced volume fraction of liquid. A better ceramic piece, i.e. one exhibiting good initial strength and a more controllable drying shrinkage could be obtained if one were able to cast or mold a blob containing a high volume % solids content of either colloidal particles (typically submicrometer size to about 2 micrometer size) and/or particles with a narrow particle size distribution (which may possibly be colloidal). Previous attempts to produce these fine particle suspensions to high solids content (> 55 vol.) have not been successful, as the conventional suspension will tend to be so viscous at this solids filling that it is not suitable for wet forming methods including drop casting, tape -moulding, extrusion and injection moulding.

Denne konvensjonelt begrensede reologi kan forstås ut fra betraktninger om innvirkning mellom kolloidale partikler. F.eks. har kolloidalt aluminiumoksyd i avionisert vann vanligvis negativt ladede overflater. Denne ladning strekker seg ut fra partikkeloverflaten og påvirker den omgivende opp-løsning. Denne "sfære" av påvirkning benevnes et diffust dobbeltlag. Når to dobbeltlag innvirker på hverandre (dvs. når to aluminiumoksydpartikler kommer nær inntil hverandre) blir partiklene avstøtt og forblir dispergert. Mens dobbelt-laget holder partiklene fra hverandre forhindrer imidlertid virkningene mellom dobbeltlagene høye faststoff-fyllinger på grunn av romlig eksklusjon. En tiltrekningskraft mellom aluminiumoksydpartiklene som motvirker og oppveier dobbelt-lagavstøtningen benevnes Van der Waals tiltrekning. Denne tiltrekningskraft er inverst proporsjonal med avstanden mellom de to partikler. Dette er en ytterligere kolloidal gjensidig innvirkning som forhindrer høye faststoff-fyllinger ettersom partiklene tvinges til å være innenfor Van der Waals påvirkningssfære. Når de er innenfor denne sfære bevirker disse tiltrekningskrefter agglomerering som fører til vesentlige viskositetsøkninger. This conventionally limited rheology can be understood from considerations of interactions between colloidal particles. E.g. colloidal alumina in deionized water usually has negatively charged surfaces. This charge extends from the particle surface and affects the surrounding solution. This "sphere" of influence is called a diffuse double layer. When two bilayers interact (ie when two alumina particles come close to each other) the particles are repelled and remain dispersed. However, while the bilayer keeps the particles apart, the interactions between the bilayers prevent high solids fillings due to spatial exclusion. An attractive force between the aluminum oxide particles that counteracts and offsets the double-layer repulsion is called Van der Waals' attraction. This attractive force is inversely proportional to the distance between the two particles. This is a further colloidal interaction that prevents high solids loadings as the particles are forced to be within the van der Waals sphere of influence. When within this sphere, these attractive forces cause agglomeration leading to significant viscosity increases.

Minskende partikkelstørrelse vil gjerne resultere i enøkning i viskositeten på grunn av en økning i den gjensidige partikkel-partikkelvirkning. Jo mindre partikkelstørrelse, desto nærmere vil partiklene være hverandre og desto større sjansen for gjensidig innvirkning ved en gitt volumandel av faststoffer. Selv i en forholdsvis fortynnet suspensjon med partikler i submikrometerområdet kan tilstedeværende Van der Waals krefter bli ganske store. Ettersom denne partikkel-partikkeltiltrekning øker øker viskositeten av suspensjonen ettersom det kreves mer og mer kraft for å bevege den ene partikkel forbi den annen. Decreasing particle size will tend to result in an increase in viscosity due to an increase in particle-particle interaction. The smaller the particle size, the closer the particles will be to each other and the greater the chance of mutual impact for a given volume proportion of solids. Even in a relatively dilute suspension with particles in the submicrometer range, the Van der Waals forces present can become quite large. As this particle-particle attraction increases, the viscosity of the suspension increases as more and more force is required to move one particle past another.

Bortsett fra en økning i viskositet er ét ytterligere problem som man støter på ved å forsøke å fremstille en høyfylt suspensjon at den gjensidige partikkel-partikkelinnvirkning kan føre til at partiklene agglomererer. Suspensjonen mister således sin homogenitet. Ved meget høye faststoff-fyllinger vil videre agglomeratene begynne å innvirke på hverandre noe som ytterligere øker viskositeten. Apart from an increase in viscosity, one further problem encountered in attempting to produce a highly packed suspension is that the particle-particle interaction can cause the particles to agglomerate. The suspension thus loses its homogeneity. With very high solids fillings, the agglomerates will also start to interact with each other, which further increases the viscosity.

For å motvirke de gjensidige partikkel-partikkelinnvirkninger tilsettes typisk et dispergeringsmiddel. Et dispergeringsmiddel er et kjemisk tilsetningsmiddel som adsorberes på partikkeloverflaten og reduserer dobbeltlag-grensevirkningen mens partiklene holdes utenfor Van der Waals påvirkningssfære. Flere typer av dispergeringsmekanismer postuleres med to primære typer dispergeringsmidler: steriske dispergeringsmidler, som utnytter størrelsen og fasongen på disperger-ingsmiddelmolekylet, og elektrostatiske dispergeringsmidler som anvender en elektrisk ladning for å bevirke dispergering. Steriske dispergeringsmidler forstås å virke ved å fremvise (i) funksjonelle grupper som fremviser sterk overflate-grensevirkning med partikkeloverflaten mens de bare er marginalt oppløselige i løsningsmidlet og (ii) stabiliserende grupper som er lettoppløselige i løsningsmidlet. Elektrostatiske dispergeringsmidler inkluderer syrer og baser som virker til å modifisere pH i det suspenderende medium. Typisk har dispersjonsmidler vært anvendt i vandige og andre oppløsninger for å skape hellbare suspensjoner av submikrometer store partikler med en maksimal faststoffandel på omtrent 50 volum%. Selv om denne maksimale faststoffandel kan være høyere hvis partiklene ikke har en snever partikkel-størrelsesfordeling kan partikler med ensartet størrelse væreønskelige for å fremstille ensartede keramikkgjenstander med ensartede egenskaper, som f.eks. reproduserbar krympning for en bestemt formgivning og for anvendelser med høy yteevne. To counteract the mutual particle-particle interactions, a dispersant is typically added. A dispersant is a chemical additive that adsorbs on the particle surface and reduces the double layer boundary effect while keeping the particles outside the van der Waals sphere of influence. Several types of dispersing mechanisms are postulated with two primary types of dispersants: steric dispersants, which utilize the size and shape of the dispersant molecule, and electrostatic dispersants, which use an electrical charge to effect dispersion. Steric dispersants are understood to work by exhibiting (i) functional groups that exhibit strong surface-interface interaction with the particle surface while being only marginally soluble in the solvent and (ii) stabilizing groups that are readily soluble in the solvent. Electrostatic dispersants include acids and bases that act to modify the pH of the suspending medium. Typically, dispersants have been used in aqueous and other solutions to create pourable suspensions of submicrometer sized particles with a maximum solids content of approximately 50% by volume. Although this maximum solids content may be higher if the particles do not have a narrow particle size distribution, particles of uniform size may be desirable to produce uniform ceramic articles with uniform properties, such as reproducible shrinkage for a specific design and for high performance applications.

Nøkkelen til å frembringe en hellbar suspensjon med en høy faststoff-fylling av kolloidale og/eller ensartet store partikler er således å tilveiebringe et effektivt dispergeringsmiddel. Den tidligere teknikk tilveiebringer ikke noe slikt dispergeringsmiddel. Det har følgelig foreligget et behov for et system for å dispergere og opprettholde et maksimalt faststoffinnhold av kolloidale og/eller smalspektret store partikler slik at den initiale styrke maksimali-seres og krympning minimaliseres, mens komponentene fremdeles opprettholdes i en hellbar eller strømningsdyktig tilstand. Thus, the key to producing a pourable suspension with a high solids loading of colloidal and/or uniformly sized particles is to provide an effective dispersant. The prior art does not provide such a dispersant. There has consequently been a need for a system to disperse and maintain a maximum solids content of colloidal and/or narrow-spectrum large particles so that the initial strength is maximized and shrinkage is minimized, while the components are still maintained in a pourable or flowable state.

Oppfinnelsen The invention

Ved oppfinnelsen er det funnet en klasse av dispergeringsmidler som innvirker med kolloidale og/eller smalspektret store partikler på en slik måte at det muliggjøre dannelse av sterkt fylte men likevel lavviskositets-suspensjoner, egnet for tallrike formeteknikker. Overraskende behøver disse systemer generelt ikke tilsetning av et organiske bindemiddel for å meddele initial styrke og problemene assosiert med avbrenning av disse organiske stoffer unngås derved. The invention has found a class of dispersants which interact with colloidal and/or narrow-spectrum large particles in such a way as to enable the formation of highly filled but nevertheless low-viscosity suspensions, suitable for numerous molding techniques. Surprisingly, these systems generally do not require the addition of an organic binder to impart initial strength and the problems associated with burning off these organic substances are thereby avoided.

Oppfinnelsen inkluderer både vandige, ikke-vandige og blandede systemer. Generelt kan et dispergeringsmiddel for vandige og blandede systemer inkludere en eller flere av de polymere eller polyelektrolytter, drøftet mer detaljert i det følgende. Et dispergeringsmiddel for ikke-vandige systemer kan generelt være et organofunksjonelt koblingsmiddel eller trietanolamin (TEOA). The invention includes both aqueous, non-aqueous and mixed systems. In general, a dispersant for aqueous and mixed systems may include one or more of the polymeric or polyelectrolytes, discussed in more detail below. A dispersing agent for non-aqueous systems can generally be an organofunctional coupling agent or triethanolamine (TEOA).

Klatter fremstilt fra suspensjoner fremstilt i samsvar med den foreliggende oppfinnelse fremviser videre overlegen initial styrke. Denne overlegne initiale styrke skyldes delvis den tettere pakning av partikler med snever partikkel-størrelsesfordeling i en suspensjon med høyt faststoffinnhold. Det er viktig at denne forbedrede initiale styrke også resulterer fra det forhold at utvalgte dispergeringsmidler virker som et bindemiddel i suspensjoner med høyt faststoffinnhold. Ytterligere detaljert og utførelsesformer av oppfinnelsen er beskrevet i det følgende. Blots prepared from suspensions prepared in accordance with the present invention further exhibit superior initial strength. This superior initial strength is due in part to the tighter packing of particles with a narrow particle size distribution in a high solids suspension. It is important that this improved initial strength also results from the fact that selected dispersants act as a binder in suspensions with a high solids content. Further details and embodiments of the invention are described below.

Som anvendt i denne fremstilling refererer betegnelsen "snever partikkelstørrelse" til partikler med størrelses-områder med et standard avvik som ikke er over 50% av den midlere partikkelstørrelse. Slike partikler kan fremstilles på en rekke måter, inklusive ved sentrifugal klassifiserings-teknikk som omhandlet i US patentansøkning 028.891 inngitt 23. mars 1987 og som det her vises til. As used herein, the term "narrow particle size" refers to particles with size ranges with a standard deviation not exceeding 50% of the mean particle size. Such particles can be produced in a number of ways, including by centrifugal classification techniques as discussed in US patent application 028,891 filed March 23, 1987 and to which reference is made herein.

Beskrivelse av spesifikke utførelsesformer Description of specific embodiments

Ved oppfinnelsen er det funnet at konvensjonelle dispergeringsmidler ikke vil tillate fremstilling av suspensjoner med høyt faststoffinnhold av kolloidale partikler og/eller partikler med en snever størrelsesfordeling og som har lav viskositet. Den fysikalske kjemi for disse typer av kolloidale partikler er markert forskjellig fra den fysikalske kjemi for konvensjonelle kolloidale partikler, slik at konvensjonelle dispergeringsmidler som er tilfredsstillende ved lave volumandeler av faststoffer er utilfredsstillende ved høyere volumandeler av faststoffer. With the invention, it has been found that conventional dispersants will not allow the production of suspensions with a high solids content of colloidal particles and/or particles with a narrow size distribution and which have a low viscosity. The physical chemistry of these types of colloidal particles is markedly different from the physical chemistry of conventional colloidal particles, so that conventional dispersants which are satisfactory at low volume fractions of solids are unsatisfactory at higher volume fractions of solids.

Til tross for disse resultater ble det funnet at visse polymere polyelektrolytter og andre sterisk virkende dispergeringsmidler vil virke tilfredsstillende ved volumandeler over 50% både i dispersjoner med kolloidal størrelse og snevert størrelsesområde. Dispergeringsmidlene må lett kunne adsorberes på partiklene og seleksjonen av dispergeringsmiddel er følgelig en funksjon av både den valgte partikkel og løs-ningsmiddel . Despite these results, it was found that certain polymeric polyelectrolytes and other sterically acting dispersants will work satisfactorily at volume fractions above 50% both in dispersions with colloidal size and narrow size range. The dispersants must be easily adsorbed on the particles and the selection of dispersant is consequently a function of both the selected particle and solvent.

Den første gruppe av dispergeringsmidler som ble funnet brukbare, særlig i vandige systemer, inkluderer de polymere poly-elektroly tter , og mer spesielt slike med en molekylvekt under omtrent 10000. Av de polymere polyelektrolytter ble det funnet at de akrylsyrebaserte polymerer og kopolymerer var særlig brukbare. Mange av disse er kommersielt tilgjenge-lige. Foretrukne typer, særlig med aluminiumoksyd i vandige systemer, inkluderer "Narlex LD-45" som er en kopolymer av polyakrylsyre med propylenglykol og utstående ammoniumsalt-grupper, videre "Narlex LD-42" som er liknende kopolymer men med utstående natriumsaltgrupper, og "DB-300" som er ammo-niumsalt av en kopolymer av akrylsyre og polypropylenglykol (samtlige kan oppnås fra National Starch and Chemical Corpo-ration, Bridgewater, NJ). "LD-45" anvendes ofte som et dis pergeringsmiddel for titanoksyd og andre uorganiske pigment-er i malingblandinger. En ytterligere fordel ved å anvende "LD-45" er at dens lave molekylvekt letter avbrenningen. Andre polymere polyelektrolytter av interesse ved oppfinnelsen inkluderer med er ikke begrenset "Darvan C" og "Darvan 821A" ammoniumpolyakrylat-kopolymer-dispergeringsmidler som kan fås kommersielt fra R.T. Vanderbilt Co., Norfolk, CT. The first group of dispersants found useful, particularly in aqueous systems, included the polymeric polyelectrolytes, and more particularly those with a molecular weight below about 10,000. Of the polymeric polyelectrolytes, the acrylic acid-based polymers and copolymers were found to be particularly useful. . Many of these are commercially available. Preferred types, particularly with alumina in aqueous systems, include "Narlex LD-45" which is a copolymer of polyacrylic acid with propylene glycol and protruding ammonium salt groups, further "Narlex LD-42" which is a similar copolymer but with protruding sodium salt groups, and "DB -300" which is the ammonium salt of a copolymer of acrylic acid and polypropylene glycol (all obtainable from the National Starch and Chemical Corporation, Bridgewater, NJ). "LD-45" is often used as a dispersant for titanium oxide and other inorganic pigments in paint mixtures. A further advantage of using "LD-45" is that its low molecular weight facilitates burning. Other polymeric polyelectrolytes of interest in the invention include but are not limited to "Darvan C" and "Darvan 821A" ammonium polyacrylate copolymer dispersants commercially available from R.T. Vanderbilt Co., Norfolk, CT.

De polymere polyelektrolytter kan dispergere et høyt volum faststoffer i ikke-vandige systemer såvel som vandige systemer. Ved en utførelsesform av oppfinnelsen ble suspensjoner på mer enn 60 volum% aluminiumoksyd fremstilt i et lavere karbon-alkoholbasert system under anvendelse av "LD-45". The polymeric polyelectrolytes can disperse a high volume of solids in non-aqueous systems as well as aqueous systems. In one embodiment of the invention, suspensions of greater than 60% by volume alumina were prepared in a lower carbon alcohol based system using "LD-45".

En annen type av dispergeringsmiddel som ble funnet å være nyttig ved fremstilling av høyt fylte men likevel hellbare dispersjoner av kolloidale og/eller smalspektret store partikler kan grovt klassifiseres som steriske dispergeringsmidler. Et slikt dispergeringsmiddel kan være et etoksykoblingsmiddel. Steriske dispergeringsmidler av interesse inkluderer de organofunksjonelle dispergeringsmidler av oksymetalltypen og deres derivater generelt benevnt organosilanestere. En foretrukket klasse av organosilanestere og deres derivater inkluderer gammaaminopropyl-trietoksysilanene og deres derivater, og spesifikt det kommersielt tilgjenge-lige som selges under betegnelsen "A174" (oppnådd fra Union Carbide Corp., Specialty Chemicals Division, Danbury, CT). Andre dispergeringsmidler av denne generelle type som også er nyttige inkluderer andre estere av organoetoksytypen og deres derivater, som f.eks. fosfatestere og deres derivater. Ved oppfinnelsen er det funnet at "RE-610", en kommersielt til-gjengelig organofosfatester (oppnådd fra GAF Corp., Wayne, NJ) er særlig foretrukket. Another type of dispersant that was found to be useful in the preparation of highly filled yet pourable dispersions of colloidal and/or narrow-spectrum sized particles can be roughly classified as steric dispersants. Such a dispersing agent may be an ethoxy coupling agent. Steric dispersants of interest include the organofunctional dispersants of the oxymetal type and their derivatives generally referred to as organosilane esters. A preferred class of organosilane esters and their derivatives includes the gammaaminopropyl-triethoxysilanes and their derivatives, and specifically that commercially available sold under the designation "A174" (obtained from Union Carbide Corp., Specialty Chemicals Division, Danbury, CT). Other dispersants of this general type which are also useful include other esters of the organoethoxy type and their derivatives, such as e.g. phosphate esters and their derivatives. In the present invention, it has been found that "RE-610", a commercially available organophosphate ester (obtained from GAF Corp., Wayne, NJ) is particularly preferred.

TEOA kan også anvendes og i en foretrukket utførelsesform dispergerte det 60 volum% submikrometer stort aluminium oksyd i alkohol mens dispersjonen likevel bibeholdt en viskositet på mindre enn omtrent 200 cP. TEOA can also be used and in a preferred embodiment it dispersed 60% by volume of submicron aluminum oxide in alcohol while the dispersion still maintained a viscosity of less than about 200 cP.

Generelt innbefatter en foretrukket utførelsesform av oppfinnelsen trinnet med å blande kolloidale partikler i størr-elsesområdet mikrometer eller submikrometerstørrelsen og/ eller med smal partikkelstørrelsesfordeling, i en litt større enn kritisk mengde væske, med dispergeringsmiddel og et passende malemedium anvendt for deagglomerering av partiklene, i en forholdsvis kort tid (mindre enn omtrent 1 time), foretrukket med pulver tilsatt væsken i trinn i en vibrasjons-mølle med høy amplityde inntil den ønskede volumandel av faststoffer oppnås. Dette blandetrinn, som foretrukket bør innbefatte blanding med høye skjærkrefter, er av kritisk betydning, og kan bety forskjellen mellom å oppnå en optimal dispersjon med en høy faststoffandel eller ikke.Alterna-tivt kan blanding finne sted ved en lavere enn ønsket volumandel faststoffer og væsken ekstraheres inntil den ønskede volumandel av faststoffer oppnås. Suspensjoner fremstilt i samsvar med den foreliggende oppfinnelse går deretter inn i en klattdannende fase hvor klattene avluftes under anvendelse av et skumfjerningsmiddel som f.eks. oktanol, og omrøres for å unngå dannelse av stripestrukturer før tildannelse av delen. In general, a preferred embodiment of the invention includes the step of mixing colloidal particles in the micrometer or submicrometer size range and/or with narrow particle size distribution, in a slightly larger than critical amount of liquid, with dispersant and a suitable grinding medium used for deagglomerating the particles, in a relatively short time (less than about 1 hour), preferably with powder added to the liquid in stages in a vibration mill with high amplitude until the desired volume fraction of solids is achieved. This mixing step, which should preferably include mixing with high shear forces, is of critical importance, and can mean the difference between achieving an optimal dispersion with a high proportion of solids or not. Alternatively, mixing can take place at a lower than desired volume proportion of solids and the liquid is extracted until the desired volume proportion of solids is achieved. Suspensions prepared in accordance with the present invention then enter a blob-forming phase where the blobs are deaerated using a defoamer such as e.g. octanol, and stirred to avoid the formation of strip structures before forming the part.

Tidligere kjente suspensjoner med volumandel faststoffer under 50% fremviser vesentlig krympning ved tørking og krever styrte tørkeprosedyrer. Det er funnet at hellbare suspensjoner av kolloidale partikler kan fremstilles med så høy volumandel faststoffer at når bare en liten mengde væske fjernes fra suspensjonen, som f.eks. ved avdamping, størkner suspensjonen meget hurtig til et faststoff med en samtidig foregående liten mengde krymping. Previously known suspensions with a volume proportion of solids below 50% exhibit significant shrinkage on drying and require controlled drying procedures. It has been found that pourable suspensions of colloidal particles can be prepared with such a high volume fraction of solids that when only a small amount of liquid is removed from the suspension, such as e.g. upon evaporation, the suspension solidifies very quickly into a solid with a concomitant small amount of shrinkage.

Det innsees at oppfinnelsen generelt kan anvendes med kolloidale partikler av keramiske oksyder og med metallpulveret. Eksempler på partikler av særlig interesse ved oppfinnelsen inkluderer men er ikke på noen måte begrenset til aluminiumoksyd, silisiumnitrid og dets legeringer, zirkoniumoksyd (inklusive delvis stabilisert) og hvilken som helst kombinasjon derav. It is understood that the invention can generally be used with colloidal particles of ceramic oxides and with the metal powder. Examples of particles of particular interest in the invention include but are in no way limited to alumina, silicon nitride and its alloys, zirconium oxide (including partially stabilized) and any combination thereof.

De følgende eksempler illustrerer oppfinnelsen. The following examples illustrate the invention.

Eksempel I Example I

Suspensjoner av aluminiumoksyd i alkohol, med mer enn 60 volum% aluminiumoksyd og viskositet mindre enn omtrent 200 centipoise, ble fremstilt på følgende måte. Tørkede aluminiumoksydpartikler med snever størrelsesfordeling med en midlere størrelse på omtrent 0,5 mikrometer og med størrelse i området fra omtrent 0,3 til 0,8 mikrometer ble blandet med isopropylalkohol og 0,5 vekt% TEOA(denne andel basert på vekten av tørket pulver) og blandet i en beholder med den passende mengde av malemedia (for deagglomerering av partikler). Blandingene ble så malt i en vibrasjonsmølle med høy amplityde i opptil omtrent 1 time og var så ferdig for bruk. Klattene fremviste høy initial styrke og størknet hurtig (omtrent 5 min. ved romtemperatur, mindre enn 1 min. ved 40<W>C) og lav krymping (omtrent 1%) ved tørking. Suspensions of alumina in alcohol, greater than 60% by volume alumina and viscosity less than about 200 centipoise, were prepared as follows. Dried alumina particles having a narrow size distribution with an average size of about 0.5 micrometers and ranging in size from about 0.3 to 0.8 micrometers were mixed with isopropyl alcohol and 0.5% by weight of TEOA (this proportion based on the weight of dried powder ) and mixed in a container with the appropriate amount of grinding media (for deagglomeration of particles). The mixtures were then milled in a high amplitude vibratory mill for up to about 1 hour and were then ready for use. The blobs exhibited high initial strength and solidified rapidly (about 5 min. at room temperature, less than 1 min. at 40<W>C) and low shrinkage (about 1%) on drying.

Eksempel II Example II

Suspensjoner av aluminiumoksyd i vann, med mer enn 60 volum% aluminiumoksyd og viskositet under omtrent 200 centipoise, ble fremstilt under anvendelse av"LD-45"som et dispergeringsmiddel. Den grunnleggende prosedyre var lik den som er beskrevet i det foregående, under anvendelse av samme type av tørkede aluminiumoksydpartikler som beskrevet i det foregående, med vann som væske i stedet for alkohol, og "LD-45" i stedet for TEOA. Konsentrasjonen av "LD-45" var 1,5 vekt% Suspensions of alumina in water, greater than 60% by volume alumina and viscosity below about 200 centipoise, were prepared using "LD-45" as a dispersant. The basic procedure was similar to that described above, using the same type of dried alumina particles as described above, with water as the liquid instead of alcohol, and "LD-45" instead of TEOA. The concentration of "LD-45" was 1.5% by weight

(basert på vekten av tørt pulver). Klattene fremviste høy (based on the weight of dry powder). The blobs displayed hay

initial styrke, hurtig størkning (omtrent 1 time ved romtemperatur, 5 timer ved 40°c, og mindre enn 1 min. ved 100°C) og lav krymping (omtrent 1%). initial strength, rapid solidification (about 1 hour at room temperature, 5 hours at 40°C, and less than 1 min. at 100°C) and low shrinkage (about 1%).

Eksempel III Example III

En suspensjon ble fremstilt generelt i samsvar med prosedyren i eksempel II, med unntagelse av at 20 ml metanol, 13 ml dimetylsulfoksyd, 7 ml etylenglykol, 23 ml "LD-45" og 206 ml vann ble anvendt sammen med 1421 g "AKP-20" aluminiumoksyd (fra Sumitomo Chemical Co., Japan). Den resulterende suspensjon hadde en viskositet på mindre enn omtrent 455 cP ved 99,8 sek<-1>. A suspension was prepared in general accordance with the procedure of Example II, except that 20 ml of methanol, 13 ml of dimethyl sulfoxide, 7 ml of ethylene glycol, 23 ml of "LD-45" and 206 ml of water were used together with 1421 g of "AKP-20 " alumina (from Sumitomo Chemical Co., Japan). The resulting suspension had a viscosity of less than about 455 cP at 99.8 sec<-1>.

Claims

1. The method of forming a dispersion of particles, characterized by (a) preparing a suspension of particles, dispersant and at least one other liquid, and (b) stirring the mixture until the particles are thoroughly dispersed, these steps being carried out to produce a pourable dispersion with more than 55% solids by volume.

2. Method as stated in claim 1, characterized in that step (a) includes the production of a suspension of particles with a narrow particle size distribution.

3. Method as stated in claim 1, characterized in that step (a) includes the preparation of a suspension of colloidal particles.

4. Method as stated in claim 1, characterized in that step (a) includes the production of a suspension of colloidal particles with a narrow particle size distribution.

5. Method as stated in claim 2, characterized in that step (a) includes the production of a suspension of ceramic particles.

6. Method as stated in claim 2, characterized in that step (a) comprises the production of a suspension of particles which are metal powders.

7. Method as stated in claim 5, characterized in that step (a) comprises the preparation of a suspension of particles selected from the group consisting of aluminum oxide, silicon carbide, silicon nitride and its alloys, zirconium oxide, partially stabilized zirconium oxide, cordierite, forsterite, mullite, titanium oxide and any combination thereof.

8. Method as set forth in claim 7, characterized in that step (a) comprises the production of a suspension of the dispersant particles and water.

9. Method as stated in claim 8, characterized in that step (a) comprises the preparation of a suspension including a polymer polyelectrolyte as a dispersant.

10. Method as stated in claim 9, characterized in that step (a) comprises the production of a suspension which includes at least one acrylic acid-based polymer or copolymer.

11. Method as stated in claim 10, characterized in that step (a) comprises the preparation of a suspension of particles, water and a dispersant selected from the group consisting of "LD-42", "LD-45", "DB-300", "Darvan C" and "Darvan 821A".

12. Method as stated in claim 6, characterized in that step (a) comprises the production of suspension particles, dispersant and at least one organic liquid.

13. Method as stated in claim 12, characterized in that step (a) comprises the preparation of a suspension including at least one alcohol.

14. Method as stated in claim 13, characterized in that step (a) comprises the preparation of a suspension including an ethoxy coupling agent as a dispersant.

15. Method as stated in claim 14, characterized in that step (a) includes preparation of a suspension including a dispersant selected from the group consisting of gamma-aminopropyl-triethoxysilane, "A-174", organophosphate esters, "RE-610" and their derivatives .

16. Method as stated in claim 13, characterized in that step (a) includes the preparation of a suspension including a dispersant including TEOA.

17. Method as stated in claim 3, characterized in that step (a) comprises the production of a suspension of ceramic particles.

18. Method as stated in claim 3, characterized in that step (a) comprises the production of a suspension of particles which are metal powders.

19. Method as stated in claim 17, characterized in that step (a) comprises the preparation of a suspension of particles selected from the group consisting of aluminum oxide, silicon nitride and its alloys, zirconium oxide, partially stabilized zirconium oxide and any combination thereof.

20. Method as stated in claim 19, characterized in that step (a) comprises the preparation of a suspension of the particles, dispersant and water.

21. Method as stated in claim 20, characterized in that step (a) comprises the preparation of a suspension including a polymer polyelectrolyte as a dispersant.

22. Method as stated in claim 21, characterized in that step (a) comprises the preparation of a suspension including at least one acrylic acid-based polymer or copolymer.

23. Method as stated in claim 21, characterized in that step (a) comprises the preparation of a suspension of particles, water and a dispersant selected from the group consisting of "LD-42", "LD-45", "DB-300", "Darvan C" and "Darvan 821A".

24. Method as stated in claim 19, characterized in that step (a) includes the preparation of a suspension including particles, dispersant and at least one organic liquid.

25. Method as stated in claim 24, characterized in that step (a) comprises the preparation of a suspension including at least one alcohol.

26. Method as stated in claim 25, characterized in that step (a) comprises the preparation of a suspension including an ethoxy coupling agent as a dispersant.

27. Method as stated in claim 25, characterized in that step (a) comprises the preparation of a suspension including a dispersant selected from the group consisting of gamma-aminopropyl-triethoxysilane, "A-174", organophosphate esters, "RE-610" and their derivatives .

28. Method as stated in claim 25, characterized in that step (a) comprises the preparation of a suspension including a dispersant including TEOA.

29. Method as stated in claim 4, characterized in that step (a) includes the production of a suspension of ceramic particles.

230. Method as stated in claim 4, characterized in that step (a) includes the production of a suspension of particles such as metal powders.

31. Method as stated in claim 29, characterized in that step (a) includes the preparation of a suspension of particles selected from the group consisting of aluminum oxide, silicon nitride and its alloys, zirconium oxide, partially stabilized zirconium oxide and any combination thereof.

32. Method as stated in claim 31, characterized in that step (a) comprises the preparation of a suspension of the particles, dispersant and water.

33. Method as stated in claim 32, characterized in that step (a) comprises the preparation of a suspension including a polymeric polyelectrolyte as a dispersant.

34. Method as stated in claim 33, characterized in that step (a) comprises the preparation of a suspension including at least one acrylic acid-based polymer or copolymer.

35. Method as stated in claim 34, characterized in that step (a) includes the preparation of a suspension of particles, water and a dispersant selected from the group consisting of "LD-42", "LD-45", "DB-300", "Darvan C" and "Darvan 821A".

36. Method as stated in claim 31, characterized in that step (a) includes the preparation of a suspension of particles, dispersant and at least one organic liquid.

37. Method as stated in claim 36, characterized in that step (a) includes the production of a suspension including at least one alcohol.

38. Method as stated in claim 37, characterized in that step (a) includes preparation of a suspension including an ethoxy coupling agent.

39. Method as set forth in claim 38, characterized in that step (a) includes preparation of a suspension including a dispersant selected from the group consisting of gamma-aminopropyl-triethoxysilane, "A-174", organophosphate esters, "RE-610" and their derivatives .

40. Method as stated in claim 37, characterized in that step (a) includes the preparation of a suspension including a dispersant including TEOA.

41. A suspension of particles, characterized in that it comprises (a) particles, (b) at least one liquid, and (c) a dispersant, in that the suspension comprises at least 55% by volume of particles that are thoroughly dispersed in the liquid and that the suspension is pourable.

42. Suspension as stated in claim 41, characterized in that the particles have a narrow size range.

43. Suspension as stated in claim 41, characterized in that the particles are colloidal.

44. Suspension as stated in claim 41, characterized in that the particles have a narrow size range and are colloidal.

45. Suspension as stated in claim 42, characterized in that the particles are ceramic particles.

46. Suspension as stated in claim 42, characterized in that the particles are metal particles.

47. Suspension as stated in claim 39, characterized in that the particles are selected from the group consisting of aluminum oxide, silicon nitride and their alloys, zirconium oxide, partially stabilized zirconium oxide, and any combination thereof.

48. Suspension as stated in claim 47, characterized in that the liquid includes water.

49. Suspension as stated in claim 48, characterized in that the dispersant includes a polymer polyelectrolyte.

50. Suspension as stated in claim 49, characterized in that the dispersant comprises an acrylic acid-based polymer or copolymer.

51. Suspension as stated in claim 50, characterized in that the dispersant is selected from the group consisting of "LD-42", "LD-45", "DB-300", "Darvan C" and "Darvan 821A".

52. Suspension as stated in claim 47, characterized in that the liquid includes at least one organic liquid.

53. Suspension as stated in claim 52, characterized in that the liquid includes at least one alcohol.

54. Suspension as stated in claim 53, characterized in that the dispersant is an ethoxy coupling agent.

55. Suspension as stated in claim 54, characterized in that the dispersant is selected from the group consisting of gamma-aminopropyltriethoxysilane, "A-174", organophosphate esters, "RE-610" and their derivatives.

56. Suspension as stated in claim 52, characterized in that the dispersant includes TEOA.

57. Suspension as stated in claim 43, characterized in that the particles are ceramic particles.

58. Suspension as stated in claim 43, characterized in that the particles are metal particles.

59. Suspension as stated in claim 47, characterized in that the particles are selected from the group consisting of aluminum oxide, silicon nitride and its alloys, zirconium oxide, partially stabilized zirconium oxide and any combination thereof.

60. Suspension as stated in claim 59, characterized in that the liquid includes water.

61. Suspension as stated in claim 60, characterized in that the dispersant comprises a polymeric polyelectrolyte.

62. Suspension as stated in claim 61, characterized in that the dispersant includes an acrylic acid-based polymer or copolymer.

63. Suspension as stated in claim 62, characterized in that the dispersant is selected from the group consisting of "LD-42", "LD-45", "DB-300", "Darvan C" and "Darvan 821A".

64. Suspension as stated in claim 59, characterized in that the liquid includes at least one organic liquid.

65. Suspension as stated in claim 64, characterized in that the liquid includes at least one alcohol.

66. Suspension as stated in claim 65, characterized in that the dispersant is an ethoxy coupling agent.

67. Suspension as stated in claim 66, characterized in that the dispersant is selected from the group consisting of gamma-aminopropyltriethoxysilane, "A-174", organophosphate esters, "RE-610" and their derivatives.

68. Suspension as stated in claim 65, characterized in that the dispersant includes TEOA.

69. Suspension as stated in claim 44, characterized in that the particles are ceramic particles.

70. Suspension as stated in claim 44, characterized in that the particles are metal particles.

71. Suspension as stated in claim 68, characterized in that the particles are selected from the group consisting of aluminum oxide, silicon nitride and its alloys, zirconium oxide, partially stabilized zirconium oxide and any combination thereof.

72. Suspension as stated in claim 70, characterized in that the liquid includes water.

73. Suspension as stated in claim 71, characterized in that the dispersant includes a polymeric polyelectrolyte.

74. Suspension as stated in claim 72, characterized in that the dispersant includes an acrylic acid-based polymer or copolymer.

75. Suspension as stated in claim 74, characterized in that the dispersant is selected from the group consisting of "LD-42", "LD-45", "DB-300", "Darvan C" and "Darvan 821A".

76. Suspension as stated in claim 70, characterized in that the liquid includes at least one organic liquid.

77. Suspension as stated in claim 75, characterized in that the liquid includes at least one alcohol.

78. Suspension as stated in claim 77, characterized in that the dispersant is an ethoxy coupling agent.

79. Suspension as stated in claim 78, characterized in that the dispersant is selected from the group consisting of gamma-aminopropyltriethoxysilane, "A-174", organophosphate esters, "RE-610" and their derivatives.

80. Suspension as stated in claim 77, characterized in that the dispersant includes TEOA.