Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/20—Conductive material dispersed in non-conductive organic material
  • H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere

Definitions

• Fiber or particulate additives can be incorporated into a wide variety of materials, such as, for example, polymers, water, polymer precursors, etc. to produce a wide variety of end products.
• Particulate additives such as fluoropolymer micropowders
• thermoplastic polymers used to produce industrial textiles such as, for example, textile articles used in filtration and dewatering processes; carpeting; fabrics for sportswear and outerwear; hot-air balloons; car and plane seats; and umbrellas.
• Incorporating fluoropolymer micropowders, such as polytetrafluoroethylene (PTFE), into such polymers can produce textiles having certain advantages, such as, for example, textiles that are easier to clean, fibers having improved tensile strength, etc.
• Fibers for example, can be added to thermoplastic polymers used to produce composites, including advanced engineering composites.
• the reinforcing effects of the fibers may significantly modify the properties of the thermoplastic polymer.
• Advanced engineering composites having polyamide fibers, such as either Kevlar® fibers, or carbon fiber, incorporated into the thermoplastic polyester matrix of the resin are widely used in articles, such as, for example, sporting goods.
• Fibers can also be incorporated into nail polish or paint coating compositions, and micropowders can be incorporated into various cosmetic products.
• U.S. Patent No. 5,370,866 relates to a colorless or colored nail polish containing, in a polish solvent system, a film-forming substance, a resin, a plasticizer, and 0.01 to 0.5 wt.% aramide fibers (poly[paraphenylene terephthalamide]).
• U.S. Patent No. 5,416,156 relates to a surface coating composition comprising, in combination, a fibrillated polymer matrix, at least one pigment, at least one binder, and at least one solvent, and a method for the manufacture thereof.
• U.S. Patent No. 4,938,952 relates to a cosmetic product including a cosmetic component as a pigment maintained within a matrix of fibrillatable polymer.
• One aspect of the invention is a slurry comprising at least one liquid medium, at least one microfiber, and at least one micropowder.
• Another aspect of the invention is a process for making a slurry comprising the at least one microfiber, the at least one micropowder, and the at least one liquid medium.
• FIG. 1 is a graph illustrating the micropowder particle size distribution of various micropowder containing slurries.
• FIG. 2 is a graph illustrating the rheology characteristics of a titanium dioxide slurry containing microfibers in comparison to a titanium dioxide slurry that does not contain microfibers.
• an amount, concentration, or other value or parameter given as a list of upper preferable values and lower preferable values is to be understood as specifically disclosing all ranges formed from any pair of an upper preferred value and a lower preferred value, regardless of whether ranges are separately disclosed.
• the present invention also provides a process for making a slurry containing at least one liquid medium, at least one microfiber, and at least one micropowder.
• the process provides improved dispersion of the microfibers and micropowders in the liquid medium, such that the particles dispersed therein are well separated and preferably do not reagglomerate. While is not intended that the present invention be bound by any particular theory, it is believed that the improved dispersion of the microfibers and micropowders is due in part to the physical interaction of particles having a dissimilar shape.
• microfiber(s) refers to "processed fiber” that can generally be described as fiber because of its aspect ratios.
• the microfibers preferably contained in the slurries, as disclosed herein, preferably have aspect ratios ranging from about 10:1 to about 1000:1 , more preferably from about 10:1 to about 500:1 , and even more preferably from about 25:1 to about 300:1.
• the microfibers have volume average lengths of from about 0.01 to about 100 microns, more preferably from about 0.1 to 100 microns, even more preferably from about 0.1 to about 50 microns, still more preferably from about 0.5 to about 50 microns, and most preferably from about 0.5 to about 25 microns.
• the microfibers preferably have diameters of from about 1 nm to about 12 microns, more preferably from about 5 nanometers to 1 micron, and most preferably from about 5 namometers to about 100 nanometers.
• the microfibers have an average surface area ranging from about 25 to about 500 m 2 /gram. These dimensions, however, are only approximations.
• the use of the term "diameter” is not intended to indicate that the microfibers are required to be cylindrical in shape or circular in cross- section.
• the aspect ratio as used herein, thus refers to the ratio between the length (largest dimension) and the smallest dimension of the microfiber.
• microfibers may also be referred to as "nanofibers", which is an indication that in at least one dimension, the size of the fiber materials is on the order of nanometers.
• Microfibers particularly when in the form of a slurry or dispersion, may also be referred to as either "micropulp", or “nanopulp”.
• microfibers is used herein to refer to the processed fibers whether or not the fibers are contained in a slurry.
• micropowder(s) is used herein to refer to finely divided, easily dispersed powders or particles with an average diameter preferably ranging from about 0.01 to about 100 microns, more preferably from about 0.1 to about 50 microns, and most preferably from about 0.5 to about 25 microns.
• the micropowders typically comprise organic or inorganic material(s).
• the microfibers are produced from fiber starting material(s) and include, but are not limited to, organic and/or inorganic microfibers.
• the fiber starting material(s) include, but are not limited to organic and/or inorganic fibers.
• a pulp such as, for example, an aramid pulp, which is particularly useful as a starting material in making the microfibers, can be prepared by refining aramid fibers to fibrillate the short pieces of aramid fiber material.
• Such pulps have been reported to have a surface area in the range of 4.2 to 15 m 2 /g, and a Kajaani weight average length in the range of 0.6 to 1.1 millimeters (mm). Such pulps also have a high volume average length in comparison to micropulps.
• Merge 1F543 aramid pulp available from DuPont, Wilmington, Delaware has a Kajaani weight average length in the range of 0.6 to 0.8 mm, and, when laser diffraction is used to measure the pulp, a volume average length of about 0.5 to 0.6 mm.
• An alternate method of making aramid pulp directly from a polymerizing solution is disclosed in U.S. Patent No. 5,028,372.
• Short fiber (sometimes called floe) can be made by cutting a continuous filament into short lengths without significantly fibrillating the fiber.
• the short fiber typically ranges from about 0.25 mm to 12 mm in length.
• the reinforcing fibers disclosed in U.S. Patent No. 5,474,842 are suitable short fibers.
• Fibrids are non-granular film-like particles having an average maximum length in the range of 0.2 to 1 mm with a length-to-width aspect ratio in the range of 5:1 to 10:1.
• the thickness dimension is on the order of a fraction of a micron.
• Aramid fibrids are well known in the art and can be made in accordance with the processes disclosed in U.S. Patent Nos. 5,209,877; 5,026,456; 3,018,091 ; and 2,999,788.
• the processes typically include adding a solution of organic polymer in solvent to another liquid that is a non-solvent for the polymer but is miscible with the solvent, and applying vigorous agitation to cause the fibrids to coagulate.
• Organic microfibers can contain any organic material(s) contained in the organic fibers.
• the organic material(s) include, but are not limited to, synthetic polymers, such as aliphatic polyamides, polyesters, polyacrylonitriles, polyvinyl alcohols, polyolefins, polyvinyl chlorides, polyvinylidene chlorides, polyurethanes, polyfluorocarbons, phenolics, polybenzimidazoles, polyphenylenetriazoles, polyphenylene sulfides, polyoxadiazoles, polyimides, and/or aromatic polyamides; natural fibers, such as cellulose, cotton, silk, and/or wool fibers; and mixtures thereof.
• synthetic polymers such as aliphatic polyamides, polyesters, polyacrylonitriles, polyvinyl alcohols, polyolefins, polyvinyl chlorides, polyvinylidene chlorides, polyurethanes, polyfluorocarbons, phenolics, polybenzimidazoles, polyphenylenetriazoles, polyphenylene sulfides,
• the commercially available organic fibers that can be used include, but are not limited to, ZYLON® PBO-AS (poly(p-phenylene-2,6- benzobisoxazole)) fiber, ZYLON® PBO-HM (poly(p-phenylene-2,6- benzobisoxazole)) fiber, available from Toyobo (Japan), and DYNEEMA® SK60 and SK71 ultra high strength polyethylene fiber, available from DSM (Netherlands); Celanese VECTRAN® HS pulp and EFT 1063-178, which are both available from Engineering Fibers Technology, Shelton, Connecticut; CFF Fibrillated Acrylic Fiber, which is available from Sterling Fibers, Inc., Pace, Florida; and Tiara Aramid KY-400S Pulp, which is available from Daicel Chemical Industries, Ltd., Sakai City, Japan.
• the organic fibers are preferably made of aromatic polyamide polymers, especially poly(p-phenylene terephthalamide) and/or poly(m-phenylene isophthalamide), which are also known as aramid fibers.
• aromatic polyamide polymers especially poly(p-phenylene terephthalamide) and/or poly(m-phenylene isophthalamide), which are also known as aramid fibers.
• an "aramid” is a polyamide having amide (-CONH-) linkages of which at least 85% are attached directly to two aromatic rings.
• the organic fibers used to make the microfibers can also contain known additives.
• the aramid fibers can have one or more other polymeric materials blended with the aramid.
• the aramid fibers can contain up to about 10%, by weight, of other polymeric materials.
• copolymers of the aramid can have either as much as 10% of one or more other diamine substituted for the diamine of the aramid, or as much as 10% of other diacid chloride substituted for the diacid chloride of the aramid.
• Such organic fibers are disclosed in U.S. Patent Nos. 3,869,430, 3,869,429, 3,767,756, and 2,999,788.
• the aromatic polyamide organic fibers used in accordance with the present invention are commercially available as KEVLAR®; KEVLAR® aramid pulp (available as merge 1 F543 from DuPont, Wilmington, DE); 1.5 millimeter (mm) KEVLAR® aramid floe (available as merge 1 F561 from DuPont, Wilmington, DE); and NOMEX® aramid fibrids (available as merge F25W from DuPont, Wilmington, DE).
• Inorganic fibers include, but are not limited to, fibers made of alumina; glass fibers; carbon fibers; carbon nanotubes; silica carbide fibers; mineral fibers made of, for example, wollastonite (CaSiOs); and whiskers, which are single crystals of materials, such as, for example, silicon carbide, boron, and boron carbide, and are more fully described in Plastics Additives, 3rd, Gachter and Muller, Hanser Publishers, New York, 1990.
• the modifying monomer can be, for example, hexafluoropropylene (HFP), perfluoro(propyl vinyl) ether (PPVE), perfluorobutyl ethylene, chlorotrifluoroethylene, or another monomer that introduces side groups into the polymer molecule.
• concentration of such copolymerized modifiers in the polymer is usually less than 1 mole percent.
• the PTFE and modified PTFE resins that can be used in this invention include those derived from suspension polymerization, as well as, those derived from emulsion polymerization.
• micropowders suitable for use in accordance with the present invention are based on powdered organic polymers, pulverized minerals, and inorganic materials that are finely divided powders, or that have been reduced to finely divided powders by a grinding device(s).
• the variously available grinding devices include, but are not limited to, a hammer mill and/or a grinder. Acceptable grinding device(s) are well-known to a person of ordinary skill in the art.
• the micropowder is a fluoropolymer. More preferably, the micropowder is a TFE polymer. Most preferably, the micropowder is a PTFE powder, such as Zonyl® MP 1600 available from DuPont,
• microfiber and micropowder containing slurries can be produced by providing 1) an organic and/or inorganic fiber starting material that has not yet been reduced to microfibers, or 2) a microfiber containing slurry that contains organic and/or inorganic fibers that have already been reduced to microfibers.
• Microfibers can be made from the organic and/or inorganic fiber starting materials. Microfibers can be made in liquid media as disclosed herein, separated from liquid, and then used as needed.
• the amount of organic and/or inorganic fiber starting material(s) preferably ranges from about 0.01 to about 50 wt.%, based on total weight of the resulting slurry containing both microfiber and micropowder, more preferably from about 0.10 to about 25 wt.%, and most preferably from about 1 to about 10 wt.%.
• the organic and/or inorganic fiber starting material(s) can be combined with the micropowder and the liquid medium using conventional mixing and pumping equipment.
• the solid component is first placed in the agitation chamber of the agitating device and the premix is then added thereto.
• the order of addition is not critical.
• the liquid medium and solid component can be combined and added to the agitating device before the starting material(s) are added thereto or the starting material(s) and solid component can be combined and added to the agitating device before the liquid medium is added thereto.
• the solid component, liquid medium, and starting material(s) can be combined and then added to the agitating device.
• the agitating devices can be batch or continuously operated.
• Batch attritors are well known. Suitable attritors include Model Nos. 01 , 1-S, 10-S, 15-S, 30-S, 100-S and 200-S supplied by Union Process, Inc. of Akron, Ohio. Another supplier of such devices is Glen Mills Inc. of Clifton, New Jersey. Suitable media mills include the Supermill HM and EHP models supplied by Premier Mills of Reading, Pennsylvania.
• the agitation of the solid component is generally controlled by the tip speed of the stirring arms or disks and the number of stirring arms/disks provided.
• a typical media mill has 4 to 10 arms/disks and the tip speed of the stirring arms/disks generally ranges from about 1500 fpm to about 3500 fpm (about 457 meters/minute to about 1067 meters/ minute), and preferably from about 2000 fpm to about 3000 fpm (about 610 meters/minute to about 914 meters/minute).
• liquid media in which the fibers used in preparing the microfibers and/or the micropowders can be dispersed for preparing the microfiber slurry can be selected from aqueous and nonaqueous solvents; monomers; water; resins; polymers; carriers; polymer precursors; and blends and mixtures thereof.
• the size of the solid component generally varies from about 0.6 mm to about 25.4 mm in diameter.
• the diameter generally varies from about 0.1 to 3.0 mm, preferably from 0.2 to 2.0 mm.
• the diameter generally varies from about 3.2 mm to 76.2 mm preferably from 3.2 mm to 9.5 mm
• the solid component is generally chemically compatible with the liquid medium and is typically made of materials selected from: glass, alumina; zirconium oxide, zirconium silicate, cerium-stabilized zirconium oxide, yttrium-stabilized zirconium oxide, fused zirconia silica, steel, stainless steel, sand, tungsten carbide, silicon nitride, silicon carbide, agate, mullite, flint, vitrified silica, borane nitrate, ceramics, chrome steel, carbon steel, cast stainless steel, plastic resin, and combinations thereof.
• the plastic resins suitable for making the solid component include, but are not limited to, polystyrene; polycarbonate; and polyamide.
• Glass suitable for the solid component includes lead-free soda lime, borosilicate, and black glass. Zirconium silicate can be fused or sintered.
• the most useful solid components are balls made of carbon steel, stainless steel, tungsten carbide, or ceramic. If desired, a mixture of balls having either the same or different sizes and being made of either the same or different materials can be used.
• Ball diameter can range from about 0.1 mm to 76.2 mm and preferably from about 0.4 mm to 9.5 mm, more preferably from about 0.7 mm to 3.18 mm.
• Solid components are readily available from various sources, including, for example, Glenn Mills, Inc., Clifton, New Jersey; Fox Industries, Inc., Fairfield, New Jersey; and Union Process, Akron, Ohio.
• the micropowder can be added either as a dry powder, or as a micropowder containing slurry.
• the micropowder as a dry powder can either be combined with the organic and/or inorganic fiber starting material(s) before the fibers are reduced to microfibers, or can be combined with the microfiber slurry, which has already been produced from the organic and/or inorganic fiber starting material(s).
• the dry powder and liquid medium can then be combined with either the organic and/or inorganic fiber starting materials, or the already prepared microfiber containing slurry via conventional mixing and pumping equipment.
• the slurry preferably contains at least about 0.5 wt.% micropowder, based on total weight of the slurry.
• the micropowder slurry can contain up to about 50 wt.% micropowder, based on total weight of the slurry, wherein the practical upper limit of the amount of micropowder is determined by slurry viscosity and material handling capabilities. More preferably, the slurry contains at least about 1 wt.% micropowder, based on total weight of the slurry, and even more preferably at least about 2 wt.% micropowder.
• the slurry preferably contains about 25 wt.% or less micropowder, based on total weight of the slurry, more preferably about 20 wt.% or less micropowder, and even more preferably about 10 wt.% or less micropowder.
• the slurry contains from about 0.5 wt.% to about 50 wt.% micropowder, based on total weight of the slurry, preferably from about 1 wt.% to about 25 wt.%, even more preferably from about 1 wt.% to about 20 wt.%, and most preferably from about 1 to about 10 wt.%.
• the micropowder slurry can either be combined with the organic and/or inorganic fiber starting material(s) before the fibers are reduced to microfibers, or can be combined with the microfiber slurry, which has already been produced from the organic and/or inorganic fiber starting material(s).
• the micropowder slurry, liquid medium, and either the organic and/or inorganic fiber starting materials, or the already prepared microfiber containing slurry can be combined with conventional mixing and pumping equipment.
• the micropowder slurry is generally prepared by the same methods as described hereinabove for preparing a slurry containing microfibers. That is, in general the micropowder is contacted with a liquid medium and optional solid component followed by agitating the micropowder, liquid medium and optional solid component in a mill, such as a ball mill to substantially uniformly disperse the micropowder in the liquid medium.
• a person of ordinary skill in the art is familiar with other acceptable processes for preparing a micropowder slurry.
• the micropowder and liquid medium can first be combined to form a premix.
• the premix can be subsequently combined with the solid component and agitated in the agitating device (when the agitating device is an attritor).
• the premix can be subsequently fed to the agitating device already containing the solid component (when using a media mill). Regardless of the nature of the agitating device, after being agitated for an effective amount of time to produce a micropowder slurry containing micropowders having the desired size and uniform distribution, the solid component is removed.
• the slurry preferably contains about 15 wt.% or less microfibers and about 30 wt.% or less micropowder, based on total weight of the slurry; more preferably about 10 wt.% or less microfibers and about 25 wt.% or less micropowder; and even more preferably about 5 wt.% or less microfibers and 20 wt.% or less micropowder.
• the microfiber and micropowder containing slurry contains from about 0.01 to about 15 wt.% microfibers and from about 0.5 to about 50 wt.% micropowder, based on total weight of the slurry; preferably from about 0.2 to about 15 wt.% microfiber and from about 1 to about 30 wt.% micropowder; more preferably from about 0.2 to about 10 wt.% microfiber and from about 2 to about 25 wt.% micropowder; even more preferably from about 0.2 to about 5 wt.% microfiber and from about 2 to about 20 wt.% micropowder; and most preferably from about 0.2 to about 2.5 wt.% microfiber and from about 5 to about 20 wt.% micropowder.
• the micropowders and either the organic and/or inorganic fiber starting material(s), or the microfibers of the microfiber containing slurry will repeatedly come into contact with, and be masticated by, the optional solid component while being agitated.
• the solid component is preferably poured into the agitation chamber of the attritor.
• the fiber, micropowder, and liquid medium can then be added directly to the agitation chamber of the attritor without premixing any of the ingredients in the stirred tank mixer. Any of the ingredients, however, can be premixed in the stirred tank mixer prior to being added to the agitation chamber of the attritor.
• the solid component is maintained in an agitated state by, for example, the at least one stirring arm of the attritor.
• the fiber or microfiber, micropowder, and liquid medium are preferably premixed in the stirred tank mixer and then pumped into the agitation chamber of the media mill.
• the solid component Prior to pumping the premix into the agitation chamber, the solid component is added to the agitation chamber.
• the premix and solid component are subsequently agitated by at least one stirring arm/disk of the mill.
• the solid component is maintained in an agitated state by, for example, the at least one stirring arm of the mill.
• the fiber or microfiber size reduction in of the process of the present invention results from both longitudinal separation of the organic and/or inorganic fibers/microfibers into substantially smaller diameter fibers along with a reduction in the length of the fibers.
• fiber length and/or diameter reductions of one, two or even greater orders of magnitude can be attained with organic and/or inorganic fiber starting material(s).
• the agitating step is continued for an effective amount of time to produce a slurry containing substantially uniformly dispersed micropowders and microfibers having the desired sizes/lengths. It may be desirable, when using a mill, to incrementally produce the microfiber and micropowder containing slurry by repeatedly passing the liquid medium containing the microfibers, and at least one micropowder through the agitation device. When a mill is used, the time for which specific components are actually in the mill determines the size of the product. When the optional solid component is used, the surface of the microfiber is fully wetted and uniformly distributed/dispersed in the slurry with minimal agglomerations or clumps. Likewise, the at least one micropowder is uniformly distributed/dispersed in the slurry with minimal agglomerations or clumps.
• the rate at which the microfiber and micropowder containing slurry is produced can be accelerated by circulating the solid component during the agitating step through an external passage typically connected near the bottom and top of the chamber of the vertical media mill.
• the rate at which the solid component is agitated depends on the physical and chemical make-up of the starting material, the size and type of the solid component, the length of time available for producing an acceptable slurry, and the size of the microfibers desired.
• the solid component Upon obtaining a satisfactory microfiber and micropowder containing slurry, the solid component is normally removed from the slurry. Typically, the solid component remains in the agitation chamber. Some conventional separation processes, however, include a mesh screen that has openings small enough for the microfiber and micropowder containing slurry to pass through, while preventing the solid component from passing through. After removing the solid component, the microfiber and micropowder slurry can be used directly. Typically, the slurry will only contain negligible grit or seed that can be visually observed.
• microfiber and micropowder containing slurries can also contain conventional including, but not limited to, dyes, pigments, antioxidants, plasticizers, UV absorbers, stabilizers, rheology control agents, flow agents, metallic flakes, toughening agents, fillers, and carbon black.
• conventional additives used will of course depend on the intended use of the microfiber and micropowder containing slurry and the desired properties of the final product being produced therefrom. It is understood that one or more of these conventional additives can be added either during the premixing step, or before, during, or at the end of the agitating step.
• Comparative Example 1 A premix slurry containing micropowder was prepared by premixing adding ethylene glycol and 3% Teflon® PTFE micropowder (Zonyl® 1600N MP sold by DuPont, Wilmington, DE) to with a tank Cowles blade mixer supplied by Premier Mill, Inc., Reading, Pennsylvania.
• the Cowles blade mixer contained a high speed agitator that operated at a speed ranging from about 100 to about 1000 rpm.
• the weight percentages were based on the total weight of the slurry. A person of ordinary skill in the art knows how to determine the amount of micropowder to add to obtain the desired micropowder weight percentage.
• the premix was observed to be very lumpy, not homogeneous at all, and separated out of the ethylene glycol if not agitated.
• the PTFE micropowder was observed to-settling quickly to the bottom of the container.
• the premix was subsequently added to a Premier SML media mill (1.5L Supermill) supplied by Premier Mill, Inc., Reading, Pennsylvania. Prior to adding the premix, however, a sample of the premix was collected to measure the particle sizes of the PTFE micropowder contained in the premix. In addition, 1035 ml of 1.0 mm solid ceramic spherical media available under the tradename Mill Mates supplied by Premier Mill, Inc., Reading, Pennsylvania was added to the media mill before the premix was added. A Beckman Coulter LS200 particle size analyzer supplied by Beckman Coulter, Inc., Fullerton, California was used to analyze the size of the micropowder particles contained in the premix.
• the particle size of the micropowder for a given mill setup i.e. mill type, media type, processing speed, etc. was controlled by the residence time of the premix in the milling chamber of the media mill. Residence time is a function of free mill volume, total liquid batch size, and total run time.
• the mean particle size of the micropowder particles contained in the Teflon® micropowder slurry samples is set forth in Table A.
• a graph depicting the particle size distribution of the micropowder particles contained in the Teflon® micropowder slurry samples is set forth in Figure 1.
• a premix slurry containing micropowder and fiber was prepared by premixing ethylene glycol, 1.5% KEVLAR ® pulp 1 F543 sold by DuPont, Wilmington, Delaware and 1.5% Teflon® PTFE micropowder (Zonyl® 1600N MP sold by DuPont, Wilmington, DE) with a Cowles blade mixer supplied by Premier Mill, Inc., Reading, Pennsylvania.
• the Cowles blade mixer contained a high speed agitator that operated at a speed ranging from about 100 to about 1000 rpm. The weight percentages were based on the total weight of the slurry.
• the premix was subsequently added to a Premier SML media mill (1.5L Supermill) supplied by Premier Mill, Inc., Reading, Pennsylvania. the media mill had a 5 plastic disk set up and a 1.38 liter working capacity. Prior to adding the premix, 1035 ml of 1.0 mm solid ceramic spherical media available under the tradename Mill Mates supplied by Premier Mill, Inc., Reading, Pennsylvania was added to the mill so that the mill contained a 75% load of spherical media.
• the particle size of the micropowder for a given mill setup i.e. mill type, media type, processing speed, etc. was controlled by the residence time of the premix in the milling chamber of the media mill. Residence time is a function of free mill volume, total liquid batch size, and total run time.
• the Zonyl® 1600N micropowder used in producing the slurries of Comparative Example 1 and Example 1 had a beginning mean micropowder particle size of 12 microns.
• the data in Table A indicate that prior to being ground the micropowder contained in the Comparative Example 1 slurry apparently underwent a considerable amount of agglomeration upon being premixed with the ethylene glycol.
• the data of Table A further indicate that the agglomerated micropowder contained in the Comparative Example 1 slurry premix was reduced by subjecting the slurry premix to 8 hours of grinding.
• the resulting Comparative Example 1 micropowder slurry still contains particles with a mean particle size of 17 microns and agglomerates as large as 194 microns.
• the micropowders contained in the Comparative Example 1 slurries were observed to readily separate out of the ethylene glycol and settle to the bottom of the container.
• a titanium dioxide premix slurry was prepared by premixing 20 wt.% titanium dioxide micropowder (Ti-Pure R-706 sold by DuPont, Wilmington, Delaware) and 80 wt.% deionized water with a Cowles blade mixer supplied by Premier Mill, Inc., Reading, Pennsylvania.
• the Cowles blade mixer contained a high-speed agitator that operated at a speed ranging from about 100 to about 1000 rpm.
• the weight percentages were based on the total weight of the slurry.
• a person of ordinary skill in the art knows how to determine the amount of micropowder and deionized water to add to obtain the desired micropowder, and deionized water weight percentages.
• the premix was added to a Premier SML media mill (1.5L Supermill) supplied by Premier Mill, Inc., Reading, Pennsylvania. Prior to adding the premix, the mill was filled to 75 vol.% with 0.7-1.2 mm Ce- stabilized zirconia media. The tip speed of the mill was set to 731.5 meters per minute (2400 fpm). The premix was run in recirculation for 720 min with a throughput of 296 g/min. Throughout the run, seven 1L samples of slurry were collected in separate sample bottles, and placed on a flat surface to study the sedimentation behavior of the particles contained in the slurry. After 8 months, the sedimentation was quantified by the ratio of the distance from the bottom of the sample bottle to the top level of the settled solids divided by the distance from the bottom of the sample bottle to the liquid meniscus. The sedimentation findings are summarized in table B.

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