CA1087933A - Coated particles and conductive compositions therefrom - Google Patents
Coated particles and conductive compositions therefromInfo
- Publication number
- CA1087933A CA1087933A CA226,759A CA226759A CA1087933A CA 1087933 A CA1087933 A CA 1087933A CA 226759 A CA226759 A CA 226759A CA 1087933 A CA1087933 A CA 1087933A
- Authority
- CA
- Canada
- Prior art keywords
- particles
- polymer
- coated
- particle
- chamber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/24—Electrically-conducting paints
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
- B01J2/006—Coating of the granules without description of the process or the device by which the granules are obtained
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
- Y10T428/2993—Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
- Y10T428/2998—Coated including synthetic resin or polymer
Abstract
ABSTRACT
Process for coating small particles less than 20 microns in size, particularly carbon particles with a polymer which comprises injecting both the particles and the coating polymer into a fluid energy mill and utilising the turbulence in the fluid energy mill to achieve the desired coating.
Optionally the polymer can be dissolved in a solvent. The coated particles find many use, for example, as fillers in plastics.
Process for coating small particles less than 20 microns in size, particularly carbon particles with a polymer which comprises injecting both the particles and the coating polymer into a fluid energy mill and utilising the turbulence in the fluid energy mill to achieve the desired coating.
Optionally the polymer can be dissolved in a solvent. The coated particles find many use, for example, as fillers in plastics.
Description
7~33 ~ ~
Fine particles in the form o~ powder, 20 microns or less, are used as additives and fillers in a wide variety of compositions, for example polymeric and coating compositions.
The final properties of the dried or cured composition as well as the ease of dispersion and the amount of filler which may be incorporated into a particular composition are controlled in large measure by the surface propertles and particle size of the particular fillers employed. Many small particle size fillers, although possessing suitable properties ,~
for particular applications, cannot be used for those applica- - -tions because they are difficult to disperse, yield highly variable products, can only be incorporated into binders at low filler volume concentrations or upon storage in the case of coating compositions tend to settle and agglomerate rendering the coating compositions useless.
Treating of fine particles with chemicals, e.g., surface active agents, to afect the particles' surface properties is not always effective to overcome the above problems. For example, the treating of a filler with an ionic surface active agent to be used in an insulative composition may , adversely affect the electrical properties of the composition so it is no longer suitable as an insulation.
Thus, for many applications, it is desirable to alter the surface properties of a particle by coating or encapsulating it in a layer of another material, for example, a polymer. If properly coated, the encapsulated particle will exhibit the surface properties of the encapsulating - material, such properties often resulting in better wetting ~ properties, ease of dispersion and compatibility with the ; 30 binder of the polymer or coating composition. Also, for some applications, it is desirable to render the particles -- 2 -- ~ Sv ~IL10~7~33 readily dispersible in a particular binder, while the particles remain chemically incompatible with that binder.
By coating the surface of the particles with a specific polymer, the final properties of the composition into whiCh the particles are dispersed or blended can be controlled.
For example, in the formulation of conductive compositions, fine particle size carbons may be coated with high polymer whi~h permits the particles to be uniformly dispersed in a plastic, yet be of Cuch a nature as to be incompatible with that plastic. Thus upon annealing, the uniformly dispersed coated conductive particles will be free to reorganize within the plastic matrix so as to form a conductive path. On the other hand, if reinforcement without appreciable conductivity is desired, the polymeric coating should be one which renders the carbon particle both easily dispersible and compatible with the plastic. Such a coating will cause each individual particle to be completely encapsulated in the plastic matrix, with little agglomeration, resulting in particles completely insulated from one another and with maximum surface area in contact with the plastic for physical reinforcement.
Encapsulation of powders with polymer compositions has to date, generally been limited to large particle size materials, in the order of 50 microns or greater. See for example Fluid Flow Analysis by G. Sharpe, American Elsevier Pub. Co., Inc., `25 N.Y. 1967 at 370, Dryin~ of Solids in the Chemical Industry by G. Nonhebel and A. Moss, CRC Press, Cleveland, Ohio (N.D.
at 211, Unit Operations of Chemical En~ineering by W. McCabe and J.~Smith, McGraw-Hill Book Co., N.Y. tN.D. 2nd ed.) at 175, and, Principles of Unit Operations by a Foust et al, Dept. of Chem. Eng., Lehigh University, Bethlehem, Pa. (N.D.) ` at 480. Such particles may be encapsulated by fluidized bed -1~7~a33 coating techni~ues if the particles are of sufficient size to be held in Suspen9ion by an upward flowing gas to form a bed o~ gas-suspended discrete particles. The polymer coating is then atomized into the chamber, coating the particles. Such a process cannot be operated successfully with fine powders. These powders tend to pack together forming large agglomerates, and thus require an excessive gas flow to fluidize the agglomerates in the bed. The excessive gas flow will transport the fine particles out of the chamber.
Attempts have been made to overcome the difficulties with ~ine particles so they may be coated with low viscosity liquids in a fluidized bed. For example in u.S~ Patent 3,237,596, an enclosed fluidized bed apparatus is provided ; 15 which ejects the particles upward, under pressure, through - a nozzle so as to reduce agglomeration, at which time they are coated with an atomized liquid sprayed downward, after which the coated particles settle into the fluidized bed. ~-Fine particles carried away by the gas flow are caught in filters and recycled to the chamber. Such a technique, although suitable for coa ing low viscosity liquids onto particles, has been found impractical for coating by high molecular weight polymers. Another example of efforts to recycle the fine powder carried away by the gas stream is found in U.S. Patent 3,110,626. This apparatus is also unsuited for coating with high molecular weight polymers, for the reason that there is no means provided for frequent ;; high velocity impact of the particles.
In order to ensure that the final product will be only discrete, coated particles, we have found it necessary -to cycle the partid es so as to cause frequent high velocity impacts between particles and coating, a process which is `
_ 4 _ ,,~ . - , . .
'`.' . : ~
not possible by the fl~idlzed bed techni~ue. The repeated impacts are in contrast to other high velocity impact processes, For example, in U.S. Patent 3,009,826, dispersion and coating o~ agglomerated particles are accomplished by propelling a stream of liquid and solid at supersonic ~
velocities against a barrier causing the solid to disperse and be coated by the liquid. Although such a process propels the particles at high speeds, it ma~e no provision ~or recy-cling the particles, thereby relying on a "one-shot" impact lo for dispersion and coating. More important, such high velocity impact against a solid barrier is inapplicable for the aoating of high polymers onto particles. The high viscosities and low flow properties of high polymers make such a technique inapplicable since it is difficult or impossible to get a uniform coating in this manner and the polymer-particle mixture will tend to coalesce and agglomerate on impact with the barrier as opposed to separating as dry coated, discrete particles.
Other proposed methods for preparing polymer coated powders include pan-coating processes, as described in U.S.
Patent 3,711,319 and micro encapsulation, as generally described in U.S. Patent 2,800,457. These processes suffer from the similar disadvantage that they are inapplicable for the coating of finely divided particulate matter in the order of 20 microns or less.
A fluid energy mill as disclosed for example in U.S.
atent 3,491,954 provides the capability of impacting agglomerated particles and coating at supersonic speeds, ; continuously recycling the particles at these speeds to prevent reagglomeration and separating out only particles of fine particle size less than 20 microns. Such mills have in the past been used for the grinding, mixing or blending `
~0~37~333 of -fine particles. Also, by maintaining the mill at a temperature below the melt temperature of a polymeric material, such mills have been used ~or the grinding and blending of high polymer particles. However, it was previously thought that the coating of discrete particlès with a high polymer in such a mill was impossible since, unlike the grinding of polymeric materials, it was necessary to cause the polymer to melt and flow about each individual particle. It was believed that the polymer, upon melting, lo was so highly viscous that it would not coat each discrete particle but rather would cause reagglomeration of the particles with the viscous polymer especially when applied in appreciable quantities. This has been a problem in other prior art techniques, and it was thought that the particle-polymer agglomerate would quickly clog the mill and depositon the sides of the chamber. For this reason, the use of fluid energy mills to coat discrete particles has been limited to liquid or molten low molecular weight materials, used in sufficiently small quantities that they would not cause reagglomeration or coalescence upon the walls of the chamber. Previously, use of a fluid energy mill to coat free-flowing powders has been limited to coating with such compositions as fatty acids, other surface active agents or waxy materials. An apparatus particularly suited for coating particles with low molecular weight materials is discussed in U.S. Patent 3,550,868.
We have now discovered that an apparatus which circulates particles at about supersonic speeds may be used ' to coat polymers on small discrete particles, which was not previously thought to be possible.
One application for finely divided coated particulate .
., -~;
~0~ 33 material in which non-coated particles suffer from all the problems previou,sly dis~u8~ed, including dif~icul~y o~
dispersion, agglomeration, and storaye stability, involves compositions containing carbon blacks. Carbon particles are usually very fine e.g., sub-micron in diameter. Carbon particl~s have found wide application in the formulation of conductive compositions in which they are incorporated at high concentrations into a non-conductive binder to render the composition conductive. Such carbon particles generally lo have high oil absorption characteristics, are different to disperse, and readily agglomerate and settle if dispersed in a fluid binder. On account of these characteristics, the amount of carbon which may be dispersed in a particular formulation is generally limited, which in turn limits the conductivity which can be obtained for such coatings. In addition, since many of the carbon or other conductive particles are inadequately dispersed, or agglomerate on ` standing, the conductivity of the final coating is highly variable and irreproducible. Thu~, it is apparent that there is a need for conductive particles which can impart predict-able and constant electrical properties to a composition - comprising the particles and a binder in which they are dispersed.
As previously discussed, in order to achieve conductive compositions with predictable and constant electrical properties, particles with very specific surface characteris-tics should be utilized. Generally, the particles should be readily dispersible in the binder to result in a uniform ~ composition yet be sufficiently :.
':
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7~33 agglomerated to provide a uniform conductive path throughout the composition.
The present invention provides a process of coating particles, comprising injecting the particles to be coated and a high polymer into a fluid energy mill, the mill dispersing, impacting, suspending and thereby coating the particles and optionally drying the coated particles if a solvent has been used, using a fluid stream ~hat is injected into the mill under pressure and at an elevated temperature. The fluid stream causes the part-icles to be dispersed and the high polymer to flow and fuse onto the dispersed particles when they impact on one another, after which the particles may be dried if a solvent has been employed, and ultimately separated out of the mill as free-flowing particulate matter.
In the case of finely divided conductive carbons, the particles so coated may be readily dispersed into a conductive composition at higher levels than was heretofore believed possible.
The present invention accordingly provides a process for coating ~-discrete particles of less than 20 microns with a high polymer coating com-prising:
injecting the polymer and particles into a chamber comprising a closed arcuate path having an outlet injecting a fluid stream into the chamber under pressure and at an elevated temperature, said fluid propelling the polymer and particles at high velocities along the path in which path said polymer and said particles undergo repeated high velocity impacts with each other thereby coating said particles with said polymer and wherein discrete particles having the polymer coating thereon are separated out of the chamber through the outlet, but agglomerated particles of greater than 20 microns are recycled around the arcuate path, coated particles produced thereby, and compositions comprising them.
In order to coat finely divided particles of less than 20 microns with high polymers, a fluid energy mill, for example one ., .
_7_ - ' ' - . . , - . . .:
.. ..
manufactured by ~luid Energy Processing and Equipment Company, Lansdale, Pa. U.S.A. is employed. Using such a mill, a high polymer ls coated onto fine particulate matter, after which it is suspended, dried (if solvent is present) and separated from the mill to yield free-flowing coated particles. By hlgh polymer is meant a material having thermoplastic properties and of sufficient molecular weight as to yield a self-supporting film having a tensile strength and Young's modulus of at least about 80% of that which obtained in the nolecular weight range where such physical properties become substantially independent of molecular weight for that particular polymer.
The molecular weight and melt viscosity will of course vary with the particular polymer utilized, but for any material, the molecular weight should in general be suff-icient to form a self-supporting film. Thus, in the case of polyethylene, molecular weights of the order of at least 6,000 or higher are preferred for use in this invention.
i ` The quantity of high polymer which can be coated onto a particulate solid by one or more of the following , procedures may be remarkably high~ The percentage of final powder product which is the coating polymer may range for e~ample from less than 1 to greater than 50% by weight.
The figure is a section through a fluid energy mill, andillustrates a process carried out in accordance with the ; invention.
Turning now to the figure, a cross-section of a fluid energy mill is shown A high polymer in a suitable ~ form and the particles to be coated are fed into a hopper ¦ 30 2 from which they are drawn into a coating chamber 6 via a ' venturi ~eeder 4. The particles and polymer may be fed into `:
i .
~7~33 the same feeder, as ghown, or may be injected via ~eparate inlets. Also, it will be understood that the coating polymer may be fed into the chamber in any suitable form, for example as a solven-t solution, a finely divided pow~er, or a gel. The choice of form will generally depend on such factors as the polymer's solubility, melting point, molecular weight, crystallization tenden-' .
- 8a -,~ .
~: ' ' , .
cies, melt and solution viscosities. Thc various suitable polymer forms will be further discussed below.
A fluid stream is fed into the chamber 6 through nozzles 10, the nozzles being so configured to cause the fluid to flow tangentially around the arcuate chamber. The fluid is preferably fed at elevated temperature and pressure and entrains the polymer and particles. The polymer and part-icles, at the lower portion of the chamber 6, are caused to collide so as to disperse the agglomerated particles and coat the polymer onto the particles.
The preferred carrier gas is steam which is injected through the nozzles at 0.21 to 5.6 kg/cm2 at a temperature of 125C to 400C. The particles are then carried by the fluid along the chamber in an arcuate path, generally designated 12, with the finely dispersed coated particles settling to the interior and the agglomerated particles being forced to the exterior of the chamber. The particles settling to the interior of the chamber flow through i an outlet 14, after which they pass through an opening defined by member 16, and through outlet 18. Particles that do not pass through the opening de-fined by member 16 and particles that have been forced to the outer regions of the chamber are returned via path 20 to coating chamber 6 for further dispersion, coating and recycling.
One suitable physical form for the polymer is a solution in an appropriate solvent. The polymer solution may be either preblended with the particles to be coated after which it is introduced into the mill, or the particles and the solution may be fed into the mill through separate inlets, the rate of feed of both materials being metered to control the quantity of the final particle coating. The solvent should desirably be immiscible with the fluid carrier in the mill. For example, where the fluid carrier gas is steam, non-polar organic polymer solvents, for example xylene, are commonly used. For the most efficient operation, solutions of high solids content but low viscosity are preferred. Minimizing the amount of solvent in the-solution minimizes heat loss upon drying in the mill.
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,, . .,,, , . ,: . . ,,. .. , : . .
Lower viscosity solutions also allow for easier metering and pumping if the coating solution is injected via a ; separate inlet.
; Where the particulate powder and the polymer solution are preblended, the amount of particular powder should be sufficient to give a dry or damp crumb-like consistency. If lesser amounts of powder yielding wet, thick slurries are used poor feeding and plugging of the inlet may result. As a consequence, the amount of coating polymer applied by using the preblending technique is limited. The amount of particles which can be incorporated into the preblend will vary depending on the particles themselves.
Another suitable form for the polymer is as a gel ; 15 in an appropriate solvent. The~polymer gel finely divided form is preblended with the particle-to be coated, and then the mixture is fed into the mill. Because the polymer solution is in a gelled form, bigher loadings of polymer , are possible than if a solution were used. This technique is suitable for those polymers which dissolve in certain solvents when hot but form gels when cool. Polyethylene and ethylene copolymers are especially suited to this appIication. ~he concentration of the polymer in the gel is governed by the character of the gel at room temperature, 25 as well as the hot solution viscosity. To be most useful, the cool gel must be friable, so that it may be broken up for preblending with the particulate powder. In practice, ~ it has been found that low density polyethylene and ethylene copolymers work well at about 20% polymer concentration.
30 High density and higher molecular weight polyethylenes -~
require a lowering of the solids content to the 10 to 15%
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.'' .' '`'' '"''-" ' ' ' 7~333 range.
Greater amounts of polymer can be applied when preblends are prepared using polymer gels rather than polymer solutions. The gel effectively holds the solvent and reduces its wetting capacity for the particulate powder. Nevertheless, the amount of polyrner which can be applied by the polymer ~el preb~end technique is also limited. Coarser particles, i.e. 1 to 20 ~m in diameter, can hold in general up to 100% by weight of polymer gel.
~n the case of very fine particles, as may be found when using carbon or hydrated silica gels, the particulate powders can accept 200% by weight or more of a 20% polyethylene gel in xyle~e and remain relatively dry.
Another suitable form for -the polymer is a dry polymer powder. The dry polymer powder may be blended with the particle to be coated, or alternatively, may be fed into the fluid energy mill by separate inlets.
When the particles to be coated and the coating polymer are preblended, it is irnportant that they be uniformly mixed so as to attain a uniform and finely divided blend of materials. A Patterson-Kelly Liquid-Solids Blender is suitable for this purpose.
When the polymer has been fed into the fluid energy mill as a solution or polymer gel, the temperature of the fluid should be sufficient to cause the gel to melt and the solvent to evaporate after being coated upon a dispersed particle. Although the invention is not to be limited in any way by the following theory, the process is believed to involve the following sequence: 1) melting of the gel particles (i~ present), 2) collision of the molten gel or the solution with the particle, 3) flow of the molten polymer material around the particle, ~) drying of the solvent.
Where the polymer is fed in as a dry powder, the fluid temperature should be sufficient to cause the polymer to melt and flow around the dispersed particles. Generally, in order to be fed in as a dry polymer, the polymer should have a melting point in the range of 50-200C, a melt index of from 5-100 in the case of polyethylene, and have a particle size of from 1-500 microns. Pulverized polyethylene and ethylene copolymers have been found to function well in this process.
Although any polymer capable of forming a self-supporting film may be used in accordance with this invention, polymers such as polyethylene, copolymers of ethylene, polypropylene, ethylene-propylene copolymers, other poly-olefins, polyviny:lldene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, various fluorine-containing copolymers (e.g. copolymers of tetrafluoro-ethylene and : hexafluoropropylene), polyvinyl chloride, copolymers of vinyl chloride, polyvinylidene chloride, silicones, poly-acryIates, polymethacrylates, polyamides, polyesters, polyimides, polycarbonates, polyethers, polyketones, phen-olic resins, polyisobutylene, polystyrene, styrene copolymers, polyvinyl acetate, vinyl acetate copolymers, polysulfones, polyacrylonitrile, polyoxymethylene, poly-urethanes, polyamines, polybutadiene, butadiene copolymers, polyisoprene, and neoprene are particularly suitable. ~.
Any fine particulate material may be coated by this process, although particularly suited for coating are carbon blacks, graphite, fine clays, talc, ground limestone, aluminum oxide, hydrated aluminum oxide, silicas, hydrated :. .:, , . ' ~ . .
, . : ..
silica gels and iron oxide. Al~o, fine organic powders used in the formulation of coatings and pla9tics may also be coated by thi~ process.
0~ particular interest i9 the coating of halogenated ~organic materials useful as flame retardents in coating and plastic formulations.
Especially suitable are compounds of the formula X ~ ~X6,.
~ N-R-N
X3~ ~ X7 x4 ~8 in which Xl to X8, which may be the same or different, are hydrogen, fluorine, chlorine, bromine, or iodine, and wherein at least one of Xl to X4 and also at least one of X5 to X8 is chlorine or bromine and wherein R is Cl to C20 alkylene, C6 to C20 cycloalkylene, C6 to C20 arylene or halogen substituted arylene, alkyl substituted arylene or fused ring arylene, or the moiety Rl-Z-R2 wherein Rl and R2, which 15'~ can be the same or different, are Cl to C20 alkylene, C6 to C20 cycloalkylene; C6 to C20 arylene, halogen substituted arylene, alkyl substituted arylene, or fused ring arylene, -~
and wherein Z iq sulfur, oxygen, isopropylidene, or a chemical bond joining Rl and R2.
Also of particular interest is the coating of conductive particles so that they are free-flowing and readily dispers-able into a binder. Such results may be obtained by this process yet, surprisingly, the coating is such that it has little effect on the conductive properties of the particles.
Although the exact nature of the coated particle is not known, it is believed that the polymer coating is sufficiently thin as not to affect the conductive properties of the particles yet sufficient to alter the surface characteris-.
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33~
tics of the particle. Alternatively, the coated particle may have a su~ficient number of uncoated areas as not to insulate the coated particle. Finally, the polymer coating and the binder into which it is dispersed should be incompatible enough to permit a sufficient amount of agglomeration of the conduc~ive particle so a conductive path is formed, if conductivity with relatively low levels of carbon is desired.
The following examples illustrate the invention:
Example 1 Carbon black, i.e. 1.7 kg of "Vulcan XC-72P"* (Cabot Corp., average particle size .03 ~n was blended with 0.227 kg of 20 % polyvinylidene fluoride (Kynar, a trademark of Pennwalt Corp) in DMF solution in a 15 litre, Patterson-Kelley "V" Type Blender until a uniform consistency was achieved. This mixture was fed through a fluid energy mill having a 288C inlet temperature 243C outlet temperature, and 5.25 kg/cm2 inlet steam pressure at a rate equal to 24.4 kg/hr. The resulting product was an extremely fine, uniform black powder, indistinguishable in appearance from the carbon starting materials. The surface properties were markedly changed, however. Using 4 % of a sodium naphthalene sulfonate wetting agent, it was possible to make a 30 % solids carbon black concentrate in water which wa9 an easily pourable fluid. In comparison, the uncoated control was stiff and completely non-fluid at this concentration.
Example II
A 25% concentration of carbon slurry made as in Example 1 was blended with the following binder composition:
* denotes a Trademark.
parts by welght 50 % solids acrylic emulsion 59 (AC61*from Rohm & Haas) Colloidal silica (40 % solids in water 200 Clay 34 Deionized water 142 Conductive elements were made with various blends of carbon slurry and binder composition generally in accordance with the method of U.S. Patent No. 3,399,451.
Resistance varied as follows:
Table I
Ratio by weight of binderResistance in - :
composition to carbon slurry ohms/s~uare :: .
1:1 260
Fine particles in the form o~ powder, 20 microns or less, are used as additives and fillers in a wide variety of compositions, for example polymeric and coating compositions.
The final properties of the dried or cured composition as well as the ease of dispersion and the amount of filler which may be incorporated into a particular composition are controlled in large measure by the surface propertles and particle size of the particular fillers employed. Many small particle size fillers, although possessing suitable properties ,~
for particular applications, cannot be used for those applica- - -tions because they are difficult to disperse, yield highly variable products, can only be incorporated into binders at low filler volume concentrations or upon storage in the case of coating compositions tend to settle and agglomerate rendering the coating compositions useless.
Treating of fine particles with chemicals, e.g., surface active agents, to afect the particles' surface properties is not always effective to overcome the above problems. For example, the treating of a filler with an ionic surface active agent to be used in an insulative composition may , adversely affect the electrical properties of the composition so it is no longer suitable as an insulation.
Thus, for many applications, it is desirable to alter the surface properties of a particle by coating or encapsulating it in a layer of another material, for example, a polymer. If properly coated, the encapsulated particle will exhibit the surface properties of the encapsulating - material, such properties often resulting in better wetting ~ properties, ease of dispersion and compatibility with the ; 30 binder of the polymer or coating composition. Also, for some applications, it is desirable to render the particles -- 2 -- ~ Sv ~IL10~7~33 readily dispersible in a particular binder, while the particles remain chemically incompatible with that binder.
By coating the surface of the particles with a specific polymer, the final properties of the composition into whiCh the particles are dispersed or blended can be controlled.
For example, in the formulation of conductive compositions, fine particle size carbons may be coated with high polymer whi~h permits the particles to be uniformly dispersed in a plastic, yet be of Cuch a nature as to be incompatible with that plastic. Thus upon annealing, the uniformly dispersed coated conductive particles will be free to reorganize within the plastic matrix so as to form a conductive path. On the other hand, if reinforcement without appreciable conductivity is desired, the polymeric coating should be one which renders the carbon particle both easily dispersible and compatible with the plastic. Such a coating will cause each individual particle to be completely encapsulated in the plastic matrix, with little agglomeration, resulting in particles completely insulated from one another and with maximum surface area in contact with the plastic for physical reinforcement.
Encapsulation of powders with polymer compositions has to date, generally been limited to large particle size materials, in the order of 50 microns or greater. See for example Fluid Flow Analysis by G. Sharpe, American Elsevier Pub. Co., Inc., `25 N.Y. 1967 at 370, Dryin~ of Solids in the Chemical Industry by G. Nonhebel and A. Moss, CRC Press, Cleveland, Ohio (N.D.
at 211, Unit Operations of Chemical En~ineering by W. McCabe and J.~Smith, McGraw-Hill Book Co., N.Y. tN.D. 2nd ed.) at 175, and, Principles of Unit Operations by a Foust et al, Dept. of Chem. Eng., Lehigh University, Bethlehem, Pa. (N.D.) ` at 480. Such particles may be encapsulated by fluidized bed -1~7~a33 coating techni~ues if the particles are of sufficient size to be held in Suspen9ion by an upward flowing gas to form a bed o~ gas-suspended discrete particles. The polymer coating is then atomized into the chamber, coating the particles. Such a process cannot be operated successfully with fine powders. These powders tend to pack together forming large agglomerates, and thus require an excessive gas flow to fluidize the agglomerates in the bed. The excessive gas flow will transport the fine particles out of the chamber.
Attempts have been made to overcome the difficulties with ~ine particles so they may be coated with low viscosity liquids in a fluidized bed. For example in u.S~ Patent 3,237,596, an enclosed fluidized bed apparatus is provided ; 15 which ejects the particles upward, under pressure, through - a nozzle so as to reduce agglomeration, at which time they are coated with an atomized liquid sprayed downward, after which the coated particles settle into the fluidized bed. ~-Fine particles carried away by the gas flow are caught in filters and recycled to the chamber. Such a technique, although suitable for coa ing low viscosity liquids onto particles, has been found impractical for coating by high molecular weight polymers. Another example of efforts to recycle the fine powder carried away by the gas stream is found in U.S. Patent 3,110,626. This apparatus is also unsuited for coating with high molecular weight polymers, for the reason that there is no means provided for frequent ;; high velocity impact of the particles.
In order to ensure that the final product will be only discrete, coated particles, we have found it necessary -to cycle the partid es so as to cause frequent high velocity impacts between particles and coating, a process which is `
_ 4 _ ,,~ . - , . .
'`.' . : ~
not possible by the fl~idlzed bed techni~ue. The repeated impacts are in contrast to other high velocity impact processes, For example, in U.S. Patent 3,009,826, dispersion and coating o~ agglomerated particles are accomplished by propelling a stream of liquid and solid at supersonic ~
velocities against a barrier causing the solid to disperse and be coated by the liquid. Although such a process propels the particles at high speeds, it ma~e no provision ~or recy-cling the particles, thereby relying on a "one-shot" impact lo for dispersion and coating. More important, such high velocity impact against a solid barrier is inapplicable for the aoating of high polymers onto particles. The high viscosities and low flow properties of high polymers make such a technique inapplicable since it is difficult or impossible to get a uniform coating in this manner and the polymer-particle mixture will tend to coalesce and agglomerate on impact with the barrier as opposed to separating as dry coated, discrete particles.
Other proposed methods for preparing polymer coated powders include pan-coating processes, as described in U.S.
Patent 3,711,319 and micro encapsulation, as generally described in U.S. Patent 2,800,457. These processes suffer from the similar disadvantage that they are inapplicable for the coating of finely divided particulate matter in the order of 20 microns or less.
A fluid energy mill as disclosed for example in U.S.
atent 3,491,954 provides the capability of impacting agglomerated particles and coating at supersonic speeds, ; continuously recycling the particles at these speeds to prevent reagglomeration and separating out only particles of fine particle size less than 20 microns. Such mills have in the past been used for the grinding, mixing or blending `
~0~37~333 of -fine particles. Also, by maintaining the mill at a temperature below the melt temperature of a polymeric material, such mills have been used ~or the grinding and blending of high polymer particles. However, it was previously thought that the coating of discrete particlès with a high polymer in such a mill was impossible since, unlike the grinding of polymeric materials, it was necessary to cause the polymer to melt and flow about each individual particle. It was believed that the polymer, upon melting, lo was so highly viscous that it would not coat each discrete particle but rather would cause reagglomeration of the particles with the viscous polymer especially when applied in appreciable quantities. This has been a problem in other prior art techniques, and it was thought that the particle-polymer agglomerate would quickly clog the mill and depositon the sides of the chamber. For this reason, the use of fluid energy mills to coat discrete particles has been limited to liquid or molten low molecular weight materials, used in sufficiently small quantities that they would not cause reagglomeration or coalescence upon the walls of the chamber. Previously, use of a fluid energy mill to coat free-flowing powders has been limited to coating with such compositions as fatty acids, other surface active agents or waxy materials. An apparatus particularly suited for coating particles with low molecular weight materials is discussed in U.S. Patent 3,550,868.
We have now discovered that an apparatus which circulates particles at about supersonic speeds may be used ' to coat polymers on small discrete particles, which was not previously thought to be possible.
One application for finely divided coated particulate .
., -~;
~0~ 33 material in which non-coated particles suffer from all the problems previou,sly dis~u8~ed, including dif~icul~y o~
dispersion, agglomeration, and storaye stability, involves compositions containing carbon blacks. Carbon particles are usually very fine e.g., sub-micron in diameter. Carbon particl~s have found wide application in the formulation of conductive compositions in which they are incorporated at high concentrations into a non-conductive binder to render the composition conductive. Such carbon particles generally lo have high oil absorption characteristics, are different to disperse, and readily agglomerate and settle if dispersed in a fluid binder. On account of these characteristics, the amount of carbon which may be dispersed in a particular formulation is generally limited, which in turn limits the conductivity which can be obtained for such coatings. In addition, since many of the carbon or other conductive particles are inadequately dispersed, or agglomerate on ` standing, the conductivity of the final coating is highly variable and irreproducible. Thu~, it is apparent that there is a need for conductive particles which can impart predict-able and constant electrical properties to a composition - comprising the particles and a binder in which they are dispersed.
As previously discussed, in order to achieve conductive compositions with predictable and constant electrical properties, particles with very specific surface characteris-tics should be utilized. Generally, the particles should be readily dispersible in the binder to result in a uniform ~ composition yet be sufficiently :.
':
. .
7~33 agglomerated to provide a uniform conductive path throughout the composition.
The present invention provides a process of coating particles, comprising injecting the particles to be coated and a high polymer into a fluid energy mill, the mill dispersing, impacting, suspending and thereby coating the particles and optionally drying the coated particles if a solvent has been used, using a fluid stream ~hat is injected into the mill under pressure and at an elevated temperature. The fluid stream causes the part-icles to be dispersed and the high polymer to flow and fuse onto the dispersed particles when they impact on one another, after which the particles may be dried if a solvent has been employed, and ultimately separated out of the mill as free-flowing particulate matter.
In the case of finely divided conductive carbons, the particles so coated may be readily dispersed into a conductive composition at higher levels than was heretofore believed possible.
The present invention accordingly provides a process for coating ~-discrete particles of less than 20 microns with a high polymer coating com-prising:
injecting the polymer and particles into a chamber comprising a closed arcuate path having an outlet injecting a fluid stream into the chamber under pressure and at an elevated temperature, said fluid propelling the polymer and particles at high velocities along the path in which path said polymer and said particles undergo repeated high velocity impacts with each other thereby coating said particles with said polymer and wherein discrete particles having the polymer coating thereon are separated out of the chamber through the outlet, but agglomerated particles of greater than 20 microns are recycled around the arcuate path, coated particles produced thereby, and compositions comprising them.
In order to coat finely divided particles of less than 20 microns with high polymers, a fluid energy mill, for example one ., .
_7_ - ' ' - . . , - . . .:
.. ..
manufactured by ~luid Energy Processing and Equipment Company, Lansdale, Pa. U.S.A. is employed. Using such a mill, a high polymer ls coated onto fine particulate matter, after which it is suspended, dried (if solvent is present) and separated from the mill to yield free-flowing coated particles. By hlgh polymer is meant a material having thermoplastic properties and of sufficient molecular weight as to yield a self-supporting film having a tensile strength and Young's modulus of at least about 80% of that which obtained in the nolecular weight range where such physical properties become substantially independent of molecular weight for that particular polymer.
The molecular weight and melt viscosity will of course vary with the particular polymer utilized, but for any material, the molecular weight should in general be suff-icient to form a self-supporting film. Thus, in the case of polyethylene, molecular weights of the order of at least 6,000 or higher are preferred for use in this invention.
i ` The quantity of high polymer which can be coated onto a particulate solid by one or more of the following , procedures may be remarkably high~ The percentage of final powder product which is the coating polymer may range for e~ample from less than 1 to greater than 50% by weight.
The figure is a section through a fluid energy mill, andillustrates a process carried out in accordance with the ; invention.
Turning now to the figure, a cross-section of a fluid energy mill is shown A high polymer in a suitable ~ form and the particles to be coated are fed into a hopper ¦ 30 2 from which they are drawn into a coating chamber 6 via a ' venturi ~eeder 4. The particles and polymer may be fed into `:
i .
~7~33 the same feeder, as ghown, or may be injected via ~eparate inlets. Also, it will be understood that the coating polymer may be fed into the chamber in any suitable form, for example as a solven-t solution, a finely divided pow~er, or a gel. The choice of form will generally depend on such factors as the polymer's solubility, melting point, molecular weight, crystallization tenden-' .
- 8a -,~ .
~: ' ' , .
cies, melt and solution viscosities. Thc various suitable polymer forms will be further discussed below.
A fluid stream is fed into the chamber 6 through nozzles 10, the nozzles being so configured to cause the fluid to flow tangentially around the arcuate chamber. The fluid is preferably fed at elevated temperature and pressure and entrains the polymer and particles. The polymer and part-icles, at the lower portion of the chamber 6, are caused to collide so as to disperse the agglomerated particles and coat the polymer onto the particles.
The preferred carrier gas is steam which is injected through the nozzles at 0.21 to 5.6 kg/cm2 at a temperature of 125C to 400C. The particles are then carried by the fluid along the chamber in an arcuate path, generally designated 12, with the finely dispersed coated particles settling to the interior and the agglomerated particles being forced to the exterior of the chamber. The particles settling to the interior of the chamber flow through i an outlet 14, after which they pass through an opening defined by member 16, and through outlet 18. Particles that do not pass through the opening de-fined by member 16 and particles that have been forced to the outer regions of the chamber are returned via path 20 to coating chamber 6 for further dispersion, coating and recycling.
One suitable physical form for the polymer is a solution in an appropriate solvent. The polymer solution may be either preblended with the particles to be coated after which it is introduced into the mill, or the particles and the solution may be fed into the mill through separate inlets, the rate of feed of both materials being metered to control the quantity of the final particle coating. The solvent should desirably be immiscible with the fluid carrier in the mill. For example, where the fluid carrier gas is steam, non-polar organic polymer solvents, for example xylene, are commonly used. For the most efficient operation, solutions of high solids content but low viscosity are preferred. Minimizing the amount of solvent in the-solution minimizes heat loss upon drying in the mill.
_g ~
,, . .,,, , . ,: . . ,,. .. , : . .
Lower viscosity solutions also allow for easier metering and pumping if the coating solution is injected via a ; separate inlet.
; Where the particulate powder and the polymer solution are preblended, the amount of particular powder should be sufficient to give a dry or damp crumb-like consistency. If lesser amounts of powder yielding wet, thick slurries are used poor feeding and plugging of the inlet may result. As a consequence, the amount of coating polymer applied by using the preblending technique is limited. The amount of particles which can be incorporated into the preblend will vary depending on the particles themselves.
Another suitable form for the polymer is as a gel ; 15 in an appropriate solvent. The~polymer gel finely divided form is preblended with the particle-to be coated, and then the mixture is fed into the mill. Because the polymer solution is in a gelled form, bigher loadings of polymer , are possible than if a solution were used. This technique is suitable for those polymers which dissolve in certain solvents when hot but form gels when cool. Polyethylene and ethylene copolymers are especially suited to this appIication. ~he concentration of the polymer in the gel is governed by the character of the gel at room temperature, 25 as well as the hot solution viscosity. To be most useful, the cool gel must be friable, so that it may be broken up for preblending with the particulate powder. In practice, ~ it has been found that low density polyethylene and ethylene copolymers work well at about 20% polymer concentration.
30 High density and higher molecular weight polyethylenes -~
require a lowering of the solids content to the 10 to 15%
~ ~ .
. .
.'' .' '`'' '"''-" ' ' ' 7~333 range.
Greater amounts of polymer can be applied when preblends are prepared using polymer gels rather than polymer solutions. The gel effectively holds the solvent and reduces its wetting capacity for the particulate powder. Nevertheless, the amount of polyrner which can be applied by the polymer ~el preb~end technique is also limited. Coarser particles, i.e. 1 to 20 ~m in diameter, can hold in general up to 100% by weight of polymer gel.
~n the case of very fine particles, as may be found when using carbon or hydrated silica gels, the particulate powders can accept 200% by weight or more of a 20% polyethylene gel in xyle~e and remain relatively dry.
Another suitable form for -the polymer is a dry polymer powder. The dry polymer powder may be blended with the particle to be coated, or alternatively, may be fed into the fluid energy mill by separate inlets.
When the particles to be coated and the coating polymer are preblended, it is irnportant that they be uniformly mixed so as to attain a uniform and finely divided blend of materials. A Patterson-Kelly Liquid-Solids Blender is suitable for this purpose.
When the polymer has been fed into the fluid energy mill as a solution or polymer gel, the temperature of the fluid should be sufficient to cause the gel to melt and the solvent to evaporate after being coated upon a dispersed particle. Although the invention is not to be limited in any way by the following theory, the process is believed to involve the following sequence: 1) melting of the gel particles (i~ present), 2) collision of the molten gel or the solution with the particle, 3) flow of the molten polymer material around the particle, ~) drying of the solvent.
Where the polymer is fed in as a dry powder, the fluid temperature should be sufficient to cause the polymer to melt and flow around the dispersed particles. Generally, in order to be fed in as a dry polymer, the polymer should have a melting point in the range of 50-200C, a melt index of from 5-100 in the case of polyethylene, and have a particle size of from 1-500 microns. Pulverized polyethylene and ethylene copolymers have been found to function well in this process.
Although any polymer capable of forming a self-supporting film may be used in accordance with this invention, polymers such as polyethylene, copolymers of ethylene, polypropylene, ethylene-propylene copolymers, other poly-olefins, polyviny:lldene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, various fluorine-containing copolymers (e.g. copolymers of tetrafluoro-ethylene and : hexafluoropropylene), polyvinyl chloride, copolymers of vinyl chloride, polyvinylidene chloride, silicones, poly-acryIates, polymethacrylates, polyamides, polyesters, polyimides, polycarbonates, polyethers, polyketones, phen-olic resins, polyisobutylene, polystyrene, styrene copolymers, polyvinyl acetate, vinyl acetate copolymers, polysulfones, polyacrylonitrile, polyoxymethylene, poly-urethanes, polyamines, polybutadiene, butadiene copolymers, polyisoprene, and neoprene are particularly suitable. ~.
Any fine particulate material may be coated by this process, although particularly suited for coating are carbon blacks, graphite, fine clays, talc, ground limestone, aluminum oxide, hydrated aluminum oxide, silicas, hydrated :. .:, , . ' ~ . .
, . : ..
silica gels and iron oxide. Al~o, fine organic powders used in the formulation of coatings and pla9tics may also be coated by thi~ process.
0~ particular interest i9 the coating of halogenated ~organic materials useful as flame retardents in coating and plastic formulations.
Especially suitable are compounds of the formula X ~ ~X6,.
~ N-R-N
X3~ ~ X7 x4 ~8 in which Xl to X8, which may be the same or different, are hydrogen, fluorine, chlorine, bromine, or iodine, and wherein at least one of Xl to X4 and also at least one of X5 to X8 is chlorine or bromine and wherein R is Cl to C20 alkylene, C6 to C20 cycloalkylene, C6 to C20 arylene or halogen substituted arylene, alkyl substituted arylene or fused ring arylene, or the moiety Rl-Z-R2 wherein Rl and R2, which 15'~ can be the same or different, are Cl to C20 alkylene, C6 to C20 cycloalkylene; C6 to C20 arylene, halogen substituted arylene, alkyl substituted arylene, or fused ring arylene, -~
and wherein Z iq sulfur, oxygen, isopropylidene, or a chemical bond joining Rl and R2.
Also of particular interest is the coating of conductive particles so that they are free-flowing and readily dispers-able into a binder. Such results may be obtained by this process yet, surprisingly, the coating is such that it has little effect on the conductive properties of the particles.
Although the exact nature of the coated particle is not known, it is believed that the polymer coating is sufficiently thin as not to affect the conductive properties of the particles yet sufficient to alter the surface characteris-.
.. . .
'~
.
33~
tics of the particle. Alternatively, the coated particle may have a su~ficient number of uncoated areas as not to insulate the coated particle. Finally, the polymer coating and the binder into which it is dispersed should be incompatible enough to permit a sufficient amount of agglomeration of the conduc~ive particle so a conductive path is formed, if conductivity with relatively low levels of carbon is desired.
The following examples illustrate the invention:
Example 1 Carbon black, i.e. 1.7 kg of "Vulcan XC-72P"* (Cabot Corp., average particle size .03 ~n was blended with 0.227 kg of 20 % polyvinylidene fluoride (Kynar, a trademark of Pennwalt Corp) in DMF solution in a 15 litre, Patterson-Kelley "V" Type Blender until a uniform consistency was achieved. This mixture was fed through a fluid energy mill having a 288C inlet temperature 243C outlet temperature, and 5.25 kg/cm2 inlet steam pressure at a rate equal to 24.4 kg/hr. The resulting product was an extremely fine, uniform black powder, indistinguishable in appearance from the carbon starting materials. The surface properties were markedly changed, however. Using 4 % of a sodium naphthalene sulfonate wetting agent, it was possible to make a 30 % solids carbon black concentrate in water which wa9 an easily pourable fluid. In comparison, the uncoated control was stiff and completely non-fluid at this concentration.
Example II
A 25% concentration of carbon slurry made as in Example 1 was blended with the following binder composition:
* denotes a Trademark.
parts by welght 50 % solids acrylic emulsion 59 (AC61*from Rohm & Haas) Colloidal silica (40 % solids in water 200 Clay 34 Deionized water 142 Conductive elements were made with various blends of carbon slurry and binder composition generally in accordance with the method of U.S. Patent No. 3,399,451.
Resistance varied as follows:
Table I
Ratio by weight of binderResistance in - :
composition to carbon slurry ohms/s~uare :: .
1:1 260
2:~ 400 : :
4:1 2,000 6.1 14,000 ::~
8:1 720,000 ' :::
Coatings formulated with this coated carbon gave predictable and uniform resistivities, compared with those achieved with uncoated carbon utilizing known dispersants ~:
and mechanical treatment. The coated carbon requires no ~` :
other mechanical work than simple stirring to get a :
25 satisfactory dispersion.
Example III
To 100 parts by weight of a 25 % carbon slurry made as in Example I was added 34 parts of graphite coated with poly-vinylidene fluoride as in Example I. The resulting 30 conductive slurry was then blended with an acrylic emulsion coating similar to Example II. Conductive elements were *Trade mark ~ . ,, . - , , :
': . . . ' , ' .. ~
- : .:
-7~ 33 made and tested as in Example II.
Table II
Ratio by Weight of graphite-carbon slurry Resistance in to composition Ohms/Square .. . . . . . . ..... . .
1:0.24 1 1:1 28 1:2.5 160 Coatings formulated using non-coated carbon particles and graphite gave very erratic resistivities and poor mechanical in~egrity. The coatings made from the coated particle~ overcame thèse weaknesses and had much lower resistivities than obtained previously.
Example IV
2.04 kg sterling MT-NS carbon black (Cabot Corp.), was blended with 2.04 kg of well-crumbled 20 % "DPD 6181" *
(ethylene ethyl acrylate copolymer from Union Carbide Corp.) gel in xylene, and thoroughly mixed in a Patterson-Kellèy Blender until a uniform consistency was achieved.
This mixture was fed through a fluid energy mill under the same conditions as in Example I. The product was uniform and very fine, with an average particle size of 4.0 ~.
(The reported particle size of the MT-NS starting material i9 0.05~). The wetting and dispersion properties were consistent with those expected for a "coated" carbon black.
The improved compatibility and bonding power of the treated carbon was demonstrated in a blend with low density poly-ethylene. A blend consisting of 300 parts of the treated carbon with 100 parts of Sinclair LDPE was prepared on a heated two-roll rubber mill. The product was a smooth, tough slab, tenæile strength 153 kg/cm2, elongation 30 %.
* denotes a Trademark In contrast, an attempt to prepare a comparable compound using untreated Sterling MT-NS at the same loading level Si.e., 249 g MT-NS and 151 g Sinclair LDPE) was unsuccess-ful. At this attempted loading level, the binding power of the resin for the carbon filler was exceeded and only a crumbled mass was obtained.
An electrical test specimen was prepared by pressing a portion of the slab in a hot press (200C) between two
4:1 2,000 6.1 14,000 ::~
8:1 720,000 ' :::
Coatings formulated with this coated carbon gave predictable and uniform resistivities, compared with those achieved with uncoated carbon utilizing known dispersants ~:
and mechanical treatment. The coated carbon requires no ~` :
other mechanical work than simple stirring to get a :
25 satisfactory dispersion.
Example III
To 100 parts by weight of a 25 % carbon slurry made as in Example I was added 34 parts of graphite coated with poly-vinylidene fluoride as in Example I. The resulting 30 conductive slurry was then blended with an acrylic emulsion coating similar to Example II. Conductive elements were *Trade mark ~ . ,, . - , , :
': . . . ' , ' .. ~
- : .:
-7~ 33 made and tested as in Example II.
Table II
Ratio by Weight of graphite-carbon slurry Resistance in to composition Ohms/Square .. . . . . . . ..... . .
1:0.24 1 1:1 28 1:2.5 160 Coatings formulated using non-coated carbon particles and graphite gave very erratic resistivities and poor mechanical in~egrity. The coatings made from the coated particle~ overcame thèse weaknesses and had much lower resistivities than obtained previously.
Example IV
2.04 kg sterling MT-NS carbon black (Cabot Corp.), was blended with 2.04 kg of well-crumbled 20 % "DPD 6181" *
(ethylene ethyl acrylate copolymer from Union Carbide Corp.) gel in xylene, and thoroughly mixed in a Patterson-Kellèy Blender until a uniform consistency was achieved.
This mixture was fed through a fluid energy mill under the same conditions as in Example I. The product was uniform and very fine, with an average particle size of 4.0 ~.
(The reported particle size of the MT-NS starting material i9 0.05~). The wetting and dispersion properties were consistent with those expected for a "coated" carbon black.
The improved compatibility and bonding power of the treated carbon was demonstrated in a blend with low density poly-ethylene. A blend consisting of 300 parts of the treated carbon with 100 parts of Sinclair LDPE was prepared on a heated two-roll rubber mill. The product was a smooth, tough slab, tenæile strength 153 kg/cm2, elongation 30 %.
* denotes a Trademark In contrast, an attempt to prepare a comparable compound using untreated Sterling MT-NS at the same loading level Si.e., 249 g MT-NS and 151 g Sinclair LDPE) was unsuccess-ful. At this attempted loading level, the binding power of the resin for the carbon filler was exceeded and only a crumbled mass was obtained.
An electrical test specimen was prepared by pressing a portion of the slab in a hot press (200C) between two
3.9 cm, 40-mesh steel wire screens to which copper strip leads had been welded. The samples was squeezed to a thickness of 0.32 cm and held in the hot press for 12 minutes. Immediately after removal from the hot press, the sample was placed in a cold press for 5 minutes. The electrical resistance of the sample was checked at this ~ ;
time and after annealing for 8 hours at 150C. The resistance in both cases was~106J~, much higher than one would expect for this high carbon loading level, indicating that the carbon particles were insulated one from the other ~` and there was little reagglomeration of the carbon particles after annealing to form a "conductive path" th~ough the specimen. The test indicated that by blending carbon particles treated with a high polymer which is compatible with the polymer into which it is blended, the carbon particles remain insulated and dispersed and will not reagglomerate even upon annealing.
Example ~
5.4 kg of a well-crumbled gel of 10 % Marlex*6003 ~HDPE, melt-index = 0.3, d=0.96 from Phillips Petroleum Co.) in xylene was thoroughly mixed with 2.72 kg of Sterling MT-NS carbon black in a Patterson-Kelley Blender f~r 5 minutes. The mixture was fed through the fluid *Trade mark .. , .. . ~ : , . , ' - :, - ' .. ,' ' ' . ., ~.~ , :, :
. . ., .. , , , : . .
energy mill set at 288C inlet temperature, 243C outlet temperature,,and 5.25 ~g/cm2 steam inlet pres~ure, at a rate equal to 22.75 kg per hour. The product was an extremely fine (approximately 1 ~), uniform powder. The wetting and surface properties of this "treated" carbon were consistent with those expected for a "coated" product.
Example VI
A mixture of 1~36 kg Vulcan XC-72P carbon black 1.36 kg of Microthene F~-500 (LDPE powder, MI=20, d=0.915, from U.S.I. Chemicals) was pre-blended in a Patterson-Kelley BIender, then passed through a ~luid energy mill set at 288C inlet temperature, 243~ outlet temperature, and 5.25 kg/cm2 inlet steam pressure at a rate equal to 27.7 kg/hr. The product was extremely fine and uniform. The average particle size was 3.75~. The wetting and surface properties of this "treated" carbon were consistent with those expected for a "coated" product.
Two 70g quantities of this "treated" carbon were ~ blende* with 180g of DFD6040 LDPE, (compatible polymer) ~and 180 g of Profax*7523 polypropylene (incompatible polymer) respectively. The blending was done in a 0.4 kg Banbury mixer for a period of 10 min~tes. The hot blends were then sheeted out into a slab approximately 0.63 cm thick on a two-roll rubber mill. Electrical property test specimens were prepared as described in Example IV. The electrical resistance of these samples was checked at their time of preparation and after two annealing periods of 150 C
for 16 hours. The results are summarized below.
*Trade mark : ~ .
R R 1st R 2nd Initial Anneal_nneal LDPE Binder ~-107 ~107 ~107 Polypropylene sinder =-10 1700 360 The results show that conductivity was poor in the case of the compatible coated carbon/polymer blend, while the conductivity was good in the case of the incompatible coated carbon/polymer blend. These differences in conductiv-ity are believed to be due to the relative extent o~
dispersion of the coated carbon in these two binders. The carbon is well dispersed in the compatible system and there-fore conducts poorly while the carbon in the incompatible system is relatively poorly dispersed and segregated into conductive channels and therefore has much better conductiv-ity.
Example VIII
"Hydral-705"* (hydrated aluminum oxide from Alcoa Aluminum Co.), 2.72 kg, and 2.3 kg of 22 % "DYNH"*
(Polyethylene from Union Carbide) gel in xylene were thoroughly premixed in a Patterson-Kelley Blender for 5 minutes. This mixture was fed through a fluid ènergy mill set at 288C inlet temperature, 243C outlet temperature, and 3.85 kg/cm inlet steam pressure, at a rate equal to 27.2 kg/hr. The product was a fine, uniform, white powder.
The particle size of the Hydral 705 before coating was 0.3~, and after coating was 1.22~. The product was totally immiscible with water, but easily miscible in mineral oil, in contrast with the untreated mineral.
A sample of this "coated" Hydral, loo g., was blended with 200 g. of DYNH (LDPE) on a hot two-roll rubber mill.
The coated filler blended in rapidly and easily, giving a 7~33 perfectly dispersed and smooth final product. In contrast, a comparable quantity of "untreated" Hydral blended into the DYNH slowly and with difficulty and the final product was obviously not as smooth.
Example VIII
A uniform mixture of 2.72 kg of Hydral-705 and 4.98 kg Mncrothene F~500 (MI=20, d.=0.915), were fed through a fluid energy mill at 288C inlet temperature, 238C outlet temperature, and 3.85 kg/cm2 inlet steam pressure, at a rate equal to 12.7 kg/~Ir. The product was essentially identical to the sample prepared in Example VII. The average particle size was 2.1~.
Example ~X
A mixture of 0.96 kg of "Cab-0-Sil"* (silica from ~abot Corp.) and 2.75 kg of well-crumbled 22 % DYNH gel in xylene were preblended in a Patterson-Kelley slender for about 5 minutes. This mixture was fed through the fluid energy mill set at 288C inlet temperature, 252C outlet temperature, and 3.85 kg/cm2 inlet steam pressure, at a rate equal to 39.4 kg/
hr. The product was a very fluffy, fine, white powder. The bulk density was more than twice that of the starting material, however. The product was totally water immiscible, but dis-persed easily in organic solvents, such as xylene, hexane, and mineral oil. These properties are in sharp contrast with those of the untreated starting material. The particle size of the starting material was 0.2~ (reported 0.01~), the particlè size of the "coated" material was 0.3~.
Example X
To the Patterson-Kelley Blender were -charged 6.7 kg of Fe34 * denotes a Trademark ~P~izer BK5099 Erom P~izer Chemical Co.) powder and 5.4~ kg of crumbled 22 %
DYNH gel in xylene. The mixture was "homogenized" for 10 minutes in the blender and then fed to the fluid energy mill set at 288C inlet temperature, 246C outlet temperature, and 3.85 kg/cm2 inlet steam pressure, at a rate equal to 27.2 kg/hr. The product was a fine, uniform black powder. The average particle size of the Fe304 before coating was 1.5~ and after coating was 6.4~. The product was totally immiscible with water, but easily wet, and dispersed in organic media such as xylene or mineral oil. These wetting properties were completely the reverse of the untreated control sample. -Example XI
time and after annealing for 8 hours at 150C. The resistance in both cases was~106J~, much higher than one would expect for this high carbon loading level, indicating that the carbon particles were insulated one from the other ~` and there was little reagglomeration of the carbon particles after annealing to form a "conductive path" th~ough the specimen. The test indicated that by blending carbon particles treated with a high polymer which is compatible with the polymer into which it is blended, the carbon particles remain insulated and dispersed and will not reagglomerate even upon annealing.
Example ~
5.4 kg of a well-crumbled gel of 10 % Marlex*6003 ~HDPE, melt-index = 0.3, d=0.96 from Phillips Petroleum Co.) in xylene was thoroughly mixed with 2.72 kg of Sterling MT-NS carbon black in a Patterson-Kelley Blender f~r 5 minutes. The mixture was fed through the fluid *Trade mark .. , .. . ~ : , . , ' - :, - ' .. ,' ' ' . ., ~.~ , :, :
. . ., .. , , , : . .
energy mill set at 288C inlet temperature, 243C outlet temperature,,and 5.25 ~g/cm2 steam inlet pres~ure, at a rate equal to 22.75 kg per hour. The product was an extremely fine (approximately 1 ~), uniform powder. The wetting and surface properties of this "treated" carbon were consistent with those expected for a "coated" product.
Example VI
A mixture of 1~36 kg Vulcan XC-72P carbon black 1.36 kg of Microthene F~-500 (LDPE powder, MI=20, d=0.915, from U.S.I. Chemicals) was pre-blended in a Patterson-Kelley BIender, then passed through a ~luid energy mill set at 288C inlet temperature, 243~ outlet temperature, and 5.25 kg/cm2 inlet steam pressure at a rate equal to 27.7 kg/hr. The product was extremely fine and uniform. The average particle size was 3.75~. The wetting and surface properties of this "treated" carbon were consistent with those expected for a "coated" product.
Two 70g quantities of this "treated" carbon were ~ blende* with 180g of DFD6040 LDPE, (compatible polymer) ~and 180 g of Profax*7523 polypropylene (incompatible polymer) respectively. The blending was done in a 0.4 kg Banbury mixer for a period of 10 min~tes. The hot blends were then sheeted out into a slab approximately 0.63 cm thick on a two-roll rubber mill. Electrical property test specimens were prepared as described in Example IV. The electrical resistance of these samples was checked at their time of preparation and after two annealing periods of 150 C
for 16 hours. The results are summarized below.
*Trade mark : ~ .
R R 1st R 2nd Initial Anneal_nneal LDPE Binder ~-107 ~107 ~107 Polypropylene sinder =-10 1700 360 The results show that conductivity was poor in the case of the compatible coated carbon/polymer blend, while the conductivity was good in the case of the incompatible coated carbon/polymer blend. These differences in conductiv-ity are believed to be due to the relative extent o~
dispersion of the coated carbon in these two binders. The carbon is well dispersed in the compatible system and there-fore conducts poorly while the carbon in the incompatible system is relatively poorly dispersed and segregated into conductive channels and therefore has much better conductiv-ity.
Example VIII
"Hydral-705"* (hydrated aluminum oxide from Alcoa Aluminum Co.), 2.72 kg, and 2.3 kg of 22 % "DYNH"*
(Polyethylene from Union Carbide) gel in xylene were thoroughly premixed in a Patterson-Kelley Blender for 5 minutes. This mixture was fed through a fluid ènergy mill set at 288C inlet temperature, 243C outlet temperature, and 3.85 kg/cm inlet steam pressure, at a rate equal to 27.2 kg/hr. The product was a fine, uniform, white powder.
The particle size of the Hydral 705 before coating was 0.3~, and after coating was 1.22~. The product was totally immiscible with water, but easily miscible in mineral oil, in contrast with the untreated mineral.
A sample of this "coated" Hydral, loo g., was blended with 200 g. of DYNH (LDPE) on a hot two-roll rubber mill.
The coated filler blended in rapidly and easily, giving a 7~33 perfectly dispersed and smooth final product. In contrast, a comparable quantity of "untreated" Hydral blended into the DYNH slowly and with difficulty and the final product was obviously not as smooth.
Example VIII
A uniform mixture of 2.72 kg of Hydral-705 and 4.98 kg Mncrothene F~500 (MI=20, d.=0.915), were fed through a fluid energy mill at 288C inlet temperature, 238C outlet temperature, and 3.85 kg/cm2 inlet steam pressure, at a rate equal to 12.7 kg/~Ir. The product was essentially identical to the sample prepared in Example VII. The average particle size was 2.1~.
Example ~X
A mixture of 0.96 kg of "Cab-0-Sil"* (silica from ~abot Corp.) and 2.75 kg of well-crumbled 22 % DYNH gel in xylene were preblended in a Patterson-Kelley slender for about 5 minutes. This mixture was fed through the fluid energy mill set at 288C inlet temperature, 252C outlet temperature, and 3.85 kg/cm2 inlet steam pressure, at a rate equal to 39.4 kg/
hr. The product was a very fluffy, fine, white powder. The bulk density was more than twice that of the starting material, however. The product was totally water immiscible, but dis-persed easily in organic solvents, such as xylene, hexane, and mineral oil. These properties are in sharp contrast with those of the untreated starting material. The particle size of the starting material was 0.2~ (reported 0.01~), the particlè size of the "coated" material was 0.3~.
Example X
To the Patterson-Kelley Blender were -charged 6.7 kg of Fe34 * denotes a Trademark ~P~izer BK5099 Erom P~izer Chemical Co.) powder and 5.4~ kg of crumbled 22 %
DYNH gel in xylene. The mixture was "homogenized" for 10 minutes in the blender and then fed to the fluid energy mill set at 288C inlet temperature, 246C outlet temperature, and 3.85 kg/cm2 inlet steam pressure, at a rate equal to 27.2 kg/hr. The product was a fine, uniform black powder. The average particle size of the Fe304 before coating was 1.5~ and after coating was 6.4~. The product was totally immiscible with water, but easily wet, and dispersed in organic media such as xylene or mineral oil. These wetting properties were completely the reverse of the untreated control sample. -Example XI
4.53 kg of N,N'~ '-diphenyl)bis-3,4,5,6-tetrabromophthalimide in particulate form useful as a flame retardant was charged to a 15 litre Patterson-Kelley Liquid Solids slender, along with 3.1 kg of well-crulnbled 22 % DYNH ~LDPE) gel in xylene. The mixture was blended for 5 minu~es. The resulting blend was of a damp, but free-flowing consistency. This material was fed through the fluid energy mill at a rate of 29.5 kg/hr. The mill was -operated at 315C inlet temperature, 260C outlet t0mperature, and at a steam inlet pressure of 2.8 kg/cm2. The product was a uniform free-flowing, fine, yellow powder. The average particle size of the starting material was 0.75~; the final coated product had an average size of 1.85~. The coated product was noticeably more oleophilic than the uncoated control.
The dispersion characteristics of the "coated" material were deter-B~ mined by compounding, in a 2.26 kg Banbury~ a composition consisting of 36 %
high density polyethylene and 17 % ethylene-propylene rubber, 36 % "coated"
material, 11 % antimony oxide. Tapes, 2.54 cm wide, 0.0127 cm thick, were extruded from this composition and the number of particles per metre counted.
A similar control sample was made up consisting of 40 % high density poly-ethylene and 32 % uncoated material, plus the other ingredients. The coated material showed an average of 560 particles, 0.051 mm or greater, per metre.
~ s (~T ~Qe ~k . . i .. . . . . . . . .
r: `.
'10~7~33 The eontrol sample showed an average of 24,300 particles/metre.
~xample XII
.
The fluid energy mill was set at 288C inlet steam tempera-ture and 260C outlet temperature. The inlet pressure was 3.5 kg/cm2.
The organic powder of Example XI was metered into the mill at a rate of 23.1 kg/hr. Simultaneously, a hot 20% solution of DYNH in xylene was sprayed into the mill at the rate of 13 litres/hr. The product was essentially identical to the sample prepared in Example XI.
The dispersion characteristics of the material were checked as in Example XI. The particle count on ~he resulting tapes was 3840 particles/metre - significantly less than the control of 24,300.
Example XIII
A well-blended mixture of 2.72 lb. of the organic powder of Example XI and 0.48 kg Microthene MU 760 ~U.S.I. Chemicals, ethylene-vinyl acetate copolymerJ M.I.=20, d.=0.94, average particle size 500 ~) was fed into the fluid energy mill set at 288C inlet temperature, 241C outlet temperature, and an inlet pressure of 3.85 kg/cm2, at a rate equal to 22 kg per hour. The product was a fine, yellow powder of average particle size 2.0 ~ (particle size starting material 0.75 ~). The dispersion characteristics of the product were determined as in Example XI. The particle count on the resulting tapes was 400 par-ticles/metre.
B Example XIV
I . Regal 660R ~ medium size, low structure) carbon black, 2.27 kg, was preblended to a uniform consistency in a Patterson-Kelley Blender with 0.54 g of Viscasii~ 0,000 Chigh molecular weight sili-cone oil, G.E. Co.). This mixture was then fed through the fluid energy mill set at 288C inlet temperature, about 260F outlet tempera-ture and 4.9 kg/cm2 inlet steam pressure at a rate of approximately 27.2 lb/hr. The product was a fine, uniform black powder.
300 parts of this "coated" carbon was compounded into 100 parts of Sinclair LDPE on a two-roll rubber mill. The compound was some-~ tes c~ d ~
: ., , - , ~: .
7~33 what stiff, but processed satisEactorily. Electrical test specimens (4) were pr0p~red as described in Example IV.
The initial resistances of the test pieces were 813, 1568, 2090, and 2554-~. The resistances of the samples after annealing for 8 hours at 150C were 377, 361, 394, and 386 J~. Further heating at 150C did not change the room temperature resistance levels appreciably.
The unusual features of this example are the higher loading level of the carbon than possible with uncoated carbon, rapid annealing rates, and good, stable levels of conductivity due presumably to the incompatible nature of the coating on the carbon with the binder resin.
Example XV
The fluid energy mill was operated at 321C inlat steam temperature and 265 outlet temperature. The inlet pressure was 3.15 kg~cm2. 5.4 kg of the organic powder of Example XI was metered into the mill at a rate of 26~4 kg/hr. Simultaneously, a solution of 500 ~. poly (N,N' -dodecamethylene pyromellitimide) dissolved in 4 litres N-methyl-2-pyrrolidone was sprayed into the mill at the rate of 333 ml/min. The product was a uniform, free-flowing, fine powder. The coated flame retardent material was shown to have improved compatibility with poly (N,N' -dodecamethylene pyromellitimide~.
.., .. . ... ~. . ~ . ..
.. ~ - . . .
The dispersion characteristics of the "coated" material were deter-B~ mined by compounding, in a 2.26 kg Banbury~ a composition consisting of 36 %
high density polyethylene and 17 % ethylene-propylene rubber, 36 % "coated"
material, 11 % antimony oxide. Tapes, 2.54 cm wide, 0.0127 cm thick, were extruded from this composition and the number of particles per metre counted.
A similar control sample was made up consisting of 40 % high density poly-ethylene and 32 % uncoated material, plus the other ingredients. The coated material showed an average of 560 particles, 0.051 mm or greater, per metre.
~ s (~T ~Qe ~k . . i .. . . . . . . . .
r: `.
'10~7~33 The eontrol sample showed an average of 24,300 particles/metre.
~xample XII
.
The fluid energy mill was set at 288C inlet steam tempera-ture and 260C outlet temperature. The inlet pressure was 3.5 kg/cm2.
The organic powder of Example XI was metered into the mill at a rate of 23.1 kg/hr. Simultaneously, a hot 20% solution of DYNH in xylene was sprayed into the mill at the rate of 13 litres/hr. The product was essentially identical to the sample prepared in Example XI.
The dispersion characteristics of the material were checked as in Example XI. The particle count on ~he resulting tapes was 3840 particles/metre - significantly less than the control of 24,300.
Example XIII
A well-blended mixture of 2.72 lb. of the organic powder of Example XI and 0.48 kg Microthene MU 760 ~U.S.I. Chemicals, ethylene-vinyl acetate copolymerJ M.I.=20, d.=0.94, average particle size 500 ~) was fed into the fluid energy mill set at 288C inlet temperature, 241C outlet temperature, and an inlet pressure of 3.85 kg/cm2, at a rate equal to 22 kg per hour. The product was a fine, yellow powder of average particle size 2.0 ~ (particle size starting material 0.75 ~). The dispersion characteristics of the product were determined as in Example XI. The particle count on the resulting tapes was 400 par-ticles/metre.
B Example XIV
I . Regal 660R ~ medium size, low structure) carbon black, 2.27 kg, was preblended to a uniform consistency in a Patterson-Kelley Blender with 0.54 g of Viscasii~ 0,000 Chigh molecular weight sili-cone oil, G.E. Co.). This mixture was then fed through the fluid energy mill set at 288C inlet temperature, about 260F outlet tempera-ture and 4.9 kg/cm2 inlet steam pressure at a rate of approximately 27.2 lb/hr. The product was a fine, uniform black powder.
300 parts of this "coated" carbon was compounded into 100 parts of Sinclair LDPE on a two-roll rubber mill. The compound was some-~ tes c~ d ~
: ., , - , ~: .
7~33 what stiff, but processed satisEactorily. Electrical test specimens (4) were pr0p~red as described in Example IV.
The initial resistances of the test pieces were 813, 1568, 2090, and 2554-~. The resistances of the samples after annealing for 8 hours at 150C were 377, 361, 394, and 386 J~. Further heating at 150C did not change the room temperature resistance levels appreciably.
The unusual features of this example are the higher loading level of the carbon than possible with uncoated carbon, rapid annealing rates, and good, stable levels of conductivity due presumably to the incompatible nature of the coating on the carbon with the binder resin.
Example XV
The fluid energy mill was operated at 321C inlat steam temperature and 265 outlet temperature. The inlet pressure was 3.15 kg~cm2. 5.4 kg of the organic powder of Example XI was metered into the mill at a rate of 26~4 kg/hr. Simultaneously, a solution of 500 ~. poly (N,N' -dodecamethylene pyromellitimide) dissolved in 4 litres N-methyl-2-pyrrolidone was sprayed into the mill at the rate of 333 ml/min. The product was a uniform, free-flowing, fine powder. The coated flame retardent material was shown to have improved compatibility with poly (N,N' -dodecamethylene pyromellitimide~.
.., .. . ... ~. . ~ . ..
.. ~ - . . .
Claims (25)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for coating discrete particles having a particle diameter not exceeding 20 microns with a polymer coating which process comprises:
injecting the polymer and particles into a chamber the walls of which define a closed arcuate path, the chamber having an outlet in its inner periphery, and so injecting a fluid stream into the chamber under pressure and at an elevated temperature that the fluid propels the polymer and particles around the chamber, in the closed arcuate path defined by its walls at a velocity sufficient to cause the polymer and the particles to undergo repeated impacts with each other whereby the particles are coated with the polymer, and sufficient to cause discrete polymer-coated particles to leave the chamber through the said outlet while agglomerated particles having a particle diameter greater than 20 microns are recycled around the arcuate path.
injecting the polymer and particles into a chamber the walls of which define a closed arcuate path, the chamber having an outlet in its inner periphery, and so injecting a fluid stream into the chamber under pressure and at an elevated temperature that the fluid propels the polymer and particles around the chamber, in the closed arcuate path defined by its walls at a velocity sufficient to cause the polymer and the particles to undergo repeated impacts with each other whereby the particles are coated with the polymer, and sufficient to cause discrete polymer-coated particles to leave the chamber through the said outlet while agglomerated particles having a particle diameter greater than 20 microns are recycled around the arcuate path.
2. A process as claimed in claim 1, wherein the particles and polymer are preblended prior to injection into the chamber.
3. A process as claimed in claim 1 or claim 2, wherein the fluid is steam, said steam being injected into the chamber at temperatures between 125°C and 400°C at a pressure between 0.2 and 6.0 kg/cm2.
4. A process as claimed in claim 1, wherein the polymer is fed into the chamber in solution.
5. A process as claimed in claim 1, wherein the polymer is fed into the chamber as a finely divided gel.
6. A process as claimed in claim 1, wherein the polymer is fed into the chamber as a dry powder.
7. A process as claimed in claim 1, wherein the particles to be coated are of carbon black, graphite, clay, talc, ground limestone, aluminium oxide, hydrated aluminium oxide, silica, hydrated silica gel or an iron oxide.
8. A process as claimed in claim 1, wherein the particles to be coated are of a halogenated organic compound.
9. A process as claimed in claim 8, wherein the halogenated organic compound has the formula in which X1 to X8, are independently selected from the group consisting of hydrogen, fluorine, chlorine, bromine, and iodine, and wherein at least one of X1 to X4 and also at least one of X5 to X8 is chlorine or bromine and wherein R is C1 to C20 alkylene, C6 to C20 cycloalkylene, C6 to C20 arylene or halogen-substituted arylene, alkyl-substituted arylene or fused ring arylene, or the moiety R1 - Z - R2 wherein R1 and R2 are independently selected from the group consisting of C1 to C20 alkylene, C6 to C20 cycloalkylene, C6 to C20 arylene, halogen-substituted arylene, alkyl-substituted arylene, and fused ring arylene, and wherein Z is sulphur, oxygen, isopropylidene, or a chemical bond joining R1 and R2.
10. A process as claimed in claim 8, wherein the particle to be coated is N,N'-(p,p'-diphenyl)bis-3,4,5,6-tetrabromo-phthalimide.
11. A process as claimed in claim 1, wherein the polymer is so coated onto conductive particles that the resulting coated particles are free-flowing and non-agglomerative but remain conductive when dispersed in a suitable binder.
12. A process as claimed in claim 11, wherein the polymer is polyvinylidene fluoride.
13, A process as claimed in claim 11 or claim 12, wherein the conductive particles are carbon.
14. An electrically conductive coated particle, comprising an electrically conductive core particle having a core diameter not exceeding 20µ which has been so coated with a polymeric material applied thereto in polymeric, substantially solvent-free form that it has been rendered free-flowing and non-agglomerative without depriving it of its electrical conductivity.
15. A coated particle as claimed in claim 14, wherein the polymeric material has been applied in the form of a dry powder.
16. A coated particle as claimed in claim 14 or claim 15, wherein the conductive core particle comprises carbon.
17. A coated particle as claimed in claim 14 or claim 15, wherein the conductive core particle comprises carbon black
18. A coated particle as claimed in claim 14, wherein the polymeric material comprises polyethylene copolymer.
19. A coated particle as claimed in claim 18, wherein the polymeric material comprises low-density polyethylene.
20. A coated particle as claimed in claim 14, wherein the polymeric material comprises polyvinylidene fluoride.
21. A process for the production of electrically conductive coated particles as claimed in claim 14, wherein a substantially solvent-free polymeric material is applied to electrically conductive core particles having a particle diameter not exceeding 20µm.
22. A process as claimed in claim 21, wherein the polymeric material is applied in the form of a dry powder.
23. A process as claimed in claim 21, wherein the polymeric material is applied to the core particles by means of a fluid stream.
24. An electrically conductive composition which comprises a dispersion of electrically conductive coated particles as claimed in claim 14 in a suitable binder.
25. A composition as claimed in claim 24 wherein the binder comprises an acrylic polymer dispersed in water.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/468,668 US3992558A (en) | 1974-05-10 | 1974-05-10 | Process of coating particles of less than 20 microns with a polymer coating |
| US468668 | 1990-01-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1087933A true CA1087933A (en) | 1980-10-21 |
Family
ID=23860745
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA226,759A Expired CA1087933A (en) | 1974-05-10 | 1975-05-12 | Coated particles and conductive compositions therefrom |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US3992558A (en) |
| JP (1) | JPS50160350A (en) |
| BE (1) | BE828906A (en) |
| CA (1) | CA1087933A (en) |
| DE (1) | DE2520636A1 (en) |
| FR (1) | FR2270070B1 (en) |
| GB (2) | GB1511741A (en) |
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| US3241520A (en) * | 1964-10-19 | 1966-03-22 | Wisconsin Alumni Res Found | Particle coating apparatus |
| US3386851A (en) * | 1965-09-16 | 1968-06-04 | Jerry W. Harlan | Preparation of polymer-coated solid materials suitable as fillers for organic polymers |
| US3408746A (en) * | 1967-03-13 | 1968-11-05 | Dow Chemical Co | Apparatus and method for recovering solids |
| US3661620A (en) * | 1969-11-26 | 1972-05-09 | Gen Tire & Rubber Co | Method of encapsulating fillers with polymers |
-
1974
- 1974-05-10 US US05/468,668 patent/US3992558A/en not_active Expired - Lifetime
-
1975
- 1975-05-08 JP JP50055332A patent/JPS50160350A/ja active Pending
- 1975-05-09 DE DE19752520636 patent/DE2520636A1/en not_active Withdrawn
- 1975-05-09 GB GB19622/75A patent/GB1511741A/en not_active Expired
- 1975-05-09 BE BE156212A patent/BE828906A/en not_active IP Right Cessation
- 1975-05-09 GB GB48593/77A patent/GB1511742A/en not_active Expired
- 1975-05-09 FR FR7514532A patent/FR2270070B1/fr not_active Expired
- 1975-05-12 CA CA226,759A patent/CA1087933A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4828882A (en) * | 1987-03-16 | 1989-05-09 | Canadian Patents & Developments Limited | Particle encapsulation technique |
Also Published As
| Publication number | Publication date |
|---|---|
| BE828906A (en) | 1975-11-10 |
| GB1511741A (en) | 1978-05-24 |
| FR2270070B1 (en) | 1979-10-19 |
| FR2270070A1 (en) | 1975-12-05 |
| US3992558A (en) | 1976-11-16 |
| DE2520636A1 (en) | 1975-11-20 |
| GB1511742A (en) | 1978-05-24 |
| JPS50160350A (en) | 1975-12-25 |
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