Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/02—Ingredients treated with inorganic substances
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L101/00—Compositions of unspecified macromolecular compounds
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
  • C01B32/152—Fullerenes
  • C01B32/156—After-treatment
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
  • C01B32/158—Carbon nanotubes
  • C01B32/168—After-treatment
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/20—Graphite
  • C01B32/21—After-treatment
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/90—Carbides
  • C01B32/914—Carbides of single elements
  • C01B32/956—Silicon carbide
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/04—Ingredients treated with organic substances
  • C08K9/06—Ingredients treated with organic substances with silicon-containing compounds

Definitions

• thermally conductive particles having volume resistivityof at least 1 at least 1 x io 6 ⁇ -cm as well as insulating compositions containing these thermally conductive particles.
• LEDs light emitting diodes
• LEDs the higher the light output of the LED, the greater the electrical energy requirement and the greater the thermal output.
• Thermal management of high power electronic devices, such as LEDs is crucial to maintain long-term functioning and safe performance of the device.
• the housing acts as a heat sink and aluminum is commonly used as the heat sink material.
• metal housing is relatively heavy and electrically conductive.
• thermally conductive yet electrically insulating particles have become a current research interest .
• the aim is to blend these into polymeric compositions to thereby provide polymeric compositions suitable for housings and other elements of high power electronic devices.
• JP Pat. App. Pub.2010-024406 discloses a method of forming a film of silicon dioxide hydrate on the surface of natural graphite in which natural graphite and tetraethoxy silicate, a coupling agent, are added to isopropanol.
• JP Pat. App. Pub.2011/089216 discloses a graphitized short fiber having a silicon carbide layer on its surface and used as a thermally conductive material that has insulating properties. The silicon carbide layer is coated by firing at over 1000 °C in silicon monoxide gas.
• JP Pat. App. Pub.2009-235650 discloses forming an insulating coating on a fibrous carbon system material.
• JP Pat. App. Pub.09-309710 and JP 08-259838 disclose the preparation of nonconductive carbonaceous powders.
• 2011/0129672 discloses a silane coating process for non-spherical hollow particles for cosmetic applications.
• U.S. Pat. No.8,110,284 discloses microcapsules which are encapsulated with a silane compound.
• U.S. Pat. No.6,919,106 discloses the preparation of porous SOG films using silane. compounds.
• thermally conductive particles that exhibit thermal conductivity with electrical insulation made by a method of mixing either a cationic surfactant or an amphoteric surfactant, a hydrolysis catalyst, and a silica precursor. Also described herein are electrically insulating polymeric compositions containing these thermally conductive particles.
• Figure 1 shows results of analysis by Auger electron spectroscopy (AES) in the depth direction of thermally conductive particles of Example 1.
• AES Auger electron spectroscopy
• Figure 2 depicts the device used to measure the volume resistivity of thermally conductive particles made in the Examples.
• Figure 3 depicts a thermally conductive particle made by methods described herein.
• the terms "light-emitting diode” or “LED” refer to a device comprising at least one light-emitting semiconductor diode, an electrical connection capable of connecting the diode to an electrical circuit, and a housing partially surrounding the diode.
• the LED may optionally have a lens that fully or partially covers the LED.
• the terms "LED housing” or “housing” refer to a structural element of an LED of which at least part, preferably all, of the structural element comprises a polymer composition and coated carbon-based particles disclosed herein and wherein the housing partially or completely surrounds the diode so as to form a cavity around the diode with the housing having an opening for the light emitted by the diode to exit.
• carbon-based particle refers to carbon based particles that are not in the form of fibers. Carbon-based particles also include carbon powders and carbon flakes. The carbon-based particle can be naturally occurring carbon or synthetic carbon. Non-fibrous carbon-based particles have an aspect ratio (length to width ratio) of less than 2. Such particles are typically round, oval, flat, or irregular in shape.
• graphite flake refers to graphite particles that are not in the form of fibers.
• Graphite flakes also includes graphite powder and graphite particles.
• the graphite can be naturally occurring graphite or synthetic graphite.
• Non-fibrous graphite or graphite flake has an aspect ratio (length to width ratio) of less than 2. Such flakes are typically round, oval, flat, or irregular in shape.
• amorphous silica precursor refers to compounds or materials which when exposed to a catalyst, results in the formation or generation of a silica based material which is useful for coating particles to make the particles electrically insulating and thermally conductive.
• collected refers to a process by which coated carbon-based particles are separated and isolated from the solution in which the particles are coated.
• the term "coated" refers to a carbon-based particle which has on its entire surface a layer of silica based material such as a Si0 2 coating.
• the layer of silica material completely encapsulates or encloses the particle.
• coated carbon-based particles refers to particles in which the exterior surface of the particle may be completely or partially coated with a material that renders the particle electrically insulating and thermally conductive.
• volume resistivity refers to electrical resistivity of a material and is a method for determining the electrical insulating capacity of a material. Volume resistivity is measured by placing the sample carbon particles in a transparent cylinder between two electrodes with terminals. The surface area of the electrode is 0.785 cm 2 . A voltage of 1000 V was applied through the terminals and the resistivity of the particles measured. The packing ratio is calculated from the weight and volume of the particles.
• the term "aspect ratio" of a particle refers to the ratio of the particle's length over its width.
• colloidal silica refers to suspensions of fine amorphous, nonporous, and typically spherical silica particles suspended in a liquid phase, and is a silica precursor used in the methods described herein.
• the liquid is typically H 2 0.
• water glass is any number of related sodium silicate substances dissolved in water.
• PDMS polydimethylsiloxane
• SiO x » refers to silica
• Aq Amphitol ® and Aq Capstone ® refer to aqueous solutions of Amphitol ® and of Capstone ® respectively, which are described in detail in the Materials section.
• I PA refers to an aqueous solution of water and isopropyl alcohol as described in Solvents section.
• Aq NH 3 and “ammonia water” refer to Aqueous Ammonia Solution, used in the methods described herein as a Hydrolysis Catalyst.
• Aq Snowtex ® refers to an aqueous solution of Snowtex ® as described in the materials section.
• HCI hydrochloric acid
• Water Glass refers to a common name for any sodium silicate compounds having the formula Na 2( Si0 2 ) n O, available in aqueous solution.
• wt% refers to weight percent.
• ⁇ refers to micrometers.
• nm refers to nanometers.
• any range set forth herein expressly includes its endpoints unless explicitly stated otherwise. Setting forth an amount, concentration, or other value or parameter as a range specifically discloses all ranges formed from any pair of any upper range limit and any lower range lim it, regardless of whether any specific range of each such possible pairs of upper and lower limits are expressly disclosed herein. To be clear, the processes, compositions, methods and articles described herein are not limited to only those specific ranges expressly stated herein.
• the silica precursor should be in colloidal form, and the carbon particles would preferably be coated by the solid silica precursor that has lost fluidity through promotion of the reaction.
• the thermally conductive particles may be removed by filtration from the mixture solution.
• compositions that comprise the silica-coated carbon particles made by the methods described herein and at least one polymer.
• - only a cationic surfactant is used; and/or - only an amphoteric surfactant is used; and/or
• a cationic surfactant when used, it is selected from the group consisting of quaternary ammonium salts, alkylamine salts, pyridinium salts, and mixtures of these; and/or
• the carbon particles are selected from the group consisting of graphite particles, carbon nanotubes, fullerene particles, carbon black, glass carbon particles, carbon fibers, silicon carbide particles, amorphous carbon, expanded graphite particles, boron carbide particles , and mixtures of these; and/or
• the silica precursor is silicon alkoxide
• the mixing of the mixed solution occurs when the temperature of the mixed solution ranges from 35°C to less than ioo°C;
• the silica-coated carbon particles have a thickness of the silica layer ranging from 30 nm to 500 nm;
• the composition when molded, exhibits a combined property of a thermal conductivity of at least l W/mK, and a volume resistivity of at least ⁇ ⁇ 10 8 ⁇ -cm; and/or
• the polymer is selected from the group consisting of organic polymers, inorganic polymers, organic-inorganic hybrid polymers, and mixtures of these; and/or
• the polymer is selected from the group consisting of polybutylene terephthalate, polyethylene terephthalate, polytrimethylene terephthalate, and at least one polyamide; and/or
• the polymer is selected from polybutylene terephalate; and/or
• the polymer is selected from at least one polyamide.
• a catalyst to a solvent are added a catalyst, carbon particles, a surfactant— either cationic or amphoteric— and a silica precursor.
• the surfactant and the carbon particles may be added first to the solvent and stirred, followed by the addition of the silica precursor. Since the silica precursor reacts with water, hydrolysis can be initiated when the carbon particles and the surfactant are uniformly present in the solvent and then the silica precursor can be effectively added, particularly when the solvent is aqueous.
• the mixing results in a mixed solution.
• the hydrolysis reaction could be promoted by regulating the temperature of the mixed solution during mixing.
• the temperature at which mixing occurs may be adjusted and is a function of the boiling point of the solvent used.
• the temperature of the mixed solution during mixing may range from 35°C to less than ioo°C.
• the temperature of the mixed solution may range from 45°C to less than 8g°C. Adjusting the temperature of the mixed solution to a range from 40°C to under 8o°C is desirable as this promotes the hydrolysis reaction of the silica precursor.
• a condensation polymerization reaction of hydrolyzed silica precursors results in the surface coating of the carbon particles with silica.
• the cationic surfactant or amphoteric surfactant acts as a binder of the silica to the carbon particles and silica.
• the silica coating may be modified in various ways. For example, mixing may occur once or be repeated to facilitate a thicker silica coating.
• a silicon rubber may be combined with the silica precursorto impart elasticity and more strength to the silica coating. The amount of silicon rubber added should be in the range of 0.5 to 20 weight parts per 100 weight parts of silica precursor.
• a silane coupling agent may beneficially be added to the mixed solution in orderto improve the compatibility of the particles with the polymer.
• mixing should occur by stirring for 30 minutes to 2 hours at a temperature of the solvent ranging from 30 to ioo°C .
• the amount of silane coupling agent may range from 1 to 10 weight parts per 100 weight parts of carbon.
• silane coupling agent there is no specific limitation on the type of silane coupling agent used, but particulary suitable are: vinyl trimethoxy silane, vinyl triethoxy silane,
• the coated carbon particles may be filtered by pouring the mixed solution through a filter with a mesh smaller than the particle diameter of the coated carbon particles.
• Silica-coated carbon particles would collect on the filter while the the solvent and the hydrolysis catalyst dissolved in the solvent pass through.
• it is expected that some hydrolysis catalyst may remain in the filtered carbon particles and may be removed by washing the filtrate with alcohol or water and then drying. Drying preferably occurs at a temperature under 2oo°C.
• the particles may set out to dry at ambient
• the resultant particle 30 include a carbon particle 31 and a silica surface coating or silica layer 32.
• particle 30 is thermally conductive yet electrically insulating and has a volume resistivity of at least 1 x 10 6 ⁇ -cm. It is expected that these methods result in a silica coating that covers the entire surface of each carbon particle. Nonetheless, even if some of the resultant particles are only partially silica-coated, the volume resistivity of each resultant particle is expected to be at least 1 x 10 6 ⁇ -cm. And, the volume resistivity of the resultant particles may range from 5.0 x 10 6 ⁇ -cm to 1 x 10 13 ⁇ -cm.
• Silica layer 32 covering carbon particle 31 in thermally conductive particle 30 contains a surfactant in silica layer 32, which is residual from the silica coating step.
• the thickness of the silica layer preferably ranges from 3onm to 500 nm because this thickness provides adequate electrical insulation.
• Carbon particles contain carbon, which includes carbon isotopes or carbon compounds. Carbon particles form the core of thermally conductive particles made by the methods described herein. Carbon material with thermal conductivity above 100 W-m "1 -K "1 would be formed into particle shape.
• Carbon particles used in the methods described herein may be selected from graphite, carbon nanotubes, fullerene, carbon black, glass carbon, carbon fibers, silicon carbide, amorphous carbon, expanding graphite, boron carbide, and mixtures of these.
• the diameter of the carbon may range from ⁇ ⁇ to 300 ⁇ , or from 5 ⁇ to 50 ⁇ , or from 15 ⁇ to 100 ⁇ .
• the particle size distribution is determined via laser diffraction and the particle diameter is reported as the median of the distribution, known as Dso.
• the microtrack (X-100) can be used as a commercial particle size distribution measurement apparatus.
• Desirable carbon particles in the methods described herein are graphite or carbon fibers.
• Graphite has a non-fibrous shape and may have an aspect ratio of less than two, meaning the particle's length is less than twice as long as its width.
• Graphite typically has a flat or plate shape, and would have length and width at least 2.5 times the thickness.
• the length or width of graphite may be 1 ⁇ to 300 ⁇ , or 5 ⁇ to 150 ⁇ , or 15 ⁇ to 100 ⁇ .
• the aspect ratio may be less than 1.5 or less than under 1.0.
• the minimum thickness of graphite may be 0.5 ⁇ and maximum thickness may be determined by the length and width of flake-shaped particles.
• Carbon fibers may have a diameter ranging from 0.5 to 50 ⁇ and an aspect ratio ranging from 3 to 15 or 4 to 10. Desirable carbon fibers may be pitch-based carbon fibers. The thickness, length, and width of graphite and the diameter of carbon fibers may be measured with an electron microscope.
• the silica precursor in the methods described herein is the source of the silica that coats graphite partices.
• Silica or SiO x is a silicon oxide and may be crystalline or amorphous.
• Amorphous silica may be used because the silica coating may be formed at low temperature.
• the silica used may contain in some part crystalline silica. Differentiation of crystalline or non-crystalline silica is done via X-ray analysis; peaks revealing crystalline structure do not appear in X-ray analysis of amorphous silica.
• the silica precursor is silicon alkoxide represented by formula (I):
• R a represents hydrocarbons with 1 to 8 identical or different, substituted or unsubstituted carbon atoms, n represents 0, 1, 2, or 3, and R 2 represents hydrocarbons with l to 8 carbon atoms.
• the silicon alkoxide is reacted with water and the hydrolysis catalyst to create silica, which is the entity that coats the carbon particles.
• the silicon alkoxide may be tetraalkoxysilane.
• the tetraalkoxysilane may be tetraethoxysilane, tetramethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetraamyloxysilane, tetraoctyloxysilane,tetranonyloxysilane,dimethoxy diethoxy silane, dimethoxy diisopropoxy silane, diethoxy diisopropoxy silane, diethoxy dibutoxy silane, diethoxy ditrityloxy silane, or mixtures of these.
• TEOS ultimately becomes Si(OH) as the hydrolysis reaction proceeds.
• a condensation polymerization reaction proceeds between two hydroxide molecules created here, and silica is created as shown below.
• the silica precursor may range from 50 to 200 weight parts per 100 weight parts of carbon.
• the methods described herein may use cationic surfactants with hydrophilic groups that dissociate in aqueous solution into cations or amphoteric surfactants that dissociate in aqueous solution into both anions and cations. These surfactants are used in these methods as binders of carbon particles and silica.
• amphoteric surfactants used in these methods include lauryl dimethyl amino acetic acid betaine, stearyl dimethyl amino acetic acid betaine, lauryl dimethyl amine oxide, lauric acid amido propyl betaine, lauryl hydroxy sulfobetaine,
• N-lauroyl-N'-carboxymethyl-N'-hydroxyethyl ethylene diamine sodium N-coconut oil fatty acid acyl-N'-carboxyethyl-N'-hydroxyethyl ethylene diamine sodium,
• oleyl-N-carboxyethyl-N-hydroxyethyl ethylene diamine sodium cocamidopropyl betaine, lauramido propyl betaine, myristamidopropyl betaine, palm kernelamidopropyl betaine, lauramidopropyl hydroxysultaine, lauramidopropyl amine oxide, and hydroxyalkyl (C12-14) hydroxyethyl sarcosine.
• Amphoteric surfactants may be amphoteric fluorinated surfactants with intramolecular perfluoroalkyls.
• An example is perfluoroalkyl betaine.
• Commerical examples of amphoteric fluorinated surfactants include Ftergent 400SW, available from Neos Co., Japan, Saffron S-231, available from AGC Chemicals Co., Japa n, and Capstone ® TMFS-50, available from E. I. du Pont de Nemours and Company, Wilmington, DE.
• Cationic surfactants may be selected from quaternary ammonium sa Its, alkylamine salts, and pyridinium salts. Quaternary ammonium salts and alkylamine salts are represented by formula (II) .
• R represents identical or different alkyls
• X represents the halogens fluorine (F), chlorine (CI), and bromine (Br).
• Examples of quaternary ammonium salts used in these methods include hexadecyl trimethyl am monium chloride, hexadecyl trimethyl ammonium bromide, octyl trimethyl ammonium chloride, octyl trimethyl ammonium bromide, decyl trimethyl a mmonium chloride, decyl trimethyl ammonium bromide, dodecyl trimethyl ammonium chloride, dodecyl trimethyl ammonium bromide, octadecyl trimethyl ammonium chloride, octadecyl trimethyl ammonium bromide, stearyl trimethyl ammonium chloride, stearyl trimethyl ammonium bromide, cetyl trimethyl am monium chloride, cetyl trimethyl ammonium bromide, distearyl dimethyl ammonium chloride, distearyl dimethyl ammonium bromide, benzalkonium chloride, benz
• long-chain monoalkyl (or alkenyl) quaternary ammonium salts with 10 to 20 carbon atoms and tri-short chain alkyl quaternary ammonium salts with 1 to 3 carbon atoms would be preferable.
• alkylamines used in these methods include trioctylamin e hydrochloride, trioctylamine hydrobromide, tridecylamine hydrochloride, tridecylamine hydrobromide, tridodecylamine hydrochloride, tridodecylamine hydrobromide, trihexadecylamine
• R represents an alkyl
• X represents the halogens fluorine (F), chlorine (C I), and bromine (Br).
• pyridinium salts used in these methods include pyridinium chloride, cetylpyridinium chloride, cetylpyridinium bromide, myristyl pyridinium chlcride, myristyl pyridinium bromide, dodecylpyridinium chloride, dodecylpyridinium bromide, ethylpyridinium chloride, ethylpyridinium bromide, hexadecylpyridinium chloride, hexadecylpyridinium bromide, butyl pyridinium chloride, butyl pyridinium bromide, methyl hexyl pyridinium chloride, methyl hexyl pyridinium bromide, methyl octyl pyridinium chloride, methyl octyl pyridinium bromide, dimethyl butyl pyr
• Cationic surfactants may include fluorinated surfactants that have fluoroalkyls, for example, perfluoro alkyl trimethyl ammonium salts.
• Commercially available surfactants include Ftergent 300 or Ftergent 310, available from Neos Co., and Saffron S-221, available from AGC Semichem ical Co.
• Desirable cation ic surfactants include hexadecyl trimethyl ammonium bromide, stearyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, trimethyl stearyl ammonium bromide, cetyl trimethyl ammonium chloride, distearyl dimethyl ammonium chloride, and mixtures of these.
• hexadecyl trimethyl ammonium bromide having formula (IV) may also be desirable.
• Cationic surfactants may contain one or more or combinations of quaternary ammonium salts, alkyl amine salts, and quaternary ammonium hydroxide.
• the amount of cationic surfactant may range from 0.5 to 10 weight parts per 100 weight parts of cairbon.
• the molecular weight of surfactant range from 50 to 5000, or from 100 to 1000, or from 300 to 500.
• Hydrolysis catalysts promote the hydrolysis reaction of silica precursors as acidic hydrolysis catalysts or basic hydrolysis catalysts.
• the methods described he rein may use acidic hydrolysis catalysts or basic hydrolysis catalysts.
• Acidic hydrolysis catalysts are proton (H + ) donors that promote the hydrolysis reaction through protonation of oxygen atoms, whereas basic hydrolysis catalysts are proton (H + ) acceptors that promote the reaction by enabling nucleophilic addition through proton transfer from carbon atoms in hydrolysis.
• Acidic hydrolysis catalysts may be used as the sole catalyst. When repeating the silica coating process as described above, basic hydrolysis catalysts and acidic hydrolysis catalysts may be alternated, which is expected to increase the strength of the silica coating.
• Hydrochloric acid may be preferable as an acidic hydrolysis and ammonia may be preferable as a basic hydrolysis catalyst.
• the amount of hydrolysis catalyst ranges from 0.5 to 10 weight parts per 100 weight parts of carbon.
• a particularly suitable solvent may be an aqueous solution that uniformly disperses the solute.
• Carbon particles, surfactants, and silica precursors can uniformly react by being uniformly dispersed.
• suitable solvents in these methods include isopropyl alcohol (IPA), methanol, ethanol, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA),
• IPA isopropyl alcohol
• MEK methyl ethyl ketone
• MIBK methyl isobutyl ketone
• PGME propylene glycol monomethyl ether
• PGMEA propylene glycol monomethyl ether acetate
• MEA monoethanolamine
• DPGDA dipropylene glyol diacrylate
• Another particularly suitable solvent is an aqueous solution of water and one or more of the following: isopropyl alcohol (IPA), methanol, ethanol, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), monoethanolamine (MEA), dipropylene glyol diacrylate (DPGDA).
• the solvent may be a mixture of water and one or more of the following: isopropyl alcohol (IPA), methanol, and ethanol.
• the solvent is an aqueous solution of water and IPA, methanol, or ethanol
• the amount of solvent ranges from 300 to 2000 weight parts per 100 weight parts of carbon and the amount of water ranges from 4 to 70 weight parts per 100 weight parts of carbon.
• compositions having electrically insulating properties may be prepared by dispersing in a polymeric medium the thermally conductive particles made by methods described herein. These compositions have both suitable electrical resistivity and suitable thermal conductivity.
• Media include polymers and other suitable media as well as combinations of media.
• Suitable polymeric media include organic polymers, inorganic polymers,
• organic-inorganic hybrid polymers include thermoplastic resins, thermosetting resins, aramid resins, and rubber, and more specifically: polyolefin resins such as polyethylene and polypropylene; polyamide resins such as nylon 6, nylon 66, nylon n, nylon 12, and aromatic polyamide; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polycyclohexylmethylene
• polyphenylene ether resin polyacetal resin, polyphenylene sulfide resin, wholly aromatic polyester resin, polyether ether ketone resin, polyethersu lfone resin, polysulfone resin, polyamide imide resin, polyimide resin, polytrimethylene terephthalate resin, fluorine resin, epoxy resin, novolak resin, isothiocyanate resin, melamine resin, urea resin, imide resin, aromatic polycarbodiimide resin, phenoxy resin, phenol resin, methacrylate resin, unsaturated polyester resin, vinyl ester resin, urea urethane resin, and resol resin.
• Copolymers in which the constituents including these resins are arbitrarily combined may also be used. These organic polymers may be used alone or in combinations. Particularly suitable organic polymers include polyamide resin, polyester resin, polyphenylene sulfide resin, and wholly aromatic polyester resin.
• Suitable inorganic polymers include, but are not limited, to silicon resin.
• Organic-inorganic hybrid polymers are polymers with silica partially compounded in the carbon framework of organic polymers. While not restricted to specific polymers, a suitable example is epoxy resin - silica hybrid polymer.
• suitable media may include organic media as necessary to dissolve these polymers or to regulate viscosity of the composition.
• the organic media may be evaporated by drying the insulating composition.
• the amount of thermally conductive particles in these compositions may range from 10 to 80 wt°/o, or from 15 to 7owt°/o, or from 20 to 60 wt°/o, of the total weight of the composition.
• These compositions may also contain additives, including antioxidants, glass fiber, and lubricants. Because of their combined property of thermal conductivity and electrical conductivity, these compositions are particularly suitable in housings or components for LED lamps as well as for insulating film applied to a substrate for the installation of electronic components.
• Carbon Particles Flake shaped graphite particles having:
• Anionic Polymer Coating In comparative examples, an aqueous solution of 0.35 g having 30 wt % poly (4-sodium styrene sulfonate) of mean molecular weight of 200,000 and available from Sigma-Aldrich, St. Louis, MO, 2.5 g of graphite flakes, and 50 g of water was mixed for five minutes at room temperature in order to form an anionic polymer coating on the surface of graphite particles. The coated graphite particles were collected by filtering this mixed solution and then further treated.
• Cationic Polymer Coating In comparative examples, an aqueous solution of 0.25 g having 20 wt % poly-diallyldimethylammonium chloride aqueous solution ofmean molecular weight of 200,000 to 350,000 and available from Sigma-Aldrich, St. Louis, MO, 50 g of deionized water, and 1.46 g of sodium chloride was mixed and the graphite particles coated with anionic polymer were added thereto and stirred for five minutes at room temperature to achieve a cationic polymer coating over the anionic polymer coating.
• Fluorinated cationic surfactant Ftergent 300, available from Neos Co., Tokyo, Japan
• Lauryl dimethyl amino acetic acid betaine 31 weight percent aqueous solution of lauryl dimethyl amino acetic betaine (a.k.a Lauryl betaine), available as AMPHITOL 20BS, from Kao Corp., Tokyo, Japan.
• AMPHITOL 20BS available as AMPHITOL 20BS, from Kao Corp., Tokyo, Japan.
• 0.071 grams of lauryl dimethyl amino acetic betaine were added to water to create an aqueous solution that had the same amount of
• Fluorinated amphoteric surfactant 27 weight percent aqueous solution of Capstone ® FS-50, available from E.I. du Pont de Nemours and Company, Wilmington, DE.
• Capstone ® FS-50 available from E.I. du Pont de Nemours and Company, Wilmington, DE.
• 0.081 grams of Capstone ® FS-50 were added to water to create an aqueous solution that had the same amount of surfactant-0.022 grams-as was used in Example 1 with CTAB
• TEOS a.k.a. tetraethoxysilane
• liquid glass also known as liquid glass, is a common name for sodium silicate compounds having the formula Na 2 Si0 2 ) n O, and available in aqueous solution.
• Carbon particles in the form of flake graphite particles were subjected to surface coating by the following method: To a solvent was added a catalyst and a surfactant, followed by the addition of flake shaped graphite with a diameter (D50) of 35 ⁇ or a diameter (D50) of 150. ⁇ . A silica precursor was added, followed by stirring for two hours at a certain temperature, either 6o°C or 8o°C, using a magnetic stirrer to result in a mixed solution in which the graphite particles become at least partially coated. The mixed solution was then filtered, the graphite particles removed and dried for one day at room temperature. The resulting graphite particles were investigated by Auger electron spectroscopy (AES), which revealed the thickness of the silica layer to be about 100 nm (see FIG. 1).
• AES Auger electron spectroscopy
• the volume resistivity of the coated carbon particles in the examples and the comparative examples was measured by the two terminal method using the device 100 shown in FIG. 2. Carbon particles 12 were packed to a height of 30 mm in a clear transparent cylinder 11 bonded to two terminal electrodes 10 on both sides. The amount packed was 0.4 g. The area of the contact surface of one terminal electrode 10 with the transparent cylinder 11 was 0.785 cm 2 . Voltage of 1000 V was applied to the cylinder between the two terminals and volume resistivity was determined.
• Silica-coated carbon particles of Example 1 were dispersed in organic solvent to prepare an insulating composition. Such compositions may be applied to at least part of a surface of an article to result in an insulated surface.
• Silica-coated carbon particles were mixed with polybutylene terephthalate and then subjected to molten kneading and injection molding using the micro compounder from DSM Research Xplore Co. and a desk-top injection molder to prepare a molded article 16 mm wide x 16 mm high x 16 mm thick.
• the volume resistivity of the molded articles was measured at 500 V applied voltage using a Hiresta UP (MCP-HT 50) resistivity meter from Mitsubishi Analytic Co.
• Table 1 shows examples of coated carbon particles made by the methods described herein.
• graphite particles were subjected to surface coating by the following method.
• the solvent was a mixture of deionized water in isopropyl alcohol.
• Ammonia water was added, followed by the addition of CTAB as the surfactant and of flake-shaped graphite having a diameter (D50) of 35 ⁇ .
• the silica precursor tetraethoxysilane (TEOS) was added to this mixture, followed by stirring for two hours at 6o°C using a magnetic stirrer.
• the mixed solution was then filtered, followed by the removal of graphite particles and drying for one day at room temperature.
• the resulting silica-coated carbon particles were investigated by Auger electron spectroscopy (AES), which revealed the thickness of the silica layer to be approximately 100 nm (see FIG. 1).
• AES Auger electron spectroscopy
• Example 2 was prepared as in Example 1, except that STAB was substituted as a cationic surfactant.
• Example 3 was prepared as in Example 1, except that dodecyl trimethyl ammonium bromide was substituted as a cationic surfactant.
• Example 4 was prepared as in Example 1, except a fluorinated surfactant-Ftergent 300 was substituted as a cationic surfactant.
• Example 5 was prepared as in Example 1, except an aqueous solution of 31% lauryl dimethyl amino acetic acid betaine— in particular, AMPHITOL ® 20BS— was substituted as an amphoteric surfactant.
• the amount of lauryl dimethyl amino acetic acid betaine added was set at 0.071 g of a lauryl dimethyl amino acetic acid betaine aqueous solution so as to reach the same 0.022 g quantity as CTAB.
• Example 6 was prepared as in Example 1, except that a fluorinated surfactant (27 wt% aqueous solution Capstone ® FS-50) was substituted as an amphoteric surfactant.
• the amount of fluorinated surfactant added was set at 0.081 g of a fluorinated surfactant aqueous solution so as to reach the same 0.022 g quantity as CTAB in Example 1.
• Example 7 was prepared as in Example 1, except ethanol was the solvent.
• Example 8 was prepared as in Example 1, except the mixing occurred at 8o°C.
• Example 10 was prepared as in Example 7, except for the further addition of 0.05 g (4 weight parts) of silane coupling agent and the change of solvent amount from 18 g (1565 weight parts) to 4.5 g (391 weight parts).
• TEOS was added to the mixed solution and reacted for two hours, followed by the addition of the silane coupling agent 3-glycidoxypropyltriethoxysilane and further heating for one hour at 6o°C .
• Example 11 was prepared as in Example 7, except for the further addition of 0.05 g (1.6 weight parts) of PDMS, change of the solvent amount from 18 g (1565 weight parts) to 4.5 g (391 weight parts), and the use of graphite having a diameter (D50) of 150 ⁇ .
• the PDMS was mixed with TEOS beforehand and then added to the mixed solution.
• Example 2 shows Comparative Examples of coated carbon particles made by methods NOT described or recited herein.
• CEi was prepared as in Example 1, except without the CTAB.
• CE2 was prepared as in Example 1, except sodium palmitate was substituted as an anionic surfactant.
• CE3 was prepared as in Example 1, except polyoxyethylene (10) cetyl ether— Brij® Cio was substituted as a nonionic surfactant.
• anionic coated graphite particles were prepared from 0.35 g of an aqueous solution of 30 wt.% poly (4-sodium styrene sulfonate), 2.5 g of graphite flakes, and 50 g of water, that had been mixed forfive minutes at room temperature in orderto form the anionic polymer coating on the surface of graphite particles. Anionic coated particles were collected by filtering the mixed solution.
• a total of 0.25 g of an aqueous solution of 20 wt.% poly-dia I lyldi methyl- ammonium chloride, 50 g of deionized water, and 1.46 g of sodium chloride (to cause colloidal silica to polymerize and form the coating on the graphite particle) were mixed; the anionic coated particles were added thereto and stirred forfive minutes at room temperature to achieve a cationic polymer overcoat on top of the anionic polymer coating. Subsequently, the mixed solution was filtered to collect the coated graphite particles.
• the overcoated graphite particles were mixed with 50 g of deionized water and 2.5 g of colloidal silica, i.e., Snowtex®, forfive minutes at room temperature to achieve an outer silica coating.
• the coated graphite particles were removed by filtering, then dried for one day at room temperature.
• 2-methyl-2-oxazoline and 2 g of acrylic acid were added and stirred for eight hours at 25°C.87 g of mixed solution were removed, after which 10 g of tetraethoxy silane and 3 g of 0.001 N dilute hydrochloric acid were added and mixed for 10 hours at 2 ° .
• the mixed solution was filtered to remove the graphite particles, which were washed and then dried for one day at room temperature.
• Table 1 shows that the volume resistivity of the particles of Ei to E8 and Eio and E11 was at least 10 4 and up to 10 8 times higher than that of any comparative example in Table 2.
• CEi to CE3 differed from the examples only in that they used neither a cationic nor amphoteric surfactant.
• the absolute increase in volume resistivity of Ei to E8 and Eio and E11 over that of CEi to CE3 clearly shows the greater effectiveness of cationic or amphoteric surfactants in forming silica coatings in the methods described herein.
• CE4 shows that colloidal silica as the source of silica in combination with a cationic surfactant produces silica coated graphite particles having very poor volume resistivity.
• CE5 shows that sodium silicate as the source of silica in combination with a hydrolysis catalyst in the absence of a surfactant produces silica coated graphite particles below the recited volume resistivity.
• CE4 and CE5 together show that, when the source of silica for coating is not a silica precursor, or, when a surfactant is not used, the silica coated graphite does not attain the recited volume resistivity.
• CE6 shows that, when using a silica precursor with a cationic surfactant but insufficient hydrolysis catalyst, the resulting silica coated graphite particle does not attain the recited volume resistivity.
• CE7 shows that, when a silane coupling agent is used in the absence of a surfactant and a silica precursor, and with insufficient hydrolysis catalyst, the resulting graphite particle does not attain the recited volume resistivity.
• Eg was prepared from a composition comprising polybutylene terephthalate as the polymer medium and silica-coated graphite particles as prepared in Example 1.
• the polybutylene terephthalate and the coated graphite particles were mixed and melt blended.
• the melt blend was injection molded using the micro compounder from DSM Research Xplore Co. and a desk-top injection molder to derive a molded test article 16 mm wide x 16 mm high x 16 mm thick.
• a molded test article CE8 was prepared as for Eg, except the composition included graphite particles that had not been coated with silica.
• a molded test article CEg was prepared as for Eg, except the composition lacked graphite particles.
• Table 3 presents the thermal conductivity and the volume resistivity of molded test articles Eg, CE8, and CEg. Although Eg and CE8 exhibited the same thermal conductivity, Eg had more than 10 10 times the volume resistivity of CE8, which shows the insulating property of silica coated graphite particles made by the methods described herein. Although CEg exhibited a substantially similar volume resistivity as Eg, its thermal conductivity was reduced five-fold. Thus, Eg shows that molded compositions containing graphite particles coated by the methods described herein exhibit a combined property of thermal conductivity and electrical insulation sufficient to whisk away or transfer heat from inside an LED housing or other high temperature electronic device while preventing electric shock.

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