JP6654562B2 - Thermally conductive electrical insulating particles and compositions - Google Patents

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority from the currently pending Japanese Patent Application No. 2013-209304, filed October 4, 2013.

  Described herein are thermally conductive particles that are also electrically insulating, resin compositions containing these particles, and methods for making them.

  In recent years, electronic devices such as LED modules and handhelds have not only been smaller and integrated, but also have greater power, which requires greater heat dissipation and electrical isolation of the components of these devices. Therefore, thermally conductive particles having excellent electrical insulation properties are required as constituent units of materials used in electronic devices.

  WO 2011/027757 discloses ceramic-coated carbon particles, which are thermally conductive, wherein the ceramic particles are added by adding a slurry of carbon particles to the slurry of ceramic particles. It is formed by adhering to carbon particles. U.S. Pat. No. 5,246,897 discloses coated graphite particles formed by a mechanical impact method in which high velocity gas flows are used to impinge the graphite particles and the coating particles. U.S. Patent No. 7,588,826 discloses coated graphite particles formed by mechanical melting in the presence of an interactive functional agent.

Described herein is a thermally conductive particle comprising a composite core and an insulating material that at least partially coats the composite core, wherein the composite core comprises an organic binder bound together by a mechanofusion process. And the volume resistivity of the thermally conductive particles is at least in the range of 1 × 10 ⁴ Ω · cm to 1 × 10 ¹⁰ Ω · cm. Also described herein is a resin composition comprising 10 to 70% by volume of these particles in addition to a thermoplastic resin, a thermosetting resin, an aramid resin, a rubber, or a mixture thereof. Also described herein is a method of making these particles.

It is sectional drawing of the heat conductive particle as described in the claim. 1 is a schematic diagram of an apparatus for measuring the volume resistivity of thermally conductive particles. It is an upper surface photograph of the molded object containing the heat conductive particle as described in the claim. It is a cross-sectional photograph of the molded article containing the thermally conductive particles described in the claims.

  The following definitions and abbreviations must be used to interpret the meaning of the terms discussed in the description and set forth in the claims.

Definitions As used herein, the term "volume resistivity" refers to the electrical resistivity of a material and determines the electrical insulating ability of the material. Volume resistivity is measured by placing sample carbon particles in a transparent cylinder between two electrodes with terminals. In the examples herein, a voltage of 500 V was applied through the terminals to measure the resistivity of the particles described herein.

  As used herein, the term “aspect ratio” of a particle refers to the ratio of the maximum length of a particle divided by its width, ie, its maximum thickness.

  As used herein, the term "composite core" refers to thermally conductive core particles bound to an organic binder by a mechanofusion process.

  As used herein, the term “thermal conductivity” or “thermal conductivity” (often denoted as k, λ, or κ) refers to a property of a material that conducts or transfers heat. Heat transfer occurs at a higher rate with high thermal conductivity materials than with low thermal conductivity materials. Correspondingly high thermal conductivity materials are widely used in heat sink applications, while low thermal conductivity materials are used as insulation. Thermal conductivity is typically measured as thermal conductance, which refers to the amount of heat that passes a unit area and thickness of a plate per unit time when its opposing faces have a temperature difference of 1 Kelvin. For a plate with thermal conductivity k, area A and thickness L, the calculated conductance is kA / L, measured in W / mK and equal to W / ° C.

  As used herein, the term "thermal diffusivity" refers to the thermal conductivity of an article divided by the density and specific heat capacity of the article at constant pressure, relative to the ability of the article to store thermal energy. Evaluate the ability to conduct thermal energy. It has SI units of m2 / s. The temperature diffusivity is usually denoted as α. ceremony,

(Where
k is the thermal conductivity (W / (m · K)),
ρ is the density (kg / m3),
c _p is the specific heat capacity (J / (kg · K))).

Abbreviations As used herein, "%" refers to percent.
As used herein, "wt%" refers to weight percent.
As used herein, "vol%" refers to volume percent.
As used herein, "hrs" refers to hours, "m" refers to minutes, and "s" refers to seconds.
As used herein, "g" refers to gram.
As used herein, “μm” refers to microns.
As used herein, “nm” refers to nanometer.
As used herein, "rpm" refers to revolutions / minute.
As used herein, "mm" refers to millimeter.
As used herein, “cm” refers to centimeter.
As used herein, “ml” refers to milliliter.
As used herein, "V" refers to bolt.
As used herein, “Ω · cm” refers to ohm centimeter.
As used herein, “W” refers to watts.
As used herein, "m" refers to meters.
As used herein, "K" refers to Kelvin.
As used herein, “mPa · s” refers to millipascal seconds.

Ranges Unless otherwise specified, any ranges set forth herein explicitly include their endpoints. By specifying amounts, concentrations, or other values or parameters as ranges, regardless of whether such pairs are separately disclosed herein, the upper and lower limits of any range. All ranges formed from any pair are disclosed. The methods and articles described herein are not limited to the specific values disclosed when defining a range in the description.

Preferred Variations of the processes, compositions, and articles described herein, whether or not identified as preferred variations,-in terms of materials, methods, steps, values, and / or ranges, etc. The disclosure of any variation herein is specifically intended to disclose any process and article that includes any combination of such materials, methods, steps, values, ranges, and the like. Any such disclosed combination is specifically intended to be a preferred variation of the processes, compositions, and articles described herein, in order to provide precise and sufficient support to the claims. ing.

Overview Thermally conductive particles are described herein, one of which is shown in FIG. 1 as element 10, which comprises a core particle 11 bonded together with an organic binder 12 and a composite core at least partially. And a composite core made of the insulating material 13.

  Also described herein is a resin composition comprising the thermally conductive particles described herein and a thermoplastic resin, a thermosetting resin, an aramid resin, a rubber, or a mixture thereof.

Also described herein is a method of at least partially coating a composite core with an insulating material, wherein the composite core includes a plurality of core particles and an organic binder that bonds the core particles together;
The core particles are thermally conductive and are selected from the group consisting of metal particles, ceramic particles, carbon-based particles, and mixtures thereof;
The insulating material is selected from the group consisting of sericite, boehmite, talc, and mixtures thereof;
Thermally conductive particles, when measured at an applied voltage of 500V on the cylinder of the thermally conductive particles having a height of 10mm in diameter and 3.0 mm, at least ^{1 × 10 4 Ω · cm~1 ×} 10 10 The volume resistivity is in the range of Ω · cm.

Thermally Conductive Particles A composite core is obtained by combining a plurality of core particles with an organic binder using a compression shear mixing method, which can be prepared to have a desired particle size or shape. The volume of the organic binder is in the range of 30 to 30 parts by volume, preferably 26 to 26 parts by volume, more preferably 22 to 22 parts by volume with respect to 100 parts by volume of the core particles.

  The composite core is partially or completely coated with an insulating layer whose thickness ranges from 0.1 to 10 μm, preferably 0.5 to 6 μm. The volume of the insulating material is in the range of 3 to 48 parts, preferably 5 to 35 parts, more preferably 10 to 32 parts for 100 parts by volume of the composite core. Such volume concentration of the insulating material and thickness of the insulating coating provide the thermally conductive particles with sufficient thermal conductivity and the desired volume resistivity as recited in the claims.

  The average particle size of the thermally conductive particles described herein ranges from 0.5 to 300 μm, preferably 20 to 250 μm, more preferably 90 to 190 μm. The average particle size may be quantified by measuring its longest axis 14 with a scanning electron microscope (SEM).

  The aspect ratio of the thermally conductive particles described herein ranges from 100 to 100, preferably 50 to 50, more preferably 35 to 35, and even more preferably 15 to 15. FIG. 1 shows the aspect ratio as the particle length (along the major axis 14) divided by the particle thickness 15. The aspect ratio of the thermally conductive particles described herein is preferably greater than 2, and preferably ranges from 3 to about 7. When the thermally conductive particles have a flat shape, molding them into an article with a resin may give the molded article anisotropic thermal conductivity.

The volume resistivity of the thermally conductive particles described herein is at least in the range of 1 × 10 Ω · cmΩ · cm, and preferably from 1.0 × 10 ^{4 to} 1.0 × 10 ¹⁸ Ω · cm. More preferably, it is in the range of 1.0 × 10 ^{4 to} 1.0 × 10 ¹⁰ Ω · cm.

In any of the thermally conductive particles, compositions or methods described herein, any or all of the following elements may be combined to provide a wide range of variations, each of which Considered inventions:
The core particles may be carbon-based particles, and / or the carbon-based particles are graphite, and / or the core particles are natural in a ratio of 3: 2 to 99: 1. And graphite and flaky carbon-based particles, and / or when a mixture of graphite and flaky carbon-based particles is used, the flaky carbon-based particles Has an average thickness less than the average thickness of the graphite; and / or the core particles are 100 parts by volume of the thermally conductive particles described herein; and / or the organic binder is the volume of the core particles. And / or the insulating material is in the range of 4 to 48 parts by volume of the core particles, and / or the organic binder is a thermosetting resin; and / or And / or the average particle size of the thermally conductive particles described herein ranges from 0.5 μm to 300 μm, and / or the insulating material is sericite, boehmite, talc, mica, and mixtures thereof. And / or-in the thermally conductive resin composition described herein, the thermally conductive particles range from 10 to 70% by volume of the total volume of the composition; and / or Or-the thermally conductive resin composition may comprise a thermoplastic resin, a thermosetting resin, an aramid resin, a rubber, or a mixture thereof.

a) Composite Core The composite core exhibits a sufficient thermal conductivity of at least 100 W · m ⁻¹ · K ⁻¹ and preferably not more than 800 W · m ⁻¹ · K ⁻¹ . The maximum occurs for composite cores having anisotropic thermal conductivity.

Core Particles The composite core may include core particles of metal, ceramic, or carbon or mixtures thereof. Metal particles include copper, silver, nickel, aluminum, and alloys thereof. Ceramic particles include aluminum nitride, silicon carbide, and alumina. The carbon-based particles include graphite, carbon nanotubes, fullerene, graphene, carbon black, glass carbon, carbon fiber, amorphous carbon, boron carbide, or mixtures thereof.

  Preferably, the composite core contains particles based on carbon. The carbon-based particles preferably contain graphite, which may be natural or synthetic, but natural is preferred due to its thermal conductivity and cost.

  In particular, the carbon-based particles are made up of a mixture of plate-like graphite, also called almost spherical and also flaky, in a spherical: flaky volume ratio of 3: 2-99: 1 and preferably in a volume ratio of 1: 1-6. : 1 included. Flake carbon-based particles that are thinner than natural graphite include expanded graphite, graphene, and mixtures thereof. Expanded graphite is flake natural graphite in which the interlayer space is expanded by chemical and thermal treatments to expand and separate graphite in the direction in which the single layers are stacked. Graphene is a flake-like particle in which carbon atoms are arranged in a hexagonal lattice. T, natural graphite is a few μm thick, while expanded graphite and graphene are less than 1 μm thick.

  By mixing relatively thick natural graphite with flake-like carbon-based particles, an almost flat thermally conductive composite core is formed. Molded articles formed using the resin composition containing substantially flat thermally conductive particles provide an anisotropic path of heat conduction, which increases the thermal conductivity of the molded article.

  The average particle size of the composite core is in the range of 1 to 150 μm, preferably 15 to 100 μm, more preferably 30 to 90 μm. The average particle size of the composite core is quantified by measuring the longest axis of the composite core with a scanning electron microscope (SEM).

  The aspect ratio of the composite core is preferably in the range of 1 or more, more preferably 2 or more, and even more preferably 5 or more. The composite core may contain two or more types of particles having different aspect ratios.

Organic Binder The composite core may be formed into a desired shape by combining one or more types of core particles together with an organic binder. Organic binders are polymers having a weight average molecular weight of at least 300. The weight average molecular weight is preferably less than 1,000,000.

  The type of the organic binder is not particularly limited, but is preferably a thermoplastic resin, a thermosetting resin, or a mixture thereof, and more preferably a thermosetting resin. Thermosetting resins include epoxy, novolak, isothiocyanate, melamine, urea, imide, aromatic polycarbodiimide, phenoxy resin, phenol, methacrylate, unsaturated polyester, vinyl ester, urea urethane, resole, and silicone, and these. And mixtures. The thermosetting resin is preferably melamine.

  The organic binder may be in solution or dispersed in a solvent. A preferred solvent is water, and an aqueous organic binder solution is preferred.

Preparation of the Composite Core The composite core may be formed by mixing the core particles with an organic binder and binding and mixing the core particles with the organic binder. The organic binder fills the gaps between the core particles and increases the mechanical strength of the core particles.

  Compression shear mixing can be used when blending the core particles with the organic binder to join the core particles. Compressive shear mixing is a method of applying compressive and shear forces to a plurality of particles (mixture of core particles and organic binder) of different materials to bond the particles together.

  Compression shear mixing may be provided using a Mechanofusion system (Hosokawa Micron Ltd.) or Theta Composer System (Tokuju Corp.). When a mechanofusion system is used, rotating blades in a compression vessel press the core particles and organic binder against the vessel inner wall, providing strong compression and shear forces to bind and mix the core particles with the organic binder. .

  When a dry particle compounding device such as NOB-130 (available from Hosokawa Micron Corporation) is used for bonding, the gap between the blades and the vessel wall is in the range of 3 to 3 mm, The rotation speed of the blade is preferably in the range of 1,000 rpm to 6,000 rpm, and more preferably in the range of 1,800 rpm to 4,500 rpm.

  When the Theta Composer System (THC model Theta Composer available from Tokuju Works) is used, the container of the system rotates in one direction, while the elliptical rotor in the container rotates in the opposite direction, Compression and shear are applied to the gap between the vessel wall and the rotor to bind and bind the core particles with the organic binder. When the gap between the rotor and the vessel wall is in the range of 3 to 3 mm, the rotational speed of the blade is preferably in the range of 1,000 rpm to 6,000 rpm, more preferably in the range of 1,800 rpm to 4,500 rpm.

  In addition, the organic binder may be diluted with a solvent before mixing with the core particles. By diluting the organic binder with a solvent, it is possible to bind the carbon particles with less binder. As long as the solvent dissolves the organic binder, the solvent may be of any type. Examples of the solvent include water, isopropyl alcohol (IPA), methanol, ethanol, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), and monoethanolamine (MEA). ), Dipropylene glycol diacrylate (DPGDA), or mixtures thereof. The solvent is preferably a solution in which the organic binder is uniformly dispersed. If the organic binder is water-soluble, the solvent is preferably water.

  The temperature at which the core particles and the organic binder are mixed is not particularly limited, but depends on the type and viscosity of the organic binder. In particular, when the organic binder is an aqueous solution, the mixing temperature is preferably in the range of 10 ° C to less than 80 ° C, more preferably in the range of 25 ° C to less than 50 ° C to avoid evaporation of water.

  The viscosity of the organic binder or the mixture of the organic binder and the solvent is preferably in the range of 0.5 to 1,000 mPa · s at 20 ° C. By adjusting the viscosity of the organic binder and the solvent during mixing, the composite core may obtain a desired shape. The composite core is almost flat at 0.5 to 100 mPa · s at 20 ° C. and becomes more spherical at 100 to 1,000 mPa · s.

  The mixing time may be adjusted so that the core particles and the organic binder are suitably bonded and mixed with each other. The mixing time is preferably in the range of 1 minute to 30 minutes, more preferably 3 minutes to 10 minutes.

b) Insulating Material The insulating material of the thermally conductive particles described herein has a volume resistivity at 20 ° C. of at least 1 × 10 ⁹ Ω · cm and preferably 1 × 10 ²² Ω · cm or less. Suitable insulating materials can be, but are not limited to, natural or synthetic, including but not limited to metal oxides, metal carbonates, carbonate minerals, metal nitrides, metal sulfides, phosphate minerals, clays Minerals, silicate minerals, glass materials, or mixtures thereof.

Metal oxides include aluminum oxide (Al ₂ O ₃ ), zinc oxide (ZnO), titanium oxide (TiO ₂ ), iron oxide (FeO), magnesium oxide (MgO), silicon oxide (SiO ₂ ), boehmite (Al ₂ O ₃ .H ₂ O), or a mixture thereof. Metal carbonates include calcium carbonate (CaCO ₃ ), magnesium carbonate (MgCO ₃ ), or mixtures thereof. Carbonate minerals include calcite (polymorphic CaCO ₃ ), aragonite (crystalline CaCO ₃ ), dolomite (CaMg (CO ₃ ) ₂ ), hydrotalcite (Mg ₆ Al ₂ CO ₃ (OH) _16. 4 (H ₂ O)), the fire gold ore _{(Mg 6 Fe 2 (CO 3} ) (OH) 16 · 4 (H 2 O)), Manaseaito _{(Mg 6 Al 2 (CO 3} ) (OH) 16 · 4H 2 O ) Or mixtures thereof. A metal nitride, boron nitride (BN), aluminum nitride (AlN), silicon nitride (Si ₃ N _4), or mixtures thereof. Metal sulfides include molybdenum sulfide (MoS ₂ ), tungsten sulfide (WS ₂ ), zinc sulfide (ZnS), or a mixture thereof. Phosphate minerals include apatite (Ca ₅ (PO ₄ ) ₃ (F, Cl, OH)), hydroxyapatite (Ca ₅ (PO ₄ ) ₃ (OH)), or mixtures thereof. Examples of the silicate mineral include minerals such as monoclinic crystalline clay (for example, serpentine ((Mg, Fe) ₃ Si ₂ O ₅ (OH) ₄ ), phyllite (Al ₂ Si ₄ O ₁₀ ) OH) ₂ ), kaolin clay, sericite (KAl ₂ AlSi ₃ O ₁₀ (OH) ₂ ), montmorillonite ((Na, Ca) _0.33 (Al, Mg) ₂ Si ₄ O ₁₀ (OH) ₂ .nH ₂ O ), Chlorite group minerals, talc, vermiculite, and smectite group minerals), mica, diatomaceous earth (SiO ₂ .nH ₂ O), or mixtures thereof.

  Since the chemical formulas of the insulating materials described above may be used for various classes of insulating materials, the thermally conductive particles described herein may include any type of insulating material specified by the chemical formula. Can be

  Suitable insulating materials include aluminum oxide (alumina), zinc oxide, talc, magnesium oxide, silicon dioxide, boehmite, boron nitride, mica, aluminum nitride, silicon nitride, zinc sulfide, or mixtures thereof. More preferred insulating materials include talc, boehmite, sericite, mica, or mixtures thereof. Talc is particularly preferred.

  The average particle size of the insulating material is preferably 10 nm to 50 μm, more preferably 100 nm to 30 μm, and more preferably 300 nm to 15 μm.

  The volume concentration of the insulating material relative to the thermally conductive core particles is from about 4 to about 40 volume percent, preferably from about 5 to about 30 volume percent, more preferably from about 8 to about 30 volume percent, and most preferably from about 10 to about 25 volume percent. It is in the range of volume percent.

Coating the Composite Core with an Insulating Material The composite core is at least partially coated with an insulating material having a volume resistivity preferably between 1 × 10 ^{9 and} 1 × 10 ²⁰ Ω · cm.

  Similar to forming a composite core, the composite core may be coated with an insulating material using a mechanofusion or theta composer system, which is essentially fused to the surface of the composite core by compression and shear forces. Is done. Alternatively, the composite core can be coated using different methods. However, to maximize manufacturing efficiency, it is preferable to use the same system to form the composite core and coat it with an insulating material. Preferably, the composite core is formed and coated using a mechanofusion process.

  A two-stage process in which the core particles and the organic binder are first subjected to compression shear mixing to form a composite core, the insulating material is added thereto, and again subjected to compression shear mixing to provide the thermally conductive particles described herein. Is preferably performed. The temperature at which the composite core is coated with the insulating material is preferably in the range below the curing temperature of the organic binder and, if a solvent is used, below the boiling point of the solvent. The coating temperature preferably ranges from 10C to less than 80C, more preferably from 25C to less than 50C. The insulating material at least partially coats the surface of the composite core, thereby providing the thermally conductive particles described herein.

  Further, the time of compression shear mixing of the composite core with the insulating material may be adjusted so that the insulating material fuses to the surface of the composite core, preferably 5 seconds to 5 minutes, more preferably 10 seconds to 120 minutes. Range of seconds.

The insulating material preferably covers or coats the entire surface of the composite core. Alternatively, the insulating material may cover or coat a sufficient portion of the surface of the composite core to maintain a volume resistivity of the thermally conductive particles of at least 1 × 10 ⁴ Ω · cm.

Resin Compositions The compositions described herein contain the thermally conductive particles described herein dispersed in a thermoplastic resin, a thermosetting resin, an aramid resin, a rubber, or a mixture thereof. I do. The compositions described herein exhibit both sufficient thermal conductivity and volume resistivity for use in moldings, films, sheets, adhesives, and the like. For example, the compositions described herein may be prepared as insulating films and applied to the surface of electronic components, or may be injection molded and used as housings for heat-generating electronic components such as LED bulb components. Good.

  With respect to thermoplastic resins, any suitable resin may be used in the compositions described herein, including polyolefin resins such as polyethylene and polypropylene, polyamide resins such as nylon 6, nylon 66, nylon 610, nylon 12, and aromatic polyamide, polyester resin such as polyethylene terephthalate, polybutylene terephthalate, and polycyclohexylmethylene terephthalate, cyclic polyester oligomer, ABS resin, polycarbonate resin, modified polyphenylene ether resin, polyacetal resin, polyphenylene sulfide resin, wholly aromatic polyester Resin, polyetheretherketone resin, polyethersulfone resin, polysulfo resin, polyamide-imide resin, etc. It may be. Further, a copolymer obtained by selectively combining components constituting these resins may be used. Thermoplastic resins may be combined. Preferably, the thermoplastic resin is selected from the group consisting of a polyamide resin, a polyester resin, a polyphenylene sulfide resin, and a wholly aromatic polyester resin.

  With respect to thermosetting resins, any suitable resin may be used in the compositions described herein, including epoxy resins, novolak resins, isothiocyanate resins, melamine resins, urea resins, imide resins, aromatic resins. A polycarbodiimide resin, a phenoxy resin, a phenol resin, a methacrylic acid resin, an unsaturated polyester resin, a vinyl ester resin, a urea urethane resin, a resole resin, and the like may be included. Preferably, the thermosetting resin contains a melamine resin, an epoxy resin, or an unsaturated polyester resin.

  Any suitable solvent may be added to the compositions described herein as long as it dissolves the resin or rubber or adjusts its viscosity. It is expected that most of the solvent will evaporate during the drying process. Suitable solvents include water, 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 glycol diacrylate (DPGDA), or mixtures thereof.

  The volume of the thermally conductive particles described herein relative to the total volume of the composition described herein is preferably 10-70% by volume, more preferably 50-50% by volume, and even more preferably 38%. ３８38% by volume. Sufficient thermal conductivity and volume resistivity are obtained when the volume percentage of thermally conductive particles relative to the total volume of the composition falls within these ranges.

  The compositions described herein may contain additives such as antioxidants, glass fibers, and lubricants.

The volume resistivity of articles made from the compositions described herein is preferably from 1.0 × 10 ^{10 to} 1.0 × 10 ¹⁸ Ω · cm, as measured at an applied voltage of 500 V. Preferably, it is in the range of 1.0 × 10 ^{13 to} 1.0 × 10 ¹⁵ Ω · cm. The thermal conductivity of the surface of a 1 mm thick molding made from the composition described herein is preferably between 0.5 W / mK and 10.0 W / mK, as estimated by the laser flash method. More preferably, it is in the range of 1.0 W / mK to 5.0 W / mK or less.

Method of making the thermally conductive particles described herein The thermally conductive particles described herein have the volumes described for the method of making them, that is, for the following two-step process. Shows resistivity: First, as shown in FIG. 1, a composite core is produced by bonding together the thermally conductive core particles and an organic binder, and then the composite core is at least partially Coat. Both the steps of preparing the composite core and coating the composite core are performed by compression shear mixing.

In particular, to produce the thermally conductive particles described herein,
First, the thermally conductive core particles and the organic binder, both described herein, are mixed for 5 minutes in a dry particle blender such as NOB-130® (available from Hosokawa Micron Corporation). Compressively shear mix at a rotation speed of 3,000 rpm to form a composite core, and then compressively shear mix the composite core and the insulating material in a dry particle blender so that the surface of the composite core is at least Being partially coated, thereby forming thermally conductive particles.

  The initial compression shear mixing time may range from about 30 seconds to about 90 minutes, and the organic binder is dissolved or suspended in a solvent, preferably water, to produce an organic binder solution or suspension. You may. The second shear mixing time may range from less than 30 seconds to about 10 minutes.

  Preferably, these particles may then be heat treated at 120 ° C. for 3 hours to remove moisture. When the organic binder is a thermosetting resin such as methylol melamine, the heat treatment may further crosslink the resin.

  The thermally conductive particles may then be added to any suitable resin or polymer described herein to form a thermally conductive resin composition.

  The present invention is illustrated by, but not limited to, the following Example (E) and Comparative Example (C).

Materials-Natural Graphite Particles-Flake graphite with an average particle size of 60 [mu] m available as graphite X-100 from ITO Graphite Co. Ltd.
-Methylol melamine (MM)-an organic binder available as Nikaresin S-176 from Nippon Carbide Industries Co. Inc.
-Aqueous polyester (PE)-a water soluble polyester available as Z730 from Goo Chemical.
-Polyamide (PA)-An aqueous polyamide suspension solution available as PA200 from Sumitomo Seika Chemicals.
-Polystyrene sodium sulfonate (SPS)-20% aqueous solution of sodium polystyrene sulfonate available as PS-50 from Tosoh Organic Chemical Co., Ltd.
-IMI FABI Co. , Ltd. Talc 1 having an average D50 particle size of 0.65 μm available as HTP Ultra5 from
-IMI FABI Co. , Ltd. Talc 2 having an average D50 particle size of 2.4 μm available as HTP2C.
-Talc 3 with an average D50 particle size of 5 μm, available as LMS200 from Fuji Talc Corporation.
-Sericite-Kinsei Magic, Co. Ltd. Fine-grained mica having an average D50 particle size of 1.6 μm, available as Sericite J.
Mica with an average D50 particle size of 5 μm available from Yamaguchi Mica.
-Boehmite with an average D50 particle size of 3-5 [mu] m, available as BMF from Kawai Line Industry.
-E. I. Titanium dioxide (TiO ₂ ) with an average D50 particle size of more than 0.5 μm, available as Tipure® R108 from du Pont de Nemours and Company [DuPont] (Wilmington, DE).
-Boron nitride (BN) with an average D50 particle size of 12 μm, available as SGP from Denki Kagaku.
- Sankyo Seiko difluoride calcium having an average D50 particle size of the available 6μm as HO # 100 from _{(Sankyo Seifun) (CaF 2)} .
-Expanded graphite obtained as EC300 from Ito Kokuen Co., Ltd.
-Polybutylene terephthalate (PBT), available as Crustin® from DuPont.

Method Measurement of Volume Resistivity The volume resistivity of the thermally conductive particles of Examples and Comparative Examples was measured by a two-terminal method using the device 20 of FIG. A transparent cylinder 22 having an inner diameter of 10 mm connected to a terminal electrode 21 at two positions on both sides was filled with graphite particles 23 to a height of 3.0 mm. The amount charged was 0.2 g. The surface area of one of the terminal electrodes 21 in contact with the transparent cylinder 22 was 0.785 cm ² . Volume resistivity was obtained by applying a voltage of 500 V on the cylinder between the two terminals.

Methods for Preparing Thermally Conductive Particles Described herein All examples of thermal conductive particles shown in the table below were prepared using Method A. Comparative Example C1 was made using Method B. Comparative Example C2 was made using Method B.

Method A: Two Compression Shear Mixing Steps for Producing Thermally Conductive Particles The first step is a step of producing a composite core by compression shear mixing graphite and an organic binder, followed by a composite core A second step of compression shear mixing with the insulating material is performed.

  The natural graphite particles and the organic binder were added into a dry particle blending device (NOB-130 (registered trademark) available from Hosokawa Micron Corporation), and compression-shear mixed at a rotation speed of 3,000 rpm for 5 minutes to form a composite. A core was formed. The organic binders in the table were obtained by dissolving or suspending certain binders in the amount of water used as a solvent to provide an organic binder solution or suspension.

  Next, an insulating material such as talc, boehmite, sericite, and mica is added to the dry particle blender holding the composite core and subjected to a second compression shear mixing at a rotation speed of 3,000 rpm for 30 seconds, An insulating layer was formed partially on the surface of the composite core, thereby resulting in thermally conductive particles. The thermally conductive particles were heat treated at 120 ° C. for 3 hours to remove residual solvent. When methylolmelamine was used as the organic binder, the heating step further crosslinked the methylolmelamine.

Method B: Single Compression Shear Mixing Step: Premix Organic Binder and Insulating Material After Addition of Thermally Conductive Core Particles and Next Compression Shear Mix All Elements of Talc and Methylol Melamine The aqueous solution was premixed together to form a talc / methylolamine mixture. This premix was not a compression shearing step. Next, the premix was added together with the natural graphite particles into the dry particle blender described in Method A and compression shear mixed for 5 minutes to form thermally conductive particles. The thermally conductive particles were heat treated at 120 ° C. for 3 hours to remove the solvent, resulting in thermally conductive particles having a volume resistivity of 8 × 10 ² Ω · cm at an applied voltage of 500V.

  This method relies on only one compression shear mixing step. Therefore, in method B, no composite core was first produced.

Method C: Single Compression Shear Mixing Step: Compression Shear Mixing Organic Binder, Thermally Conductive Core Particles and Insulating Material Together This method has no premixing step and all the components are added together, Compression shear mixed. The natural graphite particles, organic binder (melamine aqueous solution) and insulating material (talc) are added together to a dry particle blender as described in Method A and compression shear mixed for 5 minutes to form thermally conductive particles did. Next, the thermally conductive particles were heat treated at 120 ° C. for 3 hours to remove the solvent, resulting in thermally conductive particles having a volume resistivity of 8 × 10 ³ Ω · cm at an applied voltage of 500V. Like Method B, Method C also relies on only one compression shear step and does not produce a composite core.

result

  Table 1 compares the volume resistivity of thermally conductive particles prepared by mechanofusion processes A, B, and C having the same rotation speed, cure temperature and time. E1 was prepared by mechanofusion process A, indicating that mechanofusion process A achieved thermally conductive particles of the stated volume resistivity, while mechanofusion process B or C achieved C2 and C3, They exhibited the stated volume resistivity.

All Examples and Comparative Examples in Table 2 were prepared by Method A and had an average length along the long axis of 131.7 μm and an average thickness of 22.5 μm, resulting in an aspect ratio of 5.85. Each of E2-E5 had a different amount of organic binder in the composite core. C3 had no organic binder and exhibited a volume resistivity of 5 Ω · cm. This is in contrast to the minimum volume resistivity of E2-E5 which was 1.5 × 10 ⁷ Ω · cm. Table 2, when the volume percent of an organic binder to the amount of the thermally conductive core particles is in the range of 3 to 20, indicating that the described volume resistivity of at least 1 × 10 ⁴ Ω · cm can be obtained.

Table 2 also shows that the thermal conductivity with two types of graphite in the composite core, formed in the same manner as in E2, except that 20 parts by volume of 100 parts by volume of natural graphite was replaced with expanded graphite. 5 illustrates particles E6. The volume resistivity of E6 was 5.5 × 10 ⁵ Ω · cm, which was almost five times the volume resistivity of E2.

  The example of Table 3 was formed in the same manner as the example of Table 2 except that the amount of the insulating material was changed. Each of E7-E10 had a different amount of insulating material, namely talc. C4 had no talc. The volume resistivity of C4 and E7 to E10 was measured as in Examples 2 to 6.

  Table 3 shows that the volume resistivity of E7-E10 increases as the amount of talc increases. The volume resistivity of E10, containing twice the amount of talc as that of E9, was the same as the volume resistivity of E9. These results indicate that relatively more effective amounts of insulating material range from about 10 to about 20 parts by volume of the total volume of the thermally conductive particles.

The heat conductive particles in Table 4 were formed in the same manner as in Examples 2 to 10, except that the average particle size of the talc insulating material was changed. E11 had talc particles of approximately the same average size as E9. E11, E12, and E13 had talc with an average particle size of 650 nm, 2.4 μm, and 5.0 particle size of 5.0 μm, respectively. Therefore, the average talc particle size of E12 was about four times the average talc particle size of E11 (E9). The average talc particle size of E13 was about twice the average talc particle size of E12, and was about 8 times the average talc particle size of E11 (E8). The volume resistivity of E11 (E9) and E12 was almost the same despite the difference of four times in the average particle size of the insulating particles. However, the reduction of the volume resistivity of E13 relative to the volume resistivity of E12 achieves optimal results when the average talc particle size is in the range of 600 nm to about 3.0 μm when talc is an insulating material. Means that. Nevertheless, in all three examples E11 to E13, the volume resistivity of the thermally conductive particles is greater than 1.0 × 10 ⁸ Ω · cm, a 10,000-fold increase over the stated minimum. Met.

  In Table 5, C5, C6, and C7, which have titanium dioxide, boron nitride, and calcium fluoride as their insulating materials, respectively, did not achieve thermally conductive particles with the stated volume resistivity. Calcium fluoride has a Mohs hardness of 4.0. Boron nitride had a particle size of about 12 μm, and C5 titanium oxide had a spherical shape with an aspect ratio of about 1.

In contrast, Table 5 shows that E14, E15, and E16, which have sericite, mica, and boehmite, respectively, as their insulating materials, each have a volume resistivity of at least the stated value of 1.0 × 10 ^4. It shows that conductive particles have been achieved. Boehmite, sericite, and mica all have a Mohs hardness value of less than 3.5 and a particle size of about 5 μm or less.

Table 6 shows the volume resistivity of the thermally conductive particles with different organic binders. Each organic binder used in Table 6 produced thermally conductive particles having a volume resistivity of at least 1 × 10 ⁴ Ω · cm at the applied voltage of 500 V. The use of methylol melamine or aqueous polyester as the organic binder resulted in thermally conductive particles with the best volume resistivity.

  Table 7 shows a resin composition in which the thermally conductive particles are dispersed in a resin, and the resin composition is injection-molded to form an article.

The resin composition described herein was prepared as follows:
67 parts by volume of the polybutylene terephthalate resin (of the total volume of the resin composition) and 7 parts by volume of the polyester elastomer were mixed at 290 ° C. for 2 minutes using an MC15 micromixer from DSM Xplore. 26 parts by volume (of the total volume of the resin composition) of the thermally conductive particles from E10 were added and stirred for a further 30 seconds at 290 ° C. to produce a resin composition.

The resin composition was injection molded at a mold temperature of 125 ° C. to produce a molded product having a length of 21 mm, a width of 16 mm, and a thickness of 1 mm (FIG. 3). A volume resistivity of at least 1.0 × 10 ¹⁴ Ω · cm on the surface of the molded article was measured by an ohmmeter (Hiresta-UP manufactured by Mitsubishi Chemical Corp.). Further, the temperature diffusivity in the injection direction of the molded article is measured by a laser flash method on a 15 mm × 15 mm area using a Bruker AXS model LFA447 NanoFlash®, and the temperature diffusivity is determined by the specific heat and density of the molded article. When calculated, it was 1.4 W / mK.

When the cross section of this molded product was observed with an electron microscope, thermally conductive particles containing the graphite-containing composite 41 and the insulating layer 42 coating the surface thereof were observed as shown in FIG. Furthermore, the thermally conductive particles were aligned almost parallel in the resin 43.
Hereinafter, the main inventions described in this specification will be listed.
(1) a composite core;
Heat conductive particles including an insulating layer,
The composite core includes a plurality of core particles and an organic binder that binds the core particles together,
The core particles are thermally conductive, selected from the group consisting of metal particles, ceramic particles, carbon-based particles, and mixtures thereof;
An insulating material coats at least a portion of the composite core;
The thermally conductive particles are at least 1 × 10 ⁴ Ω · cm to 1 × 10 ⁴ when measured at an applied voltage of 500 V on a cylinder of the thermally conductive particles having a diameter of 10 mm and a height of 3.0 mm. Thermally conductive particles exhibiting a volume resistivity in the range of ¹⁰ Ω · cm.
(2) The thermally conductive particles according to (1), wherein the core particles are carbon-based particles.
(3) The thermally conductive particles according to (1), wherein the carbon-based particles are graphite.
(4) the core particles are particles based on natural graphite and flake carbon in a ratio of 3: 2 to 99: 1;
The thermally conductive particles according to (1) or (2), wherein the flake-like carbon-based particles have an average thickness smaller than the average thickness of the natural graphite.
(5) The core particles are 100 parts by volume,
The heat conduction according to (1) or (2), wherein the organic binder is in a range of 3 to 25 parts by volume of the core particles, and the insulating material is in a range of 4 to 48 parts by volume of the core particles. Sex particles.
(6) the core particles are particles based on natural graphite and flake carbon in a ratio of 3: 2 to 99: 1;
The thermally conductive particles according to (5), wherein the flake-like carbon-based particles have an average thickness smaller than the average thickness of the natural graphite.
(7) The thermally conductive particles according to (1) or (2), wherein the organic binder is a thermosetting resin.
(8) The thermally conductive particles according to (6), wherein the organic binder is a thermosetting resin.
(9) The thermally conductive particles according to (1) or (2), wherein the average particle size of the thermally conductive particles is in a range of 0.5 μm to 300 μm.
(10) The thermally conductive particles according to (8), wherein the average particle diameter of the thermally conductive particles is in a range of 0.5 μm to 300 μm.
(11) The thermally conductive particles according to (1) or (2), wherein the insulating material is selected from the group consisting of sericite, boehmite, talc, mica, and a mixture thereof.
(12) The thermally conductive particles according to (10), wherein the insulating material is selected from the group consisting of sericite, boehmite, talc, mica, and a mixture thereof.
(13) A method for producing thermally conductive particles comprising a step of at least partially coating a composite core with an insulating material,
The composite core includes a plurality of core particles and an organic binder that binds the core particles together,
The core particles are thermally conductive, selected from the group consisting of metal particles, ceramic particles, carbon-based particles, and mixtures thereof;
The insulating material is selected from the group consisting of sericite, boehmite, talc, mica, and mixtures thereof;
The thermally conductive particles are at least 1 × 10 ⁴ Ω · cm to 1 × 10 ⁴ when measured at an applied voltage of 500 V on a cylinder of the thermally conductive particles having a diameter of 10 mm and a height of 3.0 mm. ^A method showing a volume resistivity in the range of ¹⁰ Ω · cm.
(14) The method according to (13), wherein the composite core is formed by applying a compressive force and a shear force to mix the core particles with the organic binder.
(15) heat conductive particles;
A resin selected from the group consisting of:
The heat conductive particles include a composite core and an insulating layer,
The composite core includes a plurality of core particles and an organic binder that binds the core particles together,
The core particles are thermally conductive, selected from the group consisting of metal particles, ceramic particles, carbon-based particles, and mixtures thereof;
An insulating material coats at least a portion of the composite core;
The thermally conductive particles are at least 1 × 10 ⁴ Ω · cm to 1 × 10 ⁴ when measured at an applied voltage of 500 V on a cylinder of the thermally conductive particles having a diameter of 10 mm and a height of 3.0 mm. Indicates a volume resistivity in the range of ¹⁰ Ωcm,
The resin composition, wherein the thermally conductive particles are in a range of 10 to 70% by volume of the total volume of the resin composition.

Claims (3)

A composite core;
Heat conductive particles including an insulating layer,
The composite core includes a plurality of core particles and an organic binder that binds the core particles together,
It said core particles, thermally conductive, and a particle element shall be the basis of carbon, graphite, or 3: 2 to 99: 1 of the graphite and flaky carbon ratio selected from particles based,
An insulating material selected from the group consisting of sericite, boehmite, talc, mica and mixtures thereof , coating at least a portion of the composite core;
The thermally conductive particles are at least 1 × 10 ⁴ Ω · cm to 1 × 10 ⁴ when measured at an applied voltage of 500 V on a cylinder of the thermally conductive particles having a diameter of 10 mm and a height of 3.0 mm. Thermally conductive particles exhibiting a volume resistivity in the range of ¹⁰ Ω · cm. A method of producing thermally conductive particles comprising a step of at least partially coating a composite core with an insulating material,
The composite core includes a plurality of core particles and an organic binder that binds the core particles together,
It said core particles, thermally conductive, and a particle element shall be the basis of carbon, graphite, or 3: 2 to 99: 1 of the graphite and flaky carbon ratio selected from particles based,
The insulating material is selected from the group consisting of sericite, boehmite, talc, mica, and mixtures thereof;
The thermally conductive particles are at least 1 × 10 ⁴ Ω · cm to 1 × 10 ⁴ when measured at an applied voltage of 500 V on a cylinder of the thermally conductive particles having a diameter of 10 mm and a height of 3.0 mm. ^A method showing a volume resistivity in the range of ¹⁰ Ω · cm. Heat conductive particles,
A resin composition comprising a thermoplastic resin, a thermosetting resin, an aramid resin, a rubber, or a resin selected from the group consisting of mixtures thereof,
The heat conductive particles include a composite core and an insulating layer,
The composite core includes a plurality of core particles and an organic binder that binds the core particles together,
It said core particles, thermally conductive, and a particle element shall be the basis of carbon, graphite, or 3: 2 to 99: 1 of the graphite and flaky carbon ratio selected from particles based,
An insulating material selected from the group consisting of sericite, boehmite, talc, mica, and mixtures thereof , coating at least a portion of the composite core;
The thermally conductive particles are at least 1 × 10 ⁴ Ω · cm to 1 × 10 ⁴ when measured at an applied voltage of 500 V on a cylinder of the thermally conductive particles having a diameter of 10 mm and a height of 3.0 mm. Indicates a volume resistivity in the range of ¹⁰ Ωcm,
The resin composition, wherein the thermally conductive particles are in a range of 10 to 70% by volume of the total volume of the resin composition.

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