JP6196779B2 - Insulating heat dissipation filler and method for producing the same - Google Patents

Description

  The present invention relates to an insulating heat dissipating filler, a method for producing the same, and a heat dissipating composition containing the filler.

  In the field of electronic equipment and the like, in recent years, the amount of heat generation has increased due to the concentration of heat sources and the increase in current capacity accompanying downsizing. In order to cope with this, a composition filled with a heat radiation filler having excellent thermal conductivity is attached to an electronic device or the like, and the generated heat is released to the outside.

  The heat dissipating filler is filled in grease or a resin sheet, and has a role of enhancing heat dissipating characteristics of electronic devices and the like, and as one of them, use of zinc oxide has been proposed (for example, Patent Document 1).

  Zinc oxide has a thermal conductivity that is almost in the middle of that of general alumina and aluminum nitride as a heat dissipating filler, and is a relatively balanced material in terms of powder physical properties such as linear expansion coefficient and hardness, and price. For this reason, various studies have been made with applicability as a heat-dissipating filler.

  By the way, for heat radiation fillers, in applications such as semiconductor integrated circuits, power devices, and multi-layer substrates where electrostatic breakdown or short-circuiting is a problem, insulation is often required at the same time as thermal conductivity. However, since zinc oxide has low volume resistivity and exhibits semiconductivity, use of zinc oxide as a heat dissipating filler leads to a decrease in the insulating properties of heat dissipating grease and heat dissipating sheet.

  The low conductive zinc oxide particles are obtained by surface-treating zinc oxide particles with at least one metal compound selected from the group consisting of Mg, Co, Ca and Ni, and have a median diameter (D50) of 1 to 10,000 μm. Zinc oxide particles are disclosed (Patent Document 2). However, in this technique, the uniform surface treatment is difficult to perform and the non-covered portion is easily exposed, so that the conductivity is not sufficiently reduced. When the entire particle is coated, a large amount of surface treatment is required and it is difficult to obtain sufficient thermal conductivity. Furthermore, there is a problem that the chemical stability of the surface-treated metal compound is low.

  Further, a technique for coating zinc oxide particles with silica is known. Patent Document 3 discloses a zinc oxide particle composition having a high-density coating layer made of silicon oxide on the surface of zinc oxide particles and having a Zn solubility in pure water or sulfuric acid aqueous solution of a certain value or less. However, this technology was made in order to reduce Zn dissolution and photocatalytic activity in zinc oxide nanoparticles for use in sunscreen cosmetics. There is no suggestion.

  Patent Document 4 discloses a core-shell particle in which a shell made of a metal oxide is formed on the surface of a core particle made of a material having a dielectric constant of 10 or more, the shell has a thickness of 1 to 500 nm, nitrogen In the pore volume histogram obtained by the adsorption method, the maximum pore volume of the shell having a pore diameter of 3 nm or less is 0.01 cc / g, and the average particle diameter in the dispersion medium is 1-1000 nm. Certain core-shell particles have disclosed zinc oxide as the metal oxide. However, this technology is intended to reduce the photocatalytic activity of zinc oxide nanoparticles used for imparting ultraviolet shielding properties to resins and cosmetics and the reaction with fluororesin. There is no description or suggestion about.

  The present inventors examined a resin composition containing zinc oxide nanoparticles as a heat dissipating filler. However, sufficient thermal conductivity and dielectric breakdown voltage were not obtained.

Japanese Patent Laid-Open No. 11-246885 JP 2011-230947 A Japanese Patent Laid-Open No. 11-302015 Republished patent WO2010 / 4814 pamphlet

  An object of the present invention is to provide a zinc oxide insulating heat dissipating filler having a high powder resistance and exhibiting a high thermal conductivity and a high dielectric breakdown voltage when blended in a resin composition, an industrial production method thereof, and the insulating heat dissipating filler. A heat dissipating composition is provided.

  The present inventors diligently studied about the zinc oxide insulating heat dissipating filler. Here, the thermal conductivity of zinc oxide is 54 W / m · K, while the thermal conductivity of crystalline silica is 6.2 W / m · K. Therefore, when zinc oxide was coated with crystalline silica, the thermal conductivity was expected to decrease. However, a filler in which an oxide coating containing at least silicon is formed on the surface of zinc oxide particles, particularly a filler whose total pore volume calculated by the BJH method based on the adsorption / desorption isotherm by nitrogen adsorption is a specific value or less. As a result, the present inventors have surprisingly found an insulating heat dissipating filler having increased powder resistance with respect to zinc oxide particles alone. In addition, the present inventors have also found that when blended with a resin composition, the same thermal conductivity is exhibited and the dielectric breakdown voltage is remarkably increased, thereby completing the present invention. Furthermore, even when an organosilicon compound is used as the silicon oxide source, the insulating heat-dissipating filler can be obtained at a low cost and in a short time by using a specific amount of the catalyst compound in a medium mainly composed of water. A method of manufacturing was found.

That is, the present invention
(1) An insulating heat dissipating filler having an oxide coating containing at least silicon on zinc oxide particles,
(2) The insulating heat radiation filler according to (1), wherein the oxide coating containing at least silicon is a dense coating,
(3) The insulating heat dissipating filler according to (1) or (2), wherein the total pore volume calculated by the BJH method based on an adsorption / desorption isotherm by nitrogen adsorption is 0.07 cm 3 / g or less,
(4) The insulating heat-radiating filler according to (1) to (3), wherein the average thickness of the coating is 2 to 100 nm,
(5) The insulating heat dissipating filler according to (1) to (4), wherein the alkali metal content relative to SiO ₂ measured by atomic absorption spectrometry is 1.5% by mass or less,
(6) The shape is a hexagonal columnar shape, the average crossed diameter (L) of the hexagonal surface is 0.2 to 40 μm, and the average height (H) in the direction perpendicular to the hexagonal surface is 0.05 to The insulating heat dissipating filler of (1) to (5) which is 50 μm,
(7) A method for producing an insulating heat dissipating filler having an oxide coating containing at least silicon on the surface of zinc oxide particles,
Having a step of mixing zinc oxide particles, an organosilicon compound, a catalyst compound, and a medium and hydrolyzing the organosilicon compound,
It is a manufacturing method of an insulating heat radiation filler,
(8) Insulating radiating filler according to (7), wherein, in the step, 50% by mass or more of the liquid medium is water, and the amount of the catalyst compound is 10 times or more in molar ratio to the amount of the organosilicon compound. Is a manufacturing method of
(9) After the said process, it is a manufacturing method of the insulating thermal radiation filler of (7) or (8) which bakes solid content containing a reaction product at 150-1000 degreeC,
(10) A heat dissipating composition comprising the insulating heat dissipating filler of (1) to (6),
It is.

  Since the insulating heat dissipating filler of the present invention has high powder resistance and exhibits high thermal conductivity and dielectric breakdown voltage when blended in a resin composition, the heat dissipating resin composition is excellent in heat dissipation and insulation. Etc. are obtained. For this reason, the heat-radiating composition of the present invention can be used as a material for efficiently dissipating heat by attaching it to an electronic device that requires insulation. Furthermore, the method for producing an insulating heat dissipating filler of the present invention is useful for industrial production because it can be densely covered with an oxide containing silicon in a low cost and in a short time.

Scanning electron micrograph of insulating heat dissipating filler sample B of Example 1 of the present invention Scanning electron micrograph of insulating heat dissipating filler sample D of Example 2 of the present invention Scanning electron micrograph of insulating heat radiation filler sample F of Example 3 of the present invention Scanning electron micrograph of heat dissipation filler sample G of Comparative Example 1

  The technical configuration and operational effects of the present invention are as follows. However, the action mechanism includes estimation, and its correctness does not limit the present invention.

  The present invention is an insulating heat dissipating filler having an oxide coating containing at least silicon on zinc oxide particles. “Coating” does not mean a state in which the entire zinc oxide particles are coated in layers, that is, not only a continuous film, but also a state in which a non-continuous film, for example, a part of the continuous film is missing. Including. The coating may be in a state where fine oxide particles are deposited, or in a state where crystalline and / or amorphous oxides are integrally connected. In particular, the powder resistance of the insulating heat dissipating filler can be sufficiently increased when the oxide containing at least silicon is in a state where 95% or more of the zinc oxide particle surface is integrally connected and layered. Therefore, it is preferable. Here, “95% or more of the surface” means “the ratio of the missing area / the total area of the filler on the plane of the scanning electron microscope image is 95% or more”. A plurality of oxide coatings containing at least silicon may be present. In addition, other substances may be present between the zinc oxide particles and the oxide coating containing at least silicon. An example of such a substance is a composite oxide of silicon and zinc. Such an oxide containing at least silicon preferably has crystallinity.

  The zinc oxide particles constituting the insulating heat dissipating filler of the present invention are those containing at least 50% by weight of ZnO exhibiting an X-ray diffraction pattern of any one of hexagonal, cubic and cubic face-centered structures. Zinc and zinc compounds such as zinc sulfate, zinc nitrate, zinc chloride and zinc acetate used in production may be contained. It may also contain sulfate radicals, nitrate radicals, chlorine, acetic acid, etc. that comprised the zinc compound used in the production, and also contains materials such as carboxylic acids, their salts, and amine compounds. May be. The zinc oxide particles preferably have good crystallinity from the viewpoint of thermal conductivity. As an index, the half-value width of 2θ = 36.5 degrees, which is the main peak of the powder X-ray diffraction spectrum, is 0.20 degrees or less. Is preferred. A half width greater than 0.20 degrees is not preferable because the crystallinity is low and the thermal conductivity is likely to be lowered.

  The oxide containing at least silicon is not an oxide containing silicon as an impurity, but an oxide in which silicon is a component constituting the structure, for example, silicon oxide, and examples thereof include silica. Is mentioned.

The insulating heat dissipating filler of the present invention has a powder resistance value measured by the following method of 1 × 10 ⁸ Ω · cm or more, preferably 1 × 10 ¹⁰ Ω · cm or more, more preferably 1 ×. 10 ¹² Ω · cm or more. Since the powder resistance is high in this way, the dielectric breakdown voltage can be increased when used in a resin composition or the like.
[Powder resistance measurement method]
0.3 g of filler is molded into a cylindrical shape (18 mmφ) at a pressure of 10 MPa, and the resistance is measured using a DC voltage application type insulation resistance tester (Model 3154 HIOKI). Calculated.
Powder resistance value = Measured value × Cylinder cross-sectional area / Cylinder thickness

  In the insulating heat dissipating filler of the present invention, the oxide containing at least silicon preferably forms a dense coating layer. When the coating is dense, the powder resistance can be increased as compared with the zinc oxide particles alone. Furthermore, when blended in the resin composition, the dielectric breakdown voltage can be remarkably increased while exhibiting a thermal conductivity equivalent to that of the zinc oxide particles alone.

The insulating heat dissipating filler of the present invention preferably has a total pore volume of 0.07 cm ³ / g or less calculated by the BJH method based on the adsorption / desorption isotherm by nitrogen adsorption. Total pore volume, more preferably not more than 0.04 cm ³ / g, more preferably not more than 0.02 cm ³ / g. The powder resistance can be further increased by reducing the total pore volume of the insulating heat dissipating filler. Moreover, when it mix | blends with a resin composition, a dielectric breakdown voltage can be raised remarkably, showing the heat conductivity equivalent to a zinc oxide particle single-piece | unit. Such an insulating heat-radiating filler having a small total pore volume can be realized by increasing the denseness of the oxide coating containing at least silicon.

  The total pore volume can be measured using, for example, an automatic specific surface area / pore distribution measuring device (BELSORP-miniII manufactured by Nippon Bell Co., Ltd.). Specifically, the sample is vacuum degassed at 150 ° C. for 3 hours, and then a nitrogen adsorption / desorption isotherm is measured under the condition of liquid nitrogen temperature (77K). The obtained nitrogen adsorption / desorption isotherm is analyzed by the BJH method to obtain pore volume and pore distribution curves. The pore diameter distribution curve obtained here is obtained by plotting the value (dV / dr) obtained by differentiating the pore volume V with the pore diameter r against the pore diameter (r). The measurement is performed in a relative pressure range of 0.30 to 0.99, and the equilibration time is 6 minutes.

  In the insulating heat dissipating filler of the present invention, the thickness of the oxide coating containing at least silicon is not particularly limited, and can be appropriately adjusted within a range in which the effects of the present invention can be obtained. Further, the coating need not have a uniform thickness, and the thickness may vary depending on the location. A preferable average thickness is 2 to 100 nm. If the thickness is too small, the powder resistance and the dielectric breakdown voltage cannot be sufficiently increased, and if the thickness is too large, the thermal conductivity tends to decrease. This preferred range is influenced by the denseness of the coating, but is more preferably 10 to 40 nm. The average thickness of the coating is obtained by measuring the dimensions of the coating cross-section at 10 locations with a scanning electron microscope and calculating the average value.

In the insulating heat dissipating filler of the present invention, the ratio of the silicon oxide amount (SiO ₂ amount) to the zinc oxide amount (ZnO amount) (SiO ₂ amount / ZnO amount) is not particularly limited, and the range in which the effects of the present invention can be obtained. Can be adjusted as appropriate. The preferred range is affected by the denseness of the coating, but is preferably 1 to 50% by mass, and more preferably 5 to 20% by mass. If this ratio is too small, the powder resistance and the dielectric breakdown voltage cannot be sufficiently increased, and if it is too large, the thermal conductivity tends to decrease. The amount of SiO ₂ / ZnO can be determined by measuring the amount of Si and the amount of Zn by fluorescent X-ray analysis and converting them to oxides.

In the insulating heat dissipating filler of the present invention, the ratio of the alkali metal amount to the SiO ₂ amount is not particularly limited, and can be appropriately adjusted within a range in which the effect of the present invention can be obtained. However, if the amount of the alkali metal is too large, the powder resistance and the dielectric breakdown voltage cannot be sufficiently increased. Therefore, the content is preferably 1.5% by mass or less, and more preferably less than 300 ppm. Examples of the alkali metal include Li, Na, K, Rb, and Cs, and it is particularly preferable to reduce the amount of Na. Measurement of the amount of alkali metal relative to the amount of SiO ₂ is performed by atomic absorption spectrometry. The measurement method will be described in detail by taking Na as an example. A sample solution prepared by dissolving an insulating heat dissipating filler with an acid containing hydrofluoric acid and diluting with pure water is used as an atomic absorption spectrometer (AA-6800, manufactured by Shimadzu Corporation). The analysis is performed at a measurement wavelength of 589 nm. The amount of Na can be reduced by using, for example, a material that does not contain Na as a raw material used for production.

  There is no restriction | limiting in particular in the magnitude | size of the insulating thermal radiation filler of this invention, You may select suitably according to a use and required performance. In general, the insulating heat-radiating filler has a median diameter (D50) of preferably 0.1 to 1000 μm because heat conduction is more likely to occur when the particle diameter is larger and heat can be radiated well. ˜100 μm is more preferable. The median diameter (D50) refers to a diameter in which the large side and the small side are equivalent when the powder is divided into two from a certain particle diameter. The particle size distribution of the composite particles is determined by a laser diffraction / scattering particle size distribution analyzer (LA-910, manufactured by Horiba, Ltd.).

  The particle shape of the insulating heat radiation filler of the present invention is not particularly limited, and examples thereof include a needle shape, a rod shape, a plate shape, and a spherical shape. Examples of the plate shape include a hexagonal plate shape, and examples of the rod shape include a hexagonal column shape. In addition, as a special shape, zinc oxide particles having a shape in which needle-like crystals are radially accumulated in different axial directions of 10 or more axes (hereinafter, may be referred to as “spotted shape”) may also be mentioned. The shape of the particles can be observed with a scanning electron microscope.

The insulating heat dissipating filler of the present invention is preferably hexagonal columnar particles. In particular, the hexagonal surface has a hexagonal column shape extending in a direction perpendicular to the hexagonal surface, and the average span diameter (L) of the hexagonal surface is 0.2 to 40 μm. It is preferable that the hexagonal columnar particles have an average height (H) in the vertical direction of 0.05 to 50 μm. The “crossing diameter” means “the length of a line connecting opposite vertices”. It is preferable to mix such specific particles because a heat conduction path can be easily formed and an insulating heat dissipating filler having excellent heat conductivity can be obtained. On the other hand, if the average cross-sectional diameter (L) of the hexagonal surface is smaller than 0.2 μm, the thermal conductivity is unfavorable, and if it is larger than 40 μm, the thermal conductivity is good. It is not preferable because it is difficult to blend in. Therefore, the average crossed diameter (L) of the hexagonal surfaces of the zinc oxide particles is more preferably 3 to 15 μm. The average height (H) in the direction perpendicular to the hexagonal surface is more preferably 1 to 50 μm. When the particle shape of the insulating heat dissipating filler of the present invention is a hexagonal column, the dimensions can also be obtained by electron microscopy. Specifically, the average diameter (L) and average height (H) of the insulating heat-dissipating filler particles are measured by measuring the diameter and height of the hexagonal surfaces of at least 20 particles from an electron micrograph. These particles are assumed to be prismatic equivalents, and the weight average span diameter and weight average height calculated by the following formula are used as a reference.

Weight average span diameter = Σ (Ln · Ln · Dn ² ) / Σ (Ln · Dn ² )
Weight average height = Σ (Dn · Ln · Dn ² ) / Σ (Ln · Dn ² )

In the above formula, n represents the number of each measured particle, Ln represents the span of the nth particle, and Dn represents the height of the nth particle. When expressed as a ratio L / H of the average crossed diameter (L) of the hexagonal surface of the zinc oxide particles and the average height (H) in the direction perpendicular to the hexagonal surface, a range of 0.004 to 800 is preferable. A range of 0.02 to 60 is more preferable. The hexagonal columnar shape includes a shape called a hexagonal plate shape. Particularly, the particles having the ratio L / H of 1 or less are particularly referred to as a hexagonal columnar shape, and the particles having an L / H of 1 or more are referred to as a hexagonal plate shape. There is a case.

  Moreover, when an electron micrograph is observed in detail, there is a constriction in the center of the hexagonal column, and there are composite particles whose diameter is smaller than both ends. A shape in which the diameters at both ends and the center of the hexagonal column are smaller than those at both ends is referred to as a shape similar to a drum (drum shape) in the present invention. (Diameter of the central portion) / (Diameter of both end portions) is preferably about 0.5 to 0.99, and more preferably about 0.7 to 0.99. Such a drum shape has a shape in which a growth twin crystal having a hexagonal plate nuclei existing in the constricted portion at the center as a symmetry plane occurs. In such a drum shape, it is possible to form a heat conduction path at both ends, and it is preferable that the center portion is small because the weight is reduced accordingly. In addition, such a drum shape is preferable because the insulating heat-radiating filler particles are easily oriented when kneaded into a resin or the like and formed, and the heat conduction path is formed with a high density.

  The composite particles of the present invention can be provided with a coating layer of an oxide such as silicon, titanium, aluminum, zirconium, tin or an inorganic compound such as a phosphate thereof on the particle surface as necessary. Further, for the purpose of imparting dispersibility to solvents, paints, plastics, and the like, an organic compound may be coated, or both the inorganic compound and the organic compound may be coated. Examples of organic compounds include (1) organosilicon compounds ((a) organopolysiloxanes (dimethylpolysiloxane, methylhydrogen polysiloxane, methylmethoxypolysiloxane, methylphenylpolysiloxane, dimethylpolysiloxanediol, dimethylpolysiloxanedi). Hydrogen or the like or copolymers thereof), (b) organosilanes (aminosilane, epoxysilane, methacrylsilane, vinylsilane, mercaptosilane, chloroalkylsilane, alkylsilane, fluoroalkylsilane, etc. or their hydrolysis products) (C) organosilazanes (hexamethylsilazane, hexamethylcyclotrisilazane, etc.), (2) organometallic compounds ((a) organotitanium compounds (aminoalkoxytitanium, phosphoric acid ester titanium) , Carboxylic acid ester titanium, sulfonic acid ester titanium, titanium chelate, phosphite titanium complex, etc.), (b) organoaluminum compound (aluminum chelate, etc.), (c) organozirconium compound (carboxylate ester zirconium, zirconium chelate) Etc.), (3) polyols (trimethylolpropane, trimethylolethane, pentaerythritol, etc.), (4) alkanolamines (monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, triol) Propanolamine etc.) or derivatives thereof (acetate, oxalate, tartrate, formate, benzoate, etc. organic acid salts), (5) higher fatty acids (stearic acid, lauric acid, oleic acid) ) Or a metal salt thereof (aluminum salt, zinc salt, magnesium salt, calcium salt, barium salt, etc.), (6) higher hydrocarbons (paraffin wax, polyethylene wax, etc.) or derivatives thereof (perfluorinated products, etc.). These organic compounds may be used singly or in combination of two or more, and the coating amount of the inorganic compound and organic compound is the same as that of zinc oxide particles having a coating containing at least silicon on the surface. On the other hand, the range of 0.1 to 50% by weight is preferable, and the range of 0.1 to 30% by weight is more preferable, and the inorganic compound or organic compound is applied to the surface of the zinc oxide particles having a coating containing at least silicon on the surface. In order to coat, it is possible to coat in an aqueous slurry of particles by adding an inorganic compound or an organic compound to neutralize it. As another method for coating the compound, an organic compound can be added and mixed during dry pulverization.

  Then, the manufacturing method of the insulating thermal radiation filler of this invention is demonstrated. The zinc oxide particles used in the present invention can be produced by a known method. Further, specially shaped zinc oxide particles such as a hexagonal column shape and a sawtooth shape can be produced in accordance with Japanese Patent Application Laid-Open Nos. 2008-254992 and 2008-254989, respectively.

  The method for forming an oxide coating containing at least silicon on the surface of the zinc oxide particles (hereinafter, “oxide coating containing at least silicon” may be referred to as “silica coating”) is not particularly limited, and is a known surface treatment. The method can be used. For example, a dispersion medium, zinc oxide particles, and a silicon compound can be mixed, and the silicon compound can be reacted with silicon oxide to adhere to the surface of the zinc oxide particles.

As an example of the above silica coating forming method, a method of forming an silica coating by adding an inorganic silicon compound to an aqueous slurry of zinc oxide and neutralizing it in a pH range of 8.0 to 10.0 will be described. As the silicon compound used in the silica coating step, sodium silicate, potassium silicate, silica sol and the like can be used, and a water-soluble compound such as sodium silicate is preferably used. As the neutralizing agent, the above acidic compound or basic compound is appropriately selected and used according to the silicon compound to be used. As sodium silicate, sodium orthosilicate, sodium sesquisilicate, sodium metasilicate and the like can be used, and sodium silicate No. 1 (SiO ₂ / Na ₂ O molar ratio is 2) which is an aqueous solution of sodium silicate, No. 2 (SiO ₂ / Na ₂ O molar ratio is 2.5), No. 3 (SiO ₂ / Na ₂ O molar ratio is 3), No. 4 (SiO ₂ / Na ₂ O molar ratio is 4), N special sodium silicate (SiO ₂ / Na ₂ O molar ratio: 3.80 to 4.10), C special sodium silicate (SiO ₂ / Na ₂ O molar ratio: 3.30 to 3.50), AP silicate (SiO ₂ / Na ₂ O molar ratio: 4.25 to 4.45) (all manufactured by Nippon Kagaku Kogyo Co., Ltd.) can be preferably used, and SiO ₂ / Na ₂ O molar ratio. Use sodium silicate of 3 or more Preferred for sodium content remaining is less. The silicon compound and the neutralizing agent may be added separately, but when an acidic compound is used as the silicon compound, the silicon compound and the basic compound of the neutralizing agent are mixed in an aqueous slurry so that zinc does not elute. While maintaining the pH in the above range, it is preferable to add them in parallel. After neutralizing the silicon compound, it is preferable to age the silicon compound for a certain period of time, desirably 10 minutes to 1 hour. When coating dense silica, the temperature during neutralization is set to 60 ° C. or higher, and the neutralization time is set to 60 minutes or longer. As the neutralizing agent, an acidic compound or a basic compound is appropriately selected and used according to the silicon compound to be used. Examples of acidic compounds include inorganic acids such as sulfuric acid and hydrochloric acid, and organic acids such as acetic acid and formic acid, and basic compounds include alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, and calcium hydroxide. And alkali metal or alkaline earth metal carbonates such as sodium carbonate and potassium carbonate, and ammonium compounds such as ammonia, ammonium carbonate and ammonium nitrate.

  As another example of the above silica coating forming method, a method of forming a silica coating by mixing zinc oxide particles, an organosilicon compound, a catalyst compound, and a medium and hydrolyzing the organosilicon compound will be described. This method is preferable because a dense silica coating is easily formed.

  The organosilicon compound may be any organosilicon compound having a hydrolyzable group, and includes, for example, silicon alkoxide and the like. From the viewpoint of forming a dense coating, alkoxysilane is preferred, and tetraalkoxysilane is more preferred. Examples of the tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetra n-propoxysilane, tetraisopropoxysilane, and the like, and tetramethoxysilane and tetraethoxysilane are preferable from the viewpoint of appropriate reaction rate. Is more preferable.

The mixing amount of the organosilicon compound is such that the ratio (SiO ₂ amount / ZnO amount) to the zinc oxide amount (ZnO amount) in which the silicon amount in the compound is converted to the silicon oxide amount (SiO ₂ amount) is 1 to 50 mass. %, Preferably 5 to 20% by mass.

  An alkali can be used as the catalyst compound. Examples of the alkali include inorganic alkalis such as ammonia, sodium hydroxide and potassium hydroxide; inorganic alkali salts such as ammonium carbonate, ammonium hydrogen carbonate, sodium carbonate and sodium hydrogen carbonate; monomethylamine, dimethylamine, trimethylamine, monoethylamine, Organic alkalis such as diethylamine, triethylamine, pyridine, aniline, choline, tetramethylammonium hydroxide, guanidine; organic acid alkalis such as ammonium formate, ammonium acetate, monomethylamine formate, dimethylamine acetate, pyridine lactate, guanidinoacetic acid, aniline acetate Examples thereof include, but are not limited to, salts.

  Among these, ammonia, ammonium carbonate, ammonium hydrogen carbonate, ammonium formate, ammonium acetate, sodium carbonate, sodium hydrogen carbonate and the like are particularly preferable from the viewpoint of reaction rate control. The alkali can be used alone or in combination of two or more selected from the above group. Moreover, alkali metal content can be reduced by using the alkali which does not contain an alkali metal as a main component. Among these, ammonia, ammonium carbonate, and ammonium hydrogen carbonate are particularly preferable, and ammonia is more preferable from the viewpoint of film formation speed, ease of residue removal, and the like.

  The addition amount of the catalyst compound can form a silica coating even if it is added in a minute amount at a molar ratio to the organosilicon compound, but it is preferably added at a molar ratio of 5 times or more. However, in the case of a solid catalyst compound, adding an amount exceeding the solubility is not preferable because it is mixed as an impurity in the filler.

  As the liquid medium, those in which the composition forms a uniform solution are preferable. For example, alcohols such as methanol, ethanol, propanol and pentanol; ethers and acetals such as tetrahydrofuran and 1,4-dioxane; acetaldehyde and the like Water such as aldehydes; ketones such as acetone, diacetone alcohol, methyl ethyl ketone; polyhydric alcohol derivatives such as ethylene glycol, propylene glycol, diethylene glycol, and the like can be used. Among these, alcohols are preferably used from the viewpoint of reaction rate control, and ethanol, methanol and propanol are particularly preferable, and ethanol is particularly preferable. As the liquid medium, one or more selected from the above group can be mixed and used.

  Since water is required for hydrolysis of the organosilicon compound, it is preferable that the liquid medium contains water. In order to effectively use the organosilicon compound, the amount of water preferably contains more than the amount required for hydrolysis of the organosilicon compound.

  As for the density | concentration of the zinc oxide particle in a liquid mixture, 1-30 mass% is preferable in 100 mass% of liquid mixtures, and 1-20 mass% is more preferable. When the concentration of the zinc oxide particles is 1% by mass or more, the production efficiency of the filler particles is good. When the concentration of the zinc oxide particles is 30% by mass or less, the filler of the present invention in which a uniform silica coating is formed can be stably produced.

  There is no particular limitation on the mixing order of the zinc oxide particles, the organosilicon compound, the catalyst compound, and the liquid medium, and they can be mixed in any order. For example, (a) preparing a dispersion containing zinc oxide particles and a medium, mixing a catalyst compound therein, and then mixing an organosilicon compound, (b) a dispersion containing zinc oxide particles and a medium The method of preparing and mixing an organosilicon compound therewith, and then mixing a catalyst compound is mentioned.

  In the step of performing the hydrolysis reaction by mixing the raw materials, the reaction temperature is not particularly limited, and the reaction can be performed at a reaction temperature of 0 to 70 ° C. The higher the temperature, the higher the silica coating formation rate. However, if the temperature is too high, it will be difficult to keep the composition constant due to the volatilization of the components, and if the temperature is too low, the silica coating formation rate will be slow and impractical. This reaction can be carried out at room temperature (10 to 30 ° C.). There is no restriction | limiting in particular also in the reaction time, You may set suitably according to the hydrolysis rate of an organosilicon compound. A reaction time of 60 minutes or more is preferable because a dense silica coating is easily formed. The reaction time can be controlled by adjusting the mixing speed of the raw materials, for example, the mixing speed of the organosilicon compound in the case of (a), and the mixing speed of the catalyst compound in the case of (b). The mixing speed can be adjusted using, for example, a tube pump. The reaction time may be adjusted by the aging time after mixing all the materials.

  After forming the silica coating, filtration and washing are carried out as necessary to separate the solid and liquid, followed by drying and dry pulverization, whereby a filler powder is obtained. For solid-liquid separation, a filter that is usually used industrially, such as a filter press or a roll press, can be used. For drying, a band heater, a batch heater, a spray dryer or the like can be used. There is no restriction | limiting in particular in drying temperature and time, Although it can set suitably, For example, it can be set to 150 degrees C or less, and can also be set to 120 degrees C or less. For dry crushing, use an impact crusher such as a hammer mill or pin mill, a grinding crusher such as a roller mill, a pulverizer, or a crusher, a compression crusher such as a roll crusher or a jaw crusher, or an airflow crusher such as a jet mill. Can do.

  Further, in the silica coating formation method using the organosilicon compound, it is surprising that 50% by mass or more of the liquid medium is water and the amount of the catalyst compound is 10 times or more in molar ratio to the amount of the organosilicon compound. Moreover, it is preferable because productivity is remarkably increased. Specifically, the addition and mixing time of the raw materials can be remarkably shortened, so that the cost is low and the productivity is increased, which is industrially useful. Specifically, the silica is dense even if the organosilicon compound is mixed in a time shorter than 60 minutes by the organosilicon compound in the case of (a) and the catalyst compound in the case of (b) in a time shorter than 60 minutes. Coating is possible. The mixing may be shorter than 30 minutes, or may be mixed all at once.

  The amount of water in the medium may be 50% by mass or more, may be 80% by mass or more, and may be 100% by mass of water. Further, the amount of the catalyst compound may be 10 times or more in molar ratio with respect to the amount of the organosilicon compound, and may be 15 times or more.

  Furthermore, it is preferable that the silica-coated zinc oxide particles are fired at a temperature of about 150 to 1000 ° C. after the hydrolysis reaction of the organosilicon compound. Combined with the fact that the crystallinity of the zinc oxide particles can be further increased, the silica coating can be further densified, the crystallinity of the silica is increased, and the adhesion between the surface of the zinc oxide particles and the silica coating is increased. Powder resistance and dielectric breakdown voltage can be increased. The firing temperature is preferably 500 to 1000 ° C, more preferably 700 to 1000 ° C. Firing can usually be performed in an atmosphere of air, oxygen, nitrogen, etc., and the firing time is suitably about 10 minutes to 10 hours. For heating and firing, a known firing apparatus such as a rotary kiln, tunnel kiln, electric furnace or the like can be used.

  The insulating heat dissipating filler of the present invention can be used as it is as a heat dissipating substrate, and can also be used as a heat dissipating composition. The heat dissipating composition of the present invention is a composition containing the insulating heat dissipating filler of the present invention, and is usually mixed with a resin composition and used as a heat dissipating resin composition. The heat radiating resin composition includes a heat radiating sheet, a heat radiating elastomer, a heat radiating multilayer substrate, a heat radiating grease, a heat radiating paint, and the like. The various heat-dissipating resin compositions are also included in the present invention.

  The heat dissipating composition of the present invention may contain a heat dissipating filler other than the insulating heat dissipating filler of the present invention. It does not specifically limit as another heat radiation filler, A well-known arbitrary thing can be used. For example, metal oxides such as zinc oxide, magnesium oxide, titanium oxide, aluminum oxide, zirconium oxide, aluminum nitride, boron nitride, silicon carbide, silicon nitride, titanium nitride, metal silicon, metal particles, carbon compounds (diamond, graphite, Graphene, carbon nanotubes, etc.). When combined with the insulating heat dissipating filler of the present invention, the other heat dissipating filler is not limited to one type, and even if the same substance has a different particle size, two or more kinds of other substances having different particle sizes can be used. It may be a combination. There is no particular limitation on the shape, and the shape may be spherical, granular, cubic, rod-shaped, hexagonal plate-shaped, scale-shaped, or the like.

  The heat dissipating composition of the present invention can be mixed with a resin and used as a heat dissipating resin composition. In this case, the resin used may be a thermoplastic resin or a thermosetting resin, and an epoxy resin, acrylic resin, phenol resin, polyphenylene sulfide (PPS) resin, polyester resin, polyamide, polyimide, polystyrene , Polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, fluororesin, polymethyl methacrylate, ethylene / ethyl acrylate copolymer (EEA) resin, polycarbonate, polyurethane, polyacetal, polyphenylene ether, polyetherimide, acrylonitrile-butadiene -Resins such as styrene copolymer (ABS) resin, liquid crystal resin (LCP), and silicone resin can be exemplified.

  The heat-dissipating resin composition of the present invention comprises (1) a thermoforming resin composition obtained by kneading a thermoplastic resin and the heat-dissipating composition in a molten state, and (2) a thermosetting resin and the above-mentioned It may be in any form such as a resin composition obtained by kneading with a heat-dissipating composition and then heat-curing.

  The blending amount of the heat dissipating composition in the heat dissipating resin composition of the present invention can be arbitrarily determined according to the performance of the resin composition, such as the intended thermal conductivity and the hardness of the resin composition. In order to sufficiently exhibit the heat dissipation performance of the heat dissipation composition, it is preferable to contain 1% by volume or more based on the total solid content in the heat dissipation resin composition. The above blending amount can be used by adjusting the blending amount according to the required heat dissipation performance. In applications where higher heat dissipation is required, it is more preferably 5% by volume or more, and 10% by volume or more. Further preferred. Thus, the heat conductivity of the heat-dissipating resin composition can be preferably 0.5 W / m · K or more, and more preferably 1.0 W / m · K or more. Specifically, in a resin composition blended with 20% by volume of insulating heat dissipating filler: 80% by volume of epoxy resin, the thermal conductivity of the resin composition is 1.0 W / m · K or more, and the dielectric breakdown voltage is 4 kV / mm. This can be done.

  In the heat-dissipating resin composition of the present invention, the resin component can be freely selected depending on the application. For example, in the case where the heat source and the heat radiating plate are mounted and adhered, a resin having high adhesiveness, low hardness, and high heat resistance such as an epoxy resin, a silicone resin, or an acrylic resin may be selected.

  When the heat-dissipating resin composition of the present invention is a resin composition for thermoforming, the resin composition is obtained by melting and kneading the thermoplastic resin and the heat-dissipating composition, for example, using a screw-type twin screw extruder. It can be manufactured by pelletizing and then molding it into a desired shape by any molding method such as injection molding.

  When the heat-dissipating resin composition of the present invention is a resin composition obtained by kneading a thermosetting resin and the heat-dissipating composition and then heat-curing, for example, it is formed by pressure molding or the like. Preferably there is. Although the manufacturing method of such a resin composition is not specifically limited, For example, a resin composition can be shape | molded and manufactured by transfer molding.

  Applications of the heat dissipating resin composition of the present invention include heat dissipating members for electronic parts, heat conductive fillers, insulating fillers for temperature measurement, and the like. For example, the heat-dissipating resin composition of the present invention can be used to transfer heat from heat-generating electronic components such as MPUs, power transistors, and transformers to heat-dissipating components such as heat-dissipating fins and heat-dissipating fans. It can be used by being sandwiched between a heat conductive component and a heat dissipation component. As a result, heat transfer between the heat-generating electronic component and the heat-dissipating component is improved, and malfunction of the heat-generating electronic component can be reduced in the long term. It can also be suitably used for connection between a heat pipe and a heat sink, and connection between a module incorporating various heating elements and a heat sink.

  The heat dissipating composition of the present invention includes a heat dissipating grease which is a heat dissipating resin composition in which a base oil containing mineral oil or synthetic oil and the heat dissipating composition are mixed.

  The blending amount of the heat dissipating composition in the heat dissipating grease of the present invention can be arbitrarily determined according to the target heat conductivity. In order to sufficiently develop the heat dissipation performance of the heat dissipation composition, it is preferable to contain 1% by volume or more based on the total amount of the heat dissipation grease. The above blending amount can be used by adjusting the blending amount according to the required heat dissipation performance. In applications where higher heat dissipation is required, it is more preferably 5% by volume or more, and 10% by volume or more. Further preferred.

  The said base oil can be used 1 type or in combination of 2 or more types of various oil-based materials, such as mineral oil, synthetic oil, silicone oil, and fluorine-type hydrocarbon oil. As the synthetic oil, hydrocarbon oil is particularly preferable. As the synthetic oil, α-olefin, diester, polyol ester, trimellitic acid ester, polyphenyl ether, alkylphenyl ether and the like can be used.

  A surfactant may be added to the heat dissipating grease of the present invention as necessary. As the surfactant, a nonionic surfactant is preferable. High thermal conductivity can be achieved by blending a nonionic surfactant.

  Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl naphthyl ether, polyoxyethylenated castor oil, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkylamide, poly Oxyethylene-polyoxypropylene glycol, polyoxyethylene-polyoxypropylene glycol ethylenediamine, decaglycerin fatty acid ester, polyoxyethylene mono fatty acid ester, polyoxyethylene difatty acid ester, polyoxyethylene propylene glycol fatty acid ester, polyoxyethylene sorbitan mono Fatty acid ester, polyoxyethylene sorbitan tri fatty acid ester, ethylene glycol mono fatty acid ester, die Glycol mono fatty acid esters, propylene glycol mono fatty acid esters, glycerol mono-fatty acid esters, pentaerythritol fatty acid monoesters, sorbitan mono fatty acid esters, Sorubitansesuki fatty esters, sorbitan tri fatty acid ester.

  The effect of the addition of the nonionic surfactant varies depending on the type and blending amount of the insulating heat radiation filler and the HLB (hydrophilic / lipophilic balance) indicating the balance between hydrophilicity and lipophilicity. In applications that do not place importance on reduction in electrical insulation and electrical resistance, such as high heat dissipation grease, anionic surfactants, cationic surfactants, and amphoteric surfactants can be used.

  The heat dissipating grease of the present invention can be prepared by mixing the above-described components using a mixing device such as a dough mixer (kneader), a gate mixer, or a planetary mixer.

  The heat dissipating grease of the present invention is used by being applied to a heat generating body or a heat dissipating body. Examples of the heating element include general power supplies; electronic devices such as power transistors for power supplies, power modules, thermistors, thermocouples, temperature sensors; and exothermic electronic components such as integrated circuit elements such as LSIs and CPUs. Examples of the heat radiating body include heat radiating parts such as heat spreaders and heat sinks; heat pipes and heat radiating plates. Application | coating can be performed by screen printing, for example. Screen printing can be performed using, for example, a metal mask or a screen mesh. By applying the heat dissipating composition between the heat generating element and the heat dissipating member, heat can be efficiently conducted from the heat generating element to the heat dissipating element. Can be removed.

  The heat dissipating composition of the present invention includes a heat dissipating coating composition which is a heat dissipating resin composition in which the heat dissipating composition is dispersed in a resin solution or dispersion. In this case, the resin used may be curable or non-curable. Specific examples of the resin include the resins exemplified as resins that can be used in the above-described resin composition. The paint may be a solvent-based one containing an organic solvent or a water-based one in which a resin is dissolved or dispersed in water.

  Although the manufacturing method of the said coating material is not specifically limited, For example, it can manufacture by mixing and disperse | distributing the required raw material and solvent using a disper, bead mill, etc., for example.

The blending amount of the heat dissipating composition in the heat dissipating coating composition of the present invention can be arbitrarily determined according to the intended thermal conductivity. In order to sufficiently develop the heat dissipation performance of the heat-dissipating composition, it is preferable to contain 1% by volume or more based on the total amount of the coating composition. The above blending amount can be used by adjusting the blending amount according to the required heat dissipation performance. In applications where higher heat dissipation is required, it is more preferably 5% by volume or more, and 10% by volume or more. Further preferred.

  The heat dissipating coating composition of the present invention can be used for the uses described in the section of the heat dissipating resin composition. In addition, it can also be used for exterior walls of buildings, building materials, industrial equipment that generates heat, such as boilers, and home appliances.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

The insulating heat dissipating filler was evaluated by the following method.
The appearance and shape of the zinc oxide particles and the insulating heat radiation filler were observed using a scanning electron microscope (s-4800, manufactured by Hitachi High-Technologies Corporation).

  The dimensions of the zinc oxide particles and the insulating heat dissipating filler are measured by measuring the spanning diameter and height of the hexagonal surface of at least 20 particles from the electron micrograph using the above-mentioned scanning electron microscope. Assuming that, the weight average span diameter and the weight average height were calculated.

    The thickness of the oxide coating containing silicon of the insulating heat dissipating filler was determined by measuring the dimensions of the coating cross section at 10 locations using the scanning electron microscope and calculating the average value.

The amount of silicon insulating radiator filler measures the Zn and Si concentration by the fluorescent X-ray analyzer (Rigaku RIX2100), was determined as the ratio of the amount of SiO ₂ with respect to ZnO amount _(SiO 2 / ZnO).

The powder resistance of the zinc oxide particles and the insulating heat-dissipating filler was obtained by forming 0.3 g of a sample into a cylindrical shape (18 mmφ) at a pressure of 10 MPa and using a DC voltage application type insulation resistance tester (Model 3154 HIOKI). The powder resistance value was calculated by the following formula.

Powder resistance value = Measured value × Cylinder cross-sectional area / Cylinder thickness

The amount of Na in the oxide coating containing silicon of the insulating heat-dissipating filler was analyzed at a measurement wavelength of 589 nm using an atomic absorption analyzer (AA-6800, manufactured by Shimadzu Corporation) and calculated as the amount of Na relative to SiO ₂ . The sample solution was prepared by dissolving the insulating heat dissipating filler with an acid containing hydrofluoric acid and diluting with pure water. In addition, when there is much Na amount in zinc oxide, after measuring Na in zinc oxide separately, you may measure Na amount of the whole filler, and may obtain | require Na amount with respect to SiO2 from the difference.

  The total pore volume of the zinc oxide particles and the insulating heat dissipating filler was measured as described above using an automatic specific surface area / pore distribution measuring device (BELSORP-miniII manufactured by Nippon Bell Co., Ltd.).

(Preparation of zinc oxide particles-1)
Zinc sulfate (0.3 mol) and citric acid (0.003 mol) were dissolved in 150 cc of pure water. Next, 500 cc of pure water is put into a 2 L four-necked flask, and the aqueous zinc sulfate solution is added to the flask. The mixture is stirred at a rotation speed of 200 rpm using a two-blade stirrer having a blade diameter of 12 cm, and 0 at room temperature. 350 cc of an aqueous solution containing 7 mol of monoethanolamine was added, the pH of the aqueous solution was adjusted to 10.0, and maintained for 30 minutes to precipitate a precipitate. Then, after heating up to 100 degreeC and ageing | curing | ripening for 1 hour, it cooled, filtered, washed with water, and dried and obtained the zinc oxide powder. This zinc oxide powder had a hexagonal plate shape with an average diameter of 2.9 μm and an average height of 1.3 μm. The half width at 2θ = 36.5 ° was 0.18 °.

(Preparation of zinc oxide particles-2)
Zinc sulfate 0.3 mol and citric acid 0.001 mol were dissolved in 150 cc of pure water. Next, 500 cc of pure water is put into a 2 L four-necked flask, and the aqueous zinc sulfate solution is added to the flask. The mixture is stirred at a rotation speed of 200 rpm using a two-blade stirrer having a blade diameter of 12 cm, and 0 at room temperature. A 350 cc aqueous solution containing 9.9 moles of monoethanolamine was added, the pH of the aqueous solution was adjusted to 10.0, and maintained for 30 minutes to precipitate a precipitate. Then, after heating up to 100 degreeC and ageing | curing | ripening for 1 hour, it cooled, filtered, washed with water, and dried and obtained the zinc oxide powder. This zinc oxide powder had a hexagonal column shape with an average diameter of 1.7 μm and an average height of 3.0 μm. The half width at 2θ = 36.5 ° was 0.18 °.

(Experiment 1)
Example 1
Preparation of zinc oxide particles 10 g of the hexagonal plate-like zinc oxide particles prepared in 1 were 56 ml of ethanol (Nacalai Tesque, special grade), 3.7 ml of pure water, and 28% aqueous ammonia (special grade, manufactured by Kanto Chemical Co.). 1 g was added to prepare a slurry. Subsequently, while stirring this slurry with a magnetic stirrer, 3.5 g of tetraethoxysilane (special grade manufactured by Nacalai Tesque) was added over 30 minutes using a tube pump. Thereafter, filtration, washing, drying, and mortar grinding were performed to obtain an insulating heat dissipating filler (sample A) of the present invention. It was 0.0040 cm < ³ > / g when the total pore volume of the sample A was measured. In addition, the water in a liquid medium is 12 mass%, and ammonia is 5 times of molar ratio with respect to tetraethoxysilane. Moreover, the sample A was baked at 700 degreeC with the electric furnace for 1 hour, and the insulating thermal radiation filler (sample B) of this invention was obtained.

(Example 2)
90 ml of pure water was added to 10 g of hexagonal plate-like zinc oxide particles to prepare a slurry. While stirring this slurry with a magnetic stirrer, 3.5 g of tetraethoxysilane was added all at once. Thereafter, 15.3 g of a 28% aqueous ammonia solution was added all at once, followed by stirring at room temperature for 1 hour. Thereafter, filtration, washing, drying, and mortar grinding were performed to obtain an insulating heat dissipating filler (sample C) of the present invention. In addition, the water in a liquid medium is 100 mass%, and ammonia is 15 times of molar ratio with respect to tetraethoxysilane. Moreover, the sample C was baked at 700 degreeC with the electric furnace for 1 hour, and the insulating thermal radiation filler (sample D) of this invention was obtained.

(Example 3)
90 ml of pure water was added to 10 g of hexagonal plate-like zinc oxide particles to prepare a slurry. The slurry was heated to 90 ° C. while stirring with a magnetic stirrer, and 11.7 g of No. 4 sodium silicate (manufactured by Nippon Chemical Industry Co., Ltd.) was added in 30 minutes using a tube pump. Thereafter, a 5% aqueous sulfuric acid solution was added in 60 minutes using a tube pump until the pH of the slurry reached 9.0, and maintained at pH = 9.0 for 1 hour. Thereafter, filtration, washing, drying, and mortar grinding were performed to obtain an insulating heat dissipating filler (sample E) of the present invention. Moreover, the sample E was baked at 700 degreeC for 1 hour with the electric furnace, and the insulating thermal radiation filler (sample F) of this invention was obtained.

(Comparative Example 1)
The hexagonal plate-like zinc oxide particles prepared in Preparation of zinc oxide particles-1 were used as a comparative heat radiation filler sample G.

  All of Samples A to F maintain the shape of the hexagonal plate-like zinc oxide particles, and it can be confirmed that the surface has a dense coating of silicon oxide. In particular, Samples A to D have a dense silicon oxide coating. I found it expensive. As representatives, scanning electron micrographs of Samples B, D, F, and G are shown in FIGS.

  Table 1 shows measured values of powder physical properties of Samples B, C, D, F and G. The insulating heat radiation filler samples B, C, D and F having an oxide coating containing silicon on the surface of zinc oxide particles of the present invention are higher in powder than the zinc oxide particle sample G having no coating. It can be seen that resistance is exhibited.

In addition, in the case of an insulating heat dissipating filler having an oxide coating containing silicon, the powder resistance tends to decrease when the total pore volume is large, but the total pore volume should be 0.07 cm ² / g or less. For example, the powder resistance is higher than that of zinc oxide without a silicon oxide coating, and it can be seen that the powder resistance is remarkably increased when it is 0.02 cm ² / g or less.

In Sample F, the Na amount / SiO ₂ amount was 1.02%. On the other hand, in samples B to D, Na is below the lower limit of detection, and Na amount / SiO ₂ is estimated to be 300 ppm or less. When the amount of Na / SiO ₂ in the oxide coating containing silicon is large, the powder resistance tends to decrease, but if the amount of Na / SiO ₂ is 1.5% by mass or less, the oxidation without silicon oxide coating It can be seen that the powder resistance is higher than that of zinc.

(Experiment 2)
Example 4
The same method as in Example 1 except that 1.9 ml of pure water, 2.6 g of 28% aqueous solution of ammonia and 1.8 g of tetraethoxysilane were used, and the sample was baked at 700 ° C. for 1 hour in an electric furnace. An insulating heat dissipating filler (sample H) of the present invention was obtained.

(Example 5)
Except for 7.4 ml of pure water, 10.2 g of 28% aqueous solution of ammonia and 7.1 g of tetraethoxysilane, the sample was fired at 700 ° C. for 1 hour in an electric furnace. An insulating heat dissipating filler (sample I) of the present invention was obtained.

  The measured values of the powder physical properties of Samples H and I are shown in Table 2 together with the values of Samples B and G. The insulating heat dissipating filler having an oxide coating containing silicon on the surface of the zinc oxide particles of the present invention can increase the powder resistance as compared with the zinc oxide particles not having the coating, and particularly the coating thickness is 10 to 40 nm. In this case, it can be seen that the powder resistance can be remarkably increased.

In addition, the insulating heat dissipating filler having the oxide coating containing silicon on the surface of the zinc oxide particles of the present invention can increase the powder resistance as compared with the zinc oxide particles not having the coating, and in particular, SiO ₂ / ZnO. It can be seen that when the ratio is 5 to 20%, the powder resistance can be remarkably increased.

(Experiment 3)
(Example 6)
Preparation of Zinc Oxide Particles The insulating heat-radiating filler of the present invention (Sample J) )

  Table 4 shows the measured values of the powder physical properties of Sample J together with the values of Sample G. The insulating heat dissipating filler having an oxide coating containing silicon on the surface of the zinc oxide particles of the present invention is compared with the zinc oxide particles not having the same coating even when the shape of the zinc oxide particles as the base material changes. It can be seen that the powder resistance can be increased.

(Experiment 4)
(Example 7)
Sample B and a thermosetting epoxy resin (jER-807, manufactured by jER) were mixed as an insulating heat dissipating filler using a stirring defoaming device (ARE-250, manufactured by THINKY) at a volume ratio of 20%: 80%. . Then, after casting in a 10φ × 5 t (mm) molding machine and curing at room temperature, drying was performed at 100 ° C. for 2 hours to obtain a heat-dissipating resin composition (Sample K).

(Example 8)
A heat-dissipating resin composition (sample L) was obtained in the same manner as in Example 7 except that sample D was used instead of sample B as the insulating heat-dissipating filler.

(Comparative Example 2)
A heat-dissipating resin composition (sample M) was used in the same manner as in Example 7 except that the heat-dissipating filler was a heat-dissipating filler obtained by firing Sample G of Comparative Example 1 in an electric furnace at 700 ° C. for 1 hour instead of Sample B. )

Samples K to M were polished so as to be pellets having a shape of 10φ × 1 t (mm), and the thermal conductivity was obtained by the following calculation formula.
Thermal conductivity = thermal diffusivity × specific heat × specific gravity / thermal diffusivity: Measured by a laser flash method (thermal constant measuring device TC-7000 ULVAC-RIKO) at an ambient temperature of 25 ° C. in accordance with JIS R 1611.
Specific heat: Measured by DSC (differential scanning calorimetry DSC6200 SII) according to JIS K 7123.
Specific gravity: Measured by an underwater substitution method based on JIS K7112.

  Using specimens K to M, a test piece having a shape of 50 mm × 50 mm and a thickness of 1 to 2 mm was prepared, and in accordance with JIS C2110-1 (test using commercial frequency AC voltage application) The dielectric breakdown voltage was measured using a high voltage withstand voltage test apparatus (YHA / D-30K-2KDR manufactured by Yamaryo Electric Co., Ltd.). The test method was a short time method, the pressure increase rate was a rate of breaking in 10 to 20 seconds, and the electrode shape was a 25 mmφ cylinder / 75 mmφ cylinder. The test atmosphere was in insulating oil, and high-pressure insulating oil RA manufactured by Taniguchi Oil was used as the insulating oil. The dielectric breakdown voltage was calculated by dividing the measured value by the thickness of each test piece.

  The results are shown in Table 4. When the insulating heat dissipating filler of the present invention is used, although it is coated with an oxide containing silicon having a low thermal conductivity, it has a thermal conductivity equivalent to that of zinc oxide particles not having the coating, and dielectric breakdown. It turns out that the heat-radiating composition which improved the voltage significantly is obtained.

  By the way, in the manufacture of the samples A and B, when covering the surface of the zinc oxide particles with the oxide containing silicon, the raw materials are gradually mixed to manufacture the insulating heat dissipating filler. On the other hand, in the method for producing samples C and D, it is not necessary to gradually mix the raw materials, and a dense silicon oxide coating can be formed even if the respective materials are mixed together. Further, it can be produced even when the liquid medium is 100% water. As described above, the performance of the insulating heat dissipating filler is significantly improved as compared with the comparative example. As described above, even when an organosilicon compound is used as a silicon oxide source, the insulating heat dissipating filler can be obtained at low cost and in a short time by using a specific amount of the catalyst compound in a medium mainly composed of water. It can be seen that this method is excellent as a method for producing.

The insulating heat dissipating filler of the present invention has high powder resistance, and by using this in a resin composition or the like, a heat dissipating composition having excellent thermal conductivity and high dielectric breakdown voltage can be obtained. For this reason, since the heat-radiating composition of the present invention can be used as a material for efficiently dissipating heat by attaching it to an electronic device that requires high insulation, the utility value is high.

Claims (7)

The zinc oxide particles have an oxide coating containing at least silicon, and the ratio of the silicon oxide amount (SiO ₂ amount) to the zinc oxide amount (ZnO amount) (SiO ₂ amount / ZnO amount) is 1 to 50 mass%. The average thickness of the coating is 2 to 100 nm,
An insulating heat dissipating filler having a total pore volume of 0.07 cm ³ / g or less calculated by the BJH method based on an adsorption / desorption isotherm by nitrogen adsorption. The insulating heat radiation filler according to claim 1, wherein the oxide coating containing at least silicon is a dense coating. The insulating heat dissipating filler according to claim 1 or 2, wherein the content of alkali metal with respect to SiO ₂ measured by atomic absorption spectrometry is 1.5% by mass or less. The shape is a hexagonal columnar shape, the average crossed diameter (L) of the hexagonal surface is 0.2 to 40 μm, and the average height (H) in the direction perpendicular to the hexagonal surface is 0.05 to 50 μm. The insulating heat dissipating filler according to claim 1. The method for producing an insulating heat dissipating filler according to claim 1, wherein the surface of the zinc oxide particle has an oxide coating containing at least silicon.
A step of mixing zinc oxide particles, an organosilicon compound, a catalyst compound, and a liquid medium to hydrolyze the organic silicon compound, wherein 50% by mass or more of the liquid medium is water;
The method for producing an insulating heat dissipating filler, wherein the amount of the catalyst compound is 10 times or more in molar ratio to the amount of the organosilicon compound. The method for producing an insulating heat dissipating filler according to claim 5, wherein the solid content including the reaction product is fired at 150 to 1000 ° C. after the step. A heat dissipating composition comprising the insulating heat dissipating filler according to any one of claims 1 to 4.

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