Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/072—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with aluminium
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/04—Ingredients treated with organic substances
  • C08K9/06—Ingredients treated with organic substances with silicon-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L63/00—Compositions of epoxy resins; Compositions of derivatives of epoxy resins

Definitions

• the present invention relates to a new surface-treated aluminum nitride powder.
• heat dissipation materials used to dissipate this heat.
• the forms of heat dissipation materials used in semiconductors are diverse, including heat dissipation sheets, semiconductor encapsulants, heat dissipation greases, heat dissipation gap fillers, and heat dissipation adhesives.
• heat dissipation materials include heat dissipation resin materials that combine resins such as silicone resins, epoxy resins, and acrylic resins with highly thermally conductive fillers.
• fillers examples include aluminum nitride, boron nitride, aluminum oxide (alumina), and zinc oxide.
• aluminum nitride which has particularly high thermal conductivity, has a thermal conductivity five times that of alumina and is attracting attention as a filler for heat dissipation materials.
• the thermal conductivity of heat-dissipating resin materials can be increased by highly filling the resin with thermally conductive fillers.
• Methods for improving the filling include increasing the affinity of the filler with the resin and removing agglomerated powder.
• Additives may also be added or the filler may be surface-treated to increase affinity with the resin.
• Epoxy resins are often used in heat-dissipating resin materials, and silane compounds with epoxy groups are often used for the surface treatment.
• a surface-treated aluminum nitride powder in which a silane compound having a polymerizable unsaturated bond in its molecule is present on the particle surface, the carbon content per m2 of the surface of the aluminum nitride powder is 0.4 ⁇ 10 ⁇ 3 g/ m2 or more and 1.6 ⁇ 10 ⁇ 3 g/ m2 or less, and the proportion of unsaturated bonds per gram of carbon present on the surface of the aluminum nitride powder, calculated from the amount of iodine determined by the Wiess method, is 2.5 ⁇ 1021 bonds/g or more and 5.5 ⁇ 1021 bonds/g or less.
• the surface-treated aluminum nitride powder of the present invention is particularly preferably one having a cumulative volume 50% particle diameter D50 of 0.3 ⁇ m to 40 ⁇ m.
• the present invention also provides a method for producing surface-treated aluminum nitride powder, which includes the steps of contacting aluminum nitride powder with a silane compound having a polymerizable unsaturated bond in the molecule, holding the mixture at a temperature below 60°C for 30 minutes or more, and then heating the mixture at a temperature of 60 to 80°C under reduced pressure.
• the surface-treated aluminum nitride powder of the present invention is an aluminum nitride powder in which a silane compound having a polymerizable unsaturated bond in the molecule is present on the particle surface, and when filled into a resin such as an epoxy resin to form a resin composition, high filling is possible, the resin composition has low viscosity, and a long usable life can be achieved.
• a resin such as an epoxy resin to form a resin composition
• the surface-treated aluminum nitride powder of the present invention is characterized in that it has a silane compound having a polymerizable unsaturated bond fixed on the particle surface.
• the silane compound may be any silane compound having a polymerizable unsaturated bond, and may be, for example, an alkoxysilane having a group having a polymerizable unsaturated bond bonded thereto, such as a (meth)acrylic group shown in a representative example below.
• the main chain to which Si and the group having a polymerizable unsaturated bond are bonded is preferably a linear hydrocarbon group, and the carbon number (not including the carbon constituting the unsaturated bond) is preferably 0 to 12.
• the carbon number is preferably 3 or more and preferably 8 or less. If the carbon number is greater than 12, it becomes difficult to satisfy the conditions of the carbon content per m2 of the surface of the aluminum nitride powder and the proportion of unsaturated bonds per gram of carbon present on the surface of the aluminum nitride powder, which are specified in the surface-treated aluminum nitride powder, and furthermore, the affinity with epoxy resin tends to be low, and the filling property and operability in the resin are reduced.
• Representative compounds that are preferably used as the silane compound having a polymerizable unsaturated bond include, for example, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 8-methacryloxyoctyltrimethoxysilane, 8-methacryloxyoctyltriethoxysilane, 8-methacryloxyoctylmethyldimethoxysilane, 8-methacryloxyoctylmethyldiethoxysilane, 8-acryloxyoctyltrimethoxysilane, 8-acryloxyoctyltriethoxysilane, 10-methacryloxydecyltrimethoxysilane, Examples of suitable silane
• the surface-treated aluminum nitride powder may be surface-treated with only one type of silane compound, or may be surface-treated with a combination of two or more types of silane compounds.
• the carbon content (weight) per 1 m2 of the surface of the aluminum nitride powder in the surface-treated aluminum nitride powder is 0.4 ⁇ 10 ⁇ 3 g/ m2 or more and 1.6 ⁇ 10 ⁇ 3 g/ m2 or less.
• the carbon content is preferably 0.5 ⁇ 10 ⁇ 3 g/m2 or more, and preferably 1.5 ⁇ 10 ⁇ 3 g/ m2 or less . It is important that the carbon content is within the above range in order to exhibit filling properties in epoxy resin and operability.
• the carbon content when the carbon content is less than 0.4 ⁇ 10 ⁇ 3 g/ m2 , the amount of silane compound present on the surface generally tends to be small, and therefore, the effects of the surface treatment of the aluminum nitride powder, such as improvement of filling properties in epoxy resin and operability during filling, cannot be expected. Furthermore, when the carbon content exceeds 1.6 ⁇ 10 -3 g/ m2 , there generally tends to be a large amount of silane compound present on the surface, and therefore the excess silane compound forms oligomers and is easily fixed to the surface.
• the oligomers fixed to the surface not only impede the effect of the surface treatment of the aluminum nitride powder, but also deteriorate the viscosity when kneaded with an epoxy resin, and become thermal resistance between the aluminum nitride particles, making it difficult for the aluminum nitride powder to exhibit its inherent high thermal conductivity.
• the carbon content per square meter of the surface of the surface-treated aluminum nitride powder is determined by the method described in the Examples.
• the number of polymerizable unsaturated bonds (proportion of unsaturated bonds present) calculated from the amount of iodine determined by the Wiess method per gram of carbon present on the surface of the aluminum nitride powder is 2.5 ⁇ 10 21 /g or more and 5.5 ⁇ 10 21 /g or less.
• the proportion of unsaturated bonds present per gram of carbon present on the surface of the surface-treated aluminum nitride powder is determined by the method described in the Examples.
• the cumulative volume 50% particle size (D50) calculated from the particle size distribution measured using an ethanol solvent with a laser diffraction scattering type particle size distribution analyzer is preferably 0.3 ⁇ m to 40 ⁇ m.
• the D50 is preferably 0.7 ⁇ m or more and preferably 27 ⁇ m or less. That is, the aluminum nitride powder having the above particle size is a particle with a relatively large specific surface area as a filler, and the area forming the interface with the resin is large, so that the effect of the present invention is particularly remarkable.
• the specific surface area is preferably in the range of 0.1 to 6.0 m 2 /g.
• the specific surface area refers to the BET specific surface area measured by a nitrogen adsorption one-point method.
• the method for producing the surface-treated aluminum nitride powder of the present invention is not particularly limited, but a method including the steps of dry contacting aluminum nitride powder having an oxide layer formed on the particle surface, the oxide layer being approximately 0.005% to 0.2% of the particle diameter, with a surface treatment agent consisting of a silane compound having a polymerizable unsaturated bond at a temperature of less than 60°C, and then heating the resulting mixture at a temperature of 60 to 80°C under reduced pressure, is preferably used.
• a surface treatment agent consisting of a silane compound having a polymerizable unsaturated bond at a temperature of less than 60°C
• the aluminum nitride powder used as the raw material for the surface treatment may be any powder produced by a conventionally known method without any particular limitation.
• the aluminum nitride powder before the surface treatment is called the "raw aluminum nitride powder".
• methods for producing the raw aluminum nitride powder include a direct nitridation method, a reduction nitridation method, and a gas phase synthesis method.
• the shape of the primary particles of the raw aluminum nitride powder is not particularly limited, and can be any shape, such as irregular, spherical, polyhedral, columnar, whisker-like, or flat.
• spherical shapes are preferred, as they have good viscosity characteristics and high reproducibility of thermal conductivity.
• the aluminum nitride particles it is preferable for the aluminum nitride particles to have a small aspect ratio. The preferred aspect ratio is 1 to 3.
• the particle size distribution of the raw aluminum nitride powder is not particularly limited, and may be appropriately determined in consideration of the change in particle size due to the surface treatment of the target surface-treated aluminum nitride powder.
• the cumulative volume 50% particle size D50 determined from the particle size distribution measured using a laser diffraction scattering type particle size distribution analyzer using an aqueous solvent is preferably 0.3 to 40 ⁇ m.
• the D50 is preferably 0.7 ⁇ m or more and preferably 27 ⁇ m or less.
• the specific surface area of the raw material aluminum nitride powder measured by the BET method is preferably 0.1 to 6.0 m 2 /g, and more preferably 0.6 m 2 /g or more and 5.5 m 2 /g or less.
• the raw aluminum nitride powder may contain impurities such as alkaline earth elements and rare earth elements derived from the raw materials or intentionally added during the synthesis process, up to about 5 parts by mass per 100 parts by mass of raw aluminum nitride powder.
• boron nitride may be contained up to about 5 parts by mass as an anti-agglomeration agent or an impurity derived from the manufacturing process.
• an amount of impurities that significantly reduces the crystallinity of aluminum nitride is not preferred as it causes a decrease in thermal conductivity.
• the aluminum nitride content in the raw aluminum nitride powder is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.
• the raw aluminum nitride powder preferably has an oxide layer on the surface of the aluminum nitride particles.
• the thickness of the oxide layer is preferably 0.005% to 0.2% of the particle diameter.
• the thickness of the oxide layer is preferably about 0.05% or more of the particle diameter, and preferably about 1.5% or less of the particle diameter.
• the thickness of the oxide layer is less than 0.005% of the particle diameter, the amount of bonding of the silane compound, which is the surface treatment agent, tends to be insufficient. If the thickness of the oxide layer exceeds 0.2% of the particle diameter, there is a concern that the thermal conductivity between the aluminum nitride particles will be hindered.
• the oxide layer may be formed by natural oxidation during storage of the raw aluminum nitride powder, or it may be formed by a deliberate oxidation treatment process.
• the oxidation treatment of the aluminum nitride powder may be carried out during the manufacturing process of the raw aluminum nitride powder, or it may be carried out as a separate process after the raw aluminum nitride powder is manufactured.
• raw aluminum nitride powder obtained by reduction nitridation has an aluminum oxide layer on its surface because it goes through an oxidation treatment process during the manufacturing process for the purpose of removing the carbon used during the reaction.
• An additional oxidation treatment process may be carried out on the aluminum nitride powder obtained by reduction nitridation.
• the raw aluminum nitride powder obtained by various methods can be heated in an oxygen-containing atmosphere, preferably at a temperature of 400 to 1,000°C, more preferably at 600 to 900°C, for preferably 10 to 600 minutes, more preferably 30 to 300 minutes, to form an aluminum oxide layer on the surface of the raw aluminum nitride particles.
• the oxygen-containing atmosphere can be, for example, oxygen, air, water vapor, or carbon dioxide, but in terms of the purpose of the present invention, treatment in air, particularly under atmospheric pressure, is preferred.
• the surface treatment is carried out, for example, by a method including a step of contacting the raw material aluminum nitride powder on which the oxide layer has been formed with a surface treatment agent comprising a silane compound having a polymerizable unsaturated bond at a temperature of less than 60° C. in a dry state, and then a step of heating at a temperature of 60 to 80° C. under reduced pressure conditions.
• the silane compound which is the surface treatment agent
• the amount of the silane compound used is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 1.0 parts by mass, per 100 parts by mass of the raw aluminum nitride powder.
• a process of removing free treating agent by carrying out a reduced pressure/heat treatment may be carried out.
• the method of contacting the aluminum nitride powder with the silane compound, which is the surface treatment agent includes a dry surface treatment method and a wet surface treatment method.
• Dry surface treatment is a method in which no solvent is used when mixing the aluminum nitride powder with the surface treatment agent.
• Wet surface treatment is a method in which a solvent is used, and a solvent drying process is required. It is important that no solvent remains in the heating process under reduced pressure conditions that follows the contact process, but because heating is required to remove the solvent, there is a high risk of polymerization of unsaturated bonds occurring. Therefore, the dry surface treatment method is more desirable because it is less likely to cause polymerization of unsaturated bonds.
• the dry mixing method in dry surface treatment includes, for example, a method of gasifying the surface treatment agent and mixing it with the powder, a method of spraying or dripping the liquid surface treatment agent and mixing it with the powder, and a method of diluting the surface treatment agent with a small amount of organic solvent to increase the amount of liquid and then spraying or dripping it.
• the dry mixing method of gasifying the surface treatment agent can be applied when performing surface treatment with a surface treatment agent consisting of a highly volatile low molecular weight silane compound.
• the dry mixing method of diluting the surface treatment agent with an organic solvent is suitable for dispersing the surface treatment agent evenly throughout the powder when the amount of the surface treatment agent is small.
• a general mixer/stirrer can be used, for example, a planetary mixer, a Henschel mixer, a super mixer, a V-type mixer, a drum mixer, a double cone mixer, and a rocking mixer. It is preferable that the dry mixer is equipped with a heating function. In addition, since powders tend to aggregate during dry mixing, it is preferable that the mixer is equipped with a mechanism for breaking up aggregates that have formed, such as a crushing blade or chopper. Furthermore, during the mixing operation, not only do the powders simply adhere to each other, but depending on the stirring mechanism, the powders may be pressed against the walls of the mixing container, forming a thick adhesion layer, which makes it impossible to maintain the mixed state of the powders.
• the walls of the mixing container are equipped with anti-adhesion measures such as a fluororesin coating, a mechanism for brushing off adhering powder such as a knocker, or a scraping mechanism with a modified stirring blade.
• anti-adhesion measures such as a fluororesin coating, a mechanism for brushing off adhering powder such as a knocker, or a scraping mechanism with a modified stirring blade.
• the step of heating under reduced pressure after dry contact at a temperature below 60°C is a step of heating at approximately 60-80°C for approximately 2-24 hours under reduced pressure.
• One of the purposes of this operation is to fix the silane compound, which is the surface treatment agent, to the aluminum nitride surface, but if necessary, an operation can also be performed to adjust the amount of silane compound in the aluminum nitride powder after the contact.
• excess surface treatment agent is removed by heating under reduced pressure, preventing the presence of excess free surface treatment agent that is not fixed to the aluminum nitride powder, and preventing the aluminum nitride powder from agglomerating due to the series of surface treatment operations.
• the pressure during reduced pressure is preferably 10 hPa or less.
• the ratio of aluminum nitride constituting the surface-treated aluminum nitride powder to the silane compound as the surface treatment agent is not limited, and the optimal amount varies depending on the particle size and specific surface area of the powder.
• the amount of the silane compound used is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, and preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, per 100 parts by mass of the raw aluminum nitride powder.
• the surface-treated aluminum nitride powder obtained by the surface treatment may undergo agglomeration, which may impair the powder properties and the ability to be filled into resin. In such a case, it is preferable to remove coarse particles by a crushing treatment or a classification treatment.
• the treatment is preferably carried out so that the cumulative volume 90% particle size D90 of the resulting surface-treated aluminum nitride powder is 100 ⁇ m or less.
• the crushing method is preferably a dry crushing method.
• a relatively mild method is also preferable so that most of the formed aggregates are not crushed. In particular, if the crushing is performed so strongly that even the primary particles are crushed, the effect of the present invention is lost.
• the crushing device include dry crushing devices such as a stone mill type grinder, a mortar mill, a cutter mill, a hammer mill, and a pin mill. Among them, a stone mill type grinder is preferable because it can selectively crush large aggregates in a short time and causes little uneven crushing.
• the atmosphere for the crushing treatment is preferably air or an inert gas. In addition, it is preferable that the humidity of the atmosphere is not too high, specifically, it is preferably less than 70%, more preferably less than 55%.
• classification may be performed as a method for removing coarse aggregated particles other than the disintegration treatment.
• Either dry classification or wet classification can be selected for classification, but if high accuracy is not required, dry classification is preferable because it eliminates the need to remove the solvent.
• dry classification air classification and a vibrating sieve can be used.
• the method and device for air classification can be selected appropriately to obtain a particle size distribution suitable for use as a filler for resin compositions.
• Air classification is a method in which powder is dispersed in an air current, and the gravity, inertial force, or centrifugal force of the particles is used to separate fine powder from coarse powder. Precision suitable for classifying particles of a few micrometers in size can be achieved with a classifier that utilizes inertial and centrifugal forces.
• Methods that utilize inertial force include, for example, the impactor type, which uses guide vanes or the like inside the device to create a swirling air current, which separates fine and coarse powders as the powder is bent into a curve by the momentum of the air current; the semi-free vortex centrifugal type, which uses centrifugal force to classify particles; and the Coanda type, which utilizes the Coanda effect.
• Classification devices that utilize inertial force include, for example, the cascade impactor, viable impactor, aero fine classifier, eddy classifier, elbow jet, and hyperplex.
• the centrifugal force method uses a vortex airflow to separate fine and coarse powders, and the devices used are free vortex type and forced vortex type.
• free vortex type devices include cyclones without guide vanes, multi-stage cyclones, turboplexes that use secondary air to promote the elimination of agglomeration, dispersion separators with guide vanes to improve classification accuracy, microspins, and microcuts.
• the forced vortex type is a device that applies centrifugal force to particles with a rotating body inside the device and further improves classification accuracy by creating a separate air flow inside the device, and examples of such devices include turbo classifiers and Donaserec.
• the crushing treatment and the classification treatment may be carried out in combination.
• the resin composition of the present invention contains an epoxy resin and a filler made of the surface-treated aluminum nitride powder.
• the filler made of the surface-treated aluminum nitride powder has excellent filling properties and operability in epoxy resins, and shows only a small increase in viscosity even when kneaded under heating, so that the pot life of the resin composition is long.
• the epoxy resin is not particularly limited, and a general epoxy resin can be used.
• epoxy resins include polyfunctional epoxy resins such as bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, biphenyl type epoxy resins, naphthalene ring-containing epoxy resins, and cyclopentadiene-containing epoxy resins.
• bisphenol A type epoxy resins, bisphenol F type epoxy resins, and biphenyl type epoxy resins are preferred.
• a general curing agent for epoxy resins can be used as a curing agent for curing the epoxy resin.
• the curing agent include a thermosetting curing agent and a photocuring agent.
• the thermosetting curing agent include amines, polyamides, imidazoles, acid anhydrides, boron trifluoride-amine complexes, dicyandiamide, organic acid hydrazides, phenol novolac resins, bisphenol novolac resins, and cresol novolac resins.
• the photocuring agent include diphenyliodonium hexafluorophosphate and triphenylsulfonium hexafluorophosphate. Among these, amines, imidazoles, and acid anhydrides are preferred.
• the content of the filler consisting of the surface-treated aluminum nitride powder in the resin composition is preferably 5% by mass or more, more preferably 13% by mass or more, and even more preferably 20% by mass or more, relative to 100% by mass of the resin composition, and is, for example, 93% by mass or less.

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