Surface-treated aluminum nitride powder

Abstract

The present invention provides an aluminum nitride powder surface-treated with a silane compound having a polymerizable unsaturated bond, wherein: when a resin composition is formed by filling an epoxy resin with the same, low viscosity and a high level of filling can be achieved, and the resin composition has a long pot life; and the surface-treated aluminum nitride powder is capable of maintaining high adhesion to a resin in a cured body. The surface-treated aluminum nitride powder according to the present invention is an aluminum nitride powder in which a silane compound having a polymerizable unsaturated bond in a molecule thereof is present on the particle surfaces, wherein the carbon content per 1 m2 of the surface of the aluminum nitride powder is 0.4×10-3 to 6×10-3 g / m2, and the rate of the presence of unsaturated bonds per 1 g of carbon present on the surface of the aluminum nitride powder calculated from an iodine quantity found via the Wijs method is 2.5×1021 to 5.5×1021 bonds / g.

Description

Surface-treated aluminum nitride powder

[0001] The present invention relates to a novel surface-treated aluminum nitride powder.

[0002] In recent years, with the increasing integration of semiconductor devices, the electronic components that make up semiconductors have become smaller and more powerful. The biggest challenge in performing high-speed, large-volume calculations is the heat generated by semiconductors, leading to an increasing demand for heat-dissipating materials. Heat-dissipating materials used in semiconductors come in a wide variety of forms, including heat-dissipating sheets, semiconductor encapsulants, thermal greases, heat-dissipating gap fillers, and heat-dissipating adhesives. Examples of these heat-dissipating materials include heat-dissipating resin materials that combine resins such as silicone resins, epoxy resins, and acrylic resins with highly thermally conductive fillers. Examples of fillers that have been used include aluminum nitride, boron nitride, aluminum oxide (alumina), and zinc oxide. Among these, aluminum nitride, which has particularly high thermal conductivity, has a thermal conductivity more than five times that of alumina and is attracting attention as a filler for heat-dissipating materials.

[0003] In general, the thermal conductivity of heat-dissipating resin materials can be increased by highly loading the resin with thermally conductive fillers. To improve the filling ability, methods such as increasing the filler's affinity with the resin or removing agglomerated powder are available. To increase the affinity with the resin, additives may be added or the filler may be surface-treated. Epoxy resins are often used in heat-dissipating resin materials, and silane compounds with epoxy groups are often used for the surface treatment.

[0004] However, when a filler surface-treated with a silane compound having an epoxy group is used, depending on the type of curing agent for the epoxy resin, the epoxy group of the surface treatment agent may react with the curing agent component, resulting in a deterioration in filling properties and operability.

[0005] On the other hand, silane compounds having polymerizable unsaturated bonds but no epoxy groups are known as surface treatment agents for fillers to be filled into epoxy resins, which can increase the affinity between the filler and the resin (see Patent Document 1). Examples of silane compounds having polymerizable unsaturated bonds include (meth)acrylic silanes. Treating aluminum nitride powder with the silane compound, which has high thermal conductivity, provides good adhesion to the resin, high thermal conductivity, and the low elasticity effect described in the document. Furthermore, because the silane compound does not have epoxy groups, it is believed that the deterioration of filling properties and operability due to the epoxy groups in the surface treatment agent will not occur.

[0006] International Publication No. 2015 / 104917

[0007] However, when aluminum nitride powder was actually surface-treated by a conventional method with a silane compound having a polymerizable unsaturated bond and then filled into an epoxy resin, it was found that the viscosity of the resin after filling increased significantly. Patent Document 1 does not describe at all that this phenomenon occurs or how to solve it, and it can be said that this is an issue that needs to be solved as soon as possible.

[0008] Therefore, an object of the present invention is to provide an aluminum nitride powder that has been surface-treated with a silane compound having a polymerizable unsaturated bond, which, when filled into an epoxy resin to form a resin composition, allows for high filling, the resin composition has low viscosity and a long usable life, and, in the cured product obtained by curing the resin composition, can maintain high adhesion to the resin.

[0009] As a result of extensive research to achieve the above-mentioned object, the present inventors discovered that the degree of viscosity increase when aluminum nitride powder is filled into an epoxy resin varies depending on the treatment conditions when the aluminum nitride powder is surface-treated with a silane compound having a polymerizable unsaturated bond. Based on this discovery, the inventors conducted further research and found that the viscosity increase becomes more pronounced as the unsaturated bonds of the silane compound having a polymerizable unsaturated bond are reduced by the surface treatment. The inventors confirmed that using a surface-treated aluminum nitride powder in which the reduction in unsaturated bonds is controlled within a specific range results in a small increase in viscosity when filled into a resin, and furthermore, is able to fully demonstrate the inherent function of the silane compound, such as improving the adhesion of the surface-treated aluminum nitride powder to the resin, thereby completing the present invention.

[0010] That is, according to the present invention, there is provided an aluminum nitride powder having a silane compound having a polymerizable unsaturated bond in the molecule present on the particle surface, the aluminum nitride powder having a surface area of ​​1 m ２ The carbon content per －３ g / m ２ 1.6 x 10 －３ g / m ２ and the proportion of unsaturated bonds present on the surface of the aluminum nitride powder per 1 g of carbon calculated from the amount of iodine determined by the Wiess method is 2.5 × 10 or less. ２１ pieces / g or more 5.5×10 ２１ The surface-treated aluminum nitride powder has a particle size of 1000p / g or less.

[0011] The silane compound is preferably a (meth)acrylic silane compound having a polymerizable unsaturated bond in the molecule.

[0012] In addition, in the surface-treated aluminum nitride powder of the present invention, the density of the silane compound is 0.4 to 5.0 particles / nm ２ is particularly preferable in order to maintain a suitable affinity with the epoxy resin.

[0013] 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 μm to 40 μm.

[0014] Furthermore, the present invention further provides a method for producing a surface-treated aluminum nitride powder, which comprises the steps of contacting an aluminum nitride powder with a silane compound having a polymerizable unsaturated bond in the molecule, maintaining the mixture at a temperature of less than 60°C for 30 minutes or longer, and then heating the mixture at a temperature of 60 to 80°C under reduced pressure.

[0015] According to the present invention, there is also provided a filler comprising the surface-treated aluminum nitride powder, a resin composition comprising an epoxy resin and the filler, and a cured product thereof. Here, the resin composition preferably contains the filler in an amount of 5 mass % or more.

[0016] The surface-treated aluminum nitride powder of the present invention is an aluminum nitride powder having a silane compound with a polymerizable unsaturated bond present on the particle surface. When filled into a resin such as an epoxy resin to form a resin composition, the resin composition can be highly filled, has low viscosity, and has a long usable life. In a cured product obtained by curing the resin composition, high adhesion between the aluminum nitride powder and the resin is maintained. Furthermore, this high adhesion is expected to highly inhibit water penetration into the cured product, thereby exhibiting high water resistance.

[0017] [Surface-treated aluminum nitride powder] The surface-treated aluminum nitride powder of the present invention is characterized by having a silane compound having a polymerizable unsaturated bond immobilized on the particle surface. The silane compound may be any silane compound having a polymerizable unsaturated bond, and may be, for example, an alkoxysilane to which a group having a polymerizable unsaturated bond is bonded, such as a (meth)acrylic group, a typical example of which will be described later. In this case, the main chain to which Si and the group having a polymerizable unsaturated bond are bonded is preferably a linear hydrocarbon group, and the number of carbon atoms therein (excluding carbon atoms constituting the unsaturated bond) is preferably 0 to 12. The number of carbon atoms is preferably 3 or more and preferably 8 or less. When the number of carbon atoms is greater than 12, the surface 1 m of the aluminum nitride powder specified in the surface-treated aluminum nitride powder is preferably 100%. ２It becomes difficult to satisfy the conditions of the carbon content per gram and the proportion of unsaturated bonds per gram of carbon present on the surface of the aluminum nitride powder, and moreover, the affinity with epoxy resin tends to be low, resulting in a decrease in fillability into resin and operability.

[0018] Representative compounds that can be suitably 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, 10-methacryloxydecyltrimethoxysilane, 10-methacryloxydecyltriethoxy ... Examples of suitable silanes include 0-methacryloxydecyltriethoxysilane, 10-methacryloxydecylmethyldimethoxysilane, 10-methacryloxydecylmethyldiethoxysilane, 10-acryloxydecyltrimethoxysilane, 10-acryloxydecyltriethoxysilane, 12-methacryloxydodecyltrimethoxysilane, 12-methacryloxydodecyltriethoxysilane, 12-methacryloxydodecylmethyldimethoxysilane, 12-methacryloxydodecylmethyldiethoxysilane, 12-acryloxydodecyltrimethoxysilane, 12-acryloxydodecyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltrichlorosilane, allyltrimethoxysilane, allyltriethoxysilane, and p-styryltrimethoxysilane. Among these, more preferred silane compounds include 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane.

[0019] 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.

[0020] In the surface-treated aluminum nitride powder, the surface 1 m ２ The carbon content (weight) per －３ g / m ２ 1.6 x 10 －３ g / m ２ The carbon content is preferably 0.5×10 －３ g / m ２ or more, preferably 1.5×10 －３ g / m ２ It is important that the carbon content is within the above range in order to exhibit good filling properties into epoxy resins and operability. －３ g / m ２ When the carbon content is less than 1.6 × 10, 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 the fillability into the epoxy resin and the operability during filling, cannot be expected. －３ g / m ２ When the surface concentration of the surface-treated aluminum nitride powder exceeds 1 m, there is generally a tendency for a large amount of silane compound to be present on the surface, and therefore the excess silane compound is likely to form oligomers and be fixed on the surface, and the oligomers fixed on the surface not only hinder the effect of the surface treatment of the aluminum nitride powder, but also worsen 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. ２ The carbon content per unit area can be determined by the method described in the Examples.

[0021] In the surface-treated aluminum nitride powder of the present invention, in addition to the requirement of the carbon content, the number of polymerizable unsaturated bonds (proportion of unsaturated bonds) 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 pieces / g or more 5.5×10 ２１ The proportion of unsaturated bonds present on the surface of the surface-treated aluminum nitride powder per 1 g of carbon can be determined by the method described in the Examples.

[0022] The Wiess method is a method described in the Examples below.

[0023] The number of the polymerizable unsaturated bonds is 2.5 × 10 ２１ When the content is less than 1 / g, the amount of treatment with the silane compound, i.e., the amount of polymerizable unsaturated bonds relative to the carbon content, is small. The small amount of polymerizable unsaturated bonds relative to the carbon content is thought to be the result of the initial polymerizable unsaturated bonds being consumed by the polymerization of the silane compounds themselves. Therefore, the polymerization of the silane compounds themselves causes aggregation between multiple aluminum nitride particles, which may impair the fillability and operability of the epoxy resin.

[0024] Surface-treated aluminum nitride powders treated with a silane compound having a large number of carbon atoms in the main chain may satisfy the above carbon content, but the ratio of the amount of polymerizable unsaturated bonds to the carbon content is small, and they tend not to satisfy the above range. In this case, too, there arises the problem that the effect of the presence of the polymerizable unsaturated bonds is small.

[0025] Although the density of the silane compound in the surface-treated aluminum nitride powder cannot be directly measured, the density of the silane compound calculated from the carbon content and information on the silane compound used is preferably 0.4 to 5.0 particles / nm ２ The density of the silane compound is preferably 0.8 particles / nm ２ or more, and preferably 4.0 particles / nm ２The information on the silane compound refers to the number of carbon atoms contained in one molecule of the silane compound, and in particular, when the silane compound is an alkoxysilane having two or more alkoxy groups, it refers to the number of carbon atoms contained in one molecule of the silane compound after the two alkoxy groups have been eliminated. The density of the silane compound can be determined by the method described in the Examples.

[0026] There are no particular limitations on other physical properties of the surface-treated aluminum nitride powder, but from the viewpoint of use as a filler, the cumulative volume 50% particle size (D50) determined from the particle size distribution measured using an ethanol solvent with a laser diffraction / scattering particle size distribution analyzer is preferably 0.3 μm to 40 μm. The D50 is preferably 0.7 μm or more and preferably 27 μm or less. That is, aluminum nitride powder having the above particle size has a relatively large specific surface area as a filler, and the area forming the interface with the resin is large, so the effects of the present invention are particularly pronounced. Specifically, the specific surface area is preferably 0.1 to 6.0 m ２ The specific surface area is in the range of / g. The specific surface area refers to a BET specific surface area measured by a nitrogen adsorption single-point method.

[0027] The surface-treated aluminum nitride powder preferably has a cumulative volume 90% particle size (D90) determined from the particle size distribution of 100 μm or less. The surface-treated aluminum nitride powder can be used, for example, as a filler.

[0028] The method for producing the surface-treated aluminum nitride powder of the present invention is not particularly limited, but a preferred method includes a step of dry-contacting aluminum nitride powder having an oxide layer formed on the particle surface to a thickness of about 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. The production method will be described in detail below.

[0029] [Raw aluminum nitride powder] The aluminum nitride powder used as a raw material for surface treatment can be any powder produced by a conventionally known method without any particular restrictions. In the present invention, aluminum nitride powder before surface treatment is referred to as "raw aluminum nitride powder." Methods for producing raw aluminum nitride powder include, for example, direct nitridation, reduction nitridation, and gas phase synthesis.

[0030] The shape of the primary particles of the raw material aluminum nitride powder is not particularly limited, and can be any shape, such as irregular, spherical, polyhedral, columnar, whisker-like, or tabular. For filler applications, spherical particles are preferred because they have good viscosity characteristics and high reproducibility of thermal conductivity. Furthermore, the smaller the aspect ratio of the aluminum nitride particles, the more preferable. The preferred aspect ratio is 1 to 3.

[0031] The particle size distribution of the raw aluminum nitride powder is not particularly limited, and may be appropriately determined taking into consideration the change in particle size due to the surface treatment of the target surface-treated aluminum nitride powder. For example, the cumulative volume 50% particle size D50 determined from the particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer using an aqueous solvent is preferably 0.3 to 40 μm. The D50 is preferably 0.7 μm or more and preferably 27 μm or less. The specific surface area of ​​the raw aluminum nitride powder measured by the BET method is preferably 0.1 to 6.0 m ２ The specific surface area is preferably 0.6 m ２ / g or more, preferably 5.5m ２ / g or less.

[0032] 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 the raw aluminum nitride powder. It may also contain boron nitride as an anti-agglomeration agent or an impurity derived from the manufacturing process, up to about 5 parts by mass. However, an amount of impurities that significantly reduces the crystallinity of aluminum nitride is not preferred because 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.

[0033] The raw aluminum nitride powder preferably has an oxide layer on the surface of the aluminum nitride particles. The oxide layer thickness is preferably 0.005% to 0.2% of the particle diameter. The oxide layer thickness is preferably at least about 0.05% of the particle diameter and preferably not more than about 1.5% of the particle diameter. This allows the silane compound, which is the surface treatment agent, to be present on the surface of the aluminum nitride particles in a range that satisfies the carbon content described above. The thickness of the oxide layer can be confirmed even after surface treatment, and its thickness remains almost unchanged from before treatment. If the oxide layer thickness 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 oxide layer thickness exceeds 0.2% of the particle diameter, there is a concern that thermal conductivity between aluminum nitride particles may be impaired.

[0034] The oxide layer may be formed by natural oxidation during storage of the raw aluminum nitride powder, or by an intentional oxidation treatment step. The oxidation treatment of the aluminum nitride powder may be carried out during the production process of the raw aluminum nitride powder, or may be carried out as a separate step after the raw aluminum nitride powder is produced. For example, raw aluminum nitride powder obtained by reduction-nitridation undergoes an oxidation treatment step during the production process in order to remove carbon used during the reaction, and therefore has an aluminum oxide layer on its surface. The aluminum nitride powder obtained by reduction-nitridation may be further subjected to an additional oxidation treatment step.

[0035] When the oxidation treatment step is added as a separate step, the preferred conditions are as follows: A 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 a temperature of 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. Examples of the oxygen-containing atmosphere that can be used include oxygen, air, water vapor, and carbon dioxide. However, in terms of the objectives of the present invention, treatment in air, particularly under atmospheric pressure, is preferred.

[0036] [Surface Treatment of Raw Aluminum Nitride Powder] In the method for producing the surface-treated aluminum nitride powder, the surface treatment is carried out, for example, by a method including a step of dry-contacting the raw 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, and then heating the resulting mixture at a temperature of 60 to 80°C under reduced pressure.

[0037] In the reaction between the raw aluminum nitride powder and the silane compound serving as the surface treatment agent, it is not necessary for all of the reactive groups of the silane compound, such as alkoxy groups, to react with the aluminum nitride; some may be free. However, if there is an excess of free silane compound, the silane compound may become a thermal resistance, resulting in a decrease in thermal conductivity.

[0038] Therefore, it is advisable to adjust the amount of the silane compound depending on the amount of hydroxyl groups on the surface of the aluminum nitride to be reacted. Specifically, a preferred adjustment method is to limit the amount of the silane compound used. The amount of the silane compound used is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 1.0 part by mass, per 100 parts by mass of the raw aluminum nitride powder. Furthermore, after the surface treatment, a step of removing free treating agent by performing a reduced pressure / heat treatment may be carried out.

[0039] In the above-mentioned manufacturing method, the method of contacting the aluminum nitride powder with the silane compound serving as the surface treatment agent includes a dry surface treatment method and a wet surface treatment method. Dry surface treatment is a method in which a solvent is not 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 step is required. It is important that no solvent remains in the heating step under reduced pressure after the contact step. However, since heating is required to remove the solvent, there is a high risk of polymerization of unsaturated bonds. Therefore, the dry surface treatment method is more desirable because it is less likely to cause polymerization of unsaturated bonds.

[0040] Dry mixing methods for dry surface treatment include, for example, gasifying the surface treatment agent and mixing it with the powder, spraying or dripping the liquid surface treatment agent and mixing it with the powder, and 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 is applicable when surface treatment is performed 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 uniformly dispersing a small amount of surface treatment agent throughout the powder. In this case, if a large amount of organic solvent is used for dilution, the liquid content of the entire powder will increase, causing aggregation. Therefore, it is desirable to determine the amount of organic solvent used to dilute the surface treatment agent to an upper limit of about 50 times by weight.

[0041] As a dry mixer, a general mixer / stirrer can be used, including, 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 desirable for the dry mixer to have a heating function. Furthermore, because powders tend to agglomerate during dry mixing, it is desirable for the mixer to be equipped with a mechanism to break up agglomerations once they have formed, such as a crushing blade or chopper. Furthermore, during the mixing operation, not only do powders simply adhere to each other, but depending on the mixing mechanism, they may be pressed against the walls of the mixing vessel, forming a thick adhesion layer, which makes it impossible to maintain the powder mixture. Therefore, it is even better to equip the walls of the mixing vessel with anti-adhesion measures such as a fluororesin coating, a mechanism to remove adhering powder such as a knocker, or a scraping mechanism with a modified stirring blade.

[0042] In the method for producing the surface-treated aluminum nitride powder, the step of heating under reduced pressure after dry contact at a temperature of less than 60°C is a step of heating for about 2 to 24 hours under reduced pressure at about 60 to 80°C. 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 of adjusting the amount of the silane compound in the aluminum nitride powder after the contact can also be performed.

[0043] In the heating step, excess surface treatment agent is removed by heating under reduced pressure, which prevents the presence of excess free surface treatment agent that is not fixed to the aluminum nitride powder and the agglomeration of the aluminum nitride powder due to the series of surface treatment operations. The pressure during reduced pressure is preferably 10 hPa or less.

[0044] The ratio of aluminum nitride constituting the surface-treated aluminum nitride powder to the silane compound serving 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 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 raw aluminum nitride powder. By using an amount of silane compound that is less than the upper limit, aggregation of the surface-treated aluminum nitride powder is prevented, the particle size distribution of the raw powder can be maintained, and the fillability into resin can be improved. On the other hand, if the amount of silane compound used is excessive, a large number of aggregated particles are generated, which makes it difficult to increase the fill rate, making it difficult to increase the thermal conductivity of the resin material.

[0045] [Treatment after Surface Treatment] The surface-treated aluminum nitride powder obtained by the surface treatment may undergo aggregation, which may impair the powder properties and fillability into resin. In such cases, it is preferable to remove coarse particles by crushing or classification.

[0046] The treatment is preferably carried out so that the cumulative volume 90% particle diameter D90 of the surface-treated aluminum nitride powder obtained is 100 μm or less.

[0047] Dry crushing is preferred as the crushing method. Furthermore, a relatively mild method is desirable so as not to crush most of the formed agglomerates. In particular, if crushing is performed so strongly that even primary particles are crushed, the effects of the present invention will be lost. Examples of crushing devices include dry crushing devices such as a stone mill, a grinding machine, a cutter mill, a hammer mill, and a pin mill. Among these, a stone mill is preferred because it can selectively crush large agglomerates in a short time and causes little uneven crushing. The atmosphere for the crushing treatment is preferably air or an inert gas. It is also preferable that the humidity of the atmosphere is not too high, specifically, preferably less than 70%, more preferably less than 55%. A classification treatment may also be performed as a method for removing coarse agglomerates other than the crushing treatment. For the classification treatment, either dry classification or wet classification can be selected. However, if high accuracy is not required, dry classification is preferred because it eliminates the need for solvent removal. Dry classification methods such as air classification and vibrating sieves can be used.

[0048] The method and device for air classification may be selected appropriately to obtain a particle size distribution suitable for use as a filler for a resin composition. Air classification is a method in which powder is dispersed in an air current and fine powder and coarse powder are separated using the gravity, inertial force, or centrifugal force of the particles. A classification device that utilizes inertial force and centrifugal force, in particular, can achieve a precision suitable for classifying particles of a few micrometers in size.

[0049] Methods that utilize inertial force include, for example, impactor types that use guide vanes or the like inside the device to create a swirling air flow, which separates fine and coarse powders when the powder is bent into a curve by the momentum of the airflow, semi-free vortex centrifugal types that apply centrifugal force to particles to classify them, and Coanda types that utilize the Coanda effect. Examples of classifiers that utilize inertial force include cascade impactors, viable impactors, aero fine classifiers, eddy classifiers, elbow jets, and hyperplexes.

[0050] The centrifugal force method separates fine and coarse particles using a vortex airflow, and examples of such devices include free vortex and forced vortex. Examples of free vortex devices include cyclones without guide blades, multi-stage cyclones, turboplexes that use secondary air to promote disaggregation, dispersion separators equipped with guide blades to improve classification accuracy, microspins, and microcuts. Forced vortex devices apply centrifugal force to particles using a rotating body inside the device, and further improve classification accuracy by creating a separate airflow inside the device, such as turboclassifiers and Donaserec. The above-mentioned disintegration and classification processes may be used in combination.

[0051] [Resin Composition] 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 heat, thereby providing a long usable time when used to form a resin composition.

[0052] The epoxy resin is not particularly limited, and a general epoxy resin can be used. Examples of the epoxy resin include polyfunctional epoxy resins such as bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins, biphenyl epoxy resins, naphthalene ring-containing epoxy resins, and cyclopentadiene-containing epoxy resins. Among these, bisphenol A epoxy resins, bisphenol F epoxy resins, and biphenyl epoxy resins are preferred.

[0053] As a curing agent for curing the epoxy resin, a common curing agent for epoxy resins can be used. Examples of the curing agent include thermosetting curing agents and photocuring agents. Examples of thermosetting curing agents include amines, polyamides, imidazoles, acid anhydrides, boron trifluoride-amine complexes, dicyandiamide, organic acid hydrazides, phenol novolac resins, bisphenol novolac resins, and cresol novolac resins. Examples of photocuring agents include diphenyliodonium hexafluorophosphate and triphenylsulfonium hexafluorophosphate. Among these, amines, imidazoles, and acid anhydrides are preferred.

[0054] Examples of the amine curing agent include chain aliphatic amines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenediamine, and diethylaminopropylamine; cyclic aliphatic polyamines such as N-aminoethylpiperazine and isophoronediamine; aliphatic aromatic amines such as m-xylenediamine; and aromatic amines such as metaphenylenediamine, diaminodiphenylmethane, and diaminodiphenylsulfone.

[0055] Imidazole curing agents include, for example, 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole trimellitate, and epoxy imidazole adducts.

[0056] Examples of acid anhydride curing agents include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bistrimellitate, maleic anhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalic anhydride, methyl endomethylene tetrahydrophthalic anhydride, methylbutenyl tetrahydrophthalic anhydride, dodecenyl succinic anhydride, hexahydrophthalic anhydride, succinic anhydride, methylcyclohexene dicarboxylic anhydride, alkylstyrene-maleic anhydride copolymer, chlorendic anhydride, and polyazelaic anhydride.

[0057] In addition to the epoxy resin and curing agent, a curing accelerator may be added as needed to effect curing. Examples of the curing accelerator include imidazole-based curing accelerators such as imidazole and 2-methylimidazole, phosphine derivatives such as triphenylphosphine, tris-p-methoxyphenylphosphine, and tricyclohexylphosphine, and cycloamidine derivatives such as 1,8-diazabicyclo[5.4.0]undec-7-ene.

[0058] Furthermore, a reactive diluent having an epoxy group may be further blended into the mixture of the epoxy resin, curing agent, and curing accelerator. Common reactive diluents can also be used. Examples of reactive diluents that can be used include n-butyl glycidyl ether, allyl glycidyl ether, styrene oxide, phenyl glycidyl ether, glycidyl methacrylate, p-sec-butylphenyl glycidyl ether, diglycidyl ether, (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, butanediol diglycidyl ether, diglycidyl aniline, and glycerin triglycidyl ether.

[0059] In the resin composition, the filler consisting of the surface-treated aluminum nitride powder can be used in a ratio of 25 to 1600 parts by mass, preferably 25 to 1500 parts by mass, per 100 parts by mass of resin. In particular, when using a surface-treated aluminum nitride powder having a particle size distribution with a D50 of 0.5 to 40 μm, it is preferable to use 25 to 640 parts by mass of the surface-treated aluminum nitride powder and combine it with other fillers other than the surface-treated aluminum nitride powder within the above-mentioned blending range to form the resin composition. The other fillers do not necessarily have to be thermally conductive fillers, but fillers that promote the hydrolysis of aluminum nitride or react with aluminum nitride to produce different compounds should be avoided. Furthermore, organic solvents may be used as long as they are removed during the process of producing the final resin molded product.

[0060] 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.

[0061] Examples of the other fillers include alumina, boron nitride, ZnO, MgO, carbon fiber, and diamond particles, as well as composite oxides such as silica, quartz, talc, mica, silica-titania, silica-zirconia, silica-barium oxide, silica-alumina, silica-calcia, silica-strontium oxide, and silica-magnesia, and silicates such as zeolite and montmorillonite.

[0062] The resin composition may contain known additives in addition to the filler, such as epoxy group-containing silanes such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; methacryl group-containing silanes such as 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-acryloxypropyltrimethoxysilane, 8-methacryloxyoctyltrimethoxysilane, 8-methacryloxyoctyltriethoxysilane, 8-methacryloxyoctylmethyldimethoxysilane, 8-methacryloxyoctylmethyldiethoxysilane, and 8-acryloxyoctyltrimethoxysilane; amino group-containing silanes such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 2-aminoethyl-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, 2-aminoethyl-3-aminopropylmethyldimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane; Alkylsilanes such as methyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, cyclohexyltrimethoxysilane, cyclohexylmethyldimethoxysilane, n-octyltriethoxysilane, n-decyltriethoxysilane, n-hexadecyltriethoxysilane, and n-octadecyltriethoxysilane; fluorinated alkylsilanes such as trifluoropropyltrimethoxysilane and trifluoropropylmethyldimethoxysilane;Examples of the additive include aromatic group-containing silanes such as phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, and diphenyldiethoxysilane; mercapto group-containing silanes such as 3-mercaptopropyltrimethoxysilane and 3-mercaptopropylmethyldimethoxysilane; vinyl-containing silanes such as vinyltrimethoxysilane and vinyltriethoxysilane; p-styryltrimethoxysilane, allyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-isocyanatopropyltriethoxysilane, and 3-ureidopropyltriethoxysilane. Additives such as silane compounds are preferably blended in an amount of 0.01 to 5 parts by mass per 100 parts by mass of the resin.

[0063] Furthermore, resin compositions containing the surface-treated aluminum nitride powder as a filler can improve the fillability and operability of the filler in epoxy resins because the surface-treated aluminum nitride powder particles have good affinity with resins. In particular, fillers that have low affinity with epoxy resins due to surface treatments that impart hydrophobicity to the aluminum nitride powder can easily penetrate water if voids are generated during curing. However, the generation of such voids is suppressed, thereby suppressing hydrolysis of the filler. Furthermore, the presence of such voids can effectively prevent a decrease in thermal conductivity.

[0064] Resin compositions containing the surface-treated aluminum nitride powder as a filler and their cured products can be used appropriately in applications requiring thermal conductivity. The resin compositions and their cured products can be used, for example, as materials for heat dissipation components for efficiently dissipating heat generated by semiconductor components installed in home appliances, automobiles, notebook personal computers, etc. Examples of heat dissipation components include heat dissipation greases, heat dissipation gels, heat dissipation sheets, phase change sheets, and adhesives. The resin compositions and their cured products can also be used, for example, as insulating layers, semiconductor encapsulants, underfills, housings, and heat dissipation fins used in metal-based substrates, printed circuit boards, and flexible substrates.

[0065] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these.

[0066] The raw materials used and the conditions for measuring the physical properties are described below.

[0067] [Raw aluminum nitride powder] A1: Aluminum nitride powder produced by reduction nitridation method, D50 = 1.20 μm, specific surface area 2.60 m ２ / g, carbon content 0.040 wt%. A2: Aluminum nitride powder produced by reduction nitridation. D50 = 0.79 μm, specific surface area 2.80 m ２ / g, carbon content 0.040 wt%. A3: Aluminum nitride powder produced by reduction nitridation. D50 = 4.95 μm, specific surface area 0.80 m ２ / g, carbon content 0.070 wt%. A4: Sintered particles of aluminum nitride powder. D50 = 35.0 μm, specific surface area 0.02 m ２ / g, carbon content 0.004 wt%.

[0068] The raw material aluminum nitride powders A1 to A4 were surface-treated using the silane compounds under the surface treatment conditions described below to produce surface-treated aluminum nitride powders.

[0069] [Aluminum oxide powder] B1: Aluminum oxide powder. CB-A20S (average particle size 22.7 μm) manufactured by Resonac. The aluminum oxide powder was used in combination with surface-treated aluminum nitride powder. The aluminum oxide powder was used without surface treatment.

[0070] [Silane compounds] MPES: 3-methacryloxypropyltriethoxysilane (Shin-Etsu Chemical Co., Ltd., >98%) MPMS: 3-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., >98%) MOMS: 8-methacryloxyoctyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., >99%) VMS: vinyltrimethoxysilane (Tokyo Chemical Industry Co., Ltd., >98%) GPES: 3-glycidoxypropyltriethoxysilane (Shin-Etsu Chemical Co., Ltd., >98%) GPMS: 3-glycidoxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., >98%) GOMS: 8-glycidoxyoctyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., >99%)

[0071] [Epoxy resin] Epoxy resin jER828 (manufactured by Mitsubishi Chemical) [Curing agent] Amine curing agent jER CureW (manufactured by Mitsubishi Chemical)

[0072] [Specific surface area] The specific surface areas of the raw aluminum nitride powder and the surface-treated aluminum nitride powder were determined by the BET method (nitrogen adsorption single-point method) using a specific surface area measuring device (Shimadzu Corporation: Flowsorb 3-2305). For the measurement, 2 g of the raw aluminum nitride powder or the surface-treated aluminum nitride powder was used, which had been previously dried at 100°C for 1 hour in a nitrogen gas flow.

[0073] [Particle size distribution] Water was used as the solvent for measuring the particle size distribution of raw aluminum nitride powder. Ethanol was used as the solvent for measuring the particle size distribution of surface-treated aluminum nitride powder. Raw aluminum nitride powder or surface-treated aluminum nitride powder was dispersed in a solvent at a concentration of 0.2 mass%, and the liquid was irradiated with ultrasonic waves at about 200 W for 3 minutes. The particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer. In the volume frequency distribution of particle sizes, the volume frequencies were accumulated from the smallest particle size, and the particle size value at which the cumulative value reached 50% was defined as D50, and the particle size value at which the cumulative value reached 90% was defined as D90. In the present invention, the D50 value is defined as the average particle size.

[0074] [Carbon Content and Silane Compound (Surface Treatment Agent) Density] The carbon content was measured using a carbon analyzer (EMIA-810W manufactured by Horiba, Ltd.). The surface-treated aluminum nitride powder or a portion of the raw aluminum nitride powder used as a sample was burned in an oxygen stream at 1350°C until no carbon dioxide gas was generated. The carbon content was calculated from the amount of carbon dioxide generated within 1 m of the surface of the powder. ２ The carbon content per unit area was determined. Specifically, the carbon content was calculated by first dividing the weight of carbon in the carbon dioxide gas by the weight of the sample to determine the carbon content in the sample, and then dividing this content by the specific surface area. The silane compound density was calculated from the carbon content in the surface-treated aluminum nitride powder after washing and information on the silane compound used. Note that, to calculate the silane compound density, the carbon content in the surface-treated aluminum nitride powder was calculated by subtracting the carbon content in the raw aluminum nitride powder from the carbon content in the surface-treated aluminum nitride powder, and dividing the result by the specific surface area of ​​the surface-treated aluminum nitride powder.

[0075] [Ratio of Unsaturated Bonds] A solution of surface-treated aluminum nitride powder dispersed in an organic solvent was added with a known concentration of iodine chloride to iodize the unsaturated bonds, and then an excess amount of potassium iodide was added to liberate unreacted iodine. The solution was colored with a starch reagent and titrated with an aqueous sodium thiosulfate solution until the color disappeared (Wijs method). The amount of unsaturated bonds was calculated from the titration results and divided by the carbon content of the surface-treated aluminum nitride powder used to determine the ratio of unsaturated bonds per gram of carbon present on the surface of the surface-treated aluminum nitride powder. Note that the carbon content of the surface-treated aluminum nitride powder was calculated by subtracting the carbon content of the raw aluminum nitride powder from the carbon content of the surface-treated aluminum nitride powder, and then dividing the result by the specific surface area of ​​the surface-treated aluminum nitride powder.

[0076] Examples 1 to 7 (Surface-treated aluminum nitride powder) A silane compound shown in Table 1 was added to a fluororesin flask in the amount (parts by mass) shown in Table 1 relative to 100 parts by mass of raw material aluminum nitride powder shown in Table 1, and the mixture was stirred for 30 minutes with a fluororesin stirring blade while maintaining the temperature at 25°C to 50°C or lower. The mixture was then vacuum heated at 80°C for 180 minutes to obtain surface-treated aluminum nitride powders A'1 to A'7. The heating temperature was controlled so as not to exceed 80°C throughout the entire process.

[0077] The surface of the obtained surface-treated aluminum nitride powder was ２ The carbon content per gram, the proportion of unsaturated bonds per gram of carbon present on the surface of the aluminum nitride powder, and other physical properties were measured. The measurement results are shown in Table 1.

[0078] Example 9 (Resin composition) 0.47 g of the surface-treated aluminum nitride powder A'1 obtained by the above method, 1.33 g of aluminum oxide powder CB-A20S, 0.12 g of epoxy resin jER828, and 0.03 g of curing agent Cure W were weighed out and kneaded in a mortar for 15 minutes to obtain a resin composition. The filling rate of the surface-treated aluminum nitride powder in the resin composition was 80%.

[0079] Examples 8, 10 to 17 Resin compositions were obtained in the same manner as in Example 9, except that the type of surface-treated aluminum nitride powder was changed as shown in Table 2, and the amounts of the surface-treated aluminum nitride powder and aluminum oxide powder mixed were changed so that the filling rate was the value shown in Table 2. The mass ratio of the amount of the surface-treated aluminum nitride powder mixed to the amount of the aluminum oxide powder mixed was the same as in Example 9.

[0080] [Kneadability] In the kneading operation, the kneadability was evaluated using the following indexes, and the results are shown in Table 2. Kneadability index Determined according to the following criteria: AA: Liquid paste BB: Solid paste that does not crack when bent CC: Solid paste that cracks when bent DD: Does not become a paste

[0081] [Usable time] The usable time was defined as follows, and the results are shown in Table 2. Usable time: The time until the paste formed in the kneadability index hardens and loses its formability. Alternatively, the time until the paste that has changed to the CC state due to changes over time disintegrates and cannot be re-formed into a paste. In other words, the time until the paste reaches the DD state.

[0082] (Cured Product) The resulting resin composition was heat-pressed at 150° C. and 20 MPa for 1 hour, and then further heated at 180° C. for 1 hour to obtain a cured product having a diameter of 10 mm and a thickness of 1.2 mm.

[0083] [Thermal Conductivity of Cured Product] The thermal diffusivity of the cured product prepared by the above method was measured by a laser flash method (using Kyoto Electronics LFA-502), and the thermal conductivity was calculated by multiplying the measured value by the specific heat and density of the resin composition. The results are shown in Table 2.

[0084] [Theoretical Density Ratio of Cured Body] The density of the cured body prepared by the above method was measured by the Archimedes method (using a Metler Toledo XS204V). Next, the theoretical density of the resin composition was determined from the density and filling rate of the filler and resin, and the theoretical density ratio of the cured body was calculated. The results are shown in Table 2. The theoretical density ratio of the cured body is a value calculated by (density of cured body / theoretical density of resin composition) x 100 (%), and it can be said that the closer to 100%, the fewer voids there are.

[0085] Comparative Examples 1 to 3 and 5 to 9 Surface-treated aluminum nitride powders A'8 to A'10 and resin compositions were obtained in the same manner as in Examples 1 and 9, except that the type and amount of silane compound were changed to those shown in Table 1, and evaluations were carried out in the same manner as in Examples 1 and 9. The results are shown in Table 2. In Comparative Examples 1 to 3, the proportion of unsaturated bonds was not measured because the silane compound did not have an unsaturated bond.

[0086] Comparative Examples 4 and 10 Surface-treated aluminum nitride powder A'11 and a resin composition were obtained in the same manner as in Examples 1 and 9, except that the surface treatment temperature (temperature during vacuum heating) was 90°C, and evaluations were carried out in the same manner as in Examples 1 and 9. The results are shown in Table 2.

[0087]

[0088]

Claims

1. An aluminum nitride powder having a silane compound having a polymerizable unsaturated bond in the molecule present on the particle surface, ２ The carbon content per －３ g / m ２ That's 1.6 x 10 －３ g / m ２ 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 2.5×10 ２１ pieces / g or more 5.5×10 ２１ The surface-treated aluminum nitride powder has a particle size distribution of 1 / g or less.

2. The surface-treated aluminum nitride powder according to claim 1, having a cumulative volume 50% particle size D50 of 0.3 μm to 40 μm.

3. A filler comprising the surface-treated aluminum nitride powder according to claim 1 or 2.

4. A resin composition containing an epoxy resin and the filler according to claim 3, the resin composition containing 5 mass % or more of the filler.

5. A cured product of the resin composition according to claim 4.

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