JP7046689B2 - Thermally conductive composite particles and resin composition containing them - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act October 17, 2017 Announced at the client conference poster session sponsored by KRI Co., Ltd.

In the present invention, a composite particle composed of two phases in which fine particles having high thermal conductivity are immobilized on the surface of a base fine particle made of an organic resin having small morphological anisotropy to form a layer, a method for producing the same, and a resin composition containing the same. It is about objects and their molded products.

Resin materials are used in various fields from their good shapeability to structural material applications to applications that require packaging and design. However, if the required performance cannot be satisfied only by the mechanical properties and thermal properties of the polymer material as a molding material, a resin composition mixed with a reinforcing material (filler) to compensate for the insufficient performance is available. You will need it. In particular, organic polymer materials have inherently poor thermal conductivity, so measures are required for long-term use in high-temperature environments. While engineering plastics and super engineering plastics with higher melting points are one of the answers for that purpose, it is known that the heat deformability is improved by blending a reinforcing filler and the heat capacity of the resin composition as a whole is lowered by blending a highly thermally conductive filler. It is a measure of.

Thermally conductive fillers mixed with resin materials include metals that also have conductivity, metal oxides and carbon-based materials, some metal oxides that have insulating properties, silicon nitride, boron nitride, and high crystallization. There are some organic substances with a degree. These materials are larger or smaller and contain morphological anisotropy in their basic molecular structure, and the size of the raw materials handled industrially has a clear aspect ratio (ratio of major axis to minor axis of fine particles). Often has a non-spherical morphology.

In such a thermally conductive filler having a non-spherical morphological anisotropy, the dispersed state in the resin composition is liable to be changed by an external factor, and in particular, the resin composition is molded by injection molding, injection molding or the like. At that time, as the resin component (matrix) flows, it is oriented along the flow direction. It is well known that this gives direction to the thermal conductivity of the molded product of the resin composition mixed with the thermally conductive filler, and the thermal conduction path formed by the contact between the thermally conductive fillers has this orientation. It is understood that it is less likely to be formed by. The biggest problem with this is that in the parts where the resin composition molded product mixed with the heat conductive filler is incorporated or in the usage environment, the direction in which the heat conductivity is most required is often the orientation direction of the heat conductive filler. It is oriented vertically and is likely to cut the heat transfer path due to flow orientation.

The most common measure to solve such a problem is to increase the blending amount of the heat conductive filler and increase the probability that the heat conductive fillers are in direct contact with each other in the resin matrix. However, in order to obtain the expected effect, the amount of the heat conductive filler compounded must be at least 30 to 40 vol% or more, and the material physical characteristics of the resin composition mixed with the heat conductive filler are the same as the original performance of the resin matrix. Will be very different. In particular, it is known that the mechanical properties and impact resistance are significantly reduced, which also affects the shapeability.

Therefore, as a concept for increasing the contact frequency between the fillers without increasing the blending amount of the thermally conductive filler, the ready-made thermally conductive fillers having different particle sizes are mixed to change the particle size distribution (Patent Document 1). , Increases the wettability between the heat conductive filler and the resin matrix component and lowers the heat resistance between them (Patent Document 2), breaks the aggregated structure of the heat conductive filler, and modifies the dispersed state in the resin composition (Patent). Improvements have been studied in terms of filler type and structure, such as document 3) and forming a network structure in a resin composition using a mixture of a fibrous filler and a lumpy filler having thermal conductivity (Patent Document 4). ..

On the other hand, instead of preparing the heat conductive filler from a single material, the morphological anisotropy of the inorganic filler composite (Patent Document 5) in which different inorganic compounds are attached to the surface of the heat conductive filler or the heat conductive filler itself. Approaches such as a method for reducing the amount of heat (Patent Document 6) have also been proposed.

In the above-mentioned numerous improvement studies, the reproducibility of the heat conduction path in the resin composition after molding, particularly the heat conduction path in the direction perpendicular to the flow direction is poor, and the amount of the heat conductive filler compounded cannot always be reduced, which is good. The current situation is that it is not difficult to say that it is a countermeasure. Furthermore, with the development of the field of power electronics, the temperature of the heat source that the molded product of the heat conductive resin composition comes into contact with is also rising, and it is becoming an environment where it is required to secure a more reliable heat conduction path and to exhibit high heat dissipation characteristics. rice field.

Japanese Unexamined Patent Publication No. 2017-14445 Japanese Unexamined Patent Publication No. 2015-108058 Japanese Unexamined Patent Publication No. 2012-255055 Japanese Unexamined Patent Publication No. 2018-21156 International release WO2013 / 039103 Japanese Unexamined Patent Publication No. 2016-216318

It is an object of the present invention to provide composite particles as a heat conductive filler that is effective for exhibiting high heat conductivity in a direction perpendicular to the flow direction of the resin matrix component at the time of molding when the resin composition is molded. do.

As a result of diligent studies to achieve the above object, the inventors of the present application have completed the invention shown below.

[1] Thermally conductive composite particles in which fine particles B having thermal conductivity are immobilized on the surface of the base fine particles A, wherein the base fine particles A are organic resins and the fine particles B are cellulose nanofibers and carbon. A thermally conductive composite particle selected from the group consisting of fibers, aluminum oxide, aluminum nitride, boron nitride, zinc oxide, magnesium oxide, beryllium oxide, diamond and various metal powders.
[2] The particle size DA of the base fine particles _A is in the range of 0.1 μm to 1000 μm, the aspect ratio (ratio of the major axis to the minor axis of the fine particles) is 2 or less, and the particle size DB of the fine particles _B is The composite particle according to the above [1], which is in the range of 0.01 μm to 500 μm and is selected so that _DA > _DB in forming the composite particle.
[3] The number of fine particles B immobilized on the surface of the base fine particles A is more than the number of fine particles B that can cover the surface area of the fine particles A by the projected area of the fine particles B, and the fine particles B are substantially continuous. The thermally conductive composite particle according to the above [1] or [2], which forms a layer of fine particles B by being present.
[4] The above-mentioned [1] to [3], wherein a silane coupling agent or an organic resin is used to immobilize the fine particles B on the surface of the fine particles A in forming the composite particles. Composite particles.
[5] Thermally conductive composite particles according to any one of the above [1] to [4], wherein the composite material is produced by an electrospray deposition method or a spray drying method.
[6] A resin composition obtained by mixing the composite particles according to any one of [1] to [5] with a thermoplastic resin or a curable resin, and a molded product thereof.

As the resin parts installed in a portion close to the heat source, a molded product of a resin composition containing a heat conductive filler is often used. The thermal conductivity of such a resin composition is primarily controlled by the amount of the filler blended, but since these parts are produced by a molding method involving the flow of a material such as injection molding or injection molding, the resin matrix is contained. It is affected by the arrangement and arrangement of fillers, and is particularly dominated by the orientation toward the surface of the molded product due to the flow orientation. That is, in the molded product of the resin composition containing the filler having a large shape anisotropy represented by the aspect ratio (ratio of the major axis to the minor axis of the filler), the thermal conductivity in the thickness direction of the molded product becomes poor. This is because the fillers cannot come into contact with each other due to the flow orientation, and it is difficult to form a so-called heat conduction path.

The composite particles of the present invention are obtained by combining a base particle having a small morphological anisotropy with a heat conductive filler, and a certain amount of the powder of the heat conductive filler is immobilized on the surface of the former to form a layer. It is characterized by constructing a heat conduction path. By selecting the base particle size to be larger than the heat conductive filler size, a long-distance heat conduction path is formed beyond the original size of the heat conductive filler. Since the base particles are not easily affected by the flow orientation in this path, it is expected that high thermal conductivity will be exhibited after molding in a manner that depends on the amount of the composite particles blended in the resin composition.

Further, the base particles constituting the composite particles of the present invention are made of an organic resin, and the organic constituting the resin composition (mixture of the organic resin matrix component and the composite particles), which is the most common form using the composite particles. A major feature is that the component / inorganic component ratio can be enriched with organic components. In the conventional resin composition composed of the heat conductive filler and the organic resin matrix, a large amount of the heat conductive filler is required for the above-mentioned heat conduction path formation, and the organic component / inorganic component ratio constituting the resin composition is required. Becomes rich in inorganic components. In such a composition, the organic component is no longer a matrix, but a binder for thermally conductive fillers. As a result, the resin composition becomes hard and brittle, and does not exhibit the properties expected of the resin in terms of mechanical properties. On the other hand, in the resin composition using the composite particles of the present invention, since the heat conductive path is constructed with substantially only a small amount of the heat conductive filler, the above-mentioned problems in terms of mechanical characteristics do not occur.

The structural schematic diagram of the composite particle of this invention. An example of SEM observation of composite particles by the electrospray deposition method.

An embodiment of the present invention will be described in detail as follows.

(Composite particles)
The heat conductive composite particles of the present invention are composite particles composed of fine particles A of an organic resin having a small base and small morphological anisotropy and a plurality of fine particles B immobilized on the surface thereof, and are subject to the conditions described later. It is a synthetic product made to meet. The high thermal conductivity of the composite particles of the present invention depends on the thermal conductivity characteristics of the fine particles B described later, and it is preferable that the fine particles A function as a base for defining the aggregated state of the fine particles B. However, it does not matter if the fine particles A are a material having thermal conductivity as a result.

The base fine particles A are preferably powders made of an organic resin, aggregates thereof, or beads. The primary particles are considered to be unit particles judging from their apparent geometrical morphology, and the secondary particles formed by aggregating a plurality of these primary particles are regarded as aggregates. The beads or powder are referred to as a form of some solid-state chemical products, and are generally particles having a size of about several μm to several mm. In the present invention, it may be an off-the-shelf product or a granulated product in the manufacturing process of composite particles described later.

The base fine particles A in the present invention preferably have a particle size _DA in the range of 0.1 μm to 1000 μm regardless of their chemical composition. More preferably, it is preferably in the range of 0.1 μm to 500 μm. More preferably, it is in the range of 0.1 μm to 100 μm.

The larger the _DA mentioned above, the larger the surface area of the fine particles A as the base for immobilizing the fine particles B, and the larger the number of the fine particles B that can be fixed to the surface of A when forming the composite particles. Become. Further, it is highly possible that the fine particles B are continuously present on the surface of the base over a long distance, which is suitable for the purpose of enhancing the heat conduction characteristics described later. On the other hand, the larger the _DA , the higher the difficulty in forming the composite particles. That is, when the composite particles are prepared by using the electrospray deposition method or the spray drying method described later, both A and B fine particles need to be supplied to the granulation site in a liquid phase. Maintaining the uniformity of the liquid phase at the time becomes difficult depending on the size of _DA . Further, the fraction of the component A in the obtained resin composition containing the composite particles tends to increase. This may reduce the mechanical properties of the resin composition and is not preferable.

It is desirable that the shape of the fine particles A is as spherical as possible. Specifically, it is desirable that the aspect ratio represented by the ratio of the major axis to the minor axis on the outer shape of the fine particles A is 2 or less. When this value exceeds 2, the morphological anisotropy becomes large, and it becomes easy to be affected by the flow orientation during the molding process of the resin composition containing the composite particles based on the fine particles A, which will be described later, and the direction perpendicular to the flow direction. It is not preferable because high thermal conductivity cannot be obtained.

The organic resin constituting the fine particles A is not particularly limited, but needs to have the above-mentioned aspect ratio and particle size. Thermoplastic resins and various curable resins are applicable as organic resins , and the former includes nylon, polyphenylene sulfide, polyamide-imide, polyether sulphon, polylactic acid, polymethylmethacrylate, urethane, polyacrylonitrile, polystyrene, fluororesins, or these. A commercially available product made of the crosslinked product of the above is exemplified. In the latter case, there is an epoxy resin, a silicone resin, or a curable resin based on an arbitrary formulation, and a rubber-like adhesive having a low elastic modulus or a tacky adhesive may be used . These fine particles may be solid or hollow.

The organic material of the fine particles A may be a polymer alloy, a polymer blend, or a nanocomposite containing a nanofiller, if necessary. In particular, the latter is effective as a method for reducing the coefficient of thermal expansion of the composite particle itself of the present invention. Represented by nanosilica that disperses well with the above-mentioned thermoplastic resins and thermosetting resins, non-swellable layered silicates such as clay and talc, and swellable layered silicates such as synthetic fluorine mica and montmorillonite. A raw material that efficiently strengthens the resin matrix component with a small amount of compound is preferably used.

Although the fine particles B are thermally conductive substances, it is preferable that the fine particles B themselves have a thermal conductivity higher than 10 W / mK. In the case of 10 W / mK or less, the thermal conductivity of the resin composition using the composite particles of the present invention brings about a remarkable performance improvement as compared with the resin composition obtained by mixing only the fine particles B, for example. Since there is no such thing, it is industrially meaningless. Specific materials include one or more powders selected from cellulose nanofibers, carbon fibers, aluminum oxides, aluminum nitride, boron nitride, zinc oxide, magnesium oxide, beryllium oxide, diamonds and various metal powders. Is preferable.

The fine particles _B in the present invention preferably have a particle size DB in the range of 0.01 μm to 500 μm regardless of their chemical composition. More preferably, it is preferably in the range of 0.01 μm to 300 μm. The fine particles A and the fine particles B used in the present invention are selected so that the particle diameters of the fine particles A and the fine particles _B are _DA > DB when forming composite particles made of the fine particles A and the fine particles B. preferable. When _DA is _DB or less, the outer shape of the composite particle becomes irregular, and a desired heat conduction path cannot be formed inside the resin composition molded product obtained by molding with flow, so that the effect of the present invention can be obtained. I can't do it.

The number of fine particles B immobilized on the surface of the base fine particles A in the composite particles of the present invention needs to be present as long as the surface area of the fine particles A can be covered by the projected area of the fine particles B. It is desirable that a part of any two fine particles B adjacent to each other on the surface of A come into contact with each other to form a layer in which the fine particles B are continuously present. When the number of the fine particles B present on the surface of the base particles A does not satisfy the above conditions, the fine particles B cannot form a continuous layer and the heat conduction path of the present invention is not formed. On the other hand, when the number of fine particles B present on the surface of the base particles A is excessive, the outer shape of the composite particles becomes irregular, and a desired heat conduction path is formed inside the resin composition molded product obtained by molding with flow. Cannot be formed, and the effect of the present invention tends to be difficult to obtain.

In the composite particle of the present invention, the fine particles B are immobilized on the surface of the base particle A, but the immobilization itself is a van der Waals force, hydrogen bond or ionic bond which is reversible as an attractive interaction. It may be a covalent bond using a silane coupling agent or the like. However, the binding force of the fine particles B adsorbed on the surface of the base particle A due to the reversible attractive interaction is not large, and the force generated from the viscosity of the resin matrix of the resin composition during molding accompanied by flow causes the force from the surface of the base particle A. May be pulled apart. Therefore, in order to form a desirable heat conduction path in the resin composition after the molding step, it is desirable to use an organic polymer or a silane coupling agent for immobilization of the fine particles B. In the former case, the molecular weight and primary structure of the polymer, etc., and in the latter case, stronger immobilization is achieved by optimally selecting the silane coupling agent in consideration of the matrix type of the resin composition.

The production of such composite particles is not limited to a specific method, but the use of granulation methods such as an electrospray deposition method and a spray-drying method is exemplified. In the case of the electrospray deposition method, a raw material mixture in which the base fine particles A, the thermally conductive fine particles B and the material for immobilizing them are dissolved or dispersed is discharged under a high piezoelectric field, and the droplets are divided by an electric field. Composite particles can be obtained by simultaneously advancing the drying of the and the solvent. On the other hand, in the case of the spray-drying method, composite particles can be obtained by spraying the above-mentioned raw material mixture at high pressure in a high-temperature atmosphere to form droplets and at the same time promote solvent drying. In either case, the raw material mixed liquid may be supplied as a single liquid, or may be individually supplied for each raw material from a plurality of nozzles.

The composite particles of the present invention are finally mixed with a thermoplastic resin or a curable resin and provided as a resin composition, and are used in applications that require high thermal conductivity as a molded product thereof. The types of thermoplastic resins and curable resins are not limited, but are industrially commonly used polyamide resins, polycarbonate resins, polyacetal resins, polyethylenes (low density, high density), EVA resins, polypropylenes, polyvinyl chloride resins, etc. Polystyrene resin, AS resin, ABS resin, PET resin, PBT resin, modified PPE resin, methacrylic resin, polyphenylsulfone resin, polysulfone resin, polyallylate resin, polyetherimide resin, PEEK resin, PPS resin, polyethersulfone resin, Thermal curing of various thermoplastic resins such as liquid crystal polymer, polyvinylidene fluoride resin, PTFE resin, PCTFE resin and thermoplastic elastomer, epoxy resin, silicone resin, phenol resin, melamine resin, urea resin, unsaturated polyester resin and polyurethane resin. Examples include sex resins.

In preparing the resin composition containing the composite particles of the present invention, the resin type of the base particles A and the resin type of the resin matrix component may be the same or different, but the final molded product. There may be restrictions depending on the molding conditions when creating. That is, from the viewpoint of maintaining the morphology of the composite particles in the molding process, when heat melt molding such as injection molding is required, it is preferable that the melting point or softening point of the base particles is higher than the molding temperature. On the other hand, in the case of a molding process in which molding is performed at a relatively low temperature and then the molding process is maintained at a high temperature by a curing reaction, the restrictions applied may be negligible.

The composite particles of the present invention exhibit isotropic thermal conductivity in the molded product of the resin composition, so that the molded product of the resin composition containing the conventional heat conductive filler can be obtained in the thickness direction of the molded product (at the time of molding). It has high thermal conductivity performance compared to the fact that poor thermal conductivity was obtained in the direction perpendicular to the flow direction). Therefore, it can be suitably used as a sealing material for power semiconductors and an amount of various heat radiating materials.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples.

<Creation of base particles>
For the base particles, the same epoxy resin as the resin matrix of the resin composition described later is used, and a predetermined amount of epoxy resin (Epicoat 828 manufactured by Mitsubishi Chemical Co., Ltd.), epoxy resin curing agent (HN-2000 manufactured by Hitachi Kasei Co., Ltd.) and a curing catalyst are mixed. Then, an N-methylpyrrolidone (NMP) solution having a solid content concentration of 25 wt% was prepared, and granulated by the electrospray deposition (ESD) method.

ESD is a drying method that utilizes an electrospray phenomenon in which a mixed liquid of raw materials as described above is quantitatively discharged under a high-voltage field to continuously generate splits of charged droplets to form fine droplets, and as a result. Fine particles can be collected on the counter electrode that is electrically grounded. No special equipment is required to obtain the composite particles of the present invention. High-voltage power supply, micro-syringe pump that can quantitatively discharge the raw material mixture, syringe with a syringe nozzle with the tip cut off vertically, grounded metal plate (collector) and chamber for adjusting the test environment as needed. The device may be assembled by a known method.

The ESD conditions need to be adjusted according to the composition of the raw material mixture, but in the case of the above-mentioned liquid composition, the discharge rate is 0.01 ml / min, the applied voltage is 20 kV, the nozzle diameter is 21 G, the nozzle-collector distance is 14 cm, and 24. Stable granulation was possible at ° C./25 to 30% RH. The epoxy resin powder collected on the collector was collected using a spatula.

<Creation of composite particles>
To prepare the composite particles, the above-mentioned epoxy resin powder, boron nitride fine particles (PT140 manufactured by Momentive, particle diameter 8 to 4 μm) and polyvinyl alcohol (polymerization degree 2,000, saponification degree 78 to 82%, manufactured by Kanto Chemical Co., Inc.) Was used. Boron nitride powder 0.5 g was added to 5 g of polyvinyl alcohol prepared in advance as a 4 wt% aqueous solution, mixed using a homogenizer (combined with IKA Ultratax T10 and shaft generator S25N-8G), and then the base particles. A raw material mixture was prepared by adding 7.5 g of the epoxy resin powder to be used and mixing the powder. The prepared mixed solution was defoamed under reduced pressure as needed.

The raw material solution was granulated using the ESD method described above. The ESD conditions were a discharge rate of 0.01 ml / min, an applied voltage of 25 kV, a nozzle diameter of 21 G, a nozzle-collector distance of 12 cm, and stable granulation at 24 ° C./25 to 30% RH. The composite particles collected on the collector were collected using a spatula and then dried in a hot air dryer at 80 ° C. for 8 hours.

<Resin composition and molding>
In order to investigate the effect of the present invention, a resin composition containing the above-mentioned composite particles was prepared. Assuming use as a heat radiating material or encapsulant, weigh a predetermined amount of composite particles, and use epoxy resin (Epicoat 828 manufactured by Mitsubishi Chemical Co., Ltd.), epoxy resin curing agent (HN-2000 manufactured by Hitachi Kasei Co., Ltd.), and reactive dilution. The material (Denacol EX-141 manufactured by Nagase ChemteX Corporation) and a curing catalyst were mixed in a predetermined amount and mixed with a thermosetting resin, and injected into a plate-shaped mold made of PTFE. Then, after performing a curing treatment at 80 ° C. for 4 hours, a resin composition molded product having a thickness of 1 mm was obtained.

Further, assuming use as a thermosetting adhesive, a predetermined amount of composite particles using the above-mentioned epoxy resin powder as base particles are weighed, and an epoxy resin (Epicoat 828), an epoxy resin curing agent (HN-2000), and a reaction are used. A thermosetting adhesive containing a predetermined amount of a sex diluent (Denacol EX-141) and a curing catalyst is mixed and applied on a PTFE plate (plate thickness 2 mm) to a thickness of 500 μm (at the same time, made of PTFE with a thickness of 300 μm). The sheet was sandwiched as a spacer), and the same PTFE plate was layered on top of it. Then, a load was lightly applied until the thermosetting adhesive layer became equivalent to the spacer made of PTFE, and the state was maintained, and the curing treatment was performed at 120 ° C. for 1 hour. Finally, all the PTFE sheets and spacers were peeled off to obtain a cured thermosetting adhesive composition having a thickness of 330 μm.

(Performance evaluation)
<Evaluation of thermal characteristics>
In the thermal characteristics evaluation of the resin composition molded product containing the composite particles of the present invention, the heat transfer coefficient measurement by temperature wave thermal analysis (ai-phase mobile manufactured by i-phase mobile) was used. Since the heat conduction coefficient, which is generally used as a thermal property, can be converted into each other by multiplying the material property value (specific heat and density), if these are known, the two have a linear relationship.

<Evaluation of bending deformability>
In order to investigate the mechanical properties of the resin composition molded product containing the composite particles of the present invention, bending deformation is sequentially applied along stainless steel rods having diameters of 3 mm, 5 mm, 8 mm, 10 mm, 12 mm, 15 mm and 20 mm at room temperature. Then, the deformation followability was investigated.

[Example 1]
The heat transfer coefficient was measured for an epoxy resin composition molded product obtained by mixing 70 wt% of the prepared composite particles. The measurement was carried out at N = 10, and two kinds of values, an arithmetic mean and the maximum value of the measurement result, were obtained. The bending deformation evaluation was carried out at N = 3, and when fracture or crack occurred due to cracking, the conditions at that time were recorded.

[Example 2]
For the epoxy resin adhesive in which 70 wt% of the prepared composite particles were mixed, the heat transfer coefficient was measured after peeling off the PTFE sheet and spacer. The measurement was carried out at N = 10, and two kinds of values, an arithmetic mean and the maximum value of the measurement result, were obtained. The bending deformation evaluation was carried out at N = 3, and when fracture or crack occurred due to cracking, the conditions at that time were recorded.

[Comparative Example 1]
The heat transfer coefficient was measured for an epoxy resin composition molded product obtained by mixing only 70 wt% of boron nitride fine particles used as a raw material for composite particles. The measurement was carried out at N = 10, and two kinds of values, an arithmetic mean and the maximum value of the measurement result, were obtained. The bending deformation evaluation was carried out at N = 3, and when fracture or crack occurred due to cracking, the conditions at that time were recorded.

[Comparative Example 2]
The heat transfer coefficient was measured for the cured product of the epoxy resin adhesive in which only the boron nitride fine particles used as the raw material of the composite particles were mixed in an amount of 70 wt%. The measurement was carried out at N = 10, and two kinds of values, an arithmetic mean and the maximum value of the measurement result, were obtained. The bending deformation evaluation was carried out at N = 3, and when fracture or crack occurred due to cracking, the conditions at that time were recorded.

[Comparative Example 3]
The heat transfer coefficient was measured for the molded product obtained by curing only the epoxy resin. The measurement was carried out at N = 10, and two kinds of values, an arithmetic mean and the maximum value of the measurement result, were obtained. The bending deformation evaluation was carried out at N = 3, and when fracture or crack occurred due to cracking, the conditions at that time were recorded.

[Comparative Example 4]
The heat transfer coefficient was measured for the molded product obtained by curing only the epoxy resin adhesive. The measurement was carried out at N = 10, and two kinds of values, an arithmetic mean and the maximum value of the measurement result, were obtained. The bending deformation evaluation was carried out at N = 3, and when fracture or crack occurred due to cracking, the conditions at that time were recorded.

The composition and performance evaluation results of Examples 1 and 2 and Comparative Examples 1 and 4 are summarized in Table 1.

From Table 1, it was shown that in any of Examples 1 and 2, the heat transfer coefficient was significantly improved as compared with Comparative Examples 1 and 2, and high thermal conductivity was exhibited. In the case of Example 2, in which the relative distance between the composite particles is further shortened prior to curing, the maximum value of the heat transfer coefficient is close to the average value, and a stable heat conduction path is formed in the system. You can see that there is. On the other hand, in the case of Example 1, since the maximum value is larger and the average value is smaller than that of Example 2 having the same composition, it can be seen that there is unevenness in the formation of the heat conduction path depending on the location. It is considered that a higher heat transfer coefficient is stably expressed by increasing the amount of the composite particles blended. Further, it can be seen that since the substantially amount of the inorganic component contributing to heat conduction is smaller than the apparent amount of the composite particles, the followability to bending deformation is excellent and the embrittlement of the molded product is suppressed.

On the other hand, in Comparative Examples 3 and 4, the heat transfer coefficient was low due to the large morphological anisotropy of the boron nitride fine particles. Comparing Comparative Examples 3 and 4, the latter, which involves a compression operation, showed a slightly higher heat transfer coefficient, but injection molding was performed because it is sensitive to the influence of the flow associated with the compression operation of the epoxy resin before curing. The result was not much different from that of Comparative Example 3. Further, the epoxy resin of Comparative Example 3 has a small amount of the reactive diluent and a high viscosity. It can be seen that the composite particles are less affected by the orientation due to the flow than the boron nitride fine particles. Further, it can be seen that in Comparative Examples 3 and 4 in which a large amount of boron nitride fine particles are blended, the followability to bending deformation is lowered and the molded product is brittle.

By using the heat conductive resin composition using the composite particles of the present invention, it is possible to produce a resin molded product, an adhesive or the like having a high heat transfer ability. It is expected to be used as a sealing material for power semiconductors for automobiles and air conditioners, which is expected to be widely used in the future, as a heat radiating material, or as an adhesive with heat radiating fins.

Claims (1)

This is a method for producing thermally conductive composite particles in which the base fine particles A having thermal conductivity are immobilized on the surface of the base fine particles A of the organic resin. The base fine particles A and the boron nitride fine particles are dispersed and immobilized. A method for producing thermally conductive composite particles by discharging a mixed solution of raw materials in which a material is dissolved under a high piezoelectric field and simultaneously advancing the division of droplets by an electric field and the drying of a solvent.

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