Thermally conductive composite particles and manufacturing method thereof

Abstract

To provide thermally conductive composite particles and a method for producing the same, which can provide high thermal conductivity to a resin composition by coating boron nitride with silica to improve affinity with the resin and increase the amount of packing in the resin composition.SOLUTION: The thermally conductive composite particles according to the present invention are formed by coating the surface of boron nitride with silica, and the coating amount of silica is less than 0.5 mass% of a mass of the boron nitride. The thermally conductive composite particles can be produced by the mechanochemical treatment of boron nitride with one or more silica selected from precipitated silica, gelled silica, and dried silica by dry process.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to thermally conductive composite particles that can increase the loading amount in a resin composition by coating the surface of boron nitride with a predetermined amount of silica, thereby imparting high thermal conductivity to the resin composition, and a method for producing the same. [Background technology]

[0002] In recent years, as electric and electronic devices such as semiconductor devices and ICs become smaller and lighter, electronic components are being mounted at higher densities, which tends to increase the amount of heat generated by electronic components. If the generated heat accumulates in electronic components, it will have a negative effect on their durability, so there is a growing need for highly thermally conductive fillers that can efficiently release the generated heat from electronic components. Examples of high thermal conductive fillers include boron nitride, aluminum nitride, silicon carbide, alumina, magnesia, etc. Among these, boron nitride exhibits excellent properties such as high thermal conductivity, insulation, and low specific gravity, but has the problem that it has low affinity with resins and a low loading amount in resin compositions because there are no functional groups on the flat surfaces of the particles. Therefore, there is a demand for thermally conductive composite particles that can be made by combining boron nitride with other materials to improve the affinity with resins, increase the loading amount, and provide resin compositions with high thermal conductivity.

[0003] Conventionally, there have been proposals for thermally conductive composite particles in which boron nitride is combined with other materials. For example, there is a disclosure of thermally conductive composite particles (first filler) in which boron nitride is coated with silica (see Patent Document 1). There is also a disclosure of thermally conductive composite particles obtained by mixing a thermally conductive filler, which is a plate-like particle or a rod-like particle, with inorganic particles and subjecting the mixture to a mechanochemical treatment, and the plate-like particle and inorganic particle include boron nitride (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-2830 A [Patent Document 2] JP 2015-214639 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the thermally conductive composite particles in which boron nitride is coated with silica as disclosed in Patent Document 1 are coated with silica, which is resistant to hydrolysis, to improve moisture resistance, since the boron nitride filled in the resin composition may hydrolyze and corrode electronic components, substrates, heat sinks, etc., and there is no description or suggestion of improving the affinity with resin to increase the amount of filling in the resin composition. In addition, there is no description or suggestion of coating boron nitride with silica by mechanochemical treatment. The thermally conductive composite particles disclosed in Patent Document 2 are formed by bonding plate-like or rod-like particles to the surface of the core inorganic particle, and reduce the anisotropy of the thermal conductivity of the filled molded body due to mechanical strength, and there is no description or suggestion of improving the affinity with resin to increase the amount of filling in the resin composition.

[0006] The present invention has been made in consideration of the above circumstances, and has an objective of providing thermally conductive composite particles and a method for producing the same, which are capable of improving affinity with resins by coating (compositing) boron nitride with silica, thereby increasing the loading amount in a resin composition and imparting high thermal conductivity to the resin composition. [Means for solving the problem]

[0007] The present inventors conducted various studies to solve the above problems and came up with the present invention. That is, the present invention relates to a thermally conductive composite particle in which the surface of boron nitride is coated with silica, and the amount of the silica coating is less than 0.5 mass% of the mass of the boron nitride. In the present invention, the amount of the silica coating may be 0.3 mass% or less of the mass of boron nitride.

[0008] The present invention also relates to a method for producing the above-mentioned thermally conductive composite particles, characterized in that boron nitride and one or more silicas selected from precipitated silica, gel silica, and dried silica are mechanochemically treated by a dry method. In the present invention, the silica may be precipitated silica. Effect of the Invention

[0009] The thermally conductive composite particles of the present invention have improved affinity with resins, and therefore can be loaded in a resin composition in a larger amount, making them useful for imparting high thermal conductivity to the resin composition.

[0010] The method for producing thermally conductive composite particles of the present invention can be carried out simply by mechanochemically treating boron nitride and silica by a dry method, and is therefore useful in that it allows the thermally conductive composite particles to be produced easily. [Brief description of the drawings]

[0011] [Figure 1] 1 is a SEM photograph of the composite particles of Example 1. [Diagram 2] 1 is a SEM photograph of boron nitride in Comparative Example 1. [Diagram 3] 1 is a SEM photograph of mechanochemically treated boron nitride of Comparative Example 2. [Figure 4] 1 is a SEM photograph of the composite particles of Comparative Example 3. [Diagram 5] FIG. 2 is an image diagram showing a case where the composite particles of Example 1 are filled in a resin and a case where the boron nitride of Comparative Example 2 is filled in a resin. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The thermally conductive composite particles of the present invention can be produced by mechanochemically treating boron nitride and silica. The boron nitride may be either hexagonal boron nitride or cubic boron nitride, but hexagonal boron nitride, which has excellent thermal conductivity, is preferred. The silica may be one or more selected from precipitated silica, gel silica, and dried silica, but precipitated silica is preferred because of its low agglomeration tendency of secondary particles (easy disaggregation) and easy disintegration.

[0013] Mechanochemical treatment is a treatment method in which mechanical energy such as shear, compression, friction, bending, and impact is applied to the target raw material to modify the surface of the raw material. The means of mechanochemical treatment are not particularly limited, and known means such as media dispersers such as ball mills, bead mills, and sand mills, and jet mill grinders can be used. The treatment time and treatment conditions of the mechanochemical treatment can be appropriately set depending on the means used.

[0014] Further, the mechanochemical treatment may be a wet method using a dispersion medium or a dry method not using a dispersion medium. For producing the thermally conductive composite particles of the present invention, the dry mechanochemical treatment is preferred.

[0015] The amount of silica coated in the thermally conductive composite particle of the present invention is less than 0.5% by mass relative to the mass of boron nitride. If the amount of silica coated is 0.5% by mass or more, the silica increases, the composite particle becomes bulky, and the viscosity of the resin composition to be filled is increased, so the kneading limit amount decreases, and the boron nitride filled in the resin composition also decreases. In addition, since silica has a low thermal conductivity, an increase in silica leads to a decrease in the thermal conductivity of the resin composition to be filled.

[0016] In addition, the amount of silica coated in the thermally conductive composite particle of the present invention is preferably 0.3 mass% or less, more preferably 0.3 mass%, based on the mass of boron nitride. If the amount of silica coated is 0.3 mass% or less, the kneading limit increases, and the amount of boron nitride filled in the resin composition also increases.

[0017] The thermally conductive composite particles of the present invention can be filled into a resin composition, particularly a substrate, a semiconductor package, or an industrial resin material, and used as a thermally conductive filler. Here, the industrial resin material is a resin material that requires corrosion resistance, chemical resistance, and processability (particularly cutting, bending, welding), and can be exemplified by industrial plates. The resin used in the resin composition is not particularly limited, and examples thereof include epoxy resin, silicone resin, melamine resin, urea resin, phenol resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyetherimide, nylon, and other polyamides, polybutylene terephthalate, polyethylene terephthalate, and other polyesters, polybenzimidazole, aramid resin, polyphenylene sulfide, fully aromatic polyester, liquid crystal polymer, polysulfone, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, acrylonitrile-acrylic rubber-styrene resin, acrylonitrile-ethylene-propylene-diene rubber-styrene resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and other general-purpose resins. EXAMPLES

[0018] Next, the present invention will be described with reference to examples, but the present invention is not limited to the following examples.

[0019] [Example 1] (Composite particles with silica coating amount of 0.3 mass %) 300 g of boron nitride (grade name: HS, manufactured by Air Brown Co., Ltd.) and 0.9 g of precipitated silica (grade name: Nipsil LP, manufactured by Tosoh Corporation) were mixed at high speed (mechanochemical treatment, dry method) using a high-speed mixer granulator to obtain composite particles with a silica coating amount of 0.3 mass% relative to the mass of boron nitride shown in Figure 1. The volume of the high-speed mixer granulator was 2 L, the mixing speed was 5000 rpm, and the mixing time was 20 minutes. The SEM photograph of the composite particles shown in Figure 1 was obtained by attaching the obtained composite particles to carbon tape and observing the surface and shape of the composite particles using a scanning electron microscope (device name: JSM-7500FA, manufactured by JEOL Ltd.). The same applies to Figures 2 to 4 below.

[0020] Comparative Example 1 (Untreated boron nitride) Boron nitride (grade name: HS, Air Brown Co., Ltd.) was used as is. As shown in Figure 2, the surface of boron nitride is smooth.

[0021] Comparative Example 2 (Mechanochemically Treated Boron Nitride) Boron nitride was mechanochemically treated in the same manner as in Example 1, except that no precipitated silica was added. The boron nitride shown in Figure 3 has a surface modified.

[0022] [Comparative Example 3] (Composite particles with silica coating amount of 0.5% by mass) 300 g of boron nitride (grade name: HS, Air Brown Co., Ltd.) and 1.5 g of precipitated silica (grade name: Nipsil LP, Tosoh Corporation) were mixed at high speed in a high-speed mixer granulator (mechanochemical treatment, dry method) to obtain composite particles with a silica coating amount of 0.5 mass% relative to the mass of boron nitride, as shown in Figure 4. The volume of the high-speed mixer granulator was 2 L, the mixing speed was 5000 rpm, and the mixing time was 20 minutes.

[0023] For each of the samples (composite particles or boron nitride) of Example 1 and Comparative Examples 1 to 3 described above, the following measurements were carried out.

[0024] 1.Moisture content The moisture absorption of the sample is evaluated. High moisture absorption can adversely affect the properties of the resin composition. Five grams of the sample was placed on a moisture meter (device name: MX-50, manufactured by A&D Co., Ltd.) and the weight loss rate upon ignition at 130°C was measured and taken as the moisture content. 2.Specific surface area Evaluate whether the sample has been crushed / ground and reduced in size by mechanochemical treatment. If the sample is reduced in size, it may lead to a decrease in thermal conductivity and an increase in moisture content (decreased moisture absorption resistance). The BET specific surface area of ​​the sample was measured using a fully automatic specific surface area measuring device (Macsorb (registered trademark) HM model-1200, manufactured by Mountec Co., Ltd.). Before the measurement, the sample was pretreated by vacuum heating and evacuation at 150°C for 30 minutes, and the measurement was performed by the BET flow method (one-point method) at a temperature close to the liquid nitrogen temperature (77K). 3.Central particle size The sample is evaluated whether it is broken down and pulverized by the mechanochemical treatment. It is well known that as the particle size of the thermally conductive filler increases, the thermal conduction path becomes longer and thicker, improving the thermal conductivity, and conversely, as the particle size decreases, the thermal conductivity decreases. In the present invention, too, if the composite particles or boron nitride are broken down and the central particle size becomes smaller, this may lead to a decrease in thermal conductivity. The sample was dispersed in a 0.2% aqueous solution of sodium hexametaphosphate, and the particle size distribution was measured using a particle size distribution measuring device (Microtrack Bell, MT3000) to read the D50 value. 4.Liquid absorption amount Ease of kneading into resin is evaluated. By making it easier to knead into resin (able to fill in a large amount), it is expected that the thermal conductivity of the resin composition will improve. The liquid absorption was measured using liquid paraffin according to the boiled linseed oil method of JIS5101-13-2. The measurement procedure is as follows. (1) 2 g of the sample was weighed and placed on a glass measurement plate. (2) Liquid paraffin was gradually added from the dropper, 4 to 5 drops at a time, and the sample was kneaded into the liquid paraffin with a palette knife. (3) The above procedure (2) was repeated, and the addition was continued until a lump of liquid paraffin and sample was formed. (4) After that, add liquid paraffin drop by drop and repeat the process until the paste becomes soft and hard. (5) The weight of liquid paraffin required to reach the end point was multiplied by 100 to obtain the amount of liquid absorbed (unit: g / 100 g). 5. Dispersion test (pH, electrical conductivity) By mechanochemical treatment, boron oxide (B 2 O3 Evaluate whether there is an increase in the content of impurities, such as the occurrence of 2 O 3 If a large amount of generated particles is generated, it may adversely affect the properties of the final product (resin composition). 10 g of the sample was added to 1 L of pure water and stirred to obtain a suspension. The pH and electrical conductivity (rate) were measured using a handy pH / electrical conductivity meter (device name: WM-32EP, manufactured by DKK-TOA Corporation). 6. Boron oxide content By mechanochemical treatment, boron oxide (B 2 O 3 Evaluate whether the occurrence of 2 O 3 If a large amount of is generated, it may have a negative effect on the properties of the final product (resin composition). It also affects the electrical conductivity and pH value. 10 g of sample was added to 1 L of pure water and stirred to separate the suspension into solid and liquid. The boron concentration was then measured using an ICP optical emission spectrometer (instrument name: Thermo Fisher Scientific, iCAP7200Duo) and the boron oxide content was calculated from the measured value. 7. Thermal Conductivity (1) 40 g of epoxy resin (Mitsui Chemicals, Epomic R140P) was placed in a 205 mL paper cup, and the sample was gradually mixed until the kneading limit was reached, and the mixing process was repeated using a planetary centrifugal mixer (Thinky ARE-310). After mixing and mixing to the kneading limit, 0.8 g of 2-ethyl-4-methylimidazole (Wako Pure Chemical Industries, Ltd.) was added, thoroughly mixed and degassed, and then heated and cured at 120°C for 2 hours. The volume filling rate at the kneading limit was calculated using the following formula. Volume filling rate of sample (vol%) = (volume of sample (cm 3 ) / (sample volume (cm 3 ) + volume of epoxy resin (cm 3 )))×100 (Formula 1) Sample volume (cm 3 ) = sample weight (g) / sample density (g / cm 3 ) (Formula 2) Volume of epoxy resin (cm 3 ) = Weight of epoxy resin (g) / Density of epoxy resin (g / cm 3 ) (Formula 3) For the densities of the samples of Comparative Examples 1 and 2, the density of boron nitride was used. In Example 1 and Comparative Example 3, the density of the sample was calculated using (Equation 4) to (Equation 6). Density of the sample (g / cm 3 ) = density of boron nitride (g / cm 3 ) × (percentage of boron nitride in the sample (mass%) / 100) + density of silica (g / cm 3 ) × (% by mass of silica in the sample / 100) (Equation 4) Percentage of boron nitride in sample (mass%) = (mass of boron nitride (g) / (mass of boron nitride (g) + mass of silica (g))) x 100 (Equation 5) Percentage of silica in sample (mass%) = (mass of silica (g) / (mass of boron nitride (g) + mass of silica (g))) × 100 (Equation 6) Density of boron nitride: 2.27g / cm 3 , Epoxy resin density: 1.16g / cm 3 , Density of precipitated silica: 2.2g / cm 3 (2) The cured resin composition was polished to prepare a test sample for measuring thermal conductivity having a diameter of 5 cm and a thickness of 2 cm. (3) Thermal conductivity measurement The test sample was kept in a thermostatic chamber at 25° C. for at least 2 hours, and then the thermal conductivity of the resin composition was measured using a rapid thermal conductivity meter (QTM-500, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0025] The measurement results of Example 1 and Comparative Examples 1 to 3 are shown in Table 1.

[0026] [Table 1]

[0027] From Table 1, the following analysis can be made for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Example 1: When the resin composition is filled with the kneading limit amount (the maximum amount that can be filled in the resin composition), the thermal conductivity of the resin composition is the highest compared to each comparative example, and the high thermal conductivity performance of boron nitride can be fully imparted to the resin composition. In addition, even though there is no difference in the kneading limit amount between Example 1 and Comparative Example 2, that is, there is no difference in the amount of boron nitride filled in the resin composition, the thermal conductivity of the resin composition filled with the kneading limit amount of Example 1 is higher than that of Comparative Example 2 because an efficient thermal conduction path is formed in Example 1. The reason for this is considered to be as follows. As shown in the left diagram of Figure 5, a small amount of minute silica on the surface of boron nitride plays the role of a spacer when kneaded with resin, and boron nitride oriented in a random direction promotes the formation of a contact point between the end face of boron nitride and the plane of boron nitride, and an efficient three-dimensional network of thermal conduction paths is formed, which is thought to increase the thermal conductivity. From this mechanism, as long as boron nitride is coated with even a small amount of silica, the thermal conductivity exceeds that of the resin composition of Comparative Example 2. Therefore, although it is not particularly convenient to set a lower limit for the amount of silica coated in the thermally conductive composite particles of the present invention, for example, the thermal conductivity exceeds that of the resin composition of Comparative Example 2 even if the amount of silica coated is 0.01 mass% or 0.05 mass% relative to the mass of boron nitride. Comparative Example 1: Since the amount of liquid absorption is higher than that of Example 1 and other comparative examples, it is understood that the affinity with the resin is the lowest and the kneading limit amount is low, so that even if the kneading limit amount is filled, a resin composition with high thermal conductivity cannot be obtained. Comparative Example 2: The surface of boron nitride is modified by mechanochemical treatment, so that its affinity with resin is increased, and the amount of liquid absorption is lower than that of Comparative Example 1, and the kneading limit amount into the resin composition is higher than that of Comparative Example 1. However, although Comparative Example 2 has a higher kneading limit amount than Comparative Example 1, there is almost no difference in the thermal conductivity of the two resin compositions, which is believed to be due to the following reasons. In Comparative Example 2, as shown in the right diagram of FIG. 5, there is no silica spacer, so when mechanochemically treated boron nitride is filled into the resin, not only is a three-dimensional network of thermal conduction paths like that in Example 1 not formed, but the contact (thermal conduction path) of boron nitride-resin-boron nitride is more than that in Example 1, and the thermal resistance of the interface between boron nitride and resin increases (thermal conductivity becomes poor). This is believed to be because of this. On the other hand, the untreated boron nitride of Comparative Example 1 has a larger median particle size than that of Comparative Example 2 (Comparative Example 1: 26.6 μm, Comparative Example 2: 18.8 μm), and therefore can form longer and thicker heat conduction paths than that of Comparative Example 2. This is thought to result in a higher thermal conductivity despite the lower kneading limit amount. Comparative Example 3: The thermal conductivity when the resin composition is filled with the kneading limit amount is slightly higher than those of Comparative Examples 1 and 2, but lower than that of Example 1, because the viscosity of the resin composition increases with the increase in the amount of coated silica, decreasing the kneading limit amount, and the thermal conductivity of the resin composition decreases with the increase in silica with low thermal conductivity. 2 O 3 The content is higher than that of Example 1, and B 2 O 3 The content of impurities such as these increases compared to Example 1, which may adversely affect the properties of the resin composition. Therefore, Comparative Example 3, in which the silica coating amount is 0.5 mass%, is considered to be the boundary point for the thermally conductive composite particles of the present invention. [Industrial Applicability]

[0028] The thermally conductive composite particles of the present invention can impart high thermal conductivity to a resin by filling the resin with the thermally conductive composite particles, and are therefore suitable for use in resin molded articles that require heat dissipation, such as electronic components.

Claims

1. A method for producing thermally conductive composite particles in which the surface of boron nitride is coated with silica, and the amount of the silica coating is less than 0.5 mass% relative to the mass of the boron nitride, characterized in that the boron nitride and one or more of the silica selected from precipitated silica, gel silica, and dried silica are mechanochemically treated by a dry method.

2. A method for producing thermally conductive composite particles in which the surface of boron nitride is coated with silica, and the amount of the silica coating is 0.3 mass% or less relative to the mass of the boron nitride, characterized in that the boron nitride and one or more of the silica selected from precipitated silica, gel method silica, and dried silica are mechanochemically treated by a dry method.

3. 3. The method for producing thermally conductive composite particles according to claim 1, wherein the silica is precipitated silica.

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