Method for producing thermally conductive filler and method for producing thermally conductive composition

Abstract

This method for producing a thermally conductive filler from a thermally conductive composition raw material containing a thermosetting resin and a thermally conductive filler includes a pyrolysis step in which the thermally conductive composition raw material is heated in a low-oxygen atmosphere with an oxygen concentration of 10 vol.% or less to pyrolyze it, and a crushing step in which the residue after pyrolysis is crushed, and the crushing step produces a thermally conductive filler by crushing the thermally conductive filler to a median particle size of 0.1 to 300 μm. The obtained thermally conductive filler is mixed with a thermosetting resin to produce a thermally conductive resin composition. This allows the thermally conductive filler to be recovered and reused from the waste of the thermally conductive composition that was previously discarded.

Description

[Technical field]

[0001] The present invention relates to a method for producing a thermally conductive filler useful for a thermally conductive composition suitable for being interposed between a heat generating portion of an electric or electronic component and a heat sink, and a method for producing a thermally conductive composition. [Background technology]

[0002] Thermally conductive silicone materials using silicone are used as heat dissipation materials for electronic components. Conventionally, scraps generated during manufacturing and materials after use are disposed of in landfills as industrial waste without being reused from the viewpoint of quality assurance, etc. In particular, when using thermosetting polymers, it is necessary to separate the polymer and the thermally conductive filler and reuse them, but an effective separation process for heat dissipation materials has not yet been put into practical use. A process has been proposed in which the polymer is thermally decomposed into monomers in a high-temperature alkaline aqueous solution, recovered, and then repolymerized, but the residues of inorganic reinforcing materials that remain as precipitates are discarded. When heat dissipation materials are treated with the same process, the thermally conductive filler that remains as residue can be reused by washing it, but this is not realistic from the viewpoint of cost and environmental burden. In recent years, there is a demand for recycling technologies suitable for heat dissipation materials in response to the increasing demand for Sustainable Development Goals (SDGs). Patent Document 1 proposes pyrolyzing silicone rubber and separating and recovering volatile siloxane and silicic acid. Patent Document 2 proposes catalytic pyrolysis of silicone rubber with alcohol and recycling the polymer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-271416 [Patent Document 2] JP 2002-187976 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, there have been no effective proposals for recycling thermally conductive fillers, and most of them have been disposed of in landfills, resulting in high disposal costs.

[0005] In order to solve the above-mentioned problems of the conventional art, the present invention provides a method for producing a thermally conductive filler and a method for producing a thermally conductive composition, which can recover and reuse a thermally conductive filler from waste of a thermally conductive composition that has been conventionally discarded. [Means for solving the problem]

[0006] One embodiment of the present invention comprises: Contains silicone polymer thermosetting resin and, A method for producing a thermally conductive filler from a thermally conductive composition raw material containing the thermally conductive filler, comprising the steps of: a pyrolysis step of heating and pyrolyzing the thermally conductive composition raw material in a low-oxygen atmosphere having an oxygen concentration of 10 vol.% or less; A crushing step of crushing the residue after the pyrolysis, The pulverization step is performed so that the median particle size is 0.1 to 300 μm. death, Manufacturing thermally conductive filler with Si atom concentration of 1 at% or less by scanning electron microscope-energy dispersive X-ray spectroscopy analysis The present invention relates to a method for producing a thermally conductive filler.

[0007] Another embodiment of the present invention relates to a method for producing a thermally conductive resin composition, in which the thermally conductive filler obtained by the above-mentioned method for producing a thermally conductive filler is mixed with a thermosetting resin to obtain a thermally conductive resin composition. Effect of the Invention

[0008] The present invention includes a pyrolysis step in which a thermally conductive composition raw material is heated in a low-oxygen atmosphere with an oxygen concentration of 10 vol.% or less to pyrolyze it, and a crushing step in which the residue after pyrolysis is crushed. In the crushing step, the raw material is crushed to have a median particle size of 0.1 to 300 μm. By using waste thermally conductive composition materials that were previously discarded as raw materials to produce a thermally conductive filler, it is possible to provide a method for producing a thermally conductive filler and a method for producing a thermally conductive composition that make it possible to reuse the waste materials. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a method of using a thermally conductive sheet according to one embodiment of the present invention. [Diagram 2] 2A-B are schematic explanatory views showing a method for measuring the thermal conductivity of a sample in one embodiment of the present invention. [Diagram 3] FIG. 3 is an SEM photograph (magnification: 500x) of the filler of Example 1 after pyrolysis and before pulverization. [Figure 4] FIG. 4 is an SEM photograph (magnification: 500 times) of the filler of Comparative Example 1 after pyrolysis and before pulverization. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention produces a thermally conductive filler from a thermally conductive composition raw material containing a thermosetting resin and a thermally conductive filler. Examples of the thermosetting resin raw material include silicone resin, epoxy resin, phenolic resin, etc. Among these, silicone resin is preferable. Examples of the thermally conductive filler are preferably at least one inorganic particle selected from the group consisting of aluminum oxide (alumina), zinc oxide, magnesium oxide, aluminum nitride, boron nitride, aluminum hydroxide, and silicon carbide. These inorganic particles have high thermal conductivity and are suitable as a TIM (Thermal Interface Material). Among these, alumina and / or aluminum nitride are preferable.

[0011] The method of the present invention comprises the following steps: 1 Pyrolysis process (1) Pyrolysis atmosphere The thermally conductive composition raw material is heated and pyrolyzed in a low-oxygen atmosphere with an oxygen concentration of 10 vol.% or less. Normal oxygen at sea level is about 21 vol.% and nitrogen is about 78 vol.%, but in the present invention, pyrolysis is performed in a dilute oxygen or oxygen-free state. The reason for this is that organic matter burns in the presence of oxygen, leaving behind residues. If residues remain, it is difficult to reuse the recycled thermally conductive filler. The oxygen concentration is preferably 7 vol.% or less, more preferably 5 vol.% or less, and even more preferably 3 vol.% or less. In addition, the low-oxygen atmosphere is preferably an inert gas flow, a mixed gas flow of 51 to 100 vol.% inert gas and 0 to 49 vol.% air, under reduced pressure conditions, or under superheated steam. When the thermally conductive composition raw material is heated and pyrolyzed in a low-oxygen atmosphere with an oxygen concentration of 10 vol.% or less, the amount of residual polymer components can be reduced. The amount of the residual polymer component is preferably 15 wt.% or less of the polymer mass before the treatment, more preferably 10 wt.% or less, and even more preferably 8 wt.% or less. The amount of the residual polymer component is a relative amount when the polymer mass before the treatment is taken as 100%. (2) Processing temperature In the thermal decomposition step, it is preferable to heat to a temperature of 400°C to 1600°C. If it is less than 400°C, the thermal decomposition is inefficient. If it exceeds 1600°C, silica and alumina react to generate mullite, which is not preferable. From the viewpoint of energy saving, it is preferable to heat to a temperature of 450 to 1000°C, and more preferably 500 to 800°C. (3) Processing time The heating retention time varies depending on the heating temperature, but is preferably 10 minutes to 10 hours, more preferably 20 minutes to 5 hours, and further preferably 30 minutes to 3 hours. In the thermal decomposition step, volatile components generated by thermal decomposition may be separated. Some of the volatile components may be reusable. 2. Crushing process The residue after pyrolysis is pulverized to a median particle size of 0.1 to 300 μm using a ball mill, pin mill, cutter mill, jet mill, bead mill, hammer mill, or automatic mortar.

[0012] After the pulverization step, it is preferable to classify the material to obtain a uniform particle size. For classification, mesh sieving, air classification, water classification, vortex classification, etc. can be used. Among these, metal mesh sieving is preferable because it can accurately uniform the particle size.

[0013] The thermally conductive filler (hereinafter also referred to as "recycled filler") obtained by the thermally conductive filler manufacturing method of the present invention has a Si atom number concentration of preferably 1 at% or less, more preferably 0.5 at% or less, and even more preferably 0.1 at% or less, as determined by SEM-EDX analysis (scanning electron microscope-energy dispersive X-ray spectroscopy analysis). This allows the purity of the intended thermally conductive filler to be increased.

[0014] The thermally conductive composition raw material preferably contains 100 to 4000 parts by mass of thermally conductive filler per 100 parts by mass of thermosetting resin, more preferably 200 to 3000 parts by mass, and even more preferably 400 to 2000 parts by mass. If the thermally conductive filler is in the above range, it can be efficiently recovered and is effective for reuse.

[0015] On the surface of the recycled filler, RaSi(OR') 4-a (wherein R is an unsubstituted or substituted hydrocarbon group having 8 to 12 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1). Examples of the alkoxysilane compound (hereinafter simply referred to as "silane") of the above chemical formula include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, and octadecyltriethoxysilane. The above silane compounds can be used alone or in combination of two or more. In particular, if fine thermally conductive particles with a volume-based median diameter D=50 of 1 μm or less are surface-pretreated with a coupling agent, they will have better mixability when compounded, improving workability, and will not adsorb platinum catalysts during the compounding process, preventing inhibition of the silicone curing reaction that cures through addition reaction.

[0016] In the method for producing a thermally conductive resin composition of the present invention, the thermally conductive filler obtained by the method for producing a thermally conductive filler is mixed with a thermosetting resin to produce a thermally conductive resin composition. The thermosetting resin is preferably a silicone polymer. Silicone polymers have high heat resistance and are suitable as thermally conductive materials: TIM (Thermal Interface Material). As examples of silicone polymers, addition-curing silicone polymers, peroxide-curing silicone polymers, or condensation-type silicone polymers are preferred. These may be used alone or in combination. Commercially available silicone polymers can be used. They can be in the form of rubber, gel, grease, putty, liquid, or the like.

[0017] The thermally conductive composition preferably contains 100 to 4000 parts by mass of the thermally conductive filler per 100 parts by mass of the thermosetting resin, more preferably 200 to 3000 parts by mass, and even more preferably 400 to 2000 parts by mass, thereby obtaining a thermally conductive composition with high thermal conductivity.

[0018] As an example, the thermally conductive composition is produced by the following steps. (1) Thermally conductive composition Thermosetting resin, thermally conductive filler, curing catalyst such as platinum if necessary, other pigments, RaSi(OR') 4-a (wherein R is an unsubstituted or substituted hydrocarbon group having 8 to 12 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1) and other such compounds are mixed and stirred using a mixing device such as a planetary mixer to form a compound (composition). Liquid compositions such as greases are made into products in this state. (2) Sheet molding When forming into a sheet, the compound is degassed for 1 to 10 minutes under reduced pressure, for example, about -0.1 Pa. Next, the compound is sandwiched between release-treated polyethylene terephthalate (PET) films, rolled to a predetermined thickness using constant speed rolls, and cured by heating at 100°C for about 10 minutes to form a thermally conductive sheet.

[0019] The recycled filler obtained in the present invention is suitable as a thermally conductive filler for a thermal interface material (TIM) that is interposed between a heat generating part of an electric / electronic component and a heat sink by reusing it in a thermally conductive composition and / or a thermally conductive sheet. The thermally conductive sheet is taken as an example of the thermally conductive material. FIG. 1 is a schematic cross-sectional view of a thermally conductive sheet according to an embodiment of the present invention incorporated in a heat dissipation structure 10. The thermally conductive sheet 11b dissipates heat generated by an electronic component 13 such as a semiconductor element, is fixed to a main surface 12a of the heat spreader 12 facing the electronic component 13, and is sandwiched between the electronic component 13 and the heat spreader 12. The thermally conductive sheet 11a is sandwiched between the heat spreader 12 and a heat sink 15. The thermally conductive sheets 11a and 11b, together with the heat spreader 12, constitute a heat dissipation member that dissipates heat from the electronic component 13. The heat spreader 12 is formed, for example, in a rectangular plate shape, and has a main surface 12a facing the electronic component 13, and a side wall 12b standing along the outer periphery of the main surface 12a. The heat spreader 12 has a thermally conductive sheet 11b provided on the main surface 12a surrounded by the side wall 12b, and a heat sink 15 provided on the other surface 12c opposite the main surface 12a via the thermally conductive sheet 11a. The electronic component 13 is, for example, a semiconductor element such as a BGA, and is mounted on a wiring board 14.

[0020] The thermally conductive composition raw material containing the thermosetting resin and the thermally conductive filler used in the present invention may be of any type, such as process waste, waste scraps, recovered products, stock products after the expiration of the usage period, prototypes, etc. The properties of the raw material may also be of any type, such as rubber, gel, grease, putty, liquid, etc. EXAMPLES

[0021] The following examples will be used for explanation. The present invention is not limited to the examples.

[0022] Various parameters were measured by the methods described below. <Thermal conductivity> The thermal conductivity of the thermally conductive silicone rubber sheet was measured by a hot disk (conforming to ISO 22007-2:2008). As shown in Fig. 2A, this thermal conductivity measuring device 1 sandwiches a sensor 2 made of a polyimide film between two samples 3a and 3b, applies a constant power to the sensor 2, generates heat constantly, and analyzes the thermal characteristics from the temperature rise value of the sensor 2. The tip 4 of the sensor 2 has a diameter of 7 mm, and as shown in Fig. 2B, it has a double spiral structure of electrodes, and an electrode 5 for applying current and an electrode for resistance value (electrode for temperature measurement) 6 are arranged at the lower part. The thermal conductivity is calculated by the following formula (Equation 1).

Equation

[0023] (Example 1) (1) Manufacturing process of the thermally conductive silicone rubber sheet Two-component room temperature curable silicone polymer (silicone component), a commercially available polyorganosiloxane: 100 g As a thermally conductive filler, a mixture of alumina with a D50 (median diameter) of 0.3 μm, alumina with a D50 of 2 μm, alumina with a D50 of 35 μm, and 3.nu filler with a D50 of 75 μm based on the volume-based cumulative particle size distribution, and alumina with an average particle diameter D50 = 5.2 μm: total amount of alumina 1400 g The above materials were mixed to make a compound, which was rolled into a sheet with a thickness of 2.0 mm and heated and cured at 100°C for 10 minutes to form a thermally conductive silicone rubber sheet. (2) Pyrolysis process The thermally conductive silicone rubber sheet was placed in an electric furnace and heated in a nitrogen gas flow from room temperature of 25° C. to 600° C. at a rate of 100° C. / hr, and held at 600° C. for 1 hour. (3) Grinding and classification process The residue after pyrolysis was pulverized in a mortar and pestle, and the pulverized material was sieved through a metal mesh with a mesh size of #150. The filler thus obtained had a D50 (median diameter) of 3.7 μm. The Si atom number concentration measured by SEM-EDX analysis (scanning electron microscope-energy dispersive X-ray spectroscopy analysis) was 0.1 or less, and the purity of the target alumina was high. The yield of the obtained alumina was 99 wt.%. Figure 3 is an SEM photograph of the filler after pyrolysis and before pulverization in Example 1. The SEM-EDX analysis is the result of point analysis of the areas on the surface of the large particles in the figure where small particle size fine powder is not attached.

[0024] Comparative Example 1 The same procedure as in Example 1 was carried out except that in the pyrolysis step, heating was performed in air instead of under a nitrogen gas flow. As a result, the obtained filler had a D50 (median diameter) of 4.0 μm, which was close to the average particle diameter of Example 1, but the Si atom number concentration by SEM-EDX analysis was 1.1 wt.%, which was higher than that of Example 1. A high Si atom number concentration means that the purity of the target alumina is low. The yield of the obtained alumina was 99 wt.%. FIG. 4 is an SEM photograph of the filler of Comparative Example 1 after pyrolysis and before pulverization. The results are shown in Table 1.

[0025] [Table 1] Note*: The detection limit of SEM-EDX analysis is 0.1 to 1 at%. Although values ​​below 0.1 at% are obtained, the reliability is extremely low, so it is indicated as 0.1 at% or less.

[0026] As is clear from Table 1, in Example 1, since heating was performed in a nitrogen gas flow, the concentration of Si atoms on the surface of the obtained alumina was low, the purity was high, and it was reusable. In contrast, in Comparative Example 1, since heating was performed in the air, the concentration of Si atoms on the alumina surface was high, making reuse difficult.

[0027] Example 2 Commercially available polyorganosiloxane, two-component room temperature curing silicone polymer (silicone component): 100 g Recycled filler obtained in Example 1: 1400 g The above materials were mixed to make a compound, which was rolled into a sheet with a thickness of 2.0 mm and heated and cured at 100°C for 10 minutes to form a thermally conductive silicone rubber sheet.

[0028] Comparative Example 2 The same procedure as in Example 3 was carried out except that 1400 g of the recycled filler obtained in Comparative Example 1 was used. The results are shown in Table 2.

[0029] [Table 2]

[0030] Example 3 The same procedure as in Example 1 was repeated except that in the pyrolysis step, the nitrogen gas flow rate was 200 ml / min, the temperature was increased from room temperature 25° C. to 600° C. at a rate of 10° C. / hr, and the temperature was maintained at 600° C. for 1 hour. The amount of residual polymer in the resulting combustion residue was analyzed using a thermogravimetric differential thermal analyzer (TG-DTA, Hitachi High-Tech Science, TG / DTA7300).

[0031] Example 4 The same procedure as in Example 3 was carried out except that in the pyrolysis step, the nitrogen gas flow rate was 180 ml / min and the air flow rate was 20 ml / min.

[0032] Comparative Example 3 The same procedure as in Example 3 was carried out except that the air flow rate in the pyrolysis step was 200 ml / min. The results are shown in Table 3.

[0033] [Table 3] Note*: The residual polymer component is the relative amount when the polymer mass before treatment is taken as 100%.

[0034] The table reveals the following: (1) In Example 3, the heating was performed under a nitrogen gas flow, so that the amount of residual polymer components was small. (2) In Example 4, the heating was performed under a mixed gas of nitrogen and air, so that the amount of residual polymer components was small. (3) In Comparative Example 5, since heating was performed under air, a large amount of polymer components remained, and the recycled filler could not be reused. [Industrial Applicability]

[0035] The recycled filler obtained by the present invention can be reused in a thermally conductive composition and / or a thermally conductive sheet, and is suitable as a thermal interface material (TIM) to be interposed between a heat generating part of an electric or electronic component and a heat sink. [Explanation of symbols]

[0036] 1. Thermal conductivity measuring device 2 Polyimide film sensor 3a, 3b Thermally conductive sheet sample 4 Sensor tip 5 Electrode for applied current 6 Resistance electrodes (temperature measurement electrodes) 10 Heat dissipation structure 11a, 11b Thermally conductive sheet 12 Heat spreader 13. Electronic Components 14 Wiring board 15 Heat sink

Claims

1. A method for producing a thermally conductive filler from a thermosetting resin containing a silicone polymer and a thermally conductive composition raw material containing a thermally conductive filler, A thermal decomposition step is performed in which the thermally conductive composition raw material is heated and thermally decomposed in a low-oxygen atmosphere with an oxygen concentration of 10 vol.% or less, The process includes a grinding step for grinding the residue after the thermal decomposition, The aforementioned grinding step involves grinding the material so that the central particle size is 0.1 to 300 μm. A method for producing a thermally conductive filler, characterized by producing a thermally conductive filler with a Si atom number concentration of 1 at% or less, as determined by scanning electron microscopy-energy dispersive X-ray spectroscopy analysis.

2. The method for producing a thermally conductive filler according to claim 1, wherein the thermal decomposition step involves heating to a temperature of 400°C to 1600°C.

3. The method for producing a thermally conductive filler according to claim 1, wherein the low-oxygen atmosphere is at least one atmosphere selected from the group consisting of an inert gas stream, a mixed gas stream of 51 to 100 vol.% inert gas and 0 to 49 vol.% air, reduced pressure conditions, and superheated steam conditions.

4. The method for producing a thermally conductive filler according to claim 1, wherein the grinding step is at least one step selected from the group consisting of a ball mill, a pin mill, a cutter mill, a jet mill, a bead mill, a hammer mill, and an automatic mortar and pestle.

5. A method for producing a thermally conductive filler according to claim 1, further comprising a classification step after the grinding step.

6. The method for producing a thermally conductive filler according to claim 5, wherein the classification step is sieving with a mesh.

7. The method for producing a thermally conductive filler according to claim 1, wherein the thermally conductive filler is at least one selected from the group consisting of alumina and aluminum nitride.

8. The method for producing a thermal conductive filler according to claim 1, wherein the thermal conductive composition raw material is blended with 100 to 4000 parts by mass of thermal conductive filler per 100 parts by mass of thermosetting resin.

9. The method for producing a thermally conductive filler according to claim 1, wherein the thermally conductive composition raw material is process waste, waste material, recovered product, stock after the expiration of the usage period, or a prototype.

10. The recycled filler obtained by the above method for manufacturing the thermally conductive filler is further processed by RaSi(OR') 4-a A method for producing a thermally conductive filler according to claim 1, wherein the surface is treated with (wherein R is an unsubstituted or substituted organic group having 8 to 12 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1).

11. A method for producing a thermally conductive resin composition, characterized by mixing a recycled filler obtained by the method for producing a thermally conductive filler according to any one of claims 1 to 10 with a thermosetting resin to obtain a thermally conductive resin composition.

12. The method for producing a thermally conductive resin composition according to claim 11, wherein the thermosetting resin is a silicone resin.

13. The method for producing the thermal conductive resin composition according to claim 11, wherein the thermal conductive composition is made by blending 100 to 4000 parts by mass of a thermal conductive filler with 100 parts by mass of a thermosetting resin.

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