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

Abstract

The present invention relates to a method for producing a thermally conductive filler from a thermally conductive composition raw material containing a thermosetting resin and a thermally conductive filler, the method comprising: a thermal decomposition step for thermally decomposing the thermally conductive composition raw material by heating the thermally conductive composition raw material in a low-oxygen atmosphere having an oxygen concentration of 10 vol.% or less; and a pulverization step for pulverizing the residue after thermal decomposition, the pulverization step being performed such that the center particle diameter is 0.1-300 [mu] m, thereby producing the thermally conductive filler. The obtained thermally conductive filler is mixed with a thermosetting resin to prepare a thermally conductive resin composition. As a result, the thermally conductive filler is recovered from the chips of the conventionally discarded thermally conductive composition and reused.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a thermally conductive filler and a method for manufacturing a thermally conductive composition, the thermally conductive filler being useful for thermally conductive compositions suitable for use between heat-generating parts and heat sinks in electrical / electronic components, etc. Background Technology

[0002] Thermally conductive silicone materials using silicone are used as heat dissipation materials for electronic components. Previously, from the perspective of ensuring quality, scraps generated during manufacturing and used materials were not reused and were disposed of as industrial waste in landfills. Especially in the case of thermosetting polymers, it is necessary to separate the polymer and thermally conductive filler for reuse, but for heat dissipation materials, an effective separation process has not yet been put into practical use. A process has been proposed to thermally decompose the polymer in a high-temperature alkaline aqueous solution, recover the monomers, and then repolymerize them; however, residues such as inorganic reinforcing materials remaining as precipitates are discarded. While it is possible to reuse the residual thermally conductive filler by cleaning when treating heat dissipation materials using the same process, this is impractical from the perspectives of cost and environmental impact. In recent years, as a countermeasure to meet the increasingly demanding Sustainable Development Goals (SDGs), recycling technologies suitable for heat dissipation materials have been sought. Patent document 1 proposes a method of thermally decomposing silicone rubber to separate it into volatile siloxanes and silicic acid for recycling. Patent document 2 proposes a method of contact thermal decomposition of silicone rubber with alcohol to recycle the polymer. Existing technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 5-271416 Patent Document 2: Japanese Patent Application Publication No. 2002-187976 Summary of the Invention The problem that the invention aims to solve

[0004] However, previous recycling methods lacked effective proposals for the reuse of thermally conductive fillers, resulting in most being disposed of through landfills. Consequently, the current situation presents a high disposal cost.

[0005] To address the aforementioned problems, the present invention provides a method for manufacturing a thermally conductive filler and a method for manufacturing a thermally conductive composition, which can recover and reuse thermally conductive fillers from debris of previously discarded thermally conductive compositions. Methods for solving problems

[0006] One embodiment of the present invention relates to a method for manufacturing a thermally conductive filler, which is a method for manufacturing a thermally conductive filler from a thermally conductive composition raw material comprising a thermosetting resin and a thermally conductive filler, comprising: a thermal decomposition step of heating the thermally conductive composition raw material in a low oxygen atmosphere with an oxygen concentration of 10 vol.% or less to perform thermal decomposition; and a pulverization step of pulverizing the residue after thermal decomposition, wherein the pulverization step is performed with a central particle size of 0.1 to 300 μm.

[0007] Another embodiment of the present invention relates to a method for manufacturing a thermally conductive resin composition, wherein a thermally conductive filler obtained by the above-described method for manufacturing thermally conductive fillers is mixed with a thermosetting resin to form a thermally conductive resin composition. Invention Effects

[0008] This invention provides a method for manufacturing a thermally conductive filler and a method for manufacturing a thermally conductive composition. The method for manufacturing the thermally conductive filler includes: a thermal decomposition step, in which the thermally conductive composition raw material is heated and thermally decomposed under a low-oxygen atmosphere with an oxygen concentration of less than 10 vol.%; and a pulverizing step, in which the residue after thermal decomposition is pulverized to a central particle size of 0.1 to 300 μm. This allows the waste material of previously discarded thermally conductive compositions to be used as raw material to manufacture the thermally conductive filler, thereby enabling the reuse of waste materials. Attached Figure Description

[0009] [ Figure 1 ] Figure 1 This is a schematic cross-sectional view illustrating a method of using a thermally conductive sheet according to one embodiment of the present invention. [ Figure 2 ] Figure 2 A~B are schematic diagrams illustrating a method for measuring the thermal conductivity of a sample in one embodiment of the present invention. [ Figure 3 ] Figure 3 This is an SEM image (500x magnification) of the filler material after thermal decomposition and before pulverization in Example 1. [ Figure 4 ] Figure 4 The image shows a SEM image (500x magnification) of the filler material after thermal decomposition and before pulverization in Comparative Example 1. Detailed Implementation

[0010] This invention relates to the manufacture of thermally conductive fillers from a thermally conductive composition containing a thermosetting resin and a thermally conductive filler. As an example, the thermosetting resin raw material includes silicone resin, epoxy resin, phenolic resin, etc. Silicone resin is preferred. As an example, the thermally conductive filler is preferably at least one inorganic particle selected from the group consisting of 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 TIM (Thermal Interface Material). Alumina and / or aluminum nitride are preferred.

[0011] The method of the present invention includes the following steps. 1. Thermal decomposition process (1) Thermal decomposition atmosphere The thermally conductive composition raw material is thermally decomposed by heating in a low-oxygen atmosphere with an oxygen concentration of 10 vol.% or less. While the typical oxygen concentration at 0 m altitude is approximately 21 vol.% and nitrogen concentration is approximately 78 vol.%, in this invention, thermal decomposition is carried out under dilute or anaerobic conditions. The reason for this is that if oxygen is present, the organic matter will burn, leaving residue. If residue remains, it becomes 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. Furthermore, the low-oxygen atmosphere is preferably under a stream of inactive gas, a mixed gas stream of 51-100 vol.% inactive gas and 0-49 vol.% air, under reduced pressure, or under superheated steam. By heating the thermally conductive composition raw material in a low-oxygen atmosphere with an oxygen concentration of 10 vol.% or less, the residual polymer content can be reduced. The residual polymer content is preferably 15 wt.% or less of the polymer mass before treatment, more preferably 10 wt.% or less, and even more preferably 8 wt.% or less. In addition, the residual polymer content is the relative amount when the mass of the polymer before treatment is set to 100%. (2) Processing temperature In the thermal decomposition process, heating to a temperature of 400°C to 1600°C is preferred. Below 400°C, thermal decomposition is inefficient. Above 1600°C, silicon dioxide reacts with alumina to form mullite, which is therefore undesirable. From an energy-saving perspective, 450°C to 1000°C is preferred, and 500°C to 800°C is more preferred. (3) Processing time The heating holding time also depends on the heating temperature, preferably 10 minutes to 10 hours, more preferably 20 minutes to 5 hours, and even more preferably 30 minutes to 3 hours. In the thermal decomposition process, volatile components generated through thermal decomposition can also be separated. These volatile components can sometimes be reused. 2. Crushing process The residue after thermal decomposition is pulverized. The pulverization process is carried out with a central particle size of 0.1~300μm. The pulverization process utilizes ball mills, pin mills, shredders, jet mills, bead mills, hammer mills, or automatic mortars.

[0012] To ensure uniform particle size after the crushing process, grading is preferable. Grading can be performed using methods such as sieving with screens, air grading, hydraulic grading, and vortex grading. Among these, sieving with metal mesh is preferred because it can accurately ensure uniform particle size.

[0013] The Si atom concentration of the thermally conductive filler (hereinafter also referred to as "recycled filler") obtained by the manufacturing method of the thermally conductive filler of the present invention, based on SEM-EDX analysis (scanning electron microscopy-energy dispersive X-ray spectrometry), is preferably 1 at% or less, more preferably 0.5 at% or less, and even more preferably 0.1 at% or less. This improves the purity of the target thermally conductive filler.

[0014] In the thermally conductive composition raw materials, 100 to 4000 parts by weight of thermally conductive filler are preferably included relative to 100 parts by weight of thermosetting resin, more preferably 200 to 3000 parts by weight, and even more preferably 400 to 2000 parts by weight. If the thermally conductive filler is within the above range, it can be efficiently recycled and is effective for reuse.

[0015] R can also be applied to the surface of the recirculation packing. a Si(OR') 4-a (Where R is an unsubstituted or substituted hydrocarbon group with 8 to 12 carbon atoms, R' is an alkyl group with 1 to 4 carbon atoms, and a is 0 or 1). Examples of alkoxysilane compounds with the above chemical formula (hereinafter referred to as "silanes") include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, and octadecyltriethoxysilane. One or more of the above silane compounds may be used. In particular, if thermally conductive particles with a median particle size D=50 of less than 1 μm are pre-treated with a coupling agent, the mixability and workability will be improved when the composite is made. Moreover, it is difficult to adsorb platinum catalyst in the composite process, and it will not hinder the curing reaction of the organosilicon cured by the addition reaction.

[0016] In the method for manufacturing the thermally conductive resin composition of the present invention, the thermally conductive filler obtained by the above-described method for manufacturing thermally conductive fillers is mixed with a thermosetting resin to prepare the 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). Examples of silicone polymers include addition-curing silicone polymers, peroxide-curing silicone polymers, and condensation-curing silicone polymers. They can be used alone or in combination. Commercially available silicone polymers can be used. The composition can be formulated into rubber, gel, grease, putty, liquid, or other forms.

[0017] In the thermally conductive composition, 100 to 4000 parts by weight of thermally conductive filler are preferably added relative to 100 parts by weight of thermosetting resin, more preferably 200 to 3000 parts by weight, and even more preferably 400 to 2000 parts by weight. This results in a thermally conductive composition with high thermal conductivity.

[0018] The thermally conductive composition is manufactured as an example through the following process. (1) Thermally conductive composition Thermosetting resin, thermally conductive filler, curing catalyst such as platinum as needed, other pigments, and R... a Si(OR') 4-a Alkoxysilane compounds, etc., represented by (where R is an unsubstituted or substituted hydrocarbon group with 8 to 12 carbon atoms, R' is an alkyl group with 1 to 4 carbon atoms, and a is 0 or 1), are mixed and stirred using a mixing device such as a planetary mixer to form a complex (composition). Liquid compositions such as lubricating greases are made into articles in this state. (2) Sheet forming process When formed into a sheet, the above-mentioned composite was degassed for 1 to 10 minutes under reduced pressure of approximately -0.1 Pa. Next, the composite was sandwiched in a polyethylene terephthalate (PET) film that had undergone demolding treatment, rolled to a specified thickness using constant speed rollers, and cured by heating at 100°C for about 10 minutes to form a thermally conductive sheet.

[0019] The recyclable filler obtained in this invention can be reused in thermally conductive compositions and / or thermally conductive sheets, and is suitable as a heat dissipation material between heat-generating parts such as electrical / electronic components and heat sinks: thermally conductive filler for TIM (Thermal Interface Material). Thermally conductive sheets will be used as an example of such heat dissipation material. Figure 1It is a schematic cross-sectional view of assembling the heat-conductive sheet in one embodiment of the present invention to the heat dissipation structure 10. The heat-conductive sheet 11b is a component for dissipating the heat emitted by an electronic component 13 such as a semiconductor element, and is fixed to the main surface 12a of the radiator 12 opposite to the electronic component 13 and is sandwiched between the electronic component 13 and the radiator 12. In addition, the heat-conductive sheet 11a is clamped between the radiator 12 and the heat absorber 15. Moreover, the heat-conductive sheets 11a, 11b and the radiator 12 together constitute a heat dissipation component for dissipating the heat of the electronic component 13. The radiator 12 is formed, for example, in a square plate shape and has a main surface 12a facing the electronic component 13 and side walls 12b erected along the outer periphery of the main surface 12a. The radiator 12 is provided with the heat-conductive sheet 11b on the main surface 12a surrounded by the side walls 12b, and in addition, the heat absorber 15 is provided on the other surface 12c opposite to the main surface 12a with the heat-conductive sheet 11a interposed therebetween. The electronic component 13 is, for example, a semiconductor element such as a BGA and is mounted on the wiring substrate 14.

[0020] The types of raw materials of the heat-conductive composition containing a thermosetting resin and a heat-conductive filler used in the present invention may be process scraps, waste scraps, product recyclables, expired inventories, prototypes, etc. The properties of the above raw materials may also be rubber, gel, grease, putty, liquid, etc., and the types are not limited. Examples

[0021] The following is an explanation using examples. The present invention is not limited to the examples.

[0022] Regarding various parameters, they are measured by the methods described below. <Thermal conductivity> The thermal conductivity of the heat-conductive silicone rubber sheet is measured by the transient plane heat source method (in accordance with ISO 22007-2:2008). As shown in Figure 2 A, the polyimide film sensor 2 is clamped by two specimens 3a, 3b, a constant power is applied to the sensor 2 to make it heat constantly, and the thermal characteristics are analyzed according to the temperature rise value of the sensor 2. The diameter of the front end 4 of the sensor 2 is 7 mm. As shown in Figure 2 B, it becomes a double helix 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 1] <SEM-EDX analysis> SEM-EDX analysis (scanning electron microscopy-energy dispersive X-ray spectrometry) was performed using a Hitachi High-Tech TM4000 Plus II benchtop electron microscope. The atomic number concentration obtained as a result of the analysis represents the ratio of the relative atomic numbers of elements in the sample. The analytical range depends on the material, but typically at 500x magnification, the analytical depth is 1~2 μm, and the analytical range is several μm to tens of μm.

[0023] (Example 1) (1) Manufacturing process of thermally conductive silicone rubber sheet As a commercially available two-component room-temperature curing silicone polymer (silicone component) of polyorganosiloxane: 100g As a thermally conductive filler, alumina with a cumulative particle size distribution based on volume (D50, median particle size) of 0.3 μm, 2 μm, 35 μm, and 75 μm was mixed, along with alumina with an average particle size of 5.2 μm: the total alumina content was 1400 g. The above materials are mixed to form a composite, rolled into a sheet with a thickness of 2.0 mm, and cured at 100°C for 10 minutes to form a thermally conductive silicone rubber sheet. (2) Thermal decomposition process The thermally conductive silicone rubber sheet was placed in an electric furnace and heated from room temperature (25°C) to 600°C at a rate of 100°C / hr (°C / hour) under a nitrogen flow, and then held at 600°C for 1 hour. (3) Crushing and grading process The residue from thermal decomposition was pulverized using a mortar and pestle. The pulverized material was then sieved through a metal mesh with a mesh size of #150. The resulting filler had a D50 (median particle size) of 3.7 μm. Based on SEM-EDX analysis (scanning electron microscopy-energy dispersive X-ray spectroscopy), the Si atom concentration was below 0.1, indicating high purity of the target alumina. The yield of the obtained alumina was 99 wt.%. Figure 3 These are SEM images of the filler material after thermal decomposition and before pulverization in Example 1. The SEM-EDX analysis is the result of point analysis on the surface of the large particles in the image where no small-diameter microparticles are attached.

[0024] (Comparative Example 1) In the pyrolysis process, heating was performed at atmosphere instead of under a nitrogen flow, otherwise the same procedure as in Example 1 was followed. As a result, the D50 (median particle size) of the resulting filler was 4.0 μm, similar to the average particle size of Example 1, but the Si atomic number concentration based on SEM-EDX analysis was 1.1 wt.%, higher than in Example 1. The high Si atomic number concentration indicates a lower purity of the target alumina. The yield of the obtained alumina was 99 wt.%. Figure 4 The image shows a SEM photograph of the packing material after thermal decomposition and before pulverization in Comparative Example 1. The results are shown in Table 1.

[0025] Note*: The detection limit for SEM-EDX analysis is 0.1~1at%. Even values ​​below 0.1at% will appear, but the reliability is extremely low, so it is marked as below 0.1at%.

[0026] As shown in Table 1, the aluminum oxide obtained in Example 1, due to heating in a nitrogen gas flow, has a low Si atom concentration and high purity, and can be reused. In contrast, Comparative Example 1, due to heating in the atmosphere, has a high Si atom concentration on the alumina surface, making it difficult to reuse.

[0027] (Example 2) As a commercially available polyorganosiloxane, i.e., a two-component room-temperature curing silicone polymer (silicone component): 100g The recirculating packing material obtained in Example 1: 1400g The above materials are mixed to form a composite, rolled into a sheet with a thickness of 2.0 mm, and cured at 100°C for 10 minutes to form a thermally conductive silicone rubber sheet.

[0028] (Comparative Example 2) Except that 1400g of the recirculated packing obtained in Comparative Example 1 was used, the procedure was carried out in the same manner as in Example 3. The results are shown in Table 2.

[0029]

[0030] (Example 3) In the pyrolysis process, the nitrogen flow rate was set to 200 ml / min, and the temperature was increased from room temperature (25°C) to 600°C at a rate of 10°C / hr, and held at 600°C for 1 hour. Otherwise, the process was the same as in Example 1. The amount of residual polymer in the obtained combustion residue was analyzed using a thermogravimetric differential calorimeter (TG-DTA, Hitachi High-Tech Science, TG / DTA7300).

[0031] (Example 4) In the thermal decomposition process, the nitrogen flow rate is 180 ml / min and the air flow rate is 20 ml / min. Otherwise, it is carried out in the same manner as in Example 3.

[0032] (Comparative Example 3) In the thermal decomposition process, the air flow rate is 200 ml / min, and otherwise it is carried out in the same manner as in Example 3. The results are shown in Table 3.

[0033] Note*: Residual polymer content is the relative amount when the mass of the polymer before treatment is set to 100%.

[0034] The following information can be found in the table. (1) In Example 3, due to heating under nitrogen flow, there is less residual polymer content. (2) In Example 4, since the heating was carried out in a mixture of nitrogen and air, there was less residual polymer content. (3) Comparative Example 5 was heated in air, so there was a lot of residual polymer content and the recycle packing could not be used. Industrial applicability

[0035] The recycle filler obtained in this invention is suitable for reuse in thermally conductive compositions and / or thermally conductive sheets as a heat dissipation material between heat-generating parts such as electrical / electronic components and heat sinks: TIM (Thermal Interface Material). Explanation of reference numerals in the attached figures

[0036] 1. Thermal conductivity measuring device 2. Sensors made of polyimide film 3a, 3b Thermally conductive sheet samples 4. Sensor front end 5. Electrodes for applying current 6. Electrodes for resistance measurement (electrodes for temperature measurement) 10. Heat dissipation structure 11a, 11b Thermally conductive sheets 12 Radiators 13 Electronic components 14 Wiring substrate 15 Heat absorber

Claims

1. A method for producing a thermally conductive filler, characterized by, A method for producing a thermally conductive filler from a thermally conductive composition raw material including a thermosetting resin and a thermally conductive filler, comprising: a thermal decomposition step of thermally decomposing the thermally conductive composition raw material in a low-oxygen atmosphere having an oxygen concentration of 10 vol.% or less; and a pulverization step of pulverizing the residue after the thermal decomposition, the pulverization step is performed so that the central particle diameter becomes 0.1 to 300 μm.

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

3. The method for producing a thermally conductive filler according to claim 1 or 2, wherein The low-oxygen atmosphere is at least one atmosphere selected from the group consisting of a non-active gas stream, a mixed gas stream of a non-active gas at 51 to 100 vol.% and air at 0 to 49 vol.%, a reduced pressure condition, and superheated water vapor.

4. The method of producing a thermally conductive filler according to any one of claims 1 to 3, wherein The pulverization step is at least one step selected from the group consisting of a ball mill, a pin mill, a chopper, a jet mill, a bead mill, a hammer mill, and an automatic mortar.

5. The method of producing a thermally conductive filler according to any one of claims 1 to 4, wherein The method further includes a classification step after the pulverization step.

6. The method of producing a thermally conductive filler according to claim 5, wherein The classification step is a screening using a screen.

7. The method of producing a thermally conductive filler according to any one of claims 1 to 6, wherein The thermosetting resin is a silicone polymer.

8. The method of producing a thermally conductive filler according to any one of claims 1 to 7, wherein The recycled filler obtained by the method for producing a thermally conductive filler has a Si atomic number concentration of 1 at% or less based on SEM-EDX analysis.

9. The method of producing a thermally conductive filler according to any one of claims 1 to 8, wherein The thermally conductive filler is at least one selected from the group consisting of alumina and aluminum nitride.

10. The method of producing a thermally conductive filler according to any one of claims 1 to 9, wherein In the thermally conductive composition raw material, 100 to 4000 parts by mass of the thermally conductive filler is compounded with respect to 100 parts by mass of the thermosetting resin.

11. The method of producing a thermally conductive filler according to any one of claims 1 to 10, wherein The thermally conductive composition raw material is a process scrap, a waste scrap, a product recycle, a stock exceeding a use period, or a trial product.

12. The method of producing a thermally conductive filler according to any one of claims 1 to 11, wherein The recycled filler obtained by the manufacturing method of the thermally conductive filler is further denoted as R a Si(OR') 4-a undergoes surface treatment, 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.

13. A method for manufacturing a thermally conductive resin composition, characterized in that, A recycled filler obtained by the method for producing a thermally conductive filler according to any one of claims 1 to 12 is mixed with a thermosetting resin to produce a thermally conductive resin composition.

14. The method of producing a thermally conductive resin composition according to claim 13, wherein The thermosetting resin is a silicone resin.

15. The method for producing a thermally conductive resin composition according to claim 13 or 14, wherein In the thermally conductive composition, 100 to 4000 parts by mass of the thermally conductive filler is compounded with respect to 100 parts by mass of the thermosetting resin.

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