A high-density boron nitride thermally conductive filler and its preparation method

Abstract

This invention provides a high-density boron nitride thermally conductive filler and its preparation method, relating to the field of nitride ceramic materials technology. The invention employs hydrophilically modified hexagonal boron nitride, using an aqueous calcium acetate solution as an additive. The boron nitride surface is hydrophilic, and under the action of water in the additive, lamellar slip occurs. Simultaneously, calcium acetate acts like a lubricant, further promoting the lamellar slip rearrangement of boron nitride. After granulation, high-density boron nitride particles are obtained. During the debinding process, calcium acetate decomposes to form calcium carbonate. During heat treatment, calcium carbonate further decomposes to form calcium oxide. The formed calcium oxide reacts with the oxide film on the surface of the boron nitride to generate a sintered liquid phase, simultaneously promoting the growth of lamellar boron nitride grains and improving the bonding strength, thereby obtaining a high-density boron nitride thermally conductive filler. When used in the preparation of polymer composites, this results in polymer composites with excellent thermal conductivity.

Description

Technical Field

[0001] This invention relates to the field of nitride ceramic materials technology, and in particular to a high-density boron nitride thermally conductive filler and its preparation method. Background Technology

[0002] Hexagonal boron nitride (BN) is a key thermally conductive filler for solving heat dissipation problems in high-power electronic devices due to its excellent thermal conductivity, dielectric properties, and chemical stability. However, in the preparation of polymer composites, the significant thickening effect of the hexagonal BN lamellar structure leads to a low filler content, greatly limiting the improvement of the composite's thermal conductivity. Spherical hexagonal BN ceramic powder is an ideal filler for preparing polymer composites with high processability, high filler content, and high thermal conductivity. Currently, spherical BN thermally conductive fillers can be prepared using methods such as spray granulation and centrifugal granulation. Due to its strong covalent bond characteristics, hexagonal BN is difficult to sinter without pressure; therefore, spherical BN prepared by these methods typically has a low density (<1.5 g / cm³). 3 During the preparation of polymer composites using high-shear dispersion, spherical boron nitride powder, due to its low density and strength, breaks down again into sheet-like powders, causing the composite to lose its processability.

[0003] The key to improving the filling performance of hexagonal nitrides lies in increasing their density. Currently, hot pressing sintering can produce nitrides with a density greater than 1.9 g / cm³. 3 Boron nitride ceramic materials have been reported to yield high-density boron nitride fillers by crushing and sieving hot-pressed boron nitride ceramics, which can meet the high-filling requirements of polymer composites. However, due to limitations in hot-pressing sintering equipment, the preparation cost of high-density boron nitride by hot-pressing sintering is high and the yield is low, limiting the application of this process in high thermal conductivity fillers. Therefore, there is an urgent need for a method to prepare high-density boron nitride with low cost and high yield. Summary of the Invention

[0004] The purpose of this invention is to provide a high-density boron nitride thermally conductive filler and its preparation method. The preparation method provided by this invention has low cost, high yield, and the prepared boron nitride thermally conductive filler has high density.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing high-density boron nitride thermally conductive filler, comprising the following steps:

[0007] (1) The hydrophilic modified hexagonal boron nitride powder was mixed with calcium acetate aqueous solution and then granulated to obtain granulated powder;

[0008] (2) The granulated powder obtained in step (1) is subjected to debinding and heat treatment in sequence to obtain high-density boron nitride thermally conductive filler.

[0009] Preferably, in step (1), the average particle size of the hydrophilic modified hexagonal boron nitride powder is 5-30 μm, and the average lamellar thickness of the hydrophilic modified hexagonal boron nitride powder is 0.5-2 μm.

[0010] Preferably, the mass concentration of the calcium acetate aqueous solution in step (1) is 5-15%.

[0011] Preferably, in step (1), the mass ratio of hydrophilic modified hexagonal boron nitride powder to calcium acetate aqueous solution is (10-20):1.

[0012] Preferably, the granulation pressure in step (1) is 200-300 MPa.

[0013] Preferably, the particle size of the granulated powder in step (1) is 50 to 500 μm.

[0014] Preferably, the temperature of glue removal in step (2) is 500-600℃, and the glue removal time is 1-4h.

[0015] Preferably, the heat treatment temperature in step (2) is 1550-1650℃ and the heat treatment time is 1-6h.

[0016] The present invention also provides a high-density boron nitride thermally conductive filler prepared by the preparation method described in the above technical solution.

[0017] Preferably, the density of the high-density boron nitride thermally conductive filler is 1.9–2.0 g / cm³. 3 The tap density of the high-density boron nitride thermally conductive filler is 0.9–1.1 g / cm³. 3 .

[0018] This invention provides a method for preparing high-density boron nitride thermally conductive filler, comprising the following steps:

[0019] (1) The hydrophilic modified hexagonal boron nitride powder is mixed with calcium acetate aqueous solution and then granulated to obtain granulated powder; (2) The granulated powder obtained in step (1) is subjected to debinding and heat treatment in sequence to obtain high-density boron nitride thermally conductive filler. This invention uses hydrophilic modified hexagonal boron nitride and calcium acetate aqueous solution as an additive. The surface of boron nitride is hydrophilic, and under the action of water in the additive, lamellar slip occurs. At the same time, calcium acetate has a similar effect to lubricating oil, which also promotes the lamellar slip rearrangement of boron nitride. After granulation, high-density boron nitride particles are obtained. During the debinding process, calcium acetate decomposes to form calcium carbonate. During the heat treatment process, calcium carbonate further decomposes to form calcium oxide. The formed calcium oxide reacts with the oxide film on the surface of boron nitride to generate a sintering liquid phase, which at the same time promotes the growth of lamellar boron nitride grains and improves the bonding strength, thereby obtaining high-density boron nitride thermally conductive filler. When preparing polymer composite materials, the polymer composite materials have excellent thermal conductivity. The preparation method provided by this invention is not limited by high-pressure sintering equipment, and has low cost and high yield. The results of the examples show that the density of the boron nitride thermally conductive filler prepared by the present invention is 1.9–2.0 g / cm³. 3 The tap density is 0.9–1.1 g / cm³. 3 . Attached Figure Description

[0020] Figure 1 The XRD pattern of the high-density boron nitride thermally conductive filler prepared in Example 1 of this invention;

[0021] Figure 2 SEM image of the high-density boron nitride thermally conductive filler prepared in Example 1 of this invention;

[0022] Figure 3 This is a SEM image of the high-density boron nitride thermally conductive filler prepared in Example 2 of the present invention. Detailed Implementation

[0023] This invention provides a method for preparing high-density boron nitride thermally conductive filler, comprising the following steps:

[0024] (1) The hydrophilic modified hexagonal boron nitride powder was mixed with calcium acetate aqueous solution and then granulated to obtain granulated powder;

[0025] (2) The granulated powder obtained in step (1) is subjected to debinding and heat treatment in sequence to obtain high-density boron nitride thermally conductive filler.

[0026] Unless otherwise specified, the present invention does not have any special limitation on the source of the raw materials, and products prepared by commercially available products or conventional preparation methods known to those skilled in the art are acceptable.

[0027] This invention involves mixing hydrophilic modified hexagonal boron nitride powder with an aqueous solution of calcium acetate and then granulating the mixture to obtain granulated powder.

[0028] In this invention, the average particle size of the hydrophilic modified hexagonal boron nitride powder is preferably 5–30 μm, more preferably 5 μm, 10 μm, 20 μm, or 30 μm; the average lamellar thickness of the hydrophilic modified hexagonal boron nitride powder is preferably 0.5–2 μm, more preferably 0.5 μm, 1 μm, 1.5 μm, or 2 μm. By limiting the average particle size and average lamellar thickness of the hydrophilic modified hexagonal boron nitride powder to the above ranges, this invention can further improve the density of boron nitride.

[0029] In this invention, the water contact angle of the hydrophilic modified hexagonal boron nitride powder is preferably <90°. This invention does not have a specific limitation on the source of the hydrophilic modified hexagonal boron nitride powder; commercially available products well-known to those skilled in the art or products prepared using conventional methods, as long as their water contact angle is <90°, are acceptable. In an embodiment of this invention, the preferred method for preparing the hydrophilic modified hexagonal boron nitride powder is to thermally oxidize the hexagonal boron nitride powder at 800°C for 4 hours in air to obtain the hydrophilic modified hexagonal boron nitride powder.

[0030] In this invention, the mass concentration of the calcium acetate aqueous solution is preferably 5-15%, more preferably 5%, 10%, 12%, or 15%. By limiting the mass concentration of the calcium acetate aqueous solution within the above range, this invention can further improve the density of boron nitride.

[0031] In this invention, the preferred mass ratio of the hydrophilic modified hexagonal boron nitride powder to the calcium acetate aqueous solution is (10-20):1, more preferably (14-20):1, and even more preferably (17-20):1. By limiting the mass ratio of the hydrophilic modified hexagonal boron nitride powder to the calcium acetate aqueous solution to the above range, this invention can further improve the density of boron nitride.

[0032] The present invention does not have any special limitations on the mixing operation of the hydrophilic modified hexagonal boron nitride powder and the calcium acetate aqueous solution. The two can be mixed evenly by means of material mixing techniques known to those skilled in the art.

[0033] In this invention, the granulation is preferably carried out in a dry roller press granulator; the granulation pressure is preferably 200-300 MPa, more preferably 200-275 MPa, and even more preferably 200-250 MPa. This invention does not impose a specific limitation on the granulation time, as long as the particle size of the granulated powder is within the specified range. Limiting the granulation pressure within the above-mentioned range further improves the density of boron nitride.

[0034] After granulation, the present invention preferably sieves the granulated product to obtain granulated powder. The present invention does not impose any special limitations on the sieving operation; any sieving technique well-known to those skilled in the art can be used to ensure that the particle size of the granulated powder is within a specified range.

[0035] In this invention, the particle size of the granulated powder is preferably 50–500 μm. By limiting the particle size of the granulated powder to this range, this invention ensures that the particle size of the prepared boron nitride is within this range, which can further improve the thermal conductivity of the composite material when used as a thermally conductive filler.

[0036] After obtaining the granulated powder, the present invention sequentially performs debinding and heat treatment on the granulated powder to obtain a high-density boron nitride thermally conductive filler.

[0037] In this invention, the temperature for degumming is preferably 500–600°C, more preferably 550–600°C; the degumming time is preferably 1–4 hours, more preferably 2–4 hours; and the degumming is preferably carried out in an air atmosphere. In this invention, during the degumming process, water in the calcium acetate aqueous solution evaporates, calcium acetate decomposes to form acetic acid and calcium carbonate, and the acetic acid volatilizes. By limiting the temperature and time of degumming within the above ranges, this invention ensures complete decomposition of calcium acetate while preventing the oxidation of boron nitride.

[0038] In this invention, the heat treatment temperature is preferably 1550–1650°C, more preferably 1600–1650°C; the heat treatment time is preferably 1–6 hours, more preferably 2–4 hours; and the heat treatment is preferably carried out in a nitrogen atmosphere. In this invention, during the heat treatment process, calcium carbonate decomposes to form calcium oxide, which reacts with the oxide film on the surface of boron nitride to generate a sintered liquid phase, promoting the growth of lamellar boron nitride grains and improving the bonding strength, resulting in a high-density boron nitride thermally conductive filler. This invention limits the heat treatment temperature and time to the above ranges, further improving the density of boron nitride.

[0039] After heat treatment, the present invention preferably cools the heat-treated product to obtain a high-density boron nitride thermally conductive filler.

[0040] The present invention does not impose any special limitations on the cooling operation; any cooling technique known to those skilled in the art can be used to cool the material to room temperature.

[0041] This invention employs hydrophilic modified hexagonal boron nitride, using calcium acetate aqueous solution as an additive. The surface of boron nitride is hydrophilic, and under the action of water in the additive, lamellar slip occurs. At the same time, calcium acetate acts like a lubricant, further promoting the lamellar slip rearrangement of boron nitride. After granulation, high-density boron nitride particles are obtained. During the debinding process, calcium acetate decomposes to form calcium carbonate. During the heat treatment process, calcium carbonate further decomposes to form calcium oxide. The formed calcium oxide reacts with the oxide film on the surface of boron nitride to generate a sintered liquid phase, which simultaneously promotes the growth of lamellar boron nitride grains and improves the bonding strength. By controlling the amount of each raw material, reaction temperature, and other process parameters, a high-density boron nitride thermally conductive filler is obtained, which gives the polymer composite material excellent thermal conductivity when it is prepared.

[0042] The present invention also provides a high-density boron nitride thermally conductive filler prepared by the preparation method described in the above technical solution.

[0043] In this invention, the density of the high-density boron nitride thermally conductive filler is preferably 1.9–2.0 g / cm³. 3 The tap density of the high-density boron nitride thermally conductive filler is preferably 0.9–1.1 g / cm³. 3 .

[0044] The boron nitride thermally conductive filler prepared by this invention has high density, which enables the polymer composite material to have excellent thermal conductivity when it is prepared.

[0045] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] The preparation method of the hydrophilic modified hexagonal boron nitride powder in each embodiment is as follows: the hexagonal boron nitride powder is thermally oxidized at 800°C for 4 hours in an air atmosphere to obtain the hydrophilic modified hexagonal boron nitride powder.

[0047] Example 1

[0048] (1) Surface hydrophilic modified hexagonal boron nitride powder with an average particle size of 5.0 μm and an average lamellar thickness of 0.5 μm was mixed evenly with a calcium acetate aqueous solution with a mass concentration of 15% (the mass ratio of surface hydrophilic modified hexagonal boron nitride powder to calcium acetate aqueous solution was 10:1), and granulated under a pressure of 300 MPa by a dry roller press granulator. Granulated powder with a particle size of 50 to 500 μm was obtained by sieving.

[0049] (2) The granulated powder obtained in step (1) is debonded at 600°C in air atmosphere for 4 hours, and then heat-treated at 1550°C in nitrogen atmosphere for 4 hours and cooled to obtain high-density boron nitride thermally conductive filler.

[0050] The particle size range of the high-density boron nitride thermally conductive filler prepared in Example 1 was measured to be 50–500 μm, and the density was 1.90 g / cm³. 3 The tap density is 0.90 g / cm³. 3 .

[0051] The high-density boron nitride thermally conductive filler prepared in Example 1 was subjected to XRD testing, and the obtained XRD pattern is shown below. Figure 1 As shown. From Figure 1 As can be seen from the data, the phase composition of the high-density boron nitride thermally conductive filler is h-BN, with no impurity phases. This may be because the impurity phases volatilize at high temperatures during the heat treatment process, or because the impurity phase content is too low to be detected.

[0052] The high-density boron nitride thermally conductive filler prepared in Example 1 was observed using scanning electron microscopy, and the SEM images are shown below. Figure 2 As shown. From Figure 2 As can be seen from the data, the prepared high-density boron nitride thermally conductive filler is composed of tightly packed, oriented lamellar BN sheets.

[0053] Example 2

[0054] (1) Surface hydrophilic modified hexagonal boron nitride powder with an average particle size of 10.0 μm and an average lamellar thickness of 1.0 μm was mixed evenly with a calcium acetate aqueous solution with a mass concentration of 12% (the mass ratio of surface hydrophilic modified hexagonal boron nitride powder to calcium acetate aqueous solution was 14:1), and granulated under a pressure of 275 MPa by a dry roller press granulator. Granulated powder with a particle size of 50 to 500 μm was obtained by sieving.

[0055] (2) The granulated powder obtained in step (1) is debonded at 600°C in air atmosphere for 4 hours, and then heat-treated at 1600°C in nitrogen atmosphere for 4 hours and cooled to obtain high-density boron nitride thermally conductive filler.

[0056] The particle size range of the high-density boron nitride thermally conductive filler prepared in Example 2 was measured to be 50–500 μm, and the density was 1.93 g / cm³. 3 The tap density is 0.97 g / cm³. 3 .

[0057] The high-density boron nitride thermally conductive filler prepared in Example 2 was subjected to XRD testing, and its phase composition was h-BN with no impurities.

[0058] The high-density boron nitride thermally conductive filler prepared in Example 2 was observed using scanning electron microscopy, and the SEM images are shown below. Figure 3 As shown. From Figure 3 As can be seen from the data, the prepared high-density boron nitride thermally conductive filler is composed of tightly packed, oriented lamellar BN sheets.

[0059] Example 3

[0060] (1) Surface hydrophilic modified hexagonal boron nitride powder with an average particle size of 20.0 μm and an average lamellar thickness of 1.5 μm was mixed evenly with a calcium acetate aqueous solution with a mass concentration of 10% (the mass ratio of surface hydrophilic modified hexagonal boron nitride powder to calcium acetate aqueous solution was 17:1), and granulated under a pressure of 250 MPa by a dry roller press granulator. Granulated powder with a particle size of 50 to 500 μm was obtained by sieving.

[0061] (2) The granulated powder obtained in step (1) is debonded at 600°C in air atmosphere for 4 hours, and then heat-treated at 1600°C in nitrogen atmosphere for 4 hours and cooled to obtain high-density boron nitride thermally conductive filler.

[0062] The particle size range of the high-density boron nitride thermally conductive filler prepared in Example 3 was measured to be 50–500 μm, and the density was 1.96 g / cm³. 3 The tap density is 1.03 g / cm³. 3 .

[0063] The high-density boron nitride thermally conductive filler prepared in Example 3 was subjected to XRD testing, and its phase composition was h-BN with no impurities.

[0064] The high-density boron nitride thermally conductive filler prepared in Example 3 was observed using a scanning electron microscope. The prepared high-density boron nitride thermally conductive filler was formed by tightly packed, oriented lamellar BN.

[0065] Example 4

[0066] (1) Surface hydrophilic modified hexagonal boron nitride powder with an average particle size of 30.0 μm and an average lamellar thickness of 2.0 μm was mixed evenly with a calcium acetate aqueous solution with a mass concentration of 5% (the mass ratio of surface hydrophilic modified hexagonal boron nitride powder to calcium acetate aqueous solution was 20:1), and granulated under a pressure of 200 MPa by a dry roller press granulator. Granulated powder with a particle size of 50 to 500 μm was obtained by sieving.

[0067] (2) The granulated powder obtained in step (1) is debonded at 600°C in air atmosphere for 4 hours, and then heat-treated at 1650°C in nitrogen atmosphere for 4 hours. After cooling, a high-density boron nitride thermally conductive filler is obtained.

[0068] The particle size range of the high-density boron nitride thermally conductive filler prepared in Example 4 was measured to be 50–500 μm, and the density was 2.0 g / cm³. 3 The tap density is 1.10 g / cm³. 3 .

[0069] The high-density boron nitride thermally conductive filler prepared in Example 4 was subjected to XRD testing, and its phase composition was h-BN with no impurities.

[0070] The high-density boron nitride thermally conductive filler prepared in Example 4 was observed using a scanning electron microscope. The prepared high-density boron nitride thermally conductive filler was formed by tightly packed, oriented lamellar BN.

[0071] Examples 5-8, Comparative Examples 1-9

[0072] Boron nitride was prepared by changing the average particle size, mass ratio of surface-modified hexagonal boron nitride powder (h-BN) to calcium acetate aqueous solution, and concentration of calcium acetate aqueous solution in Example 1 according to Table 1. The density and tap density of the obtained boron nitride are shown in Table 1.

[0073] Table 1 shows the average particle size, mass ratio of surface-modified hexagonal boron nitride powder to calcium acetate aqueous solution, concentration of calcium acetate aqueous solution, density and tap density of the prepared boron nitride in Examples 5-8 and Comparative Examples 1-9.

[0074]

[0075]

[0076] As shown in Table 1, when the average particle size of the surface-hydrophilic modified hexagonal boron nitride powder is less than 5 μm or greater than 30 μm, the density and tap density of the obtained boron nitride both decrease. When the mass ratio of surface-hydrophilic modified hexagonal boron nitride powder to calcium acetate aqueous solution is higher than 10:1 or lower than 20:1, the density and tap density of the obtained boron nitride both decrease. When the concentration of calcium acetate is less than 5 wt% or greater than 15%, the density and tap density of the obtained boron nitride both decrease, and when it is higher than 15%, impurity phase formation is detected.

[0077] Examples 9-12, Comparative Examples 10-13

[0078] Boron nitride was prepared by changing the granulation pressure and heat treatment temperature in Example 2 according to Table 2. The density and tap density of the prepared boron nitride are shown in Table 2.

[0079] Table 2 shows the granulation pressure, heat treatment temperature, density, and tap density of the boron nitride prepared in Examples 9-12 and Comparative Examples 10-13.

[0080] Example 9 200 1600 1.91 0.90 Example 10 250 1600 1.93 0.94 Example 11 300 1600 1.95 1.01 Example 12 275 1650 1.92 0.94 Comparative Example 10 175 1600 1.81 0.79 Comparative Example 11 325 1600 1.95 1.01 Comparative Example 12 275 1500 1.89 0.88 Comparative Example 13 275 1700 1.87 0.86

[0081] As can be seen from Table 2, when the granulation roller pressure is less than 200 MPa, the density and tap density of the obtained boron nitride both decrease, while when it is greater than 300 MPa, the density and tap density do not increase significantly; when the sintering temperature is below 1550℃ or above 1650℃, the density and tap density of the obtained boron nitride both decrease.

[0082] Application examples

[0083] The high-density boron nitride prepared in Examples 1-4 was mixed with bisphenol A type E51 epoxy resin under vacuum conditions. The mass ratio of boron nitride to bisphenol A type E51 epoxy resin was 50:50 (the mass content of boron nitride in the polymer composite material was 50%). The polymer composite material was obtained by curing at 160°C for 4 hours.

[0084] The thermal conductivity of the prepared polymer composite material was measured using the flat plate thermal conductivity method, and the results are shown in Table 3.

[0085] Table 3 Thermal conductivity of polymer composites prepared from high-density boron nitride in Examples 1-4

[0086] Example 1 1.81 Example 2 1.87 Example 3 1.92 Example 4 1.98

[0087] As can be seen from Table 3, the high-density boron nitride thermally conductive filler prepared in this invention has a high filling amount in the polymer composite material, and the prepared polymer composite material has excellent thermal conductivity.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-density boron nitride thermally conductive filler, comprising the following steps: (1) The hydrophilic modified hexagonal boron nitride powder is mixed with calcium acetate aqueous solution and then granulated to obtain granulated powder; the average particle size of the hydrophilic modified hexagonal boron nitride powder is 5~30μm, and the average lamellar thickness of the hydrophilic modified hexagonal boron nitride powder is 0.5~2μm; the mass concentration of the calcium acetate aqueous solution is 5~15%; the mass ratio of the hydrophilic modified hexagonal boron nitride powder to the calcium acetate aqueous solution is (10~20):1; the granulation is carried out in a dry roller press granulator; (2) The granulated powder obtained in step (1) is subjected to debinding and heat treatment in sequence to obtain high-density boron nitride thermally conductive filler.

2. The preparation method according to claim 1, characterized in that, The granulation pressure in step (1) is 200~300MPa.

3. The preparation method according to claim 1, characterized in that, The particle size of the granulated powder in step (1) is 50~500μm.

4. The preparation method according to claim 1, characterized in that, The temperature for discharging glue in step (2) is 500~600℃, and the discharging time is 1~4h.

5. The preparation method according to claim 1, characterized in that, The heat treatment temperature in step (2) is 1550~1650℃, and the heat treatment time is 1~6h.

6. The high-density boron nitride thermally conductive filler prepared by the preparation method according to any one of claims 1 to 5.

7. The high-density boron nitride thermally conductive filler according to claim 6, characterized in that, The density of the high-density boron nitride thermally conductive filler is 1.9~2.0 g / cm³. 3 The tap density of the high-density boron nitride thermally conductive filler is 0.9~1.1 g / cm³. 3 .

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