THERMAL CONDUCTIVE FILLER AND PREPARATION METHOD THEREOF

Abstract

A method to prepare a thermal conductive filler, particularly a thermal conductive filler for preparation of a thermal conductive material with reduced viscosity, comprising the step of dry mixing a platelet boron nitride with a fumed silica or a fumed metal oxide with a primary particle size of 1-200 nm. A thermal conductive filler, a thermal conductive material and an electronic device are also provided.

Claims

1-15. (canceled)

16. A method for preparing a thermal conductive filler, comprising the step: (i) dry mixing a platelet boron nitride and a fumed silica or a fumed metal oxide with a primary particle size of about 1-200 nm, and optionally the following steps; (ii) mixing a silane into the mixture obtained in step (i); (iii) heating the mixture obtained in step (ii).

17. The method of claim 16, wherein step (i) does not comprise calcination or chemical treatment of the boron nitride.

18. The method of claim 16, wherein the mixing in step (i) is done at a speed of above 100 rpm for at least 5 seconds.

19. The method of claim 16, wherein the average particle size of the platelet boron nitride is 1-50 μm.

20. The method of claim 16, wherein the amount of the fumed silica or fumed metal oxide is 0.1-10 wt. % based on the weight of the boron nitride.

21. The method of claim 16, wherein: the fumed metal oxide comprises a primary particle size of 5-100 nm; the platelet boron nitride comprises an average particle size of 1-50 μm; and the fumed silica or fumed metal oxide is present in an amount of 2-5 wt. % based on the weight of the boron nitride.

22. The method of claim 16, wherein the fumed silica or fumed metal oxide is selected from the group consisting of: fumed hydrophilic silicas; fumed hydrophilic metal oxides; fumed hydrophobic silicas; and fumed hydrophobic metal oxides.

23. The method of claim 22, wherein the fumed silica or the fumed metal oxide is a fumed hydrophobic silica or a fumed hydrophobic metal oxide.

24. The method of claim 22, wherein: the fumed metal oxide comprises a primary particle size of 5-100 nm; the platelet boron nitride comprises an average particle size of 1-50 μm; and the fumed silica or fumed metal oxide is present in an amount of 2-5 wt. % based on the weight of the boron nitride.

25. The method of claim 16, comprising the steps: (i) dry mixing a platelet boron nitride and a fumed silica or a fumed metal oxide with a primary particle size of about 1-200 nm; (ii) mixing a silane into the mixture obtained in step (i); (iii) heating the mixture obtained in step (ii).

26. The method of claim 25, wherein the fumed silica or fumed metal oxide is selected from the group consisting of: fumed hydrophilic silicas; fumed hydrophilic metal oxides; fumed hydrophobic silicas; and fumed hydrophobic metal oxides.

27. The method of claim 25, wherein the fumed silica or fumed metal oxide is a fumed hydrophobic silica or a fumed hydrophobic metal oxide.

28. The method of claim 25, wherein: the fumed metal oxide comprises a primary particle size of 5-100 nm; the platelet boron nitride comprises an average particle size of 1-50 μm; and the fumed silica or fumed metal oxide is present in an amount of 2-5 wt. % based on the weight of the boron nitride.

29. Thermal conductive material comprising: A) a resin material; B) a thermal conductive filler made by the method of claim 16 dispersed in the resin material; C) a solvent, preferably methyl ethyl ketone; D) a cross-linker; and optionally E) a catalyst.

30. The thermal conductive material of claim 29, wherein the method for making the thermal conductive filler of paragraph B) comprises the steps: (i) dry mixing a platelet boron nitride and a fumed silica or a fumed metal oxide with a primary particle size of about 1-200 nm; (ii) mixing a silane into the mixture obtained in step (i); (iii) heating the mixture obtained in step (ii).

31. The thermal conductive material of claim 30, wherein the method for making the thermal conductive filler of paragraph B) does not comprise calcination or chemical treatment of boron nitride.

32. The thermal conductive material of claim 30, wherein, in paragraph i), the fumed silica or fumed metal oxide is selected from the group consisting of: fumed hydrophilic silicas; fumed hydrophilic metal oxides; fumed hydrophobic silicas; and fumed hydrophobic metal oxides.

33. The thermal conductive material of claim 32, wherein the fumed silica or fumed metal oxide is a hydrophobic silica or a fumed hydrophobic metal oxide.

34. A thermal conductive filler comprising a platelet boron nitride powder, wherein fumed silica or fumed metal oxide particles are physically fixed on the surface of the platelet boron nitride powder, and the average particle size of the platelet boron nitride is 1-50 μm; the fumed silica or fumed metal oxide has a primary particle size of 1-200 nm; and the amount of the fumed silica or fumed metal oxide is 0.1-10 wt. %, based on the weight of the boron nitride.

35. The thermal conductive filler of claim 34, wherein: the average particle size of the platelet boron nitride is 2-20 μm; the fumed silica or the fumed metal oxide has a primary particle size of 5-100 nm; and the amount of the fumed silica or the fumed metal oxide is 2-5 wt. % based on the weight of the boron nitride.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0070] FIG. 1 shows SEM photos of the thermal conductive filler prepared in Sample E of Example 1. FIG. 1A shows a low magnification (50000×) SEM photo, FIG. 1B shows a high magnification (200000×) SEM photo.

[0071] FIG. 2 shows the viscosity of the epoxy thermal conductive materials with different surface treated hBN PCTP 12 prepared in Example 1.

[0072] FIG. 3 shows the viscosity of the epoxy thermal conductive materials with different surface treated hBN PCTP 12 with or without silane treatment, prepared in Example 2.

[0073] FIG. 4 shows the viscosity of the epoxy thermal conductive materials with different surface treated hBN PCTP 8 prepared in Example 3.

[0074] FIG. 5 shows the viscosity of the epoxy thermal conductive materials with different mixing speed for Sample D prepared in Example 4.

[0075] FIG. 6 shows the viscosity of the epoxy thermal conductive materials with different amount of AEROSIL® R 711 in boron nitride, prepared in Example 5.

[0076] FIG. 7 shows the viscosity of the PPE thermal conductive materials with different surface treated hBN prepared in Example 6.

[0077] FIG. 8 shows the viscosity of the polybutadiene thermal conductive materials with different surface treated hBN prepared in Example 7.

[0078] FIG. 9 shows the viscosity of the epoxy thermal conductive materials with different surface treated hBN PCTP 12 prepared in Comparative Example 6.

DETAILED DESCRIPTION OF THE INVENTION

[0079] To describe the content and effects of the present invention in detail, the present invention will be further described below in combination with the examples and comparative examples and with the related drawings.

Equipment

[0080] The SEM photos were taken by Sirion 200 SEM from ThermoFisher Scientific (Oregon, USA).

[0081] Before SEM test, the thermal conductive filler sample was coated with gold by an ion sputter coater (Model ETD-2000C from Beijing Elaborate Technology Development Co., Ltd., Beijing, China) for 30 s.

[0082] The mixing was performed by dual asymmetric centrifugal mixing which was carried out with a SpeedMixer from FlackTek, Inc. (South Carolina, USA). The Turbula® T2F mixer from WAB Machaniery (Shenzhen) Co., Ltd. (Guangdong, China) was used in Example 4.

[0083] The viscosity was determined by a Brookfield DV-II+Pro Viscometer (Brookfield Co., Middleboro, Mass., USA). The measurements were tested under speeds of 6 rpm and 60 rpm.

[0084] The thermal conductivity was tested by laser flash method with a LFA 467 HyperFlash light flash apparatus from Netzsch-Geratebau GmbH, Germany.

Materials

[0085] The hBN used in the examples were PCTP 8 and PCTP 12 from Saint-Gobain. Table 1 listed the parameters of these two hBN samples. The AEROSIL® silicas, SIPERNAT® silicas and AEROXIDE® aluminum oxides from Evonik Industries AG were employed in examples or comparative examples. The ADMAFINE® silicas are from Admatechs Company Limited. The parameters of these silica or metal oxides are listed in Table 2.

TABLE-US-00001 TABLE 1 parameters of different boron nitride samples Average particle Tamped BET specific Sample size, μm density, g/cm3 surface area, m2/g PCTP 8 8 0.5 3 PCTP 12 12 0.5 4

TABLE-US-00002 TABLE 2 parameters of different silicas and metal oxides Primary/ Tamped BET Silica or median density, surface area, metal oxide particle size g/L m2/g AEROSIL ® 200 12 nm 50 200 AEROSIL ® R 974 12 nm 50 200 AEROSIL ® R 711 12 nm 60 200 AEROXIDE ® Alu C 13 nm 50 100 AEROXIDE ® Alu C 13 nm 50 100 805 SIPERNAT ® 622 4.5 μm 70 180 LS ADMAFINE ® 0.2~0.3 μm — 13~18 SO-C1 ADMAFINE ® 0.7~1.3 μm —   3~5.5 SO-C4 ADMAFINE ® 1.8~2.3 μm — 1.3~2.5  SO-C6 * Primary particle size for AEROSIL ® fumed silicas and AEROXIDE ® fumed aluminas, and median particle size for SIPERNAT ® precipitated silicas and ADMAFINE ® silicas. AEROSIL ® R 974 and AEROSIL ® R 711 are hydrophobic fumed silicas. AEROSIL® 200 is a hydrophilic fumed silica. AEROXIDE ® Alu C 805 is a hydrophobic fumed aluminum oxide. AEROXIDE ® Alu C is a hydrophilic fumed aluminum oxide. SIPERNAT ® 622 LS is a hydrophilic precipitated silica. ADMAFINE ® SO-C1, ADMAFINE ® SO-C4, ADMAFINE ® SO-C6 are hydrophilic silicas made by vaporized metal combustion method, and such silicas are not within the scope of the fumed silica of the invention.

[0086] The silanes used in the examples were Dynasylan® Glymo (3-glycidyloxypropyltrimethoxysilane), Dynasylan® 6498, which is a vinyl silane concentrate (oligomeric siloxane) containing vinyl and ethoxy groups, Dynasylan® MEMO which is a methacrylfunctional silane, and Dynasylan® 6598 which is an oligomeric siloxane containing vinyl, propyl and ethoxy groups. All these silanes are commercially available from Evonik Industries AG.

[0087] The resins used in the examples were D.E.R.™ 331 Liquid Epoxy Resin (from Dow Chemical), which is a liquid reaction product of epichlorohydrin and bisphenol A, NORYL™ SA9000, a polyphenylene ether (PPE) resin from SABIC, and POLYVEST® HT, a hydroxyl-terminated liquid polybutadiene resin from Evonik Industries AG.

[0088] In the examples, the cross-linker used was commercial 2-cyanoguanidine and the catalyst was commercial 2-methylimidazole to solidify the epoxy resin.

Comparative Examples 1 and 2

[0089] Thermal conductive material Sample A without silica/metal oxide nor silane treatment was prepared as Comparative Example 1 as follows:

[0090] 28 g D.E.R.™ 331 epoxy resin, 24 g methyl ethyl ketone (MEK) as a solvent and 28 g of a boron nitride PCTP 12 were mixed together with the dual asymmetric centrifugal mixing at 2500 rpm for 30 s.

[0091] Thermal conductive material Sample B with silane but without any oxide treatment was prepared as Comparative Example 2 as follows:

[0092] 50 g of boron nitride PCTP 12 was placed in a 50 mL plastic vessel. Then 1 g Dynasylan® Glymo was added into the vessel, followed by tumbling with dual asymmetric centrifugal mixing at 2500 rpm for 30 s, then the mixture was heated in an oven at 105° C. for 1 hour to obtain a thermal conductive filler. After the thermal conductive filler was prepared, 28 g D.E.R.™ 331 epoxy resin, 24 g methyl ethyl ketone (MEK) as a solvent and 28 g treated boron nitride were mixed together with the dual asymmetric centrifugal mixing at 2500 rpm for 30 s.

[0093] The final thermal conductive materials were tested for viscosity under the rotor speed of 6 rpm and 60 rpm with a Brookfield DV-II+Pro Viscometer.

Example 1

[0094] Thermal conductive material Samples C-G were prepared as follows, [0095] a) preparation of thermal conductive fillers: [0096] 1) 47.5 g of boron nitride PCTP 12 was placed in a 50 mL plastic vessel. [0097] 2) Next, 2.5 g of AEROSIL® 200 or AEROSIL® R 974 or AEROSIL® R 711 or AEROXIDE® Alu C or AEROXIDE® Alu C 805 was put into the vessel. [0098] 3) The mixture in the vessel was tumbled with a dual asymmetric centrifugal mixer at 2500 rpm for 30 s. [0099] 4) Then 1 g Dynasylan® Glymo was added into the vessel, followed by tumbling with dual asymmetric centrifugal mixing at 2500 rpm for 30 s, then the mixture was heated in an oven at 105° C. for 1 hour.

[0100] In the prepared thermal conductive filler, the loading of fumed silica or fumed metal oxide was 5 wt. % and loading of silane was 2 wt. % based on the weight of untreated boron nitride. [0101] b) preparation of thermal conductive materials:

[0102] After the thermal conductive filler was prepared, 28 g D.E.R.™ 331 epoxy resin, 24 g methyl ethyl ketone (MEK) as solvent and 28 g thermal conductive filler (treated boron nitride) were mixed together with the dual asymmetric centrifugal mixing at 2500 rpm for 30 s. The content of thermal conductive filler in the thermal conductive material was 50% after the solvent MEK was evaporated.

[0103] The final thermal conductive materials were tested for viscosity under the rotor speed of 6 rpm and 60 rpm with a Brookfield DV-II+Pro Viscometer.

[0104] The viscosity results are summarized in Table 3. The comparison graphs are shown in FIG. 2.

TABLE-US-00003 TABLE 3 Effect of different fumed silica or fumed metal oxide in thermal conductive materials with PCTP 12 hBN on viscosity at 6 rpm and 60 rpm wt. % Fumed Viscosity Viscosity silica or fumed wt. % at 6 rpm, at 60 rpm, Samples Description metal oxide Silane cP cP A PCTP 12 0 0 3099 886 B PCTP 12/Dynasylan ® 0 2% 1300 450 Glymo C PCTP 12/AEROSIL ® 5% AEROSIL ® 2% 210 107 200/Dynasylan® Glymo 200 D PCTP 12/AEROSIL ® 5% AEROSIL ® 2% 85 61 R 711/Dynasylan® Glymo R 711 E PCTP 12/AEROSIL ® 5% AEROSIL ® 2% 160 66 R974/Dynasylan ® Glymo R974 F PCTP 12/AEROXIDE ® 5% 2% 90 69 Alu C/Dynasylan ® Glymo AEROXIDE ® Alu C G PCTP 12/AEROXIDE ® 5% 2% 10 38 Alu C 805/Dynasylan® AEROXIDE ® Glymo Alu C 805

[0105] As shown in Table 3 and FIG. 2, compared with Comparative Examples 1 and 2 (Samples A and B), all the fumed oxides tried in Samples C-G of Example 1 could greatly decrease the viscosity. Notably, thermal conductive materials with AEROSIL® R 974 and AEROSIL® R 711 treated hBN showed lower viscosity than the one with AEROSIL® 200, and similarly, thermal conductive material with AEROXIDE® Alu C 805 showed lower viscosity than the one with AEROXIDE® Alu C. This indicated that hydrophobic fumed silica or fumed metal oxides performed better in viscosity decrease than hydrophilic fumed silica or fumed metal oxides.

[0106] FIG. 1 shows SEM photos of the thermal conductive filler prepared in Sample E of Example 1. FIG. 1A shows that fumed silica AEROSIL® R 974 particles are homogeneously distributed on the surface of hBN. FIG. 1B shows that fumed silica AEROSIL® R 974 particles are attached to the surface of hBN. The photos indicate that fumed silica or fumed metal oxides could be attached on the surface of hBN with good dispersibility.

Example 2

hBN without Silane Treatment

[0107] The viscosity reduction performance of thermal conductive fillers without silane treatment were tested in comparison with those in Example 1.

[0108] Samples H and I were prepared with the same method as for Sample C in Example 1 except that no silane was added (0 wt. % silane).

[0109] The sample information and viscosity results are summarized in Table 4.

TABLE-US-00004 TABLE 4 Effect of different fumed silica or fumed metal oxide in thermal conductive materials with PCTP 12 hBN on viscosity at 6 rpm and 60 rpm, with or without silane treatment viscosity viscosity wt. % fumed wt. % at 6 rpm, at 60 rpm, samples description oxide silane cP cP A PCTP 12 0 0 3099 886 B PCTP 12/ 0 2% 1300 450 Dynasylan ® Glymo C PCTP 12/ 5% 2% 210 107 AEROSIL ® AEROSIL ® 200/Dynasylan ® 200 Glymo H PCTP 12/ 5% 0 250 92.5 AEROSIL ® AEROSIL ® R 711 R 711 D PCTP 12/ 5% 2% 85 61 AEROSIL ® R AEROSIL ® 711/Dynasylan® R 711 Glymo I PCTP 12/ 5% 0 34 46 AEROXIDE ® AEROXIDE ® Alu C 805 Alu C 805 G PCTP 12/ 5% 2% 10 38 AEROXIDE ® AEROXIDE ® Alu C 805/ Alu C 805 Dynasylan ® Glymo

[0110] As shown in Table 4 and FIG. 3, in comparison with Comparative Examples 1 and 2 (Samples A and B), Sample H of Example 2 treated with hydrophobic fumed silica but without silane showed substantially decreased viscosity similar to Sample C of Example 1, indicating that hydrophobic fumed silica could reach similar viscosity decrease performance as hydrophilic fumed silica with silane. In comparison with Sample D of Example 1, the viscosity reduction of Sample H of Example 2 was worse, indicating that treatment with both hydrophobic fumed silica and silane could further decrease the viscosity compared with treatment with hydrophobic fumed oxide only. Similarly, among Samples A, B, I, G, Sample I of Example 2 treated with hydrophobic alumina had an obviously decreased viscosity, but the viscosity reduction was less than for Sample G of Example 1 with both alumina and silane treatment. It shows that hydrophobic oxide could obviously reduce the viscosity when silane was not used, but silane treatment could further decrease the viscosity.

Comparative Example 3

Different Boron Nitride

[0111] Sample J was prepared as Comparative Example 3 with the same method as for Sample A of Comparative Example 1 except that boron nitride PCTP 8 was used in this example instead of PCTP 12.

Example 3

Different Boron Nitride

[0112] Samples K and L of Example 3 were prepared with the same method as Sample C of Example 1 except that boron nitride PCTP 8 was used in this example instead of PCTP 12.

[0113] The viscosity results of Samples J, K and L are summarized in Table 5. FIG. 4 compares the performance.

TABLE-US-00005 TABLE 5 Effect of different fumed silica or fumed metal oxide in thermal conductive materials with PCTP 8 hBN on viscosity at 6 rpm and 60 rpm wt. % Fumed wt. % Viscosity at Viscosity at Samples Description silica or oxide Silane 6 rpm, cP 60 rpm, cP J PCTP 8  0 0 3359 1100 K PCTP 8/AEROSIL ® 5% AEROSIL ® 2% 60 65 200/Dynasylan ® Glymo 200 L PCTP 8/AEROSIL ® R 5% AEROSIL ® 2% 55 57 711/Dynasylan ® Glymo 200

[0114] As shown in Table 5 and FIG. 4, similarly to PCTP 12, fumed silica and metal oxides show significant viscosity decrease effect on PCTP 8 samples. It can be concluded that the method of the invention is effective to different hBN materials.

Example 4

Different Mixing Speed

[0115] Compared with Example 1, different mixing speed was applied in this example.

[0116] Thermal conductive material samples D-101, D-1000, D-1500 and D-2500 were prepared with different mixing speeds. Low speed Turbula mixing at 101 rpm and high speed dual asymmetric centrifugal mixing at 1000 rpm, 1500rpm and 2500rpm were applied in the mixing of PCTP 12 boron nitride and 5 wt. % AEROSIL® R 711, and also applied in mixing of PCTP 12 boron nitride and 2 wt. % saline Dynasylan® Glymo. The other steps were same as Sample D of Example 1.

[0117] The viscosity results at different mixing speeds are summarized in FIG. 5. Compared with the viscosity of Sample A in Comparative Example 1, the viscosity of the thermal conductive materials decreased gradually when the fumed silica and the silane was added under the mixing speed of 101 rpm, 1000 rpm, 1500 rpm and 2500 rpm, respectively. In addition, the viscosity at mixing speed 1500 rpm and 2500 rpm showed significant decrease compared to the viscosity at mixing speed 101 rpm and 1000 rpm. The viscosity at mixing speed 2500 rpm showed significant decrease when compared to the viscosity at mixing speed 1500 rpm. Such reduction of viscosity is surprising and indicates that mixing speed is important to viscosity decrease. For this example, mixing speed above 101 rpm in preparation of thermal conductive filler was effective in decreasing the viscosity of the thermal conductive material, and mixing speed above 1500 rpm was preferred to reach a better effect.

Example 5

Different Fumed Oxide Loading

[0118] To study the influence of different fumed silica loading, thermal conductive materials with 0 wt. %, 2 wt. %, 5 wt. %, 7 wt. %, 10 wt. %, respectively, of AEROSIL® R 711 in boron nitride was prepared with the same method as for Sample D of Example 1 except for the different silica loading.

[0119] The viscosity results with the rotor speed of 6 rpm and 60 rpm are summarized in FIG. 6.

[0120] Addition of AEROSIL® R 711 could significantly reduce the viscosity of the thermal conductive material, but the viscosity increased only slightly when the amount of AEROSIL® R 711 was more than 5wt. %. The optimum loading for the lowest viscosity was between 2 wt. % to 5 wt. %.

Comparative Examples 4 and 5

Different Resin for Thermal Conductive Materials

[0121] The thermal conductive material Sample M without any metal oxide or silane treatment was prepared as Comparative Example 4 as follows.

[0122] 56 g 50 wt. % PPE resin solution with MEK as solvent was added with 28 g hBN PCTP 12. The mixture was mixed with a dual asymmetric centrifugal mixing under 2500 rpm for 30 s.

[0123] The thermal conductive material Sample N with silane but without oxide treatment was prepared as Comparative Example 5 as follows.

[0124] 50 g of boron nitride PCTP 12 was placed in a 50 mL plastic vessel. Then 1 g of Dynasylan® 6498 was added into the vessel, followed by tumbling with dual asymmetric centrifugal mixing at 2500 rpm for 30 s, then the mixture was heated in an oven at 105° C. for 1 hour to obtain a thermal conductive filler. After the thermal conductive filler was prepared, 28 g of this thermal conductive filler was added to 56 g 50 wt. % PPE resin solution with MEK as a solvent. Then the mixture was mixed by the dual asymmetric centrifugal mixer at 2500 rpm for 30 s to obtain thermal conductive material Sample N.

Example 6

Different Resin for Thermal Conductive Material

[0125] In this example, a different resin, polyphenylene ether (PPE) resin NORYL™ SA9000 was used.

[0126] Thermal conductive materials Samples O, P and Q of Example 6 were prepared as follows, [0127] a) Thermal conductive fillers (surface treated hBN) of Samples O, P and Q were prepared by the same method as thermal conductive fillers of Samples C, D, G respectively in Example 1 except that Dynasylan® 6498 was chosen as silane for surface treatment instead of Dynasylan® Glymo. [0128] b) Then a 50 wt. % PPE resin NORYL™ SA9000 solution was prepared in MEK solvent by adding 500 g NORYL™ SA9000 into 500 g MEK solvent in a beaker. Magnetic stirrer was used to make the PPE dissolved in MEK solvent. Then 56 g 50 wt. % PPE solution was added with 28 g the above prepared thermal conductive fillers. The mixture was mixed with dual asymmetric centrifugal mixing under 2500 rpm for 30 s.

[0129] The final thermal conductive materials were tested for viscosity under the rotor speed of 6 rpm and 60 rpm with Brookfield DV-II+Pro Viscometer. The viscosity is shown in FIG. 7 and Table 6.

TABLE-US-00006 TABLE 6 Effect of different fumed silica or fumed metal oxide in thermal conductive materials with PCTP 12 hBN on viscosity of PPE resin at 6 rpm and 60 rpm wt. % Fumed silica or wt. % Viscosity at Viscosity at Samples Description fumed metal oxide Silane 6 rpm, cP 60 rpm, cP M PCTP 12 0 0 4755 2434 N PCTP 12/Dynasylan ® 0 2% 3433 1936 6498 O PCTP 12/AEROSIL ® 5% AEROSIL ® 200 2% 1533 1005 200/Dynasylan ® 6498 P PCTP 12/AEROSIL ® R 5% AEROSIL ® 2% 1692 1020 711/Dynasylan® 6498 R 711 Q PCTP 12/AEROXIDE ® 5%AEROXIDE  ® 2% 1488  928 Alu C 805/Dynasylan ® Alu C805 6498

[0130] FIG. 7 and Table 6 show that fumed silica and metal oxides decrease the viscosity of the PPE thermal conductive material. This indicates the viscosity reduction effect of the thermal conductive filler of the invention can be applied to different thermal conductive materials with various resins.

Comparative Example 1

PH

[0131] Thermal conductive material Sample R without silica/metal oxide or silane treatment was prepared according to the same method as that of Sample A of Comparative Example 1 except that hydroxyl-terminated liquid polybutadiene POLYVEST® HT was used in Comparative Example 1-PH instead of D.E.R.™ 331 epoxy resin.

Example 7

Different Resin for Thermal Conductive Material

[0132] In this example, a different resin, hydroxyl-terminated liquid polybutadiene POLYVEST® HT was used.

[0133] Thermal conductive materials Samples S and T of Example 7 were prepared as follows, [0134] a) Thermal conductive fillers (surface treated hBN) of Samples S and T were prepared by the similar method as thermal conductive fillers of Sample G in Example 1 except that Dynasylan® MEMO was used for Sample S and Dynasylan® 6598 was used for Sample T as silane for surface treatment instead of Dynasylan® Glymo. [0135] b) Then a 50 wt. % polybutadiene POLYVEST® HT solution was prepared in MEK solvent by adding 500 g POLYVEST® HT into 500 g MEK solvent in a beaker. Magnetic stirrer was used to make the POLYVEST® HT dissolved in MEK solvent. Then 50 g 50 wt. % POLYVEST® HT solution was added with 25 g the above prepared thermal conductive fillers. The mixture was mixed with dual asymmetric centrifugal mixing under 2500 rpm for 30 s.

[0136] The final thermal conductive materials were tested for viscosity under the rotor speed of 6 rpm and 60 rpm with Brookfield DV-II+Pro Viscometer. The viscosity is shown in FIG. 8 and Table 7.

TABLE-US-00007 TABLE 7 Effect of different fumed silica or fumed metal oxide in thermal conductive materials with PCTP 12 hBN on viscosity of polybutadiene resin at 6 rpm and 60 rpm wt.% Fumed silica Viscosity Viscosity or fumed metal wt. % at 6 rpm, at 60 rpm, Samples Description oxide Silane cP cP R PCTP 12 0 0 1940 662 S PCTP 12/AEROXIDE ® 5% AEROXIDE ® 2%  540 202 Alu C 805/Dynasylan ® Alu C 805 MEMO T PCTP 12/AEROXIDE ® 5% AEROXI E ® 2%  530 214 Alu C 805/Dynasylan ® Alu C 805 6598

[0137] FIG. 8 and Table 7 show that the fumed silica and metal oxides treatment to boron nitride in Example 7 decrease the viscosity of the polybutadiene thermal conductive material. This confirms the conclusion that the viscosity reduction effect of the thermal conductive filler of the invention can be applied to different thermal conductive materials with various resins.

Comparative Example 6

Viscosity Affected by Silica with Different Particle Sizes

[0138] Thermal conductive material Samples U, V, W, X with silica of different particle size were prepared as Comparative Example 6 as follows: [0139] a) preparation of thermal conductive fillers: [0140] 1) 47.5 g of boron nitride PCTP 12 was placed in a 50 mL plastic vessel. [0141] 2) Next, 2.5 g of ADMAFINE® SO-C1 or ADMAFINE® SO-C4 or ADMAFINE® SO-C6 or SIPERNAT® 622 LS was put into the vessel. [0142] 3) The mixture in the vessel was tumbled with a dual asymmetric centrifugal mixer at 2500 rpm for 30 s. [0143] 4) Then 1 g Dynasylan® Glymo was added into the vessel, followed by tumbling with dual asymmetric centrifugal mixing at 2500 rpm for 30 s, then the mixture was heated in an oven at 105° C. for 1 hour.

[0144] In the prepared thermal conductive filler, the loading of fumed silica or fumed metal oxide was 5 wt. % and loading of silane was 2 wt. % based on the weight of untreated boron nitride. [0145] b) preparation of thermal conductive materials:

[0146] After the thermal conductive filler was prepared, 28 g D.E.R.™ 331 epoxy resin, 24 g methyl ethyl ketone (MEK) as solvent and 28 g thermal conductive filler (treated boron nitride) were mixed together with the dual asymmetric centrifugal mixing at 2500 rpm for 30 s. The content of thermal conductive filler in the thermal conductive material was 50% after the solvent MEK was evaporated.

TABLE-US-00008 TABLE 8 Effect of different particle size silica in thermal conductive materials with PCTP 12 hBN on viscosity at 6 rpm and 60 rpm viscosity viscosity wt. % fumed wt. % at 6 rpm, at 60 rpm, Samples description oxide silane cP cP U PCTP 12/ 5% 2% 131  67 ADMAFINE ® ADMAFINE® SO-C1/Dynasylan ® SO-C1 Glymo V PCTP 12/ 5% 2%  94  70 ADMAFINE ® ADMAFINE® SO-C4/Dynasylan ® SO-C4 Glymo W PCTP 12/ 5% 2% 254  78 ADMAFINE ® ADMAFINE® SO-C6/Dynasylan® SO-C6 Glymo X PCTP 12/ 5% 2% 660 213 SIPERNAT ® SIPERNAT® 622 LS/Dynasylan ® 622 LS Glymo

[0147] As shown in Table 8 and FIG. 9, the large size silica ADMAFINE® SO-C1, ADMAFINE®

[0148] SO-C4, ADMAFINE® SO-C6 and SIPERNAT® 622 LS also decreased the viscosity of thermal conductive materials compared to Sample B with silane but without any oxide treatment prepared in Comparative Example 2. Compared to Sample D and G of Example 2, such silicas with particle size above 200 nm (0.2 μm) showed much worse viscosity reduction performance than AEROXIDE® Alu C 805 and AEROSIL® R 711. More importantly, as shown in following Example 8, such silicas with particle size above 200 nm showed much lower thermal conductivities of thermal conductive materials compared with thermal conductive materials with silicas of particle size below 200 nm thus such silicas are inferior for use in thermal conductive materials and are not within the scope of the oxides in the invention.

Example 8

Thermal Conductivity Test in Epoxy Resin Thermal Conductive Materials

[0149] Thermal conductivity of the thermal conductive materials was measured according to the procedure as follows:

[0150] To 80 g of each of the thermal conductive materials Sample A, B, D, G, U, V, W, X prepared in Comparative Example 1, Comparative Example 2, Example 1 and Comparative Example 6, 1.6 g of a cross-linker 2-cyanoguanidine and 0.015 g of a catalyst 2-methylimidazole were added. Then dual asymmetric centrifugal mixing at 2500 rpm for 30 s was applied to mix it well. The final mixture was dried under 60° C. and 20 mbar in a vacuum oven for 24 hours to remove the solvent and bubbles. Then each sample was placed to an oven at 120° C. for 8 hours to get thermal conductive material Sample A′, B′, D′, G′, U′, V′, W′, X′ respectively. The thermal conductivities of the samples were tested, and the results are shown in Table 9.

[0151] As shown in Table 9, the thermal conductive material Samples D′ and G′ showed similar thermal conductivities as Samples A′ and B′ which contained no oxides. Therefore, addition of fumed silica or fumed metal oxide didn't decrease the thermal conductivity of thermal conductive materials.

[0152] In Table 9, thermal conductive material Samples U′, V′, W′, X′ showed lower thermal conductivities than Samples A′, B′, D′, G′. This indicated that large particle size silica such as ADMAFINE® SO-C1, ADMAFINE® SO-C4, ADMAFINE® SO-C6 and SIPERNAT® 622 LS decreased the thermal conductive performance of boron nitride due to their relatively large particle sizes. By contrast, fumed silica and oxides according to the invention (such as AEROXIDE® Alu C 805 and AEROSIL® R 711) could achieve both low viscosity and high thermal conductivity.

TABLE-US-00009 TABLE 9 Thermal conductivity for different prepared samples in epoxy resin wt. % of h-BN wt. % silica wt. % Thermal PCTP 12 or metal Glymo conductivity, Sample in resin oxides in resin in resin W/mK A′ 50 0 0 1.8 B′ 50 0 1% 2.0 D′ 47.5 2.5 AEROSIL ®R 1% 1.8 711 G′ 47.5 2.5 AEROXIDE ® 1% 2.0 Alu C805 U′ 47.5 2.5 ADMAFINE ® 1% 1.2 SO-C1 V′ 47.5 2.5 ADMAFINE ® 1% 1.3 SO-C4 W′ 47.5 2.5 ADMAFINE ® 1% 1.5 SO-C6 X′ 47.5 2.5 SIPERNAT ® 1% 1.5 622 LS

[0153] As used herein, terms such as “comprise(s)” and the like as used herein are open terms meaning ‘including at least’ unless otherwise specifically noted.

[0154] All references, tests, standards, documents, publications, etc. mentioned herein are incorporated herein by reference. Where a numerical limit or range is stated, the endpoints are included. Also, all values and subranges within a numerical limit or range are specifically included as if explicitly written out.

[0155] The above description is presented to enable a person skilled in the art to make and use the invention and is provided in the context of a particular application and its requirements. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, this invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and features disclosed herein. In this regard, certain embodiments within the invention may not show every benefit of the invention, considered broadly.