Hexagonal boron nitride powder and production process therefor
A hexagonal boron nitride powder whose maximum absorption peak within the range of 3,100 to 3,800 cm −1 of the diffuse reflectance fourier transform infrared spectrum is existent at 3,530 to 3,590 cm −1 and which is able to provide high heat conductivity, dielectric strength and copper foil peel strength to a resin composition obtained by filling the powder into a resin, and a process for producing the above boron nitride powder by mixing together an oxygen-containing boron compound, a carbon source having a sulfur concentration of 1,000 to 10,000 ppm and an oxygen-containing calcium compound in a specific ratio and reduction nitriding the mixture.
1. A hexagonal boron nitride powder whose maximum absorption peak within the range of 3,100 to 3,800 cm −1 is existent at 3,530 to 3,590 cm −1 in the diffuse reflectance fourier transform infrared spectrum.
2. The hexagonal boron nitride powder according to claim 1 , wherein the (B/A) ratio of absorption peak height A derived from boron nitride at around 800 cm −1 and maximum absorption peak height B within the range of 3,530 to 3,590 cm −1 of the diffuse reflectance fourier transform infrared spectrum is not lower than 0.02.
3. The hexagonal boron nitride powder according to claim 1 which has a specific surface area of not more than 15 m 2 /g.
4. The hexagonal boron nitride powder according claim 1 which has an oxygen concentration of not more than 0.3 mass %.
5. A resin composition comprising the hexagonal boron nitride powder of claim 1 .
6. A resin composition comprising the hexagonal boron nitride powder of claim 1 and an aluminum oxide powder and/or an aluminum nitride powder.
7. A heat conductive insulating sheet made of the resin composition of claim 5 .
8. A radiation insulation member for electronic parts which comprises the heat conductive insulating sheet of claim 7 .
9. A process for producing a hexagonal boron nitride powder, comprising the steps of:
mixing together an oxygen-containing boron compound, a carbon source and an oxygen-containing calcium compound to ensure that the B/C ratio (elemental ratio) of B contained in the oxygen-containing boron compound and C contained in the carbon source becomes 0.75 to 0.85 and the amount of the oxygen-containing calcium compound becomes 10 to 15 parts by mass in terms of CaO based on 100 parts by mass of the total in terms of B 2 O 3 of the oxygen-containing boron compound and C of the carbon source;
heating and reduction nitriding the mixture in a nitrogen atmosphere at 1,450 to 1,550° C. for 4 hours or more and at 1,650 and 2,100° C. for 2 hours or more; and
removing a by-product except boron nitride existent in the reaction product by acid cleaning, wherein
the carbon source has a sulfur concentration of 1,000 to 10,000 ppm.
10. The hexagonal boron nitride powder according to claim 2 which has a specific surface area of not more than 15 m 2 /g.
11. The hexagonal boron nitride powder according to claim 2 which has an oxygen concentration of not more than 0.3 mass %.
12. The hexagonal boron nitride powder according to claim 3 which has an oxygen concentration of not more than 0.3 mass %.
13. A resin composition comprising the hexagonal boron nitride powder of claim 2 .
14. A resin composition comprising the hexagonal boron nitride powder of claim 3 .
15. A resin composition comprising the hexagonal boron nitride powder of claim 4 .
16. A resin composition comprising the hexagonal boron nitride powder of claim 2 and an aluminum oxide powder and/or an aluminum nitride powder.
17. A resin composition comprising the hexagonal boron nitride powder of claim 3 and an aluminum oxide powder and/or an aluminum nitride powder.
18. A resin composition comprising the hexagonal boron nitride powder of claim 4 and an aluminum oxide powder and/or an aluminum nitride powder.
19. A heat conductive insulating sheet made of the resin composition of claim 6 .