High solids hBN slurry, hBN paste, spherical hBN powder, and methods of making and using them

Abstract

The present invention relates to a method for making a hexagonal boron nitride slurry and the resulting slurry. The method involves mixing from about 0.5 wt. % to about 5 wt. % surfactant with about 30 wt. % to about 50 wt. % hexagonal boron nitride powder in a medium under conditions effective to produce a hexagonal boron nitride slurry. The present invention also relates to a method for making a spherical boron nitride powder and a method for making a hexagonal boron nitride paste using a hexagonal boron nitride slurry. Another aspect of the present invention relates to a hexagonal boron nitride paste including from about 60 wt. % to about 80 wt. % solid hexagonal boron nitride. Yet another aspect of the present invention relates to a spherical boron nitride powder, a polymer blend including a polymer and the spherical hexagonal boron nitride powder, and a system including such a polymer blend.

What is claimed: 
     
       1. A method for making spherical boron nitride powder comprising:
 providing a hexagonal boron nitride slurry;   spray drying the slurry under conditions effective to produce spherical boron nitride powder comprising spherical agglomerates of boron nitride platelets; and   sintering the spherical boron nitride powder.   
     
     
       2. The method according to  claim 1 , wherein the hexagonal boron nitride slurry comprises from about 30 wt. % to about 50 wt. % hexagonal boron nitride powder. 
     
     
       3. The method according to  claim 1 , wherein the spherical boron nitride powder has a tap density of about 0.4 g/cc to about 0.7 g/cc. 
     
     
       4. The method according to  claim 1 , wherein the sintering is carried out at a temperature of from about 1800° C. to about 2400° C. 
     
     
       5. The method according to  claim 1 , wherein the spherical agglomerates of boron nitride platelets have an average agglomerate diameter of from about 10 microns to about 500 microns. 
     
     
       6. The method according to  claim 5 , wherein the majority of boron nitride agglomerates have an average diameter of from about 30 microns to about 150 microns. 
     
     
       7. The method according to  claim 1  further comprising;
 classifying the spherical boron nitride powder under conditions effective to obtain a desired agglomerate size distribution. 
 
     
     
       8. The method according to  claim 7 , wherein the classifying is selected from the group consisting of screening, air classifying, and elutriation. 
     
     
       9. A spherical boron nitride powder comprising spherical agglomerates of boron nitride platelets. 
     
     
       10. The spherical boron nitride powder according to  claim 9 , wherein the spherical boron nitride powder has a tap density of about 0.4 g/cc to about 0.7 g/cc. 
     
     
       11. The spherical boron nitride powder according to  claim 9 , wherein the spherical agglomerates of boron nitride platelets have an average agglomerate diameter of from about 10 microns to about 500 microns. 
     
     
       12. The spherical boron nitride powder according to  claim 11 , wherein the majority of boron nitride agglomerates have an average diameter of from about 30 microns to about 150 microns. 
     
     
       13. A method for making a hexagonal boron nitride paste comprising:
 providing a hexagonal boron nitride slurry and   treating the slurry under conditions effective to produce a hexagonal boron nitride paste comprising from about 60 wt. % to about 80 wt. % solid hexagonal boron nitride.   
     
     
       14. The method according to  claim 13 , wherein the hexagonal boron nitride slurry comprises from about 30 wt. % to about 50 wt. % hexagonal boron nitride solids loading. 
     
     
       15. The method according to  claim 13 , wherein said treating comprises placing the slurry in a plaster mold. 
     
     
       16. The method according to  claim 13 , wherein said treating comprises vacuum filtration. 
     
     
       17. A hexagonal boron nitride paste comprising from about 60 wt. % to about 80 wt. % solid hexagonal boron nitride in a medium. 
     
     
       18. The hexagonal boron nitride paste according to  claim 17 , wherein the medium is an aqueous medium. 
     
     
       19. The hexagonal boron nitride paste according to  claim 18 , wherein the medium is a non-aqueous medium selected from the group consisting of isopropyl alcohol, methanol, and ethanol. 
     
     
       20. A polymer blend comprising:
 a polymer, and   a powder phase comprising spherical agglomerates of hexagonal boron nitride platelets, wherein the powder phase is distributed homogeneously within the polymer.   
     
     
       21. The polymer blend according to  claim 20 , wherein the powder phase has a tap density of about 0.4 g/cc to about 0.7 g/cc. 
     
     
       22. The polymer blend according to  claim 20 , wherein the polymer is selected from the group consisting of melt-processable polymers, polyesters, phenolics, silicone polymers, acrylics, waxes, thermoplastic polymers, low molecular weight fluids, and epoxy molding compounds. 
     
     
       23. The polymer blend according to  claim 20 , wherein the polymer blend comprises from about 30 wt. % to about 80 wt. % spherical boron nitride powder. 
     
     
       24. The polymer blend according to  claim 20 , wherein the polymer blend has a thermal conductivity of from about 1 W/mK to about 15 W/mK. 
     
     
       25. The polymer blend according to  claim 20 , wherein the spherical agglomerates of hexagonal boron nitride platelets have an average agglomerate diameter of from about 10 microns to about 500 microns. 
     
     
       26. The polymer blend according to  claim 25 , wherein the majority of spherical agglomerates have an average diameter of from about 30 microns to about 150 microns. 
     
     
       27. A system comprising:
 a heat source;   a heat sink; and   a thermally conductive material connecting the heat source to the heat sink, wherein the thermally conductive material comprises a powder phase comprising spherical agglomerates of hexagonal boron nitride platelets.   
     
     
       28. The system according to  claim 27 , wherein the powder phase has a tap density of about 0.4 g/cc to about 0.7 g/cc. 
     
     
       29. The system according to  claim 27 , wherein the heat source is an integrated circuit chip, power module or transformer. 
     
     
       30. The system according to  claim 27 , wherein the heat sink is finned aluminum, copper, berilium or diamond. 
     
     
       31. The system according to  claim 27 , wherein the thermally conductive material comprises from about 30 wt. % to about 80 wt. % spherical boron nitride powder. 
     
     
       32. The system according to  claim 27 , wherein the thermally conductive material has a thermal conductivity of from about 1 W/mK to about 15 W/mK. 
     
     
       33. The system according to  claim 27 , wherein the spherical agglomerates of hexagonal boron nitride platelets have an average agglomerate diameter of from about 10 microns to about 500 microns. 
     
     
       34. The system according to  claim 33 , wherein the majority of spherical agglomerates have an average diameter of from about 30 microns to about 150 microns. 
     
     
       35. The system according to  claim 27 , wherein the thermally conductive material is a polymer. 
     
     
       36. The system according to  claim 35 , wherein the polymer is selected from the group consisting of melt-processable polymers, polyesters, phenolics, silicone polymers, acrylics, waxes, thermoplastic polymers, low molecular weight fluids, and epoxy molding compounds. 
     
     
       37. A spherical boron nitride powder comprising spherical agglomerates of hexagonal boron nitride platelets having an average agglomerate diameter of from 20 microns to 74 microns.  
     
     
       38. The spherical boron nitride powder according to claim 37, wherein the boron nitride agglomerates have an average diameter of from 38 microns to 74 microns.  
     
     
       39. The spherical boron nitride powder according to claim 38, wherein the boron nitride agglomerates have an average diameter of from 38 microns to 53 microns.  
     
     
       40. The spherical boron nitride powder according to claim 37, wherein the spherical boron nitride powder has a tap density of about 0.4 g/cc to about 0.7 g/cc.  
     
     
       41. A spherical boron nitride powder comprising spherical agglomerates of hexagonal boron nitride platelets having an average agglomerate diameter of from 10 microns to 38 microns.  
     
     
       42. The spherical boron nitride powder according to claim 41, wherein the boron nitride agglomerates have an average diameter of from 20 microns to 38 microns.  
     
     
       43. The spherical boron nitride powder according to claim 41, wherein the spherical boron nitride powder has a tap density of about 0.4 g/cc to about 0.7 g/cc. 
     
     
       44. A spherical boron nitride powder comprising spherical agglomerates of hexagonal boron nitride platelets, wherein the powder has an agglomerate size distribution, based on diameter of the agglomerates, of:
 (i) 10 microns to 38 microns, or   (ii) 20 microns to 38 microns, or   (iii) 20 microns to 74 microns, or   (iv) 38 microns to 74 microns, or   (v) 38 microns to 53 microns.