Ground expanded graphite agglomerates, methods of making, and applications of the same
The present disclosure relates to ground expanded graphite agglomerate compositions, methods for making such agglomerates, their use as conductive additive, and conductive composites including such ground expanded graphite agglomerates. The disclosure also pertains to methods for making such composites and the use of such composites in preparing thermally conductive materials. The agglomerates may be characterized by a certain softness allowing the agglomerates to dissolve, e.g., through shear forces applied during compounding, thereby leading to an improved feedability and a highly homogenous distribution of the expanded graphite material in the composite matrix.
1. Graphite agglomerates comprising ground expanded graphite particles compacted together, wherein said agglomerates are in granular form having a size ranging from about 100 μm to about 10 mm.
2. The graphite agglomerates of claim 1 , wherein said agglomerates are in granular form having a size ranging from about from about 200 μm to about 4 mm.
3. The graphite agglomerates of claim 1 , wherein said agglomerates have a tap density ranging from about 0.08 to about 1.0 g/cm 3 .
4. The graphite agglomerates of claim 1 , wherein said agglomerates have a tap density ranging from about 0.08 to about 0.6 g/cm 3 .
5. The graphite agglomerates of claim 1 , wherein said agglomerates have a tap density ranging from about 0.12 to about 0.3 g/cm 3 .
6. The graphite agglomerates of claim 1 , wherein the ground expanded graphite particles have a mean particle size (d 50 ) ranging from about 5 μm to about 500 μm.
7. The graphite agglomerates of claim 1 , wherein the ground expanded graphite particles have a mean particle size (d 50 ) ranging from about 20 μm to about 200 μm.
8. The graphite agglomerates of claim 1 , wherein the ground expanded graphite particles have a mean particle size (d 50 ) ranging from about 30 μm to about 100 μm.
9. The graphite agglomerates of claim 1 , wherein at least about 10 wt % of the agglomerates remain above a 250 μm Mesh sieve after soft vibrating sieving.
10. The graphite agglomerates of claim 1 , wherein at least about 25 wt % of the agglomerates remain above a 250 μm Mesh sieve after soft vibrating sieving.
11. The graphite agglomerates of claim 1 , wherein at least about 40 wt % of the agglomerates remain above a 250 μm Mesh sieve after soft vibrating sieving.
12. The graphite agglomerates of claim 1 , wherein said agglomerates have a specific BET surface area ranging from about 8 m 2 /g to about 200 m 2 /g.
13. The graphite agglomerates of claim 1 , wherein said agglomerates have a specific BET surface area ranging from about 15 m 2 /g to about 50 m 2 /g.
14. The graphite agglomerates of claim 1 , wherein a conductive polymer including the graphite agglomerates has substantially the same thermal conductivity and mechanical properties as a polymer composite prepared with ground expanded graphite instead of the graphite agglomerates.
15. The graphite agglomerates of claim 1 , wherein less than about 20% (w/w) of the agglomerates remaining on the 250 μm Mesh sieve after soft vibrating sieving remain on the sieve when subjected to mechanical water flushing sieving according to EN ISO 787-18:1983 (250 μm Mesh size, 10 minutes sieving time).
16. The graphite agglomerates of claim 1 , wherein less than about 10% (w/w) of the agglomerates remaining on the 250 μm Mesh sieve after soft vibrating sieving remain on the sieve when subjected to mechanical water flushing sieving according to EN ISO 787-18:1983 (250 μm Mesh size, 10 minutes sieving time).
17. The graphite agglomerates of claim 1 , wherein less than about 2% (w/w) of the agglomerates remaining on the 250 μm Mesh sieve after soft vibrating sieving remain on the sieve when subjected to mechanical water flushing sieving according to EN ISO 787-18:1983 (250 μm Mesh size, 10 minutes sieving time).
18. The graphite agglomerates of claim 1 , wherein the maximum output of the ground expanded graphite agglomerates in a Brabender FlexWall DDW-MD5-FW40 Plus-50 gravimetric dosimeter is at least about 6 kg/h at a tap density of about 0.125 g/cm 3 and at least about 12 kg/h at a tap density of about 0.25 g/cm 3 .
19. The graphite agglomerates of claim 1 , wherein said agglomerates comprise at least one further component in particulate form, wherein the weight ratio of the ground expanded graphite to the at least one other component ranges from about 95:5 to about 5:95.
20. The graphite agglomerates of claim 19 , wherein said further component is selected from the group consisting of natural graphite, synthetic graphite, carbon black, boron nitride, aluminium nitride, carbon fibers, carbon nanofibers, carbon nanotubes, graphene, coke, silver powders, copper powders, aluminium oxide powders, steel fibers, PAN, graphite fibers, silicon carbide, graphene, or combinations thereof.
21. A method for making ground expanded graphite agglomerates as defined in claim 1 , comprising compacting ground expanded graphite particles together to form the ground expanded graphite agglomerates.
22. The method of claim 21 , wherein the compacting comprises compacting the ground expanded graphite particles together with at least one further component in particulate form to yield ground expanded graphite agglomerates, wherein the weight ratio of the ground expanded graphite to the at least one other component ranges from about 95:5 to about 5:95.
23. The method of claim 22 , wherein said further component is selected from the group consisting of natural graphite, synthetic graphite, carbon black, boron nitride, aluminium nitride, carbon fibers, carbon nanofibers, carbon nanotubes, graphene, coke, silver powders, copper powders, aluminium oxide powders, steel fibers, PAN, graphite fibers, silicon carbide, graphene, or combinations thereof.
24. The method of claim 21 , wherein agglomeration is accomplished by a process selected from the group consisting of:
i) employing a roller compactor, wherein the tap density is adjusted by virtue of the feeding rate, the roll gap and the sieve size,
wherein the ground expanded graphite particles are fed with the help of a screw to a couple of counter-rotating rolls to yield a pre-agglomerate, followed by a fine agglomeration step whereby the pre-agglomerates are pushed through a sieve which assists in defining the desired agglomerate size;
ii) employing a flat die pelletizer, wherein the tap density is adjusted by the gap between the rolls, the die and die size, and the knives speed,
wherein the ground expanded graphite particles are pressed through a die by pan grinder rolls, followed by cutting the pre-agglomerated graphite particles to the desired size with suitable means such as rotating knives;
iii) employing a pin mixer pelletizer or a rotary drum pelletizer, wherein the tap density is adjusted by the feeding rate, the moisture content, the choice and concentration of the additives and the pin shaft or drum rotating speed, respectively;
iv) a fluidized bed process;
v) a spray dryer process; or
vi) a fluidized bed spray dryer process.
25. The method of claim 21 , wherein the method further comprises grinding an expanded graphite material to form ground expanded graphite particles.
26. The method of claim 21 , wherein the expanded graphite is made by:
intercalating a graphite material; and
thermally expanding the graphite material to form an expanded graphite material.
27. A conductive composite comprising the graphite agglomerates of claim 1 .
28. A conductive polymer comprising:
an expanded graphite material chosen from the group consisting of:
ground expanded graphite agglomerates as defined in claim 1 ; and
compacted expanded graphite particles; and
a polymer matrix.
29. The conductive polymer of claim 28 , wherein the polymer matrix is formed by a polyolefin, a polyamide, a polyester, an acrylic or acetate, a polyimide, a thio/ether polymer, an elastomer, a thermoplastic elastomer, thermosetting resins, copolymers thereof, or mixtures of any of the foregoing materials.
30. A method for making the conductive polymer as defined in claim 28 , comprising feeding the ground expanded graphite agglomerates to an extruder, thereby mixing the polymer and agglomerates, followed by moulding of the resulting conductive polymer into the desired form.
31. A thermally and/or electrically conductive material comprising the conductive polymer of claim 28 .