Method of continuously producing bipolar separator plates from plastic filled with electrically conductive particles
For continuously producing a band-shaped plate material from plastic filled with electrically conductive particles, which can be sub-divided into bipolar separator plates or blanks for bipolar separator plates, the particles and the plastic are compounded into a compound, the compound is ground into a powder, the powder is spread out into a preform, and the preform is, preferably isobarically, hot-pressed between a lower belt and an upper belt of a double belt press into a plate material.
1. A method of continuously producing a band-shaped plate material from plastic filled with electrically conductive particles, the band-shaped plate material being sub-dividable into bipolar separator plates or blanks for bipolar separator plates, the method comprising
compounding the electrically conductive particles and the plastic into a compound, wherein the electrically conductive particles make up between 75% and 90% by weight of the compound,
cryogenically grinding the compound into a powder,
spreading out the powder into a preform, and
hot-pressing the preform between a lower belt and an upper belt of a double belt press into the band-shaped plate material.
2. The method of claim 1 , wherein the compound is cryogenically ground into the powder at a temperature below −70° C.
3. The method of claim 2 , wherein the compound is cryogenically ground into the powder at an expenditure of energy of at least 2.000 J/g Compound.
4. The method of claim 2 , wherein the compound is cryogenically ground into the powder at an expenditure of energy of between 4.000 J/g compound to 8.000 J/g compound.
5. The method of claim 1 , wherein the electrically conductive particles and the plastic are compounded into the compound in a screw extruder.
6. The method of claim 1 , wherein the electrically conductive particles and the plastic are compounded into the compound in a double screw extruder whose screws are rotationally driven in a same sense of rotation.
7. The method of claim 1 , wherein the electrically conductive particles are selected from carbon black, graphite particles and CNTs.
8. The method of claim 1 , wherein the plastic is a thermoplastic.
9. The method of claim 1 , wherein the plastic is a polyethylene (PE) or a polypropylene (PP).
10. The method of claim 1 , wherein the powder has a particle size distribution in which at least 90% per weight of the powder are made up by particles that are smaller than 100 μm.
11. The method of claim 1 , wherein the plastic is a thermoplastic on the basis of polyolefins and wherein the preform is hot-pressed into the band-shaped plate material at a temperature in a range between 170° C. and 260° C.
12. The method of claim 1 , wherein the preform is hot-pressed into the band-shaped plate material at an increased pressure which is increased by a pressure increase in a range between 0.5 MPa to 10 MPa over ambient pressure.
13. The method of claim 12 , wherein the preform is isobarically hot-pressed into the band-shaped plate material.
14. The method of claim 12 , wherein the preform is hot-pressed into the band-shaped plate material within a period of time in a range between 13 s and 215 s.
15. The method of claim 13 , wherein the band-shaped plate material, into which the preform has been hot-pressed, is cooled between the upper belt and the lower belt of the double belt press down to a temperature in a range between 100° C. and ambient temperature.
16. The method of claim 15 , wherein, in cooling down the plate material, the increased pressure at which the preform has been hot-pressed into the plate material is kept, until the plate material exits out of the double belt press.
17. The method of claim 16 , wherein the plate material is cooled between the lower belt and the upper belt of the double belt press for a period of time in a range between 6 s and 115 s.
18. The method of claim 1 , wherein the plate material is sub-divided into the bipolar separator plates or the blanks for bipolar separator plates, respectively, or rolled up into a coil downstream of the double belt press.
19. The method of claim 1 , wherein the band-shaped plate material is contoured at at least one of its two main sides, when the band-shaped plate material is still hot.
20. The method of claim 1 , wherein the plate material into which the preform has been hot-pressed has a thickness in a range between 0.4 mm and 2.5 mm.
21. A method of continuously producing a band-shaped plate material from plastic filled with electrically conductive particles, the band-shaped plate material being sub-dividable into bipolar separator plates or blanks for bipolar separator plates, the method comprising
compounding the electrically conductive particles and the plastic into a compound, wherein the electrically conductive particles make up between 75% and 90% by weight of the compound,
high-energetically grinding the compound into a powder at an expenditure of energy of between 4.000 J/g compound to 8.000 J/g compound,
spreading out the powder into a preform, and
hot-pressing the preform between a lower belt and an upper belt of a double belt press into the band-shaped plate material.
22. A method of continuously producing a band-shaped plate material from plastic filled with electrically conductive particles, the band-shaped plate material being sub-dividable into bipolar separator plates or blanks for bipolar separator plates, the method comprising
selecting the plastic from thermoplastics on the basis of polyolefins,
selecting the electrically conductive particles from carbon black, graphite particles and CNTs,
compounding the electrically conductive particles and the plastic into a compound, wherein the electrically conductive particles make up between 75% and 90% by weight of the compound,
cryogenically grinding the compound into a powder at a temperature below −70° C., wherein the powder has a particle size distribution in which at least 90% per weight of the powder are made up by particles that are smaller than 100 μm,
spreading out the powder into a preform,
isobarically hot-pressing the preform between a lower belt and an upper belt of a double belt press into the band-shaped plate material, wherein the band-shaped plate material into which the preform has been hot-pressed has a thickness in a range between 0.4 mm and 2.5 mm, and
cooling the band-shaped plate material, into which the preform has been hot-pressed, between the upper belt and the lower belt of the double belt press by at least 20 degrees Kelvin, wherein, in cooling down the band-shaped plate material, an increased pressure at which the preform has been hot-pressed into the band-shaped plate material is kept, until the band-shaped plate material exits out of the double belt press.