Process for the impregnation of carbon fiber bundles, resin-impregnated carbon fiber bundle, shaped body and intermediate body for silicization

Abstract

A process for the impregnation of carbon fiber bundles enables the carbon fiber bundles to be impregnated with a curable liquid resin without the impregnated fiber bundles sticking together. The fiber bundles are present in a mechanically generated fluidized bed during the impregnation and are held in the fluidized bed until the resin has been cured or at least dried. A resin-impregnated carbon fiber bundle, a shaped body and an intermediate body for silicization are also provided.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENT EXAMPLES

Referring now in detail to an example of the invention, the production of bundles of carbon fibers held together by a carbonized binder was carried out according to the second variant of the above-described process, i.e. bundles having the desired dimensions were cut from a laminate sheet which had been pressed to the desired thickness and were then carbonized at 900° C. The fiber bundles had a length of 9 mm, a width of 1 mm and a thickness of 0.2 mm.

Impregnation was carried out in a heatable mixing dryer which was equipped with ETS® blades. The fiber bundles were subjected to a fluidized bed having a Froude number of from 0.7 to 0.8 and preheated to a temperature of 130° C. This was reached after 5-10 minutes. A liquid phenolic resin was then introduced in an amount of 30% of the initial mass of the fiber bundles. For the introduction of resin, the Froude number was increased to a value of 2 and maintained at this higher value for from 1 to 3 minutes. The Froude number was then reduced again to 0.7-0.8 and the fiber bundles were kept in the fluidized bed for a further 5-7 minutes. During this time, the mixer was no longer heated so that the fiber bundles could cool down to temperatures in the range from 95 to 115° C.

In further experiments, the Froude number was increased to values up to 4 for the mixing phase under otherwise identical conditions.

The liquid resin was always taken up completely by the fiber bundles. In the material taken from the mixer after drying, the fiber bundles were not stuck together, i.e. free-flowing impregnated fiber bundles were obtained. Damage to the fiber bundles by the shear forces acting in the mixer was not observed.

Claims

1. A process for the impregnation of bundles of carbon fibers with a curable resin present in liquid form, the process comprising the following steps: keeping the carbon fiber bundles in a mechanically generated fluidized bed during impregnation with the curable resin; andkeeping the carbon fiber bundles in the fluidized bed until the resin has been cured or at least dried so that the bundles no longer stick together.

2. The process according to claim 1, which further comprises keeping the carbon fiber bundles in the mechanically generated fluidized bed during the following phases: a preheating phase in which the carbon fiber bundles are heated to a temperature sufficient for curing or drying of the impregnation resin,a mixing phase commencing with the addition of the impregnation resin to the carbon fiber bundles, anda curing or drying phase during which the impregnation resin in the fiber bundles cures or dries.

3. The process according to claim 2, which further comprises preheating the carbon fiber bundles to a temperature of at least 130° C.

4. The process according to claim 2, wherein: the heating-up phase has a duration of from 5 to 10 minutes,the mixing phase has a duration of from 1 to 5 minutes, andthe curing or drying phase has a duration of at least 5 minutes.

5. The process according to claim 4, wherein the mixing phase has a duration of not more than 3 minutes.

6. The process according to claim 2, which further comprises generating the fluidized bed with a mixing dryer.

7. The process according to claim 6, wherein the mixing dryer is equipped with blades.

8. The process according to claim 6, which further comprises setting a rotational speed of the mixing dryer to from 30 to 60 rotations per minute during the preheating phase and during the curing or drying phase, and increasing the rotational speed of the mixer to up to 100 rotations per minute during the mixing phase.

9. The process according to claim 6, which further comprises setting a Froude number to less than 1 during the preheating phase and during the curing or drying phase, and increasing the Froude number to from 1.5 to 4 during the mixing phase.

10. The process according to claim 9, which further comprises increasing the Froude number to not more than 2.5 during the mixing phase.

11. The process according to claim 1, wherein the resin is a phenolic resin or another carbonizable resin.

12. The process according to claim 1, wherein the carbon fiber bundles take up an amount of resin of up to 35% of an initial mass of the carbon fiber bundles.

13. The process according to claim 1, wherein the carbon fibers in the fiber bundles to be impregnated are held together by a carbonized binder.

14. The process according to claim 13, which further comprises producing the carbon fiber bundles held together by the carbonized binder by the following steps: impregnation of at least one roving including a plurality of parallel carbon fiber filaments with a carbonizable binder so as to yield a prepreg,pressing of at least one impregnated roving or a plurality of parallel impregnated rovings to form a unidirectional laminate sheet including parallel filaments and having a defined thickness, combined with curing of the binder by heat treatment so as to yield a dimensionally stable laminate sheet of defined thickness,carbonization of the binder in the unidirectional laminate sheet, andcutting of the unidirectional laminate sheet, which may have been separated into individual bands, to yield segments or fiber bundles of defined width and length.

15. The process according to claim 13, which further comprises producing the carbon fiber bundles held together by the carbonized binder by the following steps: impregnation of at least one roving including a plurality of parallel carbon fiber filaments with a carbonizable binder so as to yield a prepreg,pressing of at least one impregnated roving or a plurality of parallel impregnated rovings to form a unidirectional laminate sheet including parallel filaments and having a defined thickness, combined with curing of the binder by heat treatment so as to yield a dimensionally stable laminate sheet of defined thickness,cutting of the unidirectional laminate sheet, which may have been separated into individual bands, to yield segments or fiber bundles of defined width and length, andcarbonization of the binder in the fiber bundles.

16. The process according to claim 14, which further comprises setting a thickness of the fiber bundles to a value in a range from 0.15 to 0.4 mm, setting a length of the fiber bundles to a value in a range from 6 to 15 mm, and setting a width of the fiber bundles to a value in a range from 0.5 to 3.5 mm.

17. The process according to claim 15, which further comprises setting a thickness of the fiber bundles to a value in a range from 0.15 to 0.4 mm, setting a length of the fiber bundles to a value in a range from 6 to 15 mm, and setting a width of the fiber bundles to a value in a range from 0.5 to 3.5 mm.

18. A resin-impregnated carbon fiber bundle, comprising: parallel carbon fibers;a carbonized binder holding said carbon fibers together; andcured impregnation resin filled into pores formed during carbonization of the binder.

19. The carbon fiber bundle according to claim 15, which further comprises a bundle thickness having a value in a range from 0.15 to 0.4 mm, a bundle length having a value in a range from 6 to 15 mm, and a bundle width having a value in a range from 0.5 to 3.5 mm.

20. The carbon fiber bundle according to claim 18, wherein said resin is a phenolic resin or another carbonizable resin.

21. The carbon fiber bundle according to claim 18, wherein an amount of said resin taken up by the carbon fiber bundle is up to 35% of an initial mass of the carbon fiber bundle.

22. A shaped body, comprising: carbon fiber bundles according to claim 20; anda carbon matrix reinforced with said carbon fiber bundles.

23. An intermediate body for silicization, the intermediate body comprising: carbon fiber bundles according to claim 20; anda carbon matrix reinforced with said carbon fiber bundles.