Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,...
Patent
1997-12-03
2000-12-12
Dixon, Merrick
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
428397, 428392, 428400, 2642111, 2642093, 26417713, 264183, 26421114, 26421115, 26421122, 26421124, B32B 1900
Patent
active
061595977
DESCRIPTION:
BRIEF SUMMARY
The invention pertains to a process for spinning fibres or filaments from a spinnable solution using a centrifuge of which the wall has one or more spinning orifices, in which process the spinning solution is jetted from the centrifuge into a coagulant inside a jacket.
Such a process is known. In Japanese laid open patent application JP 27021/79 it is described how an optically anisotropic spinning solution of a para-aramid, e.g., poly(paraphenylene terephthalamide), is spun with the aid of a centrifuge. Four examples serve to explain how the solution is introduced into a centrifuge having 25 or 50 spinning orifices of 0.08 or 0.1 mm in diameter and extruded through the spinning orifices at a rotational speed in the range of 70 to 1000 revolutions per minute (rpm). The solution then ends up in a coagulant flowing downward at 2 or 5 cm distance from the centrifuge. The coagulated fibres are collected batchwise and washed for 24 hours. The properties of the resulting fibres are such as will give them a certain commercial value.
Such a process has a low productive capacity and high times of passage, int. al., because the fibres are processed batchwise.
One way of increasing the productive capacity consists in raising the centrifuge's rotational speed. However, doing so has other highly disadvantageous effects, which accounts for the comparatively low rotational speeds in the examples of the aforementioned patent application. The maximum rotational speed at which fibres of fair quality can actually be spun using the above-described technique is of the order of 1000 rpm. Rotational speeds in excess of this recommended value produce an unacceptable number of fibre breaks. Moreover, aerosol is formed between the centrifuge and the coagulant flowing along the jacket. Such conditions produce poor and irregular fibre properties (tobacco-like appearance) as well as a dangerous and contaminated working environment due to the aerosol often containing a strong acid.
Fibre properties have to satisfy ever higher demands. In a conventional wet spinning process, such as described in U.S. Pat. No. 4,320,081, the resulting fibres have properties substantially superior to those of the fibres obtained by the process according to the aforementioned Japanese patent application (higher strength and modulus). A conventional wet spinning process employs a large number of spinning orifices per spinneret (say, 1000), so the productive capacity is high also. However, because of the comparatively low winding speed (some hundreds of meters per minute), which is comparable to the productive capacity per spinning orifice, and the process's high susceptibility to foreign substances in the spinning solution (requiring thorough filtration and shutting down of the process when one or more of the spinning orifices has clogged up), this process also produces an expensive product. Especially when it is to be processed into pulp, which is used, e.g., as friction and packing material, such a fibre is really too expensive.
In other words, what is wanted is a process having a higher productive capacity than the existing wet spinning processes and by means of which fibres can be made which are less expensive and possess comparable or superior properties for a particular purpose, such as pulp. Preferably, it should be possible to spin less pure spinning solutions and spinning solutions made of already somewhat coagulated polymers by means of such a process.
These objectives are attained using the process according to the invention, by centrifugally spinning a spinnable solution, with the inner radius of the jacket being at least 35% wider than the radius of the outer circumference of the centrifuge.
Preferably, the inner radius of the jacket is at least 50% wider than the radius of the outer circumference of the centrifuge and does not exceed 350% or, more preferably, 200%.
It was found that this will make it possible to substantially increase the rotational speed of the centrifuge, even to 5000 rpm or higher per minute. Further, the process according
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Jelijs Roelof
Meerman Johannes Jacobus
Akzo Nobel nv
Dixon Merrick
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