Note: Descriptions are shown in the official language in which they were submitted.
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Composition containinq short Aramid fibres
Description
The present invention relates to a composition
which contains at least synthetic organic short Aramid
fibres and a filler.
Compositions of this type are described, for
example, in EP-A-261 820. The known composition i~ used
for the production of fibrous materials. The known
composition is less suitable for the production of
mouldings which are intended to have particularly high
strength, such as, for example, flat seals.
It is therefore the object of the present
invention to provide a composition, in particular for the
production of mouldings which are intended to have a
particularly high strength. It is also the object of the
present invention to provide a process for the production
of this composition.
This object is achieved according to the inven-
tion, for a composition of the initially mentioned type,in that at least some of the fillers have a Moh~s hard-
ness of between 2 and 9 and in that the short fibres are
split into several fibrils at their ends. In particular,
the short fibres have cracks, protruding fibrils and,
preferably, splitting along the fibre axis.
Fillers which have proved particularly suitable
are Al4Si40lo(0H)B having a Moh's hardness of about 2 to
2.5 and zinc oxide having a Moh's hardness of about 4.
The Moh's hardness is determined by the method which is
described in Fahrenwald Trans. Am. Inst. Mining. Mat.
Engrs. 112, 88, 1943.
The specified ob~ect according to the invention
can be achieved, in the case of a process in which the
short Aramid fibres and at least one filler are mixed,
in that 20 - 900 ~ by weight, based on the weight of the
short Aramid fibres, of a filler which has at least a
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Moh's hardness of 2 but at most a Moh's hardness which,
as a function of the microcavities having a size H which
are contained on average in the short Aramid fibres,
satisfies the condition
M = 2.75 x 10 3 X H - 2
the sizes H of the micro cavities being able to assume
values of between 2000 and 5000 ~ (Angstrom), are added
to the short Aramid fibres and in that the resulting
mixture is introduced into a mixer, which is capable of
transferring high shear forces to the mixture, and is
mixed until the ends of the short Aramid fibres in the
mixture have severa~ split ends. Fillers which have
proved most suitable are, in particular, minerals, such
as, for example, kaolin, magnesium oxide, white clay,
zinc oxide, aluminium oxide, barytes, quartz or mineral
fibres (obtainable under the trade names Inorphil and
Rockwool). However, the only fillers which can be used
are those which have the requisite Moh's hardness.
Mixers able to transfer high shear forces which
can be used are those mixers known for the production of
Aramid pulp which possess a high power consumption and a
low rotor speed. The so-called Banburry mixer with
tangential rotor blad~s has proved particularly suitable
in this context. However, mixers in which the mixture is
abrasively treated between two discs are also suitable.
In the case of the ma~ority of mixers, care must
be taken that they are well cooled. In the case of
Banburry mixers in particular, it has proved particularly
advantageous to maintain a temperature of at most 80C in
the composition during mixing.
Short Aramid fibres which have an average length
of about 6 mm are particularly suitable for mixing into
the composition. An excellent composition for the
production of mouldings, in particular of flat seals, is
achieved in this way.
The invention is illustrated in more detail with
reference to the following drawings.
In the drawings
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Figure 1 shows a short Aramid fibre of
the type known from the known
prior art, and
Figure 2 shows a short Aramid fibre as
used according to the inven-
tion.
Figure l shows a short Aramid fibre 1 according
to the prior art. The short fibre 1 has frayed ends 2 and
a few, not very pronounced, fibrils 3 as well as a few
cracXs 4 along the fibre axis.
The short Aramid fibre 11 contained in the
composition according to the invention is shown in Figure
2. In contrast to the prior art, the short fibre 11 has
several split fibrils 12 at its ends. The fibrils 13 and
the cracks 14 along the fibre axis are more frequent and
more pronounced than in the prior art and, in addition,
the short fibres 11 can also have splitting 15 along the
fibre axis.
