Note: Descriptions are shown in the official language in which they were submitted.
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AN ELEC~ROSTATICALLY SPUN FIBRE OF A POLYMER BASE MATERIAL
This invention relates to an electrostatically spun fibre of a
polymer base material, this fibre havlng a marked~y porous surface structure
and, preferably, a strip-form profile.
DE-OS 20 32 072 refers to a fibre of the above described type.
This is obtained by the electro-static spinning oE dissolved high polymer
materials, for example, polystyrene, cellulose ester, or a polycarbonate
dissolved in an easily vaporized organic solvent. The fibres display a more or
less broken surface structure that does not continue into the interior of the
fibre. The strength of such fibres reaches only a small order of magnitude and
technical use proved possible an].y in those cases in which, in th;s regard,
no great demands were imposed. DE-OS 20 32 072 thus refers only to use in
a fine-dust filter in which a layer of such f;bres is stretched between air-
permeable covering layers.
This invention undertakes the task of further developing such a fibre
with regard to improved strength and an improved pore structure.
Under the terms of this invention, this problem is solved by the
use of an electrostatically spun fibre of a polymer base material which is
characteriæed by the fact that the polymer material displays a molecular
structure that is amorphous or at least only partially crystallized, by the
fact that the surface structure is a component part of a foamed layer, and by
the fact that this surrounds a fibre core that it, in the main9 free of pores.
Thus the invention provides an electrostatically spun fibre of a
single polymer material that displays a markedly porous surface s~ructure wherein
the polymer material has an amorphous molecular structure or is at least only
partially crystallized, the surface structure being composed of a foamed layer
which has a substantially uniform distribution therethrough of open or closed
c~ll pores of a substantially uniform size and this foamed layer surrounds
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a fibre core which is substantially free of pores.
The profile of the proposed fibre is correspnndingly characterized by
two areas that are clearly dlfferentiated from each other, and in which the
polymer material is present in completely different forms.
The fibre core is almost completely free of pores and forces that are
introduced are thus transmitted regularly over its complete cross-section.
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The proposed fibres display a minimum tensile strength that can be guaranteed
in every case and which is always ensured.
Because of the absence of pores it is, moreover, possible to effect a
considerable increase Ln the strength oE the fibre core by the use of
conventiona:l stretching methods. According to a preferred method it is
foreseen that a suitable molecular orientation is imparted to the fibre core
even when the fibre is being spun and before it is applied to a carrier. The
stretching of the fibres that is achieved in this manner can be indicated as-2
to 5~fold in comparison with a normal electrostatically spun fibre which has a
completely amorphous molecular structure.
The foamed layer that surrounds the fibre core is characterized by an
extremely high level of regularity with regards to thickness as well as to the
size and distribution of the pores that it contains. The layer consists of
the same material as the fibre core although the degree of molecular
orientation is regularly considerably less, which can facilitate the thermal
welding of two superimposed fibres, depending on the material that is used in
each case. The pores that are contained in the layer can be either open or
closed cells. Insofar as open pores are involved, it is preferred that these
are arranged in the main perpendicular to the surface in a cross-section that
for the most part remains constant, and that they penetrate the layer
completely. Pores of this type are suitable for the application of secondary
materials, for example, a cleaning or disinfecting substance whereby the
spectrum of use for the proposed fibres in textile surface structures of the
most varied types ls greatly increased. In general, the pores are not
compressible. Substances that are incorporated in them are for this reason
not completely washed out on first use; rather, they modify the
characteristics of a suitably configured surface structure gradually until it
is completely worn~out.
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Particles, liquids, or gases can be trapped or adsorbed, respectively in
or on the pores, having been separated out from a carrier current. Separating
mechanisms of tllis type are especLally effectlve on accolmt of the foamed
surf~lce structure that continues into the depth (of the fibre).
Because of the mechanical anchoring of the binding fLlms, colour
absorption and resistance to rubbing is far better than in the case of polymer
fibres having smooth or only slightly ~meven surfaces.
In one version in which the foamed layer contains predominantly closed
cells, the fibres are characterized by great surface softness and fullness for
a very low specific weight and great strength. Fibres of this kind will
absorb no moisture and depending on the polymer material that is used they can
be completely resistant to rot. In combination with conventtonal staple
fibres they are well suited for the productlon of textile surface structures
for use in the clothing industry, and particularly for the production of
heat-retaining clothing interlinings.
The yrofile of the proposed fibres can be varied within a very broad
spectru~. It is preferred that they have a dumb-bell like profile, i.e., a
shape that corresponds more or less to a figure eight laying on its side and
having a width of approximately 2.5 to 3.S times as great as its maximum
thickness. The breadth can be varied in the range from 1-12 micronsO In t:he
case of a round cross-section the pores should have a diameter of 0.01 to
0.5 microns, and preEerably a diameter of 0.05 to 0.2 microns, in which case
the proportion of opened pores to the total surface area of the layer amounts
to 1 to 99%, preferably 10 to 70%. The surface proportion of the foamed layer
to the profile of the total fibre amounts to 40 to 80%, preferably 60%.
The proposed fibre can be processed either alone or in conjunction with
other fibres to any type of textile surface structure, particularly for
fabrics or to single-layer or multi-layer fleece materials. Natural and
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synthetic fibres as well as staple and continuous fibres are also considered
as other ELbres~ Insofar as these other fibres display a marked degree of
curlirless, surface structures havlng great elasriclty and fullness ~ ll be
obtained, which permits the preferred application in relation to the
production of absorption fllters or damping materials for air-generated
noises.
The drawings which accompany this description relate to an open-pore
fibre of the type described in the invention at a magnification factor of 7000
to 14000 respectively. These drawings include:
Figure 1 which shows a sector of an open-pore fibre in plan view of this
invention; and
Figure 2 which is a cross-section of the Eibre according to Figure 1.
From Figure 2 it can be plainly seen that the pores are oriented mainly
perpendicular to the surface and that they penetrate the whole of the foamed
layer and t~at the foamed layer is differentiated very clearly from the fibre
core by a line of separation~ The foamed layer surrounds the complete
pore-free fibre core with an even thickness on all sides. The somewhat less
sharp reproduction of the foamed layer in the lower portion of Figure 2 is
attributable to photographic difficulties in connection with representation at
the required scale.
I~e fibre that is shown is a polycarbonate fibre that is produced from a
solution of polycarbonate in methylene chloride by electrostatic methods~
Equally good results can also be obtained with the use of a spinning solution
composed as follows:
88 parts of methylene chloride and 12 parts polystyrene.
86 parts of ~ethylene chloride and 14 parts PVC.
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