BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for making improved-sealability polypropylene
fibers, the fibers made thereby and non-woven textile materials including said fibers.
[0002] As known, non-woven textile materials are conventionally made starting from fibers
which are caused to adhere to one another by subjecting said fibers to a sealing process
performed on heated calendering apparatus, or in hot-air ovens or the like.
[0003] Prior fibers used for making non-woven fabrics have a main drawback of requiring
a comparatively high temperature for mutually sealing the fibers. The sealing operation,
in particular, involves a high power cost as well as processing difficulties. The
latter mainly depend on the fact that, because of the thermal processing, the fibers
tend to degrade and loose the desired mechanical properties.
SUMMARY OF THE INVENTION
[0004] Accordingly, the main object of the present invention is to provide a novel method
for making polypropylene fibers having high mechanical strength properties, as required
for making a good quality non-woven fabric, and having melting temperatures less than
those of prior fibers used for a like application.
[0005] Another object of the present invention is to provide a novel method which is specifically
designed for making improved-sealability polypropylene fibers.
[0006] Yet another object of the present invention is to provide an improved sealability
polypropylene fiber which can be made at a temperature less than the melting temperature
of the polypropylene material.
[0007] Yet another object of the present invention is to provide such a non-woven textile
material which presents very good strength properties.
[0008] According to one aspect of the present invention, the above mentioned objects, as
well as yet other objects, which will become more apparent hereinafter, are achieved
by a non-woven textile material according to the present invention, having the features
defined respectively in the independent claims 1, 6 and 11.
[0009] Advantageous and preferred embodiments of the invention are defined in the dependent
claims.
[0010] Thus, the method according to the invention allows to easily make polypropylene fibers
suitable for making a non-woven textile material having very high mechanical strength
properties.
[0011] In particular, the fibers made by the inventive method are provided with very good
sealability or sealing properties. This result, moreover, is achieved by processing
said fibers at a temperature less than the melting temperature of the fibers, with
a consequent high saving of power.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The above and yet other objects and advantages of the present invention will become
more apparent hereinafter from the following detailed disclosure of some preferred
embodiments of the inventive method and system, which are illustrated, by way of a
non limitative example, in the figures of the accompanying drawings, where:
Figure 1 is a schematic view illustrating a system for making improved sealability
fibers according to the present invention;
Figure 2 is a cross-sectional view illustrating a fiber made by the system shown in
Figure 1;
Figure 3 illustrates an exemplary non-woven textile material made by using the fibers
shown in Figure 2;
Figure 4 is a perspective view illustrating, on an enlarged scale, two fibers of the
textile material of Figure 3;
Figure 5 is a detail of a mutual sealing section of the fibers of Figure 4;
Figure 6 is a cross-sectional view illustrating a sheath-core type of fiber, according
to the present invention;
Figure 7 is a further cross-sectional view, illustrating a side-by-side type of fiber
according to the present invention;
Figure 8 illustrates a strength and MD elongation diagram;
and
Figure 9 illustrates a strength and CD elongation diagram.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] The system shown in Figure 1 comprises a first extruder 1, which is loaded with a
set amount of molten polypropylene material 2, as well as a second extruder 3, provided
for supplying a polypropylene copolymer 4 having a melting temperature less than the
melting temperature of the polypropylene material 2. Advantageously, the preferred
copolymers would be constituted by copolymers having a melting temperature of about
140-150°C.
[0014] The polypropylene 2 proper and the low melting copolymer 4 thereof are supplied to
a mixer 5 from the outlet of which a conglomerated mass 6 having a substantially heterogeneous
structure of the two mentioned polymers is supplied.
[0015] Said mass 6 is sent to a die assembly 7 of a conventional apparatus for making short-spinning
fibers, filaments 9 being ejected by the die holes 8.
[0016] Said filaments 7, as seen in cross section as shown in Figure 2, present a heterogeneous
structure or composition constituted by granules or portions of low melting copolymer
4, dispersed through the polypropylene 2 mass.
[0017] Thus, by the disclosed method, and using a polypropylene - polypropylene copolymer
mixture, the polypropylene copolymer being preferably included in an amount of 20-30%
by weight with respect to the total polymeric mass, fibers having a count of 2.2 dtex
and a sealability of 8-10N at a temperature of 148°C (i.e. the copolymer 4 melting
temperature) have been obtained.
[0018] Actually, as is shown in Figures 3 to 5, the non-woven textile material or fabric
15 made by calendering the fibers 9, or by a like method, as a high strength owing
to the mutual sealing of said fibers 9 at the level of the low melting copolymer 4
portions appearing on the surfaces of said fibers.
[0019] The remaining mass of polypropylene 2, melting at a temperature greater than that
used in the calendering process, is held unaltered, thereby providing the non-woven
textile material with very good mechanical properties, typical of fibers made exclusively
of polypropylene.
[0020] In the variation shown in Figure 6, the polypropylene material 2 and polypropylene
copolymer 4 are processed for providing two-component fibers, and, more specifically,
sheath-core fibers.
[0021] In this case, the filaments 12 comprise a polypropylene core 2, encompassed or sheathed
by a low melting copolymer 4 outer sheath. Thus, by this method, carried out starting
from a polypropylene copolymer having a melting temperature of 148°C and in an amount
of 20-30% by weight based on the total polymeric mass weight, sheath-core fibers have
been obtained, having a high mechanical strength and a sealability of 10-12 N. These
results, in turn, caused an increase or improvement of the toughness and strength
properties, as well as of the ultimate C.D. elongation (cross direction elongation)
and M.D. (machine direction) ultimate elongation of the non-woven fabric or textile
material made by said fibers. Actually, in a case of a non-woven textile material
of 19.5 g/m
2, with a calendering speed of 200 m/min and at a sealing temperature of 147-149°C,
have been obtained the following values: M.D. = 39.11 N and C.D. = 9.56 N, with respective
ultimate elongations of 44.87% and 86.55%, which values would be indicative of a very
good product, according to the present art standards (see Figure 8 and 9, respectively).
The same disclosed method can also be advantageously used for making fibers of 0.5
to 30 dtex values.
[0022] According to a modified embodiment shown in Figure 7, the filaments 14 have a structure
in which the component providing the sealing of the fibers consists of the low-melting
copolymer portion 4 thereof.
[0023] The invention, as disclosed and illustrated, is susceptible to several modifications
and variations all of which will come within the scope of the accompanying claims.
[0024] Thus, for example, the fibers could be also provided with a multiple component construction,
of any desired configuration, including two different low melting copolymers, in combination
with a set amount of polypropylene.
[0025] Moreover, instead of the two disclosed extruders, it would be also possible to use
a single extruder, including one or more screws for processing simultaneously the
two copolymers.
[0026] In this connection, it is desired to point out that an amount of 100% low melting
(148°C) polypropylene copolymer has been also processed, but the obtained results
have not provided the desired sealability properties, since the fiber softened through
the overall cross-section thereof thereby loosing its mechanical strength properties.
1. A method for making improved-sealability polypropylene fibers, characterized in that
said method comprises the step of extruding fibers comprising polypropylene and at
least a polypropylene copolymer having a melting temperature less than the polypropylene
melting temperature, thereby providing fibers having one or more outer surfaces constituted,
at least partially, by said at least a low melting polypropylene copolymer.
2. A method according to Claim 1, characterized in that said method comprises the step
of extruding a mixture of molten masses of polypropylene and said at least a low-melting
polypropylene copolymer, to provide heterogeneous structure fibers including said
polypropylene and low-melting polypropylene copolymer.
3. A method according to Claim 1, characterized in that said method comprises the step
of extruding said polypropylene and said at least a low melting polypropylene copolymer
by a sheath-core extruding process.
4. A method according to Claim 1, characterized in that said method comprises the step
of extruding said polypropylene and said at least a low-melting polypropylene copolymer
by a side-by-side extruding process.
5. A method according to Claim 1, characterized in that said method comprises the step
of extruding said polypropylene and said at least a low-melting polypropylene copolymer
to provide fibers having a composite construction and geometry.
6. An improved sealability polypropylene fiber, characterized in that said polypropylene
fiber has a heterogeneous structure including polypropylene (2) and at least a polypropylene
copolymer (4) said polypropylene copolymer (4) having a melting temperature less than
the melting temperature of said polypropylene (2), at least a portion of the surface
of said fiber comprising said at least a low-melting polypropylene copolymer (4).
7. A fiber according to Claim 6, characterized in that said fiber comprises a two-component
sheath-core fiber (12) including an outer sheath comprising said low-melting polypropylene
copolymer (4) and a core consisting only of polypropylene (2).
8. A fiber according to Claim 6, characterized in that said fiber comprises a side-by-side
fiber (14), including the two polypropylene (2) and low-melting polypropylene copolymer
(4) components.
9. A fiber according to Claim 8, characterized in that said fiber has a count of 1 to
70 dtex and comprises a polypropylene copolymer having a melting temperature of 148°C.
10. A fiber according to Claim 9, characterized in that said fiber has a sealability of
10-12 N for 2.2 dtex fibers.
11. A non-woven textile material, of the type comprising a plurality of mutually thermosealed
filaments, characterized in that said filaments comprise fibers having a heterogeneous
structure including polypropylene (2) and at least a polypropylene copolymer (4) having
a melting temperature less than the melting temperature of said polypropylene, at
least a portion of the outer surface of said fibers comprising said at least a low-
melting polypropylene copolymer.
12. A material according to Claim 11, characterized in that said filaments comprise two-component
sheath-core fibers, including an outer sheath comprising said low-melting polypropylene
copolymer (4) and a core consisting exclusively of said polypropylene (2).
13. A material according to Claim 11, characterized in that said filaments comprise side-by-side
fibers including the two polypropylene (2) and low-melting polypropylene copolymer
(4) components.
14. A material according to one or more of Claims 11 to 13, characterized in that said
filaments are sealed to one another at that portion of the outer surface of said fibers
formed by said low-melting polypropylene copolymer (4), thereby providing a great
power saving in a non-woven material making process.
15. A material according to Claim 14, characterized in that said fibers have a count of
1 to 70 dtex and comprise a polypropylene copolymer having a melting temperature of
148°C.
16. A material according to Claim 15, characterized in that said fibers have a sealability
of 10-12 N for fibers of 2.2 dtex.
17. A material according to Claim 16, characterized in that said material comprises a
non-woven fabric having a weight of 19.5 g/m
2 and including fibers of 2.2 dtex and 40 mm cut, said fabric, upon calendering at
a calendering speed of 200 m/min and at a calendering temperature of 147-149°C, having
the following values:
M.D. = 39.11 N, with an elongation of 44.87%;
C.D. = 9.56 N, with an elongation of 86.55%.
18. A use of the fibers according to any preceding claims 6 to 10 for making non-woven
textile materials.