(19)
(11) EP 1 001 057 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
17.05.2000 Bulletin 2000/20

(21) Application number: 99113122.8

(22) Date of filing: 07.07.1999
(51) International Patent Classification (IPC)7D01F 8/06, D04H 1/42, D04H 1/54
(84) Designated Contracting States:
AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE
Designated Extension States:
AL LT LV MK RO SI

(30) Priority: 12.11.1998 IT MI982458

(71) Applicant: FARE' S.p.A.
I-21054 Fagnano Olona Varese (IT)

(72) Inventor:
  • Fare, Rosaldo
    21054 Fagnano Olona (Varese) (IT)

(74) Representative: Cicogna, Franco 
Ufficio Internazionale Brevetti Dott.Prof. Franco Cicogna Via Visconti di Modrone, 14/A
20122 Milano
20122 Milano (IT)

   


(54) Method for making heat-sealable polypropylene fibers, the fibers made thereby and non-woven textile materials including said fibers


(57) A method for making improved-sealability polypropylene fibers comprises a step of extruding fibers (9) made of polypropylene (2) and at least a polypropylene copolymer (4) having a melting temperature less than that of the melting temperature of the polypropylene material. The fibers have an outer surface which has high sealability properties owing to the provision, on at least a part of the outer surface, of the low-melting copolymer.




Description

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/m2, 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.


Claims

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/m2 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.
 




Drawing
















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